2

Departamento de Física - Facultad de Ciencias Exactas Universidad Nacional de La Plata

IFLP (CONICET) Telephone: +54 (0) 221 4246062 - Fax: +54 (0) 221 4252006

hk2010@fisica.unlp.edu.ar

Sponsors

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Organization

Chairman Alberto F. Pasquevich

Organizing Committee Mario Rentería Laura C. Damonte Marcelo R. Ceolín Cecilia von Reichenbach Germán N. Darriba

Scientific Committee Jorge Tocho Marcos Sade Néstor Bolognini Gustavo Lozano Liliana Arraechea Ezequiel Albano Daniel Pasquevich Daniel A. Gomez Dumm Horacio Garda Julián Sereni

Collaborators Cecilia Y. Chain Facundo Pasquevich Sergio Ferrari Rubén Quille Ramos Diego Richard

Prof. Emil Bose during the exhibition of experiments in physics performed in March 29th, 1911, at 3 p.m., at the amphiteatre of the Institute of Physics (UNLP).

Table of contents Invited Talks ................................................................................................................... 7 Oral Contributions ....................................................................................................... 17

A- Nuclear Physics ..................................................................................................... 19 B- Particle Physics...................................................................................................... 25 C- Condensed Matter Physics .................................................................................... 29 D- Soft Matter Physics ............................................................................................... 53 E- Physical Chemistry ................................................................................................ 61 F- Medical Physics ..................................................................................................... 65 G- Optics .................................................................................................................... 71 H- Biophysics ............................................................................................................. 75 I- Humanistics ............................................................................................................ 85 K- Physics and Mathematics ...................................................................................... 91 L- Computational Physics .......................................................................................... 95

Poster Session................................................................................................................ 99 C- Condensed Matter Physics .................................................................................. 101 E- Physical Chemistry .............................................................................................. 131 G- Optics .................................................................................................................. 143 H- Biophysics ........................................................................................................... 151 I- Humanistics .......................................................................................................... 159 J- Physics and Astronomy ........................................................................................ 163 K- Physics and Mathematics .................................................................................... 167 L- Computational Physics ........................................................................................ 173

Author Index ............................................................................................................... 183 Keywords Index .......................................................................................................... 189

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7

Invited Talks

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I-1- Defect-induced magnetic order in non-magnetic oxides

Esquinazi P.

University of Leipzig, Division of Superconductivity and Magnetism, Germany

Covalently bonded oxides, like ZnO, MgO, Al2O3, TiO2, SrTiO3, among others, are thought to be “non-magnetic”. The term “non-magnetic” means actually that they are expected to show only a diamagnetic response when a magnetic field is applied. Experimental results of the last years, however, indicate that this is not quite correct.

After the failure to obtain reproducible ferromagnetism through doping with transition-metals and rare-earth ions in some of the oxides listed above, scientists started to realize that the influence of defects (like vacancies or non-magnetic ad-atoms) on triggering magnetic order might be non-negligible, like in the case of graphite, the paradigm for defect-induced magnetic order.

In my talk I will review experimental evidence that supports the existence of defect-induced magnetic order as well as main theoretical concepts and results used to explain this magnetic phenomenon. The following issues will be shortly discussed:

Upon doping, cation as well as oxygen vacancies may play an important role in triggering this phenomenon. On the other hand, recent experimental results show that few percent hydrogen is enough to make ZnO ferromagnetic without the need of vacancies.

In general, the amount of the obtained ferromagnetic mass remains relatively small, forcing us to take care of the properties of the near surface region as well as the magnetic impurities contribution.

A delicate balance between defect density and lattice order is necessary. Therefore, the systematic production of large amount of defect-induced ferromagnetic mass remains a main experimental challenge nowadays. This challenge might be partially circumvented in nanostructures with large surface to volume ratios.

Finally, defect-induced magnetic coupling is not actually weak but the contrary, it appears to be stronger than the one in 3d-ferromagnetic alloys, for example. Keywords: oxides, lattice defects, magnetic order, diluted magnetic semiconductors

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I-2- A stable In – defect complex found in GaN, AlN and AlxGa1-xN

Hamidi S.1, Kessler P.1, Lorenz K.2, and Vianden R.1

1Helmholtz - Institut für Strahlen- und Kernphysik, University of Bonn, Germany;

2Instituto Tecnológico e Nuclear, Sacavém, Portugal

Indium is used in most of the commercially available nitride devices based on GaN or AlN in order to tailor the materials properties to the desired application. Its concentration ranges from a few percent In content to the formation of veritable ternary alloys. Usually, In is added during the growth process. However, for certain applications it might be important to vary the In content on a wafer laterally so that doping by ion implantation would be the method of choice. In both cases it is interesting to study the interaction of In with defects present in the host lattices, since segregation and/or the formation of In – defect complexes might influence the performance of the final device.

We employed a nuclear technique, namely the perturbed angular correlation (PAC) to measure the (hyperfine) interaction of an electric field gradient (EFG) at the site of a radioactive Indium probe with the quadrupole moment Q of the intermediate state of a γ-γ - cascade in the daughter nucleus. Since the EFG is characteristic for the distribution of ionic and electronic charges in the lattice surrounding of the probe nucleus any deviations from the perfect lattice symmetry can be detected with high accuracy.

The experimental results in GaN, AlN, and AlxGa1-xN (x = 0.04 – 0.97) show that In forms a complex with a defect which is stable up to 1000 K (Fig 1.). Due to the hyperfine parameters of the defect it is suggested that a single nitrogen vacancy trapped at the In probe is causing the observed EFG. Keywords: semiconductors, defects, wide band gap, PAC Email: vianden@hiskp.uni-bonn.de

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I-3- Thermodynamics of a single (macro-)molecule

Rampf F.1, Strauch T.1, Binder K.1, Taylor M. P.2, Paul W.3

1Johannes Gutenberg University, Germany; 2Hiram College, USA;

3Martin Luther University, Germany

Thermodynamics is concerned with the states and transformation between states of macroscopic samples of matter. Most prominently, our description of phase transitions and the singularities in thermodynamic properties associated with them requires the so-called thermodynamic limit, in which the number of constituents goes to infinity and the occupied volume goes to infinity, but keeping the density constant. How can this apply to a single molecule?

Single, linear macromolecules can occur as open random coil structures or as dense, collapsed globular structures, and the transition between these conformational states can be controlled by the type of the solvent the macromolecule is immersed in. In the last 20 years it has also become possible to study these conformational transitions of isolated macromolecules by means of light scattering. The synthesis of such molecules with switchable conformational states follows principles of bio-mimetic design. After all, we are made of such smart polymers, most notably proteins. Most proteins perform their function in the so-called native state, which is special globular state of a macromolecule.

Theoretically, the coil-globule transition of a single macromolecule has first been described in a mean-field theory almost 50 years ago. With the advent of computer simulation techniques and our understanding that many properties, and among those the qualitative features of the coil-globule transition, are universal for all linear macromolecules, many studies of the conformational transition of single chains have been performed. However, only several years ago it has become possible by transferring newly developed Monte Carlo simulation techniques to this problem to unravel the complete thermodynamic behavior of single macromolecules. This has, as a first result, shed new light on the question of the crystallization of macromolecules and we could show a close similarity between the phase diagram topologies of simple liquids and of linear homopolymers.

And very interestingly, there exists also a large degree of communality between the thermodynamics of the simplest common homopolymers and of proteins, two subjects which were considered completely seperate before.

Keywords: Monte Carlo simulations, statistical mechanics, proteins, coil-globule transition Email: wolfgang.paul@physik.uni-halle.de

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I-4- Polymers in nanopores

Stühn, B., Engel, M., Khaneft, M.

Condensed Matter Physics, Darmstadt Technical University, Germany

Materials with structures on the scale of nanometers are of great interest with respect to application as well as for fundamental studies. In particular in combination with polymers nanopores are expected to give rise to confinement effects as the size of the molecules and the structural sizes are comparable. Here we use porous membranes that are produced by heavy ion tracks in polymers or by electrochemical etching of aluminum. Both systems provide cylindrical nanopores that are oriented perpendicular to the membrane surface. We show how these highly oriented materials may be characterized using small angle X-ray scattering (SAXS).

The flow of homopolymers into these pores is studied using time resolved SAXS experiments. The results are discussed within classical flow theories and compared with recent computer simulations.

A specific problem arises for the microphase separation of block copolymers within the pore as the domain structure competes with confinement. A meso structure is observed that is induced by the pore geometry.

As an outlook we present results on the confinement of polymers in multi wall carbon nanotubes. Small angle neutron scattering is used to determine the polymer conformation.

Keywords: nanoporous membranes, polymer, small angle scattering, neutron scattering Email: stuehn@fkp.physik.tu-darmstadt.de

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I-5- Latest developments at the Pierre Auger Observatory

Allekotte I.1, for the Pierre Auger Collaboration

1Centro Atómico Bariloche and Instituto Balseiro, C.N.E.A. and Univ. Nac. de Cuyo,

Bariloche, Argentina

Cosmic rays of the highest energies constitute a still unresolved enigma for modern science: their sources, mechanism of production and propagation through the cosmos are still unknown, many decades after their discovery. The Pierre Auger Observatory, built by an international collaboration of 18 countries, was conceived to study these ultra-high energy cosmic rays with unprecedentedly high statistics and precision. We describe the design, performance and scientific goals of the Auger Observatory, and present the most recent results obtained. We also describe the progress achieved in recent research and development projects which will enhance the capabilities of the Auger Observatory.

Keywords: cosmic rays, Pierre Auger Observatory, astroparticle physics Email: ingo@cab.cnea.gov.ar

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I-6- National Laboratories for Materials Sciences in South-America

Aldo F. Craievich

Instituto de Física, Universidade de São Paulo, São Paulo - SP, Brazil

Tunable and powerful photon and neutron beams produced by large instruments (electron storage rings and nuclear reactors, respectively) are widely used in order to investigate the structure and related properties of inorganic and organic materials. The first synchrotron source in the southern hemisphere is a second generation 1.37 GeV UVX electron storage ring, designed and built at the National Synchrotron Light Laboratory (LNLS), Campinas, Brazil, and open to users in 1997. Fourteen UV and X-ray beam lines are now in operation at LNLS that are currently used by more than 2000 scientists/year. LNLS users come from many Brazilian research centers, and also from foreign institutions, most of them from Argentina. In order to illustrate the applications of the LNLS synchrotron light source, a few results of recent investigations related to structure and properties of nanomaterials will be presented. New projects associated to large facilities for investigations of materials under more favorable conditions are currently being discussed in Brazil and Argentina. These projects are (i) a third generation 3.0 GeV electron storage ring (Sirius) and several associated beam lines to be installed at LNLS, (ii) one or two synchrotron beam lines to be installed around the Sirius source, to be funded by the Argentine government, (iii) a 30 Mwatt multipurpose nuclear reactor equipped with several neutron beam lines to be built at Ipero, São Paulo State, by the Instituto de Pesquisas Nucleares (IPEN), Brazil, and (iv) a similar multipurpose nuclear reactor with neutron beam lines to be constructed in Argentina by the Comisión Nacional de Energía Atómica (CNEA). When the mentioned new photon and neutron sources and beam lines will be in operation, the South-American scientific community will have open access to an excellent set of large experimental facilities, whose main features will be comparable to, and in several aspects better than, those of synchrotron and neutron sources currently in operation in developed countries. Keywords: Synchrotron radiation, LNLS, Nuclear reactors, National laboratories Email: craievich@if.usp.br

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I-7- Antes de la visita de Albert Einstein a la Argentina

Gangui A.1, Ortiz E.L.2

1Instituto de Astronomía y Física del Espacio, CONICET; 2Imperial College, London

En este trabajo desarrollaremos algunos momentos clave que marcaron el viaje de Einstein a nuestro país. Mencionaremos además las relaciones, contactos académicos y referencias escritas que hubo -o dejó de haber- entre los principales actores científicos -extranjeros y nacionales- involucrados en la introducción de las ideas relativistas en la Argentina en las primeras décadas del siglo 20. Keywords: Historia de la ciencia, Relatividad, Ciencia en contexto Email: gangui@df.uba.ar

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Oral Contributions

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A- Nuclear Physics

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OA-1- Nonmesonic weak decay of Lambda hypernuclei

Bauer E.

Departamento de Física, Universidad Nacional de La Plata e IFLP (CONICET),

Argentina

A consistent microscopic diagrammatic approach is applied for the calculation of the nucleon emission spectra in the non-mesonic weak decay of Lambda-hypernuclei, together with the evaluation of the non-mesonic decay widths. We adopt a nuclear matter formalism extended to finite nuclei via the local density approximation, a one-meson exchange weak transition potential including the exchange of the complete octets of pseudoscalar and vector mesons and a Bonn nucleon--nucleon strong potential. Ground state correlations and final state interactions, at second order in the nucleon--nucleon interaction, are introduced on the same footing for all the isospin channels of one- and two-nucleon induced decays. Single and double-coincidence nucleon spectra are predicted for 12

ΛC and compared with recent KEK and FINUDA data. The key role played by quantum interference terms allows us to the predictions obtained with intranuclear cascade codes. Discrepancies with data remain for proton emission. Keywords: Lambda-hypernuclei, non-mesonic weak decay, two-nucleon induced decay Email: bauer@fisica.unlp.edu.ar

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OA-2- The future of neutrino physics in Argentina: The ANDES

proyect

Civitarese O.1 1Department of Physics. University of La Plata. Argentina

In this talk we shall discuss the possible configuration of the recently proposed

ANDES laboratory. We shall outline the main aspects of neutrino, dark matter and double beta decay measurements, in conection with the proyect, and discuss the status of the leading experiments in the field. Keywords: Measurements of neutrino physics at the ANDES lab. Email: osvaldo.civitarese@fisica.unlp.edu.ar

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OA-3- Charged and neutral current neutrino-nucleon scattering and

pion production

Mariano A.E 1, Barbero C.A.1

1Universidad Nacional de la Plata, Argentina

One-pion production in neutrino scattering off nucleons and nuclei plays and important role as a source of relevant data on hadronic structure and in the analysis of neutrino oscillation experiments. Here we develop a consistent model to describe these processes in the case of charged and neutral currents, which treats the resonant and background contributions to the cross sections in a coherent way. Previously we have used this model to describe the elastic and radiative pion-nucleon scattering and pion-photoproduction reactions. Here we have extended the model to describe the single-pion production in charged and neutral current neutrino-nucleon scattering for πN invariant-mass distributions up to 2 GeV. For that purpose we include the effects of finite size of hadrons by introducing an appropriate form factor. Good agreement is found between our results and available experimental data for the total cross sections and the invariant-mass distributions of the πN system, as well as with simulations in the case of scattering on free nucleons. Keywords: neutrino, nucleon, scattering, resonances Email: mariano@fisica.unlp.edu.ar

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OA-4- La Radioquimica en la Argentina: Formacion y Desarrollo del

Grupo Buenos Aires

Pahissa Campá J.1

1CNEA, Argentina

La radioquímica, como ciencia, es una de las bases fundamentales de un plan nuclear. Baste con decir que la evidencia de la fisión del uranio que fue lo que dio origen al desarrollo de toda la actividad nuclear actual, fue descubierta por un radioquímico alemán, el célebre profesor Otto Hahn, quien recibió el premio Nobel por dicho descubrimiento. En Argentina tuvimos, a partir de los principios de la década de los 50´s del siglo pasado la gran oportunidad de contar con la presencia de uno de sus discípulos, el profesor Walter Seelmann-Eggebert, que fue el creador e impulsor de un grupo de excelencia de radioquímicos, conocido internacionalmente como el “grupo Buenos Aires” y cuyos integrantes a lo largo de tiempo han desempeñado roles de gran importancia en el plan nuclear argentino. Keywords: radioquímica, uranio, fisión, grupo Buenos Aires Email: pahissa@cnea.gov.ar

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B- Particle Physics

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OB-1- Composition of Ultra High Energy Cosmic Rays at the Pierre

Auger Observatory

Wahlberg H.1,*

1Universidad Nacional de La Plata - IFLP Conicet

The mass composition of ultra-high energy cosmic rays is a critical issue to

understand their origin and nature. The Pierre Auger Observatory is a hybrid instrument which provides a powerful environment for the determination of the primary mass. The Observatory is located in Malargue (Argentina) and consists of 1660 water Cherenkov detectors equally spaced on a triangular grid (1.5 km) over an area of approximately 3000 km2. Overlooking at the array there are 4 different sites with 6 Fluorescence Detector telescopes. Different parameters sensitive to the primary mass are discussed. Their energy dependence and a comparisons with predictions from different models are also presented. (*) For the Pierre Auger Collaboration. Keywords: Mass Composition, Cosmic Rays, Pierre Auger, Hadronic Models Email: wahlberg@fisica.unlp.edu.ar

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OB-2- Induced electric dipole in Heisenberg-Euler nonlinear

Electromagnetism

Falomir H.

IFLP - CONICET, Departamento de Física - Fac. de Ciencias Exactas, UNLP,

Argentina.

The linearity of Maxwell equations leads to the superposition principle in Classical Electrodynamics. But quantum fluctuations in the QED vacuum induce nonlinear effects leading to a breakdown of this superposition principle [1,2]. These quantum fluctuations make the vacuum to appear as an electrically and magnetically polarizable medium, leading to effects as the scattering of light by light and the vacuum birefringence and light diffraction by a strong standing electromagnetic field [3,4]. Due to the extreme smallness of the expected effects, high-intensity lasers with fields up to 1014 Volt/m have recently been considered to put in evidence such violation of the superposition principle [5]. However, modern lasers still do not provide field strengths sufficiently high to make these effects observable. Recent theoretical results [6,9] open up an unexpected pathway to observe a first ever signal due to these non-linear electromagnetic field interactions. In [6] it was found that an electrically neutral particle with a magnetic dipole moment, such as the neutron, develops an induced electric dipole moment when immersed in an intense quasi-static external electric field. This provides an additional contribution to the amplitude of neutron scattering by the electric field of heavy nuclei [7], effect that could be several orders of magnitude larger than those expected in experiments with laser light, thus opening the possibility of being observed. [1] W. Heinsenberg and H. Euler, Consequences of Dirac's Theory of Positrons, Z. Phys. 98 (1936) 714. [2] V. Weisskopf, The electrodynamics of the vacuum based on the quantum theory of electrons, English translation in Early Quantum Electrodynamics: A source book, A.I. Miller Edt. Cambridge University Press (1994). [3] H. Euler and B. KÄockel, On the scattering of light from light in the Dirac Theory, Naturwiss 23, (1935) 246. [4] E. Brezin and C. Itzykson, Physical Review D3, (1971) 618. [5] A. Di Piazza, K.Z. Hatsagortysan, C.H. Keitel, Phys. Rev. Lett. 97, 083603 (2008). [6] C.A. Dominguez, H. Falomir, M. Ipinza, S. Kohler, M. Loewe y J.C. Rojas, Physical Review D80, 033008 (2009), arXiv:0808.2897 [hep-ph]. [7] O. Zimmer, C.A. Domínguez, H. Falomir and M. Loewe, Observability of an induced electric dipole moment of the neutron from non-linear QED, in preparation. [8] O. Zimmer, C.A. Domínguez, H. Falomir and M. Loewe, Breakdown of the super- position principle for electromagnetic ‾elds in neutron scattering, proposal number 3-15-66 to the ILL, FEB/2011. [9] C.A. Dominguez, H. Falomir, M. Ipinza, M. Loewe y J.C. Rojas, Mod. Phys. Lett. A24:1857-1862, (2009), arXiv:0808.2897 [hep-ph].

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C- Condensed Matter Physics

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OC-1- Polarization and elementary excitations of exciton-polariton

Bose–Einstein condensates in lateral traps

Trallero-Giner C.1, Núñez-Fernández Y.1,2, Vasilevskiy M. I.2, Kavokin A.V.3, Liew T. C. H.4

1Universityof Havana, Cuba; 2Universidade do Minho, Portugal; 3University of Southampton, UK; 4Ecole Polytechnique Fédérale de Lausanne, Switzerland

Bose-Einstein condensates (BEC’s) of exciton-polaritons in a semiconductor

microcavity have been demonstrated experimentally by several groups and it has been

shown that it is possible to confine such a BEC in a parabolic lateral trap induced by

local elastic strain. The stationary properties of the condensate can be described by the

Gross-Pitaevskii equation (GPE). In the realistic limit of weakly interacting polaritons,

the non-linear term in GPE can be considered as a perturbation with respect to the

potential of the trap, which allows for a convenient analytical description of the BEC

ground state. We show that the ground state of the condensate is characterized by a non-

uniform vector polarization. Using similar approach elementary excitations in the

condensate can be described by two coupled Bogolyubov equations. We derive a

complete set of phonon-type modes and present the dependence of their energies on 2

hmNα=Λ (α is the exciton-exciton interaction constant, m is the polariton

effective mass and N is the total number of particles). Owing to the axial symmetry the

(zero-order in Λ) excited states, nε ( K,2,1=n ), are ( )1+n -fold degenerate. The

interaction lifts the degeneracy although the states with non-zero angular momentum

remain two-fold degenerate. Also, an analysis of the polarization degree of the

condensate is performed as a function of the number of polaritons in the trap. We extend

the method of calculation including the effect of a magnetic field on the condensate. In

the present case the Zeeman splitting and the spin repulsive interactions are included

and the system can be described by two coupled spinor GPEs for the two circularly

polarized σ± components of the polariton condensates .We generalize our description of

the Bogolyubov-type elementary excitation to this case. Keywords: Nonlinear optics, Polaritons, Magnetic nanostructures Email: trallero@df.ufscar.br

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OC-2- Enhancement and inhibition of coherent phonon emission in

acoustic nanocavities

Fainstein A.1, Lanzillotti-Kimura N. D.1,2, Perrin B.2, Jusserand B.2, Soukiassian A.3, and Schlom D. G. 3

1Centro Atómico Bariloche and Instituto Balseiro, Argentina; 2INSP, CNRS-Université

Pierre et Marie Curie, France; 3Cornell University, USA

Changing the spontaneous light emission rate and spectra of atoms or excitons through the modification of the photon density of states (DOS) has been the subject of significant efforts following Purcell's proposal and demonstration in the microwave domain. This has been accomplished either by changing the dielectric boundaries close to the emitting species, or more fundamentally by embedding the emitter in an optical microcavity. Depending on the tuning of the emitter spectra with maxima or minima of the modified photonic DOS, the emission can be either enhanced or inhibited.

In the field of phononics, and specifically in the search of phonon ``lasing'', for efficient monochromatic THz acoustic sources, and for the control of heat at the nanoscale, these ideas have been very little applied so far. We will describe recent pump-probe time resolved reflectivity experiments along these lines performed in a hybrid air-Ni metal-BaTiO3/SrTiO3 oxide mirror phonon cavity. These experiments demonstrate that the generated coherent acoustic phonon spectra of the impulsively excited metallic film can be inhibited or enhanced in the phonon cavity with respect to a Ni film directly grown on a SrTiO3 substrate. The experiments are compared with simulations that highlight the role of the phonon density of states in the coherent acoustic generation, extending concepts at the base of cavity-quantum-electrodynamics to the field of phononics. The prospects of observing the Purcell-effect in phonon systems based on the presented results will be addressed. On-going research on an alternative scheme based on semiconductor cavities that confine simultaneously light and GHz-hypersound and that are interesting candidates for the observation of stimulated phonon emission will be also commented. Keywords: Condensed Matter, Picosecond Acoustics, Coherent Phonon Emission, Semiconductor and Oxide Nanocavities Email: afains@cab.cnea.gov.ar

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OC-3- Recent developments in the bilayer ruthenate Sr3Ru2O7

Grigera S.A.1,2

1Instituto de Fisica de Liquidos y Sistemas Biologicos, CONICET-UNLP, La Plata

Argentina, 1School of Physics and Astronomy, University of St Andrews, St Andrews, UK.

Low-temperature phase transitions and the associated quantum critical points are

a major field of research, but one in which experimental information about thermodynamics is sparse. Thermodynamic information is vital for the understanding of quantum many-body problems. In this talk I will discuss combined measurements of the magnetocaloric effect and specific heat that allow a comprehensive study of the entropy of Sr3Ru2O7, a quantum critical system in which magnetic field is used as a tuning parameter. I will also discuss recent developments in the measurement of transport properties of this system. Keywords: Strongly correlated systems, Ruthenates, Nematicity. Email: sag@iflysib.unlp.edu.ar

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OC-4- Barkhausen effect in ferromagnetic thin films

Buceta R. C., Muraca D.

Instituto de Investigaciones Físicas de Mar del Plata, UNMdP and CONICET

The Barkhausen jumps (or avalanches) of magnetic domain-walls [MDW]

between succesive pinned configurations, due the competition among magnetic external driving force and substratum quenched disorder, appear in bulk materials and thin films. For ferromagnetic thin films with exchange (or short-range) interactions, we introduce a model based in rules for the MDW evolution, that include disorder and driving force effects. We simulate in 2-dimensions with Monte Carlo dynamics, calculate numerically distributions of sizes and durations of the jumps and find power-law critical behavior. The jump-size exponent is compared with experimental results for thin films and other models, such as like random-field and random-bond disorder, or functional renormalization group. The model allows us to review current issues in the study of avalanches of the MDW in thin films with ferromagnetic interactions and opens a new approach to describe these materials with dipolar (or long-range) interactions. Keywords: ferromagnetic thin films, Barkhausen effect, Monte Carlo dynamic, scaling Email: rbuceta@mdp.edu.ar

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OC-5- Evaluation of entanglement observables in spin systems

Matera J.M.1,2, Rossignoli R.1,3,Canosa N.1,2

1Depto. de Física-IFLP, FCE, Universidad Nacional de La Plata, Argentina 2CONICET 3CIC

The study of quantum entanglement in many-body systems is of great

importance for both quantum information science and condensed matter physics. In this contribution we describe some recent developments [1] for evaluating entanglement observables in general interacting quantum many-body systems and in particular in quantum spin systems. Based on the path integral representation of the partition function obtained through the Hubbard-Stratonovich transformation and a proper treatment of the different contributions to the path integral, a robust yet tractable general approximation scheme is derived, which contains as a particular case the so-called random phase approximation. This allows to relate the entanglement properties of general systems to those in more simple and solvable systems, where they can be more easily evaluated, like bosonic systems with quadratic interactions. Results for different entanglement observables such as the pairwise concurrence, the block entropy and the negativity between arbitrary subsystems are shown for different spin systems and compared with exact results when available.

[1] J.M. Matera, R. Rossignoli, N. Canosa, Phys. Rev. A 82, 052332 (2010); Phys. Rev. A 78, 042319 (2008). Keywords: Quantum Entanglement, Many-Body Systems, Spin Chains, Quantum Information Email: matear@fisica.unlp.edu.ar

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OC-6- Quantum Discord: A new measure of quantum correlations for

mixed states

Ciliberti L.1,2, Canosa N.1,2, Rossignoli R.1,3

1Depto. de Física-IFLP, FCE, Universidad Nacional de La Plata, Argentina

2CONICET 3CIC

Quantum discord is a measure of quantum correlations which is not equivalent to the standard measures of entanglement in the case of mixed quantum states: It can be non-zero even when entanglement vanishes. Interest on the discord has been triggered by the recent discovery that it may be responsible for the exponential speedup obtained in certain quantum algorithms based on mixed quantum states (mixed state quantum computation), where entanglement is negligible. In this contribution we describe the quantum discord and evaluate this quantity exactly for typical states of spin pairs in a spin chain with XY Heisenberg couplings in a transverse field [1]. It is shown that its behavior can differ considerably from that of the pairwise entanglement at low fields, reaching full range in the vicinity of special critical points. We also discuss possible entropic generalizations of this measure, which could simplify the evaluation in general systems yet detecting the same type of correlations. [1] L. Ciliberti, R. Rossignoli, N. Canosa, Phys. Rev. A 82, 042316 (2010); Phys. Rev. A 82, 052342 (2010). Keywords: Quantum Correlations, Quantum entanglement, Spin Chains, Quantum Information Email: rossigno@fisica.unlp.edu.ar ciliberti@fisica.unlp.edu.ar

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OC-7- Polycrystalline silicon thin film solar cells

Schmidt J.A.

INTEC (CONICET-UNL), Santa Fe, Argentina

The photovoltaic industry has had an important development in the last years, growing more than 30 % annually. The photovoltaic market is currently dominated by the technology based on crystalline silicon (c-Si), with a market share in terms of modules production of around 78 %. However, the need to lower the prices of photovoltaic electricity pushes towards a reduction in the production costs of silicon solar cells. To achieve this goal, approaches that use less material and lower temperatures are needed, known as thin films approaches. Polycrystalline silicon (poly-Si), deposited as a thin film on glass, offers the possibility to combine the low-cost potential of thin films with the proven stability and high efficiency of crystalline silicon.

In this presentation, we give an overview of different deposition and processing techniques that can be used to obtain thin poly-Si films on glass substrates. We discuss the direct deposition of poly-Si on glass by thermal CVD at intermediate temperatures, starting from chlorosilane precursors. This is an attractive technique since the substrate, the chemical precursors and the process are all of low cost. We also present the technique of metal-induced crystallization of amorphous silicon, which allows producing large crystalline grains (sizes over 100 microns) at low temperatures (below 600 ºC) by means of thermally activated solid phase transformations. Specifically, we focus on the use of nickel as the metallic mediator for inducing silicon crystallization, and its influence on grain nucleation and growth. We analyze the relevant concept of solid phase epitaxial growth of a poly-Si film on a previously crystallized seed layer. The pre- or post-crystallization doping possibilities, together with their own advantages and disadvantages, are addressed. We also present results of different techniques for the structural characterization of thin poly-Si films. Raman spectroscopy, reflectance in the UV region, X-rays diffraction, optical microscopy, SEM and AFM are shown as valuable tools to follow the crystal growth and to test the crystalline quality of the resulting material.

Finally, we discuss the application of the introduced techniques in the development and design of polycrystalline silicon thin film solar cells. Among others, we present the process used by the German company CSG Solar A.G. (CSG ≡ Crystalline Silicon on Glass), based on solid phase crystallization. This process is at industrial level, producing photovoltaic modules with efficiencies of up to 8 % and mini-modules with efficiencies slightly larger than 10 %.

Some concluding remarks about the prospective utilization of solar energy as an alternative energy source are also presented. Keywords: Solar Energy, Polycrystalline Silicon, Thin Films, Photovoltaic Cells Email: jschmidt@intec.unl.edu.ar

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OC-8- Magnetic nanomaterials for biomedical applications

Sánchez F.H., Fernández van Raap M.B.., Mendoza Zélis P., Pasquevich G., Stewart S., Bruvera I., De Sousa E.L., Laborde C.

Departamento de Física-IFLP, FCE-UNLP, Argentina

The diversity of biomedical magnetic nanomaterials (MNM) increases

continuously and so their many applications do. MNM in the form of particles, rods, tubes, films, aerogels, etc., continuously find potential new uses in diagnosis, prevention, and therapy of many diseases.

MNM are especially suitable for biomedical applications because their sizes are on the scale of the natural, biologic nanomachines. On the other hand, due to their large surface/volume ratio and small confinement volume they may present enhanced reactivity and quantum effects which posse new challenges to their understanding, design and fabrication. There are several promising applications of MNM in diagnosis and on site therapy. While currently artificial materials are far less sophisticated than their natural counterparts they may perform functions not existing in nature. Among these, the improvement of magnetic resonance imaging, magnetic separation, targeting delivery of drugs and genes, and localized hyperthermia therapy can be mentioned. Magnetic nanoparticles can help cell level detection of diseases and cell level therapies due to the following features: their relaxation time at body temperature in the absence of an external field is short enough as to prevent their agglomeration, they have a sufficiently strong response to moderate magnetic fields which easies their external manipulation, they can be functionalized for biocompatibility, to evade the immunological system and to deliver specific drugs, and they can be externally activated by RF fields to kill malignant cells by hyperthermia and/or by releasing chemicals. For several of these applications the materials must be designed to have preselected values of particle size and size dispersion, shape, saturation magnetization, supermoment relaxation time at body temperature, and magnetic ordering temperature. They must also be structurally and magnetically characterized in detail after each fabrication stage, in order to correlate their biomedical performance with their physical properties and determine research paths to further improve their efficiency for a given application. On the other hand DC applicators must be capable of inducing localized magnetic forces larger than the average hydrodynamic drag forces, thus retaining the particles in the treatment area, and RF applicators must provide fields with optimum amplitudes and frequencies.

During this talk, besides introducing the above mentioned topics, a discussion will be presented on the expected behavior of MNM in a biological system, based on the estimation of the order of magnitude of interaction energies, forces and torques to which they are submitted due to external (applied) as well as inner fields. Keywords: Nanomaterials, Magnetic, Biomedical Applications Email: sanchez@fisica.unlp.edu.ar

39

OC-9- Unusual thermodynamic behavior in the vicinity of a T = 0

quantum critical point

Sereni J.G.

Bajas Temperaturas, Centro At\'omico Bariloche (CNEA), S.C. de Bariloche, Argentina A quantum critical point is defined as the limit of a second order magnetic transition driven to zero temperature (T=0) by a non-thermal parameter such as pressure or composition. Approaching the critical region, very low temperature specific heat (Cm) measurements performed on three exemplary intermetallic compounds (c.f. ferromagnetic CePd1-xRhx and antiferromagnetics CeIn3-xSnx and CeCu6-xAux) show unusual features in their respective magnetic phase boundaries. While the concentration (x) dependence of their respective ordering temperatures TC(x) and TN(x) turn from a

canonical negative curvature to a positive one, the corresponding maxima of their Cm/T

(at T=TC,N) exhibit a constant value.

Around the critical concentration (xcr , defined as T=TC,N → 0) the experimental parameters show peculiar thermal dependencies known as non-Fermi-liquid behaviors. The most relevant is Cm(T)/T which tends to diverge as T→ 0 because of the presence of quantum fluctuations related to the T=0 quantum critical point. Actually, in real

systems Cm(T))/T flattens at very low temperature preventing a non-thermodynamical singularity at zero temperature. Furthermore, a detailed experimental study performed on CeIn3-xSnx allowed to

detect an anomalous reduction of the entropy around xcr with respect to the value

expected for a magnetic doublet ground state of the Ce ion: Sm = R Ln2. Coincidentally, at that concentration the volume variation V(T), extracted from low temperature thermal expansion measurements, shows a non-monotonous behavior for T→0. These abnormal behaviors indicate the presence of non-thermal (or canonical) excitations at very low energy, which are probably originated in quantum tuneling effects. This contribution of quantum nature has to be taken into account to understand the ground state formation within the constrains of the third law of thermodynamics. Keywords: Quantum Criticality, Specific Heat, Entropy, Third law of thermodynamics Email: jsereni@cab.cnea.gov.ar

40

OC-10- Unconventional magnetization processes in spin-ice Dy2Ti2O7

Borzi R.A.1

1Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas, CONICET-UNLP,

La Plata Argentina

Spin ice is a deceptively simple frustrated system. Composed of Ising spins on the vertices of a pyrochlore lattice with ferromagnetic interactions, it has a ground state formally equivalent to that of protons in the eponymous water ice. In this talk, I will discuss experimental studies and numerical simulations performed at low temperatures on the spin ice material Dy2Ti2O7. I will show that its low energy excitations can be described by an object with local properties similar to point-like magnetic monopoles, and discuss their role in non-equilibrium low temperature phenomena.

Keywords: Magnetic Frustration, spin-ice. Email: r.chufo@gmail.com

41

OC-11- Spherical nano and microscopic material produced by fast

process

Cabanillas E.D.1, Ratner M.J.2

1CONICET and CNEA, Argentina; 2CNEA, Argentina

In this work we show that thermal different processes, used in industry, also produce material with interesting properties: spherical shape, nano and microscopic dimensions, density, specific area, chemical composition, crystal structure, etc. The industrial process we used were: electroerosion, laser ablation, plasma cutting and arc furnaces, in this processes the debries were our object of syudy. All of them have in common the swift heating and after cooling of material. The obtained temperatures reach the fussion and also the evaporation points and after that a fast cooling occurs. The source of heating are: electromagnetic light in the case of laser ablation, arc discharge in electroerosion, plasma cutting and arc furnaces. We show the processes and the obtained materials with their physical characteristics. Keywords: nano and micro particles, laser ablation, plasma ablation, electroerosion Email: cabanill@cnea.gov.ar

42

OC-12- On the origin of exciton formation in dye doped Alq3 OLEDs

Gómez J.A.1, Castro F.A.2, Nüesch F.3, Zuppiroli L.4, Graeff C.F.O. 5

1FFLCRP-USP, Brazil; 2NPL, UK; 3EMPA, Switzerland; 4EPFL, Switzerland; 5FC-UNESP, Brazil

Electrically Detected Magnetic Resonance (EDMR) was used to investigate the

influence of dye doping on spin-dependent exciton formation in Aluminum (III) 8-hydroxyquinoline (Alq3) based OLEDs with different device structures. 4-(dicyanomethylene)-2-methyl-6-2-[(4-diphenylamino)-phenyl]ethyl-4H-pyran DCM-TPA) and 5,6,11,12-tetraphenylnaphthacene (Rubrene) were used as dopants. Results at room temperature show significant differences on the EDMR spectra (g-factor and linewidth) of doped and undoped devices. Signals from DCM-TPA and Rubrene dye doped OLEDs showed strong temperature dependence, with signal intensity increasing by 2 (~1) orders of magnitude below 200 K (225 K) for DCM-TPA (Rubrene) doped OLEDs, while undoped devices shows almost no temperature dependence. By adding a “spacer” layer of undoped Alq3 at the recombination zone, we could use the bias voltage to shift the recombination from doped to undoped region and correlate that with changes in the EDMR spectrum. Our results are clear evidence that charge trapping on the dopant followed by recombination is the main mechanism of light emission for the investigated materials.

Keywords: OLEDs; Exciton formation; Dye Doped OLEDs; DCM-TPA; Rubrene; EDMR Email: graeff@fc.unesp.br

43

OC-13- Study of PbTixHf1-xO3 for 0≤≤≤≤x≤≤≤≤1 by thermal analysis (DSC)

and impedance (IS) and perturbed angular correlation (PAC)

spectroscopies

Alonso R.E.1, De la Rubia M.A.2, López-García A.3, De Frutos J.4

1Departamento de Física, Fac. Cs. Exactas, Universidad Nacional de la Plata, Calles 115 y 49, 1900 La Plata, Argentina 2Instituto de Cerámica y Vidrio (CSIC), Madrid

España 3Instituto de Física La Plata, CONICET, La Plata, Argentina 4Departamento de Física Aplicada a las Tecnologías de la Información, ETSI Telecomunicación (UPM),

Ciudad Universitaria s/n 28040 Madrid, España

The objective of this contribution is to study the influence of Ti partial substitution by Hf in the perovskite-type crystalline structure of PbTiO3. Samples of PbTi1-xHfxO3 with composition 0≤x≤1 have been prepared by the high temperature reaction procedure. Phase transitions have been determined by DSC and IS. As a consequence of cation substitution changes in the different phase transitions temperatures TC were observed. All prepared samples showed by both techniques one phase transition in the temperature range between 230 and 460ºC. The agreement in the measured values of TC taking into account the use of different characterisation techniques is remarkable. A linear dependence of TC with composition is observed. With these results and known crystalline structures of pure PbTiO3 and PbHfO3 the phase diagram of PbTi1-xHfxO3 is presented including a morphotropic phase transsition observed at x~0.5. From the PAC analysis the electronic disorder for samples with x = 0,25, 0.5 and 0.75 was studied.

Keywords: PAC, impedance spectroscopy, thermal analysis, perovskite Email: alonso@fisica.unlp.edu.ar

44

OC-14- Surface topography on epitaxial thin films and their

correlation to transport properties

Mendoza A.1

1Physics Department, Universidad Nacional de Colombia, Bogotá, Colombia

This paper deals with the macroscopic structure of thin epitaxially grown films and their correlation to transport properties. Thin films result from condensation of the evaporated constituents onto a substrate material. Substrate temperature and pressures are used to ensure first the thermodynamically stability of the desired phase, and second that the phase is kinetically allowed to form at the applied growth conditions. Epitaxial films are structurally aligned with the substrate material. Consequently the epitaxial growing layer will adopt the crystal structure and the same orientation as the flat crystalline surface of the substrate. The most frequent case of growth is heteroepitaxy, namely the growth of a layer with a chemical composition and structural parameters different form those of the substrate. Epitaxially grown films of a given material present both a crystalline structure on an atomic scale and a crystalline structure on a macroscopic scale, that is, inhomogeneities such as defects, domains or phases within the crystal under investigation. In this paper the focus of the discussion lies on the effects of dislocations, domain size, domain formation and domain mobility on the transport properties. For this purpose it will be we consider atomic force microscopy (AFM) and magnetic force microscopy (MFM) as imaging techniques. In the first case the spiral growth by the formation of screw dislocations in epitaxial YBaCuO/STO is visualized by AFM. Dislocations as a morphological defect have some direct consequences for the pinning of vortices which determines the maximum current density which can be passed without dissipation in high temperature superconducting thin films. The second case has to do with the magnetic domains structure present in epitaxial LaCaMnO3/STO thin films. The low temperature behaviour of the magnetic domains by variation of the magnetic field, was studied in situ by magnetic force microscopy .The distribution and sizes of the domains were correlate with the cycles of magnetic hysteresis and with the magneto-resistance. Epitaxial thin films, were grown by D.C. reactive sputtering in the thin film group U. Valle, Cali. Colombia. Keywords: surface morphology, transport properties, magnetic domains. Email: gamendozab@unal.edu.co

45

OC-15- The physics behind magnetic hyperthermia

Fernández van Raap M.B.1, Sánchez F.H.1, Pasquevich G.1, Mendoza Zélis P.1, Stewart S.1, De Sousa E.L.1, Bruvera I.1, Laborde C.1, Girardin P.1

1IFLP-CONICET, CCT-La Plata and Departamento de Física, Facultad de Ciencias

Exactas, Universidad Nacional de La Plata, C. C. 67, 1900 La Plata, Argentina

Magnetic nanoparticles (MNP) are multifunctional objects which show growing

interest in biomedical applications for both diagnosis and therapy. Due to their nanometric size they can interact with living cells and can be internalized. The MNPs locate in intracellular membrane bound vesicles known as endosomes. Localization at the nanoscale is clearly seen by electron microscopy. Once internalized, the functionality of these magnetic agents is exported into the cells. The MNP magnetic moment acts as a mediator and allows non invasive long distance manipulation.

In fact, they are used as agents for various strategies like: enhancement in magnetic resonant imaging, selective cell separation, drug delivery and local heat dissipation.

In the latter, named magnetic hyperthermia, temperature increase is achieved when the MNP is subjected to an alternating magnetic field in the radio frequency range. The heating power is governed by the mechanisms of magnetic energy dissipation for single-domain particles (Brown and Néel relaxations) and is highly sensitive to MNP properties like size, magnetic anisotropy, and saturation magnetization; to solvent viscosity, and to the magnetic field frequency f and amplitude H0. The MNP power lost can be improved increasing both f and H0, but this rise is limited by physiological issues i.e there is a maximum value of the product f H0 to which human bodies can be exposed without discomfort. MNP are subjected to other restrictions aside to biocompatibility and toxicity. Even local hyperthermia offers numerous advantages as a novel cancer therapy; however, it requires for small tumours a remarkably high heating power of more than 1 kWg−1 for heat agents.

In the present talk the current state of knowledge in nanoparticle properties, their internalization and magnetic intracellular hyperthermia in discussed. Keywords: magnetic hyperthermia, magnetic nanoparticles, cellular magnetic labelling. Email: raap@fisica.unlp.edu.ar

46

OC-16- Advances in the theory of strongly correlated electrons from

fruitful Argentine-German collaborations

Hallberg, K.

Instituto Balseiro and Centro Atómico Bariloche, CNEA and CONICET, Argentina

I will summarise work done in collaboration with several German groups since

1995 in the field of strongly correlated electrons systems. In particular I will mention results in the analysis of hole motion in an arbitrary spin background, the development of the ubiquitous Densoty Matrix Renormalisation Group numerical technique and its applications to spin chains, impurity systems and carbon nanotubes, and, finally, the calculation of transport properties through nanoscopic systems leading to the observation of charge and spin separation.

These collaborations have been very fruitful and fostered not only the development of new numerical techniques in the groups involved, but also long standing collaborations and friendships.

Keywords: strong correlations, numerical simulations, electronic transport, nanoscopoic systems Email: karen@cab.cnea.gov.ar

47

OC-17- Electronic Structure Calculations using Augmented Wave

Methods: applications to the study of local properties

Petrilli H.M.

Universidade de São Paulo, Instituto de Física, DFMT, CP 66318,CEP05315-970, São Paulo, SP, Brazil

Here we focus on recent applications of ab initio electronic structure calculations in the framework of the Kohn-Sham scheme of the Density Functional Theory (DFT) performed in our Nanomol Group (www.nanomol.if.usp.br) in São Paulo, Brazil.The so called Augmented Wave Methods are specially well suited to obtain local electronic, magnetic and structural properties. Special attention is given to electric and magnetic hyperfine quantities which are compared to measurements performed by Mossbauer Spectroscopy , Perturbed Angular Correlations (PAC) and resonance techniques .

The Projector Augmented Wave (PAW), the Linearized Augmented Plane Wave (FP-LAPW), as embodied in the Wien code, and the Real Space Linear Muffin-tin Orbital in the Atomic Sphere Approximation (RS-LMTO-ASA) have been recently used in our group to study systems which range from molecules with biological or technological interest and conducting polymers to doped oxide semiconductors, intermetallic phases, nanomagnetism,etc. Keywords: Electronic Structure, DFT , Ab-initio calculations, hyperfine properties Email: hmpetril@if.usp.br

48

OC-18- Theoretical study of the thermodynamic properties of stable

and metastable intermetallics of the Cu-In-Sn and related systems for

lead-free soldering applications

Ramos de Debiaggi S.B.1,2, Deluque Toro C.1, Cabeza G.2,3,

Fernández Guillermet A.2,4

1Facultad de Ingeniería, Universidad Nacional del Comahue, Argentina; 2CONICET; 3Departamento de Física, Universidad Nacional del Sur, Argentina; 4Centro Atómico

Bariloche-Instituto Balseiro, Argentina

The physico-chemical properties of the intermetallic phases (IPs) occurring in the Cu-In phase diagram have been the subject of various studies in connection with the design of lead-free materials based on the Cu-In-Sn system, to be used in diffusion soldering methods. The knowledge of the properties of the IPs formed at the interconnection zone is of great importance for defining the final properties of the joints. On the other hand, the experimental information on the structural and thermodynamic properties of the relevant IPs is not enough for a detailed phase stability analysis of the soldering process. As a consequence, there has been a considerable interest in the development of predictive approaches to the thermodynamics and phase equilibria of the Cu-In-Sn alloys and related materials relevant for lead-free soldering applications.

A possible approach, usually known as the CALPHAD (“Calculation of Phase Diagrams”) method is based on the use of models for the Gibbs energy (Gm) of the involved phases. The method makes use of information on the binary systems to construct the Gm functions for ternary and higher-order phases. In particular, a CALPHAD analysis of the Cu-In-Sn system has been performed using the Compound Energy Formalism (CEF). In the CEF, the ternary IPs are treated using two-sublattice models of the type (Cu)a(In,Sn)b with one sublattice occupied by Cu and the other occupied by a mixture on In and Sn. The key parameters in the CEF are the Gm of the compounds generated by assuming that each sublattice is fully occupied alternatively by each one of the involved elements. Usually these Gm parameters are evaluated by fitting the model expressions to experimental data. However, in view of the general lack of input information, it is necessary to search for alternative ways to predict such thermodynamic quantities.

The general purpuse of the present study is to explore the possibility of using theoretical “ab-initio” calculations to gain information on various IPs of interest for the basic understanding as well as the CEF treatment of the Cu-In-Sn and related systems. Using ab-initio calculations based on the density-functional theory and the projector augmented-wave method (PAW) using the VASP code we investigate the structural and cohesive properties of several stable, metastable or hypothetical Cu-In and Cu-Sn compounds. With the new information obtained in the present study, trends are established in the structural properties, the energy of formation from the elements at 0 K and other relevant quantities. We also compare the present results with those obtained in a CEF treatment of the Cu-In-Sn intermetallics. Keywords: lead-free soldering alloys, Cu-In-Sn alloys, Compound Energy Formalism, ab-initio calculations. Email: afg@cab.cnea.gov.ar

49

OC-19- Unusual mechanical properties related to stress induced

martensitic transformations in Cu-Al-Be single crystals

Sade M.1,2,3, Yawny A. 1,2,3, Lovey F.C.1,3, Torra V. 4

1Centro Atómico Bariloche, CNEA; 2CONICET; 3 Instituto Balseiro, UNCuyo, (ARGENTINA); 4 Universidad Politécnica de Cataluña, Barcelona, (SPAIN)

Cu based shape memory alloys exhibit a martensitic phase transition between a

metastable bcc structure and a monoclinic 18R structure. This phase transition can be either thermally or mechanically induced. Relevant specific systems which show this behavior are Cu-Zn-Al, Cu-Al-Ni and Cu-Al-Be alloys. The present work focuses on Cu-Al-Be single crystals. In case the 18R martensite is induced by the application of a stress at a constant temperature (higher than a critical temperature referred to as Af) a stress-deformation curve with a distinct plateau is obtained. As a result, a single crystal of 18R martensite is obtained. If the mechanical load is now removed, the transformation reverts back to the original austenitic single crystal. This phenomenon is referred in the literature as pseudoelasticity or superelasticity. The retransformation however occurs at a lower stress giving rise to a mechanical hysteresis with the consequent dissipation of energy in the closed transformation – retransformation cycle. These characteristics make shape memory alloys attractive candidates for potential applications as dampers in mechanical (vibrations) or civil structures (seismic activity). In order to asses on that possibility, an in depth study of the mechanisms involved is required.

In the present work the pseudoelastic behavior of Cu-Al-Be single crystals is studied, both under cuasistatic and dynamic conditions in the temperature range from 303 K to 393 K. Tensile tests performed at slow crosshead speed show a dependence of the hysteresis associated to the stress induced β-18R transformation with temperature. The critical stresses of the β-18R transition have been determined giving a negative curvature parabolic dependence on temperature. The effect is more noticeable for the retransformation stress and a consequent increment in the stress hysteresis with temperature is observed. The deformation associated to the stress induced β-18R transition has also been found to depend on temperature. These singular features can be understood in terms of a structural distortion of the 18R martensite that occurrs in the considered temperature range. The strain associated to the structural distortion and the temperature dependence of its critical stress were determined. The resulting entropy change was thus calculated, resulting fifty times smaller than the entropy change between β and 18R. The possible mechanisms responsible of this structural distortion of the 18R structure are discussed. Pseudoelastic cycling at a higher frequency introduces new features as a strong stabilization of the martensite during the tests, which leads to the noticeable interaction between nondiffusive phase transitions and diffusion in the involved structures. Keywords: Martensitic Phase Transitions, Pseudoelasticity, CuAlBe Single Crystals , Mechanical Behavior Email: sade@cab.cnea.gov.ar

50

OC-20- The role of atomic layer deposition in the fabrication of

microelectronic devices

Van Eek, S.M., Kreher, S.

FHR Anlagenbau GmbH – Centrotherm Photovoltaics Group, Dresden, Germany

With ALD (Atomic Layer Deposition) reactors, ultra-thin functional layers can be deposited which combine surface conformity with excellent homogeneity in terms of layer thickness.

The principles for ALD will be discussed applied to the sample layer Al2O3. The use of ALD in the fabrication of microelectronic devices will be discussed

together with a short explanation of the processes and technologies used in microelectronics today.

Keywords: Atomic Layer Deposition, alumina, microlectronics Email: vaneek@fhr.de

51

OC-21- Structural effects of deuteration in H-bonded systems

Koval S.1, Tosatti E.2 , Kohanoff J.3, Lasave J.1, and Migoni R.1

1 Instituto de Física Rosario (CONICET-UNR), Argentina; 2 SISSA, Trieste, Italy;

3 Queen's University, Belfast, North Ireland, UK

In 1939 Robertson and Ubbelohde observed that Deuterium substitution for Hydrogen may lead to structural changes in H-bonded compounds.1 H-bonded ferroelectrics, whose transition happens when Hydrogens order off-centred in the bridges, show a dramatic isotope effect on Tc upon deuteration. Typical is the KDP (KH2PO4) family of materials. In 1960 Blinc et al.2 explained this effect in KDP based on the supposition that H tunnels between two equivalent off-centred positions in the bridge between PO4 tetrahedra. However, the Ubbelohde effect was not taken into account. In fact, the lattice constants of KDP grow significatively upon deuteration. Since 1978, X-ray and high-resolution neutron measurements in H-bonded ferroelectrics showed linear correlation between Tc and several structural parameters, particularly the O-H···O bridge length.3 Thus the tunneling model required to be revised. By means of ab-initio DFT calculations we found that the observed bistable H distribution in the bridges can only be explained if correlated motions of H clusters are considered, the required cluster size being extremely large if relaxation of the heavier atoms is not allowed.4 Thus, the mass change alone, due to deuteration, is not enough to explain the huge isotope effect in Tc. It is necessary to consider the structural changes arising from nucleae localization grow in the H-bridges upon deuteration, which is accompanied by electronic localization. This weakens the H-bond, which becomes then longer and leads to further localization, and so long, in a self-consistent form. This process was qualitatively simulated through a model we had proposed.4 By means of analogous calculations we explain the origin of antiferroelectricity in the isomorphous compound ADP, where A (NH4) substitutes K in KDP. ADP shows also a huge isotope effect upon deuteration. The feedback effect between tunneling and structural modifications observed in the H-bonded ferroelectrics is a phenomenon of wider implications, particularly important in many biological process. [1] Robertson J.M. and Ubbelohde A.R.; Proc. Royal Soc. London A 170, 222 (1939) [2] Blinc R.; J. Chem. Solids 13,204 (1960) [3] McMahon et al.; Nature 348, 317 (1990) [4] Koval S., Kohanoff J., Migoni R. and Tosatti E.; Phys. Rev. Lett. 89, 187602 (2002) Keywords: ferroelectric, H-bond, KDP, ab-initio e-mail: rmigoni@ifir-conicet.gov.ar

52

53

D- Soft Matter Physics

54

55

OD-1- Studies on biomembrane models

Oliveira R.G.1

1CIQUIBIC-Departamento de Química Biológica, Fac. C. Químicas, Universidad Nacional de Córdoba, Argentina

Cell membranes are lamellar structures formed by the self-assembling of lipid

bilayers associated with proteins. Due to the amphipathic nature of these molecules, they form a monomolecular layer at the air/water interface in a half membrane-like structure. These films (monolayers) can be studied in a Langmuir trough as a function of temperature, molecular area and surface pressure, rendering valuable thermodynamic data, analogous to the conventional temperature, volume and pressure phase diagrams. Langmuir troughs can be coupled to other equipment, like fluorescence and Brewster angle microscopes, as well as electrodes to measure and apply electrostatic fields. This allows observing and manipulating the membrane interface from top at the micrometer level, and studying membrane domains. Additionally, thickness at the nanometer level can be estimated. For accurate determination of the out-of-plane structure (scattering length density profile) as well the in-plane (acyl chain order), powerful x-ray scattering sources (high brilliance synchrotron beamlines) are needed. Monolayers are especially useful because they allow for manipulation and observations very difficult to achieve in other systems. On the other hand, bilayers and multilayers can be studied in aqueous suspension by using weaker x-ray (or neutron) beam sources. Although less manipulable, these are more similar to the structure of the biological membrane. In this presentation, we show results on natural systems like spinal cord myelin, mainly concerning the membrane homogeneity-heterogeneity problem, and the influence of ions and other environmental variables. The addition of Na+ or Ca2+ in myelin leads to a permanent phase separation along the compression isotherm. On the contrary, the suppression of salts leads to phase homogenization at high surface pressure. A similar trend is observed in multilayers.

Keywords: biomembrane, biophysics, cell membrane, Email: oliveira@fcq.unc.edu.ar

56

OD-2- Dynamical heterogeneities and phase separation in a

supercooled liquid

Cammarota C.1, Cavagna A.2, Giardina I.2,Gradenigo G.3, Grigera T. S.4, Parisi G.1,

Verrocchio P.3

1Dipartimento di Fisica, Sapienza Università di Roma, Italy; 2Istituto Sistemi

Complessi, CNR, Roma, Italy; 3Dipartimento di Fisica, Università di Trento, Italy; 4INIFTA y Departamento de Fisica, Universidad Nacional de La Plata, Argentina

We study dynamic heterogeneities in a model glass-former whose overlap with a

reference configuration is constrained to a fixed value. We find that the system phase-separates into regions of small and large overlap, indicating that a nonzero surface tension plays an important role in the formation of dynamical heterogeneities. We calculate an appropriate thermodynamic potential and find evidence of a Maxwell's construction consistent with a spinodal decomposition of two phases. Our results suggest that even in standard, unconstrained systems dynamic heterogeneities are the expression of an ephemeral phase-separating regime ruled by a finite surface tension. Keywords: supercooled liquids, dynamical heterogeneities, surface tension, Monte Carlo simulations Email: tgrigera@inifta.unlp.edu.ar

57

OD-3- Conformations of flexible charged polymers in the framework

of continuous solvent models

Roig A.R.1, Alessandrini J.L.2,3

1Facultad de Ingeniería, Universidad Nacional de La Plata, Argentina; 2Departamento de Física e IFLP, Facultad de Ciencias Exactas, Universidad Nacional de La Plata;

3CIC, Provincia de Buenos Aires, Argentina

The exact treatment of the electrostatics of polyelectrolytes dissolved in polar solvents is beyond the present computational facilities but continuous solvent models capture the relevant physics of the problem. The electrostatic component of the solvation energy depends on the instantaneous conformation of the solute and its exact contribution for polyelectrolytes requires the numerical solution of Poisson equation (or the Poisson Boltzmann equation, in the presence of added salt) for each equilibrium configuration.

The Generalized Born model gives an approximate treatment of the solvation energy assuming paiwise interactions between charged monomers, described by spheres with effective size, the Born radius. These parameters are typically treated in macromolecules like proteins as adjustable parameters that reflects the effects of the water structure in the vecinity of each ion. But, for flexible polyelectrolytes, they depend also on the solute conformation.

Monte Carlo simulations of the equilibrium conformations of flexible polyelectrolyte models with electrostatic solvation energy included were performed using conformational dependent Born radii evaluated with appropiate algorithms. The electrostatic swelling of the polyelectrolytes appears to be higher than that predicted by mean field theories. Keywords: Electrostatics, Polyelectrolytes, Solvent models, Born radius Email: alessan@fisica.unlp.edu.ar

58

OD-4- Adsorption of classical fluids on planar walls

Szybisz L.1,2,3, Sartarelli S.A.4

1CONICET, Argentina; 2CAC-CNEA, Argentina; 3DF-FCEyN-UBA, Argentina; 4IDH-UNGS, Argentina

The adsorption of noble classical gases on single planar walls and filling of slits

with identical walls are investigated in the frame of a density functional theory. It is assumed that fluid atoms interact via a recently proposed effective attractive pair potential [1] with strength, εff, which reproduces the experimental data of the surface tension of the liquid-vapor interface at the bulk coexistence curve interface over the entire range of temperatures, T, from the triple point, Tt, to the critical point, Tc [1,2]. The behavior of the adsorbate in the cases of substrates of alkali metals and alkaline-earth metal Mg is analyzed as a function of temperature. The adsorption on the walls is described by ab initio potentials characterized by a well depth, Wsf. In this way the systems were studied in the framework of a realistic approach.

The wetting properties were studied over the entire range temperatures between Tt and Tc. Above the wetting temperature Tw the adsorption isotherms for alkali metals show first-order phase transitions exhibiting prewetting lines (PW). The PW lines terminate at the critical prewetting temperature, Tcpw. We found that for small coverages, a slit built up of two identical planar walls is always filled by forming two symmetric vapor films, one at each wall. For increasing coverage the behavior depends on the ratio Wsf /εff and temperature T. In the case of alkali metals, asymmetric density profiles are obtained leading to the so-called spontaneous symmetry breaking (SSB) effect [3]. These asymmetric solutions occur even above Tw in a range of average densities ρ*ssb1 < ρ*av < ρ*ssb2, which diminishes with increasing temperature and eventually the SSB disappears at a critical temperature, Tsb, which coincides with Tcpw observed in the adsorption on a single wall. For T>Tcpw the slit is filled symmetrically up to the phase transition to capillary condensation. In this way a correlation between the disappearance of the SSB effect and the end of prewetting lines observed in the adsorption on a one-wall planar substrate is established.

In summary, it was found that when for a given adsorbate-substrate combination the adsorption on a single wall exhibits a first-order wetting transition then asymmetric profiles always appear in the filling of an equivalent slit. It is shown that for a rather strongly attractive surfaces reentrant asymmetric filling may be obtained at a fixed value of T.

[1] S. A. Sartarelli, L. Szybisz, and I. Urrutia, Phys. Rev. E 79, 011603 (2009). [2] S. A. Sartarelli and L. Szybisz, Phys. Rev. E 80, 052602 (2009). [3] S. A. Sartarelli and L. Szybisz, J. Chem. Phys. 132, 064701 (2010).

Keywords: Fluid Structure, Density Functional, Wetting, Adsorbed Films Email: szybisz@tandar.cnea.gov.ar

59

OD-5- Application of field-cycling NMR relaxometry to the study of

ultrasound-induced effects in the molecular dynamics and order of

mesomorphic materials

Anoardo E.1

1Facultad de Matemática, Astronomía y Física – Universidad Nacional de Córdoba.

Instituto de Física Enrique Gaviola – CONICET. Córdoba – Argentina.

A salient characteristic of nuclear magnetic resonance (NMR) techniques is the possibility to scan nuclear spins evolutions within a broad Larmor frequency range. Special instrumentation was developed to extend nuclear spin relaxation studies up to proton Larmor frequencies in the sub-kilohertz regime, a technique known as field-cycling NMR relaxometry. This presentation refers to an experimental version where the sample under study is simultaneosly subjected to ultrasonic irradiation. The fact that ultrasound couples slecetively to the collective dynamics of liquid crystals, offers new insights for the study of the molecular dynamics in these materials using NMR relaxation.

The experimental technique was successfully used to detect different ordered states created in a nematic specimen through magnetoacoustic manipulation. Depending on the initial order imposed to the molecular system, the acoustic and magnetic cycles of the experiment and the sample temperature, metastable states displaying long-term memory effects can be created within the volume. It was show that NMR relaxometry at low fields is highly sensitive to the presence of such metastable states in the volume. Keywords: NMR relaxometry, field-cycling, ultrasound, mesomorphic materials. Email: anoardo@famaf.unc.edu.ar

60

OD-6- Flujos de líquidos poliméricos confinados entre sustratos

blandos: inversión de flujo y aplicaciones a Microfluídica

Pastorino C.1, Muelller M.2

1Centro Atómico Constituyentes CNEA-CONICET, Av. Gral Paz 1499, San Martín

(1650), Pcia. Buenos Aires Argentina; 2Institut für Theoretische Physik, Georg-August-Universität, Goettingen, Alemania

El presente trabajo se enmarca dentro del emergente campo de la Microfluídica.

En él, el volumen de líquido involucrado está en la escala de los picolitros, con lo cuál la superficie confinante es significativa respecto del volumen y ejerce una influencia importante en la dinámica en volumen del líquido. Presentaremos el estudio de flujos de fluidos poliméricos confinados entre sustratos blandos, mediante simulaciones numéricas de dinámica molecular. Utilizamos cadenas fijadas a una pared rígida (cepillo polimérico) como modelo de sustrato blando deformable, que forma una interfase con el líquido para un determinado rango de densidades de fijado. Encontramos un movimiento cíclico de las cadenas fijadas, que da origen a una inversión del flujo total (densidad de momento) en una región particular del sustrato, cercana la interfase líquido-cepillo. El efecto es lo suficientemente significativo como para invertir la velocidad de trazadores ubicados en la interfase líquido-cepillo. Analizaremos las posibilidades de su utilización en separación de moléculas y señalización en desarrollos de microfluídica.

Keywords: Microfluídica, polímeros, dinámica molecular

61

E- Physical Chemistry

62

63

OE-1- An analysis of the carboxylate stretching vibrations in the Cu(II)

complexes of amino acids

Baran E.J.1, Torre M.H.2

1Universidad Nacional de La Plata, Facultad de Ciencias Exactas, Centro de Química Inorgánica (CEQUINOR, CONICET/UNLP), La Plata, Argentina; 2Universidad de la

República, Facultad de Química, Cátedra de Química Inorgánica, Montevideo, R.O. del Uruguay

Besides iron and zinc, copper is the most ubiquitous transition metal present in living organisms, and is involved in a large number of important functions and processes. Copper metalloenzymes are present in oxidases (laccases, ascorbate oxidase, galactose oxidase, amine oxidases), participate in oxygenation and dismutation reactions (plastocyanins, tyrosinases, superoxide dismutases) and even in oxygen transport in arthropods and mollusks (hemocyanins). On the other hand, copper compounds and, in particular, Cu(II) complexes present great pharmacological interest as several of them show an important number of effects, including anti-inflammatory, antiulcer, anticonvulsant and even anti-tumoral activity. In this context, copper complexes of most of the simplest amino acids showed a particular relevance, appearing even useful for copper supplementation in human and veterinary medicine. Due to the commented importance of these complexes, since the last ten years we have been investigating, in a systematic way, their vibrational-spectroscopic behaviour by means of IR and Raman measurements.

In this presentation the behavior of the stretching vibrations related to the carboxylate groups of nineteen Cu(II) complexes from amino acids (aa) of general composition Cu(aa)2 or Cu(aa)2⋅nH2O is analyzed on the basis of the previously reported vibrational spectroscopic data and on the structural characteristics of these complexes.

Some general trends and tendencies are remarked and discussed. Some of the experimentally obtained results are also analyzed on the basis of the molecular orbital approach of Nara et al. (J. Phys. Chem. 100 (1996) 19812). In all cases, the spectroscopic results are consistent with the monodentate binding of the COO- groups to the metal center.

Finally, brief comments on the spectroscopic behaviour of a series of polymeric Cu(II) complexes of dipeptides are also presented.

Keywords: Copper(II), Amino acids, Carboxylate, Stretching vibrations. Email: baran@quimica.unlp.edu.ar

64

OE-2- Bonding analysis of Pd2H2 systems adsorbed

on graphene layers

López-Corral I.1, Germán E.1, Volpe M.A.2, Brizuela G.P.1, Juan A.1

1IFISUR, UNS-CONICET, Argentina; 2PLAPIQUI, UNS-CONICET, Argentina

In this work we report a bonding study of the adsorption of Pd2H2 systems on a

graphene layer, using the density-functional theory and the SIESTA code [1,2]. We modelled the graphene sheet by means of a periodically repeated tetragonal unit cell, consisting of 24 C atoms in a plane honeycomb structure. Different adsorption sites on the carbon surface and both molecular as dissociative Pd2H2 coordination structures were considered.

Our results show that the adsorption of the Pd2 dimer in a parallel approach respect to the graphene sheet is only 260 meV stronger than the adsorption of two individual Pd atoms located on remote sites, so palladium shows less preference to cluster than other transition metals adsorbed on carbon surfaces [3]. According to previous studies [4], we verified by means of Mulliken analysis that the C−Pd bonding involves a small donation from Pd 4d to C 2s orbitals and a higher back-donation from C 2p to Pd 5s orbitals. In presence of dihydrogen, both dissociative (PdH)2 and not dissociative Pd2(H2) systems are originated, developing similar binding energies for the bridge (at the midpoint of a C−C bond) or top (above a C atom) sites. On the contrary, adsorbed single Pd atoms originate preferably a molecular Pd(H2) structure, with a relaxed but not dissociated H−H bond [5]. As a result of the support interaction, Pd−Pd and Pd−H bonds are elongated regarding the un-supported Pd2H2 coordination structures, and the C−Pd interactions results weakened with respect to the free-H graphene/Pd2 system, reducing both donation from Pd 4d to C 2s orbitals as back-donation from C 2p to Pd 5s orbitals.

Finally, we found that the Pd−H bonding in the not dissociative adsorbed PdH2 and Pd2H2 systems comes from two cooperatively coupled intermolecular donor-acceptor delocalizations: the σ donation from H2 σ orbital to Pd 5s orbitals, and the π back-donation from Pd 4d orbital to H2 σ* orbitals. The analysis of the hydrogen molecular orbital occupation in these structures reveals that a second Pd atom adsorbed nearly to the PdH2 system enhances the σ donation and the π back-donation, destabilizing the H−H interaction, but these changes are small in all cases. In this way, we could assume that the dimerization effect for carbon-supported Pd atoms is limited and could not impact negatively on the hydrogen uptake of Pd-decorated graphene-based materials. [1] P. Ordejón, E. Artacho and J.M. Soler, Phys. Rev. B 53, R10441 (1996). [2] J.M. Soler, E. Artacho, J.D. Gale, A. García, J. Junquera, P. Ordejón and D. Sánchez-Portal, J. Phys.: Condens. Matter 14, 2745 (2002). [3] Q. Sun, Q. Wang, P. Jena and Y. Kawazoe, J. Am. Chem. Soc. 127, 14582 (2005). [4] I. Efremenko and M. Sheintuch, J. Catal. 214 (2003) 53–67. [5] I. López-Corral, E. Germán, A. Juan, M.A. Volpe and G.P. Brizuela, J. Phys. Chem. C (in press). Keywords: Graphene, Palladium, Hydrogen storage, DFT. Email: cajuan@criba.edu.ar

65

F- Medical Physics

66

67

OF-1- Magnetic field-assisted gene delivery

Casalini M.B.1, Schwerdt J. I.1, Mykhaylyk O.2, Morel G.R.1, Sánchez F.H.3, Goya R.G.1

1INIBIOLP-Histology B, University of La Plata (UNLP), Argentina; 2 Klinikum rechts

der Isar der TUM, München, Germany; 3 Institute of Physics, UNLP, Argentina

Gene therapy has undergone a remarkable development in the last 20 years with important advances having been made in the improvement of gene transfer and expression technology.

The association of viral vector-based gene delivery with nanotechnology now offers the possibility to develop more efficient and less invasive gene therapy strategies for a number of major pathologies like Parkinson´s and Alzheimer´s disease. This approach combines Magnetic Drug Targeting (MDT) and magnetofection, two novel methodologies based on the use of magnetic nanoparticles (MNP). The concept of MDT was introduced in 1978 by the group led by K. J. Widder and its goal is to concentrate magnetically responsive therapeutic complexes in target areas of the body by means of external magnetic fields. So far, the main application of MDT has been cancer therapy. Typically, magnetic microparticles (µm sized) or MNP (nm sized) associated to a therapeutic drug are intravascularly injected near the tumor blood supply and are concentrated into the tumor by means of an external magnetic field. This strategy has shown promising results in clinical trials. Magnetofection is a methodology developed in the early 2000’s by the group led by C. Plank in Munich. It is based on the association of MNP with nonviral or viral vectors in order to optimize gene delivery in the presence of a magnetic field.

In order to implement magnetofection in the brain we have constructed two adenoviral vectors, RAd-DsRed2 which expresses DsRed2, a red fluorescent protein from Discosoma, and RAd-GFP a vector expressing green fluorescent protein (GFP). The vectors were constructed by the two-plasmid method. These vectors were or are to be complexed with four types of magnetic nanoparticles (MNP) termed, PEI-Mag2 (S9), SO-Mag6-125, PB Mag1-4 and AdenoMag, all possessing a magnetite core and different polymeric coatings. Non complexed vectors were tested at varying multiplicities of infection (MOI) in different cell lines (HEK 293, B92, N2a and A549 cells) and showed pancellular expression of the corresponding reporter gene. In the rat brain, the vectors showed appropriate levels of expression in the hypothalamus, substantia nigra and the ependymal cell layer. Subsequently, MNP-RAd complexes were generated and tested on the above cell lines under the influence of an external magnetic field. Magnetic field-assisted reporter gene delivery (magnetotransduction) led to a MNP-dose dependent enhancement of gene expression. We conclude that our MNP-RAd complexes are suitable for magnetotransduction in vitro. These magnetic adenovectors are to be used in in vivo magnetotransduction studies in the rat brain. Keywords: nanotechnology –magnetic nanoparticles – gene delivery - magnetofection Email: goya@isis.unlp.edu.ar

68

OF-2- Current Status of Accelerator-Based Boron Neutron Capture

Therapy

Kreiner A.J.1,2,3, Bergueiro J.1,3, Di Paolo H.1,2, Castell W.1, Thatar Vento V.1,3, Cartelli D.1,3, Kesque J.M.1, Valda A.A.1,2, Ilardo J.C.1, Baldo M.1, Erhardt J.1, Debray M.E.1,2, Somacal H.R.1,2, Estrada L.1, Suarez Sandin J.C.1, Igarzabal M.1, Huck H.1,2, Padulo J.1, Minsky D.M.1,2,3,Herrera M.1,2,3, Gonzalez S.J.1,3,Capoulat M.E.1,2,3.

1CNEA, Argentina; 2UNSAM, Argentina; 3CONICET, Argentina.

The direct use of proton and heavy ion beams for radiotherapy is a well

established cancer treatment modality, which is becoming increasingly widespread due to its clear advantages over conventional photon-based treatments. This strategy is suitable when the tumor is spatially well localized. Also the use of neutrons has a long tradition. Here Boron Neutron Capture Therapy (BNCT) stands out, though on a much smaller scale, being a second-generation promising alternative for tumors which are diffuse and infiltrating.

On this sector, so far only nuclear reactors have been used as neutron sources. In this paper we describe the current situation worldwide as far as the use of accelerator-based neutron sources for BNCT is concerned (so-called Accelerator-Based (AB)-BNCT).

In particular we discuss the present status of an ongoing project to develop a folded Tandem-ElectroStatic-Quadrupole (TESQ) accelerator at the Atomic Energy Commission of Argentina. The project goal is a machine capable of delivering 30 mA of 2.4 MeV protons to be used in conjunction with a neutron production target based on the 7Li(p,n)7Be reaction. These are the specifications needed to produce sufficiently intense and clean epithermal neutron beams to perform BNCT for deep-seated tumors in less than an hour. Keywords: BNCT, Accelerator-based BNCT, Tandem-Electrostatic Quadrupole, Medical physics Email: kreiner@tandar.cnea.gov.ar

69

OF-3- Single-channel ionic conductances in smooth muscle cells from

human umbilical artery. Martín P.1, Roldán Palomo A.R.1, Enrique N.1, Rebolledo A.1, Piccinini L.1, Vilche M.1,

Milesi V. 1 1 GINFIV, Depto. de Ciencias Biológicas, Fac. de Ciencias Exactas, UNLP, Argentina.

Our aim was to study the diversity of ionic channels activated by voltage stimuli in isolated human umbilical artery (HUA) smooth muscle cells. We used the patch-clamp technique in the cell-attached (CA) and the inside-out (IO) configurations.

The experiments were performed in symmetric K+ conditions recording the stationary activity of channels in CA configuration and after that, the patch was excised and new recordings were performed in IO configuration (K+ symmetric condition and a very low Ca2+ concentration facing with the intracellular side of the membrane patch). In such recording conditions, selective K+ channels and non selective cationic channels would be recorded, both of which have important physiological roles in vascular smooth muscle. K+ channels are important for the maintenance and regulation of cell membrane potential, its activation producing hyperpolarization and less cell excitability, while the activation of non selective cationic channels induce depolarization and increase cell excitability.

More that one type of channel appeared in each membrane patch. In the CA configuration (52 cells) the frequency of apparition of the different conductance values was: 29 % of the cells showed high conductance channels (range: 200-300 pS); 61% and 50 % showed intermediate conductances included in the range of 100-200 pS and 50-100 pS, respectively; and finally, 27 % of the cells showed channels in the low conductance range (50-30 pS). In all cases, the frequency of apparition of ionic channels diminished in the IO configuration, where the values for the same ranges of conductances were: 15 % for high conductances, 30 % and 32% for intermediate conductances and 17% for low conductances. It is important to note that, in contrast to the CA configuration where the cell is intact, in IO the membrane patch is detached from the cell and so, the ionic channels whose activity depend on intracellular factors may have disappeared or diminished. Alternatively, some channels may have been inhibited by intracellular factors in CA configuration and once detached form the cell could become active. Some of these properties were further studied: for example, in HUA smooth muscle cells, an increase in Ca2+ concentration in the solution facing the intracellular side of cell membrane increased the activity of some K+ ionic channels, such as the high-conductance voltage and Ca2+ activated K+ channel, which is highly expressed in smooth muscle cells. A decrease in the pH (from 7.4 to 6.8) of the solution in contact with the intracellular side of cell membrane activated high and intermediate ionic conductances. We also tested on IO patches the effects of intracellular second messengers like arachidonic acid, observing that this substance is able to activate high and intermediate ionic conductances. So far, we have presented a description of ionic channels present in these native smooth muscle cells and the effect of some of their physiological regulators. Further research is necessary to increase the knowledge of the electrophysiological properties of the complete diversity of ionic channels and their possible mechanisms of regulation. Keywords: patch clamp, ionic channels, smooth muscle cells Email: piterdb@yahoo.com

70

71

G- Optics

72

73

OG-1- Secrecy in Optics

Tebaldi, M.1, Bolognini, N.1,2, Torroba, R.1

1Centro de Investigaciones Ópticas (CCT-La Plata, CIC) and UID OPTIMO, Facultad de Ingeniería, Universidad Nacional de La Plata, Argentina. 2Facultad de Ciencias

Exactas, Universidad Nacional de La Plata, La Plata, Argentina

Protecting information from unauthorized users is the main task for encrypting methods. Optical processing, due to its inherent parallelism, represents an important alternative in this field. These optical methods are based on protecting the information to be transmitted by transforming the original data into white-noise data. Then, the signals should be hidden to human perception, keeping in consequence secret. The digital recording and processing allows the practical implementation with a reasonable quality.

In all cases, the key codes should be difficult to find by chance and the decryption procedure should be relatively easy for receivers with the correct keys. To successfully retrieve the input information it is necessary not only to know the key code, but also to know the extra optical parameters. Then, the optical parameters (for instance polarization, wavelengths, etc) act as extra encryption keys, thus improving the robustness.

Indeed, these optical parameters are suitable to store multiple encrypted images in a single recording medium in order to bring the chance for multiple users. In multiplexing arrangements, the encryption of an input image is associated to a determined status of the optical encrypting parameters. There exist a bi-univocal relation between each input image and its encrypted version.

We can extend the idea to a single user with the capability of decoding a whole sequence of individually encrypted but associated events. This new concept thus involves the idea of encoding a dynamic situation. Besides, to retrieve the complete dynamic input information, it is necessary not only to properly decrypt the images but also to compose them in a synchronized way.

Keywords: Optical encryption, Opto-digital image processing, Fourier Optics, Speckle. Email: robertot@ciop.unlp.edu.ar

74

75

H- Biophysics

76

77

OH-1- Electric field effects on the structure, function and dynamics of

redox proteins

Murgida D.H.

INQUIMAE-Department of Inorganic Chemistry, School of Sciences, University of Buenos Aires, Argentina

Most of the biochemical and biophysical processes of redox proteins take place

at membranes and thus under the influence of strong local electric fields which are likely to affect the structure as well as the reaction mechanism and dynamics. To analyse such electric field effects we have employed biomimetic interfaces for protein attachment that consist of membrane models deposited on nanostructured metal electrodes. For such devices, surface enhanced resonance Raman and infrared absorption spectroscopy are powerful techniques to disentangle the complex interfacial processes of proteins in terms of rotational diffusion, electron transfer, as well as protein and cofactor structural changes. The atomistic interpretation of the experiments is guided by molecular dynamics (MD) simulations and electron pathways calculations of the biomimetic complexes. Using this approach we have investigated a variety of heme soluble proteins (cyt-c; cyt-b562, cyt-c6, iso-cyt-c) that act as electron shuttles in photosynthetic and respiratory chains of different organisms, as well as membrane terminal respiratory enzymes.

In general terms it is concluded that the overall ET rates are determined by the interplay of protein dynamics and tunnelling probabilities at the different conformations along the dynamics, which in turn is strongly modulated by the local electric field. It is also shown that sufficiently strong electric fields are able to induce reversible structural changes of the proteins, affecting thermodynamic and kinetic parameters of the ET reactions. Based on these results it is hypothesized that transmembrane potentials play a regulatory role in respiration and photosynthesis via a feedback inhibition mechanism. In addition, it is shown that electric field effects may be functional for the switch from the redox to the peroxidase function of cytochrome c, one of the key events in programmed cellular death. Keywords: Raman, protein electron transfer, protein dynamics, electric field effects Email: dhmurgida@qi.fcen.uba.ar

78

OH-2- Photosensitized protein modification

Borsarelli C.D.1, Jovin T.M.,2 Alarcón E.3, Aspee A.3

1INQUINOA-CONICET. Universidad nacional de Santiago del Estero (UNSE), Argentina; 2MPI-Biophysical Chemistry, Germany; 3Universidad de Santiago de Chile

(USACH), Chile. Most proteins are virtually transparent to the photochemically active portion of

the solar spectrum (320-700 nm), making unfeasible photochemical processes for direct excitation of their aromatic amino acids. However, given the organized and macromolecular nature of proteins, they have specific interaction sites with many natural or artificial molecules that can act as photosensitizers. These molecules strongly absorb in the UVA-Vis spectrum and the interaction of the photosensitizer excited states with some of the amino acid residues and / or dissolved oxygen induces the formation of reactive intermediates that can modify the structure and function of the protein.

In the present work, we present a couple of examples of photosensitized protein modification. First, the new photophysical and photochemical properties of an adduct formed between zinc phthalocyanine (ZnPc) and bovine serum albumin (BSA) and the photo-induced oxidative modification of the protein are discussed.

The second example of photosensitized protein modification will be on the formation of covalent oligomers of α-synuclein (αS) produced by photo-oxidative generation of tyrosyl radicals using the photosensitizer redox system formed by Ru(II) trisbipyridyl dication complex (Ru(bpy)3

2+ and ammonium persulfate (APS). In this case, the formation kinetics and spectroscopical properties of di-tyrosine crossing protein oligomers (e.g. dimers, trimers, ... n-mers) as a function of irradiation was evaluated.

These above results demonstrate that depending on the photosensitizer association and/or the nature of the photoinduced process (electron or energy transfer) can influence both the photophysical properties of the sensitizer and the protein photochemical modification (e.g. photo-oxidation, photo-crosslinking, etc.).

CBD acknowledges the financial support of the ANPCyT (PICT2006-1090), CONICET, and Alexander von Humboldt Foundation of Germany for a Georg Forster Fellowship. Keywords: Photochemistry, Proteins, Spectroscopy, Kinetics Email: cborsarelli@yahoo.com.ar; cborsa@unse.edu.ar

79

OH-3- Advances in the development of bioabsorbable scaffolds for

dermo-epidermal tissue engineering: hydrophilic enhancement and

hydrophobic recovery of PHAs

Hermida, E.B.1,2, Arenas, C.D.1

1 Instituto Sabato, UNSAM-CNEA & U. A. Materiales, CNEA, 2 CONICET

Advances in medicine and tissue engineering promote the development of new

materials, particularly bioabsorbable materials that could be used as scaffolds for skin regeneration. These materials must be suitable for cell growth and proliferation, and have to degrade in non-toxic substances once the scaffold has fulfilled its purpose.

Several polyhydroxyalkanoates (PHAs) are bioplastics produced by microorganisms that proved to be bioabsorbable. However, they are highly hydrophobic and this is a disadvantage for cell fixation and growth. Other important point is the size and interconnection of the pores since the scaffold must allow cells to migrate, grow and keep its normal functionality.

This contribution explores the effect of plasma treatments to enhance the hydrophilicity of compression moulded scaffolds of poly(hydroxybutyrate) (PHB) poly(hydroxyburyrate-co-hydroxyvalerate) (PHBV), two of the well-known PHAs. Furthermore, we analyzed the hydrophobic recovery in different environments and determine the condition that assures a retardation of the ageing effect. AFM images aid to follow the roughness changes after the plasma treatment, due to the rearrangement of the amorphous chains of PHBV that have high mobility at room temperature. Keywords: bioabsorbable scaffold, tissue engineering, polyhydroxybutyrate, hydrophilicity. Email: ehermida@cnea.gov.ar

80

OH-4- Evaluating the significance of Noise Correlation in the neural

code

Montani F.1

1IFLYSIB, Universidad Nacional de La Plata, La Plata, Argentina.

Simultaneous recordings from multiple neural units allow us to investigate the activity of very large neural ensembles. To understand how large ensembles of neurons process sensory information it is necessary to development suitable statistical models to describe the response variability of the recorded responses. We investigate the internal dynamic of LFPs and action potential signals obtained from multisite extracellular microelectrode recordings of rat visual cortex using an Information Theoretical Approach, and by means of analytically solvable models. Our findings show that decoding algorithms should take the correlational structure of the neural activity into account, making the problem high dimensional, and that the low frequency bands play a crucial role in internal dynamics of the rhythmic activity patterns in the brain. Keywords: Neural code, Information Geometry, Noise Correlation, Rhythmic activity patterns Email: fmontani@gmail.com

81

OH-5- Protein amyloidoses: From biophysics to disease therapy

Fernández C.O.1,2, Zweckstetter M.2, Griesinger C.2

1Institute of Molecular and Cell Biology of Rosario,National University of Rosario, CONICET, Rosario, Argentina; 2Max Planck Institute for Biophysical Chemistry,

Göttingen, Germany

The misfolding of proteins into a toxic conformation is proposed to be at the molecular foundation of a number of neurodegenerative disorders including Alzheimer and Parkinson’s disease. One common and defining feature of protein misfolding diseases is the formation and deposition of amyloid-like fibrils. The aggregation of the protein alpha-synuclein (AS) is a critical step in the etiology of Parkinson’s disease (PD) and other neurodegenerative synucleinopathies. The study of the structural and toxic mechanisms related to AS amyloid formation is critical to advance in the design of a therapeutic strategy. The identification of aggregation inhibitors and the investigation of their mechanism of action are fundamental in the quest to mitigate the pathological consequences of amyloid formation. By the combined application of a battery biochemical and biophysical tools we have addressed structural and molecular unresolved details related to the mechanistic rules that direct the anti-amyloid effect of small molecules on AS amyloid fibril formation.

Keywords: Neurodegeneration, Amyloid, Structural Biology, NMR E-mail: fernandez@ibr.gov.ar

82

OH-6- Structure-function relationships in apolipoprotein A-I:

Functional importance of the helix registry in discoidal HDL

Prieto E.D., Cuellar L.A., Cabaleiro L.V., Garda H.A.

Instituto de Investigaciones Bioquímicas de La Plata (INIBIOLP). CONICET/UNLP

Apolipoprotein A-I (apoAI), the main protein of high density lipoproteins (HDL), plays a key role in cholesterol homeostasis and prevention of cardiovascular diseases. This amphitropic protein exchanges among a lipid-free and different lipid-bound forms during its functional cycle. It is composed of a series of amphipathic α-helical repeats that fold in a globular bundle. Upon lipid binding, the bundle is opened and helix-helix interactions are substituted by helix-lipid interactions. Most of the amphipathic α-helical repeats have a type A charge distribution in the helix polar face. This charge distribution allows the interaction with membrane or HDL surfaces with the long helix axis parallel to the lipid surface, forming electrostatic interactions with the phospholipid polar groups and hydrophobic interactions with the hydrocarbon chains. However, some α-helical repeats as the 3-4 pair, have a different charge distribution at their polar face and behave differently. We have previously detected (J Biol Chem 276:16978, 2001) that this apoAI region inserts very deeply into the membrane lipid bilayer. More recently, we determined the membrane insertion topology and proposed that an intermolecular bundle of both 3-4 helix pairs in a membrane bound apoAI dimer is inserted with the long helix axis roughly perpendicular to the membrane surface (Biochemistry 50:466, 2011).

Discoidal HDL complexes (dHDL) are key intermediates in HDL biogenesis. The proposed intermolecular bundle of the 3-4 helix pairs can also be formed in dHDL, where it could act as a reversible membrane-anchoring domain to modulate lipid exchange with membranes. Most of the present knowledge of dHDL is based on studies with reconstituted complexes of dimeric apoAI obtained by cholate-dialysis. However, dHDL can also be generated by the spontaneous reaction with phospholipid vesicles at the temperature range of the gel/liquid-crystalline phase transition, a process that could be mechanistically similar to the "in vivo" apoAI lipidation. Recent studies from our lab evidenced that spontaneously generated dHDL are more active in promoting cell cholesterol efflux than those obtained by cholate dialysis. Measurements of intermolecular distances by fluorescence resonance energy transfer (FRET) in dimeric dHDL reconstituted with a series of single tryptophan mutants and extrinsically labeled cysteine mutants, indicate that: a) Dimeric dHDL obtained by cholate dialysis are a mixture of coexisting configurations with variable helix registry. As reported by others, they contain a main population with helices 5 of each monomer in juxtaposition (LL5/5 configuration) and a minor population with helix 5 of one monomer in contact with helix 2 of the other (LL5/2 registry); and b) In dimeric dHDL spontaneously generated at the phospholipid phase transition, data indicate the existence of only one population with the LL5/2 configuration. Together, these data indicate that only the LL5/2 configuration is active in promoting cell cholesterol efflux. This fact can be explained on the basis of the intermolecular bundle of the 3-4 helix pairs that can only be formed with the LL5/2, but not with the LL5/5 registry.

Keywords: Apolipoprotein A-I, High Density Lipoproteins, Fluorescence Resonance Energy Transfer, Cell Cholesterol Efflux Email: hgarda@atlas.med.unlp.edu.ar

83

OH-7- Physical principles underlying the structural stability of helical

membrane proteins

González Flecha F.L.

Laboratorio de Biofísica Molecular, Instituto de Química y Fisicoquímica Biológicas,

Universidad de Buenos Aires- CONICET, Argentina

Membrane proteins constitute a large fraction of proteomes, and a number of pathologies appear to be related to alterations in their folding. The native folded conformation of membrane proteins resides in a free energy minimum, which is determined by interactions of the peptide chains with each other, with the lipid bilayer, and with water. While a considerable amount of literature deals with the structural energetics of water-soluble proteins, relatively little is known about the forces that determine the stability of membrane proteins. This is likely rooted in the experimental difficulties linked to their characterization, such as low-yield purification, scarcity of adequate heterologous expression systems, and poor stability in solubilization detergents. In addition, their intrinsic physicochemical properties required for adaptation to the complexity of the heterogeneous membrane–water environment also appear to hamper efforts to characterize their reversible unfolding. To date, there are only five α-helical membrane proteins for which reversible unfolding have been thermodynamically characterized. In this work we will discuss the current view on the stability of this biologically and biotechnologically important class of membrane proteins against unfolding induced by heat, pressure, chemical denaturants and freezing. It can be noted that some intrinsic properties resemble features of soluble proteins, but there are distinct differences arising from specific interactions within the membrane. Keywords: Membrane protein unfolding, Thermodynamics, P ATPases, Email: lgf@qb.ffyb.uba.ar

84

OH-8- Applications of Positron Annihilation Spectroscopy to the study

of biological systems

Chain C.Y.1,2, Pasquevich A.F.1-3

1Departamento de Física, Facultad de Ciencias Exactas,

Universidad Nacional de La Plata, Argentina; 2 Instituto de Física La Plata (IFLP)-CONICET; 3 Comisión de Investigaciones Científicas- Provincia de Buenos Aires,

Argentina.

Positron Annihilation Spectroscopy (PAS) is a branch of γ- ray spectroscopy that gives information of the positron lifetime and the kinetic energy spectrum of the electrons in the material under study. The physical basis of positron annihilation resides in its capability to sense electron density in the bulk of the material. Several complementary methods are used to characterize porous materials using PAS. Among these techniques, the most common are Positron Annihilation Lifetime Spectroscopy (PALS), Doppler-broadening Spectroscopy (DBS) and Angular Correlation of Annihilation Radiation (ACAR).

PALS gives account of the characteristic positron lifetimes in the material of study, fact that is associated with the size and relative fraction of the nano- free volumes or nanopores present in the sample. In DBS the Doppler broadening of the annihilation radiation is measured while ACAR focuses in the relative angle between the two 511 keV gamma rays that result from the annihilation. DBS and ACAR are designed to be sensitive to the momentum of the electron-positron pair at the moment of the annihilation. This momentum can probe the electronic and physical environment in which the positrons are implanted. In addition, the combination of PALS and DBS provides a powerful tool for the identification of defects.

In spite of the success of PAS in probing atomic and molecular defects in solids and semiconductors, the technique has been scarcely applied in life science research. Meanwhile, in the last two decades, this spectroscopy has been used to study free volume properties and free radical status in a variety of chemical and biological systems including polymers, contact lenses and biomembranes. Among the biological field, it is worth mentioning the investigations on protein dynamics and tumoral tissues. A brief discussion of the mentioned topics and the advantages and disadvantages of these types of studies is presented. Keywords: polymers, contact lenses, proteins, tissues Email: yamil@fisica.unlp.edu.ar

85

I- Humanistics

86

87

OI-1- Fundadores, pioneros y tradición:

Usos del pasado en la conmemoración de una institución científica

argentina

Spivak L’Hoste A.1

1Conicet/ Universidad Nacional de General San Martín, Argentina

El 1º de agosto de 2005 se celebró el cincuenta aniversario del Instituto Balseiro, un centro argentino de excelencia en la formación de grado y postgrado de físicos e ingenieros que está ubicado en la ciudad de San Carlos de Bariloche al norte de la Patagonia argentina. Ese aniversario motivó la organización de una jornada conmemorativa que fue dividida en dos momentos: un acto público realizado en un teatro del centro de la ciudad y un almuerzo destinado exclusivamente a los miembros de la institución y llevado a cabo en su propio predio. Esos momentos, pese a variar en las prácticas y ejercicios que le dieron forma, definieron un mismo eje de festejo: la celebración de la tradición. Esto es, de una versión legitimada del pasado que resaltó, en particular, la importancia de aquellas personas que se señalaron como los responsables de la puesta en funcionamiento de dicho instituto.

Esta presentación tiene por objetivo sintetizar algunos de los resultados de un análisis etnográfico de esa conmemoración elaborado en el marco de mi tesis doctoral en ciencias sociales. Más precisamente, tiene por objeto presentar aquellos resultados relacionados con las modalidades y los efectos de la representación y transmisión –la performance- de esa tradición al seno de dicha ceremonia. Desde una perspectiva más general intentaré mostrar, además, como esta propuesta metodológica y analítica resulta pertinente a la hora de descifrar algunas de las dinámicas de las instituciones científicas y contribuir de esa manera a las reflexiones de los llamados estudios sociales de la ciencia y la tecnología. Palabras clave: conmemoración, tradición, etnografía, institución científica. Email: anaspivak17@gmail.com

88

OI-2- Cien años de la visita de Marconi a la Argentina

Linares C.

Para los festejos del centenario de la Revolucion de Mayo se invitaron a personalidades relevantes del momento.Marconi fue una de ellas ya que había conmocionado al mundo con su sistema de Radiotelegrafia.Pero el verdadero motivo de la visita era establecer la posibilidad de instalar una estación de Comunicaciones con Europa y Canada. En ese momento Marconi estaba en una feroz batalla técnica y comercial con Alemania,ya que los Sistemas de la TELEFUNKEN lo superaban en rendimiento y debía defender su sistema. ¿Quién triunfo? Lo desarrollare en mi charla con abundante información. Palabras clave: Marconi, centenario, Telefunken, radiotelegrafía

89

OI-3- On the scientific work of Richard Gans in La Plata

Galles, C.D.

FCEIA, Universidad Nacional de Rosario, Argentina

The German physicist, Richard Gans (1880–1954), carried out significant

research at La Plata National University. During his first stay there, from 1912 to 1925, he was Director of the Institute of Physics. Among his research dating from this period, his work on quantum physics and the phenomena of the diffusion of light, over which he conducted a veritable experimental battle with Raman, are of particular interest, as well as that he did on ferromagnetism and colloids. These works were published in the journal Contribución al estudio de las ciencias físicas y matemáticas published by the Faculty of Physics, Mathematics and Astronomy at this university and in german journals. After spending more than two decades in Germany, Gans returned to La Plata in 1947. The research he carried out at this time show him to be fully versed in modern developments. In this paper the scope of his research will be reviewed, paying particular attention to certain of his works. Keywords: La Plata, Gans, History, Physics Email: galles@fceia.unr.edu.ar

90

OI-4- Margrete Heiberg-Bose: pionera de las ciencias exactas en la

Argentina

von Reichenbach M.C.

Departamento de Física, Facultad de Ciencias Exactas,

Universidad Nacional de La Plata, Argentina Las investigaciones sobre los comienzos de las ciencias exactas en Argentina, a comienzos del siglo XX, descuidaron hasta hace unos años la figura de un personaje central en la implantación de la física. Posteriores indagaciones permitieron poner en valor la trayectoria de Margrete Heiberg de Bose, la primera profesora en física a nivel universitario. Olvidada o soslayada en los primeros relatos de la historia del Instituto de Física de La Plata, posteriormente sus aportes fueron estudiados y puestos en valor. La presente comunicación apunta a completar la información sobre su formación y su carrera científica, y las características de su vínculo con otros científicos del momento, en especial con su colega y esposo Emil Bose.

Keywords: Margrete Heiberg de Bose, Instituto de Física de La Plata, Emil Bose. Email: cecilia@fisica.unlp.edu.ar

91

K- Physics and Mathematics

92

93

OK-1- Exploding Dissipative Solitons

Descalzi O.

Facultad de Ingeniería, Universidad de los Andes, Santiago – Chile

We investigate the route to exploding dissipative solitons in the complex cubic-quintic Ginzburg-Landau equation, as the bifurcation parameter, the distance from linear onset, is increased. We find for large class of initial conditions the sequence: stationary localized solutions, oscillatory localized solutions with one frequency, oscillatory localized solutions with two frequencies, exploding localized solutions. The transition between localized solutions with one and with two frequencies, respectively, is analyzed in detail. It is found to correspond to a forward Hopf bifurcation for these localized solutions as the bifurcation parameter is increased. In addition, we make use of power spectra to characterize all time-dependent states. On the basis of all informations available, we conclude that the sequence oscillatory localized solutions with one frequency, oscillatory localized solutions with two frequencies, exploding dissipative solitons can be interpreted as the analogue of the Ruelle - Takens – Newhouse route to chaos for spatially localized solutions.

Keywords: solitons, Ginzburg-Landau, Hopf bifurcation

94

OK-2- Generalized statistical complexity measure:

a new tool for dynamical systems

Rosso O.A.1,2

1Instituto de Cálculo, UBA, Argentina; 2 Departamento de Física, UFMG, Brazil

López-Ruiz, Mancini and Calbet have proposed a statistical complexity

measure, based on the notion of “disequilibrium”, as a quantifier of the degree of physical structure in a time series Given a probability distribution P and its associate information measure I[P], an amount of “disorder” associated to the state of a system, the LMC-statistical complexity, is the product of a normalized entropy H (normalized Shannon-entropy) times the disequilibrium Q, given by the Euclidean “distance” from P to the uniform distribution Pe. The statistical complexity vanishes both for a totally random process and for a purely periodic one. Martín, Plastino and Rosso improved on this measure by suitably modifying the distance-component (in the concomitant probability space). The obtained MPR-statistical complexity is (i) able to grasp essential details of the dynamics, (ii) an intensive quantity, and (iii) capable of discerning among different degrees of periodicity and chaos. The MPR-statistical complexity can be viewed as a functional that characterizes the probability distribution P associated to the time series generated by the dynamical system under study. It quantifies not only randomness but also the presence of correlational structures. In this seminar, selection of the information measure I and generalized disorder, as well as, election of distance D and generalized disequilibrium are reviewed. Evaluation of the probability distribution P associated to a dynamical system or time series under study is a physical problem. Additional improvements can be expected if the underlying probability distribution is “extracted” by more appropriate consideration regarding causal effects in the system’s dynamics. Several well-known model-generated time series, usually regarded as being of either stochastic or chaotic nature, are analyzed. The main achievement of this approach is the possibility of clearly distinguishing between them in the HxC (Entropy-Complexity plane) representation space, something that is rather difficult otherwise. In addition, recent applications to time series from biological (epileptic EEG records, deformation of red blood cells, Alzheimer disease, etc.) and physics systems (stochastic resonance, econophysics, literature, ENSO/El Niño, etc.) will be reviewer. Keywords: entropy, statistical complexity, dynamical systems, time series analysis Email: aorosso@gmail.com

95

L- Computational Physics

96

97

OL-1- Computational study of hydrogen storage in carbon-based

materials

Sigal A.1, Rodríguez C. R. 3, Rojas M. 2, Leiva E.P.M. 2

1Facultad de Matemática Astronomía y Física; 2Facultad de Ciencias Química;

3Facultad de Ciencias Exactas, Físicas y Naturales, Universidad Nacional de Córdoba, Ciudad Universitaria, 5000 Córdoba, Argentina

The future of hydrogen economy strongly depends on the development of

hydrogen storage systems for vehicle applications. In this respect, carbonaceous materials appear very attractive, since they provide a light, high surface area and low- cost option. In recent times, the addition of metal atoms (transition, earth-alkali) has been suggested as a way to increase their capacity for hydrogen storage, since these materials alone do not meet the targets suggested by organizations like the Department of Energy of USA (DOE).

In the present work we analyze by means of density functional (DFT) calculations the possibility of hydrogen storage in carbonaceous materials decorated by metals, as well as the role placed by interferents present in the air. Particularly important is the case of oxygen, since recent studies show that this molecule appears as the main competitor and inhibitor for hydrogen adsorption [1, 2].

As a model system, we consider a graphene layer decorated by Ni, Ti, Cu, Pt and K atoms, among others. Local minima are determined by the technique of conjugate gradients, as implemented in the SIESTA [3] computer code. The reaction coordinate for different reactions (oxidation, hydride formation) is obtained using the nudged elastic band method [4]. Some of the difficulties found for the experimental implementation of these storage media can be understood from the present results. In the case of the Ti decoration, it is found that oxygen adsorbs spontaneous and irreversibly on the Ti adatom, strongly inhibiting hydrogen adsorption. In the case of the Ni decoration, the results are more encouraging but oxygen still represents an important hindrance for hydrogen storage. The entropic contribution for hydrogen adsorption is also analyzed, showing that it also deliver an important counterbalance to the favorable hydrogen adsorption energy.

[1] M.I. Rojas, E.P.M. Leiva, Phys. Rev. B 76 155415 (2007). [2] A. Sigal, M.I. Rojas, E.P.M. Leiva, Inter. J. of Hydrogen Energy (2011), doi:10.1016/j.ijhydene.2010.12.024 [3] J. M. Soler, E. Artacho, J. D. Gale, A. García, J. Junquera, P. Ordejón, D. Sánchez-Portal, J. Phys.: Condens. Matter 14 2745 (2002). [4] G. Henkelman, B.P. Uberuaga, H. Jonsson, J. Chem. Phys. 113 (2000) 9901-04. G. Henkelman, H. Jonsson, J. Chem. Phys. 113 (2000) 9978-85. Keywords: DFT calculations, hydrogen storage Email: eze_leiva@yahoo.com.ar

98

OL-2- First-principles studies on the properties of molecular wires

Castillo E., Zoloff Michoff M.E., Vélez P., Negre C., Sánchez C.G., Leiva E.P.M.

Departamento de Matemática y Física, Facultad de Ciencias Químicas, Universidad

Nacional de Córdoba, Argentina

Molecular electronics is an emerging field which has the ultimate objective of using individual molecules as constituting parts of electronic circuits. This developing technology, which represents the non plus ultra of circuit miniaturization, has the potential of replacing the actual semiconductor devices. Using molecules as building blocks is appealing, since it allows tailoring the properties of the contact either by modifying the nature of the anchoring group or by introducing different substituents on the molecule. However, dealing with such small objects has a number of handicaps that makes these systems the subject of extensive experimental and theoretical research. The present work is devoted to report on recent progress on the first-principles modelling of these tiny objects that were represented as molecular wires. By this term, we mean the thinnest contact that can be achieved between two conducting tips, made of a monatomic metallic wire with a molecule inserted in it.

Some of the subjects that will be analyzed are:

• Binding energy and rupture force of different molecular wires. • Long-term stability of pure and contaminated monatomic nanowires. • Effect of different molecular “alligator clips” for a given metal: S, N,

COOH groups. • Inclusion of a benzene group with different substituents in the wire. • Use of different metals for the contact electrodes. • Studies of the system conductance for selected systems.

Keywords: DFT calculations, nanowires Email: eze_leiva@yahoo.com.ar

99

Poster Session

100

101

C- Condensed Matter Physics

102

103

PC-1- Influence of the zirconia content on the densification, thermal

behaviour and properties of reinforced Zircon Zirconia (ZrSiO4m-

ZrO2) ceramic composites

Rendtorff N.M. 1,2,3, Suárez G. 1,2, Sakka Y.3, Aglietti E.F. 1,2

1CETMIC, Argentina; 2Dpto. de Química, Fac. de Ciencias Exactas, UNLP,

Argentina.; 3FPPG Nano Ceramics Center, NIMS, Japan.

In many industrial applications, components are required to work in extremely hard conditions, particularly at very high temperatures for long times. For these applications, new ceramic matrix composites have been designed, with both micro and nano-sized reinforcing particles, located at inter or intra-granular positions, this can improve mechanical and thermomechanical performances as well as strongly reduce creep rate.

Zirconia containing ceramics have attracted great attention to industrial applications in oxygen pumps, sensors, fuel cells, and thermal barrier coatings due to their excellent electrical, thermal, and mechanical properties.

Many attempts are in progress to develop biphasic and tri-phasic systems or even tetra-phasic systems. Particularly much interest is still being carried out in dispersed zirconia containing ceramic composites with different contents of different types of ZrO2 grains.

In this work a series of zircon zirconia (ZrSiO4-ZrO2) ceramic composites have been obtained by slip casting of concentrated aqueous dispersions in alumina porous molds and presureless sintering.

A densification study was carried out together with a microstructure characterization.

The final mechanical properties were evaluated and correlated with the zirconia content (0-30 vol %) the mechanical characterization using Vickers Hardness, and the dynamic elastic modulus. Both were strongly influenced by the incorporation of the zirconia particles to the microstructure evidencing the existence of some reinforcement mechanisms.

A thermal behavior evaluation was carried out; the correlation between the thermal expansion coefficients with the zirconia follows a mixing rule with some deviation. This deviation could be correlated with the microcracks developed during the processing caused by the thermal expansion mismatch together with the monoclinic particular dilatometric behavior. During a heating-cooling cycle, zirconia undergoes a martensitic transformation from monoclinic to tetragonal and vice versa which presents special hysteresis in the dilatometry curve at temperatures between 800-1100ºC, the limiting threshold composition for this particular thermal behavior was established in more than 10 %vol of zirconia, from this the martensitic transformation temperatures were evaluated and compared with the ones resulting from the differential thermal analysis. Keywords: Zirconia, ceramic composites, thermal behaviour, martensitic transformation. E-mail: rendtorff@cetmic.unlp.edu.ar

104

PC-2- Zirconia Calcia solid solution formation by high energy milling

of pure oxides; influence of Calcia content.

Suárez G. 1,2, Rendtorff N.M. 1,2, Aglietti E.F. 1,2.

1CETMIC, Argentina; 2Dpto. de Química, Fac. de Ciencias Exactas, UNLP, Argentina.

There are several applications of zirconia ceramics as a structure material or solid electrolyte; the polymorphic variety thermodynamically stable at room temperature is the monoclinic zirconia (m-ZrO2). It is well known that by adding cations in the structure of zirconia can be fully or partially stabilized in cubic (c-ZrO2) or tetragonal (t-ZrO2) forms. These structures present different (better) mechanical and electrical properties. Stabilized zirconia can be achieved by chemical stabilization or by heating treatment. In this second case the high temperatures (≥ 1100 º C) is responsible for the cation inter diffusion in the zirconia matrix.

The mechanochemical activation processing has proved to be an effective technique to enhance a solid-state reaction at relatively low temperatures. In such a process, the mechanical effects of milling, such as reduction of particle size and mixture homogenization, are accompanied by chemical effects, such as partial decomposition of salts or hydroxides resulting in very active reactants.

The objective of the present work is to establish the influence of the CaO proportion (3%, 8% and 13% molar) in the ZrO2-Ca+2 solid solution formation by High energy milling of pure oxides mixtures. A second objective is to evaluate the efficiency of the processing proposed and to characterize both textural and structural evolution of the mixtures during the milling processes.

The textural and structural evolution were studied by specific area measurements (BET), XRD analysis and SEM, Particularly the apparent crystallite sizes of m-ZrO2 and t-ZrO2 in the milled mixtures were calculated through the Scherrer equation. It is well known that Zirconia presents several metastable phases identified as t-ZrO2, t´-ZrO2, t´´-ZrO2, c-ZrO2, etc. As a first approach all the zirconia phases were assumed to be tetragonal and quantified by the Toraya method. However a more accurate atomic configuration determination such as Perturbed Angular Correlations (PAC) is stipulated for the following stage of this research. Finally the evolution of the particle size and morphology of the powders were examined by scanning electron microscopy SEM.

Solid-state reaction was induced by the HEM treatments, Nano crystalline ZrO2-Ca+2 solid solution powders were easily obtained directly from the high energy milling on stoichiometric mixtures of the pure oxides at room temperature.

Firstly a decrease of the crystallinity of the reactants was observed with short HEM treatments (≤ 5 minutes); this was accompanied by the disappearance of CaO diffraction peaks and the partial appearance of the tetragonal phase at room temperature. The Solid solution formation and stabilization were directly proportional to the amount of CaO added. Furthermore the solid solution proportion was increased asymptotically with the HEM time, obtaining complete stabilization of the tetragonal solid solution with long milling treatments (60 min) and higher Calcia proportions. Keywords: Zirconia, Calcia, mechanical alloying, XRD E-mail: rendtorff@cetmic.unlp.edu.ar

105

PC-3- Nuclear electric quadrupole interactions of 111

Cd in the heavy-

fermion compound CeCoIn5 compounds.

Forker M1, Silva P.R.J.1, Baggio-Saitovich E.1, Saitovich H.1, Ramos S.1, Alonso R.E.2,

Errico L.A. 2, 3, Taylor M.A.2.

1Centro Brasileiro de Pesquisas Físicas, 22290-180 Rio de Janeiro, Brasil; 2Departamento de Física & Instituto de Física La Plata (IFLP-CCT-La Plata,

CONICET-UNLP), Facultad de Ciencias Exactas, Universidad Nacional de La Plata; 3Universidad Nacional del Noroeste de la Provincia de Buenos Aires (UNNOBA), CP

2700, Buenos Aires, Argentina.

The nuclear electric quadrupole interaction of the probe nucleus 111Cd on the In sites of the heavy-fermion compound CeCo(In1-xSnx)5; x = 0.01 has been investigated in the temperature range 15 ≤ T ≤ 290 K by perturbed angular correlation spectroscopy. Single crystals of CeCo(In1-xSnx)5 grown from an In flux by combining stoichiometric amounts of Ce and Co with excess In were doped with the PAC probes 111Cd by diffusion at 700 K of radioactive 11I In from a carrier-free solution of 111InCl3 into the host lattice.

Apart from a sizeable fraction of non-reacted In metal, the PAC spectra contain contributions of two In-sites related to the CeCoIn5 structure, an axial symmetric and an asymmetric site. The 11ICd electric field gradient (EFG) of these sites differs substantially from the two EFG values determined by NQR measurements for the probe 115In on sites 1c and 4i of CeCoIn5, both with respect to strength and symmetry. For an insight into the mechanism leading to these differences, an ab initio study of the structural and electronic properties of Cd on In sites of CeCoIn5 is under way. Keywords: TDPAC, CeCoIn5, ab initio, EFG Email: forker@hiskp.uni-bonn.d

106

PC-4- Magnetic Field influence in the behavior of the transient

photoconductivity of ferromagnetic ZnO thin films

Khalid M.2, Zapata C.1, Heluani S. P.1 and Esquinazi P.2

1Division of Superconductivity and Magnetism, University of Leipzig, D-04103 Leipzig,

Germany, 2Laboratorio de Física del Sólido, Dpto. de Física, FCEyT, Universidad Nacional de Tucumán , Argentina.

Transient photoconductivity and magnetotransport measurements were used to investigate the spin dependent photoconductivity in magnetic ZnO thin films grown under N2 pressure. Spin dependent photoconductivity was measured at different temperature between 300 and 15 K in ZnO ferromagnetic and nonmagnetic films growth on c-plane Al2O3. There is a correlation between the magneto photoconductivity and the existence of defect-induced magnetic order already reported in these films. The role of traps and the effect of magnetic field on the transient photoconductivity is slow down the recombination process enhancing the photocarriers. The experimental results support theoretical predictions of the spin dependent recombination process in diluted magnetic semiconductors.

Keywords: Photoconductivity, Magnetotransport, Semiconductor. Email: sperez@herrera.unt.edu.ar

107

PC-5- Thermodynamics in a complete description of Landau

diamagnetism

Olivares F.1, Pennini F. 2,3, Curilef S.3

1Departamento de Física- Facultad de Ciencias Exactas- UNLP, La Plata, Argentina;

2IFLP/CONICET-Departamento de Física- Facultad de Ciencias Exactas- UNLP, La Plata, Argentina;3Departamento de Física. Universidad Católica del Norte, Av.

Angamos 0610, Antofagasta. Chile.

In the present study we analyze some consequences that come from revised

measures as the Wehrl entropy and the Fisher information for the problem of a particle in a magnetic field starting from a complete description of the Husimi function. We discuss in the most complete form (three dimensions) some results related to measures in contrast with the incomplete form (two dimensions) shown in previous contributions. Some limiting cases as high and low temperatures are discussed. From the present reasoning, it is suggested that the formulation in two dimensions is sufficient unto itself to explain the problem whenever the length of the cylindrical geometry of the system is large enough. Otherwise, it is not possible to work in all finite temperatures, a natural lower temperature bound emerges from the analysis when three dimensions are considered

Keywords: Husimi distributions, Wherl entropies, Fisher information, Thermodynamics Email: folivares@fisica.unlp.edu.ar

108

PC-6- Study of sheared self-propelled suspensions: Arrest of

coarsening and suppression of giant density fluctuations

Saracco G. P1., Gonnella G2, Marenduzzo D.3, Orlandini E4

1INIFTA, Argentina; 2 Bari University, Italy; 3Edinburgh University, Scotland; 4

Padova University, Italy We study the effect of a linear shear flow on a collection of interacting active, self-propelled particles modelled via the Vicsek model. The imposed flow has a dramatic effect on the behaviour of the model. We find that in the presence of shear there is no order-disorder transition, and that coarsening of the domains is arrested. Shear also suppresses the so-called giant density fluctuations which are observed in the quiescent limit. Keywords: Condensed matter physics, far from equilibrium behavior, matter structure, biophysics Email: gsaracco@inifta.unlp.edu.ar

109

PC-7- Synthesis and cell internalization of magnetite nanoparticles for

magnetic hyperthermia applications.

De Sousa E.L.1., Girardin P1., Fernández van Raap M.B.1., Pasquevich G.1., Mendoza

Zélis P.1. Bruvera I. 1., Sánchez F.H.1., Goya R.G.2, Sosa Y.E.2

1IFLP, UNLP La Plata, Argentina; 2INIBIOLP-UNLP, Argentina

Magnetic hyperthermia treatment appears as a viable alternative or complementary procedure for localized cancerous tumors therapy. The treatment consists of locally injecting magnetic nanoparticles (MNP) into the tumor and exposing it to an oscillating magnetic field in the radio frequency range. When exposed to this field, the MNP dissipates energy causing a temperature increase in the zone that contains nanoparticles, inducing tumor cell death by apoptosis at or above 42°C. MNP energy dissipation is characterized by the specific power loss parameter (SLP) which expresses the power absorbed by the MNP from the field per mass unit of MNP.

13 nm size magnetite nanoparticles with saturation magnetization of 60 emu/g, were synthesized by co-precipitation route using iron salts and a strong base, and finally set into aqueous suspension. Their physical properties were characterized with various techniques and suggest their adequacy for hyperthermia treatment and cell internalization requirements. Measured SPL value for this solution, using a coil fed with a signal of 260 kHz and amplitude of 500 Oe (39.8 kA m-1), was 203 W g-1.

Internalization methodology for anionic magnetic nanoparticles, which is achieved, for instance, by adsorption of citrate anions to the ferric oxide surface, is known to be well established in various tumoural and normal cells. Here, bare MNP nanoparticle were internalizated in A549 cells from human lung adenocarcinoma for two NP concentrations of 20 and 50 µg/ml. MNP incorporation into cells follows the endocytic pathway. It is observed that MNP concentration inside cells is larger and more densely packed for the larger MNP concentration. Confocal, atomic force and transmission electron microscopies were used to image the in vitro uptake of nanoparticles by A549 cells. Keywords: iron oxide nanoparticles, tumoural cell, magnetic hyperthermia, magnetic labelling Email: raap@fisica.unlp.edu.ar

110

PC-8- Transport properties of TCO-coated macroporous silicon

structures

Garcés F.A.1, Acquaroli L.N.1, Urtega R.1 Dussan A.2, Koropecki R.R.1, Arce R.D.1

1INTEC UNL-CONICET, Argentina; 2Universidad Nacional, Colombia.

In this work we present the electrical and photonic characterization of a

semiconductor (Silicon Porous)/TCO (Transparent Conductor Oxide) junction obtained by the deposition of SnO2 and ZnO onto porous silicon, using the Sol-Gel technique. The porous silicon was prepared by the electrochemical anodization of a silicon wafer. The anodization conditions were chosen so as to produce a macroporous system, with pore size ranging in 0.8 to 1 µm diameter. The transport of charge carriers through the interface was studied from measurements of current-voltage curves in dark and under illumination.. The SnO2 was doped with fluorine, and the ZnO was doped with aluminium. We analyzed the effects of the dopant concentration on the electrical properties of the junction. By fitting the I-V characteristic we evaluated the series resistance, ideality factor, reverse saturation current and photo-generated current. The values obtained for the ideality factor are quite high, between 9 and 20. This behaviour can be attributed to formation of thin layer of SiO2 at interface TCO/Silicon porous. The results were analysed in relation with the structural properties of the grown films, such as lattice parameter and the crystallite size obtained by X-ray diffraction.

Additionally, the light emission of porous silicon/TCO heterojunction was measured under the passage of electrical current for different applied voltages. The measured signal was collected by a photodiode as a function of time. The light intensity increases with increasing applied voltage, following a trend similar to that observed for the current in the J-V curves. This phenomenon, known as electroluminescence, has been rarely observed in macroporous silicon. Keywords: Porous silicon, TCO, Sol-Gel Email: rarce@intec.unl.edu.ar

111

PC-9- Analyzes of the structure of Agx(Ge0.25Se0.75)1-x bulk glasses

employing 119

Sn Mössbauer effect and XAFS

Conde Garrido J.M.1,2, Lede E.J.2, Ureña M.A.1,2,3, Rocca J.A.1, Arcondo B.1,2

1Facultad de Ingeniería, UBA; 2INTECIN (UBA-CONICET); 3CIC, CONICET

The zone rich in Se in the equilibrium phase diagram of Ag-Ge-Se system presents a large gap of miscibility in the liquid phase that solidifies, upon a fast cooling process, as an intrinsically inhomogeneous glass. The non-homogeneous morphology of these glasses depends on the atomic fraction of Ag (x). These glasses consist of Ag rich zones surrounded by a Ag depleted matrix for x < 0.08 whereas they consist of Ag depleted zones surrounded by a Ag rich matrix for x > 0.10. Evidence of a spinodal decomposition is observed for 0.08 ≤ x ≤ 0.10. On the other hand, these glasses present an abrupt change in their conductivity at x ≈ 0.08. They are semiconductors for x<0.08 whereas they are fast ionic conductors for x ≥ 0.08. This fact has been attributed to their particular morphology. In this work, the structure of these glasses is analyzed for 0 ≤ x ≤ 0.25 employing Mössbauer spectroscopy, on samples doped with substitutional 119Sn, and X-ray absorption spectroscopy (Ge and Se K edges).

In the Mössbauer spectra two main 119Sn (i.e. Ge) environments were observed. One of them, corresponding to Sn4+ tetrahedrally coordinated by 4 Se, is the main contribution for all sample spectra. The other contribution, present in the spectrum of sample with x=0.25, may be attributed to Sn2+. In agreement with these results the best fit of Xanes spectra (Ge edge) corresponded to a superposition of two Ge environments that may be correlated to those mentioned above. Xanes spectra (Se edge) provides a complementary insight revealing two different environments of Se, whose relative abundance depends almost linearly on the concentration of Ag. Accordingly, these environments may be asociated to Se-Ge and Se-Ag. These results suggest that the structure of both glassy phases that coexist in each non homogeneous sample, that is the phase with high Ag concentration and that with lower Ag concentration, are not qualitatively different as Ge and Se environments are practically the same in both phases. Keywords: non-homogeneous glasses; fast ionic conductors; Mössbauer spectroscopy, XAFS spectroscopy. Email: barcond@fi.uba.ar

112

PC-10- Dielectric and magnetic properties of mechanically milled

nanosized cupric oxide

Bianchi A.1,2,4, Junciel L. D.2,4, Osorio S.3, Echeverría G.1,2,4, Ayala A.5, Mercader R.

C.2, Torriani I. L.6, Punte G.1,2

1LANADI e 2IFLP (CCT-La Plata), 3Departamento de Física, FCE and 4Facultad de Ingeniería UNLP, Argentina.5Departamento de Física, Universidade Federal do Ceará, Fortaleza, Brasil. 6DFMC-UNICAMP y LNLS, Campinas, SP, Brasil

Cupric oxide (CuO) has been the subject of permanent attention since the advent of the Cu-based high-Tc superconductors in 1987. Its C2/c monoclinic crystal structure is unique among the 3d transition-metal monoxides and departs considerably from the simple NaCl-type structure common to most of them. The crystal structure of CuO can be viewed as made up of two types of zigzag Cu–O–Cu chains running along the [10‾ 1 ] and [101] directions. The system undergoes two successive magnetic transitions; one to an incommensurate antiferromagnetic (AF) phase between TN1=230 K and TN2=213 K, and a second one to a commensurate AF phase below TN2. This magnetic behavior seems to be ruled by the dominant magnetic interaction along the [10‾ 1 ] chain. The angle involved in this super exchange path, ≈ 146° (intermediate between 90 and 180), seems to be responsible for the spiral order arising from the competing AF and ferromagnetic interactions, while maintaining a high effective J, which in turn induces a magnetoelectric multiferroic behavior at 230K. In addition, CuO is a charge-transfer insulator, but micro-traces of Cu3+ turn it into a semiconductor. All the reported studies in the literature demonstrate the great importance that the microstructure and grain size have on the magnetic and dielectric properties. Trying to add to the knowledge of the relation between the magnetic and dielectric properties of the title system, we have produced nanostructures by controlled mechanical milling of high purity commercial CuO for different times up to 12 h. The structural and microstructural properties of all samples were studied by X-ray diffraction, SAXS and SEM. For increasing milling time, crystal-cell expansion, grain-size diminution, and strain and surface fractality growth have been observed. The dependence of the magnetic moment with the applied magnetic field (0 ≤ H ≤ 18 kOe) showed for all the samples the presence at RT of hysteresis loops, whose characteristic values (saturation magnetization, coercitivity and remanence) raise with milling time. Impedance spectroscopy at RT (in the 1Hz to 1 MHz range) showed a remarkable reduction of the real impedance component value when going from commercial CuO (40 kΩ) to the 12 h milled sample (3.3 kΩ). Besides, the imaginary component of the impedance, Z”, as function of frequency also shows a noticeable modification when compared to commercial CuO (maximum at 1.4 x 105 Hz), while in the nanostructured samples, the Z” maximum values lie at frequencies higher than the measured range. In this work we discuss the relationship between the magnetic and dielectric properties of the studied samples with their structural and microstructural properties dependence on the milling time. Keywords: CuO, nanostructure, nanomagnetism, impedance spectroscopy Email: bianchi@fisica.unlp.edu.ar

113

PC-11- Evidence of existence of metastable SrFe12O19 nanoparticles

Martinez Garcia R.1, Bilovol V.1, Socolovsky L. M.1, Pirota K.2

1Laboratorio de Sólidos Amorfos, INTECIN, Facultad de Ingeniería, Universidad de Buenos Aires, Paseo Colón 850 C1063ACV, Buenos Aires, Argentina; 2Instituto de Física “Gleb Wataghin”, UNICAMP, 13083-970 Campinas SP, Brasil.

The existence of metastable hexaferrite is reported. Synthesis of strontium

hexaferrite, SrFe12O19, at 400ºC was realized under controlled oxygen atmosphere. Such technique allows obtaining SrFe12O19 at lower temperatures than those used by traditional methods (above to 800ºC). Phase transformation occurred during a measurement of magnetization vs. temperature (heating up to 625ºC). The heat treatment induces a change from SrFe12O19 to γ-Fe2O3 (as main phase), and SrFeO2.74 to Sr2Fe2O5. Together with these phase transformations, an increment of the amount of SrCO3 is detected. Magnetic study of the samples, before and after the heating, supports the structural analysis conclusions. Up to our knowledge, this is the first report of the existence of metastable SrFe12O19.

Keywords: Metastable strontium hexaferrite; Iron oxide nanopowders; Phase transformation Email: rmartinez@fi.uba.ar

114

PC-12- Fluidity on metallic eutectic alloys

Morando C.1-2, Garbellini O.1-3, Fornaro O.1-2 y Palacio H.1-3

1IFIMAT, Dep. de Física, Facultad de Ciencias Exactas, UNCPBA, MT-CICPBA 2 CONICET, 3CICPBA

Eutectic alloys have a great importance both from academic as technological

point of view. For technological applications such casting, welding and joining, these systems offer lower melting point than the pure elements and good fluidity.

The fluidity is the measure of the distance travelled by the metal until it is stopped by solidification when the liquid metal is forced to flow through a channel of small cross section and is called Fluidity Length (LF). The process that takes place is a combination of the dynamic progress of the vein with the solidification of liquid metal. Physical variables associated with the process are: metalostatic pressure, heat extraction rate at the metal-mold interface, overheating of the liquid metal and the physico-chemical properties of metal or alloy (latent heat of fusion, density, viscosity, surface tension and solidification mode). Also the alloy chemical composition plays a fundamental role on the resultant fluidity length. In general, pure metals and alloys of eutectic composition have the highest values of fluidity, whilst intermediate composition alloys with greater solidification range shows lesser fluidity lengths. This behavior also shows a relation with the solidification structures.

Eutectic systems are classified in two groups: regular and irregular. The criteria used for this are: the entropy of fusion and the volume fraction of phases. If both phases have low entropy of fusion exhibit a regular or nonfaceted-nonfaceted morphology. If one phase has high and the other low entropy then the eutectic morphology results irregular or faceted-nonfaceted type.

Based on the results obtained by the authors in previous works, the aim of this work is to analize the fluidity of binary and ternary metallic alloys, with composition close to the eutectic composition, in terms of solidification microstructure. The fluidity measurements were carried out in linear fluidity tests corresponding to the Al-rich corner of the AlCuSi and AlAgCu diagram, and Sn based alloys, extensively used for important industrial applications. The purpose was to determine the physical mechanism involved in experiments and the relationships between morphology of growth, microstructure and fluidity length, and so to predict the behavior of proeutectic, intermediate composition alloys of the same diagram.

Keywords: eutectic systems, solidification structures, fluidity. Email: cmorando@exa.unicen.edu.ar, carinamorando@yahoo.com.ar

115

PC-13- Ordering in ββββ Cu-Zn-Al shape memory alloys

Lanzini F1, 2., Romero R.1, 2, Cuniberti A.1, 3

1Instituto de Física de Materiales Tandil, Facultad de Ciencias Exactas, Universidad Nacional del Centro de la Pcia. de Buenos Aires, Argentina; 2CICPBA; 3CONICET

Cu-based alloys belong to the Hume-Rothery alloys group, for which the

stability of different phases at different compositions and temperatures depends, mainly, on the average number of conduction electrons per atom ratio, e/a. At e/a around 1.48 and high temperature these alloys show a bcc structure called β phase. Within the Cu-based alloys, the Cu-Zn-Al system is one of the most investigated due to its excellent shape memory properties, associated with the martensitic transformation. The Cu-Zn-Al β phase is not stable at low temperatures, however it can be retained in metastable state by quenching. During cooling, it can exhibit two ordering transitions: A2 (bcc desordered) → B2 (CsCl type), and B2 → L21 (Heusler structure). Different long range order states can be obtained under quenching. It is worth noting that the order degree affects several physical properties, including the martensitic transformation critical temperatures.

This work is devoted to the study of the ordering process and its effects on the martensitic transformation. Samples with different compositions have been quenched from high temperatures, and subject to isothermal aging. Ordering was followed by electrical resistometry and mechanical test. It is found that the ordering kinetics does not follow a simple exponential law. The influence of quenching and ageing temperatures is discussed and compared with published data. The interplay between nearest and next-nearest neighbours is studied.

Keywords: Cu-Zn-Al shape memory alloys, atomic order, order kinetics Email: flanzini@exa.unicen.edu.ar

116

PC-14- Amorphous-crystal transition of Ge-Sb-Te thin films using

resistivity measurements.

Rocca J.A.1, Fontana M.1,2,3, Arcondo B.1,2, Molina Ruiz M.4, Rodriguez Viejo J.4

1Facultad de Ingeniería, UBA; 2INTECIN (UBA-CONICET); 3CIC, CONICET 4Grup de Nanomaterials i Microsistemes, Departament de Física, Universitat

Autònoma de Barcelona, Spain

Phase change materials show unique properties that have motivated important

technological applications. Ge-Sb-Te is one of the most significant systems that exhibit

these properties. GeSbTe alloys are employed in optical data storage (DVD

technologies) and are candidates for future electronic storage application.

In this work, films of compositions Ge13Sb5Te82 (atomic %) were obtained by pulsed

laser deposition, using a Nd:YAG laser ( = 266 nm). Atomic force microscopy (AFM)

was employed to characterize the films thickness.

The crystallization of the Ge13Sb5Te82 thin film was studied using the

temperature dependence of sheet resistance measurements and by means of the nano-

calorimetric technique at ultra-fast heating rates (5x104 K/s). The crystallization

temperature is determined in both measurements. In the resistance measurements, the

films were put into a conventional electric furnace in vacuum upon a heating rate about

1.8 K/m. The value of the resistance falls three orders of magnitude in a small

temperature range (400-440 K). In the nano-calorimetric measurements the onset

temperature of the transformation is about 520 K. The crystallization products have

been characterized by X-ray diffraction with Cu(Kα) radiation. These results are

compared with those obtained in a previous work for amorphous samples that were

rapidly quenched from the liquid state.

Keywords: Phase change memories; Chalcogenide glasses; Resistivity, Crystallization. Email: mfontan@fi.uba.ar

117

PC-15- Hydrophobic silica xerogel as host for antioxidants

Revuelta M.V.1,2, Fernández van Raap M.B.3*, Mendoza Zélis P.3, Sánchez F.H.3, Castro G.R.1,4

1CINDEFI-Universidad Nacional de La Plata (UNLP, La Plata, Argentina), 2Universidad Nacional de Cuyo (Mendoza, Argentina), 3IFLP-UNLP (La Plata,

Argentina), 4Tufts University (Ma, USA) The application of xerogels as a host matrix for bioactive substances has found

an intensified interest in the last decade. Composite xerogels are promising tools for industrial applications in the areas of fortified food packaging and drug delivery because they are chemically inert and non-harmful to human body.

The aims of the present work is to study hydrophobic silica xerogel as a carrier for drug delivery, using sensitive molecules like ascorbic acid (AA) to be applied in food packaging. AA is an essential nutrient in human diet with antioxidant properties as well. Free AA stability is very sensitive to environmental conditions such as temperature, light, oxygen, pH and water activity. Therefore ambient conditions cause a decrease in its biological activity. AA encapsulation and/or entrapment in an inert matrix are alternatives to keep AA activity protected and therefore for the development of AA-fortified food.

AA was encapsulated by a sol-gel process in an organic-inorganic hybrid matrix. A one-step synthesis was optimised for the preparation of silica–drug composites by using tetraethyl orthosilicate (TEOS) and methyltrimethoxysilane (MTMS) as precursors at different molar ratios. The presence of methyl groups decrease the amount of silanol groups which results in a more hydrophobic silica surface.

Characterization of AA loaded and unloaded xerogels were performed with FTIR and XRD. FTIR analysis of silica xerogels showed the characteristic vibrational peaks of SiO2 at 780 cm-1 (Si-O(b), bending mode) and 1070 cm-1 (Si-O(s), asymmetric stretching mode). However, when AA was entrapped in the xerogel, the carbonyl stretching (C=O(s)) mode of AA was shifted from 1754 cm-1 to 1738 cm-1 indicating a strong interaction with the matrix. In addition, a displacement of at least one hydroxyl group strectching (O-H(s)) mode was shifted from 3624 cm-1 to 3628 cm-1, that could be possibly because of H-bridge formation with SiO2 matrix.

X-ray analysis showed two broad reflection lines at 2θ = 11 and 23 degrees corresponding to amorphous silica. For loaded xerogels the structure is expanded, the 11 degree peak shift to lower angles. Results indicate that AA molecules were incorporated into the silica structure.

Kinetic of AA release from silica xerogel granules was followed at 37ºC and 150 rpm. AA concentrations were quantified by high performance liquid chromatography (HPLC). The hidrophobic silica gel was very stable in aqueous medium pH 5. About 60% of AA was released from the dried-gel between 3 to 4 hours. The release of AA from dried-silica granules could be diffusion controlled. The effective diffusion constant of AA from dried-gel in aqueous solution obtained through Crank model was 4.12x10‐7 cm2/s.

Keywords: hydrophobic xerogel, sol-gel, ascorbic acid, drug delivery Email: raap@fisica.unlp.edu.ar

118

PC-16- Ab initio study of F-centers in alkali halides

Hoya J.1, Laborde J.I.1, Richard D.1,2, Rentería M.1,2.

1Departamento de Física, Facultad de Ciencias Exactas, Universidad Nacional de La Plata (UNLP), CC 67, 1900 La Plata, Argentina. 2Instituto de Física La Plata (IFLP,

CONICET), La Plata, Argentina.

The structural and electronic properties of an electron trapped at vacant anion sites in alkali halides (F-center) have been investigated using ab initio electronic band structure calculations with the super-cell method.

We used the Full-Potential Augmented-Plane Waves plus local orbital (FP-APW+lo) method in the framework of the Density Functional Theory (DFT), with a vacancy dilution of 1:64 in order to determine the spatial electronic charge density and band structure of the studied compounds. The defect introduces a donor level which has s-character. According to the dipole selection rule, the allowed F-center optical transition was also determined. Despite of the underestimated transition energies we could obtain a qualitative agreement with the known experimental UV/Vis absorption energies.

Keywords: alkali halide, defect, F-center, ab initio Email: richard@fisica.unlp.edu.ar

119

PC-17- Synthesis, structure and properties of Finemet-like alloys

Silveyra J.M.1, Cremaschi V.J.1

1Lab. de Sólidos Amorfos, INTECIN, University of Buenos Aires-CONICET, Argentina

Since the first synthesis of nanocrystalline Fe-based alloys in Fe-Si-B-Nb-Cu

system in 1988 by Yoshizawa et al., a special interest has been devoted to improving the performance of the material from academic research to industry. The good soft magnetic properties of this system result in a variety of practical uses such as transformer cores, inductive devices, magnetic shielding, sensors, etc. Nanocrystalline Fe-Si-B-Nb-Cu alloys are obtained by devitrification from amorphous state and reveal an ultrafine grain structure of DO3-FeSi with grain sizes around 10-20 nm and random orientation, embedded in a ferromagnetic amorphous matrix. Due to their production inherent low thickness (~20 um) and relatively high electrical resistivity (~7.4 g/cm3), these materials exhibit excellent soft magnetic properties in a wide range of frequencies up to several hundred kHz, competing with those of Co-based amorphous alloys and MnZn ferrites. The saturation magnetization and dc coercive force are ~1 T and ~0.6 A/m, respectively. Finemet is the well-known trademark of the alloy Fe73.5Si13.5B9Nb3Cu1 and Vitroperm is the trademark of the alloy Fe73.5Si15.5B7Nb3Cu1.

Effects of a partial replacement of Nb by Mo on the Finemet alloy has rarely been investigated and it was reported to maximize the magnetic permeability while it can provide cost savings because Mo is more abundant and cheaper than Nb. According to the materials science tetrahedron, the optimization of the performance of a material lies in the triangle defined by the interrelationship among its synthesis, structure and properties.

In the present work the triangle synthesis-nanostructure-magnetic properties of Mo-doped Finemets is explored. The wide variety of techniques includes XRD, TEM, Mössbauer spectroscopy, Bitter technique, DSC, DTA, TGA under magnetic field, resistivity, dilatometry, magnetoresistance measurements, dc and ac magnetic measurements as well as ab initio calculations and simple balance models. Keywords: Finemet, Molybdenum, amorphous and nanocrystalline materials Email: jsilveyra@fi.uba.ar

120

PC-18- Impedance Spectroscopy Study at Different Bias Voltages of

Core-shell p-n GaAs Nanowire Photovoltaic Devices

Tirado M.1, Sandoval C.1, Caram J.1, Comedi D.1, 2

Czaban J.A.3, LaPierre R.R.3

1Dep. Physics, FACET, Universidad Nacional de Tucumán, S.M. de Tucumán, Argentina; 2Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET); 3McMaster University, Hamilton, ON Canada.

Great efforts are currently being made to develop new schemes for the

manufacturing of nanowire (NW) devices. Recently, photovoltaic (PV) p-n junction devices employing semiconductor nanowires (NWs) have received attention due to their enormous potential for lower cost and greater energy conversion efficiency compared to conventional thin film devices [1]. However, the current status of PV devices is far from satisfactory due to laboratory efficiencies that are much lower than the theoretical limits. Some of the problems may include charge carrier trapping at the NW surface or core-shell interface, insufficient control of dopant distribution across the NWs, and high contact resistance [2]. Hence, efforts are being made to improve their electrical characterization to give a more complete description of the device performance, which should be an important feedback to the fabrication procedure.

Electrical impedance measurements performed over broad frequency and bias ranges provide information of the whole measured system: bulk material and interfaces. In this work, we present an impedance spectroscopy study of core-shell GaAs NW PV devices aimed at determining charge conduction and trapping mechanisms. Samples having two distinct p and n spatial distributions and with Te as the n-dopant, were studied over the 103–107 Hz frequency and the −1.5 to 1.5 V bias ranges, using HP 4192A Impedance Analyzer*. For a large n-core/p-shell overlap region within the NWs in a coaxial geometry, the p–n junction properties (DC rectification and p–n depletion capacitance) are found to prevail. When the excitation frequency is increased above around 104 Hz, the device responses are found to decay abruptly, an effect that can be attributed to carrier trapping at and release from deep bandgap levels. By comparing the estimated trap energies with those reported in the literature for planar GaAs surfaces, the deep levels are attributed to NW surface states. Electrostatic calculations in the NW core-shell geometry show that NW surfaces lie within or very close to the depletion region, backing the above results. An increasing conductance with increasing frequency for low bias is observed, suggesting hopping transport through localized states. For large bias values, the conductance increases exponentially with bias and is frequency independent, indicating conduction through extended states in this regime [3].

[1] J. A. Czaban, D. A. Thompson, and R. R. LaPierre, Nano Lett., 9 (2009) 148-154. [2] B. Tian, T. J. Kempa, and C. M. Lieber, Chem. Soc. Rev., 38, (2009) 16-24. [3] J. Caram, C. Sandoval, M. Tirado, D. Comedi, J. Czaban, D. A. Thompson and R. R. LaPierre, Nanotechnology 21 (2010) 134007-134013. * Instrument supplied by the Volkswagen Foundation, Hannover, Germany.

Keywords: impedance spectroscopy, photovoltaic devices, core-shell nanowire, semiconductor. Email: mtirado@herrera.unt.edu.ar

121

PC-19- Al-doped Zinc Oxide nanocrystalline powders prepared by

mechanical milling

Ferrari, S., Damonte L.C.

Departamento Física, Universidad Nacional de la Plata, La Plata Buenos Aires Argentina.

The interest in new materials of nano-sized scale for applications in industry, medicine and other fields has led to research in the many ways of producing them with good efficiency trying to improve the quality of the final products. Of the many techniques of obtaining nanomaterials, mechanical ball-milling has the virtues of being efficient in producing large amount of material, leading to the incorporation of doping material into the main structure and/or creating blends, alloys, non-equilibrium phases and oxide-reduction reactions, etc. This is of particular importance in the study of semiconductors, like ZnO, whose electrical, optical and other properties can be ameliorated with doping. The aim of this article is to study ZnO powders doped with different amounts (5, 10 and 30 at%) of Al metal powder using mechanical milling. The structural ZnO changes were analyzed by X-ray diffraction (XRD), while defect creation with milling was followed by Positron Annihilation Lifetime Spectroscopy (PALS). Progress incorporation of aluminum into the wurtzite ZnO structure and, under certain circumstances, ZnO reduction was observed. After 16 hours of milling ternary oxides of the form Zn1-xAlxO were obtained in all samples.

Email:damonte@fisica.unlp.edu.ar, ferrari@fisica.unlp.edu.ar

122

PC-20- Magnetic hyperfine field at Zn sites in RZn (R = Gd, Tb, Dy)

compounds measured by PAC spectroscopy with 111

Cd

Bosch-Santos B., Carbonari A.W., Cabrera-Pasca G. A., Saxena R. N.

Instituto de Pesquisas Energéticas e Nucleares, IPEN-CNEN/SP, São Paulo, Brazil

In this work, we have investigated magnetic properties of the ferromagnetic RZn (R = Gd, Tb, Dy) compounds by perturbed γ-γ angular correlation (PAC) spectroscopy using 111In→111Cd ( t1/2 = 85 ns, and g-factor 0.306) as probe nuclei. The study of magnetic properties of rare earth and zinc (RZn) compounds is interesting because rare earth elements present a localized magnetism associated with 4f electrons, and these electrons do not participate in chemical bonds, as a consequence the RZn magnetic properties originate from the 4f electrons of rare earth. The compounds exhibit the cubic CsCl structure and the Curie temperatures are around 268 K, 204 K and 139 K, respectively for GdZn, TbZn and DyZn.

The PAC spectroscopy provides information about the hyperfine interaction between nuclear external fields and nuclear moments of probe nuclei at a certain atomic site in the crystalline structure of the compound, and consequently allows extracting information of the involved hyperfine parameters, as well as the characterization of structural as well as magnetic transitions of the crystal. This technique is based on the emission of two gamma radiations in a cascade as a result from the decay of the excited states of the probe nucleus.

The RZn compounds (R = 99.9% e Zn = 99.999% purity) were prepared by arc-melting the constituent elements. Carrier-free 111In was diffused into the samples sealed in vacuum and annealed at 800 ºC. Samples have been characterized by X-ray diffraction, and it was observed a major fraction corresponding to the expected structure. PAC measurements were carried out in the temperature range of 10 K to 295 K.

The results show that the temperature dependence of magnetic field can be fitted by the Brillouin function for J = 7/2, J = 6 and J = 15/2, respectively for GdZn, TbZn and DyZn and the Curie temperature as well as the extrapolated value of the magnetic hyperfine field at 0 K could be extracted from these fitting for each compound. These results are discussed in terms of spin polarized model. Keywords: rare-earth compounds, magnetic hyperfine field, PAC spectroscopy, hyperfine interactions Email: carbonar@ipen.br

123

PC-21- Influence of the conductive substrate on the properties of

nanostructured electrodeposited Zinc Oxide layers

Reyes Tolosa M.D1, Orozco Messana J. 1, Lima A.N.C. 1, Camaratta R. 1, Bolink H.J. 2, Sessolo M. 2, Brine H., Damonte L.C. 3, Hernandez-Fenollosa M.A. 1.

1Instituto de Tecnología de Materiales, Universidad Politécnica de Valencia, Camí de

Vera s/n, 46071, Valencia, Spain 2Universidad de Valencia

3 Departamento Física, Universidad Nacional de la Plata, La Plata Buenos Aires Argentina

Three types of transparent conductive oxides on glass substrates were used for

analyze their influence on ZnO nanostructured films electrochemically: i) ZnO prepared by spray pyrolysis; ii) ZnO prepared by radio frequency magnetron sputtering; iii) commercial ITO (In2O3:Sn) covered glass substrates. Although thin, these primary oxide layers play an important role on the properties of the nanostructured films grown on top of them. Additionally, these primary oxide layers prevent direct hole combination in hybrid organic-inorganic solid state solar cells. We show that the properties of the ZnO nanostructured films depend strongly on the type of primary oxide covered substrate used. Additionally, we will present the effect of the primary layers on the performance of hybrid solar cells based on the three types of ZnO nanostructured films and the organic p-type semiconductor regio-regular poly(3-hexylthiophene) (P3HT). The photovoltaic cells obtained by these methods have been characterized by scanning electron microscopy and I-V measurements under a solar simulator. Keywords: nanocrystalline ZnO, photovoltaic cells, nanostructured films Email: damonte@fisica.unlp.edu.ar

124

PC-22- SAXS study of PVP capped Pt nanoparticles:The capping effect

Giovanetti L.J.1, Ramallo-López J.M. 1, Requejo F.G. 1, Craievich A.F.2, Salmeron M. 3, and Koebel M.M. 3

1INIFTA, Facultad de Ciencias Exactas, UNLP. - La Plata Bs.As Argentina

2Instituto de Física, Universidade de São Paulo - São Paulo - São Paulo SP Brazil 3Lawrence Berkeley National Laboratory - Berkeley CA United States of America

In most technological applications the control over the access to nanoparticle

surface is a key issue to understand the nature and role of nanoparticle surfaces and interfaces. Soft-chemistry methods allows for achieving the preparation of very small metallic particles by capping them with different types of polymers so as avoiding aggregation effects in further processing. The capping shell formed by the polymers could affect the accessibility to the nanoparticle surface so information on their density and size is important. We present here a detailed study by small-angle X-ray scattering (SAXS) of several dilute sets of Pt nanoparticles capped with poly(N-vinyl-2-pyrrolidone) (PVP) and embedded in ethanol. Four colloidal solutions with different nanoparticles average sizes are analyzed. A preliminary TEM characterization of the four studied samples indicated the presence of spherical Pt nanoparticles with average diameters approximately equal to 3, 4, 5 and 7 nm, respectively. Over the high q range, the SAXS curves of all studied colloidal solutions exhibit oscillations that are classically expected from a set of spherical nano-objects with a rather narrow size distribution. Over the intermediate q-range, all SAXS curves obey Guinier law and yield Guinier average radii that are compatible with those estimated from the features of SAXS oscillations at high q. However, positive deviations from Guinier law can be noticed in all SAXS curves over the very small q range. Three tentative models were initially proposed to fit the whole experimental SAXS curves, (i) a classical two electron-density model consisting of a dilute set of Pt nanoparticles with homogeneous electron density and bimodal radius distribution, surrounded by an also homogeneous solvent, this model assuming that the contrast in electron density between PVP capping and solvent can be neglected; (ii) the same model as (i), but in this case consisting of a single mode radius distribution of nanoparticles and allowing for the clustering of a fraction of them; and (iii) a complex model of nanoparticles, with a log-normal radius distribution, consisting of a homogenous Pt core surrounded by a shell exhibiting a variable and non negligible contrast in electron density with respect to the solvent. The SAXS curves derived from the three proposed models were fitted to the experimental SAXS patterns of all samples. A comparative analysis of the different features of the proposed models and quality of best SAXS fittings was performed. This analysis suggests that model (iii) is the most consistent with our experimental results. Thus, this SAXS study would indicate that PVP capping – i. e. flexible PVP polymer chains grafting to the surface of Pt core - promotes the formation of a shell with a gradient in electron density that surrounds the Pt nanoparticle core, being the contrast in electron density between shell and solvent high enough to induce noticeable effects on SAXS patterns.This work was supported by the Brazilian Synchrotron Light Laboratory (LNLS) under proposal D11A - SAXS1 5854, by ANPCyT (PICT 06-17492 and 25515), UNLP and CONICET (PIP6075) from Argentina. Keywords: Nanoparticles, SAXS, agglomeration. Email: lisandro@fisica.unlp.edu.ar

125

PC-23- α-Al2O3 Slabs: a local environment study

Darriba G.N.1, Faccio R.2, and Rentería M.1

1Departamento de Física e Instituto de Física La Plata (IFLP, CCT La Plata, CONICET-UNLP), Facultad de Ciencias Exactas, Universidad Nacional de La Plata,

CC 67, 1900 La Plata, Argentina 2Cryssmat-Lab., DETEMA. Facultad de Química. Universidad de la República,

Uruguay.

In this work we performed an ab initio/DFT study of structural and electronic properties of the (001) α-Al2O3 surface. For this study we used two methods with different basis set: the Augmented Plane Wave plus local orbital (APW+lo) and a linear combination of numerical localized atomic orbital basis sets, employing the Wien2K code and SIESTA code, respectively. In order to calculate the structural and electronic properties of the reconstructed surface, we calculated the final equilibrium atomic positions with the SIESTA code and then we calculated the Electric-Field Gradient (EFG) tensor with the APW+lo code at the optimized positions.

Using this procedure we found equilibrium structures with less energy than those obtained by using only the APW+lo method. The EFG tensor and the local structure for Al were study as a function of the depth from the surface, for relaxed structures. We found that distances down to 6 Å from the surface are sufficient to converge the EFG and the Al-O distances to bulk values. The predicted bulk EFG is in good agreement with the experimental results. These results can be used for local probe purposes, for example in the case of doping, with important sensitivity for probes located close to the top of the surface, in particular for distances lower than 6 Å. Keywords: DFT; Alumina; Electric-Field Gradient; SIESTA, APW+lo; Surfaces. Email: darriba@fisica.unlp.edu.ar

126

PC-24- PALS study and ab-initio calculations on mechanical milled

ZnSe and ZnTe powders

Hoya J.1, Laborde J.I.1 and Damonte L.C.1,2

1Departamento de Física, Facultad de Ciencias Exactas, Universidad Nacional de La

Plata (UNLP), CC 67, 1900 La Plata, Argentina 2Instituto de Física La Plata (IFLP, CONICET), La Plata, Argentina

II-VI semiconductors are of interest due to their potential application as

photovoltaic devices like hybrid solar cells. The efficiency of these devices may be improved mainly increasing charge carriers densities and interfacial processes. In order to reach this last purpose nanocrystalline materials are the best option as solar cells constituents. In this work we present a structural characterization of nanocrystalline ZnSe and ZnTe semiconductors obtained by mechanical milling. The samples were analyzed by X-ray diffraction (XRD) and positron annihilation lifetime (PALS) measurements. PALS results were compared with ab-initio simulations using the MIKA program. The two component density functional theory framework (TC-DFT) with the generalized gradient approximation (GGA) was applied. Keywords: nanocrystalline semiconductors, positron annihilation, mechanical milling, Email: damonte@fisica.unlp.edu.ar

127

PC-25- Defects studies in pure and doped In2O3 single crystals by PAC

Quille R.A.1,a, Chain C.Y.1,b, Damonte L.C.1,c, Pasquevich A.F.1,d

1Departamento de Física, Facultad de Ciencias Exactas, UNLP -Argentina. Instituto de

Física La Plata, CONICET. aBecario CONICET, bBecaria UNLP, cInvestigador CONICET, dInvestigador CICPBA.

The indium oxide electronic properties, pure or impurity doped, as massive

material or thin films, irrespective of its morphology, i.e. nanoparticles or nanowires, are of high interest due to their potential technological applications. Perturbed Angular Correlations (PAC) measurements on pure and doped In2O3 using 111In as radioactive probe are presented. Already the first paper on the application of the PAC technique to an oxide found the electron capture after effects (AE) for 111In/ 111Cd probes in In2O3. The 111In isotope decays via EC to the 7/2+ state of 111Cd and after 170 ps the first γ quanta of the PAC cascade is emitted. The EC-decay caused a hole in the K-shell, which is filled by X-ray and/or Auger transitions. Within 0.01 ps further Auger processes produce additional holes in higher shells. Therefore, the 111Cd-atom is highly ionized after its creation and electrons are needed to stabilize its electron shell. It depends strongly on the properties of the matrix (metal, semiconductor, and insulator) whether enough electrons are available in time or not. In metals the missing electrons are fast supplied and no AE is observed. But in semiconductors or insulators the relaxation time of the excited electron shell may be longer than the mean lifetime of the hyperfine-sensitive intermediate state in 111Cd (122 ns), leading to time-dependent (fluctuating) EFGs and damped PAC perturbation functions G22(t) Many different experiments have proven that the EC after-effect is, without doubts, the origin of this damping of the R(t) functions. Implantations at ISOLDE/CERN of the 48 min isotope 111mCd into different bixbyite oxides showed no after-effect, the same was observed in the PAC-experiments with the 181Hf/ 181Ta. In both cases, no EC-decay can distort the probe’s electron shell and no additional electron is needed. The existence of these after effects depends on the oxide purity. In this communication are presented results obtained with indium oxides samples contaminates with different impurities. An equimolar mixture of OCd and In2O3 doped with 111In and overnight calcinated at 1273 K in normal air atmosphere, results in In2O3 doped with Cd impurities. Additionally, In2O3 doped with C was made: a mixture of indium metal and carbon, in a porcelain crucible, loosely cover was overnight calcinated at 1273 K. In this way crystals of In2O3 grew on the walls and cover of the crucible. Later the crystals were doped with 111In. PAC spectra of both samples were studied as a function of temperature. The obtained results show pronounced differences, which can be ascribed to the donor or acceptor character of the impurities.

Keywords: decay after effects, perturbar angular correlations (PAC), indium oxide. Email: pasquevi@fisica.unlp.edu.ar

128

PC-26- Dynamic hyperfine interactions in 111

In-doped ZnO

Muñoz E.L. 1, Mercurio M.E.2, Pereira L.F.D.2., Cordeiro M.R.2, Carbonari A.W.2, and Rentería M..1

1Departamento de Física e Instituto de Física La Plata (IFLP, CCT La Plata, CONICET-UNLP), Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CC 67, 1900 La

Plata, Argentina, e-mail:munoz@fisica.unlp.edu.ar 2 Instituto de Pesquisas Energéticas y Nucleares-IPEN-CNEN/SP, São Paulo, Brazil

During the last 25 years, dynamic hyperfine interactions have been observed in

several Time-Differential γ-γ Perturbed-Angular-Correlation (PAC) experiments when the probe isotope 111Cd, obtained after the electron-capture (EC) decay of its parent 111In, was used in certain semiconducting and insulator oxides. These dynamic interactions are originated in the electronic relaxation of the probe atom, usually called “after-effects” (AE), which follows the EC decay of the 111In isotope. This relaxation must occur during the life time of the intermediate-sensitive-nuclear state of the γ-γ cascade, time-window in which we measure the hyperfine interaction at the probe nucleus with external fields by means of the PAC technique. Up to now it was believed that the ECAE can only be detected if the probe atom was a non-isovalent impurity in the system under study.

Following these ideas, we present here results of PAC experiments performed in an oxide, ZnO, were the 111Cd probe atom is an isovalent impurity. But this time the observed behavior will be analyzed enlighten by recent ab initio calculations of the electric-field gradients (EFG) as a function of the charge state of the Cd atom. PAC experiments carried out on 111In-diffused polycrystalline ZnO have been performed in order to measure the EFG at (111In (EC)→) 111Cd nuclei located at the cation site of the ZnO crystal structure. The PAC experiments were performed in the temperature range 77 K-1075 K. The presence of dynamic hyperfine interactions with low intensity was observed, fitting the spectra with a perturbation factor based in the Bäverstam and Othaz model [U. Bäverstam et al., Nucl. Phys. A 186, 500 (1972)]. The experimental results were compared with ab initio calculations performed with the Full-Potential Augmented Plane Wave plus local orbital (FP-APW+lo) method, in the framework of the Density Functional Theory (DFT), using the Wien2K code. The dependence of the EFG at the Cd sites as a function of the charge state of the supercell was determined. From this ab initio-experimental comparison we can correlate the strength dynamic hyperfine interaction with the dependence of the EFG on the charge state of the impurity Cd atom. Keywords: ZnO, Ab initio calculations, PAC, EFG Email: munoz@fisica.unlp.edu.ar

129

PC-27- PAC and ab initio study of the dynamic hyperfine interactions

at 111

In-doped Sc2O3 semiconductor

Muñoz E.L.1, Richard D.1, Carbonari A.W.2, Errico L.A.1,3 and Rentería M.1.

1Departamento de Física e Instituto de Física La Plata (IFLP, CCT La Plata, CONICET-UNLP), Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CC 67, 1900 La

Plata, Argentina, e-mail:munoz@fisica.unlp.edu.ar 2 Instituto de Pesquisas Energéticas y Nucleares-IPEN-CNEN/SP, São Paulo, Brazil

3 Universidad Nacional del Noroeste Bonaerense (UNNOBA), Monteagudo 2772, CP 2700 Pergamino, Argentina.

The combined experimental and theoretical approach based on electric-field

gradient (EFG) determinations by means of hyperfine interaction measurements and ab initio predictions at impurity atoms has been shown to be a powerful tool to unravel structural and electronic characterizations of impurities in solids, in particular in semiconductor oxides [1-3] In this work, PAC experiments using 111In-difussed Sc2O3 polycrystals have been performed at the IPEN facility in order to measure the Electric-Field Gradient (EFG) at (111In (EC)) 111Cd nuclei located at the cation site of the semiconductor lattice. The experimental results are compared with ab initio calculations performed with the Full-Potential Augmented Plane Wave plus local orbital (FP-APW+lo) method in the framework of the Density Functional Theory (DFT).

The PAC experiments were carried out in the temperature range 10 K – 900 K. The PAC spectra obtained in these measurements shows two very well-defined quadrupole frequencies along the whole temperature range, pointing to the fact that 100% of the probes are located at both nonequivalent cation sites of the bixbyite structure. Nevertheless, the spectra are dampened at certain intermediate temperatures, indicating the presence of dynamic hyperfine interactions that were analyzed with a perturbation factor based on the Bäverstam and Othaz model [4,5]. The FPAPW+lo calculations were performed using the Wien2K code. From the ab initio-experimental comparison, we can conclude that the Cd impurities localized at the axially symmetric D sites of the crystal structure do not present dynamic interactions while that the Cd probes localized at the asymmetric C sites present appreciable dynamic interactions attributed to the so-called after-effects that follow the electron-capture decay of the 111In parent isotope of the 111Cd impurity tracer. This scenario could be supported in terms of the EFG behaviour, predicted by the ab initio calculations, at Cd impurities as a function of the charge state of the impurity located at the different cation sites of the structure. [1] Anisotropic Relaxations Introduced by Cd Impurities in Rutile TiO2: First-Principles Calculations and Experimental Support. L.A. Errico, G. Fabricius, M. Rentería, P. de la Presa, and M. Forker. Physical

Review Letters 89, 55503 (2002). [2] Metal Impurities in an Oxide: Ab Initio Study of Electronic and Structural Properties of Cd in Rutile TiO2. L.A. Errico, G. Fabricius, and M. Rentería. Physical Review B 67, 144104 (2003). [3] Metal Impurities in an Oxide: Ab Initio Study of Electronic and Structural Properties of Cd in Rutile TiO2. G. N. Darriba, L. A. Errico, P. D. Eversheim, G. Fabricius, and M. Rentería. Physical Review B

79, 115213 (2009). [4] U. Bäverstam, R. Othaz, N. De Sousa and B. Ringström, Nucl. Phys. A186, 500 (1972). [5] A. Abragam and R. V. Pound, Phys. Rev. 92, 943 (1953).

130

PC-28- Electric-Field Gradients at 181

Ta impurities in Sc2O3

semiconductor

Richard D.1, Muñoz E.L.1, Errico L.A.1,2, Eversheim P.D.3, Rentería M.1

1Departamento de Física and Instituto de Física La Plata (IFLP, CONICET), Facultad de Ciencias Exactas, Universidad Nacional de La Plata (UNLP), CC 67, 1900 La Plata, Argentina; 2Universidad Nacional del Noroeste Bonaerense (UNNOBA), Monteagudo 2772, 2700 Pergamino, Argentina; 3Helmholtz-Institut für Strahlen- und Kernphysik

(H-ISKP), Universität Bonn, Nussallee 1416, 53115 Bonn, Germany.

In this work we present a combined ab initio and experimental study of 181Ta-doped Sc2O3 semiconductor. An extrapolation to 0 K of the experimental electric-field gradient (EFG) results obtained by Perturbed Angular Correlations (PAC) as a function of temperature suggested a reinterpretation of the charge state of the impurity in this semiconductor.

The experimental temperature dependence of the EFGs at 181Ta probes located at defect-free cation sites C and D of the Sc2O3 structure was determined in the range 373 K - 1173 K.

The theoretical calculations were performed at diluted Ta impurities located at both cationic sites, using the Full-Potential Augmented PlaneWave plus Local Orbital (FP-APW+lo) method in the framework of the Density Functional Theory (DFT), with a impurity dilution of 1:32. The structural atomic relaxations and the EFGs were studied for different charge states of the cell in order to simulate different ionization states of the double donor Ta impurity (with a neutral cell, and removing 1 or 2 electrons from the cell). These APW+lo results were found to be in excellent agreement with the experimental values.

Keywords: ab initio, scandium oxide, bixbyite, semiconductor. Email: richard@fisica.unlp.edu.ar

131

E- Physical Chemistry

132

133

PE-1- Phase change materials for thermal packaging of agricultural

products

Bouciguez, A.C.1, Lara, M.A.2, Villa, L. T.3

1INENCO (UNSA–CONICET), 2IFIR (UNR–CONICET), 3INIQUI (UNSA–CONICET)

The agricultural products need adequate condition temperature and controlled atmosphere of storage and transport. Each product needs different temperature condition; it must be maintained into a certain range, which guarantees the conservation of its organoleptic characteristic during a certain period of time.

All the biological products generate heat (respiration rate). When they are stored, little changes takes place, and the respiration rate produce heat, which must be taken into account when cooling and storing those products.

Temperature is an important factor in any chemical reaction with heat generation. Fruits, vegetables, flowers, etc. produce high respiration rate when they are storage. Nearly all vegetables have a minimal and a maximum respiration rate for each temperature. To estimate the respiration rate, when the product is storage at equilibrium state, the lower value might be used to estimate the storage temperature; the higher value might be used for calculating the heat load for the first or two days. The best results in the packing are obtained when the temperature is approximately constant. Variations of one or two degree can produce a quickly ripening and increase the risk of putrefaction. A way of keeping the product at constant temperature is removing its internal heat generation.

The use of phase change materials (PCM) is proposed for these purposes. It is placed in container specially designed, which are positioned along the wall with the agricultural products. The dimensions of the packing (width, length and height) are big in comparison to the wall thickness containers, so convective effects can be neglected, and the heat flux is practically one-dimensional. The PCM is initially solid at the melting point; when it is heated, the liquid phase appears and the solid initial phase stays at the fusion temperature. So, it is necessary to study the distribution temperature only in one phase: the liquid one. For this reason that mathematical situation is named: “One phase Stefan problem”. It is important to say that the interface position, which is a priory unknown, must be determined too. In such a way, the performance of PCM is studied in relation to know the interface position and the temperature distribution inside it to maintain the agricultural product in adequate condition of temperature during a certain period of time.

For the PCM, a defined melting point, a high latent heat of fusion per unit mass, a high specific heat, a constant density in the operation range temperature, and a similar density in the liquid and solid phase, are required. Besides, they must be chemically stable, and not corrosive, nor flammable, nor toxic and nor explosive.

Some animal fatty substances can be used for that purposes, with density around 1100 kg/m3, latent heat in the order of 150 kJ/kg, specific heat about 1500 J/kg ºC and thermal conductivity about 0.2 W/m ºC in the liquid phase and 0.4 W/m ºC in the solid one. Its melting point must be in the order of the temperature condition of the agricultural products. It is possible to obtain artificial substances which present phase change at different temperature.

Keywords: Phase change material (PCM); Interface position; Packing; Melting point. Email: acbouciguez@gmail.com

134

PE-2- Soil particle distribution; influence of the organic matter content

Filgueira R.R.1,2, Sarli G. O.1, Fournier L.L.1, Gelati P.R.1, Soracco C.G.1,2, Lozano L.A.1,2

1Facultad de Ciencias Agrarias y Forestales, Universidad Nacional de La Plata,

Argentina; 2CONICET, Argentina

Particle size distribution (PSD) in soil is one of the more interesting soil physical

properties. The information provided by PSD are often used to infer soil functioning

and use. The traditional method of characterizing particle sizes in soils is to divide the

array of possible particle sizes into three arbitrary separable size ranges: sand, silt and

clay. An alternative to this approach is to measure and display the complete distribution

of particle sizes. Sieves can be used to separate and determine the content of the

relatively large particles of sand and coarse silt. However the common source of PSD

data is the process of sedimentation of particles in water and the most popular

techniques are the hydrometer method and the pipet method. Both methods are based on

the Stoke’s law and employ the relationship among time, travel distance, and the

diameter of a sphere subject to sedimentation in a viscous liquid.

Cumulative PSD have been analyzed with both mass-size and mass-time scaling models, assuming a fractal mass-size distribution for particles settling in a liquid. The objective of this study was to investigate the influence of organic matter content (OM) on particle aggregation using Fractal dimension (D) of soil PSD obtained from mass-time and mass-size data. Five soils from Argentina, with different textures and OM, where sampled and used in the measurements. Two treatments were employed; 1) dispersing the particles with hydrogen peroxide and sodium hydroxide (T1), 2) dispersing the particles only with sodium hydroxide (T2). Experimental data were fitted to power law relations by regression methods. Significant differences in D values were found. For T1, D values ranged from 2.617 to 2.702 with R2 ranging from 0.960 to 0.999. For T2, D values ranged from 2.396 to 2.560 with R2 ranging from 0.950 to 0.992. Both theoretical models used could fit data sets in the silt domain with a high determination coefficient and the resulting fractal dimension values, for each soil, were similar within 1.2 % of variation. The OM in the soil plays an important role on aggregation at the very early stages of soil formation. Keywords : mass-size scaling; mass-time scaling; fractal dimension; fragmentation Email: fisica@agro.unlp.edu.ar

135

PE-3- The relationship among organic matter and specific surface in a

soil

Filgueira R.R.1,2, Sarli G.O.1, Gelati P.R.1, Soracco C.G.1,2, Lozano L.A.1,2, Arnal P.2,3

1Facultad de Ciencias Agrarias y Forestales, Universidad Nacional de La Plata,

Argentina; 2CONICET, Argentina; 3CETMIC, Argentina

The specific surface area (SSA) of soil organic matter (OM) has been worldwide considered to range from 500 to 800 m2 g-1, based on data of ethylene glycol (EG) retention before and after the removal of OM of soil samples with H2O2. However, measurements with the Brunauer, Emmett and Teller method (BET), using N2 adsorption at 77 K, resulted in values of SSA for OM two order of magnitude smaller than the former ones. It was apparent that an overestimation of the effect of MO on SSA resulted when polar solvents were used.

Some authors reported a positive relationship between the soil OM content and the SSA, but others found that large amounts of OM in soil resulted in reduced SSA when the BET method was used.

With the objective to contribute to a better knowledge about the OM role in edaphological processes, determinations of SSA in samples from a Typic argiudoll with different OM contents and constant clay contents (around 20%) were made. Measurements were carried out with N2 at 77 K, and the isotherms were interpreted with the BET model. Values of OM content and SSA ranged from 2.8 to 11.5 % and 7 to 18 m2 g-1, respectively. Elimination of OM with H2O2 increased SSA in all cases. Results showed a negative non linear relationship between SSA and the OM content of the samples. The increments in SSA, normalized by the content of removed OM, suggested that the adsorption of MO on the mineral surface is not uniform. Keywords : nitrogen adsorption, BET method, micropores, Typic argiudoll Email: fisica@agro.unlp.edu.ar

136

PE-4- Polymerization of acrylic monomers under microwave energy.

Oberti T.G.1, Cortizo M.S.1, Alessandrini J.L.2,3

1INIFTA, Universidad Nacional de La Plata (UNLP), Argentina; 2Departamento de Física e IFLP, Facultad de Ciencias Exactas, UNLP; 3 CIC, Provincia de Buenos Aires,

Argentina

The use of the microwave energy as a new methodology for carrying out more safe, clean and efficient chemical reactions was known for a long time 1 and has spread rapidly to the field of polymer science 2. Due to the fact that free radical polymerization is the most important industrial polymerization technique, the effect of the microwave energy on the polymerization of a series of acrylic monomers: benzyl acrylate (BA), p-nitrobenzyl acrylate (pNBA) and 2-ethylhexyl acrylate (2EHA), was studied in detail.

The homopolymerization and copolymerization of those monomers was carried out under both microwave and thermal conditions. In all cases, high conversion percent was obtained with low time of reaction under microwave conditions.

In the case of BA, the average molecular weight and polydispersity index decrease with increase of the reaction time. Moreover, the molecular weight distribution becomes bimodal by increasing the microwave power, indicating the existence of chain transfer reactions, as confirmed by nuclear magnetic resonance spectra 3.

Homopolymerization of pNBA lead to low molecular weight polymers under all experimental conditions: power, time, type and concentration of initiator, solution and mass. This anomaly was tentatively attributed to chain transfer reactions to monomer, a mechanism that was confirmed by theoretical calculations 4.

In contrast, the molecular weight and polydispersity obtained for the case of 2EHA were high and decrease with increasing the initiator concentration and the reduction of microwave power and reaction time.

From the comparision of the resulting homopolymers under similar reaction conditions (E = 42.0 kJ), the following order of reactivity: 2EHA > BA> pNBA was obtained.

The copolymerization of BA and pNBA with diisopropyl fumarate (DIPF) was also studied. The copolymerizations showed the same trend to reactivity as the homopolymerizations, obtaining the following order of reactivity: BA-co-DIPF5 > pNBA-co-DIPF6.

[1] Lidström P, Tierney J, Wathey B, Westman J (2001), Tetrahedron 57:9225-9283. [2] Bogdal D, Penczek P, Pielichowski J, Prociak A (2003), Adv Polym Sci 163:194-263. [3] Oberti TG, Schiavoni MM, Cortizo, (2008), Rad Phys Chem 77:597-604. [4] Oberti TG, Lavecchia MJ, Cortizo MS, (2010 on line), http://www.springerlink.com/content/108465/?Content+Status=Accepted [5] Oberti TG, Cortizo MS, Alessandrini JL, (2010), J Macromol Sci, Part A 47:725-731. [6] Oberti TG, Cortizo MS, Alessandrini JL, RITEQ-2010, Córdoba, Argentina. Keywords: Microwave Energy, Free Radical Polimerization, Acrylic Monomers, Copolymerization. Email: toberti@inifta.unlp.edu.ar

137

PE-5- Accurate replication of noise-sustained chemical patterns

Izús G.G.1, Deza R.R.1, Sánchez A.D.1

1IFIMAR (UNMdP-CONICET), Argentina

The DIFICI mechanism (differential-flow-induced chemical instability)—pre-dicted (and experimentally observed in the ferroin-catalyzed Belousov–Zhabotinsky re-action inside a quasi-1D flow tube) shortly after the first unambiguous experimental ob-servation of a Turing structure—opened a new highway to research on pattern formation in autocatalytic chemical systems. Its convective nature was soon recognized in numeri-cal simulations and then theoretically established in models.

In order to elucidate the mechanisms underlying the formation of dissipative structures in reaction–diffusion systems with flow, one must distinguish between abso-lute and convective instabilities. In an absolutely unstable regime, local perturbations of the steady state grow exponentially at the beginning in a Eulerian description. In the convectively unstable regime, perturbations are advected more rapidly than their rate of spreading. Macroscopic patterns called noise-sustained structures (NSS) emerge in the latter regime if noise (or an external forcing) is present during a time interval, and dis-appear through the boundaries when these are switched off (thus recovering the homo-geneous state). Some time ago, NSS were reported to arise in a system with Gray–Scott kinetics in a packed-bed reactor (known to undergo a DIFICI toward a convectively un-stable regime) [1].

In this work, two identical copies of such a system are coupled in master-slave configuration and submitted to independent spatiotemporal Gaussian white noise sources. Numerical simulation of two-dimensional reactors with uniform and Poiseuille flows reveals that the slave system replicates to a very high degree of precision and the convective patterns arising in the master one due to the presence of noise. The quality of this synchronization is assessed through several measures. A convective instability in the synchronization manifold is theoretically predicted and numerically confirmed [2]. [1] B. von Haeften and G.G. Izús, Phys. Rev. E 67, 056207 (2003). [2] G.G. Izús, R.R. Deza and A.D. Sánchez, J. Chem. Phys. 132, 234112 (2010). Keywords: DIFICI mechanism, convective instability, noise-sustained structures, syn-chronization Email: deza@mdp.edu.ar

138

PE-6- Stabilizing transient nanopatterns in heterogeneous catalysis

Mangioni S.E.1, Deza R.R.1

1IFIMAR (UNMdP-CONICET), Argentina

The development of novel experimental techniques allowing atomic resolution in real time (e.g. field ion microscopy and fast scanning tunneling microscopy) has revolutionized the 40-yr old field of nonequilibrium pattern formation in heterogeneous catalysis, by showing that fast kinetic processes typically lead to nanoscale patterns (which in turn enables self-assembled nanostructured surfaces).

Ertl and Mikhailov among others showed theoretically that transient nanoscale patterns might result from the interplay of reactions and (either direct or bulk-mediated) attractive potential interactions between adsorbate molecules. They shaped and sub-stanced a nonlocal mesoscopic kinetic equation which properly describes the behavior of surface-adsorbed particles experiencing attractive lateral interactions, and which can be written as a reaction–diffusion equation with field-dependent coefficients. When a nonequilibrium chemical reaction is incorporated, these patterns become stable and grow. Recently, that goal has been achieved by means of a particular multiplicative noise [1]. However, the complexity of the nonlocal kinetic equations has somewhat ob-scured the underlying physical mechanism leading to nanoscale pattern formation. In order to clarify the issue, we resorted to a simplified model that reproduces qualitatively the results of the studies carried out on the complete model [2].

Our primary assumptions are the following: 1) the patterns are approximately harmonic in shape; 2) the qualitative dynamics can be studied by focusing on the ex-trema and zero point of the field. As a further convenient simplification, we replace the drift term in the original kinetic equation by a cubic one. Using these assumptions, we catalog the subtle effects that underlie pattern formation by sub-dominant attractive forces, showing that such stable patterns arise from interplay between attractive forces (which favor the pattern) and diffusion. We also clarify the relationship between the domain of attractive forces and the dominant attractor, and point out the crucial depend-ence of the phenomenon on a single parameter p. A final surprising result is that nonlin-earity is not formally required to produce a pattern based on the balance between diffu-sion and attractive forces. Our analysis reveals that such a mechanism may largely tran-scend the context in which it was found. [1] S.E. Mangioni, Physica A 389, 1799 (2010). [2] S.E. Mangioni and R.R. Deza, Phys. Rev. E 82, 042101 (2010). Keywords: heterogeneous catalysis, nanopatterns, sub-dominant attractive forces, mul-tiplicative noise Email: deza@mdp.edu.ar

139

PE-7- Synthesis and Characterization of CaCO3-Biopolymers Hybrid

Microparticles for Tissue Engineering.

Bosio V.E.1, Calvignac B.2, Boury F. 2, Castro G.R.1,3

1CINDEFI-Universidad Nacional de La Plata (UNLP, La Plata, Argentina), 2INSERM U646, “Ingénierie de la Vectorisation Particulaire” (Université d’Angers, France),

3Tufts University (Ma, USA) Focus on the development of hybrid materials has been received high attention

in Medicine amongst other fields for bone repair and/or replace using minimally invasive surgery (MIS). The aim of the present work is study the synthesis and characterization of novel hybrid microparticles (hMPs) based on biopolymers and calcium carbonate for potential use in bone regeneration. The hMPs were also developed, as potential carrier of specific molecules towards the damaged zone to use in cancer therapies, and/or increase the repair efficiency and help tissue differentiation.

Calcium carbonate were selected as calcium source, to made the hMPs matrices who will incorporate the biopolymer-active drug complexes. Development of the hMPs were synthesize by coprecipitation method in presence of biopolymers. Doxorubicin, an anticancer drug, was used as molecule model to screen 10 biopolymers. Hyaluronic acid, three types of pectins and other three types of carragenines were selected based on the interaction with the drug. Optimal synthesis conditions were determined based on stability and gelification performance of each biopolymer.

hMPs characterization were performed by chemical and physical structure analysis, morphology, size and physiological pH stability. Fluorescence microscopy was used to determine the presence of the biopolymers in the CaCO3 matrices. hMPs structural analysis were performed with FTIR and Raman spectroscopies. Physical structure was determined by XRD and hMPs morphology including the size, shape, and surface properties were examined using a SEM.

In order to determine the presence of the biopolymer blended into the matrices, biopolymers derivatized with fluorescent probes were synthesized. Fluorescence microscopy revealed the presence of biopolymers incorporated to inorganic matrices and confirmed by FTIR and Raman spectroscopies. Also, the spectroscopies allowed to detect the presence of vaterite and calcite crystaline structures of CaCO3. XRD analysis showed about 70/30 % vaterite/calcite in biopolymer absence, and an increase vaterite percentage up to 95% depending on the biopolymer type. hMPs stability in physiological buffer solutions was increased in presence of the biopolymers. SEM images revealed that all types of MPs were approximately spherical in shape with a average diameter 1–5 µm. In addition, all types of MPs have shown the smooth outer surface.

Keywords: CaCO3 microparticles, hybrid materials, tissue engineering, drug delivery Email: grcastro@gmail.com

140

PE-8- Thermochemical properties of chlorine oxides ClOx (x=3-6) and

Cl2Oy (y=3-8)

Cobos C.J., Croce A.E., Sanservino M.A.

INIFTA, Facultad de Ciencias Exactas, Universidad Nacional de La Plata. Casilla de

Correo 16, Sucursal 4, La Plata (1900), Argentina

It is largely accepted that simple chlorine oxides are key participants in the catalytic destruction of stratospheric ozone. Due to this, the kinetics the photochemistry and the thermochemistry of these species have been extensively investigated to try to explain the ozone loss since the discovery of the Antarctic “ozone hole”. However, the detection in polar stratosphere of elevated concentrations of ClO and OClO has increased the interest for the possible formation of higher oxides acting as temporary reservoirs or intermediate species in complex-forming bimolecular reactions. High-level quantum chemical methods provide at present accurate values for diverse molecular properties, some of them not easily attainable from experiments. In particular, the energetic of gas-phase reactions can be normally predicted within the so called “chemical accuracy” of 1 kcal mol-1. In this context, standard enthalpies of formation at 298 K, ∆Hf,298, for a large number of chorine oxides were in the present study derived. For this, the composite quantum-chemical models G3MP2B3, G3B3, their associated Bond Additivity Corrections (BAC) methods BAC-G3MP2B3 and BAC-G3B3 and the last generation G4MP2 and G4 model chemistries were employed. The performance of hybrid functionals such as B3LYP, B98, O3LYP in conjunction with the large 6-311+G(3d2f) basis set is also investigated. The ∆Hf,298 were computed from both total atomization and, more accurately, from isodesmic energies. The resulting average values (in kcal mol-1) derived from the ab initio calculations are the following: ClClO (30.2±0.5), ClClO2 (28.1±1.7), ClOClO (38.5±0.4), (ClO)2 (38.6±0.4), OClClO (51.7±1.7), OOCl2 (50.7±0.6), ClO3 (43.5±0.5), ClO4 (55.4±0.6), ClOClO2 (31.2±0.7), ClClO3 (34.7±0.9), ClOClO3 (37.4±0.7), O3ClOO (41.2±0.6), ClOOClO (45.0±0.4), (OClO)2 (41.3±2.5), O2ClOClO2 (49.7±0.8), O3ClOOCl (55.5±0.5), O3ClOClO (62.6±0.6), O3ClOOO (52.9±2.6), O3ClOClO2

(52.8±0.8), O3ClOClO3 (62.0±1.1) and O3ClOOClO3 (78.5±0.1). From the above data, enthalpy changes for forty Cl−O bond breaking unimolecular reactions ranging from 2.3 kcal mol-1 (OOCl2→ClOO+Cl) and 73.8 kcal mol-1

(O3ClOO→ClO4+O) have been predicted. In addition, the existence of the following novel exothermic chemical reactions (in kcal mol-1) passing from ground-state rovibrational excited adducts, are proposed: ClO3+Cl→ClOClO2

*→OClO+ClO (−25.6); ClO4+Cl→ClOClO3

*→ClO3+ClO (−16.6); ClO4+ClO→O3ClOOCl*→ClO3+ClOO (−12.5); ClO4+ClO→O3ClOOCl*→O3ClOO+Cl (−9.5); ClO4+ClO→O3ClOClO*→ ClO3+OClO (−13.6); ClO3+O3→O3ClOOO*→ClO4+O2 (−22.2); ClO3+ClO3→ O3ClOClO2

*→ClO4+OClO (−9.0) and 2 ClO4→O3ClOOClO3*→O3ClOO+ClO3

(−26.1). Keywords: Chlorine oxides, Enthalpies of formation, Bond dissociation energies, Ab initio calculations Email: acroce@inifta.unlp.edu.ar

141

PE-9- Cogeneration and clean development mechanism

Sosa M.I.

GECCU, Facultad de Ingeniería, Universidad Nacional de La Plata, Argentina

The objective of this paper is to review restrictions of cogeneration systems installation and to discuss them in function of the financial credit for reduction of greenhouse gases emissions by using the Clean Development Mechanism.

Argentine presents nowadays a low investment in generation power plants. Certainly several thermoelectrical plants will enter in operation soon, but this will not solve the increasing industrial energetic demand. Other solutions must be found in order to avoid an energetic crisis, as well as to contribute to a rational use of primary energetic resources. The argentine industrial sector has a high thermal demand, ten times higher as the electrical one. The industrial sector presents a high cogeneration potential, theoretically 4 GW, which represents a 38 % contribution to the central distribution system. Cogeneration systems have to be considered as capital intensive projects subject to the effects of the economy of scale. This implies that in order to install such systems, keeping in mind the rational use of energy, the industry should face a high inversion.

On the other hand, cogeneration systems imply thermal and electrical generation with high reduction of Greenhouse effect gases, that is to say reduction of carbon oxides emission, due to the fact of combustible diminution.

Therefore a way to it make this possible is to apply for a certificate of gas emissions reduction. The evolution of Greenhouse effect emissions represents the best way to point out national government compromise with the surroundings. Kyoto Protocol looks forward to stabilize Greenhouse effect gas emission concentrations in the atmosphere at a level that should prevent dangerous anthropogenic interference with the climate system. Developed countries have now an opportunity to take the lead in combating climate change and its adverse known effects. Therefore, clean development mechanism represents a cooperative action between developed and developing countries. Keywords: Cogeneration, Rational use of energy, Clean development mechanism, Reduction of greenhouse emissions Email: misosa@ing.unlp.edu.ar

142

143

G- Optics

144

145

PG-1- Spectral study of ionized noble gases related with laser physics

and astrophysics

Reyna Almandos J. 1, Bredice F. 1, Raineri M.1, Gallardo M.1

1Centro de Investigaciones Opticas, La Plata, Argentina

In this presentation we report an overview of some studies concerning the spectral analysis of different ions of noble gases with implications to astronomy and laser physics. Studies of emission spectra of noble gas ions have been carried out in La Plata for more than forty years, several of them in collaboration with other groups. Knowledge of atomic parameters of neon, argon, krypton and xenon in intermediate and high degrees of ionization is important not only to understand laser emission mechanisms, but also to help in the study of different plasma conditions. The spectra were excited using pulsed discharges and recorded from the VUV to the IR regions. In some cases temporal resolution was used. From these studies new energy levels, lifetimes, wavelengths, intensities of the observed transitions and oscillator strengths were established. To support the analysis, regularities belonging to the atomic structure, relativistic Hartree-Fock and Dirac-Fock calculations were used.

Keywords: Optical Spectroscopy, Atomic Structure Email: jreyna@ciop.unlp.edu.ar

146

PG-2- Homogeneous solutions for elliptically polarized light in a ring

cavity with a non-linear metamaterial

Mártin D.A.1,2, Hoyuelos M.L.1,2

1Universidad Nacional de Mar del Plata, Argentine; 2IFIMAR (CONICET)

Ring cavities with flat mirrors filled with a Kerr-like nonlinear material can

present bistability, i.e. for certain values of parameters, assuming a linearly polarised incoming and outcoming electromagnetic beam, two possible stable homogeneous steady state solutions can occur. Because of that, nonlinear ring cavities have been proposed as optical switching and memory storage devices.

Here, we generalise the previous analysis. Evolution equations and stationary homogeneous solutions for cavity electric and magnetic field amplitudes are studied. Negative and positive refractive index materials are considered. Not only electric nonlinearities but also magnetic nonlinearities, which could be relevant in metamaterials, are allowed. The degree of freedom of polarization of the incident beam is also taken into account.

It is found that considering a magnetic nonlinearity increases the variety of possible qualitatively different solutions. A classification of solutions is proposed in terms of the number of bifurcations. Keywords: Ring cavities, Optical bistability, Kerr-like nonlinearity, Metamaterials Email: danielalejandromartin@gmail.com, hoyuelos@mdp.edu.ar

147

PG-3- Regeneration of optical pulses using the Radon-Wigner

transform

Bulus Rossini L.A.1,2, Costanzo Caso P.A.1,2, Duchowicz R.1,2, Sicre E.E.3

1Centro de Investigaciones Opticas (CCT CONICET La Plata - CIC), Argentina; 2Universidad Nacional de La Plata, Facultad de Ingeniería, Argentina;

3Intec, Universidad Argentina de la Empresa, Argentina

A generalization of the Fourier transform or spectrum of a signal, namely the fractional Fourier transform (FRT), allows to obtain the Radon-Wigner transform (RWT) when the fractional order p of the FRT is varied from 0 (only temporal information) to 1 (only spectral information or ordinary Fourier transform). In this way, the whole RWT display can be considered as a dual phase-space signal representation. Although originally employed for space optics applications, the RWT can be translated to the temporal domain using the spatial-time analogy so becoming a useful tool for different optical pulse processing operations. For the case of a pulse distorted and/or broadened under transmission in a certain optical channel, the complete RWT display of the pulse complex amplitude gives information about the specific fractional order p = pC which has associated an irradiance showing partial symmetry and compression effects. Thus, if the FRT of order pC can be applied to the distorted pulse, the obtained time-varying irradiance gives rise to a compressed and partially reshaped pulse.

In this work we analyze a photonic implementation of the temporal FRT irradiance by combining chromatic dispersion transmission and phase modulation of the pulse to be processed. For analysis purposes, as the complete RWT should be obtained, it is very unpractical to get an experimental implementation since it would require both, a very precise adjustment and the continuous variation of the device parameters. For this reason the RWT should be numerically produced. The RWT computational generation implies to know amplitude and phase information of the pulse, something which is not the case in most applications. This problem can be solved in two different ways: i) Through an experimental amplitude and phase recoverying process, or ii) by a numerical modelling of the pulse. The second approach can be only applied if there is a partial knowledge of the fiber optic channel where the pulse was propagated. From the numerical RWT display one or several fractional orders pC are chosen for synthesizing a particular, required time waveform using our proposed setup. To illustrate this approach, different FRT irradiances are generated and combined in order to modulate a continuous wave laser source. In this way, the regeneration of a pulse is performed by selecting the FRT irradiances which, when combined, can shape the desired waveform; e.g. a symmetry operation on a deformed pulse can be readily done. On the other hand, conditions for deriving the fractional orders pC needed to regenerate an originally symmetrical pulse are theoretically obtained. A scaling operation of the FRT is also explored in order to have a more versatile and functional pulse regeneration. Some important applications concerning with long haul optical communications are illustrated such as: second and third order chromatic dispersion compensation and partial mitigation of some nonlinear effects. Keywords: Optical processing, Fiber optics, Phase-space representations Email: esicre@uade.edu.ar

148

PG-4- Temporal and spectral properties of an all-fiber APM laser with

two-coupled cavities of different lengths

Paulucci E.1,2, Sicre E.E.3, Russo N.A.1, Duchowicz R.1,2

1Centro de Investigaciones Opticas (CCT CONICET La Plata - CIC), Argentina;

2Universidad Nacional de La Plata, Facultad de Ingeniería, Argentina; 3Intec, Universidad Argentina de la Empresa, Argentina

Some properties of a two coupled cavities all-fiber laser as a function of the ratio

between their optical lengths are analyzed in this work. The operation of this additive-pulse mode-locking (APM) laser is based on the coherent addition of pulses that interact on a central reflective element which is a common component for both cavities. The developed model derive the non-linear Schrödinger equation to resolve the propagation of fields through the Split-Step method, together with the T-matrix method for obtaining the reflectivity and transmittance characteristics of the fiber Bragg gratings (FBG´s) employed as feedback elements of the system. This is composed of an active primary cavity generated by an erbium-doped fiber and two fiber Bragg gratings (FBG1 and FBG2), and a passive cavity made with an appropriate length of standard optical fiber, delimited by FBG2 and the end of the fiber (4% reflectivity). The main parameters taken into account for defining the output of the laser are: the group velocity dispersion, the self-phase modulation, the gain factor that includes the effects of self- and cross- saturation, fiber losses and dispersion of the FBG. The emission generated, is analyzed in time and/or frequency domains, for different ratios between both cavities lengths. Numerical results for the pulse width and the peak power of the output, obtained from the application of the analytical model, are compared with experimental values measured by varying the length of the auxiliary cavity. These results show a decrease in the temporal width with a corresponding increase in the repetition frequency of the pulses, when the auxiliary cavity length is reduced with respect to the main cavity length. The experimental results are in good agreement with those obtained with the simulations. Keywords: Fiber Laser, Additive Pulse Mode Locking, Laser Modeling, Fiber Bragg Grating Email: emanuelp@ciop.unlp.edu.ar

149

PG-5- Measurement of thermal expansion post-curing Bis-GMA resins

with a fiber optic interferometric sensor

Arenas G. F.1, Duchowicz R.2,3

1 Laboratorio Láser, Facultad de Ingeniería, Universidad Nacional de Mar del Plata,

Argentina. 2 Facultad de Ingeniería, Universidad Nacional de La Plata.

3 Centro de Investigaciones Opticas (CCT CONICET La Plata-CIC, La Plata, Argentina.

In this paper we present a simple technique to measure thermal contraction of samples of Bis-GMA photocuring resin using a Fizeau fiber optic interferometer and a thermocouple previously embedded in the specimen before photo-polymerized. After introducing the sample in a thermostatic bath operating in heating/cooling cycles, measurement are performed by recording the contraction of the heated sample, in its cooling cycle, using a fiber optic Fizeau interferometer to determine the length changes simultaneously with the temperature evolution obtained with the thermocouple. Contrasting these two values, it is possible to determine the coefficient of thermal expansion (CTE) in a simple form. Moreover, not only possible to obtain the average CTE, but its value as a function of temperature can be determined, which is potentially useful to characterize many physical situations of interest in industry and research. For the specific case under study, coefficients of the monomer and vitrified resins were obtained. Solid samples of the Bis-GMA resin thermal expansion coefficient values range from 120 x 10-6 1/K and 290 x 10-6 1/K. These results are in agreement with classical methods, offering a simpler experimental stage and more compact. Measurement of contraction is optically stable, intrinsically self-calibrating and noninvasive. Since it provides information in time, it may be suitable to study shrinkage profiles and kinetic of polymerization. Furthermore it can be applied to other materials such as glass, rubber, metals, etc. Keywords: Interferometry, Thermal Expansion, Fiber Optic, photocuring. Email: ricardod@ciop.unlp.edu.ar

150

PG-6- Plasmonic Bindings in Elliptic Dimers

Abraham Ekeroth R.M.1,2, Lester M.F.1,3

1IFAS-Universidad Nacional del Centro de la Provincia de Buenos Aires, Argentina; 2Fellow of CONICET, Argentina; 3Member of CONICET, Argentina

In this work we study the electromagnetic wave interaction with a 2D system

composed by two metallic nanoparticles (nps) with elliptical cross sections. Through an exact integral formalism, we study (in a numerical form) the near and far fields, and the latter through the optical cross sections. Particularly, we are interested in the field dependence on the geometrical parameters of the system (distance between the nps, rotation’s angles, radii). In addition we show how the plasmonic resonances play a relevant role in both the near and far fields, and we explore the physical mechanisms involved in photonic bindings in complex systems. Keywords: Plasmonics, Dimers, Metallic Nanotubes Email: mabraham@exa.unicen.edu.ar

151

H- Biophysics

152

153

PH-1- Fluorescence sensing of alpha-synuclein amyloid aggregation

Celej M.S.1, Caarls W.2, Demchenko A.3, Jares-Erijman E.4, Jovin T.M.5

1National University of Córdoba, Argentina; 2Delft University of Technology, The Netherlands; 3Palladin Institute, Ukraine; 4National University of Buenos Aires,

Argentina; 5MPI for Biophysical Chemistry, Germany

Parkinson’s disease (PD) is a movement disorder characterized by the presence in the mid-brain of intracytoplasmatic inclusions (Lewy bodies), of which the main fibrillar constituent is the 140-aa protein α-synuclein (AS). AS is located presynaptically and functions in vesicle release and trafficking. Three missense point mutations (A53T, A30P and E46K) in the AS gene lead to early onset PD.

The kinetics of AS aggregation is consistent with a nucleation-propagation mechanisms, starting from nucleation centers and progressing via oligomerization to an elongation phase leading to the formation of the characteristic fibrils. Cytotoxicity is currently attributed to the action of intermediate species rather than the end-state amyloid fibrils. These prefibrillar structures are generally not revealed by classical amyloid indicators. In a search for improved fluorescence tools for studying amyloid formation, we reported the use of N-arylaminonahthalene sulfonate derivatives as noncovalent probes of AS fibrillation [1].

The mature amyloid fibrils have an unbranched rod-like morphology and are formed by interwound protofilaments. The core structure is a stack of β-sheets, the strands of which are perpendicular to main axis of the fibril. Of particular interest is the ability of the β-sheet network within this canonical cross-β structure to adapt to point mutations. It is known that fibrils formed by AS familial mutants exhibit subtle differences in ultrastructural features as compared to the WT protein. We showed that AS variants differ in their supramolecular fibrillar organization as sensed by a novel dual-emission color probe. These differences can be interpreted in terms of distinctive polarity and hydration of the binding sites [2]. [1] Celej MS, Jares-Erijman EA, Jovin TM, Biophys. J. (2008)94:4867-4879. [2] Celej MS, Caarls W, Demchenko A, Jovin TM, Biochemistry (2009)48:7465-7472. Keywords: amyloids, alpha-synuclein, Parkinson’s disease, fluorescence. Email: mcelej@mail.fcq.unc.edu.ar

154

PH-2- Rheology of human erythrocytes: A fractional analysis

Korol A.M.1, Deza J.I.2, Deza R.R.2

1UNR, Argentina; 2IFIMAR (UNMdP-CONICET), Argentina

The clinical practice usually links symptomatology with the visual microscopy

inspection of red blood cells. Erythrocytes from healthy donors are discocytes (bicon-cave discs) in the absence of shear stress, with a mean diameter of about 7.8 µm. This is regarded as the footprint of their optimal ability to adapt in flow (they are able to pass through capillaries with diameter down to 3 µm in some cases, changing noticeably their shape in the process). Other shapes, like the agglutinates and aggregates seen in diabetic patient samples, should then exhibit different viscoelastic properties. It is thus useful for clinical practice to count with an independent quantitative assessment of the viscoelastic properties themselves, in order to test the foregoing hypothesis.

Light diffraction under Fraunhofer conditions may be applied to obtain quanti-tative information of diffracting particles such as suspended erythrocytes. Under shear stress, the cells in dilute suspension take a triaxial ellipsoidal shape, with the major axis oriented towards the shear field direction. The laser beam traverses perpendicularly a thin layer of the erythrocyte suspension and is diffracted producing a Fraunhofer dif-fraction pattern that is either circular (when the healthy mammalian erythrocyte mem-branes are at rest) or elliptical (when they become deformed by a shear stress field).

When laser light is applied during a creep–recovery process, the light intensity dynamically changes along the major axis of the elliptic diffraction pattern. This change has been determined photometrically, with a home-made device called “erythrodefor-meter”. The steep rise of the creep curves cannot be accounted for by finite combination of classical models of viscoelasticity. In the present work, that behavior is qualitatively reproduced by a linear model containing a fractional time derivative of the shear strain, for parameters typical of living matter. Keywords: Erythrocytes, diffractometry, viscoelasticity, fractional calculus Email: deza@mdp.edu.ar

155

PH-3- Noise effects in excitable antiphase FitzHugh–Nagumo networks

Cascallares G. 1, Izús G.G.1,2, Sánchez A.D.1,2, Deza R.R.1,2

1UNMdP, Argentina; 2IFIMAR (UNMdP-CONICET), Argentina

The analytical finding some time ago [1] of an exact nonequilibrium potential valid in the excitable regime of the FitzHugh–Nagumo model (a useful two-variable re-duction of the Hodgkin–Huxley one) enabled a new perspective in the study of noise-driven synchronization in excitable FitzHugh–Nagumo networks with phase-repulsive (antiphase) coupling, describing e.g. intracellular calcium oscillations in cultures of hu-man epileptic astrocytes [2]. By monitoring its global nonequilibrium potential in the limit of adiabatic driving, we study the dynamics of bipartite bidirectional graphs whose nodes are excitable FitzHugh–Nagumo units submitted to a common subthreshold har-monic signal and independent Gaussian white noises with a common intensity η [3].

In the “nearest-neighbor” case (ring topology), transitions between two macro-scopic regimes—a “rest” state and an “activated” one with almost half of the neurons excited, forming a staggered structure—are observed by varying η. Both states alternate with the signal in a spatiotemporally synchronized way. Measures of activation and co-herent behavior become maximal for intermediate values of η. These collective effects are explained in terms of the system's nonequilibrium potential, which allows moreover a theoretical estimation of the minimum η-levels for activation and synchronization.

The same is done for excitable regular networks with extended antiphase cou-pling, where the minimum η-levels for short-wavelength phase instability, network syn-chronization and depinning of “defects” (groups of contiguous inhibited neurons on an antiphase background)—as well as the parameter dependence of the most probable de-fect length—are theoretically predicted from the system's nonequilibrium potential, and numerically confirmed. The competition between extended antiphase and “in phase” (diffusive) couplings is also briefly discussed. [1] G. Izús, R.R. Deza and H.S. Wio, Phys. Rev. E 58, 93 (1998); ibid., Comp. Phys.

Comm. 121-122, 406 (1999). [2] G. Balázsy, A. Cornell-Bell, A.B. Neiman and F. Moss, Phys. Rev. E 64, 041912

(2001). [3] G.G. Izús, A.D. Sánchez and R.R. Deza, Physica A 388, 967 (2009); G.G. Izús and

A.D. Sánchez, Physica A 389, 1931 (2010). Keywords: Nonequilibrium potential, antiphase coupling, FitzHugh–Nagumo model, synchronization Email: deza@mdp.edu.ar

156

PH-4- Protein misfolding associated to mild modifications of local

cellular pH: Amyloid-like aggregation of human apolipoprotein A-I

variants

Ramella N., Tricerri M. A., Rimoldi O.J.

INIBIOLP-CONICET. Fac. Ciencias Medicas, UNLP. Argentina

The native folding of proteins is critical to fulfill their biological functions.

Some proteins are structurally unstable and thus, small changes in the medium are clue to induce a pathological conformation. Amyloidosis is characterized by extra cellular deposits of anomalous fibrilar proteins. Human apolipoproteinA-I (apoA-I ) is not usually associated with this pathology, but some natural single mutants induce severe amyloidosis in patients. In order to get insight on the local cellular environment that promotes this anomalous aggregation, we studied the influence of low pH (a microenvironment associated to inflammation) that, in vivo, could induce protein misfolding and toxicity. We expressed and purified two natural- occurring apoA-I mutants: Gly26Arg (a substitution mutant with a gain in a positive charge), and Lys107-0 (showing a deletion of a Lisine residue). Structural analysis shows that acidic pH induces a strong conformational shift, decreasing the cooperative denaturation pattern, and the hydrophobic cavities present in the native state of the protein. This means that misfolding could be associated with intermediate folding states, and protonation of residues. Even though natural pathological mutants show higher tendency to aggregate as amyloid-like structures, wt apoA-I also is sensitive to acid-induced misfolding. Proteins show a significant structural arrangement between pH 5 and 6, suggesting strong influence of protein charge in such events. In addition, low pH enhances the binding of apoA-I and the mutants to heparin, a component of the cellular matrix that could help to retain the protein in injured environments being substrate for oxidative aggression. We conclude that local pH is clue to ensure the native conformation of apoA-I, and natural mutants are more sensitive to mild modifications, eliciting protein pathological rearrangement. Keywords: apolipoprotein A-I, protein misfolding, amyloidosis. Email: aletricerri@yahoo.com

157

PH-5- Synchronization of bursting oscillators by a common noise

source

Savino G.V.1, Formigli C.M.1, Deza J.I.2, Deza R.R.2,3

1UNT, Argentina; 2UNMdP, Argentina; 3IFIMAR (UNMdP-CONICET), Argentina

Neuron synchronization is nowadays an active research issue, for its fundamen-tal role in many complex brain functions (memory, control, thought, etc.). Even appar-ently simple questions are still mysterious: it is not yet understood why (and how) do neurons use either single spikes or bursts to transmit, encode and process information. Since a single neuron typically receives random inputs from other 104, the neurocom-putational paradigm finally arising will necessarily have noise as a central ingredient. Previous studies have shown that—against common sense—noise may improve neuron synchronization. To the best of our knowledge, such paradoxical noise effect has still not been reported in any of the very few actual physical devices that emulate the spiking and bursting neuron electrical activity.

In particular, our analog electronic circuit [1] is based on the same operating principles (conductance change) as neurons—analogues for potentials, currents and conductances can be easily identified—and exhibits the same bifurcation scenarios as the Hodgkin–Huxley model. Through a single parameter (a conductance) our circuit can be set into different self-oscillating regimes: single spikes at chaotic interspike intervals, and two- and three-spike bursts interspersed with single spikes. The phase portrait shows a stable limit cycle and a saddle point, originating the stable and unstable mani-folds necessary to get noise-induced phase synchronization according with previous theoretical models [2].

Here we present experimental evidences of the noise-induced phase synchroni-zation and frequency matching of two nonidentical and weakly-coupled analog models of the biological neuron. These are naturally nonidentical due to their component’s value dispersion, and unavoidably coupled—even if not deliberately done—when using a common noise source. By applying to two such circuits a common noise of increasing intensity, their initially very different instantaneous frequencies increase and match, and the system’s self-oscillation becomes periodic. We show that this effect is noise-medi-ated rather than due to the (very) weak coupling. The histograms, frequency spectra, correlation and recurrence plots show the measured activation and excursion times as the frequencies of both oscillators become equal for a definite noise intensity. Moreo-ver, the plots for different noise intensities of the spike-sequence phase differences be-tween the two circuits as time goes on show plateau with different duration, indicating phase synchronization [2] induced by the common noise. Complete synchronization [2] has never been observed. [1] G.V. Savino and C.M. Formigli, BioSystems 97, 9 (2009); G.V. Savino, C.M. For-

migli and R.R. Deza, proceedings RPIC (2007), paper 341. [2] C. Zhou and J. Kurths, Phys. Rev. Lett. 88, 230602 (2002); C. Zhou, J. Kurths and

B. Hu, Phys. Rev. Lett. 87, 014101 (2002). Keywords: neuron, synchronization, bursting oscillator, bifurcations Email: gsavino@herrera.unt.edu.ar

158

Novel lipid binding proteins from relevant parasitic helminths:

structure-function analysis based on biophysical techniques.

Ibáñez, M.1; Rey, F.1; Pórfido, J. L.1; Silva, V.1; Franchini, G.R.1; Kennedy, M.2;

Cooper, A.2; Smith, B.2; Córsico, B.1

1INIBIOLP, Facultad de de Ciencias Médicas, UNLP, Argentina.; 2Institute of Biomedical & Life Sciences, University of Glasgow, United Kingdom

Parasitic helminths express lipid-binding proteins (LBPs) that are structurally

distinct from those of their host. These proteins bind a wide range of lipid classes such as fatty acids, retinoids, eicosanoids, triglycerides, phospholipids and cholesterol. Due to helminth’s limited lipid metabolism, LBP’s have been proposed to participate in parasites development and in the interaction with the host. To understand the mechanisms involved, we have selected four important types of LBPs from highly pathogenic helminth parasites: a) a novel class of fatty acid and retinol binding protein with a structure that has no known counterpart, b) relatives of the fatty acid binding protein family, including members that are structurally modified in ways that are unique to nematodes, c) Antigen B, a member of a new family of ligand binding proteins present in cestodes, and d) nematode polyprotein allergens/antigens. Their atomic structures are under analysis employing NMR spectroscopy, for which we have already obtained high quality data and full structure determination is in progress. Protein-ligand interactions have also been studied by NMR, observing changes in NMR spectra, when stripped and reloaded samples are compared, evidencing conformational changes produced during the binding process. We are also analyzing their ligand-binding parameters (n, K, ∆H and ∆S) employing fluorescence-based systems and ITC. The studies confirm these LBPs bind natural ligands and fluorescent analogues in the sub-micromolar range. Additionally, protein-membrane interaction assays are being performed in vitro in order to characterize LBPs’ possible functions. Structural and functional studies will enhance our understanding of the unique features of helminth LBPs that may be related to the survival of the organisms and could be used as potential drug targets. Keywords: Lipid Binding Proteins, Parasite, Fatty Acids, NMR Email: bcorsico@med.unlp.edu.ar

159

I- Humanistics

160

161

PI-1- The Audion of the “Instituto de Física de La Plata”

Santoro A.¹,²,³

¹IAR-CONICET; ²AWA, USA; ³TCA, USA

This article report the advance of the wireless electronics in Argentina in early 1920, particularly in the “Instituto de Física de La Plata”, in which was made an electronic tube or Audion, device in that time, representative of the “state of the art” of the electronics. Keywords: History, Electronics, Physics, Electron tubes Email: abel@iar.unlp.edu.ar

162

163

J- Physics and Astronomy

164

165

PJ-1 Automatic optimization of experiments with digital output

Calabria M.F.1, Deza J.I.1, Deza R.R.1,2

1UNMdP, Argentina; 2IFIMAR (UNMdP-CONICET), Argentina

The phenomenon of noise-enhanced signal transmission (or noise-enhanced

propagation) has been a subject of theoretical and experimental research for more than a decade. Intimately related as it is to the phenomenon of array-enhanced stochastic reso-nance, it relies for its appearance on the cooperation of noise and coupling. Hence in any experiment involving the phenomenon, the system’s parameters must be adjusted in order to maximize its response to a low-frequency signal.

As a mock-up of synaptic transmission between neurons, we considered some time ago a chain of damped and unidirectionally coupled bistable oscillators (double-well potentials) [1]. A low-frequency signal was fed at the input of the first unit, its out-put fed with coupling intensity ε′ as input to the next unit, and so on. Moreover, inde-pendent additive Gaussian white noises with intensity D were injected at each element, thus building a cascade representative of a transmission line with noise. The theory was formulated with an analogical focus, measuring the signal-to-noise ratio (SNR) at the output of the last unit, and a region was numerically found in the (ε′, D) plane such that the output SNR expressed in dB was largest.

Having recently developed a custom data acquisition and control hardware [2] and as a step in our experimental program, we committed ourselves to verify that pre-diction and find an equivalent region that maximizes the output response of a chain of Schmitt triggers to a low-frequency signal. We automatically optimize the units’ input parameters with the goal of achieving maximal coherence between the last oscillator’s response and the input signal. The optimization is carried out by means of a genetic al-gorithm, using as measures of input–output coherence either the Hamming distance or the mutual information, and as input parameters the signal-to-noise ratio and the switching threshold of each oscillator. In the uniform case, the optimal setup is basically the same, regardless of which coherence measure is employed. [1] R. Perazzo, L. Romanelli and R.R. Deza. Phys. Rev. E 61, R3287 (2000). [2] M.F. Calabria and R.R. Deza. Rev. Sci. Instr. 81, 114702 (2010). Keywords: noise-enhanced propagation, data acquisition and control, genetic algorithm, mutual information Email: deza@mdp.edu.ar

166

167

K- Physics and Mathematics

168

169

PK-1- Perturbation theory on the non-commutative plane

with a singular potential

Nieto M.1, Pisani P.A.G.2, Falomir H.2

1Departamento de Física- Facultad de Ciencias Exactas- UNLP, La Plata, Argentina;

2IFLP/CONICET-Departamento de Física- Facultad de Ciencias Exactas- UNLP, La Plata, Argentina

The generalization of Schrödinger operators to the noncommutative plane can be

carried out by means of the Bopp shift / 2i i ij jX x pε θ= − . Since the noncommutative

coordinates are then represented by differential operators, the subsequent generalization of the Schrödinger Hamiltonian ( )V X−∆ + changes drastically its character as a linear

operator on the Hilbert space. In particular, positive powers nX of the coordinates in the potential ( )V X correspond to differential operators of order n whereas an inverse

square 21/ R , as in the case that we present. As a consequence, the spectral properties of this kind of Hamiltonians are

different from the well-known properties of second order Schrödinger operators. We present an example of how analyticity in one of the parameters of the Hamiltonian, namely the noncommutativity parameterθ , is spoiled as a consequence of this non-local representation of the Schrödinger potential. This result is to be remarked since many of the known studies of problems in noncommutative spaces rely on expansions in powers of the parameterθ .

In particular, we have studied the case of a singular potential and showed that the spectrum is not analytic in the noncommutativity parameter. We have considered on the noncommutative plane a perturbation proportional to the inverse squared distance to

the origin, 2/ Rα . Since this perturbation is represented by a bounded operator, the spectrum can be computed perturbatively in α and the non-analyticity of the energies in θ emerges explicitly as logarithmic cuts in 0θ = .

Keywords: Noncommutative Quantum Mechanics, Singular Potential, Perturbation Theory, Spectrum of energies Email: mnieto@fisica.unlp.edu.ar

170

PK-2- Exact static patterns in a fractional diffusion–reaction system

Deza J.I.1, Deza R.R.1, Wio H.S.2

1IFIMAR (UNMdP-CONICET), Argentina; 2IFCA (UC-CSIC), Spain

Diffusion–reaction systems are a paradigm in the research on nonequilibrium phenomena, its origins being associated to people like A. Kolmogorov, R. A. Fisher, and A. M. Turing. Besides its applications in chemistry and physics, the diffusion–reac-tion framework has been a useful approach for understanding (among other issues) morphogenesis and population dynamics, cardiac tissue physiology, and neural signal-ing. Viewed from the theory of stochastic processes, diffusion is characterized by a lin-ear time-dependence of the variance. Often, however, one finds examples of anomalous diffusion, in which the variance grows as a power α of time: in fractal substrata there is “subdiffusion” (α<1), whereas in chaotic systems and search processes involving Lévy walks there is “superdiffusion” (α>1). Whereas in the theory of stochastic processes, diffusion is adequately described by random walks, anomalous diffusion calls for a de-scription in terms of continuous-time random walks, which consider a (non δ–like) waiting-time distribution for the random walk.

Now, it is a marvel of scientific endeavor that again and again, apparently use-less mathematics comes to the rescue when physics is at the crossroads: this time, frac-tional calculus. It occurs indeed, that the continuous-time random walk description of anomalous diffusion is equivalent (from a macroscopic point of view) to a PDE with fractional time derivative [1]. Here we report on the analytical finding of exact static nonequilibrium patterns in a model fractional diffusion–reaction equation on a bounded domain. We consider the hot-spot model [2], which mimics general bistable diffusion–reaction models (e.g. those with a cubic reaction term) through a piecewise-linear “re-action term”. The original equation is converted into a spatially fractional diffusion–re-action equation. The fact that the domain is bounded allows using the Laplace transform method when the (spatial) fractional derivatives are defined in the sense of Caputo. [1] R. Hilfer (ed.), Applications of Fractional Calculus in Physics, World Scientific,

Singapore, 1999. [2] H.S. Wio, An Introduction to Stochastic Processes and Nonequilibrium Statistical

Physics, World Scientific, Singapore, 1994. Keywords: Diffusion–reaction systems, anomalous diffusion, continuous-time random walks, fractional calculus Email: deza@mdp.edu.ar

171

PK-3- Variational formulation of the KPZ equation

Wio H.S.1, Revelli J.A.2, Deza R.R.3

1IFCA (UC-CSIC), Spain; 2IFEG (UNC-CONICET), Argentina; 3IFIMAR (UNMdP-CONICET), Argentina

During the last decades, the research focus in statistical physics has shifted to-

ward phenomena far from equilibrium (e.g. turbulence, chemical reactions, biological systems, economic and social patterns). Among them, the understanding of surface and interface growth kinetics at microscopic and mesoscopic levels constitutes a major challenge in physics and materials science. Thus, the methods from static critical phe-nomena have been exploited in this field as a first approach to obtain scaling properties, symmetries, morphology of patterns in a driven state, etc.

It is still commonly believed that the nontrivial spatiotemporal behavior of sev-eral nonequilibrium systems stems from the nonvariational character of their dynamics, wrongly implying the nonexistence of a Lyapunov function(al): a Lyapunov-like func-tion(al)—the so-called nonequilibrium potential (NEP)—does exist for a very general dynamical system (the complex Ginzburg–Landau equation); it is formally defined as the solution of a Hamilton–Jacobi-like equation, and eventually obtained through a small gradient expansion. The confusion associated with the qualification of “nonvaria-tional” arises from the idea that for systems having nontrivial (limit cycle, chaotic) at-tractors, the dynamics cannot be deduced from the minimization of a potential playing the role of the free energy in equilibrium systems. This does not preclude the existence of a Lyapunov function(al) whose local minima identify the attractors of the system. Once the system has reached an attractor that is not a fixed point, the dynamics proceeds inside the attractor driven by nonvariational contributions to the dynamical flow, that do not change the value of the Lyapunov functional (i.e. the dynamics is not completely determined once the indicated functional is known—a situation having known examples even in equilibrium statistical mechanics). The NEP characterizes the global properties of the dynamics (attractors and their relative)—or nonlinear)—stability, height of the barriers separating attractions basins, etc) offering the possibility of studying transitions among them due to (thermal) fluctuations.

We present a variational formulation for the Kardar–Parisi–Zhang (KPZ) equa-tion of interface growth, leading to a thermodynamic-like potential whose knowledge allows to prove global shift invariance properties previously conjectured by other authors [1,2]. We also show a few results about the form of the stationary probability distribution function for arbitrary dimensions. The procedure used for KPZ can be ex-tended to derive more general forms suitable for other nonlinear kinetic equations, and cases with density dependent surface tension. [1] H.S. Wio, Int. J. Bif. Chaos 19, 2813 (2009). [2] H.S. Wio, J.A. Revelli, R.R. Deza, C. Escudero and M.S. de la Lama, Europhys.

Lett. 89, 40008 (2010); ibid., Phys. Rev. E 81, 066706 (2010); ibid., Phil. Trans. Roy. Soc. A 369, 396 (2011).

Keywords: KPZ equation, variational formulation, nonequilibrium potential, global shift invariance Email: deza@mdp.edu.ar

172

PK-4- Two Quantum Mechanical Problems on the Noncommutative

Plane.

Vega F.G., Pisani P.A.G., Falomir H.

IFLP, Argentina

We study the non-relativistic quantum mechanical problem of a particle in the

non-commutative plane in the presence of two central potentials. The first one is given by V(R)=V0H(R2-r0

2), where H is Heaviside function, and the second one is V(R)=V0δ(R2-r0

2), where delta is Dirac´s delta; V0 is a constant and R2 is the distance to the origin in the non-commutative plane. Using the spectral decomposition of the differential operator R2 one obtains a recurrence relation that can be explicitly solved. (In this way, an implicit equation for the spectrum is obtained). This recursion determine the spectrum of the Hamiltonian in terms of trascendental functions. We also analyse the particular limit in which V0 tends to infinite -for both cases- and the consequent simplification of the problem. This limit could be considered as an extension to the non-commutative plane of the problem of a particle in a disc subject to Dirichlet boundary conditions, an approach to the a non-commutative disc. Finally, we discuss the pole structure of the zeta function associated to these Hamiltonians.

Keywords: Spectral Functions, Non-Commutative Field Theory Email: fvega@fisica.unlp.edu.ar

173

L- Computational Physics

174

175

PL-1- Density gap in equilibrium states of packings of polygonal grains

Carlevaro C.M.1, Pugnaloni L.A.1

1Instituto de Física de Líquidos y Sistemas Biológicos (CONICET La Plata, UNLP),

Calle 59 Nro 789,1900 La Plata, Argentina

The packing fraction of a tapped granular bed is studied for different polygonal grains via simulations, focusing on equilibrium states. We find a unexpected sharp transition for packings of polygons with more than 13 vertices signaled by a discontinuity in the packing fraction at a particular tapping intensity. A discussion on the nature of this transition is presented. Keywords: Granular Matter, Phase Transitions, Static Packings Email: luis@iflisib.unlp.edu.ar

176

PL-2- Monte Carlo simulations of the effect of nonmagnetic impurities

on the wetting transition in confined Ising films

Cotes S.M.1,2, Albano E.V.2,3

1INIFTA, Universidad Nacional de La Plata, CCT-La Plata CONICET, Argentina; 2IFLYSIB, Universidad Nacional de La Plata, CCT-La Plata CONICET, Argentina;

3Physics Department, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, La Plata, Argentina.

In the first part of this work we present the results of a systematic exploration of

the effect caused by the introduction of nonmagnetic impurities (or defects) on the stabilization of the interface between two magnetic domains of opposite magnetic orientation. Those defects are simulated as spin vacancies along the center of confined 2-D Ising films, which have competing magnetic fields acting on the confinement walls.

The calculations are performed for different LxM film sizes, and by using the standard Metropolis dynamics. In the absence of defects, the film is characterized by an interface running along the M-direction, which is induced by the competing surface fields. That interface undergoes a localization-delocalization transition that is the precursor of a true wetting transition taking place in the thermodynamic limit.

When the density of defects is relatively low, our results show that the wetting phase transition is of second order, as in the absence of defects. On the other hand, when the density of nonmagnetic impurities is relatively high, a pinning effect of the interface gives rise to a first-order wetting phase transition.

The observed transitions are characterized by measuring relevant properties such as magnetization profiles, cumulants, magnetization fluctuations, etc., as a function of the density of defects.

In the second part of this work we present the preliminar results of the exploration of the effect of introducing sets of vacancies regularly placed in a triangular geometry along the center of the confined Ising film. We observed the movement of the interface assissted by a weak bulk magnetic film, hb.

Keywords: Ising model, Monte Carlo, thin films, defects. Email: cotes@inifta.unlp.edu.ar

177

PL-3- Granular flow and evacuation of pedestrians in panic

situations. Experimental verification of the "faster is slower" effect.

Gago P.A.1, Parisi D.R.2, Pugnaloni L.A.1

1Instituto de Líquidos de Física y Sistemas Biológicos (CONICET) La Plata, Argentina. 2Instituto Tecnológico de Buenos Aires (CONICET) C. A. de Buenos Aires, Argentina.

Previous works have demonstrated, by using simulation models, that the

evacuations times of pedestrian from a room depends non-linearly on the “force of desire”. In the models studied, the evacuation times decreases when the desire force increases for low force of desire. However, for large desire forces, the evacuation times increase. This effect has been termed "faster is slower". In the models, a high desire force corresponds to panic situations, where pedestrians enter in close contact in a desperate attempt to exit the room. For this reason, no controlled experiments have been carried out to verify the "faster is slower" effect. However, a number of similarities have been suggested between pedestrian flow and granular flow. We exploit these analogous properties in the agent-agent (individuals or grains) interactions to study evacuation times in granular silos and so extrapolate some conclusions on pedestrian flow. We used a quasi-two-dimensional silo, filled with glass spheres. The equivalent to the desire force is controlled by varying the silo inclination, that is, the projection of the acceleration of gravity in the plane of the silo. The exit hole used is about 4 particle diameters. This small aperture is frequently jammed during the discharge. To break the jamming arches and obtain a complete evacuation, we vibrated the silo.

We show that there exist an optimal inclination angle of the silo that minimizes the mean evacuation time. This originates in a competition between the increased flow rate as the inclinations is increased and the increased stability of the jamming arches that have longer survival times at higher inclinations. This constitute a poof of the "faster is slower" effect in granular flow. We present a discussion on the implications for pedestrian flow. Keywords: granular flow, pedestrian traffic, jamming Email: luis@iflisib.unlp.edu.ar

178

PL-4- Stochastic resonance between moving extended attractors

dell’Erba M.G.1, Izús G.G.1, Deza R.R.1, Wio H.S.2

1IFIMAR (UNMdP-CONICET), Argentina; 2IFCA (UC-CSIC), Spain

Since its discovery 30 years ago, stochastic resonance (SR) has become a para-

digm of the constructive effects of fluctuations on nonlinear systems. SR is a very well-studied phenomenon in concentrated (or zero-dimensional) systems, where numerous instances and applications have been discovered. Regarding nonlinear media, much of the analytical work in SR has been done on transitions between stable static patterns in reaction–diffusion systems [2] exploiting the nonequilibrium analog of a free energy: the nonequilibrium potential.

Our concern here is with SR in the transitions between counterpropagating sta-ble traveling fronts. In particular, we consider systems undergoing a nonequilibrium Ising–Bloch front bifurcation (NIB), a pitchfork bifurcation where an Ising wall ex-changes stability with a pair of counterpropagating and opposite-chirality Bloch walls, which is an important pattern-forming mechanism. The NIB front bifurcation of the FitzHugh–Nagumo model with nondiffusing inhibitor provides a beautiful instance of an extended bistable system made up of propagating (Bloch) fronts. Moreover, these fronts are chiral and parity-related, and the barrier between them is nonetheless but a station-ary Ising front.

Here we demonstrate, in the neighborhood of the NIB and by means of numeri-cal simulation, the presence of stochastic resonance in the transition between Bloch fronts of opposite chiralities when an additive noise is included. A scaling law of the signal-to-noise ratio with the distance to the critical point is theoretically characterized in terms of an effective nonequilibrium potential, and numerically observed [1,2]. [1] H.S. Wio, J.A. Revelli, M.A. Rodríguez, R.R. Deza and G.G. Izús, Eur. Phys. J. B 69, 71 (2009). [2] M.G. dell’Erba, G.G. Izús, R.R. Deza and H.S. Wio, Eur. Phys. J. D (2011) DOI: 10.1140/epjd/e2010-00269-2 Keywords: nonequilibrium Ising–Bloch front bifurcation, stochastic resonance, non-equilibrium potential, scaling law Email: deza@mdp.edu.ar

179

PL-5- Consistent spatial discretization of the KPZ equation

Wio H.S.1, Revelli J.A.2, Deza R.R.3, Escudero C.4

1IFCA (UC-CSIC), Spain; 2IFEG (UNC-CONICET), Argentina; 3IFIMAR (UNMdP-

CONICET), Argentina; 4UAM, Spain

Surface- and interface-growth processes lie at the heart of multibillion-dollar in-dustries like semiconductor and pharmaceutical ones, besides their crucial role in biol-ogy and environmental chemistry. That is why the appearance a quarter of century ago of a highly successful phenomenological mesoscopic model—the stochastic nonlinear PDE known as the Kardar–Parisi–Zhang (KPZ) equation—was so celebrated.

Its suitability for analytical work, its explicit symmetries, and its prediction of an exact dynamic scaling relation for a one-dimensional substratum, led people to adopt it as the “standard” model to describe the growth of rough interfaces, and it readily be-came a paradigm of nonequilibrium growth processes. Some of its interesting properties from a theoretical viewpoint are its exact mappings to the Burgers equation and to a dif-fusion equation with multiplicative noise, whose field can be interpreted as the re-stricted partition function of the directed polymer problem. The feature that made it so successful and interesting is the phenomenologically grounded “gradient-squared” term (a.k.a. “the KPZ term”).

The usual discretization choices in finite-difference schemes have been centered Laplacian and gradient. This choice respects a discrete form of Galilean invariance (re-lated to tilting invariance of the particle flow in microscopic growth models and thought to be at the heart of exact scaling relations in one spatial dimension). Other choices re-spect instead a fluctuation–dissipation theorem (also peculiar of 1D). We show that all those choices are inconsistent and moreover, that neither Galilean invariance nor the fluctuation–dissipation theorem are really an issue. We even propose a highly accurate spatial discretization scheme, which accelerates the setting of the asymptotic scaling regime. [1] H.S. Wio, J.A. Revelli, R.R. Deza, C. Escudero and M.S. de la Lama, Europhys. Lett. 89, 40008 (2010); ibid., Phys. Rev. E 81, 066706 (2010); ibid., Phil. Trans. Roy. Soc. A 369, 396 (2011). Keywords: KPZ equation, consistent discretization, Galilean invariance, fluctuation–dissipation Email: deza@mdp.edu.ar

180

PL-6- Tricritical behavior of Blume Capel model: a study of the Short-

Time Dynamic evolution of the metastable phases in the coexistence

region

Bab M. A.1 and Figueiredo W.2.

1Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas, Facultad de

Ciencias Exactas, UNLP-CCT La Plata CONICET, Argentina 2Departamento de Fisica, Universidade Federal de Santa Catarina, Brasil.

We have studied the nonequilibrium dynamic evolution of the Blume Capel Model-S=1 in the coexistence region close to tricritical point. As is well known, the metastable phase becomes unstable at the spinodal point and presents divergences in the susceptibility and relaxation times. By assuming that this behaviour is analogous to that observed in continuous phase transitions, the spinodal lines were obtained from short-time dynamic evolution of the relevant physical observables, such as the order parameter and its second moment, which follow a power law within the short-time regime. We have shown that the obtained spinodal lines agree with the thermodynamical spinodals in mean field (long-ranged) systems. The results allowed us to determine the tricritical point as well as the tricritical exponents. Keywords: Blume Capel Model, Short-time dynamics, spinodal, tricritical point. Email: mbab@inifta.unlp.edu.ar

181

PL-7- On the interplay between spatial and time symmetry in dynamic

and kinetic processes occurring in fractal media

Bab M. A.

Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas, Facultad de Ciencias Exactas, UNLP-CCT La Plata CONICET, La Plata, Argentina

The understanding of the kinetic and dynamic behaviour of the wide variety of

phenomena and processes, taking place in fractal media, is a challenging issue of increasing interdisciplinary interest. As is well known deterministic fractals are built iteratively from a generating cell, as consequence these exhibit discrete scale invariance (DSI) symmetry. DSI means that the fractal is scale invariant only between scales whose ratio is an integer power of the size of the generating cell b, named fundamental scaling ratio. Recent results report a subtle interplay between dynamic and kinetic processes and the DSI symmetry of the underlying fractal where the considered process takes, which leads to time DSI in the behaviour of the relevant observables. The hallmark of the time DSI is the observation of a log-periodic modulation on the dynamics or kinetics that is characterized by a well-defined fundamental time scaling

ratio, τ. Both fundamental scaling ratios are linked according to zb /1τ= , where z is the dynamic exponent of the corresponding physical process. In order to discuss this point, four paradigmatic cases will be addressed in detail: kinetics of diffusion-controlled reaction among random walker; the voter model that involves coarsening dynamic driven by interfacial noise in absence of surface tension; the contact process as representative of an epidemic propagation exhibiting irreversible critical behaviour; and the Ising model that represents a broad universality of reversible critical phenomena. Keywords: Fractal, Reversible phase transition, irreversible phase transition, contact process Email: mbab@inifta.unlp.edu.ar

182

183

Author Index

184

185

Abraham Ekeroth R.M.,150

Acquaroli L.N., 110 Aglietti E.F., 103, 104 Alarcón E., 78 Albano E.V., 176 Alessandrini J.L., 57, 136 Allekotte I., 13 Alonso R.E., 43, 105 Anoardo E., 59 Arce R.D., 110 Arcondo B., 111, 116 Arenas G. F., 149 Arenas, C.D., 79 Arnal P., 135 Aspee A., 78 Ayala A., 112 Bab M. A., 180, 181 Baggio-Saitovich E., 105 Baldo M., 68 Baran E.J., 63 Barbero C.A., 23 Bauer E., 21 Bergueiro J., 68 Bianchi A., 112 Bilovol V., 113 Binder K., 11 Bolink H.J., 123 Bolognini, N., 73 Borsarelli C.D., 78 Borzi R.A., 40 Bosch-Santos B., 122 Bosio V.E., 139 Bouciguez, A.C., 133 Boury F., 139 Bredice F., 145 Brine H., 123 Brizuela G.P., 64 Bruvera I., 38, 45, 109 Buceta R. C, 34 Bulus Rossini L.A., 147 Caarls W., 153 Cabaleiro L.V., 82 Cabanillas E.D., 41 Cabeza G., 48 Cabrera-Pasca G. A., 122 Calabria M.F., 165 Calvignac B., 139 Camaratta R., 123 Cammarota C., 56

Canosa N., 35, 36 Capoulat M.E., 68 Caram J., 120 Carbonari A.W., 122, 128, 129 Carlevaro C.M., 175 Cartelli D., 68 Casalini M.B., 67 Cascallares G., 155 Castell W., 68 Castillo E., 98 Castro F.A., 42 Castro G.R., 117, 139 Cavagna A., 56 Celej M.S., 153 Chain C.Y., 84, 127 Ciliberti L., 36 Civitarese O., 22 Cobos C.J., 140 Comedi D., 120 Conde Garrido J.M., 111 Cooper A., 158 Cordeiro M.R., 128 Córsico B., 158 Cortizo M.S., 136 Costanzo Caso P.A., 147 Cotes S.M., 176 Craievich A.F., 14, 124 Cremaschi V.J., 119 Croce A.E., 140 Cuellar L.A., 82 Cuniberti A., 115 Curilef S., 107 Czaban J.A., 120 Damonte L.C., 121, 123, 126, 127 Darriba G.N., 125 De Frutos J., 43 De la Rubia M.A., 43 De Sousa E.L., 38, 45, 109 Debray M.E., 68 dell’Erba M.G., 178 Deluque Toro C., 48 Demchenko A., 153 Descalzi O., 93 Deza J.I., 154, 157, 165, 170 Deza R.R., 137, 138, 154, 155, 157,

165, 170, 171, 178, 179 Di Paolo H., 68 Duchowicz R., 147, 148, 149 Dussan A., 110

186

Echeverría G., 112 Engel, M., 12 Enrique N., 69 Erhardt J., 68 Errico L.A., 105, 129, 130 Escudero C., 179 Esquinazi P., 9, 106 Estrada L., 68 Eversheim P.D., 130 Faccio R., 125 Fainstein A, 32 Falomir H., 28, 169, 172 Fernández C.O., 81 Fernández Guillermet A., 48 Fernández van Raap M.B., 38, 45, 109,

117 Ferrari, S., 121 Figueiredo W., 180 Filgueira R.R., 134, 135 Fontana M., 116 Forker, M, 105 Formigli C.M., 157 Fornaro O., 114 Fournier L.L., 134 Franchini G.R., 158 Gago P.A., 177 Gallardo M., 145 Galles, C.D., 89 Gangui A., 15 Garbellini O.1, 114 Garcés F.A., 110 Garda H.A., 82 Gelati P.R., 134, 135 Germán E., 64 Giardina I., 56 Giovanetti L.J., 124 Girardin P., 45 Gómez J.A., 42 Gonnella G, 108 González Flecha F.L., 83 Gonzalez S.J., 68 Goya R.G., 67, 109 Gradenigo G., 56 Graeff C.F.O., 42 Griesinger C., 81 Grigera S.A., 33 Grigera T. S., 56 Hallberg, K., 46 Hamidi S., 10 Heluani S. P., 106

Hermida, E.B., 79 Hernandez-Fenollosa M.A., 123 Herrera M., 68 Hoya J., 118, 126 Hoyuelos M.L., 146 Huck H., 68 Ibáñez M., 158 Igarzabal M., 68 Ilardo J.C., 68 Izús G.G., 137, 155, 178 Jares-Erijman E., 153 Jovin T.M., 78, 153 Juan A., 64 Junciel L. D., 112 Jusserand B., 32 Kavokin A.V., 31 Kennedy M., 158 Kesque J.M., 68 Kessler P, 10 Khalid M., 106 Khaneft, M., 12 Koebel M.M., 124 Kohanoff J., 51 Korol A.M., 154 Koropecki R.R., 110 Koval S., 51 Kreher, S., 50 Kreiner A.J., 68 Laborde C., 38, 45 Laborde J.I., 118, 126 Lanzillotti-Kimura N. D., 32 Lanzini F, 115 LaPierre R.R., 120 Lara, M.A., 133 Lasave J., 51 Lede E.J., 111 Leiva E.P.M., 97, 98 Lester M.F., 150 Liew T. C. H., 31 Lima A.N.C., 123 Linares C., 88 López-Corral I., 64 López-García A., 43 Lorenz K, 10 Lovey F.C., 49 Lozano L.A., 134, 135 Mangioni S.E., 138 Marenduzzo D., 108 Mariano A.E, 23 Mártin D.A., 146

187

Martín P., 69 Martinez Garcia R., 113 Matera J.M., 35 Mendoza A., 44 Mendoza Zélis P., 38, 45, 109, 117 Mercader R. C., 112 Mercurio M.E., 128 Migoni R., 51 Milesi V., 69 Minsky D.M., 68 Molina Ruiz M., 116 Montani F., 80 Morando C., 114 Morel G.R., 67 Muelller M., 60 Muñoz E.L., 128, 129, 130 Muraca D., 34 Murgida D.H., 77 Mykhaylyk O., 67 Negre C., 98 Nieto M., 169 Nüesch F., 42 Núñez-Fernández Y., 31 Oberti T.G., 136 Olivares F, 107 Oliveira R.G., 55 Orlandini E, 108 Orozco Messana J., 123 Ortiz E.L., 15 Osorio S., 112 Padulo J., 68 Pahissa Campá J., 24 Palacio H., 114 Parisi D.R., 177 Parisi G., 56 Pasquevich A.F., 84, 127 Pasquevich G., 38, 45, 109 Pastorino C., 60 Paul W., 11 Paulucci E., 148 Pennini F., 107 Pereira L.F.D., 128 Perrin B., 32 Petrilli H.M., 47 Piccinini L., 69 Pirota K., 113 Pisani P.A.G., 169, 172 Pórfido J. L, 158 Prieto E.D., 82 Pugnaloni L.A., 175, 177

Punte G., 112 Quille R.A., 127 Raineri M., 145 Ramallo-López J.M., 124 Ramella N., 156 Ramos de Debiaggi S.B., 48 Ramos S., 105 Rampf F., 11 Ratner M.J., 41 Rebolledo A., 69 Rendtorff N.M., 103, 104 Rentería M., 118, 125, 128, 129, 130 Requejo F.G., 124 Revelli J.A., 171, 179 Revuelta M.V., 117 Rey F., 158 Reyes Tolosa M.D, 123 Reyna Almandos J., 145 Richard D., 118, 129, 130 Rimoldi O.J., 156 Rocca J.A., 111, 116 Rodríguez C. R., 97 Rodriguez Viejo J., 116 Roig A.R., 57 Rojas M., 97 Roldán Palomo A.R., 69 Romero R., 115 Rossignoli R., 35, 36 Rosso O.A., 94 Russo N.A., 148 Sade M., 49 Saitovich H., 105 Sakka Y., 103 Salmeron M., 124 Sánchez A.D., 137, 155 Sánchez C.G., 98 Sánchez F.H., 38, 45, 67, 109, 117 Sandoval C., 120 Sanservino M.A., 140 Santoro A., 161 Saracco G. P, 108 Sarli G.O., 134, 135 Sartarelli S.A., 58 Savino G.V., 157 Saxena R. N., 122 Schlom D. G., 32 Schmidt J.A., 37 Schwerdt J. I., 67 Sereni J.G., 39 Sessolo M., 123

188

Sicre E.E., 147, 148 Sigal A., 97 Silva P.R.J., 105 Silva V., 158 Silveyra J.M., 119 Smith B., 158 Socolovsky L. M., 113 Somacal H.R., 68 Soracco C.G., 134, 135 Sosa M.I., 141 Sosa Y.E., 109 Soukiassian A., 32 Spivak L’Hoste A., 87 Stewart S., 38, 45 Strauch T., 11 Stühn, B., 12 Suárez G., 103, 104 Suarez Sandin J.C., 68 Szybisz L., 58 Taylor M. P., 11 Taylor M.A., 105 Tebaldi, M., 73 Thatar Vento V., 68 Tirado M., 120 Torra V., 49 Torre M.H., 63

Torriani I. L., 112 Torroba, R., 73 Tosatti E., 51 Trallero-Giner C, 31 Tricerri M. A., 156 Ureña M.A., 111 Urtega R., 110 Valda A.A., 68 Van Eek, S.M., 50 Vasilevskiy M. I, 31 Vega F.G., 172 Vélez P., 98 Verrocchio P., 56 Vianden R., 10 Vilche M., 69 Villa, L. T., 133 Volpe M.A., 64 von Reichenbach M.C., 90 Wahlberg H., 27 Wio H.S., 170, 171, 178, 179 Yawny A., 49 Zapata C., 106 Zoloff Michoff M.E., 98 Zuppiroli L., 42 Zweckstetter M., 81

189

Keywords Index

190

191

ab initio, 51, 109, 122, 134 Ab initio calculations, 47, 48, 132, 146 Accelerator-based BNCT, 70 Acrylic Monomers, 141 Additive Pulse Mode Locking, 154 Adsorbed Films, 58 alkali halide, 122 alpha-synuclein, 159 Alumina, 129, 50 Amino acids, 63 amorphous and nanocrystalline

materials, 123 Amyloid, 84 amyloidosis, 162 amyloids, 159 anomalous diffusion, 176 antiphase coupling, 161 apolipoprotein A-I, 162 Apolipoprotein A-I, 85 APW+lo, 129 ascorbic acid, 121 Atomic layer deposition, 50 atomic order, 119 Atomic Structure, 151 Barkhausen effect, 34 BET method, 140 bifurcations, 163 bioabsorbable scaffold, 82 Biomedical Applications, 38 biomembrane, 55 biophysics, 55, 112 bixbyite, 134 Blume Capel Model, 186 BNCT, 70 Bond dissociation energies, 146 Born radius, 57 bursting oscillator, 163 CaCO3 microparticles, 145 Calcia, 108 Carboxylate, 63 CeCoIn5, 109 Cell Cholesterol Efflux, 86 cell membrane, 55 cellular magnetic labelling, 45 ceramic composites, 107 centenario, 88 Chalcogenide glasses, 120 Chlorine oxides, 146 Ciencia en contexto, 15

Clean development mechanism, 147 Cogeneration, 147 Coherent Phonon Emission, 32 coil-globule transition, 11 Compound Energy Formalism, 48 Condensed Matter, 32 Condensed matter physics, 112 conmemoración, 91 consistent discretization, 185 contact lenses, 88 contact process, 187 continuous-time random walks, 176 convective instability, 143 Copolymerization, 141 Copper(II), 63 core-shell nanowire, 124 Cosmic Rays, Pierre Auger, 27 Crystallization, 120 CuAlBe Single Crystals, 49 Cu-In-Sn alloys, 48 CuO, 116 Cu-Zn-Al shape memory alloys, 119 data acquisition and control, 171 DCM-TPA, 42 decay after effects, 131 defect, 122 defects, 10, 182 Density Functional, 58 DFT, 47, 64, 129 DFT calculations, 101, 102 diffractometry, 160 Diffusion–reaction systems, 176 DIFICI mechanism, 143 diluted magnetic semiconductors, 9 Dimers, 150 dinámica molecular, 60 drug delivery, 121, 145 Dye Doped OLEDs, 42 dynamical heterogeneities, 56 dynamical systems, 98 EDMR, 42 EFG, 109, 132 electric field effects, 80 Electric-Field Gradient, 129 electroerosion, 41 Electron tubes, 167 Electronic Structure, 47 electronic transport, 46 Electronics, 167

192

Electrostatics, 57 Emil Bose, 90 Enthalpies of formation, 146 entropy, 98 Entropy, 39 Erythrocytes, 160 etnografía, 91 eutectic systems, 118 Exciton formation, 42 far from equilibrium behavior, 112 fast ionic conductors, 115 Fatty Acids, 158 F-center, 122 ferroelectric, 51 ferromagnetic thin films, 34 Fiber Bragg Grating, 154 Fiber Laser, 154 Fiber Optic, 155 Fiber optics, 153 field-cycling, 59 Finemet, 123 Fisher information, 111 fisión, 24 FitzHugh–Nagumo model, 161 fluctuation–dissipation, 185 Fluid Structure, 58 fluidity, 118 fluorescence, 159 Fluorescence Resonance Energy

Transfer, 85 Fourier Optics, 76 Fractal, 187 fractal dimension, 139 fractional calculus, 160, 176 fragmentation, 139 Free Radical Polimerization, 141 Galilean invariance, 185 Gans, 93 gene delivery, 68 genetic algorithm, 171 Ginzburg-Landau, 93 global shift invariance, 177 granular flow, 183 Granular Matter, 181 Graphene, 64 grupo Buenos Aires, 24 Hadronic Models, 27 H-bond, 51 heterogeneous catalysis, 144 High Density Lipoproteins, 85

Historia de la ciencia, 15 History, 93, 167 Hopfbifurcation, 93 Husimi distributions, 111 hybrid materials, 145 hydrogen storage, 101 Hydrogen storage, 64 hydrophilicity, 82 hydrophobic xerogel, 121 hyperfine interactions, 126 hyperfine properties, 47 impedance spectroscopy, 116, 124, 43 indium oxide, 131 Information Geometry, 83 institución científica, 91 Instituto de Física La Plata, 90 Interface position, 138 Interferometry, 155 ionic channels, 71 iron oxide nanoparticles, 113 Iron oxide nanopowders, 117 irreversible phase transition, 187 Ising model, 182 jamming, 183 Kerr-like nonlinearity, 152 Kinetics, 81 Koval S., 51 KPZ equation, 177, 185 La Plata, 93 Lambda-hypernuclei, 21 Lasave J., 51 laser ablation, 41 Laser Modeling, 154 lattice defects, 9 lead-free soldering alloys, 48 Lipid Binding Proteins, 158 LNLS, 14 Magnetic, 38 magnetic domains, 44 Magnetic Frustration, 40 magnetic hyperfine field, 126 magnetic hyperthermia, 45, 113 magnetic labelling, 113 Magnetic nanoestructures, 31 magnetic nanoparticles, 45, 68 magnetic order, 9 magnetofection, 68 Magnetotransport, 110 Many-Body Systems, 35 Marconi, 88

193

Margaret Heigberg de Bose, 90 Martensitic Phase Transitions, 49 martensitic transformation, 107 Mass Composition, 27 mass-size scaling, 139 mass-time scaling, 139 matter structure, 112 Measurements of neutrino physics at the

ANDES lab, 22 mechanical alloying, 108 Mechanical Behavior, 49 mechanical milling, 130 Medical physics, 70 Membrane protein unfolding, 87 mesomorphic materials, 59 Metallic Nanotubes, 150 Metamaterials, 152 Metastable strontium hexaferrite, 117 microelectronics, 50 Microfluídica, 60 micropores, 140 Microwave Energy, 141 Molybdenum, 123 Monte Carlo, 182 Monte Carlo dynamic, 34 Monte Carlo simulations, 11, 56 Mössbauer spectroscopy, 115 multiplicative noise, 144 mutual information, 171 nano and micro particles, 41 nanocrystalline semiconductors, 130 nanocrystalline ZnO, 127 nanomagnetism, 116 Nanomaterials, 38 Nanoparticles, 128 nanopatterns, 144 nanoporous membranes, 12 nanoscopoic systems, 46 nanostructure, 116 nanostructured films, 127 nanotechnology, 68 nanowires, 102 National laboratories, 14 Nematicity, 33 Neural code, 83 Neurodegeneration, 84 neuron, 163 neutrino, nucleon, 23 neutron scattering, 12 nitrogen adsorption, 140

NMR, 84, 158 NMR relaxometry, 59 Noise Correlation, 83 noise-enhanced propagation, 171 noise-sustained structures, 143 Non-Commutative Field Theory, 178 Noncommutative Quantum Mechanics,

175 nonequilibrium Ising–Bloch front

bifurcation, 184 nonequilibrium potential, 177, 184 Nonequilibrium potential, 161 non-homogeneous glasses, 115 Nonlinear optics, 31 non-mesonic weak decay, 21 Nuclear reactors, 14 numerical simulations, 46 OLEDs, 42 Optical bistability, 152 Optical encryption, 76 Optical processing, 153 Optical Spectroscopy, 151 Opto-digital image processing, 76 order kinetics, 119 oxides, 9 P ATPases, 87 PAC, 10, 132, 43 PAC spectroscopy, 126 Packing; Melting point, 138 Palladium, 64 Parasite, 158 Parkinson’s disease, 159 patch clamp, 71 pedestrian traffic, 183 perovskite, 43 perturbar angular correlations (PAC),

131 Perturbation Theory, 175 Phase change material (PCM), 138 Phase change memories, 120 Phase transformation, 117 Phase Transitions, 181 Phase-space representations, 153 Photochemistry, 81 Photoconductivity, 110 photocuring, 155 photovoltaic cells, 127 Photovoltaic Cells, 37 photovoltaic devices, 124 Physics, 93, 167

194

Picosecond Acoustics, 32 plasma ablation, 41 Plasmonics, 150 Polaritons, 31 Polycrystalline Silicon, 37 Polyelectrolytes, Solvent models, 57 polyhydroxybutyrate, 82 polymer, 12 polímeros, 60 polymers, 88 Porous silicon, 114 positron annihilation, 130 protein dynamics, 80 protein electron transfer, 80 protein misfolding, 162 proteins, 88 Proteins, 81 Pseudoelasticity, 49 Quantum Correlations, 36 Quantum Criticality, 39 Quantum entanglement, 36 Quantum Entanglement, 35 Quantum Information, 35, 36 radioquímica, 24 radiotelegrafía, 88 Raman, 80 rare-earth compounds, 126 Rational use of energy, 147 Reduction of greenhouse emissions, 147 Relatividad, 15 Resistivity, 120 Reversible phase transition, 187 Rhythmic activity patterns, 83 Ring cavities, 152 Rubrene, 42 Ruthenates, 33 SAXS, 128 scaling, 34 scaling law, 184 scandium oxide, 134 scattering, resonances, 23 semiconductor, 124, 134 Semiconductor, 110 Semiconductor and Oxide Nanocavities,

32 semiconductors, 10 Short-time dynamics, 186 SIESTA, 129 Singular Potential, 175 small angle scattering, 12

smooth muscle cells, 71 Solar Energy, 37 sol-gel, 121 Sol-Gel, 114 solidification structures, 118 solitons, 93 Specific Heat, 39 Speckle, 76 Spectral Functions, 178 Spectroscopy, 81 Spectrum of energies, 175 Spin Chains, 35, 36 spin-ice, 40 spinodal, 186 Static Packings, 181 statistical complexity, 98 statistical mechanics, proteins, 11 stochastic resonance, 184 Stretching vibrations, 63 strong correlations, 46 Strongly correlated systems, 33 Structural Biology, 84 sub-dominant attractive forces, 144 supercooled liquids, 56 surface morphology, 44 surface tension, 56 Surfaces, 129 Synchrotron radiation, 14 synchronization, 143, 161, 163 Tandem-Electrostatic Quadrupole, 70 TCO, 114 TDPAC, 109 Telefunken, 88t thermal analysis, 43 thermal behaviour, 107 Thermal Expansion, 155 Thermodynamics, 87, 111 thin films, 37, 182 Third law of thermodynamics, 39 time series analysis, 98 tissue engineering, 82, 145 tissues, 88 Tosatti E., 51 tradición, 91 transport properties, 44 tricritical point, 186 tumoural cell, 113 two-nucleon induced decay, 21 Typic argiudoll, 140 ultrasound, 59

195

uranio, 24 variational formulation, 177 viscoelasticity, 160 Wetting, 58 Wherl entropies, 111 XAFS spectroscopy, 115 XRD, 108 Zirconia, 107, 108 ZnO, 132

196

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