Colóquios e Seminários

Colóquio IF/USP: “A questão energética”

O colóquio será transmitido ao vivo na IPTV/USP.

Para assistir on-line, acesse www.iptv.usp.br

Café com física: “Scattering Amplitudes as a Flux-Tube Gas”

I will survey recent progress in the quest for an exact formulation of gauge theories. I will describe recent progress in looking for a new description of Quantum Field Theory, based on so-called Integrability techniques, which bypasses the use of traditional Feynman diagram perturbative techniques and promises to greatly improve our understanding of finite coupling quantum fields. More precisely, we shall propose the first non-perturbative formulation of planar scattering amplitudes in a non-abelian Gauge theory (N=4 Super Yang-Mills Theory) or, equivalently, polygonal Wilson loops. The construction is based on the Operator Product Expansion approach and introduces a new decomposition of the Wilson loop in terms of fundamental building blocks named Pentagon transitions. These transitions satisfy a simple relation to the worldsheet S-matrix on top of the so called Gubser-Klebanov-Polyakov vacuum which allows us to bootstrap them at any value of the coupling.

Seminários do CCMC: “Desenvolvimento de nanotubos de óxidos metálicos e nanopartículas metálicas”

O desenvolvimento de nanoestruturas avançadas de óxidos metálicos semicondutores com capacidade de absorção de luz solar na faixa do espectro visível é uma das áreas da ciência que ganhou muita atenção nas duas últimas décadas. Isso se deve às expectativas que os óxidos metálicos vêm gerando na possibilidade de sua utilização na produção fotocatalítica de hidrogênio e na fabricação de células solares mais eficientes para a geração de energias renováveis. Em especial, a geração fotocatalítica de hidrogênio a partir da água, fotocatalisador semicondutor e energia solar, constitui um dos processos mais desafiadores e promissores para a geração de energia limpa da atualidade. O desenvolvimento de nanotubos de óxidos metálicos é muito atraente para as aplicações fotocatalíticas, uma vez que materiais com geometria 1D têm-se mostrado muito eficientes para o transporte de cargas sobre a superfície, quando comparados com materiais maciços “bulk” ou de geometria esférica. Além disso, o rendimento da produção fotocatalítica de H2 pode ser drasticamente aumentada quando se utiliza nanopartículas metálicas sobre a superfície dos óxidos metálicos como cocatalisadores da reação. Neste trabalho, os desafios e as perspectivas para a produção eficiente de H2 utilizando água, luz solar e nanotubos de óxidos metálicos serão abordados. A síntese de crescimento de nanotubos de óxidos metálicos por anodização e um método físico de deposição de nanopartículas “limpas” sem utilizar precursores orgânicos como agentes redutores ou estabilizadores serão discutidos.

Seminário Especial (Grupo de Polímeros): Electron transport and reactivity through single molecule”

Electron transfer is one of the most fundamental processes in many important systems with relevance to areas such as biology, solar energy conversion, from respiration to photosynthesis, molecular electronics, electrochemistry, catalysis, and information storage. Therefore, understanding interfacial electron transfer between molecules and electrodes, and their dynamics at the molecular level, is important for fundamental science as well as for technological applications. However, the most of the present knowledge of interfacial electron transfer between molecules and electrodes mainly relies on ensemble averaged spectroscopic and electrochemical measurements. Thus, our understanding of the interfacial electron transfer dynamics at the molecular level is very limited. The ability to measure and to control charge transport at the molecular level represents a key step towards the understanding of local structure, electronic conductance, and electrochemical charge transfer in active nanometer-scale molecular systems at well-defined solid|liquid interfaces.

Among various experimental approaches, single-molecule junctions formed in a metal-substrate|molecule|STM-tip configuration has contributed significantly to the fundamental understanding of the principles required to realize molecular-scale electronic components, switches, transducers and sensors. In this talk we will discusse the interfacial and electronic properties of molecular systems sandwiched between two electrodes at the molecular scale in a metal-substrate|molecule|STM-tip configuration.

Seminário do Grupo de Polímeros: “Nonlinear imaging in turbid biological media”

Nonlinear microscopy (NLM) has emerged as a powerful technique for biological imaging in a label-free manner. Two-photon fluorescence imaging of neural activity, coherent Raman scattering imaging of lipid-rich assemblies, second-harmonic generation imaging of collagen structures and sensitive screening of pharmaceuticals, are just a few representative examples. Despite the tremendous impact of NLM, all of nonlinear imaging modalities can only image at shallow depths because deeper penetration imaging into biological specimens is hindered by scattering phenomena. In the first part of this presentation, and in order to present the current state-of-the-art nonlinear imaging capabilities, I will present a study of depolarization effects due to scattering on polarization-resolved coherent anti-Stokes Raman scattering imaging of opaque spinal cords myelin sheaths. The results highlight how scattering can lead to erratic conclusions and also how shallow nonlinear imaging is currently possible on biological specimens. I will then present how we used wavefront shaping (WS) technique to image through strongly scattering media in order to enhance the (imaging) penetration depth. After an explanation of WS fundamentals, I will show how we successfully imaged nonlinear sources of second-harmonic photons after strongly scattering medium, at a sub-diffraction limited resolution. These results demonstrate that nonlinear imaging deep in biological specimens is no longer limited to shallow depths.

Seminário internacional do Grupo de Nanomedicina: “Multiplex electrochemical DNA platform”

Current EU regulations on the mandatory labelling of genetically modified organisms (GMOs) with a minimum content of 0.9% would benefit from the availability of reliable and rapid methods to detect and quantify DNA sequences specific for GMOs. Different genosensors have been developed to this aim, mainly intended for GMOs screening. A remaining challenge, however, is the development of genosensing platforms for GMO quantification, which should be expressed as the number of event-specific DNA sequences per taxon-specific sequences. We report a simple and sensitive multiplexed electrochemical approach for the quantification of Roundup-Ready Soybean (RRS). Results indicate that the method could be applied for GMO quantification below the European labeling threshold level (0.9%), offering a general approach for the rapid quantification of specific GMO events in foods.

Colloquium diei: “Ultrafast process im many electron systems”

After a general introduction to time-dependent density-functional theory, several recent applications of the theory will be presented: We study the laser-induced ultrafast demagnetization of solid Fe, Co and Ni; we investigate the dynamics of chemical bonds and address the question, how much time an electron needs to make a transition from one state to another; we study molecular junctions focussing on cases where, after turning on a bias, no steady state is achieved; and finally we combine time-dependent density functional theory with optimal control theory to find laser pulses specifically tailored to enhance a single peak in the harmonic spectrum of atoms.

Journal Club: Topological Insulators and Quantum Spin Liquids

Topological states of matter is an umbrella term to designate phases of matter with very different physical origin, such as the Quantum Hall Effect (QHE), the topological insulators (TI) and the quantum spin liquids (QSL). Because of the differences, it is at first glance hard to see any relation between these states, giving the appearance that the branch of topological condensed mater theory is completely fragmented. In spite of that some connections were recently found between the QHE, TIs and QSLs, opening new guidances to look for models that support topological phases. In this seminar, such connections will be introduced. The focus will be on a correspondence between a modified Kitaev honeycomb model and the Haldane model and on 3D strongly correlated systems in the strong spin-orbit regime. The first case inspired the generation of tight-binding models that supports either a QSL or a TI phase, establishing a method of generating certain types of desired states. In the second case, we review the research into systems that have a combination of the key elements for the generation of topologically non-trivial phases.

Colloquium diei: “Relação dos jovens com o saber e com a escola na sociedade contemporânea”

Que sentido tem para um jovem o fato de ir à escola, o fato de estudar (ou não estudar) na escola, o fato de aprender e compreender, quer na escola quer fora dela? De acordo com os alunos, o que é “uma aula interessante”? Na lógica dos alunos, quem é responsável do sucesso ou do fracasso escolar: o aluno ou o professor? Qual a diferença entre “aprender na escola” e “aprender na vida”? Por que, apesar da inegável desigualdade social frente à escola, encontram-se também nas famílias populares alunos bem-sucedidos e nas classes médias alunos fracassados?

Essas questões e mais algumas outras foram investigadas, na França, no Brasil e em alguns outros países, pelas pesquisas sobre a relação dos alunos com o saber e com a escola. Respaldada em pesquisas de campo desenvolvidas na França, no Brasil e em alguns outros países, a teoria da relação com o saber associa abordagens pedagógicos, psicanalíticos, sociológicos, antropológicos e didáticos.

Seminário do Grupo de Óptica: “A Quantitative Study of In Vivo Protoporphyrin IX Fluorescence”

Photodynamic therapy (PDT) relies on the interaction between light, oxygen and a photosensitive chemical: Protoporphyrin IX (PpIX). Louise will talk about the current study being performed at Hospital Amaral Carvalho in Jahu city, where the build up of PpIX in different skin lesions is measured using the fluorescence signal produced by the drug. The research will help to gain more understanding of the kinetics and dynamics of the PDT treatment process as well as help to generate more accurate computer models. Initial results show that the PpIX builds up in the lesion linearly with time over the 3 hours of occlusive treatment.

Journal club: “Impurity-induced bound states in superconductors with spin-orbit coupling”

We study the effect of strong spin-orbit coupling on bound states induced by impurities in superconductors. The presence of spin-orbit coupling breaks the SU(2)-spin symmetry and causes the superconducting order parameter to have generically both singlet (s-wave) and triplet (p-wave) components. As a result, impurity induced bound states corresponding to different angular momentum channels hybridize and display a number of qualitatively different features from that of the well-known Yu-Shiba-Rusinov states in conventional s-wave superconductors. In particular, we find that in the presence of spin-orbit coupling the spectrum of the impurity induced bound states depends on the orientation of the magnetic moment of the impurity. Our predictions can be used to distinguish the symmetry of the order parameter and have implications for the Majorana proposals based on chains of magnetic atoms placed on the surface of superconductors with strong spin-orbit coupling [1].

[1] S. Nadj-Perge, I. K. Drozdov, J. Li, H. Chen, S. Jeon, J. Seo, A. H. MacDonald, B. A. Bernevig, and A. Yazdani, Science (2014).

Journal club: “Impurity-induced bound states in superconductors with spin-orbit coupling”

We study the effect of strong spin-orbit coupling on bound states induced by impurities in superconductors. The presence of spin-orbit coupling breaks the SU(2)-spin symmetry and causes the superconducting order parameter to have generically both singlet (s-wave) and triplet (p-wave) components. As a result, impurity induced bound states corresponding to different angular momentum channels hybridize and display a number of qualitatively different features from that of the well-known Yu-Shiba-Rusinov states in conventional s-wave superconductors. In particular, we find that in the presence of spin-orbit coupling the spectrum of the impurity induced bound states depends on the orientation of the magnetic moment of the impurity. Our predictions can be used to distinguish the symmetry of the order parameter and have implications for the Majorana proposals based on chains of magnetic atoms placed on the surface of superconductors with strong spin-orbit coupling [1].

[1] S. Nadj-Perge, I. K. Drozdov, J. Li, H. Chen, S. Jeon, J. Seo, A. H. MacDonald, B. A. Bernevig, and A. Yazdani, Science (2014).

Journal club: “Impurity-induced bound states in superconductors with spin-orbit coupling”

We study the effect of strong spin-orbit coupling on bound states induced by impurities in superconductors. The presence of spin-orbit coupling breaks the SU(2)-spin symmetry and causes the superconducting order parameter to have generically both singlet (s-wave) and triplet (p-wave) components. As a result, impurity induced bound states corresponding to different angular momentum channels hybridize and display a number of qualitatively different features from that of the well-known Yu-Shiba-Rusinov states in conventional s-wave superconductors. In particular, we find that in the presence of spin-orbit coupling the spectrum of the impurity induced bound states depends on the orientation of the magnetic moment of the impurity. Our predictions can be used to distinguish the symmetry of the order parameter and have implications for the Majorana proposals based on chains of magnetic atoms placed on the surface of superconductors with strong spin-orbit coupling [1].

[1] S. Nadj-Perge, I. K. Drozdov, J. Li, H. Chen, S. Jeon, J. Seo, A. H. MacDonald, B. A. Bernevig, and A. Yazdani, Science (2014).

Seminário do Grupo de Óptica: “Fenômenos fotoinduzidos em vidros calcogenetos”

Os vidros calcogenetos pertencem a um importante grupo de materiais inorgânicos que possuem um ou mais elementos calcogênios (S, Se ou Te) em sua composição, ligados covalentemente com formadores de rede tais como As, Ge, Sb, P. Esses materiais apresentam boa estabilidade térmica e química, alto índice de refração e transparência na região do infravermelho.

Uma das propriedades bastante estudada nos vidros nesses materiais vítreos é a fotossensibilidade, que apresenta uma variedade de fenômenos fotoinduzidos como fotoexpansão, fotocristalização, fotodissolução, etc. Estes fenômenos têm sido estudados extensivamente, levando a inúmeras aplicações como, por exemplo: mídia para armazenamento de informações ópticas, grades holográficas eficientes, microlentes, células solares, etc. A fotossensiblilidade nos vidros calcogenetos ocorre devido a tendência de mudança nas ligações químicas, quando exposto à luz com comprimento de onda próximo a borda de absorção. O mecanismo envolve a criação de pares de elétrons-buraco, que mudam a valência dos átomos vizinhos e suas ligações químicas, criando assim defeitos. Estes estados induzidos pela luz são fisicamente próximos uns dos outros, assim possibilitando a quebra e restauração de ligações ou mesmo a formação de novas ligações químicas, resultando assim em uma mudança macroscópica nas propriedades físicas do material, proporcionando uma ampla variedade de fenômenos fotoinduzidos.

Café com física: “Molecular Imaging in Oncology”

Molecular imaging is emerging as an incredibly powerful tool in oncology research. With unprecedented specificity to capture some of the key cancer hallmarks (e.g., proliferation), it can assess pharmacodynamic effects of various therapies on tumor response. A general overview of molecular imaging, its potential and limitations will be presented in the lecture. An example of a pharmacodynamic study using 3′-deoxy-3′[(18)F]-fluorothymidine, [(18)F]-FLT PET/CT in assessing response to anti-angiogenic therapies (VEGFR TKI) will be shown. Patient-specific modeling of tumor response to VEGFR TKI based on FLT PET/CT molecular imaging will be used to illustrate intimate connection between tumor modeling and molecular imaging-based clinical trials.

Seminário do Grupo de Óptica: “Scaling in cold few-atom systems in different dimensions”

Close to s-wave Feshbach resonances two and few-atom systems can come near the continuum threshold, and three atoms in the state of zero angular momentum presents the Efimov or Thomas effect when the scattering length is large or the range of the s-wave interaction tends to zero. In this limit the binding energy and sizes of three-body systems in zero angular momentum states are dependent on a three-body single scale, showing universal and model independent correlations between these quantities. In two dimensions the relevant s-wave scales are the pair binding energy, which leads to model independent laws for the dependence of the three-body bound state energies on these quantities. The continuous transition between these different scaling behaviors in three-boson systems by continuously squeezing one dimension will be also discussed. The four-boson system in 3 dimensions in the limit of s-wave zero range forces exhibits a scaling behavior with a new single scale, which appears, in particular, in the position of the four-body resonant recombination. Range correction to this scaling law will be shown and results compared to the experimental data.

Seminários do Laboratório de Química Medicinal e Computacional

Seminário 1

Título: Development of selective trypanocidal compounds targeted against the glycolytic enzymes of the parasites

Data: 20 de novembro

Hora: 13h30

Local: IFSC área II (1º piso, sala 1)

Palestrante: Paul A. M. Michels (University of Edinburgh– Reino Unido)

Seminário 2

Título: Avaliação da atividade anti-Trypanosomatidae e potencial mecanismo de ação de compostos ciclopaladados

Data: 20 de novembro

Hora: 14h30

Local: IFSC área II (1º piso, sala 1)

Palestrante: Marcia Graminha (Unesp)