Colóquios e Seminários

Seminário especial do Grupo de Polímeros: Duc Trong Duong

One of the biggest challenges in the field of semiconducting polymers is the fundamental understanding of crystallization kinetics and thin film growth. The difficulties facing such studies stem from the inherently short crystallization times of these materials and the relatively slow techniques available for characterizing nanoscale microstructures. To overcome these limitations, we chose to investigate the polymer poly(3-ethylhexylthiophene) (P3EHT). Due to its low melting point, P3EHT exhibits slow crystallization kinetics when quenched at room temperature from the melt, which is a rare property among semiconducting polymers. We perform quantitative analyses of x-ray diffraction patterns and optical absorption spectra P3EHT thin films and are able to monitor the evolution of aggregates and crystallites as well as the recrystallization kinetics as a function of time. Here we find that the growths of individual aggregates and crystallites along the three packing directions are indeed anisotropic and exhibit different growth rates. Furthermore, we show that crystallization kinetics depend on a number of parameters including film thickness, molecular weights and quenching temperatures, which is all attributed to chain confinement effects. Finally we also correlate the evolution of thin film microstructure to electronic properties and charge transport. From these measurements, we directly observe the onset of charge percolation in thin film and demonstrate that polymer tie chains are responsible for efficient charge transport.

Seminário do Grupo de Óptica: “Curriculum Lattes”

Neste seminário será feita uma apresentação da Plataforma Lattes, para conhecimento dos mecanismos e suas funcionalidades para busca, cadastro e atualização das produções Bibliográficas, Técnica e Artística. A importância da atualização do Curriculum Lattes faz com que a vida profissional, cientifica e intelectual dos alunos e pesquisadores tenha mais visibilidade e transparência permitindo uma avaliação global através das agências de fomento, instituições de pesquisa, empresas etc.

Journal Club: “Indirect dark matter search and the positron fraction measurement”

The Alpha Magnetic Spectrometer (AMS-02) is a large acceptance particle physics detector, operating onboard the International Space Station (ISS) since May 2011. The main goals of AMS-02 are the search for antimatter and dark matter, and the precise measurements of cosmic rays composition and flux.

The study of the electromagnetic component of the cosmic rays, namely electrons, positrons, is of primary importance in the search for primordial antimatter and dark matter in the Universe.

The present seminary will describe the methods to identify electrons and positrons in cosmic rays in GeV to TeV region, and will describe the performances of AMS-02 in this context. Particular emphasis will be given to the latest AMS positron fraction measurement, that will be published this week.

Café com física: “O detector biológico de infravermelho mais preciso do mundo”

Não se sabe como este detetor funciona. Após descrevê-lo, serão apresentados dados experimentais e as dificuldades para propor um modelo minimamente realista. Tal como o nosso olho, que consegue detectar um só fóton, desconfiamos que este seja um “aparelho” explorando os limites da fisica.

Seminário do Grupo de Óptica: “Biophotonic Technologies to Improve Global Health”

In this presentation Dr. Rebecca will talk about translating research that integrates advances in nanotechnology and molecular imaging with microfabrication technologies to develop optical imaging systems that are inexpensive, portable, and provide point-of-care diagnosis. This basic and translational research is highly collaborative and has led to new technologies to improve the early detection of cancers and other diseases, especially in impoverished settings.

Seminário: “Monitoramento da Resistência do Plasmodium falciparum”

Chloroquine (CQ), a cost effective antimalarial drug with a relatively good safety profile and therapeutic index, is no longer used by itself to treat patients with Plasmodium falciparum due to CQ-resistant strains. P. vivax, representing over 90% of malaria cases in Brazil, despite reported resistance, is treated with CQ as well as with primaquine to block malaria transmission and avoid late P. vivax malaria relapses. Resistance to CQ and other antimalarial drugs influences malaria control, thus monitoring resistance phenotype by parasite genotyping is helpful in endemic areas.

Journal Club: “Controlling spin-correlations in double quantum dots”

In the last decades, a great effort has been invested in understanding how to utilize the spin degree of freedom of confined electrons as a component of a quantum computation device or in spintronics. In this regard, one of the main challenges is to be able to construct, control and manipulate entangled states between spins.

First, for a double quantum dot system in a parallel geometry, I will demonstrate that by combining the effects of a flux and driving an electrical current through the structure, the spin correlations between electrons localized in the dots can be controlled at will. In particular a current can induce spin correlations even if the spins are uncorrelated in the initial state. Therefore, we are able to engineer an entangled state in this double-dot structure. Using a canonical transformation, I will provide an intuitive explanation for the results, related to Ruderman-Kittel-Kasuya-Yoshida physics driven by the bias.

In the second part of this talk I will consider the two quantum dots structure to study the decay of a maximally entangled state between the dots. The system is prepared in a perfect singlet and then coupling one of the dots to electronic baths. Two cases can be identified: In a first regime a direct electronic current cause decoherence and the entanglement, as well as spin correlations, decay exponentially fast. A second regime is found for zero or small voltages and beyond the mixed-valence regime; in this case virtual tunneling processes dominate and lead to a slower loss of coherence.

A combination of these two effects, the formation and destruction of a singlet state using a bias, can be proposed as a mechanism to control the entanglement between electrons in quantum dots.

Seminário Grupo de Óptica: “Pesquisa Clínica e Desenvolvimento de Novos Medicamentos”

A consultora científica da Novartis Biociências S.A. abordará neste seminário informações para o suporte na elaboração e desenvolvimento de projetos de pesquisa clínica e desenvolvimento de novos medicamentos, dando continuidade à apresentação sobre o papel do consultor científico Medical Science Liaison.

Ana Paula é Fisioterapeuta pela Universidade Estadual de Londrina (2002), Mestre em Bioengenharia pela USP (2004), doutora em Ciências Endocrinológicas pela UNIFESP (2008), com período “sanduíche” na Université de Lyon, França e pós-doutora pela UNIFESP (2009).

Foi docente do departamento de Fisioterapia da UNICASTELO São Paulo (2009-2011) e coordenadora do Programa de Reabilitação e Atividade Física direcionada ao Osteoporótico por sete anos na UNIFESP. Atualmente trabalha como consultora científica na área de Reumatologia na Novartis Biociências.

Journal Club: “Extended OFT+U+V method with on-site and inter-site electronic interactions”

A generalization of the popular DFT+U method based on the extended Hubbard model that includes on-site and inter-site electronic interactions is presented. The generalized corrective Hamiltonian is designed to study systems for which electrons are not completely localized on atomic states and hybridization between orbitals from different sites plays an important role. The application of the the extended functional to archetypal Mott-chargetransfer (NiO) and covalently bonded insulators (Si and GaAs) deminstrates its versatility and the possiblity to obtain a unifying and equally accurate description for a broad range of very diverse systems.

Seminário do Grupo de Biofísica: “Synchrotron Radiation Circular Dichroism Spectroscopy of Proteins”

Synchrotron Radiation Circular Dichroism (SRCD) spectroscopy is an emerging method in Structural Biology which is enabling many exciting new applications in biology and chemistry. It can provide information on molecular structure and function that is complementary to other methods such as crystallography, electron microscopy, SAXS and NMR spectroscopy, as it enables examination of the secondary and tertiary structures and dynamics of molecules in solution. It has thus far been used to study a variety of proteins, carbohydrates, nucleic acids and nanomaterials in different environments (solutions, hydrated films, membranes, micelles, suspensions, crystallisation conditions, and emulsions).

SRCD beamlines are now operational at synchrotrons across Europe and Asia (China, Taiwan, Japan, the UK, Denmark, Germany and France) although there are as yet no such beamlines in the Americas.

I will describe the advantages of SRCD (as compared to the well-established method of circular dichroism spectroscopy using lab-based instruments) due to the high UV and VUS light flux provided by the synchrotron: collection of data to lower wavelengths (resulting in increased information content), improved signal-to-noise levels (enabling the measurement of subtle static and dynamic changes), measurements in the presence of absorbing components (buffers, salts, lipids, and detergents and under physiological conditions), and fast dynamic measurements for kinetics studies.

I will then discuss examples of the use of SRCD (including collaborative studies we have done with Brazilian investigators) for studying protein structures, macromolecular complex formation, thermal stability, protein folding and unfolding, mutations in proteins associated with disease states, drug binding (including its potential as a drug development screen), and characterisation of natively disordered proteins that do not crystallise.

Hence this talk will describe how SRCD spectroscopy represents a novel physics-based method that can provide important and exciting new static and dynamic structural information for the biological, chemical and material sciences.

Café com física: “Atividade espontânea e avalanches em dinâmica neural”

Os progressos tecnológicos em computação e instrumentação científica nas duas últimas décadas abriram importantes linhas de pesquisa em Neurociência. O notável aumento na capacidade de aquisição e processamento de sinais eletrofisiológicos tem levado a um “dilúvio de dados” cuja interpretação é desafiadora e exige abordagens teórico/computacionais. Neste seminário, vou discutir algumas investigações que vêm sendo desenvolvidas nesse contexto, enfatizando em particular algumas abordagens que sugerem (i) que conceitos de criticalidade da física estatística podem ser relevantes na análise de “avalanches” de atividade neural e (ii) que, em algumas situações, os padrões estatísticos de respostas estimuladas de redes neurais podem ser praticamente independentes da natureza dos estímulos, de modo que a atividade espontânea desses redes (determinada por sua topologia) pode ser preditiva para algumas de suas propriedades funcionais (sob estímulo).

Seminário do Grupo de Óptica: “Água, luz, cargas e engenharia”

Apesar de ser comum e parte fundamental da nossa vida, a água ainda tem muitos mistérios e aplicações a serem obtidas dela e com ela. O seminário faz uma visita a certos aspectos encontrados na interface da água com outros meios, como metais, géis ou orgânicos. Além da existência de uma região chamada Camada Dupla (Double Layer) nessas interfaces, originadas do potencial eletroquímico das substâncias, ocorre também a formação de uma zona adicional denominada de Zona de Exclusão (Exclusion Zone). Nesta última se mostra a formação de uma estrutura ordenada da água dando lugar a propriedades de caráter sólido e líquido e motivou a denomina-la de uma quarta fase da água,. A partir daí vem a verificação de fenômenos interessantes e das possíveis aplicações práticas e estimulam a busca de outras novas.

Seminário Grupo Fotônica: “Optochemically organized filaments of light: from WaveguIDe Encoded…”

Optochemical organization is a powerful single-step route that employs low-intensity incandescent light to generate complex, optically functional 3-D polymer architectures. In this technique, we exploit the instability of broad light beams in photopolymerizing media and their spontaneous division into large populations (> 10, 000 cm-3) of self-trapped filaments. Each filament is a microscopic thread of light, which inscribes a polymer channel – a multimode waveguide – along its path. By employing multiple, spatially modulated beams, we can corral filaments into a richly diverse collection of lattices with square, near-cubic, simple cubic, BCC and woodpile geometries.

This seminar highlights two recently developed applications of our approach to optochemical organization. The first is a WaveguIDe Encoded Intersecting (WIDEI) lattice – which like an insect’s compound eye – possesses a significantly enhanced field of view. Because they are fabricated in flexible, robust photopolymer media, WIDEI lattices could serve as intelligent encapsulants of light-harvesting devices or light-shaping conformal coatings on LEDs. More generally, this approach opens pathways to a fundamentally new generation of planar, flexible, thin film optics that can capture, steer, guide, transmit and focus light. The second application exploits the interactions of optochemically organizing filaments to elicit the spontaneous transfer of information between light beams and develop a new technology to encode optical data.

Filosofísica: “O que é filosofia da ciência?” e “Indutivismo do método científico”

Os seminários de hoje são parte de uma série de dez discussões ligadas aos temas mais centrais da Filosofia da Ciência. Nessa segunda, os tópicos 1 e 2, “O que é Filosofia da Ciência” e “Indutivismo e método científico”. No primeiro veremos um panorama geral do que é a área acadêmica de Filosofia da Ciênca, as principais discussões e desafios, bem como uma breve análise histórica dos temas. No segundo tópico, teremos o início do conteúdo de fato das discussões, delineando o cenário teórico anterior aos principais pensadores modernos da área e apresentando a principal concepção de Ciência que está associada ao senso comum.

Filosofísica: “O que é ciência? E como fazer essa pergunta”

O que é Ciência? Você já fez essa pergunta? Mais do que isso, já tentou respondê-la seriamente?

Neste seminário discutiremos, sob a luz dos trabalhos de John M. Ziman, um dos tópicos mais centrais da Filosofia da Ciência, os chamados ‘critérios de demarcação’. Tentaremos, aqui, mais do que responder à questão inicial, entender qual seria o melhor modo de formulá-la.

Seminário do Grupo de Óptica: “Ultra-cold atomic systems: polar molecules and quantum correlations”

This talk is divided into two parts: in the first part I will present our experimental set-up in Nottingham towards the realisation of mixtures of cold molecules, and in the second part I will show our recent theoretical results on genuine tripartite entanglement in Bose-Einstein condensates.

Polar Molecules

The research field of ultra-cold molecules has grown in the last decade bringing many researchers to investigate the unique properties of these fascinating systems. Their additional internal degrees of freedom compared to the atoms, make ultra-cold molecules suitable candidates for the study of new physical phenomena with an impact on a large variety of fields, including atomic, molecular and optical physics, chemistry, quantum information science and quantum simulations, condensed matter physics and cosmology. Our goal is to realise lithium-caesium mixtures, which are especially interesting with respect to studying stationary and mobile impurities, transport measurements and exotic phases in optical lattices. I will present details of our optical and vacuum set-up, and discuss the state of the art of our experiment. I will furthermore present a proposal for a scheme to create and manipulate cold polar molecules close to the surface of an atom chip. I will give details of the required magnetic field to ramp the molecules over the Feshbach resonance and show that it is possible to polarise them by apply a potential between the chip surface and a copper ring placed below it.

Quantum Correlations

We investigate the genuine multipartite nonlocality of three-mode Gaussian states of continuous variable systems. For pure states, we present a simplified procedure to obtain the maximum violation of the Svetlichny inequality based on displaced parity measurements, and we analyze its interplay with genuine tripartite entanglement measured via Rényi-2 entropy. The maximum Svetlichny violation admits tight upper and lower bounds at fixed tripartite entanglement. As an example, we study a system represented by a Bose-Einstein condensate interacting with a ring cavity field in the presence of a strong off-resonant pumping laser. The state of this system can be described by a three-mode Gaussian state, where two are the atomic modes corresponding to atoms populating upper and lower momentum sidebands and the third mode describes the scattered cavity field light. We show that, as a consequence of the collective atomic recoil lasing mechanism, the state of the system exhibits genuine tripartite entanglement and nonlocality, which can be revealed by a robust violation of the Svetlichny inequality when performing displaced parity measurements.