Colóquios e Seminários

Café com física: “High-accuracy numerical methods in classical field theories”

Even though there is a wide range of numerical methods to treat partial differential equations (PDEs), our interests lie in those which render highly accurate solutions, ideally close to machine precision. In this context, pseudo-spectral methods are probably the best choice, as they have the remarkable capability of providing exponential convergence rate when the underlying problem admits a regular solution. Therefore, the aim of this talk is to give an introductory discussion to such spectral-methods applied to some problems in classical field theories. I shall first concentrate on examples concerning PDEs restricted to spatial coordinates (typically elliptic equations), a field where spectral methods find their most common application. Then I will discuss our efforts to further extend those methods to the realm of hyperbolic equations, where a spectral approximation is also considered in the time direction.

Palestra: “Symmetry approach to integrability of differential equations”

We´ll discuss the symmetry approach to integrability of partial differential equations with two independet variables. Main definitions are given and examples have been considered. A classification of integrable equations of the Korteweg-de Vries type is presented. We show that some special classes of integrable polynomial multi-component models are closely related to Jordan and left-symmetric algebras and to Jordan triple systems.

Journal Club: “Spin-orbit coupling and spin relaxation in graphene”

Intrinsic spin-orbit coupling in graphene is relatively weak, some tens of micro eVs [1-3]. On one hand, this is nice, as the projected intrinsic spin relaxation is also slow, on the order of microseconds. On the other hand, a greater value for the spin-orbit interaction is desired for spin manipulation and spin-orbit induced phenomena, such as the (quantum) spin Hall effect. In this talk I will review basics of the spin-orbit physics in graphene and show how to effectively increase the value of the spin-orbit interaction by adding adatoms [3]. Examples will be hydrogen, fluorine, and copper adatoms. I will present our first-principles results as well as phenomenological model Hamiltonians which should be useful to study model spin transport and spin relaxation. I will also discuss the spin relaxation problem in graphene: experiments get the spin relaxation times of 100 ps, orders of magnitude below what is theoretically expected [4]. The cause appears to be extrinsic, due to impurities. I will argue that the mechanism is resonant scattering by a small concentration of magnetic moments (wherever they come from) [5].

[1] M. Gmitra, S. Konschuh, C. Ertler, C. Ambrosch-Draxl, and J. Fabian, Phys. Rev. B 80, 235431 (2009).

[2] S. Konschuh, M. Gmitra, and J. Fabian, Phys. Rev. B 82, 245412 (2010).

[3] M. Gmitra, D. Kochan, and J. Fabian, Phys. Rev. Lett. 110, 246602 (2013).

[4] W. Han, R. Kawakami, M. Gmitra, and J. Fabian, Nature Nanotechnology 9, 794 (2014)

[5] D. Kochan, M. Gmitra, and J. Fabian, Phys. Rev. Lett. 112, 116602 (2014).

Seminário: “Crystal Engineering of Task-Specific Materials”

That composition and structure profoundly impact the properties of crystalline solids has provided impetus for exponential growth in the field of crystal engineering over the past 20 years. This lecture will address how crystal engineering has evolved from structure design (form) to control over bulk properties (function). Strategies for the generation of two classes of functional crystalline materials will be addressed: Multicomponent pharmaceutical materials, MPMs, such as cocrystals have emerged as a fixture at the preformulation stage of drug development. This results from their modular and designable nature which facilitates the discovery of a wide range of new crystal forms of active pharmaceutical ingredients, APIs, with changed physicochemical properties. However, this does not mean that cocrystal discovery is yet routine. The concepts of “supramolecular heterosynthons” and “ionic cocrystals” will be explained as they pertain to the design of MPMs. We shall address the profound impact that cocrystallization can have upon solubility and bioavailability by presenting three case studies including one that addresses brain bioavailability of lithium.

Metal-Organic Materials (MOMs) that are built from metal or metal cluster “nodes” and organic “linkers” have captured the imagination of materials scientists because they are amenable to crystal engineering and they offer unprecedented levels of porosity. A familyof MOMs,pillared grids, that afford exceptional control over composition, pore size and binding energy,will be detailed. Unprecedented selectivity for carbon capture in narrow pore MOMs will be highlighted. In summary, this lecture will emphasize how the crystal engineering approach to materials design offers a paradigm shift from the more random, high-throughput methods that have traditionally been utilized in materials discovery and development with respect to pharmaceutical materials and porous materials. In short, how do we make the right material for the right application?

Astro-Cosmo-Particle Journal Club

A proposta do programa é reunir estudantes e cientistas interessados para discutir temas relevantes na física de partículas, cosmologia e astrofísica de partículas.

Todos estão convidados a participar das reuniões, mas se recomenda a leitura do artigo com antecedência, para que se possa acompanhar a discussão.

Para saber qual artigo será discutido, clique aqui.

Journal club: “Effective Field Theory @LHC”

The discovery of the Higgs boson at the LHC completes the Standard Model (SM). Otherwise, we know that this is not the end as Dark Matter, neutrino masses and other issues stay without an explanation. The physics Beyond Standard Model becomes a necessity and there are a lot of models on the market, so how to make sure that we are not missing any signal of new physics? The effective field theory (EFT) permits a model independent approach that makes it possible to translate the analysis to any model. I will discuss what is an EFT and latter, apply the analysis to a recent measurement of lepton flavor violating Higgs decays.

Colloquium diei: História e atividades da IBM Research – Brasil

Nesta palestra, o Prof. Ulisses Thibes Mello irá discutir a história da instalação do Centro de Pesquisas da IBM no Brasil, nesses últimos cinco anos, como também irá descrever as áreas-foco do laboratório (recursos naturais, computação cognitiva, sistemas de engajamento e tecnologias industriais).

O palestrante descreverá, também – e de forma breve -, os principais projetos da IBM nessas áreas (eg., inversão sísmica, análise de dados de media social, otimização estocástica aplicada à mineração, bem como nanotecnologia aplicada à recuperação de hidrocarbonetos).

A palestra cobrirá, ainda, modelos de colaboração com empresas e universidades e será transmitida pela IPTV.

Assessoria de Comunicação

Colloquium diei: “História e atividades IBM Research – Brasil”

Na palestra será discutida a história da instalação do centro de pesquisas da IBM no Brasil nesses últimos cinco anos como também serão descritas as áreas foco do laboratório (recursos naturais, computação cognitiva, sistemas de engajamento, e tecnologias industriais). Serão descritos brevemente os principais projetos nessas áreas (eg., inversão sísmica, analise de dados de media social, otimização estocástica aplicada a mineração, e nanotecnologia aplicada a recuperação de hidrocarbonetos). Também serão cobertos modelos de colaboração com empresas e universidades.

Seminário do Grupo de Polímeros: “Printed (Bio)Electronics”

Initially in this talk, the fabrication of an all-printed and flexible biosensor for antioxidants will be described in order to illustrate the techniques and approaches explored by our group in the field of printed bioelectronics [1]. The research work comprised the following steps: i) formulation of an enzyme-containing bioink with both good printability in the large-area, roll-to-roll (R2R) compatible, rotogravure printing method, and preserved catalytic activity after printing; ii) deposition of sub-100 µm Au interdigitated electrodes by inkjet printing; iii) deposition of large-area, patterned, bioactive films onto flexible substrates (PET and PEN); iv) testing of the all-printed device in electrical impedance biosensing. In a second moment, results from two other projects will be discussed. The first project comprises the fabrication of flexible inkjet-printed Au circuits that were used as a biomedical device for the early detection of pressure ulcers on skin [2]. The second project is a current initiative from our group in which electronic components (printed resistor, capacitor and transistor) are being deposited exclusively by inkjet-printing. These components will be further combined to build more complex devices as inverters and (in the long-term) all-printed, low-cost, RFID tags. In general, the aim of the presentation is to illustrate capabilities and interest from the Bernhard Gross Polymer Group in the area of Printed (Bio)Electronics.

References

[1] PAVINATTO, F. J.; PASCHOAL, C. W. A.; ARIAS, A. C. Printed and flexible biosensor for antioxidants using interdigitated ink-jetted electrodes and gravure-deposited active layer. Biosensors and Bioelectronics, v. 67, p. 553-559, 2015.

[2] SWISHER, S. L, LIN, M. C.; LIAO, A.; LEEFLANG, E. J.; KHAN, Y.; PAVINATTO, F. J.; MANN, K.; NAUJOKAS, A.; YOUNG, D.; ROY, S.; HARRISON, M. R.; ARIAS, A. C.; SUBRAMANIAN, V.; MAHARBIZ, M. Impedance sensing device enables early detection of pressure ulcers in vivo. Nature Communications, Accepted for Publication, 2015.

Café com física: “Nanowetting: Liquid-Solid Interaction at the Nanometer Scale”

Nanoscale science and technology has the potential to transform processes involving liquids in various industries. However, a combination of suitable experimental techniques and computational methods is needed in order to reveal the fundamentals of surface wetting phenomena at the nanoscale. Specifically, the understanding of liquid-solid interaction at the nanoscale is hoped to improve existing oil reservoir models up to the macroscale with potential benefits for enhanced oil recovery.

In this seminar, I will present results obtained with a novel measurement platform that enables the nanoscale characterization of tiny amounts of liquids having volumes of the order of 10 attoliter. The analysis of high-resolution optical and topographical data measured on the same oil droplet reveals how droplet shape and surface wetting behavior are influenced by local properties of the surface. The experimental results are compared with results obtained by molecular dynamics simulations which take into consideration the properties of the local chemical environment. I will discuss the future direction of this research and how the results could be applied in the domain of natural resources management.

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.