Colóquios e Seminários

Café com física: “Persistência induzida por amnésia em Random Walks”

O expoente de Hurst (H) tem sido amplamente utilizado para caracterizar o tipo de difusão em estudos envolvendo caminhantes aleatórios rotulados na literatura como Random Walks. A dependência de H com o alcance da memória apresenta um desafio adicional, particularmente quando danos são introduzidos no perfil de memória. A característica mais notável desses problemas é o surgimento de uma fase superdifusiva com assinatura log-periódica associada à memória de longo alcance, que surge numa região não usual do diagrama de fases, onde o feedback é negativo. Vamos discutir esses problemas sob os pontos de vista numérico e analítico.

Seminário do Grupo de Óptica: “Terapia Fotodinâmica combinada à radioterapia”

A terapia fotodinâmica (TFD) e a radioterapia são técnicas já conhecidas no tratamento do câncer. A TFD consiste na interação entre fotossensibilizador, luz e oxigênio molecular; que combinados causam morte celular. Já radioterapia é uma técnica que utiliza radiação ionizante para tratamento de tumores. A associação entre a TFD e a radioterapia foi pouco estudada até o momento e poderia aumentar o dano causado ao tecido enquanto diminui os efeitos colaterais provenientes da radioterapia. O objetivo desse estudo é avaliar o dano da combinação entre TFD e radioterapia. Nesse seminário serão abordados os resultados obtidos pela aluna no Dartmouth College, EUA. Durante o estágio foram realizadas medidas de reflectância e fluorescência para acompanhar a resposta da radioterapia e terapia fotodinâmica mostrando os produtos do dano vascular, como, tamanho do vaso e concentração de met-hemoglobina e bilirubina, além da saturação de oxigênio. Os experimentos foram realizados em pele normal de ratos wistar e posteriormente em tumores de pele em camundongos nude, onde foi acompanhado o crescimento do tumor após os tratamentos.

Seminário do Grupo de Óptica: “Confocal microscopy: past, present and future”

This seminar shall focus the essentials of confocal microscopy, applications and perspectives, particularly based on the experience of Dr. Sheppard.

Journal club: Spin-orbit interaction and related transport phenomena in 2D electron and hole systems

Spin-orbit interaction is responsible for many physical phenomena which are under intensive study currently. Here we discuss several of them.

The first phenomenon is the edge spin accumulation, which appears due to spin-orbit interaction in 2D mesoscopic structures in the presence of a charge current. We consider the case of a strong spin-orbit-related splitting of the electron spectrum, i.e., the spin precession length is small compared to the mean free path l. The structure can be either in a ballistic regime (when the mean free path is the largest scale in the problem) or in a quasi-ballistic regime (when l is much smaller than the sample size).

We show how the physics of edge spin accumulation in different situations should be understood from the point of view of unitarity of boundary scattering. Using transparent method of scattering states, we are able to explain some previously puzzling theoretical results. In particular, we clarify the important role of the form of the spin-orbit Hamiltonian, the role of the boundary conditions, etc.. The relation between the edge spin density and the bulk spin current in different regimes is discussed.

Besides, we consider several new transport phenomena which appear in the presence of spin-orbit interaction, for example, magnetotransport phenomena in an external classical magnetic field. In particular, a new mechanism of negative magnetoresistance appears which is due to destruction of spin fluxes by the magnetic field, and which can be really pronounced in 2D systems with strong scatterers.

Seminário do Grupo de Óptica: “Diagnóstico óptico de processos patológicos bucais”

Neste seminário serão abordados aspectos relevantes de processos patológicos bucais importantes para as pesquisas utilizando as técnicas espectroscópicas. Algumas lesões bucais, como leucoplasia e câncer bucal, serão mencionadas com relação à epidemiologia e fatores etiológicos. Resultados envolvendo a utilização das técnicas de espectroscopia Raman e FT-IR em amostras ex vivo e in vitro, assim como publicações recentes também serão apresentadas. Por fim, a utilização da espectrosocopia Raman in vivo, em um sistema portátil, será abordada como projeto de pesquisa atual do nosso laboratório, visando o diagnóstico precoce e minimamente invasivo das leões bucais.

High energy physics seminars: “Cosmic and Superconducting Strings”

Topological defects (aka topological solitons) appear in field theory models with spontaneous symmetry breaking and a non-trivial vacuum manifold. Cosmic strings are created whenever a U(1) symmetry gets spontaneously broken and are the topological defect that seems most important from the point of view of cosmological applications. There are several reasons for this: on the one hand it is believed that cosmic strings might be linked to the fundamental strings of String theory and on the other essentially all models that try to embed the Theory of Inflation into the scheme of Grand Unification predict the production of cosmic strings. Furthermore, the analysis of recent Cosmic Microwave Background (CMB) data suggests that cosmological models containing cosmic strings provide a better fit to both the temperature as well as polarization anisotropy data than inflaton and/or dust models alone. In the first part of my talk, I will discuss the “zoo” of cosmic strings available and also mention their gravitational properties. In the second part of my talk I will concentrate on superconducting strings. These are current-carrying strings, which can have an additional internal structure in the form of bosonic or fermionic fields. This internal structure can lead to the formation of vortons, i.e. loops of cosmic string that are balanced against collapse by a non-vanishing angular momentum.

Para mais informações, acesse http://www.ifsc.usp.br/~lattice/hepseminar/

Formulações Nanoestruturadas contendo Curcumina

A terapia fotodinâmica (TFD) é uma modalidade terapêutica que combina o uso de luz, oxigênio molecular (O2) e compostos fotossensíveis para causar a morte às células-alvo. A curcumina é um composto antioxidante natural, de cor amarela, extraída do açafrão (Curcuma longa Linn), que possui várias atividades farmacológicas, tais como anti-inflamatória, antimicrobiana e anticâncer, e que também pode ser utilizada como fotossensibilizador (FS) na TFD. No entanto, a curcumina possui propriedades altamente hidrofóbicas, o que resulta em uma baixa biodisponibilidade sistêmica e dificulta suas aplicações. As principais estratégias para superar tais limitações são baseadas no carregamento do composto em nanocarregadores, que são variáveis, como as nanopartículas poliméricas, micelas, ciclodextrinas, dispersões sólidas, emulsões, lipossomas, transportadores de peptídeos, entre outras. Os nanocarregadores devem ser capazes de incorporar o FS, sem que ele perca ou altere sua atividade. Assim, com o objetivo de melhorar sua estabilidade e otimizar sua ação fotodinâmica, a curcumina foi encapsulada em nanopartículas de PLGA (polímero) e caracterizada quanto ao seu tamanho, potencial zeta, perfil de liberação. Para avaliar sua eficiência in vitro, a mesma foi testada em fungo e bactérias (Gram positiva e Gram negativa), uma vez que a inativação fotodinâmica de microrganismos é considerada uma alternativa promissora para infecções resistentes. Posteriormente, os resultados obtidos foram comparados com os da curcumina em sua forma livre (solução aquosa), a fim de verificar se a formulação de nanopartículas obteve melhor desempenho.

Café com Física Especial – Quantum Information Science with Trapped Ca+ Ions

In this talk, the basic toolbox of the Innsbruck quantum computer based on strings of trapped Ca+ ions will be reviewed [1] and an overview will be given on our current experiments in the field of quantum information science.

For quantum information processing, the toolbox operations are used to encode one logical qubit in entangled states distributed over seven trapped-ion qubits. We demonstrate the capability of the code to detect one bit flip, phase flip or a combined error of both, regardless on which of the qubits they occur.

Furthermore, we apply combinations of the entire set of logical single-qubit Clifford gates on the encoded qubit to explore its computational capabilities [2].

With the quantum toolbox both analog and digital quantum simulations are carried out [3].

The basic simulation procedure will be presented and its application will be discussed for a variety of spin Hamiltonians.

Including a carefully controlled dissipation mechanism, the toolbox even allows for the quantum simulation of open systems [4].

With long ion strings, the quantum toolbox is applied to investigate the propagation of entanglement in a quantum many-body system represented by the trapped-ion qubits [5].

[1] P. Schindler et al., New. J. Phys. 15, 123012 (2013).

[2] D. Nigg, M. Müller et al., Science 345, 302 (2014).

[3] R. Blatt and C. F. Roos, Nature Phys. 8, 277 (2012).

[4] J. T. Barreiro et al., Nature 470, 486 (2011).

[5] P. Jurcevic, et al., Nature 511, 202 (2014).

Prof. Rainer Blatt – Institute for Experimental Physics – University of Innsbruck – Institute for Quantum Optics and Quantum Information – Austrian Academy of Sciences.

Seminário do Grupo de Óptica: “Ressonâncias de Fano no espalhamento de luz por nanopartículas”

A ressonância de Fano, descoberta no ramo da física atômica por Ugo Fano, é uma característica marcante de sistemas quânticos abertos. Sendo um fenômeno de interferência, essa ressonância também se manifesta em óptica clássica e pode ser descrita dentro do formalismo de Lorenz-Mie. Com os avanços técnicos na engenharia de nanoestruturas plasmônicas e metamateriais, o “efeito Fano” tem se tornado uma importante ferramenta para o controle das interações dos modos eletromagnéticos no espalhamento de luz por nanopartículas. Graças ao perfil assimétrico da ressonância de Fano, que possui um pico de ressonância muito próximo espectralmente de uma antirressonância, sistemas exibindo o efeito Fano são altamente sensíveis ao ambiente dielétrico local. De fato, a interferência entre os modos reemitidos pelo centro espalhador no dielétrico circundante pode dar origem tanto ao aumento de intensidade do campo eletromagnético próximo quanto à sua supressão ressonante. Neste seminário, abordaremos algumas das modernas aplicações envolvendo ressonâncias de Fano em plasmônica, bem como resultados teóricos que publicamos recentemente acerca deste tema .

T. J. Arruda, F. A. Pinheiro e A. S. Martinez, “Electromagnetic energy within coated spheres containing dispersive metamaterials.” J. Opt., 14 (065101), 2012.

T. J. Arruda, A. S. Martinez e F. A. Pinheiro, “Unconventional Fano effect and off-resonance field enhancement in plasmonic coated spheres,” Phys. Rev. A, 87 (043841), 2013.

T. J. Arruda, F. A. Pinheiro e A. S. Martinez, “Electromagnetic energy within single-resonance chiral metamaterial spheres,” J. Opt. Soc. Am. A, 30:1205-1212, 2013.

T. J. Arruda, A. S. Martinez e F. A. Pinheiro, “Electromagnetic energy within coated cylinders at oblique incidence and applications to graphene coatings,” J. Opt. Soc. Am. A, 31:1811-1819, 2014.

T. J. Arruda, A. S. Martinez e F. A. Pinheiro, “Omnidirectional absorption and off-resonance field enhancement in dielectric cylinders coated with graphene layers,” J. Opt. Soc. Am. A, 32: 943-948, 2015.

Seminário: “Multi-chanel MRI”

Transmitting and receiving radio frequency signals for NMR signal excitation and response has been developed since the first crossed-pair coils used by Bloch for his co-discovery (together with Purcell) of NMR in 1945. In a more modern sense using multiple transmit and receive channels in parallel to acquire more signal from more volume, and/or to target specific regions of interest more optimally, multi-channel MRI has been under development and in practice since my presentation of “Parallel Imaging for MRI” in poster at the 1986 New York Academy of Science meeting. Of course multi-channel receive arrays, and parallel imaging with them, took off with Pete Roemer’s patent in 1989 followed by the advent of parallel imaging from Sodickson’s SMASH in 1996 followed by Pruessmann’s SENSE techniques, and still represent the State-of-the-Art in clinics today. All the while, multi-channel transmit approaches to solve problems and enhance performance especially for ultra-high field MRI have been pursued by myself and others since the first 2T system in 1984. In 1992 and since I have demonstrated both the need for and the application of what is known today as B1 shimming. I have used this term to more broadly apply to the ability and utility of manipulating the RF EM field generated by a coil, over five degrees of freedom (phase, magnitude, frequency, space, time), by adjusting the currents on multiple, independent coil elements or channels accordingly. Multi-channel transmit demonstrated use and potential for optimizing RF field uniformity, SAR, SNR, transmit efficiency, speed, and other benefits, especially important in modern, ultra-high field MRI where the shorter Larmor wavelengths are leading to increasing interference patterns and loss adversely effecting the success and safety of human studies. Additional avenues of multi-channel MRI development in our lab include on-coil, channel dedicated RF/analog front-ends and channel dedicated, FPGA facilitated, automated tune, match, and isolation functions for the ultimate versatility and optimization of RF technology and techniques for MRI. Finally, new research in simulation and validation of multi-channel RF safety principles and practices will be presented.

Seminário do Grupo de Cristalografia: “New methodologies for examining neuronal ensembles”

When using drugs of abuse, learned associations are formed between the drugs and stimuli present in the drug-taking environment. With continued use, these stimuli can become cues that promote drug relapse. We have identified sparsely distributed patterns of neurons in the brain called ‘neuronal ensembles’ that are selectively activated by drug-related cues and thought to encode the learned associations that mediate drug seeking behavior. The talk will discuss new approaches — Daun02 inactivation, FACS sorting of activated neurons, Fos-GFP and c-Fos-Tetop::iCre transgenic rats — that have been used to selectively target and study activated neuronal ensembles in models of conditioned drug effects and relapse.

High energy physics seminars: “Phenomenology of new heavy quarks at the LHC”

New heavy quarks are predicted in various scenarios of new physics; depending on their nature they can mix with SM quarks or they can even mediate the production of dark matter states. Theoretically-motivated scenarios of new physics in general predict the

existence of multiple new quarks with different couplings with the SM states or dark matter. Experimental searches of new quarks at the LHC, on the other hand, have so far mostly tested minimal extensions of the SM with new quarks which specific decay patterns. No signals have been detected, pushing mass limits above 600-800 GeV, depending on different assumptions about their couplings to SM states. The reinterpretation of mass bounds from experimental searches to test theoretical models is therefore not always straightforward.

Para informações sobre os próximos seminários, acesse

http://www.ifsc.usp.br/~lattice/hepseminar/

I will describe model independent methods to recast data from experimental searches. These methods can be used to test general scenarios with any number of extra quarks which can mix with all SM families or couple to dark matter.

Journal club: “Glycerol Adsorption on Platinum Surfaces: A Density Function Theory Investigation”

Several studies have suggested glycerol as a candidate for hydrogen production (C3H5(OH)3 + 3H2O ⟶ 3CO2 + 7H2, ΔH = 225.29 kJ/mol). The promising results of steam reforming of glycerol on the Pt, Pd, Ni and Cu-based materials have been obtained in several experimental studies, however, the interaction mechanism between glycerol and transition-metal surfaces is still not well-understood. In this talk, the interaction mechanism between glycerol and Pt surfaces along with the adsorption, structural and electronic properties of glycerol on (111), (100), (110) Pt surfaces will be discussed based on initio dispersion corrected density functional theory calculations [1]. Moreover, the role of the defects on the Pt surface on the adsorption properties of glycerol will be also highlighted [2].

The obtained results play an important role on improvement of our basic understanding of the interaction of glycerol molecule with open and close-packed Pt surfaces and the surface with defects, which can help in design of new catalysts for glycerol reforming reaction.

[1] P. Tereshchuk and J. L. F. Da Silva, J. Phys. Chem. C 118, 15251 (2014).

[2] P. Fernandez, J. F. Gomes, C. A. Angelucci, P. Tereshchuk, C. A. Martins, G. A. Camara, M. E. Martins, J. L. F. Da Silva, G. Tremiliosi-Filho, ACS Catalysis 5, 4227 (2015).

Astro-Cosmo-Particle Journal Club: “Teste da invariância de Lorentz com raios cósmicos”

Nosso objetivo é reunir estudantes e cientistas interessados em discutir temas relevantes da física de partículas, cosmologia e astrofisica de partículas. Todos estão convidados a participar das reuniões, mas aconselhamos que se leia o artigo com antecedência, para que se possa acompanhar a discussão.

O artigo escolhido para próxima discussão pode ser acessado no endereço eletrônico http://iopscience.iop.org/1475-7516/2009/04/022

Café com física: “Frequency- and Gradient-Modulated MRI: Imaging with Extreme Field Inhomogeneity”

MRI has evolved into an incredibly powerful tool due to impressive innovations over the past 3-4 decades. However, the general approach used to obtain MR images has not deviated significantly from Lauterbur’s original MRI experiment (1). That is, in state-of-the-art MRI, the pulse sequence used to generate spatially-encoded signals for imaging requires two basic elements: a sufficiently short RF pulse to excite all resonance frequencies of interest simultaneously, followed by a finite time during which magnetization is allowed to evolve in the presence of a field gradient to encode their spatial locations. This universal approach to MR imaging is optimal only under stringent experimental conditions. Specifically, frequency variation due to field inhomogeneity and magnetic susceptibility must be limited to a small fraction of the Larmor frequency, γB0. Although recent advances have improved the ability of Fourier-based imaging to tolerate B0 inhomogeneity, these improvements fall short of meeting the technical requirements for human imaging using small and portable magnets. For example, MRI of the human brain cannot be performed with the subject’s body from the shoulder down placed outside the magnet bore. No MRI technology has ever been conceived to accomplish this; that is, until possibly recently. Namely, spatiotemporal encoding (2-7) has the capability to go far beyond standard Fourier imaging in terms of tolerating B0 inhomogeneity, allowing B0 to vary by a significant fraction of the nominal field.

Improved tolerance to B0 inhomogeneity with spatiotemporal-encoded MRI has already been demonstrated by us and others. However, these improvements were limited because B0 compensation was restricted to one or possibly two spatial directions simultaneously. Now, due to the recent invention of 3D frequency-swept excitation pulses in STEREO (7), in combination with parallel transmit “beam-steering”, multi-coil shimming, and simultaneous transmit and receive electronics, it should be possible to fully compensate extreme B0 inhomogeneity and thus accomplish MR imaging of brain using a small and portable head-only magnet. STEREO, which stands for steering resonance over the object (7), produces non- Fourier based images by moving a localized resonant region along a curved trajectory in space such that the excitation itself is spatially selective and temporally sequential. In STEREO, the gradients are modulated to produce a “spatial rapid passage”. By producing a sweeping 3D-selective excitation in time, temporal adjustments to the pulse can be made to compensate for the spatial variation of B0 and B1 as the “resonant region” traverses through space. Simultaneous RF transmission and signal detection preserves ultrashort-T2* signals. This method of achieving spatial isolation is particularly novel in MR imaging and opens opportunities for numerous novel applications that could not be considered with standard Fourier-based techniques.

Seminário do Grupo de Óptica: “Dinâmica de transporte de fotossensibilizadores em células”

Nos últimos anos, os estudos de técnicas fotônicas não invasivas têm ganhado destaque devido à preocupação com a saúde. Nestes estudos, o uso de fotossensibilizadores na terapia fotodinâmica desempenha um papel fundamental para os avanços da área, e tem sido utilizado com sucesso em diversas aplicações, tais como a redução de contaminantes ambientais, descontaminação de alimentos e tratamento de infecções localizadas, infecções fúngicas, acnes e câncer, Apesar de tal sucesso, a dinâmica de transporte dessas substâncias fotossensíveis nos alvos a serem tratados ainda não é um processo completamente compreendido. Assim, torna-se importante estudar a dinâmica de difusão e a entrada desses fotossensibilizadores em células e bactérias. Neste projeto, pretende-se utilizar técnicas como microscopia confocal e espectroscopia de fluorescência correlacionada (FCS), de modo a compreender tal transporte em bactérias gram-positivas e gram-negativas, e buscar diferenças na dinâmica de difusão entre elas. Do mesmo modo comparativo também serão estudadas células tumorais e sadias. Espera-se com este projeto caracterizar e modelar toda dinâmica de transporte destes fotossensibilizadores em bactérias gram-positivas e gram-negativas, buscando encontrar diferenças entre os grupos de modo a possibilitar a seletividade de um único grupo de interesse para terapia fotodinâmica.