em FÃ­sica e Astronomia da UFSC

Dias 5 a 9 de Maio de 2014.

# Resumos Submetidos

Lista de resumos de todas as apresentaÃ§Ãµes (poster:Â Â e oral:Â ) submetidos atÃ© o momento.

Estudo da mobilidade de um fluido tipo Ã¡gua sujeito a um confinamento unidimensional
Patricia Ternes Dallagnollo ; Evy A. Salcedo Torres
Usando simulaÃ§Ãµes por dinÃ¢mica molecular estudaremos a mobilidade de um sistema unidimensional de partÃ­culas que interagem atravÃ©s de um potencial de duas escalas sujeitas a um campo confinante.
Bayesian framework to wavelet estimation and linearized acoustic inversion
L. P. Figueiredo; M. Santos; M. Roisenberg; W. Figueiredo
Seismic inversion is an important tool widely used in Geophysical problems to infer the subsurface properties through seismic wave measurements. In particular, it can improve exploration and management success in the petroleum industry, since it estimates the elastic properties from the seismic data, which has a great correlation with many petrophysical properties. The major challenge of seismic inversion method is to integrate all different kinds of data in order to obtain an accurate and high-resolution set of subsurface parameters, also characterizing the uncertainties of the results of the inversion.
In this work, we show how a seismic inversion method based on a Bayesian framework can be applied on post-stack seismic data to estimate the wavelet, the seismic noise level and the subsurface acoustic impedance. We propose a different linearized forward model and discuss in detail how some stochastic quantities are defined in a geophysical interpretation. The forward model and the Gaussian assumption for the likelihood distributions enable to obtain the conditional distributions. The method is divided in two sequential steps: the wavelet and noise level estimation, in which the posterior distribution is obtained via a Monte Carlo method (Gibbs sampling algorithm), and the acoustic inversion, which uses the proposal forward model and the results of the first step. In the second step, the posterior distribution for acoustic impedance is analytically obtained. Therefore, the maximum a posteriori impedance can be calculated, yielding a very fast inversion algorithm.
In the wavelet estimation, the method presents good results without any assumption about the wavelet phase. The estimated wavelet, and the mean value of noise level yield good results when used as fixed quantities in the proposed acoustic inversion method. The methodology appears to be a good choice for acoustic inversion, due to the possibility of integrating prior knowledge, as the low frequency model, seismic correlation function and wavelet characteristics, in the inversion results conditioned to seismic traces. The similarity between the MAP solution and the Constrained Sparse Spike Inversion indicates the feasibility and reliability of the proposed method. The covariance matrices calculations of the multivariate Gaussian distributions are important procedures to incorporate results of the prior knowledge into the inversion, which directly influences its quality.
HistÃ³rias de FormaÃ§Ã£o Estelar e Morfologia de GalÃ¡xias Post-Starburst em Baixo Redshift.
Ariel Werle, Abilio Mateus.
GalÃ¡xias post-starburst(PSB) apresentam espectros com fortes linhas de absorÃ§Ã£o na sÃ©rie de Balmer e linhas de emissÃ£o negligenciÃ¡veis, indicando uma predominÃ¢ncia de populaÃ§Ãµes estelares jovens e nenhum sinal de formaÃ§Ã£o estelar atual.
Combinando dados do Sloan Digital Sky Survey com a sÃ­ntese espectral do STARLIGHT, selecionamos uma amostra de 403 galÃ¡xias post-starburst em uma amostra limitada em volume de 162538 objetos com redshift entre 0.04 e 0.095. Dados do STARLIGHT foram usados para recuperar as histÃ³rias de formaÃ§Ã£o estelar(SFH) destas galÃ¡xias.
Nossos resultados mostram que galÃ¡xias post-starburst tÃªm um desenvolvimento extremamente lento quando comparadas com outras galÃ¡xias, suas massas estelares atuais sÃ£o comparÃ¡veis Ã s de galÃ¡xias star-forming, porÃ©m, enquanto galÃ¡xias star-forming formam sua massa de maneira contÃ­nua, galÃ¡xias post-starburst apresentam uma forte descontinuidade em sua taxa de formaÃ§Ã£o estelar por volta de 3Gyr atrÃ¡s, formando atÃ© 40% de sua massa no perÃ­odo entre 3 bilhÃµes e 50milhÃµes de anos atrÃ¡s e cessando sua formaÃ§Ã£o estelar em seguida.
A alta quantidade de massa formada nos Ãºltimos 3Gyr pode indicar que estas galÃ¡xias sÃ£o remanescentes de fusÃµes com galÃ¡xias de massa comparÃ¡vel, o que Ã© verificado em redshifts mais altos, porÃ©m, dados do Galaxy Zoo mostram que apenas 14,5% das galÃ¡xias PSB em nossa amostra apresentam vestÃ­gios de fusÃµes e menos de 1% apresentam fusÃµes evidentes, uma justificativa para este resultado Ã© que o tempo caracterÃ­stico para que o espectro de uma galÃ¡xia apresente caracterÃ­sticas de post-starburst apÃ³s uma fusÃ£o Ã© maior do que o tempo necessÃ¡rio para o desaparecimento dos vestÃ­gios desta fusÃ£o, esta hipÃ³tese Ã© compatÃ­vel com a baixa incidÃªncia de galÃ¡xias espirais em nossa amostra de galÃ¡xias PSB.
Correcoes de N Finito ao Modelo de Polyakov--Nambu-Jona-Lasinio
Tulio E. Restrepo, Juan C. Macias, Gabriel N. Ferrari.
Utilizamos Teoria de perturbaÃ§Ã£o Optimizada no modelo de Nambu-Jona-Lasinio, para ir alem dos resustados em campo medio para a termodinÃ¢mica do modelo e comparar os nossos resultados com os resutados da QCD na rede.
Dilution Effect in one-dimensional Potts model with long-range interactions: a mean-field renormalisation-group approach
C. E. K. Soares; N. S. Branco; J. R. de Sousa
Long-distance interactions may play an important role in many physical phenomena as, for example, in ionic systems, in uncharged particles immersed in a critical fluid, and in the Kondo problem. From a theoretical point of view, one may be interested in the effects on the critical behavior of models in which interactions fall off with distance at different rates. This problem has been extensively studied in the literature and some exact and precise results are available. Much less is known when disorder is present in models with longe-range interactions. Therefore, in this work we address this matter, using a site-disordered Ising model with ferromagnetic interactions decaying with distance $r$ as $\sim 1/r^p$, for 1 e we want to study the $q=3$ Potts model, which presents first-order transitions for some values of $p$, we intend to employ a Monte Carlo algorithm to treat this model. This algorithm allows for an efficient way to simulate models with long-distance interactions (essentially, with the same efficiency as for models with short-range interactions).
Quantum Flow in the Phase Space in the Coherent State Representation
Matheus Veronez; Marcus A. M. de Aguiar
In this work we derive a general construction for a phase space flow for the Husimi function of a quantum system. For the case of unitary time evolution the flow equations obtained are continuity-like equations made of a classical term (Liouville Equation) plus quantum corrections. The presence of non-classical terms leads to the existence of new features not observed in classical flows, namely: displacement of stagnation points and momentum inversion. We have also shown that the zeros of the Husimi function are saddle points of the flow, and we have topological evidence that they are always followed by a center of the flow.
EvoluÃ§Ã£o quÃ­mica de galÃ¡xias com formaÃ§Ã£o estelar
Marielli de Souza Schlickmann, Roberto Cid Fernandes, Natalia Vale Asari, Grazyna StazÃ¬nska
Os elementos quÃ­micos sÃ£o transformados no interior estelar, por isso, a taxa com que as estrelas sÃ£o formadas nas galÃ¡xias, dita a maneira como essas evoluem quimicamente. O estudo da evoluÃ§Ã£o quÃ­mica em galÃ¡xias, pela paleontologia das galÃ¡xias, ou seja, pela decomposiÃ§Ã£o espectral em populaÃ§Ãµes estelares simples, mostrou que hÃ¡ uma forte correlaÃ§Ã£o entre massa estelar (M$_*$) e metalicidade (Z) do gÃ¡s. A introduÃ§Ã£o da taxa de formaÃ§Ã£o estlear (SFR) atual nas galÃ¡xias, calibrada pela luminosidade de H$_\alpha$, mostrou posteriormente que M$_*$, Z e SFR tambÃ©m estÃ£o fortemente correlacionadas. Nesse trabalho introduzimos a SFH - a SFR como funÃ§Ã£o do tempo - Ã  relaÃ§Ã£o M$_*$ -- Z. A SFH Ã© um produto do cÃ³digo de sÃ­ntese espectral de nosso grupo o {\sc{starlight}}, que pode nos levar ao passado da formaÃ§Ã£o estelar das galÃ¡xias. Vamos apresentar os resultados encontrados atÃ© aqui em nosso estudo, que pretende elucidar quais fenÃ´menos devem ter maior influÃªncia na forma da SFH das galÃ¡xias.
Brain Oscillations and New Synchronization Phase Transitions of Kuramoto oscillators
Caio L. Tiedt; Mauricio Girardi-Schappo; Marcelo H. R. Tragtenberg
Neural synchronization is a phenomenon related to information transmission between brain areas, cognitive
functions, perceptual and motor skills and memory. It is also connected to mental illnesses like epilepsy,
isolated seizures, AlzheimerÂ´s disease, ParkinsonÂ´s disease, autism and schizophrenia. This work is related to the critical state of the brain: the order of the synchronization transition.
The Kuramoto model is a paradigm in the study of synchronization phenomena in many areas, including
Physics, Biology and Chemistry. It consists of a network of phase oscillators. An order parameter is defined in order to identify synchronized states. The transition between the
incoherent to synchronized state is continuous for oscillators with well-centered distributed
natural frequencies {w_i}, like in the cases of Lorentzian or the Gaussian
distributions. On the other hand, for a uniform distribution the transition is discontinuous.We aim to study the behavior of the synchronization transition for Kuramoto oscillators with
an all-to-all interaction and distributions from the uniform to one-peaked.
We discretize the Gaussian and Lorentzian distributions as podia with 2m+1 steps.
The result in the two cases are piecewise uniform distributions.
The system presents a continuous phase transition on the interaction parameter for any piecewise uniform distribution
for 100 oscillators. However, for 1000 oscillators,
we find discontinuous transition for distributions with many steps.There is a critical
value of m such that the transition becomes continuous.
We studied the effect of an additive noise term in the interaction parameter on a uniform
distribution of {w_i}. The discontinuous phase transition remains discontinuous
for large values of the noise.
Dynamical Behaviors and Phase Diagrams of a Computationally Efficient Map-based Neuron Model
Rafael V. Stenzinger; Jheniffer J. Gonsalves; MaurÃ­cio Girardi-Schappo; Marcelo H. R. Tragtenberg
The KTz is a neuron model with the membrane potential described by the discrete time recursion relation x(t+1) = f(u(t)), where f is a sigmoidal function, u(t )= [x(t) â€“ K . y(t) + z(t) + I(t)] / T, I(t) is an external current and z(t) is a slow current. The case f(u) = tanh(u) was extensively studied, being called the KTz model (Kuva et al., 2001). It has many dynamical behaviors of a neuron and excitable systems: excitable fixed point, fast and slow regular spiking, bursts and spikes with plateau, among others. Because the hyperbolic tangent compromises the computational efficiency of the model, we replace it by a logistic function f(u) = u / [1 +|u|], which have a similar asymptotic behavior. Initially, we focus our attention on the KT model, a special case of the KTz, where the external current I(t) and the variable z(t) are set equal to zero. We determine with details the complete phase diagram of the KT logistic model: fixed points, cycles and the co-stability region between fixed points and cycles. This phase diagram is very similar to the original KT model, but is more analytically tractable (Tragtenberg and Yokoi, 1995; Kinouchi and Tragtenberg, 1996). The myriad of dynamical behaviors of the logistic KTz model are also described and compared with the original one. Finally, we make qualitative and quantitative comparisons between the computational efficiency of the hyperbolic tangent model and the logistic model.
Quantum Speed Limit para um elÃ©tron relativÃ­stico em um campo magnÃ©tico uniforme
David Velasco - Eduardo Duzzioni
Saber o quÃ£o rÃ¡pido um sistema fÃ­sico pode processar informaÃ§Ã£o Ã© uma tarefa extremadamente importante no campo da computaÃ§Ã£o. A resposta a esta pergunta Ã© o foco central do presente estudo, ao investigar o tempo mÃ­nimo necessÃ¡rio para que um sistema quÃ¢ntico relativÃ­stico mude para um estado ortogonal ao estado inicial.