Anomalous diffusion : a basic mechanism for the evolution of inhomogeneous systems

In this article we review classical and recent results in anomalous diffusion and provide mechanisms useful for the study of the fundamentals of certain processes, mainly in condensed matter physics, chemistry and biology. Emphasis will be given to some methods applied in the analysis and characterization of diffusive regimes through the memory function, the mixing condition (or irreversibility), and ergodicity. Those methods can be used in the study of small-scale systems, ranging in size from single-molecule to particle clusters and including among others polymers, proteins, ion channels and biological cells, whose diffusive properties have received much attention lately

Scanning electron microscopy and machine learning reveal heterogeneity in capsular morphotypes of the human pathogen Cryptococcus spp.

Phenotypic heterogeneity is an important trait for the development and survival of many microorganisms including the yeast Cryptococcus spp., a deadly pathogen spread worldwide. Here, we have applied scanning electron microscopy (SEM) to defne four Cryptococcus spp. capsule morphotypes, namely Regular, Spiky, Bald, and Phantom. These morphotypes were persistently observed in varying proportions among yeast isolates. To assess the distribution of such morphotypes we implemented an automated pipeline capable of (1) identifying potentially cell-associated objects in the SEM-derived images; (2) computing object-level features; and (3) classifying these objects into their corresponding classes. The machine learning approach used a Random Forest (RF) classifer whose overall accuracy reached 85% on the test dataset, with per-class specifcity above 90%, and sensitivity between 66 and 94%. Additionally, the RF model indicates that structural and texture features, e.g., object area, eccentricity, and contrast, are most relevant for classifcation. The RF results agree with the observed variation in these features, consistently also with visual inspection of SEM images. Finally, our work introduces morphological variants of Cryptococcus spp. capsule. These can be promptly identifed and characterized using computational models so that future work may unveil morphological associations with yeast virulence

Processos estocásticos não-Markovianos

Tese (doutorado)—Universidade de Brasília, Instituto de Física, 2007.Modelos de Langevin, que levam em consideração flutuações térmicas, têm aplicação nas mais variadas áreas. Neste trabalho serão estudados fenômenos relacionados a processos difusivos que podem ser modelados por equações de Langevin normais e generalizadas. Daremos bastante ênfase ao papel do ruído ao mostrar que sua forma é determinante para as propriedades difusivas do sistema em consideração, seja no caso Markoviano ou no não-Markoviano. Estudaremos como o ruído determina a forma da função de correlação em sistemas governados por equações de Langevin generalizadas e como influi no tipo de difusão apresentado pelo sistema. Ainda enfocaremos o caso extremo de difusão, denominado difusão balística, e mostraremos algumas de suas propriedades peculiares, como a violação das condições de mistura e de ergodicidade. _______________________________________________________________________________________ ABSTRACTLangevin models, which take into account thermal fluctuations, have been applied in many areas. In this work, phenomena related to diffusive processes which can be modelled by normal and generalized Langevin equations will be studied. Emphasis will be given to the role played by noise, since its characteristics are determinant for the diffusive properties of the system, both in the Markovian and in the non-Markovian cases. We will show how the noise determines the form of the correlation function in systems governed by generalized Langevin equations and how it affects the type of diffusion presented by the system. We will also focus on a extreme case of diffusion, termed ballistic motion, and show some of its peculiar properties, such as a violation of the conditions of mixing and of ergodicity

Estratégias evolutivas de populações

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Estratégias evolutivas de populações

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Estratégias evolutivas de populações

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Estratégias evolutivas de populações

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Estratégias evolutivas de populações

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Estratégias evolutivas de populações

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Cooperation in diffusive spatial games

Random diffusion is shown to be an important mechanism on fostering cooperative behavior among simple agents (memoryless, unconditional cooperators or defectors) living on a spatially structured environment. In particular, under the Prisoner's Dilemma framework, when allowing the agents to move with the simple "always-move" rule, we find that cooperative behavior is not only possible but may even be enhanced. In addition, for a broad range of densities, mobile cooperators can more easily invade a population of mobile defectors, when compared with the fully viscous, immobile case. Thus, such simple mobility pattern may have played a fundamental role both in the onset and development of cooperative behavior, paving the way to more complex, individual and group, motility rules