Artigos
URI permanente para esta coleçãohttps://locus.ufv.br/handle/123456789/11797
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Item Electrocrystallization under magnetic fields: experiment and model(Physica A: Statistical Mechanics and its Applications, 2005-05-25) Mansur Filho, J. C.; Silva, A. G.; Carvalho, A. T. G.; Martins, M. L.We report some experimental results for quasi-two-dimensional electrocrystallization of copper under magnetic fields. Such results are theoretically investigated by large scale simulations of a DLA-like model in which random walkers can move along circular vortices enhanced by the Lorentz force. In addition, a sticking probability is used to take into account the complex reaction dynamics at the cathode surface. Our results indicate that the convective motion does not change the nature of the normal diffusive regime, but increases dramatically the diffusion constant by a factor of up to six. The characteristic features (morphology and scaling laws) of both random walks and growing electrodeposits under a perpendicular magnetic field are determined.Item Epidemic spreading in a scale-free network of regular lattices(Physica A: Statistical Mechanics and its Applications, 2007-04-15) Silva, S. L.; Ferreira, J. A.; Martins, M. L.The susceptible-infected-susceptible (SIS) epidemics in a scale-free network in which each node is a square lattice itself is investigated through large-scale computer simulations. The model combines a local contact process among individuals in a node (or city) with stochastic long-range infections due to people traveling between cities interconnected by the national transportation scale-free network. A nonzero epidemic threshold is found and it is approached with a power-law behavior by the density of infected individuals, as observed in the small-world network of Watts and Strogatz. Also, the epidemic propagation follows a 1/f , hierarchical dynamics from the highly connected square lattices to the smaller degree nodes in outbreaks with sizes distributed accordingly a Gaussian function.Item Multiscale models for the growth of avascular tumors(Physics of Life Reviews, 2007-06) Martins, M. L.; Ferreira Jr., S. C.; Vilela, M. J.In the past 30 years we have witnessed an extraordinary progress on the research in the molecular biology of cancer, but its medical treatment, widely based on empirically established protocols, still has many limitations. One of the reasons for that is the limited quantitative understanding of the dynamics of tumor growth and drug response in the organism. In this review we shall discuss in general terms the use of mathematical modeling and computer simulations related to cancer growth and its applications to improve tumor therapy. Particular emphasis is devoted to multiscale models which permit integration of the rapidly expanding knowledge concerning the molecular basis of cancer and the complex, nonlinear interactions among tumor cells and their microenvironment that will determine the neoplastic growth at the tissue level.Item Effects of vascularization on cancer nanochemotherapy outcomes(Physica A: Statistical Mechanics and its Applications, 2016-08-01) Paiva, L. R.; Ferreira, S. C.; Martins, M. L.Cancer therapy requires anticancer agents capable of efficient and uniform systemic delivery. One promising route to their development is nanotechnology. Here, a previous model for cancer chemotherapy based on a nanosized drug carrier (Paiva et al., 2011) is extended by including tissue vasculature and a three-dimensional growth. We study through computer simulations the therapy against tumors demanding either large or small nutrient supplies growing under different levels of tissue vascularization. Our results indicate that highly vascularized tumors demand more aggressive therapies (larger injected doses administrated at short intervals) than poorly vascularized ones. Furthermore, nanoparticle endocytic rate by tumor cells, not its selectivity, is the major factor that determines the therapeutic success. Finally, our finds indicate that therapies combining cytotoxic agents with antiangiogenic drugs that reduce the abnormal tumor vasculature, instead of angiogenic drugs that normalize it, can lead to successful treatments using feasible endocytic rates and administration intervals.Item A multiscale model for plant invasion through allelopathic suppression(Biological Invasions, 2009-09-18) Souza, D. R. de; Martins, M. L.; Carmo, F. M. S.In the present paper, we propose and study by numerical simulations a multiscale model for plant invasion based on allelopathic suppression in a homogeneous environment. The negative effects on seed production and germination, establishment and mortality of native plants generated by the root-secreted alien phytotoxin constitute the basic mechanism contributing to invasiveness. We obtained the invasion patterns, their success probabilities, the time evolution of plant populations, the gyration radius and the border roughness of the invaded region. As an important result, it was observed that, in addition to the phytotoxin nature (synthesis and degradation rates, diffusivity and phytotoxic threshold), invasive patterns and invasion success depend on the kind of native plants present in the area. In fact, both success and invasion speed decrease in the presence of resistant native plants. Also, self-affine invasion fronts are smooth (Hurst exponent H = 1) in the absence of resistant plants, but are rough (H ≠ 1) on the contrary. Furthermore, if the resistant native species are randomly distributed on the landscape, the invasion front exhibits long-range correlations (H ∼ 0.76), while its border is anti-correlated (H ∼ 0.20), if resistant plants are distributed in patches. Finally, the cluster size distribution functions of resistant plants are exponentials with characteristic cluster sizes increasing in time.Item Multiscale models for biological systems(Current Opinion in Colloid & Interface Science, 2010-04) Martins, M. L.; Ferreira Jr., S. C.; Vilela, M. J.Life, amazingly rich in diversity of shapes and functions, explores the limits of extreme complexity in nature. In this review we shall discuss in general terms the use of multiscale mathematical and computer models to study the dynamics of biological systems. These models permit integration of the rapidly expanding knowledge concerning the molecular basis of biology and its complex, nonlinear relationship with the emerging shapes and functions of cells, tissues and organs in living organisms.Item Cellular automata model for citrus variegated chlorosis(Physical Review E., 2000-06-14) Martins, M. L.; Ceotto, G.; Alves, S. G.; Bufon, C. C. B.; Silva, J. M.; Laranjeira, F. F.A cellular automata model is proposed to analyze the progress of citrus variegated chlorosis epidemics in São Paulo orange plantations. In this model epidemiological and environmental features, such as motility of sharpshooter vectors that perform Lévy flights, level of plant hydric and nutritional stress, and seasonal climatic effects, are included. The observed epidemic data were quantitatively reproduced by the proposed model on varying the parameters controlling vector motility, plant stress, and initial population of diseased plants.