Navegando por Autor "Ferreira Jr., S. C."
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Item Absorbing state transition in a one-dimensional contact replication process(Physical Review E, 2004-09-29) Ferreira Jr., S. C.In this work, the contact process (CP) is modified in order to model a contact replication process (CRP) for monoclonal reproduction. The occupation rates of an empty site depend on the nearest-neighbor and next- nearest-neighbor sites. The CRP exhibits an absorbing state transition studied through cluster approximations and Monte Carlo simulations. The critical rate obtained from simulations,λc = 2.0263(4), is smaller than that for CP. However, the CRP critical exponents are in agreement with those for CP and, consequently, the model belongs to the directed percolation universality class.Item Effects of the mean free path and relaxation in a model for the aggregation of particles in superfluid media(The Journal of Chemical Physics, 2009-06-30) Alves, S. G.; Vilesov, A. F.; Ferreira Jr., S. C.In this paper, we study a two-dimensional model for the growth of molecular clusters in superfluid helium at low temperature. In the model, particles of diameter a follow random ballistic moves of length ␦ = a − 256a. Upon attachment on the cluster surface, particles allow one-step relaxation to the nearest twofold coordinated site. Average coordination numbers of particles show that in the presence of relaxation the screening for incoming particles modifies the microscopic structure of the cluster. These results are in qualitative agreement with experimental aggregation of methane in He droplets, in which large abundance of fully coordinated sites is observed. The average coordination number increases with ␦ , showing that screening is relevant when relaxation is present. As the cluster size increases, the corresponding structure clusters changes from a compact to a fractal, typical of ballistic and diffusion limited models, respectively. A scaling ansatz describing the crossover between the two regimes is proposed.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 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.