Papers by Rita Maria Zorzenon dos Santos
Journal of Theoretical Biology, Jul 1, 1993
Using a simple mathematical model of the Jerne network, we investigate the conditions of antigen ... more Using a simple mathematical model of the Jerne network, we investigate the conditions of antigen presentation that result in tolerance to pairs of antigens with complementary shapes, such as hormones and receptors. This study is motivated by the prevalence of auto-immune diseases involving hormones or neurotransmitters and their respective receptors as self-antigens. The model shows that, in order to ensure full tolerance to coupled antigens in those conditions that ensure tolerance to isolated antigens, both antigens have to be presented simultaneously in similar conditions. This result suggests a possibility for preventing some auto-immune diseases.
Physics Letters, Mar 1, 1985
Within a real space renormalization group framework, we study the criticality (phase diagram, and... more Within a real space renormalization group framework, we study the criticality (phase diagram, and critical thermal and crossover exponents) of the spin-l/2 anisotropic quantum Heisenberg ferromagnet on a simple cubic lattice. The results obtained are in satisfactory agreement with known results whenever available.
American Journal of Physics, Mar 1, 1979
arXiv (Cornell University), Jun 4, 2003
In this paper we review the trajectory of a model proposed by Stauffer and Weisbuch in 1992 to de... more In this paper we review the trajectory of a model proposed by Stauffer and Weisbuch in 1992 to describe the evolution of the immune repertoire and present new results about its dynamical behavior. Ten years later this model, which is based on the ideas of the immune network as proposed by Jerne, has been able to describe a multi-connected network and could be used to reproduce immunization and aging experiments performed with mice. Besides its biological implications, the physical aspects of the complex dynamics of this network is very interesting per se. The immunization protocol is simulated by introducing small and large perturbations (damages), and in this work we discuss the role of both. In a very recent paper we studied the aging effects by using auto-correlation functions, and the results obtained apparently indicated that the small perturbations would be more important than the large ones, since their cumulative effects may change the attractor of the dynamics. However our new results indicate that both types of perturbations are important. It is the cooperative effects between both that lead to the complex behavior which allows to reproduce experimental results.
Nucleation and Atmospheric Aerosols, 2003
ABSTRACT This text summarizes a series of four lectures presented at the PASI on Modern Challenge... more ABSTRACT This text summarizes a series of four lectures presented at the PASI on Modern Challenges in Statistical Mechanics. The idea was to give to the students a flavor of the biological aspects involved in the dynamics of infection and the spread of diseases, the complexity of the systems involved, and how we can improve our modeling of such systems by using different approaches in order to get closer to experimental results. In a huge universe of publications about the subject, we restrict the list of references to the ones that may be useful to the students and will lead them to other important work. Therefore, the text should not be taken as a review of the subject, but rather as an introductory text for physicists about the dynamics of infection and spread of diseases and the role of biological physics in this interdisciplinary field.
Physica A: Statistical Mechanics and its Applications, 2001
ABSTRACT
arXiv (Cornell University), Jul 12, 2001
In this paper we revisit the Mackey-Glass model for blood-forming process, which was proposed to ... more In this paper we revisit the Mackey-Glass model for blood-forming process, which was proposed to describe the spontaneous fluctuations of the blood cell counts in normal individuals and the first stage of chronic myelocytic (or granylocytic) leukemia (CML). We obtain the bifurcation diagram as a function of the time delay parameter and show that the onset of leukemia is related to instabilities associated to the presence of periodic windows in the midst of a chaotic regime. We also introduce a very simple modification in the death rate parameter in order to simulate the accumulation of cells and the progressive increase of the minima counts experimentally observed in the final stage of the disease in CML patients. The bifurcation diagram as a function of the death rate parameter is also obtained and we discuss the effects of treatments like leukapheresis.
Hidrocarbonetos aromaticos policiclicos foram incorporados em bicamadas umidas de Dipalmitil Leci... more Hidrocarbonetos aromaticos policiclicos foram incorporados em bicamadas umidas de Dipalmitil Lecitina (DPL), no intuito de detectar as mudancas estruturais induzidas na membrana modelo hospedeira. Foram obtidos diagramas de difracao a baixo ângulo para os sistemas: DPL, DPL - pireno, DPL - 3, 4- benzopireno e DPL - 1, 2, 5, 6 - dibenzantraceno. Estes diagramas, subsequentemente, foram analisados usando-se as intensidades das reflexoes lamelares. A distribuicao de densidade eletronica normal ao plano da bicamada foi calculada pela sintese de Fourier, com resolucao de 7.5 Ao. No caso do pireno, o mapa de densidade eletronica mostra uma leve perturbacao da estrutura na regiao hidrofobica, proxima ao grupo glicerol. Este resultado concorda com as experiencias de NMR realizadas por Vanderkooi e colaboradores (J. Chem. Phys., 63, 3662, 1975). Para os sistemas de DPL - 3,4 - benzopireno a distorcao na regiao da queda abrupta existente no centro de simetria do perfil de densidade eletronica e similar aquela observada para as amostras de DPL - pireno. A incorporacao do 1, 2, 5, 6 - dibenzantraceno dentro das bicamadas afeta bastante o empacotamento das cadeias, por perturbacoes ao longo das cadeias de carbono e na regiao do centro da bicamada correspondente aos grupos terminais Abstract
Journal of Theoretical Biology, 1993
Using a simple mathematical model of the Jerne network, we investigate the conditions of antigen ... more Using a simple mathematical model of the Jerne network, we investigate the conditions of antigen presentation that result in tolerance to pairs of antigens with complementary shapes, such as hormones and receptors. This study is motivated by the prevalence of auto-immune diseases involving hormones or neurotransmitters and their respective receptors as self-antigens. The model shows that, in order to ensure full tolerance to coupled antigens in those conditions that ensure tolerance to isolated antigens, both antigens have to be presented simultaneously in similar conditions. This result suggests a possibility for preventing some auto-immune diseases.
American Journal of Physics, 1979
We use a cellular automata model to study the evolution of HIV infection and the onset of AIDS. T... more We use a cellular automata model to study the evolution of HIV infection and the onset of AIDS. The model takes into account the global features of the immune response to any pathogen, the fast mutation rate of the HIV and a fair amount of spatial localization. Our results reproduce quite well the three-phase pattern observed in T cell and virus counts of infected patients, namely, the primary response, the clinical latency period and the onset of AIDS. We have also found that the infected cells may organize themselves into special spatial structures since the primary infection, leading to a decrease on the concentration of uninfected cells. Our results suggest that these cell aggregations, which can be associated to syncytia, leads to AIDS.
AIP Conference Proceedings, 2003
ABSTRACT This text summarizes a series of four lectures presented at the PASI on Modern Challenge... more ABSTRACT This text summarizes a series of four lectures presented at the PASI on Modern Challenges in Statistical Mechanics. The idea was to give to the students a flavor of the biological aspects involved in the dynamics of infection and the spread of diseases, the complexity of the systems involved, and how we can improve our modeling of such systems by using different approaches in order to get closer to experimental results. In a huge universe of publications about the subject, we restrict the list of references to the ones that may be useful to the students and will lead them to other important work. Therefore, the text should not be taken as a review of the subject, but rather as an introductory text for physicists about the dynamics of infection and spread of diseases and the role of biological physics in this interdisciplinary field.
Parallel computing is becoming increasingly important for solving technological and scientific pr... more Parallel computing is becoming increasingly important for solving technological and scientific problems. In fact, the most powerful computers in the world are now parallel machines. In this paper we utilize a low-cost parallel computing environment, based on the UNIX operating system and the PVM (Parallel Virtual Machine) and MPI (Message Passing Interface) communication protocols, to compute the dynamical evolution of one-dimensional cellular automata with large numbers of sites. Specifically, we develop and validate parallel binary PVM and MPI implementations, analyse their parallel performance measures, and use the relatively faster MPI implementation to obtain some results for cellular automata with large numbers of sites.
Journal of Physics C: Solid State Physics, 1988
ABSTRACT The authors study both the pure anisotropic and the anisotropically diluted transverse I... more ABSTRACT The authors study both the pure anisotropic and the anisotropically diluted transverse Ising model at zero temperature on the square lattice. In the former the coupling along each Cartesian direction are allowed to be different, whereas in the latter it is the bond concentration which may be different along the Cartesian directions. By means of a position space renormalisation group scheme, they find that in both cases the isotropic systems are stable with respect to anisotropy perturbations. They also discuss their results in view of a recently proposed criterion for the stability of pure systems of fixed points with respect to correlated dilution.
International Journal of Modern Physics C, 1998
Cellular automata are very simple systems that can exhibit complex dynamics on its time evolution... more Cellular automata are very simple systems that can exhibit complex dynamics on its time evolution. Over the last decade there have been many applications of cellular automata to modeling of biological systems. Those applications have been stimulated by the study of complex systems which has brought many insights into the cooperative and global behavior of the biological systems. Along with this discussion we present two different applications of deterministic and also of probabilistic cellular automata that are used to model the dynamics involved in cooperative and collective behavior of the immune system. In the first example, we use a deterministic cellular automata to model the time evolution of the immune repertoire, as a network, according to the Jerne's theory. Using this model we could reproduce some recent experimental results about immunization and aging of the immune system. In the second example, we use a probabilistic cellular automata model to study the evolution of...
International Journal of Modern Physics C, 2001
In this paper, we study the dynamics of a multi-connected network which has been used recently to... more In this paper, we study the dynamics of a multi-connected network which has been used recently to simulate the evolution of the immune repertoire. In particular, we used this model to reproduce experimental results about immunization and aging performed with mice. Here, we investigate the main features which are responsible for those effects by obtaining the cluster size and the activation time distributions. We observe a power law behavior for the activation time distribution below and at the critical region whereas the cluster size distribution exhibits a characteristic length scale in the biologically relevant region of the parameter space. Only at the transition, we obtain a power law behavior for this distribution. The characteristic cluster size is responsible for the loss of plasticity during the time evolution of the system, leading to aging effects, while the absence of a characteristic time scale in the activation time is associated with memory effects.
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Papers by Rita Maria Zorzenon dos Santos