Navegando por Autor "Arashiro, Everaldo"
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Item An alternative order parameter for the 4-state Potts model.(2006) Fernandes, Henrique Almeida; Arashiro, Everaldo; Felício, José Roberto Drugowich de; Caparica, Álvaro de AlmeidaWe have investigated the dynamic critical behavior of the two-dimensional 4-state Potts model using an alternative order parameter first used by Vanderzande [J. Phys. A 20 (1987) L549] in the study of the Z(5) model. We have estimated the global persistence exponent θg by following the time evolution of the probability P(t) that the considered order parameter does not change its sign up to time t. We have also obtained the critical exponents θ, z, ν, and β using this alternative definition of the order parameter and our results are in complete agreement with available values found in literature.Item A comparative study of the dynamic critical behavior of the four-state Potts like models.(2009) Arashiro, Everaldo; Fernandes, Henrique Almeida; Felício, José Roberto Drugowich deWe investigate the short-time critical dynamics of the Baxter–Wu (BW) and n=3 Turban (3TU) models to estimate their global persistence exponent θg. We conclude that this new dynamical exponent can be useful in detecting differences between the critical behavior of these models which are very difficult to obtain in usual simulations. In addition, we estimate again the dynamical exponents of the four-state Potts (FSP) model in order to compare them with results previously obtained for the BW and 3TU models and to decide between two sets of estimates presented in the current literature. We also revisit the short-time dynamics of the 3TU model in order to check if, as already found for the FSP model, the anomalous dimension of the initial magnetization x0 could be equal to zero.Item Efeitos da dinâmica sucessional de florestas neotropicais pluviais sobre sua estrutura, composição e biomassa no contexto das mudanças globais.(2012) Lanna, João Monnerat; Carneiro, Tiago Garcia de Senna; Kozovits, Alessandra Rodrigues; Carneiro, Tiago Garcia de Senna; Arashiro, Everaldo; Kampel, Silvana AmaralAs mudanças globais observadas nos últimos anos são indicadas como evidências de eventos mais drásticos preditos para o futuro, como contínuas alterações nos padrões de precipitação e incremento da temperatura média global. Indica-se como causa das mudanças globais o incremento atmosférico de gases do efeito estufa, cujas concentrações tendem a aumentar progressivamente no séc. XXI sob qualquer cenário de desenvolvimento humano. Como principais consequências das mudanças globais sobre as Florestas Neotropicais Pluviais, a intensificação dos períodos de seca e o aumento da concentração atmosférica de CO2 têm potencial para gerar profundas alterações sobre estes ecossistemas. Espera-se que a intensificação do estresse hídrico causado pelos eventos de seca aumente a mortalidade florestal, principalmente para espécies de madeira leve, e reduza a produtividade primária líquida destes ambientes. As mudanças esperadas para o incremento atmosférico de CO2 compreendem aumento da produtividade primária líquida (PPL) com crescimento mais intensificado para as espécies de madeira leve. Para avaliar os efeitos destes cenários sobre a dinâmica sucessional florestal, um modelo de crescimento florestal individual e espacialmente explícito é utilizado na realização de experimentos simulados. Nestes modelos as árvores são consideradas individualmente e seu ciclo de vida é integralmente simulado. Foram conduzidos experimentos independentes onde a floresta se desenvolveu por mil anos sobre taxas de crescimento ou mortalidade intensificadas. Os resultados produzidos a partir da simulação dos processos sucessionais sob cenários de intensificação de crescimento e morte ilustram alterações semelhantes às observadas e preditas pela ciência. Tais resultados incluem alterações na estrutura e composição florestal indicando perda de biomassa pela floresta em ambos os experimentos. Porém, a interpretação dos resultados do modelo indica que a dinâmica de clareiras atuou como principal direcionador das mudanças na composição e biomassa florestal observadas. Estes resultados indicam que a dinâmica sucessional florestal deve ser considerada em estudos que busquem analisar a longo prazo os impactos das mudanças climáticas sobre as florestas tropicais pluviais.Item Estudo de modelos de conservação de paridade por crescimento de superfícies.(2015) Santos, Felipe Aguiar Severino dos; Arashiro, EveraldoNesse trabalho, investigamos o fenômeno de crescimento da superfície gerada pela deposição do tipo solido sobre sólido (SOS) segundo as regras que definem os autômatos celulares estocásticos propostos por Grassberger (modelos A e B), e pela propagação de danos no modelo de Ising unidimensional submetido a uma dinâmica proposta por Hinrichsen e Domany (HD). Esses modelos não pertencem à classe de universalidade da percolação direcionada (DP) e apresentam novos valores para expoentes críticos, cuja origem se deve à conservação de paridade (PC). Determinamos o expoente de persistência local _, expoente de crescimento _w, válido em tempos curtos, assim como os outros expoentes críticos associados ao crescimento de superfície (_ e z). Nossas estimativas para os expoentes _w, _ e z, se comparam bem com os resultados obtidos a partir de razões de inteiros propostas por Jensen para os expoentes _, || _ e __ . Além disso, através da introdução de um campo externo no modelo A de Grassberger mapeamos a transição da classe de universalidade da PC para a DP através do expoente _w.Item Melanin-like units concentration effects in melanin-like/vanadium pentoxide hybrid compounds.(2001) Arashiro, Everaldo; Zampronio, Elaine Cabrini; Brunello, Carlos Alberto; Lassali, Tânia Aparecida Farias; Oliveira, Herenilton Paulino; Graeff, Carlos Frederico de OliveiraAn intercalated material has been prepared consisting of a regular alternation of organic/inorganic layers. The films were obtained by reacting 3,4-dihydroxy-phenylalanine (dl-DOPA) with varying concentrations in a solution with freshly prepared HVO3, which suffered a oxidative polymerization/intercalation ‘in situ’ process, forming a green suspension, in which after de-hydration at room temperature produces a nanocomposite with a dark blue metallic color. Films (C8H9NO2)xV2O5•nH2O were characterized using FT–IR, ESR, powder X-ray diffraction, conductivity, and cyclic voltammetry. The X-ray diffractograms indicate that the lamellar structure of the V2O5 is preserved for low concentrations of melanin-likeunits (x<0.02), but the inter-planar space increases from 1.2 nm to ca. 1.5 nm. The FT–IR and ESR spectra confirm that the V2O5 structure is preserved, however the presence of melanin-likeunits induces the reduction of V(V) ions to V(IV) ions. The melanin insertion is observed to increase the stability and reproducibility of the electrochemical insertion/de-insertion of Li+. The incorporation of melanin-like structures increases the conductivity, followed by a decrease in its temperature activation energy.Item New applications of an old individual-based model for biological dynamics.(2023) Ferreira, Fabíola Keesen; Silva, Alcides Volpato Carneiro de Castro e; Pinheiro, Carlos Felipe Saraiva; Arashiro, Everaldo; Ligeiro, Yan; Grelle, Carlos Eduardo de ViveirosA simplified representation or interpretation of reality using conceptual and mathematical models plays a role in understanding important phenomena, especially biological ones. Based on Medawar’s mutation accumulation theory, which predicts that the strength of natural selection decreases with age, favouring the accumulation of deleterious genes to be expressed at advanced ages, an individual-based model (IBM) published in 1995 was designed to demonstrate the biological ageing mechanism, with each individual being represented by a bitstring in a chronological manner. This model is called Penna Model (Penna, 1995) in honour of the creator, the physicist Thadeu Josino Pereira Penna. For this first time, this article carries out a systematic review of the use of Penna Model to assess its applicability in other phenomena and biological mechanisms. Our results indicate that the model was extensively explored and improved by researchers from different parts of the world, through small changes in the structure and base parameters of the model aimed at the biological phenomena of interest including Ecology, Evolutionary Ecology and Genetics issues. These changes have allowed the use of the model in other biological phenomena besides aging, with studies in systems of predation, competition, fragmentation, natural selection, speciation, genetics, immunology, epidemiology and others. The model is highlighted as a fairly flexible tool for applied biological dynamics of simple use, with the possibility of implementing different scales - temporal or spatial; and different languages - computational, logical or numerical; in addition to the possibility of inserting parameters that modify the individual and/or population that allow consistent results for decision-making.Item Pseudocapacitive behavior of Ti/RhOx+Co3O4 electrodes in acidic medium : application to supercapacitor development.(2004) Souza, Adriana Rodrigues de; Arashiro, Everaldo; Golveia, Helder; Lassali, Tânia Aparecida FariasMixtures of RhOx+Co3O4 have been electrochemically studied by cyclic voltammetry in acid solution as a function of composition. The electrodes were prepared by thermal decomposition at 400 °C of mixtures of nitrate precursors. Their electrochemical behavior shows substantial dependence on the electrode’s composition. The Co site controls the electrochemical behavior of the system in the 5–10 mol.% Rh composition range. A significant increase in the electrodes’ active area is observed for compositions corresponding to more than 10 mol.% RhOx in admixture with Co3O4. Above 10 mol.% Rh, the voltammetric curves become more similar to that for RhOx and then RhOx becomes able to stabilize the Co3O4 in the mixture. Electrodes of this kind have been found to perform as good materials in electrochemical capacitor applications, exhibiting specific capacitances of 500–800 F g−1 over to 20–60 mol.% RhOx composition range. The large specific capacitance exhibited by this system arises from a combination of the double-layer capacitance and the pseudocapacitance associated with Rh surface redox-type reactions.Item Recruitment and entropy decrease during trail formation by foraging ants.(2020) Lourenço, Giselle Martins; Ferreira, Fabíola Keesen; Fagundes, Roberth; Luna, P.; Silva, Alcides Volpato Carneiro de Castro e; Ribeiro, Sérvio Pontes; Arashiro, EveraldoSocial insects utilise a complex spatial orientation system mediated by chemical signals. This study investigated how the foraging behaviour of ants (Dorymyrmex thoracicus) varies depending on the quantity of an available resource using a feld experiment. Further, we demonstrated computationally that ant displacement is compatible with a model based on pheromone deposition. Our experiment tested how the resource size (large or small) and availability (one or two simultaneous patches) of resources ofered infuence the number of recruited ants (trafc fow) and the speed of trafc fow both moving towards a resource and returning to the colony. The results showed that the returning fow was higher than the going fow independent of resource. The trafc fow towards a single resource was higher than the fow for either of two simultaneous resources patches ofered; thus, multiple resources sources split the fow, regardless of the fact that resource size did not afect foraging choices. Our results indicated that the ants used an orientation mechanism that can be reproduced by a theoretical computer model. With our model, we showed that initially, the displacement of ants followed no clearly detectable pattern. However, with increasing levels of ant recruitment and consequent pheromone deposition on the most used trails, returning displacement revealed the formation of shorter and more organised trails. The model revealed key transition between periods of order and disorder that continued until the fow of information reached an organised state (Shannon entropy). This study highlights an exceptional mechanism of foraging optimisation in eusocial insects.Item Short-time critical dynamics of the Baxter-Wu model(2003) Arashiro, Everaldo; Felício, José Roberto Drugowich deWe study the early time behavior of the Baxter-Wu model, an Ising model with three-spin interactions on a triangular lattice. Our estimates for the dynamic exponent z are compatible with results recently obtained for two models which belong to the same universality class of the Baxter-Wu model: the two-dimensional four-state Potts model and the Ising model with three-spin interactions in one direction. However, our estimates for the dynamic exponent theta of the Baxter-Wu model are completely different from the values obtained for those models. This discrepancy could be related to the absence of a marginal operator in the Baxter-Wu model.Item Short-time dynamics of helix-coil transition in polypeptides(2006) Arashiro, Everaldo; Felício, José Roberto Drugowich de; Hansmann, Ulrich H. E.We study the critical relaxation of the helix-coil transition in all-atom models of polyalanine chains. We show that at the critical temperature the decay of a completely helical conformation can be described by scaling relations that allow us estimating the pertinent critical exponents. The present approach opens a new way for characterizing transitions in proteins and may lead to a better understanding of their folding mechanism. An application of the technique to the 34-residue human parathyroid fragment PTH(1-34) supports universality of the helix-coil transition in homopolymers and (helical) proteins.Item Simulação computacional para populações em ambientes fragmentados : estudo de caso com o macaco-prego-de-crista, Sapajus robustus.(2013) Ferreira, Fabíola Keesen; Arashiro, Everaldo; Pinheiro, Carlos Felipe Saraiva; Martins, Waldney PereiraModelos computacionais têm sido comumente utilizados para simular sistemas complexos tais como a dinâmica de comunidades biológicas. O estudo de populações sujeitas ao fenômeno de perda e fragmentação do habitat, transformação de áreas contínuas em áreas pequenas, geralmente circundada por matrizes antrópicas, tem sido o foco de muitos estudos dentro do âmbito da conservação. Assim, o objetivo do presente estudo foi desenvolver um modelo computacional, a partir da modificação do reconhecido Penna Model de envelhecimento biológico, a fim de se avaliar o comportamento de populações sujeitas aos efeitos de ambientes fragmentados, modelo denominada "Modelo Penna de Fragmentação". Como objeto de estudo foram utilizados os dados biológicos do macaco-prego-de-crista, espécie de primata (Sapajus robustus) ameaçada de extinção, cuja distribuição geográfica dentro do bioma Mata Atlântica se insere no cenário de intensa fragmentação do habitat. Foi realizada uma classificação de uso e ocupação do solo - utilizando técnicas de processamento digital de imagens e geoprocessamento - em uma área contida dentro da distribuição geográfica de S. robustus, a fim de se obter um panorama da estrutura da paisagem na qual a espécie está inserida. As simulações do modelo evidenciaram o comportamento demográfico esperado em função de três principais aspectos que acometem populações sujeitas a perda e fragmentação do habitat: tamanho populacional efetivo, área e conformação dos fragmentos e os efeitos deletérios devido à baixa variabilidade genética, considerando populações pequenas e isolados. A análise da paisagem revelou que a região apresenta-se com uma composição fragmentada, com predominância de matrizes antrópicas bem como classes de regeneração da paisagem que não são capazes de abrigar populações viáveis de Sapajus robustus. A classificação servira, ainda, de subsidio para a continuidade da simulação do modelo considerando população e espaço geográfico, na expectativa de gerar uma ferramenta capaz de demonstrar o comportamento de populações no tempo real e futuro, servindo de auxílio para ações de conservação e manejo.Item Simulação de propriedades fractais de perfis de fratura.(2015) Miranda, Otacílio Ricardo Gonçalves de; Machado, Romuel Figueiredo; Arashiro, Everaldo; Machado, Romuel Figueiredo; Rodrigues, Áttila Leães; Menezes Sobrinho, Ismael Lima; Pinheiro, Carlos Felipe SaraivaAlém de sua relevância tecnológica a investigação da mecânica da fratura ainda atrai a atenção dos físicos. Neste trabalho estamos interessados nas propriedades geométricas geradas pela fratura de um meio continuo sob a ação de tensões aplicadas em suas bordas. Neste caso, o campo tensorial de tensões é dado pelas soluções das equações de Michel-Beltrami (equações MB) da teoria da elasticidade linear. Essas equações elípticas são similares a equação de Laplace da eletrostática. Este fato nos motivou a elaborar um modelo para fratura baseado no modelo de ruptura dielétrica que é conhecido por gerar padrões de descarga fractais. A cada passo as equações MB são solucionadas numericamente usando um algoritmo SOR e um novo sitio de uma rede quadrada é adicionado ao padrão da trinca com uma probabilidade proporcional a u onde u é proporcional à densidade de energia elástica no sitio que é uma função do campo tensorial de tensões e é um parâmetro relacionado a desordem e não-homogeneidades do meio. Nossos resultados mostram que a dimensão fractal d da trinca está relacionada ao modo como a energia elástica é distribuída ao longo da trinca durante o processo de fratura: d é próxima de 1:0 quando a energia é concentrada nas pontas ( > 1:0) e maior do que 1:0 quando a energia é espalhada pela trinca.Item Simulations of populations of Sapajus robustus in a fragmentedlandscape.(2017) Ferreira, Fabíola Keesen; Silva, Alcides Volpato Carneiro de Castro e; Arashiro, Everaldo; Pinheiro, Carlos Felipe SaraivaThe study of populations subject to the phenomenon of loss and fragmentation of habitat, transformingcontinuous areas into small ones, usually surrounded by anthropogenic matrices, has been the focus ofmany researches within the scope of conservation. The objective of this study was to develop a com-puter model by introducing modifications to the renowned Penna model for biological aging, in order toevaluate the behavior of populations subjected to the effects of fragmented environments. As an objectof study, it was used biological data of the robust tufted capuchin (Sapajus robustus), an endangered pri-mate species whose geographical distribution within the Atlantic Rain Forest is part of the backdrop ofintense habitat fragmentation. The simulations showed the expected behavior based on the three mainaspects that affects populations under intense habitat fragmentation: the population density, area andconformation of the fragments and deleterious effects due the low genetic variability in small and isolatedpopulations. The model showed itself suitable to describe changes in viability and population dynamicsof the species crested capuchin considering critical levels of survival in a fragmented environment andalso, actions in order to preserve the species should be focused not only on increasing available area butalso in dispersion dynamicsItem A smooth path to plot hydrogen atom via Monte Carlo method.(2019) Lobo, Pedro Henrique Fernandes; Arashiro, Everaldo; Silva, Alcides Volpato Carneiro de Castro e; Pinheiro, Carlos Felipe SaraivaIn this paper, we show how to build a basic computer program using the Monte Carlo method to display the hydrogen atomic orbitals. For this, in a heuristic way, we applied a von Neumann acceptance-rejection method in simple problems of potential wells, and we end with the hydrogen orbitals representation. In this technique, we spread points uniformly on the 1D and 2D charts of probability density distributions, then we filtered points under these “curves or surfaces”, and we extended this logic to 3D cases. Throughout the work, we also made some comments to help beginner students better understand the term “wave function” present in the Schrödinger equation. Also, we made all source code available at a third-party platform, for any purpose under the MIT license. Keywords: hydrogen atom, quantum mechanics, Monte Carlo method, Neumann acceptance-rejection method.Item The stochastic nature of predator prey cycles.(2009) Castro, Tânia Tomé Martins de; Rodrigues, Áttila Leães; Arashiro, Everaldo; Oliveira, Mário José deWe study by numerical simulations the time correlation function of a stochastic lattice model describing the dynamics of coexistence of two interacting biological species that present time cycles in the number of species individuals. Its asymptotic behavior is shown to decrease in time as a sinusoidal exponential function from which we extract the dominant eigenvalue of the evolution operator related to the stochastic dynamics showing that it is complex with the imaginary part being the frequency of the population cycles. The transition from the oscillatory to the nonoscillatory behavior occurs when the asymptotic behavior of the time correlation function becomes a pure exponential, that is, when the real part of the complex eigenvalue equals a real eigenvalue. We also show that the amplitude of the undamped oscillations increases with the square root of the area of the habitat as ordinary random fluctuations.Item Time correlation function in systems with two coexisting biological species.(2008) Arashiro, Everaldo; Rodrigues, Áttila Leães; Oliveira, Mário José de; Castro, Tânia Tomé Martins deWe study a stochastic lattice model describing the dynamics of coexistence of two interacting biological species. The model comprehends the local processes of birth, death, and diffusion of individuals of each species and is grounded on interaction of the predator-prey type. The species coexistence can be of two types: With self-sustained coupled time oscillations of population densities and without oscillations. We perform numerical simulations of the model on a square lattice and analyze the temporal behavior of each species by computing the time correlation functions as well as the spectral densities. This analysis provides an appropriate characterization of the different types of coexistence. It is also used to examine linked population cycles in nature and in experiment.Item Voltammetric characterization of an iridium oxide-based system : the pseudocapacitive nature of the Ir0.3Mn0.7O2 electrode.(2002) Grupioni, Andrea Alves Ferreira; Arashiro, Everaldo; Lassali, Tânia Aparecida FariasMixtures of IrO2+MnO2 (30:70 mol%) have been electrochemically studied by cyclic voltammetry (CV) in acid solution. The crystalline structure, morphology and the electrochemical properties of the electrodes have been studied as a function of the annealing temperature. X-ray diffraction analysis (XRD), show absence of Mn2O3 phase formation and suggest the possible of formation of a solid solution of IrO2 and MnO2 mainly between 400 and 450 °C. The voltammetric behavior depends on the potential cycle number and annealing temperature employed in the preparation of the oxide layer. A good potential window in aqueous H2SO4 and high electroactive area are obtained due to the contribution of Ir redox transitions. Energy-dispersive X-ray (EDX) and scanning electron microscopy (SEM) analysis suggest an enrichment of the Ir content on the surface at the cost of the dissolution of the manganese present in the film when the electrode is submitted to the continuous potential scan. The electrodes have been found to perform well in electrochemical capacitor applications with a specific capacitance close to 550 F g−1. The large capacitance exhibited by this system arises from a combination of the double-layer capacitance and pseudocapacitance associated with surface redox-type reactions.