oalib

Publish in OALib Journal

ISSN: 2333-9721

APC: Only $99

Submit

Any time

4 ( 1 )

2020 ( 7 )

2019 ( 613 )

2018 ( 918 )

Custom range...

Search Results: 1 - 10 of 556775 matches for " L. R. D. da; "
All listed articles are free for downloading (OA Articles)
Page 1 /556775
Display every page Item
Colored noise and memory effects on formal spiking neuron models
L. A. da Silva,R. D. Vilela
Quantitative Biology , 2015, DOI: 10.1103/PhysRevE.91.062702
Abstract: Simplified neuronal models capture the essence of the electrical activity of a generic neuron, besides being more interesting from the computational point of view when compared to higher dimensional models such as the Hodgkin-Huxley one. In this work, we propose a generalized resonate-and-fire model described by a generalized Langevin equation that takes into account memory effects and colored noise. We perform a comprehensive numerical analysis to study the dynamics and the point process statistics of the proposed model, highlighting interesting new features like: i) non-monotonic behavior (emergence of peak structures, enhanced by the choice of colored noise characteristic time-scale) of the coefficient of variation (CV) as a function of memory characteristic time-scale, ii) colored noise-induced shift in the CV, and iii) emergence and suppression of multimodality in the interspike interval (ISI) distribution due to memory-induced subthreshold oscillations. Moreover, in the noise-induced spike regime, we study how memory and colored noise affects the coherence resonance (CR) phenomenon. We found that for sufficiently long memory, CR is not only suppressed, but also the minimum of the CV $\times$ noise intensity curve that characterizes the presence of CR may be replaced by a maximum. The aforementioned features allow to interpret the interplay between memory and colored noise as an effective control mechanism to neuronal variability. Since both variability and non-trivial temporal patterns in the ISI distribution are ubiquitous in biological cells, we hope the present model can be useful in modeling real aspects of neurons.
Estudo da intercala??o de compostos organicos em caulins na forma ácida
Fernandes, M. V. da S.;Silva, L. R. D. da;
Ceramica , 2011, DOI: 10.1590/S0366-69132011000200014
Abstract: the feasibility of using major clays such as kaolin in the adsorption processes, can occur through chemical modification by intercalation in their structures phyllite. samples of kaolin in the region of northeast brazil, one white and one gray of a portion of the region borborema-served in the state of paraiba, were interspersed with dimethylsulfoxide, oxalic acid and citric acid. the characterization natural and modified techniques were used x-ray diffraction, thermal analysis and absorption spectroscopy in the infrared.
Efeito do glutaraldeído na adsor??o de extrato proteico da Ipomoea Batatas (L) Lam na superficie de uma zeólita analcima
Gondim, A. C. S.;Silva, L. R. D. da;
Ceramica , 2005, DOI: 10.1590/S0366-69132005000300008
Abstract: the analcime zeolite (na16al16si32o96.nh2o) was treated with hydrochloric acid 0.25 mol.l-1, followed by the funcionalization with glutaraldehyde and immersed in the proteic extract obtained from gross extract of sweet potato pulp (ipomoea batatas (l) lam), which presents in its composition the polyphenol oxidase enzyme (ppo). other samples were submitted to the same procedure with characterizations by scanning electron microscopy, fourier transform infrared spectroscopy and thermogravimetry.
Recursive-search method for ferromagnetic ising systems: combination with a finite-size scaling approach
Silva P. C. da,Fulco U. L.,Nobre F. D.,Silva L. R. da
Brazilian Journal of Physics , 2002,
Abstract: A method for obtaining critical properties of physical systems is presented. Based on a recursive relation involving a physical parameter of the system, it drives the system spontaneously to the critical point, providing an efficient way to estimate critical properties. The method is illustrated for several ferromagnetic Ising systems on well-known Bravais lattices. A finite-size scaling approach is performed, by applying the method on lattices of different sizes. The efficiency of the method is confirmed by evaluating critical temperatures, as well as critical exponents, that turn up to be in good agreement with those available in the literature, with a relatively small computational effort.
Diffusion in stochastic sandpiles
S. D. da Cunha,Ronaldo R. Vidigal,L. R. da Silva,Ronald Dickman
Physics , 2009, DOI: 10.1140/epjb/e2009-00367-0
Abstract: We study diffusion of particles in large-scale simulations of one-dimensional stochastic sandpiles, in both the restricted and unrestricted versions. The results indicate that the diffusion constant scales in the same manner as the activity density, so that it represents an alternative definition of an order parameter. The critical behavior of the unrestricted sandpile is very similar to that of its restricted counterpart, including the fact that a data collapse of the order parameter as a function of the particle density is only possible over a very narrow interval near the critical point. We also develop a series expansion, in inverse powers of the density. for the collective diffusion coefficient in a variant of the stochastic sandpile in which the toppling rate at a site with $n$ particles is $n(n-1)$, and compare the theoretical prediction with simulation results.
Decomposition kinetics of gaseous ozone in peanuts
Alencar, Ernandes R. de;Faroni, Lêda R. D.;Martins, Marcio A.;Costa, André R. da;Cecon, Paulo R.;
Engenharia Agrícola , 2011, DOI: 10.1590/S0100-69162011000500011
Abstract: this study was conducted to evaluate the decomposition kinetics of gaseous ozone in peanut grains. this evaluation was made with 1-kg peanut samples, moisture contents being 7.1 and 10.5% wet basis (w.b.), placed in 3-liter glass containers. the peanut grains were ozonated at the concentration of 450 μg l-1, at 25 and 35 oc, with gas flow rates of 1.0 and 3.0 l min-1. time of saturation was determined by quantifying the residual concentration of ozone after the gas passed through the grains to constant mass. the decomposition kinetics of ozone was evaluated after the grain mass was ozone-saturated. for the peanut grains whose moisture content was 7.1% (w.b.), at 25 and 35oc and with flow rates of 1.0 and 3.0 l min-1, the values obtained for time of saturation of gaseous ozone ranged between 173 and 192 min; the concentration of saturation was approximately 260 μg l-1. for the grains whose moisture content was 10.5% (w.b.), a higher residual concentration of gaseous ozone was obtained at 25 oc, that of 190 μg l-1. as regards the half-life of ozone, the highest value obtained was equivalent to 7.7 min for grains ozonated at 25 oc, while for those with moisture content of 10.5% at 35 oc, half-life was 3.2 min. in the process of ozone decomposition in peanut grains, temperature was concluded to be the key factor. an increase of 10 oc in the temperature of the grains results in a decrease of at least 43% in the half-life of ozone.
Estudo morfométrico e estereológico digital da mucosa do intestino delgado de crian?as eutróficas e desnutridas com diarréia persistente
Pires, Ana L.G.;Silveira, Themis R. da;Silva, Vinícius D. da;
Jornal de Pediatria , 2003, DOI: 10.1590/S0021-75572003000400011
Abstract: objectives: to test the hypothesis that the proximal small intestines of children with persistent diarrhea present morphometric and stereologic changes proportional to their nutritional status, using microscope images stored in a computer. methods: cross-sectional study with 65 pediatric patients, whose ages ranged from 4 months to 5 years, with persistent diarrhea for over 14 days. the nutritional assessment was performed according to the z-scores for weight/age (w/a), weight/height (w/h) and height/age (h/a) ratios, divided into: well-nourished = z > 2sd and malnourished = z < -2sd; well-nourished = z > 2sd, nutritional risk = z < -1sd and malnourished = z < -2sd; and continuously, in descending order, using the nchs charts. after obtaining the computer images using the software scion image, villous height, crypt depth, mucosal thickness, total mucosal thickness, and villous/crypt ratio were measured in the fragments of the small intestinal mucosa, enlarged 100 times. when images were enlarged 500 times, enterocyte height, nuclear height and brush-border height were measured. stereologic analysis was performed using cycloid arcs. results: for w/a, w/h and h/a z-scores, divided into two nutritional status categories, no statistically significant difference was observed in regard to villous height, crypt depth, mucosal thickness, total mucosal thickness and villous/crypt ratio. enterocyte height presented the most significant difference between well-nourished and malnourished groups, for w/a and w/h ratios, with a 500x enlargement, although this difference was not statistically significant. when z-scores were subdivided into three nutritional status categories, a digital morphometric analysis showed a statistically significant difference for villous/crypt ratio between the well-nourished and slightly malnourished group and the well-nourished and mild to severe malnourished group (p = 0.048). the villous/crypt ratio was higher among well-nourished children. using the
Estudo morfométrico e estereológico digital da mucosa do intestino delgado de crian as eutróficas e desnutridas com diarréia persistente
Pires Ana L.G.,Silveira Themis R. da,Silva Vinícius D. da
Jornal de Pediatria , 2003,
Abstract: OBJETIVOS: testar a hipótese de que a mucosa do intestino delgado proximal de crian as com diarréia persistente apresenta altera es morfométricas e estereológicas proporcionais ao estado nutricional, utilizando captura de imagens através de microscópio acoplado ao computador. MéTODOS: estudo transversal incluindo 65 pacientes pediátricos, com idade entre quatro meses e cinco anos, com diarréia de mais de 14 dias de dura o, avaliados pelos escores z, divididos em eutróficos = z > 2 DP e desnutridos = z < -2DP; eutróficos = z > 2 DP, risco nutricional = z < -1DP e desnutridos = z < -2DP; e de maneira contínua em ordem decrescente, utilizando-se as tabelas do NCHS. Após a captura das imagens através do programa Scion Image, foram medidas a altura dos vilos, a profundidade das criptas, a espessura da mucosa, a espessura total da mucosa e a rela o vilo/cripta (100 aumentos) e a altura do enterócito, altura do núcleo e do bordo em escova (500 aumentos). A análise estereológica foi feita através de arcos ciclóides. RESULTADOS: para os escores z P/I, P/E e E/I, divididos em duas categorias de estado nutricional, n o houve diferen a estatisticamente significante quanto às medidas da altura dos vilos, profundidade das criptas, espessura da mucosa, espessura total da mucosa e rela o vilo/cripta. A altura do enterócito foi a característica que apresentou maior diferen a entre os grupos eutróficos e desnutridos, para os índices P/I e P/E, em 500 aumentos, sem atingir significancia estatística. No entanto, para três categorias de estado nutricional, a análise morfométrica digitalizada mostrou diferen a estatisticamente significante para a rela o vilo/cripta entre eutróficos e desnutridos leves e entre eutróficos e desnutridos moderados e graves (p=0,048). A rela o vilo/cripta foi maior nos eutróficos. Através do coeficiente de correla o linear de Spearman, a altura do enterócito, a altura do núcleo do enterócito e a do bordo em escova mostraram clara associa o com os índices P/I (r=0,25;p=0,038) e P/E (r=0,029; p=0,019). A altura do núcleo do enterócito e a do bordo em escova mostraram, ainda, associa o com o índice P/E. CONCLUS ES: as correla es encontradas entre o estado nutricional e a morfometria das variáveis da mucosa do intestino delgado relacionaram-se ao peso dos pacientes. Embora estas associa es tenham sido de magnitude fraca a moderada, há uma tendência à diminui o do tamanho do enterócito, do seu núcleo e do bordo em escova, à medida que aumenta o grau de desnutri o.
Competing long-range bonds and site dilution in the one-dimensional bond-percolation problem
Fulco, U. L.;Silva, L. R. da;Nobre, F. D.;Lucena, L. S.;
Brazilian Journal of Physics , 2003, DOI: 10.1590/S0103-97332003000300032
Abstract: the long-range bond-percolation problem, on a linear chain (d = 1), in the presence of diluted sites (with an occupancy probability ps for an active site) is studied by means of a monte carlo simulation. the occupancy probability for a bond between two active sites i and j, separated by a distance rij is given by pij = , where p represents the usual occupancy probability between nearest-neighbor sites. this model allows one to analyse the competition between long-range bonds (which enhance percolation) and diluted sites (which weaken percolation). by varying the parameter a (a > 0), one may find a crossover between a nonextensive regime and an extensive regime; in particular, the cases a = 0 and a ? ¥ represent, respectively, two well-known limits, namely, the mean-field (infinite-range bonds) and first-neighbor-bond limits. the percolation order parameter, p¥, was investigated numerically for different values of a and ps. two characteristic values of a were found, which depend on the site-occupancy probability ps, namely, a1(ps) and a2(ps) (a2(ps) > a1(ps) > 0). the parameter p¥ equals unit, "p > 0, for 0 < a < a1(ps) and vanishes, "p < 1, for a > a2(ps). in the interval a1(ps) < a < a2(ps), the parameter p¥ displays a familiar behavior, i.e., 0 for p < pc(a) and finite otherwise. it is shown that both a1(ps) and a2(ps) decrease with the inclusion of diluted sites. for a fixed ps, it is shown that a convenient variable, p* o p*(p, a, n), may be defined in such a way that plots of p¥ versus p* collapse for different sizes and values of a in the nonextensive regime.
Competing long-range bonds and site dilution in the one-dimensional bond-percolation problem
Fulco U. L.,Silva L. R. da,Nobre F. D.,Lucena L. S.
Brazilian Journal of Physics , 2003,
Abstract: The long-range bond-percolation problem, on a linear chain (d = 1), in the presence of diluted sites (with an occupancy probability p s for an active site) is studied by means of a Monte Carlo simulation. The occupancy probability for a bond between two active sites i and j, separated by a distance r ij is given by p ij = , where p represents the usual occupancy probability between nearest-neighbor sites. This model allows one to analyse the competition between long-range bonds (which enhance percolation) and diluted sites (which weaken percolation). By varying the parameter a (a > 0), one may find a crossover between a nonextensive regime and an extensive regime; in particular, the cases a = 0 and a ¥ represent, respectively, two well-known limits, namely, the mean-field (infinite-range bonds) and first-neighbor-bond limits. The percolation order parameter, P¥, was investigated numerically for different values of a and p s. Two characteristic values of a were found, which depend on the site-occupancy probability p s, namely, a1(p s) and a2(p s) (a2(p s) > a1(p s) > 0). The parameter P¥ equals unit, "p > 0, for 0 < a < a1(p s) and vanishes, "p < 1, for a > a2(p s). In the interval a1(p s) < a < a2(p s), the parameter P¥ displays a familiar behavior, i.e., 0 for p < p c(a) and finite otherwise. It is shown that both a1(p s) and a2(p s) decrease with the inclusion of diluted sites. For a fixed p s, it is shown that a convenient variable, p* o p*(p, a, N), may be defined in such a way that plots of P¥ versus p* collapse for different sizes and values of a in the nonextensive regime.
Page 1 /556775
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.