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Search Results: 1 - 10 of 449879 matches for " L. R. da Silva "
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Generating more realistic complex networks from power-law distribution of fitness
Mendes, G. A.;da Silva, L. R.;
Brazilian Journal of Physics , 2009, DOI: 10.1590/S0103-97332009000400013
Abstract: in this work we analyze the implications of using a power law distribution of vertice's quality in the growth dynamics of a network studied by bianconi and barabási. using this suggested distribution we show the degree distribution interpolates the barabási et al. model and bianconi et al. model. this modified model (with power law distribution) can help us understand the evolution of complex systems. additionally, we determine the exponent gamma related to the degree distribution, the time evolution of the average number of links,< ki >∝ (t/i)β (i coincindes with the input-time of the ith node), the average path length and the clustering coefficient.
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.
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.
A photometric and spectroscopic survey of solar twin stars within 50 parsecs of the Sun: I. Atmospheric parameters and color similarity to the Sun
G. F. Porto de Mello,R. da Silva,L. da Silva,R. V. de Nader
Physics , 2013, DOI: 10.1051/0004-6361/201322277
Abstract: Solar twins and analogs are fundamental in the characterization of the Sun's place in the context of stellar measurements, as they are in understanding how typical the solar properties are in its neighborhood. They are also important for representing sunlight observable in the night sky for diverse photometric and spectroscopic tasks, besides being natural candidates for harboring planetary systems similar to ours and possibly even life-bearing environments. We report a photometric and spectroscopic survey of solar twin stars within 50 pc of the Sun. Hipparcos absolute magnitudes and (B-V)_Tycho colors were used to define a 2 sigma box around the solar values, where 133 stars were considered. Additional stars resembling the solar UBV colors in a broad sense, plus stars present in the lists of Hardorp, were also selected. All objects were ranked by a color-similarity index with respect to the Sun, defined by uvby and BV photometry. Moderately high-resolution, high-S/N spectra were used for a subsample of equatorial-southern stars to derive Teff, log g, and [Fe/H] with average internal errors better than 50 K, 0.20 dex, and 0.08 dex, respectively. Ages and masses were estimated from theoretical HR diagrams. The color-similarity index proved very successful. We identify and rank new excellent solar analogs, which are fit to represent the Sun in the night sky. Some of them are faint enough to be of interest for moderately large telescopes. We also identify two stars with near-UV spectra indistinguishable from the Sun's. We present five new "probable" solar twin stars, besides five new "possible" twins. Masses and ages for the best solar twin candidates lie very close to the solar values, but chromospheric activity levels range somewhat. We propose that the solar twins be emphasized in the ongoing searches for extra-solar planets and SETI searches.
Effect of Ultrasound and Xylanase Treatment on the Physical-Mechanical Properties of Bleached Eucalyptus Kraft Pulp  [PDF]
Larisse A.R. Batalha, Juliana C. da Silva, Carolina M. Jardim, Rubens C. Oliveira, Jorge L. Colodette
Natural Resources (NR) , 2011, DOI: 10.4236/nr.2011.22017
Abstract: The modification on the fiber structure of bleached eucalyptus kraft pulp is a very attractive alternative for improve- ments in the properties of paper production. The enzymatic treatment by xylanases and ultrassonic treatments modify the characteristics of the fibers, has been reported. Therefore, the purpose of this study was to evaluate the influence of ultrasonic waves as a facilitator of the action of enzymes (hemicellulase) by modifying the physicochemical nature of fiber eucalyptus Kraft pulp, in order to improve the physical and mechanical properties of the paper. But it was observed the that idea of ultrasound acts as facilitator for action of enzymes can’t be affirmed, since in most properties XA-1 and XA-2 were equal statistically. It may be noted that the junction of ultrasound and xylanase provided improves on tensile index, specific elastic modulus and tensile energy absorption and a decrease of tear index on the mechanical properties of handsheet and it increased the opacity when the ultrasound was applied before xylanase.
D-aminoácidos em biologia: mais do que se julga
Silva, Jo?o J. R. Fraústo da;Silva, José Armando L. da;
Química Nova , 2009, DOI: 10.1590/S0100-40422009000200046
Abstract: it is still frequently referred, even in reference text-books, that the d-enantiomers of amino acids are not present in living organisms, which is not right. in the present revision/informative paper we describe a large number of d-amino acids that are present in all forms of organisms, from bacteria to human beings, in the free state, in peptides and in proteins, and give a short overview of their characteristics, physiological interaction and roles.
Lattices with variable and constant occupation density and q-exponential distribution
Cavalcante da Silva, P;Corso, G;da Silva, L.R;
Revista mexicana de física , 2008,
Abstract: in this paper we test the hypothesis that q-exponential distribution fits better on distributions arising from lattices with a heterogeneous topology than a homogeneous topology. we compare two lattices: the first is the typical square lattice with a constant occupation density p (the lattice used in standard percolation theory), and the second is a lattice constructed with a gradient of p. in the homogeneous lattice the occupied number of neighbors of each cell is the same (on average) for the full lattice, otherwise in the p-gradient lattice this number changes along the lattice. in this sense the p-gradient lattice shows a more complex topology than the homogeneous lattice. we fit the q-exponential and the stretched exponential distribution on the cluster size distribution that arises in the lattices. we observe that the q-exponential fits better on the p-gradient lattice than on a constant p lattice. on the other hand, the stretched exponential distribution fits equally well on both lattices.
Lattices with variable and constant occupation density and q-exponential distribution
P. Cavalcante da Silva,G. Corso,L.R. da Silva
Revista mexicana de física , 2008,
Abstract: En este trabajo se prueba la hipotesis de que la distribución q-exponencial se adapta mejor en distribuciones derivadas de redes con una topología heterogenea que en una topología homogenea. Se comparan dos redes: la primera es la típica red cuadrada con una densidad de ocupación constante p (la red estandar de la percolación), y la segunda es una red construida con un gradiente de ocupación p. En la red homogénea, el número de vecinos ocupados de cada celda es el mismo (en promedio), pero por otro lado, en la red con p-gradiente, este número sufre cambio a lo largo de la red. En este sentido, la p-gradiente red muestra una topología mas compleja que la red homegénea. Nos ajustamos la q-exponencial y la distribucion exponencial estirada sobre la distribución de clusters de las redes. Observamos que la q-exponencial encaja mejor en la red p-gradiente que en una red con p constante. Por otro lado, la distribución exponencial estirada encaja bien en ambas redes.
Evaluation of Milk Compositional Quality and Mammary Gland Health of Dairy Herds in the Southwestern Brazilian Amazon  [PDF]
Luciana G. Brito, José R. Vieira Júnior, Fábio da S. Barbieri, Rodrigo B. Rocha, Marivaldo R. Figueiró, Websten C. da Silva, Gilvania L. O. Carvalho, José de Arimatéia Silva, Guilherme N. Souza
Open Journal of Veterinary Medicine (OJVM) , 2016, DOI: 10.4236/ojvm.2016.69018
Abstract: Samples of raw milk from bulk cooling tanks were collected in five municipalities of the Southwestern Brazilian Amazon to establish the prevalence of Staphylococcus aueus and Streptococcus agalactiae, as well as to evaluate the milk composition and its correlation with the bulk tank somatic cell count (BTSCC). A total of 250 samples were collected to investigate the causal agents of bovine mastitis in whole milk, from 50 bulk milk tanks in each municipality. Under laboratory conditions, the samples were diluted to 1/10 and 1/100, and samples of 0.1 ml from each dilution were plated in triplicate on selective media for Staphylococcus aureus and Streptococcus agalactiae. To evaluate the correlation between the major milk components (fat, protein and lactose) and the BTSCC, samples were collected for 18 months from 73 dairy herds. The presence of the above-mentioned contagious mastitis pathogens was detected in 97.2% (243/250) of refrigerated raw milk samples evaluated. Analysis of the major milk components and BTSCC demonstrated that during the study period, fat compo-nent showed the largest variance, followed by protein and lactose, which also showed significant variances.
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