Roberto da Silva

Faculdade de Medicina de São José do Rio Preto, Rio Preto, São Paulo, Brazil

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Publications (122)119.7 Total impact

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    ABSTRACT: This paper refers to the new proposal of pre-treatment of sugarcane bagasse with microwave associated to glycerol, seeking greater release of fermentable sugars during enzymatic hydrolysis. The residue was subjected to microwave irradiation for 5 min with distilled water, phosphoric acid (pH 3.0) and glycerol (100%) before being enzymatically hydrolyzed using cellulase enzyme extract Myceliophthora thermophila M.7.7. and the commercial enzyme cocktail Celluclast 1.5 L. A variety of analyses including measurement of BET surface analysis, MET, TGA, DTG, DSC, ATR-FTIR and PAD-HPLC were used to facilitate the understanding of the physical and chemical characteristics of the solid fraction resulting from pre-treatment. Infrared spectra of untreated and treated bagasse in microwave irradiation and glycerol showed significant differences in the regions 1635, 1600 and 1510 related vibration of the aromatic ring, and the band at 1100 cm−1 is attributed to an overlap of C–O–H elongation of primary and secondary alcohols and at 980 cm−1 to stretching of glycosidic linkages C–O–C. The thermal analysis showed that the bagasse treated in a microwave irradiation and glycerol has higher thermal stability compared to the untreated bagasse. The experimental results indicated that 5.4 and 11.3% w/w of lignin and xylan fractions, respectively, are degraded after pretreatment of bagasse in microwave heating with glycerol. The highest yields of hydrolysis of hemicellulose (22.4%) and cellulose (40.2%) w/w were obtained in the reaction mixture containing the enzyme and Celluclast commercial cane bagasse treated in a microwave irradiation and glycerol after 24 h of incubation. The association of microwave and glycerol is a new alternative to deconstruction of lignocellulose structure.
    Applied Energy. 01/2014; 122:189–195.
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    Roberto da Silva, Silvio R. Dahmen
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    ABSTRACT: Is football (soccer) a universal sport? Beyond the question of geographical distribution, where the answer is most certainly yes, when looked at from a mathematical viewpoint the scoring process during a match can be thought of, in a first approximation, as being modeled by a Poisson distribution. Recently, it was shown that the scoring of real tournaments can be reproduced by means of an agent-based model (da Silva et al. (2013) [24]) based on two simple hypotheses: (i) the ability of a team to win a match is given by the rate of a Poisson distribution that governs its scoring during a match; and (ii) such ability evolves over time according to results of previous matches. In this article we are interested in the question of whether the time series represented by the scores of teams have universal properties. For this purpose we define a distance between two teams as the square root of the sum of squares of the score differences between teams over all rounds in a double-round-robin-system and study how this distance evolves over time. Our results suggest a universal distance distribution of tournaments of different major leagues which is better characterized by an exponentially modified Gaussian (EMG). This result is corroborated by our agent-based model.
    Physica A: Statistical Mechanics and its Applications. 01/2014; 398:56–64.
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    ABSTRACT: An iterated version of ultimatum game, based on generalized probabilistic strategies, which are mathematically modeled by accepting proposal functions is presented. These strategies account for the behavior of the players by mixing levels of altruism and greed. We obtained analytically the moments of the payoff of the players under such a generalization. Our analysis is divided into two cases: (i) no memory players, where players do not remember previous decisions, and (ii) one-step memory players, where the offers depend on players’ last decision. We start considering the former case. We show that when the combination of the proposer’s altruism and responder’s greed levels balances the proposer’s greedy and responder’s altruism levels, the average and variance of the payoff of both players are the same. Our analysis is carried out considering that the acceptance of an offer depends on: (a) a fixed probability pp or (b) the value offered. The combination of cases (i) and (a) shows that there exists a pp value that maximizes the cumulative gain after nn iterations. Moreover, we show n×pn×p diagrams with ïso-average” and ïso-variance” of the cumulative payoff. Our analytical results are validated by Monte Carlo simulations. For the latter case, we show that when players have no memory (i), there are cutoff values, which the variance of the proposer’s cumulative payoff presents local maximum and minimum values, while for the responder, the same amount presents a global maximum. Case (b) combined with one-step memory players (ii), we verified, via MC simulations that, for the same number of iterations, the responder obtains different cumulative payoffs by setting different cutoff values. This result composes an interesting pattern of stripes in the cutoff per nn diagrams. Simultaneously, looking at variance of this amount, for the responder player in a similar diagram, we observe regions of iso-variance in non trivial patterns which depend on initial value of the proposal. Our contributions detailed by analytical and MC simulations are useful to design new experiments in the ultimatum game in stochastic scenarios.
    Physica A: Statistical Mechanics and its Applications 01/2014; 412:54–65. · 1.68 Impact Factor
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    ABSTRACT: Lipases have important applications in biotechnological processes, motivating us to produce, purify, immobilize and perform a biochemical characterization of the lipase from Rhizomucor pusillus. The fungus was cultivated by solid state fermentation producing lipolytic activity of about 0.5 U/mL(4U/g). A partial purification by gel filtration chromatography in Sephacryl S-100 allowed obtaining a yield of about 85% and a purification factor of 5.7. Our results revealed that the purified enzyme is very stable with some significant differences in its properties when compared to crude extract. The crude enzyme extract has an optimum pH and temperature of 7.5˚C and 40˚C, respectively. After purification, a shift of the optimum pH from 7 to 8 was observed, as well as a rise in optimum- temperature to 60˚C and an increase in stability. The enzyme was immobilized on CNBr-Agarose and Octyl-Agarose supports, having the highest immobilization yield of 94% in the second resin. The major advantage of immobilization in hydrophobic media such as Octyl is in its hyper activation, which in this case was over 200%, a very interesting finding. Another advantage of this type of immobilization is the possibility of using the derivatives in biotechnological appli- cations, such as in oil enriched with omega-3 as the results obtained in this study display the hy- drolysis of 40% EPA and 7% DHA from sardine oil, promising results compared to the literature.
    Advances in Enzyme Research. 12/2013; 4(1):79-90.
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    ABSTRACT: We have investigated the time-dependent regime of a two-dimensional metamagnetic model at its tricritical point via Monte Carlo simulations. First, we obtained the temperature and magnetic field corresponding to the tricritical point of the model by using a refinement process based on optimization of the coefficient of determination in the log-log fit of magnetization decay as a function of time. With these estimates in hand, we obtained the dynamic tricritical exponents θ and z and the static tricritical exponents ν and β by using the universal power-law scaling relations for the staggered magnetization and its moments at an early stage of the dynamic evolution. Our results at the tricritical point confirm that this model belongs to the two-dimensional Blume-Capel model universality class for both static and dynamic behaviors, and they also corroborate the conjecture of Janssen and Oerding for the dynamics of tricritical points.
    Computer Physics Communications 11/2013; 184(11):2371-2377. · 2.41 Impact Factor
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    ABSTRACT: Statistics of soccer tournament scores based on the double round robin system of several countries are studied. Exploring the dynamics of team scoring during tournament seasons from recent years we find evidences of superdiffusion. A mean-field analysis results in a drift velocity equal to that of real data but in a different diffusion coefficient. Along with the analysis of real data we present the results of simulations of soccer tournaments obtained by an agent-based model which successfully describes the final scoring distribution [da Silva et al., Comput. Phys. Commun. 184, 661 (2013)]. Such model yields random walks of scores over time with the same anomalous diffusion as observed in real data.
    Physical Review E 08/2013; 88(2):022136. · 2.31 Impact Factor
  • Current Opinion in Biotechnology 07/2013; 24, Supplement 1:S139. · 7.86 Impact Factor
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    ABSTRACT: Several mushroom species have been pointed out as sources of antioxidant compounds, in addition to their important nutritional value. Agaricus blazei and Lentinus edodes are among the most studied species all over the world, but those studies focused on their fruiting bodies instead of other presentations, such as powdered preparations, used as supplements. In the present work the chemical composition (nutrients and bioactive compounds) and antioxidant activity (free radical scavenging activity, reducing power and lipid peroxidation inhibition) of dried powder formulations of the mentioned mushroom species (APF and LPF, respectively) were evaluated. Powder formulations of both species revealed the presence of essential nutrients, such as proteins, carbohydrates and unsaturated fatty acids. Furthermore, they present a low fat content (<2g/100g) and can be used in low-calorie diets, just like the mushrooms fruiting bodies. APF showed higher antioxidant activity and higher content of tocopherols and phenolic compounds (124 and 770μg/100g, respectively) than LPF (32 and 690μg/100g). Both formulations could be used as antioxidant sources to prevent diseases related to oxidative stress.
    Food Chemistry 06/2013; 138(4):2168-73. · 3.33 Impact Factor
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    ABSTRACT: Polygalacturonases are enzymes involved in the degradation of pectic substances, being extensively used in food industries, textile processing, degumming of plant rough fibres, and treatment of pectic wastewaters. Polygalacturonase (PG) production by thermophilic fungus Thermoascus aurantiacus on solid-state fermentation was carried out in culture media containing sugar cane bagasse and orange bagasse in proportions of 30% and 70% (w/w) at 45°C for 4 days. PG obtained was purified by gel filtration and ion-exchange chromatography. The highest activity was found between pH 4.5 and 5.5, and the enzyme preserved more than 80% of its activity at pH values between 5.0 and 6.5. At pH values between 3.0 and 4.5, PG retained about 73% of the original activity, whereas at pH 10.0 it remained around 44%. The optimum temperature was 60-65°C. The enzyme was completely stable when incubated for 1 hour at 50°C. At 55°C and 60°C, the activity decreased 55% and 90%, respectively. The apparent molecular weight was 29.3 kDa, K m of 1.58 mg/mL and V max of 1553.1 μ mol/min/mg. The presence of Zn(+2), Mn(+2), and Hg(+2) inhibited 59%, 77%, and 100% of enzyme activity, respectively. The hydrolysis product suggests that polygalacturonase was shown to be an endo/exoenzyme.
    Enzyme research. 01/2013; 2013:438645.
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    ABSTRACT: In this work, we study the critical behavior of second-order points, specifically the Lifshitz point (LP) of a three-dimensional Ising model with axial competing interactions [the axial-next-nearest-neighbor Ising (ANNNI) model], using time-dependent Monte Carlo simulations. We use a recently developed technique that helps us localize the critical temperature corresponding to the best power law for magnetization decay over time: 〈M〉_{m_{0}=1}∼t^{-β/νz}, which is expected of simulations starting from initially ordered states. We obtain original results for the dynamic critical exponent z, evaluated from the behavior of the ratio F_{2}(t)=〈M^{2}〉_{m_{0}=0}/〈M〉_{m_{0}=1}^{2}∼t^{3/z}, along the critical line up to the LP. We explore all the critical exponents of the LP in detail, including the dynamic critical exponent θ that characterizes the initial slip of magnetization and the global persistence exponent θ_{g} associated with the probability P(t) that magnetization keeps its signal up to time t. Our estimates for the dynamic critical exponents at the Lifshitz point are z=2.34(2) and θ_{g}=0.336(4), values that are very different from those of the three-dimensional Ising model (the ANNNI model without the next-nearest-neighbor interactions at the z axis, i.e., J_{2}=0), i.e., z≈2.07 and θ_{g}≈0.38. We also present estimates for the static critical exponents β and ν, obtained from extended time-dependent scaling relations. Our results for static exponents are in good agreement with previous works.
    Physical Review E 01/2013; 87(1-1):012131. · 2.31 Impact Factor
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    ABSTRACT: We propose a novel algorithm that outputs the final standings of a soccer league, based on a simple dynamics that mimics a soccer tournament. In our model, a team is created with a defined potential(ability) which is updated during the tournament according to the results of previous games. The updated potential modifies a teams' future winning/losing probabilities. We show that this evolutionary game is able to reproduce the statistical properties of final standings of actual editions of the Brazilian tournament (Brasileir\~{a}o). However, other leagues such as the Italian and the Spanish tournaments have notoriously non-Gaussian traces and cannot be straightforwardly reproduced by this evolutionary non-Markovian model. A complete understanding of these phenomena deserves much more attention, but we suggest a simple explanation based on data collected in Brazil: Here several teams were crowned champion in previous editions corroborating that the champion typically emerges from random fluctuations that partly preserves the gaussian traces during the tournament. On the other hand, in the Italian and Spanish leagues only a few teams in recent history have won their league tournaments. These leagues are based on more robust and hierarchical structures established even before the beginning of the tournament. For the sake of completeness, we also elaborate a totally Gaussian model (which equalizes the winning, drawing, and losing probabilities) and we show that the scores of the "Brasileir\~{a}o" cannot be reproduced. Such aspects stress that evolutionary aspects are not superfluous in our modeling. Finally, we analyse the distortions of our model in situations where a large number of teams is considered, showing the existence of a transition from a single to a double peaked histogram of the final classification scores. An interesting scaling is presented for different sized tournaments.
    Computer Physics Communications 07/2012; 184(3). · 2.41 Impact Factor
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    ABSTRACT: Twenty-seven thermophilic and thermotolerant fungal strains were isolated from soil, decaying organic matter and sugarcane piles based on their ability to grow at 45°C on medium containing corn straw and cardboard as carbon sources. These fungi were identified in the genera Aspergillus, Thermomyces, Myceliophthora, Thermomucor and Candida. The majority of the isolated strains produced xylanase and cellulases under solid state fermentation (SSF). The highest cellulase and xylanase productions were obtained by the cultivation of the strains identified as Aspergillus fumigatus M.7.1 and Myceliophthora thermophila M.7.7. The enzymes from these strains exhibited maximum activity at pH 5.0 and at 60 and 70ºC. The endo-glucanase from A. fumigatus was stable from 40°C to 65°C and both endo-glucanase and xylanase from M. thermophila were stable in this temperature range when in absence of substrate. The enzymes were stable from pH 4.0 to 9.0.
    Brazilian Journal of Microbiology 07/2012; 43(3):1062-71. · 0.76 Impact Factor
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    ABSTRACT: The extension of Boltzmann-Gibbs thermostatistics, proposed by Tsallis, introduces an additional parameter $q$ to the inverse temperature $\beta$. Here, we show that a previously introduced generalized Metropolis dynamics to evolve spin models is not local and does not obey the detailed energy balance. In this dynamics, locality is only retrieved for $q=1$, which corresponds to the standard Metropolis algorithm. Non-locality implies in very time consuming computer calculations, since the energy of the whole system must be reevaluated, when a single spin is flipped. To circumvent this costly calculation, we propose a generalized master equation, which gives rise to a local generalized Metropolis dynamics that obeys the detailed energy balance. To compare the different critical values obtained with other generalized dynamics, we perform Monte Carlo simulations in equilibrium for Ising model. By using the short time non-equilibrium numerical simulations, we also calculate for this model: the critical temperature, the static and dynamical critical exponents as function of $q$. Even for $q\neq 1$, we show that suitable time evolving power laws can be found for each initial condition. Our numerical experiments corroborate the literature results, when we use non-local dynamics, showing that short time parameter determination works also in this case. However, the dynamics governed by the new master equation leads to different results for critical temperatures and also the critical exponents affecting universality classes. We further propose a simple algorithm to optimize modeling the time evolution with a power law considering in a log-log plot two successive refinements.
    Physical Review E 06/2012; 85(6):066707. · 2.31 Impact Factor
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    ABSTRACT: Prato cheeses were manufactured using coagulant from Thermomucor indicae-seudaticae N31 or a commercial coagulant. Cheeses were characterised using the following analysis: yield; fat; acidity; moisture; ash; salt; pH; total nitrogen; total protein; NS-pH 4.6/NT*100; NS-TCA 12%/NT*100; casein electrophoresis; and RP-HPLC. The results were statistically analysed and revealed that the proteolytic indices were not significantly different throughout the 60 days of ripening of cheeses made with either coagulant. Even though there were some quantitative differences in the peptide profile of cheeses, the enzyme from T. indicae-seudaticae N31 was used in the production of good quality Prato cheese without having to change the established technological parameters of the process.
    Food Chemistry. 02/2012; 130(4):859–865.
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    ABSTRACT: We propose a foundational model to explain properties of the retention time distribution of particle transport in a random medium. These particles are captured and released by distributed theoretical plates in a random medium as in standard chromatography. Our approach differs from current models, since it is not based on simple random walks, but on a directed and coordinated movement of the particles whose retention time dispersion in the column is due to the imprisonment time of the particle spent in the theoretical plates. Given a pair of fundamental parameters (lambdac,lambdae) the capture and release probabilities, we use simple combinatorial methods to predict the Probability Distribution of the retention times. We have analyzed several distributions typically used in chromatographic peak fits. We show that a log-normal distribution with only two parameters describes with high accuracy chromatographic distributions typically used in experiments. This distribution show a better fit than distributions with a larger number of parameters, possibly allowing for better control of experimental data. Combinatorial methods are used to explain particle residence time in random media. Strong correspondence with traditional stochastic methods which are employed in chromatography. Discrete regime is better described by more complex variations of the negative binomial distributions. On the other hand, continuous approximation is best fitted by a log-normal distribution.
    Physica A: Statistical Mechanics and its Applications 01/2012; 391:1-7. · 1.68 Impact Factor
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    ABSTRACT: Many discussions have enlarged the literature in Bibliometrics since the Hirsh proposal, the so called $h$-index. Ranking papers according to their citations, this index quantifies a researcher only by its greatest possible number of papers that are cited at least $h$ times. A closed formula for $h$-index distribution that can be applied for distinct databases is not yet known. In fact, to obtain such distribution, the knowledge of citation distribution of the authors and its specificities are required. Instead of dealing with researchers randomly chosen, here we address different groups based on distinct databases. The first group is composed by physicists and biologists, with data extracted from Institute of Scientific Information (ISI). The second group composed by computer scientists, which data were extracted from Google-Scholar system. In this paper, we obtain a general formula for the $h$-index probability density function (pdf) for groups of authors by using generalized exponentials in the context of escort probability. Our analysis includes the use of several statistical methods to estimate the necessary parameters. Also an exhaustive comparison among the possible candidate distributions are used to describe the way the citations are distributed among authors. The $h$-index pdf should be used to classify groups of researchers from a quantitative point of view, which is meaningfully interesting to eliminate obscure qualitative methods.
    Physica A: Statistical Mechanics and its Applications 11/2011; · 1.68 Impact Factor
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    ABSTRACT: The seedless grapes BRS Clara and BRS Morena, developed in Brazil, are currently growing in popularity due to their premium texture and taste. However, there are no reports on the polyphenoloxidase (PPO) from these cultivars. In this paper, active and latent PPO from BRS Clara and BRS Morena seedless grapes were extracted using the non-ionic detergents Triton-X-100 (active) and Triton-X-114 (latent), and their catecholase activities were characterized. The PPO extracted using Triton-X-110 exhibited maximum activities at pH 6.0 and at 25 °C. Above 30 °C, a gradual decline in activities was noted, with complete inactivation at 60 °C. The PPO from grapes extracted with Triton-X-114 was activated with 0.2% of the ionic detergent sodium dodecyl sulfate (SDS), and exhibited maximum activities at pH 5.5 and at 30 °C. It was stable until the temperature reached 60 °C.
    Plant Physiology and Biochemistry 11/2011; 49(11):1251-8. · 2.78 Impact Factor
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    ABSTRACT: This work is an exploratory study of the possibility of promoting the consumption of Syzygium cumini fruit by adding its extract to orange juice making good use of its functional (antioxidant) properties. S. cumini fruit extract was characterized in terms of its anthocyanin content (2.11 g/100 g expressed in cyanidine-3-glucoside equivalents), total phenolic compounds (360 mg/100 g expressed in gallic acid equivalents) and antioxidant capacity evaluated by the 2,2-diphenyl-1-picrylhydrazyl free radical scavenging method. The effects of the addition of S. cumini fruit crude extract as well as its chromatographic fractions on the juice were assessed chemically by headspace solid-phase micro-extraction and gas chromatography coupled with a mass spectrometry detector. Only six compounds had their chromatographic peak intensities clearly changed and the results are discussed in terms of the inhibition of the formation of 2-octanone, hexanol, α-copaene, and α-panasinsene and the conservation of octyl acetate and p-menth-1-en-9-ol. Sensory evaluation of orange juice with and without S. cumini crude extract addition did not show any significant differences in the sensorial profile, discriminative and acceptance tests.
    International Journal of Food Sciences and Nutrition 10/2011; 63(3):273-7. · 1.26 Impact Factor
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    ABSTRACT: In Brazil, several little economically explored fruits have good potential as raw material for the agro-industry. This study aimed to produce and determine the physical-chemical and sensory characteristics of light jambolan jelly. This fruit has intense purple color, which gave the jellies - both standard and light - a quite attractive visual aspect. The light jellies exhibited similar physical-chemical characteristics to the ones developed through the conventional method and; with the proportion of sweeteners used, the caloric values of the formulations were reduced to the range of 41 to 53%, attending the requirements of the Brazilian legislation for this type of product. The sensory profile obtained for the 4 light formulations developed, clearly showed the tasters' preference for the jelly elaborated with the association of cyclamate and saccharin. Thus, the results revealed good perspectives for the application of this fruit in the food industry.
    Ciência e Tecnologia de Alimentos 09/2011; 31(3):666-673. · 0.33 Impact Factor
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    08/2011; , ISBN: 978-953-307-447-4

Publication Stats

491 Citations
119.70 Total Impact Points


  • 2006–2014
    • Faculdade de Medicina de São José do Rio Preto
      Rio Preto, São Paulo, Brazil
  • 2004–2014
    • Universidade Federal do Rio Grande do Sul
      • • Institute of Physics
      • • Instituto de Informática
      Pôrto de São Francisco dos Casaes, Rio Grande do Sul, Brazil
  • 2013
    • Universidade Estadual de Minas Gerais (UEMG)
      Fructal, Minas Gerais, Brazil
  • 1998–2013
    • São Paulo State University
      • Instituto de Biociências, Letras e Ciências Exatas
      San Paulo, São Paulo, Brazil
  • 2005
    • Instituto de Botânica
      San Paulo, São Paulo, Brazil
  • 2002–2004
    • University of São Paulo
      • Departamento de Física Matemática (FMA) (São Paulo)
      São Paulo, Estado de Sao Paulo, Brazil