Extending the kinetic solution of the classic Michaelis-Menten model of enzyme action

The principal aim of studies of enzyme-mediated reactions has been to provide comparative and quantitative information on enzyme-catalyzed reactions under distinct conditions. The classic Michaelis-Menten model (Biochem Zeit 49:333, 1913) for enzyme kinetic has been widely used to determine important parameters involved in enzyme catalysis, particularly the Michaelis-Menten constant (K (M) ) and the maximum velocity of reaction (V (max) ). Subsequently, a detailed treatment of the mechanisms of enzyme catalysis was undertaken by Briggs-Haldane (Biochem J 19:338, 1925). These authors proposed the steady-state treatment, since its applicability was constrained to this condition. The present work describes an extending solution of the Michaelis-Menten model without the need for such a steady-state restriction. We provide the first analysis of all of the individual reaction constants calculated analytically. Using this approach, it is possible to accurately predict the results under new experimental conditions and to characterize and optimize industrial processes in the fields of chemical and food engineering, pharmaceuticals and biotechnology.

Solution Polymerization of N-vinylcaprolactam in 1,4-dioxane. Kinetic Dependence on Temperature, Monomer, and Initiator Concentrations

The kinetics of the solution free radical polymerization of N-vinylcaprolactam, in 1,4-dioxane and under various polymerization conditions was studied. Azobisisobutyronitrile and 3-mercaptopropionic acid were used as initiator and as chain transfer agent (CTA), respectively. The influence of monomer and initiator concentrations and polymerization temperature on the rate of polymerizations (R(p)) was investigated. In general, high conversions were obtained. The order with respect to initiator was consistent with the classical kinetic rate equation, while the order with respect to the monomer was greater than unity. The overall activation energy of 53.6 kJ mol(-1) was obtained in the temperature range 60-80 degrees C. The decreasing of the absolute molecular weights when increasing the CIA concentration was confirmed by GPC/SEC/LALS analyses. It was confirmed by UV-visible analyses the effect of molecular weights on the lower critical solution temperature of the polymers. It was also verified that the addition of the CTA influenced the kinetic of the polymerizations. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 118: 229-240, 2010

Adsorption of Cr(VI) from aqueous solution by hydrous zirconium oxide

A type of ZrO(2)center dot nH(2)O Was synthesized and its Cr(VI) removal potential was investigated in this study. The kinetic study, adsorption isotherm, pH effect, thermodynamic study and desorption were examined in batch experiments. The kinetic process was described by a pseudo-second-order rate model very well. The Cr(VI) adsorption tended to increase with a decrease of pH. The adsorption data fitted well to the Langmuir model. The adsorption capacity increased from 61 to 66 mg g(-1) when the temperature was increased from 298 to 338 K. The positive values of both Delta H degrees and Delta S degrees suggest an endothermic reaction and increase in randomness at the solid-liquid interface during the adsorption. Delta G degrees values obtained were negative indicating a spontaneous adsorption process. The effective desorption of Cr(VI) on ZrO(2)center dot nH(2)O could be achieved using distilled water at pH 12. (C) 2009 Elsevier B.V. All rights reserved.

Banana as Adjunct in Beer Production: Applicability and Performance of Fermentative Parameters

Traditionally, the raw materials for beer production are barley, hops, water, and yeast, but most brewers use also different adjuncts. During the alcoholic fermentation, the contribution of aroma compounds from other ingredients to the final beer flavor depends on the wort composition, on the yeast strain, and mainly on the process conditions. In this context, banana can also be a raw material favorable to alcoholic fermentation being rich in carbohydrates and minerals and providing low acidity. In this work, the objective was to evaluate the performance of wort adjusted with banana juice in different concentrations. For this, static fermentations were conducted at 15 degrees C at pilot scale (140 L of medium). The addition of banana that changed the concentration of all-malt wort from 10 degrees P to 12 and 15 degrees P were evaluated (degrees P is the weight of the extract or the sugar equivalent in 100 g solution, at 20 degrees C). The results showed an increase in ethanol production, with approximately 0.4 g/g ethanol yield and 0.6 g/L h volumetric productivity after 84 h of processing when concentrated wort was used. Thus, it was concluded that banana can be used as an adjunct in brewing methods, helping in the development of new products as well as in obtaining concentrated worts.

Selection of new glass-forming compositions in Al-La system using a combination of topological instability and thermodynamic criteria

A combination of an extension of the topological instability ""lambda criterion"" and a thermodynamic criterion were applied to the Al-La system, indicating the best range of compositions for glass formation. Alloy compositions in this range were prepared by melt-spinning and casting in an arc-melting furnace with a wedge-section copper mold. The GFA of these samples was evaluated by X-ray diffraction, differential scanning calorimetry and scanning electron microscopy. The results indicated that the gamma* parameter of compositions with high GFA is higher, corresponding to a range in which the lambda parameter is greater than 0.1, which are compositions far from Al solid solution. A new alloy was identified with the best GFA reported so far for this system, showing a maximum thickness of 286 mu m in a wedge-section copper mold. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.

Corrosion behavior of Ti-xNb-13Zr alloys in Ringer`s solution

Ti-6Al-4V alloy has been widely used in restorative surgery due to its high corrosion resistance and biocompatibility. Nevertheless, some studies showed that V and Al release in the organism might induce cytotoxic effects and neurological disorders, which led to the development of V-free alloys and both V- and Al-free alloys containing Nb, Zr, Ta, or Mo. Among these alloys, Ti-13Nb-13Zr alloy is promising due to its better biomechanical compatibility than Ti-6Al-4V. In this work, the corrosion behavior of Ti, Ti-6Al-4V, and Ti-xNb-13Zr alloys (x=5, 13, and 20) was evaluated in Ringer`s solution (pH 7.5) at 37 degrees C through open-circuit potential measurements, potentiodynamic polarization, and electrochemical impedance spectroscopy. Spontaneous passivity was observed for all materials in this medium. Low corrosion current densities (in the order of 10(-7) A/cm(2)) and high impedance values (in the order of 10(5) Omega cm(2) at low frequencies) indicated their high corrosion resistance. EIS results showed that the passivating films were constituted of an outer porous layer (very low resistance) and an inner compact layer (high resistance), the latter providing the corrosion resistance of the materials. There was evidence that the Ti-xNb-13Zr alloys were more corrosion resistant than both Ti and Ti-6Al-4V in Ringer`s solution.

Noise reduction in biomedical speech signal processing based on time and frequency Kalman filtering combined with spectral subtraction

The goal of this paper is to study and propose a new technique for noise reduction used during the reconstruction of speech signals, particularly for biomedical applications. The proposed method is based on Kalman filtering in the time domain combined with spectral subtraction. Comparison with discrete Kalman filter in the frequency domain shows better performance of the proposed technique. The performance is evaluated by using the segmental signal-to-noise ratio and the Itakura-Saito`s distance. Results have shown that Kalman`s filter in time combined with spectral subtraction is more robust and efficient, improving the Itakura-Saito`s distance by up to four times. (C) 2007 Elsevier Ltd. All rights reserved.

Experimental Analysis of Structural Change and Rheological Behavior of Macromolecular Solutions with Guar and Xanthan Gums in Crossflow Microfiltration Processing

The present paper reports on the structural change and rheological behavior of mixtures of macromolecular suspensions (guar and xanthan gums) in crossflow microfiltration processing. Mixtures in suspension of guar and xanthan gums at low concentrations (1,000 ppm) and different proportions were processed by microfiltration with membrane of nominal pore size of 0.4 mu m. The rheological behavior of the mixtures was investigated in rotational viscometers at two different temperatures, 25 and 40 C, at the beginning and at the end of each experiment. The shear stress (t) in function of the shear rate (gamma) was fitted and analyzed with the power-law model. All the mixtures showed flow behavior index values (n) lower than 1, characterizing non-Newtonian fluids (pseudoplastic). The samples of both mixtures and permeates were also analyzed by absorbency spectroscopy in infrared radiation. The absorbency analysis showed that there is good synergism between xanthan and guar gums without structure modifications or gel formation in the concentration process by microfiltration.

Chaos-Galerkin solution of stochastic Timoshenko bending problems

This paper presents an accurate and efficient solution for the random transverse and angular displacement fields of uncertain Timoshenko beams. Approximate, numerical solutions are obtained using the Galerkin method and chaos polynomials. The Chaos-Galerkin scheme is constructed by respecting the theoretical conditions for existence and uniqueness of the solution. Numerical results show fast convergence to the exact solution, at excellent accuracies. The developed Chaos-Galerkin scheme accurately approximates the complete cumulative distribution function of the displacement responses. The Chaos-Galerkin scheme developed herein is a theoretically sound and efficient method for the solution of stochastic problems in engineering. (C) 2011 Elsevier Ltd. All rights reserved.

Galerkin Solution of Stochastic Beam Bending on Winkler Foundations

In this paper, the Askey-Wiener scheme and the Galerkin method are used to obtain approximate solutions to stochastic beam bending on Winkler foundation. The study addresses Euler-Bernoulli beams with uncertainty in the bending stiffness modulus and in the stiffness of the foundation. Uncertainties are represented by parameterized stochastic processes. The random behavior of beam response is modeled using the Askey-Wiener scheme. One contribution of the paper is a sketch of proof of existence and uniqueness of the solution to problems involving fourth order operators applied to random fields. From the approximate Galerkin solution, expected value and variance of beam displacement responses are derived, and compared with corresponding estimates obtained via Monte Carlo simulation. Results show very fast convergence and excellent accuracies in comparison to Monte Carlo simulation. The Askey-Wiener Galerkin scheme presented herein is shown to be a theoretically solid and numerically efficient method for the solution of stochastic problems in engineering.

Sorption aspects for unconsolidated materials of the Sao Carlos region (SP), Brazil

The transport of liquid and gaseous pollutants through porous geological media depends on the physical and chemical characteristics of the unconsolidated material, rocks and water associated with the characteristics of the pollutants. Of these characteristics, the sorption aspect is of fundamental importance and is a function of the mineral proportions, pH, Eh and void aspects encountered in the porous media. In the Sao Carlos region, located in the eastern-central part of the 9 ate of Sao Paulo, Brazil, there are basically two types of unconsolidated materials: the first is a residual from sandstones cemented with fines and the secondarily composed of claystones, siltstones and conglomerates from the Cretaceous Period that constitute the Itaqueri Formation; the second is a sandy sediment of the Tertiary Period. These geological conditions are found in areas where chemical products are disposed of characterized as either diffuse or point pollutions sources. Because of this situation, a study was developed to evaluate the sorption aspects of some inorganic cations that are frequently found in these sources, in varied concentrations. Taken into consideration were their physical/chemical properties, such as: specific weight, grain size, mineralogy, cationic exchange capacity, pH, hydraulic conductivity. Batch tests were run using solutions of KCl, ZnCl(2) and CuCl center dot H(2)O at three different pH values, and then with a combined solution (KCl + ZnCl(2) + CuCl center dot H(2)O), also at three different pH values.

Solution of a heterogeneous modeling of a horizontal-flow anaerobic immobilized biomass (HAIB) reactor by the sequencing method

A modeling study was completed to develop a methodology that combines the sequencing and finite difference methods for the simulation of a heterogeneous model of a tubular reactor applied in the treatment of wastewater. The system included a liquid phase (convection diffusion transport) and a solid phase (diffusion reaction) that was obtained by completing a mass balance in the reactor and in the particle, respectively. The model was solved using a pilot-scale horizontal-flow anaerobic immobilized biomass (HAIB) reactor to treat domestic sewage, with the concentration results compared with the experimental data. A comparison of the behavior of the liquid phase concentration profile and the experimental results indicated that both the numerical methods offer a good description of the behavior of the concentration along the reactor. The advantage of the sequencing method over the finite difference method is that it is easier to apply and requires less computational time to model the dynamic simulation of outlet response of HAIB.

Thermoplastic starch modified during melt processing with organic acids: The effect of molar mass on thermal and mechanical properties

Thermoplastic starch (TPS) was modified with ascorbic acid and citric acid by melt processing of native starch with glycerol as plasticizer in an intensive batch mixer at 160 degrees C. It was found that the molar mass decreases with acid content and processing time causing the reduction in melting temperature (T(m)). As observed by the results of X-ray diffraction and DSC measurements, crystallinity was not changed by the reaction with organic acids. T(m) depression with falling molar mass was interpreted on the basis of the effect of concentration of end-chain units, which act as diluents. FTIR did not show any appreciable change in starch chemical compositions, leading to the conclusion that the main changes observed were produced by the variation in molar mass of the material. We demonstrated that it is possible to decrease melt viscosity without the need for more plasticizer thus avoiding side-effects such as an increase in water affinity or relevant changes in the dynamic mechanical properties. (C) 2010 Elsevier B.V. All rights reserved.

Quality of martensitic stainless steel type AISI-420 utilized in the manufacture surgical implements

Until now the martensitic stainless steel type AISI-420 is widely used in the manufacture of surgical implements. These implements present premature corrosion problems identified after cleaning, sterilization and cutting edge loss and/or rupture during the surgical processes.. This study evaluates the steel as to the chemical composition, hardness, microstructure and pitting corrosion resistance in a solution of enzyme detergent diluted in water by anodic cyclic polarization. This mixture is used in the cleaning of surgical implements that are submerged in this solution for 2 h before cleaning and sterilization. The results show steels with martensite microstructures in the ferrite phase, together with impurities. These presented low pitting potential values in compariston to steels with a fully martensitic microstructure.

Compatible Ternary Blends of Chitosan/poly(vinyl alcohol)/poly(lactic acid) Produced by Oil-in-Water Emulsion Processing

Ternary compatible blends of chitosan, poly(vinyl alcohol), and poly(lactic acid) were prepared by an oil-in-water (O/W) emulsion process. Solutions of chitosan in aqueous acetic acid, poly(vinyl alcohol) (PVA) in water, and poly(lactic acid) (PLA) in chloroform were blended with a high shear mixer. PVA was used as an emulsifier to stabilize the emulsion and to reduce the interfacial tension between the solid polymers in the blends-produced. It proved to work very well because the emulsions were stable for periods of days or weeks and compatible blends were obtained When PVA was added. This effect was attributed to a synergistic effect of PVA and chitosan because the binary blends PVA/PLA and chitosan/PLA were completely incompatible; The blends were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermal mechanical analysis (TMA), stress strain tests, and Fourier transform infrared spectroscopy (FTIR). The results indicated that despite the fact that the system contained distinct phases some degree of molecular miscibility occurred when the three components were present in the blend.