Iskanje po katalogu digitalne knjižnice

Opis: Proteinase from Carica papaya latex was tested on its thermal stability at atmospheric pressure and in supercritical carbon dioxide, near-critical propane and dimethyl-ether. In supercritical carbon dioxide at 300 bar thermalactivation of the examined proteinase was improved in the comparison toatmospheric pressure. In propane and dimethyl-ether (300 bar) activity of the examined proteinase decreased. Influence of compressionžexpansion cycles on residual activity of the same proteinase in supercritical carbon dioxide (300 bar and 50 °C) was studied, as well. Different ways of transition from supercritical to low-pressure-state were used which affected residual activityof the proteinase.Addition of water in the system increased activity of proteinase from C. papaya, which was incubated in supercritical carbon dioxide for 24 h. Optimum amount of water was found to be between 0.5 and 0.7 g/L.
Ključne besede: chemical processing, high pressure technology, supercritical CO2, proteinase, thermal stability, pressure stability, enzyme activity, water content, dense gases
Objavljeno v DKUM: 01.06.2012; Ogledov: 2015; Prenosov: 32
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Opis: This paper presents a novel approach to the determination of passive soil pressures: using the upper-bound method within the framework of limit analysistheory. It is based on a three-dimensional, kinematically admissible, rotational, hyperbolical failure mechanism. The failure mechanism is composed of the central and two lateral bodies, which are connected by a common velocity field. This approach is similar to two-dimensional stability analyses, where the log spiral potential failure surface is considered. The front surface of the central body interacts with the retaining wallč the uppersurface can be loaded by surcharge loadingč and the log spiral segment defines the curved failure surface of the central part. The cross sections of the lateral bodies are in agreement with the cross section of the central body. On the outer side, they are laterally bounded by a curved and kinematically admissible hyperbolic surface, which is defined by enveloping the hyperbolical half cones and part of the case surface of the leading half cone. The results give values for the passive soil pressure coefficients that are for most cases lower than the values determined by the upper-bound method of limit analysis for a translational failure mechanism, as published in the literature.
Ključne besede: geomechanics, soil-structure interaction, limit analysis, earth pressures, passive pressure, failure surface
Objavljeno v DKUM: 01.06.2012; Ogledov: 1923; Prenosov: 113
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Opis: Sugar fatty acid esters are nonionic surfactants, which are used for personal care products, cosmetic applications, and as emulsifiers for food. In recent years, enzymatic synthesis of sugar fatty acid esters is attracting keen attention as a new manufacturing method for future application. Reaction parameters of lipase-catalyzed synthesis of fructose fatty acid esters in organic solvent were optimized in a batch reactor at atmospheric pressure. Optimum conditions for reaction performed in organic solvent at atmospheric pressure were 10% (wžw of substrates) of lipase from Candida antarctica B, 12.14% (wžw of reaction mixture) of molecular sieves at 60 C, and stirring rate of 600 rpm. Esterification of fructose and palmitic acid was performed insupercritical carbon dioxide with and without addition of cosolvent (organicsolvent) at 60 C. Effect of pressure on enzyme activity was studied.
Ključne besede: chemical processing, high pressure technology, supercritical CO2, esterification, organic solvent, lipase catalysed synthesis, fructose fatty esters, Candida antarctica B, enzyme activity
Objavljeno v DKUM: 01.06.2012; Ogledov: 2400; Prenosov: 218
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Opis: The paper describes modelling approach to computational simulation of surface crack growth subjected to lubricated rolling-sliding contact conditions. The model considers the size and orientation of the initial crack, normal and tangential loading due to rolling-sliding contact and the influence of fluid trapped inside the crack by a hydraulic pressure mechanism. The motion of the contact sliding load is simulated with different load cases. The strain energy density (SED) and maximum tangential stress (MTS) crack propagation criteria are modified to account for the influence of internal pressure along the crack surfaces due to trapped fluid. The developed model is used to simulate surface crack growth on a gear tooth flank, which has been also experimentally tested. It is shown that the crack growth path, determined with modified crack propagation criteria, is more accurately predicted than by using the criteria in its classical form.
Ključne besede: fracture mechanics, numerical methods, contact loading, finite element analysis, internal pressure, maximum tangential stress, strain energy density, surface crack growth
Objavljeno v DKUM: 01.06.2012; Ogledov: 2689; Prenosov: 102
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Opis: Solid-liquid phase transitions of vanillin, ethylvanillin, o-vanillin and o-ethylvanillin in presence of compressed CO2 were determined with the modified capillary method. Furthermore, the solubilities of the above mentioned vanillins in supercritical CO2 were measured at 313.2, 333.2 and 353.2 K and in the pressure range 8-30 MPa using a static-analytic method. The experimental equilibrium solubility data have been fitted to the Peng-Robinson equation in combination with two parameter van der Waals mixing rules and binary parameters were determined from the best fit. Results showed that the phase equilibria of vanillins in dense CO2 are influenced by the position of the hydroxyl group bound to the aromatic ring. Under the pressure of CO2 the melting point depression and also the solubility of both o-vanillins was higher than those of p-vanillins. Oppositely, the alchoxy group (methoxy or ethoxy) showed no significant influence on the solubility of vanillins.
Ključne besede: chemical processing, high pressure technology, CO2, phase equilibria, vanillin isomers, data, ring substituents
Objavljeno v DKUM: 01.06.2012; Ogledov: 2270; Prenosov: 53
Povezava na celotno besedilo