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[en] Lunar materials and derivatives such as glass may possess very high tensile strengths compared to equivalent materials on earth because of the absence of hydrolytic weakening processes on the moon and in the hard vacuum of free space. Hydrolyzation of Si-O bonds at crack tips or dislocations reduces the strength of silicates by about an order of magnitude in earth environments. However, lunar materials are extremely anhydrous and hydrolytic weakening will be suppressed in free space. Thus, the geomechanical properties of the moon and engineering properties of lunar silicate materials in space environments will be very different than equivalent materials under earth conditions where the action of water cannot be conveniently avoided. Possible substitution of lunar glass for structural metals in a variety of space engineering applications enhances the economic utilization of the moon. 26 references, 3 figures, 2 tables
[en] This paper describes the implementation of a new approach to estimating the probability of damaging, in-vessel, steam explosions, which significantly reduces the problem of properly accounting for uncertainty in the physics. The program comprises separation of macrophysics from microphysics, greatly improved modelling of the macrophysics, probabilistic quantification of microphysical uncertainties, and the propagation of probability through the models by a modified L.H.S. method. The approach is suitable for a wide range of similar problems
[en] A cation-exchange method was used for determining the average cationic charge of polonium species present in hydrolytic equilibrium in solutions. This method is based on measurements of the distribution ratio of polonium at a constant internal hydrogen-ion concentration of the cation-exchanger phase. In 1.0 mol dm-3(H, Na)ClO4 and 1.0 mol dm-3 (H, Na)NO3 solutions at -log[H+] = 1.0, tracer concentrations of polonium(IV) were found to exist in the mean chemical forms of Po(OH)sub(3.43)sup(0.53+) and Po(OH)sub(2.83)(NO3)sub(0.60)sup(0.57+), respectively. The formation of cationic polymerized species was also estimated in region of 4 <= -log[H+] in a 1.0 mol dm-3 (H, Na)ClO4 solution. (author)
[en] The kinetic and chemical mechanisms of AChE-catalyzed hydrolysis of short-chain thiocholine esters are relatively well documented. Up to propanoylthiocholine (PrTCh) the chemical mechanism is general acid-base catalysis by the active site catalytic triad. The chemical mechanism for the enzyme-catalyzed butyrylthio-choline(BuTCh) hydrolysis shifts to a parallel mechanism in which general base catalysis by E199 of direct water attack to the carbonyl carbon of the substrate. (Selwood, T., et al. J. Am. Chem. Soc. 1993, 115, 10477-10482) The long chain thiocholine esters such as hexanoylthiocholine (HexTCh), heptanoylthiocholine (HepTCh), and octanoylthiocholine (OcTCh) are hydrolyzed by electric eel acetylcholinesterase (AChE). The kinetic parameters are determined to show that these compounds have a lower Michaelis constant than BuTCh and the pH-Rate profile showed that the mechanism is similar to that of BuTCh hydrolysis. The solvent isotope effect and proton inventory of AChE-catalyzed hydrolysis of HexTCh showed that one proton transfer is involved in the transition state of the acylation stage. The relationship between the dipole moment and the Michaelis constant of the long chain thiocholine esters showed that the dipole moment is the most important factor for the binding of a substrate to the enzyme active site
[en] Technological characteristics of some active dyes have been considered. Diffusion-sorption characteristics, reaction ability, fixation rate and hydrolysis of dyes have been studied. The kinetic curves of sorption of studied active dyes have been discussed. Kinetic curves of dependence of fixation rate of studied dyes have been studied.
[en] In this article the results of the investigation on the processes of adsorption, hydrolysis and consumption of COD (chemical oxygen demand) in both aerobic and anaerobic reactors to laboratory scale, their relationship with the conditions of illumination, half of support and concentration of oxygen, and their possible application in aerobic post-treatment of anaerobic leachates are presented. The investigation consists of an experimental assembly and a theoretical development of search of descriptor equations of the global process, and rates of occurrence of the particular processes. The experimental assembly was carried out with four reactors to laboratory scale subjected to different conditions of light, half of support and concentration of oxygen; it had two phases: one of evaluation of the effect of the different conditions in the efficiency of the reactors, and another of evaluation of the kinetic constants in the reactor of better acting and their application in aerobic treatment of anaerobic leachates
[en] The increasing use of biodegradable devices in tissue engineering and regenerative medicine means it is essential to study and understand their degradation behaviour. Accelerated degradation systems aim to achieve similar degradation profiles within a shorter period of time, compared with standard conditions. However, these conditions only partially mimic the actual situation, and subsequent analyses and derived mechanisms must be treated with caution and should always be supported by actual long-term degradation data obtained under physiological conditions. Our studies revealed that polycaprolactone (PCL) and PCL-composite scaffolds degrade very differently under these different degradation conditions, whilst still undergoing hydrolysis. Molecular weight and mass loss results differ due to the different degradation pathways followed (surface degradation pathway for accelerated conditions and bulk degradation pathway for simulated physiological conditions). Crystallinity studies revealed similar patterns of recrystallization dynamics, and mechanical data indicated that the scaffolds retained their functional stability, in both instances, over the course of degradation. Ultimately, polymer degradation was shown to be chiefly governed by molecular weight, crystallinity susceptibility to hydrolysis and device architecture considerations whilst maintaining its thermodynamic equilibrium
[en] Systematic trends of mononuclear and polynuclear hydrolysis constants of tetravalent actinide ions were analyzed by using an electrostatic hard sphere model. The effective charges of actinide ions were introduced into the model by considering possible contributions non-electrostatic interactions of actinide ions in addition to those of ordinary electrostatic ones. The systematic trends of hydrolysis constants were well fitted by the present model, and the parameter values such as the effective charges of actinide ions were determined. Some predictions were made and discussed in comparison with the solubility curves of tetravalent actinides. (author)
[en] Highlights: • MTSR vs process temperature profile may present S-shape in isothermal semibatch reactors. • Quantitative relationship between Xac,max and Damköhler number is first developed. • A theoretical criterion has be developed to determine the dependency of MTSR on T. • The criterion states that MTSR will increase with T increasing if the value of criterion is negative. - Abstract: Semibatch reactors (SBRs) are commonly used to conduct exothermic reaction in the pharmaceutical and fine chemical industries. From the thermal safety point of view, low MTSR (maximum temperature of synthesis reactions) is desirable. We have found that MTSR vs process temperature (T) profile favorably present S-shape in isothermal homogeneous SBRs involving highly exothermic or slow reactions. However, the criterion to determine the dependency of MTSR on T has been not thoroughly studied. In this work, such a theoretical criterion will be developed based on the fact that the derivative of MTSR to T is zero at the reaction temperature at which the lowest value of MTSR is obtained and experimentally validated by the hydrolysis reaction of acetic anhydride. To develop such a criterion, the quantitative relationship between the maximum accumulation Xac,max and Damköhler number (Da) for isothermal homogeneous semibatch reactions of arbitrary kinetic orders is first developed and numerically verified.