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Poly(acrylonitrile-methylmethacrylate-sodium vinylsulfonate) membranes were subjected to seven different chemical modifications and the amount of the newly formed groups was measured for each membrane. Urease was then covalently immobilized onto the modified membranes and the amount of bound protein was determined. The kinetic parameters V(max) and K(m) of the immobilized urease were studied under static and dynamic conditions. Results showed that the rate of the enzyme reaction was higher for the membranes modified with NH(2)OH . H(2)SO(4), NH(2)NH(2) . H(2)SO(4), NaOH + EDA and NaOH + GA + EDA. It was confirmed that the reaction rate, measured under dynamic conditions, was higher than that one determined under static conditions. The influence of Cu(II) ions, as inhibitors, on the enzyme reaction kinetics (V(i) and K(i)) was also investigated. It turned out that the most sensitive membranes towards Cu(II) were those modified with NH(2)NH(2) . H(2)SO(4), NaOH + EDA and H(2)O(2). The results initiated further investigations on the influence of other heavy metal ions (Cd(II), Zn(II), Ni(II) and Pb(II)) over urease bound to a NH(2)OH . H(2)SO(4)-modified membrane. It was found that the inhibition effect of the heavy metal ions over immobilized urease decreases in the order: Cu(II) > Cd(II) > Zn(II) > Ni(II) > Pb(II). [Diagram: see text] 相似文献
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Katya Arishtirova Barbara Pawelec Rodimir N. Nikolov J. L. G. Fierro Sonia Damyanova 《Reaction Kinetics and Catalysis Letters》2007,91(2):241-248
The effect of Pt/Ni ratio on the surface properties and catalytic behavior of bimetallic PtNi catalysts for reforming of methane
with CO2 was studied. The TPR, FTIR of adsorbed CO and XPS data showed that introduction of a small amount of Pt (0.3 – 0.5 wt.%)
into the Ni catalyst leads to a decrease of the NiO size, its easy reduction and a uniform distribution of the nickel metal
particles. 相似文献
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A mechanical system that models swimming using a pair of two-chain extremities is considered. The motion of the system under study is similar to swimming of a frog and some other animals, in which lower extremities play the main role. This type of motion is characteristic of competitive breaststroke swimming. 相似文献
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F.L. Chernous’ko 《Journal of Applied Mathematics and Mechanics》2011,75(5):493-500
The rectilinear motion of a system of two interacting bodies when there is a dry friction force acting on both of them is considered. It is assumed that the relative velocity of the bodies can vary practically instantaneously, while the distance between them has upper and lower limits. The periodic motion of the system as a whole is constructed, and the mean velocity of motion and the energy costs per unit of path are determined. The optimum values of the parameters for which the highest mean velocity is reached with the superimposed limitations are obtained. 相似文献
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The elastic deformation of plastic foams with a low (< 6%) volume fraction of solid phase is described based on a 4-rod equivalent
element. A criterion is proposed which allows one to determine the parameter of structure of this element. Based on an analysis
of the equivalent element, a procedure is developed for constructing the compression diagram of plastic foams in the region
of large (> 70%) strains. The calculation results are compared with data found in the literature and experimental results
for polyurethane foams obtained by the present authors.
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Translated from Mekhanika Kompozitnykh Materialov, Vol. 41, No. 5, pp. 619–632, September–October, 2005. 相似文献
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Mono- and polyamines can catalyze the hydrolysis and condensation of organosilicate starting materials in biomimetic silica synthesis pathways at circum-neutral pHs and room temperature. Our study is focused on understanding the mechanistic role of amines in catalyzing the hydrolysis process that precedes condensation. We have conducted (29)Si NMR experimental studies over a range of temperature and pHs for the hydrolysis rates of trimethylethoxysilane (TMES), a model compound with only one hydrolyzable bond, combined with quantum mechanical hybrid density functional theory calculations of putative intermediate and transition-state structures for TMES and tetramethyl orthosilicate (TMOS). Comparison of calculated energies with experimentally determined activation energies indicates that amine catalysis of TMES is primarily a consequence of the amine's acidity at neutral pH. The proton released by the amine is transferred to the organosilicate, producing a protonated ethoxy leaving group that can be displaced by water in an S(N)2 reaction. For TMOS, the activation energy of proton-transfer coupled with S(N)2 substitution is comparable to that for Corriu's nucleophile-activated nucleophilic displacement, such that the mechanism of amine-catalyzed hydrolysis is dependent mostly on the ambient pH conditions as well as the type of amine. The relevance of our results to biological silica precipitation is discussed. 相似文献
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N.N. Bolotnik T.Yu. Figurina F.L. Chernous’ko 《Journal of Applied Mathematics and Mechanics》2012,76(1):1-14
The rectilinear motion of a two-body system is considered. One of the bodies (the main body) interacts with a resistive environment, while the other body (the internal body) interacts with the main body but does not interact with the environment. The force applied to the internal body leads to a reaction that acts on the main body and produces a change in its velocity, which causes a change in the resistance of the environment to the motion of the main body. Thus, by controlling the motion of the internal body, one can control the external force acting on the main body and, as a consequence, the motion of the entire system. A periodic motion of the internal body relative to the main body, which generates the motion of the main body with periodically changing velocity and the maximum displacement for the period, is constructed for a wide class of laws of resistance of the environment to the motion of the main body.The principle of motion considered is appropriate for mobile mini- and micro-robots. The body (housing) of such robots can be hemetically sealed and smooth, without protruding parts, which enables these robots to be used for the non-destructive inspection of miniature engineering structures such as thin pipe-lines, as well as in medicine. Problems of optimizing the control modes for such systems are of interest both to researchers in the field of optimal control and to specialists in applied mechanics and robotics. 相似文献