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A two-dimensional steady-sate analysis of semi-infinite brittlecrack growth at a constant subcritical rate in an unboundedfully-coupled thermoelastic solid under mixed-mode thermomechanicalloading is made. The loading consists of normal and shear tractionsand heat fluxes applied as point sources (line loads in theout-of-plane direction). A related problem is solved exactly in an integral transformspace, and robust asymptotic forms used to reduce the originalproblem to a set of integral equations. The equations are partiallycoupled and exhibit operators of both Cauchy and Abel types,yet can be solved analytically. The temperature change field at a distance from the moving crackedge is then constructed, and its dominant term is found tobe controlled by the imposed heat fluxes. The role of this termis, indeed, enhanced if the heat fluxes serve to render thecrack as a net heat source/sink for the solid, as opposed tobeing a transmitter of heat across its plane. More generally,the influence of the thermoelastic coupling on this field, aswell as other functions, is found to increase with crack speed. 相似文献
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Lieza M. Danan Zhihao Yu Peter J. Ludden Weitao Jia Kevin L. Moore Julie A. Leary 《Journal of the American Society for Mass Spectrometry》2010,21(9):1633-1642
Human tyrosylprotein sulfotransferases catalyze the transfer of a sulfuryl moiety from the universal sulfate donor PAPS to
the hydroxyl substituent of tyrosine residues in proteins and peptides to yield tyrosine sulfated products and PAP. Tyrosine
sulfation occurs in the trans-Golgi network, affecting an estimated 1% of the tyrosine residues in all secreted and membrane-bound
proteins in higher order eukaryotes. In this study, an effective LC-MS-based TPST kinetics assay was developed and utilized
to measure the kinetic properties of human TPST-2 and investigate its catalytic mechanism when G protein-coupled CC-chemokine
receptor 8 (CCR8) peptides were used as acceptor substrates. Through initial rate kinetics, product inhibition studies, and
radioactive-labeling experiments, our data strongly suggest a two-site ping-pong model for TPST-2 action. In this mechanistic
model, the enzyme allows independent binding of substrates to two distinct sites, and involves the formation of a sulfated
enzyme covalent intermediate. Some insights on the important amino acid residues at the catalytic site of TPST-2 and its covalent
intermediate are also presented. To our knowledge, this is the first detailed study of the reaction kinetics and mechanism
reported for human TPST-2 or any other Golgi-resident sulfotransferase. 相似文献
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Danan LM Yu Z Hoffhines AJ Moore KL Leary JA 《Journal of the American Society for Mass Spectrometry》2008,19(10):1459-1466
Protein tyrosine O-sulfation, a widespread post-translational modification, is mediated by two Golgi enzymes, tyrosylprotein
sulfotransferase-1 and-2. These enzymes catalyze the transfer of sulfate from the universal sulfate donor 3′-phosphoadenosine-5′-phosphosulfate
(PAPS) to the hydroxyl group of tyrosine residues to form tyrosine O-sulfate ester and PAP. More than 60 proteins have been identified to be tyrosine sulfated including several G protein-coupled
receptors, such as CC-chemokine receptor 8 (CCR8) that is implicated in allergic inflammation, asthma, and atherogenesis.
However, the kinetic properties of purified tyrosylprotein sulfotransferase (TPST)-1 and −2 have not been previously reported.
Moreover, currently there is no available quantitative TPST assay that can directly monitor individual sulfation of a series
of tyrosine residues, which is present in most known substrates. We chose an MS-approach to address this limitation. In this
study, a liquid chromatography electrospray ionisation mass spectrometry (LC/ESI-MS)-based TPST assay was developed to determine
the kinetic parameters of individual TPSTs and a mixture of both isozymes using CCR8 peptides as substrates that have three
tyrosine residues in series. Our method can differentiate between mono-and disulfated products, and our results show that
the Km,app for the monosulfated substrate was 5-fold less than the nonsulfated substrate. The development of this method is the initial
step in the investigation of kinetic parameters of the sequential tyrosine sulfation of chemokine receptors by TPSTs and in
determining its catalytic mechanism. 相似文献
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第十七届全国中学生物理竞赛预赛试题获得中学物理教师的普遍好评.题目灵活,难度适中,既能与中学物理教学相衔接,又能考出考生的能力与水平,而且结合了一些近代物理知识,起到了很好的导向作用. 相似文献
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2,3-Diazido-2,3-dideoxy-beta-D-mannopyranoside derivatives were synthesized in order to prepare beta-glycosides of 2,3-diacetamido-2,3-dideoxy-D-mannuronic acid, a rare moiety of bacterial oligosaccharides. A direct glycosyl donor, 4,6-di-O-acetyl-2,3-diazido-2,3-dideoxy-alpha-D-mannopyranosyl bromide, was prepared, and its synthetic capacity was tested in glycosylation reactions. An indirect route was also elaborated: 3-azido-3-deoxy-beta-D-glucopyranosides were converted into beta-D-mannopyranosides. The cis vicinal diazido function successfully tolerated the conditions of mild acidic hydrolysis, tritylation, Jones oxidation, TEMPO oxidation, acetolysis, and bromination with TiBr(4). 相似文献
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Amita Gupta Alexei Yu Ganin Parmanand Sharma Vikrant Agnihotri LM Belova KV Rao Mikhail E Kozlov AA Zakhidov RH Baughman 《Pramana》2002,58(5-6):1051-1059
We present studies of novel nanocomposites of BiNi impregnated into the structure of opals as well as inverse opals. Atomic force microscopy and high resolution elemental analyses show
a highly ordered structure and uniform distribution of the BiNi filler in the matrix. These BiNi-based nanocomposites are
found to exhibit distinct ferromagnetic-like ordering with transition temperature of about 675 K. As far as we know there
exists no report in literature on any BiNi compound which is magnetic. 相似文献
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如图所示,光滑绝缘水平面上的M、N两点各放完全相同的金属球A和B,A和B的带电量分别为-2Q和-Q. 相似文献
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Mediterranean Journal of Mathematics - This paper represents a continuation of Barboteu et al. (Analysis of a contact problem with unilateral constraint and slip-dependent friction, Math... 相似文献
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层状盐岩力学特性研究进展 总被引:31,自引:0,他引:31
盐岩具有孔隙度低,渗透率小,损伤自恢复和塑性变形能力大等特性.本文着眼于深部盐岩能源地下储备,在简要介绍国内外盐岩力学特性研究现状基础上,着重综述了近期关于层状沉积型盐岩工程力学特性研究的进展.层状盐岩压缩试验表明泥质硬石膏夹层对盐岩体的变形和破坏特性有明显的影响,揭示了复合岩体的变形和破坏机制;层状盐岩流变试验表明层状盐岩的蠕变主要由盐岩层控制,硬夹层的存在对溶腔围岩的长期蠕变起到抑制作用;为了深入了解界面的力学特性,开展了层状盐岩直接剪切试验、间接拉伸试验和界面微观分析试验,试验表明层状盐岩体中盐岩夹层界面具有较强的黏结力,这十分有利于盐岩溶腔的密闭性和稳定性;针对特殊的层状岩体提出了复合岩体Cosserat介质扩展本构模型,并应用于层状盐岩构造中能源储库稳定性分析中.最后指出了层状盐岩工程力学特性研究中值得关注的几个重点研究方向. 相似文献