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排序方式: 共有283条查询结果,搜索用时 15 毫秒
161.
V. I. Torgashev A. A. Volkov A. A. Bush E. S. Zhukova S. N. Migunov A. N. Lobanov B. P. Gorshunov 《Physics of the Solid State》2007,49(9):1652-1657
The reflection spectrum R(ν) and transmission spectrum Tr(ν) of polycrystalline solid solutions Bi0.5Sr0.5FeO2.75 are studied for the first time using submillimeter and IR spectroscopy in the frequency range 7 < ν < 4000 cm?1 at temperatures of 10–300 K. A large difference is found between the magnitudes of the dielectric susceptibility measured by contact (at a frequency of 103 Hz) and noncontact (THz range) methods. It is suggested that powerful relaxation excitations exist at frequencies below 100 cm?1 (“subphonon” region). The possible origin of the excitations is discussed. 相似文献
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Bush MF Forbes MW Jockusch RA Oomens J Polfer NC Saykally RJ Williams ER 《The journal of physical chemistry. A》2007,111(32):7753-7760
The gas-phase structures of protonated and alkali-metal-cationized lysine (Lys) and epsilon-N-methyllysine (Lys(Me)) are investigated using infrared multiple photon dissociation (IRMPD) spectroscopy utilizing light generated by a free electron laser, in conjunction with ab initio calculations. IRMPD spectra of Lys.Li(+) and Lys.Na(+) are similar, but the spectrum for Lys.K(+) is different, indicating that the structure of lysine in these complexes depends on the metal ion size. The carbonyl stretch of a carboxylic acid group is clearly observed in each of these spectra, indicating that lysine is nonzwitterionic in these complexes. A detailed comparison of these spectra to those calculated for candidate low-energy structures indicates that the bonding motif for the metal ion changes from tricoordinated for Li and Na to dicoordinated for K, clearly revealing the increased importance of hydrogen-bonding relative to metal ion solvation with increasing metal ion size. Spectra for Lys(Me).M(+) show that Lys(Me), an analogue of lysine whose side chain contains a secondary amine, is nonzwitterionic with Li and zwitterionic with K and both forms are present for Na. The proton affinity of Lys(Me) is 16 kJ/mol higher than that of Lys; the higher proton affinity of a secondary amine can result in its preferential protonation and stabilization of the zwitterionic form. 相似文献
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二氧化硅悬浮体和水解聚丙烯酰胺体系的流变性 总被引:6,自引:0,他引:6
研究了二氧化硅悬浮体的流变性。在固体含量较少的情况下, 体系呈Newton型;固体含量达到一定程度以后, 产生三维结构, 为假塑性体系。三维结构的固体含量与pH值有关。实验证实, 在等电点(i,e, p)附近三维结构最为疏松。还研究了水解聚丙烯酰胺(HPAM)对悬浮体流变性能的影响。HPAM破坏了二氧化硅粒子聚集体结构, 呈絮凝体结构, 并出现触变性。当高聚物在固体表面覆盖一半时, 具有最大触变性和动剪切力。HPAM的水解度达到一定程度, 由于对固体粒子由“强”吸附转变为“弱”吸附, 固体粒子“屏蔽”了高分子间的相互作用, 出现了负触变性现象。在流动时粒子会脱附, 静止以后又产生吸附, 这种吸附与脱附是产生负触变性的主要原因。HPAM水解过度或用量过多, 均会减弱负触变性现象。 相似文献
167.
Emma K. Grant David J. Fallon H. Christian Eberl Ken G. M. Fantom Francesca Zappacosta Cassie Messenger Nicholas C. O. Tomkinson Jacob T. Bush 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(48):17483-17488
The CDK family plays a crucial role in the control of the cell cycle. Dysregulation and mutation of the CDKs has been implicated in cancer and the CDKs have been investigated extensively as potential therapeutic targets. Selective inhibition of specific isoforms of the CDKs is crucial to achieve therapeutic effect while minimising toxicity. We present a group of photoaffinity probes designed to bind to the family of CDKs. The site of crosslinking of the optimised probe, as well as its ability to enrich members of the CDK family from cell lysates, was investigated. In a proof of concept study, we subsequently developed a photoaffinity probe‐based competition assay to profile CDK inhibitors. We anticipate that this approach will be widely applicable to the study of small molecule binding to protein families of interest. 相似文献
168.
Kapustin V. I. Li I. P. Shumanov A. V. Moskalenko S. O. Bush A. A. Lebedinskii Yu. Yu. 《Technical Physics》2019,64(5):720-729
Technical Physics - High-resolution X-ray diffraction method (XRD) is used to determine sizes and crystallographic orientation of the nanocrystallites of the Pd and Pd5Ba phases in... 相似文献
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Majidi C Groff RE Maeno Y Schubert B Baek S Bush B Maboudian R Gravish N Wilkinson M Autumn K Fearing RS 《Physical review letters》2006,97(7):076103
High dry friction requires intimate contact between two surfaces and is generally obtained using soft materials with an elastic modulus less than 10 MPa. We demonstrate that high-friction properties similar to rubberlike materials can also be obtained using microfiber arrays constructed from a stiff thermoplastic (polypropylene, 1 GPa). The fiber arrays have a smaller true area of contact than a rubberlike material, but polypropylene's higher interfacial shear strength provides an effective friction coefficient of greater than 5 at normal loads of 8 kPa. At the pressures tested, the fiber arrays showed more than an order of magnitude increase in shear resistance compared to the bulk material. Unlike softer materials, vertical fiber arrays of stiff polymer demonstrate no measurable adhesion on smooth surfaces due to high tensile stiffness. 相似文献