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81.
Christopher R. Weinberger Andrew T. Jennings Keonwook Kang Julia R. Greer 《Journal of the mechanics and physics of solids》2012,60(1):84-103
The strength of true metallic nanowires and nanopillars (diameters below 100 nm) is known to be higher than the strength of bulk metals and is most likely controlled by dislocation nucleation from free surfaces. Dislocation nucleation is a thermally activated process that is sensitive to both temperature and strain rate. However, most simulations rely on high strain rate molecular dynamics to investigate strength and nucleation, which is limited by short molecular dynamics time scales. In this work, the energetics of dislocation nucleation in gold nanowires are computed using atomistic simulations, and transition state theory is used to estimate the strength at experimental strain rates revealing detailed information outside the realm accessible to molecular dynamics simulations. This allows investigation into the competition between thermally activated dislocation nucleation and other failure mechanisms such as elastic and structural instabilities. Additionally, the mechanisms of dislocation nucleation are compared against analytical continuum models which allow a better understanding of the nucleation process including the effects of the wire surfaces. This study helps clarify and consolidate our understanding of the nature of dislocation nucleation in small structures. 相似文献
82.
The amount of correlation attainable between the components of a quantum system is constrained if the system is closed. We provide some examples, largely from the field of quantum thermodynamics, where knowing the maximal possible variation in correlations is useful. The optimization problem it raises requires us to search for the maximally and minimally correlated states on a unitary orbit, with and without energy conservation. This is fully solvable for the smallest system of two qubits. For larger systems, the problem is reduced to a manageable, classical optimization. 相似文献
83.
René Roy Craig A. Laferrière Apdrzej Gamian Harold J. Jennings 《Journal of carbohydrate chemistry》2013,32(1):161-165
Abstract A simplified procedure for the synthesis of acetochloroneuraminic acid is described starting from the methyl ester. N-acetyl neuraminic acid α-allyl glycoside was prepared in high yield using silver salicylate as catalyst. Reductive ozonolysis of the allyl group, followed by direct reductive ami nation to protein carriers, gave immunogenic neoglycoproteins. Copolymerization of the α-allyl glycoside with acrylamide produced a water-soluble pseudopolysaccharide useful for the EL ISA technique. 相似文献
84.
David A. Glenar Andrew R. Hill Donald E. Jennings James W. Brault 《Journal of Molecular Spectroscopy》1985,111(2):403-414
Absorption features from vibrational transitions of silicon monoxide have been observed in sunspot umbrae between 1070 and 1225 cm?1 using the Fourier transform spectrometer (FTS) at the McMath Solar Telescope of the National Solar Observatory, located at Kitt Peak. Sunspots are a source of high-temperature spectra not easily obtained in the laboratory. Measurements were made of 937 28SiO, 29SiO, and 30SiO fundamental and hot band transitions in the umbral spectrum extending to v = 10 and J = 80. All three isotopic species were treated together to derive 10 Dunham rotation-vibration coefficients. 相似文献
85.
86.
C.R. Pollock F.R. Petersen D.A. Jennings J.S. Wells A.G. Maki 《Journal of Molecular Spectroscopy》1984,107(1):62-71
The absolute frequencies of 39 lines in the 0002-0000, 2001-0000, and 1201-0000 bands of N2O in the range 4300–4800 cm?1 have been measured by heterodyne frequency techniques. The lines were each measured in Doppler-limited absorption, with a color-center laser as a tunable probe of the N2O and two stabilized CO2 lasers as reference frequencies. New rovibrational constants have been fitted to these measurements. Tables of calculated transition frequencies are given, with estimated absolute uncertainties as small as 10?4 cm?1. The pressure shifts of four lines have been measured, and the values fall within the range of 0 to ?2 MHz/kPa (0 to ?0.2 MHz/Torr). 相似文献
87.
88.
An enantioselective synthesis of (S)-(+)-3-aminomethyl-5-methylhexanoic acid via asymmetric hydrogenation 总被引:2,自引:0,他引:2
Burk MJ De Koning PD Grote TM Hoekstra MS Hoge G Jennings RA Kissel WS Le TV Lennon IC Mulhern TA Ramsden JA Wade RA 《The Journal of organic chemistry》2003,68(14):5731-5734
A concise enantioselective synthesis of (S)-(+)-3-aminomethyl-5-methylhexanoic acid (1, Pregabalin) has been developed. The key step is the asymmetric hydrogenation of a 3-cyano-5-methylhex-3-enoic acid salt 2 with a rhodium Me-DuPHOS catalyst, providing the desired (S)-3-cyano-5-methylhexanoate 3 in very high ee. Subsequent hydrogenation of the nitrile 3 with a heterogeneous nickel catalyst provides Pregabalin 1 in excellent overall yield and purity. 相似文献
89.
Walter Jennings 《Journal of separation science》1980,3(12):601-608
Fused silica is an evolutionary product of continuing efforts to improve our chromatographic capabilities. It offers the normal user new horizons in inertness, chromatographic reproducibility, ease of column installation, and possibilities in on-column trapping. Since this writing, chemically bonded phases in several film thicknesses became available on fused silica columns, and these are especially well suited to on-column injections. The use of fused silica syringe needles to inject directly onto fused silica columns seems particularly interesting. Evolution is, of course, a continuous process and it would appear that we can expect continuing developments in this exciting area. 相似文献
90.