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排序方式: 共有178条查询结果,搜索用时 15 毫秒
171.
We describe novel composite pulse sequences which act as general rotors and thus are particularly suitable for nuclear magnetic resonance quantum computation. The resonance offset tailoring to enhance nutations approach permits perfect compensation of off-resonance errors at two selected frequencies placed symmetrically around the frequency of the radiofrequency source. 相似文献
172.
Brask JK Fickes MG Sangtrirutnugul P Durà-Vilà V Odom AL Cummins CC 《Chemical communications (Cambridge, England)》2001,(17):1676-1677
The iminophosphinimide complexes [Ar(R)N]3M(NPNBut) (M = V, Nb) were prepared from the corresponding anionic nitride species ([Ar(R)N]3M identical to NNa)2 by way of a four-step synthetic strategy. 相似文献
173.
We propose a technique for achieving phase matching in Brillouin scattering in a dielectric fiber doped by three-level Lambda-type ions. This can lead to a dramatic increase of efficiency of ponderomotive nonlinear interaction between the electromagnetic waves and holds promise for applications in quantum optics such as squeezing and quantum nondemolition measurements. 相似文献
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176.
Christian G Stranger R Petrie S Yates BF Cummins CC 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(15):4264-4272
The reaction pathway for the interaction of CO with three-coordinate TaIII, WIII and ReIII complexes (modelled on the experimental [M{N(tBu)Ar}3] system) has been explored by using density functional methods. Calculations show that CO binds without a barrier to [Re(NH2)3], forming the encounter complex [OC--Re(NH2)3], which is stabilized by approximately 280 kJ mol-1 relative to the reactants. The binding of [Ta(NH2)3] to the oxygen terminus of CO is inhibited by a barrier of only 20 kJ mol-1 and is followed by spontaneous cleavage of the C--O bond to form the products [C--Re(NH2)3] and [O--Ta(NH2)3]. The salient features of the potential energy surface are more favourable to CO cleavage than the analogous N2 cleavage by [Mo(NH2)3], which is less exothermic (335 vs. 467 kJ mol-1) and is impeded by a significant barrier (66 kJ mol-1). The ReIII/TaIII/CO system therefore appears to be an excellent candidate for cleaving the exceptionally strong C--O bond under mild laboratory conditions. The related WIII/TaIII dimer, which significantly weakens but does not cleave the CO bond, may be a suitable alternative when the chemistry is to be performed on activated CO rather than on the strongly bound oxide and carbide cleavage products. 相似文献
177.
E. Galvin M. M. Morshed C. Cummins S. Daniels C. Lally B. MacDonald 《Plasma Chemistry and Plasma Processing》2013,33(6):1137-1152
The surface texture and chemistry of WE43 absorbable magnesium stents (AMS) and tube specimens processed by chemical and reactive ion etching (RIE) were investigated. Tube specimens were produced in three different conditions, namely as-received, chemically etched and plasma etched. The results of scanning electron microscopy, atomic force microscopy and energy dispersive X-ray spectroscopy studies showed that plasma etching and cleaning reduced surface roughness by 10 % compared to chemical etching alone, and completely removed surface deposits remaining from the chemical etch process. The same combination of chemical and plasma etching processes was employed to produce AMS. Expansion tests demonstrated uniform stent expansion characteristics and confirmed the viability of the device. The results of this study show that RIE is an effective surface modification technique for absorbable magnesium devices. 相似文献
178.
This review covers the subject of pheromones, attractants and other chemical cues of aquatic invertebrates, fishes and amphibians (including salamanders and anurans). Major topics include the sex pheromones of gastropods, salamanders and a giant tree frog, and the conspecific attraction of sperm to ova of some of the organisms and animals described in this review. 相似文献