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21.
The syntheses of new cyano-substituted derivatives of arachno-6,8-C(2)B(7)H(13) have been achieved through the addition reactions of the arachno-6,8-C(2)B(7)H(12)(-) (1-) anion with cyano-activated olefins. The reaction of PSH+1- with tetracyanoethylene (TCNE) yielded the unusual bridging compound PSH(+)endo-6-endo-7-[micro(2)-(C(CN)(2))(2)]-arachno-6,8-C(2)B(7)H(12)(-) (PSH+2-)) resulting from cycloaddition of the TCNE at the C6-B7 edge of the anion. Consistent with its hypho skeletal electron count, an X-ray crystallographic study and DFT/GIAO calculations confirm 2(-) has a more open structure than 1-. The reaction of 1- with acrylonitrile resulted in the formation of endo-6-(NCCH(2)CH(2))-arachno-6,8-C(2)B(7)H(11)(-) (3-), which, upon acidification, afforded endo-6-(NCCH(2)CH(2))-arachno-6,8-C(2)B(7)H(12) (3) in high yield. X-ray crystallographic and DFT/GIAO studies established that the cyanoethyl fragment in 3 is substituted at the endo-position of the C6 cage-carbon. Heating 3 in THF at 50 degrees C or in toluene at 110 degrees C resulted in the quantitative isomerization of the cyanoethyl-substituent from the endo- to the exo-position at C6 to yield exo-6-(NCCH(2)CH(2))-arachno-6,8-C(2)B(7)H(12) (4). This is the first example of an endo to exo isomerization to be observed at a cage-carbon of a carborane. While heating 3 resulted in isomerization to 4, heating 3- in the presence of a small amount of 3 yielded the new ethylene-bridged 10-vertex tricarbaborane micro(6,9)-(CH(2)CH(2))-arachno-5,6,9-C(3)B(7)H(11) (5) resulting from reduction of the 3- pendant nitrile group, followed by deammination and carbon insertion. 相似文献
22.
A new method to tune the peak loss of mechanically formed long-period fiber gratings (MLPFGs) is proposed. Periodic arrayed metal wires are used to obtain the gratings along a single mode fiber (SMF). Self-maintaining gratings are achieved by the bonding force of an UV-adhesive between two glass plates. The initial index modulation formed at room temperature creates a maximum attenuation of −9 dB and −12 dB for coated and uncoated SMF, respectively. By changing the temperature, the peak loss is tuned due to the large thermal expansion of the UV-adhesive. Thermally tunable characteristics caused by the coating layer of the SMF are also described and compared with the results of the device with an uncoated SMF. 相似文献
23.
OXA-17, an extended-spectrum β-lactamase (ESBL) conferring severe antibiotic resistance, hydrolytically inactivates β-lactam antibiotics, inducing a lack of eradication of pathogenic bacteria by oxyimino β-lactams and not helping hospital infection control. Thus, the enzyme is a potential target for developing antimicrobial agents against pathogens producing ESBLs. OXA-17 was purified and crystallized at 298 K. X-ray diffraction data from OXA-17 crystal have been collected to 1.85 Å resolution using synchrotron radiation. The crystal of OXA-17 belongs to space group P212121, with unit-cell parameters a = 48.37, b = 101.12, and c = 126.07 Å. Analysis of the packing density shows that the asymmetric unit probably contains two molecules with a solvent content of 54.6%. 相似文献
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Major weapon system acquisition programmes often require high initial purchase cost which can be a burden for the procurement of a highly reliable system. In order to avoid the tendency of acquiring a less expensive weapon system with lower performance, a cost of ownership (COO) model can be applied to assess the lifetime cost of the weapon system. In many existing cost estimation models for weapon systems, the failure rate of the system is assumed to be constant and the functional relationship between the initial purchase cost and maintenance cost is not well defined. In this paper, we propose a revised COO model where random effects models are employed to accommodate the variations of the system failure frequency and repair time. It is expected that our model can contribute to the cost-effective procurement of spare engines for the Korean Navy acquisition programme within the limited national defence budget. 相似文献
26.
A double lambda four-level system could be implemented with biexcitonic transitions on GaAs quantum well. We observed that the phase dependent biexcitonic transition could be explained by interference between one-photon and three-photon transition in a double lambda four-level system. An ultralow-light switch pulse could control 80% of biexcitonic absorption, which demonstrated all-optical switching with biexcitonic double lambda system. 相似文献
27.
ENVIRONMENTAL VARIABILITY OF MODAL PROPERTIES 总被引:5,自引:0,他引:5
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We study the structure of the complement of an F-bundle over a graph G when it can be expressed as an F-bundle over another graph G. In particular, we compute the characteristie polynomial of the complement of an F-bundle when its voltages lie in and abelian subgroup Г of Aut(F) which acts freely and transitively on the vertices of the fiber F Some applications to regular embeddings of graph bundles into Euclidean spaces are also discussed 相似文献
30.
Numerical investigation of hydroplaning characteristics of three-dimensional patterned tire 总被引:6,自引:0,他引:6
J.R. Cho H.W. Lee J.S. Sohn G.J. Kim J.S. Woo 《European Journal of Mechanics - A/Solids》2006,25(6):914-926
Hydroplaning characteristics of patterned tire on wet road are investigated by making use of finite volume and finite element methods. A detailed 3-D patterned tire model is constructed by our in-house modeling program and the rainwater flow is considered as incompressible and inviscid. Meanwhile, the fluid–structure interaction between the highly complicated tire tread and the rainwater flow is effectively treated by the general coupling method. Through the numerical experiments, the rainwater flow drained through tire grooves, hydrodynamic pressure and contact force are investigated and compared with those of the three-grooved tire model. 相似文献