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861.
A facile procedure for the synthesis.of quinoxalines is being reported starting from benzil and 1,2-diaminobenzene. Thereactions were carried out catalyst-free, solvent-free and under microwave irradiation conditions in high yield (84-98%) with short time (3-6 rain) and environmental benign, as well as convenient operation. The structures of all the compounds have been confirmed on the basis of their IR, 1H NMR, and/or 13C NMR, mass spectral data.  相似文献   
862.
Four 1, 2, 3-trisubstituted imidazolinium iodides which were used as 5,10 -+CPh-THF model (7—10) at formic acid oxidation level were synthesized. The benzylidyne group (phenyl-substituted one carbon unit) transfer reactions from these compounds to Grignard reagent were investigated, and the reactions of these compounds with KBH4 and NaOH were also studied.  相似文献   
863.
通过构建一个随机甬数族,本方案可成功地为用户分配密钥,使合法用户以概率为1地获得解密,而用户的密钥存储仅为(l 1)个.在系统开始运行前,每一个用户从每一个密钥池获得一个密钥.对于退出用户,广播中心只需用他们所不拥有的其他(辅助)密钥加密会话密钥即可;而对于未退出用户,在一定程度上他们总可以找到一个密钥与广播中心在加密会话密钥时所使用的密钥相匹配.本方案较目前基于二叉树结构的广播加密方案(如SD)在密钥存储量上有显著的优势,同时在一定条件下可使传输成本最小.  相似文献   
864.
A convenient route for the synthesis of 3,4-dihydrocoumarin derivates from salicylaldehyde derivates and 1,3-dicarbonyl compounds under solvent-free microwave irradiation conditions was described. In this way, a range of compounds was obtained in moderate to good yields in a short reaction time.  相似文献   
865.
Two new natural products, tenelate A ( 1 ) and B ( 2 ), together with the known compound, tenellic acid C ( 3 ), were isolated from the mangrove endophytic fungus Talaromyces sp. (SBE‐14), from the South China Sea. Their structures were elucidated by spectroscopic methods, mainly 1D and 2D NMR techniques. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   
866.
Polyoxymethylene/thermoplastic polyurethane (POM/TPU) blends containing 10–30 wt % of TPU were electrospun using hexafluoroisopropanol as the solvent. The average fiber diameter increases with the increase in TPU content from 0.68 μm for neat POM fibers to 0.92 μm for POM/TPU 7:3 blend fibers due to the increase in solution viscosity. Core/sheath structure with the major component POM as the core and the minor component TPU as the sheath was observed by transmission electron microscopy and further confirmed by surface N contents of the blend fiber mats. The crystalline melting point and the degree of crystallinity of POM have no obvious change by coelectrospinning with TPU due to lack of interaction between POM and TPU as revealed by Fourier transform infrared spectroscopy. Tensile tests showed that the unusual high ductility of POM fiber mat could be further increased by coelectrospinning with 10 or 20 wt % TPU without significantly decreasing the stiffness and strength. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1853–1859, 2009  相似文献   
867.
In this paper, a new one-step explicit method of fourth order is derived. The new method is proved to be A-stable and L-stable, and it gives exact results when applied to the test equation y'=λy with Re(λ)<0, Also several numerical examples are included.  相似文献   
868.
869.
The Hamiltonian in the framework of eight-band effective-mass approximation of the zinc-blende nanowires and nanorods in the presence of external homogeneous magnetic field is given in the cylindrical coordinate. The electronic structure, optical properties, magnetic energy levels, and g factors of the nanowires and nanorods are calculated. It is found that the electron states consist of many hole-state components, due to the coupling of the conduction band and valence band. For the normal bands which are monotone functions of |kz|, long nanorods can be modeled by the nanowires, the energy levels of the nanorods approximately equal the values of the energy band E(kz) of the nanowires with the same radius at a special kz, where kz is the wave vector in the wire direction. Due to the coupling of the states, some of the hole energy bands of the nanowires have their highest points at kz≠0. Especially, the highest hole state of the InSb nanowires is not at the kz=0 point. It is an indirect band gap. For these abnormal bands, nanorods can not be modeled by the nanowires. The energy levels of the nanorods show an interesting plait-like pattern. The linear polarization factor is zero, when the aspect ratio L/2R is smaller than 1, and increases as the length increases. The gz and gx factors as functions of the kz, radius R and length L are calculated for the wires and rods, respectively. For the wires, the gz of the electron ground state increases, and the gz of the hole ground state decreases first, then increases with the kz increasing. For the rods, the gz and gx of the electron ground state decrease as the R or the L increases. The gx of the hole ground state decreases, the gz of the hole ground state increases with the L increasing. The variation of the gz of the wires with the kz is in agreement with the variation of the gz of the rods with the L.  相似文献   
870.
In this paper we will provide a theory for an extrapolation algorithm of band-limited signals with sampling errors or low noises. The main result is as follows: Suppose thatf(t) is in L2 and is a continuous Ω band-limited signal. Then for any positive numbers T, A(>T) and ε, there exists a δ>0 such that when the sampling errors (or noises) off(t) on [−T, T] is less than δ we can extrapolate the values off(t) on the interval [−A, A] such that the difference between the extrapolated value and the exact value off(t) does not exceed ε.  相似文献   
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