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991.
Cerium ammonium nitrate (CAN) catalyzed the three-component domino reaction between aromatic amines, α,β-unsaturated aldehydes, and ethyl acetoacetate, providing an efficient new entry into 1,4-dihydropyridines. This new reaction requires very mild reaction conditions, has water as the only side product and is complementary to the classical Hantzsch synthesis in that it is well suited to the preparation of N-aryl-5,6-unsubstituted dihydropyridines. Experiments in the presence of a radical trap suggest that a one-electron oxidative mechanism can be excluded and that CAN acts as a Lewis acid. 相似文献
992.
Metaheuristics are a class of approximate methods designed to solve hard combinatorial optimization problems arising within various different areas. The importance of metaheuristics results from their ability to continue the search beyond a local optimum so that near-optimal or optimal solutions are efficiently found. In order to solve the backhauling problem associated with mixed and simultaneous delivery and pick-ups, this paper presents a hybrid algorithm which is comprised of the two metaheuristics of tabu search and variable neighbourhood descent. The primary challenge associated with backhauling consists of creating routes in which vehicles are not only required to deliver goods, but also to perform pick-ups at customer locations. The problems associated with these two categories of problems, however, have received little attention in the literature to date. A set of examples taken from the literature with Euclidean cost matrices are presented. Finally, some numerical results are illustrated to show the effectiveness of the proposed approach. 相似文献
993.
An ethanolic solution of CuCl / ethylendiamine reacts with 1.3‐bis‐ (phenyltriazene)benzene in THF leading to the deprotonation of the bis triazene ligand to give orange crystals of [CuII(en)3][CuI4{(NNN‐Ph)2C6H4}3], an example of a rare complex salt of copper with mixed valence states. In the anion complex [CuI4{(NNNPh)2C6H4}3]2? the copper(I) ions are disposed linearly as single, bridged pairs in the two extremes of an axis, each of them presenting a trigonal bipyramidal alike coordination arrangement. 相似文献
994.
The shapes of Dicke-narrowed spectral lines in the fundamental P-branch of CO in Ar are studied by comparing high-resolution measurements and theoretical calculations. The measured spectra were recorded at temperatures between 214 and 324 K, and at pressures between 0.025 and 1 atm. The calculations are based on solving a transport/relaxation equation for the appropriate off-diagonal element of the density matrix; they use a realistic intermolecular potential to determine the speed-dependent collisional broadening, and a rigid sphere potential to determine the Dicke narrowing. It is found that the calculations can reproduce the measured spectra within the experimental noise under all conditions, but that the magnitude of the Dicke narrowing in the measured spectra is 70-90% less than predicted from the mass diffusion constant. A revised view of the collision operator resolves the discrepancy in principle, and leads to a better understanding of the line shape problem in general. 相似文献
995.
We have found two different regimes in the kinetics of the YBCO formation depending on the water partial pressure at a constant temperature and total flow rate of the carrier gas. The first regime at low partial water pressure shows continual kinetics curves until the end of YBCO growth and the reaction is controlled chemically. The second regime at high partial water pressure shows irreproducible steps in the kinetics curves during the thin films YBCO growth. In this work we suggest that there is formation of a boundary layer of water (Nernst layer) when the partial water pressure is higher than 20 hPa at 795 °C for a total gas flow rate lower than 2.4 × 10−2 m s−1. These irreproducible steps dues probably to a water boundary layer formation can be eliminated by increasing the stirring rate of the carrier gas. The reaction order of YBa2Cu3O7−x formation respect to the water pressure is n = 0.5 when the water boundary layer is not formed, but the apparent reaction order respect to the partial water pressure is zero or negative when the gas flow rate of the carrier gas is not big enough for the elimination of this water layer. This work also evidences that there is an intermediate step in the kinetics curves before the formation of YBCO. This step, which starts at low temperature during the heating ramp (400 °C) is attributed to the partial elimination of F from the BaF2 precursor to form oxyfluoride compounds. So, at low total flow gas rates and low partial water pressures, the reaction is controlled by diffusion mechanism due to the formation of a HF boundary layer (Nernst layer), because the apparent order of YBCO formation is one respect to the stirring rate. Nevertheless, at high flow gas rates and low partial water pressures, the YBCO formation is controlled chemically, then the apparent order respect to the stirring rate is zero and the HF Nernst layer is eliminated. The apparent Ea for the oxyfluoride formation at low temperatures is only 18 Kj/mol indicating that this intermediate reaction is controlled by diffusion mechanism even at high stirring rate and relatively low partial water pressure. The apparent Ea for the YBCO formation at partial water pressures higher than 20 hPa for a total flow rate of 2.4 × 10−2 m s−1 is only 32 Kj/mol, indicating that the reaction control is mainly diffusive or mixed (diffusive and chemist). 相似文献
996.
Antonio Luiz P. S. Campos Adaildo Gomes d''Assunção Marcos A. Barbosa de Melo 《International Journal of Infrared and Millimeter Waves》2002,23(1):123-133
The analysis of periodic structures on anisotropic substrates is presented for incident millimeter waves. Frequency selective surface structures composed by a periodic array of conducting crossed dipoles on anisotropic layers are analyzed. A full-wave analysis for the problem of scattering is performed. The formulation uses the moment method in combination with the immitance approach, in the Fourier domain, to determine the scattering parameters of the considered structures. A set of entire-domain type basis functions is used in the expansion for the unknown induced current. This analysis is computationally efficient, and its accuracy is verified by the agreement between results obtained in this work and those available in the literature, for particular cases. 相似文献
997.
998.
H. Beiro Da Veiga 《纯数学与应用数学通讯》1993,46(2):221-259
The main result of this paper (which is completely new, apart from our previous and less general result proved in reference [9]) states that the nonlinear system of equations (1.11) (or, equivalently, (1.10)) that describes the motion of an inviscid, compressible (barotropic) fluid in a bounded domain Ω, gives rise to a strongly well-posed problem (in the Hadamard classical sense) in spaces Hk(Ω), k ≧ 3; see Theorem 1.4 below. Roughly speaking, if (an, ?n) → (a, ?) in Hk × Hk and if fn → f in ??2(0, T;Hk), then (vn, gn) → (v, g) in ?? (0, T; Hk × Hk). The method followed here (see also [8]) also applies to the non-barotropic case p = p(ρ, s) (see [10]) and to other nonlinear problems. These results are based upon an improvement of the structural-stability theorem for linear hyperbolic equations. See Theorem 1.2 below. Added in proof: The reader is referred to [29], Part I, for a concise explanation of some fundamental points in the method followed here. © 1993 John Wiley & Sons, Inc. 相似文献
999.
A. Gizon J. Genevey B. Weiss Gh. Căta-Danil J. Gizon D. Barnéoud R. Béraud D. Bucurescu T. von Egidy A. Emsallem C. F. Liang P. Paris I. Penev A. Plochocki 《Zeitschrift für Physik A Hadrons and Nuclei》1997,359(1):11-17
Low-lying levels of the 129La isotope have been investigated through the β+/EC decay of 129Ce. The radioactive nuclei were produced in the 94Mo+40Ca reaction at a bombarding energy of 255 MeV and transported with a He-jet system. On-line mass separation was used to select the 129Ce beta-decay γ-γ-t, X- γ- t, e?-γ -t coincidence measurements as well as time multi-analysis were performed. Internal conversion electrons were recorded with a magnetic selector and multipolarities deduced. The level scheme of 129La is discussed and compared with the calculations made in the frame of the neutron-proton Interacting Boson-Fermion Model (IBFM-2). 相似文献
1000.