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941.
C. R. Bector S. Chandra M. K. Bector 《Journal of Optimization Theory and Applications》1989,60(2):243-260
Using a parametric approach, duality is presented for a minimax fractional programming problem that involves several ratios in the objective function.The first author is thankful to Natural Science and Engineering Research Council of Canada for financial support through Grant A-5319, and the authors are thankful to the anonymous referees for useful suggestions. 相似文献
942.
Asha K. Nadipuram 《Tetrahedron letters》2006,47(3):353-356
The thermolysis of 1,2-dialkynylimidazoles in benzene solution affords high yields of 7-phenyl-5H-cyclopentapyrazines, which presumably form by solvent trapping of cyclopentapyrazine carbene intermediates. In cases where dialkynylimidazole contains side chains that can participate in intramolecular carbene C-H insertion or olefin addition, these processes compete with solvent addition to afford novel tri- and tetracyclic pyrazines, which can be obtained in good yield when the thermolysis is carried out in hexafluorobenzene. 相似文献
943.
A. E. Batalov V. K. Malinovsky A. M. Pugachev N. V. Surovtsev A. P. Shebanin 《Physics of the Solid State》2002,44(3):497-499
Low-frequency Raman scattering in the orientationally disordered phase of a polycrystalline C60 film is investigated. By analogy with disordered media (glasses), the low-frequency Raman spectra are interpreted in terms of light scattering by localized vibrational states. 相似文献
944.
Despite its capability of high spatial resolution, simulation of turbulent flows with traditional Lagrangian (front tracking) scheme is often discouraged by numerical instability caused by clustering of marker nodes and topological changes of fronts. Contour advection surgery (CAS), being a robust front tracking scheme, can limit the growth of front complexity during simulation without jeopardizing accuracy or efficiency. This allows it to open up an advantage over traditional front-tracking schemes. It has already been demonstrated that CAS, with incorporation of the reaction sheet model, can accurately simulate the propagation and advection of a turbulent premixed V-shaped flame. In this study, it is further tested with 10 values of vortex circulation. A range of upstream turbulence levels of 1.8–19.8% was obtained. Results indicate that upstream turbulence increase the average flame length, flame zone area and the overall burning rate. Flame surface density Σ was also estimated. Maximum values of Σ obtained lie in the range 0.1–1.4 mm−1. Skewness towards the burnt region was observed in all profiles of Σ. Similar to results from laboratory experiments, it was found that Σ values decreases with upstream turbulence. From this study, the ability of CAS to cope with intense turbulence is demonstrated and a better quantitative understanding on the scheme has also been acquired. 相似文献
945.
Due to the discovery of Au as a catalyst for low temperature CO oxidation, the adsorption of CO on Au surfaces has attracted a lot of attention recently. On stepped and rough single crystal surfaces as well as on deposited particles two characteristic desorption states above 100 K have been observed via TPD. We have studied Au deposits on graphite in order to elucidate the nature of these desorption peaks in more detail. For this purpose, Au was deposited at 100 K and 300 K on HOPG as a weakly interacting support. In analogy to other supports, we obtain two desorption states (∼140 K and ∼170 K) whose relative intensities depend strongly on the deposition temperature with the high temperature peak being much more pronounced for the 100 K deposits. After annealing to 600 K, both states drastically lose intensity. XP spectra, on the other hand, show virtually no decrease of the Au 4f intensity as would be expected for desorption or significant changes of the particle morphologies. We conclude that both desorption peaks are defect-related and connected with under-coordinated Au atoms that are lost for the most part upon annealing. These sites could be located at the perimeter of dendritic islands or on small, defect-rich particles in addition to larger particles not adsorbing CO at 100 K. Preliminary STM results are in favour of the second interpretation. 相似文献
946.
Polycrystalline Sn1−xMnxO2 (0≤x≤0.05) diluted magnetic semiconductors were prepared by solid-state reaction method and their structural and magnetic properties had been investigated systematically. The three Mn-doped samples (x=0.01, 0.03, 0.05) undergo paramagnetic to ferromagnetic phase transitions upon cooling, but their Curie temperatures are far lower than room temperature. The magnetization cannot be attributed to any identified impurity phase. It is also found that the magnetization increases with increasing Mn doping, while the ratio of the Mn ions contributing to ferromagnetic ordering to the total Mn ions decreases. 相似文献
947.
A complete optical characterization in the visible region of thin copper oxide films has been performed by ellipsometry. Copper
oxide films of various thicknesses were grown on thick copper films by low temperature thermal oxidation at 125 °C in air
for different time intervals. The thickness and optical constants of the copper oxide films were determined in the visible
region by ellipsometric measurements. It was found that a linear time law is valid for the oxide growth in air at 125 °C.
The spectral behaviour of the optical constants and the value of the band gap in the oxide films determined by ellipsometry
in this study are in agreement with the behaviour of those of Cu2O, which have been obtained elsewhere through reflectance and transmittance methods. The band gap of copper oxide, determined
from the spectral behaviour of the absorption coefficient was about 2 eV, which is the generally accepted value for Cu2O. It was therefore concluded that the oxide composition of the surface film grown on copper is in the form of Cu2O (cuprous oxide). It was also shown that the reflectance spectra of the copper oxide–copper structures exhibit behaviour
expected from a single layer antireflection coating of Cu2O on Cu.
Received: 19 July 2001 / Accepted: 27 July 2001 / Published online: 17 October 2001 相似文献
948.
949.
This paper presents an improved generalized differential quadrature (GDQ) method for the investigation of the effects of boundary conditions on the free vibration characteristics of truncated conical panels. The truncated conical panel is an important geometrical shape in the fields of aerospace, marine and structural engineering. However, despite this importance, few works in free vibration analysis have dealt with this particular geometry. In this work, the vibration characteristics of clamped and simply supported truncated conical shells are obtained for various circumferential wave numbers. Further, the effects of the vertex and subtended angles on the frequency parameters are also examined in detail. Due to limited published results in the open literature, results for a range of cases are compared with those generated from the commercial finite element solver McNeal-Schwendler Corporation Nastran, and excellent agreement is observed. 相似文献
950.
Combinations of problem structuring methods with hard OR methodologies are seldom described in the literature. This paper will reflect on the barriers to such combinations that can be seen at the philosophical level—paradigm incommensurability—and cognitive level—type of personality and difficulty of switching paradigm. This paper examines the combination of Soft Systems Methodology and Discrete Event Simulation within an Intermediate Care case study. The paper will argue, by way of the practical application, that these problems are not insurmountable and that the result can be seen as interplay of the soft and hard paradigms. The idea of yin and yang is proposed as a metaphor for this process. 相似文献