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91.
92.
Dmitri I. Popov Mohammed Z. Tahar Sergei A. Nemov 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):453
The Hall coefficient and resistivity were measured on a series of samples of InTe in Pb0.4Sn0.6Te solid solutions with varying indium content from 0 to 5 molar%. All samples show a p-type conductivity with the concentration of holes 1019 cm−3 at 77 K. A considerable decrease of mobility calculated from the measurements was observed in the samples with high content of In. The contribution to the mobility, directly related to the scattering of holes into In atoms, was determined, and the scattering crosssection was estimated. We observed a drastic increase in the scattering crosssection with the rise of In content, which can be explained by the resonance scattering of holes into the band of quasi-local states of In. This result can also be explained with the use of the Breit–Wigner formula. The location of the In states in the valence band was also calculated using the Kane model. 相似文献
93.
Tahar AyadYves Génisson Alexandre VerduMichel Baltas Liliane Gorrichon 《Tetrahedron letters》2003,44(3):579-582
The use of a trans α,β-epoxyaldehyde as a precursor of d-ribo-phytosphingosines was studied. The highly stereoselective alkylation of the aldehyde with a diorganozinc reagent was ensured through double asymmetric induction. The regioselective opening of the epoxide in turn gives access to an azide from which a C10 phytosphingosine can be easily prepared. 相似文献
94.
Fabien Chauny Richard Loulou Sylvie Sadones François Soumis 《The Journal of the Operational Research Society》1991,42(1):39-47
The two-dimensional cutting-stock problem consists of laying out a specified list of rectangular pieces on rectangular sheets, in such a way as to minimize the number of sheets used. A pattern is a combination of piece widths whose sum does not exceed the sheet's width. We present a new heuristic algorithm for this problem based on an approach with two phases: strategic phase and tactical phase. The first phase takes a global view of the problem and proposes a list of patterns to the second phase, which in turn is in charge of actually laying out these patterns on sheets. The strategic module relaxes the global problem to a one-dimensional cutting-stock problem and solves it using linear programming, while the tactical module is a recursive algorithm based on repeated knapsack operations and other heuristics. 相似文献
95.
Berhal F Esseiva O Martin CH Tone H Genet JP Ayad T Ratovelomanana-Vidal V 《Organic letters》2011,13(11):2806-2809
Two new atropisomeric electron-poor chiral diphosphine ligand analogues of SYNPHOS were prepared, and their electronic properties are described. These two ligands afforded high performance for the Rh-catalyzed asymmetric 1,4-addition of arylboronic acids to α,β-unsaturated carbonyl compounds at room temperature. 相似文献
96.
ABSTRACTWe investigated the alignment director of a frustrated cholesteric liquid crystal (CLC) confined in a planar cell. Three cells with different confinement ratio (c?=?d/p) (where p is the pitch and d is the cell thickness) are prepared. Under an electric field, the CLC planar texture is transformed into a cholesteric fingerprint (CF). The results showed that CF contrast depends on c. When c?≈?2, CLC stripes are formed by a periodic CF, with a period equal to the CLC pitch. The CF is developed and slowly extended to the whole cell surface along the rubbing direction and the contrast of the grating stripes keeps unchangeable. Yet, the CLC finger borders have a different light intensity. However, when c?≈?1, the CF contrast increases with time. When c?1, an isolated CF is obtained whose borders contrast change by varying the angle θ between the polarizer and the CFs. 相似文献
97.
This article describes an experimental procedure conducted to estimate and investigate the transient thermal contact conductance (or thermal contact resistance) between the electrodes and workpieces during resistance spot welding. A fine thermal metrology was developed to collect thermal histories near the welding region. Indeed, the electrode tip was instrumented with several interior microthermocouples for measuring the transient temperature response during the welding process. A simple mathematical model, using an inverse heat transfer method, was built for the estimation of the transient heat transfer coefficient from interior transient temperature measurements. A simple resistance welding case of two steel sheets was investigated. The initial transient values of thermal contact conductance were found to be in agreement with those observed in the dry copper–steel solid contact case. At the end of the process, the transient heat transfer coefficient reaches a high value corresponding to the best heat transfer phenomenon at the interface during the welding process. When the metal is melted, the contact quality increases due to the high-applied electrode force. Higher electrode force and heating temperatures produce lower thermal contact resistance. The results obtained show the capabilities and the power of the coupled thermal metrology and transient inverse technique developed to investigate thermal history of resistance spot welding. 相似文献
98.
Imen Ben Naceur Moez Guettari Ghazi Kassab Tahar Tajouri 《Journal of Macromolecular Science: Physics》2013,52(11):2171-2182
The aim of this work was to study the rheological behavior of water in-oil microemulsion formulated with AOT (sodium bis(2-ethylhexyl) sulfoccinate) in isooctane over a temperature range from 25°C to 55°C for the oil/AOT volume fraction φ m =0.1 and various AOT and H2O molar ratios, W0, ranging from 0 to 45. The apparent viscosity was measured vs. shear rate by a rotational concentric cylinder viscometer. It was shown that above s?1, the solutions utilized behaved as Newtonian liquids. The absolute viscosities were deduced from the shear stress- shear rate rheograms. For W0 < 17, the solutions behaved as simple fluids, where the viscosities decrease as the temperature increases. However, an opposite behavior was observed for W0 > 17; the viscosity remained constant and then increased above a critical temperature, Tc, depending on W0. For the molar ratio W0,c = 17; the studied viscosity remained constant, η(W0,c) = (1.17 ± 0.04) cP, for the temperature range studied. Thus, a simple–complex fluid transition was evident in the studied system. For the simple fluids, W0 < W0,c, the total activation energy vs. W0 showed three linear parts. The different slopes were attributed to the change of the microscopic structure of the formed micelles. For the critical molar ratio W0,c = 17, the total activation energy vanished. So, according to the Eyring lattice model, the jump of the formed micelles from one site to another was not permitted and the entire molecular groups were in vibration and rotation motions. For W0 > W0,c, where the formed micelles were fully hydrated, the relative viscosity of the studied solutions vs. temperature was fitted according a polynomial law, where the exponent was found to be dependent on W0. 相似文献
99.
100.
The paper deals with the existence of weak positive solutions for a new class of quasilinear singular elliptic systems involving critical Caffarelli–Kohn–Nirenberg exponent with sign-changing weight functions using the method of sub-super solutions. Our results are natural extensions from the previous ones in [3]. 相似文献