排序方式: 共有83条查询结果,搜索用时 125 毫秒
51.
Mohamed Nazih Rhimi Riadh El-Bahi 《International Journal of Theoretical Physics》2008,47(4):1095-1111
The Landau problem of a charged particle in a plane with a uniform perpendicular magnetic field is analysed in two oscillator
modes. The coherent states for the problem have been found out using a general definition of displaced states. The time evolution
and the associated nonadiabatic geometric phase for both initially displaced and non-displaced wave packets have been studied.
The path integral is derived in a simple way through the calculation of Gaussian integrals via the concept of coherent state
wavefunctions. 相似文献
52.
Michihisa Koyama Riadh Sahnoun Nozomu Hatakeyama Hiromitsu Takaba Carlos A. Del Carpio 《Applied Surface Science》2008,254(23):7774-7776
Efficient development of highly functional porous materials, used as catalysts in the automobile industry, demands a meticulous knowledge of the nano-scale interface at the electronic and atomistic scale. However, it is often difficult to correlate the microscopic interfacial interactions with macroscopic characteristics of the materials; for instance, the interaction between a precious metal and its support oxide with long-term sintering properties of the catalyst. Multi-scale computational chemistry approaches can contribute to bridge the gap between micro- and macroscopic characteristics of these materials; however this type of multi-scale simulations has been difficult to apply especially to porous materials. To overcome this problem, we have developed a novel mesoscopic approach based on a porous structure simulator. This simulator can construct automatically irregular porous structures on a computer, enabling simulations with complex meso-scale structures. Moreover, in this work we have developed a new method to simulate long-term sintering properties of metal particles on porous catalysts. Finally, we have applied the method to the simulation of sintering properties of Pt on alumina support. This newly developed method has enabled us to propose a multi-scale simulation approach for porous catalysts. 相似文献
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54.
The present paper investigates Gaussian bilateral inequalities in view of solving related probability maximization problems. Since the function f representing the probability of satisfaction of a given Gaussian bilateral inequality is not concave everywhere, we first state and prove a necessary and sufficient condition for negative semi-definiteness of the Hessian. Then, the (nonconvex) problem of globally maximizing f over a given polyhedron in \(\mathbb {R}^{n}\) is adressed, and shown to be polynomial-time solvable, thus yielding a new-comer to the (short) list of nonconvex global optimization problems which can be solved exactly in polynomial time. Application to computing upper bounds to the maximum joint probability of satisfaction of a set of m independent Gaussian bilateral inequalities is discussed and computational results are reported. 相似文献
55.
Sahnoun R Fujimura Y Kabuto K Takeuchi Y Noyori R 《The Journal of organic chemistry》2007,72(21):7923-7929
The origin of conformational preference in alpha-cyano-alpha-fluorophenylacetic acid (CFPA) methyl ester that is a model system of alpha-cyano-alpha-fluoro-p-tolylacetic acid (CFTA) esters was theoretically investigated by means of DFT and MP2 calculations. Two stable conformations having the C-F bond syn and anti to the C=O bond, respectively, were obtained for CFPA methyl ester. A small energy difference (0.9 kcal mol-1 at the MP2(fc)/6-31++G(d,p)) was found between the two conformations. From the molecular orbital analysis based on the Natural Bond Orbital analysis and supported by calculations using the Orbital Deletion Procedure technique, we found that sigma-(sigma*+pi*)(C=O) and sigma-sigma*(Ph) and pi(Ph)-sigma* hyperconjugations are the main factors responsible for the conformational preference. The role of the fluorine atom on the stereogenic center was also clarified. 相似文献
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57.
Mariem Saada Hanen Wasli Ins Jallali Rim Kboubi Karl Girard-Lalancette Vakhtang Mshvildadze Riadh Ksouri Jean Legault Susana M. Cardoso 《Molecules (Basel, Switzerland)》2021,26(19)
The fractionation of the methanolic extract (MeOH-E) of Retama raetam (Forssk.) Webb & Berthel and further analysis by thin layer chromatography resulted in four fractions (F1, F2, F3 and F4) that, in parallel with the MeOH-E, were screened for antioxidant, cytotoxic, antidiabetic and antibacterial properties. In addition, chemical characterization of their bioactive molecules was performed using LC-DAD-ESI/MSn. The results indicated that F3 was the most promising regarding antioxidant and cytotoxicity abilities, possibly due to its richness in flavonoids class, particularly isoflavones. In turn, F1 was characterized by the presence of the most polar compounds from MeOH-E (organic acids and piscidic acid) and showed promising abilities to inhibit α-amylase, while F4, which contained prenylated flavonoids and furanoflavonoids, was the most active against the tested bacteria. The gathered results emphasize the distinct biological potentials of purified fractions of Retama raetam. 相似文献
58.
Amel Ben Abda Riadh Ben Fatma Damien Tromeur-Dervout 《Comptes Rendus Mathematique》2010,348(1-2):93-97
This Note is concerned with the severely ill-posed Cauchy–Helmholtz problem. This Cauchy problem being rephrased through an “interfacial” equation, we resort to an Aitken–Schwarz method for solving this equation. Numerical trials highlight the efficiency of the present method. 相似文献
59.
The container was introduced as a universal carrier for various goods in the 1960s and soon became a standard worldwide transportation.
The competitiveness of a container seaport is marked by different success factors, particularly the time in port for ships.
Operational problems of container terminals is divided into several problems, such as assignment of vessels, loading/unloading
and storage of the containers, quay cranes scheduling cite, planning yard cranes cite and assignment of storage containers
cite. In this work, the study will focus on piloting yard trucks. Two different types of vehicles can be used, namely automated
guided vehicles (AGVs) and lifting vehicles (LVs). An AGV receives a container from a quay crane and transports containers
over fixed path. LVs are capable of lifting a container from the ground by itself. The model that we consider is formulated
as a mixed integer programming problem, and the difficulty arises when the number of binary variables increases. There are
a lot of algorithms designed for mixed integer programming problem such as Branch and Bound method, cutting plane algorithm,
. . . By using an exact penalty technique we treat this problem as a DC program in the context of continuous optimization.
Further, we combine the DCA with the classical Branch and Bound method for finding global solutions. 相似文献
60.
Faraz Rajput Antonio Colantuoni Salim Bayahya Riadh Dhane Phillip Servio Milan Maric 《Journal of polymer science. Part A, Polymer chemistry》2018,56(21):2445-2457
Amphiphilic block copolymers of short poly(styrene) (PS) or poly(2,3,4,5,6-pentafluorostyrene) (PPFS) segments with comparatively longer poly(vinyl acetate) or poly(vinylpyrrolidone) (PVP) segments are synthesized using a 2-cyanopropan-2-yl N-methyl-N-(pyridin-4-yl)dithiocarbamate switchable reversible addition–fragmentation chain transfer (RAFT) agent toward application as kinetic gas hydrate inhibitors (KHIs). Polymerization conditions are optimized to provide water-soluble block copolymers by first polymerizing more activated monomers such as S and PFS to form a defined macro chain-transfer agent (linear degree of polymerization with conversion, comparatively low dispersity) followed by chain extensions with less activated monomers VAc or VP by switching to the deprotonated form of the RAFT agent. The critical micelle concentrations of these amphiphilic block copolymers (after VAc unit hydrolysis to vinyl alcohol units) are measured using zeta surface potential measurements to estimate physical behavior once mixed with the hydrates. A PS-poly(vinyl alcohol) block copolymer improved inhibition to 49% compared to the pure methane–water system with no KHIs. This inhibition was further reduced by 27% by substituting the PS with a more hydrophobic PPFS. A block copolymer of PS–PVP exhibited 20% greater inhibition than the PVP homopolymer and substituting PS with a more hydrophobic PPFS resulted in a 35% further decreased in methane KHI. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2445–2457, 56, 2445–2457 相似文献