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141.
Arash?KhatibiEmail author Golshid?Baharian Banafsheh?Behzad Sheldon?H.?Jacobson 《Mathematical Methods of Operations Research》2015,81(3):317-336
The sequential stochastic assignment problem (SSAP) allocates N workers to N IID sequentially arriving tasks so as to maximize the expected total reward. This paper studies two extensions of the SSAP. The first one assumes that the values of any two consecutive tasks are dependent on each other while the exact number of tasks to arrive is unknown until after the final arrival. The second extension generalizes the first one by assuming that the number of workers is also random. Optimal assignment policies for both problems are derived and proven to have the same threshold structure as the optimal policy of the SSAP. 相似文献
142.
143.
144.
Control of chaos in permanent magnet synchronous motor by using optimal Lyapunov exponents placement
Permanent Magnet Synchronous Motor (PMSM) experiences chaotic behavior for a certain range of its parameters. In this case, since the performance of the PMSM degrades, the chaos should be eliminated. In this Letter, the control of the undesirable chaos in PMSM using Lyapunov exponents (LEs) placement is proposed that is also improved by choosing optimal locations of the LEs in the sense of predefined cost function. Moreover, in order to provide the physical realization of the method, nonlinear parameter estimator for the system is suggested. Finally, to show the effectiveness of the proposed methodology, the simulation results for applying this control strategy are provided. 相似文献
145.
Vibration analysis of single-layered graphene sheets (SLGSs) is investigated using nonlocal continuum plate model. To this end, Eringens's nonlocal elasticity equations are incorporated into the classical Mindlin plate theory for vibrations of rectangular nanoplates. In contrast to the classical model, the nonlocal model developed in this study has the capability to evaluate the natural frequencies of the graphene sheets with considering the size-effects on the vibrational characteristics of them. Solutions for frequencies of the free vibration of simply-supported and clamped SLGSs are computed using generalized differential quadrature (GDQ) method. Then, molecular dynamics (MD) simulations for the free vibration of various SLGSs with different values of side length and chirality are employed, the results of which are matched with the nonlocal model ones to derive the appropriate values of the nonlocal parameter relevant to each boundary condition. It is found that the value of the nonlocal parameter is independent of the magnitude of the geometrical variables of the system. 相似文献
146.
Cabezas MG Bateni A Montanero JM Neumann AW 《Langmuir : the ACS journal of surfaces and colloids》2006,22(24):10053-10060
Drop shape techniques, such as axisymmetric drop shape analysis, are widely used to measure surface properties, as they are accurate and reliable. Nevertheless, they are not applicable in experimental studies dealing with fluid configurations that do not present an apex. A new methodology is presented for measuring interfacial properties of liquids, such as surface tension and contact angles, by analyzing the shape of an axisymmetric liquid-fluid interface without use of apex coordinates. The theoretical shape of the interface is generated numerically as a function of surface tension and some geometrical parameters at the starting point of the interface, e.g., contact angle and radius of the interface. Then, the numerical shape is fitted to the experimental profile, taking the interfacial properties as adjustable parameters. The best fit identifies the true values of surface tension and contact angle. Comparison between the experimental and the theoretical profiles is performed using the theoretical image fitting analysis (TIFA) strategy. The new method, TIFA-axisymmetric interfaces (TIFA-AI), is applicable to any axisymmetric experimental configuration (with or without apex). The versatility and accuracy of TIFA-AI is shown by considering various configurations: liquid bridges, sessile and pendant drops, and liquid lenses. 相似文献
147.
Single crystals of [mppyr][NdI6] and [bmpyr][NdI6][Tf2N] are the first surprising examples of how the cation of an ionic liquid determines the compound formation from an ionic liquid. Depending upon the variation of the length of the alkyl chain of the quaternary pyrrolidinium cation (C3 and C4, respectively), incorporation of the anion of the ionic liquid, [Tf2N]-, can either be evoked or suppressed. 相似文献
148.
The first homoleptic alkaline earth bis(trifluoromethanesulfonyl)imide (Tf2N) complexes [mppyr]2[Ca(Tf2N)4], [mppyr]2[Sr(Tf2N)4], and [mppyr][Ba(Tf2N)3] were crystallized from a solution of the respective alkaline earth bis(trifluoromethanesulfonyl)imide and the ionic liquid [mppyr][Tf2N] (mppyr = 1,1-N-methyl-N-propylpyrrolidinium). In the calcium and strontium compounds, the alkaline earth metal (AE) is coordinated by four bidentately chelating Tf2N ligands to form isolated (distorted) square antiprismatic [AE(Tf2N)4]2- complexes which are separated by N-methyl-N-propylpyrrolidinium cations. In contrast, the barium compound, [mppyr][Ba(Tf2N)3], forms an extended structure. Here the alkaline earth cation is surrounded by six oxygen atoms belonging to three Tf2N- anions which coordinate in a bidentate chelating fashion. Three further oxygen atoms of the same ligands are linking the Ba2+ cations to infinite (infinity)(1)[Ba(Tf2N)3] chains. 相似文献
149.
Kamel Hooman Alireza Pourshaghaghy Arash Ejlali 《应用数学和力学(英文版)》2006,27(5):617-626
The viscous dissipation effect on forced convection in a porous saturated circular tube with an isoflux wall is investigated on the basis of the Brinkman flow model. For the thermally developing region, a numerical study is reported while a perturbation analysis is presented to find expressions for the temperature profile and the Nusselt number for the fully developed region. The fully developed Nusselt number found by numerical solution for the developing region is compared with that of asymptotic analysis and a good degree of agreement is observed. 相似文献
150.
Arash Daghighi Kiumars Ghowsi Mohammad Reza Nilforoushan 《Journal of solution chemistry》2010,39(7):959-966
A new automated technique was developed for online monitoring of the conductance of a conductive type of cell. Shining metal
electrodes were used for the conductometry measurements and the frequency of the input signal was swept from a few hertz to
1 MHz. A theoretical model was developed based on the voltage dividing technique. The model was in good agreement with the
experimental results. Conductances of simple electrolytes such as HCl and micellar solutions were compared. Solutions of HCl
with concentrations as low as 45 μmol⋅L−1 were investigated. Critical micellar concentrations of two types of micelles, SDS and CPC, were also measured. It was shown
that this voltage divider circuit can be used for automated online conductometric titrations. 相似文献