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排序方式: 共有131条查询结果,搜索用时 15 毫秒
21.
Stratos Ioannidis Oualid Jouini Angelos A. Economopoulos Vassilis S. Kouikoglou 《Annals of Operations Research》2013,209(1):115-138
We consider problems of inventory and admission control for make-to-stock production systems with perishable inventory and impatient customers. Customers may balk upon arrival (refuse to place orders) and renege while waiting (withdraw delayed orders) during stockouts. Item lifetimes and customer patience times are random variables with general distributions. Processing, setup, and customer inter-arrival times are however assumed to be exponential random variables. In particular, the paper studies two models. In the first model, the system suspends its production when its stock reaches a safety level and can resume later without incurring any setup delay or cost. In the second model, the system incurs setup delays and setup costs; during stockouts, all arriving customers are informed about anticipated delays and either balk or place their orders but cannot withdraw them later. Using results from the queueing literature, we derive expressions for the system steady-state probabilities and performance measures, such as profit from sales and costs of inventory, setups, and delays in filling customer orders. We use these expressions to find optimal inventory and admission policies, and investigate the impact of product lifetimes and customer patience times on system performance. 相似文献
22.
Ioannis G. Tigelis Jean-Yves Raguin Zisis C. Ioannidis George P. Latsas Angelos J. Amditis 《International Journal of Infrared and Millimeter Waves》2008,29(4):432-442
The dispersion characteristics of a circular cylindrical waveguide with periodic surface corrugations consisting of rectangular
grooves with smoothing are examined using the Space Harmonic Method (SHM). The whole structure is divided into two regions,
one describing the propagation volume and one inside the grooves. In the first region, the Floquet theorem is applicable and
the field distribution is expressed as a summation of spatial Bloch components, whereas in the second one an appropriate Fourier
expansion of standing waves is used. Applying the boundary conditions an infinite system of equations is obtained, which is
solved numerically by truncation. Several cases are considered, including the limiting cases of a sinusoidal and a rectangular
corrugation profile, to check the accuracy of the method proposed as well as its dependence on the corrugation profile. Numerical
results are presented only for transverse magnetic modes, although the formalism can be easily extended to include all kinds
of waves that can in principle propagate in such a structure. 相似文献
23.
Georghiou Angelos Kuhn Daniel Wiesemann Wolfram 《Computational Management Science》2019,16(4):545-576
Computational Management Science - Dynamic decision-making under uncertainty has a long and distinguished history in operations research. Due to the curse of dimensionality, solution schemes that... 相似文献
24.
Global approximation to arbitrary cost functions: A Bayesian approach with application to US banking
Panayotis G. Michaelides Efthymios G. Tsionas Angelos T. Vouldis Konstantinos N. Konstantakis 《European Journal of Operational Research》2015
This paper proposes and estimates a globally flexible functional form for the cost function, which we call Neural Cost Function (NCF). The proposed specification imposes a priori and satisfies globally all the properties that economic theory dictates. The functional form can be estimated easily using Markov Chain Monte Carlo (MCMC) techniques or standard iterative SURE. We use a large panel of U.S. banks to illustrate our approach. The results are consistent with previous knowledge about the sector and in accordance with mathematical production theory. 相似文献
25.
The novel separation of a 3-hydroxyproline containing a semi-synthetic macrocyclic antifungal agent from its structurally related 4-hydroxyproline isomer using capillary electrochromatography (CEC) is described. The molecular weight of the two compounds is 1093 Daltons and they differ only in the placement of a proline -OH group. The separation is achieved using capillaries packed or coated with ODS particles (C18) or with glycerol bound to silica through a carbon chain linker. The presence of a transition metal (Ni(II), Ag(I), Zn(II), or Cu(II)) as buffer additive in the phosphate buffer (pH=2.5):CH3CN (75:25, v/v) is essential to achieve a baseline separation. HPLC columns packed with similar ODS particles showed no selectivity. Capillaries packed or coated with C18 material under similar conditions showed partial selectivity compared to the glycerol capillaries. Some fundamental aspects of CEC, such as capillary temperature, applied voltage, and buffer composition were varied in order to study the mechanism of the separation. This mechanistic study included the testing of first and second row transition metal ions (individually or in combination), the use of organic solvents, the use of an ion pair reagent, and the use of β- and γ-cyclodextrin to assess the impact on the separation. The resolution was dependent on the metal ion concentration and is consistent with a mechanism of metal-oxygen complexation through the hydroxyl groups of the two isomers and glycerol. 相似文献
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One‐Dimensional Arsenic Allotropes: Polymerization of Yellow Arsenic Inside Single‐Wall Carbon Nanotubes
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Martin Hart Dr. Ji Chen Prof. Angelos Michaelides Prof. Andrea Sella Prof. Milo S. P. Shaffer Dr. Christoph G. Salzmann 《Angewandte Chemie (International ed. in English)》2018,57(36):11649-11653
The pnictogen nanomaterials, including phosphorene and arsenene, display remarkable electronic and chemical properties. Yet, the structural diversity of these main group elements is still poorly explored. Here we fill single‐wall carbon nanotubes with elemental arsenic from the vapor phase. Using electron microscopy, we find chains of highly reactive As4 molecules as well as two new one‐dimensional allotropes of arsenic: a single‐stranded zig‐zag chain and a double‐stranded zig‐zag ladder. These linear structures are important intermediates between the gas‐phase clusters of arsenic and the extended sheets of arsenene. Raman spectroscopy indicates weak electronic interaction between the arsenic and the nanotubes which implies that the formation of the new allotropes is driven primarily by the geometry of the confinement. The relative stabilities of the new arsenic structures are estimated computationally. Band‐gap calculations predict that the insulating As4 chains become semiconducting, once converted to the zig‐zag ladder, and form a fully metallic allotrope of arsenic as the zig‐zag chain. 相似文献