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Any solution to facility location problems will consider determining the best suitable locations with respect to certain criteria. Among different types of location problems, involving emergency service system (ESSs) are one of the most widely studied in the literature, and solutions to these problems will mostly aim to minimize the mean response time to demands. In practice, however, a demand may not be served from its nearest facility if that facility is engaged in serving other demands. This makes it a requirement to assign backup services so as to improve response time and service quality. The level of backup service is a key, strategic-level planning factor, and must be taken into consideration carefully. Moreover, in emergency service operations conducted in congested demand regions, demand assignment policy is another important factor that affects the system performance. Models failing to adopt sufficient levels of backup service and realistic demand assignment policies may significantly deteriorate the system performance.Considering the classic p-median problem (pMP) location model, this paper investigates the effects of backup service level, demand assignment policy, demand density, and number of facilities and their locations on the solution performance in terms of multiple metrics. For this purpose, we adopt a combined optimization and simulation approach. We will first modify the classic pMP to account for distances to backup services. Next, we employ a discrete event simulation to evaluate the performance of location schemes obtained from the deterministic mathematical model. Our results provide insights for decision-makers while planning ESS operations. 相似文献
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Wai CM Kulyako Y Yak HK Chen X Lee SJ 《Chemical communications (Cambridge, England)》1999,(24):2533-2534
Strontium (Sr(2+)) can be selectively extracted from aqueous solutions into supercritical fluid CO(2) at 60 °C and 100 atm with dicyclohexano-18-crown-6 (DC18C6) using CF(3)(CF(2))(6)CO(2) (-) (PFOA(-)) or CF(3)(CF(2))(6)CF(2)SO(3) (-) (PFOSA(-)) as a counter anion; at a mole ratio of Sr(2+) : DC18C6 : PFOA(-) = 1:10:50, the extraction of Sr (5.6 × 10(-5) M) from water at pH 3 is near quantitative whereas Ca(2+) and Mg(2+) at equal concentration are only extracted to a level of 7 and 1%, respectively; PFOSA(-) is an effective counter anion for selective extraction of Sr(2+) from 1.3 M HNO(3) with DC18C6 in supercritical CO(2). 相似文献
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Revenue management can be used in many industries where there is a limited, perishable capacity and the market can be segmented. In this paper we focus on the sales of event tickets in the Sports and Entertainment industries, where tickets are sold exclusively as season tickets initially or as single events later in the selling horizon. We specifically study the optimal time to switch between these market segments dynamically as a function of the state of the system. Under Poisson demand processes, we find the optimal switching time is a set of time thresholds that depends on the remaining inventory and time left in the horizon. We use numerical experiments to show that significant profit improvements can be obtained by dynamically deciding the optimal switch time over the case when the date is announced in advance. We also study an extension where ??early switch to a low-demand event?? is allowed. 相似文献
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M. Yakıt Ongun 《中国科学A辑(英文版)》2007,50(2):217-230
In this paper we consider the nonselfadjoint (dissipative) Schrödinger boundary value problem in the limit-circle case with an eigenparameter in the boundary condition. Since the boundary conditions are nonselfadjoint, the approach is based on the use of the maximal dissipative operator, and the spectral analysis of this operator is adequate for the boundary value problem. We construct a selfadjoint dilation of the maximal dissipative operator and its incoming and outgoing spectral representations, which make it possible to determine the scattering matrix of the dilation. We construct a functional model of the maximal dissipative operator and define its characteristic function in terms of solutions of the corresponding Schrödinger equation. Theorems on the completeness of the system of eigenvectors and the associated vectors of the maximal dissipative operator and the Schrödinger boundary value problem are given. 相似文献
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Wall thickness of siliceous MCM‐41 could be controlled systematically up to 36.1 Å. A reasonable model explaining formation of thicker MCM‐41 walls, not enlarging pore channel is proposed on the basis of TGA and 13C MAS NMR data of samples. Thermal restructuring process under mild basic condition favors the silica redeposition on silica wall and building up thicker wall. Most mesostructure of calcined MCM‐41 with thicker wall was retained even after hydrothermal treatment in boiling water for 14 days. To our best knowledge, the excellent hydrothermal stability of the MCM‐41 silica reported herein has not been described before and facilitates practical applications of mesoporous molecular sieves in future. 相似文献
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Dry ice-originated supercritical and liquid carbon dioxide extraction of organic pollutants from environmental samples 总被引:1,自引:0,他引:1
Packed in a high-pressure vessel and under calculated conditions, dry ice can be used as a source of carbon dioxide for supercritical CO2 extraction or liquid CO2 of organic compounds from environmental samples. Coupled with a fluid modifier such as toluene, dry ice-originated supercritical CO2 (Sc CO2) achieves quantitative extraction of many volatile organic compounds (VOCs) and semivolatile organic compounds (SOCs) including polycyclic aromatic hydrocarbons (PAHs), n-alkanes, and polychlorinated biphenyls (PCBs) from solid matrices. Compared to contemporary manual or automated supercritical fluid extraction (SFE) technologies, this novel technique simplifies SFE to a minimum requirement by eliminating the need of a high-pressure pump and any electrical peripherals associated with it. This technique is highly suitable to analytical areas where sample preservation is essential but difficult in the sampling field, or where sample collection, sample preparation, and analysis are to be done in the field. 相似文献
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Mediha Kök Şahin Ata Zehra Deniz Yakıncı Yıldırım Aydoğdu 《Journal of Thermal Analysis and Calorimetry》2018,133(2):845-850
In the present study, a ternary CuAl-based alloy was produced by adding 2% chromium, niobium, titanium and hafnium instead of 2% copper from the Cu88Al12 (% in mass) shape memory alloy, and the phase changes in the alloy were examined. As a result of the X-ray analyses performed at room temperature, the α phase, which is rich in copper, was detected in the main sample, i.e., the Cu88Al12 alloy, and the β 1 1 and γ 1 ? phases were detected in the four of the Cu86Al12Cr2, Cu86Al12Nb2, Cu86Al12Ti2 and Cu86Al12Hf2 alloys. All of phases were clearly seen in SEM images. As a result of the mapping performed during chemical analysis, it was observed clearly that there appeared a precipitation phase in the Cu86Al12Cr2, Cu86Al12Nb2, Cu86Al12Ti2 alloys due to the additions. It was also observed that the additions were effective in forming a martensite phase in the Cu88Al12 alloy. In differential scanning calorimetry (DSC) measurements, which were taken to support these measurements, no martensitic phase transformations were detected in dual primary alloy (Cu88Al12); however, a clear martensite phase transformation was detected in ternary alloys (Cu86Al12Cr2, Cu86Al12Nb2, Cu86Al12Ti2 and Cu86Al12Hf2) in the first DSC measurement. Then, when the DSC cycle was applied to the ternary alloy, both the austenite transformation and martensite transformation temperatures were clearly seen, and it was claimed that all the alloys showed high-temperature shape memory alloy properties. 相似文献
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Observation of autosoliton propagation in a dispersion-managed optical transmission system controlled by in-line nonlinear fiber loop switches is reported for what is believed to be the first time. The system is based on a strong dispersion map with large amplifier spacing. Operation at transmission rates of 10 and 40 Gbits/s is demonstrated. 相似文献