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41.
Computation of approximate optimal policies in a partially observed inventory model with rain checks
Alain Bensoussan Metin Cakanyildirim Suresh P. Sethi Ruixia ShiAuthor vitae 《Automatica》2011,(8):1589-1604
This paper proposes a new methodology to solve partially observed inventory problems. Generally, these problems have infinite-dimensional states that are conditional distributions of the inventory level. Our methodology involves linearizing the state transitions via unnormalized probabilities. It then uses an appropriate functional basis to represent the state. Considering the speed and stability of computations, we choose truncated Chebyshev polynomials as the basis. We use Fast Fourier Transforms along with an appropriate discretization of inventory levels to speed up the computations. These main ideas are blended to obtain an iterative algorithm to solve a partially observed inventory model with rain checks. In this model, the inventory manager (IM) does not know the inventory level when it is positive. Otherwise, the IM fully observes it. This model provides a context to illustrate our methodology, which applies to other such models. Although this model has been studied mathematically in the literature, the use of our algorithm provides a numerical approximation of the optimal order quantities. These are compared to the orders released under a base mean-stock policy, where the IM replaces the unobserved inventory level with its mean and applies the well-known base stock policy. We show numerically that the optimal order quantity is very close to the base mean-stock order quantity, when the variance of the inventory distribution is small. When the mean of the inventory distribution is large, the optimal order quantity is more than the base mean-stock quantity, and it is the other way around when the mean is small or negative. These insights are explained via uncertainty and information effects and their interplay. We expect this interplay to show up in other partially observed inventory models. 相似文献
42.
Synthesis and characterization of poly(N-(2-(thiophen-3-yl)methylcarbonyloxyethyl)maleimide) and its spectroelectrochemical properties 总被引:1,自引:0,他引:1
A new monomer; N-(2-(thiophen-3-yl)methylcarbonyloxyethyl) maleimide (NMT) was synthesized. The chemical structure of the
monomer was characterized by Nuclear Magnetic Resonance (1H-NMR) and Fourier Transform Infrared (FTIR) Spectroscopy. Electrochemical polymerization of NMT was performed in acetonitrile
(AN)/borontrifloride ethylether (BFEE) solvent mixture (1:1, v/v) where tetrabutylammonium tetrafluoroborate (TBAFB) was utilized
as the supporting electrolyte. The resulting conducting polymer was characterized by Fourier Transform Infrared (FTIR) Spectroscopy,
thermal analyses and Scanning Electron Microscopy (SEM). Electrical conductivity was measured by the four-probe technique.
The spectroelectrochemical behavior and switching ability of P(NMT) film were investigated by UV–Vis spectrophotometry. P(NMT)
revealed color changes between yellow and blue in the reduced and oxidized states respectively. 相似文献
43.
Optimization of Multireservoir Systems by Genetic Algorithm 总被引:1,自引:1,他引:0
Application of optimization techniques for determining the optimal operating policy of reservoirs is a major issue in water
resources planning and management. As an optimization Genetic Algorithm, ruled by evolution techniques, have become popular
in diversified fields of science. The main aim of this study is to explore the efficiency and effectiveness of genetic algorithm
in optimization of multi-reservoirs. A computer code has been constructed for this purpose and verified by means of a reference
problem with a known global optimum. Three reservoirs in the Colorado River Storage Project were optimized for maximization
of energy production. Besides, a real-time approach utilizing a blend of online and a posteriori data was proposed. The results
obtained were compared to the real operational data and genetic algorithm was found to be effective and can be utilized as
an alternative technique to other traditional optimization techniques. 相似文献
44.
Environmental concerns and limited resource of petroleum fuels have caused interests in the development of alternative fuels for internal combustion (IC) engines. For diesel engines, alcohols are receiving increasing attention because they are oxygenated and renewable fuels. Therefore, in this study, the effect of injection timing on the exhaust emissions of a single cylinder, naturally aspirated, four-stroke, direct injection diesel engine has been experimentally investigated by using methanol-blended diesel fuel from 0% to 15% with an increment of 5%. The tests were conducted for three different injection timings (15°, 20° and 25 °CA BTDC) at four different engine loads (5 Nm, 10 Nm, 15 Nm, 20 Nm) at 2200 rpm. The experimental test results showed that Bsfc, NOx and CO2 emissions increased as BTE, smoke opacity, CO and UHC emissions decreased with increasing amount of methanol in the fuel mixture. When compared the results to those of original injection timing, NOx and CO2 emissions decreased, smoke opacity, UHC and CO emissions increased for the retarded injection timing (15 °CA BTDC). On the other hand, with the advanced injection timing (25 °CA BTDC), decreasing smoke opacity, UHC and CO emissions diminished, and NOx and CO2 emissions boosted at all test conditions. In terms of Bsfc and BTE, retarded and advanced injection timings gave negative results for all fuel blends in all engine loads. 相似文献
45.
Sheet metal hydroforming is a deep drawing process that uses a pressure medium for load transmission. The process is mainly influenced by the control of the blank holder force and the fluid pressure. This report describes investigations of a newly developed process-control system. Process variables can be controlled by the sealing state of the tool. The detection is performed by a CCD-camera system that allows the continuous recording of occurring leakages. Different control strategies can be used to control the multiple process parameters. This paper describes the performance and the limits of the aforementioned technology. 相似文献
46.
This study investigates the effect of ZrO2 on phase transformation of alumina. Alumina and alumina–zirconia composite powders were produced by the precipitation method from aluminum sulfate and zirconium sulfate precursors. Precipitates obtained at 15 °C were dried at 80 °C for 72 h, and then calcinated at four different temperatures; 1000 °C, 1100 °C, 1200 °C and 1300 °C for 1 h. Powders calcinated at 1300 °C were pressed uniaxially and sintered at 1600 °C for 1 h. XRD and DSC analyses showed that the presence of zirconia retarded the transformation to α-alumina. SEM studies on the powders calcinated at 1300 °C revealed that both alumina and alumina–zirconia particles were 100–300 nm in size and of near spherical shape. Zirconia additions inhibited abnormal grain growth of alumina and provided homogeneous, equaxied grain structure. 相似文献
47.
In this paper, the compensation advantage of the first-generation current conveyor (CCI) over the second-generation current
conveyor (CCII) in tunable circuits is shown. For this purpose, a new floating frequency dependent negative resistor (FDNR)
simulator using three CCIs is presented and employed in a third-order high-pass filter. The compensation feature of the CCI
is shown for the proposed high-pass filter. As a second example, the presented compensation method is tested in a second-order
band-pass filter constructed with two CCIs. Applying the proposed compensation technique, the CCI-based circuits can operate
in lower biasing currents, which result in lower power consumption. 相似文献
48.
Precipitation of phosphate minerals from liquid swine manure is an established means of reducing the orthophosphate (OP) concentration. This project investigated the usefulness of a chemical equilibrium model, Visual Minteq, for prescribing the amendments needed to maximize struvite precipitation from liquid swine manure and thus reduce the OP phosphorus concentration. The actual concentrations of Mg(2+), Ca(2+), K(+), OP, NH(4)(+), alkalinity and pH from a liquid swine manure system were used as inputs to the model. The model was modified to remove species with extremely low formation rates, because they would not significantly precipitate in the reaction occurring in a short retention-time process such as those envisioned for swine manure struvite-formation reactors. Using the model's output, a series of 19-L reactors were used to verify the results. Verification results demonstrated that Visual Minteq can be used to pre-determine the concentration of amendments required to maximize struvite recovery. 相似文献
49.
Ipek Akin Mikinori Hotta Filiz Cinar Sahin Onuralp Yucel Gultekin Goller Takashi Goto 《Journal of the European Ceramic Society》2009,29(11):2379-2385
ZrB2–SiC composites were prepared by spark plasma sintering (SPS) at temperatures of 1800–2100 °C for 180–300 s under a pressure of 20 MPa and at higher temperatures of above 2100 °C without a holding time under 10 MPa. Densification, microstructure and mechanical properties of ZrB2–SiC composites were investigated. Fully dense ZrB2–SiC composites containing 20–60 mass% SiC with a relative density of more than 99% were obtained at 2000 and 2100 °C for 180 s. Below 2120 °C, microstructures consisted of equiaxed ZrB2 grains with a size of 2–5 μm and α-SiC grains with a size of 2–4 μm. Morphological change from equiaxed to elongated α-SiC grains was observed at higher temperatures. Vickers hardness of ZrB2–SiC composites increased with increasing sintering temperature and SiC content up to 60 mass%, and ZrB2–SiC composite containing 60 mass% SiC sintered at 2100 °C for 180 s had the highest value of 26.8 GPa. The highest fracture toughness was observed for ZrB2–SiC composites containing 50 mass% SiC independent of sintering temperatures. 相似文献
50.