1,721,194 research outputs found
Petri net modeling and scheduling for cyclic job shops with blocking
No full textCyclic scheduling is an effective scheduling method in the repetitive discrete manufacturing environment. We investigate the scheduling problem for general cyclic job shops with blocking where each machine has an input buffer of finite capacity. We develop Petri net models for the-shops. We propose a sequential buffer control policy that restricts the jobs to enter the input buffer of the next machine in a specified sequence. We show that the scheduling model of a cyclic shop with finite buffers under such a buffer control policy can be transformed into a scheduling model of a cyclic shop with no buffer that can be modeled as a timed marked graph. In addition, we characterize the structural properties for deadlock detection. Finally, we present a mixed integer programming model to find an optimal deadlock-free schedule that minimizes the cycle time. (C) 1998 Elsevier Science Ltd. All rights reserved.
A tabu search procedure for periodic job shop scheduling
No full textWe consider job shops where an identical mixture of items is repetitively produced. We discuss the sequencing problem that finds the processing order at each machine that maximizes the throughput rate of the mixtures or equivalently minimizes the cycle time. We present an effective tabu search procedure for the problem. To do this, we characterize the neighborhood structure that generates feasible solutions by reversing the order of two operations on a critical circuit in the associated graph. We develop an efficient method of approximately evaluating the cycle times of neighborhood solutions. Computational results are reported. Copyright (C) 1996 Elsevier Science Lt
Synthesis, Characterization and Electrical Properties of the Novel Polymer Electrolyte Based on Polyesters Containing EO Moiety
No full textAn intelligent tutoring system for introductory C language course
No full textIn this paper, we describe a system called C-Tutor, an intelligent tutoring system (ITS) for novice C programmers. A program analyzer is the most important part of the ITS for programming. Our program analyzer is a compound of a reverse engineering system and a didactic system. Since a novice program usually contains many bugs, information about the intentions of the programmer is inevitable to recognize a buggy program. In our approach, the intentions of a programmer are automatically extracted as a problem description from a sample program by a reverse engineering system called GOES (GOal Extraction System). Based on the problem description, students' programs are recognized by a didactic system called ExBug (Execution-guided deBugger). As a learning environment, Curriculum Network constructs the knowledge base as genetic graphs to teach programming. C-Tutor is a complete ITS which provides both a program analyzer and a learning environment. Tested with real students' programs, program analyzer gives acceptable recognition results. Program analyzer and learning environment are closely related so that students can learn C language during programming. New problems can be easily set because GOES automatically generates problem descriptions for program analyzers. This makes C-Tutor a more practical tutoring system for a real C language course. (C) 1997 Elsevier Science Ltd
Electrical properties of CuInSe2-films prepared by evaporation of Cu2Se and In2Se3 compounds
No full textWe prepared CuInSe2 films by evaporating In2Se3 and Cu2Se compounds instead of elemental sources, The resulting CuInSe2 film grown at 680 degrees C had a smooth and dense microstructure with the grain size of 2 similar to 3 mu m. But the CuInSe2 films were Cu-rich, with a low resistivity of about 0.1 Omega cm. So we conducted H-2 post annealing to control the electrical resistivity and composition of CuInSe2 films. In a H-2 atmosphere, the resistivity increased to about 100 Omega cm by annealing at 350 degrees C for 1 h. The resistivity decreased again when the annealing temperature was above 350 degrees C, This resistivity change might be related to the contents of Cu, In, Se atoms and the valency states of Cu and In ions in the films. We discussed the reason of resistivity change caused by H-2 post annealing in this paper
Effect of first-stage temperature on Cu(In,Ga)Se-2 solar cells using the evaporation of binary selenide compounds
No full textCu(In,Ga)Se-2 films were prepared by a three-stage process using the evaporation of In2Se3, Ga2Se3, Cu2Se, and Se. In the first stage, the (In,Ga)(2)Se-3 layer was deposited at the substrate temperatures of 150degreesC and 325degreesC by the evaporation of In2Se3, Ga2Se3, and Se. The CIGS film had small grains with a bi-layer morphology at 150degreesC, while the film had large grains without the bi-layer morphology at 325degreesC. As the first-stage temperature increased, the CdS/ Cu(In,Ga)Se2 solar efficiency was improved from 9.3% to 11.7% for 0.21 cm 2 active area. The efficiency improvement was attributed to the reduction of the recombination at the CdS/ Cu(In,Ga)Se-2 interface and recombination within Cu(In,Ga)Se-2 film bulk due to the increase of Cu(In,Ga)Se-2 grain size. These findings were supported by the increased hole density, reduced reverse saturation current, and enhanced spectral response with increasing the first-stage temperature. (C) 2002 Elsevier Science B.V. All rights reserved
Analytic initialization of nonequilibrium iodine and xenon distributions for core transient simulation
No full textIn a core transient simulation, the initial condition of the simulation should be consistent with the real core state. The initial iodine and xenon distributions, which cannot be measured in the core, have significant effects on the transient with xenon dynamics of a pressurized water reactor. In simulating the transient starting from a nonequilibrium xenon state, accurate initialization of the nonequilibrium iodine and xenon distribution is essential to predict the core transient behavior. An initialization method that uses the iodine and xenon states to predict a core transient starting from a nonequilibrium xenon condition is developed through the analytical treatment of the relationship between power and the iodine and xenon distributions. An application of this method tr;provided by simulating a transient in the start-up test of Yonggwang Unit 3
Pilot-scale SBR and MF operation for the removal of organic and nitrogen compounds from greywater
No full textA pilot plant of SBR (Sequencing Batch Reactor) and MF (microfiltration) process was operated in order to treat and reuse the greywater produced from an office building. The performance of SBR for greywater was satisfactory as the effluent had 20 mg/l, 5 mg/l, and 0.5 mg/l of SCOD, BOD, and ammonia, respectively. The cyclic operation of SBR used in this study proved more effective in nitrification and denitrification than the conventional SBR operation. However, the most effective mode was step-feed SBR for denitrification. The decanting system of this SBR discharged the effluent fairly well without sludge washout. However, it was difficult to maintain constant concentration of suspended solid from the SBR process. Thus, additional filtration was needed to get adequate water quality for water reuse. MF could remove residual suspended solids and pathogens as well from the SBR effluent. The suspended solids of final effluent were around 1 mg/l and allowed using the treated water for some purposes. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.This research is supported by KOWACO and SAM KWANG AQUA-CLEAR, INC. The author is grateful for their valued assistance
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