1,722,046 research outputs found
ON THE SCORE FUNCTIONS OF THE 2-SAMPLE LOCALLY OPTIMUM RANK TEST STATISTIC FOR RANDOM SIGNALS IN ADDITIVE NOISE
No full textIn this correspondence the test statistic of the two-sample locally optimum rank detector is derived for weak random signals in additive noise. It is shown that the two-sample locally optimum rank detector for random signals has interesting similarities to the one-sample locally optimum rank detector for random signals. The detector may also be viewed as a generalization of the two-sample locally optimum rank detector for known signals. Some examples and properties of the score functions constituting the locally optimum rank test statistic are investigated.Korea Science and Engineering
Foundation (KOSEF) under Grant 941-0900-040-2
Coherent Nuclear Wave Packets in Q States by Ultrafast Internal Conversions in Free Base Tetraphenylporphyrin
No full textPersistence of vibrational coherence in electronic transition has been noted especially in biochemical systems. Here, we report the dynamics between electronic excited states in free base tetraphenylporphyrin (H2TPP) by time-resolved fluorescence with high time resolution. Following the photoexcitation of the B state, ultrafast internal conversion occurs to the Q(x) state directly as well as via the Q(y) state. Unique and distinct coherent nuclear wave packet motions in the Q(x) and Q(y) states are observed through the modulation of the fluorescence intensity in time. The instant, serial internal conversions from the B to the Q(y) and Q(x) states generate the coherent wave packets. Theory and experiment show that the observed vibrational modes involve the out-of-plane vibrations of the porphyrin ring that are strongly coupled to the internal conversion of H2TPP.1110sciescopu
Parallel processing of 3D rigid-viscoplastic finite element analysis using domain decomposition and modified block Jacobi preconditioning technique
No full textIn three-dimensional finite element analysis of forging processes, a large number of elements is needed for improvement in the accuracy of solutions. This results in increased computation time and memory requirements, which still remain major problems for effective three-dimensional metal forming analyses. In the present study, a parallel computation technique was adopted for rigid-viscoplastic approach in order to increase the computational efficiency. The domain decomposition algorithm and preconditioned conjugate gradient (CG) iterative solver were used for parallel computation, and a new preconditioning technique was proposed. In the proposed preconditioning technique, the block Jacobi preconditioner was applied to interior degrees of freedom with the Jacobi preconditioner being applied to interface degrees of freedom of each sub-domain. Using the proposed parallel computation and preconditioning techniques, simple upsetting simulations of a cubic type workpiece were carried out. From simulation results, it was found that the proposed method is more efficient compared to both the conventional CG and the Jacobi preconditioned conjugate gradient (J-PCG) solving techniques. (C) 2002 Elsevier Science B.V. All rights reserved.The authors wish to thank the Korean Research and Development Information Center (KORDIC) for providing invaluable computing time in CRAY T3E-900 parallel super computer
Three-dimensional thermo-viscoplastic analysis of compression molding of sheet molding compounds with fiber volume fraction prediction
No full textSMC (Sheet Molding Compounds) is a thermosetting material which consists of unsaturated polyester resin and other additives reinforced with randomly distributed chopped fiberglass strands. While the incorporation of chopped short fiberglass strands into the thermosetting SMC resin has added strength and stiffness to molded parts, a better understanding of overall effects of SMC resin components, mold geometries and processing variables on flow characteristics and mechanical performance of the molded parts is complicated. Thus, a three-dimensional rigid thermo-viscoplastic finite element program including chemical reaction and fiber volume fraction prediction was developed in the present study and applied to the analysis of compression molding of SMC charge. The rheological characteristics of the SMC charge were modeled by a power law as a function of strain rate and temperature based on compression test data. To investigate the effects of dwelling time, mold closing speed, friction, and mold temperature on mold filling and curing, series of three-dimensional molding simulations of the SMC charge block were carried out using various molding parameters such as mold closing speeds of 45 mm/min and 250 mm/min, mold temperatures of 130 degrees C and 150 degrees C, and constant shear frictional factors of 0.1 and 0.8. The calculated fiber volume fraction distribution for plane strain condition was compared to the experimental result obtained from scanning electron microscope available in the literature. From this study, it was found that the currently developed three-dimensional finite element program coupled with heat transfer and chemical reaction can provide valuable information in understanding flow characteristics, fiber volume fraction distribution, and the curing behavior of SMC compression molding in detail.The authors thank the grant from the Cray Research. Inc.
under which this work was possible
MULTI-PROJECT SCHEDULING WITH EXPLICIT LATENESS COSTS
No full textWe propose a heuristic procedure for planning and scheduling multiple projects subject to limited resource availabilities. We depart from previous research in that explicit lateness costs for each project are considered. Our procedure involves aggregate analysis using linear programming to determine target resource loading profiles for each project that optimize trade-offs of lateness costs among projects, followed by detailed multi-project scheduling consistent with the target profiles. Target profiles and detailed schedules are iteratively modified through N iterations, where N is the number of projects. The procedure can be used to jointly schedule previously committed and newly proposed projects, as well as to assign due dates to proposed projects. We compare the performance of our procedure to that of the traditional minimum slack heuristic, as well to a simple extension of the minimum slack rule that accounts for lateness costs. On a set of 60 multi-project test problems adapted from the Patterson set of single-project problems, results are very favorable for our proposed algorithm.X1113sciescopu
Three-dimensional finite element analysis of non-isothermal shape rolling
No full textIn shape rolling, prediction of deformations such as spread, elongation, and draft, pressure distribution between rolls and the workpiece, and forming load is important in designing proper roll grooves and pass sequences. Since initial temperature of the workpiece is in the range 11001200 degreesC, temperature distribution of the workpiece is a significant factor which influences the mechanical properties due to variation of microstructure in rolled products. Thus, variation of the workpiece temperature distribution during shape rolling should be considered at the design stage. In the present study, a three-dimensional finite element program for analyzing shape rolling processes considering heat transfer is developed based on rigid thermo-viscoplastic approach. Using the developed program, square-oval, round-oval, and square-diamond passes were simulated at different friction conditions with and without temperature effects. From the present simulation results, the non-isothermal and frictional effects on deformed shape, stress and temperature distributions of the workpiece, and forming loads were investigated. Also, in order to apply the developed program to more complex rolling problems, shape rolling of H-beam was simulated. The developed program will be useful in generating the database for designing roll pass and profile design in shape rolling. (C) 2002 Elsevier Science B.V. All rights reserved
SCHEDULING OF STORAGE-RETRIEVAL ORDERS UNDER A JUST-IN-TIME ENVIRONMENT
No full textWe consider the problem of scheduling storage and retrieval orders under dual-command operations in a unit-load automated storage/retrieval system. The objective is to minimize the weighted sum of earliness and tardiness penalties about a common due date. We propose four heuristics based upon a two-step approach where dual-command cycles are formed first and then optimally scheduled. A mixed-integer programming model is also formulated to obtain an optimal solution. Performances of the heuristics are compared in the simulation tests. Computational results show that some heuristics perform favourably.X117sciescopu
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