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In this study we compare the recording performance of 4 mm metal particle (MP) and Ba-ferrite (BF) tapes using helical scan digital audio tape (DAT) mechanisms and heads. At low bit densities the MP tapes have higher output signal and SNR compared with the BF tapes, but at high bit densities the reverse is true. This superior recording performance of the BF tapes, along with their immunity to environmental corrosion, recommends them as the media of choice for 4 mm data recording applications. 相似文献
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Klaus Jansen Lorant Porkolab 《Journal of Algorithms in Cognition, Informatics and Logic》2002,45(2):592
We study preemptive and non-preemptive versions of the general multiprocessor job shop scheduling problem: Given a set of n tasks each consisting of at most μ ordered operations that can be processed on different (possibly all) subsets of m machines with different processing times, compute a schedule (preemptive or non-preemptive, depending on the model) with minimum makespan where operations belonging to the same task have to be scheduled according to the specified order. We propose algorithms for both preemptive and non-preemptive variants of this problem that compute approximate solutions of any positive ε accuracy and run in O(n) time for any fixed values of m, μ, and ε. These results include (as special cases) many recent developments on polynomial time approximation schemes for scheduling jobs on unrelated machines, multiprocessor tasks, and classical open, flow and job shops. 相似文献
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Markus Poppenberg Klaus Schmitt Zhi-Qiang Wang 《Calculus of Variations and Partial Differential Equations》2002,14(3):329-344
Variational techniques are applied to prove the existence of standing wave solutions for quasilinear Schr?dinger equations
containing strongly singular nonlinearities which include derivatives of the second order. Such equations have been derived
as models of several physical phenomena. The nonlinearity here corresponds to the superfluid film equation in plasma physics.
Direct methods of the calculus of variations and minimax methods like the Mountain Pass Theorem are used. The difficulties
introduced by the nonconvex functional are substantially different from the semilinear case.
Received: 21 March 2000 / Accepted: 23 February 2001 / Published online: 25 June 2001 相似文献