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191.
This paper is concerned with characterizing the transient behavior of general queueing systems, which is widely known to be notoriously difficult. The objective is to develop a statistical methodology, integrated with extensive offline simulation and preliminary queueing analysis, for the estimation of a small number of transfer function models (TFMs) that quantify the input–output dynamics of a general queueing system. The input here is the time-varying arrival rate of jobs to the system; the time-dependent output performances include the departure rate of jobs and the mean of the work in process (i.e., number of jobs in the system). The resulting TFMs are difference equations, like the discrete approximations of the ordinary differential equations provided by an analytical approach, while possessing the high fidelity of simulation. Our method is expected to overcome the shortcomings of the existing transient analysis approaches, i.e., the computational burden of simulation and the lack of fidelity of analytical queueing models. 相似文献
192.
An Experimental Technique for Spalling of Concrete 总被引:1,自引:0,他引:1
The spalling strength of concrete is measured by examining the strain wave profiles in a polymer buffer bar behind the slender
concrete bar specimen placed between a large diameter (Φ100 mm) Hopkinson bar and the buffer bar. The experimental results indicate that the spalling strength is related to not only
the compressive strength of concrete but also the impact velocities (the loading rates). The rate effect of spalling strength
mainly results from the different cracking paths in concrete under different impact velocities. However when the input compressive
stress to specimen exceeds the threshold required to trigger the compressive damage, the spalling strength decreases due to
the evolution and cumulation of compressive damage in concretes. The repeated impact loading experiments indicate that damage
plays an important role in the spallation process of concrete. The high speed video of the spalling fracture process shows
that multiple spalling fractures may occur in the scab and damage accumulation resulting from stress wave propagation in scab
is the main reason for the producing of multiple spallations. 相似文献
193.
A newly developed multi-axial testing technique for sheet materials is employed to investigate the inelastic response of a temper-rolled stainless steel 301LN under isothermal quasi-static loading conditions at room temperature. The experimental technique consists of a flat sheet specimen, which is subject to combinations of shear and normal loading using a custom-made dual-actuator system. The large deformation behavior under monotonic loading is determined along more than 20 distinct radial paths in the stress space. The experimental results indicate that Hill's quadratic yield function along with an associated flow rule provides a good approximation of the initial yield behavior of this anisotropic two-phase FCC/BCC sheet material. Based on the experimental data for radial monotonic loading, it is concluded that conventional isotropic-kinematic hardening models cannot successfully describe the strain hardening of this austenitic steel. Instead, a non-associated anisotropic hardening model is proposed that relates the increase in yield strength to an isothermal martensitic transformation kinetics law. The comparison of the model predictions with the experimental results shows very good agreement for all biaxial and uniaxial experiments. 相似文献
194.
In this study plate-impact pressure-shear friction experiments are employed to investigate dynamic slip resistance and time-resolved growth of molten metal films during dry metal-on-metal slip under extreme interfacial conditions. By employing a tribo-pair comprising of a hard tool-steel against a relatively low melt-point metal (7075-T6 Al alloy), interfacial normal stress of up to 5 GPa and slip speeds of approximately 250 m/s have been achieved. These extreme interfacial conditions are conducive to the development of molten metal film at the tribo-pair interface. A Lagrangian finite element code is developed to understand the evolution of the thermo-mechanical fields and their relationship to the observed slip response. The code accounts for dynamic effects, heat conduction, contact with friction, and full thermo-mechanical coupling. At temperatures below the melting point of the tribo-pair materials are described as isotropic, thermally softening, elastic–viscoplastic solids. For material elements with temperatures in excess of the melt temperature a purely Newtonian fluid constitutive model is employed. 相似文献
195.
J. Gemmer G. Mahler 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(3):385-393
For a bi-partite quantum system defined in a finite dimensional Hilbert-space we investigate in what sense entanglement change
and interactions imply each other. For this purpose we introduce an entanglement-operator, which is then shown to represent
a non-conserved property for any bi-partite system and any type of interaction. This general relation does not exclude the
existence of special initial product states, for which the entanglement remains small over some period of time, despite interactions.
For this case we derive an approximation to the full Schr?dinger-equation, which allows the treatment of the composite systems
in terms of product states. The induced error is estimated. In this factorization-approximation one subsystem appears as an
effective potential for the other. A pertinent example is the Jaynes-Cummings model, which then reduces to the semi-classical
rotating wave approximation.
Received 8 June 2001 相似文献
196.
P. Hello 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,15(3):373-383
In this paper we study several means of compensating for thermal lensing which, otherwise, should be a source of concern for
future upgrades of interferometric detectors of gravitational waves. The methods we develop are based on the principle of
heating the cold parts of the mirrors. We find that thermal compensation can help a lot but can not do miracles. It seems
finally that the best strategy for future upgrades (“advanced configurations”) is may be to use thermal compensation together
with another substrate materials than silica, for example sapphire.
Received 26 April 2001 相似文献
197.
V.I. Yukalov 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,13(1):83-91
An ensemble of resonance atoms is considered, which are doped into a medium with well developed polariton effect, when in
the spectrum of polariton states there is a band gap. If an atom with a resonance frequency inside the polariton gap is placed
into the medium, the atomic spontaneous emission is suppressed. However, a system of resonance atoms inside the polariton
gap can radiate when their coherent interaction is sufficiently strong. Thus the suppression of spontaneous emission for a
single atom can be overcome by a collective of atoms radiating coherently. Conditions when such collective effects can appear
and their dynamics are analysed.
Received 7 June 2000 相似文献
198.
199.
研究在自学考试中设立物理实验课操作性考试的目的 ,报告考试的设计、组织实施的情况 ,总结经验。 相似文献
200.
基于MATLAB的自动控制实验模拟软件的设计 总被引:1,自引:1,他引:0
针对传统自动控制实验课时紧张、实验设备扩展性能差、操作复杂等不足,分析了MATLAB语言的特点及其功能强大的控制系统工具箱(Control System Toolbox)在自动控制领域的应用,提出了用该语言编制交互性能良好的模拟软件用来进行自动控制实验,并以所开发的“基于MATLAB环境的自动控制实验模拟系统”为例,分析了运用软件进行自动控制的模拟实验比传统实验方法的优越性。 相似文献