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51.
The characteristic wind curve (CWC) was com- monly used in the previous work to evaluate the operational safety of the high-speed trains exposed to crosswinds. How- ever, the CWC only provide the dividing line between safety state and failure state of high-speed trains, which can not evaluate the risk of derailment of high-speed trains when ex- posed to natural winds. In the present paper, a more realistic approach taking into account the stochastic characteristics of natural winds is proposed, which can give a reasonable and effective assessment of the operational safety of high-speed trains under stochastic winds. In this approach, the longitudi- nal and lateral components of stochastic winds are simulated based on the Cooper theory and harmonic superposition. An algorithm is set up for calculating the unsteady aerody- namic forces (moments) of the high-speed trains exposed to stochastic winds. A multi-body dynamic model of the rail vehicle is established to compute the vehicle system dynamic response subjected to the unsteady aerodynamic forces (mo- ments) input. Then the statistical method is used to get the mean characteristic wind curve (MCWC) and spread range of the high-speed trains exposed to stochastic winds. It is found that the CWC provided by the previous analyticalmethod produces over-conservative limits. The methodol- ogy proposed in the present paper can provide more signif- icant reference for the safety operation of high-speed trains exposed to stochastic winds. 相似文献
52.
Shou-Kuan Zhao 《中国物理 B》2022,31(3):30307-030307
The Loschmidt echo is a useful diagnostic for the perfection of quantum time-reversal process and the sensitivity of quantum evolution to small perturbations. The main challenge for measuring the Loschmidt echo is the time reversal of a quantum evolution. In this work, we demonstrate the measurement of the Loschmidt echo in a superconducting 10-qubit system using Floquet engineering and discuss the imperfection of an initial Bell-state recovery arising from the next-nearest-neighbor (NNN) coupling present in the qubit device. Our results show that the Loschmidt echo is very sensitive to small perturbations during quantum-state evolution, in contrast to the quantities like qubit population that is often considered in the time-reversal experiment. These properties may be employed for the investigation of multiqubit system concerning many-body decoherence and entanglement, etc., especially when devices with reduced or vanishing NNN coupling are used. 相似文献
53.
54.
基于LabVIEW激光引信回波模拟装置设计 总被引:4,自引:1,他引:3
激光引信回波模拟装置是激光引信测试设备的重要组成部分。介绍了激光引信回波模拟装置的组成,设计了用于该装置的硬件电路和软件控制系统。硬件电路采用单片机完成控制指令的接收和控制信号的产生,使用串行扩展芯片GM8125将单片机AT89S52的串行口扩展成5个,满足了激光引信回波模拟装置串口资源要求。软件控制系统基于LabVlFⅣ设计,主要包括串口通信程序和控制指令的产生程序,控制指令经串口通信传送给硬件电路。实验结果表明,该装置满足激光引信测试设备的要求。 相似文献
55.
A.G. Kofman 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(2):153-165
The electromagnetically induced transparency (EIT) with a (near-)resonant chaotic (amplitude-phase fluctuating, Gaussian-Markovian)
coupling field is studied theoretically. The Fourier transform of the steady-state EIT spectrum, which determines a nonstationary
probe absorption, is also considered. This quantity equals the average diagonal element of the (reduced) evolution operator
of the coupled transition (the evolution function). The exact solution in the form of a continued fraction is obtained and
used to perform numerical calculations. Moreover, a number of approximate analytical results are obtained, which, together
with the results of previous publications, describe the EIT and the evolution function in all possible regimes. In particular,
in the constructive-interference case the EIT increases with the coupling-field bandwidth ν at sufficiently small ν. For a strong field, the maximum of the transparency as a function
of ν is less than that for a monochromatic field of the same average intensity. In contrast, for a weak field, there is a
range of ν values, where the field fluctuations do not affect the EIT. The latter result is shown to hold for a broad class of stochastic fields.
Received 31 December 2000 and Received in final form 14 May 2001 相似文献
56.
Generation of time-dependent ultra-short optical pulse trains in the presence of self-steepening effect
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Starting from the extended nonlinear Schr?dinger equation in
which the self-steepening effect is included, the evolution and the
splitting processes of continuous optical wave whose amplitude is
perturbed into time related ultra-short optical pulse trains in an
optical fibre are numerically simulated by adopting the split-step
Fourier algorithm. The results show that the self-steepening effect
can cause the characteristic of the pulse trains to vary with time,
which is different from the self-steepening-free case where the
generated pulse trains consist of single pulses which are identical
in width, intensity, and interval, namely when pulses move a certain
distance, they turn into the pulse trains within a certain time
range. Moreover, each single pulse may split into several
sub-pulses. And as time goes on, the number of the sub-pulses will
decrease gradually and the pulse width and the pulse intensity will
change too. With the increase of the self-steepening parameter, the
distance needed to generate time-dependent pulse trains will
shorten. In addition, for a large self-steepening parameter and at
the distance where more sub-pulses appear, the corresponding
frequency spectra of pulse trains are also wider. 相似文献
57.
Manuel Gadella Sebastin Fortín Juan Pablo Jorge Marcelo Losada 《Entropy (Basel, Switzerland)》2022,24(6)
We review some results in the theory of non-relativistic quantum unstable systems. We account for the most important definitions of quantum resonances that we identify with unstable quantum systems. Then, we recall the properties and construction of Gamow states as vectors in some extensions of Hilbert spaces, called Rigged Hilbert Spaces. Gamow states account for the purely exponential decaying part of a resonance; the experimental exponential decay for long periods of time physically characterizes a resonance. We briefly discuss one of the most usual models for resonances: the Friedrichs model. Using an algebraic formalism for states and observables, we show that Gamow states cannot be pure states or mixtures from a standard view point. We discuss some additional properties of Gamow states, such as the possibility of obtaining mean values of certain observables on Gamow states. A modification of the time evolution law for the linear space spanned by Gamow shows that some non-commuting observables on this space become commuting for large values of time. We apply Gamow states for a possible explanation of the Loschmidt echo. 相似文献
58.
基于激光不同波段的探测传输特点,通过分析典型微小摄像头的回波传输特性,提出了一种针对多波长激光特征检测微小摄像头的研究方案。利用几何光学和波动光学理论,分析微小摄像头结构及其反射光谱特征,计算并仿真了一定探测距离下的回波光场,在此基础上搭建多波长激光检测系统。实验结果表明,在一定的景深范围内,具有红外截止滤光片的微小摄像头对可见光的回波光斑衍射环特征明显、条纹对比度高且可探测距离远;近红外波段的目标回波功率低、后向散射干扰严重,可探测距离近;短波红外波段几乎不受红外截止滤光片影响,且1550 nm处于人眼安全波段。实验结果与数值分析、理论仿真结果一致,验证了短波红外激光用于探测微小摄像头的可行性。 相似文献
59.
礁石和海洋动物引起的混响是主动声纳最严重的干扰, 如何区分礁石、鱼群和水中目标一直是制约主动声纳识别技术的难点问题. 针对礁石与目标回波难以区分的问题, 从特征识别的应用角度, 研究水中复杂目标全方位回波亮点特征的有效表征和应用方式, 基于目标回波亮点模型, 提出拷贝相关器输出的目标散射函数估计方法, 给出对目标回波亮点相对关系进行定量分析的目标回波特征统计表征方式, 并基于湖上实验提取了物理机理明确的目标回波亮点统计特征, 使得目标时间-角度谱中所蕴含的目标特征信息能够很直接地转化为主动声纳易于应用的目标特征.
关键词:
水中目标
回波亮点
统计特征 相似文献
60.