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排序方式: 共有331条查询结果,搜索用时 15 毫秒
51.
52.
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
53.
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
54.
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
55.
G. Huang C. Hang L. Deng 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,40(3):437-444
We study stable propagation of multiple shape-preserving optical
pulses in an inhomogeneously broadened multi-level atomic medium.
By analytically solving the Maxwell-Schr?dinger equations
governing the evolution of N coupled optical fields and atomic
amplitudes we show that N pulsed optical waves coupling to
(N+1)-levels can be automatically matched with the same soliton
waveform and identical yet very slow propagation velocity. Several
sets of coupled soliton solutions for two different (N+1)-level
models are given and their stability is studied by using a
numerical simulation. 相似文献
56.
本文计算了红宝石中Al核自旋跳变引起的R1[4A2(S=-3/2)→2E(S=-1/2)]回波衰减。用随机电报过程描述每个Al核自旋(i)跳变引起Cr共振频率的起伏Δi,这个过程对光子回波衰减的贡献〈Ei(t21)〉可以用解析式表示。首先计算核自旋(i)跳变的总速率Wi及它引起的Δi,求出〈Ei(t21)〉。设对Cr光失相起主要贡献的每个Al核自旋跳变近似是独立的,所以总的回波强度是所有Al引起的〈Ei(t)21〉的乘积。计算得到非指数的回波衰减,以I=I0exp〔-(4t/tm)x〕拟合,x=2.56,tm=50.6μs,与实验及计算机模拟的结果一致. 相似文献
57.
An analytical expression for a signal of the single-pulse echo generated in nonresonant pulse excitation of an inhomogeneously broadened two-level quantum system has been obtained, with the reversible and irreversible relaxation taken into account. It is shown that the rate of decay of the single-pulse echo is determined by the rate of reversible and irreversible transverse relaxation. It has been established that the contribution of the reversible and irreversible relaxations to decay of the single-pulse echo depends on the ratio between the detuning of the pulse-carrying frequency from resonance to the Rabi frequency. The difference between the times of transverse irreversible relaxation measured in manganese ferrite MnFe2O4 by the methods of single and two-pulse echo of nuclear magnetic resonance has been explained within the framework of the theoretical expressions obtained. 相似文献
58.
F. Weigand D.E. Demco B. Blümich H.W. Spiess 《Solid state nuclear magnetic resonance》1996,6(4):357-365
Different procedures based on parameters of the wideline NMR absorption spectrum are presented to obtain localized molecular mobility contrast for imaging of solid polymers. For this purpose a 1H-NMR imaging technique with magic sandwich echoes is used for acquiring localized wideline spectra. With samples composed of polystyrene and high impact strength polystyrene, and polycarbonate and low density polyethylene a spatial difference in NMR absorption spectrum lineshape and linewidth is displayed. Furthermore, the spatial distribution of rigid and mobile domains in a heterogeneous polymer can be derived from the NMR spectral components. It is demonstrated that a van Vleck moment analysis can be performed from spatially resolved magic echo decays. The second (M2) and fourth (M4) moments of the rigid components show considerable variation with the spatial composition of the investigated samples. 相似文献
59.
Franciszek Hennel 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,134(2):206-213
The method to reduce the ghost artifact in echo-planar imaging (EPI) using a phase correction derived from the image data (M. H. Buonocore and L. Gao,Magn. Reson. Med.38, 89 (1997)) is generalized to multishot (interleaved) EPI, where the artifact takes the form of multiple ghosts. The method is shown to be much more sensitive to noise when applied to standard interleaved data than is the case with single-shot EPI, because the calculation must be based on high-order ghosts of low intensity. A modified interleaving scheme is proposed for multishot EPI in which the initial trajectory direction alternates in consecutive shots and the number of shots is odd. With this scheme, only a single ghost shifted by one-half of the field of view appears just as in the single-shot EPI, and the image-based phase correction can be applied with the usual sensitivity to noise. 相似文献
60.
Furihata K Fujimoto T Tsutsui A Machinami T Tashiro M 《Magnetic resonance in chemistry : MRC》2005,43(12):1044-1048
ROESY pulse sequences are presented and evaluated to identify bound waters in the cyclic tetrasaccharide. The first experiment incorporated the double-pulsed field gradient spin-echo (DPFGSE) for selective water excitation at the initial portion of the pulse sequence. Although long, shaped pulses were used in DPFGSE to achieve the highly selective excitation of water resonance that is very close to resonances of the cyclic tetrasaccharide, the approach was not effective because of the loss of sensitivity. Concomitant use of long delays and moderate length of shaped pulses in the portion of DPFGSE gained more sensitivity. A simple approach incorporating spin-echo with long delays instead of DPFGSE also afforded a sensitive spectrum. Practical aspects of these ROESY experiments are illustrated using the cyclic tetrasaccharide cyclo-{-->6}-alpha-D-Glcp-(1-->3)-alpha-D-Glcp-(1-->6)-alpha-D-Glcp-(1-->3)-alpha-D-Glcp-(1-->). 相似文献