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941.
Statistical energy analysis (SEA) is commonly used in industry to predict high-frequency vibrational response of structures. Since only local modes are used in SEA, only high-frequency responses can be predicted. This study extends SEA to the middle-frequency region by additionally using global modes. Methods using impedance matrices that can be found by NASTRAN are developed. Then the results are post processed to determine coupling loss factors. 相似文献
942.
A dual-frequency Nd: YAG laser which can output two frequencies with frequency difference of more than 5 gigaherz is developed. By inserting and moving an intracavity quartz crystal wedge in diode pumped Nd:YAG laser, It can be obtained and tuned frequency difference in a wide frequency range. The stabilization of frequency difference in free state is much better than that of birefringent dual-frequency He-Ne lasers at similar laboratory conditions. With such a large tunable frequency difference i.e. short synthetic wavelength, the laser may be used as the light source of absolute distance interferometers. In our experiment, the methods for tuning frequency difference by rotating and applying a tunable force on the intracavity quartz plate are also studied. 相似文献
943.
Axel Jahn 《International Journal of Satellite Communications and Networking》2001,19(2):169-203
Efficient resource management is mandatory to achieve maximum system capacity for next generation communications systems. Resource management deals with the available spectral band, time, power, and space for a transmission signal. It includes (i) the frequency planning, (ii) the selection of transmit power, and (iii) the assignment of the channels and access nodes to the users. The paper presents a generalized notation as well as graph algorithms for resource management problems. Impairment graphs can be used for frequency planning, whereas flow graphs are suitable for channel access problems. To evaluate the performance of the resource management, service criteria (such as blocking or the carrier to interference ratio C/I) or efficiency criteria (bandwidth requirements) can be derived from the graphs. The resource management techniques are applied to satellite networks with non‐geostationary orbits yielding time‐variant network topologies. As a simple example, the channel assignment and capacity optimization of the EuroSky Way system are shown. Furthermore, a comparison of fixed, dynamic and hybrid channel allocation schemes (FCA, DCA, HCA) for a typical MEO satellite scenario is given. Satellite diversity and its impact on bandwidth requirement and transmission quality is also examined. Finally, it is shown how spread spectrum systems can be investigated with the presented tools. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
944.
P. Sigmund 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,12(1):111-116
Second-harmonic cross-correlation operates a selection in time-phase among the randomly de-phased contributions to an optical
field that propagated through a scattering medium. It can thus be used to selectively detect the weak contribution remaining
coherent with the incident field.
Received 7 May 1999 相似文献
945.
P. Nielaba J. L. Lebowitz H. Spohn J. L. Vallés 《Journal of statistical physics》1989,55(3-4):745-767
We investigate the behavior of a two-level quantum system in contact with a classical heat bath, e.g., a solute particle with internal degrees of freedom immersed in a solvent of massive particles. Using a combination of analytical and numerical methods, we obtain precise information about localization, time-displaced correlation functions, and the frequency-dependent susceptibility of such solute particles. We find that these quantities can have a strong dependence on the density of the solvent fluid, with the maximum changes from the behavior of the corresponding isolated quantum system occurring in many cases at very low densities. We compare the exact results with those obtained by path integral Monte Carlo. There is good agreement with the imaginary time correlations, but analytic continuation to real time proves elusive: even with the best numerical data on the former, we can only get very gross features of the latter. 相似文献
946.
We investigate the ratio of spin precession frequency to orbital frequency for a spinning charged particle confined to circular
orbit in the equatorial plane of a compact object, with a uniform magnetic field, as described by the Wald and the Ernst potentials.
In order to see the difference in behaviours for particles with differentg values we consider the cases of electron and proton separately. 相似文献
947.
In the Shubnikov–de Haas oscillation spectrum of doped InAs/AlSb structures, high-amplitude peaks are established at combination
frequencies. It is demonstrated that they are caused by a significant contribution of intersubband scattering to the processes
of electron-electron interaction.
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 32–38, December, 2008. 相似文献
948.
949.
Ziqiang Yang Chengliang Ge Zheng Liang 《International Journal of Infrared and Millimeter Waves》2000,21(11):1887-1896
Reported in this paper are the results of an experiment to produce high-power microwave radiation from a gas-filled backward wave oscillator (BWO) driven by a relativistic electron beam without external guiding magnetic field. A peak power for background gas pressure at 5.25 mTorr has been observed as argon pressure from 0.75 mTorr to 15 mTorr. Operating frequency of the oscillator has been measured at 9.6 ± 0.4 GHz. The results of PIC simulation are in good agreement with the experimental results. A reasonable explanation is given for experimental results by PIC simulation. 相似文献
950.
高分辨率影像(HRI)亮度信号二维空间频谱分析 总被引:1,自引:0,他引:1
主要分析了HRI亮度信号的空间频谱特性,并逐步建立其二维频谱的数学模型和二维抽样谱模型。 相似文献