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Yang Ruike Wu Zhensen You Jinguang 《International Journal of Infrared and Millimeter Waves》2003,24(8):1383-1392
The influence of sand and dust storms on modern MMW and satellite communication systems reliability have been paid more attention to. The attenuations induced by sand and dust storms are estimated by means of Mie-theory and Rayleigh approximation, in the case of the tenuous distribution of particles. With the particle density increasing, however, these method become inadequate, the multiple scattering effects then become dominant for attenuation estimation. The attenuations considering multiple scattering effects are estimated by Monte-Carlo and four fluxes method at horizontal paths. At slant paths, based on multi-layer media model, the attenuations considering multiple scattering effects are calculated by layered Monte-Carlo method at 100, 37, 24, and 14GHz. It is shown that the multiple scattering effects should be considered at the attenuation prediction in the sand and dust storm, which the visibility is about 0.5km and smaller than 0.5km and frequency is about 20GHz. Above 30GHz, the multiple scattering effects due to sand and dust particles should be considered, as visibility is about 1km and smaller than 1km at slant paths. 相似文献
13.
The present paper reports the dislocation unpinning model of acoustic emission (AE) from alkali halide crystals. Equations
are derived for the strain dependence of the transient AE pulse rate, peak value of the AE pulse rate and the total number
of AE pulse emitted. It is found that the AE pulse rate should be maximum for a particular strain of the crystals. The peak
value of the AE pulse rate should depend on the volume and strain rate of the crystals, and also on the pinning time of dislocations.
Since the pinning time of dislocations decreases with increasing strain rate, the AE pulse rate should be weakly dependent
on the strain rate of the crystals. The total number of AE should increase linearly with deformation and then it should attain
a saturation value for the large deformation. By measuring the strain dependence of the AE pulse rate at a fixed strain rate,
the time constantτ
s for surface annihilation of dislocations and the pinning timeτ
p of the dislocations can be determined. A good agreement is found between the theoretical and experimental results related
to the AE from alkali halide crystals. 相似文献
14.
The purpose of the present study was to describe the effects ofacute laryngitis on some aerodynamic, acoustic, and perceptual measures. Eleven subjects with diagnosed acute laryngitis due to upper respiratory infection were recorded during a laryngitic episode and 1 week to 10 days after amelioration of the laryngitic condition. Fundamental frequency values, collapsed across the five vowels, were significantly reduced in the laryngitic compared with the normal speaking condition. The decrease in fundamental frequency associated with acute laryngitis suggests an increase in the mass of the vocal folds. In addition, aerodynamic values differed significantly for the laryngitic condition compared with the normal speaking condition, suggesting the presence of laryngeal hypofunction. Perceptual data indicated that speakers in the laryngitic condition were judged to have a hoarse voice when compared with the normal speaking condition. 相似文献
15.
Mitigating the effects of explosive blasts has been an important concern for a long time. Water-mist presents an attractive option due to its easy availability, extensive use in the fire suppression area, and non-toxicity. However, its ability to mitigate the effects of blasts is unclear. This research uses multiphase numerical simulations to elucidate some of the issues associated with using water-mist to mitigate explosive blasts in unconfined spaces. Initial multidimensional simulations examine the effect of water-mist on the blast wave generated by a TNT explosive. Results show that the droplets are generally swept outward with the shock wave and in general do not penetrate into the secondary fireball. The water-mist does, however, mitigate the shock-front through vaporization and momentum extraction. Further simulations show that momentum extraction has the dominant role in mitigating the leading shock wave. Parametric studies indicate that droplet size and mass loading play a secondary role to the total amount of water between the observer and the explosive blast. This is a promising result for using water-mist for blast-mitigation, because it suggests that water-mist can be as effective as having a more dense “water wall” surrounding the explosive. 相似文献
16.
L.B.Magalas 《物理学进展》2006,26(3):258-276
本文广泛地收集了有关内耗,力学谱,超声衰减方面的专著及会议文集。反映了20世纪在此领域的英文,俄文出版的书籍。也列出了历次国际会议及前苏联,乌克兰,中国的国内会议。文中包括了点缺陷,电,声子,位错,晶界,电畴等诸方面在内的内耗与力学谱工作。 相似文献
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章利用基于三次B样条插值的边界元方法,对振动体外部声辐射问题进行了研究,对CHIEF法及其改进方法作了进一步的改进,提出在加权余量意义下,通过把内部Helmholtz积分方程与其对内点坐标取导后的方程式作线性叠加,在域外构作的一个小体积块上进行积分以形成补充方程,经与表面Helmholtz积分方程相结合,来求解任意频率下的声辐射问题,并以脉动球和摆动球作为算例,说明本提出的方法能够有效地克服在特殊频率处解的非唯一性问题。 相似文献
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