Monte Carlo Simulation of Optical Properties of Wake Bubbles

Based on Mie scattering theory and the theory of multiple light scattering, the light scattering properties of air bubbles in a wake are analysed by Monte Carlo simulation. The results show that backscattering is enhanced obviously due to the existence of bubbles, especially with the increase of bubble density, and that it is feasible to use the Monte Carlo method to study the properties of light scattering by air bubbles.     

全息凹面光栅单色仪

此种单色仪专配焦比约为F/3的全息凹面光栅。在机械结构简单的前提下,设计了一种新光路,使其聚焦精度尽可能地提高。设计的基本思想是在濑谷-布岗(Seya-Namioka)和Johnson装置的基础上另选转轴的位置,并选用两个标准波长来校正光谱,这类似于三点统调法。所得结果比濑谷-布岗装置和Johnson装置都有改善。按照这种设计装架了JS-II型凹面光栅单色仪。仪器可在波长为2500?至10000?范围内工作,在3500?至6500?范围内,由于聚焦偏离而引起的分辨率损失不超过1?。 关键词：     

不确定中立型线性随机时滞系统的鲁棒稳定性

建立了中立型随机微分时滞方程的LaSalle不变原理,然后应用LaSalle不变原理讨论了不确定中立型随机时滞系统的随机渐近稳定和几乎必然指数稳定的代数判据, 同时给出示例说明结果的有效性．     

Design of Broadband L-band Erbium Doped Fiber Amplifier

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润滑油对超临界压力CO_2对流换热特性影响

本文对含有少量润滑油对冷却条件下水平细圆管中超临界压力二氧化碳的对流换热特性进行了实验研究,并与相应不含润滑油的工况及已有经验关联式进行对比。实验结果表明,润滑油会使冷却工况下超临界压力二氧化碳的对流换热恶化,尤其是二氧化碳温度在准临界温度附近时,恶化现象更显著。本文提出了用于计算含润滑油时冷却工况下超临界压力二氧化碳对流换热的经验关联式,其计算结果与90%以上实验数据的偏差在25%以内。     

Enhancing sound absorption using periodic micro-perforated structure with porous layer

To get desired sound absorption,we proposed a novel periodic composite structure comprised of micro-perforated plates(MPPs),porous materials and air cavities.The composite structure is then solved using an equivalent circuit model,with equivalent fluid porous model and Maa's theory.Distributed four-pole elements are used to handle structures which are not compact compared to the sound wavelength.The model procedures are validated and confirmed as satisfactory by published results and finite-element results.Analysis conducted on a single layer shows that,compared with traditional MPP,the porous addition can increase sound absorption in the low-to-medium frequency range;however,the advantage of porous materials in the high-frequency range is lost.Meanwhile,by arranging the porous materials in parallel and controlling their filling ratios,the absorption curve of the composite structure can be tuned.As to periodic composite structures,it is found that the influence of layer number N is mainly in the low-to-medium frequency range.When N varies,the half-absorption bandwidth increases over 40%(≥380 Hz) compared with a single layer.Compared with multi-layered MPPs,N=2 and N=4 produce an increase of bandwidth by 50%(≥400 Hz) and 30%(≥300 Hz) respectively.As N increases,the sound absorption is better but the enhancement weakens as it tends to the limit of the composite structure.These results show the potential enhancements that can be made to the traditional MPP,which can benefit the research on wideband noise reduction in the low-to-medium frequency range.     

反正切Finsler度量与Randers度量射影等价(英文)

本文研究了反正切Finsler度量F=α+εβ+βarctan(β/α)与Randers度量F=α+β射影等价,这里α和α表示流形上的两个黎曼度量,β和β表示流形上的两个非零的1-形式.利用射影等价具有相同的Douglas曲率的性质,获得了这两类度量射影等价的充要条件.     

基于模糊因素的载人航天器乘员舱内人-机界面工效学评价研究

载人航天器乘员舱内人－机界面的工效学评价是决定能否进行载人空间飞行的重要依据之一，由于人－机界面本身的复杂性，使得对其评价有一定的难度。本文在模糊理论的基础上，首先对舱内人－机界面工效学评价各参数进行随机模糊分析，据此建立工效学模糊综合评价模型，最后进行了实例研究。结果表明，对于同一个评价对象，应用该方法更能接近实际。     

基于时延和相位估计的合成孔径声呐运动补偿研究

合成孔径声呐成象的难点之一在于孔径上载体的运动不稳定性影响了合成孔径上水听器接收的信号的相干性,其结果将导致图像的畸变和分辨率的降低。首先讨论了运动误差对合成孔径声呐(SAS)成像的影响及运动补偿的必要性。在分析位移相位中心运动补偿法的基础上,提出了一种改进算法。该方法首先估计时延,然后再对剩余误差进行相位估计,从而扩大了算法适用的运动误差范围。文中给出了利用该方法的计算机仿真结果和部分水池实验结果,从结果可以看出,该方法有效地修正了在合成孔径上由于介质和载体不稳定带来的不相干性,提高了成像的质量。