正弦波型高频动态压力光学校准系统及其应用

动态压力是气动部件表面的关键气动参数。光学压力敏感涂料（PSP）测量技术在测量气动部件表面动态压力方面具有全域测量、不影响流场自身的优势，而光学压力敏感涂料的动态响应特性则是进行动态压力测量的决定性因素。基于声学驻波管原理，自主设计并组建了正弦波型高频动态压力光学校准系统，主要包含有驻波管型校准舱、声源、激光源、高频压力传感器、光电倍增管以及测控系统。对动态压力光学校准系统及某新型快响压敏涂料的实验结果表明，所组建的动态压力校准系统可产生最短响应时间12.5 μs、最大压力幅值为4.37 kPa的正弦型动态压力，其有效动态频响范围为0.4~20.0 kHz（50 μs~2.5 ms），不确定度小于0.004 9%；校准系统合理的光路布局可进行快响压敏涂料动态特性的校准，所测涂料可用于动态频响不高于9.1 kHz（响应时间为109.9 μs）的非定常流场的压力测量。     

内置开孔隔墙的高速铁路隧道压力波数值模拟方法

基于一维可压缩非定常不等熵流动模型、薄壁孔口出流模型以及广义黎曼变量特征线法,发展了单列车通过内置开孔隔墙隧道的压力波数值分析方法.与国外试验结果比较验证本文建立的计算方法的正确合理性基础上,通过对不同开孔率的计算得出采用过大的开孔率将导致一维流动模型计算时出现较大的数值振荡,分析了计算结果震荡可能的—维流动模型适用性的原因.同时,通过对隔墙中开孔和不开孔的模拟计算,得出隔墙开孔可较大幅度的减缓压力波,为今后研究和隧道内设置开孔隔墙提供了有益的启示.     

消除粘性项高阶离散数值振荡的半结点-结点交错方法

通常的粘性项处理方法是连续两次采用结点型中心差分格式求得.但是,通过两次采用高阶结点型中心格式求得的粘性项易在流场中的"间断"附近产生数值振荡.本文采用多种格式,通过求解一维Burgers方程来充分展示了这种振荡现象.为了消除这种数值振荡,一种半结点型的高阶紧致格式被用来求解粘性项.Fourier频谱分析表明,这种格式具有非常优越的保频谱性能.一维和二维的数值计算结果表明,通过"半结点-结点"交错采用这种半结点型格式的方法可以非常有效地避免粘性项高阶离散可能导致的数值振荡.     

Effects of adiabaticity and non-adiabaticity of dust charge fluctuation on the propagation of the dust ion acoustic waves in inhomogeneous dusty plasma

A theoretical investigation has been made for adiabatic positive and negative dust charge fluctuations on the propagation of dust-ion acoustic waves (DIAWs) in a weakly inhomogeneous, collisionless, unmagnetized dusty plasmas consisting of cold positive ions, stationary positively and negatively charged dust particles and isothermal electrons. The reductive perturbation method is employed to reduce the basic set of fluid equations to the variable coefficients Korteweg–de Vries (KdV) equation. Either compressive or rarefactive solitons are shown to exist depending on the critical value of the ion density, which in turn, depends on the inhomogeneous distribution of the ion. The dissipative effects of non-adiabatic dust charge variation has been studied which cause generation of dust ion acoustic shock waves governed by KdV-Burger (KdVB) equation. The results of the present investigation may be applicable to some dusty plasma environments, such as dusty plasma existing in polar mesosphere region.     

Ion- and electron-acoustic solitons and double layers in multi-component space plasmas

A general model for the ion- and electron-acoustic solitons and double layers in a multi-component unmagnetized plasma consisting of background electrons, counter-streaming electron beams and ions is discussed. The model is based on the multi-fluid equations and the Poisson equation, and uses the Sagdeev pseudo-potential techniques. For identical counter-streaming electron beams and depending upon the plasma parameters, three types of solutions, namely, ion-acoustic, slow and fast electron-acoustic soliton/double layer, are possible. Generally, the ion acoustic solitons have positive potentials, slow-electron acoustic solitons have negative potentials and fast electron-acoustic solitons and double layers can have either positive or negative potentials depending on the core electron density. As beam speed is increased, first ion-acoustic and then slow electron-acoustic solitons disappear. At large beam speed, only fast electron-acoustic solitons/double layers survive. The results may be relevant to the observations of the electrostatic solitary waves (ESWs) observed in the Earth’s magnetosphere.     

Nonlinear dust Alfvén modes

Nonlinear modes are investigated in magnetized dusty plasmas, where the dust dynamics is modelled by a number of cold, highly negatively charged and very massive fluids, besides ordinary electrons and protons. Several low-frequency motions occur which are typical for the dust components, some of them described by model equations such as the derivative nonlinear Schrödinger equation for electromagnetic waves. One can include equilibrium drifts and even fluctuations in the grain charges. Most of the preceding conclusions are relevant for different kinds of astrophysical and heliospheric plasmas.     

Remote sounding of atmospheric gravity waves with satellite limb and nadir techniques

Recent advances in satellite techniques hold great potential for mapping global gravity wave (GW) processes at various altitudes. Poor understanding of small-scale GWs has been a major limitation to numerical climate and weather models for making reliable forecasts. Observations of short-scale features have important implication for validating and improving future high-resolution numerical models. This paper summarizes recent GW observations and sensitivities from several satellite instruments, including MLS, AMSU-A, AIRS, GPS, and CLAES. It is shown in an example that mountain waves with horizontal wavelengths as short as 30 km now can be observed by AIRS, reflecting the superior horizontal resolution in these modern satellite instruments. Our studies show that MLS, AMSU-A and AIRS observations reveal similar GW characteristics, with the observed variances correlated well with background winds. As a complementary technique, limb sounding instruments like CRISTA, CLAES, and GPS can detect GWs with better vertical but poorer horizontal resolutions. To resolve different parts of the broad GW spectrum, both satellite limb and nadir observing techniques are needed, and a better understanding of GW complexities requires joint analyses of these data and dedicated high-resolution model simulations.     

A Self-Consistent Determination of the Temperature Profile and The Magnetic Field Geometry in Winds of Late-Type Stars

Cool giant and supergiant stars generally present low velocity winds with high mass-loss rates. Several models have been proposed to explain the acceleration process of these winds. Although dust is known to be present in these objects, the radiation pressure on these particles is uneffective in reproducing the observed physical parameters of the wind. The most promising acceleration mechanism cited in the literature is the transference of momentum and energy from Alfvén waves to the gas. Usually, these models consider the wind to be isothermal. We present a stellar wind model in which the Alfvén waves are used as the main acceleration mechanism, and determine the temperature profile by solving the energy equation taking into account both the radiative losses and the wave heating. We also determine, self-consistently, the magnetic field geometry as the result of the competition between the magnetic field and the thermal pressure gradient. As the main result, we show that the magnetic geometry presents a super-radial index in the region where the gas pressure is increasing. However, this super-radial index is greater than that observed for the solar corona.     

Cassini Radio Science

Cassini radio science investigations will be conducted both during the cruise (gravitational wave and conjunction experiments) and the Saturnian tour of the mission (atmospheric and ionospheric occultations, ring occultations, determinations of masses and gravity fields). New technologies in the construction of the instrument, which consists of a portion on-board the spacecraft and another portion on the ground, including the use of the Ka-band signal in addition to that of the S- and X-bands, open opportunities for important discoveries in each of the above scientific areas, due to increased accuracy, resolution, sensitivity, and dynamic range.This revised version was published online in July 2005 with a corrected cover date.     

非线性动力Alfven波的演化

本文讨论了非线性动力Alfven波在1＞＞β＞＞me／mi条件下形成孤子解的限制条件，表明只有亚Alfven速度才能形成压缩型孤子．由动力Alfven波孤子和湍流产生的极大纵向电子速度不会超过本底电子热速度，但由此产生的纵向电场在小尺度范围可以很强，这可能对太阳风的能量传输与粒子加速产生一定影响．