Investigation of Electric Discharges in the Vicinity of a Charged Aerosol Cloud and Their Interaction with a Laser-Induced Spark

It is experimentally demonstrated that an extended laser-induced spark developed in the vicinity of a grounded electrode and having a structure in the form of separate spherical plasma formations may intercept the channel of a leader discharge developing from the grounded electrode to an artificially charged aerosol cloud. The interception occurs with the electric field intensity in the vicinity of the electrode being close to the value required for an upward positive leader. It is registered that the presence of a laser-induced spark in the vicinity of the electrode causes a manifold reduction of the time of stable leader formation. It is found that the emergence of an extended laser-induced spark of a CO₂ laser in the vicinity of the boundaries of a highly charged aerosol cloud does not provoke a discharge to ground from the cloud.     

用MLP法求强非线性保守系统的次谐共振周期解

在两种改进的LP解法的基础上，将它们结合起来，用于求强非线性保守系统的次谐共振周期解。研究了Dufling方程的1／3亚谐共振周期解和2次超谐共振周期解，结果表明本方法既可求得一类强非线性保守系统的次谐共振周期解又能提高解的计算精度。     

环形溶蚀器大气颗粒物采集系统条件实验研究

为确定环形溶蚀器大气颗粒物采集系统的最优化条件,于2008年夏季与冬季在北京市进行了关于优化环形溶蚀器涂渍溶液浓度的条件实验。结果表明:为保障大气中酸碱性气体的去除效率达到95%以上,环形溶蚀器中柠檬酸涂渍溶液的优化浓度在夏季和冬季分别为6%与3%;环形溶蚀器中碳酸钠涂渍溶液的优化浓度在夏季和冬季分别为2%与4%。讨论说明在特定地点特定时间利用环形溶蚀器大气颗粒物采集系统采样前,确定环形溶蚀器涂层溶液优化浓度的必要性。     

R134a通过短管流动的试验研究

短管机构在汽车空调、家用空调和热泵系统中得到越来越广泛的应用。目前，关于提供通过短管机构ＣＦＣ替代物性能研究方面的数据很少。本文给出了ＣＦＣ替代物Ｒ１３４ａ通过短管机构的流动特性试验研究。在很宽的操作条件下，通过试验研究了Ｒ１３４ａ流过短管机构的性能参数变化。长径比在７￣２０范围内，冷凝温度为３５℃￣５４℃时，过冷度可达１３．９℃，短管入口干度可达１０％左右。对进入短管的两相流和过冷液体性能进行了     

“沸腾法气溶胶发生和静电采样法”在扫描电镜表征超细粉体中的应用

该文介绍了一种为扫描电镜表征超细粉体制备样品的新方法—“沸腾法气溶胶发生和静电采样法”。将粉体悬浮在分散剂中,沸腾产生高浓度的气溶胶,利用静电沉积原理,将气溶胶状态的粉体粒子均匀收集至样品台,由扫描电镜进行表征。此法能打破由于存放或运输过程中因挤压、吸潮等引起的粒子团聚,较为真实的反映粉体原貌。该文也给出TTiO2超细粉末表征的实例。     

行波热声发电系统自激振荡的非线性动力学研究

利用非线性热声网络模型建立了一种行波热声发电系统的简化动力学演化方程,考察了系统自激振荡过程。重点探究非线性热声效应的影响,并与仅考虑线性热声效应的情况进行对比。结果表明,当仅考虑线性热声效应时,振荡曲线不断增大,无法达到稳定值;而考虑非线性热声效应时,自激振荡最后达到稳定幅值。进一步研究得出,系统电机的非线性阻尼系数越大,系统稳定后的振荡幅值越小。对不同电机非线性阻尼系数时系统产生的振荡曲线作频谱分析,计算结果和实际情况相近。最后考察了回热器未达临界温度梯度时系统的自激振荡过程。     

基于注入锁模光纤激光器的OTDM时钟提取技术实验研究

提出了一个新的全光时钟提取方案 :用非均匀复用后的OTDM信号去驱动主动锁模光纤环行激光器中的调制器件 ,得到复用前的单路时钟光脉冲 ,并且成功地从 2×10Gb/sOTDM信号中提取出 10GHz的单路时钟光脉冲     

参激非线性振子不稳定区域的实验研究

对一端固定、一端滑动、受轴向简谐激励的屈曲梁的非线性动力学行为进行了实验研究。对固定的参数激励频率和阻尼，当参数激励幅值较小时梁的运动是周期的，但大幅值激励会使运动通过倍周期分岔变为混沌。实验得到了动态响应在参数平面上的分布，并研究了阻尼对分布区域的影响。实验结果为全面了解系统解的分布及该类结构的动力学设计提供了有价值的资料。     

Experimental and Numerical Investigation of the Fracture of Obstacles by Groups of High-Speed Bodies

The processes of high-speed interaction of several compact bodies with obstacles of finite thickness are studied experimentally and numerically in a three-dimensional statement of the problem. In experiments, the number of particles in a homogeneous flow varied from two to seven. The density of flow (distance between the particles) was also variable. In numerical calculations, we simulated the collisions of four particles with an obstacle for the cases of frontal impacts and asymmetric impacts separated in time. We present the numerically determined configurations of the bodies, the distributions of the specific volume of microdefects in the obstacle, and the experimental data on changes in the area and the mass of backside cleavage fragments. We also study the distinctive features of the processes of deformation and fracture of obstacles depending on the intensity of interaction between the particles.     

The effectiveness of an air cleaner in controlling droplet/aerosol particle dispersion emitted from a patient's mouth in the indoor environment of dental clinics

Dental healthcare workers (DHCWs) are at high risk of occupational exposure to droplets and aerosol particles emitted from patients'' mouths during treatment. We evaluated the effectiveness of an air cleaner in reducing droplet and aerosol contamination by positioning the device in four different locations in an actual dental clinic. We applied computational fluid dynamics (CFD) methods to solve the governing equations of airflow, energy and dispersion of different-sized airborne droplets/aerosol particles. In a dental clinic, we measured the supply air velocity and temperature of the ventilation system, the airflow rate and the particle removal efficiency of the air cleaner to determine the boundary conditions for the CFD simulations. Our results indicate that use of an air cleaner in a dental clinic may be an effective method for reducing DHCWs'' exposure to airborne droplets and aerosol particles. Further, we found that the probability of droplet/aerosol particle removal and the direction of airflow from the cleaner are both important control measures for droplet and aerosol contamination in a dental clinic. Thus, the distance between the air cleaner and droplet/aerosol particle source as well as the relative location of the air cleaner to both the source and the DHCW are important considerations for reducing DHCWs'' exposure to droplets/aerosol particles emitted from the patient''s mouth during treatments.     

脉动流场中旋进旋涡流量计流体振动特性的实验研究

研究了脉动流场中旋进旋涡流量计流体振动特性。在自行设计的实验装置中使用压电式压力传感器对50mm口径的旋进旋涡流量计在脉动干扰流场中的流体振动特性进行试验研究,明确了流体脉动对旋进旋涡效应的影响因素。实验研究表明,流体脉动干扰与旋进旋涡效应的脉动压力为线性叠加关系;流体脉动干扰的能量耗散作用将导致旋进旋涡效应的衰减,从而扩展旋进旋涡流量计测量的下限。并提出了新的设计,以利用对称脉动压力信号差分处理和改善测量系统的电磁屏蔽性能来减弱流场波动对该类流量计的影响。     

Investigation of Flow in the Vicinity of Porous Material on a Cylindrical Body Subjected to Flow

The results are given of an experimental investigation of the distribution of velocity components in a flow of air in the vicinity of a hemispherical permeable blunting of a cylindrical body under conditions of low injection intensity. A numerical simulation of the flow structure is performed for the parameters corresponding to those used in the experiments. Comparison of the results of physical and numerical simulation revealed a number of special features of flow in the boundary layer on a curved surface under conditions of its gasdynamic conjugation with the inner cavity.     

An Experimental Study on the Interaction of Thermal Loading and Mechanical Loading in Membrane Structures

Abstract: Maintenance of membrane structures geometry is crucial for them to be utilised in some space missions, including membrane antennae being developed at the Canadian Space Agency. In the harsh space environment, thermal loading and mechanical loading both can cause the distortion of membrane surfaces. Their effects on surface distortion will interact with each other. In order to properly design active control system, the interaction needs to be well understood. An experimental setup is designed for this purpose. A square membrane is subjected to mechanical loading provided by corner tension forces and thermal loading provided by a ceramic heater. Surface profile of the membrane is measured using the photogrammetry technique. In cases of symmetric thermal loading and asymmetric thermal loading, different mechanical loading cases are evaluated in terms of mitigating surface distortions. Some results are compared and explained using numerical results. Finally, the controllability of membrane structures is discussed using the results from these experiments.     

周期永磁场作用下的螺旋线行波管非线性返波振荡分析

螺旋线行波管中返波振荡是影响行波管设计的重要问题,行波管中当高频信号滞后于高压信号或者高频信号脉宽小于高压信号时,也就是在高电压信号的上升和下降沿,这时没有高频信号但返波振荡也有可能被激起,这在以往是被忽略的,本文从瓦因斯坦的波导激励理论出发,导出了在布里渊条件下此种特殊情况的非线性返波振荡工作方程;分析了周期永磁场的磁场周期和磁场强度抑制返波振荡的效果,同时考虑了损耗因子、空间电荷场、不同磁场位形对抑制返波振荡效果的影响,从理论上说明了该方法的有效性,为行波管的设计和优化提供了依据.     

钢管混凝土短柱支座隔震房屋试验研究

对钢管砼短柱进行了伪静力试验研究,由此确立了短柱支座的恢复力模型。其恢复力模型曲线丰满、呈仿锤型、不出现下降段。滞回性能与钢材相近。在此基础上,利用钢管砼隔震支座对一幢四层砖混房屋模型进行了地震模拟振动台试验。试验结果表明,钢管砼短柱具有良好的隔震性能,施工方便、操作简单、容易推广,是一种新型的隔震支座。     

热端管长度对涡流管性能影响的实验研究

研制了不同热端管长度的涡流管,并以空气作为工作介质,通过实验研究了热端管长度对涡流管能量分离性能的影响.实验结果表明:对于常温涡流管,在入口压力为0.5MPa的情况下,相同冷流率时,随着热端管长度的增加,涡流管的制冷温度效应、单位制冷量和制冷系数增加,而其制热温度效应无显著的规律;对同一热端管长的涡流管,随着冷流率的增加,涡流管的制冷温度效应、单位制冷量和制冷系数增加,且在冷流率为40%～50%时出现峰值,而制热温度效应随冷流率的增加而增加,在冷流率范围内未出现峰值.     

An original approximate method for estimating the invariant probability distribution of a large class of multi-dimensional nonlinear stochastic oscillators

This paper proposes an original method for obtaining analytical approximations of the invariant probability density function of multi-dimensional Hamiltonian dissipative dynamic systems under Gaussian white noise excitations, with linear non-conservative parts and nonlinear conservative parts. The method is based on an exact result and a heuristic argument. Its pertinence is attested by numerical tests.