FDTD Numerical Simulation of Absorption of Microwaves in an Unmagnetized Atmosphere Plasma

Numerical simulations based on the finite-difference-time-domain （FDTD） approximation to multi-fluid equations for positive ions, negative ions and electrons are used to study high frequency electromagnetic wave propagation and absorption in an unmagnetized plasma layer. The interaction between the incident high frequency wave and the plasma layer shows that the existence of negative ions and the nonlinear effect reduces the power absorption capability of the plasma. Parameter dependences of the effects are calculated and discussed.     

强流脉冲离子束模型及辐照靶材能量沉积的模拟研究

强流脉冲离子束(IPIB)及其在靶材中沉积的能量是研究束流与靶材作用的基础.根据三束材料改性国家重点实验室从俄罗斯引进TEMPⅡ型加速器实测的磁绝缘二极管(MID)的加速电压波形及法拉第杯检测到的MID焦点处离子流密度波形,对其进行拟合得到高斯脉冲分布模型,以此为基础采用Monte Carlo方法模拟了离子在铝靶内沉积的能量,得到了一个脉冲内靶材内沉积的能量的时空演化规律.计算了单能离子束以20°～40°角入射铝靶情形.不同能量的单能H+束和C+束以一定角度入射时的最大射程比垂直入射时都要小,表面处单位长度沉积的能量随入射角的增加而增多.IPIB入射铝靶时变化规律同单能离子束.同时对H+和C+二维入射靶材情况也进行了模拟研究.     

房地产市场羊群行为研究——以北京市场为例

从资产价格的角度研究存在于北京市房地产市场的羊群行为。利用检验证券市场羊群行为的基于GCAPM的测度方法,对北京市房地产市场进行实证分析,结果表明,2003年之前北京市场不存在明显的羊群行为,2003年之后存在显著的羊群行为。     

基于模糊诊断理论的航空发动机自动停车故障原因的分析

针对某型航空发动机空中自动停车故障诊断中故障症状与故障原因之间关系极为复杂、不确定等问题,提出了该型发动机故障的模糊诊断方法,建立了发动机自动停车故障模糊诊断的数值理论模型,利用专家知识动态建立了模糊诊断矩阵过程模型,并结合具体自动停车故障案例,实现了该型发动机自动停车故障的模糊诊断,验证了该方法应用于发动机系统故障诊断中的可行性.     

Alfvénic Fluctuations in an Interplanetary Coronal Mass Ejection Observed Near 1 AU

As for the present situation of coronal mass ejection(CME) triggering models,the distributions of Alfvén waves in flux ropes are different from model to model,and thus examining those distributions in interplanetary coronal mass ejection(ICME) is an effective way to connect ICME observations with these theoretical models of CME triggering.However,previous observations of Alfvénic fluctuations in ICMEs were rare with locations ranging from 0.3 AU to 0.68 AU only,which is usually explained as rapid dissipation of those remnant waves.Here we present an observation of Alfvén waves in a magnetic cloud(MC) near 1 AU,in situ detected by WIND in February 17～20,2011.The MC was generated by a CME accompanied with the first X-class flare in the 24 th solar cycle.The slope of the power spectral densities of magnetic fluctuation in the MC,are similar to those modes in ambient solar wind,but more anisotropic.The results will also be helpful for studies of CME theories and ICME thermodynamics.     

基于锁相热象法的金属疲劳特性评估方法研究

红外热象法作为一种无损、实时及非接触的测试技术,已应用于疲劳研究中。传统的疲劳试验方法存在试验周期长、耗费试件多等不足,而新兴的热象法可以快速确定金属材料或构件的疲劳极限。文中基于能量耗散理论,借助于先进的锁相热象技术,快速准确地测定Q235钢的疲劳极限。同时还对疲劳极限的热评估方法进行改进,以保证测试结果的准确性,有助于提供该类疲劳试验方法标准化依据。研究还表明,锁相热象法在健康监测中具有潜在的应用价值。     

脉冲电子束辐照中增强扩散效应的数值计算

针对强流脉冲电子束(HCPEB)表面改性的特点，采用适当的数学模型和数值模拟的方法，对9Cr18钢经Ti离子注入后又使用强流脉冲电子束表面辐照处理中产生的增强扩散效应进行了研究，计算结果与实验结果较为吻合。分析表明，扩散激活能的下降是导致增强扩散的主要原因，这与HCPEB改性过程产生的非平衡辐照缺陷浓度密切相关。     

Dynamics of Dust in a Plasma Sheath with Magnetic Field

Dynamics of dust in a plasma sheath with a magnetic field was investigated using a single particle model. The result shows that the radius, initial position, initial velocity of the dust particles and the magnetic field do effect their movement and equilibrium position in the plasma sheath. Generally, the dust particles with the same size, whatever original velocity and position they have, will locate at the same position in the end under the net actions of electrostatic, gravitational, neutral collisional, and Lorentz forces. But the dust particles will not locate in the plasma sheath if their radius is beyond a certain value.     

Electrostatic Modes of Dusty Plasmas in a Uniform Magnetic Field

Electrostatic dusty plasma waves in a uniform magnetic field are studied.Unless the magnetic field is extremely strong,the dust particles can hardly be magnetized,while however,electrons and ions are easily done so.Electrostatic modes in such dusty plasmas can then be investigated by making use of the “Moderately magnetized” assumption of magnetized electrons and ions,and unmagnetized dust particles.In a high frequency range,due to the existence of dust component.both frequencies of Langmuir waves(parallel to the magnetic field)and upper hybrid waves(perpendicular to the field) are reduced.In the frequency range of ion waves,besides the effect on dust-ion-acoustic waves propagating parallel to the magnetic field.the frequency of ion cyclotron waves perpendicular to the magnetic field is also enhanced.In a very low dust frequency range,we find an “ion-cyclotron-dust-acoustic” mode propagating across the field line with a frequency even slower than dust acoustic waves.     

Effects of Ion Temperature on Collisionless and Collisional RF Sheath

A numerical two-fluid simulation of the non-ionized radio frequency （rf） sheath model, has been carried out. This model is ＂global＂ and thus applicable to the sheath, pre-sheath and plasma regions, In the model all variables in the ion force balance equation, including the electrical force, ion pressure and neutral particle friction, are considered. The model is solved through a finite difference scheme and sheath characteristics are obtained. The effects of the ion temperature on both the collisionless and collisional sheath characteristics are discussed. Then it is concluded that 1） the model is in a good agreement with Bohm Theorem; 2） the ion temperature has significant effects on the rf sheath characteristics. The effects are far more significant on a collisional rf sheath than on a collisionless sheath.