Identification of the wave-particles interaction in space plasma using higher-order statistics

The interaction of wave-particles and wave-wave in the space plasmas are essentially non-linear or non-Gaussian processes. Using the higher-order statistical analyses methods (higher-order moments and bi-tri correlation or bi-tri spectrum), its physical properties can be described. The question addressed in this paper is that of the usefulness of higher-order statistical analysis for identification of the wave-particles interaction in space plasmas. The signals handled are from the ARCAD-3 ISOPROBE experiment on ELF frequency range, then strong electrostatic turbulence and electron density irregularities. Second and third order statistical analyses are applied: first, on time series associated with each type of measurement, then, on the two types. All results are presented for one typical case. Correlation functions estimated over the corresponding time intervals point out the existence of a, non-linear interaction between these fluctuations and electrostatic filed. Supported by National Natural Science Foundation of China Zhao Zhenyu; born in 1952, Ph. D.     

Higher-order statistics and nonlinear processes in space plasmas

Statistics of order 2 (variance, auto and cross-correlation functions, auto and cross-power spectra) and 3 (skewness, auto and cross-bicorrelation functions, auto and cross-bispectra) are used to analyze the wave-particle interaction in space plasmas. The signals considered here are medium scale electron density irregularities and ELF/ULF electrostatic turbulence. Nonlinearities are mainly observed in the ELF range. They are independently pointed out in time series associated with fluctuations in electronic density and in time series associated with the measurement of one electric field component. Peaks in cross-bicorrelation function and in mutual information clearly show that, in well delimited frequency bands, the wave-particle interactions are nonlinear above a certain level of fluctuations. The way the energy is transferred within the frequencies of density fluctuations is indicated by a bi-spectra analysis. Supported by the National Natural Science Foundation of China Zhao Zhengyu: born in 1952. Doctor, Associate professor     

An interpretation of density holes observed by Cluster and Double Star in solar wind

To interpret density holes in the solar wind,which are nonlinear structures observed by Cluster and Double Star,we propose an electrostatic ion fluid model.We derive the Sagdeev potential from the magnetohydrodynamic(MHD)equations and study the characteristics of nonlinear structures in our model.The results show that density depletions(or holes)can develop from linear ion acoustic waves or ion cyclotron waves in space plasmas when parameters such as Mach number,initial electric field and ratio of ion to electron temperature satisfy certain conditions.In our model,the relative density depletion(or density holes)is from 0 to 1, and the time duration of density holes is from 2 s to more than 98 s.These are in good agreement with the observations by Cluster and Double Star in the solar wind.Our model also shows that the density holes should be accompanied by bipolar electric field solitary structures,which have also been observed by Cluster in the solar wind.     

带转动的相对论电子束在非中性等离子体柱状波导中传输的稳定性分析

首先利用相对论电子束的自电场与自磁场所产生的径向力平衡方程,计算出相对论电子束在稳态非中性等离子体填充的柱状波导中传输的转动频率。然后运用 MHD 方程,求得电子束静电扰动的本征方程和色散关系。发现电子束与非中性等离子体相互作用的不稳定性增长特性及静电扰动在高频长波被显著放大。     

High-speed flowing plasmas in the Earth’s plasma sheet

A research topic of great interest to the space physics community is the observation of plasmas flowing at hundreds of kilometers per second in the Earth’s plasma sheet. Although considerable effort has been made to understand the source of fast-flowing plasmas, many questions remain unanswered about the mechanisms that produce high-speed flows and the effects they have on magnetospheric disturbances, especially their contributions to magnetospheric convection and substorms. In this paper, we discuss briefly the history of high-speed flows and review the proposed mechanisms, signatures of high-speed flows in auroras and their interaction with the background plasma. We then summarize the relationships between high-speed flows and magnetic structures, discuss questions associated with substorms, and finally pose several important scientific questions that need to be addressed.     

相对论正负电子对等离子体色散关系

等离子体色散关系是研究等离子体中波及其不稳定性的基础。本文以正电子温度与电子温度之比为参数,对无磁化、无碰撞、各向同性、正负电子对等离子体纵波和横波的色散方程进行解析计算,对正负电子对双温等离子体纵波和横波进行研究,得到长波支和短波支的色散关系。基于纵波和横波解析色散曲．线的不连续性,进而采用数值计算的方法求解完整的正负电子对双温等离子体纵波和横波的色散方程,得到其数值解。纵波和横波的数值解色散曲线可将解析上的长波和短波衔接起来,得到较为全面的色散图像。     

利用ABEEM模型在分子形貌轮廓上计算几个五元环配合物的分子静电势

分子的许多物理和化学性质都与其静电势密切相关.分子静电势是指分子在空间某一位置产生的分子静电作用势能,分子之间的相互作用可以通过静电势这个物理量来表述.利用ABEEMσπ模型计算出回归到各原子位点的电荷分布,结合自编Fortran程序可快速计算得到分子的静电势,将其投影到分子形貌轮廓上,即可得到在分子形貌上的静电势分布图.笔者选取咪唑、吡唑、噻吩、噻唑和异噻唑等五元环配合物作为模型分子,分别采用从头计算方法和ABEEM模型方法计算它们的分子静电势,并将其投影到分子形貌上.通过比较,ABEEM模型方法不仅可以快速计算分子的静电势,且与从头计算所得结果一致.     

原油中水滴在电场中的凝聚行为

利用静态电凝聚装置和显微摄影对文题进行研究,考察了水滴直径和油样含水量与电场强度和停留时间的关系。结果表明:水滴的平均粒径和最大平均粒径在低电压下随停留时间的延长而缓慢增大,5min后逐步趋向定值;当场强超过3000V/cm时,水滴粒径在2min之内增长到最大值,然后下降,场强越高,其增长速度和下降速度越快。油样的含水量在电场中停留一段时间后开始下降。电场强度越大,脱水过程开始得越早。在不同的场强下油样含水量的下降速度都是先快后慢。就脱水效率而言,存在一个最佳停留时间。对于绝缘电极来说,交流电场的凝聚脱水效果要高于直流电场。     

FDTD(2,4)算法的数值色散特性及其在微带天线中的应用研究

该文研究了在时间上采用2阶差分、空间上采用4阶差分的高阶FDTD(2，4)数值方法，推导出其三维差分公式，并详细分析了其数值色散特性．另外，将PML吸收边界有效地应用于微带天线的计算，并与传统FDTD(2，2)数值结果进行了对比．结果证明高阶FDTD(2，4)算法能够有效减小数值色散和相速误差，而且可以降低对计算机内存的要求，减小计算量，适用的计算频段更高．     

货车干摩擦阻尼的线性化研究

应用统计线性化和能量等效方法，求解货车非线性阻尼的当量线性值，并计算分析了Ｃ６２Ａ型货车车体的垂向振动响应．分析结果表明统计线性化方法可用于求解货车非线性阻尼的当量线性值。     

带时滞项的高阶Kirchhoff方程的拉回吸引子

研究了带有时滞项的高阶Kirchhoff方程的拉回吸引子的存在性.首先利用解的有界性验证了拉回吸引集的存在性,接着借助sobolev空间的紧嵌入证明了该初边值问题产生的过程是紧的,最后得到了拉回吸引子的存在性.     

高阶时频分布在滚动轴承故障诊断中的应用研究

滚动轴承故障信号是非高斯、非线性、非平稳信号,由于调制性,使用幅值谱分析方法无法找到轴承故障频率。将高阶时频分布——主要是Wigner双谱分析方法应用于滚动轴承的故障诊断,计算滚动轴承振动信号的高阶时频分布,并对其沿时间轴切片,分析了切片的幅值谱。针对不同故障轴承,对其振动信号幅值谱、高阶时频分布及其切片谱的对比分析表明,高阶时频及其切片谱性能优于幅值谱。     

变质量任意阶非线性非完整系统相对于非惯性系的广义Noether定理

全面研究了Noether定理的发展历史与现状。定义m次相对速度空间,构造变质量力学系统相对于非惯性系的Lagrange函数,建立变质量任意阶非线性非完整系统相对于非惯性参考系的万有D'Alembert-Lagrange变分原理,提出并证明了这类系统的广义Noether定理,研究了其守恒量,并加以讨论。惯性系和常质量系统的各种Noether定理均是本文定理的特款。     

Intense plasma waves at and near the solar wind termination shock

Plasma waves are a characteristic feature of shocks in plasmas, and are produced by non-thermal particle distributions that develop in the shock transition layer. The electric fields of these waves have a key role in dissipating energy in the shock and driving the particle distributions back towards thermal equilibrium. Here we report the detection of intense plasma-wave electric fields at the solar wind termination shock. The observations were obtained from the plasma-wave instrument on the Voyager 2 spacecraft. The first evidence of the approach to the shock was the detection of upstream electron plasma oscillations on 1 August 2007 at a heliocentric radial distance of 83.4 au (1 au is the Earth-Sun distance). These narrowband oscillations continued intermittently for about a month until, starting on 31 August 2007 and ending on 1 September 2007, a series of intense bursts of broadband electrostatic waves signalled a series of crossings of the termination shock at a heliocentric radial distance of 83.7 au. The spectrum of these waves is quantitatively similar to those observed at bow shocks upstream of Jupiter, Saturn, Uranus and Neptune.     

Condition Monitoring of Turbines Using Nonlinear Mapping Method

Aiming at the non-linear nature of the signals generated from turbines,curvilinear component analysis (CCA),a novel nonlinear projection method that favors local topology conservation is presented for turbines conditions monitoring.This is accomplished in two steps.Time domain features are extracted from raw vibration signals,and then they are projected into a two-dimensional output space by using CCA method and form regions indicative of specific conditions,which helps classify and identify turbine states visually.Therefore,the variation of turbine conditions can be observed clearly with the trajectory of image points for the feature data in the two-dimensional space,and the occurrence and development of failures can be monitored in time.     

基于时空影响域的地震网络构造方法

针对地震系统表现出的时空复杂性,提出一种基于时空影响域的地震网络构造方法,根据震级的大小确定地震在时间和空间上的直接影响范围.实验结果表明,所提方法构造的地震网络在不同时间跨度下均表现出稳定的无标度特征,幂指数在1到2之间,节点的出入度呈现正相关性;网络的平均聚集系数在大地震来临之后迅速增大,然后随时间推移逐渐减小,最终恢复平稳;通过地震数据所构成的基于时空影响域的网络表现出一定的统计规律,可以帮助分析地震系统的内在联系.     

闽宁对口帮扶系统发展动力学模型及其应用

把经济学时空引进模型体系,建立起讨论模型的严格时空参照系,提出供需和管理三大经济位势,提出经济渗透率、空隙度、饱和度、粘滞度等参数,建立了经济力学流动工程;引进空间作用函数,改进空间相互作用模型;广义定义资源概念,给出资源优化配置决策模型,使其适用于广泛的应用场合,在此基础上,阐述了闽宁对口帮扶系统发展的动力机制和运行机制,并提出了定性和定量相结合的系统分析方法,供决策参考。     

狭缝型微空心阴极维持放电等离子体

为在高气压条件下获得稳定、大体积的放电等离子体,实验研究了氩气中的狭缝型微空心阴极放电(SMHCD)特性. 设计了包括SMHCD的三电极放电系统,并利用SMHCD作为预电离源(等离子体阴极),在不同放电条件下测试了该系统的放电特性并讨论了其放电模式. 结果表明,SMHCD具有微空心阴极放电的特性,在适当条件下可以形成稳定的辉光放电. 利用SMHCD离子源可以获得大体积、高气压的狭缝型微空心阴极维持放电(SMSD)等离子体. SMSD具有普通直流辉光放电的特性,且SMHCD本身的放电电流以及第三电极处所加的电压对SMSD的形成有十分重要的作用. 该系统可以产生大面积均匀等离子体.     

磁流变液沉降稳定性改进及对流变性能的影响

对影响磁流变液沉降稳定性的颗粒表面性质、固／液界面性质和大小颗粒之间相互作用等因素进行了实验研究和探讨,实验结果表明：磁流变悬浮液体的稳定性取决于固相颗粒这间的静电排斥作用或固－液界面分子构型所产生的空间阻效应;对于颗粒径度较大的分散体系,通过改善粒子表面的结构,依靠体系的结构力学性质改善粗大颗粒悬浮液体的沉降稳定性。     

子午线轮胎模态分析的有限元方法

轮胎的动态特性是影响车辆整体性能的重要指标之一,文章在充分考虑轮胎材料的各种非线性特性的基础之上,应用ANSYS软件建立了用于子午线轮胎动态特性分析的非线性有限元模型,并针对该模型进行了模态分析,得到了其固有频率及相应的振型。结果证明,该方法具有一定工程实用价值,为轮胎的后续动态分析奠定了基础,并为轮胎特性对整车性能影响的研究提供参考依据。