径向收缩的等离子体的运动不稳定性

<正> 近几年来,人们详细地研究过等离子体某些运动状态的不稳定性,如Rayleigh-Taylor不稳定性和Kelvin-Helmholtz不稳定性等等。本文先根据雪铲模型讨论收缩效应的运动不稳定性,其次指出,在径向运动情形下,稳定性不只和加速度有关,而且也和速度等其它因素有关,因此,它并不相当于平面情形的Rayleig-Taylor不稳定性。 1.收缩效应的运动不稳定性在雪铲模型里,如果假定在某时刻t_1出现径向、周向和轴向的微扰动γ,θ,z,并以初始时刻to的位置θo、Zo以及时刻t为自变量,则在假定(γ,θ,z)的形式为(γ(t),-iθ(t),-iz(t))eimθo+ikzσ之后,就可得到线性化的扰动方程(采用高斯单位)为:

Numerical simulation of coherent structure in two-dimensional compressible mixing layers

The coherent structure in two-dimensional mixing layers is simulated numerically with the compressible Navier-Stokes equations. The Navier-Stokes equations are discretized with high-order accurate upwind compact schemes. The process of development of flow structure is presented: loss of stability, development of Kelvin-Helmholtz instability, rolling up and pairing. The time and space development of the plane mixing layer and influence of the compressibility are investigated.

Complete solution of the columbus problem for large-disturbance cases

The Columbus problem has been rigorously solved by Lyapunov's direct approach to the continuous system in gencral cases of large disturbance and the theory has proved to be in strict consistency with Kelvin's experiments.

On the non-linear stability theory of spinning solid bodies with liquid-filled cavities and its application to the columbus problem

In this paper, we first present a system of differential-integral equations for the largedisturbance to the general case that any arbitrarily shaped solid body with a cavity contain-ing viscous liquid rotates uniformly around the principal axis of inertia, and then develop aweakly non-linear stability theory by the Lyapunov direct approach. Applying this theoryto the Columbus problem, we have proved the consistency between the theory and Kelvin'sexperiments.

可压缩轴对称射流三维拟序结构的演化

采用高精度差分方法对空间发展轴对称可压缩射流流场进行直接数值模拟，计算结果显示了射流失稳后首先出现Kelvin-Helmholtz非稳定特征，流动的进一步发展，非线性效应的增长导致轴对称涡环的二次失稳和流向涡的产生，并给出了拟序结构的三维演化过程，计算结果证实了轴对称射流中二闪失稳，流向涡的产生是增强流动混合及流动产生转捩的重要机制。

平面酞菁弱取向外延薄膜的KPFM研究

载流子传输一直是有机半导体研究中最核心的问题，通过弱外延生长方法可制备高取向、大面积连续的平面酞菁化合物薄膜，其迁移率可达到单晶水平。本论文中应用建立起来的有机半导体开尔文探针力显微镜(KPFM)表征方法，从微观水平研究了这种弱取向外延薄膜和常规的多晶有机半导体薄膜中结构和电特性的关系。 1. 建立了有机半导体的KPFM表征方法。KPFM用微探针方法同时获得样品的表面形貌和电势，本文第二章中论述了KPFM的工作原理、操作方法和成像机制，解释了相关的有机半导体表面态的问题。并且定量验证我们所建立的这种方法的可靠性。 2. 运用KPFM研究了多晶态的有机半导体CuPc和F16CuPc，直接观察到晶界势垒的存在，说明CuPc晶界处存在类施主的缺陷能级，F16CuPc晶界处存在类受主的缺陷能级，这两两种缺陷态分别俘获空穴和电子，使晶界周围的载流子耗尽而形成空间电荷区，限制了载流子的传输，我们从实验的角度证明了有机半导体中晶界限制载流子传输的理论。另外得到多晶CuPc高能量分辨的局域功函图像，越是π电子暴露的表面其功函越高。 3. 在导电的H-Si(111)衬底上制备出6P诱导弱取向生长的CuPc和F16CuPc薄膜，比较了和SiO2衬底上的弱外延生长薄膜的特征。KPFM观察到在CuPc界面处的能带弯曲和空穴累积，这大大降低了载流子传输沟道内CuPc晶界的势垒，从而其迁移率得到很大提高，这说明6P除了具有在结构上诱导使酞菁取向的作用外，还具有电子结构上的效应。另外研究了6P弱外延生长的亚单层F16CuPc薄膜，直接观察到在6P-F16CuPc界面存在强烈的电荷累积，这从微观上说明了有机异质结的电特性。

多孔材料的合成和表征及离子液体中电化学沉积的研究

在BMIMPF6和BMIMBF4两种室温离子液体中研究了银和铂在玻碳电极上的电化学行为，采用电化学沉积方法制得了纳米颗粒银膜以及纳米颗粒铂膜。银和铂在上述两种室温离子液体中的电化学沉积过程为受扩散控制的三维瞬间（或渐进）成核／半球生长模式。在两种室温离子液体中所得纳米颗粒银膜对拉曼探针分子呈现出极强的表面增强拉曼散射效应。将室温离子液体中所得纳米颗粒铂膜用于甲醇的电化学催化氧化，结果表明其电催化性能优于水溶液中制得的纳米颗粒铂膜。报道了一种高比表面三维纳米多孔铂膜电极的制备方法。于室温条件下在玻碳电极上电沉积得到均一的RCu合金，然后基于脱合金成分腐蚀原理，选择性地阳极溶出RCu合金中的铜组分，从而得到纳米多孔铂膜电极。与多晶铂电极相比，这种通过脱合金成分腐蚀方法而得到的纳米多孔铂电极其比表面积至少可提高500倍。该方法简单、有效、具有可行性。这种纳米多孔铂膜电极表现出了高度的稳定性，并对氧的电化学还原和甲醇的电化学氧化有着显著的催化活性，在燃料电池和生物传感器等方面有很好的应用前景。电化学阻抗谱（EIS）表明，与多晶铂电极相比，脱合金成分腐蚀后所得纳米多孔铂电极的电荷迁移电阻大大降低，其电催化活性得到极大增强。采用电化学蚀刻技术在乙醇／HF溶液中制备得到了多孔硅，利用光致发光、Kelvin探针力显微镜以及拉曼散射等技术研究了阳极化过程相关的多孔硅表面微结构的变化。在较小的蚀刻电流密度和较短的蚀刻时间情况下，多孔硅表面呈现出簇状的浅丘形貌。随着电流密度和极化时间的增大，多孔硅表面层的形貌起伏和相应的表面势变化越来越大。此外，当逐渐增加电化学蚀刻电流密度和蚀刻时间时，观察到越来越强的光致发光以及拉曼散射峰的红移和非对称性展宽。当蚀刻时间不变而逐渐增加电流密度时，光致发光出现蓝移现象。有意思的是，当蚀刻电流密度不变而逐渐增加蚀刻时间时，光致发光的峰位置出现红移。

The main factor influencing the tensile properties of surface nano-crystallized graded materials

The improved mechanical properties of surface nano-crystallized graded materials produced by surface severe plastic deformation ((SPD)-P-2) are generally owing to the effects of the refined structure, work-hardened region and compressive residual stress. However, during the (SPD)-P-2 process, residual stress is produced simultaneously with work-hardened region, the individual contribution of these two factors to the improved mechanical properties remains unclear. Numerical simulations are carried out in order to answer this question. It is found that work hardening predominates in improving the yield strength and the ultimate tensile strength of the surface nano-crystallized graded materials, while the influence of the residual stress mainly emerges at the initial stage of deformation and decreases the apparent elastic modulus of the surface nano-crystallized graded materials, which agrees well with the experimental results. (C) 2010 Elsevier B.V. All rights reserved.

岩体中应力波幅值随时空衰减的关系

把岩石抽象为Kelvin-Voigt黏弹性体, 应用复数理论建立了应力波在岩石中传播时的振动频率和波动频率的关系, 在此基础上, 研究了岩石和含有一组平行结构面的岩体中应力波幅值随时间和随空间衰减的关系. 研究表明, 应力波在岩石的传播过程中, 频率是影响应力波幅值衰减的的主要因素; 应力波在含有1组平行结构面岩体的传播过程中, 由于结构面的存在, 影响了应力波能量的传播, 其幅值随时空衰减系数主要由结构面间距及其反射系数决定, 结构面间距减小和反射系数增加, 幅值随传播距离的衰减系数增加和随时间的衰减系数减小, 而结构面的黏性系数增加, 幅值随传播距离的衰减系数增加, 但随时间的衰减系数变化很小. 上述结论对岩体结构探测具有重要的指导意义

Isotype heterojunction between organic crystalline semiconductors

We report the effect of n-n isotype organic heterojunction consisting of copper hexadecafluorophthalocyanine (F16CuPc) and phthalocyanatotin (IV) dichloride (SnCl2Pc). Their interfacial electronic structure was observed by Kelvin probe force microscopy (KPFM), and there is band bending in two materials, resulting in an electron accumulation region in F16CuPc layer and an electron depletion region in SnCl2Pc layer. The forming of organic heterojunction was explained by carriers flowing through the interface due to thermal emission of electrons. Furthermore, the carrier transport behavior parallel and vertical to heterojunction interface was also revealed by their heterojunction field-effect transistor with normally on operation mode and heterojunction diodes with rectifying property.

Electrochemical investigations of micro-droplets formed on metals during the deliquescence of salt particles in atmosphere

CORROSION; WATER; SPECTROSCOPY; CHLORIDE; ZINC; NUCLEATION; INTERFACE; ELECTRODE; SURFACES; GROWTH

Dynamics of intraseasonal sea level and thermocline variability in the equatorial Atlantic during 2002-03

Satellite and in situ observations in the equatorial Atlantic Ocean during 2002-03 show dominant spectral peaks at 40-60 days and secondary peaks at 10-40 days in sea level and thermocline within the intraseasonal period band (10-80 days). A detailed investigation of the dynamics of the intraseasonal variations is carried out using an ocean general circulation model, namely, the Hybrid Coordinate Ocean Model (HYCOM). Two parallel experiments are performed in the tropical Atlantic Ocean basin for the period 2000-03: one is forced by daily scatterometer winds from the Quick Scatterometer (QuikSCAT) satellite together with other forcing fields, and the other is forced by the low-passed 80-day version of the above fields. To help in understanding the role played by the wind-driven equatorial waves, a linear continuously stratified ocean model is also used. Within 3 degrees S-3 degrees N of the equatorial region, the strong 40-60-day sea surface height anomaly (SSHA) and thermocline variability result mainly from the first and second baroclinic modes equatorial Kelvin waves that are forced by intraseasonal zonal winds, with the second baroclinic mode playing a more important role. Sharp 40-50-day peaks of zonal and meridional winds appear in both the QuikSCAT and Pilot Research Moored Array in the Tropical Atlantic (PIRATA) data for the period 2002-03, and they are especially strong in 2002. Zonal wind anomaly in the central-western equatorial basin for the period 2000-06 is significantly correlated with SSHA across the equatorial basin, with simultaneous/ lag correlation ranging from-0.62 to 0.74 above 95% significance. Away from the equator (3 degrees-5 degrees N), however, sea level and thermocline variations in the 40-60-day band are caused largely by tropical instability waves (TIWs). On 10-40-day time scales and west of 10 degrees W, the spectral power of sea level and thermocline appears to be dominated by TIWs within 5 degrees S-5 degrees N of the equatorial region. The wind-driven circulation, however, also provides a significant contribution. Interestingly, east of 10 W, SSHA and thermocline variations at 10 40- day periods result almost entirely from wind-driven equatorial waves. During the boreal spring of 2002 when TIWs are weak, Kelvin waves dominate the SSHA across the equatorial basin (2 degrees S-2 degrees N). The observed quasi-biweekly Yanai waves are excited mainly by the quasi-biweekly meridional winds, and they contribute significantly to the SSHA and thermocline variations in 1 degrees-5 degrees N and 1 degrees-5 degrees S regions.

Long-Wave Dynamics of Sea Level Variations during Indian Ocean Dipole Events

Long-wave dynamics of the interannual variations of the equatorial Indian Ocean circulation are studied using an ocean general circulation model forced by the assimilated surface winds and heat flux of the European Centre for Medium-Range Weather Forecasts. The simulation has reproduced the sea level anomalies of the Ocean Topography Experiment (TOPEX)/Poseidon altimeter observations well. The equatorial Kelvin and Rossby waves decomposed from the model simulation show that western boundary reflections provide important negative feedbacks to the evolution of the upwelling currents off the Java coast during Indian Ocean dipole (IOD) events. Two downwelling Kelvin wave pulses are generated at the western boundary during IOD events: the first is reflected from the equatorial Rossby waves and the second from the off-equatorial Rossby waves in the southern Indian Ocean. The upwelling in the eastern basin during the 1997-98 IOD event is weakened by the first Kelvin wave pulse and terminated by the second. In comparison, the upwelling during the 1994 IOD event is terminated by the first Kelvin wave pulse because the southeasterly winds off the Java coast are weak at the end of 1994. The atmospheric intraseasonal forcing, which plays an important role in inducing Java upwelling during the early stage of an IOD event, is found to play a minor role in terminating the upwelling off the Java coast because the intraseasonal winds are either weak or absent during the IOD mature phase. The equatorial wave analyses suggest that the upwelling off the Java coast during IOD events is terminated primarily by western boundary reflections.

Intraseasonal variability of Indian Ocean sea surface temperature during boreal winter: Madden-Julian Oscillation versus submonthly forcing and processes

[ 1] Intraseasonal variability of Indian Ocean sea surface temperature (SST) during boreal winter is investigated by analyzing available data and a suite of solutions to an ocean general circulation model for 1998 - 2004. This period covers the QuikSCAT and Tropical Rainfall Measuring Mission (TRMM) observations. Impacts of the 30 - 90 day and 10 - 30 day atmospheric intraseasonal oscillations (ISOs) are examined separately, with the former dominated by the Madden-Julian Oscillation (MJO) and the latter dominated by convectively coupled Rossby and Kelvin waves. The maximum variation of intraseasonal SST occurs at 10 degrees S - 2 degrees S in the wintertime Intertropical Convergence Zone (ITCZ), where the mixed layer is thin and intraseasonal wind speed reaches its maximum. The observed maximum warming ( cooling) averaged over ( 60 degrees E - 85 degrees E, 10 degrees S - 3 degrees S) is 1.13 degrees C ( - 0.97 degrees C) for the period of interest, with a standard deviation of 0.39 degrees C in winter. This SST change is forced predominantly by the MJO. While the MJO causes a basin-wide cooling ( warming) in the ITCZ region, submonthly ISOs cause a more complex SST structure that propagates southwestward in the western-central basin and southeastward in the eastern ocean. On both the MJO and submonthly timescales, winds are the deterministic factor for the SST variability. Short-wave radiation generally plays a secondary role, and effects of precipitation are negligible. The dominant role of winds results roughly equally from wind speed and stress forcing. Wind speed affects SST by altering turbulent heat fluxes and entrainment cooling. Wind stress affects SST via several local and remote oceanic processes.

Roles of equatorial waves and western boundary reflection in the seasonal circulation of the equatorial Indian Ocean

An ocean general circulation model (OGCM) is used to study the roles of equatorial waves and western boundary reflection in the seasonal circulation of the equatorial Indian Ocean. The western boundary reflection is defined as the total Kelvin waves leaving the western boundary, which include the reflection of the equatorial Rossby waves as well as the effects of alongshore winds, off-equatorial Rossby waves, and nonlinear processes near the western boundary. The evaluation of the reflection is based on a wave decomposition of the OGCM results and experiments with linear models. It is found that the alongshore winds along the east coast of Africa and the Rossby waves in the off-equatorial areas contribute significantly to the annual harmonics of the equatorial Kelvin waves at the western boundary. The semiannual harmonics of the Kelvin waves, on the other hand, originate primarily from a linear reflection of the equatorial Rossby waves. The dynamics of a dominant annual oscillation of sea level coexisting with the dominant semiannual oscillations of surface zonal currents in the central equatorial Indian Ocean are investigated. These sea level and zonal current patterns are found to be closely related to the linear reflections of the semiannual harmonics at the meridional boundaries. Because of the reflections, the second baroclinic mode resonates with the semiannual wind forcing; that is, the semiannual zonal currents carried by the reflected waves enhance the wind-forced currents at the central basin. Because of the different behavior of the zonal current and sea level during the reflections, the semiannual sea levels of the directly forced and reflected waves cancel each other significantly at the central basin. In the meantime, the annual harmonic of the sea level remains large, producing a dominant annual oscillation of sea level in the central equatorial Indian Ocean. The linear reflection causes the semiannual harmonics of the incoming and reflected sea levels to enhance each other at the meridional boundaries. In addition, the weak annual harmonics of sea level in the western basin, resulting from a combined effect of the western boundary reflection and the equatorial zonal wind forcing, facilitate the dominance by the semiannual harmonics near the western boundary despite the strong local wind forcing at the annual period. The Rossby waves are found to have a much larger contribution to the observed equatorial semiannual oscillations of surface zonal currents than the Kelvin waves. The westward progressive reversal of seasonal surface zonal currents along the equator in the observations is primarily due to the Rossby wave propagation.