冲击加载下铝中孔洞长大的微观机理分析

 利用扫描电镜和透射电镜观测了冲击加载后高纯铝损伤状态孔洞的分布,发现在冲击波加载后,高纯铝中出现了大量的孔洞,孔洞大小多集中在百纳米尺度,分布不均匀,且呈现出带状形貌,局部区域的孔洞在冲击波作用下优先发展,孔洞长大,形成微米级的大孔洞。进一步的观测发现,在孔洞周围出现了大量的位错发射,发射方向位于{111}晶面上,是面心立方金属的密排面。运用分子动力学模拟进行了对比研究,验证了位错发射方向与观测结果是一致的。     

Multiple-Relaxation-Time Lattice Boltzmann Approach to Richtmyer-Meshkov Instability

The aims of the present paper are twofold. At first, we further study the Multiple-Relaxation-Time (MRT) Lattice Boltzmann (LB) model proposed in [Europhys. Lett. 90 (2010) 54003]. We discuss the reason why the Gram-Schmidt orthogonalization procedure is not needed in the construction of transformation matrix M; point out a reason why the Kataoka-Tsutahara model [Phys. Rev. E 69 (2004) 035701(R)] is only valid in subsonic flows.The von Neumann stability analysis is performed. Secondly, we carry out a preliminary quantitative study on the Richtmyer-Meshkov instability using the proposed MRT LB model. When a shock wave travels from a light medium to a heavy one, the simulated growth rate is in qualitative agreement with the perturbation model by Zhang-Sohn. It is about half of the predicted value by the impulsive model and is closer to the experimental result. When the shock wave travels from a heavy medium to a light one, our simulation results are also consistent with physical analysis.     

用NND格式模拟Kelvin-Helmholtz不稳定性

使用局部Steger-Warming通量分裂方法,利用NND有限差分格式求解守恒型流体力学方程组,实现对Kelvin-Helmholtz不稳定性的数值模拟.数值模拟给出的线性增长率与线性稳定性分析给出的结果相符合,得到锐利的界面变形图像.     

关于铁的势函数的研究

本文介绍了由Voter-Chan提出的嵌入式原子势模型(EAM),运用该原子势计算了单晶铁的弹性常数和在高压下的固固相变.模拟结果显示此EAM势描述铁的弹性常数与实验值有一定的偏离,但是却比较好的反映了铁在高压下的相变.此EAM势模型可以用来进一步研究铁在极端条件下的相变过程等,对相变的微观机制进行更细致深入的研究.     

带电导体椭球表面的电荷密度与电场

利用极限情形推断了带电导体椭球表面的电荷密度与电场强度.     

Acceleration of Initially Moving Electrons by a Copropagation Intense Laser Pulse

Acceleration of an initially moving electron by a copropagation ultra-short ultra-intense laser pulse in vacuum is studied. It is shown that when appropriate laser pulse parameters and focusing conditions axe imposed, the acceleration of electron by ascending front of laser pulse can be much stronger compared to the deceleration by descending part. Consequently, the electron can obtain significantly high net energy gain. We also report the results of the new scheme that enables a second-step acceleration of electron using laser pulses of peak intensity in the range of 1019 - 1020 Wμm^2/cm^2. In the first step the electron acceleration from rest is limited to energies of a few MeV, while in the second step the electron acceleration can be considerably enhanced to about 100 MeV energy.     

原子团簇对飞秒激光的吸收

使用800nm飞秒脉冲激光研究了Xe,Ar,He等原子团簇对激光的吸收.实验结果表明,脉冲阀门的工作压力、所使用的气体种类等因素对团簇的尺寸及团簇对激光的吸收影响很大.在阀门工作压力为20×10⁵Pa、激光功率密度为1×10¹⁵W/cm²的条件下,Xe团簇对激光的吸收高达45%.激光预脉冲的存在会降低原子团簇对激光能量的吸收.离子能量测量结果表明,团簇对激光的高效吸收导致较高离子温度等离子体的生 关键词： 原子团簇 飞秒激光 能量吸收效率 高能离子     

Optical diagnostics of femtosecond laser plasmas

Optical diagnostics of evolution of plasmas produced by ultrashort laser pulses is carried out using a femtosecond probing beam. The time sequence of plasma shadowgrams and interferograms are obtained. The filamentation instability in high-density region induces the local density modification. Large-scale toroidal magnetic fields confine plasma expansion in the transverse direction, resulting in the formation of a plasma jet. The plasma expansion along the target normal direction is found to scale as t^1/2.     

Two-Dimensional Rayleigh-Taylor Instability in Incompressible Fluids at Arbitrary Atwood Numbers

The Rayleigh-Taylor instability in two-dimensional incompressible fluids at arbitrary Atwood numbers is studied by expanding the perturbation velocity potential to third order. The second and third harmonic generation effects of single-mode perturbation are analyzed, as well as the nonlinear correction to the exponential growth of the fundamental modulation. The mode coupling coefficients are dependent on the Atwood numbers. Our simulations support the weakly nonlinear results. We find that the ratio of the nonlinear saturation amplitude ηs and the perturbation wavelength λ is dependent on the Atwood number AT and the relation is ηs/λ=（1/π）[√2/5/√（1＋3AT2 ）].     

Ray tracing method for the grazing incidence flat-field imaging soft X-ray spectrometer

A ray tracing method is introduced for helping adjustment and spectra analysis of the grazing incidence flat-field imaging soft X-ray spectrometer. For a single point source, the spectra images obtained by separate components, the toroidal mirror, and the grazing incidence flat-field concave grating with varied line spaces are given respectively. The calculated spectral images of the single point source by the spectrometer are also given for comparison with measurements with different experimental alignments.