复合材料层板纯剪实验

本文提出一个测量复合材料层板面内剪切性质的方板纯剪试验法。首先对方法的可靠性进行试验检验,然后对两种复合材料层板的剪切行为进行试验。     

The evolution of mirror type magnetic fluctuations in the magnetosheath based on multipoint observations

Two orbits were selected in January–February 2006 when the separation between the Cluster spacecraft was large and mirror type magnetic field fluctuations were observed by all spacecraft in different regions of the terrestrial magnetosheath. Minimum variance analysis was applied to find the mirror type fluctuations, and the amplitude of the fluctuations was determined individually. Mirror mode structures are moving along the streamlines frozen in the plasma. A model was developed for the calculation of plasma flowtime from the bow shock to the observation point. The growth rate of the field strength perturbations was estimated by comparing the amplitudes of fluctuations observed simultaneously at distant locations (∼10,000 km) based on the assumption that δB ∼ exp(γt). The obtained growth rate values were about an order of magnitude smaller than those provided by linear models and they decreased in the inner regions of the magnetosheath, indicating some saturation in the growth of the waves when proceeding towards the magnetopause. The results of these two case studies suggest that mirror type fluctuations originate from the compression region downstream of the quasi-perpendicular bow shock, and the growth of the fluctuations cannot be described by linear approximations.     

相对论性离子束（环束）流引起的电磁不稳定性

在相对论性框架下，研究了冷离子流产生的右旋共振模，非共振模电磁不稳定性的特征结果表明，非共振模不稳定性增长率受离子流初始参数影响较大，而右旋共振模的增长率则受离子流初始参数影响较小。此结果可应用于太阳高能离子流通过低日冕区和地球磁层辐射带俘获的高能质子情形。     

Shock Wave Interaction with the Magnetopause

The magnetopause is in continuous motion and shock waves and impulsive acceleration events can occur. As an example, we show that the interaction of an interplanetary shock with the bow shock can generate a shock wave that after passing through the magnetosheath can interact with the magnetopause. In fluid dynamics, when a shock wave encounters a fluid discontinuity, the interface may become unstable and form bubbles and spikes. We consider this Richtmyer-Meshkov instability in magnetohydrodynamics. At the dayside magnetopause, the instability tends to be stabilized by the magnetic field. However, the shock wave interaction can initiate magnetic field reconnection for the southward IMF, which may be important in strong interplanetary shock events. This revised version was published online in August 2006 with corrections to the Cover Date.     

新型工具电极制造方法

用电火花加工复杂形状模腔的关键之一是工具电极的制造。为了解决一般电极材料价高，复杂型腔难以加工等问题，通过试验研究，推出了一种以石膏和塑料为基本材料，采用非金属电镀工艺制造工具电极的新方法。     

细晶铸造对K418合金拉伸性能的影响

测试了不同温度下细晶铸造和普通铸造Ｋ４１８合金的拉伸性能。结果表明，细晶铸造明显改善了合金的极限位伸强度和屈服强度，室温和６００℃的合金拉伸强度和晶粒平均直径符合Ｈａｌｌ－Ｐｅｔｃｈ关系。     

Daytime VHF amplitude scintillations recorded at an Indian low-latitude station,Waltair (17.7°N, 83.3°E) during 1997–2003

In this research, it is presented the daytime amplitude scintillations recorded at VHF frequency (244 MHz) at an Indian low-latitude station, Waltair (17.7°N, 83.3°E) during seven continuous years (1997–2003). Contrary to the nighttime scintillation seasonal trends, the occurrence of daytime scintillations maximizes during summer followed by winter and the equinox seasons. The fade depths, scintillation indices and the patch durations of daytime scintillations are meager when compared with their nighttime counterparts. A co-located digital high frequency (HF) ionosonde radar confirms the presence of sporadic (Es) layers when daytime scintillations are observed. The presence of daytime scintillations is evident when the critical frequency of the Es-layer (foEs) is ≥4 MHz and Es-layers are characterized by a highly diffuse range spread Es echoes as can be seen on ionograms. It is surmised that the gradient drift instability (GDI) seems to be the possible mechanism for the generation of these daytime scintillations. It is quite likely that the spread Es-F-layer coupling is done through polarization electric fields (Ep) that develop inside the destabilized patches of sporadic E layers, which are mapped up to the F region along the field lines as to initiate the daytime scintillations through the GDI mechanism. Further, the presence of additional stratification of ionosphere F-layer, popularly known as the F3-layer, is observed on ionograms once the Es-layers and daytime scintillations are ceased.     

Two-stream instability generation in the lunar ionosphere

The Two-stream Instability (TSI) generation is studied analytically in the lunar ionosphere. The TSI is a tiny perturbation in the electron plasma density, due to which an electric field grows with time and this growth is facilitated by the electron plasma in the background. In lunar ionosphere, the TSI comes into existence when the solar wind interacts unhindered with the tenuous lunar electron plasma in the surface bound exosphere. In this study, the conditions which allow the TSI to form and the subsequent instability growth with time i.e. the growth factor, is estimated. Initially, the threshold condition for the TSI to take place is determined. Thereafter, the solar wind and lunar plasma parameter contribution to trigger TSI is investigated along with the effect of these parameters in the evolution of TSI. The plasma TSI evolution with the passage of time is also depicted in phase space diagram with Particle-In-Cell simulations.     

部分球壳分布离子流激发的电磁不稳定性

在离子环束流和低频电磁波相互作用的过程中廓了环束流将演化成具有投掷角展宽的部分球壳速度分布离子流,其投掷角展宽随时间增大,低频右旋电磁不稳定性增长率峰值,总的说来也逐渐增大,并向高频短波方向移动,与此相反,低频左旋电磁不稳定性增长率峰值,当投掷 角展宽等于０时,大于右旋不稳定性峰值,但随着投掷角展宽增加而迅速低于右 性增长率峰值,并向工波方向移动。     

一种多晶石墨的拉伸蠕变行为

对一种多晶石墨材料进行了拉伸蠕变试验后,用ＲＡＭＡＮＯＲＵ１０００拉曼光谱仪对蠕变前后的试样作了分析,并用扫描电镜观察了蠕变前后试样纵向剖面的孔隙变化。结果表明：在１７００℃,０．７ＭＰａ的应力作用下多晶石墨材料不发生明显蠕变。蠕变初期可用ε－ε０＝Ａｔｎ进行描述,在不同温度和应力下ｎ值从０．４８５～０．８之间变化。在同一应力条件下,随温度提高,ｎ值增大。激光拉曼光谱仪和扫描电镜分析表明,多晶石墨蠕变后石墨化程度增加、孔隙增多、变大。