Keck observations of ROSAT ultra-luminous X-ray source candidates

We present results of optical follow-up observations of candidate ultra-luminous X-ray sources (ULXs). Using Keck optical spectroscopy, 17 of the candidates from the Colbert and Ptak [Colbert, E.J.M., Ptak, A.F. A catalog of candidate intermediate-luminosity X-ray objects. ApJS 143, 25–45, 2002] catalog have been identified; this is one of the largest sets of optical identifications of such objects thus far. Fifteen are background active galactic nuclei (AGN); two are foreground stars in our Galaxy. These findings are consistent with background and foreground object expectations, as derived from log N–log S relations. Also, the results are briefly discussed in terms of the spiral-galaxy/ULX connection.     

Grid-Adaptive Computations of Magnetized Jets

We present grid-adaptive numerical simulations of magnetized plasma jets, modeled by means of the compressible magnetohydrodynamic equations. The Adaptive Mesh Refinement strategy makes it possible to investigate long-term jet dynamics where both large-scale and small-scale effects are at play. We extend recent findings for uniformly magnetized, periodic shear layers to planar and fully 3D extended jet segments. The jet lengths cover multiple, typically 10, axial wavelengths of the fastest growing Kelvin–Helmholtz (KH) like modes. The dominant linear MHD instabilities of the jet flows are quantified by means of MHD spectroscopic analysis. In cases characterized by sonic Mach numbers about unity and large plasma beta values, both single and double shear layers (planar jets) manifest self-organizing trends to large scales, e.g. by continuous pairing/merging between co-rotating vortices, simultaneously with the introduction of small-scale features by magnetic reconnection events. The vortices form as a result of KH unstable shear-flow layers, and their coalescence arises from the growth of subharmonic modes at multiple wavelengths of the fastest growing KH instability. In extended two-dimensional jet segments, we investigate how varying jet width alters this coalescence process occurring at both edges, e.g. by introducing Batchelor-like coupling between counter-rotating vortices formed at opposing weakly magnetized, close shear layers. Finally, periodic segments of supersonic magnetized jets are simulated in two- and three-dimensional cases, which are characterized by violent shock-dominated transients.     

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.     

高职高专院校建设数字化校园过程中应注意的问题

21世纪以来,数字化和信息化成为现代社会的主要标志。高职高专院校为了提高自己的管理水平,跟上时代的步伐,也都在着手数字化校园的建设。本文从数字化校园的基本概念入手,介绍数字化校园的组成、建设内容、建设步骤以及建设过程中应注意的问题,并给出了数字化校园的基本模型。     

CAM后置处理研究

分析了数控加工后置处理技术的特征、面临的问题和当前的发展趋势,介绍了应用通用后置处理器开发定制专用后置处理器的实践。     

Effects of the photo-ionized absorber on the continuum spectra of EXO 0748–676

We report on the analysis of XMM-Newton archival data of EXO 0748–676. We studied changes of the continuum spectra due to the presence of photo-ionized plasma on the line of sight. We show that the ionization degree of the plasma could change largely during the X-ray bursts and the dips. These changes can significantly modify the soft-band spectrum, which was in fact observed from EXO 0748–676. We discuss the effect of the photo-ionized plasma on the continuum spectra in comparison with a frequently used model such as partial covering absorption.     

巨型晶闸管在大型直流电动机拖动中的应用

巨型晶闸管在国内首次成功地用于大型风洞的动力系统──大型直流电动机拖动系统中，使大型直流拖动的控制系统简化，１０００—３０００ｋＷ系统简化到一个三相全控桥式整流电路，或两个三相全控桥式整流电路并联输出的技术问题上，而且由于系统简单化，潜在的故障因素减少，可靠性增强，维护的工作量也大大减少。本文介绍风洞动力控制系统的实用调速方法，以及用计算机控制速压的方法。     

航行情报服务(AIS)及其属性初探

本篇首次运用情报的广义属性从理论上分析和概括了航行情报的定义、宗旨和有关性质,并给出了航行情报服务的流程图和交流图。对促进和加强这一学科的教学研究有一定的参考意义。     

模拟JJ—7飞机纵向摆动试飞研究

本文论述了BW-1变稳机空中飞行模拟H-7飞机发生两次纵向摆动时飞行状态特性,通过试飞研究其飞行品质,校核驾驶员诱发振荡(PIO)发生的可能性;并对解决PIO的方案进行了验证试飞研究,提出了排除PIO较适宜的参数值.试飞证明,空中飞行模拟试验是研究PIO的有效方法之一.     

化学气相反应法在C/C复合材料抗氧化处理中的应用

通过把硅蒸气渗入预制体孔隙与碳直接反应生成SiC的化学气相反应(CVR)方法,提高初始密度和预制体结构均不同的C／C复合材料的抗氧化能力,研究了C／C复合材料的密度变化与微观结构,并对其进行了氧化试验。结果表明,因CVR温度、C／C复合材料初始密度不同,抗氧化处理后的密度增加量有显著不同。针刺炭布C／C／SiC复合材料在马福炉中于1160℃经65min氧化后,其失重率仅2．6％,而密度为1．95g／cm^3的同结构C／C复合材料相在同条件下失重率高达32％。