空间滤波器阵列结构优化设计

给出了新型大型激光装置阵列化空间滤波器结构优化设计。对大口径阵列化光束超长程传输、光路控制、光束质量控制,以及支撑稳定性、震动隔离、离轴调节等关键技术进行了分析研究,对物理方案和参数进行分解。运用Pro/E软件建立阵列化空间滤波器三维实体模型,给出了阵列化空间滤波器的总体结构解决方案。对关键部件和技术指标进行了详细分析,采取了新颖的结构和相应的技术措施;运用ANSYS分析软件对结构刚性、强度、振型等指标进行分析,通过有限元仿真与CAD环境的双向嵌入优化结构;为给装置结构的适应性找到可靠的评估依据,对影响稳定性较大的器件和单元进行了微振动测试和分析。理论分析和测试结果表明,该方案达到了优化设计,是可行的。     

Scanning electron microscopic observations on micro-organisms in the root nodules of Tribulus terrestris L. (Zygophyllaceae)

Scanning electron microscopic observations were made on the micro-organisms of root nodules of Tribulus terrestris L. The results showed that nodules of T. terrestris contained dual infection consisting of Rhizobium sp. and Newmania karachiensis. Based on these observations, T. terrestris should be grouped with nonlegume Parasponia-type bacterial nodules.     

基于双CPU的激光打标机控制系统设计

中介绍了基于双CPU控制的激光打标机系统的结构组成、地址编排、软件设计以及LCD液晶屏的汉字显示技术。该系统打标速度快、精确度高,可连续不间断运行。适于在任何大小、异形工作上标刻图,标记清晰、永久、美观,且可有效防伪。     

激光准直高斯光斑中心位置计算方法分析

结合一种用于大孔同轴度测量的激光准直系统,分析高斯光斑能量中心坐标的几种常用计算方法:对称法、曲线拟合法和重心法。准直系统用单模尾纤半导体激光器作光源,用CCD探测器接收激光光斑。重心法计算时该实验装置实验室内6m距离上的方向稳定性达到1 5×10-6的量级。实验表明重心法有效利用光斑全场数据,对光强分布缺陷不敏感,分辨率和示值重复性都优于对称法和曲线拟合法。     

Evaluation of thermal conductivity from temperature profiles

A new dynamic technique for the measurement of thermal conductivity is being developed at IMGC. The experiment consists in bringing the specimen to high temperatures with a current pulse and in measuring the temperature profiles during the free cooling period. Different techniques can be used to extract the information on thermal conductivity from the profiles. The numerical computation of thermal conductivity from the experimental temperature profiles in absolute space is possible, but it is difficult and cumbersome because one must know and take into the account the exact position of the infinitesimal elements of the specimen in different profiles. Computations in tube-space (a fictitious space where no thermal expansion occurs) are simpler and lead to less complex numerical computations. Complementary techniques to evaluate thermal conductivity as a function of temperature or at constant temperature are presented with a discussion of advantages and disadvantages of each method. Computer simulations have tested the precision of the complex software. Numerically generated temperature profiles from known thermophysical properties have been obtained and thermal conductivity has been recomputed from the profiles. The relative difference using different computational approaches and different fitting functions is always less than 0.1%.Paper presented at the Third Workshop on Subsecond Thermophysics, September 17–18, 1992, Graz, Austria.     

Premelting transition in uranium dioxide

Thermal analysis of the cooling curves of small samples of uranium dioxide, laser heated in a high-pressure autoclave on a subsecond time scale to a temperature just below the melting point, reveals, in the case of nominally stoichiometric UO_2.00, a significant -like heat capacity peak, indicating a premelting transition in this material. The results are discussed and a simple model is presented in terms of which the observed behavior can be described.Summary of a paper presented at the Third Workshop on Subsecond Thermophysics, September 17–18, 1992, Graz, Austria. Because of its length, the full paper was published in a regular issue of this journal (Vol. 14, No. 2, 1993).     

Dielectric function and electrical resistivity of liquid carbon determined by femtosecond spectroscopy

Femtosecond pump-probe reflectance of graphite and diamond targets following intense laser irradiation is used to measure the optical properties of the pressurized liquid carbon phase while it retains an optically sharp surface before expanding hydrodynamically as a hot plasma. These measurements allow the historically elusive liquid phase of carbon to be characterized optically for the first time. A Drude dielectric model of the reflectance spectrum 1 ps after excitation just above the melting threshold reveals a poorly conducting liquid metal with a dc resistivity 625±75 · cm. The optically determined resistivity decreases with increasing sample excitation. The initial stages of hydrodynamic surface expansion of Al, W, and C targets are also quantitatively characterized by time-resolved reflectance, revealing the expansion speed as well as further dielectric properties of the high-temperature-pressure phase.Paper presented at the Third Workshop on Subsecond Thermophysics, September 17–18, 1992, Graz, Austria.     

石榴石中Cr^3＋的电子结构与晶场强度的关系

本文对掺铬的GGG(Ca,Mg,Zr),GGG,YGG和YAG四种晶体进行了自旋极化的SCC-DV-X_α计算。首次报道了它们的10Dq计算值,与实验值符合得很好,并讨论了中心离子和配位体之间的距离与该计算值的关系。还计算得到了二重态~2E_3的能量值,从而阐明了YAG_2cr~(3+)只能发射窄带荧光,而GGG(Ca,Mg,Zr):Cr~(3+)能发射强的宽带荧光的机理。     

高精度切割新技术的研究现状

电火花切割、等离子切割、激光切割和超高压水切割是工业上广泛应用的高精度切割方法：电火花切割具有很高的材料利用率和接近于磨削水平的加工精度和加工表面粗糙度,但加工效率过低;等离子切割速度快,但切割过程中噪声大、烟尘多、辐射大,而且作为等离子切割机关键部件的喷嘴、电极和割炬在目前技术条件下都是易损件,无形中增加了切割成本;激光切割切割速度快、切缝小、切割材料表面质量好,但是切割材料厚度偏低,目前仅用于薄板切割;超高压水切割是一种冷态切割方式,切割材料无热变形,表面质量极佳,但切割成本过高。结合实践经验,提出了三条选用切割工艺的原则：特殊的场合选用特定的切割方法;利用热切割方法满足加工工艺要求时,则无需采用超高压水切割;在等离子切割和激光切割都能满足加工要求的情况下,最好选用等离子切割.     

大型机组轴系对中方法探讨

针对大型机组的对中问题和常用的对中方法及适用范围进行了全面分析,采用激光对中仪进行大型机组轴系对中,测量精度高、操作简便、适用面广。分析了国内外激光对中仪的发展近况,根据目前国内相关研究讨论其不足之处以及发展方向。