渡越辐射及其在北京自由电子激光置束测中的应用

 在北京自由电子激光器装置的性能改进中,采用了基于渡越辐射的电子束诊断方法。描述了渡越辐射应用于电子束参数测量的基本理论,介绍了BFEL中利用渡越辐射进行的实验方案,并报导了初步的结果。     

一种新型光电式液位传感器

本文介绍一种新型光电式液位传感器的设计原理、光路的理论分析。该传感器具有液位测量准确、反应灵敏、防暴、使用寿命长等优点,是一种有很大实用价值的新型液位传感器。     

Investigations of heavy ion tracks in polyethylene naphthalate films

The heavy ion beam (with fluence 3x10⁸ ion/cm²) from a cyclotron has been used for irradiation of thin polyethylene naphthalate (PEN) films. Latent tracks in these polymeric films have been sensitized by UV radiation and then chemically etched in NaOH solution. The etching process parameters have been controlled by the electroconductivity method. After etching, parameters of samples have been examined by SEM and bubble point methods (Coulter® Porometer II instrument). Results have shown good quality of PEN track membranes with pore sizes in the range: 0.1 – 0.5 μm. The described procedure is known for thin polythylene terephthalate (PET) films. Taking into consideration that PEN films have got better mechanical, thermal, gas barrier as well as better chemical resistance properties in comparison with PET films, the possibility of application of such membranes is much wider.     

Reflection of cold atoms from an array of current-carrying wires

We report the realization of a new type of magnetostatic mirror for slowly moving atoms which comprises a planar array of parallel wires alternately carrying electric current in opposite directions. One of the features of this atomic mirror is that the magnetic field may be readily varied, switched or modulated by altering the current in the wires. Reflection signals close to 100% at a pulsed current of 3 A are demonstrated for a beam of free-falling laser-cooled cesium atoms at normal incidence. The current dependence of the reflection signals exhibits structure which is associated with the sequential onset of reflection of cesium 6² S _1/2 , F=4 atoms in the m=+4, +3, +2 and +1 magnetic states. Measurements of the spatial distribution of the reflected atoms indicate the reflection is predominantly specular at currents of 3 A. Received: 31 August 1998 / Accepted: 6 October 1998     

Neutralization of specularly reflecting ions on a clean (001) surface of SnTe

Neutral fractions of specularly reflected beams have been measured for the glancing-angle incidence of (0.2-0.5) MeV ions on a clean (001) surface of SnTe. The measured fractions have been compared with the results calculated by a classical model for charge exchanges and by a model based on the first-order perturbation theory. The experimental and calculated results have differed greatly. The disagreements are attributed to collisions with valence electrons on the surface. The electron capture cross-sections of (0.2-0.5) MeV ions for valence electrons have been derived, based on the measured neutral fraction and distribution of valence electrons for jellium background positive charges, and are found to be about ten times larger than those for the outermost electrons of Sn and Te atoms calculated by the classical model. Received: 23 October 1998     

多程放大器光束空间分布的优化设计

This paper focuses on measuring straightness of large-scale dimension by using laser diode fiber alignment, diffraction imaging technique and a CCD camera. In this method, we use a laser diode fiber alignment beam as the datum reference of straightness, deviation of the measured from this datum, can be detected by a CCD camera directly. Also a novel image processing algorithm is presented. The experiment result shows that the measurement range of L (m), the measurement accuracy of the system is 3+2.3×10-6L(\mm).     

Optical and Electrical Properties of the PLT Films with Various Compositions Deposited by Sol-Gel Process

In order to study optical and electrical properties of (Pb_1-xLa_x)TiO₃ (PLT) films with varying La concentration, the PLT films were deposited by sol-gel process. X-ray diffraction revealed that a pseudocubic phase of the PLT film became dominant with increasing La concentration due to decrease of lattice constant of c-axis. Three-dimensional atomic force microscopy images showed that the grain size and root mean square surface roughness decreased by addition of La. The optical band gap of the PLT films became wider when Pb was substituted with La. The addition of La increased the transparency of the PbTiO₃ film and shifted the threshold for initiation of absorption to shorter wavelength. Hysteresis loops of the PLT films showed that remanent polarization and coercive field decreased with increasing La concentration. In addition, we modified the surface of the PLT film with La concentration of 5% using a keV oxygen ion beam at different doses. The optical band gap of the PLT film was changed by the oxygen ion beam irradiation although the XRD patterns and the transmittance values were not significantly changed. In measuring AFM images of the surface of modified PLT film, significant changes of the grain shape and size were not found. Moreover, polarization and dielectric constant were not changed after oxygen ion irradiation. These results suggested that addition of La could affect the optical and electrical properties of the PbTiO₃ and PLT films and that surface modification by oxygen ion beam modification with 1 keV energy can change the surface property but not bulk property.     

非均质Timoshenko梁的边界镇定

In this paper,the boundary stabilization of the Timoshenko equation of a nonuniform beam,with clamped boundary condition at one end and with bending moment and shear force controls at the other end,is considered.It is proved that the system is exponentially stabilizable when the bending moment and shear force controls are simultaneously applied.The frequency domain method and the multiplier technique are used.     

斜梁在热状态下非线性振动分岔

利用Ｇａｌｅｒｋｉｎ原理及Ｍｅｌｎｉｋｏｖ函数法研究了斜梁在热状态下的非线性振动分岔,并讨论分析了温度、长高比、倾斜角对斜梁发生混沌运动区域的影响．     

弹性支承圆弧梁内力分析

以现代桥梁及房屋结构为工程背景,提出弹性支承曲线梁计算模型,按结构力学方法推导出弹性支承圆弧梁的内力计算公式,分析讨论了竖向和抗扭弹性支承对内力的影响．