The computer modeling of lanthanum in the framework of faujasite: Part 1. Anhydrous lanthanum zeolite

Structures having a La³⁺ ion assigned to various sites in an idealized faujasite framework have been modeled using potentials developed from the study of oxides and successfully applied to zeolites. An initial structure is relaxed to minimum energy at constant pressure with all species free to move. The resulting lattice energy is used as a measure of the stability of the structure. On this basis, it is shown that distortion of the framework and the combined effect of many relatively long-range electrostatic interactions cause simple analyses based on high symmetry and short-range interactions to be unreliable. In particular, it is shown that the chance of an isolated La³⁺ ion's occupying an SI' site is comparable to that of its occupying an SI site, and, indeed, the SI' site can be the preferred location. This finding serves to clarify the interpretation of the X-ray diffraction data for single-crystal La-FAU. A further significant finding is that SII sites can be expected to have a higher population of La³⁺ ions in such structures than they have usually been thought to have.     

Removal of 60Co by zeolites and clays

The use of NaY zeolite, erionite, and bentonite in the removal of radioactive cobalt from aqueous solutions has been investigated. Ion-exchange experiments were performed either with inactive cobalt solutions or labeled solutions containing ⁶⁰Co. XRD patterns were used to determine if cell parameters were alike and to verify if the crystallinity of the aluminosilicates was maintained during experiments. The cobalt content was determined by neutron activation analysis. According to the exchange behavior, the selectivity sequence to retain cobalt is bentonite < erionite < Y zeolite.     

环境材料研究的基本理论问题

讨论了环境材料领域的基本理论问题,包括目标、出发点、概念的内涵及其判据,明确提出了环境材料研究的方法,指出环境分析是环境材料研究的核心特征和基本要素,并给出了环境材料研究的定义.对这些基本理论问题的讨论旨在促进环境材料学及其学科范式的建立与发展.     

Pulse shape discrimination with a 100 MHz flash ADC system

We have developed an electronic system based on a 100 MHz flash ADC for analysing the shape of the signals issued from photomultipliers. The purpose of this system is to improve appreciably the pulse shape discrimination (PSD) technique by means of the full knowledge on the time dependence of the collected light for electrons and heavy particles in the scintillating medium. We have obtained, without any particular optimisation, an order of magnitude improvement in the rejection of the electrons with a heavy particle efficiency of 93%.     

Inspection of laminates and adhesive bonds by pulse-video thermography

The use of thermography in NDT has been extended in recent years by the application of transient heat sources and the rapid scanning of the subsequent thermal fields by TV/video-compatible infrared imagers. Such a system is called pulse video thermography (PVT) and its use has been demonstrated in many practical cases. Limitations are however set by the nature of the thermal diffusion process, and their exact definition in practice is discussed from both theoretical and experimental points of view.     

广义Rayleigh商在四元数体中的推广及其在图象信息融合中的应用

在力学、物理学及系统工程理论中,常会遇到形如AX=λBX的广义特征值问题。本文将复数域中的广义特征值问题向四元数体加以推广、通过详细的数学推导证明其正确性。同时说明该问题在基于Fisher模式分类法的信息融各技术中的应用,并结出详细的数学证明。     

窄带三次谐波转换的逆问题

以分步离散傅里叶变换和四阶R-K法为基础,给出了解决激光三次谐波转换逆问题(即已知输出三倍频光场分布以及三次谐波转换器参数的情况下,求解输入基频光场分布)的方法,对三次谐波转换的逆问题进行了数值计算和分析,并讨论了逆算的初始光场条件对迭代计算次数及计算精度的影响。结果表明,对于设定的输出三倍频光场分布,可通过逆解三次谐波转换过程及数值迭代方法,求得相应的输入基频光场分布。     

用二元位相光栅进行激光束叠加的研究

基于标量衍射理论,系统探讨了二元位相光栅实现激光束叠加的理论和位相光栅设计方法,利用新型遗传模拟退火混合算法得到优化的光栅参数,给出其用于分束和耦合时的模拟结果,并讨论实际误差对位相光栅耦合效率的影响.二元位相光栅用于激光束叠加有结构简单,调节灵活的优点,可以有效地提高激光束的功率密度和系统的整体性能.     

调幅式调制盘红外导引头的主动干扰

为了干扰调幅式调制盘系统,根据调幅式调制盘红外导引头的工作原理,采用数值模拟的方式分析了两种主动干扰红外导引头的方法。结果表明,缓变幅度的干扰辐射会使导引头获得的目标方位信息产生偏差,但无法使目标摆脱导引头的跟踪;而重复频率近似等于调制盘系统调制波形载频的光脉冲会干扰导引头接收到的目标信号,使导引头失去目标。干扰辐射强度近似等于目标辐射强度,即可实现干扰。