Vibration Characteristics of Acoustically Levitated Object with Rigid and Elastic Reflectors

Levitation stability is a crucial factor that influences acoustic levitation capability. We present two sample-including models for a single-axis acoustic levitator with either a rigid or elastic reflector. Numerical analysis shows that, with the rigid reflector, both the decay time from initial disturbance and the vibration amplitude increase with sample density, which is unfavorable for levitation stability. However, with the elastic reflector, the decay time and the vibration amplitude are greatly reduced by choosing appropriate parameters of the reflector. Experimental results agree well with theoretical predictions, indicating that levitation stability can be remarkably enhanced by replacing the rigid reflector with an elastic reflector.     

自由电子激光器的新进展

本文对自由电子激光器的工作原理、实验装置以及自由电子激光辐射的基本特征等进行了详细介绍，在系统综述自由电子激光器的发展动态的基础上，指出了这一研究领域的发展趋势。     

基于CASE推理的排样算法

优化排料的目的是根据给定待排样品对板材进行最优切割使得板材的利用率尽可能的高。本文提出一种基于ＣＡＳＥ推理的优化排样算法，基本思想是对每块板材的布局都进行ＣＡＳＥ推理，选取ＣＡＳＥ中的最佳布局，若没有相应的ＣＡＳＥ、则调用启发式算法搜索。算法不但避免了组合爆炸，加快了排料速度，而且具有满意的材料利用率。实际应用表明算法是成功的。     

垃圾填埋场防渗技术的现状

论述了目前垃圾填埋场防渗系统的类型、材料和垂直防渗系统的施工方法等,指出了我国在垃圾填埋场防渗方面存在的问题,并提出了需要加强研究的方向。     

水稻钵苗行栽机试验

介绍了研制成功的水稻钵苗行栽机的构造和工作原理，以及样机的性能指标检测和生产试验．试验结果表明：该机的检测项目均达到或超过设计指标，满足水稻生产要求；采用水稻钵苗行栽机作业与人工抛秧相比具有生产效率高、秧苗分布均匀、直立度好等特点；与插秧相比具有栽植深度适宜、植伤轻、缓苗快的优点，作业质量显著提高；每公顷可增产558kg，增产幅度达到10．0％，具有明显的增产效果．水稻钵苗行栽机是目前较为理想的一种水稻移栽机械．     

基于图文法的对象操作可视化

讨论对象的操作可视化,将其连续操作映射为图的剪枝与拼接,对其连续操作映射为图文法的推导,这不仅可视化了查询语言,也有利于可视化对象的设计过程。     

光柄筒冠花核糖体DNA ITS区序列

测定中国特有植物光西风筒化的ＩＴＳ区序列,分析了其结构特征,Ｇ＋Ｃ百分含质量及序列变异性,并比较了光西风筒冠花与其他被子植物的ＩＴＳ区序列特征。光柄筒冠花的ＩＴＳ区和５．８Ｓ ＤＮＡ的总长度为６０９个核苷酸。其中ＩＴＳ－１为２０７ｂｐ,ＩＴＳ－２为２３６ｂｐ,５．８ＳｒＤＮＡ为１６６ｂｐ;总的ω（Ｇ＋Ｃ）为５９．１１％,其中ＩＴＳ－１为６４．２５％,ＩＴＳ－２为５７．６３％和５．８ＳｒＤＮＡ为５３     

论实验教学中的科学素质培养

科学素质是人才素质的组成部分,实验教学在科学素质的形成中起着重要的促进作用。在实验教学中进行科学素质教育,对开发学生的创造力与创新思维、提高学生的综合素质、培养新世纪的合格人才将起重要作用     

PHYSICAL CHARACTERISTICS OF ELECTROMAGNETIC LEVITATION PROCESSING

Electromagnetic levitation has developed from a pure physical phenomenon into a practical containerless processing technique in the fields of both applied physics and materials science. In order to obtain a better understanding of this processing technique, two typical levitation coils were designed and the physical characteristics in levitation droplets suspended in these two coils, such as electromangetic field, levitation force field, total levitation force, and power absorption, were analyzed numerically and calculated in this paper. It was found that the eddy current density, together with the magnetic flux density and levitation force density, increases rapidly with radius as it approaches sample surface. The maximum levitation force produced by coil A is larger than that of coil B, whereas the levitated sample can obtain less power absorption at the equilibrium position in the former coil than that in the latter one. Moreover, the calculated results also demonstrated that the levitation ability decreases as the atomic number increases. The larger the material's electrical resistivity, the easier the samples can obtain more power absorption.