Steps and facets at the surface of soft crystals

We consider the shape of crystals which are soft in the sense that their elastic modulus μ is small compared to their surface tension γ, more precisely μa < γ where a is the lattice spacing. We show that their surface steps penetrate inside the crystal as edge dislocations. As a consequence, these steps are broad with a small energy which we calculate. We also calculate the elastic interaction between steps a distance d apart, which is a 1/d ² repulsion. We finally calculate the roughening temperatures of successive facets in order to compare with the remarkable shapes of lyotropic crystals recently observed by Pieranski et al. [#!Pieranski!#,#!EPJ!#]. Good agreement is found. Received 25 June 2001     

Ronchi光栅光密度的一种测试方法

本文提出利用衍射光栅的反射特性,在自光图像处理系统中对光栅进行实时无损伤检验.这种方法灵敏度高、简便易行,有较高的实用价值.理论与实验结果一致.     

狭缝光栅自由立体显示器立体可视区域的研究

提出了反映观察区域某一点是否是合适的立体观察点立体图像质量因子的概念.根据狭缝光栅自由立体显示器的结构和工作原理并应用几何光学知识,分析得出了立体图像质量因子的计算公式,并给出了立体显示器的立体图像质量因子的计算结果.通过定义立体图像质量因子的阈值,得到狭缝光栅自由立体显示器的立体可视区域.     

基于“慕课”的物理类微课程设计探索

“慕课”起步,微课程先行!鉴于目前微课程设计缺乏规范模式,本文旨在对此进行深入探讨．在微课程设计缺乏充分的理论基础支持的前提下,本文首先利用文献综述法归纳得出微课程的基本特征,据此确定微课程设计原则;其次以此原则为指导,借鉴远程开放教育的设计模式,类比探索出微课程设计的基本模式;最后将这种微课程设计模式应用于物理类课程,并结合物理类课程特点进行实证分析,成功实现了物理类微课程设计．教学实践活动进一步检验了本文构建的微课程设计模式切实可行、效果良好．     

Dosimetric characterization of the Exradin W1 plastic scintillator detector through comparison with an in-house developed scintillator system

New commercial dosimetry systems need careful characterization and can benefit from the comparison with similar, in-house developed solutions. A comparison between such two dosimetry systems, both based on fibre-coupled organic plastic scintillator detectors, is presented. One system is the Exradin W1, fully commercialized by Standard Imaging, while the other system is the non-commercial ME40 system, developed by DTU Nutech with the aim of fundamental dosimetric research. Both systems employ plastic scintillator detectors that can be considered similar in design, calibrated using the same method, but differing primarily in the signal detection hardware. The two systems were compared with respect to essential dosimetric properties, with the purpose of testing their performance under conditions less well discussed in the literature. A Farmer ionization chamber was used as the primary reference of the comparison. The study demonstrated that the Cerenkov light ratio calibration coefficient of both systems was not constant, but changed systematically with photon beam quality to a maximum difference of 1.1%. Calibration with respect to stem effect correction should therefore be performed for every investigated beam quality when using plastic scintillator detectors. Both systems were found to be dose rate independent, even for the highest instantaneous dose rate evaluated (1.5 mGy per pulse). Low-dose measurements revealed large uncertainties for both systems, although the ME40 system handled short beam deliveries under reference conditions with accuracy and precision within 0.4%. Changes in response due to field size dependence were investigated and found to be as large as 3.3% for the W1 and 5.4% for the ME40, biasing output factor measurements in large fields. Great caution is therefore advised if using either system for measurements in large fields or under circumstances where the fibre irradiation geometry is unfavourable. Measurements of reference dose to water yielded differences up to 1.5% when compared with the Farmer ionization chamber for all investigated beam qualities.     

探索物质微观结构的历史回顾——纪念夸克提出50周年

1964年盖尔曼和兹威格分别提出“基本粒子”由夸克或艾斯组成。至今,这一领域仍是粒子物理研究的前沿领域。经过50年的发展,夸克(艾斯)理论取得诸多辉煌成就。文章简要地回顾了夸克的提出过程及随后实验和理论方面的进展。     

基于连续光谱分析的在线水质检测信号处理研究

在线光谱水质检测仪器是现代水资源环境监测技术的重要发展方向之一,具有多参数监测和准确度高、重复性好的技术优势,然在线被测水样的光谱信号处理是其关键核心技术,为此,基于连续光谱分析,建立了在线被测水样光谱测量信号的数学模型,提出了基于双波长光强比值不变性的光谱测量信号系统误差处理方法,并结合小波多分辨率滤波噪声处理技术,系统研究了基于在线被测水质参数光谱特征的背景干扰处理方法。以上信号处理方法应用于自主研制的多参数光谱水质监测仪器,在线检测标准环境水样及实际环境水样中的化学需氧量、六价铬和阴离子表面活性剂等水质参数,并与国家标准分析方法展开了现场对比测试,仪器的关键参数重复性(相对标准偏差RSD≤10%)与准确度(实际水样比对试验相对误差A≤10%)均达到并优于国家环境保护技术标准要求,表明该信号处理方法能够有效消除在线水质检测光谱测量信号的系统误差及噪声与背景干扰,对于提升光谱水质监测仪器的技术性能具有重要的作用。     

量子频标中的原子物理

频率是自然界中测量得最准的物理量.量子频标是频率的测量标准,它是利用原子跃迁谱线的稳定而准确的频率作为参考频率.频标研究中存在几乎所有的原子物理问题,如原子结构与光谱、原子与电磁场的相互作用以及原子碰撞等问题值得深入研究.本文就量子频标的基本原理和应用,量子频标中存在的原子物理问题做以简要评述.     

Compression evaluation of surgery video recordings retaining diagnostic credibility (compression evaluation of surgery video)

Wider dissemination of medical digital video libraries is affected by two correlated factors, resource effective content compression that directly influences its diagnostic credibility. It has been proved that it is possible to meet these contradictory requirements halfway for long-lasting and low motion surgery recordings at compression ratios close to 100 (bronchoscopic procedures were a case study investigated). As the main supporting assumption, it has been accepted that the content can be compressed as far as clinicians are not able to sense a loss of video diagnostic fidelity (a visually lossless compression). Different market codecs were inspected by means of the combined subjective and objective tests toward their usability in medical video libraries. Subjective tests involved a panel of clinicians who had to classify compressed bronchoscopic video content according to its quality under the bubble sort algorithm. For objective tests, two metrics (hybrid vector measure and hosaka Plots) were calculated frame by frame and averaged over a whole sequence.     

中国医学物理学的过去、现在与未来

医学物理（medical physics，MP）是把物理学的原理和方法应用于人类疾病的预防、诊断、治疗和保健的一门交叉学科，是物理学与医学实践相结合的一门独立的分支学科．它是研究人类疾病诊、治过程中的物理现象，并用物理方法表达这种现象．医学物理包括放射肿瘤物理（rsdiation oncdogy physics，ROP）、医学影像物理（medical imaong physics，MIP）、核医学物理（nuclear medicine physics，NMP），其他非电离辐射如核磁、超声、微波、射频、激光等物理因子在医学中的应用，和保健物理（heath physics，HP）等分支内容．医学物理学和生物医学工程学（biomedical engineefing，BME）是一对栾生的兄弟学科，分别从物理学的角度（前者）和工程学的角度（后者）研究人类疾病诊断、治疗及健康保健过程中的生命现象和采取相应的物理措施和工程手段。医学物理学与物理医学（physical medicine，PM）是完全两个不同的概念，前者是物理学的分支，后者是医学的分支．自上世纪60年代以来，中国医学物理学有了很大的进展，推动了中国现代放射肿瘤学、核医学和医学影像学的发展；成立了自己的学术组织，并成为国际医学物理组织（IOMP）的成员国组织．随着中国逐步奔入小康社会，为适应人民大众对健康的需求和现代化医院发展的需要，中国医学物理应该加快发展．