Physical and dosimetric aspects of a multileaf collimation system used in the dynamic mode for implementing intensity modulated radiotherapy

The use of a multileaf collimator in the dynamic mode to perform intensity modulated radiotherapy became a reality at our institution in 1995. Unlike treatment with static fields using a multileaf collimator, there are significant dosimetric issues which must be assessed before dynamic therapy can be implemented. We have performed a series of calculations and measurements to quantify head scatter for small fields, collimator transmission, and the transmission through rounded leaf ends. If not accounted for, these factors affect the delivered dose to the prostate by 5%-20% for a typical plan. Data obtained with ion chambers and radiographic film are presented for both 6 and 15 MV x-ray beams. The impact on the delivered dose of the mechanical accuracy of the multileaf collimator, achieved during leaf position calibration and maintained during dose delivery, is also discussed.     

Multimode parameter extraction for multiconductor transmissionlines via single-pass FDTD and signal-processing techniques

We present two approaches to extract the broadband multimode parameters of guided wave structures from a single-pass finite-difference time-domain (FDTD) simulation. They include a two-dimensional (2-D) Fourier transform (FT) algorithm and a super-resolution estimation of signal parameters via rotational invariance technique (ESPRIT) algorithm. Comparison is made to show the superiority of the super-resolution approach. As a typical application, a three-line coupled microstrip structure is studied. After a single-pass FDTD simulation, broadband multimode parameters such as propagation constants, modal-field templates, and modal impedances are extracted and verified against published data obtained by the spectral-domain method. The main feature of this parameter-extraction methodology is that it decouples the computational electromagnetics engine (in this case, the FDTD simulator) from the post-processing parameter-extraction algorithm, thus providing more flexibility and connectivity among the various simulation tools     

GIS技术与微机制图

地理信息系统（ＧＩＳ）随着信息社会的发展愈发显示出强大的生命力。本文简要叙述ＧＩＳ的重要作用及其发展进程中涌出出来的四个设计模型，总结了运用ＧＩＳ国产软件平台ＭＡＰＧＩＳ制作遥感地质构造解译图的工作步骤和技术方法。     

珠江口盆地开平凹陷油气聚集条件分析

珠江口盆地自新生代以来,曾先后受到不同方向张应力的作用,造成了不同时期构造体系的交叉叠合.中中新世以来构造运动强烈,并具有东强西弱的特点,对油气的运移与聚集产生了重要影响.开平凹陷的剧烈断裂和断陷活动始于始新世,并在同期沉积了巨厚的文昌组.晚渐新世以后,由于断裂活动非常微弱,在成熟的烃源岩与其上地层之间缺乏有效的油源断层,因而自生自储、近距离运移可能是开平凹陷油气聚集的基本特征.在凹陷内部,因重力滑动和欠压实泥岩共同作用所形成的KPll-1构造带可能是该区最具有油气远景的地区.     

Genetic mapping of a major susceptibility locus for juvenile myoclonic epilepsy on chromosome 15q

The epilepsies are a group of disorders characterised by recurrent seizures caused by episodes of abnormal neuronal hyperexcitability involving the brain. Up to 60 million people are affected worldwide and genetic factors may contribute to the aetiology in up to 40% of patients. The most common human genetic epilepsies display a complex pattern of inheritance. These are categorised as idiopathic in the absence of detectable structural or metabolic abnormalities. Juvenile myoclonic epilepsy (JME) is a distinctive and common variety of familial idiopathic generalised epilepsy (IGE) with a prevalence of 0.5-1.0 per 1000 and a ratio of sibling risk to population prevalence (lambda(s)) of 42. The molecular genetic basis of these familial idiopathic epilepsies is entirely unknown, but a mutation in the gene CHRNA4, encoding the alpha4 subunit of the neuronal nicotinic acetylcholine receptor (nAChR), was recently identified in a rare Mendelian variety of idiopathic epilepsy. Chromosomal regions harbouring genes for nAChR subunits were therefore tested for linkage to the JME trait in 34 pedigrees. Significant evidence for linkage with heterogeneity was found to polymorphic loci encompassing the region in which the gene encoding the alpha7 subunit of nAChR (CHRNA7) maps on chromosome 15q14 (HLOD = 4.4 at alpha = 0.65; Z(all) = 2.94, P = 0.0005). This major locus contributes to genetic susceptibility to JME in a majority of the families studied.     

鲁布革水电厂计算机监控系统的更新改造

鲁布革水电厂原Ｒ３０计算机监控系统更新改造过程中，重点研究了与原西门子ＲＴＵ的数据交换，机组功率调节和线路定功率调节的实现有关问题，在对３号机组计算机监控系统改造试验的基础上，成功地实现了计算机监控系统的整体改造，改造后采用的国产ＮＡＲＩＳＳＪ－３０００计算机监控系统实用可靠，功能完善，配置灵活，具有国际，国内领先水平。     

Cervicovaginal foetal fibronectin in the prediction of preterm labour in a low-risk population

Ten groups of 14 immunosuppressed NMRI-mice (nu/nu) were raised and kept under germ-reduced conditions. The control animals were fed a germ-reduced diet, nine other groups received the same diet with selegiline (CAS 14611-51-9, Deprenyl) or lipoic acid (thioctic acid, CAS 62-46-4) admixed at various amounts. The 50% survival rate, the total life span of each group and the areas under the curves were determined to evaluate life expectancy as compared to the controls. The racemate of lipoic acid at high dosage (350 mg/kg body weight) reduced the life span significantly. The S(-)-enantiomer of lipoic acid (75 mg/kg body weight) increased the 50% survival rate, whereas the physiologic R(+)-enantiomer (9 mg/kg body weight) expanded the total life span of its group. Alteration of only one out of three parameters was not considered significant. All other groups except for one did not differ from controls: only animals which obtained 75 micrograms selegiline per kg of body weight and per day exerted increased life expectancies by all three parameters. This group exhibited also in statistical evaluation a significantly (p < 0.05) prolongated survival time up to about 200% as compared to the control animals.     

低合金高强度钢的微观组织和疲劳裂纹扩展行为

用透射电镜观察了３０ＣｒＭｎＳｉＮｉ２Ａ钢等温的微观组织，疲劳裂纹扩展行为、裂纹尖端塑性区和位错结构，结果表明，等温状态组织由马氏体和贝氏体组成。在一个奥氏体晶粒内一般存在四个板条领域、裂纹尖端的塑性区内存在主位错带，疲劳断裂的基本组织单元为板条晶或板条束。裂纹遇到板条束界时方向发生较大偏斜。     

虚拟企业图纸数据传输

图纸数据是企业间合作需交换的一种重要的信息。本文分析了虚拟企业环境下企业之间交换图纸数据的要求，提出了一种具体的解决方案，并给出实例。     

一种新型基于石英的热光型光开关

一种采用基于石英的平面光波回路技术（PLC）制造的热光型光开关正越来越引起关注，它具有低耦合损耗、高稳定性及适于大规模集成等优点。首先描述了采用热光相移器构成马赫-曾德于涉仪（MZI）结构的热光型光开关，然后讨论2×2MZI热光型开关的工作原理及基本特性，最后介绍了由2×2MZI热光型开关单元构成的大规模光开关阵列以及一种采用悬梁式结构热光相移器的低功率消耗的光开关。