Correction for photon attenuation in SPECT: analytical framework, average attenuation factors, and a new hybrid approach

We provide a unified framework for the investigation of convergence properties of the iterative algorithms for photon attenuation correction in SPECT, including the iterative Chang method--a commonly used approach in which an average attenuation factor calculated over all projection angles is employed in a pointwise correction scheme. A new average attenuation factor calculated along the projection line is introduced, which can compensate exactly for the attenuation effect in the case of a uniform activity distribution. We propose a new hybrid approach in which we use this new average attenuation factor initially and then shift to the iterative Chang method in later iterations. This hybrid approach was evaluated in a simulation study by use of a computer-generated phantom with both non-uniform activity and non-uniform attenuation distributions. The results demonstrate that this hybrid approach improves the convergence speed of the iterative Chang method and produces reconstructed images of high quality.     

用EVA复配物改善高含蜡原油低温流动性的研究

本文研究了采用化学处理剂改善南海高含蜡原油的低温流动性,结果表明,添加150ppm EVA复合化学处理剂,原油低温流动性得到明显改善,凝固点由32℃降至11.5℃,表观粘度降低86.9%,1;℃时屈服值降低98%。同时考察了添加温度,冷却速度以及化学处理剂的化学组成和结构对改善原油低温流动性的影响。根据南海高含蜡原油中蜡的组成和正构烷烃的碳数分布及其对不同结构的EVA的感受性,讨论了化学处理剂改善原油低温流动性的机理,指出,EVA中乙烯链长与原油中正构烷烃链长相近时才能形成共晶,起到改变原油中蜡的结晶形态的作用,达到降凝减粘效果。     

Glass-ceramics of barium strontium titanate for high energy density capacitors

Barium strontium titanate glass-ceramics were successfully produced with one major crystalline phase when Al₂O₃ was added to the melt. A dielectric constant of 1000 and a breakdown strength of 800 kV/cm was achieved; however the energy density was only measured to be 0.3–0.9 J/cm³. These energy density values were lower than anticipated due to the presence of dendrites and pores in the microstructure. Using BaF₂ as a refining agent improved the microstructure and doubled the energy density for BST 80/20 samples. However, no refining agent reduced the increasing amount of hysteresis that developed with increasing applied electric field. This phenomenon is believed to be due to interfacial polarization.     

飞行器火工装置的冲击隔离结构方案实验研究

飞行器由于采用了××炸药索作为级间分离及壁板减重的火工装置，当火工品引炸时，对周围的仪器支架和脱拔插头产生高达３００００ｇ的冲击加速度。为保护仪器支架和脱拔插头，本文，总结了多种隔冲击结构方案的试验结果，选出了一种最佳方案，即二级硅橡胶缓冲器与阻尼复合结构的结合形式。该方案可使冲击加速度衰减至１６０ｇ以下。测的是周向过载。４结语粘弹阻尼复合结构用于高频响、高过载的冲击衰减系统尚是一种新的尝试。由于本课题所设计的缓冲支架采用了多级隔冲方式，冲击载荷传递的环节多，而且是三维冲击响应，载荷的波形复杂，不确定因素多，无法采用理论分析的方法进行研究。虽然如此，缓冲器的隔冲特性以及粘弹阻尼复合结构的减振性能还是可以估算的。这方面的理论问题有待于进一步研究。从试验角度而言，本次试验已解决了飞行器的仪器盒及脱拔插头的隔冲击振动问题，证明所设计的隔冲击支架满足使用要求。通过对不同支承界面联接方式的研究，选出了较佳的支承结构形式，即文中的标准状态。该结构形式隔冲击性能好，衰减倍数大，安装和更换方便，防热性能好。试验数据表明，仪器架的衰减倍数大于４００倍，脱拔插头支架大于２９０倍；在最大过载约３００００ｇ，最大响应频率约２２．４     

MERLIN: a device diagnosis system based on analytic models

An approach to computer-aided interpretation of parametric test data for integrated circuit process-problem diagnosis is presented. In contrast to a conventional expert system, which reasons with a knowledge base consisting of rules acquired from human experts, the system presented centers its knowledge around analytic device equations. By using equations as the basis of the system knowledge, a more universal, well-organized, and concise level of knowledge is encoded. With the use of objects to present this knowledge, a great deal of useful information outside that described by only the symbolic expressions can be represented, and extension to qualitative or numeric models should be straightforward. The result is an expressive, well-organized, easily built, and easily maintained knowledge base. The authors describe the system's interactive graphical displays and the automatic data interpretation algorithms. Examples evaluating n-channel metal oxide semiconductor (NMOS) parameter variations, interconnect parameter variations, and interconnect yields are used for illustration     

一种微机控制的多测头凸轮轴测量系统

本文介绍一种由机械装置，高精度圆光栅编码器，光栅位移传感器，微型计算机，接口控制电路等组成的多测头凸轮轴测量系统，该系统安装调整方便，定位准确，测量精度高，操作简单，工作可靠，能快速实现对凸轮轴的自动测量。     

MCS接枝共聚物的结构和形态

将甲基丙烯酸甲酯（ＭＭＡ）、苯乙烯（Ｓ）在氯化聚乙烯（ＣＰＥ）存在下进行悬浮接枝共聚，获得ＭＣＳ树脂。本文着重考察了ＭＣＳ树脂的化学结构及胶粒形态。结果表明，确实发生了接枝共聚。ＣＰＥ用量、ＲＳＨ含量、引发剂浓度、反应温度、溶胀时间及聚合转化率对ＭＣＳ树脂的接枝率、接枝效率均有影响。ＭＣＳ树脂是接枝共聚物、ＭＭＡ／Ｓ共聚物与ＭＭＡ均聚物的混合物，橡胶相ＣＰＥ在ＭＣＳ树脂中的分散情况为“海岛结构”，     

论军事院校文化建设与管理

校园文化直接影响高质量人才的培养和塑造。校园文化包括：求实的校风，优良的环境，活跃的学术，良好的素质，丰富的文化生活。讲究科学方法，抓好校园文化建设，是建设高质量军事院校的关键。     

V型天线的行波加载公式

本文研究了ｖ型天线上电流分布与阻抗加载的关系，导出了支持天线上行波电流的阻抗加载公式。讨论了天线张角、振子半径以及振子长度与加载量的关系和规律，说明了加载Ｖ型天线的宽带特性。文中还计算了在高斯脉冲激励下，不同加载量的天线上瞬态电流的分布，由此可以表明所导加载公式的正确性与重要性。