非晶硒对X射线光电转换特性的研究

非晶硒X射线光电导具有很高的固有空间分辨率,有可能研制探测X射线成象的平板化数字器件,在探测X射线成象方面倍受注目.它对X射线的光电转换特性和灵敏度是重要的性能参数之一.我们制作了约400μm厚的非晶硒膜,在1～12.5V/μm场强范围,0.2～12mR/s照射率范围测量了X射线光电流值.实验结果显示,非晶硒具有线性的光电转换特性,其灵敏度随场强的增加而增加.计算表明,对于医疗诊断常用的轫致辐射X射线谱,用X射线在非晶硒中产生一电子-空穴对所需的能量W±约50eV(10V/μm场强)     

多巴胺D3受体显像剂的前体合成及其^19F的标记

自从多巴胺D3受体亚型克隆成功[1]以来,对D3受体功能的研究引起了极大的兴趣.它主要分布于哺乳动物大脑中与认知和情感功能相关的边缘脑区,特别是嗅结节、马列加氏岛和前脑基质的侧坐核隔膜,而且与抗精神病药物具有很高的亲和性,具有特殊的神经药理学意义[2].     

Illusory possibilities and imagining counterparts

Given Kripke’s semantic views, a statement, such as ‘Water is H₂O’, expresses a necessary a posteriori truth. Yet it seems that we can conceive that this statement could have been false; hence, it appears that we can conceive impossible states of affairs as holding. Kripke used a de dicto strategy and a de re strategy to address three illusions that arise with respect to necessary a posteriori truths: (1) the illusion that a statement such as ‘Water is H₂O’ possibly expresses a falsehood, (2) the illusion that conceivability can fail to latch on to a genuine metaphysical possibility, and (3) the illusion that one can access a real metaphysical possibility by conceiving that water is not H₂O. In this paper I argue that while Kripke’s de dicto strategy dispels (1), his strategies do not enable him to dispel (2) and (3).     

Approximating ideal diffractive optical systems

In numerical wave optics involving diffractive optical elements one is required, at some point, to form a multiplicative matrix factorization. This paper is concerned with such representations and related approximations of ideal diffractive optical systems. Various simple diffractive optical elements are used. The basic factoring problem being highly nonlinear, a minor parallelism in terms of beam splitters and beam combiners makes the task computationally much more tractable and versatile. This gives rise to several matrix nearness problems of geometric nature.