Direct measurement of free-volume hole distributions in polymers by using a positronium probe

We have directly measured the free-volume hole distributions in semicrystalline polypropylene by positron lifetime annihilation spectroscopy. A Laplace inversion technique was engaged to analyze the positron lifetime spectra measured under quasi-isotropic external pressures of 0, 4.2, and 14.7 kbar into continuous lifetime distributions. The hole radii distributions as determined from the ortho-positronium lifetime distributions are found to be between 4.0 and 0.5 Å and to have maxima at 3.0, 1.9, and 1.1 Å under the external pressures of 0, 4.2, and 14.7 kbar, respectively. © 1992 John Wiley & Sons, Inc.     

Vortex breakdown over a delta wing with oscillating leading edge flaps

 The effects of oscillating leading-edge flaps on leading-edge vortices and vortex breakdown were investigated for a delta wing with upward-deflected flaps. The variation of breakdown location revealed hysteresis loops. The time-averaged breakdown location over one cycle may move upstream or downstream compared to the quasi-steady case, depending on the amplitude of flap oscillations and angle of attack. Measurements of the phase-averaged velocity upstream of breakdown did not reveal any correlation to the response of breakdown location. The effect of oscillating flaps is largest when the breakdown location is near the trailing-edge region in the static case. Received: 2 February 1997/Accepted: 7 April 1997     

实际光栅系统分辨本领的实验验证

本文通过光栅衍射实验对钠光双线结构的观测，验证了实际光栅系统的分辨本领。     

蛇鞭的化学成分研究Ⅰ.蛇鞭中新化合物异亮氨酸-苏氨酸-2-甲基-环己胺的分离和结构测定

从黑眉锦蛇（Ｅｌａｐｈｅ　ｔａｅｎｉｕｒｕｓ）的蛇鞭中分离得到一个淡黄色固体化合物，用ＩＲ、~１Ｈ－ＮＭＲ、~（１３）Ｃ－ＮＭＲ、ＭＳ等现代波谱方法鉴定其化学结构为异亮氨酸－苏氨酸－２－甲基－环己胺。该化合物是一个未见文献报道的新化合物。     

度规光学中的聚焦定理及其应用

度规光学中的聚焦定理被导出。给出了光束的聚焦，散焦和陷的条件。讨论了分析在静态曲对称介质中的应用。     

On convergence of a semi-analytical method for American option pricing

We examine the valuation of American put options by a semi-analytical method, and obtain the prior estimate and the convergence of the approximate solution. Our proofs are based on the embedding theorem in Sobolev space and the theory of functional analysis, in particular, the theory of weak compactness. The results in this paper theoretically confirm empirical observations that these methods are accurate and computationally efficient.     

Effect of magnetic field on the TC and magnetic properties for the aligned MnBi compound

In the compound MnBi, a first-order transition from the paramagnetic to the ferromagnetic state can be triggered by an applied magnetic field and the Curie temperature increases nearly linearly with an increase in magnetic field by ∼2 K/T. Under a field of 10 T, T_C increases by 20 and 22 K during heating and cooling, respectively. Under certain conditions a reversible magnetic field or temperature induced transition between the paramagnetic and ferromagnetic states can occur. A magnetic and crystallographic H-T phase diagram for MnBi is given. Magnetic properties of MnBi compound aligned in a Bi matrix have been investigated. In the low temperature phase MnBi, a spin-reorientation takes place during which the magnetic moments rotate from being parallel to the c-axis towards the basal plane at ∼90 K. A measuring Dc magnetic field applied parallel to the c-axis of MnBi suppresses partly the spin-reorientation transition. Interestingly, the fabricated magnetic field increases the temperature of spin-reorientation transition T_s and the change in magnetization for MnBi. For the sample solidified under 0.5 T, the change in magnetization is ∼70% and T_s is ∼91 K.     

固态富马酸单乙酯在变温1H MAS与CRAMPS研究

富马酸单乙酯(FAME)的单脉冲¹H MAS谱由-高分辨成分与-宽线谱成分组成.高分辨成分可由Hahn回波脉冲序列单独获得.文中通过变温¹H MAS与CRAMPS实验对两组分的性质进行了系统的研究.发现当温度趋于样品的熔点时,其¹H CRAMPS谱可观察到化学位移明显区别的两套谱,它们分别对应于¹H MAS谱的高分辨与宽线组分.实验表明:高分辨成分来自FAME样品的-塑性相,而宽线组分来自通常的刚性相.文中所给出的实验事实充分说明¹H MAS与CRAMPS技术是研究有机塑性固体的强有力的工具.     

直线感应加速器加速腔物理设计与研究

简要介绍直线感应加速器（ＬＩＡ）加速腔物理设计的几个关键问题．讨论了加速电压及其平顶和腔参数的关系．对腔的耦合阻抗与束流不稳定性的关系作了概念性介绍，分析了降低耦合阻抗的途径．并给出两个加速腔设计原型．     

用于扩展目标自适应光学校正的相关波前传感器的理论和实验

研究了使用非相干、扩展光源的波前误差测量技术，分析了使用强度透过串型像面掩模的扩展目标相关波前探测原理，讨论了模拟目标的选择问题，探讨了根据目标图像生成像面掩模图像、进而制作像面掩模的方法，给出了所生成的像面掩模图像的典型结果，进行了以强度透过率型掩模为特征的单子孔径扩展目标波前传感器原理实验，比较了两种不同掩模的波前探测效果，获得了与理论分析一致的实验结果。