连续函数孔径在编码孔径成象中的应用

本文探讨了哥伯环带作为编码孔径的γ射线成象中应用。理论分析和计算机模拟表明，在采用相关解码时，哥伯环带孔径的成像性能优于菲涅耳环带孔径。     

A strong law of large numbers for iterated functions of independent random variables

We study sequences of random variables obtained by iterative procedures, which can be thought of as nonlinear generalizations of the arithmetic mean. We prove a strong law of large numbers for a class of such iterations. This gives rise to the concept of generalized expected value of a random variable, for which we prove an analog of the classical Jensen inequality. We give several applications to models arising in mathematical physics and other areas.     

On the law of the iterated logarithm

An analogue of the law of the iterated logarithm for Brownian motion in Banach spaces is proved where the expression √2 loglog s is replaced by a positive non-decreasing function satisfying certain conditions.     

轴外点光源复振幅分布函数的讨论

在处理点光源球面波复振幅传播、交换等问题时,为了简化数学运算。通常应用菲涅耳近似,以二次曲面代替球面,但是,当离轴角较大时,菲涅耳近似的误差较大,明显地与实验现象不符。本文从点光源理想球面波复振幅分布函数出发,采用一种准菲涅耳近似,导出了轴外点光源复。振幅分布函数较为准确的简单表示式,该式同样能简化运算,而且还能满意地解释一些实验现象。     

Antenna Measurement on Cylindrical Surface in Fresnel Region Using Direct Far‐Field Measurement System

The small anechoic chambers built by many small‐/medium‐sized companies and universities present difficulties in testing electrically large antennas because the chamber size cannot satisfy the far‐field criterion of large antennas. In this paper, a method for Fresnel‐region measurement on a cylindrical surface with variation of the measurement height is proposed and verified by both calculations and experiments. We implement the proposed method using a direct far‐field measurement system by adding a few supporting structures. The results show good accuracy.     

用菲涅耳衍射理论分析双光栅成像效应

从理论上对双光栅成像效应现象进行研究,分别从菲涅耳衍射理论和平面透射光栅的菲涅耳衍射公式出发,分析了物光波经过两个平行放置的平面透射光栅组成的系统衍射后的复振幅分布。分析结果表明,在理想状态下,当两个光栅的放置位置满足一定条件时,在第二个光栅后面可以观察到一个清晰的原物体图像。理论分析解释了两个光栅在双光栅成像效应中的作用,得到了双光栅成像效应发生时,两个光栅的空间频率、衍射光级数以及光栅放置位置之间的关系式,这与实验所得结果相一致。     

基于衍射微透镜的光学加速度传感器设计

提出了一种基于菲涅耳衍射微透镜的新型光学加速度传感器,它能够解决导航系统中惯性传感器普遍存在的抗电磁干扰和电磁冲击能力差等缺陷。其传感原理是把一个反光膜平行地置于衍射微透镜的后方,加速度的变化会改变反光膜的位置,根据微透镜前方会聚点处光强的变化,感知加速度的大小。介绍了传感器及其动力学系统的工作原理,并对衍射微透镜和动力学系统的微弹性机械结构进行了设计和加工,最后对传感器的性能和误差进行了分析。原理验证性实验的结果表明这种新型光学加速度传感器的原理正确,并且结构简单,灵敏度高。     

透过检测中的准直镜精度容限

在干涉检验过程中,被检元件的面形误差检测精度受到干涉仪系统结构的影响,从而降低测量结果的可靠性。为了得到较高的检测精度,必须对检测系统进行分析,建立测量误差和系统结构的关联度。根据菲涅耳衍射近似理论,就菲佐干涉仪中的准直镜和标准镜面形误差对透过检测的影响进行了研究。通过对波前相位传递情况的分析,得出波前误差和系统结构参量的相关性,去除空腔系统误差,优化结构参量,并建立准直镜误差容限表达式。经计算得出,当被检面形变误差为0.2λ时,测试误差可以达到0.02λ,而对准直镜的面形误差要求只需0.8λ。     

Constant flux relation for aggregation models with desorption and fragmentation

We study mass fluxes in aggregation models where mass transfer to large scales by aggregation occurs alongside desorption or fragmentation. Two models are considered: (1) a system of diffusing, aggregating particles with influx and outflux of particles (in-out model); and (2) a system of diffusing aggregating particles with fragmentation (chipping model). Both these models can exist in phases where probability distributions are power laws. In these power law phases, we argue that the two point correlation function should have a certain homogeneity exponent. These arguments are based on the exact constant flux scaling valid for simple aggregation with input. Predictions are compared with Monte Carlo simulations.     

Existence and Regularity of Purely Viscous Polymer Flow

In this article we study purely viscous nonstationary flow of quasi-Newtonian fluids with share dependent viscosity obeying the power-law and the Carreau's law. We prove the existence and regularity of the solution using the Galerkin's procedure.