The use of antiphased zones in an acoustic Fresnel lens for a scanning sonar transmitter

A simple acoustic Fresnel lens is described, which, when used with a plane array of sonar transducer elements, produces a wide beam in azimuth. Test results are compared to computed beam plots and good agreement between theory and measurement was found when all the array elements were in phase. When alternate zones are 180° out of phase, the lens can be reduced in thickness as the step height is halved; however, more careful placing of the transducer elements is required. Such a reduction in lens thickness could be desirable at low operating frequencies, or if a very wide sound beam is desired.     

在超短脉冲照射下光栅的瞬时Talbot效应的研究

本文给出了光栅在超短脉冲照射下其瞬时Fresnel衍射光场的解析解.对该解析解的数值计算表明:当脉冲光波的半极大值全宽Δτ在几十个fs内,光栅的瞬时Talbot自成象现象消失,且Δτ越小或距离越远,瞬时光强波形与初始波形差异较大.而当Δτ达到ps的数值级时,瞬时Talbot自成象现象是存在的.     

A tail empirical process approach to some nonstandard laws of the iterated logarithm

We show that a number of nonstandard laws of the iterated logarithm have limiting constants which may be expressed as the extreme values of functionals off, wheref varies over suitable compact sets of functions. By solving the corresponding extremal problems, we show how these constants are generated. In addition, several new laws are presented.     

Notes on a generalized Fresnel class

In this paper we establish a theorem for the generalized Fresnel class F _A1,A2 ensuring that various functions are in F _A1,A2. We also prove a translation theorem for the analytic Feynman integral of functions in F _A1,A2.This research was supported in part by the Basic Science Research Program, Ministry of Education.     

SLLN for Weighted Independent Identically Distributed Random Variables

For any sequence {a _k } with sup for some q>1, we prove that converges to 0 a.s. for every {X _n } i.i.d. with E(|X ₁|)< and E(X ₁)=0; the result is no longer true for q=1, not even for the class of i.i.d. with X ₁ bounded. We also show that if {a _k } is a typical output of a strictly stationary sequence with finite absolute first moment, then for every i.i.d. sequence {X _n { with finite absolute pth moment for some p> 1, converges a.s.     

再现实像的大视角菲涅尔全息图的制作

本文给出一种大视角菲涅尔全息图的制作方法,由此法制得的全息图可再现出物体的正视实像。此法整个过程无需大孔径透镜,而且再现像无任何畸变。文中给出了原理性实验结果。     

Laws of the iterated logarithm for partial sum processes indexed by functions

We establish a bounded and a compact law of the iterated logarithm for partial sum processes indexed by classes of functions. We assume a growth condition on the metric entropy under bracketing. Examples show that our results are sharp. As a corollary we obtain new results for weighted sums of independent identically distributed random variables.     

菲涅耳衍射公式误差相位的讨论

根据波动光学的理论,对菲涅耳近场衍射公式误差相位的影响进行了分析。以单缝衍射为例,讨论了误差相位与计算精度的联系。结合菲涅耳线波带片焦面光强分布的计算,对比了菲涅耳衍射公式与基尔霍夫衍射公式的计算结果,说明在不满足误差相位近似条件下使用菲涅耳衍射公式带来的影响。最后对影响波带片焦面光强分布的几个因素进行了讨论。