Issues in Optical Diffraction Theory

This paper focuses on unresolved or poorly documented issues pertaining to Fresnel’s scalar diffraction theory and its modifications. In Sec. 2 it is pointed out that all thermal sources used in practice are finite in size and errors can result from insufficient coherence of the optical field. A quarter-wave criterion is applied to show how such errors can be avoided by placing the source at a large distance from the aperture plane, and it is found that in many cases it may be necessary to use collimated light as on the source side of a Fraunhofer experiment. If these precautions are not taken the theory of partial coherence may have to be used for the computations.In Sec. 3 it is recalled that for near-zone computations the Kirchhoff or Rayleigh-Sommerfeld integrals are applicable, but fail to correctly describe the energy flux across the aperture plane because they are not continuously differentiable with respect to the assumed geometrical field on the source side. This is remedied by formulating an improved theory in which the field on either side of a semi-reflecting screen is expressed as the superposition of mutually incoherent components which propagate in the opposite directions of the incident and reflected light.These components are defined as linear combinations of the Rayleigh-Sommerfeld integrals, so that they are rigorous solutions of the wave equation as well as continuously differentiable in the aperture plane. Algorithms for using the new theory for computing the diffraction patterns of circular apertures and slits at arbitrary distances z from either side of the aperture (down to z = ± 0.0003 λ) are presented, and numerical examples of the results are given. These results show that the incident geometrical field is modulated by diffraction before it reaches the aperture plane while the reflected field is spilled into the dark space. At distances from the aperture which are large compared to the wavelength λ these field expressions are reduced to the usual ones specified by Fresnel’s theory. In the specific case of a diffracting half plane the numerical results obtained were practically the same as those given by Sommerfeld’s rigorous theory.The modified theory developed in this paper is based on the explicit assumption that the scalar theory of light cannot explain plolarization effects. This premise is justified in Sec. 4, where it is shown that previous attempts to do so have produced dubious results.     

严寒地区输水渠道滑坡快速维修方法

在北疆严寒地区输水明渠滑坡维修中，由于施工工期短，施工环境恶劣，施工断面狭小，特别在深挖方滑坡段，大型施工机械不易作业，效率降低。如何组织好滑坡段维修各工序的高效衔接，是节约维修时间，提高供水保证率的关键。结合多年渠道滑坡维修实践经验，重点讨论渠道滑坡快速维修的方法。     

明流隧洞反弧段水力及空化特性研究

明流隧洞反弧段是最容易发生空蚀的部位。本文根据势流理论,运用解析函数的 Riemann—Hilbert 混合边值问题理论,导出了计算二维明流泄洪洞反弧段水力特性的边界积分方程,对反弧段的时均压强,时均流速及水深的分布进行了计算。结合对曲边边界层动量积方程的分析,探讨了反弧末端易于发生空蚀破坏的原因。     

关于信息产业技术革命的若干思考

我国国民经济高层决策与规划的着眼点，是实行国民经济工业化与信息化相结合的发展战略．本文就世界信息产业技术革命的趋势、意义、现状以及在我国现有条件下建立国民经济信息网络平台的策略问题提出了浅见．     

短波信道的噪声监测

提出一种短波信道自动监测系统，采用频道估算技术和噪声监测方法，使最佳工作频率的选择及噪声电平的自动实时测量成为现实，并通过试验得出频道噪声随时间变化的情况。     

多功能单片计算机数据采集系统

本文对计算机数据采集系统和紊流流变仪作了一般性介绍，给出紊流流变仪所配用的单片微型计算机数据采集系统的设计方案，并着重分析了系统的输入与输出通道．     

窄通道内小传热面的混合与受迫对流换热研究

通过实验研究了垂直矩形窄通道内小尺寸加热元件在助流和反流条件下对流体的热传过程,详细探讨了混合对流的换热特性,并给出一系列实验关联式,用以计算混合对流条件下的换热率。当Re_L>2500时,无论助流或反流均不受Ra_L~*的影响;当Re_L<350时,对于助流,其换热率与Ra_L~(*0.065)成正比;在350相似文献   

冷弯薄壁卷边槽钢开孔腹板屈曲性能分析

本文用有限元方法分析了受压卷边槽钢开孔腹板的屈曲性能,给出了与孔径d、相邻板件宽度a有关的开孔板稳定系数K的计算公式。通过对所作21根腹板带孔的冷弯薄壁卷边槽钢短柱段试验结果的分析,讨论了开孔腹板的屈曲特点,提出了确定开孔腹板屈曲荷载的方法。理论计算与试验结果吻合较好。     

公路涎流冰防治技术试验研究—截水积冰沟设计原则探讨

本文在查明三十一支线一公里处涎流冰的成因及形成条件的基础上,论证了防治公路诞流冰工程建筑物的设计原则,并根据这一原则阐述了截水积冰沟的设计要点及试验使用中的效果,从而为防治涎流冰的危害提了一定经验.