Ka波段超小型同腔混频收发前端

给出一种用于测量运动目标多普勒信号的毫米波同腔混频收发前端，分析了工作原理和性能参数，并给出实验结果。该前端具有小体积、高强度、低功耗、高灵敏度、易于调试和批量生产等优点，已应用于多种毫米波近距离测距系统。     

Dynamic stresses created by the sudden appearance of a transverse crack in periodically layered composites

The time-dependent stress field generated by the sudden appearance of a transverse crack in a periodically layered composite that is subjected to a remote loading is determined. The resulting two-dimensional elastodynamic problem is solved by combining two approaches. In the first one, the representative cell method, which has been presently generalized to dynamic problems, is employed for the construction of the time-dependent Green’s functions generated by the displacement jumps along the crack line. This is performed in conjunction with the application of the double finite discrete Fourier transform. Thus the original problem for the cracked periodic composite is reduced to the problem of a domain with a single period in the transform space. The second approach is based on a wave propagation in composites theory which has been presently generalized to admit arbitrary types of loading. This theory is based on the elastodynamic continuum equations where the transformed time-dependent displacement vector is expressed by a second-order expansion, and the equations of motion and the various interfacial and boundary conditions are imposed in the average (integral) sense. The time-dependent field in any observation point in the plane can be obtained by the application of the inverse transform. This field is valid as long as no reflected waves from external boundaries have been arrived. Results along the crack line as well as the full field are given for cracks of various lengths for Mode I, II and III deformations. In particular the dynamic magnification with respect to the static case is determined at the interface within the first unbroken stiff layer.     

引力波定位和通信技术

本文提出了利用引力波对飞行器和其它运动目标进行识别、跟踪和定化的理论.同时讨论了引力波通信原理和可能的技术方案.引力波通信的发射和接收,放大器原理在文末作了介绍.     

Wavelet Analysis of Soil Mass Images for Particle Size Determination

A method for determination of average grain size from images of fairly uniform particle size soil masses is presented. The procedure utilizes two-dimensional wavelet decomposition of gray scale images. Earlier attempts to quantify grain sizes based on the statistics of co-occurrence matrices suffered from dependence on the illumination intensity and soil color. By normalizing the energy distribution from wavelet decomposition the effects of these previously problematic factors have been eliminated. A general relationship between the center of area beneath the normalized energy distribution and the perceived particle size in pixels per diameter (PPD) is established. A sample problem demonstrates that the proposed wavelet decomposition method provides accurate grain sizes for a wide range of magnification levels as long as the resulting PPD is between approximately 1 and 50.     

Time-Domain Boundary Element Method for Underground Structures in Orthotropic Media

Based on the fundamental solutions due to Dirac’s δ function for transversely isotropic media, a numerical scheme for wave propagation in two-dimensional orthotropic media is developed within the boundary element method in the time domain. Criteria for selection of the time and space discretizations for convergent and accurate results are established. The applicability and accuracy of the scheme are verified by a number of benchmark problems including dynamic responses of an orthotropic half plane under uniform harmonic surface loadings and a circular cavern in slightly orthotropic media under the incidence of pseudo-P and -SV waves. The procedure is then applied to examine wave propagation for an underground tunnel with different ratios of orthotropy in the media. The effects of different wave parameters and ratios of orthotropy on dynamic response of the tunnel are presented.     

Large Scale Particle Image Velocimetry for Low Velocity and Shallow Water Flows

Large scale particle image velocimetry (LSPIV) is an extension of quantitative imaging techniques for measurements of water surface velocities using inexpensive standard video equipment. The present Technical Note describes capabilities and limitations of LSPIV for low velocity shallow flows. Measurements in low velocity shallow flume flows were performed to investigate the LSPIV sensitivity to seeding density and time interval between successive images. The results show that the accuracy of the LSPIV technique does not deteriorate as the flow velocity is reduced to as low as 0.015 m/s provided an adequate seeding and suitable time difference between images are selected. The results suggest that LSPIV is well-suited for flow fields with small velocities that are often below the limit of detection of most conventional devices.     

Effective Soil Density for Propagation of Small Strain Shear Waves in Saturated Soil

This technical note defines an “effective soil density” that controls the velocity of small strain shear waves in saturated soil. Biot theory indicates that the ratio of effective density to saturated density will generally range from 0.75 to 1.0 and is a function of specific gravity of solids, porosity, hydraulic conductivity, and shear wave frequency. For many geotechnical applications, effective density will be equal to saturated density for low hydraulic conductivity soils (clays and silts) and may be less than saturated density for high hydraulic conductivity soils (clean sands and gravels). The findings are relevant to applications involving the propagation of small strain shear waves through saturated soil, and in particular for laboratory and field tests in which shear modulus is back-calculated from measured shear-wave velocity.     

金电解电源装置的优化设计与应用

详细介绍金电解电源装置整流回路的串联电路、并联电路及串并混合电路等不同的电路设计形式、波形及特点，通过分析，优选出最佳的电路形式，并经生产实践证明，采用这种串、并联混合电路形式的电源装置，可以很好地解决金电解生产中的阳极钝化现象，并且电解速度快。与普通的可调恒流或恒压的电解电源相比，能取得更好的经济效益。     

Wave Equation Analyses of Fiber-Reinforced Polymer Composite Piling

Fiber-reinforced polymer (FRP) composites represent an alternative construction material without many of the performance disadvantages of traditional materials. The use of FRP as a pile material can eliminate deterioration problems of conventional piling materials in waterfront environments and aggressive soils. The driveability of traditional piling can be predicted using wave equation analysis of piles (WEAP). The input parameters used in WEAP are obtained by back-analyses of actual case histories. The properties of FRP piling differ from those of conventional piling, so conventional WEAP input parameters may not work as well for FRP composite piling. In this paper, WEAP input parameters for three composite pile types are calibrated using available driving records. The driveability of FRP composite piling is also compared with that of piling made of conventional materials such as timber, steel, and concrete.     

Laser Imagery Technique for Measuring Dispersed Droplets in Water

A nonintrusive method, based on the planar laser imagery technique, was developed to capture images of droplets dispersed in turbulent flow without disturbing the flow field. The methodology and technique of capturing the images, processing, recognition, and measurement were presented. Experimental findings show that this is a workable method in laboratory investigations of droplet dispersion. Results of droplet size distribution obtained and their comparison with those in the literature indicated that the proposed nonintrusive method was successful at capturing fast-moving droplets in turbulent flow without disturbing the flow field. The image processing methodology adopted to recognize and measure the droplets was found to be efficient and effective. The results of the normalized droplet size distribution (number frequency) depicts clearly discernible self-similarity characteristics.