物探新技术在山地采空洞穴探查中的应用

本文简要介绍了几种物探新技术对采空洞穴的异常机理．并结合实例，对这些方法在山地采空洞穴探查中的应用效果进行了探讨．     

A simplified exact expression of SEP for cross QAM in AWGN channel from M × N rectangular QAM and its usefulness in Nakagami-m fading channel

This paper derives a simple exact expression of symbol error probability (SEP) for general order cross QAM constellation in the presence of additive white Gaussian noise (AWGN) channel. The key idea is to obtain this novel expression from a simple analysis of the corresponding rectangular QAM. The analysis of the expression involves simple one dimensional Gaussian Q functions unlike other complex SEP expressions. A simple tight bound approximation of the proposed exact SEP is also given, which provides performance improvement over the existing SEP approximations, particularly for low signal to noise ratios (SNRs). Also, with the help of simulation results, we show that the proposed approximation is in excellent agreement with the exact SEP curve. Moreover, the proposed expressions prove to be useful for accurate estimation of the SEP in Nakagami-m fading channel, including the special case of Rayleigh fading (m = 1).     

A multi-criteria comparative analysis of different Rayleigh fading channel simulators

In this paper, an in-depth comparative analysis of the most accepted and approved Rayleigh fading channel simulators is presented. Our study addresses the three common methods for generating time-correlated Rayleigh fading processes: the inverse discrete Fourier transform (IDFT) method, the filtering white Gaussian noise (FWGN) method and the sum-of-sinusoids (SOS) method. Totally seven models, including the recently proposed models, are analyzed and compared with Clarke's reference model. We use four quantitative measures for judicious assessment of the quality of generated processes in terms of both first-order and second-order statistics. Additionally, these measures cover analysis in time domain as well as in frequency domain. An evaluation of the computational effort is also depicted. The simulation results suggest that the recently published Wang's model is very attractive and it outperforms all SOS-based models. We conclude that Zheng and Xiao's first model remains the best choice among Zheng and Xiao's family models. Several other important remarks and conclusions about the accuracy and the capability of the different Rayleigh fading simulators are driven from this study.     

Evaluation of behavior of the secondary columns in semi-supported steel shear walls

Semi-supported steel shear walls (SSSW), whose steel plate is connected to secondary columns rather than main columns of the frame, have been considered as an alternative steel shear walls to the traditional type. Many investigations have been made for proportionate designing of components of SSSW system. One of the important issues in this regard is the out of plane buckling of the secondary columns. In this paper, the plastic theory of structures is utilized to find out the axial force distribution, along the compressive column. Then, using energy method, for an assumed shear wall with specific geometry and material and a given shear force, the maximum overturning moment that makes the compressive secondary column buckles, can be determined. Repeating this method, for various shear forces, makes it possible to draw some interaction curves between overturning moments and shear forces. These curves can be used to analyze and design of semi-supported steel shear walls.     

Subsurface crack determination by one-sided ultrasonic measurements

Corrosion of steel reinforcement in concrete is a common type of damage. The cracks propagate from the steel bar to the surface without giving any visual sign prior to surface crack formation. As long as the surface material is intact, the sensitivity of the longitudinal wave velocity to the subsurface cracks is doubtful. In this paper, cracks were created in steel fiber reinforced concrete specimens by four point bending. Wave measurements took place on the intact surfaces (compression side) using common acoustic emission transducers. Although there was no visual sign of the crack, Rayleigh as well as longitudinal wave velocities clearly decreased relative to those of the sound material. Other parameters like the amplitude and the experimental scatter of the waves were much more sensitive to damage. Numerical simulations were conducted in order to make a parametric study concerning the depth of the sound layer, the propagating wavelength and the measured wave parameters and propose a firm methodology. It is concluded that by scanning a surface with simple acoustic one-sided measurements, the identification of the location of the subsurface damage is possible, while the propagating wave gives information about the depth of the crack.     

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.     

偶氮胭脂红B与蛋白质的共振瑞利散射研究

在酸性条件下,蛋白质与偶氮胭脂红B(ABX)结合形成离子缔合物,使ABX微弱的共振瑞利散射(RRS)急剧增强.研究了ABX与牛血清白蛋白(BSA)相应的光谱特征,影响因素及适宜的反应条件,建立了一种定量测量蛋白质的新方法.该方法灵敏度高,蛋白质的检出限在30.6～38.7μg/L之间,线性范围宽,反应迅速,操作简单.该法已经应用于人尿样、牛血清及奶粉中蛋白质含量的测定,样品的相对标准偏差小于1.9%,回收率在 96.2%～102.2%之间,结果与考马斯亮蓝法(CBB)无差异.     

一种简单有效的CDMA信号DOA估计方法

针对直接序列扩频同步码分多址(CDMA)通信系统，提出了一种基于均匀直线天线阵的CDMA信号波达方向(DOA)估计新方法。该方法利用解扩后干扰已被抑制的特点，以及不同天线上加性噪声的不相关性，利用简单的2阶统计平均来提取信号的DOA。新方法不需要计算阵列输出的空间相关矩阵，与存在的任何方法相比，计算量大为减少。仿真结果表明，在平坦瑞利衰落信道中具有良好的性能。     

Average channel capacity for Rayleigh fading spread spectrum MIMO systems

In this paper, a novel approach to the problem of estimating the average channel capacity (in the Shannon sense) assigned to each user of a spread spectrum (SS) multiple‐input multiple‐output (MIMO) system operating in a Rayleigh fading environment, is presented. The analysis leads to a closed‐form expression which fully conforms to the upper bound of the channel capacity value of a non‐fading AWGN channel when the transmitted signal bandwidth tends to infinity proving the validity of the described analysis. Copyright © 2006 John Wiley & Sons, Ltd.     

旋转矩阵法抗多用户间干扰

研究了一种新的MIMO系统下多用户间干扰抑制技术(旋转矩阵法),此方法增加了码字间的欧氏距离,降低成对差错率,与传统方法(TDMA/CDMA)系统相比:保证了频带利用率;并对接收机进行设计,为降低算法复杂度采用了MMSEML分组接收机。仿真证明,在没有编码、不用正交信号、在高信噪比下,系统可明显降低用户间干扰,而MMSEML接收机降低算法复杂度的同时在信噪比22dB时,误码率可达到3·3E3。