Direct evaluation of singular integrals in elastoplastic analysis by the boundary element method

This paper presents a new method for the direct and accurate evaluation of strongly singular integrals in the sense of Cauchy principal values and weakly singular integrals over quadratic boundary elements in three-dimensional stress analysis and quadratic internal cells in two-dimensional elastoplastic analysis by the boundary element method. A quadratic triangle polar co-ordinate transformation technique is applied to reduce the order of singularity of the singular integrals. Next, a form of Stokes' theorem is introduced in order to remove the singularity in the Cauchy principal value integrals; therefore, the evaluation of these integrals can be carried out by standard Gaussian quadrature. Numerical examples of 2-D elastoplastic problems and a 3-D elastic problem show the effectiveness and efficiency of the method.     

石家庄市室内氡及其子体浓度

本文报道了用双滤膜法对石家庄市室内空气中氡及其子体浓度的调查结果。47个房间室内氡年平均浓度为17.0Bq·m~(-3),氡子体平均浓度是7.14Bq·m~(-3)。氡及其子体浓度的日变化是清晨4—8时出现峰值。季节变化是夏秋季低,冬季高,全年的最低值出现在8月,最高值出现在11月。     

Localized audio watermarking technique robust against time-scale modification

Synchronization attacks like random cropping and time-scale modification are very challenging problems to audio watermarking techniques. To combat these attacks, a novel content-dependent localized robust audio watermarking scheme is proposed. The basic idea is to first select steady high-energy local regions that represent music edges like note attacks, transitions or drum sounds by using different methods, then embed the watermark in these regions. Such regions are of great importance to the understanding of music and will not be changed much for maintaining high auditory quality. In this way, the embedded watermark has the potential to escape all kinds of distortions. Experimental results show strong robustness against common audio signal processing, time-domain synchronization attacks, and most distortions introduced in Stirmark for Audio.     

A wavelet-based procedure for process fault detection

To detect faults in a time-dependent process, we apply a discrete wavelet transform (DWT) to several independently replicated data sets generated by that process. The DWT can capture irregular data patterns such as sharp "jumps" better than the Fourier transform and standard statistical procedures without adding much computational complexity. Our wavelet coefficient selection method effectively balances model parsimony against data reconstruction error. The few selected wavelet coefficients serve as the "reduced-size" data set to facilitate an efficient decision-making method in situations with potentially large-volume data sets. We develop a general procedure to detect process faults based on differences between the reduced-size data sets obtained from the nominal (in-control) process and from a new instance of the target process that must be tested for an out-of-control condition. The distribution of the test statistic is constructed first using normal distribution theory and then with a new resampling procedure called "reversed jackknifing" that does not require any restrictive distributional assumptions. A Monte Carlo study demonstrates the effectiveness of these procedures. Our methods successfully detect process faults for quadrupole mass spectrometry samples collected from a rapid thermal chemical vapor deposition process     

热带城市垃圾典型组分的热解特性研究

对热带城市垃圾的几种典型组分进行了热解实验，得到了它们的失重曲线，通过对失重曲线进行分析，得到了这几种典型组分的热解规律，并通过建立热解动力学模型，求出了其中两种组分的活化能E和频率因子A。     

超高相对分子质量聚乙烯纤维研究进展

介绍了超高分子质量聚乙烯纤维的制备、表面改性及应用的研究进展 ,指出了今后超高分子质量聚乙烯纤维的研究及应用的发展方向     

Iterative receivers for space-time block-coded OFDM systems indispersive fading channels

We consider the design of iterative receivers for space-time block-coded orthogonal frequency-division multiplexing (STBC-OFDM) systems in unknown wireless dispersive fading channels, with or without outer channel coding. First, we propose a maximum-likelihood (ML) receiver for STBC-OFDM systems based on the expectation-maximization (EM) algorithm. By assuming that the fading processes remain constant over the duration of one STBC code word and by exploiting the orthogonality property of the STBC as well as the OFDM modulation, we show that the EM-based receiver has a very low computational complexity and that the initialization of the EM receiver is based on the linear minimum mean square error (MMSE) channel estimate for both the pilot and the data transmission. Since the actual fading processes may vary within one STBC code word, we also analyze the effect of a modeling mismatch on the receiver performance and show both analytically and through simulations that the performance degradation due to such a mismatch is negligible for practical Doppler frequencies. We further propose a turbo receiver based on the maximum a posteriori-EM algorithm for STBC-OFDM systems with outer channel coding. Compared with the previous noniterative receiver employing a decision-directed linear channel estimator, the iterative receivers proposed here significantly improve the receiver performance and can approach the ML performance in typical wireless channels with very fast fading, at a reasonable computational complexity well suited for real-time implementations     

DC-DC变换器突加负载时的动态性能研究

提出了一种能够有效改善DC-DC变换器动态性能的方案。该方案是在全桥电路基础上并联一单端正激变换电路，使变换器负载从10%轻载突加到100%满载时，其暂态过程小于1μs输出电压达到设计要求。文中对具体电路进行了详细分析，并通过仿真进行了验证。     

利用闲置设备生产均三甲苯的探索

介绍了利用闲置设备工业化生产均三甲苯的方法,并从理论上研究了生产的可行性。探讨了提高均三甲苯产品纯度和收率的途径。     

提高综合勘测实力开拓岩土工程市场

随着西北勘测设计研究院（以下简称西北院）勘测总队所承担的黄河龙￣青段、白龙江流域等河段前期综合勘测工作的相继结束，拥有２０００多名职工的勘测队伍面临着何去何从的重大选择。在此转折关头，勘测总队面对现实，审时度势，抓住机遇，开拓前进，及时转轨变型，制定了本单位发展的战略和方向，使勘测总队由单一勘测业务转变为集勘测与岩土工程施工为一身的新型综合队伍。几年来，经过全体职工的奋发努力，缍获得了１９９５年￣