BEMD在复杂背景下弱小目标检测中的应用

针对复杂背景下的弱小目标检测与识别问题,提出了一种基于二维经验模态分解(Bidimensional Empirical Mode Decomposition,BEMD)的检测算法。待检测的原图像经过BEMD分解筛选出多个二维的内蕴模函数(Intrinsic Mode Functions,IMF)和趋势图像,使用全局门限法分割各个IMF,将处理后的IMFs综合成一个分割出待检测目标的结果图像。实验结果表明,该方法使用简洁的步骤,有效、准确地检测出弱小目标。     

Litter fall, litter stocks and decomposition rates in rainforest and agroforestry sites in central Amazonia

The sustainability of agroforestry systems in Amazonia was assessed from their litter dynamics and decomposition. Litter fall and litter stocks were determined from July 1997 to March 1999 in four sites in central Amazonia: a primary rainforest, a 13-year-old secondary forest, and two sites of a polyculture forestry system which consisted of four planted tree species of commercial use amidst upcoming secondary growth. The average annual litter fall in the undisturbed primary rainforest (FLO) was 8.4 t ha^–1 year^–1, which is within the range of litter fall in other rainforests in the region. It was similar in one of the two polyculture sites (8.3 t ha^–1 year^–1), but lower in the secondary forest and in the second polyculture site. In the litter fall in secondary forest and agroforestry sites, the leaf portion was higher (76–82% of total litter fall) than in FLO, due to reduced fine matter and wood fall. Leaf litter fall variability was much lower in the plantation sites than in the forests, which is explained by the much more homogeneous stand structure of the plantations. The quality of the produced litter, measured as C/N ratio, differed significantly between the primary forest site and one polyculture and the secondary forest site. The cumulative input of nitrogen through litter fall was 144 kg ha^–1 year^–1 in FLO, and 91–112 kg ha^–1 year^–1 in the polycultures and the secondary forest. Litter fall was not correlated with soil parameters, but had a significant linear regression with canopy closure. For the primary rainforest, litter fall was also (inversely) correlated with monthly rainfall. Litter fall was higher in the first year (1997–1998; an El Niño period) than in 1998–1999. Litter stocks on the forest floor were highest in the secondary forest (24.7 t ha^–1), and much lower in the polyculture sites (15.1–16.2 t ha^–1) and the primary forest (12.0 t ha^–1). There were no differences in the relative N content (C/N ratio) of the litter stocks between the sites, but the larger stocks led to higher absolute N contents in the litter layer in the secondary forest. From the monthly values of litter stocks (S) and litter fall (P), the decomposition coefficient k _e=P/S was calculated, which was, on average, highest for the primary forest (0.059), followed by the polyculture systems (0.040–0.042), and by the secondary forest (0.024). Thus, due to low decomposition rates, the secondary forest site showed large litter accumulations in spite of a relatively low litter fall. In contrast, the primary forest showed high litter fall but low stocks, due to high decomposition rates. The decomposition coefficients of the polyculture systems ranged between the primary and the secondary forest. The reduced decomposition rates in the man-managed agroecosystems indicate quantitative and/or qualitative changes in the decomposer communities of these systems that lead to a higher build-up of litter stocks on the forest floor. However, the decomposer systems in the polyculture sites still were more functional than in the site of non-managed secondary growth. Thus, from a soil biological viewpoint, ecologically sustainable low-input agroforestry in Amazonia will benefit from the application of these polyculture systems.     

关于单向板肋梁楼盖主梁永久荷载分项系数取用的思考

指出了现行教材中现浇单向板肋梁楼盖主梁内力计算时永久荷载荷载分项系数取用存在的错误,分析了该错误对计算结果的影响,提出了解决方法和笔者对问题重要性的认识,供同行参考。     

New explicit formulas for the effective piezoelectric coefficients of binary 0-3 composites

The explicit formula for the effective dielectric constant of binary 0-3 composites (Poon and Shin, J. Mat. Sc. 39 (2004) 1277–1281) is extended into two explicit formulas for the prediction of the elastic properties of macroscopically isotropic 0-3 composites. By combining them with the explicit effective dielectric formula into a calculation scheme (Wong et al., J. Appl. Phys. 90 (2001) 4690), we obtained two new explicit formulas for the prediction of the d ₃₁ and d ₃₃ values for binary 0-3 piezoelectric composites. These two explicit formulas are applicable even when the inclusion volume fraction is high. Comparing with existing experimental data, they are found to fit more favorably than those predicted by Wong et al. and others. Also, being explicit makes these formulas much easier to be embedded into other effective property calculations for binary 0-3 composite materials.     

具有随机系数和带间隙的自激振动问题的人工神经网络解法

利用人工神经网络技术(BP网络)研究具有随机系数和带有间隙的初轧机自激振动问题,提出了一种Runge-Kutta法和人工神经网络相结合的求解方法。即利用数值计算和BP网络建立随机系数和稳态振幅之间的关系,从而直接计算出稳态振幅的统计特性。计算结果表明:采用所提出的方法求解,通用性好且可提高计算精度,并得到了间隙与稳态振幅的均值有关,与标准离差无关的有用结论。     

聚乙烯钢塑复合管导热系数的测定

聚乙烯钢塑复合管是新一代替代传统管道的新型管材，其导热系数的测试及相关的数据目前还没有报导。本文利用一维、稳态传热的基本规律，采用相对简单易行、测试成本低、较能真实反映实际情况的测试装置，对成都某企业的聚乙烯钢塑复合管导热系数进行了测试，获取了较满意的测试结果，并对测试结果的准确性进行了分析。所采用的测试方法及所获取的数据，对相应的生产厂家、设计、施工单位具有一定的指导意义。     

变系数三阶线性微分方程的一个新的可解类型

通过自变量变换，将一类变系数三阶线性微分方程化为三阶常系数线性微分方程，从而得到变系数三阶线性微分方程的一个新的可解类型，推广了著名的三阶Eulcr方程。     

Performance evaluation of continuous production lines with machines having different processing times and multiple failure modes

This paper presents an approximate analytical method for the performance evaluation of asynchronous production lines with deterministic processing times, multiple failure modes and finite buffer capacity. The discrete flow of parts is approximated by a continuous flow of material. The technique developed here is based on the approximate evaluation of a K machine line by the evaluation of K−1 two-machine lines: unlike previous work on this subject, the multiple failure approach allows to consider real and virtual failure modes for each building block in which the original line is decomposed. Indeed, to reproduce in each two-machine lines the flow of material observed in the related buffer of the original line, real failures are used to take into account the reliability of the physical machines while virtual failures are introduced to model the different interruptions of flow that can arise inside the line thus preventing machines from working. To assess the accuracy of the proposed method, extensive simulation and numerical experiments have been carried out.     

Regularization Techniques for Numerical Approximation of PDEs with Singularities

The rate of convergence for numerical methods approximating differential equations are often drastically reduced from lack of regularity in the solution. Typical examples are problems with singular source terms or discontinuous material coefficients. We shall discuss the technique of local regularization for handling these problems. New numerical methods are presented and analyzed and numerical examples are given. Some serious deficiencies in existing regularization methods are also pointed out.     

Vague集中的分解定理与相似度量

1 引言目前,在计算机科学及应用的多种领域中,模糊集起着重要的作用。因而其理论及应用都得到了迅速的发展。Vague集从一定意义上讲在对事物属性的描述上较模糊集提供了更多的选择方式,因而已在学术界和工程技术界引起了广泛关注。事实上,Vague集正成为当前模糊信息处理中的一个新兴课题。当前相对于应用而言,Vague集的理论研究方面有待