汉江上游干支流沉积物细菌群落多样性和影响因素

为了解汉江上游干支流沉积物细菌多样性以及确定性过程和随机性过程在沉积物细菌群落构建过程中的相对重要性,基于Illumina高通量测序技术,分析了环境因子对细菌群落组成的影响,采用非度量多维尺度(NMDS)排序探究了季节之间沉积物细菌群落的差异,并结合中性群落模型和标准化随机率量化了确定性过程和随机过程对群落构建的影响。结果表明:汉江上游及其支流细菌群落主要由变形菌门(Proteobacteria)、拟杆菌门(Bacteroidetes)、蓝藻门(Cyanophyta)、浮霉菌门(Planctomycetes)和酸杆菌门(Acidobacteria)等组成；细菌群落在不同季节有显著差异；地理距离和环境因子对细菌群落结构影响较小,确定性过程并未在细菌群落组成中起到主导作用；随机过程很大程度上影响了群落在秋季和春季的组成,是沉积物细菌群落构建的主导因素。     

Comparison of two low-hazard organic solvents as individual and cosolvents for the fabrication of polysulfone membranes

Petroleum-derived solvents commonly used in membrane fabrication are often hazardous and toxic, so the investigation of safer alternatives is important. In this study, two low-hazard solvents, methyl 5-(dimethylamino)-2-methyl-5-oxopentanoate (Rhodiasolv® PolarClean) and gamma-valerolactone (GVL), were investigated as sole solvents and as cosolvents to cast polysulfone membranes via nonsolvent induced phase inversion. Normalized viscosity was introduced as an indicator of dope solution homogeneity and was used to compare the required time of mixing to achieve full dissolution of the polymer in the different solvents/solvent mixtures. All dope solutions made with low-hazard solvents were found to be more viscous than those made with traditional solvents, which meant additional mixing time was needed, and that fabricated membranes were morphologically different. With respect to operation, membranes cast from dope solutions containing equal amounts of PolarClean and GVL displayed the most similar flux curves and solute rejection to those made using the traditional solvent tested.     

一种低信噪比环境下的语音端点检测算法

端点检测技术是语音信号处理的关键技术之一，为提高低信噪比环境下端点检测的准确率和稳健性，提出了一种非平稳噪声抑制和调制域谱减结合功率归一化倒谱距离的端点检测算法。该算法首先通过抑制非平稳噪声再采用调制域谱减消除残余噪声来提升信噪比，减少语音失真。然后再提取每帧信号的功率归一化倒谱系数，计算每帧信号与背景噪声的功率归一化倒谱距离。最后将该倒谱距离作为检测参数，采用双门限判决方法进行端点检测。实验结果表明，该端点检测算法对语音帧和噪声帧具有较好的区分性。此外，在低信噪比环境下，所提出的算法对于不同类型的噪声都具有较好的稳健性。     

公路工程区域报价的多样性及其统一性

通过对产生公路工程区域报价多样性的原因进行分析，提出了规范与统一报价的具体措施，并指出投标阶段关系到产品的质量与投资者实施项目的标底。     

Stochastic response of hysteretic systems

This paper deals with approximate stochastic response of hyseretic structures under white noise excitation, based on It stochastic differential equations. Instead of the original system an equivalent nonlinear system is considered, in which the drift vector is given by a series expansion of the order n 1 in terms of the state variables. n = 1 represents the well-known case of equivalent linearization. Components in the drift vector representing the nonanalytical constitutive equations are replaced by a cubic polynomial expansion. The hierarchy of statistical moment equations is closed by a cumulant neglect closure scheme. The method has been applied to a bilinear single degree-of-freedom system subjected to white noise excitation, for which an equivalent system with a cubic series expansion to the constitutive equation is considered. The results obtained are compared with those of numerical simulation and alternative methods, and they provide substantial improvements compared to equivalent linearization.     

Postflashover fires — an overview of the research at the national research council of Canada (NRCC), 1970–1985

The NRCC model of fully developed compartment fires is discussed. Although the mathematics involved is quite simple, it allows a rather comprehensive simulation of the fire process. The model offers an explanation for the findings that ventilation control is related to the pyrolysis mechanism and is not a result of scarcity of air in the fire compartment, and that thermal feedback is of secondary importance in the burning (pyrolysis) of cellulosic fuels. Another feature of the model is the introduction of the normalized heat load concept. The normalized heat load is a scalar quantity that depends on the total heat absorbed by the compartment boundaries during the fire incident, and is practically independent of the temperature history of the fire. A simple explicit formula has been proposed and proved experimentally to describe the normalized heat load for real-world fires with fair accuracy. The normalized heat load concept offers a simple means for converting fire severities into fire resistance requirements, and makes it possible to design buildings for prescribed levels of structural fire safety. The potential of fires to spread by convection and the expected characteristics of fires of noncharring plastics are also discussed. Reference: T. Z. Harmathy, Postflashover Fires—An Overview of the Research at the National Research Council of Canada (NRCC), 1970–1985,Fire Technology, Vol. 22, No. 3, August 1986, p. 210.     

基于分数阶Fourier变换累积量的目标检测算法

传统的信号检测和噪声分离方法只限于在时域或是频域进行,如果信号和背景噪声有很强的时频耦合,就难以在时频域得到好的检测结果。对此提出了分数阶Fourier变换累积量算法,该算法具有解除时频耦合和抑制噪声的特性,当选择合适的旋转角度使之与处理信号相匹配,就可以在分数阶Fourier域获得较好的检测结果。仿真结果表明,分数阶Fourier累积量算法的检测性能优于分数阶Fourier变换和4阶累积量算法,展现了分数阶Fourier变换累积量算法有优越的信号处理性能。     

基于三阶循环平稳度准则的盲源分离算法

通过研究循环平稳信号的特性和分析传统的基于二阶统计量的盲源分离算法,在二阶循环平稳度的基础上提出了三阶循环平稳度的概念,并推导出了利用三阶循环累积量平稳度作为分离准则的新盲源分离算法。本算法可以在复杂噪声的情况下有效的分离平稳信号和循环平稳信号。仿真结果表明该算法能够抑制混合信号中的强噪声,算法简单,实时性好。     

计及UPFC的电力系统多阶段多目标无功优化算法

统一潮流控制器(UPFC)并联侧连续的无功调节能力为电力系统无功优化提供了新的控制手段。基于此,首先建立适用于新型UPFC拓扑的UPFC稳态模型;然后考虑无功设备动作次数的约束,明确多目标无功优化问题的目标函数和约束条件,建立计及UPFC的多目标无功优化模型;接着,提出一种多阶段方法对其进行求解,其中,第一阶段将原问题进行松弛并采取归一化的方法统一多个目标的量纲,第二阶段基于规格化平面约束法获取松弛问题的Pareto最优候选解集,并给出折衷解的选取方法,第三阶段基于三角罚函数法对折衷解中的整数变量进行归整,获取原问题的最优折衷整数解。最后,对南京西环网实际等值系统进行算例测试,验证了算法的有效性及UPFC在无功优化问题中的应用前景。     

一种基于遥感指数的城市建筑用地信息提取新方法

提出了一种利用仿建筑用地指数提取城市建筑用地信息的新方法。首先利用近红外波段和绿波段构建仿归一化建筑指数,再将其与土壤调节植被指数和归一化水体指数相结合,进而构建仿建筑用地指数,最后利用仿建筑用地指数提取城市建筑用地信息。仿建筑用地指数影像将建筑用地信息增强,通过影像分割、去小面元以及合并邻近面元处理,可以准确提取城市建筑用地信息,实验精度可达89.5%。