海洋环境参数对Scholte波特性的影响

采用半无限海底的Scholte波模型并将其推广至分层海底,在直角坐标系下利用流体和弹性体中的波动方程,提出基于水平分层弹性海底模型的Scholte波的求解方法,结合简正波理论分析了Scholte波的频散特性及其质点运动轨迹和质点位移的传播特性,并分析了海洋环境参数(声速与海底参数)对Scholte波传播特征的影响.结果表明,Scholte波受海底介质中横波声速的影响最大,其频散曲线转折点可用于估算弹性沉积层厚度.     

基于改进的TF-IDF与隐朴素贝叶斯的情感分类研究

为了提高情感分类准确率,提出了一种基于改进的TF-IDF与隐朴素贝叶斯的情感分类研究。通过改进的TF-IDF算法提取文本特征词,并根据属性之间的依赖关系添加隐藏的父节点,增强了属性之间的依赖关系,提高了情感分类的准确性。实验结果表明,在平均宏查准率、宏查全率和宏F1值在改进之后的算法分别提高了5%、8%和6%。     

基于光流块统计特征的视频异常行为检测算法

提出了一种基于光流块统计特征的视频异常行为检测算法.该算法首先对训练集视频序列的光流场进行分块及预处理,而后提取光流块的统计特征,所提取的块统计特征同时包括了光流块的幅度信息和相位信息,通过训练集得到的光流块统计特征训练出对应的正常行为的高斯混合模型(GMM).测试集通过同样的方式提取光流块统计特征,通过计算所提取统计特征以多大的概率属于GMM判定所检测光流块的异常程度.实验结果表明,该算法能够在一定程度上解决运动物体一致性和部分遮挡问题,并提高了异常行为检测的准确率.     

超声波法在检测导堤表面混凝土结构中的应用

基于超声波无损检测理论,建立了超声波检测混凝土结构强度的预测方法.以吴淞导堤表面混凝土质量检测为案例,比较分析了4 200个超声波法预测的和400个现场钻孔取芯实测的混凝土强度值.结果表明,混凝土强度实测值和预测值均近似服从正态分布,概率峰值区间分别位于12~16MPa和9~15MPa,分布密度分别为28%和23.26%,强度分布区域均为3~25MPa,且均小于设计值,预测结果和实测值吻合度较高.     

Insights from the genome of the biotrophic fungal plant pathogen Ustilago maydis

Ustilago maydis is a ubiquitous pathogen of maize and a well-established model organism for the study of plant-microbe interactions. This basidiomycete fungus does not use aggressive virulence strategies to kill its host. U. maydis belongs to the group of biotrophic parasites (the smuts) that depend on living tissue for proliferation and development. Here we report the genome sequence for a member of this economically important group of biotrophic fungi. The 20.5-million-base U. maydis genome assembly contains 6,902 predicted protein-encoding genes and lacks pathogenicity signatures found in the genomes of aggressive pathogenic fungi, for example a battery of cell-wall-degrading enzymes. However, we detected unexpected genomic features responsible for the pathogenicity of this organism. Specifically, we found 12 clusters of genes encoding small secreted proteins with unknown function. A significant fraction of these genes exists in small gene families. Expression analysis showed that most of the genes contained in these clusters are regulated together and induced in infected tissue. Deletion of individual clusters altered the virulence of U. maydis in five cases, ranging from a complete lack of symptoms to hypervirulence. Despite years of research into the mechanism of pathogenicity in U. maydis, no 'true' virulence factors had been previously identified. Thus, the discovery of the secreted protein gene clusters and the functional demonstration of their decisive role in the infection process illuminate previously unknown mechanisms of pathogenicity operating in biotrophic fungi. Genomic analysis is, similarly, likely to open up new avenues for the discovery of virulence determinants in other pathogens.     

The distillation and volatility of ionic liquids

It is widely believed that a defining characteristic of ionic liquids (or low-temperature molten salts) is that they exert no measurable vapour pressure, and hence cannot be distilled. Here we demonstrate that this is unfounded, and that many ionic liquids can be distilled at low pressure without decomposition. Ionic liquids represent matter solely composed of ions, and so are perceived as non-volatile substances. During the last decade, interest in the field of ionic liquids has burgeoned, producing a wealth of intellectual and technological challenges and opportunities for the production of new chemical and extractive processes, fuel cells and batteries, and new composite materials. Much of this potential is underpinned by their presumed involatility. This characteristic, however, can severely restrict the attainability of high purity levels for ionic liquids (when they contain poorly volatile components) in recycling schemes, as well as excluding their use in gas-phase processes. We anticipate that our demonstration that some selected families of commonly used aprotic ionic liquids can be distilled at 200-300 degrees C and low pressure, with concomitant recovery of significant amounts of pure substance, will permit these currently excluded applications to be realized.     

Involvement of small Ras GTPases and their effectors in chronic renal disease

The mechanisms involved in the development of renal fibrosis are poorly understood. Small Ras GTPases control cell proliferation, differentiation, cellular growth and apoptosis, with cell-specific expression in the kidney. Cytokines, high glucose medium or advanced glycation end-products activate Ras in different renal cells. Increased Ras activation has been found in experimental tubulointerstitial fibrosis. Transforming growth factor-β1 (TGF-β1) and Ras signalling pathways are close related: TGF-β1 overcomes Ras mitogenic effects, and Ras counteracts TGF-β signalling. However, Ras activation is also an intracellular signal transduction point for several molecules (e.g. TGF-β1) involved in kidney damage. Ras isoforms play different roles in regulating extracellular matrix synthesis in fibroblasts and mesangial cells. These data give evidence for a role for Ras in renal fibrosis, but no reviews are available on the role of p21 Ras in this process. Thus, our goal is to review the role of Ras activation and signalling in renal fibrosis. Received 7 June 2007; received after revision 17 September 2007; accepted 1 October 2007     

杆系结构静/动力学计算的直接方法

针对有限单元法计算精度受网格密度制约的问题,提出一种求任意复杂杆系静、动力学问题精确解的方法.该方法基于节点分析法,逐个节点列位移相容方程和内力平衡方程,以谱系数作为未知数,杆件变形和截面内力则采用相应问题的精确解来描述.用代数符号化的方式,对方程系数矩阵的组建过程进行了详细描述,为通用程序编制提供依据.对建模过程中的分布式载荷和铰接接头的处理方法进行了探讨并给出处理方法.通过平面钢架屈曲分析和空间管路谐响应分析,证实所提方法具有计算精度高、划分单元数少的特点,特别适合于需要精确解的场合.     

Unique astrocyte ribbon in adult human brain contains neural stem cells but lacks chain migration

The subventricular zone (SVZ) is a principal source of adult neural stem cells in the rodent brain, generating thousands of olfactory bulb neurons every day. If the adult human brain contains a comparable germinal region, this could have considerable implications for future neuroregenerative therapy. Stem cells have been isolated from the human brain, but the identity, organization and function of adult neural stem cells in the human SVZ are unknown. Here we describe a ribbon of SVZ astrocytes lining the lateral ventricles of the adult human brain that proliferate in vivo and behave as multipotent progenitor cells in vitro. This astrocytic ribbon has not been observed in other vertebrates studied. Unexpectedly, we find no evidence of chains of migrating neuroblasts in the SVZ or in the pathway to the olfactory bulb. Our work identifies SVZ astrocytes as neural stem cells in a niche of unique organization in the adult human brain.