Imaging of Titan from the Cassini spacecraft

Titan, the largest moon of Saturn, is the only satellite in the Solar System with a substantial atmosphere. The atmosphere is poorly understood and obscures the surface, leading to intense speculation about Titan's nature. Here we present observations of Titan from the imaging science experiment onboard the Cassini spacecraft that address some of these issues. The images reveal intricate surface albedo features that suggest aeolian, tectonic and fluvial processes; they also show a few circular features that could be impact structures. These observations imply that substantial surface modification has occurred over Titan's history. We have not directly detected liquids on the surface to date. Convective clouds are found to be common near the south pole, and the motion of mid-latitude clouds consistently indicates eastward winds, from which we infer that the troposphere is rotating faster than the surface. A detached haze at an altitude of 500 km is 150-200 km higher than that observed by Voyager, and more tenuous haze layers are also resolved.     

高职院校思想政治教育的顶层设计、品牌创建、基地拓展与实效检验

高职院校思想政治教育的顶层设计、品牌创建、基地拓展与实效检验这四项重大工程或环节,是做好思想政治教育的关键因素。必须牢牢把握顶层设计的要素、品牌创建的特征、基地拓展的原则、实效检验的角度和层面等,以提高人才培养工作的质量和水平。     

North-south geological differences between the residual polar caps on Mars

Polar processes can be sensitive indicators of global climate, and the geological features associated with polar ice caps can therefore indicate evolution of climate with time. The polar regions on Mars have distinctive morphologic and climatologic features: thick layered deposits, seasonal CO2 frost caps extending to mid latitudes, and near-polar residual frost deposits that survive the summer. The relationship of the seasonal and residual frost caps to the layered deposits has been poorly constrained, mainly by the limited spatial resolution of the available data. In particular, it has not been known if the residual caps represent simple thin frost cover or substantial geologic features. Here we show that the residual cap on the south pole is a distinct geologic unit with striking collapse and erosional topography; this is very different from the residual cap on the north pole, which grades into the underlying layered materials. These findings indicate that the differences between the caps are substantial (rather than reflecting short-lived differences in frost cover), and so support the idea of long-term asymmetry in the polar climates of Mars.     

膝褶带构造及其地球物理正演

通过构建一系列理想的膝褶带地质模型, 利用四阶有限差分法单炮记录正演模拟方法, 对各类型膝褶带在地震反射剖面上的图像几何学特征进行了正演。正演结果分析表明: 1) 在地震剖面上, 膝褶带变形样式不同于断层构造样式, 膝褶带在地震剖面上具有一定宽度, 带内地震信息呈低振幅、信息模糊或空白带; 2) 膝褶带内外角之间的变化, 即膝褶带内地层产状的倾角变化, 对地震反射信息影响巨大; 3) 在膝褶带内地层陡立或近于直立的情况下, 地震反射界面从膝褶带外向内追踪困难, 且发生反射界面信息假象。这些地球物理正演结果为实际地震剖面的构造解释、膝褶与断裂构造的区分提供基本的参考。     

试论虚拟经济

虚拟经济是指用货币符号表现商品价值及虚拟资本持有和交易的活动。相对于实体经济来说，虚拟经济有其虚拟性，但它的存在却是一个客观事实。从虚拟经济的运行背景、基本特征、虚拟经济和实体经济的关系、我国虚拟经济的现状等方面进行了探讨。     

论西门庆

《金瓶梅词话》中最重要的人物形象西门庆蕴含了丰富的社会、文化及人性的内涵 ,是一个复杂深刻的文学形象。封建社会之中的新兴暴发商人是其本质特征 ,在罪恶的社会时代之中所难以避免的人生悲剧 ,是其政治人生的主要蕴涵。情感的真诚和纵欲的疯狂和罪恶是其情场行为中所昭示的人性深度的主要内容。     

闸门水下自振频率的分析与计算

本文根据闸门在水体中振动的特性,对闸门振动时所受的随动水体的附加质量力和粘性阻尼力进行了分析.由于闸门动力特性与闸门本身的结构特性,支座方式,起吊机构的特性,在闸门槽中的紧固程度及闸门面板的水平倾角等有关,在计算闸门水上,水下的自振频率时,视县体情况分别将门体简化成刚性体或平面(空间)弹性刚架.根据上述原理、编制了相应程序.实例计算表明,附加质量力对水下闸门的自振频率有明显的影响.     

当前西藏产业结构存在的问题及原因分析

西藏和平解放六十年来,经济发展成效显著,产业结构不断得以优化,但各产业之间以及产业内部各部门、各层次之间还存在诸多问题,在一定程度上制约了西藏经济的跨越式发展。西藏三次产业结构的主要问题是结构偏离度大而产业高度化程度低,各次产业内的问题则主要表现为各子产业发展失衡和不均衡现象突出,产业发展尚处于低级阶段。文章认为社会经济体制发展基础薄弱而市场化程度低下;高原地理特征、气候条件和资源禀赋制约;人口相对稀少、分散加上受教育程度相对低,是产业发展相对滞缓的原因。     

Field regulation of single-molecule conductivity by a charged surface atom

Electrical transport through molecules has been much studied since it was proposed that individual molecules might behave like basic electronic devices, and intriguing single-molecule electronic effects have been demonstrated. But because transport properties are sensitive to structural variations on the atomic scale, further progress calls for detailed knowledge of how the functional properties of molecules depend on structural features. The characterization of two-terminal structures has become increasingly robust and reproducible, and for some systems detailed structural characterization of molecules on electrodes or insulators is available. Here we present scanning tunnelling microscopy observations and classical electrostatic and quantum mechanical modelling results that show that the electrostatic field emanating from a fixed point charge regulates the conductivity of nearby substrate-bound molecules. We find that the onset of molecular conduction is shifted by changing the charge state of a silicon surface atom, or by varying the spatial relationship between the molecule and that charged centre. Because the shifting results in conductivity changes of substantial magnitude, these effects are easily observed at room temperature.     

从《岷州广仁禅院碑》看河陇吐蕃佛教文化的特色

毕功于宋神宗元丰七年的《岷州广仁禅院碑》，是我们研究北宋时期河陇吐蕃佛教化方方面面的珍贵实物资料，碑铭历史和客观地记录了缘边地区佛教化的鲜明特色。     

Great Himalayan earthquakes and the Tibetan plateau

It has been assumed that Himalayan earthquakes are driven by the release of compressional strain accumulating close to the Greater Himalaya. However, elastic models of the Indo-Asian collision using recently imaged subsurface interface geometries suggest that a substantial fraction of the southernmost 500 kilometres of the Tibetan plateau participates in driving great ruptures. We show here that this Tibetan reservoir of elastic strain energy is drained in proportion to Himalayan rupture length, and that the consequent growth of slip and magnitude with rupture area, when compared to data from recent earthquakes, can be used to infer a approximately 500-year renewal time for these events. The elastic models also illuminate two puzzling features of plate boundary seismicity: how great earthquakes can re-rupture regions that have already ruptured in recent smaller earthquakes and how mega-earthquakes with greater than 20 metres slip may occur at millennia-long intervals, driven by residual strain following many centuries of smaller earthquakes.     

基于GMM和二分类特征筛选的多级音频分类方法

采用同一种特征参数——Mel倒谱系数及其动态参数区分纯语音、带背景语音、乐器音、歌声和环境音.根据该特征参数的特点以及各类音频之间的差异,给出了一种区分性模型训练和特征筛选相结合的多级二分类音频分类方法,即为各级建立GMM(Gaussian mixture model)模型的同时挑选出使当前模型区分程度达到最大的特征子集.对长约2 h的音频数据集的测试结果表明,该方法相对于特征筛选前的分类系统,平均误识率下降了约23.5%,且各二分类子系统的特征维数也有明显地减少.     

伪并行遗传算法在供水管网优化调度中的应用

讨论了基于微观水力模型的多水源大型供水管网优化调度问题的主要特征，并提出了求解该问题的改进遗传算法．首先，针对决策变量的结构提出二进制-实数混合编码策略；其次，设计并实现了多种群进化的伪并行遗传算法．将本算法与单一群体进化算法同时应用于实际管网的优化调度求解，结果表明，通过个体迁移策略，伪并行遗传算法可以加速优化搜索的进程，显著改善解的质量，并有效节省运行调度费用．     

Analysis of pore system model and physical property of coal reservoir in the Qinshui Basin

The Qinshui Basin in China is a major area for exploration and development of high rank coalbed methane. Due to the high rank coal and complicated pore system, no substantial breakthrough in the exploration and development of coalbed methane has been made until now. Many systematic tests show that a pore system of coal reservoir has some features as follows: the porosity is relatively low; the pore system is dominated by micropores and transition pores; mesopores take the second place, and macropores are nearly absent, which is exceedingly adverse for production of coal-bed methane. However, testing data also revealed the differential development for the pore of high rank coal reservoirs in the Qinshui Basin, which necessarily led to the different physical properties of desorption, diffusion and permeability. This paper classifies the testing data using cluster analysis method and selects the typical samples to establish four pore system models, analyzes the differences of reservoir physical property, and provides a guidance for the exploration and development of coalbed methane in the Qinshui Basin.     

高原太阳辐射的利弊及防护措施

太阳辐射是最基本气象学资源,并对光合作用提供了积极的辐射能源,强烈地影响着气候,并为蒸发作用提供能量。这意味着太阳辐射给气候的变化传播能量。太阳辐射在时间和空间上的分配细节如对气象、水文、农业、白天所需的日光,太阳能的利用进行数据估计至关重要。因此,太阳辐射对不同特定区域的气候起着重要的作用,对农业、气象和水文具有实质的影响。文章结合青藏高原特殊的气候、地理等特征,阐述太阳辐射对气候的重要作用和人们在户外（太阳底下）作业时,应该采取的防护措施。     

Coexistence of A- and B-form DNA in a single crystal lattice

It is well known that DNA can exist in a variety of conformations which can be interconverted by relatively mild changes in conditions. The in vivo conformation of DNA is usually thought to be the B form, but there is recent evidence that other conformations may be important in DNA-protein recognition. Different fragments of DNA crystallized under virtually identical conditions can form A, B or Z helices. A fragment that adopted an A conformation in a crystal was found in the B conformation in solution, whereas NMR spectroscopy of A-DNA films revealed the presence of a substantial amount of disordered B-DNA. Until now, however, a DNA fragment of a given sequence has not been crystallized in more than one global conformation. We report here an X-ray diffraction study of crystals of the DNA octamer dGGBrUABrUACC. In addition to a 'framework' of A-DNA, which gives discrete X-ray reflections, there are partially disordered B-DNA helices, recognized by their diffuse scattering features.     

Genome of the marsupial Monodelphis domestica reveals innovation in non-coding sequences

We report a high-quality draft of the genome sequence of the grey, short-tailed opossum (Monodelphis domestica). As the first metatherian ('marsupial') species to be sequenced, the opossum provides a unique perspective on the organization and evolution of mammalian genomes. Distinctive features of the opossum chromosomes provide support for recent theories about genome evolution and function, including a strong influence of biased gene conversion on nucleotide sequence composition, and a relationship between chromosomal characteristics and X chromosome inactivation. Comparison of opossum and eutherian genomes also reveals a sharp difference in evolutionary innovation between protein-coding and non-coding functional elements. True innovation in protein-coding genes seems to be relatively rare, with lineage-specific differences being largely due to diversification and rapid turnover in gene families involved in environmental interactions. In contrast, about 20% of eutherian conserved non-coding elements (CNEs) are recent inventions that postdate the divergence of Eutheria and Metatheria. A substantial proportion of these eutherian-specific CNEs arose from sequence inserted by transposable elements, pointing to transposons as a major creative force in the evolution of mammalian gene regulation.     

基于发音特征的发音偏误趋势检测研究

为了提升计算机辅助发音训练(CAPT)系统中发音偏误趋势(PET)的检测效果,确保反馈信息的准确性与有效性,提出一种基于对数似然比的发音特征方法。该方法将多个基于深度神经网络的发音特征提取器用于生成帧级别的对数似然比,然后将对数似然比组成的发音特征用于PET的检测,为学习者提供发音位置和发音方法的正音信息。实验结果表明,发音特征对PET的检测效果优于常用声学特征(MFCC,PLP和f Bank),当发音特征与MFCC特征相结合时,可以进一步提升性能,达到错误接受率为5.0%,错误拒绝率为30.8%,诊断正确率为89.8%的检测效果。     

Hominoid nasal region polymorphism and its phylogenetic significance

The morphology of the nasal bones and their articulations with the adjoining frontal and maxillary bones have recently been reported in Nature and elsewhere to be diagnostic of hominoid taxa, and cladistic analysis based on these features has been used to assign two immature Plio-Pleistocene hominoids (AL 333-105 and Taung) to different lineages (Paranthropus and Homo, respectively). Because earlier studies had established that hominoid crania are highly variable intraspecifically, it seemed desirable to try to replicate the study reporting a consistently different pattern for each hominoid taxon. My results show extensive polymorphism in the nasal region within every taxon of extant pongids, including several rather clear examples, in extant Pan troglodytes, of that recently hypothesized to be a 'paranthropine' pattern. These findings underscore the substantial risks inherent in cladistic analyses using very restricted character sets to assign individual specimens to particular taxa.     

The development of allergic inflammation

Allergic disorders, such as anaphylaxis, hay fever, eczema and asthma, now afflict roughly 25% of people in the developed world. In allergic subjects, persistent or repetitive exposure to allergens, which typically are intrinsically innocuous substances common in the environment, results in chronic allergic inflammation. This in turn produces long-term changes in the structure of the affected organs and substantial abnormalities in their function. It is therefore important to understand the characteristics and consequences of acute and chronic allergic inflammation, and in particular to explore how mast cells can contribute to several features of this maladaptive pattern of immunological reactivity.