中国早期具刺疑源类的演化及生物地层学意义

本文以我国元古代至早寒武世梅树村阶中发现的具刺疑源类化石为基础，结合最近研究的新资料，通过对具刺疑源类化石组合特征、形态对比、微细结构和演经关系的研究，并与国内外资料广泛为对比。探讨了我国早期具刺疑源类的演化阶段、各阶段的组合特征及生物地展学意义，论证了我国早期具刺疑原类的演化发展趋势。     

三门峡市冰雹出现规律与防雹工作探讨

利用1971-2005年三门峡市冰雹天气过程资料,分析了冰雹时空分布特征、主要影响系统、本站要素指标及雷达回波特征等,结果表明:渑池县降雹次数最多,灵宝次之,卢氏最少;降雹集中在4-8月,13-19时降雹几率最高.三门峡降雹的天气形势主要有蒙古-华北冷槽、冷涡型和西北气流型.受上述天气系统影响时,500 hPa有冷平流,若地面连续2～3天增温增湿,有可能出现冰雹天气.此外,雹云雷达回波强度＞50 dBz,云顶高度＞10 km,云顶温度＜-40℃,垂直积分液态含水量有明显的跃升.是降雹的前兆.     

考虑钙质砂细观颗粒形状影响的液体拖曳力系数试验

钙质砂作为南海岛礁填筑常用的岩土材料,其渗透性很大程度上决定着填筑后土体的固结和沉降。拖曳力系数是表达流体对土体颗粒表面力的参数,也是表征颗粒状土体渗透能力的一个重要参数,目前国内外对钙质砂拖曳力系数的研究十分有限。首先引入一个修正的三维参数 对钙质砂这种天然非规则颗粒材料的形状进行定量描述,然后开展一系列单个钙质砂颗粒在液体中沉降试验,利用高速相机记录颗粒沉降过程,结合图像处理技术获得颗粒沉降平衡速度Ut,进而计算出拖曳力系数CD和雷诺数Re,最后拟合出包含CD、Re及 三个参数的钙质砂拖曳力系数半经验模型。结果发现,在相同雷诺数条件下钙质砂的形状系数 越大,拖曳力系数越小。通过与其他研究结果对比发现,其表面微孔隙越发育,拖曳力系数越小的规律。该模型能够考虑不规则颗粒形状对拖曳力系数的影响,从而提高对土体渗透性预测的精度,对南海岛礁填筑工程中钙质砂固结和沉降的计算也具有重要意义。     

四川盆地—大巴山结合带地壳构造特征:深反射地震约束的重磁解释

大巴山位于四川盆地北部、秦岭南缘,以发育大规模的中生代逆冲推覆构造为世人瞩目,其地壳尺度结构与构造特征对于理解扬子克拉通和华北克拉通的碰撞过程有重要意义.本文基于深反射地震剖面和宽角反射与折射地震数据的约束,结合地质与钻井资料,通过重磁场分析拟合解释,对四川盆地北部—大巴山地壳尺度的构造进行综合研究,建立了地壳断面结构与构造模型.模型显示,四川盆地北部基底和沉积盖层变形差异较大,且上下地壳具有解耦性,上地壳向北延伸至紫阳断裂一带;而下地壳与上地壳拆离,向北延伸远至安康断裂一带.研究区莫霍面起伏较大,自南向北先加深后抬升,在大巴山下出现Moho的构造叠置,这种现象源于大陆地块(扬子克拉通)下地壳向大巴山—秦岭造山带下的俯冲.类似的现象也出现在西昆仑山下,即塔里木盆地下地壳向西昆仑山下俯冲,俯冲板片前缘出现Moho的叠置.     

地形对于气流运动影响的数值研究

建立了二维、非静力平衡的数值模式，研究地形对上游气流的阻挡以及大振幅背风波谷与下坡风的形成。结果表明：地形的阻挡效应受地形高度、大气层结及地形非对称性等因子的影响。数值试验与理论分析都证明地形越高、层结越稳定时阻挡作用越强；同样条件下，迎风坡坡度大的地形容易对气流形成阻挡。此外，分析了地形高度、大气层结、地形非对称性以及基本入流大小对背风波谷及下坡风强度影响的规律，并通过一次实际观测对数值模拟结果进行了检验。     

Directed movements in probabilistic time geography

This article studies probabilistic time geography for space–time prisms, that is, for situations where observers know the location of an agent at one time and then again at another time. In the intervening period, the agent would have moved freely, according to its time budget. The article demonstrates that the probability of finding the agent somewhere in the space–time prism is not equally distributed, so any attempt of a quantitative time geographic analysis must consider the actual probability distribution. This article develops, implements, and demonstrates this distribution. A preceding article introduced probabilistic time geography for space–time cones. With cones and prisms, the elementary space–time volumes of time geography are provided.     

Bender Elements在测试土样剪切波速中的应用

本文以作者在香港理工大学土木与结构工程系设计制作的一套BenderElements为例,介绍了BenderElements的原理、发展历史、应用范围、使用方法和注意事项等。BenderElements是由压电陶瓷材料制成的,在拉伸、压缩作用下,会产生正、负电荷,反过来,给它施加正、负电荷后,它又可产生弯曲振动,正是利用它的这一特性,将其作成接收和发射装置,来测试土样的剪切波速Vs。BenderElements在安装使用时,防水和静电屏蔽十分关键。Vs可在场地地震反应、液化判别、动力基础设计、检测地基改良效果等方面获得应用。震相识别的原则是接收信号的第一个峰值为到时。     

SAR image despeckling with a multilayer perceptron neural network

Speckle noise in synthetic-aperture radar (SAR) images severely hinders remote sensing applications; therefore, the appropriate removal of speckle noise is crucial. This paper elaborates on the multilayer perceptron (MLP) neural-network model for SAR image despeckling by using a time series of SAR images. Unlike other filtering methods that use only a single radar intensity image to derive their parameters and filter that single image, this method can be trained using archived images over an area of interest to self-learn the intensity characteristics of image patches and then adaptively determine the weights and thresholds by using a neural network for image despeckling. Several hidden layers are designed for feedforward network training, and back-propagation stochastic gradient descent is adopted to reduce the error between the target output and neural-network output. The parameters in the network are automatically updated in the training process. The greatest advantage of MLP is that once the despeckling parameters are determined, they can be used to process not only new images in the same area but also images in completely different locations. Tests with images from TerraSAR-X in selected areas indicated that MLP shows satisfactory performance with respect to noise reduction and edge preservation. The overall image quality obtained using MLP was markedly higher than that obtained using numerous other filters. In comparison with other recently developed filters, this method yields a slightly higher image quality, and it demonstrates the powerful capabilities of computer learning using SAR images, which indicate the promising prospect of applying MLP to SAR image despeckling.     

Occurrence of brackish water phytoplankton species at a closed coral reef in Nansha Islands, South China Sea

The phytoplankton assemblage of Zhubi Reef, a closed coral reef in Nansha Islands (South China Sea, SCS) was studied in June 2007. A total of 92 species belonging to 53 genera and four phyla have been identified. The dominant taxa in the lagoon were the diatom Chaetoceros and cyanobacteria Nostoc and Microcystis, while in reef flats were cyanobacteria Trichodesmium erythraeum, dinoflagellates Gymnodinium and Prorocentrum. The species richness and diversity were consistently lower in the lagoon than in reef flats. Classification and nMDS ordination also revealed significant dissimilarity in phytoplankton community structure between the reef flat and lagoon, with statistical difference in species composition and abundance between them (ANOSIM, p = 0.025). Nutrient concentrations also spatially varied, with ammonium-enrichment in the lagoon, while high Si-concentration existed in reef flat areas. Both nutrient levels and currents in SCS may play important roles in determining the composition and distribution of microalgae in Zhubi Reef and SCS.     

海藻糖类的气相色谱分析 Ⅱ.红藻及红藻多糖中D-半乳糖和3, 6-内醚半乳糖的测定

红藻中的糖类主要以多糖形式存在(琼胶、卡拉胶等)，其中主要的单糖组分是D-半乳糖和3, 6-内醚半乳糖，除此之外还含有少晕的木糖、葡萄糖及甘露糖等成分。由于各单糖的相互干扰，难以用比色等着通化学分析方法对每一种单糖准确地定性定量。作者曾研究过褐藻中单糖的气相色谱测定法, 但该法不能测定3, 6-内醚半乳糖，囚为这种内醚糖对酸水解不稳定。据Dutton和Nozawa等人报道, 将多糖经甲醇分解后进行气相色谱分析，结果令人满意。本文用琼胶(Difco bacto-agar)作代表，研究探讨了红藻胶甲醇-HCI分解的条件，确定了红藻胶中D-半乳糖和3, 6-内醚半乳糖的气相色谱分析方法，并将其应用于红藻中D-半乳糖和3, 6-内醚半乳糖的分析。