Determination of probability distributions for Strahler stream lengths based on Poisson process and DEM

Abstract

One of the basic tasks in geomorphologic analysis is to know the probability distributions of the stream lengths of different orders. In practical applications, this information is useful for basin rainfall-runoff modelling. The objective of this study is to determine the length distributions of the Strahler streams. A Poisson process was used to derive the theoretical distributions. The result showed that the length distribution of the first-order stream is an exponential distribution and the second-order or higher order stream length is a gamma distribution. In order to verify the theoretical distributions, a digital elevation model (DEM) was adopted to calculate the stream lengths of four basins in Taiwan. Kolmogorov-Smirnov and chi-square tests were used to test the goodness-of-fit of the data. Results showed that the length distributions of the first- and second-order streams analysed by using DEM correspond with those from the derived distribution method.     

On applying viewshed analysis for determining least-cost paths on Digital Elevation Models

The concept of computing least-cost paths has been proposed and discussed for a few decades but only in simplified form due to the limited computational resources in the past. With the advancement of computer technology in speed and data storage, it is now possible to implement least-cost path algorithms with realistic conditions. In this paper, we present our implementations of least-cost paths by integrating viewshed information computed from digital elevation models. Our implementations and analyses include four possible types of paths. They are scenic paths, strategic paths, hidden paths, and withdrawn paths. While possible applications of these least-cost paths include planning of civil engineering, military and environmental planning, other extensions can be formulated without much difficulty.     

The 2011 Tohoku-Oki earthquake's influence on the Asian plates and Korean geodetic network

本研究分析了2011年3月11日发生的Mw9.0日本东北地区太平洋近海地震对亚洲地区和韩国国内GPS卫星常年跟踪站的位移影响.为此,利用了日本东北地区太平洋近海地震发生前后两周(2011年3月4日到3月18日)的GPS站点数据,包括震中附近地区(韩国,中国,中国台湾地区,日本和俄罗斯)55个GPS卫星常年跟踪站和284个IGS全球跟踪站,并采用GAMIT/GL,OBK软件进行处理和平差,估算出所有GPS站点的同震形变.结果显示,日本东北地区太平洋近海地震引起的同震形变影响在亚洲地区比较明显,包括日本和附近国家,距离震中2702 km的中国武汉(WUHN)站也观测到同震形变.为精确分析日本东北地区太平洋近海地震对韩国国家大地控制网的影响.通过GAMIT/GLLOBK软件计算出韩国GPS卫星常年跟踪站之间的基线长度变形,并分析出弹性变形量.结果表明:大部分GPS站点均向震中方向膨胀,且向震中的垂直方向收缩,由日本东北地区太平洋近海地震导致的最大剪应变达到韩国国家大地控制网年均变形率的约7倍,对韩国的地壳产生14.5～57.7 mm的水平位移,并导致韩国国家大地控制网产生弹性变形,因此,在不及时更新维护韩国国家大地控制网的情况下,GPS测量成果将会发生最大20 mm的位置误差.     

Aragonite in the Murray (CM2) carbonaceous chondrite: Implications for parent body compaction and aqueous alteration

Abstract— The matrix of the CM2 carbonaceous chondrite Murray contains rare micrometer‐sized prismatic crystals of aragonite that formed during late‐stage parent body aqueous alteration. The aragonite was identified by X‐ray microanalysis coupled with electron backscatter diffraction (EBSD), TEM selected area electron diffraction and cathodoluminescence spectroscopy. The sixteen crystals found all occur within loose and elongate submillimeter‐sized clusters and one cluster is present in each of the two thin sections studied. Orientation determinations using EBSD show that the c axes of aragonite crystals within each cluster lie roughly in a plane, itself aligned approximately parallel to the long axis of the host cluster. Aragonite is inferred to have crystallized after calcite but before completion of static/impact‐related compaction. The clusters developed by growth of aragonite within films of aqueous fluids that had a relatively high Mg/Ca ratio. These fluids were focused within zones of high porosity and permeability along a weak compactional fabric in the matrix and this fabric is also likely to have influenced the orientations of aragonite crystals as they grew. These results suggest that aragonite probably occurs in most of those carbonaceous chondrites that have undergone moderate degrees of parent body aqueous alteration and may provide further insights into the evolution of pore fluid compositions and volumes and the chronology of asteroidal evolution.     

日本凋毛藻(Griffithsia japonica)硫氧还蛋白基因及其编码的蛋白特征

从日本凋毛藻的表达序列标记EST库中筛选到2条全长的编码硫氧还蛋白的cDNA序列,分别命名为GjTRX1和GjTRX2。将这2条基因编码的蛋白序列与其它藻类(包括酵母)进行比较,结果表明不同物种及同一物种间TRX的相似性都较差,除GjTRX2编码的蛋白序列外,所有蛋白在活性位点序列WCGPC处都完全保守。推测GjTRX1属于细胞质内分布的硫氧还蛋白。GjTRX1序列推导的蛋白二级结构单元与以往报道的传统上保守的TRX的二级结构单元类型一致,但是顺序有所不同。     

Hack's law of debris-flow basins

Hack's law was originally derived from basin statistics for varied spatial scales and regions.The exponent value of the law has been shown to vary between 0.47 and 0.70,causing uncertainty in its application.This paper focuses on the emergence of Hack's law from debris-flow basins in China.Over 5,000 debris-flow basins in different regions of China with drainage areas less than 100km2 are included in this study.Basins in the different regions are found to present similar distributions.Hack's law is derived fi'om maximum probability and conditional distributions,suggesting that the law should describe some critical state of basin evolution.Results suggest the exponent value is approximately 0.5.Further analysis indicates that Hack's law is related to other scaling laws underlying the evolution of a basin and that the exponent is not dependent on basin shape but rather on the evolutionary stage.A case study of a well known debris-flow basin further confirms Hack's law and its implications in basin evolution.     

Hack＇s law of debris-flow basins

Hack＇s law was originally derived from basin statistics for varied spatial scales and regions. The exponent value of the law has been shown to vary between 0.47 and 0.70, causing uncertainty in its application. This paper focuses on the emergence of Hack＇s law from debris-flow basins in China. Over 5,000 debris-flow basins in different regions of China with drainage areas less than 100km^2 are included in this study. Basins in the different regions are found to present similar distributions. Hack＇s law is derived from maximum probability and conditional distributions, suggesting that the law should describe some critical state of basin evolution. Results suggest the exponent value is approximately 0,5. Further analysis indicates that Hack＇s law is related to other scaling laws underlying the evolution of a basin and that the exponent is not dependent on basin shape but rather on the evolutionary stage. A case study of a well known debris-flow basin further confirms Hack＇s law and its implications in basin evolution.     

Pier scour monitoring system by bed-level image tracking

A scour monitoring system with a micro camera tracking the bed-level images is proposed in this study.Two image recognition algorithms have been developed to support the bed-level image tracking approach.Through the laboratory experiments of pier scour,this study demonstrates that the proposed system is able to accurately monitor the scour-depth evolution in real time.In addition,five commonly-used temporal scour models are employed to simulate scour-depth evolution and their results are compared with monitoring data.In general,the results indicate that the proposed scour monitoring system has the potential for further applications in the field.     

贵阳次生林不同演替阶段土壤微生物生物量与反硝化酶活性的研究

土壤营养元素赋存状态和微生物活性是喀斯特地区生态恢复的关键质量指标,温室气体N2O的排放是全球变暖的重要因子。研究了雨季贵阳不同演替阶段森林表层土壤（0～10cm）微生物生物量（SMB）、反硝化酶活性（DEA）、无机氮（N）库和N转化特征,并与玉米地、茂兰喀斯特原始森林土壤做了对比分析。结果表明,微生物群落对土壤水分条件响应强烈,土壤有效N的增加有助于微生物群落的增长,土壤N转化速率越快,微生物N同化作用越低。人为干扰（火烧和农业活动）会增加或降低土壤SMB、增加潜在的气态N流失。总的来说,不同演替阶段土壤SMB、DEA和土壤N库均有显著差异,随植被恢复土壤SMB呈上升趋势,温室气体N2O的排放量呈下降趋势,气态N流失形态从N2O转变为N2,N循环过程趋于优化,表明自发演替是退化喀斯特森林恢复的可靠方式。     

波浪作用下饱和砂质海床土体与管线相互作用规律研究

针对波浪引起的饱和砂质海床土体和管线相互作用问题,将Biot动力固结理论与笔者课题组提出的砂土液化变形弹塑性本构模型相耦合,较为合理地再现了简谐波浪作用下较浅饱和砂质海床中管线周围可液化海床土体的超静孔隙水压力瞬态累积变化规律与液化过程。数值计算结果与Sumer等的试验规律一致。结果表明：由于管线的存在,改变了饱和砂质海床液化区域的空间分布。液化首先由管线下部土体开始产生,随着波浪荷载的持续作用,液化区域沿着管线外壁向上演化;同时海床表层土体产生液化并向深层发展,最终管线周围土体都发生液化,这是导致空管上浮的主要原因。当饱和砂质海床中存在管线时,管线附近海床土体液化深度明显变深。超静孔压累积和渗透力变化的耦合作用是导致饱和砂质海床土体产生液化的原因。与将海床土体视为饱和弹性多孔介质相比,可考虑液化全过程的弹塑性动力分析能更为合理地揭示实际波浪作用下饱和砂质海床土体的渗流场和应力场的瞬态时空演变规律。