Investigating the geomorphic characteristics of an Amazonian headwater stream draining a páramo ecosystem     

Christopher P. Ely 《自然地理学》2019,40(2):164-185

Páramos are neotropical alpine grasslands located in the northern Andes of South America. Although they cover important headwater regions, little is known about the hydro-geomorphic characteristics of páramo river systems, which are increasingly being impacted by human use and climate change. The objective of this research is to characterize the geomorphology of the Ningar River, Ecuador, an Amazonian headwater river that drains a 22.7 km2 páramo sub-basin, by (1) classifying the geomorphology based on common geomorphic classifications, (2) deriving downstream hydraulic geometry relationships, and (3) performing a global comparison with mountain river systems. Common geomorphic field surveying techniques were used to acquire the necessary data. Results suggest that the Ningar River has similar form-function characteristics as other known mountain headwater streams and corresponds to commonly known stream classification systems, but displays more of an alluvial character than might be expected for montane headwater streams as a result of a convexity in the stream’s longitudinal profile. Additionally, preliminary analyses suggest that other páramo headwater streams may exhibit similar characteristics; thus, the findings of this research are important for future management and protection of these valuable headwater ecosystems.  相似文献   

变速海水运动感应电磁场数值模拟及特征分析     

周春  李予国  张宝强 《海洋与湖沼》2019,50(2):261-268

海水是一种高电导率的流体,根据电磁感应定律,运动的海水切割地磁场会在海水中产生感应电流,从而产生感应电磁场。本文从麦克斯韦方程出发,推导出一维速度场海水运动感应电磁场偏微分方程,利用电磁场水平分量在海表面和海底面上的连续性条件,得到海水运动感应电磁场表达式,并编写了Fortran计算程序。计算了常速度海水运动感应电磁场,并与格林函数法计算结果进行了对比,两种方法的计算结果一致。计算了变速度(即海水运动速度随深度变化)海水运动感应电磁场,并讨论了海水运动周期和海底介质电导率对海水运动感应电磁场的影响。计算结果表明:海水运动周期和海底介质电导率对常速度海水运动和变速度海水运动感应电磁场都有影响,但影响程度不同。在本文所述模型和参数条件下,海水运动感应电场和感应磁场振幅分别可达6μV/m和10nT,这与海洋大地电磁响应的量级相当。因而在处理海洋大地电磁数据时,海水运动感应电磁响应是不可忽略的噪音干扰,需要采用必要的压制手段。  相似文献   

A nonlinear inversion of InSAR-observed coseismic surface deformation for estimating variable fault dips in the 2008 Wenchuan earthquake     

《International Journal of Applied Earth Observation and Geoinformation》2019

Satellite Interferometric Synthetic Aperture Radar (InSAR) is playing an increasingly important role in the observation of coseismic surface deformation caused by earthquakes, and has been used to invert for subsurface fault structure and reveal earthquake source mechanisms. However, the mapping of complex non-planar or curved (e.g., listric-shaped) faults still remains a challenging task due to variable dips along the underground depth and the impenetrability of the deep crust. Here, we develop a set of new inversion algorithms to determine the listric fault geometry with InSAR- and GPS-observed surface deformation as the significant constraints. The fault surface with variable dip angles is discretized into consecutive sub-fault layers along the down-dip direction. A nonlinear iteration algorithm is used to minimize the objective function to determine the dip angle for each sub-fault layer. The proposed method is first tested using synthetic data to show its effectiveness for retrieval of varying fault geometry dips, and then applied to the 2008 Mw 7.9 Wenchuan earthquake that ruptured the Yingxiu-Beichuan fault for over 320 km along the southwest-northeast strike. The inversion shows that the dip angle of the seismogenic fault is up to 76° near the surface layer, and gradually decreases along the down-dip direction. A significant decrease in dip occurs within the depths of 6–15 km with a dip of 32° at a depth of 15 km. The dip angle decreases to 2° at a depth of 20 km, and finally merges with the subparallel PengGuan fault, which is basically consistent with geological investigations and seismic waveform data inversion. Using the inferred fault geometry, the slip model associated with the event is estimated. Five high-slip concentrations along the strike of the Yingxiu-Beichuan fault are recognized. The inversion misfit of InSAR data is reduced to 7.1 cm with a significant improvement compared to previous studies.  相似文献   

基于拓扑优化方法的船体支柱布局优化设计     

朱俊侠  吴嘉蒙  蔡诗剑  于大鹏 《海洋工程》2019,37(4):70-79

船体支柱的布局影响到船舶功能性舱室的布置及相应的结构设计,而目前支柱布局多依赖母型船或者工程师设计经验,缺少基于数学优化的技术支撑。变密度的拓扑优化方法可将属于离散变量优化的支柱布局问题转化为连续变量优化问题。通过悬臂梁—支柱结构的算例,验证了该方法用于解决支柱布局优化问题的可行性。针对某型VLCC的支柱—大跨度甲板结构的支柱布局优化问题,根据布置限制条件设定了支柱优化设计域,选择了两种不同的优化目标函数进行支柱的布局优化设计,最后对优化结果进行了对比分析。结果表明,本方法具有较好的可行性,无需过多设计经验即可优化得到结构性能较好的支柱布局方案,可为此类的支柱布局优化设计提供技术支撑。  相似文献   

A simple but accurate ultraviolet limb-scan spherically-layered radiative-transfer-model based on single-scattering physics   总被引：2，自引：0，他引：2  

郭霞  吕达仁  吕曜 《大气科学进展》2007,24(4):619-630

Here we present a study focusing on atmospheric limb-scattered radiative characteristics in the ultraviolet band by using a limb-scan spherically-layered radiative-transfer-model based on the single-scattering approximation, which was developed by the present authors. We have applied an accurate numerical integration technique involving an auto-adaptive modified-space step, which assured high accuracy and simplification. Comparisons were made to the newly released spherical radiative transfer model, SCIATRAN2.0, which was developed by Institute of Remote Sensing/Institute of Environmental Physics （IUP/IFE） at University of Bremen and to measurements collected via an ultraviolet spectrometer on the Solar Mesospheric Explorer （SME） satellite, which was launched in October, 1981. Preliminary results indicate that the present model provides a good interpretation of the earth-limb scattered ultraviolet radiance, and thus, is suitable for the study of the ultraviolet-limb radiative-transfer problem with high accuracy.  相似文献   

一种基于GIS的多模型统计结果的自动综合方法   总被引：3，自引：2，他引：1  

陈永良  伍伟  刘大有 《物探化探计算技术》1999,21(4):319-322

当用多种统计数学模型预测矿产资源靶区时,预测结果往往是不同的,需要进一步的统计综合。本文探讨了ＧＩＳ矿产资源统计预测中,将不同统计预测结果进行自动综合的计算机算法,以ＭａｐＩｎｆｏ 为软件平台,用ＭａｐＢａｓｉｃ语言编制了算法的计算机程序,在该软件平台中实现了多模型统计预测结果的自动综合。  相似文献   

再论全球变网格多层原始方程差分模式的设计     

廖洞贤 《应用气象学报》1999,10(2):141-150

在修正的MM4和一个有限域变网格差分模式的基础上,设计了全球变网格多层原始方程差分模式。可以证明:设计的模式具有质量、能量守恒等整体性质,并具有正确的动、位能转换关系。为了克服高纬地区经线辐合带来的时间步长须取得很小的问题,给出了不进行滤波处理并仍能保持整体性质的解决办法。  相似文献   

利用几何学方法判定东坪金矿区的断层性质及位移量     

杨再红 《地质与勘探》1999,35(2):45-48

论述了利用单纯几何关系确定断层性质及位移量（两盘标志层或矿层对位置）的方法,对矿山探矿与采矿工程的布置有重要的现实意义。  相似文献   

Self-Similar Fold Evolution Under Prescribed End-Shortening     

Chris J. Budd  Giles W. Hunt  Mark A. Peletier 《Mathematical Geology》1999,31(8):989-1005

The evolution of single-layer folds under prescribed end-shortening conditions displays folds of varying wavelength. We investigate a simple model of this kind and characterize the long-term behaviour of fold profiles. In particular we determine the evolution of the axial load and the variation of the wavelength, and we show that fold profiles are highly self-similar.  相似文献   

基于变轴力柱恢复力模型的钢框筒地震反应分析     

陈以一  刘永明  岳昌智 《世界地震工程》2000,16(4):47-52

建立了考虑轴力变化影响的钢结构杆件的恢复力模型,介绍了模型构成和经试验比较得到的模型的适用性,采用这一模型,对钢框筒结构进行了多维地震作用下的非线性分析,对这类结构的弹塑性特征进行了考察。  相似文献