Analysis of the environmental sensitivities of a typical dynamic epikarst system at the Nongla monitoring site, Guangxi, China   总被引：6，自引：0，他引：6  

Zhang Cheng  Yuan Daoxian  Cao Jianhua 《Environmental Geology》2005,47(5):615-619

Nongla, a typical karst dynamic system (KDS) monitoring site, is located at Nongla Village, Mashan County, Guangxi, China. The data from a Greenspan CTDP300 multichannel data logger indicates that the KDS is highly sensitive to environmental changes. Multi-day and diurnal physico-chemical composition of epikarst spring water is quite different under different climatic conditions. During a day with no rainfall, water temperature and air temperature have similar variations. Electrical conductivity (EC) has good positive correlation with pH value and water temperature. During rainstorms, the physico-chemical composition of the spring water is initially strongly effected by dilution, pH and EC drop rapidly. However, half to one hour later, EC returns to normal and the CO₂ effects will be the dominant physical effect. This is due to the high fissure rates and high permeability in the epikarst zone. Dilution effects were observed during the entire rainstorm event,whereas, it only acts during the earliest period of light rain. Therefore, it is necessary to examine the water–rock–CO₂ combination as a whole system to explain the hydrochemical behavior of epikarst processes.  相似文献   

A multiphase approach for evaluating the horizontal and rocking impedances of pile group foundations          下载免费PDF全文

V.T. Nguyen  G. Hassen  P. de Buhan 《国际地质力学数值与分析法杂志》2016,40(10):1454-1471

This paper advocates the use of a multiphase model, already developed for static or quasi‐static geotechnical engineering problems, for simulating the behaviour of piled raft foundations subject to horizontal as well as rocking dynamic solicitations. It is shown that such a model, implemented in a FEM code, yields appropriate predictions for the foundation impedance characteristics, provided that shear and bending effects in the piles are taken into account, thus corroborating the findings of the asymptotic homogenization theory. Besides, it is notably pointed out that such a multiphase‐based computational tool makes it possible to assess the dynamic behaviour of pile groups in a much quicker way than when using direct numerical simulations, which may face oversized problems when large pile groups are concerned. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

A new bounding surface model for thermal cyclic behaviour          下载免费PDF全文

C. Zhou  K.Y. Fong  C.W.W. Ng 《国际地质力学数值与分析法杂志》2017,41(16):1656-1666

To accurately predict soil volume changes under thermal cycles is of great importance for analysing the performance of many earth structures such as the energy pile and energy storage system. Most of the existing thermo‐mechanical models focus on soil behaviour under monotonic thermal loading only, and they are not able to capture soil volume changes under thermal cycles. In this study, a constitutive model is proposed to simulate volume changes of saturated soil subjected to cyclic heating and cooling. Two surfaces are defined and used: a bounding surface and a memory surface. The bounding surface and memory surface are mainly controlled by the preconsolidation pressure (a function of plastic volumetric strain) and the maximum stress experienced by the soil, respectively. Under thermal cycles, the distance of the two surfaces and plastic modulus increase with an accumulation of plastic strain. By adopting the double surface concept, a new elastoplastic model is derived from an existing single bounding surface thermo‐mechanical model. Comparisons between model predictions and experimental results reveal that the proposed model is able to capture soil volume changes under thermal cycles well. The plastic strain accumulates under thermal cycles, but at a decreasing rate, until stabilization. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

试析GIS技术在房产测绘中的作用     

张怀兴  陆春雨  石龙 《测绘与空间地理信息》2016,(5):164-165

以GIS技术在房产测绘中的作用探索研究为题展开论述。首先,介绍了GIS技术操作简单、工作效率高、功能全面,可以实现全天候工作的优势特点。然后,结合测绘行业方面的相关经验,提出该技术在房产测绘中的作用。最后,对GIS技术的改进做了简单分析。希望可以提高GIS技术在房产测绘中的工作效率,促进我国房产事业的长期、稳定发展。  相似文献   

雷暴闪电放电活动对电离层影响的研究进展          下载免费PDF全文

张义军  张阳 《应用气象学报》2016,27(5):570-576

雷暴中的闪电放电能够产生强静电场以及电磁辐射场,从而对空间电离层产生重要影响,引起电离层电子密度分布的扰动。研究表明:闪电放电引起电离层扰动的方式有两种:直接耦合和间接耦合。其中,直接耦合主要来自于闪电产生的准静电场及电磁场的作用,在甚低频 (VLF) 反射信号上表现出快VLF事件, 而间接耦合主要是闪电低频电磁波在传播过程中与磁层相互作用,在辐射带产生闪电诱导电子沉降 (LEP) 现象。雷暴闪电活动能够改变电离层从D层到F层的电子密度分布,影响对流层大气和电离层之间的场,导致中高层瞬态放电淘气精灵 (elves) 及红闪 (sprite) 等现象的激发。闪电VLF传输反射信号可用于反演电离层密度的变化,目前已成为一种探测电离层扰动的常用方法,而引起电离层扰动的强度不但和闪电放电参量密切相关,也和闪电放电过程、类型有关。该文重点阐述了闪电放电与电离层直接耦合和间接耦合作用以及导致的相关现象。  相似文献   

Use of an inside buffer method to extract the extent of urban areas from DMSP/OLS nighttime light data in North China     

Minghong Tan 《地理信息系统科学与遥感》2016,53(4):444-458

Defense Meteorological Satellite Program (DMSP)/Operational Linescan System (OLS) nighttime imagery provides a valuable data source for mapping urban areas. However, the spatial extents of large cities are often overestimated because of the effect of over-glow from nighttime light if a fixed thresholding technique is used. In the work reported here, an inside buffer method was developed to solve this issue. The method is based on the fact that the area overestimated is proportional to the extent of the lit area if a fixed threshold is used to extract urban areas in a region/county. Using this method, the extents of urban areas in North China were extracted and validated by interpretations from Landsat Thematic Mapper images. The results showed that the lit areas had a significant linear relationship with the urban areas for 120 representative cities in North China in 2000, with an R² value of over 0.95. This demonstrates that the inside buffer method can be used to extract urban areas. The validation results showed that the inside buffer model developed in 2000 can be directly used to extract the extent of urban areas using more recent nighttime light imagery. This is of great value for the timely updating of urban area databases in large regions or countries.  相似文献   

西北太平洋气候和海洋环境变化对柔鱼空间分布的影响     

余为  陈新军  易倩  高郭平  陈勇 《海洋学报(英文版)》2016,35(3):108-116

Ommastrephes bartramii is an ecologically dependent species and has great commercial values among the AsiaPacific countries. This squid widely inhabits the North Pacific, one of the most dynamic marine environments in the world, subjecting to multi-scale climatic events such as the Pacific Decadal Oscillation(PDO). Commercial fishery data from the Chinese squid-jigging fleets during 1995–2011 are used to evaluate the influences of climatic and oceanic environmental variations on the spatial distribution of O. bartramii. Significant interannual and seasonal variability are observed in the longitudinal and latitudinal gravity centers(LONG and LATG) of fishing ground of O. bartramii. The LATG mainly occurred in the waters with the suitable ranges of environmental variables estimated by the generalized additive model. The apparent north-south spatial shift in the annual LATG appeares to be associated with the PDO phenomenon and is closely related to the sea surface temperature(SST)and sea surface height(SSH) on the fishing ground, whereas the mixed layer depth(MLD) might contribute limited impacts to the distribution pattern of O. bartramii. The warm PDO regimes tend to yield cold SST and low SSH, resulting in a southward shift of LATG, while the cold PDO phases provid warm SST and elevated SSH,resulting in a northward shift of LATG. A regression model is developed to help understand and predict the fishing ground distributions of O. bartramii and improve the fishery management.  相似文献   

2001年秋季风对坦帕湾盐度平衡的影响     

韩树宗  朱君  范永斌  戚洪帅  王星驰 《海洋学报(英文版)》2016,35(9):67-73

利用三维高分辨率有限体积的近海海域模型FVCOM来分析2001年秋季期间风作用对坦帕湾区域盐度平衡的影响。为了区分风的影响,分别设计了两个实验：一个由潮汐和河流作为驱动,另一个由潮汐、河流以及风场共同驱动。结论如下：首先,风作用会使盐度产生变化,能够明显地使坦帕湾内的盐度增加,并导致水平和垂直方向上盐度梯度的减少;随后,本文分析了坦帕湾区域内的盐度平衡,主要的盐度平衡来自于全部（水平和垂直方向上）平流的盐度流量分歧以及除去海峡底部的垂直方向上盐度流量分歧;最后,对由风引起的盐度变化进一步进行分析,结果表明风作用不能改变盐度平衡地位的相对重要性,由风引起的盐度平衡改变高度依靠于特殊的地形,除此之外,全部平流盐度流量分歧和垂直散布盐度通量分歧能够抵消,并且两者都远大于水平散步盐度流量分歧。  相似文献   

基于神经网络的南太平洋长鳍金枪鱼渔场预报   总被引：2，自引：1，他引：1  

ESMAEILZADEH Marjan  KARBASSI Abdolrez  MOATTAR Faramarz 《海洋学报(英文版)》2016,35(10):28-36

南太平洋长鳍金枪鱼是我国远洋渔业的重点捕捞对象;对南太平洋长鳍金枪鱼进行准确的渔场预报;可以提高捕捞效率;提高渔业的生产能力。本研究根据1993-2010年南太平洋长鳍金枪鱼的延绳钓生产数据以及海洋卫星遥感数据（海水表面温度;SST;海面高度;SSH）和ENSO（El Niño-Southern Oscillation）指标;采用DPS（data processing system）数据处理系统中的BP人工神经网络模型;以渔获产量（单位时间的渔获尾数）和单位捕捞努力量渔获量（CPUE;Catch per unit of effort）分别作为中心渔场的表征因子;并作为BP模型的输出因子;以月、经度、纬度、SST、SSH和ENSO指标等作为输入因子;分别构建4-3-1;5-4-1;5-3-1;6-5-1;6-4-1;6-3-1等BP模型结构;比较渔场预报模型优劣。研究结果表明;以CPUE作为输出因子的BP人工神经网络结构总体上较优;其中以6-4-1模型结构为最优;相对误差只有0.006 41。研究认为;以CPUE为输出因子的6-4-1结构的人工神经网络模型;能够准确预报南太平洋长鳍金枪鱼的渔场位置。  相似文献   

基于船位监控系统的拖网捕捞努力量提取方法研究   总被引：6，自引：1，他引：5  

张胜茂  张衡  唐峰华  樊伟  黄华文 《海洋科学》2016,40(3):146-153

为了基于船位监控系统提取拖网捕捞努力量,通过统计航速获得3个峰值,拖网作业在第2个峰值,即1~2.1 m/s,拖网作业航向差一般在–50°~50°。利用航速、航向差阈值设定,把拖网船状态划分为慢速、作业、航行,然后提取出捕捞作业状态点,1 423艘拖网船共提取到处于捕捞状态的点318 433个,合计拖网捕捞时间15 921 h,利用反距离加权插值法生成捕捞强度分布变化趋势图。捕捞努力量在渔业资源研究中是重要的参考值之一,与传统的捕捞努力量计算方法相比,该方法具有实时、大范围、快速、分辨率高的特点,能够用于辅助渔业资源保护。  相似文献