The problem of the Quaternary, geological environment and desertification   总被引：2，自引：0，他引：2  

L. Nianfeng  T. Jie  Z. Dianfa 《Environmental Geology》1999,38(1):7-12

 The Quaternary geological environment supplied mankind with a habitat and rich natural resources such as forest, meadow, water, etc. Mankind has developed to modern civilization through a very long history. During the last 100 years the area of desertification has been expanding, natural resources have been consumed, and eco-environments plundered. Mankind felled forests, cultivated grassland, and increased farmland because of unceasing increasing population and the need for materials. In a period of 50–100 years, mankind's destruction could change good meadow into desert. The following examples are evidence: Shangdu grassland in Inner Mongolia and the west grassland of Jilin Province have been changing into desert rapidly. Two concepts of destructive power (D) and bearing capacity (B) can be used to describe this process. When D<B, the ecosystem keeps good circulation, D=B, eco-balance reaches critical state, and D>B, ecosystem loses balance, the environment is destroyed and developed toward desert. The law of destructive power increasing with time accords with logistic curves and can be expressed by a logistic model. Destructive power (D) increases with decrease of bearing capacity (B);D and B represent a reciprocal relation. With a logistic model the developing process of desertification can be studied and the developing rate and strength of change can be forecasted. Received: 20 July 1998 · Accepted: 1 December 1998  相似文献   

金沙江下游支流黑水河松新电站幼鱼下行过坝研究     

李冬晴  柯森繁  许家炜  焦易林  白天翔  成必新  陶宇  王永猛  石小涛  孙干 《湖泊科学》2023,35(3):985-997

梯级小水电的开发一定程度上破坏了河流连通性并阻碍了鱼类洄游通道。黑水河流域松新坝址为了满足鱼类上行产卵修建了松新鱼道,然而作为洄游物种生命周期中的关键行为,鱼类下行洄游的需求也同等重要。为了寻求一种可行、高效、低损伤的下行过鱼方式,了解河流中不同环境因素对鱼类下行效率的影响,本研究在金沙江下游支流黑水河松新水电站补水通道开展鱼类下行过坝效果评估研究。针对两种鲤科鱼类(棒花鱼Abbottina rivularis和短须裂腹鱼Schizothorax wangchiachii)幼鱼和两种鳅科鱼类(短体副鳅Paracobitis potanini和红尾副鳅Paracobitis variegatus)幼鱼各放鱼90尾,定量分析鱼种、水体透明度、放鱼位置、流量、水温、水位等因素对鱼类下行效率的影响。结果表明:棒花鱼、短须裂腹鱼、短体副鳅、红尾副鳅的下行率依次为22.22%(20尾)、28.89%(26尾)、8.89%(8尾)、15.56%(14尾);幼鱼下行成功率与上游河道水温呈正相关趋势,且放鱼位置、鱼种、上游河道水温和流量均对鱼类下行成功率有显著影响。通过构建二元Logistic回归模型识...  相似文献   

我国海洋资源环境经济复合系统演化研究 ——基于Logistic模型的实证分析     

宋泽明  宁凌 《海洋科学》2021,45(8):21-33

随着我国各项海洋事业和活动有序推进,实现海洋资源、环境、经济协调可持续,对海洋高质量发展具有重要意义。从资源、环境和经济3个层面构建我国海洋复合系统,运用熵权TOPSIS方法进行测算,通过建立Logistic模型,对我国海洋资源环境经济复合系统演化过程进行拟合分析和趋势预测。得到相关研究结论：海洋资源环境经济复合系统是基于海洋资源、环境、经济相互作用、相互制约而形成的,其系统演化过程受到经济增长机制和生态平衡机制的影响;海洋资源环境经济复合系统及其子系统的演化规律符合Logistic法则,海洋资源子系统最大演化度高于海洋环境、经济子系统;海洋资源环境经济复合系统及海洋资源、经济子系统演化度的增长率较大,正处于成熟阶段,而海洋环境子系统演化度达到饱和状态,正处于衰退阶段。基于上述研究结论,提出有效措施建议。  相似文献   

结合多混沌映射和输出反馈的图像加密算法   总被引：1，自引：1，他引：0  

朱从旭  黄大足  郭迎 《武汉大学学报(信息科学版)》2010,(5)

提出了一种结合多个Logistic混沌映射和逐段正弦混沌映射的图像加密算法。通过m个Logistic混沌映射的多次迭代,分别产生m个分段正弦混沌映射的初值和参数值,由m个分段正弦混沌映射迭代产生图像加密密钥序列,并引入密文输出反馈机制,对图像像素值逐点进行2轮异或加密。实验表明,该算法使密文对明文和密钥都充分敏感,加密图像像素值具有类随机均匀分布特性,相邻像素具有零相关特性,而且算法具有密钥空间大、加密速度快的优越性。  相似文献   

共享社会经济路径下中国各省城市化水平预测     

丁小江  钟方雷  毛锦凰  宋晓谕  黄春林 《气候变化研究进展》2018,14(4):392-401

城市化水平预测与减缓及适应气候变化研究息息相关。基于国家统计局2005—2015年全国各省区城镇和乡村人口,以各省区2015年人均地区生产总值为指标进行分组,结合IPCC 5种共享社会经济路径（SSPs）的发展特征设置模型参数,运用Logistic模型预测了我国各省区2016—2050年城市化水平。结果表明,到2050年,各省区（除天津、北京、上海、西藏外）在5种典型SSPs下城市化水平收敛于75%左右。其中,SSP1、SSP3、SSP4、SSP5路径下,各省城市化水平比较趋同。而在SSP2路径下,全国总体上从东部到西部城市化程度逐渐降低,空间分布具有明显梯次递减性。5种SSPs路径下城市化速度方面,基本上呈现出中西部快而东部慢、西南快而东北慢的空间分布格局。同时,高收入省份不同路径下的城市化水平差别小,而中低收入省份的差别较大。  相似文献   

Indicator Kriging without Order Relation Violations   总被引：2，自引：1，他引：1  

Raimon Tolosana-Delgado  Vera Pawlowsky-Glahn  Juan-Jose Egozcue 《Mathematical Geosciences》2008,40(3):327-347

Indicator kriging (IK) is a spatial interpolation technique aimed at estimating the conditional cumulative distribution function (ccdf) of a variable at an unsampled location. Obtained results form a discrete approximation to this ccdf, and its corresponding discrete probability density function (cpdf) should be a vector, where each component gives the probability of an occurrence of a class. Therefore, this vector must have positive components summing up to one, like in a composition in the simplex. This suggests a simplicial approach to IK, based on the algebraic-geometric structure of this sample space: simplicial IK actually works with log-odds. Interpolated log-odds can afterwards be easily re-expressed as the desired cpdf or ccdf. An alternative but equivalent approach may also be based on log-likelihoods. Both versions of the method avoid by construction all conventional IK standard drawbacks: estimates are always within the (0,1) interval and present no order-relation problems (either with kriging or co-kriging). Even the modeling of indicator structural functions is clarified.  相似文献   

Selection of coherent deposit-type locations and their application in data-driven mineral prospectivity mapping   总被引：2，自引：1，他引：1  

E.J.M. Carranza  M. Hale  C. Faassen 《Ore Geology Reviews》2008,33(3-4):536-558

Data-driven prospectivity mapping can be undermined by dissimilarity in multivariate spatial data signatures of deposit-type locations. Most cases of data-driven prospectivity mapping, however, make use of training sets of randomly selected deposit-type locations with the implicit assumption that they are coherent (i.e., with similar multivariate spatial data signatures). This study shows that the quality of data-driven prospectivity mapping can be improved by using a training set of coherent deposit-type locations. Analysis and selection of coherent deposit-type locations was performed via logistic regression, by using multiple sets of deposit occurrence favourability scores of univariate geoscience spatial data as independent variables and binary deposit occurrence scores as dependent variable. The set of coherent deposit-type locations and three sets of randomly selected deposit-type locations were each used in data-driven prospectivity mapping via application of evidential belief functions. The prospectivity map based on the training set of coherent deposit-type locations resulted in lower uncertainty, better goodness-of-fit to the training set, and better predictive capacity against a cross-validation set of economic deposits of the type sought. This study shows that explicit selection of training set of coherent deposit-type locations should be applied in data-driven prospectivity mapping.  相似文献   

一种矢量线数据零水印算法     

李文德  闫浩文  王中辉  张黎明  禄小敏 《测绘科学》2017,42(3)

为了满足矢量地理空间数据高精度和零扰动的实用性需要,该文提出一种零水印算法。首先利用Logistic混沌映射置乱原始水印图像;然后对原始矢量线数据进行离散傅里叶变换,获得离散傅里叶变换后的相位值,并将相位值由弧度值转换为角度值;接着随机选取均匀分布的角度值,向下取整后转换为相应的二进制形式,得到二值矩阵;最后将置乱后的水印图像与由相位值构成的二值矩阵进行异或操作,从而构造出零水印图像。实验结果表明,该算法能够抵抗常见的平移、缩放等几何攻击,并且对数据格式转换攻击、投影变换攻击具有较好的鲁棒性。  相似文献   

Construction and assessment of a logistic regression model applied to short-term forecasting of thunderstorms in León (Spain)     

Jos Luis Snchez  Eduardo García Ortega  Jos Luis Marcos 《Atmospheric Research》2001,56(1-4)

Forecasting thunderstorms is one of the most difficult tasks in weather prediction due to the scarce knowledge on how to characterise the mechanisms taking part in the formation of thunderstorms. New tools based upon the objective recognition of appropriate conceptual models have been developed in the last years. A good example of this are the statistical models, based on variables that characterise the preconvective atmospheric conditions.This paper presents the results obtained by applying a short-term forecast model to thunderstorms during the summer periods in León (Spain). This model makes use of the logistic function as a binary forecasting technique determining storm/no storm. The logistic function used was a combination of 15 previously selected meteorological variables. The model has been constructed with the data collected on 152 occasions, and it has been verified on 77 other occasions.The skill scores obtained show that the use of statistical models combining the data, provided by variables characterizing the preconvective conditions and the triggering mechanisms, represent an important step in the difficult task of short-term thunderstorm forecasting.  相似文献   

Comparison of spatial and aspatial logistic regression models for landmine risk mapping     

《Applied geography (Sevenoaks, England)》2016

Landmines continue to affect the lives of millions of people living in war-torn countries. One major challenge in humanitarian mine action (HMA) is finding new and integrated approaches to land release, which remains a slow and costly process. The use of geographic information systems (GIS) in HMA can improve the land release process by efficient mapping and prioritizing of landmine risk areas. This study explores the usage of aspatial and spatial regression techniques to construct a predictive geo-statistical model for landmine risk mapping in a small 160 km² municipality in Bosnia and Herzegovina (BiH) and a large 4500 km² region in Colombia. The first application of logistic geographically weighted regression to landmine risk mapping is presented. The results show that in the BiH study area, the effect of local parameters that influence the distribution of landmine risk varies significantly across the study area. Conversely, in the Colombia case study the effect of explanatory variables remains more homogeneous over the study area. We produced two landmine risk maps for each study area, based on aspatial and spatial regression models. Risk maps are classified into five classes, i.e. very low, low, medium, high, and very high risk. The landmine risk maps created through the usage of these innovative methodologies improve the assessment of risk and prioritization of the land release process in mine-contaminated areas, compared to existing approaches.  相似文献