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784.
河流水质预测的因素状态网络模型研究 总被引:6,自引:0,他引:6
建立了一种河流水质预测的因素状态人工神经网络模型,其算例的计算结果表明,这一种方法有着极大的研究意义和广阔的应用前景。 相似文献
785.
Incorporating anthropogenic variables into a species distribution model to map gypsy moth risk 总被引:1,自引:0,他引:1
Christopher D. Lippitt John Rogan James Toledano Florencia Sangermano J. Ronald Eastman Victor Mastro Alan Sawyer 《Ecological modelling》2008
This paper presents a novel methodology for multi-scale and multi-type spatial data integration in support of insect pest risk/vulnerability assessment in the contiguous United States. Probability of gypsy moth (Lymantria dispar L.) establishment is used as a case study. A neural network facilitates the integration of variables representing dynamic anthropogenic interaction and ecological characteristics. Neural network model (back-propagation network [BPN]) results are compared to logistic regression and multi-criteria evaluation via weighted linear combination, using the receiver operating characteristic area under the curve (AUC) and a simple threshold assessment. The BPN provided the most accurate infestation-forecast predictions producing an AUC of 0.93, followed by multi-criteria evaluation (AUC = 0.92) and logistic regression (AUC = 0.86) when independently validating using post model infestation data. Results suggest that BPN can provide valuable insight into factors contributing to introduction for invasive species whose propagation and establishment requirements are not fully understood. The integration of anthropogenic and ecological variables allowed production of an accurate risk model and provided insight into the impact of human activities. 相似文献
786.
A Graph-Theory Framework for Evaluating Landscape Connectivity and Conservation Planning 总被引:9,自引:0,他引:9
Abstract: Connectivity of habitat patches is thought to be important for movement of genes, individuals, populations, and species over multiple temporal and spatial scales. We used graph theory to characterize multiple aspects of landscape connectivity in a habitat network in the North Carolina Piedmont (U.S.A).. We compared this landscape with simulated networks with known topology, resistance to disturbance, and rate of movement. We introduced graph measures such as compartmentalization and clustering, which can be used to identify locations on the landscape that may be especially resilient to human development or areas that may be most suitable for conservation. Our analyses indicated that for songbirds the Piedmont habitat network was well connected. Furthermore, the habitat network had commonalities with planar networks, which exhibit slow movement, and scale-free networks, which are resistant to random disturbances. These results suggest that connectivity in the habitat network was high enough to prevent the negative consequences of isolation but not so high as to allow rapid spread of disease. Our graph-theory framework provided insight into regional and emergent global network properties in an intuitive and visual way and allowed us to make inferences about rates and paths of species movements and vulnerability to disturbance. This approach can be applied easily to assessing habitat connectivity in any fragmented or patchy landscape. 相似文献
787.
李北枝 《湖南环境生物职业技术学院学报》2008,14(3):27-30
介绍一些经常性的网络安全问题,以及用一种相应的防御对策——网络防火墙,它技术的核心思想是在不安全的网络环境中构造一个相对安全的子网环境.讨论了实现防火墙的两种主要技术手段:一种是基于分组过滤技术(Packet filtering),它的代表是在筛选路由器上实现的防火墙功能;一种是基于代理技术(Proxy),它的代表是应用层网关上实现的防火墙功能.参5. 相似文献
788.
The ensemble Kalman Filter (EnKF) applied to a simple fire propagation model by a nonlinear convection-diffusion-reaction
partial differential equation breaks down because the EnKF creates nonphysical ensemble members with large gradients. A modification
of the EnKF is proposed by adding a regularization term that penalizes large gradients. The method is implemented by applying
the EnKF formulas twice, with the regularization term as another observation. The regularization step is also interpreted
as a shrinkage of the prior distribution. Numerical results are given to illustrate success of the new method. 相似文献
789.
对9种垂直流人工湿地基质进行了对磷的等温吸附试验.结果表明,在溶液磷浓度为100~500mg/L条件下,9种基质中以草炭的吸附量为最高,达到2439.56mg/kg;砾石的吸附量最低,仅为188.67mg/kg;其余基质表现出高炉渣土>高炉渣>煤灰渣土>耕层土>煤灰渣>中粗砂土>中粗砂的规律.供试基质的容重和密度与磷吸附量呈极显著性负相关关系;基质的颗粒直径D80和不均匀系数K80与磷吸附量呈显著性正相关关系.基质的CEC、有机质、有效Fe和交换性Al的含量与磷吸附量呈极显著性正相关关系;pH值与磷吸附量呈极显著性负相关关系. 相似文献
790.