Distance Threshold Values Research Articles

基于景观连接度的森林景观恢复研究——以巩义市为例

PDF HTML阅读 XML下载 导出引用 引用提醒 基于景观连接度的森林景观恢复研究——以巩义市为例 DOI: 10.5846/stxb201108171210 作者: 作者单位: 河南大学资源与环境研究所,河南大学环境规划学院,河南大学资源与环境研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金资助项目(41071118) Landscape connectivity analysis for the forest landscape restoration: a case study of Gongyi City Author: Affiliation: Institute of Natural Resources and Environmental Science Research,Henan University,Institute of Natural Resources and Environmental Science Research,Henan University,College of Environment Planning,Henan University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:景观连接度是研究景观促进或阻碍生物体或某种生态过程在斑块间运动的程度。基于景观连接度原理,借用景观连接度指数,在地理信息系统支持下,探讨了巩义市丘陵和低山地区森林景观在不同景观距离阈值下连接度的变化,确定了分析森林景观连接度的合适距离阈值。在此基础上分析了要恢复为森林景观的农业斑块的重要值的大小,确定了对要恢复为森林景观的每一农业景观斑块对新形成的森林景观的连接度贡献大小,并结合区域地形特征,明确了森林恢复之初的重要斑块的选取及恢复的先后次序。结果显示,在不同的距离阈值下,低山地区森林景观的整体连通性指数值(IIC)都大于丘陵地区森林景观的IIC值;森林景观的适宜距离阈值,在丘陵地区可选择750 m,在低山地区可选择500 m,或者更小尺度;通过农业景观斑块重要值(dIIC)确定的对森林景观连接度作用起"非常高"和"高"的斑块的数量非常少,但对森林景观连接度的贡献作用却比较大。提出的基于景观连接来分析在森林恢复时重要斑块的选取的方法,具有一定的可操作性与实用性,对区域生态恢复和生态建设具有重要意义。 Abstract:Landscape connectivity is the degree to which the landscape facilitates or impedes the movement of organisms or ecological processes among patches. The maintenance of landscape connectivity is one of the key issues in ecological conservation and construction. The Conversion From Farmland to Forest is a long-term ecological project in China. However, along with the rapid urbanization and industrialization in China, the relationships between landscape connectivity and forest restoration has not been fully explored. The emergent questions concern the connectivity of restored forest landscapes, whether or not this connectivity benefits the local flora and fauna, and how to evaluate the importance of agricultural patches that are to be converted prior to the onset of forest restoration. Based on the theory of landscape connectivity, the forest connectivity in Gongyi City, Henan Province is investigated using indicators such as the number of components (NC), the integral index of connectivity (IIC) and the importance value of IIC (dIIC). With the help of GIS, we examined how landscape connectivity of the forest in the hilly and low mountain areas varied according to distance threshold values ranging from 50 meters to 10000 meters, and identified the most appropriate distance threshold values for analyzing forest landscape connectivity. On this basis, we then looked into the importance values of the agricultural patches that were to be converted, determined the contribution of each pre-conversion agricultural patch to the connectivity of the future forest landscape, and elucidated the selection criteria and restoration priorities of important patches in the early stages of forest restoration according to local topographical features. The results show that the low mountain forest has higher IIC values than the forest in the hilly areas under all distance thresholds. The most appropriate distance threshold for hilly areas is 750 meters, and 500 meters or less for low mountains. The dIIC values indicate that few patches are in the "very high" and "high" categories of contribution to forest landscape connectivity: three arid land patches in the hilly areas (respectively 35.14, 20.16 km2 and 15.39 km2 in descending order of importance value, accounting for 17.06%, 9.79% and 7.47% of the total hilly arid land area) and five arid land patches in the low mountains (respectively 3.65, 2.47, 1.35, 1.96 km2 and 1.15 km2 in descending order of importance value, accounting for 10.05%, 6.80%, 3.71%, 5.38% and 3.167% of the total low mountain arid land area). We also determined the preferable sequence of converting farmland to forest according to the topographical features, especially the slope characteristics, of the arid land patches in the "very high" and "high" categories. The case study shows that the analysis of landscape connectivity should be used as a criterion for selecting important patches in forest restoration planning. The analytical method introduced in this paper is relatively easy to implement, and thus has application potentials in ecological restoration management. 参考文献 相似文献 引证文献

Development of a Method To Consistently Quantify the Structural Distance between Scaffolds and To Assess Scaffold Hopping Potential

We introduce a method to determine a structural distance between any pair of molecular scaffolds. The development of this approach was motivated by the need to accurately evaluate scaffold hopping studies in virtual screening and medicinal chemistry and assess the degree of difficulty involved in facilitating a transition from one structure to another. In order to consistently derive structural distances, scaffolds of different composition and topology are subjected to molecular editing procedures that abstract from original scaffolds in a defined manner until compositional and topological equivalence can be established. Pairs of corresponding scaffold representations are transformed into one-dimensional atom sequences that are aligned using approaches adapted from biological sequence comparison. From best scoring atom sequence alignments, interscaffold distances are derived. The algorithm is evaluated at different levels including the analysis of a series of model scaffolds with defined chemical changes, a scaffold library, and scaffolds from reference compounds and hits of successful virtual screening applications. It is demonstrated that chemically intuitive scaffold distances are obtained for pairs of scaffolds with varying composition and topology. Distance threshold values for close and remote structural relationships between scaffolds are also determined. The methodology is made publicly available in order to provide a basis for a consistent assessment of scaffold hopping ability and to aid in the evaluation and comparison of virtual screening methods.

Small-World and Random Networks in Contact Maps of Protein Channels

Although it is estimated that protein channels constitute large portion of all proteins, the number of their experimental structures is extremely small compared to other proteins. Lipid environment and great size of the channels impede the development. Improvement could contribute to drug design and resolving mechanisms of channelopathies. Modeling 3D structure of transmembrane channels can be enhanced by constraints defined by their contact sites distribution, supporting proper selection of protein decoys in the modeling process. We represent a protein as a network of contact sites and characterize topology of the graph. As a contact site we consider residues within a defined distance between protein backbone C alpha (or beta) atoms that are separated by a certain number of amino acids. Characteristics of the graph model is tested, with regard to protein secondary structure and location of the residues in the membrane or outside. We investigate how the topological characteristics of protein channels compare to other proteins and how definition of the contact site, in terms of the distance and separation threshold values, affects the network topology. The results indicate that the graph model of ionic channel has distinct features. The network topology of proteins proved sensitive to the contact site definition, showing that the graph obeys typical real world network characteristics (“small-world” graph) only if the distance and the separation in the contact site definition are within certain limits, which are not always in accordance with typically assumed. Otherwise a random (Erdos-Renyi) network is observed. Transmembrane helices are much less sensitive to the contact site definition and fall into the “small world” more easily than other structures.

Molecular taxonomy of phytopathogenic fungi: a case study in Peronospora.

BackgroundInappropriate taxon definitions may have severe consequences in many areas. For instance, biologically sensible species delimitation of plant pathogens is crucial for measures such as plant protection or biological control and for comparative studies involving model organisms. However, delimiting species is challenging in the case of organisms for which often only molecular data are available, such as prokaryotes, fungi, and many unicellular eukaryotes. Even in the case of organisms with well-established morphological characteristics, molecular taxonomy is often necessary to emend current taxonomic concepts and to analyze DNA sequences directly sampled from the environment. Typically, for this purpose clustering approaches to delineate molecular operational taxonomic units have been applied using arbitrary choices regarding the distance threshold values, and the clustering algorithms.MethodologyHere, we report on a clustering optimization method to establish a molecular taxonomy of Peronospora based on ITS nrDNA sequences. Peronospora is the largest genus within the downy mildews, which are obligate parasites of higher plants, and includes various economically important pathogens. The method determines the distance function and clustering setting that result in an optimal agreement with selected reference data. Optimization was based on both taxonomy-based and host-based reference information, yielding the same outcome. Resampling and permutation methods indicate that the method is robust regarding taxon sampling and errors in the reference data. Tests with newly obtained ITS sequences demonstrate the use of the re-classified dataset in molecular identification of downy mildews.ConclusionsA corrected taxonomy is provided for all Peronospora ITS sequences contained in public databases. Clustering optimization appears to be broadly applicable in automated, sequence-based taxonomy. The method connects traditional and modern taxonomic disciplines by specifically addressing the issue of how to optimally account for both traditional species concepts and genetic divergence.

A general pairwise key predistribution scheme for wireless sensor networks

This paper develops a general hypercube-based key predistribution scheme for establishing pairwise keys between sensor nodes using polynomials, which is parameterized by the dimension of hypercube and the Hamming distance threshold variables. The scheme addresses the weaknesses of existing key predistribution schemes, which have either worse security or lower efficiency. It exhibits a nice property—when the Hamming distance between any two neighboring sensor nodes is less than the pre-defined threshold, the pairwise key can be established directly. Extensive performance and security analysis shows that by increasing Hamming distance threshold value, we can trade off the resilience against node capture attack for higher probability of direct pairwise key establishment, so as to save the energy consumption which is the most important issue for sensor networks.

Chirality and protein folding

There are several simple criteria of folding to a native state in model proteins. One of theminvolves crossing of a threshold value of the root mean square deviation distance away fromthe native state. Another checks whether all native contacts are established, i.e. whether theinteracting amino acids come closer than some characteristic distance. We useGo-like models of proteins and show that such simple criteria may prompt oneto declare folding even though fragments of the resulting conformations have awrong sense of chirality. We propose that a better condition of folding shouldaugment the simple criteria with the requirement that most of the local values of thechirality should be nearly native. The kinetic discrepancy between the simple andcompound criteria can be substantially reduced in the Go-like models by providing theHamiltonian with a term which favours native values of the local chirality. We studythe effects of this term as a function of its amplitude and compare it to othermodels such as ones with side groups and ones with angle-dependent potentials.

Using curvature features in a multiclassifier OCR system

This paper proposes a new method for character recognition which is based on a novel sequential multiclassifier scheme that uses curvature features in conjunction with other outstanding features. The curvature features are obtained according to the slopes of the character edge pixels. These slopes are observed from certain outer and inner character directions, are grouped according to slope type, and are evaluated according to the areas of the orthogonal triangles which have as hypotenuse the resulting slope lines. Through the multiclassifier technique, different feature types can be used for each character, and combined in a sequential way. Using this approach the recognition rate becomes greater in comparison with single classifiers. To improve the effectiveness of the multiclassifier, a technique has been developed that gives the optimum distance threshold value for each classifier in order to decide with certainty for a character. In this way, characters having very close feature vectors can be distinguished. The proposed method gives highly accurate results with low error rates even if a different recognition font set is used, or in the case of the recognition of deformed fonts. Experimental results with Latin and Greek characters show that the recognition rate can exceed 99.7%.

Method of verifying a speaker

An improved method of verifying the speaker from whom long term spectral characteristics have been derived during a learning phase. Mean values and distance thresholds have been calculated and stored. Improved recognition is obtained by incorporating into the stored values additional values of speech samples in ranges situated outside the distance threshold value. When, during verification, a speech sample not situated within the distance threshold value is encountered its distance from the additionally stored speech samples is successively determined and compared with the separate distance threshold value. The speaker is rejected only if the speech sample to be verified is not situated at a sufficiently small distance from any of the additionally stored speech samples. The method thus increases the recognition range to better approximate the actual distribution of speech samples of the learning phase.