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991.
将森林看成空气和植物组成的混合物, 应用两相混合物折射模型求解了森林的等效介电常数, 通过与实验结果的对比, 验证了该模型的正确性. 将该森林介电常数求解方法引入到抛物方程的森林模型中, 改进了抛物方程的森林模型. 相对于传统的森林环境电波传播模型, 该模型能考虑森林各组成要素对电波传播的影响, 更适合于实际不同地区、不同种类植物分布的森林环境中电波传播特性的求解. 此外, 引入了非均匀网格技术, 有效提高了大区域森林环境中电波传播问题的求解效率.最后基于该模型仿真分析了森林的植物体积含量、重量含水量等要素对电波传播特性的影响.
关键词:
森林
抛物方程
非均匀网格
电波传播 相似文献
992.
A.A. Al-Ghamdi Nadia Abdel Aal Waleed E. Mahmoud 《Polymer Degradation and Stability》2009,94(6):980-986
Poly(vinyl Chloride)/graphite nanosheet/nickel (PVC/GN) nancomposites are new alternative candidates for electrostatic charge dissipation and electromagnetic interference shielding applications due to their lightweight, ease processing and tunable conductivities. The structures of the nanocomposites were examined by means of scanning electron microscopy (SEM) and X-ray analysis. The mechanical properties such as hardness, modulus of elasticity and elongation at break as a function of GN content were examined. The applicability of the nanocomposites as electrostatic charge dissipation was tested in terms of displaying the variation of decay voltage with time. In addition, the dielectric properties such as real and imaginary permittivity of composites as functions of frequency were investigated. Finally, the electromagnetic properties were measured in the frequency range from 1 to 12 GHz and compared with theoretical modeling. The highest shielding effectiveness at microwave frequency of these nanocomposites was 47 dB which is realistic for defense applications like radar evasion. 相似文献
993.
994.
S. Haberman 《Insurance: Mathematics and Economics》1985,4(3):207-224
A discussion is presented of the effect for married women of the introduction of home responsibility credits, earned while they are looking after children or elderly or infirmed relatives, on their entitlement to National Insurance Basic Pensions in the U.K. These credits were introduced in 1978 and three long-term projections are described of the changes in Basic Pension entitlements for future retiring cohorts. 相似文献
995.
996.
997.
In this paper we present a second-order nonlinear dynamical system modelling the interactions of trees and damaging insects in a forest. With this model we discuss the influence of acidic deposition, an increase of which can cause sudden insect infestations and the collapse of the forest ecosystem. The analysis is carried out by finding the bifurcations of the system and by proving that under suitable conditions, such bifurcations can be catastrophic. The conditions for bifurcation can be explicitly given, and this facilitates the biological interpretation of the results. 相似文献
998.
999.
Aforest cover of a graph is a spanning forest for which each component has at least two nodes. We consider the convex hull of incidence vectors of forest covers in a graph and show that this polyhedron is the intersection of the forest polytope and the cover polytope. This polytope has both the spanning tree and perfect matching polytopes as faces. Further, the forest cover polytope remains integral with the addition of the constraint requiring that, for some integerk, exactlyk edges be used in the solution.Research done while thae authors were visiting the Institut für Ökonometrie und Operations Research, Universität Bonn, West Germany.Financial support provided by the Natural Sciences and Engineering Research Council, Canada and the German Research Association (Deutsche Forschungsgemeneinschaft, SFB 303). 相似文献
1000.
Willem Albers 《Statistics & probability letters》1984,2(1):1-4
In the disclosure problem already collected data are disclosed only to such extent that the individual privacy is protected to at least a prescribed level. For this problem estimators are introduced which are both simple and efficient. 相似文献