共查询到18条相似文献,搜索用时 203 毫秒
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推导出了部分相干平顶光束在湍流大气中传输的等效曲率半径的解析表达式,详细地研究了湍流对其等效曲率半径的影响.研究表明,湍流使得等效曲率半径R减小,但是只有当湍流足够强时等效曲率半径极小值出现的位置zmin才会改变.在弱湍流中,R随着光束相干长度β的增大而增大;但是在强湍流中,R随着β的增大而减小.R随着光束阶数M(N)的增大而缓慢减小.若β越大、
关键词:
等效曲率半径
湍流
部分相干平顶光束 相似文献
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MC与$lt;i$gt;M$lt;/i$gt;$lt;sub$gt;$lt;i$gt;n$lt;/i$gt;+1$lt;/sub$gt;$lt;i$gt;AC$lt;/i$gt;$lt;sub$gt;$lt;i$gt;n$lt;/i$gt;$lt;/sub$gt;稳定性与电子特征的第一性原理研究 下载免费PDF全文
研究MC与Mn+1ACn(M=Sc, Ti, V, Cr, Mn; A=Al, Si, P, S; n=1, 2, 3)结构的稳定性与电子特征有利于探究三元层状结构Mn+1ACn稳定性的内在原因和设计新型Mn+1ACn结构. 第一性原理计算研究表明, M-3d与C-2p轨道间的电子转移对MC与Mn+1ACn 的形成焓有较大影响. 供电子能力较强的前过渡金属可以形成稳定的MC结构. 计算结果显示, MC结构是缺电子体系, 其趋向于与具有一定供电子能力的MA结构结合形成Mn+1ACn. 与M2PC和M2SC 相比, M2AlC和M2SiC可以更为容易地被分离成二维 M2C结构.
关键词:
MAX相结构
第一性原理
电子结构
过渡金属碳化物 相似文献
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系统研究了核磁共振碳谱与化学位移和规律,以及拓扑图论方法在定量结构波谱关系(QSSR)中的应用.本文基于路径长度矢量p=p1,p2,p3,…,pm)组合研究提出了一种新的整数型拓扑图论指数M=(p1+p2)+(p1-p3),并发现它与烷烃13C NMR化学位移和有良好线性相关性:回归方程及其统计参数为CSS=+14.329* M-21.089;n=65,R=0.991,SD=7.684,F=3648.021,U=215381.656,Q=3719.563;交互校验CV结果为:R=0.990,R2(01)=0.981,SD(01)=8.086,F(01)=3288.113,U(01)=214982.172,Q(01)=4119.042. 相似文献
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系统研究了核磁共振碳谱与化学位移和规律,以及拓扑图论方法在定量结构波谱关系(QSSR)中的应用.本文基于路径长度矢量p=p1,p2,p3,…,pm)组合研究提出了一种新的整数型拓扑图论指数M=(p1+p2)+(p1-p3),并发现它与烷烃13C NMR化学位移和有良好线性相关性:回归方程及其统计参数为CSS=+14.329* M-21.089;n=65,R=0.991,SD=7.684,F=3648.021,U=215381.656,Q=3719.563;交互校验CV结果为:R=0.990,R2(01)=0.981,SD(01)=8.086,F(01)=3288.113,U(01)=214982.172,Q(01)=4119.042. 相似文献
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依据粗粒化方法,将中国1961—2002年逐日平均温度序列转化为由5个特征字符{R,r,e,d,D}构成的温度符号序列.以符号序列中的125种3字串组成的温度波动模态为网络的节点(即连续4d的温度波动组合),并按照时间顺序连边,构建有向加权的温度波动网络,进而将温度波动模态间的相互作用等综合信息蕴含于网络的拓扑结构之中.对随机序列和Lorenz系统的混沌序列分别构建随机和混沌波动网络.计算三种网络的度与度分布、聚类系数、最短路径长度等动
关键词:
气候变化
气候复杂网络
拓扑结构 相似文献
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提出了一种实现节点结构互异的复杂网络的混沌同步方法.以异结构混沌系统作为节点构造复杂网络,基于Lyapunov稳定性定理确定了复杂网络中连接节点的耦合函数的形式.以Rssler系统、Coullet系统以及Lorenz系统作为网络节点构成的复杂网络为例,仿真模拟发现,整个复杂网络存在稳定的混沌同步现象.此方法不但可以实现任意混沌系统作为节点的网络混沌同步,而且网络节点数对整个复杂网络同步的稳定性也无影响,因而,具有一定的普适性.
关键词:
混沌同步
复杂网络
异结构
Lyapunov稳定性定理 相似文献
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针对真实世界中大规模网络都具有明显聚类效应的特点, 提出一类具有高聚类系数的加权无标度网络演化模型, 该模型同时考虑了优先连接、三角结构、随机连接和社团结构等四种演化机制. 在模型演化规则中, 以概率p增加单个节点, 以概率1–p增加一个社团. 与以往研究的不同在于新边的建立, 以概率φ在旧节点之间进行三角连接, 以概率1–φ进行随机连接. 仿真分析表明, 所提出的网络度、强度和权值分布都是服从幂律分布的形式, 且具有高聚类系数的特性, 聚类系数的提高与社团结构和随机连接机制有直接的关系. 最后通过数值仿真分析了网络演化机制对同步动态特性的影响, 数值仿真结果表明, 网络的平均聚类系数越小, 网络的同步能力越强.
关键词:
无标度网络
加权网络
聚类系数
同步能力 相似文献
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In the study of complex networks,it is commonly believed that the eigenratio λ2/λ N of the Laplacian matrix of a network represents the network synchronizability,especially for symmetric networks.This paper gives two counterexamples to show that this is not true for the case where the network has a disconnected synchronized region.Consequently,a simple answer is presented to the question of when the eigenratio λ2/λ N does represent the network synchronizability. 相似文献
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Enhancing the synchronizability of networks by rewiring based on tabu search and a local greedy algorithm 总被引:1,自引:0,他引:1 下载免费PDF全文
By considering the eigenratio of the Laplacian matrix as the synchronizability measure, this paper presents an efficient method to enhance the synchronizability of undirected and unweighted networks via rewiring. The rewiring method combines the use of tabu search and a local greedy algorithm so that an effective search of solutions can be achieved. As demonstrated in the simulation results, the performance of the proposed approach outperforms the existing methods for a large variety of initial networks, both in terms of speed and quality of solutions. 相似文献
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Does the eigenratio λ<sub>2</sub>/λ<sub>N</sub> represent the synchronizability of a complex network? 下载免费PDF全文
In the study of complex networks,it is commonly believed that the eigenratio λ2/λ N of the Laplacian matrix of a network represents the network synchronizability,especially for symmetric networks.This paper gives two counterexamples to show that this is not true for the case where the network has a disconnected synchronized region.Consequently,a simple answer is presented to the question of when the eigenratio λ2/λ N does represent the network synchronizability. 相似文献
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In this paper, subgraphs and complementary graphs are used to analyze network synchronizability. Some sharp and attainable bounds are derived for the eigenratio of the network structural matrix, which characterizes the network synchronizability, especially when the network’s corresponding graph has cycles, chains, bipartite graphs or product graphs as its subgraphs. 相似文献
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The first step in the counting operator analysis of the spectrum of any model Hamiltonian H is the choice of a Hermitean operator M in such a way that the third commutator with H is proportional to the first commutator. Next one calculates operators R and R† which share some of the properties of creation and annihilation operators, and are such that M becomes a counting operator. The spectrum of H is then decomposed into multiplets, not determined by symmetries of H, but by those of a reference Hamiltonian Href, which is defined by Href=H−R−R†, and which commutes with M. Finally, we introduce the notion of stable eigenstates. It is shown that under rather weak conditions one stable eigenstate can be used to construct another one. 相似文献
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Håkan Andréasson 《Communications in Mathematical Physics》2007,274(2):409-425
In a previous work [1] matter models such that the energy density ρ ≥ 0, and the radial- and tangential pressures p ≥ 0 and q, satisfy p + q ≤ Ωρ, Ω ≥ 1, were considered in the context of Buchdahl’s inequality. It was proved that static shell solutions of the spherically
symmetric Einstein equations obey a Buchdahl type inequality whenever the support of the shell, [R
0, R
1], R
0 > 0, satisfies R
1/R
0 < 1/4. Moreover, given a sequence of solutions such that R
1/R
0 → 1, then the limit supremum of 2M/R
1 was shown to be bounded by ((2Ω + 1)2 − 1)/(2Ω + 1)2. In this paper we show that the hypothesis that R
1/R
0 → 1, can be realized for Vlasov matter, by constructing a sequence of static shells of the spherically symmetric Einstein-Vlasov
system with this property. We also prove that for this sequence not only the limit supremum of 2M/R
1 is bounded, but that the limit is ((2Ω + 1)2 − 1)/(2Ω + 1)2 = 8/9, since Ω = 1 for Vlasov matter. Thus, static shells of Vlasov matter can have 2M/R
1 arbitrary close to 8/9, which is interesting in view of [3], where numerical evidence is presented that 8/9 is an upper bound
of 2M/R
1 of any static solution of the spherically symmetric Einstein-Vlasov system. 相似文献
17.
S. V. Goupalov 《JETP Letters》2010,92(8):507-510
When electron states in carbon nanotubes are characterized by two-dimensional wave vectors with the components K
1 and K
2 along the nanotube circumference and cylindrical axis, respectively, then two such vectors symmetric about a M-point in the reciprocal space of graphene are shown to be related by the time-reversal operation. To each carbon nanotube
there correspond five relevant M-points with the following coordinates: K
1(1) = N/2R, K
2(1)= 0; K
1(2) = M/2R, K
2(2)= −π/T; K
1(3)= (2N −M)/2R, K
2(3)= π/T; K
1(4)= (M + N)/2R, K
2(4)= -π/T, and K
1(5)= (N − M)/2R, K
2(5)= π/T, where M and N are the integers relating the chiral, C
h
, symmetry, R, and translational, T, vectors of the nanotube by N
R = C
h
+ M
T, T = |T|, and R is the nanotube radius. The states at the edges of the one-dimensional Brillouin zone, which are symmetric about the M-points with K
2 = ±π/T, are shown to be degenerate due to the time-reversal symmetry. 相似文献
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As a first step toward a proper treatment of compact objects in binary systems the attraction force of two massive bodies connected by a rod is calculated in a post-Newtonian expansion. Contrary to a calculation by Weyl und Bach we start without specializing the internal structure of the bodies. We consider general anisotropic pressures and do not require axial symmetry for the bodies. We calculate the attraction force first in a post-Newtonian approximation and then (in paper II) we shall be concerned with the post-post-Newtonian approximation. In both approximations we obtain Newton's attraction forceM
S1
M
S2/R
2 plus terms of order 1/R
3 and higher, whereM
S1,M
S2 are the Schwarzschild masses of the bodies. 相似文献