共查询到20条相似文献,搜索用时 15 毫秒
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评价网络中节点的信息传播影响力对于理解网络结构与网络功能具有重要意义.目前,许多基于最短路径的指标,如接近中心性、介数中心性以及半局部(SP)指标等相继用于评价节点传播影响力.最短路径表示节点间信息传播途径始终选择最优方式,然而实际上网络间的信息传播过程更类似于随机游走,信息的传播途径可以是节点间的任一可达路径,在集聚系数高的网络中,节点的局部高聚簇性有利于信息的有效扩散,若只考虑信息按最优传播方式即最短路径传播,则会低估节点信息传播的能力,从而降低节点影响力的排序精度.综合考虑节点与三步内邻居间的有效可达路径以及信息传播率,提出了一种SP指标的改进算法,即ASP算法.在多个经典的实际网络和人工网络上利用SIR模型对传播过程进行仿真,结果表明ASP指标与度指标、核数指标、接近中心性指标、介数中心性指标以及SP指标相比,可以更精确地对节点传播影响力进行排序. 相似文献
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声信号在海水中能够传播上千千米,远距离声传播与近距离声传播的特性不同.本文利用西太平洋声源与接收最远距离近2000 km的水声实验数据,对实验海区的海洋环境信息、实验使用的接收垂直阵信息进行处理,分析大洋完全声道环境下,远距离声传播能量衰减规律和多途到达结构特性.在远距离传播能量衰减规律方面,随着传播距离增大,海水吸收对声能衰减的作用凸显,海水吸收系数的选取对声场能量预报的准确性至关重要.较低频信号海水吸收较小,中心频率100 Hz的声信号,传播距离从1000—2000 km,传播损失仅增大6 dB左右.深海声道远距离声传播多途到达结构特性方面,实验海区温跃层声速较高,使得到达接收点的本征声线数目更多,多途到达结构更复杂,海面反射声线形成的到达结构处在整体到达结构的靠前位置,且能量相对较强;受西北太平洋副热带模态水的影响,声速剖面存在双跃层结构,导致部分声线到达接收点的时间较早,多途到达结构在时间轴上的长度延长. 相似文献
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The radiation directivity of a complicated conformal array of underwater acoustic transducers is presented based on the boundary "element method. It includes the element directivity of each transducer, the natural beam pattern and the controlled beam pattern of the transducer array. At first, the boundary element model of the conformal array is built up, and then the boundary condition is exerted on the model according to the design and environment in which the transducer array is used, and the radiation directivity of the conformal array is calculated. An experiment has been done to measure the directivity in an anechoic water tank. The calculated and the experimental results are compared and analyzed. They are consistent to each other. It is shown that the boundary element method together with the detailed calculations is successful to simulate and predict the radiation directivity of an underwater acoustic transducer array. 相似文献
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本文指出只有在光场与物质、光场与光场之间的相互作用可忽略时,物质被线性极化,光才遵守独立传播定律.当光场与物质、各光场之间的相互作用不能忽略时,物质的极化是非线性的,光场不再遵守独立传播定律. 相似文献
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ZHANGHai-Xia WUShi-Shu 《理论物理通讯》2003,40(3):357-362
In an approximation where the baryon current conservation is violated, the contribution of the κμκυ terms in the vector meson propagator may not vanish. Their effects on the baryon and meson spectral functions and on the consequences of self-consistency are studied in the relativistic self-consistent Hartree-Fock approximation by means of the σ-ω model. Two cases where the κμκυ terms are and are not neglected are compared. It is found that there is a marked change in the baryon spectral function which becomes more peaked in the latter case. Such a change remains even by a proper readjustment of parameters. The effects of self-consistency in the σ-ω model are qualitatively the same in both cases, though quantitatively there is some significant difference. 相似文献
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光的波动说的奠基人惠更斯在1690年对光的传播作如下解释:[1]“某一瞬间波阵面上各点各自作为新光源,由它们发出的球面子波的包络面就是下一个波阵面.”这就是著名的惠更斯原理.1816年菲涅耳把惠更斯原理数学公式化[2],成功地解释了衍射现象.在惠更斯-菲涅耳的理论中有一个明显的不合理之处即只考虑球面子波向前传播的那一部分,不加说明地舍弃了球面子波向后传播的另一部分.300年来,物理学家一直回避这个问题,没有明确地给予回答. 在菲涅耳的理论中必须引入一个比例系数K,假定子波是以振幅1/ 、位相 /2来传播的,这在当时仅仅是为了计算上的… 相似文献
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