基于抛物方程的短波电离层传播数值模拟研究

短波电离层传播损耗的计算对电离层基础研究与短波通信、天波超视距雷达等应用有重要意义，以往主要采用半经验模型.文中基于电磁波传播的抛物方程方法，实现对短波电离层传播损耗空间分布的数值计算，该方法可同时考虑电磁波传播的折射、反射、绕射和吸收等效应.根据电子浓度剖面数据，仿真计算了不同频点和天线波束宽度情况下的电离层传播损耗，从折射效应引起的传播模式、反射点高度、地面落区位置方面，与射线描迹结果进行对比，两者具有一致性.此外，进一步仿真分析了电离层的吸收效应.研究结果初步表明了抛物方程方法预测电离层传播的有效性及其强大的功能.     

树冠中电波传播路径损耗的研究及模型的建立

运用随机介质中波的传播和散射理论,解出了电波经过树叶和树枝时散射场的表达式,然后利用平均场的近似方法,计算出电波经过树冠时传播常数的表达式,建立了树冠中电波传播路径损耗的数学模型.通过实验测量了常见树种的相关参数,并代入该模型进行了计算,计算结果与文献提供的测量值吻合较好.     

D2D通信中用户意识与信息耦合传播建模分析

设备到设备(D2D)通信中信息传输过程不仅受物理通信条件影响,还与用户动态属性密切相关。为探讨信息传输与用户意识扩散之间的内在关系,该文将信息传输与用户意识扩散视作两种传播过程,并引入过程影响因子刻画两者相互作用。进一步地,建立了一种信息与用户意识耦合传播动力学模型,并进行了全面分析。其中,理论分析证明了模型平衡点的存在唯一性及其全局稳定性,这揭示了D2D通信中信息与用户意识耦合传播的最终状态。实验分析也验证了该理论结果。同时,与传统模型和未考虑过程影响的传播模型对比发现所提模型能扩大信息传播规模且能更准确刻画信息传播过程。     

Dynamic model of computer viruses under the effect of removable media and external computers

This paper investigates the propagation of computer viruses and establishes a novel propagation model. In contrast to the existing models, this model can directly indicate the impact of removable media and external computers on the propagation of computer virus. The stability results of equilibrium point are derived by Hurwitz criterion and Bendixson Dulac criterion. The effectiveness of the proposed results is shown by numerical simulation. In order to show the superiority of the proposed model, some comparisons with the existing models are presented. The acceptable threshold and the reasonable strategies for suppressing the propagation of computer virus are also suggested, respectively.     

基于机载ADS-B信号地空传播试验数据分析

地空传播特性是机载无线电系统设计的重要依据, 电波传播试验数据是建立地空传播预测模型的基础.为了深入研究航空移动业务电波传播特性, 利用机载ADS-B(automatic dependent surveillance broadcast)信号开展了地空传播试验, 对试验数据进行的分析表明, 实测传播损耗与ITU-R P.528-3模型预测损耗及自由空间传播损耗的变化趋势一致; 同时, 还利用抛物方程方法对不同折射条件下的ADS-B信号传播进行了仿真, 仿真的地空传播衰落特征与实测数据有较好的一致性.分析结果表明, 利用机载ADS-B信号取得的地空传播试验数据是可靠的, 这对今后利用ADS-B信号积累传播数据, 改进传播预测模型具有重要意义.     

Narrowband Short Range Directive Channel Propagation Loss in Indoor Environment at Three Frequency Bands

Propagation loss models for indoor environment are presented. The narrowband directive channel propagation loss in indoor environment at three frequency bands namely (2.4, 3.3 and 5.5) GHz is measured. Sets of directive panel antennas are used in the measurements. RF signal generator and a spectrum analyzer are used in the measurement campaign. It is found that propagation loss is sensitive to the scenario configuration. It is noticed that the propagation loss can be modelled by a single slope propagation model or two slopes propagation model.     

A joint finite-difference and FFT full vectorial beam propagationscheme

A full vectorial beam propagation scheme is developed and it is applied on 3-dimensional waveguide structures. The formulation is based on the coupled wave equations for the transverse electric field. Each propagation step is performed by utilizing both the FFT and a finite-difference implementation. Under this perspective the offered advantages of FFT and finite-differences are exploited within a single propagation step resulting in a joint propagation scheme. The scheme is applied on a step-index circular fiber where analytical solutions are readily available for cross-checking. Moreover, the dependence of the phase constant on the reference refractive index is discussed. The polarized modes and the effective mode indices are derived in the case of rib waveguides by performing propagation along imaginary distance. Further, the rib waveguide coupler is examined and the energy transfer is simulated     

Delay fault propagation in synchronous sequential circuits

Compared with the propagation of logic errors produced by stuck-at faults, the propagation of gate delay fault effects in sequential circuits poses some particular problems. The authors first describe the propagation conditions of such faults then define the propagation rules of these faults which are used in a new delay fault simulation process for synchronous sequential circuits     

Three-dimensional beam propagation analysis of nonlinear opticalfibers and optical logic gates

A three-dimensional (3-D) beam propagation method is described for the analysis of nonlinear optical fibers, where the finite element and finite difference methods are, respectively, utilized for discretizing the fiber cross section and the propagation direction. For efficient evaluation of wide-angle beam propagation Pade approximation is applied to the differential operator along the propagation direction. In order to improve the efficiency and accuracy of solutions, isoparametric elements and numerical integration formulae derived by Hammer et al. are introduced. The propagation characteristics of nonlinear optical fibers with linear core and nonlinear cladding are analyzed, and unique features of nonlinear guided-wave propagation are investigated. Furthermore, all-optical logic gates with practical, 3-D geometry consisting of optical fibers and a nonlinear film are proposed, and their operations of Boolean arithmetic are demonstrated     

空心傍轴高斯光束的传输特性

推导了空心高斯光束经过傍轴光学系统的传输模型;利用导出的公式计算分析了卒心高斯光束在自由空间的传输特性;最后利用Matlab对传输方程进行模拟仿真.结果表明:高斯光束的阶数n和沿傍轴的传输距离z是控制空心光束的主要参数.随着阶数n的增大,高斯光束逐渐变为空心高斯光束,且中心暗斑和亮环的半径也相应增加;当传输距离z增大时...     

Modeling of the Division Point of Different Propagation Mechanisms in the Near-Region Within Arched Tunnels

An accurate characterization of the near-region propagation of radio waves inside tunnels is of practical importance for the design and planning of advanced communication systems. However, there has been no consensus yet on the propagation mechanism in this region. Some authors claim that the propagation mechanism follows the free space model, others intend to interpret it by the multi-mode waveguide model. This paper clarifies the situation in the near-region of arched tunnels by analytical modeling of the division point between the two propagation mechanisms. The procedure is based on the combination of the propagation theory and the three-dimensional solid geometry. Three groups of measurements are employed to verify the model in different tunnels at different frequencies. Furthermore, simplified models for the division point in five specific application situations are derived to facilitate the use of the model. The results in this paper could help to deepen the insight into the propagation mechanism within tunnel environments.     

High precision analysis of finlines on semiconductor substrate

In this study, the effect of the metallization thickness in finlines on semiconcuctor substrate is researched. The propagation parameters are computed to measure the inluence of the metallization. The theory and numerical results are presented to the propagation constant and characteristic impedance of the bilateral and unilateral finlines. The full wave analysis of the transverse transmission line — TTL method is used to determine the electromagnetic fields of the structure in Fourier transform domain — FTD. Applying the suitable boundary conditions, the moment method and expanding the fields in a set of suitable bases functions, a homogeneous matrix system is obtained and the propagation constant is computed. The characteristic impedance is obtained using the relation of the voltage in the slot and the transmitted power by the structure. Computational programs are developed to obtain numerical results to the propagation parameters composed by the propagation constant and characteristic impedance.     

Physical characteristics of urban micro-cellular propagation

The characteristics of the propagation in micro-cellular environments at a carrier frequency of 1.98 GHz are investigated by wide band measurements, complemented by theoretical model calculations. The spatial variations of the complex impulse response were measured with a high time resolution allowing via the scattering function the extraction of detailed information about the wave propagation process. The analysis of a large number of different real propagation configurations leads to a characterization of the most relevant urban micro-cellular propagation mechanisms: propagation in lined streets under line-of-sight conditions, coupling into side streets and propagation effects near street intersections. The wide band channel behavior during the transition of a mobile antenna from directly illuminated into shadowed areas has been considered in particular detail, since this is a crucial situation for a mobile communications system     

电波在有耗分层媒质中传播的频域特性研究

本文在频率域上研究了电波在分层媒质中的传播特性，提出了一种新的电波在有耗分层媒质中的传播的频域模型，利用计算机仿真分析了电波在层状媒质中的传播的频率特性，得出了各介质参数及电波频率与传播持性的关系。     

Two-Layer Coupled Network Model for Topic Derivation in Public Opinion Propagation

In view of the fact that news can generate derivative topics when it spreads through micro-blogs,a two-layer coupled SEIR public opinion propagation model is proposed in this paper.The model divides the process of public opinion propagation into two layers:the original topic layer and the derived topic layer.Messages are transmitted separately by the SEIR model in the two topic layers,which are independent and interactive.The influence of the topic derivation rate on the propagation trend is established by solving for the equilibrium point and propagation threshold.Further,we establish the relationship between the original topic and the derived topic by simulation.This paper uses the Baidu index to demonstrate the correctness of the model.The relationship between the derived topic and the original topic is verified by adjusting the parameters by the control variable method.The results show that the proposed model is consistent with the propagation of actual public opinion.     

Ka-band Earth-space propagation research in Japan

Earth-space propagation studies in Japan were originally concerned with measuring atmospheric absorption and rain attenuation by means of a suntracker and a radiometer, following which a number of long-term experiments were performed using various experimental and commercial satellites. The first experiments involving Ka-band Earth-space propagation measurements in Japan were carried out in 1977 using the Engineering Test Satellite Type II, and since 1978, these experiments have been conducted using Japan's domestic communication satellite. Based on these studies to date, the understanding of Earth-space propagation characteristics at higher frequency bands, modeling of propagation channels, and development of countermeasure technologies have shown dramatic progress. In Japan at present, advanced propagation studies are under way in wideband digital-transmission satellite systems for the forthcoming multimedia era. This paper summarizes recent study activities concerning wave propagation in Ka-band Earth-space paths and related topics, such as radiometeorology in Japan. Last, future plans for conducting Ka-band and millimeter-wave propagation experiments by using the Japanese experimental satellite “COMETS” and rain observations in tropical regions by “TRMM” are introduced briefly     

P2P网络中激发型蠕虫传播动态建模

 鉴于激发型蠕虫的巨大危害性,本文在考虑网络动态变化的情况下对激发型蠕虫的传播进行了深入地研究,提出了激发型蠕虫动态传播数学模型和免疫模型,并基于动态传播数学模型推导出了激发型蠕虫不会泛滥的充分条件.大规模仿真实验验证了传播模型的有效性和蠕虫不会泛滥充分条件的正确性.基于传播模型的分析表明,下载率是影响蠕虫传播的关键因素,蠕虫基本繁殖率是衡量蠕虫传播能力的关键指标.基于实测P2P网络数据和传播模型,预测和估计了激发型蠕虫的传播能力、传播速度和危害性,指出尽早重视P2P激发型蠕虫特别是尽早找到检测和控制方法的重要性和迫切性.     

聚焦光束的傅里叶数值算法研究

由于取样定理的限制 ,常规的基于快速傅里叶变换 (FFT)光束传输模拟算法不能进行任意焦距聚焦光束的传输过程的模拟。为此提出了一种新算法 :将球面波因子提出 ,将会聚光束的传输过程转化为非会聚光束的传输 ,从而间接地求得了聚焦光束的光场分布。利用Fresnel数对两种传输过程的关系和聚焦光束的传输特性作了分析     

神经网络方法在降雨去极化效应预报中的应用

利用神经网络中的ＢＰ算法，通过在已知的传播路径上降雨同极化衰减ＣＰＡ来预算降雨去极化分辨率ＸＰＤ，且将计算结果与其他算法进行了对比。本文的工作是神经网络方法在建立电波大气传输效应预报模型应用中的有益尝试。     

Propagation of magnetostatic surface waves in a ferrite plate magnetized by a spatially periodic transverse field

Propagation of magnetostatic surface waves (MSSWs) in a ferrite plate magnetized by a spatially periodic transverse field has been considered. The parameters of MSSW propagation have been calculated by the Hamilton-Auld method. It is shown that only noncollinear MSSWs, whose wave-beam trajectories as well as wave numbers and angles, which determine the directions of the vectors of the phase and group velocities, are described by functions that are periodic in the direction of the wave propagation, can exist in this field. The period of these functions is determined by the period of the spatially periodic field. The frequency range of existence of the collinear waves is narrower than that of the waves in a uniformly magnetized plate. The characteristics of wave propagation in a nonuniform spatially periodic field are compared to the characteristics of wave propagation in nonuniform fields of known types.