Surface tension driven flow on a thin reaction front

Surface tension driven convection affects the propagation of chemical reaction fronts in liquids. The changes in surface tension across the front generate this type of convection. The resulting fluid motion increases the speed and changes the shape of fronts as observed in the iodate-arsenous acid reaction. We calculate these effects using a thin front approximation, where the reaction front is modeled by an abrupt discontinuity between reacted and unreacted substances. We analyze the propagation of reaction fronts of small curvature. In this case the front propagation equation becomes the deterministic Kardar-Parisi-Zhang (KPZ) equation with the addition of fluid flow. These results are compared to calculations based on a set of reaction-diffusion-convection equations.     

Determination of the Kardar–Parisi–Zhang equation from experimental data with a small number of configurations

We introduce an inverse method to determine the parameters of the Kardar–Parisi–Zhang equation corresponding to an evolving interface which requires a small number of configurations as input data. Our approach presents advantages for applications in real world scenarios since it does not require small time intervals between fronts. The method is applied to a restricted solid-on-solid model and a stochastic cellular automata model for fire front propagation.     

A simple model for friction detachment at an interface of finite size mimicking Fineberg’s experiments on uneven loading

This work presents a model and simulation results for the friction detachment of a finite sized interface, following previous results on the phenomenon by Ben-David and Fineberg, namely “experiments demonstrating that the ratio of shear to normal force needed to move contacting bodies can, instead, vary systematically with controllable changes in the external loading configuration”. In particular, we extend a previous one-dimensional simulation model by Bar-Sinai with colleagues to a quasi 2D model to allow for a tilting of one of the contacting blocks. While Bar-Sinai with colleagues postulate that the presence of “slow fronts” of detachment (an order of magnitude lower than the usual Rayleigh fronts as in crack propagation) is due to a strengthening term in the friction law, which is not always measured in unlubricated contacts, we find slow fronts also with a purely weakening law.     

Propagation through heterogeneous substrates in simple excitable media models

The interaction of waves and obstacles is simulated by adding heterogeneities to a FitzHugh-Nagumo model and a cellular automata model. The cellular automata model is formulated to account for heterogeneities by modelling the interaction between current sources and current sinks. In both models, wave fronts propagate if the size of the heterogeneities is small, and block if the size of the heterogeneities is large. For intermediate values, wave fronts break up into numerous spiral waves. The theoretical models give insights concerning spiral wave formation in heterogeneous excitable media. (c) 2002 American Institute of Physics.     

Investigation of transient processes at liquid boiling under nonstationary heat generation conditions

The paper presents results on experimentally investigated dynamics of boiling development and formation of film boiling zones under stepwise heat generation on a horizontally and vertically oriented cylindrical surface in a large volume of Freon-21. Experimental data on the expectation time and boiling temperature, the propagation velocity and structure of evaporation and boiling fronts for different heat flux density both in saturated liquid and in subcooling conditions are obtained. Results of experiments on investigating the nucleation forms under development of nonstationary heat release crisis caused by heat loading on the vertical heater immersed into the volume of liquid (water, ethanol) subcooled to saturation temperature are presented. A calculation ratio for determining the expectation time to the beginning of intense vaporization in water is proposed and compared with experimental data obtained on surfaces with different-size roughness. Peculiarities of evolution of evaporation fronts from incipient bubbles are investigated in the experiments with ethanol. Data on the evaporation front velocity as a function of wall overheating are obtained. The obtained experimental data on the propagation velocity of self-sustained evaporation fronts are compared with the known calculated data.     

Wave fronts in inhomogeneous neural field models

In this work we investigate the influence of inhomogeneities on wave front propagation in an excitatory neural field model describing synaptic activity in the absence of delays. This allows the derivation of the spatial (and hence temporal) behaviour of the front velocity under the assumption that the front is approximatively homogeneous in a very small time window. With this assumption we can also derive the spatiotemporal behaviour of the membrane potential analytically in the vicinity of the wave front. In addition to this we investigate stationary solutions such as standing wave fronts and localised activity (so-called bumps) to determine the existence condition of travelling and standing fronts. Numerical results are included to point out the accordance of theory and simulation.     

磁性量子元胞自动机拐角结构的理论模拟和实验

磁性量子元胞自动机拐角结构是一种同时含有铁磁耦合和反铁磁耦合的电路. 理论模拟了外加时钟场作用下铸铁磁性材料拐角结构的信号传递. 采用微磁仿真给出了信号传递的磁化演化图, 结果证实了铸铁纳磁体能够实现含有两种冗长耦合结构的稳定转换. 实验制备了相应的拐角结构, 扫描电子显微图和磁力显微图结果显示了成功的电路图案和正确的两种耦合方式信号传递.     

Multi-value cellular automata model for mixed bicycle flow

In this paper, we investigate mixed bicycle flow using the multi-value cellular automata (CA) model. Two types of bicycles with different maximum speed are considered in the system. The system of mixed bicycles is investigated under both deterministic and stochastic regimes. It is shown under the deterministic case that there appear multiple states both in congested flow and free flow regions. Analytical analysis is carried out and is in good agreement with the simulation results. Under the stochastic case, the multiple states effect disappears only when both slow and fast bicycles are randomized. Spacetime plots are presented to show the evolution of mixed bicycle flow.     

The propagation of discontinuities in non-homogeneous thermoviscoelastic media

In this study, the propagation of plane, cylindrical and spherical dilatational waves in non-homogeneous thermoviscoelastic media is investigated by employing the notion of singular surfaces and the method of characteristics. The inhomogeneity of the medium is such that the material properties depend in an arbitrary manner on the co-ordinate coinciding with the direction of the propagation. An integral type constitutive equation is considered for the heat flux which permits a finite propagation speed for thermal disturbances. It is found that the application of a dynamic input on the boundary surface gives rise to two different wave fronts along which mechanical and thermal effects are coupled. The growth and decay equations describing the change of the strength of the discontinuities on these two wave fronts are then obtained. By integrating the growth and decay equations along the rays the solutions valid at the wave fronts are found. The solutions are then reduced to two special cases: in one the heat flux equation is taken as the so-called modified Fourier equation, and in the other as the classical Fourier equation. The effects of inhomogeneity, geometry of the wave front, thermomechanical coupling and material internal friction on the strength of the discontinuity are discussed.     

基于元胞自动机考虑传播延迟的复杂网络病毒传播研究

基于元胞自动机,研究传播延迟对复杂网络病毒传播动力学行为的影响,提出一种新的易染状态-感染状态-易染状态(SIS)传播模型.研究表明,传播延迟的存在显著降低了网络的传播临界值,增强了网络中病毒爆发的危险性.研究还发现,随着传播延迟的增大,病毒的感染程度以及传播速率都明显增大.此外,SIS传播模型不仅能够反映病毒的平均传播趋势,而且可以描述病毒随时间的动态演化过程以及病毒的爆发和消亡等概率事件,从而有效地克服了利用平均场方法构建的微分方程模型只能反映病毒平均传播趋势的局限性.同时,还给出有效控制网络中病毒传 关键词： 复杂网络 病毒传播 元胞自动机 传播延迟     

Traveling waves and chaotic properties in cellular automata

Traveling wave solutions of cellular automata (CA) with two states and nearest neighbors interaction on one-dimensional (1-D) infinite lattice are computed. Space and time periods and the number of distinct waves have been computed for all representative rules, and each velocity ranging from 2 to 22. This computation shows a difference between spatially extended systems, generating only temporal chaos and those producing as well spatial complexity. In the first case wavelengths are simply related to the velocity of propagation and the dispersivity is an affine function, while in the second case (which coincides with Wolfram class 3), the dispersivity is multiform and its dependence on the velocities is highly random and discontinuous. This property is typical of space-time chaos in CA. (c) 1999 American Institute of Physics.     

鼓泡床内气固两相流的变尺度格子气模拟

基于格子气自动机的建模思想,建立气固两相流的变尺度格子气模型,用微观层次的气固作用规则描述两相流的宏观行为.二维流场空间被离散成两层不同尺度的正六边形网格,固体颗粒和气体粒子分别在各自的网格上运动;在格子气自动机基本规则基础上设计气固相作用规则和附加演化规则;确定模型宏观物理量的统计计算方法,并根据相似原理建立模型物理量与真实物理量之间的转换关系.用建立的模型对鼓泡床内气固流动行为进行模拟,通过比较发现,变尺度格子气模型的模拟结果与文献中的实验结果和双流体模型的模拟结果吻合较好,且平均相对误差更小,表明建模方法的正确性和模型的有效性.     

Effect of hydrogen content in titanium on the structure of the front and the specific features of the combustion of a Ti + 0.5C granular mixture in a cocurrent nitrogen flow

Specific features of the combustion of a titanium–carbon black granular mixture in a quartz tube blown with nitrogen is studied. In contrast to the previous studies, titanium with increased hydrogen content is used. The gas flow (cocurrent filtration) is produced by applying a fixed pressure differential less than 1 atm across the inlet and outlet of the tube. The characteristics of the combustion of a Ti + 0.5C granular mixture in a nitrogen flow are investigated. It is shown that an increased content of hydrogen in titanium leads to the formation of a two-front combustion wave. It is demonstrated that the first and second fronts of the two-front structure arise due to the interaction of the charge with nitrogen. The velocities of propagation of the fronts increase with the nitrogen pressure differential.     

Dynamics of A + B --> C reaction fronts in the presence of buoyancy-driven convection

The dynamics of A+B-->C fronts in horizontal solution layers can be influenced by buoyancy-driven convection as soon as the densities of A, B, and C are not all identical. Such convective motions can lead to front propagation even in the case of equal diffusion coefficients and initial concentration of reactants for which reaction-diffusion (RD) scalings predict a nonmoving front. We show theoretically that the dynamics in the presence of convection can in that case be predicted solely on the basis of the knowledge of the one-dimensional RD density profile across the front.     

节点抗攻击存在差异的无尺度网络恶意软件传播研究

在考虑节点抗攻击能力存在差异情形下,研究了恶意软件在无尺度网络中的传播行为.基于元胞自动机理论,建立了节点具有攻击差异的恶意软件传播模型.通过定义脆弱性函数,以描述不同度节点的抗攻击差异,使得模型更具普遍性.研究了不同形式的脆弱性函数对恶意软件在无尺度网络中的传播临界值和时间演化的影响.研究表明,节点抗攻击能力的差异对传播行为会产生重要影响,如导致传播临界值改变、传播速度减缓.研究指出,脆弱性函数是网络选择适合的免疫策略的重要依据.     

基于元胞自动机的复杂信息系统安全风险传播研究

基于元胞自动机建立复杂信息系统安全风险传播模型, 研究复杂信息系统安全风险在最近邻耦合网络、 随机网络,　Watts-Strogatz 小世界网络和Barabasi-Albert无标度网络 四种网络拓扑下的传播问题. 通过研究安全风险传播模型在四种网络拓扑下安全风险的传播阈值, 与现有的传播阈值研究成果进行比较, 验证模型的正确性, 并分析验证网络拓扑结构中度分布的异质化程度越高传播阈值越小的结论. 通过对安全风险的传播演化趋势进行研究, 分析验证网络度分布的异质化程度越高、安全风险影响范围越小、传播速度越快的结论, 并指出度分布的异质化程度越高、模型后期的免疫机制对控制安全风险传播的效果越缓慢. 通过对安全风险在传播最早期就趋于消亡的情况进行研究, 分析得出安全风险在传播之初就趋于消亡的消亡率与传播率之间呈现近似负指数的关系, 并且初期的感染源越多安全风险的消亡率越低. 分析了影响复杂信息系统安全风险传播的关键要素, 对复杂信息系统中安全风险传播的控制具有指导作用. 关键词： 复杂信息系统 复杂网络 安全风险传播 元胞自动机     

Broadband modeling of downslope propagation in a penetrable wedge

Sound propagation in a wedge-shaped environment with a penetrable bottom is simulated with broadband adiabatic mode, coupled mode, and parabolic equation model computations. Simulated results are compared to measured data taken in a tank experiment by Tindle et al. The coupled mode formalism is shown to predict, in agreement with that experiment, that modal wave fronts in penetrable wedges are approximately circular arcs centered at the apex of the wedge for a source near the apex. It is also shown that for wedge angles up to 6 degrees, the received waveforms are well approximated by the adiabatic waveforms time-shifted by a depth-dependent interval to account for the curvature of the modal wave fronts. A small deviation from circularity in the modal wave fronts is possibly observed in the 6 degrees case.     

Structures of Strong Shock Waves in Dense Plasmas

Structures of strong shock waves in dense plasmas are investigated via the steady-state Navier-Stokes equations and Poisson equation. The structures from nuid simulation agree with the ones from kinetic simulation. The effects of the transport coeffcients on the structures are analysed. The enhancements of the electronic heat conduction and ionic viscosity both will broaden the width of the shock fronts, and decrease the electric fields in the fronts.