A mixing propagation model of computer viruses and countermeasures

Based on the CMC antivirus strategy proposed by Chen and Carley, a mixing propagation model of computer viruses and countermeasures is suggested. This model has two potential virus-free equilibria and two potential endemic equilibria. The existence and global stability of these equilibria are fully investigated. From the obtained results it can be deduced that the CMC strategy is efficacious in deracinating viruses.     

Mathematical modeling and computer simulation of fire phenomena

An approach to the study of gas phase combustion and convection processes in fires using a combination of mathematical analysis and computer simulation is presented. It seeks to solve the governing equations directly (if approximately) by decomposing the fire into a large-scale convective and radiative transport problem coupled to a small-scale thermal-element model of combustion and radiative emission. The thermal-element model solves the combustion equations in a local Lagrangian coordinate system convected by the large-scale motion, which in turn is driven by the heat released by the combustion processes. The large-scale flow is studied using finite-difference techniques to solve large-eddy simulations of the Navier-Stokes equations. The basic theory behind the methodology is outlined and sample results of both large- and small-scale phenomena are presented. An analytical model of a large eddy is used to show how the simulation can be assembled to yield radiation feedback from a fire plume to a target surface.     

A computer model of pulse wave and input impedance in human arteries

To predict the propagation of pressure and flow pulses in arterial system and the variation of vascular input impedance, a branched and tapered tube model is studied through one-dimensional transient flow analysis. Coupling the continuity and momentum equations yields a group of quasilinear hyperbolic partial differential equations which can be solved numerically by using the method of characteristics. Several boundary conditions of the arterial system are also simplified suitably. The propagation of the pulses of the arterial system and the vascular input impedance is calculated on computer by using the dimensions and the physiological data of the arterial system. The results point out that the pressure and flow pulses of the arterial system and the vascular input impedance produced by this theoretical model is consistent quite well with the experimental results published.     

The seismic pulse in a semi-infinite medium

Summary In a foregoing paper the present author developed methods for studying the transient field from a vertical electric antenna placed in the vicinity of the plane boundary of two semi-infinite dielectric media.As the theory involved is applicable to the comparable elastodynamic pulse problem the present paper deals with the field from a buried transient longitudinal source in an elastic half space.The method appears to be relatively simple and is also applicable to the more general problem in which two elastic semi-infinite solids are separated by a plane boundary.     

The application of the Lattice Boltzmann method to the one-dimensional modeling of pulse waves in elastic vessels

The one-dimensional nonlinear equations for the blood flow motion in distensible vessels are considered using the kinetic approach. It is shown that the Lattice Boltzmann (LB) model for non-ideal gas is asymptotically equivalent to the blood flow equations for compliant vessels at the limit of low Knudsen numbers. The equations of state for non-ideal gas are transformed to the pressure-luminal area response. This property allows to model arbitrary pressure-luminal area relations. Several test problems are considered: the propagation of a sole nonlinear wave in an elastic vessel, the propagation of a pulse wave in a vessel with varying mechanical properties (artery stiffening) and in an artery bifurcation, in the last problem Resistor–Capacitor–Resistor (RCR) boundary conditions are considered. The comparison with the previous results shows a good precision.     

Primary pulse transmission in coupled steel granular chains embedded in PDMS matrix: Experiment and modeling

We present an experimental study of primary pulse transmission in coupled ordered steel granular chains embedded in poly-di-methyl-siloxane (PDMS) elastic matrix. Two granular one-dimensional chains are considered (an ‘excited’ and an ‘absorbing’ one), each composed of 11 identical steel beads of 9.5 mm diameter with the centerline of the chain spaced at fixed distances of 0.5, 1.5 or 2.5 mm apart. We directly force one of the chains (the excited one) by a transient pulse and measure, by means of laser vibrometry, the primary transmitted pulses at the end beads of both chains and at the first bead of the absorbing chain. It is well known that the dynamics of this type of ordered granular media is strongly nonlinear due, (i) to Hertzian interactions between adjacent beads, and (ii) to possible bead separations in the absence of compressive forces and ensuing collisions between neighboring beads. Accordingly, we develop a strongly nonlinear theoretical model that takes into account the coupling of the granular chains due to the PDMS matrix, with the aim to model primary pulse transmission in this system. After validating the model with experimental measurements, we employ it in a predictive fashion to estimate energy transfer between chains as a function of the interspatial distance between chains. Furthermore, based on this model we perform predictive matrix design to achieve maximum energy transfer from the excited to the absorbing chain, and provide a theoretical explanation of the nonlinear dynamics governing energy transfer (including energy equi-partition) in this system.     

Analysis of computer virus propagation behaviors over complex networks: a case study of Oregon routing network

Nonlinear Dynamics - This paper mainly aims to explore the propagation behaviors of computer virus over complex networks under the combined effects of network topology and removable storage media....     

The total reflection of a sound pulse of arbitrary form

The problem of a sound pulse of arbitrary form incident on a half space with an angle of incidence greater than the critical angle is discussed. Formulae are obtained for the transmitted and reflected pressure fields. An expression is obtained for the energy flux across the interface, and it is shown that the net energy flow per unit area over all time is zero.     

大型渡槽动力建模研究

根据渡槽系薄壁杆件结构的特点,提出了渡槽薄壁结构空间动力分析模型。采用空间梁段单元进行离散,考虑渡槽横向、竖向、纵向、自由扭转和约束扭转变形,由能量原理推导给出了渡槽槽身结构的单元刚度矩阵、质量矩阵的显示表达式;渡槽支架采用空间梁单元模拟;渡槽支架与槽身联贯的盆式橡胶支认采用弹性元件单元模拟。文中具体计算了某大型渡槽的模态,计算结果表明：该模型计算渡槽结构的固有频率与理论解和用大型结构分析程序SAP计算的结果良好接近。本文模型计算简单,使用方便,是大型渡槽动力分析的实用模型。     

Experimental study of an air-breathing pulse detonation engine ejector

Experimental studies were performed in order to improve the understanding of the performance of ejector driven by an air-breathing pulse detonation engine (PDE) with a convergent nozzle. This research utilized a gasoline-air PDE at four different operating frequencies of 8 Hz, 10 Hz, 12 Hz and 15 Hz. The performance of PDE-ejector was quantified by thrust measurements. The effects of single ejector length and axial location on thrust augmentation were investigated. It was found that the single ejector with L/D of 2 showed the best performance and the maximum thrust augmentation occurred at a downstream placement of +1 tube diameter. The performances of two-stage and three-stage ejectors were also investigated. The results indicated that both the overlap ratio and the flow area between two stages should not be too large. The performance of the two-stage ejector was not as sensitive as single-stage ejector to axial position in current conditions. The three-stage ejector behaved better than the two-stage ejector but worse than the single-stage ejector in this work. A maximum thrust augmentation of 1.8 was obtained with an L/D of 2 at a downstream placement of +1 position and 15 Hz operating frequency.     

The effect of anisotropy on the integral representation of a cylindrical pulse

Summary The infinite medium Green's function for a two dimensional anisotropic scalar wave equation is obtained in closed form using a technique developed by De Hoop¹). The effect of anisotropy on the complex contour integral representation of this Green's function is explicitly exhibited.Publication 367, Institute of Geophysics and Planetary Physics, University of California, Los Angeles.     

Impact of <Emphasis Type="Italic">θ</Emphasis>-burst stimulation on memory mechanism: modeling study

The information stored in working memory can be transformed into the system of long-term memory due to the long-term potential (LTP) mechanism. The θ-burst stimulation (TBS) can be used as an LTP induction protocol in some experiments, but it has not been used in the models related to memory. In this work, an improved Camperi-Wang (C-W) model with the Ca²⁺ subsystem-induced bistability is adopted, and the TBS is simulated to be the initial stimuli of this model. With the evolution of the effects of the stimuli properties such as the cycle, the amplitude, and the duty ration on the memory mechanism of this model, the TBS can be adopted to activate working memory models and produce long-term memory. The study helps to propose the relationship between working memory and long-term memory, which lays a theoretical basis for the study of the neural mechanism of long-term memory.     

The possibility of measuring flow velocity using a low-intensity periodic pulse discharge

A direct method of measuring the flow velocity in a supersonic wind tunnel by creating a low-intensity periodic pulse discharge is proposed.     

Experimental study and modeling of particle drying in a continuously-operated horizontal fluidized bed

Multistage fluidized beds are frequently used for product drying in industry. One advantage of these fluidized beds is that they can achieve a high throughput, when operated continuously. In this study, γ-Al₂O₃ particles were dried in a pilot-scale horizontal fluidized bed, without considering any comminution effects. For each experiment, the particle moisture content distribution and residence time distribution were determined. To take into account particle back mixing in our experiments, a one-dimensional population balance model that considers particle residence time was introduced into a fluidized bed-drying model. Experimental particle residence time distributions were reproduced using a tank-in-series model. Subsequently, the moisture content distribution was implemented, as a second dimension to the population balance in this model. These two-dimensional simulations were able to describe the experimental data, especially the spread in the residual particle moisture distribution, much more accurately than one-dimensional simulations. Using this novel two-dimensional model, the effects of different operating parameters (process gas temperature, solid feed rate, superficial air velocity) on the particle moisture content distribution were systematically studied.     

A study of transient elastic wave propagation in a bimaterial modeling the thorax

The transient response of an elastic bimaterial, made out of a “hard” medium and a “soft” medium, welded at a plane interface, have been investigated by using an integral transform technique that permits isolation of the pressure and shear waves contributions to the wave-field. The method, often referred to as the generalized ray/Cagniard-de Hoop method (GR/CdH), is briefly presented. The wave motion is generated alternatively by a buried point source of strain rate and by a point force perpendicular to the free surface of the bimaterial. New simplified solutions are derived for points located on the axis perpendicular to the interfaces and passing through the source. Owing to the formalism, an approximation to the strain energy is shown to be readily obtained. The numerical schemes for the implementation of the exact three-dimensional GR/CdH are presented. Numerical examples are concerned with the propagation of an impact wave in the thorax modeled as a bimaterial (thoracic wall–lung). The effects of the weak coupling between the thoracic wall and the lung are investigated. The distributions of transient strain energies, respectively carried by the pressure and the shear waves in the media representing the lung, are plotted.     

Finite deformation of a polymer: experiments and modeling

The response of a polymer (polytetrafluoroethylene) to quasi-static and dynamic loading is determined and modeled. The polytetrafluoroethylene is extremely ductile and highly nonlinear in elastic as well as plastic behaviors including elastic unloading. Constitutive model developed earlier by Khan, Huang and Liang (KHL) is extended to include the responses of polymeric materials. The strain rate hardening, creep, and relaxation behaviors of polytetrafluoroethylene were determined through extensive experimental study. Based on the observation that both viscoelastic and viscoplastic deformation of polytetrafluoroethylene are time dependent and nonlinear, a phenomenalogical viscoelasto–plastic constitutive model is presented by a series connection of a viscoelastic deformation module (represented by three elements standard solid spring dashpot model), and a viscoplastic deformation module represented by KHL model. The KHL module is affected only when the stress exceeds the initial yield stress. The comparison between the predictions from the extended model and experimental data for uniaxial static and dynamic compression, creep and relaxation demonstrate that the proposed constitutive model is able to represent the observed time dependent mechanical behavior of polytetrafluoroethylene polytetrafluoroethylene qualitatively and quantitatively.     

脉搏波本构关系实验研究的探索

脉搏波本构关系决定着脉搏波的传播特征。如何通过实验研究来确定脉搏波本构关系,以及如何通过这些方法从现有文献数据来获得脉搏波本构关系,是当前研究的核心之一。本文中探索了3个可行途径：(1)由实测脉搏波波速对压力的关系C(p)进行反分析（无创法）;(2)直接对脉搏波p-V本构关系进行实测（有创法）;(3)由一系列实测脉搏波波形进行Lagrange反分析（无创法）。采用上述方法,根据现有文献数据,发现由C(p)关系的Rogers-Huang简化式可推得指数型p(V)本构关系;由MK-Hughes式可推得对数型p(V)本构关系。脉搏波传播特性随非线性本构参数发生显著变化。按中医体质分类观点,相应的脉搏波本构关系原则上也有不同类型,因人而定。在这个意义上,脉搏波的Lagrange反分析具有广阔发展前景,但它对正确选择测点和提高测量敏感性和精度等方面提出了更高要求。