网络蠕虫的演化

针对复杂生态环境中网络蠕虫对传播率的演化选择问题,给出了一个蠕虫传播模型.运用动力学分析方法得到了模型的平衡态及其稳定性条件,并进行了仿真验证.在理论分析的基础上,利用随机算法仿真了不同传播率对蠕虫传播的影响.仿真结果表明,复杂生态环境更有利于具有小传播率的蠕虫.对该类蠕虫,进一步仿真了防病毒技术对其影响.结果表明,加强杀毒系统对小传播率蠕虫的查杀能力和引入竞争性蠕虫能有效遏制该类蠕虫的传播     

利用正三棱锥前向展开法追踪三维温度场声线路径

声波在温度梯度场中传播路径的弯曲效应是影响声学法温度场重建精度的一个重要因素,使用正三棱锥前向展开方法对三维温度梯度场中声波的真实传播路径进行研究,并在具体的温度场模型中对该声线追踪算法进行了仿真计算和分析,仿真结果表明,该方法能够很好地追踪三维温度场声波的真实传播路径.     

基于实测的无线信道仿真分析

在建设WCDMA网络前,为了获得符合本地区实际环境的无线传播模型,提高覆盖预测的准确性,为网络规划打好基础,必须进行传播模型的校正.介绍了利用实地无线信道测试数据修正经典传播模型以估计无线信道的方法和原理、数据采集的基本原则以及如何利用SIMULINK仿真工具包构建无线信道工作模型.仿真结果表明,该方法有效且可行.     

基于改进SIR模型的项目隐性知识转移因素解析

隐性知识作为组织重要资产,其成功转移与吸收对项目成败具有重要作用。隐性知识转移绩效受到转移主体比例、知识模糊性、接触率、学习意愿、遗忘率等因素的影响。通过类比分析传染病传播机制与项目隐性知识转移过程,引入SIR模型(susceptible infected recovered model),基于项目成员类型与知识传递过程,建立项目隐性知识转移改进SIR模型,围绕各因素变化对知识转移绩效影响进行仿真分析,进而发现隐性知识转移规律。结果表明,知识模糊性、遗忘率对知识转移绩效具有负向作用;组织成员接触率、学习意愿对转移绩效具有正向作用,可以有效降低其他因素的负向作用。因此,为促进隐性知识转移,应增加知识传播途径、知识学习者人数,提高成员间接触率,降低知识遗忘率,构建项目学习型组织共同体。     

人因可靠性仿真

为了改进人因可靠性分析中时间接口、误差传播等方面的不足,进行了人因可靠性仿真方法研究.对仿真中的关键问题如仿真模型建立、仿真流程设计、仿真误差分析和仿真规模确定等进行了深入的理论分析并给出了合理的解决方案.并以核电工程中广为应用的THERP+ HCR方法为原型,给出了人因可靠性仿真的实现实例.仿真结果表明,前述理论分析...     

空调塑料材料的碰撞失效模拟研究

研究空调内机塑料材料ABS-121H在跌落工况下的力学行为。通过准静态、动态拉伸力学实验和失效实验,分别建立了不同应变率下材料弹塑性模型及LS-DYNA软件的GISSMO失效模型,并通过整机零部件实验及仿真对材料弹塑性模型和失效模型准确性进行验证。结果表明:考虑应变率效应的材料弹塑性模型可以准确反映结构的加速度和刚度,GISSMO失效模型可以准确预测材料复杂应力状态下的断裂失效行为。该研究为空调跌落仿真的材料模型建立提供参考。     

硅微加速度计的建模与仿真

根据物体相对运动理论,采用能量法表述了建立硅微加速度计功能组件模型的一般方法,并以Verlog-A为模型编码语言实现了硅微加速度计参数化组件模型.利用这些参数化的功能组件模型,在Saber仿真平台上构建了电容式微加速度计系统级模型,并进行了仿真.频域仿真结果表明系统的谐振频率相对于有限元模态分析结果,计算精度相差在3%以内;时域仿真结果表明使用该系统级模型能够快速进行复杂机电耦合系统时域行为分析,输出电压仿真结果与实测值相差在7.5%以内.     

浅海声速剖面对吊放声纳探测距离的影响

吊放声纳的作用距离不仅和自身设备性能有关,还和海洋水声环境特性及吊放声纳入水深度有着密切的关系.本文阐述了浅海不同声速剖面中的声传播特性,通过仿真声线轨迹分析了几种典型的浅海声速剖面对声传播的影响.通过对声纳、水声环境以及目标的模型化计算,利用射线模型仿真了几种不同声速剖面情况下吊放声纳的主动作用距离.分析了吊放声纳入...     

多普勒效应对水下高速运动目标被动定位的影响及其抑制方法

为改善水下高速运动目标被动定位精度,通过仿真分析给出抑制多普勒效应的方法。首先介绍了基本的水下信号模型和水下声传播信道模型,分析了多普勒效应对被动定位的影响,给出抑制方案。随后分析了所给出方案的性能,并且通过仿真,分析了出现误差的原因,得到了提高定位精度的关键因素。仿真结果表明,该方案可以有效抑制多普勒效应对被动定位的影响,具有较强的实用性。     

航空声纳双基地探测模型及仿真

从双基地声纳方程出发,分析了航空双基地探测条件下,声传播模型、目标特性模型、环境噪声模型以及混响模型的优化选择,提出了航空双基地声纳性能预测方法,并针对典型的海洋环境进行了仿真实验.仿真结果表明该模型和仿真方法能预测不同态势下航空双基地声纳的信号余量和检测概率,可为航空声纳优化使用提供参考.     

LiF:Mg,Cu,P 'pin worms': miniature detectors for brachytherapy dosimetry

Dose measurements in brachytherapy 192Ir implants are often difficult due to large dose gradients and complex photon spectra. Therefore, tissue-equivalent detectors with a high spatial resolution, such as the highly promising LiF:Mg,Cu,P thermoluminescent detectors (TLDs) are required. It was the aim of the present work to ascertain if miniature LiF:Mg,Cu,P TLDs can effectively measure the dose distribution around 192Ir implants. 'Pin worm' TLDs (type MCP, diameter 0.6 mm, length 2 mm) were compared with GR-200R (SSDL, Beijing) rods cut in half. The TLDs were tested for reproducibility and energy dependence using high dose rate (HDR) and low dose rate (LDR) brachytherapy units. 192Ir measurements were performed in a tissue equivalent phantom accommodating hollow needles and catheters routinely used in brachytherapy. Pin worms had an average reproducibility of less than +/-2% (1 SD) and a detection limit of less than 10 microGy. The small dimensions of the pin worms allowed their placement within brachytherapy needles and catheters. The measured relative dose distribution was in good agreement with the predictions of a computerised treatment planning system (ADAC Pinnacle); however, limitations in the TLD energy correction did not allow for absolute dose comparison.     

The influence of plasticizer molecular weight on spreading droplet size of HPMC aqueous solutions using an indirect method

Film coating is a complex process that involves many factors. To ensure spreading and/or film capability, plasticizers are added. The role of different molecular weights of polyethylene glycol on the behavior of hydroxypropylmethylcellulose (HPMC) with different grades was determined and compared with values for the film without the plasticizer using a real method for spreading. The droplet size, distribution, and shape were analyzed as the criterion. The results show that the polymer grades and plasticizer types are important in droplet size formation.     

Wetting and spreading of molten aluminium against AlN surfaces

Wetting and spreading of molten aluminium against AlN substrates were investigated between 1100 and 1290°C. The contact angles decreased linearly with time under isothermal conditions between 1100 and 1200°C. The isothermal rate of spreading of molten aluminium against AlN substrates was constant between 1220 and 1290°C and the rate increased exponentially with increasing temperature. Crystals of Al4C3 nucleated and grew on the substrate surface beneath the liquid. However, the formation of Al4C3 may not be solely responsible for the changes in contact angle and spreading. It is postulated that carbon contamination from the substrate and/or experimental equipment coupled with the low oxygen partial pressure of the chamber in the presence of graphite, were primarily responsible for the observed contact angle and spreading phenomena. The activation energy for the spreading process was 448 kJ mol-1, suggesting the presence of some chemical reaction at the interface. Carbon-rich aluminium may be initiating a continuous surface reaction with the AlN substrates by reducing the native oxide layer on the substrate surface.     

Dynamical Interaction Between Information and Disease Spreading in Populations of Moving Agents

Considering dynamical disease spreading network consisting of moving individuals, a new double-layer network is constructed, one where the information dissemination process takes place and the other where the dynamics of disease spreading evolves. On the basis of Markov chains theory, a new model characterizing the coupled dynamics between information dissemination and disease spreading in populations of moving agents is established and corresponding state probability equations are formulated to describe the probability in each state of every node at each moment. Monte Carlo simulations are performed to characterize the interaction process between information and disease spreading and investigate factors that influence spreading dynamics. Simulation results show that the increasing of information transmission rate can reduce the scale of disease spreading in some degree. Shortening infection period and strengthening consciousness for self-protection by decreasing individual’s scope of activity both can effectively reduce the final refractory density for the disease but have less effect on the information dissemination. In addition, the increasing of vaccination rate or decreasing of long-range travel can also reduce the scale of disease spreading.     

Design and evaluation of a high data rate optical wireless system for the diffuse indoor channel using barker spreading codes and RAKE reception [optical wireless communications]

The performance of a high data rate optical wireless system (OWS) over the diffuse indoor infrared channel based on direct sequence spread spectrum (DSSS) techniques is highly sensitive to the properties of the aperiodic autocorrelation function and the spreading factor of the spreading sequence used. Ideally, the aperiodic autocorrelation function should have zero sidelobes in order to eliminate intersymbol interference caused by multipath propagation. In practice, such an ideal sequence does not exist in the binary field when data modulation is applied. For high data rates, a small spreading factor is desired in order to avoid an excessive system bandwidth. The family of Barker sequences is investigated in a DSSS-OWS. The Barker sequences are binary spreading sequences which exhibit small aperiodic autocorrelation values and short spreading factors. The system bit error rate (BER) performance is characterized on the diffuse indoor infrared channel when using RAKE reception. Results of BER against Eh/NQ are presented with data rate and spreading factor as parameters. The results demonstrate that of the seven Barker sequences existing, the length three Barker sequence {0 0 1} provides the best system design trade-off in respect of good BER performance and low implementation complexity.     

Investigations into the evaporation of liquefied gases spreading on land

This paper deals with the results of a theoretical study of the evaporation of liquefied gases spreading on land.Firstly it is shown that the evaporation rate of the above-mentioned liquids on nonpenetrable media can be calculated with the theory of heat transfer from a semi-infinite medium. Calculating the evaporation rate of liquids on penetrable media, it then appears that the porosity of the medium has an appreciable influence on the evaporation rate. The presence of moisture in the capillaries must also be taken into account.Finally the evaporation of cooled liquids spreading on land has been calculated, and it is assumed that the liquid spreads until a minimum layer thickness is reached.This study leads to the conclusion that the results of the calculated evaporation of liquefied gases on land are well in line with the experimental data relative hereto, although the model describing the spreading of such liquids on land cannot be verified due to the lack of experimental data existing at this time.     

A model for oil spreading in cold waters

A model for oil spreading on sea is developed based on forces acting in the horizontal dimension. It consists of conservation laws for volume and momentum. The model is valid for a complex slick geometry, and is suitable for coupling to a discrete element ice model or other complex boundaries, for example coast lines. The numerical interpretation of the model is based on a finite difference approach.     

The behavior of membrane proteins in monolayers at the gas–water interface: comparison between photosystem II, rhodopsin and bacteriorhodopsin

It has been postulated, without supporting evidence, for decades that proteins are denatured once spread in monolayers at the gas–water interface. In the present study, the effect of different experimental conditions on the structure of three membrane proteins has been investigated by polarization modulated infrared reflection absorption spectroscopy in situ in monolayers at the gas–water interface. We have found that photosystem II core complex (PS II CC) is less sensitive to denaturation than rhodopsin. In fact, denaturation of rhodopsin could only be prevented when spreading was performed at 4°C. In contrast, bacteriorhodopsin was found to remain native when monolayer spreading was performed in conditions that were found to denature both PS II CC and rhodopsin. This behavior may be explained by the two-dimensional crystalline structure of bacteriorhodopsin. In conclusion, conditions can be found where the native structure of membrane proteins is maintained after their spreading in monolayers at the gas–water interface.     

A numerical study of the scalar field in turbulent round jet with co-flowing stream

The influence of co-flow on a turbulent binary gas mixing round jet is numerically studied using a first and a second order turbulence closure models. The objective of the study is to obtain a better understanding of the flow structure and mixing process in turbulent variable-density jets. Comparisons between recently published experimental results and mean mixture fraction, the scalar turbulent fluctuation, and the jet spreading rate, feature reasonably good agreements. It is mainly shown that the co-flow reduces the jet spreading rate, but on the otherhand increases the mixing efficiency.An erratum to this article can be found at