Modelling and characterisation of Mo2C precipitation and cementite dissolution during tempering of Fe–C–Mo martensitic steel

Abstract

The precipitation and Ostwald ripening behaviour of needle shaped Mo₂C particles during the tempering of a ternary Fe-C-Mo martensitic steel have been characterised and modelled, taking account of local equilibrium, the capillarity effect, and the simultaneous enrichment and dissolution of cementite. Particles of Mo₂C are represented as paraboloids of revolution, with the tip radius chosen to yield the maximum lengthening rate. Transmission electron microscopy has been used to validate the theory; measurements of the average length, volume fraction, and number density of particles showed good agreement with experimental observations.     

异构车载自组网中两级资源调度机制研究

WiMAX网络和WAVE网络中资源调度方式不同,但又需要在移动网关节点处进行互通。为此,提出一种基于反馈的两级资源调度机制。在WiMAX网络中采用基于权重的轮询调度,针对WAVE网络提出一种基于反馈的EDCA接入方式,使节点各业务的发送速率契合WiMAX 网络中的调度规则。仿真结果表明,相比同类方法,该机制使系统的平均传输时延降低至20 ms,网关节点处的排队队长缩短了50%。     

面向装配设计的标准件库的研究与开发

在对标准件库技术现状分析的基础上，针对装配设计的特点，开发了面向装配的标准件库CAD系统。介绍了系统的总体框架，并重点论述标准件在装配设计中关联技术的实现方法。     

Statistical Modeling at 18 GHz Using of Broadband Wireless LAN Channels Directive Antennas

Measurements of indoor radio channels in thefrequency domain were carried out in acommunicationslaboratoryat 18-19 GHz using directiveantennas of beamwidths equal to 25 V × 53 H.Statistical modeling of the channel parameters wasderived from 800 data profiles. The main resultsobtained are: (1) The arrival times of the multipathcomponents have a clustering property, with itsstatistical distribution fitting very well to themodified Poisson process; (2) the amplitudes of themultipath components and the mid-scale power attenuationobey the log-normal distribution; (3) the power decreasewith the antenna separation exponentially, with theexponent around 1.9 for Line-of-Sight (LOS) locations,2.7 for non-line-of-sight (NLOS) locations, and 2.2 forboth LOS and NLOS locations; (4) the RMS Dels are generally quite small, with a global meanvalue of 4.8 ns, and standard deviation value of 5.3 ns.Its statistical distribution was found to follow thenormal distribution for the same antenna separation aswell as for all the measurement data with differentantenna separations; (5) the RMS delay spread isinversely proportional to the channel coherencebandwidth, with the proportional coefficient greater forLOS data than for NLOS data, and also decaying with theincrement of antenna separations.     

基于WAVE和XMPP的车队即时通信系统

在分析车队通信采用的三种通信方式的基础上,提出一种基于车辆通信标准WAVE(车载环境下的无线接入)和即时通信标准协议XMPP(可扩展的消息和出席信息协议)的车队即时通信系统WXMIM(WAVE and XMPP based Motorcade Instant Messaging System),对其应用场景、协议框架和通信流程进行介绍,并在Android平台下进行主要功能的实现,结果证明本系统能够满足车队即时通信的要求。     

WAVE协议栈下基于高斯混合模型的无线定位研究

无线定位是车联网中各应用的基础,对实时性和精度要求更高。基于此,本文提出了一个在WAVE系统下基于混合高斯模型的位置指纹定位算法。该算法由离线训练和在线定位两部分组成,采用GMM对离线训练阶段的指纹数据库进行聚类建模处理,并在定位阶段对结果采用多点均值方法,不仅降到了系统定位误差,也减少了定位阶段的运算量,提高了定位的实时性。实验结果表明,该算法有较好的定位精度和实时性,为WAVE环境下的快速定位进一步研究提供有效参考价值。     

车间通信技术的研究

近年来,随着汽车的日益普及和汽车电子产业的迅速发展,人们利用车间通信技术来解决驾车安全问题,并帮助建立智能交通系统,提高交通管理效率.然而,高速移动、变化的汽车行驶环境,需要与之相应的通信和网络技术的支持.本文将介绍车间通信的主要应用以及实现车间通信的主流技术.     

Dissemination of safety messages in IEEE 802.11p/WAVE vehicular network: Analytical study and protocol enhancements

Multi-channel IEEE WAVE 1609.4 protocol has been proposed to guarantee the co-existence of safety and non-safety applications over the same Vehicular Ad hoc NETwork (VANET) scenario. While the usage of multi-channel avoids the risk of collisions between applications allocated on different frequencies, its implementation on a single-radio transceiver poses some major concerns about the effective utilization of the channel resources. In this paper, we study the performance of safety applications over multi-channel single-radio VANETs, and we present three novel contributions in this regard. First, we propose an analytical analysis and a simulation study of IEEE 1609.4. We show the harmful impact of synchronous channel switching on the message delay and delivery ratio. Second, we investigate the problem of dissemination of safety broadcast messages over multi-channel VANETs, where the network is intermittently disconnected, due to the alternation of control and service intervals. Finally, we propose a WAVE-enhanced Safety message Delivery (WSD) scheme to enable fast dissemination of safety messages over multi-channel VANETs, while guaranteeing compatibility with the existing WAVE stack. To this aim, we formulate the dissemination problem as a multi-channel scheduling problem. We further introduce cooperation among vehicles to reduce the dissemination latency. Simulation study shows the ability of the WSD scheme to enhance the performance of IEEE 1609.4 in terms of message delay and delivery ratio under different topologies and various applications.     

超变量几何相关性技术WAVE及应用

20世纪80年代参数化特征建模技术的崛起，使得零件的编辑修改更加方便，数据的可重复利用率和产品设计效率大大提高。是CAD技术的突破。但是。参数化特征建模技术是基于零部件级的技术。而超变量几何相关性技术WAVE是基于装配级的全相关总体参数化技术，特别适合于大型复杂产品的设计，是产品系列化、变型产品的快速设计变更的强有力工具，是参数化造型设计与系统工程的有机结合，是CAD技术的新突破。     

Analysis of adjacent channel interference using distribution function for V2X communication systems in the 5.9‐GHz band for ITS

Many use cases have been presented on providing convenience and safety for vehicles employing wireless access in vehicular environments and long‐term evolution communication technologies. As the 70‐MHz bandwidth in the 5.9‐GHz band is allocated as an intelligent transportation system (ITS) service, there exists the issue that vehicular communication systems should not interfere with each other during their usage. Numerous studies have been conducted on adjacent interfering channels, but there is insufficient research on vehicular communication systems in the ITS band. In this paper, we analyze the interference channel performance between communication systems using distribution functions. Two types of scenarios comprising adjacent channel interference are defined. In each scenario, a combination of an aggressor and victim network is categorized into four test cases. The minimum requirements and conditions to meet a 10% packet error rate are analyzed in terms of outage probability, packet error rate, and throughput for different transmission rates. This paper presents an adjacent channel interference ratio and communication coverage to obtain a satisfactory performance.