基于马尔科夫链的60 GHz 点对点通信移动性优化

由于60 GHz通信在空气中可能会有高达20 dB的信号衰减,因此通信的范围和质量都可能受到影响．为此,IEEE 802.11 ad标准引入了能够定向增强信号和控制信号传播方向的波束成形技术来提高通信质量．然而,设备位置移动对波束成形的影响较大,它可能会导致通信质量下降甚至中断．为保证通信通畅,文中针对IEEE 802.11ad定义的点对点场景提出了波束成形优化算法．该算法基于马尔科夫链模型预测下一时刻设备的位置,并且提前调整相应的波束方向．该算法利用动态设备的相对位置和波束转动角度信息,代替了原波束成形方法中的波束扫描等过程．在仿真实验中,通过信息交互次数验证了该算法的有效性,提高了波束成形过程的效率,并且使该过程中的能量消耗降低了60％．     

水面舰船锚装置设计探讨

锚装置是水面舰船上的一个重要设备,其设计优劣直接关系舰船的安全性和操作方便性。本文根据以往多型舰船锚装置的设计经验,总结了锚装置主要组成部件的设计选型原则及计算方法等,供业内人员共同探讨,亦可为初学者提供设计指导。     

航运服务产业链的内涵与生成机理

为研究航运服务产业链的内涵与生成机理,在对国内外相关文献梳理的基础上,提出了航运服务产业链的定义,分析其产业构成.在对航运服务产业链生成的三类研究路径分析的基础上,构建了一个综合分析框架:外部促进、内部驱动和适应性选择.根据该分析框架,分析了航运服务产业链生成的外生机理和内生机理,归纳了其生成的动力.     

基于供应链的造船企业供应商关系管理研究

文章基于供应链的内涵,以当前造船企业供应商关系管理所面临的难题为切入点,从造船企业供应商关系管理的现状与存在的问题出发,阐述加强供应商关系管理的重要意义,提出了造船企业供应商关系管理的考评、激励、开发等一系列方法与策略。     

An exploration of shoppers travel mode choice in visiting convenience stores in the UK

Using data from over 2000 convenience store customers within and outside London, this paper explores how individuals access their convenience stores and how significant the influence of their socio-demographics, shopping types and trip chaining is to their mode choice in visiting the stores. Trip chaining is found to be crucial in influencing customers' mode choice and their visit frequency. The application of logit models also shows that frequent shoppers are the ones most likely to visit the stores on foot. Interestingly, the estimation results also show that the location's density, shopping types and the day of the week are not significant in influencing travel modes. Customers who live in the most deprived areas are less likely to use a private car in visiting the stores.     

应用型海运本科院校航运经贸专业群建设研究

专业群建设是应用型本科院校实现内涵发展,提升外部竞争力的重要途径．广州航海学院应充分发挥行业办学传统及新建本科院校的后发优势,借鉴应用型海运本科专业建设实践经验,把握我国航运服务业产业链发展的高端化趋势,对接航运服务业构建航运特色经贸专业群,实现专业人才培养与服务产业发展的双重贡献．     

A simulation of the simple Mohring model to predict patronage and value of resources consumed for enhanced bus services

Choosing between the competing approaches to providing enhanced bus services requires the ability to predict the effects on patronage and overall benefits to society in terms of Value of Resources Consumed (VRC) of any proposed change. One common approach uses the Mohring model of 1972 and its successors to optimise one or more aspects of the supply of transit services given various level of demand. This paper simulates the operation of a simple circular bus route using the equations of a basic Mohring type model and a Decision Support System (DSS) to endogenise demand under the assumption that there is a fixed demand for travel but commuters can choose between the bus and private vehicle. The selected approach recognises that demand for a particular mode of travel is predicated on the speed of the vehicle in service which is itself determined by the demand for that vehicle (in this model or boarding and alighting time) rather than being determined exogenously. This creates an iterative feedback mechanism whereby changes to the attributes of the bus and car alter mode choice and the speed in service of the bus which, in turn, alters mode choice. The simulation is used to predict changes to patronage and VRC under scenarios regarding changes to the transport network (in terms of fares and running costs, frequency and spacing of bus stops) using parameters from both a Multinomial Logit (MNL) and a Mixed Multinomial Logit (MMNL). The results demonstrate that there are large differences in the size and, in some cases, direction of predicted changes to patronage, VRC and revenue, depending on whether the parameters of the MNL or MMNL model are used.     

基于投影和密度的高维数据流聚类算法

在经典数据流的聚类算法基础之上,提出了一种基于投影和密度的高维数据流聚类算法——HpDenStream,该算法结合滑动窗口技术,采用投影算法对高维数据流进行降维处理,并运用密度聚类算法对降维后的数据进行异常数据检测。仿真实验结果表明:该方法占用的存储空间小,算法的工作量少,并提高了算法的执行效率。     

有限水深三维脉动源格林函数数值算法研究

由于柯西主值积分的奇异性和贝塞尔函数的振荡性,有限水深情况下复杂格林函数及其导数的精确数值求解一直是浅水中波浪水动力计算的难点,因此寻找格林函数的精确数值解显得非常重要.通过对格林函数奇异项进行变形推导,文中给出了一种去掉了奇点的新积分形式.另外通过改进前人推导的Gauss-Laguerre积分方法,给出了一种改进的新Gauss-Laguerre积分方法.格林函数及其导数的数值结果显示文中给出的两种新方法可以有效地计算复杂格林函数及其导数值.最后对这两种方法、级数解以及传统的Gauss-Laguerre积分方法的计算精度和效率进行了比较研究,结果显示文中给出的两种方法的计算精度高于传统的Gauss-Laguerre积分方法,但其计算效率低于级数解.但在接近于0的近场附近级数解失真,而文中提出的改进的新Gauss-Laguerre积分方法可以获得正确结果.同时当频率和水深均较大时级数解失真,而文中提出的方法也可以获得正确结果.最后针对这些方法的优缺点,该文提出了建议的策略用于计算有限水深格林函数.     

海外散货码头多点系泊结构设计

海外干散货码头常设有多点系泊结构,船舶等待装船时系泊使用,其适应性强,有较强的成本优势,在国内采用尚不广泛。总结吉布提盐业码头项目和几内亚铝业GAC码头项目中多点系泊结构的设计经验,研究多点系泊结构的荷载、工况组合以及锚块、锚链、浮筒和快速脱缆钩等设计方法,并结合optimoor软件对理论计算结果进行了数值分析验证。