A continuous approximation model for time definite many-to-many transportation

Time definite freight transportation carriers provide very reliable scheduled services between origin and destination terminals. They seek to reduce transportation costs through consolidation of shipments at hubs, but are restricted by the high levels of service to provide less circuitous routings. This paper develops a continuous approximation model for time definite transportation from many origins to many destinations. We consider a transportation carrier serving a fixed geographic region in which demand is modeled as a continuous distribution and time definite service levels are imposed by limiting the maximum travel distance via the hub network. Analytical expressions are developed for the optimal number of hubs, hub locations, and transportation costs. Computational results for an analogous discrete demand model are presented to illustrate the behavior observed with the continuous approximation models.     

Bus running time prediction using a statistical pattern recognition technique

Abstract

Given that real-time bus arrival information is viewed positively by passengers of public transit, it is useful to enhance the methodological basis for improving predictions. Specifically, data captured and communicated by intelligent systems are to be supplemented by reliable predictive travel time. This paper reports a model for real-time prediction of urban bus running time that is based on statistical pattern recognition technique, namely locally weighted scatter smoothing. Given a pattern that characterizes the conditions for which bus running time is being predicted, the trained model automatically searches through the historical patterns which are the most similar to the current pattern and on that basis, the prediction is made. For training and testing of the methodology, data retrieved from the automatic vehicle location and automatic passenger counter systems of OC Transpo (Ottawa, Canada) were used. A comparison with other methodologies shows enhanced predictive capability.     

Using non-real-time Automatic Vehicle Location data to improve bus services

Although real-time Automatic Vehicle Location (AVL) data is being utilised successfully in the UK, little notice has been given to the benefits of historical (non-real-time) AVL data. This paper illustrates how historical AVL data can be used to identify segments of a bus route which would benefit most from bus priority measures and to improve scheduling by highlighting locations at which the greatest deviation from schedule occurs. A new methodology which uses historical AVL data and on-bus passenger counts to calculate the passenger arrival rate at stops along a bus route has been used to estimate annual patronage and the speed of buses as they move between stops. Estimating the patronage at stops using AVL data is more cost-effective than conventional methods (such as surveys at stops which require much more manpower) but retains the benefits of accuracy and stop-specific estimates of annual patronage. The passenger arrival rate can then be used to calculate how long buses spend at stops. If the time buses spend at stops is removed from the total time it takes the bus to traverse a link, the remaining amount of time can be assumed to be the time the bus spends moving and hence the moving speed of the bus can be obtained. It was found that estimation of patronage and the speed of buses as they move between stops using AVL data produced results which were comparable with those obtained by other methods. However the main point to note is that this new method of estimating patronage has the potential to provide a larger and superior data set than is otherwise available, at very low cost.     

战略装车点选址模型研究

分析了建立区域战略装车点的政策性原则和关联因素,并根据铁路运输生产实际模拟了在供需均衡条件下选站建点系统架构,构建战略装车点多点选址多类变量混合0-1非线性规划模型(MSLSLP)。模型以社会总成本最小化为出发点,协同考虑决策者和客户双方利益,将选站建点的改扩建费用、可变费用和代表客户利益的运输成本共同纳入目标体系。将建立战略装车点后的运输特点要求与相关选址模型的共性约束相结合构造约束条件,使其更具针对性。最后,以相当规模数值算例验证了模型的有效性和可行性。     

基于多声纳基阵FDOA的联合定位技术及精度分析

主要对基于单平台多声纳基阵多普勒频率差的联合定位技术和精度进行了分析和推导,给出系统具体的定位公式和误差计算公式,并对系统的模型误差进行了分析.最后通过仿真,分析不同基阵布阵情况下的受控区域内GDOP的分布情况及基线和目标的深度等对GDOP的影响.仿真结果表明,定位误差与目标和基阵的位置、布阵形式等有关,定位误差随基线长度的增加而减小,当基线增大到一定长度时,定位误差最终趋向稳定,达到最小.     

Generating complete all-day activity plans with genetic algorithms

Activity-based demand generation contructs complete all-day activity plans for each member of a population, and derives transportation demand from the fact that consecutive activities at different locations need to be connected by travel. Besides many other advantages, activity-based demand generation also fits well into the paradigm of multi-agent simulation, where each traveler is kept as an individual throughout the whole modeling process. In this paper, we present a new approach to the problem, which uses genetic algorithms (GA). Our GA keeps, for each member of the population, several instances of possible all-day activity plans in memory. Those plans are modified by mutation and crossover, while bad instances are eventually discarded. Any GA needs a fitness function to evaluate the performance of each instance. For all-day activity plans, it makes sense to use a utility function to obtain such a fitness. In consequence, a significant part of the paper is spent discussing such a utility function. In addition, the paper shows the performance of the algorithm to a few selected problems, including very busy and rather non-busy days.     

Pole location control design of an active suspension system with uncertain parameters

This paper addresses the problem of robust control design for an active suspension quarter-car model by means of state feedback gains. Specifically, the design of controllers that assure robust pole location of the closed-loop system inside a circular region on the left-hand side of complex plane is investigated. Three sufficient conditions for the existence of a robust stabilizing state feedback gain are presented as linear matrix inequalities: (i) the quadratic stability based gain; (ii) a recently published condition that uses an augmented space and has been here modified to cope with the pole location specification; (iii) a condition that uses an extended number of equations and yields a parameter-dependent state feedback gain. Unlike other parameter-dependent strategies, neither extensive gridding nor approximations are needed. In the suspension model, the sprung mass, the damper coefficient and the spring constant are considered as uncertain parameters belonging to a known interval (polytope type uncertainty). It is shown that the parameter-dependent gain proposed allows one to impose the closed-loop system pole locations that in some situations cannot be obtained with constant feedback gains.     

基于DTA的OD估计方法的交通检测器优化布置模型研究

论文在探讨了动态交通分配和动态0D估计背景下的交通检测器优化问题的基础上，提出了基于DTA的动态OD估计方法的交通检测器布置原则；从预算，对路网中交通流量信息的覆盖程度，对关键路段的检测、对重复检测器的剔除等方面对路网交通检测方案进行约束，建立了交通检测器优化布置模型；最后将遗传算法用于交通检测器优化布置模型的求解，证明了基于DTA的动态0D估计方法的交通检测器优化布置模型的有效性。论文方法概念清楚、操作简单，是交通检测器优化布置的一种可行方法。     

车身薄壁件形位公差的分析与研究

根据汽车车身薄壁件的功能要求，提出了车身薄壁件采用形位公差的必要性，并指出了现行形位公差用于车身设计时所存在的问题。在对现行形位公差标准进行适当的补充的基础上，建立一个比较切合实际和较为完善的汽车车身薄壁件形位公差体系，并在南京汽车制造厂得到了实际应用。     

基于纹理特征和彩色特征的车牌定位算法

车牌定位是车牌自动识别系统的关键。提出了一种以纹理特征为主要手段，以彩色特征为辅助手段的多特征定位算法，对不同背景和光照条件下的各类车牌图像进行了实验，结果表明该算法是一种可行的方法。