Physical distribution from a warehouse: Vehicle coverage and inventory levels

This paper studies the costs involved in distributing items from a warehouse or depot to randomly scattered customers on a day-to-day basis. Two trade-offs are explored simultaneously. The first one arises because by accumulating large inventories at the depot it is possible to build more efficient distribution tours. This trade-off has already been explored for both distribution of goods (Burns et al., 1983) and passengers (Daganzo et al., 1977; Hendrickson, 1978). Another tradeoff, which involves the length of individual vehicle tours (Clarens and Hurdle, 1975), balances the inventory inside the vehicles against the transportation cost. Banks et al. (1982) have considered both of these tradeoffs simultaneously in the context of passenger transportation, but used a somewhat unrealistic model for vehicle routing. This paper is similar to the latter reference but uses a different routing strategy. It also illustrates how the nature of the objects carried (cheap goods, expensive goods, people, etc.) affects the optimal configuration of the distribution system and the overall distribution costs. Usually there is an optimum partitioning of the service area into districts and an optimum dispatching frequency in each district. The results can vary tremendously, depending on factors such as: the inventory carrying cost per item per unit time, the transportation costs, the demand per unit area and unit time, the average distance from the depot, the average vehicle speed and the time per stop.As an illustration of the ideas, a hypothetical limousine service from an airport is analyzed. The example is used to demonstrate how dramatically the optimal system configuration depends on the nature of the items carried.     

Transit performance evaluation in the U.S.A.

Performance of transit agencies in the United States improved during the 1980s. At the beginning of the decade, Americans had become disenchanted with transit; legislation was passed that required agencies to report performance and accept regular audits. Theory underlying these policies is examined in four components: dimensions for policy objectives, indicators, information systems and incentives. Three programs are examined: federal triennial reviews that monitor compliance with planning and grant requirements, California performance audits that analyze goals and track performance on five indicators and the Los Angeles program that encourages improvement by offering incentive payments for better-than-average performance. The California audits have been the most successful.     

通用大宇沉浮录·上篇·

2002年通用汽车决定收购倒闭的韩国大宇汽车组建通用大宇汽车技术公司(GMDAT)时,曾引来业界一片质疑之声,甚至通用董事会中也有成员持怀疑态度。现在回头来看,通用收购大宇是一件无比明智的决定。这家以打造低制造成本、低级别车型的公司经过几年的发展。不仅实现高速增长,还成为了通用面向欧洲、亚洲甚至北美市场重要的研发中心,以及公司全球发展计划中的核心组成部分。为了更深入地了解大宇的发展,Global Insight特别就该收购案中的战略关系,以及就过去五年里改变大宇的关键因素等问题,采访了曾任通用大宇汽车和科技公司总裁兼首席执行官,现升任通用汽车亚太区总裁的Nick Reilly先生。     

Optimal control of brakes and steering for autonomous collision avoidance using modified Hamiltonian algorithm

ABSTRACT

This paper considers the problem of collision avoidance for road vehicles, operating at the limits of friction. A two-level modelling and control methodology is proposed, with the upper level using a friction-limited particle model for motion planning, and the lower level using a nonlinear 3DOF model for optimal control allocation. Motion planning adopts a two-phase approach: the first phase is to avoid the obstacle, the second is to recover lane keeping with minimal additional lateral deviation. This methodology differs from the more standard approach of path-planning/path-following, as there is no explicit path reference used; the control reference is a target acceleration vector which simultaneously induces changes in direction and speed. The lower level control distributes vehicle targets to the brake and steer actuators via a new and efficient method, the Modified Hamiltonian Algorithm (MHA). MHA balances CG acceleration targets with yaw moment tracking to preserve lateral stability. A nonlinear 7DOF two-track vehicle model confirms the overall validity of this novel methodology for collision avoidance.     

全球去煤化亚洲正提速

对于煤炭,丧钟已然敲响,而石油和天然气也时日不多.中国率先做出了在2060年之前实现净零排放的承诺,随后日本和韩国也称将在2050年实现同样目标,这些表态给金融市场发出了响亮而明确的信号. 在世界其他地区开始转向自己国内更为便宜的可再生能源之后,化石燃料出口国曾寄厚望于在亚洲地区的煤炭进口,然而以上近期的转变只能让他们...