编者的话

<正>北汽福田与戴姆勒,双方采用了以对等出资筹建新中重卡合资公司的模式,成立的合资公司只采用福田欧曼单一品牌。注入奔驰技术的新产品上将被烙上"FOTON"的LOGO,而提供戴姆勒核心动力的产品,则在驾驶室上打上"戴姆勒动力"的字样。     

严峻问题

今年关于太平洋航线有两个不确定因素,即美国进口量增长将会大大放缓,同时美国出口量会继续增加.因此,几乎所有其他的问题都是不确定的:进口量是否会增长还是会减少?     

Host specificity in copepod parasites of deep-sea fishes

Parasitic copepods belonging to two orders, Siphonostomatoida and Poecilostomatoida, are frequently reported from fish hosts in the deep sea. Three families of copepods are most commonly encountered, Sphyriidae, Lernaeopodidae and Chondracanthidae, but members of another four families, Hatschekiidae, Pennellidae, Philichthyidae and Hyponeoidae, are occasionally recorded. These parasites utilise various deep demersal fishes as hosts, especially species of the most abundant families, Macrouridae, Moridae, Synaphobranchidae and Alepocephalidae. Host specificity levels are variable, as for shallow-water fishes. In contrast, few parasites are regularly reported from fishes inhabiting the pelagic water column away from the bottom and away from the near-surface zone. Only the pennellids Sarcotretes scopeli and Cardiodectes medusaeus appear common on pelagic fishes, in the Atlantic and Pacific respectively. Host specificity levels in these two pennellid species are relatively low. It is speculated that the difficulty of encountering a host in the vast pelagic biome has restricted the diversity of parasitic copepods that have successfully colonized pelagic fishes.     

Access control policies without inside queues: Their properties and public policy implications

An access control policy that eliminates all queues beyond the entry points to a network has obvious benefits, which include smooth travel and predictable travel times inside the network. Yet it has never been proven, to the best of our knowledge, whether excluding inside queues yields sub-optimal network performance or, in other words, allowing inside queues can actually further reduce the system travel cost. Moreover, it is not clear whether an optimal control policy derived from efficiency considerations can also be a fair policy to all road users. This paper provide answers to these questions in the context of a monocentric network. By analyzing the structure of the access control problem considering all feasible policies (with/without inside queues), we show that the minimal system cost realizable by access control can be obtained without directly solving a non-convex optimization program, and can indeed always be achieved by a control policy excluding all of the inside queues. These optimal policies are defined by a polyhedral set and a Finite Generation Algorithm can be applied to derive the analytical form of this set. The optimal policies are not unique in general, thus making it possible to achieve both minimal system cost and fairness simultaneously.     

Factors affecting the environmental impact of pavement wear

Wear at the interface between flexible pavements and tires influences pavement life, pavement cycle costs, and tire consumption, and is a source of environmental harm. Wear-related processes evolve over time and are affected by a number of boundary conditions, such as interface fluids, water and fuels. We develop a model explaining and predicting mass losses in flexible pavements under carefully controlled conditions, and with estimation of the related environmental costs. We also employed an accelerated loading test. Under normal conditions, the environmental impact of pavement wear is not greatly influenced by mix type or volumetrics. Indeed, the presence of hazmat materials, traditional, dense mixes have an environmental impact that is appreciably lower than that of porous European mixes.     

Equilibria of bilateral taxi–customer searching and meeting on networks

This paper proposes an equilibrium model to characterize the bilateral searching and meeting between customers and taxis on road networks. A taxi driver searches or waits for a customer by considering both the expected searching or waiting time cost and ride revenue, and a customer seeks a taxi ride to minimize full trip price. We suppose that the bilateral taxi–customer searching and meeting occurs anywhere in residential and commercial zones or at prescribed taxi stands, such as an airport or a railway station. We propose a meeting function to spell out the search and meeting frictions that arise endogenously as a result of the distinct spatial feature of the area and the taxi–customer moving decisions. With the proposed meeting function and the assumptions underlying taxi–customer search behaviors, the stationary competitive equilibrium achieved at fixed fare prices is determined when the demand of the customers matches the supply of taxis or there is market clearing at the prevailing searching and waiting times in every meeting location. We establish the existence of such an equilibrium by virtue of Brouwer’s fixed-point theorem and demonstrate its principal operational characteristics with a numerical example.     

Tests on ultimate strength of hull box girders made of high tensile steel

The experimental results of the collapse of three box girders subjected to pure bending moment are presented. The structures are made of high tensile steel of 690 MPa of nominal yield stress reinforced with bar stiffeners of the same material. The moment curvature curves are presented covering the pre- and post-collapse regions. The modes of collapse for each box girder are discussed considering the variation on the panel's slenderness. The concept of efficiency of high tensile steel structures is introduced. The concept is very useful to identify the governing parameters affecting the ultimate strength of 3D structures under predominant bending moment.     

Socio-demographic and built environment influences on the odds of being overweight or obese: The Atlanta experience

This paper explores the association of socio-demographic and built environment characteristics on the odds of being overweight and obese using data from the Atlanta SMARTRAQ travel survey. A new methodological framework based on a multinomial logit (MNL) model and an enhanced odds ratio plot is presented. The use of an MNL model overcomes limitations of many prior studies that employ a sequence of binary logit models to examine multiple weight categories. The use of an enhanced odds ratio plot provides important information into the relative importance of socio-demographic and built environment characteristics. Several new findings for the Atlanta area result from this study. Socio-demographic variables, including age and educational attainment, exhibit a non-linear relationship with the odds of being overweight or obese. Gender, age, ethnicity, and educational attainment are strongly associated with the odds of being overweight or obese, while income and number of students between 5 and 16 years old in the household have smaller effects. Built environment characteristics such as increased net residential densities and enhanced street connectivity are associated with reductions in the odds of being overweight and/or obese. Relative to socio-demographic variables, however, such built environment characteristics have a much smaller impact on describing the odds of being overweight or obese.