A systemic overview of non‐motorized transportation for developing countries: An agenda for action

All through the twentieth century transportation planning and the implementation of transportation facilities in the developing world was heavily weighted toward motorized transportation (MT), despite the fact that non‐motorized transportation (NMT) constitutes a significant proportion of all trips. However, in the last two decades many researchers and practitioners all across the world have recognized the importance and advantages of NMT, and their investigations and findings have contributed toward identifying, if not mitigating, some of the more glaring problems in these countries. Unfortunately, most of these investigations have been performed in a piece‐meal and disjointed fashion. This paper explores the complex and sometimes poorly understood set of relationships between transportation and its links to a myriad of other factors, such as landuse, sustainability, safety, energy, ethical issues, value of time, telecommunication, environmental justice, and equity. The main objective of this paper is to provide a systemic overview of NMT by describing its multi‐dimensional aspects and to assist developing countries in formulating an “Agenda for Action”.     

A cross-section analysis of stock returns: The case of shipping firms

This paper undertakes an analysis of the determinants of the cross-section of expected stock returns of 19 shipping companies listed in the US, Norway, Stockholm and London. Various factors, including company stock market beta, divided yield, and financial leverage have been identified in the finance literature as determinants of share price performance. We capitalize on these findings and add one more industry specific factor, the average age of the company's fleet, to quantitatively analyse the determinants of the performance of shipping shock returns. We use the Fama-MacBeth methodology to empirically test whether the five factors above have a significant effect on shipping stocks' performance. Our results indicate that the industry specific factor (the average age of the fleet) plus financial leverage, are significant in explaining shipping stocks' returns, wheras the stock market beta and the dividend yield are far less significant.     

Multiobjective pricing of bus-subway services in Santiago,Chile

Presently, the surface transit system in Santiago, Chile is private and atomized. It operates in competition with the subway, covering long distances and causing congestion in the central business district. As the subway operates below capacity, integrated services with a common fare have been identified as both operatively and financially possible, making better use of resources and avoiding negative externalities. A multi-objective approach is formulated and applied to determine the price of the combined service, accounting for both users' benefits and operators' profit. The role of different parameters in the financial and operative constraints is analyzed in particular, as well as the conflicting nature of the objective functions. The non-inferior set of solutions is constructed and analyzed both in the decision variables space and in the objectives space, and solutions are compared against the present conditions.     

A two-layer model of the Rhine plume

The outflow of Rhine water into the shallow Southern Bight of the North Sea leads to almost discontinuous vertical density distributions and sharp frontal structures around the river mouth. Strong tidal motion, wind and baroclinic effects have large influence on the dynamics and dispersion of river water. A three-dimensional tidal model, including advective and diffusive transport of salinity, is used in the two-layer mode for simulation of Rhine water outflow to quantify the interaction of the different processes and the effect on dispersion and mixing of river water. Layer depths are adjusted in a way that no advective transports between upper and lower layer take place in case of sufficiently stable stratification. In case of weak or no stratification the upper layer depth is fixed, and advective transports between layers are computed. Model results show frontal eddy development and (limited) growing internal waves due to baroclinic instability. Comparisons with observational data are presented.     

Multicriteria ranking of urban transportation system alternatives

This paper presents the fundamentals of a new method to rank urban transportation system alternatives, taking into consideration multiple criteria. Those criteria can be quantifiable or not. The new method is founded on Utility Theory and it makes use of absolute weighting and pairwise comparisons. It has important practical advantages over other existing methods, the most important among those advantages being its capability to be understood and accepted by professionals and by the public. A numerical example is included in the paper.     

Meroplankton abundance in the Northeast Water Polynya: Insights from oceanographic parameters and benthic abundance patterns

We investigated meroplankton (planktonic larvae of benthic organisms) abundance and distribution in the Northeast Water (NEW) Polynya, located on the northeast coast of Greenland, from July 15 to August 15, 1992. Meroplankton was present at all sites visited (0.03–84.83 individuals per m³); at one station meroplankton comprised 8.28% of total zooplankton. Total meroplankton abundance was correlated with total zooplankton abundance and total benthic infaunal abundance but was not correlated with either microscopic carbon concentration or primary productivity. Examination of distribution data for barnacle nauplii and adults indicated that both adults and larvae were concentrated at the same locations. Patterns of distribution were also examined for stelleroid plutei, polychaete larvae and trochophores. There were distinct geographic patterns in total and class-specific meroplankton distributions, with maximal abundances occurring over the Belgica Bank and in the eastern regions of the Westwind Trough and minimal abundances in the Belgica Trough. The apparent control of meroplankton distribution by the hydrography of the region, coupled with the correlation between meroplankton, zooplankton and adult infaunal abundance, reinforces the hypothesis that hydrography plays a major role in controlling the distribution of biota in the NEW polynya (Ambrose and Renaud, 1995; Ashjian et al., 1995, 1997-this volume; Smith et al., 1995; Piepenburg et al., 1997-this volume).     

Dynamic tyre friction models for combined longitudinal and lateral vehicle motion

An extension to the LuGre dynamic friction model from longitudinal to longitudinal/lateral motion is developed in this paper. Application of this model to a tyre yields a pair of partial differential equations that model the tyre-road contact forces and aligning moment. A comparison of the steady-state behaviour of the dynamic model with existing static tyre friction models is presented. This comparison allows one to determine realistic values of the parameters for the new dynamic model. Via the introduction of a set of mean states we reduce the partial differential equations to a lumped model governed by a set of three ordinary differential equations. Such a lumped form describes the aggregate effect of the friction forces and moments and it can be useful for control design and online estimation. A method to incorporate wheel rim rotation is also proposed. The proposed model is evaluated by comparing both its steady-state as well as its dynamic characteristics via numerical simulations. The results of the simulations corroborate steady-state and dynamic/transient tyre characteristics found in the literature.     

PWM逆变器供电异步电机传动的去耦直接控制

提出一种用于脉宽调制(PWM)逆变器供电异步电机的转矩和定子磁通直接控制方法.这种被称为去耦直接控制(DDC)的基础是一个去耦矩阵,它允许对定子磁通和转矩单独控制.将该方法和著名的直接磁场定向控制(FOC)和定子磁通矢量控制(SFVC)进行比较.提出了2种基于DDC的方案.第一种是确定定子电压矢量,以便转矩和磁通跟踪其各自在一个采样周期内的基准轨迹.第二种是利用PI控制器分别控制转矩和定子磁通误差的动态特性.与FOC和SFVC相似,这些方法均考虑到了整个电机动态特性范围内不需要坐标变换,并可大幅度地降低计算工作量.这2处控制方案已经完成试验,并且与FOC和SFVC进行了比较.试验结果表明,所提出的PI-DDC控制非常有效.