遮阳棚对隧道进出口明暗适应的影响规律研究北大核心CSCD

为研究隧道进出口路段驾驶员明暗适应的特性及遮阳棚对明暗适应过程的影响规律,文章依托紫荆隧道(无遮阳棚)及巴朗山隧道(有遮阳棚)进行驾驶试验,以驾驶员瞳孔直径及其变化速率为研究参数,分析遮阳棚对隧道进出口路段明暗适应的缓冲效果。研究结果表明:暗适应过程90%以上发生在洞内段,明适应过程54.61%以上发生在洞内段;在隧道进口段暗适应过程中,通过遮阳棚时间为2 s时,最大瞳孔直径变化速率下降4.84%,通过遮阳棚时间为5 s时,最大瞳孔直径变化速率下降33.58%;在隧道出口段明适应过程中,通过遮阳棚时间为2 s时,最大瞳孔直径变化速率下降38.75%,通过遮阳棚的时间为5 s时,最大瞳孔直径变化速率下降49.97%。     

Assessment of economic impacts from unexpected events with an interregional commodity flow and multimodal transportation network model

Loss and damage caused by unscheduled events, especially earthquakes, have sudden and significant impacts not only on the region’s economy where the event occurs but also on other regions. The New Madrid Seismic Zone, located in the center of the United States, could have great impacts on economic activities related to this area, if a major earthquake occurred. Based on the 1993 US Commodity Flow Survey [US Commodity Flow Survey, 1993. Available from: <http://www.bts.gov/ntda/cfs/prod.html>], more than 42% of total commodity flows in the US are related to the greater Midwest, which includes the New Madrid Seismic Zone. If a catastrophic earthquake occurred in this area, the indirect damages could spread far beyond the region, and could have sizable impacts on other regions. A model of interregional commodity flows, incorporating regional input–output relationships, and the corresponding transportation network flows, was applied to assess the economic impacts of such an unexpected event. The economic impacts from the event are described for three hypothetical scenarios, analyzing the magnitude and the extent of the direct and indirect impacts. These analytical results may be used to propose strategic management of the recovery and reconstruction efforts after the event.     

Book review

According to the latest BIMCO and Drewry reports, there is a global shortage of officers for the worlds’ merchant fleet. This article focuses on the South African labour market for officers and examines some of the maritime education and training challenges facing these officers in accessing global labour markets. The paper argues that despite processes of globalisation, the nation state can still be an important actor in shaping global labour markets. Using a qualitative approach, interviews were conducted with 10 key informants in the maritime human resources management sectors in South Africa. Interview data was analysed and coded for themes using NVivo qualitative data analysis software (QSR International Pty Ltd., Version 10, London, UK). This was theoretically informed by Braun &; Clarke’s six-step method of thematic analysis. This was combined with a review of labour market statistics to demonstrate that the key challenges facing South African officers are the lack of training berth availability and the lack of South African ship ownership. The solutions adopted by the state includes a limited adoption of best practices adopted by global MET institutions in the United Kingdom, Australia, Singapore, Taiwan and Nigeria. The article contributes to filling the gap in empirical-based maritime studies that are located on Africa.     

Seaport Development and Coastal Management Programs: A National Overview

Oysters have been harvested on the east coast of Australia for many thousands of years. Coastal Aboriginal communities used the extensive estuarine oyster resource and may have farmed oysters by establishing shell cultch beds in shallow areas of estuaries. The British colonization of Australia commenced in 1788 and oysters were initially used for food and production of lime. Concerns about unsustainable exploitation led to introduction of legislation that directed the oyster industry to aquaculture in 1884. Translocation of oyster stock for fattening, from New Zealand to Australian east coast estuaries, was encouraged. Here evidence is presented that this activity resulted in “mudworm disease” appearing in oyster farming estuaries on the Australian east coast between 1880 and 1900. The pandemic permanently destroyed natural sub-tidal oyster reefs and forced the oyster industry to adopt avoidance farming techniques including intertidal farming to cope with mudworm.     

采用单电压源逆变器双异步电动机结构提高机车传动系统的性能

介绍了一种特殊的多电机多变流器系统(MMS)结构,即专为轨道牵引设计的单逆变器双电机结构.牵引设备必须具有良好的转矩响应,为了控制两台电动机的转矩,可以采用基于传统磁场定向控制(FOC)的协调控制结构.单逆变器双异步电动机传动系统可以提高机车性能,降低由内部和外部干扰产生的不良影响,对其系统性能与传统的机车传动控制系统的性能进行了比较.机车制造商已对仿真模型进行了确认.根据结果对这2种控制方式进行了性能分析,而且考虑了该牵引系统中的4种特性干扰.     

Estimating the inefficiency in the Norwegian bus industry from stochastic cost frontier models

A stochastic cost frontier function based on data from 170 of the 175 Norwegian subsidized bus companies is estimated under two alternative presumptions regarding the distribution of the inefficency among the bus operators. When the inefficiency is assumed to be half-normally distributed, the average inefficiency in the industry is estimated to be 13.7 per cent. This calculated value is nearly halved (7.2 per cent) when the exponential distribution is applied, while the ranking of the companies according to inefficiency is unchanged. By regressing the estimated inefficiency values for each company on some exogenous variables describing its ownership structure and the subsidy policy which it faces, it is seen that inefficiency of the companies which negotiate with the public authorities over the subsidy amounts is slightly higher than the inefficiency of the companies which face a subsidy policy based on cost norms. Our analysis gives, however, no significant differences in the efficiency between privately owned bus companies and publicly owned bus operators, and shows only minor economies of scale.     

Sequential optimization approach for the multi‐class user equilibrium problem in a continuous transportation system

We consider a city region with several facilities that are competing for customers of different classes. Within the city region, the road network is dense, and can be represented as a continuum. Customers are continuously distributed over space, and they choose a facility by considering both the transportation cost and market externalities. More importantly, the model takes into account the different transportation cost functions and market externalities to which different customer classes are subjected. A logit‐type distribution of demand is specified to model the decision‐making process of users' facility choice. We develop a sequential optimization approach to decompose the complex multi‐class and multi‐facility problem into a series of smaller single‐class and single‐facility sub‐problems. An efficient solution algorithm is then proposed to solve the resultant problem. A numerical example is given to demonstrate the effectiveness and potential applicability of the proposed methodology.     

Does Weight matter? A Statistical analysis of the SSY Capesize index

This paper examines the statistical properties of 19 dry cargo rate series, which are used in the construction of index numbers measuring dry cargo market conditions for Capesize vessels. It is shown that the series are extremely highly correlated. They are also non-stationary. The presence of cointegration is established. It is argued that this implies that rebasing the index numbers using different weights makes little difference to the information derived from the index itself, because of the high correlation between the series and the presence of cointegration. Changing the weighting structure does not alter the information derived from the index in any material way because of these properties.     

Heterogeneous traffic flow modelling for an arterial using grid based approach

A grid based modelling approach akin to cellular automata (CA) is adopted for heterogeneous traffic flow simulation. The road space is divided into a grid of equally sized cells. Moreover, each vehicle type occupies one or more cell as per its size unlike CA traffic flow model where each vehicle is represented by a single cell. Model needs inputs such as vehicle size, its maximum speed, acceleration, deceleration, probability constants, and arrival pattern. The position and speed of the vehicles are assumed to be discrete. The speed of each vehicle changes according to its interactions with other vehicles, following some stochastic rules depending on the circumstances. The model is calibrated and validated using real data and VISSIM. The results indicate that grid based model can reasonably well simulate complex heterogeneous traffic as well as offers higher computational efficiency needed for real time application.     

Robust control of traffic networks under uncertain conditions

Uncertainty of traffic network operations has been a subject of lively debate in the last decade. However, little effort has been put in developing control frameworks that are not only aimed at improving the average performance of the system, but also at improving the system robustness and reliability. In fact, it can be argued that most of the current control approaches are only aimed at improving the efficiency, which can even be counterproductive from a robustness point of view. The main contributions of this article is the proposition of a new control framework based on the notion of controlled Markov processes, which explicitly takes into account the uncertainty in predicted traffic conditions and system performance. Furthermore, in contrast to traditional optimal control approaches, the objective function can include general statistic of the random system performance, such as the mean, standard deviation or 95‐percentile. The contribution aims to make clear how different performance function specifications yield different control strategies. This is shown for a relatively simple case study.