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Transportation - Travel is one of the most important facilitators of life and has been widely acknowledged as a prerequisite for economic and social activity. Research developing in recent decades... 相似文献
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To identify the potential relationship between Pheaocystis globosa bloom conditions and seawater properties, a hydrobiological survey was performed in the inshore waters of the Eastern English Channel over the course of the phytoplankton spring bloom. Chlorophyll concentration, auto- and hetero/mixotrophic composition of protists and standing stock, and seawater viscosity were measured weekly from March to June 2004. The decline of the bloom is characterized by a massive foam formation in the turbulent surf zone. Before foam formation, seawater viscosity significantly increased, showing a significant positive correlation with chlorophyll concentration. In contrast, after foam formation this correlation was negative, seawater viscosity kept increasing despite a sharp decrease in chlorophyll concentrations. No significant correlation has been found between seawater viscosity and the composition of the phytoplankton assemblages observed during the survey. However, significant positive correlations have been found between seawater viscosity and both the size and the abundance of P. globosa colonies. From the correlation patterns observed between chlorophyll concentration and seawater viscosity, we suggest that the rheological properties of seawater are mainly driven by extracellular materials associated with colony formation and maintenance rather than by cell composition and standing stock. 相似文献
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HE Tseng J. Asgari D. Hrovat P. van der Jagt A. Cherry S. Neads 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2005,43(3):199-216
In the pursuit of an objective rating on vehicle stability performance, it is always desirable to reduce disturbances and inconsistencies during experimental evaluations, especially the ones introduced by human drivers. This paper presents the development of a steering robot designed for closed-loop steering tasks during evasive manoeuvres. It describes the controller structure and discusses experimental results, in addition to simulation/vehicle model verifications and theoretical control analysis. 相似文献
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Vincent A.C. van den Berg 《Transportation Research Part A: Policy and Practice》2012,46(10):1608-1622
Most dynamic models of congestion pricing use fully time-variant tolls. However, in practice, tolls are uniform over the day, or at most have just a few steps. Such uniform and step tolls have received surprisingly little attention from the literature. Moreover, most models that do study them assume that demand is insensitive to the price. This seems an empirically questionable assumption that, as this paper finds, strongly affects the implications of step tolling for the consumer. In the bottleneck model, first-best tolling has no effect on the generalised price, and thus consumer surplus remains the same as without tolling. Conversely, under price-sensitive demand, step tolling increases the price, making the consumer worse off. The more steps the toll has, the closer it approximates the first-best toll, thereby increasing the welfare gain and making consumers better off. This indicates the importance for real-world tolls to have as many steps as possible: this not only raises welfare, but may also increase the political acceptability of the scheme by making consumers better off. 相似文献
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Maksym Spiryagin Peter Wolfs Colin Cole Sebastian Stichel Mats Berg Plöchl Manfred 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2017,55(8):1241-1264
The main task for heavy haul railway operators is to reduce the cost of exported minerals and enhance the long-term viability of rail transport operations through increasing productivity by running longer and heavier trains. The common opinion is that this is achievable by means of implementation of high adhesion locomotives with advanced AC traction technologies. Modern AC high adhesion locomotives are very complex mechatronic systems and can be designed with two alternative traction topologies of either bogie or individual axle controls. This paper describes a modelling approach for these two types of AC traction systems with the application of an advanced co-simulation methodology, where an electrical system and a traction algorithm are modelled in Matlab/Simulink, and a mechanical system is modelled in a multibody software package. Although the paper concentrates on the analysis of the functioning for these two types of traction control systems, the choice of reference slip values also has an influence on the performance of both systems. All these design variations and issues have been simulated for various adhesion conditions at the wheel–rail interface and their influence on the high traction performance of a locomotive equipped with two three-axle bogies has been discussed. 相似文献
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Land use can influence walking (measured by the number of steps) and so the health of people. This paper presents the result of empirical research on the impact of regional population densities (inhabitants per inhabitable area) on the number of steps (all steps, both outdoors and indoors). With data collected from almost 11,000 respondents in 148 Japanese regions, we estimate polynomial regression models, the total number of steps being the dependent variable and densities being the main independent variable. Regional population density significantly affects the number of steps after controlling for individual and household attributes. The estimated population density that maximizes the number of steps is around 11,000?persons/km2. Increasing densities, up to levels of around 11,000?inhabitants/km2, could increase walking and consequently the health of inhabitants. The population density elasticity of the number of steps is 0.046–0.049 in a simple log linear regression model without a peak. 相似文献
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This paper uses observations from before and during the Stockkholm congestion charging trial in order to validate and improve a transportation model for Stockholm. The model overestimates the impact of the charges on traffic volumes while at the same time it substantially underestimates the impact on travel times. These forecast errors lead to considerable underestimation of economic benefits which are dominated by travel time savings. The source of error lies in the static assignment that is used in the model. Making the volume-delay functions (VDFs) steeper only marginally improves the quality of forecast but strongly impacts the result of benefit calculations. We therefore conclude that the dynamic assignment is crucial for an informed decision on introducing measures aimed at relieving congestion. However, in the absence of such a calibrated dynamic model for a city, we recommend that at least a sensitivity analysis with respect to the slope of VDFs is performed. 相似文献
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Over the past decade, activity scheduling processes have gained increasing attention in the field of transportation research. However, still little is known about the scheduling of social activities even though these activities account for a large and growing portion of trips. This paper contributes to this knowledge. We analyze how the duration of social activities is influenced by social activity characteristics and characteristics of the relationship between the respondent and the contacted person(s). To that end, a latent class accelerated hazard model is estimated, based on social interaction diary data that was collected in the Netherlands in 2008. Chi-square tests and analyses of variance are used to test for significant relations between the latent classes and personal and household characteristics. Findings suggest that the social activity characteristics and the characteristics of the relationship between the socializing persons are highly significant in explaining social activity duration. This shows that social activities should not be considered as a homogenous set of activities and it underlines the importance of including the social context in travel-behavior models. Moreover, the results indicate that there is a substantial amount of latent heterogeneity across the population. Four latent classes are identified, showing different social activity durations, and different effects for both categories of explanatory variables. Latent class membership can be explained by household composition, socio-economic status (education, income and work hours), car ownership and the number of interactions in 2 days. 相似文献
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