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861.
Silvana N.R. Birchenough Sin E. Boyd Roger A. Coggan David S. Limpenny William J. Meadows Hubert L. Rees 《Journal of Marine Systems》2006,62(3-4):204
This study presents the results of a trial assessment based on a combination of sampling techniques at a dredged material disposal site located off the North East coast of the UK, over 2001 to 2004. The site was surveyed with a high-resolution sidescan sonar system producing a mosaic with 100% coverage of the survey area. Benthic communities and sediments were ground-truthed using a Hamon grab with a video camera. Additionally, the area was also sampled in 2003 with a Sediment Profile Imaging (SPI) camera, which complemented other techniques by providing in situ information on sediment quality, and biogenic activities. An assessment is made of the benefits of combining the results from conventional methods, principally using grab samples, with those from acoustic techniques and optical imaging devices to determine seafloor and macrobenthic conditions. This information has the potential to contribute to the enhancement of routine monitoring programmes within UK waters. 相似文献
862.
David A. Hensher 《Transportation》2006,33(3):205-222
A feature of recent developments in choice models that enable estimation of the distribution of willingness to pay (WTP) is
that the sign of the distribution can change over the range. Behaviourally this often makes little sense for attributes such
as travel time on non-discretionary travel, despite a growing recognition of positive utility over some travel time ranges.
This can in part be attributed to the analytical distribution that is selected (except the cumbersome lognormal), many of
which are unconstrained over the full range. Although a number of analysts have imposed constraints on various distributions
for random parameters that can satisfy the single-sign condition, these restrictions are, with rare exception, only satisfied
for the mean and the standard deviation estimates of a random parameter. When heterogeneity around the mean and/or heteroscedasticity
around the standard deviation is allowed for, however, the constraint condition is often not satisfied. Given the popularity
of distributions other than the lognormal, in order to satisfy the sign condition under the most general form of parameterisation,
we need to impose a global sign condition. In this paper we show how this might be achieved in the context of the valuation
of travel time savings for car commuters choosing amongst an offered set of route-specific travel times and costs. We illustrate
the impact of the constraint under a globally constrained Rayleigh distribution for total travel time parameterisation, contrasting
the evidence with a multinomial logit model and a range of other distributional assumptions within the mixed logit framework.
Discussions with Bill Greene, John Rose, Ken Train and especially Juan de Dios Ortuzar have been invaluable as have the comments
of referees. 相似文献
863.
In this paper, a new methodology is presented for computing time-optimal obstacle avoidance maneuvers for ground vehicles. Usually, the problem of obstacle avoidance is addressed in two parts. In the first part a path is planned. In the second an appropriately designed vehicle controller tracks the desired path. In view of the fact that the main problem concerning emergency maneuvers remains the development of an optimal control for minimum time and maximum maneuverability — with respect to the slip risk due to saturation of the tire forces — the authors propose an alternative approach. Considering that the time optimal control according to Pontryagin’s Maximum Principle (PMP) is of bang-bang type the investigations concern the minimum order and magnitude bang-bang control for “feedforward” steering maneuvers with the target of minimizing the computation time and simplifying the algorithm. This is accomplished by keeping the basic PMP logic but transforming the computational algorithm from an exact to a least squares control problem. Furthermore, the paper addresses how to solve the problem of guiding the vehicle from a non rest to a rest position. Simulations of obstacle avoidance maneuvers illustrate the performance of the controller. 相似文献
864.
865.
A. Esnaola I. Ulacia B. Elguezabal E. Del Pozo De Dios J. J. Alba I. Gallego 《International Journal of Automotive Technology》2016,17(6):1013-1022
The development and validation of a modular composite impact structure is presented in the present paper. Quasi-static and dynamic impact tests of the composite components and a full frontal crash test of a vehicle prototype with composite impact structures manufactured by a new UV-pultrusion process have been performed. The results have demonstrated the feasibility of composite impact structures for crash applications with high specific energy absorption values compared with current metallic crash structures. Furthermore, due to the high production capacity of this new manufacturing process, cost-effective composite impact structures for mass-production of conventional cars may be feasible. Finally, a multimaterial numerical model as design tool for crashworthiness applications has also been validated. Different accelerations measured in the crash test have been accurately predicted as well as the crash behaviour of the composite impact structures. 相似文献
866.
T. A. Arentze H. J. P. Timmermans 《Transportation Research Part C: Emerging Technologies》2000,8(1-6)
Current geographic information systems typically offer limited analytical capabilities and lack the flexibility to support spatial decision making effectively. Spatial decision support systems aim to fill this gap. Following this approach, this paper describes an operational system for integrated land-use and transportation planning called Location Planner. The system integrates a wide variety of spatial models in a flexible and easy-to-use problem solving environment. Users are able to construct a model out of available components and use the model for impact analysis and optimization. Thus, in contrast to existing spatial decision support systems, the proposed system allows users to address a wide range of problems. The paper describes the architecture of the system and an illustrative application. Furthermore, the potentials of the system for land-use and transportation planning are discussed. 相似文献
867.
Key to the predictive understanding of many nearshore marine ecosystems is the transport of larvae by ocean circulation processes. Many species release thousands to billions of larvae to develop in pelagic waters, but only a few lucky ones successfully settle to suitable habitat and recruit to adult life stages. Methodologies for predicting the larval dispersal are still primitive, and simple diffusive analyses are still used for many important applications. In this study, we investigate mechanisms of larval dispersal using idealized simulations of time-evolving coastal circulations in the California Current system with Lagrangian particles as models for planktonic larvae. Connectivity matrices, which describe the source-to-destination relationships for larval dispersal for a given larval development time course, are used to diagnose the time–space dynamics of larval settlement. The resulting connectivity matrices are shown to be a function of several important time scales, such as the planktonic larval duration, the frequency and duration of larval release events and inherent time scales for the coastal circulations. Many important fishery management applications require knowledge of fish stocks on a year-to-year or generation-to-generation basis. For these short time scales (typically less than 1 year), larval dispersal is generally far from a simple diffusive process and the consideration of the stochastic and episodic nature of larval dispersal is required. This work provides new insights into the spatial–temporal dynamics of nearshore fish stocks. 相似文献
868.
In this paper, we extend previous analyses of temporal effects by examining the factors associated with activity generation and duration over four waves of the Puget sound transportation panel survey (PSTPS). A Cox proportional hazards model was specified for each of five activities: visiting, appointment, free time, personal business, and shopping. For each activity, the duration times are modeled with an emphasis on examining important higher order interactions. The results suggest that activity durations have changed significantly over the survey period. Many of the differences in activity durations over time were significant, and often associated with increasing numbers of children in the household and higher order interactions between sex and the sequencing of activities. 相似文献
869.
870.
C. Sanchez-Rebollo A. Carnicero 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2013,51(4):554-569
Dynamic simulation methods have become essential in the design process and control of the catenary–pantograph system, overall since high-speed trains and interoperability criteria are getting very trendy. This paper presents an original hardware-in-the-loop (HIL) strategy aimed at integrating a multicriteria active control within the catenary–pantograph dynamic interaction. The relevance of HIL control systems applied in the frame of the pantograph is undoubtedly increasing due to the recent and more demanding requirements for high-speed railway systems. Since the loss of contact between the catenary and the pantograph leads to arcing and electrical wear, and too high contact forces cause mechanical wear of both the catenary wires and the strips of the pantograph, not only prescribed but also economic and performance criteria ratify such a relevance. Different configurations of the proportional-integral-derivative (PID) controller are proposed and applied to two different plant systems. Since this paper is mainly focused on the control strategy, both plant systems are simulation models though the methodology is suitable for a laboratory bench. The strategy of control involves a multicriteria optimisation of the contact force and the consumption of the energy supplied by the control force, a genetic algorithm has been applied for this purpose. Thus, the PID controller is fitted according to these conflicting objectives and tested within a nonlinear lumped model and a nonlinear finite element model, being the last one validated against the European Standard EN 50318. Finally, certain tests have been accomplished in order to analyse the robustness of the control strategy. Particularly, the relevance or the plant simulation, the running speed and the instrumentation time delay are studied in this paper. 相似文献