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271.
Russell David Brancato Mary Sue Bennett H. Jesse 《Journal of Marine Science and Technology》1996,1(4):230-238
The results of three national monitoring programs in the United States (U.S.) that measure concentrations of tributyltin (TBT)
are compared. Regional and site comparisons are made of changes in TBT concentrations since passage of the Organotin Antifouling
Paint Control Act (OAPCA) in 1988. The monitoring programs compared are the U.S. LongTerm Monitoring Program conducted by
a consortium of tributyltin manufacturers, the National Oceanic and Atmospheric Administration's National Status and Trends
Mussel Watch project, and the U.S. Navy's TBT monitoring program. All of the monitoring results demonstrate declining TBT
concentrations over time. These declines have occurred rapidly (within a few years) and are considerable (56%–71% decrease
in TBT concentrations in water, 47%–55% decrease in sediments, and 40%–82% decrease in bivalve tissues). Mean TBT concentrations
in water are generally below the current U.S. Environmental Protection Agency marine chronic water quality criterion of 10ng/L.
These results indicate that the OAPCA has been effective in reducing TBT concentrations in the aquatic environment. 相似文献
272.
Y. Shen M. F. Golnaraghi G. R. Heppler 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2007,45(4):297-312
In this paper, a load-leveling suspension system with a magnetorheological (MR) damper is investigated. In this suspension system, the MR damper is connected to a spring to form a load-leveling suspension system. The system effective stiffness and damping can be adjusted by controlling the MR damper. The characteristics of a load-leveling suspension system are studied first. When the linear damper is replaced with an MR damper, the averaging method is adopted to obtain the steady-state response of the nonlinear system. A comparison demonstrates that the results of the averaging method are in good agreement with those obtained by numerical simulations. The analytical results are then verified experimentally. The load-leveling suspension system studied here is able to adjust both suspension stiffness and damping and, hence, it may provide more effective vibration control in a wider frequency range, when the damper is controlled. 相似文献
273.
274.
This paper addresses the issue of using before and after surveys to evaluate behavioural changes in response to transport
policies and investments, a procedure that, we argue is done far too rarely in this profession. Further, it demonstrates very
clearly that, in almost all conceivable cases, there are considerable economies to be obtained by using a panel (again, under-utilised
in our profession) to undertake evaluation, rather than successive independent cross-sectional surveys. The paper also addresses
the critical issue of sample size requirements for measuring changes of a relatively small magnitude in travel behaviour;
i.e., to state, with 95% confidence, that if there is a ∂ percent change in behaviour for the sample, there is a ∂ percent ± e
percent change in the behaviour of the population, where e is the sampling error. In this paper, we present a method for calculating such sample size requirements from first principles
and demonstrate the applicability both hypothetically and then empirically using data from the Puget Sound Transportation
Panel. The formulation enables designers of before and after surveys to investigate the trade-offs between the statistical
accuracy of their predictions and the sample size requirements systematically, without the need to specify ∂ a priori. This
latter point is crucial, we argue, because we have limited information on ∂, yet, as we explain here, it drives the sample
size requirements using alternative, well-cited approaches for calculating sample sizes to assess behavioural change. The
results have important ramifications both for those implementing transport policies intended to produce behavioural change,
especially when a cost-benefit evaluation of the policy is desired, and for those interpreting the results reported in previous
studies. 相似文献
275.
276.
R.Schmidt 《变流技术与电力牵引》2003,(6):28-30
用变流器向德国铁路16.7 Hz电网供电是一种价格低廉的标准化方法.文章介绍了这种开发的基本特点以及在中央和地方电网中的应用实例. 相似文献
277.
Roesner R 《变流技术与电力牵引》2003,(1):25-28
逆变器用于高压时,将电力半导体器件串联是众所周知的方法.本文介绍了一种先进的驱动器/吸收器方案,该方案可以产生自己所需的电源电压,不需要外部电源.另外,电压分配和吸收性能得到最优化,吸收能量可以再生到逆变器的直流环节.还介绍了从1台实际的IGCT逆变器获得的测量结果. 相似文献
278.
D. Swaroop Assistant Professor R. Huandra Graduate Student 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1998,30(5):319-344
This paper investigates the problem of designing Intelligent Cruise Control (ICC) algorithms for partially and fully automated highways. ICC algorithms must guarantee that density disturbances attenuate as they propagate upstream. Such a desirable property of traffic is dependent on the spacing policy employed by automated vehicles and on the availability of information required to synthesize a string stable control law consistent with the employed spacing policy. The first part of the paper is concerned with the design of the spacing policy and the latter part is concerned with synthesizing ICC algorithms. Various other issues relating to the design of ICC are also discussed. 相似文献
279.
Dietrich R. Bergmann 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1973,2(3):139-154
Vehicle dwell times are perhaps the most unpredictable parameters of station operations because of occasional passenger intervention. This paper reports on an investigation involving theoretical and Monte Carlo techniques to ascertain the sensitivity of station throughput to randomness in dwell times. Alternative configurations of vehicle loading positions, e.g., loading positions in parallel, in series, or in a series-parallel combination, are considered in an effort to rank the configurations by their associated performance levels. 相似文献
280.