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861.
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Reliable research synthesis is of high significance for a transport policy which tries to base its decisions on available
empirical evidence. There is growing doubt whether the frequently used narrative approach provides a scientifically defensible
way of synthesising a body of quantitative research results. The present paper demonstrates meta-analysis as a more objective
and powerful alternative for this task. For this purpose evaluation data synthesised in two earlier narrative reviews on the
effectiveness of work travel plans [Cairns et al. Making travel plans work: research report (former), Department for Transport,
Local Government and the Regions (DTLR), London, 2002; Smarter choices—changing the way we travel. (Final report of the research project: The influence of soft factor interventions
on travel demand. Research report for the Department for Transport.) London. Retrieved 1 December 2005, from , 2004] are meta-analytically re-analysed and compared with the conclusions drawn from the narrative synthesis of these data. Our
meta-analyis provides only limited support for the conclusion that addressing parking is the hallmark of successful work travel
plans. Our meta-analysis indicates that site and organisational factors as well as characteristics of the monitoring process
are significant predictors of effective work travel plans, whereas Cairns et al. view little evidence for the impact of these
factors. 相似文献
865.
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
866.
目前新疆地区主要干线等级公路的车辆超载现象十分严重,从而对沥青路面造成很大的损伤和破坏,使其正常使用寿命大大降低。以新疆某干线公路典型的半刚性路面结构为例,针对车辆超载情况并考虑到超载时轮胎接地压力为非均匀分布的特点,运用三维有限元方法分析了路面弯沉、轴载及基层模量之间的关系以及超载对路面使用寿命的影响。 相似文献
867.
Martin F. Diez-Picazo 《WMU Journal of Maritime Affairs》2007,6(2):241-247
A cross-cutting Maritime Policy can ensure that climate change threats and challenges in regards to seas and oceans are dealt
with in a wide policy framework that takes into account the impacts that climate change may have on other sectors and vice
versa. 相似文献
868.
Genetic algorithms (GAs) can powerfully search for parameters in a large multidimensional design space. Thus, the principle
can be applied to preliminary series propeller design problems with multiple considerations. In the present study, B-series
propeller design was conducted using a GA for both hydrodynamic efficiency and vibration consideration. The objective function
was set by users who could freely weight the relative importance of efficiency and vibration. GAs were successfully shown
to be able to obtain an optimal set of parameters leading to efficient performance and low vibration. 相似文献
869.
ZHU Guang-ping SUN Hui ZHANG Ming-hui 《船舶与海洋工程学报》2007,6(2):64-69
Array calibration is important in engineering practice. In this paper, fast calibration methods for a ULA's gain and phase errors both in far and near fields are proposed. In the far field, using a single sound source without exact orientation, this method horizontally rotates the array exactly once, performs eigen value decomposition for the covariance matrix of received data, then computes the gain and phase error according to the formulas. In the near field, using the same single sound source, it is necessary to rotate the array horizontally at most three times, build equations according to geometric relations, then solve them. Using the formula proposed in this paper, spherical waves are modified into plane waves. Then eigen values decomposition is performed. These two calibration methods were shown to be valid by simulation and are fast, accurate and easy to use. Finally, an analysis of factors influencing estimation precision is given. 相似文献
870.
磷化参数与磷化质量息息相关,控制好磷化参数是稳定和提高磷化质量的前提。本文结合生产实际详细介绍各种磷化参数对磷化效果的影响。 相似文献