支架法在海中箱梁现浇施工中的应用

针对海中箱梁现浇施工中的工程量大、工期紧迫、悬臂法施工不能满足工期要求和施工难度大等问题，文章结合青岛海湾大桥箱梁现浇施工实践，介绍以钢管桩支撑作为承载基础，采用贝雷梁与碗扣式支架相结合的支架，成功地解决现浇箱梁施工难题的方法。     

Catching the tail: Empirical identification of the distribution of the value of travel time

Recent methodological advances in discrete choice analysis in combination with certain stated choice experiments have allowed researchers to check empirically the identification of the distribution of latent variables such as the value of travel time (VTT). Lack of identification is likely to be common and the consequences are severe. E.g., the Danish value of time study found the 15% right tail of the VTT distribution to be unidentified, making it impossible to estimate the mean VTT without resorting to strong assumptions with equally strong impact on the resulting estimate. This paper analyses data generated from a similar choice experiment undertaken in Sweden during 2007-2008 in which the range of trade-off values between time and money was significantly increased relative to the Danish experiment. The results show that this change allowed empirical identification of effectively the entire VTT distribution. In addition to informing the design of future choice experiments, the results are also of interest as a validity test of the stated choice methodology. Failure in identifying the right tail of the VTT would have made it difficult to maintain that respondents’ behaviour is consistent with utility maximisation in the sense intended by the experimenter.     

基于声电类比法的管系气柱固有频率的计算

基于平面波动理论与电学系统方程的等价,建立管道气柱单元声学等效电路.采用MATLAB/SIMULINKL软件,通过谐振法对气柱系统进行电路仿真,得到其各阶固有频率,并与传递矩阵法计算结果相比较,误差很小,说明采用声电类比法计算气柱固有频率是有效的.     

Role of the Railways in the Future of Air Transport

Abstract

The role of the railways in the air transport industry is usually limited to provision of access to airports. However, the development of high-speed rail networks and the congestion and environmental problems faced by the air transport industry suggest the railways could have a greater role in working with the airlines to provide an integrated transport service for medium-distance journeys (up to 800 km). Many air journeys involve two flights and a transfer at a hub airport. The alternative being investigated here would replace air journeys by a rail journey and a flight, and a transfer between them at the hub airport. Such integration could offer a positive alternative to aircraft on some routes and lead to railway journeys to airports becoming part of air transport services, and not only to provide access to them. Integration could therefore provide a better use of available air capacity rather than duplicating some high-speed rail routes and services.     

数字图像处理技术在隧道围岩收敛量测中应用的初步研究

文章系统地总结了国内外图像处理技术在隧道工程中的应用现状和隧道变形收敛量测的各种方法,并对各种方法的优缺点进行了详细分析;尝试了应用数字图像处理技术对隧道围岩收敛进行量测的新方法(二次比较法);编制了一套隧道图像处理系统(TUNNEL IMAGE PROCESSING SYSTEM,简称TIPS)。室内试验证明,本系统对距离的量测结果是可靠的,灵敏度和精度达到了相关要求。本研究成果可供有关人员在现场实用研究中参考。     

原油管道检测器通过能力评价方法

为了探明管道内部通过能力,保证管道内部腐蚀检测器的顺利投放,制定了由泡沫检测器到几何尺寸检测器的管道通过能力检测流程,并将此方法在多条原油管线上进行了验证。结果表明：该方法能准确地识别管线上的变形尺寸大小,并对变形部位进行定位。根据检测结果对管道通过能力进行评价,对不符合要求的管段及时进行修复,保证了后期检测的顺利进行。此外,在检测的过程中有效地清理了管道内部污物,提高检测器通过能力及管道的输油效率。     

Problems of the carless in the United Kingdom and the United States

An examination of current population statistics shows that in the U.S. more than half of the population is without immediate access to a car, and in the U.K. more than three-fifths of the population is without access to a car. This phenomenon has been accentuated by national investment in both countries in major highway programs. The term carless refers to more than just households that own no cars. It extends, in households with cars to those without licenses (old and young), the handicapped, and even the licensed drivers who have no access to the family car when it is in use elsewhere (e.g. at work). The most severely effected are those in urban areas and especially the urban poor. Transportation expenses are limited for the poor when other family expenditures (food, shelter) take a high priority. Once the work trip has been satisfied, money for other trips, for the poor, is not always available. One solution to cost-free travel is pedestrianism (walking), but this too is difficult in urban areas where the pedestrian has been overlooked in favor of the car. Solutions to problems of the carless include dial-a-ride, better public transit, and better design of urban form.     

川气东送天然气管道线路水合物形成预测

为了更好地预测、分析和处理水合物造成的不良后果,以川气东送管道为例讨论了天然气水合物的形成原因,提出了输气管线水合物预测模型,并建立了水合物形成预测的压力和温度计算模型,编制了“水合物预测软件”,预测该管道线路和场站的水合物形成条件和易形成水合物的区域.文中通过以上方法很好地预测了川气东送管道水合物的形成区域及情况,该预测方法可用于天然气管道线路水合物的形成预测.     

Is it the labor unions’ fault? Dissecting the causes of the impaired technical efficiencies of the legacy carriers in the United States

Data envelopment analysis is used to evaluate the technical efficiencies of a number of major passenger airlines in the United States at transforming their inputs (labor, fuel and fleet-wide seating capacity) into available seat-miles. A tobit regression model is then used to identify the underlying drivers of airline efficiency, as measured by the data envelopment analysis efficiency score. The impact of unionization on airline efficiency is found to be statistically insignificant, controlling for the influences of other hypothesized determinants of airline efficiency: the average age of an airline’s fleet, the average size of its aircraft, its average stage length, the extent to which the airline relies of hubbing within its route structure, the percent of its passenger enplanements that are international, and whether the airline is a legacy carrier. The statistically significant drivers of airline efficiency, at a ten percent level of significance, are average aircraft size, average stage length and the extent to which the airline relies on hubbing and connecting flights within its route structure. The stage length variable is not significant at a five percent level of significance, however. An increase in average aircraft size or in average stage length enhances an airline’s efficiency whereas an increase in hubbing reduces it.     

On the income elasticity of the value of travel time

Transport infrastructure is long-term and in appraisal it is necessary to value travel time savings for future years. This requires knowing how the value of time (VTT) will develop over time as incomes grow. This paper investigates if the cross-sectional income elasticity of the VTT is equal to inter-temporal income elasticity. The study is based on two identical stated choice experiments conducted with a 13 year interval. Results indicate that the relationship between income and the VTT in the cross-section has remained unchanged over time. As a consequence, the inter-temporal income elasticity of the VTT can be predicted based on cross-sectional income elasticity. However, the income elasticity of the VTT is not a constant but increases with income. For this reason, the average income elasticity of the VTT in the cross-sections has increased between the two survey years and can be expected to increase further over time.     

Evaluating the efficiency of the Essential Air Service program in the United States

Essential Air Service (EAS) is a federally funded program in the United States that provides connecting, commercial air service between rural communities and their nearest large or medium commercial hub airport. During fiscal year 2010, $170 million dollars were spent to provide this service to 107 communities in the US. However, with significant variations in subsidies to each airport (ranging from $427,757 to $3,082,403) and marked differences in passengers served, there are serious concerns regarding the overall efficiency of the EAS program. The purpose of this paper is to use data envelopment analysis integrated in a geographic information system for evaluating service efficiencies at the community level. Policy implications and strategies to improve the EAS program are discussed.     

绝热材料下沉对蒸汽管道热损失的影响

文中从绝热材料下沉的角度，利用形状因子法对高温蒸汽管线保温问题进行了探讨。通过理论分析和实验测试，得出了“复合硅酸盐保温涂料＋复合硅酸盐保温型材＋复合硅酸盐保温涂料”的保温结构，可有效改善绝热材料的下沉问题。     

On the calibration of the combined distribution-assignment model

We consider a model which combines gravity model trip distribution and equilibrium assignment. This model contains a free parameter which must be fixed using supplementary information, that is, the model must be calibrated. It is natural to ask which supplementary information is sufficient to determine the free parameter. We show here that under very weak hypotheses each of the quantities, the entropy H or the total assignment cost F, is alone sufficient to determine the free parameter. In contrast, it is shown by means of a counterexample that even under very strong hypotheses, the total cost C is not sufficient.     

The effect of the oil crisis on the growth in the ownership and use of cars

Since the oil crisis of 1973, a number of studies have been made in various countries of the effects of the rise in petrol prices on the level of traffic flow, but rather fewer have attempted to delineate the complex chain of reactions within the car market set off by this impulse. We attempt to do this, using data from the UK.Since 1966 during the prediction stage of the first London Transportation Study it became obvious that low income and high income households had different rates of growth of car ownership, mainly because low income households bought cheap, old cars which vary in quantity and price differently from expensive, new cars. The Greater London Council therefore sponsored a study of car prices by age and size, starting from 1957 annually, and since the oil crisis, evaluated monthly. This has enabled us to examine the strong change in trend that had occurred, with large cars depreciating 15% per annum more than the smallest. The quantities of cars of each size registered each month are available from national statistics and this enables us to say that the previous 1% per annum increase in car size was arrested, with new cars becoming substantially smaller.A model of the car market has been developed which relates on the one hand the price distribution of cars by age, and on the other hand the price. distribution of the stock of cars owned at each household income level. Via the expenditure on car purchase at each household income level and the distribution of the length of time between purchase and resale of cars, a fully dynamic model has been developed to relate expenditure flow and stock. This enables us to test the effect of different trends on the dynamic equilibrium in the car market.The implications of the two trends noted above on the prediction of future car ownership growth are discussed, with the standstill since the oil crisis attributed to petrol prices via the split in household expenditure between purchase and use.     

武汉长江隧道盾构段结构型式研究

武汉长江隧道是我国在高水压、强透水地层中修建的第一条大直径盾构隧道,且左侧河床历年冲淤变化幅度较大,如何选择合理的隧道结构型式是工程设计必须考虑的关键问题.为此,在国内外现有单层管片衬砌和全环双层衬砌的基础上,研究提出了一种新型的“管片衬砌+非封闭内衬”的双层衬砌结构该结构在不增加隧道开挖直径的前提下,允分利用圆形隧道底部和两侧的富余空间现浇钢筋混凝土,并与车道板结构共同组成非封闭二次衬砌结构,可以大幅度地减少河床冲淤变化时的结构横向变形,并确保隧道底部与两侧这些重点部位的防水性能及结构长期稳定性,是一种值得推荐的创新结构方案.     

紧邻有轨电车高架桥基坑施工安全保障措施

结合苏州太湖大道改造工程阳山西路隧道基坑工程,文章分析了紧邻有轨电车高架桥基坑施工时存在的风险及相应安全保证措施,研究了各主要施工工序的控制要点,并对施工期间可能出现的风险提出了针对性的应急措施,不仅可以确保基坑的安全和稳定,而且将基坑施工对高架桥的影响降到最低,安全保障措施可供类似工程参考。     

A review of the state of the art of personal rapid transit

The paper begins with a review of the rational for development of personal rapid transit, the reasons it has taken so long to develop, and the process needed to develop it. Next I show how the PRT concept can be derived from a system‐significant equation for life‐cycle cost per passenger‐mile as the system that minimizes this quantity. In the bulk of the paper I discuss the state‐of‐the‐art of a series of technical issues that had to be resolved during the development of an optimum PRT design. These include capacity, switching, the issue of hanging vs. supported vehicles, guideways, vehicles, control, station operations, system operations, reliability, availability, dependability, safety, the calculation of curved guideways, operational simulation, power and energy. The paper concludes with a listing of the implications for a city that deploys an optimized PRT system.     

浅覆土砂层土压平衡盾构始发掘进对环境的影响分析

盾构始发和到达安全掘进控制技术是困扰盾构隧道施工的主要难题之一。盾构进出洞施工中,面临掌子面失稳、土体坍塌、涌水涌砂、地表沉陷、盾构"抬头及磕头"等诸多施工风险。本文从基坑及隧道的破坏模式,塑性区分布范围出发,通过有限差分法针对易受扰动的浅埋砂层地层盾构始发段进行了研究,为加固区范围大小的选择提供了依据。研究表明,在不采取加固措施时,基坑开挖后隧道始发段的竖向位移、拱底的隆起和最大纵向挤出变形量均过大,显示基坑将发生坍塌等破坏。当盾构始发段主要加固措施为旋喷桩,加固后的土体的物理参数得到了显著的提升。本文在此基础上得出了旋喷桩的合理加固区域。     

Determinants of the willingness-to-pay for reducing the environmental impacts of road transportation

This paper examines the willingness-to-pay of people living in a number of villages in Navarre, in the Spanish Pyrenees to reduce noise and air pollution. Several models are used for estimation based on contingent valuation, noting that those living near roads are willing to pay more to reduce air and noise pollution. In addition, younger people, the better educated, and the more environmentally aware individuals are also willing to pay more to reduce those externalities.     

Measuring the environmental efficiency of the global aviation fleet

This research analyses the environmental footprint of the airline industry in an attempt to highlight potential paths for improvement. We develop a directional economic-environmental distance function (DEED) which accounts for the production of both desirable and undesirable output and the potential for constrained increases in input utilization. This research applies the modeling framework to analyze the potential to reduce noise and airborne pollutants emitted by aircraft–engine combinations given the current state of aeronautical technology. The global aircraft–engine market is viewed from the regulatory perspective in order to compare the single environmental and operational efficient frontier to that of the airline carriers, and environmental objectives. The results of DEED are then applied in order to substitute the fleets serving Schipol, Amsterdam and Arlanda, Stockholm airports in June 2010 with the benchmark aircraft. The results highlight the inefficiencies of the current airline fleets and that the IPCC values of externalities are a magnitude of TEN too low to encourage changes in the global fleet hence the need for government intervention.