Computing airfare elasticities or opening Pandora's box

Airfare elasticities are crucial for policy instruments for the stakeholders of tourism industry. Modellers attempting to estimate these elasticities face several challenges in the absence of microeconomic data on consumer preferences. The aim of this paper is to offer a critical analysis of the practice of computing airfare elasticities from tourism demand studies. It identifies and discusses potential sources of measurement errors in the data and drawbacks that investigators face and assesses their implications for the estimated parameters in the respective models. The use of price of crude oil and distance between origin and destination as proxies for transportation costs are evaluated. It is recommended that authors be more systematic in reporting their results. They need to comment on the limitations of their elasticity estimates since these have repercussions on policy recommendations made based on their results.     

内河船舶航行香港航线防止空气污染的检验与管理

内河船舶航行香港航线,应满足香港《商船（防止空气污染）规例》的要求,并持有防止空气污染证书。本文结合香港规例、内河船检法规及中国海事局文件要求,按照新船与现有船舶进行区分,介绍了航行香港的内河船舶防止空气污染方面的检验要求,并提出相应的管理建议。关键词：内河船舶防止空气污染检验要求     

Aircraft trajectory forecasting using local functional regression in Sobolev space

This paper considers the problem of short to mid-term aircraft trajectory prediction, that is, the estimation of where an aircraft will be located over a 10–30 min time horizon. Such a problem is central in decision support tools, especially in conflict detection and resolution algorithms. It also appears when an air traffic controller observes traffic on the radar screen and tries to identify convergent aircraft, which may be in conflict in the near future. An innovative approach for aircraft trajectory prediction is presented in this paper. This approach is based on local linear functional regression that considers data preprocessing, localizing and solving linear regression using wavelet decomposition. This algorithm takes into account only past radar tracks, and does not use any physical or aeronautical parameters. This approach has been successfully applied to aircraft trajectories between several airports on the data set that is one year air traffic over France. The method is intrinsic and independent from airspace structure.     

基于NASTRAN的某商用车空调压缩机支架性能仿真研究

文章基于有限元法,采用Nastran软件,对某商用车空调压缩机系统进行了CAE模态,强度和疲劳分析分析结果显示,空调压缩机及支架NVH模态,强度和耐久性能满足设计目标。     

基于LQR控制的现代客车自适应空气悬架

长期在不良工况的道路上驾驶会降低驾驶员的乘坐舒适性。随着人们对乘坐舒适性需求不断提升,空气弹簧的优势尤为明显。文章提出了一种基于LQR控制策略的自适应空气悬架系统的创新设计方案,提出的LQR控制器采用粒子群算法进行优化。以客车空气悬架为研究对象,采用MATLAB软件对空气悬架系统的被动和自适应动力学模型进行了设计和仿真。仿真结果表明,自适应空气悬架系统在保证车辆稳定性的同时,降低了车辆在随机道路上的最大位移幅值,从而提高了车辆的平顺性。     

潜艇舱室大气中金属元素的X-射线荧光光谱法检测

建立了X-射线荧光光谱仪对潜艇舱室大气中Cr、Mn、Fe、Co、Ni、Cu等10种金属元素的快速分析方法。利用醋酸纤维素微孔滤膜对潜艇舱室大气进行采样,用X射线荧光光谱仪对滤膜进行检测,可同时检测10种金属元素。方法具有简便准确、元素分析含量适应范围宽等优点。方法的相对标准偏差在0.99%~3.04%,回收率在94.2%~98.4%。     

信号电气设备空气断路器的种类和选用

城轨交通信号系统的各设备负载都由电源屏和UPS统一供电,而能达到各负载分路供电的电气元件则是通过空气断路器完成.在信号系统的维护过程中,空气断路器选择不当,可能带来很多麻烦.因此,从断路器的种类、功能、应用等几方面,详细介绍了断路器选用时的注意事项.     

无缝线路现场移动式气压焊接质量的控制

长钢轨焊接是铺设无缝线路的一个极其特殊和重要的过程,原因在于其内部质量的好坏不能通过后续检验来判定,直接危及运输行车安全;其几何外形尺寸的平顺是保证无缝线路正常运用的关键。钢轨焊接质量不良,将使线路维修工作后患无穷,因此有效控制钢轨焊接质量成为目前急需探讨和解决的新课题。     

机车及动车组车体内部空气过滤的标准介绍

通过制定标准、规定统一的技术要求,有利于在生产和运用环节对车体空气过滤器进行规范并进行有效的质量控制,对提高机车及动车组的运用可靠性和过滤器的质量、延长机车使用寿命和可靠性,有相当重要的意义。