The impact of strategic management and fleet planning on airline efficiency - A random effects Tobit model based on DEA efficiency scores

As a result of the liberalisation of airline markets; the strong growth of low cost carriers; the high volatility in fuel prices; and the recent global financial crisis, the cost pressure that airlines face is very substantial. In order to survive in these very competitive environments, information on what factors impact on costs and efficiency of airlines is crucial in guiding strategic change. To evaluate key determinants of 58 passenger airlines’ efficiency, this paper applies a two-stage Data Envelopment Analysis (DEA) approach, with partially bootstrapped random effects Tobit regressions in the second stage. Our results suggest that the effects of route optimisation, in the sense of average stage length of the fleet, are limited to airline technical efficiency. We show that airline size and key fleet mix characteristics, such as aircraft size and number of different aircraft families in the fleet, are more relevant to successful cost management of airlines since they have significant impacts on all three types of airline efficiency: technical, allocative and, ultimately, cost efficiency. Our results also show that despite the fuel saving benefits of younger aircraft, the age of an airline’s fleet has no significant impact on its technical efficiency, but does have a positive impact on its allocative and cost efficiency.     

替苹果新主塑造形象

蒂姆·库克(Tim Cook)先生,从苹果教主乔布斯手上接过CEO的黄金棒后,自此整个科技世界恐怕都会聚焦在你的身上吧。懂得你的人,都知道你那低调与默默耕耘的作风,以及相对温逊的性格,与乔布斯那万丈光芒汇聚的前台身影恰成对比。谁能忘记是你一手把苹果从一堆濒临失效的制造供应链上拯救过来?今天大家趋     

金属的咆哮 机械的诗歌

2009年底,三大艺术机构向公众展出了粗加工金属制成的艺术品,原型皆来自汽车。这是一场远距离的,围绕材料以及汽车地位的对话。第一件,也许是最具冲击力的一件作品,来自于Jeremy Deller的装置艺术作品,该作品获得了2004年泰纳奖(Turner Prize)。作为一个天生具备挑衅精神的英国艺术家,Deller于10月11月在芝加哥MCA展示了他的作品《它就是它,关于伊拉克的谈话(It iswhat it is:Conversation about Iraq)》。     

疏浚管道加气输送阻力特性研究

针对绞吸式挖泥船在输送泥浆过程中遇到阻力大,易堵管,能耗高等问题,分析了加气助送的可行性,在不同管道参数、泥浆参数、流量参数的条件下,采用分层流动模型和段塞流动模型对其进行了计算.结果表明在分层流动状态下,输入一定流量的气体会减小管道的阻力,在段塞流动状态下,输入气体会增大管道的阻力.     

羟基锡酸锌包覆氢氧化镁

采用均匀沉淀法制取羟基锡酸锌,通过单因实验法考察了包覆质量比、包覆时间及包覆温度三个因素对ZnSn(OH)6包覆Mg(OH)2的包覆效果的影响,并且结合超声分散和共沸蒸馏制备了包覆效果较好的ZnSn(OH)6包覆Mg(OH)2.通过X射线衍射(XRD)、扫描电镜(SEM)、热重分析(DTA-TG)及能谱分析(EDX)等...     

切换混杂系统的优化控制

针对一类切换混杂系统模型对其进行最优化控制.首先给出了混杂系统模型,按照极大值原理给出了最优控制问题应满足的的必要条件,运用极大值原理算法对其进行优化控制研究,实现该混杂系统的全局最优,得出结论,证明了优化策略的有效性.     

变点交叉多目标遗传算法在作业车间调度中的应用

针对传统多目标遗传算法在求解作业车间调度问题时收敛速度慢和容易陷入局部最优化的不足,提出一种采用变点交叉方式的多目标遗传算法.运算初期采用多点交叉的方式,在于提高收敛速度.在运算后期逐步减少交叉点,直至采用两点交叉、单点交叉的方式,避免丢失最优解导致早熟收敛.同时设计一种交互权重将多目标问题变为单一目标问题,体现决策者...     

大型油轮系靠泊外海开敞式码头的船舶撞击力计算

船舶撞击码头所产生的撞击力,是码头设计时的重要荷载,合理确定它的值很重要。由于相关影响因素很多,船舶撞击力计算公式尚存在一定差异,特别是针对大型油轮系靠泊外海开敞式码头时的船舶撞击力。分析国内外各种计算理论中的几个代表性公式,并进行比较分析。国内行业规范对船舶撞击力的计算值相较国外研究成果及物理试验结果均偏小,为了合理确定大型油轮系靠泊外海开敞式码头时的船舶撞击力值,对现行《港口工程荷载规范》采用的计算公式提出了改进建议。     

通过水下储能系统的蓄电池单元的流:三个接触的似花结构的球状物(英文)

An LES simulation of flow over an accumulator unit of an underwater compressed air energy storage facility was conducted. The accumulator unit consists of three touching underwater balloons arranged in a floral configuration. The structure of the flow was examined via three dimensional iso surfaces of the Q criterion. Vortical cores were observed on the leeward surface of the balloons. The swirling tube flows generated by these vortical cores were depicted through three dimensional path lines. The flow dynamics were visualized via time series snapshots of two dimensional vorticity contours perpendicular to the flow direction; revealing the turbulent swinging motions of the aforementioned shedding-swirling tube flows. The time history of the hydrodynamic loading was presented in terms of lift and drag coefficients. Drag coefficient of each individual balloon in the floral configuration was smaller than that of a single balloon. It was found that the total drag coefficient of the floral unit of three touching balloons, i.e. summation of the drag coefficients of the balloons, is not too much larger than that of a single balloon whereas it provides three times the storage capacity. In addition to its practical significance in designing appropriate foundation and supports, the instantaneous hydrodynamic loading was used to determine the frequency of the turbulent swirling-swinging motions of the shedding vortex tubes; the Strouhal number was found to be larger than that of a single sphere at the same Reynolds number.     

电动助力转向用无刷直流电机直接转矩控制方法研究

结合EPS系统的功能特点,提出1种适用于汽车转向的无刷直流电机(BLDC)系统直接转矩控制(DTC)方法,以提升汽车转向系统的控制性能。从BLDC系统的转矩特性和磁链特性的关系入手,根据电机系统的转矩、磁链跟踪误差及定子磁链所处扇区号,查询预先规划的离线查找表(LUT),直接输出最优的电压空间矢量。并基于Matlab/Simulink仿真平台进行BLDC调速系统的仿真实验。结果表明,DTC方法可以对电磁转矩脉动进行有效控制,而且能大大提高BLDC的动、稳态驱动性能,提供了1种适用于电动助力转向EPS系统控制的新思路。