对外汉语专业的英美文学选读课教学初探

英美文学选读课有助于对外汉语专业的学生全面掌握语言文字的魅力,领略不同文化的精神内涵,肩负起自身的文化使命。笔者通过两年多的教学实践,以教学活动过程为背景,从预热、选材、学习、反思四个阶段,总结出了几点经验。     

Quasi-optimal feedback control for an isolated intersection under oversaturation

How to manage signalized intersections under oversaturated conditions is a long-standing problem in traffic science and engineering. However, although research works in this area date back to 1960s, an on-line control strategy with theoretically bounded performance is missing, even for the control of an isolated intersection under oversaturation. This paper makes one step further in this area by proposing a QUEUE-based quasi-optimal feedback control (abbreviated as QUEUE) strategy for an isolated oversaturated intersection. The QUEUE strategy is intuitive, simple, and proved to match the off-line optimum in the case of constant demand. More importantly, the bounds of sub-optimality of the QUEUE strategy can be specified quantitatively in general piece-wise constant demand cases. To better deal with the maximum queue constraints, the oversaturation period is divided into the queuing period and the dissipation period with two different objectives. In the queuing period, the primary objective is to keep the queue length within the maximum value; but for the dissipation period, the primary objective is to eliminate all queues at the earliest time. Interestingly, we found that both control objectives can be realized with the same QUEUE strategy. Numerical examples show that the QUEUE strategy approximates the off-line optimum very well. The average sub-optimality in comparison with the off-line optimum in the challenging conditions with Poisson distributed random demand is below 5%.     

Improved driver responses at intersections with red signal countdown timers

Traffic Signal Countdown Timers (TSCTs) are innovative, practical and cost effective technologies with the potential to improve efficiency at signalized intersections. The purpose of these devices is to assist motorists in decision-making at signalized intersections with real-time signal duration information. This study focused specifically on driver responses in the presence of a Red Signal Countdown Timer (RSCT). A Linear Mixed Effect (LME) model was developed to predict the effect of RSCT on the headway of the first vehicle waiting on a red signal. The model predicted 0.72 s reduction in the headway of the first queued vehicle resulting from the presence of RSCT, while the observed difference in mean headway was 0.82 s. This result is suggestive of a reduction in start-up lost time at signalized intersections, i.e., an improvement in signalized intersection efficiency when an RSCT is present.     

COVID-19疫情对我国港航业发展影响的调查和应对措施

针对2020年春节期间发生的新型冠状病毒肺炎(COVID-19)疫情给我国的经济发展带来严重影响的状况,为客观地了解此次疫情对我国港航业发展的影响,以广州航运交所开展的问卷调查收集的数据为样本,对与此次疫情相关的数据进行梳理分析。在此基础上,结合已有研究,提出在该疫情的影响下港航业应采取的应对措施。统计分析结果表明,面对不确定性因素,提振市场信心是对恢复港航企业发展最有效,也是最容易忽视的因素,在应对该疫情过程中,需予以重视。     

小半径曲线梁桥弯曲效应分析

为提高小半径曲线梁桥的安全性,利用三维空间结构分析程序,对不同曲率半径桥梁结构的结构内力和位移进行了计算和比较,分析了桥跨的内力、位移与弯桥圆心角的关系,并对其设计和计算提出了相应的建议。     

原油一段脱水达标新工艺在FPSO上的应用

随着海洋石油工业的高速发展,需要有越来越多的陆上石油处理工艺移植到海上平台上。通过对南海西部海域文昌13-1/2油田原油处理工艺流程及关键设备的研究、分析、不断优化和总结,证明了其先进性、可靠性和适应性,除完全能够满足生产的要求外,同时可以将这一工艺流程推广和应用到其他项目中,对工艺设计、甚至标准化设计都具有借鉴意义。     

京张高铁八达岭景区设站研究

京张高铁经八达岭景区设地下站,地下站埋深较深,且经过全国重点风景名胜区八达岭景区,涉及工程结构安全、铁路运营安全、旅游安全、文物安全,以及对景区景观、环境的影响等方面的问题,使得八达岭地下站成为各方关注的焦点。通过对八达岭地下站涉及的相关问题进行综合分析,认为在八达岭景区设站是必要的。通过方案比选,滚天沟地下站方案在技术上是可行的,车站设于滚天沟广场地下,游客乘降方便,有利于改善八达岭景区的交通拥堵状况,运输方式低碳、环保、安全、快捷,是相对较优的方案。最终选定在八达岭长城景区设置埋深102 m的地下车站作为实施方案。     

Customers’ selections between premium electric taxis and liquefied petroleum gas taxis

Reducing roadside emissions is a common challenge in metropolitan cities. In Hong Kong, conventional liquefied petroleum gas taxis are one of the main contributors to roadside emissions as they operate on the streets 24 h a day with a long daily driving mileage. Moreover, these taxis suffer from a severely poor service reputation. To enhance the environmental friendliness and service quality of the taxi industry, this study explores the market potential of operating premium electric taxis in the dispatching mode. A stated preference survey was conducted to 1410 taxi customers about their taxi-riding choices between premium electric taxis and conventional liquefied petroleum gas taxis. In total, 5640 observations were obtained and used to develop a series of binary logistic regression models with different model formulations for the determination of the significant factors influencing customers’ selections. The findings indicate that walk time to and wait time for taxis were the most critical concerns to the customers, and they were more willing to take premium taxis if their journey distance was longer and their desired improvement on taxi service quality was greater. The socio-demographic status of taxi customers also influences their choices. The associated policy implications are discussed for promoting taxis with better service quality and fewer roadside emissions. The findings provide some policy insights to other international cities that have a similar taxi market to Hong Kong.     

Recursive expected conditional value at risk in the fleet renewal problem with alternative fuel vehicles

We study the fleet portfolio management problem faced by a firm deciding which alternative fuel vehicles (AFVs) to choose for its fleet to minimise the weighted average of cost and risk, in a stochastic multi-period setting. We consider different types of technology and vehicles with heterogeneous capabilities. We propose a new time consistent recursive risk measure, the Recursive Expected Conditional Value at Risk (RECVaR), which we prove to be coherent. We then solve the problem for a large UK based company, reporting how the optimal policies are affected by risk aversion and by the clustering for each type of vehicle.     

Reliable route guidance: A case study from Chicago

Reliable route guidance can be obtained by solving the reliable a priori shortest path problem, which finds paths that maximize the probability of arriving on time. The goal of this paper is to demonstrate the benefits and applicability of such route guidance using a case study. An adaptive discretization scheme is first proposed to improve the efficiency in computing convolution, a time-consuming step used in the reliable routing algorithm to obtain path travel time distributions. Methods to construct link travel time distributions from real data in the case study are then discussed. Particularly, the travel time distributions on arterial streets are estimated from linear regression models calibrated from expressway data. Numerical experiments demonstrate that optimal paths are substantially affected by the reliability requirement in rush hours, and that reliable route guidance could generate up to 5-15% of travel time savings. The study also verifies that existing algorithms can solve large-scale problems within a reasonable amount of time.