建构主义学习理论及其倡导的教学模式

本文简要分析了建构主义全新的学习理论以及受其理论影响而形成的教学模式,并结合其基本理论阐述了对大学英语教学的启示。文章认为,教学模式和教学方法的改革离不开现代外语教学理论的指导,建构主义学习理论对传统的教学理论和观念提出了挑战,为大学英语教学模式的转变提供了理论依据。     

不同沥青混凝土路面结构的大温差温度行为分析

为基于环境因素的大温差地区选择适宜的沥青混凝土路面结构提供理论依据。考虑沥青混合料的感温特性,将路面结构视为层间接触的不连续层状体系,应用ABAQU S的瞬态热分析和热-结构耦合求解技术,对不同基层类型沥青混凝土路面结构在低温大温差作用下的温度场与温度应力响应等温度行为特性进行分析。分析结果表明:采用级配碎石、掺2%水泥的级配碎石以及沥青稳定碎石等柔性基层的沥青混凝土路面结构组合,具有优良的抗环境温度变化作用的性能,是高寒、低温大温差地区值得推荐选用的沥青混凝土路面结构。     

Auction-based tolling systems in a connected and automated vehicles environment: Public opinion and implications for toll revenue and capacity utilization

Autonomous and connected vehicles are expected to enable new tolling mechanisms, such as auction-based tolls, for allocating the limited roadway capacity. This research examines the public perception of futuristic auction-based tolling systems, with a focus on the public acceptance of such systems over current tolling practices on highways (e.g., dynamic and fixed tolling methodologies). Through a stated-preference survey, responses from 159 road-users residing in Virginia are elicited to understand route choice behavior under a descending price auction implemented on a hypothetical two-route network. Analysis of the survey data shows that there is no outright rejection of the presented auction-based tolling among those who are familiar with the current tolling methods. While males strongly support the new method, no clear pattern emerges among other demographic variables such as income and education level, and age. While high income respondents and regular commuters are more likely to pay higher tolls, no statistical significance between different genders, age groups, household sizes, and education levels is found. Based on the modeling results and the hypothetical road network, it is found that descending price tolling method yields higher average toll rates, and generates at least 70% more revenue when travel time saving is 30 min, and improves capacity utilization of the toll road significantly compared to fixed tolls.     

Adapting the shipping sector to stricter emissions regulations: Fuel switching or installing a scrubber?

This paper examines how the existing fleet in the shipping industry can be adapted to the new emission regulations through the two main techniques that currently exist: (a) the use of low-sulphur marine diesels; and (b) the installation of scrubbers. A method is presented here for drawing up an economic assessment of both these techniques under uncertainty. It enables the best option to be selected at any given time taking into account fuel prices (spot and futures), scrubber installation costs, the time that the vessel operates in an Emission Control Area (ECA) and the remaining useful lifetime of the vessel. The paper also considers the possibility of an unexpected change from a non-ECA navigation area to an ECA. The assessment is carried out in a manner consistent with marine diesel and crude oil spot and futures market quotes. Our results show the net present value of investing in the installation of scrubbers and investing in changing fuel types for different assumptions on how vessels are operated. We also analyse increases in fuel consumption and CO₂ emissions as a consequence of using scrubbers and how they affects the financial analysis if such incremental emissions must be paid under a CO₂ pricing mechanism.     

Continuous approximation models for mixed load school bus routing

School bus routing is a complex and expensive transportation problem for many public school districts. Typical school bus routes serve a single school, but mixed load school bus routes carry students for more than one school at the same time. A mixed load policy reduces the number of stops and distance to pick up and drop off children, but it can increase travel distance by visiting multiple schools. This paper provides a general strategic analysis using continuous approximation models to assess the conditions under which mixed loading is likely to be beneficial. We also present a case study for a semi-rural Missouri school district to illustrate the application of the models in practice. Results show that mixed load routing is more beneficial for larger districts, when a large percentage of bus stops are shared by students of different schools, and when schools are closer together.     

Impact of stop-and-go waves and lane changes on discharge rate in recovery flow

In an effort to uncover traffic conditions that trigger discharge rate reductions near active bottlenecks, this paper analyzed individual vehicle trajectories at a microscopic level and documented the findings. Based on an investigation of traffic flow involving diverse traffic situations, a driver’s tendency to take a significant headway after passing stop-and-go waves was identified as one of the influencing factors for discharge rate reduction. Conversely, the pattern of lane changers caused a transient increase in the discharge rate until the situation was relaxed after completing the lane-changing event. Although we observed a high flow from the incoming lane changers, the events ultimately caused adverse impacts on the traffic such that the disturbances generated stop-and-go waves. Based on this observation, we regard upstream lane changes and stop-and-go waves as the responsible factors for the decreased capacity at downstream of active bottlenecks. This empirical investigation also supports the resignation effect, the regressive effect, and the asymmetric behavioral models in differentiating acceleration and deceleration behaviors.     

市场经济条件下的航海职业教育模式研究

在市场经济条件下，依据高等职业教育人才培养的特点及对航海职业教师的素质的要求，针对当前航运业对高级人才的基本要求和需求情况，“订单”培养与航运企业联合办学是符合市场需求的人才培养的新模式．     

渐变能隙超晶格结构中的施主杂质性质的研究

本文研究了渐变能隙超晶格结构中类氢施主杂质的性质。使用无限深抛物线势阱模拟这一结构,在有效质量近似下,用变分法计算了抛物线势阱中施主杂质的基态和几个低激发态的束缚能。给出了这些状态的束缚能随势阱焦距(Al 成分的变化率)、杂质的位置变化的规律,并将所得的结果与方势阱的实验结果进行比较,得出了一些有意义的结果。     

双壳驳模型的结构设计及约束扭转试验研究

本文从双壳驳模型结构设计、扭转试验技术两方面作了系统介绍。 在指导畸变模型设计的理论上,提出了两个独立的几何参数L、t的概念,基本解决了这类模型所必然存在的构件厚度与其它几何尺度不能取同一相似倍数的问题,从而使模型试验结果对实船进行相关预报成为可能。 在约束扭转试验技术方面,设计中采用了双滑轮悬吊支承,油顶-滑轮自平闭式加载系统,百分表随动臂架变形测量装置等,形成一套新的弯、扭组合测试技术,与国外类似试验相比,模型的边界条件更为合理。 本文结论对于箱形结构模型是适用的;所介绍的试验技术对于集装箱船、双体船、工程船和海洋平台等大比例尺模型试验具有一定的参考价值。