The fleet size and mix pollution-routing problem

This paper introduces the fleet size and mix pollution-routing problem which extends the pollution-routing problem by considering a heterogeneous vehicle fleet. The main objective is to minimize the sum of vehicle fixed costs and routing cost, where the latter can be defined with respect to the cost of fuel and CO₂ emissions, and driver cost. Solving this problem poses several methodological challenges. To this end, we have developed a powerful metaheuristic which was successfully applied to a large pool of realistic benchmark instances. Several analyses were conducted to shed light on the trade-offs between various performance indicators, including capacity utilization, fuel and emissions and costs pertaining to vehicle acquisition, fuel consumption and drivers. The analyses also quantify the benefits of using a heterogeneous fleet over a homogeneous one.     

Walking short distances. The socioeconomic drivers for the use of proximity in everyday mobility in Barcelona

Many studies have found that cities, with residents that are co-located with jobs and services in compact and diverse urban environments, generate positive outputs for a number of areas of social policy, with issues ranging from environmental to social and including public health. This evidence supports promoting rich and thriving neighbourhoods in order to encourage short distance mobility. In this context, we use a wide travel survey (EMQ06), undertaken in Spain, to measure short-distance travelling within Barcelona and to assess how distinct social groups make use of the local scale for their everyday mobility. The effects of socioeconomics and access to transport are discussed, prior to applying a Chi-squared Automatic Interaction Detection (CHAID) method, in order to explore heterogeneity among the different social groups, in terms of local travelling. We found that nearly a quarter of all daily mobility in Barcelona is performed with a local trip, and that short trips are more frequently undertaken for personal purposes. Also, age, gender and access to private transport appear as significant factors. Overall, our results suggest that a proximity scale is being used by those groups with greater time–space constraints, such as working women or low income people without access to private vehicles, opening important implications on transport policy regarding the design of proximity-prone environments.     

国内外疏浚市场现状及发展

随着世界经济的发展，航道、港口等疏浚丁程不断上马，近几年疏浚市场十分红火。本文介绍了同内外疏浚市场的现状及发展。国内疏浚市场正处于供不应求阶段，巨大的挖泥船需求给中国造船业带来了新的契机。     

精细操作 适应定线——长江船舶定线制航路与驾驶技术研究

文章针对长江江苏段定线制航路的引入,解读定线制规定的正确运用,分析船队航法与操作习惯的改变,研究适应定线制航路通行的安全对策。     

论政党模式与政府创新的限度——一种比较分析的视角

政党是现代政治的常见现象,不同的政党对政府创新的影响是不一样的。本文以政党与社会的关系作为分析的逻辑起点,按照“政党—社会→执政党类型→执政方式→政府创新的限度”的分析路径,比较两种不同类型政党对政府创新限度的影响：他们是“全能主义—国家化执政党—领导控制—技术式创新”模式和“政治市场—交易型执政党—开放竞争—政府企业化”模式,在此基础上进行一个尝试性的小结。     

世界LNG海运市场回顾与展望

LNG海上贸易作为世界天然气贸易的一种重要方式,得到了快速的发展。分析了世界LNG海运市场运量和运力的情况,并对未来市场的发展进行了展望。     

班轮运输船队规划模型与仿真

为提高班轮运输系统的优化配置水平,满足班轮运输组织定期、定时服务的要求,根据班轮多港口挂靠和货物直达运输航线形式的特点,以规划期内船队营运现金流量折现值最大为目标,建立了班轮船队规划混合整数非线性规划模型.针对该模型的特点,设计了拉格朗日松弛启发式混合算法.以某航运公司班轮船队为例进行分析.结果表明:本文提出的启发式算法实现了多航线、多型船、大规模班轮船队规划问题的优化求解,能得到规划期内的航线配船、发船频率及船队建设优化方案.本文建立的模型能综合考虑航线的货流预测、船舶装载率、船舶租入租出等多种影响班轮船队规划的因素,适用于同一航线上配置相同船型的典型班轮运输模式,为班轮船队规划决策提供了支持.     

需求不确定状态下的航班机型分配问题研究

机型分配问题是飞机、机组排班问题的基础,是整个航班计划中的关键环节。文章针对市场需求高度不确定的情况,建立了两阶段随机混合整数规划模型,其中第一阶段考虑机族层次的分配,确保每个航节均分配1种且仅有1种机族,第二阶段根据进一步的市场需求信息及预测,考虑每个航节所分配的机族内具体机型的分配问题。针对建立的模型,设计了Benders分解算法,并通过算例验证了该模型较传统确定型模型更具有效性,能够为航空公司的机型分配提供决策支持。     

政府投资项目建设过程中影响工程投资的问题及建议

针对政府投资项目中存在的一些不规范性,该文从五个方面较为详细地阐述了存在的问题,分析了产生这些问题的原因,并提出了相关的建议。