Identification and interpretation of spatial–temporal mismatch between taxi demand and supply using global positioning system data

Taxis provide a type of on-demand mobility service in urban transportation. There are growing concerns regarding the level of service of taxis in satisfying residents’ mobility demand. However, the mismatch between demand and supply of taxi services has not been resolved even with the introduction of app-based vehicle services. In this study, three indicators are constructed using the Shanghai taxi global positioning system (GPS) dataset to reveal the spatial–temporal mismatch pattern. The issue is further analyzed via a case study, in which seven regions with frequent mismatch patterns are identified in the time period from 21:00 to 22:00. Then, a multinomial logistic regression model is employed to identify the demographic and built-environment factors contributing to the taxi mismatch problem. The study results show that population density, residential areas, the number of points of interest, and road density have significant relationships with the taxi undersupply. In contrast, the areas of commercial lands, as well as the other two transportation-related factors, that is, the number of bus stops and the distance to nearest subway station, are observed to be statistically significant for both “oversupply” and “undersupply” conditions. This study provides valuable insights for identifying mismatch patterns and interpreting the mismatch problem as a function of spatially explicit factors that are of great use for urban governance, especially in the improvement of taxi efficiency, taxi management, and urban planning.     

舰船刚性阻振质量基座中频振动特性研究

有限元与统计能量混合法(FE-SEA)将计算低频响应的有限元法(FEM)与计算高频响应的统计能量法(SEA)结合起来,有效解决了FEM计算量大而SEA计算不准的中频域问题。提出在舰船弹性基座中引入刚性减振器,即在舰船基座与船体结构连接部位布设刚性阻振质量,并采用基于FE-SEA混合法的VA One软件对舰船刚性阻振质量基座的中频振动特性进行了研究。结果表明,刚性阻振质量对中高频结构噪声可起到明显的隔振作用,而对低频结构噪声的减振效果则不明显,甚至没有减振效果,这对刚性阻振技术在实艇基座减振降噪设计中的应用具有一定的实际工程价值。     

刚性阻振质量在舰船基座设计中的应用研究

基于阻抗失配原理,分析刚性阻振质量阻隔振动波传递的特性,提出在舰船弹性基座中引入刚性减振器．即在舰船基座与船体结构连接部位布设刚性阻振质量．并利用有限元法对基座舱段耐压壳体及基座板结构的振动传递特性进行数值仿真研究。研究结果表明：对于中高频结构噪声,刚性阻振质量能有效降低基座舱段耐压壳体的振动及声辐射,而对于低频结构噪声,阻振质量的减振效果不明显,甚至没有减振效果。这对刚性阻振技术在实艇减振降噪中的应用具有重要的参考意义。     

运能不匹配的城市轨道交通换乘方案研究

城市轨道交通换乘站有别于普通车站,其影响因素众多,应重点考虑换乘客流对车站设计方案的影响。在运能不匹配的情况下,对同台换乘、节点换乘、通道换乘等多种换乘方式的客流承载力进行验算,得到不同换乘方式承担大换乘客流的风险能力。当运能不匹配的轨道交通线路间换乘时,首先应选择合理的换乘节点,尽量采用多点换乘,避免大换乘客流集中产生风险,其次应适当增加换乘车站规模。当换乘站位于大断面区段存在较大客流风险时,应慎重选择同台换乘方式,可考虑通道换乘;当换乘站位于客流小断面区段存在较小的客流风险时,可优先选择换乘便捷的同台换乘或者节点换乘。总之,运能不匹配的换乘站应依据不同的客流特征选择合理的换乘方式,在满足换乘能力的前提下,优先选择换乘便捷、服务水平高的换乘方式。     

A 1.5 bit/s Pipelined Analog-to-Digital Converter Design with Independency of Capacitor Mismatch

A new technique which is named charge temporary storage technique (CTST) was presented to improve the linearity of a 1.5 bit/s pipelined analog-to-digital converter (ADC). The residual voltage was obtained from the sampling capacitor, and the other capacitor was just a temporary storage of charge. Then, the linearity produced by the mismatch of these capacitors was eliminated without adding extra capacitor error-averaging amplifiers. The simulation results confirmed the high linearity and low dissipation of pipelined ADCs implemented in CTST, so CTST was a new method to implement high resolution, small size ADCs.     

沿海航标管理及维护运行信息化探讨

文中介绍了我国沿海航标管理及维护运行信息化建设的背景,提出了航标信息化建设的设计方案,从设计原则、方法、航标数据库、总体框架等几方面进行论述,从而实现对航标业务及信息数据的规范化、智能化管理。     

船舶阻抗失配基座对平面弯曲波传递的阻抑特性

研究了船舶阻抗失配基座对平面弯曲波传递的阻抑特性.基于波动理论,根据不均质结构中波型转换、阻抗特性,推导并给出了振动波入射不同连接形式的船舶基座结构的透声系数及隔声量公式,归纳了隔振性能随基座板架厚度比及频率变化规律,讨论了基座连接结构处板架固定方式对隔振性能的影响.在理论分析基础上,构造含阻振质量的阻抗失配基座.数值结果表明阻抗失配基座显著增大了基座的输入机械阻抗,加剧了振动波在船体板架中的波形转换、散射和反射,显著提高了舰船基座结构的隔振效果.     

Ichthyoplankton in the neritic and coastal zone of Antarctica and Subantarctic islands: A review

Since the article published by Loeb et al. [Loeb, V.J., Kellermann, A., Koubbi, P., North, A.W., White, M., 1993. Antarctic larval fish assemblages: a review. Bull. Mar. Sci. 53(2), 416–449.] about Antarctic ichthyoplankton, many surveys were carried out in different sectors of the Southern Ocean focusing on different aspects of the ecology of fish larvae. Some of these researches were conducted in the Subantarctic Kerguelen Islands and others on the continental shelf off Terre Adélie and Georges V land. Oceanographic and geographic features influence fish larvae ecology such as island mass effects, gyres, canyons. Antarctic fishes show also temporal segregation of spawning which induces temporal succession of early stage larvae. This avoids competition and probably the predation on early stages for species having few recruits. In that case, we have to understand how these larvae can deal with the match–mismatch with their preys and how they find sufficient food to survive. But our knowledge on Antarctic fish larvae is still insufficient as we do not know larvae for quite a lot of species and because of the difficulty to sample during winter.