移动IPv6关键协议技术的研究

综述了移动IPv6关键协议技术研究方面的一些最新的工作,分析了移动IPv6的基本原理,着重论述了移动IPv6所面临的问题,包括最小移动、快速切换、平滑切换等扩展协议,以及服务质量、通信安全等。     

Annual uptake of atmospheric CO2 by the Weddell Sea derived from a surface layer balance, including estimations of entrainment and new production

Data from two cruises, one in April/May 1996 and one in December/January 1993, covering the same wide area in the offshore Weddell Sea, were used to derive the annual extent of entrainment and the capacity of the biological pump. The former property was obtained with the help of dissolved oxygen data, whereas the latter was approximated with nutrients. Especially the data from April/May, representing the initial state of the winter surface layer, were crucial to assess the annual extent of these processes. The results were applied to our carbon dioxide data. The annual increase of the Total CO₂ (TCO₂) concentration in the surface layer due to vertical transport amounts to 16.3 μmol kg⁻¹. An entrainment rate of deep water in the surface layer amounting to 35±10 m yr⁻¹ was deduced. The compensating, biologically mediated TCO₂ reduction was calculated to be larger than the TCO₂ increase due to vertical transport. Since the balance of these two processes determines whether the Weddell Sea is a source or a sink of CO₂, this indicates that the Weddell Sea, albeit upwelling area, is definitely a sink for atmospheric CO₂ on an annual basis. This conclusion is further supported by contemplations that the biological drawdown of CO₂ in the Weddell Sea as a whole is probably underestimated by our calculations. The new production for the Weddell Sea on a per unit area basis was found to be much higher than that for the Antarctic Ocean, when the latter value is being obtained by traditional biological methods. On the other hand, the CO₂ uptake by the Weddell Sea on a per unit area basis is somewhat smaller than the CO₂ uptake by the world ocean.     

The unmet travel needs of the older population: a review of the literature

Unmet travel needs can be defined as trips and activities that people need or would like to do more, but for a variety of reasons they are prevented from doing so. This paper provides a critical evaluation of the literature focused on unmet travel needs, with the aim of assessing the scope of existing studies on this topic and better understanding the full context of older people’s mobility. This narrative review identifies how travel needs in later life have been assessed, and the barriers that affect the ability of older people to fulfil these needs. Due to the heterogeneity of older people and differences in research approaches, the analysis of the literature is not conclusive in terms of identifying the real impact of the analysed variables and measures on unrealised mobility. Nevertheless, of the studies analysed, on average at least one-third of older people report unmet travel needs. This situation was found to worsen with age, and women were reported to be more affected than men. The pursuit of leisure, and in particular visiting friends and family, was found to be the activity most associated with unmet travel needs.     

河道水流冲刷对推移质运动形态影响试验研究

水流冲刷下的床面是推移质运动的场所,研究微观床面形态对推移质运动的影响,有利于探究床面上推移质运动的规律,对河道治理有较好的促进作用。经过系列水槽试验,选取具有代表性的视频,采用图像识别技术,对视频中运动的物体进行标记,分析推移质在床面运动的规律,探究水流冲刷对推移质运动形态的影响。结果表明：大颗粒在床面上的运动方向与水流方向形成一个小于30°的、路径较直的夹角;小颗粒在床面的运动受近底流速的影响,聚集体会对河床表面水流进行树枝型分流,导致小颗粒的运动方向时刻变化,与水流方向夹角范围在0°～90°,在2个聚集体之间加速较为明显;不同形态的聚集体的稳定性不同,且聚集体之间可相互转化。     

沉埋施工法水底隧道数据库及其现实意义

为加速我国沉理随道的发展,引进国外先进技术,作者搜集了世界上已 建成的沉埋阵道货料,并建成了沉理施工法水底随道数据库。该库包括 沉理隧道的设计、施工、运榆管理等方面的内容。利用该库可快速地查 找各种经验数据和有关典道的乎面、纵剖面和横剖面图,为工程技术人 员研完和决策提供依据。为了使用方便,叶现有词组软件作了改进,并 开发了动态输出报表等一些新功能。      

基于离散元法的铁路沿线非饱和边坡流动与冲击分析

为降低降雨入渗对铁路边坡安全性的影响,对云南普洱市一铁路修建现场区域内存在的典型非饱和边坡进行稳定性分析.引入了黏附-再黏附模型,并通过模型试验以及离散元法分析不同参数条件下的土体崩塌特征和支护下的最大冲击力.研究结果表明:引入黏附-再黏附模型后的离散元法能很好地再现黏聚力作用下非饱和土边坡的崩塌行为;通过将非饱和土的...     

The utilisation and user characteristics of Uber services in London

ABSTRACT

Ridesourcing services such as Uber are nowadays a common feature within available transport options of many cities around the world (E.g. London & San Francisco). There has been much publicity about the potential impacts of ridesourcing services and how (or if) they should be managed or regulated without an objective understanding of who uses these services and why, as well as its current and future implications for public transport (PT).

Ridesourcing is part of a broader tech-driven, mobile app-based sharing phenomenon – the ‘sharing economy’ – which has disrupted traditional market models and industries, for example, the transport industry, where new players such as Uber have emerged and have quickly become part of the urban transport landscape. Uber has been at the forefront in disrupting the transport sector since its first launch in 2010 (San Francisco, USA). Since its launch, Uber has generated extensive media coverage and debate among policymakers, transport planners and transport authorities on how these services are affecting traditional transport modes such as buses and taxis. However, without objective empirical data – in terms of impacts on trip making characteristics, PT ridership and congestion – policymakers and transport regulators are yet to fully understand the real impacts ridesourcing services are having on the transport network.

This paper is part of broader research that aims to provide insights and empirical-based evidence on how Uber services are used (UberX and Uberpool) in London. A comprehensive survey was undertaken using a detailed questionnaire, issued to UberX and Uberpool users in London to gather detailed data on who uses the Uber services, why they use it and what are the trip purposes, in order to understand Uber user demographics and what effects (if any) Uber services are having on PT usage and trip making characteristics in London. The final findings provide important insights on Uber user demographics, trip purposes, types of trips replaced, impact on car ownership and why travellers use Uber services.     

舰船加筋复合材料层合板的导纳分析

应用有限元法对加筋复合材料层合板结构进行固有振动特性和导纳特性分析。基于一阶剪切理论的复合材料层合板理论，采用4节点Mindlin壳单元进行结构离散，通过动力学原理建立结构动力学有限元方程，并编制出相应的计算机程序。针对双向加筋复合材料结构进行分析，讨论不同结构模态阻尼系数、不同激励位置、不同边界条件和加筋的疏密程度对结构原点导纳及跨点导纳的影响。依据计算结果，可以进一步研究舰船复杂结构振动能量的传递和隔振效果，为追求最佳振动和声学设计提供分析方法。     

Household Mobility Tool Ownership: Modeling Interactions between Cars and Season Tickets

This paper moves beyond traditional models of car ownership in that we propose a framework for modeling household-level decisions to acquire specific types and numbers of mobility tools to fulfill the mobility needs of household members. The framework is applied to a data set collected during the winter and spring of 2000/2001 in the German city Karlsruhe via an interactive web-based stated response survey in which respondents could optimize their household mobility tool sets through on-line feedback concerning the estimated costs of the sets. In our analysis, bivariate ordered probit models are estimated for three combinations of mobility tools: season tickets (i.e., transit passes) and cars, season tickets and small cars and season tickets and large cars. In all instances, strong substitution effects are found – that is, as the number of season tickets increases, the number of cars decreases. This finding underscores the need to move beyond simple models of car ownership to comprehensive models of mobility tool ownership. As demonstrated by our research, failure to do so is likely to lead to biased results.