On the distribution of dissolved lead in the Loire estuary and the North Biscay continental shelf, France

The dissolved lead was studied in the whole salinity gradient of the system composed of the Loire estuary and the North Biscay continental shelf. About 130 samples were collected in winter 2001 and spring 2002 during Nutrigas and Gasprod campaigns (Programme PNEC-Golfe de Gascogne, RV Thalassa) and metal measurements were conducted on board by Potentiometric Stripping Analysis. In the Loire estuary, levels of dissolved lead ranged from 0.15 to 0.24 nM and from 0.04 to 0.26 nM in winter and spring, respectively. Compared to the concentrations reported in 1987 and 1990 (0.4–1.7 nM; Boutier, B., Chiffoleau, J.F., Auger, D., Truquet, I., 1993. Influence of the Loire river on dissolved lead and cadmium concentrations in coastal waters of Brittany. Estuar. Coast. Shelf S., 36:133–143, Estuarine, Coastal and Shelf Science 36, 133–143) our study indicated much lower values. The fall in concentration in the estuary could be attributed to the stopping of activity of Octel, a big manufacturer of tetra alkyl lead. Discharge in dissolved metal to the continental shelf by the Loire river was assessed as 7.5 and 1.9 kg day^− 1 for winter and spring, respectively. On the continental shelf, levels of dissolved lead varied within 0.06 and 0.27 nM in winter (0.15 ± 0.06 nM, sd = 1.96, n = 49), whereas concentrations measured in spring were in the range 0.06–0.17 nM (0.09 ± 0.03 nM, sd = 1.96, n = 60). This difference in metal concentration was related to the amounts of rainfall that have fallen over the continental shelf: estimations of inputs by this way (74 and 32 kg day^− 1 in winter and spring, respectively) appeared to be significantly higher than inputs from the Loire river (7.5 and 1.9 kg day^− 1 in winter and spring, respectively). The distributions of dissolved metal in the surface waters highlighted the role of suspended particular matter (SPM) for a rapid “trapping” of lead near the mouth of the estuary. The vertical distributions showed, in the stratified area, a biological transfer of lead between winter and spring from surface waters to the halocline.     

新开发的轮对设计方法

轮对设计在车轮磨耗方面正面临着严格的新规范 ,以降低外形车削的要求 ,并减轻质量 ,以减少对轨道的侵蚀 ,且在可靠性、运行安全性和寿命周期成本都没有不利影响的情况下 ,实现所有要求。与此同时 ,由于车辆有既在小半径曲线 ,又在高速线路上运行的趋向 ,在普通线路上提高了运行速度 ,以及由于低级维护而使线路质量和车辆质量有所降低 ,所以轮对的运行作用正在变化。为此 ,开发了一整套程序 ,以便为高速列车设计振动小、噪声低、寿命周期成本最佳的轮对 ,也为城市轨道车辆设计新型的使用铝制轮毂、钢制车轴和轮辋的轻型混合车轮。该程序以采…     

新型快餐盒生物降解性能试验方法研究

通过固体培养微生物侵蚀试验、液体培养微生物侵蚀试验、降解过程中纤维素酶活性测定、纤维素酶侵蚀试验和降解过程中 Ｃ Ｏ２ 生成体积分数的测定等试验结果分析，认为固体培养微生物侵蚀试验、纤维素酶侵蚀试验及 Ｃ Ｏ２ 生成量测定试验可用于评价新型快餐盒生物降解性能。     

A “horizontal Sverdrup mechanism” may control the spring bloom around small oceanic islands and over banks

One of the most basic paradigms in marine ecology is the “Sverdrup mechanism,” where the spring bloom is retarded if the surface mixed layer is too deep, due to the algae being mixed vertically out of the euphotic layer. A similar mechanism may operate in vertically homogeneous water over a small shallow area, surrounded by deep waters, if the horizontal exchange is sufficiently intense. In systems with inter-annual variations in the horizontal exchange rate, this may induce inter-annual variations in the timing and intensity of the spring bloom. A numerical primary production model with circular symmetry and prescribed horizontal exchange rate is developed. Using the Faroe Shelf as an example, the model and observations show that the timing and intensity of the spring bloom in the shallow parts of the system may be critically dependent upon the rate of the horizontal exchange. Numerical experiments confirm that the effect of horizontal exchange on the spring bloom is less pronounced for banks than for shelf systems around islands of similar scales, and that the effect increases in importance as the horizontal scale is reduced.     

Exploring the distances people walk to access public transport

ABSTRACT

A shift from private motorised transport to more active transportation can, among other things, deliver significant health benefits. The main disadvantage of active transport (in particular walking) for most people compared to private motorised transport is the limited range. Public transport (PT) can complement the use of active modes and extend their range. Therefore, there might be potential to increase physical activity through an increase in PT use. This article takes a closer look at how walking relates to the use of PT by examining existing literature on the topic. It aims to study how far people walk to and from PT and what key factors influence this. Scopus, Transport Research International Documentation and Web of Science have been searched systematically for relevant articles, conference papers and books. After screening of titles and abstracts, 41 relevant publications were identified. Studies were included if they quantified the amount of walking (measured as either distance or time) that is directly related to the use of PT. Studies that quantified walking using general measures of daily physical activity or daily walking or that used stated preference designs were excluded. The PT systems considered in this paper are mass transport systems in urban areas, either road- or rail-based, with fixed schedules and stops. Demand responsive transport services, which can offer door-to-door travel, are not considered, as these systems can to a large extent eliminate the need to walk. In the identified publications, a large variety of walking distances and times have been reported, and these seem to be highly context-specific. The paper establishes the evidence for the wide range of factors that influence walking related to PT, which have been categorised as personal, PT-related, environmental, and journey-related. The different methods that have been used are discussed by critically analysing their advantages and limitations. Only a limited number of these methods used allow for an accurate assessment of the walking distances to and from PT. The paper concludes with suggestions for future research, such as a need for more accurate measurement of walking and research in different geographical areas to shed light on underlying influences of culture and climate.     

An exploratory analysis of observed and latent variables affecting intercity train service quality in developing countries

Transportation - Service quality (SQ) and customer satisfaction as perceived by 1037 passengers on intercity train services in Bangladesh were examined using structural equation modeling to explain...     

高速铁路车辆车轴的疲劳设计方法

从19世纪早期铁路运营开始,车轴的疲劳设计就是工程设计人员在材料的疲劳研究方面的一个难点。为了保证高速铁路系统的安全,一些杰出的研究人员进行了大量的投资和试验,并且在材料、制造、热处理和设计方法等方面取得了很大进步。比较欧洲和日本在高速铁路车辆车轴疲劳设计上的原理,认为在新干线车辆和TGV,ICE之间存在一些区别。疲劳强度的危险部位主要是容易受到磨损和疲劳损伤的压装配合部位,如轮座、齿轮座和制动盘座等部位。在欧洲,车轴压装部位采用大直径使危险部位平滑;在日本采用高频硬化的方法提高压装部位的疲劳强度,同时在车轴的压装部位附近设置了应力释放槽。多年来,新干线的车轴经过磁粉探伤没有发现疲劳磨损裂纹,这表明高速铁路车轴的安全性多年的改进是成功的。     

Practical Frequency and Time Optimal Design of Passive Linear Vibration Isolation Mounts

Summary In this paper we examine a linear one-degree of freedom vibration isolator mount. The linearity of the system allows us to analyze its frequency and time response characteristics analytically. Optimal damping and stiffness values for the isolator are obtained by minimizing certain cost functions, which are the Root Mean Square (RMS) of the absolute acceleration and the relative displacement. These RMS cost functions are used to create a design chart for the isolator parameters. This is very useful particularly in the presence of physical constraints such as a limit in relative displacement. The time response of the system for a unit step input is also considered to gain an insight into the transient characteristics of the system. We obtain an optimal value for the damping ratio of the system in order to minimize the transmitted acceleration. Combining the frequency and time response analyses leads to an optimal value for the mount natural frequency and damping ratio satisfying both time and frequency domains. The results are verified numerically using measured acceleration as input.     

Deep water mass characteristics and interannual variability in the North and Central Aegean Sea

The characteristics and interannual variability of the deep water masses in the North and Central Aegean Sea are being investigated through the data sets of the Hellenic Navy Hydrographic Service (HNHS) and the MEDATLAS 1997 project. In the period between 1987 and 1993, the densest deep water in the Mediterranean has been produced in the Aegean Sea (with σ_θ densities reaching up to 29.6 kg/m³), contributing to what has been called the Eastern Mediterranean Transient. The examination of time series of mean integrated values of θ, S and σ_θ below the depth of 500 dbar reveals the significant deep water density increase after 1987 in all of the deep basins in the area. Data suggest that the density increase of 1987–1988 is mainly attributed to a temperature drop, while in 1993, an even more intense density increase is observed, characterized this time by an abrupt salinity increase. We assume that the increased salinity necessary to produce deep water masses with the observed characteristics was not locally produced but rather advected from the Levantine through the South Aegean. After 1993, no new deep water formation episodes have been observed. A series of Θ–S diagrams derived from HNHS CTD casts covering the period between 1993 and 2000, depict the different characteristics of the deep water masses in the area. As 1993 marks the end of the formation period, observed differences between basins in that year must be attributed to different deep water formation sites. Thereafter, the stagnating deep water in the North and Central Aegean basins has been slowly gaining buoyancy by losing salt and gaining heat. The rate at which this phenomenon takes place varies between different deep basins. It is suggested that these variations are linked to the different volumes of each basin as well as to the general circulation features of the Aegean Sea.     

韩国HSR 350x型高速动车组的开发

韩国在引进法国TGV之后于2004年4月1日启动了韩国特快列车(KTX)的运营,从此韩国便开始步入了高速铁路时代,这被称为"内陆运输革命".此外,韩国通过名为"高速铁路技术开发"的国家研发项目,自主研制出350型高速试验动车组(HSR 350x),在2003年9月汉城至釜山高速试验线上运行时,其运行速度超过了300 km/h.HSR 350x作为最佳技术成果载入韩国铁路史.HSR 350x是韩国工程技术人员研制的,从概念设计到在线试验共用了6年的时间.按既定目标该动车组投入Honam高速线的商业运营以及在先期的运行中确定其与地面设施的兼容性.这样,韩国能充分利用自己的技术设计高速铁路、开发主要设备和生产动车组.也就是说,韩国通过修建汉城至釜山的高速铁路线,能进一步掌握高速铁路的建造、管理与维护技术.这一巨大成果将使韩国成为世界上拥有最佳高速铁路技术水平的国家之一.详细介绍了HSR 350x型高速动车组及其主要核心设备的开发.