Circulation on the Armorican shelf (Bay of Biscay) in autumn

Three drifters drogued at 65 m were launched on a transect on the Armorican shelf of the Bay of Biscay for 4 years. The experiments were conducted in autumn. They revealed a north-westward, poleward current over the 100 m isobath and a very weak eastward current over depths comprised between 120 and 150 m. A model was used to assess the role of residual tidal currents and wind-induced circulation. The results show that the former are quite weak and the latter do not explain the average velocity of over 10 cm s^− 1. It is thought that this current is mainly driven by the density gradient induced by the breakdown of stratification. Hydrological data and satellite images from the period are discussed, in the light of this hypothesis.     

法国混合动力式AGC列车

介绍了法国混合动力式AGC列车的结构特点,以及运用前景.     

Geographical variation in traffic-related mortality and morbidity among pedestrians in Quebec, 1983-1988

In this study we analyze the dmographic and geographical distribution of pedestrian accidents (n=28,452) in the Quebec Municipalités régionales de comté (MRC) reported between January 1, 1983 and December 31, 1988. In order to be able to make comparisons between MRCs, we have created in Comparative Mortality Index and a Comparative Morbidity Index. We use a logistic regression model to single out explanatory factors. The main tendencies which are apparent in the demographic analysis are an overrepresentation of young persons and elderly persons in the accident statistics, and that men are more at risk than women. Men 15 years and under and men 65 years and over are more at risk of being involved in a fatal pedestrian accident. The geographic analysis show that among men, the average mortality rate is one and a half times greater in rural MRCs than in urban MRCs; among women, rural mortality is two and a half times greater than urban mortality. In the case of non-severe injuries we note an over-representation of urban MRCs. Young persons 15 years or less who live in an urban, populated zone are those most at risk of being involved in a pedestrian accident. Identifying high risk groups or areas is a prerequisite step for injury prevention and control.     

Microphytobenthos biomass at Kerguelen's Land (Subantarctic Indian Ocean): repartition and variability during austral summers

Microphytobenthos biomass has been measured at several coastal sites on the SE of the main island of the Kerguelen Archipelago (Indian Ocean), during several austral summers (1985–1992), using a conventional fluorometric method. Heterogeneity tests, conducted on two different intertidal sites (Port-Aux-Français, PAF; and Port-Raymond, PRA), showed low standard deviations, whereas the mean concentrations were highly different. Pigment concentrations showed a high variability related to the characteristics of the sediments: from low biomass in coarse intertidal sand, submitted to intense scouring (0.32±0.31 μg Chl a g⁻¹ dw, 0.29±0.14 μg Phaeo g⁻¹ dw) to high biomass in intertidal muddy sand in sheltered areas, particularly along estuaries (54 μg Chl a, 15 μg Phaeo g⁻¹ dw at Korrigan). The subtidal muddy sediments under a Macrocystis pyrifera (Linné) and Durvillaea antarctica (Chamisso in Choris) belt exhibited high concentrations in phaeopigment (Phaeo) (up to 136±83 μg g⁻¹ dw; PRA), while the concentration of chlorophyll a (Chl a) was relatively low. The dense macroalgal canopy supports an important epiphytic diatom biomass (mainly the genera Cocconeis Ehrenberg and Grammatophora Ehrenberg), which is sedimenting after degradation and is in part responsible of the high levels of Phaeo in all sediments. Macroalgal debris were observed, but diatom frustules were dominant in most surficial subtidal sediments. A circatidal mud, in the Morbihan Bay, made of a sponge spicule mat (50 m deep; 4.96 μg Chl a g⁻¹ dw), showed a very low Chl a/Phaeo ratio (0.1), while it reached up to 6 in intertidal sand. Surprisingly, a penguin rookery beach, at the east side of Courbet Peninsula, was characterized by a very low biomass (0.07±0.04 μg Chl a g⁻¹ dw), while it was nutrient enriched, particularly with nitrates.In comparison with the data at the similar latitude, but in temperate regions from the Northern Hemisphere, the microphytobenthos biomass, recorded at Kerguelen's Land, exhibited relatively high pigment concentrations, particularly the Phaeo, and supported a dense and diversified subtidal macrofauna composed of polychaetes (particularly Thelepus extensus Hutchings and Glasby), sea urchins, mytillids and gammarids. The exuberant macroalgal canopy, coastal indentations and low tidal amplitude must be in part responsible of these large benthic primary and secondary biomasses.     

The Available Methods to Calculate the Wheel/Rail Forces in Non Hertzian Contact Patches and Rail Damaging

In the present paper, the methods used in railway dynamics to take into account the non Hertzian multi contact patches occurring on a wheel, are summarised. Some application cases are presented as well as an explanation of the so called “squat” rail deterioration.     

出行服务的发展:无限可能的时代

面对燃油价格过高、全球气候变暖等一系列问题,寻求＂共享＂交通资源与可持续发展势在必行。围绕公共自行车、自助汽车、车辆租借、社会服务目的的购车贷款、拼车几种交通系统的创新方式,以美国、法国等发达国家为例分析这几种创新方式的特点、经验以及发展前景。最后,指出交通问题没有万能的解决方式,需因地制宜,并根据某一种创新方式对个人的益处以及整体使用者的数量两个方面对其进行评价。     

Cavitation erosion research in France: the state of the art

An important part of the French research program on cavitation erosion, conducted from 1980 to 1995, was devoted to pitting. Histograms of pit size have been extensively used to characterise the hydrodynamic aggressiveness of a cavitating flow. Numerous erosion tests, limited to the incubation period, were carried out on similar test sections, for different velocities, liquids, length scales, and materials. Scaling laws were discussed and two kinds of methods for prediction of the erosion rate were proposed. The first one is based upon the estimation of the aggressiveness of the prototype cavitating flow, from pitting tests on a model and the simulation of the prototype histogram of pits on an appropriate device. The second one is based upon a correlation between the advanced stage of erosion and the incubation period, consisting of a proper adimensionalization of the mass-loss curve. After several years of research and the development of special facilities, devices and techniques, more deterministic procedures for predicting cavitation erosion could now be developed, based not upon erosion tests, but upon the characterization of the aggressiveness of the cavitating flow in terms of impact loads and the analysis of the mechanical and metallurgical response of the material to successive impacts.     

Influence of residual stresses and geometric imperfections on the elastoplastic collapse of cylindrical tubes under external pressure

The buckling problem of a circular cylindrical shell has long been widely investigated due to its great importance in the design of aerospace and marine structures. Geometric imperfections and residual stresses are inevitable in practice and have been so far frequently considered in analytical and numerical predictions. But little attention has been paid until now on the combined influence of such initial defects on the critical and often unstable response of such elastoplastic structures. In this paper, a shell finite element is designed within the total Lagrangian formulation framework to deal with the elastoplastic buckling and post-buckling of thin cylindrical tubes under external pressure and axial compression. A specific experimental process will be introduced in order to measure residual stresses in the shell very accurately, so as to include them in the numerical calculations. The present formulation will enable us to describe the complete non-linear solutions, namely the critical pressures (bifurcation and limit (collapse) loads), the bifurcation modes and the bifurcated equilibrium branches up to advanced post-critical states. Comparisons will be made between numerical results and the experimental critical value and deformation patterns of a new generation profiler. Furthermore, the combined effects of geometric imperfections, residual stresses and plasticity will be analyzed.     

Train-to-wayside wireless communication in tunnel using ultra-wide-band and time reversal

The capabilities of ultra-wide-band (UWB) technology make it a viable candidate for fourth generation wireless communication. This paper proposes the use of UWB radio technology and time-reversal (TR) technique for underground train-to-wayside communication systems. UWB technology has the potential to offer simultaneous ground-to-train communication, train location and obstacle detection in front of the trains. Time-reversal channel prefiltering facilitates signal detection and helps reducing interference. Thus, UWB–TR combination provides a challenging, economically sensible, as well as technically effective alternative solution to existing signaling technologies used in urban transport systems. This paper concentrates on the communication function and reports simulation and measurement performance evaluation of such combinations, respectively in a deterministic tunnel channel model and in real tunnel environments. A new approach is also proposed to ensure multiple access (MA) communication using modified-orthogonal waveforms.