全球海事界的盛会——第十三届中国国际海事展览会

12月6日，作为亚洲最具权威的海事展览会，第13届中国国际海事展览会在上海新国际博览中心隆重开幕！虽然最近上海气温骤降，但两年一届的中国国际海事展览会依然吸引了来自全球海事业界的众多人士，大家齐聚上海，现场气氛火爆。[编者按]     

An examination of the determinants of day-to-day variability in individuals' urban travel behavior

Day-to-day variability in individuals' travel behavior (intrapersonal variability) has been recognized in conceptual discussions, yet the analysis and modeling of urban travel are typically based on a single day record of each individual's travel. This paper develops and examines hypotheses regarding the determinants of intrapersonal variability in urban travel behavior.Two general hypotheses are formulated to describe the effects of motivations for travel and related behavior and of travel and related constraints on intrapersonal variability in weekday urban travel behavior. Specific hypotheses concerning the effect of various sociodernographic characteristics on intrapersonal variability are derived from these general hypotheses. These specific hypotheses are tested empirically in the context of daily trip frequency using a five-day record of travel in Reading, England.The empirical results support the two general hypotheses. First, individuals who have fewer economic and role-related constraints have higher levels of intrapersonal variability in their daily trip frequency. Second, individuals who fulfil personal and household needs that do not require daily participation in out-of-home activities have higher levels of intrapersonal variability in their daily trip frequency.     

Urban travel demand: The impact of Box-Cox transformations with nonspherical residual errors

We develop an algorithm for solving regression models with Box-Cox transformations on both the dependent and independent variables, while simultaneously taking into account corrections for serial correlation of several orders and for heteroscedasticity. The latter correction is of a general form which contains as special cases most specifications of heteroscedasticity found in practice. We apply the procedure to three urban travel demand functions, two of which are currently used in their linear form by the Montreal Transit Authority, and analyze more than 100 specifications. Our results show that taking into account nonsphericalness of the residuals has a major impact on model parameter estimates, notably on those which determine the functional form of the model, and that, conversely, modifications of the functional form have strong implications for both the structure of autocorrelation and the importance of heteroscedasticity; moreover, we find interactions between autocorrelation and heteroscedasticity structures. We introduce a special measure of elasticity for variables which contain zero observations, particularly dummy variables. Moreover, we find that elasticities of demand and implicit values of time depend to a large extent on the stochastic specification of the model.     

Rail freight transportation: A review of recent optimization models for train routing and empty car distribution

This paper describes two types of rail transportation problems in detail. These are train routing and makeup, and empty car distribution problems. Some of the recent optimization models which address these problems are reviewed and the areas for potential improvements in rail transportation literature are identified. The type of interactions which exist between routing, makeup, and empty car distribution decisions are highlighted and potential areas for future research are identified.     

钢桥构件按疲劳寿命服从威布尔分布的可靠度计算

本文根据失效率函数h(二)讨论了假定疲劳寿命服从对数正态分布的不合理之处,并 在假定疲劳寿命服从威布尔分布的基础上导出钢桥构件疲劳可靠度的计算式。      

提速客车转向架转臂的拓扑优化设计

为设计出易于安装及落车的提速客车转向架转臂结构,基于变密度法和非线性接触有限元法对转臂进行了拓扑优化和强度分析。以HyperMesh/Optistruct为拓扑优化分析平台,创建了转臂的拓扑优化模型;以I-DEAS软件为多体接触分析平台,建立和分析了新型转臂的多体接触有限元模型。结果表明:新型转臂结构在满足使用强度的要求下,不仅从整体上改善了结构的应力分布,使应力分布更趋均匀,而且转臂的质量也比现有结构的质量下降了9.7%。     

USS Boone (FFG 28) Emergent Underwater Rudder Replacement

On November 30, 2006, USS Boone (FFG 28) lost all steering control in the Mediterranean Sea due to a lost rudder. Within hours of the casualty, numerous US Navy and contractor activities sprung into action to coordinate and complete an emergent voyage repair to return USS Boone to service to support the Global War on Terrorism. The Navy faced a large hurdle to identify and transport a replacement rudder to Rota, Spain, and prepare and carry out an extremely complex repair procedure. Pearl Harbor Naval Shipyard personnel removed the replacement rudder from USS Crommelin (FFG 37) in Pearl Harbor Naval Shipyard and transported the rudder to Rota, Spain. The Navy's Supervisor of Salvage and Diving developed the repair procedure and coordinated the repair operation, which involved over 30 US Navy and contractor divers. The repair team completed the rudder replacement on December 28, 2006 and returned USS Boone to underway operations.     

Long-term changes of inorganic nutrients in the Lagoon of Venice (Italy)

The paper aims at investigating the trends of the concentrations of dissolved inorganic nitrogen (DIN) and phosphorous in the Lagoon of Venice, Italy, in the last 35 years. The trend analysis of ammonia nitrogen, nitrate nitrogen and reactive phosphorus (RP) yielded rather different results. The decrease in ammonia nitrogen concentration, in particular, in the basin influenced by severe industrial discharges, is accurately described by a negative exponential model. The nitrate concentration did not show significant interannual trends, while wide seasonal variations have been detected. Reactive phosphorus concentration increased until the end of the 1970s at the stations close to the industrial area as well as in those influenced by river discharges and by sewages of the city of Venice. The sudden decrease that followed was most likely related with environmental policies, namely the improvement of wastewater purification treatments and the regulation of phosphorus use in detergents.     

A reduced-gravity model of the Catalan Sea

A reduced-gravity model is used to study the effects of the wind on the upper layer circulation in the Catalan Sea. The model parameters were set by observed features of the circulation in the basin. It is shown that the results are particularly sensitive to the open sea boundary conditions. Simulations were done using the following boundary fluxes: (i) mean values estimated by Bethoux (1980) and (ii) more recent geostrophic transports computed from hydrographic data by Font et al. (1988). The latter seem to lead to more realistic circulation patterns. The influence of seasonal winds (climatological data) on the dynamics is clear, especially during the winter.     

Physical–biological coupling in spore dispersal of kelp forest macroalgae

The physical–biological linkages controlling the dispersal of spores produced by macroalgae that reside in kelp forests are complicated and laced with feedbacks. Here we discuss the fundamental elements of these interactions. Biological considerations include spore swimming and sinking speeds, their periods of viability in the plankton, and the height of spore release above the seafloor, which together determine the durations over which spores can be swept by horizontal currents before they contact the seafloor. Morphologies and material properties of canopy forming kelps may also influence the drag exerted on passing waters by the kelps, the plants' ability to persist in the face of rapid flows, and thereby the degree to which impinging currents are redirected around, or slowed within, kelp forests. Macroalgal life histories, and the size of spore sources as controlled by the dimensions of kelp forests and the density and fecundity of individuals within them, influence effective dispersal distances as well. Physical considerations encompass the mean speed, direction, and timescales of variability of currents relative to spore suspension times, the interaction of surface gravity waves with currents in producing turbulence in the benthic boundary layer, wind-driven surface mixing, water stratification, and shoreline bathymetry and substratum roughness, all of which can affect the interplay of vertical and horizontal transport of macroalgal spores. Intricate within-forest processes may induce attenuation of current speeds and consequent reductions in seabed shear, along with simultaneous production of small-scale turbulence in kelp wakes. Slower mean currents and smaller eddy scales in turn may attenuate vertical mixing within forests, thus extending spore suspension times. Further complexities likely arise due to changes in the relative rates of horizontal and vertical dispersion, modifications to the overall profiles of vertical mixing, and the creation of fine-scale secondary flows around kelp individuals and substratum features. Under conditions of more rapid currents, submergence of the surface canopy and the establishment of skimming flows at the canopy–fluid interface may introduce additional coherent flow structures that alter rates of fluid exchange to and from the forest. Many of these coupled physical–biological processes are just beginning to be examined in a rigorous fashion in kelp forests, but their potential importance is clear.