VICTREX(R)PEEK(R)聚合物使极端条件下的密封工序轻而易举

在汽车中,密封件和垫圈始终起着非常重要的作用.为了满足现今苛刻的技术要求,开发人员越来越多转向使用耐高温材料,以用于制造发动机、变速器、转向系统和燃油注入系统的密封件.     

Hydrographic structure and zooplankton abundance and diversity off Paita, northern Peru (1994 to 2004) — ENSO effects, trends and changes

The objective of the present study was to verify possible spatial, seasonal, and inter-annual changes in the zooplankton off Paita (northern Peru), an upwelling area located closely to the limits of cold Humboldt Current and warm Equatorial Surface Waters. Zooplankton was sampled at subsurface on 53 occasions from August 1994 to December 2004 at four stations located 2 to 30 km offshore with a WP-2 net (300 µm). Extremely high surface water temperatures combined with low salinities were observed during the 1997/98 El Niño up to 29.0 °C) and in April 2002 (up to 25.0 °C). Temperatures more than 2 °C above monthly average were also observed in October 1994, in April 2000, and in November 2004. Significant trends were observed for oxygen concentration (increase) and several horizontal and vertical gradients. Among the copepods (72% of all individuals), the most abundant species were Paracalanus parvus (28%), Acartia tonsa (26%), and Calanus sp. (10%). The strong 1997–98 El Niño (EN) event led to drastic changes in species composition that were reversed during the 1998–99 La Niña (LN) event. Community parameters such as total abundance, diversity, equitability and species richness displayed marked variations associated with the 1997–98 EN and long-term trends. Long-term trends were significant for several vertical and horizontal temperature and oxygen gradients, indicating an increase in upwelling intensity at the shelf during the study period. 10-year-trends were also significant for total zooplankton abundance (increase) and community evenness (J, decline). Our data confirmed the importance of the weak EN in 2002/03 for the study region. Within the trend of increasing zooplankton abundance, a sharp step or shift was observed from 1999 to 2000. When using sequential t-tests to detect shifts in (x + 1) transformed abundance data, a significant rupture was found between the last sampling in 1999 and the first sampling in 2000. Also, a substantial decrease in diel variability occurred after 1999, probably due to changes in vertical migration patterns. The considerable increase in zooplankton abundance over the study period, the ENSO effect, and the 1999–2000 transition are discussed with regard to synchronicity with other zooplankton time series. The present study contributes with the first evidence from an important area located in the Humboldt Current for synchronous trends and changes that were previously observed elsewhere in the Pacific. Our results demonstrated the importance of long-term zooplankton monitoring studies in upwelling areas, and confirms the idea of dramatic changes in pelagic ecosystem structure occurring in the East Pacific.     

Reconstructions of marine environmental conditions and scenarios for future changes

Long-term changes of environmental conditions are fundamentally important for many sectors in the maritime industry. Observational evidence from which such long-term changes may be reliably derived is often limited. Here we briefly illustrate the present situation and present an approach on how quasirealistic environmental models can be used in combination with existing data to reconstruct recent long-term changes and to derive scenarios of future developments. We concentrate on variables of primary importance for the maritime industry, namely wind-storms, wind-waves and storm surges. Examples are provided for the North Sea area.     

Advanced Contact Mechanics-Road and Rail

The development of contact theories and numerical formula for various applications is a field which expands rapidly. This publication focuses on the rolling contact problem both for tire-road and wheel-rail contact. For the tire-road application a central problem is the modeling of the composite structure of the tire under internal pressure and axle load. One actual contact problem is the rolling on soft soil, which is discussed as the main application. In the wheel-rail case the contact area is much smaller and much more emphasis has been laid on the treatment of material changes, wear and creep phenomena. These approaches are discussed in detail as well as a more recent finite element formulation following the arbitrary Lagrange-Eulerian concept. Ideas about damage mechanisms finish the article.     

德国信号设备升级

德国铁路正在引进各种最新的尖端控制中心系统，旨在进行更有效和更灵活的运行操作。德国铁路（DB）运营控制中心（OCC）是欧洲铁路运输自动化最全面的方案之一，铁路运输调度和运行控制正愈来愈趋于集成化和自动化。直到最近，列车调度和运输调度（如进路排列）均是在铁路的不同区域、不同地点并使用不同的技术设施进行的独立工作。目前，正在把这两项功能逐步在运营控制中心紧密绑定。     

Reducing the climate change impacts of aviation by restricting cruise altitudes

Two of the ways in which air travel affects climate are the emission of carbon dioxide and the creation of high-altitude contrails. One possible impact reduction strategy is to significantly reduce the formation of contrails. This could be achieved by limiting the cruise altitude of aircraft. If implemented, this could severely constrain air space capacity, especially in parts of Europe. In addition, carbon emissions would likely be higher due to less efficient aircraft operation at lower cruise altitudes. This paper describes an analysis of these trade-offs using an air space simulation model as applied to European airspace. The model simulates the flight paths and altitudes of each aircraft and is here used to calculate emissions of carbon dioxide and changes in the journey time. For a one-day Western European traffic sample, calculations suggest annual mean CO₂ emissions would increase by only 4% if cruise altitudes were restricted to prevent contrail formation. The change in journey time depended on aircraft type and route, but average changes were less than 1 min. Our analysis demonstrates that altitude restrictions on commercial aircraft could be an effective means of reducing climate change impacts, though it will be necessary to mitigate the increased controller workload conflicts that this will generate.     

The impact of urban form on automobile travel: disentangling causation from correlation

A longstanding question within the field of transportation demand management is the strength of the relationship between urban form and mobility behavior. Although several studies have identified a strong correlation between these variables, there is as yet scant evidence to support policy interventions that target land use as a means of influencing travel. To the contrary, some of the more recent research has cast skepticism on the proposition that the relationship is causative, recognizing the possibility that households endogenously self-select themselves into communities that support their preferences for particular transportation modes. Focusing on individual automobile travel, the present study seeks to contribute to this line of inquiry by estimating econometric models on a panel of travel-diary data collected in Germany between 1996 and 2003. Specifically, we employ the two-part model (2PM)—a procedure involving probit and OLS estimators—to assess the determinants of the discrete decision to use the car and the continuous decision of distance traveled. Beyond modeling variables that capture the urban form features that are commonly suggested to influence mobility behavior, including mixed use and public transit, this study employs instrumental variables to control for potential endogeneity emerging from the simultaneity of residential and mode choices. Unlike much of the work to date, our results suggest that urban form has a causative impact on car use, a finding that is robust to alternative econometric specifications.