Nutrient cycling and primary production in the marine systems of the Arctic and Antarctic

Primary production events in both the Arctic and the Antarctic are highly localized. Carbon-14 incubations that did not account for this caused antarctic primary production estimates to be revised too far downwards from the historic view of high productivity. The primary production regime in the Arctic is even more heterogeneous than in the Antarctic. Arctic primary production rates are in the process of being revised upwards because of a better spatial and temporal distribution of incubation experiments and a re-awakening of interest in estimating new production from the distribution of chemical variables. Similarly, recent examination of temporal changes in nitrate concentrations and recognition of the importance of ice-edge blooms has caused antarctic primary productivity to be revised upwards. In both the Arctic and the Antarctic, the ratio of “new” to total primary production is high, and neglect of this fact can lead to an underestimation of the potential that these regions have for influencing global cycles of bioactive chemicals. Some recent data on temporal changes in nitrate from Fram Strait emphasize the poor state of our knowledge by suggesting an unexpectedly high “new” production rate of 1 g C m⁻² d⁻¹ for a 35 day experiment that encountered an early Phaeocystis bloom. Chemical distributions suggest that new production over the shelf seas that border the Polar Basin is about 50 g Cm⁻² yr⁻¹.The shelves in the Arctic Ocean's marginal and adjacent seas comprise 25% of the total global continental shelf. These extensive shallow regions have much higher rates of primary production than the Polar Basin and may be globally significant sites of denitrification. Globally significant silica deposition could occur on these shelves or on the adjacent slopes.Because of the differences in geomorphology and stratification, global warming is likely to increase primary production in the Arctic and will probably decrease antarctic primary production.In addition to sharing high ratios of “new” to total primary production, high ammonium concentrations occur in the Arctic and Antarctic. It is possible that these accumulations arise from a strong repression of nitrification at low temperatures.     

机车轮对装配应力的数值分析

提出了一套模拟车轮装配全过程的数值分析程序，分析轮对配合面内的接触应力分布，在轴对称模型基础上，模拟分析了整体直辐板车轮与车轴之间的过盈配合接触现象，详细地讨论了过盈配公差和加工精度对配合面内的接触应力分面和摩擦滑动的影响；在三维模型基础上，模拟分析了论心－轮箍型斜辐板车轮与车轴的两个过盈配合面内的接触压力分布，研究了不同过盈配合量，轮箍厚度和垂向外载荷对接触压应力分布的影响。     

The performance of route modification and demand stabilization strategies in stochastic vehicle routing

A key concern in managing vehicle routing operations under stochastic demands is whether, on the basis of travel distance, route modification yields materially greater logistical efficiency than fixed routes. This research uses statistical calibration as the primary technique to develop a robust and tractable model for estimating this difference in logistical efficiency. Based on features such as the models predictive accuracy and generalizability, it constitutes a substantive improvement over existing models. The present study also expands the range of predictive models relevant to vehicle routing under stochastic demands with models to estimate the transportation and inventory effects of persuading customers to stabilize their ordering patterns.     

美国拉臂钩技术发展及应用现状

我叫大卫·泽洛斯特里克,是斯泰勒工业有限公司的董事长.斯泰勒工业有限公司是美国第一家拉臂钩制造商,成立于1990年,座落于美国爱荷华州的加纳区.     

编者的话

2008年重卡各车型的销量格局比较稳定，牵引车仍旧是重卡市场中份额最大的车型。而载货车和自卸车的市场份额也势均力敌。重卡各吨位销量还是以总质量19～26t为主，但份额稍有下滑，而1～19t和26～32t的市场份额各有一个百分点的增长。今年1—5月是近年来重卡车型格局变化最大的一次，自卸车市场迅速扩张，牵引车市场的萎缩，使原来三足鼎立的格局发生了翻天覆地的变化。目前，我国正处于大规模基础设施建设中。新开工项目比较集中，形成了自卸车的销售高峰。在前5个月销售的重卡中，自卸车占到了相当大的比重，市场份额几乎翻倍。部分企业自卸车的销量占到总销量的近一半甚至更多。预计这种势头还将持续一段时期。     

Highway expenditures and non-metropolitan employment

Using data on state highway expenditures and employment from 30 Minnesota non-metropolitan counties over a 25-year period, possible interactions between transportation and employment are investigated. While crosssectional analysis suggests no significant interactions, causality tests and time-series analyses indicate that highway expenditures affect manufacturing and retail employment, and employment influences expenditures. Although expenditure increases cause employment improvements in the short-term, long-term effects are less favorable. Highway expenditures respond quickly to increased needs caused by retail improvements.     

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.     

Short sea shipping: a Canadian perspective

Short sea shipping has begun to receive attention from governments worldwide, as they seek to reduce traffic congestion and greenhouse gases. Despite a long coastline and its interest in international maritime affairs, the Canadian government had, until 2003, placed greater emphasis on resolving the issues of other transport modes. In July 2003, Canada and the United States signed a Memorandum of Cooperation on Sharing Short Sea Shipping Information and Experience. Subsequently, the federal government embarked on an assessment of short sea shipping through a series of workshops. This paper explores the key issues with respect to further development of short sea shipping from a Canadian perspective. It examines the critical limitations and impediments to further growth of short sea services in Canada and trans-border trade with the USA, and identifies a number of questions Canadian policymakers need to answer.     

欧洲跨境运输用司机台

就欧洲铁路跨境运输用司机台项目开发了能方便今后铁路跨境运输的司机台.该司机台的特点是改善了司机台的人机工程学、可单手操作牵引制动转换开关和使用了现代化的终端技术.在仿真运行中对具有功能的演示司机台进行了首批试验,获得大家的高度肯定.