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991.
Quantitative estimation of the influence of surface thermal fronts over chlorophyll concentration at the Patagonian shelf 总被引:1,自引:0,他引:1
Andrs L. Rivas 《Journal of Marine Systems》2006,63(3-4):183-190
Eighteen-year (1985–2002) mean monthly SST Pathfinder data with 9 km spatial resolution have been used to estimate surface gradients by finite differences. Then the seasonal climatological means have been calculated from the intensity of these gradients, and surface thermal fronts present in the Patagonian Continental Shelf (PCS) have been located. Moreover, 6 years (1998–2003) of SeaWiFS data with approximately 4 km spatial resolution have been used to estimate monthly composite images of surface chlorophyll concentration, after which seasonal climatological means distributions have been generated. Both seasonal distributions have been analyzed together and by combining the knowledge of oceanographic processes and phytoplankton responses to light and nutrient availability, regions where the presence of a thermal front affects photosynthetic activity have been identified. Subjective criteria have been applied to define eighteen areas where phytoplankton biomass is influenced by the presence of a thermal front. In these areas, the surface chlorophyll (spatial mean and total), its relationship with the surface chlorophyll of the whole region, and the seasonal evolution of this relationship have been calculated. All frontal areas cover less than 15% of the total surface, but they contribute with over 23% of the phytoplankton annual mean biomass. Considered as a group, during summer they show high chlorophyll values very similar to those in spring. During the cold period, when the water column is vertically mixed in practically the whole of PCS, the influence of physical fronts over the biological production is minimum. The frontal zone image remains clearly defined during summer, when approximately 85% of the area will have a determined mean chlorophyll concentration, while the other 15% has a 2.45 times larger value. While three pattern trends have been identified in the frontal areas, only two of them condition the pattern of the group, due to their horizontal extension. 相似文献
992.
JAMES S. WEBSTER HOWARD FIREMAN DILLON A. ALLEN ADRIAN J. MACKENNA JOHN C. HOOTMAN 《Naval Engineers Journal》2007,119(2):35-48
The US Navy has been studying the technical and cost impacts associated with the availability and cost of fossil fuel contrasted with nuclear energy alternatives for surface combatants and amphibious warfare ships. Over the past 2 years these efforts have grown in maturity to examine the tactical and strategic implications of our Navy's dependence on fossil fuels from technical, economic, and military perspectives. This paper will present three major topics:
Given the US Navy's dependence on fossil fuels and the expected increase in cost and reduced availability of fossil fuel, propulsion system investment decisions made today will have a profound impact on the future tactical and strategic roles of the US Navy surface fleet. This paper lays the foundation for providing robust and flexible technology decision opportunities for the Navy's future. 相似文献
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Background research on alternative energy sources.
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A survey discussion of current and future power and propulsion system technologies.
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An overview of principal Naval Sea Systems Command studies on the integration of alternative power and propulsion system technologies into notional surface combatants, submarines, and amphibious warfare ships.
Given the US Navy's dependence on fossil fuels and the expected increase in cost and reduced availability of fossil fuel, propulsion system investment decisions made today will have a profound impact on the future tactical and strategic roles of the US Navy surface fleet. This paper lays the foundation for providing robust and flexible technology decision opportunities for the Navy's future. 相似文献
993.
This paper quantifies the potential environmental benefit of short sea shipping. Critical strategic issues relevant to formulating
public policy are developed. Coastal shipping has traditionally been a major sector of the maritime industry. This continues
to be the case in the European Union, but the sector has diminished in relative importance in North America as the transport
industry has become increasingly dominated by less environmentally-friendly interstate trucking and railroads. Congestion
threatens to overwhelm overland carriage and limit economic growth. An alternative strategy is to revitalize coastal shipping
as short sea shipping to alleviate traffic congestion and enhance economic development by maintaining freight flow efficiency.
Because ship transport offers higher fuel economy and lower emission of harmful pollutants, the environmental benefits of
short sea shipping over land transportation can be quantified and used to inform public policy. 相似文献
994.
在九月召开的国际航空货运协会世界航空货运论坛上&;#183;波音公司发布了其两年一度的世界航空货运预测报告,其中鲜有特别的内容。 相似文献
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本文通过实际案例阐述了在我国目前公路建设广泛开展建设——经营——转让 (BOT)条件下 ,中国铁路工程总公司以限定概算、总额包干的建设项目管理承包 (PMC)模式 ,参与公路工程建设的实践 相似文献
998.
Ney Roitman Carlos Magluta Ronaldo C. Batista Ricardo W. Capllonch 《Marine Structures》1996,9(10):991-1002
The structural elastic behaviour of steel pipelines during on-bottom pull-in procedure is investigated experimentally by using small scale models. Despite the lack of a sea-bed soil pipeline interaction effect in the model, it is possible to show that the unevenness of the sea-bed surface and the non-uniform distribution of friction forces can lead to large deflection bending stresses, higher than the numerical results yielded by standard software packages commonly used for design calculations. Due to foreseen difficulties in overcoming the drawbacks in practical and numerical procedures, the off-bottom pull-in operation arises as an attractive alternative even for shallow waters. 相似文献
999.
A stated preference experiment was performed in Calgary in Canada to examine how people are influenced in the selection of a departure time for a hypothetical trip to see a movie. A total of 635 complete observations were obtained. In each observation the respondent was presented with a set of possible departure time scenarios and asked to indicate the order of preference for these scenarios. Each scenario was described by specifying the automobile travel time, the expected arrival time relative to the movie start time, the parking cost, the probability of being at least ten minutes late for the movie and the length of time the movie had been running. This forced the respondent to trade off between conditions regarding these attributes. Age, gender and frequency of movie attendance were also recorded. The observations thus obtained were used to estimate the parameter values for a range of alternative utility functions in logit models representing this choice behaviour. The results indicate that all of the attributes included have significant effects on departure time choice in the situation being considered. They also indicate that travellers are prepared to arrive roughly two minutes early for each minute of travel time saved; that the money value of driving time for trips to recreational activities is about half that for trips to work; that one additional percent in the probability of arriving late is equivalent to roughly 0.20 Canadian dollars or 1.93 minutes drive time; and that there is a preference for a non-zero expected early arrival time regardless of the associated probability of arriving late. Some of these results are novel and others are consistent with findings for work trips in work done by others, which is seen to add credence to the approach being used here. 相似文献
1000.
J.C. Wu T.S. Liu 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1996,26(6):431-448
This study deals with dynamics and control of a rider-motorcycle system model in Hamiltonian form. The model is established to account for not only the motorcycle dynamics but also changes in rider's postures. Tyre forces are treated as external forces and rider's control actions contain three actuation torques. The Hamiltonian system is subject to dissipation effects due to tyre forces and rider's control torques. In addition to the total Hamiltonian, a generalized free energy is employed in formulation. Lyapunov's second method provides sufficient conditions for stability. Variable structure system (VSS) control is used to account for stabilization control exerted by the rider. Simulation results validate the proposed method. 相似文献