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Gas transfer velocities of CO2 and CH4 in a tropical reservoir and its river downstream 总被引:4,自引:0,他引:4
Frdric Gurin Gwenaël Abril Dominique Sera Claire Delon Sandrine Richard Robert Delmas Alain Tremblay Louis Varfalvy 《Journal of Marine Systems》2007,66(1-4):161
We have measured simultaneously the methane (CH4) and carbon dioxide (CO2) surface concentrations and water–air fluxes by floating chambers (FC) in the Petit-Saut Reservoir (French Guiana) and its tidal river (Sinnamary River) downstream of the dam, during the two field experiments in wet (May 2003) and dry season (December 2003). The eddy covariance (EC) technique was also used for CO2 fluxes on the lake. The comparison of fluxes obtained by FC and EC showed little discrepancies mainly due to differences in measurements durations which resulted in different average wind speeds. When comparing the gas transfer velocity (k600) for a given wind speed, both methods gave similar results. On the lake and excluding rainy events, we obtained an exponential relationship between k600 and U10, with a significant intercept at 1.7 cm h− 1, probably due to thermal effects. Gas transfer velocity was also positively related to rainfall rates reaching 26.5 cm h−1 for a rainfall rate of 36 mm h− 1. During a 24-h experiment in dry season, rainfall accounted for as much as 25% of the k600. In the river downstream of the dam, k600 values were 3 to 4 times higher than on the lake, and followed a linear relationship with U10. 相似文献
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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. 相似文献
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Aileen P. Maypa Alan T. White Elline Caňares Raffy Martinez Rose Liza Eisma-Osorio Porfirio Aliňo 《Coastal management》2013,41(5):510-524
Quantifying progress in management of marine protected areas (MPAs) is crucial to marine conservation and fisheries management in the Philippines. This study compiles data on the status, occurrence, and management gaps of MPAs through coordination with multiple organizations supporting and guiding MPAs in the Philippines. MPA management effectiveness was measured using a MPA Rating System. Since 2002 the modal MPA rating levels increased from level 1 (initiated) to level 4 (sustained) in 2008/9. This upward trend is attributed to factors that promoted both the establishment and improved management of MPAs. Analysis indicated that: (1) most MPAs struggle with budgetary constraints or lack of sustainable financing and (2) overall the MPAs are being maintained and progressing with notable improvement in management despite a range of difficulties encountered during the implementation process. For MPAs in the Visayan Region for which biophysical data were available, the MPA Rating System was used to assess the effectiveness of local government capacity building on MPA coral reef health. Our results suggest that MPAs with higher ratings are likely to have better reef health conditions. 相似文献
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Wilderness traditionally has been a terrestrial resource designation. This study examined user perceptions related to the existence of wilderness in the Great Barrier Reef Marine Park (GBRMP), and raises questions about the efficacy of the GIS based Australian National Wilderness Inventory (ANWI) as a method of inventorying and analyzing wilderness settings in the absence of such perceptions. Three hundred eighty‐three users of the GBRMP were surveyed. Results indicated that over 80% of the respondents believed that wilderness existed in the park, and that it existed both above and below the surface of the water. Characteristics of wilderness related to human presence, natural features, and remoteness were found to be important to marine wilderness. Responses revealed that remoteness (physical distance) from human development may warrant less weight in the designation of marine wilderness than implied as necessary by the ANWI. We discuss implications for selecting areas as wilderness and using the wilderness designation in marine settings. 相似文献
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The transport planning and its decision making involve a large number of goals and more than one alternative to be evaluated. This analysis comprises technical and financial features up to social and environmental impacts. We show how the AHP is a useful tool in this procedure, and evaluate several objectives and impacts of the implantation of the third metro line in the city of Sao Paulo, Brazil, where there were two alternative outlines and one of them to be selected. 相似文献
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ALSTOM在城市轨道交通方面的经验可以回溯到70年以前向巴黎地铁供货的年代.从那时起,公司就不断地积累其在各种地铁系统中的专业特长和独到的经验,无论是橡胶轮或钢轮,钢、不锈钢或铝合金车体,铰接或常规列车组运行,人工还是无人驾驶的系统. 相似文献
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An agent‐based simulation model to assess the impacts of introducing a shared‐taxi system: an application to Lisbon (Portugal) 下载免费PDF全文
This paper presents a new concept of urban shared‐taxi services. The proposed system has a new organisational design and pricing scheme that aims to use the capacity in traditional taxi services in a more efficient way. In this system, a taxi acting in ‘sharing’ mode offers lower prices to its clients, in exchange for them to accept sharing the vehicle with other persons who have compatible trips (time and space). The paper proposes and tests an agent‐based simulation model in which a set of rules for space and time matching between a request of a client and the candidate shared taxis is identified. It considers that the client is only willing to accept a maximum deviation from his or her direct route and establishes an objective function for selecting the best candidate taxi. The function considers the minimum travel time combination of pickup and drop‐off of all the pool of clients sharing each taxi while allowing to establish a policy of bonuses to competing taxis with certain number of occupants. An experiment for the city of Lisbon is presented with the objectives of testing the proposed simulation conceptual model and showing the potential of sharing taxis for improving mobility management in urban areas. Results show that the proposed system may lead to significant fare and travel time savings to passengers, while not jeopardising that much the taxi revenues. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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Dominique Lord Fred Mannering 《Transportation Research Part A: Policy and Practice》2010,44(5):291-305
Gaining a better understanding of the factors that affect the likelihood of a vehicle crash has been an area of research focus for many decades. However, in the absence of detailed driving data that would help improve the identification of cause and effect relationships with individual vehicle crashes, most researchers have addressed this problem by framing it in terms of understanding the factors that affect the frequency of crashes – the number of crashes occurring in some geographical space (usually a roadway segment or intersection) over some specified time period. This paper provides a detailed review of the key issues associated with crash-frequency data as well as the strengths and weaknesses of the various methodological approaches that researchers have used to address these problems. While the steady march of methodological innovation (including recent applications of random parameter and finite mixture models) has substantially improved our understanding of the factors that affect crash-frequencies, it is the prospect of combining evolving methodologies with far more detailed vehicle crash data that holds the greatest promise for the future. 相似文献
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Our aim is to investigate the behavior of submerged supple nets. This work generates many problems owing to the discontinuous
and highly flexible nature of the nets. Only the action of external forces can bring an infinitely flexible structure like
a net into a definite shape. When considering supple nets immersed in a fluid, these external forces themselves depend on
the net geometry. A numerical method to solve this fluid-structure coupling problem is proposed, and is applied to fish farms.
In order to validate the calculation model of the hydrodynamic forces on the mesh sides, we measured the hydrodynamic forces
on a plane panel of netting spread across a transverse current. We thus proved that the Landweber model modified according
to the Richtmeyer formula as regards friction gives good results. The calculated shape of the fixed net cage is qualitatively
in accordance with flume tank observations. We have adapted the algorithm to the study of the dynamic behavior of floating
fish farms. 相似文献
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