Boussinesq-type modelling using an unstructured finite element technique     

Ole R. Srensen  Hemming A. Schffer  Lars S. Srensen 《Coastal Engineering》2004,50(4):181-198

A model for solving the two-dimensional enhanced Boussinesq equations is presented. The model equations are discretised in space using an unstructured finite element technique. The standard Galerkin method with mixed interpolation is applied. The time discretisation is performed using an explicit three-step Taylor–Galerkin method. The model is extended to the surf and swash zone by inclusion of wave breaking and a moving boundary at the shoreline. Breaking is treated by an existing surface roller model, but a new procedure for the detection of the roller thickness is devised. The model is verified using four test cases and the results are compared with experimental data and results from an existing finite difference Boussinesq model.  相似文献   

Environmental consequence analyses of fish farm emissions related to different scales and exemplified by data from the Baltic--a review   总被引：3，自引：0，他引：3  

Gyllenhammar A  Håkanson L 《Marine environmental research》2005,60(2):211-243

The aim of this work is to review studies to evaluate how emissions from fish cage farms cause eutrophication effects in marine environments. The focus is on four different scales: (i) the conditions at the site of the farm, (ii) the local scale related to the coastal area where the farm is situated, (iii) the regional scale encompassing many coastal areas and (iv) the international scale including several regional coastal areas. The aim is to evaluate the role of nutrient emissions from fish farms in a general way, but all selected examples come from the Baltic Sea. An important part of this evaluation concerns the method to define the boundaries of a given coastal area. If this is done arbitrarily, one would obtain arbitrary results in the environmental consequence analysis. In this work, the boundary lines between the coast and the sea are drawn using GIS methods (geographical information systems) according to the topographical bottleneck method, which opens a way to determine many fundamental characteristics in the context of mass balance calculations. In mass balance modelling, the fluxes from the fish farm should be compared to other fluxes to, within and from coastal areas. Results collected in this study show that: (1) at the smallest scale (<1 ha), the "footprint" expressing the impact areas of fish cage farm often corresponds to the size of a "football field" (50-100 m) if the annual fish production is about 50 ton, (2) at the local scale (1 ha to 100 km2), there exists a simple load diagram (effect-load-sensitivity) to relate the environmental response and effects from a specific load from a fish cage farm. This makes it possible to obtain a first estimate of the maximum allowable fish production in a specific coastal area, (3) at the regional scale (100-10,000 km2), it is possible to create negative nutrient fluxes, i.e., use fish farming as a method to reduce the nutrient loading to the sea. The breaking point is to use more than about 1.1 g wet weight regionally caught wild fish per gram feed for the cultivated fish, and (4) at the international scale (>10,000 km2) related to the Baltic Proper, the contribution from fish farms to the overall nutrient fluxes are very small. We have also given two case-studies at the local scale where the impact of the fish farm emissions are greatest and the idea is to identify coastal areas unsuitable and suitable for fish cage farms and the reasons why. It should also be stressed that the results presented here are exemplified using emissions from fish farms, but that the underlying principles to evaluate the ecosystem effects of nutrient discharges from point source emissions are valid in a wider and more general perspective.  相似文献   

Sea Grant in Latin America?: Adapting the US Sea Grant model of linked applied research,extension, and education to a Latin American Context—Is there a fit?     

S. Matthew Wilburn  James Tobey  Jill Hepp  Stephen Olsen  Barry Costa-Pierce 《Marine Policy》2007

This paper explores the application of the US Sea Grant model of applied research, extension, and education to two case studies in Latin America: Coastal Ecuador and the Gulf of Fonseca. The analysis is based on a series of meetings and roundtables with in-country partners and leaders of the US Sea Grant program. We conclude that the Sea Grant model provides an institutional structure that Latin America lacks and the model's features would improve governance of marine and coastal resources through more effective linkages between coastal communities, universities, and policy/decision makers at local, national, and international levels.  相似文献   

Answers to the comments by M. Vermeer on L. E. Sjöberg (2007) “The topographic bias by analytical continuation in physical geodesy” J Geod 81:345–350     

Lars E. Sjöberg 《Journal of Geodesy》2008,82(7):451-452

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Geodetic intersection on the ellipsoid     

Lars E. Sjöberg 《Journal of Geodesy》2008,82(9):565-567

Through each of two known points on the ellipsoid a geodesic is passing in a known azimuth. We solve the problem of intersection of the two geodesics. The solution for the latitude is obtained as a closed formula for the sphere plus a small correction, of the order of the eccentricity of the ellipsoid, which is determined by numerical integration. The solution is iterative. Once the latitude is obtained, the longitude is determined without iteration.  相似文献   

Indigenous soil knowledge among the Fulani of northern Burkina Faso: linking soil science and anthropology in analysis of natural resource management     

Lars Krogh  Bjarke Paarup-Laursen 《GeoJournal》1997,43(2):189-197

The indigenous soil knowledge among the Fulani subsistence farmers in two villages of northern Burkina Faso is examined, analysed and assessed with the aim of evaluating its adequacy for sustaining soil fertility and for the appropriateness of tapping indigenous knowledge in development programmes. The analytical framework is a multidisciplinary approach combining soil science and anthropology. The results show a high degree of consistency between the science-based western soil classification and the Fulani soil classification although the routes of generation are different. The farmers are aware of and active in management of soil fertility based on their experience, but express no thorough understanding of the mechanisms of plant growth. The soil knowledge is applied in the farming strategies which, as a primary aim, seek to minimize the risk of harvest failure. However, the analysis also suggests that the knowledge is no part of a free-standing knowledge body which can be separated from the actual agricultural performance. The farmers express a general concern about the present state of the environment and degradation processes; however, there is no motivation to take active control of and manage the bush area. This is in contrast with the way millet cultivators actively manage their fields. An explanation of this is suggested by the division between the two Fulani ethnic subgroups, the FulBe who are the former masters and the RimayBe, the former slaves.  相似文献   

Evidence for the depletion of ammonia in the Uranus atmosphere     

Samuel Gulkis  Michael A. Janssen  Edward T. Olsen 《Icarus》1978,34(1):10-19

The theoretical disk brightness temperature spectra for Uranus are computed and compared with the observed microwave spectrum. It is shown that the emission observed at short centimeter wavelengths originates deep below the region where ammonia would ordinarily begin to condense. We demonstrate that this result is inconsistent with a wide range of atmospheric models in which the partial pressure of NH₃ is given by the vapor-pressure equation in the upper atmosphere. It is estimated that the ammonia mixing ratio must be less than 10^?6 in the 150 to 200°K temperature range. This is two orders of magnitude less than the expected mixing ratio based on solar abundances. The evidence for this depletion and a possible explanation are discussed.  相似文献   

Reservoir description using dynamic parameterisation selection with a combined stochastic and gradient search     

Lars Kristian Nielsen  Sam Subbey  Mike Christie  Trond Mannseth 《Computational Geosciences》2006,10(3):321-342

There is a correspondence between flow in a reservoir and large scale permeability trends. This correspondence can be derived by constraining reservoir models using observed production data. One of the challenges in deriving the permeability distribution of a field using production data involves determination of the scale of resolution of the permeability. The Adaptive Multiscale Estimation (AME) seeks to overcome the problems related to choosing the resolution of the permeability field by a dynamic parameterisation selection. The standard AME uses a gradient algorithm in solving several optimisation problems with increasing permeability resolution. This paper presents a hybrid algorithm which combines a gradient search and a stochastic algorithm to improve the robustness of the dynamic parameterisation selection. At low dimension, we use the stochastic algorithm to generate several optimised models. We use information from all these produced models to find new optimal refinements, and start out new optimisations with several unequally suggested parameterisations. At higher dimensions we change to a gradient-type optimiser, where the initial solution is chosen from the ensemble of models suggested by the stochastic algorithm. The selection is based on a predefined criterion. We demonstrate the robustness of the hybrid algorithm on sample synthetic cases, which most of them were considered insolvable using the standard AME algorithm.  相似文献   

Blessed with Tourists: The Borderlands of Religion and Tourism in San Antonio by Thomas S. Bremer     

Daniel H. Olsen 《The Professional geographer》2006,58(4):503-504

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Late-Glacial and Early Holocene Environmental and Climatic Change at Lake Tambichozero, Southeastern Russian Karelia     

Barbara Wohlfarth  Ludmila Filimonova  Ole Bennike  Leif Bjrkman  Lars Brunnberg  Nadja Lavrova  Igor Demidov  Gran Possnert 《Quaternary Research》2002,58(3):261

High-resolution lithostratigraphy, mineral magnetic, carbon, pollen, and macrofossil analyses, and accelerator mass spectrometry ¹⁴C measurements were performed in the study of a sediment sequence from Lake Tambichozero, southeastern Russian Karelia, to reconstruct late-glacial and early Holocene aquatic and terrestrial environmental changes. The lake formed ca. 14,000 cal yr B.P. and the area around the lake was subsequently colonized by arctic plants, forming patches of pioneer communities surrounded by areas of exposed soil. A minor rise in lake productivity and the immigration of Betula pubescens occurred ca. 11,500 cal yr B.P. The rise in summer temperatures probably led to increased melting of remnant ice and enhanced erosion. The distinct increase in lake productivity and the development of open Betula-Populus forests, which are reconstructed based on plant macrofossil remains, indicate stable soils from 10,600 cal yr B.P. onward. Pinus and Picea probably became established ca. 9900 cal yr B.P.  相似文献