A Linear Programming Model for Seabed Oil-Gas Pipe Network

This paper analyzes the pipe network system of oil-gas collection and transportation foroffshore oilfield development.A"0-1"integer linear programming model is constructed to optimize theinvestment of seabed pipe network.The mathematical model is solved by the spanning tree method ofgraph theory and network analysis.All spanning trees of a network graph compose all the feasible solu-tions of the mathematical model.The optimal solution of the model is the spanning tree with the minimumcost among all spanning trees.This method can be used to optimize the seabed pipe network system andgive a minimum cost plan for the development of offshore marginal oilfield groups.     

Objective analysis of the structure of three-dimensional atmospheric fronts

A computational method for diagnosing three-dimensional atmospheric fronts from temperature, wind, and geopotential fields on a three-dimensional regular grid is proposed. The criterion, which serves for the diagnosis of atmospheric fronts, is discussed. The weights of the input information about the mentioned fields are optimized based on the maximal difference between the correlation functions for (a) pairs of particles separated by the front and (b) pairs from one synoptic mass. These weights were different for different baric levels. The correlation functions and the optimization of weights were estimated on the basis of the archive of fields of the NCEP objective analysis on the half-degree latitude-longitude grid and data from aerological observations. The results of numerical experiments on the construction of atmospheric fronts are presented. Applying the described method to fields predicted for a term of up to 36 h showed that errors in the prognostic models introduce a relatively weak distortion into the geometry of atmospheric fronts.     

小气候、雪盖及土壤湿度对高山生态系统功能的影响

1 Introduction High mountain landscapes above the tree-line are often regarded as close to nature, although human impact has obviously changed the environment, partly exceeding its carrying capac- ity (L?ffler, 2000). Due to their fragility regarding expected environmental changes and an increasing land use pressure in many regions, high mountain landscapes recently became a major focus within the discussion on a sustainable development in a worldwide (Messerli and Ives, 1997), and regional p…     

THE TROPICS: ENVIRONMENTS AND HUMAN IMPACTS UNDERSTOOD AND REINTERPRETED

In the 1950s, few people had travelled widely through different parts of the tropics and interpretations on tropical landforms, soils, vegetation and climate largely rested on impressions gained from residence or long sojourns in particular tropical countries. Most academic geography on the tropics was then written by expatriates and lacked the perspective gained from long experience of tropical regions. Particular problems of understanding arose as people attempted to extrapolate from one part of the tropics to another. Since then, understanding has advanced enormously, largely through the efforts of tropical scientists working in their own institutions and through the greater technological ability to study tropical lands both remotely and through easier field access. The establishment of a number of field stations, aimed primarily at the biological sciences, but also facilitating the work of geographers, has been a major stimulus to this effort. Concerns over practical issues, particularly local development and global climatic change have prompted new avenues of research, many of which have been assisted by the great increase in data collection in tropical countries. For the future, South-South dialogue between tropical physical geographers is needed to improve their ability to ask meaningful questions so that they can contribute to teach the rest of their discipline more about serious applied and applicable geography.     

HUMAN GEOGRAPHY OF THE AMERICAN TROPICS: A FORTY-YEAR REVIEW

For a decade or so after World War II, human geographers working in the American tropics found socio-political conditions and resultant research topics little changed from those before the war. This was in contrast to the Old World tropics where decolonization processes and the demands of economic development and new nation building produced divergent research currents, For the first half of the period under review, the American tropics continued to be the province largely of geographers with culturalhistorical questions grounded in natural historical bases. The legacy is Humboldt's; the practitioners most notably students of Carl Sauer or German counterparts such as Carl Troll. French and British regionalist approaches, strong in the region before World War II, survived less successfully. By the 1980s, however, broad pan-tropical currents of geographic discourse and debate had become established. New practices and theories were formulated and tested as North Atlantic geographers borrowed from antipodean innovators and others working in the Asian and African tropics. Since the 1980s, there have been greater efforts at dialogue and collaboration with host country colleagues. As might be expected in this era of ‘globalization’, national research styles and agendas have become less evident. This paper offers a highly selective map of research nodes within tropical Americanist geography since the early 1950s. The selection of examples includes qualitative criteria, but more importantly, research that signify stasis or intensification as well as turning points and departures in the overall development of this literature. The contours of this history suggest some highly evolved, even idiosyncratic enterprises, but in the main, it is an unfolding that suggests broad congruencies with human geographic work elsewhere in the tropics.     

Aquaculture intensification under land and water limitations

Two intensive aquaculture systems are described in which high yields are obtained for relatively low inputs of land area, water and supplementary feed. The one is a polyculture of a number of fish species in deep cotton irrigation reservoires (5–7 m deep) in Israel. The large volume of water in these reservoirs improves the oxygen regime and dilutes catabolites excreted by the fish. This allows the increase of fish density to 10,000–18,000 fish ha^–1. It also enables the increase of the resevoir's productivity by manuring with liberal amounts of animal wastes. Yields obtained in this system reach over 10 ton ha^–1 yr^–1 at very low feed conversion rates. The second system is practiced in Taiwan for the culture of red tilapia. Pond water is stirred mechanically by paddlewheels to create a gentle current around a central water outlet. This supplies ample oxygen and concentrates wastes in the center of the pond, from where it is removed twice daily, thus alleviating the build-up of catabolite concentration in the pond. Densities of fish amount to 215,000 to 430,000 fish ha^–1, and the yields are accordingly high reaching more than 200 ton ha^–1 yr^–1. The ecological principles involved in these systems are discussed.     

No geology without marine geology

Summary A brief review is offered of the many problems where knowledge of the ocean floors and of marine processes in shallow water is indispensable for the further advancement of geology. The subject of turbidity currents is treated in greater detail, to demonstrate the interrelation of several aspects of marine geology with sedimentologic and paleogeographic investigations.