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151.
The purpose of the paper is to state general properties of theoretical market areas of cities. We consider two centers on the Euclidean plane, several models describing the spatial influence of a center, and a general, continuous, and strictly increasing transportation cost function. Derived properties of market areas concern area measure, topological bounds, emptiness, boundedness, connectedness, convexity, and the membership of a city to its own market area. In particular, it is shown how the shape of market areas changes with the transportation cost function. Finally, prospects for further research are presented. 相似文献
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Pey-Chun Chen Pierre Hansen Brigitte Jaumard Hoang Tuy 《Journal of regional science》1992,32(4):467-486
ABSTRACT. Weber's problem consists of locating a facility in the plane in such a way that the weighted sum of Euclidean distances to n given points be minimum. The case where some weights are positive and some are negative is shown to be a d.-c. program (i.e., a global optimization problem with both the objective function and constraint functions written as differences of convex functions), reducible to a problem of concave minimization over a convex set. The reduced problem is then solved by outer-approximation and vertex enumeration. Moreover, locational constraints can be taken into account by combining the previous algorithm with an enumerative procedure on the set of feasible regions. Finally, the algorithm is extended to solve the case where obnoxiousness of the facility is assumed to have exponential decay. Computational experience with n up to 1000 is described. 相似文献
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Zone pricing consists in determining simultaneously several delivered prices together with the zones where these prices apply. A model and algorithm are proposed to determine optimal facility locations, prices, tariff-zones, and market areas in order to maximize the firm's profit under zone pricing. The resulting nonlinear mixed-integer program is tackled by projecting the objective function on the price space, solving repeatedly uncapacitated facility location problems for fixed values of the prices. The implicit profit function so defined is optimized by branch-and-bound. Computational results are reported. 相似文献
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Pierre Taminiaux 《European Legacy》2009,14(6):685-695
This article studies Paul Valéry's personal reflection on photography, as it appears in his essay “Le Discours du Centenaire de la Photographie,” based on a speech given at the Sorbonne in 1939 to members of the French Academy. It stresses the relationship between this essay and the French poet's writings on painting and aesthetics, in particular his work on Corot. Moreover, it analyzes the synthetic character of Valéry's critical approach, which attempts to bring together the language of poetry, philosophy and science when dealing with this utterly modern visual language. Photography is celebrated here as a unique art form that can at the same time imitate and reproduce nature perfectly, while allowing mankind to create a cosmological vision of life and the universe. In other words, the poet underlines in this text the utmost modernity of photography, at a time when many in France were still reluctant to acknowledge its artistic identity. 相似文献