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Hellen JA 《GeoJournal》1981,5(4):369-384
Egypt's general population growth since 1805 is reviewed, with particular reference to the effect of changes in fertility and mortality since 1906 and factors affecting these variables. The rapidity of mortality decline is stressed and the nature of the epidemiological transition considered. In the light of population projections Egypt's population policies are described, and the diffusion of family planning since 1965 particularly is examined on a governorate basis. Finally, the success of the Population and Development Project set up in 1977 in instituting a radically new approach to family planning is presented. 相似文献
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Modeling fracture porosity development using simple growth laws 总被引：2，自引：0，他引：2
A model of porosity development has been developed to investigate general relationships between simple fracture aperture growth laws and fracture porosity in evolved fracture arrays in aquifers. The growth of fracture apertures in two-dimensional orthogonal arrays with initially spatially uncorrelated lognormal aperture distributions has been studied, where aperture growth rate is proportional to an exponent of the flow rate through each fracture. The evolved arrays show geometrical phase changes as a function of the aperture growth rate exponent, e, and the standard deviation of the initial aperture distribution, sigma(z). Low values of e and sigma(z) lead to bimodal aperture distributions, where apertures parallel to flow are preferentially enlarged. At moderate values of e and sigma(z), there is a transition to a regime of more complex geometries consisting of networks of channel-like structures of preferentially enlarged apertures. At larger values of e, array-spanning channel-like paths of preferentially enlarged apertures develop, where the tortuosity of the channel-like paths is a linear function of sigma(z). Following an initial growth phase, during which dynamically stable aperture configurations develop, arrays undergo simple amplification. The geometry of the evolved aperture fields is diverse and they can be highly complex; consequently, parameterization and prediction of their evolution in terms of the initial aperture distributions and growth rate laws is not trivial. 相似文献
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