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A Laplace-transform analytic element method (LT-AEM) is described for the solution of transient flow problems in porous media. Following Laplace transformation of the original flow problem, the analytic element method (AEM) is used to solve the resultant time-independent modified Helmholtz equation, and the solution is inverted numerically back into the time domain. The solution is entirely general, retaining the mathematical elegance and computational efficiency of the AEM while being amenable to parallel computation. It is especially well suited for problems in which a solution is required at a limited number of points in space–time, and for problems involving materials with sharply contrasting hydraulic properties. We illustrate the LT-AEM on transient flow through a uniform confined aquifer with a circular inclusion of contrasting hydraulic conductivity and specific storage. Our results compare well with published analytical solutions in the special case of radial flow. 相似文献
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This paper focuses on the use of the provision of public housing in Israel as a political measure, in addition to its benign role of providing shelter. In the early stages of Jewish settlement in the country the Right controlled most towns and cities, while Labour was engaged in building a rural base. As urban growth attracted many of the newly arrived workers, Labour found it necessary to become politically active in the urban sphere. This has been done through the provision of a variety of services, among which was the provision of housing with a view to recruiting their political support. Two strategies were adopted. One was the penetration of existing towns by building public housing estates, the other was the establishment of new urban centres. These strategies have enabled Labour to attain local political hegemony in many cities, but while the provision of public housing proved to be as effective political tool in the short run, it has failed to secure a lasting impact. 相似文献
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Shlomo Hasson 《The Professional geographer》1984,36(1):11-18
Humanistic geography represents a duality of reason and feeling, science and ethics. As a scientific approach, it is concerned with uncovering the truth regarding people's experiential relationship with place. It does not regard the phenomena under consideration as merely an object of research, rather it bears an ethical message of concern for those objects, be they human beings, nature or place. This study expands on the ethical dimension conveyed by humanistic geography via Buber's work, trying to show that his dialogical philosophy and humanism is a logical extension of this message. I seek to convey an action-oriented frame of reference for geographers that may lead to a shift from passive reflection about people and place, to an active role in making Buber's “perfect space’ possible. 相似文献
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Black holes are extremely dense and compact objects from which light cannot escape. There is an overall consensus that black holes exist and many astronomical objects are identified with black holes. White holes were understood as the exact time reversal of black holes, therefore they should continuously throw away material. It is accepted, however, that a persistent ejection of mass leads to gravitational pressure, the formation of a black hole and thus to the “death of while holes”. So far, no astronomical source has been successfully tagged a white hole. The only known white hole is the Big Bang which was instantaneous rather than continuous or long-lasting. We thus suggest that the emergence of a white hole, which we name a ‘Small Bang’, is spontaneous - all the matter is ejected at a single pulse. Thus, unlike black holes, white holes cannot be continuously observed rather their effect can only be detected around the event itself. γ-ray bursts are the most energetic explosions in the universe. Long γ-ray bursts were connected with supernova eruptions. There is a new group of γ-ray bursts, which are relatively close to Earth, but surprisingly lack any supernova emission. We propose identifying these bursts with white holes. White holes seem like the best explanation of γ-ray bursts that appear in voids. We also predict the detection of rare gigantic γ-ray bursts with energies much higher than typically observed. 相似文献
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Monica Riva Shlomo P. Neuman Alberto Guadagnini 《Stochastic Environmental Research and Risk Assessment (SERRA)》2013,27(1):195-207
Earth and environmental variables are commonly taken to have multivariate Gaussian or heavy-tailed distributions in space and/or time. This is based on the observation that univariate frequency distributions of corresponding samples appear to be Gaussian or heavy-tailed. Of particular interest to us is the well-documented but heretofore little noticed and unexplained phenomenon that whereas the frequency distribution of log permeability data often seems to be Gaussian, that of corresponding increments tends to exhibit heavy tails. The tails decay as powers of ? $ \alpha $ where 1 < $ \alpha $ < 2 is either constant or grows monotonically toward an asymptote with increasing separation distance or lag. We illustrate the latter phenomenon on 1-m scale log air permeabilities from pneumatic tests in 6 vertical and inclined boreholes completed in unsaturated fractured tuff near Superior, Arizona. We then show theoretically and demonstrate numerically, on synthetically generated signals, that whereas the case of constant $ \alpha $ is consistent with a collection of samples from truncated sub-Gaussian fractional Lévy noise, a random field (or process) subordinated to truncated fractional Gaussian noise, the case of variable $ \alpha $ is consistent with a collection of samples from truncated sub-Gaussian fractional Lévy motion (tfLm), a random field subordinated to truncated fractional Brownian motion. Whereas the first type of signal is relatively regular and characterized by Lévy index $ \alpha $ , the second is highly irregular (punctuated by spurious spikes) and characterized by the asymptote of $ \alpha $ values associated with its increments. We describe a procedure to estimate the parameters of univariate distributions characterizing such signals and apply it to our log air permeability data. The latter are found to be consistent with a collection of samples from tfLm with $ \alpha $ slightly smaller than 2, which is easily confused with a Gaussian field (characterized by constant $ \alpha $ = 2). The irregular (spiky) nature of this signal is typical of observed fractured rock properties. We propose that distributions of earth and environmental variable be inferred jointly from measured values and their increments in a way that insures consistency between these two sets of data. 相似文献
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Wang XS Neuman SP Strack OD Verruijt A Jamali M Seymour B Bear J Cheng AH 《Ground water》2011,49(2):133-42; discussion 142-3