108,632 research outputs found
Geografia delle risorse idriche
No full textThe Table presents in numerical and cartographic form, the results of a systematic survey of articles concerning water as a resource, published in five international geographic reviews (Annals of the Association of American Geographers, Applied Geography, Political Geography, Transactions of the Institute of British Geographers, L'Espace Géographique), during 10 years (1994-2004). Part 1 pertains to M. Fiori (pp. 561-562); part 2 (pp. 563-564) to G. Galeandro
Concentration fluctuations in aquifer transport: A rigorous first-order solution and applications
No full textFlow and transport take place in a formation of spatially variable conductivity K(x). The latter is modeled as a lognormal stationary random space function. With Y = ln K, the structure is characterized by the mean [Y], the variance sigma(Y)(2), the horizontal and vertical integral scales I-h and I-v. The fluid velocity field V(x), driven by a constant mean head gradient, has a constant mean U and a stationary two-point covariance. Transport of a conservative solute takes place by advection and by pore-scale dispersion (PSD), that is assumed to be characterized by the constant longitudinal and transverse dispersivities alpha(dL) and alpha(dT). The local solute concentration C(x, t), a random function of space and time, is characterized by its statistical moments. While the mean concentration [C] was investigated extensively in the past, the aim here is to determine the variance sigma(C)(2), a measure of concentration fluctuations. This is achieved in a Lagrangean framework, continuous limit of the particle-tracking procedure, by adopting a few approximations. The present study is a continuation of a previous one (Dagan, G., Fiori, A., 1997. The influence of pore-scale dispersion on concentration statistical moments in transport through heterogeneous aquifers. Water Resour. Res., 33, 1595-1606) and extends it as follows: (i) it is shown that the indepence of the advective component of a solute particle trajectory from the trajectory component associated with PSD, is a rigorous first-order approximation in sigma(Y)(2). This independence, that was conjectured in the work of Dagan and Fiori (Dagan, G., Fiori, A., 1997. The influence of pore-scale dispersion on concentration statistical moments in transport through heterogeneous aquifers. Water Resour. Res., 33, 1595-1606), simplifies considerably the solution; (ii) the covariance of two-particle trajectories, needed in order to evaluate sigma(C)(2), is rederived, correcting for an error in the previous work. The general results are applied to determining CVC = sigma(C)/[C] at the center of a small solute body, of initial size much smaller than I-h = I-v, as function of sigma(gamma)(2), t' = tU/I and Pe = UI/D-dT = I/alpha(dT). Though PSD reduces considerably CVC as compared with advective transport (Pe = infinity), its value is still quite large for time intervals of interest in applications. This finding is in agreement with the analysis of field data by Fitts (Fitts, C.R., 1996. Uncertainty in deterministic groundwater transport models due to the assumption of macrodispersive mixing: evidence from the Cape Cod (Massachussets, USA) and Borden (Ontario, Canada) tracer tests. J. Contam. Hydrol., 23, 69-84). (C) 2000 Elsevier Science B.V. All rights reserved
Concentration fluctuations in transport by groundwater: Comparison between theory and field experiments RID A-2321-2010
No full textIn a recent work [Dagan and Fiori, 1997] we developed a Lagrangian theoretical framework to compute the concentration variance in transport of a conservative solute in a heterogeneous formation of random stationary structure. This variance, a measure of concentration fluctuations in the plume, depends on the spreading effect of advection and on the mixing effect of pore-scale dispersion. Comparison between theory and the numerical simulations of Graham and McLaughlin [1989] showed very good agreement. Here we compare the same theoretical formulae with the field measurements at Borden Site and Cape God. We rely on the analysis of these experiments carried out by Fitts [1996], who characterized the concentration fluctuations by a global measure. The latter is the standard deviation of the logarithm of the ratio between measured and modeled concentrations over the entire plume and at different times. The theoretical relationships require computing the two particles trajectories' covariances. We simplify the computations considerably by taking advantage of the anisotropy of the heterogeneous structures of the two aquifers. Thus the major effect of advection is in the shearing of the plume in the longitudinal direction, whereas pore-scale dispersion acts mainly through its transverse effect in the vertical direction. We found a good agreement between theory and experiments by using parameter values determined independently in the past, provided that the values of transverse pore-scale dispersivities were 0.5 mm for Cape Cod and 0.44 mm for Borden Site. These values are somewhat smaller than the vertical macrodispersivities inferred from measurements
Geometrie parziali ed insiemi di permutazioni
No full textLet G be a partial geometry in the sense of R.C. Bose. In this paper the author defines a set M of permutations on the points of G and determines conditions relative to the geometry g in order that M should be maximal according to M.Deza
Time-dependent transport in heterogeneous formations of bimodal structures: 2. Results
No full textThe theoretical results of part 1 [Dagan and Fiori, 2003] for modeling time-dependent, advective transport of a conservative solute in porous formations of bimodal structure are applied to illustrate the behavior of a few trajectory statistical moments as function of time, of the permeability contrast kappa, and of the inclusions volume density n. The computations are carried out for circular (2D) and spherical (3D) inclusions to represent isotropic media. Advective transport is solved by studying the distortion of a thin plume, linear (2D) or planar (3D), normal to the mean velocity U and moving through a single inclusion. The deformation of the plume is determined from the residual trajectories of solute particles that are derived numerically by a quadrature. The longitudinal macrodispersivity is defined by alpha(L)(t; n, kappa)=(2U)(-1) dX(11)/dt, where X-11 is the trajectories second moment in the mean flow direction. The general behavior of the time-dependent longitudinal dispersivity alpha(L)(t; n, kappa) and, in particular, its constant, large time limit are examined. The tendency of alpha(L) to the "Fickian'' limit with time depends strongly on the conductivity contrast; in particular, for low permeable inclusions (kappamuch less than1) it may be extremely slow. It is shown that the first-order approximation in the conductivity contrast kappa is of limited validity (0.3<κ<2). The transverse moment X-22 tends asymptotically to a constant value. The analysis of the trajectory high order moments shows that the probability density function (pdf) of the solute trajectories tends to normality at large time. Similar to the "Fickian'' limit the normal distribution may be reached at very large time in presence of low conductivity inclusions, with the pdf characterized by significant tailing for the trailing part of the pdf
On the Sources of the Kantian Distinction between Voluntary and Involuntary Imagination. Remarks on Platner, Meier and Tetens
No full textThe purpose of this article is to highlight some possible sources of Kant's theory of empirical imagination, with particular reference to the distinction between its voluntary and involuntary use. It will be shown that Kant the discussion of the subject is not limited to the mere repetition or extension of Baumgarten's conception, but is affected by other influences, unified by the importance they attach to the psycho-physiological investigation of mental phenomena. Through the analysis of the reflections and the transcripts of the anthropology lectures, the contribution stresses how, not only Platner, but also Meier's Anfangsgründe aller schönen Wissenschaften may have offered relevant insights to the first elaboration of the above distinction. Moreover, the Kantian conception of fantasy, as involuntary imagination, is compared with some passages of Tetens' Philosophische Versuche, before being described in its peculiar caracters
Effective conductivity of an anisotropic heterogeneous medium of random conductivity distribution
No full text"\"The paper deals with the effective conductivity tensor K(ef) of anisotropic random media subject to mean uniform flux. The hydraulic conductivity K field is modeled as a collection of spheroidal disjoint inclusions of different, isotropic and independent Y = ln K; the latter is a random variable with given distribution of variance sigma(2)(Y). Inclusions are embedded in homogeneous background of anisotropic conductivity K(0). The K field is anisotropic, characterized by the anisotropy ratio f, ratio of the vertical and horizontal integral scales of K. We derive K(ef) by accurate numerical simulations; the numerical model for anisotropic media is presented here for the first time, and it generalizes a previously developed model for isotropic formations [I. Jankovic, A. Fiori, and G. Dagan, Multiscale Model. Simul., 1 (2003), pp. 40-56]. The numerical model is capable of solving complex three-dimensional flow problems with high accuracy for any configuration of the spheroidal inclusions and arbitrary K distribution. The numerically derived K(ef) for a normal Y is compared with its prediction by (i) the self-consistent solution K(sc), (ii) the first-order approximation in sigma(2)(Y), and (iii) the exponential conjecture [L. J. Gelhar and C. L. Axness Water. Resour. Res., 19 (1983), pp. 161-180]. It is found that the self-consistent solution K(sc) is very accurate for a broad range of the values of the parameters sigma(2)(Y), f and for the densest inclusions packing. In contrast, the first-order solution strongly deviates from K(ef) for large sigma(2)(Y), as expected, and the exponential conjecture is generally unable to correctly represent the effective conductivity. The numerical solution for the potential is expressed as an infinite series of spheroidal harmonics, attached to the interior and exterior of each inclusion, which accounts for the nonlinear interaction between neighboring inclusions.\"
Come «accordare le cetre lascive a’ sacri concenti»: i Fiori celesti di G. B. Andreini
No full text[ITA] Lo studio analizza un manoscritto seicentesco di materia lirico-devozionale, registrato con il titolo di Fiori celesti sotto il nome del famoso attore-autore Giovan Battista Andreini, che nei tardi anni Trenta del secolo avrebbe oπerto in dono al «principe Ippolito Estense» questa breve raccolta poetica, letteralmente raccogliendo non solo importanti motivi tematici e formali tipici del periodo barocco, rintracciabili attraverso mappature intertestuali mirate, ma anche interi componimenti dell’Andreini ripresi da altre sue opere più, o meno, celebri, quali il Teatro celeste e Il Sacrificio. - [ENG] How to «tune lascivious citharas to sacred harmonies»: Fiori celesti by G. B. Andreini ·
This study analyses a 17th-century manuscript containing devotional poems, registered with the title Fiori celesti [Celestial Flowers] to the name of the renowned actor-author Giovan Batti- sta Andreini, who in the late 30s of the 17th century would oπer this short poetry collection to the «prince Ippolito Estense», indeed collecting not only typically baroque thematic and formal Leitmotifs, detectable by careful intertextual mapping, but also full poems derived from other works that Andreini published, more or less famously, such as Celestial Theatre and The Sacrifice
Simulation of One Dimensional Subband Transport in Ultra-Short Silicon Nanowire Transistors
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