Effects of pore-scale dispersion,degree of heterogeneity,sampling size,and source volume on the concentration moments of conservative solutes in heterogeneous formations     

Daniele Tonina  Alberto Bellin 《Advances in water resources》2008

Pore-scale dispersion (PSD), aquifer heterogeneity, sampling volume, and source size influence solute concentrations of conservative tracers transported in heterogeneous porous formations. In this work, we developed a new set of analytical solutions for the concentration ensemble mean, variance, and coefficient of variation (CV), which consider the effects of all these factors. We developed these models as generalizations of the first-order solutions in the log-conductivity variance of point concentration proposed by [Fiori A, Dagan G. Concentration fluctuations in aquifer transport: a rigorous first-order solution and applications. J Contam Hydrol 2000;45(1–2):139–163]. Our first-order solutions compare well with numerical simulations for small and moderate formation heterogeneity and from small to large sampling and source volumes. However, their performance deteriorates for highly heterogeneous formations. Successively, we used our models to study the interplay among sampler size, source volume, and PSD. Our analysis shows a complex and important interaction among these factors. Additionally, we show that the relative importance of these factors is also a function of plume age, of aquifer heterogeneity, and of the measurement location with respect to the mean plume center of gravity. We found that the concentration moments are chiefly controlled by the sampling volume with pore-scale dispersion playing a minor role at short times and for small source volumes. However, the effect of the source volume cannot be neglected when it is larger than the sampling volume. A different behavior occurs for long periods, which may be relevant for old contaminations, or for small injection volumes. In these cases, PSD causes a significant dilution, which is reflected in the concentration statistics. Additionally, at the center of the mean plume, where high concentrations are most likely to occur, we found that sampling volume and PSD are attenuating mechanisms for both concentration ensemble mean and coefficient of variation, except at very large source and sampler sizes, where the coefficient of variation increases with sampler size and PSD. Formation heterogeneity causes a faster reduction of the ensemble mean concentrations and a larger uncertainty at the center of the mean plume. Therefore, our results highlight the importance of considering the combined effect of formation heterogeneity, exposure volume, PSD, source size, and measurement location in performing risk assessment.  相似文献   

Subsurface mass redistributions at Mount Etna (Italy) during the 1995–1996 explosive activity detected by microgravity studies     

Gennaro Budetta  Daniele Carbone  & Filippo Greco 《Geophysical Journal International》1999,138(1):77-88

Gravity changes are presented from a series of field microgravity surveys conducted at Mt Etna between August 1994 and November 1996, a period including the 1995–1996 explosive summit activity. Data were collected along a microgravity network of 69 stations at a monthly to annual sampling rate, depending on each subarray of the network.
  Results show that seasonal changes in water level within the volcano may induce gravity changes of up to 20  μgal on Etna's southern slope, and indicate that significant magma movement occurred within and below Etna's edifice between 1994 and 1996. In particular, between September 1994 and October 1995, a mass increase of 2 × 10¹⁰  kg occurred 2000  m beneath the summit craters. Between October 1995 and July 1996 this mass was lost, while another 2 × 10¹⁰  kg was injected at about 1000  m  a.s.l. into the 1989 fracture system. From the gravity data alone, it is not possible to distinguish whether the first shallow intrusion (1994–1995) was then injected laterally into the 1989 fracture, or summit activity was fed by the first shallow intrusion, while new magma entered the 1989 fracture system.
  While magma was being redistributed within the volcanic edifice, measurements along an E–W-trending profile on the southern slope of the volcano detected some 1.5 × 10¹¹  kg of magma accumulating 2–3  km below sea level between October 1995 and November 1996.  相似文献   

Rotating magnetopolytropes: spherical figures of equilibrium due to balance of magnetic field and rotation     

Daniele Galli 《Astrophysics and Space Science》1993,204(1):111-127

In this paper we compute spherical figures of equilibrium resulting from the balance of toroidal magnetic field and rotation. These two distortion effects are assumed to act on rotating magneto-polytropic constant-mass sequences, that is, sequences with each of their members having mass constant and equal to that of the corresponding nondistorted model.  相似文献   

Transformations of Benzene Photoinduced by Nitrate Salts and Iron Oxide     

Daniele?Borghesi  Davide?Vione  Valter?Maurino  Claudio?MineroEmail author 《Journal of Atmospheric Chemistry》2005,52(3):259-281

This paper reports the results of a study on the transformation of benzene in the presence of solid nitrate salts (NaNO₃, NH₄NO₃) under irradiation in a gas-solid photoreactor. Sodium and ammonium nitrate have been chosen as representative of the composition of atmospheric particulate, benzene as a model aromatic molecule. The purpose is to simulate the transformations that aromatic compounds undergo on the surface of dispersed particles in the atmosphere. Irradiation of sodium nitrate causes hydroxylation and nitration of benzene, yielding phenol and nitrobenzene. This is most likely due to the generation of ^•OH and ^•NO₂ radicals upon nitrate photolysis, with ^•OH + O₂ leading to the formation of phenol and ^•OH + ^•NO₂ yielding nitrobenzene. The percentage of oxygen in the reaction environment influences the transformation pathways, with phenol formation being favoured and nitrobenzene formation depressed by high O₂ concentration. In the presence of hematite (α-Fe₂O₃, another component of atmospheric particulate) very relevant formation of nitrobenzene takes place even with 21% oxygen (simulated air), indicating that the interaction between hematite and nitrate can lead to the formation of aromatic nitroderivatives on the surface of atmospheric particulate. The effect of hematite is possibly due to protonation of peroxynitrite, formed upon nitrate photoisomerisation, to peroxynitrous acid, a powerful nitrating agent. A similar effect leads to relevant formation of nitrobenzene under atmospheric conditions upon irradiation of the acid salt ammonium nitrate.  相似文献   

Pretunnel technology: applications and design methods     

Fulvio?TononEmail author  Armando?Mammino  Daniele?Vanni  Pier?Giorgio?Borghi  Alessandro?Bertero 《Geotechnical and Geological Engineering》2005,23(5):487-518

The Pretunnel technology allows the final or preliminary lining to be built ahead of a tunnel face. The paper shows how this technology has been used for mechanizing the full-face excavation of large tunnels in difficult ground conditions with minimum settlements. Analytical methods are presented for the analysis of the lining both in deep and shallow applications. Fields of applicability are established using results of parametric studies based on the methods proposed.  相似文献   

Occurrence of potentially pathogenic vibrios in the marine environment of the Straits of Messina (Italy)     

Gugliandolo C  Carbone M  Fera MT  Irrera GP  Maugeri TL 《Marine pollution bulletin》2005,50(6):692-697

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Chemical speciation of arsenic in different marine organisms: Importance in monitoring studies     

Fattorini D  Alonso-Hernandez CM  Diaz-Asencio M  Munoz-Caravaca A  Pannacciulli FG  Tangherlini M  Regoli F 《Marine environmental research》2004,58(2-5):845-850

Arsenic is a widely distributed element in the marine environment. Inorganic and organic compounds have extremely different toxicological effects, and their characterization is thus of great utility when monitoring and assessing the impact of arsenic pollution. In this study both the levels of total arsenic and its chemical speciation were analyzed in several marine organisms collected from Cienfuegos Bay (Cuba) following an episode of acute As-contamination. Fish from the more impacted site were characterized by elevated concentrations of arsenic (up to 500 microg/g d.w.) and inorganic species represented the predominant forms in muscle tissues of these organisms.  相似文献   

Failure to protect beaches under slowly rising sea level     

Alisha Summers  Charles H. Fletcher  Daniele Spirandelli  Kristian McDonald  Jin-Si Over  Tiffany Anderson  Matthew Barbee  Bradley M. Romine 《Climatic change》2018,147(3-4):427-439

The increase in population and the improvement of life standards are stretching the boundaries between water-energy-land management, and demanding innovative and holistic solutions. This article proposes an approach for increasing the water availability of two or more water basins taking into consideration land use and wind patterns, and was named Land, Water, and Wind Watershed Cycle (L3WC). This approach can be applied to one watershed or a combination of watersheds. In the first case, if wind patterns blow mainly in the opposite direction of the main river flow, plantations with high water demand should be focused on the lowest part of the basin. The transpired moisture would then return to the basin with the wind and possibly increase the water availability of the basin. Applying this method to a series of basins, water is transposed from one basin to another, used for irrigated agriculture, returned to the atmosphere with evapotranspiration and pushed back to the basin where the water was extracted by the wind. Case studies of this methodology are presented in the São Francisco basin and between the Tocantins, Amazonas, and Paraná basins and the São Francisco basin in Brazil. The São Francisco basin was selected because it is located in a dry region, its flow has considerably reduced in the past decade and because the trade winds blow constantly from the ocean into the continent all year around. L3WC is a strategy to plan the allocation of water consumption in a watershed, taking into account wind patterns to support the sustainable development of a region. It has the potential of increasing water availability and creating a climate change adaptation mechanism to control the climate and reduce vulnerability to climatic variations.  相似文献   

The influence of hydrogeological properties,seawater intrusion and refreshening on the quality of groundwater used for irrigation in an agricultural coastal plain in North Sardinia,Italy     

Daniele Pittalis  Alberto Carletti  Giorgio Ghiglieri  Fulvio Celico 《Environmental Earth Sciences》2016,75(11):963

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A shell model for anisotropic magnetohydrodynamic turbulence     

Vincenzo Carbone  Pierluigi Veltri 《地球物理与天体物理流体动力学》2013,107(1-3):153-181

Abstract

In this paper, starting from the spectral DIA equations obtained by Veltri et al. (1982), describing the spectral dynamical evolution of magnetohydrodynamic (MHD) turbulence in the presence of a background magnetic field B ₀, we have derived an approximate form of these equations (shell model) more appropriate for numerical integration at high Reynolds numbers.

We have studied the decay of an initially isotropic state, with an initial imbalance between the energies for the two signs of the cross-helicity. Reynolds numbers up to 10⁵ have been considered.

Numerical results show that the nonlinear energy cascade behaves anisotropically in the k-space, i.e. in the spectra there is a prevalence of the wavevectors perpendicular to B ₀ with respect to the parallel wavevectors. This anisotropic effect, which is due to the presence of the background magnetic field, can be understood in terms of the so-called ‘‘Alfvén effect''.

A different source of anisotropy, due to the difference of the energy transfer for the two polarizations perpendicular to k, is recovered, but its effect is found to be mainly concentrated in the injection range.

Only little differences have been found, in the inertial range, in the spectral indices from the Kraichnan 3/2 value, which is valid for an isotropic spectrum. A form for the anisotropic spectrum can be recovered phenomenologically from our results. Values of the spectral indices quite different from the Kraichnan 3 2 value are obtained only when we consider stationary states with different forcing terms for the two modes of Alfvén wave propagation.

The comparison of our results with the observations of the v and B fluctuations in the interplanatery space shows that the anisotropy found in interplanetary fluctuations might be attributed only partially to the result of a nonlinear energy cascade.  相似文献