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P M Adler

Publications and source records attributed to P M Adler.

15 recordsLinked to original sources
PubMed2006

Thermodiffusional transport of electrolytes in compact clays.

The macroscopic Soret coefficient S(T) was measured for three porous media, namely mica, glass powder, and natural compact clay. At a mean temperature of T = 25 degrees C and with NaCl, S(T) for mica and glass powder was found to be equal to (3.1+/-0.7) x 10(-3) K(-1) and close to values for a free medium in agreement with theoretical predictions which are obtained under the assumption that the pressure gradient and the electric field are negligible on the pore scale. The main result is that for clay S(T) was found five times larger, presumably because of extra couplings with electrical phenomena. This latter measurement was confirmed by an independent technique based on the membrane potential.

Journal Article↗
PubMed2005

Electrokinetic phenomena in saturated compact clays.

The membrane potential, the pressure difference, and the concentration difference induced by an applied concentration gradient through samples of compact clay were measured as functions of sodium chloride concentration and of porosity. The results of some previous numerical predictions are recalled to be functions of a characteristic length scale which can be derived from conductivity and permeability. Generally, the experimental data were in agreement with these numerical predictions. Therefore, nondiagonal coupling coefficients can be derived with acceptable precision from the diagonal coefficients.

Journal Article↗
PubMed2005

Nuclear-magnetic-resonance diffusion simulations in two phases in porous media.

Time-dependent diffusion simulations which can be measured by nuclear magnetic resonance (NMR) were numerically performed in consolidated reconstructed porous media saturated by two immobile fluids. The phase distributions were obtained by an immiscible lattice Boltzmann technique which incorporates interfacial tension and wetting. The apparent diffusion coefficient in each fluid was determined by a random walk algorithm. Permeability and conductivity tensors were calculated by finite-difference schemes. The major properties valid for a single phase could be generalized to two phases. First, the characteristic length Lambda introduced by Johnson et al.[Phys. Rev. Lett. 57, 2564 (1986)] is of the order of twice the phase volume to surface ratio. Second, the apparent diffusion coefficients for all porosities, saturations, and phases can be represented by a single dimensionless curve.

Journal Article↗
PubMed2005

Nuclear magnetic resonance diffusion with surface relaxation in porous media.

Nuclear magnetic resonance (NMR) diffusion simulations with surface relaxation were performed numerically in unconsolidated and consolidated porous media by a random walk technique. Two uniform and nonuniform models of surface relaxation were proposed and compared. The apparent diffusion coefficient and extinction function were determined and studied in the fast, slow and intermediate diffusion regimes of relaxation. According to theoretical predictions, it was observed that the extinction function does not depend on surface relaxivity parameter rho 2 in the slow diffusion regime. The apparent diffusion coefficients are independent of rho 2 in the fast diffusion regime and tend to be superposed onto a single curve in the slow one. The evolution of the apparent diffusion coefficients is gathered by a reduced representation in the fast diffusion regime.

Journal Article↗
PubMed2005

Percolation of three-dimensional fracture networks with power-law size distribution.

The influence of various parameters such as the domain size, the exponent of the power law, the smallest radius, and the fracture shape on the percolation threshold of fracture networks has been numerically studied. For large domains, the adequate percolation parameter is the dimensionless fracture density normalized by the product of the third moment of fracture radii distribution and of the shape factor; for networks of regular polygons, the dimensionless critical density depends only slightly on the parameters of radii distribution and on the shape of fractures; a model is proposed for the percolation threshold for fractures with elongated shapes. In small domains, percolation is analyzed in terms of the dimensionless fracture density normalized by the sum of two reduced moments of the radii distribution; this provides a general description of the network connectivity properties whatever the dominating percolation mechanism; the fracture shape is taken into account by using excluded volume in the definition of dimensionless fracture density.

Journal Article↗
PubMed2005

Deposition in porous media and clogging on the field scale.

Deposition is modeled as a first order reaction on the Darcy scale for porous media which are statistically homogeneous. An elementary analytical solution is derived. A parametric study was done with a three-dimensional code which is briefly described and checked in media where the solution is known. The role of the parameters, including the artificial ones, is discussed with an illustrative example. When the Damköhler number is small, deposition causes smooth changes to the porosity field; the evolution of porosity is well described by the analytical solution. Very different results are obtained for large Damköhler numbers. The influence of the correlation of the initial porosity field is studied.

Journal Article↗
PubMed2004

Macroscopic permeability of three-dimensional fracture networks with power-law size distribution.

Fracture network permeability is investigated numerically by using a three-dimensional model of plane polygons uniformly distributed in space with sizes following a power-law distribution. Each network is triangulated via an advancing front technique, and the flow equations are solved in order to obtain detailed pressure and velocity fields. The macroscopic permeability is determined on a scale which significantly exceeds the size of the largest fractures. The influence of the parameters of the fracture size distribution--the power-law exponent and the minimal fracture radius--on the macroscopic permeability is analyzed. Eventually, a general expression is proposed, which is the product of a dimensional measure of the network density, weighted by the individual fracture conductivities, and of a fairly universal function of a dimensionless network density, which accounts for the influences of the fracture shapes and of the parameters of their size distribution. Two analytical formulas are proposed which successfully fit the numerical data over a wide range of network densities.

Journal Article↗
PubMed2004

Macroscopic diffusion on rough surfaces.

We consider diffusion on rough and spatially periodic surfaces. The macroscopic diffusion tensor D is determined by averaging the local fluxes over the unit cell. D is proved to be the unit tensor for macroscopically isotropic surfaces. For general surfaces, an asymptotic analysis is applied, when the ratio of the oscillation amplitude to the size of the unit cell is a small parameter epsilon. The microscopic field is determined up to O(epsilon(6)) in analytical form and an algorithm is derived to calculate higher order terms. We also deduce general analytical formulas for D up to O(epsilon(6)) and derive an algorithm to compute D as a series in epsilon(2).

Journal Article↗
PubMed2003

Thermodiffusion in compact clays.

An experimental cell has been devised in order to measure the Soret coefficients in a compact clay, namely argilite, when a concentration difference of a binary mixture is applied simultaneously with a temperature difference. Temperature gradients have been imposed in the same direction as concentration gradients or in the opposite one. The sign of the Soret coefficients is related to the respective direction of these gradients. Generally, mass transfer was found to be enhanced by the Soret effect. Experimental values of the Soret coefficient are given.

Journal Article↗
PubMed2003

Two-phase flow through fractured porous media.

Two-phase flow in fractured porous media is investigated by means of a direct and complete numerical solution of the generalized Darcy equations in a three-dimensional discrete fracture description. The numerical model applies to arbitrary fracture network geometry, and to arbitrary distributions of permeabilities in the porous matrix and in the fractures. It is used here in order to obtain the steady-state macroscopic relative permeabilities of random fractured media. Results are presented as functions of the mean saturation and are discussed in comparison with simple models.

Journal Article↗
PubMed2003

Transport properties of compact clays. II. Diffusion.

An experimental system was constructed in order to measure the diffusion coefficient in three types of porous media, namely mica, sodic montmorillonite, and natural compact clay. Several salts at various concentrations were used for the measurements in order to investigate the influence of these factors. Influence of porosity was also studied. In a first approximation, all the results can be summarized by a simple Archie's law independent of the clay and of the solute. The diffusion and electric formation factors have also been systematically compared; they generally agree for large porosities, while they disagree for small porosities for clay and montmorillonite.

Journal Article↗
PubMed2001

Grain reconstruction of porous media: application to a low-porosity Fontainebleau sandstone.

The fundamental issue of reconstructing a porous medium is examined anew in this paper, thanks to a sample of low-porosity Fontainebleau sandstone that has been analyzed by computed microtomography. Various geometric properties are determined on the experimental sample. A statistical property, namely, the probability density of the covering radius, is determined. This is used in order to reconstruct a porous medium by means of a Poissonian generation of polydisperse spheres. In a second part, the properties of the real experimental sample and of the reconstructed one are compared. The most important success of the present reconstruction technique is the fact that the numerical sample percolates despite its low porosity. Moreover, other geometrical features and conductivity are found to be in good agreement.

Journal Article↗
PubMed1986

Stool examination: culture versus Gram stain.

Presented is a methodology for efficient, cost-effective collection, transport, culture, and microscopic examination of infectious diarrhea. A critical review of the literature is included, as are guidelines for workup and management of the disease complex in the emergency department.

Diagnosis, Differential↗
PubMed1986

Serum glucose changes after administration of 50% dextrose solution: pre- and in-hospital calculations.

A prospective clinical trial was conducted to estimate the rise in serum glucose level after an intravenous bolus of 50 ml of 50% dextrose solution (D-50) in the emergency department setting. Fifty one subjects with altered levels of consciousness were studied. Of these, 23 patients were known diabetics, and 28 were not diabetic. The change in glucose level for the total study group ranged from a low of 37 mg/dl to a high of 370 mg/dl, with a mean of 166 +/- 77 mg/dl. The mean for the diabetic and non-diabetic groups were 177 +/- 80 mg/dl and 154 +/- 75 mg/dl. These results suggest that serum glucose levels cannot be quantitatively predicted after a single intravenous bolus of D-50.

Adolescent↗