408 Matching Results

Search Results

Advanced search parameters have been applied.

Scale dependence of the effective matrix diffusion coefficient:some analytical results

Description: Matrix diffusion is an important process affecting solutetransport in fractured rock, and the matrix diffusion coefficient is akey parameter for describing this process. Previous studies haveindicated that the effective matrix-diffusion coefficient values,obtained from a number of field tracer tests, are enhanced in comparisonwith local values and may increase with test scale. In thiscommunication, we develop analytical expressions for the effective matrixdiffusion coefficient for two simple fracture-matrix systems, anddemonstrate that heterogeneities in the rock matrix at different scalescontribute to the scale dependence of the effective matrix diffusioncoefficient.
Date: May 30, 2005
Creator: Liu, H. H.; Zhang, Y. Q. & Molz, F. J.
Partner: UNT Libraries Government Documents Department

Growth of Uniform Ga{sub 1-x}In{sub x}Sb Bulk Crystals by Self-Solute Feeding Technique

Description: Compositionally homogeneous, crack-free bulk crystals of Ga{sub 1-x}In{sub x}Sb with x as high as 0.4 has been grown for the first time using a self-solute feeding method. A balance between the growth rate and the spacing between the solute and the growth interface has been found to be crucial in maintaining uniform alloy composition.
Date: August 29, 2003
Creator: Dutta, P.S.; Rajagopalan, G.; Gutmann, R.J. & Nichols, G.
Partner: UNT Libraries Government Documents Department

A Technique for Estimating the Time of Travel of Water in Indiana streams

Description: Abstract: Estimates of the travel time of waterborne particles in streams is important for pollution studies and in the event of spills of contaminants. This report provides data for the 16 Indiana streams on which time-of-travel information has been obtained and a means for estimating the velocity of any naturally flowing stream in Indiana with a drainage area of 80 square miles (210 square kilometers) or more. Measured velocity rates compiled from the time-of-travel data collected in Indiana are related to 25, 50, 100, and 200 percent of the average discharge of streams shown in this report. Velocities at these discharges are significantly related to their respective watershed characteristics (average discharge and slope).Generalized relations of the velocities as functions of the streams' watershed characteristics are developed as multivariate regression equations using the data from each of the measured streams.
Date: March 1976
Creator: Eikenberry, S. E. & Davis, L. G.
Partner: UNT Libraries Government Documents Department

Comment on "Thermochemical Investigations of Associated Solutions: Calculation of Solute-Solvent Equilibrium Constants from Solubility Measurements"

Description: This article provides comments on "Thermochemical Investigations of Associated Solutions: Calculation of Solute-Solvent Equilibrium Constants from Solubility Measurements," published in the Journal of Pharmaceutical Sciences in 1983.
Date: July 1, 1987
Creator: Acree, William E. (William Eugene)
Partner: UNT College of Arts and Sciences

Generation of Compositionally Graded Ga{sub 1-x}In{sub x}Sb Seed by Solute Diffusion

Description: Compositionally graded single crystalline <100> seed of Ga{sub 1-x}In{sub x}Sb has been grown in a single experiment using a solute diffusion method. The present technique is simple and less time consuming compared to the conventional boot-strapping approach previously used for generating ternary seeds. Starting from an InSb <100> single crystalline seed, a seed of Ga{sub 0.6}In{sub 0.4}Sb has been grown. The effect of temperature gradient on the crystalline quality of seeds grown using this method has been discussed.
Date: August 29, 2002
Creator: Dutta, P.S.; Rajagopalan, G.; Gutmann, R.J. & Nichols, G.
Partner: UNT Libraries Government Documents Department

Activity Coefficients at Infinite Dilution for Organic Solutes Dissolved in Three 1-Alkyl-1-methylpyrrolidinium Bis(trifluoromethylsulfonyl)imide Ionic Liquids Bearing Short Linear Alkyl Side Chains of Three to Five Carbons

Description: Article discussing activity coefficients at infinite dilution for organic solutes dissolved in three 1-alkyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquids bearing short linear alkyl side chains of three to five carbons.
Date: July 30, 2013
Creator: Mutelet, Fabrice; Hassan, El-Sayed R. E.; Stephens, Timothy W.; Acree, William E. (William Eugene) & Baker, Gary A.
Partner: UNT College of Arts and Sciences

Supplemental Material: Enthalpy of Solvation Correlations for Gaseous Solutes Dissolved in Linear Alkanes (C5 thru C16) Based on the Abraham Model

Description: This document includes supplemental material to an article titled "Enthalpy of solvation correlations for gaseous solutes dissolved in linear alkanes (C5 thru C16) based on the Abraham model," published in QSAR & Combinatorial Science.
Date: June 2007
Creator: Mintz, Christina; Burton, Katherine; Acree, William E. (William Eugene) & Abraham, M. H. (Michael H.)
Partner: UNT College of Arts and Sciences

Abraham Model Linear Free Energy Relationships as a Means of Extending Solubility Studies to Include the Estimation of Solute Solubilities in Additional Organic Solvents

Description: This article calculates Abraham model solute descriptors for 5-nitro-8-hydroxyquinoline, 2-methyl-6-nitroaniline, and terephthaldialdehyde using experimental solubility data taken from papers published in The Journal of Chemical Thermodynamics in 2016.
Date: July 21, 2016
Creator: Acree, William E. (William Eugene); Horton, Melissa Y.; Higgins, Elizabeth & Abraham, M. H. (Michael H.)
Partner: UNT College of Arts and Sciences

A modified invasion percolation model for low-capillary number immiscible displacements in horizontal rough-walled fractures: Influence of local in-plane

Description: The authors develop and evaluate a modified invasion percolation (MIP) model for quasi-static immiscible displacement in horizontal fractures. The effects of contact angle, local aperture field geometry, and local in-plane interracial curvature between phases are included in the calculation of invasion pressure for individual sites in a discretized aperture field. This pressure controls the choice of which site is invaded during the displacement process and hence the growth of phase saturation structure within the fracture. To focus on the influence of local in-plane curvature on phase invasion structure, they formulate a simplified nondimensional pressure equation containing a dimensionless curvature number (C) that weighs the relative importance of in-plane curvature and aperture-induced curvature. Through systematic variation of C, they find in-plane interracial curvature to greatly affect the phase invasion structure. As C is increased from zero, phase invasion fronts transition from highly complicated (IP results) to microscopically smooth. In addition, measurements of fracture phase saturations and entrapped cluster statistics (number, maximum size, structural complication) show differential response between wetting and nonwetting invasion with respect to C that is independent of contact angle hysteresis. Comparison to experimental data available at this time substantiates predicted behavior.
Date: January 28, 2000
Partner: UNT Libraries Government Documents Department

Partition of solutes from the gas phase and from water to wet and dry di-n-butyl ether: a linear free energy relationship analysis

Description: Article on the partition of solutes from the gas phase and from water to wet and dry di-n-butyl ether and a linear free energy relationship analysis.
Date: August 13, 2001
Creator: Abraham, M. H. (Michael H.); Zissimos, Andreas M. & Acree, William E. (William Eugene)
Partner: UNT College of Arts and Sciences

Fick's Insights on Liquid Diffusion

Description: In 1855, Adolph Fick published ''On Liquid Diffusion'', mathematically treating salt movements in liquids as a diffusion process, analogous to heat diffusion. Less recognized is the fact that Fick also provided a detailed account of the implications of salt diffusion to transport through membranes. A careful look at Fick (1855) shows that his conceptualization of molecular diffusion was more comprehensive than could be captured with the mathematical methods available to him, and therefore his expression, referred to as Fick's Law, dealt only with salt flux. He viewed salt diffusion in liquids as a binary process, with salt moving in one way and water moving in the other. Fick's analysis of the consequences of such a binary process operating in a hydrophilic pore in a membrane offers insights that are relevant to earth systems. This paper draws attention to Fick's rationale, and its implications to hydrogeological systems. Fick (1829-1901; Figure 1), a gifted scientist, published the first book on medical physics (Fick, 1858), discussing the application of optics, solid mechanics, gas diffusion, and heat budget to biological systems. Fick's paper is divisible into two parts. The first describes his experimental verification of the applicability of Fourier's equation to liquid diffusion. The second is a detailed discussion of diffusion through a membrane. Although Fick's Law specifically quantifies solute flux, Fick visualized a simultaneous movement of water and stated, ''It is evident that a volume of water equal to that of the salt passes simultaneously out of the upper stratum into the lower.'' (Fick, 1855, p.30). Fick drew upon Fourier's model purely by analogy. He assumed that concentration gradient impelled salt movement, without inquiring why concentration gradient should constitute a driving force. As for water movement, he stated intuitively, ''a force of suction comes into play on each side of the membrane, proportional ...
Date: October 7, 2004
Creator: Narasimhan, T.N.
Partner: UNT Libraries Government Documents Department

Flow channeling and analysis of tracer tests in heterogeneous porous media

Description: Flow and solute transport through porous medium with strongly varying hydraulic conductivity are studied by numerical simulations. The heterogeneity of the porous medium is defined by {sigma} and {lambda}{prime}, which are, respectively, the standard deviation of natural log of permeability values and its correlation range {lambda} divided by transport distance L. The development of flow channeling as a function of these two parameters is demonstrated. The results show that for large heterogeneities, the flow is highly channelized and solute is transported through a few fast paths, and the corresponding breakthrough curves show a high peak at very early times, much shorter than the mean residence time. This effect was studied for a converging radial flow, to simulate tracer tests in a fracture zone or contact-thickness aquifer. It is shown that {sigma}{sup 2}{lambda}{prime} is an appropriate parameter to characterize the tracer dispersion and breakthrough curves. These results are used to study tracer breakthrough data from field experiments performed with nonsorbing tracers. A new procedure is proposed to analyze the results. From the moments of the residence-time distribution represented by the breakthrough curves, the heterogeneity of the porous medium, as characterized by {sigma}{sup 2}{lambda}{prime} and the mean residence time t{sub o}, may be determined.
Date: November 3, 2001
Creator: Moreno, Luis & Tsang, Chin-Fu
Partner: UNT Libraries Government Documents Department

Linear Free Energy Relationship Correlations for Enthalpies of Solvation of Organic Solutes into Room-Temperature Ionic Liquids Based on the Abraham Model with Ion-Specific Equation Coefficients

Description: Article discussing the linear free energy relationship correlations for enthalpies of solvation of organic solutes into room-temperature ionic liquids based on the Abraham model with ion-specific equation coefficients.
Date: August 3, 2009
Creator: Sprunger, Laura M.; Achi, Sai S.; Acree, William E. (William Eugene) & Abraham, M. H. (Michael H.)
Partner: UNT College of Arts and Sciences

A macroscopic relationship for preferential flow in the vadose zone: Theory and Validation

Description: Preferential flow commonly observed in unsaturated soils allows rapid movement of solute from the ground surface or vadose zone to the groundwater, bypassing a significant volume of unsaturated soil and increasing the risk of groundwater contamination. A variety of evidence indicates that complex preferential flow patterns observed from fields are fractals. This paper discusses a macroscopic rela-tionship for modeling preferential flow in the vadose zone. Conceptually, the flow domain can be di-vided into active and inactive regions. Flow occurs preferentially in the active region (characterized by fractals), and inactive region is simply bypassed. The portion of the active region was found to be a power function of saturation. The validity of this macroscopic relationship is demonstrated by its consistency with field observations and the related numerical experiments.
Date: February 15, 2010
Creator: Liu, H.H. & Zhang, R.D.
Partner: UNT Libraries Government Documents Department

Lattice Boltzmann simulation of solute transport in heterogeneous porous media with conduits to estimate macroscopic continuous time random walk model parameters

Description: Lattice Boltzmann models simulate solute transport in porous media traversed by conduits. Resulting solute breakthrough curves are fitted with Continuous Time Random Walk models. Porous media are simulated by damping flow inertia and, when the damping is large enough, a Darcy's Law solution instead of the Navier-Stokes solution normally provided by the lattice Boltzmann model is obtained. Anisotropic dispersion is incorporated using a direction-dependent relaxation time. Our particular interest is to simulate transport processes outside the applicability of the standard Advection-Dispersion Equation (ADE) including eddy mixing in conduits. The ADE fails to adequately fit any of these breakthrough curves.
Date: October 20, 2008
Creator: Anwar, S.; Cortis, A. & Sukop, M.
Partner: UNT Libraries Government Documents Department

Field-Scale Effective Matrix Diffusion Coefficient for FracturedRock: Results From Literature Survey

Description: Matrix diffusion is an important mechanism for solutetransport in fractured rock. We recently conducted a literature survey onthe effective matrix diffusion coefficient, Dem, a key parameter fordescribing matrix diffusion processes at the field scale. Forty fieldtracer tests at 15 fractured geologic sites were surveyed and selectedfor study, based on data availability and quality. Field-scale Dem valueswere calculated, either directly using data reported in the literature orby reanalyzing the corresponding field tracer tests. Surveyed dataindicate that the effective-matrix-diffusion-coefficient factor FD(defined as the ratio of Dem to the lab-scale matrix diffusioncoefficient [Dem]of the same tracer) is generally larger than one,indicating that the effective matrix diffusion coefficient in the fieldis comparatively larger than the matrix diffusion coefficient at therock-core scale. This larger value could be attributed to the manymass-transfer processes at different scales in naturally heterogeneous,fractured rock systems. Furthermore, we observed a moderate trend towardsystematic increase in the emDFmDDF value with observation scale,indicating that the effective matrix diffusion coefficient is likely tobe statistically scale dependent. The FD value ranges from 1 to 10,000for observation scales from 5 to 2,000 m. At a given scale, the FD valuevaries by two orders of magnitude, reflecting the influence of differingdegrees of fractured rock heterogeneity at different sites. In addition,the surveyed data indicate that field-scale longitudinal dispersivitygenerally increases with observation scale, which is consistent withprevious studies. The scale-dependent field-scale matrix diffusioncoefficient (and dispersivity) may have significant implications forassessing long-term, large-scale radionuclide and contaminant transportevents in fractured rock, both for nuclear waste disposal and contaminantremediation.
Date: March 28, 2005
Creator: Zhou, Quanlin; Liu, Hui Hai; Molz, Fred J.; Zhang, Yingqi & Bodvarsson, Gudmundur S.
Partner: UNT Libraries Government Documents Department

Scale dependency of the effective matrix diffusion coefficient

Description: It has been recognized that matrix diffusion is an important process for retarding solute transport in fractured rock. Based on analyses of tracer transport data from a number of field tests, we demonstrate for the first time that the effective matrix-diffusion coefficient may be scale dependent and generally increases with test scale. A preliminary theoretical explanation of this scale dependency is also presented, based on the hypothesis that solute travel paths within a fracture network are fractals.
Date: May 30, 2003
Creator: Liu, H. H.; Bodvarsson, G. S. & Zhang, G.
Partner: UNT Libraries Government Documents Department

Radioactivity of Potassium Solutions: A Comparison of Calculated Activity to Measured Activity from Gross Beta Counting and Gamma Spectroscopy

Description: In order to determine if the measured beta activity for a solution containing potassium was exactly as predicted, particularly since the CES gas counter is not calibrated specifically with K-40, an experiment was conducted to compare measured activities from two radioanalytical methods (gamma spectroscopy and gas proportional counting) to calculated activities across a range of potassium concentrations. Potassium, being ubiquitous and naturally radioactive, is a well-known and common interference in gross beta counting methods. By measuring the observed beta activity due to K-40 in potassium-containing solutions across a wide range of concentrations, it was found that the observed beta activity agrees well with the beta activity calculated from the potassium concentration measured by standard inorganic analytical techniques, such as ICP-OES, and that using the measured potassium concentration to calculate the expected beta activity, and comparing this to the observed beta activity to determine if potassium can account for all the observed activity in a sample, is a valid technique. It was also observed that gamma spectroscopy is not an effective means of measuring K-40 activity below approximately 700 pCi/L, which corresponds to a solution with approximately 833 mg/L total potassium. Gas proportional counting for gross beta activity has a much lower detection limit, typically 20-50 picoCi/L for a liquid low in total dissolved solids, which corresponds to a potassium concentration of approximately 30-70 ppm K.
Date: July 26, 2005
Creator: Gaylord, R F
Partner: UNT Libraries Government Documents Department