bluuebunny/crossref_metadata_2025_split huggingface dataset:
Permeability Changes in Layered Sediments: Impact of Particle Release
Authors: Blume Theresa , Weisbrod Noam , Selker John S. 
Published: December 2005

AbstractOne of the mechanisms of sudden particle release from grain surfaces in natural porous media is a decrease in salt concentration of the permeating fluid to below the critical salt concentration. Particle release can cause a change in hydraulic conductivity of the matrix, either by washing out the fines and thus increasing the pore sizes or by the plugging of pore constrictions. The phenomenon of permeability changes as a result of particle detachment was investigated in a series of column experiments. Coarse and fine sediments from the Hanford Formation in southeast Washington were tested. Columns were subject to a pulse of highly saline solution (NaNO3) followed by a fresh water shock causing particle release. Outflow rates and changes in hydraulic head as well as electric conductivity and pH were monitored over time. No permeability decrease occurred within the coarse matrix alone. However, when a thin layer of fine sediment was embedded within the coarse material (mimicking field conditions at the Hanford site), permeability irreversibly decreased to 10% to 20% of the initial value. Evidence suggests that most of this permeability decrease was a result of particles detached within the fine layer and its subsequent clogging. An additional observation was a sudden increase in pH in the outflow solution, generated in situ during the fresh water shock. Because layered systems are common in natural settings, our results suggest that alteration between sodium solution and fresh water can lead to particle release and subsequently reduce the overall permeability of the matrix.
Dynamic Optimal Ground Water Remediation Including Fixed and Operation Costs
Authors: Chang Liang‐Cheng , Hsiao Chin‐Tsai 
Published: December 2005

AbstractIn time‐varying ground water remediation, the lack of an optimal control algorithm to simultaneously consider fixed costs and time‐varying operating costs makes it nearly impossible to obtain an optimal solution. This study presents a novel algorithm that integrates a genetic algorithm (GA) and constrained differential dynamic programming (CDDP) to solve this time‐varying ground water remediation problem. A GA can easily incorporate the fixed costs associated with the installation of wells. However, using a GA to solve for time‐varying policies would dramatically increase the computational resources required. Therefore, the CDDP is used to handle the subproblems associated with time‐varying operating costs. A hypothetical case study that incorporates fixed and time‐varying operating costs is presented to demonstrate the effectiveness of the proposed algorithm. Simulation results indicate that the fixed costs can significantly influence the number and locations of wells, and a notable total cost savings can be realized by applying the novel algorithm herein.
Origin of Shallow Ground Water in an Alluvial Aquifer as Determined by Isotopic and Chemical Procedures
Authors: Rains Mark Cable , Mount Jeffrey F. 
Published: December 2005

AbstractIn this study, we identify the origin of shallow ground water that supports regionally unique plant and wildlife habitats in a riparian and reservoir‐fringe system using isotopic and chemical procedures. This study was conducted where Little Stony Creek flows into East Park Reservoir on the east front of the Coast Range, northern California. Little Stony Creek water, Hyphus Creek water, Franciscan Complex regional ground water, Great Valley Group regional ground water, and local shallow ground water were collected during wet and dry seasons and were analyzed for deuterium, oxygen‐18, temperature, pH, redox potential, conductivity, and major cation and anion concentrations. Turnover in the local flow system is rapid indicating that local shallow ground water is dependent on recent recharge. Local shallow ground water is recharged primarily by Little Stony Creek water and Franciscan Complex ground water. In the wet season, Little Stony Creek is the more prominent source of local shallow ground water, and the ratio of Little Stony Creek water to Franciscan Complex ground water decreases with distance from the channel. In the dry season, Franciscan Complex ground water is the more prominent source of local shallow ground water, and the ratio of Little Stony Creek water to Franciscan Complex ground water decreases with distance down the valley. Franciscan Complex ground water discharges to local shallow ground water throughout the year, primarily because the local flow system is a regional low that lies perpendicular to the Franciscan Complex ground water flowpath. Little Stony Creek is a more prominent source of ground water in the wet season than in the dry season because Little Stony Creek flows continuously through the alluvial reach in the wet season and intermittently through the alluvial reach in the dry season. Extensive ground water withdrawals from the Franciscan Complex flow system could reduce the amount of water available to the local flow system, particularly during the dry season, and could substantially reduce the geographic extent of the regionally unique plant and wildlife habitats.
Comparison of an Algebraic Multigrid Algorithm to Two Iterative Solvers Used for Modeling Ground Water Flow and Transport
Authors: Detwiler Russell L. , Mehl Steffen , Rajaram Harihar , Cheung Wendy W. 
Published: December 2005

AbstractNumerical solution of large‐scale ground water flow and transport problems is often constrained by the convergence behavior of the iterative solvers used to solve the resulting systems of equations. We demonstrate the ability of an algebraic multigrid algorithm (AMG) to efficiently solve the large, sparse systems of equations that result from computational models of ground water flow and transport in large and complex domains. Unlike geometric multigrid methods, this algorithm is applicable to problems in complex flow geometries, such as those encountered in pore‐scale modeling of two‐phase flow and transport. We integrated AMG into MODFLOW 2000 to compare two‐ and three‐dimensional flow simulations using AMG to simulations using PCG2, a preconditioned conjugate gradient solver that uses the modified incomplete Cholesky preconditioner and is included with MODFLOW 2000. CPU times required for convergence with AMG were up to 140 times faster than those for PCG2. The cost of this increased speed was up to a nine‐fold increase in required random access memory (RAM) for the three‐dimensional problems and up to a four‐fold increase in required RAM for the two‐dimensional problems. We also compared two‐dimensional numerical simulations of steady‐state transport using AMG and the generalized minimum residual method with an incomplete LU‐decomposition preconditioner. For these transport simulations, AMG yielded increased speeds of up to 17 times with only a 20% increase in required RAM. The ability of AMG to solve flow and transport problems in large, complex flow systems and its ready availability make it an ideal solver for use in both field‐scale and pore‐scale modeling.
Effects of Land Use on Ground Water Quality in the Anoka Sand Plain Aquifer of Minnesota
Authors: Trojan Michael D. , Maloney Jennifer S. , Stockinger James M. , Eid Erin P. , Lahtinen Mark J. 
Published: December 2005

AbstractWe began a study, in 1996, to compare ground water quality under irrigated and nonirrigated agriculture, sewered and nonsewered residential developments, industrial, and nondeveloped land uses. Twenty‐three monitoring wells were completed in the upper meter of an unconfined sand aquifer. Between 1997 and 2000, sampling occurred quarterly for major ions, trace inorganic chemicals, volatile organic compounds (VOCs), herbicides, and herbicide degradates. On single occasions, we collected samples for polynuclear aromatic hydrocarbons (PAHs), perchlorate, and coliform bacteria. We observed significant differences in water chemistry beneath different land uses. Concentrations of several trace inorganic chemicals were greatest under sewered urban areas. VOC detection frequencies were 100% in commercial areas, 52% in sewered residential areas, and <10% for other land uses. Median nitrate concentrations were greatest under irrigated agriculture (15,350 μg/L) and nonsewered residential areas (6080 μg/L). Herbicides and degradates of acetanilide and triazine herbicides were detected in 86% of samples from irrigated agricultural areas, 68% of samples from nonirrigated areas, and <10% of samples from other land uses. Degradates accounted for 96% of the reported herbicide mass. We did not observe seasonal differences in water chemistry, but observed trends in water chemistry when land use changes occurred. Our results show land use is the dominant factor affecting shallow ground water quality. Trend monitoring programs should focus on areas where land use is changing, while resource managers and planners must consider potential impacts of land use changes on ground water quality.
Retracted: A Single Recovery Type Curve from Theis' Exact Solution
Authors: Samani Nozar , Pasandi M. 
Published: December 2005

AbstractThe following article from Ground Water Volume 41, Issue 5, September 2003, “A Single Recovery Type Curve from Theis' Exact Solution” by Nozar Samani and M. Pasandi, published online on December 13, 2005, in Wiley InterScience (http://www.interscience.wiley.com), has been retracted by the journal Editor‐in‐Chief, Mary P. Anderson, and Wiley‐Blackwell following discovery that the article was plagiarized. This retraction supersedes the Notice of Plagiarism, which was published in Ground Water Volume 42, Issue 1, January 2004.
Using Temperature to Test Models of Flow Near Yucca Mountain, Nevada
Authors: Painter Scott , Winterle James , Armstrong Amit 
Published: December 2005

AbstractGround water temperatures in the fractured volcanic aquifer near Yucca Mountain, Nevada, have previously been shown to have significant spatial variability with regions of elevated temperatures coinciding roughly with near‐vertical north‐south trending faults. Using insights gained from one‐dimensional models, previous investigators have suggested upwelling along faults from an underlying aquifer as a likely explanation for this ground water temperature pattern. Using a three‐dimensional coupled flow and heat‐transport model, we show that the thermal high coinciding with the Paintbrush fault zone can be explained without significant upwelling from the underlying aquifer. Instead, the thermal anomaly is consistent with thermal conduction enhanced slightly by vertical ground water movement within the volcanic aquifer sequence. If more than ‐400 m3/day of water enters the volcanic aquifer from below along a 10 km fault zone, the calculated temperatures at the water table are significantly greater than the measured temperatures. These results illustrate the potential limitations in using one‐dimensional models to interpret ground water temperature data, and underscore the value in combining temperature data with fully coupled three‐dimensional simulations.
The Effect of Critical pH on Virus Fate and Transport in Saturated Porous Medium
Authors: Guan Huade , Schulze‐Makuch Dirk , Schaffer Steve , Pillai Suresh D. 
Published: December 2005

AbstractSeveral viral transport experiments were conducted in a model aquifer l m long, using bacteriophages MS2 and φX174 at various pH (4.6 to 8.3) conditions, to increase our understanding of virus behavior in ground water. The results indicate the existence of a critical pH at which the virus behavior changes abruptly. This is supported by data from field and batch experiments. The critical pH is determined to be 0.5 unit below the highest isoelectric point of the virus and porous medium. When water pH is below the critical pH, the virus has an opposite charge to at least one component of the porous medium, and is almost completely and irreversibly removed from the water. This suggests that electrostatic attraction at a subcritical water pH condition is an important factor controlling virus attenuation in ground water. The concept of critical pH can assist in the design of geologic barriers for preventing viral contamination in ground water.
Influence of Aquifer Properties on Phytoremediation Effectiveness
Authors: Matthews Daniel W. , Massmann Joel , Strand Stuart E. 
Published: December 2005

AbstractRecent research has shown that planting deep‐rooted trees, such as poplar, can take up and degrade important ground water pollutants such as trichloroethylene (TCE) as they transpire water from the capillary fringe of shallow contaminated aquifers. The effect of hydrogeologic factors on the minimum plantation area needed to prevent downgradient migration of contaminated ground water is not well known. Accordingly, the objective of this research was to identify the hydrogeologic parameters that control phytoremediation effectiveness. We used a numerical ground water flow model to evaluate the effect that natural variations in hydrogeologic parameters and growing season duration have on the minimum plantation area required for capture. We found that the plantation area that was needed to completely capture a ground water contamination plume was directly proportional to aquifer horizontal hydraulic conductivity, saturated thickness, and ground water gradient. The plantation area needed for capture increased non‐linearly with increasing plume width, aquifer anisotropy, and decreasing growing season duration. The plantation area needed for capture was generally insensitive to aquifer‐specific yield and storativity. Steady‐state simulations can be used to predict the plantation area needed for capture in many applications. A particularly important finding of this work is that evapotranspiration fluxes through plantations appropriately sized to contain the plume substantially exceeded the ground water flux through the plume itself.
Aquifer Parameter Estimation from Surface Resistivity Data
Authors: Niwas Sri , de Lima Olivar A.L 
Published: December 2005

AbstractThis paper is devoted to the additional use, other than ground water exploration, of surface geoelectrical sounding data for aquifer hydraulic parameter estimation. In a mesoscopic framework, approximated analytical equations are developed separately for saline and for fresh water saturations. A few existing useful aquifer models, both for clean and shaley sandstones, are discussed in terms of their electrical and hydraulic effects, along with the linkage between the two. These equations are derived for insight and physical understanding of the phenomenon. In a macroscopic scale, a general aquifer model is proposed and analytical relations are derived for meaningful estimation, with a higher level of confidence, of hydraulic parameter from electrical parameters. The physical reasons for two different equations at the macroscopic level are explicitly explained to avoid confusion. Numerical examples from existing literature are reproduced to buttress our viewpoint.
Transport of Three Herbicides in Ground Water at Twin Lake Test Site, Chalk River, Ontario, Canada
Authors: Maloszewski P. , Zuber A. , Bedbur E. , Matthess G. 
Published: December 2005

AbstractA field tracer test performed under natural flow conditions at the Twin Lake test site, Chalk River Laboratories of the Atomic Energy of Canada Ltd. in Chalk River, Ontario, Canada, using tritium and three herbicides (Chlor‐toluron, Terbuthylazine, and Pendimethalin) was interpreted using the dispersion equation with a combined reaction model. The reaction model couples an instantaneous equilibrium reaction governed by a linear adsorption isotherm with a reversible or irreversible kinetic reaction of the first order, and decay. An improved interpretation method consists of a simultaneous fitting of theoretical concentration and mass‐recovery curves to the experimental data, which leads to a more reliable determining of reaction models and improves the accuracy of fitting. Tritium served as the reference tracer to determine the flow velocity, dispersivity, and the recovery of the herbicides. Chlortoluron was slightly delayed by equilibrium exchange with strongly reduced concentration due to an irreversible kinetic reaction and/or decay. Terbuthilazine was slightly delayed by equilibrium exchange, with strongly reduced concentration due to a reversible kinetic reaction with some influence of decay. A strong equilibrium reaction and a strong reversible kinetic reaction without degradation governed the transport of Pendimethalin, reducing considerably its concentration. The results obtained show that simulations based only on Kd and decay constant, especially if these parameters are found in the laboratory, may considerably differ from those performed with reaction parameters determined in properly performed field tests. The dominant reaction types, and the values of parameters found in the study, supply useful information on the transport of the investigated herbicides in sandy aquifers under natural flow conditions.
Ground Water Discharge and Nitrate Flux to the Gulf of Mexico
Authors: Dowling Carolyn B. , Poreda Robert J. , Hunt Andrew G. , Carey Anne E. 
Published: December 2005

AbstractGround water samples (37 to 186 m depth) from Baldwin County, Alabama, are used to define the hydrogeology of Gulf coastal aquifers and calculate the subsurface discharge of nutrients to the Gulf of Mexico. The ground water flow and nitrate flux have been determined by linking ground water concentrations to 3H/3He and 4He age dates. The middle aquifer (A2) is an active flow system characterized by postnuclear tritium levels, moderate vertical velocities, and high nitrate concentrations. Ground water discharge could be an unaccounted source for nutrients in the coastal oceans. The aquifers annually discharge 1.1 ± 0.01 × 108 moles of nitrate to the Gulf of Mexico, or 50% and 0.8% of the annual contributions from the Mobile‐Alabama River System and the Mississippi River System, respectively.In southern Baldwin County, south of Loxley, increasing reliance on ground water in the deeper A3 aquifer requires accurate estimates of safe ground water withdrawal. This aquifer, partially confined by Pliocene clay above and Pensacola Clay below, is tritium dead and contains elevated 4He concentrations with no nitrate and estimated ground water ages from 100 to 7000 years. The isotopic composition and concentration of natural gas diffusing from the Pensacola Clay into the A3 aquifer aids in defining the deep ground water discharge. The highest 4He and CH4 concentrations are found only in the deepest sample (Gulf State Park), indicating that ground water flow into the Gulf of Mexico suppresses the natural gas plume. Using the shape of the CH4‐He plume and the accumulation of 4He rate (2.2 ± 0.8 μcc/kg/1000 years), we estimate the natural submarine discharge and the replenishment rate for the A3 aquifer.
Assembly of CS1 Pili: the Role of Specific Residues of the Major Pilin, CooA
Authors: Starks Angela M. , Froehlich Barbara J. , Jones Tamara N. , Scott June R. 
Published: December 2005

ABSTRACT

CS1 pili are important virulence factors of enterotoxigenic
Escherichia coli
strains associated with human diarrheal disease. They are the prototype for a family of pili that share extensive sequence similarity among their structural and assembly proteins. Only four linked genes,
cooB
,
cooA
,
cooC
, and
cooD
, are required to produce CS1 pili in
E. coli
K-12. To identify amino acids important for the function of the major pilin CooA, we used alanine substitution mutagenesis targeting conserved residues in the N and C termini of the protein. To test function, we examined
cooA
mutants for the ability to agglutinate bovine erythrocytes. Each hemagglutination-negative (HA
−
)
cooA
mutant was examined to identify its assembly pathway defect. CooA has been shown to be degraded in the absence of CooB (K. Voegele, H. Sakellaris, and J. R. Scott, Proc. Natl. Acad. Sci. USA
94:
13257-13261, 1997). We found several HA
−
cooA
mutants that produced no detectable CooA, suggesting that recognition by CooB is mediated by residues in both the N and C termini of CooA. In addition, we found that alanine substitution for some of the conserved residues in the C-terminal motif “AGxYxG(x
6
)T,” which is found in all subunits of this pilus family, had no effect on pilus formation. However, alanine substitution for some of the alternating hydrophobic residues within this motif prevented CooA from interacting with CooD, which serves as both the tip adhesin and nucleation protein for pilus formation. Thus, it appears that some, but not all, of the residues in both the N and C termini of CooA play a critical role in the intermolecular interactions of the major pilin with the other structural and assembly proteins. We anticipate that the results obtained here for CS1 pili in enterotoxigenic
E. coli
will help develop an understanding of the pilus assembly pathway used by CS1 family members in several important human pathogens.
Generation of DNA-Free
Escherichia coli
Cells by 2-Aminopurine Requires Mismatch Repair and Nonmethylated DNA
Authors: Matic Ivan , Ekiert Damian , Radman Miroslav , Kohiyama Masamichi 
Published: December 2005

ABSTRACT

Undirected mismatch repair initiated by the incorporation of the base analog 2-aminopurine kills DNA-methylation-deficient
Escherichia coli dam
cells by DNA double-strand breakage. Subsequently, the chromosomal DNA is totally degraded, resulting in DNA-free cells.
Isolation of RNA Polymerase from
Clostridium difficile
and Characterization of Glutamate Dehydrogenase and rRNA Gene Promoters In Vitro and In Vivo
Authors: Mani Nagraj , Dupuy Bruno , Sonenshein Abraham L. 
Published: December 2005

ABSTRACT

Clostridium difficile
is the primary causative agent of antibiotic-associated diarrheal disease. To facilitate molecular genetic analysis of gene expression in this organism, methods were developed to study transcriptional regulation in vitro and in vivo. That is,
C. difficile
RNA polymerase was partially purified and shown to bind to and initiate transcription in vitro from bona fide
C. difficile
promoters for rRNA and glutamate dehydrogenase genes. In addition, primer extension analyses and a β-glucuronidase reporter system were used to quantitate transcription from these promoters in vivo. With these tools in hand, it is now possible to characterize the behavior of any
C. difficile
gene in vivo and to study the regulation of its expression in detail.