Showing papers by "Clemson University published in 1997"
TL;DR: A paradigm for developing unidimensional scales is offered as a means of formally defining unidimensionality, distinguishing the concept from traditional reliability-based metrics, and describing a structured technique for empirically testing its existence.
Abstract: The development and psychometric evaluation of scales which measure unobservable (latent) phenomena continues to be an issue of high interest among researchers within the information systems community. Accurate measurement of structurally complex constructs provides a potentially powerful means for empirically exploring relationships between information technology and individual, organizational, and industrial phenomena. In exploratory contexts, measurement properties of psychometric scales are evaluated using traditional techniques such as item-to-total correlations, reliability analysis, and exploratory factor analysis. In instances of strong theoretical rationale, contemporary techniques, such as confirmatory factor analysis, are utilized as a means of assessing model efficacy. An essential, but often overlooked, property of measurement which is assumed in both exploratory and confirmatory statistical techniques is unidimensionality. Scales which are unidimensional measure a single trait. This property is a basic assumption of measurement theory and is absolutely essential for unconfounded assessment of variable interrelationships in path modeling. In this paper, a paradigm for developing unidimensional scales is presented and illustrated. Built on similar frameworks within the disciplines of psychology, education and marketing research, this paradigm is offered as a means of formally defining unidimensionality, distinguishing the concept from traditional reliability-based metrics, and describing a structured technique for empirically testing its existence.
932 citations
TL;DR: In this paper, a study was conducted to ascertain the positive and/or negative effects that other customers may have upon one's service experience, using the critical incident technique, data were gathered from 486 customers regarding satisfying or dissatisfying episodes with service organizations that were the result of other customer's presence.
726 citations
TL;DR: The use of chemical solution deposition for the fabrication of perovskite thin films is reviewed in this paper, where a variety of approaches including sol−gel, chelate, and metalloorganic decomposition have all been employed with success in the preparation of these materials.
Abstract: The use of chemical solution deposition for the fabrication of perovskite thin films is reviewed. A variety of approaches including sol−gel, chelate, and metalloorganic decomposition have all been employed with success in the preparation of these materials. For a number of perovskite compounds, thin-film properties that equal those of the bulk materials have been obtained. Various aspects of the solution chemistries for the three different routes are discussed, and the effects of solution precursor properties on the conversion of the as-deposited film to the desired perovskite phase are discussed. The roles that thermodynamic and kinetic factors have on this transformation process are also reviewed. Finally, some of the applications for solution-derived thin films currently under development are reviewed, and the inherent limitations of the deposition technique for device manufacture are considered.
499 citations
University of Washington1, University of Illinois at Urbana–Champaign2, Yale University3, Los Alamos National Laboratory4, University of North Carolina at Chapel Hill5, Duke University6, California Institute of Technology7, University of Texas at El Paso8, University of Arizona9, University of California, Santa Cruz10, University of Texas at Austin11, Ohio State University12, Clemson University13
TL;DR: A review of low energy nuclear experiments and theory, stellar modeling over a wide range of mass and composition, and abundance studies of many hundreds of stars can be found in this paper.
Abstract: Forty years ago Burbidge, Burbidge, Fowler, and Hoyle combined what we would now call fragmentary evidence from nuclear physics, stellar evolution and the abundances of elements and isotopes in the solar system as well as a few stars into a synthesis of remarkable ingenuity. Their review provided a foundation for forty years of research in all of the aspects of low energy nuclear experiments and theory, stellar modeling over a wide range of mass and composition, and abundance studies of many hundreds of stars, many of which have shown distinct evidence of the processes suggested by B2FH. In this review we summarize progress in each of these fields with emphasis on the most recent developments.
498 citations
TL;DR: In this paper, the authors investigate whether inside managers are added to corporate boards for efficiency or entrenchment purposes, and find that the expected benefits of an inside manager's expert knowledge clearly out weigh the expected costs of managerial entrenchments only when managerial and outside shareholders interests are closely aligned.
420 citations
TL;DR: In this paper, the authors present a comparison of multiple comparative methods in theory and methods for quality assurance in the field of quality assurance. Journal of Quality Technology: Vol. 29, No. 3, No 3, pp. 359-359.
Abstract: (1997). Multiple Comparisons: Theory and Methods. Journal of Quality Technology: Vol. 29, No. 3, pp. 359-359.
402 citations
TL;DR: In this article, the relationships between fear expectancy, disgust sensitivity, desire for modem comforts, and preference for wildland and built environments and related activiffes were examined. Using a populatio...
Abstract: The relationships between fear expectancy, disgust sensitivity, desire for modem comforts, and preference for wildland and built environments and related activiffes were examined. Using a populatio...
342 citations
TL;DR: Cloning a gene (MAC1) encoding adenylate cyclase, a membrane-bound enzyme that catalyzes the production of cAMP from ATP, confirms that cell signaling involving cAMP plays a central role in the development and pathogenicity of M. grisea.
Abstract: Magnaporthe grisea, the causal agent of rice blast disease, differentiates a specialized infection structure called an appressorium that is crucial for host plant penetration. Previously, it was found that cAMP regulates appressorium formation. To further understand the cellular mechanisms involved in appressorium formation, we have cloned a gene (MAC1) encoding adenylate cyclase, a membrane-bound enzyme that catalyzes the production of cAMP from ATP, by using a polymerase chain reaction-based strategy. The entire gene was isolated and subcloned from a large insert bacterial artificial chromosome library. Sequence characterization showed that MAC1 has a high degree of identity with other adenylate cyclase genes from several filamentous fungi as well as yeasts. Gene deletion resulted in reduced vegetative growth, conidiation, and conidial germination. Transformants lacking MAC1 were unable to form appressoria on an inductive surface and were unable to penetrate susceptible rice leaves. mac1- transformants were also sterile and produced no perithecia. Appressorium formation was restored in the presence of exogenous cAMP derivatives. These results confirm that cell signaling involving cAMP plays a central role in the development and pathogenicity of M. grisea.
342 citations
01 Dec 1997
TL;DR: A variety of techniques to carry out highly accurate data value predictions are investigated, including monitoring the strides by which the results produced by different instances of an instruction change and combining these two predictors to form a hybrid predictor.
Abstract: Data dependences (data flow constraints) present a major hurdle to the amount of instruction-level parallelism that can be exploited from a program. Recent work has suggested that the limits imposed by data dependences can be overcome to some extent with the use of data value prediction. That is, when an instruction is fetched, its result can be predicted so that subsequent instructions that depend on the result can use this predicted value. When the correct result becomes available, all instructions that are data dependent on that prediction can be validated. This paper investigates a variety of techniques to carry out highly accurate data value predictions. The first technique investigates the potential of monitoring the strides by which the results produced by different instances of an instruction change. The second technique investigates the potential of pattern-based two-level prediction schemes. Simulation results of these two schemes show improvements over the existing method of predicting the last outcome. In particular, some benchmarks show improvement with the stride-based predictor and others show improvement with the pattern-based predictor. To do uniformly well across benchmarks, we combine these two predictors to form a hybrid predictor. Simulation analysis of the hybrid predictor shows its overall prediction accuracy to be better than that of the component predictors across all benchmarks.
308 citations
TL;DR: Three G protein α subunit genes have been cloned and characterized from Magnaporthe grisea and it is found that magB¯ transformants failed to form perithecia, whereas magA¯ and magC¯ transformant did not produce mature asci.
Abstract: Three G protein α subunit genes have been cloned and characterized from Magnaporthe grisea: magA is very similar to CPG-2 of Cryphonectria parasitica; magB is virtually identical to CPG-1 of Crypho...
301 citations
TL;DR: In this paper, a fault location and diagnosis scheme is proposed to accurately identify the location of a fault upon its occurrence, based on the integration of information available from disturbance recording devices with knowledge contained in a distribution feeder database.
Abstract: This paper presents new techniques for locating and diagnosing faults on electric power distribution feeders. The proposed fault location and diagnosis scheme is capable of accurately identifying the location of a fault upon its occurrence, based on the integration of information available from disturbance recording devices with knowledge contained in a distribution feeder database. The developed fault location and diagnosis system can also be applied to the investigation of temporary faults that may not result in a blown fuse. The proposed fault location algorithm is based on the steady-state analysis of the faulted distribution network. To deal with the uncertainties inherent in the system modeling and the phasor estimation, the fault location algorithm has been adapted to estimate fault regions based on probabilistic modeling and analysis. Since the distribution feeder is a radial network, multiple possibilities of fault locations could be computed with measurements available only at the substation. To identify the actual fault location, a fault diagnosis algorithm has been developed to prune down and rank the possible fault locations by integrating the available pieces of evidence. Testing of the developed fault location and diagnosis system using field data has demonstrated its potential for practical use.
TL;DR: This chapter discusses recent developments that provide new insight into the molecular mechanism regulating induction and function of appressoria, and topics include attachment to the leaf surface; environmental cues that signal germ-tube growth and appressorium formation; mechanisms for sensing environmental cues; endogenous signaling pathways; and mechanisms of penetration from theappressorium.
Abstract: Fungal pathogens have evolved elaborate strategies to gain access to plant tissues. For many pathogens, following attachment of spores to the leaf surface, germ tubes emerge and grow across the surface, often in response to particular environmental cues and to a specific location. At an appropriate site, polar elongation of the germ tube ceases, the tip attaches to the surface and swells to form an appressorium, a uniquely organized infection structure. Following a period of maturation, a hypha then emerges at the plant interface and penetrates into the plant tissues. This chapter discusses recent developments that provide new insight into the molecular mechanism regulating induction and function of appressoria. Topics include attachment to the leaf surface; environmental cues that signal germ-tube growth and appressorium formation; mechanisms for sensing environmental cues; endogenous signaling pathways; and mechanisms of penetration from the appressorium.
TL;DR: In this paper, a vorticity-based approach is used to evaluate the effect of counterrotating vortices in the boundary layers of a film-hole flowfield.
Abstract: A previously documented systematic computational methodology is implemented and applied to a jet-in-crossflow problem in order to document all of the pertinent flow physics associated with a film-cooling flowfield Numerical results are compared to experimental data for the case of a row of three-dimensional, inclined jets with length-to-diameter ratios similar to a realistic film-cooling application A novel vorticity-based approach is included in the analysis of the flow physics Particular attention has been paid to the downstream coolant structures and to the source and influence of counterrotating vortices in the crossflow region It is shown that the vorticity in the boundary layers within the film hole is primarily responsible for this secondary motion Important aspects of the study include: (1) a systematic treatment of the key numerical issues, including accurate computational modeling of the physical problem, exact geometry and high-quality grid generation techniques, higher-order numerical discretization, and accurate evaluation of turbulence model performance; (2) vorticity-based analysis and documentation of the physical mechanisms of jet-crossflow interaction and their influence on film-cooling performance; (3) a comparison of computational results to experimental data; and (4) comparison of results using a two-layer model near-wall treatment versus generalized wall functions Solution of the steady, time-averaged Navier-Stokes equations were obtained for all cases using an unstructured/adaptive grid, fully explicit, time-marching code with multigrid, local time stepping, and residual smoothing acceleration techniques For the case using the two-layer model, the solution was obtained with an implicit, pressure-correction solver with multigrid The three-dimensional test case was examined for two different film-hole length-to-diameter ratios of 175 and 35, and three different blowing ratios, from 05 to 20 All of the simulations had a density ratio of 20, and an injection angle of 35 deg An improved understanding of the flow physics has provided insight into future advances to film-cooling configuration design In addition, the advantages and disadvantages of the two-layer turbulence model are highlighted for this class of problems
TL;DR: The recent design of an in vitro assay combined with the identification of Bchl-biosynthetic enzyme genes has now made it possible to address the question of regulation of Mg-chelatase.
Abstract: Mg-chelatase catalyses the insertion of Mg into protoporphyrin IX (Proto). This seemingly simple reaction also is potentially one of the most interesting and crucial steps in the (bacterio)chlorophyll (Bchl/Chl)-synthesis pathway, owing to its position at the branch-point between haem and Bchl/Chl synthesis. Up until the level of Proto, haem and Bchl/Chl synthesis share a common pathway. However, at the point of metal-ion insertion there are two choices: Mg2+ insertion to make Bchl/Chl (catalysed by Mg-chelatase) or Fe2+ insertion to make haem (catalysed by ferrochelatase). Thus the relative activities of Mg-chelatase and ferrochelatase must be regulated with respect to the organism's requirements for these end products. How is this regulation achieved? For Mg-chelatase, the recent design of an in vitro assay combined with the identification of Bchl-biosynthetic enzyme genes has now made it possible to address this question. In all photosynthetic organisms studied to date, Mg-chelatase is a three-component enzyme, and in several species these proteins have been cloned and expressed in an active form. The reaction takes place in two steps, with an ATP-dependent activation followed by an ATP-dependent chelation step. The activation step may be the key to regulation, although variations in subunit levels during diurnal growth may also play a role in determining the flux through the Bchl/Chl and haem branches of the pathway.
TL;DR: The identity of a novel growth factor in uterine fluids as a highly truncated form of CTGF is revealed and show that the N-terminal two-thirds of the CTGF primary translation product is not required for mitogenic activity or heparin binding.
TL;DR: In this paper, high-speed cyclic voltammetry was used to measure rates for ferrocene oxidation/reduction in a series of self-assembled monolayers formed by coadsorption of N-(mercaptoalkyl)ferrocenecarboxamide ((C5H5)Fe(C 5H4)CONH(CH2)nSH where n = 7−10, and 15) with mercapto alcohol (HO(CH 2)n+1SH) on gold.
Abstract: High-speed cyclic voltammetry was used to measure rates for ferrocene oxidation/reduction in a series of self-assembled monolayers formed by coadsorption of N-(mercaptoalkyl)ferrocenecarboxamide ((C5H5)Fe(C5H4)CONH(CH2)nSH where n = 7−10, and 15) with mercapto alcohol (HO(CH2)n+1SH where n = 7−10, and 15) on gold. Standard electron-transfer rate constants were obtained as a function of chain length and from these rate constants, a β value (describing the exponential decay of rate with adsorbate chain length) of 1.1 methylene-1 or 0.85 A-1 was obtained. The rate data were also used to estimate coupling factors, |VAB|, describing the long-range electronic coupling between the immobilized ferrocene groups and the underlying gold electrode. Electronic coupling factors varied from a low of 0.06 cm-1 for the long-chain monolayer (18 bonds in the pathway linking ferrocene to the electrode) to a high of 6.5 cm-1 for the short-chain monolayer (10 bonds linking ferrocene to the electrode). The latter value is in go...
TL;DR: This paper presents an alternative approach to distribution circuit state estimation using a probabilistic extension of the radial load flow algorithm while accounting for real-time measurements as solution constraint.
Abstract: Past work on distribution circuit state estimation has focused on the adoption of a transmission state estimator approach, without necessarily accounting for the specific requirement of a distribution circuit-based analysis. On distribution circuits, typically, there are very few available real-time measurements, and thus, researchers have treated customer load demand estimates as pseudo-measurements in a weighted-least-squares formulation. This can lead to convergence problems and also, the approach effectively assumes that all bus load demands are normally distributed (Gaussian) which may not be valid on distribution circuits. This paper presents an alternative approach to distribution circuit state estimation using a probabilistic extension of the radial load flow algorithm while accounting for real-time measurements as solution constraint. The algorithm which takes advantage of the radial nature of distribution circuits also accounts for other issues specific to distribution circuits. Namely, the algorithm accounts for nonnormally distributed loads, incorporates the concept of load diversity (load correlation) and can interact with a load allocation routine. The effectiveness of the algorithm is illustrated through comparisons made with Monte Carlo simulations.
TL;DR: In this paper, the authors extend the Carlino and Mills and Boarnet models of local development to test for the presence and direction of rural area linkages to urban areas in Functional Economic Areas (FEAs).
Abstract: In this article we extend the Carlino and Mills and Boarnet models of local development to test for the presence and direction of rural area linkages to urban areas in Functional Economic Areas (FEAs). In a sample of southern FEAs, we detect a mix of spillover and backwash effects from urban core and fringe areas to their rural hinterlands. Rural-area population and employment both grew faster than average between 1980 and 1990 if in an FEA with a pattern of urban decentralization.
TL;DR: Results provide direct evidence that P2c contributes to the invasion and spread of A. flavus during infection of cotton bolls and other factors not evaluated in this study also contribute to aggressiveness.
Abstract: Isolates of Aspergillus flavus can be differentiated based on production of the polygalacturonase P2c. One group of isolates produces P2c, whereas the other group does not. In general, the group that produces P2c causes more damage and spreads to a greater extent in cotton bolls than those isolates that do not produce P2c. To determine whether P2c contributes to disease, the expression of pecA, the gene previously determined to encode P2c, was genetically altered. Adding the pecA gene to a strain previously lacking the gene resulted in the ability to cause significantly more damage to the intercarpellary membrane and the ability spread to a greater extent within the adjacent locule compared to the abilities of a control transformant. Conversely, eliminating the expression of pecA by targeted disruption caused a significant reduction in aggressiveness compared to that of a nondisrupted control transformant. These results provide direct evidence that P2c contributes to the invasion and spread of A. flavus during infection of cotton bolls. However, other factors not evaluated in this study also contribute to aggressiveness.
TL;DR: In this paper, the physics of the film cooling process for shaped, streamwise-injected, inclined jets is studied for blowing ratio (M = 1.25, 1.88), density ratio (DR), and length-to-diameter ratio (L/D = 4) parameters typical of gas turbine operations.
Abstract: The physics of the film cooling process for shaped, streamwise-injected, inclined jets is studied for blowing ratio (M = 1.25, 1.88), density ratio (DR = 1.6), and length-to-diameter ratio (L/D = 4) parameters typical of gas turbine operations. A previously documented computational methodology is applied for the study of five distinct film cooling configurations: (1) cylindrical film hole (reference case); (2) forward-diffused film hole; (3) laterally diffused film hole; (4) inlet shaped film hole, and (5) cusp-shaped film hole. The effect of various film hole geometries on both flow and thermal field characteristics is isolated, and the dominant mechanisms responsible for differences in these characteristics are documented. Special consideration is given to explaining crucial flow mechanisms from a vorticity point of view. It is found that vorticity analysis of the flow exiting the film hole can aid substantially in explaining the flow behavior downstream of the film hole. Results indicate that changes in the film hole shape can significantly alter the distribution of the exit-plane variables, therefore strongly affecting the downstream behavior of the film. Computational solutions of the steady, Reynolds-averaged Navier-Stokes equations are obtained using an unstructured/adaptive, fully implicit, pressure-correction solver. Turbulence closure is obtained via the high-Reynolds-number {kappa}-{epsilon}more » model with generalized wall functions. Detailed field results as well as surface phenomena involving adiabatic film effectiveness {eta} and heat transfer coefficient (h) are presented. When possible, computational results are validated against corresponding experimental cases from data found in the open literature. Detailed comparisons are made between surface and field results of the film hole shapes investigated in this work; design criteria for optimizing downstream heat transfer characteristics are then suggested.« less
TL;DR: The results suggest that these compounds exert their inhibitory effects through cannabinoid CB1 receptors in the myenteric plexus preparation, but mainly through CB2-like cannabinoid receptors inThe vas deferens.
TL;DR: In this article, a non-incremental self-consistent scheme for elastic-viscoplastic deformations is proposed and compared with the Taylor's upper bound for both time dependent and time independent plasticity.
TL;DR: There are tissue and gender-related differences for basal ChE and CaE activity and the in vitro sensitivity of CaE or ChE to CPF-oxon is highly tissue-specific, suggesting that the number of binding sites does play a role in the detoxification potential of a tissue.
TL;DR: In this article, the effect of elemental substitutions on the properties of the ferromagnetic, conducting, highly magnetoresistive compound ${\mathrm{La}}{2/3}{Ca}}_{1/3}{\mathm{MnO}}_{3}$ has been studied.
Abstract: The effect of elemental substitutions on the properties of the ferromagnetic, conducting, highly magnetoresistive compound ${\mathrm{La}}_{2/3}{\mathrm{Ca}}_{1/3}{\mathrm{MnO}}_{3}$ has been studied. The results of Co doping and Ni doping on the Mn site and Gd doping on the La site are reported. These compounds were investigated by x-ray diffraction, magnetization measurements, resistivity measurements, thermopower measurements, and by paramagnetic resonance. The result of replacing La by Gd atoms is to lower the ferromagnetic (or metal-insulator) transition temperature, an effect which is shown to be due to bond bending caused by the lattice adjusting to the size differential between the La and Gd ions. On the other hand, the reduction of the magnetic transition temperature when Mn ions are replaced with Co or Ni ions is not attributed to changes in the size of the ions. Instead, we ascribe the lowering of the ferromagnetic transition temperature to a weakening of the double-exchange interaction between two unlike ions. The resistivity and Seebeck coefficient in these materials have been investigated as a function of elemental substitution. The magnetic polaron theory of Zhang is used, phenomenologically, to provide a quantitative explanation of these transport properties. In addition, the effect of these elemental substitutions on the linewidths of the paramagnetic resonances is studied and is discussed in terms of exchange narrowing and spin-lattice relaxation.
TL;DR: This database of basic anatomic geometry defines the anatomic relationships of the proximal humerus and glenoid cavity that allow for a precise bone-implant fit and assesses the match between the shape of existing components and the patient's anatomy.
TL;DR: A review of the literature on tropical ecotoxicology, with an emphasis on Latin America and the Caribbean, is presented in this article, where the authors outline the special issues that must be addressed as the field of tropical ecology progresses and also address priority areas for immediate research in the tropics.
Abstract: Ecotoxicology has focused almost exclusively on countries and ecosystems in temperate zones. Tropical ecosystems, which combined contain as much as 75% of the global biodiversity, have been neglected. Tropical ecosystems are under increasing threat of development and habitat degradation from population growth and urbanization, agricultural expansion, deforestation, and mining. Some of these activities also lead to the release of toxic substances into the environment. Little research in ecotoxicology has been carried out in tropical environments. Techniques and procedures developed for temperate environments are often applied, even though physical and chemical environmental parameters in the tropics can be very different. Most research has focused on water quality and aquatic toxicology. The regulatory environment also varies among countries. We present a review of the literature on tropical ecotoxicology, with an emphasis on Latin America and the Caribbean. We also address priority areas for immediate research in the tropics. These include large-scale agricultural activities, especially banana, pineapple, and soybean farming, and gold mining with the associated heavy use of mercury. We outline the special issues that must be addressed as the field of tropical ecotoxicology progresses.
TL;DR: Despite a relatively low level of polymorphism in the species, AFLP markers were found to be more efficient in mapping the melon genome than RAPD or microsatellite markers.
Abstract: Genetic maps facilitate the study of genome structure and evolution, and the identification of monogenic traits or Mendelian components of quantitative traits. We evaluated 228 RAPD, microsatellite and AFLP markers for linkage analysis in melon (Cucumis melo L.) varieties MR-1 (resistant to Fusarium wilt, powdery and downy mildews) and Ananas Yokneum (AY; susceptible to these diseases) and constructed a detailed genetic map. The mapping population consisted of 66 backcross progenies derived from AY×(MR-1×AY). Despite a relatively low level of polymorphism in the species, AFLP markers were found to be more efficient in mapping the melon genome than RAPD or microsatellite markers. The map contains 197 AFLPs, six RAPDs and one microsatellite marker assigned to 14 major and six minor linkage groups, and covers 1942 cM with the average distance between adjacent markers of approximately 10 cM. The maximum distance allowed between markers is 27.5 cM. About 11% of the intervals (20 out of 173) are over 20 cM (but less than 27.5 cM). The map has immediate utility for identifying markers linked to disease resistance genes that are suitable for marker-assisted breeding. The use of microsatellite markers for integration with other maps is also discussed.
TL;DR: In this article, a vorticity and momentum-based approach was implemented to document how the symmetric, counterrotating vortex structure typically found in the crossflow region in streamwise injection cases, becomes asymmetric with increasing compound angle injection, leading to a large, single vortex system at {Phi} = 90 deg and fundamentally alters the interaction of the coolant jet and hot crossflow.
Abstract: Detailed analyses of computational simulations with comparisons to experimental data were performed to identify and explain the dominant flow mechanisms responsible for film cooling performance with compound angle injection, {Phi}, of 45, 60, and 90 deg. A novel vorticity and momentum based approach was implemented to document how the symmetric, counterrotating vortex structure typically found in the crossflow region in streamwise injection cases, becomes asymmetric with increasing {Phi}. This asymmetry eventually leads to a large, single vortex system at {Phi} = 90 deg and fundamentally alters the interaction of the coolant jet and hot crossflow. The vortex structure dominates the film cooling performance in compound angle injection cases by enhancing the mixing of the coolant and crossflow in the near wall region, and also by enhancing the lateral spreading of the coolant. The simulations consist of fully elliptic and fully coupled solutions for field results in the supply plenum, film hole, and crossflow regions and includes surface results for adiabatic effectiveness {eta} and heat transfer coefficient h. Realistic geometries with length-to-diameter ratio of 4.0 and pitch-to-diameter ratio of 3.0 allowed for accurate capturing of the strong three-way coupling of flow in this multiregion flowfield. The cooling configurations implemented in thismore » study exactly matched experimental work used for validation purposes and were represented by high-quality computational grid meshes using a multiblock, unstructured grid topology. Blowing ratios of 1.25 and 1.88, and density ratio of 1.6 were used to simulate realistic operating conditions and to match the experiments used for validation. Predicted results for {eta} and h show good agreement with experimental data.« less
TL;DR: In this article, a numerical simulation study of air sparging for the removal of nonaqueous phase liquids (NAPLs) from the subsurface is presented.
Abstract: A numerical simulation study of air sparging for the removal of nonaqueous phase liquids (NAPLs) from the subsurface is presented. These simulations were performed using the T2VOC integrated finite-difference, multiphase-flow, contaminant transport code. The code is used to model two-dimensional air sparging experiments from Ji et al. (1993) which include both homogeneous and heterogeneous permeability distributions. The model predicts the experimental gas plume shape and behavior very well. Field-scale simulations using a radially symmetric, cylindrical mesh are then used to model hypothetical DNAPL and LNAPL spills and air sparging remediation performance in various hydrogeologic settings. Both homogeneous and heterogeneous systems are considered. The results of the study indicate that the sparging-induced gas pressure increase, or ``positive pressure,`` measured at steady state below the water table, closely corresponds to both the subsurface gas distribution and the effective zone of contaminant reduction. Because this positive pressure is easily measured in the field with a simple monitoring device, it can be used to realistically define the sparging radius of influence.