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Simulations of Turbulent Flows with Strong Shocks and Density Variations: Final Report

Description: The target of this SciDAC Science Application was to develop a new capability based on high-order and high-resolution schemes to simulate shock-turbulence interactions and multi-material mixing in planar and spherical geometries, and to study Rayleigh-Taylor and Richtmyer-Meshkov turbulent mixing. These fundamental problems have direct application in high-speed engineering flows, such as inertial confinement fusion (ICF) capsule implosions and scramjet combustion, and also in the natural occurrence of supernovae explosions. Another component of this project was the development of subgrid-scale (SGS) models for large-eddy simulations of flows involving shock-turbulence interaction and multi-material mixing, that were to be validated with the DNS databases generated during the program. The numerical codes developed are designed for massively-parallel computer architectures, ensuring good scaling performance. Their algorithms were validated by means of a sequence of benchmark problems. The original multi-stage plan for this five-year project included the following milestones: 1) refinement of numerical algorithms for application to the shock-turbulence interaction problem and multi-material mixing (years 1-2); 2) direct numerical simulations (DNS) of canonical shock-turbulence interaction (years 2-3), targeted at improving our understanding of the physics behind the combined two phenomena and also at guiding the development of SGS models; 3) large-eddy simulations (LES) of shock-turbulence interaction (years 3-5), improving SGS models based on the DNS obtained in the previous phase; 4) DNS of planar/spherical RM multi-material mixing (years 3-5), also with the two-fold objective of gaining insight into the relevant physics of this instability and aiding in devising new modeling strategies for multi-material mixing; 5) LES of planar/spherical RM mixing (years 4-5), integrating the improved SGS and multi-material models developed in stages 3 and 5. This final report is outlined as follows. Section 2 shows an assessment of numerical algorithms that are best suited for the numerical simulation of compressible flows involving turbulence and shock phenomena. ...
Date: October 1, 2012
Creator: Lele, Sanjiva
Partner: UNT Libraries Government Documents Department

Development of combinatorial bacteria for metal and radionuclide bioremediation

Description: The grant concerned chromate [Cr(VI)] bioremediation and it was our aim from the outset to construct individual bacterial strains capable of improved bioremediation of multiple pollutants and to identify the enzymes suited to this end. Bacteria with superior capacity to remediate multiple pollutants can be an asset for the cleanup of DOE sites as they contain mixed waste. I describe below the progress made during the period of the current grant, providing appropriate context.
Date: June 15, 2006
Creator: A. C. Matin, Ph. D.
Partner: UNT Libraries Government Documents Department

Nanosensors as Reservoir Engineering Tools to Map Insitu Temperature Distributions in Geothermal Reservoirs

Description: The feasibility of using nanosensors to measure temperature distribution and predict thermal breakthrough in geothermal reservoirs is addressed in this report. Four candidate sensors were identified: melting tin-bismuth alloy nanoparticles, silica nanoparticles with covalently-attached dye, hollow silica nanoparticles with encapsulated dye and impermeable melting shells, and dye-polymer composite time-temperature indicators. Four main challenges associated with the successful implementation of temperature nanosensors were identified: nanoparticle mobility in porous and fractured media, the collection and detection of nanoparticles at the production well, engineering temperature sensing mechanisms that are both detectable and irreversible, and inferring the spatial geolocation of temperature measurements in order to map temperature distribution. Initial experiments were carried out to investigate each of these challenges. It was demonstrated in a slim-tube injection experiment that it is possible to transport silica nanoparticles over large distances through porous media. The feasibility of magnetic collection of nanoparticles from produced fluid was evaluated experimentally, and it was estimated that 3% of the injected nanoparticles were recovered in a prototype magnetic collection device. An analysis technique was tailored to nanosensors with a dye-release mechanism to estimate temperature measurement geolocation by analyzing the return curve of the released dye. This technique was used in a hypothetical example problem, and good estimates of geolocation were achieved. Tin-bismuth alloy nanoparticles were synthesized using a sonochemical method, and a bench heating experiment was performed using these nanoparticles. Particle growth due to melting was observed, indicating that tin-bismuth nanoparticles have potential as temperature nanosensors
Date: June 15, 2011
Creator: Ames, Morgan
Partner: UNT Libraries Government Documents Department

Dynamic spatial organization of multi-protein complexes controlling microbial polar organization, chromosome replication, and cytokinesis

Description: This project was a program to develop high-throughput methods to identify and characterize spatially localized multiprotein complexes in bacterial cells. We applied a multidisciplinary “systems engineering” approach to the detailed characterization of localized multi-protein structures in vivo – a problem that has previously been approached on a fragmented, piecemeal basis.
Date: June 18, 2012
Creator: McAdams, Harley; Shapiro, Lucille; Horowitz, Mark; Andersen, Gary; Downing, Kenneth; Earnest, Thomas et al.
Partner: UNT Libraries Government Documents Department

Doublet Tracer Testing in Klamath Falls, Oregon

Description: A tracer test was carried out in a geothermal doublet system to study the injection behavior of a developed reservoir known to be fractured. The doublet produces about 320 gpm of 160 F water that is used for space heating and then injected; the wells are spaced 250 ft apart. Tracer breakthrough was observed in 2 hours and 45 minutes in the production well, indicating fracture flow. However, the tracer concentrations were low and indicated porous media flow; the tracers mixed with a reservoir volume much larger than a fracture.
Date: December 15, 1983
Creator: Gudmundsson, J.S.; Johnson, S.E.; Horne, R.N.; Jackson, P.B. & Culver, G.G.
Partner: UNT Libraries Government Documents Department

Simulation of Radon Transport in Geothermal Reservoirs

Description: Numerical simulation of radon transport is a useful adjunct in the study of radon as an in situ tracer of hydrodynamic and thermodynamic numerical model has been developed to assist in the interpretation of field experiments. The model simulates transient response of radon concentration in wellhead geofluid as a function of prevailing reservoir conditions. The radon simulation model has been used to simulate radon concentration response during production drawdown and two flowrate transient tests in vapor-dominated systems. Comparison of model simulation with experimental data from field tests provides insight in the analysis of reservoir phenomena such as propagation of boiling fronts, and estimates of reservoir properties of porosity and permeability thickness.
Date: December 15, 1983
Creator: Semprini, Lewis & Kruger, Paul
Partner: UNT Libraries Government Documents Department

Slug Test Data Analysis in Reservoirs with Double Porosity Behaviour

Description: Pressure analysis for a slug test which corresponds to the flow period of a Drill Stem test is extended to wells in reservoirs with double-porosity behaviour. Solutions are obtained for either pseudo-steady state or transient interporosity flow. The distinctive specific features of both solutions are identified. Results presented are applicable to both naturally-fractured and layered reservoirs with the more permeable layer connecting to the wellbore. Type curves based on the pseudo-steady or transient interporosity flow are presented. These type curves are similar to the existing homogenous single layer type curve with addition of interporosity flow lines indicating double-porosity behaviour.
Date: December 15, 1983
Creator: Mateen, Khalid & Ramey, Henry J. Jr.
Partner: UNT Libraries Government Documents Department

Matrix Diffusion and its Effect on the Modeling of Tracer Returns from the Fractured Geothermal Reservoir at Wairakei, New Zealand

Description: Tracer tests performed at the geothermal reservoir at Wairakei, New Zealand have been analyzed, using a mathematical and physical model in which tracer flows through individual fractures with diffusion into the surrounding porous matrix. Model calculations matched well with the observed tracer return profiles. From the model, first tracer arrival times and the number of individual fractures (the principal conduits of fluid flow in the reservoir) joining the injector-producer wells can be determined. if the porosity, adsorption distribution coefficient, bulk density and effective diffusion coefficient are nown, fracture widths may be estimated. Hydrodynamic dispersion down the length of the fracture is a physical component not taken into account in this model. Future studies may be warranted in order to determine the necessity of including this factor. In addition to the tracer profile matching by the matrix diffusion model, comparisons with a simpler fracture flow model by Fossum and Horne (1982) were made. The inclusion of the matrix diffusion effects was seen to significantly improve the fit to the observed data.
Date: December 15, 1983
Creator: Jensen, Clair L. & Horne, Roland N.
Partner: UNT Libraries Government Documents Department

Fracture Characterization in Enhanced Geothermal Systems by Wellbore and Reservoir Analysis

Description: This report highlights the work that was done to characterize fractured geothermal reservoirs using production data. That includes methods that were developed to infer characteristic functions from production data and models that were designed to optimize reinjection scheduling into geothermal reservoirs, based on these characteristic functions. The characterization method provides a robust way of interpreting tracer and flow rate data from fractured reservoirs. The flow-rate data are used to infer the interwell connectivity, which describes how injected fluids are divided between producers in the reservoir. The tracer data are used to find the tracer kernel for each injector-producer connection. The tracer kernel describes the volume and dispersive properties of the interwell flow path. A combination of parametric and nonparametric regression methods were developed to estimate the tracer kernels for situations where data is collected at variable flow-rate or variable injected concentration conditions. The characteristic functions can be used to calibrate thermal transport models, which can in turn be used to predict the productivity of geothermal systems. This predictive model can be used to optimize injection scheduling in a geothermal reservoir, as is illustrated in this report.
Date: June 30, 2012
Creator: Roland N. Horne, Kewen Li, Mohammed Alaskar, Morgan Ames, Carla Co, Egill Juliusson, Lilja Magnusdottir
Partner: UNT Libraries Government Documents Department

Heat Transfer in Nonisothermal Liquid Injection Experiments in Porous Media

Description: This paper discusses an analysis of the heat transfer phenomena in the bench-scale experiments being carried out in the Stanford Geothermal Program. The basis of this analysis was a series of simplified mathematical models of heat and mass transport in fine-grained porous media. The analysis determined that the thermal capacity of the coreholder system caused heat losses from the core which were not steady at early and medium times. This phenomenon had not been recognized previously. This was in spite of the fact that various authors previously had attempted to match the experimental behavior under discussion with their sophisticated computer models. These computer models did not account for the transient nature of the heat losses from the core. 8 refs., 3 figs.
Date: December 3, 1976
Creator: Atkinson, Paul G.
Partner: UNT Libraries Government Documents Department

Heat extracted from the long term flow test in the Fenton Hill HDR reservoir

Description: A long-term flow test was carried out in the Fenton Hill HDR Phase-2 reservoir for 14 months during 1992-1993 to examine the potential for supplying thermal energy at a sustained rate as a commercial demonstration of HDR technology. The test was accomplished in several segments with changes in mean flowrate due to pumping conditions. Re-test estimates of the extractable heat content above a minimum useful temperature were based on physical evidence of the size of the Fenton Hill reservoir. A numerical model was used to estimate the extent of heat extracted during the individual flow segments from the database of measured production data during the test. For a reservoir volume of 6.5x10{sup 6}m{sup 3}, the total heat content above a minimum temperature of 150{degree} C was 1.5x10{sup 15}J. For the total test period at the three sustained mean flowrates, the integrated heat extracted was 0.088x10{sup 15}J, with no discernable temperature decline of the produced fluid. The fraction of energy extracted above the abandonment temperature was 5.9%. On the basis of a constant thermal energy extraction rate, the lifetime of the reservoir (without reservoir growth) to the abandonment temperature would be 13.3 years, in good agreement with the pre-test estimate of 15.0 years for the given reservoir volume.
Date: January 20, 1994
Creator: Kruger, Paul & Robinson, Bruce
Partner: UNT Libraries Government Documents Department


Description: An extensive study of the Thermal Shallow Reservoir at The Geysers was performed in 1982 to improve our understanding of the source and flow patterns of steam in the shallow anomaly and how they relate to the Thermal 4 blowout. This project included gathering and analyzing pressure transient, enthalpy, tracer and chemical data and developing a reservoir model that was consistent with this data. Following the pressure transient testing and analysis, a convection-plume with lateral-flow model was proposed. Subsequent analysis of enthalpy, tracer and chemical data corroborated this model. The high flowrate wells--Thermal 4, Thermal 10, Thermal 11 and Magma 1--produce from the high-pressure, high-permeability upflow zone. The source of this upflow is a limited fracture system connecting the shallow anomaly with the underlying main reservoir. The outlying low-pressure, low-permeability wells are supplied by lateral flow of steam from the central area. The pressure gradient from the core to the periphery is caused by condensation in the flanks.
Date: January 22, 1985
Creator: Mogen, P.; Pittinger, L. & Magers, M.
Partner: UNT Libraries Government Documents Department

Effects of Temperature and Saturation on the Velocity and Attenuation of Seismic Waves in Rocks: Applications to Geothermal Reservoir Evaluation

Description: In the evaluation of a geothermal resource it is critical to know the reservoir geometry, temperature, saturation, state of saturants, pore pressure, porosity and permeability. These are the parameters which will determine the production feasibility and cost effectivness of a geothermal prospect. The increasing sophistication of seismic wave data collection and processing and recent exerimental work on factors governing wave propagation in rocks has stimulated increased interest in the use of active seismic techniques to determine the in situ physical state of crustal rocks for engineering applications. In this paper we review experimental work showing how wave velocities in rocks are sensitive to parameters of interest to geothermal exploration; effective pressure, the degree of water saturation of the pores, and the bulk modulus of the pore phase. Seismic attenuation is even more sensitive to the degree of saturation and the microgeometry of the pores. Both velocity and attenuation are strongly temperature dependent and reflect thermal fracturing of the rocks at elevated temperatures. By combining data on attenuation and velocity of compressional and shear waves considerably greater constraints may be placed on the environmental state of the rocks than on the basis of P velocities alone.
Date: December 18, 1980
Creator: Jones, Terry; Murphy, William & Nur, Amos
Partner: UNT Libraries Government Documents Department

The Dynamics of Adsorption on Clean and Adsorbate-Modified Transition Metal and Metal Oxide Surfaces

Description: Research directed toward understanding the dynamical factors governing the adsorption of molecules typically involved in heterogeneous catalytic processes has been continued. Adsorption is the first step in any catalytic process, and predictions of rates of adsorption are fundamental to calculations of rates of catalytic reactions. Dissociative adsorption can occur either directly upon impact with the surface or as the result of the migration of a temporarily trapped species across the surface. Alkane activation exhibits both of these pathways for reaction on metal surfaces. We have focused on the dynamics of dissociative adsorption of low molecular weight alkanes on single crystal surfaces of platinum group metals. The overall objective of these studies was to make a quantitative comparison of the dissociation probabilities of C{sub 2}-C{sub 4} alkanes on different metals in order to assess the effects of the structures of the different alkanes and the intrinsic differences of the metals on reactivity. First, an unusual and somewhat unexpected difference is observed in the reactivity of linear and branched alkanes. Further, the reactivity of each alkane is significantly higher on Pt(111) than on Pd(111). It has also been observed that the trapping probabilities for the alkanes are higher on Pd(111) due to a larger dissipation of energy to lattice vibrations upon collision, suggesting that energy dissipation in the reaction coordinate into phonons may be involved in dissociative adsorption. We have thus focused on the dynamics of dissociative adsorption of low molecular weight alkanes on single crystal surfaces of platinum, palladium and nickel in order to assess the role of energy dissipation from the incident molecule and the differences of the reactivity of the different metals. We observe that the reactivity of each of the alkanes studied to date differs by only a small amount. On the contrary, due to the dissipation of ...
Date: March 31, 2006
Creator: Madix, Robert J.
Partner: UNT Libraries Government Documents Department


Description: Turkey is classified among countries which have high geothermal energy potential. Geological and geophysical explorations are continuing in promising areas. However primary emphasis was given to Western Anatolia during the last decade. As a result of these efforts Kizildere field was developed and power plant was put into operation in February 14, 1984. This paper summarizes the power plant, production problems encountered in wells during the last nine months and future field development plans.
Date: January 22, 1985
Creator: Okandan, E, & Polat, T.
Partner: UNT Libraries Government Documents Department

Buoyancy Induced Boundary Layer Flows in Geothermal Reservoirs

Description: Most of the theoretical study on heat and mass transfer in geothermal reservoirs has been based on numerical method. Recently at the 1975 NSF Workshop on Geothermal Reservoir Engineering, Cheng presented a number of analytical solutions based on boundary layer approximations which are valid for porous media at high Rayleigh numbers. according to various estimates the Rayleigh number for the Wairakei geothermal field in New Zealand is in the range of 1000-5000, which is typical for a viable geothermal field consisting of a highly permeable formation and a heat source at sufficiently high temperature. The basic assumption of boundary layer theory is that heat convective heat transfer takes place in a thin porous layer adjacent to heated or cooled surfaces. Indeed, numerical solutions suggest that temperature and velocity boundary layers do exist in porous media at high Rayleigh numbers. It is worth mentioning that the large velocity gradient existing near the heated or cooled surfaces is not due to viscosity but is induced by the buoyancy effects. The present paper is a summary of the work that we have done on the analytical solutions of heat and mass transfer in a porous medium based on the boundary layer approximations since the 1975 Workshop. As in the classical convective heat transfer theory, boundary layer approximations in porous layer flows can result in analytical solutions. Mathematically, the approximations are the first-order terms of an asymptotic expansion which is valid for high Rayleigh numbers. Comparison with experimental data and numerical solutions show that the approximations are also accurate at moderate values of Rayleigh numbers. For problems with low Rayleigh numbers where boundary layer is thick, higher-order approximations must be used. 9 refs., 5 figs.
Date: December 1, 1976
Creator: Cheng, Ping
Partner: UNT Libraries Government Documents Department

Two Phase Streaming Potentials

Description: The streaming potentials generated by the flow of both liquid and gas through either a Pyrex capillary tube or else an unconsolidated Pyrex porous medium were investigated. This mixture of distilled water plus nitrogen gas simulated wet stream but allowed experiments to be run at room temperature. Single-phase flow of distilled water alone resulted in a constant voltage-to-pressure drop ratio, E/∆p, of +0.15 v/psi for the capillary tube and -0.52 v/psi for the porous medium. For both single- and two-phase flow through the capillary tube, the upstream potential was always positive relative to the downstream electrode while the opposite was true for the porous medium. The maximum two-phase potentials generated in the porous medium were about four times as great as those generated in the capillary tube for similar gas fractions, Γ. For the capillary tube experiments the potentials generated when Γ < ≈ 0.5 were equal to or slightly less than those for single-phase flow, while for the porous medium the potentials were always greater than those for single-phase flow. When Γ > ≈ 0.5 for both kinds of flow systems Γ had a profound effect on streaming potential and reached a pronounced maximum when 0.94 < Γ < 0.99. The implications of these streaming potentials for geothermal exploration and delineation of geothermal reservoirs is also discussed in the paper. 7 figs., 10 refs.
Date: January 20, 1987
Creator: Marsden, S.S. & Wheatall, M.W.
Partner: UNT Libraries Government Documents Department


Description: In bringing you up to date on DOE's geothermal R and D programs, they are going to emphasize first those elements that may be of special interest to a reservoir engineering audience, because the activities in support of an improved understanding of hydrothermal reservoirs deserve attention. Reservoir definition, brine injection, and reservoir stimulation technologies are major elements of the Hydrothermal Research Program, and in total they account for nearly 50% of the fiscal year (FY) 1985 hydrothermal research budget. These elements fall into the essential R and D category; that is, while some basic technologies have been borrowed from the petroleum industry for geothermal service, they are often ill-suited to geothermal requirements, and cannot be used without significant technological innovations. Into this category fall the current reservoir technology, brine injection, and reservoir stimulation projects that are listed in Table 1. The reservoir technology projects include: (1) development of methods for characterizing and mapping reservoir parameters, processes, and spatial dimensions; (2) development of methods to predict and monitor reservoir changes from fluid extraction; (3) evaluation of existing methods and development of new methods for predicting the location and mapping faults and fractures in geothermal reservoirs; and (4) testing of new analysis techniques using field case studies. Brine injection projects include: (1) development of physical and mathematical models to determine the behavior of geothermal reservoirs during injection; (2) tracer testing to determine rapid flow paths between wells; and (3) analysis of pressure responses in the field to injection into one or more wells.
Date: January 22, 1985
Creator: Mock, J.E. & Marshall, J.R.
Partner: UNT Libraries Government Documents Department


Description: The Nesjavellir High Temperature Geothermal Field is located in the Northern part of the Hengill Geothermal Area, which has been estimated to be one of the largest geothermal areas in iceland. Drilling started at Nesjavellir some 20 years ago with five wells. In 1982 a renewed exploration phase began and five additional wells have been drilled during the last three years. The pressure distribution within the geothermal system is very inhomogeneous in both horizontal and vertical directions. Variations in temperature are also considerable. The highest pressure and temperature is found in the southwestern part of the investigated area and both pressure and temperature decreases towards northeast. There seem to be four different zones of pressure potential in the system, which require the existence of both horizontal and vertical barriers in the system. Some parts of the geothermal system are in two-phase condition whereas other parts are in single phase liquid condition. The chemical composition of the fluid seem to be relatively uniform and a common origin of the fluid is assumed. The transmissivity of wells is in the range (1,3-3,5) 10{sup -8} m{sup 3}/Pa {center_dot} s whereas the flowing enthalpy ranges from 1200-2100 kJ/kg. The thermal output of wells are 40-60 MW. The geothermal system at Nesjavellir shows a high degree of three-dimensional variation, but a simple conceptual model described in the paper, seem to be in agreement with all observation made so far in the field.
Date: January 22, 1985
Creator: Stefansson, V.
Partner: UNT Libraries Government Documents Department

The effects of adsorption on injection into geothermal reservoirs

Description: The effects of an adsorbing phase on the injection of liquid and eventual production of vapor from a low-porosity, vapor dominated geothermal reservoir was studied. The magnitude of delay caused by adsorption, diffusion partitioning, preferential partitioning, and permeability variation were compared. Results were then compared to measured tracer production data at the Geysers to determine the most likely delay mechanism for injected tracer at the Geysers. A one-dimensional numerical model describing vapor flow in a porous medium in the presence of a sorbing phase was used to investigate the delay of injected tracer caused solely by the sorbing phase. An analytical model was used to describe delay effects due to diffusion partitioning of tracer from the vapor phase into the liquid phase. Properties of steam and tracer used in Geysers tracer studies were compared to determine the effects of preferential partitioning. Finally, a streamline model of a tracer study was used to determine the magnitude of permeability delays possible using permeability values measured at the Geysers. It was concluded that adsorption alone has very little effect on the delay of injected tracer indicating that little recharge of the adsorbed mass occurs for a typical injection program at the Geysers. Diffusion partitioning was shown to have a larger effect on tracer delay than adsorption while preferential partition was shown to have no effect. Permeability variation was shown to have the largest effect on tracer delay. Tracer delay was shown to be approximated closely by known permeability variations even when adsorption and diffusion effects are ignored.
Date: January 20, 1994
Creator: Hornbrook, John W. & Horne, Roland N.
Partner: UNT Libraries Government Documents Department

Geothermal Reservoir Engineering Research

Description: This report first describes reservoir engineering within the broad field of petroleum engineering. The report next describes the general pattern of reservoir engineering in terms of performance observations, hypothesis construction and testing, and reservoir development planning, and emphasizes the importance of searching for the hypothesis about the nature of the reservoir system derived from all known facts instead of a model that includes only selected fact. The history since 1900 of gas, oil, and geothermal reservoir engineering research is briefly described.
Date: December 1, 1976
Creator: Ramey, H.J. Jr. & Miller, Frank G.
Partner: UNT Libraries Government Documents Department

Experimental Investigation and High Resolution Simulation of In-Situ Combustion Processes

Description: This final technical report describes work performed for the project 'Experimental Investigation and High Resolution Numerical Simulator of In-Situ Combustion Processes', DE-FC26-03NT15405. In summary, this work improved our understanding of in-situ combustion (ISC) process physics and oil recovery. This understanding was translated into improved conceptual models and a suite of software algorithms that extended predictive capabilities. We pursued experimental, theoretical, and numerical tasks during the performance period. The specific project objectives were (i) identification, experimentally, of chemical additives/injectants that improve combustion performance and delineation of the physics of improved performance, (ii) establishment of a benchmark one-dimensional, experimental data set for verification of in-situ combustion dynamics computed by simulators, (iii) develop improved numerical methods that can be used to describe in-situ combustion more accurately, and (iv) to lay the underpinnings of a highly efficient, 3D, in-situ combustion simulator using adaptive mesh refinement techniques and parallelization. We believe that project goals were met and exceeded as discussed.
Date: April 30, 2008
Creator: Gerritsen, Margot & Kovscek, Tony
Partner: UNT Libraries Government Documents Department

Experimental Investigation and High Resolution Simulator of In-Situ Combustion Processes

Description: Accurate simulation of in-situ combustion processes is computationally very challenging because the spatial and temporal scales over which the combustion process takes place are very small. In this current and thirteenth report, we report on our continuing development of a Virtual Kinetic Cell model and our continuing experimental program.
Date: December 31, 2006
Creator: Gerritsen, Margot & Kovscek, Anthony R.
Partner: UNT Libraries Government Documents Department