Contaminant Organic Complexes: Their Structure and Energetics in Surface Decontamination Processes

Contaminant Organic Complexes: Their Structure and Energetics in Surface Decontamination Processes

Date: December 13, 2005
Creator: Myneni, Satish C. B.
Description: Siderophores are biological macromolecules (400-2000 Da) released by bacteria in iron limiting situations to sequester Fe from iron oxyhydroxides and silicates in the natural environment. These molecules contain hydroxamate and phenolate functional groups, and exhibit very high affinity for Fe{sup 3+}. While several studies were conducted to understand the behavior of siderophores and their application to the metal sequestration and mineral dissolution, only a few of them have examined the molecular structure of siderophores and their interactions with metals and mineral surfaces in aqueous solutions. Improved understanding of the chemical state of different functional moieties in siderophores can assist in the application of these biological molecules in actinide separation, sequestration and decontamination processes. The focus of our research group is to evaluate the (a) functional group chemistry of selected siderophores and their metal complexes in aqueous solutions, and (b) the nature of siderophore interactions at the mineral-water interfaces. We selected desferrioxamine B (desB), a hydroxamate siderophore, and its small structural analogue, acetohydroxamic acid (aHa), for this investigation. We examined the functional group chemistry of these molecules as a function of pH, and their complexation with aqueous and solid phase Fe(III). For solid phase Fe, we synthesized all naturally occurring Fe(III)-oxyhydroxides ...
Contributing Partner: UNT Libraries Government Documents Department
On the structure, propagation, and stabilization of laminar premixed flames. Final report

On the structure, propagation, and stabilization of laminar premixed flames. Final report

Date: July 1999
Creator: Law, Chung K.
Description: The primary objective of the funded program was to qualitatively understand and quantitatively determine the structure and dynamics of laminar premixed flames. The investigation was conducted using laser-based experimentation, computational simulation with detailed chemistry and transport, and activation energy asymptotic analysis. Highlights of accomplishments were discussed in the annual reports submitted to the program monitor for this project. Details are reported in the thirty journal publications cited in the journal article list which is the major component of this final report.
Contributing Partner: UNT Libraries Government Documents Department
Biological physics

Biological physics

Date: September 24, 1998
Creator: unknown
Description: Major goals of biological physics are the understanding of biological systems in physical terms and the study of concepts and laws of complex systems.
Contributing Partner: UNT Libraries Government Documents Department
Geochemical constraints on the longevity and environmental habitat of subsurface microbial communities

Geochemical constraints on the longevity and environmental habitat of subsurface microbial communities

Date: June 1, 2000
Creator: Onstott, Tullis C.
Description: No abstract prepared.
Contributing Partner: UNT Libraries Government Documents Department
The symbiosis of carbon-dioxide sequestration and hydrogen fuel: what is its significance for the long-term global energy system. Final progress report July 1998 - July 2000

The symbiosis of carbon-dioxide sequestration and hydrogen fuel: what is its significance for the long-term global energy system. Final progress report July 1998 - July 2000

Date: September 8, 2000
Creator: Socolow, Robert H.; Ogden, Joan M. & Williams, Robert H.
Description: This study examined the implications of the ''fuel decarbonization/carbon sequestration'' strategy for the world energy system.
Contributing Partner: UNT Libraries Government Documents Department
Trace Metal Bioremediation: Assessment of Model Components from Laboratory and Field Studies to Identify Critical Variables

Trace Metal Bioremediation: Assessment of Model Components from Laboratory and Field Studies to Identify Critical Variables

Date: February 14, 2003
Creator: Jaffe, Peter & Rabitz, Herschel
Description: The objective of this project was to gain an insight into the modeling support needed for the understanding, design, and operation of trace metal/radionuclide bioremediation. To achieve this objective, a workshop was convened to discuss the elements such a model should contain. A ''protomodel'' was developed, based on the recommendations of the workshop, and was used to perform sensitivity analysis as well as some preliminary simulations in support for bioremediation test experiments at UMTRA sites. To simulate the numerous biogeochemical processes that will occur during the bioremediation of uranium contaminated aquifers, a time-dependent one-dimensional reactive transport model has been developed. The model consists of a set of coupled, steady state mass balance equations, accounting for advection, diffusion, dispersion, and a kinetic formulation of the transformations affecting an organic substrate, electron acceptors, corresponding reduced species, and uranium. This set of equations is solved numerically, using a finite element scheme. The redox conditions of the domain are characterized by estimating the pE, based on the concentrations of the dominant terminal electron acceptor and its corresponding reduced specie. This pE and the concentrations of relevant species are passed to a modified version of MINTEQA2, which calculates the speciation and solubilities of the species ...
Contributing Partner: UNT Libraries Government Documents Department
COARSE-GRID SIMULATION OF REACTING AND NON-REACTING GAS-PARTICLE FLOWS

COARSE-GRID SIMULATION OF REACTING AND NON-REACTING GAS-PARTICLE FLOWS

Date: October 2004
Creator: Sundaresan, Sankaran
Description: Many processes involved in coal utilization involve handling of fine particles, their pneumatic transport, and their reactions in fluidized beds, spouted beds and circulating fluidized beds. One of the factors limiting our ability to simulate these processes is the hydrodynamics encountered in them. Two major issues that contribute to this limitation are lack of good and computationally expedient models for frictional interaction between particles, and models to capture the consequences of mesoscale structures that are ubiquitous in gas-solid flows. This project has focused on the development of these models through a combination of computer simulations and experiments. The principal goal of this project, funded under the ''DOE Vision 21 Virtual Demonstration Initiative'' is better simulation of circulating fluidized bed performance. The principal challenge funded through this cooperative agreement is to devise sound physical models for the rheological characteristics of the gas-particle mixtures and implement them in the open-domain CFD code MFIX. During the course of this project, we have made the following specific advances. (a) We have demonstrated unequivocally that sub-grid models are essential to capture, even qualitatively correctly, the macroscale flow structures in gas-particle flows in vertical risers. To this end, we developed sub-grid models of different levels of ...
Contributing Partner: UNT Libraries Government Documents Department
Precipitation and Deposition of Aluminum-Containing Phases in Tank Wastes

Precipitation and Deposition of Aluminum-Containing Phases in Tank Wastes

Date: January 12, 2005
Creator: Dabbs, Daniel M. & Aksay, Ilhan A.
Description: Aluminum-containing phases compose the bulk of solids precipitating during the processing of radioactive tank wastes. Processes designed to minimize the volume of high-level waste through conversion to glassy phases require transporting waste solutions near-saturated with aluminum-containing species from holding tank to processing center. The uncontrolled precipitation within transfer lines results in clogged pipes and lines and fouled ion exchangers, with the potential to shut down processing operations.
Contributing Partner: UNT Libraries Government Documents Department
COARSE-GRID SIMULATION OF REACTING AND NON-REACTING GAS-PARTICLE FLOWS

COARSE-GRID SIMULATION OF REACTING AND NON-REACTING GAS-PARTICLE FLOWS

Date: March 2004
Creator: Sundaresan, Sankaran
Description: The principal goal of this project, funded under the ''DOE Vision 21 Virtual Demonstration Initiative'' is virtual demonstration of circulating fluidized bed performance. We had proposed a ''virtual demonstration tool'', which is based on the open-domain CFD code MFIX. The principal challenge funded through this grant is to devise and implement in this CFD code sound physical models for the rheological characteristics of the gas-particle mixtures. Within the past year, which was the third year of the project, we have made the following specific advances. (a) We have completed a study of the impact of sub-grid models of different levels of detail on the results obtained in coarse-grid simulations of gas-particle flow. (b) We have also completed a study of a model problem to understand the effect of wall friction, which was proved in our earlier work to be very important for stable operation of standpipes in a circulating fluidized bed circuit. These are described in a greater detail in this report.
Contributing Partner: UNT Libraries Government Documents Department
Grand Challenge Problems in Environmental Modeling and Remediation: Groundwater Contaminant Transport (Partnerships in Computational Science)

Grand Challenge Problems in Environmental Modeling and Remediation: Groundwater Contaminant Transport (Partnerships in Computational Science)

Date: March 11, 1999
Creator: Celia, M. A.
Description: The over-reaching goal of the Groundwater Grand Challenge component of the Partnership in Computational Science (PICS) was to develop and establish the massively parallel approach for the description of groundwater flow and transport and to address the problem of uncertainties in the data and its interpretation. This necessitated the development of innovative algorithms and the implementation of massively parallel computational tools to provide a suite of simulators for groundwater flow and transport in heterogeneous media. This report summarizes the activities and deliverables of the Princeton University component of the Groundwater Grand Challenge project funded through the High Performance Computing grand challenge program of the Department of Energy from 1995 through 1998. Seven institutions were primarily involved in this project: Brookhaven National Laboratory, Oak Ridge National Laboratory, Princeton University, SUNY at Stony Brook, Texas A&M University, The University of South Carolina, and the University of Texas at Austin, with contributing efforts from the Westinghouse Savannah River Technology Center. Each institution had primary responsibility for specific research components, but strong collaboration among all institutions was essential for the success of the project and in producing the final deliverables. PICS deliverables include source code for the suite of research simulators and auxiliary HPC ...
Contributing Partner: UNT Libraries Government Documents Department
CONCEPTUAL DESIGN OF OPTIMIZED FOSSIL ENERGY SYSTEMS WITH CAPTURE AND SEQUESTRATION OF CARBON DIOXIDE

CONCEPTUAL DESIGN OF OPTIMIZED FOSSIL ENERGY SYSTEMS WITH CAPTURE AND SEQUESTRATION OF CARBON DIOXIDE

Date: May 1, 2004
Creator: Ogden, Joan M.
Description: In this third semi-annual progress report, we describe research results from an ongoing study of fossil hydrogen energy systems with CO{sub 2} sequestration. This work was performed under NETL Award No. DE-FC26-02NT41623, during the six-month period September 2003 through March 2004. The primary objective of the study is to better understand system design issues and economics for a large-scale fossil energy system co-producing H{sub 2} and electricity with CO{sub 2} sequestration. This is accomplished by developing analytic and simulation methods for studying the entire system in an integrated way. We examine the relationships among the different parts of a hydrogen energy system, and attempt to identify which variables are the most important in determining both the disposal cost of CO{sub 2} and the delivered cost of H{sub 2}. A second objective is to examine possible transition strategies from today's energy system toward one based on fossil-derived H{sub 2} and electricity with CO{sub 2} sequestration. We are carrying out a geographically specific case study of development of a fossil H{sub 2} system with CO{sub 2} sequestration, for the Midwestern United States, where there is presently substantial coal conversion capacity in place, coal resources are plentiful and potential sequestration sites in deep ...
Contributing Partner: UNT Libraries Government Documents Department
CONCEPTUAL DESIGN OF OPTIMIZED FOSSIL ENERGY SYSTEMS WITH CAPTURE AND SEQUESTRATION OF CARBON DIOXIDE

CONCEPTUAL DESIGN OF OPTIMIZED FOSSIL ENERGY SYSTEMS WITH CAPTURE AND SEQUESTRATION OF CARBON DIOXIDE

Date: December 2003
Creator: Ogden, Joan M.
Description: In this second semi-annual progress report, we describe research results from an ongoing study of fossil hydrogen energy systems with CO{sub 2} sequestration. This work was performed under NETL Award No. DE-FC26-02NT41623, during the six-month period March 2003 through September 2003. The primary objective of the study is to better understand system design issues and economics for a large-scale fossil energy system co-producing H{sub 2} and electricity with CO{sub 2} sequestration. This is accomplished by developing analytic and simulation methods for studying the entire system in an integrated way. We examine the relationships among the different parts of a hydrogen energy system, and attempt to identify which variables are the most important in determining both the disposal cost of CO{sub 2} and the delivered cost of H{sub 2}. A second objective is to examine possible transition strategies from today's energy system toward one based on fossil-derived H{sub 2} and electricity with CO{sub 2} sequestration. We are carrying out a geographically specific case study of development of a fossil H{sub 2} system with CO{sub 2} sequestration, for the Midwestern United States, where there is presently substantial coal conversion capacity in place, coal resources are plentiful and potential sequestration sites in deep ...
Contributing Partner: UNT Libraries Government Documents Department
CONCEPTUAL DESIGN OF OPTIMIZED FOSSIL ENERGY SYSTEMS WITH CAPTURE AND SEQUESTRATION OF CARBON DIOXIDE

CONCEPTUAL DESIGN OF OPTIMIZED FOSSIL ENERGY SYSTEMS WITH CAPTURE AND SEQUESTRATION OF CARBON DIOXIDE

Date: June 26, 2003
Creator: Ogden, Joan M.
Description: In this semi-annual progress report, we describe research results from an ongoing study of fossil hydrogen energy systems with CO{sub 2} sequestration. This work was performed under NETL Award No. DE-FC26-02NT41623, during the six-month period September 2002 through March 2003. The primary objective of the study is to better understand system design issues and economics for a large-scale fossil energy system co-producing H{sub 2} and electricity with CO{sub 2} sequestration. This is accomplished by developing analytic and simulation methods for studying the entire system in an integrated way. We examine the relationships among the different parts of a hydrogen energy system, and attempt to identify which variables are the most important in determining both the disposal cost of CO{sub 2} and the delivered cost of H{sub 2}. A second objective is to examine possible transition strategies from today's energy system toward one based on fossil-derived H{sub 2} and electricity with CO{sub 2} sequestration. We are carrying out a geographically specific case study of development of a fossil H{sub 2} system with CO{sub 2} sequestration, for the Midwestern United States, where there is presently substantial coal conversion capacity in place, coal resources are plentiful and potential sequestration sites in deep saline ...
Contributing Partner: UNT Libraries Government Documents Department
Final report for ''Global survey of carbon dioxide in the ocean''

Final report for ''Global survey of carbon dioxide in the ocean''

Date: July 1998
Creator: Sarmiento, J. L.; Key, R. M. & Sabine, C. L.
Description: No abstract prepared.
Contributing Partner: UNT Libraries Government Documents Department
Thermochemical studies of the stability of nitrides and oxynitrides

Thermochemical studies of the stability of nitrides and oxynitrides

Date: January 29, 1999
Creator: unknown
Description: No abstract prepared.
Contributing Partner: UNT Libraries Government Documents Department
Up-Scaling Geochemical Reaction Rates for Carbon Dioxide (CO2) in Deep Saline Aquifers

Up-Scaling Geochemical Reaction Rates for Carbon Dioxide (CO2) in Deep Saline Aquifers

Date: February 28, 2013
Creator: Peters, Catherine A
Description: Geochemical reactions in deep subsurface environments are complicated by the consolidated nature and mineralogical complexity of sedimentary rocks. Understanding the kinetics of these reactions is critical to our ability to make long-term predictions about subsurface processes such as pH buffering, alteration in rock structure, permeability changes, and formation of secondary precipitates. In this project, we used a combination of experiments and numerical simulation to bridge the gap between our knowledge of these reactions at the lab scale and rates that are meaningful for modeling reactive transport at core scales. The focus is on acid-driven mineral dissolution, which is specifically relevant in the context of CO2-water-rock interactions in geological sequestration of carbon dioxide. The project led to major findings in three areas. First, we modeled reactive transport in pore-network systems to investigate scaling effects in geochemical reaction rates. We found significant scaling effects when CO2 concentrations are high and reaction rates are fast. These findings indicate that the increased acidity associated with geological sequestration can generate conditions for which proper scaling tools are yet to be developed. Second, we used mathematical modeling to investigate the extent to which SO2, if co-injected with CO2, would acidify formation brines. We found that there ...
Contributing Partner: UNT Libraries Government Documents Department
Integration of Carbon, Nitrogen, and Oxygen Metabolism in Escherichia coli--Final Report

Integration of Carbon, Nitrogen, and Oxygen Metabolism in Escherichia coli--Final Report

Date: October 22, 2012
Creator: Rabinowitz, Joshua D; Wingreen, Ned s; Rabitz, Herschel A & Xu, Yifan
Description: A key challenge for living systems is balancing utilization of multiple elemental nutrients, such as carbon, nitrogen, and oxygen, whose availability is subject to environmental fluctuations. As growth can be limited by the scarcity of any one nutrient, the rate at which each nutrient is assimilated must be sensitive not only to its own availability, but also to that of other nutrients. Remarkably, across diverse nutrient conditions, E. coli grows nearly optimally, balancing effectively the conversion of carbon into energy versus biomass. To investigate the link between the metabolism of different nutrients, we quantified metabolic responses to nutrient perturbations using LC-MS based metabolomics and built differential equation models that bridge multiple nutrient systems. We discovered that the carbonaceous substrate of nitrogen assimilation, α-ketoglutarate, directly inhibits glucose uptake and that the upstream glycolytic metabolite, fructose-1,6-bisphosphate, ultrasensitively regulates anaplerosis to allow rapid adaptation to changing carbon availability. We also showed that NADH controls the metabolic response to changing oxygen levels. Our findings support a general mechanism for nutrient integration: limitation for a nutrient other than carbon leads to build-up of the most closely related product of carbon metabolism, which in turn feedback inhibits further carbon uptake.
Contributing Partner: UNT Libraries Government Documents Department
Quantitative Tools for Dissection of Hydrogen-Producing Metabolic Networks-Final Report

Quantitative Tools for Dissection of Hydrogen-Producing Metabolic Networks-Final Report

Date: October 19, 2012
Creator: Rabinowitz, Joshua D.; Dismukes, G.Charles.; Rabitz, Herschel A. & Amador-Noguez, Daniel
Description: During this project we have pioneered the development of integrated experimental-computational technologies for the quantitative dissection of metabolism in hydrogen and biofuel producing microorganisms (i.e. C. acetobutylicum and various cyanobacteria species). The application of these new methodologies resulted in many significant advances in the understanding of the metabolic networks and metabolism of these organisms, and has provided new strategies to enhance their hydrogen or biofuel producing capabilities. As an example, using mass spectrometry, isotope tracers, and quantitative flux-modeling we mapped the metabolic network structure in C. acetobutylicum. This resulted in a comprehensive and quantitative understanding of central carbon metabolism that could not have been obtained using genomic data alone. We discovered that biofuel production in this bacterium, which only occurs during stationary phase, requires a global remodeling of central metabolism (involving large changes in metabolite concentrations and fluxes) that has the effect of redirecting resources (carbon and reducing power) from biomass production into solvent production. This new holistic, quantitative understanding of metabolism is now being used as the basis for metabolic engineering strategies to improve solvent production in this bacterium. In another example, making use of newly developed technologies for monitoring hydrogen and NAD(P)H levels in vivo, we dissected the ...
Contributing Partner: UNT Libraries Government Documents Department
Enhancement of Bacterial Transport in Aerobic and Anaerobic Environments: Assessing the Effect of Metal Oxide Chemical Heterogeneities

Enhancement of Bacterial Transport in Aerobic and Anaerobic Environments: Assessing the Effect of Metal Oxide Chemical Heterogeneities

Date: September 30, 2005
Creator: Onstott, T.C.
Description: The goal of our research was to understand the fundamental processes that control microbial transport in physically and chemically heterogeneous aquifers and from this enhanced understanding determine the requirements for successful, field-scale delivery of microorganisms to metal contaminated subsurface sites. Our specific research goals were to determine; (1) the circumstances under which the preferential adsorption of bacteria to Fe, Mn, and Al oxyhydroxides influences field-scale bacterial transport, (2) the extent to which the adhesion properties of bacterial cells affect field-scale bacterial transport, (3) whether microbial Fe(III) reduction can enhance field-scale transport of Fe reducing bacteria (IRB) and other microorganisms and (4) the effect of field-scale physical and chemical heterogeneity on all three processes. Some of the spin-offs from this basic research that can improve biostimulation and bioaugmentation remediation efforts at contaminated DOE sites have included; (1) new bacterial tracking tools for viable bacteria; (2) an integrated protocol which combines subsurface characterization, laboratory-scale experimentation, and scale-up techniques to accurately predict field-scale bacterial transport; and (3) innovative and inexpensive field equipment and methods that can be employed to enhance Fe(III) reduction and microbial transport and to target microbial deposition under both aerobic and anaerobic conditions.
Contributing Partner: UNT Libraries Government Documents Department
Ultra-High Intensity Magnetic Field Generation in Dense Plasma

Ultra-High Intensity Magnetic Field Generation in Dense Plasma

Date: January 8, 2014
Creator: Fisch, Nathaniel J
Description: I. Grant Objective The main objective of this grant proposal was to explore the efficient generation of intense currents. Whereasthefficient generation of electric current in low-­‐energy-­‐ density plasma has occupied the attention of the magnetic fusion community for several decades, scant attention has been paid to carrying over to high-­‐energy-­‐ density plasma the ideas for steady-­‐state current drive developed for low-­‐energy-­‐ density plasma, or, for that matter, to inventing new methodologies for generating electric current in high-­‐energy-­‐density plasma. What we proposed to do was to identify new mechanisms to accomplish current generation, and to assess the operation, physics, and engineering basis of new forms of current drive in regimes appropriate for new fusion concepts.
Contributing Partner: UNT Libraries Government Documents Department
Hydrogen as an Indicator to Assess Biological Activity During Trace-Metal Bioremediation

Hydrogen as an Indicator to Assess Biological Activity During Trace-Metal Bioremediation

Date: September 27, 2005
Creator: Peter R. Jaffe, John Komlos, Derick Brown
Description: Trace-metal and/or radionuclide bioremediation schemes require that specific redox conditions be achieved at given zones of an aquifer. Tools are therefore needed to identify the terminal electron acceptor processes (TEAPs) that are being achieved during bioremediation in an aquifer. Dissolved hydrogen (H2) concentrations have been shown to correlate with specific TEAPs during bioremediation in an aquifer. Theoretical analysis has shown that these steady-state H2 levels are solely dependent upon the physiological parameters of the hydrogen-consuming microorganisms, with H2 concentrations increasing as each successive TEAP yields less energy for bacterial growth. The objective of this research was to determine if H2 can still be used as an indicator of TEAPs during a uranium bioremediation scheme where an organic substrate is injected into the subsurface and organisms may consume H2 and carbon simultaneously. In addition, the effect of iron bioavailability on H2 concentrations during iron reduction was observed. The first phase of research determined the effect of a competing electron donor (acetate) on the kinetics of H2 utilization by Geobacter sulfurreducens in batch cultures under iron reducing conditions. The results indicate that, though the Monod kinetic coefficients describing the rate of H2 utilization under iron-reducing conditions correlate energetically with the coefficients found ...
Contributing Partner: UNT Libraries Government Documents Department
Systematic Effects in Type-1a Supernovae Surveys from Host Galaxy Spectra

Systematic Effects in Type-1a Supernovae Surveys from Host Galaxy Spectra

Date: August 23, 2013
Creator: Strauss, Michael A.
Description: The physical relation between the properties of Type Ia supernovae and their host galaxies is investigated. Such supernovae are used to constrain the properties of dark energy, making it crucial to understand their physical properties and to check for systematic effects relating to the stellar populations of the progenitor stars from which these supernovae arose. This grant found strong evidence for two distinct populations of supernovae, and correlations between the progenitor stellar populations and the nature of the supernova light curves.
Contributing Partner: UNT Libraries Government Documents Department
Corridor One: An Integrated Distance Visualization Environment for SSI and ASCI Applications

Corridor One: An Integrated Distance Visualization Environment for SSI and ASCI Applications

Date: July 15, 1999
Creator: Li, K.; Finkelstein, A. & Funkhouser, T.
Description: The Corridor One project is a three-year integrated research project that combines the forces of six leading-edge laboratory and university groups working in the area of visualization, distributed computing and high-performance networking to develop and to deploy the most advanced, integrated distance visualization environment.
Contributing Partner: UNT Libraries Government Documents Department
Configurational forces in solid nanostructures

Configurational forces in solid nanostructures

Date: June 12, 2006
Creator: Suo, Zhigang
Description: The DOE grant (DE-FG02-99ER45787) to Princeton University, entitled Configurational Forces in Solid Nanostructures, was intended to cover the four-year period from September 1999 to September 2003. Effective 1 July 2003, the PI will relocate from Princeton to join the Harvard faculty. Princeton University will submit the Final Financial Report, the Final Property Report, and the Final Patent Report. The expenditures to date are $261,513 with %8,487 remaining of the awarded amount of $320,000. Harvard University will submit a request for the remaining amount. This Final Technical Report covers from the period between September 1999 to June 2003. Three Ph.D. students, Wei Lu, Yanfei Gao and Wei Hong, admitted to Princeton in the fall of 1998, 1999, 2002, respectively, have been dedicated to this project. Wei Lu earned his Ph.D. in August 2001, and is now an assistant professor at The University of Michigan, Ann Arbor. Yanfei Gao earned his Ph.D. in February 2003, and is now a post-doc at Brown University. The amount of funding covers one student at a time. All three students received first-year fellowships from Princeton University. In the Mechanical and Aerospace Engineering Department, to fulfill a doctoral degree requirement, every student serves as a teaching assistant ...
Contributing Partner: UNT Libraries Government Documents Department
FIRST PREV 1 2 3 4 5 NEXT LAST