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Solidification Modeling of a Spiral Casting to Determine Material Fluidity (open access)

Solidification Modeling of a Spiral Casting to Determine Material Fluidity

In casting, fluidity is the measure of the distance a metal can flow in a channel before being stopped by solidification. During mold filling, the metal loses heat to the surrounding mold, thereby cooling and becoming more viscous until the leading portion solidifies and no further flow is possible. A coupled heat-transfer and fluid-flow modeling of a spiral, involving the use of thermophysical properties to determine material fluidity, has been conducted. Simulations of these experiments utilized the Casting Process Simulator (CaPS) software developed at Argonne National Laboratory. Two types of spiral geometries with different assumptions were considered: (1) a two-dimensional laterally stretched spiral and (2) a three-dimensional lateral spiral. The computer extent of mold filling is in good agreement with the experimental results. Time required by the metal/gas interface to attain specific positions in the spiral arm also compares favorably with the experimental results. The influence of process variables, especially pour time, is discussed. The CaPS software has been used as a computational tool to investigate the validity of the dimensionality assumptions and to evaluate the ability of CaPS to model fluidity adequately.
Date: February 1994
Creator: Ahuja, S.; Domanus, H. M.; Schmitt, R. C.; Chuzhoy, L. & Grabel, J. V.
System: The UNT Digital Library
Long-term sealing analyses for US Strategic Petroleum Reserve (SPR) caverns (open access)

Long-term sealing analyses for US Strategic Petroleum Reserve (SPR) caverns

It is inevitable that sealing and abandonment will someday occur in a SPR cavern or caverns. To gain insight into the long-term behavior of a typical SPR cavern following sealing and abandonment, a suite of mechanical finite-element calculations was performed. The initial analyses predict how quickly and to what extent a cavern pressurizes after it is plugged. The analyses also examine the stability of the cavern as it changes shape due to the excessive pressures generated as the salt creeps and the brine in the cavern thermally expands. These large-scale analyses do not include the details of the plug but assume a good seal is established in the cavern wells. In another series of analyses, the potential for forming a leak at the plug is evaluated. A cement plug, emplaced in the casing seat of a cavern well, is loaded using the predicted brine pressures from the cavern analyses. The plugged casing analyses examine the potential for forming a leak path in and along the interfaces of salt, casing, and cement plug. In the last set of analysis, the dimensional scale of the problem is further reduced to examine a preexisting crack along a casing/salt interface. The cracked interface is …
Date: February 1, 1994
Creator: Ehgartner, B.
System: The UNT Digital Library
Trade and Environment: Treatment in Recent Agreements--GATT and NAFTA (open access)

Trade and Environment: Treatment in Recent Agreements--GATT and NAFTA

This report reviews some of the concerns surrounding the environment work program and other environmental issues. It briefly describes work underway in the Organization for Economic Cooperation and Development (OECD), and current thinking underlying development of U.S. positions on trade and the environment in the GATT.
Date: February 24, 1994
Creator: Fletcher, Susan R. & Tiemann, Mary
System: The UNT Digital Library
[Amended order of dismissal: PWA v Mark William Nelson] (open access)

[Amended order of dismissal: PWA v Mark William Nelson]

Amended order of dismissal in PWA v Nelson.
Date: February 28, 1994
Creator: unknown
System: The UNT Digital Library
Petroleum marketing monthly, January 1994 (open access)

Petroleum marketing monthly, January 1994

The Petroleum Marketing Monthly (PMM) is designed to give information and statistical data about a variety of crude oils and refined petroleum products. The publication provides statistics on crude oil costs and refined petroleum products sales for use by industry, government, private sector analysts, educational institutions, and consumers. Data on crude oil include the domestic first purchase price, the f.o.b. and landed cost of imported crude oil, and the refiners` acquisition cost of crude oil. Sales data for motor gasoline, distillates, residuals, aviation fuels, kerosene, and propane are presented.
Date: February 1, 1994
Creator: unknown
System: The UNT Digital Library
[Aluminum Coordination and Active Sites on Aluminas, Y-Zeolites and Pillared Layered Silicates]. Progress Report (open access)

[Aluminum Coordination and Active Sites on Aluminas, Y-Zeolites and Pillared Layered Silicates]. Progress Report

This report is organized in four sections. In the first the authors will outline structural features which are common to all fine grained alumina, as well as to non-framework alumina in zeolites. This section will be followed by a study of the surface vs. bulk coordination of aluminum. The third section will deal with measurement of the number of acid sites and the scaling of their strength. The fourth and last section will describe three model reactions: the isomerization of 1-butene and of 2 cis-butene; the isomerization and disproportionation of oxtho-xylene; and the transformation of trichloroethane into vinyl chloride followed by the polymerization of the vinyl chloride. The relationship between chemical activity and selectivity and what is known of the local structure of the active catalytic sites will be underlined. Other kinds of zeolites besides Y zeolite have been studied. Instead of the aluminum pillared silicates they found it more interesting to study the substitution of silicon by aluminum in a layered structure containing a permanent porosity (aluminated sepiolite).
Date: February 1, 1994
Creator: Fripiat, J. J.
System: The UNT Digital Library
Magnetless magnetic fusion (open access)

Magnetless magnetic fusion

The authors propose a concept of thermonuclear fusion reactor in which the plasma pressure is balanced by direct gas-wall interaction in a high-pressure vessel. The energy confinement is achieved by means of the self-contained toroidal magnetic configuration sustained by an external current drive or charged fusion products. This field structure causes the plasma pressure to decrease toward the inside of the discharge and thus it should be magnetohydrodynamically stable. The maximum size, temperature and density profiles of the reactor are estimated. An important feature of confinement physics is the thin layer of cold gas at the wall and the adjacent transitional region of dense arc-like plasma. The burning condition is determined by the balance between these nonmagnetized layers and the current-carrying plasma. They suggest several questions for future investigation, such as the thermal stability of the transition layer and the possibility of an effective heating and current drive behind the dense edge plasma. The main advantage of this scheme is the absence of strong external magnets and, consequently, potentially cheaper design and lower energy consumption.
Date: February 1, 1994
Creator: Beklemishev, A. D. & Tajima, T.
System: The UNT Digital Library
Rocky Mountain area petroleum product availability with reduced PADD IV refining capacity (open access)

Rocky Mountain area petroleum product availability with reduced PADD IV refining capacity

Studies of Rocky Mountain area petroleum product availability with reduced refining capacity in Petroleum Administration for Defense IV (PADD IV, part of the Rocky Mountain area) have been performed with the Oak Ridge National Laboratory Refinery Yield Model, a linear program which has been updated to blend gasolines to satisfy constraints on emissions of nitrogen oxides and winter toxic air pollutants. The studies do not predict refinery closures in PADD IV. Rather, the reduced refining capacities provide an analytical framework for probing the flexibility of petroleum refining and distribution for winter demand conditions in the year 2000. Industry analysts have estimated that, for worst case scenarios, 20 to 35 percent of PADD IV refining capacity could be shut-down as a result of clean air and energy tax legislation. Given these industry projections, the study scenarios provide the following conclusions: The Rocky Mountain area petroleum system would have the capability to satisfy winter product demand with PADD IV refinery capacity shut-downs in the middle of the range of industry projections, but not in the high end of the range of projections. PADD IV crude oil production can be maintained by re-routing crude released from PADD IV refinery demands to satisfy increased …
Date: February 1, 1994
Creator: Hadder, G. R. & Chin, S. M.
System: The UNT Digital Library
LAHET Code System/CINDER`90 validation calculations and comparison with experimental data (open access)

LAHET Code System/CINDER`90 validation calculations and comparison with experimental data

The authors use the Los Alamos LAHET Code System (LCS)/CINDER`90 suite of codes in a variety of spallation neutron source applications to predict neutronic performance and as a basis for making engineering decisions. They have broadened their usage of the suite from designing LANSCE and the next generation of spallation neutron sources for materials science and nuclear physics research to designing a target system for Accelerator Production of Tritium and Accelerator Transmutation of Waste. While designing, they continue to validate the LCS/CINDER`90 code suite against experimental data whenever possible. In the following, they discuss comparisons between calculations and measurements for: integral neutron yields from a bare-target of lead; fertile-to-fissile conversion yields for thorium and depleted uranium targets; dose rates from the LANSCE tungsten target; energy deposition in a variety of light and heavy materials; and neutron spectra from LANSCE water and liquid hydrogen moderators. The accuracy with which the calculations reproduce experimental results is an indication of their confidence in the validity of their design calculations.
Date: February 1, 1994
Creator: Brun, T. O.; Beard, C. A.; Daemen, L. L.; Pitcher, E. J.; Russell, G. J. & Wilson, W. B.
System: The UNT Digital Library
United States Department of Energy Budget Highlights FY 1995 (open access)

United States Department of Energy Budget Highlights FY 1995

The Department of Energy is entrusted to contribute to the welfare of the Nation by providing the scientific and educational foundation or the technology, policy, and institutional leadership necessary to achieve efficiency in energy use, diversity in energy sources, and access to technical information required for a more productive and competitive economy, improved environmental quality, and a secure national defense.
Date: February 1, 1994
Creator: O`Leary, H. R.
System: The UNT Digital Library
Research priorities for occupational radiation protection (open access)

Research priorities for occupational radiation protection

The Subpanel on Occupational Radiation Protection Research concludes that the most urgently needed research is that leading to the resolution of the potential effects of low-level ionizing radiation. This is the primary driving force in setting appropriate radiation protection standards and in directing the emphasis of radiation protection efforts. Much has already been done in collecting data that represents a compendium of knowledge that should be fully reviewed and understood. It is imperative that health physics researchers more effectively use that data and apply the findings to enhance understanding of the potential health effects of low-level ionizing radiation and improve the risk estimates upon which current occupational radiation protection procedures and requirements depend. Research must be focused to best serve needs in the immediate years ahead. Only then will we get the most out of what is accomplished. Beyond the above fundamental need, a number of applied research areas also have been identified as national priority issues. If effective governmental focus is achieved on several of the most important national priority issues, important occupational radiation protection research will be enhanced, more effectively coordinated, and more quickly applied to the work environment. Response in the near term will be enhanced and …
Date: February 1, 1994
Creator: unknown
System: The UNT Digital Library
Groundwater maps of the Hanford Site, June 1993 (open access)

Groundwater maps of the Hanford Site, June 1993

The Groundwater Maps of the Hanford Site, June 1993 is an update of the series of reports that document the configuration of the uppermost unconfined aquifer beneath the Hanford Site. This report series presents the semiannual water level measurements taken at site groundwater monitoring wells each June and December and the groundwater maps derived from these measurements. These reports document the changes in the groundwater level at Hanford as the site has transitioned from nuclear material production to environmental restoration and remediation. In addition, these reports provide water level data to support the various site characterization and groundwater monitoring programs currently in progress on the Hanford Site. Groundwater Maps of the Hanford Site are prepared for the US Department of Energy, Office of Environmental Restoration and Waste Management, by the Hanford Site Operations and Engineering Contractor, Westinghouse Hanford Company (WHC). This document fulfills reporting requirements specified in WHC (1993), Section 8.0 {open_quotes}Water Quality{close_quotes} and also described in the Environmental Monitoring Plan for the Hanford Site (DOE-RL 1991). Maps depicting the water table beneath the Hanford Site south of the Columbia River are presented in this report. Appendix A lists the well identification number, depth to water, casing elevating and the …
Date: February 1, 1994
Creator: Kasza, G. L.; Hartman, M. J.; Jordan, W. A. & Weekes, D. C.
System: The UNT Digital Library
Guidance for establishment and implementation of a national sample management program in support of EM environmental sampling and analysis activities (open access)

Guidance for establishment and implementation of a national sample management program in support of EM environmental sampling and analysis activities

The role of the National Sample Management Program (NSMP) proposed by the Department of Energy`s Office of Environmental Management (EM) is to be a resource for EM programs and for local Field Sample Management Programs (FSMPs). It will be a source of information on sample analysis and data collection within the DOE complex. Therefore the NSMP`s primary role is to coordinate and function as a central repository for information collected from the FSMPs. An additional role of the NSMP is to monitor trends in data collected from the FSMPs over time and across sites and laboratories. Tracking these trends will allow identification of potential problems in the sampling and analysis process.
Date: February 18, 1994
Creator: unknown
System: The UNT Digital Library
Uranium-contaminated soils: Ultramicrotomy and electron beam analysis (open access)

Uranium-contaminated soils: Ultramicrotomy and electron beam analysis

Uranium-contaminated soils from the U.S. Department of Energy (DOE) Fernald Site, Ohio, have been examined by a combination of scanning electron microscopy with backscattered electron imaging (SEM/BSE) and analytical electron microscopy (AEM). The inhomogeneous distribution of particulate uranium phases in the soil required the development of a method for using ultramicrotomy to prepare transmission electron microscopy (TEM) thin sections of the SEM mounts. A water-miscible resin was selected that allowed comparison between SEM and TEM images, permitting representative sampling of the soil. Uranium was found in iron oxides, silicates (soddyite), phosphates (autunites), and fluorite (UO{sub 2}). No uranium was detected in association with phyllosilicates in the soil.
Date: February 1, 1994
Creator: Buck, E. C.; Dietz, N. L.; Bates, J. K. & Cunnane, J. C.
System: The UNT Digital Library
Summary of work completed under the Environmental and Dynamic Equipment Qualification research program (EDQP) (open access)

Summary of work completed under the Environmental and Dynamic Equipment Qualification research program (EDQP)

This report documents the results of the main projects undertaken under the Environmental and Dynamic Equipment Qualification Research Program (EDQP) sponsored by the U.S. Nuclear Regulatory Commission (NRC) under FIN A6322. Lasting from fiscal year 1983 to 1987, the program dealt with environmental and dynamic (including seismic) equipment qualification issues for mechanical and electromechanical components and systems used in nuclear power plants. The research results have since been used by both the NRC and industry. The program included seven major research projects that addressed the following issues: (a) containment purge and vent valves performing under design basis loss of coolant accident loads, (b) containment piping penetrations and isolation valves performing under seismic loadings and design basis and severe accident containment wall displacements, (c) shaft seals for primary coolant pumps performing under station blackout conditions, (d) electrical cabinet internals responding to in-structure generated motion (rattling), and (e) in situ piping and valves responding to seismic loadings. Another project investigating whether certain containment isolation valves will close under design basis conditions was also started under this program. This report includes eight main section, each of which provides a brief description of one of the projects, a summary of the findings, and an …
Date: February 1, 1994
Creator: Steele, R. Jr.; Bramwell, D. L.; Watkins, J. C. & DeWall, K. G.
System: The UNT Digital Library
Optimization of the engineering design for the Lansing District Cooling System by comparative analysis of the impact of advanced technologies on a conventional design approach. Volume 1 (open access)

Optimization of the engineering design for the Lansing District Cooling System by comparative analysis of the impact of advanced technologies on a conventional design approach. Volume 1

The Lansing Board of Water and Light (LBWL) began investigating development of a cooling district in the Lansing Downtown in 1989 in order to retain and build summer load for its steam utility. A feasibility study was conducted in conjunction with SFT, Inc. and ZBA, Inc. which addressed many factors such as marketability of the product, impact on the summer steam load, distribution system development, system design, probable capital and operating costs, reliability and environmental and other regulatory impacts on a preliminary feasibility basis. The Phase I study completed in September of 1989 provided highly promising results for establishing a District Cooling System (DCS). An existing chilled water production facility owned by the State of Michigan was identified as a potential location for a DCS plant. With these changes a review of the feasibility with a new set of alternatives and sensitivities was evaluated. This enhancement to the Phase I Study was nearing completion when the LBWL in conjunction with Energy, Mines and Resources Canada proposed to conduct the Phase II project in conjunction with DOE. The project was structured to proceed along a dual track to demonstrate the impact of the application of various innovative technologies.
Date: February 1, 1994
Creator: unknown
System: The UNT Digital Library
Description of work for 200-UP-1 characterization of monitoring wells (open access)

Description of work for 200-UP-1 characterization of monitoring wells

This description of work (DOW) details the field activities associated with the drilling, soil sampling, and construction of groundwater monitoring and dual-use wells in the 200-UP-1 Operable Unit (Tasks 2, 3, and 5 in the 200-UP-1 RI/FS Work Plan DOE/RL 1993a) and will serve as a field guide for those performing the work. It will be used in conjunction with the Remedial Investigation/Feasibility Study Work Plan for the 200-UP-1 Groundwater operable Unit (DOE-RL 1993a, [LFI]) and Site Characterization Manual (WHC 1988a). Groundwater wells are being constructed to characterize the vertical and horizontal extent of the Uranium and {sup 99}{Tc} plumes and to define aquifer properties such as hydraulic communication between aquifers and hydrostratigraphy. Some of these wells may be utilized for extraction purposes during the IRM phase anticipated at this operable unit and are being designed with a dual use in mind. These data will be used to optimize the Interim Remedial Measures (IRM) for the cleanup of these two plumes. The data will also be used with later Limited Field Investigation (LFI) data to perform a Qualitative Risk Assessment (QRA) for the operable unit. The locations for the proposed groundwater wells are presented in Figure 1. The contaminants of …
Date: February 1, 1994
Creator: Innis, B. E. & Kelty, G. G.
System: The UNT Digital Library
Tomographic data developed using the ABEM RAMAC borehole radar system at the Mixed Waste Landfill Integrated Demonstration (open access)

Tomographic data developed using the ABEM RAMAC borehole radar system at the Mixed Waste Landfill Integrated Demonstration

The ABEM RAMAC borehole radar system was run as part of the Mixed Waste Landfill Integrated Demonstration for Sandia National Laboratories at Kirtland AFB. Tomograms were created between three test boreholes-UCAP No. 1, UCAP No. 2, and UCAP No. 3. These tomograms clearly delineate areas of amplitude attenuation and residual time of arrival or slowness differences. Plots for slowness were made using both the maximum and minimum of the first arrival pulse. The data demonstrates that the ABEM RAMAC 60-MHz pulse sampling radar system can be used to collect usable data in a highly conductive environment.
Date: February 18, 1994
Creator: MacLeod, G. A.; Barker, D. L. & Molnar, S.
System: The UNT Digital Library
Pulse radiolysis of alkanes: A time-resolved electron paramagnetic resonance study (open access)

Pulse radiolysis of alkanes: A time-resolved electron paramagnetic resonance study

Time-resolved spin-echo-detected electron paramagnetic resonance (EPR) was applied to examine short-lived alkyl radicals formed in pulse radiolysis of liquid alkanes. It was found that the ratio of yields of penultimate and interior radicals in n-alkanes at the instant of their generation is temperature-independent and is ca. 1.25 times greater than the statistical quantity. This higher-than-statistical production of penultimate radicals indicates that the fast ion molecule reactions involving radical cations are a significant route of radical generation. The analysis of spin-echo kinetics in n-alkanes suggests that the alkyl radicals are emissively polarized in spur reactions. this initial polarization rapidly increases with shortening of the aliphatic chain. Another finding is that a long-chain structure of these radicals results in much higher rate of Heisenberg spin exchange relative to the recombination rate. The relative yields of hydrogen abstraction and fragmentation for various branched alkanes are estimated. It is concluded that the fragmentation occurs prior to the formation of radicals in an excited precursor species. Effects of phenolic and alkene additives in radiolysis of n-alkanes are examined. It is demonstrated that phenoxy radicals are produced in dissociative capture of electrons and alkane holes. Another route is a reaction of phenols with free hydrogen atoms. …
Date: February 14, 1994
Creator: Shkrob, I. A. & Trifunac, A. D.
System: The UNT Digital Library
Improved electroacoustic dewatering (EAD) belt press for food products. Phase 3, Technical progress report (open access)

Improved electroacoustic dewatering (EAD) belt press for food products. Phase 3, Technical progress report

Battelle`s electroacoustic dewatering (EAD) process improves the performance of mechanical dewatering processes for several food products (such as corn fiber) by superimposing electric and ultrasonic fields. EAD has the potential to save 0.027 to 0.035 quad/yr energy by 1995 in the food processing industry, which consumed 0.15 to 0.18 quad in 1986. This report covers Phase III for demonstrating the EAD prototype on corn wet milling products (corn fiber and gluten); only Task 1 (prototype preparation and planning) was completed. EAD performance was examined in the laboratory; availability of a test site was examined. The single-roll, postdewatering EAD belt press prototype can accept material predewatered by a screw press, centrifuge, or any other mechanical dewatering device. The two-belt system, utilizing a copper-polymer cathode belt, performed as well as the three-belt system used in Phase II.
Date: February 1, 1994
Creator: unknown
System: The UNT Digital Library
Draft final feasibility study report and proposed plan for Operable Unit 4, response to comments: Fernald Environmental Management Project, Fernald, Ohio (open access)

Draft final feasibility study report and proposed plan for Operable Unit 4, response to comments: Fernald Environmental Management Project, Fernald, Ohio

This report contains questions and comments regarding a risk evaluation and possible remedial action of Operable Unit 4 at the Feed Materials Production Center at Fernald, Ohio. Attention is focused on the US EPA Region V feasibility study and on the CRARE. The CRARE is a post-remediation time frame document.
Date: February 1, 1994
Creator: unknown
System: The UNT Digital Library
Separations techniques for recovery and/or removal of toxic metals from spent textile dyebaths (open access)

Separations techniques for recovery and/or removal of toxic metals from spent textile dyebaths

The Textile Resource Conservation Project (TReC) is a major initiative of the American Textile Partnership (AMTEX) focusing on energy and the environment. The largest proposed project in the TReC is Raw Material Recovery and Reuse. The main task within the Raw Material Recovery and Reuse Project is Textile Chemical Recovery. The initial focus of this task is the separation/removal of colorants from solution. Screening studies were performed at a number of US Department of Energy National Laboratories to identify promising technologies for the treatment and recovery of dyes containing toxic metals. These dyes were chosen because of the environmental concern associated with their disposal. The research group at Pacific Northwest Laboratory (PNL) took two approaches to the removal and recovery of the toxic metals in the dyes. One approach was to react or destroy the organic fraction of the dye, releasing the metals for conventional separation such as ion exchange. PNL evaluated the Rapid Thermal Decomposition of precursors in Solution (RTDS) and Corona Discharge processes for metal release. The other approach was to separate and concentrate the dye, metal-complex intact, from the bulk of the spent solution. Membrane separation was evaluated for recovery of the dyes with the metals left …
Date: February 1, 1994
Creator: Babocsi, E. E. & Hallen, R. T.
System: The UNT Digital Library
4f heavy fermion photoelectron spectra do not exhibit the Kondo scale (open access)

4f heavy fermion photoelectron spectra do not exhibit the Kondo scale

It has been the authors contention for some time that the Single Impurity Anderson Model (SIAM), as extended by Gunnarsson and Schonhammer (GS), or the non-crossing approximation (NCA), does not correctly describe the 4f photoelectron spectra of heavy fermions. Recently, they have concentrated on Yb heavy fermions since in these materials the Kondo resonance (KR) is fully occupied and thus accessible via photoemission. In particular, they have repeatedly pointed out that the width, position, spectral weight, lineshape, and temperature dependence of the features assumed to be the KR and its sidebands, are nearly independent of the Kondo temperature, T{sub K}, while at the same time bearing a striking resemblance to the simple 4f core level spectra of pure Yb metal, or of Lu in isostructural Lu compounds. It is important to resolve these issues in view of the fundamental nature of the problem. Here, the authors chose to test the bulk vs. surface hypothesis by performing measurements on YbCu{sub 2}Si{sub 2} and YbAl{sub 3} single crystals at hv {approx} 120 eV (UPS) and hv {approx} 1,500 eV(XPS) to see if the n{sub f}, hole occupancy, values increase markedly at XPS energies as the electron escape depth increases by about a …
Date: February 1, 1994
Creator: Arko, A. J.; Joyce, J. J.; Andrews, A. B.; Blyth, R. I. R.; Bartlett, R. J.; Fisk, Z. et al.
System: The UNT Digital Library
Fermi surface instability at 0.4K in a heavy-fermion YbBiPt: SDW? (open access)

Fermi surface instability at 0.4K in a heavy-fermion YbBiPt: SDW?

The authors report results of resistivity measurements of heavy-fermion compound YbBiPt at ambient and hydrostatic pressures of up to {approx} 6kbars and in magnetic field up to 1 Tesla. They interpret the rise of resistivity below 0.4K as partial gaping of the Fermi surface. From the temperature dependence of resistivity they obtain the value of the weak coupling energy gap of {Delta}{sub 0}/k{sub B}T{sub c} = 1.65 {+-} 0.15. Magnetic field -- transition temperature phase diagram follows the weak coupling BCS expression remarkably well from T{sub c} to T{sub c}/4. These results support identification of 0.4K transition as a Spin Density Wave formation.
Date: February 1, 1994
Creator: Movshovich, R.; Lacerda, A.; Canfield, P. C.; Thompson, J. D. & Fisk, Z.
System: The UNT Digital Library