Active-Interrogation Measurements of Induced-Fission Neutrons from Low-Enriched Uranium (open access)

Active-Interrogation Measurements of Induced-Fission Neutrons from Low-Enriched Uranium

Protection and control of nuclear fuels is paramount for nuclear security and safeguards; therefore, it is important to develop fast and robust controlling mechanisms to ensure the safety of nuclear fuels. Through both passive- and active-interrogation methods we can use fast-neutron detection to perform real-time measurements of fission neutrons for process monitoring. Active interrogation allows us to use different ranges of incident neutron energy to probe for different isotopes of uranium. With fast-neutron detectors, such as organic liquid scintillation detectors, we can detect the induced-fission neutrons and photons and work towards quantifying a sample’s mass and enrichment. Using MCNPX-PoliMi, a system was designed to measure induced-fission neutrons from U-235 and U-238. Measurements were then performed in the summer of 2010 at the Joint Research Centre in Ispra, Italy. Fissions were induced with an associated particle D-T generator and an isotopic Am-Li source. The fission neutrons, as well as neutrons from (n, 2n) and (n, 3n) reactions, were measured with five 5” by 5” EJ-309 organic liquid scintillators. The D-T neutron generator was available as part of a measurement campaign in place by Padova University. The measurement and data-acquisition systems were developed at the University of Michigan utilizing a CAEN V1720 …
Date: July 1, 2012
Creator: Dolan, J. L.; Marcath, M. J.; Flaska, M.; Pozzi, S. A.; Chichester, D. L.; Tomanin, A. et al.
System: The UNT Digital Library
ACTUAL-WASTE TESTS OF ENHANCED CHEMICAL CLEANING FOR RETRIEVAL OF SRS HLW SLUDGE TANK HEELS AND DECOMPOSITION OF OXALIC ACID (open access)

ACTUAL-WASTE TESTS OF ENHANCED CHEMICAL CLEANING FOR RETRIEVAL OF SRS HLW SLUDGE TANK HEELS AND DECOMPOSITION OF OXALIC ACID

Savannah River National Laboratory conducted a series of tests on the Enhanced Chemical Cleaning (ECC) process using actual Savannah River Site waste material from Tanks 5F and 12H. Testing involved sludge dissolution with 2 wt% oxalic acid, the decomposition of the oxalates by ozonolysis (with and without the aid of ultraviolet light), the evaporation of water from the product, and tracking the concentrations of key components throughout the process. During ECC actual waste testing, the process was successful in decomposing oxalate to below the target levels without causing substantial physical or chemical changes in the product sludge.
Date: January 12, 2012
Creator: Martino, C.; King, W. & Ketusky, E.
System: The UNT Digital Library
ADAPTING A CERTIFIED SHIPPING PACKAGE FOR STORAGE APPLICATIONS (open access)

ADAPTING A CERTIFIED SHIPPING PACKAGE FOR STORAGE APPLICATIONS

For years shipping packages have been used to store radioactive materials at many DOE sites. Recently, the K-Area Material Storage facility at the Savannah River Site became interested in and approved the Model 9977 Shipping Package for use as a storage package. In order to allow the 9977 to be stored in the facility, there were a number of evaluations and modifications that were required. There were additional suggested modifications to improve the performance of the package as a storage container that were discussed but not incorporated in the design that is currently in use. This paper will discuss the design being utilized for shipping and storage, suggested modifications that have improved the storage configuration but were not used, as well as modifications that have merit for future adaptations for both the 9977 and for other shipping packages to be used as storage packages.
Date: June 5, 2012
Creator: Loftin, B. & Abramczyk, G.
System: The UNT Digital Library
Adaptive Sampling using Support Vector Machines (open access)

Adaptive Sampling using Support Vector Machines

Reliability/safety analysis of stochastic dynamic systems (e.g., nuclear power plants, airplanes, chemical plants) is currently performed through a combination of Event-Tress and Fault-Trees. However, these conventional methods suffer from certain drawbacks: • Timing of events is not explicitly modeled • Ordering of events is preset by the analyst • The modeling of complex accident scenarios is driven by expert-judgment For these reasons, there is currently an increasing interest into the development of dynamic PRA methodologies since they can be used to address the deficiencies of conventional methods listed above.
Date: November 1, 2012
Creator: Mandelli, D. & Smith, C.
System: The UNT Digital Library
Adaptive Wavenumber Estimation for Mode Tracking in a Shallow Ocean Environment (open access)

Adaptive Wavenumber Estimation for Mode Tracking in a Shallow Ocean Environment

None
Date: June 28, 2012
Creator: Candy, J V
System: The UNT Digital Library
Addressing Control of Hazardous Energy (COHE) Requirements in a Laser Safety Program (open access)

Addressing Control of Hazardous Energy (COHE) Requirements in a Laser Safety Program

OSHA regulation 29CFR1910.147 specifies control of hazardous energy requirements for 'the servicing and maintenance of machines and equipment in which the unexpected energization or start up of the machines or equipment, or release of stored energy could cause injury to employees.' Class 3B and Class 4 laser beams must be considered hazardous energy sources because of the potential for serious eye injury; careful consideration is therefore needed to safely de-energize these lasers. This paper discusses and evaluates control of hazardous energy principles in this OSHA regulation, in ANSI Z136.1 ''Safe Use of Lasers,'' and in ANSI Z244.1 ''Control of Hazardous Energy, Lockout/Tagout and Alternative Methods.'' Recommendations are made for updating and improving CoHE (control of hazardous energy) requirements in these standards for their applicability to safe laser operations.
Date: February 15, 2012
Creator: Woods, Michael
System: The UNT Digital Library
AdS/QCD and Applications of Light-Front Holography (open access)

AdS/QCD and Applications of Light-Front Holography

Light-Front Holography leads to a rigorous connection between hadronic amplitudes in a higher dimensional anti-de Sitter (AdS) space and frame-independent light-front wavefunctions of hadrons in 3 + 1 physical space-time, thus providing a compelling physical interpretation of the AdS/CFT correspondence principle and AdS/QCD, a useful framework which describes the correspondence between theories in a modified AdS5 background and confining field theories in physical space-time. To a first semiclassical approximation, where quantum loops and quark masses are not included, this approach leads to a single-variable light-front Schroedinger equation which determines the eigenspectrum and the light-front wavefunctions of hadrons for general spin and orbital angular momentum. The coordinate z in AdS space is uniquely identified with a Lorentz-invariant coordinate {zeta} which measures the separation of the constituents within a hadron at equal light-front time. The internal structure of hadrons is explicitly introduced and the angular momentum of the constituents plays a key role. We give an overview of the light-front holographic approach to strongly coupled QCD. In particular, we study the photon-to-meson transition form factors (TFFs) F{sub M{gamma}}(Q{sup 2}) for {gamma}{gamma}* {yields} M using light-front holographic methods. The results for the TFFs for the {eta} and {eta}' mesons are also presented. Some …
Date: February 16, 2012
Creator: Brodsky, Stanley J.; /SLAC /Southern Denmark U., CP3-Origins; Cao, Fu-Guang; U., /Massey; de Teramond, Guy F. & U., /Costa Rica
System: The UNT Digital Library
AdS/QCD, Light-Front Holography, and Sublimated Gluons (open access)

AdS/QCD, Light-Front Holography, and Sublimated Gluons

The gauge/gravity duality leads to a simple analytical and phenomenologically compelling nonperturbative approximation to the full light-front QCD Hamiltonian - 'Light-Front Holography', which provides a Lorentz-invariant first-approximation to QCD, and successfully describes the spectroscopy of light-quark meson and baryons, their elastic and transition form factors, and other hadronic properties. The bound-state Schroedinger and Dirac equations of the soft-wall AdS/QCD model predict linear Regge trajectories which have the same slope in orbital angular momentum L and radial quantum number n for both mesons and baryons. Light-front holography connects the fifth-dimensional coordinate of AdS space z to an invariant impact separation variable {zeta} in 3+1 space at fixed light-front time. A key feature is the determination of the frame-independent light-front wavefunctions of hadrons - the relativistic analogs of the Schroedinger wavefunctions of atomic physics which allow one to compute form factors, transversity distributions, spin properties of the valence quarks, jet hadronization, and other hadronic observables. One thus obtains a one-parameter color-confining model for hadron physics at the amplitude level. AdS/QCD also predicts the form of the non-perturbative effective coupling {alpha}{sub s}{sup AdS} (Q) and its {beta}-function with an infrared fixed point which agrees with the effective coupling a{sub g1} (Q{sup 2}) extracted …
Date: February 16, 2012
Creator: Brodsky, Stanley J. & de Teramond, Guy F.
System: The UNT Digital Library
Adsorption of Atmospheric Gases on Pu Surfaces (open access)

Adsorption of Atmospheric Gases on Pu Surfaces

Surface adsorption represents a competition between collision and scattering processes that depend on surface energy, surface structure and temperature. The surface reactivity of the actinides can add additional complexity due to radiological dissociation of the gas and electronic structure. Here we elucidate the chemical bonding of gas molecules adsorbed on Pu metal and oxide surfaces. Atmospheric gas reactions were studied at 190 and 300 K using x-ray photoelectron spectroscopy. Evolution of the Pu 4f and O 1s core-level states were studied as a function of gas dose rates to generate a set of Langmuir isotherms. Results show that the initial gas dose forms Pu{sub 2}O{sub 3} on the Pu metal surface followed by the formation of PuO{sub 2} resulting in a layered oxide structure. This work represents the first steps in determining the activation energy for adsorption of various atmospheric gases on Pu.
Date: March 29, 2012
Creator: Nelson, A J; Holliday, K S; Stanford, J A; Grant, W K; Erler, R G; Allen, P G et al.
System: The UNT Digital Library
AN ADVANCED CALIBRATION PROCEDURE FOR COMPLEX IMPEDANCE SPECTRUM MEASUREMENTS OF ADVANCED ENERGY STORAGE DEVICES (open access)

AN ADVANCED CALIBRATION PROCEDURE FOR COMPLEX IMPEDANCE SPECTRUM MEASUREMENTS OF ADVANCED ENERGY STORAGE DEVICES

With the increasing demand for electric and hybrid electric vehicles and the explosion in popularity of mobile and portable electronic devices such as laptops, cell phones, e-readers, tablet computers and the like, reliance on portable energy storage devices such as batteries has likewise increased. The concern for the availability of critical systems in turn drives the availability of battery systems and thus the need for accurate battery health monitoring has become paramount. Over the past decade the Idaho National Laboratory (INL), Montana Tech of the University of Montana (Tech), and Qualtech Systems, Inc. (QSI) have been developing the Smart Battery Status Monitor (SBSM), an integrated battery management system designed to monitor battery health, performance and degradation and use this knowledge for effective battery management and increased battery life. Key to the success of the SBSM is an in-situ impedance measurement system called the Impedance Measurement Box (IMB). One of the challenges encountered has been development of an accurate, simple, robust calibration process. This paper discusses the successful realization of this process.
Date: June 1, 2012
Creator: Morrison, William H.; Christophersen, Jon P.; Bald, Patrick & Morrison, John L.
System: The UNT Digital Library
Advanced divertor configurations with large flux expansion. (open access)

Advanced divertor configurations with large flux expansion.

None
Date: June 11, 2012
Creator: et. al, V
System: The UNT Digital Library
Advanced Electric Submersible Pump Design Tool for Geothermal Applications (open access)

Advanced Electric Submersible Pump Design Tool for Geothermal Applications

Electrical Submersible Pumps (ESPs) present higher efficiency, larger production rate, and can be operated in deeper wells than the other geothermal artificial lifting systems. Enhanced Geothermal Systems (EGS) applications recommend lifting 300 C geothermal water at 80kg/s flow rate in a maximum 10-5/8-inch diameter wellbore to improve the cost-effectiveness. In this paper, an advanced ESP design tool comprising a 1D theoretical model and a 3D CFD analysis has been developed to design ESPs for geothermal applications. Design of Experiments was also performed to optimize the geometry and performance. The designed mixed-flow type centrifugal impeller and diffuser exhibit high efficiency and head rise under simulated EGS conditions. The design tool has been validated by comparing the prediction to experimental data of an existing ESP product.
Date: May 31, 2012
Creator: Qi, Xuele; Turnquist, Norman & Ghasripoor, Farshad
System: The UNT Digital Library
Advanced High-Speed 16-Bit Digitizer System (open access)

Advanced High-Speed 16-Bit Digitizer System

The fastest commercially available 16-bit ADC can only perform around 200 mega-samples per second (200 MS/s). Connecting ADC chips together in eight different time domains increases the quantity of samples taken by a factor of eight. This method of interleaving requires that the input signal being sampled is split into eight identical signals and arrives at each ADC chip at the same point in time. The splitting of the input signal is performed in the analog front end containing a wideband filter that impedance matches the input signal to the ADC chips. Each ADC uses a clock to tell it when to perform a conversion. Using eight unique clocks spaced in 45-degree increments is the method used to time shift when each ADC chip performs its conversion. Given that this control clock is a fixed frequency, the clock phase shifting is accomplished by tightly controlling the distance that the clock must travel, resulting in a time delay. The interleaved ADC chips will now generate digital data in eight different time domains. These data are processed inside a field-programmable gate array (FPGA) to move the data back into a single time domain and store it into memory. The FPGA also contains …
Date: May 1, 2012
Creator: unknown
System: The UNT Digital Library
Advanced Horizontal Well Recirculation Systems for Geothermal Energy Recovery in Sedimentary Formations (open access)

Advanced Horizontal Well Recirculation Systems for Geothermal Energy Recovery in Sedimentary Formations

There is increased recognition that geothermal energy resources are more widespread than previously thought, with potential for providing a significant amount of sustainable clean energy worldwide. Recent advances in drilling, completion, and production technology from the oil and gas industry can now be applied to unlock vast new geothermal resources, with some estimates for potential electricity generation from geothermal energy now on the order of 2 million megawatts. Terralog USA, in collaboration with the University of California, Irvine (UCI), are currently investigating advanced design concepts for paired horizontal well recirculation systems, optimally configured for geothermal energy recovery in permeable sedimentary and crystalline formations of varying structure and material properties. This two-year research project, funded by the US Department of Energy, includes combined efforts for: 1) Resource characterization; 2) Small and large scale laboratory investigations; 3) Numerical simulation at both the laboratory and field scale; and 4) Engineering feasibility studies and economic evaluations. The research project is currently in its early stages. This paper summarizes our technical approach and preliminary findings related to potential resources, small-scale laboratory simulation, and supporting numerical simulation efforts.
Date: September 30, 2012
Creator: Bruno, Mike; Detwiler, Russell L.; Lao, Kang; Serajian, Vahid; Elkhoury, Jean; Diessl, Julia et al.
System: The UNT Digital Library
ADVANCED OXIDATION: OXALATE DECOMPOSITION TESTING WITH OZONE (open access)

ADVANCED OXIDATION: OXALATE DECOMPOSITION TESTING WITH OZONE

At the Savannah River Site (SRS), oxalic acid is currently considered the preferred agent for chemically cleaning the large underground Liquid Radioactive Waste Tanks. It is applied only in the final stages of emptying a tank when generally less than 5,000 kg of waste solids remain, and slurrying based removal methods are no-longer effective. The use of oxalic acid is preferred because of its combined dissolution and chelating properties, as well as the fact that corrosion to the carbon steel tank walls can be controlled. Although oxalic acid is the preferred agent, there are significant potential downstream impacts. Impacts include: (1) Degraded evaporator operation; (2) Resultant oxalate precipitates taking away critically needed operating volume; and (3) Eventual creation of significant volumes of additional feed to salt processing. As an alternative to dealing with the downstream impacts, oxalate decomposition using variations of ozone based Advanced Oxidation Process (AOP) were investigated. In general AOPs use ozone or peroxide and a catalyst to create hydroxyl radicals. Hydroxyl radicals have among the highest oxidation potentials, and are commonly used to decompose organics. Although oxalate is considered among the most difficult organic to decompose, the ability of hydroxyl radicals to decompose oxalate is considered to …
Date: February 29, 2012
Creator: Ketusky, E. & Subramanian, K.
System: The UNT Digital Library
Advanced Test Reactor National Scientific User Facility Partnerships (open access)

Advanced Test Reactor National Scientific User Facility Partnerships

In 2007, the United States Department of Energy designated the Advanced Test Reactor (ATR), located at Idaho National Laboratory, as a National Scientific User Facility (NSUF). This designation made test space within the ATR and post-irradiation examination (PIE) equipment at INL available for use by researchers via a proposal and peer review process. The goal of the ATR NSUF is to provide researchers with the best ideas access to the most advanced test capability, regardless of the proposer's physical location. Since 2007, the ATR NSUF has expanded its available reactor test space, and obtained access to additional PIE equipment. Recognizing that INL may not have all the desired PIE equipment, or that some equipment may become oversubscribed, the ATR NSUF established a Partnership Program. This program enables and facilitates user access to several university and national laboratories. So far, seven universities and one national laboratory have been added to the ATR NSUF with capability that includes reactor-testing space, PIE equipment, and ion beam irradiation facilities. With the addition of these universities, irradiation can occur in multiple reactors and post-irradiation exams can be performed at multiple universities. In each case, the choice of facilities is based on the user's technical needs. …
Date: March 1, 2012
Creator: Marshall, Frances M.; Allen, Todd R.; Benson, Jeff B.; Cole, James I. & Thelen, Mary Catherine
System: The UNT Digital Library
Advanced Test Reactor National Scientific User Facility Progress (open access)

Advanced Test Reactor National Scientific User Facility Progress

The Advanced Test Reactor (ATR) at the Idaho National Laboratory (INL) is one of the world’s premier test reactors for studying the effects of intense neutron radiation on reactor materials and fuels. The ATR began operation in 1967, and has operated continuously since then, averaging approximately 250 operating days per year. The combination of high flux, large test volumes, and multiple experiment configuration options provide unique testing opportunities for nuclear fuels and material researchers. The ATR is a pressurized, light-water moderated and cooled, beryllium-reflected highly-enriched uranium fueled, reactor with a maximum operating power of 250 MWth. The ATR peak thermal flux can reach 1.0 x1015 n/cm2-sec, and the core configuration creates five main reactor power lobes (regions) that can be operated at different powers during the same operating cycle. In addition to these nine flux traps there are 68 irradiation positions in the reactor core reflector tank. The test positions range from 0.5” to 5.0” in diameter and are all 48” in length, the active length of the fuel. The INL also has several hot cells and other laboratories in which irradiated material can be examined to study material radiation effects. In 2007 the US Department of Energy (DOE) designated …
Date: October 1, 2012
Creator: Marshall, Frances M.; Allen, Todd R.; Cole, James I.; Benson, Jeff B. & Thelen, Mary Catherine
System: The UNT Digital Library
Advanced Wind Turbine Controls Reduce Loads (Fact Sheet) (open access)

Advanced Wind Turbine Controls Reduce Loads (Fact Sheet)

NREL's National Wind Technology Center provides the world's only dedicated turbine controls testing platforms.
Date: March 1, 2012
Creator: unknown
System: The UNT Digital Library
Advanced X-Band Test Accelerator for High Brightness Electron and Gamma Ray Beams (open access)

Advanced X-Band Test Accelerator for High Brightness Electron and Gamma Ray Beams

In support of Compton scattering gamma-ray source efforts at LLNL, a multi-bunch test stand is being developed to investigate accelerator optimization for future upgrades. This test stand will enable work to explore the science and technology paths required to boost the current 10 Hz monoenergetic gamma-ray (MEGa-Ray) technology to an effective repetition rate exceeding 1 kHz, potentially increasing the average gamma-ray brightness by two orders of magnitude. Multiple bunches must be of exceedingly high quality to produce narrow-bandwidth gamma-rays. Modeling efforts will be presented, along with plans for a multi-bunch test stand at LLNL. The test stand will consist of a 5.5 cell X-band rf photoinjector, single accelerator section, and beam diagnostics. The photoinjector will be a high gradient standing wave structure, featuring a dual feed racetrack coupler. The accelerator will increase the electron energy so that the emittance can be measured using quadrupole scanning techniques. Multi-bunch diagnostics will be developed so that the beam quality can be measured and compared with theory. Design will be presented with modeling simulations, and layout plans.
Date: July 3, 2012
Creator: Marsh, Roark; Anderson, Scott; Barty, Christopher; Chu, Tak Sum; Ebbers, Chris; Gibson, David et al.
System: The UNT Digital Library
Advancement of isotope separation for the production of reference standards (open access)

Advancement of isotope separation for the production of reference standards

Idaho National Laboratory (INL) operates a mass separator that is currently producing high purity isotopes for use as internal standards for high precision isotope dilution mass spectrometry (IDMS). In 2008, INL began the revival of the vintage 1970’s era instrument. Advancements thus far include the successful upgrading and development of system components such as the vacuum system, power supplies, ion-producing components, and beam detection equipment. Progress has been made in the separation and collection of isotopic species including those of Ar, Kr, Xe, Sr, and Ba. Particular focuses on ion source improvements and developments have proven successful with demonstrated output beam currents of over 10 micro-amps 138Ba and 350nA 134Ba from a natural abundance source charge (approximately 2.4 percent 134Ba). In order to increase production and collection of relatively high quantities (mg levels) of pure isotopes, several advancements have been made in ion source designs, source material introduction, and beam detection and collection. These advancements and future developments will be presented.
Date: March 1, 2012
Creator: Horkley, Jared; McGrath, Christopher; Edwards, Andrew; Knighton, Gaven; Carney, Kevin; Davies, Jacob et al.
System: The UNT Digital Library
ADVANCES IN HEXAVALENT CHROMIUM REMOVAL AT HANFORD (open access)

ADVANCES IN HEXAVALENT CHROMIUM REMOVAL AT HANFORD

At the Hanford Site, chromium was used as a corrosion inhibitor in the reactor cooling water and was introduced into the groundwater as a result of planned and unplanned discharges from reactors during plutonium production since 1944. Beginning in 1995, groundwater treatment methods were evaluated leading to the use of pump and treat facilities with ion exchange using Dowex 21 K, a regenerable strong base anion exchange resin. This required regeneration of the resin, which is currently performed offsite. Resin was installed in a 4 vessel train, with resin removal required from the lead vessel approximately once a month. In 2007, there were 8 trains (32 vessels) in operation. In 2008, DOE recognized that regulatory agreements would require significant expansion in the groundwater chromium treatment capacity. Previous experience from one of the DOE project managers led to identification of a possible alternative resin, and the contractor was requested to evaluate alternative resins for both cost and programmatic risk reductions. Testing was performed onsite in 2009 and 2010, using a variety of potential resins in two separate facilities with groundwater from specific remediation sites to demonstrate resin performance in the specific groundwater chemistry at each site. The testing demonstrated that a …
Date: January 30, 2012
Creator: Neshem, D. O. & Riddelle, J.
System: The UNT Digital Library
Advances in High Throughput Screening of Biomass Recalcitrance (Poster) (open access)

Advances in High Throughput Screening of Biomass Recalcitrance (Poster)

This was a poster displayed at the Symposium. Advances on previous high throughput screening of biomass recalcitrance methods have resulted in improved conversion and replicate precision. Changes in plate reactor metallurgy, improved preparation of control biomass, species-specific pretreatment conditions, and enzymatic hydrolysis parameters have reduced overall coefficients of variation to an average of 6% for sample replicates. These method changes have improved plate-to-plate variation of control biomass recalcitrance and improved confidence in sugar release differences between samples. With smaller errors plant researchers can have a higher degree of assurance more low recalcitrance candidates can be identified. Significant changes in plate reactor, control biomass preparation, pretreatment conditions and enzyme have significantly reduced sample and control replicate variability. Reactor plate metallurgy significantly impacts sugar release aluminum leaching into reaction during pretreatment degrades sugars and inhibits enzyme activity. Removal of starch and extractives significantly decreases control biomass variability. New enzyme formulations give more consistent and higher conversion levels, however required re-optimization for switchgrass. Pretreatment time and temperature (severity) should be adjusted to specific biomass types i.e. woody vs. herbaceous. Desalting of enzyme preps to remove low molecular weight stabilizers and improved conversion levels likely due to water activity impacts on enzyme structure and …
Date: June 1, 2012
Creator: Turner, G. B.; Decker, S. R.; Tucker, M. P.; Law, C.; Doeppke, C.; Sykes, R. W. et al.
System: The UNT Digital Library
Advances in NIF Shock Timing Experiments (open access)

Advances in NIF Shock Timing Experiments

None
Date: July 10, 2012
Creator: Robey, H. F.; Celliers, P. M.; Moody, J. D. & MacKinnon, A. J.
System: The UNT Digital Library
Advances in Superresolution Optical Fluctuation Imaging (SOFI) (open access)

Advances in Superresolution Optical Fluctuation Imaging (SOFI)

None
Date: May 15, 2012
Creator: Dertinger, T.; Pallaoro, A.; Braun, G.; Ly, S.; Laurence, T. A. & Weiss, S.
System: The UNT Digital Library