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Renewal, Modulation, and Superstatistics in Times Series (open access)

Renewal, Modulation, and Superstatistics in Times Series

Article discussing two different approaches, referred to as renewal and modulation, to generate time series with a nonexponential distribution of waiting times.
Date: April 27, 2006
Creator: Allegrini, Paolo; Barbi, Francesco; Grigolini, Paolo & Paradisi, Paolo
System: The UNT Digital Library
System-level modeling for geological storage of CO2 (open access)

System-level modeling for geological storage of CO2

One way to reduce the effects of anthropogenic greenhousegases on climate is to inject carbon dioxide (CO2) from industrialsources into deep geological formations such as brine formations ordepleted oil or gas reservoirs. Research has and is being conducted toimprove understanding of factors affecting particular aspects ofgeological CO2 storage, such as performance, capacity, and health, safetyand environmental (HSE) issues, as well as to lower the cost of CO2capture and related processes. However, there has been less emphasis todate on system-level analyses of geological CO2 storage that considergeological, economic, and environmental issues by linking detailedrepresentations of engineering components and associated economic models.The objective of this study is to develop a system-level model forgeological CO2 storage, including CO2 capture and separation,compression, pipeline transportation to the storage site, and CO2injection. Within our system model we are incorporating detailedreservoir simulations of CO2 injection and potential leakage withassociated HSE effects. The platform of the system-level modelingisGoldSim [GoldSim, 2006]. The application of the system model is focusedon evaluating the feasibility of carbon sequestration with enhanced gasrecovery (CSEGR) in the Rio Vista region of California. The reservoirsimulations are performed using a special module of the TOUGH2 simulator,EOS7C, for multicomponent gas mixtures of methane and CO2 or methane andnitrogen. …
Date: April 24, 2006
Creator: Zhang, Yingqi; Oldenburg, Curtis M.; Finsterle, Stefan & Bodvarsson, Gudmundur S.
System: The UNT Digital Library
Chemical imaging of biological materials by NanoSIMS using isotopic and elemental labels (open access)

Chemical imaging of biological materials by NanoSIMS using isotopic and elemental labels

The NanoSIMS 50 combines unprecedented spatial resolution (as good as 50 nm) with ultra-high sensitivity (minimum detection limit of {approx}200 atoms). The NanoSIMS 50 incorporates an array of detectors, enabling simultaneous collection of 5 species originating from the same sputtered volume of a sample. The primary ion beam (Cs{sup +} or O{sup -}) can be scanned across the sample to produce quantitative secondary ion images. This capability for multiple isotope imaging with high spatial resolution provides a novel new approach to the study of biological materials. Studies can be made of sub-regions of tissues, mammalian cells, and bacteria. Major, minor and trace element distributions can be mapped on a submicron scale, growth and metabolism can be tracked using stable isotope labels, and biogenic origin can be determined based on composition. We have applied this technique extensively to mammalian and prokaryotic cells and bacterial spores. The NanoSIMS technology enables the researcher to interrogate the fate of molecules of interest within cells and organs through elemental and isotopic labeling. Biological applications at LLNL will be discussed.
Date: April 10, 2006
Creator: Weber, P K; Fallon, S J; Pett-Ridge, J; Ghosal, S & Hutcheon, I D
System: The UNT Digital Library
A Coupled Model for Natural Convection and Condensation in HeatedSubsurface Enclosures Embedded in Fractured Rock (open access)

A Coupled Model for Natural Convection and Condensation in HeatedSubsurface Enclosures Embedded in Fractured Rock

In heated tunnels such as those designated for emplacementof radioactive waste at Yucca Mountain, axial temperature gradients maycause natural convection processes that can significantly influence themoisture conditions in the tunnels and in the surrounding fractured rock.Large-scale convection cells would provide an effective mechanism foraxial vapor transport, driving moisture out of the formation away fromthe heated tunnel section into cool end sections (where no waste isemplaced). To study such processes, we have developed and applied anenhanced version of TOUGH2 (Pruess et al., 1999) adding a new module thatsolves for natural convection in open cavities. The new TOUGH2 simulatorsimultaneously handles (1) the flow and energy transport processes in thefractured rock; (2) the flow and energy transport processes in thecavity; and (3) the heat and mass exchange at the rock-cavity interface.The new module is applied to simulate the future thermal-hydrological(TH) conditions within and near a representative waste emplacement tunnelat Yucca Mountain. Particular focus is on the potential for condensationalong the emplacement section, a possible result of heat outputdifferences between individual waste packages.
Date: April 14, 2006
Creator: Halecky, N.; Birkholzer, J. T.; Webb, S. W.; Peterson, P. F. & Bodvarsson, G. S.
System: The UNT Digital Library
Cobra-IE Evaluation by Simulation of the NUPEC BWR Full-Size Fine-Mesh Bundle Test (BFBT) (open access)

Cobra-IE Evaluation by Simulation of the NUPEC BWR Full-Size Fine-Mesh Bundle Test (BFBT)

The COBRA-IE computer code is a thermal-hydraulic subchannel analysis program capable of simulating phenomena present in both PWRs and BWRs. As part of ongoing COBRA-IE assessment efforts, the code has been evaluated against experimental data from the NUPEC BWR Full-Size Fine-Mesh Bundle Tests (BFBT). The BFBT experiments utilized an 8 x 8 rod bundle to simulate BWR operating conditions and power profiles, providing an excellent database for investigation of the capabilities of the code. Benchmarks performed included steady-state and transient void distribution, single-phase and two-phase pressure drop, and steady-state and transient critical power measurements. COBRA-IE effectively captured the trends seen in the experimental data with acceptable prediction error. Future sensitivity studies are planned to investigate the effects of enabling and/or modifying optional code models dealing with void drift, turbulent mixing, rewetting, and CHF.
Date: April 26, 2006
Creator: Burns, C. J. and Aumiler, D. L.
System: The UNT Digital Library
DSP-Based dual-polarity mass spectrum pattern recognition for bio-detection (open access)

DSP-Based dual-polarity mass spectrum pattern recognition for bio-detection

The Bio-Aerosol Mass Spectrometry (BAMS) instrument analyzes single aerosol particles using a dual-polarity time-of-flight mass spectrometer recording simultaneously spectra of thirty to a hundred thousand points on each polarity. We describe here a real-time pattern recognition algorithm developed at Lawrence Livermore National Laboratory that has been implemented on a nine Digital Signal Processor (DSP) system from Signatec Incorporated. The algorithm first preprocesses independently the raw time-of-flight data through an adaptive baseline removal routine. The next step consists of a polarity dependent calibration to a mass-to-charge representation, reducing the data to about five hundred to a thousand channels per polarity. The last step is the identification step using a pattern recognition algorithm based on a library of known particle signatures including threat agents and background particles. The identification step includes integrating the two polarities for a final identification determination using a score-based rule tree. This algorithm, operating on multiple channels per-polarity and multiple polarities, is well suited for parallel real-time processing. It has been implemented on the PMP8A from Signatec Incorporated, which is a computer based board that can interface directly to the two one-Giga-Sample digitizers (PDA1000 from Signatec Incorporated) used to record the two polarities of time-of-flight data. By using …
Date: April 21, 2006
Creator: Riot, V; Coffee, K; Gard, E; Fergenson, D; Ramani, S & Steele, P
System: The UNT Digital Library
Process Control Minitoring by Stress Response (open access)

Process Control Minitoring by Stress Response

Environmental contamination with a variety of pollutants hasprompted the development of effective bioremediation strategies. But howcan these processes be best monitored and controlled? One avenue underinvestigation is the development of stress response systems as tools foreffective and general process control. Although the microbial stressresponse has been the subject of intensive laboratory investigation, theenvironmental reflection of the laboratory response to specific stresseshas been little explored. However, it is only within an environmentalcontext, in which microorganisms are constantly exposed to multiplechanging environmental stresses, that there will be full understanding ofmicrobial adaptive resiliency. Knowledge of the stress response in theenvironment will facilitate the control of bioremediation and otherprocesses mediated by complex microbial communities.
Date: April 17, 2006
Creator: Hazen, Terry C. & Stahl, David A.
System: The UNT Digital Library
Structures in Molecular Clouds: Modeling (open access)

Structures in Molecular Clouds: Modeling

We attempt to predict the observed morphology, column density and velocity gradient of Pillar II of the Eagle Nebula, using Rayleigh Taylor (RT) models in which growth is seeded by an initial perturbation in density or in shape of the illuminated surface, and cometary models in which structure is arises from a initially spherical cloud with a dense core. Attempting to mitigate suppression of RT growth by recombination, we use a large cylindrical model volume containing the illuminating source and the self-consistently evolving ablated outflow and the photon flux field, and use initial clouds with finite lateral extent. An RT model shows no growth, while a cometary model appears to be more successful at reproducing observations.
Date: April 20, 2006
Creator: Kane, J. O.; Mizuta, A.; Pound, M. W.; Remington, B. A. & Ryutov, D. D.
System: The UNT Digital Library
The Education and Outreach Project of ATLAS - A New Participant inPhysics Education (open access)

The Education and Outreach Project of ATLAS - A New Participant inPhysics Education

The ATLAS experiment at the Large Hadron Collider at CERN has a substantial collaborative Education and Outreach project. This article describes its activities and how it promotes physics to students around the world. With the extraordinary possibility to make groundbreaking discoveries, the ATLAS Experiment [1] at the Large Hadron Collider at CERN can play an important role in promoting contemporary physics at school. For many years ATLAS has had a substantial collaborative Education and Outreach (E&O) project in which physicists from various parts of the world take part. When the experiment begins in 2007, students from around the world will be analyzing data using cutting-edge technology. The unprecedented collision energies of the Large Hadron Collider allow ATLAS to decode the 'events' that unfold after the head-on collisions of protons (Fig. 1). The scientific results from these events will reveal much about the basic nature of matter, energy, space, and time. Students and others will be excited as they try to find events that may be signs for dark matter, extra dimensions of space, mini-black holes, string theory, and other fundamental discoveries. Science education and outreach and the promotion of awareness and appreciation of physics research have become important tasks for …
Date: April 15, 2006
Creator: Barnett, R. Michael & Johansson, K. Erik
System: The UNT Digital Library
Indoor Thermal Comfort, an Evolutionary Biology Perspective (open access)

Indoor Thermal Comfort, an Evolutionary Biology Perspective

As is becoming increasingly clear, the human species evolvedin the East African savannah. Details of the precise evolutionary chainremain unresolved however it appears that the process lasted severalmillion years, culminating with the emergence of modern Homo sapiensroughly 200,000 years ago. Following that final evolutionary developmentmodern Homo sapiens relatively quickly populated the entire world.Clearly modern Homo sapiens is a successful, resourceful and adaptablespecies. In the developed societies, modern humans live an existence farremoved from our evolutionary ancestors. As we have learned over the lastcentury, this "new" lifestyle can often result in unintendedconsequences. Clearly, our modern access to food, shelter, transportationand healthcare has resulted in greatly expanded expected lifespan butthis new lifestyle can also result in the emergence of different kinds ofdiseases and health problems. The environment in modern buildings haslittle resemblance to the environment of the savannah. We strive tocreate environments with little temperature, air movement and lightvariation. Building occupants often express great dissatisfaction withthese modern created environments and a significant fraction even developsomething akin to allergies to specific buildings (sick buildingsyndrome). Are the indoor environments we are creating fundamentallyunhealthy -- when examined from an evolutionary perspective?
Date: April 15, 2006
Creator: Stoops, John L.
System: The UNT Digital Library
Characterization of chemical bonding in low-k dielectric materialsfor interconnect isolation: a xas and eels study (open access)

Characterization of chemical bonding in low-k dielectric materialsfor interconnect isolation: a xas and eels study

The use of low dielectric constant materials in the on-chipinterconnect process reduces interconnect delay, power dissipation andcrosstalk noise. To achieve the requirements of the ITRS for 2007-2009minimal sidewall damage from etch, ash or cleans is required. In chemicalvapor deposited (CVD) organo-silicate glass (OSG) which are used asintermetal dielectric (IMD) materials the substitution of oxygen in SiO2by methyl groups (-CH3) reduces the permittivity significantly (from 4.0in SiO2 to 2.6-3.3 in the OSG), since the electronic polarizability islower for Si-C bonds than for Si-O bonds. However, plasma processing forresist stripping, trench etching and post-etch cleaning removes C and Hcontaining molecular groups from the near-surface layer of OSG.Therefore, compositional analysis and chemical bonding characterizationof structured IMD films with nanometer resolution is necessary forprocess optimization. OSG thin films as-deposited and after plasmatreatment are studied using X-ray absorption spectroscopy (XAS) andelectron energy loss spectroscopy (EELS). In both techniques, the finestructure near the C1s absorption or energy loss edge, respectively,allows to identify C-H, C-C, and C-O bonds. This gives the opportunity todifferentiate between individual low-k materials and their modifications.The O1s signal is less selective to individual bonds. XAS spectra havebeen recorded for non-patterned films and EELS spectra for patternedstructures. The chemical bonding is compared for as-deposited …
Date: April 10, 2006
Creator: Hoffmann, P.; Schmeisser, D.; Engelmann, H. J.; Zschech, E.; Stegmann, H.; Himpsel, F. et al.
System: The UNT Digital Library
Borehole Seismic Monitoring of Injected CO2 at the Frio Site (open access)

Borehole Seismic Monitoring of Injected CO2 at the Frio Site

As part of a small scale sequestration test (about 1500 tonsof CO2) in a saline aquifer, time-lapse borehole seismic surveys wereconducted to aid in characterization of subsurface CO2 distribution andmaterial property changes induced by the injected CO2. A VSP surveydemonstrated a large increase (about 75 percent) in seismic reflectivitydue to CO2 injection and allowed estimation of the spatial extent of CO2induced changes. A crosswell survey imaged a large seismic velocitydecrease (up to 500 m/s) within the injection interval and provided ahigh resolution image of this velocity change which maps the subsurfacedistribution of CO2 between two wells. Numerical modeling of the seismicresponse uses the crosswell measurements to show that this small CO2volume causes a large response in the seismic reflectivity. This resultdemonstrates that seismic detection of small CO2 volumes in salineaquifers is feasible and realistic.
Date: April 21, 2006
Creator: Daley, Thomas M.; Myer, Larry R.; Hoversten, G.M.; Peterson, JohnE. & Korneev, Valeri A.
System: The UNT Digital Library
A sampling-based Bayesian model for gas saturation estimationusing seismic AVA and marine CSEM data (open access)

A sampling-based Bayesian model for gas saturation estimationusing seismic AVA and marine CSEM data

We develop a sampling-based Bayesian model to jointly invertseismic amplitude versus angles (AVA) and marine controlled-sourceelectromagnetic (CSEM) data for layered reservoir models. The porosityand fluid saturation in each layer of the reservoir, the seismic P- andS-wave velocity and density in the layers below and above the reservoir,and the electrical conductivity of the overburden are considered asrandom variables. Pre-stack seismic AVA data in a selected time windowand real and quadrature components of the recorded electrical field areconsidered as data. We use Markov chain Monte Carlo (MCMC) samplingmethods to obtain a large number of samples from the joint posteriordistribution function. Using those samples, we obtain not only estimatesof each unknown variable, but also its uncertainty information. Thedeveloped method is applied to both synthetic and field data to explorethe combined use of seismic AVA and EM data for gas saturationestimation. Results show that the developed method is effective for jointinversion, and the incorporation of CSEM data reduces uncertainty influid saturation estimation, when compared to results from inversion ofAVA data only.
Date: April 4, 2006
Creator: Chen, Jinsong; Hoversten, Michael; Vasco, Don; Rubin, Yoram & Hou,Zhangshuan
System: The UNT Digital Library
Field Survey of Parabolic Trough Receiver Thermal Performance: Preprint (open access)

Field Survey of Parabolic Trough Receiver Thermal Performance: Preprint

This paper describes a technique that uses an infrared camera to evaluate the in-situ thermal performance of parabolic trough receivers at operating solar power plants.
Date: April 1, 2006
Creator: Price, H.; Forristall, R.; Wendelin, T.; Lewandowski, A.; Moss, T. & Gummo, C.
System: The UNT Digital Library
Solid Deuterium-Tritium Surface Roughness In A Beryllium Inertial Confinement Fusion Shell (open access)

Solid Deuterium-Tritium Surface Roughness In A Beryllium Inertial Confinement Fusion Shell

Solid deuterium-tritium (D-T) fuel layers for inertial confinement fusion experiments were formed inside of a 2 mm diameter beryllium shell and were characterized using phase-contrast enhanced x-ray imaging. The solid D-T surface roughness is found to be 0.4 {micro}m for modes 7-128 at 1.5 K below the melting temperature. The layer roughness is found to increase with decreasing temperature, in agreement with previous visible light characterization studies. However, phase-contrast enhanced x-ray imaging provides a more robust surface roughness measurement than visible light methods. The new x-ray imaging results demonstrate clearly that the surface roughness decreases with time for solid D-T layers held at 1.5 K below the melting temperature.
Date: April 19, 2006
Creator: Kozioziemski, B J; Sater, J D; Moody, J D; Montgomery, D S & Gautier, C
System: The UNT Digital Library
Time-dependent seismic tomography of the Coso geothermal area, 1996-2004 (open access)

Time-dependent seismic tomography of the Coso geothermal area, 1996-2004

Local-earthquake tomographic images were calculated for each of the years 1996 - 2004 using arrival times from the U.S. Navy’s permanent seismometer network at the Coso geothermal area, California. The results show irregular strengthening with time of the wave-speed ratio VP/VS at shallow depths. These changes result predominately from progressive relative increase in VS with respect to VP, and could result from processes associated with geothermal operations such as decrease in fluid pressure and the drying of argillaceous minerals such as illite.
Date: April 1, 2006
Creator: Julian, B.R.; Foulger, G.R.; Richards-Dinger, K. & Monastero, F.
System: The UNT Digital Library
Letting The Sun Shine On Solar Costs: An Empirical InvestigationOf Photovoltaic Cost Trends In California (open access)

Letting The Sun Shine On Solar Costs: An Empirical InvestigationOf Photovoltaic Cost Trends In California

None
Date: April 12, 2006
Creator: Wiser, Ryan; Bolinger, Mark; Cappers, Peter & Margolis, Robert
System: The UNT Digital Library
Preliminary optical design for a 2.2 degree diameter prime focus corrector for the Blanco 4 meter telescope (open access)

Preliminary optical design for a 2.2 degree diameter prime focus corrector for the Blanco 4 meter telescope

We describe a five element corrector for the prime focus of the 4 meter Blanco telescope at the Cerro Tololo Inter-American Observatory (CTIO) in Chile that will be used in conjunction with a new mosaic CCD camera as part of the proposed Dark Energy Survey (DES). The corrector is designed to provide a flat focal plane and good images in the SDSS g, r, i, and z filters. We describe the performance in conjunction with the scientific requirements of the DES, particularly with regard to ghosting and weak-lensing point spread function (PSF) calibration.
Date: April 1, 2006
Creator: Kent, S.; Bernstein, R.; Abbott, T.; Bigelow, B.; Brooks, D.; Doel, P. et al.
System: The UNT Digital Library
SIMULATION AND ANALYSIS OF MICROWAVE TRANSMISSION THROUGH ANELECTRON CLOUD, A COMPARISON OF RESULTS (open access)

SIMULATION AND ANALYSIS OF MICROWAVE TRANSMISSION THROUGH ANELECTRON CLOUD, A COMPARISON OF RESULTS

Simulation studies for transmission of microwaves through electron clouds show good agreement with analytic results. The electron cloud produces a shift in phase of the microwave. Experimental observation of this phenomena would lead to a useful diagnostic tool for accessing the local density of electron clouds in an accelerator. These experiments are being carried out at the CERN SPS and the PEP-II LER at SLAC and is proposed to be done at the Fermilab main injector. In this study, a brief analysis of the phase shift is provided and the results are compared with that obtained from simulations.
Date: April 15, 2006
Creator: Sonnad, Kiran G.; Furman, Miguel; Veitzer, Seth A. & Cary, John
System: The UNT Digital Library
Rhamm-/- mice are defective in skin wound repair due to aberrantERK1,2 signaling in fibroblast migration (open access)

Rhamm-/- mice are defective in skin wound repair due to aberrantERK1,2 signaling in fibroblast migration

None
Date: April 3, 2006
Creator: Tolg, Cornelia; Hamilton, Sara R.; Kooshesh, Pari; McCarthy,James B.; Bissell, Mina J. & Turley, Eva A.
System: The UNT Digital Library
EVALUATION OF RADIONUCLIDE ACCUMULATION IN SOIL DUE TO LONG-TERM IRRIGATION (open access)

EVALUATION OF RADIONUCLIDE ACCUMULATION IN SOIL DUE TO LONG-TERM IRRIGATION

Radionuclide accumulation in soil due to long-term irrigation is an important part of the model for predicting radiation dose in a long period of time. The model usually assumes an equilibrium condition in soil with a constant irrigation rate, so that radionuclide concentration in soil does not change with time and can be analytically solved. This method is currently being used for the dose assessment in the Yucca Mountain project, which requires evaluating radiation dose for a period of 10,000 years. There are several issues associated with the method: (1) time required for the equilibrium condition, (2) validity of constant irrigation rate, (3) agricultural land use for a long period of time, and (4) variation of a radionuclide concentration in water. These issues are evaluated using a numerical method with a simple model built in the GoldSim software. Some key radionuclides, Tc-99, Np-237, Pu-239, and Am-241 are selected as representative radionuclides. The results indicate that the equilibrium model is acceptable except for a radionuclide that requires long time to accumulate in soil and that its concentration in water changes dramatically with time (i.e. a sharp peak). Then the calculated dose for that radionuclide could be overestimated using the current equilibrium …
Date: April 16, 2006
Creator: Wu, De Wesley
System: The UNT Digital Library
Modeling the impact of sea-spray on particle concentrations in a coastal city (open access)

Modeling the impact of sea-spray on particle concentrations in a coastal city

An atmospheric chemistry-transport model is used to assess the impacts of sea-spray chemistry on the particle composition in and downwind of a coastal city--Vancouver, British Columbia. Reactions in/on sea-spray affect the entire particle ensemble and particularly the size distribution of particle nitrate. Urban air quality, and particularly airborne particles, is a major concern in terms of human health impacts. Sea-spray is known to be a major component of the particle ensemble at coastal sites yet relatively few air quality models include the interaction of gases with sea-spray and the fate of the particles produced. Sea-spray is not an inert addition to the particle ensemble because heterogeneous chemistry in/on sea-spray droplets changes the droplets composition and the particle size distribution, which impacts deposition and the ion balance in different particle size fractions. It is shown that the ISOPART model is capable of simulating gas and particle concentrations in the coastal metropolis of Vancouver and the surrounding valley. It is also demonstrated that to accurately simulate ambient concentrations of particles and reactive/soluble gases in a coastal valley it is absolutely critical to include heterogeneous chemistry in/on sea-spray. Partitioning of total particle-NO{sub 3}{sup -} between sea-spray and NH{sub 4}NO{sub 3} is highly sensitive …
Date: April 19, 2006
Creator: Pryor, S C; Barthelmie, R J; Schoof, J T; Binkowski, F S; Monache, L D & Stull, R B
System: The UNT Digital Library
A Universe Without Weak Interactions (open access)

A Universe Without Weak Interactions

None
Date: April 4, 2006
Creator: Harnik, Roni; Kribs, Graham D. & Perez, Gilad
System: The UNT Digital Library
Insertion of a self-splicing intron into the mtDNA of atriploblastic animal (open access)

Insertion of a self-splicing intron into the mtDNA of atriploblastic animal

Nephtys longosetosa is a carnivorous polychaete worm that lives in the intertidal and subtidal zones with worldwide distribution (pleijel&rouse2001). Its mitochondrial genome has the characteristics typical of most metazoans: 37 genes; circular molecule; almost no intergenic sequence; and no significant gene rearrangements when compared to other annelid mtDNAs (booremoritz19981995). Ubiquitous features as small intergenic regions and lack of introns suggested that metazoan mtDNAs are under strong selective pressures to reduce their genome size allowing for faster replication requirements (booremoritz19981995Lynch2005). Yet, in 1996 two type I introns were found in the mtDNA of the basal metazoan Metridium senile (FigureX). Breaking a long-standing rule (absence of introns in metazoan mtDNA), this finding was later supported by the further presence of group I introns in other cnidarians. Interestingly, only the class Anthozoa within cnidarians seems to harbor such introns. Although several hundreds of triploblastic metazoan mtDNAs have been sequenced, this study is the first evidence of mitochondrial introns in triploblastic metazoans. The cox1 gene of N. longosetosa has an intron of almost 2 kbs in length. This finding represents as well the first instance of a group II intron (anthozoans harbor group I introns) in all metazoan lineages. Opposite trends are observed within …
Date: April 14, 2006
Creator: Valles, Y.; Halanych, K. & Boore, J.L.
System: The UNT Digital Library