Resource Type

120 Matching Results

Results open in a new window/tab.

Spatial Bias in Field-Estimated Unsaturated Hydraulic Properties (open access)

Spatial Bias in Field-Estimated Unsaturated Hydraulic Properties

Hydraulic property measurements often rely on non-linear inversion models whose errors vary between samples. In non-linear physical measurement systems, bias can be directly quantified and removed using calibration standards. In hydrologic systems, field calibration is often infeasible and bias must be quantified indirectly. We use a Monte Carlo error analysis to indirectly quantify spatial bias in the saturated hydraulic conductivity, K{sub s}, and the exponential relative permeability parameter, {alpha}, estimated using a tension infiltrometer. Two types of observation error are considered, along with one inversion-model error resulting from poor contact between the instrument and the medium. Estimates of spatial statistics, including the mean, variance, and variogram-model parameters, show significant bias across a parameter space representative of poorly- to well-sorted silty sand to very coarse sand. When only observation errors are present, spatial statistics for both parameters are best estimated in materials with high hydraulic conductivity, like very coarse sand. When simple contact errors are included, the nature of the bias changes dramatically. Spatial statistics are poorly estimated, even in highly conductive materials. Conditions that permit accurate estimation of the statistics for one of the parameters prevent accurate estimation for the other; accurate regions for the two parameters do not overlap …
Date: December 21, 2000
Creator: HOLT,ROBERT M.; WILSON,JOHN L. & GLASS JR.,ROBERT J.
System: The UNT Digital Library
Dense optical-electrical interface module (open access)

Dense optical-electrical interface module

The DOIM (Dense Optical-electrical Interface Modules) is a custom-designed optical data transmission module employed in the upgrade of Silicon Vertex Detector of CDF experiment at Fermilab. Each DOIM module consists of a transmitter (TX) converting electrical differential input signals to optical outputs, a middle segment of jacketed fiber ribbon cable, and a receiver (RX) which senses the light inputs and converts them back to electrical signals. The targeted operational frequency is 53 MHz, and higher rate is achievable. This article outlines the design goals, implementation methods, production test results, and radiation hardness tests of these modules.
Date: December 21, 2000
Creator: Chang, Paul
System: The UNT Digital Library
Tests of quark mass textures (open access)

Tests of quark mass textures

The classic hints on the structure of the quark mass matrices are shortly reviewed and the possibility of obtaining further information through precise texture analysis is discussed with the aid of a specific example.
Date: December 21, 2000
Creator: unknown
System: The UNT Digital Library
The underlying event in large transverse momentum charged jet and Z-boson production (open access)

The underlying event in large transverse momentum charged jet and Z-boson production

The authors study the behavior of the underlying event in large transverse momentum charged jet and Z-boson production at 1.8 TeV and compare with the QCD Monte-Carlo models. The data indicate that neither ISAJET or HERWIG produce enough charged particles (with p{sub T} > 0.5 GeV/c) from the beam-beam remnant component and that ISAJET produces too many charged particle from initial-state radiation. PYTHIA which uses multiple parton scattering to enhance the underlying event does the best job describing the data.
Date: December 21, 2000
Creator: Field, Rick
System: The UNT Digital Library
From a {nu} factory to {mu} super + mu super {minus} Colliders (open access)

From a {nu} factory to {mu} super + mu super {minus} Colliders

An important feature of a {mu}-storage ring {nu}-source is that it can be extended to the possibility of a future high-energy muon collider. The neutrino source provides a useful physics device that initiates key technologies required for future {mu}{sup +}-{mu}{sup {minus}} Colliders, but with much less demanding parameter requirements. These technologies include high-intensity {mu}-production, {mu}-capture, {mu}-cooling, {mu}-acceleration and multiturn {mu} storage rings. {mu}{sup +}-{mu}{sup {minus}} colliders require a similar number of muons, but they require that the muons be cooled to a much smaller phase space and formed into a small number of bunches, and both positive and negative bunches must be simultaneously captured. These differences are discussed, and the extension of the {nu}-source to {mu}{sup +}-{mu}{sup {minus}} collider specifications is described.
Date: December 21, 2000
Creator: Neuffer, David
System: The UNT Digital Library
Dijet production by double pomeron exchange at the Tevatron (open access)

Dijet production by double pomeron exchange at the Tevatron

The authors report the observation of dijet events with a Double Pomeron Exchange topology produced in {bar p}p collisions at {radical}s = 1,800 GeV. The events are characterized by a leading antiproton, two jets in the central pseudorapidity region, and a rapidity gap on the outgoing proton side. Results on kinematics, production rates, and comparisons with corresponding results from single diffractive and inclusive dijet production are presented.
Date: December 21, 2000
Creator: Terashi, Koji
System: The UNT Digital Library
Search for second and third generation leptoquarks at CDF (open access)

Search for second and third generation leptoquarks at CDF

The authors report the results of a search for second and third generation leptoquarks using 88 pb{sup {minus}1} of data recorded by the Collider Detector at Fermilab. Color triplet technipions, which play the role of scalar leptoquarks, are investigated due to their potential production in decays of strongly coupled color octet technirhos. Events with a signature of two heavy flavor jets and missing energy may indicate the decay of a second (third) generation leptoquark to a charm (bottom) quark and a neutrino. As the data is found to be consistent with Standard Model expectations, mass limits are determined.
Date: December 21, 2000
Creator: Haas, Richard
System: The UNT Digital Library
Collectivity of the ''Three-Phonon'' Region in {sup 100}Ru (open access)

Collectivity of the ''Three-Phonon'' Region in {sup 100}Ru

We have studied the quadrupole degree of freedom in a typical vibrational nucleus, {sup 100}Ru. From inelastic neutron scattering at the Van de Graaff accelerator of the University of Kentucky, lifetimes of states in {sup 100}Ru were determined. Absolute transition rates or limits thereon were extracted and compared to the theoretical description of this nucleus.
Date: December 21, 1999
Creator: Genilloud, L.; Brown, T.B.; Corminboeuf, G & Garrett, P.
System: The UNT Digital Library
Double-Diffusive Finger Convection: Flow Field Evolution in a Hele-Shaw Cell (open access)

Double-Diffusive Finger Convection: Flow Field Evolution in a Hele-Shaw Cell

Double-diffusive finger convection is a hydrodynamic instability that can occur when two components with different diffusivities are oppositely stratified with respect to the fluid density gradient as a critical condition is exceeded. Laboratory experiments were designed using sodium chloride and sucrose solutions in a Hele-Shaw cell. A high resolution, full field, light transmission technique was used to study the development of the instability. The initial buoyancy ratio (R{sub p}), which is a ratio of fluid density contributions by the two solutes, was varied systematically in the experiments so that the range of parameter space spanned conditions that were nearly stable (R{sub p} = 2.8) to those that were moderately unstable (R{sub p} = 1.4). In systems of low R{sub p}, fingers develop within several minutes, merge with adjacent fingers, form conduits, and stall before newer-generated fingers travel through the conduits and continue the process. Solute fluxes in low R{sub p} systems quickly reach steady state and are on the order of 10{sup {minus}6} m{sup 2} sec{sup {minus}1}. In the higher R{sub p} experiments, fingers are slower to evolve and do not interact as dynamically as in the lower R{sub p} systems. Our experiment with initial R{sub p} = 2.8 exhibited …
Date: December 21, 2000
Creator: Cooper, Clay A.; Glass, Robert J., Jr. & Tyler, Scott W.
System: The UNT Digital Library
Chemical Solution Processing of Strontium Bismuth Tantalate Films (open access)

Chemical Solution Processing of Strontium Bismuth Tantalate Films

We describe Chemical Solution Deposition (CSD) processes by which Strontium Bismuth Tantalate (SBT) thin films can be prepared at temperatures as low as 550 C. In this paper, we will present strategies used to optimize the properties of the films including solution chemistry, film composition, the nature of the substrate (or bottom electrode) used, and the thermal processing cycle. Under suitable conditions, {approximately} 1700 {angstrom} films can be prepared which have a large switchable polarization (2P{sub r} > 10{micro}C/cm{sup 2}), and an operating voltage, defined as the voltage at which 0.80 x 2P{sub r} max is switched, 2.0V. We also describe an all-alkoxide route to SBT films from which SBT can be crystallized at 550 C.
Date: December 21, 1998
Creator: Boyle, T.J. & Lakeman, C.D.E.
System: The UNT Digital Library
Solar Heat-Pipe Receiver Wick Modeling (open access)

Solar Heat-Pipe Receiver Wick Modeling

Stirling-cycle engines have been identified as a promising technology for the conversion of concentrated solar energy into usable electrical power. In previous experimented work, we have demonstrated that a heat pipe receiver can significantly improve system performance-over a directly-illuminated heater head. The design and operating conditions of a heat pipe receiver differ significantly from typical laboratory heat pipes. New wick structures have been developed to exploit the characteristics of the solar generation system. Typically, these wick structures allow vapor generation within the wick. Conventional heat pipe models do not handle this enhancement yet it can more than double the performance of the wick. In this study, I develop a steady-state model of a boiling-enhanced wick for a solar heat pipe receiver. The model is used for design-point calculations and is written in FORTRAN90. Some limited comparisons have been made with actual test data.
Date: December 21, 1998
Creator: Andraka, C. E.
System: The UNT Digital Library
High-resolution electron microscopy studies of the precipitation of copper under neutron irradiation in an Fe-1.3WT % Cu alloy. (open access)

High-resolution electron microscopy studies of the precipitation of copper under neutron irradiation in an Fe-1.3WT % Cu alloy.

We have studied by electron microscopy the copper-rich precipitates in an Fe-1.3wt%Cu model alloy irradiated with neutrons to doses of 8.61 x 10{sup {minus}3} dpa and 6.3 x 10{sup {minus}2} dpa at a temperature of {approximately}270 C. In the lower dose material a majority (ca. 60%)of the precipitates visible in high-resolution electron microscopy were timed 9R precipitates of size {approximately}2-4 nm, while ca. 40% were untwinned. In the higher dose material, a majority (ca. 75%) of visible precipitates were untwinned although many still seemed to have a 9R structure. The average angle {alpha} between the herring-bone fringes in the twin variants was measured as 125{degree}, not the 129{degree} characteristic of precipitates in thermally-aged and electron-irradiated material immediately after the bcc{r_arrow}9R martensitic transformation. We argue that these results imply that the bcc{r_arrow}9R transformation of small (<4 nm) precipitates under neutron irradiation takes place at the irradiation temperature of 270 C rather than after subsequent cooling. Preliminary measurements showed that precipitate sizes did not depend strongly on dose, with a mean diameter of 3.4 {+-} 0.7 nm for the lower dose material, and 3.0 {+-} 0.5 nm for the higher dose material. This result agrees with the previous assumption that the lack …
Date: December 21, 1998
Creator: Nicol, A. C.
System: The UNT Digital Library
Geotechnical Issues in Total System Performance Assessments of Yucca Mountain (open access)

Geotechnical Issues in Total System Performance Assessments of Yucca Mountain

A Total System Performance Assessment (TSPA) of Yucca Mountain consists of integrated sub-models and analyses of natural and engineered systems. Examples of subsystem models include unsaturated-zone flow and transport, seepage into drifts, coupled thermal hydrologic processes, transport through the engineered barrier system, and saturated-zone flow and transport. The TSPA evaluates the interaction of important processes among these subsystems, and it determines the impact of these processes on the overall performance measures (e.g., dose rate to humans). This paper summarizes the evaluation, abstraction, and combination of these subsystem models in a TSPA calculation, and it provides background on the individual TSPA subsystem components that are most directly impacted by geotechnical issues. The potential impact that geologic features, events, and processes have on the overall performance is presented, and an evaluation of the sensitivity of TSPA calculations to these issues is also provided.
Date: December 21, 1999
Creator: HO,CLIFFORD K.; HOUSEWORTH,JIM & WILSON,MICHAEL L.
System: The UNT Digital Library
Properties and orientation of antiferroelectric lead zirconate thin films grown by MOCVD. (open access)

Properties and orientation of antiferroelectric lead zirconate thin films grown by MOCVD.

Single-phase polycrystalline PbZrO{sub 3} (PZ) thin films, 3000-6000 {angstrom} thick, have been grown by metal-organic chemical vapor deposition (MOCVD) on (111)Pt/Ti/SiO{sub 2}/Si substrates at {approximately}525 C. X-ray diffraction analysis indicated that the PZ films grown on (111)Pt/Ti/SiO{sub 2}/Si (Pt/Ti/Si) showed preferred pseudocubic (110) orientation. In contrast, PZ films grown on 150 {angstrom} thick PbTiO{sub 3} (PT) template layers exhibited a pseudocubic (100) preferred orientation, and PZ films deposited on TiO{sub 2} template layers consisted of randomly oriented grains. The PZ films grown on Pt/Ti/Si with or without templates exhibited dielectric constants of 120-200 and loss tangents of 0.03-0.01. The PZ films with (110) orientation exhibited an electric-field-induced transformation from the antiferroelectric phase to the ferroelectric phase with a polarization of {approx}34 {micro}C/cm{sup 2}, and the energy that was stored during switching was 7.1 J/cm{sup 3}. The field needed to excite the ferroelectric state and that needed to revert to the antiferroelectric state were 350 and 250 kV/cm, respectively. Relationships between the MOCVD processing and the film microstructure and properties are discussed.
Date: December 21, 1998
Creator: Chen, N.
System: The UNT Digital Library
Fate of neptunium in an anaerobic, methanogenic microcosm. (open access)

Fate of neptunium in an anaerobic, methanogenic microcosm.

Neptunium is found predominantly as Np(IV) in reducing environments, but Np(V) in aerobic environments. However, currently it is not known how the interplay between biotic and abiotic processes affects Np redox speciation in the environment. In order to evaluate the effect of anaerobic microbial activity on the fate of Np in natural systems, Np(V) was added to a microcosminoculated with anaerobic sediments from a metal-contaminated fresh water lake. The consortium included metal-reducing, sulfate-reducing, and methanogenic microorganisms, and acetate was supplied as the only exogenous substrate. Addition of more than 10{sup {minus}5} M Np did not inhibit methane production. Total Np volubility in the active microcosm, as well as in sterilized control samples, decreased by nearly two orders of magnitude. A combination of analytical techniques, including VIS-NIR absorption spectroscopy and XANES, identified Np(IV) as the oxidation state associated with the sediments. The similar results from the active microcosm and the abiotic controls suggest that microbian y produced Mn(II/HI) and Fe(II) may serve as electron donors for Np reduction.
Date: December 21, 1998
Creator: Banaszak, J. E.
System: The UNT Digital Library
Incorporation of radionuclides from the electrometallurgical treatment of spent fuel into a ceramic waste form. (open access)

Incorporation of radionuclides from the electrometallurgical treatment of spent fuel into a ceramic waste form.

An electrometallurgical process is being developed at Argonne National Laboratory to treat spent metallic nuclear fuel. In this process, the spent nuclear fuel is electrorefined in a molten salt to separate uranium from the other constituents of the fuel. The treatment process generates a contaminated chloride salt that is incorporated into a ceramic waste form. The ceramic waste form, a composite of socialite and glass, contains the fission products (rare earths, alkalis, alkaline earth metals, and halides) and transuranic radionuclides that accumulated in the electrorefiner salt. These radionuclides are incorporated into zeolite A, which can fully accommodate the salt in its crystal structure. The radionuclides are incorporated into the zeolite by high-temperature blending or by ion exchange. In the blending process the salt and zeolite are simply tumbled together at >450 C (723 K), but in the ion exchange process, which yields a product more highly concentrated in fission products, the molten salt is passed through a bed of the zeolite. In either case, the salt-loaded zeolite A is mixed with glass frit and hot isostatically pressed to produce a monolithic leach resistant waste form. Zeolite is converted to sodalite during hot pressing. This paper presents experimental results on the …
Date: December 21, 1998
Creator: Pereira, C.
System: The UNT Digital Library
Search for SUSY with missing E{sub T} and jets at CDF (open access)

Search for SUSY with missing E{sub T} and jets at CDF

Events with signatures involving large missing transverse energy (E{sub T}) are among the quintessential search modes for R-parity conserving supersymmetry. CDF has conducted two recent analyses for supersymmetry which use E{sub T} and jets. The E{sub T} and monojet signature is employed to determine process independent limits for the production of new physics beyond the Standard Model and then applied to models of spontaneous breaking of supersymmetry to determine limits on the supersymmetry breaking parameter and the gravitino mass. Direct searches for scalar top and scalar bottom quarks within the framework of supersymmetric models are performed using a signature of E{sub T} and two heavy flavor jets. Since the data is found to be consistent with Standard Model expectations, limits are determined in the mass planes m({tilde {chi}}{sub 1}{sup 0})-m({tilde t}{sub 1}) and m({tilde {chi}}{sub 1}){sup 0}-m({tilde b}{sub 1}).
Date: December 21, 2000
Creator: CDF, Search for SUSY with Missing ET and Jets at
System: The UNT Digital Library
Ba{sub 1{minus}x}Sr{sub x}TiO{sub 3} thin film sputter-growth processes and electrical property relationships for high frequency devices (open access)

Ba{sub 1{minus}x}Sr{sub x}TiO{sub 3} thin film sputter-growth processes and electrical property relationships for high frequency devices

Precise control of Ba{sub 1{minus}x}Sr{sub x}Ti0{sub 3} (BST) film composition is critical for the production of high-quality BST thin films. Specifically, it is known that nonstoichiometry greatly affects the electrical properties of BST film capacitors. The authors are investigating the composition-microstructure-electrical property relationships of polycrystalline BST films produced by magnetron sputter-deposition using a single target with a Ba/Sr ratio of 50/50 and a (Ba+Sr)/Ti ratio of 1.0. It was determined that the (Ba+Sr)/Ti ratios of these BST films could be adjusted from 0.73 to 0.98 by changing the total (Ar+O{sub 2}) process pressure, while the O{sub 2}/Ar ratio did not strongly affect the metal ion composition. The crystalline quality as well as the measured dielectric constant, dielectric tunability, and electrical breakdown voltage of BST films have been found to be strongly dependent on the composition of the BST films, especially the (Ba+Sr)/Ti ratio. The authors discuss the impact of BST film composition control, through film deposition and process parameters, on the electrical properties of BST capacitors for high frequency devices.
Date: December 21, 1999
Creator: Im, J.; Auciello, O.; Streiffer, S. K.; Baumann, P. K.; Eastman, J. A.; Kaufman, D. Y. et al.
System: The UNT Digital Library
Disorder-driven nonequilibrium melting studied by electron diffraction, brillouis scattering, and molecular dynamics (open access)

Disorder-driven nonequilibrium melting studied by electron diffraction, brillouis scattering, and molecular dynamics

In the present paper, a brief overview of the electron diffraction, Brillouin scattering and molecular dynamics studies of radiation-induced amorphization of ordered intermetallic compounds is presented. In these studies, measured changes in the velocity of surface acoustic phonons, lattice constant, and the Bragg-Williams long-range order parameter induced by irradiation were compared with the results of computer simulations of defect-induced amorphization. The results indicate that progressive chemical disordering of the superlattice structure during irradiation is accompanied by an expansion of the lattice and a large change in sound velocity corresponding to a {approximately} 50% decrease in the average shear modulus. The onset of amorphization occurs when the average shear modulus of the crystalline compound becomes equal to that of the amorphous phase. This elastic softening criterion for the onset of amorphization and the dependence of the average shear modulus on the long-range-order parameter are in excellent agreement with molecular dynamics simulations. Both the experimental observations and computer simulations confirm the predictions of the generalized Lindemann melting criterion which stipulates that thermodynamic melting of a defective crystal occurs when the sum of the dynamic and static mean-square atomic displacements reaches a critical value identical to that for melting of the defect-free crystal. …
Date: December 21, 1999
Creator: Okamoto, P. R.; Lam, N. Q. & Grimsditch, M.
System: The UNT Digital Library
Synchronization of multiple coupled rf-SQUID flux qubits (open access)

Synchronization of multiple coupled rf-SQUID flux qubits

Article demonstrating a practical strategy for synchronizing the properties of compound Josephson junction (CJJ) radio frequency monitored superconducting quantum interference device (rf-SQUID) qubits on a multi-qubit chip.
Date: December 21, 2009
Creator: Harris, R.; Brito, F.; Berkley, A. J.; Johansson, J.; Johnson, M. W.; Lanting, T. et al.
System: The UNT Digital Library
Averages of B-Hadron, C-Hadron, and Tau-Lepton Properties as of Early 2012 (open access)

Averages of B-Hadron, C-Hadron, and Tau-Lepton Properties as of Early 2012

This report talks about Averages of B-Hadron, C-Hadron, and Tau-Lepton Properties as of Early 2012
Date: December 21, 2012
Creator: Amhis, Y.; /LPHE, Lausanne; Banerjee, Sw.; U., /Victoria; Bernhard, R.; U., /Freiburg et al.
System: The UNT Digital Library
Molecular signatures in the progression of COVID-19 severity (open access)

Molecular signatures in the progression of COVID-19 severity

Authors of the article discuss that to uncover genes and pathways involved in the differential clinical manifestations of COVID-19 they developed a novel gene co-expression network-based pipeline that uses gene expression obtained from different SARS-CoV-2 infected human tissues. Their study shines a new light on genes and their networks (modules) that drive the progression of COVID-19 from moderate to extremely severe condition, which could aid development of new therapeutics to combat COVID-19.
Date: December 21, 2022
Creator: De, Ronika & Azad, Rajeev K.
System: The UNT Digital Library
Highly Unstable Double-Diffusive Finger Convection in a Hele-Shaw Cell: Baseline Experimental Data for Evaluation of Numerical Models (open access)

Highly Unstable Double-Diffusive Finger Convection in a Hele-Shaw Cell: Baseline Experimental Data for Evaluation of Numerical Models

An experimental investigation was conducted to study double-diffusive finger convection in a Hele-Shaw cell by layering a sucrose solution over a more-dense sodium chloride (NaCl) solution. The solutal Rayleigh numbers were on the order of 60,000, based upon the height of the cell (25 cm), and the buoyancy ratio was 1.2. A full-field light transmission technique was used to measure a dye tracer dissolved in the NaCl solution. They analyze the concentration fields to yield the temporal evolution of length scales associated with the vertical and horizontal finger structure as well as the mass flux. These measures show a rapid progression through two early stages to a mature stage and finally a rundown period where mass flux decays rapidly. The data are useful for the development and evaluation of numerical simulators designed to model diffusion and convection of multiple components in porous media. The results are useful for correct formulation at both the process scale (the scale of the experiment) and effective scale (where the lab-scale processes are averaged-up to produce averaged parameters). A fundamental understanding of the fine-scale dynamics of double-diffusive finger convection is necessary in order to successfully parameterize large-scale systems.
Date: December 21, 2000
Creator: Pringle, Scott E.; Cooper, Clay A. & Glass, Robert J., Jr.
System: The UNT Digital Library
Application of a General Computer Algorithm Based on the Group-Additivity Method for the Calculation of Two Molecular Descriptors at Both Ends of Dilution: Liquid Viscosity and Activity Coefficient in Water at Infinite Dilution (open access)

Application of a General Computer Algorithm Based on the Group-Additivity Method for the Calculation of Two Molecular Descriptors at Both Ends of Dilution: Liquid Viscosity and Activity Coefficient in Water at Infinite Dilution

This paper presents the application of a commonly used computer algorithm based on the group-additivity method for the calculation of the liquid viscosity coefficient at 293.15 K and the activity coefficient at infinite dilution in water at 298.15 K or organic molecules.
Date: December 10, 2017
Creator: Naef, Rudolf & Acree, William E. (William Eugene)
System: The UNT Digital Library