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Characterization of the sorption of gaseous and organic solutes onto polydimethyl siloxane solid-phase microextraction surfaces using the Abraham model

Description: Article on the characterization of the sorption of gaseous and organic solutes onto polydimethyl siloxane solid-phase microextraction surfaces using the Abraham model.
Date: December 21, 2007
Creator: Sprunger, Laura M.; Proctor, Amy; Acree, William E. (William Eugene) & Abraham, M. H. (Michael H.)
Partner: UNT College of Arts and Sciences

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

Description: 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 fission product uptake of the zeolite as a function of time and salt composition.
Date: December 21, 1998
Creator: Pereira, C.
Partner: UNT Libraries Government Documents Department

Fate of neptunium in an anaerobic, methanogenic microcosm.

Description: 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.
Partner: UNT Libraries Government Documents Department

Geotechnical Issues in Total System Performance Assessments of Yucca Mountain

Description: 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.
Partner: UNT Libraries Government Documents Department

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

Description: 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 of coarsening in precipitates formed under neutron irradiation is a consequence of the partial dissolution of larger precipitates by high-energy cascades.
Date: December 21, 1998
Creator: Nicol, A. C.
Partner: UNT Libraries Government Documents Department

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

Description: 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.
Partner: UNT Libraries Government Documents Department

Pressure Induced Phase Transformation of Pb(Zr(0.95)Ti(0.05))O(3) Based Ceramics: Grain Size Dependence

Description: A substantial decrease in hydrostatic ferroelectric (FE) to antiferroelectric (AFE) transformation pressure was measured for Pb(Zr{sub 0.949}Ti{sub 0.051}){sub 0.989}Nb{sub 0.0182}O{sub 3} ceramics with decreasing grain size. The 150 MPa decrease in hydrostatic FE to AFE transformation pressure over the grain size range of 8.5 {micro}m to 0.7{micro}m was shown to be consistent with enhanced internal stress with decreasing grain size. Further, the Curie Point decreased and the dielectric constant measured at 25 C increased with decreasing grain size. All three properties: dielectric constant magnitude, Curie point shift and FE to AFE phase transformation pressure were shown to be semi-quantitatively consistent with internal stress differences on the order of 100 MPa. Calculations of Curie point shifts from the Clausius-Clapeyron equation, using internal stress levels derived from the hydrostatic depoling characteristics, were consistent with measured values.
Date: December 21, 1999
Creator: TUTTLE,BRUCE A.; VOIGT,JAMES A.; SCOFIELD,TIMOTHY W.; ASELAGE,TERRENCE L.; RODRIGUEZ,MARK A.; YANG,PIN et al.
Partner: UNT Libraries Government Documents Department

Monte Carlo Simulations of Phosphate Polyhedron Connectivity in Glasses

Description: Monte Carlo simulations of phosphate tetrahedron connectivity distributions in alkali and alkaline earth phosphate glasses are reported. By utilizing a discrete bond model, the distribution of next-nearest neighbor connectivities between phosphate polyhedron for random, alternating and clustering bonding scenarios was evaluated as a function of the relative bond energy difference. The simulated distributions are compared to experimentally observed connectivities reported for solid-state two-dimensional exchange and double-quantum NMR experiments of phosphate glasses. These Monte Carlo simulations demonstrate that the polyhedron connectivity is best described by a random distribution in lithium phosphate and calcium phosphate glasses.
Date: December 21, 1999
Creator: ALAM,TODD M.
Partner: UNT Libraries Government Documents Department

Development of integrated mechanistically-based degradation-mode models for performance assessment of high-level waste containers

Description: Alloy 22 [UNS NO60221] is now being considered for construction of high level waste containers to be emplaced at Yucca Mountain and elsewhere. In essence, this alloy is 20.0-22.5% Cr, 12.5-14.5% MO, 2.0-6.0% Fe, 2.5-3.5% W, with the balance being Ni. Other impurity elements include P, Si, S, Mn, Co and V. Cobalt may be present at a maximum concentration of 2.5%. Detailed mechanistic models have been developed to account for the corrosion of Alloy 22 surfaces in crevices that will inevitably form. Such occluded areas experience substantial decreases in pH, with corresponding elevations in chloride concentration. Experimental work has been undertaken to validate the crevice corrosion model, including parallel studies with 304 stainless steel.
Date: December 21, 1998
Creator: Estill, J C; Farmer, J C; Gordon, S R & McCright, R D
Partner: UNT Libraries Government Documents Department

Chemical Solution Processing of Strontium Bismuth Tantalate Films

Description: 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.
Partner: UNT Libraries Government Documents Department

Defining Requirements for Improved Photovoltaic System Reliability

Description: Reliable systems are an essential ingredient of any technology progressing toward commercial maturity and large-scale deployment. This paper defines reliability as meeting system fictional requirements, and then develops a framework to understand and quantify photovoltaic system reliability based on initial and ongoing costs and system value. The core elements necessary to achieve reliable PV systems are reviewed. These include appropriate system design, satisfactory component reliability, and proper installation and servicing. Reliability status, key issues, and present needs in system reliability are summarized for four application sectors.
Date: December 21, 1998
Creator: Maish, A.B.
Partner: UNT Libraries Government Documents Department

Precision measurements at a muon collider

Description: We discuss the potential for making precision measurements of M{sub W} and M{sub T} at a muon collider and the motivations for each measurement. A comparison is made with the precision measurements expected at other facilities. The measurement of the top quark decay width is also discussed.
Date: December 21, 1995
Creator: Dawson, S.
Partner: UNT Libraries Government Documents Department

Testing and Development of a 30-kVA Hybrid Inverter: Lessons Learned and Reliability Implications

Description: A 30-kVA Trace Technologies hybrid power processor was specified and tested at the Sandia inverter test facility. Trace Technologies involving the control system, in response to suggestions made modifications, primarily by Sandia and Arizona Public Service (APS) personnel. The modifications should make the inverter more universally applicable and less site-specific so that it can be applied in various sites with minimal field interaction required from the design engineer. The project emphasized the importance of battery management, generator selection, and site load management to the performance and reliability of hybrid power systems.
Date: December 21, 1998
Creator: Ginn, J.W.
Partner: UNT Libraries Government Documents Department

Solar Heat-Pipe Receiver Wick Modeling

Description: 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.
Partner: UNT Libraries Government Documents Department

Safe venting of ``red oil`` runaway reactions

Description: Calorimetry testing of Tri-n-butyl phosphate (TBP) saturated with strong nitric acid was performed to determine the relationship between vent size and pressure buildup in the event of a runaway reaction. These experiments show that runaway can occur in an open system, but that even when runaway is induced in the TBP/HN0{sub 3} system, dangerous pressure buildup will be prevented with practical vent size.
Date: December 21, 1994
Creator: Paddleford, D.F. & Fauske, H.K.
Partner: UNT Libraries Government Documents Department

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

Description: 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.
Partner: UNT Libraries Government Documents Department

Neutron transfer kernels in the resonance domain in the harmonic crystal model.

Description: To describe neutron scattering the resonance domain of the nuclear fuel isotopes, the static model is widely in use in nuclear data processing codes. With this model the influence of chemical binding on the transfer cross section is not taken into account since the nucleus is considered to be in rest and isolated in the laboratory system. Further, the application of the free gas model to the resonant scattering of neutrons shows that the up-scattering probability is strongly dependent on the incident neutron energy. If the latter is smaller than the resonance energy then the free gas model predicts an enormous chance for the neutron to gain energy after collision. Neither the static nor free gas model is adequate to describe the resonant scattering of neutrons in a crystal. This fact can induce non-negligible errors in reactor calculations and, in particular, in the estimation of the Doppler coefficient. In the present paper the author proposes the theoretical study of the possibility to estimate the neutron transfer cross sections in the harmonic crystal approximation.
Date: December 21, 1999
Creator: Naberejnev, D. G.
Partner: UNT Libraries Government Documents Department

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

Description: 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. In this broader view of melting, the crystal-to-glass transformation is a disorder-driven nonequilibrium melting process occurring at temperatures below the Kauzmann isentropic glass-transition temperature.
Date: December 21, 1999
Creator: Okamoto, P. R.; Lam, N. Q. & Grimsditch, M.
Partner: UNT Libraries Government Documents Department

Long-term operating experience for the ATLAS superconducting resonators

Description: Portions of the ATLAS accelerator have been operating now for over 21 years. The facility has accumulated several million resonator-hours of operation at this point and has demonstrated the long-term reliability of RF superconductivity. The overall operating performance of the ATLAS facility has established a level of beam quality, flexibility, and reliability not previously achieved with heavy-ion accelerator facilities. The actual operating experience and maintenance history of ATLAS are presented for ATLAS resonators and associated electronics systems. Solutions to problems that appeared in early operation as well as current problems needing further development are discussed.
Date: December 21, 1999
Creator: Pardo, R. & Zinkann, G.
Partner: UNT Libraries Government Documents Department

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

Description: 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.
Partner: UNT Libraries Government Documents Department

Spatial Bias in Field-Estimated Unsaturated Hydraulic Properties

Description: 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 in parameter space. False cross-correlation between estimated parameters is created because estimates of K{sub s} also depend on estimates of {alpha} and both parameters are estimated from the same data.
Date: December 21, 2000
Creator: HOLT,ROBERT M.; WILSON,JOHN L. & GLASS JR.,ROBERT J.
Partner: UNT Libraries Government Documents Department