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619 Matching Results
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Order and disorder in the local and long-range structure of the spin-glass pyrochlore, Tb{sub 2}Mo{sub 2}O{sub 7}
To understand the origin of the spin-glass state in molybdate pyrochlores, the structure of Tb{sub 2}Mo{sub 2}O{sub 7} is investigated using two techniques: the long-range lattice structure was measured using neutron powder diffraction (NPD), and local structure information was obtained from the extended x-ray absorption fine structure (EXAFS) technique. While the long-range structure appears generally well ordered, enhanced mean-squared site displacements on the O(1) site and the lack of temperature dependence of the strongly anisotropic displacement parameters for both the Mo and O(1) sites indicate some disorder exists. Likewise, the local structure measurements indicate some Mo-Mo and Tb-O(1) nearest-neighbor disorder exists, similar to that found in the related spin-glass pyrochlore, Y{sub 2}Mo{sub 2}O{sub 7}. Although the freezing temperature in Tb{sub 2}Mo{sub 2}O{sub 7}, 25 K, is slightly higher than in Y{sub 2}Mo{sub 2}O{sub 7}, 22 K, the degree of local pair distance disorder is actually less in Tb{sub 2}Mo{sub 2}O{sub 7}. This apparent contradiction is considered in light of the interactions involved in the freezing process.
Date:
February 11, 2011
Creator:
Jiang, Yu; Huq, Ashfia; Booth, Corwin H.; Ehlers, Georg; Greedan, John E. & Gardner, Jason S.
Object Type:
Article
System:
The UNT Digital Library
SUPERIMPOSED MESH PLOTTING IN MCNP
The capability to plot superimposed meshes has been added to MCNP{trademark}. MCNP4C featured a superimposed mesh weight window generator which enabled users to set up geometries without having to subdivide geometric cells for variance reduction. The variance reduction was performed with weight windows on a rectangular or cylindrical mesh superimposed over the physical geometry. Experience with the new capability was favorable but also indicated that a number of enhancements would be very beneficial, particularly a means of visualizing the mesh and its values. The mathematics for plotting the mesh and its values is described here along with a description of other upgrades.
Date:
February 1, 2001
Creator:
HENDRICKS, J.
Object Type:
Article
System:
The UNT Digital Library
Performance of a tapered pulse tube
In a well instrumented pulse tube refrigerator having 1,500 W of cooling power at 125 K, the authors have measured the figure of merit of a tapered pulse tube at several operating points. At operating points near the operating point for which the taper was designed, the figure of merit is 0.96. This is close to the theoretical optimum figure of merit 0.97 calculated for this pulse tube considering only two loss mechanisms: heat conduction in the metal pulse tube wall and ordinary thermoacoustic heat transport in the gas within a few thermal penetration depths of the wall. At operating points farther from the design operating point, the measured figure of merit is much lower, as streaming driven convection adds a third loss mechanism.
Date:
February 1, 1998
Creator:
Swift, G.; Allen, M. & Woolan, J.J.
Object Type:
Article
System:
The UNT Digital Library
Runoff and erosion from a rapidly eroding pinyon-juniper hillslope
The dramatic acceleration of erosion associated with the expansion of pinyon-juniper woodlands over the past 100 years has been a widely recognized but poorly understood phenomenon. A more complete understanding will come only through long-term observations of erosion and related factors. To this end, we are conducting a study of a small (1-ha) catchment in a rapidly eroding pinyon-juniper woodland. Since July 1993, we have been collecting data on runoff, erosion, and weather conditions in the catchment, as well as on the topography, soils, and vegetation. Our preliminary results suggest that (1) the catchment is currently in a cycle of accelerated erosion that began concomitant with a shift from ponderosa pine forest to pinyon-juniper woodland that was initiated by a prolonged drought; (2) the intercanopy soils cannot be sustained at the current erosion rates and will be mostly stripped away in about a century; (3) large summer thunderstorms are the most important agents of erosion (4) erosion increases dramatically as the scale increases; (5) runoff makes up <10% of the water budget.
Date:
February 1, 1996
Creator:
Wilcox, B.P.; Davenport, D. W.; Pitlick, J. & Allen, C.D.
Object Type:
Article
System:
The UNT Digital Library
Magnetic field dependence of resistivity minima in amorphous La--Gd--Au alloys with high Gd content. [(La/sub 100-x/Gd/sub x/)/sub 80/Au/sub 20/, x = 8 to 40]
Magnetoresistivity measurements are performed in fields up to 40 kOe on some concentrated amorphous La--Gd--Au alloys exhibiting characteristics of a spin-glass. The negative magnetoresistivity at low temperature is found to be roughly proportional to the square of the magnetization. The resistivity minima in these alloys are attributed to a mechanism of electron scattering from magnetic clouds coupled by the RKKY interactions, in qualitative agreement with analysis of remanent magnetization data. 4 figures, 1 table.
Date:
February 1, 1977
Creator:
Poon, S. J.; Durand, J. & Yung, M.
Object Type:
Report
System:
The UNT Digital Library
Gyrokinetic particle simulation of neoclassical transport
A time varying weighting ({delta} f) scheme for gyrokinetic particle simulation is applied to a steady state, multi-species simulation of neoclassical transport. Accurate collision operators conserving momentum and energy are developed and implemented. Simulation results using these operators are found to agree very well with neoclassical theory. For example, it is dynamically demonstrated in these multispecies simulations that like-particle collisions produce no particle flux and that the neoclassical fluxes are ambipolar for an ion-electron plasma. An important physics feature of the present scheme is the introduction of toroidal sheared flow to the simulations. Simulation results are in agreement with the existing analytical neoclassical theory of Hinton and Wong. The poloidal electric field associated with toroidal mass flow is found to enhance density gradient driven electron particle flux and the bootstrap current while reducing temperature gradient driven flux and current. Finally, neoclassical theory in steep gradient profile relevant to the edge regime is examined by taking into account finite banana width effects. In general, the present work demonstrates a valuable new capability for studying important aspects of neoclassical transport inaccessible by conventional analytical calculation processes.
Date:
February 1, 1995
Creator:
Lin, Z.; Tang, W. M. & Lee, W. W.
Object Type:
Report
System:
The UNT Digital Library
Hopple for Horses.
Patent for a new and improved hopple for horses. This design "consists in the combination of two curved or bent pieces which are to go around the horses ankles . . . [each with] three links and a ring . . . allow[ing] the horse to walk slowly about, permitting [it] to graze at leisure, and enabling [it] to be easily caught when desired" (lines 14-34).
Date:
February 12, 1884
Creator:
Cottle, Julius O. & Ivie, Rufus
Object Type:
Patent
System:
The Portal to Texas History
Beam profiles from multiple aperture sources
Using a rapidly convergent approximation scheme, formulas are given for beam intensity profiles everywhere. In the first approximation, formulas are found for multiple aperture sources, such as a TFTR design, and integrated power for rectangular plates downstream for Gaussian beamlets. This analysis is duplicated for Lorentzian beamlets which should provide a probable upper bound for off-axis loading as Gaussian beamlets provide a probable lower bound. Formulas for beam intensity profiles are found everywhere. In first approximation, formulas are found for downstream intensity of multiple sources and integrated power for rectangular plates.
Date:
February 1, 1979
Creator:
Whealton, J.H.
Object Type:
Report
System:
The UNT Digital Library
Quantifying the surface-subsurface biogeochemical coupling during the VERTIGO ALOHA and K2 studies
A central question addressed by the VERTIGO (VERtical Transport In the Global Ocean) study was 'What controls the efficiency of particle export between the surface and subsurface ocean'? Here, we present data from sites at ALOHA (N Central Pacific Gyre) and K2 (NW subarctic Pacific) on phytoplankton processes, and relate them via a simple planktonic foodweb model, to subsurface particle export (150-500 m). Three key factors enable quantification of the surface-subsurface coupling: a sampling design to overcome the temporal lag and spatial displacement between surface and subsurface processes; data on the size-partitioning of Net Primary Production (NPP) and subsequent transformations prior to export; estimates of the ratio of algal- to faecal-mediated vertical export flux. At ALOHA, phytoplankton were characterized by low stocks, NPP, F{sub v}/F{sub m} (N-limited), and were dominated by picoplankton. The HNLC waters at K2 were characterized by both two-fold changes in NPP and floristic shifts (high to low proportion of diatoms) between deployment 1 and 2. Prediction of export exiting the euphotic zone was based on size-partitioning of NPP, a copepod-dominated foodweb and a ratio of 0.2 (ALOHA) and 0.1 (K2) for algal:faecal particle flux. Predicted export was 20-22 mg POC m{sup -2} d{sup -1} at ALOHA …
Date:
February 25, 2008
Creator:
Boyd, P. W.; Gall, M. P.; Silver, M. W.; Bishop, J. K. B.; Coale, Susan L. & Bidigare, Robert R.
Object Type:
Article
System:
The UNT Digital Library
Status report to DOE Nuclear Data Committee
This status report includes brief reports on measurements and calculations of quantities for nuclear data applications and data for reactor safety. Separate abstracts were prepared for those items with a significant amount of data. (RWR)
Date:
February 16, 1978
Creator:
Anderson, J. D.; Browne, J. C. & Struble, G. L.
Object Type:
Report
System:
The UNT Digital Library
Observation of off-Hugoniot shocked states with ultrafast time resolution
We apply ultrafast single shot interferometry to determine the pressure and density of argon shocked from up to 7.8 GPa static initial pressure in a diamond anvil cell. This method enables the observation of thermodynamic states distinct from those observed in either single shock or isothermal compression experiments, and the observation of ultrafast dynamics in shocked materials. We also present a straightforward method for interpreting ultrafast shock wave data which determines the index of refraction at the shock front, and the particle and shock velocities for shock waves in transparent materials. Based on these methods, we observe shocked thermodynamic states between the room temperature isotherm of argon and the shock adiabat of cryogenic argon at final shock pressures up to 28 GPa.
Date:
February 23, 2010
Creator:
Armstrong, M; Crowhurst, J; Bastea, S & Zaug, J
Object Type:
Article
System:
The UNT Digital Library
A high precision model of Booster Tune Control
N/A
Date:
February 1, 2002
Creator:
Brown, K.; Vanasselt, W. & Meng, W.
Object Type:
Report
System:
The UNT Digital Library
Geologic framework and hot dry rock geothermal potential of the Castle Dome area, Yuma County, Arizona
The Castle Dome Mountains and surrounding ranges constitute a voluminous pile of silicic volcanic rocks within the Basin and Range province of southwestern Arizona. Previously reported as Cretaceous and Quaternary in age, these volcanics all are of late Oligocene to early Miocene age as indicated by five new K-Ar dates. Reconnaissance field studies indicate that the volcanic section locally has undergone large rotations that contrast with the usual structural style of the Basin and Range and resemble the thin-skinned rotational tectonics documented for earlier, mid-Tertiary extensional deformation in ranges to the north and northeast. Significant geothermal potential of the Castle Dome area is suggested by a shallow depth to the Curie isotherm and by the apparent presence of a good electrical conductor at anomalously shallow depth in the crust. Warm wells exist in the area and Shearer (1979) reported a geothermal gradient of about 70/sup 0/C/km in a dry well near the center of the gravity low. Radiogenic heat production in the silicic batholith inferred above constitutes a reasonable candidate for a shallow regional heat source.
Date:
February 1, 1981
Creator:
Gutmann, J.T.
Object Type:
Report
System:
The UNT Digital Library
Measuring Energy-Saving Retrofits: Experiences from the Texas Loanstar Program
In 1988 the Governor`s Energy Management Center of Texas received approval from the US Department of Energy to establish a $98.6 million state-wide retrofit demonstration revolving loan program to fund energy-conserving retrofits in state, public school, and local government buildings. As part of this program, a first-of-its-kind, statewide Monitoring and Analysis Program (MAP) was established to verify energy and dollar savings of the retrofits, reduce energy costs by identifying operational and maintenance improvements, improve retrofit selection in future rounds of the LoanSTAR program, and initiate a data base of energy use in institutional and commercial buildings located in Texas. This report discusses the LoanSTAR MAP with an emphasis on the process of acquiring and analyzing data to measure savings from energy conservation retrofits when budgets are a constraint. This report includes a discussion of the program structure, basic measurement techniques, data archiving and handling, data reporting and analysis, and includes selected examples from LoanSTAR agencies. A summary of the program results for the first two years of monitoring is also included.
Date:
February 1, 1996
Creator:
Haberl, J. S.; Reddy, T. A.; Claridge, D. E.; Turner, W. D.; O`Neal, D. L. & Heffington, W. M.
Object Type:
Report
System:
The UNT Digital Library
Experimental results on the two-stage, Venetian Blind, direct energy converter
Some preliminary results obtained from experiments designed to test the feasibility of the Venetian Blind, direct energy-conversion concept are discussed. A two-stage unit was built and tested and found to have an overall efficiency of 65% for an energy spread of from 330 to 1000 eV. The calculated efficiency was 69% leaving a 4% discrepancy. This discrepancy seems to result from the slight transparency in the backward direction of the ribbons of the converter. (auth)
Date:
February 1, 1974
Creator:
Moir, R. W. & Barr, W. L.
Object Type:
Report
System:
The UNT Digital Library
Final report on LDRD Project: In situ determination of composition and strain during MBE
Molecular Beam Epitaxy (MBE) of semiconductor heterostructures for advanced electronic and opto-electronic devices requires precise control of the surface composition and strain. The development of advanced in situ diagnostics for real-time monitoring and process control of strain and composition would enhance the yield, reliability and process flexibility of material grown by MBE and benefit leading-edge programs in microelectronics and photonics. The authors have developed a real-time laser-based technique to measure the evolution of stress in epitaxial films during growth by monitoring the change in the wafer curvature. Research has focused on the evolution of stress during the epitaxial growth of Si{sub x}Ge{sub 1{minus}x} alloys on Si(001) substrates. Initial studies have observed the onset and kinetics of strain relaxation during the growth of heteroepitaxial layers. The technique has also been used to measure the segregation of Ge to the surface during alloy growth with monolayer sensitivity, an order of magnitude better resolution than post-growth characterization. In addition, creation of a 2-dimensional array of parallel beams allows rapid surface profiling of the film stress that can be used to monitor process uniformity.
Date:
February 1, 1997
Creator:
Chason, E.; Floro, J.A.; Reno, J. & Klem, J.
Object Type:
Report
System:
The UNT Digital Library
Advanced research and technology, direct utilization: recovery of minerals from coal fly ash. Fossil energy program. Technical progress report, 1 October 1980-31 December 1980
The purpose of this research is to develop methods to process fly ash for the separation and use of an iron-rich fraction, for the recovery of metals, primarily Al and Ti, and for use of the process residues. Research during this report period of the HiChlor process for the extraction of alumina and titania by high-temperature chlorination of a fly ash-reductant mixture included investigation of the simulation of the reactions as a design tool, the assembly of a unit to measure reaction kinetic rates and particle specific surface areas and porosities, and the design of equipment to measure necessary chloride product separation data. A pretreatment chlorination reaction using CO and Cl/sub 2/ was found to be capable of removing 80% of the iron with only minimal alumina and silica reaction. Development of the lime-soda sinter process includes the collection of data on the phenomenon of auto-disintegration of lime-fly ash sinters. Results indicate that it is the presence of minor constituents having +5 pr +6 valence cations of a size that can enter the lattice of the calcium silicate which prevent sinter auto-disintegration.
Date:
February 1, 1981
Creator:
Burnet, G.; Weiss, S. J. & Murtha, M. J.
Object Type:
Report
System:
The UNT Digital Library
Spectral analysis of the turbulent mixing of two fluids
The authors describe a spectral approach to the investigation of fluid instability, generalized turbulence, and the interpenetration of fluids across an interface. The technique also applies to a single fluid with large variations in density. Departures of fluctuating velocity components from the local mean are far subsonic, but the mean Mach number can be large. Validity of the description is demonstrated by comparisons with experiments on turbulent mixing due to the late stages of Rayleigh-Taylor instability, when the dynamics become approximately self-similar in response to a constant body force. Generic forms for anisotropic spectral structure are described and used as a basis for deriving spectrally integrated moment equations that can be incorporated into computer codes for scientific and engineering analyses.
Date:
February 1996
Creator:
Steinkamp, M. J.
Object Type:
Report
System:
The UNT Digital Library
Evidence of Transformation Bursts During Thermal Cycling of a Pu-Ga Alloy
The thermodynamics and kinetics of the fcc (delta) to monoclinic (alpha-prime) phase transformation and its reversion in a plutonium-gallium alloy have been studied using differential scanning calorimetry, resistometry, and dilatometry. Under ambient conditions, the delta phase is metastable in a Pu-2.0 at% Ga alloy. Thermal cycling to below the ambient temperature results in a partial transformation to the alpha-prime phase; this transformation is composition-invariant and exhibits martensitic behavior. Because this transformation results in an unusually invariant large 25% volume contraction that cannot be fully accommodated by purely elastic adjustments, the transformation mode is expected to involve burst formation of individual alpha-prime particles. However, upon cooling, these individual bursts were not resolved by the above techniques, although signals corresponding to the overall accumulation of many alpha-prime particles were observed. On the other hand, upon heating, signals from differential scanning calorimetry, resistometry, and dilatometry showed a series of discrete changes occurring in periodic increments beginning at approximately 32 C. These features correspond to the cooperative reversion of many alpha-prime particles to the delta phase; they appear to be the result of an interplay between the autocatalytically driven reversion of a cascade of individual martensite units, and self-quenching caused by small changes of …
Date:
February 9, 2005
Creator:
Blobaum, K M; Krenn, C R; Mitchell, J N; Haslam, J J; Wall, M A; Massalski, T B et al.
Object Type:
Article
System:
The UNT Digital Library
Inhalation developmental toxicology studies: Teratology study of methyl ethyl ketone in mice: Final report
Methyl ethyl ketone (MEK) is a widely used industrial solvent which results in considerable human exposure. In order to assess the potential for MEK to cause developmental toxicity in rodents, four groups of Swiss (CD-1) mice were exposed to 0, 400, 1000 or 3000 ppM MEK vapors, 7 h/day, 7 dy/wk. Ten virgin females and approx.30 plug-positive females per group were exposed concurrently for 10 consecutive days (6--15 dg for mated mice). Body weights were obtained throughout the study period, and uterine and fetal body weights were obtained at sacrifice on 18 dg. Uterine implants were enumerated and their status recorded. Live fetuses were sexed and examined for gross, visceral, skeletal, and soft-tissue craniofacial defects. Exposure of pregnant mice to these concentrations of MEK did not result in apparent maternal toxicity, although there was a slight, treatment-correlated increase in liver to body weight ratios which was significant for the 3000-ppM group. Mild developmental toxicity was evident at 3000-ppM as a reduction in mean fetal body weight. This reduction was statistically significant for the males only, although the relative decrease in mean fetal body weight was the same for both sexes. 17 refs., 4 figs., 10 tabs.
Date:
February 1, 1989
Creator:
Mast, T. J.; Dill, J. A.; Evanoff, J. J.; Rommereim, R. L.; Weigel, R. J. & Westerberg, R. B.
Object Type:
Report
System:
The UNT Digital Library
Radiochemical analyses of water samples collected postshot in the vicinity of Tatum Dome, Mississippi. Technical letter: Dribble 42
On the basis of the analytical methods used, preliminary radiochemical analysis of the water samples collected after the Salmon event indicate that no detectable level of radioactive contamination exists. Samples were obtained from the calcite caprock at a depth of 934 to 1,006 feet and through intervening aquifers to aquifer 1 at a depth of 365 to 421 feet from the surface. The water sample collected from the calcite caprock was taken within approximately 1,700 feet of the detonation. Periodic sampling of the wells will continue and more refined analytical techniques will be used in analyzing the samples. After the hydrologic test wells have been better developed by bailing, additional isotopes will be investigated.
Date:
February 8, 1965
Creator:
Janzer, V. J. & Rucker, S. J.
Object Type:
Report
System:
The UNT Digital Library
Perspectives Gained in an Evaluation of Uncertainty, Sensitivity, and Decision Analysis Software
The following software packages for uncertainty, sensitivity, and decision analysis were reviewed and also tested with several simple analysis problems: Crystal Ball, RiskQ, SUSA-PC, Analytica, PRISM, Ithink, Stella, LHS, STEPWISE, and JMP. Results from the review and test problems are presented. The study resulted in the recognition of the importance of four considerations in the selection of a software package: (1) the availability of an appropriate selection of distributions, (2) the ease with which data flows through the input sampling, model evaluation, and output analysis process, (3) the type of models that can be incorporated into the analysis process, and (4) the level of confidence in the software modeling and results.
Date:
February 24, 1999
Creator:
Davis, F. J. & Helton, J. C.
Object Type:
Article
System:
The UNT Digital Library
Health physics aspects of nuclear radiations from deuterium beam injectors
Estimations are made for X-ray generation from the accelerator column of various neutral beam injectors. For the case of deuterium beam operation where 2.5-MeV D-D neutrons pose a serious health physics concern, neutron and tritium production rates from beam targets are calculated for different beam energies. Biological doses from these radiations and shielding requirements are discussed.
Date:
February 1, 1978
Creator:
Kim, J.
Object Type:
Report
System:
The UNT Digital Library
Implementation of State Solar Incentives: Financial Programs.
None
Date:
February 28, 1979
Creator:
Ashworth, J.
Object Type:
Report
System:
The UNT Digital Library