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Investigation of Sodium Distribution in Phosphate Glasses Using Spin-Echo {sup 23}Na NMR
The spatial arrangement of sodium cations for a series of sodium phosphate glasses, xNa{sub 2}O(100-x)P{sub 2}O{sub 5} (x<55), were investigated using {sup 23}Na spin-echo NMR spectroscopy. The spin-echo decay rate is a function of the Na-Na homonuclear dipolar coupling and is related to the spatial proximity of neighboring Na nuclei. The spin-echo decay rate in these sodium phosphate glasses increases non-linearly with higher sodium number density, and thus provides a measure of the Na-Na extended range order. The results of these {sup 23}Na NMR experiments are discussed within the context of several structural models, including a decimated crystal lattice model, cubic dilation lattice model, a hard sphere (HS) random distribution model and a pair-wise cluster hard sphere model. While the experimental {sup 23}Na spin-echo M{sub 2} are described adequately by both the decimated lattice and the random HS model, it is demonstrated that the slight non-linear behavior of M{sub 2} as a function of sodium number density is more correctly described by the random distribution in the HS model. At low sodium number densities the experimental M{sub 2} is inconsistent with models incorporating Na-Na clustering. The ability to distinguish between Na-Na clusters and non-clustered distributions becomes more difficult at higher …
Date:
September 16, 1999
Creator:
ALAM, TODD M.; BOYLE, TIMOTHY J.; BROW, RICHARD K.; CLICK, CAROL C.; CONZONE, SAM; McLAUGHLIN, JAY et al.
Object Type:
Article
System:
The UNT Digital Library
Data Torturing and the Misuse of Statistical Tools
Statistical concepts, methods, and tools are often used in the implementation of statistical thinking. Unfortunately, statistical tools are all too often misused by not applying them in the context of statistical thinking that focuses on processes, variation, and data. The consequences of this misuse may be ''data torturing'' or going beyond reasonable interpretation of the facts due to a misunderstanding of the processes creating the data or the misinterpretation of variability in the data. In the hope of averting future misuse and data torturing, examples are provided where the application of common statistical tools, in the absence of statistical thinking, provides deceptive results by not adequately representing the underlying process and variability. For each of the examples, a discussion is provided on how applying the concepts of statistical thinking may have prevented the data torturing. The lessons learned from these examples will provide an increased awareness of the potential for many statistical methods to mislead and a better understanding of how statistical thinking broadens and increases the effectiveness of statistical tools.
Date:
August 16, 1999
Creator:
Abate, Marcey L.
Object Type:
Article
System:
The UNT Digital Library
Development of a Real-Time Beryllium Air Monitor Utilizing Microwave Induced Plasma Spectroscopy (MIPAES)
This is the final report of a one-year, Laboratory-Directed Research and Development (LDRD) Program Development project at the Los Alamos National laboratory (LANL). The focus of this development has been an innovative beryllium air monitor for on-site' real-time continuous monitoring which overcomes limitations of the previous techniques for beryllium monitoring. A bench-top instrument has been set up and the performance of the instrument has been tested based on a solution aerosol. The sensitivity obtained with the instrument is sufficient to ensure workers can respond at airborne levels well below current exposure regulations. With this versatile, real-time monitor, worker exposure can be greatly reduced.
Date:
July 16, 1999
Creator:
Abeln, S.; Duan, Y.-A.; Olivares, J. A.; Koby, M. & Scopsick, R. C.
Object Type:
Report
System:
The UNT Digital Library
Growth and Fabrication of GaN/AlGaN Heterojunction Bipolar Transistor
A GaN/AlGaN heterojunction bipolar transistor structure with Mg doping in the base and Si Doping in the emitter and collector regions was grown by Metal Organic Chemical Vapor Deposition in c-axis Al(2)O(3). Secondary Ion Mass Spectrometry measurements showed no increase in the O concentration (2-3x10(18) cm(-3)) in the AlGaN emitter and fairly low levels of C (~4-5x10(17) cm (-3)) throughout the structure. Due to the non-ohmic behavior of the base contact at room temperature, the current gain of large area (~90 um diameter) devices was <3. Increasing the device operating temperature led to higher ionization fractions of the mg acceptors in the base, and current gains of ~10 were obtained at 300 degree C.
Date:
March 16, 1999
Creator:
Abernathy, C. R.; Baca, A. G.; Cao, X. A.; Cho, H.; Dang, G. T.; Donovan, S. M. et al.
Object Type:
Article
System:
The UNT Digital Library
High Precision Droplet Based New Form Manufacturing
In collaboration with the University of California at Irvine (UCI), we are working on a new technology that relies on the precise deposition of nanoliter molten-metal droplets that are targeted onto a substrate by electrostatic charging and deflection. By this way, three-dimensional (3D) structural materials can be manufactured microlayer by microlayer. Because the volume of the droplets are small, they rapidly solidify on impact, bringing forth a material component with fine grain structures which lead to enhanced material properties (e.g., strength). UCI is responsible for an experimental investigation of the manufacturing feasibility of this process. LLNL has unique expertise in the computational modeling of 3D heat transfer and solid mechanics and has the large-scale computer resources necessary to model this large system. Process modeling will help move this technology from the bench-top to an industrial process. Applications at LLNL include rapid prototyping of metal parts and manufacturing new alloys by co-jetting different metals.
Date:
September 16, 1999
Creator:
Aceves, S.; Hadjiconstantinou, N.; Miller, W. O.; Orme, M.; Sahai, V. & Shapiro, A. B.
Object Type:
Report
System:
The UNT Digital Library
Recombination Lifetime of InxGa1-xAs Alloys Used in Thermophotovoltaic Converters
The family of ternary compounds of composition InxGa1-xAs are of considerable interest for thermophotovoltaic energy converters. The recombination lifetimes of the various compositions are critical to the successful application of these materials as efficient converters. Here we will describe experimental results on the composition. In0.53Ga0.47 that is lattice-matched to InP. We will also describe lifetime results on the compositions In0.68Ga0.32As, with bandgap of 0.60 eV to compositions In0.78Ga0.22As with a bandgap of 0.50 eV. Double heterostructure confinement devices have been made over a range of both n- and p-type doping. These results are preliminary, but the goal is to obtain the radiative and Auger recombination coefficients for the alloys in this composition range.
Date:
February 16, 1999
Creator:
Ahrenkiel, R. K.; Ellingson, R.; Johnston, S.; Webb, J.; Carapella, J. & Wanlass, M.
Object Type:
Article
System:
The UNT Digital Library
Three-Body Breakup Dynamics in Dissociative Recombination
Using the CRYRing Facility in Stockholm Coupled with an MCP-CCD detector, and a differential stopping foil, we have determined dynamic parameters in the three-body dissociative recombination of H<sub>2</sub>O<sup>+</sup>. These include the distribution between the O(<sup>3</sup>P) and O(<sup>1</sup>D) channels, the distribution of H atom recoil energies in the O(<sup>3</sup>P) channel and the distribution of angles between the two departing H atoms.
Date:
June 16, 1999
Creator:
Al-Khalili, A.; Datz, S.; Derkatch, A.; Larsson, M.; Rosén, S.; Shi, W. et al.
Object Type:
Article
System:
The UNT Digital Library
The Very Large Hadron Collider
I present some of the current ideas about a Very Large Hadron Collider [1] which could eventually extend the high energy frontier beyond that of the Large Hadron Collider (LHC) or any other machine seriously conceived at this time.
Date:
February 16, 1999
Creator:
Albrow, Michael G.
Object Type:
Article
System:
The UNT Digital Library
Oral History Interview with Frederick J. Holland, Jr., February 16, 1999
Access:
Use of this item is restricted to the UNT Community
Transcript of an interview with Frederick J. Holland, Jr., an Army Air Forces veteran, concerning his experiences in the China-Burma-India Theater during World War II. Holland discusses his early employment with REA Express; basic training, Fort Miles Standish, Massachusetts, 1942; his transfer to the Air Force and assignment to Patterson Field, Dayton, Ohio, 1942; Officer Candidate School, Miami, Florida, 1943; assignment to India; assignment to Dum Dum Airport, Calcutta, 1943; his role in supervising and shipping cargo over "The Hump" (Himalaya Mountains) to China; assignment to Baruipur Airport, Calcutta; his role in the development and operation of the first mobile conveyor unit to load and unload cargo; awarding of the Bronze Star for his invention. Appendix includes one leaf that gives history of the mobile conveyor and one leaf that shows four images of the mobile conveyor.
Date:
February 16, 1999
Creator:
Alexander, William J. & Holland, Frederick J., Jr.
Object Type:
Book
System:
The UNT Digital Library
Oral History Interview with Nick Sanchez, February 16, 1999
Access:
Use of this item is restricted to the UNT Community
Interview with Nick Sanchez, a Army Air Force WWII veteran from Laredo, Texas. Sanchez discusses working in radio when the war began, becoming a radio technician in the Army Air Force, deployment to India and operations there, going missing in China after surviving a plane crash, and the end of the war. In appendix are an autobiographical sketch of Sanchez's service, a copy of a diary recording his experience "bailing-out," and his official military statement of the event.
Date:
February 16, 1999
Creator:
Alexander, William J. & Sanchez, Nick
Object Type:
Book
System:
The UNT Digital Library
The Oklahoma Daily (Norman, Okla.), Vol. 83, No. 106, Ed. 1 Tuesday, February 16, 1999
Student newspaper of the University of Oklahoma in Norman, Oklahoma that includes national, local, and campus news along with advertising.
Date:
February 16, 1999
Creator:
Allam, Heather
Object Type:
Newspaper
System:
The Gateway to Oklahoma History
The Oklahoma Daily (Norman, Okla.), Vol. 83, No. 142, Ed. 1 Friday, April 16, 1999
Student newspaper of the University of Oklahoma in Norman, Oklahoma that includes national, local, and campus news along with advertising.
Date:
April 16, 1999
Creator:
Allam, Heather
Object Type:
Newspaper
System:
The Gateway to Oklahoma History
Integrated Micro-Optical Fluorescence Detection System for Microfluidic Electrochromatography
The authors describe the design and microfabrication of an extremely compact optical system as a key element in an integrated capillary-channel electrochromatograph with laser induced fluorescence detection. The optical design uses substrate-mode propagation within the fused silica substrate. The optical system includes a vertical cavity surface-emitting laser (VCSEL) array, two high performance microlenses and a commercial photodetector. The microlenses are multilevel diffractive optics patterned by electron beam lithography and etched by reactive ion etching in fused silica. Two generations of optical subsystems are described. The first generation design is integrated directly onto the capillary channel-containing substrate with a 6 mm separation between the VCSEL and photodetector. The second generation design separates the optical system onto its own module and the source to detector length is further compressed to 3.5 mm. The systems are designed for indirect fluorescence detection using infrared dyes. The first generation design has been tested with a 750 nm VCSEL exciting a 10{sup -4} M solution of CY-7 dye. The observed signal-to-noise ratio of better than 100:1 demonstrates that the background signal from scattered pump light is low despite the compact size of the optical system and meets the system sensitivity requirements.
Date:
September 16, 1999
Creator:
Allerman, Andrew A.; Arnold, Don W.; Asbill, Randolph E.; Bailey, Christopher G.; Carter, Tony Ray; Kemme, Shanalyn A. et al.
Object Type:
Article
System:
The UNT Digital Library
The Growth of InGaAsN for High Efficiency Solar Cells by Metalorganic Chemical Vapor Deposition
InGaAsN alloys are a promising material for increasing the efficiency of multi-junction solar cells now used for satellite power systems. However, the growth of these dilute N containing alloys has been challenging with further improvements in material quality needed before the solar cell higher efficiencies are realized. Nitrogen/V ratios exceeding 0.981 resulted in lower N incorporation and poor surface morphologies. The growth rate was found to depend on not only the total group III transport for a fixed N/V ratio but also on the N/V ratio. Carbon tetrachloride and dimethylzinc were effective for p-type doping. Disilane was not an effective n-type dopant while SiCl4 did result in n-type material but only a narrow range of electron concentrations (2-5e17cm{sup -3}) were achieved.
Date:
September 16, 1999
Creator:
Allerman, Andrew A.; Banks, James C.; Gee, James M.; Jones, Eric D. & Kurtz, Steven R.
Object Type:
Article
System:
The UNT Digital Library
Ensemble: 1999-11-10 - UNT African Percussion Ensemble
Access:
Use of this item is restricted to the UNT Community
Ensemble recital performed at the UNT College of Music.
Date:
November 16, 1999
Creator:
Alorwoyie, Gideon Foli
Object Type:
Sound
System:
The UNT Digital Library
Extraction of Substructural Flexibility from Global Frequencies and Mode Shapes
A computational procedure for extracting substructure-by-substructure flexibility properties from global modal parameters is presented. The present procedure consists of two key features: an element-based direct flexibility method which uniquely determines the global flexibility without resorting to case-dependent redundancy selections; and, the projection of cinematically inadmissible modes that are contained in the iterated substructural matrices. The direct flexibility method is used as the basis of an inverse problem, whose goal is to determine substructural flexibilities given the global flexibility, geometrically-determined substructural rigid-body modes, and the local-to-global assembly operators. The resulting procedure, given accurate global flexibility, extracts the exact element-by-element substructural flexibilities for determinate structures. For indeterminate structures, the accuracy depends on the iteration tolerance limits. The procedure is illustrated using both simple and complex numerical examples, and appears to be effective for structural applications such as damage localization and finite element model reconciliation.
Date:
July 16, 1999
Creator:
Alvin, K. F. & Park, K. C.
Object Type:
Article
System:
The UNT Digital Library
Quantum Well Width Dependence of Threshold Current Density in InGaN Lasers
The quantum confined Stark effect was found to result in a strong quantum well width dependence of threshold current density in strained group-III nitride quantum well lasers. For an In{sub 0.2}Ga{sub 0.8}N/GaN structure with quantum well width in the neighborhood of 3.5nm, our analysis shows that the reduction in spontaneous emission loss by the electron-hole spatial separation outweighs the corresponding reduction in gain to produce a threshold current density minimum.
Date:
March 16, 1999
Creator:
Amano, H.; Chow, W.W.; Han, J. & Takeuchi, T.
Object Type:
Article
System:
The UNT Digital Library
Cs, Sr, and Ba Sorption on Clays and Fe-Oxides
Technical guidance for performance assessment (PA) of low-level radioactive waste (LLRW) sites is currently dependent upon experimental retardation factors (K{sub D}'s) to predict radionuclide transport. Accurate predictions of waste transport or retardation will require mechanistic models of radionuclide sorption so as to be applicable to a wide range of soil/groundwater environments. To that end, we have investigated Cs{sup +}, Sr{sup +}, and Ba{sup 2+} sorption on several clay and Fe-oxide minerals. Relative metal binding strengths for montmorillonite clay decrease from Ba{sup 2+} to Sr{sup +}, which is similar to that sorption trend noticed for kaolinite. Molecular dynamics simulations for kaolinite suggest that Cs{sup +} is sorbed at aluminol (010) edge sites as an inner-sphere complex and weakly sorbed as an outer-sphere complex on (001) basal surfaces. Sorption is thought to occur on similar sites for smectite clays, however, the basal plane residual charge and its increased basal plane exposure should have a greater influence on metal sorption. On the other hand, phase transformation kinetics (e.g., ferrihydrite to goethite) is a very important control of metal sorption and resorption for Fe-oxides/hydroxides. These results provide a basis for understanding and predicting metal sorption on complex soil minerals.
Date:
June 16, 1999
Creator:
Anderson, H. L.; Brady, P. V.; Cygan, R. T.; Gruenhagen, S. E.; Nagy, K. L. & Westrich, H. R.
Object Type:
Article
System:
The UNT Digital Library
Applications of Multivariate Statistical Analysis (MSA) in Microanalysis
Recent improvements in computer hardware and software for the acquisition, storage and analysis of series of spectra and images allow for a change in strategy for quantitative microanalysis. For example, in the area of X-ray microanalysis, whereas compositional analysis and elemental distributions have been traditionally performed using point microanalysis and simple intensity mapping from a ROI, respectively, the two tasks are now routinely performed simultaneously through X-ray spectrum-imaging, where full spectra are acquired from pixels in a two-dimensional array of points on the specimen. Commercially available software now allows for the acquisition and storage of such spectrum-images, perhaps comprising as much as 100 MBytes of data or more. A variety of post-acquisition processing tools are provided by the developer to allow the extraction of both X-ray intensity maps, with or without rudimentary background subtraction, or full spectra from pixels of interest. In order to maximize the extraction of information from these large data sets, a number of linear and nonlinear methods are currently being explored that identify statistically significant variations among the series of spectra without a priori assumptions about the content of the data set. Among these methods, linear multivariate statistical analysis (MSA) has a number of significant advantages, …
Date:
February 16, 1999
Creator:
Anderson, I. M.
Object Type:
Article
System:
The UNT Digital Library
Harnessing the power of the new SMP cluster architecture
In 1993, members of our team collaborated with Silicon Graphics to perform the first full-scale demonstration of the computational power of the SMP cluster supercomputer architecture. That demonstration involved the simulation of homogeneous, compressible turbulence on a uniform grid of a billion cells, using our PPM gas dynamics code. This computation was embarrassingly parallel, the ideal test case, and it achieved only 4.9 Gflop/s performance, slightly over half that achievable by this application on the most expensive supercomputers of that day. After four to five solid days of computation, when the prototype machine had to be dismantled, the simulation was only about 20% completed. Nevertheless, this computation gave us important new insights into compressible turbulence and also into a powerful new mode of cost-effective, commercially sustainable supercomputing [S]. In the intervening 6 years, the SMP cluster architecture has become a fundamental strategy for several large supercomputer centers in the US, including the DOE's ASCI centers at Los Alamos National Laboratory and at the Lawrence Livermore National Laboratory and the NSF's center NCSA at the University of Illinois. This SMP cluster architecture now underlies product offerings at the high-end of performance from SGI, IBM, and HP, among others. Nevertheless, despite many …
Date:
June 16, 1999
Creator:
Anderson, S. E.; Cohen, R. H.; Curtis, B. C.; Dannevik, W. P.; Dimits, A. M.; Dinge, D. et al.
Object Type:
Article
System:
The UNT Digital Library
Extruded plastic scintillation detectors
As a way to lower the cost of plastic scintillation detectors, commercially available polystyrene pellets have been used in the production of scintillating materials that can be extruded into different profiles. The selection of the raw materials is discussed. Two techniques to add wavelength shifting dopants to polystyrene pellets and to extrude plastic scintillating strips are described. Data on light yield and transmittance measurements are presented.
Date:
April 16, 1999
Creator:
Anna Pla-Dalmau, Alan D. Bross and Kerry L. Mellott
Object Type:
Article
System:
The UNT Digital Library
Isentropic Compression Experiments on the Z Accelerator
This paper provides a brief review of experimental techniques for producing dynamic isentropic compression of samples to pressures of several hundred GPa. Traditional gun launch techniques include use of buffer plates, such as fused silica, that exhibit negative curvature to their stress-strain response and graded-density impactors. Graded-density impactors have been used to study isentropic compression of specimens to pressures exceeding 2 Mbar on high-impedance materials. A recent development includes the use of the Sandia Z Accelerator to produce magnetic compression in planar specimens to pressures of a few hundred kbar over time scales of 100 ns. These techniques have been successfully applied to isentropic compression of iron to 300 kbar and copper to 130 kbar. The iron results indicate that it is possible to study the polymorphic phase change that occurs at 130 kbar and also the kinetic properties of the transformation. The copper results indicate that with further improvements in progress it should be possible to measure continuous isentropic compression curves in materials of interest to pressures exceeding 1 Mbar. The Z accelerator is limited to peak currents of about 20 MA. By reconfiguring the anode-cathode geometry it should be possible to obtain constant current density and thus driving …
Date:
June 16, 1999
Creator:
Asay, J.R.
Object Type:
Article
System:
The UNT Digital Library
High Capacity High Speed Optical Data Storage System Based on Diffraction-Free Nanobeam. Final Report, 09-02-98 to 03-17-99
Physical Optics Corporation (POC) investigated the development of an optical data storage system built around a current well-engineered high-speed optical disk system with an innovative diffraction-free micro-optical element to produce a beam {approximately}250 nm wide with {approximately}4-5 mm depth of focus, allowing the system to address data at {approximately}100 Mbits/second and to store it 100 to 1,000 times more densely ({approximately}10 Gbit/in.{sup 2}) than in present systems. In Phase 1 of this project POC completed a thorough feasibility study by system design and analysis, successfully demonstrated fabrication of the key components, and conducted a proof-of-principle experimental demonstration. Specifically, production of a subwavelength ({approximately}380 nm) large depth of focus ({approximately}4-5 mm) addressing beam was demonstrated by fabricating a special microdiffractive optical element and recording this beam on a standard optical recording disk coated with a photopolymer material.
Date:
June 16, 1999
Creator:
Aye, Tin
Object Type:
Report
System:
The UNT Digital Library
Productivity and Injectivity of Horizontal Wells
The generation of suitable simulation grids for heterogeneous media and specific discretization issues that arise. Streamlines and equipotentials are used to define our base grids. Since streamlines are concentrated in high velocity regions they provide a natural means of clustering fine grid cells in crucial flow regions. For complex configurations and particularly for strongly heterogeneous regions the resulting grid cells can become very distorted due to extremely high curvatures. Two types of cell centered formulation are examined together with a cell vertex-point distributed scheme. Important distinctions are found for highly distorted cells. The new grids are tested for accuracy in terms of critical breakthrough parameters and it is shown that a much higher level of grid resolution is required by conventional simulators in order to achieve results that are comparable with those computed on relatively coarse streamline-potential grids.
Date:
November 16, 1999
Creator:
Aziz, Khalid; Hewett, Thomas A.; Arbabi, Sepehr & Smith, Marilyn
Object Type:
Report
System:
The UNT Digital Library