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Ion-assisted laser deposition of intermediate layers for YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} thin film growth on polycrystalline and amorphous substrates

Description: The growth of YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (YBCO) high-temperature superconductor thin films has largely been limited to deposition on single-crystal substrates to date. In order to expand the range of potential applications, growth on polycrystalline and amorphous substrates is desirable. In particular, the deposition of YBCO thin films with high critical current densities on polycrystalline metal alloys would allow the manufacture of superconducting tapes. However, it is shown that it … more
Date: November 1, 1993
Creator: Reade, R. P.
Partner: UNT Libraries Government Documents Department
open access

Quantum-limited detection of millimeter waves using superconducting tunnel junctions

Description: The quasiparticle tunneling current in a superconductor-insulator- superconductor (SIS) tunnel junction is highly nonlinear. Such a nonlinearity can be used to mix two millimeter wave signals to produce a signal at a much lower intermediate frequency. We have constructed several millimeter and sub-millimeter wave SIS mixers in order to study high frequency response of the quasiparticle tunneling current and the physics of high frequency mixing. We have made the first measurement of the out-of-p… more
Date: September 1, 1991
Creator: Mears, C. A.
Partner: UNT Libraries Government Documents Department
open access

Models to evaluate magnicon architectures and designs suitable for high-perveance beams

Description: The magnicon, a new high-power, radio frequency (rf) deflection- modulated amplifier, was recently developed at the Institute for Nuclear Physics in Novosibirsk, Russia. The first magnicon achieved a peak output power of 2.6 MW for 50-{mu}s pulses at a frequency of 915 MHz with a dc-to-rf conversion efficiency of 73%. The conversion efficiency achieved by the original magnicon represents a significant improvement over state-of-the-art conventional velocity- and density-modulated devices. Theref… more
Date: March 1, 1994
Creator: Rees, D. E.
Partner: UNT Libraries Government Documents Department
open access

Bimolecular reaction dynamics from photoelectron spectroscopy of negative ions

Description: The transition state region of a neutral bimolecular reaction may be experimentally investigated by photoelectron spectroscopy of an appropriate negative ion. The photoelectron spectrum provides information on the spectroscopy and dynamics of the short lived transition state and may be used to develop model potential energy surfaces that are semi-quantitative in this important region. The principles of bound {yields} bound negative ion photoelectron spectroscopy are illustrated by way of an exa… more
Date: November 1, 1992
Creator: Bradforth, S. E.
Partner: UNT Libraries Government Documents Department
open access

Threshold photodetachment spectroscopy of negative ions

Description: This thesis is concerned with the development and application of high resolution threshold photodetachment spectroscopy of negative ions. Chapter I deals with the principles of our photodetachment technique, and in chapter II a detailed description of the apparatus is presented. The threshold photodetachment spectra of I{sup {minus}}, and SH{sup {minus}}, presented in the last sections of chapter II, indicated that a resolution of 3 cm{sup {minus}1} can be achieved using our technique. In chapt… more
Date: December 1, 1991
Creator: Kitsopoulos, T. N.
Partner: UNT Libraries Government Documents Department
open access

Spectroscopy of transient neutral species via negative ion photoelectron spectroscopy

Description: Negative ion photoelectron spectroscopy has been used to study two types of transient neutral species: bound free radicals (NO{sub 2} and NO{sub 3}) and unstable neutral species ([IHI] and [FH{sub 2}]). The negative ion time-of-flight photoelectron spectrometer used for these experiments is described in detail.
Date: December 1, 1991
Creator: Weaver, A.
Partner: UNT Libraries Government Documents Department
open access

Impulse-based methods for fluid flow

Description: A Lagrangian numerical method based on impulse variables is analyzed. A relation between impulse vectors and vortex dipoles with a prescribed dipole moment is presented. This relation is used to adapt the high-accuracy cutoff functions of vortex methods for use in impulse-based methods. A source of error in the long-time implementation of the impulse method is explained and two techniques for avoiding this error are presented. An application of impulse methods to the motion of a fluid surrounde… more
Date: May 1, 1995
Creator: Cortez, R.
Partner: UNT Libraries Government Documents Department
open access

The growth of epitaxial iron oxides on platinum (111) as studied by X-ray photoelectron diffraction, scanning tunneling microscopy, and low energy electron diffraction

Description: Three complementary surface structure probes, x-ray photoelectron diffraction (XPD), scanning tunneling microscopy (STM), and low-energy electron diffraction (LEED) have been combined in a single instrument. This experimental system has been utilized to study the structure and growth mechanisms of iron oxide films on Pt(111); these films were formed by first depositing a single overlayer of Fe with a certain coverage in monolayers (ML`s), and then thermally oxidizing it in an oxygen atmosphere.… more
Date: May 1, 1995
Creator: Kim, Y. J.
Partner: UNT Libraries Government Documents Department
open access

Excited state carrier dynamics in CdS{sub x}Se{sub 1-x} semisconductor alloys as studied by ultrafast fluorescence spectroscopy

Description: This dissertation discusses studies of the electron-hole pair dynamics of CdS{sub x}Se{sub 1-x} semiconductor alloys for the entire compositional range from x = 1 to x = 0 as examined by the ultrafast fluorescence techniques of time correlated single photon counting and fluorescence upconversion. Specifically, samples with x = 1, .75, .5, .25, and 0 were studied each at a spread of wavelengths about its respective emission maximum which varies according to {lambda} = 718nm - 210x nm. The decays… more
Date: August 1, 1995
Creator: Gadd, S. E.
Partner: UNT Libraries Government Documents Department
open access

Oxidation studies on small atom doped TI*5*SI*3*

Description: This report described the oxidation and oxidation resistance of Ti{sub 5}Si{sub 3}, along with a discussion on general material properties. Single crystal studies of Ti{sub 5}Si{sub 3}Z{sub x} are included.
Date: November 1, 1995
Partner: UNT Libraries Government Documents Department
open access

Characterization of Zns-GaP Naon-composites

Description: It proved possible to produce consistent, high-quality nanocrystalline ZnS powders with grain sizes as small as 8 nm. These powders are nano-porous and are readily impregnated with GaP precursor, although inconsistently. Both crystal structure and small grain size of the ZnS can be maintained through the use of GaP. Heat treatment of the impregnated powders results in a ZnS-GaP composite structure where the grain sizes of the phases are on the order of 10--20 nm. Conventional powder processing … more
Date: December 9, 1993
Creator: Todd, V.
Partner: UNT Libraries Government Documents Department
open access

Dynamics of inelastic and reactive gas-surface collisions

Description: The dynamics of inelastic and reactive collisions in atomic beam-surface scattering are presented. The inelastic scattering of hyperthermal rare gaseous atoms from three alkali halide surfaces (LiF, NaCl, GI)was studied to understand mechanical energy transfer in unreactive systems. The dynamics of the chemical reaction in the scattering of H(D) atoms from the surfaces of LIF(001) and the basal plane of graphite were also studied.
Date: April 1, 1995
Creator: Smoliar, L.A.
Partner: UNT Libraries Government Documents Department
open access

A transport based one-dimensional perturbation code for reactivity calculations in metal systems

Description: A one-dimensional reactivity calculation code is developed using first order perturbation theory. The reactivity equation is based on the multi-group transport equation using the discrete ordinates method for angular dependence. In addition to the first order perturbation approximations, the reactivity code uses only the isotropic scattering data, but cross section libraries with higher order scattering data can still be used with this code. The reactivity code obtains all the flux, cross secti… more
Date: February 1, 1995
Creator: Wenz, T. R.
Partner: UNT Libraries Government Documents Department
open access

Effects of pore fluids in the subsurface on ultrasonic wave propagation

Description: This thesis investigates ultrasonic wave propagation in unconsolidated sands in the presence of different pore fluids. Laboratory experiments have been conducted in the sub-MHz range using quartz sand fully saturated with one or two liquids. Elastic wave propagation in unconsolidated granular material is computed with different numerical models: in one-dimension a scattering model based on an analytical propagator solution, in two dimensions a numerical approach using the boundary integral equa… more
Date: May 1, 1998
Creator: Seifert, P.K.
Partner: UNT Libraries Government Documents Department
open access

A quasi-model-independent search for new high p{_}T physics at DO

Description: We present a new quasi-model-independent strategy (''Sleuth'') for searching for physics beyond the standard model. We define final states to be studied, and construct a rule that identifies a set of relevant variables for any particular final state. A novel algorithm searches for regions of excess in those variables and quantifies the significance of any detected excess. This strategy is applied to search for new high p{_}T physics in approximately 100 pb{sup -1} of proton-anti-proton collisio… more
Date: December 11, 2000
Creator: Knuteson, Bruce O.
Partner: UNT Libraries Government Documents Department
open access

A compact, discrete CsI(Tl) scintillator/Si photodiode gamma camera for breast cancer imaging

Description: Recent clinical evaluations of scintimammography (radionuclide breast imaging) are promising and suggest that this modality may prove a valuable complement to X-ray mammography and traditional breast cancer detection and diagnosis techniques. Scintimammography, however, typically has difficulty revealing tumors that are less than 1 cm in diameter, are located in the medial part of the breast, or are located in the axillary nodes. These shortcomings may in part be due to the use of large, conven… more
Date: Autumn 2000
Creator: Gruber, Gregory J.
Partner: UNT Libraries Government Documents Department
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