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Trace Elemental Analysis of Ashes in the Combustion of the Binder Enhanced d-RDF by Inductively Coupled Plasma Atomic Emission Spectroscopy

Description: Incineration is an attractive solution to the problems of disposing of municipal solid wastes and supplying energy. Because up to 25 percent of the waste in refuse-derived-fuel systems is ash, the physical and chemical characteristics of ash become more and more important for its potential impacts and methods suitable for their disposal. Trace elements concentration in ash is of great interest because of its relationship to regulatory criteria under the Resource Conservation and Recovery Act (RCRA) regarding toxicity and hazards. The applications of a microwave oven sample dissolution method has been tested on a variety of standard reference materials, with reproducible and accurate results. Fourteen trace elements, As, Ba, Be, Cd, Cr, Cu, Hg, Ni, Pb, Sb, Se, Tl, V, and Zn, from the dissolved ash samples were determined by inductively coupled plasma atomic emission spectrometry.
Date: November 1988
Creator: Tai, Chia-Hui
Partner: UNT Libraries

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

Structural oxidation state studies of the manganese cluster in the oxygen evolving complex of photosystem II

Description: X-ray absorption spectroscopy (XAS) was performed on Photosystem II (PSII)-enriched membranes prepared from spinach to explore: (1) the correlation between structure and magnetic spin state of the Mn cluster in the oxygen evolving complex (OEC) in the S{sub 2} state; and (2) the oxidation state changes of the Mn cluster in the flash-induced S-states. The structure of the Mn cluster in the S{sub 2} state with the g{approx}4 electron paramagnetic resonance (EPR) signal (S{sub 2}-g4 state) was compared with that in the S{sub 2} state with multiline signal (S{sub 2}-MLS state) and the S{sub 1} state. The S{sub 2}-g4 state has a higher XAS inflection point energy than that of the S{sub 1} state, indicating the oxidation of Mn in the advance from the S{sub 1} to the S{sub 2}-g4 state. Differences in the edge shape and in the extended X-ray absorption fine structure (EXAFS) show that the structure of the Mn cluster in the S{sub 2}-g4 state is different from that in the S{sub 2}-MLS or the S{sub 1} state. In the S{sub 2}-g4 state, the second shell of backscatterers from the Mn absorber contains two Mn-Mn distances of 2.73 {angstrom} and 2.85 {angstrom}. Very little distance disorder exists in the second shell of the S{sub 1} or S{sub 2}-MLS states. The third shell of the S{sub 2}-g4 state at about 3.3 {angstrom} also contains increased heterogeneity relative to that of the S{sub 2}-MLS or the S{sub 1} state. Various S-states were prepared at room-temperature by saturating, single-turnover flashes. The flash-dependent oscillation in the amplitude of the MLS was used to characterize the S-state composition and to construct {open_quotes}pure{close_quotes} S-state Mn K-edge spectra. The edge position shifts to higher energy by 1.8 eV upon the S{sub 1} {yields} S{sub 2} transition.
Date: November 1, 1994
Creator: Liang, W.
Partner: UNT Libraries Government Documents Department

Electroproduction of Photons and of Pawns on the Proton in Quadrimoment of Transfer Q2=1.0GeV2. Measure Cross Sections and Extraction of Polarizabilities Generalities; Electroproduction de Photons et de Pions sur le Proton au Quadrimoment de Transfert Q2=1.0GeV2. Mesure des Sections Efficaces et Extraction des Polarisabilites Generalisees

Description: In hadronic physics, the nucleon structure and the quarks confinement are still topical issues. The neutral pion electroproduction and virtual Compton scattering (VCS) reactions allow us to access new observables that describe this structure. This work is focused on the VCS experiment performed at Jefferson Lab in 1998.
Date: November 6, 2001
Creator: Laveissiere, Geraud
Partner: UNT Libraries Government Documents Department

Synthesis, characterization and physical properties of Al-Cu-Fe quasicrystalline plasma sprayed coatings

Description: Our lab has been working with plasma spraying of both high pressure gas atomized (HPGA) and cast and crushed quasicrystal powders. A major component of this research includes comparative studies of PAS coatings formed with starting powders prepared by both techniques. In addition, a thorough investigation of the effects of starting powder particle size on coating microstructure is included. During the course of the overall research, an interest developed in forming Al-Cu-Fe materials with finer grain sizes. Therefore, a brief study was performed to characterize the effect of adding boron to Al-Cu-Fe materials prepared by different techniques. In addition to characterizing the microstructural features of the above materials, oxidation and wear behavior was also examined.
Date: November 9, 1995
Creator: Daniel, S.
Partner: UNT Libraries Government Documents Department

Application of the Environmental Protection Agency`s data quality objective process to environmental monitoring quality control

Description: The United States Environmental Protection Agency`s (EPA) Data Quality Objectives (DQO) process was applied to two environmental monitoring networks for the purpose of optimizing field quality control sampling to give the highest quality monitoring data with minimal impact on resources. The DQO process, developed primarily to aid in cleanup and restoration activities, is a systematic approach to designing sampling, and analysis programs with improved efficiency, cost savings, and measureable and traceable data quality. The two monitoring- networks studied had not been subjected to the systematic review and analysis of the DQO process defined by the EPA. The two monitoring networks studied had relied upon field duplicates or replicates as the main source of field quality control data. Sometimes, both duplicate and routine sample were analyzed by the same analytical laboratory; at other times they were analyzed by different laboratories. This study identified some potential inconsistencies between analytical data and reporting limits from two different laboratories. Application of the EPA DQO process resulted in recommendations for changes in the field quality control sampling program, allowed new insight into the monitoring data, and raised several issues that should be the subject of further investigation.
Date: November 1, 1995
Creator: Garcia, L.M.
Partner: UNT Libraries Government Documents Department

Inertial fusion energy: A clearer view of the environmental and safety perspectives

Description: If fusion energy is to achieve its full potential for safety and environmental (S&E) advantages, the S&E characteristics of fusion power plant designs must be quantified and understood, and the resulting insights must be embodied in the ongoing process of development of fusion energy. As part of this task, the present work compares S&E characteristics of five inertial and two magnetic fusion power plant designs. For each design, a set of radiological hazard indices has been calculated with a system of computer codes and data libraries assembled for this purpose. These indices quantify the radiological hazards associated with the operation of fusion power plants with respect to three classes of hazard: accidents, occupational exposure, and waste disposal. The three classes of hazard have been qualitatively integrated to rank the best and worst fusion power plant designs with respect to S&E characteristics. From these rankings, the specific designs, and other S&E trends, design features that result in S&E advantages have been identified. Additionally, key areas for future fusion research have been identified. Specific experiments needed include the investigation of elemental release rates (expanded to include many more materials) and the verification of sequential charged-particle reactions. Improvements to the calculational methodology are recommended to enable future comparative analyses to represent more accurately the radiological hazards presented by fusion power plants. Finally, future work must consider economic effects. Trade-offs among design features will be decided not by S&E characteristics alone, but also by cost-benefit analyses. 118 refs., 35 figs., 35 tabs.
Date: November 1, 1996
Creator: Latkowski, J.F.
Partner: UNT Libraries Government Documents Department

The influence of ambient medium density on laser ablation processes

Description: Interest in high flux transport processes has grown in recent years along with the ability and need to manipulate systems with microscopic length and time scales. These systems present unique engineering challenges. Because the time and length scales associated with these problems are very small, assumptions of local equilibrium, physical and mathematical smoothness of boundaries and the unambiguous definition of thermodynamic fields can not be automatically made, even though they may ultimately be acceptable. Furthermore, the observations are made on macroscopic or integrated scales. The large difference in scales between the temporal evolution of the process and the observation requires careful consideration of the claims made regarding the system`s microscopic, temporal behavior. In particular, consistency of a proposed model with observed results does not guarantee uniqueness, or predictive accuracy for the model. For these reasons, microscale heat transfer systems demand a careful consideration of the framework within which the experimentation and analysis are conducted.
Date: November 1, 1995
Creator: Kilgo, M.M. III
Partner: UNT Libraries Government Documents Department

A study of the interaction of x-rays and acoustic, stress and shock waves in solids

Description: The primary emphasis of this thesis involves an investigation of techniques for the control and modulation of x-ray radiation through acoustic perturbation of solids. The use of x-ray diffraction and x-ray optical techniques for the study of acoustic fields and atomic motion was also investigated. Analysis of the basic properties of x-ray propagation in solids reveals that practical methods for x-ray control or modulation must involve changes in the spatial configuration of x-ray scatterers. Numerical methods for the study of x-ray propagation in acoustically perturbated crystals are formulated. In developing these methods special emphasis has been placed on Borrmann transmission in thick crystals. Modulation and shuttering (on a micro-second timescale) of x-rays are experimentally demonstrated. A quantitative investigation of the basic interactions used to produce modulation and shuttering is presented. Agreement between the experimental observations and the theoretical predictions is within experimental error. An analytical investigation of the basic potential and limitations of x-ray modulation shuttering and control devices is presented. Basic design criteria for x-ray modulation devices is formulated and applied to practical configurations.
Date: November 1, 1976
Creator: Hauer, A.
Partner: UNT Libraries Government Documents Department

Compact Intracloud Discharges

Description: No abstract prepared.
Date: November 1, 1998
Creator: Smith, D.A.
Partner: UNT Libraries Government Documents Department

A study of non-equilibrium phonons in GaAs/AlAs quantum wells

Description: In this thesis we have studied the non-equilibrium phonons in GaAs/AlAs quantum wells via Raman scattering. We have demonstrated experimentally that by taking into account the time-reversal symmetry relation between the Stokes and anti-Stokes Raman cross sections, one can successfully measure the non-equilibrium phonon occupancy in quantum wells. Using this technique, we have studied the subject of resonant intersubband scattering of optical phonons. We find that interface roughness plays an important role in resonant Raman scattering in quantum wells. The lateral size of the smooth regions in such interface is estimated to be of the order of 100 {Angstrom}. Through a study of photoluminescence of GaAs/AlAs quantum wells under high intensity laser excitation, we have found that band nonparabolicity has very little effect on the electron subband energies even for subbands as high as a few hundred meV above the lowest one. This finding may require additional theoretical study to understand its origin. We have also studied phonon confinement and propagation in quantum wells. We show that Raman scattering of non-equilibrium phonons in quantum wells can be a sensitive measure of the spatial extent of the longitudinal optical (LO) phonons. We deduce the coherence length of LO phonons in GaAs/Al{sub x}Ga{sub 1-x}As quantum wells as a function of the Al concentration x.
Date: November 1, 1996
Creator: Su, Zhenpeng
Partner: UNT Libraries Government Documents Department

Fourier transform photoelectron diffraction and its application to molecular orbitals and surface structure

Description: Photoemission intensities from the molecular orbitals of c(2x2)CO/Pt(111) over a wide photon energy range were measured and analyzed by the same methods developed for structural studies using core levels. The 4{sigma} orbital center of gravity is found to be concentrated between the C and O atoms, while that of the 5{sigma} orbital lies between the C atom and the Pt surface. The C 1s photoelectron diffraction was used to determine the adsorption geometry. The earlier ambiguity that multiple scattering is needed to correctly model a {chi} curve while single scattering is sufficient for understanding major peaks in the ARPEFS-FTS is clarified by studying the clean Ni(111) surface. In the normal emission case, several different combinations of scattering events have similar path length differences (PLDs), and can either cancel each other or enhance the corresponding FT peak. In the off-normal case the degeneracy is greatly reduced due to the lower degree of symmetry. In normal emission AR PEFS, up to third order multiple scattering is needed to describe fully both the {chi} curve and its FT spectrum. To improve the spectral resolution in the ARPEFS-FT analysis, several new spectral analysis methods are introduced. With both autocorrelation autoregression (ACAR) and autocorrelation eigenvector (ACE), we can produce a reliable power spectrum by following the order-closing procedure. The best spectra are usually obtained when the autocorrelation sequence is computed with lags up to half the data range. A simple way of determining surface adsorption sites is proposed as follows: First use a single scattering cluster for possible adsorption sites to construct the geometrical PLDs from the strong backscattering events; then compare these PLDs with those obtained from the ARPEFS-FT analysis of the experimental data. After the preferred adsorption site is determined, fine tune the interlayer distances according to the positional R-factor.
Date: November 30, 1998
Creator: Zhou, Xin
Partner: UNT Libraries Government Documents Department

Modeling interfacial area transport in multi-fluid systems

Description: Many typical chemical engineering operations are multi-fluid systems. They are carried out in distillation columns (vapor/liquid), liquid-liquid contactors (liquid/liquid) and other similar devices. An important parameter is interfacial area concentration, which determines the rate of interfluid heat, mass and momentum transfer and ultimately, the overall performance of the equipment. In many cases, the models for determining interfacial area concentration are empirical and can only describe the cases for which there is experimental data. In an effort to understand multiphase reactors and the mixing process better, a multi-fluid model has been developed as part of a research effort to calculate interfacial area transport in several different types of in-line static mixers. For this work, the ensemble-averaged property conservation equations have been derived for each fluid and for the mixture. These equations were then combined to derive a transport equation for the interfacial area concentration. The final, one-dimensional model was compared to interfacial area concentration data from two sizes of Kenics in-line mixer, two sizes of concurrent jet and a Tee mixer. In all cases, the calculated and experimental data compared well with the highest scatter being with the Tee mixer comparison.
Date: November 1, 1996
Creator: Yarbro, S.L.
Partner: UNT Libraries Government Documents Department

Transport processes in directional solidification and their effects on microstructure development

Description: The processing of materials with unique electronic, mechanical, optical and thermal properties plays a crucial role in modern technology. The quality of these materials depend strongly on the microstructure and the solute/dopant fields in the solid product, that are strongly influenced by the intricate coupling of heat and mass transfer and melt flow in the growth systems. An integrated research program is developed that include precisely characterized experiments and detailed physical and numerical modeling of the complex transport and dynamical processes. Direct numerical simulation of the solidification process is carried out that takes into account the unsteady thermo-solutal convection in the vertical Bridgman crystal growth system, and accurately models the thermal interaction between the furnace and the ampoule by appropriately using experimentally measured thermal profiles. The flow instabilities and transitions and the nonlinear evolution following the transitions are investigated by time series and flow pattern analysis. A range of complex dynamical behavior is predicted with increasing thermal Rayleigh number. The route to chaos appears as: steady convection {r_arrow} transient mono-periodic {r_arrow} transient bi-periodic {r_arrow} transient quasi-periodic {r_arrow} transient intermittent oscillation-relaxation {r_arrow} stable intermittent oscillation-relaxation attractor. The spatio-temporal dynamics of the melt flow is found to be directly related to the spatial patterns observed experimentally in the solidified crystals. The application of the model to two phase Sn-Cd peritectic alloys showed that a new class of tree-like oscillating microstructure develops in the solid phase due to unsteady thermo-solutal convection in the liquid melt. These oscillating layered structures can give the illusion of band structures on a plane of polish. The model is applied to single phase solidification in the Al-Cu and Pb-Sn systems to characterize the effect of convection on the macroscopic shape and disorder in the primary arm spacing of the cellular/dendritic freezing front. The apparently puzzling experimental observation of ...
Date: November 8, 1999
Creator: Mazumder, Prantik
Partner: UNT Libraries Government Documents Department

Surface plasmon enhanced interfacial electron transfer and resonance Raman, surface-enhanced resonance Raman studies of cytochrome C mutants

Description: Surface plasmon resonance was utilized to enhance the electron transfer at silver/solution interfaces. Photoelectrochemical reductions of nitrite, nitrate, and CO{sub 2} were studied on electrochemically roughened silver electrode surfaces. The dependence of the photocurrent on photon energy, applied potential and concentration of nitrite demonstrates that the photoelectrochemical reduction proceeds via photoemission process followed by the capture of hydrated electrons. The excitation of plasmon resonances in nanosized metal structures resulted in the enhancement of the photoemission process. In the case of photoelectrocatalytic reduction of CO{sub 2}, large photoelectrocatalytic effect for the reduction of CO{sub 2} was observed in the presence of surface adsorbed methylviologen, which functions as a mediator for the photoexcited electron transfer from silver metal to CO{sub 2} in solution. Photoinduced reduction of microperoxidase-11 adsorbed on roughened silver electrode was also observed and attributed to the direct photoejection of free electrons of silver metal. Surface plasmon assisted electron transfer at nanostructured silver particle surfaces was further determined by EPR method.
Date: November 8, 1999
Creator: Zheng, Junwei
Partner: UNT Libraries Government Documents Department

A Spatial Discretization Scheme for Solving the Transport Equation on Unstructured Grids of Polyhedra

Description: In this work, we develop a new spatial discretization scheme that may be used to numerically solve the neutron transport equation. This new discretization extends the family of corner balance spatial discretizations to include spatial grids of arbitrary polyhedra. This scheme enforces balance on subcell volumes called corners. It produces a lower triangular matrix for sweeping, is algebraically linear, is non-negative in a source-free absorber, and produces a robust and accurate solution in thick diffusive regions. Using an asymptotic analysis, we design the scheme so that in thick diffusive regions it will attain the same solution as an accurate polyhedral diffusion discretization. We then refine the approximations in the scheme to reduce numerical diffusion in vacuums, and we attempt to capture a second order truncation error. After we develop this Upstream Corner Balance Linear (UCBL) discretization we analyze its characteristics in several limits. We complete a full diffusion limit analysis showing that we capture the desired diffusion discretization in optically thick and highly scattering media. We review the upstream and linear properties of our discretization and then demonstrate that our scheme captures strictly non-negative solutions in source-free purely absorbing media. We then demonstrate the minimization of numerical diffusion of a beam and then demonstrate that the scheme is, in general, first order accurate. We also note that for slab-like problems our method actually behaves like a second-order method over a range of cell thicknesses that are of practical interest. We also discuss why our scheme is first order accurate for truly 3D problems and suggest changes in the algorithm that should make it a second-order accurate scheme. Finally, we demonstrate 3D UCBL's performance on several very different test problems. We show good performance in diffusive and streaming problems. We analyze truncation error in a 3D problem and demonstrate robustness in ...
Date: November 1, 2000
Creator: Thompson, K.G.
Partner: UNT Libraries Government Documents Department

The intergroup protocols: Scalable group communication for the internet

Description: Reliable group ordered delivery of multicast messages in a distributed system is a useful service that simplifies the programming of distributed applications. Such a service helps to maintain the consistency of replicated information and to coordinate the activities of the various processes. With the increasing popularity of the Internet, there is an increasing interest in scaling the protocols that provide this service to the environment of the Internet. The InterGroup protocol suite, described in this dissertation, provides such a service, and is intended for the environment of the Internet with scalability to large numbers of nodes and high latency links. The InterGroup protocols approach the scalability problem from various directions. They redefine the meaning of group membership, allow voluntary membership changes, add a receiver-oriented selection of delivery guarantees that permits heterogeneity of the receiver set, and provide a scalable reliability service. The InterGroup system comprises several components, executing at various sites within the system. Each component provides part of the services necessary to implement a group communication system for the wide-area. The components can be categorized as: (1) control hierarchy, (2) reliable multicast, (3) message distribution and delivery, and (4) process group membership. We have implemented a prototype of the InterGroup protocols in Java, and have tested the system performance in both local-area and wide-area networks.
Date: November 1, 2000
Creator: Berket, K.
Partner: UNT Libraries Government Documents Department

Studies of beam dynamics in relativistic klystron two-beam accelerators

Description: Two-beam accelerators (TBAs) based upon free-electron lasers (FELs) or relativistic klystrons (RK-TBAs) have been proposed as efficient power sources for next generation high-energy linear colliders. Studies have demonstrated the possibility of building TBAs from X-band ({approximately}8-12 GHz) through Ka band ({approximately} 30-35 GHz) frequency regions. Provided that further prototyping shows stable beam propagation with minimal current loss and production of good quality, high-power rf fields, this technology is compatible with current schemes for electron-positron colliders in the multi-TeV center-of-mass scale. A new method of simulating the beam dynamics in accelerators of this type has been developed in this dissertation. There are three main components to this simulation. The first is a tracking algorithm to generate nonlinear transfer maps for pushing noninteracting particles through the external fields. The second component is a 3D Particle-In-Cell (PIC) algorithm that solves a set of Helmholtz equations for the self-fields, including the conducting boundary condition, and generates impulses that are interleaved with the nonlinear maps by means of a split-operation algorithm. The Helmholtz equations are solved by a multi-grid algorithm. The third component is an equivalent circuit equation solver that advances the modal rf cavity fields in time due to excitation by the modulated beam. The RTA project is described, and the simulation code is used to design the latter portions of the experiment. Detailed calculations of the beam dynamics and of the rf cavity output are presented and discussed. A beamline design is presented that will generate nearly 1.2 GW of power from 40 input, gain, and output rv cavities over a 10 m distance. The simulations show that beam current losses are acceptable, and that longitudinal and transverse focusing techniques are sufficient capable of maintaining a high degree of beam quality along the entire beamline. Additional experimental efforts are also described.
Date: November 1, 1999
Creator: Lidia, Steven M.
Partner: UNT Libraries Government Documents Department

Kinetics and mechanism of the oxidation of alkenes and silanes by hydrogen peroxide catalyzed by methylrhenium trioxide (MTO) and a novel application of electrospray mass spectrometry to study the hydrolysis of MTO

Description: Conjugated dienes were oxidized by hydrogen peroxide with methylrhenium trioxide (MTO) as catalyst. Methylrhenium bis-peroxide was the major reactive catalyst present. Hydroxyalkenes and trisubstituted silane were also tested. Mechanisms for each of these reactions are presented.
Date: November 8, 1999
Creator: Tan, Haisong
Partner: UNT Libraries Government Documents Department

Improving the design and analysis of superconducting magnets for particle accelerators

Description: High energy particle accelerators are now the primary means of discovering the basic building blocks of matter and understanding the forces between them. In order to minimize the cost of building these machines, superconducting magnets are used in essentially all present day high energy proton and heavy ion colliders. The cost of superconducting magnets is typically in the range of 20--30% of the total cost of building such machines. The circulating particle beam goes through these magnets a large number of times (over hundreds of millions). The luminosity performance and life time of the beam in these machines depends significantly on the field quality in these magnets. Therefore, even a small error in the magnetic field shape may create a large cumulative effect in the beam trajectory to throw the particles of the magnet aperture. The superconducting accelerator magnets must, therefore, be designed and constructed so that these errors are small. In this thesis the research and development work will be described 3which has resulted in significant improvements in the field quality of the superconducting magnets for the Relativistic Heavy Ion Collider (RHIC). The design and the field quality improvements in the prototype of the main collider dipole magnet for the Superconducting Super Collider (SSC) will also be presented. RHIC will accelerate and collide two counter rotating beams of heavy ions up to 100 GeV/u and protons up to 250 GeV. It is expected that RHIC will create a hot, dense quark-gluon plasma and the conditions which, according to the Big Bang theory, existed in the early universe.
Date: November 1, 1996
Creator: Gupta, R.C.
Partner: UNT Libraries Government Documents Department

Elemental speciation in biomolecules by LC-ICP-MS with magnetic sector and collision cell instruments

Description: A methodology that can monitor and identify inorganic elements in biological and environmental systems was developed. Size exclusion chromatography (SEC) separates biomolecules, which are then nebulized by a microconcentric nebulizer. The resulting aerosol is desolved and introduced into either a high resolution ICP-MS device or a quadrupole device with a collision cell. Because of the high sensitivity and spectral resolution and high sample introduction efficiency, many unusual or difficult elements, such as Cr, Se, Cd and U, can be observed at ambient levels bound to proteins in human serum. These measurements are made in only a few minutes without preliminary isolation and preconcentration steps. Serum samples can be titrated with spikes of various elements to determine which proteins bind a given metal and oxidation state. Experiments concerning the effects of breaking disulfide linkages and denaturation on metal binding in proteins were also investigated. Elemental distribution in liver extract was also obtained.
Date: November 8, 1999
Creator: Wang, Jin
Partner: UNT Libraries Government Documents Department