Digital Commons Network^™

Comparison Of Deep Centers In Semiinsulating Liquid-Encapsulated Czochralski And Vertical-Gradient Freeze Gaas, Z-Q. Fang, David C. Look

Physics Faculty Publications

Three‐inch, semi‐insulating (SI) GaAs, grown by the vertical gradient freeze (VGF) technique, has been studied by IR absorption, temperature‐dependent dark current and Hall‐effect, thermally stimulated current (TSC), and photoinduced current transient spectroscopy and has been compared with undoped, SI GaAs, both As‐rich and Ga‐rich, grown by the high‐pressure liquid‐encapsulated Czochralski method. The results clearly indicate that (1) the VGF GaAs contains less EL2, which suggests a less As‐rich crystal stoichiometry; (2) in some VGF samples activation energies of 0.43 or 0.46 eV are deduced from temperature‐dependent carrier concentration or resistivity measurements, respectively, and (3) VGF samples often show a thermal …

Quenching And Rotational Energy Transfer In Molecular Bromine: Br2(B), Dean A. Massman

Theses and Dissertations

This study investigates the rotational energy transfer processes of optically excited bromine molecules in the presence of several collision partners. Resolved laser induced fluorescence spectra of collisionally populated rotational states were analyzed by means of Stern Volmer analysis. Total rotational removal rate coefficients and state-to-state rotational removal rate coefficients for the v'=11,J'=35 level of Br₂(B) were obtained for collisions with Br₂(X), He, Ar and Xe. Rotational removal rate coefficients were also obtained for the v'11, J'=26 and 47; v'=14, J'=36 states of Br₂(B) with collisions with Ar. Total rotational removal rate for Br_{2 …}

The Process-Controlled Magnetic Properties In Nanostructured Fe/Ag Composite Films, Y.Z. Zhang, Sy_Hwang Liou, R.J. Deangelis, K.W. Lee, C.P. Reed, A. Nazareth

Sy-Hwang Liou Publications

Nanostructured Fe/Ag composite films were prepared by magnetron sputtering using a single target. Correlations between the microstructure and magnetic properties, in particular the effects of cluster-size distribution in the films, are discussed. The cluster-size distribution was calculated by analyzing the width and shape of the x-ray-diffraction peaks. The average cluster size in the films increased from 42 to 295 Å and from 38 to 320 Å in the systems of 41 and 27 vol % of Fe, respectively, as the substrate temperature increased from 100 to 500 °C. The maximum magnetic coercivity, as high as 900 Oe, has been observed …

Effect Of Interfacial Microstructure On Magnetic Properties Of Dysprosium Multilayers, Z.S. Shan, B. Jacobsen, Sy_Hwang Liou, David J. Sellmyer

Sy-Hwang Liou Publications

Nanostructured multilayers of Dy/M (M=Ta, Cu, Y, and Co) have been investigated. Correlations between the microstructure and the magnetic properties, in particular the effects of interfacial structure, are discussed. The temperature and layer-thickness dependences of anisotropy of these Dy/M multilayers can be interpreted reasonably in light of the model previously developed for the perpendicular anisotropy in amorphous multilayers.

Magneto-Optic And Optical Characterization Of Tb/Co Compositionally Modulated Amorphous Films, Liang-Yao Chen, Ping He, S. Nafis, William A. Mcgahan, John A. Woollam, David J. Sellmyer

David Sellmyer Publications

Amorphous Tb/Co compositionally modulated films were deposited on Si substrates with different modulation layer thicknesses ranging from about 2.5 to 15 Å. The nominal Tb to Co layer thickness ratios were systematically varied and the complex refractive index (n and k) and polar magneto-optical Kerr effects (rotation and ellipticity) were measured in the 3000–8000-Å spectral range as well. The samples were divided into two groups. In one group, the thickness of the Co layers was fixed, the Tb layer thickness varied. In the second group, the thickness of the Tb layer was fixed, and that of the Co …

Fourier Transform Infrared (Ftir) Spectroscopy Analysis Of Combustion Aerosol, Gary Jacquin

Opportunities for Undergraduate Research Experience Program (OURE)

In conjunction with my co-op program at McDonnell-Douglas, my current OURE project is the analysis of combustion aerosols using Fourier Transform Infrared (FTIR) Spectroscopy. Aerosol science is a very important field as it is concerned with atmospheric chemistry, atmospheric physics, climate, public health, and environmental issues.

In the Cloud and Aerosol Sciences Laboratory (CASL) at UMR, combustion aerosols are generated by an in-house designed torch or burner. The fuels, JP4 and JP5, are provided by McDonnell-Douglas. Some other commercial fuels are also used. The primary objective of my OURE project was to generate and collect combustion aerosols for chemical analysis. …

Combustion Aerosol Morphology, Ronald P. Holland

Opportunities for Undergraduate Research Experience Program (OURE)

The following report entitled Carbon Aerosol Morphology is the result of research done through the University of Missouri--Rolla Graduate School program entitled Opportunities for Undergraduate Research Experience (OURE). My appointment was for the Summer - 1990 with the Cloud and Aerosol Sciences Laboratory, Department of Physics, located in Norwood Hall. The goal of this appointment was to study the size and morphology of combustion aerosols whose characteristics are dependent on the history of the particle, e.g. exposure to chemicals, scavenging effects, and other time dependent factors. Computer image processing software is available in the department for this purpose.

Removal Of Chlorine From Chlorine-Nitrogen Mixture In A Film Of Liquid Water, Sarwan S. Sandhu

Chemical and Materials Engineering Faculty Publications

In industry there are many examples of absorption of a gas with or without chemical reaction in the liquid phase. In physical absorption, a particular gaseous component is removed from a gas mixture due to its larger solubility in the liquid phase solvent. The removal of butane and pentane from a refinery gas mixture by a heavy oil in the liquid phase is an example of physical absorption. In absorption with chemical reaction, the gaseous component to be removed transfers across the gas-liquid interface due to a difference in the bulk chemical potentials or concentrations in the two phases. The …

Transport Anomalies In The High-Temperature Hopping Conductivity And Thermopower Of Sr-Doped La(Cr,Mn)O,₃, Ryne P. Raffaelle, Harlan U. Anderson, Don M. Sparlin, Paul Ernest Parris

Materials Science and Engineering Faculty Research & Creative Works

A minimum exists in the electrical conductivity of the perovskite-type ceramic LaCr_1-xMn_xO₃ as a function of Mn content near x=0.05. This minimum has been explained in terms of a crossover from multiple trapping to percolation among energetically lower Mn sites. In this paper electrical conductivity and Seebeck measurements are presented on a similar series in which 10 mol % Sr was substituted for La in order to increase the small polaron concentration through the compensation of Sr ions according to the Verway mechanism. The data suggests that there is an apparent suppression of the Verway …

Magnetic-Field Distributions In Zinc-Nickel Ferrite, T. A. Dooling, Desmond C. Cook

Physics Faculty Publications

The Mössbauer effect has been used to study the microscopic magnetic properties of the cubic microwave ferrite (Zn_0.41Ni_0.59)Fe₂O₄ at 300 K. The magnetically split spectrum is broad and unresolved due to the overlap of the hyperfine magnetic fields at the tetrahedral and octahedral sites. This is caused by a distribution of magnetic fields at each site. The distribution is especially large and asymmetric at the octahedral site and is due to the fact that the iron atoms at this site are influenced by the presence of both iron and zinc at the tetrahedral …

Phase Changes In Plasma‐Sprayed Zinc‐Nickel Ferrite, T. A. Dooling, Desmond C. Cook

Physics Faculty Publications

The magnetic and crystalline properties of a plasma‐sprayed coating of the microwave absorbing zinc‐nickel ferrite, (Zn_0.41Ni_0.59 )Fe₂O₄ have been studied at 300 K using the Mössbauer effect and x‐ray diffraction (XRD). Both techniques indicate that the plasma‐sprayed material separated into two phases. The first is a nickel‐rich phase with magnetic fields of 47.5 and 44.5 T at the tetrahedral and octahedral sites, respectively. The second is a zinc‐rich phase, zinc meta‐ferrite, having a small magnetic field of 4.2 T. The quadrupole splitting of this second phase is ΔE=0.34 mm s⁻¹, …

An Erasable Optical Memory Based On Stimulated Electronic Transition Concept, James D. Satira

Electrical & Computer Engineering Theses & Dissertations

Erasable optical memory systems with a high storage density and a large data transfer rate are required for many real time data acquisition systems such as those placed aboard NASA's space born platforms. A new concept for erasable optical memory involving stimulated electronic transitions (SET) will meet these requirements. The SET concept useful in erasable optical storage systems was demonstrated in MgS and SrS doped with Eu and Sm. The optical properties of these materials were studied. The reading and writing wavelengths for these samples were determined to be 950 and 514 nm respectively. The peaks of the emission spectra …

Third‐Order, Nonlinear Optical Interactions Of Some Benzporphyrins, D.V.G.L.N. Rao, Francisco J. Aranda, Joseph F. Roach, David E. Remy

Physics Faculty Publications

We measured third‐order, nonlinear optical susceptibility χ⁽³⁾ for a series of tetrabenzporphyrins in solution in tetrahydrofuran at 532 nm using degenerate four‐wave mixing with picosecond pulses and obtained values of molecular second hyperpolarizability 〈γ〉. The corresponding macroscopic χ⁽³⁾ values calculated for nine compounds with different substituent groups are four to five orders larger than CS₂. For five of the compounds the χ⁽³⁾ values are in the range 1.2–2.8×10⁻⁸ esu. Our experiments indicate that the nonlinearity is predominately electronic in origin with a response time faster than the 15 ps resolution of our system.

Biomineralization Of Iron Sulfides In Magnetotactic Bacteria From Sulfidic Environments, Dennis A. Bazylinski, Richard B. Frankel, Anthony J. Garratt-Reed, Stephen Mann

Physics

No abstract provided.

A Study Of The Liquid-Solid Interface During Rapid Resolidification Of Cooper-Titanium Using Molecular Dynamics, Craig L. Loisel

Theses and Dissertations

The behavior of the liquid-solid interface during resolidification of a condensed copper-titanium crystal is studied by atomistic simulation. A system of 1080 atoms (540 of each type) was simulated. The interface was created using monte carlo techniques and resolidification was performed by molecular dynamics. Resolidification was attempted at temperatures of 1200 K, 1100 K, 1000 K, 900 K, 818 K and 773 K. The liquid-solid interface was found to move only at 773 K, resulting in a chemically disordered crystal. The interface velocity observed in the simulation is 6.6 m/s which agrees well with the theoretical value of 5.5 m/ …

Calculated Point Defect Properties Of The Intermetallic Compounds Nickel Titanium (Niti) And Iron Titanium (Feti), Russell T. Lutton

Theses and Dissertations

Atomistic simulation with a modified version of the DYNAMO code was used to calculate the point defect properties of the intermetallic compounds nickel titanium and iron titanium. The calculated energies are believed to be experimentally accurate to within ± 0.1 eV. Vacant Ni or Fe lattice sites were preferred and had energies of 6.356 eV for NiTi and 5.899 eV for FeTi. Removing a Ti atom resulted in a neighboring antisite defect caused by migration of a Ni or Fe atom into the vacant Ti site. These configurations had energies of 7.024 eV for NiTi and 6.336 eV for FeTi. …

High Altitude Neutral Particle Transport Using The Monte Carlo Simulation Code Mcnp With Variable Density Atmosphere, David L. Monti

Theses and Dissertations

The Monte Carlo transport code, MCNP was modified for purposes of two dimensional neutron-photon transport modelling in a variable density atmosphere. Calculations were performed using cylindrical (r, z) geometry and a point isotropic neutron-photon source at an elevation of 40 kilometers. Neutron and photon fluence results were computed using ring detectors for field points at constant range versus source elevation angle and for field points at constant altitude versus radius. Comparisons between the modified and unmodified versions of MCNP showed a decrease in run time by a factor of two was possible. Only a fraction of the spatial cells previously …

The Jovian Ionospheric E Region, Y. H. Kim, Jane L. Fox

Physics Faculty Publications

We have constructed a model of the Jovian ionosphere that includes direct photoionization of hydrocarbon molecules. A high resolution solar spectrum was synthesized from Hinteregger's solar maximum spectrum (F79050N) and high resolution cross sections for photoabsorption by H₂ bands in the range 842 to 1116 Å were constructed. Two strong solar lines and about 30% of the continuum flux between 912 and 1116 Å penetrate below the methane homopause despite strong absorption by CH₄ and H₂. We find that hydrocarbons (mainly C₂H₂) are ionized at a maximum rate of 55 cm^{−3 …}

Phenomena Relating To Charge In Insulators: Macroscopic Effects And Microscopic Causes, Jacques Cazaux, Claude Le Gressus

Scanning Microscopy

Conservation of current under steady-state conditions makes it possible to determine the sign of charges trapped in an insulator subjected to ionizing radiation. The maximum value of the surface potential can thus be estimated.

On the basis of a given trapped charge distribution, the pattern of the electrical field and of the potential can thus be established, and the influence of the shape of the sample and its environment can be clearly shown. Change of trapped charges with time (at the start and after irradiation) is then examined. Finally, the microscopic causes of trapping of charge is suggested by analogy …

Revised Global Model Of Thermosphere Winds Using Satellite And Ground-Based Observations, A E. Hedin, M A. Biondi, R G. Burnside, G Hernandez, R M. Johnson, T L. Killeen, C Mazaudier, J W. Meriwether, J E. Salah, R W. Smith, N W. Spencer, Vincent B. Wickwar, T S. Virdi

All Physics Faculty Publications

Thermospheric wind data obtained from the Atmosphere Explorer E and Dynamics Explorer 2 satellites have been combined with wind data for the lower and upper thermosphere from ground-based incoherent scatter radar and Fabry-Perot optical interferometers to generate a revision (HWM90) of the HWM87 empirical model and extend its applicability to 100 km. Comparison of the various data sets with the aid of the model shows in general remarkable agreement, particularly at mid and low latitudes. The ground-based data allow modeling of seasonal/diurnal variations, which are most distinct at mid latitudes. While solar activity variations are now included, they are found …

Raman Scattering And Lattice-Dynamical Calculations Of Alkali-Metal Sulfates, D. Liu, H. M. Lu, John R. Hardy, F. G. Ullman

John R. Hardy Papers

Raman-scattering measurements on single crystals of K₂SO₄, Rb₂SO₄, and Cs₂SO₄ have been made at both room and liquid-nitrogen temperatures. Lattice-dynamical calculations, based on a rigid-ion model using the Gordon-Kim method to calculate the short-range potentials, were performed. The influence of the alkali-metal ions on the lattice-dynamical properties of the crystals is discussed.

Optical Property Measurements In Turbid Media Using Frequency Domain Photon Migration, Bruce J. Tromberg, Lars O. Svaasand, Tsong-Tseh Tsay, Richard C. Haskell, Michael W. Berns

All HMC Faculty Publications and Research

In frequency domain photon migration (FDPM), amplitude-modulated light is launched into a turbid medium, e.g. tissue, which results in the propagation of density waves of diffuse photons. Variations in the optical properties of the medium perturb the phase velocity and amplitude of the diffusing waves. These parameters can be determined by measuring the phase delay and demodulation amplitude of the waves with respect to the source. More specifically, the damped spherical wave solutions to the homogeneous form of the diffusion equation yield expressions for phase (φ) and demodulation (m) as a function of source distance, modulation frequency, absorption coefficient (β), …

The Venus Ultraviolet Aurora: A Soft Electron Source, Jane L. Fox, A. I. F. Stewart

Physics Faculty Publications

The Pioneer Venus Orbiter Ultraviolet Spectrometer has recorded continuous but variable emissions of atomic oxygen at 1304 and 1356 Å in images of the nightside of Venus. We show that the observed intensities are consistent with the presence of precipitation of soft electrons into the nightside thermosphere. Model calculations are presented in which upper and lower limits to the magnitude of the electron flux necessary to produce the observed intensities are derived. Constraints are imposed on the energy spectrum of the electrons by the measured ion densities and by the predicted intensities of other emissions that have not been detected.

Electric Field Induced Emission As A Diagnostic Tool For Measurement Of Local Electric Field Strengths, A. N. Dharamsi, K. H. Schoenbach

Bioelectrics Publications

The phenomenon of electric field induced (EFI) emission is examined in several diatomic and polyatomic molecules. The possibility of using this phenomenon as a diagnostic tool to measure, nonintrusively, the strength and direction of local electric fields in plasmas is discussed. An estimate of the EFI signal emitted in a typical application plasma is given. This yields a lower bound on the detector sensitivity necessary to exploit EFI emission in practical applications. It is concluded that, at present, the EFI signal could be measured by some very sensitive infrared detection schemes available. Current progress in infrared detector technology, if maintained, …

Microscopic Irreversibility And Gibbs Entropy, John D. Ramshaw

Physics Faculty Publications and Presentations

In a recent paper of the same title [J. Non-Equilib. Thermodyn., 15 (1990), 151], Liboff observed that the fine-grained Gibbs entropy of a canonical Hamiltonian system remains constant in time even for Hamiltonians that are not even in momenta and consequently violate time-reversal invariance (TRI). Here we extend this observation to non-canonical Hamiltonian systems, including systems with singular Poisson tensors and pseudo-Hamiltonian systems that violate the Jacobi identity. Necessary and sufficient conditions are given for the Gibbs entropy to be constant in such systems. The concept of TRI is not in general meaningful for such systems, but it is shown …

Nonlinear-Interaction Of A Detonation Vorticity Wave, D. G. Lasseigne, T. L. Jackson, M. Y. Hussaini

Mathematics & Statistics Faculty Publications

The interaction of an oblique, overdriven detonation wave with a vorticity disturbance is investigated by a direct two-dimensional numerical simulation using a multidomain, finite-difference solution of the compressible Euler equations. The results are compared to those of linear theory, which predict that the effect of exothermicity on the interaction is relatively small except possibly near a critical angle where linear theory no longer holds. It is found that the steady-state computational results whenever obtained in this study agree with the results of linear theory. However, for cases with incident angle near the critical angle, moderate disturbance amplitudes, and/or sudden transient …

Magnetic Fine Particles In Biological Systems, Dominic P.E. Dickson, Richard B. Frankel

Physics

Two examples of biological magnetic fine particles are considered: iron-storage proteins and magnetotactic bacteria. These cover many aspects of this field, including the use of well-defined biological systems for testing theoretical models, using magnetic properties to distinguish between different biological materials, producing magnetic materials by biological processes, and using optimised biological magnetic systems as a guide to the production of synthetic magnetic materials.

Defect Structure, Nonstoichiometry, And Phase Stability Of Ca-Doped Ycro3, G. F. Carini, Harlan U. Anderson, M. M. Nasrallah, Don M. Sparlin

Materials Science and Engineering Faculty Research & Creative Works

The dependence of the defect structure of Ca-doped YCrO₃ on oxygen activity and temperature was investigated by high temperature thermogravimetric measurements. Defect models developed from electrical conductivity data obtained in a previous study were used to interpret the thermogravimetric data. A correlation was found between the electrical conductivity and the thermogravimetric data which suggested that these data were concomitantly dependent on the acceptor dopant and oxygen vacancy dependance of the thermodynamic parameters. Kröger-Vink type diagrams showing the regions of stability with respect to oxygen activity and temperature were constructed. The TGA data show that Ca-doped YCrO₃ is even …

Electrical Conductivity, Seebeck Coefficient And Defect Chemistry Of Ca-Doped Ycro3, G. F. Carini, Harlan U. Anderson, Don M. Sparlin, M. M. Nasrallah

Materials Science and Engineering Faculty Research & Creative Works

The electrical transport behavior and defect structure of Ca-doped YCrO₃ were studied using electrical conductivity and Seebeck coefficient measurements as a function of oxygen activity and temperature. Defect models derived from the electrical conductivity data were found to adequately relate the concentration of charge carriers to the acceptor dopant and oxygen vacancy concentrations. Thermodynamic properties were calculated and found to be consistent with the model. Activation energy and carrier mobility data were also obtained. The analysis of the electrical conductivity, Seebeck and mobility data suggest that the conduction process in Ca-doped YCrO₃ occurs via the small polaron hopping …

Effects Of Sample Orientation On The Corrosion Of Zinc In Ammonium Sulfate And Sodium Hydroxide Solutions, D. Abayarathna, Edward Boyd Hale, Thomas J. O'Keefe, Y. M. Wang, D. Radovic

Physics Faculty Research & Creative Works

The corrosion and electrochemical properties of three zinc single crystal surfaces with different orientations have been investigated. In near-neutral 1 M (NH₄)₂SO₄, the corrosion rates on all three surfaces were found to be similar. However, the SEM morphologies of the corresponding corroded surfaces were markedly different from each other, but consistent with preferential attack of {1120} surfaces. In alkaline 0.5 N NaOH solution, the three sample orientations showed significantly different reactivities, with the (1120) surface exhibiting the highest reactivity and corrosion rate. Here, passivation ultimately occurred and the difference in the corrosion performance of …