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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 …

Rotationally Resolved Laser Spectroscopy Of The 3s2Σ+ ← 2p2ii Transition In 6li20ne And 7li20ne Van Der Waals Molecules, Chang Jae Lee

Physics Theses & Dissertations

The rotationally resolved absorption spectrum of the ⁶Li²⁰Ne and ⁷Li²⁰Ne 3s²Σ⁺ ← 2p² II transition has been observed. For each isotope, thirteen vibrational transitions from four vibrational levels (v"=0, 1, 2, and 3) of the lower 2p² II to six (v’=0, 1, 2, 3, 4, and 5) of the upper 3s*Σ⁺ electronic state have been rotationally analyzed. Adiabatic potentials and dissociation energies for both states have been obtained through an inverse perturbation analysis. For the 2p²II state, a well depth of 212(5) cm^-1 and an …

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 …

Intraconfiguration Interactions In Barium 6p1/2Nf Autoionizing States, Xiao Wang, J. Greg Story, William E. Cooke

Physics Faculty Research & Creative Works

Measurements are reported of the energies and linewidths of the J=2, 3, and 4 components of the 6p_1/214f and 6p_1/219f states of barium. These states are anomalously broad, having autoionization lifetimes of approximately 1/2 of a classical Rydberg orbit period, and previously measurements have discerned no differences among the various J components. This work shows that the differences can be observed, and are consistent with calculations. The variations between states would be large if the states were LS coupled, but the large 6p ionic fine-structure forces recoupling into jj configurations. The spherical symmetry of the 6p …

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.

Polarized X-Ray-Emission Studies Of Methyl Chloride And The Chlorofluoromethanes, Dennis W. Lindle, P. L. Cowan, T. Jach, R. E. Lavilla, R. D. Deslattes, Rupert C. Perera

Chemistry and Biochemistry Faculty Research

A new technique sensitive to molecular orientation and geometry, and based on measuring the polarization of x-ray emission, has been applied to the Cl-containing molecules methyl chloride (CH₃Cl) and the chlorofluoromethanes (CF₃Cl, CF₂Cl₂, and CFCl₃) in the gas phase. Upon selective excitation using monochromatic synchrotron radiation in the Cl K-edge (Cl 1s) near-threshold region, polarization-selective x-ray emission studies reveal highly polarized molecular valence x-ray fluorescence for all four molecules. The degree and the orientation of the polarized emission are observed to be sensitive to the incident excitation energy near …

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/ …

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 …

Selective Area Deposition Of Boron On Si(111) Induced By Synchrotron Radiation, R.A. Rosenberg, F.K. Perkins, D.C. Mancini, G.R. Harp, B.P. Tonner, S. Lee, Peter A. Dowben

Peter Dowben Publications

We have performed the first deposition of boron on Si(111) induced by broadband synchrotron radiation (SR). Contamination-free thin films were grown at room temperature using decaborane (B₁₀H₁₄) as the source gas. After deposition the films were examined using photoelectron microscopy, which showed that film growth was limited to the region illuminated by SR. The temperature of the substrate rose less than 10 K. These results indicate that gas-phase excitations are not important and that the films are deposited by a nonthermal, photoinduced mechanism. Masked exposures demonstrate the potential of this technique for patterned deposition.

First-Order Amplitude For General State-To-State Transitions In Hydrogen By Projectile Impact, Jack C. Straton

Physics Faculty Publications and Presentations

The closed analytic form for bound-state transitions due to projectile impact is found in the intermediate representation. The coordinate integral is obtained by evaluating the remaining two integrals in the general multicenter integral derived previously [J.C. Straton, Phys. Rev. A 41, 71 (1990)]. Evaluating the remaining time integral depends upon relating a sum of modified Bessel functions of the second kind K_N+1/2(z) to a simple polynomial in 1/z. The results of Van Den Bos and De Heer [Physica 34, 333 (1967)] are shown to be missing a phase factor of (-i)^(l′+l)

High-Resolution Photoelectron Spectrometry Study Of Conjugate Shakeup Processes In The Li 1s Threshold Region, B. Langer, J. Viefhaus, Oliver Hemmers, A. Menzel, U. Becker

Environmental Studies Faculty Publications

Partial cross sections and angular-distribution asymmetry parameters of diagram and satellite lines associated with Li 1s photoionization were measured using synchrotron-radiation excitation. Special emphasis was given to a high-resolution study of the ¹P and ³P conjugate shakeup satellite lines testing qualitative predictions of the conjugate shakeup model: increasing σ and decreasing β values towards threshold, both being verified. Comparison with recent relaxed Hartree-Fock calculations shows good agreement for the ¹P satellite, but demonstrates also that the present theory does not seem to be able to describe the cross-section behavior of the ³P satellite correctly.

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 …

Gaussian Reference Auid And Interpretation Of Quantum Geometrodynamics, Karel V. Kucha, Charles G. Torre

Aerospace, Physics, and Space Science Faculty Publications

The of vacuum geometrodynamics is turned into a Schrödinger equation by imposing the normal Gaussian coordinate conditions with s and then restoring the coordinate invariance of the action by parametrization. This procedure corresponds to coupling the gravitational field to a reference fluid. The source appearing in the Einstein law of gravitation has the structure of a heat-conducting dust. When one imposes only the Gaussian time condition but not the Gaussian frame conditions, the heat flow vanishes and the dust becomes incoherent. The canonical description of the fluid uses the Gaussian coordinates and their conjugate momenta as the fluid variables. The …

Anomaly In The Dynamic Behavior Of The Electroclinic Effect Below The Nematicsmectic-A Phase Transition, Zili Li, Robert B. Akins, Gregory A. Dilisi, Charles Rosenblatt, Rolfe G. Petschek

Faculty Scholarship

The electroclinic effect and dielectric response have been investigated in the British Drug House material SCE12 over its entire 15-K smectic-A range. Near the smectic-Asmectic-C*-phase transition both the electroclinic coefficient and dynamic response behave normally, the former diverging and the latter exhibiting a critical slowing down on approaching TA-C* from above. Similar behavior is seen in the dielectric response. Approximately 10 to 12 K above TA-C*, however, it was found that the electroclinic relaxation time levels off and even begins to increase again on approaching the nematicsmectic-A transition from below. The magnitude of the electroclinic coefficient, however, decreases monotonically on …

Composite Operator Renormalization And The Trace Anomaly, David G. Robertson

Physics Faculty Scholarship

The general connection between the renormalization of elementary fields and couplings and of appropriate composite operators is discussed. A general method is presented for computing the anomalous dimension matrix of the lagrangian composite operators, to all orders in perturbation theory, in terms of the elementary beta functions and anomalous dimensions. The trace anomaly for a general field theory is determined.

A Search For Embedded Young Stellar Objects In And Near The Ic 1396 Complex, Richard Schwartz, Bruce Wilking, Armen Giulbudagian

Physics Faculty Works

The IRAS data base is used to locate young stellar object candidates in and near the IC 1396 complex located in the Cepheus OB2 association. Co-added survey data are used to identify all sources with a flux density Snu(100) greater than 10 Jy and with Snu(100) greater than Snu(60). The 15 sources located at the positions of globules and dark clouds are further analyzed using the in-scan slices to assess the source profiles

Nonequilibrium Processes In Polymers Undergoing Interchange Reactions. Part 2: Reaction-Diffusion Processes, Alejandro Garcia, J. Pojman, D. Kondepudi, C. Van De Broeck

Faculty Publications

A reactiodffusion system of polymers undergoing interchange reactions is studied. The equation that describes the dynamics of the system is similar to the Boltzmann equation for a gas of hard spheres. We consider a one-dimensionsl system in which the average length and the concentrations at the boundaries are fixed. The resulting steady states are obtained analytically and with numerical integration of equations obtained by using a local equilibrium approximation. Monte Carlo simulations of experimentally realizable conditions were performed and compared. The results reveal a nonlinear distribution of molecular concentration and mass. The entropy of the polymer distributions is calculated as …

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 …

Onset Of Convection For Autocatalytic Reaction Fronts: Laterally Unbounded System, Boyd F. Edwards, J. W. Wilder, K. Showalter

All Physics Faculty Publications

The linear stability of exothermic autocatalytic reaction fronts that convert unreacted fluid into a lighter reacted fluid is considered using the viscous thermohydrodynamic equations. For upward front propagation and a thin front, the discontinuous jump in density at the front is reminiscent of the Rayleigh-Taylor problem of an interface between two immiscible fluids, whereas the vertical thermal gradient near the front is reminiscent of the Rayleigh-Bénard problem of a fluid layer heated from below. The problem is also similar to flame propagation, except that here the front propagation speed is limited by catalyst diffusion rather than by activation kinetics. For …

Cellular Track Model Of Biological Damage To Mammalian Cell Cultures From Galactic Cosmic Rays, Francis A. Cucinotta, Robert Katz, John W. Wilson, Lawrence W. Townsend, John E. Nealy, Judy L. Shinn

Robert Katz Publications

The quality factor (QF) as defined in International Commission on Radiological Protection report no. 26 (ICRP 26, ref. 1) or in International Commission on Radiation Units and Measurements report no. 40 (ICRU 40, ref. 2) is not expected to be a valid method for assessing the biological risk for deep space missions where the high-energy heavy ion (HZE) particles of the galactic cosmic rays (GCR) are of major concern. No human data for cancer induction from the HZE particles exist, and information on biological effectiveness is expected to be taken from experiments with animals and cultured cells (ref. 3). Experiments …

The Photorefractive Effect In Batio3, Tom Savard

Honors Theses, 1963-2015

The photorefractive effect was observed in a sample of BaTiO, crystal. In two-beam coupling experiments, the crystal failed to amplify the signal beam even though experimental configurations that provided other researchers with large gains were used. However, beam fanning, a two-beam coupling effect, was observed. The unmeasurable gain of our crystal in twc-beam coupling experiments might be due to multiple domains in the crystal or competition between hole and electron charge carriers. In addition, a self-pumped phase conjugate mirror was made using the "cat" configuration. The formation of the phase conjugate mirror in the crystal was observed using the image …

The Solution Space Of The Unitary Matrix Model String Equation And The Sato Grassmannian, Konstantinos N. Anagnostopoulos, Mark Bowick, Albert Schwarz

Physics - All Scholarship

The space of all solutions to the string equation of the symmetric unitary one-matrix model is determined. It is shown that the string equation is equivalent to simple conditions on points V 1 and V 2 in the big cell Gr (0) of the Sato Grassmannian Gr. This is a consequence of a well-defined continuum limit in which the string equation has the simple form [P; Q \Gamma ] = 1, with P and Q \Gamma 2 \Theta 2 matrices of differential operators. These conditions on V 1 and V 2 yield a simple system of first order differential equations …

Magnetic-Field-Induced Alignment-To-Orientation Conversion In Sodium, G. W. Schinn, Xianming Han

Scholarship and Professional Work - LAS

We report a detailed investigation of excited-state alignment-to-orientation conversion in the presence of an external magnetic field. This counterintuitive phenomenon occurs under intermediate-coupling conditions. A weak, linearly polarized, cw laser beam was used to excite and align the Na 3P3/2 state in an atomic beam along the z direction. The degree of circular polarization of the resulting fluorescence was detected along the z direction as a function of magnetic-field strength. The spectrally integrated transitions originating from individual F levels of the 3S1/2 state yield a maximum circular-polarization fraction of ∼40%; integrating the circular polarization over all the allowed 3S1/2-3P3/2 transitions …

Fine‐Structure Mixing Within The Zn(43pj) Multiplet By Collisions With The Noble Gases, Xianming Han, J. F. Kelly

Scholarship and Professional Work - LAS

Measurements of rate coefficients for intramultiplet state transfer of Zn(4 ³ P ₁→4 ³ P _J’) by collisions with the rare gases are presented. The state‐to‐state binary rate coefficients are derived from least‐squares fittings of the time‐resolved triexponential behavior of the 4 ³ P ₁fluorescence. These rate coefficients were studied systematically over a temperature range of 690–1100 K in order to characterize the velocity dependence of the collisional coupling. The systematic behavior of the rate coefficients with varying temperature and noble gas species is qualitatively consistent with a nearly adiabatic coupling limit for noncrossing levels.

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), …

Systematic Variation Of Transport And Thermodynamic Properties With Degree Of Reduction In Nd1.85ce0.15cuo4-, Nathanael A. Fortune, K. Murata, M. Ishibashi, Y. Yokoyama, Y. Nishihara

Physics: Faculty Publications

Superconductivity only occurs in Nd1.85Ce0.15CuO4- after heat treatment in a reducing at- mosphere; yet we find the oxygen loss during reduction to be remarkably small. To better understand the physical role of reduction, we have systematically varied the degree of reduction in a series of ceramic samples by varying the partial pressures of oxygen and argon in the reducing atmosphere, keeping the total pressure constant. We find that small increases in the degree of reduction strongly increase the apparent carrier density and the superconducting Meissner fraction. We also find that there is an optimal degree of reduction to produce a …

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.

K-Shell Ionization Measurements For Light Incident Icons, Rahul Mehta, George Bissinger

Journal of the Arkansas Academy of Science

The ionization of the K-shell in targets of copper, silver, dysprosium and gold was investigated with incident ion beams of proton and helium ions in the range 0.5 MeV/u to 3 MeV/u. The x-rays were detected by a HpGe detector. K-shell x-ray production cross section were determined by normalization of the x-ray yield to the incident beam flux, the Rutherford-scattered ions and the nuclear-Coulomb excited gamma ray yield. The multiple normalization procedures minimize the errors in these cross section measurements. The data are compared with the predictions of the ECPSSR theory for K-shell ionization. The atomic number dependence of these …

First-Principles Study Of Phase Transitions In Kno3, H. M. Lu, John R. Hardy

John R. Hardy Papers

We report a first-principles simulation study of phase transitions in KNO₃, using our recently developed method for treating ionic molecular solids. With the interionic potentials calculated from ab initio electron charge densities of the ions, our structural static relaxation gave close fits to both the normal room-temperature (α-phase) and the ferroelectric (γ-phase) structures. Our supercell molecular-dynamics calculations closely simulated the transitions from the α phase and γ phase to the high-temperature disordered β phase, and successfully reproduced the abnormally large c-axis thermal expansion observed in experiment. Both transitions were found to be initiated by the rotations of the …

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 …