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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 …

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 …

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 …

A Mössbauer-Effect Study Of A Series Of R₂Fe₁₄C Hard Magnetic Materials, Gary J. Long, Oran Allan Pringle, Gaya Kanishka Marasinghe, Fernande Grandjean, K. H. Buschow

Chemistry Faculty Research & Creative Works

The ⁵⁷Fe Mössbauer-effect spectra of the series of hard magnetic materials, R₂Fe₁₄C, where R is Nd, Gd, Tb, Dy, Ho, and Lu, have been measured at 295 K. All of these carbides exhibit uniaxial magnetic anisotropy. The spectra resemble those obtained for the related R ₂Fe₁₄B compounds and have been fit with the model used earlier for Nd₂Fe₁₄B. The magnitude of the hyperfine field on each site, as a function of rare earth, parallels the Curie temperature; the maximum hyperfine fields and the maximum Curie temperature are observed …

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 …

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 …

Long-Range Dipole Field Effects On H– Detachment Processes Above The H(N=2) Threshold, Anthony F. Starace

Anthony F. Starace Publications

The long-range dipole field interaction between a low energy electron and the hydrogen atom in the n = 2 state is shown to be the key for understanding significant features of a number of H^– detachment processes. Collisional, single photon, and two-photon detachment processes are examined, each of which is shown to be sensitive to different aspects of low-energy H(n=2)–e^– interactions. Specifically, these detachment processes are best suited respectively for exhibiting the finite threshold cross sections for certain ¹S^e, ¹P⁰, and ¹D^e final-state channels, the shape resonance in one of …

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.

Fluctuations In Astronomical Masers, Moshe Elitzur

Physics and Astronomy Faculty Publications

The radiation of astronomical masers fluctuates on the time scale 1/Gamma, where Gamma is the levels' loss rate. These intensity fluctuations reflect fluctuations of the level poulations around their mean, steady state values over the length scale λ_c = c/Γ. In saturated masers, the intensity fluctuations are dominated by passage through the unsaturated core. The effects of the saturated zones and of the seed radiation that the masers amplify can be neglected.

These fluctuations may have been detected in recent observations by Clegg and Cordes (1991) of Galactic H II/OH masers, providing a possible direct determination of the …

Polarization Of Astronomical Maser Radiation, Moshe Elitzur

Physics and Astronomy Faculty Publications

The polarization of maser radiation when the source is permeated by an aligned magnetic field is derived for arbitrary angular momenta of the transition states. This generalization is made possible by an analysis of the structure of the propagating waves in a frame aligned with the magnetic axis. The key elements in determining the polarization properties are the assumption of independent and incoherent pump and loss processes for all magnetic sublevels, and the beaming of maser radiation. The radiation propagating in the direction of maximal intensity growth is polarized according to the solutions derived by Goldreich, Keeley, and Kwan for …

Relativistic Wave Equation For Anyons, R. Jackiw, V. Parameswaran Nair

Publications and Research

Construction of one-particle states as unitary representations of the Poincare algebra in 2 + 1 dimensions shows that an anyon has one polarization state. However, for nonzero spin manifestly linear and covariant realizations of Lorentz transformations require more than one field component, and an infinite number is needed when the value of spin is not an integer or half-integer. We discuss the relation between these two aspects of Poincare symmetry. In particular, we construct a relativistic equation for anyons where the number of physical polarizations is reduced to one by virtue of a gauge symmetry or equivalent constraint.

Synthesis And Superconducting Properties Of Tl-Ba-Ca-Cu-O Films, Sy_Hwang Liou, V.K. Chan, F. Foong, W.Y. Lee, Y.S. Gou, T.M. Uen

Sy-Hwang Liou Publications

Tl-Ba-Ca-Cu-O superconducting films were synthesized by sputtering either from a single target or from two oxide targets in a symmetric configuration. Films were zero resistance T_c of up to 122 K were obtained after various postannealing treatments at 870-950°C under an oxygen atmosphere. The composition of the films is not very homogeneous on the submicrometer scale. The critical current of these films at 77 K is in the 103-A/cm²-10⁴-A/cm² range, which is much smaller than that of films prepared on SrTiO₃ and LaAlO₃ substrates. The low critical current density in these films …

Redox Capacity Of Apo Mammalian Ferritin, Gerald D. Watt, Richard B. Frankel

Physics

No abstract provided.

Iron Biominerals: An Overview, Richard B. Frankel

Physics

No abstract provided.

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.

Realization Of A Measurement Of A Weak Value, N. W M Ritchie, J. Greg Story, Randall G. Hulet

Physics Faculty Research & Creative Works

We present the first realization of a measurement of a weak value, a concept recently introduced by Aharonov, Albert, and Vaidman (AAV). Our experiment uses a birefringent crystal to separate the two linear-polarization components of a laser beam by a distance small compared to the laser-beam waist. This weak measurement is followed by a strong measurement which translates the centroid of the beam by a distance far larger than the birefringence-induced separation. In addition, we present data corresponding to orthogonal initial and final states, for which the weak value is not defined. This interference effect may have application in the …

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 …

Intercellular Junctions, Motility, And Magnetosome Structure In A Multicellular Magnetotactic Prokaryote, Frank G. Rodgers, Richard P. Blakemore, Nancy A. Blakemore, Richard B. Frankel, Dennis A. Bazylinski, Denise Maratea, Christine Rodgers

Physics

A many-celled, magnetotactic, prokaryote obtained from brackish water possessed intercellular connections at points of contact between the outer membranes of constituent cells. These connections structurally resembled the "gap junctions" found in eukaryotes. Each aggregate organism consisted of 10 to 30 individual gram-negative cells containing material with the appearance of poly-𝛽-hydroxybutyrate and magnetosomes of unusual arrangement, structure and composition. The aggregate, which possessed prokaryotic-type flagella arranged at the outward surfaces of each cell, showed motility indicative of coordination between individual component cells. These results suggest that this organism is a multicellular prokaryote.

Theory Of An Atomic Beam Splitter Based On Velocity-Tuned Resonances, Scott Glasgow, P. Meystre, M. Wilkens, E. M. Wright

Faculty Publications

We develop the theory of an atomic beam splitter in which a monoenergetic beam of two-level atoms is incident normally to a classical standing-wave light field. The incident atomic wave function can be split into two coherent components with transverse momenta ±(2n + 1)fzk using velocity-tuned resonances, where n is the order of the resonance. We discuss the cases of zero- and first-order resonances in detail, and show that the velocity-tuned resonances are renormalized due to a high-frequency Stark shift. Numerical results that display the effects of a finite momentum spread in the incident atomic beam are presented.

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. …

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 …

Recent Advances In The Comparison Of Matter— And Antimatter—Atom Collisions, D. R. Schultz, Ronald E. Olson, C. O. Reinhold

Physics Faculty Research & Creative Works

The relatively recent advent of low energy antimatter projectiles has spurred a rapid advance in the comparison of matter- and antimatter-atom collisions. These experimental studies have in turn stimulated a great deal of theoretical effort to explain their results, and together both theory and experiment have shed new light on the dynamics of ion-atom collisions. Here we review these developments with particular emphasis on the processes of ionization and charge transfer. © 1991 IOP Publishing Ltd.

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.

Relativistic Approach For E± Scattering From Argon, Sultana N. Nahar, J. M. Wadehra

Physics and Astronomy Faculty Research Publications

Differential and integrated elastic, integrated total cross sections as well as various polarization parameters–the spin polarization P and the parameters T and U describing the change in the polarization vector during scattering–for the scattering of electrons and positrons from argon in the energy range of 3–300 eV are calculated using the relativistic Dirac equation. The real part of the projectile-target interaction is represented by a sum of model potentials. The phase shifts for large angular momenta ħl are calculated using the Born approximation. The relativistic calculations for the differential and integrated elastic cross sections obtained using the pure real potential …

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)

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 …}

Substrate-Induced Magnetic Ordering Of Rare-Earth Overlayers, Peter A. Dowben, D. Lagraffe, Dongqi Li, A. Miller, Ling Zhang, L. Dottl, M. Onellion

Peter Dowben Publications

We have studied the magnetic ordering of terbium overlayers on Cu(100) and Ni(111), using angle-resolved photoemission. The 5p_3/2 to 5p_1/2 shallow-core-level branching ratios in different photoemission geometries provide a measure of the magnetic ordering in rare-earth-metal overlayers as a result of final-state effects in photoemission. We find that ferromagnetic substrates order paramagnetic terbium overlayers. This induced magnetic ordering is not a crystal-field effect and can be modeled by Ginzburg-Landau theory. Application of Ginzburg-Landau theory to our results suggests that the correlation length of paramagnetic terbium κ^-1 is between 2.5 and 3.5 Å. Reversible increases in …

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 …