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Electron Paramagnetic Resonance Of Gd3+ Ions In The Superconductor Gdba2Cu3OX, F. Mehran, S. E. Barnes, C. C. Tsuei, T. R. Mcguire

Physics Articles and Papers

EPR from Gd³⁺ ions in the high-T_c≃90 K superconductor GdBa₂Cu₃O_x is reported. The temperature dependence of the linewidth and intensity of the Gd³⁺ ions in the vicinity of T_c are related to the corresponding characteristics of the Cu²⁺ ions.

Paramagnetic Resonance Of Cu2+ Ions In The Superconductor Y0.2Ba0.8CuoX, F. Mehran, S. E. Barnes, T. R. Mcguire, W. J. Gallagher, R. L. Sandstrom, T. R. Dinger, D. A. Chance

Physics Articles and Papers

A strong paramagnetic resonance signal characteristic of Cu²⁺ ions in ‖x²-y²〉 states is observed in the high-T_c≊90 K superconductor Y_0.2Ba_0.8CuO_x. The line intensity of the ioniclike signal shows a deviation from Curie behavior at T≳T_c. It is speculated that the phase that is responsible for the signal is an example of an Anderson lattice with an unusually high Kondo temperature.

Observation Of Al2O3: Cr3+ Magnetic Resonance Via Solitons In Long Josephson Junctions, F. Mehran, S. E. Barnes, C. C. Chi, R. L. Sandstrom, C. P. Umbach

Physics Articles and Papers

We have detected the zero-field electron-spin resonance signal of Al₂O₃ with ∼1000 ppm Cr³⁺ using an edge Josephson junction. The sample comprises the substrate upon which the junction was fabricated and the coupling to the electron-spin resonance is via the solitons which exist in these "long" devices.

Theoretical Study Of The Effect Of Ionospheric Return Currents On The Electron Temperature, Robert W. Schunk, Jan Josef Sojka, M. D. Bowline

All Physics Faculty Publications

An electron heat flow can occur in a partially ionized plasma in response to either an electron temperature gradient (thermal conduction) or an electron current (thermoelectric heat flow). The former process has been extensively studied, while the latter process has received relatively little attention. Therefore a time-dependent three-dimensional model of the high-latitude ionosphere was used to study the effect of field-aligned ionospheric return currents on auroral electron temperatures for different seasonal and solar cycle conditions as well as for different upper boundary heat fluxes. The results of this study lead to the following conclusions: (1) The average, large-scale, return current …

Recoil-Ion Production From Zero-Impact-Parameter H+-Ar And H+-Kr Collisions At 20-70 Kev, Akio Itoh, M. Eugene Rudd

M. Eugene Rudd Publications

Recoil ions emitted at 70° from H⁺-Ar and at 50° and 70° from H+-Kr collisions at 20-70 keV were analyzed by an electrostatic spectrometer. Ions selected in this way result from collisions at very small, essentially zero, impact parameters. Charge states up to 6 + were identified in the spectrum. The cross section for each charge state was measured. The data indicate that these close collisions produce a larger fraction of ions in high charge states than more distant collisions.

Hemispherical Emissivity Of V, Nb, Ta, Mo, And W From 300 To 1000 K, S. X. Cheng, P. Cebe, L. M. Hanssen, D. Mark Riffe, A. J. Sievers

All Physics Faculty Publications

The hemispherical emissivities of five transition elements, V, Nb, Ta, Mo, and W, have been measured from 300 to 1000 K, complementing earlier higher-temperature results. These low-temperature data, which are similar, are fitted to a Drude model in which the room-temperature parameters have been obtained from optical measurements and the temperature dependence of the dc resistivity is used as input to calculate the temperature dependence of the emissivity. A frequency-dependent free-carrier relaxation rate is found to have a similar magnitude for all these elements. For temperatures larger than 1200 K the calculated emissivity is always greater than the measured value, …

A Substorm Resulting From Energy Storage In The Magnetosphere, T S. Jorgensen, K Larsen, W J. Heikkila, Vincent B. Wickwar, G Haerendel

All Physics Faculty Publications

In order to study the problem whether magnetospheric substorms are directly driven by solar wind energy or result from unloading of such energy temporarily stored in the magnetosphere, it is necessary to investigate substorms following long quiescent periods and to observe solar wind parameters in proximity of the magnetsosphere as well as many high-latitude ionosphere parameters with good temporal resolution.

In this study we present such observations obtained on November 29, 1984 by the AMPTE-IRM spacecraft just outside the bow shock and by the Sondrestrom incoherent scatter radar plus several other instruments in the earth's polar region.

We infer from …

A Theoretical Study Of The Lifetime And Transport Of Large Ionospheric Density Structures, Robert W. Schunk, Jan Josef Sojka

All Physics Faculty Publications

Large-scale density structures are a common feature in the high-latitude ionosphere. They have been observed in the dayside cusp, polar cap, and nocturnal auroral region. Relative to background densities, the perturbations associated with large-scale structures vary from about 10% to a factor of 100. The lifetime and transport characteristics of “large” ionospheric structures (factor of 10 to 100) were studied with the aid of a three-dimensional time-dependent ionospheric model. Both density depletions and enhancements were considered. A density structure was created at a specific location in the high latitude F region and the subsequent evolution was followed for different seasonal …

Lower-Thermospheric Winds At High Latitude, R M. Johnson, Vincent B. Wickwar, R G. Roble, J G. Luhmann

All Physics Faculty Publications

Observations made of the high-latitude E-region with the Chatanika, Alaska (65° N), incoherent scatter radar facility during the summer months of 1976 to 1982 are presented. Fourteen 24-h experiments were performed with altitude resolution between 9 and 24 km. Ion drifts measured during these experiments have been analysed to obtain neutral winds at lower-thermospheric heights. Tidal oscillations are the predominant feature of the neutral winds from 90 to 125 km. The semidiurnal oscillation is particularly strong, attaining peak amplitudes of ≈50 m/s at 110 km. Average semidiurnal tidal phases are in good agreement with previous mid- to hight-latitude observations. …

Theoretical Study Of The High-Latitude Ionosphere’S Response To Multicell Convection Patterns, Jan Josef Sojka, Robert W. Schunk

All Physics Faculty Publications

It is well known that convection electric fields have an important effect on the ionosphere at high latitudes and that a quantitative understanding of their effect requires a knowledge of the plasma convection pattern. When the interplanetary magnetic field (IMF) is southward, plasma convection at F region altitudes displays a two-cell pattern with antisunward flow over the polar cap and return flow at lower latitudes. However, when the IMF is northward, multiple convection cells can exist, with both sunward flow and auroral precipitation (theta aurora) in the polar cap. The characteristic ionospheric signatures associated with multicell convection patterns were studied …

Optical And Radar Characterization Of A Short-Lived Auroral Event At High Latitude, A Vallance-Jones, R L. Gattinger, P Shih, J W. Meriwether, Vincent B. Wickwar, J D. Kelly

All Physics Faculty Publications

Observations of optical emission intensities and incoherent scatter radar returns in the magnetic zenith were compared in a study carried out at Sondre Stromfjord (Λ = 76.1°) in Greenland. The results were used to test the consistency of a theoretical model of ion chemistry and optical emissions in aurora and to explore the accuracy of relations between optical measurements and the average energy of the incident electrons. The incident primary electron spectrum and its temporal variation were inferred from zenith electron density profiles from the radar. The inferred primary energy spectrum at the peak intensity of the event approximated a …

The Aperiodic Crystal Picture And Free Energy Barriers In Glasses, Randall W. Hall, Peter G. Wolynes

Collected Faculty Scholarship

The aperiodic crystal picture associates the glass transition with freezing into a nonperiodic structure. Dynamics in the glassy state involves activated jumps between different aperiodic free energy minima. Activation barriers may be estimated through the use of freezing theory and the theory of dense solids. The results resemble, but are distinct from, free volume theory. Reasonable fits to experimental data are obtained.

Nonorthogonal Configuration-Interaction Calculations Of Molecular States: The Low-Lying Molecular States Of Arhsup+ And Two-Electron Charge Exchange In Ar-H+ Collisions, Gordon A. Gallup

Gordon Gallup Publications

A nonorthogonal configuration-interaction procedure has been used to calculate adiabatic energy curves of ArH⁺. The basis functions are a mixture of typical molecular-orbital configurations and typical valence-bond (Heitler-London) configurations. This gives an economical description of the wave functions, allowing an easy tracing of various diabatic states through the adiabatic states and a clear identification of the asymptotic states. The results are used to rationalize the unexpectedly large production of Ar²⁺+H^- from collisions of H⁺ with Ar.

Heterotic String From Four-Dimensional Geometry, James Thomas Wheeler

All Physics Faculty Publications

In any conformally invariant metric-connection theory of 4-dimensional spacetime, there are 26 ways that a body can distort. This follows from the absence of any preferred metric, and is equivalent to the ability of an observer to consider objects on any given world line to be distortion free. Within the simplest conformally invariant theory of distortions that allow metric compatible spaces as trivial solutions, we find the maximal classical solution. This solution corresponds to the bosonic sector of the heterotic string: 26 left-moving fields plus 10 right-moving fields.

Brst Structure Of General Relativity In Terms Of New Variables, Charles G. Torre

All Physics Faculty Publications

The structure of the Poisson-brackets algebra of constraints of general relativity is reexamined using the recently introduced spinorial variables. Three different combinations of constraints are analyzed and their relative merits are discussed. In each case we construct the corresponding expression of the Becchi-Rouet-Stora-Tyutin charge. These expressions provide a point of departure for a nonperturbative quantization scheme for general relativity.

Determination Of Dissociation Energies And Thermal Functions Of Hydrogen‐Bond Formation Using High Resolution Ftir Spectroscopy, B. A. Wofford, M. E. Eliades, Shannon Lieb, J. W. Bevan

Scholarship and Professional Work - LAS

A technique which employs high resolution Fourier transform infrared spectroscopy is demonstrated for evaluation of hydrogen bonddissociation energiesD ₀ and D _e . Results for HCN‐‐HF give a D ₀=20.77(22) and D _e =28.77(45) kJ/mol which are compared with previously determined values obtained from microwave absolute intensity measurements and a b i n i t i o molecular orbital calculations. Rovibrational band information available for HCN‐‐HF also permits evaluation of thermal functions of dimer formation in kJ/mol: ΔU ^○ _298.2 =20.1(2), ΔH ^○ _298.2 =22.6(2), ΔG ^○ _298.2 =59.4(2), ΔS ^○ _298.2 =−0.1235.

Molecular Dynamics In Hydrogen‐Bonded Interactions: A Preliminary Experimentally Determined Harmonic Stretching Force Field For Hcn‐‐‐Hf, B. A. Wofford, Shannon Lieb, J. W. Bevan

Scholarship and Professional Work - LAS

Observation of the 2ν₁ overtone band in the hydrogen‐bonded complex HCN‐‐‐HF permits evaluation of the anharmonicity constant X _{1 1}=−116.9(1) cm^{− 1} and determination of the anharmonicity corrected fundamental frequency ω₁. This information, and available data from previous rovibrational analyses in the common and perdeuterated isotopic species of HCN‐‐‐HF, offer an opportunity for calculation of an approximate stretching harmonic force field. With the assumptions f _{1 2}=f _{2 4}=0.0, the remaining force constants (in mdyn/Å) are evaluated as: f _{1 1}=8.600(20), f _{2 2}=6.228(9), f _{3 3}=19.115(40), f _{4 …}

A Viable Form Of Weyl’S Theory, James Thomas Wheeler

All Physics Faculty Publications

A reinterpretation of the Weyl vector in a Weyl geometry is shown to yield Dirac’s 1951 classical theory of the electron, thereby avoiding the most obvious problems of measurement inherent in Weyl’s original geometric formulation of electromagnetism. This paves the way for the consistency of recent metric-connection theories, for which similar questions of measurement can arise.

Limit Theorems In The Area Of Large Deviations For Some Dependent Random Variables, Narasinga Rao Chaganty, Jayaram Sethuraman

Mathematics & Statistics Faculty Publications

A magnetic body can be considered to consist of n sites, where n is large. The magnetic spins at these n sites, whose sum is the total magnetization present in the body, can be modelled by a triangular array of random variables (X(n) 1,..., X(n) n). Standard theory of physics would dictate that the joint distribution of the spins can be modelled by dQ_n(x) = z_n^-1 exp[ -H_n(x)]Π dP(x_j), where x = (x₁,..., x_n) ∈ Rⁿ, where H_n is the Hamiltonian, z_n is …

Electrical Characterization Of Ion Implantation Into Gaas, David C. Look

Physics Faculty Publications

Recent advances in the characterization of ion‐implanted samples have included whole wafer mapping (topography) and depth profiling techniques. We review several methods for mapping electrical parameters, including the dark‐spot resistance (DSR), and the microwave photoconductance techniques. In addition, we suggest a new photo‐Hall technique which would allow mobility and carrier‐concentration mapping as well as that of resistivity . Finally, we review methods for obtaining ρ, μ, and depth profiles, with particular emphasis on the application of the magnetoresistance techniques in actual field‐effect transistor structures.

Measurement Of The Condensation Coefficient Of Water In The Umr Simulation Chamber, Daniel R. White, James L. Kassner, John C. Carstens, Donald E. Hagen, John L. Schmitt, Darryl J. Alofs, Alfred R. Hopkins, Max B. Trueblood, Max W. Alcorn, William L. Walker

Physics Faculty Research & Creative Works

The UMR Cloud Simulation Facility is described. The facility is designed to provide a controlled environment simulating the conditions of natural atmospheric processes. It consists of two cooled-wall expansion cloud chambers and peripheral instrumentation for generation and characterization of aerosols used for cloud formation studies. Results of initial studies of the growth of warm cloud droplets and inferred measurements of the condensation coefficient are described.

Electron Transmission Study Of The Temporary Negative Ion States Of Selected Benzenoid And Conjugated Aromatic Hydrocarbons, Paul Burrow, J.A. Michejda, K.D. Jordan

Paul Burrow Publications

Electron transmission spectroscopy is utilized to determine the vertical electron affinities and to characterize the temporary anion states of a series of alternant hydrocarbons including benzene, naphthalene, anthracene, tetracene, styrene, and cis- and trans-stilbene. The vibrational structure present in the low lying resonances is interpreted in light of the charge distributions of the temporarily occupied orbitals. The energies of the anion states are compared with the predictions of PPP, PPP-CI, and HAM calculations, the pairing theorem and with the results from optical absorption measurements on the ground state anions in rigid glasses.

Electron Correlation Effects In Nonresonant Multiphoton Ionization Processes, Anthony F. Starace

Anthony F. Starace Publications

The role of electron correlations in nonresonant multiphoton processes of atoms is presented. The evidence for the validity of a lowest order perturbation theory (LOPT) approach for the laser field in the case of nonresonant processes is sketched. The growing consensus for a LOPT interpretation of even the multiply-charged ion spectra obtained with high intensity lasers is reviewed. Finally, a review of those specific electron correlation processes within LOPT that are important for the quantitative prediction of two-photon ionization cross sections is presented and some of their effects on calculated generalized cross sections are exhibited.

Test Of Quasiclassical Theories Of Redistribution In Atomic Collisions, Ronald James Bieniek

Physics Faculty Research & Creative Works

The first numerical tests, for a real system, of the Quasi classical description of redistribution of polarized radiation through atomic collisions are presented. Polarization results are reported for red-wing redistribution of Sr (1S0 1P1) in the presence of Ar colliders. They compare favorably to recent quantal, nonadiabatic computations. It is shown that the effects of bent trajectories are important. Modified Quasi classical formulas to account for some of these are presented and tested. The results indicate that Quasi classical analysis can be used to probe the transformation from molecular to atomic states as atoms separate in a half-collision. © 1987 …

Saddle-Point Electrons In Ionizing Ion-Atom Collisions, Ronald E. Olson, Timothy James Gay, H. G. Berry, Edward Boyd Hale, V. D. Irby

Physics Faculty Research & Creative Works

We have studied H⁺+He ionizing collisions, and find that electrons stranded between the two postcollision Coulomb centers dominate the ejected-electron spectra for intermediate (100 keV) projectile energies. The importance of these electrons is clearly established by our classical calculations which are in qualitative agreement, in both shape and magnitude, with experimental spectra taken by us, and with earlier measurements. These saddle-point electrons are produced by a classically understandable mechanism, and are unambiguously observed at nonzero scattering angles. © 1987 The American Physical Society.

Compactification Of The Twisted Heterotic String, V. Parameswaran Nair, Alfred Shapere, Andrew Strominger, Frank Wilczek

Publications and Research

We consider compactifications of the recently discovered tachyon free non-supersymmetric string on tori of Lorentzian self dual lattices. The one loop cosmological constant is computed as a function of the parameters characterizing the lattices. When the lattice parameters are treated as dynamical variables, their equations of motion require extremization of A. This extremization determines the allowed gauge groups and mass spectra. We explicitly find some extremes of A, valid to all orders in perturbation theory. A very general duality relation between compactifications is demonstrated, which leads to an equivalence of compactifications on tori of radii R aud 1/R.

Comment On "Orientation, Alignment, And Hyperfine Effects On Dissociation Of Diatomic Molecules To Open Shell Atoms", Mark D. Havey, Linda L. Vahala

Electrical & Computer Engineering Faculty Publications

A recent paper in this journal [Y. B. Band e t a l., J. Chem. Phys. 8 4, 3762 (1986)] reported parameters describing orientation and alignment produced, in an axial recoil limit, by one photondissociation of diatomic molecules. Reported also were values, applicable to the resonance transitions of the alkali atoms, for orientation and alignment depolarization coefficients. Most of the numerical values reported for the coefficients were incorrect, in some cases by as much as a factor of 2. We report a tabulation of correct depolarization coefficients applicable to the resonance transitions of common alkali isotopes. Further, the coefficients …

Sensitivity Of The Ellipsometric Parameters To The Angle Of Incidence For Gaas, Jie-Fang Li

Masters Theses

"Ellipsometry was used to study a 10¹⁸ si-doped GaAs substrate and a 5 μm metal organic chemical vapor deposited (MOCVD) GaAs film on a similar substrate. The sensitivity of Ψ and Δ to Ø was studied, and the region of highest sensitivity was found for both samples. The optical constants for the 10¹⁸ Si-doped GaAs substrate and the 5 μm GaAs film were found to be N₂ = (3.768-0.491j) and N₂ = (3.704-0􀁐599j), respectively. The dependence of the sensitivity of Ψ and Δ to Ø was also calculated for various optical constants"-- Abstract. p. ii

Parametric Equation Of State For The N-Vector Model And Polymers, Rolfe G. Petschek

Faculty Scholarship

We introduce a new parametric form for the scaling equation of state of the n-vector model of magnetism correct to first order in μ=4-d. It is based on the equation of state of Schaaumlfer and Horner in a general parametric form proposed earlier by Schofield, Litster, and Ho. We integrate it to obtain the scaling part of the free energy F(T,H) of the n-vector model, correct to order μ, for general n. We use it to discuss the behavior of polymer solutions and equilibrium polymerization. This equation of state of the n0, T

On A Ferromagnetic With A Three‐Spin Interaction, Harry A. Brown

Physics Faculty Research & Creative Works

No abstract provided.