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Transitions And Modulated Phases In Centrosymmetric Ferroelectrics: Mean-Field And Renormalization-Group Predictions, George A. Hinshaw Jr., Rolfe G. Petschek

Faculty Scholarship

A variety of ferrodisplacive transitions have Landau expansions which involve terms proportional to p2(p), i.e., three powers of the order parameter (p) and one gradient (). Such expansions have also been suggested for polymeric liquid crystals. We have studied a rotationally invariant, centrosymmetric ferroelectric in which the order parameter is a vector. The pp term leads to modulated phases when it is large enough. The modulated phase close to the uniform-modulated transition and the location of the transition are discussed as a function of dimensionless parameters in a simple model for the free energy. Modifications expected from dangerous irrelevant variables …

Versatile New Metalorganic Process For Preparing Superconducting Thin Films, M.E. Gross, M. Hong, Sy_Hwang Liou, P.K. Gallagher, J. Kwo

Sy-Hwang Liou Publications

A new technique for producing thin films of the high-temperature perovskite superconductors, LnBa₂Cu₃O_7-x, where Ln represents a rare-earth element, using spin-on metalorganic precursors is described. Pyrolysis of the spin-coated films, consisting of mixed metal (2-ethyl hexanoates), leads to black films up to several microns thick whose degree of orientation is a function of the processing temperature and duration. Representative films of Y Ba₂Cu₃O_7-x on MgO begin to exhibit orientation with the c axis perpendicular to the film plane at heat treatments above 900 °C. The superconducting behavior of a …

Critical Dimensions For Chiral Bosons, Luca Mezincescu, Rafael I. Nepomechie

Physics Articles and Papers

We give the Lagrangian formulation of a Bose model in 1+1 dimensions which describes a free chiral Lie-algebra-valued current. This model is a non-Abelian generalization of the chiral scalar model of Siegel. Both the Abelian and non-Abelian actions have a gauge invariance, which becomes anomalous when the models are quantized. The condition that this anomaly be canceled coincides with the string no-ghost condition.

Alternative Feynman-Diagram Method For The General-Spin Kondo Problem, S. E. Barnes

Physics Articles and Papers

We introduce a new method of replacing spin operators with pseudofermions. For a spin value S there are 2S pseudofermions each of which can have spin ‘‘up’’ or ‘‘down’’. In contrast to the standard Abrikosov method which has 2S+1 inequivalent fermions, i.e., one for each S_z value, the present pairs are all equivalent. It follows that the general spin expression is obtained by multiplying the S=(1/2 result by a ceratin combinational factor. This aids in the construction of rotationally invariant solutions for the general-spin Kondo problem for the case when n≤2S, where n is the number of conduction-electron scattering …

Experiments With Disposable Hypodermic Syringes, Glen T. Clayton, Thomas O. Callaway, Harry D. Downing

Faculty Publications

No abstract provided.

Comparison Of Simultaneous Chatanika And Millstone Hill Temperature Measurements With Ionospheric Model Predictions, C. E. Rasmussen, Jan Josef Sojka, Robert W. Schunk, Vincent B. Wickwar, O. De La Beaujariere, J. Foster, J. Holt

All Physics Faculty Publications

As part of the MITHRAS program, the Chatanika and Millstone Hill incoherent scatter radars made coordinated observations of the polar ionosphere on June 27 and 28, 1981. The temperature data obtained during these days were compared with predictions made by a high-latitude ionospheric model. The comparison of the temperature measurements and the results of the ionospheric model depend on the assumptions made both in reducing the data and on the inputs that are needed by the model. The deduction of electron temperature from radar measurements depends upon a knowledge of the mean ion mass as a function of altitude. The …

A Model Study Of How Electric Field Structures Affect The Polar Cap F Region, Jan Josef Sojka, Robert W. Schunk

All Physics Faculty Publications

A three-dimensional time-dependent ionospheric model was used to study how electric field structures affect the polar F region. The electric field structures are represented by elongated Volland two-cell models whose dimensions range from tens to 1000 km. These model structures are intended to represent the polar cap electric field for IMF B_z northward conditions. A statistical method is used to generate a set of these structures. Their electric field strength and polarity are varied in order to study the F region’s dependence on this magnetospheric input. For electric field structures whose size and electric field strengths are consistent with …

A Photochemical Equilibrium Model For Ionospheric Conductivity, C. E. Rasmussen, Robert W. Schunk, Vincent B. Wickwar

All Physics Faculty Publications

A photochemical equilibrium model of the high-latitude ionosphere has been developed. This model provides densities of the ionospheric constituents, N₂ ⁺, O₂ ⁺, O⁺, and NO⁺, from 85 km to approximately 220 km. These densities are then used to calculate Pedersen and Hall conductivities. A comparison of the model results with Arecibo and Chatanika radar observations was made, covering periods of solar minimum and solar maximum. The comparison showed the model to predict ionospheric densities to within 50% and conductivities to within 40% in the illuminated portion of the ionosphere. In regions …

Observations Of Auroral E Region Plasma Waves And Electron Heating Witheiscat And A Vhf Radar Interferometer, J. Providakes, D. T. Farley, B. G. Fejer, J. Sahr, W. E. Swartz, I. Haggstrom, A. Hedberg, J. A. Nordling

All Physics Faculty Publications

Two radars were used simultaneously to study naturally occurring electron heating events in the auroral E-region ionosphere. During a joint campaign in March 1986 the Cornell University Portable Radar Interferometer (CUPRI) was positioned to look perpendicular to the magnetic field to observe unstable plasma waves over Tromsø, Norway, while EISCAT measured the ambient conditions in the unstable region. On two nights EISCAT detected intense but short lived (< 1 min) electron heating events during which the temperature suddenly increased by a factor of 2–4 at altitudes near 108 km and the electron densities were less than 7 × 104 cm−3. On the second of these nights CUPRI was operating and detected strong plasma waves with very large phase velocities at precisely the altitudes and times at which the heating was observed. The altitudes, as well as one component of the irregularity drift velocity, were determined by interferometric techniques. From the observations and our analysis, we conclude that the electron temperature increases were caused by plasma wave heating and not by either Joule heating or particle precipitation.

Low-Temperature Ion Beam Mixing In Metals, S J. Kim, M A. Nicolet, R S. Averback, David Peak

All Physics Faculty Publications

A systematic study of ion-beam mixing of tracer impurities in thin metal films at low temperatures has been conducted. We have investigated the dependence of ion mixing on two matrix properties: atomic mass and cohesive energy. We have also studied the dependence of ion mixing on tracer impurity properties: its heat of mixing with the matrix and its thermal diffusivity in the matrix. The matrices investigated were thin films of C, Al, Ti, Fe, Ni, Cu, Mo, Ru, Ag, Hf, Ta, W, Pt, and Au. The tracer impurities, Al, Ti, Cr, Mn, Fe, Ni, Cu, Y, Nb, Mo, Ru, Ag, …

The Treatment Of Exchange In Path Integral Simulations Via An Approximate Pseudopotential, Randall W. Hall

Collected Faculty Scholarship

An approximate form that includes the effects of exchange is suggested for the short time propagator used in path integral simulations. The form is inspired physically by the approximation made in Hartree–Fock treatments of atoms and molecules. The approximate propagator is used with q u a n t i t a t i v e accuracy in two systems: an ideal gas of fermions localized in a three‐dimensional harmonic well and the triplet state of the sodium dimer.

The Rainbow And The Achromatic Telescope: Two Case Studies, M. Eugene Rudd

M. Eugene Rudd Publications

From the history of science we can learn not only some science and some history, but also something about how science is done and how it interacts with technology.
The First case study chosen illustrates the development of an understanding of a phenomenon of nature-one that has been observed with awe and wonder for as long as man has walked the Earth, but has only been well understood in the last 200 years. Some of the greatest thinkers of all time have worked on the problems of the rainbow.
The second study shows how an important invention became possible only …

Spin-Exchange Cross Section For Electron Excitation Of Na 3s 3p Determined By A Novel Spectroscopic Technique, Xianming Han, G. W. Schwinn, A. Gallagher

Scholarship and Professional Work - LAS

An experimental technique is described which enables determination of the partial cross sections for electron excitation of atoms as a function of changes in spin and orbital angular momentum. This method provides a good signal-to-noise ratio in the energy region near threshold, and could be used to study long- or short-lived excited states of many atomic systems. Measurements for Na 3S−3P, near-threshold excitation are reported here. The results are generally in good agreement with the close-coupling calculations of D. L. Moores and D. W. Norcross [J. Phys. B 5, 1482 (1972)] for the largest ΔmS and ΔmL components of …

The Spectroscopy And Molecular Dynamics Of The High Frequency Ν1 6 Intermolecular Vibrations In Hcn‐‐‐Hf And Dcn‐‐‐Df, B. A. Wofford, M. W. Jackson, Shannon Lieb, J. W. Bevan

Scholarship and Professional Work - LAS

Gas phase rovibrational analysis of the high frequency intermolecular hydrogen bonded bending overtone 2ν⁰ ₆ [ν₀=1132.4783(2) cm^{− 1}] in HCN‐‐‐HF and its corresponding perdeuterated fundamental ν¹ ₆ [ν₀=409.1660(2) cm^{− 1}] are reported. Evaluated rovibrational parameters provide the basis for quantitative modeling of the molecular dynamics associated with this vibration. A quantum mechanical calculation permits determination of the quadratic and quartic force constants K _{6 6}=537(17) and K _{6 6 6 6}=4.98(12) cm^{− 1} which in turn are used to estimate the pertinent cubic band stretching interaction constants …

Erratum: Determination Of Dissociation Energies And Thermal Functions Of Hydrogen Bond Formation Using High Resolution Ftir Spectroscopy [J. Chem. Phys. 8 7, 5674 (1987)], B. A. Wofford, M. E. Eliades, Shannon Lieb, J. W. Bevan

Scholarship and Professional Work - LAS

Erratum

Spectral Momentum Density From Graphite From (E,2e) Spectroscopy: Comparison With First Principles Calculations, Chao Gao, A. L. Ritter, Jr Dennison, N. A. W. Holzwarth

Journal Articles

We have measured the spectral momentum density p(E,q) of graphite by (e,2e) spectroscopy for momentum parallel and perpendicular to the crystal c axis. In the independent-electron approximation, p(E,q) = Σ_G |U_k(G)|² δ(q-k-G)δ(E-E(k)) where the one-electron wave function is Ψ_k(r) = e^ik•rΣ_GU_k(G)e^iG•r and G is a reciprocal-lattice vector. The measurements covered a range of momentum parallel to the c axis equal to 0 ≤ |q| ≤ 1.84Å^-1 and a …

Contact Resistance Measurements In Gaas Mesfet's And Modfet's By The Magneto‐Tlm Technique, David C. Look

Physics Faculty Publications

The standard transmission‐line model (TLM) for specific contact resistivity measurements of planar contacts is improved in two ways: (i) the addition of a magnetic field, which gives the mobility and carrier concentration of the bulk material, and the mobility of the material under the contact; and (ii) an extension to two layers, which makes the model applicable to MODFET structures. The results are applied to MESFET material, and MODFET material. One conclusion concerning the latter material is that the electrons directly beneath the annealed Au/Ge/Ni contacts have lower mobility than those in the bulk, but still …

Anomalous Magnetic Properties Of Some High-Temperature Magnetic Superconductors, P. H. Hor, R. L. Meng, C. W. Chu, C. Y, Huang, R, B. Frankel

Physics

No abstract provided.

Spectral Densities And Nuclear Spin Relaxation In Solids, Peter A. Beckmann

Physics Faculty Research and Scholarship

We investigate the properties of ten spectral densities relevant for nuclear spin relaxation studies in solids. This is preceded by a brief review of nuclear spin relaxation in solids which includes a discussion of the appropriate spin-dependent interactions and the various relaxation rates which can be measured. Also, the link between nuclear spin relaxation and dielectric relaxation is discussed. Where possible and/or appropriate each of the spectral densities is expressed as a continuous distribution of Bloembergen-Purcell-Pound (or Debye) spectral densities 2ξ /(1 + ξ2 ω2) for nuclear Larmor angular frequency ω and correlation time ξ. The spectral densities are named …

Nuclear-Spin Relaxation In Molecular Solids With Reorienting Methyl And T-Butyl Groups: The Spectral Density And The State Of The Solid, Peter A. Beckmann, Audrey I. Hill, Ellen B. Kohler, Hong Yu

Physics Faculty Research and Scholarship

We have measured the temperature T dependence of the proton Zeeman relaxation rate R in polycrystalline 1,3-di-t-butylbenzene (1,3-DTB) at Larmor frequencies of ω/(2π)=8.50, 22.5, and 53.0 MHz. The relaxation is caused by the modulation of the methyl proton dipole-dipole interactions by the reorientation of the t-butyl groups [C(CH3)3] and their three constituent methyl groups (CH3).

There are two solid phases which either have a large hysteresis of at least 90 K, or are both stable below 200 K. The sample melts at 262 K. We interpret the high-temperature phase R-versus-T−1data with three models. First, we adopt a one-correlation-time model using …

Generation Of Moire Contours With Acousto-Optic Cells, Joel H. Blatt, Huey-Chin Chang Ho, Eddie H. Young

Aerospace, Physics, and Space Science Faculty Publications

Moire contours are seen on a curved surface viewed through a grating when the surface is illuminated with a matched grating. We have been able to replace both the projection and viewing physical gratings with gratings of variable spacing generated in acousto-optic cells, and have been able to observe and record Moire contours. The gratings are generated by amplitude modulating 70 MHz AO cells with a 1 to 10 MHz square wave. The gratings become visible on the curved object by strobing the illuminating laser beam with 50 nsec pulses by means of an AO modulator. Data is given showing …

Argon Metastable-Cadmium Dihalide Energy Transfer Collisions In A Flowing Afterglow, Christopher L. Bohler, Laird D. Schearer

Physics Faculty Research & Creative Works

The energy dependence of dissociating collisions between argon metastable atoms and cadmium dihalide molecules have been studied in a flowing afterglow apparatus. The fluorescence spectra obtained in the range of 3000-7600 Å which result from the Ar(3P2) + CdX2 interactions indicate a dominant dissociative excitation production mechanism. The emission spectra are used to narrow the uncertainty in the currently accepted values for the dissociation energy of the CdX2 molecules. The Wigner spin rule (conservation of total electronic spin) was verified for these processes as shown by the dominance of final state triplet production as compared to the virtual absence of …

Multi Gluon Scattering: A String Based Calculation, David Kosower, Bum-Hoon Lee, V. Parameswaran Nair

Publications and Research

We suggest the use of open bosonic string theory to compute multigluon scattering in QCD, since gauge invariance ,cyclic symmetry etc. are manifest in this approach. The method is illustrated by the computation of five gluon scattering.

A New Search For Interstellar C3, Charles L. Joseph, Theodore P. Snow, C Gregory Seab

Physics Faculty Publications

A new, very sensitive search for interstellar triatomic carbon has resulted in upper limits for a few diffuse clouds of order 10¹⁰ cm ^{– 2}, or about 10 ^{– 11} with respect to hydrogen. These limits are consistent with recent cold diffuse cloud chemistry models, but may be in conflict with shocked cloud models such as those invoked to explain CH ⁺ abundances. Our results may also be argue against linear carbon-chain molecules as carriers of the diffuse interstellar bands.

An Optically Controlled Closing And Opening Semiconductor Switch, K. H. Schoenbach, V. K. Lakdawala, R. Germer, S. T. Ko

Electrical & Computer Engineering Faculty Publications

A concept for a bulk semiconductor switch is presented, where the conductivity is increased and reduced, respectively, through illumination with light of different wavelengths. The increase in conductivity is accomplished by electron ionization from deep centers and generation of bound holes. The reduction of conductivity is obtained by hole ionization from the excited centers and subsequent recombination of free electrons and holes. The transient behavior of electron and hole density in a high power semiconductor (GaAs:Cu) switch is computed by means of a rate equation model. Changes in conductivity by five orders of magnitude can be obtained.

Measurements Of The Drag On Spheres Falling Through The Air, J. G. Ross, Stephen R. Addison, N.O (Jack) Gaiser

Journal of the Arkansas Academy of Science

No abstract provided.

Magnetite And Magnetotaxis In Microorganisms, Richard B. Frankel, R. P. Blakemore

Physics

No abstract provided.

Aerosol Evolution And Metamorphosis During And After Haze (Fog) Formation Over The Bay Of Naples, Josef Podzimek, H. Andriambeloma, A. De Maio, M. Ianniruberto, R. Montmory, E. Sansone, G. Spezie, G. Stowell

Physics Faculty Research & Creative Works

No abstract provided.

A Study Of Vapor Phase Self-Initiated Thermal Polymerization Of Styrene With An Expansion Chamber, John L. Schmitt

Physics Faculty Research & Creative Works

Studies of the self-initiated polymerization of styrene have been performed in the uniform environment of an expansion cloud chamber, using nucleation of liquid monomer drops for detection. These studies are the first of this kind in an expansion chamber and, although preliminary and designed to explore feasibility, have yielded many interesting results. The occurrence of the self-initiated nonterminated gas phase processes, previously observed in a diffusion cloud chamber, has now been confirmed in an expansion chamber. At 15 °C the initiation rate is measured to be 2 to 6 radicals cm-3 s-1 and the propagation constant is approximately 6X10-21 cm3 …

Solution Manual Of University Physics: Mechanics, Yimin Wang, Clifton Keller

All Books

No abstract provided.