Digital Commons Network^™

Electronic Structure And Properties Of Sputtered Ta-Cu Films , K.D. Aylesworth, Sitaram Jaswal, M.A. Engelhardt, Z.R. Zhao, David J. Sellmyer

David Sellmyer Publications

Films of Ta_xCu_1-x have been produced in a co-sputtering system with dc- and rf-sputtering guns and a substrate attached to a rapidly rotating, water-cooled table. Samples were produced in the composition range 0.1≤x≤0.9. X-ray diffraction and electrical resistivity data between 4.2 and 300 K have been obtained. Diffraction measurements show that for 0.6≤x≤0.9 the samples are glassy. The room-temperature resistivities follow the Mooij correlation with a zero temperature coefficient of resistivity at a resistivity of 35 μΩ cm. The resistivity-versus-temperature data for Ta_0.90Cu_0.10 are compared to the extended Ziman-Faber theory …

Reply To Lung Cancer Risk From Rn In Chinese Study, Werner Hofmann, Robert Katz, Zhang Chunxiang

Robert Katz Publications

We are writing in response to comments by V. A. Archer (Archer 1987) on our study of lung cancer incidence in two Chinese areas, designated as the high background and the control area (Hofmann et al. 1986). In his comments, he asserts that the epidemiological data suffer from two serious defects.

Driven 3-State Model And Its Analytic Solutions, C. E. Carroll, Foek T. Hioe

Physics Faculty/Staff Publications

For an atom or molecule in which two transitions are driven by laser beams, a three‐state model is used. Transitions among the three states are caused only by the oscillating electric fields of the laser beams. The amplitudes and detunings of the two laser beams, which are various functions of the time, appear in the Schrödinger equation for the atom or molecule. In certain cases, the Schrödinger equation can be solved analytically, to find transition probabilities and the probability of no transition. This is done by using Clausen’s special function, or by assuming that the sum of the two detunings …

Anomalous Layering Of Fe(C0) Adsorbed On Graphite, John R. Dennison, H. Taub, F. Y. Hansen, H. Shechter, R. Brener

All Physics Faculty Publications

Synchrotron x-ray diffraction experiments reveal the adsorption of iron pentacarbonyl [Fe(CO)₅] on graphite basal-plane surfaces to be an extreme example of incomplete wetting in which only one solid layer of film coexists with bulk particles. Upon heating through the monolayer melting point, the amount of coexisting bulk solid first increases and then decreases. This anomalous layering behavior has not been observed in other systems exhibiting incomplete wetting, and we suggest that it is related to the steric properties of the Fe(CO)₅ molecule.

Review Of The Advancement Of Science, And Its Burdens By Gerald Holton, David W. Hafemeister

Physics

No abstract provided.

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 …

Effects Of Transport Coherence On The Mutual Annihilation Of Excitons, Demet Gulen, Vasudev M. Kenkre, Robert S. Knox, Paul Ernest Parris

Physics Faculty Research & Creative Works

We report results of a theoretical investigation into the mutual annihilation of tight-binding excitons. The results are in apparent contradiction with intuitive expectations and provide corrections to expressions given by one of the present authors (V.M.K.) in an earlier analysis. A part of that analysis was based on a mapping of the dynamics of two mobile, mutually annihilating excitons onto the dynamics of a single exciton migrating in the presence of a fixed trap. We find that while this equivalence is valid for incoherent, randomly walking particles in an ordered system, it does not hold for an arbitrary degree of …

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 …

Bacterial Biomagnetism And Geomagnetic Field Detection By Organisms, Richard P. Blakemore, Nancy A. Blakemore, Richard B. Frankel

Physics

No abstract provided.

Nonlocal Symmetries And Backlund Transformations For The Self-Dual Yang-Mills System, C. J. Papachristou, Kent B. Harrison

Faculty Publications

The observation is made that generalized evolutionary isovectors of the self-dual Yang–Mills equation, obtained by "verticalization'' of the geometrical isovectors derived in a previous paper [J. Math. Phys. 28, 1261 (1987)], generate Bäcklund transformations for the self-dual system. In particular, new Bäcklund transformations are obtained by "verticalizing'' the generators of point transformations on the solution manifold. A geometric ansatz for the derivation of such (generally nonlocal) symmetries is proposed.

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 …

Comparison Of Effective Medium Procedures For Optical Modeling Of Laminar Structures, David D. Allred, Robert F. Edgerton

Faculty Publications

This study addresses the question, "How can the optical properties of matter in ultrathin amorphous nonmetallic films in multilayers best be determined from reflectance (R) and transmission (T) measurements?" A blue shift in the band gap of plasma CVD a-Si:H/a-SiNx:H multilayers was reported several years ago. It was suggested that the shift in the band gap, Eg, Relative to bulk a-Si:H as given by the Tauç plot was due to quantum confinement effects. The purpose of this study is to evaluate the usefulness of various effective media theories (EMT) for determining the optical constants of materials in a multilayer and …

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.