Physical Sciences and Mathematics Commons^™

Radar Interferometry: A New Technique For Studyingplasma Turbulence In The Ionosphere, D. T. Farley, H. M. Ierkic, Bela G. Fejer

Bela G. Fejer

A new radar interferometer technique has been developed and used successfully at the Jicamarca Radio Observatory in Peru to study the strong nighttime plasma turbulence in the equatorial electrojet. The technique represents a major step forward in radar probing of turbulent irregularities such as (but not limited to) those in the electrojet. In many situations it provides far more information than previous Doppler measurements. We form the cross spectrum of the backscattered signals received from approximately overhead on two antennas, separated in this case along an east-west baseline, as well as the individual power spectra. From the phase of the …

Angular Differential And Total Cross Sections For The Excitation Of Atomic Hydrogen To Its N=2 State By Helium Ions, Judith E. Aldag, Jerry Peacher, Paul J. Martin, V. C. Sutcliffe, Jacob M. George, E. Redd, Thomas J. Kvale, D. M. Blankenship, John T. Park

Physics Faculty Research & Creative Works

Differential cross sections for 15-100 keV He⁺ excitation of atomic hydrogen to its n=2 level have been determined for c.m. angles from 0 to 8 mrad. The differential cross sections are obtained from an analysis of the angular distribution of the scattered ions which have lost an energy corresponding to the excitation of the target to its n=2 level. The shape of the differential cross section changes rapidly with increasing incident energy. At 15 keV, the differential cross section falls off by a factor of 5 in 6 mrad. At 100 keV, the differential cross section decreases by nearly …

Ammonia Adsorption And Decomposition On A Ni(Ll0) Surface, M. Grunze, M. Golze, R.K. Driscoll, Peter A. Dowben

Peter Dowben Publications

We report UPS/XPS results for ammonia adsorption and decomposition on a Ni(1 10)-surface. At T < 130 K molecular adsorption of NH ₃ is observed to proceed with an initial sticking coefficient of s ₀-0.1. Increasing the temperature of the nickel surface above 150 K results in partial dissociation of the adsorbed NH ₃ molecules. The intermediate species are tentatively identified by their photoelectron spectra as NH-fragments. At temperatures above 350 K only atomic nitrogen is observed to populate the surface after NH ₃-exposures. Our data show a similar reactivity of the Ni(ll0) surface in the NH ₃-decomposition reaction as found on iron-single crystal …

Compendium Of Bag-Model Matrix-Elements Of The Weak Non-Leptonic Hamiltonian, Jf Donoghue, E Golowich, Br Holstein, Wa Ponce

Barry R Holstein

A comprehensive list of baryon and meson single-particle matrix elements of the nonleptonic weak Hamiltonian is presented.

Raman Investigation Of The Charge-Density-Wave Mixed-Crystal System 1t-Tas2-XSeX, J.R. Duffey, Roger D. Kirby

Roger Kirby Publications

The results of Raman scattering measurements on the mixed-crystal system 1T- TaS_2-xSe_x in the commensurate charge-density-wave state are reported. In the pure compounds, our measurements indicate that a strong LA-TA phonon interaction at the distortion wave-vector results in additional coupled charge-density-wave-lattice excitations. These excitations can be followed over the whole range of concentrations in the mixed crystals. The concentration dependences of the mode frequencies are treated using an effective oscillator model.

Landau Free Energy Form At The F Point Of The Roverline3 Structure, Dorian M. Hatch, Daniel L. Decker

Faculty Publications

A free energy form compatible with the F point of the trigonal D63d(Roverline3c) symmetry is constructed. It is a function of the order parameter, elastic strain, and the stress. The resulting free energy exhibits a close formalistic analogy to the stressed cubic perovskite structures and their associated multicriticality.

Four-Color And Hβ Photometry Of The Galactic Cluster Ngc 7790, Edward G. Schmidt

Edward Schmidt Publications

Observations have been obtained on the four-color and Hβ system of 16 stars in the field of NGC 7790. These represent virtually all of the stars which are in the B-star region of the cluster color-magnitude diagram. I discuss the membership of these stars and find three which are possibly field stars. The remaining stars indicate a true distance modulus of 11.98 ± 0.13 for the cluster and a color excess of E(b – y) = 0.403.

Effect Of Polarization And Absorption On Differential Cross Sections And Angular Correlation Parameters For Electron Excitation Of Helium, M. E. Stewart, Don H. Madison

Physics Faculty Research & Creative Works

The effects of local polarization and absorption potentials on differential cross sections and angular correlation parameters are studied within the distorted-wave approximation for electron excitation of the 2 ¹P state of helium. For examining the effect of local polarization, we have compared a recent numerical self-consistent adiabatic polarization potential for helium with the commonly used hydrogenic adiabatic polarization potential. Different radial regions for the polarization potential were studied to determine their contribution to the overall effect of polarization. Calculations are also presented which show the effects of different strengths for a local absorption potential.

Observation Of The Transition From Semiconductor To High-Tc Superconductor In (Snxeu1-X)Ymo6s8 Under High Pressure, D. W. Harrison, K. C. Lim, J. D. Thompson, C. Y. Huang, Paul D. Hambourger, H. L. Luo

Physics Faculty Publications

Pressure-induced high-temperature superconductivity is observed in semiconducting (Sn_xEu_1-x)_yMo₆S₈, where 0<~x<~0.1 and y=1.0 and 1.2, having a carrier concentration ≃10¹⁹/cm³ at 4.2 K as determined from Hall-effect measurements. Above a threshold pressure ≃7 kbar, superconductivity appears with dT_c/dP≃2 K/kbar. The maximum superconducting temperature (T_c∼10 K), reached at ∼ 12 kbar, represents the highest pressure-induced T_c in any semiconductor. For P>~13 kbar, the temperature-dependent resistance appears metallic.

Application Of Discrete-Basis-Set Methods To The Dirac Equation, Gordon W. F. Drake, S. P. Goldman

Physics Publications

Variational solutions to the Dirac equation in a discrete L2 basis set are investigated. Numerical calculations indicate that for a Coulomb potential, the basis set can be chosen in such a way that the variational eigenvalues satisfy a generalized Hylleraas-Undheim theorem. A number of relativistic sum rules are calculated to demonstrate that the variational solutions form a discrete representation of the complete Dirac spectrum including both positive-and negative-energy states. The results suggest that widely used methods for constructing L2 representations of the nonrelativistic electron Green's function can be extended to the Dirac equation. As an example, the relativistic basis sets …

Relativistic Two-Photon Decay Rates Of 2s12 Hydrogenic Ions, S. P. Goldman, Gordon W. F. Drake

Physics Publications

Rates are calculated for the decay of metastable 2s12 ions to the ground state by the simultaneous emission of two photons. The calculation includes all relativistic and retardation effects, and all combinations of photon multipoles which make significant contributions up to Z=100. Summations over intermediate states are performed by constructing a finite-basis-set representation of the Dirac Green's function. The estimated accuracy of the results is 10 ppm for all Z up to 100. The decay rates are about 20 (Z)2% larger than an earlier calculation by Johnson owing to the inclusion of higher-order retardation effects. The general question of gauge …

Electron-Spin-Resonance Modes And The Edwards-Anderson Theory Of The Spin-Glass State, S. E. Barnes

Physics Articles and Papers

It is shown that the ESR modes observed in Cu: Mn alloys can be explained in terms of an Edwards-Anderson-type theory for a spin-glass when an anisotropy energy is included. Unlike other theories, the present one involves the conventional form for this anisotropy, U_K=Ksin²θ, where θ is the angle the local microscopic magnetization makes with the symmetry rather than equilibrium direction. The present theory is distinguished by a predicted, but as yet unobserved, angular dependence of single-crystal samples with axial symmetry.

Driven "Portulum": A Rolling Ball As A Simple Oscillating System, Laurence A. Marschall

Physics and Astronomy Faculty Publications

A classroom demonstration, a variation of the simple swinging pendulum, is described. In our "portulum," a ball, driven by short blasts of air, rolls along a curved tube. The design of this device, its construction, and its usefulness to the teaching of physics are discussed. It is also shown that the oscillations of the rolling ball have the same mathematical form as the oscillations of the ball swinging along the same path, but with a lower frequency.

Wave Demonstration Device, Glen T. Clayton, Harry D. Downing, Thomas O. Callaway

Faculty Publications

Students often have difficulty gaining an understanding of wave motion without effective demonstrations being performed in the lecture. Many excellent approaches utilizing ripple tanks, waves on a spring, chain, rope, etc., are customarily employed. Perhaps the most well-known device for demonstrating many of the effects of wave motion is the shive or bell wave motion machine.¹ The purpose of the present note is to describe a simple, inexpensive device which can be easily constructed by a teacher or student and can be used to demonstrate many of the properties of wave motion.

Structure-Factor Measurements In 4he At Saturated Vapor Pressure For 1.38<~T<~4.24 K, Robert Hallock, H. N. Robkoff

Robert Hallock

We present the results of measurements of the liquid structure factor, S(k), for liquid 4He at saturated vapor pressure at seven temperatures between 1.38 and 4.24 K over the momentum-transfer range k<~5.1 Å-1. The results are compared with previous measurements carried out by both x-ray and neutron scattering techniques. Comparison with recent theoretical work emphasizes the importance of higher-order correlations and more realistic potentials in the description of the liquid. Measurements in the vicinity of the λ transition document a loss in spatial order as the liquid is cooled through Tλ.

Phase Separation In 3he-4he Mixture Films, Robert Hallock, F. M. Ellis, M. D. Miller, R. A. Guyer

Robert Hallock

We report detailed observations of the propagation of third sound in 3He-4He mixture films as a function of temperature and 3He concentration. The data are consistent with a simple model for the film and we conclude that thin 3He-4He mixture films exhibit nearly complete phase separation.

O++ In The Venusian Ionosphere, Jane L. Fox, G. A. Victor

Physics Faculty Publications

It is shown that the revised photochemical theory for O⁺⁺ in the earth's ionopshere, where double photoionization of O is the dominant source, is consistent with recent O⁺⁺ measurements on Venus. A rate coefficient of 1.5 × 10⁻¹⁰ cm³ s⁻¹ for O⁺⁺ + O is obtained, and the possible importance of O⁺⁺ chemistry on minor atomic ions and airglow emissions is explored.

How Do College Students Solve Proportion Problems?, Melvin C. Thorton, Robert Fuller

Robert G. Fuller Publications

Problems which could be solved using proportional reasoning were administered nationwide by college faculty to their own science classes during a three year period. The reasoning of more than 8000 students covering three sections of the country was classified as concrete, transitional, or formal using Piagetian categories. Data from the West closely replicated that from the Midwest on similar metric conversion tasks. Student performance changed noticeably with a different problem format. The percentages of students using a ratio formula, ratio attempt, or intuitive methods of solution held approximately constant over time, task, and section of the country. The data shows …

Effective Swarm Parameters And Transport Coefficients In Co2 Laser Mixtures, R. A. Sierra, H. L. Brooks, A. J. Sommerer, S. R. Foltyn, Kaare J. Nygaard

Physics Faculty Research & Creative Works

A pulsed electron swarm technique has been used to obtain effective attachment and ionization cross-sections as well as electron drift velocities in mixtures of CO₂ laser interest. In binary CO₂:N 2 mixtures, below a reduced electric field of E/N=60*10 -17 V cm2, attachment was the principal ion production process. (N is the total gas number density.) The reduced attachment coefficients measured were small and in excellent agreement with numerical predictions. In ternary mixtures of He:CO₂:N2, positive ion formation described by Townsend's first ionisation coefficient played a more important role over the same range of E/N. …

N,L Distributions In Aq++H Electron-Capture Collisions, R. (Ronald) E. Olson

Physics Faculty Research & Creative Works

The classical-trajectory Monte Carlo method has been used to determine product-state distributions in Aq++HA(q-1)+(nl)+H+ electron-capture collisions at energies 50 and 100 keV/amu for fully stripped ions in charge states q=1to 20. In the energy region studied, the electron-capture products are found to populate predominately principal quantum numbers around nmq34. Such behavior implies the captured electron tries to preserve both its original orbital energy and dimensions after the electron-capture collision. The orbital-angular-momentum quantum numbers l are more highly peaked than statistical to large l values for nnm. © 1981 The American Physical Society.

Simultaneous X-Ray And Optical Observations Of An Ursae Majoris During A Low State, Paula Szkody, Edward G. Schmidt, Lidia Crosa, Robert Schommer

Edward Schmidt Publications

X-ray observations throughout the orbital cycle of AN UMa during its low state were conducted with the Einstein Observatory simultaneously with ground-based optical UBV photometry and spectroscopy. The observed low X-ray flux of 7 × 10^–13 ergs cm^–2 s^–1 is a factor of 40 below the high-state X-ray flux, and F_x/F_opt is about a factor of 50 lower than for AM Her and 2A 0311–227. There is marginal evidence for an X-ray eclipse coincident with an optical minimum and for increased X-ray flux at magnetic phase 0.4 which does not correlate with any optical …

Study Of Iron In Magnetotactic Bacteria, Richard B. Frankel, Richard P. Blakemore

Physics

Bacteria have recently been discovered directing their movements by sensing the earth's magnetic field. They contain arrays of crystals of lodestone or magnetite which they synthesize from iron in the ocean. The discovery of the same type of crystals in the abdomens of honey bees and the brains of homing pigeons suggests that nature is not oblivious to the earth's magnetic field. The biological mechanism for sensing magnetic fields has never been determined. These bacteria are capable of biologically synthesizing highly purified single domain magnets that would be very expensive to produce chemically.

The tiny perfect magnetite crystals made by …

Mossbauer Spectroscopy Of Iron-Containing Dermal Granules From Molpadia Intermedia, S. Ofer, G. C. Papaefthymiou, R. B. Frankel, H. A. Lowenstam

Physics

Dermal granules containing hydrous ferric oxide cores from Molpadia intermedia were studied by Mössbauer spectroscopy from 1.5 t0 300 K and in magnetic fields up to 80 kOersted at 4.2 K. A magnetic phase transition to an antiferromagnetically ordered state is observed at 10 K. The results are compared with the magnetic behavior of micellar cores of ferritin from eukaryotes and iron-storage materials from prokaryotes.

An Intense Wave/Particle Event In The Auroral Ionosphere, A. D. Johnstone, Jan Josef Sojka, W. Gibbons, B. K. Madahar, L.J. C. Woolliscroft

All Physics Faculty Publications

An intense burst of VLF waves, at frequencies just above the local proton gyrofrequency, was observed shortly after each of two intense bursts of field‐aligned suprathermal electrons (E < 250eV) by instruments carried on a sounding rocket flown in diffuse aurora. If the two phenomena are associated with each other, the implication is that the electron acceleration occurred nearby, in a relatively small volume.

Theoretical Predictions For Ion Composition In The High-Latitude Winter F-Region For Solar Minimum And Low Magnetic Activity, Jan Josef Sojka, W. John Raitt, Robert W. Schunk

All Physics Faculty Publications

We combined a simple plasma convection model with an ionospheric-atmospheric density model in order to study the ion composition in the high-latitude winter F-region at solar minimum for low geomagnetic activity. Our numerical study produced time-dependent, 3-dimensional, ion density distributions for the ions NO+, O2 +, N2 +, O+, N+, and He+. We covered the high-latitude ionosphere above 54°N magnetic latitude and at altitudes between 160 and 800 km for a time period of 1 complete day. From our study we found the following (1) The ion composition exhibits a significant variation with latitude, local time, altitude, and universal time. …

Auroral Plasma Lines: A First Comparison Of Theory And Experiment, E. S. Oran, Vincent B. Wickwar, W. Kofman, A. Newman

All Physics Faculty Publications

In this preliminary report on low-energy (0.3 to 3 eV) secondary electrons in the auroral E layer (90 to 150 km), we compare intensities of plasma lines observed with the Chatanika radar to theoretical predictions obtained from a detailed numerical model. The model calculations are initiated with a flux of energetic auroral primary electrons which enter the atmosphere and lose energy to electrons, ions, and neutrals through a combination of elastic and inelastic collisions. This flux is chosen in order that the total calculated ionization rate matches one that is deduced from the radar measurements. From these same calculations the …

Radar Measurements Of High-Latitude Ion Composition Between 140 And 300 Km Altitude, J. D. Kelly, Vincent B. Wickwar

All Physics Faculty Publications

The Chatanika radar has been used to measure the ratio of atomic (O⁺) ions to molecular (O₂ ⁺, NO⁺) ions in the high-latitude ionosphere. The radar results agreed well with simultaneous in situ rocket data, giving confidence in the radar method of deducing ion composition. Measurements made over long periods of time show seasonal variations, diurnal variations, and variations due to auroral processes. The transition altitude, where the number densities of atomic and molecular ions are equal, is a convenient parameter for describing the composition variation with altitude or ‘composition altitude profile.’ The transition …

Plasma Density Features Associated With Strong Convection In The Winter High-Latitude F Region, Jan Josef Sojka, W. John Raitt, Robert W. Schunk

All Physics Faculty Publications

We combined a simple plasma convection model with an ionospheric-atmospheric composition model in order to study the plasma density features associated with strong convection in the winter high-latitude F region. Our numerical study produced time-dependent, three-dimensional, ion density distributions for the ions NO+, O2 +, N2 +, O+, N+, and He+. We covered the high-latitude ionosphere above 42° N magnetic latitude and at altitudes between 160 and 800 km for a time period of one complete day. From our study, we found the following: (1) For strong convection, the electron density exhibits a significant variation with altitude, latitude, longitude, and …

Energization Of Ionospheric Ions By Electrostatic Hydrogen Cyclotron Waves, Nagendra Singh, Robert W. Schunk, Jan Josef Sojka

All Physics Faculty Publications

Interactions between ionospheric ions and a monochromatic electrostatic hydrogen cyclotron wave were studied numerically for conditions corresponding to the auroral plasma. Strong heating of the minority ions He⁺, He⁺⁺, and O⁺ were observed. The fraction of the initial ion population which underwent heating was found to strongly depend on the mass, charge, and initial temperature of the ion species.

A Theoretical Study Of The High-Latitude Winter F Region At Solar Minimum For Low Magnetic Activity, Jan Josef Sojka, W. J. Raitt, Robert W. Schunk

All Physics Faculty Publications

We combined a simple plasma convection model with an ionospheric-atmospheric composition model in order to study the high-latitude winter F region at solar minimum for low magnetic activity. Our numerical study produced time dependent, three-dimensional ion density distributions for the ions NO+, O2 +, N2 +, O+, N+, and He+. We covered the high-latitude ionosphere above 54°N magnetic latitude and at altitudes between 160 and 800 km for a time period of one complete day. The main result we obtained was that high-latitude ionospheric features, such as the ‘main trough,’ the ‘ionization hole,’ the ‘tongue of ionization,’ the ‘aurorally produced …