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1983

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Articles 31 - 60 of 122

Full-Text Articles in Physics

Atomic Photoionization, Anthony F. Starace Aug 1983

Atomic Photoionization, Anthony F. Starace

Anthony F. Starace Publications

We present here a brief overview of the theory of atomic photoionization. The main aim is to describe current theoretical understanding of the dynamics of the photon-atom collision process. In particular the discussion focuses on those kinds of electron correlation that have been found to be most important for photoionization processes. The general theoretical formulation of the interaction between an incident photon and an N-electron atom is presented first. This is followed by a description of those quantitative and qualitative features of the photoionization cross section that can be understood within a central potential model. The particle-hole type of electron …

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25th Rocky Mountain Conference Aug 1983

25th Rocky Mountain Conference

Rocky Mountain Conference on Magnetic Resonance

Abstracts and meeting program from the 25th annual meeting of the Rocky Mountain Conference, co-sponsored by the Rocky Mountain Section of the Society for Applied Spectroscopy and the Rocky Mountain Chromatography Discussion Group. Held in Denver, Colorado, August 14-17, 1983.

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Simple And Direct Determination Of Complex Refractive Index And Thickness Of Unsupported Or Embedded Thin Films By Combined Reflection And Transmission Ellipsometry At 45° Angle Of Incidence, R. M.A. Azzam Aug 1983

Simple And Direct Determination Of Complex Refractive Index And Thickness Of Unsupported Or Embedded Thin Films By Combined Reflection And Transmission Ellipsometry At 45° Angle Of Incidence, R. M.A. Azzam

Electrical Engineering Faculty Publications

Measurements of the polarization states (represented by complex numbers Xr and Xt, respectively) of light reflected and transmitted by an unsupported or embedded thin film, for totally polarized light (with nonzero p and s components) incident at 45°, permit simple, direct, and explicit determination of the film's complex refractive index N1 independently of film thickness or input polarization. If α = Xr/Xt, we find that α = rs + rs-1, where rs is Fresnel’s complex reflection coefficient of the ambient-film interface for the s polarization at …

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Hole Transport In Pure And Doped Gaas, H. J. Lee, David C. Look Aug 1983

Hole Transport In Pure And Doped Gaas, H. J. Lee, David C. Look

Physics Faculty Publications

We have used a two-band model (heavy and light holes) to calculate the transport properties ofp-type GaAs. The scattering mechanisms included are acoustic-mode deformation potential, acoustic-mode piezoelectric potential, polar- and nonpolar-mode deformation potential, ionized impurity, and space charge. Interband scattering is included explicitly for the optical phonons and phenomenologically for the acoustic phonons. The intraband polar optical-mode scattering, for which a relaxation time cannot be defined, was calculated by using the numerical method of Fletcher and Butcher. The acoustic deformation-potential parameter and the coupling coefficient for interband scattering were calculated by fitting the theory to Hall-mobility data for both pure …

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Low Compensation Vapor-Phase Epitaxial Gallium-Arsenide, P. C. Colter, David C. Look, D. C. Reynolds Aug 1983

Low Compensation Vapor-Phase Epitaxial Gallium-Arsenide, P. C. Colter, David C. Look, D. C. Reynolds

Physics Faculty Publications

Vapor phase epitaxial gallium arsenide (GaAs) layers, with lower compensation ratios than any reported heretofore, have been reproducibly grown by the Ga/H2/AsCl3 method. One of these samples has been studied extensively by electrical measurements and shows an acceptor concentration of (2.0 ± 0.7)X1013 cm-3 , and a compensation rate of NA/ND = 0.06 ± 0.02. These numbers are supported by magnetophotothermal spectroscopy and photoluminescence measurements. The preparation involves growth on [211A] substrates, and a pregrowth bakeout of the Ga source, which results in a significantly lower Zn acceptor concentration in the layer. …

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Center-Of-Mass Properties Of Composite Systems Subject To Non-Linear External Interactions, James A. Lock Aug 1983

Center-Of-Mass Properties Of Composite Systems Subject To Non-Linear External Interactions, James A. Lock

Physics Faculty Publications

If two bound nonrelativistic quantum particles are each subject to a nonlinear external potential, their Schrödinger equation does not separate in relative and center-of-mass coordinates. For this case, the details of internal state of the composite affect its center-of-mass properties. The extent of this internal state influence is examined for an exactly soluble one-dimensional model system.

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Apl And The Numerical Solution Of High-Order Linear Differential Equations, N. A. Gershenfeld, Edward H. Schadler , '81, Oleksa-Myron Bilaniuk Aug 1983

Apl And The Numerical Solution Of High-Order Linear Differential Equations, N. A. Gershenfeld, Edward H. Schadler , '81, Oleksa-Myron Bilaniuk

Physics & Astronomy Faculty Works

An Nth‐order linear ordinary differential equation is rewritten as a first‐order equation in an N×N matrix. Taking advantage of the matrix manipulation strength of the APL language this equation is then solved directly, yielding a great simplification over the standard procedure of solving N coupled first‐order scalar equations. This eases programming and results in a more intuitive algorithm. Example applications of a program using the technique are given from quantum mechanics and control theory.

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Unification Of Ernst-Equation Backlund Transformations Using A Modified Wahlquist-Estabrook Technique; Wahlquist-Estabrook, B. Kent Harrison Aug 1983

Unification Of Ernst-Equation Backlund Transformations Using A Modified Wahlquist-Estabrook Technique; Wahlquist-Estabrook, B. Kent Harrison

Faculty Publications

The three known Backlund transformations for the Ernst equation are derived using a modification of the Wahlquist-Estabrook prolongation procedure. The modification requires that the equation to be studied be cast into a set of differential forms and their exterior derivatives, such that all coefficients are constant (a "CC ideal''). Analysis of the resulting equations produces 16 solutions composed of the three basic transformations combined with identity and other essentially trivial transformations. The group structure of the transformations is discussed. A Backlund transformation (already known) for the Ernst-Maxwell equations can be found by the same method. Promising generalizations are mentioned.

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Order Of Phase Transitions In A Field Theory, V. Parameswaran Nair Jul 1983

Order Of Phase Transitions In A Field Theory, V. Parameswaran Nair

Publications and Research

The relation between the gauge or global nature of a symmetry being broken and the order of the associated phase transition is clarified. First-order phase transitions in gauge theories are related to the asymptotic freedom of the Φ3 interaction in six dimensions. Spontaneous violation of lepton number in the standard electroweak theory provides a nontrivial illustration of our results.

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Activity Coefficient And The Einstein Relation, Peter T. Landsberg, Albert G. Guy Jul 1983

Activity Coefficient And The Einstein Relation, Peter T. Landsberg, Albert G. Guy

Aerospace, Physics, and Space Science Faculty Publications

A connection between the activity coefficient of current carriers and the Einstein relations is established by two methods, one based on normal semiconductor concepts and one based on irreversible thermodynamics. The connection holds for all densities of states, for Fermi degeneracy, and in the presence of heavy doping.

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Equatorial Disturbance Dynamo Electric Fields, Bela G. Fejer, M. F. Larsen, D. T. Farley Jul 1983

Equatorial Disturbance Dynamo Electric Fields, Bela G. Fejer, M. F. Larsen, D. T. Farley

Bela G. Fejer

F-region vertical drift data from Jicamarca, Peru show that equatorial east-west electric fields are sometimes perturbed 16-24 hours after the onset of geomagnetic storms. These disturbance dynamo electric fields, which must be caused primarily by the action of neutral winds at low and middle latitudes, decrease and sometimes even reverse the quiet time electric field pattern during both daytime and nighttime. The long delay excludes the possibility that gravity waves are responsible and suggests that the thermospheric circulation is disturbed. The data also show that after some storms there are no such delayed disturbances, a fact which may be due …

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Maximum Minimum Reflectance Of Parallel-Polarized Light At Interfaces Between Transparent And Absorbing Media, R. M.A. Azzam Jul 1983

Maximum Minimum Reflectance Of Parallel-Polarized Light At Interfaces Between Transparent And Absorbing Media, R. M.A. Azzam

Electrical Engineering Faculty Publications

The pseudo-Brewster angle ØpB, of minimum reflectance Rpm for the parallel (p) polarization, of an interface between a transparent and an absorbing medium is determined by Im{(∊ - u)[1 - (1 + ∊-1)u]2} = 0, where ∊ is the complex ratio of dielectric constants of the media and u = sin2øpB. It is shown that, for a given value of the normal-incidence amplitude reflectance |r|, there is an associated normal-incidence phase shift, δ = δmm, that leads to maximum minimum parallel reflectance, …

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Study Of Prenucleation Ion Clusters: Correlation Between Ion Mobility Spectra And Size Distributions, Sung-Ho Suck Salk, Donald E. Hagen, James L. Kassner Jul 1983

Study Of Prenucleation Ion Clusters: Correlation Between Ion Mobility Spectra And Size Distributions, Sung-Ho Suck Salk, Donald E. Hagen, James L. Kassner

Physics Faculty Research & Creative Works

Additional studies regarding our earlier electrothermodynamic theory are presented. Comparisons to recent expansion cloud chamber ion mobility measurements are made, indicating general agreement with observations. This theory predicts more stable and ordered structure for prenucleation ion-water cluster systems than accounted for by the classical Thomson's theory. In the limiting case of the dielectric constant ε = 1, our monopole electrostatic energy term contributed by the foreign ion center precisely converges to that of Thomson. Predicted ion cluster size distributions are found to correlate well with ion cluster size spectra obtained from the ion mobility measurements of hydrated ion clusters and …

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Highly Excited States Of A Hydrogen Atom In A Strong Magnetic Field, John B. Delos, Stephen Knudson, D. W. Knudson Jul 1983

Highly Excited States Of A Hydrogen Atom In A Strong Magnetic Field, John B. Delos, Stephen Knudson, D. W. Knudson

Arts & Sciences Articles

Classical trajectories and semiclassical energy eigenvalues are calculated for an atomic electron in a high Rydberg state in an external magnetic field. With the use of perturbation theory, a classical trajectory is described as a Kepler ellipse with orbital parameters evolving slowly with time. As they evolve, the ellipse rocks, tilts, and flips in space, but the length of its major axis remains approximately constant. Exact numerical calculations verify that perturbation theory is quite accurate for the cases considered (principal quantum number ≃ 30, magnetic field ≲ 6 T). Action variables are calculated from perturbation theory and from exact trajectories, …

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Dissociative Attachment In Hcl, Dcl, And F2, J. N. Bardsley, J. M. Wadehra Jun 1983

Dissociative Attachment In Hcl, Dcl, And F2, J. N. Bardsley, J. M. Wadehra

Physics and Astronomy Faculty Research Publications

Resonant scattering models, using nonlocal decay widths, are developed for dissociative attachment of slow electrons to diatomic molecules. Cross sections are obtained for HCl and DCl in several initial rotational and vibrational states, and the dependence of the average attachment cross section upon the rotational and vibrational temperature is examined. For F_2 the cross section for ground state molecules agrees well with experiment above 0.2 eV but shows no zero energy peak. The attachment cross section is higher for vibrationally excited molecules, but the enhancement is much less than that found in H_2 and HCl.

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Second-Order Phase Transitions, Inflationary Universe, And Formation Of Galaxies, V. Parameswaran Nair Jun 1983

Second-Order Phase Transitions, Inflationary Universe, And Formation Of Galaxies, V. Parameswaran Nair

Publications and Research

At the critical point of a second-order phase transition, statistical fluctuations are correlated and enhanced in amplitude. We explore this phenomenon in the early universe as a possible mechanism for the formation of galaxies. In an inflationary universe, such dynamical effects on galactic scales are consistent with the constraints imposed by the horizon. Spontaneous breakdown of lepton number provides a model where these ideas are realized. The two-point correlation function for density fluctuations is calculated and agrees with the observed correlation for galaxies. An estimate of the density contrast is shown to be of the required magnitude.

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A Study Of The 0.1-Ev Conversion Acceptor In Gaas, David C. Look, Gernot S. Pomrenke Jun 1983

A Study Of The 0.1-Ev Conversion Acceptor In Gaas, David C. Look, Gernot S. Pomrenke

Physics Faculty Publications

Two semi-insulating liquid-encapsulated Czochralski GaAs cyrstals, one Cr-doped and the other undoped, were annealed at 750°C for 15 min in flowing H2. Each sample converted to conducting p type in the near-surface region, due to the formation of acceptors at E∪ + 0.1 eV. We have studied this phenomenon by electrical, optical, and analytical profiling techniques, and have determined conclusively that the acceptors in our samples are not related to Mn accumulation, a commonly accepted explanation. It is argued that the O.I-e V center may arise from several possible sources, each exhibiting a VGa -like state at …

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Momentum-Transfer Scaling In Hydrogen-Isotope Collision Systems, Eduard P. Rille, Jerry Peacher, Thomas J. Kvale, E. Redd, D. M. Blankenship, John T. Park Jun 1983

Momentum-Transfer Scaling In Hydrogen-Isotope Collision Systems, Eduard P. Rille, Jerry Peacher, Thomas J. Kvale, E. Redd, D. M. Blankenship, John T. Park

Physics Faculty Research & Creative Works

The differential cross sections for excitation of atomic hydrogen isotopes to their n=2 states by proton or deutron impact are found to follow a simple scaling relationship. The momentum-transfer-scaled differential excitation cross sections, for a projectile velocity of 1.26 a.u., produce one differential cross-section curve for all four possible hydrogen-isotope collision systems. The experimental results are in excellent agreement with our Glauber-approximation calculations.

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An Elementary Development Of Mass-Energy Equivalence, Daniel J. Steck, Frank Rioux May 1983

An Elementary Development Of Mass-Energy Equivalence, Daniel J. Steck, Frank Rioux

Physics Faculty Publications

No abstract provided.

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Defect Nature Of The 0.4-Ev Center In O-Doped Gaas, David C. Look, S. Chaudhuri, J. R. Sizelove May 1983

Defect Nature Of The 0.4-Ev Center In O-Doped Gaas, David C. Look, S. Chaudhuri, J. R. Sizelove

Physics Faculty Publications

We have studied the Ec - 0.4 e V center in O-doped GaAs by a combination of temperature-dependent Hall-effect measurements, spark-source mass spectroscopy, and secondary-ion mass spectroscopy. The conclusion is that neither 0 nor any other impurity can account for the O.4-eV center; therefore, it is a pure defect.

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Structural Studies Of Low Temperature Ice Iₕ Using A Central Force Potential Model, Peter W. Deutsch, Barbara N. Hale, Richard C. Ward, Donald A. Reago Jr. Apr 1983

Structural Studies Of Low Temperature Ice Iₕ Using A Central Force Potential Model, Peter W. Deutsch, Barbara N. Hale, Richard C. Ward, Donald A. Reago Jr.

Physics Faculty Research & Creative Works

The revised central force potentials of Stillinger and Rahman [J. Chem. Phys. 68, 666 (1978)] are used to study the binding energy, structure, and multipole moments of a periodic ice Ih sample with a unit cell of 192 water molecules. The initial configuration for the unit cell has each oxygen in a wurtzite structure and intramolecular H-O-H angles symmetrically positioned in the tetrahedral O-O-O angles. Hydrogens are placed such that the total dipole moment for the unit cell is zero and the diagonal quadrupole moments are small (≲ 10-28 esu cm2). Subject to these restrictions, a …

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Using Nuclear Resonance Excitation To Observe United Atoms In Symmetric Ion-Atom Collisions, James M. Feagin, Ladislov Kocbach Apr 1983

Using Nuclear Resonance Excitation To Observe United Atoms In Symmetric Ion-Atom Collisions, James M. Feagin, Ladislov Kocbach

Department of Physics and Astronomy: Faculty Publications

We consider nuclear resonance excitation as a means to observe the distribution of united-atom orbitals in symmetric ion-atom collisions. We develop this possibility with the application of a two-state adiabatic model to an analysis of a 8Be nuclear resonance experiment. To test our model, and to provide a more direct determination of the nuclear resonance width, we propose that the 8Be experiment be repeated with metastable helium targets.

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Generalized Bohr-Sommerfeld Rules For Anomalies With Applications To Symmetry Breakdown And Decoupling, A. P. Balachandran, V. P. Nair, C. G. Trahern Mar 1983

Generalized Bohr-Sommerfeld Rules For Anomalies With Applications To Symmetry Breakdown And Decoupling, A. P. Balachandran, V. P. Nair, C. G. Trahern

Publications and Research

In the presence of anomalies, the requirement that a classical symmetry group G has a proper action on the fermion measure or in the effective Lagrangian description imposes Bohr-Sommerfeld conditions on the anomalies, and often implies that G is broken to a subgroup H as well. We show these results in this paper and apply them to QCD and SU(5). In particular, constraints on the QCD order parameter are derived, and an argument is presented which suggests that the breakdown of the chiral flavor symmetry and the emergence of some sort of generation structure in QCD may be natural.

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Science And Society Test Viii: The Arms Race Revisited, David W. Hafemeister Mar 1983

Science And Society Test Viii: The Arms Race Revisited, David W. Hafemeister

Physics

Approximate numerical estimates are developed in order to quantify a variety of aspects of the arms race. The results of these calculations are consistent with either direct observations or with more sophisticated calculations. This paper will cover some of the following aspects of the arms race: (1) the electromagnetic pulse (EMP); (2) spy satellites; (3) ICBM accuracy; (4) NAVSTAR global positioning satellites; (5) particle and laser beam weapons; (6) the neutron bomb; and (7) war games.

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Studies Of Self-Focusing Instability At Arecibo, D. T. Farley, C. Lahoz, Bela G. Fejer Mar 1983

Studies Of Self-Focusing Instability At Arecibo, D. T. Farley, C. Lahoz, Bela G. Fejer

Bela G. Fejer

Precisely simultaneous radar and satellite measurements at the altitude of reflection of a strong HF heating wave above the Arecibo Observatory were made on June 7, 1977. Parametric instabilities produce strong enhancements in the plasma line and ion line incoherent scatter radar echoes. These echoes also exhibit periodic deep fading that is attributed to a self-focusing instability. This explanation was confirmed by the in situ observation of electron density fluctuations with peak-to-peak amplitudes reaching at least 3% and a spatial dependence that corresponded closely to the radar fading pattern, at least for irregularity wavelengths ranging from a few hundred meters …

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Soliton States In The Quantum-Chromodynamic Effective Lagrangian, A. P. Balachandran, V. Parameswaran Nair, S. G. Rajeev, A. Stern Mar 1983

Soliton States In The Quantum-Chromodynamic Effective Lagrangian, A. P. Balachandran, V. Parameswaran Nair, S. G. Rajeev, A. Stern

Publications and Research

The work of Skyrme has shown that the SU(2)×SU(2) chiral model has nontrivial topological sectors which admit solitons for generic chiral Lagrangians. In this paper, we study such models in the presence of baryon fields. The baryon number and strangeness of the solitons, and the bound states of the nucleon to the soliton are investigated. It is found that long-lived levels with large baryon number B and strangeness (≳6 in magnitude) and masses somewhere in the range 1.8 to 5.6 GeV must exist. Some of these levels have half-integral electric charge and exotic relation between B and spin s (e.g., …

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Homogeneous Nucleation Rate Measurements For Water Over A Wide Range Of Temperature And Nucleation Rate, Ronald C. Miller, Robert J. Anderson, James L. Kassner, Donald E. Hagen Mar 1983

Homogeneous Nucleation Rate Measurements For Water Over A Wide Range Of Temperature And Nucleation Rate, Ronald C. Miller, Robert J. Anderson, James L. Kassner, Donald E. Hagen

Physics Faculty Research & Creative Works

An expansion cloud chamber was used to measure the homogeneous nucleation rate for water over a wide range of temperature from 230-290 K and nucleation rates of 1-106 drops cm-3 s-1. The comprehensive and extensive nature of this data allows a much more detailed comparison between theory and experiment than has previously been possible. The expansion chamber technique employs continuous pressure measurement and an adiabatic pulse of supersaturation to give the time history of supersaturation and temperature during the nucleation. The resulting drop concentration is determined using photographic techniques. The experimental observations are presented in tabular …

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Quantum Theory Of Slow Atomic Collisions, John B. Delos Mar 1983

Quantum Theory Of Slow Atomic Collisions, John B. Delos

Arts & Sciences Articles

Quantum-mechanical and semiclassical theories of slow atomic collisions are reviewed, with attention to electron-translation factors and their effects.

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Exciton Trapping And Sensitized Luminescence: A Generalized Theory For All Trap Concentrations, Vasudev M. Kenkre, Paul Ernest Parris Mar 1983

Exciton Trapping And Sensitized Luminescence: A Generalized Theory For All Trap Concentrations, Vasudev M. Kenkre, Paul Ernest Parris

Physics Faculty Research & Creative Works

The generalized-master-equation theory of sensitized luminescence in molecular crystals is extended to cover arbitrary guest concentrations by making use of a recently introduced formalism. Central to the formalism is a quantity termed the ν function, which is an ensemble average of the sum of host propagators over guest-influenced host sites. A variety of experimentally relevant sensitized luminescence observables, such as the host (and guest) luminescence intensity, the quantum yields, and the energy-transfer rates are simply related to the ν function. It is shown how the latter can be calculated for exciton motion possessing an arbitrary degree of coherence, dimensionality, and …

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Dislocations And The Nematic To Smectic-A Transition For Arbitrary Values Of K1, Anthony Day, T. Lubensky, A. Mckane Feb 1983

Dislocations And The Nematic To Smectic-A Transition For Arbitrary Values Of K1, Anthony Day, T. Lubensky, A. Mckane

Anthony Roy Day

The de Gennes model is used to derive the energy of interacting dislocations in smectic-A liquid crystals. This energy reduces to the energy of interacting vortices in type-II superconductors when the splay elastic constant K1 is zero and to that derived from the Landau-Peierls elastic energy when spatial variations are slow on a scale of the bend and twist penetration depths. Furthermore, it has a well-defined K1→∞ limit. The dislocation energy is used to study the nematic—to—smectic-A transition as a function of K1 in two dimensions and in 4-ε dimensions. No evidence for the Nelson-Toner, anisotropic critical point is found …

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