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Collision-Induced Bands Of Lithium-Rare Gas Molecules, Wen Jong Wang

Physics Theses & Dissertations

Lithium vapor is optically excited by two-step laser excitation of the 3d state in the presence of the rare gases He, Ne, Ar, Kr, and Xe. Collision induced bands are observed in Li-Ar, Li-Kr, and Li-Xe mixtures. The bands are believed to be due to transitions to the dissociating 2s~ ground state from states above the 2p state of the Li-RG molecules. The Li-Ar, Li-Kr, and Li-Xe 3sб -2sб collision induced bands are progressively shifted, for the heavier rare gases, further to the red of the asymptotic atomic Li 3s-2s energy difference. A qualitative comparison is made between the spectra …

Anomalies In Chemical Equilibria Near Critical Points Of Dilute Solutions, Rolfe G. Petschek

Faculty Scholarship

We show that a recent prediction that the extent of reaction of a very dilute solute near the critical point of an almost pure solvent will show strong variation with temperature at fixed volume is in error. We give arguments to show that the behavior is at most weakly singular in the sense of Griffiths and Wheeler, point out the error in the earlier argument, and show that experiments adduced as evidence for the earlier argument are subject to alternative explanation. We also consider a prediction about the behavior near the critical point of a dissociating solvent.

Search For Fractional Charges In Water, David C. Joyce, Peter C. Abrams, Roger W. Bland, Robert T. Johnson, Michael A. Lindgren, Maureen H. Savage, Marion H. Scholz, Betty A. Young, Christopher L. Hodges

Physics

Results are presented from a search for fractional charges in water from a variety of natural sources. About 30 000 water drops have been measured, comprising 51 μg of water and dissolved materials. No evidence for fractional charge was seen.

Magnetic Field Behavior Of A Josephson-Junction Array: Two-Dimensional Flux Transport On A Periodic Substrate, Richard A. Webb, Richard F. Voss, G. Grinstein, P. M. Horn

Faculty Publications

This Letter reports measurements down to 3 mK of the magnetic field dependence of the resistance and critical current of a weakly coupled periodic array of Josephson junctions. Below 700 mK the resistance is an oscillatory function of field. The temperature dependence of the resistance for integral numbers of flux quanta per cell suggests the existence of a Kosterlitz-Thouless transition involving the unbinding of defects in the flux lattice.

The Application Of Exact Electrodiffusion Theory To Ion Transport Across Lipid Bilayer Membranes, Scott Cohen

Dissertations and Theses

The question of how ions interact with each other and with the potential energy barrier in thin lipid bilayer membranes has interested investigators for several years. The application of electrodiffusion theory to the study of this question is the central theme of this work. We have calculated current-voltage curves for barriers of various shapes and heights, in each case by means of numerically integrating the exact electrodiffusion equation as well as this same equation in the constant field approximation. We have also calculated the total charge in the membrane for the same conditions under which we have calculated the current-voltage …

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 …

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.

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 …

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.

Electrical-Properties Of Low-Compensation Gaas, David C. Look, P. C. Colter

Physics Faculty Publications

Recently we have reproducibly grown vapor-phase epitaxial GaAs, with less than 10% compensation, in an AsC1₃-Ga-H₂ reactor. The low-temperature electrical properties of such samples are quite interesting, with neutral-impurity scattering and screening being much more important than usual. The Hall mobility is typically above 10⁵ cm²/V sec at 5 K and has two maxima as a function of temperature, the usual one near 50 K and another near 9 K, The latter phenomenon has not been observed before, to our knowledge, The mobility and carrier concentration temperature dependences for a low-compensation sample and a …

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 …

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 Ø_pB, of minimum reflectance R_pm 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 = sin²ø_pB. It is shown that, for a given value of the normal-incidence amplitude reflectance |r|, there is an associated normal-incidence phase shift, δ = δ_mm, that leads to maximum minimum parallel reflectance, …

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.

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 V_Ga -like state at …

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 E_c - 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.

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.

Transient Two Dimensional Ground-Water Flow: A Comparison Of Computed And Analytical Results, Robert Jan Fennema

Civil & Environmental Engineering Theses & Dissertations

The exact analytical solution of the transient-flow equation is compared with the finite difference solution. The finite difference program, written by the author, uses an iterative alternating direction implicit procedure to solve the linearized partial differential equation. A second order accurate central difference method is employed to solve the equation in two dimensions.

Variable cell spacing to divide the physical domain, a weighting factor and a time acceleration function were used to investigate rate of convergence and accuracy of the numerical solution. The exact integral solution to the one-dimensional form of the flow equation i n radial coordinates is used …

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.

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.

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 …

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., …

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 …

Interpretation Of Anomalies In The Raman Spectrum Of K2Seo4 In Terms Of Oxygen Sublattice Disorder, Nestor Massa, Frank Ullman, John R. Hardy

John R. Hardy Papers

Raman scattering from K₂SeO₄ crystals has been studied in the (20-800)-K temperature range. Three portions of the spectrum are discussed: defect-induced scattering, primarily below 100 cm^-1, the external mode spectrum below 200 cm^-1, and the internal mode spectra in two regions, 300-500 and 800-950 cm^-1. The temperature dependence of the low-frequency, defect-induced scattering has been correlated (in previous studies) with the temperature dependence of certain nonzero-wave-vector phonons that have been observed by others using inelastic neutron scattering. Close to the incommensurate transition temperature, T_i= 129 K, a large enhancement …

Single-Reflection Film—Substrate Half-Wave Retarders With Nearly Stationary Reflection Properties Over A Wide Range Of Incidence Angles, R. M.A. Azzam, M. Emdadur Rahman Khan

Electrical Engineering Faculty Publications

The complex reflection coefficient for the p polarization of a transparent film on an absorbing or transparent substrate can be made equal to the negative of that for the s polarization, and hence the film—substrate system acts as a half-wave retarder (HWR), by proper selection of film refractive index N₁, film thickness d, and angle of incidence Φ. This condition, which generally holds only at normal incidence, becomes possible at oblique incidence also if N₁ is within a certain range, 1 < N₁ < N̂₁ . For a given substrate and given N₁, …

Gravity‐Induced Density And Concentration Profiles In Binary Mixtures Near Gas–Liquid Critical Lines, R. F. Chang, J. M. H. Levelt Sengers, T. Doiron, J. Jones

Physics Publications

We have calculated gravity‐induced density and concentration gradients using scaled equations of state fashioned after that of Leung and Griffiths for binary mixtures near gas–liquid critical lines. The mixtures considered here are those of helium‐3 and helium‐4 and of carbon dioxide and ethane. Our calculations show that the density profiles for both mixtures in any proportion of the components are similar to those of pure fluids. The concentration gradients in the helium mixture have the same appearance as the density gradients. In the carbon dioxide–ethane system, however, the form of the concentration profile varies greatly, depending on the overall composition. …

Intermediate-Band Photometry Of Stars In Three Clusters Containing Classical Cepheids, Edward G. Schmidt

Edward Schmidt Publications

Four-color and Hβ photometry has been carried out of stars in three sparse and distant clusters which are thought to contain Cepheids. From these data the distance moduli and color excesses of the clusters have been derived. In general the new values agree with those in the literature but are somewhat more precise.

Interactive Computer Graphics: The Arms Race, David W. Hafemeister

Physics

No abstract provided.

Comparison Of Model High-Latitude Electron Densities With Millstone Hill Observations, Jan Josef Sojka, Robert W. Schunk, J. V. Evans, J. M. Holt, R. H. Wand

All Physics Faculty Publications

Model predictions of the diurnal variations of plasma convection velocities and electron densities in the high-latitude ionosphere were compared with Millstone Hill incoherent scatter radar observations for an equinox day on which there was moderate magnetic activity. On the observation day, three major morphological features were evident at 500 km, including a dayside high density region, a nightside mid-latitude trough, and a region of slightly enhanced densities in the auroral zone. Although the dayside high density region was due to solar EUV radiation, it was not symmetrical about local noon (1000-1900 LT sector) owing to the effect of horizontal transport. …

Experimental Evidence For The Acceleration Of Thermal Electrons By Ion Cyclotron Waves In The Magnetosphere, A. J. Norris, J.F. E. Johnson, Jan Josef Sojka, G. L. Wrenn, N. Cornilleau-Wehrlin, S. Perraut, A. Roux

All Physics Faculty Publications

Ion cyclotron waves (ICWs) at frequencies just above f He+ , the helium gyrofrequency, are often observed by the ESA satellites GEOS 1 and GEOS 2. Young et al. (1981) have shown the close connection between these ICWs and the presence of thermal He+ ions in the outer magnetosphere. The purpose of this paper is to provide experimental evidence for the acceleration of thermal electrons by the large amplitude ICWs. The wave power in the ultra low frequency (ULF) range near f He+ is compared with the distribution function of low energy electrons, measured by instruments aboard the GEOS satellites. …

Fluorescence Quenching At High Quencher Concentrations, David Peak, T C. Werner, R M. Dennin Jr., J K. Baird

All Physics Faculty Publications

Chemical reactions occurring in dense media at high reactant concentrations can be described by rate ‘‘constants’’ which are actually functions of concentration. We present a theoretical model in which this so‐called rate constant ‘‘renormalization’’ occurs for the specific case of fluorescence quenching in solution. We show that both the quenching and the excitation rate constants can become concentration dependent. We fit our theory to several sets of experimental data—our own and some from the literature—and show that excellent agreement is obtained by varying a single free parameter, namely, the efficiency with which a fluorophore‐quencher collision leads to a quench of …