Digital Commons Network^™

Diffusion-Limited Reactions In Spherical Cavities, Amy Lisa Graves, Elizabeth L. Grossman , '92, Dane D. Morgan Iii, '92, B. J. Berne

Physics & Astronomy Faculty Works

We study a quenching reaction occurring at sinks within a spherical cavity and at the cavity surface. One may think of reactions at these two, distinct locations as two, coupled reactive channels. Reactions of the type D* + A-->D + A are studied in the limit of nondilute A, present at both locations, and dilute D, present within the cavity. We use a Monte Carlo algorithm to compute mean rates, pseudo-first-order rates and branching ratios, and compare with results obtained by assuming that the two reactive channels operate in parallel. The ratio of activities of the two channels are …

Self Organization And A Dynamical Transition In Traffic Flow Models, Alan Middleton, Ofer Biham, Dov Levine

Physics - All Scholarship

A simple model that describes traffic flow in two dimensions is studied. A sharp {\it jamming transition } is found that separates between the low density dynamical phase in which all cars move at maximal speed and the high density jammed phase in which they are all stuck. Self organization effects in both phases are studied and discussed.

Magnetization And 57Fe Hyperfine Fields In Y2Fe17Z3- Δ (Z=H, C, Or N) Interstitial Compounds, Qi-Nian Qi, Hong Sun, Ralph Skomski, J.M.D. Coey

Ralph Skomski Publications

Measured magnetization and ⁵⁷Fe hyperfine fields at T∼0 K for Y₂Fe₁₇ and Y₂Fe₁₇Z_{3- δ} , with Z=H, C, or N and δ∼0.5, are analyzed to determine the influence of the interstitial atoms on the 3d magnetism. All are weak ferromagnets with a nearly-full 3d subband, although when Z=N, the magnetic moment of 38.1μ_B is very close to the fully saturated value of 39.4μ_B. On a local scale, the order of hyperfine fields B_hf^4f (=35 T)> B_hf^6g (=33 T)> B_hf^{12j …}

Native Donors And Acceptors In Molecular-Beam Epitaxial Gaas Grown At 200 Degrees C, David C. Look, D. C. Walters, M. Mier, C. E. Stutz, S. K. Brierley

Physics Faculty Publications

Absorption measurements at 1.1 and 1.2 μm were used along with the known electron and hole photoionization cross sections for EL2 to determine deep donor (EL2‐like) and acceptor concentrations N_D=9.9×10¹⁹ and N_A=7.9×10¹⁸ cm⁻³, respectively, in a 2‐μm‐thick molecular‐beam epitaxial GaAs layer grown at 200 °C on a 2‐in.‐diam semi‐insulating wafer. Both lateral and depth uniformities of N_D over the wafer were excellent as was also the case for the conductivity. Band conduction was negligible compared to hopping conduction at 296 K as evidenced by the lack of a measurable Hall coefficient.

Prediction Of Paper Color: A Process Simulation Approach, Mayank Chaturvedi

Masters Theses

A simulation model was developed for a dye mixing process and for the prediction of the optical properties of the paper. The model was integrated with the MAPPS (Modular Analysis of Pulp and Paper Systems) simulation software package. The model was validated using dyed handsheets made in a laboratory and dyed paper made on a pilot papermachine. Validation comprised of prediction of the optical properties of the handsheets and the machine-made paper which contained various combinations of three non-fluorescent dyes. Sheet reflectances were predicted at 20 nanometer intervals for discrete light wavelength range of 400 to 700 nanometers and verified …

Mechanisms For Gaas Surface Passivation By A Molecular-Beam Epitaxial Cap Layer Grown At 200-Degrees-C, David C. Look, D. C. Walters, C. E. Stutz, K. R. Evans, J. R. Sizelove

Physics Faculty Publications

A thin, undoped, molecular beam epitaxial (MBE) GaAs cap layer grown on top of an n‐type conductive layer significantly reduces the free‐electron depletion from the latter. By analyzing electron transfer to surface, interface, and bulk acceptor states in the cap, as a function of cap thickness, we show that either (1) the usual E_C−0.7 eV surface states are absent, (2) a dense donor near E_C−0.4 eV exists or (3) a high donor interface charge (∼5×10¹² cm⁻²) is present. Any of these conclusions constitutes an important new aspect of low‐temperature MBE GaAs.

Three Dimensional Quantum Gravity Coupled To Ising Matter, Simon Catterall, Ray L. Renken, John B. Kogut

Physics - All Scholarship

We establish the phase diagram of three--dimensional quantum gravity coupled to Ising matter. We find that in the negative curvature phase of the quantum gravity there is no disordered phase for ferromagnetic Ising matter because the coordination number of the sites diverges. In the positive curvature phase of the quantum gravity there is evidence for two spin phases with a first order transition between them.

Water Masers In W49n - The Youngest Stellar Jet?, Mordecai-Mark Mac Low, Moshe Elitzur

Physics and Astronomy Faculty Publications

Observations by Gwinn, Moran, and Reid of the proper motions of water masers in W49N show that they have an elongated distribution expanding from a common center. Features with high space velocity only occur far from the center, while low-velocity features occur at all distances. It is proposed that water masers in star-forming regions occur in expanding shells swept up by high-velocity winds from young, massive stars during the early phases of the expansion. In W49N, confinement of the bubble by a density distribution with an axial cavity can explain both the velocity field and the shape of the maser …

Limaçon Of Pascal Locus Of The Complex Refractive Indices Of Interfaces With Maximally Flat Reflectance-Versus-Angle Curves For Incident Unpolarized Light, R. M.A. Azzam

Electrical Engineering Faculty Publications

For an interface between two isotropic media the power reflectance R_v (ø) is an even function, R_v (ø) = R_v (--), of the angle of incidence ø; hence all the odd derivatives, R_v⁽ⁿ⁾ = dⁿ R_v /døⁿ (n odd), are identically 0 at ø = 0, independent of the incident polarization v. When the incident light is unpolarized (v = u), the second derivative, R_u⁽²⁾, is also 0 at ø = 0, so that the flatness of the R_u -versus-ø curve …

Direct Measurement Of The Van Der Waals Interaction Between An Atom And Its Images In A Micron-Sized Cavity, V. Sandoghdar, C. I. Sukenik, E. A. Hinds, S. Haroche

Physics Faculty Publications

The authors have measured by laser spectroscopy the energy of interaction between a sodium atom and its images in the walls of a micron-sized cavity. This cavity-QED study is the first direct quantitative test of the Lennard-Jones van der Waals interaction as a function of controlled atom-surface separation and mean-square electric dipole moment.

Crystalline Orientations Of Tl2Ba2Ca2Cu3OΧ Grains On Mgo, Srtio3, And Laalo3 Substrates, Sy_Hwang Liou, C.Y. Wu

Sy-Hwang Liou Publications

Crystalline orientations of Tl₂Ba₂Ca₂Cu₃O_χ grains in magnetron sputtered films on MgO (001), SrTiO₃ (001), and LaAlO₃ (001) substrates were investigated by scanning electron microscopy. In contrast to the nearly single crystalline films on the lattice matched substrates SrTiO₃ and LaAlO₃, films on the MgO (001) substrate, being polycrystalline in nature, exhibit several preferred in-plane grain orientations. These orientations agree well with a simplified theory of near-coincidence site lattices between Tl₂Ba₂Ca₂Cu₃O_χ and MgO.

Double Differential Cross Sections For State-Selective Electron Capture By Low-Energy Ar4+ And Ar5+ Ions From He And Ar, Serefettin Yaltkaya

Masters Theses

Doubly differential cross sections, in angle and energy, for state-selective single-electron capture from He and Ar by Ar⁴⁺ and Ar⁵⁺ ions have been studied experimentally at laboratory impact energies of 25q, 50q, and lOOq eV (q = 4 and 5, where q is the ion charge state) and at laboratory scattering angles between 0° and 5.5°, by means of translational energy spectroscopy. The translational energy-gain spectra show that only a few final states are selectively populated. Final-state transition probabilities were found to depend strongly on the charge state of the projectile ion and the ionization potential of the …

Some Stability Problems In Droplet Formation And Breakup (Report Lstm 351/T/92)., Nihad E. Daidzic

Aviation Department Publications

In this study the instability of droplets and cylindrical jets is investigated. The understanding of these processes has both academic and practical value. Instability of cylindrical jets is theoretically investigated for infinitesimal and finite, but small initial amplitudes (linear and nonlinear stability). For droplets, only linear theory is presented. It is assumed that the capillary force play a dominant role. It is determined that the viscosity exerts a damping effect. In the first section we give an introduction, after which the linear stability theory of cylindrical liquid jets is presented. In the third section the nonlinear jet stability theory is …

Tamm States In Finite Semiconductor Superlattices: Influence Of Accumulation And Depletion Layers, Roger H. Yu

All Faculty Scholarship for the College of the Sciences

We discuss the electronic-level structure of finite semiconductor superlattices and the influence of accumulation and depletion regions on the surface localized states (Tamm states). Exact solutions of the Poisson and Schrödinger equations are obtained self-consistently, through use of a nonuniform jellium model. Both high-energy and low-energy Tamm states are found.

Rayleigh-Brillouin Scattering To Determine One-Dimensional Temperature And Number Density Profiles Of A Gas Flow Field, James A. Lock, Richard G. Seasholtz, W. Trevor John

Physics Faculty Publications

Rayleigh-Brillouin spectra for heated nitrogen gas were measured by imaging the output of a Fabry-Perot interferometer onto a CCD array The spectra were compared with the theoretical 6-moment model of Rayleigh-Brillouin scattering convolved with the Fabry-Perot instrument function. Estimates of the temperature and a dimensionless parameter proportional to the number density of the gas as functions of position in the laser beam were calculated by least-squares deviation fits between theory and experiment.

Thermal Rounding Of The Charge Density Wave Depinning Transition, Alan Middleton

Physics - All Scholarship

The rounding of the charge density wave depinning transition by thermal noise is examined. Hops by localized modes over small barriers trigger ``avalanches'', resulting in a creep velocity much larger than that expected from comparing thermal energies with typical barriers. For a field equal to the $T=0$ depinning field, the creep velocity is predicted to have a {\em power-law} dependence on the temperature $T$; numerical computations confirm this result. The predicted order of magnitude of the thermal rounding of the depinning transition is consistent with rounding seen in experiment.

Selective Area, Synchrotron Radiation Induced, Delta Doping Of Silicon, R.A. Rosenberg, S.P. Frigo, Sunwoo Lee, Peter A. Dowben

Peter Dowben Publications

We have used broadband synchrotron radiation to induce selective area surface doping of boron into silicon. The source of the boron was nido-decaborane (B₁₀H₁₄) adsorbed on Si(111) at 100 K. Irradiation caused decomposition of the adsorbed molecule which lead to an enhanced concentration of free boron in the irradiated area. Using Si 2p core level photoelectron spectroscopy, the surface chemical composition and Fermi level position in both the irradiated and unirradiated regions were determined. The downward movement of the Fermi level was greater in the irradiated region than in the unirradiated region, and greater …

Evidence For The Formation Of Metallic Mercury Overlayers On Si(111), Dongqi Li, Jiandi Zhang, Sunwoo Lee, Peter A. Dowben

Peter Dowben Publications

A strongly chemisorbed Hg species is observed following the adsorption of Hg on Si(111) at 110 K. This strongly chemisorbed Hg species and subsequently weakly chemisorbed Hg species are observed to be metallic in the photoemission final state as determined by resonant photoemission and the reduction of photovoltaic charging. We postulate that the strongly chemisorbed Hg species on Si(111) is more metallic at dilute coverages than Hg adsorbed on Cu(100).

Mutual Information, Strange Attractors, And The Optimal Estimation Of Dimension, J. M. Martinerie, Alfonso M. Albano, A. I. Mees, P. E. Rapp

Physics Faculty Research and Scholarship

It has been shown that the appropriate setting of data windows is crucial to a successful estimation of a time-series correlation dimension using the Grassberger-Procaccia algorithm [Physica 9D, 189 (1983); Phys. Rev. Lett. 50, 346 (1983)], and it has been proposed that the first minimum of the corresponding mutual-information function may be an appropriate window value. We have tested this hypothesis against data generated by the Rossler equations, the Lorenz equations, and a three-dimensional irrational torus. We conclude that mutual information is not consistently successful in identifying the optimal window.

Incorporation Of Si And Al In Low Temperature Mbe Gaas, M. O. Manasreh, K. R. Evans, C. E. Stutz, David C. Look

Physics Faculty Publications

The localized vibrational modes (LVMs) of silicon donor (Si_Ga) and aluminum isovalent (Al_Ga) impurities in molecular beam epitaxial GaAs layers grown at various temperatures are studied using the infrared absorption technique. It is found that the total integrated absorption of these impurities LVMs is decreased as the growth temperature decreases. This finding suggests a nonsubstitutional incorporation of Si and Al in GaAs layers grown at 200 °C. On the other hand, a subtitutional incorporation is obtained in GaAs layers grown at temperatures higher than 350 °C. A recovery of the Si_Ga LVMs in GaAs layers …

Senior Theses: Department Of Physical Sciences, Patrick M. Higgins, Timothy Howard, Leah Carol Ross

Morehead State Theses and Dissertations

1992 Senior Theses from the Department of Physical Science at Morehead State University.

The Abundance, Diversity, and Stratigraphy of the Upper Crab Orchard Formation, Lewis County, Kentucky by Patrick M. Higgins.

The Modification of Flemion for Use in a Solid Electrolyte Battery by Timothy Howard.

Simple Analog Computers by Leah Carol Ross.

Dephasing Processes In Glasses With Strong Strain Interactions, Ulrich Zürcher, R. Silbey

Physics Faculty Publications

Spectral diffusion decay is calculated for a glass modeled by two level systems which are strongly coupled to phonons. The spin-phonon interaction induces an effective spin-spin interaction which dominates the energy scale. We show that spectral diffusion is a property of macroscopic local fields which fluctuate on time scales that are much longer than the spin-phonon relaxation time T1. We assume for the spectral diffusion a Gaussian distribution and derive a self-consistent equation for its variance which is nonlocal in time. At high temperatures, the variance grows linearly with time while at low temperatures, we find strong deviations from simple …

Assessing The Contributions Of Surface Waves And Complex Rays To Far-Field Mie Scattering By Use Of The Debye Series, Edward A. Hovenac, James A. Lock

Physics Faculty Publications

The contributions of complex rays and the secondary radiation shed by surface waves to scattering by a dielectric sphere are calculated in the context of the Debye-series expansion of the Mie scattering amplitudes. Also, the contributions of geometrical rays are reviewed and compared with those of the Debye series. Interference effects among surface waves, complex rays, and geometrical rays are calculated, and the possibility of observing these interference effects is discussed. Experimental data supporting the observation of a surface-wave-geometrical-ray-interference pattern are presented.

Optical Caustics In Natural Phenomena, James A. Lock, James H. Andrews

Physics Faculty Publications

When observing a distant point source of light through a water droplet adhering to a pane of glass near one's eye or the scattering of light from raindrops, one often sees optical caustics. In this paper, diffraction integrals are used to investigate these caustics. The caustic shapes are related to divergences in the stationary phase method for approximating the diffraction integrals. These divergences correspond to the coalescing of two or more geometrical light rays in ray optics or the coalescing of two or more regions of stationary phase in wave optics. The number of coalescing light rays is related to …

Thermal Conductivity Of Thermoelectric Si0.8‐Ge0.2 Alloys, D. P. White, P. G. Clemens

Physics Faculty Publications

The thermal conductivity of heavily doped, n-type Si-Ge alloys has been studied from 300 to 1200 K. The scattering rate of several phonon scattering mechanisms has been calculated, including intrinsic scattering, mass defect and distortion scattering, phonon-electron scattering, and scattering by inclusions. These rates were then used to calculate the lattice thermal conductivity. The electronic component of the thermal conductivity was calculated from the calculated Lorenz ratio and measured values of the electrical conductivity. The total thermal conductivity was then compared to measured values for a specimen studied by Vining et al.

Incorporation Of Silicon And Aluminum In Low-Temperature Molecular-Beam Epitaxial Gaas, M. O. Manasreh, K. R. Evans, C. E. Stutz, David C. Look, Joseph Hemsky

Physics Faculty Publications

The localized vibrational modes (LVMs) of silicon donor (Si_Ga) and aluminum isovalent (Al_Ga) impurities in molecular beam epitaxial GaAs layers grown at various temperatures are studied using the infrared absorption technique. It is found that the total integrated absorption of these impurities LVMs is decreased as the growth temperature decreases. This finding suggests a nonsubstitutional incorporation of Si and Al in GaAs layers grown at 200 °C. On the other hand, a subtitutional incorporation is obtained in GaAs layers grown at temperatures higher than 350 °C. A recovery of the Si_Ga LVMs in GaAs layers …

Review: 'Optical Fiber Communications' (2nd Edition), By Gerd Keiser, Bradley D. Duncan

Electro-Optics and Photonics Faculty Publications

If first impressions are worth anything (and they usually are), I would have to admit that my first impression of the second edition of Gerd Keiser's now popular text Optical Fiber Communications was quite good. My compliments are hereby extended to the publisher for choosing a rather handsome cover and dust jacket. It stands in strong contrast to the text's first edition, which still ranks as probably the ugliest book I own, with color choices ranging from dull cream and "baby" blue to pale pink! I am now happy to say that this older version has been discretely·retired to the …

The Three-Line Magnetic Hyperfine Spectrum Of 57Fe, Norman A. Blum, Richard B. Frankel

Physics

Longitudinal magnetization of a ⁵⁷Co in iron metal foil source and an iron metal foil absorber in a uniform external magnetic field results in a simple three-line magnetic hyperfine absorption spectrum. Measurement of the spectral splitting as a function of applied magnetic field yields the ⁵⁷Fe excited-and ground-state g-factors.

Transmission Studies Of Explosive Vaporization Of A Transparent Liquid Film On An Opaque Solid Surface Induced By Excimer-Laser-Pulsed Irradiation, P.T. Leung, Nhan Do, Leander Klees, Wing P. Leung, Frank Tong

Physics Faculty Publications and Presentations

Examines the dynamics of the explosion of a liquid film by an ultraviolet excimer pulsed laser studied experimentally on top of an amorphous silicon film deposited on fused quartz. Background on thermal physics of superheated pure or mixed liquids; Techniques for surface temperature measurement; Experimental of probe laser and pulsed excimer laser.

An Embedded Ring Approach To The Vibrational Dynamics Of Disordered Two-Dimensional Materials, Timothy Edwin Doyle

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

A theoretical approach was developed to model the vibrational dynamics of amorphous, two-dimensional materials. The materials were modeled as continuous random networks (CRN's) comprising an assemblage of planar rings of diverse size. In-plane vibrational modes for symmetric 4-, 5-, 6-, 7-, and 8-membered rings were examined. Vibrational states of isolated rings were modified by coupling the rings to a continuous network to represent rings embedded in a CRN. An effective force constant was used to couple the ring vibrations to the network's collective motions. Potentials were approximated with the use of a central force model (bond-stretching force constant) and a …