Digital Commons Network^™

Energy Deposition Of Energetic Silicon Atoms Within A Silicon Lattice, P. Zecher, D. Wang, J. Rapaport, C. Jeff Martoff, Betty A. Young

Physics

The energy dependence of the ionization produced in silicon by recoiling silicon atoms was measured in the 4–54-keV energy interval. It is found that the fraction of the recoil energy that is dissipated as ionization follows an E^1/2 dependence which agrees well with the predictions of the theory of Lindhard et al. [Mat. Fys. Medd. 33, 10 (1963)].

Polymerization On The Diamond Hierarchical Lattice: The Migdal-Kadanoff Renormalization-Group Scheme, Miron Kaufman, J. E. Touma

Physics Faculty Publications

The thermodynamics of the equilibrium polymerization model (grand-canonical ensemble of self-avoiding walks) in two dimensions is worked out by means of the Migdal-Kadanoff renormalization-group technique. This method involves renormalization-group flows in an eight-dimensional parameter space. At the critical point the number of relevant fields (positive exponents) is four. The leading exponent value differs by less than 1% from the (presumed) exact value. The results are exact for the polymerization problem defined on the diamond hierarchical lattice. Some results are peculiar to this lattice and are not expected to hold for Bravais lattices. For instance, the polymerized phase (infinite polymerization index) …

Rovibrationally Enhanced Dissociative Electron Attachment To Molecular Lithium, J M. Wadehra

Physics and Astronomy Faculty Research Publications

We have investigated the role played by initial rovibrational excitation of Li_2 on the cross sections and rates for dissociative electron attachment to the molecule. For a given internal energy, the vibrational excitation enhances the attachment cross section more than the rotational excitation. The attachment cross sections and the attachment rates reach their maximum values when the process of dissociative attachment to rovibrationally excited molecules is still endoergic and, furthermore, these quantities stay close to their maximum values even when the process changes from being endoergic to exoergic. The upper bounds on the cross sections and the rates for dissociative …

Decay Of Molecules At Spherical Surfaces: Nonlocal Effects, P.T. Leung

Physics Faculty Publications and Presentations

The decay rates for molecules in the vicinity of a metallic sphere are investigated in a phenomenological approach for very close molecule-surface distances d. The Fuchs-Claro model [Phys. Rev. B 35, 3722 (1987)] is adopted to describe the polarizability of the sphere with the nonlocal dielectric response being accounted for within the hydrodynamic description. The results show significant differences when compared with those obtained previously within a local description for dlsim50 Aring, with extra resonances observed in the high-frequency regime, a phenomenon similar to that noted previously by Ruppin (1982), in his calculation of the extinction cross section for such …

Structure And Morphology Of Magnetite Anaerobically-Produced By A Marine Magnetotactic Bacterium And A Dissimilatory Iron-Reducing Bacterium, N. H. C. Sparks, Stephen Mann, D. A. Bazylinski, D. R. Lovley, H. W. Jannasch, Richard B. Frankel

Physics

Intracellular crystals of magnetite synthesized by cells of the magnetotactic vibroid organism, MV-1, and extracellular crystals of magnetite produced by the non-magnetotactic dissimilatory iron-reducing bacterium strain GS-15, were examined using high-resolution transmission electron microscopy, electron diffraction and ⁵⁷Fe Mo¨ssbauer spectroscopy. The magnetotactic bacterium contained a single chain of approximately 10 crystals aligned along the long axis of the cell. The crystals were essentially pure stoichiometric magnetite. When viewed along the crystal long axis the particles had a hexagonal cross-section whereas side-on they appeared as rectangules or truncated rectangles of average dimension, 53 × 35 nm. These findings are explained …

The Effect Of Hot Dense Hydrogen And Argon In A Ballistic Compressor On The Structure And Composition Of Pure Iron, David Samuel Silver

Dissertations and Theses

An experimental study of pure iron foil exposed to a hot, dense hydrogen and argon gas mixture in a ballistic compressor yielded evidence of structural and compositional changes of the metal due to the presence of the hydrogen gas. Three iron foils have been compared, one of unexposed pure iron, another of pure iron exposed to a mixture of hydrogen and argon gas, and the third of pure iron exposed to argon alone. Exposure to these high temperature, high pressure gases took place in a ballistic compressor.

Line formations were found on the surface of the iron foil exposed to …

Chiral Phase Transition For Su(N) Gauge Theories Via An Effective Lagrangian Approach, Joseph Schechter, Francesco Sannino

Physics - All Scholarship

We study the chiral phase transition for vector-like SU(N) gauge theories as a function of the number of quark flavors N_f by making use of an anomaly-induced effective potential. We modify an effective potential of a previous work, suggested for N_f < N, and apply it to larger values of N_f where the phase transition is expected to occur. The new effective potential depends explicitly on the full \beta-function and the anomalous dimension \gamma of the quark mass operator. By using this potential we argue that chiral symmetry is restored for \gamma <1. A perturbative computation of \gamma then leads to an estimate of the critical value N_f^c for the transition.

Analytic Variational Method For Hamiltonian Lattice Gauge Theory In 3+ 1 Dimensions, Ming C. Huang, Mohammad W. Katoot

Aerospace, Physics, and Space Science Faculty Publications

We present an analytic d in 3 + 1 dimensions for Hamiltonian lattice gauge theory. This method is based on Batrouni's mean-plaquette method and space integration. The Abelianized Bianchi identities are used and a detailed study of the number of identities that are needed and the validity of this approximation is given. The we use is the product of single-plaquette wave functions. The guage group we consider here is SU(2), but the method is valid for any gauge theory. We apply this method to calculate the 0++ glueball mass, and, in addition, the results of the string tension (scaling is …

Analytic Solution Of The Two-State Problem, C. E. Carroll, Foek T. Hioe

Physics Faculty/Staff Publications

An exact solution of the time-dependent Schrodinger equation is obtained for a simple model with only two quantum states. The calculated transition probability involves only exponential and hyperbolic functions.

A Kähler-Chern-Simons Theory And Quantization Of Instanton Moduli Spaces, V. P. Nair, Jeremy Schiff

Publications and Research

A five dimensional field theory is introduced which is an analogue of three dimensional Chern-Simons theory. The reduced phase space in the theory is a moduli phase of instantons in four dimensional Euclidean gauge theory, with a symplectic structure induced by the Donaldson u-map. Issues related to quantization are discussed.

Fast-Wave Current Drive Above The Slow-Wave Density Limit, D. P. Sheehan, R. Mcwilliams, N. S. Wolf, D. Edrich

Physics and Biophysics: Faculty Scholarship

Fast-wave and slow-wave current drive near the mean gyrofrequency were compared in the Irvine Torus. The slow-wave current drive density limit observation was extended by an order of magnitude in wave frequency compared to previous tokamak results. At low densities, the fast-wave antenna was observed to launch slow waves which drove currents that suffered from the current drive density limit identical to waves launched from the slow-wave antenna. At higher densities, current was driven by the fast-wave antenna while none was driven by the slow-wave antenna.

Photoluminescence Studies In Znxcd1-Xte Single Crystals, David D. Allred, Jesus González-Hernández, Elías López-Cruz, Worth P. Allred

Faculty Publications

The crystalline quality of ZnxCd1-xTe single crystals prepared by a modified Bridgman method with 0≤x≤0.05 has been analyzed using photoluminescence. The spectrum of a typical sample is dominated by lines originating from the recombination of free and bound excitons. Lines due to free excitons in their ground and first excited states are observed in both the pure CdTe and the mixed crystals. Excitons bound to Dc vacancies are observed in the pure CdTe crystal but not in the mixed crystal. Weaker and broader features appearing at energies below the exciton emission range were associated with transitions involving free-to-bound and bound-to-bound …

Hydrogen Adsorption On The Β N-Covered W(100) Surface: An Infrared Study Of The W–Hstretch, D. Mark Riffe, A. J. Sievers

All Physics Faculty Publications

The adsorption of hydrogen on the c(2×2) β-N-covered W(100) surface has been studied with infrared and thermal-desorption spectroscopies. A new dipole-active vibrational absorption due to chemisorbed hydrogen has been discovered. Its center frequency (1738 cm^-1 for minimal H₂ adsorption), isotopic dependence (1252 cm^-1 for D₂ adsorption and the existence of both lines for HD adsorption), absorption strength versus β-N coverage, and effective dynamic charge e^*/ε_∞≥0.12e lead to the assignment of the W-H stretch associated with a top-bonded H species. The vibration has been studied in detail on the highly ordered surface characterized …

Size‐Inconsistency Effects In Molecular Properties For States With Valence‐Rydberg Mixing: The Low‐Lying Π→Π∗ States Of Ethylene And Butadiene, Robert J. Cave

All HMC Faculty Publications and Research

Ab initio results for the low‐lying 1B1u states of ethylene are used to discuss size‐inconsistency effects on calculated molecular properties for states where valence‐Rydberg mixing is important. Results for the expectation value of x2, x being the coordinate perpendicular to the plane of the molecule, are presented from quasidegenerate variational perturbation theory and multireference configuration‐interaction calculations. These results are compared with values from previous studies. It is argued that size inconsistency in configuration‐interaction studies can have a significant effect on estimated molecular properties. Calculations on several low‐lying states of butadiene are also reported where similar size‐inconsistency effects are found.

Nematic Electroclinic Effect, Zili Li, Gregory A. Dilisi, Rolfe G. Petschek, Charles Rosenblatt

Faculty Scholarship

A tilt of the principal axis of the optical dielectric tensor linear in a transverse electric field was observed for a surface-stabilized nematic liquid crystal. The electroclinic coefficient d/dE was observed to increase rapidly on approaching the nematicsmectic-A phase transition from above. This was not expected, and indicates that the incipient translational order is important to the electroclinic effect. The data are consistent with a critical exponent only over a narrow range of temperature, and in this range the apparent exponent is not that expected from theory. In addition, dielectric data are presented for this transition, and birefringence results are …

Surface And Interface Free-Carrier Depletion In Gaas Molecular Beam Epitaxial Layers: Demonstration Of High Interface Charge, David C. Look, C. E. Stutz, K. R. Evans

Physics Faculty Publications

Molecular beam epitaxial GaAs layers of electron concentration 1.69×10¹⁷ cm⁻³, and various thicknesses d=0.25, 0.50, 1.00, and 2.00 μm, have been grown on semi‐insulating GaAs substrates and characterized by the Hall effect and capacitance‐voltage (C‐V) techniques. A plot of sheet Hall concentration n_s vs d gives accurate values of (N_D−N_A) and (w_s+w_i), the sum of the surface and interface free‐carrier depletion widths, respectively. The C‐V measurements verify the value of N_D−N_{A …}

First-Principles Simulations Of Ionic Molecular Solids: The Phase Transitions In K2Seo4, H. M. Lu, John R. Hardy

John R. Hardy Papers

We present a new approach to first-principles simulations of the statics and dynamics of ionic molecular crystals. It is shown that the new method gives very realistic simulations of the phase transitions in K₂SeO₄ and that a double-well type of structure in the potential-energy surface is the driving mechanism of these phase transitions.

Eta' To Eta Pi Pi Decay As A Probe Of A Possible Lowest-Lying Scalar Nonet, Joseph Schechter, Amir H. Fariborz

Physics - All Scholarship

We study the eta' to eta pi pi decay within an effective chiral Lagrangian approach in which the lowest lying scalar meson candidates sigma(560) and kappa(900) together with the f0(980) and a0(980) are combined into a possible nonet. We show that there exists a unique choice of the free parameters of this model which, in addition to fitting the pi pi and pi K scattering amplitudes, well describes the experimental measurements for the partial decay width of eta' to eta pi pi and the energy dependence of this decay. As a by-product, we estimate the a0(980) width to be 70 …

Corrugation In The Nitrogen-Graphite Potential Probed By Inelastic Neutron Scattering, F. Y. Hansen, L. W. Bruch, H. Taub, V. L. Frank, H. J. Lauter, John R. Dennison

All Physics Faculty Publications

Inelastic neutron spectra of the commensurate √3 ×3 herringbone monolayer phase of nitrogen physisorbed on the graphite (002) surface at low temperature have been compared with lattice dynamics calculations of the polycrystalline-averaged one-phonon coherent neutron cross section. The observed zone-center energy gap of ∼0.4 THz in the acoustic-phonon branches is a factor of 2 larger than calculated from central atom-atom potentials. We conclude that current models of the corrugation in the adatom substrate potential greatly underestimate the lateral restoring forces in this relatively simple molecular film.

Surface And Interface Free-Carrier Depletion In Gaas Molecular-Beam Epitaxial Layers: Demonstration Of High Interface Charge, David C. Look, C. E. Stutz, K. R. Evans

Physics Faculty Publications

Molecular beam epitaxial GaAs layers of electron concentration 1.69×10¹⁷ cm⁻³, and various thicknesses d=0.25, 0.50, 1.00, and 2.00 μm, have been grown on semi‐insulating GaAs substrates and characterized by the Hall effect and capacitance‐voltage (C‐V) techniques. A plot of sheet Hall concentration n_s vs d gives accurate values of (N_D−N_A) and (w_s+w_i), the sum of the surface and interface free‐carrier depletion widths, respectively. The C‐V measurements verify the value of N_D−N_{A …}

Alkali Metal Adsorbates On W(110): Ionic, Covalent, Or Metallic?, D. Mark Riffe, G. K. Wertheim, P. H. Citrin

All Physics Faculty Publications

The photoemission signal from the first atomic layer of W(110) is used to assess the nature of the interaction between the surface atoms of the metal substrate and the adsorbates Na, K, and Cs for coverages up to 1 atomic layer. Our results indicate that there is little or no charge transfer from the alkali metal to the W surface, even in the limit of low coverage. The satellite structure of the photoemission lines of the outermost p shell of the alkali metals confirms this conclusion. While contrary to the conventional picture of alkali-metal-charge donation, these findings fully support recent …

Biomineralization Of Ferrimagnetic Greigite (Fe3s4) And Iron Pyrite (Fes2) In A Magnetotactic Bacterium, Stephen Mann, Nicholas C.H. Sparks, Richard B. Frankel, Dennis A. Bazylinski, Holger W. Jannasch

Physics

The ability of magnetotactic bacteria to orientate and navigate along geomagnetic field lines is due to the controlled intracellular deposition of the iron oxide mineral, magnetite (Fe₃O₄)^1,2. The function and crystal chemical specificity of this mineral has been considered to be unique amongst the prokaryotes³. Moreover, the bacterial production of magnetite may represent a significant contribution to the natural remanent magnetism of sediments^4,5. Here we report, the intracellular biomineralization of single crystals of the ferrimagnetic iron sulphide, greigite (Fe₃S₄), in a multicellular magnetotactic bacterium common in …

Quantum Measurement And Geometry, James Thomas Wheeler

All Physics Faculty Publications

A model for the interpretation of spacetime as a Weyl geometry is proposed, based on the hypothesis that a system moves on any given path with a probability which is inversely proportional to the resulting change in length of the system. The results of physical measurements are calculated as the product of Weyl-conjugate gauge-dependent probabilities for the detection of conjugate objects. Each probability, expressed as a Wiener integral, is the Green's function for a diffusion equation. If the line integral of the Weyl field equals the action functional divided by ℏ this equation provides the stochastic equivalent of the Schrödinger …

Perturbations Of Gravitational Instantons, Charles G. Torre

Aerospace, Physics, and Space Science Faculty Publications

Ashtekar's spinorial formulation of general relativity is used to study perturbations of gravitational instantons corresponding to finite-action solutions of the Euclidean Einstein equations (with a nonzero cosmological constant) possessing an anti-self-dual Weyl curvature tensor. It is shown that, with an appropriate "on-shell" form of infinitesimal gauge transformations, the space of solutions to the can be described in terms of an elliptic complex; the cohomology of the complex defines gauge-inequivalent perturbations. Using this elliptic complex we prove that there are no nontrivial solutions to the linearized instanton equation on conformally anti-self-dual Einstein spaces with a positive cosmological constant. Thus, the space …

The Circumstellar Structure Of Iras 16293-2422: C18o, Nh3 , And Co Observations, Lee Mundy, H. Wootten, Bruce Wilking

Physics Faculty Works

Interferometric observations of the (C-18)O and (C-12)O J = 1-0 transitions, and the NH3 (1, 1) and (2, 2) transitions toward the young far-IR source IRAS 16293-2422 are presented. The data reveal elongated gas structures which are aligned perpendicular to the axis of a bipolar outflow and to the local magnetic field direction. By combining the interferometric data with single-dish spectra of the (C-18)O and (C-17)O lines, a comprehensive model for the IRAS 16293-2422 region is developed. In this model, the compact (C-18)O line and 40 K dust emission arise from rotating material within which the central heat source is …

All-Electronic Peierls Instability In The Infinite-U Mean-Field Theory For The Hubbard Model, S. E. Barnes

Physics Articles and Papers

It is shown, for a small hole doping relative to half filling, that the large-U limit of the Hubbard model (or J=0 limit of the t-J model) exhibits an all-electron Peierls instability towards a state with a charge-density wave. The resulting gap in the spinon spectrum renders the model an insulator.

Spin-Disordered Ground State For A Nearly Half-Filled Hubbard Model, S. E. Barnes

Physics Articles and Papers

Following Nagaoka, the ground state of the large-U nearly half-filled Hubbard model is ‘‘ferromagnetic.’’ However, because of the anisotropic exchange energy J_A, the physical Nagaoka ground state is nondegenerate and comprises a totally disordered spin state, i.e., a linear combination of all possible spin arrangements. For this ground state the susceptibility is Pauli-like but of a magnitude associated with a narrow band of width ∼J_A while the holons, i.e., the charge excitations, correspond to spinless fermions with a band of width 2zt. Associated with the spinon sector are very poorly defined spin waves, i.e., bosons, with a …

Methyl Reorientation In Methylphenanthrenes. Ii. Solid-State Proton Spin-Lattice Relaxation In The 1-Ch3, 9-Ch3, And 1-Cd3, 9-Ch3 Systems, F B. Mallory, C. W. Mallory, K. G. Conn, Peter A. Beckmann

Physics Faculty Research and Scholarship

We report proton Zeeman relaxation rates R as a function of temperature T at 8.5 and 53 MHz in polycrystalline 1,9-dimethylphenanthrene (1,9-DMP) and l-trideuteriomethyl-9-methylphenanthrene (1, 9-DMP[1-d3]). The data are interpreted using a Davidson-Cole spectral density for intramolecular reorientation and the implications of this are discussed. R vs T−1data for 1,9-DMP[1-d3] are used to determine the parameters that characterize the reorientation of the 9-methyl group. By assuming that the parameters characterizing the dynamics of the 9-methyl group are the same in 1,9-DMP and 1,9-DMP[1-d3], we subtract out the R vs T−1 contribution of the 9-methyl group in 1,9-DMP to …

Improved Resolution Of A 6m Torodial Grating Monochromator, G. K. Wertheim, J. E. Rowe, D. Mark Riffe, N. V. Smith

All Physics Faculty Publications

We report a modification of the AT&T Bell Laboratories 6m toroidal grating monochromator at the National Synchrotron Light Source at Brookhaven National Laboratory which provides greatly improved resolution at midrange without the use of a movable exit slit. This modification is based on detailed ray tracing calculation, using the precedures developed by Haber, Howells, and McKinney and Howells, modified to include the holographic correction terms to the focusing equations. To maintain the optimum resolution requires an exit slit assembly movable over a distance of ∼20 cm. However, we show that an additional fixed slit 16.8 cm closer to the grating …

Iron Compounds In Brazilian Pre-Columbian Pigments Identified By 57Fe Mossbauer Spectroscopy And X-Ray Powder Diffraction, F. F.T. De Araujo, M. A.B. De Araujo, R. B. Frankel, G. C. Papaefthymiou, V. W. Vieira

Physics

Mossbauer spectroscopy and X-ray powder diffraction have been used to identify iron compounds in pre-Columbian pigments, probably used for art decorating, collected from the oldest archaeological site of Early Man presently known in American at Sao Raimundo Nonato, in Northeastern Brazil. The iron compounds were identified as being alpha-Fe203 (haematite) with full Morin transition supressed and small particles of alpha-FeOOH (goethite).