Physical Sciences and Mathematics Commons^™

Specific Heat And Critical Fields Of The Organic Superconductor Β″–(Bedt-Ttf)2sf5ch2cf2so3, S. Wanka, J. Hagel, D. Beckmanm, J. Wosnitza, J. A. Schlueter, Jack M. Williams, P. G. Nixon, Rolf Walter Winter, Gary L. Gard

Chemistry Faculty Publications and Presentations

We report on specific-heat, magnetization, and ac-susceptibility measurements of β″–(BEDT-TTF)₂SF₅CH₂CF₂SO₃, an organic superconductor with Tc=4.5 K, where BEDT-TTF stands for bis(ethylenedithio)-tetrathiafulvalene. The jump of the specific heat C at Tc and the exact form of the specific heat difference between C in the superconducting (B=0 T) and in the normal (B=3.5 T) state can be well described by BCS theory with strong coupling. We estimate an electron-phonon coupling parameter λ≈1.1. From measurements of C in magnetic fields we extract the upper critical field Bc₂(T). Low-field dc-magnetization measurements were used to determine the temperature dependence of the lower critical field Bc₁. …

The Surface Plasmon Enhancement Effect On Adsorbed Molecules At Elevated Temperatures, P.T. Leung, Hai-Pang Chiang, W. S. Tse

Physics Faculty Publications and Presentations

The surface plasmon enhancement effect on adsorbed molecules at elevated substrate temperatures is studied theoretically using surface enhanced Raman scattering (SERS) as an example. The surface structure is idealized to be a monodisperse spherical particle with its nonlocal dielectric response accounted for. The temperature effects are modeled using a temperature-dependent collision frequency in the Drude model. Numerical results show that only a small decrease in the SERS enhancement ratio occurs for temperatures up to the melting point of the substrate, even for scattering close to the surface plasmon resonance frequency of the metal. More definitive results are subjected to more …

Measurement Of The Total Cross Section For E+E-→Hadrons At √S=10.52 Gev, R. Ammar, Kenneth A. Bloom, Cleo Collaboration

Kenneth Bloom Publications

Using the CLEO detector at the Cornell Electron Storage Ring, we have made a measurement of R≡ σ(e⁺e^- → hadrons)/σ(e⁺e^-→μ⁺μ^-)=3.56± 0.01± 0.07 at √s= 10.52 GeV. This implies a value for the strong coupling constant of α_s(10.52 GeV) =0.20±0.01±0.06, or α_s (M_Z)=0.13±0.005±0.03.

Thermal Equilibrium Of Warm Clouds Of Charge With Small Aspect Ratio, Deborah L. Paulson, Ross L. Spencer

Faculty Publications

Global thermal equilibrium computations are presented for non-neutral plasmas whose radial size is much larger than their axial thickness. Axial and radial density profiles are computed for both ideal and nonideal Penning trap fields. Simple results are obtained in the limits of both low and high central density. Comparison is made to the grid calculations of Mason et al. [Phys. Plasmas 3 (5), 1502 (1996)].

Density Fluctuations In Vibrated Granular Materials , E.R. Nowak, J.B. Knight, E. Ben-Naim, H.M Jaeger, S.R. Nagel

Eli Ben-Naim

We report systematic measurements of the density of a vibrated granular material as a function of time. Monodisperse spherical beads were confined to a cylindrical container and shaken vertically. Under vibrations, the density of the pile slowly reaches a final steady-state value about which the density fluctuates. We have investigated the frequency dependence and amplitude of these fluctuations as a function of vibration intensity Γ. The spectrum of density fluctuations around the steady state value provides a probe of the internal relaxation dynamics of the system and a link to recent thermodynamic theories for the settling of granular material. In …

Electron-Irradiation-Induced Deep Level In N-Type Gan, Z-Q. Fang, Joseph W. Hemsky, David C. Look, M. P. Mack

Physics Faculty Publications

Deep-level transient spectroscopy measurements of n-type GaN epitaxial layers irradiated with 1-MeV electrons reveal an irradiation-induced electron trap at E_C−0.18 eV. The production rate is approximately 0.2 cm⁻¹, lower than the rate of 1 cm⁻¹ found for the N vacancy by Hall-effect studies. The defect trap cannot be firmly identified at this time. ©1998 American Institute of Physics.

The Nature Of The Continuum Limit In The 2d Rp^2 Gauge Model, Simon Catterall, M. Hasenbusch, R. R. Horgan, R. Renken

Physics - All Scholarship

The RP(2) gauge model is studied in 2D. We use Monte-Carlo renormalization techniques for blocking the mean spin-spin interaction, , and the mean gauge field plaquette. The presence of the O(3) renormalized trajectory is verified and is consistent with the known three-loop beta-function. The first-order `vorticity' transition observed by Solomon et al. is confirmed, and the location of the terminating critical point is established. New scaling flows in (,) are observed associated with a large exponent kappa in the range 4~5. The scaling flows give rise to a strong cross-over effect between regions of high and low vorticity …

Novel Doubly Excited States Produced In Negative Ion Photodetachment, Anthony F. Starace

Anthony F. Starace Publications

Eigenchannel R-matrix calculations for photodetachment partial cross sections of H^–, Li^–, Na^–, and Aℓ^– provide results that are dominated by high doubly-excited states and that are in excellent agreement with available measurements. Propensity rules for doubly-excited states developed for H^– apply also for heavier targets. However, states not observed in H^– may be observed in the heavier target spectra owing to the non-Coulomb core. Finally the signature of particular doubly excited states changes drastically from one partial cross section to another.

Fluctuation Properties Of Precipitation. Part Ii: Reconsideration Of The Meaning And Measurement Of Raindrop Size Distributions, A. R. Jameson, Alexander Kostinski

Department of Physics Publications

For M drop size categories, rain is frequently viewed simply as the superposition of M,statistically independent Poisson-distributed drop fluxes each described by its own mean concentration. Implicit in such a Poissonian model is the assumption of uncorrelated counts among the drops. However, it is well known that drop size distributions are the result of the processes of collision, coalescence, and breakup, which should lead to correlations.

This inconsistency is resolved in this work. Using 1-min disdrometer measurements, two-point cross-correlation functions are used to show that drop counts at different sizes are correlated rather than independent. Moreover, it is argued …

Crossing Of Disclinations In Nematic Slabs, T. Ishikawa, Oleg Lavrentovich

Oleg Lavrentovich

It is shown experimentally that crossing and intercommutation of disclinations in a bounded nematic cell depend on surface orientation of the director and the relative strength of disclinations. Lines of opposite strength switch the pinned ends between the bounding plates and vanish independently of each other if the surface orientation is tangential. In contrast, tilted surface orientation preserves the stability of lines.

Single Magnetic Domains In Magnetotactic Bacteria, Richard B. Frankel, Jin-Ping Zhang, Dennis A. Bazylinski

Physics

Magnetotactic bacteria construct an internal, permanent magnetic dipole based on single magnetic domain particles of magnetite or greigite. The organisms exert a high degree of control over the size and morphology of the particles. This may be relevant in distinguishing biogenic from nonbiogenic iron mineral particles.

Review Of The Future Of U.S. Nuclear Weapons Policy, David W. Hafemeister

Physics

No abstract provided.

Biomineralization Of Magnetic Iron Minerals In Bacteria, Richard B. Frankel, Dennis A. Bazylinski, Dirk Schϋler

Physics

Magnetotactic bacteria orient and migrate along magnetic field lines. This ability is based on a submicron assembly of single-magnetic domain iron mineral particles that elegantly solves the problem of how to construct a magnetic dipole that is large enough to be oriented in the geomagnetic field at ambient temperature, yet fit inside a micron-sized cell. The solution is based on the ability of the bacteria to accumulate high concentrations of iron, and control the deposition, size and orientation of a specific iron mineral at specific locations in the cell.

Suppression Of Switchable Polarization In Kdp By Ionizing Radiation, Timothy D. Usher

Physics Faculty Publications

Switching curves were obtained from KH₂PO₄ single crystals exposed to x-ray radiation for various time intervals, up to 8 h. The applied electric field was varied between 370 and 740 V/cm, as well. The temperature was held constant at 99 K. The switching curves were fit to a three-parameter nucleation and growth model based on the original works by Johnson and Mehl, and independently by Avrami. The two dynamic parameters, characteristic time t_c, and effective domain wall dimensionality n, produced values consistent with unirradiated studies, however, they did not show any clear dependancy on …

Theoretical Treatment Of Quasibound Resonances In Two-Color Resonant Four-Wave Mixing Spectroscopy, F. Di Teodoro, Elizabeth Mccormack

Physics Faculty Research and Scholarship

A treatment of continuum states in the application of diagrammatic perturbation theory to calculate the signal produced in two-color resonant four-wave mixing (TC-RFWM) spectroscopy is developed. The third-order susceptibility is significantly modified from that obtained when considering only discrete states. To illustrate the contribution of continuum states, the line profile of a quasibound resonance arising from the configuration interaction of bound and continuum states is derived. Analytic expressions for line profiles are presented for two specific experimental implementations of TC-RFWM used in gas-phase spectroscopic studies. While the TC-RFWM line profiles are found to be very distinct from the line profiles …

Phase And Risetime Dependence Using Rf Pulses In Multiphoton Processes, W. M. Griffith, Michael W. Noel, T. F. Gallagher

Physics Faculty Research and Scholarship

With this experiment we demonstrate that excitation of a two-state system with radio-frequency fields differing in phase by 90° produces nonintuitively different results, even for very long pulses. In addition, we show how the phase dependence of the transition probability of long pulses can be easily understood by using the single cycle time propagator. Finally, we have found surprising results for real pulses in the strong-field regime, i.e., pulses having appreciable rise and fall times.

Optimal Renormalization Scale And Scheme For Exclusive Processes, Stanley J. Brodsky, Chueng-Ryong Ji, Alex Pang, David G. Robertson

Physics Faculty Scholarship

We use the Brodsky-Lepage-Mackenzie (BLM) method to fix the renormalization scale of the QCD coupling in exclusive hadronic amplitudes such as the pion form factor and the photon-to-pion transition form factor at large momentum transfer. Renormalization-scheme-independent commensurate scale relations are established which connect the hard scattering subprocess amplitudes that control exclusive processes to other QCD observables such as the heavy quark potential and the electron-positron annihilation cross section. The commensurate scale relation connecting the heavy quark potential, as determined from lattice gauge theory, to the photon-to-pion transition form factor is in excellent agreement with γe⃗ π0e data assuming that the …

Novel Electronic And Magnetic Properties Of Ultrathin Chromium Oxide Films Grown On Pt(111), P S. Robbert, H Geisler, C A. Ventrice Jr, J Van Ek, S Chaturvedi, J A. Rodriguez, M Kuhn, U Diebold

Physics Faculty Publications

The growth of epitaxial metal–oxide films on lattice-mismatched metal substrates often results in the formation of unique overlayer structures. In particular, epitaxial chromium oxide films grown on Pt(111) exhibit a p(2×2) symmetry through the first two monolayers of growth which is followed by a (√3×√3)R30° phase that is attributed to the growth of a Cr₂O₃(0001) overlayer. Ultraviolet photoelectron spectroscopy measurements have been performed on the CrO_x/Pt(111) system. The electronic structures of CrO₂, Cr₂O₃, and Cr₃O₄ were calculated using the linear muffin-tin orbital method in …

Dynamics And Instabilities Near The Glass Transition: From Clusters To Crystals, Saroj K. Nayak, Puru Jena, Keith D. Ball, R. Stephen Berry

Physics Publications

Molecular dynamics simulation has been used to explore the evolution, kinetics, and dynamics of a liquid–glass transition in clusters and bulk matter. We demonstrate a dynamical indicator that characterizes the onset of the glass transition in clusters and is consistent with other indicators of glass transitions in bulk systems. This criterion, based on changes in chaotic behavior as measured by the largest Liapunov exponent, reveals aspects of the microscopic processes associated with the phase change from liquid to glass, and provides a connection between the thermodynamic and dynamical behavior of systems and their multidimensional potential surfaces.

Atomic And Electronic Structure Of Neutral And Charged Sinom Clusters, Saroj K. Nayak, B. K. Rao, S. N. Khanna, P. Jena

Physics Publications

Using molecular orbital approach and the generalized gradient approximation in the density functional theory, we have calculated the equilibrium geometries, binding energies, ionization potentials, and vertical and adiabatic electron affinities of SinOm clusters (n⩽6,m⩽12). The calculations were carried out using both Gaussian and numerical form for the atomic basis functions. Both procedures yield very similar results. The bonding in SinOm clusters is characterized by a significant charge transfer between the Si and O atoms and is stronger than in conventional semiconductor clusters. The bond distances are much less sensitive to cluster size than seen for metallic clusters. Similarly, calculated energy …

Geodetic Vlbi Observations Of Egret Blazars, B. Glenn Piner, Kerry A. Kingham

Physics

We present VLBI observations of the EGRET quasars 0202+149, CTA 26, and 1606+106, as well as additional analysis of VLBI observations of 1156+295 presented in a previous letter. We have produced 8 and 2 GHz VLBI images at 11 epochs, 8 epochs, and 12 epochs, spanning the years 1989-1996, of 0202+149, CTA 26, and 1606+106, respectively. The VLBI data have been taken from the Washington VLBI correlator's geodetic database. We have measured the apparent velocities of the jet components and find that CTA 26 and 1606+106 are superluminal sources, with average apparent speeds of 8.9 and 2.9 h-1c …

Critical Point In Ferroelectric Langmuir-Blodgett Polymer Films, Stephen Ducharme, A.V. Bune, L.M. Blinov, V.M. Fridkin, S.P. Palto, A.V. Sorokin, S.G. Yudin

Stephen Ducharme Publications

The ferroelectric critical point has been found in a ferroelectric polymer by exploring the influence of the electric field on the paraelectric-ferroelectric phase transition. Dielectric and pyroelectric measurements on 30-monolayer-thick films of the crystalline copolymer poly(vinylidene fluoride-trifluoroethylene) grown by Langmuir-Blodgett deposition show a single hysteresis loop below the zero-field phase transition temperature T_c0=80±10 °C, double hysteresis loops between T_c0 , and the critical temperature T_cr=145±5 °C, and no hysteresis above T_cr where the critical electric field is E_cr=0.93±0.1X10⁹ V/m.

Electron Attachment Energies Of The Dna Bases, Kayvan Aflatooni, Gordon A. Gallup, Paul Burrow

Paul Burrow Publications

Injection of electrons into the empty π* molecular orbitals of uracil and the DNA bases creates short-lived anion states whose energies have been determined by electron scattering. A common range of attachment energies into the lowest orbitals is observed in all the bases. Evidence for nuclear motion during the lifetimes of the anions is found in all the compounds except adenine. These properties of the bases as bridge sites along the π-stack of DNA, namely, the effective degeneracy of the anion energies and the strong excitation of vibration, are key parameters for theories of electron-transfer rate, some of …

Patterns On Liquid Surfaces: Cnoidal Waves, Compactons And Scaling, Andrei Ludu

Andrei Ludu

Localized patterns and nonlinear oscillation formation on the bounded free surface of an ideal incompressible liquid are analytically investigated. Cnoidal modes, solitons and compactons, as traveling non-axially symmetric shapes are discussed. A finite-difference differential generalized Korteweg-de Vries equation is shown to describe the three-dimensional motion of the fluid surface and the limit of long and shallow channels one re-obtains the well-known KdV equation. A tentative expansion formula for the representation of the general solution of a nonlinear equation, for given initial condition is introduced on a graphical-algebraic basis. The model is useful in multilayer fluid dynamics, cluster formation, and nuclear …

Wavelets And Quantum Algebras, Andrei Ludu

Andrei Ludu

No abstract provided.

Diffusion Of Low Molecular Mass Substances In Glassy Polymers, Sergey Sobolev

Sergey Sobolev

No abstract provided.

Mass Transfer With Chemical Reaction In The Process Of Ammonia Desorption From Aqueous Solutions Containing Carbon Dioxide, Wojciech M. Budzianowski

Wojciech Budzianowski

No abstract provided.

Local Structural Heterogeneities In Liquid Water Under Pressure, M. Canpolat, Francis W. Starr, M. R.S. Lahijany, A. Scala, O. Mishima, S. Havlin, H. E. Stanley

Francis Starr

No abstract provided.

Cell Size Dependence Of Transport Coefficients In Stochastic Particle Algorithms, Alejandro Garcia, F. Alexander, B. Alder

Faculty Publications

Using the Green–Kubo theory, the dependence of the viscosity and thermal conductivity on cell size is obtained explicitly for stochastic particle methods such as direct simulation Monte Carlo (DSMC) and its generalization, the consistent Boltzmann algorithm (CBA). These analytical results confirm empirical observations that significant errors occur when the cell dimensions are larger than a mean free path.

High-Resolution Image Reconstruction From A Sequence Of Rotated And Translated Frames And Its Application To An Infrared Imaging System, Russell C. Hardie, Kenneth J. Barnard, John G. Bognar, Ernest E. Armstrong, Edward A. Watson

Electrical and Computer Engineering Faculty Publications

Some imaging systems employ detector arrays that are not sufficiently dense to meet the Nyquist criterion during image acquisition. This is particularly true for many staring infrared imagers. Thus, the full resolution afforded by the optics is not being realized in such a system. This paper presents a technique for estimating a high-resolution image, with reduced aliasing, from a sequence of undersampled rotated and translationally shifted frames. Such an image sequence can be obtained if an imager is mounted on a moving platform, such as an aircraft. Several approaches to this type of problem have been proposed in the literature. …