Physical Sciences and Mathematics Commons^™

Novel Switching Phenomena In Ferroelectric Langmuir-Blodgett Films, A. Bune, Stephen Ducharme, V.M. Fridkin, L. Blinov, S. Palto, N. Petukhova, S. Yudin

Stephen Ducharme Publications

We have established ferroelectric switching and observed a novel conductance switching phenomenon in ferroelectric polymer films fabricated by the Langmuir–Blodgett technique. The films consist of 10–30 monolayers (ML) of a copolymer of vinylidene fluoride (70%) and trifluoroethylene (30%), exhibiting a first-order ferroelectric phase transition at 70 °C and nearly rectangular ferroelectric and conductance hysteresis at 24 °C. Ferroelectric switching is accompanied by switching of the conductance by three orders of magnitude. A model describing this switching phenomenon is proposed.

Measured Stark Widths Of A 425,94 Nm Ari Spectral Line, Ljiljana Skuljan, Vladimir Milosavljevic, Aleksandar Sreckovic, Stevan Djenize

Articles

No abstract provided.

Locally Optimally Emitting Clouds And The Origin Of Quasar Emission Lines, Jack Baldwin, Gary J. Ferland, Kirk Korista, Dima Verner

Physics and Astronomy Faculty Publications

The similarity of quasar line spectra has been taken as an indication that the emission line clouds have preferred parameters, suggesting that the environment is subject to a fine-tuning process. We show here that the observed spectrum is a natural consequence of powerful selection effects. We computed a large grid of photoionization models covering the widest possible range of cloud gas density and distance from the central continuum source. For each line only a narrow range of density and distance from the continuum source results in maximum reprocessing efficiency, corresponding to "locally optimally emitting clouds" (LOCs). These parameters depend on …

Singular Vertices And The Triangulation Space Of The D-Sphere, Simon Catterall, G. Thorleifsson, John B. Kogut, R. Renken

Physics - All Scholarship

By a sequence of numerical experiments we demonstrate that generic triangulations of the D-sphere for D>3 contain one {\it singular} (D-3)-simplex. The mean number of elementary D-simplices sharing this simplex increases with the volume of the triangulation according to a simple power law. The lower dimension subsimplices associated with this (D-3)-simplex also show a singular behaviour. Possible consequences for the DT model of four-dimensional quantum gravity are discussed.

Broad Ne Viii Λ744 Emission From The Quasar Pg 1148+549, Fred Hamann, Joseph C. Shields, Gary J. Ferland, Kirk T. Korista

Physics and Astronomy Faculty Publications

We discuss the probable detection of broad Ne VIII λ774 emission from the z_ɛ = 0.978 quasar PG 1148+549, and we use spectral synthesis calculations to study the physical conditions in the line-forming gas. The theoretical predictions and the measured line wavelength both support Ne VIII λ774 as the most likely identification.

Our calculations show that Ne VIII λ774 forms in hotter and more highly ionized gas than previously recognized in the broad emission line region. If the gas is photoionized by a standard active galactic nucleus continuum, the observed Ne VIII equivalent width, the Ne VIII/O VI flux …

The Anomalous Mössbauer Fraction Of Ferritin And Polysaccharide Iron Complex (Pic), M. E. Y. Mohie-Eldin, Richard B. Frankel, L. Gunther, G. C. Papaefthymiou

Physics

Mössbauer studies of the ubiquitous protein molecule ferritin and its synthetic "biomimic" polysaccharide iron complex (PIC) exhibit an anomaly in the Mössbauer spectrum wherein the recoil free fraction f-factor has a sharp drop with respect to temperature as the temperature rises above 30 K for mammalian ferritin and 60 K for PIC. The anomaly coincides with the disappearance of hyperfine splitting, which is due to superparamagnetic relaxation above the blocking temperature. Different absorbers were used to experimentally investigate the effect of absorber thickness on the Mössbauer spectrum. The anomaly persists for thin absorbers. Also, spectra treated with FFT procedures …

Local Magnetic Properties Of Antiferromagnetic Febr2, J. Peloth, R. A. Brand, Takele Seda, M. M. Pereira De Azevedo, W. Kleeman, Ch. Binek, J. Kushauer, D. Bertrand

Physics & Astronomy

The antiferromagnet FeBr₂ has been studied by Mössbauer spectroscopy in external fields both in the metamagnetic region below the multicritical temperature T_MCP and in the second-order transition region above. The local magnetization shows that the metamagnetic transition occurs by spin flips, as in simple models. However, in the second-order transition region, the local magnetization of the sublattice oriented antiparallel to the external field varies continuously but remains parallel to the c axis. This can only be understood if the external magnetic field induces strong transversal spin precession of the moments on the antiparallel sublattice. This shows that the …

Effect Of Disorder On Synchronization In Prototype 2-Dimensional Josephson Arrays, Adam S. Landsberg, Yuri Braiman, Kurt Wiesenfeld

WM Keck Science Faculty Papers

We study the effects of quenched disorder on the dynamics of two-dimensional arrays of overdamped Josephson junctions. Disorder in both the junction critical currents and resistances is considered. Analytical results for small arrays are used to identify a physical mechanism which promotes frequency locking across each row of the array, and to show that no such locking mechanism exists between rows. The intrarow locking mechanism is surprisingly strong, so that a row can tolerate large amounts of disorder before frequency locking is destroyed.

Methods For Generating Quasi-Exactly Solvable Potentials, Asim Gangopadhyaya, Avinash Khare, Uday P. Sukhatme

Physics: Faculty Publications and Other Works

We describe three different methods for generating quasi-exactly solvable potentials, for which a finite number of eigenstates are analytically known. The three methods are respectively based on (i) a polynomial ansatz for wave functions; (ii) point canonical transformations; (iii) supersymmetric quantum mechanics. The methods are rather general and give considerably richer results than those available in the current literature.

Local Magnetic Properties Of Antiferromagnetic Febr2, J. Pelloth, R.A. Brand, S. Takele, M.M. Pereira De Azevedo, Wolfman Kleemann, Christian Binek, J. Kushauer, D. Bertrand

Christian Binek Publications

The antiferromagnet FeBr₂ has been studied by Mössbauer spectroscopy in external fields both in the metamagnetic region below the multicritical temperature T_MCP and in the second-order transition region above. The local magnetization shows that the metamagnetic transition occurs by spin flips, as in simple models. However, in the second-order transition region, the local magnetization of the sublattice oriented antiparallel to the external field varies continuously but remains parallel to the c axis. This can only be understood if the external magnetic field induces strong transversal spin precession of the moments on the antiparallel sublattice. This shows that the …

Failure Of The Optical Theorem For Gaussian-Beam Scattering By A Spherical Particle, James A. Lock, Joseph T. Hodges, Gérard Gouesbet

Physics Faculty Publications

It is shown that when an electromagnetic wave with some degree of amplitude rolloff in the transverse direction is scattered by a spherical particle, the optical theorem is not valid. For such shaped beams the extinction cross section may be written as an infinite series in powers of the reciprocal of the beam width. The imaginary part of the forward-scattering amplitude is shown to be the first term in this series. Two approximations to based on the dominance of diffraction in the forward direction for w(0) greater than or similar to a, where w(0) is the beam half-width and a …

Transitions Between Convective Patterns In Chemical Fronts, Y. Wu, D. A. Vasquez, Boyd F. Edwards, J. W. Wilder

All Physics Faculty Publications

We present a theory for the transition from nonaxisymmetric to axisymmetric convection in iodate-arsenous acid reaction fronts propagating in a vertical slab. The transition takes place away from the onset of convection, where a convectionless flat front becomes unstable to a nonaxisymmetric convective front. The transition is studied by numerically solving a reaction-diffusion equation coupled with nonlinear hydrodynamics in a two-dimensional slab.

Single Molecule Emission Characteristics In Near-Field Microscopy, Randy X. Bian, Robert C. Dunn, X. Sunney Xie, P.T. Leung

Physics Faculty Publications and Presentations

In near-field scanning optical microscopy (NSOM), the measured fluorescence lifetime of a single dye molecule can be shortened or lengthened, sensitively dependent on the relative position between the molecule and aluminum coated fiber tip. The modified lifetimes and other emission characteristics are simulated by solving Maxwell equations with the finite-difference time-domain (FDTD) method. The 2D computation reveals insight into the lifetime behaviors and provides guidance for nonperturbative spectroscopic measurements with NSOM. This new methodology is capable of predicting molecular emission properties in front of a metal/dielectric interface of arbitrary geometry.

Observation Of Beam-Induced Changes In The Polarization Of Balmer-Α Radiation Emitted Following Beam--Tilted-Foil Transmission, Wang Qi, David D. Allred, Larry V. Knight, Douglas L. Harper, Royal G. Albridge, Norman H. Tolk

Faculty Publications

Measurements of the circular polarization of Balmer-α radiation emitted by excited hydrogen atoms, following the transmission of (20-50)-keV protons through thin, tilted amorphous carbon foils, exhibit markedly unexpected behavior as a function of exposure of the foil to the proton beam. Specifically, the circular polarization changes from an initially well understood tilt-angle dependence to a behavior which, for low tilt angles, gives the opposite handedness of circular polarization from that predicted. In addition, the degree of alignment, indicated by the linear Stokes parameter M/I, is enhanced also as a function of dose. These changes in the tilt-angle dependence of the …

Upper-Tropospheric Aerosol Sampled During Project Fire Ifo Ii, Donald E. Hagen, Josef Podzimek, Max B. Trueblood

Physics Faculty Research & Creative Works

Aerosols can play a role in the cloud formation process through the heterogeneous nucleation mechanism, and in turn, once formed, cirrus clouds can impact the ambient aerosol through scavenging and other collection mechanisms. University of Missouri aerosol sampling facilities were employed on aircraft for in situ collection and characterization of the particulates near cirrus cloud level. Tandem differential mobility analyzer and impactor techniques were used to measure aerosol size distribution, hydration capability, and particle composition information. Evidence of aerosol layering was observed near the tropospause, and there was a tendency toward depletion of the ambient aerosol at both ends of …

Forming B1-XCX Semiconductor Devices By Chemical Vapor Deposition, Peter A. Dowben

Peter Dowben Publications

Active semiconductor devices including heterojunction diodes and thin film transistors are formed by PECVD deposition of a boron carbide thin film on an N-type substrate. The boron to carbon ratio of the deposited material is controlled so that the film has a suitable band gap energy. Boron carbides such as B_4.7C, B_7.2C and B₁₉C have suitable band gap energies between 0.8 and 1.7 eV. The stoichiometry of the film can be selected by varying the partial pressure of precursor gases, such as nido pentaborane and methane. The precursor gas or gases are energized, e.g., …

Simple Description Of Pion-Pion Scattering To 1 Gev, Joseph Schechter, Masayasu Harada, Francesco Sannino

Physics - All Scholarship

Motivated by the 1/Nc expansion, we present a simple model of pion-pion scattering as a sum of a `current-algebra' contact term and resonant pole exchanges. The model preserves crossing symmetry as well as unitarity up to 1.2 GeV. Key features include chiral dynamics, vector meson dominance, a broad low energy scalar (sigma) meson and a `Ramsauer-Townsend' mechanism for the understanding of the 980 MeV region. We discuss in detail the `regularization' (corresponding to rescattering effects) necessary to make all these nice features work.

Evidence For Crystal-Field Splitting In Surface-Atom Photoemission From Potassium, G. K. Wertheim, D. Mark Riffe

All Physics Faculty Publications

Photoemission spectra from the shallow 3p_3/2 core levels of the surface atoms of metallic potassium exhibit the effects of a small but measurable crystal-field splitting of ∼38 meV. It manifests itself mainly as an apparent angle-dependent modulation of the spin-orbit splitting. This phenomenon may, in general, interfere with accurate determinations of surface-atom core-level shifts.

The Geometry And Kinematics Of The Broad-Line Region In Ngc 5548 From Hst And Iue Observations, Ignaz Wanders, Mike R. Goad, Kirk T. Korista, Bradley M. Peterson, Keith Horne, Gary J. Ferland, Anuradha P. Koratkar, Richard W. Pogge, Joseph C. Sheilds

Physics and Astronomy Faculty Publications

The spatial and radial velocity distribution of broad-line-emitting gas in the Seyfert 1 galaxy NGC 5548 is examined through the process of reverberation mapping, which is done by detailed comparison of continuum and emission-line variations. Recent spectroscopic monitoring of NGC 5548 with HST and IUE allows us to resolve the "transfer function" (TF) that relates the continuum and emission-line variability. We also examine the radial velocity-resolved TFs, and confirm that predominantly radial motions of the line-emitting clouds can be excluded. We find that a broad-line region comprised of clouds that are orbiting a central source of mass ~10⁸ M …

Tailoring Of The Magnetic Properties Of Smco5:Nb0.33Cr0.67 Nanocomposites Using Mechanical Alloying, Richard L. Schalek, Diandra Leslie-Pelecky, John Knight, David J. Sellmyer, Steven C. Axtell

David Sellmyer Publications

Nanocomposite structures composed of ferromagnetic particles dispersed in a matrix are systems in which the magnetic properties can be tailored by varying the size and spacing of the ferromagnetic particles. Nanocomposites of SmCo₅ in a non-magnetic Nb_0.33Cr_0.67 matrix exhibit a wide variety of magnetic properties. SmCo₅ powder is premilled prior to mechanical alloying. The premilliing results in a maximum coercivity of 16 kOe after 2 hours of milling, and an enhanced remanence ratio. Both features may be due to exchange anisotropy and/or exchange coupling between hard and soft ferromagnetic phases. The nanocomposite samples show that, …

Magnetic Switching Volumes Of Cosm Thin Films For High Density Longitudinal Recording, E.W. Singleton, Z.S. Shan, Y.S. Jeong, David J. Sellmyer

David Sellmyer Publications

For a high density recording media, the magnetic switching volume is of great importance when considering media noise and thermal stability. CoSm//Cr films have been prepad and the influence of the Cr underlayer thickness and of the magnetic layer preparation conditions on the magnetic switching volume have been investigated through magnetic viscosity and remnance curve measurements. The measured switching volumes ranged from 3.0 to 15.2x10^-18 cm³, and implications regarding noise and thermal stability are discussed.

A Quasiparticle Trap Assisted Transition Edge Sensor For Phonon Mediated Particle Detection, K. D. Irwin, S. W. Nam, Blas Cabrera, B. Chugg, Betty A. Young

Physics

ABSTRACT We have demonstrated the operation of composite superconducting tungsten and aluminum transition‐edge sensors which take advantage of quasiparticle trapping and electrothermal feedback. We call these devices W/Al QETs (quasiparticle‐trap‐assisted electrothermal feedback transition‐edge sensors). The quasiparticle trapping mechanism makes it possible to instrument large surface areas without increasing sensor heat capacity, thus allowing larger absorbers and reducing phonon collection times. The sensor consists of a 30‐nm‐thick superconducting tungsten thin film with T_c∼80 mK deposited on a high‐purity silicon substrate. The W film is patterned into 200 parallel lines segments, each 2 μm wide and 800 μm long. Eight …

Analysis Of Ladar Range Resolution Enhancement By Sinusoidal Phase Modulation, Leonard T. Masters, Martin B. Mark, Bradley D. Duncan

Electro-Optics and Photonics Faculty Publications

The ability of a ladar system to resolve two or more separate returns from a combined echo is related to the effective correlation bandwidth of the pulse emitted by the ladar system. Phase modulation of an outgoing pulse introduces additional frequency components, which increases the effective correlation bandwidth of the pulse and thus improves the range resolution of the system. In this paper, we discuss the general theoretical basis for achieving improved range resolution using a modulated waveform and a matched filter receiver. We then demonstrate these concepts by considering the particular case of improved range resolution for a sinusoidally …

Spin Polarization Of The Conduction Bands Of Gd(0001)*, Dongqi Li, J. Pearson, S.D. Bader, D. N. Mcilroy, C. Waldfried, Peter A. Dowben

Peter Dowben Publications

Angle- and spin-resolved photoemission was utilized to investigate the 5d bulk bands and the surface state of Gd(0001) in the temperature range of 130 - 350 K. The bulk bands at 1-2 eV below the Fermi energy E_F show Stoner-like behavior, while the temperature dependence of the surface state near E_F indicates spin-mixing behavior due to fluctuating local 5d moments. The secondary electron spectra of the Gd surfaces both before and after initial oxygen adsorption show a polarization dip at low kinetic energies due to the extra scattering channel for minority electrons via the unoccupied 4ƒ level. The …

Magnetic Properties And Structure Of Fe/Pt Thin Films, C.P. Luo, David J. Sellmyer

David Sellmyer Publications

The structural transfqmation from fcc to fct and relevant magnetic properties of initially multilayered Fe/Pt films were studied. When the as-deposited FePt films were annealed at the temperature of 300°C and up, the fct-phase was formed. Rather square hysteresis loops and large coercivities were measured from the annealed films. The films annealed at 300°C retain a layered structure.

High Resolution Electron Microscopy And Nano-Probe Study Of Cosm/Cr Films, Yi Liu, David J. Sellmyer, B. W. Robertson, Z.S. Shan, Sy_Hwang Liou

Sy-Hwang Liou Publications

The crystal structure of the crystallites in CoSm thin films deposited on Cr underlayer was studied by nanodiffraction and high resolution electron microscopy (HREM). It was found that the crystallites have a closed-packed structure. Some nanodiffraction patterns taken from different crystallites using a two nanometer probe can be indexed by two layer stacking AB (HCP structure), three layer stacking ABC (FCC structure), and four layer stacking ABAC (double hexagonal structure), suggesting that a particular local stacking mode could exist. [112^-0] HREM images confirmed that stacking sequence changes within one crystallite. In local regions, random stacking, and unit cells …

Image Restoration Of Dispersion-Degraded Images From A Liquid-Crystal Beam Steerer, Ronald J. Broessel, Vince Dominic, Russell C. Hardie

Electrical and Computer Engineering Faculty Publications

Liquid-crystal arrays represents one of the first practical technologies capable of steering light by electronic control only. We use such a device to steer the field of view of a broadband imaging sensor. Unfortunately, dispersion degrades the image quality by smearing out details in the image and by introducing multiple diffraction orders (echoes) at the detector plane. We present a method to compensate for these unwanted effects and thus restore the broadband images obtained with the beam steerer. We use the beam-propagation method to find the wavelength-dependent impulse response, from which we determine the appropriate Wiener filter. When training data …

Aliasing Reduction In Staring Infrared Imagers Utilizing Subpixel Techniques, Joseph C. Gillette, Thomas M. Stadtmiller, Russell C. Hardie

Electrical and Computer Engineering Faculty Publications

We introduce and analyze techniques for the reduction of aliased signal energy in a staring infrared imaging system. A standard staring system uses a fixed two-dimensional detector array that corresponds to a fixed spatial sampling frequency determined by the detector pitch or spacing. Aliasing will occur when sampling a scene containing spatial frequencies exceeding half the sampling frequency. This aliasing can significantly degrade the image quality. The aliasing reduction schemes presented here, referred to as microscanning, exploit subpixel shifts between time frames of an image sequence. These multiple images are used to reconstruct a single frame with reduced aliasing. If …

Magnetic And Magneto-Optical Properties Of MnXCubi ( X =0.75 - 3.5 ) Films, Jian Chen, K. Wierman, Roger D. Kirby, David J. Sellmyer

Department of Physics and Astronomy: Faculty Publications

Magnetic and magneto-optical properties of Mn_xCuBi ( x = 0.75 - 3.5) thin films are presented. With increasing Mn concentration x, the perpendicular anisotropy constant (K_u the remanence squareness (S = M_r/M_s) and the coercivity (H_c)the perpendicular hysteresis loop increase. Remanence squareness as high as 0.95 has been obtained. Kerr rotation (θ_k) and ellipticity (η_k) spectra from all samples measured from substrate side are similar, with θ_k exhibiting a broad peak in the blue wavelength region with maximum Kerr rotation up to 0.7 degrees.

Magnetic And Magneto-Optical Properties Of MnXCubi ( X =0.75 - 3.5 ) Films†, Jian Chen, K. Wierman, Roger D. Kirby, David J. Sellmyer

Department of Physics and Astronomy: Faculty Publications

Abstract - Magnetic and magneto-optical properties of Mn_xCuBi ( x = 0.75 - 3.5) thin films are presented. With increasing Mn concentration x, the perpendicular anisotropy constant (K_u), the remanence squareness (S = M_r/M_s) and the coercivity (H_c ), of the perpendicular hysteresis loop increase. Remanence squareness as high as 0.95 has been obtained. Kerr rotation (Ө_k) and ellipticity (η_k) spectra from all samples measured from substrate side are similar, with Ө_k exhibiting a broad peak in the blue wavelength region with maximum Kerr rotation up …