Digital Commons Network^™

Comparison Of Magnetic Properties Of Polysaccharide Iron Complex (P.I.C.) And Ferritin, M. E. Y. Mohie-Eldin, Richard B. Frankel, L. Gunther

Physics

The synthetic polysaccharide iron complex (PIC) molecule has been suggested as a ‘biomimic’, i.e. a counterpart, to the naturally occurring biological molecule ferritin with respect to its magnetic properties based on the identification of ferrihydrite as the major mineral in both. Magnetization measurements were used to investigate the magnetic properties of PIC in relation to those of ferritin, as well as to identify differences in such properties between naturally occurring ferritin, which we designate here as Ferritin I, and ferritin with an artificially high content of Fe²⁺ ions bound to its core, which is designated here as Ferritin II. …

Emitted Current Instability From Silicon Field Emission Emitters Due To Sputtering By Residual Gas Ions, W.I. Karain, Larry V. Knight, David D. Allred, A. Reyes-Mena

Faculty Publications

We have fabricated arrays of silicon field emitters using semiconductor lithography techniques. The density of the tips was 10^5/cm^2. The maximum current that can be extracted from each emitter is limited by resistive heating. We have investigated how the electron current emitted changes under constant applied voltage. We found that the current is very sensitive to the vacuum conditions. We attribute this to sputtering of the emitters due to ionized residual gas molecules. The poorer the vacuum, the higher the instability in the current. We studied this phenomenon at 10^6 and 10-x Torr. The model of two concentric spherical shells …

Raman Spectroscopic Study Of The Formation Of T-Mosi2 From Mo/Si Multilayers, Ming Cai, David D. Allred, A. Reyes-Mena

Faculty Publications

We have used Raman spectroscopy, large- and small-angle x-ray diffraction spectroscopy of sputter-deposited, vacuum-annealed, soft x-ray Mo/Si thin-film multilayers to study the physics of silicide formation. Two sets of multilayer samples with d-spacing 8.4 and 2.0 nm have been studied. Annealing at temperatures above 800 °C causes a gradual formation of amorphous MoSi2 interfaces between the Si and Mo layers. The transition from amorphous to crystalline MoSi2 is abrupt. The experimental results indicate that nucleation is the dominant process for the early stage and crystallization is the dominant process after nucleation is well advanced. In the thicker multilayer, a portion …

A Magnetic, Neutron Diffraction, And Mössbauer Spectral Study Of Nd₂Fe₁₅Ga₂ And The Tb₂Fe₁₇₋ₓgaₓ Solid Solutions, Zhong Bo Hu, William B. Yelon, Sanjay R. Mishra, Gary J. Long, Oran Allan Pringle, D. P. Middleton, K. H. J. Buschow, Fernande Grandjean

Physics Faculty Research & Creative Works

An x-ray diffraction study of the substitution of gallium in Tb ₂Fe₁₇ to form the Tb₂Fe_17-xGa_x solid solutions indicates that the compounds adopt the rhombohedral Th₂Zn₁₇ structure. The unit cell volume and the a-axis lattice parameter increase linearly with increasing gallium content. The c-axis lattice parameter increases linearly from x=0 to 6 and then decreases between x=7 and 8. Magnetic studies show the Curie temperature increases by ~150° above that of Tb₂Fe₁₇ to reach a maximum between x=3 and 4, and then decreases with further increases in …

Strong Magnetic Field Effects And Molecular Processes With Applications To White Dwarfs, Phillip C. Stancil

Physics Theses & Dissertations

Radiative transitions of hydrogenlike atoms in external magnetic fields of strength applicable to magnetic white dwarfs, i.e. B < 10³ megagauss, have been investigated for field-free principal quantum numbers n < 6. Finite proton mass corrections are included. Relativistic corrections are also investigated. Transition probabilities are determined using the length, velocity, and acceleration forms of the electric dipole operator. Discrepancies between previous calculations and magnetic white dwarf observations of low-lying boundbound transitions have been studied. New results for high-lying transitions are also obtained.

The transition probability for the hydrogenlike 2s two-photon decay has been investigated and shown to increase substantially with field strength. The computed two-photon spectra show resonances and interference minima. Anomalous Zeeman depolarization features are found in computed two-photon polarization spectra of alkali atoms in laboratory strength magnetic fields. A previously observed fine structure depolarization feature is shown to decay with decreasing field strength.

Investigation Of Computational And Spectral Analysis Methods For Aeroacoustic Wave Propagation, Florence Odile Vanel

Mechanical & Aerospace Engineering Theses & Dissertations

Most computational fluid dynamics (CFD) schemes are not adequately accurate for solving aeroacoustics problems, which have wave amplitudes several orders of magnitude smaller yet with frequencies larger than the flow field variations generating the sound. Hence, a computational aeroacoustics (CAA) algorithm should have minimal dispersion and dissipation features. A dispersion relation preserving (DRP) scheme is, therefore, applied to solve the linearized Euler equations in order to simulate the propagation of three types of waves, namely: acoustic, vorticity, and entropy waves. The scheme is derived using an optimization procedure to ensure that the numerical derivatives preserve the wave number and angular …

Projectile And Electron Spectra Resulting From Positron-Argon Collisions, R. A. Sparrow, Ronald E. Olson

Physics Faculty Research & Creative Works

A three-body classical trajectory Monte-Carlo calculation is used to evaluate the differential cross sections for the ejected electron, as well as the projectile scattering for 50, 100 and 150 eV e++Ar0 electron removal collisions. In the ionized eleciron spectra both the electron capture to the continuum (ecc) and binary peak structures are observed. The theoretical ecc peak is diffuse and shifted to lower energies than expected from simple arguments. The calculated double differential cross sections for electron ejection have been compared to experiment, When the experimental apparatus function of Moxom et al is used to convolute the theoretical spectra, good …

Experimental Stark Shift Of Several Nii And Oii Spectral Lines, Mara Scepanovic, Vladimir Milosavljevic, Stevan Djenize, Mihajlo Platisa, Jaroslav Labat

Articles

Stark shift of four NII and seven OII spectral lines have been measured for the first time in the linear low pressure pulsed arc plasma and compared with existing theoretical values.

Heavy Meson Radiative Decays And Light Vector Meson Dominance, Joseph Schechter, Pankaj Jain, Arshad Momen

Physics - All Scholarship

Electromagnetic interactions are introduced in the effective chiral Lagrangian for heavy mesons which includes light vector particles. A suitable notion of vector meson dominance is formulated. The constraints on the heavy meson -light vector and heavy meson-light pseudoscalar coupling constants are obtained using experimental D^* \ra D \, \gamma branching ratios. These constraints are compared with values estimated from semi-leptonic transition amplitudes as well as from extension of the light meson coupling pattern. Application to the heavy baryon spectrum in the ``bound state " model is made.

State-Selective Electron Capture In He²⁺-H2 Collisions, L. Meng, Ronald E. Olson, H. O. Folkerts, R. Hoekstra

Physics Faculty Research & Creative Works

A classical phase-space model of the hydrogen molecule which includes both electrons and nuclear centers is utilized to study state selective electron capture for collisions with alpha particles at intermediate impact energies (30-200 keV amu‑1), The calculations are performed within the framework of the classical trajectory Monte Carlo method. The direct one-electron transfer process and the transfer ionization reaction which becomes increasingly important at the higher impact energies are directly included in the cross section determinations. Photon emission spectroscopy experiments were conducted to obtain line emission cross sections for capture to the He+(np) states, n = 2-5, for energies from …

Light Cone Quantization Of Gauge Fields, Gary Mccartor, David G. Robertson

Physics Faculty Scholarship

Light-cone quantization of gauge field theory is considered. With a careful treatment of the relevant degrees of freedom and where they must be initialized, the results obtained in equal-time quantization are recovered, in particular the Mandelstam-Leibbrandt form of the gauge field propagator. Some aspects of the “discretized” light-cone quantization of gauge fields are discussed.

Photoconductivity And Grating Response Time Of A Photorefractive Polymer, Brian E. Jones, Stephen Ducharme, Martin M Liphardt, Arosha Goonesekera, James M. Takacs, Lei Zhang, Rajan Athalye

Stephen Ducharme Publications

We report the photoconductive properties and photorefractive grating response time of a polymer mixture composed of 40-wt. % dissolved diethylamino-benzaldehyde diphenyl hydrazone (DEH) and the non-cross-linking epoxy polymer Bisphenol A 4,4'-nitroaminostilbene. The films have improved photoconductive sensitivities as high as 2.1 × 10^–10 cm/(W Ω) at a wavelength of 650 nm with a corresponding reduction of the grating response time constant to 0.11 ± 0.02 s at an intensity of 1 W/cm². The nitro-aminostilbene chromophore is deduced to be the source of photogenerated charge carriers on the basis of a comparison of the wavelength dependence of the …

Observation Of A Metastable Defect Transition In Gaas, David C. Look, Z-Q. Fang, J. R. Sizelove

Physics Faculty Publications

We show that the well-known 0.15-eV donor in bulk GaAs quenches under IR-light illumination and that the quenched (metastable) state has an electronic transition energy about 0.14 eV deeper than the ground state and can be observed by temperature-dependent-resistivity and Hall-effect measurements. The quenched state thermally recovers by an Auger-like process at a rate of r=2.3×10^-12 nv_n exp(-0.18/kT). Many of the properties exhibited by this donor are similar to those predicted theoretically for the complex defect As_Ga-V_As.

A Protostellar Jet Model For The Water Masers In W49n, Mordecai-Mark Mac Low, Moshe Elitzur, James M. Stone, Arieh Königl

Physics and Astronomy Faculty Publications

Observations by Gwinn, Moran, & Reid of the proper motions of water masers in W49N show that they have 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. We propose that these observations can be interpreted in terms of a shell of shocked molecular gas that is driven by the expanding cocoon of a high-velocity protostellar jet. We present three-dimensional numerical simulations in support of this interpretation and argue that this source provides a unique oppurtunity for a detailed study of jet-driven cocoons.

Anisotropic Wormhole: Tunneling In Time And Space, Marco Cavaglia, Vittorio De Alfaro, Fernado De Felice

Physics Faculty Research & Creative Works

We discuss the structure of a gravitational Euclidean instanton obtained through coupling of gravity to electromagnetism. This Euclidean solution can be interpreted as a tunneling to a hyperbolic space (baby universe) or alternatively as a static wormhole that joins two asymptotically flat spaces of a Reissner-Nordström type solution.

Laser-Rf Double Resonance Measurements Of The Hyperfine Structure Of V Ii, Gregory Michael Matous

Masters Theses

We have measured the hyperfine structure of ⁵¹V II using the technique of collinear fast-ion-beam laser spectroscopy. The output of a dye laser was applied collinearly to an accelerated 50 ke V ion beam to produce laser induced fluorescence spectra for the metastable 3d³4s and 3d⁴ configurations. The technique of laserradio- frequency double resonance, which utilizes an optical photon to deplete a hyperfine state and an rf photon to repopulate the state, was used to measure the hyperfine intervals to a high precision. These measurements of the hyperfine intervals allowed the determination of the magnetic …

On The Linear Extrapolation To Low Doses, Robert Katz, Michael P. R. Waligórski

Robert Katz Publications

While radiobiological data are conveniently fitted by a linear quadratic formula to data of limited dynamic range at doses typically exceeding 1 Gy, they are extrapolated linearly to doses below a milligray for the evaluation of low dose RBEs. However a single relativistic electron passing through a cell nucleus deposits a “dose” there in the neighborhood of a milligray. The validity of the linear extrapolation then rests on the demonstration that a single electron transit through a cell nucleus can cause inactivation or mutation or can lead to cancer induction. The extrapolation made is a huge one, of some three …

The Excitation Mechanism Of Praseodymium-Doped Semiconductors, Paul L. Thee

Theses and Dissertations

This study on praseodymium Pr luminescence in Al_xGa_1-xAs was conducted to enhance the understanding of the excitation mechanism. Pr was implanted at 390 keV with doses from 5 x 10¹² to 5 x 10¹³ cm² into Al_xGa_1-xAs x0.0 to 0.50 wafers which were annealed using the rapid thermal annealing RTA method. Low temperature photoluminescence PL was conducted using an Ar-ion laser and Ge detector. PL emissions of Pr from all hosts include peaks near 1.3 and 1.6 µm which are assigned to the intra-4f transitions of 1G4 yielding 3H5 …

Spatio-Temporal Pattern Recognition Using Hidden Markov Models, Kenneth H. Fielding

Theses and Dissertations

A new spatio-temporal method for identifying 3D objects found in 2D image sequences is presented. The Hidden Markov Model technique is used as a spatio-temporal classification algorithm to identify 3D objects by the temporal changes in observed shape features. A new information theoretic argument is developed that proves identifying objects based on image sequences can lead to higher classification accuracies than single look methods. A new distance measure is proposed that analyzes the performance of Hidden Markov Models in a multi-class pattern recognition problem. A three class problem identifying moving light display objects provides experimental verification of the sequence processing …

A Diffraction-Based Model Of Anisoplanatism Effects In Adaptive Optic Systems, Steven E. Troxel

Theses and Dissertations

This dissertation presents a new model for computing the angle dependent performance measures of an adaptive-optics system. By incorporating diffraction caused by the index-of-refraction variations of the atmosphere, the phase and amplitude fluctuations of the propagating wave are computed. New theory is presented, that uses the diffraction-based propagation model to yield optical transfer function (OTF) expressions that are more accurate as compared to current theory that neglects diffraction. An evaluation method for calculating the OTF is presented that utilizes a layered atmospheric model and normalized OTF expressions. The diffraction model is also used to present the first OTF signal-to-noise ratio …

Low Temperature Performance Of Field Effect Transistors, Wei Zhu

Theses

The low temperature static characteristics of silicon junction field-effecttransistors (JFETs) have been investigated and analysed. The followingchanges were observed after cooling down the transistors: pinch-offvoltage and transconductance increases; and drain current is changedas a function of the drain-source voltage. It was found that there wasan increase in the amplifying properties and a reduction in noise voltageof cooled transistors. In addition, the temperature and voltage dependenceof leakage current have been studied. Temperatures below 77K are ofinterest in evaluating effects of impurity freezeout and temperatureabove 77K are important since actual device temperature will be aboutthe ambient. Operation of FET circuits at liquid …

Nmr Computer Simulation Of Glassy And Powdered Samples : Application To Studies Of Sodium Borovanadate Glasses, Xian-Quan Zhang

Theses

A computer program is devised to simulate the nuclear magnetic resonance (NMR) spectra observed in powdered and glassy samples in the presence of both nuclear quadrupole and anisotropic chemical shift interactions. This method is performed for the central transition of NMR spectra of nuclei with half-integral spin I. Typical theoretical behavior of the powder pattern is discussed and the "noise" and "error" in the simulated spectra are analyzed. The computer simulation method is applied to the studies of 11B NMR spectra of the sodium borovanadate glass system for which a structural model is presented in the range for which glasses …

Low-Temperatures Vortex Dynamics In Twinned Superconductors, M. Cristina Marchetti, Valerii M. Vinokur

Physics - All Scholarship

We discuss the low-temperature dynamics of magnetic flux lines in samples with a family of parallel twin planes. A current applied along the twin planes drives flux motion in the direction transverse to the planes and acts like an electric field applied to {\it one-dimensional} carriers in disordered semiconductors. As in flux arrays with columnar pins, there is a regime where the dynamics is dominated by superkink excitations that correspond to Mott variable range hopping (VRH) of carriers. In one dimension, however, rare events, such as large regions void of twin planes, can impede VRH and dominate transport in samples …

Scaling Behavior Of Fluctuations In Systems With Continuous Symmetry, Ulrich Zürcher

Physics Faculty Publications

In nematic liquid crystals, director fluctuations correpond to the dynamical mode that is critical for all temperatures in zero external fields. The Hurst exponent characterizes the temporal behavior of the mean square displacement of director fluctuations, 〈[δn(r,t)-δn(r,0)]2〉∼t2H. We find H=1/2 in finite fields and H=3/4 in zero field. This result differs from that of Zhang et al. [Phys. Rev. Lett. 70, 1834 (1993)] who find a Hurst exponent that varies continuously from H≃1 in zero field to H≃1/2 in moderate fields.

The Cataclysmic Variable Hx Pegasi = Pg 2337 + 123: Caught On The Rise To Maximum, F. A. Ringwald

Dartmouth Scholarship

A radial velocity study of the Hα emission line of the cataclysmic variable HX Peg = PG 2337 + 123 shows that its orbital period is 0.2008 ± 0.0005 d (4.82 h). Magnitudes from Harvard College Observatory archive plates suggest that it is either a dwarf nova or a VY Scl star. The quiescent spectrum shows KIλλ 7665, 7699 Å in absorption, consistent with the presence of an unusual subdwarf-K mass-losing star.

At the beginning of the second night of the run, O Iλ 7773 Å was in absorption. Near midnight, the continuum rose rapidly into maximum, …

Ac Response Of The Flux-Line Liquid In High-Tc Superconductors, Lee-Wen Chen, M. Cristina Marchetti

Physics - All Scholarship

We use a hydrodynamics theory to discuss the response of a viscous flux-line liquid to an ac perturbation applied at the surface of the sample. The theory incorporates viscoelastic effects and describes the crossover between liquid-like and solid-like response of the vortex array as the frequency of the perturbation increases. A large viscosity from flux-line interactions and entanglement leads to viscous screening of surface fields. As a result, two frequency-dependent length scales are needed to describe the penetration of an ac field. For large viscosities the imaginary part of the ac permeability can exihibit, in addition to the well-know peak …

Magnetic And Magneto-Optic Properties Of Sputtered Co/Ni Multilayers, Y. B. Zhang, P. He, John A. Woollam, J. X. Shen, Roger D. Kirby, David J. Sellmyer

Roger Kirby Publications

We have investigated the magnetic and magneto-optic properties of Co/Ni multilayers deposited on Ag and Au buffer layers. The samples with Au buffer layers show perpendicular magnetic anisotropy, but those with Ag buffer layers do not. The. structure and degree of crystalline alignment of the buffer layer are evidently crucial to development of perpendicular magnetic anisotropy. We also present the results of polar Kerr rotation measurements as a function of wavelength and layer thickness of the multilayers.

Magnetic And Magneto-Optical Properties Of Mn5(Ge1-XMX)3 Alloys With M=Sn, Pb, Y. Zhang, A.P. Runge, Z.S. Shan, David J. Sellmyer

David Sellmyer Publications

We report on the magnetic and magneto-optical properties of the intermetallic alloys Mn₅(Ge_1-xM_x)₃, where M=Sn, Pb. Generally, these alloys were ordered ferromagnetically at T≥300 K for x<0.3. The structure of Mn₅(Ge_1-xSn_x)₃ remains in the hexagonal Mn₅Si₃ (hP16) phase up to x=0.25 and then changes to Ni₂In (hP6) as x approaches 1. The magnetization and Curie temperature of these alloys is largest for small x and reach a minimum value near x=0.5. The room temperature Polar Kerr rotation, however, …

Electronic Structure And Curie Temperature Of Yfe12-XMoXNY Compounds, A.S. Fernando, J.P. Woods, Sitaram Jaswal, D. Welipitiya, B.M. Patterson, David J. Sellmyer

David Sellmyer Publications

The electronic structures of YFe_12-xMo_xN_y , where x=1.0, 2.0 and y=0, 0.7, have been studied with photoemission and spin-polarized calculations. The peak near the Fermi level in the energy distribution curves (EDC) becomes successively broader with larger Mo concentration. The features in the calculated density of state at 1.3 and 2.7 eV are not readily seen in the EDC, and this may be due to lifetime effects in these compounds. Finally, changes in Curie temperature (T_c) with the change of N or Mo concentration are compared with prediction of the …

Magnetic Properties Of Nd(Fe,Ti) 12 And Nd(Fe,Ti) 12NX Films Of Perpendicular Texture, D. Wang, David J. Sellmyer, I. Panagiotopoulos, D. Niarchos

David Sellmyer Publications

Nd(Fe,Ti)₁₂ and Nd(Fe,Ti)₁₂N_x films textured with c axis perpendicular to the film plane were synthesized by sputtering. For the Nd(Fe,Ti)₁₂ films a spin reorientation took place at about 170 K. For the Nd(Fe,Ti)₁₂N_x films, the anisotropy field is about 85 kOe at room temperature and 130 kOe at 5 K, corresponding to a coercivity of 2.7 and 12 kOe, respectively. Initial magnetization curves show a behavior characteristic of nucleation type of magnetization reversal mechanism. Attempts were made to fit the experimental data with Kronmüller's magnetization reversal model. The results suggest that nucleation …