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Articles 1 - 16 of 16
Full-Text Articles in Physical Sciences and Mathematics
Quantum Entanglement Of Anisotropic Magnetic Nanodots, Ralph Skomski, Andrei Y. Istomin, Anthony F. Starace, David J. Sellmyer
Quantum Entanglement Of Anisotropic Magnetic Nanodots, Ralph Skomski, Andrei Y. Istomin, Anthony F. Starace, David J. Sellmyer
Department of Physics and Astronomy: Faculty Publications
Anisotropic magnetic nanodots are promising physical realizations of qubits for quantum computing at finite temperature owing to their well-separated low-lying energy levels and scalability. The entanglement of two interacting magnetic nanodots is investigated and shown both analytically and numerically to be resonantly dependent on their interaction strength and on differences in their properties. These results provide criteria for fabricating and coupling magnetic nanodots so that their low-lying eigenstates can be significantly entangled.
The Spectra Of Type Ii Cepheids. Iii. The Hα Line And Helium Emission In Long-Period Stars, Edward G. Schmidt, Dale Johnston, Kevin M. Lee, Shawn Langan, Peter R. Newman, Stephanie A. Snedden
The Spectra Of Type Ii Cepheids. Iii. The Hα Line And Helium Emission In Long-Period Stars, Edward G. Schmidt, Dale Johnston, Kevin M. Lee, Shawn Langan, Peter R. Newman, Stephanie A. Snedden
Department of Physics and Astronomy: Faculty Publications
We have obtained Hα profiles from 175 spectra of 37 Cepheids with periods longer than 8 days. About two-thirds of the stars are likely type II Cepheids. In contrast to the situation among short-period stars, the velocity of Hα relative to the metal-line spectrum is not a useful parameter for distinguishing type I and type II Cepheids. On the other hand, at periods longer than 11 days and shorter than 34 days strong emission is observed in many stars and appears to be a good discriminator of type. On this basis we identify one probable type I Cepheid at a …
The Nuclear Reddening Curve For Active Galactic Nuclei And The Shape Of The Infrared To X-Ray Spectral Energy Distribution, C. Martin Gaskell, René W. Goosmann, Robert R. J. Antonucci, David H. Whysong
The Nuclear Reddening Curve For Active Galactic Nuclei And The Shape Of The Infrared To X-Ray Spectral Energy Distribution, C. Martin Gaskell, René W. Goosmann, Robert R. J. Antonucci, David H. Whysong
Department of Physics and Astronomy: Faculty Publications
We present extinction curves derived from the broad emission lines and continua of samples of 72 radio-loud and 1018 radio-quiet active galactic nuclei (AGNs). The curves are significantly flatter in the UV than curves for the local interstellar medium. The reddening curves for the radio-quiet Large Bright Quasar Survey quasars are slightly steeper than those of the radio-loud quasars in the UV, probably because of additional reddening by dust farther out in the host galaxies of the former. The UV extinction curves for the radio-loud AGNs are very flat. This is explicable with slight modifications to standard Mathis-Rumpl-Nordsieck dust models: …
Surface Structure Of Ultrathin Copolymer Films Of Ferroelectric Vinylidene Fluoride (70%) With Trifluoroethylene (30%) On Graphite, Lei Cai, Hongwei Qu, Chenxi Lu, Stephen Ducharme, Peter A. Dowben, Jiandi Zhang
Surface Structure Of Ultrathin Copolymer Films Of Ferroelectric Vinylidene Fluoride (70%) With Trifluoroethylene (30%) On Graphite, Lei Cai, Hongwei Qu, Chenxi Lu, Stephen Ducharme, Peter A. Dowben, Jiandi Zhang
Department of Physics and Astronomy: Faculty Publications
The structure and local structural distortions, through the polarization manipulation, of crystalline films of ferroelectric vinylidene fluoride (70%) with trifluoroethylene (30%) [P(VDF-TrFE)] copolymer on graphite were studied by scanning tunneling microscopy (STM). A quasispiral twist in C[Single Bond]C bonds with rotations about the polymer chain axis was observed by high-resolution STM, indicating a surface relaxation of the strained copolymer films. Such a relaxation behavior appears to be linked to the observed local dipole rotations accompanied by the reversal of the local polarization with biasing the STM tip. A structure model is proposed based upon the observations
Photometry Of Type Ii Cepheids. I. The Long-Period Stars, Edward G. Schmidt, Dale Johnston, Shawn Langan, Kevin M. Lee
Photometry Of Type Ii Cepheids. I. The Long-Period Stars, Edward G. Schmidt, Dale Johnston, Shawn Langan, Kevin M. Lee
Department of Physics and Astronomy: Faculty Publications
We present 1256 new photometric observations of 36 Cepheids with periods longer than 8 days. The majority are likely type II Cepheids, but we have included about a dozen classical Cepheids for comparison purposes, a few stars of uncertain type, and one putative RV Tauri star. We discuss the appearance of the light curves, the Fourier parameters, and the light-curve stability in terms of differentiation between type I and type II Cepheids. Although we encounter the same difficulties as previous investigators in using these parameters for this purpose, we are able to identify some stars of particular interest, including several …
Lognormal X-Ray Flux Variations In An Extreme Narrow-Line Seyfert 1 Galaxy, C. Martin Gaskell
Lognormal X-Ray Flux Variations In An Extreme Narrow-Line Seyfert 1 Galaxy, C. Martin Gaskell
Department of Physics and Astronomy: Faculty Publications
We show that the large variations in the X-ray flux of the extreme narrow-line Seyfert 1 galaxy IRAS 13224– 3809, measured during a 10 day ASCA observation, have a two-parameter lognormal distribution of multiplicative standard deviation σmult = 2.7 and that the amplitude of variability at any given moment is proportional to the flux level. We find similar behavior in earlier ROSAT soft X-ray monitoring. There is no evidence of a nonvariable component. The flux-dependent behavior of the variability rules out linear shot-noise models. Although at first glance the variations of the ASCAlight curve for IRAS 13224–3809 appear …
Circular Dichroism At Equal Energy Sharing In Photo-Double-Ionization Of He, Andrei Y. Istomin, N. L. Manakov, A. V. Meremianin, Anthony F. Starace
Circular Dichroism At Equal Energy Sharing In Photo-Double-Ionization Of He, Andrei Y. Istomin, N. L. Manakov, A. V. Meremianin, Anthony F. Starace
Department of Physics and Astronomy: Faculty Publications
Interference between dipole and quadrupole transition amplitudes in photo-double-ionization of He by an elliptically polarized vuv photon is shown to induce circular dichroism in the case of equal energy sharing. The magnitude of this retardation-induced dichroic effect is estimated and its impact on the nondipole asymmetries of the triply differential cross section is demonstrated.
Optical Variability Of Narrow-Line Seyfert 1 Galaxies, Elizabeth S. Klimek, C. Martin Gaskell, Cecilia H. Hedrick
Optical Variability Of Narrow-Line Seyfert 1 Galaxies, Elizabeth S. Klimek, C. Martin Gaskell, Cecilia H. Hedrick
Department of Physics and Astronomy: Faculty Publications
We present results of a broadband photometric study of the optical variability of six narrow-line Seyfert 1 (NLS1) galaxies observed at 172 epochs. We searched for microvariability on 33 nights. Strong evidence for microvariability was found only for our lowest luminosity object, NGC 4051, on one night. Weaker evidence suggests such variability on a few other nights for two other objects, but the data are not as convincing. Intranight variability in NLS1’s is thus concluded to be rare and of low amplitude. We give illustrations of how variable image quality can produce spurious variability. We find that for well-studied non-NLS1’s …
Focused Ion Beam Milled Copt Magnetic Force Microscopy Tips For High Resolution Domain Images, L. Gao, Lanping Yue, T. Yokota, Ralph Skomski, Sy-Hwang Liou, H. Takahoshi, Hitoshi Saito, S. Ishio
Focused Ion Beam Milled Copt Magnetic Force Microscopy Tips For High Resolution Domain Images, L. Gao, Lanping Yue, T. Yokota, Ralph Skomski, Sy-Hwang Liou, H. Takahoshi, Hitoshi Saito, S. Ishio
Department of Physics and Astronomy: Faculty Publications
Abstract—High-coercivity CoPt magnetic force microscope tips have been modified by focused ion beam milling to improve the resolution of magnetic domain images. The magnetic materials around the apex have been removed, leaving a 30-nm diameter magnetic particle at the tip end. Due to the smaller amount of magnetic material, the stray field from this new tip is significantly reduced, and the spatial resolution of the magnetic domain images is improved. The tip is used to obtain high-resolution domain images of a CoCrPt-SiO2/Ru perpendicular recording medium with linear recording densities from 800 to 1000 kfci. Magnetic patterns of 900 kfci, corresponding …
Hysteresis Of Granular Fept:Ag Films With Perpendicular Anisotropy, M. L. Yan, Ralph Skomski, Arti Kashyap, L. Gao, Sy-Hwang Liou, David J. Sellmyer
Hysteresis Of Granular Fept:Ag Films With Perpendicular Anisotropy, M. L. Yan, Ralph Skomski, Arti Kashyap, L. Gao, Sy-Hwang Liou, David J. Sellmyer
Department of Physics and Astronomy: Faculty Publications
Intergranular interactions in nanostructured FePt:Ag thin films and their effect on magnetic hysteresis are investigated. The films, produced by multilayer deposition plus rapid thermal annealing, consist of FePt nanoparticles embedded in a silver matrix. They are investigated by magnetization measurements and magnetic force microscopy. Analytical model calculations, supported by micromagnetic simulations, are used to elucidate the relation between coercivity, hysteresis-loop slope, and spatial correlations during magnetization reversal. The analytical calculations yield simple expressions for the loop slope and the coercivity as a function of the intergranular exchange. Small intergranular exchange enhances the coercivity, but for strong exchange there is a …
Simulations Of Ferroelectric Polymer Film Polarization: The Role Of Dipole Interactions, Chun-Gang Duan, Wai-Ning Mei, Wei-Guo Yin, Jianjun Liu, J. R. Hardy, Stephen Ducharme, Peter A. Dowben
Simulations Of Ferroelectric Polymer Film Polarization: The Role Of Dipole Interactions, Chun-Gang Duan, Wai-Ning Mei, Wei-Guo Yin, Jianjun Liu, J. R. Hardy, Stephen Ducharme, Peter A. Dowben
Department of Physics and Astronomy: Faculty Publications
We present a systematic study of the dipole alignment in the polyvinylidene fluoride (PVDF) films using first-principles total energy calculations. The ground state of a single layer film is a state with all the dipoles lying parallel to the film plane. This can also be explained by a dipole-dipole interaction model. The induced mirror charges on conducting substrates or substrates with a non-negligible dielectric response play an important role in aligning the polarization perpendicular to the film. From fitting the ab initio calculations, we obtain an effective monomer dipole moment of 4.7×10–30 C m. This corresponds to a spontaneous …
Kapitza-Dirac Diffraction Without Standing Waves: Diffraction Without A Grating?, Olga Smirnova, Daniel L. Freimund, Herman Batelaan, Misha Ivanov
Kapitza-Dirac Diffraction Without Standing Waves: Diffraction Without A Grating?, Olga Smirnova, Daniel L. Freimund, Herman Batelaan, Misha Ivanov
Department of Physics and Astronomy: Faculty Publications
We discuss electron diffraction from two counterpropagating light waves with two different frequencies.We show that, even though these waves do not form a standing wave, electron diffraction similar to the conventional Kapitza-Dirac effect, i.e., scattering on a standing wave, is still possible. The nonlinear response of the electron to the laser fields creates a stationary diffraction grating from which the same electron scatters.
Low-Pressure Source Of Slow Metastable Rare Gas Atoms, M. H.L. Van Der Velden, Herman Batelaan, E. Te Sligte, H. C.W. Beijerinck, E. J.D. Vredenbregt
Low-Pressure Source Of Slow Metastable Rare Gas Atoms, M. H.L. Van Der Velden, Herman Batelaan, E. Te Sligte, H. C.W. Beijerinck, E. J.D. Vredenbregt
Department of Physics and Astronomy: Faculty Publications
We investigate the properties of a commercial inverted magnetron pressure gauge for use as a source of slow metastable rare gas atoms. We find that the velocity distribution of the atoms as well as the pressure dependence of the output flux agree with a simple model. This shows that the low-velocity output of the source is enhanced over the Maxwell–Boltzmann form due to a velocity-dependent excitation probability. For argon, the center-line intensity per unit area of the source is measured to be greater than 4.2x1015 Ar 1s5 atoms/(s srm2) at a pressure of 23 mPa. …
Perturbative Analysis Of The Triply Differential Cross Section And Circular Dichroism In Photo-Double-Ionization Of He, Andrei Y. Istomin, N. L. Manakov, Anthony F. Starace
Perturbative Analysis Of The Triply Differential Cross Section And Circular Dichroism In Photo-Double-Ionization Of He, Andrei Y. Istomin, N. L. Manakov, Anthony F. Starace
Department of Physics and Astronomy: Faculty Publications
We extend application of our lowest-order perturbative approach (in electron-electron correlation) for analysis of photo-double-ionization (PDI) of He [A.Y. Istomin et al., J. Phys. B 35, L543 (2002)] to excess energies up to 450 eV and to analysis of circular dichroism. We find that account of electron correlation in the final state to first order provides predictions for the triply differential cross section and circular dichroism that are in reasonable agreement with absolute data for excess energies up to 80 eV. For an excess energy of 450 eV, account of electron correlation in both initial and final states is necessary …
Nondipole Effects In Photo-Double-Ionization Of He By A Vuv Photon, Andrei Y. Istomin, N. L. Manakov, A. V. Meremianin, Anthony F. Starace
Nondipole Effects In Photo-Double-Ionization Of He By A Vuv Photon, Andrei Y. Istomin, N. L. Manakov, A. V. Meremianin, Anthony F. Starace
Department of Physics and Astronomy: Faculty Publications
We present a dynamical model-independent, ab initio parametrization of the quadrupole transition amplitude for photo-double-ionization of He. An asymmetry of the triple differential cross section induced by the nondipole corrections is discussed and shown to be significant even for an excess energy as low as 80 eV. We provide predictions for two different kinds of experiments in which nondipole effects should be observable with current experimental capabilities.
The Case For An Optically-Thick High-Velocity Broad-Line Region, Stephanie A. Snedden, C. Martin Gaskell
The Case For An Optically-Thick High-Velocity Broad-Line Region, Stephanie A. Snedden, C. Martin Gaskell
Department of Physics and Astronomy: Faculty Publications
A combined analysis of the profiles of the main broad quasar emission lines in both Hubble Space Telescope and optical spectra shows that while the profiles of the strong UV lines are quite similar, there is frequently a strong increase in the Lyα/Hα ratio in the high-velocity gas. We show that the suggestion that the high velocity gas is optically-thin presents many problems. We show that the relative strengths of the high velocity wings arise naturally in an optically-thick BLR component. An optically-thick model successfully explains the equivalent widths of the lines, the Lyα/Hα ratios and flatter Balmer decrements in …