Digital Commons Network^™

Micromagnetic Localization, Ralph Skomski

Ralph Skomski Publications

The localization of nucleation modes in inhomogeneous ferromagnets and its influence on the coercivity are investigated. From the formal analogy between quantum mechanics and micromagnetics follows that anisotropy inhomogeneities may cause localization. The nucleation modes of one-dimensional arrays, such as multilayers composed of hard and soft magnetic materials, are localized even if the superlattice exhibits a nearly ideal periodicity. Gaussian distributions of the layer thicknesses lead to Urbach tails and very low coercivities, but a maximum thickness l_m of the soft layers suppresses the Urbach tails. The related problem of magnetic viscosity leads to a supersymmetric Fokker–Planck description where …

Pressure Ionization And Line Merging In Strongly Coupled Plasmas Produced By 100-Fs Laser Pulses, M. Nantel, G. Ma, S. Gu, C.Y. Côté, J. Itatani, Donald Umstadter

Donald Umstadter Publications

Time- and space-resolved extreme ultraviolet spectra of carbon plasmas, created with 100-fs laser pulses, are obtained with the novel technique of picosecond jitter-free streak-camera averaging. Spectroscopic diagnostics indicate electron densities and temperatures evolving from 10²³ to 10²¹ cm^-3 and 80 to 50 eV, respectively, implying less than one particle in a Debye sphere at early times. The emission reveals conditions of extreme pressure ionization and line merging. Comparisons of the experimental spectra with numerical simulations validate the use of the Inglis-Teller limit for line merging, and confirm that pressure ionization models based on the Debye-Huckel potential are …

Search For Inclusive B→Sl+L-, S. Glenn, Kenneth A. Bloom, Cleo Collaboration

Kenneth Bloom Publications

We have searched for the effective flavor changing neutral-current decays b→sl⁺l^- using an inclusive method. We set upper limits on the branching ratios B(b→ se⁺e^-) < 5.7 X 10^-5, B(b→ sμ⁺μ^-) < 5.8 X 10^-5 and Bb→se⁺μ^-) < 2.2 3 10^-5 [at 90% confidence level (C.L.)]. Combing the dielectron and dimuon decay modes we find b→sl⁺l^-) < 4.2 X 10^-5 (at 90% C.L.).

Orthogonal Polynomial Projectors For The Projector Augmented Wave Method Of Electronic Structure Calculations, N. A. W. Holzwarth, G. E. Matthews, A. R. Tackett, Rodney Dunning

Chemistry & Physics Faculty Publications

The projector augmented wave (PAW) method for electronic structure calculations developed by Blochl [Phys. Rev. B 50, 17 953 (1994)] has been very successfully used for density functional studies. It has the numerical advantages of pseudopotential techniques while retaining the physics of all-electron formalisms. We describe a method for generating the set of atom-centered projector and basis functions that are needed for the PAW method. This scheme chooses the shapes of the projector functions from a set of orthogonal polynomials multiplied by a localizing weight factor. Numerical benefits of the scheme result from having direct control of the …

Polydispersivity Of Non-Critical Field-Induced Fluctuations In Febr2, Christian Binek

Christian Binek Publications

The field and temperature dependence of the complex low-frequency susceptibility of the metamagnet FeBr2 exhibits large anomalies in the vicinity of the second-order phase boundary Hc(T). The low-frequency losses reflect polydispersive dynamics with a broad distribution of relaxation times peaking at τ ≈ 0.2 s. The dispersion, χ versus ƒ, is well described within Chamberlin's model of dynamically coupled domains. The heterogeneous glass-like response gives rise to the intuitive picture of a magnetic fluid of high viscosity.

Observation Of The Radiative Decay D*+→D+Γ, J. Bartelt, Kenneth A. Bloom, Cleo Collaboration

Kenneth Bloom Publications

We have observed a signal for the decay D^*+→D⁺γ at a significance of 4 standard deviations. From the measured branching ratio B(D^*+→D⁺γ)/ B(D^*+→ D⁺+pi⁰ = 0.055 ± 0.014 ± 0.010 we find B(D^*+→D⁺γ)= 0.017 ± 0.004 ± 0.003, where the first uncertainty is statistical and the second is systematic. We also report the highest precision determination of the remaining D^*+ branching fractions.

Known Source Detection Predictions For Higher Order Correlators, Lisa A. Pflug, George E. Ioup, Juliette W. Ioup

Physics Faculty Publications

The problem addressed in this paper is whether higher order correlation detectors can perform better in white noise than the cross correlation detector for the detection of a known transient source signal, if additional receiver information is included in the higher order correlations. While the cross correlation is the optimal linear detector for white noise, additional receiver information in the higher order correlations makes them nonlinear. In this paper, formulas that predict the performance of higher order correlation detectors of energy signals are derived for a known source signal. Given the first through fourth order signal moments and the noise …

Confocal Microscopy: A Powerful Tool For Biological Research, Amit Singh, K. P. Gopinathan

Biology Faculty Publications

Conventional light microscopy allows the observation of living as well as fixed cells and tissues to generate two-dimensional images. The out-of-focus information often obscures the ultrastructural details, especially in thick specimens with overlapping structures. The earliest available light microscopy visualized the objects in hydrated state in two-dimensions during their temporal development. The emergence of electron microscopy (EM) provided superb resolution of ultrastructural details, but it was applicable only for objects in the dehydrated state and thereby potentially introducing handling artifacts. The usefulness of optical methods, however, has been limited by the poor depth discrimination. Often, the fluorescence and reflectance images …

Particle Concentration Characterization For Jet Engine Emissions Under Cruise Conditions, Jonathan D. Paladino, Philip D. Whitefield, Donald E. Hagen, Alfred R. Hopkins, Max B. Trueblood

Chemistry Faculty Research & Creative Works

Airborne particle measurements during NASA project SUCCESS have shown that particle concentration profiles serve as good indicators of aircraft exhaust plume encounters. During exhaust plume penetrations there is a strong anticorrelation between the ratio of nonvolatile/total particulates and Nitrogen Oxide (NO) concentrations. an increase in fuel sulfur content was found to increase the total particle emission index, while the nonvolatile emission index remained unchanged. the EI's increased by a factor of 2.6 as the fuel sulfur increased from 70 - 700 ppm. the large particle size distribution (200-400 nm) was seen as a good long term indicator of an aircraft …

Measurement Of B(D0 → K-Π+) Using Partial Reconstruction Of B̅ → D*+Xℓ- Ν̅, M. Artuso, Kenneth A. Bloom, Cleo Collaboration

Kenneth Bloom Publications

We present a measurement of the absolute branching fraction for D⁰ → K^-π⁺ using the reconstruction of the decay chain B̅ → D*⁺Xℓ^- ν̅ where only the lepton and the low-momentum pion from the D*⁺ are detected. With data collected by the CLEO II detector at the Cornell Electron Storage Ring, we have determined Ɓ(D⁰ → K^-π⁺)= [3.81 ± 0.15(stat) ± 0.16(syst)]%.

Evidence For A Scalar Kappa(900) Resonance In Pi-K Scattering, Joseph Schechter, Deirdre Black, Amir H. Fariborz, Francesco Sannino

Physics - All Scholarship

Motivated by the 1/N_c\ expansion, we study a simple model in which the pi-K scattering amplitude is the sum of a current-algebra contact term and resonance pole exchanges. This phenomenological model is crossing symmetric and, when a putative light strange scalar meson, kappa, is included, satisfies the unitarity bounds to well above 1 GeV. The model also features chiral dynamics, vector meson dominance and appropriate interference between the established scalar K*(1430) resonance and its predicted background. We briefly discuss the physical significance of the results and directions for further work.

Dynamic And Chemical Aspects Of The Mesospheric Na ‘Wall’ Event On 9 October 1993 During The Aloha Campaign, G. R. Swenson, J. Qian, J. M.C. Plane, P. J. Espy, Michael J. Taylor, D. N. Turnbull, R. P. Lowe

All Physics Faculty Publications

On October 9, 1993, observations were made from the National Center for Atmospheric Research Electra aircraft during a flight from Maui, Hawaii, toward a low-pressure system NW of the island, a flight of 7 hours in total. The leading edge (wall) of a bright airglow layer was observed 900 km NW of Maui at 0815 UT, which was traveling at 75 m s−1 toward the SE, reaching Haleakala, Maui, about 3.25 hours later [see Swenson and Espy, 1995]. An intriguing feature associated with the event was the large increase in the mesospheric Na column density at the wall (∼180%). The …

Application Of Tomographic Inversion In Studying Airglow In The Mesopause Region, T. Nygren, Michael J. Taylor, M. S. Lehtinen, M. Markkanen

All Physics Faculty Publications

It is pointed out that observations of periodic nightglow structures give excellent information on atmospheric gravity waves in the mesosphere and lower thermosphere. The periods, the horizontal wavelengths and the phase speeds of the waves can be determined from airglow images and, using several cameras, the approximate altitude of the luminous layer can also be determined by triangulation. In this paper the possibility of applying tomographic methods for reconstructing the airglow structures is investigated using numerical simulations. A ground-based chain of cameras is assumed, two-dimensional airglow models in the vertical plane above the chain are constructed, and simulated data are …

Scaling Studies Of Spheromak Formation And Equilibrium, Cameron G. R. Geddes , '97, Thomas W. Kornack , '98, Michael R. Brown

Physics & Astronomy Faculty Works

Formation and equilibrium studies have been performed on the Swarthmore Spheromak Experiment (SSX). Spheromaks are formed with a magnetized coaxial plasma gun and equilibrium is established in both small (d(small)=0.16 m) and large (d(large)=3d(small)=0.50 m) copper flux conservers. Using magnetic probe arrays it has been verified that spheromak formation is governed solely by gun physics (in particular the ratio of gun current to flux, mu(0)I(gun)/Phi(gun)) and is independent of the flux conserver dimensions. It has also been verified that equilibrium is well described by the force free condition del xB=lambda B (lambda=constant), particularly early in decay. Departures from the force-free …

Nonlocal Theory Of Dissociative Electron Attachment To H2 And Hf Molecules, Gordon A. Gallup, Y. [Yuanguang] Xu, Ilya I. Fabrikant

Gordon Gallup Publications

We develop a method for calculation of dissociative electron attachment cross sections based on the Fano- Feshbach projection-operator approach. The coupling between the diabatic state and electron continuum is calculated with the inclusion of orthogonality scattering and long-range electron-molecule interaction. The dynamics of nuclear motion in the non-local complex potential is treated by semiclassical theory. We apply the theory to the calculation of dissociative attachment to the H₂ and HF molecules. Our results for attachment to ground-state hydrogen molecules and the near-threshold vibrational enhancement of H₂ are essentially the same as previous non-local results. However, the shape of …

Thermal Lattice Boltzmann Simulations Of Variable Prandtl Number Turbulent Flows, Min Soe, George Vahala, Pavol Pavlo, Linda L. Vahala, Hudong Chen

Electrical & Computer Engineering Faculty Publications

Thermal lattice Boltzmann (TLBE) models that utilize the single relaxation time scalar Bhatnagar, Gross, and Krook collision operator have an invariant Prandtl number. For flows with arbitrary Prandtl number, a matrix collision operator is introduced. The relaxation parameters are generalized so that the transport coefficients become density independent. TLBE simulations are presented for two-dimensional free decaying turbulence induced by a strongly perturbed double velocity shear layer for various Prandtl numbers.

Steps Toward Determination Of The Size And Structure Of The Broad-Line Region In Active Galactic Nuclei, Xii: Ground-Based Monitoring Of 3c 390.3, M. Dietrich, Bradley M. Peterson, P. Albrecht, M. Altmann, A. J. Barth, P. J. Bennie, R. Bertram, N. G. Bochkarev, H. Bock, J. M. Braun, A. Burenkov, S. Collier, L.-Z. Fang, O. P. Francis, A. V. Filippenko, C. B. Foltz, W. Gassler, C. Martin Gaskell, M. Geffert, K. K. Ghosh, R. W. Hilditch, R.K. Honeycutt, K. Horne, J. P. Huchra, Shai Kaspi, M. Kummel, K. M. Leighly, D. C, Leonard, Yu. F. Malkov, V. Mikhailov, H. Richard Miller, A. C. Morrill, J. Noble, Paul T. O'Brien, T. D. Oswalt, S. P. Pebley, M. Pfeiffer, V. I. Pronik, B.-C. Qian, J. W. Robertson, A. Robinson, Kenneth S. Rumstay, J. Schmoll, S. G. Sergeev, E. A. Sergeeva, A. I. Shapovalova, D. R. Skillman, Stephanie A. Snedden, S. Soundararajaperumal, G. M. Stirpe, J. Tao, G. W. Turner, R. M. Wagner, S. J. Wagner, J. Y. Wei, H. Wu, W. Zheng, Z. L. Zhou

C. Martin Gaskell Publications

Results of a ground-based optical monitoring campaign on 3C 390.3 in 1994-1995 are presented. The broadband fluxes (B, V , R, and I), the spectrophotometric optical continuum flux F_λ(5177 Å), integrated emission-line fluxes of Hα, Hβ, Hγ, He _I λ5876, and He _II λ4686 all show a nearly monotonic increase with episodes of milder short-term variations superposed. The amplitude of the continuum variations increases with decreasing wavelength (4400-9000 Å). The optical continuum variations follow the variations in the ultraviolet and X-ray with time delays, measured from the centroids of the crosscorrelation functions, typically around …

Search For The Decay B→DS1+(2536)X, M. Bishai, Kenneth A. Bloom, Cleo Collaboration

Kenneth Bloom Publications

We have searched for the decay B→D_s1⁺ (2536)X and measured an upper limit for the inclusive branching fraction of B(B→D_s1⁺X) < 0.96% at the 90% confidence level. This limit is small compared with the total expected B→D‾^(*)D^(*) KX rate. Assuming factorization, the D_s1⁺ 1 decay constant is constrained to be f_Ds1⁺ < 114 MeV at the 90% confidence level, at least 2.5 times smaller than that of D_s.

Crossover From Pure Ising To Random-Exchange Dominated Behavior Of The Two-Dimensional Antiferromagnet Rb2Co1-XMgXF4, Christian Binek, Wolfgang Kleemann, David P. Belanger

Christian Binek Publications

The temperature dependence of the uniform susceptibility χ of diluted two-dimensional Ising antiferromagnets Rb₂Co_1-xMg_xF₄, 0<~xN(x), but also in relation to the “local” phase transition temperatures TN′ throughout the Griffiths regime, T_N(x)<~T_N′<~T_N(0), a satisfactory quantitative description of χ vs T is deduced for any x above the percolation threshold. ©1998 The American Physical Society

Material Evaluation By Pulsed Diode Laser Optoacoustics, Xiaodong Xu

Electrical & Computer Engineering Theses & Dissertations

Pulsed diode laser optoacoustic diagnostics were carried out to characterize solid sample materials. The apparatus developed is compact, portable, cost-effective and therefore very promising for both industrial as well as laboratory applications. To our knowledge, this is the first time that optoacoustic characterization and measurement have been performed with a diode laser. The method was successfully applied to measure the thickness of a multilayer structure non-intrusively. Internal cracks of the material were detected by this technique.

A theory for optoacoustic signal generation, propagation and detection is given. A numerical analysis technique is developed to solve for the expected signal. In …

Rainbow Scattering By A Cylinder With A Nearly Elliptical Cross Section, Charles L. Adler, James A. Lock, Bradley R. Stone

Physics Faculty Publications

We both theoretically and experimentally examine the behavior of the first-and the second-order rainbows produced by a normally illuminated glass rod, which has a nearly elliptical cross section, as it is rotated about its major axis. We decompose the measured rainbow angle, taken as a function of the rod's rotation angle, into a Fourier series and find that the rod's refractive index, average ellipticity, and deviation from ellipticity are encoded primarily in the m = 0, 2, 3 Fourier coefficients, respectively. We determine these parameters for our glass rod and, where possible, compare them with independent measurements. We find that …

The Ultraviolet-Optical Albedo Of Broad Emission Line Clouds, Kirk Korista, Gary J. Ferland

Physics and Astronomy Faculty Publications

We explore the effective UV-optical albedos of a variety of types of broad emission line clouds, as well as their possible effects on the observed spectra of active galactic nuclei (AGNs). An important albedo source in moderately ionized ionization-bounded clouds is that which is due to neutral hydrogen: Rayleigh scattering of continuum photons off the extreme damping wings of Lyα. The photons resulting from this scattering mechanism may contribute significantly to the Lyα emission line, especially in the very broad wings. In addition, line photons emitted near 1200 Å (e.g., N V λ1240) that stream toward the neutral portion of …

Temperature Variations And N/O In The Orion Nebula From Hst Observations, R. H. Rubin, P. G. Martin, R. J. Dufour, Gary J. Ferland, J. A. Baldwin, J. J. Hester, D. K. Walter

Physics and Astronomy Faculty Publications

Using the Goddard High Resolution Spectrograph (GHRS) and the Faint Object Spectrograph (FOS) on the Hubble Space Telescope, we measured the flux of the N II] (2s2p^{3 5}S₂ --> 2s²2p^{2 3}P_2,1) lines at λ_vac = 2143.45, 2139.68 Å in the Orion Nebula--the first detection of these lines in an H II region. In order to assess the N⁺/O⁺ ratio, we also measured the flux of the [O II] (2p³²P^o_1/2,3/2-->2p³⁴S^o_3/2) lines at λ_{vac …}

Event Shape Analysis Of Deep Inelastic Scattering Events With A Large Rapidity Gap At Hera, J. Breitweg, M. Derrick, D. Krakauer, S. Magill, D. Mikunas, B. Musgrave, J. Repond, R. Stanek, R. L. Talaga, R. Yoshida, H. Zhang, Margarita C. K. Mattingly, F. Anselmo, P. Antonioli, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, G. Cara Romeo, G. Castellini, L. Cifarelli, F. Cindolo, A. Contin, M. Corradi, S. De Pasquale, I. Gialas, P. Giusti, G. Iacobucci, G. Laurenti

Faculty Publications

A global event shape analysis of the multihadronic final states observed in neutral current deep inelastic scattering events with a large rapidity gap with respect to the proton direction is presented. The analysis is performed in the range 5 ≤ Q2 ≤ 185 GeV2 and 160 ≤ W ≤ 250 GeV, where Q2 is the virtuality of the photon and W is the virtual-photon proton centre of mass energy. Particular emphasis is placed on the dependence of the shape variables, measured in the γ * -pomeron rest frame, on the mass of the hadronic final state, MX. With increasing MX …

The Texture Of Clouds, A. R. Jameson, Alexander Kostinski, R A. Black

Department of Physics Publications

Using a precise definition of clustering, it is shown that in two tropical cumulus clouds, droplets appear to be bunched over distances ranging from at least a kilometer or more down to several centimeters. A statistical framework is proposed for quantifying clustering in terms of a Poisson probability mixture. While these observations require further substantiation in many different clouds, droplet clustering may play a role in diverse phenomena from the coalescence growth of raindrops to the scattering of radiation by clouds.

Temporal Contrast In Ti:Sapphire Lasers: Characterization And Control, Marc Nantel, Jiro Itatani, An-Chun Tien, Jerome Faure, Daniel Kaplan, Marcel Bouvier, Takashi Buma, Paul Van Rompay, John Nees, Peter P. Pronko, Donald P. Umstadter, Gerald A. Mourou

Donald Umstadter Publications

As ultrafast lasers achieve ever higher focused intensities on target, the problem of ensuring a clean laser-solid interaction becomes more pressing. In this paper, we give concrete examples of the deleterious effects of low-contrast interactions, and address the problem of subpicosecond laser intensity contrast ratio on both characterization and control fronts. We present the new technique of high-dynamic-range plasma-shuttered streak camera contrast measurement, as well as two efficient and relatively inexpensive ways of improving the contrast of short pulse lasers without sacrificing on the output energy: a double-pass Pockels cell (PC), and clean high-energy-pulse seeding of the regenerative amplifier.

Onset Of Superconductivity In Decreasing Fields For General Domains, Andrew J. Bernoff, Peter Sternberg

All HMC Faculty Publications and Research

Ginzburg–Landau theory has provided an effective method for understanding the onset of superconductivity in the presence of an external magnetic field. In this paper we examine the instability of the normal state to superconductivity with decreasing magnetic field for a closed smooth cylindrical region of arbitrary cross-section subject to a vertical magnetic field. We examine the problem asymptotically in the boundary layer limit (i.e., when the Ginzburg–Landau parameter, k, is large). We demonstrate that instability first occurs in a region exponentially localized near the point of maximum curvature on the boundary. The transition occurs at a value of the …

Linear Reconstruction Of Non-Stationary Image Ensembles Incorporating Blur And Noise Models, Stephen D. Ford

Theses and Dissertations

Two new linear reconstruction techniques are developed to improve the resolution of images collected by ground-based telescopes imaging through atmospheric turbulence. The classical approach involves the application of constrained least squares (CLS) to the deconvolution from wavefront sensing (DWFS) technique. The new algorithm incorporates blur and noise models to select the appropriate regularization constant automatically. In all cases examined, the Newton-Raphson minimization converged to a solution in less than 10 iterations. The non-iterative Bayesian approach involves the development of a new vector Wiener filter which is optimal with respect to mean square error (MSE) for a non-stationary object class degraded …

Highly Anisotropic Elasticity Of A Dendrimeric Liquid Crystal, A. J. Jin, Michael R. Fisch, M. P. Mahajan, Karl A. Crandall, P. Chu, C.-Y. Huang, V. Percec, Rolfe G. Petschek, Charles Rosenblatt

Faculty Scholarship

Magnetic and electrical Freedericksz measurements were performed on the second generation monodendritic liquid crystal G2(OH). The deduced elastic constants were found to be exceptionally anisotropic: the splay elastic constant K11 is more than an order of magnitude larger than the bend elastic constant K33, and the twist constant K22 is approximately twice K33. The results are discussed in terms of molecular conformations.

The Nomad Experiment At The Cern Sps, Nomad Collaboration, J. Altegoer, M. Anfreville, C. Angelini, P. Astier, M. Authier, D. Autiero, A. Baldisseri, M. Baldo-Ceolin, G. Ballocchi, M. Banner, S. Basa, G. Bassompierre, K. Benslama, I. Bird, B. Blumenfeld, F. Bobisut, J. Bouchez, S. Bunyatov, S. Boyd, Roberto Petti, Et. Al.

Faculty Publications

The NOMAD experiment is a short base-line search for ν_μ − ν_τ oscillations in the CERN neutrino beam. The ντ's are searched for through their charged current interactions followed by the observation of the resulting τ− through its electronic, muonic or hadronic decays. These decays are recognized using kinematical criteria necessitating the use of a light target which enables the reconstruction of individual particles produced in the neutrino interactions. This paper describes the various components of the NOMAD detector: the target and muon drift chambers, the electromagnetic and hadronic calorimeters, the preshower and transition radiation …