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Scaling Behavior In Soliton Models, Joseph Schechter, Masayasu Harada, F. Sannino, H. Weigel

Physics - All Scholarship

In the framework of chiral soliton models we study the behavior of static nucleon properties under rescaling of the parameters describing the effective meson theory. In particular we investigate the question of whether the Brown--Rho scaling laws are general features of such models. When going beyond the simple Skyrme model we find that restrictive constraints need to be imposed on the mesonic parameters in order to maintain these scaling laws. Furthermore, in the case when vector mesons are included in the model it turns out that the isoscalar form factor no longer scales according to these laws. Finally we note …

Relativistic Momentum, Paul Finkler

Paul Finkler Papers

Introductory treatments of relativistic dynamics rely on the invariance of momentum conservation (i.e., on the assumption that momentum is conserved in all inertial frames if it is conserved in one) to establish the relationship for the momentum of a particle in terms of its mass and velocity. By contrast, more advanced treatments rely on the transformation properties of the four-velocity and/or proper time to obtain the same result and then show that momentum conservation is invariant. Here, we will outline a derivation of that relationship that, in the spirit of the more advanced treatments, relies on an elemental feature of …

The Observatory That Never Was, M. Eugene Rudd

M. Eugene Rudd Publications

Astronomy has been taught at the University of Nebraska since it first opened its doors in 1871, but for almost half of this time the university had no telescope larger than a Cinch Brashear refractor. Goodwin DeLoss Swezey, the astronomy professor at the turn of the century, had a small observatory built on campus to house this and other astronomical instruments.
Despite Swezey's ambitions for a larger telescope, the university's resources were limited. So he proposed to build a 12-inch refractor himself with the help of Charles S. Minnich, a nearby country doctor and amateur astronomer. Not only could Minnich …

Reconnecting The Sciences, John Eggebrecht, Raymond Dagenais, Don Dosch, Norman J. Merczak, Margaret N. Park, Susan C. Styer, David Workman

Faculty Publications & Research

During the last three years at the Illinois Mathematics and Science Academy, we have been working on a partial reconstruction of Whitehead's "one subject matter," a course reconnecting biology, chemistry, earth and space sciences, and physics into an Integrated Science program.

Critical Point For The Blue-Phase-Iii-Isotropic Phase Transition In Chiral Liquid Crystals, Z. Kutnjak, C. W. Garland, Colin G. Schatz , '97, Peter J. Collings, C. J. Booth, J. W. Goodby

Physics & Astronomy Faculty Works

The highly chiral compound S,S-4 ''-(methylbutyl)phenyl-4'-(methylbutyl) biphenyl carboxylate (S,S-MBBPC) undergoes a continuous supercritical evolution from the isotropic (I) phase to the third blue phase (BPI III). Mixtures of S,S-MBBPC and its racemate have been studied with high-resolution calorimetry capable of quantitative latent heat determinations and with optical activity measurements. Both experiments indicate that the first-order BP III-I transition line ends at a critical point when the chiral mole fraction X(c) similar or equal to 0.45. Analysis of C-p and optical activity data for the near-critical mixture with X = 0.45 indicates mean-field behavior instead of the theoretically predicted Ising fluctuation …

The Interaction Of Intense Laser Pulses With Atomic Clusters, T. Ditmire, Thomas D. Donnelly, A. M. Rubenchik, R. W. Falcone, M. D. Perry

All HMC Faculty Publications and Research

We examine the interaction of intense, femtosecond laser radiation with the large (50–200 Å) clusters produced in pulsed gas jets. Both experiment and simulation show that the plasmas produced during these interactions exhibit electron temperatures far in excess of that predicted by above-threshold ionization theory for a low-density gas. Efficient heating of the clusters by the laser is followed by rapid expansion of the clusters and long-lived x-ray emission from hot, decaying, underdense plasma.

Polarization Stability And Dynamics In A Model For A Polarization-Isotropic Laser That Goes Beyond Third-Order Lamb Theory, N. B. Abraham, Mark Matlin, R. S. Gioggia

Physics Faculty Research and Scholarship

Instabilities and dynamical pulsations are common features of solutions of a model that includes the material variable dynamics for a laser with a polarization isotropic resonator and with a homogeneously broadened j=1 --> j=0 transition. These resemble in some respects features found in third-order Lamb theories under anisotropic conditions, such as splitting of the optical field into two relatively independent orthogonally polarized modes with different optical frequencies. At higher intensities the amplitudes and frequencies of these modes exhibit such strong coupling that a ''two-mode'' description loses its usefulness or effectiveness. Various periodic attractors with strong intensity and polarization pulsations are …

Far-Ultraviolet Stellar Photometry: Fields Centered On Ρ Ophiuchi And The Galactic Center, Edward G. Schmidt, George R. Carruthers

Edward Schmidt Publications

Far-ultraviolet photometry is presented for 121 objects in a 20" diameter field centered on ρ Oph and for 649 objects in a field covering the Galactic center. Broadband magnitudes with effective wavelengths of 1375 Å and 1781 Å are given. The Galactic center field overlaps two fields which were discussed in an earlier paper. Eighty-eight percent of the ultraviolet objects in the ρ Oph field were identified with visible stars using the SIMBAD database, while only 9% of the objects are blends of early-type stars too close together to separate with our resolution. The photometric calibration was studied in detail, …

Auger Electron Spectroscopy Of Free Argon Clusters, A. Knop, D.N. Mcilroy, Peter A. Dowben, E. Ruhl

Peter Dowben Publications

Auger electron spectra and Auger yields of free argon clusters in the Ar(2p) excitation regime are reported. The Auger yield spectra show characteristic changes as a function of cluster size. The results indicate that the Auger yield signal originates primarily from the surface of the clusters. The results are compared to bulk-sensitive experimental techniques, such as total electron yields (TEY), zero kinetic energy electron (ZEKE) spectra for variable size clusters, as well as Auger yield spectra of condensed argon multilayers.

Percus-Yevick Approximation For Fluids With Spontaneous Partial Order: Results For A Separable Model, Hua Zhong, Rolfe G. Petschek

Faculty Scholarship

Recently we have applied the Percus-Yevick approximation to nematic fluids with partial spontaneous order using a diagrammatic implementation of a Ward identity. In this paper we apply the method to study the isotropic-nematic phase transition of a separable model, where the interparticle potential independently depends on the spatial separation and the relative orientation of the particles. This approach allows us to study the transition directly without other approximations besides the Percus-Yevick closure itself. Previous works of the integral equation method on phase transitions were based on the stability criterion or coexistence condition derived from a truncated density functional expansion. By …

Characterization Of Spatial And Temporal Anisotropy In Turbulent Mixing Layers Using Optical Techniques, Patrick J. Gardner

Theses and Dissertations

The optical aberrations induced by mixing layers of dissimilar gases are recorded and analyzed in order to characterize the spatial and temporal properties of the flow. Laser light was propagated through a mixing layer of Helium and Nitrogen gas, having velocities of 8.5 m/sec and 1.5 m/sec, respectively. The light was propagated in a direction perpendicular to the plane of the mixing layer. The mixing layer was evaluated in two experimental regimes: free turbulent mixing, where the mixing layer spreads into the surrounding air; and channel flow, where the mixing layer is confined to a rectangular channel. The optical perturbations …

Surface-Enhanced Raman Scattering At Elevated Temperatures, P.T. Leung, M. H. Hider, Erik J. Sánchez

Physics Faculty Publications and Presentations

The effect on surface-enhanced Raman scattering due to the increase in temperature of the metallic substrate is studied via a simple model for physisorbed molecules. Surface roughness is represented by a spherical or spheroidal island, and the temperature effects on the surface plasmon are accounted for via a slightly modified Ujihara model. It is found that the enhancement ratio in general decreases as substrate temperature increases. For noble metals like silver, this temperature effect is particularly pronounced at scattering frequencies close to that of the surface-plasmon resonance; and for frequencies well below the surface plasmon frequency, the enhancement ratio is …

An Instrument For Experimental Secondary Electron Emission Investigations, With Application To The Spacecraft Charging Problem, Robert Davies

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Secondary electron emission (SEE) and incident-particle backscattering are important processes accompanying the impact of energetic electrons and ions on surfaces. The phenomena play a key role in the buildup of electrical charge on spacecraft surfaces. and are therefore of particular interest to scientists attempting to model spacecraft charging. In response to a demonstrated need for data, techniques for determining total secondary electron (SE) and backscatter (BS) yields S and n, and associated scattering-angle-resolved, scattering-energy-resolved, and simultaneous angle-energy-resolved yields have been developed. Further, an apparatus capable of making the necessary measurements for experimental determination of these quantities-for conducting materials in …

A Study Of The Gradient Drift Instability In The High-Latitude Ionosphere Using The Utah State University Time Dependent Ionospheric Model, Mahesh Subramanium

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Research over the years has established that the Gradient Drift Instability process causes small-scale irregularities, mostly along the edges of the high-latitude polar cap patches. Studying these irregularities will help in the development of a Global Scale Ionospheric model, which is a central part of a global space weather forecast system. Much theoretical work has been done with varying degrees of complexity to study this instability in the high latitude patches.

In this work we have used the Utah State University Time Dependent Ionospheric Model to model the high-latitude patches, calculate the growth rate of the instability, and perform a …

Simulations Of Electrostatic Modes Of Non-Neutral Plasmas With Small Aspect Ratio In A Penning Trap, Grant W. Mason, Ross L. Spencer, Jonathan A. Bennett

Faculty Publications

The dependence on induced charge, experimental geometry, and temperature of electrostatic modes in very low aspect ratio non-neutral plasmas in a Penning trap is considered. The modes are of interest as non-destructive diagnostics of the shape of the plasmas. These investigations include equilibrium calculations of plasma shapes and profiles at finite temperature and particle-in-cell simulations of axisymmetric modes. The results of the simulations are compared to the zero-temperature theory by Dubin [Phys. Rev. Lett. 66, 2076 (1991)] taken to first-order in the aspect ratio and to experimental measurements by Weimer et al. [Phys. Rev. A 49, 3842 (1994)]. In general, …

Fabrication Of Large Arrays Of Micron-Scale Magnetic Features By Selective Area Organometallic Chemical Vapor Deposition, D. Welipitiya, Y.L. He, Jiandi Zhang, P.I. Oden, T. Thundat, R.J. Warmack, Ismail Gobulukoglu, Z.S. Shan, David J. Sellmyer, Peter A. Dowben

Peter Dowben Publications

We demonstrate that it is possible to deposit a wide range of magnetic features, using photoassisted selective area organometallic chemical vapor deposition. Large arrays of identical micron-scale Ni features were deposited on a Si(111) wafer by this method. Their magnetic properties were studied by alternating gradient force magnetometry as well as magnetic force microscopy. Our morphological and magnetic measurements show that the structures are spatially well defined, and the magnetic properties are related to the structural shapes of the features. This method can be adapted to the fabrication of smaller-scale magnetic and electronic devices. ©1996 American Institute of Physics.

Very High Density Clumps And Outflowing Winds In Qso Broad-Line Regions, J. A. Baldwin, Gary J. Ferland, K. T. Korista, R. F. Carswell, F. Hamann, M. M. Phillips, D. A. Verner, Belinda J. Wilkes, R. E. Williams

Physics and Astronomy Faculty Publications

Intercomparison of the spectra of seven high-luminosity quasi-stellar objects (QSOs) shows that there is a gradation of properties in their broad emission-line regions (BELRs) that can be understood as differing mixtures of different gas components. Six of these seven objects have unusually narrow BELR profiles, which greatly facilitates the disentangling of blends and measuring of weak lines. In the QSO 0207 - 398, the BELR is made up of at least three kinematically distinct components; its spectrum is in fact a composite of the spectra of the more homogeneous BELRs in the QSOs at either end of our sequence of …

The Chemical Enrichment Of Gas In Broad Absorption Line Qsos: Rapid Star Formation In The Early History Of Galaxies, Kirk Korista, Fred Hamann, Jason W. Ferguson, Gary J. Ferland

Physics and Astronomy Faculty Publications

Utilizing spectra from ground-based and Hubble Space Telescope observations, Korista et al. identified at least 12 broad absorption lines in the broad absorption line (BAL) QSO 0226-1024 (z_em = 2.256), many for the first time. In the present paper we use seven of their measured column densities to investigate the BAL gas ionization equilibrium and metallicity. We assume that the metal abundances follow the rapid star formation (RSF) models of Hamann & Ferland or are simply scaled from solar ratios to (1) limit the free parameters in constraining the overall metallicity and (2) test the applicability of such a …

High Metal Enrichments In Luminous Quasars, Gary J. Ferland, Jack A. Baldwin, Kirk T. Korista, Fred Hamann, R. F. Carswell, Mark Phillips, Belinda J. Wilkes, Robert E. Williams

Physics and Astronomy Faculty Publications

We discuss observations of the broad emission line in luminous intermediate redshift quasars, with emphasis on Q0207 -398. This object has relatively sharp lines, allowing us to deconvolve the profiles into distinct components. In this paper we examine the high ionization region, which we show must be matter-bounded, partially transparent to ionizing radiation. We measure a large N V λ1240/He II λ1640 ratio in Q0207-398, but detailed calculations predict this ratio to be ~1 for standard cloud properties. We show that no choice of incident continuum, ionizing photon flux, density, or even the appeal to nonradiative energy sources, can reproduce …

Magnetic Properties Of Nanometer-Size Copt Particles, Sy_Hwang Liou, Yi Liu, S.S. Malhotra, M. Yu, David J. Sellmyer

Sy-Hwang Liou Publications

We have prepared nanometer-size, isolated CoPt particles. The particles in the range of 100–300 nm in diameter were formed by annealing thin films in the temperature range of 550–800 °C. Films with magnetic coercivity as high as 30 kOe were achieved. The results indicate that the high magnetic coercivity was obtained because the crystallite size approaches that of noninteracting single-domain particles.

Magnetic Viscosity And Switching Volumes Of Annealed Fe/Pt Multilayers, C.P. Luo, Z.S. Shan, David J. Sellmyer

David Sellmyer Publications

Magnetic viscosity and the phenomenon of the sweep-rate dependence of the coercivity are important for the characterization of magnetic recording media. The activation volume of magnetization reversal or switching volume is directly related to medium noise. The magnetic viscosity behavior of annealed Fe/Pt multilayers was studied and the switching volumes were obtained by both measurements of the sweep-rate dependence of coercivity and time dependence of magnetization. It is found that samples with larger coercivities have smaller switching volumes, and an estimate of the magnetic grain diameter is about 9 nm. The coercivity mechanisms are also discussed.

Mössbauer Study Of Permanent-Magnet R2Fe17-XMXCY Compounds, I. A. Al-Omari, E.W. Singleton, Y. Zheng, George C. Hadjipanayis, David J. Sellmyer

David Sellmyer Publications

We report Fe⁵⁷ Mössbauer spectroscopy studies of the effect of carbon doping on the magnetic properties of the Fe sites of R₂Fe_17-xM_xC_y, and of the presence of multiple phases in these systems. In this study two systems, Sm₂Fe₁₄Al₃C_y, where y=0, 1.0, 2.0, and 3.0, and Nd₂Fe_14.54Si_2.46C_y, where y=0, 0.432, and 2.544, were measured at room temperature and analyzed. The ternary compounds R₂Fe_17-xM_xC_y studied here have the …

Spin Polarization Of The Conduction Bands And Secondary Electrons 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 4f level. The temperature dependencies …

Magnetic Properties And Magnetization Reversal In Co/Au Multilayers (Abstract), Z. S. Shan, J. X. Shen, Roger D. Kirby, David J. Sellmyer

Roger Kirby Publications

We report studies of magnetic properties in CoX Å/Au60 Å multilayers (X = 5,6,7,8,12,20 Å), which were prepared by sputtering on Si(111) substrates, with emphasis on the magnetization reversal. Magnetization reversal was investigated by measurements of initial magnetization curves, minor loops, coercivity as a function of the maximum field of minor loops, temperature dependence of magnetic properties using Kronmüller’s model, time decay of Kerr rotation angle UK, and the field-sweep speed dependence of coercivity H_c(dH_a/dt) at room and/or low temperature. It is found that (1) the thermal activation volumes determined by H_{c …}

Magnetic And Magneto-Optical Properties Of MnXPt1–X–YZnY, Kurt W. Wierman, Roger D. Kirby

Roger Kirby Publications

In this work we have prepared thin films of the ternary alloy Mn_xPt_1–x–yZn_y by magnetron sputtering onto quartz substrates. We have found a wide range of compositions which are strongly ferromagnetic at room temperature. A transition from a cubic to tetragonal phase with decreasing Pt content is confirmed by x-ray diffraction. X-ray diffraction measurements also show a strong (001) reflection consistent with long range order along the c axis for the tetragonal phase. These films show large complex Kerr rotations (up to 0.7°) in the visible spectrum. This combined with their anisotropic structure suggests …

Co-Sm (1̅100)[0001]//Cr (1̅21̅)[ 1̅01] Epitaxy And Its Effects On Magnetic Properties Of Co-Sm//Cr Films, Yi Liu, David J. Sellmyer, B. W. Robertson

David Sellmyer Publications

It is well known that the Cr underlayer plays a critical role in generating large in-plane coercivity in Co-based magnetic thin films. In this paper we report in detail the Co-Sm (1̅100)[0001]//Cr (1̅21̅)[ 1̅01] epitaxy revealed by high resolution electron microscopy. The lattice mismatch between Co-Sm (1̅100) and Cr (1̅21̅) is less than 2%, suggesting an energetically favorable configuration. The high anisotropy observed in Co-Sm films is discussed by this epitaxial relation.

Site Affinity Of Substituents In Nd₂Fe₁₇₋ₓtₓ (T=Cu,Zr,Nb,Ti,V) Alloys, William B. Yelon, Z. Hu, William Joseph James, G. K. Marasinghe

Physics Faculty Research & Creative Works

In order to understand the magnetic properties of the substituted rare-earth-iron alloys, it is especially important to know the location of the substitutional atoms within the iron lattice. The site distributions of some nontransition-metal substituents in the substituted Nd₂Fe_17-xT_x alloys have previously been reported. Here we report the site distributions of some transition-metal substituents (Cu,Zr,Nb,Ti,V) in the Nd₂Fe_17-xT_x alloys and compare them with those of the nontransition-metal substituted compounds. Rietveld analysis of neutron powder diffraction data indicates that the nontransition-metal substituents show very similar site affinity at low substituent content. …

Magnetic Field-Mediated Alignment Of A Nematic Liquid Crystal At A Polymer Surface Exposed To Ultraviolet Light, Rolfe G. Petschek, Charles Rosenblatt

Faculty Scholarship

A nematic liquid crystalline cell utilizing a substrate coated with polyvinylcinnamate was subjected to UV polarized light in the presence of a magnetic field. After removing the cell from the field it was found that the pretilt angle was large and both temporally and thermally robust. Irradiation in the absence of a field resulted in a rapid decay of the pretilt angle to zero, corresponding to planar alignment.

Magnetic Hardening Of Melt-Spun Nanocomposite Nd2Fe14B/Fe Magnets, I. Panagiotopoulos, L. Withanawasam, A.S. Murthy, George C. Hadjipanayis, E.W. Singleton, David J. Sellmyer

David Sellmyer Publications

Coercivity optimization studies were done on melt-spun nanocomposite Nd₄R₂Fe_87-xNbT_xB₆ (R=Nd,Y,Dy; T=Ag,Cu) isotropic ribbon samples. The maximum attainable coercivities, after adjusting the annealing time, were found to be very sensitive to the annealing temperatures. The optimum magnetic properties [H_c=3.9 kOe, (BH) _max=10 MGOe] were obtained by annealing at 750–775 °C for a few minutes. Optimization by flash annealing gave similar results. Microstructural studies show that the grain size is greater than the theoretically predicted grain size for optimum coupling between the hard and the soft phase. With the …

Superparamagnetic Magnetic Force Microscopy Tips, P.F. Hopkins, John Moreland, S.S. Malhotra, Sy_Hwang Liou

Sy-Hwang Liou Publications

We report on magnetic force microscopy (MFM) images of a thin-film magnetic recording head taken using batch micromachined silicon tips coated with nanocomposite Fe₆₀ (SiO₂)₄₀ and Fe₇₀ (SiO₂)₃₀ films. The small Fe grain size (<10 nm) and dilute Fe volume fraction (0.29–0.4) of these granular films produce tip coatings of low remanence and essentially zero coercivity, reduced by the superparamagnetic properties of these films. We have used these tips to obtain MFM images of the write field of the head with high spatial and magnetic-field resolution. In comparison to images taken using commercial Co₈₅Cr₁₅-coated tips, these MFM images show reduced tip memory effects and clearly delineate the gap field from the pole pieces.