Physical Sciences and Mathematics Commons^™

Analysis Of The Shadow-Sausage Effect Caustic, James A. Lock, Charles L. Adler, Diana Ekelman, Jonathan Mulholland, Brian Keating

Physics Faculty Publications

We analyze the optical caustic produced by light refracted at the curved meniscus surrounding a cylindrical rod standing partially out of a liquid-filled container. When the rod is tilted from the vertical or when light is diagonally incident, the caustic is a four-cusped astroid with two of its cusps obscured by the rod's shadow. If a portion of the flat end of the rod is raised above the water level, the caustic evolves into a pattern of five interlocking cusps. The five cusps result from symmetry breaking of a three-cusped surface perturbation caustic. (C) 2003 Optical Society of America.

Simulating Coronas In Color, Stanley D. Gedzelman, James A. Lock

Physics Faculty Publications

Coronas are simulated in color by use of the Mie scattering theory of light by small droplets through clouds of finite optical thickness embedded in a Rayleigh scattering atmosphere. The primary factors that affect color, visibility, and number of rings of coronas are droplet size, width of the size distribution, and cloud optical thickness. The color sequence of coronas and iridescence varies when the droplet radius is smaller than similar to6-mum. As radius increases to approximately 3.5 mum, new color bands appear at the center of the corona and fade as they move outward. As the radius continues to increase …

Light And Color In The Open Air: Introduction To The Feature Issue, Charles L. Adler, James A. Lock

Physics Faculty Publications

This special feature of Applied Optics reports the results of new experimental and theoretical research concerning a number of naked-eye optical phenomena, including ice-crystal halo displays, mirages, rainbows, glories, optical caustics, clear-sky phenomena, cloud coronas, cloud iridescence, and the extinction of skylight. (C) 2003 Optical Society of America.

Experimental Observation Of Total-Internal-Reflection Rainbows, Charles L. Adler, James A. Lock, Jonathon Mulholland, Brian Keating, Diana Ekelman

Physics Faculty Publications

A new class of rainbows is created when a droplet is illuminated from the inside by a point light source. The position of the rainbow depends on both the index of refraction of the droplet and the position of the light source, and the rainbow vanishes when the point source is too close to the center of the droplet. Here we experimentally measure the position of the transmission and one-internal-reflection total-internal-reflection rainbows, and the standard (primary) rainbow, as a function of light-source position. (C) 2003 Optical Society of America.

Photoproduction Of The Ω Meson On The Proton At Large Momentum Transfer, M Battaglieri, M Brunoldi, R De Vita, B Asavapibhop, R S. Hicks, D Lawrence, R Miskimen, Gerald Alvin Peterson

Gerald Alvin Peterson

The differential cross section, dσ/dt, for ω meson exclusive photoproduction on the proton above the resonance region (2.6

Absolute Orientation-Dependent Anisotropic Tin(111) Island Step Energies And Stiffnesses From Shape Fluctuation Analyses, S. Kodambaka, S. V. Khare, V. Petrova, Duane D. Johnson, I. Petrov, J. E. Greene

Duane D. Johnson

In situ high-temperature (1165–1248 K) scanning-tunneling microscopy was used to measure temporal fluctuations about the anisotropic equilibrium shape of two-dimensional TiN(111) adatom and vacancy islands on atomically smooth TiN(111) terraces. The equilibrium island shape was found to be a truncated hexagon bounded by alternating 〈110〉 steps, which form [100] and [110] nanofacets with the terrace. Relative step energies β as a function of step orientation φ were obtained from the inverse Legendre transformation of the equilibrium island shape to within an orientation-independent scale factor λ, the equilibrium chemical potential of the island per unit TiN area. We find that for …

Electronic Structure Of Eras(100), Takashi Komesu, Hae-Kyung Jeong, Jaewu Choi, C.N. Borca, Peter A. Dowben, A.G. Petukhov, B.D. Schultz, C.J. Palmstrom

Peter Dowben Publications

The experimental band structure of the rare-earth pnictide erbium arsenide (ErAs), grown epitaxially on GaAs(100), has been mapped out using photoelectron spectroscopy and inverse photoemission spectroscopy. The electronic structure is dominated by bulk bands qualitatively consistent with the calculated band structure. A number of additional nondispersing 4 f multiplet levels can be identified in the valence-band structure as well as at least one surface resonance band. From symmetry selection rules, photoemission provides strong evidence that the Δ₅ (or e) symmetry bands are a consequence of hybridization between Er and As, while the Δ ₁ (or a₁) symmetry …

Tt̅ Production Cross Section In Pp̅ Collisions At √S = 1.8 Tev, V. M. Abazov, Gregory R. Snow, D0 Collaboration

Gregory Snow Publications

Results are presented on a measurement of the tt̅ pair production cross section in pp̅ collisions at √s = 1.8 TeV from nine independent decay channels. The data were collected by the DØ experiment during the 1992–1996 run of the Fermilab Tevatron Collider. A total of 80 candidate events is observed with an expected background of 38.8±3.3 events. For a top quark mass of 172.1 GeV/c², the measured cross section is 5.69 ±1.21(stat) ±1.04(syst) pb.

Neutron Diffraction, Structural And Magnetic Properties Of (La1-Ypry)0.9na0.1mno3, S. Megdiche, Mohamed Ellouze, A. Cheikh-Rouhou, Q. Cai, William B. Yelon

Physics Faculty Research & Creative Works

A systematic study of the structural and magnetic properties of the diluted perovskite manganite oxides (La_1-yPr_y)_0.9Na_0.1MnO₃ (0.2≤y≤0.8) had been carried on. in this study, the average ionic radius 〈rA〉 of a cation site was systematically varied while keeping fixed the carrier concentration (Mn³⁺/Mn⁴⁺ ratio). X-Ray diffraction investigations showed a structural transition from the rhombohedral to the orthorhombic system for 0.33≤y≤0.5. the unit cell volume decreases with increasing Pr³⁺ content. Magnetic measurements showed that our synthesized samples exhibit a paramagnetic to ferromagnetic transition with decreasing temperature. Neutron diffraction …

High-Field Magnetic Resonant Properties Of Β’–(Et)2sf5cf2so3, Gary L. Gard, Rolf Walter Winter, J. A. Schlueter, Brian H. Ward, E. Jobiliong, A. P. Reyes, P. Kuhns, J. Krzystek, J. S. Brooks, S. A. Zvyagin, B. Rutel

Chemistry Faculty Publications and Presentations

The charge transfer salt β′-(ET)₂SF₅CF₂SO₃, which has previously been considered a spin-Peierls material with a TSP;33 K, is examined using high-resolution high-field sub-millimeter/millimeter wave electron spin resonance (ESR), and nuclear magnetic resonance (NMR) techniques. A peak in the nuclear spin-lattice relaxation behavior in fields of 8 T, accompanied by a broadening and paramagnetic shift of the resonance line, indicates a phase transition at Tc~20 K. A pronounced change in the high-field ESR excitation spectra at ~24 T, observed at Tc~20 K, may indicate the onset of antiferromagnetic (AFM) correlations of the low temperature phase in β′-(ET)₂SF₅CF₂SO₃. Peculiarities of the low-temperature …

The Mass Of Quasar Broad Emission Line Regions, J. A. Baldwin, Gary J. Ferland, K. T. Korista, F. Hamann, M. Dietrich

Physics and Astronomy Faculty Publications

We show that the mass of ionized gas in the broad-line regions (BLRs) of luminous quasars is at least several hundred M_☉, and probably of the order of 10³-10⁴ M_solar. BLR mass estimates in several existing textbooks suggest lower values but pertain to much less luminous Seyfert galaxies or include only a small fraction of the ionized/emitting volume of the BLR. The previous estimates also fail to include the large amounts of BLR gas that emit at low efficiency (in a given line) but that must be present based on reverberation and other …

Study Of The Azimuthal Asymmetry Of Jets In Neutral Current Deep Inelastic Scattering At Hera, S. Chekanov, D. Krakauer, S. Magill, B. Musgrave, J. Repond, R. Yoshida, Margarita C. K. Mattingly, P. Antonioli, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, G. Cara Romeo, L. Cifarelli, F. Cindolo, A. Contin, M. Corradi, S. De Pasquale, P. Giusti, G. Iacobucci, A. Margotti, R. Nania, F. Palmonari, A. Pesci, G. Sartorelli, A. Zichichi, G. Aghuzumtsyan, D. Bartsch, I. Brock

Faculty Publications

The azimuthal distribution of jets produced in the Breit frame in high-Q2 deep inelastic e+p scattering has been studied with the ZEUS detector at HERA using an integrated luminosity of 38.6 pb-1. The measured azimuthal distribution shows a structure that is well described by next-to-leading-order QCD predictions over the Q2 range considered, Q2 > 125 GeV2. © 2002 Elsevier Science B.V. All rights reserved.

Electrical And Spectroscopic Studies Of The Effects Of Dc Electric Fields On Pre-Mixed Propane-Air Flames, S D. Marcum, G D. Gillen, B N. Ganguly

Physics

The effects of DC electric fields on temperature distributions within pre-mixed propane-air flames have been measured by the technique of thin filament pyrometry (TFP). We have focussed on the dramatic electric-field-induced modifications of the shape and size of the inner cone and the concomitant changes in the temperature profiles of fuel-rich mixtures with equivalence ratios of 1-1.35. Temperature profile measurements show large decreases in the reaction zone volume that is dependent upon the applied voltage polarity, indicating that electron impact excitation is not responsible for the observed effects. Additionally, the observed flame temperature profile modifications are not strongly dependent on …

Nonvolatile Memory Element Based On A Ferroelectric Polymer Langmuir-Blodgett Film, Timothy J. Reece, Stephen Ducharme, A.V. Sorokin, Matt Poulsen

Stephen Ducharme Publications

We report the operation of a potential nonvolatile bistable capacitor memory element consisting of a metal gate, a 170 nm thick ferroelectric Langmuir–Blodgett film of vinylidene fluoride (70%) with trifluoroethylene (30%) copolymer, and a 100 nm thick silicon-oxide insulating layer, all deposited on an n-type silicon semiconductor substrate. The device exhibited clear capacitance hysteresis as the gate voltage was cycled between ±25 V, with a capacitance dynamic range of 8:1 and threshold voltage shift of 2.8 V. The results are in good agreement with the model of Miller and McWhorter [J. Appl. Phys. 72, 5999 (1992)].

Low-Mobility Solar Cells: A Device Physics Primer With Application To Amorphous Silicon, Eric A. Schiff

Physics - All Scholarship

The properties of pin solar cells based on photogeneration of charge carriers into lowmobility materials were calculated for two models. Ideal p- and n-type electrode layers were assumed in both cases. The first, elementary case involves only band mobilities and direct electron–hole recombination. An analytical approximation indicates that the power in thick cells rises as the 1 4 power of the lower band mobility, which reflects the buildup of space-charge under illumination. The approximation agrees well with computer simulation. The second model includes exponential bandtail trapping, which is commonly invoked to account for very low hole drift mobilities in amorphous …

Bandtail Limits To Solar Conversion Efficiencies In Amorphous Silicon Solar Cells, Kai Zhu, Weining Wang, Eric A. Schiff, Jianjun Liang, S. Guha

Physics - All Scholarship

We describe a model for a-Si:H based pin solar cells derived primarily from valence bandtail properties. We show how hole drift-mobility measurements and measurements of the temperature-dependence of the open-circuit voltage VOC can be used to estimate the parameters, and we present VOC(T) measurements. We compared the power density under solar illumination calculated with this model with published results for as-deposited a-Si:H solar cells. The agreement is within 4% for a range of thicknesses, suggesting that the power from as-deposited cells is close to the bandtail limit.

Hole Drift-Mobility Measurements In Contemporary Amorphous Silicon, S. Dinca, Eric A. Schiff, V. Vlahos, C. R. Wronski, Q. Yuan

Physics - All Scholarship

We present hole drift-mobility measurements on hydrogenated amorphous silicon from several laboratories. These temperature-dependent measurements show significant variations of the hole mobility for the differing samples. Under standard conditions (displacement/field ratio of 2×10-9 cm2/V), hole mobilities reach values as large as 0.01 cm2/Vs at room-temperature; these values are improved about tenfold over drift-mobilities of materials made a decade or so ago. The improvement is due partly to narrowing of the exponential bandtail of the valence band, but there is presently little other insight into how deposition procedures affect the hole drift-mobility.

Amorphous Silicon Based Solar Cells, Xunming Deng, Eric A. Schiff

Physics - All Scholarship

Crystalline semiconductors are very well known, including silicon (the basis of the integrated circuits used in modern electronics), Ge (the material of the first transistor), GaAs and the other III-V compounds (the basis for many light emitters), and CdS (often used as a light sensor). In crystals, the atoms are arranged in near-perfect, regular arrays or lattices. Of course, the lattice must be consistent with the underlying chemical bonding properties of the atoms. For example, a silicon atom forms four covalent bonds to neighboring atoms arranged symmetrically about it. This “tetrahedral” configuration is perfectly maintained in the “diamond” lattice of …

Ferroelectric-Field-Induced Tuning Of Magnetism In The Colossal Magnetoresistive Oxide La1Àxsrxmno3, X. Hong, A. Posadas, A. Lin, C. H. Ahn

Xia Hong Publications

A ferroelectric field effect approach is presented for modulating magnetism in the colossal magnetoresistive oxide La_1-xSr_xMnO₃ (LSMO). The ferromagnetic Curie temperature of ultrathin LSMO films was shifted by 35 K reversibly using the polarization field of the ferroelectric oxide Pb(Zr_xTi_1-x)O₃ in a field effect structure. This shift was also observed in magnetoresistance measurements, with the maximum magnetoresistance ratio at 6 T increasing from 64% to 77%. This model system approach does not introduce substitutional disorder or structural distortion, demonstrating that regulating the carrier concentration alone changes the magnetic phase transition …

Temperature Variations From Hubble Space Telescope Spectroscopy Of The Orion Nebula, R. H. Rubin, P. G. Martin, R. J. Dufour, Gary J. Ferland, K. P. M. Blagrave, X.-W. Liu, J. F. Nguyen, J. A. Baldwin

Physics and Astronomy Faculty Publications

We present Hubble Space Telescope (HST)/STIS long-slit spectroscopy of NGC 1976. Our goal is to measure the intrinsic line ratio [O III] 4364/5008 and thereby evaluate the electron temperature (T_e) and the fractional mean-square T_e variation (t²_A)across the nebula. We also measure the intrinsic line ratio [N II] 5756/6585 in order to estimate T_e and t²_A in the N⁺region. The interpretation of the [N II] data is not as clear cut as the [O III] data because of a higher sensitivity to knowledge …

Measurement Of The Index Of Refraction Of A Flat Zinc Germanium Phosphide Wafer In The Infrared, Glen Gillen, Shekhar Guha

Physics

We have developed and tested a novel application of interferometry to determine the absolute refractive index of individual infrared materials having flat and parallel surfaces without alteration of the sample in any way, and measured no for ZnGeP₂.

The Temporally Filtered Navier-Stokes Equations: Propertes Of The Residual Stress, C. D. Pruett, T. B. Gatski, Chester E. Grosch, W. D. Thacker

CCPO Publications

Recent interest in the development of a unifying framework among direct numerical simulations, large-eddy simulations, and statistically averaged formulations of the Navier-Stokes equations, provides the motivation for the present paper. Toward that goal, the properties of the residual (subgrid-scale) stress of the temporally filtered Navier-Stokes equations are carefully examined. This includes the frame-invariance properties of the filtered equations and the resulting residual stress. Causal time-domain filters, parametrized by a temporal filter width 0infinity, the residual stress is equivalent to the long-time averaged stress, and the Reynolds-averaged Navier-Stokes equations are recovered from the temporally filtered equations. The predicted behavior at the …

Magnetic Core Loss Of Ultrahigh Strength Feco Alloys, Xuemei Cheng, X. K. Zhang, D. Z. Zhang, S. H. Lee, A. Duckham, T. P. Weihs, R. C. Cammarata, John Q. Xiao, C. L. Chien

Physics Faculty Research and Scholarship

Hiperco^® 50 alloy heat treated between 450 and 650 °C exhibits superior mechanical properties. We report the measurements of the ac core loss at various frequencies up to 4500 Hz of the Hiperco^® 50 alloy samples annealed at 450 and 650 °C. The 650 °C annealed specimens have lower ac core loss than the 450 °C annealed ones. The total core loss, consisting of contributions from hysteresis core loss and eddy-current core loss, depends on the frequency f as af+bf². The eddy current loss of a single laminate is minor compared to the hysteresis loss.

Magnetic Properties Of Epitaxial Mn-Doped Zno Thin Films, Xuemei Cheng, C. L. Chien

Physics Faculty Research and Scholarship

Epitaxial ZnO thin film doped with 7% Mn have been made by reactive rf magnetron sputtering onto (1120) sapphire substrates at 400 °C. X-ray diffraction measurements reveal that the Zn_0.93Mn_0.07O film has a (0001) wurtzite single-crystal structure with a rocking curve width od 0.98°. UV-VIS absorption spectra show a band gap of 3.25 eV for pure ZnO films and 3.31 eV for the Zn_0.93Mn_0.07O film with states extending into the gap. The Auger electron spectroscopy shows homogeneous distribution of Mn in the film. The magnetic properties of the Zn_0.93Mn_{0.07 …}

Study Of The Cabibbo-Suppressed Decay Modes D0→Π−Π+ And D0→K−K+, Abaz Kryemadhi

Educator Scholarship & Departmental Newsletters

Using data from the FOCUS (E831) experiment at Fermilab, we present a new measurement for the branching ratios of the Cabibbo-suppressed decay modes D0→π−π+ and D0→K−K+. We measured: Γ(D0→K−K+)/Γ(D0→π−π+)=2.81±0.10(stat)±0.06(syst), Γ(D0→K−K+)/Γ(D0→K−π+)=0.0993±0.0014(stat)±0.0014(syst), and Γ(D0→π−π+)/Γ(D0→K−π+)=0.0353±0.0012(stat)±0.0006(syst). These values have been combined with other experimental data to extract the ratios of isospin amplitudes and the phase shifts for the D→KK and D→ππ decay channels.

Ultrafine Nife2o4 Powder Fabricated From Reverse Microemulsion Process, Jiye Fang, Narayan Shama, Le Duc Tung, Eun Young Shin, Charles J. O'Connor, Kevin L. Stokes, Gabriel Caruntu, John B. Wiley, Leonard Spinu, Jinke Tang

Physics Faculty Publications

NiFe2O4 ultrafine powder with high crystallinity has been prepared through a reverse microemulsion route. The composition in starting solution was optimized, and the resulting NiFe2O4 was formed at temperature of around 550–600 °C, which is much lower than that observed from the solid-state reaction. Magnetic investigation indicates that samples are soft-magnetic materials with low coercivity and with the saturation magnetization close to the bulk value of Ni ferrite.

Self-Assembly Of Fept Nanoparticles Into Nanorings, Weilie L. Zhou, Jibao He, Jiye Fang, Tuyet-Anh Huynh, Trevor J. Kennedy, Kevin L. Stokes, Charles J. O'Connor

Physics Faculty Publications

The application of nanoparticles as quantum dots in nanoelectronics demands their arrangement in ordered arrays. Shape controlled self-assembly is a challenge due to the difficulties of obtaining proper self-assembling parameters, such as solvent concentration, organic ligands, and nanoparticle size. In this article, hard magnetic FePt nanoparticles were synthesized using a combination approach of reduction and thermal decomposition. The nanoparticles are about 4.5 nm and appeared as truncated octahedral enclosed by the

{100} and {111}

crystal facets of fcc structure. The nanoparticles are of hexagonal close packing and orient randomly in the self-assembly nanoarrays. By diluting the solution for large-area self-assembly, …

Mim And Nonlinear Least-Squares Inversions Of Aem Data In Barataria Basin, Louisiana, Melissa Whitten Bryan, Kenneth W. Holladay, Clyde J. Bergeron Jr., Juliette W. Ioup, George E. Ioup

Physics Faculty Publications

An airborne electromagnetic survey was performed over the marsh and estuarine waters of the Barataria basin of Louisiana. Two inversion methods were applied to the measured data to calculate layer thicknesses and conductivities: the modified image method (MIM) and a nonlinear least-squares method of inversion using two two-layer forward models and one three-layer forward model, with results generally in good agreement. Uniform horizontal water layers in the near-shore Gulf of Mexico with the fresher (less saline, less conductive) water above the saltier (more saline, more conductive) water can be seen clearly. More complex near-surface layering showing decreasing salinity/conductivity with depth …

Kerr-Resonance-Condition-Coupled Enhancement In Magneto-Optic Media, A. De, A. Puri

Physics Faculty Publications

We derive an expression for cyclotron frequency ω_c, which sets Re[ϵ₊ϵ₋]=1 in a magneto-optic (MO) substrate, at any incident photon energy. Thereby, at any desired part of the optical spectrum, large Kerr effects can be obtained, which are generally known to occur either at the free-charge-carrier-plasma-resonance frequency ω_p, or at frequencies where active electronic transitions take place. Under these conditions, ω_p is seen to play a very different role; it is seen that for any ω, the magnitude of the Kerr resonance in a single MO (InSb here) substrate increases …

The Ionizing Efficiency Of The First Stars, Aparna Venkatesan, James W. Truran

Physics and Astronomy

We investigate whether a single population of first stars could have influenced both the metal enrichment and reionization of the high-redshift intergalactic medium (IGM), by calculating the generated ionizing radiation per unit metal yield as a function of the metallicity of stellar populations. We examine the relation between the ionizing radiation and carbon created by the first stars, since the evidence for the widespread enrichment of the IGM at redshifts z about 3-4 comes from the detection of C IV absorption. We find that the number of ionizing photons per baryon generated in association with the detected IGM metallicity may …