Digital Commons Network^™

Neutral Dissociation Of Hydrogen Following Photoexcitation Of Hcl At The Chlorine K Edge, D. L. Hansen, J. Cotter, G. R. Fisher, K. T. Leung, R. Martin, Paul Neill, Rupert C. Perera, I. A. Sellin, Marc Simon, Y. Uehara, B. Vanderford, S. B. Whitfield

Chemistry and Biochemistry Faculty Research

Time-of-flight mass spectroscopy was used to study the relaxation dynamics of HCl following photoexcitation in the vicinity of the Cl K edge (~2.8 keV) using monochromatic synchrotron radiation. At the lowest resonant excitation to the 6ơ* antibonding orbital, almost half of the excited molecules decay by emission of a neutral H atom, mostly in coincidence with a highly charged Cln1 ion. The present work demonstrates that neutral-atom emission can be a significant decay channel for excited states with very short lifetimes (1 fs). [S1050-2947(98)03604-X]

Electrophoretic Deposition Of Polymer Chains On An Adsorbing Surface In (2+1) Dimensions: Conformational Anisotropy And Nonuniversal Coverage, Grace M. Foo, Ras B. Pandey

Faculty Publications

Electrophoretic deposition of polymer chains flowing in a (2 + 1)-dimensional system is studied by computer simulations. Steady-state surface coverage θ_j is found to decay with the chain's length, i.e., θ_j∼L_c^-a with a nonuniversal exponent α≃0.0-0.9 depending on the magnitude of driving field and temperature. Conformational crossover occurs for chains from a surface or wall to an adjacent bulk region with different scaling exponents for their longitudinal and transverse spread.

Measurement Of The Branching Fractions Of ΛC+→Pk̅N (Π), M. S. Alam, Kenneth A. Bloom, Cleo Collaboration

Kenneth Bloom Publications

Using data recorded by the CLEO-II detector at CESR, we report new measurements of the branching fractions for the decays of the charmed baryon Λ_c⁺ into pK^-π⁺π⁰, pK⁰, pK⁰π⁺π^-, and pK⁰π⁰, all measured relative to pK^-π⁺. The relative branching fractions are 0.67±0.04±0.11,0.46±0.02±0.04,0.52±0.04±0.05, and 0.66±0.05±0.07, respectively.

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.

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

Solvable Model Of Two-Dimensional Dilaton Gravity Coupled To A Massless Scalar Field, Marco Cavaglia

Physics Faculty Research & Creative Works

We present a solvable model of two-dimensional dilaton-gravity coupled to a massless scalar field. We locally integrate the field equations and briefly discuss the properties of the solutions. For a particular choice of the coupling between the dilaton and the scalar field the model can be interpreted as the two-dimensional effective theory of 2+1 cylindrical gravity minimally coupled to a massless scalar field.

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 …

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.

The Effects Of Fabry-Perot Fringing On The Sensitivity Of A Wavelength Modulation Experiment, Patrick C. Shea

Electrical & Computer Engineering Theses & Dissertations

Parasitic Fabry-Perot etaloning plagues many experiments which use wavelength modulation spectroscopy. This fringing, which is an artifact that almost always appears in such experiments, arises from multiple reflections in the optical elements in the experimental apparatus. The etaloning plays a detrimental role and limits the ultimate sensitivity of wavelength modulation spectroscopy experiments. The research described in this thesis investigates this phenomenon. Experimental results are presented which show that when the Q-factor of the parasitic etalon is smaller that that of the absorption line being measured, significant improvement in the Signal to Fringe Noise Ratio can be obtained through the use …

Perc Report 1998 - Research In Physics Education Group, University Of Nebraska - Lincoln

Research in Physics Education Group

The work of the University of Nebraska-Lincoln Research in Physics Education Group has two main thrusts. One is to examine student reasoning and the other is to use multiple forms of media to improve the teaching and learning of physics. Multiple projects are underway in the summer of 1998 which are related to these interests.

Synthesis, Molecular Structure, And Reactivity Of Dinuclear Copper(Ii) Complexes With Carboxylate-Rich Coordination Environments, Richard C. Holz, John M. Bradshaw, Brian Bennett

Physics Faculty Research and Publications

The dinucleating ligand N,N‘-(2-hydroxy-5-methyl-1,3-xylylene)bis(N-(carboxymethyl)glycine) (CH₃HXTA) has been used to synthesize the dinuclear Cu(II) bis(pyridine) complex Na[Cu₂(CH₃HXTA)(Py)₂]·1.5(1,4-dioxane) (Na(1)):  triclinic space group P1̄ (a = 12.550(3) Å, b = 13.413(3) Å, c = 13.540(4) Å, α = 117.12(2)°, β = 104.70 (2)°, and γ = 92.13(2)°). The structure shows two distinct distorted square pyramidal Cu(II) centers with each Cu(II) ion bound by two carboxylate oxygen atoms, one amine nitrogen atom, a phenolate oxygen atom, and one pyridine nitrogen atom. The Cu--Cu separation is 3.531 Å, …

Valence Intersubband Lasers With Inverted Light-Hole Effective Mass, Greg Sun, Y. Lu, Jacob B. Khurgin

Physics Faculty Publications

We propose a novel intersubband laser based on transition between the ground-state heavy-hole subband (HH1) and light-hole subband (LH1) in a k-space region where the light-hole effective mass is inverted. The laser structure can be electrically pumped with a simple quantum cascade scheme. Our calculation shows that with only a small fraction of the carrier population in the upper subband (LH1), it is possible to achieve population inversion between the two subbands locally in K space where the light-hole effective mass is inverted. Optical gain in excess of 150/cm can be achieved with a pumping current density on the …

Evolution Of A Plasma Waveguide Created During Relativistic-Ponderomotive Self-Channeling Of An Intense Laser Pulse, Shouyuan Chen, G.S. Sarkisov, Anatoly Maksimchuk, R. Wagner, Donald P. Umstadter

Donald Umstadter Publications

An on-axis plasma density depression channel was observed during and after the passage of a relativistically and ponderomotively self-guided laser pulse through a plasma. Optical interferometry was used to produce time-resolved plasma density distributions, revealing the formation of a plasma waveguide. These results were complemented by the guiding of a collinear trailing pulse.

Amplification Of High-Order Rainbows Of A Cylinder With An Elliptical Cross Section, James A. Lock, Charles L. Adler, Bradley R. Stone, Patrick D. Zajak

Physics Faculty Publications

The intensity of high-order rainbows for normally incident light and certain rotation angles of a cylinder with an elliptical cross section is greatly amplified with respect to the intensity for a circular cross-sectional cylinder. The amplification is due to a number of the internal reflections occurring past the critical angle for total internal reflection, and the effect is especially strong for odd-order rainbows, beginning with the third order. Experimentally, the fourth-and the fifth-order rainbows of a nearly elliptical cross-sectional glass rod were observed and analyzed. (C) 1998 Optical Society of America.

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 …

Ray Theory Analysis Of The Shadow Blister Effect, James A. Lock

Physics Faculty Publications

When an extended light source such as the Sun illuminates two objects so that their shadows lie close to each other, the shadow of one of the objects occasionally appears to bulge out toward the shadow of the other. This effect is caused by the overlap of the penumbras of the shadows and is analyzed here with ray theory. A laboratory demonstration of this phenomenon is performed and compared with theoretical predictions. (C) 1998 Optical Society of America.

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 …}

Computer Intensive Physics, Robert Fuller

Robert G. Fuller Publications

In the abstract packet for the conference is an article of references about ideas from cognitive studies that help us teach physics (Fuller, 1998). There is also a pamphlet of references to innovative physics teaching programs in the United States and many of those programs have world-wide web sites so you can access information about those programs from Portugal (O'Kuma, 1998).

I want to talk about my research project last year, which I now call "Computer Intensive Physics", but it really started out as paper-less physics.

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.

Ampte/Cce‐Scatha Simultaneous Observations Of Substorm‐Associated Magnetic Fluctuations, S. Ohtani, K. Takahashi, T. Higuchi, A. T. Y. Lui, Harlan E. Spence, J. F. Fennell

Physics & Astronomy

This study examines substorm-associated magnetic field fluctuations observed by the AMPTE/CCE and SCATHA satellites in the near-Earth tail. Three tail reconfiguration events are selected, one event on August 28, 1986, and two consecutive events on August 30, 1986. The fractal analysis was applied to magnetic field measurements of each satellite. The result indicates that (1) the amplitude of the fluctuation of the north-south magnetic component is larger, though not overwhelmingly, than the amplitudes of the other two components and (2) the magnetic fluctuations do have a characteristic timescale, which is several times the proton gyroperiod. In the examined events the …

Full-Wave Modeling Of Small-Scale Gravity Waves Using Airborne Lidar And Observations Of The Hawaiian Airglow (Aloha-93) O(1s) Images & Coincident Na Wind/Temperature Lidar Measurements, M. P. Hickey, Michael J. Taylor, C. S. Gardner, C. R. Gibbons

All Physics Faculty Publications

Measurements were made of mesospheric gravity waves in the OI (5577 Å) nightglow observed from Maui, Hawaii, during the Airborne Lidar and Observations of Hawaiian Airglow (ALOHA-93) campaign. Clear, monochromatic gravity waves were observed on several nights. By using a full-wave model that realistically includes the major physical processes in this region, we have simulated the propagation of four waves through the mesopause region and calculated the O(1 S) nightglow response to the waves. Mean winds derived from Na wind/temperature lidar observations were employed in the computations. Wave amplitudes were calculated based on the requirement that the observed and simulated …

Observational Limits For Lidar, Radar And Airglow Imager Measurements Of Gravity Wave Parameters, C. S. Gardner, Michael J. Taylor

All Physics Faculty Publications

By examining the observational limits and biases for lidar, radar, and airglow imager measurements of middle atmosphere gravity waves, we provide plausible explanations for the characteristics of the monochromatic wave parameters that have been reported during the past decade. The systematic dependencies of vertical and horizontal wavelength on wave period, reported in many lidar and some radar studies, are associated with diffusive damping. The prominent waves with the largest amplitudes, most often observed by lidars and radars, are those with vertical phase speeds near the diffusive damping limit. The narrow range of horizontal phase velocities of the waves seen by …

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 …

Joint Wavelet Transform Correlation With Separated Target And Reference Planes, Boon Yi Soon, Mohammad A. Karim, Russell C. Hardie, Mohammad S. Alam

Electrical and Computer Engineering Faculty Publications

In recent years, we realize the usefulness of feature extraction for optical correlator and hereby, we investigate the capability of Laplace operator in feature extraction of multiple targets. The first-order terms and the false alarm terms in the correlation output would be removed using electronic power spectrum subtraction technique. Most importantly, the entire magneto-optic SLM is completely utilized for displaying only targets in the input scene. A new cost efficient hardware implementation is proposed and aforementioned result of the proposed system is evaluated through computer simulation.

Numerical Analysis Of Bose-Einstein Condensation In A Three-Dimensional Harmonic Oscillator Potential, Martin K. Ligare

Faculty Journal Articles

Bose–Einstein condensation is the anomalous accumulation of particles in the ground state of a system of bosons, when compared with the population in a system of particles obeying classical statistics. I use undergraduate-level statistical mechanics and a symbolic algebra computer program to study the occupation numbers of the energy levels of a finite number of noninteracting particles confined in a three-dimensional harmonic oscillator potential. I also calculate the heat capacity of the gas. The harmonic oscillator potential simplifies the calculations and approximates the conditions of the recent experiments achieving Bose–Einstein condensation in laser-cooled alkali vapors.

Double Photoionization Of Helium, James A.R. Samson, Wayne C. Stolte, Z. X. He, Y. Lu, J. N. Cutler, R. J. Bartlett

Chemistry and Biochemistry Faculty Research

The cross sections for double photoionization of helium and the ratios of double to single ionization have been measured from the double-ionization threshold to 820 eV. The results are in very good agreement with several recent calculations.