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Science On The Great Plains: The History Of Physics And Astronomy At The University Of Nebraska-Lincoln, M. Eugene Rudd Jan 1992

Science On The Great Plains: The History Of Physics And Astronomy At The University Of Nebraska-Lincoln, M. Eugene Rudd

M. Eugene Rudd Publications

The year 1988 marked the 100th anniversary of the founding of the Department of Physics at the University of Nebraska. While the year passed without fanfare in the department, DuaneJaecks, one of the members of the faculty, suggested to the author that it would be a good time to write a history of what is now the Department of Physics and Astronomy. He not only provided the initial impetus for the project, but has also given it his continual help and encouragement. While the initial plan was to write only a brief, informal departmental history, the project, like Topsy, grew. …

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Spatial Correlation Between Ch, Cn And The Diffuse Interstellar Band Carriers, J Krelowski, T P. Snow, C G. Seab, J Papaj Jan 1992

Spatial Correlation Between Ch, Cn And The Diffuse Interstellar Band Carriers, J Krelowski, T P. Snow, C G. Seab, J Papaj

Physics Faculty Publications

Observations are presented of the diffuse interstellar bands at 5780 and 5797 A and of the ultraviolet lines of CH and CN in the light of six bright stars which lie behind isolated interstellar clouds. It is found that CN and CH are only present when the 5797 band is deeper than the 5780 one. Comparisons with satellite measurements of the UV extinction show that the shape of the extinction curve is linked to the same band ratio in these stars. The results support a previous suggestion that the various components of the absorption spectrum of an isolated cloud (the …

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Unitary One Matrix Models: String Equation And Flows, Konstantinos N. Anagnostopoulos, Mark Bowick Jan 1992

Unitary One Matrix Models: String Equation And Flows, Konstantinos N. Anagnostopoulos, Mark Bowick

Physics - All Scholarship

We review the Symmetric Unitary One Matrix Models. In particular we discuss the string equation in the operator formalism, the mKdV flows and the Virasoro Constraints. We focus on the -function formalism for the flows and we describe its connection to the (big cell of the) Sato Grassmannian Gr (0) via the Plucker embedding of Gr (0) into a fermionic Fock space. Then the space of solutions to the string equation is an explicitly computable subspace of Gr (0) \Theta Gr (0) which is invariant under the flows.

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Translational Correlations In The Vortex Array At The Surface Of A Type-Ii Superconductor, M. Cristina Marchetti, David R. Nelson Jan 1992

Translational Correlations In The Vortex Array At The Surface Of A Type-Ii Superconductor, M. Cristina Marchetti, David R. Nelson

Physics - All Scholarship

We discuss the statistical mechanics of magnetic flux lines in a finite-thickness slab of type-II superconductor. The long wavelength properties of a flux-line liquid in a slab geometry are described by a hydrodynamic free energy that incorporates the boundary conditions on the flux lines at the sample's surface as a surface contribution to the free energy. Bulk and surface weak disorder are modeled via Gaussian impurity potentials. This free energy is used to evaluate the two-dimensional structure factor of the flux-line tips at the sample surface. We find that surface interaction always dominates in determining the decay of translational correlations …

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Empirical Relations Between Static And Dynamic Exponents For Ising Model Cluster Algorithms, Paul D. Coddington, Clive F. Baillie Jan 1992

Empirical Relations Between Static And Dynamic Exponents For Ising Model Cluster Algorithms, Paul D. Coddington, Clive F. Baillie

Physics - All Scholarship

We have measured the autocorrelations for the Swendsen-Wang and the Wolff cluster update algorithms for the Ising model in 2, 3 and 4 dimensions. The data for the Wolff algorithm suggest that the autocorrelations are linearly related to the specific heat, in which case the dynamic critical exponent zW int,E = α/ν. For the Swendsen-Wang algorithm, scaling the autocorrelations by the average maximum cluster size gives either a constant or a logarithm, which implies that zSW int,E = β/ν for the Ising model.

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Monte Carlo Study Of A Simple Model Bulk-Ice-Ih System: P-T Melting Behavior At Constant Volume, K. Han, Barbara N. Hale Jan 1992

Monte Carlo Study Of A Simple Model Bulk-Ice-Ih System: P-T Melting Behavior At Constant Volume, K. Han, Barbara N. Hale

Physics Faculty Research & Creative Works

An NVT Metropolis Monte Carlo computer simulation is used to examine the P-T behavior of a constant-density model periodic ice-Ih sample near melting. The ice unit cell with density 0.904 g/cm3 consists of 192 rigid water molecules interacting via the revised central-force potentials (RSL2) of Stillinger and Rahman [J. Chem. Phys. 68, 666 (1978)] with a cutoff. Intramolecular parameters are determined from a minimization of the total potential energy of the ice-Ih structure at 0 K. In the P-T plot, emergence of the liquid-solid coexistence region is signaled by a change in sign of dP/dT (when expansion occurs upon …

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Pressure And Temperature Effects On The Energy Of Formation For Silicon Clusters, Sung-Ho Suck Salk, Chen K. Lutrus, Donald E. Hagen, T. Oshiro, Steven M. Beck, Gary L. Loper Jan 1992

Pressure And Temperature Effects On The Energy Of Formation For Silicon Clusters, Sung-Ho Suck Salk, Chen K. Lutrus, Donald E. Hagen, T. Oshiro, Steven M. Beck, Gary L. Loper

Physics Faculty Research & Creative Works

At present most theoretical studies of atomic clusters are limited to their physical properties referred to 0 K. To the best of our knowledge, there exists no theoretical study of the simultaneous dependence of cluster formation and cluster-size distributions on both pressure and temperature. In the present work both pressure and temperature effects on the formation of silicon clusters are explored. A universal semiempirical formula is obtained to show a general trend in the variation of binding energy as a function of cluster size for both atomic and molecular clusters.

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Energetic Protons And Deuterons Emitted Following Μ⁻ Capture By ³He Nuclei, W. J. Cummings, G. E. Dodge, S. S. Hanna, B. H. King, S. E. Kuhn, Y. M. Shin, R. Helmer, R. B. Schubank, N. R. Stevenson, U. Wienands, Y. K. Lee, G. R. Mason, B. E. King, K. S. Chung, J. M. Lee, D. P. Rosenzweig Jan 1992

Energetic Protons And Deuterons Emitted Following Μ⁻ Capture By ³He Nuclei, W. J. Cummings, G. E. Dodge, S. S. Hanna, B. H. King, S. E. Kuhn, Y. M. Shin, R. Helmer, R. B. Schubank, N. R. Stevenson, U. Wienands, Y. K. Lee, G. R. Mason, B. E. King, K. S. Chung, J. M. Lee, D. P. Rosenzweig

Physics Faculty Publications

Spectra of energetic protons and deuterons emitted following negative muon capture from rest in 3He have been measured for the first time. Significant capture strength is observed at high energy transfers (mμ- Ev >60 MeV) for the two-body and three-body breakup channels, indicative of the importance of nucleon-nucleon correlations and meson exchange currents in the capture process. A simple plane wave impulse approximation calculation reproduces the proton spectrum reasonably well, but underpredicts the deuteron rate at the highest energies by a large factor.

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Homogeneous Nucleation Of Liquid From The Vapor Phase In An Expansion Cloud Chamber, John L. Schmitt Jan 1992

Homogeneous Nucleation Of Liquid From The Vapor Phase In An Expansion Cloud Chamber, John L. Schmitt

Physics Faculty Research & Creative Works

A Wilson expansion cloud chamber has been used to measure the homogeneous vapor-to-liquid nucleation of several materials over the past decade. These data, representing nucleation rate as a function of temperature and supersaturation ratio for toluene, nonane, and water measured in our center, have been re-examined and are presented both in graphical form and as a table of selected data points. The latter is included for ease of comparison with theory. Measurements of the binary homogeneous nucleation of ethanol-water (E-W) mixtures are also presented. The expansion chamber experimental technique and data reduction technique are discussed.

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Classical Calculation Of High-Energy Electron Capture In 5-Mev Proton-Hydrogen Collisions, D. R. Schultz, C. O. Reinhold, Ronald E. Olson Jan 1992

Classical Calculation Of High-Energy Electron Capture In 5-Mev Proton-Hydrogen Collisions, D. R. Schultz, C. O. Reinhold, Ronald E. Olson

Physics Faculty Research & Creative Works

The existence of the classical Thomas peak in the angular distribution of projectiles undergoing capture in collisions of 5-MeV protons with atomic hydrogen is explored using the three-body, three-dimensional classical-trajectory Monte Carlo technique. A method that selects only that portion of the initial phase space which yields capture at this energy was developed to make the calculation tractable due to the extremely small cross section. The spectrum obtained displays only a small shoulder near the angle predicted by Thomas on the basis of successive classical binary collisions and the total (integral) cross section is overestimated by a factor of 26 …

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Proteolytic Modification Of The Ca²-Release Mechanism Of Sarcoplasmic Reticulum In Skeletal Muscle, Ute Goerke Jan 1992

Proteolytic Modification Of The Ca²-Release Mechanism Of Sarcoplasmic Reticulum In Skeletal Muscle, Ute Goerke

Dissertations and Theses

Calcium ions are important mediators in the mechanism of contraction and relaxation of muscle fibers. Depolarization of sarcolemma and transverse tubule causes an increase of myoplasmic ca2+ concentration which induces contraction of the myofibrils. In skeletal muscle fibers, the intracellular Ca2+ concentraton is regulated by an extensive membrane system, the sarcoplasmic reticulum (SR). Ca2+-release from SR is initiated by depolarization of the transverse tubule via a process referred to as excitation-contraction coupling. The Ca2+ - release channel located in the junctional SR plays an important role in this mechanism.

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Adsorption Of Halogenated Phenolate Ions To Egg-Phosphatidylcholine Vesicles, Andreas Blochel Jan 1992

Adsorption Of Halogenated Phenolate Ions To Egg-Phosphatidylcholine Vesicles, Andreas Blochel

Dissertations and Theses

In this study, parameters for the adsorption of several halogenated phenolate ions to egg-phosphatidylcholine vesicles have been determined by microelectrophoresis.

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Density Effect In Cu K-Shell Ionization By 5.1-Gev Electrons, W. E. Meyerhof, D. G. Jensen, D. M. Kawall, S. E. Kuhn, D. W. Spooner, Z. E. Meziani, D.. N. Faust Jan 1992

Density Effect In Cu K-Shell Ionization By 5.1-Gev Electrons, W. E. Meyerhof, D. G. Jensen, D. M. Kawall, S. E. Kuhn, D. W. Spooner, Z. E. Meziani, D.. N. Faust

Physics Faculty Publications

We have made an absolute measurement of the Cu K-shell impact ionization cross section by 5.1-GeV electrons, which demonstrates directly a density effect predicted by Fermi in 1940. By determining the ratio of the K x-ray yield from a thin front and back layer of the target by a novel grazing emission method, we have verified the effect of transition radiation on the x-ray production, suggested by Sorensen and reported by Bak et al.

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Principal Linear Polarization States Of An Optical System, R. M.A. Azzam Jan 1992

Principal Linear Polarization States Of An Optical System, R. M.A. Azzam

Electrical Engineering Faculty Publications

The constraint on the Jones matrix of an optical system such that there exist two linear polarization states at its input that are mapped onto two corresponding linear states at its output is derived. These principal linear polarization (PLP) states, which characterize a broad range of systems, are also found in terms of the Jones matrix elements. Special cases when the PLP states are orthogonal, collapse onto one state, or become infinite in number are indicated. For a deterministic or nondeterministic optical system described by a Mueller matrix, the existence of two PLP states places a constraint on only 3 …

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Effect Of Magnetic And Density Fluctuations On The Propagation Of Lower Hybrid Waves In Tokamaks, George Vahala, Linda L. Vahala, Paul T. Bonoli Jan 1992

Effect Of Magnetic And Density Fluctuations On The Propagation Of Lower Hybrid Waves In Tokamaks, George Vahala, Linda L. Vahala, Paul T. Bonoli

Electrical & Computer Engineering Faculty Publications

Lower hybrid waves have been used extensively for plasma heating, current drive, and ramp-up as well as sawteeth stabilization, The wave kinetic equation for lower hybrid wave propagation is extended to include the effects of both magnetic and density fluctuations. This integral equation is then solved by Monte Carlo procedures for a toroidal plasma. It is shown that even for magnetic/density fluctuation levels on the order of 10-4, there are significant magnetic fluctuation effects on the wave power deposition into the plasma. This effect is quite pronounced if the magnetic fluctuation spectrum is peaked within the plasma. For …

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Effect Of Fluctuations On Lower Hybrid Power Deposition And Hard X-Ray Detection, George Vahala, Linda L. Vahala, Paul T. Bonoli Jan 1992

Effect Of Fluctuations On Lower Hybrid Power Deposition And Hard X-Ray Detection, George Vahala, Linda L. Vahala, Paul T. Bonoli

Electrical & Computer Engineering Faculty Publications

The hard X-ray intensity radial profiles from lower hybrid current drive experiments are interpreted as being correlated with fluctuations in the bulk plasma. This view seems to be dictated by comparing the hard X-ray data for various n║ with the Monte Carlo solutions of the lower hybrid wave energy deposition on plasma electrons. Information on internal magnetic fluctuations may, under certain conditions, be unfolded from a n║ scan of the hard X-ray profiles.

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Charge-State Equilibrium And Nonequilibrium Modeling Of The Carbon-Pellet Plasma Interaction, A. G. Elcashlan, G. A. Gerdin, L. L. Vahala, P. B. Parks Jan 1992

Charge-State Equilibrium And Nonequilibrium Modeling Of The Carbon-Pellet Plasma Interaction, A. G. Elcashlan, G. A. Gerdin, L. L. Vahala, P. B. Parks

Electrical & Computer Engineering Faculty Publications

Self-consistent equilibrium and nonequilibrium charge-state models are formulated for the spherical expansion of low-Z pellet vapor as an inviscid perfect gas of constant ratio of specific heats being heated volumetrically by the incident electrons of a thermonuclear plasma. The two models are found to be in agreement in the region where the ratio of the ionization length ζj to pellet radius rp is less than unity, but a single parameter, such as the magnitude of this ratio on the sonic surface, is insufficient to determine whether an equilibrium model will be valid for all regions of the ablatant …

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Schroedinger Equation With Spherically Averaged Potentials, C. A. Hughes Jan 1992

Schroedinger Equation With Spherically Averaged Potentials, C. A. Hughes

Journal of the Arkansas Academy of Science

Using a method adapted from few—body hyperspherical techniques, an approach to the solution of the Schroedinger equation with nonspherical potentials is discussed. The method is to spherically average the potential over spherical angles and then solve the resulting set of coupled differential equations. A discussion of how this method is applied to the Stark effect is presented.

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Development Of A Variable Wavelength Flame Infrared Emission Gas Chromatography Detector, Weiqun Zhang, M. Keith Hudson, Mokhtar Mofidi Jan 1992

Development Of A Variable Wavelength Flame Infrared Emission Gas Chromatography Detector, Weiqun Zhang, M. Keith Hudson, Mokhtar Mofidi

Journal of the Arkansas Academy of Science

No abstract provided.

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Comparison Of Two Models For Breakdown Waves, Debra Burris, Mostafa Hemmati Jan 1992

Comparison Of Two Models For Breakdown Waves, Debra Burris, Mostafa Hemmati

Journal of the Arkansas Academy of Science

In this paper, the two theories concerning the propagation of breakdown waves are compared. The two theories are as follows: 1. The photoionization theory, in which the driving force of the propagation is the electromagnetic radiation from the hot gas generated at the electrode with the greatest potential gradient. 2. The electron fluid dynamical theory, in which the driving force of the propagation is the partial pressure of the high temperature electron gas generated in the neighborhood of the pulsed electrode. Successes in explaining the experimental data will be compared.

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Self-Consistent Determination Of Low-Za Pellet Ablation And Pellet Penetration, Linda L. Vahala, Glenn Gerdin, A. G. El Cashlan, Paul Parks Jan 1992

Self-Consistent Determination Of Low-Za Pellet Ablation And Pellet Penetration, Linda L. Vahala, Glenn Gerdin, A. G. El Cashlan, Paul Parks

Electrical & Computer Engineering Faculty Publications

The ablation dynamics of LiT pellets are solved self-consistently over a modest range of parameters using a surface dissociation model. The self-consistently determined parameters are then used to modify the standard low-Z pellet penetration codes. Since LiT pellets have certain advantages over carbon [in particular, Li conditioning of the walls and T for refueling a D-T reaction], the penetration of LiT into fusion plasmas is considered.

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Electromagnetic Wave Scattering From Magnetic Fluctuations In Tokamaks, L. L. Vahala, G. Vahala, N. Bretz Jan 1992

Electromagnetic Wave Scattering From Magnetic Fluctuations In Tokamaks, L. L. Vahala, G. Vahala, N. Bretz

Electrical & Computer Engineering Faculty Publications

Cross sections are calculated for electromagnetic wave scattering and mode transformation from magnetic and density fluctuations in a homogeneous plasma. For the special case of scattering perpendicular to the magnetic field, density fluctuations scatter ordinary to ordinary and extraordinary to extraordinary modes-but cannot transform these modes. On the other hand, magnetic fluctuations perpendicular to the field can transform modes but cannot scatter on a single branch. For incident frequencies on the order of the electron plasma frequency or gyrofrequency, the cross sections for scattering and transformation due to field and density fluctuations have a similar value. Estimates are given for …

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Competition Between Superconductivity And A New 20 K Phase In -(Bedt-Ttf)2i3: Specific Heat Measurements, Nathanael A. Fortune, K. Murata, K. Ikeda, T. Takahashi Jan 1992

Competition Between Superconductivity And A New 20 K Phase In -(Bedt-Ttf)2i3: Specific Heat Measurements, Nathanael A. Fortune, K. Murata, K. Ikeda, T. Takahashi

Physics: Faculty Publications

We present here direct calorimetric evidence for a new transition at T*=22.25 K in the metallic state of quasi-2D organic superconductor -(BEDT-TTF)2I3 at ambient pressure, as suggested by our previous measurement of the temperature-dependent Hall coefficient RH(T). The apparent reduction in the effective electronic density of states at T* quantitatively explains for the first time the suppression of Tc from the pressure-stabilized eehigh-Tcee value of 8 K to the ambient-pressure cooled eelow-Tcee value of 1.5 K.

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Bounds On The Polymer-Length Distribution In Equilibrium Polymerization, Rolfe G. Petschek Jan 1992

Bounds On The Polymer-Length Distribution In Equilibrium Polymerization, Rolfe G. Petschek

Faculty Scholarship

We obtain upper bounds on the polymer-length distribution in a class of models for equilibrium polymerization. This rules out a recent claim for the existence of a collapsed phase in which a nonzero fraction of the monomers are in infinite polymer(s). We discuss the behavior of finite systems, in which a collapse of sorts does occur, and indicate how this collapse disappears in the thermodynamic limit.

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Plasma As A High-Charge-State Projectile Stripping Medium, G. D. Alton, R. A. Sparrow, Ronald E. Olson Jan 1992

Plasma As A High-Charge-State Projectile Stripping Medium, G. D. Alton, R. A. Sparrow, Ronald E. Olson

Physics Faculty Research & Creative Works

The classical trajectory Monte Carlo model has been used to computationally study the charge-state distributions that result from interactions between a high-energy, multielectron projectile and neutral and fully ionized targets. These studies are designed to determine the properties of a plasma for producing highly stripped ions as a possible alternative to gas and foil strippers that are commonly used to enhance the charge states of energetic ion beams. The results of these studies clearly show that a low-atomic-number, highly ionized plasma can yield higher charge states than a neutral target of the same density. The effect is principally attributable to …

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Track Structure Model For Damage To Mammalian Cell Cultures During Solar Proton Events, Francis A. Cucinotta, J. W. Wilson, L. W. Townsend, J. L. Shinn, Robert Katz Jan 1992

Track Structure Model For Damage To Mammalian Cell Cultures During Solar Proton Events, Francis A. Cucinotta, J. W. Wilson, L. W. Townsend, J. L. Shinn, Robert Katz

Robert Katz Publications

Solar proton events (SPEs) occur infrequently and unpredictably, thus representing a potential hazard to interplanetary space missions. Biological damage from SPEs will be produced principally through secondary electron production in tissue, including important contributions due to delta rays from nuclear reaction products. We review methods for estimating the biological effectiveness of SPEs using a high energy proton model and the parametric cellular track model. Results of the model are presented for several of the historically largest flares using typical levels and body shielding.

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Comment On Ncrp Report No. 104, "The Relative Biological Effectiveness Of Radiations Of Different Quality", Robert Katz Jan 1992

Comment On Ncrp Report No. 104, "The Relative Biological Effectiveness Of Radiations Of Different Quality", Robert Katz

Robert Katz Publications

The validity of a linear extrapolation to lowest fluences of charged particles demands that the transit of a single charged particle through the target volume is capable of inducing the chain of events leading to an observable end-point. This is always the case for one-hit detectors. It is not always the case for biological cells and tissues (Katz and Hofmann 1982).
By way of example, Cole ct al. (1980) found that, on average, some 500 electrons pass into the nucleus of a CHO cell for inactivation. Similarly, Warters et al. (1977) found that some 500 tritium decays in the nucleus …

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Lattice- And Molecular-Dynamics Studies Of Phase Transitions In Csliso4, V. Katkanant Jan 1992

Lattice- And Molecular-Dynamics Studies Of Phase Transitions In Csliso4, V. Katkanant

John R. Hardy Papers

We report results of a simulation of the phase transitions in CsLiSO4. These are based on our previously developed method for calculating parameter-free potential-energy surface for ionic molecular crystals. Our lattice-dynamical and molecular-dynamics studies show that the roomtemperature (Pnam) phase is unstable and transforms to the observed low-temperature (P1121/n) phase over approximately 200–280 K. The unstable modes of the Pnam phase have maximum instability at the zone center, which indicates a possible phase transformation without a cell multiplication. The rotational ordering of tetrahedral SOM4 2- was found to be …

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Phase Transitions In K2Zncl4, H. M. Lu, John R. Hardy Jan 1992

Phase Transitions In K2Zncl4, H. M. Lu, John R. Hardy

John R. Hardy Papers

It is shown that the potential-energy surface in K2ZnCl4 contains a double-well structure, very similar to some of the other A2BX4 compounds (e.g., K2SeO4, Rb2ZnCl4), except that the double well is much deeper and broader, giving rise to a highly disordered high-temperature phase as observed experimentally. A lattice-dynamics study of the Pna21 structure shows an instability with the wave vector q=0.5b*+(0.5±δ)c*, providing an explanation to the incommensurate phase transition reported recently.

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An Attempt To Observe Mott Scattering Optically, J. E. Furst, Timothy J. Gay, W. M. K. P. Wijayaratna, K. Bartschat, H. Geesmann, M. A. Khakoo, D. H. Madison Jan 1992

An Attempt To Observe Mott Scattering Optically, J. E. Furst, Timothy J. Gay, W. M. K. P. Wijayaratna, K. Bartschat, H. Geesmann, M. A. Khakoo, D. H. Madison

Timothy J. Gay Publications

We report an attempt to make an optical observation of Matt scattering, involving the first studies of inelastic collisions between polarized electrons and a heavy noble gas. Polarization fractions of light emitted by the 5p56p[5/7],(3D3) state of Xe following impact excitation in an axial collision geometry were measured as a funclion of the incident electron energy, and compared with distorted-wave Bom calculations. The theoretical and experimental results agree qualitatively in the energy range where cascade contributions to the photon signal are small. We failed to measure non-zero values of the linear polarization fraction η …

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