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Radiative Transfer In Astronomical Masers. Iii. Filamentary Masers, Moshe Elitzur, Christopher F. Mckee, David J. Hollenbach Jan 1991

Radiative Transfer In Astronomical Masers. Iii. Filamentary Masers, Moshe Elitzur, Christopher F. Mckee, David J. Hollenbach

Physics and Astronomy Faculty Publications

This paper, the last in a series, presents the complete solution of a filamentary maser. The contribution of rays emanating from the filament sidewall is essential for the solution self-consistency during saturation. We develop an integral equation to calculate this contribution, devise an iteration scheme to solve it, and perform the first two iterations. The solution provides complete expressions for the distributions of intensity and flux across the source as functions of position and direction with regard to the axis. One consequence of radiation beaming, somewhat surprising at first, is that the filament appears smaller when viewed off-axis, at angles …

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Gaussian Reference Auid And Interpretation Of Quantum Geometrodynamics, Karel V. Kucha, Charles G. Torre Jan 1991

Gaussian Reference Auid And Interpretation Of Quantum Geometrodynamics, Karel V. Kucha, Charles G. Torre

Aerospace, Physics, and Space Science Faculty Publications

The of vacuum geometrodynamics is turned into a Schrödinger equation by imposing the normal Gaussian coordinate conditions with s and then restoring the coordinate invariance of the action by parametrization. This procedure corresponds to coupling the gravitational field to a reference fluid. The source appearing in the Einstein law of gravitation has the structure of a heat-conducting dust. When one imposes only the Gaussian time condition but not the Gaussian frame conditions, the heat flow vanishes and the dust becomes incoherent. The canonical description of the fluid uses the Gaussian coordinates and their conjugate momenta as the fluid variables. The …

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Anomaly In The Dynamic Behavior Of The Electroclinic Effect Below The Nematicsmectic-A Phase Transition, Zili Li, Robert B. Akins, Gregory A. Dilisi, Charles Rosenblatt, Rolfe G. Petschek Jan 1991

Anomaly In The Dynamic Behavior Of The Electroclinic Effect Below The Nematicsmectic-A Phase Transition, Zili Li, Robert B. Akins, Gregory A. Dilisi, Charles Rosenblatt, Rolfe G. Petschek

Faculty Scholarship

The electroclinic effect and dielectric response have been investigated in the British Drug House material SCE12 over its entire 15-K smectic-A range. Near the smectic-Asmectic-C*-phase transition both the electroclinic coefficient and dynamic response behave normally, the former diverging and the latter exhibiting a critical slowing down on approaching TA-C* from above. Similar behavior is seen in the dielectric response. Approximately 10 to 12 K above TA-C*, however, it was found that the electroclinic relaxation time levels off and even begins to increase again on approaching the nematicsmectic-A transition from below. The magnitude of the electroclinic coefficient, however, decreases monotonically on …

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Composite Operator Renormalization And The Trace Anomaly, David G. Robertson Jan 1991

Composite Operator Renormalization And The Trace Anomaly, David G. Robertson

Physics Faculty Scholarship

The general connection between the renormalization of elementary fields and couplings and of appropriate composite operators is discussed. A general method is presented for computing the anomalous dimension matrix of the lagrangian composite operators, to all orders in perturbation theory, in terms of the elementary beta functions and anomalous dimensions. The trace anomaly for a general field theory is determined.

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A Search For Embedded Young Stellar Objects In And Near The Ic 1396 Complex, Richard Schwartz, Bruce Wilking, Armen Giulbudagian Jan 1991

A Search For Embedded Young Stellar Objects In And Near The Ic 1396 Complex, Richard Schwartz, Bruce Wilking, Armen Giulbudagian

Physics Faculty Works

The IRAS data base is used to locate young stellar object candidates in and near the IC 1396 complex located in the Cepheus OB2 association. Co-added survey data are used to identify all sources with a flux density Snu(100) greater than 10 Jy and with Snu(100) greater than Snu(60). The 15 sources located at the positions of globules and dark clouds are further analyzed using the in-scan slices to assess the source profiles

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Resistivity And Thermoelectric-Power Measurements Of PrXY1-XBa2Cu3O7-Δ Up To 1200 K And An Electronic-Structure Analysis, B. Fisher, J. Genossar, L. Patlagan, J. Ashkenazi Jan 1991

Resistivity And Thermoelectric-Power Measurements Of PrXY1-XBa2Cu3O7-Δ Up To 1200 K And An Electronic-Structure Analysis, B. Fisher, J. Genossar, L. Patlagan, J. Ashkenazi

Physics Articles and Papers

We report measurements of absolute thermoelectric power and resistivity in PrxY1-xBa2Cu3O7-δ, as function of x and δ, over a wide temperature range. At high temperature, the substitution of Pr for Y does not affect the thermopower and resistivity; Pr behaves then as a trivalent ion: Pr3+. For small x and δ the effects of substitution of Y by Pr and of oxygen deficiency on the low-temperature resistivity are additive. A simple electronic-structure model is proposed to account for thermopower as function of temperature, x, and δ.

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Flux States For The Infinite-U Limit Of The Hubbard Model, S. E. Barnes Jan 1991

Flux States For The Infinite-U Limit Of The Hubbard Model, S. E. Barnes

Physics Articles and Papers

For finite doping, δ, relative to half filling, it is shown, within the confines of a mean-field auxiliary-operator formulation, for the strictly infinite-U, i.e., J=0, limit of the two-dimensional Hubbard model, that the spinons generate a fictitious magnetic flux to which holons are subject and vice versa. For small doping, a flux state is the absolute ground state and has 1-δ=2p/q, where p/q is a rational fraction and the flux per plaquette is Φ=(p/q)Φ0, where Φ0 is the flux quantum. This phenomenon can be viewed upon as an all-electron Peierls instability or as broken statistical symmetry.

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Nonequilibrium Processes In Polymers Undergoing Interchange Reactions. Part 2: Reaction-Diffusion Processes, Alejandro Garcia, J. Pojman, D. Kondepudi, C. Van De Broeck Jan 1991

Nonequilibrium Processes In Polymers Undergoing Interchange Reactions. Part 2: Reaction-Diffusion Processes, Alejandro Garcia, J. Pojman, D. Kondepudi, C. Van De Broeck

Faculty Publications

A reactiodffusion system of polymers undergoing interchange reactions is studied. The equation that describes the dynamics of the system is similar to the Boltzmann equation for a gas of hard spheres. We consider a one-dimensionsl system in which the average length and the concentrations at the boundaries are fixed. The resulting steady states are obtained analytically and with numerical integration of equations obtained by using a local equilibrium approximation. Monte Carlo simulations of experimentally realizable conditions were performed and compared. The results reveal a nonlinear distribution of molecular concentration and mass. The entropy of the polymer distributions is calculated as …

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Silicon (2p) Surface Core-Level Line Shape Of Si(111)—B, J. E. Rowe, G. K. Wertheim, D. Mark Riffe Jan 1991

Silicon (2p) Surface Core-Level Line Shape Of Si(111)—B, J. E. Rowe, G. K. Wertheim, D. Mark Riffe

All Physics Faculty Publications

Several recent structural studies of the Si(111)–B ((3)1/2×(3)1/2) surface have established that the boron atoms occupy substitutional sites in the second full Si layer and have Si adatoms directly above them. High‐resolution (∼80–100 meV) Si(2p) core‐level photoemission was used to determine the B‐induced perturbation of the surface Si atoms. The samples were prepared by surface segregation from Si(111) wafers (∼1.5 at. % B) after thermally removing the thin protective oxide layer on the surface. Photoemission spectra for photon energies from 110 to 140 eV show three peaks, indicative of at least two well‐separated spin‐orbit …

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Modeling Radon Transport And Entry, Michael John Bergmann Jan 1991

Modeling Radon Transport And Entry, Michael John Bergmann

Honors Theses, 1963-2015

Techniques and devices for measuring the emanation power and permeabdity of soil samples are developed. A Monte Carlo simulation is used to model the transport of radon to 112 basements in Minnesota. Correlation between this model and the measured indoor radon concentration is compared to other leading models' correlations. This model has been found to have the strongest correlation.

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A Deformation Theory Of Self-Dual Einstein Spaces, Charles G. Torre Jan 1991

A Deformation Theory Of Self-Dual Einstein Spaces, Charles G. Torre

All Physics Faculty Publications

The self-dual Einstein equations on a compact Riemannian 4-manifold can be expressed as a quadratic condition on the curvature of an $SU(2)$ (spin) connection which is a covariant generalization of the self-dual Yang-Mills equations. Local properties of the moduli space of self-dual Einstein connections are described in the context of an elliptic complex which arises in the linearization of the quadratic equations on the $SU(2)$ curvature. In particular, it is shown that the moduli space is discrete when the cosmological constant is positive; when the cosmological constant is negative the moduli space can be a manifold the dimension of which …

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Harmonic Gauge In Canonical Gravity, K. V. Kuchal, Charles G. Torre Jan 1991

Harmonic Gauge In Canonical Gravity, K. V. Kuchal, Charles G. Torre

All Physics Faculty Publications

The Isham-Kuchař representation theory of the spacetime diffeomorphism group in canonical geometrodynamics is implemented in the context of harmonic coordinate conditions. The representation is carried by either an extended phase space, consisting of the cotangent bundle over the space of three-metrics, spacelike embeddings, and Lagrange multipliers which serve to enforce the harmonic gauge in the action, or by a reduced space in which the multipliers are eliminated. The approach used here is applicable to any generally covariant theory and to any coordinate conditions. The physical interpretation of the diffeomorphism Hamiltonians is discussed and compared with the analogous interpretation given by …

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Field-Aligned Current Associated With A Distorted Two-Cell Convection Pattern During Northward Interplanetary Magnetic Field, Lie Zhu, Robert W. Schunk, Jan Josef Sojka Jan 1991

Field-Aligned Current Associated With A Distorted Two-Cell Convection Pattern During Northward Interplanetary Magnetic Field, Lie Zhu, Robert W. Schunk, Jan Josef Sojka

All Physics Faculty Publications

A systematic study of the influence of the ionospheric conductance on the field-aligned current associated with a distorted two-cell convection pattern during northward interplanetary magnetic field (IMF) has been conducted. Our modeling results indicate that the NBZ current can be associated with the distorted two-cell convection for most of the ionospheric conductivity conditions. It is shown that the conductivity conditions related to the seasonal variation and the aurora activity can significantly influence the basic features of the field-aligned current associated with a distorted two-cell convection pattern. It is found that the increase of the field-aligned current in the polar cap …

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Ionospheric Physics, Jan Josef Sojka Jan 1991

Ionospheric Physics, Jan Josef Sojka

All Physics Faculty Publications

The author has taken a parochial view of the subject matter
under the title of ionospheric physics. Physics is used as the
key to separating this section of the aeronomy review from the
other aeronomy reports. Specifically, work categorized as
chemistry, optical emissions, and thermosphere will not be
reviewed in this section. However, coupling to the
thermosphere and more specifically to the magnetosphere is
considered. A brief section is also included on active
experiments which is a productive area in plasma physics and
also to some extent in ionospheric physics, but one that has
fallen on hard times with regard …

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Revised Global Model Of Thermosphere Winds Using Satellite And Ground-Based Observations, A E. Hedin, M A. Biondi, R G. Burnside, G Hernandez, R M. Johnson, T L. Killeen, C Mazaudier, J W. Meriwether, J E. Salah, R W. Smith, N W. Spencer, Vincent B. Wickwar, T S. Virdi Jan 1991

Revised Global Model Of Thermosphere Winds Using Satellite And Ground-Based Observations, A E. Hedin, M A. Biondi, R G. Burnside, G Hernandez, R M. Johnson, T L. Killeen, C Mazaudier, J W. Meriwether, J E. Salah, R W. Smith, N W. Spencer, Vincent B. Wickwar, T S. Virdi

All Physics Faculty Publications

Thermospheric wind data obtained from the Atmosphere Explorer E and Dynamics Explorer 2 satellites have been combined with wind data for the lower and upper thermosphere from ground-based incoherent scatter radar and Fabry-Perot optical interferometers to generate a revision (HWM90) of the HWM87 empirical model and extend its applicability to 100 km. Comparison of the various data sets with the aid of the model shows in general remarkable agreement, particularly at mid and low latitudes. The ground-based data allow modeling of seasonal/diurnal variations, which are most distinct at mid latitudes. While solar activity variations are now included, they are found …

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Onset Of Convection For Autocatalytic Reaction Fronts: Laterally Unbounded System, Boyd F. Edwards, J. W. Wilder, K. Showalter Jan 1991

Onset Of Convection For Autocatalytic Reaction Fronts: Laterally Unbounded System, Boyd F. Edwards, J. W. Wilder, K. Showalter

All Physics Faculty Publications

The linear stability of exothermic autocatalytic reaction fronts that convert unreacted fluid into a lighter reacted fluid is considered using the viscous thermohydrodynamic equations. For upward front propagation and a thin front, the discontinuous jump in density at the front is reminiscent of the Rayleigh-Taylor problem of an interface between two immiscible fluids, whereas the vertical thermal gradient near the front is reminiscent of the Rayleigh-Bénard problem of a fluid layer heated from below. The problem is also similar to flame propagation, except that here the front propagation speed is limited by catalyst diffusion rather than by activation kinetics. For …

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Pretransitional Optical Activity In Chiral Smectic Liquid Crystals, K. C. Frame, J. L. Walker, Peter J. Collings Jan 1991

Pretransitional Optical Activity In Chiral Smectic Liquid Crystals, K. C. Frame, J. L. Walker, Peter J. Collings

Physics & Astronomy Faculty Works

Pretransitional optical activity measurements in smectic liquid crystals of both law and high chirality are reported. In the low chirality sample, p-(n-(decyloxybenzylidene)-p-amino-(2-methylbutyl)cin-namate (DOBAMBC), the results indicate that the optical activity in both the isotropic phase just above the smectic A phase and in the smectic A phase just above the smectic C* phase can be explained in terms of a Landau-deGennes free energy with no coupling between the chiral modes. In the high chirality sample, 1-methylheptyl 4′-[(4″-tetradecyloxyphenyl)propioloyloxy]biphenyl-4-carboxylate (14P|M7), the data in the isotropic phase above the recently discovered smectic A* phase cannot be explained in this way, even when coupling …

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A Comparison Of Pressure Induced And Concentration Induced Smectic A-Nematic-Isotropic Triple Points, J. L. Walker, Peter J. Collings Jan 1991

A Comparison Of Pressure Induced And Concentration Induced Smectic A-Nematic-Isotropic Triple Points, J. L. Walker, Peter J. Collings

Physics & Astronomy Faculty Works

No abstract provided.

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Exact And Asymptotic Scaling Solutions For Fragmentation With Mass Loss, M. Cai, Boyd F. Edwards, H. Han Jan 1991

Exact And Asymptotic Scaling Solutions For Fragmentation With Mass Loss, M. Cai, Boyd F. Edwards, H. Han

All Physics Faculty Publications

Exact and asymptotic solutions to a linear rate equation for fragmentation with mass loss are presented. Solutions for spatially discrete random bond annihilation illustrate the mutual exclusiveness of the fragmentation and recession terms in the rate equation. Exact solutions for deterministic equal fragment recession show that continuous mass loss between fragmentation events can be approximated by discrete mass loss during fragmentation events when this mass loss is small. Evidence that continuous and discrete mass loss preclude shattering mass loss, the loss of mass to zero-mass particles due to runaway fragmentation, is presented. General asymptotic scaling forms, general solutions reflecting arbitrary …

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Raman Scattering And Lattice-Dynamical Calculations Of Alkali-Metal Sulfates, D. Liu, H. M. Lu, John R. Hardy, F. G. Ullman Jan 1991

Raman Scattering And Lattice-Dynamical Calculations Of Alkali-Metal Sulfates, D. Liu, H. M. Lu, John R. Hardy, F. G. Ullman

John R. Hardy Papers

Raman-scattering measurements on single crystals of K2SO4, Rb2SO4, and Cs2SO4 have been made at both room and liquid-nitrogen temperatures. Lattice-dynamical calculations, based on a rigid-ion model using the Gordon-Kim method to calculate the short-range potentials, were performed. The influence of the alkali-metal ions on the lattice-dynamical properties of the crystals is discussed.

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Cellular Track Model Of Biological Damage To Mammalian Cell Cultures From Galactic Cosmic Rays, Francis A. Cucinotta, Robert Katz, John W. Wilson, Lawrence W. Townsend, John E. Nealy, Judy L. Shinn Jan 1991

Cellular Track Model Of Biological Damage To Mammalian Cell Cultures From Galactic Cosmic Rays, Francis A. Cucinotta, Robert Katz, John W. Wilson, Lawrence W. Townsend, John E. Nealy, Judy L. Shinn

Robert Katz Publications

The quality factor (QF) as defined in International Commission on Radiological Protection report no. 26 (ICRP 26, ref. 1) or in International Commission on Radiation Units and Measurements report no. 40 (ICRU 40, ref. 2) is not expected to be a valid method for assessing the biological risk for deep space missions where the high-energy heavy ion (HZE) particles of the galactic cosmic rays (GCR) are of major concern. No human data for cancer induction from the HZE particles exist, and information on biological effectiveness is expected to be taken from experiments with animals and cultured cells (ref. 3). Experiments …

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The Quantum Magneto Effect Of Bismuth, Omar Kerem Durdag Jan 1991

The Quantum Magneto Effect Of Bismuth, Omar Kerem Durdag

Honors Theses, 1963-2015

Using a standard field modulation technique, the de Haas-van Alphen effect was measured in bismuth for various crystal orientations. Measurements performed using a d.c. magnetic field that was ramped up from -0.05 T to -0.6 T at 4.2 K with a w.01 T modulating field. Data shows a variation of dHvA period with orientation that is in good agreement with the results of Bhargava'.

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The Photorefractive Effect In Batio3, Tom Savard Jan 1991

The Photorefractive Effect In Batio3, Tom Savard

Honors Theses, 1963-2015

The photorefractive effect was observed in a sample of BaTiO, crystal. In two-beam coupling experiments, the crystal failed to amplify the signal beam even though experimental configurations that provided other researchers with large gains were used. However, beam fanning, a two-beam coupling effect, was observed. The unmeasurable gain of our crystal in twc-beam coupling experiments might be due to multiple domains in the crystal or competition between hole and electron charge carriers. In addition, a self-pumped phase conjugate mirror was made using the "cat" configuration. The formation of the phase conjugate mirror in the crystal was observed using the image …

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The Solution Space Of The Unitary Matrix Model String Equation And The Sato Grassmannian, Konstantinos N. Anagnostopoulos, Mark Bowick, Albert Schwarz Jan 1991

The Solution Space Of The Unitary Matrix Model String Equation And The Sato Grassmannian, Konstantinos N. Anagnostopoulos, Mark Bowick, Albert Schwarz

Physics - All Scholarship

The space of all solutions to the string equation of the symmetric unitary one-matrix model is determined. It is shown that the string equation is equivalent to simple conditions on points V 1 and V 2 in the big cell Gr (0) of the Sato Grassmannian Gr. This is a consequence of a well-defined continuum limit in which the string equation has the simple form [P; Q \Gamma ] = 1, with P and Q \Gamma 2 \Theta 2 matrices of differential operators. These conditions on V 1 and V 2 yield a simple system of first order differential equations …

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Gaussian Reference Fluid And Interpretation Of Quantum Geometrodynamics, Karel Kucha, Charles G. Torre Jan 1991

Gaussian Reference Fluid And Interpretation Of Quantum Geometrodynamics, Karel Kucha, Charles G. Torre

All Physics Faculty Publications

The Wheeler-DeWitt equation of vacuum geometrodynamics is turned into a Schrödinger equation by imposing the normal Gaussian coordinate conditions with Lagrange multipliers and then restoring the coordinate invariance of the action by parametrization. This procedure corresponds to coupling the gravitational field to a reference fluid. The source appearing in the Einstein law of gravitation has the structure of a heat-conducting dust. When one imposes only the Gaussian time condition but not the Gaussian frame conditions, the heat flow vanishes and the dust becomes incoherent. The canonical description of the fluid uses the Gaussian coordinates and their conjugate momenta as the …

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Magnetic-Field-Induced Alignment-To-Orientation Conversion In Sodium, G. W. Schinn, Xianming Han Jan 1991

Magnetic-Field-Induced Alignment-To-Orientation Conversion In Sodium, G. W. Schinn, Xianming Han

Scholarship and Professional Work - LAS

We report a detailed investigation of excited-state alignment-to-orientation conversion in the presence of an external magnetic field. This counterintuitive phenomenon occurs under intermediate-coupling conditions. A weak, linearly polarized, cw laser beam was used to excite and align the Na 3P3/2 state in an atomic beam along the z direction. The degree of circular polarization of the resulting fluorescence was detected along the z direction as a function of magnetic-field strength. The spectrally integrated transitions originating from individual F levels of the 3S1/2 state yield a maximum circular-polarization fraction of ∼40%; integrating the circular polarization over all the allowed 3S1/2-3P3/2 transitions …

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Fine‐Structure Mixing Within The Zn(43pj) Multiplet By Collisions With The Noble Gases, Xianming Han, J. F. Kelly Jan 1991

Fine‐Structure Mixing Within The Zn(43pj) Multiplet By Collisions With The Noble Gases, Xianming Han, J. F. Kelly

Scholarship and Professional Work - LAS

Measurements of rate coefficients for intramultiplet state transfer of Zn(4 3 P 1→4 3 P J’) by collisions with the rare gases are presented. The state‐to‐state binary rate coefficients are derived from least‐squares fittings of the time‐resolved triexponential behavior of the 4 3 P 1fluorescence. These rate coefficients were studied systematically over a temperature range of 690–1100 K in order to characterize the velocity dependence of the collisional coupling. The systematic behavior of the rate coefficients with varying temperature and noble gas species is qualitatively consistent with a nearly adiabatic coupling limit for noncrossing levels.

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Optical Property Measurements In Turbid Media Using Frequency Domain Photon Migration, Bruce J. Tromberg, Lars O. Svaasand, Tsong-Tseh Tsay, Richard C. Haskell, Michael W. Berns Jan 1991

Optical Property Measurements In Turbid Media Using Frequency Domain Photon Migration, Bruce J. Tromberg, Lars O. Svaasand, Tsong-Tseh Tsay, Richard C. Haskell, Michael W. Berns

All HMC Faculty Publications and Research

In frequency domain photon migration (FDPM), amplitude-modulated light is launched into a turbid medium, e.g. tissue, which results in the propagation of density waves of diffuse photons. Variations in the optical properties of the medium perturb the phase velocity and amplitude of the diffusing waves. These parameters can be determined by measuring the phase delay and demodulation amplitude of the waves with respect to the source. More specifically, the damped spherical wave solutions to the homogeneous form of the diffusion equation yield expressions for phase (φ) and demodulation (m) as a function of source distance, modulation frequency, absorption coefficient (β), …

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Modulated, Frequency-Locked, And Chaotic Cross-Waves, William B. Underhill, Seth Lichter, Andrew J. Bernoff Jan 1991

Modulated, Frequency-Locked, And Chaotic Cross-Waves, William B. Underhill, Seth Lichter, Andrew J. Bernoff

All HMC Faculty Publications and Research

Measurements were made of the wave height of periodic, quasi-periodic, and chaotic parametrically forced cross-waves in a long rectangular channel. In general, three frequencies (and their harmonics) may be observed: the subharmonic frequency and two slow temporal modulations — a one-mode instability associated with streamwise variation and a sloshing motion associated with spanwise variation. Their interaction, as forcing frequency, f, and forcing amplitude, a, were varied, produced a pattern of Arnold tongues in which two or three frequencies were locked. The overall picture of frequency-locked and -unlocked regions is explained in terms of the Arnold tongues predicted by …

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Systematic Variation Of Transport And Thermodynamic Properties With Degree Of Reduction In Nd1.85ce0.15cuo4-, Nathanael A. Fortune, K. Murata, M. Ishibashi, Y. Yokoyama, Y. Nishihara Jan 1991

Systematic Variation Of Transport And Thermodynamic Properties With Degree Of Reduction In Nd1.85ce0.15cuo4-, Nathanael A. Fortune, K. Murata, M. Ishibashi, Y. Yokoyama, Y. Nishihara

Physics: Faculty Publications

Superconductivity only occurs in Nd1.85Ce0.15CuO4- after heat treatment in a reducing at- mosphere; yet we find the oxygen loss during reduction to be remarkably small. To better understand the physical role of reduction, we have systematically varied the degree of reduction in a series of ceramic samples by varying the partial pressures of oxygen and argon in the reducing atmosphere, keeping the total pressure constant. We find that small increases in the degree of reduction strongly increase the apparent carrier density and the superconducting Meissner fraction. We also find that there is an optimal degree of reduction to produce a …

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