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Articles 1 - 30 of 63
Full-Text Articles in Astrophysics and Astronomy
High-Temperature Calcium Vapor Cell For Spectroscopy On The 4s2 1s0-4s4p 3p1 Intercombination Line, Christopher J. Erickson, Brian Neyenhuis, Dallin S. Durfee
High-Temperature Calcium Vapor Cell For Spectroscopy On The 4s2 1s0-4s4p 3p1 Intercombination Line, Christopher J. Erickson, Brian Neyenhuis, Dallin S. Durfee
Faculty Publications
We have demonstrated a high-temperature vapor cell for absorption spectroscopy on the Ca intercombination line. The cell uses a dual-chamber design to achieve the high temperatures necessary for an optically dense vapor while avoiding the necessity of high-temperature vacuum valves and glass-to-metal seals. We have observed over 50% absorption in a single pass through the cell. Although pressure broadening in the cell prevented us from performing saturated-absorption spectroscopy, the broadening resulted in higher signal-to-noise ratios by allowing us to probe the atoms with intensities much greater than the 0.2µW/cm2 saturation intensity of the unbroadened transition. The techniques presented in this …
Nonmetal Ordering In Tic1-Xnx: Ground-State Structure And The Effects Of Finite Temperature, Gus L. W. Hart, Brian Kolb
Nonmetal Ordering In Tic1-Xnx: Ground-State Structure And The Effects Of Finite Temperature, Gus L. W. Hart, Brian Kolb
Faculty Publications
The TiC1-xNx system has long been prized in industry because of its desirable thermodynamic and hardness characteristics. Previous studies have not produced comprehensive results describing the ordering tendencies of TiC1-xNx at any temperature. We apply the mixed-basis cluster expansion and Monte Carlo methods to the problem and find a fascinating array of ground-state structures occurring at precise nitrogen-concentration intervals of ∆x=1/16 and related to each other by simple (201) quasisuperlattice motifs. Thermodynamic Monte Carlo results indicate that the critical ordering temperatures at all concentrations are well below room temperature. short-range ordering develops at T ≈ 800 K and exhibits the …
Electromagnetism In Gravitational Collapse, Craig Ernest Skinfill
Electromagnetism In Gravitational Collapse, Craig Ernest Skinfill
Theses and Dissertations
A numerical approach to including electromagnetism with general relativity is developed using GRAXI as a starting point. We develop a mathematical model describing electromagnetism coupled to a scalar field in an evolving axisymmetric spacetime. As there are numerous formulations of electromagnetism, we evalute different formulations in a limited flat space case. The full curved space system is then developed, using the flat case as a guide to implementing electromagnetism. This model is then implemented using GRAXI as a code base.
Ultracold Neutral Plasma Expansion In Two Dimensions, E. A. Cummings, J. E. Daily, Dallin S. Durfee, Scott D. Bergeson
Ultracold Neutral Plasma Expansion In Two Dimensions, E. A. Cummings, J. E. Daily, Dallin S. Durfee, Scott D. Bergeson
Faculty Publications
An isothermal model of ultracold neutral plasma expansion is extended to systems without spherical symmetry. It is used to interpret new fluorescence measurements on ultracold neutral calcium plasmas. For a self-similar expansion, the fluid equations are solved both analytically and numerically. The density and velocity solutions are used to predict fluorescence signals induced by a laser beam weakly focused into the plasma. Despite the simplicity of the model, predicted fluorescence signals reproduce major features of the experimental data
Multivalued Logic, Neutrosophy And Schrodinger Equation, Florentin Smarandache, Victor Christianto
Multivalued Logic, Neutrosophy And Schrodinger Equation, Florentin Smarandache, Victor Christianto
Branch Mathematics and Statistics Faculty and Staff Publications
This book was intended to discuss some paradoxes in Quantum Mechanics from the viewpoint of Multi-Valued-logic pioneered by Lukasiewicz, and a recent concept Neutrosophic Logic. Essentially, this new concept offers new insights on the idea of ‘identity’, which too often it has been accepted as given. Neutrosophy itself was developed in attempt to generalize Fuzzy-Logic introduced by L. Zadeh. While some aspects of theoretical foundations of logic are discussed, this book is not intended solely for pure mathematicians, but instead for physicists in the hope that some of ideas presented herein will be found useful. The book is motivated by …
Fluorescence Measurements Of Expanding Strongly Coupled Neutral Plasmas, E. A. Cummings, J. E. Daily, Dallin S. Durfee, Scott D. Bergeson
Fluorescence Measurements Of Expanding Strongly Coupled Neutral Plasmas, E. A. Cummings, J. E. Daily, Dallin S. Durfee, Scott D. Bergeson
Faculty Publications
We report new detailed density profile measurements in expanding strongly coupled neutral calcium plasmas. Using laser-induced fluorescence techniques, we determine plasma densities in the range of 10^5 to 10^9 cm^-3 with a time resolution limit as small as 7 ns. Strong coupling in the plasma ions is inferred directly from the fluorescence signals. Evidence for strong coupling at late times is presented, confirming a recent theoretical result.
Acoustics Of The Salt Lake Tabernacle: Characterization And Study Of Spatial Variation, Sarah Rollins
Acoustics Of The Salt Lake Tabernacle: Characterization And Study Of Spatial Variation, Sarah Rollins
Theses and Dissertations
In order to preserve the acoustics of the Salt Lake Tabernacle after the seismic renovation of 2005-2006, it was necessary to characterize these acoustics immediately preceding the renovation. This thesis discusses the characterization process that began with the measurement of hundreds of impulse responses for five different source positions and several receiver locations throughout the hall seating areas. The acoustics were further characterized by deriving various parameters from these responses that correlate with subjective preferences for music and speech. Impulse responses were also generated by a CATT-Acoustic™ computer model of the Tabernacle for the same purpose. The parameter values were …
Pumping Or Mixing System Using A Levitating Magnetic Element, Aexandre N. Terentiev
Pumping Or Mixing System Using A Levitating Magnetic Element, Aexandre N. Terentiev
Physics and Astronomy Faculty Patents
A system capable of pumping or mixing fluids using a rotating magnetic element or bearing levitated by a cold superconducting element is disclosed.
The H Ii Region/Pdr Connection: Self-Consistent Calculations Of Physical Conditions In Star-Forming Regions, Nicholas Paul Abel, Gary J. Ferland, G. Shaw, Peter A. M. Van Hoof
The H Ii Region/Pdr Connection: Self-Consistent Calculations Of Physical Conditions In Star-Forming Regions, Nicholas Paul Abel, Gary J. Ferland, G. Shaw, Peter A. M. Van Hoof
Physics and Astronomy Faculty Publications
We have performed a series of calculations designed to reproduce infrared diagnostics used to determine physical conditions in star-forming regions. We self-consistently calculate the thermal and chemical structure of an H II region and photodissociation region (PDR) that are in pressure equilibrium. This differs from previous work, which used separate calculations for each gas phase. Our calculations span a wide range of stellar temperatures, gas densities, and ionization parameters. We describe improvements made to the spectral synthesis code Cloudy that made these calculations possible. These include the addition of a molecular network with ~1000 reactions involving 68 molecular species and …
Using Genetic Algorithms To Map First-Principles Results To Model Hamiltonians: Application To The Generalized Ising Model For Alloys, Gus L. W. Hart, Volker Blum, Michael J. Walorski, Alex Zunger
Using Genetic Algorithms To Map First-Principles Results To Model Hamiltonians: Application To The Generalized Ising Model For Alloys, Gus L. W. Hart, Volker Blum, Michael J. Walorski, Alex Zunger
Faculty Publications
The cluster expansion method provides a standard framework to map first-principles generated energies for a few selected configurations of a binary alloy onto a finite set of pair and many-body interactions between the alloyed elements. These interactions describe the energetics of all possible configurations of the same alloy, which can hence be readily used to identify ground state structures and, through statistical mechanics solutions, find finite-temperature properties. In practice, the biggest challenge is to identify the types of interactions which are most important for a given alloy out of the many possibilities. We describe a genetic algorithm which automates this …
Numerical Integration Of The Teukolsky Equation In The Time Domain, Enrique Pazos-Avalos, Carlos O. Lousto
Numerical Integration Of The Teukolsky Equation In The Time Domain, Enrique Pazos-Avalos, Carlos O. Lousto
Physics and Astronomy Faculty Publications and Presentations
We present a fourth-order convergent, (2+1)-dimensional, numerical formalism to solve the Teukolsky equation in the time domain. Our approach is first to rewrite the Teukolsky equation as a system of first-order differential equations. In this way we get a system that has the form of an advection equation. This is then used in combination with a series expansion of the solution in powers of time. To obtain a fourth-order scheme we kept terms up to fourth derivative in time and use the advectionlike system of differential equations to substitute the temporal derivatives by spatial derivatives. This scheme is applied to …
Integral Neutron Multiplicity Measurements From Cosmic Ray Interactions In Lead, Thomas E. Ward, Alexander A. Rimsky-Korsakov, Nikolai A. Kudryashev, Denis E. Beller
Integral Neutron Multiplicity Measurements From Cosmic Ray Interactions In Lead, Thomas E. Ward, Alexander A. Rimsky-Korsakov, Nikolai A. Kudryashev, Denis E. Beller
Transmutation Sciences Physics (TRP)
Sixty element 3He neutron multiplicity detector systems were designed, constructed and tested for use in cosmic ray experiments with a 30-cm cube lead target. A series of measurements were performed for the cosmic ray configuration at ground level (3 meters water equivalent, mwe), in the St. Petersburg metro tunnel (185 mwe), and in the Pyhäsalmi mine in Finland (583 and 1185 mwe). Anomalous coincidence events with charged cosmic ray particles at sea level produced events with 100-120 neutrons due possibly to the total disintegration of the Pb nucleus. These events were also detected at 185 mwe, but the particles …
Direct Enumeration Of Alloy Configurations For Electronic Structural Properties, Gus L. W. Hart, Peter A. Graf, Kwiseon Kim, Wesley B. Jones
Direct Enumeration Of Alloy Configurations For Electronic Structural Properties, Gus L. W. Hart, Peter A. Graf, Kwiseon Kim, Wesley B. Jones
Faculty Publications
We present and apply an approach to directly enumerate the band gaps and effective masses of all possible zinc blende-based alloy configurations whose unit cell contains up to a specified number of atoms. This method allows us to map the space of band gaps and effective masses versus alloy composition and atomic configuration. We demonstrate that a large number of band gaps and effective masses are available. We also discuss convergence of the method with respect to unit cell size and the combined optimization of band gap and effective mass for AlGaAs and GaInP semiconductor alloys.
Cross Sections Fall 2005, Department Of Physics And Astronomy
Cross Sections Fall 2005, Department Of Physics And Astronomy
Cross Sections
No abstract provided.
An Acoustical Analysis Of Domes Coupled To Rooms, With Special Application To The Darussholah Mosque, In East Java, Indonesia, Sentagi Sesotya Utami
An Acoustical Analysis Of Domes Coupled To Rooms, With Special Application To The Darussholah Mosque, In East Java, Indonesia, Sentagi Sesotya Utami
Theses and Dissertations
Concave surfaces are often considered to be detrimental or precarious in room acoustics, especially because of the impact they have on the distribution of sound energy. However, it is often difficult to avoid such surfaces in buildings with specific architectural functions. A primary example of this involves mosques, which are sacred places of worship for Muslims. In keeping with the Islamic architectural style, most mosques incorporate a symbolic centralized domed ceiling as part of their room structures. These domes are open on the bottom and coupled to the acoustic spaces below. In many cases, the lower spaces may be idealized …
New Correlation Effects In Nonrelativistic Atomic Photoionization In The High Energy Limit, Chieh Jen Yang
New Correlation Effects In Nonrelativistic Atomic Photoionization In The High Energy Limit, Chieh Jen Yang
Physics and Astronomy Theses
The effect of initial state correlation on high-energy dipole photoionization is considered and it is shown that for almost all atomic electron the asymptotic high-energy dependence is E-7/2, and the dominant transition is an ionization plus excitation satellite transition. This is demonstrated in numerical calculations of the photoionization of Ge4p2 1S and Sn 5p2 1S.
Rest Frame Variability Characteristics Of Blazars, John Patrick Mcfarland
Rest Frame Variability Characteristics Of Blazars, John Patrick Mcfarland
Physics and Astronomy Dissertations
Blazars exhibit the most extreme variability of the class of objects known asactive galactic nuclei (AGN). They are characterized by a featureless continuum, high polarization, and variability at all wavelengths and timescales. The amplitude of optical variations can range from less than 0.1 magnitude on the timescale of minutes to hours, to greater than 5.0 magnitudes on timescales of months to years, and gamma-ray variability amplitudes can span a range of as much as three orders of magnitude in a time-scale as short as a few days. These characteristics are consistent with a supermassive black hole accreting matter at the …
Spectral Line Synthesis For Hot Stars, Wenjin Huang
Spectral Line Synthesis For Hot Stars, Wenjin Huang
Physics and Astronomy Dissertations
I developed a spectrum synthesis method to investigate the physical properties of hot OB main sequence (MS) stars, which are often rapid rotators. The code realistically simulates the surface conditions of rapidly rotating stars, considering the rotationally-deformed stellar shape and gravity darkening effect. Comparing the synthesized absorption line profiles with the observed spectra of the member stars of 19 young Galactic clusters, I determined the projected rotational velocities of 496 stars. The average surface temperature and gravity for most of these objects were then derived from H$\gamma$ line fits. The polar gravity of each star was estimated as a good …
J-Resolved He I Emission Predictions In The Low-Density Limit, R. P. Bauman, R. L. Porter, Gary J. Ferland, K. B. Macadam
J-Resolved He I Emission Predictions In The Low-Density Limit, R. P. Bauman, R. L. Porter, Gary J. Ferland, K. B. Macadam
Physics and Astronomy Faculty Publications
Determinations of the primordial helium abundance are used in precision cosmological tests. These require highly accurate He I recombination rate coefficients. Here we reconsider the formation of He I recombination lines in the low-density limit. This is the simplest case, and it forms the basis for the more complex situation in which collisions are important. The formation of a recombination line is a two-step process, beginning with the capture of a continuum electron into a bound state and followed by radiative cascade to ground. The rate coefficient for capture from the continuum is obtained from photoionization cross sections and detailed …
An Improved Flexible Neutron Detector For Powder Diffraction Experiments, Thomas Kevin Mcknight
An Improved Flexible Neutron Detector For Powder Diffraction Experiments, Thomas Kevin Mcknight
Theses and Dissertations
Large amounts of money are being applied to the construction of the next generation of spallation sources for neutron scattering. Neutron powder diffraction instruments will be an important element of these facilities and the incorporation of detectors into these instruments with a high neutron capture efficiency is desirable. A new detector design named the Flexible Embedded Fiber Detector (FEFD) has been developed and tested for this thesis. This detector is based on wavelength shifting fibers embedded in a zinc-sulfide lithium-fluoride based scintillator. The virtue of this design is that the detecting surface can be curved around the Debye-Scherrer rings. This …
Black Spaghetti: A Numerical Model Of Gravitational Collapse In 4 + 1 Spacetime, Michael P. Christenson
Black Spaghetti: A Numerical Model Of Gravitational Collapse In 4 + 1 Spacetime, Michael P. Christenson
Theses and Dissertations
We investigate spherically-symmetric gravitational collapse in the presence of a single "large" extra dimension through the use of analytical and numerical techniques. This has bearing on higher-dimensional ideas concerning hypothetical objects called "black strings," or black holes extending into an extra circular dimension, which dimension we hereinafter label zeta. These putative objects were first seriously considered as elements of string theory but have relevance in simpler, higher-dimensional generalization of Einstein's general relativity. We assume a universe topologically consisting of a two-dimensional Lorentzian manifold crossed with the sphere, crossed again with the circle. We model the formation of a uniform black …
Representations For Understanding The Stern-Gerlach Effect, Jared R. Stenson
Representations For Understanding The Stern-Gerlach Effect, Jared R. Stenson
Theses and Dissertations
The traditional explanation of the Stern-Gerlach effect carries with it several very subtle assumptions and approximations. We point out the degree to which this fact has affected the way we practice and interpret modern physics. In order to gain a more complete understanding of the Stern-Gerlach effect beyond the standard approximations and assumptions it typically carries, we introduce the inhomogeneous Stern-Gerlach effect in which the strong uniform field component is removed. This change allows us to easily identify precession as a critical concept. It also provides us with a means by which to study precession and analyze it critically. By …
Novel Neutron Detector For N-N Scattering Length Measurement, Eva Wilcox
Novel Neutron Detector For N-N Scattering Length Measurement, Eva Wilcox
Theses and Dissertations
The neutron-neutron (n-n) scattering length is a fundamental parameter in nuclear physics; however, measurements are plagued with large uncertainties caused by neutron detector cross talk. Many experimentalists also rely upon computer code to calibrate their neutron detectors. Experiments give one of two different numbers but there is still no adequate explanation for this discrepancy. We have developed a new neutron detector expressly for the purpose of improving the n-n scattering length measurement. It offers two important advantages: 1) minimal cross talk and 2) high counting efficiency. We calibrated the detector from 1 MeV to 6 MeV at 1 MeV increments. …
Phase-Matching Optimization Of Laser High-Order Harmonics Generated In A Gas Cell, Julia Robin Miller Sutherland
Phase-Matching Optimization Of Laser High-Order Harmonics Generated In A Gas Cell, Julia Robin Miller Sutherland
Theses and Dissertations
Ten-millijoule, thirty-five femtosecond, 800 nm (~40 nm bandwidth) laser pulses are used to study high-order harmonic generation in helium- and neon-filled gas cells of various lengths. Harmonic orders in the range of 50 to 100 are investigated. A semi-infinite cell geometry produces brighter harmonics than cells of sub-centimeter length. In the semi-infinite geometry, the gas occupies the region from the focusing lens to a thin exit foil near the laser focus. Counter-propagating light is used to directly probe where the high harmonics are generated within the laser focus and to investigate phase matching. The phase matching under optimized harmonic generation …
A Multi-Instrument Study Of The Helix Nebula Knots With The Hubble Space Telescope, C. R. O'Dell, W. J. Henney, Gary J. Ferland
A Multi-Instrument Study Of The Helix Nebula Knots With The Hubble Space Telescope, C. R. O'Dell, W. J. Henney, Gary J. Ferland
Physics and Astronomy Faculty Publications
We have conducted a combined observational and theoretical investigation of the ubiquitous knots in the Helix Nebula (NGC 7293). We have constructed a combined hydrodynamic + radiation model for the ionized portion of these knots and have accurately calculated a static model for their molecular regions. Imaging observations in optical emission lines were made with the Hubble Space Telescope's STIS, operating in a "slitless" mode, complemented by WFPC2 images in several of the same lines. The NICMOS camera was used to image the knots in H2. These observations, when combined with other studies of H2 and …
Dynamo Regimes With A Nonhelical Forcing, Pablo D. Mininni, Yannick Ponty, David C. Montgomery, Jean-Francois Pinton
Dynamo Regimes With A Nonhelical Forcing, Pablo D. Mininni, Yannick Ponty, David C. Montgomery, Jean-Francois Pinton
Dartmouth Scholarship
A three-dimensional numerical computation of magnetohydrodynamic dynamo behavior is described. The dynamo is mechanically forced with a driving term of the Taylor-Green type. The magnetic field development is followed from negligibly small levels to saturated values that occur at magnetic energies comparable to the kinetic energies. Although there is locally a nonzero helicity density, there is no overall integrated helicity in the system. Persistent oscillations are observed in the saturated state for not-too-large mechanical Reynolds numbers, oscillations in which the kinetic and magnetic energies vary out of phase but with no reversal of the magnetic field. The flow pattern exhibits …
Commutation Relations For Functions Of Operators, Mark K. Transtrum, Jean-Francois S. Van Huele
Commutation Relations For Functions Of Operators, Mark K. Transtrum, Jean-Francois S. Van Huele
Faculty Publications
We derive an expression for the commutator of functions of operators with constant commutations relations in terms of the partial derivatives of these functions. This result extends the well-known commutation relation between one operator and a function of another operator. We discuss the range of applicability of the formula with examples in quantum mechanics
Erratum: Computing The M = 1 Diocotron Frequency Via An Equilibrium Calculation In Non-Neutral Plasmas, Ross L. Spencer
Erratum: Computing The M = 1 Diocotron Frequency Via An Equilibrium Calculation In Non-Neutral Plasmas, Ross L. Spencer
Faculty Publications
Equation 14 in this paper contains errors.
Molecular Hydrogen In Star-Forming Regions: Implementation Of Its Microphysics In Cloudy, G. Shaw, Gary J. Ferland, N. P. Abel, P. C. Stancil, P. A. M. Van Hoof
Molecular Hydrogen In Star-Forming Regions: Implementation Of Its Microphysics In Cloudy, G. Shaw, Gary J. Ferland, N. P. Abel, P. C. Stancil, P. A. M. Van Hoof
Physics and Astronomy Faculty Publications
Much of the baryonic matter in the universe is in the form of H2, which includes most of the gas in Galactic and extragalactic interstellar clouds. Molecular hydrogen plays a significant role in establishing the thermal balance in many astrophysical environments and can be important as a spectral diagnostic of the gas. Modeling and interpretation of observations of such environments requires a quantitatively complete and accurate treatment of H2. Using this microphysical model of H2, we present illustrative calculations of prototypical astrophysical environments. This work forms the foundation for future investigations of these and …
The Effect Of Inharmonic Partials On Pitch Of Piano Tones, Brian E. Anderson, William J. Strong
The Effect Of Inharmonic Partials On Pitch Of Piano Tones, Brian E. Anderson, William J. Strong
Faculty Publications
Piano tones have partials whose frequencies are sharp relative to harmonic values. A listening test was conducted to determine the effect of inharmonicity on pitch for piano tones in the lowest three octaves of a piano. Nine real tones from the lowest three octaves of a piano were analyzed to obtain frequencies, relative amplitudes, and decay rates of their partials. Synthetic inharmonic tones were produced from these results. Synthetic harmonic tones, each with a twelfth of a semitone increase in the fundamental, were also produced. A jury of 21 listeners matched the pitch of each synthetic inharmonic tone to one …