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2010

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Articles 61 - 90 of 276

Full-Text Articles in Astrophysics and Astronomy

Optical Discovery Of An Apparent Galactic Supernova Remnant G159.6+7.3, Robert A. Fesen, Dan Milisavljevic Sep 2010

Optical Discovery Of An Apparent Galactic Supernova Remnant G159.6+7.3, Robert A. Fesen, Dan Milisavljevic

Dartmouth Scholarship

Deep Hα images of portions of a faint 3° × 4° Hα shell centered at l = 1596, b = 73 seen on the Virginia Tech Spectral Line Survey images revealed the presence of several thin emission filaments along its eastern limb. Low-dispersion optical spectra of two of these filaments covering the wavelength range of 4500-7500 Å show narrow Hα line emissions with velocities around –170 ± 30 km s–1. Both the morphology and spectra of these filaments are consistent with a Balmer-dominated shock interpretation and we propose that these optical filaments indicate that the large Hα emission …

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Discovery Of Cyclic Spot Activity On The G8 Giant Hd 208472, Orkun Özdarcan, Serdar Evren, Klaus G. Strassmeier, Thomas Granzer, Gregory W. Henry Sep 2010

Discovery Of Cyclic Spot Activity On The G8 Giant Hd 208472, Orkun Özdarcan, Serdar Evren, Klaus G. Strassmeier, Thomas Granzer, Gregory W. Henry

Information Systems and Engineering Management Research Publications

We present and analyze 17 consecutive years of UBVRI time-series photometry of the spotted giant component of the RS CVn binary HD 208472. Our aim is to determine the morphology and the evolution of its starspots by using periodsearch techniques and two-spot light-curve modelling. Spots on HD208472 always occur on hemispheres facing the observer during orbital quadrature and flip their location to the opposite hemisphere every approximately six years. The times when the spots change their preferential hemisphere correspond to times when the light curve amplitudes are the smallest and when abrupt changes of the photometric periods are observed. During …

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Local Group Dwarf Spheroidals: Correlated Deviations From The Baryonic Tully-Fisher Relation, Stacy S. Mcgaugh Sep 2010

Local Group Dwarf Spheroidals: Correlated Deviations From The Baryonic Tully-Fisher Relation, Stacy S. Mcgaugh

Faculty Scholarship

Local Group dwarf spheroidal satellite galaxies are the faintest extragalactic stellar systems known. We examine recent data for these objects in the plane of the Baryonic Tully-Fisher Relation (BTFR). While some dwarf spheroidals adhere to the BTFR, others deviate substantially. We examine the residuals from the BTFR and find that they are not random. The residuals correlate with luminosity, size, metallicity, ellipticity, and susceptibility of the dwarfs to tidal disruption in the sense that fainter, more elliptical, and tidally more susceptible dwarfs deviate farther from the BTFR. These correlations disfavor stochastic processes and suggest a role for tidal effects. We …

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The Climate Of Hd 189733b From Fourteen Transits And Eclipses Measured By Spitzer, Eric Agol, Nicolas B. Cowan, Heather A. Knutson, Drake Deming, Jason H. Steffen, Gregory W. Henry, David Charbonneau Sep 2010

The Climate Of Hd 189733b From Fourteen Transits And Eclipses Measured By Spitzer, Eric Agol, Nicolas B. Cowan, Heather A. Knutson, Drake Deming, Jason H. Steffen, Gregory W. Henry, David Charbonneau

Information Systems and Engineering Management Research Publications

We present observations of six transits and six eclipses of the transiting planet system HD 189733 taken with the Spitzer Space Telescope's Infrared Array Camera (IRAC) at 8 μm, as well as a re-analysis of previously published data. We use several novel techniques in our data analysis, the most important of which is a new correction for the detector "ramp" variation with a double-exponential function, which performs better and is a better physical model for this detector variation. Our main scientific findings are (1) an upper limit on the variability of the dayside planet flux of 2.7% (68% confidence); (2) …

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A Hot Jupiter Orbiting The 1.7 M☉ Subgiant Hd 102956*, John Asher Johnson, Brendan P. Bowler, Andrew W. Howard, Gregory W. Henry, Geoffrey W. Marcy, Howard Isaacson, John Michael Brewer, Debra A. Fischer, Timothy D. Morton, Justin R. Crepp Sep 2010

A Hot Jupiter Orbiting The 1.7 M☉ Subgiant Hd 102956*, John Asher Johnson, Brendan P. Bowler, Andrew W. Howard, Gregory W. Henry, Geoffrey W. Marcy, Howard Isaacson, John Michael Brewer, Debra A. Fischer, Timothy D. Morton, Justin R. Crepp

Information Systems and Engineering Management Research Publications

We report the detection of a giant planet in a 6.4950 day orbit around the 1.68 M☉ subgiant HD 102956. The planet has a semimajor axis a = 0.081 AU and a minimum mass MPsin i =0.96 MJup. HD 102956 is the most massive star known to harbor a hot Jupiter, and its planet is only the third known to orbit within 0.6 AU of a star more massive than 1.5 M☉. Based on our sample of 137 subgiants with M⋆>1.45 M☉, we find that 0.5%–2.3% of A-type stars harbor a close-in planet (a < 0.1 AU) with MPsin i > 1 MJup, consistent with hot-Jupiter …

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The California Planet Survey. I. Four New Giant Exoplanets*, Andrew W. Howard, John Asher Johnson, Geoffrey W. Marcy, Debra A. Fischer, Jason T. Wright, David Bernat, Gregory W. Henry, Kathryn M. G. Peek, Howard Isaacson, Kevin Apps, Michael Endl, William D. Cochran, Jeff A. Valenti, Jay Anderson, Nikolai E. Piskunov Sep 2010

The California Planet Survey. I. Four New Giant Exoplanets*, Andrew W. Howard, John Asher Johnson, Geoffrey W. Marcy, Debra A. Fischer, Jason T. Wright, David Bernat, Gregory W. Henry, Kathryn M. G. Peek, Howard Isaacson, Kevin Apps, Michael Endl, William D. Cochran, Jeff A. Valenti, Jay Anderson, Nikolai E. Piskunov

Information Systems and Engineering Management Research Publications

We present precise Doppler measurements of four stars obtained during the past decade at Keck Observatory by the California Planet Survey (CPS). These stars, namely, HD 34445, HD 126614, HD 13931, and Gl 179, all show evidence for a single planet in Keplerian motion. We also present Doppler measurements from the Hobby-Eberly Telescope (HET) for two of the stars, HD 34445 and Gl 179, that confirm the Keck detections and significantly refine the orbital parameters. These planets add to the statistical properties of giant planets orbiting near or beyond the ice line, and merit follow-up by astrometry, imaging, and space-borne …

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Veritas Search For Vhe Gamma-Ray Emission From Dwarf Spheroidal Galaxies, P. T. Reynolds, Et. Al. Sep 2010

Veritas Search For Vhe Gamma-Ray Emission From Dwarf Spheroidal Galaxies, P. T. Reynolds, Et. Al.

Physical Sciences Publications

Indirect dark matter searches with ground-based gamma-ray observatories provide an alternative for identifying the particle nature of dark matter that is complementary to that of direct search or accelerator production experiments. We present the results of observations of the dwarf spheroidal galaxies Draco, Ursa Minor, Boötes 1, and Willman 1 conducted by the Very Energetic Radiation Imaging Telescope Array System (VERITAS). These galaxies are nearby dark matter dominated objects located at a typical distance of several tens of kiloparsecs for which there are good measurements of the dark matter density profile from stellar velocity measurements. Since the conventional astrophysical background …

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Biofunctionalization And Immobilization Of A Membrane Via Peptide Binding (Cr3-1, S2) By A Monte Carlo Simulation, Ras B. Pandey, Hendrik Heinz, Jie Feng, Barry L. Farmer Sep 2010

Biofunctionalization And Immobilization Of A Membrane Via Peptide Binding (Cr3-1, S2) By A Monte Carlo Simulation, Ras B. Pandey, Hendrik Heinz, Jie Feng, Barry L. Farmer

Faculty Publications

A coarse-grained computer simulation model is used to study the immobilization of a dynamic tethered membrane (representation of a clay platelet) in a matrix of mobile peptide chains CR3-1:(1)Trp-(2)Pro-(3)Ser-(4)Ser-(5)Tyr-(6)Leu-(7)Ser-(8)Pro-(9)Ile-(10)Pro-(11)Tyr-(12)Ser and S2:(1)His-(2)Gly-(3)Ile-(4)Asn-(5)Thr-(6)Thr-(7)Lys-(8)Pro-(9)Phe-(10)Lys-(11)Ser-(12)Val on a cubic lattice. Each residue interacts with the membrane nodes with appropriate interaction and executes their stochastic motion with the Metropolis algorithm. Density profiles, binding energy of each residue, mobility, and targeted structural profile are analyzed as a function of peptide concentration. We find that the binding of peptides S2 is anchored by lysine residues ((7)Lys,(10)Lys) while peptides CR3-1 do not bind to membrane. The membrane slows down …

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Predictions For The Rates Of Compact Binary Coalescences Observable By Ground-Based Gravitational-Wave Detectors, J. Abadie, B. P. Abbott, R. Abbott, M. Abernathy, T. Accadia, F. Acernese, C. Adams, R. Adhikari, P. Ajith, B. Allen, G. Allen, E. Amador Ceron, R. S. Amin, S. B. Anderson, W. G. Anderson, F. Antonucci, S. Aoudia, M. A. Arain, M. Araya, M. Aronsson, K. G. Arun, Y. Aso, S. Aston, P. Astone, D. E. Atkinson, P. Aufmuth, C. Aulbert, S. Babak, P. Baker, G. Ballardin, S. Ballmer, Tiffany Z. Summerscales Sep 2010

Predictions For The Rates Of Compact Binary Coalescences Observable By Ground-Based Gravitational-Wave Detectors, J. Abadie, B. P. Abbott, R. Abbott, M. Abernathy, T. Accadia, F. Acernese, C. Adams, R. Adhikari, P. Ajith, B. Allen, G. Allen, E. Amador Ceron, R. S. Amin, S. B. Anderson, W. G. Anderson, F. Antonucci, S. Aoudia, M. A. Arain, M. Araya, M. Aronsson, K. G. Arun, Y. Aso, S. Aston, P. Astone, D. E. Atkinson, P. Aufmuth, C. Aulbert, S. Babak, P. Baker, G. Ballardin, S. Ballmer, Tiffany Z. Summerscales

Faculty Publications

We present an up-to-date, comprehensive summary of the rates for all types of compact binary coalescence sources detectable by the initial and advanced versions of the ground-based gravitational-wave detectors LIGO and Virgo. Astrophysical estimates for compact-binary coalescence rates depend on a number of assumptions and unknown model parameters and are still uncertain. Themost confident among these estimates are the rate predictions for coalescing binary neutron stars which are based on extrapolations from observed binary pulsars in our galaxy. These yield a likely coalescence rate of 100 Myr-1 per MilkyWay Equivalent Galaxy (MWEG), although the rate could plausibly range from 1 …

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A Portable Neutron Spectroscope (Nspect) For Detection, Imaging And Identification Of Nuclear Material, James M. Ryan, Chris Bancroft, Peter F. Bloser, U Bravar, Dominique Fourguette, Colin Frost, Liane Larocque, Mark L. Mcconnell, Jason S. Legere, Jane Pavlich, Greg Ritter, Greg Wassick, Joshua Wood, R S. Woolf Sep 2010

A Portable Neutron Spectroscope (Nspect) For Detection, Imaging And Identification Of Nuclear Material, James M. Ryan, Chris Bancroft, Peter F. Bloser, U Bravar, Dominique Fourguette, Colin Frost, Liane Larocque, Mark L. Mcconnell, Jason S. Legere, Jane Pavlich, Greg Ritter, Greg Wassick, Joshua Wood, R S. Woolf

Space Science Center

We have developed, fabricated and tested a prototype imaging neutron spectrometer designed for real-time neutron source location and identification. Real-time detection and identification is important for locating materials. These materials, specifically uranium and transuranics, emit neutrons via spontaneous or induced fission. Unlike other forms of radiation (e.g. gamma rays), penetrating neutron emission is very uncommon. The instrument detects these neutrons, constructs images of the emission pattern, and reports the neutron spectrum. The device will be useful for security and proliferation deterrence, as well as for nuclear waste characterization and monitoring. The instrument is optimized for imaging and spectroscopy in the …

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Quiescent X-Ray Emission From Cen X-4: A Variable Thermal Component, Edward M. Cackett, Edward F. Brown, Jon M. Miller, Rudy Wijnands Sep 2010

Quiescent X-Ray Emission From Cen X-4: A Variable Thermal Component, Edward M. Cackett, Edward F. Brown, Jon M. Miller, Rudy Wijnands

Physics and Astronomy Faculty Research Publications

The nearby neutron star low-mass X-ray binary, Cen X-4, has been in a quiescent state since its last outburst in 1979. Typically, quiescent emission from these objects consists of thermal emission (presumably from the neutron star surface) with an additional hard power-law tail of unknown nature. Variability has been observed during quiescence in Cen X-4 on both timescales as short as hundreds of seconds and as long as years. However, the nature of this variability is still unknown. Early observations seemed to show it was all due to a variable hard X-ray tail. Here, we present new and archival observations …

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Relativistic Particle Acceleration In Tangled Magnetic Fields, Stephen O'Sullivan, Brian Reville, Andrew Taylor Sep 2010

Relativistic Particle Acceleration In Tangled Magnetic Fields, Stephen O'Sullivan, Brian Reville, Andrew Taylor

Conference papers

We present simulations of the transport of fast particles through three-dimensional turbulent magnetic field configurations. A time dependency is imposed on the plane wave modes used in constructing these fields such than acceleration via the second-order Fermi process is possible. We consider simulations of models with low and high turbulence levels for non-relativistic waves. The predictions of quasi-linear theory are discussed with respect to the simulation data. We conclude that for pure stochastic acceleration via Alfvén waves to be plausible as the generator of UHECR in Cen A, the baryon number density would need to be several orders of magnitude …

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Probing The Evolving Massive Star Population In Orion With Kinematic And Radioactive Tracers, R. Voss, R. Diehl, J. S. Vink, Dieter H. Hartmann Sep 2010

Probing The Evolving Massive Star Population In Orion With Kinematic And Radioactive Tracers, R. Voss, R. Diehl, J. S. Vink, Dieter H. Hartmann

Publications

Context. Orion is the nearest star-forming region to host a significant number of young and massive stars. The energy injected by these OB stars is thought to have created the Eridanus superbubble. Because of its proximity, Orion is a prime target for a detailed investigation of the interaction between massive stars and their environment. Aims. We study the massive star population of Orion and its feedback in terms of energy and mass, in order to compare the current knowledge of massive stars with kinematic and radioactive tracers in the surrounding interstellar medium (ISM). Methods. We assembled a census of the …

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Relativistic Lines And Reflection From The Inner Accretion Disks Around Neutron Stars, Edward M. Cackett, Jon M. Miller, David R. Ballantyne, Didier Barret, Sudip Bhattacharyya, Martin Boutelier, M. Coleman Miller, Tod E. Strohmayer, Rudy Wijnands Sep 2010

Relativistic Lines And Reflection From The Inner Accretion Disks Around Neutron Stars, Edward M. Cackett, Jon M. Miller, David R. Ballantyne, Didier Barret, Sudip Bhattacharyya, Martin Boutelier, M. Coleman Miller, Tod E. Strohmayer, Rudy Wijnands

Physics and Astronomy Faculty Research Publications

A number of neutron star low-mass X-ray binaries (LMXBs) have recently been discovered to show broad, asymmetric Fe K emission lines in their X-ray spectra. These lines are generally thought to be the most prominent part of a reflection spectrum, originating in the inner part of the accretion disk where strong relativistic effects can broaden emission lines. We present a comprehensive, systematic analysis of Suzaku and XMM-Newton spectra of 10 neutron star LMXBs, all of which display broad Fe K emission lines. Of the 10 sources, 4 are Z sources, 4 are atolls, and 2 are accreting millisecond X-ray pulsars …

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Compact Binaries In Star Clusters - I. Black Hole Binaries Inside Globular Clusters, J. M.B. Downing, M. J. Benacquista, M. Giersz, R. Spurzem Sep 2010

Compact Binaries In Star Clusters - I. Black Hole Binaries Inside Globular Clusters, J. M.B. Downing, M. J. Benacquista, M. Giersz, R. Spurzem

Physics & Astronomy Faculty Publications

We study the compact binary population in star clusters, focusing on binaries containing black holes, using a self-consistent Monte Carlo treatment of dynamics and full stellar evolution. We find that the black holes experience strong mass segregation and become centrally concentrated. In the core the black holes interact strongly with each other and black hole-black hole binaries are formed very efficiently. The strong interactions, however, also destroy or eject the black hole-black hole binaries. We find no black hole-black hole mergers within our simulations but produce many hard escapers that will merge in the Galactic field within a Hubble time. …

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The Sensitivity Of The Parkes Pulsar Timing Array To Individual Sources Of Gravitational Waves, D. R.B. Yardley, G. B. Hobbs, Fredrick A. Jenet, J. P.W. Verbiest, Z. L. Wen, R. N. Manchester, W. A. Coles, W. Van Straten, M. Bailes Sep 2010

The Sensitivity Of The Parkes Pulsar Timing Array To Individual Sources Of Gravitational Waves, D. R.B. Yardley, G. B. Hobbs, Fredrick A. Jenet, J. P.W. Verbiest, Z. L. Wen, R. N. Manchester, W. A. Coles, W. Van Straten, M. Bailes

Physics & Astronomy Faculty Publications

We present the sensitivity of the Parkes Pulsar Timing Array to gravitational waves (GWs) emitted by individual supermassive black hole binary systems in the early phases of coalescing at the cores of merged galaxies. Our analysis includes a detailed study of the effects of fitting a pulsar timing model to non-white timing residuals. Pulsar timing is sensitive at nanoHertz frequencies and hence complementary to Laser Interferometer Gravitational-Wave Observatory and Laser Interferometer Space Antenna. We place a sky-averaged constraint on the merger rate of nearby (z < 0.6) black hole binaries in the early phases of coalescence with a chirp mass of 1010 M⊙ of less than one merger every 7 yr. The prospects for future GW astronomy of this type with the proposed Square Kilometre Array telescope are discussed. © 2010 The Authors. Journal compilation © 2010 RAS.

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A Detailed Model Atmosphere Analysis Of Cool White Dwarfs In The Sloan Digital Sky Survey, Mukremin Kilic, Ted Von Hippel, Et Al. Sep 2010

A Detailed Model Atmosphere Analysis Of Cool White Dwarfs In The Sloan Digital Sky Survey, Mukremin Kilic, Ted Von Hippel, Et Al.

Publications

We present optical spectroscopy and near-infrared photometry of 126 cool white dwarfs (WDs) in the Sloan Digital Sky Survey (SDSS). Our sample includes high proper motion targets selected using the SDSS and USNO-B astrometry and a dozen previously known ultracool WD candidates. Our optical spectroscopic observations demonstrate that a clean selection of large samples of cool WDs in the SDSS (and the SkyMapper, Pan-STARRS, and the Large Synoptic Survey Telescope data sets) is possible using a reduced proper motion diagram and a tangential velocity cut-off (depending on the proper motion accuracy) of 30 km s–1. Our near-infrared observations reveal eight …

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Monster In The Dark: The Ultraluminous Grb 080607 And Its Dusty Environment, Dieter H. Hartmann, D. A. Perley, A. N. Morgan, A. Updike, F. Yuan, C. W. Awkerlof, A. A. Miller, J. S. Bloom, S. B. Cenko, W. Li Aug 2010

Monster In The Dark: The Ultraluminous Grb 080607 And Its Dusty Environment, Dieter H. Hartmann, D. A. Perley, A. N. Morgan, A. Updike, F. Yuan, C. W. Awkerlof, A. A. Miller, J. S. Bloom, S. B. Cenko, W. Li

Publications

We present early-time optical through infrared photometry of the bright gamma-ray burst GRB 080607, starting only 6 s following the initial trigger in the rest frame. Complemented by our previously published spectroscopy, this high-quality photometric dataset allows us to solve for the extinction properties of the redshift 3.036 sightline, giving perhaps the most detailed information on the ultraviolet continuum absorption properties of any sightline outside our Local Group to date. The extinction properties are not adequately modeled by any ordinary extinction template (including the average Milky Way, Large Magellanic Cloud, and Small Magellanic Cloud curves), partially because the 2175 A …

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Simulations Of A Monolithic Lanthanum Bromide Gamma-Ray Detector, Camden Ertley, Chris Bancroft, Peter F. Bloser, Taylor Connor, Jason S. Legere, Mark L. Mcconnell, James M. Ryan Aug 2010

Simulations Of A Monolithic Lanthanum Bromide Gamma-Ray Detector, Camden Ertley, Chris Bancroft, Peter F. Bloser, Taylor Connor, Jason S. Legere, Mark L. Mcconnell, James M. Ryan

Space Science Center

We have been working on the development of a detector design for a large area coded aperture imaging system operating in the 10-600 keV energy range. The detector design is based on an array of Lanthanum Bromide (LaBr3) scintillators, each directly coupled to a Hamamatsu 64-channel multi-anode photomultiplier tube (MAPMT). This paper focuses on the development of the GEANT4-based simulations as an aid in the optimization of the detector design. The simulations have been validated by comparisons with various laboratory data sets. We will summarize the current status and latest findings from this study.

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On The Transit Potential Of The Planet Orbiting Iota Draconis, Stephen R. Kane, Sabine Reffert, Gregory W. Henry, Debra A. Fischer, Christian Schwab, Kelsey I. Clubb, Christoph Bergmann Aug 2010

On The Transit Potential Of The Planet Orbiting Iota Draconis, Stephen R. Kane, Sabine Reffert, Gregory W. Henry, Debra A. Fischer, Christian Schwab, Kelsey I. Clubb, Christoph Bergmann

Information Systems and Engineering Management Research Publications

Most of the known transiting exoplanets are in short-period orbits, largely due to the bias inherent in detecting planets through the transit technique. However, the eccentricity distribution of the known radial velocity planets results in many of those planets having a non-negligible transit probability. One such case is the massive planet orbiting the giant star iota Draconis, a situation where both the orientation of the planet's eccentric orbit and the size of the host star inflate the transit probability to a much higher value than for a typical hot Jupiter. Here we present a revised fit of the radial velocity …

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Modeling Broadband X-Ray Absorption Of Massive Star Winds, M. A. Leutenegger, David H. Cohen, J. Zsargó, Erin Marie Martell , '09, James Paton Macarthur , '11, S. P. Owocki, M. Gagné, D. J. Hillier Aug 2010

Modeling Broadband X-Ray Absorption Of Massive Star Winds, M. A. Leutenegger, David H. Cohen, J. Zsargó, Erin Marie Martell , '09, James Paton Macarthur , '11, S. P. Owocki, M. Gagné, D. J. Hillier

Physics & Astronomy Faculty Works

We present a method for computing the net transmission of X-rays emitted by shock-heated plasma distributed throughout a partially optically thick stellar wind from a massive star. We find the transmission by an exact integration of the formal solution, assuming that the emitting plasma and absorbing plasma are mixed at a constant mass ratio above some minimum radius, below which there is assumed to be no emission. This model is more realistic than either the slab absorption associated with a corona at the base of the wind or the exospheric approximation that assumes that all observed X-rays are emitted without …

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On The Disappearance Of The Broad-Line Region In Low-Luminosity Active Galactic Nuclei, Moshe Elitzur, Luis C. Ho Aug 2010

On The Disappearance Of The Broad-Line Region In Low-Luminosity Active Galactic Nuclei, Moshe Elitzur, Luis C. Ho

Physics and Astronomy Faculty Publications

The disk-wind scenario for the broad-line region (BLR) and toroidal obscuration in active galactic nuclei (AGNs) predicts the disappearance of the BLR at low luminosities. In accordance with the model predictions, data from a nearly complete sample of nearby AGNs show that the BLR disappears at luminosities lower than 5 × 1039(M/107 M⊙)2/3 erg s-1, where M is the black hole mass. The radiative efficiency of accretion onto the black hole is ≲10-3 for these sources, indicating that their accretion is advection-dominated.

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Long-Lived Time-Dependent Remnants During Cosmological Symmetry Breaking: From Inflation To The Electroweak Scale, Marcelo Gleiser, Noah Graham, Nikitas Stamatopoulos Aug 2010

Long-Lived Time-Dependent Remnants During Cosmological Symmetry Breaking: From Inflation To The Electroweak Scale, Marcelo Gleiser, Noah Graham, Nikitas Stamatopoulos

Dartmouth Scholarship

Through a detailed numerical investigation in three spatial dimensions, we demonstrate that long-lived time-dependent field configurations emerge dynamically during symmetry breaking in an expanding de Sitter spacetime. We investigate two situations: a single scalar field with a double-well potential and an SU(2) non-Abelian Higgs model. For the single scalar, we show that large-amplitude oscillon configurations emerge spontaneously and persist to contribute about 1.2% of the energy density of the Universe. We also show that for a range of parameters, oscillon lifetimes are enhanced by the expansion and that this effect is a result of parametric resonance. For the SU(2) case, …

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Acoustical Analysis Of A Horn-Loaded Compression Drivers Using Numerical Analysis, Daniel Ross Tengelsen Aug 2010

Acoustical Analysis Of A Horn-Loaded Compression Drivers Using Numerical Analysis, Daniel Ross Tengelsen

Theses and Dissertations

Two numerical techniques, the boundary-element method (BEM) and the finite-difference method (FDM), are used for simulating the radiation from horn-loaded compression drivers and from an infinitely-baffled, finite-length pipe. While computations of the horn-loaded compression driver are in steady state, transient analysis of the finite-length pipe is studied as a precursor to transient analysis within the horn-loaded compression driver. BEM numerical simulations show promise for the development of new designs. Numerical simulations serve as a good tool for time and cost-effective prototyping as poor designs are detected before they are built.

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Perpendicular Ion Heating By Low-Frequency Alfvén-Wave Turbulence In The Solar Wind, Benjamin D. G. Chandran, Bo Li, Barrett N. Rogers, Eliot Quataert, Kai Germaschewski Aug 2010

Perpendicular Ion Heating By Low-Frequency Alfvén-Wave Turbulence In The Solar Wind, Benjamin D. G. Chandran, Bo Li, Barrett N. Rogers, Eliot Quataert, Kai Germaschewski

Dartmouth Scholarship

We consider ion heating by turbulent Alfvén waves (AWs) and kinetic Alfvén waves (KAWs) with wavelengths (measured perpendicular to the magnetic field) that are comparable to the ion gyroradius and frequencies ω smaller than the ion cyclotron frequency Ω. We focus on plasmas in which β < 1, where β is the ratio of plasma pressure to magnetic pressure. As in previous studies, we find that when the turbulence amplitude exceeds a certain threshold, an ion's orbit becomes chaotic. The ion then interacts stochastically with the time-varying electrostatic potential, and the ion's energy undergoes a random walk. Using phenomenological arguments, we derive an analytic expression for the rates at which different ion species are heated, which we test by simulating test particles interacting with a spectrum of randomly phased AWs and KAWs. We find that the stochastic heating rate depends sensitively on the quantity ε = δv ρ/v ⊥, where v ⊥ (v ∥) is the component of the ion velocity perpendicular (parallel) to the background magnetic field B 0, and δv ρ (δB ρ) is the rms amplitude of the velocity (magnetic-field) fluctuations at the gyroradius scale. In the case …

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Temperature And Variability Of Three Ionian Volcanoes, Daniel R. Allen Aug 2010

Temperature And Variability Of Three Ionian Volcanoes, Daniel R. Allen

Theses and Dissertations

Cassini spacecraft images of Io obtained during its flyby of Jupiter in late 2000 and early 2001 were used to determine the lava composition and eruption style of three faint hotspots, Pillan, Wayland, and Loki. We found a maximum color temperature of 1130+/-289 K for Pillan and maximum color temperatures of 1297+/-289 K and 1387+/-287 K for Wayland and Loki, respectively. These temperatures are suggestive of basaltic lava. The temperatures with the best signal-to-noise ratios also suggested basaltic lava and were found to be 780+/-189 K, 1116+/-250 K, and 1017+/-177 K for Pillan, Wayland, and Loki, respectively. Pillan showed increased …

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Potassium Chlorate Decomposition Under High Pressure, Harrison Ruiz, Michael G. Pravica, Martin Galley Aug 2010

Potassium Chlorate Decomposition Under High Pressure, Harrison Ruiz, Michael G. Pravica, Martin Galley

Undergraduate Research Opportunities Program (UROP)

High pressure physics involves placing various substances under high pressure and observing changes in that substance. In this experiment this high amount of pressure is induced using a diamond anvil cell. A diamond anvil cell uses a metal gasket to hold the sample between two diamonds, which will press on the sample to reach high pressures. High pressures are reached with a moderate amount of force by exerting that force over a small area. Diamonds are used for the compression because of their hardness and ability to resist compression. The pressure being exerted on the sample using a diamond anvil …

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Properties Of Z≥6 Galaxies In Cosmological Sph Simulations, Jason Jaacks Aug 2010

Properties Of Z≥6 Galaxies In Cosmological Sph Simulations, Jason Jaacks

Undergraduate Research Opportunities Program (UROP)

Recent upgrades to the Hubble Space Telescope have given observers their deepest look into our Universe yet, seeing nearly 13 billion years into the past. This new observational data has presented those of us that use simulations to study the early Universe a benchmark opportunity to evaluate the ability of these codes to reproduce the photometric properties being observed. Establishing this agreement allows us to probe deeper into the physical properties such as mass, star formation histories and star formation rates of these early galaxies. This research lays the ground work for examining the contribution of primordial galaxies to the …

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Mutation Size Optimizes Speciation In An Evolutionary Model, Nathan Dees, Sonya Bahar Aug 2010

Mutation Size Optimizes Speciation In An Evolutionary Model, Nathan Dees, Sonya Bahar

Physics Faculty Works

The role of mutation rate in optimizing key features of evolutionary dynamics has recently been investigated in various computational models. Here, we address the related question of how maximum mutation size affects the formation of species in a simple computational evolutionary model. We find that the number of species is maximized for intermediate values of a mutation size parameter μ; the result is observed for evolving organisms on a randomly changing landscape as well as in a version of the model where negative feedback exists between the local population size and the fitness provided by the landscape. The same result …

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How Lightning Tortuosity Affects The Electromagnetic Fields By Augmenting Their Effective Distance, S L. Meredith, S K. Earles, I N. Kostanic, Niescja E. Turner, C E. Otero Aug 2010

How Lightning Tortuosity Affects The Electromagnetic Fields By Augmenting Their Effective Distance, S L. Meredith, S K. Earles, I N. Kostanic, Niescja E. Turner, C E. Otero

Physics and Astronomy Faculty Research

A novel approach for developing the electromagnetic fields from a lightning return stroke which follows a tortuous path will be presented. The proposed model is unique in that it recognizes that the symmetrical tortuosity of lightning directly impacts the observable distance r, which in turn, alters the resulting electromagnetic fields. In the literature, lightning return stroke models typically employ the assumption that the cloud-to-ground path is straight. Although this assumption yields fairly consistent results across an array of varying approaches, it does not account for lightning's natural physical appearance. Furthermore, straight-line models only account for the cloud-to-ground discharges and do …

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