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Faculty Publications

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Articles 481 - 510 of 685

Full-Text Articles in Astrophysics and Astronomy

Searches For Periodic Gravitational Waves From Unknown Isolated Sources And Scorpius X-1: Results From The Second Ligo Science Run, B. Abbott, R. Abbott, R. Adhikari, J. Agresti, P. Ajith, B. Allen, R. Amin, S. B. Anderson, W. G. Anderson, M. Arain, M. Araya, H. Armandula, M. Ashley, S. Aston, P. Aufmuth, C. Aulbert, S. Babak, S. Ballmer, H. Bantilan, B. C. Barish, C. Barker, D. Barker, B. Barr, P. Barriga, M. A. Barton, K. Bayer, K. Belczynski, S. J. Berukoff, J. Betzwieser, P. T. Beyersdorf, B. Bhawal, Tiffany Z. Summerscales Oct 2007

Searches For Periodic Gravitational Waves From Unknown Isolated Sources And Scorpius X-1: Results From The Second Ligo Science Run, B. Abbott, R. Abbott, R. Adhikari, J. Agresti, P. Ajith, B. Allen, R. Amin, S. B. Anderson, W. G. Anderson, M. Arain, M. Araya, H. Armandula, M. Ashley, S. Aston, P. Aufmuth, C. Aulbert, S. Babak, S. Ballmer, H. Bantilan, B. C. Barish, C. Barker, D. Barker, B. Barr, P. Barriga, M. A. Barton, K. Bayer, K. Belczynski, S. J. Berukoff, J. Betzwieser, P. T. Beyersdorf, B. Bhawal, Tiffany Z. Summerscales

Faculty Publications

We carry out two searches for periodic gravitational waves using the most sensitive few hours of data from the second LIGO science run. Both searches exploit fully coherent matched filtering and cover wide areas of parameter space, an innovation over previous analyses which requires considerable algorithm development and computational power. The first search is targeted at isolated, previously unknown neutron stars, covers the entire sky in the frequency band 160-728.8 Hz, and assumes a frequency derivative of less than 4×10-10Hz/s. The second search targets the accreting neutron star in the low-mass x-ray binary Scorpius X-1 and covers the frequency bands …

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Search For Gravitational Wave Radiation Associated With The Pulsating Tail Of The Sgr 1806-20 Hyperflare Of 27 December 2004 Using Ligo, B. Abbott, R. Abbott, R. Adhikari, J. Agresti, P. Ajith, B. Allen, R. Amin, S. B. Anderson, W. G. Anderson, M. Arain, M. Araya, H. Armandula, M. Ashley, S. Aston, P. Aufmuth, C. Aulbert, S. Babak, S. Ballmer, H. Bantilan, B. C. Barish, C. Barker, D. Barker, B. Barr, P. Barriga, M. A. Barton, K. Bayer, K. Belczynski, J. Betzwieser, P. T. Beyersdorf, B. Bhawal, I. A. Bilenko, Tiffany Z. Summerscales Sep 2007

Search For Gravitational Wave Radiation Associated With The Pulsating Tail Of The Sgr 1806-20 Hyperflare Of 27 December 2004 Using Ligo, B. Abbott, R. Abbott, R. Adhikari, J. Agresti, P. Ajith, B. Allen, R. Amin, S. B. Anderson, W. G. Anderson, M. Arain, M. Araya, H. Armandula, M. Ashley, S. Aston, P. Aufmuth, C. Aulbert, S. Babak, S. Ballmer, H. Bantilan, B. C. Barish, C. Barker, D. Barker, B. Barr, P. Barriga, M. A. Barton, K. Bayer, K. Belczynski, J. Betzwieser, P. T. Beyersdorf, B. Bhawal, I. A. Bilenko, Tiffany Z. Summerscales

Faculty Publications

We have searched for gravitational waves (GWs) associated with the SGR 1806-20 hyperflare of 27 December 2004. This event, originating from a Galactic neutron star, displayed exceptional energetics. Recent investigations of the x-ray light curve's pulsating tail revealed the presence of quasiperiodic oscillations (QPOs) in the 30-2000 Hz frequency range, most of which coincides with the bandwidth of the LIGO detectors. These QPOs, with well-characterized frequencies, can plausibly be attributed to seismic modes of the neutron star which could emit GWs. Our search targeted potential quasimonochromatic GWs lasting for tens of seconds and emitted at the QPO frequencies. We have …

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Upper Limits On Gravitational Wave Emission From 78 Radio Pulsars, B. Abbott, R. Abbott, R. Adhikari, J. Agresti, P. Ajith, B. Allen, R. Amin, S. B. Anderson, W. G. Anderson, M. Arain, M. Araya, H. Armandula, M. Ashley, S. Aston, P. Aufmuth, C. Aulbert, S. Babak, S. Ballmer, H. Bantilan, B. C. Barish, C. Barker, D. Barker, B. Barr, P. Barriga, M. A. Barton, K. Bayer, K. Belczynski, J. Betzwieser, P. T. Beyersdorf, B. Bhawal, I. A. Bilenko, Tiffany Z. Summerscales Aug 2007

Upper Limits On Gravitational Wave Emission From 78 Radio Pulsars, B. Abbott, R. Abbott, R. Adhikari, J. Agresti, P. Ajith, B. Allen, R. Amin, S. B. Anderson, W. G. Anderson, M. Arain, M. Araya, H. Armandula, M. Ashley, S. Aston, P. Aufmuth, C. Aulbert, S. Babak, S. Ballmer, H. Bantilan, B. C. Barish, C. Barker, D. Barker, B. Barr, P. Barriga, M. A. Barton, K. Bayer, K. Belczynski, J. Betzwieser, P. T. Beyersdorf, B. Bhawal, I. A. Bilenko, Tiffany Z. Summerscales

Faculty Publications

We present upper limits on the gravitational wave emission from 78 radio pulsars based on data from the third and fourth science runs of the LIGO and GEO 600 gravitational wave detectors. The data from both runs have been combined coherently to maximize sensitivity. For the first time, pulsars within binary (or multiple) systems have been included in the search by taking into account the signal modulation due to their orbits. Our upper limits are therefore the first measured for 56 of these pulsars. For the remaining 22, our results improve on previous upper limits by up to a factor …

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First Cross-Correlation Analysis Of Interferometric And Resonant-Bar Gravitational-Wave Data For Stochastic Backgrounds, B. Abbott, R. Abbott, R. Adhikari, J. Agresti, P. Ajith, B. Allen, R. Amin, S. B. Anderson, W. G. Anderson, M. Arain, M. Araya, H. Armandula, M. Ashley, S. Aston, P. Aufmuth, C. Aulbert, S. Babak, S. Ballmer, H. Bantilan, B. C. Barish, C. Barker, D. Barker, B. Barr, P. Barriga, M. A. Barton, K. Bayer, K. Belczynski, J. Betzwieser, P. T. Beyersdorf, B. Bhawal, I. A. Bilenko, Tiffany Z. Summerscales Jul 2007

First Cross-Correlation Analysis Of Interferometric And Resonant-Bar Gravitational-Wave Data For Stochastic Backgrounds, B. Abbott, R. Abbott, R. Adhikari, J. Agresti, P. Ajith, B. Allen, R. Amin, S. B. Anderson, W. G. Anderson, M. Arain, M. Araya, H. Armandula, M. Ashley, S. Aston, P. Aufmuth, C. Aulbert, S. Babak, S. Ballmer, H. Bantilan, B. C. Barish, C. Barker, D. Barker, B. Barr, P. Barriga, M. A. Barton, K. Bayer, K. Belczynski, J. Betzwieser, P. T. Beyersdorf, B. Bhawal, I. A. Bilenko, Tiffany Z. Summerscales

Faculty Publications

Data from the LIGO Livingston interferometer and the ALLEGRO resonant-bar detector, taken during LIGO's fourth science run, were examined for cross correlations indicative of a stochastic gravitational-wave background in the frequency range 850-950 Hz, with most of the sensitivity arising between 905 and 925 Hz. ALLEGRO was operated in three different orientations during the experiment to modulate the relative sign of gravitational-wave and environmental correlations. No statistically significant correlations were seen in any of the orientations, and the results were used to set a Bayesian 90% confidence level upper limit of Ωgw(f)≤1.02, which corresponds to a gravitational-wave strain at 915 …

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Anomalous Magnetic Field Dependence Of The T1 Spin Lifetime In A Lightly Doped Gaas Sample, John S. Colton, M. E. Heeb, P. Schroeder, A. Stokes, L. R. Wienkes, A. S. Bracker May 2007

Anomalous Magnetic Field Dependence Of The T1 Spin Lifetime In A Lightly Doped Gaas Sample, John S. Colton, M. E. Heeb, P. Schroeder, A. Stokes, L. R. Wienkes, A. S. Bracker

Faculty Publications

The T1 spin lifetime of a lightly doped n-type GaAs sample has been measured via time-resolved polarization spectroscopy under a number of temperature and magnetic field conditions. Lifetimes up to 19 μs have been measured. The magnetic field dependence of T1 shows a nonmonotonic behavior, where the spin lifetime first increases, then decreases, then increases again with field. The initial increase in T1 is understood to be due to correlation between electrons localized on donors. The decrease in T1 is likely due to phonon-related spin-orbit relaxation. The final increase in T1 with B indicates a suppression of the spin-orbit relaxation …

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Grating Lobe Reduction In Transducer Arrays Through Structural Filtering Of Supercritical Plates, Brian E. Anderson, Stephen A. Hambric, Jack W. Hughes Mar 2007

Grating Lobe Reduction In Transducer Arrays Through Structural Filtering Of Supercritical Plates, Brian E. Anderson, Stephen A. Hambric, Jack W. Hughes

Faculty Publications

The effect of placing a structural acoustic filter between water and the transducer elements of an array to help reduce undesirable grating lobes is investigated. A supercritical plate is mounted to transducer elements with a thin decoupling polyurethane layer between the transducers and the plate. The plate acts as a radiation/incidence angle filter to pass energy at angles near normal incidence, but suppress energy at large incidence angles. Grating lobe reduction is achieved at the expense of limiting the available steering of the main lobe. Within this steer angle limitation, the main lobe can be steered as normal while the …

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Bounds And Conditions: A Kolob In Our Solar System?, David D. Allred Mar 2007

Bounds And Conditions: A Kolob In Our Solar System?, David D. Allred

Faculty Publications

In 2003, Dialogue ran adjacent essays by two scientists, David Tolman and David Allred. The two Davids had been students together at Princeton, attending the same student ward. Decades after Princeton, Tolman had left Mormonism and Allred had stayed. Their essays are a fascinating juxtaposition. In the course of his piece, David Allred ventured for a few paragraphs into a discussion of the planet Jupiter and its role as a governor and protector in our solar system—a type of Kolob. Although the other author dismissed the topic as “fanciful physics,” my own interest was piqued. I asked Dr. Allred, who …

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Strain-Based Electrical Properties Of Systems Of Carbon Nanotubes Embedded In Parylene, David D. Allred, Jon Brame, Johnathan Goodsell, Stephanie Getty Jan 2007

Strain-Based Electrical Properties Of Systems Of Carbon Nanotubes Embedded In Parylene, David D. Allred, Jon Brame, Johnathan Goodsell, Stephanie Getty

Faculty Publications

We have fabricated flexible electronic devices to test the strain-based change in resistance of a network of single-walled carbon nanotubes (SWCNTs) for use in microscale, high resolution magnetometry. To do this, we first develop a simple, reliable method to obtain catalyst nanoparticles for carbon nanotube growth through indirect, thin-film evaporation. Next we fabricate a two-terminal SWCNT device on a rigid substrate. We then transfer the device, intact, to a flexible substrate for strain testing. Herein, we report progress in growth and measurement techniques.

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Algorithm Refinement For Fluctuating Hydrodynamics, Alejandro Garcia, S. Williams, J. B. Bell Jan 2007

Algorithm Refinement For Fluctuating Hydrodynamics, Alejandro Garcia, S. Williams, J. B. Bell

Faculty Publications

This paper introduces an adaptive mesh and algorithm refinement method for fluctuating hydrodynamics. This particle-continuum hybrid simulates the dynamics of a compressible fluid with thermal fluctuations. The particle algorithm is direct simulation Monte Carlo (DSMC), a molecular-level scheme based on the Boltzmann equation. The continuum algorithm is based on the Landau–Lifshitz Navier–Stokes (LLNS) equations, which incorporate thermal fluctuations into macroscopic hydrodynamics by using stochastic fluxes. It uses a recently developed solver for the LLNS equations based on third-order Runge–Kutta. We present numerical tests of systems in and out of equilibrium, including time-dependent systems, and demonstrate dynamic adaptive refinement by the …

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The Star Pile In Abell 545, R. Salinas, T. Richtler, M. J. West, Aaron J. Romanowsky, Y. Schuberth Jan 2007

The Star Pile In Abell 545, R. Salinas, T. Richtler, M. J. West, Aaron J. Romanowsky, Y. Schuberth

Faculty Publications

Context.Struble (1988, ApJ, 330, L25) found what appeared to be a cD halo without cD galaxy in the center of the galaxy cluster Abell 545. This remarkable feature has been passed almost unnoticed for nearly twenty years. Aims.Our goal is to review Struble's claim by providing a first (preliminary) photometric and spectroscopic analysis of this "star pile". Methods.Based on archival VLT-images and long-slit spectra obtained with Gemini-GMOS, we describe the photometric structure and measure the redshift of the star pile and of the central galaxy. Results.The star pile is indeed associated with Abell 545. Its velocity is higher by about …

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Numerical Methods For The Stochastic Landau-Lifshitz Navier-Stokes Equations, Alejandro Garcia, J. B. Bell, S. Williams Jan 2007

Numerical Methods For The Stochastic Landau-Lifshitz Navier-Stokes Equations, Alejandro Garcia, J. B. Bell, S. Williams

Faculty Publications

The Landau-Lifshitz Navier-Stokes (LLNS) equations incorporate thermal fluctuations into macroscopic hydrodynamics by using stochastic fluxes. This paper examines explicit Eulerian discretizations of the full LLNS equations. Several computational fluid dynamics approaches are considered (including MacCormack’s two-step Lax-Wendroff scheme and the piecewise parabolic method) and are found to give good results for the variance of momentum fluctuations. However, neither of these schemes accurately reproduces the fluctuations in energy or density. We introduce a conservative centered scheme with a third-order Runge-Kutta temporal integrator that does accurately produce fluctuations in density, energy, and momentum. A variety of numerical tests, including the random walk …

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The Pn.S Elliptical Galaxy Survey: Data Reduction, Planetary Nebula Catalog, And Basic Dynamics For Ngc 3379, N. G. Douglas, N. R. Napolitano, Aaron J. Romanowsky, L. Coccato, K. Kuijken, M. R. Merrifield, M. Arnaboldi, O. Gerhard, K. C. Freeman, H. R. Merrett, E. Noordermeer, M. Capaccioli Jan 2007

The Pn.S Elliptical Galaxy Survey: Data Reduction, Planetary Nebula Catalog, And Basic Dynamics For Ngc 3379, N. G. Douglas, N. R. Napolitano, Aaron J. Romanowsky, L. Coccato, K. Kuijken, M. R. Merrifield, M. Arnaboldi, O. Gerhard, K. C. Freeman, H. R. Merrett, E. Noordermeer, M. Capaccioli

Faculty Publications

We present results from Planetary Nebula Spectrograph (PN.S) observations of the elliptical galaxy NGC 3379 and a description of the data reduction pipeline. We detected 214 planetary nebulae, of which 191 are ascribed to NGC 3379 and 23 to the companion galaxy NGC 3384. Comparison with data from the literature shows that the PN.S velocities have an internal error of lesssim20 km s-1 and a possible offset of similar magnitude. We present the results of kinematic modeling and show that the PN kinematics is consistent with absorption-line data in the region where they overlap. The resulting combined kinematic data set, …

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Search For Gravitational-Wave Bursts In Ligo Data From The Fourth Science Run, B. Abbott, R. Abbott, R. Adhikari, J. Agresti, P. Ajith, B. Allen, R. Amin, S. B. Anderson, W. G. Anderson, M. Arain, M. Araya, H. Armandula, M. Ashley, S. Aston, P. Aufmuth, C. Aulbert, S. Babak, S. Ballmer, H. Bantilan, B. C. Barish, C. Barker, D. Barker, B. Barr, P. Barriga, M. A. Barton, K. Bayer, K. Belczynski, J. Betzwieser, P. T. Beyersdorf, B. Bhawal, I. A. Bilenko, Tiffany Z. Summerscales Jan 2007

Search For Gravitational-Wave Bursts In Ligo Data From The Fourth Science Run, B. Abbott, R. Abbott, R. Adhikari, J. Agresti, P. Ajith, B. Allen, R. Amin, S. B. Anderson, W. G. Anderson, M. Arain, M. Araya, H. Armandula, M. Ashley, S. Aston, P. Aufmuth, C. Aulbert, S. Babak, S. Ballmer, H. Bantilan, B. C. Barish, C. Barker, D. Barker, B. Barr, P. Barriga, M. A. Barton, K. Bayer, K. Belczynski, J. Betzwieser, P. T. Beyersdorf, B. Bhawal, I. A. Bilenko, Tiffany Z. Summerscales

Faculty Publications

The fourth science run of the LIGO and GEO 600 gravitational-wave detectors, carried out in early 2005, collected data with significantly lower noise than previous science runs. We report on a search for short-duration gravitational-wave bursts with arbitrary waveform in the 64-1600 Hz frequency range appearing in all three LIGO interferometers. Signal consistency tests, data quality cuts and auxiliary-channel vetoes are applied to reduce the rate of spurious triggers. No gravitational-wave signals are detected in 15.5 days of live observation time; we set a frequentist upper limit of 0.15 day-1 (at 90% confidence level) on the rate of bursts with …

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Ordering Tendencies In The Binary Alloys Of Rh, Pd, Ir, And Pt: Density Functional Calculations, Gus L. W. Hart, Brian Kolb, Stefan Müller, David B. Botts Oct 2006

Ordering Tendencies In The Binary Alloys Of Rh, Pd, Ir, And Pt: Density Functional Calculations, Gus L. W. Hart, Brian Kolb, Stefan Müller, David B. Botts

Faculty Publications

The binary alloys of Rh, Pd, Ir, and Pt are important because of their high catalytic potential. We report in this paper that the Rh1-xIrx and Rh1-xPtx systems, long thought to phase separate at low temperatures, actually exhibit miscibility over the entire concentration and temperature range. We find low critical ordering temperatures, indicating that long-range order is unlikely to be observed experimentally. These results are compared with previous theoretical predications for the other binary alloys of Rh, Pd, Ir, and Pt and with calculations performed here on the Pt1-xIrx and Pd1-xIrx systems. We discuss these results and investigate the mechanisms …

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Fourier Spectroscopy Of Ultrashort Laser Pulses, Scott D. Bergeson, Justin Peatross Sep 2006

Fourier Spectroscopy Of Ultrashort Laser Pulses, Scott D. Bergeson, Justin Peatross

Faculty Publications

We describe a Fourier-transform spectrometer appropriate for use in an undergraduate optics laboratory. The modular design, which uses off-the-shelf equipment, is suitable for determining the spectra of ultrashort pulsed and continuous light sources. The spectrometer does not require equal step sizes for the motion of the mirror. An algorithm interpolates the phase of both a reference and an unknown light beam at equal intervals before performing the Fourier transform. The interferometer scan and the phase and spectral analysis are performed in a few seconds, making the apparatus a useful tool for teaching concepts of temporal coherence and Fourier spectroscopy.

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Mesoscopic Domain Average Engineering Simulations Of Ferroelectric Perovskites Compared With Multidomain Group Theoretical Predictions, Brandon J. Keith, Dorian M. Hatch Aug 2006

Mesoscopic Domain Average Engineering Simulations Of Ferroelectric Perovskites Compared With Multidomain Group Theoretical Predictions, Brandon J. Keith, Dorian M. Hatch

Faculty Publications

Engineered, multidomain ferroelectrics are of current interest for mechatronic and optical applications. Previously [D. M. Hatch et al., J. Appl. Phys. 94, 5220 (2003)], we presented a set of tables/symmetry rules showing all possible domain average engineered multidomain structures arising from [100]-, [110]-, and [111]-ordering ferroelectric transitions from a Pm[overline 3]m perovskite structure. In this work we test those predictions against three-dimensional mesoscopic fast quench simulations under various electric/stress field combinations and find excellent agreement with multidomain group theory. These simulations use a Langevin strain-displacement/polarization evolution strategy and are important to developing processing conditions for materials with precise domain structures.

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Understanding Dc-Bias Sputtered Thorium Oxide Thin Films Useful In Euv Optics, William R. Evans, Sarah C. Barton, Michael Clemens, David D. Allred Aug 2006

Understanding Dc-Bias Sputtered Thorium Oxide Thin Films Useful In Euv Optics, William R. Evans, Sarah C. Barton, Michael Clemens, David D. Allred

Faculty Publications

We use spectroscopic ellipsometry to determine the optical constants of seven thin-film ThO2 samples deposited by radio-frequency sputtering, thickness ranging between 24 and 578 nm, for the spectral range of 1.2 to 6.5. We used a hollow-cathode light source and vacuum monochromator to measure constants at 10.2 eV. None of the deposition parameters studied including DC-bias voltages successfully increased the n of (that is, densify) thoria films. The value of n at 3.0 eV is 1.86 ± 0.04. We find compelling evidence to conclude that the direct bad gap is at ~5.9 eV, clarifying the results of others, some of …

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Compositional Stability Of Fept Nanoparticles On Sio2/Si During Annealing, Richard R. Vanfleet, B. Yao, R. V. Petrova, K. R. Coffey Apr 2006

Compositional Stability Of Fept Nanoparticles On Sio2/Si During Annealing, Richard R. Vanfleet, B. Yao, R. V. Petrova, K. R. Coffey

Faculty Publications

The loss of Fe due to oxidation or diffusion into the substrate can prevent the successful preparation of well-ordered, stoichiometric, FePt nanoparticles. In this work we report the composition changes during annealing observed for small (<10 nm) FePt nanoparticles on thermally grown SiO2 layers on Si wafer substrates. Additionally, we describe the use of a controlled reducing gas mixture, Ar+H2+H2O, to reduce the loss of Fe.

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Compact Solid-State Laser Source For 1s-2s Spectroscopy In Atomic Hydrogen, Scott D. Bergeson, N. Kolachevsky, J. Alnis, T. W. Hansch Feb 2006

Compact Solid-State Laser Source For 1s-2s Spectroscopy In Atomic Hydrogen, Scott D. Bergeson, N. Kolachevsky, J. Alnis, T. W. Hansch

Faculty Publications

We demonstrate a compact solid-state laser source for high-resolution two-photon spectroscopy of the 1S-2S transition in atomic hydrogen. The source emits up to 20 mW at 243 nm and consists of a 972 nm diode laser, a tapered amplifier, and two doubling stages. The diode laser is actively stabilized to a high-finesse cavity. We compare the new source to the stable 486 nm dye laser used in previous experiments and record 1S-2S spectra using both systems. With the solid-state laser system, we demonstrate a resolution of the hydrogen spectrometer of 6×10^11, which is promising for a number of high-precision measurements …

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Finding The Radial Parallel Temperature Profile In A Non-Neutral Plasma Using Equilibrium Calculations On Experimental Data, Grant W. Hart, Bryan G. Peterson Feb 2006

Finding The Radial Parallel Temperature Profile In A Non-Neutral Plasma Using Equilibrium Calculations On Experimental Data, Grant W. Hart, Bryan G. Peterson

Faculty Publications

In 1992, Eggleston et al. [D. L. Eggleston et al., Phys. Fluids B 4, 3432 (1992)] reported on a technique for measuring the radial temperature profile in a pure-electron plasma confined in a Malmberg-Penning trap by partially dumping the plasma onto a charge collector at the end of the trap. For short plasmas and short confining rings, the assumptions in their paper are violated and a more general calculation is needed. This paper presents a variation of the standard equilibrium calculation to find the temperature profile of a pure-electron plasma. Eggleston's shortcut "evaporation" temperature method is found to require a …

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A Deep Kinematic Survey Of Planetary Nebulae In The Andromeda Galaxy Using The Planetary Nebula Spectrograph, H. R. Merrett, M. R. Merrifield, N. G. Douglas, K. Kuijken, Aaron J. Romanowsky, N. R. Napolitano, M. Arnaboldi, M. Capaccioli, K. C. Freeman, O. Gerhard, L. Coccato, D. Carter, N. W. Evans, M. I. Wilkinson, C. Halliday, T. J. Bridges Jan 2006

A Deep Kinematic Survey Of Planetary Nebulae In The Andromeda Galaxy Using The Planetary Nebula Spectrograph, H. R. Merrett, M. R. Merrifield, N. G. Douglas, K. Kuijken, Aaron J. Romanowsky, N. R. Napolitano, M. Arnaboldi, M. Capaccioli, K. C. Freeman, O. Gerhard, L. Coccato, D. Carter, N. W. Evans, M. I. Wilkinson, C. Halliday, T. J. Bridges

Faculty Publications

We present a catalogue of positions, magnitudes and velocities for 3300 emission-line objects found by the Planetary Nebula Spectrograph in a survey of the Andromeda galaxy, M31. Of these objects, 2615 are found likely to be planetary nebulae (PNe) associated with M31. The survey area covers the whole of M31's disc out to a radius of Graphic. Beyond this radius, observations have been made along the major and minor axes, and the Northern Spur and Southern Stream regions. The calibrated data have been checked for internal consistency and compared with other catalogues. With the exception of the very central, high …

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Planetary Nebula Velocities In The Disc And Bulge Of M31, C. Halliday, D. Carter, T. J. Bridges, Z. C. Jackson, M. I. Wilkinson, D. P. Quinn, N. W. Evans, N. G. Douglas, H. R. Merrett, Aaron J. Romanowsky, K. Kuijken, M. J. Irwin Jan 2006

Planetary Nebula Velocities In The Disc And Bulge Of M31, C. Halliday, D. Carter, T. J. Bridges, Z. C. Jackson, M. I. Wilkinson, D. P. Quinn, N. W. Evans, N. G. Douglas, H. R. Merrett, Aaron J. Romanowsky, K. Kuijken, M. J. Irwin

Faculty Publications

We present radial velocities for a sample of 723 planetary nebulae in the disc and bulge of M31, measured using the WYFFOS fibre spectrograph on the William Herschel Telescope. Velocities are determined using the [O III] λ5007 emission line. Rotation and velocity dispersion are measured to a radius of 50 arcmin (11.5 kpc), the first stellar rotation curve and velocity dispersion profile for M31 to such a radius. Our kinematics are consistent with rotational support at radii well beyond the bulge effective radius of 1.4 kpc, although our data beyond a radius of 5 kpc are limited. We present tentative …

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Wide-Field Kinematics Of Globular Clusters In The Leo I Group, G. Bergond, S. E. Zepf, Aaron J. Romanowsky, R. M. Sharples, K. L. Rhode Jan 2006

Wide-Field Kinematics Of Globular Clusters In The Leo I Group, G. Bergond, S. E. Zepf, Aaron J. Romanowsky, R. M. Sharples, K. L. Rhode

Faculty Publications

We present wide-field spectroscopy of globular clusters around the Leo I group galaxies NGC 3379 and NGC 3384 using the FLAMES multi-fibre instrument at the VLT. We obtain accurate radial velocities for 42 globular clusters (GCs) in total, 30 for GCs around the elliptical NGC 3379, eight around the lenticular NGC 3384, and four which may be associated with either galaxy. These data are notable for their large radial range extending from 0$\farcm$7 to 14$\farcm$5 (2 to 42 kpc) from the centre of NGC 3379, and small velocity uncertainties of about 10 km s-1. We combine our sample of 30 …

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The Araucaria Project. An Accurate Distance To Ngc 6822 From Near-Infrared Photometry Of Cepheid Variables, W. Gieren, G. Pietrzyński, K. Nalewajko, I. Soszyński, F. Bresolin, R.-P. Kudritzki, D. Minniti, Aaron J. Romanowsky Jan 2006

The Araucaria Project. An Accurate Distance To Ngc 6822 From Near-Infrared Photometry Of Cepheid Variables, W. Gieren, G. Pietrzyński, K. Nalewajko, I. Soszyński, F. Bresolin, R.-P. Kudritzki, D. Minniti, Aaron J. Romanowsky

Faculty Publications

We have measured near-infrared magnitudes in the J and K bands for 56 Cepheid variables in the Local Group galaxy NGC 6822 with well-determined periods and optical light curves in the V and I bands. Using the template light-curve approach of Soszyński and coworkers, accurate mean magnitudes were obtained from these data, which allowed us to determine with unprecedented accuracy the distance to NGC 6822 from a multiwavelength period-luminosity solution in the VIJK bands. From our data, we obtain a distance to NGC 6822 of (m - M)0 = 23.312 ± 0.021 (random error) mag, with an additional systematic uncertainty …

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Estimating Hydrodynamic Quantities In The Presence Of Microscopic Fluctuations, Alejandro Garcia Jan 2006

Estimating Hydrodynamic Quantities In The Presence Of Microscopic Fluctuations, Alejandro Garcia

Faculty Publications

This paper discusses the evaluation of hydrodynamic variables in the presence of spontaneous fluctuations, such as in molecular simulations of fluid flows. The principal point is that hydrodynamic variables such as fluid velocity and temperature must be defined in terms of mechanical variables such as momentum and energy density). Because these relations are nonlinear and because fluctuations of mechanical variables are correlated, care must be taken to avoid introducing a bias when evaluating means, variances, and correlations of hydrodynamic variables. The unbiased estimates are formulated; some alternative, incorrect approaches are presented as cautionary warnings. The expressions are verified by numerical …

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Hydrodynamic Description Of The Adiabatic Piston, Alejandro Garcia, M. M. Mansour Jan 2006

Hydrodynamic Description Of The Adiabatic Piston, Alejandro Garcia, M. M. Mansour

Faculty Publications

A closed macroscopic equation for the motion of the two-dimensional adiabatic piston is derived from standard hydrodynamics. It predicts a damped oscillatory motion of the piston towards a final rest position, which depends on the initial state. In the limit of large piston mass, the solution of this equation is in quantitative agreement with the results obtained from both hard disk molecular dynamics and hydrodynamics. The explicit forms of the basic characteristics of the piston’s dynamics, such as the period of oscillations and the relaxation time, are derived. The limitations of the theory’s validity, in terms of the main system …

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High-Temperature Calcium Vapor Cell For Spectroscopy On The 4s2 1s0-4s4p 3p1 Intercombination Line, Christopher J. Erickson, Brian Neyenhuis, Dallin S. Durfee Dec 2005

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 …

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Nonmetal Ordering In Tic1-Xnx: Ground-State Structure And The Effects Of Finite Temperature, Gus L. W. Hart, Brian Kolb Dec 2005

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 …

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Ultracold Neutral Plasma Expansion In Two Dimensions, E. A. Cummings, J. E. Daily, Dallin S. Durfee, Scott D. Bergeson Dec 2005

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

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Fluorescence Measurements Of Expanding Strongly Coupled Neutral Plasmas, E. A. Cummings, J. E. Daily, Dallin S. Durfee, Scott D. Bergeson Nov 2005

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.

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