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Articles 1291 - 1320 of 1383

Full-Text Articles in Physical Sciences and Mathematics

White Dwarfs In Common Proper Motion Binary Systems: Mass Distribution And Kinematics, Nicole M. Silvestri, Terry D. Oswalt, Matt A. Wood, J. Allyn Smith, I. Neill Reid, Edward M. Sion Jan 2001

White Dwarfs In Common Proper Motion Binary Systems: Mass Distribution And Kinematics, Nicole M. Silvestri, Terry D. Oswalt, Matt A. Wood, J. Allyn Smith, I. Neill Reid, Edward M. Sion

Publications

We present the mass distribution, gravitational redshifts, radial velocities, and space motions of white dwarf stars in common proper motion binary systems. The mass distribution we derive for the 41 DA white dwarfs in this study has a mean of 0.68 ± 0.04 MꙨ. This distribution has a slightly higher mean and larger dispersion than most previous white dwarf studies. We hypothesize that this is due to a higher fraction of cool (average Teff ̴ 10,000 K), hence old, white dwarfs in our sample. Our results indicate that samples made up of predominantly cool, old white dwarf stars …

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White Dwarfs In Open Clusters: New Tests Of Stellar Evolution And The Age Of The Galaxy, Ted Von Hippel Jan 2001

White Dwarfs In Open Clusters: New Tests Of Stellar Evolution And The Age Of The Galaxy, Ted Von Hippel

Publications

White dwarf cooling theory and very deep observations in star clusters provide a new tool to test stellar evolution theory and time scales. In particular, white dwarf cooling theory is now testing the degree of enhanced core mixing in stars with turnoff ages of 1 to 2 Gyr. More generally, I show the good overall agreement between white dwarf and modern isochrone ages over the range 0.1 to 4 Gyr.

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Break Out Session: The Future Of White Dwarf Observing, Ted Von Hippel Jan 2001

Break Out Session: The Future Of White Dwarf Observing, Ted Von Hippel

Publications

On Thursday, June 15, 2000 the conference participants joined on of four afternoon break out sessions. Our break out session was charged with addressing the the following questions: Astronomy is changing. Eight to ten meter telescopes looking towards the edge of the Universe will dominate the astronomical landscape. Queue scheduling, large surveys, and the current emphasis towards the red end of the spectrum will also affect us. What consequences do these changes imply for our field? How can we convince telescope assignment committees to grand observing time to proposers from our community?

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The Savannah River Site: Site Description, Land Use And Management History, David L. White, Karen F. Gaines Dec 2000

The Savannah River Site: Site Description, Land Use And Management History, David L. White, Karen F. Gaines

Publications

The 78,000-ha Savannah River Site, which is located in the upper Coastal Plain of South Carolina along the Savannah River, was established as a nuclear production facility in 1951 by the Atomic Energy Commission. The site’s physical and vegetative characteristics, land use history, and the impacts of management and operations are described. Aboriginal and early European settlement was primarily along streams, where much of the farming and timber cutting have occurred. Woodland grazing occurred in the uplands and lowlands. Land use intensity increased after the Civil War and peaked in the 1920s. Impacts from production of cotton and corn, naval …

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Secular Variations Of Atomic Oxygen In The Mesopause Region Induced By Transient Gravity Wave Packets, Michael P. Hickey Ph.D., R. L. Walterscheid, Philip G. Richards Nov 2000

Secular Variations Of Atomic Oxygen In The Mesopause Region Induced By Transient Gravity Wave Packets, Michael P. Hickey Ph.D., R. L. Walterscheid, Philip G. Richards

Publications

We employ a 2-dimensional, time-dependent, fully nonlinear model of minor species in the mesopause region and our Spectral Full-Wave Model to simulate the response of atomic oxygen (O) to a gravity wave packet in the mesopause region. We demonstrate that gravity waves affect the time-averaged distribution of O in the mesosphere and lower thermosphere (MLT) region through the constituent fluxes the waves induce. Our conclusions are based on simulations of two wave packets that violate the non-acceleration conditions through transience and dissipation. The net cycle-averaged effect of the waves is to significantly increase (by as much as 50%) the O …

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Book Review: 3-D Atlas Of Stars And Galaxies, T. D. Oswalt Nov 2000

Book Review: 3-D Atlas Of Stars And Galaxies, T. D. Oswalt

Publications

This document is Dr. Oswalt’s review of 3-D Atlas of Stars and Galaxies by Richard Monkhouse and John Cox Springer, 2000. 95p, 1-85233-189-5 $42.00.

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Resolving Ambiguities In Gravity Wave Propagation Directions Inherent In Satellite Observations: A Simulation Study, Michael P. Hickey Ph.D., Jason S. Brown Sep 2000

Resolving Ambiguities In Gravity Wave Propagation Directions Inherent In Satellite Observations: A Simulation Study, Michael P. Hickey Ph.D., Jason S. Brown

Publications

We simulate space-based, sub-limb viewing observations of airglow brightness fluctuations caused by atmospheric gravity wave interactions with the O2 atmospheric airglow, and we demonstrate that, due to the geometry associated with such observations, the brightness fluctuations observed for the optically thick 0–0 band emission will always appear stronger for waves traveling towards the observer (satellite). The effect should be most noticeable for waves having relatively small vertical wavelengths (∼10 km) and horizontal wavelengths of 50 km or greater. For waves of short (∼100 km) horizontal wavelength, the brightness fluctuation anisotropy with respect to viewing direction may also be evident in …

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The White Dwarf Cooling Age Of The Open Cluster Ngc 2420, Ted Von Hippel, Gerard Gilmore Sep 2000

The White Dwarf Cooling Age Of The Open Cluster Ngc 2420, Ted Von Hippel, Gerard Gilmore

Publications

We have used deep HST WFPC2 observations of two fields in NGC 2420 to produce a cluster color-magnitude diagram down to V ≈ 27. After imposing morphological selection criteria we find eight candidate white dwarfs in NGC 2420. Our completeness estimates indicate that we have found the terminus of the WD cooling sequence. We argue that the cluster distance modulus is likely to be close to 12.10 with E(B-V) = 0.04. With these parameters we find a white dwarf cooling age for NGC 2420 of 2.0 ± 0.20 (1 σ) Gyr. The 0.20 Gyr uncertainty includes errors in the photometry, …

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Characterization Of An Isolate That Uses Vinyl Chloride As A Growth Substrate Under Aerobic Conditions, Matthew F. Verce, Ricky L. Ulrich, David L. Freedman Aug 2000

Characterization Of An Isolate That Uses Vinyl Chloride As A Growth Substrate Under Aerobic Conditions, Matthew F. Verce, Ricky L. Ulrich, David L. Freedman

Publications

An aerobic enrichment culture was developed by using vinyl chloride (VC) as the sole organic carbon and electron donor source. VC concentrations as high as 7.3 mM were biodegraded without apparent inhibition. VC use did not occur when nitrate was provided as the electron acceptor. A gram-negative, rod-shaped, motile isolate was obtained from the enrichment culture and identified based on biochemical characteristics and the sequence of its 16S rRNA gene as Pseudomonas aeruginosa, designated strain MF1. The observed yield of MF1 when it was grown on VC was 0.20 mg of total suspended solids (TSS)/mg of VC. Ethene, acetate, glyoxylate, …

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Mpi Collective Operations Over Ip Multicast, Amy Apon, H A. Chen, Y O. Carrasco May 2000

Mpi Collective Operations Over Ip Multicast, Amy Apon, H A. Chen, Y O. Carrasco

Publications

Many common implementations of Message Passing Inter- face (MPI) implement collective operations over point-to-point operations. This work examines IP multicast as a framework for collective operations. IP multicast is not reliable. If a receiver is not ready when a message is sent via IP multicast, the message is lost. Two techniques for ensuring that a message is not lost due to a slow receiving process are examined. The techniques are implemented and compared experimentally over both a shared and a switched Fast Ethernet. The average performance of collective operations is improved as a function of the number of participating processes …

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An Elliptic Equation With Spike Solutions Concentrating At Local Minima Of The Laplacian Of The Potential, Gregory S. Spradlin May 2000

An Elliptic Equation With Spike Solutions Concentrating At Local Minima Of The Laplacian Of The Potential, Gregory S. Spradlin

Publications

We consider the equation −ԑ2∆u + V (z)u = f(u) which arises in the study of nonlinear Schrödinger equations. We seek solutions that are positive on RN and that vanish at infinity. Under the assumption that f satisfies super-linear and sub-critical growth conditions, we show that for small ԑ there exist solutions that concentrate near local minima of V. The local minima may occur in unbounded components, as long as the Laplacian of V achieves a strict local minimum along such a component. Our proofs employ vibrational mountain-pass and concentration compactness arguments. A penalization technique developed by Felmer and del …

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The Wiyn Open Cluster Study: A New Color-Magnitude Diagram For M35 - A Twin Of The Pleiades, Ted Von Hippel, Vera Kozhurina-Platais, Imants Platais, Pierre Demarque, Ata Sarajedini Jan 2000

The Wiyn Open Cluster Study: A New Color-Magnitude Diagram For M35 - A Twin Of The Pleiades, Ted Von Hippel, Vera Kozhurina-Platais, Imants Platais, Pierre Demarque, Ata Sarajedini

Publications

M35 (NGC 2168) is rich, young, and in some regards a bet­ter laboratory for stellar cluster research at 100 million years than the Pleiades. Yet, while M35 has been the subject of intriguing photometric, astrometric, and theoretical studies, to the best of our knowledge no pub­lished CCD-based photometry exists for this cluster. We have obtained relatively wide-field (23' x23') precise UBVRJ CCD photometry for M35 as part of the WIYN Open Cluster Study (WOCS) at the 0.9m telescope at Kitt Peak National Observatory. The photometry extends from the main sequence turn off to beyond V = 19. We find that …

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Book Review: The Birth Of Time: How Astronomers Measured The Age Of The Universe, T. D. Oswalt Jan 2000

Book Review: The Birth Of Time: How Astronomers Measured The Age Of The Universe, T. D. Oswalt

Publications

This document is Dr. Oswalt’s review of The Birth of Time : How Astronomers Measured the Age of the Universe by John Gribbin. Yale, 2000 237p, 0-300-08346-7 $22.50.

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(Teff,Log G,[Fe/H]) Classification Of Low-Resolution Stellar Spectra Using Artificial Neural Networks, Shawn Snider, Yuan Qu, Carlos Allende Prieto, Ted Von Hippel, Timothy C. Beers, Christopher Sneden, David L. Lambert, Silvia Rossi Dec 1999

(Teff,Log G,[Fe/H]) Classification Of Low-Resolution Stellar Spectra Using Artificial Neural Networks, Shawn Snider, Yuan Qu, Carlos Allende Prieto, Ted Von Hippel, Timothy C. Beers, Christopher Sneden, David L. Lambert, Silvia Rossi

Publications

New generation large-aperture telescopes, multi-object spectrographs, and large format detectors are making it possible to acquire very large samples of stellar spectra rapidly. In this context, traditional star-by-star spectroscopic analysis are no longer practical. New tools are required that are capable of extracting quickly and with reasonable accuracy important basic stellar parameters coded in the spectra. Recent analyses of Artificial Neural Networks (ANNs) applied to the classification of astronomical spectra have demonstrated the ability of this concept to derive estimates of temperature and luminosity. We have adapted the back-propagation ANN technique developed by von Hippel et al. (1994) to predict …

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Wiyn Open Cluster Study. Ii. Ubvri Ccd Photometry Of The Open Cluster Ngc 188, Ata Sarajedini, Ted Von Hippel, Vera Kozhurina-Platais, Pierre Demarque Dec 1999

Wiyn Open Cluster Study. Ii. Ubvri Ccd Photometry Of The Open Cluster Ngc 188, Ata Sarajedini, Ted Von Hippel, Vera Kozhurina-Platais, Pierre Demarque

Publications

We present high-precision UBVRI CCD photometry of the old open cluster NGC 188. Our color-magnitude diagram extends from near the red giant branch tip to as faint as ~5 mag below the main-sequence turnoff. From an analysis of these data along with published photometry for M67, we draw the following conclusions: (1) From the UBV two-color diagram, we find a reddening of E(B ̶ V) = 0.04 ± 0.02 for M67 and E(B ̶ V) = 0.09 ± 0.02 for NGC 188. (2) Based on main-sequence fitting to solar abundance isochrones, the distance moduli …

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Enhanced Biotransformation Of Carbon Tetrachloride By Acetobacterium Woodii Upon Addition Of Hydroxocobalamin And Fructose, Syed A. Hashsham, David L. Freedman Oct 1999

Enhanced Biotransformation Of Carbon Tetrachloride By Acetobacterium Woodii Upon Addition Of Hydroxocobalamin And Fructose, Syed A. Hashsham, David L. Freedman

Publications

The objective of this study was to evaluate the effect of hydroxocobalamin (OH-Cbl) on transformation of high concentrations of carbon tetrachloride (CT) by Acetobacterium woodii (ATCC 29683). Complete transfor-mation of 470 􀀀M (72 mg/liter [aqueous]) CT was achieved by A. woodii within 2.5 days, when 10 􀀀M OH-Cbl was added along with 25.2 mM fructose. This was approximately 30 times faster than A. woodii cultures (live or autoclaved) and medium that did not receive OH-Cbl and 5 times faster than those controls that did receive OH-Cbl, but either live A. woodii or fructose was missing. CT transformation in treatments with …

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A Review Of Automated Stellar Spectral Classification And Surveys, Ted Von Hippel, Coryn A.L. Bailer-Jones Sep 1999

A Review Of Automated Stellar Spectral Classification And Surveys, Ted Von Hippel, Coryn A.L. Bailer-Jones

Publications

Modern spectroscopic surveys and automated classifiers are becoming so inextricably linked that it is difficult even to summarize one without discussing the other. Some of the automated classifiers are being built because of current analysis needs, though with a clear anticipation of future, larger surveys. Other automated classifiers are being designed specifically for future surveys. Automated classifiers may be applied to databases already in hand, to real-time analysis at the telescope, or one day to on-board satellite analysis where the raw data are too bulky to save and transmit. In addition, many current spectroscopic surveys target galaxies. These surveys may …

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Observations And Interpretation Of Gravity Wave Induced Fluctuations In The O I (557.7 Nm) Airglow, G. Schubert, R. L. Walterscheid, Michael P. Hickey Ph.D., C. A. Tepley Jul 1999

Observations And Interpretation Of Gravity Wave Induced Fluctuations In The O I (557.7 Nm) Airglow, G. Schubert, R. L. Walterscheid, Michael P. Hickey Ph.D., C. A. Tepley

Publications

Observations of fluctuations in the intensity and temperature of the O I (557.7 nm) airglow taken at Arecibo in 1989 are reported and interpreted on the assumption that they are caused by gravity waves propagating through the emission layer. The data give the magnitude of Krassovsky's ratio as 3.5 ± 2.2, at periods between about 5 and 10 hours. Comparison with theory shows that the gravity waves responsible for the measured airglow variations must have long wavelengths of several thousand kilometers. The observed phases of Krassovsky's ratio are in good agreement with theoretically predicted values at the long wavelengths and …

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Evaluation Of Real-Time Fiber Communications For Parallel Collective Operations, Amy Apon, Parvathi Rajagopal Apr 1999

Evaluation Of Real-Time Fiber Communications For Parallel Collective Operations, Amy Apon, Parvathi Rajagopal

Publications

Real-Time Fiber Communications (RTFC) is a gigabit speed network that has been designed for damage tolerant local area networks. In addition to its damage tolerant characteristics, it has several features that make it attractive as a possible interconnection technology for parallel applications in a cluster of workstations. These characteristics include support for broadcast and multicast messaging, memory cache in the network interface card, and support for very fine grain writes to the network cache. Broadcast data is captured in network cache of all workstations in the network providing a distributed shared memory capability. In this paper, RTFC is introduced. The …

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Load Dependent Single Chain Models Of Multichain Closed Queueing Networks, Amy Apon, Lawrence Dowdy Mar 1999

Load Dependent Single Chain Models Of Multichain Closed Queueing Networks, Amy Apon, Lawrence Dowdy

Publications

No abstract provided.

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A Note On Gravity Wave-Driven Volume Emission Rate Weighted Temperature Perturbations Inferred From O₂ Atmospheric And O I 5577 Airglow Observations, Michael P. Hickey Ph.D., Richard L. Walterscheid Mar 1999

A Note On Gravity Wave-Driven Volume Emission Rate Weighted Temperature Perturbations Inferred From O₂ Atmospheric And O I 5577 Airglow Observations, Michael P. Hickey Ph.D., Richard L. Walterscheid

Publications

A full-wave dynamical model and chemistry models that simulate ground-based observations of gravity wave-driven O₂ atmospheric and O I 5577 airglow fluctuations in the mesopause region are used to demonstrate that for many observable gravity waves modeling is required to infer temperature perturbation amplitudes from airglow observations. We demonstrate that the amplitude of the altitude-integrated volume emission rate weighted temperature perturbation differs by at least about 30% from the amplitude of the temperature perturbation of the major gas in the vicinity of the peak of the airglow volume emission rate for gravity waves with horizontal phase speeds less than about …

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Thermal Plasmaspheric Morphology: Effect Of Geomagnetic And Solar Activity, Mark Anthony Reynolds, G. Ganguli, J.A. Fedder, J. Lemaire, R.R. Meier, D.J. Melendez-Alvira Jan 1999

Thermal Plasmaspheric Morphology: Effect Of Geomagnetic And Solar Activity, Mark Anthony Reynolds, G. Ganguli, J.A. Fedder, J. Lemaire, R.R. Meier, D.J. Melendez-Alvira

Publications

A multispecies kinetic model of the thermal plasma in the plasmasphere is used to predict the spatial dependence of the hydrogen ion and helium ion density and temperature for different levels of geomagnetic and solar activity. The particular convection electric field model chosen is intended for the time intervals between substorms. The plasma density and temperature in the equatorial plane are found to exhibit a local-time variation that is sensitive to the details of the convection electric field. In particular, the parallel temperature increases with altitude and the perpendicular temperature decreases with altitude, except in the postmidnight sector, features that …

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Wiyn Open Cluster Study. I. Deep Photometry Of Ngc188, Ted Von Hippel, Ata Sarajedini Oct 1998

Wiyn Open Cluster Study. I. Deep Photometry Of Ngc188, Ted Von Hippel, Ata Sarajedini

Publications

We have employed precise and carefully calibrated V - and I - band photometry of NGC 188 at WIYN Observatory to explore the cluster luminosity function (LF) and study the cluster white dwarfs. Our photometry is offset by V = 0.052 (fainter) from that of Sandage and Eggen & Sandage. All published photometry for the past three decades has been based on these two calibrations, which are in error by 0.05 ± 0.01. We employ the Pinsonneault et al. fiducial open cluster main sequence to derive a distance modulus of 11.43 ± 0.08 and E(B - V )=0.09, with …

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Weyl-Type Fields With Geodesic Lines Of Force, Brendan Guilfoyle Sep 1998

Weyl-Type Fields With Geodesic Lines Of Force, Brendan Guilfoyle

Publications

The static electrogravitational equations are studied and it is shown that an aligned type D metric which has a Weyl-type relationship between the gravitational and electric potential has shearfree geodesic lines of force. All such fields are then found and turn out to be the fields of a charged sphere, charged infinite rod and charged infinite plate. A further solution is also found with shearing geodesic lines of force. This new solution can have m > |e| or m < |e|, but cannot be in the Majumdar-Papapetrou class (in which m = |e|). It is algebraically general and has flat equipotential surfaces.

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Detection Of Intergalactic Red-Giant-Branch Stars In The Virgo Cluster, Henry C. Ferguson, Ted Von Hippel, Nial R. Tanvir Aug 1998

Detection Of Intergalactic Red-Giant-Branch Stars In The Virgo Cluster, Henry C. Ferguson, Ted Von Hippel, Nial R. Tanvir

Publications

It has been suspected for nearly 50 years that clusters of galaxies contain a population of intergalactic stars, ripped from galaxies during cluster formation or when the galaxies’ orbits take them through the cluster center. Support for the existence of such a population of free-floating stars comes from measurements of the diffuse light in clusters and from recent detections of planetary nebulae with positions and/or velocities far removed from any observed cluster galaxy. 10 , 11 But estimates for the mass of the diffuse population and its distribution relative to the galaxies are still highly uncertain. Here we report the …

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Semi-Automated Extraction Of Digital Objective Prism Spectra, Coryn A.L. Bailer-Jones, Ted Von Hippel, Mike Irwin Aug 1998

Semi-Automated Extraction Of Digital Objective Prism Spectra, Coryn A.L. Bailer-Jones, Ted Von Hippel, Mike Irwin

Publications

We describe a method for the extraction of spectra from high dispersion objective prism plates. Our method is a catalogue driven plate solution approach, making use of the Right Ascension and Declination coordinates for the target objects. In contrast to existing methods of photographic plate reduction, we digitize the entire plate and extract spectra off-line. This approach has the advantages that it can be applied to CCD objective prism images, and spectra can be re-extracted (or additional spectra extracted) without having to re-scan the plate. After a brief initial interactive period, the subsequent reduction procedure is completely automatic, resulting in …

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White Dwarf Cosmochronometry. I. Monte Carlo Simulations Of Proper-Motion ̶ And Magnitude-Limited Samples Using Schmidt’S 1/Vmax Estimator, Matt A. Wood, Terry D. Oswalt Apr 1998

White Dwarf Cosmochronometry. I. Monte Carlo Simulations Of Proper-Motion ̶ And Magnitude-Limited Samples Using Schmidt’S 1/Vmax Estimator, Matt A. Wood, Terry D. Oswalt

Publications

Observationally, white dwarf stars are a remarkably homogeneous class with a minimum observed Teff ~4000 K. Theoretically, the physics that determines their cooling timescales is relatively more straightforward than that which determines main-sequence evolutionary timescales. As a result, the white dwarf luminosity function has for the last decade been used as a probe of the age and star formation rate of the Galactic disk, providing an estimated local disk age of ~10 Gyr with estimated total uncertainties of roughly 20%. A long-standing criticism of the technique is that the reality of the reported downturn in the luminosity function (LF) …

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Contribution Of White Dwarfs To Cluster Masses, Ted Von Hippel Apr 1998

Contribution Of White Dwarfs To Cluster Masses, Ted Von Hippel

Publications

I have undertaken a literature search through 1997 July 31 of white dwarfs (WDs) in open and globular clusters. I have tried to make a careful evaluation in each case of the likelihood that the object is a WD and that it is a cluster member. The results are presented for 13 open clusters and 11 globular clusters. Currently there are 36 single WDs and Ðve WDs in binaries known among the open clusters, and 340 single WDs and 11 WDs in binaries known among the globular clusters. From these data, I have calculated WD mass fractions for four open …

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Contribution Of White Dwarfs To Cluster Masses, Ted Von Hippel Apr 1998

Contribution Of White Dwarfs To Cluster Masses, Ted Von Hippel

Publications

I have undertaken a literature search through 1997 July 31 of white dwarfs (WDs) in open and globular clusters. I have tried to make a careful evaluation in each case of the likelihood that the object is a WD and that it is a cluster member. The results are presented for 13 open clusters and 11 globular clusters. Currently there are 36 single WDs and Ðve WDs in binaries known among the open clusters, and 340 single WDs and 11 WDs in binaries known among the globular clusters. From these data, I have calculated WD mass fractions for four open …

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Steps Toward Determination Of The Size And Structure Of The Broad-Line Region In Active Galactic Nuclei. Xii. Ground-Based Monitoring Of 3c 390.3, M. Dietrich, Terry D. Oswalt, B. M. Peterson, P. Albrecht, M. Altmann, Et Al. Apr 1998

Steps Toward Determination Of The Size And Structure Of The Broad-Line Region In Active Galactic Nuclei. Xii. Ground-Based Monitoring Of 3c 390.3, M. Dietrich, Terry D. Oswalt, B. M. Peterson, P. Albrecht, M. Altmann, Et Al.

Publications

Results of a ground-based optical monitoring campaign on 3C 390.3 in 1994-1995 are presented. The broadband fluxes (B, V, R, and I), the spectrophotometric optical continuum flux and the Fλ(5177 Å),integrated emission-line fluxes of Hᵪ Hβ, Hᵧ, He I λ5876 and He II λ4686 all show a nearly monotonic increase with episodes of milder short-term variations superposed. The amplitude of the continuum variations increases with decreasing wavelength (4400-9000 Å). The optical continuum variations follow the variations in the ultraviolet and X-ray with time delays, measured from the centroids of the cross-correlation functions, typically around …

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