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Articles 61 - 90 of 105
Full-Text Articles in Astrophysics and Astronomy
Starbursts Versus Truncated Star Formation In Nearby Clusters Of Galaxies, James A. Rose, Alejandro E. E. Gaba, Nelson Caldwell, Brian Chaboyer
Starbursts Versus Truncated Star Formation In Nearby Clusters Of Galaxies, James A. Rose, Alejandro E. E. Gaba, Nelson Caldwell, Brian Chaboyer
Dartmouth Scholarship
We present long-slit spectroscopy, B - and R -bandpass imaging, and 21 cm observations of a sample of early-type galaxies in nearby clusters, which are known to be either in a star-forming phase or to have had star formation that recently terminated. From the long-slit spectra, obtained with the Blanco 4 m telescope, we ‹nd that emission lines in the star-forming cluster galaxies are signi‹cantly more centrally concentrated than in a sample of ‹eld galaxies. The broadband imaging reveals that two currently starforming early-type galaxies in the Pegasus I cluster have blue nuclei, again indicating that recent star formation has …
Gas Mass Fractions And The Evolution Of Low Surface Brightness Dwarf Galaxies, Stacy S. Mcgaugh
Gas Mass Fractions And The Evolution Of Low Surface Brightness Dwarf Galaxies, Stacy S. Mcgaugh
Faculty Scholarship
The optical and H I properties are presented for a sample of low surface brightness (LSB) dwarf galaxies, cataloged from the Second Palomar Sky Survey. Gas mass fractions for LSB dwarfs reach the highest levels of any know galaxy type (fg = 95%), confirming that their low stellar densities are due to inefficient conversion of gas mass into stellar mass. Comparison with star formation models indicates that the blue optical colors of LSB dwarfs are not due to low metallicity or to recent star formation and can only be explained by a dominant stellar population less than 5 Gyr in …
Long‐Term Vri Photometry Of Small‐Amplitude Red Variables. I. Light Curves And Periods, John R. Percy, Joseph B. Wilson, Gregory W. Henry
Long‐Term Vri Photometry Of Small‐Amplitude Red Variables. I. Light Curves And Periods, John R. Percy, Joseph B. Wilson, Gregory W. Henry
Information Systems and Engineering Management Research Publications
We report up to 5000 days of VRI photometry, from a robotic photometric telescope, of 34 pulsating red giants, namely, TV Psc, EG And, Z Psc, RZ And, 4 Ori, RX Lep, UW Lyn, η Gem, μ Gem, ψ1 Aur, V523 Mon, V614 Mon, HD 52690, Y Lyn, BC CMi, X Cnc, UX Lyn, RS Cnc, VY UMa, ST UMa, TU CVn, FS Com, SW Vir, 30 Her, α1 Her, V642 Her, R Lyr, V450 Aql, V1293 Aql, δ Sge, EU Del, V1070 Cyg, W Cyg, and μ Cep, as well as a few variable comparison stars. V …
Energy Content Of The Stormtime Ring Current, Niescja E. Turner, D N. Baker, T I. Pulkkinen, J L. Roeder, J F. Fennell, V K. Jordanova
Energy Content Of The Stormtime Ring Current, Niescja E. Turner, D N. Baker, T I. Pulkkinen, J L. Roeder, J F. Fennell, V K. Jordanova
Physics and Astronomy Faculty Research
Given the important role the ring current plays in magnetospheric energetics, it is essential to understand its strength and evolution in disturbed times. There are currently three main methods for deducing the strength of the ring current: measuring ground magnetic perturbations, measuring high-altitude magnetic perturbations, or directly measuring ring current particles. The use of ground magnetometers is the most convenient, and many use the ground magnetometer-derived Dst index as a proxy for the ring current. Recent work suggests, however, that a substantial portion of Dst may not be caused only by the ring current but also by local induction effects …
Heating And Ionization Of The Intergalactic Medium By An Early X-Ray Background, Aparna Venkatesan, Mark L. Giroux, J Shull
Heating And Ionization Of The Intergalactic Medium By An Early X-Ray Background, Aparna Venkatesan, Mark L. Giroux, J Shull
Physics and Astronomy
Observational studies indicate that the intergalactic medium (IGM) is highly ionized up to redshifts just over 6. A number of models have been developed to describe the process of reionization and the effects of the ionizing photons from the first luminous objects. In this paper we study the impact of an X-ray background, such as high-energy photons from early quasars, on the temperature and ionization of the IGM prior to reionization, before the fully ionized bubbles associated with individual sources have overlapped. X-rays have large mean free paths relative to EUV photons, and their photoelectrons can have significant effects on …
Molecular Simulations Of Sound Wave Propagation In Simple Gases, Alejandro Garcia, N. Hadjiconstantinou
Molecular Simulations Of Sound Wave Propagation In Simple Gases, Alejandro Garcia, N. Hadjiconstantinou
Faculty Publications
Molecular simulations of sound waves propagating in a dilute hard sphere gas have been performed using the direct simulation Monte Carlo method. A wide range of frequencies is investigated, including very high frequencies for which the period is much shorter than the mean collision time. The simulation results are compared to experimental data and approximate solutions of the Boltzmann equation. It is shown that free molecular flow is important at distances smaller than one mean free path from the excitation point.
10 New Γ Doradus And Δ Scuti Stars, Gregory W. Henry, Francis C. Fekel, Anthony B. Kaye, Ann Kaul
10 New Γ Doradus And Δ Scuti Stars, Gregory W. Henry, Francis C. Fekel, Anthony B. Kaye, Ann Kaul
Information Systems and Engineering Management Research Publications
We present high-resolution spectroscopy and precision photometry of five new γ Doradus and five new δ Scuti variables. The five new γ Doradus variables substantially increase the number of confirmed stars of this class. All 10 stars fall in the spectral class range F0–F2, but they are cleanly separated into two groups by their luminosity and photometric periods. However, the period gap between the γ Doradus and δ Scuti stars is becoming very narrow since we confirm that HD 155154 is a γ Doradus star with the shortest periods reported to date (the shortest of its four periods is ∼0.312 …
Can Post T Tauri Stars Be Found? Yes!, Eric L.N. Jensen
Can Post T Tauri Stars Be Found? Yes!, Eric L.N. Jensen
Physics & Astronomy Faculty Works
I review the observational challenges of finding post T Tauri stars (PTTS), defined here as low-mass, pre-main-sequence stars with ages of 10(7)-10(8) yr. Such stars are difficult to find because they are less active than younger T Tauri stars, and they may not be associated with molecular gas. They are useful for studying the evolution of circumstellar disks and stellar activity between the 10(6)-yr ages of nearby star-forming regions and the main sequence. However, care must be taken in the search process so that the selection criteria used to locate such stars do not bias the sample used for subsequent …
Disk Clearing In The Young Binary Ak Sco, Eric L.N. Jensen
Disk Clearing In The Young Binary Ak Sco, Eric L.N. Jensen
Physics & Astronomy Faculty Works
The pre-main-sequence spectroscopic binary AK Sco is surrounded by a circumbinary disk. Yet while this disk must be somewhat disturbed by the binary at its center, there is no evidence from current data that it has a cleared central hole like those seen in some young binaries, nor that accretion from the outer disk has been cut off. Indeed, most of its spectral and photometric diagnostics are indistinguishable from those of young single stars. Why doesn't this system show any evidence of disturbance of its disk? It may be that the center of the disk is indeed largely cleared, but …
Disks In Young Binary Systems: Unresolved Millimeter-Wave Observations, Eric L.N. Jensen
Disks In Young Binary Systems: Unresolved Millimeter-Wave Observations, Eric L.N. Jensen
Physics & Astronomy Faculty Works
Observations at millimeter and submillimeter wavelengths are sensitive to the total mass of circumstellar and circumbinary dust in a multiple system, and in some cases single-dish observations can help constrain the location of disk material in spite of their lack of spatial resolution. Young binary stars show a great diversity of disk properties, with a large part of the variation accounted for by binary separation. Many of the closest binaries (those with separations a less than a few AU) harbor massive circumbinary disks. Binaries with a greater than or equal to 100 AU tend to have massive circumstellar disks. In …
Ring Current Ion Composition During Solar Minimum And Rising Solar Activity: Polar/Cammice/Mics Results, T I. Pulkkinen, N Yu Ganushkina, D N. Baker, Niescja E. Turner, J F. Fennell, J L. Roeder, T A. Fritz, M Grande, B Kellett, G Kettmann
Ring Current Ion Composition During Solar Minimum And Rising Solar Activity: Polar/Cammice/Mics Results, T I. Pulkkinen, N Yu Ganushkina, D N. Baker, Niescja E. Turner, J F. Fennell, J L. Roeder, T A. Fritz, M Grande, B Kellett, G Kettmann
Physics and Astronomy Faculty Research
This paper shows statistical results of the ring current ion composition and its variability as a function of solar cycle and magnetospheric activity for 3 < L < 8. Spin-averaged energetic particle (1-200 keV) measurements from Polar are combined with geomagnetic indices as well as solar wind and interplanetary observations from the Wind spacecraft during a period from September 1996 to March 1999. The statistics are performed both for time-averaged values for all periods as well as for peak flux values during geomagnetic storms (defined as Dst < -50 nT) that occurred during this period. The average O+ energy density increases by about a factor of 5 during the rising phase of the solar cycle from the minimum values in 1996, while the average values of H+ and He show variability but no consistently increasing trend. The O+ flux is small (below 10%) compared with the hydrogen flux, and the average energy density ranges from a few percent at solar minimum to ∼10% at high solar activity time in …
Study Of 5 And 10 Mm Thick Czt Strip Detectors, John R. Macri, Pierre C. Dufour, L A. Hamel, M Julien, Mark L. Mcconnell, M Mcclish, James M. Ryan, Mark Widholm
Study Of 5 And 10 Mm Thick Czt Strip Detectors, John R. Macri, Pierre C. Dufour, L A. Hamel, M Julien, Mark L. Mcconnell, M Mcclish, James M. Ryan, Mark Widholm
Space Science Center
We report progress in the study of 5 and 10 mm thick CZT strip detectors featuring orthogonal coplanar anode contacts. This novel anode geometry combines the advantages of pixel detectors with those of double-sided strip detectors. Like pixel detectors, these are electron-only devices that perform well as hard x-ray and y-ray spectrometers and imagers even in the thicker configurations required for reasonable detection efficiency at 1 MeV. Like double-sided strip detectors in an N x N configuration, these detectors require only 2N readout channels to form N2 “pixels”. Unlike doublesided strip detectors, all signal contacts for spectroscopy and 3- d …
Comptel Gamma-Ray Observations Of The C4 Solar Flare On 20 January 2000, C A. Young, M B. Arndt, K Bennett, A Connors, H Debrunner, R Diehl, Mark L. Mcconnell, R S. Miller, G Rank, James M. Ryan, V Schonfelder, C Winkler
Comptel Gamma-Ray Observations Of The C4 Solar Flare On 20 January 2000, C A. Young, M B. Arndt, K Bennett, A Connors, H Debrunner, R Diehl, Mark L. Mcconnell, R S. Miller, G Rank, James M. Ryan, V Schonfelder, C Winkler
Space Science Center
The “Pre-SMM” (Vestrand and Miller 1998) picture of gamma-ray line (GRL) flares was that they are relatively rare events. This picture was quickly put in question with the launch of the Solar Maximum Mission (SMM). Over 100 GRL flares were seen with sizes ranging from very large GOES class events (X12) down to moderately small events (M2). It was argued by some (Bai 1986) that this was still consistent with the idea that GRL events are rare. Others, however, argued the opposite (Vestrand 1988; Cliver, Crosby and Dennis 1994), stating that the lower end of this distribution was just a …
Sontrac—A Scintillating Plastic Fiber Tracking Detector For Neutron And Proton Imaging Spectroscopy, James M. Ryan, John R. Macri, Mark L. Mcconnell, R S. Miller
Sontrac—A Scintillating Plastic Fiber Tracking Detector For Neutron And Proton Imaging Spectroscopy, James M. Ryan, John R. Macri, Mark L. Mcconnell, R S. Miller
Space Science Center
SONTRAC (SOlar Neutron TRACking imager and spectrometer) is a conceptual instrument intended to measure the energy and incident direction of 20–150 MeV neutrons produced in solar flares. The intense neutron background in a low-Earth orbit requires that imaging techniques be employed to maximize an instrument’s signal-to-noise ratio. The instrument is comprised of mutually perpendicular, alternating layers of parallel, scintillating, plastic fibers that are viewed by optoelectronic devices. Two stereoscopic views of recoil proton tracks are necessary to determine the incident neutron’s direction and energy. The instrument can also be used as a powerful energetic proton imager. Data from a fully …
Comptel Observations Of The Blazars 3c 454.3 And Cta 102, S Zhang, W Collmar, V Schonfelder, H Bloemen, W Hermsen, Mark L. Mcconnell, K Bennett, O R. Williams
Comptel Observations Of The Blazars 3c 454.3 And Cta 102, S Zhang, W Collmar, V Schonfelder, H Bloemen, W Hermsen, Mark L. Mcconnell, K Bennett, O R. Williams
Space Science Center
We have analyzed the two blazars of 3C 454.3 and CTA 102 using all available COMPTEL data from 1991 to 1999. In the 10–30 MeV band, emission from the general direction of the sources is found at the 4σ-level, being consistent with contributions from both sources. Below 10 MeV only 3C 454.3 is significantly detected, with the strongest evidence (5.6 σ) in the 3–10 MeV band. Significant flux variability is not observed for both sources, while a low emission is seen most of the years in the 3–10 MeV light curve for 3C 454.3. Its time-averaged MeV spectrum suggests a …
Comptel Observations Of The Virgo Blazars 3c 273 And 3c 279, W Collmar, V Schonfelder, S Zhang, H Bloemen, W Hermsen, Mark L. Mcconnell, K Bennett, O R. Williams
Comptel Observations Of The Virgo Blazars 3c 273 And 3c 279, W Collmar, V Schonfelder, S Zhang, H Bloemen, W Hermsen, Mark L. Mcconnell, K Bennett, O R. Williams
Space Science Center
We report the main MeV properties (detections, light curves, spectra) of the Virgo blazars 3C 273 and 3C 279 which were derived from a consistent analysis of all COMPTEL Virgo observations between 1991 and 1997.
Bayesian Multiscale Deconvolution Applied To Gamma-Ray Spectroscopy, C A. Young, A Connors, E Kolaczyk, Mark L. Mcconnell, G Rank, James M. Ryan, V Schonfelder
Bayesian Multiscale Deconvolution Applied To Gamma-Ray Spectroscopy, C A. Young, A Connors, E Kolaczyk, Mark L. Mcconnell, G Rank, James M. Ryan, V Schonfelder
Space Science Center
A common task in gamma-ray astronomy is to extract spectral information, such as model constraints and incident photon spectrum estimates, given the measured energy deposited in a detector and the detector response. This is the classic problem of spectral “deconvolution” or spectral inversion. The methods of forward folding (i.e., parameter fitting) and maximum entropy “deconvolution” (i.e., estimating independent input photon rates for each individual energy bin) have been used successfully for gamma-ray solar flares (e.g., Rank, 1997; Share and Murphy, 1995). These methods have worked well under certain conditions but there are situations were they don’t apply. These are: 1) …
Gamma-Ray Spectral Variability Of Cygnus X-1, Mark L. Mcconnell, K Bennett, H Bloemen, W Collmar, W Hermsen, L Kuiper, W Paciesas, B F. Phlips, J Poutanen, James M. Ryan, V Schonfelder, H Steinle, A W. Strong, A A. Zdziarski
Gamma-Ray Spectral Variability Of Cygnus X-1, Mark L. Mcconnell, K Bennett, H Bloemen, W Collmar, W Hermsen, L Kuiper, W Paciesas, B F. Phlips, J Poutanen, James M. Ryan, V Schonfelder, H Steinle, A W. Strong, A A. Zdziarski
Space Science Center
We have used observations from CGRO to study the variation in the MeV emission of Cygnus X-1 between its low and high X-ray states. These data provide a measurement of the spectral variability above 1 MeV. The high state MeV spectrum is found to be much harder than that of the low state MeV spectrum. In particular, the power-law emission seen at hard X-ray energies in the high state spectrum (with a photon spectral index of 2.6) is found to extend out to at least 5 MeV, with no evidence for any cutoff. Here we present the data and describe …
Energetic Proton Spectra In The 11 June 1991 Solar Flare, C A. Young, K Bennett, A Connors, R Diehl, Mark L. Mcconnell, G Rank, James M. Ryan, R Suleiman, V Schonfelder, C Winkler
Energetic Proton Spectra In The 11 June 1991 Solar Flare, C A. Young, K Bennett, A Connors, R Diehl, Mark L. Mcconnell, G Rank, James M. Ryan, R Suleiman, V Schonfelder, C Winkler
Space Science Center
The June 11, 1991 gamma-ray flare seen by the Compton Gamma-ray Observatory (CGRO) displays several features that make it a dynamic and rich event. It is a member of a class of long duration gamma-ray events with both 2.223 MeV and greater than 8 MeV emission for hours after the impulsive phase. It also contains an inter-phase between the impulsive and extended phases that presents a challenge to the standard gamma-ray line (GRL) flare picture. This phase has strong 2.223 MeV emission and relatively weak 4.44 MeV emission indicative of a very hard parent proton spectrum. However, this would indicate …
X- And Gamma-Ray Observations Of The 15 November 1991 Solar Flare, M B. Arndt, A Connors, J Lockwood, Mark L. Mcconnell, R Suleiman, James M. Ryan, C A. Young, G Rank, V Schonfelder, H Debrunner, K Bennett, O R. Williams, C Winkler
X- And Gamma-Ray Observations Of The 15 November 1991 Solar Flare, M B. Arndt, A Connors, J Lockwood, Mark L. Mcconnell, R Suleiman, James M. Ryan, C A. Young, G Rank, V Schonfelder, H Debrunner, K Bennett, O R. Williams, C Winkler
Space Science Center
This work expands the current understanding of the 15 November 1991 Solar Flare. The flare was a well observed event in radio to gamma-rays and is the first flare to be extensively studied with the benefit of detailed soft and hard X-ray images. In this work, we add data from all four instruments on the Compton Gamma Ray Observatory. Using these data we determined that the accelerated electron spectrum above 170 keV is best fit with a power law with a spectral index of −4.6, while the accelerated proton spectrum above 0.6 MeV is fit with a power law of …
The Milagro Gamma-Ray Observatory, J E. Mcenery, R Atkins, W Benbow, D Berley, M L. Chen, D G. Coyne, B L. Dingus, D E. Dorfan, R W. Ellsworth, D Evans, A Falcone, L Fleysher, R Fleysher, G Gisler, J A. Goodman, T J. Haines, C M. Hoffman, S Hugenberger, L A. Kelley, I Leonor, Mark L. Mcconnell, J F. Mccullough, R S. Miller, A I. Mincer, M F. Morales, P Nemethy, James M. Ryan, B Shen, A Shoup, C Sinnis, A J. Smith, G W. Sullivan, O T. Tumer, K Wang, M O. Wascko, S Westerhoff, D A. Williams, G B. Yodh
The Milagro Gamma-Ray Observatory, J E. Mcenery, R Atkins, W Benbow, D Berley, M L. Chen, D G. Coyne, B L. Dingus, D E. Dorfan, R W. Ellsworth, D Evans, A Falcone, L Fleysher, R Fleysher, G Gisler, J A. Goodman, T J. Haines, C M. Hoffman, S Hugenberger, L A. Kelley, I Leonor, Mark L. Mcconnell, J F. Mccullough, R S. Miller, A I. Mincer, M F. Morales, P Nemethy, James M. Ryan, B Shen, A Shoup, C Sinnis, A J. Smith, G W. Sullivan, O T. Tumer, K Wang, M O. Wascko, S Westerhoff, D A. Williams, G B. Yodh
Space Science Center
The Milagro water Cherenkov detector began full operation in January 2000. This detector is capable of monitoring the Northern sky at energies above 500 GeV for sources of equivalent strength to the Crab Nebula over one year of integration. We report on the current performance and sensitivity of Milagro.
Effective Field Theory For The Small-X Evolution, I. Balitsky
Effective Field Theory For The Small-X Evolution, I. Balitsky
Physics Faculty Publications
The small-x behavior of structure functions in the saturation region is determined by the non-linear generalization of the BFKL equation. I suggest the effective field theory for the small-x evolution which solves formally this equation. The result is the 2+1 functional integral for the structure functions at small x.
Hα Imaging With Hubble Space Telescope-Nicmos Of An Elusive Damped Lyα Cloud At Z = 0.61, Nicolas Bouché, James D. Lowenthal, Jane C. Charlton, Matthew A. Bershady, Christopher W. Churchill, Charles C. Steidel
Hα Imaging With Hubble Space Telescope-Nicmos Of An Elusive Damped Lyα Cloud At Z = 0.61, Nicolas Bouché, James D. Lowenthal, Jane C. Charlton, Matthew A. Bershady, Christopher W. Churchill, Charles C. Steidel
Astronomy: Faculty Publications
Despite previous intensive ground-based imaging and spectroscopic campaigns and wideband Hubble Space Telescope (HST) imaging of the z = 0.927 QSO 3C 336 field, the galaxy that hosts the damped Lyα system along this line of sight has eluded detection. We present a deep narrowband Hα image of the field of this zabs = 0.656 damped Lyα absorber, obtained through the F108N filter of NICMOSI on board the HST. The goal of this project was to detect any Hα emission 10 times closer than previous studies to unveil the damped absorber. We do not detect Hα emission between 0".05 and …
Designing Adaptive Low-Dissipative High Order Schemes For Long-Time Integrations, Helen Yee, Bjorn Sjögreen
Designing Adaptive Low-Dissipative High Order Schemes For Long-Time Integrations, Helen Yee, Bjorn Sjögreen
United States National Aeronautics and Space Administration: Publications
A general framework for the design of adaptive low-dissipative high order schemes is presented. It encompasses a rather complete treatment of the numerical approach based on four integrated design criteria: (1) For stability considerations, condition the governing equations before the application of the appropriate numerical scheme whenever it is possible. (2) For consistency, compatible schemes that possess stability properties, including physical and numerical boundary condition treatments, similar to those of the discrete analogue of the continuum are preferred. (3) For the minimization of numerical dissipation contamination, efficient and adaptive numerical dissipation control to further improve nonlinear stability and accuracy should …
White Dwarfs In Common Proper Motion Binary Systems: Mass Distribution And Kinematics, Nicole M. Silvestri, Terry D. Oswalt, Matt A. Wood, Jonathan Allyn Smith, Iain Neill Reid, Edward M. Sión
White Dwarfs In Common Proper Motion Binary Systems: Mass Distribution And Kinematics, Nicole M. Silvestri, Terry D. Oswalt, Matt A. Wood, Jonathan Allyn Smith, Iain Neill Reid, Edward M. Sión
Aerospace, Physics, and Space Science Faculty 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 M⊙. 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 tend to …
Multi-Phase Transport Study Of Relativistic Nuclear Collisions, Bin Zhang, C. M. Ko, Bao-An Li, Ziwei Lin, Subrata Pal
Multi-Phase Transport Study Of Relativistic Nuclear Collisions, Bin Zhang, C. M. Ko, Bao-An Li, Ziwei Lin, Subrata Pal
Journal of the Arkansas Academy of Science
A multi-phase transport model (AMPT) is developed for the study of hot and dense matter produced in relativistic nuclear collisions. This model includes both initial partonic and final hadronic scattering. Using the AMPT model, we study the momentum distributions of charged particles such as protons, antiprotons, pions, and kaons in central heavy ion collisions at Super Proton Synchrotron (SPS) and Relativistic Heavy Ion Collider (RHIC) energies. The results are consistent with experimental data at these energies. They indicate a significant nuclear shadowing but a relative weak jet quenching in the initial dense matter. Antiproton to proton ratio at mid-rapidity increases …
Exclusive Electroproduction Of ᵠ Mesons At 4.2 Gev, M. Bektasoglu, L. Ciciani, G. E. Dodge, T. A. Forest, C. E. Hyde-Wright, S. E. Kuhn, L. M. Qin, F. Sabatié, L. B. Weinstein, Et Al., The Clas Collaboration
Exclusive Electroproduction Of ᵠ Mesons At 4.2 Gev, M. Bektasoglu, L. Ciciani, G. E. Dodge, T. A. Forest, C. E. Hyde-Wright, S. E. Kuhn, L. M. Qin, F. Sabatié, L. B. Weinstein, Et Al., The Clas Collaboration
Physics Faculty Publications
We studied the exclusive reaction ep → e' p' ᵠ using the ᵠ →K+K- decay mode. The data were collected using a 4.2 GeV incident electron beam and the CEBAF Large Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility. Our experiment covers the range in Q2 from 0.7 to 2.2 GeV2and W from 2.0 to 2.6 GeV. Taken together with all previous data, we find a consistent picture of ᵠ production on the proton. Our measurement shows the expected decrease of the t slope with the vector-meson formation time c Δ t …
Break Out Session: The Future Of White Dwarf Observing, Ted Von Hippel
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?
White Dwarfs In Open Clusters: New Tests Of Stellar Evolution And The Age Of The Galaxy, Ted Von Hippel
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.
Building Blocks For Reliable Complex Nonlinear Numerical Simulations, Helen Yee
Building Blocks For Reliable Complex Nonlinear Numerical Simulations, Helen Yee
United States National Aeronautics and Space Administration: Publications
This chapter describes some of the building blocks to ensure a higher level of confidence in the predictability and reliability (PAR) of numerical simulation of multiscale complex nonlinear problems. The focus is on relating PAR of numerical simulations with complex nonlinear phenomena of numerics. To isolate sources of numerical uncertainties, the possible discrepancy between the chosen partial differential equation (PDE) model and the real physics and/or experimental data is set aside. The discussion is restricted to how well numerical schemes can mimic the solution behavior of the underlying PDE model for finite time steps and grid spacings. The situation is …