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Articles 1201 - 1230 of 1383
Full-Text Articles in Physical Sciences and Mathematics
Integral/Spi Limits On Electron-Positron Annihilation Radiation From The Galactic Plane, B. J. Teegarden, K. Watanabe, P. Jean, J. Knödlseder, V. Lonjou, J. P. Roques, G. K. Skinner, P. Von Ballmoos, G. Weidenspointer, A Bazzano, Y M. Butt, A Decourchelle, A C. Fabian, A Goldwurm, M Gudel, D C. Hannikainen, Dieter H. Hartmann
Integral/Spi Limits On Electron-Positron Annihilation Radiation From The Galactic Plane, B. J. Teegarden, K. Watanabe, P. Jean, J. Knödlseder, V. Lonjou, J. P. Roques, G. K. Skinner, P. Von Ballmoos, G. Weidenspointer, A Bazzano, Y M. Butt, A Decourchelle, A C. Fabian, A Goldwurm, M Gudel, D C. Hannikainen, Dieter H. Hartmann
Publications
The center of our Galaxy is a known strong source of electron-positron 511 keV annihilation radiation. Thus far, however, there have been no reliable detection of annihilation radiation outside of the central radian of our Galaxy. One of the primary objectives of the INTEGRAL (International Gamma-Ray Astrophysics Laboratory mission, resolution, coded-apeture gamma-ray telescope with an unprecedented combination of sensitivity, angular resolution, and energy resolution. We resport results from the first 10 months of observation. During this period a significant fraction of the observing time was spent in or near the Galactic plan. No positive annihilation flux was detected outside of …
Book Review: The New Amateur Astronomer, T. D. Oswalt
Book Review: The New Amateur Astronomer, T. D. Oswalt
Publications
This document is Dr. Oswalt’s review of The New Amateur Astronomer by Martin Mobberley. Springer, 2004 229p, 1852336633 $34.95
The Chromospheric Activity And Ages Of M Dwarf Stars In Wide Binary Systems, Nicole M. Silvesteri, T. D. Oswalt, Suzanne L. Hawley
The Chromospheric Activity And Ages Of M Dwarf Stars In Wide Binary Systems, Nicole M. Silvesteri, T. D. Oswalt, Suzanne L. Hawley
Publications
We investigate the relationship between age and chromospheric activity for 139 M dwarf stars in wide binary systems with white dwarf companions. The age of each system is determined from the cooling age of its white dwarf component. The current limit for activity-age relations found for M dwarfs in open clusters is 4 Gyr. Our unique approach to finding ages for M stars allows for the exploration of this relationship at ages older than 4 Gyr. The general trend of stars remaining active for a longer time at later spectral type is confirmed. However, our larger sample and greater age …
The Dyad Theory Of Classical And Quantum Physics, Preston Jones
The Dyad Theory Of Classical And Quantum Physics, Preston Jones
Publications
The 4-space equations of hydrodynamics, electrodynamics, and quantum mechanics are developed using the dyad calculus. Gravity is found to couple hydrodynamics, electrodynamics, and quantum mechanics through the 4- space metric and differential operator. Expanding the 4-space equations of electrodynamics a time varying metric is shown to dissipate electromagnetic energy.
Robust Control Techniques For State Tracking In The Presence Of Variable Time Delays, Jarrett Goodell, Marc Compere, Miguel Simon, Wilford Smith, Ronnie Wright, Mark Brudnak
Robust Control Techniques For State Tracking In The Presence Of Variable Time Delays, Jarrett Goodell, Marc Compere, Miguel Simon, Wilford Smith, Ronnie Wright, Mark Brudnak
Publications
In this paper, a distributed driver-in-the-Ioop and hardware-in-the-Ioop simulator is described with a driver on a motion simulator at the U.S. Army TARDEC Ground Vehicle Simulation Laboratory (GVSL). Realistic power system response is achieved by linking the driver in the GVSL with a full-sized hybrid electric power system located 2,450 miles away at the TARDEC Power and Energy Systems Integration Laboratory (P&E SIL), which is developed and maintained by Science Applications International Corporation (SAIC). The goal is to close the loop between the GVSL and P&E SIL over the Internet to provide a realistic driving experience in addition to realistic …
A Full-Wave Investigation Of The Use Of A ‘‘Cancellation Factor’’ In Gravity Wave–Oh Airglow Interaction Studies, Michael P. Hickey Ph.D., Yonghui Yu
A Full-Wave Investigation Of The Use Of A ‘‘Cancellation Factor’’ In Gravity Wave–Oh Airglow Interaction Studies, Michael P. Hickey Ph.D., Yonghui Yu
Publications
Atmospheric gravity waves (GWs) perturb minor species involved in the chemical reactions of airglow emissions in the upper mesosphere and lower thermosphere. In order to determine gravity wave fluxes and the forcing effects of gravity waves on the mean state (which are proportional to the square of the wave amplitude), it is essential that the amplitude of airglow brightness fluctuation be related to the amplitude of major gas density fluctuation in a deterministic way. This has been achieved through detailed modeling combining gravity wave dynamics described using a full-wave model with the chemistry relevant to the airglow emission of interest. …
Transient Non-Linear Heat Conduction Solution By A Dual Reciprocity Boundary Element Method With An Effective Posteriori Error Estimator, Eduardo Divo, Alain J. Kassab
Transient Non-Linear Heat Conduction Solution By A Dual Reciprocity Boundary Element Method With An Effective Posteriori Error Estimator, Eduardo Divo, Alain J. Kassab
Publications
A Dual Reciprocity Boundary Element Method is formulated to solve non-linear heat conduction problems. The approach is based on using the Kirchhoff transform along with lagging of the effective non-linear thermal diffusivity. A posteriori error estimate is used to provide effective estimates of the temporal and spatial error. A numerical example is used to demonstrate the approach.
Onset Conditions For Equatorial Spread F Determined During Equis Ii, D. L. Hysell, M. F. Larsen, C. M. Swenson, Aroh Barjatya, T. F. Wheeler, M. F. Sarango, Et.Al
Onset Conditions For Equatorial Spread F Determined During Equis Ii, D. L. Hysell, M. F. Larsen, C. M. Swenson, Aroh Barjatya, T. F. Wheeler, M. F. Sarango, Et.Al
Publications
An investigation into the dynamics and layer structure of the postsunset ionosphere prior to the onset of equatorial spread F (ESF) took place during the NASA EQUIS II campaign on Kwajalein Atoll on August 7 and 15, 2004. On both nights, an instrumented rocket measured plasma number density and vector electric fields to an apogee of about 450 km. Two chemical release rockets were launched both nights to measure lower thermospheric wind profiles. The Altair UHF/VHF radar was used to monitor coherent and incoherent scatter. In both experiments, strong plasma shear flow was detected. Periodic, patchy bottom-type scattering layers were …
The Initial-Final Mass Relationship: Spectroscopy Of White Dwarfs In Ngc 2099 (M37), Jasonjot Singh Kalirai, Ted Von Hippel, Et Al.
The Initial-Final Mass Relationship: Spectroscopy Of White Dwarfs In Ngc 2099 (M37), Jasonjot Singh Kalirai, Ted Von Hippel, Et Al.
Publications
We present new observations of very faint white dwarfs (WDs) in the rich open star cluster NGC 2099 (M37). Following deep, wide-field imaging of the cluster using the Canada-France-Hawaii Telescope, we have now obtained spectroscopic observations of candidate WDs using both the Gemini Multi-Object Spectrograph on Gemini North and the Low-Resolution Imaging Spectrometer on Keck. Of our 24 WD candidates (all fainter than V = 22.4), 21 are spectroscopically confirmed to be bona fide WDs, four or five of which are most likely field objects. Fitting 18 of the 21 WD spectra with model atmospheres, we find that most WDs …
Discovery Of Co Gas In The Inner Disk Of Tw Hydrae, Terrence W. Rettig, Joe Haywood, Theodore Simon, Sean D. Brittain, Erika Gibb
Discovery Of Co Gas In The Inner Disk Of Tw Hydrae, Terrence W. Rettig, Joe Haywood, Theodore Simon, Sean D. Brittain, Erika Gibb
Publications
We report the detection of rovibrationally excited CO emission from the inner disk of the classical T Tauri star (cTTS) TW Hya. We observe ~6 × 1021 g of CO gas with a rotational temperature of 430 ± 40 K. The linearity of the excitation plot suggests that the CO is optically thin. Atypical for cTTSs, hot CO was not detected, implying that TW Hya has cleared its inner disk region out to a radial distance of ~0.5 AU. We discuss implications for the structure of the disk as it relates to replenishment and planet formation.
Generalised Surfaces In ℝ³, Brendan Guilfoyle, Wilhelm Klingenberg
Generalised Surfaces In ℝ³, Brendan Guilfoyle, Wilhelm Klingenberg
Publications
The correspondence between 2-parameter families of oriented lines in ℝ³ and surfaces in Tℙ¹ is studied, and the geometric properties of the lines are related to the complex geometry of the surface. Congruences generated by global sections of Tℙ¹ are investigated, and a number of theorems are proven that generalise results for closed convex surfaces in ℝ³.
Discovery Of The Near-Ir Afterglow And Of The Host Of Grb 030528, A. Rau, J. Greiner, S. Klose, M. Salvato, J. M. Castro Cerón, Dieter H. Hartmann, A. Fruchter, A. Levan, N. R. Tanvir, J. Gorosabel
Discovery Of The Near-Ir Afterglow And Of The Host Of Grb 030528, A. Rau, J. Greiner, S. Klose, M. Salvato, J. M. Castro Cerón, Dieter H. Hartmann, A. Fruchter, A. Levan, N. R. Tanvir, J. Gorosabel
Publications
The rapid dissemination of an arcmin-sized HETE-2 localization of the long-duration X-ray flash GRB 030528 led to a ground-based multi-observatory follow-up campaign. We report the discovery of the near-IR afterglow, and also describe the detection of the underlying host galaxy in the optical and near-IR bands. The afterglow is classified as “optically dark” as it was not detected in the optical band. The K-band photometry presented here suggests that the lack of optical detection was simply the result of observational limitations (lack of rapid and deep observations plus high foreground extinction). Simple power law fits to the afterglow in the …
Coordinate Conditions For A Uniformly Accelerated Or Static Plane Symmetric Metric, Preston Jones, Lucas Wanex
Coordinate Conditions For A Uniformly Accelerated Or Static Plane Symmetric Metric, Preston Jones, Lucas Wanex
Publications
The coordinate conditions for three exact solutions for the metric components of a coordinate system with constant acceleration or of a static plane symmetric gravitational field are presented. First, the coordinate condition that the acceleration of light is constant is applied to the field equations to derive the metric of a coordinate system of constant acceleration. Second, the coordinate conditions required to produce the metrics of Rindler and Lass are applied to the field equations to calculate the components of these two metrics and the coordinate velocities and coordinate accelerations for light of these two metrics are compared to the …
Geocoronal Hydrogen Studies Using Fabry-Perot Interferometers, S. M. Nossal, E. J. Mierkiewicz, F. L. Roesler, J. Bishop, R. J. Reynolds
Geocoronal Hydrogen Studies Using Fabry-Perot Interferometers, S. M. Nossal, E. J. Mierkiewicz, F. L. Roesler, J. Bishop, R. J. Reynolds
Publications
Ground based Fabry-Perot observations of solar excited geocoronal hydrogen fluorescence emissions are one of the primary means of studying the neutral upper atmosphere [Atreya et al., 1975; Meriwether et al., 1980; Yelle and Roesler, 1985; Shih et al., 1985; Kerr et al., 2001a,b; He et al., 1993; Nossal et al., 1993, 1998, 2004; Bishop et al., 2001; Mierkiewicz, 2002; and references therein]. Excellent reviews of early ground-based geocoronal Balmer α observations are found in: Krassovsky et al. [1966], Krassovsky [1971], Donahue [1964, 1966], Tinsley [1974], Fahr and Shizgal [1983] and Kerr et al. [2001a]. Instruments onboard satellites and rockets also …
Probing A Grb Progenitor At A Redshift Of Z=2: A Comprehensive Observing Campaign Of The Afterglow Of Grb 030226, S. Klose, J. Greiner, A. Rau, A. A. Henden, Dieter H. Hartmann, A. Zeh, C. Reis, N. Masetti, D. Malesani, E. Guenther
Probing A Grb Progenitor At A Redshift Of Z=2: A Comprehensive Observing Campaign Of The Afterglow Of Grb 030226, S. Klose, J. Greiner, A. Rau, A. A. Henden, Dieter H. Hartmann, A. Zeh, C. Reis, N. Masetti, D. Malesani, E. Guenther
Publications
We report results from a comprehensive follow-up observing campaign of the afterglow of GRB 030226, in-cluding VLTspectroscopy, VLT polarimetry, and Chandra X-ray observations. In addition, we present BOOTES-1 wide-field observations at the time of the occurrence of the burst. First observations at ESO started 0.2 days after the event when the gamma ray burst (GRB) afterglow was at a magnitude of R $19 and continued until the afterglow had faded below the detection threshold (R > 26). No underlying host galaxy was found. The optical light curve shows a break around 0.8 days after the burst, which is achromatic within the …
The White Dwarf Luminosity Function: The Shape Of Things To Come, Ted Von Hippel, M. Kilie, J. Munn, K. Williams, J. Libert, D. E. Winget, T. S. Metcalfe, Et Al.
The White Dwarf Luminosity Function: The Shape Of Things To Come, Ted Von Hippel, M. Kilie, J. Munn, K. Williams, J. Libert, D. E. Winget, T. S. Metcalfe, Et Al.
Publications
We describe a new survey for cool white dwarfs that supplements Sloan Digital Sky Survey photometry with USNO proper motions and followup spectroscopy. To date we have discovered and spectroscopically confirmed 80 new moderate temperature and cool white dwarfs. We have also found a handful of high-velocity white dwarfs and we expect a sizable fraction of these to be thick disk or possibly halo objects. Our survey is designed to find 104 new white dwarfs, although only 60 will be among the faintest white dwarfs (MV 16), where most of the age-sensitivity resides. We discuss an extension of our survey …
The Correlation Of Lithium And Beryllium In F And G Cluster Dwarf Stars, Ann Merchant Boesgaard, Eric Armengaud, Constantine P. Deliyannis, Alex Stephens, Jeremy R. King
The Correlation Of Lithium And Beryllium In F And G Cluster Dwarf Stars, Ann Merchant Boesgaard, Eric Armengaud, Constantine P. Deliyannis, Alex Stephens, Jeremy R. King
Publications
Although Li has been extensively observed in main-sequence field and cluster stars, there are relatively fewer observations of Be. We have obtained Keck HIRES spectra of 36 late F and early G dwarfs in order to study the Li-Be correlation we found previously in the temperature regime of 5900–6650 K. The sample size for this temperature range with detectable and (usually) depleted Li and Be is now 88, including Li and Be abundances in both cluster and field stars. Therefore we can now investigate the influence of other parameters such as age, temperature, and metallicity on the correlation. The Be …
Asymptotic Accuracy Of Geoacoustic Inversions, Michele Zanolin, Ian Ingram, Aaron Thode, Nicholas C. Makris
Asymptotic Accuracy Of Geoacoustic Inversions, Michele Zanolin, Ian Ingram, Aaron Thode, Nicholas C. Makris
Publications
Criteria necessary to accurately estimate a set of unknown geoacoustic parameters from remote acoustic measurements are developed in order to aid the design of geoacoustic experiments. The approach is to have estimation error fall within a specified design threshold by adjusting controllable quantities such as experimental sample size or signal-to-noise ratio (SNR). This is done by computing conditions on sample size and SNR necessary for any estimate to have a variance that (1) asymptotically attains the Cramer–Rao lower bound (CRLB) and (2) has a CRLB that falls within the specified design error threshold. Applications to narrow band deterministic signals received …
Photometric Identification Of Cool White Dwarfs, M. Kilic, D. E. Winget, Ted Von Hippel, C. F. Claver
Photometric Identification Of Cool White Dwarfs, M. Kilic, D. E. Winget, Ted Von Hippel, C. F. Claver
Publications
We investigate the use of a narrowband DDO51 filter for photometric identification of cool white dwarfs. We report photometric observations of 30 known cool white dwarfs with temperatures ranging from 10,000 K down to very cool temperatures (3500 K). Follow-up spectroscopic observations of a sample of objects selected using this filter and our photometric observations show that DDO51 filter photometry can help select cool white dwarf candidates for follow-up multiobject spectroscopy by rejecting 65% of main-sequence stars with the same broadband colors as the cool white dwarfs. This technique is not selective enough to efficiently feed single-object spectrographs. We present …
Lorentz-Violating Electrostatics And Magnetostatics, Quentin G. Bailey, V. Alan Kostelecký
Lorentz-Violating Electrostatics And Magnetostatics, Quentin G. Bailey, V. Alan Kostelecký
Publications
Electromagnetostatics experiments show promise for improving existing sensitivities to parity-odd coefficients for Lorentz violation in the photon sector.
Redefining The Empirical Zz Ceti Instability Strip, Anjum S. Mukadam, Ted Von Hippel, Et Al.
Redefining The Empirical Zz Ceti Instability Strip, Anjum S. Mukadam, Ted Von Hippel, Et Al.
Publications
We use the new ZZ Ceti stars (hydrogen-atmosphere white dwarf variables; DAVs) discovered within the Sloan Digital Sky Survey (Mukadam et al. 2004) to redefine the empirical ZZ Ceti instability strip. This is the first time since the discovery of white dwarf variables in 1968 that we have a homogeneous set of spectra acquired using the same instrument on the same telescope, and with consistent data reductions, for a statistically significant sample of ZZ Ceti stars. The homogeneity of the spectra reduces the scatter in the spectroscopic temperatures, and we find a narrow instability strip of width ~950 K, from …
Spin Mass Of An Electron Liquid, Zhixin Qian, Giovanni Vignale, D C. Marinescu
Spin Mass Of An Electron Liquid, Zhixin Qian, Giovanni Vignale, D C. Marinescu
Publications
We show that in order to calculate correctly the spin current carried by a quasiparticle in an electron liquid one must use an effective ‘‘spin mass’’ ms that is larger than both the band mass mb, which determines the charge current, and the quasiparticle effective mass m, which determines the heat capacity. We present two independent estimates of the spin mass enhancement, ms=mb, in two- and three-dimensional electron liquids, based on (i) previously calculated values of the Landau parameters and (ii) a recent theory of the dynamical local field factor in the spin channel. Both methods yield a significant spin …
Book Review: Sky Vistas: Astronomy For Binoculars And Richestfield Telescopes, T. D. Oswalt
Book Review: Sky Vistas: Astronomy For Binoculars And Richestfield Telescopes, T. D. Oswalt
Publications
This document is Dr. Oswalt’s review of Sky Vistas : Astronomy for Binoculars and Richestfield Telescopes by Craig Crossen and Gerald Rhemann Springer, 2004 279p, 3211008519 $69.95
The Li Overabundance Of J37: Diffusion Or Accretion?, J F. Ashwell, R D. Jeffries, C P. Deliyannis, A Steinhauer, Jeremy R. King
The Li Overabundance Of J37: Diffusion Or Accretion?, J F. Ashwell, R D. Jeffries, C P. Deliyannis, A Steinhauer, Jeremy R. King
Publications
In September 2002 the discovery of a super Li-rich F-dwarf (J37) in NGC 6633, an iron poor analogue of the better studied Hyades and Praecepe open clusters, was announced. This unique star was thought to be the smoking gun for the action of diffusion, models of which predict a narrow ”Li-peak” at approximately the correct temperature. However, with more detailed studies into J37s abundance pattern this star provides firm evidence for the accretion of planetesimals or other material from the circumstellar environment of new born stars. Thanks to the specific predictions made about the behaviour of Be abundances, (the most …
Lorentz-Violating Electromagnetostatics, Quentin G. Bailey
Lorentz-Violating Electromagnetostatics, Quentin G. Bailey
Publications
In this talk, the stationary limit of Lorentz-violating electrodynamics is discussed. As illustrated by some simple examples, the general solution includes unconventional mixing of electrostatic and magnetostatic effects. I discuss a high-sensitivity null-type measurement, exploiting Lorentz-violating electromagnetostatic effects, that could improve existing limits on parity-odd coefficients for Lorentz violation in the photon sector.
Proper Motion Objects In The Hubble Deep Field, M. Kilic, Ted Von Hippel, Et Al.
Proper Motion Objects In The Hubble Deep Field, M. Kilic, Ted Von Hippel, Et Al.
Publications
Using the deepest and finest resolution images of the universe acquired with the Hubble Space Telescope and a similar image taken 7 yr later for the Great Observatories Origins Deep Survey, we have derived proper motions for the point sources in the Hubble Deep Field–North. Two faint blue objects, HDF 2234 and HDF 3072, are found to display significant proper motion, 10:0 ± 2:5 and 15:5 ± 3:8 mas yr¯1. Photometric distances and tangential velocities for these stars are consistent with disk white dwarfs located at ~500 pc. The faint blue objects analyzed by Ibata et al. and Mendez & …
The Near-Infared Survey Of The N49 Region Around The Soft Gamma Repeater Sgr 0526-66, S. Klose, A. A. Henden, U. Geppert, J. Greiner, H. H. Guetter, Dieter H. Hartmann, C. Kouveliotou, C. B. Luginbuhl, B. Stecklum, F. J. Vrba
The Near-Infared Survey Of The N49 Region Around The Soft Gamma Repeater Sgr 0526-66, S. Klose, A. A. Henden, U. Geppert, J. Greiner, H. H. Guetter, Dieter H. Hartmann, C. Kouveliotou, C. B. Luginbuhl, B. Stecklum, F. J. Vrba
Publications
We report the results of a deep near-infrared survey with the Very Large Telescope/Infrared Spectrometer and Array Camera of the environment of the supernova remnant N49 in the Large Magellanic Cloud, which contains the soft gamma repeater SGR 0526-66. Two of the four confirmed SGRs are potentially associated with compact stellar clusters. We thus searched for a similar association of SGR 0526-66 and imaged a young stellar cluster at a projected distance of ∼30 pc from the SGR. This constitutes the third cluster–SGR link and lends support to scenarios in which SGR progenitors originate in young dusty clusters. If confirmed, …
The Upper Limit For Ch4 In The Protostellar Disk Toward Hl Tauri, E L. Gibb, T Rettig, Sean D. Brittain, R Haywood, Theodore Simon, C Kulesa
The Upper Limit For Ch4 In The Protostellar Disk Toward Hl Tauri, E L. Gibb, T Rettig, Sean D. Brittain, R Haywood, Theodore Simon, C Kulesa
Publications
We used high-resolution infrared spectra of the heavily embedded T Tauri star HL Tau to search for evidence of absorption due to the R0, R1, and R2 gas-phase CH4 ν3 lines near 3.3 μm. From this, we report a 3 σ upper limit of 1.3 × 1015 cm-2 for the CH4 gas column density toward HL Tau. Our results are compared to those found for CO gas toward this source and to the recent model for chemistry in the inner (10 AU) disks around T Tauri stars by Markwick et al. We find that the upper limit of methane ice+gas …
Cluster Observations Of Magnetic Field Fluctuations In The High-Altitude Cusp, K. Nykyri, P. J. Cargill, E. Lucek, T. Horbury, B. Lavraud, A. Balogh, M. W. Dunlop, Et Al.
Cluster Observations Of Magnetic Field Fluctuations In The High-Altitude Cusp, K. Nykyri, P. J. Cargill, E. Lucek, T. Horbury, B. Lavraud, A. Balogh, M. W. Dunlop, Et Al.
Publications
High-resolution (22 vector/s) magnetic field data from Cluster FGM instrument are presented for the highaltitude cusp crossing on 17 March 2001. Despite the quiet solar wind conditions, the cusp was filled with magnetic field turbulence for much of the crossing. Large-scale fluctuations show some correlation between spacecraft but the higher frequency fluctuations show no correlation, indicating that the length scales of these waves are smaller than the spacecraft separation (500 km). In many intervals, there are clear peaks in the wave power around the ion cyclotron frequency (~1 Hz), and there is some evidence for waves at the first harmonic …
Book Review: The Edge Of Infinity: Supermassive Black Holes In The Universe, T. D. Oswalt
Book Review: The Edge Of Infinity: Supermassive Black Holes In The Universe, T. D. Oswalt
Publications
This document is Dr. Oswalt’s review of The Edge of Infinity : Supermassive Black Holes in the Universe by Fulvio Melia. Cambridge, 2003 148p, 0-521-81405-7 $30.00.