7,707 research outputs found
High-Resolution Spectroscopy of Ursa Major Moving Group Stars
We use new and extant literature spectroscopy to address abundances and
membership for UMa moving group stars. We first compare the UMa, Coma, and
Hyades H-R diagrams via a homogeneous set of isochrones, and find that these
three aggregates are essentially coeval. Our spectroscopy of cool UMa dwarfs
reveals striking abundance anomalies--trends with Teff, ionization state, and
excitation potential--like those recently seen in young cool M34, Pleaides, and
Hyades dwarfs. In particular, the trend of rising 7774 Ang-based OI abundance
with declining Teff is markedly subdued in UMa compared to the Pleiades,
suggesting a dependence on age or metallicity. Despite disparate sources of Li
data,our homogeneous analysis indicates that UMa members evince remarkably
small scatter in the Li-Teff plane for Teff>5200 K. Significant star-to-star
scatter suggested by previous studies is seen for cooler stars. Comparison with
the consistently determined Hyades Li-Teff trend reveals differences
qualitatively consistent with this cluster's larger [Fe/H] (and perhaps
slightly larger age). However, quantitative comparison with standard stellar
models indicates the differences are smaller than expected, suggesting the
action of a fourth parameter beyond age, mass, and [Fe/H] controlling Li
depletion.Comment: To appear in Publ. Astron. Soc. Pacif. (September 2005
Hybrid propulsion technology program: Phase 1, volume 1
A number of booster propulsion system concepts are being considered for the next generation of manned and unmanned space launch vehicles. The one propulsion system concept that has potential for reducing costs with increased safety, reliability, and performance is hybrid propulsion (HP). A HP system may be thought of as a liquid propulsion system with solid fuel or a solid propulsion system with a liquid oxidizer. The liquid propulsion features that are most attractive are the higher specific impulse, clean exhaust, separated propellants, and oxidizer loading just prior to launch. The most attractive solid propulsion features includes low life cycle costs, no rotating machinery, compact size, and a robust case. In addition, a HP system has a robust LO2 tank; provides thrust control for ignition, to alleviate flight loads, and for thrust termination; and uses an inert grain that is not sensitive to anomalies such as cracks, voids, and separations. The object is to develop the technology to enable the application of HP to manned and unmanned space launch vehicles. This program will identify the necessary technology, acquire that technology, and demonstrate that technology. This volume is the executive summary
Hybrid propulsion technology program: Phase 1. Volume 3: Thiokol Corporation Space Operations
Three candidate hybrid propulsion (HP) concepts were identified, optimized, evaluated, and refined through an iterative process that continually forced improvement to the systems with respect to safety, reliability, cost, and performance criteria. A full scale booster meeting Advanced Solid Rocket Motor (ASRM) thrust-time constraints and a booster application for 1/4 ASRM thrust were evaluated. Trade studies and analyses were performed for each of the motor elements related to SRM technology. Based on trade study results, the optimum HP concept for both full and quarter sized systems was defined. The three candidate hybrid concepts evaluated are illustrated
Atmospheric nitric oxide measurement techniques Final report
Optical radar technique for measuring vertical density distribution of neutral nitric oxide in earth atmospher
Lithium in the Upper Centaurus Lupus and Lower Centaurus Crux Subgroups of Scorpius-Centaurus
We utilize spectroscopically derived model atmosphere parameters and the
\ion{Li}{1} subordinate line and the doublet to
derive lithium abundances for 12 members of the Upper-Centaurus Lupus (UCL) and
Lower-Centaurus Crux (LCC) subgroups of the Scorpius Centaurus OB Association.
The results indicate any intrinsic Li scatter in our 0.9-1.4 stars
is limited to dex, consistent with the lack of dispersion in
stars in the 100 Myr Pleiades and 30-50 Myr IC 2391 and
2602 clusters. Both ab initio uncertainty estimates and the derived abundances
themselves indicate that the 6104 line yields abundances with
equivalent or less scatter than is found from the 6708 doublet as a
result of lower uncertainties for the subordinate feature, a result of low
sensitivity to broadening in the subordinate feature. Because NLTE corrections
are less susceptible to changes in surface gravity and/or metallicity for the
6104 {\AA} line, the subordinate Li feature is preferred for deriving lithium
abundances in young Li-rich stellar association stars with K.Comment: Accepted for publication in Astronomical Journal (abstract shortened
for astro-ph submission
Fe I and Fe II Abundances of Solar-Type Dwarfs in the Pleiades Open Cluster
We have derived Fe abundances of 16 solar-type Pleiades dwarfs by means of an
equivalent width analysis of Fe I and Fe II lines in high-resolution spectra
obtained with the Hobby - Eberly Telescope and High Resolution Spectrograph.
Abundances derived from Fe II lines are larger than those derived from Fe I
lines (herein referred to as over-ionization) for stars with Teff < 5400 K, and
the discrepancy (deltaFe = [Fe II/H] - [Fe I/H]) increases dramatically with
decreasing Teff, reaching over 0.8 dex for the coolest stars of our sample. The
Pleiades joins the open clusters M 34, the Hyades, IC 2602, and IC 2391, and
the Ursa Major moving group, demonstrating ostensible over-ionization trends.
The Pleiades deltaFe abundances are correlated with Ca II infrared triplet and
Halpha chromospheric emission indicators and relative differences therein.
Oxygen abundances of our Pleiades sample derived from the high-excitation O I
triplet have been previously shown to increase with decreasing Teff, and a
comparison with the deltaFe abundances suggests that the over-excitation
(larger abundances derived from high excitation lines relative to low
excitation lines) and over-ionization effects that have been observed in cool
open cluster and disk field main sequence (MS) dwarfs share a common origin.
Star-to-star Fe I abundances have low internal scatter, but the abundances of
stars with Teff < 5400 K are systematically higher compared to the warmer
stars. The cool star [Fe I/H] abundances cannot be connected directly to
over-excitation effects, but similarities with the deltaFe and O I triplet
trends suggest the abundances are dubious. Using the [Fe I/H] abundances of
five stars with Teff > 5400 K, we derive a mean Pleiades cluster metallicity of
[Fe/H] = +0.01 +/- 0.02.Comment: 32 pages, 7 figures, 7 tables; accepted by PAS
Two-photon mediated resonance production in e+e- collisions: cross sections and density matrices
Earlier described model amplitudes are used in this paper to evaluate both
cross sections and density matrices for two-photon mediated resonance
production in e^+e^- collisions. All 25 q\bar{q} low-lying ^1S_0, ^3P_J and
^1D_2 resonances can thus be treated. Two independent methods are described to
obtain the resonance production density matrices and cross sections. These
density matrices combined with a resonance decay density matrix give the
detailed angular distributions of the resonance decay products. For two
particular decays, \chi_{c2},\chi_{c1}\to\gamma J/\psi the details are given.
Several numerical results are presented as well.Comment: 27 pages, 4 figure
Voice Of The Lilies : Reverie
https://digitalcommons.library.umaine.edu/mmb-ps/2941/thumbnail.jp
A Critical and Comparative Analysis of John Calvin\u27s and the Early Friends\u27 Doctrine of the Word of God
The question has been raised since the inception of the Friends or Quaker movement, What position do the Friends hold in reference to a basis of authority for their proposed and propounded doctrines? This basis of authority was first questioned by various religious leaders of the day when George Fox went about preaching against the cold, dead, formalism of the churches in England, and remains a matter of some debate today.
Since the beginning of the Friends movement, it has held the Bible in great reverence and has used it as a basis of their teaching. Other groups, too, considered the Bible their source of authority -- groups such as John Calvin brought into being. We find that Calvin\u27s approach to Christianity was logical and systematic, whereas George Fox preached a purely experiential religion. They both used the Bible as their authority, yet they arrived at the widely divergent conceptions of Christina rules and faith.
Every theological system has some thing or some one as a basis of its authority. For the Christian religion this source is called the Word of God. But in the consideration of defining the Word of God, it would seem every separate group in Christianity has a different view of what the term consists. When there are divergent views on what the Word of God consists there will be different views of Christina doctrine and faith.
It is proposed to state as concisely as possible the views of John Calvin and the early Friends in an attempt to discover where and for what reasons there is this divergence of views between them.
Some theologians feel that within the scope of the term Word of God are involved more than merely the written Scriptures. It is essential that three phases of study be undertaken here for all are directly related to such a study in any group. These phases or areas are 1) Revelation in general 2) Revelation in regard to the Word of God, and 3) Revelation in regard to the Sacraments.
Some of the specific problems to be considered are: 1) How has God revealed Himself to man and does He still reveal Himself: Is revelation finished? 2) Of what does the Word of God consist -- i.e. is it limited to the written Word, and if so, to what extent? If not, what are the other phases of the Word of God? 3) Of what do the sacraments consist and what part do they play in the salvation of man? Are they essential to salvation? If there any real merit or value between the spiritual and physical or corporeal elements
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