2,459 research outputs found
Apollo experience report: A use of network simulation techniques in the design of the Apollo lunar surface experiments package support system
A case study of data-communications network modeling and simulation is presented. The applicability of simulation techniques in early system design phases is demonstrated, and the ease with which model parameters can be changed and comprehensive statistics gathered is shown. The discussion of the model design and application also yields an insight into the design and implementation of the Apollo lunar surface experiments package ground-support system
The Velocity Field of Quasar Broad Emission Line Gas
In this Letter, the broad emission line (BEL) profiles of superluminal
quasars with apparent jet velocities, , (ultraluminal QSOs, or
ULQSOs hereafter) are studied as a diagnostic of the velocity field of the BEL
emitting gas in quasars. The ULQSOs are useful because they satisfy a very
strict kinematical constraint, their parsec scale jets must be propagating
within of the line of sight. We know the orientation of these
objects with great certainty. The large BEL FWHM, , in ULQSOs tend to indicate that the BEL gas has a larger
component of axial velocity (either random or in a wind) along the jet
direction than previously thought.Comment: To appear in ApJ Letter
The Deep SWIRE Field III. WIYN Spectroscopy
We present the results of spectroscopy using HYDRA on the WIYN 3.5m telescope
of objects in the deep SWIRE radio field. The goal of the project was to
determine spectroscopic redshifts for as many of the brighter objects in the
field as possible, especially those detected in the radio and at 24 microns.
These redshifts are primarily being used in studies of galaxy evolution and the
connection of that evolution to AGN and star-formation. Redshifts measured for
365 individual objects are reported. The redshifts range from 0.03 to 2.5,
mostly with z < 0.9. The sources were selected to be within the WIYN HYDRA
field of approximately 30' in radius from the center of the SWIRE deep field,
10h46m00s, 59d 01'00" (J2000). Optical sources for spectroscopic observation
were selected from a r-band image of the field. A priority list of
spectroscopic targets was established in the following order: 20cm detections,
24 micron detections, galaxies with r < 20 and the balance made up of fainter
galaxies in the field. We provide a table listing the galaxy positions,
measured redshift and error, and note any emission lines that were visible in
the spectrum. In practice almost all the galaxies with r < 19 were observed
including all of the radio sources and most of the 24 microns sources with r <
20 and a sample of radio sources which had fainter optical counterparts on the
r-band image.Comment: 6 pages, 3 tables, 2 figures, full electronic tables at
http://www.aoc.nrao.edu/~fowen/papers/SWIRE/WIYNpaper3/, accepted ApJ Suppl
Serie
Chandra Detection of Highest Redshift (z~6) Quasars in X-rays
We report on Chandra observations of three quasars SDSSP J083643+005453,
SDSSP J103027+052455, and SDSSP J130608+035626 at redshifts 5.82, 6.28 and 5.99
respectively. All the three sources are clearly detected in the X-ray band, up
to rest frame energies of ~55 keV. These observations demonstrate the
unprecedented sensitivity of Chandra to detect faint sources in relatively
short exposure times (5.7--8.2 ksec). The broad band X-ray properties of these
highest redshift quasars do not appear to be any different from their lower
redshift cousins. Spectra of the sources could not be determined with only few
counts detected. Observations with XMM-Newton will be able to constrain the
spectral shapes, if they are simple. Determination of complex spectra in a
reasonable amount of time, however, will have to await next generation of X-ray
missions.Comment: Submitted to ApJ Letter
Blob ejection from advection-dominated accretion flow: observational consequences
There is increasing evidence for the presence of an optically thin
advection-dominated accretion flow (ADAF) in low luminosity active galactic
nuclei and radio-loud quasars. The present paper is devoted to explore the fate
of a blob ejected from an ADAF, and to discuss its observational consequences.
It is inevitable for the ejected blob to drastically expand into its
surroundings. Consequently, it is expected that a group of relativistic
electrons should be accelerated, which may lead to nonthermal flares, since a
strong shock will be formed by the interaction between the blob and its
surroundings. Then the blob cools down efficiently, leading to the appearance
of recombination lines about s after its ejection from an ADAF. We apply
this model to NGC 4258 for some observational prediction, and to PKS 2149--306
for the explanation of observational evidence. Future simultaneous observations
of recombination X-ray lines and continuum emission are highly desired to test
the present model.Comment: 4 pages in emulateapj.sty, no figure. Accepted by ApJ Letter
Stability, reliability and cross-mode correlations of tests in a recommended 8-minute performance assessment battery
A need exists for an automated performance test system to study drugs, agents, treatments, and stresses of interest to the aviation, space, and environmental medical community. The purpose of this present study is to evaluate tests for inclusion in the NASA-sponsored Automated Performance Test System (APTS). Twenty-one subjects were tested over 10 replications with tests previously identified as good candidates for repeated-measure research. The tests were concurrently administered in paper-and-pencil and microcomputer modes. Performance scores for the two modes were compared. Data from trials 1 to 10 were examined for indications of test stability and reliability. Nine of the ten APT system tests achieved stability. Reliabilities were generally high. Cross-correlation of microbased tests with traditional paper-and-pencil versions revealed similarity of content within tests in the different modes, and implied at least three cognition and two motor factors. This protable, inexpensive, rugged, computerized battery of tests is recommended for use in repeated-measures studies of environmental and drug effects on performance. Identification of other tests compatible with microcomputer testing and potentially capable of tapping previously unidentified factors is recommended. Documentation of APTS sensitivity to environmental agents is available for more than a dozen facilities and is reported briefly. Continuation of such validation remains critical in establishing the efficacy of APTS tests
Apollo experience report - a use of network simulation techniques in the design of the Apollo lunar surface experiments package support system
A case study of data-communications network modeling and simulation is presented. The applicability of simulation techniques in early system design phases is demonstrated, and the ease with which model parameters can be changed and comprehensive statistics gathered is shown. The discussion of the model design and application also yields an insight into the design and implementation of the Apollo lunar surface experiments package ground-support system
Fluorescence of thermal control coatings on S0069 and A0114
Many of the thermal control surfaces exposed to the space environment during the 5.8 year LDEF mission experienced changes in fluorescence. All of the thermal control coatings flown on LDEF experiments S0069 and A0114 were characterized for fluorescence under ambient conditions. Some of the black coatings, having protective overcoats, appear bright yellow under ultraviolet exposure. Urethane based coatings exhibited emission spectra shifts toward longer wavelengths in the visible range. Zinc oxide pigment based coatings experienced a quenching of fluorescence, while zinc orthotitanate pigment based and other ceramic type coatings had no measurable fluorescence
Fluorescence measurements of the thermal control experiments coatings on LDEF S0069 and A0114
Fluorescence measurements were made on the thermal control coatings from the Long Duration Experiment Facility (LDEF) S0069, Thermal Control Surfaces Experiment (TCSE); and the A0114, Interaction of Atomic Oxygen with Material Surfaces in Low Earth orbit. Fluorescence was observed in two types of thermal control coatings and is attributed to pigments or binders. In addition, fluorescence measurement on the silver Teflon from the front cover of TCSE led to confirmation of damage (cracking) to the metal layers during application
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