2,821 research outputs found
The Twin Astrographic Catalog (TAC) Version 1.0
A first version of the Twin Astrographic Catalog (TAC) of positions for
705,679 stars within has been produced.
The sky coverage of the TAC is complete to over 90\% in that area. The limiting
magnitude is about B=11.5. Positions are based on plates taken with the
U.S. Naval Observatory Twin Astrograph (blue, yellow lens) at epochs
1977--1986. The TAC is supplemented by proper motions which are obtained from a
combination with a re--reduced Astrographic Catalog (AC). Some AC zones are
available now and a complete northern hemisphere is expected by fall 1996.
Proper motions of almost all TAC stars will be generated as the AC work
progresses. The average precision of a catalog position is 90 mas per
coordinate at epoch of observation. A large fraction of that error is
introduced by the currently available reference stars. The inherent precision
of the TAC data is considerably better. The precision of the proper motions is
currently 2.5 to 4 mas/yr. Magnitude--dependent systematic errors have been
found and preliminarily corrected. The final reduction of this plate material
will be performed with the Hipparcos catalog in 1997. The TAC is about 3 times
more precise than the PPM or ACRS in the northern hemisphere at current epochs
and contains about 3 times more stars. The TAC has a higher star density than
the Tycho catalog and provides independent, high precision positions for a
large fraction of the Tycho stars at an epoch about 10 years earlier than the
Tycho mean epoch. The TAC version 1.0 data are released as the AC zones become
available. For latest information, look at the US Naval Observatory World Wide
Web page http://aries.usno.navy.mil/ad/tac.html.Comment: 22 pages LaTex, accepted by AJ, scheduled for Nov., no figures
provided, needs aasms4.st
Manual control of yaw motion with combined visual and vestibular cues
Measurements are made of manual control performance in the closed-loop task of nulling perceived self-rotation velocity about an earth-vertical axis. Self-velocity estimation was modelled as a function of the simultaneous presentation of vestibular and peripheral visual field motion cues. Based on measured low-frequency operator behavior in three visual field environments, a parallel channel linear model is proposed which has separate visual and vestibular pathways summing in a complementary manner. A correction to the frequency responses is provided by a separate measurement of manual control performance in an analogous visual pursuit nulling task. The resulting dual-input describing function for motion perception dependence on combined cue presentation supports the complementary model, in which vestibular cues dominate sensation at frequencies above 0.05 Hz. The describing function model is extended by the proposal of a non-linear cue conflict model, in which cue weighting depends on the level of agreement between visual and vestibular cues
Brorfelde Schmidt CCD Catalog (BSCC)
The Brorfelde Schmidt CCD Catalog (BSCC) contains about 13.7 million stars,
north of +49 deg Declination with precise positions and V, R photometry. The
catalog has been constructed from the reductions of 18,667 CCD frames observed
with the Brorfelde Schmidt Telescope between 2000 and 2007. The Tycho-2 catalog
was used for astrometric and photometric reference stars. Errors of individual
positions are about 20 to 200 mas for stars in the R = 10 to 18 mag range.
External comparisons with 2MASS and SDSS reveal possible small systematic
errors in the BSCC of up to about 30 mas. The catalog is supplemented with J,
H, and K_s magnitudes from the 2MASS catalog. The catalog data file (about 550
MB ASCII, compressed) will be made available at the Strasbourg Data Center
(CDS).Comment: 16 pages, 22 figures, 2 tables, accepted by A
Study of fault tolerant software technology for dynamic systems
The major aim of this study is to investigate the feasibility of using systems-based failure detection isolation and compensation (FDIC) techniques in building fault-tolerant software and extending them, whenever possible, to the domain of software fault tolerance. First, it is shown that systems-based FDIC methods can be extended to develop software error detection techniques by using system models for software modules. In particular, it is demonstrated that systems-based FDIC techniques can yield consistency checks that are easier to implement than acceptance tests based on software specifications. Next, it is shown that systems-based failure compensation techniques can be generalized to the domain of software fault tolerance in developing software error recovery procedures. Finally, the feasibility of using fault-tolerant software in flight software is investigated. In particular, possible system and version instabilities, and functional performance degradation that may occur in N-Version programming applications to flight software are illustrated. Finally, a comparative analysis of N-Version and recovery block techniques in the context of generic blocks in flight software is presented
A Radio--Optical Reference Frame VIII. CCD observations from KPNO and CTIO: internal calibration and first results
In this pilot investigation, precise optical positions in the FK5 system are
presented for a set of 16 compact extragalactic radio sources, which will be
part of the future radio--optical reference frame. The 0.9 m KPNO and CTIO
telescopes equipped with 2K CCD's have been used for this project. The
astrometric properties of these instruments are investigated in detail. New
techniques of using wide field CCD observations for astrometry in general are
developed. An internal precision of 5 to 31 mas in position per single exposure
is found, depending on the brightness of the object. The tie to the primary
optical reference system is established by photographic astrometry using
dedicated astrographs on both hemispheres. An accuracy of mas per
source is estimated for the multi--step reduction procedure when based on the
future Hipparcos catalog, while the FK5--based positions suffer from system
errors of 100 to 200 mas as compared to the radio positions. This work provides
a contribution to the international effort to link the Hipparcos instrumental
coordinate system to the quasi--inertial VLBI radio reference frame. Precise
radio and optical astrometry of a large sample of compact extragalactic sources
will also contribute to the astrophysics of these objects by comparing the
respective centers of emission at the optical and radio wavelengths.Comment: AAS v.4 LaTeX, 2 parts on 1 file (main text + deluxetable), accepted
by AJ, Dec.95, fig. with reprint
The second US Naval Observatory CCD Astrograph Catalog (UCAC2)
The second USNO CCD Astrograph Catalog, UCAC2 was released in July 2003.
Positions and proper motions for 48,330,571 sources (mostly stars) are
available on 3 CDs, supplemented with 2MASS photometry for 99.5% of the
sources. The catalog covers the sky area from -90 to +40 degrees declination,
going up to +52 in some areas; this completely supersedes the UCAC1 released in
2001. Current epoch positions are obtained from observations with the USNO
8-inch Twin Astrograph equipped with a 4k CCD camera. The precision of the
positions are 15 to 70 mas, depending on magnitude, with estimated systematic
errors of 10 mas or below. Proper motions are derived by utilizing over 140
ground-and space-based catalogs, including Hipparcos/Tycho, the AC2000.2, as
well as yet unpublished re-measures of the AGK2 plates and scans from the NPM
and SPM plates. Proper motion errors are about 1 to 3 mas/yr for stars to 12th
magnitude, and about 4 to 7 mas/yr for fainter stars to 16th magnitude. The
observational data, astrometric reductions, results, and important information
for the users of this catalog are presented.Comment: accepted by AJ, AAS LaTeX, 14 figures, 10 table
Fewer of Whom? Climate-Based Population Policies Infringe Marginalized People\u27s Reproductive Autonomy
A comparison of head and manual control for a position-control pursuit tracking task
Head control was compared with manual control in a pursuit tracking task involving proportional controlled-element dynamics. An integrated control/display system was used to explore tracking effectiveness in horizontal and vertical axes tracked singly and concurrently. Compared with manual tracking, head tracking resulted in a 50 percent greater rms error score, lower pilot gain, greater high-frequency phase lag and greater low-frequency remnant. These differences were statistically significant, but differences between horizontal- and vertical-axis tracking and between 1- and 2-axis tracking were generally small and not highly significant. Manual tracking results were matched with the optimal control model using pilot-related parameters typical of those found in previous manual control studies. Head tracking performance was predicted with good accuracy using the manual tracking model plus a model for head/neck response dynamics obtained from the literature
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