13,497 research outputs found
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 StarScan plate measuring machine: overview and calibrations
The StarScan machine at the U.S. Naval Observatory (USNO) completed measuring
photographic astrograph plates to allow determination of proper motions for the
USNO CCD Astrograph Catalog (UCAC) program. All applicable 1940 AGK2 plates,
about 2200 Hamburg Zone Astrograph plates, 900 Black Birch (USNO Twin
Astrograph) plates, and 300 Lick Astrograph plates have been measured. StarScan
comprises of a CCD camera, telecentric lens, air-bearing granite table, stepper
motor screws, and Heidenhain scales to operate in a step-stare mode. The
repeatability of StarScan measures is about 0.2 micrometer. The CCD mapping as
well as the global table coordinate system has been calibrated using a special
dot calibration plate and the overall accuracy of StarScan x,y data is derived
to be 0.5 micrometer. Application to real photographic plate data shows that
position information of at least 0.65 micrometer accuracy can be extracted from
course grain 103a-type emulsion astrometric plates. Transformations between
"direct" and "reverse" measures of fine grain emulsion plate measures are
obtained on the 0.3 micrometer level per well exposed stellar image and
coordinate, which is at the limit of the StarScan machine.Comment: 24 pages, 8 figures, accepted for PAS
Risk stratification with cardiac troponin I in acute coronary syndromesââEditorials published in the Journal of the American College of Cardiology reflect the views of the authors and do not necessarily represent the views of JACC or the American College of Cardiology.
Understanding the Role of Endothelial Progenitor Cells in Cardiovascular Disease, Coronary Artery Lesion Progression, and In-Stent RestenosisââEditorials published in JACC: Cardiovascular Interventions reflect the views of the authors and do not necessarily represent the views of JACC: Cardiovascular Interventions or the American College of Cardiology.
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Five-Point Likert Items: t test versus Mann-Whitney-Wilcoxon (\u3ci\u3eAddendum added October 2012\u3c/i\u3e)
Likert questionnaires are widely used in survey research, but it is unclear whether the item data should be investigated by means of parametric or nonparametric procedures. This study compared the Type I and II error rates of the t test versus the Mann-Whitney-Wilcoxon (MWW) for five-point Likert items. Fourteen population distributions were defined and pairs of samples were drawn from the populations and submitted to the t test and the t test on ranks, which yields the same results as MWW. The results showed that the two tests had equivalent power for most of the pairs. MWW had a power advantage when one of the samples was drawn from a skewed or peaked distribution. Strong power differences between the t test and MWW occurred when one of the samples was drawn from a multimodal distribution. Notably, the Type I error rate of both methods was never more than 3% above the nominal rate of 5%, even not when sample sizes were highly unequal. In conclusion, for five-point Likert items, the t test and MWW generally have similar power, and researchers do not have to worry about finding a difference whilst there is none in the population.Accessed 61,170 times on https://pareonline.net from October 06, 2010 to December 31, 2019. For downloads from January 1, 2020 forward, please click on the PlumX Metrics link to the right
Bullying and Victimization in Elementary Schools: A Comparison of Bullies, Victims, Bully/Victims, and Uninvolved Preadolescents
Research on bullying and victimization largely rests on univariate analyses and on reports from a single informant. Researchers may thus know too little about the simultaneous effects of various independent and dependent variables, and their research may be biased by shared method variance. The database for
this Dutch study was large (N = 1,065) and rich enough to allow multivariate analysis and multisource information. In addition, the effect of familial vulnerability for internalizing and externalizing disorders was studied. Gender, aggressiveness, isolation, and dislikability were most strongly related to bullying and victimization. Among the many findings that deviated from or enhanced the univariate knowledge
base were that not only victims and bully/victims but bullies as well were disliked and that parenting was unrelated to bullying and victimization once other factors were controlled.
Navigating the path home:Pioneering hospital-to-home transitions for children with medical complexity
status: Published onlin
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