1,126 research outputs found
A Survey of Proper Motion Stars. XVII. A Deficiency of Binary Stars on Retrograde Galactic Orbits and the Possibility that omega Centauri is Related to the Effect
We find a deficiency of binary stars moving on strongly retrograde Galactic
orbits. No binary deficiencies are seen for U or W velocities, however. From
theoretical analyses, we rule out preferential disruption of pre-existing
binary stars due to encounters with massive perturbers. We also rule out
globular clusters as the source of the effect since prograde motions are more
likely to create such an effect. We search for star streams and find one
possible candidate, but it is not on a retrograde orbit and probably represents
the remains of a cluster that has passed too near the Galactic center. Based on
a very small number of stars, we find that about the right fraction of stars on
retrograde Galactic orbits share some chemical similarities to the cluster
omega Cen, suggesting that its parent galaxy could be the explanation.Comment: To appear in the Astronomical Journal (March 2005 issue
Designing for multi-user interaction in the home environment: Implementing social translucence
© 2016 ACM. Interfaces of interactive systems for domestic use are usually designed for individual interactions although these interactions influence multiple users. In order to prevent conflicts and unforeseen influences on others we propose to leverage the human ability to take each other into consideration in the interaction. A promising approach for this is found in the social translucence framework, which was originally described by Erickson & Kellogg. In this paper, we investigate how to design multi-user interfaces for domestic interactive systems through two design cases where we focus on the implementation of social translucence constructs (visibility, awareness, and accountability) in the interaction. We use the resulting designs to extract design considerations: interfaces should not prescribe behavior, need to offer sufficient interaction alternatives, and previous settings need to be retrievable. We also identify four steps that can be integrated in any design process to help designers in creating interfaces that support multi-user interaction through social translucence
Multi-Segment Computerized Adaptive Testing for Educational Testing Purposes
Computerized adaptive testing (CAT) was initially developed as a psychometric tool for the efficient estimation of the ability of a student. Because of technological and psychometrical developments, CAT can now meet practical conditions and can also have other purposes than the mere estimation of ability. It can be applied in not only summative but also formative settings. In this paper, attention is given to the goals of testing in education and the different CAT algorithms serving these purposes. In particular, the approach of multi-segment adaptive testing is described. A multi-segment CAT consists of a number of segments, each with its own algorithm and branching rules. In this approach, practical constraints can be implemented in CATs. Furthermore, having a different testing purpose per segment for possibly different parts of the population is possible. The method will be illustrated with a CAT that has been developed as a part of an operational student monitoring system, which is a spelling test of Dutch words
Search for low instability strip variables in the young open cluster NGC 2516
In this paper we revise and complete the photometric survey of the
instability strip of the southern open cluster NGC 2516 published by Antonello
and Mantegazza (1986). No variable stars with amplitudes larger than
were found. However by means of an accurate analysis based on a new statistical
method two groups of small amplitude variables have been disentangled: one with
periods (probably Scuti stars) and one with periods
. The position in the HR diagram and the apparent time-scale may
suggest that the stars of the second group belong to a recently discovered new
class of variables, named Dor variables. They certainly deserve
further study. We also present a comparison between the results of the
photometric survey and the available pointed ROSAT observations of this
cluster.Comment: 7 pages, 2 ps figures. Accepted for P.A.S.
Underwater acoustic communication over Doppler spread channels
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1997.Includes bibliographical references (p. 297-307).by Trym H. Eggen.Ph.D
The Age of the Oldest Stars in the Local Galactic Disk From Hipparcos Parallaxes of G and K Subgiants
We review the history of the discovery of field subgiant stars and their
importance in the age dating of the Galactic disk. We use the cataloged data
from the Hipparcos satellite in this latter capacity. Based on Hipparcos
parallaxes accurate to 10% or better, the absolute magnitude of the lower
envelope of the nearly horizontal subgiant sequence for field stars in the H-R
diagram for B-V colors between 0.85 and 1.05 is measured to be M_V = 4.03 +/-
0.06. The age of the field stars in the solar neighborhood is found to be 7.9
+/- 0.7 Gyr by fitting the theoretical isochrones for [Fe/H] = +0.37 to the
lower envelope of the Hipparcos subgiants. The same grid of isochrones yields
ages, in turn, of 4.0 +/- 0.2 Gyr, 6.2 +/- 0.5 Gyr, and 7.5 to 10 Gyr for the
old Galactic clusters M67, NGC188, and NGC6791. The ages of both the Galactic
disk in the solar neighborhood and of NGC6791 are, nevertheless, likely between
3 and 5 Gyr younger than the oldest halo globular clusters, which have ages of
13.5 Gyr. The most significant results are (1) the supermetallicity of the
oldest local disk stars, and (2) the large age difference between the most
metal-poor component of the halo and the thick and thin disk in the solar
neighborhood. These facts are undoubtedly related and pose again the problem of
the proper scenario for the timing of events in the formation of the halo and
the Galactic disk in the solar neighborhood. [Abstract Abridged]Comment: 44 pages, 12 Figures; accepted for publication in PASP; high
resolution versions of Figures 1, 2, 6 and 9 available at
http://bubba.ucdavis.edu/~lubin/Sandage
- …