22,208 research outputs found
Probing the Galaxy I. The galactic structure towards the galactic pole
Observations of (B-V) colour distributions towards the galactic poles are
compared with those obtained from synthetic colour-magnitude diagrams to
determine the major constituents in the disc and spheroid. The disc is
described with four stellar sub-populations: the young, intermediate, old, and
thick disc populations, which have respectively scale heights of 100 pc, 250
pc, 0.5 kpc, and 1.0 kpc. The spheroid is described with stellar contributions
from the bulge and halo. The bulge is not well constrained with the data
analyzed in this study. A non-flattened power-law describes the observed
distributions at fainter magnitudes better than a deprojected R^{1/4}-law.
Details about the age, metallicity, and normalizations are listed in Table 1.
The star counts and the colour distributions from the stars in the intermediate
fields towards the galactic anti-centre are well described with the stellar
populations mentioned above. Arguments are given that the actual solar offset
is about 15 pc north from the galactic plane.Comment: 11 pages TeX, 4 separate pages with additional figures, accepted for
publication in A&
Precise LIGO Lensing Rate Predictions for Binary Black Holes
We show how LIGO is expected to detect coalescing binary black holes at
, that are lensed by the intervening galaxy population. Gravitational
magnification, , strengthens gravitational wave signals by ,
without altering their frequencies, which if unrecognised leads to an
underestimate of the event redshift and hence an overestimate of the binary
mass. High magnifications can be reached for coalescing binaries because the
region of intense gravitational wave emission during coalescence is so small
(100km), permitting very close projections between lensing caustics and
gravitational-wave events. Our simulations incorporate accurate waveforms
convolved with the LIGO power spectral density. Importantly, we include the
detection dependence on sky position and orbital orientation, which for the
LIGO configuration translates into a wide spread in observed redshifts and
chirp masses. Currently we estimate a detectable rate of lensed events
\rateEarly{}, that rises to \rateDesign{}, at LIGO's design sensitivity limit,
depending on the high redshift rate of black hole coalescence.Comment: 5 pages, 4 figure
Validation of the English and Chinese versions of the Quick-FLIC quality of life questionnaire.
A useful measure of quality of life should be easy and quick to complete. Recently, we reported the development and validation of a shortened Chinese version of the Functional Living Index-Cancer (FLIC), which we called the Quick-FLIC. In the present study of 327 English-speaking and 221 Chinese-speaking cancer patients, we validated the English version of the Quick-FLIC and further assessed the Chinese version. The 11 Quick-FLIC items were administered alongside the 11 remaining items of the full FLIC, but there appeared to be little context effect. Validity of the English version of the Quick-FLIC was attested by its strong correlation with two other measures of quality of life, and its ability to detect differences between patients with different performance status and treatment status (each P<0.001). Its internal consistency (alpha=0.86) and test-retest reliability (intraclass correlation=0.76) were also satisfactory. The measure was responsive to changes in performance status (P<0.001). The Chinese version showed similar characteristics. The Quick-FLIC behaved in ways that are highly comparable with the FLIC, even though the Quick-FLIC comprised only 11 items whereas the FLIC comprised 22. Further research is required to see whether the use of shorter instruments can improve data quality and response rates, but the fact that shorter instruments place less burden on the patients is itself inherently important
The galactic disc age-metallicity relation
New ages are computed for stars in the Solar Neighbourhood from the
Edvardsson et al. (1993) data set. Distances derived from the Hipparcos
parallaxes were adopted to obtain reliable ages (uncertainty less than 12%) for
a subset of stars. There is no apparent age-metallicity relation for stars with
an age less than 10 Gyr. Only if we consider older stars a slope of ~0.07
dex/Gyr appears. This relation is compared with those obtained from other
methods, i.e. galactic open clusters, stellar population synthesis (star
counts), and chemical evolution models.Comment: 4 pages LaTeX, 3 postscript figures, to appear in proceedings ``1997
Pacific RIM conference on Stellar Astrophysics'', August 13-16, 1997, Hong
Kong (China), K.L. Chan, K.S. Cheng and H.P. Singh (eds.), ASP Conference
Serie
Frustrated multiband superconductivity
We show that a clean multiband superconductor may display one or several
phase transitions with increasing temperature from or to frustrated
configurations of the relative phases of the superconducting order parameters.
These transitions may occur when more than two bands are involved in the
formation of the superconducting phase and when the number of repulsive
interband interactions is odd. These transitions are signalled by slope changes
in the temperature dependence of the superconducting gaps.Comment: 5 pages, 3 figure
Non-magnetic impurities in two- and three- dimensional Heisenberg antiferromagnets
In this paper we study in a large-S expansion effects of substituting spins
by non-magnetic impurities in two- and three- dimensional Heisenberg
antiferromagnets in a weak magnetic field. In particular, we demonstrate a
novel mechanism where magnetic moments are induced around non-magnetic
impurities when magnetic field is present. As a result, Curie-type behaviour in
magnetic susceptibility can be observed well below the Neel temperature, in
agreement with what is being observed in and
compounds.Comment: Latex fil
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