3,607 research outputs found
Optical Interferometry of early-type stars with PAVO@CHARA. I. Fundamental stellar properties
We present interferometric observations of 7 main-sequence and 3 giant stars
with spectral types from B2 to F6 using the PAVO beam combiner at the CHARA
array. We have directly determined the angular diameters for these objects with
an average precision of 2.3%. We have also computed bolometric fluxes using
available photometry in the visible and infrared wavelengths, as well as
space-based ultraviolet spectroscopy. Combined with precise \textit{Hipparcos}
parallaxes, we have derived a set of fundamental stellar properties including
linear radius, luminosity and effective temperature. Fitting the latter to
computed isochrone models, we have inferred masses and ages of the stars. The
effective temperatures obtained are in good agreement (at a 3% level) with
nearly-independent temperature estimations from spectroscopy. They validate
recent sixth-order polynomial (B-V)- empirical relations
\citep{Boyajian2012a}, but suggest that a more conservative third-order
solution \citep{vanBelle2009} could adequately describe the
(V-K)- relation for main-sequence stars of spectral type A0 and
later. Finally, we have compared mass values obtained combining surface gravity
with inferred stellar radius (\textit{gravity mass}) and as a result of the
comparison of computed luminosity and temperature values with stellar
evolutionary models (\textit{isochrone mass}). The strong discrepancy between
isochrone and gravity mass obtained for one of the observed stars,
\,Lyr, suggests that determination of the stellar atmosphere parameters
should be revised.Comment: 13 pages, 9 figures, accepted for publication in MNRA
Diagnosis and grading of radiographic osteoporotic vertebral deformity by general radiologists after a brief self-learning period
Background: The expanded semi-quantitative (eSQ) osteoporotic vertebral deformity (OVD) classification has minimal, mild, moderate, moderately-severe, severe, and collapsed grades with <20%, 20-25%, >25%-1/3, >1/3-40%, >40%-2/3, >2/3 vertebral height loss respectively. This study evaluates the performance of using this grading criterion by radiology readers who did not have former training in OVD assessment. Methods: Spine radiographs of 44 elderly women with 278 normal appearing vertebrae and 65 OVDs were selected, with two senior readers agreed the reference reading. Three readers from Italy and three readers from China were invited to evaluate these radiographs after reading five reference articles including one detailing eSQ criteria with illustrative examples. Before the second round of reading, the readers were asked to read an additional explanatory document. For the readers in Italy an additional on-line demonstration was given on how to measure vertebral height loss in another five cases of OVD. Two Chinese readers had a third round of reading after a 90 minutes' on-line lecture. Results: The final absolute agreement rate with the reference reading (i.e., exactly the same grading as the reference) ranged between 46.2% to 68.2% for the six readers, and the final relative agreement (with one eSQ grade difference allowed) ranged between 78.5% to 92.5%. The >1 grade disagreement rate was all below 11%, and mostly below 7%. The missed OVD were mostly minimal grade. The rate for missing a ≥ mild OVD was <4.5%, and false positive rate was generally <1.4% among the final reading. If the minimal grade was removed and the remaining gradings were converted to Genant's semi-quantitative (GSQ) grading, the mean kappa values against the reference reading for SQ grades-1,2,3 were 0.813, 0.814, and 0.916 respectively. Conclusions: This study demonstrates good performance of the six learner readers for assessing radiographic after a brief self-learning period
A novel detection method for voltage sags
Author name used in this publication: K. W. E. ChengAuthor name used in this publication: X. D. XueAuthor name used in this publication: C. D. XuAuthor name used in this publication: Y. B. CheAuthor name used in this publication: D. H. WangAuthor name used in this publication: P. DongPower Electronics Research CentreRefereed conference paper2006-2007 > Academic research: refereed > Refereed conference paperVersion of RecordPublishe
Rotationally-modulated g-modes in the rapidly-rotating delta Scuti star Rasalhague (alpha Ophiuchi)
Despite a century of remarkable progress in understanding stellar interiors,
we know surprisingly little about the inner workings of stars spinning near
their critical limit. New interferometric imaging of these so-called ``rapid
rotators'' combined with breakthroughs in asteroseismology promise to lift this
veil and probe the strongly latitude-dependent photospheric characteristics and
even reveal the internal angular momentum distribution of these luminous
objects. Here, we report the first high precision photometry on the
low-amplitude delta cuti variable star Rasalhague (alpha Oph, A5IV, 2.18 Msun,
omega/omega_c~0.88) based on 30 continuous days of monitoring using the MOST
satellite. We have identified 57+/-1 distinct pulsation modes above a
stochastic granulation spectrum with a cutoff of ~26 cycles per day.
Remarkably, we have also discovered that the fast rotation period of 14.5~hours
modulates low-frequency modes (1-10 day periods) that we identify as a rich
family of g-modes (|m| up to 7). The spacing of the g-modes is surprisingly
linear considering Coriolis forces are expected to strongly distort the mode
spectrum, suggesting we are seeing prograde ``equatorial Kelvin'' waves (modes
l=m). We emphasize the unique aspects of Rasalhague motivating future detailed
asteroseismic modeling -- a source with a precisely measured parallax distance,
photospheric oblateness, latitude temperature structure, and whose low-mass
companion provides an astrometric orbit for precise mass determinations.Comment: Accepted for publication in Astrophysical Journa
Development of an automotive HID electronic ballast based microprocessor
Author name used in this publication: D. H. WangAuthor name used in this publication: K. W. E. ChengAuthor name used in this publication: P. DongAuthor name used in this publication: X. D. XueAuthor name used in this publication: K. DingAuthor name used in this publication: Y. B. CheAuthor name used in this publication: C. D. XuPower Electronics Research CentreRefereed conference paper2006-2007 > Academic research: refereed > Refereed conference paperVersion of RecordPublishe
Imaging the Algol Triple System in H Band with the CHARA Interferometer
Algol (Beta Per) is an extensively studied hierarchical triple system whose
inner pair is a prototype semi-detached binary with mass transfer occurring
from the sub-giant secondary to the main-sequence primary. We present here the
results of our Algol observations made between 2006 and 2010 at the CHARA
interferometer with the Michigan Infrared Combiner in the H band. The use of
four telescopes with long baselines allows us to achieve better than 0.5 mas
resolution and to unambiguously resolve the three stars. The inner and outer
orbital elements, as well as the angular sizes and mass ratios for the three
components are determined independently from previous studies. We report a
significantly improved orbit for the inner stellar pair with the consequence of
a 15% change in the primary mass compared to previous studies. We also
determine the mutual inclination of the orbits to be much closer to
perpendicularity than previously established. State-of-the-art image
reconstruction algorithms are used to image the full triple system. In
particular an image sequence of 55 distinct phases of the inner pair orbit is
reconstructed, clearly showing the Roche-lobe-filling secondary revolving
around the primary, with several epochs corresponding to the primary and
secondary eclipses
Allogenic Mesenchymal Stem Cell Transplantation Ameliorates Nephritis in Lupus Mice Via Inhibition of B-Cell Activation
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