53 research outputs found
Low Cohomogeneity and Polar Actions on Exceptional Compact Lie Groups
We study isometric Lie group actions on the compact exceptional groups E6,
E7, E8, F4 and G2 endowed with a biinvariant metric. We classify polar actions
on these groups. We determine all isometric actions of cohomogeneity less than
three on E6, E7, F4 and all isometric actions of cohomogeneity less than 20 on
E8. Moreover we determine the principal isotropy algebras for all isometric
actions on G2.Comment: 27 pages; introduction rewritten; references updated; final version;
to appear in Transformation Group
GALEX J201337.6+092801: The lowest gravity subdwarf B pulsator
We present the recent discovery of a new subdwarf B variable (sdBV), with an
exceptionally low surface gravity. Our spectroscopy of J20136+0928 places it at
Teff = 32100 +/- 500, log(g) = 5.15 +/- 0.10, and log(He/H) = -2.8 +/- 0.1.
With a magnitude of B = 12.0, it is the second brightest V361 Hya star ever
found. Photometry from three different observatories reveals a temporal
spectrum with eleven clearly detected periods in the range 376 to 566 s, and at
least five more close to our detection limit. These periods are unusually long
for the V361 Hya class of short-period sdBV pulsators, but not unreasonable for
p- and g-modes close to the radial fundamental, given its low surface gravity.
Of the ~50 short period sdB pulsators known to date, only a single one has been
found to have comparable spectroscopic parameters to J20136+0928. This is the
enigmatic high-amplitude pulsator V338 Ser, and we conclude that J20136+0928 is
the second example of this rare subclass of sdB pulsators located well above
the canonical extreme horizontal branch in the HR diagram.Comment: 5 pages, accepted for publication in ApJ Letter
On the volume formulas of cones and orthogonal multi-cones in S-n(1) and H-n(-1)
In the study of n-dimensional spherical or hyperbolic geometry, n >= 3, the volume of various objects such as simplexes, convex polytopes, etc. often becomes rather difficult to deal with. In this paper, we use the method of infinitesimal symmetrization to provide a systematic way of obtaining volume formulas of cones and orthogonal multiple cones in S-n(1) and H-n(-1)
Single molecule fluorescence spectroscopy
Single molecule spectroscopy can uncover fluctuation averaged out in ensemble measurements. In addition, single molecule spectroscopy naturally implies ultra-sensitive measurements, which should play important role in future proteomics and genomic research. Fluorescence method is the most commonly used single molecule detection. In this paper, we will use single conjugated polymer fluorescence spectroscopy to illustrate the power of this technique
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