330,573 research outputs found
A More Precise Extraction of |V_{cb}| in HQEFT of QCD
The more precise extraction for the CKM matrix element |V_{cb}| in the heavy
quark effective field theory (HQEFT) of QCD is studied from both exclusive and
inclusive semileptonic B decays. The values of relevant nonperturbative
parameters up to order 1/m^2_Q are estimated consistently in HQEFT of QCD.
Using the most recent experimental data for B decay rates, |V_{cb}| is updated
to be |V_{cb}| = 0.0395 \pm 0.0011_{exp} \pm 0.0019_{th} from B\to D^{\ast} l
\nu decay and |V_{cb}| = 0.0434 \pm 0.0041_{exp} \pm 0.0020_{th} from B\to D l
\nu decay as well as |V_{cb}| = 0.0394 \pm 0.0010_{exp} \pm 0.0014_{th} from
inclusive B\to X_c l \nu decay.Comment: 7 pages, revtex, 4 figure
Optical study of phase transitions in single-crystalline RuP
RuP single crystals of MnP-type orthorhombic structure were synthesized by
the Sn flux method. Temperature-dependent x-ray diffraction measurements reveal
that the compound experiences two structural phase transitions, which are
further confirmed by enormous anomalies shown in temperature-dependent
resistivity and magnetic susceptibility. Particularly, the resistivity drops
monotonically upon temperature cooling below the second transition, indicating
that the material shows metallic behavior, in sharp contrast with the
insulating ground state of polycrystalline samples. Optical conductivity
measurements were also performed in order to unravel the mechanism of these two
transitions. The measurement revealed a sudden reconstruction of band structure
over a broad energy scale and a significant removal of conducting carriers
below the first phase transition, while a charge-density-wave-like energy gap
opens below the second phase transition.Comment: 5 pages, 6 figure
Calibration of LAMOST Stellar Surface Gravities Using the Kepler Asteroseismic Data
Asteroseismology is a powerful tool to precisely determine the evolutionary
status and fundamental properties of stars. With the unprecedented precision
and nearly continuous photometric data acquired by the NASA Kepler mission,
parameters of more than 10 stars have been determined nearly consistently.
However, most studies still use photometric effective temperatures (Teff) and
metallicities ([Fe/H]) as inputs, which are not sufficiently accurate as
suggested by previous studies. We adopted the spectroscopic Teff and [Fe/H]
values based on the LAMOST low-resolution spectra (R~1,800), and combined them
with the global oscillation parameters to derive the physical parameters of a
large sample of stars. Clear trends were found between {\Delta}logg(LAMOST -
seismic) and spectroscopic Teff as well as logg, which may result in an
overestimation of up to 0.5 dex for the logg of giants in the LAMOST catalog.
We established empirical calibration relations for the logg values of dwarfs
and giants. These results can be used for determining the precise distances to
these stars based on their spectroscopic parameters.Comment: 22 pages, 13 figures and 3 tables, accepted for publication in
Astronomical Journal. Table 3 is available at
http://lwang.info/research/kepler_lamost
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