1,389 research outputs found
Absolute dimensions of detached eclipsing binaries. III. The metallic-lined system YZ Cassiopeiae
The bright binary system YZ Cassiopeiae is a remarkable laboratory for
studying the Am phenomenon. It consists of a metallic-lined A2 star and an F2
dwarf on a circular orbit, which undergo total and annular eclipses. We present
an analysis of 15 published light curves and 42 new high-quality echelle
spectra, resulting in measurements of the masses, radii, effective temperatures
and photospheric chemical abundances of the two stars. The masses and radii are
measured to 0.5% precision: M_A = 2.263 +/- 0.012 Msun, M_B = 1.325 +/- 0.007
Msun, R_A = 2.525 +/- 0.011 Rsun and R_B = 1.331 +/- 0.006 Rsun. We determine
the abundance of 20 elements for the primary star, of which all except scandium
are super-solar by up to 1 dex. The temperature of this star (9520 +/- 120 K)
makes it one of the hottest Am stars. We also measure the abundances of 25
elements for its companion (Teff = 6880 +/- 240 K), finding all to be solar or
slightly above solar. The photospheric abundances of the secondary star should
be representative of the bulk composition of both stars. Theoretical stellar
evolutionary models are unable to match these properties: the masses, radii and
temperatures imply a half-solar chemical composition (Z = 0.009 +/- 0.003) and
an age of 490-550 Myr. YZ Cas therefore presents a challenge to stellar
evolutionary theory.Comment: Accepted for publication in MNRAS. 15 pages, 9 tables, 7 figure
Stability of 1-D Excitons in Carbon Nanotubes under High Laser Excitations
Through ultrafast pump-probe spectroscopy with intense pump pulses and a wide
continuum probe, we show that interband exciton peaks in single-walled carbon
nanotubes (SWNTs) are extremely stable under high laser excitations. Estimates
of the initial densities of excitons from the excitation conditions, combined
with recent theoretical calculations of exciton Bohr radii for SWNTs, suggest
that their positions do not change at all even near the Mott density. In
addition, we found that the presence of lowest-subband excitons broadens all
absorption peaks, including those in the second-subband range, which provides a
consistent explanation for the complex spectral dependence of pump-probe
signals reported for SWNTs.Comment: 4 pages, 4 figure
The PiSpec: A Low-Cost, 3D-Printed Spectrometer for Measuring Volcanic SO2 Emission Rates
Spectroscopy has been used to quantify volcanic gas emission rates, most commonly SO2, for a number of decades. Typically, commercial spectrometers costing 1000s USD are employed for this purpose. The PiSpec is a new, custom-designed, 3D-printed spectrometer based on smartphone sensor technology. This unit has â1 nm spectral resolution and a spectral range in the ultraviolet of â280â340 nm, and is specifically configured for the remote sensing of SO2 using Differential Optical Absorption Spectroscopy (DOAS). Here we report on the first field deployment of the PiSpec on a volcano, to demonstrate the proof of concept of the deviceâs functionality in this application area. The study was performed on Masaya Volcano, Nicaragua, which is one of the largest emitters of SO2 on the planet, during a period of elevated activity where a lava lake was present in the crater. Both scans and traverses were performed, with resulting emission rates ranging from 3.2 to 45.6 kg sâ1 across two measurement days; these values are commensurate with those reported elsewhere in the literature during this activity phase (Aiuppa et al., 2018; Stix et al., 2018). Furthermore, we tested the PiSpecâs thermal stability, finding a wavelength shift of 0.046 nm/âC between 2.5 and 45âC, which is very similar to that of some commercial spectrometers. Given the low build cost of these units (â500 USD for a one-off build, with prospects for further price reduction with volume manufacture), we suggest these units hold considerable potential for volcano monitoring operations in resource limited environments
Perfect hypermomentum fluid: variational theory and equations of motion
The variational theory of the perfect hypermomentum fluid is developed. The
new type of the generalized Frenkel condition is considered. The Lagrangian
density of such fluid is stated, and the equations of motion of the fluid and
the Weyssenhoff-type evolution equation of the hypermomentum tensor are
derived. The expressions of the matter currents of the fluid (the canonical
energy-momentum 3-form, the metric stress-energy 4-form and the hypermomentum
3-form) are obtained. The Euler-type hydrodynamic equation of motion of the
perfect hypermomentum fluid is derived. It is proved that the motion of the
perfect fluid without hypermomentum in a metric-affine space coincides with the
motion of this fluid in a Riemann space.Comment: REVTEX, 23 pages, no figure
Ki67 expression levels are a better marker of reduced melanoma growth following MEK inhibitor treatment than phospho-ERK levels
The loss of tumour phospho-extracellular responsive kinase (pERK) positivity is the major treatment biomarker for mitogen-activated protein kinase/extracellular responsive kinase (MEK) inhibitors. Here, we demonstrate that there is a poor correlation between pERK inhibition and the anti-proliferative effects of MEK inhibitors in melanoma cells. We suggest that Ki67 is a better biomarker for future clinical studies
Evidence for the Early Evolutionary Loss of the M20D Auxin Amidohydrolase Family from Mosses and Horizontal Gene Transfer from Soil Bacteria of Cryptic Hydrolase Orthologues to Physcomitrella patens
Inactive auxin conjugates are accumulated in plants and hydrolyzed to recover phytohormone action. A family of metallopeptidase orthologues has been conserved in Plantae to help regulate auxin homeostatic levels during growth and development. This hydrolase family was recently traced back to liverwort, the most ancient extant land plant lineage. Liverwortâs auxin hydrolase has little activity against auxin conjugate substrates and does not appear to actively regulate auxin. This finding, along with data that shows moss can synthesize auxin conjugates, led to examining another bryophyte lineage, Physcomitrella patens. We have identified and isolated three M20D hydrolase paralogues from moss. The isolated enzymes strongly recognize and cleave a variety of auxin conjugates, including those of indole butyric and indole propionic acids. These P. patens hydrolases not only appear to be âcrypticâ, but they are likely to have derived from soil bacteria through Horizontal Gene Transfer. Additionally, support is presented that the plant-type M20D peptidase family may have been universally lost from mosses after divergence from the common ancestor with liverwort
Abundance analysis of two late A-type stars HD 32115 and HD 37594
We have performed abundance analysis of two slowly rotating, late A-type
stars, HD 32115 (HR 1613) and HD 37594 (HR 1940), based on obtained echelle
spectra covering the spectral range 4000-9850 AAngstrom. These spectra allowed
us to identify an extensive line list for 31 chemical elements, the most
complete to date for A-type stars. Two approaches to abundance analysis were
used, namely a ``manual'' (interactive) and a semi-automatic procedure for
comparison of synthetic and observed spectra and equivalent widths. For some
elements non-LTE (NLTE) calculations were carried out and the corresponding
corrections have been applied. The abundance pattern of HD 32115 was found to
be very close to the solar abundance pattern, and thus may be used as an
abundance standard for chemical composition studies in middle and late A stars.
Further, its H-alpha line profile shows no core-to-wing anomaly like that found
for cool Ap stars and therefore also may be used as a standard in comparative
studies of the atmospheric structures of cool, slowly rotating Ap stars. HD
37594 shows a metal deficiency at the level of -0.3 dex for most elements and
triangle-like cores of spectral lines. This star most probably belongs to the
Delta Scuti group.Comment: 10 pages, 4 figure
The sub-millimetre evolution of V4334 Sgr (Sakurai's Object)
We report the results of monitoring of V4334 Sgr (Sakurai's Object) at 450
microns and 850 microns with SCUBA on the James Clerk Maxwell Telescope. The
flux density at both wavelengths has increased dramatically since 2001, and is
consistent with continued cooling of the dust shell in which Sakurai's Object
is still enshrouded, and which still dominates the near-infrared emission.
Assuming that the dust shell is optically thin at sub-millimetre wavelengths
and optically thick in the near-infrared, the sub-millimetre data imply a
mass-loss rate during 2003 of ~3.4(+/0.2)E-5 for a gas-to-dust ratio of 75.
This is consistent with the evidence from 1-5micron observations that the
mass-loss is steadily increasing.Comment: 5 pages, 4 eps figures, accepted for publication in MNRA
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