12,972 research outputs found
RAT0455+1305: another pulsating hybrid sdB star
RAT0455+1305 was discovered during the Rapid Temporal Survey which aims in
finding any variability on timescales of a few minutes to several hours. The
star was found to be another sdBV star with one high amplitude mode and
relatively long period. These features along with estimation of T_eff and log g
makes this star very similar to Balloon 090100001. Encouraged by prominent
results obtained for the latter star we have decided to perform white light
photometry on RAT0455+1305. In 2009 we used the 1.5m telescope located in San
Pedro Martir Observatory in Mexico. Fourier analysis confirmed the dominant
mode found in the discovery data, uncovered another peak close to the dominant
one, and three peaks in the low frequency region. This shows that RAT0455+1305
is another hybrid sdBV star pulsating in both p- and g-modes.Comment: Proceedings of The Fourth Meeting on Hot Subdwarf Stars and Related
Objects held in China, 20-24 July 2009. Accepted for publication in
Astrophysics & Space Scienc
Darth Fader: Using wavelets to obtain accurate redshifts of spectra at very low signal-to-noise
We present the DARTH FADER algorithm, a new wavelet-based method for
estimating redshifts of galaxy spectra in spectral surveys that is particularly
adept in the very low SNR regime. We use a standard cross-correlation method to
estimate the redshifts of galaxies, using a template set built using a PCA
analysis on a set of simulated, noise-free spectra. Darth Fader employs wavelet
filtering to both estimate the continuum & to extract prominent line features
in each galaxy spectrum. A simple selection criterion based on the number of
features present in the spectrum is then used to clean the catalogue: galaxies
with fewer than six total features are removed as we are unlikely to obtain a
reliable redshift estimate. Applying our wavelet-based cleaning algorithm to a
simulated testing set, we successfully build a clean catalogue including
extremely low signal-to-noise data (SNR=2.0), for which we are able to obtain a
5.1% catastrophic failure rate in the redshift estimates (compared with 34.5%
prior to cleaning). We also show that for a catalogue with uniformly mixed SNRs
between 1.0 & 20.0, with realistic pixel-dependent noise, it is possible to
obtain redshifts with a catastrophic failure rate of 3.3% after cleaning (as
compared to 22.7% before cleaning). Whilst we do not test this algorithm
exhaustively on real data, we present a proof of concept of the applicability
of this method to real data, showing that the wavelet filtering techniques
perform well when applied to some typical spectra from the SDSS archive. The
Darth Fader algorithm provides a robust method for extracting spectral features
from very noisy spectra. The resulting clean catalogue gives an extremely low
rate of catastrophic failures, even when the spectra have a very low SNR. For
very large sky surveys, this technique may offer a significant boost in the
number of faint galaxies with accurately determined redshifts.Comment: 22 pages, 15 figures. Accepted for publication in Astronomy &
Astrophysic
Hamiltonian formulation of systems with linear velocities within Riemann-Liouville fractional derivatives
The link between the treatments of constrained systems with fractional
derivatives by using both Hamiltonian and Lagrangian formulations is studied.
It is shown that both treatments for systems with linear velocities are
equivalent.Comment: 10 page
Formulation strategies for enhancing growth of akkermansia muciniphila and its survival through lyophilisation and storage at air ambient
Gut bacterium Akkermansia muciniphila has been recognized as a new potential probiotic due to promising outcomes in the prevention and treatment of several human diseases. However, despite its multiple beneficial effects, its viability is compromised by the presence of oxygen. This has so far precluded its application namely in the development of nutraceutical/therapeutic formulations. In order to enhance growth of A. muciniphila and its survival through lyophilisation and storage at air ambient, formulation strategies are presented based on use of prebiotic compounds, antioxidants and cryoprotectants. According to our best knowledge, there is no information regarding lyophilisation procedures involving A. muciniphila as well as
its subsequent storage at ambient air.info:eu-repo/semantics/publishedVersio
Type O pure radiation metrics with a cosmological constant
In this paper we complete the integration of the conformally flat pure
radiation spacetimes with a non-zero cosmological constant , and , by considering the case . This is a
further demonstration of the power and suitability of the generalised invariant
formalism (GIF) for spacetimes where only one null direction is picked out by
the Riemann tensor. For these spacetimes, the GIF picks out a second null
direction, (from the second derivative of the Riemann tensor) and once this
spinor has been identified the calculations are transferred to the simpler GHP
formalism, where the tetrad and metric are determined. The whole class of
conformally flat pure radiation spacetimes with a non-zero cosmological
constant (those found in this paper, together with those found earlier for the
case ) have a rich variety of subclasses with zero,
one, two, three, four or five Killing vectors
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