18,673 research outputs found
SACY - a Search for Associations Containing Young stars
The scientific goal of the SACY (Search for Associations Containing
Young-stars) was to identify possible associations of stars younger than the
Pleiades Association among optical counterparts of the ROSAT X-ray bright
sources. High-resolution spectra for possible optical counterparts later than
G0 belonging to HIPPARCOS and/or TYCHO-2 catalogs were obtained in order to
assess both the youth and the spatial motion of each target. More than 1000
ROSAT sources were observed, covering a large area in the Southern Hemisphere.
The newly identified young stars present a patchy distribution in UVW and XYZ,
revealing the existence of huge nearby young associations. Here we present the
associations identified in this survey.Comment: 8 pages, 2 figures, to appear in the Proceedings of Open Issues in
Local Formation and Early Stellar Evolution, Ouro Preto, Brazi
Spin-Torque-Induced Rotational Dynamics of a Magnetic Vortex Dipole
We study, both experimentally and by numerical modeling, the magnetic
dynamics that can be excited in a magnetic thin-film nanopillar device using
the spin torque from a spatially localized current injected via a
10s-of-nm-diameter aperture. The current-driven magnetic dynamics can produce
large amplitude microwave emission at zero magnetic field, with a frequency
well below that of the uniform ferromagnetic resonance mode. Micromagnetic
simulations indicate that the physical origin of this efficient microwave
nano-oscillator is the nucleation and subsequent steady-state rotational
dynamics of a magnetic vortex dipole driven by the localized spin torque. These
results show this novel implementation of a spintronic nano-oscillator is a
promising candidate for microwave technology applications.Comment: 19 pages, 4 figures
Quantum Cosmology of Fab Four John Theory with Conformable Fractional Derivative
We study a quantization via fractional derivative of a nonminimal derivative coupling cosmological theory, namely, the Fab Four John theory. Its Hamiltonian version presents the issue of fractional powers in the momenta. That problem is solved here by the application of the so-called conformable fractional derivative. This leads to a Wheeler\u2013DeWitt equation of second order, showing that a Bohm\u2013de Broglie interpretation can be constructed. That combination of fractional quantization and Bohmian interpretation provides us a new quantization method, in which the quantum potential is the criterion to say if a quantum solution is acceptable or not to be further studied. We show that a wide range of solutions for the scale factor is possible. Among all of those, a bouncing solution analogous to the perfect fluid cosmology seems to deserve special attention
On the binary nature of 1RXS J162848.1-415241
We present spectroscopy of the optical counterpart to 1RXS J162848.1-41524,
also known as the microquasar candidate MCQC J162847-4152. All the data
indicate that this X-ray source is not a microquasar, and that it is a
single-lined chromospherically active binary system with a likely orbital
period of 4.9 days. Our analysis supports a K3IV spectral classification for
the star, which is dominant at optical wavelengths. The unseen binary component
is most likely a late-type (K7-M) dwarf or a white dwarf. Using the high
resolution spectra we have measured the K3 star's rotational broadening to be
vsini = 43 +/- 3 km/s and determined a lower limit to the binary mass ratio of
q(=M2/M1)>2.0. The high rotational broadening together with the strong CaII H &
K / Halpha emission and high-amplitude photometric variations indicate that the
evolved star is very chromospherically active and responsible for the
X-ray/radio emission.Comment: 15 pages, 5 figures, accepted for publication in Ap
Vortices in atomic-molecular Bose-Einstein condensates
The structure and stability of vortices in hybrid atomic-molecular
Bose-Einstein condensates is analyzed in the framework of a two-component
Gross-Pitaevskii-type model that describes the stimulated Raman-induced
photoassociation process. New types of topological vortex states are predicted
to exist in the coherently coupled two-component condensates even without a
trap, and their nontrivial dynamics in the presence of losses is demonstrated.Comment: 7 pages, 6 figure
Megadepth: efficient coverage quantification for BigWigs and BAMs
Motivation
A common way to summarize sequencing datasets is to quantify data lying within genes or other genomic intervals. This can be slow and can require different tools for different input file types.
Results
Megadepth is a fast tool for quantifying alignments and coverage for BigWig and BAM/CRAM input files, using substantially less memory than the next-fastest competitor. Megadepth can summarize coverage within all disjoint intervals of the Gencode V35 gene annotation for more than 19 000 GTExV8 BigWig files in approximately 1 h using 32 threads. Megadepth is available both as a command-line tool and as an R/Bioconductor package providing much faster quantification compared to the rtracklayer package.
Availability and implementation
https://github.com/ChristopherWilks/megadepth, https://bioconductor.org/packages/megadepth.
Supplementary information
Supplementary data are available at Bioinformatics online
Orbital motion of the young brown dwarf companion TWA 5 B
With more adaptive optics images available, we aim at detecting orbital
motion for the first time in the system TWA 5 A+B. We measured separation and
position angle between TWA 5 A and B in each high-resolution image available
and followed their change in time, because B should orbit around A. The
astrometric measurement precision is about one milli arc sec. With ten year
difference in epoch, we can clearly detect orbital motion of B around A, a
decrease in separation by ~ 0.0054 arc sec per year and a decrease in position
angle by ~ 0.26 degrees per year. TWA 5 B is a brown dwarf with ~ 25 Jupiter
masses (Neuh\"auser et al. 2000), but having large error bars (4 to 145 Jupiter
masses, Neuh\"auser et al. 2009). Given its large projected separation from the
primary star, ~ 86 AU, and its young age ~ 10 Myrs), it has probably formed
star-like, and would then be a brown dwarf companion. Given the relatively
large changes in separation and position angle between TWA 5 A and B, we can
conclude that they orbit around each other on an eccentric orbit. Some evidence
is found for a curvature in the orbital motion of B around A - most consistent
with an elliptic (e=0.45) orbit. Residuals around the best-fit ellipse are
detected and show a small-amplitude (~ 18 mas) periodic sinusoid with ~ 5.7 yr
period, i.e., fully consistent with the orbit of the inner close pair TWA 5
Aa+b. Measuring these residuals caused by the photocenter wobble - even in
unresolved images - can yield the total mass of the inner pair, so can test
theoretical pre-main sequence models.Comment: 6 pages, 4 figures, accepted for publication in A&A; corrected typo
in amplitude below Fig.
Experimental balance to estimate efficiency in the use of nitrogen in rabbit breeding
[EN] Defining the composition and properties of manure in livestock production is critical in order to minimise possible environmental impacts stemming from its management. In this study, a nitrogen balance was carried out during two identical fattening periods (Experiments 1 and 2) in growing rabbits from weaning (age 28 d and live weight about 0.6 kg) to slaughter (age 61 d and live weight about 1.8 kg). The breeding conditions were typical for Spanish rabbit production. The objectives were to quantify the total nitrogen excreted by the animals and to estimate the average efficiency in the use of this nutrient, in comparison to other species. Animal weight, feed intake, and the production of faeces and urine were monitored weekly in a set of eight cages with nine rabbits in each, performing weekly analyses for nitrogen content in feed, urine and faeces. The overall nitrogen excretion was 50.2 g N per animal in Experiment 1 and 46.9 g N per animal in Experiment 2, which corresponded to about 58% of the total nitrogen intake. Urine and faeces contributed to overall nitrogen excretion in approximately the same proportions. The nitrogen excretion ratio was 40 grams per kilogram of animal produced. According to this ratio, rabbit breeding is less efficient in the use of nitrogen than raising broilers, but more than fattening pigs.The authors thank the Spanish Ministry of Education and Science for the economic support to conduct this study (Project GASFARM AGL2005-07297).Calvet Sanz, S.; Estellés Barber, F.; Hermida, B.; Blumetto, O.; Torres Salvador, AG. (2008). Experimental balance to estimate efficiency in the use of nitrogen in rabbit breeding. World Rabbit Science. 16(4). https://doi.org/10.4995/wrs.2008.615SWORD16
The Relationship Between X-ray Luminosity and Duty Cycle for Dwarf Novae and their Specific Frequency in the Inner Galaxy
We measure the duty cycles for an existing sample of well observed, nearby
dwarf novae using data from AAVSO, and present a quantitative empirical
relation between the duty cycle of dwarf novae outbursts and the X-ray
luminosity of the system in quiescence. We have found that , where
DC stands for duty cycle. We note that there is intrinsic scatter in this
relation greater than what is expected from purely statistical errors. Using
the dwarf nova X-ray luminosity functions from \citet{Pretorius12} and
\citet{Byckling10}, we compare this relation to the number of dwarf novae in
the Galactic Bulge Survey which were identified through optical outbursts
during an 8-day long monitoring campaign. We find a specific frequency of X-ray
bright () Cataclysmic Variables undergoing
Dwarf Novae outbursts in the direction of the Galactic Bulge of
. Such a specific frequency would give
a Solar neighborhood space density of long period CVs of
pc. We advocate the use of specific
frequency in future work, given that projects like LSST will detect DNe well
outside the distance range over which .Comment: 9 pagers, 4 figures Accepted for publication in MNRA
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