866 research outputs found
Proyecciones de población escolar de Costa Rica, 1977-1990
Incluye Bibliografí
Addressing conflict between fishermen and the Titicaca Grebe ( Rollandia microptera ) through diet analysis
Human–wildlife conflict is often a driver of species declines, and understanding the material basis of this conflict is the first step in addressing it. The Titicaca Grebe Rollandia microptera is an endangered endemic species found solely in the Lake Titicaca watershed of Peru and Bolivia, and has experienced population declines due to fisheries bycatch. Human fishers often have negative opinions of the Titicaca Grebe, because they consider it as a competitor for declining fish stocks. We tested that assumption by an analysis of the bird's diet and found that the Titicaca Grebe does not compete with fishers for more lucrative fish species such as trout Oncorhynchus sp. and Pejerrey Odontesthes bonariensis, but does compete for the less desirable (to human fishers) native Orestias sp
Dating young open clusters using delta Scuti stars. Results for Trumpler 10 and Praesepe
Aims. The main goal of this work is to date young open clusters using
Sct stars. Seismic indices such as the large separation and the
frequency at maximum power can help to constrain the models to better
characterise the stars. We propose a reliable method to identify some radial
modes, which gives us greater confidence in the constrained models. Methods. We
extract the frequency content of a sample of Sct stars belonging to
the same open cluster. We estimate the low-order large separation by means of
different techniques and the frequency at maximum power for each member of the
sample. We use a grid of models built with the typical parameters of
Sct stars, including mass, metallicity and rotation as independent variables,
and determine the oscillation modes. We select the observed frequencies whose
ratios match those of the models. Once we find a range of radial modes matching
the observed frequencies, mainly the fundamental mode, we add it to the other
seismic parameters to derive the stellar age. Assuming star groups have similar
chemistry and age, we estimate their mean age by computing a weighted
probability density function fit to the age distribution of the seismically
constrained models. Results. We estimate the age of Trumpler 10 to be
Myr, and that of Praesepe to be Myr. In this
latter case, we find two apparent populations of Sct stars in the same
cluster, one at Myr and another at Myr. This may be
due to two different formation events, different rotational velocities of the
members in our sample of stars (as rapid rotation may modify the observed large
separation), or to membership of unresolved binary systems.Comment: 20 pages, 25 figure, uses the open-source code MultiModes (see
https://github.com/davidpamos/MultiModes). It will be published in A&
JPCam: A 1.2Gpixel camera for the J-PAS survey
JPCam is a 14-CCD mosaic camera, using the new e2v 9k-by-9k 10microm-pixel
16-channel detectors, to be deployed on a dedicated 2.55m wide-field telescope
at the OAJ (Observatorio Astrofisico de Javalambre) in Aragon, Spain. The
camera is designed to perform a Baryon Acoustic Oscillations (BAO) survey of
the northern sky. The J-PAS survey strategy will use 54 relatively narrow-band
(~13.8nm) filters equi-spaced between 370 and 920nm plus 3 broad-band filters
to achieve unprecedented photometric red-shift accuracies for faint galaxies
over ~8000 square degrees of sky. The cryostat, detector mosaic and read
electronics is being supplied by e2v under contract to J-PAS while the
mechanical structure, housing the shutter and filter assembly, is being
designed and constructed by a Brazilian consortium led by INPE (Instituto
Nacional de Pesquisas Espaciais). Four sets of 14 filters are placed in the
ambient environment, just above the dewar window but directly in line with the
detectors, leading to a mosaic having ~10mm gaps between each CCD. The massive
500mm aperture shutter is expected to be supplied by the Argelander-Institut
fur Astronomie, Bonn. We will present an overview of JPCam, from the filter
configuration through to the CCD mosaic camera. A brief outline of the main
J-PAS science projects will be included.Comment: 11 pages and 9 figure
Evidence for a black hole in the historical X-ray transient A 1524-61 (=KY TrA)
We present VLT spectroscopy, high-resolution imaging and time-resolved
photometry of KY TrA, the optical counterpart to the X-ray binary A 1524-61. We
perform a refined astrometry of the field, yielding improved coordinates for KY
TrA and the field star interloper of similar optical brightness that we locate
arcsec SE. From the spectroscopy, we refine the radial velocity
semi-amplitude of the donor star to km s by employing
the correlation between this parameter and the full-width at half-maximum of
the H emission line. The -band light curve shows an ellipsoidal-like
modulation with a likely orbital period of d (
h). These numbers imply a mass function M. The
KY TrA de-reddened quiescent colour is consistent
with a donor star of spectral type K2 or later, in case of significant
accretion disc light contribution to the optical continuum. The colour allows
us to place a very conservative upper limit on the companion star mass, M, and, in turn, on the binary mass ratio, . By exploiting the correlation between the binary inclination and the
depth of the H line trough, we establish deg. All these
values lead to a compact object and donor mass of
M and M, respectively, thus confirming the
black hole nature of the accreting object. In addition, we estimate a distance
toward the system of kpc.Comment: 7 pages, 5 figure
Black hole mass and spin measurements through the Relativistic Precession Model: XTE J1859+226
The X-ray light curves of accreting black holes and neutron stars in binary
systems show various types of quasi-periodic oscillations (QPOs), the origin of
which is still debated. The Relativistic Precession Model identifies the QPO
frequencies with fundamental time scales from General Relativity, and has been
proposed as a possible explanation of certain types of such oscillations. Under
specific conditions (i.e., the detection of a particular QPOs triplet) such a
model can be used to obtain self-consistent measurements of the mass and spin
of the compact object. So far this has been possible only in the black hole
binary GRO J1655-40. In the RXTE/PCA data from the 1999-2000 outburst of the
black hole transient XTE J1859+226 we found a QPO triplet, and used the the
Relativistic Precession Model to obtain high-precision measurements of the
black hole mass and spin - M = (7.85+/-0.46) Msun, a* = 0.149+/-0.005 - the
former being consistent with the most recent dynamical mass determination from
optical measurements. Similarly to what has been already observed in other
black hole systems, the frequencies of the QPOs and broad-band noise components
match the general relativistic frequencies of particle motion close to the
compact object predicted by the model. Our findings confirm previous results
and further support the validity of the Relativistic Precession Model, which is
the only electromagnetic-measurement-based method that so far has consistently
yielded spins close to those from the gravitational waves produced by merging
binary black holes.Comment: 8 pages, 5 figures, accepted for publication in MNRA
Androgens and Cardiovascular Risk Factors in Polycystic Ovary Syndrome
Polycystic Ovary Syndrome (PCOS) is the most common endocrine disorder in reproductive-aged women. Clinical or biochemical signs of androgen excess is a cardinal feature of the syndrome and are present in approximately 80% of women with PCOS. Increased blood pressure and insulin resistance, two major cardiovascular risk factors, are frequently present in women with PCOS. This chapter aims to highlight the fundamental role of androgens in mediating the increased blood pressure and insulin resistance in women with PCOS. This chapter is also a call for action to develop new pharmacological therapies that target the androgen synthesis and androgen receptor activation dysregulation present in women with PCOS. These novel therapies will allow to prevent or mitigate the excess androgen-mediated cardiovascular risk factors that affect women with PCOS
African Ancestry Is Associated with Asthma Risk in African Americans
Asthma is a common complex condition with clear racial and ethnic differences in both prevalence and severity. Asthma consultation rates, mortality, and severe symptoms are greatly increased in African descent populations of developed countries. African ancestry has been associated with asthma, total serum IgE and lower pulmonary function in African-admixed populations. To replicate previous findings, here we aimed to examine whether African ancestry was associated with asthma susceptibility in African Americans. In addition, we examined for the first time whether African ancestry was associated with asthma exacerbations.After filtering for self-reported ancestry and genotype data quality, samples from 1,117 self-reported African-American individuals from New York and Baltimore (394 cases, 481 controls), and Chicago (321 cases followed for asthma exacerbations) were analyzed. Genetic ancestry was estimated based on ancestry informative markers (AIMs) selected for being highly divergent among European and West African populations (95 AIMs for New York and Baltimore, and 66 independent AIMs for Chicago). Among case-control samples, the mean African ancestry was significantly higher in asthmatics than in non-asthmatics (82.0±14.0% vs. 77.8±18.1%, mean difference 4.2% [95% confidence interval (CI):2.0-6.4], p<0.0001). This association remained significant after adjusting for potential confounders (odds ratio: 4.55, 95% CI: 1.69-12.29, p = 0.003). African ancestry failed to show an association with asthma exacerbations (p = 0.965) using a model based on longitudinal data of the number of exacerbations followed over 1.5 years.These data replicate previous findings indicating that African ancestry constitutes a risk factor for asthma and suggest that elevated asthma rates in African Americans can be partially attributed to African genetic ancestry
The orbital period, black hole mass and distance to the X-ray transient GRS 1716-249 (=N Oph 93)
We present evidence for a 0.278(8) d (=6.7 h) orbital period in the X-ray
transient GRS 1716-249 (=N Oph 93), based on a superhump modulation detected
during the 1995 mini-outburst plus ellipsoidal variability in quiescence. With
a quiescent magnitude of r=23.19+-0.15 N Oph 93 is too faint to warrant a full
dynamical study through dedicated time-resolved spectroscopy. Instead, we apply
the FWHM-K2 correlation to the disc Halpha emission line detected in Gran
Telescopio Canarias spectra and obtain K2=521+-52 km/s. This leads to a mass
function f(M)=4.1+-1.2 Msun, thus indicating the presence of a black hole in
this historic X-ray transient. Furthermore, from the depth of the Halpha trough
and the quiescent light curve we constrain the binary inclination to i=61+-15
deg, while the detection of superhumps sets an upper limit to the donor to
compact star mass ratio q=M2/M1<=0.25. Our de-reddened (r-i) colour is
consistent with a ~K6 main sequence star that fills its Roche lobe in a 0.278 d
orbit. Using all this information we derive a compact object mass
M1=6.4+3.2-2.0 Msun at 68 per cent confidence. We also constrain the distance
to GRS 1716-249 to 6.9+-1.1 kpc, placing the binary ~0.8 kpc above the Galactic
Plane, in support of a large natal kick.Comment: Accepted for publication in MNRAS, 12 pages, 9 figures, 2 Table
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