1,180 research outputs found
The envelope of the power spectra of over a thousand \delta Scuti stars. The - scaling relation
CoRoT and Kepler high-precision photometric data allowed the detection and
characterization of the oscillation parameters in stars other than the Sun.
Moreover, thanks to the scaling relations, it is possible to estimate masses
and radii for thousands of solar-type oscillating stars. Recently, a \Delta\nu
- \rho relation has been found for \delta Scuti stars. Now, analyzing several
hundreds of this kind of stars observed with CoRoT and Kepler, we present an
empiric relation between their frequency at maximum power of their oscillation
spectra and their effective temperature. Such a relation can be explained with
the help of the \kappa-mechanism and the observed dispersion of the residuals
is compatible with they being caused by the gravity-darkening effect
Evidence of chaotic modes in the analysis of four delta Scuti stars
Since CoRoT observations unveiled the very low amplitude modes that form a
flat plateau in the power spectrum structure of delta Scuti stars, the nature
of this phenomenon, including the possibility of spurious signals due to the
light curve analysis, has been a matter of long-standing scientific debate. We
contribute to this debate by finding the structural parameters of a sample of
four delta Scuti stars, CID 546, CID 3619, CID 8669, and KIC 5892969, and
looking for a possible relation between these stars' structural parameters and
their power spectrum structure. For the purposes of characterization, we
developed a method of studying and analysing the power spectrum with high
precision and have applied it to both CoRoT and Kepler light curves. We obtain
the best estimates to date of these stars' structural parameters. Moreover, we
observe that the power spectrum structure depends on the inclination,
oblateness, and convective efficiency of each star. Our results suggest that
the power spectrum structure is real and is possibly formed by 2-period island
modes and chaotic modes
Evidence of amplitude modulation due to Resonant Mode Coupling in the delta Scuti star KIC5892969
A study of the star KIC5892969 observed by the Kepler satellite is presented.
Its three highest amplitude modes present a strong amplitude modulation. The
aim of this work is to investigate amplitude variations in this star and their
possible cause. Using the 4 years-long observations available, we obtained the
frequency content of the full light curve. Then, we studied the amplitude and
phase variations with time using shorter time stamps. The results obtained are
compared with the predicted ones for resonant mode coupling of an unstable mode
with lower frequency stable modes. Our conclusion is that resonant mode
coupling is consistent as an amplitude limitation mechanism in several modes of
KIC5892969 and we discuss to which extent it might play an important role for
other delta Scuti stars
Enzymatic hydrolysis of esters from 2-carboxy-6- methoxy-2,3-dihydrobenzofuran acid
In this work we describe the results of the enzymatic hydrolysis of esters from 2-carboxy-6-methoxy-2,3-dihydrobenzofuran acid using Candida antarctica lipase supported on acrylic resin, with enantiomeric excesses ranging between 80 to 99%
Influence of crystalline orientation on the thermal-energy convertion efficiency in shape memory alloys
A theoretical study about the influence of crystalline orientation on the energy conversion efficiency of two shape memory alloys is present. The study consider single crystal samples in simple tension. The results showed higher properties for of the NiTi than Cu-Al-Be, especially in the temperature-increment (ΔT) necessary for get a conversion energy cycle. However, the study showed a crystalline orientation favorable for Cu-Al-Be
On paraquaternionic submersions between paraquaternionic K\"ahler manifolds
In this paper we deal with some properties of a class of semi-Riemannian
submersions between manifolds endowed with paraquaternionic structures, proving
a result of non-existence of paraquaternionic submersions between
paraquaternionic K\"ahler non locally hyper paraK\"ahler manifolds. Then we
examine, as an example, the canonical projection of the tangent bundle, endowed
with the Sasaki metric, of an almost paraquaternionic Hermitian manifold.Comment: 13 pages, no figure
Distributional and reproductive aspects of the bigeye thresher shark (Alopias superciliosus) in the Atlantic ocean
Captura asociada a la pesquería de palangre de superficie dirigida a pez espadaThe bigeye thresher shark, Alopias supercilious is sometimes caught as bycatch in
pelagic longline fisheries targeting tunas and swordfish in the Atlantic Ocean. As part
of an ongoing cooperative program for fisheries and biological data collection, fishery
observer data from various fishing nations and projects were compiled and analyzed.
Those data sets include information on geographic location of the observations, as well
as size, sex and in some cases maturity stage. A total of 4371 bigeye threshers were
recorded throughout the Atlantic Ocean between 1992 and 2013, with the sizes ranging
from 70 to 305 cm FL (fork length). Considerable variability was observed in the catchat-
size, with particular emphasis on the tropical region where the mean sizes tended to
be smaller than in the other regions. The expected distribution of juvenile and adult
specimens also showed considerable variability, and the sex-ratios varied between
regions and size classes. Maturity ogives were fitted to data from 642 specimens, with
the median sizes at maturity estimated at 208.6 cm FL (corresponding to 349.1 cm TL)
for females and 159.2 cm FL (corresponding to 269.8 cm TL) for males. In addition, a
segmented regression model (SRM) was used for males, and two breakpoints (Bk1:
122.5cm FL, Bk2: 173.3cm FL) estimated, identifying transitions between the three
different maturity stages for male sharks (immature, maturing and mature). Only a few
pregnant females were recorded, always with the presence of two embryos (one per
uterus), and were distributed predominantly in the tropical northeast Atlantic closer the
African continent, and in the southwest region, with those regions possibly serving as
nursery areas for this species. These reproductive parameters, and especially the
estimated median sizes at maturity and low fecundity, highlight the vulnerability of this
species, reinforcing that the bigeye thresher tends to mature at a larger size than the
other species of the Alopiidae family. The biological and distributional patterns
presented can help managers adopt more informed and efficient conservation measures
for this species.En prensa0,000
Hypertension as a Risk Factor for Hip Fracture
Producción CientíficaArterial hypertension is a chronic disease in which prevalence
increases with age, as occurs in osteoporosis. It is
clinically silent and is only revealed in the form of complications,
an aspect that it also shares with osteoporosis.
Various alterations of calcium metabolism have been described
in association with hypertension; such alterations
can cause decreased bone mass, the principal determining
factor of fracture.1,2 Another important factor is the occurrence
of falls. Hypertensive patients may experience a
greater number of falls resulting from fainting associated
with diminished baroreflex sensitivity or hypotension secondary
to therapy.3,4 The purpose of this study was to
assess the effect of hypertension and its various therapeutic
alternatives on the risk of hip fracture.2015-09-0
Control of D-STATCOM during unbalanced grid faults based on DC voltage oscillations and peak current limitations
The safe operation of grid connected power converters during abnormal condition is a key issue in order to guarantee its operation and to avoid undesired trips. In this paper different control strategies for the operation of a D-STATCOM are introduced, where the reference currents are determined in such a way that not only none of the phase currents goes over the limits, but also the DC voltage fluctuations remain in safe operation limit. Fluctuating active power interchange, during unbalanced condition leads to DC voltage oscillation. Severe unbalanced condition and small DC capacitor selection (to meet the size and cost constraints) intensify the DC voltage oscillation. Therefore, the contribution of this paper lays on the combination of the DC voltage oscillations and the current limit control. The effectiveness of three proposed control strategies are verified by simulating a D-STATCOM tied to an industrial distribution network. Moreover a scaled scenario has been reproduced experimentally which shows that the results cope well with the analytical equations and the simulation results.Peer ReviewedPostprint (author's final draft
First release of the IPHAS catalogue of new extended planetary nebulae
Date of Acceptance: 30/06/2014We present the first results of our search for new, extended planetary nebulae (PNe) based on careful, systematic, visual scrutiny of the imaging data from the Isaac Newton Telescope Photometric Ha Survey of the Northern Galactic plane (IPHAS). The newly uncovered PNe will help to improve the census of this important population of Galactic objects that serve as key windows into the late-stage evolution of low- to intermediate-mass stars. They will also facilitate study of the faint end of the ensemble Galactic PN luminosity function. The sensitivity and coverage of IPHAS allows PNe to be found in regions of greater extinction in the Galactic plane and/or those PNe in a more advanced evolutionary state and at larger distances compared to the general Galactic PN population. Using a set of newly revised optical diagnostic diagrams in combination with access to a powerful, new, multiwavelength imaging data base, we have identified 159 true, likely and possible PNe for this first catalogue release. The ability of IPHAS to unveil PNe at low Galactic latitudes and towards the Galactic Anticentre, compared to previous surveys, makes this survey an ideal tool to contribute to the improvement of our knowledge of the whole Galactic PN population.Peer reviewe
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