1,952 research outputs found
Science and Business
There are two kinds of scientists in evolutionary studies that need a space of debate: the specialists in evolutionary studies in business and all other evolutionary scientists in general. The themes of the discussion are the behaviour, growth, reproduction, and organizational structures of the firm
Modeling non-thermal emission from stellar bow shocks
Runaway O- and early B-type stars passing throughout the interstellar medium
at supersonic velocities and characterized by strong stellar winds may produce
bow shocks that can serve as particle acceleration sites. Previous theoretical
models predict the production of high energy photons by non-thermal radiative
processes, but their efficiency is still debated. We aim to test and explain
the possibility of emission from the bow shocks formed by runaway stars
traveling through the interstellar medium by using previous theoretical models.
We apply our model to AE Aurigae, the first reported star with an X-ray
detected bow shock, to BD+43 3654, in which the observations failed in
detecting high energy emission, and to the transition phase of a supergiant
star in the late stages of its life.From our analysis, we confirm that the
X-ray emission from the bow shock produced by AE Aurigae can be explained by
inverse Compton processes involving the infrared photons of the heated dust. We
also predict low high energy flux emission from the bow shock produced by BD+43
3654, and the possibility of high energy emission from the bow shock formed by
a supergiant star during the transition phase from blue to red supergiant.Bow
shock formed by different type of runaway stars are revealed as a new possible
source of high energy photons in our neighbourhood
X-ray flares on the UV Ceti-type star CC Eridani: a "peculiar" time-evolution of spectral parameters
Context: Weak flares are supposed to be an important heating agent of the
outer layers of stellar atmospheres. However, due to instrumental limitations,
only large X-ray flares have been studied in detail until now.
Aims: We used an XMM-Newton observation of the very active BY-Dra type binary
star CC Eri in order to investigate the properties of two flares that are
weaker than those typically studied in the literature.
Methods: We performed time-resolved spectroscopy of the data taken with the
EPIC-PN CCD camera. A multi-temperature model was used to fit the spectra. We
inferred the size of the flaring loops using the density-temperature diagram.
The loop scaling laws were applied for deriving physical parameters of the
flaring plasma. We also estimated the number of loops involved in the observed
flares.
Results: A large X-ray variability was found. Spectral analysis showed that
all the regions in the light curve, including the flare segments, are
well-described by a 3-T model with variable emission measures but,
surprisingly, with constant temperatures (values of 3, 10 and 22 MK). The
analysed flares lasted ~ 3.4 and 7.1 ks, with flux increases of factors
1.5-1.9. They occurred in arcades made of a few tens of similar coronal loops.
The size of the flaring loops is much smaller than the distance between the
stellar surfaces in the binary system, and even smaller than the radius of each
of the stars. The obtained results are consistent with the following ideas: (i)
the whole X-ray light curve of CC Eri could be the result of a superposition of
multiple low-energy flares, and (ii) stellar flares can be scaled-up versions
of solar flares.Comment: 14 pages, 12 figures. Accepted for publication in Astronomy &
Astrophysic
La custodia del territorio como instrumento complementario para la protección de los espacios naturales
La presente nota analiza la evolución normativa de la custodia del territorio como estrategia complementaria de protección de los espacios naturales caracterizada por las notas de participación y voluntariedad y que goza de una creciente vitalidad y posibilidades de futuro. En especial, se trata de subrayar la evolución de los mecanismos de protección que, si bien descansaban en el ejercicio unilateral de potestades administrativas, de modo creciente se orientan a estrategias acordadas con los sectores interesados y afectados, como modo de conseguir mayor apoyo social y colaboración de los particulares en la consecución de los fines de interés general, en este caso, la utilización racional de los recursos naturales, la garantía del derecho a disfrutar de un medio ambiente adecuado y el más cabal cumplimiento de los deberes de protección
El nuevo régimen de la reutilización de las aguas depuradas: en especial las novedades en el nuevo Plan Hidrológico de la demarcación del Segura
La reutilización de las aguas depuradas constituye una práctica adecuada para incrementar la disponibilidad del recurso. Sin embargo, las implicaciones sanitarias que pudiera conllevar hacen necesario la instauración de un marco jurídico que otorgue seguridad a los diferentes sectores implicados. La incorporación de las aguas regeneradas a la gestión integral del dominio público hidráulico implica, a su vez, su consideración en los nuevos planes hidrológicos recientemente aprobados. En la Demarcación Hidrográfica del Segura, donde el recurso se encuentra sometido a una intensa presión por los actuales y potenciales usuarios, la reutilización puede representar un relevante recurso adicional
Deep XMM-Newton observation of the Eta Chamaleontis cluster
The members of the Eta Chamaleontis cluster are in an evolutionary stage in
which disks are rapidly evolving. It also presents some peculiarities, such as
the large fraction of binaries and accretion disks, probably related with the
cluster formation process. Its proximity makes this stellar group an ideal
target for studying the relation between X-ray emission and those stellar
parameters. The main objective of this work is to determine general X-ray
properties of the cluster members in terms of coronal temperature, column
density, emission measure, X-ray luminosity and variability. We also aim to
establish the relation between the X-ray luminosity of these stars and other
stellar parameters, such as binarity and presence of accretion disks. A study
of flare energies for each flare event and their relation with some stellar
parameters is also performed. We used proprietary data from a deep XMM-Newton
observation pointed at the core of the Eta Chamaleontis cluster. Specific
software for the reduction of XMM-Newton data was used for the analysis of our
observation. For the detection of sources, we used the wavelet-based code
PWDetect. General coronal properties were derived from plasma model fitting. We
also determined variability of the Eta Chamaleontis members in the EPIC
field-of-view. A total of six flare-like events were clearly detected in five
different stars. For them, we derived coronal properties during the flare
events and pseudo-quiescent state separately. In our observations, stars that
underwent a flare event have higher X-ray luminosities in the pseudo-quiescent
state than cluster members with similar spectral type with no indications of
flaring, independently whether they have an accretion disk or not. Observed
flare energies are typical of both pre-main and main-sequence M stars. We
detected no difference between flare energies of stars with and without an
accretion disk.Comment: Accepted for publication in Astronomy and Astrophysics. 12 pages, 30
individual figure
Formation of X-ray emitting stationary shocks in magnetized protostellar jets
X-ray observations of protostellar jets show evidence of strong shocks
heating the plasma up to temperatures of a few million degrees. In some cases,
the shocked features appear to be stationary. They are interpreted as shock
diamonds. We aim at investigating the physics that guides the formation of
X-ray emitting stationary shocks in protostellar jets, the role of the magnetic
field in determining the location, stability, and detectability in X-rays of
these shocks, and the physical properties of the shocked plasma. We performed a
set of 2.5-dimensional magnetohydrodynamic numerical simulations modelling
supersonic jets ramming into a magnetized medium and explored different
configurations of the magnetic field. The model takes into account the most
relevant physical effects, namely thermal conduction and radiative losses. We
compared the model results with observations, via the emission measure and the
X-ray luminosity synthesized from the simulations. Our model explains the
formation of X-ray emitting stationary shocks in a natural way. The magnetic
field collimates the plasma at the base of the jet and forms there a magnetic
nozzle. After an initial transient, the nozzle leads to the formation of a
shock diamond at its exit which is stationary over the time covered by the
simulations (~ 40 - 60 yr; comparable with time scales of the observations).
The shock generates a point-like X-ray source located close to the base of the
jet with luminosity comparable with that inferred from X-ray observations of
protostellar jets. For the range of parameters explored, the evolution of the
post-shock plasma is dominated by the radiative cooling, whereas the thermal
conduction slightly affects the structure of the shock.Comment: Accepted for publication in Astronomy and Astrophysic
Recent changes in women’s Olympic shooting and effects in performance
In 2018, the Olympic shooting regulations were modified to increase the number of women’s
shots from 40 to 60, equaling the number given to men. This research presented in this
paper addresses two research issues: (1) has the performance of women’s shooting
changed as a result of this increase in the number of shots? and (2) with the equalized number
of shots in place, do women and men perform differently? This study included 292
shooters who competed in the 2016 and/or 2018 European Championships who all obtained
top-50 results. Our sample included balanced quotas for sports (50% pistol and 50% rifle)
and by category (50% women and 50% men). Both championships were held in the same
facilities and in the same month of the season, but with the difference that in 2016, women
had 40 shots and in 2018 they had 60 shots. We observed that women’s performances did
not diminish for the pistol or the rifle category when their number of shots were increased.
Men and women shot equally well with rifles, although the men’s performance with pistols
was higher than that of women. We concluded that sports in which physical strength is a
minor factor, as in the case of shooting, should revise their regulations in the interest of
greater gender equality in sport
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