367 research outputs found
Criterios de intervención y recomendaciones de diseño a sismo en las estructuras de patrimonio histórico
This paper describes the peculiar conditions of historic masonry structures subjected to seismic actions.
The present seismic standards govern modern constructures with columns and beams; but masonry buildings are built upon a base of gravity systems, which work on compression, as stone materials with no tractions.
In another hand, the appearance of cracks, until now, was the reason for a diagnosis of decay.
Our present knowledge about classic building materials, techniques and construction stages indicates that old buildings must be considered and analyzed from a particular viewpoint.
Finally, some recommendations of seismic designs for masonry structures are included.En este artículo se describen las condiciones particulares de las estructuras históricas sujetas a acciones sísmicas.
Las actuales normas sísmicas están hechas desde el edificio moderno de vigas y pilares, siendo los edificios de fábrica sistemas de gravedad que trabajan a compresión, como materiales pétreos sin tracciones.
Por otra parte, la aparición de grietas, hasta hoy, era motivo de diagnóstico por ruina.
Nuestro actual conocimiento de los materiales clásicos, sus técnicas y fases de construcción, nos muestran que los edificios antiguos deben ser vistos y analizados desde un punto de vista particular.
Finalmente, se incluyen algunas recomendaciones de diseño sísmico para estructuras de fábrica
Hsp70 Chaperones and Type I PRMTs Are Sequestered at Intranuclear Inclusions Caused by Polyalanine Expansions in PABPN1
Genomic instability at loci with tandem arrays of simple repeats is the cause for many neurological, neurodegenerative and neuromuscular diseases. When located in coding regions, disease-associated expansions of trinucleotide repeats are translated into homopolymeric amino acid stretches of glutamine or alanine. Polyalanine expansions in the poly(A)-binding protein nuclear 1 (PABPN1) gene causes oculopharyngeal muscular dystrophy (OPMD). To gain novel insight into the molecular pathophysiology of OPMD, we studied the interaction of cellular proteins with normal and expanded PABPN1. Pull-down assays show that heat shock proteins including Hsp70, and type I arginine methyl transferases (PRMT1 and PRMT3) associate preferentially with expanded PABPN1. Immunofluorescence microscopy further reveals accumulation of these proteins at intranuclear inclusions in muscle from OPMD patients. Recombinant PABPN1 with expanded polyalanine stretches binds Hsp70 with higher affinity, and data from molecular simulations suggest that expansions of the PABPN1 polyalanine tract result in transition from a disordered, flexible conformation to a stable helical secondary structure. Taken together, our results suggest that the pathological mutation in the PABPN1 gene alters the protein conformation and induces a preferential interaction with type I PRMTs and Hsp70 chaperones. This in turn causes sequestration in intranuclear inclusions, possibly leading to a progressive cellular defect in arginine methylation and chaperone activity
The CARMENES search for exoplanets around M dwarfs: Radial-velocity variations of active stars in visual-channel spectra
Previous simulations predicted the activity-induced radial-velocity (RV)
variations of M dwarfs to range from cm/s to km/s, depending on
various stellar and activity parameters. We investigate the observed relations
between RVs, stellar activity, and stellar parameters of M dwarfs by analyzing
CARMENES high-resolution visual-channel spectra (m), which were
taken within the CARMENES RV planet survey during its first months of
operation. During this time, of the CARMENES-sample stars were observed
at least five times. From each spectrum we derived a relative RV and a measure
of chromospheric H emission. In addition, we estimated the chromatic
index (CRX) of each spectrum, which is a measure of the RV wavelength
dependence. Despite having a median number of only measurements per star,
we show that the RV variations of the stars with RV scatter of m/s and a
projected rotation velocity km/s are caused mainly by activity.
We name these stars `active RV-loud stars' and find their occurrence to
increase with spectral type: from for early-type M dwarfs
(MV) through for mid-type M dwarfs (MV) to
for late-type M dwarfs (MV). Their RV-scatter amplitude is
found to be correlated mainly with . For about half of the stars, we
also find a linear RVCRX anticorrelation, which indicates that their
activity-induced RV scatter is lower at longer wavelengths. For most of them we
can exclude a linear correlation between RV and H emission. Our results
are in agreement with simulated activity-induced RV variations in M dwarfs. The
RV variations of most active RV-loud M dwarfs are likely to be caused by dark
spots on their surfaces, which move in and out of view as the stars rotate.Comment: A&A accepte
Hollow Fiber Membranes of PCL and PCL/Graphene as Scaffolds with Potential to Develop In Vitro Blood—Brain Barrier Models
There is a huge interest in developing novel hollow fiber (HF) membranes able to modulate neural differentiation to produce in vitro blood–brain barrier (BBB) models for biomedical and pharmaceutical research, due to the low cell-inductive properties of the polymer HFs used in current BBB models. In this work, poly(ε-caprolactone) (PCL) and composite PCL/graphene (PCL/G) HF membranes were prepared by phase inversion and were characterized in terms of mechanical, electrical, morphological, chemical, and mass transport properties. The presence of graphene in PCL/G membranes enlarged the pore size and the water flux and presented significantly higher electrical conductivity than PCL HFs. A biocompatibility assay showed that PCL/G HFs significantly increased C6 cells adhesion and differentiation towards astrocytes, which may be attributed to their higher electrical conductivity in comparison to PCL HFs. On the other hand, PCL/G membranes produced a cytotoxic effect on the endothelial cell line HUVEC presumably related with a higher production of intracellular reactive oxygen species induced by the nanomaterial in this particular cell line. These results prove the potential of PCL HF membranes to grow endothelial cells and PCL/G HF membranes to differentiate astrocytes, the two characteristic cell types that could develop in vitro BBB models in future 3D co-culture systems.This research was funded by IDIVAL (INNVAL 17/20), MINECO/EIG-Concert Japan (X-MEM PCI2018-092929 project, International Joint Program 2018) and MINECO/Spain Feder (CTM-2016-75509-R project)
The CARMENES search for exoplanets around M dwarfs: Nine new double-line spectroscopic binary stars
Context. The CARMENES spectrograph is surveying ~300 M dwarf stars in search
for exoplanets. Among the target stars, spectroscopic binary systems have been
discovered, which can be used to measure fundamental properties of stars. Aims.
Using spectroscopic observations, we determine the orbital and physical
properties of nine new double-line spectroscopic binary systems by analysing
their radial velocity curves. Methods. We use two-dimensional cross-correlation
techniques to derive the radial velocities of the targets, which are then
employed to determine the orbital properties. Photometric data from the
literature are also analysed to search for possible eclipses and to measure
stellar variability, which can yield rotation periods. Results. Out of the 342
stars selected for the CARMENES survey, 9 have been found to be double-line
spectroscopic binaries, with periods ranging from 1.13 to ~8000 days and orbits
with eccentricities up to 0.54. We provide empirical orbital properties and
minimum masses for the sample of spectroscopic binaries. Absolute masses are
also estimated from mass-luminosity calibrations, ranging between ~0.1 and ~0.6
Msol . Conclusions. These new binary systems increase the number of double-line
M dwarf binary systems with known orbital parameters by 15%, and they have
lower mass ratios on average.Comment: Accepted for publication in A&A. 17 pages, 4 figure
Magnetic fields in M dwarfs from the CARMENES survey
M dwarfs are known to generate the strongest magnetic fields among
main-sequence stars with convective envelopes, but the link between the
magnetic fields and underlying dynamo mechanisms, rotation, and activity still
lacks a consistent picture. In this work we measure magnetic fields from the
high-resolution near-infrared spectra taken with the CARMENES radial-velocity
planet survey in a sample of 29 active M dwarfs and compare our results against
stellar parameters. We use the state-of-the-art radiative transfer code to
measure total magnetic flux densities from the Zeeman broadening of spectral
lines and filling factors. We detect strong kG magnetic fields in all our
targets. In 16 stars the magnetic fields were measured for the first time. Our
measurements are consistent with the magnetic field saturation in stars with
rotation periods P<4d. The analysis of the magnetic filling factors reveal two
different patterns of either very smooth distribution or a more patchy one,
which can be connected to the dynamo state of the stars and/or stellar mass.
Our measurements extend the list of M dwarfs with strong surface magnetic
fields. They also allow us to better constrain the interplay between the
magnetic energy, stellar rotation, and underlying dynamo action. The high
spectral resolution and observations at near-infrared wavelengths are the
beneficial capabilities of the CARMENES instrument that allow us to address
important questions about the stellar magnetism.Comment: 13 pages of main text, 14 pages of online material, 2 table
A Machine Learning approach for correcting radial velocities using physical observables
Precision radial velocity (RV) measurements continue to be a key tool to
detect and characterise extrasolar planets. While instrumental precision keeps
improving, stellar activity remains a barrier to obtain reliable measurements
below 1-2 m/s accuracy. Using simulations and real data, we investigate the
capabilities of a Deep Neural Network approach to produce activity free Doppler
measurements of stars. As case studies we use observations of two known stars
(Eps Eridani and AUMicroscopii), both with clear signals of activity induced RV
variability. Synthetic data using the starsim code are generated for the
observables (inputs) and the resulting RV signal (labels), and used to train a
Deep Neural Network algorithm. We identify an architecture consisting of
convolutional and fully connected layers that is adequate to the task. The
indices investigated are mean line-profile parameters (width, bisector,
contrast) and multi-band photometry. We demonstrate that the RV-independent
approach can drastically reduce spurious Doppler variability from known
physical effects such as spots, rotation and convective blueshift. We identify
the combinations of activity indices with most predictive power. When applied
to real observations, we observe a good match of the correction with the
observed variability, but we also find that the noise reduction is not as good
as in the simulations, probably due to the lack of detail in the simulated
physics. We demonstrate that a model-driven machine learning approach is
sufficient to clean Doppler signals from activity induced variability for well
known physical effects. There are dozens of known activity related observables
whose inversion power remains unexplored indicating that the use of additional
indicators, more complete models, and more observations with optimised sampling
strategies can lead to significant improvements in our detrending capabilities
HADES RV Programme with HARPS-N at TNG. VII. Rotation and activity of M-Dwarfs from time-series high-resolution spectroscopy of chromospheric indicators
We aim to investigate the presence of signatures of magnetic cycles and
rotation on a sample of 71 early M-dwarfs from the HADES RV programme using
high-resolution time-series spectroscopy of the Ca II H & K and Halpha
chromospheric activity indicators, the radial velocity series, the parameters
of the cross correlation function and the V-band photometry. We used mainly
HARPS-N spectra, acquired over four years, and add HARPS spectra from the
public ESO database and ASAS photometry light-curves as support data, extending
the baseline of the observations of some stars up to 12 years. We provide
log(R'hk) measurements for all the stars in the sample, cycle length
measurements for 13 stars, rotation periods for 33 stars and we are able to
measure the semi-amplitude of the radial velocity signal induced by rotation in
16 stars. We complement our work with previous results and confirm and refine
the previously reported relationships between the mean level of chromospheric
emission, measured by the log(R'hk), with the rotation period, and with the
measured semi-amplitude of the activity induced radial velocity signal for
early M-dwarfs. We searched for a possible relation between the measured
rotation periods and the lengths of the magnetic cycle, finding a weak
correlation between both quantities. Using previous v sin i measurements we
estimated the inclinations of the star's poles to the line of sight for all the
stars in the sample, and estimate the range of masses of the planets GJ 3998 b
and c (2.5 - 4.9 Mearth and 6.3 - 12.5 Mearth), GJ 625 b (2.82 Mearth), GJ 3942
b (7.1 - 10.0 Mearth) and GJ 15A b (3.1 - 3.3 Mearth), assuming their orbits
are coplanar with the stellar rotation.Comment: 19 pages, 16 figures, 10 table
HADES RV Programme with HARPS-N at TNG VI. GJ 3942 b behind dominant activity signals
Short- to mid-term magnetic phenomena on the stellar surface of M-type stars
cannot only resemble the effects of planets in radial velocity data, but also
may hide them. We analyze 145 spectroscopic HARPS-N observations of GJ 3942
taken over the past five years and additional photometry to disentangle stellar
activity effects from genuine Doppler signals as a result of the orbital motion
of the star around the common barycenter with its planet. To achieve this, we
use the common methods of pre-whitening, and treat the correlated red noise by
a first-order moving average term and by Gaussian-process regression following
an MCMC analysis. We identify the rotational period of the star at 16.3 days
and discover a new super-Earth, GJ 3942 b, with an orbital period of 6.9 days
and a minimum mass of 7.1 Me. An additional signal in the periodogram of the
residuals is present but we cannot claim it to be related to a second planet
with sufficient significance at this point. If confirmed, such planet candidate
would have a minimum mass of 6.3 Me and a period of 10.4 days, which might
indicate a 3:2 mean-motion resonance with the inner planet
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