1,189 research outputs found
Los valles tectónicos recientes de Rubielos de la Cerida (Teruel)
[Resumen] La actividad tectónica cuaternaria y reciente ha dado lugar en este área a un conjunto de depresiones alargadas de orientación submeridiana, enmarcadas por fallas, que constituyen valles tectónicos[Abstract] Quaternary and recent tectonic activity led to a series of elongated depressions in the studied area of roughly N-S orientation, framed by faults, and developping as tectonic valleys
The IACOB project. VI. On the elusive detection of massive O-type stars close to the ZAMS
The apparent lack of massive O-type stars near the zero-age main sequence (at
ages < 2 Myr) is a topic widely discussed. Different explanations for this
elusive detection have been proposed, but no firm conclusions have been reached
yet. We reassess this empirical result benefiting from the high-quality
spectroscopic observations of >400 Galactic O-type stars gathered by the IACOB
and OWN surveys. We used temperatures and gravities from a iacob-gbat/fastwind
spectroscopic analysis to locate our sample in the Kiel and spectroscopic HR
diagrams. We evaluated the completeness of our sample of stars, observational
biases using information from the Galactic O star catalog (GOSC), systematics
of our methodology, and compare with other recent studies using smaller samples
of Galactic O-type stars. We base our discussion on the spectroscopic HR
diagram to avoid the use of uncertain distances. We performed a detailed study
of the young cluster Trumpler-14 as an example of how Gaia cluster distances
can help to construct the associated classical HR diagram. The apparent lack of
massive O-type stars near the ZAMS with masses between 30 and 70 Msol persist
even when spectroscopic results from a large, non-biased sample of stars are
used. We do not find correlation between the dearth of stars and observational
biases, limitations of our methodology, or the use of spectroscopic HR diagram
instead of the classical one. Investigating the efficiency of mass accretion
during the formation process we conclude that an adjustment of the accretion
rate towards lower values could reconcile the hotter boundary of detected
O-type stars and the theoretical birthline. Last, we discuss that the presence
of a small sample of O2-O3.5 stars found closer to the ZAMS might be explained
taking into account non-standard star evolution (e.g. binary interaction,
mergers, or homogeneous evolution).Comment: 20 pages, 15 figures, accepted for publication in Astronomy &
Astrophysic
MorfologÃa de vertientes y neotectónica en el Macizo de Javalambre (provincia de Teruel)
[Resumen] El modelado actual de las vertientes del macizo de Javalambre es consecuencia de tres tipos principales de procesos que actúan a partir de su elevación a comienzos del Plioceno -superior: (a) la dinámica periglaciar, (b) una etapa de activida~ tect6nica ocurrida hacia el Pleistoceno medio-superior, y (c) deslizamientos gravitacionales, translacionales y rotacionales producidos a favor de un sustrato plástico en las áreas de mayor incisión de la red -fluvial.Abstract] The present slope form in Javalambre area results from three principal types of processes which are active after its elevation in the early Upper Pliocene: (a) periglacial dynamics, (b) a tectonic phase in Middle-Upper Pleistocene, and (c) gravitational, translational and rotational landslides generated over plastic rocks in zones with a intensive fluvial incisio
Agroforestry Systems in Cuba: Some Aspects of Animal Production
The silvopastoral systems, that nowadays constitute scientific achievements of the Grasses and Forages Research Station Indio Hatuey , have been developed from the results of investigations that were carried out since the 1980s, to improve the productivity of natural pastures through the introduction of valuable herbaceous species and tree legumes. Those investigations also determined the essential elements of pasture management such as the optimal stocking rates for low input systems and suitable methods of grazing to obtain sustainability of grasslands
Influence of the Ni-Co/Al-Mg catalyst loading in the continuous aqueous phase reforming of the bio-oil aqueous fraction
The effect of catalyst loading in the Aqueous Phase Reforming (APR) of bio-oil aqueous fraction has been studied with a Ni-Co/Al-Mg coprecipitated catalyst. Because of the high content of water in the bio-oil aqueous fraction, APR could be a useful process to convert this fraction into valuable products. Experiments of APR with continuous feeding of aqueous solution of acetol, butanol and acetic acid as the only compound, together with a simulated and a real aqueous fraction of bio-oil, were carried out. Liquid products in the liquid effluent of the APR model compounds were quantified and the reaction pathways were revised. The increase of catalyst loading produced an increase of gas production and a gas with higher alkanes content. Acetol was the compound with the highest reactivity while the conversion of acetic acid was very low. The presence of acetic acid in the feed caused catalyst deactivation
B-type supergiants in the SMC: Rotational velocities and implications for evolutionary models
High-resolution spectra for 24 SMC and Galactic B-type supergiants have been
analysed to estimate the contributions of both macroturbulence and rotation to
the broadening of their metal lines. Two different methodologies are
considered, viz. goodness-of-fit comparisons between observed and theoretical
line profiles and identifying zeros in the Fourier transforms of the observed
profiles. The advantages and limitations of the two methods are briefly
discussed with the latter techniques being adopted for estimated projected
rotational velocities (\vsini) but the former being used to estimate
macroturbulent velocities. Only one SMC supergiant, SK 191, shows a significant
degree of rotational broadening (\vsini 90 \kms). For the remaining
targets, the distribution of projected rotational velocities are similar in
both our Galactic and SMC samples with larger values being found at earlier
spectral types. There is marginal evidence for the projected rotational
velocities in the SMC being higher than those in the Galactic targets but any
differences are only of the order of 5-10 \kms, whilst evolutionary models
predict differences in this effective temperature range of typically 20 to 70
\kms. The combined sample is consistent with a linear variation of projected
rotational velocity with effective temperature, which would imply rotational
velocities for supergiants of 70 \kms at an effective temperature of 28 000 K
(approximately B0 spectral type) decreasing to 32 \kms at 12 000 K (B8 spectral
type). For all targets, the macroturbulent broadening would appear to be
consistent with a Gaussian distribution (although other distributions cannot be
discounted) with an half-width varying from approximately 20 \kms
at B8 to 60 \kms at B0 spectral types.Comment: 4 figures, 8 pages, submitted to Astronomy and Astrophysic
Controls on space–time distribution of soft-sediment deformation structures: Applying palaeomagnetic dating to approach the apparent recurrence period of paleoseisms at the Concud Fault (eastern Spain)
This work describes soft-sediment deformation structures (clastic dykes, load structures, diapirs, slumps, nodulizations or mudcracks) identified in three sections (Concud, Ramblillas and Masada Cociero) in the Iberian Range, Spain. These sections were logged from boreholes and outcrops in Upper Pliocene-Lower Pleistocene deposits of the Teruel-Concud Residual Basin, close to de Concud normal fault. Timing of the succession and hence of seismic and non-seismic SSDSs, covering a time span between ~ 3.6 and ~ 1.9 Ma, has been constrained from previous biostratigraphic and magnetostratigraphic information, then substantially refined from a new magnetostratigraphic study at Masada Cociero profile. Non-seismic SSDSs are relatively well-correlated between sections, while seismic ones are poorly correlated except for several clusters of structures. Between 29 and 35 seismic deformed levels have been computed for the overall stratigraphic succession. Factors controlling the lateral and vertical distribution of SSDSs are their seismic or non-seismic origin, the distance to the seismogenic source (Concud Fault), the sedimentary facies involved in deformation and the observation conditions (borehole core vs. natural outcrop). In the overall stratigraphic section, seismites show an apparent recurrence period of 56 to 108 ka. Clustering of seismic SSDSs levels within a 91-ka-long interval records a period of high paleoseismic activity with an apparent recurrence time of 4.8 to 6.1 ka, associated with increasing sedimentation rate and fault activity. Such activity pattern of the Concud Fault for the Late Pliocene-Early Pliocene, with alternating periods of faster and slower slip, is similar to that for the most recent Quaternary (last ca. 74 ka BP). Concerning the research methods, time occurrence patterns recognized for peaks of paleoseismic activity from SSDSs in boreholes are similar to those inferred from primary evidence in trenches. Consequently, apparent recurrence periods calculated from SSDS inventories collected in borehole logs close to seismogenic faults are comparable to actual recurrence times of large paleoearthquakes
Carbon and oxygen in HII regions of the Magellanic Clouds: abundance discrepancy and chemical evolution
We present C and O abundances in the Magellanic Clouds derived from deep
spectra of HII regions. The data have been taken with the Ultraviolet-Visual
Echelle Spectrograph at the 8.2-m VLT. The sample comprises 5 HII regions in
the Large Magellanic Cloud (LMC) and 4 in the Small Magellanic Cloud (SMC). We
measure pure recombination lines (RLs) of CII and OII in all the objects,
permitting to derive the abundance discrepancy factors (ADFs) for O^2+, as well
as their O/H, C/H and C/O ratios. We compare the ADFs with those of other HII
regions in different galaxies. The results suggest a possible metallicity
dependence of the ADF for the low-metallicity objects, but more uncertain for
high-metallicity objects. We compare nebular and B-type stellar abundances and
we find that the stellar abundances agree better with the nebular ones derived
from collisionally excited lines (CELs). Comparing these results with other
galaxies we observe that stellar abundances seem to agree better with the
nebular ones derived from CELs in low-metallicity environments and from RLs in
high-metallicity environments. The C/H, O/H and C/O ratios show almost flat
radial gradients, in contrast with the spiral galaxies where such gradients are
negative. We explore the chemical evolution analysing C/O vs. O/H and comparing
with the results of HII regions in other galaxies. The LMC seems to show a
similar chemical evolution to the external zones of small spiral galaxies and
the SMC behaves as a typical star-forming dwarf galaxy.Comment: Accepted for publication in MNRAS, 17 pages, 11 figures, 8 table
Agroforestry Systems in Cuba: Some Aspects of Animal Production
The silvopastoral systems, that nowadays constitute scientific achievements of the Grasses and Forages Research Station “Indio Hatuey , have been developed from the results of investigations that were carried out since the 1980s, to improve the productivity of natural pastures through the introduction of valuable herbaceous species and tree legumes. Those investigations also determined the essential elements of pasture management such as the optimal stocking rates for low input systems and suitable methods of grazing to obtain sustainability of grasslands
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