70 research outputs found
Transferability of vegetation recovery models based on remote sensing across different fire regimes
P. 441-451Aim
To evaluate the transferability between fire recurrence scenarios of postâfire vegetation cover models calibrated with satellite imagery data at different spatial resolutions within two Mediterranean pine forest sites affected by large wildfires in 2012.
Location
The northwest and east of the Iberian Peninsula.
Methods
In each study site, we defined three fire recurrence scenarios for a reference period of 35 years. We used image texture derived from the surface reflectance channels of WorldViewâ2 and Sentinelâ2 (at a spatial resolution of 2 m Ă 2 m and 20 m Ă 20 m, respectively) as predictors of postâfire vegetation cover in Random Forest regression analysies. Percentage vegetation cover was sampled in two sets of field plots with a size roughly equivalent to the spatial resolution of the imagery. The plots were distributed following a stratified design according to fire recurrence scenarios. Model transferability was assessed within each study site by applying the vegetation cover model developed for a given fire recurrence scenario to predict vegetation cover in other scenarios, iteratively.
Results
For both wildfires, the highest model transferability between fire recurrence scenarios was achieved for those holding the most similar vegetation community composition regarding the balance of species abundance according to their plantâregenerative traits (root mean square error [RMSE] around or lower than 15%). Model transferability performance was highly improved by fineâgrained remoteâsensing data.
Conclusions
Fire recurrence is a major driver of community structure and composition so the framework proposed in this study would allow land managers to reduce efforts in the context of postâfire decisionâmaking to assess vegetation recovery within large burned landscapes with fire regime variability.S
Fuentes de informaciĂłn en odontologĂa
In this work a tour of the main sources of medical information of interest in dentistry is carried out. Its objective is to present to the students, professors, researchers and professionals of the dentistry a selection of quality resources that allow to develop their respective functions of learning, teaching, investigation and exercise of the health care, with guarantees of knowing the sources of information more complete and updated. To do this we have reviewed the most recent bibliography on the subject and visited the web sites of the main medical and scientific information resources (databases, scientific search engines, editorial portals, research repositories, open access platforms and directories, etc.), from which we have obtained descriptive information about them, analyzed their performance and contrasted their level of dental information. From this analysis we extract a selection of sources of information and search tools that we believe cover with a high level of quality all areas of the scientific production in dentistry. We conclude that there are hardly any sources of secondary information of dentistry beyond the specific primary sources of information (monographs, theses, conference proceedings, journals, etc.). Health sciences or multidisciplinary, which collect documents of dentistry. Most of the selected sources are open access or, with payment being the access to the full text, allow open bibliographic consultations of interest for their content in dental information. Some are totally closed payment resources but usually consulted because there is some type of subscription or purchase consortium in universities and health centers. And others we believe deserve to be so for their specificity and quality. We note an important and qualified progress of the information resources in open access
Could Edge-Lit Type Ia Supernovae be Standard Candles
The progenitors of Type Ia supernovae (SNe Ia) have not been identified.
Though they are no longer fashionable we investigate the consequences if a
significant number of SNe Ia were edge-lit detonations (ELDs) of carbon/oxygen
white dwarfs that have accreted a critical mass of helium. Our best
understanding of the Phillips relation between light curve speed and peak
luminosity assigns both these phenomena to the amount of Ni produced. In
ELDs there are two sites of Ni synthesis. If the peak luminosity is
determined primarily by the C/O ratio in the core it is primarily a function of
its progenitor's initial mass. If the light curve decay speed is determined by
the total mass of iron group elements ejected this is a function of the total
mass of the ELD at the time of explosion. In general these two masses are
correlated and an empirical relation between peak luminosity and light curve
shape can be expected. However when we perform population synthesis for
progenitors of different metallicities we find a systematic shift in this
relation that would make distant SNe Ia fainter than those nearby. The
abundances of alpha-rich isotopes, such as Ca, in the solar system
indicate that only about 40 per cent of SNe Ia are edge-lit so any systematic
effect that could be present would be correspondingly diluted. If we examine
only the small subset of ELDs that accrete from a naked helium star, rather
than a He white dwarf, the systematic effect disappears.Comment: 14 pages, 3figure
Redshift-space limits of bound structures
An exponentially expanding Universe, possibly governed by a cosmological
constant, forces gravitationally bound structures to become more and more
isolated, eventually becoming causally disconnected from each other and forming
so-called "island universes". This new scenario reformulates the question about
which will be the largest structures that will remain gravitationally bound,
together with requiring a systematic tool that can be used to recognize the
limits and mass of these structures from observational data, namely redshift
surveys of galaxies. Here we present a method, based on the spherical collapse
model and N-body simulations, by which we can estimate the limits of bound
structures as observed in redshift space. The method is based on a theoretical
criterion presented in a previous paper that determines the mean density
contrast that a spherical shell must have in order to be marginally bound to
the massive structure within it. Understanding the kinematics of the system, we
translated the real-space limiting conditions of this "critical" shell to
redshift space, producing a projected velocity envelope that only depends on
the density profile of the structure. From it we created a redshift-space
version of the density contrast that we called "density estimator", which can
be calibrated from N-body simulations for a reasonable projected velocity
envelope template, and used to estimate the limits and mass of a structure only
from its redshift-space coordinates.Comment: Contains 12 pages, 12 figures and 8 table
Binary Star Origin of High Field Magnetic White Dwarfs
White dwarfs with surface magnetic fields in excess of MG are found as
isolated single stars and relatively more often in magnetic cataclysmic
variables. Some 1,253 white dwarfs with a detached low-mass main-sequence
companion are identified in the Sloan Digital Sky Survey but none of these is
observed to show evidence for Zeeman splitting of hydrogen lines associated
with a magnetic field in excess of 1MG. If such high magnetic fields on white
dwarfs result from the isolated evolution of a single star then there should be
the same fraction of high field white dwarfs among this SDSS binary sample as
among single stars. Thus we deduce that the origin of such high magnetic fields
must be intimately tied to the formation of cataclysmic variables. CVs emerge
from common envelope evolution as very close but detached binary stars that are
then brought together by magnetic braking or gravitational radiation. We
propose that the smaller the orbital separation at the end of the common
envelope phase, the stronger the magnetic field. The magnetic cataclysmic
variables originate from those common envelope systems that almost merge. We
propose further that those common envelope systems that do merge are the
progenitors of the single high field white dwarfs. Thus all highly magnetic
white dwarfs, be they single stars or the components of MCVs, have a binary
origin. This hypothesis also accounts for the relative dearth of single white
dwarfs with fields of 10,000 - 1,000,000G. Such intermediate-field white dwarfs
are found preferentially in cataclysmic variables. In addition the bias towards
higher masses for highly magnetic white dwarfs is expected if a fraction of
these form when two degenerate cores merge in a common envelope. Similar
scenarios may account for very high field neutron stars.Comment: 6 pages, 1 figure, accepted by MNRA
CLASH-VLT: The stellar mass function and stellar mass density profile of the z=0.44 cluster of galaxies MACS J1206.2-0847
Context. The study of the galaxy stellar mass function (SMF) in relation to
the galaxy environment and the stellar mass density profile, rho(r), is a
powerful tool to constrain models of galaxy evolution. Aims. We determine the
SMF of the z=0.44 cluster of galaxies MACS J1206.2-0847 separately for passive
and star-forming (SF) galaxies, in different regions of the cluster, from the
center out to approximately 2 virial radii. We also determine rho(r) to compare
it to the number density and total mass density profiles. Methods. We use the
dataset from the CLASH-VLT survey. Stellar masses are obtained by SED fitting
on 5-band photometric data obtained at the Subaru telescope. We identify 1363
cluster members down to a stellar mass of 10^9.5 Msolar. Results. The whole
cluster SMF is well fitted by a double Schechter function. The SMFs of cluster
SF and passive galaxies are statistically different. The SMF of the SF cluster
galaxies does not depend on the environment. The SMF of the passive population
has a significantly smaller slope (in absolute value) in the innermost (<0.50
Mpc), highest density cluster region, than in more external, lower density
regions. The number ratio of giant/subgiant galaxies is maximum in this
innermost region and minimum in the adjacent region, but then gently increases
again toward the cluster outskirts. This is also reflected in a decreasing
radial trend of the average stellar mass per cluster galaxy. On the other hand,
the stellar mass fraction, i.e., the ratio of stellar to total cluster mass,
does not show any significant radial trend. Conclusions. Our results appear
consistent with a scenario in which SF galaxies evolve into passive galaxies
due to density-dependent environmental processes, and eventually get destroyed
very near the cluster center to become part of a diffuse intracluster medium.Comment: A&A accepted, 15 pages, 13 figure
CLASH-VLT: The mass, velocity-anisotropy, and pseudo-phase-space density profiles of the z=0.44 galaxy cluster MACS 1206.2-0847
We use an unprecedented data-set of about 600 redshifts for cluster members,
obtained as part of a VLT/VIMOS large programme, to constrain the mass profile
of the z=0.44 cluster MACS J1206.2-0847 over the radial range 0-5 Mpc (0-2.5
virial radii) using the MAMPOSSt and Caustic methods. We then add external
constraints from our previous gravitational lensing analysis. We invert the
Jeans equation to obtain the velocity-anisotropy profiles of cluster members.
With the mass-density and velocity-anisotropy profiles we then obtain the first
determination of a cluster pseudo-phase-space density profile. The kinematics
and lensing determinations of the cluster mass profile are in excellent
agreement. This is very well fitted by a NFW model with mass M200=(1.4 +- 0.2)
10^15 Msun and concentration c200=6 +- 1, only slightly higher than theoretical
expectations. Other mass profile models also provide acceptable fits to our
data, of (slightly) lower (Burkert, Hernquist, and Softened Isothermal Sphere)
or comparable (Einasto) quality than NFW. The velocity anisotropy profiles of
the passive and star-forming cluster members are similar, close to isotropic
near the center and increasingly radial outside. Passive cluster members follow
extremely well the theoretical expectations for the pseudo-phase-space density
profile and the relation between the slope of the mass-density profile and the
velocity anisotropy. Star-forming cluster members show marginal deviations from
theoretical expectations. This is the most accurate determination of a cluster
mass profile out to a radius of 5 Mpc, and the only determination of the
velocity-anisotropy and pseudo-phase-space density profiles of both passive and
star-forming galaxies for an individual cluster [abridged]Comment: A&A in press; 22 pages, 19 figure
Fuentes documentales y recursos docentes en OdontopediatrĂa y Ortodoncia
214 p. : il. ; 24 c
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