155 research outputs found
Educar en empatía a niños de 0 a 6 años
La etapa de Educación infantil se constituye como un período clave ya que en
ella se sientan las bases de todo el aprendizaje posterior del individuo. El fin principal
de esta etapa educativa es favorecer no sólo el desarrollo físico e intelectual del niño
sino también su desarrollo afectivo y social. Teniendo en cuenta este fin, el presente
trabajo refleja la importancia de educar la capacidad empática de los niños de 0 a 6
años. Para ello, se aborda un estudio sobre las perspectivas teóricas expuestas por
diferentes autores sobre el concepto de “empatía”. Una vez aclarado, se describe el
desarrollo evolutivo de esta capacidad desde prácticamente el nacimiento del niño hasta
los 6 años de edad. Dado que a estas edades la familia y la escuela se erigen como los
contextos básicos de aprendizaje por parte del niño, se recalca la importancia de que
padres y maestros eduquen en empatía a los más pequeños.
Palabras clave: empatía, niño, emociones, sentir, Educación infantil, comprender,
capacidad empática, sentimientos, aula, infancia
Photoelectric cross-sections of gas and dust in protoplanetary disks
We provide simple polynomial fits to the X-ray photoelectric cross-sections
(0.03 < E < 10keV) for mixtures of gas and dust found in protoplanetary disks.
Using the solar elemental abundances of Asplund et al. (2009) we treat the gas
and dust components separately, facilitating the further exploration
evolutionary processes such as grain settling and gain growth. We find that
blanketing due to advanced grain-growth (a_max > 1 micron) can reduce the X-ray
opacity of dust appreciably at E_X ~ 1keV, coincident with the peak of typical
T Tauri X-ray spectra. However, the reduction of dust opacity by dust settling,
which is known to occur in protoplanetary disks, is probably a more significant
effect. The absorption of 1-10keV X-rays is dominated by gas opacity once the
dust abundance has been reduced to about 1% of its diffuse interstellar value.
The gas disk establishes a floor to the opacity at which point X-ray transport
becomes insensitive to further dust evolution. Our choice of fitting function
follows that of Morrison & McCammon (1983), providing a degree of
backward-compatibility.Comment: 34 pages, 7 figures. To be published in in Ap
Resistive double-diffusive instability in the dead-zones of protostellar disks
We outline a novel linear instability that may arise in the dead-zones of
protostellar disks, and possibly the fluid interiors of planets and
protoplanets. In essence it is an axisymmetric buoyancy instability, but one
that would not be present in a purely hydrodynamical gas. The necessary
ingredients for growth include a negative radial entropy gradient (of any
magnitude), weak magnetic fields, and efficient resistive diffusion (in
comparison with thermal diffusion). The character of the instability is local,
axisymmetric, and double-diffusive, and it attacks lengths much shorter than
the resistive scale. Like the axisymmetric convective instability, it draws its
energy from the negative radial entropy gradient; but by utilising the
diffusing magnetic field, it can negate the stabilising influence of rotation.
Its nonlinear saturated state, while not transporting appreciable angular
momentum, could drive radial and vertical mixing, which may influence the
temperature structure of the disk, dust dynamics and, potentially, planet
formation.Comment: 16 pages, 5 figures. MNRAS Accepted. V2: cosmetic changes to bring in
line with MNRAS versio
Neon Fine-Structure Line Emission By X-ray Irradiated Protoplanetary Disks
Using a thermal-chemical model for the generic T-Tauri disk of D'Alessio et
al. (1999), we estimate the strength of the fine-structure emission lines of
NeII and NeIII at 12.81 and 15.55 microns that arise from the warm atmosphere
of the disk exposed to hard stellar X-rays. The Ne ions are produced by the
absorption of keV X-rays from the K shell of neutral Ne, followed by the Auger
ejection of several additional electrons. The recombination cascade of the Ne
ions is slow because of weak charge transfer with atomic hydrogen in the case
of Ne2+ and by essentially no charge transfer for Ne+. For a distance of 140pc,
the 12.81 micron line of Ne II has a flux of 1e-14 erg/cm2s, which should be
observable with the Spitzer Infrared Spectrometer and suitable ground based
instrumentation. The detection of these fine-structure lines would clearly
demonstrate the effects of X-rays on the physical and chemical properties of
the disks of young stellar objects and provide a diagnostic of the warm gas in
protoplanetary disk atmospheres. They would complement the observed H2 and CO
emission by probing vertical heights above the molecular transition layer and
larger radial distances that include the location of terrestrial and giant
planets.Comment: 24 pages, 5 figure
Essential role of the Cdk2 activator RingoA in meiotic telomere tethering to the nuclear envelope
Cyclin-dependent kinases (CDKs) play key roles in cell cycle regulation. Genetic analysis in mice has revealed an essential role for Cdk2 in meiosis, which renders Cdk2 knockout (KO) mice sterile. Here we show that mice deficient in RingoA, an atypical activator of Cdk1 and Cdk2 that has no amino acid sequence homology to cyclins, are sterile and display meiotic defects virtually identical to those observed in Cdk2 KO mice including non-homologous chromosome pairing, unrepaired double-strand breaks, undetectable sex-body and pachytene arrest. Interestingly, RingoA is required for Cdk2 targeting to telomeres and RingoA KO spermatocytes display severely affected telomere tethering as well as impaired distribution of Sun1, a protein essential for the attachment of telomeres to the nuclear envelope. Our results identify RingoA as an important activator of Cdk2 at meiotic telomeres, and provide genetic evidence for a physiological function of mammalian Cdk2 that is not dependent on cyclins
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Polyploidy on Islands: Its Emergence and Importance for Diversification.
Whole genome duplication or polyploidy is widespread among floras globally, but traditionally has been thought to have played a minor role in the evolution of island biodiversity, based on the low proportion of polyploid taxa present. We investigate five island systems (Juan Fernández, Galápagos, Canary Islands, Hawaiian Islands, and New Zealand) to test whether polyploidy (i) enhances or hinders diversification on islands and (ii) is an intrinsic feature of a lineage or an attribute that emerges in island environments. These island systems are diverse in their origins, geographic and latitudinal distributions, levels of plant species endemism (37% in the Galapagos to 88% in the Hawaiian Islands), and ploidy levels, and taken together are representative of islands more generally. We compiled data for vascular plants and summarized information for each genus on each island system, including the total number of species (native and endemic), generic endemicity, chromosome numbers, genome size, and ploidy levels. Dated phylogenies were used to infer lineage age, number of colonization events, and change in ploidy level relative to the non-island sister lineage. Using phylogenetic path analysis, we then tested how the diversification of endemic lineages varied with the direct and indirect effects of polyploidy (presence of polyploidy, time on island, polyploidization near colonization, colonizer pool size) and other lineage traits not associated with polyploidy (time on island, colonizer pool size, repeat colonization). Diploid and tetraploid were the most common ploidy levels across all islands, with the highest ploidy levels (>8x) recorded for the Canary Islands (12x) and New Zealand (20x). Overall, we found that endemic diversification of our focal island floras was shaped by polyploidy in many cases and certainly others still to be detected considering the lack of data in many lineages. Polyploid speciation on the islands was enhanced by a larger source of potential congeneric colonists and a change in ploidy level compared to overseas sister taxa
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Polyploidy on Islands: Its Emergence and Importance for Diversification.
Whole genome duplication or polyploidy is widespread among floras globally, but traditionally has been thought to have played a minor role in the evolution of island biodiversity, based on the low proportion of polyploid taxa present. We investigate five island systems (Juan Fernández, Galápagos, Canary Islands, Hawaiian Islands, and New Zealand) to test whether polyploidy (i) enhances or hinders diversification on islands and (ii) is an intrinsic feature of a lineage or an attribute that emerges in island environments. These island systems are diverse in their origins, geographic and latitudinal distributions, levels of plant species endemism (37% in the Galapagos to 88% in the Hawaiian Islands), and ploidy levels, and taken together are representative of islands more generally. We compiled data for vascular plants and summarized information for each genus on each island system, including the total number of species (native and endemic), generic endemicity, chromosome numbers, genome size, and ploidy levels. Dated phylogenies were used to infer lineage age, number of colonization events, and change in ploidy level relative to the non-island sister lineage. Using phylogenetic path analysis, we then tested how the diversification of endemic lineages varied with the direct and indirect effects of polyploidy (presence of polyploidy, time on island, polyploidization near colonization, colonizer pool size) and other lineage traits not associated with polyploidy (time on island, colonizer pool size, repeat colonization). Diploid and tetraploid were the most common ploidy levels across all islands, with the highest ploidy levels (>8x) recorded for the Canary Islands (12x) and New Zealand (20x). Overall, we found that endemic diversification of our focal island floras was shaped by polyploidy in many cases and certainly others still to be detected considering the lack of data in many lineages. Polyploid speciation on the islands was enhanced by a larger source of potential congeneric colonists and a change in ploidy level compared to overseas sister taxa
Dust amorphization in protoplanetary disks
High-energy irradiation of the circumstellar material might impact the
structure and the composition of a protoplanetary disk and hence the process of
planet formation. In this paper, we present a study on the possible influence
of the stellar irradiation, indicated by X-ray emission, on the crystalline
structure of the circumstellar dust. The dust crystallinity is measured for 42
class II T Tauri stars in the Taurus star-forming region using a decomposition
fit of the 10 micron silicate feature, measured with the Spitzer IRS
instrument. Since the sample includes objects with disks of various
evolutionary stages, we further confine the target selection, using the age of
the objects as a selection parameter. We correlate the X-ray luminosity and the
X-ray hardness of the central object with the crystalline mass fraction of the
circumstellar dust and find a significant anti-correlation for 20 objects
within an age range of approx. 1 to 4.5 Myr. We postulate that X-rays represent
the stellar activity and consequently the energetic ions of the stellar winds
which interact with the circumstellar disk. We show that the fluxes around 1 AU
and ion energies of the present solar wind are sufficient to amorphize the
upper layer of dust grains very efficiently, leading to an observable reduction
of the crystalline mass fraction of the circumstellar, sub-micron sized dust.
This effect could also erase other relations between crystallinity and
disk/star parameters such as age or spectral type.Comment: accepted for publication by A&
A Spitzer survey of mid-infrared molecular emission from protoplanetary disks I: Detection rates
We present a Spitzer InfraRed Spectrometer search for 10-36 micron molecular
emission from a large sample of protoplanetary disks, including lines from H2O,
OH, C2H2, HCN and CO2. This paper describes the sample and data processing and
derives the detection rate of mid-infrared molecular emission as a function of
stellar mass. The sample covers a range of spectral type from early M to A, and
is supplemented by archival spectra of disks around A and B stars. It is drawn
from a variety of nearby star forming regions, including Ophiuchus, Lupus and
Chamaeleon. In total, we identify 22 T Tauri stars with strong mid-infrared H2O
emission. Integrated water line luminosities, where water vapor is detected,
range from 5x10^-4 to 9x10^-3 Lsun, likely making water the dominant line
coolant of inner disk surfaces in classical T Tauri stars. None of the 5
transitional disks in the sample show detectable gaseous molecular emission
with Spitzer upper limits at the 1% level in terms of line-to-continuum ratios
(apart from H2). We find a strong dependence on detection rate with spectral
type; no disks around our sample of 25 A and B stars were found to exhibit
water emission, down to 1-2% line-to-continuum ratios, in the mid-infrared,
while almost 2/3 of the disks around K stars show sufficiently intense water
emission to be detected by Spitzer. Some Herbig Ae/Be stars show tentative
H2O/OH emission features beyond 20 micron at the 1-2 level, however, and one of
them shows CO2 in emission. We argue that the observed differences between T
Tauri disks and Herbig Ae/Be disks is due to a difference in excitation and/or
chemistry depending on spectral type and suggest that photochemistry may be
playing an important role in the observable characteristics of mid-infrared
molecular line emission from protoplanetary disks.Comment: 19 pages, accepted for publication in Ap
Empirical Constraints on Turbulence in Protoplanetary Accretion Disks
We present arcsecond-scale Submillimeter Array observations of the CO(3-2)
line emission from the disks around the young stars HD 163296 and TW Hya at a
spectral resolution of 44 m/s. These observations probe below the ~100 m/s
turbulent linewidth inferred from lower-resolution observations, and allow us
to place constraints on the turbulent linewidth in the disk atmospheres. We
reproduce the observed CO(3-2) emission using two physical models of disk
structure: (1) a power-law temperature distribution with a tapered density
distribution following a simple functional form for an evolving accretion disk,
and (2) the radiative transfer models developed by D'Alessio et al. that can
reproduce the dust emission probed by the spectral energy distribution. Both
types of models yield a low upper limit on the turbulent linewidth (Doppler
b-parameter) in the TW Hya system (<40 m/s), and a tentative (3-sigma)
detection of a ~300 m/s turbulent linewidth in the upper layers of the HD
163296 disk. These correspond to roughly <10% and 40% of the sound speed at
size scales commensurate with the resolution of the data. The derived
linewidths imply a turbulent viscosity coefficient, alpha, of order 0.01 and
provide observational support for theoretical predictions of subsonic
turbulence in protoplanetary accretion disks.Comment: 18 pages, 9 figures, accepted for publication in Ap
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