4,828 research outputs found
Las Platyperigea Smith, 1894 (insectivora. Lepidoptera) de Cataluña y Baleares
Abstract not availabl
Fossil biomass preserved as graphitic carbon in a late paleoproterozoic banded iron formation metamorphosed at more than 550°C
Metamorphism is thought to destroy microfossils, partly through devolatilization and graphitization of biogenic organic matter. However, the extent to which there is a loss of molecular, elemental and isotope signatures from biomass during high-temperature metamorphism is not clearly established. We report on graphitic structures inside and coating apatite grains from the c. 1850 Ma Michigamme silicate banded iron formation from Michigan, metamorphosed above 550°C. Traces of N, S, O, H, Ca and Fe are preserved in this graphitic carbon and X-ray spectra show traces of aliphatic groups. Graphitic carbon has an expanded lattice around 3.6 Å, forms microscopic concentrically-layered and radiating polygonal flakes and has homogeneous δ13C values around −22‰, identical to bulk analyses. Graphitic carbon inside apatite is associated with nanometre-size ammoniated phyllosilicate. Precursors of these metamorphic minerals and graphitic carbon originated from ferruginous clayrich sediments with biomass. We conclude that graphite coatings and inclusions in apatite grains indicate fluid remobilization during amphibolite-facies metamorphism of precursor biomass. This new evidence fills in observational gaps of metamorphosed biomass into graphite and supports the existence of biosignatures in the highly metamorphosed iron formation from the Eoarchean Akilia Association, which dates from the beginning of the sedimentary rock record
VLA Observations of the Infrared Dark Cloud G19.30+0.07
We present Very Large Array observations of ammonia (NH3) (1,1), (2,2), and
CCS (2_1-1_0) emission toward the Infrared Dark Cloud (IRDC) G19.30+0.07 at
~22GHz. The NH3 emission closely follows the 8 micron extinction. The NH3 (1,1)
and (2,2) lines provide diagnostics of the temperature and density structure
within the IRDC, with typical rotation temperatures of ~10 to 20K and NH3
column densities of ~10^15 cm^-2. The estimated total mass of G19.30+0.07 is
~1130 Msun. The cloud comprises four compact NH3 clumps of mass ~30 to 160
Msun. Two coincide with 24 micron emission, indicating heating by protostars,
and show evidence of outflow in the NH3 emission. We report a water maser
associated with a third clump; the fourth clump is apparently starless. A
non-detection of 8.4GHz emission suggests that the IRDC contains no bright HII
regions, and places a limit on the spectral type of an embedded ZAMS star to
early-B or later. From the NH3 emission we find G19.30+0.07 is composed of
three distinct velocity components, or "subclouds." One velocity component
contains the two 24 micron sources and the starless clump, another contains the
clump with the water maser, while the third velocity component is diffuse, with
no significant high-density peaks. The spatial distribution of NH3 and CCS
emission from G19.30+0.07 is highly anti-correlated, with the NH3 predominantly
in the high-density clumps, and the CCS tracing lower-density envelopes around
those clumps. This spatial distribution is consistent with theories of
evolution for chemically young low-mass cores, in which CCS has not yet been
processed to other species and/or depleted in high-density regions.Comment: 29 pages, 9 figures, accepted for publication by ApJ. Please contact
the authors for higher resolution versions of the figure
Geometry of Empty Space is the Key to Near-Arrest Dynamics
We study several examples of kinetically constrained lattice models using
dynamically accessible volume as an order parameter. Thereby we identify two
distinct regimes exhibiting dynamical slowing, with a sharp threshold between
them. These regimes are identified both by a new response function in
dynamically available volume, as well as directly in the dynamics. Results for
the selfdiffusion constant in terms of the connected hole density are
presented, and some evidence is given for scaling in the limit of dynamical
arrest.Comment: 11 page
Psathyrella globosivelata Gröger, un fong rar i interessant citat per primera vegada a Catalunya
Es descriu , es comenta i s'il·lustra Psathyr ella globosivelata Groger, una especie rara i
sorprenent del genere Psathyr ella. D'acord amb la informació de que disposem, creiem que aquesta és
la primera citació d'aquesta espec ie a Catalunya i a la Península Ibérica,Arare and intere sting species of the genus Psathyr ella: P. globosivelata Groger, is
described , discussed and illustrated. To our knowl edge, this is its first record for Catalonia and the
Iberian Peninsula.Se describe, se comenta y se ilustra Psathyr ella globosivelata Groger, una especie
rara e interesante del género Psathyr ella. De acuerdo con la información que disponemos, creemo s
que ésta es la primera vez que se cita en Cataluña y en la Península Ibérica
Dense gas and exciting sources of the molecular outflow in the AFGL 437 star-forming region
We present Very Large Array (VLA) high resolution observations of the
NH3(1,1) and NH3(2,2) molecular transitions towards the high mass star forming
region AFGL 437. Our aim was to investigate if the poorly collimated CO
molecular outflow previously detected in the region is the result of a
projection effect, with no intrinsic bipolarity, as suggested by Gomez et al.
We complemented our observations with radio continuum archived data from the
VLA at 2 and 3.6 cm, and with unpublished public data at 450 {\mu}m taken with
Submillimetre Common-User Bolometer Array at the James Clerk Maxwell Telescope.
Ammonia emission was found mainly in three clumps located at the south and east
of the position of the compact infrared cluster of AFGL 437, where the CO
outflow seemed to have its origin. One of the NH3(1,1) clumps coincides with
the maximum of NH3(2,2) and with a local peak of emission at 450 {\mu}m. A near
infrared source (s11) is also found at that position. Our continuum map at 2 cm
shows extended elongated emission associated with the infrared source AFGL
437W. This elongated morphology and its spectral index between 3.6 and 2 cm
(\simeq 0.4) suggest the presence of a jet in AFGL 437W. We suggest that
several molecular bipolar outflows may exist in the region. The observed CO
outflow would be the superposition of those individual outflows, which would
explain its low degree of collimation observed at larger scales.Comment: 9 pages, 5 figures, 3 tables, accepted by MNRA
Spectral index of the H2O-maser emitting planetary nebula IRAS 17347-3139
We present radio continuum observations of the planetary nebula (PN) IRAS
17347-3139 (one of the only two known to harbour water maser emission), made to
derive its spectral index and the turnover frequency of the emission. The
spectrum of the source rises in the whole frequency range sampled, from 2.4 to
24.9 GHz, although the spectral index seems to decrease at the highest
frequencies (0.79+-0.04 between 4.3 and 8.9 GHz, and 0.64+-0.06 between 16.1
and 24.9 GHz). This suggests a turnover frequency around 20 GHz (which is
unusual among PNe, whose radio emission usually becomes optically thin at
frequencies < 10 GHz), and a relatively high emission measure (1.5 x 10^9
cm^{-6} pc). The radio continuum emission has increased by a factor of ~1.26 at
8.4 GHz in 13 years, which can be explained as expansion of the ionized region
by a factor of ~1.12 in radius with a dynamical age of ~120 yr and at an
expansion velocity of ~5-40 km/s. These radio continuum characteristics,
together with the presence of water maser emission and a strong optical
extinction suggest that IRAS 17347-3139 is one of the youngest PNe known, with
a relatively massive progenitor star.Comment: Five pages, 2 figures, accepted by MNRA
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