2,592 research outputs found
Pressure Tuning of an Ionic Insulator into a Heavy Electron Metal: An Infrared Study of YbS
Optical conductivity [] of YbS has been measured under
pressure up to 20 GPa. Below 8 GPa, is low since YbS is an
insulator with an energy gap between fully occupied 4 state and unoccupied
conduction () band. Above 8 GPa, however, increases
dramatically, developing a Drude component due to heavy carriers and
characteristic infrared peaks. It is shown that increasing pressure has caused
an energy overlap and hybridization between the band and 4 state, thus
driving the initially ionic and insulating YbS into a correlated metal with
heavy carriers
The planetary nebula population in the halo of M87
We investigate the diffuse light in the outer regions of the nearby
elliptical galaxy M87 in the Virgo cluster, using planetary nebulas (PNs) as
tracers. The surveyed areas (0.43 squared degrees) cover M87 up to a radial
distance of 150 kpc, in the ransition region between galaxy halo and
intracluster light (ICL). All PNs are identified through the on-off band
technique using automatic selection criteria based on the distribution of the
detected sources in the colour-magnitude diagram and the properties of their
point-spread function. We extract a catalogue of 688 objects down to
m_5007=28.4, with an estimated residual contamination from foreground stars and
background Lyalpha galaxies, which amounts to ~35% of the sample. This is one
of the largest extragalactic PN samples in number of candidates, magnitude
depth, and radial extent, which allows us to carry out an unprecedented
photometric study of the PN population in the outer regions of M87. We find
that the logarithmic density profile of the PN distribution is shallower than
the surface brightness profile at large radii. This behaviour is consistent
with the superposition of two components associated with the halo of M87 and
with the ICL, which have different luminosity specific PN numbers, the ICL
contributing three times more PNs per unit light. Because of the depth of this
survey we are also able to study the shape of the PN luminosity function (PNLF)
in the outer regions of M87. We find a slope for the PNLF that is steeper at
fainter magnitudes than the standard analytical PNLF formula and adopt a
generalised model that treats the slope as a free parameter. Comparing the PNLF
of M87 and the M31 bulge, both normalised by the sampled luminosity, the M87
PNLF contains fewer bright PNs and has a steeper slope towards fainter
magnitudes.Comment: 16 pages, 13 figures, 5 tables, accepted for publication in A&
Galaxy types in the Sloan Digital Sky Survey using supervised artificial neural networks
Supervised artificial neural networks are used to predict useful properties of galaxies in the Sloan Digital Sky Survey, in this instance morphological classifications, spectral types and redshifts. By giving the trained networks unseen data, it is found that correlations between predicted and actual properties are around 0.9 with rms errors of order ten per cent. Thus, given a representative training set, these properties may be reliably estimated for galaxies in the survey for which there are no spectra and without human intervention
Bryozoan stable carbon and hydrogen isotopes: relationships between the isotopic composition of zooids, statoblasts and lake water
0000-0001-7279-715XŠ Springer International Publishing Switzerland 2015. The attached document is the authors' final accepted version of the journal article. You are advised to consult the publisher's version if you wish to cite from it
Optical Conductivity and Electronic Structure of CeRu4Sb12 under High Pressure
Optical conductivity [s(w)] of Ce-filled skutterudite CeRu4Sb12 has been
measured at high pressure to 8 GPa and at low temperature, to probe the
pressure evolution of its electronic structures. At ambient pressure, a
mid-infrared peak at 0.1 eV was formed in s(w) at low temperature, and the
spectral weight below 0.1 eV was strongly suppressed, due to a hybridization of
the f electron and conduction electron states. With increasing external
pressure, the mid-infrared peak shifts to higher energy, and the spectral
weight below the peak was further depleted. The obtained spectral data are
analyzed in comparison with band calculation result and other reported physical
properties. It is shown that the electronic structure of CeRu4Sb12 becomes
similar to that of a narrow-gap semiconductor under external pressure.Comment: 8 pages, 9 figure
Intracluster stars in the Virgo cluster core
We have investigated the properties of the diffuse light in the Virgo cluster
core region, based on the detection of intracluster planetary nebulae (PNe) in
four fields. We eliminate the bias from misclassified faint continuum objects,
using improved Monte Carlo simulations, and the contaminations by high redshift
Ly galaxies, using the Ly luminosity function in blank fields.
Recent spectroscopic observations confirm that our photometric PN samples are
well-understood. We find that the diffuse stellar population in the Virgo core
region is inhomogeneous on scales of 30'-90': there exist significant
field-to-field variations in the number density of PNe and the inferred amount
of intracluster light, with some empty fields, some fields dominated by
extended Virgo galaxy halos, and some fields dominated by the true intracluster
component. There is no clear trend with distance from M87. The mean surface
luminosity density, its rms variation, and the mean surface brightness of
diffuse light in our 4 fields are L
arcmin, L arcmin, and
mag arcsec respectively. Our results indicate that
the Virgo cluster is a dynamically young environment, and that the intracluster
component is associated at least partially with local physical processes like
galaxy interactions or harassment. We also argue, based on kinematic evidence,
that the so-called 'over-luminous' PNe in the halo of M84 are dynamically
associated with this galaxy, and must thus be brighter than and part of a
different stellar population from the normal PN population in elliptical
galaxies.Comment: 31 pages, 6 figure. In press on the Astronomical Journa
Narrow band imaging in [OIII] and Halpha to search for ICPNe in the Virgo cluster
We have identified intracluster planetary nebulae in a Virgo cluster core
field by imaging with the Subaru Suprime-Cam through two narrow band filters
centered at the redshifted wavelengths of the [OIII] \AA and the
H \AA lines; broad-band images in V and R were
acquired to check for emission in the adjacent continuum. Emission line objects
in Virgo are then selected from the two-color diagram ([OIII] -- Halpha) vs.
([OIII] -- (V+R)), which is calibrated using PNe in M84 (Jacoby et al. 1990).
Using both [OIII] and Halpha allows us to distinguish bona-fide planetary
nebulae from high redshift emission-line galaxies at the bright end of the
[OIII] luminosity function. Spectroscopic observations of a subsample of these
objects were made at the TNG and at the VLT, in a region around M84 and in an
intracluster field respectively. The observations confirm the efficiency of the
combined [OIII]+H imaging to identify true PNe. We also obtained the
first spectrum of an intracluster PN which shows the [OIII] doublet with S/N >
10 and its Halpha emission. From the results based on the spectroscopic
follow-up, we derive a lower limit to the fraction of the Virgo cluster light
contributed by the intracluster stars at the surveyed position in the cluster
core: it amounts to 10%.Comment: 32 pages,11 figures, in press on AJ, February 200
A rare presentation of the Klinefelter's syndrome
A 16 years old boy with Chronic Renal Failure (CRF) was not suspected of having Klinefelter's syndrome until he complained of painful gynecomastia. He was under haemodialysis for 2 years. At first, he was in an approximately full pubertal development (P5, G5), but he had a small and a firm testis (length 2.2cm) and some degree of facial male pattern hair. He also had a decreased upper to lower body segment ratio and despite having chronic renal failure, he was taller than his parents and siblings. His laboratory tests showed high levels of FSH and normal levels of LH and testosterone. With regards to all these findings, we suspected that there might be an occult Klinefelter's syndrome. So, we made his karyotype that showed a 47XXY pattern. Because there are only a few number of cases that have occult Klinefelter's syndrome in the basis of chronic renal failure, we decided to report this case
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