240 research outputs found
The Nuclear Stellar Cluster in the Seyfert~1 Galaxy NGC 3227: High Angular Resolution NIR Imaging and Spectroscopy
NIR high angular resolution speckle imaging and imaging spectroscopy of the
nuclear region (10'' ~ 840pc) of the Seyfert1 galaxy NGC3227 are presented. A
nuclear stellar cluster is slightly resolved in the J and H band with
increasing contribution to the NIR continuum from the K to the J band. The
stellar absorption lines are extended compared to the neighboring continuum
suggesting a cluster size of ~ 70pc FWHM. Analysis of those lines suggests that
the stars are contributing about 65% (40%) of the total continuum emission in
the H (K) band in a 3.6'' aperture. Population synthesis in conjunction with
NIR spectral synthesis indicates an age of 25 to 50 Myr when red supergiants
contribute most to the NIR light. This is supported by published optical data
on the MgIb line and the CaII triplet. Although a higher age of ~ 0.5 Gyr where
AGB stars dominate the NIR light can not be excluded, the observed parameters
are at the limit of those expected for a cluster dominated by AGB stars.
However, in either case the resolved stellar cluster contributes only about ~
15 % of the total dynamical mass in the inner 300pc implying another much older
stellar population. Pure constant star formation over the last 10 Gyr can be
excluded. Therefore, at least two star formation/starburst events took place in
the nucleus of NGC3227. Since such sequences in the nuclear star formation
history are also observed in the nuclei of other galaxies a link between the
activity of the star formation and the AGN itself seems likely.Comment: accepted for publication in the Astrophysical Journal, 46 pages, 15
figure
Sub-bandgap spectral photo-response analysis of Ti supersaturated Si
We have analyzed the increase of the sheet conductance (ÎGâĄ) under spectral illumination in high dose Ti implanted Si samples subsequently processed by pulsed-laser melting. Samples with Ti concentration clearly above the insulator-metal transition limit show a remarkably high ÎGâĄ, even higher than that measured in a silicon reference sample. This increase in the ÎG⥠magnitude is contrary to the classic understanding of recombination centers action and supports the lifetime recovery predicted for concentrations of deep levels above the insulator-metal transition
Counterterms and dual holographic anomalies in CS gravity
The holographic Weyl anomaly associated to Chern-Simons gravity in 2n+1
dimensions is proportional to the Euler term in 2n dimensions, with no
contributions from the Weyl tensor. We compute the holographic energy-momentum
tensor associated to Chern-Simons gravity directly from the action, in an
arbitrary odd-dimensional spacetime. We show, in particular, that the
counterterms rendering the action finite contain only terms of the Lovelock
type.Comment: 10 pages, no figure
Influence of the AlN interlayer thickness on the photovoltaic properties of In-rich AlInN on Si heterojunctions deposited by RF sputtering
We report the influence of the AlN interlayer thickness (0-15 nm) on the
photovoltaic properties of Al0.37In0.63N on Si heterojunction solar cells
deposited by radio frequency sputtering. The poor junction band alignment and
the presence of a 2-3 nm thick amorphous layer at the interface mitigates the
response in devices fabricated by direct deposition of n-AlInN on p-Si(111).
Adding a 4-nm-thick AlN buffer layer improves the AlInN crystalline quality and
the interface alignment leading to devices with a conversion efficiency of 1.5%
under 1-sun AM1.5G illumination. For thicker buffers the performance lessens
due to inefficient tunnel transport through the AlN. These results demonstrate
the feasibility of using In-rich AlInN alloys deposited by radio frequency
sputtering as novel electron-selective contacts to Si-heterojunction solar
cells
Thermodynamics of Black Holes in Two (and Higher) Dimensions
A comprehensive treatment of black hole thermodynamics in two-dimensional
dilaton gravity is presented. We derive an improved action for these theories
and construct the Euclidean path integral. An essentially unique boundary
counterterm renders the improved action finite on-shell, and its variational
properties guarantee that the path integral has a well-defined semi-classical
limit. We give a detailed discussion of the canonical ensemble described by the
Euclidean partition function, and examine various issues related to stability.
Numerous examples are provided, including black hole backgrounds that appear in
two dimensional solutions of string theory. We show that the Exact String Black
Hole is one of the rare cases that admits a consistent thermodynamics without
the need for an external thermal reservoir. Our approach can also be applied to
certain higher-dimensional black holes, such as Schwarzschild-AdS,
Reissner-Nordstrom, and BTZ.Comment: 63 pages, 3 pdf figures, v2: added reference
Thermoplastic elastomer with advanced hydrophilization and bonding performances for rapid (30 s) and easy molding of microfluidic devices
One of the most important area of research in microfluidic technologies focuses on the identification and characterisation
of novel materials with enhanced properties and versatility. Here we present a fast, easy and inexpensive microstructuration
method for the fabrication of novel, flexible, transparent and biocompatible microfluidic devices. Using a simple
hot-press, we demonstrate the rapid (30s) production of various microfluidic prototypes embossed in a commercially-available
soft thermoplastic elastomer (sTPE). This styrenic block copolymer (BCP) material is as flexible as PDMS and as
thermoformable as classical thermoplastics. It exhibits high fidelity in replication using SUâ8 and epoxy master
molds in a highly convenient low-isobar (0.4 bar) and iso-thermal process. Microfluidic devices can then be easily
sealed using either a simple hot plate or even room-temperature assembly, allowing them so sustain liquid pressure
of 2 and 0.6 bars respectively. The excellent sorption and biocompatibility properties of the microchips were validated
via a standard rhodamine dye assay as well as a sensitive yeast cell-based assay. The morphology and composition of
the surface area after plasma treatment for hydrophilization purposes are stable and show constant and homogenous
distribution of the block nanodomains (⌠22° after 4 days). These domains, which are evenly distributed at the nanoscale,
therefore account for a uniform and convenient surface at a âmicrofluidic scale deviceâ. To our knowledge, this is
the first thermoplastic elastomer material that can be used for fast and reliable fabrication and assembly of
microdevices while maintaining a high and stable hydrophilicity
Holographic renormalization and supersymmetry
Holographic renormalization is a systematic procedure for regulating
divergences in observables in asymptotically locally AdS spacetimes. For dual
boundary field theories which are supersymmetric it is natural to ask whether
this defines a supersymmetric renormalization scheme. Recent results in
localization have brought this question into sharp focus: rigid supersymmetry
on a curved boundary requires specific geometric structures, and general
arguments imply that BPS observables, such as the partition function, are
invariant under certain deformations of these structures. One can then ask if
the dual holographic observables are similarly invariant. We study this
question in minimal N = 2 gauged supergravity in four and five dimensions. In
four dimensions we show that holographic renormalization precisely reproduces
the expected field theory results. In five dimensions we find that no choice of
standard holographic counterterms is compatible with supersymmetry, which leads
us to introduce novel finite boundary terms. For a class of solutions
satisfying certain topological assumptions we provide some independent tests of
these new boundary terms, in particular showing that they reproduce the
expected VEVs of conserved charges.Comment: 70 pages; corrected typo
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