782 research outputs found
Evidence for two spatially separated UV continuum emitting regions in the Cloverleaf broad absorption line quasar
Testing the standard Shakura-Sunyaev model of accretion is a challenging task
because the central region of quasars where accretion takes place is unresolved
with telescopes. The analysis of microlensing in gravitationally lensed quasars
is one of the few techniques that can test this model, yielding to the
measurement of the size and of temperature profile of the accretion disc. We
present spectroscopic observations of the gravitationally lensed broad
absorption line quasar H1413+117, which reveal partial microlensing of the
continuum emission that appears to originate from two separated regions: a
microlensed region, corresponding to the compact accretion disc; and a
non-microlensed region, more extended and contributing to at least 30\% of the
total UV-continuum flux. Because this extended continuum is occulted by the
broad absorption line clouds, it is not associated with the host galaxy, but
rather with light scattered in the neighbourhood of the central engine. We
measure the amplitude of microlensing of the compact continuum over the
rest-frame wavelength range 1000-7000 \AA. Following a Bayesian scheme, we
confront our measurements to microlensing simulations of an accretion disc with
a temperature varying as . We find a most likely source
half-light radius of cm (i.e., 0.002\,pc) at
0.18\,m, and a most-likely index of . The standard disc
() model is not ruled out by our data, and is found within the 95\%
confidence interval associated with our measurements. We demonstrate that, for
H1413+117, the existence of an extended continuum in addition to the disc
emission only has a small impact on the inferred disc parameters, and is
unlikely to solve the tension between the microlensing source size and standard
disc sizes, as previously reported in the literature.Comment: Accepted for publication in Astronomy and Astrophysics. 12 pages.
Minor changes w.r.t. v1 (language editing, Fig. 5-6
Experimental ratchet effect in superconducting films with periodic arrays of asymmetric potentials
A vortex lattice ratchet effect has been investigated in Nb films grown on
arrays of nanometric Ni triangles, which induce periodic asymmetric pinning
potentials. The vortex lattice motion yields a net dc-voltage when an ac
driving current is applied to the sample and the vortex lattice moves through
the field of asymmetric potentials. This ratchet effect is studied taking into
account the array geometry, the temperature, the number of vortices per unit
cell of the array and the applied ac currents.Comment: 15 pages, figures include
Dramatic reductions in water uptake observed in novel POSS nanocomposites based on anhydride-cured epoxy matrix resins
© 2015.A methylnadic anhydride-cured diglycidylether of bisphenol A, is prepared and characterised and a mono-epoxy POSS reagent added (0.5-4wt-%) to produce a series of nanocomposites. Two reaction mechanisms are observed involving esterification at lower temperatures (60-180°C) and etherification at temperatures above 180°C. Using the Ozawa and Kissinger methods, the activation energy for the first reaction was found to be 87-90kJ/mol and 122-124kJ/mol for the second reaction. Incorporation of POSS into the epoxy-anhydride network increases the Tg and cross-link density, indicating a more rigid network, but the values do not follow a trend based solely on POSS content. The char yield increases with POSS content with very little change in the degradation temperature. Incorporation of POSS (1wt-%) can reduce the moisture uptake in the cured resin by ~25% at 75% relative humidity. This is accompanied by a lower impact on glass transition temperature: the Tg is reduced by 10K at saturation, compared with 31K for the unmodified epoxy
LandsCare: a system of payments for environmental services based on the beauty of the landscape
LandsCare is a smart-phone guide and a website on rural territories that use a system of payment for environmental services (PES) that tries to contribute to preserve and to valorise the natural and cultural local landscape. It develops a series of instruments to try to facilitate the interrelation of all the agents of a rural territory, including visitors pursuing a common objective, taking care of the common landscape and obtaining added value from it. LandsCare aspires to be the first global system of conservation and PES operating through smart-phones and based on the beauty of the landscape. LandsCare software is currently used by different NGOs and public administrations from different countries and regions. The present article describes the LandsCare system of rural development and payment for environmental services. It explains its components with the aim of becoming a global instrument facilitating countries’ rural development and ecotourism
Microlensing in H1413+117 : disentangling line profile emission and absorption in a broad absorption line quasar
On the basis of 16 years of spectroscopic observations of the four components
of the gravitationally lensed broad absorption line (BAL) quasar H1413+117,
covering the ultraviolet to visible rest-frame spectral range, we analyze the
spectral differences observed in the P Cygni-type line profiles and have used
the microlensing effect to derive new clues to the BAL profile formation. We
confirm that the spectral differences observed in component D can be attributed
to a microlensing effect lasting at least a decade. We show that microlensing
magnifies the continuum source in image D, leaving the emission line region
essentially unaffected. We interpret the differences seen in the absorption
profiles of component D as the result of an emission line superimposed onto a
nearly black absorption profile. We also find that the continuum source and a
part of the broad emission line region are likely de-magnified in component C,
while components A and B are not affected by microlensing. We show that
microlensing of the continuum source in component D has a chromatic dependence
compatible with the thermal continuum emission of a standard Shakura-Sunyaev
accretion disk. Using a simple decomposition method to separate the part of the
line profiles affected by microlensing and coming from a compact region from
the part unaffected by this effect and coming from a larger region, we
disentangle the true absorption line profiles from the true emission line
profiles. The extracted emission line profiles appear double-peaked, suggesting
that the emission is occulted by a strong absorber, narrower in velocity than
the full absorption profile, and emitting little by itself. We propose that the
outflow around H1413+117 is constituted by a high-velocity polar flow and a
denser, lower velocity disk seen nearly edge-on.Comment: Accepted for publication in Astronomy and Astrophysic
The ACS Virgo Cluster Survey IV: Data Reduction Procedures for Surface Brightness Fluctuation Measurements with the Advanced Camera for Surveys
The Advanced Camera for Surveys (ACS) Virgo Cluster Survey is a large program
to image 100 early-type Virgo galaxies using the F475W and F850LP bandpasses of
the Wide Field Channel of the ACS instrument on the Hubble Space Telescope
(HST). The scientific goals of this survey include an exploration of the
three-dimensional structure of the Virgo Cluster and a critical examination of
the usefulness of the globular cluster luminosity function as a distance
indicator. Both of these issues require accurate distances for the full sample
of 100 program galaxies. In this paper, we describe our data reduction
procedures and examine the feasibility of accurate distance measurements using
the method of surface brightness fluctuations (SBF) applied to the ACS Virgo
Cluster Survey F850LP imaging. The ACS exhibits significant geometrical
distortions due to its off-axis location in the HST focal plane; correcting for
these distortions by resampling the pixel values onto an undistorted frame
results in pixel correlations that depend on the nature of the interpolation
kernel used for the resampling. This poses a major challenge for the SBF
technique, which normally assumes a flat power spectrum for the noise. We
investigate a number of different interpolation kernels and show through an
analysis of simulated galaxy images having realistic noise properties that it
is possible, depending on the kernel, to measure SBF distances using
distortion-corrected ACS images without introducing significant additional
error from the resampling. We conclude by showing examples of real image power
spectra from our survey.Comment: ApJS, in press, complete version of the paper at the link:
http://www.physics.rutgers.edu/~pcote/acs/publications.htm
A gravitationally lensed quasar discovered in OGLE
Indexación: Scopus; Web of Science.We report the discovery of a new gravitationally lensed quasar (double) from the Optical Gravitational Lensing Experiment (OGLE) identified inside the ~670deg2 area encompassing the Magellanic Clouds. The source was selected as one of ~60 'red W1-W2' mid-infrared objects from WISE and having a significant amount of variability in OGLE for both two (or more) nearby sources. This is the first detection of a gravitational lens, where the discovery is made 'the other way around', meaning we first measured the time delay between the two lensed quasar images of -132 < tAB < -76 d (90 per cent CL), with the median tAB ~-102 d (in the observer frame), and where the fainter image B lags image A. The system consists of the two quasar images separated by 1.5 arcsec on the sky, with I ~20.0mag and I ~19.6mag, respectively, and a lensing galaxy that becomes detectable as I ~21.5 mag source, 1.0 arcsec from image A, after subtracting the two lensed images. Both quasar images show clear AGN broad emission lines at z=2.16 in the New Technology Telescope spectra. The spectral energy distribution (SED) fitting with the fixed source redshift provided the estimate of the lensing galaxy redshift of z ~0.9 ± 0.2 (90 per cent CL), while its type is more likely to be elliptical (the SED-inferred and lens-model stellar mass is more likely present in ellipticals) than spiral (preferred redshift by the lens model). © 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society.https://academic.oup.com/mnras/article/476/1/663/483368
Lattice effects and current reversal in superconducting ratchets
Competition between the vortex lattice and a lattice of asymmetric artificial
defects is shown to play a crucial role in ratchet experiments in
superconducting films. We present a novel and collective mechanism for current
reversal based on a reconfiguration of the vortex lattice. In contrast to
previous models of vortex current reversal, the mechanism is based on the
global response of the vortex lattice to external forces.Comment: 12 pages, 7 figure
Black Silicon with high density and high aspect ratio nanowhiskers
Physical properties of black Silicon (b-Si) formed on Si wafers by reactive
ion etching in chlorine plasma are reported in an attempt to clarify the
formation mechanism and the origin of the observed optical and electrical
phenomena which are promising for a variety of applications. The b-Si
consisting of high density and high aspect ratio sub-micron length whiskers or
pillars with tip diameters of well under 3 nm exhibits strong photoluminescence
(PL) both in visible and infrared, which are interpreted in conjunction with
defects, confinement effects and near band-edge emission. Structural analysis
indicate that the whiskers are all crystalline and encapsulated by a thin Si
oxide layer. Infrared vibrational spectrum of Si-O-Si bondings in terms of
transverse-optic (TO) and longitudinal-optic (LO) phonons indicates that
disorder induced LO-TO optical mode coupling can be an effective tool in
assessing structural quality of the b-Si. The same phonons are likely coupled
to electrons in visible region PL transitions. Field emission properties of
these nanoscopic features are demonstrated indicating the influence of the tip
shape on the emission. Overall properties are discussed in terms of surface
morphology of the nano whiskers
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