63,963 research outputs found
Interoperability between Multimedia Collections for Content and Metadata-Based Searching
Artiste is a European project developing a cross-collection search system for art galleries and museums. It combines image content retrieval with text based retrieval and uses RDF mappings in order to integrate diverse databases. The test sites of the Louvre, Victoria and Albert Museum, Uffizi Gallery and National Gallery London provide their own database schema for existing metadata, avoiding the need for migration to a common schema. The system will accept a query based on one museum’s fields and convert them, through an RDF mapping into a form suitable for querying the other collections. The nature of some of the image processing algorithms means that the system can be slow for some computations, so the system is session-based to allow the user to return to the results later. The system has been built within a J2EE/EJB framework, using the Jboss Enterprise Application Server
Band-Limited Coronagraphs using a halftone-dot process: II. Advances and laboratory results for arbitrary telescope apertures
The band-limited coronagraph is a nearly ideal concept that theoretically
enables perfect cancellation of all the light of an on-axis source. Over the
past years, several prototypes have been developed and tested in the
laboratory, and more emphasis is now on developing optimal technologies that
can efficiently deliver the expected high-contrast levels of such a concept.
Following the development of an early near-IR demonstrator, we present and
discuss the results of a second-generation prototype using halftone-dot
technology. We report improvement in the accuracy of the control of the local
transmission of the manufactured prototype, which was measured to be less than
1%.
This advanced H-band band-limited device demonstrated excellent contrast
levels in the laboratory, down to 10-6 at farther angular separations than 3
lambda/D over 24% spectral bandwidth. These performances outperform the ones of
our former prototype by more than an order of magnitude and confirm the
maturity of the manufacturing process.
Current and next generation high-contrast instruments can directly benefit
from such capabilities. In this context, we experimentally examine the ability
of the band-limited coronagraph to withstand various complex telescope
apertures.Comment: Accepted in ApJ - under pres
Cross-correlation of the CMB and radio galaxies in real, harmonic and wavelet spaces: detection of the integrated Sachs-Wolfe effect and dark energy constraints
We report the first detection of the ISW effect in wavelet space, at scales
in the sky around 7 degrees with a significance of around 3.3 sigma, by
cross-correlating the WMAP first-year data and the NRAO VLA Sky Survey (NVSS).
In addition, we present a detailed comparison among the capabilities of three
different techniques for two different objectives: to detect the ISW and to put
constraints in the nature of the dark energy. The three studied techniques are:
the cross-angular power spectrum (CAPS, harmonic space), the correlation
function (CCF, real space) and the covariance of the Spherical Mexican Hat
Wavelet (SMHW) coefficients (CSMHW, wavelet space). We prove that the CSMHW is
expected to provide a higher detection of the ISW effect for a certain scale.
This prediction has been corroborated by the analysis of the data. The SMHW
analysis shows that the cross-correlation signal is caused neither by
systematic effects nor foreground contamination. However, by taking into
account the information encoded in all the multipoles/scales/angles, the CAPS
provides slightly better constraints than the SMHW in the cosmological
parameters that define the nature of the dark energy. The limits provided by
the CCF are wider than for the other two methods. Two different cases have been
studied: 1) a flat Lambda-CDM universe and 2) a flat universe with an equation
of state parameter different from -1. In the first case, the CAPS provides (for
a bias value of b = 1.6) 0.59 < Lambda density < 0.84 (at 1 sigma CL).
Moreover, the CAPS rejects the range Lambda density < 0.1 at 3.5 sigma, which
is the highest detection of the dark energy reported up to date. In the second
case, the CAPS gives 0.50 < dark energy density < 0.82 and -1.16 < w < 0.43 (at
1 sigma CL).Comment: 12 pages, 7 figures, accepted for publication in MNRAS. Analysis
redone. Changes in the estimation of the cosmological parametres. Additional
comparison between wavelets and more standard technique
Coherent diffraction of thermal currents in Josephson tunnel junctions
We theoretically investigate heat transport in temperature-biased Josephson
tunnel junctions in the presence of an in-plane magnetic field. In full analogy
with the Josephson critical current, the phase-dependent component of the heat
flux through the junction displays coherent diffraction. Thermal transport is
analyzed in three prototypical junction geometries highlighting their main
differences. Notably, minimization of the Josephson coupling energy requires
the quantum phase difference across the junction to undergo \pi-slips in
suitable intervals of magnetic flux. An experimental setup suited to detect
thermal diffraction is proposed and analyzed.Comment: 6.5 pages, 4 color figures, updated versio
Multiplicative local linear hazard estimation and best one-sided cross-validation
This paper develops detailed mathematical statistical theory of a new class of cross-validation techniques of local linear kernel hazards and their multiplicative bias corrections. The new class of cross-validation combines principles of local information and recent advances in indirect cross-validation. A few applications of cross-validating multiplicative kernel hazard estimation do exist in the literature. However, detailed mathematical statistical theory and small sample performance are introduced via this paper and further upgraded to our new class of best one-sided cross-validation. Best one-sided cross-validation turns out to have excellent performance in its practical illustrations, in its small sample performance and in its mathematical statistical theoretical performance
High-contrast imaging at small separation: impact of the optical configuration of two deformable mirrors on dark holes
The direct detection and characterization of exoplanets will be a major
scientific driver over the next decade, involving the development of very large
telescopes and requires high-contrast imaging close to the optical axis. Some
complex techniques have been developed to improve the performance at small
separations (coronagraphy, wavefront shaping, etc). In this paper, we study
some of the fundamental limitations of high contrast at the instrument design
level, for cases that use a combination of a coronagraph and two deformable
mirrors for wavefront shaping. In particular, we focus on small-separation
point-source imaging (around 1 /D). First, we analytically or
semi-analytically analysing the impact of several instrument design parameters:
actuator number, deformable mirror locations and optic aberrations (level and
frequency distribution). Second, we develop in-depth Monte Carlo simulation to
compare the performance of dark hole correction using a generic test-bed model
to test the Fresnel propagation of multiple randomly generated optics static
phase errors. We demonstrate that imaging at small separations requires large
setup and small dark hole size. The performance is sensitive to the optic
aberration amount and spatial frequencies distribution but shows a weak
dependence on actuator number or setup architecture when the dark hole is
sufficiently small (from 1 to 5 /D).Comment: 13 pages, 18 figure
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