43,604 research outputs found
Facet-Based Browsing in Video Retrieval: A Simulation-Based Evaluation
In this paper we introduce a novel interactive video retrieval approach which uses sub-needs of an information need for querying and organising the search process. The underlying assumption of this approach is that the search effectiveness will be enhanced when employed for interactive video retrieval. We explore the performance bounds of a faceted system by using the simulated user evaluation methodology on TRECVID data sets and also on the logs of a prior user experiment with the system. We discuss the simulated evaluation strategies employed in our evaluation and the effect on the use of both textual and visual features. The facets are simulated by the use of clustering the video shots using textual and visual features. The experimental results of our study demonstrate that the faceted browser can potentially improve the search effectiveness
Simulated evaluation of faceted browsing based on feature selection
In this paper we explore the limitations of facet based browsing which uses sub-needs of an information need for querying and organising the search process in video retrieval. The underlying assumption of this approach is that the search effectiveness will be enhanced if such an approach is employed for interactive video retrieval using textual and visual features. We explore the performance bounds of a faceted system by carrying out a simulated user evaluation on TRECVid data sets, and also on the logs of a prior user experiment with the system. We first present a methodology to reduce the dimensionality of features by selecting the most important ones. Then, we discuss the simulated evaluation strategies employed in our evaluation and the effect on the use of both textual and visual features. Facets created by users are simulated by clustering video shots using textual and visual features. The experimental results of our study demonstrate that the faceted browser can potentially improve the search effectiveness
Clustering of Primordial Black Holes. II. Evolution of Bound Systems
Primordial Black Holes (PBHs) that form from the collapse of density
perturbations are more clustered than the underlying density field. In a
previous paper, we showed the constraints that this has on the prospects of PBH
dark matter. In this paper we examine another consequence of this clustering:
the formation of bound systems of PBHs in the early universe. These would
hypothetically be the earliest gravitationally collapsed structures, forming
when the universe is still radiation dominated. Depending upon the size and
occupation of the clusters, PBH merging occurs before they would have otherwise
evaporated due to Hawking evaporation.Comment: 23 pages, 1 figure. Submitted to PR
Cosmological Parameters from Observations of Galaxy Clusters
Studies of galaxy clusters have proved crucial in helping to establish the
standard model of cosmology, with a universe dominated by dark matter and dark
energy. A theoretical basis that describes clusters as massive,
multi-component, quasi-equilibrium systems is growing in its capability to
interpret multi-wavelength observations of expanding scope and sensitivity. We
review current cosmological results, including contributions to fundamental
physics, obtained from observations of galaxy clusters. These results are
consistent with and complementary to those from other methods. We highlight
several areas of opportunity for the next few years, and emphasize the need for
accurate modeling of survey selection and sources of systematic error.
Capitalizing on these opportunities will require a multi-wavelength approach
and the application of rigorous statistical frameworks, utilizing the combined
strengths of observers, simulators and theorists.Comment: 53 pages, 21 figures. To appear in Annual Review of Astronomy &
Astrophysic
Voronoi Tessellations and the Cosmic Web: Spatial Patterns and Clustering across the Universe
The spatial cosmic matter distribution on scales of a few up to more than a
hundred Megaparsec displays a salient and pervasive foamlike pattern. Voronoi
tessellations are a versatile and flexible mathematical model for such weblike
spatial patterns. They would be the natural asymptotic result of an evolution
in which low-density expanding void regions dictate the spatial organization of
the Megaparsec Universe, while matter assembles in high-density filamentary and
wall-like interstices between the voids. We describe the results of ongoing
investigations of a variety of aspects of cosmologically relevant spatial
distributions and statistics within the framework of Voronoi tessellations.
Particularly enticing is the finding of a profound scaling of both clustering
strength and clustering extent for the distribution of tessellation nodes,
suggestive for the clustering properties of galaxy clusters. Cellular patterns
may be the source of an intrinsic ``geometrically biased'' clustering.Comment: 10 pages, 9 figures, accepted for publication as long paper in
proceedings Fourth International Symposium on Voronoi Diagrams in Science and
Engineering (ISVD 2007), ed. C. Gold, IEEE Computer Society, July 2007. For
high-res version see
http://www.astro.rug.nl/~weygaert/tim1publication/vorwey.isvd07.pd
The Dark Energy Survey
We describe the Dark Energy Survey (DES), a proposed optical-near infrared
survey of 5000 sq. deg of the South Galactic Cap to ~24th magnitude in SDSS
griz, that would use a new 3 sq. deg CCD camera to be mounted on the Blanco 4-m
telescope at Cerro Telolo Inter-American Observatory (CTIO). The survey data
will allow us to measure the dark energy and dark matter densities and the dark
energy equation of state through four independent methods: galaxy clusters,
weak gravitational lensing tomography, galaxy angular clustering, and supernova
distances. These methods are doubly complementary: they constrain different
combinations of cosmological model parameters and are subject to different
systematic errors. By deriving the four sets of measurements from the same data
set with a common analysis framework, we will obtain important cross checks of
the systematic errors and thereby make a substantial and robust advance in the
precision of dark energy measurements.Comment: White Paper submitted to the Dark Energy Task Force, 42 page
Revealing modified gravity signal in matter and halo hierarchical clustering
We use a set of N-body simulations employing a modified gravity (MG) model
with Vainshtein screening to study matter and halo hierarchical clustering. As
test-case scenarios we consider two normal branch Dvali-Gabadadze-Porrati
(nDGP) gravity models with mild and strong growth rate enhancement. We study
higher-order correlation functions up to and associated
hierarchical amplitudes . We find that
the matter PDFs are strongly affected by the fifth-force on scales up to
Mpc, and the deviations from GR are maximised at . For reduced
cumulants , we find that at small scales Mpc the MG is
characterised by lower values, with the deviation growing from in the
reduced skewness up to even in . To study the halo clustering we
use a simple abundance matching and divide haloes into thee fixed number
density samples. The halo two-point functions are weakly affected, with a
relative boost of the order of a few percent appearing only at the smallest
pair separations (Mpc). In contrast, we find a strong MG signal
in 's, which are enhanced compared to GR. The strong model exhibits a
level signal at various scales for all halo samples and in all
cumulants. In this context, we find that the reduced kurtosis to be an
especially promising cosmological probe of MG. Even the mild nDGP model leaves
a imprint at small scales Mpc, while the stronger model
deviates from a GR-signature at nearly all scales with a significance of
. Since the signal is persistent in all halo samples and over a range
of scales, we advocate that the reduced kurtosis estimated from galaxy
catalogues can potentially constitute a strong MG-model discriminatory as well
as GR self-consistency test.Comment: 19 pages, 11 figures, comments are welcom
Cosmological constraints on Lorentz violating dark energy
The role of Lorentz invariance as a fundamental symmetry of nature has been
lately reconsidered in different approaches to quantum gravity. It is thus
natural to study whether other puzzles of physics may be solved within these
proposals. This may be the case for the cosmological constant problem. Indeed,
it has been shown that breaking Lorentz invariance provides Lagrangians that
can drive the current acceleration of the universe without experiencing large
corrections from ultraviolet physics. In this work, we focus on the simplest
model of this type, called ThetaCDM, and study its cosmological implications in
detail. At the background level, this model cannot be distinguished from
LambdaCDM. The differences appear at the level of perturbations. We show that
in ThetaCDM, the spectrum of CMB anisotropies and matter fluctuations may be
affected by a rescaling of the gravitational constant in the Poisson equation,
by the presence of extra contributions to the anisotropic stress, and finally
by the existence of extra clustering degrees of freedom. To explore these
modifications accurately, we modify the Boltzmann code CLASS. We then use the
parameter inference code Monte Python to confront ThetaCDM with data from
WMAP-7, SPT and WiggleZ. We obtain strong bounds on the parameters accounting
for deviations from LambdaCDM. In particular, we find that the discrepancy
between the gravitational constants appearing in the Poisson and Friedmann
equations is constrained at the level 1.8%.Comment: 17 pages, 5 figure
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