3,573 research outputs found
Automatic Metadata Generation using Associative Networks
In spite of its tremendous value, metadata is generally sparse and
incomplete, thereby hampering the effectiveness of digital information
services. Many of the existing mechanisms for the automated creation of
metadata rely primarily on content analysis which can be costly and
inefficient. The automatic metadata generation system proposed in this article
leverages resource relationships generated from existing metadata as a medium
for propagation from metadata-rich to metadata-poor resources. Because of its
independence from content analysis, it can be applied to a wide variety of
resource media types and is shown to be computationally inexpensive. The
proposed method operates through two distinct phases. Occurrence and
co-occurrence algorithms first generate an associative network of repository
resources leveraging existing repository metadata. Second, using the
associative network as a substrate, metadata associated with metadata-rich
resources is propagated to metadata-poor resources by means of a discrete-form
spreading activation algorithm. This article discusses the general framework
for building associative networks, an algorithm for disseminating metadata
through such networks, and the results of an experiment and validation of the
proposed method using a standard bibliographic dataset
Multi-wavelength VLTI study of the puffed-up inner rim of a circumbinary disc
The presence of stable, compact circumbinary discs of gas and dust around
post-asymptotic giant branch (post-AGB) binary systems has been well
established. We focus on one such system: IRAS 08544-4431. We present an
interferometric multi-wavelength analysis of the circumstellar environment of
IRAS 08544-4431. The aim is to constrain different contributions to the total
flux in the H, K, L, and N-bands in the radial direction. The data from
VLTI/PIONIER, VLTI/GRAVITY, and VLTI/MATISSE range from the near-infrared,
where the post-AGB star dominates, to the mid-infrared, where the disc
dominates. We fitted two geometric models to the visibility data to reproduce
the circumbinary disc: a ring with a Gaussian width and a flat disc model with
a temperature gradient. The flux contributions from the disc, the primary star
(modelled as a point-source), and an over-resolved component are recovered
along with the radial size of the emission, the temperature of the disc as a
function of radius, and the spectral dependencies of the different components.
The trends of all visibility data were well reproduced with the geometric
models. The near-infrared data were best fitted with a Gaussian ring model
while the mid-infrared data favoured a temperature gradient model. This implies
that a vertical structure is present at the disc inner rim, which we attribute
to a rounded puffed-up inner rim. The N-to-K size ratio is 2.8, referring to a
continuous flat source, analogues to young stellar objects. By combining
optical interferometric instruments operating at different wavelengths we can
resolve the complex structure of circumstellar discs and study the
wavelength-dependent opacity profile. A detailed radial, vertical, and
azimuthal structural analysis awaits a radiative transfer treatment in 3D to
capture all non-radial complexity.Comment: 8 pages, 5 figures, accepted for publication in A&A Letter
Model selection in High-Dimensions: A Quadratic-risk based approach
In this article we propose a general class of risk measures which can be used
for data based evaluation of parametric models. The loss function is defined as
generalized quadratic distance between the true density and the proposed model.
These distances are characterized by a simple quadratic form structure that is
adaptable through the choice of a nonnegative definite kernel and a bandwidth
parameter. Using asymptotic results for the quadratic distances we build a
quick-to-compute approximation for the risk function. Its derivation is
analogous to the Akaike Information Criterion (AIC), but unlike AIC, the
quadratic risk is a global comparison tool. The method does not require
resampling, a great advantage when point estimators are expensive to compute.
The method is illustrated using the problem of selecting the number of
components in a mixture model, where it is shown that, by using an appropriate
kernel, the method is computationally straightforward in arbitrarily high data
dimensions. In this same context it is shown that the method has some clear
advantages over AIC and BIC.Comment: Updated with reviewer suggestion
Direct Measurement of Kirkwood-Rihaczek distribution for spatial properties of coherent light beam
We present direct measurement of Kirkwood-Rihaczek (KR) distribution for
spatial properties of coherent light beam in terms of position and momentum
(angle) coordinates. We employ a two-local oscillator (LO) balanced heterodyne
detection (BHD) to simultaneously extract distribution of transverse position
and momentum of a light beam. The two-LO BHD could measure KR distribution for
any complex wave field (including quantum mechanical wave function) without
applying tomography methods (inverse Radon transformation). Transformation of
KR distribution to Wigner, Glauber Sudarshan P- and Husimi or Q- distributions
in spatial coordinates are illustrated through experimental data. The direct
measurement of KR distribution could provide local information of wave field,
which is suitable for studying particle properties of a quantum system. While
Wigner function is suitable for studying wave properties such as interference,
and hence provides nonlocal information of the wave field. The method developed
here can be used for exploring spatial quantum state for quantum mapping and
computing, optical phase space imaging for biomedical applications.Comment: 27 pages, 14 figure
Ranking Spaces for Predicting Human Movement in an Urban Environment
A city can be topologically represented as a connectivity graph, consisting
of nodes representing individual spaces and links if the corresponding spaces
are intersected. It turns out in the space syntax literature that some defined
topological metrics can capture human movement rates in individual spaces. In
other words, the topological metrics are significantly correlated to human
movement rates, and individual spaces can be ranked by the metrics for
predicting human movement. However, this correlation has never been well
justified. In this paper, we study the same issue by applying the weighted
PageRank algorithm to the connectivity graph or space-space topology for
ranking the individual spaces, and find surprisingly that (1) the PageRank
scores are better correlated to human movement rates than the space syntax
metrics, and (2) the underlying space-space topology demonstrates small world
and scale free properties. The findings provide a novel justification as to why
space syntax, or topological analysis in general, can be used to predict human
movement. We further conjecture that this kind of analysis is no more than
predicting a drunkard's walking on a small world and scale free network.
Keywords: Space syntax, topological analysis of networks, small world, scale
free, human movement, and PageRankComment: 11 pages, 5 figures, and 2 tables, English corrections from version 1
to version 2, major changes in the section of introduction from version 2 to
A cylindrical Penning trap for capture, mass selective cooling, and bunching of radioactive ion beams
A Penning trap ion accumulator, cooler, and buncher for low energy ion beams has been developed for the ISOLTRAP mass spectrometer at ISOLDE/CERN. A cylindrical electrode configuration is used for the creation of a nested trapping potential. This is required for efficient accumulation of externally produced ions and for high mass selectivity by buffer gas cooling. The design goal of a mass resolving power of about has been achieved. Isobar separation has been demonstrated for radioactive rare earth ion beams delivered by the ISOLDE on-line mass separator
Quantitative Analysis of Bloggers Collective Behavior Powered by Emotions
Large-scale data resulting from users online interactions provide the
ultimate source of information to study emergent social phenomena on the Web.
From individual actions of users to observable collective behaviors, different
mechanisms involving emotions expressed in the posted text play a role. Here we
combine approaches of statistical physics with machine-learning methods of text
analysis to study emergence of the emotional behavior among Web users. Mapping
the high-resolution data from digg.com onto bipartite network of users and
their comments onto posted stories, we identify user communities centered
around certain popular posts and determine emotional contents of the related
comments by the emotion-classifier developed for this type of texts. Applied
over different time periods, this framework reveals strong correlations between
the excess of negative emotions and the evolution of communities. We observe
avalanches of emotional comments exhibiting significant self-organized critical
behavior and temporal correlations. To explore robustness of these critical
states, we design a network automaton model on realistic network connections
and several control parameters, which can be inferred from the dataset.
Dissemination of emotions by a small fraction of very active users appears to
critically tune the collective states
The reporting of distribution power quality surveys
Power quality surveys can contain a large amount of data for many sites and several utilities. A reporting format needs to be adopted which gives useful insights without sacrificing detail. It is recommended that a three level structure be adopted with site, network and utility component styles. The first of these is the presentation of the raw data in slightly abbreviated form while the second allows all sites in one network to be ranked according to severity of their power quality disturbances. Utility reporting allows comparison between the overall power quality performance of different utilities in benchmarking studies. Some new data analysis algorithms are proposed to show how the reporting styles should be implemented
Production and trapping of carbon clusters for absolute mass measurements at ISOLTRAP
Singly-charged carbon clusters C/sub n//sup +/ (n >or= 1) have been produced by laser-induced desorption and fragmentation of C/sub 60/ fullerenes and have been injected into and stored in the Penning trap system of the ISOLTRAP mass spectrometer at ISOLDE/CERN. The present study is the first step to extend the until now direct mass measurements at ISOLTRAP to absolute mass measurements by using clusters of /sup 12/C. (10 refs)
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