5,573 research outputs found
Automatic Classification of Text Databases through Query Probing
Many text databases on the web are "hidden" behind search interfaces, and
their documents are only accessible through querying. Search engines typically
ignore the contents of such search-only databases. Recently, Yahoo-like
directories have started to manually organize these databases into categories
that users can browse to find these valuable resources. We propose a novel
strategy to automate the classification of search-only text databases. Our
technique starts by training a rule-based document classifier, and then uses
the classifier's rules to generate probing queries. The queries are sent to the
text databases, which are then classified based on the number of matches that
they produce for each query. We report some initial exploratory experiments
that show that our approach is promising to automatically characterize the
contents of text databases accessible on the web.Comment: 7 pages, 1 figur
Pilot Experiments with Electrodialysis and Ozonation for the Production of a Fertilizer from Urine
Pilot tests were performed with a process combination of electrodialysis and ozonation for the removal of micropollutants and the concentration of nutrients in urine. In continuous and batch experiments, maximum concentration factors up to 3.5 and 4.1 were obtained, respectively. The desalination capacity did not decrease significantly during continuous operation periods of several weeks. Membrane cleaning after 195 days resulted in approximately 35% increase in desalination rate. The Yeast Estrogen Screen (YES), a bioassay that selectively detects oestrogenic compounds, confirmed that about 90% of the oestrogenic activity was removed by electrodialysis. HPLC analysis showed that ibuprofen was removed to a high extent, while other micropollutants were below the detection limit. In view of the fact that ibuprofen is among the most rapidly transported micropollutants in electrodialysis processes, this result indicates that electrodialysis provides an effective barrier for micropollutants. Standardised plant growth tests were performed in the field with the salt solution resulting from the treatment by electrodialysis and subsequent ozonation. The results show that the plant height is comparable to synthetic fertilisers, but the crop yield is slightly lower. The latter is probably caused by volatilisation losses during field application, which can be prevented by improved application technologies
Homography-based ground plane detection using a single on-board camera
This study presents a robust method for ground plane detection in vision-based systems with a non-stationary camera. The proposed method is based on the reliable estimation of the homography between ground planes in successive images. This homography is computed using a feature matching approach, which in contrast to classical approaches to on-board motion estimation does not require explicit ego-motion calculation. As opposed to it, a novel homography calculation method based on a linear estimation framework is presented. This framework provides predictions of the ground plane transformation matrix that are dynamically updated with new measurements. The method is specially suited for challenging environments, in particular traffic scenarios, in which the information is scarce and the homography computed from the images is usually inaccurate or erroneous. The proposed estimation framework is able to remove erroneous measurements and to correct those that are inaccurate, hence producing a reliable homography estimate at each instant. It is based on the evaluation of the difference between the predicted and the observed transformations, measured according to the spectral norm of the associated matrix of differences. Moreover, an example is provided on how to use the information extracted from ground plane estimation to achieve object detection and tracking. The method has been successfully demonstrated for the detection of moving vehicles in traffic environments
Magnetic Field Effects on Quasiparticles in Strongly Correlated Local Systems
We show that quasiparticles in a magnetic field of arbitrary strength can
be described by field dependent parameters. We illustrate this approach in the
case of an Anderson impurity model and use the numerical renormalization group
(NRG) to calculate the renormalized parameters for the levels with spin
, , resonance width
and the effective local quasiparticle interaction . In the Kondo or strong correlation limit of the model the progressive
de-renormalization of the quasiparticles can be followed as the magnetic field
is increased. The low temperature behaviour, including the conductivity, in
arbitrary magnetic field can be calculated in terms of the field dependent
parameters using the renormalized perturbation expansion. Using the NRG the
field dependence of the spectral density on higher scales is also calculated.Comment: 15 pages, 17 figure
Bayesian Network Structure Learning with Permutation Tests
In literature there are several studies on the performance of Bayesian
network structure learning algorithms. The focus of these studies is almost
always the heuristics the learning algorithms are based on, i.e. the
maximisation algorithms (in score-based algorithms) or the techniques for
learning the dependencies of each variable (in constraint-based algorithms). In
this paper we investigate how the use of permutation tests instead of
parametric ones affects the performance of Bayesian network structure learning
from discrete data. Shrinkage tests are also covered to provide a broad
overview of the techniques developed in current literature.Comment: 13 pages, 4 figures. Presented at the Conference 'Statistics for
Complex Problems', Padova, June 15, 201
Realizing Exactly Solvable SU(N) Magnets with Thermal Atoms
We show that thermal fermionic alkaline-earth atoms in a flat-bottom trap
allow one to robustly implement a spin model displaying two symmetries: the
symmetry that permutes atoms occupying different vibrational levels of
the trap and the SU() symmetry associated with nuclear spin states. The
high symmetry makes the model exactly solvable, which, in turn, enables the
analytic study of dynamical processes such as spin diffusion in this SU()
system. We also show how to use this system to generate entangled states that
allow for Heisenberg-limited metrology. This highly symmetric spin model should
be experimentally realizable even when the vibrational levels are occupied
according to a high-temperature thermal or an arbitrary non-thermal
distribution.Comment: 12 pages, 5 figures (including supplemental materials
Brain structure in pediatric Tourette syndrome
Previous studies of brain structure in Tourette syndrome (TS) have produced mixed results, and most had modest sample sizes. In the present multicenter study, we used structural magnetic resonance imaging (MRI) to compare 103 children and adolescents with TS to a well-matched group of 103 children without tics. We applied voxel-based morphometry methods to test gray matter (GM) and white matter (WM) volume differences between diagnostic groups, accounting for MRI scanner and sequence, age, sex and total GM+WM volume. The TS group demonstrated lower WM volume bilaterally in orbital and medial prefrontal cortex, and greater GM volume in posterior thalamus, hypothalamus and midbrain. These results demonstrate evidence for abnormal brain structure in children and youth with TS, consistent with and extending previous findings, and they point to new target regions and avenues of study in TS. For example, as orbital cortex is reciprocally connected with hypothalamus, structural abnormalities in these regions may relate to abnormal decision making, reinforcement learning or somatic processing in TS
A Calculation of the ESR Parameters of the Hydrogen Bonded Complex Radical (H2NO ... HF)
The isotropic constant (a) and the dipolar tensor (B) have
been calculated for the radical H2NO bonded to HF. The semiempirical
SCF (INDO) method has been used to describe the electronic
configuration of the complex radical H2NO ... HF. It is
suggested that a and B of the proton from HF are amenable to
experimental verification
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