36,460 research outputs found
Inductive Logic Programming in Databases: from Datalog to DL+log
In this paper we address an issue that has been brought to the attention of
the database community with the advent of the Semantic Web, i.e. the issue of
how ontologies (and semantics conveyed by them) can help solving typical
database problems, through a better understanding of KR aspects related to
databases. In particular, we investigate this issue from the ILP perspective by
considering two database problems, (i) the definition of views and (ii) the
definition of constraints, for a database whose schema is represented also by
means of an ontology. Both can be reformulated as ILP problems and can benefit
from the expressive and deductive power of the KR framework DL+log. We
illustrate the application scenarios by means of examples. Keywords: Inductive
Logic Programming, Relational Databases, Ontologies, Description Logics, Hybrid
Knowledge Representation and Reasoning Systems. Note: To appear in Theory and
Practice of Logic Programming (TPLP).Comment: 30 pages, 3 figures, 2 tables
Toroidal crossings and logarithmic structures
We generalize Friedman's notion of d-semistability, which is a necessary
condition for spaces with normal crossings to admit smoothings with regular
total space. Our generalization deals with spaces that locally look like the
boundary divisor in Gorenstein toroidal embeddings. In this situation, we
replace d-semistability by the existence of global log structures for a given
gerbe of local log structures. This leads to cohomological descriptions for the
obstructions, existence, and automorphisms of log structures. We also apply
toroidal crossings to mirror symmetry, by giving a duality construction
involving toroidal crossing varieties whose irreducible components are toric
varieties. This duality reproduces a version of Batyrev's construction of
mirror pairs for hypersurfaces in toric varieties, but it applies to a larger
class, including degenerate abelian varieties.Comment: 34 pages, 1 figure, notational changes, to appear in Adv. Mat
Attend Refine Repeat: Active Box Proposal Generation via In-Out Localization
The problem of computing category agnostic bounding box proposals is utilized
as a core component in many computer vision tasks and thus has lately attracted
a lot of attention. In this work we propose a new approach to tackle this
problem that is based on an active strategy for generating box proposals that
starts from a set of seed boxes, which are uniformly distributed on the image,
and then progressively moves its attention on the promising image areas where
it is more likely to discover well localized bounding box proposals. We call
our approach AttractioNet and a core component of it is a CNN-based category
agnostic object location refinement module that is capable of yielding accurate
and robust bounding box predictions regardless of the object category.
We extensively evaluate our AttractioNet approach on several image datasets
(i.e. COCO, PASCAL, ImageNet detection and NYU-Depth V2 datasets) reporting on
all of them state-of-the-art results that surpass the previous work in the
field by a significant margin and also providing strong empirical evidence that
our approach is capable to generalize to unseen categories. Furthermore, we
evaluate our AttractioNet proposals in the context of the object detection task
using a VGG16-Net based detector and the achieved detection performance on COCO
manages to significantly surpass all other VGG16-Net based detectors while even
being competitive with a heavily tuned ResNet-101 based detector. Code as well
as box proposals computed for several datasets are available at::
https://github.com/gidariss/AttractioNet.Comment: Technical report. Code as well as box proposals computed for several
datasets are available at:: https://github.com/gidariss/AttractioNe
Comparing Poynting flux dominated magnetic tower jets with kinetic-energy dominated jets
Magnetic Towers represent one of two fundamental forms of MHD outflows.
Driven by magnetic pressure gradients, these flows have been less well studied
than magneto-centrifugally launched jets even though magnetic towers may well
be as common. Here we present new results exploring the behavior and evolution
of magnetic tower outflows and demonstrate their connection with pulsed power
experimental studies and purely hydrodynamic jets which might represent the
asymptotic propagation regimes of magneto-centrifugally launched jets.
High-resolution AMR MHD simulations (using the AstroBEAR code) provide insights
into the underlying physics of magnetic towers and help us constrain models of
their propagation. Our simulations have been designed to explore the effects of
thermal energy losses and rotation on both tower flows and their hydro
counterparts. We find these parameters have significant effects on the
stability of magnetic towers, but mild effects on the stability of hydro jets.
Current-driven perturbations in the Poynting Flux Dominated (PDF) towers are
shown to be amplified in both the cooling and rotating cases. Our studies of
the long term evolution of the towers show that the formation of weakly
magnetized central jets within the tower are broken up by these instabilities
becoming a series of collimated clumps which magnetization properties vary over
time. In addition to discussing these results in light of laboratory
experiments, we address their relevance to astrophysical observations of young
star jets and outflow from highly evolved solar type stars.Comment: 11 pages, 4 figures, accepted for publication in the High Energy
Density Physics Journal corresponding to the proceedings of the 9th
International Conference on High Energy Density Laboratory Astrophysics, May
4, 2012, Tallahassee Florid
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