3,734 research outputs found
A Tractable Extension of Linear Indexed Grammars
It has been shown that Linear Indexed Grammars can be processed in polynomial
time by exploiting constraints which make possible the extensive use of
structure-sharing. This paper describes a formalism that is more powerful than
Linear Indexed Grammar, but which can also be processed in polynomial time
using similar techniques. The formalism, which we refer to as Partially Linear
PATR manipulates feature structures rather than stacks.Comment: 8 pages LaTeX, uses eaclap.sty, to appear in EACL-9
Optimal Union-Find in Constraint Handling Rules
Constraint Handling Rules (CHR) is a committed-choice rule-based language
that was originally intended for writing constraint solvers. In this paper we
show that it is also possible to write the classic union-find algorithm and
variants in CHR. The programs neither compromise in declarativeness nor
efficiency. We study the time complexity of our programs: they match the
almost-linear complexity of the best known imperative implementations. This
fact is illustrated with experimental results.Comment: 12 pages, 3 figures, to appear in Theory and Practice of Logic
Programming (TPLP
Parallel Natural Language Parsing: From Analysis to Speedup
Electrical Engineering, Mathematics and Computer Scienc
Realization of tree adjoining grammars with unification
The syntactic generator of the WIP system is based on the representation formalism "Tree Adjoining Grammars" (TAGs). We have extended the formalism by associating elementary rules of the grammar (trees) with feature structures, leading to "Tree Adjoining Grammars with Unification" (UTAGs). The extended formalism facilitates a compact and adequate representation of complex syntactic features. The contradiction between the monotonic operation of unification and the combination operation for trees - adjunction - that is nonmonotonic in a way can be solved by several approaches to realization. Two of them are presented in this work and compared with respect to the restrictions that are given by the system, i.e., the adequacy of the realization for incremental and parallel generation. It can be shown that UTAGs are subsumed by FTAGs (Feature Structure based TAGs) that have been defined by Vijay-Shanker and Joshi. That is why the results for realization can be applied to both UTAGs and a restricted version of FTAGs
CP Violation and Neutrino Oscillations
We review the basic mechanisms of neutrino mass generation and the
corresponding structure of the lepton mixing matrix. We summarize the status of
three-neutrino oscillation parameters as determined from current observations,
using state-of-the-art solar and atmospheric neutrino fluxes, as well as latest
experimental data as of September 2007. We also comment on recent attempts to
account for these results and to understand flavour from first principles. We
discuss extensively the prospects for probing the strength of CP violation in
two near term accelerator neutrino oscillation experiments, T2K and NOvA, as
well as possible extensions such as T2KK and a second large off-axis detector
near the NOvA detector. We also briefly discuss the possibility of probing the
effect of Majorana phases in future neutrinoless double beta decay searches and
discuss other implications of leptonic CP violation such as leptogenesis.
Finally we comment on the issue of robustness of the current oscillation
interpretation and possible ways of probing for non-standard neutrino
interactions in precision oscillation studies.Comment: 78 pages, 46 figures, minor misprint corrections, a few new
references and an acknowledgement to a funding agency. Review to be published
in Prog. Part. Nucl. Phy
Quantum Gravity: General Introduction and Recent Developments
I briefly review the current status of quantum gravity. After giving some
general motivations for the need of such a theory, I discuss the main
approaches in quantizing general relativity: Covariant approaches (perturbation
theory, effective theory, and path integrals) and canonical approaches (quantum
geometrodynamics, loop quantum gravity). I then address quantum gravitational
aspects of string theory. This is followed by a discussion of black holes and
quantum cosmology. I end with some remarks on the observational status of
quantum gravity.Comment: 21 pages, 6 figures, invited contribution for "Annalen der Physik",
v2: minor corrections, additional reference
Un outil pour développer et tester les grammaires d’unification polarisées
Ce mémoire présente un outil informatique pour développer et tester des grammaires d’unification polarisées, conçu entre autres pour faciliter la validation expérimentale du formalisme de la grammaire d’unification Sens-Texte (GUST) de Kahane & Lareau. Les fondements théoriques du formalisme GUP sont d’abord expliqués, puis nous décrivons la conception du module et l’évaluons avec un fragment de la grammaire GUST.This thesis presents a computer tool to develop and test polarized unification grammars that was built, namely, to help validate experimentally Kahane & Lareau’s Meaning-Text Unification Grammar (MTUG) formalism. We first describe the theory behind the PUG formalism, then we explain how the module was developed and we test it using a fragment of the MTUG grammar
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