3,926 research outputs found
Local supersymmetry in supergravity
We have studied the local supersymmetry in two D = 4 supergravity models, with
N = 1 and N = 2, given the Lagrangians. We have used a simple method based on
the differential of the action H, which provides an alternative systematic derivation of
the gauge field variations in the first order formalism. This method may be used to find
non-relativistic limits of supergravity models.Departamento de FĂsica TeĂłrica, AtĂłmica y Ă“pticaMáster en FĂsic
A Full Non-Monotonic Transition System for Unrestricted Non-Projective Parsing
Restricted non-monotonicity has been shown beneficial for the projective
arc-eager dependency parser in previous research, as posterior decisions can
repair mistakes made in previous states due to the lack of information. In this
paper, we propose a novel, fully non-monotonic transition system based on the
non-projective Covington algorithm. As a non-monotonic system requires
exploration of erroneous actions during the training process, we develop
several non-monotonic variants of the recently defined dynamic oracle for the
Covington parser, based on tight approximations of the loss. Experiments on
datasets from the CoNLL-X and CoNLL-XI shared tasks show that a non-monotonic
dynamic oracle outperforms the monotonic version in the majority of languages.Comment: 11 pages. Accepted for publication at ACL 201
Parsing as Reduction
We reduce phrase-representation parsing to dependency parsing. Our reduction
is grounded on a new intermediate representation, "head-ordered dependency
trees", shown to be isomorphic to constituent trees. By encoding order
information in the dependency labels, we show that any off-the-shelf, trainable
dependency parser can be used to produce constituents. When this parser is
non-projective, we can perform discontinuous parsing in a very natural manner.
Despite the simplicity of our approach, experiments show that the resulting
parsers are on par with strong baselines, such as the Berkeley parser for
English and the best single system in the SPMRL-2014 shared task. Results are
particularly striking for discontinuous parsing of German, where we surpass the
current state of the art by a wide margin
Transition-based Semantic Role Labeling with Pointer Networks
Semantic role labeling (SRL) focuses on recognizing the predicate-argument
structure of a sentence and plays a critical role in many natural language
processing tasks such as machine translation and question answering.
Practically all available methods do not perform full SRL, since they rely on
pre-identified predicates, and most of them follow a pipeline strategy, using
specific models for undertaking one or several SRL subtasks. In addition,
previous approaches have a strong dependence on syntactic information to
achieve state-of-the-art performance, despite being syntactic trees equally
hard to produce. These simplifications and requirements make the majority of
SRL systems impractical for real-world applications. In this article, we
propose the first transition-based SRL approach that is capable of completely
processing an input sentence in a single left-to-right pass, with neither
leveraging syntactic information nor resorting to additional modules. Thanks to
our implementation based on Pointer Networks, full SRL can be accurately and
efficiently done in , achieving the best performance to date on the
majority of languages from the CoNLL-2009 shared task.Comment: Final peer-reviewed manuscript accepted for publication in
Knowledge-Based System
Arc-eager parsing with the tree constraint
The arc-eager system for transition-based dependency parsing is widely used in natural language processing despite the fact that it does not guarantee that the output is a well-formed dependency tree. We propose a simple modification to the original system that enforces the tree constraint without requiring any modification to the parser training procedure. Experiments on multiple languages show that the method on average achieves 72% of the error reduction possible and consistently outperforms the standard heuristic in current use.Ministerio de Ciencia e InnovaciĂłn | Ref. TIN2010-18552-C03-01Xunta de Galicia | Ref. CN 2012/319Xunta de Galicia | Ref. CN 2012/31
Chaotic image encryption using hopfield and hindmarsh–rose neurons implemented on FPGA
Chaotic systems implemented by artificial neural networks are good candidates for data encryption. In this manner, this paper introduces the cryptographic application of the Hopfield and the Hindmarsh–Rose neurons. The contribution is focused on finding suitable coefficient values of the neurons to generate robust random binary sequences that can be used in image encryption. This task is performed by evaluating the bifurcation diagrams from which one chooses appropriate coefficient values of the mathematical models that produce high positive Lyapunov exponent and Kaplan–Yorke dimension values, which are computed using TISEAN. The randomness of both the Hopfield and the Hindmarsh–Rose neurons is evaluated from chaotic time series data by performing National Institute of Standard and Technology (NIST) tests. The implementation of both neurons is done using field-programmable gate arrays whose architectures are used to develop an encryption system for RGB images. The success of the encryption system is confirmed by performing correlation, histogram, variance, entropy, and Number of Pixel Change Rate (NPCR) tests
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