1,553 research outputs found
Remarks on the consistency of minimal deviations from General Relativity
We study the consequences of the modification of the phase space structure of
General Relativity imposed by breaking the full diffeomorphism invariance but
retaining the time foliation preserving diffeomorphisms. We examine the
different sectors in phase space that satisfy the new structure of constraints.
For some sectors we find an infinite tower of constraints. In spite of that, we
also show that these sectors allow for solutions, among them some well known
families of black hole and cosmologies which fulfill all the constraints. We
raise some physical concerns on the consequences of an absolute Galilean time,
on the thermodynamical pathologies of such models and on their unusual vacuum
structure.Comment: latex 28 pages, 1 figure. Added comments and a reference. Text
improved
Food-bridging: a new network construction to unveil the principles of cooking
In this manuscript we propose, analyse, and discuss a possible new principle
behind traditional cuisine: the Food-bridging hypothesis and its comparison
with the food-pairing hypothesis using the same dataset and graphical models
employed in the food-pairing study by Ahn et al. [Scientific Reports, 1:196
(2011)].
The Food-bridging hypothesis assumes that if two ingredients do not share a
strong molecular or empirical affinity, they may become affine through a chain
of pairwise affinities. That is, in a graphical model as employed by Ahn et
al., a chain represents a path that joints the two ingredients, the shortest
path represents the strongest pairwise chain of affinities between the two
ingredients.
Food-pairing and Food-bridging are different hypotheses that may describe
possible mechanisms behind the recipes of traditional cuisines. Food-pairing
intensifies flavour by mixing ingredients in a recipe with similar chemical
compounds, and food-bridging smoothes contrast between ingredients. Both
food-pairing and food-bridging are observed in traditional cuisines, as shown
in this work.
We observed four classes of cuisines according to food-pairing and
food-bridging: (1) East Asian cuisines, at one extreme, tend to avoid
food-pairing as well as food-bridging; and (4) Latin American cuisines, at the
other extreme, follow both principles. For the two middle classes: (2)
Southeastern Asian cuisines, avoid food-pairing and follow food-bridging; and
(3) Western cuisines, follow food-pairing and avoid food-bridging
Factoid question answering for spoken documents
In this dissertation, we present a factoid question answering system, specifically tailored for Question Answering (QA) on spoken documents.
This work explores, for the first time, which techniques can be robustly adapted from the usual QA on written documents to the more difficult spoken documents scenario. More specifically, we study new information retrieval (IR) techniques designed for speech, and utilize several levels of linguistic information for the speech-based QA task. These include named-entity detection with phonetic information, syntactic parsing applied to speech transcripts, and the use of coreference resolution.
Our approach is largely based on supervised machine learning techniques, with special focus on the answer extraction step, and makes little use of handcrafted knowledge. Consequently, it should be easily adaptable to other domains and languages.
In the work resulting of this Thesis, we have impulsed and coordinated the creation of an evaluation framework for the task of QA on spoken documents. The framework, named QAst, provides multi-lingual corpora, evaluation questions, and answers key. These corpora have been used in the QAst evaluation that was held in the CLEF workshop for the years 2007, 2008 and 2009, thus helping the developing of state-of-the-art techniques for this particular topic.
The presentend QA system and all its modules are extensively evaluated on the European Parliament Plenary Sessions
English corpus composed of manual transcripts and automatic transcripts obtained by three different Automatic Speech Recognition (ASR) systems that exhibit significantly different word error rates. This data belongs to the CLEF 2009 track for QA on speech transcripts.
The main results confirm that syntactic information is very useful for learning to rank question candidates, improving results on both manual and automatic transcripts unless the ASR quality is very low. Overall, the performance of our system is comparable or better than the state-of-the-art on this corpus, confirming the validity of our approach.En aquesta Tesi, presentem un sistema de Question Answering (QA) factual, especialment ajustat per treballar amb documents orals.
En el desenvolupament explorem, per primera vegada, quines tècniques de les habitualment emprades en QA per documents escrit són suficientment robustes per funcionar en l'escenari més difÃcil de documents orals. Amb més especificitat, estudiem nous mètodes de Information Retrieval (IR) dissenyats per tractar amb la veu, i utilitzem diversos nivells d'informació linqüÃstica. Entre aquests s'inclouen, a saber: detecció de Named Entities utilitzant informació fonètica, "parsing" sintà ctic aplicat a transcripcions de veu, i també l'ús d'un sub-sistema de detecció i resolució de la correferència.
La nostra aproximació al problema es recolza en gran part en tècniques supervisades de Machine Learning, estant aquestes enfocades especialment cap a la part d'extracció de la resposta, i fa servir la menor quantitat possible de coneixement creat per humans. En conseqüència, tot el procés de QA pot ser adaptat a altres dominis o altres llengües amb relativa facilitat.
Un dels resultats addicionals de la feina darrere d'aquesta Tesis ha estat que hem impulsat i coordinat la creació d'un marc d'avaluació de la taska de QA en documents orals. Aquest marc de treball, anomenat QAst (Question Answering on Speech Transcripts), proporciona un corpus de documents orals multi-lingüe, uns conjunts de preguntes d'avaluació, i les respostes correctes d'aquestes. Aquestes dades han estat utilitzades en les evaluacionis QAst que han tingut lloc en el si de les conferències CLEF en els anys 2007, 2008 i 2009; d'aquesta manera s'ha promogut i ajudat a la creació d'un estat-de-l'art de tècniques adreçades a aquest problema en particular.
El sistema de QA que presentem i tots els seus particulars sumbòduls, han estat avaluats extensivament utilitzant el corpus EPPS (transcripcions de les Sessions Plenaries del Parlament Europeu) en anglès, que cónté transcripcions manuals de tots els discursos i també transcripcions automà tiques obtingudes mitjançant tres reconeixedors automà tics de la parla (ASR) diferents. Els reconeixedors tenen caracterÃstiques i resultats diferents que permetes una avaluació quantitativa i qualitativa de la tasca. Aquestes dades pertanyen a l'avaluació QAst del 2009.
Els resultats principals de la nostra feina confirmen que la informació sintà ctica és mol útil per aprendre automà ticament a valorar la plausibilitat de les respostes candidates, millorant els resultats previs tan en transcripcions manuals com transcripcions automà tiques, descomptat que la qualitat de l'ASR sigui molt baixa. En general, el rendiment del nostre sistema és comparable o millor que els altres sistemes pertanyents a l'estat-del'art, confirmant aixà la validesa de la nostra aproximació
Un modelo numérico para el análisis no lineal de estructuras laminares de revolución de hormigón pretensado
Se lia desarrollado un método numérico de análisis para el estudio de la respuesta no lineal, por la geometrÃa y el material, de estructuras laminares de revolución de hormigón armado y pretensado. Para ello se ha utilizado el Método de los Elementos Finitos. La geometrÃa de la lámina se modeliza mediante elementos isoparamétricos de tres nodos. Mediante un modelo niulticapa se representa el armado y la variación de las propiedades del hormigón en el espesor
de la lámina. El liormigón se considera sometido a un estado biaxial de tensiones en la lámina, y uiiiasial en los anillos rigidizadores. El método incluye la modelización del pretensado y de sus efectos estructurales. El modelo desarrollado ha sido implementado numéricamente en el
programa de ordenador AXSHL. El correcto funcionamiento del método ha sido comprobado
mediante la comparación con resultados de ejemplos de solución analÃtica o numérica conocida. Los ejemplos numéricos presentados ilustran la validez del modelo realizado para la predicción de la capacidad última de estas estructuras, y de su comportamiento bajo altos niveles de carga eii general.In this paper, a numerical method for the nonlinear geometric and material analysis of
asisyinmetric reinforced and prestressed concrete shell structures, is presented. This method is based on the Finite Element Teclinique of analysis. Tlie shell geometry has been modelled by isoparan~etric elements of tliree nodes. A multi-layered model is used to describe the reinforcemeiit and the changes in tlie concrete properties across the shell thicl<ness. Concrete is assumed to be submitted to a biasial stress state in tlie shell, and a uniasial stress state in
the ring-beams. Tlie metliod includes the inodelling of prestressing and its structural effects. Based on the preseiit niimerical inodel, a coiiiputer program (AXSIIL) has been developed. Tlie niimerical metliod has beeil proved to yield good results by coinparison witli examples wliose
solution is known aiialiticaly or nuinerically. Tlie numerical examples included in this paper also sliow tlie capability of tlie preseiit model to predict tlie ultimate load of sucli structures as
well as tlieir general beliavior uiider liigli load levels.Peer Reviewe
The almost isomorphism relation for simple regular rings
A longstanding open problem in the theory of von Neumann regular rings is the question of whether every directly finite simple regular ring must be unit-regular. Recent work on this problem has been done by P. Menal, K.C . O'Meara, and the authors. To clarify some aspects of these new developments, we introduce and study the notion of almost isomorphism between finitely generated projective modules over a simple regular ring
A new view on exoplanet transits: Transit of Venus described using three-dimensional solar atmosphere Stagger-grid simulations
Stellar activity and, in particular, convection-related surface structures,
potentially cause fluctuations that can affect the transit light curves.
Surface convection simulations can help the interpretation of ToV. We used
realistic three-dimensional radiative hydrodynamical simulation of the Sun from
the Stagger-grid and synthetic images computed with the radiative transfer code
Optim3D to provide predictions for the transit of Venus in 2004 observed by the
satellite ACRIMSAT. We computed intensity maps from RHD simulation of the Sun
and produced synthetic stellar disk image. We computed the light curve and
compared it to the ACRIMSAT observations and also to the light curves obtained
with solar surface representations carried out using radial profiles with
different limb-darkening laws. We also applied the same spherical tile imaging
method to the observations of center-to-limb Sun granulation with HINODE. We
managed to explain ACRIMSAT observations of 2004 ToV and showed that the
granulation pattern causes fluctuations in the transit light curve. We
evaluated the contribution of the granulation to the ToV. We showed that the
granulation pattern can partially explain the observed discrepancies between
models and data. This confirms that the limb-darkening and the granulation
pattern simulated in 3D RHD Sun represent well what is imaged by HINODE. In the
end, we found that the Venus's aureole contribution during ToV is less intense
than the solar photosphere, and thus negligible. Being able to explain
consistently the data of 2004 ToV is a new step forward for 3D RHD simulations
that are becoming essential for the detection and characterization of
exoplanets. They show that the granulation have to be considered as an
intrinsic incertitude, due to the stellar variability, on precise measurements
of exoplanet transits of, most likely, planets with small diameters.Comment: Accepted for publication in Astronomy and Astrophysic
Comentaris a les llistes d'aus capturades a Mallorca de B. Nadal, perÃode 1970-1982
Comentaris a les llistes d’Aus capturades a Mallorca, perÃode 1970- 1982. El present article és un recull de comentaris i observacions sobre les espècies més interessants que s’anomenen al treball d’en Bartomeu Nadal. Es fa una comparació dels estatus actuals de les espècies de les llistes amb la quantitat d’exemplars capturats i les dates de captura. Per algunes espècies es suggereix un canvi de l’estatus actual.Commentaries on the lists of Birds captured in Mallorca by B. Nadal, during the periods 1970-1982. This article is the recollection of commentaries and observations on the most interesting species mentioned in Tomeu Nadal’s work.We compare the current status of the species on his lists with the quantity and dates of the birds captured. For some of the species a change of status is suggested
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