4,683 research outputs found
Textual Economy through Close Coupling of Syntax and Semantics
We focus on the production of efficient descriptions of objects, actions and
events. We define a type of efficiency, textual economy, that exploits the
hearer's recognition of inferential links to material elsewhere within a
sentence. Textual economy leads to efficient descriptions because the material
that supports such inferences has been included to satisfy independent
communicative goals, and is therefore overloaded in Pollack's sense. We argue
that achieving textual economy imposes strong requirements on the
representation and reasoning used in generating sentences. The representation
must support the generator's simultaneous consideration of syntax and
semantics. Reasoning must enable the generator to assess quickly and reliably
at any stage how the hearer will interpret the current sentence, with its
(incomplete) syntax and semantics. We show that these representational and
reasoning requirements are met in the SPUD system for sentence planning and
realization.Comment: 10 pages, uses QobiTree.te
Social capital at work How family, friends and civic ties relate to labour market outcomes
This paper investigates the extent to which an individual's 'stock' of social capital relates to labour force outcomes, over and above more well established determinants. In particular, it examines how family and kinship networks, friends and neighbours relate to individual labour market outcomes, compared with the role of civic ties and institutional networks. Using data collected from a national random sample of 1500 Australians, the paper investigates the relative impact of trust, bonding, bridging and linking relationships upon labour force status and successful job search method.
Anaphora and Discourse Structure
We argue in this paper that many common adverbial phrases generally taken to
signal a discourse relation between syntactically connected units within
discourse structure, instead work anaphorically to contribute relational
meaning, with only indirect dependence on discourse structure. This allows a
simpler discourse structure to provide scaffolding for compositional semantics,
and reveals multiple ways in which the relational meaning conveyed by adverbial
connectives can interact with that associated with discourse structure. We
conclude by sketching out a lexicalised grammar for discourse that facilitates
discourse interpretation as a product of compositional rules, anaphor
resolution and inference.Comment: 45 pages, 17 figures. Revised resubmission to Computational
Linguistic
Microbial diversity in the thermal springs within Hot Springs National Park
The thermal water systems of Hot Springs National Park (HSNP) in Hot Springs, Arkansas exist in relative isolation from other North American thermal systems. The HSNP waters could therefore serve as a unique center of thermophilic microbial biodiversity. However, these springs remain largely unexplored using culture-independent next generation sequencing techniques to classify species of thermophilic organisms. Additionally, HSNP has been the focus of anthropogenic development, capping and diverting the springs for use in recreational bathhouse facilities. Human modification of these springs may have impacted the structure of these bacterial communities compared to springs left in a relative natural state. The goal of this study was to compare the community structure in two capped springs and two uncapped springs in HSNP, as well as broadly survey the microbial diversity of the springs. We used Illumina 16S rRNA sequencing of water samples from each spring, the QIIME workflow for sequence analysis, and generated measures of genera and phyla richness, diversity, and evenness. In total, over 700 genera were detected and most individual samples had more than 100 genera. There were also several uncharacterized sequences that could not be placed in known taxa, indicating the sampled springs contain undescribed bacteria. There was great variation both between sites and within samples, so no significant differences were detected in community structure between sites. Our results suggest that these springs, regardless of their human modification, contain a considerable amount of biodiversity, some of it potentially unique to the study site
Magnetorotational Turbulence and Dynamo in a Collisionless Plasma
We present results from the first 3D kinetic numerical simulation of
magnetorotational turbulence and dynamo, using the local shearing-box model of
a collisionless accretion disc. The kinetic magnetorotational instability grows
from a subthermal magnetic field having zero net flux over the computational
domain to generate self-sustained turbulence and outward angular-momentum
transport. Significant Maxwell and Reynolds stresses are accompanied by
comparable viscous stresses produced by field-aligned ion pressure anisotropy,
which is regulated primarily by the mirror and ion-cyclotron instabilities
through particle trapping and pitch-angle scattering. The latter endow the
plasma with an effective viscosity that is biased with respect to the
magnetic-field direction and spatio-temporally variable. Energy spectra suggest
an Alfv\'en-wave cascade at large scales and a kinetic-Alfv\'en-wave cascade at
small scales, with strong small-scale density fluctuations and weak
non-axisymmetric density waves. Ions undergo non-thermal particle acceleration,
their distribution accurately described by a kappa distribution. These results
have implications for the properties of low-collisionality accretion flows,
such as that near the black hole at the Galactic center.Comment: 6 pages, 6 figures, accepted for publication in Physical Review
Letter
Representing scope in intuitionistic deductions
AbstractIntuitionistic proofs can be segmented into scopes which describe when assumptions can be used. In standard descriptions of intuitionistic logic, these scopes occupy contiguous regions of proofs. This leads to an explosion in the search space for automated deduction, because of the difficulty of planning to apply a rule inside a particular scoped region of the proof. This paper investigates an alternative representation which assigns scope explicitly to formulas, and which is inspired in part by semantics-based translation methods for modal deduction. This calculus is simple and is justified by direct proof-theoretic arguments that transform proofs in the calculus so that scopes match standard descriptions. A Herbrand theorem, established straightforwardly, lifts this calculus to incorporate unification. The resulting system has no impermutabilities whatsoever — rules of inference may be used equivalently anywhere in the proof. Nevertheless, a natural specification describes how λ-terms are to be extracted from its deductions
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