34 research outputs found
Algorithms for Analysing the Temporal Structure of Discourse
We describe a method for analysing the temporal structure of a discourse
which takes into account the effects of tense, aspect, temporal adverbials and
rhetorical structure and which minimises unnecessary ambiguity in the temporal
structure. It is part of a discourse grammar implemented in Carpenter's ALE
formalism. The method for building up the temporal structure of the discourse
combines constraints and preferences: we use constraints to reduce the number
of possible structures, exploiting the HPSG type hierarchy and unification for
this purpose; and we apply preferences to choose between the remaining options
using a temporal centering mechanism. We end by recommending that an
underspecified representation of the structure using these techniques be used
to avoid generating the temporal/rhetorical structure until higher-level
information can be used to disambiguate.Comment: EACL '95, 8 pages, 1 eps picture, tar-ed, compressed, uuencoded, uses
eaclap.sty, a4wide.sty, epsf.te
Temporal Relations: Reference or Discourse Coherence?
The temporal relations that hold between events described by successive
utterances are often left implicit or underspecified. We address the role of
two phenomena with respect to the recovery of these relations: (1) the
referential properties of tense, and (2) the role of temporal constraints
imposed by coherence relations. We account for several facets of the
identification of temporal relations through an integration of these.Comment: To appear in the Proceedings of ACL-94, Student Session. 5 pages,
LaTeX source, requires lingmacros. Comments are welcom
Multiple-grid acceleration of Lax-Wendroff algorithms
A technique for accelerating the convergence of a one-step Lax-Wendroff method to a steady-state solution is discussed and its applicability extended to the more general class of two-step Lax-Wendroff methods. Several two-step methods which lead to quite efficient multiple grid algorithms are discussed. Computational results are presented using the full two dimensional Euler equations for both subcritical and shocked supercritical flows. Extensions and generalizations are mentioned
An Empirical Approach to Temporal Reference Resolution
This paper presents the results of an empirical investigation of temporal
reference resolution in scheduling dialogs. The algorithm adopted is primarily
a linear-recency based approach that does not include a model of global focus.
A fully automatic system has been developed and evaluated on unseen test data
with good results. This paper presents the results of an intercoder reliability
study, a model of temporal reference resolution that supports linear recency
and has very good coverage, the results of the system evaluated on unseen test
data, and a detailed analysis of the dialogs assessing the viability of the
approach.Comment: 13 pages, latex using aclap.st
Radiation-hydrodynamical modelling of Core-Collapse Supernovae: light curves and the evolution of photospheric velocity and temperature
We have developed a relativistic, radiation-hydrodynamics Lagrangian code,
specifically tailored to simulate the evolution of the main observables (light
curve, evolution of photospheric velocity and temperature) in core-collapse
supernova (CC-SN) events. The distinctive features of the code are an accurate
treatment of radiative transfer coupled to relativistic hydrodynamics, a
self-consistent treatment of the evolution of the innermost ejecta taking into
account the gravitational effects of the central compact remnant, and a fully
implicit Lagrangian approach to the solution of the coupled non-linear finite
difference system of equations. Our aim is to use it as numerical tool to
perform calculations of grid of models to be compared with observation of
CC-SNe. In this paper we present some testcase simulations and a comparison
with observations of SN 1987A, as well as with the results obtained with other
numerical codes. We also briefly discuss the influence of the main physical
parameters (ejected mass, progenitor radius, explosion energy, amount of
\chem{56}{Ni}) on the evolution of the ejecta, and the implications of our
results in connection with the possibility to "standardize" hydrogen-rich
CC-SNe for using them as candles to measure cosmological distances.Comment: Accepted for publication in ApJ (16 pages, 22 figures