1,145 research outputs found
Existence and homogenization of the Rayleigh-B\'enard problem
The Navier-Stokes equation driven by heat conduction is studied. As a
prototype we consider Rayleigh-B\'enard convection, in the Boussinesq
approximation. Under a large aspect ratio assumption, which is the case in
Rayleigh-B\'enard experiments with Prandtl number close to one, we prove the
existence of a global strong solution to the 3D Navier-Stokes equation coupled
with a heat equation, and the existence of a maximal B-attractor. A rigorous
two-scale limit is obtained by homogenization theory. The mean velocity field
is obtained by averaging the two-scale limit over the unit torus in the local
variable
An Abstract Machine for Unification Grammars
This work describes the design and implementation of an abstract machine,
Amalia, for the linguistic formalism ALE, which is based on typed feature
structures. This formalism is one of the most widely accepted in computational
linguistics and has been used for designing grammars in various linguistic
theories, most notably HPSG. Amalia is composed of data structures and a set of
instructions, augmented by a compiler from the grammatical formalism to the
abstract instructions, and a (portable) interpreter of the abstract
instructions. The effect of each instruction is defined using a low-level
language that can be executed on ordinary hardware.
The advantages of the abstract machine approach are twofold. From a
theoretical point of view, the abstract machine gives a well-defined
operational semantics to the grammatical formalism. This ensures that grammars
specified using our system are endowed with well defined meaning. It enables,
for example, to formally verify the correctness of a compiler for HPSG, given
an independent definition. From a practical point of view, Amalia is the first
system that employs a direct compilation scheme for unification grammars that
are based on typed feature structures. The use of amalia results in a much
improved performance over existing systems.
In order to test the machine on a realistic application, we have developed a
small-scale, HPSG-based grammar for a fragment of the Hebrew language, using
Amalia as the development platform. This is the first application of HPSG to a
Semitic language.Comment: Doctoral Thesis, 96 pages, many postscript figures, uses pstricks,
pst-node, psfig, fullname and a macros fil
Amalia -- A Unified Platform for Parsing and Generation
Contemporary linguistic theories (in particular, HPSG) are declarative in
nature: they specify constraints on permissible structures, not how such
structures are to be computed. Grammars designed under such theories are,
therefore, suitable for both parsing and generation. However, practical
implementations of such theories don't usually support bidirectional processing
of grammars. We present a grammar development system that includes a compiler
of grammars (for parsing and generation) to abstract machine instructions, and
an interpreter for the abstract machine language. The generation compiler
inverts input grammars (designed for parsing) to a form more suitable for
generation. The compiled grammars are then executed by the interpreter using
one control strategy, regardless of whether the grammar is the original or the
inverted version. We thus obtain a unified, efficient platform for developing
reversible grammars.Comment: 8 pages postscrip
On the Similarities Between Native, Non-native and Translated Texts
We present a computational analysis of three language varieties: native,
advanced non-native, and translation. Our goal is to investigate the
similarities and differences between non-native language productions and
translations, contrasting both with native language. Using a collection of
computational methods we establish three main results: (1) the three types of
texts are easily distinguishable; (2) non-native language and translations are
closer to each other than each of them is to native language; and (3) some of
these characteristics depend on the source or native language, while others do
not, reflecting, perhaps, unified principles that similarly affect translations
and non-native language.Comment: ACL2016, 12 page
Reef society and the tyranny of data
Modern science now approaches divergent processes in many areas, including health assessments of marine eco-systems and social aspects of marine species. Scientific data have long enjoyed a reputation for objectivity but incidents of science-for-hire, data spinning/skewing and political jading are more frequent than ever. In the field of reef creature sensitivity, technical treatises can “logically” explain away what a person of average education can clearly observe on any given reef. Western medicine discounted anecdotal evidence of any cure outside the 4% margin of error until those cures demanded attention and in some cases application. Modern science must now enter an age of practical truth, with data presented, interpreted and peer-reviewed in a common-sense context without regard for political or commercial expediency. A wealth of empirical content combined with credible observations and even a dose of empathy for social order in gill-breathing species makes Balcombe’s new book a welcome contribution
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