22,510 research outputs found
A virtual environment for the design and simulated construction of prefabricated buildings
The construction industry has acknowledged that its current working practices are in need of substantial improvements in quality and efficiency and has identified that computer modelling techniques and the use of prefabricated components can help reduce times, costs, and minimise defects and problems of on-site construction. This paper describes a virtual environment to support the design and construction processes of buildings from prefabricated components and the simulation of their construction sequence according to a project schedule. The design environment can import a library of 3-D models of prefabricated modules that can be used to interactively design a building. Using Microsoft Project, the construction schedule of the designed building can be altered, with this information feeding back to the construction simulation environment. Within this environment the order of construction can be visualised using virtual machines. Novel aspects of the system are that it provides a single 3-D environment where the user can construct their design with minimal user interaction through automatic constraint recognition and view the real-time simulation of the construction process within the environment. This takes this area of research a step forward from other systems that only allow the planner to view the construction at certain stages, and do not provide an animated view of the construction process
Using torsion to manipulate spin currents
We address the problem of quantum particles moving on a manifold
characterised by the presence of torsion along a preferential axis. In fact,
such a torsion may be taylored by the presence of a single screw dislocation,
whose Burgers vector measures the torsion amplitude. The problem, first treated
in the relativistic limit describing fermions that couple minimally to torsion,
is then analysed in the Pauli limit We show that torsion induces a geometric
potential and also that it couples generically to the phase of the wave
function, giving rise to the possibility of using torsion to manipulate spin
currents in the case of spinor wave functions. These results emerge as an
alternative strategy for using screw dislocations in the design of
spintronic-based devices
Speech Recognition by Composition of Weighted Finite Automata
We present a general framework based on weighted finite automata and weighted
finite-state transducers for describing and implementing speech recognizers.
The framework allows us to represent uniformly the information sources and data
structures used in recognition, including context-dependent units,
pronunciation dictionaries, language models and lattices. Furthermore, general
but efficient algorithms can used for combining information sources in actual
recognizers and for optimizing their application. In particular, a single
composition algorithm is used both to combine in advance information sources
such as language models and dictionaries, and to combine acoustic observations
and information sources dynamically during recognition.Comment: 24 pages, uses psfig.st
Beyond Word N-Grams
We describe, analyze, and evaluate experimentally a new probabilistic model
for word-sequence prediction in natural language based on prediction suffix
trees (PSTs). By using efficient data structures, we extend the notion of PST
to unbounded vocabularies. We also show how to use a Bayesian approach based on
recursive priors over all possible PSTs to efficiently maintain tree mixtures.
These mixtures have provably and practically better performance than almost any
single model. We evaluate the model on several corpora. The low perplexity
achieved by relatively small PST mixture models suggests that they may be an
advantageous alternative, both theoretically and practically, to the widely
used n-gram models.Comment: 15 pages, one PostScript figure, uses psfig.sty and fullname.sty.
Revised version of a paper in the Proceedings of the Third Workshop on Very
Large Corpora, MIT, 199
Similarity-Based Models of Word Cooccurrence Probabilities
In many applications of natural language processing (NLP) it is necessary to
determine the likelihood of a given word combination. For example, a speech
recognizer may need to determine which of the two word combinations ``eat a
peach'' and ``eat a beach'' is more likely. Statistical NLP methods determine
the likelihood of a word combination from its frequency in a training corpus.
However, the nature of language is such that many word combinations are
infrequent and do not occur in any given corpus. In this work we propose a
method for estimating the probability of such previously unseen word
combinations using available information on ``most similar'' words.
We describe probabilistic word association models based on distributional
word similarity, and apply them to two tasks, language modeling and pseudo-word
disambiguation. In the language modeling task, a similarity-based model is used
to improve probability estimates for unseen bigrams in a back-off language
model. The similarity-based method yields a 20% perplexity improvement in the
prediction of unseen bigrams and statistically significant reductions in
speech-recognition error.
We also compare four similarity-based estimation methods against back-off and
maximum-likelihood estimation methods on a pseudo-word sense disambiguation
task in which we controlled for both unigram and bigram frequency to avoid
giving too much weight to easy-to-disambiguate high-frequency configurations.
The similarity-based methods perform up to 40% better on this particular task.Comment: 26 pages, 5 figure
The Market of Foreign Exchange Hedge in Brazil: Reactions of Financial Institutions to Interventions of the Central Bank
Between 1999 and 2002, Brazil's Central Bank sold expressive amounts of dollar indexed debt and foreign exchange swaps. This paper shows that in periods of high volatility of the exchange rate, first semester of 1999 and second semester of 2002, the Central Bank of Brazil increased the foreign exchange hedge, but the financial institutions used this to reduce their foreign exchange exposure. In contrast, increases in foreign hedge during periods of low volatility of the exchange rate were transferred to the productive sector.foreign exchange swaps, central bank interventions, foreign exchange risk
Conjugacy classes of p-cycles of type D in alternating groups
We classify the conjugacy classes of p-cycles of type D in alternating
groups. This finishes the open cases in arXiv:0812.4628. We also determine all
the subracks of those conjugacy classes which are not of type D.Comment: Second paragraph of subsection 2.2 rewritten. 4-th sentence of
subsection 2.4 rewritten. More explanations added in Remark 2.4. Lemma 2.5
and Corollary 2.7 added. Appendix removed and put it as Remark 3.1. Remark
3.2 (former 3.1) reorganized. References: [Da], [EGSS], [H], [IS] added,
[GPPS] removed. Communications in Algebra (2014
- …