6,084 research outputs found
Computational methods and software systems for dynamics and control of large space structures
Two key areas of crucial importance to the computer-based simulation of large space structures are discussed. The first area involves multibody dynamics (MBD) of flexible space structures, with applications directed to deployment, construction, and maneuvering. The second area deals with advanced software systems, with emphasis on parallel processing. The latest research thrust in the second area involves massively parallel computers
On the first k moments of the random count of a pattern in a multi-states sequence generated by a Markov source
In this paper, we develop an explicit formula allowing to compute the first k
moments of the random count of a pattern in a multi-states sequence generated
by a Markov source. We derive efficient algorithms allowing to deal both with
low or high complexity patterns and either homogeneous or heterogenous Markov
models. We then apply these results to the distribution of DNA patterns in
genomic sequences where we show that moment-based developments (namely:
Edgeworth's expansion and Gram-Charlier type B series) allow to improve the
reliability of common asymptotic approximations like Gaussian or Poisson
approximations
Importance sampling the union of rare events with an application to power systems analysis
We consider importance sampling to estimate the probability of a union
of rare events defined by a random variable . The
sampler we study has been used in spatial statistics, genomics and
combinatorics going back at least to Karp and Luby (1983). It works by sampling
one event at random, then sampling conditionally on that event
happening and it constructs an unbiased estimate of by multiplying an
inverse moment of the number of occuring events by the union bound. We prove
some variance bounds for this sampler. For a sample size of , it has a
variance no larger than where is the union
bound. It also has a coefficient of variation no larger than
regardless of the overlap pattern among the
events. Our motivating problem comes from power system reliability, where the
phase differences between connected nodes have a joint Gaussian distribution
and the rare events arise from unacceptably large phase differences. In the
grid reliability problems even some events defined by constraints in
dimensions, with probability below , are estimated with a
coefficient of variation of about with only sample
values
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