27,138 research outputs found
Design optimisation of multistage depressed collectors for high efficiency travelling wave tubes using genetic algorithm.
The design of a symmetric and an asymmetric collector has been optimised using the genetic algorithm. The improvement in collector efficiency in both cases is remarkable
Consistency of a recursive estimate of mixing distributions
Mixture models have received considerable attention recently and Newton
[Sankhy\={a} Ser. A 64 (2002) 306--322] proposed a fast recursive algorithm for
estimating a mixing distribution. We prove almost sure consistency of this
recursive estimate in the weak topology under mild conditions on the family of
densities being mixed. This recursive estimate depends on the data ordering and
a permutation-invariant modification is proposed, which is an average of the
original over permutations of the data sequence. A Rao--Blackwell argument is
used to prove consistency in probability of this alternative estimate. Several
simulations are presented, comparing the finite-sample performance of the
recursive estimate and a Monte Carlo approximation to the permutation-invariant
alternative along with that of the nonparametric maximum likelihood estimate
and a nonparametric Bayes estimate.Comment: Published in at http://dx.doi.org/10.1214/08-AOS639 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
A comparison of the Benjamini-Hochberg procedure with some Bayesian rules for multiple testing
In the spirit of modeling inference for microarrays as multiple testing for
sparse mixtures, we present a similar approach to a simplified version of
quantitative trait loci (QTL) mapping. Unlike in case of microarrays, where the
number of tests usually reaches tens of thousands, the number of tests
performed in scans for QTL usually does not exceed several hundreds. However,
in typical cases, the sparsity of significant alternatives for QTL mapping
is in the same range as for microarrays. For methodological interest, as well
as some related applications, we also consider non-sparse mixtures. Using
simulations as well as theoretical observations we study false discovery rate
(FDR), power and misclassification probability for the Benjamini-Hochberg (BH)
procedure and its modifications, as well as for various parametric and
nonparametric Bayes and Parametric Empirical Bayes procedures. Our results
confirm the observation of Genovese and Wasserman (2002) that for small p the
misclassification error of BH is close to optimal in the sense of attaining the
Bayes oracle. This property is shared by some of the considered Bayes testing
rules, which in general perform better than BH for large or moderate 's.Comment: Published in at http://dx.doi.org/10.1214/193940307000000158 the IMS
Collections (http://www.imstat.org/publications/imscollections.htm) by the
Institute of Mathematical Statistics (http://www.imstat.org
Effective field theory for spinor dipolar Bose Einstein condensates
We show that the effective theory of long wavelength low energy behavior of a
dipolar Bose-Einstein condensate(BEC) with large dipole moments (treated as a
classical spin) can be modeled using an extended Non-linear sigma model (NLSM)
like energy functional with an additional non-local term that represents long
ranged anisotropic dipole-dipole interaction. Minimizing this effective energy
functional we calculate the density and spin-profile of the dipolar
Bose-Einstein condensate in the mean-field regime for various trapping
geometries. The resulting configurations show strong intertwining between the
spin and mass density of the condensate, transfer between spin and orbital
angular momentum in the form of Einstein-de Hass effect, and novel topological
properties. We have also described the theoretical framework in which the
collective excitations around these mean field solutions can be studied and
discuss some examples qualitatively.Comment: Latex + 3 eps figures, accepted for publication in a special issue of
EPJB on "Novel Quantum Phases and Mesoscopic Physics in Quantum Gases
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