41,973 research outputs found
Polydispersity Effects in the Dynamics and Stability of Bubbling Flows
The occurrence of swarms of small bubbles in a variety of industrial systems
enhances their performance. However, the effects that size polydispersity may
produce on the stability of kinematic waves, the gain factor, mean bubble
velocity, kinematic and dynamic wave velocities is, to our knowledge, not yet
well established. We found that size polydispersity enhances the stability of a
bubble column by a factor of about 23% as a function of frequency and for a
particular type of bubble column. In this way our model predicts effects that
might be verified experimentally but this, however, remain to be assessed. Our
results reinforce the point of view advocated in this work in the sense that a
description of a bubble column based on the concept of randomness of a bubble
cloud and average properties of the fluid motion, may be a useful approach that
has not been exploited in engineering systems.Comment: 11 pages, 2 figures, presented at the 3rd NEXT-SigmaPhi International
Conference, 13-18 August, 2005, Kolymbari, Cret
Optimal random sampling designs in random field sampling
A Horvitz-Thompson predictor is proposed for spatial sampling when the characteristic of interest is modeled as a random field. Optimal sampling designs are deduced under this context. Fixed and variable sample size are considered
Maxwell Superalgebras and Abelian Semigroup Expansion
The Abelian semigroup expansion is a powerful and simple method to derive new
Lie algebras from a given one. Recently it was shown that the -expansion of
leads us to the Maxwell algebra
. In this paper we extend this result to superalgebras, by proving
that different choices of abelian semigroups lead to interesting
Maxwell Superalgebras. In particular, the minimal Maxwell superalgebra
and the -extended Maxwell superalgebra recently found by the Maurer Cartan expansion procedure, are
derived alternatively as an -expansion of . Moreover we show that new minimal Maxwell superalgebras type
and their -extended generalization can be obtained
using the -expansion procedure.Comment: 31 pages, some clarifications in the abstract,introduction and
conclusion, typos corrected, a reference and acknowledgements added, accepted
for publication in Nuclear Physics
N=1 Supergravity and Maxwell superalgebras
We present the construction of the supergravity action from the minimal
Maxwell superalgebra , which can be derived from the
superalgebra by applying the abelian
semigroup expansion procedure. We show that , pure supergravity can
be obtained alternatively as the MacDowell-Mansouri like action built from the
curvatures of the Maxwell superalgebra . We extend this
result to all minimal Maxwell superalgebras type . The
invariance under supersymmetry transformations is also analized.Comment: 22 pages, published versio
OPTIMAL RANDOM SAMPLING DESIGNS IN RANDOM FIELD SAMPLING
A Horvitz-Thompson predictor is proposed for spatial sampling when the characteristic of interest is modeled as a random field. Optimal sampling designs are deduced under this context. Fixed and variable sample size are considered.
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