589 research outputs found
RBF neural net based classifier for the AIRIX accelerator fault diagnosis
The AIRIX facility is a high current linear accelerator (2-3.5kA) used for
flash-radiography at the CEA of Moronvilliers France. The general background of
this study is the diagnosis and the predictive maintenance of AIRIX. We will
present a tool for fault diagnosis and monitoring based on pattern recognition
using artificial neural network. Parameters extracted from the signals recorded
on each shot are used to define a vector to be classified. The principal
component analysis permits us to select the most pertinent information and
reduce the redundancy. A three layer Radial Basis Function (RBF) neural network
is used to classify the states of the accelerator. We initialize the network by
applying an unsupervised fuzzy technique to the training base. This allows us
to determine the number of clusters and real classes, which define the number
of cells on the hidden and output layers of the network. The weights between
the hidden and the output layers, realising the non-convex union of the
clusters, are determined by a least square method. Membership and ambiguity
rejection enable the network to learn unknown failures, and to monitor
accelerator operations to predict future failures. We will present the first
results obtained on the injector.Comment: 3 pages, 4 figures, LINAC'2000 conferenc
Applications of Frobenius Algebras to Representation Theory of Schur Algebras
AbstractA Schur algebra is a subalgebra of the group algebraRGassociated to a partition ofG, whereGis a finite group andRis a commutative ring. For two classes of Schur algebras we study the relationship between indecomposable modules over the Schur algebra and overRG, but we discuss this problem in a more general context. Further we develop a character theory for Schur algebras; in particular, we express primitive central idempotents in terms of trace functions and we derive orthogonality relations for trace functions. These results are also presented in a more general context, namely for Frobenius algebras over rings. Moreover, we focus on class functions on Schur algebras
Average characteristic polynomials in the two-matrix model
The two-matrix model is defined on pairs of Hermitian matrices of
size by the probability measure where
and are given potential functions and \tau\in\er. We study averages
of products and ratios of characteristic polynomials in the two-matrix model,
where both matrices and may appear in a combined way in both
numerator and denominator. We obtain determinantal expressions for such
averages. The determinants are constructed from several building blocks: the
biorthogonal polynomials and associated to the two-matrix
model; certain transformed functions and \Q_n(v); and finally
Cauchy-type transforms of the four Eynard-Mehta kernels , ,
and . In this way we generalize known results for the
-matrix model. Our results also imply a new proof of the Eynard-Mehta
theorem for correlation functions in the two-matrix model, and they lead to a
generating function for averages of products of traces.Comment: 28 pages, references adde
Non-colliding Brownian Motions and the extended tacnode process
We consider non-colliding Brownian motions with two starting points and two
endpoints. The points are chosen so that the two groups of Brownian motions
just touch each other, a situation that is referred to as a tacnode. The
extended kernel for the determinantal point process at the tacnode point is
computed using new methods and given in a different form from that obtained for
a single time in previous work by Delvaux, Kuijlaars and Zhang. The form of the
extended kernel is also different from that obtained for the extended tacnode
kernel in another model by Adler, Ferrari and van Moerbeke. We also obtain the
correlation kernel for a finite number of non-colliding Brownian motions
starting at two points and ending at arbitrary points.Comment: 38 pages. In the revised version a few arguments have been expanded
and many typos correcte
The influence of microgravity on invasive growth in Saccharomyces cerevisiae
This study investigates the effects of microgravity on colony growth and the morphological transition from single cells to short invasive filaments in the model eukaryotic organism Saccharomyces cerevisiae. Two-dimensional spreading of the yeast colonies grown on semi-solid agar medium was reduced under microgravity in the Sigma 1278b laboratory strain but not in the CMBSESA1 industrial strain. This was supported by the Sigma 1278b proteome map under microgravity conditions, which revealed upregulation of proteins linked to anaerobic conditions. The Sigma 1278b strain showed a reduced invasive growth in the center of the yeast colony. Bud scar distribution was slightly affected, with a switch toward more random budding. Together, microgravity conditions disturb spatially programmed budding patterns and generate strain-dependent growth differences in yeast colonies on semi-solid medium
Non-intersecting squared Bessel paths at a hard-edge tacnode
The squared Bessel process is a 1-dimensional diffusion process related to
the squared norm of a higher dimensional Brownian motion. We study a model of
non-intersecting squared Bessel paths, with all paths starting at the same
point at time and ending at the same point at time . Our
interest lies in the critical regime , for which the paths are tangent
to the hard edge at the origin at a critical time . The critical
behavior of the paths for is studied in a scaling limit with time
and temperature . This leads to a critical
correlation kernel that is defined via a new Riemann-Hilbert problem of size
. The Riemann-Hilbert problem gives rise to a new Lax pair
representation for the Hastings-McLeod solution to the inhomogeneous Painlev\'e
II equation where with
the parameter of the squared Bessel process. These results extend
our recent work with Kuijlaars and Zhang \cite{DKZ} for the homogeneous case
.Comment: 54 pages, 13 figures. Corrected error in Theorem 2.
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