1,858 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
Coupling and higher-order effects in the 12C(d,p)13C and 13C(p,d)12C reactions
Coupled channels calculations are performed for the 12C(d,p)13C and
13C(p,d)12C reactions between 7 and 60 MeV to study the effect of inelastic
couplings in transfer reactions. The effect of treating transfer beyond Born
approximation is also addressed. The coupling to the 12C 2+ state is found to
change the peak cross-section by up to 15 %. Effects beyond Born approximation
lead to a significant renormalization of the cross-sections, between 5 and 10 %
for deuteron energies above 10 MeV, and larger than 10 % for lower energies. We
also performed calculations including the remnant term in the transfer
operator, which has a small impact on the 12C(d,p)13C(g.s.) and
13C(p,d)12C(g.s.) reactions. Above 30 MeV deuteron energy, the effect of the
remnant term is larger than 10 % for the 12C(d,p)13C(3.09 MeV) reaction and is
found to increase with decreasing neutron separation energy for the 3.09 MeV
state of 13C. This is of importance for transfer reactions with weakly bound
nuclei.Comment: 7 pages, 7 figures, submitted to Phys. Rev.
Random parking, Euclidean functionals, and rubber elasticity
We study subadditive functions of the random parking model previously
analyzed by the second author. In particular, we consider local functions
of subsets of and of point sets that are (almost) subadditive in
their first variable. Denoting by the random parking measure in
, and by the random parking measure in the cube
, we show, under some natural assumptions on , that there
exists a constant such that % % almost surely. If is the counting measure of in , then we
retrieve the result by the second author on the existence of the jamming limit.
The present work generalizes this result to a wide class of (almost)
subadditive functions. In particular, classical Euclidean optimization problems
as well as the discrete model for rubber previously studied by Alicandro,
Cicalese, and the first author enter this class of functions. In the case of
rubber elasticity, this yields an approximation result for the continuous
energy density associated with the discrete model at the thermodynamic limit,
as well as a generalization to stochastic networks generated on bounded sets.Comment: 28 page
The form and function of avian rictal bristles
Although mechanoreception is present throughout the animal kingdom, it is still relatively under-studied and poorly understood, especially in nocturnal birds. A particular type of facial feather, the rictal bristles, are thought to carry out a similar tactile function to mammalian whiskers, of which they superficially resemble. If they do, such a function could enhance foraging behaviour and facilitate obstacle avoidance, especially in dark, complex habitats. However, as rictal bristles are the least described of any feather, little is known about them. Therefore, this thesis characterises rictal bristle form and function by describing: i) bristle morphology and follicle anatomy, ii) the development of rictal bristles, and iii) the associated mechanosensory brain areas. It will also explore: iv) rictal bristle evolution and v) function. Results in this thesis demonstrated that rictal bristle morphology and the presence of mechanoreceptors around the follicle varied between species. Specifically, diurnal species did not have mechanoreceptors around their bristle follicles and had shorter bristles. Associated mechanosensory brain areas also varied between species, but there was no clear association between the neuroanatomy, rictal bristle morphology or foraging traits. Rictal bristles were absent in two species of altricial hatchlings, and only emerged after their eyes opened. Stimulation of the rictal region in these chicks led to behavioural feeding responses, especially coinciding with when chicks started to feed independently. Rictal bristle evolution underwent multiple events of disappearance and gain during avian evolution, and therefore, the presence and morphology of the rictal bristles also varied between orders, families and genera. Short rictal bristles with barbs at the base were likely to be present in the common ancestor of the phylogeny (108 mya). Rictal bristle presence and length were associated with nocturnality and foraging methods, and diet is also likely to be associated with rictal bristle length. Consequently, this thesis suggests that, in adult birds, rictal bristles are likely to act as facial tactile sensors in species that forage in low-light conditions in complex habitats. Rictal bristles are may, therefore, play a role in collision avoidance, foraging and eye protection. Species foraging in the daytime might have rictal bristles with a reduced tactile function. However, identifying rictal bristle function is challenging and demands further investigation. This thesis provides the first comparative description of avian rictal bristle form and function, and is an important foundation for further investigation of the sense of touch in birds
Détection et classification de courroies défectueuses par analyse acoustique. Comparaison entre une approche temps-fréquence et une approche statistique d'ordre supérieur.
Les développements récents en traitement du signal ont permis de nouvelles approches en matière de détection et de classification de signaux à faible RSB. Nous proposons dans cet article une comparaison de trois approches d'un problème de détection à hypothèses multiples, la première issue de la théorie classique de la détection, la suivante s'appuyant sur une analyse temps-fréquence des signaux, et la dernière exploitant l'apport des statistiques d'ordre supérieur. Ces approches sont tout d'abord testées en simulation, pour être ensuite appliquées dans un contexte industriel, à la détection et à la classification de courroies défectueuses sur une turbine de séchage en vue d'un contrôle acoustique de qualité
On well-posedness, stability, and bifurcation for the axisymmetric surface diffusion flow
In this article, we study the axisymmetric surface diffusion flow (ASD), a
fourth-order geometric evolution law. In particular, we prove that ASD
generates a real analytic semiflow in the space of (2 + \alpha)-little-H\"older
regular surfaces of revolution embedded in R^3 and satisfying periodic boundary
conditions. We also give conditions for global existence of solutions and prove
that solutions are real analytic in time and space. Further, we investigate the
geometric properties of solutions to ASD. Utilizing a connection to
axisymmetric surfaces with constant mean curvature, we characterize the
equilibria of ASD. Then, focusing on the family of cylinders, we establish
results regarding stability, instability and bifurcation behavior, with the
radius acting as a bifurcation parameter for the problem.Comment: 37 pages, 6 figures, To Appear in SIAM J. Math. Ana
Cosmological Consequences of Nearly Conformal Dynamics at the TeV scale
Nearly conformal dynamics at the TeV scale as motivated by the hierarchy
problem can be characterized by a stage of significant supercooling at the
electroweak epoch. This has important cosmological consequences. In particular,
a common assumption about the history of the universe is that the reheating
temperature is high, at least high enough to assume that TeV-mass particles
were once in thermal equilibrium. However, as we discuss in this paper, this
assumption is not well justified in some models of strong dynamics at the TeV
scale. We then need to reexamine how to achieve baryogenesis in these theories
as well as reconsider how the dark matter abundance is inherited. We argue that
baryonic and dark matter abundances can be explained naturally in these setups
where reheating takes place by bubble collisions at the end of the strongly
first-order phase transition characterizing conformal symmetry breaking, even
if the reheating temperature is below the electroweak scale GeV. We
also discuss inflation as well as gravity wave smoking gun signatures of this
class of models.Comment: 22 pages, 7 figure
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