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 $S$ of subsets of $\mathbb{R}^d$ and of point sets that are (almost) subadditive in their first variable. Denoting by $\xi$ the random parking measure in $\mathbb{R}^d$, and by $\xi^R$ the random parking measure in the cube $Q_R=(-R,R)^d$, we show, under some natural assumptions on $S$, that there exists a constant $\bar{S}\in \mathbb{R}$ such that % $$\lim_{R\to +\infty} \frac{S(Q_R,\xi)}{|Q_R|}\,=\,\lim_{R\to +\infty}\frac{S(Q_R,\xi^R)}{|Q_R|}\,=\,\bar{S}$$ % almost surely. If $\zeta \mapsto S(Q_R,\zeta)$ is the counting measure of $\zeta$ in $Q_R$, 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 $\sim 100$ GeV. We also discuss inflation as well as gravity wave smoking gun signatures of this class of models.Comment: 22 pages, 7 figure