Semi-classical analysis of a random walk on a manifold

We prove a sharp rate of convergence to stationarity for a natural random walk on a compact Riemannian manifold $(M,g)$. The proof includes a detailed study of the spectral theory of the associated operator.Comment: Published in at http://dx.doi.org/10.1214/09-AOP483 the Annals of Probability (http://www.imstat.org/aop/) by the Institute of Mathematical Statistics (http://www.imstat.org

Gibbs/Metropolis algorithms on a convex polytope

This paper gives sharp rates of convergence for natural versions of the Metropolis algorithm for sampling from the uniform distribution on a convex polytope. The singular proposal distribution, based on a walk moving locally in one of a fixed, finite set of directions, needs some new tools. We get useful bounds on the spectrum and eigenfunctions using Nash and Weyl-type inequalities. The top eigenvalues of the Markov chain are closely related to the Neuman eigenvalues of the polytope for a novel Laplacian.Comment: 21 pages, 1 figur

Organizational and Individual Determinants of Atypical Employment: The Case of Multiple Jobholding and Self-Employment

Traditionally, the company has been attributed relative control over employees' career paths, particularly in the case of very active organizational management. However, the growing need for organizational flexibility has led to the increasing recourse to atypical work, which in turn contributes to consolidating new careers in which the themes of control and autonomy acquire new meaning. Of these forms of atypical work, multiple jobholding and self-employment have particularly intrigued researchers. Using data compiled by Statistics Canada, we have sought to identify, through logistic regression analyses, the factors that influence the probability of belonging to these two categories of atypical employment. Our results suggest that the influence factors are not identical for the non-standard two job categories studied. Sector of activity, sex and the absence of promotion have a considerable impact on the probability of joining the ranks of the self-employed, whereas professional category and frequency of movement significantly influence the probability of belonging to the multiple jobholder group. Our results also show that the makeup of the populations engaging in these two forms of atypical work is not homogeneous, and that belonging to one of these groups does not necessarily entail precarious living and working conditions. Le rôle traditionnel de la gestion de carrière attribuait à l'entreprise un certain contrôle sur le cheminement des individus, dans la mesure où la prise en charge organisationnelle était très active. Toutefois, le besoin incessant de flexibilité organisationnelle, qui mène à l'utilisation croissante du travail atypique, contribue à la consolidation des nouvelles carrières dans lesquelles les thèmes du contrôle et de l'autonomie sont questionnés. Parmi ces formes de travail atypique, le cumul d'emplois et le travail autonome/à son compte ont particulièrement retenu l'attention des chercheurs. En utilisant des données produites par Statistique Canada, nous avons cherché à identifier, par l'entremise des analyses de régression logistique, les facteurs qui influencent la probabilité de faire partie de ces deux catégories d'emploi atypique. Nos résultats suggèrent que les facteurs d'influence ne sont pas les mêmes pour les deux catégories d'emploi non standard considérées. Le secteur d'activité, le sexe et les promotions jouent davantage sur la probabilité de joindre les effectifs des autonomes/à son compte alors que la catégorie professionnelle, la fréquence du mouvement et l'absence de promotion influencent davantage la probabilité d'appartenir au groupe des cumulards. Finalement, nos résultats montrent que les effectifs de ces deux types de travail atypique ne sont pas homogènes et que l'appartenance à l'un ou l'autre de ces groupes n'implique pas exclusivement la précarité des conditions de vie et de travail.Multiple jobholding, self-employment, new career, Travail atypique, cumul d'emplois, travail autonome/à son compte, flexibilité organisationnelle

Bubble formation at a flexible orifice with liquid cross-flow

In waste water treatment, biological processes for denitrification and nitrification are performed using oxidation ditches. In these reactors, the mixing and the aeration functions are dissociated: a bubble cloud is generated from flexible membrane spargers and is subjected to a horizontal liquid flow. The objective of this paper is to study the effects of the liquid crossflow on the bubble formation at a single flexible orifice in water. The several forces acting on the forming bubble have been modelled in order to understand the dynamics of the bubble growth and detachment. The bubble detachment is controlled by the drag force due to the liquid motion and not by the buoyancy force. The experimental analysis of the bubble growth has shown that, under liquid cross-flow conditions, the bubbles move downstream and are flattened during their growth (position of the bubble centre of gravity, bubble inclination angle). The bubbles spread over the orifice surface, and the advancing and the receding bubble angles were measured. The detached bubbles have significantly smaller sizes and higher frequencies when compared to bubble formation under quiescent liquid conditions

High numerical aperture holographic microscopy reconstruction with extended z range

An holographic microscopy reconstruction method compatible with high numerical aperture microscope objective (MO) up to NA=1.4 is proposed. After off axis and reference field curvature corrections, and after selection of the +1 grating order holographic image, a phase mask that transforms the optical elements of the holographic setup into an afocal device is applied in the camera plane. The reconstruction is then made by the angular spectrum method. The field is first propagated in the image half space from the camera to the afocal image of the MO optimal plane (plane for which MO has been designed) by using a quadratic kernel. The field is then propagated from the MO optimal plane to the object with the exact kernel. Calibration of the reconstruction is made by imaging a calibrated object like an USAF resolution target for different positions along $z$. Once the calibration is done, the reconstruction can be made with an object located in any plane $z$. The reconstruction method has been validated experimentally with an USAF target imaged with a NA=1.4 microscope objective. Near-optimal resolution is obtained over an extended range ($\pm 50~\mu$m) of $z$ locations

Holographic microscopy reconstruction in both object and image half spaces with undistorted 3D grid

We propose an holographic microscopy reconstruction method, which propagates the hologram, in the object half space, in the vicinity of the object. The calibration yields reconstructions with an undistorted reconstruction grid i.e. with orthogonal $x$, $y$ and $z$ axis and constant pixels pitch. The method is validated with an USAF target imaged by a $\times$60 microscope objective, whose holograms are recorded and reconstructed for different USAF locations along the longitudinal axis: -75 to +75 $\mu$m. Since the reconstruction numerical phase mask, the reference phase curvature and MO form an afocal device, the reconstruction can be interpreted as occurring equivalently in the object or in image half space

Microtraps for neutral atoms using superconducting structures in the critical state

Recently demonstrated superconducting atom-chips provide a platform for trapping atoms and coupling them to solid-state quantum systems. Controlling these devices requires a full understanding of the supercurrent distribution in the trapping structures. For type-II superconductors, this distribution is hysteretic in the critical state due to the partial penetration of the magnetic field in the thin superconducting film through pinned vortices. We report here an experimental observation of this memory effect. Our results are in good agreement with the redictions of the Bean model of the critical state without adjustable parameters. The memory effect allows to write and store permanent currents in micron-sized superconducting structures and paves the way towards new types of engineered trapping potentials.Comment: accepted in Phys. Rev.

Foreground-Background Ambient Sound Scene Separation

Ambient sound scenes typically comprise multiple short events occurring on top of a somewhat stationary background. We consider the task of separating these events from the background, which we call foreground-background ambient sound scene separation. We propose a deep learning-based separation framework with a suitable feature normaliza-tion scheme and an optional auxiliary network capturing the background statistics, and we investigate its ability to handle the great variety of sound classes encountered in ambient sound scenes, which have often not been seen in training. To do so, we create single-channel foreground-background mixtures using isolated sounds from the DESED and Audioset datasets, and we conduct extensive experiments with mixtures of seen or unseen sound classes at various signal-to-noise ratios. Our experimental findings demonstrate the generalization ability of the proposed approach

The flow structure behind vortex generators embedded in a decelerating turbulent boundary layer

The objective of the present work is to analyse the behaviour of a turbulent decelerating boundary layer under the effect of both passive and active jets vortex generators (VGs). The stereo PIV database of Godard and Stanislas [1, 2] obtained in an adverse pressure gradient boundary layer is used for this study. After presenting the effect on the mean velocity field and the turbulent kinetic energy, the line of analysis is extended with two points spatial correlations and vortex detection in instantaneous velocity fields. It is shown that the actuators concentrate the boundary layer turbulence in the region of upward motion of the flow, and segregate the near-wall streamwise vortices of the boundary layer based on their vorticity sign