Efficient implementation of Markov chain Monte Carlo when using an unbiased likelihood estimator

When an unbiased estimator of the likelihood is used within a Metropolis--Hastings chain, it is necessary to trade off the number of Monte Carlo samples used to construct this estimator against the asymptotic variances of averages computed under this chain. Many Monte Carlo samples will typically result in Metropolis--Hastings averages with lower asymptotic variances than the corresponding Metropolis--Hastings averages using fewer samples. However, the computing time required to construct the likelihood estimator increases with the number of Monte Carlo samples. Under the assumption that the distribution of the additive noise introduced by the log-likelihood estimator is Gaussian with variance inversely proportional to the number of Monte Carlo samples and independent of the parameter value at which it is evaluated, we provide guidelines on the number of samples to select. We demonstrate our results by considering a stochastic volatility model applied to stock index returns.Comment: 34 pages, 9 figures, 3 table

Aspect freudien des rites et de leurs répétitions

La mention de la perspective freudienne concernant les rites et leur dimension religieuse se réduit souvent à la seule caractéristique de névrose obsessionnelle. Or, les textes freudiens suivent une orientation différente fondée sur la découverte de l’inconscient. Ce parcours montre d’abord que l’origine de cette assimilation entre rites et névrose obsessionnelle repose sur un mode particulier de recherche de satisfaction. En revanche, l’hystérie donne lieu à une quête de satisfaction différente qui conduit néanmoins à une autre forme de pratiques rituelles. Trois exemples contemporains indiquent la pertinence de l’analyse freudienne. En accordant une importance particulière au sens des rites, voire même à leur dimension symbolique, Freud opère un double renversement

Orientation lacanienne sur les rites

Rites et religion ne conduisent pas inexorablement au constat freudien de la névrose universelle. En effet, les pratiques rituelles n’occupent pas un seul discours. Cette diversité ne soustrait pas les rites au point de vue freudien mais conduit à une autre lecture, celle de l’opération des signifiants. L’orientation lacanienne permet de la mettre en évidence et de la déployer dans sa façon particulière de produire des effets de sens.Rites and religion do not lead inexorably to the Freudian claim of a universal neurosis. In effect, ritual practices do not occupy a single discourse. This diversity does not remove rites from a Freudian point of view but leads to another reading, that of the operation of signifiers. A Lacanian orientation reveals and displays this operation in its particular fashion of producing effects of meaning

Simplified numerical approach for incremental sheet metal forming process

The current work presents a finite element approach for numerical simulation of the incremental sheet metal forming (ISF) process, called here ‘‘ISF-SAM’’ (for ISF-Simplified Analysis Modelling). The main goal of the study is to develop a simplified FE model sufficiently accurate to simulate the ISF process and quite efficient in terms of CPU time. Some assumptions have been adopted regarding the constitutive strains/stresses equations and the tool/sheet contact conditions. A simplified contact procedure was proposed to predict nodes in contact with the tool and to estimate their imposed displacements. A Discrete Kirchhoff Triangle shell element called DKT12, taking into account membrane and bending effects, has been used to mesh the sheet. An elasto-plastic constitutive model with isotropic hardening behaviour and a static scheme have been adopted to solve the nonlinear equilibrium equations. Satisfactory results have been obtained on two applications and a good correlation has been shown compared to experimental and numerical results, and at the same time a reduction of CPU time more than 60% has been observed. The bending phenomenon studied through the second application and the obtained results show the reliability of the DKT12 element

New Generation of Multi-Bands S-X-Ka Ground Station for Smallsats

The LEGION 400 is the new generation of 4m-class antenna system released by Safran Data Systems. Originally designed for Mega-Constellations, the LEGION 400 benefits from a unique tri-band S/X/Ka concentric feed, patented by Safran, combined with a lean and an ultra accurate pedestal. Safran Data Systems offers its customers total flexibility in building up a scalable ground segment for the long term, with a true one-stop-shop for the complete system, including antenna, radome, RF, baseband, station Monitoring & Control as well as scheduler. The LEGION 400 is applicable whether you need to support smallsats, launch vehicles or telecom constellations

How to estimate the differential acceleration in a two-species atom interferometer to test the equivalence principle

We propose a scheme for testing the weak equivalence principle (Universality of Free Fall) using an atom-interferometric measurement of the local differential acceleration between two atomic species with a large mass ratio as test masses. A apparatus in free fall can be used to track atomic free-fall trajectories over large distances. We show how the differential acceleration can be extracted from the interferometric signal using Bayesian statistical estimation, even in the case of a large mass and laser wavelength difference. We show that this statistical estimation method does not suffer from acceleration noise of the platform and does not require repeatable experimental conditions. We specialize our discussion to a dual potassium/rubidium interferometer and extend our protocol with other atomic mixtures. Finally, we discuss the performances of the UFF test developed for the free-fall (0-g) airplane in the ICE project (\verb"http://www.ice-space.fr"

The effects of bar-spiral coupling on stellar kinematics in the Galaxy

We investigate models of the Milky Way disc taking into account simultaneously the bar and a two-armed quasi-static spiral pattern. Away from major resonance overlaps, the mean stellar radial motions in the plane are essentially a linear superposition of the isolated effects of the bar and spirals. Thus, provided the bar is strong enough, even in the presence of spiral arms, these mean radial motions are predominantly affected by the Galactic bar for large scale velocity fluctuations. This is evident when comparing the peculiar line-of-sight velocity power spectrum of our coupled models with bar-only models. However, we show how forthcoming spectroscopic surveys could disentangle bar-only non-axisymmetric models of the Galaxy from models in which spiral arms have a significant amplitude. We also point out that overlaps of low-order resonances are sufficient to enhance stellar churning within the disc, even when the spirals amplitude is kept constant. Nevertheless, for churning to be truly non-local, stronger or (more likely) transient amplitudes would be needed: otherwise the disc is actually mostly unaffected by churning in the present models. Finally, regarding vertical breathing modes, the combined effect of the bar and spirals on vertical motions is a clear non-linear superposition of the isolated effects of both components, significantly superseding the linear superposition of modes produced by each perturber separately, thereby providing an additional effect to consider when analysing the observed breathing mode of the Galactic disc in the extended Solar neighbourhood.Comment: 13 pages, 12 figures. MNRAS. Accepted for publication. v2 is the published versio