Multi-GPU maximum entropy image synthesis for radio astronomy

The maximum entropy method (MEM) is a well known deconvolution technique in radio-interferometry. This method solves a non-linear optimization problem with an entropy regularization term. Other heuristics such as CLEAN are faster but highly user dependent. Nevertheless, MEM has the following advantages: it is unsupervised, it has a statistical basis, it has a better resolution and better image quality under certain conditions. This work presents a high performance GPU version of non-gridding MEM, which is tested using real and simulated data. We propose a single-GPU and a multi-GPU implementation for single and multi-spectral data, respectively. We also make use of the Peer-to-Peer and Unified Virtual Addressing features of newer GPUs which allows to exploit transparently and efficiently multiple GPUs. Several ALMA data sets are used to demonstrate the effectiveness in imaging and to evaluate GPU performance. The results show that a speedup from 1000 to 5000 times faster than a sequential version can be achieved, depending on data and image size. This allows to reconstruct the HD142527 CO(6-5) short baseline data set in 2.1 minutes, instead of 2.5 days that takes a sequential version on CPU.Comment: 11 pages, 13 figure

Ethnic Xenophobia as Symbolic Politics: A Cross-National Study of Anti-Migrant Activism from Brussels to Beirut

Xenophobia is examined almost exclusively as a prejudice of advanced western nations. I argue that the field of study of xenophobia must be re-conceptualized in order for comparative, cross-regional inquiry to take place. With a new concept of ethnic xenophobia, this dissertation examines the determinants and causal mechanisms of ethnic xenophobic activity across developed and developing countries. I integrate studies of xenophobia and theories of ethnic threat to explain that political elites rely on structural dimensions of threat to convert native anxieties into ethnic xenophobia through the use of anti-migrant myths and symbols. I extend Stuart Kaufman’s theory of symbolic politics to further explain how elites mobilize ethnic xenophobic activity in order to gain or maintain political advantage among the native selectorate in their respective competitions for power. I use a Heckman Selection Model and a Structural Equation Model to test this theory across 14,000 cases of ethnic xenophobic activity targeting refugees for seventy-two developed and developing countries from 1990 to 2014. The results suggest that elites- across both developed and developing countries- do indeed exploit native anxieties in the aftermath of structural crises and events to provoke and mobilize hostilities toward migrants. A most-different systems design is also used to illustrate the causal mechanisms of the argument across two pairs of cases, including Kenya and the Netherlands and Lebanon and the United States. These cases provide additional support to the cross-regional explanation of ethnic xenophobic activity. This research opens the door to further exploration of similarities in the patterns and trends of ethnic xenophobia and anti-migrant intolerance across different country contexts. The results suggest that efforts for the protection of migrants against such expressions of prejudice require improvement; and that relationships between native and migrant populations matter a great deal for the exploitation of fears and anxieties by political elites especially in and around elections

Art, artiste, artisan. Introduction.

International audienceCe texte introduit un volume collectif. Sans pour autant proposer une lecture linéaire ou évolutionniste du phénomène artistique, le présent ouvrage interroge ces trois catégories, art, artiste, artisan, à travers le prisme de l’histoire de l’art et de l’archéologie. L’ambition affichée consiste plutôt à déconstruire l’idée d’une appréhension universelle de l’art qui ne serait forgée que par la tradition occidentale ou par ses catégories habituelles.Redonner une place aux acteurs de la production artistique, en s’interrogeant sur leur statut social, sur leurs pratiques techniques, leurs savoir-faire ainsi que sur la perception que nous en avons comme sur la conscience qu’ils ont d’eux-mêmes, en sont les lignes directrices. On y explore la frontière entre technique et esthétique, entre création et production, avec le souhait de se rapprocher d’une anthropologie de l’art, encore très timide dans le champ de l’histoire de l’art. Cette publication aborde différents volets, théoriques, offrant un cadre de réflexion, ou au contraire appliqués aux aires chrono-culturelles habituelles, proposant des éclairages précis. Plusieurs types de sources sont sollicités en fonction des périodes : sources directes (objets, écrits, enquête orale, etc.) ou indirectes (parallèles ethnographiques, modèles, etc.).Portée par la section d’antique du département d’histoire de l’art et d’archéologie de l’université Blaise Pascal (Clermont-Ferrand 2), cette publication s’inscrit dans une dynamique de réflexion collective et transdisciplinaire qui caractérise les travaux menés dans le cadre de l’axe “Dynamiques culturelles et artistiques” du CHEC (Centre d’Histoire “Espaces et Cultures” de l’université Blaise Pascal). À cet égard, elle rassemble les travaux de ses enseignants-chercheurs, toutes périodes confondues et accueille ceux de collègues d’institutions proches

Timescale of open-reservoir evolution beneath the south Cleft segment, Juan de Fuca ridge

International audienceLavas erupted at the southern end of the intermediate Juan de Fuca ridge (Cleft segment) are mostly cogenetic and their chemical diversity results from melt evolution in an open magma system. In the present study, we apply a theoretical model allowing the time evolution of this periodically recharged and tapped magma chamber to be estimated. In our mathematical procedure, the melt quantity supplied to the reservoir varies through time following a sinusoidal function. The rare earth element concentrations in the refilling melt were calculated on the basis of the REE distribution in lavas. This theoretical composition is akin to that previously estimated for a Mg#70 MORB from mineralogical and chemical data. Then, we approached the temporal evolution of the reservoir using a set of suitable parameters deduced from the geometry of the crust and magma system beneath the Cleft segment. Particularly, we considered two end-members scenarios for the melt repartition through the magma reservoir beneath the Cleft segment: the "gabbro glacier" model (crystal nucleation and growth occur within one single melt lens and crystals subside vertically and laterally) and the "sheeted sill" model (crystallization takes place within a network of connected sills located at various depths within the crust). We estimated that the magma chamber is refilled every thousand years and that the melt resides approximately one hundred years within the reservoir

Cdk1, Plks, Auroras, and Neks: the mitotic bodyguards.

In: Li JJ, Li SA, Mohla S, Rochefort H, Maudelonde T, (eds), 2008, Hormonal Carcinogenesis V : Proceedings of the Fifth International Symposium, New York, Springer-Verlag. (Adv. Exp. Med. Biol. 617)International audienceThe coordination of progression through mitosis is mainly orchestrated by protein phosphorylation insured by several serine/threonine kinases. In this short review we will focus on the four main mitotic kinase families: the cyclin-dependent kinase: Cdks, the polo-like kinases: Plks, the Aurora kinases and the NIMArelated kinases: Nerks

Low intrusive coupling of implicit and explicit integration schemes for structural dynamics: application to low energy impacts on composite structures

Simulation of low energy impacts on composite structures is a key feature in aeronautics. Unfortunately they are very expensive: on the one side, the structures of interest have large dimensions and need fine volumic meshes (at least locally) in order to capture damages. On the other side small time steps are required to ensure the explicit algorithms stability which are commonly used in these kind of simulations [4]. Implicit algorithms are in fact rarely used in this situation because of the roughness of the solutions that leads to prohibitive expensive time steps or even to non convergence of Newtonlike iterative processes. It is also observed that rough phenomenons are localized in space and time (near the impacted zone). It may therefore be advantageous to adopt a multiscale space/time approach by splitting the structure into several substructures owning there own space/time discretization and their own integration schemes. The purpose of this decomposition is to take advantage of the specificities of both algorithms families: explicit scheme focuses on rough areas while smoother (actually linear) parts of the solutions are computed with larger time steps with an implicit scheme. We propose here an implementation of the Gravouil-Combescure method (GC) [1] by the mean of low intrusive coupling between the implicit finite element analysis (FEA) code Z-set and the explicit FEA code Europlexus. Simulations of low energy impacts on composite stiffened panels are presented. It is shown on this application that time step ratios up to 5000 can be reached. However, computations related to the explicit domain still remain a bottleneck in terms of cpu time