Overlapping stochastic block models with application to the French political blogosphere

Complex systems in nature and in society are often represented as networks, describing the rich set of interactions between objects of interest. Many deterministic and probabilistic clustering methods have been developed to analyze such structures. Given a network, almost all of them partition the vertices into disjoint clusters, according to their connection profile. However, recent studies have shown that these techniques were too restrictive and that most of the existing networks contained overlapping clusters. To tackle this issue, we present in this paper the Overlapping Stochastic Block Model. Our approach allows the vertices to belong to multiple clusters, and, to some extent, generalizes the well-known Stochastic Block Model [Nowicki and Snijders (2001)]. We show that the model is generically identifiable within classes of equivalence and we propose an approximate inference procedure, based on global and local variational techniques. Using toy data sets as well as the French Political Blogosphere network and the transcriptional network of Saccharomyces cerevisiae, we compare our work with other approaches.Comment: Published in at http://dx.doi.org/10.1214/10-AOAS382 the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org

Wrinkles, folds and plasticity in granular rafts

We investigate the mechanical response of a compressed monolayer of large and dense particles at a liquid-fluid interface: a granular raft. Upon compression, rafts first wrinkle; then, as the confinement increases, the deformation localizes in a unique fold. This characteristic buckling pattern is usually associated to floating elastic sheets and as a result, particle laden interfaces are often modeled as such. Here, we push this analogy to its limits by comparing the first quantitative measurements of the raft morphology to a theoretical continuous elastic model of the interface. We show that although powerful to describe the wrinkle wavelength, the wrinkle-to-fold transition and the fold shape, this elastic description does not capture the finer details of the experiment. We describe an unpredicted secondary wavelength, a compression discrepancy with the model and a hysteretic behavior during compression cycles, all of which are a signature of the intrinsic discrete and frictional nature of granular rafts. It suggests also that these composite materials exhibit both plastic transition and jamming dynamics.Comment: 10 pages, including Supplementary Information. Submitted to Physical Review Material

Application of Laguerre based adaptive predictive control to Shape Memory Alloy (SMA) actuators

This paper discusses the use of an existing adaptive predictive controller to control some Shape Memory Alloy (SMA) linear actuators. The model consists in a truncated linear combination of Laguerre filters identified online. The controller stability is studied in details. It is proven that the tracking error is asymptotically stable under some conditions on the modelling error. Moreover, the tracking error converge toward zero for step references, even if the identified model is inaccurate. Experimentalcresults obtained on two different kind of actuator validate the proposed control. They also show that it is robust with regard to input constraints.ANR MAFESM

Liquidity costs: a new numerical methodology and an empirical study

We consider rate swaps which pay a fixed rate against a floating rate in presence of bid-ask spread costs. Even for simple models of bid-ask spread costs, there is no explicit strategy optimizing an expected function of the hedging error. We here propose an efficient algorithm based on the stochastic gradient method to compute an approximate optimal strategy without solving a stochastic control problem. We validate our algorithm by numerical experiments. We also develop several variants of the algorithm and discuss their performances in terms of the numerical parameters and the liquidity cost

The Hydraulic Jump in Liquid Helium

We present the results of some experiments on the circular hydraulic jump in normal and superfluid liquid helium. The radius of the jump and the depth of the liquid outside the jump are measured through optical means. Although the scale of the apparatus is rather small, the location of the jump is found to be consistent with the assumption that the jump can be treated as a shock, if the surface tension is taken into account. The radius of the jump does not change when going down in temperature through the lambda point; we think that the flow is supercritical. A remarkable feature of the experiment is the observation of stationary ripples within the jump when the liquid is superfluid.Comment: Submitted to the proceedings of the 24th International Conference on Low Temperature Physics. 2 figure

Introduction of variability in pantograph-catenary dynamic simulations

Currently, pantograph-catenary dynamic simulations codes are mainly based on deterministic approaches. However, the contact force between catenary and pantograph depends on many key parameters that are not always quantified precisely. To get a better chance of addressing extreme or combinations of critical conditions, methodologies to consider variability are thus necessary. Aerodynamic forces and geometrical irregularities of catenaries are thought to be significant sources of variability in measurement and this paper proposes methods to take them into account. Results are compared with measurements to see the importance of the considered parameters with respect to global variability observed in measurements

Analyse de données spatiales du marché du travail. Application aux 260 communes wallonnes.

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Analyse de données spatiales du marché du travail. Application aux 260 communes wallonnes

L’analyse de données spatiales permet d’appréhender des phénomènes en général ignorés de l’analyse économique standard. Dans le cadre du marché du travail, en particulier, l’approche spatiale peut révéler l’importance de la concentration spatiale du chômage, les corrélations dans l’espace de la qualification de la force de travail, la propagation dans l’espace des chocs d’emplois, enfin les raisons possibles de la persistance d’un niveau de chômage élevé dans certains secteurs géographiques. Ce papier tente d’adresser ces questions en appliquant des techniques d’analyse spatiale à des données des 260 communes de la Wallonie. L’objectif est d’abord méthodologique et exploratoire : après une première partie descriptive utilisant les techniques d’analyse de données spatiales, on procède à l’estimation d’un modèle de chômage et d’offre de travail avec ou sans termes de corrélations spatiales. Les conclusions d’étape permettent d’éclairer le rôle de la mobilité du travail et des politiques intra-régionales

Nonthermal Plasma Technology as a Versatile Strategy for Polymeric Biomaterials Surface Modification: A Review

In modern technology, there is a constant need to solve very complex problems and to fine-tune existing solutions. This is definitely the case in modern medicine with emerging fields such as regenerative medicine and tissue engineering. The problems, which are studied in these fields, set very high demands on the applied materials. In most cases, it is impossible to find a single material that meets all demands such as biocompatibility, mechanical strength, biodegradability (if required), and promotion of cell-adhesion, proliferation, and differentiation. A common strategy to circumvent this problem is the application of composite materials, which combine the properties of the different constituents. Another possible strategy is to selectively modify the surface of a material using different modification techniques. In the past decade, the use of nonthermal plasmas for selective surface modification has been a rapidly growing research field. This will be the highlight of this review. In a first part of this paper, a general introduction in the field of surface engineering will be given. Thereafter, we will focus on plasma-based strategies for surface modification. The purpose of the present review is twofold. First, we wish to provide a tutorial-type review that allows a fast introduction for researchers into the field. Second, we aim to give a comprehensive overview of recent work on surface modification of polymeric biomaterials, with a focus on plasma-based strategies. Some recent trends will be exemplified. On the basis of this literature study, we will conclude with some future trends for research