Lower bounds on data collection time in sensory networks

Data collection, i.e., the aggregation at the user location of information gathered by sensor nodes, is a fundamental function of sensory networks. Indeed, most sensor network applications rely on data collection capabilities, and consequently, an inefficient data collection process may adversely affect the performance of the network. In this paper, we study via simple discrete mathematical models, the time performance of the data collection and data distribution tasks in sensory networks. Specifically, we derive the minimum delay in collecting sensor data for networks of various topologies such as line, multiline, and tree and give corresponding optimal scheduling strategies. Furthermore, we bound the data collection time on general graph networks. Our analyses apply to networks equipped with directional or omnidirectional antennas and simple comparative results of the two systems are presented

Scheduling algorithms for wireless ad-hoc sensor networks

We define a simple discrete mathematical model for wireless ad-hoc sensor networks and study the problems of data distribution and data collection which arise in those networks. We show how those tasks can be optimally performed on tree sensor networks that use directional antennas. Furthermore we compare the performance of a network equipped with directional antenna elements with one equipped with omnidirectional antenna elements and show the former outperforms the latter by 50% at most on a line network

Experimental Analysis of the nonlinear Vibrations of a rigid Rotor in Gas Foil Bearings

Air bearings and gas foil bearings (GFBs) in particular are characterized by a low-loss operation at high rotational speeds and temperatures, because of their adequate and relatively low lubrication viscosity. Further advantages are the simple design of the bearing and the omission of an oil system. A disadvantage is the low fluid viscosity, which limits the load capacity and damping capacity of the bearing. Even though the bearing wall, which is elastic and sensitive to friction, compensates the mentioned disadvantages by self-regulating the lubrication film and providing external damping. GFBs always show a tendency for nonlinear subharmonic vibrations. In this paper, the nonlinear vibration behavior of a rigid rotor in gas foil bearings is investigated. The rotor is accelerated to approx. 60 000 rpm by means of an impulse turbine. Waterfall charts for a variation of static and dynamic unbalance are recorded using transient coast-downs. The experiments show a variety of nonlinear effects. Their causes are analyzed experimentally. In addition to self-excitation by the fluid film, the rotor is sensitive to high unbalances and the resulting forced vibrations. The nonlinear, progressive system behavior results in excitation orders of 1/2 Ω, 1/3 Ω, and 1/4 Ω that modulate additional frequencies

Existence and classification of bb-contact structures

A $b$-contact structure on a $b$-manifold $(M,Z)$ is a singular Jacobi structure on $M$ satisfying a transversality condition along the hypersurface $Z$. We show that, in three dimensions, $b$-contact structures with overtwisted three-dimensional leaves satisfy an existence $h$-principle that allows prescribing the induced singular foliation. We give a method to classify $b$-contact structures on a given $b$-manifold and use it to give a classification on $S^3$ with either a two-sphere or an unknotted torus as the critical surface. We also discuss generalizations to higher dimensions.Comment: 27 pages. Minor correction

Model-free based water level control for hydroelectric power plants

International audienceAutomatic water level control methods for open channels have difficulties to keep good performances for a large range of flow and significant unknown disturbances. A new concept called "model-free control" is applied in this paper for hydroelectric run-of-the river power plants. To modulate power generation, a level trajectory is planned for cascaded power plants. Numerous dynamic simulations show that with a simple and robust control algorithm, the set-point is followed even in severe operating conditions

Vers une commande sans mod\`ele pour am\'enagements hydro\'electriques en cascade

A new concept called "Model-Free Control" is applied to hydroelectric run-of-the river power plants, with severe constraints and operating conditions. Numerous computer simulations display excellent results, which are obtained thanks to simple and robust algorithms

Une "commande sans modèle" pour aménagements hydroélectriques en cascade

International audienceOn aborde, par la "commande sans modèle", la régulation du niveau d'eau dans un aménagement hydraulique, soumis à de fortes contraintes, pour produire de l'électricité. Les nombreuses simulations numériques fournissent d'excellents résultats, obtenus grâce à des algorithmes robustes et simples

Disparity-compensated view synthesis for s3D content correction

International audienceThe production of stereoscopic 3D HD content is considerably increasing and experience in 2-view acquisition is in progress. High quality material to the audience is required but not always ensured, and correction of the stereo views may be required. This is done via disparity-compensated view synthesis. A robust method has been developed dealing with these acquisition problems that introduce discomfort (e.g hyperdivergence and hyperconvergence...) as well as those ones that may disrupt the correction itself (vertical disparity, color difference between views...). The method has three phases: a preprocessing in order to correct the stereo images and estimate features (e.g. disparity range...) over the sequence. The second (main) phase proceeds then to disparity estimation and view synthesis. Dual disparity estimation based on robust block-matching, discontinuity-preserving filtering, consistency and occlusion handling has been developed. Accurate view synthesis is carried out through disparity compensation. Disparity assessment has been introduced in order to detect and quantify errors. A post-processing deals with these errors as a fallback mode. The paper focuses on disparity estimation and view synthesis of HD images. Quality assessment of synthesized views on a large set of HD video data has proved the effectiveness of our method

Atom transfer radical polymerization of MMA with a macromolecular ligand in a fluorinated solvent and in supercritical carbon dioxide

Macromolecular fluorinated ligands were prepared according to a three-step strategy that consists of the random copolymerization of heptadecafluorodecyl acrylate and 2-hydroxyethylacrylate, followed by the esterification of the pendant hydroxyl groups with acryloyl chloride and the Michael-type addition of tetraethyldiethylenetriamine onto the acrylic double bonds of the polymeric chains. These fluorinated macroligands were successfully used in the atom transfer radical polymerization of MMA catalyzed by a copper salt in a fluorinated solvent. The polymerization control was analyzed in relation to the copper salt, the initiator and the molecular weight and composition of the macroligand before being extended to the heterogeneous ATRP of MMA in scCO2