École Polytechnique Fédérale de Lausanne
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Cooperative Localization for Autonomous Underwater Vehicles
No full textThis paper describes an algorithm for distributed acoustic navigation for Autonomous Underwater Vehicles (AUVs). Whereas typical AUV navigation systems utilize pre-calibrated arrays of static transponders, our work seeks to create a fully mobile network of AUVs that perform acoustic ranging and data exchange with one another to achieve cooperative positioning for extended duration missions over large areas. The algorithm enumerates possible solutions for the AUV trajectory based on dead-reckoning and range-only measurements provided by acoustic modems that are mounted on each vehicle, and chooses the trajectory via minimization of a cost function based on these constraints. The resulting algorithm is computationally efficient, meets the strict bandwidth requirements of available AUV modems, and has potential to scale well to networks of large numbers of vehicles. The method has undergone extensive experimentation, and results from three different scenarios are reported in this paper, each of which utilizes MIT SCOUT Autonomous Surface Craft (ASC) as convenient platforms for testing. In the first experiment, we utilize three ASCs, each equipped with a Woods Hole acoustic modem, as surrogates for AUVs. In this scenario, two ASCs serve as Communication/Navigation Aids (CNAs) for a third ASC that computes its position based exclusively on GPS positions of the CNAs and acoustic range measurements between platforms. In the second scenario, an undersea glider is used in conjunction with two ASCs serving as CNAs. Finally, in the third experiment, a Bluefin12 AUV serves as the target vehicle. All three experiments demonstrate the successful operation of the technique with real ocean data.DISA
Compressive sampling
Get PDFThe ten articles in this special section provide the reader with specific insights into the basic theory, capabilities, and limitations of compressed sensing (CS).LCAVWritten as Guest Editor
Iterative Demosaicking Accelerated: Theory and Fast Noniterative Implementations
Get PDFColor image demosaicking is a key process in the digital imaging pipeline. In this paper, we present a rigorous treatment of a classical demosaicking algorithm based on alternating projections (AP). Since its publication, the AP algorithm has been widely cited and served as a benchmark in a flurry of papers in the demosaicking literature. Despite its impressive performances, a relative weakness of the AP algorithm is its high computational complexity. In our work, we provide a rigorous analysis of the convergence of the AP algorithm based on the concept of contraction mapping. Furthermore, we propose an efficient noniterative implementation of the AP algorithm in the polyphase domain. Numerical experiments show that the proposed noniterative implementation achieves the same results obtained by the original AP algorithm at convergence, but is about an order of magnitude faster than the latter.LCA
Implementing a NAT and Firewall traversal library
Get PDFImplementing a NAT and Firewall traversal libraryLSI
Dynamic Cost-Efficient Replication in Data Clouds
Get PDFHardware failures in current data centers are common partly due to the higher data scales supported. Data replication is the common approach for improving availability. However, mostly static replication approaches have been proposed, i.e. the number of replicas and their locations are fixed. Moreover, the geographical diversity of data locations has not explicitly been considered. In this paper, we propose a cost-efficient replication scheme across data centers that dynamically adapts the number of replicas employed per partition to the query load, while maintaining availability guarantees in case of failures. Our approach employs a virtual economy that is experimentally proved in a simulated environment to achieve load balancing among data servers at the minimum cost.LSI
Production and properties of substituted LaFeO3-perovskite tubular membranes for partial oxidation of methane to syngas
No full textTubular membranes of La0.6Ca0.4Fe0.75Co0.25O3−δ and La0.5Sr0.5Fe1−yTiyO3−δ (y = 0, 0.2) for the application of partial oxidation of methane to syngas were produced by thermoplastic extrusion and investigated by oxygen permeation measurements. The optimum ceramic content in the feedstock for extrusion was found to be 51 vol% as a result of rheology measurements. Tubes with an outer diameter of 4.8–5.5mmand thickness of 0.25–0.47mm were produced with densities higher than 95% of the theoretical density. The oxygen permeation flux of the tubular membranes wasmeasured with air on one side and Ar or Ar +CH4 mixture on the other side. The oxygen permeation rate decreased with Ti-substitution while it was considerably increased by introduction of 5% methane into the system. The normalized oxygen fluxes in air/Ar gradient at 900 ◦C were measured to be 0.06, 0.051, and 0.012 mol cm−2 s−1 for LCFC, LSF, and LSFT2, respectively, and 0.18 mol cm−2 s−1 for LSFT2 with 5% methane.LENIdoi:10.1016/j.jeuceramsoc.2006.10.00
Reduced Basis Methods and A Posteriori Error Estimators for Heat Transfer Problems
Get PDFThis paper focuses on the parametric study of steady and unsteady forced and natural convection problems by the certified reduced basis method. These problems are characterized by an input-output relationship in which given an input parameter vector — material properties, boundary conditions and sources, and geometry — we would like to compute certain outputs of engineering interest — heat fluxes and average temperatures. The certified reduced basis method provides both (i) a very inexpensive yet accurate output prediction, and (ii) a rigorous bound for the error in the reduced basis prediction relative to an underlying expensive high-fidelity finite element discretization. The feasibility and efficiency of the method is demonstrated for three natural convection model problems: a scalar steady forced convection problem in a rectangular channel is characterized by two parameters — Peclet number and the aspect ratio of the channel — and an output –- the average temperature over the domain; a steady natural convection problem in a laterally heated cavity is characterized by three parameters — Grashof and Prandtl numbers, and the aspect ratio of the cavity — and an output — the inverse of the Nusselt number; and an unsteady natural convection problem in a laterally heated cavity is characterized by two parameters — Grashof and Prandtl numbers— and a timedependent output — the average of the horizontal velocity over a specified area of the cavity.CMCSSCI-SB-SDpresented in the Computational Section of the conference. EPFL-IACS report 05.2009, peer reviewed