École Polytechnique Fédérale de Lausanne
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On a theorem of H. Reiter concerning the map and a theorem of C. Herz concerning the algebras . (A propos d'un théorème de H. Reiter concernant l'application et d'un théorème de C. Herz concernant les algèbres )
No full textCAHRUExp. No.2
Sparse Sampling of Signal Innovations
Get PDFSparse sampling of continuous-time sparse signals is addressed. In particular, it is shown that sampling at the rate of innovation is possible, in some sense applying Occam's razor to the sampling of sparse signals. The noisy case is analyzed and solved, proposing methods reaching the optimal performance given by the Cramer-Rao bounds. Finally, a number of applications have been discussed where sparsity can be taken advantage of. The comprehensive coverage given in this article should lead to further research in sparse sampling, as well as new applications. One main application to use the theory presented in this article is ultra-wide band (UWB) communications.LIBLCA
Fracture behavior of low-density replicated aluminum alloy foams
No full textTensile tests have been performed on replicated aluminum alloy foams of relative density between 4.5% and 8%. During the test the electrical resistance was measured with a four-point set-up and the displacements along the gage section were measured using a digital image correlation (DIC) technique. Right from the start of the tensile test, the strain as observed at the surface with DIC is not uniformly distributed over the sample, but concentrates in bands; this is attributed to density variations. The peak strain, i.e. the strain at the ultimate tensile strength (UTS), increases with decreasing density for densities below 5.5%. For densities above 5.5% fracture occurs in the band with the highest strain, yielding a roughly constant peak strain (near 1.5%). Resistivity data indicate an increased contribution of strut bending compared to stretching for densities below 5.5%, causing a decreased rate of damage accumulation and an increase in the tolerance to damage. Incremental strain maps show that the increased damage tolerance in the low-density samples allows initially formed deformation bands to harden resulting in multiple bands to be involved in the fracture process. (C) 2008 Elsevier B.V. All rights reserved.LM
Structural analysis of a composite bridge structure combining UHPFRC and prestressed concrete
Get PDFReinforced concrete being the most applied construction material today performs very well in most applications but still lacks durability under severe environmental conditions. Especially existing structures built decades ago show degradation. Using Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) to improve durability is a promising option seen the extraordinary performance of this material when applied in a composite section. Restrained shrinkage of the overlay plays an important role in this type of application. A conceptual bridge cross section combining UHPFRC and reinforced concrete has been numerically analysed. Two main parameters, tensile strength and strain hardening capacity, were varied. The analysis indicates the importance of strain hardening of UHPFRC and the influence of its tensile strength on the structural response under restrained shrinkage (deformation controlled loading) and traffic loads (force controlled loading). The results validate the concept of using a UHPFRC layer to improve the structural durability of concrete constructions.MC
Interval consensus: from quantized gossip to voting
Get PDFWe design distributed and quantized average consensus algorithms on arbitrary connected networks. By construction, quantized algorithms cannot produce a real, analog average. Instead, our algorithm reaches consensus on the quantized interval that contains the average. We prove that this consensus in reached in finite time almost surely. As a byproduct of this convergence result, we show that the majority voting problem is solvable with only 2 bits of memory per agent.LCAVINDY