École Polytechnique Fédérale de Lausanne
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Very high resolution digital elevation models: do they improve models of plant species distribution ?
No full textLASI
Microstructure and Hydroabrasive Wear Behavior of High-Velocity Oxy-Fuel Thermally Sprayed Wc-Co(Cr) Coatings
No full textSand erosion tests were performed on WC-Co and WC-CoCr coatings deposited by the high velocity oxy-fuel spraying method. Several analytical techniques, including X-ray diffraction, Auger electron spectroscopy and energy-dispersive spectroscopy in a transmission electron microscope were used to characterize the microstructures formed during powder processing and spraying. It was found that a substantial fraction of WC decomposed into W2C or reacted with the cobalt matrix to form ternary carbides such as Co3W3C and other mixed compounds. In both cases the binder phase had a nanocrystalline structure of size 4-8 nm containing tungsten, cobalt, carbon and chromium elements. The addition of chromium inhibits to a large extent the decomposition of WC and avoids the formation of metallic tungsten. In addition, chromium improved the erosion resistance by several times compared with the WC-Co coating. Scanning electron microscopy showed that the CoCr matrix binds carbides better than the cobalt matrix, thereby inhibiting carbide loss at the spray particle boundaries. The hydroabrasive wear behaviour of coatings and the mechanisms for material removal are discussed with respect to the microstructures formed during spraying.CRPPSP
Apparent fracture toughness master curves derived from specimen-size-independent Weibull master curves
No full textThe objective of this paper is to show that apparent fracture toughness master curves can be derived from experimental Weibull master curves of materials undergoing an amount of stable crack growth prior to failure, facilitating the identification of the type of toughening mechanisms operating in the investigated materials. (C) 1998 Elsevier Science S.A. All rights reserved.CRPPSP
Frequency response identification of the dynamics of a Tokamak plasma
No full textIn this paper we describe the application of an H-infinity system identification procedure to a Tokamak. The work is motivated by the need to create linear models which are suitable for controller design and which may be used to validate different models derived from physics principles. The paper develops an H-infinity system identification algorithm and demonstrates its successful application to the Tokamak a configuration variable (TCV). Each of the required steps is detailed, from the design of identification experiments through to the creation of low-order models from a combination of Hankel model reduction and Chebycheff approximation. The method described in this paper is a worst-case identification technique, in that it aims to minimize the H-infinity error between the identified model and the true plant. Such a model is particularly well suited for robust controller design. The identified model of TCV is compared with various physics-based models.CRPPSP
The stable set polytope of quasi-line graphs
Get PDFIt is a long standing open problem to find an explicit description of the stable set polytope of claw-free graphs. Yet more than 20 years after the discovery of a polynomial algorithm for the maximum stable set problem for claw-free graphs, there is even no conjecture at hand today. Such a conjecture exists for the class of quasi-line graphs. This class of graphs is a proper superclass of line graphs and a proper subclass of claw-free graphs for which it is known that not all facets have 0/1 normal vectors. Ben Rebea's conjecture states that the stable set polytope of a quasi-line graph is completely described by clique-family inequalities. Chudnovsky and Seymour recently provided a decomposition result for claw-free graphs and proved that Ben RA a's conjecture holds, if the quasi-line graph is not a fuzzy circular interval graph.. In this paper, we give a proof of Ben Rebea's conjecture by showing that it also holds for fuzzy circular interval graphs. Our result builds upon an algorithm of Bartholdi, Orlin and Ratliff which is concerned with integer programs defined by circular ones matricesDISOP
Quasi CW Room Temperature Operation of 1.52 microns InGaAsP/AlGaAs VCSELs obtained by Localised Fusion
No full textLP
Fuzzynet: Zero-maintenance Ringless Overlay
Get PDFMany structured overlay networks rely on a ring invariant as a core network connectivity element. The responsibility ranges of the participating peers and navigability principles (greedy routing) heavily depend on the ring structure. For correctness guarantees, each node needs to eagerly maintain its immediate neighboring links - the ring invariant. However, the ring maintenance is an expensive task and it may not even be possible to maintain the ring invariant continuously under high churn, particularly as the network size grows. Furthermore, routing anomalies in the network, peers behind firewalls and Network Address Translators (NATs) create non-transitivity effects, which inevitably lead to the violation of the ring invariant. We argue that reliance on the ring structure is a serious impediment for real life deployment and scalability of structured overlays. In this paper we propose an overlay called Fuzzynet, which does not rely on the ring invariant, yet have all the functionalities of structured overlays. Fuzzynet takes the idea of lazy overlay maintenance further by dropping any explicit connectivity and data maintenance requirement, relying merely on the actions performed when new Fuzzynet peers join the network. We show that with sufficient amount of neighbors (O(logN), comparable to traditional structured overlays), even under high churn, data can be retrieved in Fuzzynet w.h.p. We validate our novel design principles by simulations as well as PlanetLab experiments and compare it with ring based overlays.LSI
Designing Micro/Nano Systems for a Safer and Healthier Tomorrow
Get PDFThe ongoing scaling and hybridisation of manufacturing technologies enables us to attain unprecedented levels performance as well as to integrate electronic and fluidic circuits with sensors and actuators. Smart micro/nano systems will be the building blocks of wearable and ambient systems, that gather and integrate heterogeneous data in real time and operate and communicate in a wireless and ultra low power code. These systems will foster a revolution in health and environmental management, with the final objective of improving security and quality of life. At the same time, they will create a large market of components and systems, and a renewed perspective for electronic design and manufacturing companies. To accomplish such an ambitious goal, new technologies and architectures must be matched and tailored to the operational environment by solving novel and challenging design and optimisation problems, through the creation of novel design methodologies and tools.LSI
