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Keshavarz-Haddad A.,Shiraz University | Riedi R.H.,Ecole dIngenieurs et dArchitectes de Fribourg
IEEE Transactions on Mobile Computing | Year: 2014

In this paper, we explore fundamental limitations of the benefit of network coding in multihop wireless networks. We study two well-accepted scenarios in the field: single multicast session and multiple unicast sessions. We assume arbitrary but fixed topology and traffic patterns for the wireless network. We prove that the gain of network coding in terms of throughput and energy saving of a single multicast session is at most a constant factor. Also, we present a lower bound on the average number of transmissions of multiple unicast sessions under any arbitrary network coding. We identify scenarios under which network coding provides no gain at all, in the sense that there exists a simple flow scheme that achieves the same performance. Moreover, we prove that the gain of network coding in terms of the maximum transport capacity is bounded by a constant factor of at most π in any arbitrary wireless network under all traditional Gaussian channel models. As a corollary, we find that the gain of network coding on the throughput of large homogeneous wireless networks is asymptotically bounded by a constant. Furthermore, we establish theorems which relate a network coding scheme to a simple routing scheme for multiple unicast sessions. The theorems can be used as criteria for evaluating the potential gain of network coding in a given wired or wireless network. Based on these criteria, we find more scenarios where network coding has no gain on throughput or energy saving. © 2014 IEEE. Source


Ang E.-T.,University of Fribourg | Schafer R.,University of Bonn | Baltensperger R.,Ecole dIngenieurs et dArchitectes de Fribourg | Wernig A.,University of Bonn | And 2 more authors.
Journal of Neuropathology and Experimental Neurology | Year: 2010

Muscle weakness in Charcot-Marie-Tooth Type 1A disease (CMT1A) caused by mutations in peripheral myelin protein 22 (PMP22) has been attributed to an axonopathy that results in denervation and muscle atrophy. The underlying pathophysiological mechanisms involved are not understood. We investigated motor performance, neuromuscular junctions (NMJs), physiological parameters, and muscle morphometry of PMP22 transgenic mice. Neuromuscular junctions were progressively lost in hindlimb muscles of PMP22 transgenic mice, but their motor performance did not completely deteriorate during the observation period. There was considerable variability, including in laterality, in deficits among the animals. Cross-sectional areas and mean fiber size measurements indicated variable myofiber atrophy in hindlimb muscles. There was substantial concomitant axonal sprouting, and loss of neuromuscular junctions was inversely correlated with the accumulated length of axonal branches. Synaptic transmission studied in isolated nerve/muscle preparations indicated variable partial muscle denervation. Acetylcholine sensitivity was higher in the mutant muscles, and maximum tetanic force evoked by direct or indirect stimulation, specific force, and wet weights were markedly reduced in some mutant muscles. In summary, there is partial muscle denervation, and axons may retain some regenerative capacity but fail to reinnervate muscles in PMP22 transgenic mice. Copyright © 2010 by the American Association of Neuropathologists, Inc. Source


Nicchiotti G.,Meggitt Sensing Systems | Giner G.,Ecole dIngenieurs et dArchitectes de Fribourg
Technical Program for MFPT 2012, The Prognostics and Health Management Solutions Conference - PHM: Driving Efficient Operations and Maintenance | Year: 2012

Cyclostationarity analysis has been proved to be very effective to detect and classify rolling bearing faults. To detect 2nd order cyclostationarity properties in signals, spectral correlation density diagrams are computed. They are frequency- frequency diagram, where peaks are associated to the bearing fault frequencies. In spectral correlation diagrams peaks due to bearing faults present typical rhomboidal patterns. However spectral correlation diagrams can result pretty complex to interpret when bearing faults are at the initial stages. From a prognostics stand point, the detection of bearing defects at an early stage is fundamental to track the fault evolution. Hough transform is a feature extraction technique used in image processing. It allows identifying arbitrary shapes within an image (straight lines or circles) in presence of low SNR values. This paper presents a novel approach for the analysis of spectral correlation density diagrams based on Hough transform. The integration of Hough transform within the framework of the spectral correlation analysis aims at improving the detection and classification of bearing defects patterns at the initial stage of the fault. A fully automated method for detection and classification of bearing faults will be presented. In such strategy the coherent (complex) Hough transform has the role to improve the robustness of the detection and the classification stage. Source


Flueck M.,Ecole Polytechnique Federale de Lausanne | Janka A.,Ecole dIngenieurs et dArchitectes de Fribourg | Rappaz J.,Ecole Polytechnique Federale de Lausanne
Lecture Notes in Computational Science and Engineering | Year: 2015

We present here a model for simulating the ferromagnetic screening effect in thin steel plates. We exhibit a domain decomposition method to solve this problem by using only Laplace equations. We then apply this on an academic situation of a steel plate placed in front of a linear conductor and on an industrial application in aluminum production. More details and proofs can be found in Flück et al. (Numerical methods for ferromagnetic plates. Scientific report, SB/MATHICSE, EPFL). © Springer International Publishing Switzerland 2015. Source


Hock S.,ZHAW Zurich University of Applied Sciences | Marti R.,Ecole dIngenieurs et dArchitectes de Fribourg | Riedl R.,ZHAW Zurich University of Applied Sciences | Simeunovic M.,Uberlandstrasse 129
Chimia | Year: 2010

The Fmoc protection group is among the most commonly used protection groups for the amino function. A fast method for the thermal deavage of this protection group under base-free conditions without the need for dibenzofulvene scavengers is presented. The advantages of this method include straightforward testability by means of a simple high-temperature NMR experiment, usually high yields, and good selectivity towards the BOC protection group and t-butyl ethers. Source

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