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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.

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.

Flueck M.,Ecole Polytechnique Federale de Lausanne | Janka A.,Ecole d'Ingenieurs et d'Architectes 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.

Moser R.,Ecole dingenieurs et darchitectes de Fribourg | Chappuis T.,Ecole dingenieurs et darchitectes de Fribourg | Vanoli E.,Ecole dingenieurs et darchitectes de Fribourg | Crelier S.,Ecole dingenieurs et darchitectes de Fribourg | Naef O.,Ecole dingenieurs et darchitectes de Fribourg
Chimia | Year: 2010

A micro-reactor coupled to a microfluidic system and an online UV/VIS spectrometer is described. The enzymatic reaction studied is the hydrolysis of the N-benzoyl-l-tyrosine ethyl ester (BTEE) to N-benzoyl-ltyrosine (BT) and ethanol, catalyzed by chymotrypsin. The production is online monitored with UV spectroscopy at 256 nm. Three different immobilization methods of the enzyme are discussed: Eupergit® C, controlled-pore glass (CPG), and Sepharose. © Schweizerische Chemische Gesellschaft.

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.

Naef O.,Ecole dingenieurs et darchitectes de Fribourg | Roch M.,Ecole dingenieurs et darchitectes de Fribourg | Chappuis T.,Ecole dingenieurs et darchitectes de Fribourg
Chimia | Year: 2010

This article discusses the screening of chemical reactions using a microreactor equipped with infrared spectroscopy as online analytics. An esterification reaction has been optimized in continuous mode with the proposed setup. The esterification did not work well due to the material of the microreactor (stainless-steel 316Ti) that catalyzed the decomposition of formic acid. However, despite the occurrence of decomposition, an optimization could be achieved with this system. © Schweizerische Chemische Gesellschaft.

Chappuis T.,Ecole dIngenieurs et dArchitectes de Fribourg | Bobowska I.,Ecole dIngenieurs et dArchitectes de Fribourg | Hengsberger S.,Ecole dIngenieurs et dArchitectes de Fribourg | Vanoli E.,Ecole dIngenieurs et dArchitectes de Fribourg | Dietsch H.,University of Fribourg
Chimia | Year: 2011

We report on the transformation via hydrogen reduction of spindle-type hematite nanoparticles into hematite/magnetite hybrid iron oxide particles. The transformation process consists of the reduction of nanoparticles powder in an autoclave using hydrogen gas at a fixed pressure of 11 bars. Both temperature and time of reduction are varied between 300°C to 360°C and 0 to 45 h. X-Ray powder diffraction data on the obtained powder and corresponding Rietveld refinement allow the amount of reduced hematite to be determined as a function of these two parameters. Kinetics parameters are measured and an estimation of the activation energy is obtained through linearization of the Arrhenius equation. While reduction is dramatically accelerated at higher temperature, the morphology of the nanoparticles only remain qualitatively unchanged at 300°C as seen from transmission electron microscopy images. The mechanisms underlying morphology changes are still under study and seem to be closely related to reactor pressure. © Schweizerische Chemische Gesellschaft.

Ecole Dingenieurs Et Darchitectes De Fribourg | Date: 2011-09-06

The present invention concerns a cutting or abrasive tool (1) such as a bur or a file that is produced by ceramic injection moulding with specific profiles or teeth. The tool can be a bur or a file that is directly produced by this process with no need for an extra treatment. Such tools are easily and cheaply produced and can be single use tools. The defect line (2) at the mould split plane location may advantageously be used as part of the abrasive or cutting profile. The tool may be made from stabilised zirconium dioxide (ZrO2), pure aluminium oxide (Al2O3) or a mixture of both. The cutting profile may include a face angle of about 5 degrees, a back angle of about 17 degrees and a gullet angle of 78 degrees (see FIG. 2).

PubMed | Imperial College London, Ecole dIngenieurs et dArchitectes de Fribourg, University of Bern, University of Nottingham and University of Birmingham
Type: Journal Article | Journal: Proceedings of the National Academy of Sciences of the United States of America | Year: 2014

Morphogenesis occurs in 3D space over time and is guided by coordinated gene expression programs. Here we use postembryonic development in Arabidopsis plants to investigate the genetic control of growth. We demonstrate that gene expression driving the production of the growth-stimulating hormone gibberellic acid and downstream growth factors is first induced within the radicle tip of the embryo. The center of cell expansion is, however, spatially displaced from the center of gene expression. Because the rapidly growing cells have very different geometry from that of those at the tip, we hypothesized that mechanical factors may contribute to this growth displacement. To this end we developed 3D finite-element method models of growing custom-designed digital embryos at cellular resolution. We used this framework to conceptualize how cell size, shape, and topology influence tissue growth and to explore the interplay of geometrical and genetic inputs into growth distribution. Our simulations showed that mechanical constraints are sufficient to explain the disconnect between the experimentally observed spatiotemporal patterns of gene expression and early postembryonic growth. The center of cell expansion is the position where genetic and mechanical facilitators of growth converge. We have thus uncovered a mechanism whereby 3D cellular geometry helps direct where genetically specified growth takes place.

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.

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