Entity

Time filter

Source Type


Kilundu B.,University of Mons | Chiementin X.,CNRS Research Group of Sciences for Engineer | Duez J.,University of Mons | Mba D.,Cranfield University
Mechanical Systems and Signal Processing | Year: 2011

Cyclostationarity is a relatively new technique that offers diagnostic advantages for analysis of vibrations from defective bearings. Similarly the Acoustic Emission (AE) technology has emerged as a viable tool for preventive maintenance of rotating machines. This paper presents an experimental study that characterizes the cyclostationary aspect of Acoustic Emission signals recorded from a defective bearing. The cyclic spectral correlation, a tool dedicated to evidence the presence of cyclostationarity, was compared with a traditional technique, the envelope spectrum. This comparison showed that the cyclic spectral correlation was most efficient for small defect identification on outer race defects though the success was not mirrored on inner race defects. An indicator, based on this cyclostationary technique, has also been proposed. It is concluded that its offers better sensitivity to the continuous monitoring of defects compared to the use of traditional temporal indicators (RMS, Kurtosis, Crest Factor). © 2010 Elsevier Ltd. All rights reserved. Source


Grossel P.,CNRS Research Group of Sciences for Engineer
Annals of Physics | Year: 2013

Complex time is often invoked about tunneling effect where the classical phase delay is completed with a crucial filter effect. Usually the complex times are obtained by considering the flux-flux correlation function, but this can be obtained by a very simple approach using the search of the maximum of the generalized complex phase function, including the amplitude of the wave function. Various aspects of the phase delay are presented in the case of wave packets impinging on simple or resonant quantum barriers. Formal links with the classical mechanics give birth to quasi-trajectories of the quantum particle, totally compatible with the quantum mechanics. © 2012 Elsevier Inc. Source


Bertucci W.,University of Reims Champagne Ardenne | Crequy S.,University of Reims Champagne Ardenne | Chiementin X.,CNRS Research Group of Sciences for Engineer
International Journal of Sports Medicine | Year: 2013

The aim of this study was to test the validity and reliability of the G-Cog which is a new BMX power meter allowing for the measurements of the power output (250 Hz) at the BMX rear wheel during actual cycling and laboratory conditions. Sprints in road cycling (6-8 s) from static start and incremental tests in the laboratory (100-400 W) have been performed to analyse the validity and reliability of the power output values by comparison with 2 devices: The PowerTap and the SRM which are considered as the gold standard. The most important finding of this study is that the G-Cog power output data were not valid and reliable during sprint and standardised laboratory tests compared with the SRM and the PowerTap devices. During the sprint and the laboratory tests the ratio limits of agreement of the power output differences between the SRM and G-Cog were 1.884×÷1.970 (95%CI=0.956-3.711) and 12.126×÷16.281 (95%CI=0.745-197.430), respectively. In conclusion, the G-Cog must be used with caution regarding the power output measurements. Nevertheless, the G-Cog could be used for the first time to analyse the determinants of the BMX performance from the pedalling profile. © Georg Thieme Verlag KG Stuttgart, New York. Source


Liger-Belair G.,CNRS Molecular and Atmospheric Spectrometry Group | Liger-Belair G.,University of Reims | Bourget M.,CNRS Research Group of Sciences for Engineer | Pron H.,CNRS Research Group of Sciences for Engineer | And 2 more authors.
PLoS ONE | Year: 2012

In champagne tasting, gaseous CO 2 and volatile organic compounds progressively invade the headspace above glasses, thus progressively modifying the chemical space perceived by the consumer. Simultaneous quantification of gaseous CO 2 and ethanol was monitored through micro-gas chromatography (μGC), all along the first 15 minutes following pouring, depending on whether a volume of 100 mL of champagne was served into a flute or into a coupe. The concentration of gaseous CO 2 was found to be significantly higher above the flute than above the coupe. Moreover, a recently developed gaseous CO 2 visualization technique based on infrared imaging was performed, thus confirming this tendency. The influence of champagne temperature was also tested. As could have been expected, lowering the temperature of champagne was found to decrease ethanol vapor concentrations in the headspace of a glass. Nevertheless, and quite surprisingly, this temperature decrease had no impact on the level of gaseous CO 2 found above the glass. Those results were discussed on the basis of a multiparameter model which describes fluxes of gaseous CO 2 escaping the liquid phase into the form of bubbles. © 2012 Liger-Belair et al. Source


Bertucci W.M.,CNRS Research Group of Sciences for Engineer | Rogier S.,CNRS Research Group of Sciences for Engineer | Reiser II. R.F.,Colorado State University
Journal of Sports Sciences | Year: 2013

Aerodynamic and rolling resistances are the two major resistances that affect road cyclists on level ground. Because of reduced speeds and markedly different tyre-ground interactions, rolling resistance could be more influential in mountain biking than road cycling. The aims of this study were to quantify 1) aerodynamic resistance of mountain-bike cyclists in the seated position and 2) rolling resistances of two types of mountain-bike tyre (smooth and knobby) in three field surfaces (road, sand and grass) with two pressure inflations (200 and 400 kPa). Mountain-bike cyclists have an effective frontal area (product of projected frontal area and drag coefficient) of 0.357 ± 0.023 m2, with the mean aerodynamic resistance representing 8-35% of the total resistance to cyclists' motion depending on the magnitude of the rolling resistance. The smooth tyre had 21 ± 15% less rolling resistance than the knobby tyre. Field surface and inflation pressure also affected rolling resistance. These results indicate that aerodynamic resistance influences mountain-biking performance, even with lower speeds than road cycling. Rolling resistance is increased in mountain biking by factors such as tyre type, surface condition and inflation pressure that may also alter performance. © 2013 Copyright © 2013 Taylor & Francis. Source

Discover hidden collaborations