CNRS Research Group of Sciences for Engineer

Reims, France

CNRS Research Group of Sciences for Engineer

Reims, France
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Maafi E.M.,University Mohammed Premier | Maafi E.M.,CNRS Research Group of Sciences for Engineer | Malek F.,University Mohammed Premier | Tighzert L.,CNRS Research Group of Sciences for Engineer
Journal of Applied Polymer Science | Year: 2010

Different polyurethane (PU) were synthesized from e-polycaprolactone diol, 4, 40-diphenyl methane diisocyanate (MDI) and bis(2-hydroxyethyl) terephthalate(BHET), using a two-stepmethod and a one-stepmethod providing regular and random distributions of starting monomers in the PUchains. Evenwith an identical molarmonomer composition, the properties of obtained PU are different depending on the method of synthesis. The structure of PU was characterized by 1Hand 13C-NMR and Fourier transform infrared spectroscopy (FTIR). The thermomechanical properties of synthesized PU were also studied demonstrating the influence of aromatic ring in the macromolecular chain.© 2009 Wiley Periodicals, Inc.

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.

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.

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.

Hadjadj A.,CNRS Research Group of Sciences for Engineer | Djellouli G.,CNRS Research Group of Sciences for Engineer | Jbara O.,CNRS Research Group of Sciences for Engineer
Applied Physics Letters | Year: 2010

We performed H2 plasma treatment of hydrogenated amorphous silicon (a-Si:H) thin films and followed by in situ spectroscopic ellipsometry measurements the kinetics of hydrogen-induced film modifications at temperatures varying from 100 to 250 °C. The time-dependence of the H-modified layer thickness dH (t) follows an exponential relation of the form dH0 [1-exp (-t/τ)]. The temperature-dependence of dH0 and τ shows a discontinuity at T=200 °C. While the activation energy of dH0 changes from 0.19 eV at T<200 °C to 0.05 eV at higher temperatures, the activation energy of τ suddenly changes from 0.15 eV to a negative value (-0.26 eV). Such a discontinuity should be linked to the thermal equilibrium temperature of undoped a-Si:H. Moreover, we found that the rate of formation of the H-modified layer rH = dH0 /τ varies in inverse proportion to the etching rate, indicating a balance between hydrogen insertion and film etching at the steady state. © 2010 American Institute of Physics.

Haussener S.,Ecole Polytechnique Federale de Lausanne | Randrianalisoa J.,CNRS Research Group of Sciences for Engineer
Journal of Physics: Conference Series | Year: 2016

The porous morphology of ceramic foams can significantly influence its heat and mass transport phenomena. Ceramic foams with dual-scale porosity provide flexibility for tailoring the coupled transport characteristics for enhanced performance. We numerically characterized the radiative transport in porous ceria foams with dual-scale porosity, i.e. exhibiting pores in the millimeter range in the micrometer range. Ceria can act as a catalyst- equivalent in high temperature thermochemical reactions for the direct synthesis of solar fuels and its bulk material properties vary significantly with wavelength. The methodology used is based on Monte Carlo methods for the solution of the volume-averaged radiative transfer equations for the determination of macroscopic optical properties such as reflectance or transmittance of a 1D slab. The exact millimeter-scale structure was incorporated by effective transport properties obtained through collision-based Monte Carlo methods. The micrometer- range strut porosity was incorporated using Mie theory and assuming independent scattering. The results allow for guiding the synthesis of ceramic foams with dual-scale porosity for enhanced radiative transport characteristics.

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.

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.

Grossel Ph.,CNRS Research Group of Sciences for Engineer | Depasse F.,CNRS Research Group of Sciences for Engineer
International Journal of Thermal Sciences | Year: 2011

Most of the time the surface of materials presents profiles of physical properties that are variable along the depth. The heat diffusion equation of current thermophysical profiles rarely accepts analytical solutions that can be introduced in a rapid minimization scheme. A thermal Riccati equation is defined in case of any continuous profiles, the solutions of which are shown to be the limit of the exact solutions for simple staircase multilayer modellings when the layers are taken thinner and thinner. Thanks to the use of iterative methods based on the thermal wave or the quadrupole descriptions, it is shown that the choice of the multilayer approach to describe continuous depth profiles of materials leads to exact solutions of the problem. © 2011 Elsevier Masson SAS. All rights reserved.

Randrianalisoa J.H.,CNRS Research Group of Sciences for Engineer | Dombrovsky L.A.,RAS Joint Institute for High Temperatures | Lipinski W.,Australian National University | Timchenko V.,University of New South Wales
International Journal of Heat and Mass Transfer | Year: 2014

Transient radiative transfer effects are pertinent to thermal treatment of superficial cancer via short-pulsed laser irradiation. Importance of the transient effects arise from relatively strong scattering and long attenuation path of radiation in human tissues in the therapeutic window until the complete absorption. Our analysis is based on transport approximation for scattering phase function and the Monte Carlo method for solving the three-dimensional radiative transfer problem. Monte Carlo simulations are used to study applicability of the quasi-steady radiative transfer approach, and demonstrate that in the biomedical problem under consideration, the quasi-steady solution for absorbed radiation power is sufficiently accurate for laser pulse duration longer than 10 ps. The simulations for superficial tissues with embedded gold nanoshells, used to increase the local volumetric absorption, show that overheating of the nanoshells with respect to the ambient biological tissue is strongly dependent on the laser pulse duration. This effect becomes considerable for laser pulse duration shorter than 1-2 ns. The quasi-steady approach for radiative transfer results in significantly underestimated temperatures of human tissues for short laser radiation pulses. The latter is explained by a relatively strong reflection of the short pulsed radiation by highly scattering human tissues. © 2014 Elsevier Ltd. All rights reserved.

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