Open Archive Toulouse Archive Ouverte

    3D digital image correlation applied to birdstrike tests

    Get PDF
    The development of new bird strike shielding materials for commercial aircrafts requires test campaigns. During these tests, measurement of the high speed deformation is needed to characterize and compare the mechanical response of the shielding samples and to correlate numerical simulations with experiments. In this work, 3D digital image correlation method is used with high speed (HSP) cameras to compute the displacement and strain fields on a large area (approximately 400mm wide) of the back side of impacted samples. Compromise on spatial resolution, frame rate of HSP camera and measurement error is discussed

    Vocal Problems in Sports and Fitness Instructors: A Study of Prevalence, Risk Factors, and Need for Prevention in France

    Get PDF
    Objectives Sports and fitness instructors (SFIs) are known for being a high-risk population for voice difficulties (VD). However, past studies have encountered various methodological difficulties in determining prevalence and risk factors for VD in SFIs, such as limited population, gender and selection biases, or poor statistical power, because VD were studied as a binary variable. The present research work addresses these issues and aims at studying the prevalence of vocal problems and risk factors in French SFIs, a population in which no such study was conducted yet. Another objective is to survey the French SFIs' habits and expectations regarding vocal prevention and care. Study design This is a cross-sectional study. Methods Three hundred and twenty SFIs answered a questionnaire, whether in an online (né=é267) or a paper (né=é53) version. The questionnaire consisted of 31 items addressing self-reported vocal difficulties, supposed risk factors, and personal health-care history, followed by the Voice Handicap Index assessment. Results Prevalence of self-reported vocal difficulties is 55%. The Voice Handicap Index is significantly associated with gender, age, and variables related to work environment (noise and music) and habits (shouting, frequency of classes), as well as with daily sleeping time. Results also indicate that a minority of the SFIs (37%) received information on vocal difficulties, whereas a majority (80%) declares being interested in participating in prevention programs. Conclusions This work confirms that SFIs are a high-risk population for VD, underlines the need for specific information programs in France, and provides relevant data for driving such preventive actions

    Structural Properties of Double-Walled Carbon Nanotubes Driven by Mechanical Interlayer Coupling

    Get PDF
    Structural identification of double-walled carbon nanotubes (DWNTs) is presented through a robust procedure based on the latest generation of transmission electron microscope, making possible a statistical analysis based on numerous nanoobjects. This approach reveals that inner and outer tubes of DWNTs are not randomly oriented, suggesting the existence of a mechanical coupling between the two concentric walls. With the support of atomic-scale modeling, we attribute it to the presence of incommensurate domains whose structures depend on the diameters and helicities of both tubes and where inner tubes try to achieve a local stacking orientation to reduce strain effect

    Mechanical properties of flax and hemp yarns designed for the manufacturing of geotextiles. Improvement of the resistance to soil born microorganisms.

    Get PDF
    Geotextiles are widely used to stabilize river banks from erosion when these ones are restored into vegetal covered areas as mentioned by European regulations. For these applications imported coir (coconut shell fibres) based geotextiles are generally used because coir fibres show a good resistance to soil degradation. In Europe, flax and hemp plants are already grown for textile, building or oil applications. By-products of these industries such as flax tows and short hemp fibres were used to manufacture yarns. The resistance to degradation via the measurement of the mechanical properties of these yarns submitted to enzymatic (cellulase) and microbial attacks (Cellvibrio gandavensis) mimicking soil degradation was evaluated. Large decreases in mechanical properties were observed, even though these ones were still higher than the as received reference coir material. After impregnation by chitosan of the fibres, the tensile properties of the yarns globally remained unchanged after severe attacks. The chitosan acts as a protection against the soil microorganism attacks. As a consequence, flax and hemp by-products could be good candidates for local manufacturing of biodegradable geotextiles

    How to Build an Average Model When Samples Are Variably Incomplete? Application to Fossil Data

    No full text
    In paleontology, incomplete samples with small or large missing parts are frequently encountered. For example, dental crowns, which are widely studied in paleontology because of their potential interest in taxonomic and phylogenetic analyses, are nearly systematically affected by a variable degree of wear that alters considerably their shape. It is then difficult to compute a significant reference surface model based on classical methods which are used to build atlases from set of samples. In this paper, we present a general approach to deal with the problem of estimating an average model from a set of incomplete samples. Our method is based on a state-of-the-art non-rigid surface registration algorithm. In a first step, we detect missing parts which allows one to focus only on the common parts to get an accurate registration result. In a second step, we try to build average model of the missing parts by using information which is available in a subset of the samples. We specifically apply our method on teeth, and more precisely on the surface in between dentine and enamel tissues (EDJ). We investigate the robustness and accuracy properties of the methods on a set of artificial samples representing a high degree of incompleteness. We compare the reconstructed complete shape to a ground-truth dataset. We then show some results on real data

    An efficient torque speed characteristic calculation method for brusbless C.A.D using optimization techniques

    Get PDF
    Nowadays, powerful tools enable to simulate the work of inverter fed machine systems. But, they generally require long calculation times and large memory capacities and many parameters, So, they are not well adapted for an iterative design. In this paper, we present an efficient model, based on optimization techniques, for current fed synchronous machines fed by means of current controlled voltage inverter which leads to very short calculation times to determine torque speed characteristic of such a actuator. The limits of the valitidy of this model are discussed and simulated results are compared to experimental ones for validation

    Analysis of the deformability of flax-fibre nonwoven fabrics during manufacturing.

    Get PDF
    The use of natural fibres for technical advanced products such as composites is widely increasing with the view to reduce the impact of the material throughout its life cycle on the environment. Some work has been performed on natural fibre based reinforcement textiles for composite materials. The mechanical and the formability behaviours of woven fabrics has particularly been characterised. However, few research work concerns the forming aptitude of nonwoven fabrics despite promising preliminary studies. In the present work, the mechanical characterizations of flax-fibre nonwoven reinforcements are carried out firstly. Then the forming tests of the nonwoven fabrics are performed to quantify their formability behaviour. The tensile and forming tests showed very different mechanical behaviours in comparison to the ones observed on woven fabrics due to the non-uniformity of nonwoven fabric. The high deformation potential of the nonwoven fabrics is established. The specific behaviour of the nonwoven fabrics is studied by analysing the local and global deformation mechanisms of the reinforcement during forming. Moreover, the manufacturing defects experienced in nonwoven fabric forming are demonstrated. The slippage/damage of network is a typical problem in the nonwoven fabric forming, which depends strongly on the fibre density (area density) of fabric and blank-holder pressure

    Marangoni-driven convection around exothermic autocatalytic chemical fronts in free-surface solution layers

    Get PDF
    Gradients of concentration and temperature across exothermic chemical fronts propagating in free-surface solution layers can initiate Marangoni-driven convection. We investigate here the dynamics arising from such a coupling between exothermic autocatalytic reactions, diffusion, and Marangoni-driven flows. To this end, we numerically integrate the incompressible Navier-Stokes equations coupled through the tangential stress balance to evolution equations for the concentration of the autocatalytic product and for the temperature. A solutal and a thermal Marangoni numbers measure the coupling between reaction-diffusion processes and surface-driven convection. In the case of an isothermal system, the asymptotic dynamics is characterized by a steady fluid vortex traveling at a constant speed with the front, deforming and accelerating it [L. Rongy and A. De Wit, J. Chem. Phys. 124, 164705 (2006)]. We analyze here the influence of the reaction exothermicity on the dynamics of the system in both cases of cooperative and competitive solutal and thermal effects. We show that exothermic fronts can exhibit new unsteady spatio-temporal dynamics when the solutal and thermal effects are antagonistic. The influence of the solutal and thermal Marangoni numbers, of the Lewis number (ratio of thermal diffusivity over molecular diffusivity), and of the height of the liquid layer on the spatio-temporal front evolution are investigated. As a chemical reaction induces changes in the temperature and in the composition of the reactive medium, it can modify the properties of the solution (density, viscosity, surface tension) and thereby trigger convective motions, which in turn affect the reaction. Such a coupling can typically be observed around reactive interfaces in liquid solutions. Two classes of convective flows are then commonly developing in solutions open to air, namely Marangoni flows arising from surface tension gradients and buoyancy flows driven by density gradients. As both flows can be induced by compositional changes as well as thermal changes and in turn modify them, the resulting experimental dynamics are often complex. The purpose of our study is to gain insight into these intricate dynamics thanks to the theoretical analysis of model systems where only one type of convective flow is present. We address here the dynamics of an exothermic autocatalytic front propagating in the presence of Marangoni flows, when the density remains uniform. The surface tension gradient across the front has both a thermal component linked to the exothermicity of the reaction and a solutal component arising from the change in the chemical composition during the reaction. We show that the thermal effects modify the properties of the isothermal system and that new dynamics such as oscillations of the concentration field can be observed when the solutal and thermal effects act antagonistically on the surface tension, provided that they act on different length scales

    Participatory methods in surveillance and control of foot-and-mouth disease : how to better involve the farmers at local scale ?

    Get PDF
    This PhD thesis aimed at evaluating the contribution of participatory epidemiology (PE) to improve the foot-and-mouth disease (FMD) surveillance and control activities, especially the involvement of farmers at local level. The first objective aimed at assessing the effectiveness of the FMD surveillance and vaccination strategy at local level by using PE approach. The second objective aimed at assessing the feasibility of applying PE tools to improve the involvement of farmers in the FMD surveillance in Vietnam. PE methods performed in our study included informal interviews (focus group and individual), scoring tools (pairwise ranking, proportional pilling, disease impact matrix scoring and disease signs matrix scoring), visualization tools (mapping, timeline, flow chart) and sociological tools called Q methodology. 122 focus groups, 467 individual interviews, 339 questionnaire surveys were performed during two field studies in 2014 and 2015. 409 sera and 152 probang samples were taken. Conventional questionnaire surveys, Bayesian modelling and laboratory test (ELISA and rtRT-PCR) was used to validate the performance of PE in FMD surveillance. Disease was considered as the most important issues in animal production. FMD was the most important disease for dairy cattle production, followed by haemorrhagic septicaemia. For beef cattle production, it was recorded in reverse order. The most important disease for pig production was porcine reproductive and respiratory syndrome while FMD was ranked fourth. Farmers showed their abilities in differential diagnostic of important diseases based on its clinical symptoms. Sero-prevalence of FMD were estimated at 23% for population 1 (bordering with Cambodia) and 31% for population 2 (locating far from the border), respectively. Sensitivity and Specificity of PE were found to be 59% and 81%, respectively. The positive and negative predictive value were found to be 48% and 86% for population 1 and 58% and 81% for population 2, respectively. The presence of serotype A, lineage A/Asia/Sea-97 and serotype O with two separate lineages, O/ME-SA/PanAsia and O/SEA/Mya-98 supported virus circulation through trans-boundary animal movement activities. Dairy farms frequently applied quarantine, disinfection and vaccination as prevention methods. Beef farms preferred cleanliness and good husbandry management practices. Pig farms considered that all prevention methods had the same importance. Three distinct discourses “Believe”, “Confidence”, “Challenge”, representing common perceptions among farmers and accounting for 57.3 % of the variance, were identified based on Q methodology. Farmers take vaccination decisions themselves without being influenced by other stakeholders and feel more secure after FMD vaccination campaigns. However, part of the studied population did not consider vaccination to be the first choice of prevention strategy. The benefitcost ratio of FMD vaccination for dairy cow production in large-scale and in small-scale and meat cattle production were 37.2, 30.0 and 7.3, respectively. The sensibility analysis showed that FMD vaccination was profitable for all of production types even through the increase of vaccine cost and decrease of market price of milk and slaughter cattle. From the focus groups organized at sentinel villages, 18 new villages were identified as potentially infected by FMD. 77 suspected animals were confirmed positive for FMD, with viral serotypes O and A. Sensitivity and specificity of participatory surveillance were recorded at 0.75 and 0.65, respectively. The effectiveness of PE in FMD surveillance system to detect outbreak in Vietnam was demonstrated. It was demonstrated that vaccination was the most effective and economic method to prevent FMD. Through the application of simple, adaptive tools which facilitate direct and active participation of farmers, PE allowed to reach a better acceptability of surveillance and to obtain qualified information

    Phase equilibria of aqueous solutions of formaldehyde and methanol: Improved approach using UNIQUAC coupled to chemical equilibria

    Get PDF
    The study of the phase equilibria involving formaldehyde is still relevant because of its presence in new processes where biomass is the raw material. The coupling between physical phase equilibria and chemical reactions makes its thermodynamic description a challenging task. In this work, an improved approach using UNIQUAC coupled to chemical equilibria was developed and compared with experimental data from the literature. The first application was done for the phase equilibria of the formaldehyde–water system and distribution of oligomers in the liquid phase was computed. The second and the third applications respectively considered the phase equilibria of the formaldehyde–methanol system and the formaldehyde–water–methanol system
    Open Archive Toulouse Archive Ouverte is based in FR
    Do you manage Open Archive Toulouse Archive Ouverte? Access insider analytics, issue reports and manage access to outputs from your repository in the CORE Dashboard!