18 research outputs found
Transition to turbulence in duct flow
No full textInternational audienceThe transition of the flow in a duct of square cross-section is studied. Like in the similar case of the pipe flow, the motion is linearly stable for all Reynolds numbers; this flow is thus a good candidate to investigate the 'bypass' path to turbulence. Initially the so-called 'linear optimal perturbation problem' is formulated and solved, yielding optimal disturbances in the form of longitudinal vortices. Such optimals, however, fail to elicit a significant response from the system in the nonlinear regime. Thus, streamwise-inhomogeneous, sub-optimal disturbances are focussed upon; nonlinear quadratic interactions are immediately evoked by such initial perturbations and an unstable streamwise-homogeneous large amplitude mode rapidly emerges. The subsequent evolution of the flow, at a value of the Reynolds number at the edge between fully developed turbulence and relaminarization, shows the alternance of patterns with two pairs of large scale vortices near opposing parallel walls. Such edge states bear a resemblance to optimal disturbance
Optimization of the propulsion of a flapping airfoil by kinematic control
No full textLa cinématique d'une aile battante bidimensionelle est controlée numériquement à travers la résolution des équations du mouvement et des sensibilités d'un écoulement incompressible à faible nombre de Reynolds. Une fonctionnelle liée à l'efficacité du vol est minimisée permettant d'optimiser la propulsion
Boundary Layer Trips for Low Reynolds Number Wind Tunnel Tests
No full textThe generation of a thick fully turbulent boundary layer is investigated in a lowspeed
wind tunnel at a nominal zero pressure gradient over the Reynolds number range
0.145×106 · Rex · 0.58×106. The wind tunnel floor natural boundary layer is laminar with
thickness ± between 5.76 mm and 8.13 mm. Different tripping devices are tested to trigger
transition so to double the boundary layer thickness and provide a fully established turbulent
velocity profile. Using a trip wire significantly increases ± but leads to an unsatisfactory
velocity profiles. Using a sandpaper strip slightly increases ± but keeps the boundary layer
laminar. Using a strip of sharp-edged silicon granules doubles boundary layer thickness
that increases up to 20 mm and the mean velocity profiles are a good fit to the logarithmic
law of the wall over the outer region of the boundary layer. The spectral decay of turbulent
kinetic energy in this outer layer is exponential and close to −5/3, indicating turbulence
equilibrium. This work is of practical interest to wind tunnel practitioners for generating
equilibrium thick turbulent boundary layers at low Reynolds numbers
Optimisation de la cinématique d'un profil battant pour des applications aux micro-drônes
No full textTOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF
Open innovation implementation pratices and firm competitiveness in Malaysian manufacturing industry
No full textMalaysia has successfully transformed from an agriculture -based economy into a resource-based economy. However, Malaysia’s endeavor to transform into an innovation-led economy is presently hindered by the lack of innovation capabilities important for business, as well as by the Malaysian policies’ lack of focus on modern concepts of innovation, such as open innovation. Despite the fact that the implementation of an open innovation concept will enhance the competence of innovation in the manufacturing sector; a theoretical framework for enhancing this implementation in Malaysia is still absent. Furthermore, the relationship between open innovation concept and firms’ competitiveness indicators is still unclear. This thesis determined the effectiveness of the local innovation policy, investigated the level of open innovation practices in the Malaysian manufacturing sector and identified the factors that influence the adoption of open innovation practices. The thesis also examined the relationship between implementing open innovation practices and firms’ competitiveness indicators. A quantitative method with a descriptive and inferential analysis was used to obtain the results of this research. The study population were 1100 manufacturing firms located in Selangor state. Based on the proposed framework which was developed by the author,a valid questionnaire was used in a self-administrated survey to collect the data. The questionnaires were answered by conducting face-to-face interviews with the participants. The participants were 281 manufacturing firms out of the 1100 firms in Selangor. The inferential analysis used was the Parametric Test (One-sample T-test), to investigate the factors included in the proposed framework. After data analyses, the author modified the proposed framework and revealed nine key factors affecting the adoption of open innovation in Malaysia. These factors were grouped into three main areas, intellectual property management in universities, government policies including laws and intellectual property management in industries. This research supports the claim that open innovation concepts have a positive impact on firms' performance, as the study revealed a significant relationship between open innovation adoption and firms’ competitiveness indicators. It was determined that if a firm increases the implementation of open innovation practices, its ability to compete in business will increase. Finally, the study showed that the Malaysian innovation policy has a significant influence on the innovation atmosphere. However, this policy needs improvement in order to support a modern approach to innovation
Factor learning portfolio optimization informed by continuous-time finance models
No full texthttps://openreview.net/forum?id=6TLqwuyg2sFirst author draf
Metallic to Insulating Transition in Disordered Pulsed Laser Deposited Silicide Thin Films
No full textA metal-to-insulating transition has been observed in iron, iron oxide, iron silicide and cobalt silicide thin films when deposited on Si substrate with a native SiOx layer. This transition produced a change in resistance of 5 orders of magnitude at a temperature of 250 K. To the best of the author\u27s knowledge, this effect has not been reported in the literature prior to this study. This work reports a systematic experimental investigation carried out to understand the fundamental mechanism involved in the manifestation of this metal-to-insulator transition. The films were deposited using the pulsed laser deposition technique (PLD) in a base vacuum of the order of 10-6 torr at 400o C and room temperature. Several experiments were systematically conducted to understand the nature of the transition and the current path. Deposition of films on different substrates and the deposition of different transition metal films were made to narrow down the physical origin of the transition in the sample. Temperature-dependent resistance measurements not only exhibited a transition but also suggested more than one conduction mechanism. This is confirmed by the data collected for the IV curves. Current and voltage have a linear relation at temperatures greater than the transition temperature, and a non-linear relation at lower temperatures. Magnetoresistance (MR) measurements revealed a quadratic dependence of the resistance on the applied magnetic field. This is an indication that the MR observed is due to Lorentz forces acting on the charge carriers. Transmission electron microscopy and x-ray photoelectron spectroscopy have identified different layers that are believed to be responsible for the observed transition
Impact of dietary methionine on respiratory tissue integrity and humoral immunity of broilers challenged with Mycoplasma gallisepticum and treated with Pulmotil AC®
No full textThe experiment was performed to determine the effect of 20% dietary DL-Methionine (Met) in excess of modern breeder requirement level compared to Tilmicosin (Pulmotil AC®) on the humoral immune response and histopathological parameters of male broilers challenged with Mycoplasma gallisepticum (MG). Birds of Treatments 1–4 remained unchallenged while those of Treatments 5–8 were challenged with MG at 10 days of age. Diets with excess Met were formulated for birds of Treatments 3, 4, 7 and 8. Broilers of Treatments 2, 3, 6 and 7 were administered Pulmotil AC® in drinking water. The 20% excess dietary Met significantly reduced tracheal deciliation, preserved the integrity of tracheal mucosal layer and significantly decreased goblet cell degeneration in MG-challenged birds. Furthermore, MG-challenged broilers administered 20% excess Met manifested higher ELISA titers against MG and a significantly higher antibody response to p33 (MG-cytadhesin putative gene) and p66 (MG-hemagglutinin protein A (pMGA)) in comparison to the other treatments. The 20% excess Met thereby maintained the health of the respiratory system and embodied an increased protection against MG-putative gene and a greater humoral response to MG challenge in broilers. © 2019, © 2019 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group
Physiological and Perceptual Responses to Incremental Exercise Testing in Healthy Men: Effect of Exercise Test Modality
No full textIn a randomized cross-over study of 15 healthy men aged 20-30 years, we compared physiological and perceptual responses during treadmill and cycle exercise test protocols matched for increments in work rate – the source of increased locomotor muscle metabolic and contractile demands. The rates of O2 consumption (V̇O2) and CO2 production (V̇CO2) were higher at the peak of treadmill vs. cycle testing (p≤0.05). Nevertheless, work rate, minute ventilation (V̇E), tidal volume (VT), breathing frequency (fR), inspiratory capacity (IC), inspiratory reserve volume (IRV), tidal esophageal (Pes,tidal) and transdiaphragmatic pressure swings (Pdi,tidal), peak expiratory gastric pressures (Pga,peak), the root mean square of the diaphragm EMG (EMGdi,rms) expressed as a percentage of maximum EMGdi,rms (EMGdi,rms%max), and dyspnea ratings were similar at the peak of treadmill vs. cycle testing (p>0.05). Ratings of leg discomfort were higher at the peak of cycle vs. treadmill exercise (p≤0.05), even though peak V̇O2 was lower during cycling. V̇O2, V̇CO2, V̇E, fR, Pes,tidal, Pdi,tidal and Pga,peak were higher (p≤0.05), while VT, IC, IRV, EMGdi,rms%max, and ratings of dyspnea and leg discomfort were similar (p>0.05) at all or most submaximal work rates during treadmill vs. cycle exercise. Our findings highlight important differences (and similarities) in physiological and perceptual responses at maximal and submaximal work rates during incremental treadmill and cycle exercise testing protocols. The lack of effect of exercise test modality on peak work rate advocates for the use of this readily available parameter to optimize training intensity determination, regardless of exercise training mode.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author
