31 research outputs found
Flow rate--pressure drop relation for deformable shallow microfluidic channels
Laminar flow in devices fabricated from soft materials causes deformation of
the passage geometry, which affects the flow rate--pressure drop relation. For
a given pressure drop, in channels with narrow rectangular cross-section, the
flow rate varies as the cube of the channel height, so deformation can produce
significant quantitative effects, including nonlinear dependence on the
pressure drop [{Gervais, T., El-Ali, J., G\"unther, A. \& Jensen, K.\ F.}\ 2006
Flow-induced deformation of shallow microfluidic channels.\ \textit{Lab Chip}
\textbf{6}, 500--507]. Gervais et. al. proposed a successful model of the
deformation-induced change in the flow rate by heuristically coupling a Hookean
elastic response with the lubrication approximation for Stokes flow. However,
their model contains a fitting parameter that must be found for each channel
shape by performing an experiment. We present a perturbation approach for the
flow rate--pressure drop relation in a shallow deformable microchannel using
the theory of isotropic quasi-static plate bending and the Stokes equations
under a lubrication approximation (specifically, the ratio of the channel's
height to its width and of the channel's height to its length are both assumed
small). Our result contains no free parameters and confirms Gervais et. al.'s
observation that the flow rate is a quartic polynomial of the pressure drop.
The derived flow rate--pressure drop relation compares favorably with
experimental measurements.Comment: 20 pages, 6 figures; v2 minor revisions, accepted for publication in
the Journal of Fluid Mechanic
Bioinspired turbine blades offer new perspectives for wind energy
Wind energy is becoming a significant alternative solution for future energy production. Modern turbines now benefit from engineering expertise, and a large variety of different models exists, depending on the context and needs. However, classical wind turbines are designed to operate within a narrow zone centred around their optimal working point. This limitation prevents the use of sites with variable wind to harvest energy, involving significant energetic and economic losses. Here, we present a new type of bioinspired wind turbine using elastic blades, which passively deform through the air loading and centrifugal effects. This work is inspired from recent studies on insect flight and plant reconfiguration, which show the ability of elastic wings or leaves to adapt to the wind conditions and thereby to optimize performance. We show that in the context of energy production, the reconfiguration of the elastic blades significantly extends the range of operating regimes using only passive, non-consuming mechanisms. The versatility of the new turbine model leads to a large increase of the converted energy rate, up to 35%. The fluid/elasticity mechanisms involved for the reconfiguration capability of the new blades are analysed in detail, using experimental observations and modelling
COUP-TFII Controls Mouse Pancreatic ÎČ-Cell Mass through GLP-1-ÎČ-Catenin Signaling Pathways
Background: The control of the functional pancreatic beta-cell mass serves the key homeostatic function of releasing the right amount of insulin to keep blood sugar in the normal range. It is not fully understood though how beta-cell mass is determined
Horizontal-axis wind turbines optimization by the use of flexible blades
LâĂ©olien est un secteur industriel en pleine expansion, qui joue un rĂŽle fondamental dans le dĂ©veloppement des Ă©nergies renouvelables. Cependant ces machines sont performantes sur une plage de fonctionnement Ă©troite. Afin dâadapter lâĂ©olienne aux changements de vent, une solution actuellement mise en place sur certaines Ă©oliennes commerciales consiste aÌ faire varier lâangle de calage (ie lâinclinaison) des pales au cours de son fonctionnement. Cette mĂ©thode de contrĂŽle actif Ă©largit la plage de hauts rendements ainsi que la plage de fonctionnement global, et amĂ©liore le dĂ©marrage de lâĂ©olienne, mais elle nâaugmente pas le rendement maximal atteint par une Ă©olienne aÌ angle de calage optimal fixeÌ. Cependant la complexitĂ©Ì de cette mĂ©thode ainsi que ses coĂ»ts de conception, de construction et de maintenance la rende inaccessible pour beaucoup dâĂ©oliennes, en particulier celles de petite taille. RĂ©cemment des recherches se sont orientĂ©es vers un contrĂŽle passif de lâangle de calage. Dans cette thĂšse nous examinons expĂ©rimentalement et thĂ©oriquement lâintĂ©rĂȘt dâutiliser des pales flexibles suivant la corde sur une Ă©olienne aÌ axe horizontal. LâĂ©tude se concentre sur deux questions : - comprendre le mĂ©canisme de reconfiguration de la pale flexible bio-inspirĂ©e : la dĂ©formation de la pale est due aÌ la compĂ©tition entre les forces aĂ©rodynamiques, qui augmentent lâangle de calage moyen, et la force centrifuge qui le diminue. Ces effets sont gouvernĂ©s par deux nombres adimensionnĂ©s, respectivement le nombre de Cauchy et le nombre centrifuge. - qualifier et quantifier le gain en performances de lâĂ©olienne : une flexibilitĂ©Ì de pale modĂ©rĂ©e Ă©largit la plage de fonctionnement, et augmente significativement le rendement de lâĂ©olienne, expĂ©rimentalement jusquâaÌ 35% sur la plage de hauts rendements. Une procĂ©dure dâoptimisation visant aÌ dĂ©terminer le matĂ©riau optimal de la pale flexible est prĂ©sentĂ©e. Ces gains obtenus en rĂ©gime stationnaire sont conservĂ©s expĂ©rimentalement en moyenne en rĂ©gime instationnaire. Deux temps caractĂ©ristiques sont identifiĂ©s : le temps de reconfiguration de la pale flexible et le temps de variation de la frĂ©quence de rotation de lâĂ©olienneWind energy is a rapidly growing branch of industry, playing a significant role in the development of renewable energies. However these machines are efficient only on a narrow working range. In order to adapt wind turbines to wind changes, some commercial machines are pitch controlled during rotation. This active control method extends the high-efficiency range and the total working range, and improves the starting phase, but it does not increase the maximum efficiency reached by a wind turbine with the fixed optimal pitch angle. However this method is complex and costly (design, construction, maintenance). Thus it becomes cost-effective only for large wind turbines. Research recently focused on passive pitch control. In this thesis, the contribution of chord wise flexible blades is studied both experimentally and theoretically. The thesis concentrates on: - the reconfiguration mechanism of the bio-inspired flexible blade : the deformation is the result of the competition between aerodynamic forces, which increase the pitch angle, and the centrifugal force, which reduces it. These two effects are governed by two dimensionless numbers, respectively the Cauchy number and the centrifugal number. - how to qualify and quantify the efficiency gains : a moderate flexibility extends the working range, and significantly increases wind turbine efficiency, up to 35% on the high-efficiency working range. An optimization procedure is presented, which aims at determining the optimal material to construct the blade. These improvements measured in steady regime are maintained on average when rotational speed is unsteady. Two characteristic times are identified: the reconfiguration time of the flexible blade and the time of variation of the rotational speed of the wind turbin
Termite graveyards. Hidden geochemical patches?
International audienceEntombment, or the production of graveyards for the disposal of dead bodies, is not only a practice of human societies but is also observed in nature, including among small invertebrates such as termites. While the influence of termites on soil dynamics has largely been studied in comparing the specific properties of their mounds and protective sheeting with those of the surrounding soil, the properties of their graveyards have never been described before. Using incipient colonies of Macrotermes natalensis reared in a controlled environment, we showed that graveyard sheeting was characterized by a much higher C content in comparison with the reference soil and protective sheeting (4.7-fold increase). As a consequence, a slight increase in the C:N ratio was measured from 8 in the reference soil to 10 in graveyard sheeting. No changes in soil particle size fractions were measured. However, lower Fe and Al contents were measured in sheeting, and micrographs obtained from scanning electron microscopy revealed the presence of calcium carbonate, or calcium oxalate crystals, in sheeting, as well as the presence of organic substances and salt crystals covering termite corpses, most likely for controlling the spread of pathogens. The presence of calcium carbonates and/or calcium oxalate was explained by the very high Ca content within termite bodies. Therefore, this study shows that termite graveyards are likely to constitute unexplored patches of nutrients in soil
Use of visual aids in general practice consultations: A questionnaire-based survey
Objectives: Visual aids (VAs) seem effective to improve doctor-patient communication. The objective was to describe how VAs are used in consultation and what French general practitioners (GPs) expect of them. Methods: Cross-sectional study using a self-administered questionnaire among French GPs in 2019. Descriptive and multinominal logistic regression analyses were performed. Results: Of the 376 respondents, 70% used VAs at least weekly and 34% daily; 94% considered VAs useful/very useful; 77% felt they did not use VAs enough. Sketches were the most used VAs and considered the most useful. Younger age was significantly associated with a higher rate of use of simple digital images. VAs were mainly used to describe anatomy and facilitate patient comprehension. Main reasons for not using VAs more often were time spent searching, lack of habit and poor quality of available VAs. Many GPs requested a database of good quality VAs. Conclusions: GPs use VAs regularly in consultations but would like to use them more often. Informing GPs of the usefulness of VAs, training them to draw adapted sketches and creating a good quality databank are some possible strategies to increase the use of VAs. Innovation: This study described in detail the use of VAs as tool for doctor-patient communication
Local circuit allowing hypothalamic control of hippocampal area CA2 activity and consequences for CA1
International audienceThe hippocampus is critical for memory formation. The hypothalamic supramammillary nucleus (SuM) sends long-range projections to hippocampal area CA2. While the SuM-CA2 connection is critical for social memory, how this input acts on the local circuit is unknown. Using transgenic mice, we found that SuM axon stimulation elicited mixed excitatory and inhibitory responses in area CA2 pyramidal neurons (PNs). Parvalbumin-expressing basket cells were largely responsible for the feedforward inhibitory drive of SuM over area CA2. Inhibition recruited by the SuM input onto CA2 PNs increased the precision of action potential firing both in conditions of low and high cholinergic tone. Furthermore, SuM stimulation in area CA2 modulated CA1 activity, indicating that synchronized CA2 output drives a pulsed inhibition in area CA1. Hence, the network revealed here lays basis for understanding how SuM activity directly acts on the local hippocampal circuit to allow social memory encoding