Caractérisation dynamique des fibres synthétiques et végétales

International audienceObjective: go further in structural and multifunctional applications• to master the natural resources• to control the mechanical properties in a specific environment• to optimize the architecturation of the composit

CMUT sensors based on circular membranes array for SHM applications

International audienceA MEMS sensor dedicated to SHM applications is presented. The MEMS is made of a Capacitive Micromachined Ultrasonic Transducer (CMUT) chip composed of circular membranes array. The radius of the membranes vary between 50 µm and 250 µm and hence the associated resonance frequencies between 80 kHz and 2 MHz. A wide frequency bandwidth is then available for acoustic measurements. A testing campaign is conducted in order to characterize the MEMS sensor's behavior when subjected to single-frequency and broadband excitation stimuli. The single-frequency excitations are produced with specific piezoelectric transducers from 300 kHz to 800 kHz. The Fast Fourier Transform (FFT) of the measured signal from the CMUT is centered as expected on the excitation frequency. The broadband excitation is obtained with a pencil lead break. In this case, the FFT of the measured signal is centered on the resonance frequency of the membrane. These characterizations point out the DC bias voltage applied to the CMUT as a major parameter for controlling the sensitivity of thesensor. The CMUT sensor proves to be sufficiently sensitive to monitor these sources. This work highlights the relevant prospective capacities of the CMUT sensor to collect data in structural health monitoring applications. This sensor technology could be externally deployed, or even integrated into a composite structure, in order to monitor the structure by the CMUT detection, either by active ultrasound tests or by passive acoustic emission

Bordering the footprint of AE sensor using a bank of sharply-defined frequency domain capacitive micromachined ultrasonic transducers

International audienceThe Acoustic Emission (AE) technique is widely used in Structural Health Monitoring (SHM) in order to detect, in real-time, small-scale damages and to evaluate their kinetics. The piezoelectric transduction is generally favored for detecting the subnanometric displacements of the surface of a material induced by the propagation of the elastic waves generated by the sudden release of energy during damage. Yet highly sensitive, this type of sensor has a great impact on the signals collected introducing interpretation biases when assigning damage families to AE signals. In this paper, new Capacitive Micromachined Ultrasonic Transducers (CMUT) have been designed and tested with the objective to decrease the footprint of AE sensors compared to conventional piezoelectric sensor. CMUT allow getting AE sensors with wide-band and flat response making them of great interest for the collection of AE signals in SHM solutions

Towards a better understanding of the CMUTs potential for SHMapplications

International audienceThe ability of Capacitive Micromachined Ultrasonic Transducer (CMUTs) todesign broadband sensors for Structural Health Monitoring (SHM) is studiedthrough both multi-frequency and bandwidth aspects. Elementary cells arecomposed of circular membranes fabricated using the standard MUMPS Process. The multi-frequency aspect, which involves different individual membranes from 50 µm to 250 µm radius, is theoretically addressed through anumerical modeling. The targeted frequency range, consistent with the SHMapplication, is then between 80 kHz and 2 MHz. Geometrical features induced by the manufacturing process greatly affect the dynamic properties ofthe membranes and this is experimentally validated. The bandwidth aspectis also addressed on an array of identical 100 µm radius membranes thusinvolving their intrinsic capabilities. Harmonic excitation with targeted frequencies 300 kHz, 530 kHz and 800 kHz, below and beyond the resonancefrequency of the membranes, are performed. The influence of the bias voltage VDC on the signal-to-noise ratio is studied according to the excitationfrequency. As a result, a signal-to-noise of 20 dB is achieved around the resonance frequency. Finally, the circular membranes array is tested for acousticemission sensing through a pencil lead break test. In spite of a low signal-tonoise ratio, acoustic events are clearly detected. The multi-frequency aspectand the large bandwidth capability of the CMUTs are hence demonstratedand highlight the adaptability of the sensor to its environment

Bordering the footprint of AE sensor using a bank of sharply-defined frequency domain capacitive micromachined ultrasonic transducers

International audienceThe Acoustic Emission (AE) technique is widely used in Structural Health Monitoring (SHM) in order to detect, in real-time, small-scale damages and to evaluate their kinetics. The piezoelectric transduction is generally favored for detecting the subnanometric displacements of the surface of a material induced by the propagation of the elastic waves generated by the sudden release of energy during damage. Yet highly sensitive, this type of sensor has a great impact on the signals collected introducing interpretation biases when assigning damage families to AE signals. In this paper, new Capacitive Micromachined Ultrasonic Transducers (CMUT) have been designed and tested with the objective to decrease the footprint of AE sensors compared to conventional piezoelectric sensor. CMUT allow getting AE sensors with wide-band and flat response making them of great interest for the collection of AE signals in SHM solutions

Viscoelastic properties of plant fibers - Dynamic analysis and nanoindentation tests

International audienceIt is now established that plant fibers are suitable reinforcements to replace or to complete synthetic fibers for composite applications. They have many well-known advantages such as being renewable, biodegradable and having high specific mechanical properties and intrinsic damping properties that can impart attractive benefits to composite materials. When compared to glass and carbon fibers reinforced polymer composites, PFCs exhibit generally higher damping properties. This is commonly attributed to the polymeric nature of the fibers. It could also result from their hierarchical structure and microstructural specificities. Indeed, damping in composite materials is induced by several microscopic level mechanisms related to the viscoelasticity of both matrix and fibers, but also by the fiber/matrix interface and the friction between fibers inside bundles or between layers. The presence of lumen could also play a role. At this stage, the damping source is not well identified, and the design and the optimization of composites, for structural applications, are then difficult. A better knowledge of the physical phenomena involved is therefore necessary

Synthesis, Photophysical, Photochemical, and Computational Studies of Coumarin-Labeled Nicotinamide Derivatives

The syntheses and photophysical/photochemical properties of two amide-tethered coumarin-labeled nicotinamides are described. Photochemical studies of 6-bromo-7-hydroxycoumarin-4-ylmethylnicotinamide (BHC-nicotinamide) revealed an unexpected solvent effect. This result is rationalized by computational studies of the different protonation states using TD-DFT with the M06L/6-311+G** method with implicit and explicit solvation models. Molecular orbital energies responsible for the λ_max excitation show that the functionalization of the coumarin ring results in a strong red-shift from 330 to 370 nm when the pH of solution is increased from 3.06 to 8.07. From this MO analysis, a model for solvent interactions has been proposed. The BHC-nicotinamide proved to be photochemically stable, which is also interpreted in terms of NBO calculations. The results provide a set of principles for the rational design of either photostable labeling reagents or photolabile cage compounds

Lysosomal acid lipase and lipophagy are constitutive negative regulators of glucose-stimulated insulin secretion from pancreatic beta cells

AIMS/HYPOTHESIS: Lipolytic breakdown of endogenous lipid pools in pancreatic beta cells contributes to glucose-stimulated insulin secretion (GSIS) and is thought to be mediated by acute activation of neutral lipases in the amplification pathway. Recently it has been shown in other cell types that endogenous lipid can be metabolised by autophagy, and this lipophagy is catalysed by lysosomal acid lipase (LAL). This study aimed to elucidate a role for LAL and lipophagy in pancreatic beta cells. METHODS: We employed pharmacological and/or genetic inhibition of autophagy and LAL in MIN6 cells and primary islets. Insulin secretion following inhibition was measured using RIA. Lipid accumulation was assessed by MS and confocal microscopy (to visualise lipid droplets) and autophagic flux was analysed by western blot. RESULTS: Insulin secretion was increased following chronic (≥ 8 h) inhibition of LAL. This was more pronounced with glucose than with non-nutrient stimuli and was accompanied by augmentation of neutral lipid species. Similarly, following inhibition of autophagy in MIN6 cells, the number of lipid droplets was increased and GSIS was potentiated. Inhibition of LAL or autophagy in primary islets also increased insulin secretion. This augmentation of GSIS following LAL or autophagy inhibition was dependent on the acute activation of neutral lipases. CONCLUSIONS/INTERPRETATION: Our data suggest that lysosomal lipid degradation, using LAL and potentially lipophagy, contributes to neutral lipid turnover in beta cells. It also serves as a constitutive negative regulator of GSIS by depletion of substrate for the non-lysosomal neutral lipases that are activated acutely by glucose

Protease-Activated Receptor-1 Antagonist F 16618 Reduces Arterial Restenosis by Down-Regulation of Tumor Necrosis Factor α and Matrix Metalloproteinase 7 Expression, Migration, and Proliferation of Vascular Smooth Muscle Cells

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