Aligned carbon nanotube based ultrasonic microtransducers for durability monitoring in civil engineering

International audienceStructural health monitoring of porous materials such as concrete is becoming a major component in our resource-limited economy, as it conditions durable exploitation of existing facilities. Durability in porous materials depends on nanoscale features which need to be monitored in situ with nanometric resolution. To address this problem, we put forward an approach based on the development of a new nanosensor, namely a capacitive micrometric ultrasonic transducer whose vibrating membrane is made of aligned single-walled carbon nanotubes (SWNT). Such sensors are meant to be embedded in large numbers within a porous material in order to provide information on its durability by monitoring in situ neighboring individual micropores. In the present paper, we report on the feasibility of the key building block of the proposed sensor: we have fabricated well-aligned, ultra-thin, dense SWNT membranes that show above-nanometer amplitudes of vibration over a large range of frequencies spanning from 100 kHz to 5 MHz

Micro−transducteur ultrasonique capacitif à membrane de nanotubes de carbone : Perspectives pour le suivi immergé de la durabilité des matériaux cimentaires

Nous présentons des éléments de la conception, la réalisation et la caractérisation d'un micro−transducteur ultrasonique capacitif haute-fréquence dont la membrane vibrante est faite de nanotubes de carbone alignés. Le dispositif est conçu spécifiquement pour l'instrumentation immergée de la microporosité des matériaux cimentaires. La modélisation élasto−acoustique du dispositif valide préliminairement son intérêt applicatif pour la métrologie de la microporosité

QUALITE DE VISION (DEVELOPPEMENT D'UNE PLATE-FORME EXPERIMENTALE POUR LA CARACTERISATION DES VERRES DIFFUSANTS)

GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Study and realization of an all-solid-state infrared absorption spectrometer (ICLAS) based on a continuous wave Cr4+:YAG laser

GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Self Pulsing, Chaos and Antiphase Dynamics in an Er3+\mathsf{Er^{3+}} Doped Fiber Laser

The temporal dynamics of an Er$^{3+}$ doped fiber laser shows various interesting modes of behaviours. In the transient regime, beating and antiphase phenomena between two orthogonal state of polarisation can be observed, while the total intensity exhibits regular relaxation oscillations. In the stationary regime a Hopf bifurcation appears leading the laser from a cw working mode to different self pulsed working modes. Under a sinusoidal modulated pumping the temporal behaviour of the fiber laser exhibits a period doubling cascade leading to chaos. A study of the influence of the laser parameters allow us to determine (in a reduce parameter spaces) a bifurcation diagram showing the boundary between the different working modes

A very promising piezoelectric property of Ta2O5 thin films. II: Birefringence and piezoelectricity

International audienceBirefringent and piezoelectric properties of Ta2O5 ceramic thin films of monoclinic and trigonal structures were analyzed. The birefringence, observed by reflected polarized light microscopy, yields information on thin film microstructures, crystal shapes and sizes and on crystallographic orientations of grains of trigonal structure. Such an information was considered for investigating piezoelectric properties by laser Doppler vibrometry and by piezoresponse force microscopy. The vibration velocity was measured by applying an oscillating electric field between electrodes on both sides of a Ta2O5 film deposited on a Si substrate which was pasted on an isolating mica sheet. In this case, it is shown that the vibration velocity results were not only from a converse piezoelectric effect, proportional to the voltage, but also from the Coulomb force, proportional to the square of the voltage. A huge piezoelectric strain effect, up to 7.6%, is found in the case of Ta2O5 of trigonal structure. From an estimation of the electrical field through the Ta2O5 thin film, this strain likely corresponds to a very high longitudinal coefficient d(33) of several thousand picorneters. Results obtained by piezoresponse force microscopy show that trigonal grains exhibit a polarization at zero field, which is probably due to stress caused expansion in the transition monoclinic-trigonal, presented in a previous article (part I). (C) 2011 Elsevier Inc. All rights reserved

A very promising piezoelectric property of Ta2O5 thin films. I: Monoclinic-trigonal phase transition

International audienceCeramic thin films of tantalum oxide of a new trigonal structure (a=12.713(7) angstrom, alpha = 28.201(0)degrees, space-group R3) were produced by thermal treatments of amorphous deposits on (001)Si wafers, either by electrostatic spray deposition or by injection metal-organic chemical vapor decomposition. This trigonal phase comes from the transformation of a monoclinic phase 11L- or 25L-Ta2O5. The transformation is reversible under oxygen atmosphere and, from results of TEM investigations, occurs mainly via atomic motions along the z unique axis of the monoclinic structure parallel to the polar three-fold axis of the trigonal structure. The non-centrosymmetry and direction of polar axis of the trigonal phase, identified by high resolution TEM imaging, indicate a possibility of very high electric dipole moments linked to a strong piezoelectricity. From results of XPS analyses of both monoclinic and trigonal structures, the binding energies remain similar to those of Ta2O5. As the formation of the trigonal structure gives rise to an important volume expansion, stresses induced in ceramic thin films are likely influencing both properties of birefringence and piezoelectricity which are presented in a 'separated article (part 11). It is mentioned that the formation of trigonal phase does not occur in bulk Ta2O5 samples, for which an incommensurate phase transition has been observed in a previous work

Prognostic Value of Serum Procalcitonin After Orthopedic Surgery in the Elderly Population

International audienceBackground: Orthopedic surgery is more and more frequent in the older patients and is associated with a high mortality rate. Although serum procalcitonin levels are associated with prognosis in young adults, data are still lacking in the elderly population, and especially after surgery. The main objective of this study was to determine the prognostic value of procalcitonin levels in a large geriatric orthopedic population, and we compared it with clinical variables and biomarkers. Methods: This is a prospective study including patients admitted in our dedicated geriatric postoperative unit, after orthopedic surgery with immediate postoperative measured procalcitonin levels. Collected data included age, sex, medical history, functional status (activities of daily living [ADL]), fracture type, Cumulative Illness Rating scale (CIRS), postoperative complications, and biological data. The primary endpoint was the 30-day mortality. Results: 436 patients (age 85 +/- 6 years) were included. Hip fracture surgery was the most frequent (n = 310; 71%), and the 30-day mortality rate was 6.9%. Compared with C-reactive protein (CRP), albumin, CIRS, and ADL, procalcitonin had the highest area under the receiver operating characteristic curve for predicting 30-day mortality (0.74; 95% CI: 0.70-0.78). Using a cutoff at 1 mu g/L, procalcitonin was more specific than CIRS to predict 30-day mortality (92 vs 77%; p <.001). In a multivariable analysis, procalcitonin level higher than 0.39 mu g/L is a significant predictor of mortality within 30 days (odds ratio 3.84; 95% CI: 1.61-9.14, p =.002). Conclusion: Elevated procalcitonin values were strongly and significantly associated with mortality within 30 days in older patients after orthopedic surgery