EPR study of Ti3+ ions formed under beta irradiation in silicate glasses.

International audienceReduction processes of Ti4+ ions in various silicate glasses have been studied by EPR spectroscopy at 20 K. Different parameters like the [Na]/[Ti] ratio, the integrated dose and Ti3+ ions ageing processes were analyzed in this work. Simulation of the Ti3+ ion EPR spectra in different Ti-doped silicate glasses has shown three different Ti3+ environment attributed to one [VI]Ti3+ and two [V]Ti3+ environment (square pyramid and trigonal bi-pyramid). The [VI]Ti3+ ion environment is observed only for [Na]/[Ti] ratios higher or equal to 68 although the two others are observed for all values of the [Na]/[Ti] ratio considered. In terms of relative proportions, the Ti3+ ions in a square pyramid of oxygen are the dominant species

L' "Arbre de Vie" de Bahreïn, entre mythe et réalité environnementale et archéologique

ArchéOrient - Le Blo

Evaluation of component mode synthesis methods for the detection of modal interaction through rotor/stator contacts

International audienceThe study of interactions through direct contact between blade-tips and outer casings in modern turbomachines may be very time-consuming when the classical finite element method is used. The construction of reduced-order models using component mode synthesis methods generally allows for dramatic increase in computational efficiency and may be used in order to improve the knowledge over these interaction phenomena. Among the available approaches, both a fixed-interface method and a free-interface method are considered here in an original manner to reduce the size of a realistic two-dimensional model. The equations of motion are solved using an explicit time integration scheme with the Lagrange multiplier method where friction is accounted for. This method offers energy momentum conserving which is a critical point to ensure the convergence of the algorithm. Moreover, it is shown that even in a non-linear framework the reduced-order models converge to the finite element solution as the number of modes included in the models increases. Considering the fixed-interface method of Craig-Bampton and the free-interface method of Craig-Chang-Martinez, it is shown that a method with fast displacement convergence may be less efficient in terms of motion convergence

Le choc des images. A propos de la table-ronde "L'iconographie de la guerre au Proche-Orient ancien"

ArchéOrient - Le Blo

Spectroscopic studies of Ti3+ ions speciation inside MgAl2O4 spinels

International audienceAn electron paramagnetic resonance (EPR) investigation on Ti-doped MgAl2O4 spinels has been made in order to study the Ti3+ sites. The study we present here concerns the angular dependencies of the Ti3+ EPR lines and the variations of the EPR spectra due to a modification of the TiO2 content or of the chemical composition from MgAl2O4 to MgAl4O7 and MgAl6O10. In all the studied samples except one, we observe the presence of both Mn2+ and Ti3+ ions. No correlation was observed between Ti3+ amount and TiO2 content; the titanium ions are located in three different sites: the octahedral B site of the spinel structure; the tetrahedral A site and a last site which remains unclear. On the contrary, the major part of the Mn2+ ions is assumed to be in the tetrahedral A site of the spinel structure and a minor part in the octahedral B site. Our work demonstrates the overall interest of EPR spectroscopy in the study of the paramagnetic optically active ions inside optical materials

Interferon-gamma release assays versus tuberculin skin testing for detection of latent tuberculosis in chronic haemodialysis patients

Background. End stage renal disease increases the risk of reactivating latent tuberculosis (LTBI). Interferon-γ release assays (IGRA) are an alternative to the tuberculin skin test (TST) for detecting LTBI. Methods. Sixty-two hemodialysis patients (46 male, 16 female, aged 65 ± 15 years) from 3 hemodialysis facilities in the Geneva area were submitted to a TST, 2 IGRA (T-SPOT.TB and QuantiFERON Gold in tube: QFT), a chest radiography, and a questionnaire to record social status, country of birth, history of prior TST, tuberculosis (TB), BCG (Bacillus of Calmette-Guérin vaccine), and any cause of immuno-suppression. LTBI was defined as prior "at risk” contact with a case of contagious TB and/or a chest X-ray suggestive of prior TB infection. Results. Positivity rate was 19% for TST, 21% for QFT and 29% for T-SPOT-TB; 8% of QFT and 11% of T-SPOT-TB were indeterminate. Agreement between IGRA was fair (κ= 0.60). After adjusting for age and BCG, OR (Odds Ratio) of having a positive QFT was 4.6-fold (p = 0.029) higher in patients with LTBI vs. those without LTBI. In contrast, no association was found between LTBI and having a positive T-SPOT.TB or a positive TST. As expected, there was a strong association between prior BCG vaccination and having a positive TST (OR 5.3, p = 0.017). QFT was the only test with a significant OR of having LTBI (adjusted OR: 4.4; 95%CI: 1.1 − 17.6; p = 0.034). Among 5 patients with definite prior TB, TST and T-SPOT.TB were positive in 1 and QFT, in 2. Conclusions. In this population, QFT was superior to TST for detecting LTBI, but both IGRAs and TST have important limitations, and are unreliable for screening for LTB

Coherent combining of mid-infrared difference frequency generators

International audienceWe report what is, to the best of our knowledge, the first experimental demonstration of coherent combining of two mid-infrared difference frequency generators by active phase control in continuous-wave regime. Using the phase relation that is inherent to the nonlinear process, we are able to phase-lock and combine the idler waves by the sole phase control of one of the pump waves. This control is done by an all fiber electro-optic modulator. Combining is achieved with an excellent efficiency with a residual phase error of λ/28

Implementation of ultrasonic sensing for high resolution measurement of binary gas mixture fractions

We describe an ultrasonic instrument for continuous real-time analysis of the fractional mixture of a binary gas system. The instrument is particularly well suited to measurement of leaks of a high molecular weight gas into a system that is nominally composed of a single gas. Sensitivity < 5 × 10−5 is demonstrated to leaks of octaflouropropane (C3F8) coolant into nitrogen during a long duration (18 month) continuous study. The sensitivity of the described measurement system is shown to depend on the difference in molecular masses of the two gases in the mixture. The impact of temperature and pressure variances on the accuracy of the measurement is analysed. Practical considerations for the implementation and deployment of long term, in situ ultrasonic leak detection systems are also described. Although development of the described systems was motivated by the requirements of an evaporative fluorocarbon cooling system, the instrument is applicable to the detection of leaks of many other gases and to processes requiring continuous knowledge of particular binary gas mixture fractions

GT2004-53372 FORCED RESPONSE PREDICTION METHODOLOGY FOR THE DESIGN OF HP COMPRESSORS BLADED DISKS

ABSTRACT This paper presents a general approach related to bladed disk forced response prediction and a typical way to use it in the design process. Firstly, a good confidence level in prediction tools must be reached. The first application is a highly instrumented HP compressor blisk representative of a real engine environment. Simulation of forced response is compared to measurements in order to check the accuracy of prediction. For this test case, the results obtained are in very good agreement with measurements. The good quality of prediction is due to the complete characterization performed on the test case: all the influent parameters were identified before testing. But during the design process, many important parameters are unknown and this level of accuracy can not be obtained. Nevertheless, forced response prediction in the early design process can provide interesting information even if uncertainties are high for some parameters. As an illustration, a second application is proposed, based on the design experience of a new HP compressor of a known engine family. Some forced response predictions were performed during development and compared afterwards with measurements obtained during engine testing. This analysis has permitted to confirm some technical choices and to assess the High Cycle Fatigue risk associated to this new engine configuration. INTRODUCTION The forced response prediction of bladed disks is the main challenge to mitigate the risk of vibration of these structures. It is a way to avoid the late discovery of High Cycle Fatigue problems. Indeed, in the current design process, engine manufacturers know the vibration levels only at the very end of the development, during engine testing, or sometimes in operation (it is difficult to cover the entire flight domain with ground testing). But forced response prediction is complex because much of the needed information is unknown at the early stages of the design process: -an accurate computation of the aerodynamic forcing function -the dynamic behavior of the structure that can be complex (high modes, mistuning, non linearity) -an estimation of the total damping, as a combination of mechanical and aeroelastic damping. Many solutions have been proposed concerning the forced response simulation tools, both for unsteady aerodynamics and for the fluid/structure coupling. This paper does not describe a new computational method but tries to address the problem of the way to use forced response prediction in the design process. This paper 's objective is to propose a general methodology coherent with an industrial context, that is to say with many unknown parameters

Découverte d’un nouvel individu de Bois de senteur blanc, Ruizia cordata Cav. dans le Nord de l’île de La Réunion et bilan des connaissances sur l’état de conservation de l’espèce (Malvales, Malvaceae, Dombeyoideae)

Abstract : Ruizia cordata Cav., a native species of Réunion Island, is critically endangered as 4 individuals are known to be left in the wild at the dawn of 2015. Today, the success of ex situ programs initiated in the past 30 years is undeniable, ensuring available genetic strains conservation for the generations to come. The finding of a well-shaped new individual in February 2015 in the North coastal cliffs of the island has made a new genetic strain available for ex situ collections. As such, the perspective of discovering other natural individuals still stands as a hope for the long term conservation of R. cordata. Résumé : Ruizia cordata Cav. est en danger critique d’extinction, seulement 4 individus naturels connus et encore en vie sont répertoriés début 2015 à La Réunion. L'introductionex situde R. cordata reste un succès indiscutable, elle assure la conservation à long terme des souches génétiques actuelles. La découverte d’un nouvel individu mâle en bon état en février 2015 sur les falaises littorales du Nord de l’île apporte un espoir pour l’avenir du taxon, avec une nouvelle souche génétique à intégrer dans les efforts de multiplication et la perspective restaurée de trouver de nouvelles stations naturelles.Keywords : habitat lost, hybridisation, endemism, genetic isolation, insular ecosystems.Mots clés : perte d'habitat, hybridation, endémisme, isolation génétique, écosystèmes insulaires