Diversity and Functional Traits of Lichens in Ultramafic Areas: A Literature Based Worldwide Analysis Integrated by Field Data at the Regional Scale

While higher plant communities found on ultramafics are known to display peculiar characteristics, the distinguishability of any peculiarity in lichen communities is still a matter of contention. Other biotic or abiotic factors, rather than substrate chemistry, may contribute to differences in species composition reported for lichens on adjacent ultramafic and non-ultramafic areas. This work examines the lichen biota of ultramafics, at global and regional scales, with reference to species-specific functional traits. An updated world list of lichens on ultramafic substrates was analyzed to verify potential relationships between diversity and functional traits of lichens in different Köppen–Geiger climate zones. Moreover, a survey of diversity and functional traits in saxicolous communities on ultramafic and non-ultramafic substrates was conducted in Valle d’Aosta (North-West Italy) to verify whether a relationship can be detected between substrate and functional traits that cannot be explained by other environmental factors related to altitude. Analyses (unweighted pair group mean average clustering, canonical correspondence analysis, similarity-difference-replacement simplex approach) of global lichen diversity on ultramafic substrates (2314 reports of 881 taxa from 43 areas) displayed a zonal species distribution in different climate zones rather than an azonal distribution driven by the shared substrate. Accordingly, variations in the frequency of functional attributes reflected reported adaptations to the climate conditions of the different geographic areas. At the regional scale, higher similarity and lower species replacement were detected at each altitude, independent from the substrate, suggesting that altitude-related climate factors prevail over putative substrate–factors in driving community assemblages. In conclusion, data do not reveal peculiarities in lichen diversity or the frequency of functional traits in ultramafic areas

Analysis of temperature measurement at material/LiF interface under moderate shock wave compression

In the field of dynamic high-pressure physics of condensed materials, the accurate knowledge of the thermodynamic state of a material is fundamental to understand its dynamic behaviour under stress. The equation of state of materials is verified in terms of pressure, density and internal energy thanks to the measurements of pressure and velocity under shock wave compression with a satisfying precision. The theoretical temperature evaluated from EOS remains discussed. So; its accurate measurement is of great interest, in particular at low temperature. However, in this range, measurements appear more difficult to perform. Because of this, a high-speed infrared three-wavelength pyrometer has been modified at CEG to perform measurements at very low temperature (<500 K). Besides, an emissive layer has been designed to increase the emissivity of the shocked surface. To reduce the uncertainty of the temperature measurement, it appears necessary to limit its emissivity to a 0.9–1 range

Thermay spray and lasers

11-13 octobre 2003International audienc

The use of a macroscopic formulation describing the effects of dynamic compaction and porosity on plasma sprayed copper

International audienceCoatings processed by thermal deposition techniques involve porosity. The Laser adhesion test developed for testing bond strength of a coating on its substrate requires a good knowledge of shock wave propagation in such media. Experiments carried out on plasma sprayed copper samples, about 14% porous, with velocity interferometer system for any reflector measurements display the discrepancy of previously used models. Hence, a one-dimensional formulation of the compaction process, based on a simple P-α model, is proposed to improve the correlation between experimental and computed data signals obtained on a plasma sprayed copper under dynamic loading. Besides, this improvement allows the estimation of the bond strength of a plasma sprayed copper on aluminum substrate

Evolutions of the LASer Adhesion Test (LASAT) for the debonding of coatings on substrates above the millimeter range thickness

International audienceHigh power laser irradiation on a substrate coated on the opposite side drives a shock whose propagation and consecutive transmission/reflexion at the interface and free surfaces can yield to important traction inside the sample and particularly at the interface. For a given system, traction at the interface can be controlled by laser settings and therefore a LASer Adhesion Test of quality (LASAT) can be realised for many couples of substrate/coating system. The debonding is detected by VISAR measurements at the opposite face to the loading. However, due to the shortness of laser shock at the origin of traction, a strong decay of the initial shock occurs above a few hundredth microns in the substrate. Therefore, debonding cannot be obtained for most samples exceeding the millimeter range thickness. Several solutions have been investigated for opening up the possibilities of the LASAT process for systems above the millimeter range. One solution would consist in generating the shock on the coating to produce traction at the interface independently of the reverberations of the substrate free surface. An analytical study of shock waves propagation into the coating/substrate system has been performed. It shows that traction can be produced at the interface only when the coating's shock impedance is much lower than that of the substrate. An experiment performed by high power laser shock of an al coating on a thick substrate evidences the debonding

Physical approach to adhesion testing using laser-driver shock waves

International audienceThis paper deals with an adhesion test of coatings using laser-driven shock waves. Physical aspects concerning laser–matter interaction, shock wave propagation and interface fracture strength are described. This comprehensive approach using two numerical codes (HUGO and SHYLAC) allows the determination of mechanisms responsible for coating debonding and a quantitative evaluation of fracture strength. From this description, a coating test protocol is also designed. To diagnose coating debonding, it is based on the analysis of experimental rear free surface velocity profiles measured by velocity interferometer system for any reflectors (VISAR). Ni electrolytic coating (70–90 µm) deposited on a Cu substrate (120–190 µm) is used for the experimental validation of the test. The fracture strength is 1.49 ± 0.01 GPa for a laser pulse duration of 10 ns at 1.064 µm

Etude de l'adhérence des dépôts de cuivre projetés plasma sur de l'aluminium par l'essai de choc laser (LASAT) : influence des propriétés métallurgiques des interfaces

National audienc