Prospection géophysique multi-méthodes du pergélisol alpin dans le Sud des Alpes Suisses

La prospection géophysique multi-méthodes du pergélisol alpin dans la Valle di Sceru (sud des Alpes suisses, Canton du Tessin) à l’aide de méthodes thermiques (température des sources et de la surface du sol), à l’aide de méthodes thermiques (température des sources et de la surface du sol), de résistivité (sondage géoélectrique) et électromagnétiques (VLF-R et conductivimètre EM31) a permis de déterminer la répartition et les caractéristiques du pergélisol dans les glaciers rocheux et les éboulis étudiés. La répartition du pergélisol dans les glaciers rocheux est assez homogène et généralement contrôlée par les conditions topoclimatiques du site. Pour les éboulis, au contraire, l’extension spatiale du pergélisol est le plus souvent hétérogène et la probabilité d’occurrence du pergélisol diminue en direction du haut du versant. Les processus qui semblent contrôler la répartition du pergélisol dans les éboulis sont les échanges d’air advectifs, la redistribution de la neige (par le vent et les avalanches) et le granoclassement longitudinal. L’étude a également permis de tester les méthodes électromagnétiques utilisées et de les valider pour la prospection du pergélisol alpin.The multi-method geophysical prospecting of alpine permafrost in the Sceru Valley (southern Swiss Alps, Ticino Canton) with thermal methods (spring temperature and ground surface temperature monitoring), DC-resistivity method (Vertical Electrical Sounding) and electromagnetic methods (VLF-R and conductivity-meter EM 31), allowed determining the permafrost distribution and characteristics in the investigated rockglaciers and talus slopes. The permafrost distribution is quite homogeneous in the rockglaciers, where it is generally controlled by the topoclimatic conditions of the site. In the talus slopes, the permafrost distribution is quite heterogeneous and the probability of permafrost occurrence decreases upslope. The main processes controlling this particular permafrost distribution are the chimney effect, the redistribution of snow by wind and avalanches and, finally, the increase of grain size downslope. The study also allowed testing electromagnetic methods and to validating their application in the prospecting of alpine permafrost

TTAS a new stilbene derivative that induces apoptosis in Leishmania infantum.

Leishmania parasites are able to undergo apoptosis (programmed cell death), similarly to mammalian cells. Recently it was demonstrated in vitro the anti-leishmanial effect of some natural and synthetic stilbenoids including resveratrol and piceatannol. In this study we evaluated the Leishmanicidal activity of a pool of stilbene derivatives which had previously shown high apoptotic efficacy against neoplastic cells. All the compounds tested were capable to decrease the parasite viability in a dose-dependent manner. Trans-stilbenes proved to be markedly more effective than cis-isomers. This was different from that observed in tumor cells in which cis-stilbenes were more potent cytotoxic agents. Trans-3,4',5-trimethoxy-3'-amino-stilbene (TTAS) was the most active stilbene showing in Leishmania infantum a LD(50) value of 2.6 μg/mL. In contrast TTAS showed a low toxicity when tested on normal hemopoietic cells. This compound induced apoptosis in parasites by disrupting the mitochondrial membrane potential. Moreover it shows the ability to block Leishmania parasites in G(2)-M phase of cell cycle in agreement with the data obtained by affinity chromatography that identify tubulin as the putative target of TTAS. In conclusion, our results indicate that some stilbene derivatives are highly effective as anti-leishmanial agents and TTAS represents a pro-apoptotic agent in Leishmania parasites that merit further in vivo investigation

Schmidt-hammer exposure ages from periglacial patterned ground (sorted circles) in Jotunheimen, Norway, and their interpretative problems

© 2016 Swedish Society for Anthropology and Geography Periglacial patterned ground (sorted circles and polygons) along an altitudinal profile at Juvflya in central Jotunheimen, southern Norway, is investigated using Schmidt-hammer exposure-age dating (SHD). The patterned ground surfaces exhibit R-value distributions with platycurtic modes, broad plateaus, narrow tails, and a negative skew. Sample sites located between 1500 and 1925 m a.s.l. indicate a distinct altitudinal gradient of increasing mean R-values towards higher altitudes interpreted as a chronological function. An established regional SHD calibration curve for Jotunheimen yielded mean boulder exposure ages in the range 6910 ± 510 to 8240 ± 495 years ago. These SHD ages are indicative of the timing of patterned ground formation, representing minimum ages for active boulder upfreezing and maximum ages for the stabilization of boulders in the encircling gutters. Despite uncertainties associated with the calibration curve and the age distribution of the boulders, the early-Holocene age of the patterned ground surfaces, the apparent cessation of major activity during the Holocene Thermal Maximum (HTM) and continuing lack of late-Holocene activity clarify existing understanding of the process dynamics and palaeoclimatic significance of large-scale sorted patterned ground as an indicator of a permafrost environment. The interpretation of SHD ages from patterned ground surfaces remains challenging, however, owing to their diachronous nature, the potential for a complex history of formation, and the influence of local, non-climatic factors