Tree-ring reconstruction of snow avalanche activity: Does avalanche path selection matter?

In the current context of anthropogenic global warming, one of the purposes of dendrogeomorphic analyses is to provide long and continuous chronologies of mass movements, so as to detect potential trends or shift related to increasing temperatures. However, on documented slopes, the comparison between historical archives and tree-ring records suggests that dendrogeomorphic reconstructions systematically underestimate the natural activity of the process under investigation. In the specific case of snow avalanches, underestimation generally amounts to 50% and the main causes generally given for this difference are related to the magnitude of past events. In this study, we hypothesize that the morphometric characteristics of avalanche paths and their forest cover could have significant impacts on the length and reliability of tree-ring reconstructions. In order to test this hypothesis, we selected four adjacent, albeit differently structured, avalanche paths from the Queyras massif (French Alps), with the aim to compare their potential for a continuous reconstruction of past avalanche activity. On the most active avalanche paths characterized by high-altitude release areas (covered only by shrubby vegetation), tree-ring reconstructions do not exceed one century in length, with recurrence intervals of high magnitude events >25 years. By contrast, on forested couloirs where lower slopes and forest coverage up to the release areas limits the intensity of events, the frequency of reconstructed snow avalanches is 2.5 times higher, the reconstructions span longer periods and the convergence rate with historical archives attest to the reliability of the dendrogeomorphic approach. These results suggest that a careful selection of couloirs is essential and that priority should be given to forested sites as (i) they allow for exhaustive and (ii) reliable reconstructions over (iii) long periods of time.

Excitation of spirals and chiral symmetry breaking in rayleigh-benard convection.

Spiral-defect populations in low-Prandtl number Rayleigh-Bénard convection with slow rotation about a vertical axis were measured in carbon dioxide at high pressure. The results indicate that spirals act like "thermally excited" defects and that the winding direction of a spiral is analogous to a magnetic spin. Rotation about a vertical axis, the spiral analog of the magnetic field, breaks the zero-rotation chiral symmetry between clockwise and counterclockwise spiral defects. Many properties of spiral-defect statistics are well described by an effective statistical-mechanical model.

A complex chromosome rearrangement with 10 breakpoints: tentative assignment of the locus for Williams syndrome to 4q33----q35.1.

An unbalanced complex chromosome rearrangement with 10 breakpoints resulting in four derivative chromosomes (1, 2, 4, and 11) was found in a girl with severe phenotypic abnormalities, many of which are characteristic of Williams syndrome. The patient was monosomic for the region 4q33----q35.1 and thus the mapping of the syndrome could tentatively be restricted to this region.