Development of Vegetation Communities in a Retrogressive Thaw Slump near Mayo, Yukon Territory : A 10-year Assessment

The vegetation in a retrogressive thaw slump, first surveyed and documented in 1987, was revisited 10 years later to investigate its subsequent development and to test a chronosequence-based successional model. The thaw slump stabilized in 1994, when the headwall became covered by organic and mineral debris. As a result, the meltwater supply from headwall ablation ceased. Alteration of environmental conditions due to stabilization of the headwall diverted the vegetation succession from the chronosequence determined in 1987. Areas that were marshy in 1987 dried up, and an area dominated by Polygonum alaskanum appeared close to the headwall. Much of the thaw slump was dominated by Salix spp. in 1997, rather than the Equisteum of 1987. However, the ground more than 200 m from the headwall, over a decade old in 1987, experienced less change in edaphic conditions, and the communities there continued to develop a structure approaching the surrounding undisturbed forest.La végétation située dans un décrochement de fonte régressif, étudiée et documentée pour la première fois en 1987, a fait l'objet d'une autre étude sur place dix ans plus tard pour examiner son évolution et tester un modèle de succession fondé sur la chronoséquence. Le décrochement de fonte s'est stabilisé en 1994, quand le mur de rimaye s'est couvert de débris organiques et minéraux. Il en a résulté que l'alimentation en eau de fonte venant de l'ablation du mur de rimaye a cessé. Le changement dans les conditions environnementales dû à la stabilisation du mur a détourné la succession végétale de la chronoséquence établie en 1987. Des zones qui étaient marécageuses en 1987 se sont asséchées, et une étendue où dominait Polygonum alaskanum apparue près du mur. En 1997, une grande partie de la zone du décrochement de fonte était dominée par des espèces Salix, plutôt qu'Equisteum, comme c'était le cas en 1987. Toutefois, le sol situé à plus de 200 m du mur de rimaye, sol vieux de dix ans en 1987, a subi moins de changement dans les conditions édaphiques, et les communautés y ont continué à évoluer vers une structure qui se rapproche de la forêt non perturbée située à la périphérie

Classification of singular Q-homology planes. I. Structure and singularities

A Q-homology plane is a normal complex algebraic surface having trivial rational homology. We obtain a structure theorem for Q-homology planes with smooth locus of non-general type. We show that if a Q-homology plane contains a non-quotient singularity then it is a quotient of an affine cone over a projective curve by an action of a finite group respecting the set of lines through the vertex. In particular, it is contractible, has negative Kodaira dimension and only one singular point. We describe minimal normal completions of such planes.Comment: improved results from Ph.D. thesis (University of Warsaw, 2009), 25 pages, to appear in Israel J. Mat

Decaying shock studies of phase transitions in MgOSiO2 systems: implications for the Super-Earths interiors

We report an experimental study of the phase diagrams of periclase (MgO), enstatite (MgSiO3) and forsterite (Mg2SiO4) at high pressures. We investigated with laser driven decaying shocks the pressure/temperature curves of MgO, MgSiO3 and Mg2SiO4 between 0.2-1.2 TPa, 0.12-0.5 TPa and 0.2-0.85 TPa respectively. A melting signature has been observed in MgO at 0.47 TPa and 9860 K, while no phase changes were observed neither in MgSiO3 nor in Mg2SiO4. An increasing of reflectivity of MgO, MgSiO3 and Mg2SiO4 liquids have been detected at 0.55 TPa -12 760 K, 0.15 TPa - 7540 K, 0.2 TPa - 5800 K, respectively. In contrast to SiO2, melting and metallization of these compounds do not coincide implying the presence of poor electrically conducting liquids close to the melting lines. This has important implications for the generation of dynamos in Super-earths mantles

A New Upper Limit for the Tau-Neutrino Magnetic Moment

Using a prompt neutrino beam in which a nu_tau component was identified for the first time, the nu_tau magnetic moment was measured based on a search for an anomalous increase in the number of neutrino-electron interactions. One such event was observed when 2.3 were expected from background processes, giving an upper 90% confidence limit of 3.9x10^-7 Bohr magnetons.Comment: 9 pages; 1 figur