Spatial Patterns of Soil Development, Methane Oxidation, and Methanotrophic Diversity along a Receding Glacier Forefield, Southeast Greenland

Increasing global annual temperature leads to massive loss of ice cover worldwide. Consequently, glaciers retreat and ice-covered areas become exposed. We report on a study from the Mittivakkat Gletscher forefield in Southeast Greenland with special focus on methanotrophy in relation to exposure time to the atmosphere. The Mittivakkat Gletscher has receded since the end of the Little Ice Age (LIA; about AD 1850) and has left behind a series of deposits of decreasing age concurrently with its recession. Soil samples from this chronosequence were examined in order to elucidate main soil variables, as well as the activity and community structure of methanotrophs, a group of microorganisms involved in regulation of atmospheric methane. Soil variables revealed poor soil development, and incubation experiments showed methane consumption rates of 2.14 nmol CH4 day−1 gsoil −1 at 22 °C and 1.24 nmol CH4 day−1 gsoil −1 at 10 °C in the LIA terminal moraine. Methane consumption was not detected in younger samples, despite the presence of high-affinity methanotrophs in all samples. This was indicated by successful amplification of partial pmoA genes, which code for a subunit of a key enzyme involved in methane oxidation. In addition, the results of the diversity study show that the diversity of the methanotrophic community at the younger, recently deglaciated site P5 is poorer than the diversity of the community retrieved from the LIA moraine. We put forward the hypothesis that aerobic methanotrophs were at very low abundance and diversity during glaciation probably due to anoxia at the ice-sediment interface and that colonization after deglaciation is not completed yet. More detailed studies are required to explain the causes of discrepancy between activity and presence of high-affinity methanotrophs and its relation to the transit from ice-covered probably anoxic to ice-free oxi

Ti3SiC2-Cf composites by spark plasma sintering: Processing, microstructure and thermo-mechanical properties

MAX phases, and particularly Ti3SiC2, are interesting for high temperature applications. The addition of carbon fibers can be used to reduce the density and to modify the properties of the matrix. This work presents the densification and characterization of Ti3SiC2 based composites with short carbon fibers using a fast and simple fabrication approach: dry mixing and densification by Spark Plasma Sintering. Good densification level was obtained below 1400 °C even with a high amount of fibers. The reaction of the fibers with the matrix is limited thanks to the fast processing time and depends on the amount of fibers in the composite. Bending strength at room temperature, between 437 and 120 MPa, is in the range of conventional CMCs with short fibers and according to the resistance of the matrix and the presence of residual porosity. Thermo-mechanical properties of the composites up to 1500 °C are also presented.This work has received funding from the European Union’s Horizon2020 “Research and innovation programme” under grant agreement No 685594 (C3HARME

Moure Romanillo, J. Alfonso: "El arte paleolítico: consideraciones a un siglo de su descubrimiento". Revista de Occidente, N° 35, pp. 121-143., 3 figs. y 1 mapa. Madrid, 1984.

Fil: Barcena, J. Roberto. Universidad Nacional de Cuyo. Facultad de Filosofía y Letra

Magic numbers, excitation levels, and other properties of small neutral math clusters (N < 50)

The ground-state energies and the radial and pair distribution functions of neutral math clusters are systematically calculated by the diffusion Monte Carlo method in steps of one math atom from 3 to 50 atoms. In addition the chemical potential and the low-lying excitation levels of each cluster are determined with high precision. These calculations reveal that the “magic numbers” observed in experimental math cluster size distributions, measured for free jet gas expansions by nondestructive matter-wave diffraction, are not caused by enhanced stabilities. Instead they are explained in terms of an enhanced growth due to sharp peaks in the equilibrium concentrations in the early part of the expansion. These peaks appear at cluster sizes which can just accommodate one more additional stable excitation. The good agreement with experiment provides not only experimental confirmation of the energy level and the chemical potential calculations, but also evidence for a new mechanism which can lead to magic numbers in cluster size distributions. By accounting for the falloff of the radial density distributions at the surface and a size-dependent surface tension, the energy levels are demonstrated to be consistent with a modified Rayleigh model of surface excitations. The compressibility coefficient of these small clusters is found to be one order of magnitude smaller than the bulk [email protected]

Inequality, welfare and order statistics

In this paper we use the distributions of order statistics to define functions with the appropriate properties and represent social preferences regarding income distributions. Following the approach of Yaari (1987, 1988), this allows constructing a set of social welfare functions from which the corresponding inequality indices are derived. The obtained measures incorporate diverse normative criteria, with different degrees of preference for equality. The generalized Gini coefficients and the family of indices proposed in Aaberge (2000) are obtained as particular cases. This approach shows that each of these families of indices characterizes the income distribution, but for a change of scale

Fabrication of radiopaque, drug loaded resorbable inferior vena cava filters

https://openworks.mdanderson.org/sumexp23/1073/thumbnail.jp

Arenas calizas para la confección de hormigones: influencia de sus finos calizos y arcillosos a nivel de morteros

For the purpose to obtain data for a next revision of the Spanish Concrete Norm about the content of fines in sands fixed to date on 5 % without exceptions, an exhaustive research project has been undertaken. Following, the results of the influence of different contents of calcareous and clayey fines in mortar mechanical properties, are shown, first step to begin the study of this influence on concretes made with limestone aggregate, presently in execution phase. Before those experimental works, a general survey at all the limestone aggregate quarries in northern area of the peninsula corresponding to the Basque Country, was accomplished. By the results obtained it seems that it will be possible to enlarge the limit untill 12-15%, if only a limited presence of clay is assured.Con el propósito de obtener datos para una próxima revisión de la Norma Española de Hormigón en cuanto al contenido en finos en arenas, actualmente fijado sin excepción en el 5%, se ha abordado un proyecto de investigación bastante exhaustivo. Se presentan a continuación los resultados de la influencia de diferentes contenidos de finos calizos y arcillosos en las propiedades mecánicas de los morteros, paso previo al estudio de dicha influencia en hormigones confeccionados con árido calizo de machaqueo, fase actualmente en ejecución. Previamente a estos trabajos experimentales se realizó una prospección general de todas las canteras de machaqueo de caliza en el área norte de la península, correspondiente al País Vasco. Por los resultados obtenidos parece que el límite podrá elevarse hasta el 12-15%, siempre que se garantice una presencia de arcilla limitada por ensayos