3,983 research outputs found
Nanostructure and properties of a Cu-Cr composite processed by severe plastic deformation
A Cu-Cr composite was processed by severe plastic deformation to investigate
the role of interphase boundaries on the grain size reduction mechanisms. The
as-deformed material exhibits a grain size of only 20nm. This gives rise to a
dramatic increase of the hardness. Some deformation induced Cu super saturated
solid solutions were clearly exhibited and it is shown that they decrease the
hardness. The formation of such supersaturated solid solution and their
influence on the mechanical properties are discussed
Dust in an extremely metal-poor galaxy: mid-infrared observations of SBS 0335-052
The metal deficient (Z = Z_sun/41) Blue Compact Dwarf Galaxy (BCD) SBS
0335-052 was observed with ISOCAM between 5 and 17 mic. With a L_12mic/L_B
ratio of 2.15, the galaxy is unexpectedly bright in the mid-infrared for such a
low-metallicity object. The mid-infrared spectrum shows no sign of the
Unidentified Infrared Bands, which we interpret as an effect of the destruction
of their carriers by the very high UV energy density in SBS 0335-052. The
spectral energy distribution (SED) is dominated by a very strong continuum
which makes the ionic lines of [SIV] and [NeIII] very weak. From 5 to 17 mic,
the SED can be fitted with a grey-body spectrum, modified by an extinction law
similar to that observed toward the Galactic Center, with an optical depth of
A_V~19-21 mag. Such a large optical depth implies that a large fraction (as
much as ~ 75%) of the current star-formation activity in SBS 0335-052 is hidden
by dust with a mass between 3x10^3 M_sun and 5x10^5 M_sun. Silicate grains are
present as silicate extinction bands at 9.7 and 18 mic can account for the
unusual shape of the MIR spectrum of SBS 0335-052. It is remarkable that such a
nearly primordial environment contains as much dust as galaxies which are 10
times more metal-rich. If the hidden star formation in SBS 0335-052 is typical
of young galaxies at high redshifts, then the cosmic star formation rate
derived from UV/optical fluxes would be underestimated.Comment: 13 pages, 4 figures, requires aaspp4.sty, accepted in Ap
A standardised method for measuring in situ denitrification in shallow aquifers: numerical validation and measurements in riparian wetlands
A tracer test to examine in situ denitrification in shallow groundwater by a piezometer with a packer system used bromide as a tracer of dilution and acetylene (10%) to block the denitrification process at the nitrous oxide stage. During the test, dissolved oxygen, nitrate (NO3-), bromide (Br-), nitrous oxide (N2O) and dissolved organic carbon (DOC) were measured. To calibrate the experimental method, comparison with numerical simulations of the groundwater transfer were carried out, taking into account the environmental characteristics. The method was tested by measurements undertaken in different environmental conditions (geology, land use and hydrology) in two riparian wetlands. Denitrification rates measured by this method ranged from 5.7 10-6 g N-NO3-L-1 h-1 to 1.97 10-3 g N-NO3-L-1 h-1 The method is applicable in shallow aquifers with a permeability from 10-2 to 10-4m s-1
Non-equilibrium intermixing and phase transformation in severely deformed Al/Ni multilayers
Al/Ni multilayers have been prepared by repeated folding and cold rolling
(F&R) of elemental foils. The thickness of Al and Ni foils is reduced down to
less than 50 nm after fifty F&R cycles. Three-dimensional atom probe analyses
clearly reveal the presence of supersaturated solid solutions and give the
evidence of deformation-induced intermixing. The formation of the solid
solutions and their transformation into the Al3Ni phase upon annealing is
discussed.Comment: 4 page
Nitrogen dynamics in the shallow groundwater of a riparian wetland zone of the Garonne, SW France: nitrate inputs, bacterial densities, organic matter supply and denitrification measurements
This study highlights the role of interactions between surface and sub-surface water of the riparian zone of a large river (the Garonne, SW
France). Information is given about the role of surface water in supplying Dissolved Organic Carbon (DOC ) to the riparian zone for nitrate
removal processes. The densities of bacteria (up to 3.3106 cell m L-1) in groundwater are strongly conditioned by the water moving during
flood events. Total bacterial densities in groundwater were related to surface water bacterial densities. In sediment, total bacteria are attached
mainly to fine particles (90 % in the fraction < 1 mm). Spatial variations in organic carbon and nitrate content in groundwater at the site
studied are correlated with exchanges between the groundwater and the river, from the upstream to the downstream part of the meander. Total
bacterial densities, nitrate and decressing organic carbon concentrations follow the same pattern. These results suggest that, in this kind of
riparian wetland, nitrate from alluvial groundwater influenced by agricultural practices may be denitrified by bacteria in the presence of
organic carbon from river surface water
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