1,316 research outputs found
The prosody of Barra Gaelic epenthetic vowels
published or submitted for publicationis peer reviewe
The maximal Beurling transform associated with squares
It is known that the improved Cotlar's inequality ,
, holds for the Beurling transform , the maximal Beurling
transform , , and the Hardy--Littlewood maximal operator . In this note we consider
the maximal Beurling transform associated with squares, namely,
, ,
being the square with sides parallel to the coordinate axis
of side length . We prove that ,
, where is the iteration of the
Hardy--Littlewood maximal operator, and cannot be replaced by .Comment: 3 figure
Transport of ferrihydrite nanoparticles in saturated porous media: role of ionic strength and flow rate
The use of nanoscale ferrihydrite particles, which are known to effectively enhance microbial degradation of a wide range of contaminants, represents a promising technology for in situ remediation of contaminated aquifers. Thanks to their small size, ferrihydrite nanoparticles can be dispersed in water and directly injected into the subsurface to create reactive zones where contaminant biodegradation is promoted. Field applications would require a detailed knowledge of ferrihydrite transport mechanisms in the subsurface, but such studies are lacking in the literature. The present study is intended to fill this gap, focusing in particular on the influence of flow rate and ionic strength on particle mobility. Column tests were performed under constant or transient ionic strength, including injection of ferrihydrite colloidal dispersions, followed by flushing with particle-free electrolyte solutions. Particle mobility was greatly affected by the salt concentration, and particle retention was almost irreversible under typical salt content in groundwater. Experimental results indicate that, for usual ionic strength in European aquifers (2 to 5 mM), under natural flow condition ferrihydrite nanoparticles are likely to be transported for 5 to 30 m. For higher ionic strength, corresponding to contaminated aquifers, (e.g., 10 mM) the travel distance decreases to few meters. A simple relationship is proposed for the estimation of travel distance with changing flow rate and ionic strength. For future applications to aquifer remediation, ionic strength and injection rate can be used as tuning parameters to control ferrihydrite mobility in the subsurface and therefore the radius of influence during field injection
Stellar Ages and Metallicities of Central and Satellite Galaxies: Implications for Galaxy Formation and Evolution
Using a large SDSS galaxy group catalogue, we study how the stellar ages and
metallicities of central and satellite galaxies depend on stellar mass and halo
mass. We find that satellites are older and metal-richer than centrals of the
same stellar mass. In addition, the slopes of the age-stellar mass and
metallicity-stellar mass relations are found to become shallower in denser
environments. This is due to the fact that the average age and metallicity of
low mass satellite galaxies increase with the mass of the halo in which they
reside. A comparison with the semi-analytical model of Wang et al. (2008) shows
that it succesfully reproduces the fact that satellites are older than centrals
of the same stellar mass and that the age difference increases with the halo
mass of the satellite. This is a consequence of strangulation, which leaves the
stellar populations of satellites to evolve passively, while the prolonged star
formation activity of centrals keeps their average ages younger. The resulting
age offset is larger in more massive environments because their satellites were
accreted earlier. The model fails, however, in reproducing the halo mass
dependence of the metallicities of low mass satellites, yields
metallicity-stellar mass and age-stellar mass relations that are too shallow,
and predicts that satellite galaxies have the same metallicities as centrals of
the same stellar mass, in disagreement with the data. We argue that these
discrepancies are likely to indicate the need to (i) modify the recipes of both
supernova feedback and AGN feedback, (ii) use a more realistic description of
strangulation, and (iii) include a proper treatment of the tidal stripping,
heating and destruction of satellite galaxies. [Abridged]Comment: 20 pages, 12 figures, submitted for publication in MNRA
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