1,559 research outputs found
A Korovkin Theorem for Abstract Lebesgue Spaces
AbstractWulbert and Meir have each obtained a Korovkin theorem for weak convergence of operators on an L1 space. Here we prove a result which includes both of these theorems and which provides a general setting for weak Korovkin type L1 convergence of operators which are not assumed positive
Replication study: a cross-country field observation study of real world PIN usage at ATMs and in various electronic payment scenarios:towards understanding why people do, or do not, shield PIN entry
In this paper, we describe the study we carried out to replicate and extend the field observation study of real world ATM use carried out by De Luca et al., published at the SOUPS conference in 2010. Replicating De Luca et al.'s study, we observed PIN shielding rates at ATMs in Germany. We then extended their research by conducting a similar field observation study in Sweden and the United Kingdom. Moreover, in addition to observing ATM users (withdrawing), we also observed electronic payment scenarios requiring PIN entry. Altogether, we gathered data related to 930 observations. Similar to De Luca et al., we conducted follow-up interviews, the better to interpret our findings. We were able to confirm De Luca et al.'s findings with respect to low PIN shielding incidence during ATM cash withdrawals, with no significant differences between shielding rates across the three countries. PIN shielding incidence during electronic payment scenarios was significantly lower than incidence during ATM withdrawal scenarios in both the United Kingdom and Sweden. Shielding levels in Germany were similar during both withdrawal and payment scenarios. We conclude the paper by suggesting a number of explanations for the differences in shielding that our study revealed
The nature of damped HI absorbers probed by cosmological simulations: satellite accretion and outflows
We use state-of-the-art cosmological zoom simulations to explore the
distribution of neutral gas in and around galaxies that gives rise to high
column density \ion{H}{i} \mbox{Ly-} absorption (formally, sub-DLAs and
DLAs) in the spectra of background quasars. Previous cosmological hydrodynamic
simulations under-predict the mean projected separations of these
absorbers relative to the host, and invoke selection effects to bridge the gap
with observations. On the other hand, single lines of sight (LOS) in absorption
cannot uniquely constrain the galactic origin. Our simulations match all
observational data, with DLA and sub-DLA LOS existing over the entire probed
parameter space ([M/H], kpc) at all redshifts
(). We demonstrate how the existence of DLA LOS at kpc from a massive host galaxy require high numerical resolution, and
that these LOS are associated with dwarf satellites in the main halo, stripped
metal-rich gas and outflows. Separating the galaxy into interstellar
("\ion{H}{i} disc") and circumgalactic ("halo") components, we find that both
components significantly contribute to damped \ion{H}{i} absorption LOS. Above
the sub-DLA (DLA) limits, the disc and halo contribute with and
per cent, respectively. Our simulations confirm analytical
model-predictions of the DLA-distribution at . At high redshift
() sub-DLA and DLAs occupy similar spatial scales, but on average
separate by a factor of two by . On whether sub-DLA and DLA LOS
sample different stellar-mass galaxies, such a correlation can be driven by a
differential covering-fraction of sub-DLA to DLA LOS with stellar mass. This
preferentially selects sub-DLA LOS in more massive galaxies in the low-
universe.Comment: 12 pages, 5 figures, submitted to MNRAS 29/01/201
Seabird Concentrations in Late Summer Along the Coasts of Devon and Ellesmere Islands, N.W.T.
The presence of large concentrations of northern fulmars and black-legged kittiwakes along coasts of Devon and Ellesmere islands was documented in 1976 and 1978 by aerial surveys. Fulmars were present along these coasts from late July until mid-September, with peaks in late August and early September along Devon Island, and mid-September along Ellesmere Island. Black-legged kittiwakes were abundant along Devon Island after mid-September, but common along Ellesmere Island from late August to late September. Densities of both species were significantly higher in front of glaciers than along coastlines.Key words: northern fulmar, black-legged kittiwake, arctic distribution, late summer, glacier front, Devon Island, Ellesmere Islan
Experiments on the fragmentation of a buoyant liquid volume in another liquid
We present experiments on the instability and fragmentation of volumes of
heavier liquid released into lighter immiscible liquids. We focus on the regime
defined by small Ohnesorge numbers, density ratios of order one, and variable
Weber numbers. The observed stages in the fragmentation process include
deformation of the released fluid by either Rayleigh-Taylor instability or
vortex ring roll-up and destabilization, formation of filamentary structures,
capillary instability, and drop formation. At low and intermediate Weber
numbers, a wide variety of fragmentation regimes is identified. Those regimes
depend on early deformations, which mainly result from a competition between
the growth of Rayleigh-Taylor instabilities and the roll-up of a vortex ring.
At high Weber numbers, turbulent vortex ring formation is observed. We have
adapted the standard theory of turbulent entrainment to buoyant vortex rings
with initial momentum. We find consistency between this theory and our
experiments, indicating that the concept of turbulent entrainment is valid for
non-dispersed immiscible fluids at large Weber and Reynolds numbers
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