15,200 research outputs found
A computation of Poisson kernels for some standard weighted biharmonic operators in the unit disc
We compute Poisson kernels for integer weight parameter standard weighted
biharmonic operators in the unit disc with Dirichlet boundary conditions. The
computations performed extend the supply of explicit examples of such kernels
and suggest similar formulas for these Poisson kernels to hold true in more
generality. Computations have been carried out using the open source computer
algebra package Maxima
Size-biased branching population measures and the multi-type condition
We investigate the condition for a general (Crump--Mode--Jagers)
multi-type branching process with a general type space by constructing a
size-biased population measure that relates to the ordinary population measure
via an intrinsic martingale . Sufficiency of the condition for a
non-degenerate limit of is proved and conditions for necessity are
investigated.Comment: Published in at http://dx.doi.org/10.3150/09-BEJ211 the Bernoulli
(http://isi.cbs.nl/bernoulli/) by the International Statistical
Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm
Stability or change in the Swedish Labour Market Regime?
From the late 1970s to the early 1990s Sweden diverted from the rest of Western Europe. The employment rate was high and unemployment was kept very low. But in the early 1990s unemployment started to rise also in Sweden. In this paper the worsened situation for low educated in general, and youth in particular, are related to two institutional factors: a changed organisation of vocational education in upper secondary schooling and changes in labour market policy, where changes in vocational education is understood as a cause and changes in labour market policy as an effect of rising obstacles for low educated. Of course, there are several other factors that have to be considered in order to get the full picture, but reforms in the upper secondary school system as well as in labour market policy are of great interest as they can be apprehended as parts of broader changes in the traditional Swedish labour market model. Studies of changes in the Swedish model can also be seen as part of a wider research interest concerning the effectiveness of competing institutional models of capitalism. It’s argued that changes in schooling are an important factor behind increasing social marginalisation and income dispersion. The focus is primarily on the ages between 20 and 24. Changes in upper secondary schooling are also valued in connection to the supply of youth measures connected to labour market policy. Since the beginning of the 1990s, there has been a huge increase of participants in programs directed to youth. This is a direct effect of rising unemployment and increasing troubles for those with unfinished upper secondary education. But it’s also possible to trace changes in labour market policy to broader institutional transformations in the Swedish labour market model. These changes will first and foremost be analysed as an expression of stronger segmentation forces.Swedish Labour Market; low educated; young adults
The detached dust and gas shells around the carbon star U Ant
Context: Geometrically thin, detached shells of gas have been found around a
handful of carbon stars. --Aims: Previous observations of scattered stellar
light in the circumstellar medium around the carbon star U Ant were taken
through filters centred on the resonance lines of K and Na. These observations
could not separate the scattering by dust and atoms. The aim of this paper is
to remedy this situation. --Methods: We have obtained polarization data on
stellar light scattered in the circumstellar medium around U Ant through
filters which contain no strong lines, making it possible to differentiate
between the two scattering agents. Kinematic, as well as spatial, information
on the gas shells were obtained through high-resolution echelle spectrograph
observations of the KI and NaD lines. --Results: We confirm the existence of
two detached shells around U Ant. The inner shell (at a radius of approx 43"
and a width of approx 2") consists mainly of gas, while the outer shell (at a
radius of approx 50" and a width of approx 7") appears to consist exclusively
of dust. Both shells appear to have an over-all spherical geometry. The gas
shell mass is estimated to be 2x10^-3 M(Sun), while the mass of the dust shell
is estimated to be 5x10^-5 M(Sun). The derived expansion velocity, from the KI
and NaD lines, of the gas shell, 19.5 km/s, agrees with that obtained from CO
radio line data. The inferred shell age is 2700 years. There is structure, e.g.
in the form of arcs, inside the gas shell, but it is not clear whether these
are due to additional shells. --Conclusions: Our results support the hypothesis
that the observed geometrically thin, detached shells around carbon stars are
the results of brief periods of intense mass loss, probably associated with
thermal pulses, and subsequent wind-wind interactions
Classifying the secondary component of the binary star W Aquilae
AIMS: The object W Aql is an asymptotic giant branch (AGB) star with a faint
companion. By determining more carefully the properties of the companion, we
hope to better constrain the properties of the AGB star. METHODS: We present
new spectral observations of the binary star W Aql at minimum and maximum
brightness and new photometric observations of W Aql at minimum brightness.
RESULTS: The composite spectrum near minimum light is predominantly from the
companion at wavelengths < 6000 . This spectrum can be
classified as F8 to G0, and the brightness of the companion is that of a dwarf
star. Therefore, it can be concluded that the companion is a main sequence
star. From this, we are able to constrain the mass of the AGB component to 1.04
- 3 and the mass of the W Aql system to 2.1 - 4.1 . Our
photometric results are broadly consistent with this classification and suggest
that the main sequence component suffers from approximately 2 mag of extinction
in the V band primarily due to the dust surrounding the AGB component.Comment: 5 pages, 1 figure, research not
Mapping rail wear transitions
This paper outlines work carried out to produce maps of
rail material wear coefficients taken from laboratory
tests run on twin disc and pin-on-disc machines as well
as those derived from measurements taken in the field.
Wear transitions are identified using the maps and
defined in terms of slip and contact pressure. Wear
regimes are related to expected wheel/rail contact
conditions and contact points (rail head/wheel tread and
rail gauge/wheel flange). Surface and sub-surface
morphologies are discussed and comparisons are made
between field and laboratory data
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