31,561 research outputs found
Testing common classical LTE and NLTE model atmosphere and line-formation codes for quantitative spectroscopy of early-type stars
It is generally accepted that the atmospheres of cool/lukewarm stars of
spectral types A and later are described well by LTE model atmospheres, while
the O-type stars require a detailed treatment of NLTE effects. Here model
atmosphere structures, spectral energy distributions and synthetic spectra
computed with ATLAS9/SYNTHE and TLUSTY/SYNSPEC, and results from a hybrid
method combining LTE atmospheres and NLTE line-formation with DETAIL/SURFACE
are compared. Their ability to reproduce observations for effective
temperatures between 15000 and 35000 K are verified. Strengths and weaknesses
of the different approaches are identified. Recommendations are made as to how
to improve the models in order to derive unbiased stellar parameters and
chemical abundances in future applications, with special emphasis on Gaia
science.Comment: 12 pages, 8 figures; accepted for publication in Journal of Physics:
Conference Series, GREAT-ESF Workshop: Stellar Atmospheres in the Gaia Er
Generalized Conformal Symmetry in D-Brane Matrix Models
We study in detail the extension of the generalized conformal symmetry
proposed previously for D-particles to the case of supersymmetric Yang-Mills
matrix models of Dp-branes for arbitrary p. It is demonstrated that such a
symmetry indeed exists both in the Yang-Mills theory and in the corresponding
supergravity backgrounds produced by Dp-branes. On the Yang-Mills side, we
derive the field-dependent special conformal transformations for the collective
coordinates of Dp-branes in the one-loop approximation, and show that they
coincide with the transformations on the supergravity side. These
transformations are powerful in restricting the forms of the effective actions
of probe D-branes in the fixed backgrounds of source D-branes. Furthermore, our
formalism enables us to extend the concept of (generalized) conformal symmetry
to arbitrary configurations of D-branes, which can still be used to restrict
the dynamics of D-branes. For such general configurations, however, it cannot
be endowed a simple classical space-time interpretation at least in the static
gauge adopted in the present formulation of D-branes.Comment: 26 pages, no figure
Some comments about Schwarzschield black holes in Matrix theory
In the present paper we calculate the statistical partition function for any
number of extended objects in Matrix theory in the one loop approximation. As
an application, we calculate the statistical properties of K clusters of D0
branes and then the statistical properties of K membranes which are wound on a
torus.Comment: 15 page
Coefficient of tangential restitution for the linear dashpot model
The linear dashpot model for the inelastic normal force between colliding
spheres leads to a constant coefficient of normal restitution,
const., which makes this model very popular for the investigation
of dilute and moderately dense granular systems. For two frequently used models
for the tangential interaction force we determine the coefficient of tangential
restitution , both analytically and by numerical integration of
Newton's equation. Although const. for the linear-dashpot model,
we obtain pronounced and characteristic dependencies of the tangential
coefficient on the impact velocity . The
results may be used for event-driven simulations of granular systems of
frictional particles.Comment: 12 pages, 12 figure
On the Bekenstein-Hawking Entropy, Non-Commutative Branes and Logarithmic Corrections
We extend earlier work on the origin of the Bekenstein-Hawking entropy to
higher-dimensional spacetimes. The mechanism of counting states is shown to
work for all spacetimes associated with a Euclidean doublet
of electric-magnetic dual brane pairs of type II
string-theory or M-theory wrapping the spacetime's event horizon plus the
complete internal compactification space. Non-Commutativity on the brane
worldvolume enters the derivation of the Bekenstein-Hawking entropy in a
natural way. Moreover, a logarithmic entropy correction with prefactor 1/2 is
derived.Comment: 17 pages, 2 figures; refs. adde
High-energy Emission from Pulsar Outer Magnetospheres
We investigate a stationary pair production cascade in the outer
magnetosphere of an isolated, spinning neutron star. The charge depletion due
to global flows of charged particles, causes a large electric field along the
magnetic field lines. Migratory electrons and/or positrons are accelerated by
this field to radiate gamma-rays via curvature and inverse-Compton processes.
Some of such gamma-rays collide with the X-rays to materialize as pairs in the
gap. The replenished charges partially screen the electric field, which is
self-consistently solved together with the energy distribution of particles and
gamma-rays at each point along the field lines. By solving the set of Maxwell
and Boltzmann equations, we demonstrate that an external injection of charged
particles at nearly Goldreich-Julian rate does not quench the gap but shifts
its position and that the particle energy distribution cannot be described by a
power-law. The injected particles are accelerated in the gap and escape from it
with large Lorentz factors. We show that such escaping particles migrating
outside of the gap contribute significantly to the gamma-ray luminosity for
young pulsars and that the soft gamma-ray spectrum between 100 MeV and 3 GeV
observed for the Vela pulsar can be explained by this component. We also
discuss that the luminosity of the gamma-rays emitted by the escaping particles
is naturally proportional to the square root of the spin-down luminosity.Comment: 24 pages, 11 figures; to appear in the inaugural (Sep) issue of
Progress in Astrophysics Researches (a new book series
State education as high-yield investment: human capital theory in European policy discourse
Human Capital Theory has been an increasingly important phenomenon in economic thought over the last 50 years. The central role it affords to education has become even more marked in recent years as the concept of the âknowledge economyâ has become a global concern. In this paper, the prevalence of Human Capital Theory within European educational policy discourse is explored. The paper examines a selection of policy documents from a number of disparate European national contexts and considers the extent to which the ideas of Human Capital Theory can be seen to be influential. In the second part of the paper, the implications of Human Capital Theory for education are considered, with a particular focus on the possible ramifications at a time of economic austerity. The paper argues that Human Capital Theory risks offering a diminished view of the person, a diminished view of education, but that with its sole focus on economic goals leaves room for educationists and others to argue for the educational, social, and moral values it ignores, and for the conception of the good life and good society it fails to mention
Simultaneous sub-second hyperpolarization of the nuclear and electron spins of phosphorus in silicon
We demonstrate a method which can hyperpolarize both the electron and nuclear
spins of 31P donors in Si at low field, where both would be essentially
unpolarized in equilibrium. It is based on the selective ionization of donors
in a specific hyperfine state by optically pumping donor bound exciton
hyperfine transitions, which can be spectrally resolved in 28Si. Electron and
nuclear polarizations of 90% and 76%, respectively, are obtained in less than a
second, providing an initialization mechanism for qubits based on these spins,
and enabling further ESR and NMR studies on dilute 31P in 28Si.Comment: 4 pages, 3 figure
Two sides of the same coin? The association between suicide stigma and suicide normalisation
Aims: Evidence suggests that suicide stigma (i.e. negative attitudes towards persons affected by suicide/suicidality) and suicide normalisation (i.e. liberal attitudes towards suicide) are both associated with increased suicide risk. Despite conceptual similarities and potential interaction, suicide stigma and suicide normalisation have usually been investigated separately. We used cross-sectional data from a community sample to test the association between suicide stigma and suicide normalisation as well as to identify their respective determinants and consequences. Methods: Participants were N = 3.269 adults recruited from an established online-panel using quotas to reflect the composition of the German general population with regard to age, gender, education and region. We collected information about suicide stigma, suicide normalisation, intentions to seek help for suicidality, current suicidality, suicide literacy, negative mood and socio-demographic variables. We used regression modelling to determine the association between suicide stigma and suicide normalisation as well as to identify their determinants and consequences
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