8,019 research outputs found
Circumstellar shells and mass loss rates: Clues to the evolution of S stars
It is the purpose of this paper to rediscuss the circumstellar properties of
S stars and to put these properties in perspective with our current
understanding of the evolutionary status of S stars, in particular the
intrinsic/extrinsic dichotomy. Accordingly, an extensive data set probing the
circumstellar environment of S stars (IRAS flux densities, maser emission, CO
rotational lines) has been collected and critically evaluated. This data set
combines new observations (9 stars have been observed in the CO J=2-1 line and
3 in the CO J=3-2 line, with four new detections) with existing material (all
CO and maser observations of S stars published in the literature). The IRAS
flux densities of S stars have been re-evaluated by co-adding the individual
scans, in order to better handle the intrinsic variability of these stars in
the IRAS bands, and possible contamination by Galactic cirrus.
Mass loss rates or upper limits have been derived for all S stars observed in
the CO rotational lines, and range from < 2 10^{-8} Msun y^{-1} for extrinsic S
stars to 10^{-5} Msun y^{-1}. These mass-loss rates correlate well with the K -
[12] color index, which probes the dust loss rate, provided that the mass loss
rate be larger than 10^{-8} Msun~y^{-1}. Small mass-loss rates are found for
extrinsic S stars, consistent with their not being so evolved (RGB or
Early-AGB) as the Tc-rich S stars. This result does not support the claim often
made in relation with symbiotic stars that binarity strongly enhances the
mass-loss rate.Comment: Astronomy & Astrophysics Suppl., 40 pages, 22 figures, 6 tables
(LaTeX). Also available at: http://astro.ulb.ac.be/Htm/ps.ht
An Institutional Framework for Heterogeneous Formal Development in UML
We present a framework for formal software development with UML. In contrast
to previous approaches that equip UML with a formal semantics, we follow an
institution based heterogeneous approach. This can express suitable formal
semantics of the different UML diagram types directly, without the need to map
everything to one specific formalism (let it be first-order logic or graph
grammars). We show how different aspects of the formal development process can
be coherently formalised, ranging from requirements over design and Hoare-style
conditions on code to the implementation itself. The framework can be used to
verify consistency of different UML diagrams both horizontally (e.g.,
consistency among various requirements) as well as vertically (e.g.,
correctness of design or implementation w.r.t. the requirements)
Developing the evidence base for adult social care practice: The NIHR School for Social Care Research
In a foreword to 'Shaping the Future of Care Together', Prime Minister Gordon Brown says that a care and support system reflecting the needs of our times and meeting our rising aspirations is achievable, but 'only if we are prepared to rise to the challenge of radical reform'. A number of initiatives will be needed to meet the challenge of improving social care for the growing older population. Before the unveiling of the green paper, The National Institute for Health Research (NIHR) announced that it has provided 15m pounds over a five-year period to establish the NIHR School for Social Care Research. The School's primary aim is to conduct or commission research that will help to improve adult social care practice in England. The School is seeking ideas for research topics, outline proposals for new studies and expert advice in developing research methods
Parameters for Twisted Representations
The study of Hermitian forms on a real reductive group gives rise, in the
unequal rank case, to a new class of Kazhdan-Lusztig-Vogan polynomials. These
are associated with an outer automorphism of , and are related to
representations of the extended group . These polynomials were
defined geometrically by Lusztig and Vogan in "Quasisplit Hecke Algebras and
Symmetric Spaces", Duke Math. J. 163 (2014), 983--1034. In order to use their
results to compute the polynomials, one needs to describe explicitly the
extension of representations to the extended group. This paper analyzes these
extensions, and thereby gives a complete algorithm for computing the
polynomials. This algorithm is being implemented in the Atlas of Lie Groups and
Representations software
Equivalence of domains for hyperbolic Hubbard-Stratonovich transformations
We settle a long standing issue concerning the traditional derivation of
non-compact non-linear sigma models in the theory of disordered electron
systems: the hyperbolic Hubbard-Stratonovich (HS) transformation of
Pruisken-Schaefer type. Only recently the validity of such transformations was
proved in the case of U(p,q) (non-compact unitary) and O(p,q) (non-compact
orthogonal) symmetry. In this article we give a proof for general non-compact
symmetry groups. Moreover we show that the Pruisken-Schaefer type
transformations are related to other variants of the HS transformation by
deformation of the domain of integration. In particular we clarify the origin
of surprising sign factors which were recently discovered in the case of
orthogonal symmetry.Comment: 30 pages, 3 figure
Departmental elections and the changing landscape of French politics
The departmental elections of March 2015 redrew the French political landscape, setting the new terms of electoral competition in advance of the regional elections of December 2015 and, more critically, the presidential election of April–May 2017. These elections saw the far-right National Front (FN) come top in both rounds only to be outmanoeuvred by the mainstream parties and prevented from winning a single department. As a case study in vote–seat distortion, the elections highlighted a voting system effective in keeping the FN out of executive power but deficient in terms of democratic representation and inadequate as a response to the new tripartite realities of France's changing political landscape
Investigation of the B -field-induced widening of the donor-electron energy distribution in n-doped (Zn,Mn)Se by resonant electron spin-flip Raman spectroscopy
Decomposition of time-covariant operations on quantum systems with continuous and/or discrete energy spectrum
Every completely positive map G that commutes which the Hamiltonian time
evolution is an integral or sum over (densely defined) CP-maps G_\sigma where
\sigma is the energy that is transferred to or taken from the environment. If
the spectrum is non-degenerated each G_\sigma is a dephasing channel followed
by an energy shift. The dephasing is given by the Hadamard product of the
density operator with a (formally defined) positive operator. The Kraus
operator of the energy shift is a partial isometry which defines a translation
on R with respect to a non-translation-invariant measure.
As an example, I calculate this decomposition explicitly for the rotation
invariant gaussian channel on a single mode.
I address the question under what conditions a covariant channel destroys
superpositions between mutually orthogonal states on the same orbit. For
channels which allow mutually orthogonal output states on the same orbit, a
lower bound on the quantum capacity is derived using the Fourier transform of
the CP-map-valued measure (G_\sigma).Comment: latex, 33 pages, domains of unbounded operators are now explicitly
specified. Presentation more detailed. Implementing the shift after the
dephasing is sometimes more convenien
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