7,762 research outputs found
On the Explosion Mechanism of SNe Type Ia
In this article we discuss the first simulations of two- and
three-dimensional Type Ia supernovae with an improved hydrodynamics code. After
describing the various enhancements, the obtained results are compared to those
of earlier code versions, observational data and the findings of other
researchers in this field.Comment: 7 pages, 4 figure
Efficient data structures for masks on 2D grids
This article discusses various methods of representing and manipulating
arbitrary coverage information in two dimensions, with a focus on space- and
time-efficiency when processing such coverages, storing them on disk, and
transmitting them between computers. While these considerations were originally
motivated by the specific tasks of representing sky coverage and cross-matching
catalogues of astronomical surveys, they can be profitably applied in many
other situations as well.Comment: accepted by A&
ArtDeco: A beam deconvolution code for absolute CMB measurements
We present a method for beam deconvolution for cosmic microwave background
(CMB) anisotropy measurements. The code takes as input the time-ordered data,
along with the corresponding detector pointings and known beam shapes, and
produces as output the harmonic a_Tlm, a_Elm, and a_Blm coefficients of the
observed sky. From these one can further construct temperature and Q and U
polarisation maps. The method is applicable to absolute CMB measurements with
wide sky coverage, and is independent of the scanning strategy. We test the
code with extensive simulations, mimicking the resolution and data volume of
Planck 30GHz and 70GHz channels, but with exaggerated beam asymmetry. We apply
it to multipoles up to l=1700 and examine the results in both pixel space and
harmonic space. We also test the method also in presence of white noise.Comment: 15 page
Libpsht - algorithms for efficient spherical harmonic transforms
Libpsht (or "library for Performant Spherical Harmonic Transforms") is a
collection of algorithms for efficient conversion between spatial-domain and
spectral-domain representations of data defined on the sphere. The package
supports transforms of scalars as well as spin-1 and spin-2 quantities, and can
be used for a wide range of pixelisations (including HEALPix, GLESP and ECP).
It will take advantage of hardware features like multiple processor cores and
floating-point vector operations, if available. Even without this additional
acceleration, the employed algorithms are among the most efficient (in terms of
CPU time as well as memory consumption) currently being used in the
astronomical community.
The library is written in strictly standard-conforming C90, ensuring
portability to many different hard- and software platforms, and allowing
straightforward integration with codes written in various programming languages
like C, C++, Fortran, Python etc.
Libpsht is distributed under the terms of the GNU General Public License
(GPL) version 2 and can be downloaded from
http://sourceforge.net/projects/libpsht.Comment: 9 pages, 8 figures, accepted by A&
Libsharp - spherical harmonic transforms revisited
We present libsharp, a code library for spherical harmonic transforms (SHTs),
which evolved from the libpsht library, addressing several of its shortcomings,
such as adding MPI support for distributed memory systems and SHTs of fields
with arbitrary spin, but also supporting new developments in CPU instruction
sets like the Advanced Vector Extensions (AVX) or fused multiply-accumulate
(FMA) instructions. The library is implemented in portable C99 and provides an
interface that can be easily accessed from other programming languages such as
C++, Fortran, Python etc. Generally, libsharp's performance is at least on par
with that of its predecessor; however, significant improvements were made to
the algorithms for scalar SHTs, which are roughly twice as fast when using the
same CPU capabilities. The library is available at
http://sourceforge.net/projects/libsharp/ under the terms of the GNU General
Public License
Following multi-dimensional Type Ia supernova explosion models to homologous expansion
The last years have witnessed a rapid development of three-dimensional models
of Type Ia supernova explosions. Consequently, the next step is to evaluate
these models under variation of the initial parameters and to compare them with
observations. To calculate synthetic lightcurves and spectra from numerical
models, it is mandatory to follow the evolution up to homologous expansion. We
report on methods to achieve this in our current implementation of
multi-dimensional Type Ia supernova explosion models. The novel scheme is
thoroughly tested in two dimensions and a simple example of a three-dimensional
simulation is presented. We discuss to what degree the assumption of homologous
expansion is justified in these models.Comment: 15 pages, 16 figures, resolution of some figures reduced to meet
astro-ph file size restriction, submitted to A&
Full-star Type Ia supernova explosion models
We present full-star simulations of Type Ia supernova explosions on the basis
of the standard Chandrasekhar-mass deflagration model. Most simulations so far
considered only one spatial octant and assumed mirror symmetry to the other
octants. Two full-star models are evolved to homologous expansion and compared
with previous single-octant simulations. Therefrom we analyze the effect of
abolishing the artificial symmetry constraint on the evolution of the flame
surface. It turns out that the development of asymmetries depends on the chosen
initial flame configuration. Such asymmetries of the explosion process could
possibly contribute to the observed polarization of some Type Ia supernova
spectra.Comment: 11 pages, 10 figures, resolution of some figures reduced to meet
astro-ph file size restriction, submitted to A&
Optically induced spin gates in coupled quantum dots using the electron-hole exchange interaction
We propose a fast optically induced two-qubit \textsc{c-phase} gate between
two resident spins in a pair of coupled quantum dots. An excited bound state
which extends over the two dots provides an effective electron-electron
exchange interaction. The gate is made possible by the electron-hole exchange
interaction, which isolates a single transition in the system. When combined
with appropriate single qubit rotations, this gate generates an entangled state
of the two spins
Caring or not caring for coworkers? An empirical exploration of the dilemma of care allocation in the workplace
Organization and management researchers praise the value of care in the workplace. However, they overlook the conflict between caring for work and for coworkers, which resonates with the dilemma of care allocation highlighted by ethicists of care. Through an in-depth qualitative study of two organizations, we examine how this dilemma is confronted in everyday organizational life. We draw on the concept of boundary work to explain how employees negotiate the boundary of their caring responsibilities in ways that grants or denies care to coworkers. We argue that the possibility of an ethics of care for coworkers requires boundary work that suspends the separation of personal and professional selves and constitutes the worker as a whole person. We contribute to research on care in organizations by showing how care for coworkers may be enabled or undermined by maintaining or suppressing the care allocation dilemma
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