1,300 research outputs found
Model Validation and Simulation
The Bauhaus Summer School series provides an international forum for an exchange of methods and skills related to the interaction between different disciplines of modern engineering science.
The 2012 civil engineering course was held in August over two weeks at Bauhaus-Universität Weimar. The overall aim was the exchange
of research and modern scientific approaches in the field of model validation and simulation between well-known experts acting as lecturers
and active students. Besides these educational intentions the social and cultural component of the meeting has been in the focus. 48 graduate and doctoral students from 20 different countries and 22 lecturers from 12 countries attended this summer school. Among
other aspects, this activity can be considered successful as it raised the
sensitivity towards both the significance of research in civil engineering
and the role of intercultural exchange.
This volume summarizes and publishes some of the results: abstracts
of key note papers presented by the experts and selected student
research works. The overview reflects the quality of this summer school.
Furthermore the individual contributions confirm that for active students
this event has been a research forum and a special opportunity
to learn from the experiences of the researchers in terms of methodology
and strategies for research implementation in their current work
Observational constraints on the progenitors of core-collapse supernovae : the case for missing high mass stars
Over the last 15 years, the supernova community has endeavoured to identify
progenitor stars of core-collapse supernovae in high resolution archival images
of their galaxies.This review compiles results (from 1999 - 2013) in a distance
limited sample and discusses the implications. The vast majority of the
detections of progenitor stars are of type II-P, II-L or IIb with one type Ib
progenitor system detected and many more upper limits for progenitors of Ibc
supernovae (14). The data for these 45 supernovae progenitors illustrate a
remarkable deficit of high luminosity stars above an apparent limit of Log L ~=
5.1 dex. For a typical Salpeter IMF, one would expect to have found 13 high
luminosity and high mass progenitors. There is, possibly, only one object in
this time and volume limited sample that is unambiguously high mass (the
progenitor of SN2009ip). The possible biases due to the influence of
circumstellar dust and sample selection methods are reviewed. It does not
appear likely that these can explain the missing high mass progenitor stars.
This review concludes that the observed populations of supernovae in the local
Universe are not, on the whole, produced by high mass (M > ~18Msun) stars.
Theoretical explosions of model stars also predict that black hole formation
and failed supernovae tend to occur above M > ~18Msun. The models also suggest
there are islands of explodability for stars in the 8-120Msun range. The
observational constraints are quite consistent with the bulk of stars above M >
~18Msun collapsing to form black holes with no visible supernovae. (Abridged).Comment: Invited review article for Publications of the Astronomical Society
of Australia, to be published in a special PASA collection on "SN1987A and
Supernovae in the Local Universe". This is the accepted version, after
referee review. Additional minor corrections to match proofs. (25 pages
A reusable iterative optimization software library to solve combinatorial problems with approximate reasoning
Real world combinatorial optimization problems such as scheduling are
typically too complex to solve with exact methods. Additionally, the problems
often have to observe vaguely specified constraints of different importance,
the available data may be uncertain, and compromises between antagonistic
criteria may be necessary. We present a combination of approximate reasoning
based constraints and iterative optimization based heuristics that help to
model and solve such problems in a framework of C++ software libraries called
StarFLIP++. While initially developed to schedule continuous caster units in
steel plants, we present in this paper results from reusing the library
components in a shift scheduling system for the workforce of an industrial
production plant.Comment: 33 pages, 9 figures; for a project overview see
http://www.dbai.tuwien.ac.at/proj/StarFLIP
The atomic simulation environment — a python library for working with atoms
The Atomic Simulation Environment (ASE) is a software package written in the Python programming language with the aim of setting up, steering, and analyzing atomistic simula- tions. In ASE, tasks are fully scripted in Python. The powerful syntax of Python combined with the NumPy array library make it possible to perform very complex simulation tasks. For example, a sequence of calculations may be performed with the use of a simple "for-loop" construction. Calculations of energy, forces, stresses and other quantities are performed through interfaces to many external electronic structure codes or force fields using a uniform interface. On top of this calculator interface, ASE provides modules for performing many standard simulation tasks such as structure optimization, molecular dynamics, handling of constraints and performing nudged elastic band calculations
SPH Simulations of Counterrotating Disk Formation in Spiral Galaxies
We present the results of Smoothed Particle Hydrodynamics (SPH) simulations
of the formation of a massive counterrotating disk in a spiral galaxy. The
current study revisits and extends (with SPH) previous work carried out with
sticky particle gas dynamics, in which adiabatic gas infall and a retrograde
gas-rich dwarf merger were tested as the two most likely processes for
producing such a counterrotating disk. We report on experiments with a cold
primary similar to our Galaxy, as well as a hot, compact primary modeled after
NGC 4138. We have also conducted numerical experiments with varying amounts of
prograde gas in the primary disk, and an alternative infall model (a spherical
shell with retrograde angular momentum). The structure of the resulting
counterrotating disks is dramatically different with SPH. The disks we produce
are considerably thinner than the primary disks and those produced with sticky
particles. The time-scales for counterrotating disk formation are shorter with
SPH because the gas loses kinetic energy and angular momentum more rapidly.
Spiral structure is evident in most of the disks, but an exponential radial
profile is not a natural byproduct of these processes. The infalling gas shells
that we tested produce counterrotating bulges and rings rather than disks. The
presence of a considerable amount of preexisting prograde gas in the primary
causes, at least in the absence of star formation, a rapid inflow of gas to the
center and a subsequent hole in the counterrotating disk. In general, our SPH
experiments yield stronger evidence to suggest that the accretion of massive
counterrotating disks drives the evolution of the host galaxies towards earlier
(S0/Sa) Hubble types.Comment: To appear in ApJ. 20 pages LaTex 2-column with 3 tables, 23 figures
(GIF) available at this site. Complete gzipped postscript preprint with
embedded figures available from http://tarkus.pha.jhu.edu/~thakar/cr3.html (3
Mb
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