533,523 research outputs found
Radiative transfer modelling of parsec-scale dusty warped discs
Warped discs have been found on (sub-)parsec scale in some nearby Seyfert
nuclei, identified by their maser emission. Using dust radiative transfer
simulations we explore their observational signatures in the infrared in order
to find out whether they can partly replace the molecular torus. Strong
variations of the brightness distributions are found, depending on the
orientation of the warp with respect to the line of sight. Whereas images at
short wavelengths typically show a disc-like and a point source component, the
warp itself only becomes visible at far-infrared wavelengths. A similar variety
is visible in the shapes of the spectral energy distributions. Especially for
close to edge-on views, the models show silicate feature strengths ranging from
deep absorption to strong emission for variations of the lines of sight towards
the warp. To test the applicability of our model, we use the case of the
Circinus galaxy, where infrared interferometry has revealed a highly elongated
emission component matching a warped maser disc in orientation and size. Our
model is for the first time able to present a physical explanation for the
observed dust morphology as coming from the AGN heated dust. As opposed to
available torus models, a warped disc morphology produces a variety of silicate
feature shapes for grazing lines of sight, close to an edge-on view. This could
be an attractive alternative to a claimed change of the dust composition for
the case of the nearby Seyfert 2 galaxy NGC 1068, which harbours a warped maser
disc as well.Comment: accepted by MNRA
Modeling and Analysis of Software Product Line Variability in Clafer
Both feature and class modeling are used in Software Product Line (SPL) engineering to model variability. Feature models are used primarily to represent user-visible characteristics (i.e., features) of products; whereas class models are often used to model types of components and connectors in a product-line architecture.
Previous works have explored the approach of using a single language to express both configurations of features and components. Their goal was to simplify the definition and analysis of feature-to-component mappings and to allow modeling component options as features. A prominent example of this approach is cardinality-based feature modeling, which extends feature models with multiple instantiation and references to express component-like, replicated features. Another example is to support feature modeling in a class modeling language, such as UML or MOF, using their profiling mechanisms and a stylized use of composition. Both examples have notable drawbacks: cardinality-based feature modeling lacks a constraint language and a well-defined semantics; encoding feature models as class models and their evolution bring extra complexity.
This dissertation presents Clafer (class, feature, reference), a class modeling language with first-class support for feature modeling. Clafer can express rich structural models augmented with complex constraints, i.e., domain, variability, component models, and meta-models. Clafer supports: (i) class-based meta-models, (ii) object models (with uncertainty, if needed), (iii) feature models with attributes and multiple instantiation, (iv) configurations of feature models, (v) mixtures of meta- and feature models and model templates, and (vi) first-order logic constraints.
Clafer also makes it possible to arrange models into multiple specialization and extension layers via constraints and inheritance. On the other hand, in designing Clafer we wanted to create a language that builds upon as few concepts as possible, and is easy to learn. The language is supported by tools for SPL verification and optimization.
We propose to unify basic modeling constructs into a single concept, called clafer. In other words, Clafer is not a hybrid language. We identify several key mechanisms allowing a class modeling language to express feature models concisely. We provide Clafer with a formal semantics built in a novel, structurally explicit way. As Clafer subsumes cardinality-based feature modeling with attributes, references, and constraints, we are the first to precisely define semantics of such models.
We also explore the notion of partial instantiation that allows for modeling with uncertainty and variability. We show that Object-Oriented Modeling (OOM) languages with no direct support for partial instances can support them via class modeling, using subclassing and strengthening multiplicity constraints. We make the encoding of partial instances via subclassing precise and general. Clafer uses this encoding and pushes the idea even further: it provides a syntactic unification of types and (partial) instances via subclassing and redefinition.
We evaluate Clafer analytically and experimentally. The analytical evaluation shows that Clafer can concisely express feature and meta-models via a uniform syntax and unified semantics. The experimental evaluation shows that: 1) Clafer can express a variety of realistic rich structural models with complex constraints, such as variability models, meta-models, model templates, and domain models; and 2) that useful analyses can be performed within seconds
A Dust Twin of Cas A: Cool Dust and 21-micron Silicate Dust Feature in the Supernova Remnant G54.1+0.3
We present infrared (IR) and submillimeter observations of the Crab-like
supernova remnant (SNR) G54.1+0.3 including 350 micron (SHARC-II), 870 micron
(LABOCA), 70, 100, 160, 250, 350, 500 micron (Herschel) and 3-40 micron
(Spitzer). We detect dust features at 9, 11 and 21 micron and a long wavelength
continuum dust component. The 21 micron dust coincides with [Ar II] ejecta
emission, and the feature is remarkably similar to that in Cas A. The IRAC 8
micron image including Ar ejecta is distributed in a shell-like morphology
which is coincident with dust features, suggesting that dust has formed in the
ejecta. We create a cold dust map that shows excess emission in the
northwestern shell. We fit the spectral energy distribution of the SNR using
the continuous distributions of ellipsoidal (CDE) grain model of pre-solar
grain SiO2 that reproduces the 21 and 9 micron dust features and discuss grains
of SiC and PAH that may be responsible for the 10-13 micron dust features. To
reproduce the long-wavelength continuum, we explore models consisting of
different grains including Mg2SiO4, MgSiO3, Al2O3, FeS, carbon, and Fe3O4. We
tested a model with a temperature-dependent silicate absorption coefficient. We
detect cold dust (27-44 K) in the remnant, making this the fourth such SNR with
freshly-formed dust. The total dust mass in the SNR ranges from 0.08-0.9 Msun
depending on the grain composition, which is comparable to predicted masses
from theoretical models. Our estimated dust masses are consistent with the idea
that SNe are a significant source of dust in the early Universe.Comment: MNRAS: accepted on June 28, 2018 and published on July 4, 201
Interstellar and Ejecta Dust in the Cas A Supernova Remnant
Infrared continuum observations provide a means of investigating the physical
composition of the dust in the ejecta and swept up medium of the Cas A
supernova remnant. Using low resolution Spitzer IRS spectra (5-35 m), and
broad-band Herschel PACS imaging (70, 100, and 160 m), we identify
characteristic dust spectra, associated with ejecta layers that underwent
distinct nuclear burning histories. The most luminous spectrum exhibits strong
emission features at and 21 m and is closely associated with
ejecta knots with strong Ar emission lines. The dust features can be reproduced
by magnesium silicate grains with relatively low Mg to Si ratios. Another dust
spectrum is associated with ejecta having strong Ne emission lines. It has no
indication of any silicate features, and is best fit by AlO dust. A
third characteristic dust spectrum shows features that are best matched by
magnesium silicates with a relatively high Mg to Si ratio. This dust is
primarily associated with the X-ray emitting shocked ejecta, but it is also
evident in regions where shocked interstellar or circumstellar material is
expected. However, the identification of dust composition is not unique, and
each spectrum includes an additional featureless dust component of unknown
composition. Colder dust of indeterminate composition is associated with
emission from the interior of the SNR, where the reverse shock has not yet
swept up and heated the ejecta. Most of the dust mass in Cas A is associated
with this unidentified cold component, which is . The
mass of warmer dust is only .Comment: 45 pages. 21 Figures. Accepted for publication in Ap
Towards Product Lining Model-Driven Development Code Generators
A code generator systematically transforms compact models to detailed code.
Today, code generation is regarded as an integral part of model-driven
development (MDD). Despite its relevance, the development of code generators is
an inherently complex task and common methodologies and architectures are
lacking. Additionally, reuse and extension of existing code generators only
exist on individual parts. A systematic development and reuse based on a code
generator product line is still in its infancy. Thus, the aim of this paper is
to identify the mechanism necessary for a code generator product line by (a)
analyzing the common product line development approach and (b) mapping those to
a code generator specific infrastructure. As a first step towards realizing a
code generator product line infrastructure, we present a component-based
implementation approach based on ideas of variability-aware module systems and
point out further research challenges.Comment: 6 pages, 1 figure, Proceedings of the 3rd International Conference on
Model-Driven Engineering and Software Development, pp. 539-545, Angers,
France, SciTePress, 201
Cosmic Rays from the Knee to the Ankle
Investigations of the energy spectrum as well as the mass composition of
cosmic rays in the energy range of PeVto EeV are important for understanding
both, the origin of the galactic and the extragalactic cosmic rays. Recently,
three modern experimental installations (KASCADE-Grande, IceTop, Tunka-133),
dedicated to investigate this primary energy range, have published new results
on the all-particle energy spectrum. In this short review these results are
presented and the similarities and differences discussed. In addition, the
effects of using different hadronic interaction models for interpreting the
measured air-shower data will be examined. Finally, a brief discussion on the
question if the present results are in agreement or in contradiction with
astrophysical models for the transition from galactic to 10 pagesextragalactic
origin of cosmic rays completes this paper.Comment: 10 pages, proceedings of TAUP 2013 conferenc
Early aspects: aspect-oriented requirements engineering and architecture design
This paper reports on the third Early Aspects: Aspect-Oriented Requirements Engineering and Architecture Design Workshop, which has been held in Lancaster, UK, on March 21, 2004. The workshop included a presentation session and working sessions in which the particular topics on early aspects were discussed. The primary goal of the workshop was to focus on challenges to defining methodical software development processes for aspects from early on in the software life cycle and explore the potential of proposed methods and techniques to scale up to industrial applications
Integrating the common variability language with multilanguage annotations for web engineering
Web applications development involves managing a high diversity of files and resources like code, pages or style sheets, implemented in different languages. To deal with the automatic generation of
custom-made configurations of web applications, industry usually adopts annotation-based approaches even though the majority of studies encourage the use of composition-based approaches to implement
Software Product Lines. Recent work tries to combine both approaches to get the complementary benefits. However, technological companies are reticent to adopt new development paradigms
such as feature-oriented programming or aspect-oriented programming.
Moreover, it is extremely difficult, or even impossible, to apply
these programming models to web applications, mainly because of
their multilingual nature, since their development involves multiple
types of source code (Java, Groovy, JavaScript), templates (HTML,
Markdown, XML), style sheet files (CSS and its variants, such as
SCSS), and other files (JSON, YML, shell scripts). We propose to
use the Common Variability Language as a composition-based approach
and integrate annotations to manage fine grained variability
of a Software Product Line for web applications. In this paper, we (i)
show that existing composition and annotation-based approaches,
including some well-known combinations, are not appropriate to
model and implement the variability of web applications; and (ii)
present a combined approach that effectively integrates annotations
into a composition-based approach for web applications. We implement
our approach and show its applicability with an industrial
real-world system.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech
The shape and composition of interstellar silicate grains
We investigate the composition and shape distribution of silicate dust grains
in the interstellar medium. The effect of the amount of magnesium in the
silicate lattice is studied. We fit the spectral shape of the interstellar 10
mu extinction feature as observed towards the galactic center. We use very
irregularly shaped coated and non-coated porous Gaussian Random Field particles
as well as a statistical approach to model shape effects. For the dust
materials we use amorphous and crystalline silicates with various composition
and SiC. The results of our analysis of the 10 mu feature are used to compute
the shape of the 20 mu silicate feature and to compare this with observations.
By using realistic particle shapes we are, for the first time, able to derive
the magnesium fraction in interstellar silicates. We find that the interstellar
silicates are highly magnesium rich (Mg/(Fe+Mg)>0.9) and that the stoichiometry
lies between pyroxene and olivine type silicates. This composition is not
consistent with that of the glassy material found in GEMS in interplanetary
dust particles indicating that these are, in general, not unprocessed remnants
from the interstellar medium. Also, we find a significant fraction of SiC
(~3%). We discuss the implications of our results for the formation and
evolutionary history of cometary and circumstellar dust. We argue that the fact
that crystalline silicates in cometary and circumstellar grains are almost
purely magnesium silicates is a natural consequence of our findings that the
amorphous silicates from which they were formed were already magnesium rich.Comment: Accepted for publication in A&
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