11,044 research outputs found
Taming Uncertainty in the Assurance Process of Self-Adaptive Systems: a Goal-Oriented Approach
Goals are first-class entities in a self-adaptive system (SAS) as they guide
the self-adaptation. A SAS often operates in dynamic and partially unknown
environments, which cause uncertainty that the SAS has to address to achieve
its goals. Moreover, besides the environment, other classes of uncertainty have
been identified. However, these various classes and their sources are not
systematically addressed by current approaches throughout the life cycle of the
SAS. In general, uncertainty typically makes the assurance provision of SAS
goals exclusively at design time not viable. This calls for an assurance
process that spans the whole life cycle of the SAS. In this work, we propose a
goal-oriented assurance process that supports taming different sources (within
different classes) of uncertainty from defining the goals at design time to
performing self-adaptation at runtime. Based on a goal model augmented with
uncertainty annotations, we automatically generate parametric symbolic formulae
with parameterized uncertainties at design time using symbolic model checking.
These formulae and the goal model guide the synthesis of adaptation policies by
engineers. At runtime, the generated formulae are evaluated to resolve the
uncertainty and to steer the self-adaptation using the policies. In this paper,
we focus on reliability and cost properties, for which we evaluate our approach
on the Body Sensor Network (BSN) implemented in OpenDaVINCI. The results of the
validation are promising and show that our approach is able to systematically
tame multiple classes of uncertainty, and that it is effective and efficient in
providing assurances for the goals of self-adaptive systems
Fitting Analysis using Differential Evolution Optimization (FADO): Spectral population synthesis through genetic optimization under self-consistency boundary conditions
The goal of population spectral synthesis (PSS) is to decipher from the
spectrum of a galaxy the mass, age and metallicity of its constituent stellar
populations. This technique has been established as a fundamental tool in
extragalactic research. It has been extensively applied to large spectroscopic
data sets, notably the SDSS, leading to important insights into the galaxy
assembly history. However, despite significant improvements over the past
decade, all current PSS codes suffer from two major deficiencies that inhibit
us from gaining sharp insights into the star-formation history (SFH) of
galaxies and potentially introduce substantial biases in studies of their
physical properties (e.g., stellar mass, mass-weighted stellar age and specific
star formation rate). These are i) the neglect of nebular emission in spectral
fits, consequently, ii) the lack of a mechanism that ensures consistency
between the best-fitting SFH and the observed nebular emission characteristics
of a star-forming (SF) galaxy. In this article, we present FADO (Fitting
Analysis using Differential evolution Optimization): a conceptually novel,
publicly available PSS tool with the distinctive capability of permitting
identification of the SFH that reproduces the observed nebular characteristics
of a SF galaxy. This so-far unique self-consistency concept allows us to
significantly alleviate degeneracies in current spectral synthesis. The
innovative character of FADO is further augmented by its mathematical
foundation: FADO is the first PSS code employing genetic differential evolution
optimization. This, in conjunction with other unique elements in its
mathematical concept (e.g., optimization of the spectral library using
artificial intelligence, convergence test, quasi-parallelization) results in
key improvements with respect to computational efficiency and uniqueness of the
best-fitting SFHs.Comment: 25 pages, 12 figures, A&A accepte
Measuring the delay time distribution of binary neutron stars. II. Using the redshift distribution from third-generation gravitational wave detectors network
We investigate the ability of current and third-generation gravitational wave
(GW) detectors to determine the delay time distribution (DTD) of binary neutron
stars (BNS) through a direct measurement of the BNS merger rate as a function
of redshift. We assume that the DTD follows a power law distribution with a
slope and a minimum merger time , and also allow the
overall BNS formation efficiency per unit stellar mass to vary. By convolving
the DTD and mass efficiency with the cosmic star formation history, and then
with the GW detector capabilities, we explore two relevant regimes. First, for
the current generation of GW detectors, which are only sensitive to the local
universe, but can lead to precise redshift determinations via the
identification of electromagnetic counterparts and host galaxies, we show that
the DTD parameters are strongly degenerate with the unknown mass efficiency and
therefore cannot be determined uniquely. Second, for third-generation detectors
such as Einstein Telescope (ET) and Cosmic Explorer (CE), which will detect BNS
mergers at cosmological distances, but with a redshift uncertainty inherent to
GW-only detections (), we show that the DTD and mass
efficiency can be well-constrained to better than 10\% with a year of
observations. This long-term approach to determining the DTD through a direct
mapping of the BNS merger redshift distribution will be supplemented by more
near term studies of the DTD through the properties of BNS merger host galaxies
at (Safarzadeh & Berger 2019).Comment: 10 pages, Accepted to ApJ Letter
Joint deprojection of Sunyaev-Zeldovich and X-ray images of galaxy clusters
We present two non-parametric deprojection methods aimed at recovering the
three-dimensional density and temperature profiles of galaxy clusters from
spatially resolved thermal Sunyaev-Zeldovich (tSZ) and X-ray surface brightness
maps, thus avoiding the use of X-ray spectroscopic data. In both methods,
clusters are assumed to be spherically symmetric and modeled with an onion-skin
structure. The first method follows a direct geometrical approach. The second
method is based on the maximization of a single joint (tSZ and X-ray)
likelihood function, which allows one to fit simultaneously the two signals by
following a Monte Carlo Markov Chain approach. These techniques are tested
against a set of cosmological simulations of clusters, with and without
instrumental noise. We project each cluster along the three orthogonal
directions defined by the principal axes of the momentum of inertia tensor.
This enables us to check any bias in the deprojection associated to the cluster
elongation along the line of sight. After averaging over all the three
projection directions, we find an overall good reconstruction, with a small
(<~10 per cent) overestimate of the gas density profile. This turns into a
comparable overestimate of the gas mass within the virial radius, which we
ascribe to the presence of residual gas clumping. Apart from this small bias
the reconstruction has an intrinsic scatter of about 5 per cent, which is
dominated by gas clumpiness. Cluster elongation along the line of sight biases
the deprojected temperature profile upwards at r<~0.2r_vir and downwards at
larger radii. A comparable bias is also found in the deprojected temperature
profile. Overall, this turns into a systematic underestimate of the gas mass,
up to 10 percent. (Abridged)Comment: 17 pages, 15 figures, accepted by MNRA
Non-parametric deprojection of NIKA SZ observations: Pressure distribution in the Planck-discovered cluster PSZ1 G045.85+57.71
The determination of the thermodynamic properties of clusters of galaxies at
intermediate and high redshift can bring new insights into the formation of
large-scale structures. It is essential for a robust calibration of the
mass-observable scaling relations and their scatter, which are key ingredients
for precise cosmology using cluster statistics. Here we illustrate an
application of high resolution arcsec) thermal Sunyaev-Zel'dovich (tSZ)
observations by probing the intracluster medium (ICM) of the \planck-discovered
galaxy cluster \psz\ at redshift , using tSZ data obtained with the
NIKA camera, which is a dual-band (150 and 260~GHz) instrument operated at the
IRAM 30-meter telescope. We deproject jointly NIKA and \planck\ data to extract
the electronic pressure distribution from the cluster core () to its outskirts () non-parametrically for the
first time at intermediate redshift. The constraints on the resulting pressure
profile allow us to reduce the relative uncertainty on the integrated Compton
parameter by a factor of two compared to the \planck\ value. Combining the tSZ
data and the deprojected electronic density profile from \xmm\ allows us to
undertake a hydrostatic mass analysis, for which we study the impact of a
spherical model assumption on the total mass estimate. We also investigate the
radial temperature and entropy distributions. These data indicate that \psz\ is
a massive ( M) cool-core cluster.
This work is part of a pilot study aiming at optimizing the treatment of the
NIKA2 tSZ large program dedicated to the follow-up of SZ-discovered clusters at
intermediate and high redshifts. (abridged)Comment: 16 pages, 10 figure
A study of the sensitivity of shape measurements to the input parameters of weak lensing image simulations
Improvements in the accuracy of shape measurements are essential to exploit
the statistical power of planned imaging surveys that aim to constrain
cosmological parameters using weak lensing by large-scale structure. Although a
range of tests can be performed using the measurements, the performance of the
algorithm can only be quantified using simulated images. This yields, however,
only meaningful results if the simulated images resemble the real observations
sufficiently well. In this paper we explore the sensitivity of the
multiplicative bias to the input parameters of Euclid-like image simulations.We
find that algorithms will need to account for the local density of sources. In
particular the impact of galaxies below the detection limit warrants further
study, because magnification changes their number density, resulting in
correlations between the lensing signal and multiplicative bias. Although
achieving sub-percent accuracy will require further study, we estimate that
sufficient archival Hubble Space Telescope data are available to create
realistic populations of galaxies.Comment: 18 pages, accepted for publications in MNRA
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