455 research outputs found
Faà di Bruno’s formula and spatial cluster modelling
AbstractThe probability generating functional (p.g.fl.) provides a useful means of compactly representing point process models. Cluster processes can be described through the composition of p.g.fl.s, and factorial moment measures and Janossy measures can be recovered from the p.g.fl. using variational derivatives. This article describes the application of a recent result in variational calculus, a generalisation of Faà di Bruno’s formula, to determine such results for cluster processes
Piece‐wise constant cluster modelling of dynamics of upwelling patterns
A comprehensive approach is presented to analyse season's coastal upwelling represented by weekly sea surface temperature (SST) image grids. Our three-stage data recovery clustering method assumes that the season's upwelling can be divided into shorter periods of stability, ranges, each to be represented by a constant core and variable shell parts. Corresponding clustering algorithms parameters are automatically derived by using the least-squares clustering criterion. The approach has been successfully applied to real-world SST data covering two distinct regions: Portuguese coast and Morocco coast, for 16 years each.LA/P/0101/2020info:eu-repo/semantics/publishedVersio
Bayesian modelling of clusters of galaxies from multi-frequency pointed Sunyaev--Zel'dovich observations
We present a Bayesian approach to modelling galaxy clusters using
multi-frequency pointed observations from telescopes that exploit the
Sunyaev--Zel'dovich effect. We use the recently developed MultiNest technique
(Feroz, Hobson & Bridges, 2008) to explore the high-dimensional parameter
spaces and also to calculate the Bayesian evidence. This permits robust
parameter estimation as well as model comparison. Tests on simulated Arcminute
Microkelvin Imager observations of a cluster, in the presence of primary CMB
signal, radio point sources (detected as well as an unresolved background) and
receiver noise, show that our algorithm is able to analyse jointly the data
from six frequency channels, sample the posterior space of the model and
calculate the Bayesian evidence very efficiently on a single processor. We also
illustrate the robustness of our detection process by applying it to a field
with radio sources and primordial CMB but no cluster, and show that indeed no
cluster is identified. The extension of our methodology to the detection and
modelling of multiple clusters in multi-frequency SZ survey data will be
described in a future work.Comment: 12 pages, 7 figures, submitted to MNRA
X-ray modelling of galaxy cluster gas and mass profiles
We present a parametric analysis of the intracluster medium and gravitating
mass distribution of a statistical sample of 20 galaxy clusters using the
phenomenological cluster model of Ascasibar and Diego. We describe an effective
scheme for the estimation of errors on model parameters and derived quantities
using bootstrap resampling. We find that the model provides a good description
of the data in all cases and we quantify the mean fractional intrinsic scatter
about the best-fit density and temperature profiles, finding this to have
median values across the sample of 2 and 5 per cent, respectively. In addition,
we demonstrate good agreement between r500 determined directly from the model
and that estimated from a core-excluded global spectrum. We compare cool core
and non-cool core clusters in terms of the logarithmic slopes of their gas
density and temperature profiles and the distribution of model parameters and
conclude that the two categories are clearly separable. In particular, we
confirm the effectiveness of the logarithmic gradient of the gas density
profile measured at 0.04 r500 in differentiating between the two types of
cluster.Comment: 8 pages, 7 figures, accepted for publication in MNRA
High Energy Phenomena in Clusters of Galaxies
Several phenomena in high energy astrophysics have been recently related to
clusters of galaxies and to cosmic ray interactions occurring inside these
structures. In many of these phenomena the observable effects depend on the
energy density of cosmic rays confined in the Intra Cluster (IC) medium, which
is a poorly known quantity. We propose here that useful indications about this
quantity can be obtained from present and future observations of galaxy
clusters in the radio and hard X-ray frequency ranges.Comment: 5 pages, 3 Figures, Latex (using espcrc2,epsfig), to appear in the
Proceedings of the TAUP97, Eds. A. DiCredico et al., in press. Send comments
to S.Colafrancesco: [email protected]
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