5,659 research outputs found
Decomposition of AGN host galaxy images
We describe an algorithm to decompose deep images of Active Galactic Nuclei
into host galaxy and nuclear components. Currently supported are three galaxy
models: A de-Vaucouleurs spheroidal, an exponential disc, and a two-component
disc+bulge model. Key features of the method are: (semi-)analytic
representation of a possibly spatially variable point-spread function; full
two-dimensional convolution of the model galaxy using gradient-controlled
adaptive subpixelling; multiple iteration scheme. The code is computationally
efficient and versatile for a wide range of applications. The quantitative
performance is measured by analysing simulated imaging data. We also present
examples of the application of the method to small test samples of nearby
Seyfert 1 galaxies and quasars at redshifts z < 0.35.Comment: 12 pages, 15 figures, accepted for publication in MNRA
The central black hole mass of the high-sigma but low-bulge-luminosity lenticular galaxy NGC 1332
The masses of the most massive supermassive black holes (SMBHs) predicted by
the M_BH-sigma and M_BH-luminosity relations appear to be in conflict. Which of
the two relations is the more fundamental one remains an open question. NGC
1332 is an excellent example that represents the regime of conflict. It is a
massive lenticular galaxy which has a bulge with a high velocity dispersion
sigma of ~320 km/s; bulge--disc decomposition suggests that only 44% of the
total light comes from the bulge. The M_BH-sigma and the M_BH-luminosity
predictions for the central black hole mass of NGC 1332 differ by almost an
order of magnitude. We present a stellar dynamical measurement of the SMBH mass
using an axisymmetric orbit superposition method. Our SINFONI integral-field
unit (IFU) observations of NGC 1332 resolve the SMBH's sphere of influence
which has a diameter of ~0.76 arcsec. The sigma inside 0.2 arcsec reaches ~400
km/s. The IFU data allow us to increase the statistical significance of our
results by modelling each of the four quadrants separately. We measure a SMBH
mass of (1.45 \pm 0.20) x 10^9 M_sun with a bulge mass-to-light ratio of 7.08
\pm 0.39 in the R-band. With this mass, the SMBH of NGC 1332 is offset from the
M_BH-luminosity relation by a full order of magnitude but is consistent with
the M_BH-sigma relation.Comment: 15 pages, 12 figures, accepted for publication in MNRA
Superconducting elliptical cavities
We give a brief overview of the history, state of the art, and future for
elliptical superconducting cavities. Principles of the cell shape optimization,
criteria for multi-cell structures design, HOM damping schemes and other
features are discussed along with examples of superconducting structures for
various applications.Comment: 25 pages, contribution to the CAS - CERN Accelerator School:
Specialised Course on RF for Accelerators; 8 - 17 Jun 2010, Ebeltoft, Denmar
Combining spectroscopic and photometric surveys using angular cross-correlations II: Parameter constraints from different physical effects
Future spectroscopic and photometric surveys will measure accurate positions
and shapes of an increasing number of galaxies. In the previous paper of this
series we studied the effects of Redshift Space Distortions (RSD), baryon
acoustic oscillations (BAO) and Weak gravitational Lensing (WL) using angular
cross-correlation. Here, we provide a new forecast that explores the
contribution of including different observables, physical effects (galaxy bias,
WL, RSD, BAO) and approximations (non-linearities, Limber approximation,
covariance between probes). The radial information is included by using the
cross-correlation of separate narrow redshift bins. For the auto correlation
the separation of galaxy pairs is mostly transverse, while the
cross-correlations also includes a radial component. We study how this
information adds to our figure of merit (FoM), which includes the dark energy
equation of state and the growth history, parameterized by . We
show that the Limber approximation and galaxy bias are the most critical
ingredients to the modelling of correlations. Adding WL increases our FoM by
4.8, RSD by 2.1 and BAO by 1.3. We also explore how overlapping surveys perform
under the different assumption and for different figures of merit. Our
qualitative conclusions depend on the survey choices and scales included, but
we find some clear tendencies that highlight the importance of combining
different probes and can be used to guide and optimise survey strategies
Numerical Simulation and Characterisation of the Packing of Granular Materials
The scientific problems related to granular matter are ubiquitous. It is currently an
active area of research for physicists and earth scientists, with a wide range of applications
within the industrial community. Simple analogue experiments exhibit behaviour that is
neither predicted nor described by any current theory. The work presented here consists
of modelling granular media using a two-dimensional combined Finite-Discrete Element
Method (FEM-DEM). While computationally expensive, as well as modelling accurately
the dynamic interactions between independent and arbitrarily shaped grains, this method
allows for a complete description of the stress state within individual grains during their
transient motion.
After a detailed description of FEM-DEM principles, this computational approach is
used to investigate the packing of elliptical particles. The work is aimed at understanding
the influence of the particle shape (the ellipse aspect ratio) on the emergent properties of
the granular matrix such as the particle coordination number and the packing density. The
diff erences in microstructure of the resultant packing are analysed using pair correlation
functions, particle orientations and pore size distributions. A comparison between frictional
and frictionless systems is carried out. It shows great diff erences not only in the calculated
porosity and coordination number, but also in terms of structural arrangement and stress
distribution. The results suggest that the particle's shape a ffects the structural order of the
particle assemblage, which itself controls the stress distribution between the pseudo-static
grains.
The study then focuses on describing the stress patterns or \force chains" naturally
generated in a frictional system. An algorithm based on the analysis of the contact
force network is proposed and applied to various packs in order to identify the force
chains. A statistical analysis of the force chains looking at their orientation, length and
proportion of the particles that support the loads is then performed. It is observed
that force chains propagate less efficiently and more heterogeneously through granular
systems made of elliptical particles than through systems of discs and it is proposed
that structural diff erences due to the particle shape lead to a signifi cant reduction in the length of the stress path that propagates across connected particles. Finally, the e ffect
of compression on the granular packing, the emergent properties and the contact force
distribution is examined. Results show that the force network evolves towards a more
randomly distributed system (from an exponential to a Gaussian distribution), and it
confi rms the observations made from simulations using discs.
To conclude, the combined finite-discrete element method applied to the study of
granular systems provides an attractive modelling strategy to improve the knowledge of
granular matter. This is due to the wide range of static and dynamic problems that can be
treated with a rigorous physical basis. The applicability of the method was demonstrated
through to a variety of problems that involve di fferent physical processes modelled with
the FEM-DEM (internal deformations, fracture, and complex geometry). With the rapid
extension of the practical limits of computational models, this work emphasizes the
opportunity to move towards a modern generation of computer software to understand
the complexity of the phenomena associated with discontinua
A review of wildland fire spread modelling, 1990-present 3: Mathematical analogues and simulation models
In recent years, advances in computational power and spatial data analysis
(GIS, remote sensing, etc) have led to an increase in attempts to model the
spread and behvaiour of wildland fires across the landscape. This series of
review papers endeavours to critically and comprehensively review all types of
surface fire spread models developed since 1990. This paper reviews models of a
simulation or mathematical analogue nature. Most simulation models are
implementations of existing empirical or quasi-empirical models and their
primary function is to convert these generally one dimensional models to two
dimensions and then propagate a fire perimeter across a modelled landscape.
Mathematical analogue models are those that are based on some mathematical
conceit (rather than a physical representation of fire spread) that
coincidentally simulates the spread of fire. Other papers in the series review
models of an physical or quasi-physical nature and empirical or quasi-empirical
nature. Many models are extensions or refinements of models developed before
1990. Where this is the case, these models are also discussed but much less
comprehensively.Comment: 20 pages + 9 pages references + 1 page figures. Submitted to the
International Journal of Wildland Fir
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