47,424 research outputs found
Portfolio of compositions
This text contains a short general description of my experience at the University of Birmingham. This is an attempt to communicate how my perception in composing music has changed and evolved. The focus is to introduce briefly my experience before I arrived at the University of Birmingham, then go through all the compositions I have worked on during my PhD programme. This attempt is to explain the main processes I have used for composing, giving a wider view of the issues that I was interested in developing. Furthermore, I will consider some technical aspects with reference to facilities that the University of Birmingham offers to students. This appears to be the right opportunity for them to explore technology almost without any restrictions. I also give some information about other nonmusical issues, which I was interested in developing in order to look into personal aesthetic directions.
My main reason for being at the University of Birmingham was to explore compositional processes different from my previous experiences, in order to enlarge my abilities and perspectives in music composition
Accounting for Stochastic Fluctuations when Analysing Integrated Light of Star Clusters. I: First Systematics
Star clusters are studied widely both as benchmarks for stellar evolution
models and in their own right. Cluster age and mass distributions within
galaxies are probes of star formation histories, and of cluster formation and
disruption processes. The vast majority of clusters in the Universe is small,
and it is well known that the integrated fluxes and colors have broad
probability distributions, due to small numbers of bright stars. This paper
goes beyond the description of predicted probability distributions, and
presents results of the analysis of cluster energy distributions in an
explicitly stochastic context. The method developed is Bayesian. It provides
posterior probability distributions in the age-mass-extinction space, using
multi-wavelength photometric observations and a large collection of Monte-Carlo
simulations of clusters of finite stellar masses. Both UBVI and UBVIK datasets
are considered, and the study conducted in this paper is restricted to the
solar metallicity. We first reassess and explain errors arising from the use of
standard analysis methods, which are based on continuous population synthesis
models: systematic errors on ages and random errors on masses are large, while
systematic errors on masses tend to be smaller. The age-mass distributions
obtained after analysis of a synthetic sample are very similar to those found
for real galaxies in the literature. The Bayesian approach on the other hand,
is very successful in recovering the input ages and masses. Taking stochastic
effects into account is important, more important for instance than the choice
of adding or removing near-IR data in many cases. We found no immediately
obvious reason to reject priors inspired by previous (standard) analyses of
cluster populations in galaxies, i.e. cluster distributions that scale with
mass as M^-2 and are uniform on a logarithmic age scale.Comment: 17 pages, 13 figures, Accepted for publication in A&A
Scale dependence of galaxy biasing investigated by weak gravitational lensing: An assessment using semi-analytic galaxies and simulated lensing data
Galaxies are biased tracers of the matter density on cosmological scales. For
future tests of galaxy models, we refine and assess a method to measure galaxy
biasing as function of physical scale with weak gravitational lensing. This
method enables us to reconstruct the galaxy bias factor as well as the
galaxy-matter correlation on spatial scales between for redshift-binned lens galaxies below redshift .
In the refinement, we account for an intrinsic alignment of source
ellipticities, and we correct for the magnification bias of the lens galaxies,
relevant for the galaxy-galaxy lensing signal, to improve the accuracy of the
reconstructed . For simulated data, the reconstructions achieve an
accuracy of (68\% confidence level) over the above -range for a
survey area and a typical depth of contemporary ground-based surveys.
Realistically the accuracy is, however, probably reduced to about ,
mainly by systematic uncertainties in the assumed intrinsic source alignment,
the fiducial cosmology, and the redshift distributions of lens and source
galaxies (in that order). Furthermore, our reconstruction technique employs
physical templates for and that elucidate the impact of central
galaxies and the halo-occupation statistics of satellite galaxies on the
scale-dependence of galaxy bias, which we discuss in the paper. In a first
demonstration, we apply this method to previous measurements in the
Garching-Bonn-Deep Survey and give a physical interpretation of the lens
population.Comment: 31 pages, 16 figures; corrected typos in Eqs. (31), (34), and (36
Temporal difference learning with interpolated table value functions
This paper introduces a novel function approximation architecture especially well suited to temporal difference learning. The architecture is based on using sets of interpolated table look-up functions. These offer rapid and stable learning, and are efficient when the number of inputs is small. An empirical investigation is conducted to test their performance on a supervised learning task, and on themountain car problem, a standard reinforcement learning benchmark. In each case, the interpolated table functions offer competitive performance. ©2009 IEEE
Investigating learning rates for evolution and temporal difference learning
Evidently, any learning algorithm can only learn on the basis of the information given to it. This paper presents a first attempt to place an upper bound on the information rates attainable with standard co-evolution and with TDL. The upper bound for TDL is shown to be much higher than for coevolution. Under commonly used settings for learning to play Othello for example, TDL may have an upper bound that is hundreds or even thousands of times higher than that of coevolution. To test how well these bounds correlate with actual learning rates, a simple two-player game called Treasure Hunt. is developed. While the upper bounds cannot be used to predict the number of games required to learn the optimal policy, they do correctly predict the rank order of the number of games required by each algorithm. © 2008 IEEE
Geometrical-based algorithm for variational segmentation and smoothing of vector-valued images
An optimisation method based on a nonlinear functional is considered for segmentation and smoothing of vector-valued images. An edge-based approach is proposed to initially segment the image using geometrical properties such as metric tensor of the linearly smoothed image. The nonlinear functional is then minimised for each segmented region to yield the smoothed image. The functional is characterised with a unique solution in contrast with the MumfordâShah functional for vector-valued images. An operator for edge detection is introduced as a result of this unique solution. This operator is analytically calculated and its detection performance and localisation are then compared with those of the DroGoperator. The implementations are applied on colour images as examples of vector-valued images, and the results demonstrate robust performance in noisy environments
The Canada-France deep fields survey-I: 100,000 galaxies, 1 deg^2: a precise measurement of \omega(\theta) to IAB~25
(abridged) Using the UH8K mosaic camera, we have measured the angular
correlation function \omega(\theta) for 100,000 galaxies over four widely
separated fields totalling ~1\deg^2 and reaching IAB~25.5. With this sample we
investigate the dependence of \omega(\theta) at 1', A_\omega(1'), on sample
median IAB magnitude in the range 19.5<I(AB-med)<24. Our results show that
A_\omega(1') decreases monotonically to IAB~25. At bright magnitudes,
\omega(\theta) is consistent with a power-law of slope \delta = -0.8 for
0.2'<\theta<3.0' but at fainter magnitudes we find \delta ~ -0.6. At the
3\sigma level, our observations are still consistent with \delta=-0.8.
Furthermore, in the magnitude ranges 18.5<IAB<24.0 and 18.5<IAB<23.0 we find
galaxies with 2.6<(V-I)AB<2.9 have A_\omega(1')'s which are ~10x higher than
field values. We demonstrate that our model redshift distributions for the
faint galaxy population are in good agreement with current spectroscopic
observations. Using these predictions, we find that for low-omega cosmologies
and assuming r_0=4.3/h Mpc, in the range 19.5<I(AB-med)<22, the growth of
galaxy clustering is \epsilon~0. However, at 22<I(AB-med)<24.0, our
observations are consistent with \epsilon>1. Models with \epsilon~0 cannot
simultaneously match both bright and faint measurements of A_\omega(1`). We
show how this result is a natural consequence of the ``bias-free'' nature of
the \epsilon formalism and is consistent with the field galaxy population in
the range 22.0<IAB<24.0 being dominated by galaxies of low intrinsic
luminosity.Comment: 20 pages, 21 figures, requires natbib.sty, accepted for publication
in Astronomy and Astrophysic
Pulsational and evolutionary analysis of the double-mode RR Lyrae star BS Com
We derive the basic physical parameters of the field double-mode RR Lyrae
star BS Com from its observed periods and the requirement of consistency
between the pulsational and evolutionary constraints. By using the current
solar-scaled horizontal branch evolutionary models of Pietrinferni et al.
(2004) and our linear non-adiabatic purely radiative pulsational models, we get
M/M(Sun) = 0.698 +/- 0.004, log(L/L(Sun)) = 1.712 +/- 0.005, T(eff) = 6840 +/-
14 K, [Fe/H] = -1.67 +/- 0.01, where the errors are standard deviations
assuming uniform age distribution along the full range of uncertainty in age.
The last two parameters are in a good agreement with the ones derived from the
observed BVIc colours and the updated ATLAS9 stellar atmosphere models. We get
T(eff) = 6842 +/- 10 K, [Fe/H] = -1.58 +/- 0.11, where the errors are purely
statistical ones. It is remarkable that the derived parameters are nearly
independent of stellar age at early evolutionary stages. Later stages,
corresponding to the evolution toward the asymptotic giant branch are most
probably excluded because the required high temperatures are less likely to
satisfy the constraints posed by the colours. We also show that our conclusions
are only weakly sensitive to nonlinear period shifts predicted by current
hydrodynamical models.Comment: Accepted for publication by MNRAS on 2008 February 01. The paper
contains 4 figures and 8 table
On the use of sensitivity tests in seismic tomography
ACKNOWLEDGEMENTS This work was partly supported by ARC Discovery Project DP120103673 and by the Research Council of Norway through its Centres of Excellence funding scheme, project number 223272. We thank Maximilliano Bezada and an anonymous referee for constructive comments which improved the original version of the manuscript. We also thank the Editor, A. Morelli, for providing additional helpful comments.Peer reviewedPublisher PD
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