777 research outputs found
Dynamics of Three Agent Games
We study the dynamics and resulting score distribution of three-agent games
where after each competition a single agent wins and scores a point. A single
competition is described by a triplet of numbers , and denoting the
probabilities that the team with the highest, middle or lowest accumulated
score wins. We study the full family of solutions in the regime, where the
number of agents and competitions is large, which can be regarded as a
hydrodynamic limit. Depending on the parameter values , we find six
qualitatively different asymptotic score distributions and we also provide a
qualitative understanding of these results. We checked our analytical results
against numerical simulations of the microscopic model and find these to be in
excellent agreement. The three agent game can be regarded as a social model
where a player can be favored or disfavored for advancement, based on his/her
accumulated score. It is also possible to decide the outcome of a three agent
game through a mini tournament of two-a gent competitions among the
participating players and it turns out that the resulting possible score
distributions are a subset of those obtained for the general three agent-games.
We discuss how one can add a steady and democratic decline rate to the model
and present a simple geometric construction that allows one to write down the
corresponding score evolution equations for -agent games
Deep Luminosity Functions and Colour-Magnitude Relations for Cluster Galaxies at 0.2 < z < 0.6
We derive deep band luminosity functions and colour-magnitude diagrams
from HST imaging for eleven clusters observed at various stages of
merging, and a comparison sample of five more relaxed clusters at similar
redshifts. The characteristic magnitude evolves passively out to ,
while the faint end slope of the luminosity function is at all
redshifts. Cluster galaxies must have been completely assembled down to out to . We observe tight colour-magnitude relations over a
luminosity range of up to 8 magnitudes, consistent with the passive evolution
of ancient stellar populations. This is found in all clusters, irrespective of
their dynamical status (involved in a collision or not, or even within
subclusters for the same object) and suggests that environment does not have a
strong influence on galaxy properties. A red sequence luminosity function can
be followed to the limits of our photometry: we see no evidence of a weakening
of the red sequence to . The blue galaxy fraction rises with redshift,
especially at fainter absolute magnitudes. We observe bright blue galaxies in
clusters at that are not encountered locally. Surface brightness
selection effects preferentially influence the detectability of faint red
galaxies, accounting for claims of evolution at the faint end.Comment: 21 pages. A series of figures for individual clusters (the full
sample) will be made available on the MNRAS website. Accepted by MNRA
Morphological evolution in situ: Disk-dominated cluster red sequences at z ~ 1.25
We have carried out a joint photometric and structural analysis of red
sequence galaxies in four clusters at a mean redshift of z ~ 1.25 using optical
and near-IR HST imaging reaching to at least 3 magnitudes fainter than .
As expected, the photometry and overall galaxy sizes imply purely passive
evolution of stellar populations in red sequence cluster galaxies. However, the
morphologies of red sequence cluster galaxies at these redshifts show
significant differences to those of local counterparts. Apart from the most
massive galaxies, the high redshift red sequence galaxies are significantly
diskier than their low redshift analogues. These galaxies also show significant
colour gradients, again not present in their low redshift equivalents, most
straightforwardly explained by radial age gradients. A clear implication of
these findings is that red sequence cluster galaxies originally arrive on the
sequence as disk-dominated galaxies whose disks subsequently fade or evolve
secularly to end up as high S\'ersic index early-type galaxies (classical S0s
or possibly ellipticals) at lower redshift. The apparent lack of growth seen in
a comparison of high and low redshift red sequence galaxies implies that any
evolution is internal and is unlikely to involve significant mergers. While
significant star formation may have ended at high redshift, the cluster red
sequence population continues to evolve (morphologically) for several Gyrs
thereafter.Comment: Accepted by MNRA
The Fornax Spectroscopic Survey --- Low Surface Brightness Galaxies in Fornax
The Fornax Spectroscopic Survey is a large optical spectroscopic survey of
ALL 14,000 objects with 16.5<Bj<19.7 in a 12 sq.deg area of sky centered on the
Fornax Cluster. We are using the 400-fibre Two Degree Field spectrograph on the
Anglo-Australian Telescope: the multiplex advantage of this system allows us to
observe objects conventionally classified as `stars' as well as `galaxies'.
This is the only way to minimise selection effects caused by image
classification or assessing cluster membership.
In this paper we present the first measurements of low surface brightness
(LSB) galaxies we have detected both in the Fornax Cluster and among the
background field galaxies. The new cluster members include some very low
luminosity (M_B approx -11.5 mag) dwarf ellipticals, whereas the background LSB
galaxies are luminous (-19.6<M_B<-17.0 mag) disk-like galaxies.Comment: To appear in "The Low Surface Brightness Universe", IAU Coll 171,
eds. J.I. Davies et al., A.S.P. Conference Series. 8 pages, LaTex, 6
encapsulated ps-figures, requires paspconf.st
A Topological Characterization Of Knots and Links Arising From Site-Specific Recombination
We develop a topological model of knots and links arising from a single (or
multiple processive) round(s) of recombination starting with an unknot, unlink,
or (2,m)-torus knot or link substrate. We show that all knotted or linked
products fall into a single family, and prove that the size of this family
grows linearly with the cube of the minimum number of crossings. Additionally,
we prove that the only possible products of an unknot substrate are either
clasp knots and links or (2,m)-torus knots and links. Finally, in the (common)
case of (2,m)-torus knot or link substrates whose products have minimal
crossing number m+1, we prove that the types of products are tightly
prescribed, and use this to examine previously uncharacterized experimental
data.Comment: 18 pages, 3 tables, 18 figures. See also arXiv:0707.3775v1 for
biological evidence for and applications of the model developed her
The Extinction Distribution in the Galaxy UGC 5041
We probe the dust extinction through the foreground disk of the overlapping
galaxy pair UGC 5041 by analyzing B,I, and H band images. The inclined
foreground disk of this infrared-selected pair is almost opaque in B at a
projected distance of ~8kpc. From the images, we estimate directly the
area-weighted distribution of differential near-IR extinction: it is nearly
Gaussian with =0.6 and sigma=0.27. For a homogenous dust
distribution and a Milky Way extinction curve, this corresponds to a face-on
distribution p(tau) with a mean of =0.34 and sigma_V=0.15. For a clumpy
dust model the optical depth estimate increases to =0.41 and
sigma_V=0.19. Even though the galaxy pair is subject to different selection
biases and our analysis is subject to different systematics, the result is
consistent with existing case studies, indicating that ~0.3 is generic
for late-type spirals near their half-light radii.
We outline how to estimate from p(tau) by how much background quasars are
underreresented, where projected within ~10kpc of nearby spirals, such as
damped Ly-alpha absorbers or gravitational lenses; from our data we derive a
factor of two deficit for flux-limited, optical surveys.Comment: 18 pages, 3 figures; To appear in the Astronomical Journa
Optical/near-infrared colours of early-type galaxies and constraints on their star formation histories
(abridged) We introduce and discuss the properties of a theoretical
(B-K)-(J-K) integrated colour diagram for single-age, single-metallicity
stellar populations. This combination of integrated colours is able to largely
disentangle the well known age-metallicity degeneracy when the age of the
population is greater than ~300 Myr. We discuss in detail the effect on this
colour-colour diagram of alpha-enhanced metal abundance ratios, the presence of
blue horizontal branch stars unaccounted for in the theoretical calibration,
and of statistical colour fluctuations in low mass stellar systems. In the case
of populations with multiple stellar generations, the luminosity-weighted mean
age obtained from this diagram is shown to be heavily biased towards the
youngest stellar components. We apply this method to several datasets for which
optical and near-IR photometry are available in the literature. For the two
Local Group dwarf galaxies NGC185 and NGC6822, the mean ages derived from the
integrated colours are consistent with the star formation histories inferred
independently from photometric observations of their resolved stellar
populations. A sample of bright field and Virgo cluster elliptical galaxies is
found to exhibit a range of luminosity-weighted mean ages from 3 to 14 Gyr,
with a mean of 8 Gyr, independent of environment, and mean metallicities at or
just above the solar value. Colour gradients are found in all of the galaxies
studied, in the sense that central regions are redder. Aperture data for five
Virgo early-type dwarf galaxies show that these galaxies appear to be shifted
to lower mean metallicities and lower mean ages (range 1 to 6 Gyr) than their
higher luminosity counterparts.Comment: (1) Liverpool John Moores University, UK; (2) University of Cardiff,
UK; (3) University of Bristol, UK; (4) INAF-Osservatorio Astronomico di
Collurania, I; 12 pages, 9 figures, MNRAS in pres
Metastable Flux Configurations and de Sitter Spaces
We derive stability conditions for the critical points of the no-scale scalar
potential governing the dynamics of the complex structure moduli and the
axio-dilaton in compactifications of type IIB string theory on Calabi-Yau
three-folds. We discuss a concrete example of a T^6 orientifold. We then
consider the four-dimensional theory obtained from compactifications of type
IIB string theory on non-geometric backgrounds which are mirror to rigid
Calabi-Yau manifolds and show that the complex structure moduli fields can be
stabilized in terms of H_{RR} only, i.e. with no need of orientifold
projection. The stabilization of all the fields at weak coupling, including the
axio-dilaton, may require to break supersymmetry in the presence of H_{NS} flux
or corrections to the scalar potential.Comment: 24 page
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