258 research outputs found
Hexagonal Tilings: Tutte Uniqueness
We develop the necessary machinery in order to prove that hexagonal tilings
are uniquely determined by their Tutte polynomial, showing as an example how to
apply this technique to the toroidal hexagonal tiling.Comment: 12 figure
Extended reagions of radio emission not associated with the AGN phenomenon as sources of acceleration of cosmic rays: The case of cD galaxies
Diffuse, non-thermal extended emission not associated with the AGN
phenomenon, found in many clusters of galaxies hosted by an AGN, are related to
the acceleration of cosmic rays. In the current work we present preliminary
evidence of absence of such formations in clusters of galaxies hosted by
optically identified cD galaxies. Our subsample consists of three powerful low
redshift radiogalaxies, centered in poor clusters of galaxies. We have searched
for radio relics and (mini)halos which could be forming as a result of the
confinement of cosmic rays by bubbles creayed by the AGN. We report on the work
in progress.Comment: 4 pages, Conference HEPRO II
Hexagonal Tilings and Locally C6 Graphs
We give a complete classification of hexagonal tilings and locally C6 graphs,
by showing that each of them has a natural embedding in the torus or in the
Klein bottle. We also show that locally grid graphs are minors of hexagonal
tilings (and by duality of locally C6 graphs) by contraction of a perfect
matching and deletion of the resulting parallel edges, in a form suitable for
the study of their Tutte uniqueness.Comment: 14 figure
Random-walk simulation of cell migration and proliferation
Cell migration and proliferation has been modelled in several works of the literature as a process similar to diffusion. However, diffusion models to simulate the proliferation and migration of cells tend to create a homogeneous distribution in the cell density, but this result is not real. Diffusion is not the mechanism of cell dispersal: cells disperse by crawling or proliferation, or are transported in a moving fluid. The use of stochastic models or other (cellular automata, models particles, etc...) can modify this limitation. Therefore, this paper presents a stochastic model (random-walk) to simulate the proliferation and migration of cells. Both processes are considered as completely stochastic as discrete. The model developed aims to predict the behavior of in vitro cell cultures performed with adult muscle satellite cells. Non homogeneous distribution of cells has been observed inside the culture well. Using previous stochastic model we have been able to predict the non homogeneous cell distribution and accurate quantitative results have been computed. In a future, the model will allow us to incorporate other aspects such as cell differentiation, incorporate several cell populations simultaneously, etc
TEMPORAL AND SPATIAL DISTRIBUTION OF POACEAE POLLEN IN AREAS OF SOUTHERN UNITED KINGDOM, SPAIN AND PORTUGAL
Overall, longer Poaceae pollen seasons coincided with earlier pollen season start dates. Winter rainfall noticeably affects
the intensity of Poaceae pollen seasons in Mediterranean areas, but this was not as important in Worcester. Weekly data
from Worcester followed a similar pattern to that of Badajoz and Évora but at a distance of more than 1500 km and 4-5
weeks later
Serendipitous discovery of a cluster of galaxies with a peculiar central galaxy
We report the serendipitous discovery of a cluster of galaxies at z=0.369.
Thirty-eight candidate members were identified based on rough broad-band
photometric redshifts, and three members were confirmed spectroscopically. The
brightest cluster galaxy (BCG) is exceptionally blue, with B-V=0.12 and
V-I=1.02. The surface-brightness profile of the BCG follows an r^(1/4)-law
profile out to 3" in all three bands. The effective radius is significantly
smaller in bluer bandpasses, resulting in a blue core and a color gradient
opposite to the metallicity-induced color gradient observed in typical
elliptical galaxies. Beyond 3" an extended envelope of emission in excess of
the r^(1/4)-law profile is observed, the position angle of which coincides with
the major axis of the galaxy cluster. The spectrum of the BCG contains strong
Balmer absorption, a minimal 4000 A break, and a broad Mg II emission line,
suggesting that the galaxy has undergone recent star formation and may harbor a
central AGN. The presence of numerous nearby bright stars makes this cluster an
interesting target for next-generation adaptive optics using natural guide
stars.Comment: 21 pages, 8 figures, accepted for publication in the Astronomical
Journa
Globular Clusters in Dense Clusters of Galaxies
Deep imaging data from the Keck II telescope are employed to study the
globular cluster (GC) populations in the cores of six rich Abell clusters. The
sample includes A754, A1644, A2124, A2147, A2151, and A2152, and spans the
redshift range z = 0.035-0.066. The clusters also range in morphology from
spiral-rich, irregular systems to centrally concentrated cD clusters rich in
early-type galaxies. Globular cluster specific frequencies S_N and luminosity
function dispersions are measured for a total of 9 galaxies in six central
fields. The measured values of S_N for the six brightest cluster galaxies
(BCGs) are all higher than typical values for giant ellipticals, in accord with
the known S_N-density correlations. The three non-BCGs analyzed also have
elevated values of S_N, confirming that central location is a primary factor.
The number of GCs per unit mass for these fields are consistent with those
found in an earlier sample, giving further evidence that GC number scales with
mass and that the S_N variations are due to a deficit of halo light, i.e., S_N
reflects mass-to-light ratio.
The discussion builds on an earlier suggestion that the GCs (both metal rich
and metal poor) around the central cluster galaxies were assembled at early
times, and that star formation halted prematurely in the central galaxies at
the epoch of cluster collapse. This is consistent with recent simulations of
BCG/cluster formation. The subsequent addition of luminous material through
cluster dynamical evolution can cause S_N to decrease, and we may be seeing the
first evidence of this. Finally, the GC luminosity function measurements are
used to constrain the relative distances of the three clusters that make up the
Hercules supercluster.Comment: Uses emulateapj.sty (included); 17 pages with 9 included PostScript
figures. Figures 1-6 are separate GIF images (so 15 figures total) available
from http://astro.caltech.edu/~jpb/clusters -- the full PostScript version of
the paper (20 pages; 2.2 Mb compressed) incorporating Figures 1-6 can also be
grabbed from this URL. Accepted for publication in A
The Origin of the Brightest Cluster Galaxies
Most clusters and groups of galaxies contain a giant elliptical galaxy in
their centres which far outshines and outweighs normal ellipticals. The origin
of these brightest cluster galaxies is intimately related to the collapse and
formation of the cluster. Using an N-body simulation of a cluster of galaxies
in a hierarchical cosmological model, we show that galaxy merging naturally
produces a massive, central galaxy with surface brightness and velocity
dispersion profiles similar to observed BCG's. To enhance the resolution of the
simulation, 100 dark halos at are replaced with self-consistent
disk+bulge+halo galaxy models following a Tully-Fisher relation using 100000
particles for the 20 largest galaxies and 10000 particles for the remaining
ones. This technique allows us to analyze the stellar and dark matter
components independently. The central galaxy forms through the merger of
several massive galaxies along a filament early in the cluster's history.
Galactic cannibalism of smaller galaxies through dynamical friction over a
Hubble time only accounts for a small fraction of the accreted mass. The galaxy
is a flattened, triaxial object whose long axis aligns with the primordial
filament and the long axis of the cluster galaxy distribution agreeing with
observed trends for galaxy-cluster alignment.Comment: Revised and accepted in ApJ, 25 pages, 10 figures, online version
available at http://www.cita.utoronto.ca/~dubinski/bcg
Classification of Complex Polynomial Vector Fields in One Complex Variable
A classification of the global structure of monic and centered one-variable
complex polynomial vector fields is presented.Comment: 57 pages, 35 figures, submitted to the Journal of Difference
Equations and Application
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