2,409 research outputs found
The Formation of Galactic Bulges
We summarise some recent results about nearby galactic bulges that are
relevant to their formation. We highlight a number of significant advances in
our understanding of the surface brightness profiles, stellar populations, and
especially the very centers of spiral galaxies. We also view our own Milky Way
as if it were an external galaxy. Our main conclusions are that bulges of
early-type spirals (S0 -- Sb) contain central nuclear components, just like
late-type spirals and most other types of galaxies. The luminosities of these
central components correlate best with total bulge luminosity, and not as well
with morphological type. Bulges of early-type spiral galaxies follow the
fundamental plane and the colour/line strength vs. luminosity relations of
elliptical galaxies. Although we have a reasonable idea about bulges of
early-type spirals we know much less about late-type bulges. However, the close
resemblance of our Milky Way Bulge to bulges in external disk galaxies makes us
suspect that bulges of late-type spirals might be very similar as well.Comment: 10 pages, invited review presented at 'Baryons in Dark Matter',
Novigrad Oct 5-9, 2004; eds. R. Dettmar, U. Klein and P. Salucci. On-line
publication at http://pos.sissa.i
Small Volume Fraction Limit of the Diblock Copolymer Problem: II. Diffuse-Interface Functional
We present the second of two articles on the small volume fraction limit of a
nonlocal Cahn-Hilliard functional introduced to model microphase separation of
diblock copolymers. After having established the results for the
sharp-interface version of the functional (arXiv:0907.2224), we consider here
the full diffuse-interface functional and address the limit in which epsilon
and the volume fraction tend to zero but the number of minority phases (called
particles) remains O(1). Using the language of Gamma-convergence, we focus on
two levels of this convergence, and derive first- and second-order effective
energies, whose energy landscapes are simpler and more transparent. These
limiting energies are only finite on weighted sums of delta functions,
corresponding to the concentration of mass into `point particles'. At the
highest level, the effective energy is entirely local and contains information
about the size of each particle but no information about their spatial
distribution. At the next level we encounter a Coulomb-like interaction between
the particles, which is responsible for the pattern formation. We present the
results in three dimensions and comment on their two-dimensional analogues
IAU Symposium 241 - Stellar Populations as Building Blocks of Galaxies
Stellar populations, building blocks of galaxies, are direct tracers of the
star formation history, the chemical enrichment and the assembly of galaxies in
the Universe. They therfore allow us to understand how galaxies formed and
evolved. This last decade has witnessed a revolution in our observations of
galaxies; with larger telescopes and new instruments we are not only able to
look deeper in the Universe, we can also study nearby galaxies with greater
detail. The fact that now is becoming possible to resolve stars up to the
distance of Virgo Cluster allows us to rigorously compare and calibrate the
analysis of the integrated light with resolved stellar populations. These
Proceedings report the considerable progress made in recent years in this
topic. Theorists and observers, researchers of resolved and unresolved stellar
populations, discussed the ingredients of stellar population models, and
rigorously compared them to new data, forcing theorists to develop more refined
models and methods to derive the physical parameters of the stellar
populations. New results from the Milky Way, the Local Group, and nearby and
distant galaxies were presented.Comment: This is the table of contents of the upcoming proceedings of IAU
Symposium 241. The book will appear in September, from Cambridge University
Press, and will also be available electronically at
http://www.journals.cambridge.org/action/displayJournal?jid=IA
Small Volume Fraction Limit of the Diblock Copolymer Problem: I. Sharp Interface Functional
We present the first of two articles on the small volume fraction limit of a
nonlocal Cahn-Hilliard functional introduced to model microphase separation of
diblock copolymers. Here we focus attention on the sharp-interface version of
the functional and consider a limit in which the volume fraction tends to zero
but the number of minority phases (called particles) remains O(1). Using the
language of Gamma-convergence, we focus on two levels of this convergence, and
derive first and second order effective energies, whose energy landscapes are
simpler and more transparent. These limiting energies are only finite on
weighted sums of delta functions, corresponding to the concentration of mass
into `point particles'. At the highest level, the effective energy is entirely
local and contains information about the structure of each particle but no
information about their spatial distribution. At the next level we encounter a
Coulomb-like interaction between the particles, which is responsible for the
pattern formation. We present the results here in both three and two
dimensions.Comment: 37 pages, 1 figur
Near-Infrared Surface Photometry of Bulges and Disks of Spiral Galaxies. The Data
We present optical and near-infrared (NIR) surface brightness and colour
profiles,in bands ranging from U to K, for the disk and bulge components of a
complete sample of 30 nearby S0 to Sbc galaxies with inclinations larger than
50 degrees. We describe in detail the observations and the determination of
colour parameters. Calibrated monochromatic and real-colour images are
presented, as well as colour index maps. This data set, tailored for the study
of the population characteristics of galaxy bulges, provides useful information
on the colours of inner disks as well. In related papers, we have used them to
quantify colour gradients in bulges, and age differentials between bulge and
inner disk.Comment: 18 pages Latex with 2 postscript figures. Accepted for New Astronomy.
This is an electronic paper; a complete preprint, including all of the tables
and figures can be found at
ftp://www.astro.rug.nl/peletier/newast/newast.htm
Applied Mathematics, the Hans van Duijn way
This is a former PhD student's take on his teacher's scientific philosophy. I
describe a set of 'principles' that I believe are conducive to good applied
mathematics, and that I have learnt myself from observing Hans van Duijn in
action.Comment: 11 page
Non-oriented solutions of the eikonal equation
We study a new formulation for the eikonal equation |grad u| =1 on a bounded
subset of R^2. Instead of a vector field grad u, we consider a field P of
orthogonal projections on 1-dimensional subspaces, with div P in L^2. We prove
existence and uniqueness for solutions of the equation P div P=0. We give a
geometric description, comparable with the classical case, and we prove that
such solutions exist only if the domain is a tubular neighbourhood of a regular
closed curve. The idea of the proof is to apply a generalized method of
characteristics introduced in Jabin, Otto, Perthame, "Line-energy
Ginzburg-Landau models: zero-energy states", Ann. Sc. Norm. Super. Pisa Cl.
Sci. (5) 1 (2002), to a suitable vector field m satisfying P = m \otimes m.
This formulation provides a useful approach to the analysis of stripe
patterns. It is specifically suited to systems where the physical properties of
the pattern are invariant under rotation over 180 degrees, such as systems of
block copolymers or liquid crystals.Comment: 14 pages, 4 figures, submitte
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