125,578 research outputs found
Cosmological interpretation of the color-magnitude diagrams of galaxy clusters
We investigate the color-magnitude diagram (CMD) of cluster galaxies in the
hierarchical -CDM cosmological scenario using both single stellar
populations and simple galaxy models. First, we analyze the effect of bursts
and mergers and companion chemical pollution and rejuvenation of the stellar
content on the integrated light emitted by galaxies. The dispersion of the
galaxy magnitudes and colors on the plane is mainly due to mixing
of ages and metallicities of the stellar populations, with mergers weighting
more than bursts of similar mass fractions. The analysis is made using the
Monte-Carlo technique applied to ideal model galaxies reduced to single stellar
populations with galaxy-size mass to evaluate mass, age and metallicity of each
object. We show that separately determining the contributions by bursts and
mergers leads to a better understanding of observed properties of CMD of
cluster galaxies. Then we repeat the analysis using suitable chemo-photometric
models of galaxies whose mass is derived from the cosmological predictions of
the galaxy content of typical clusters. Using the halo mass function and the
Monte-Carlo technique, we derive the formation redshift of each galaxy and its
photometric history. These are used to simulate the CMD of the cluster
galaxies. The main conclusion is that most massive galaxies have acquired the
red color they show today in very early epochs and remained the same ever
since. The simulations nicely reproduce the Red Sequence, the Green Valley and
the Blue Cloud, the three main regions of the CMD in which galaxies crowd.Comment: Accepted for publication in Ap
What do we know about the proton spin structure?
A brief summary of the theoretical and experimental knowledge of the spin
structure of the proton is presented. The helicity distributions of quark and
gluons are discussed, together with their related sum rules. The transversity
distribution is also introduced with possible strategies for its measurement.
Novel spin dependent and \bfk_\perp unintegrated distribution and
fragmentation functions are discussed, in connection with a new and rich
phenomenology of transverse single spin asymmetries.Comment: 8 pages, 5 figures, talk delivered at GDH02, July 3-6 2002, Genova,
Ital
Local automorphisms of finite dimensional simple Lie algebras
Let be a finite dimensional simple Lie algebra over an
algebraically closed field of characteristic . A linear map
is called a local automorphism if for
every in there is an automorphism of
such that . We prove that a linear map
is local automorphism if and only if
it is an automorphism or an anti-automorphism.Comment: 14 page
A classification of spherical conjugacy classes
Let G be a simple algebraic group over an algebraically closed field k. We
classify the spherical conjugacy classes of G.Comment: 36 page
Bohr’s Relational Holism and the classical-quantum Interaction
In this paper I present and critically discuss the main strategies that Bohr used and could have used to fend off the charge that his interpretation does not provide a clear-cut distinction between the classical and the quantum domain. In particular, in the first part of the paper I reassess the main arguments used by Bohr to advocate the indispensability of a classical framework to refer to quantum phenomena. In this respect, by using a distinction coming from an apparently unrelated philosophical corner, we could say that Bohr is not a revisionist philosopher of physics but rather a descriptivist one in the sense of Strawson. I will then go on discussing the nature of the holistic link between classical measurement apparatuses and observed system that he also advocated. The oft-repeated conclusion that Bohr’s interpretation of the quantum formalism is untenable can only be established by giving his arguments as much force as possible, which is what I will try to do in the following by remaining as faithful as possible to his published work
Oscillatory Dynamics in Rock-Paper-Scissors Games with Mutations
We study the oscillatory dynamics in the generic three-species
rock-paper-scissors games with mutations. In the mean-field limit, different
behaviors are found: (a) for high mutation rate, there is a stable interior
fixed point with coexistence of all species; (b) for low mutation rates, there
is a region of the parameter space characterized by a limit cycle resulting
from a Hopf bifurcation; (c) in the absence of mutations, there is a region
where heteroclinic cycles yield oscillations of large amplitude (not robust
against noise). After a discussion on the main properties of the mean-field
dynamics, we investigate the stochastic version of the model within an
individual-based formulation. Demographic fluctuations are therefore naturally
accounted and their effects are studied using a diffusion theory complemented
by numerical simulations. It is thus shown that persistent erratic oscillations
(quasi-cycles) of large amplitude emerge from a noise-induced resonance
phenomenon. We also analytically and numerically compute the average escape
time necessary to reach a (quasi-)cycle on which the system oscillates at a
given amplitude.Comment: 25 pages, 9 figures. To appear in the Journal of Theoretical Biolog
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