3,485 research outputs found
Age spreads in clusters and associations: the lithium test
We report the evidence that several low-mass stars (<~0.4 Msun) of the Orion
and Upper Scorpius clusters have lithium abundances well below the interstellar
value. Due to time-dependent depletion, our result implies stellar ages greater
than ~5 Myr, suggesting that star formation has been proceeding for a long time
in these systems.Comment: to appear in IMF@50: The Initial Mass Function 50 years later, eds.
E. Corbelli et al. (Kluwer Acad. Press), 2004, in pres
Diffusion in scale-free networks with annealed disorder
The scale-free (SF) networks that have been studied so far contained quenched
disorder generated by random dilution which does not vary with the time. In
practice, if a SF network is to represent, for example, the worldwide web, then
the links between its various nodes may temporarily be lost, and re-established
again later on. This gives rise to SF networks with annealed disorder. Even if
the disorder is quenched, it may be more realistic to generate it by a
dynamical process that is happening in the network. In this paper, we study
diffusion in SF networks with annealed disorder generated by various scenarios,
as well as in SF networks with quenched disorder which, however, is generated
by the diffusion process itself. Several quantities of the diffusion process
are computed, including the mean number of distinct sites visited, the mean
number of returns to the origin, and the mean number of connected nodes that
are accessible to the random walkers at any given time. The results including,
(1) greatly reduced growth with the time of the mean number of distinct sites
visited; (2) blocking of the random walkers; (3) the existence of a phase
diagram that separates the region in which diffusion is possible from one in
which diffusion is impossible, and (4) a transition in the structure of the
networks at which the mean number of distinct sites visited vanishes, indicate
completely different behavior for the computed quantities than those in SF
networks with quenched disorder generated by simple random dilution.Comment: 18 pages including 8 figure
A simple algorithm to test for linking to Wilson loops in percolation
A simple burning or epidemic type of algorithm is developed in order to test
whether any loops in percolation clusters link a fixed reference loop, a
problem considered recently by Gliozzi, Lottini, Panero, and Rago in the
context of gauge theory. We test our algorithm at criticality in both 2d, where
the behavior agrees with a theoretical prediction, and in 3d.Comment: v1: A third figure added with additional simulation results. Small
corrections als
Disorder induced brittle to quasi-brittle transition in fiber bundles
We investigate the fracture process of a bundle of fibers with random Young
modulus and a constant breaking strength. For two component systems we show
that the strength of the mixture is always lower than the strength of the
individual components. For continuously distributed Young modulus the tail of
the distribution proved to play a decisive role since fibers break in the
decreasing order of their stiffness. Using power law distributed stiffness
values we demonstrate that the system exhibits a disorder induced brittle to
quasi-brittle transition which occurs analogously to continuous phase
transitions. Based on computer simulations we determine the critical exponents
of the transition and construct the phase diagram of the system.Comment: 6 pages, 6 figure
On Site Percolation on Correlated Simple Cubic Lattice
We consider site percolation on a correlated bi-colored simple cubic lattice.
The correlated medium is constructed from a strongly alternating bi-colored
simple cubic lattice due to anti-site disordering. The percolation threshold is
estimated. The cluster size distribution is obtained. A possible application to
the double 1:1 perovskites is discussed.Comment: 10 pages, 12 figures, Submitted to IJMP
Monte Carlo Simulation of Deffuant opinion dynamics with quality differences
In this work the consequences of different opinion qualities in the Deffuant
model were examined. If these qualities are randomly distributed, no different
behavior was observed. In contrast to that, systematically assigned qualities
had strong effects to the final opinion distribution. There was a high
probability that the strongest opinion was one with a high quality.
Furthermore, under the same conditions, this major opinion was much stronger
than in the models without systematic differences. Finally, a society with
systematic quality differences needed more tolerance to form a complete
consensus than one without or with unsystematic ones.Comment: 8 pages including 5 space-consuming figures, fir Int. J. Mod. Phys. C
15/1
Modelling linguistic taxonomic dynamics
This paper presents the results of the application of a bit-string model of
languages (Schulze and Stauffer 2005) to problems of taxonomic patterns. The
questions addressed include the following: (1) Which parameters are minimally
ne eded for the development of a taxonomic dynamics leading to the type of
distribution of language family sizes currently attested (as measured in the i
number of languages per family), which appears to be a power-law? (2) How may
such a model be coupled with one of the dynamics of speaker populations leading
to the type of language size seen today, which appears to follow a log-normal
distribution?Comment: 18 pages including 9 figure
Quail Methodology: Where are We and Where Do We Need to Be?
I review and evaluate methods used for population estimation, determination of survival, radio-tagging, habitat analysis and evaluation, and study design and analysis. I conclude that rigorously designed call-count surveys are likely to provide the best information on quail population trends across time and space. More intensive techniques such as line transects and mark-recapture may be appropriate if the resources are available. Radio-tagging can be a very useful technique; however, in many cases, triangulation error and effects of equipment on the birds may render results suspect. Therefore, caution is urged when using radio-tagging. Approaches to habitat analysis and evaluation are described. I discuss the importance of replication in study design and the use of appropriate and rigorous statistics. I suggest we consider statistical power more in the interpretation of results. Generally, we have the techniques available to meet our needs, but implementation has been less than ideal in many cases. Finally, the dichotomy between researchers and managers needs to be bridged. Better communication of needs by managers and cooperation by researchers should lead to positive results concerning our quail resources
Crossover transition in bag-like models
We formulate a simple model for a gas of extended hadrons at zero chemical
potential by taking inspiration from the compressible bag model. We show that a
crossover transition qualitatively similar to lattice QCD can be reproduced by
such a system by including some appropriate additional dynamics. Under certain
conditions, at high temperature, the system consist of a finite number of
infinitely extended bags, which occupy the entire space. In this situation the
system behaves as an ideal gas of quarks and gluons.Comment: Corresponds to the published version. Added few references and
changed the titl
- …