48,513 research outputs found
Constraints on the topology of the universe from the 2-yr COBE data
The cosmic microwave background (CMB) is a unique probe of cosmological
parameters and conditions. There is a connection between anisotropy in the CMB
and the topology of the Universe. Adopting a universe with the topology of a
3-Torus, or a universe where only harmonics of the fundamental mode are
allowed, and using 2-years of COBE/DMR data, we obtain constraints on the
topology of the Universe. Previous work constrained the topology using the
slope information and the correlation function of the CMB. We obtain more
accurate results by using all multipole moments, avoiding approximations by
computing their full covariance matrix. We obtain the best fit for a cubic
toroidal universe of scale 7200h^{-1} Mpc for n=1. The data set a lower limit
on the cell size of 4320h^{-1} Mpc at 95% confidence and 5880h^{-1} Mpc at 68%
confidence. These results show that the most probable cell size would be around
1.2 times larger than the horizon scale, implying that the 3-Torus topology is
no longer an interesting cosmological model.Comment: Minor revisions to match published version. 14 pages, with 4 figures
included. Color figures and links at
http://www.sns.ias.edu/~angelica/topology.htm
Coherence and incoherence in extended broad band triplet interaction
In the present analysis we study the transition from coherent to incoherent
dynamics in a nonlinear triplet of broad band combs of waves. Expanding the
analysis of previous works, this paper investigates what happens when the band
of available modes is much larger than that of the initial narrower combs
within which the nonlinear interaction is not subjected to selection rules
involving wave momenta. Here selection rules are present and active, and we
examine how and when coherence can be defined.Comment: 6 pages, 2 figure
Death by starvation in May-Leonard models
We consider the dynamics of spatial stochastic May-Leonard models with mutual
predation interactions of equal strength between any two individuals of
different species. Using two-dimensional simulations, with two and three
pecies, we investigate the dynamical impact of the death of individuals after a
given threshold number of successive unsuccessful predation attempts. We find
that the death of these individuals can have a strong impact on the dynamics of
population networks and provide a crucial contribution to the preservation of
coexistence.Comment: 7 pages, 9 figure
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