48,347 research outputs found
Line-strength indices and velocity dispersions for 148 early-type galaxies in different environments
We have derived high quality line-strength indices and velocity
dispersions for a sample of 148 early-type galaxies in different
environments. The wavelength region covered by the observations
( to 6600 Ã…) includes the Lick/IDS indices
H, Mg1, Mg2, Mgb, Fe5015, Fe5270, Fe5335, Fe5406,
Fe5709, Fe5782, NaD, TiO1 and TiO2. The data are intended to
address possible differences of the stellar populations of early-type
galaxies in low- and high-density environments. This paper describes
the sample properties, explains the data reduction and presents the
complete list of all the measurements. Most galaxies of the sample
(85%) had no previous measurements of any Lick/IDS indices and for
30% of the galaxies we present first-time determinations of their
velocity dispersions. Special care is taken to identify galaxies with
emission lines. We found that 62Â per cent of the galaxies in the
sample have emission lines, as measured by the equivalent width of the
[OIII] 5007Å line, EW[OIII] > 0.3 Å
Ising Ferromagnet: Zero-Temperature Dynamic Evolution
The dynamic evolution at zero temperature of a uniform Ising ferromagnet on a
square lattice is followed by Monte Carlo computer simulations. The system
always eventually reaches a final, absorbing state, which sometimes coincides
with a ground state (all spins parallel), and sometimes does not (parallel
stripes of spins up and down). We initiate here the numerical study of
``Chaotic Time Dependence'' (CTD) by seeing how much information about the
final state is predictable from the randomly generated quenched initial state.
CTD was originally proposed to explain how nonequilibrium spin glasses could
manifest equilibrium pure state structure, but in simpler systems such as
homogeneous ferromagnets it is closely related to long-term predictability and
our results suggest that CTD might indeed occur in the infinite volume limit.Comment: 14 pages, Latex with 8 EPS figure
Corrections to Finite Size Scaling in Percolation
A 1/L-expansion for percolation problems is proposed, where L is the lattice
finite length. The square lattice with 27 different sizes L = 18, 22 ... 1594
is considered. Certain spanning probabilities were determined by Monte Carlo
simulations, as continuous functions of the site occupation probability p. We
estimate the critical threshold pc by applying the quoted expansion to these
data. Also, the universal spanning probability at pc for an annulus with aspect
ratio r=1/2 is estimated as C = 0.876657(45)
Scaling behavior of explosive percolation on the square lattice
Clusters generated by the product-rule growth model of Achlioptas, D'Souza,
and Spencer on a two-dimensional square lattice are shown to obey qualitatively
different scaling behavior than standard (random growth) percolation. The
threshold with unrestricted bond placement (allowing loops) is found precisely
using several different criteria based upon both moments and wrapping
probabilities, yielding p_c = 0.526565 +/- 0.000005, consistent with the recent
result of Radicchi and Fortunato. The correlation-length exponent nu is found
to be close to 1. The qualitative difference from regular percolation is shown
dramatically in the behavior of the percolation probability P_(infinity) (size
of largest cluster), the susceptibility, and of the second moment of finite
clusters, where discontinuities appears at the threshold. The critical
cluster-size distribution does not follow a consistent power-law for the range
of system sizes we study L 2
for larger L.Comment: v2: Updated results in original version with new data; expanded
discussion. v3: Resubmitted version. New figures, reference
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