3,401 research outputs found
Quasi-isometrically embedded subgroups of Thompson's group F
The goal of this paper is to construct quasi-isometrically embedded subgroups
of Thompson's group which are isomorphic to \fz^n for all . A result
estimating the norm of an element of Thompson's group is found. As a corollary,
Thompson's group is seen to be an example of a finitely presented group which
has an infinite-dimensional asymptotic cone.Comment: AMS-Tex file, 8 page
Molecular line probes of activity in galaxies
The use of specific tracers of the dense molecular gas phase can help to
explore the feedback of activity on the interstellar medium (ISM) in galaxies.
This information is a key to any quantitative assessment of the efficiency of
the star formation process in galaxies. We present the results of a survey
devoted to probe the feedback of activity through the study of the excitation
and chemistry of the dense molecular gas in a sample of local universe
starbursts and active galactic nuclei (AGNs). Our sample includes also 17
luminous and ultraluminous infrared galaxies (LIRGs and ULIRGs). From the
analysis of the LIRGs/ULIRGs subsample, published in Gracia-Carpio et al.(2007)
we find the first clear observational evidence that the star formation
efficiency of the dense gas, measured by the L_FIR/L_HCN ratio, is
significantly higher in LIRGs and ULIRGs than in normal galaxies. Mounting
evidence of overabundant HCN in active environments would even reinforce the
reported trend, pointing to a significant turn upward in the Kennicutt-Schmidt
law around L_FIR=10^11 L_sun. This result has major implications for the use of
HCN as a tracer of the dense gas in local and high-redshift luminous infrared
galaxies.Comment: 4 pages, 2 figures, contributed paper to Far-Infrared Workshop 07
(FIR 2007
Computational explorations in Thompson's group F
We describe the results of some computational explorations in Thompson's
group F. We describe experiments to estimate the cogrowth of F with respect to
its standard finite generating set, designed to address the subtle and
difficult question whether or not Thompson's group is amenable. We also
describe experiments to estimate the exponential growth rate of F and the rate
of escape of symmetric random walks with respect to the standard generating
set.Comment: 16 pages, 2 figures, 5 table
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