1,794 research outputs found
How Turing parasites expand the computational landscape of digital life
Why are living systems complex? Why does the biosphere contain living beings
with complexity features beyond those of the simplest replicators? What kind of
evolutionary pressures result in more complex life forms? These are key
questions that pervade the problem of how complexity arises in evolution. One
particular way of tackling this is grounded in an algorithmic description of
life: living organisms can be seen as systems that extract and process
information from their surroundings in order to reduce uncertainty. Here we
take this computational approach using a simple bit string model of coevolving
agents and their parasites. While agents try to predict their worlds, parasites
do the same with their hosts. The result of this process is that, in order to
escape their parasites, the host agents expand their computational complexity
despite the cost of maintaining it. This, in turn, is followed by increasingly
complex parasitic counterparts. Such arms races display several qualitative
phases, from monotonous to punctuated evolution or even ecological collapse.
Our minimal model illustrates the relevance of parasites in providing an active
mechanism for expanding living complexity beyond simple replicators, suggesting
that parasitic agents are likely to be a major evolutionary driver for
biological complexity.Comment: 13 pages, 8 main figures, 1 appendix with 5 extra figure
Dressed tunneling approximation for electronic transport through molecular transistors
A theoretical approach for the non-equilibrium transport properties of
nanoscale systems coupled to metallic electrodes with strong electron-phonon
interactions is presented. It consists in a resummation of the dominant Feynman
diagrams from the perturbative expansion in the coupling to the leads. We show
that this scheme eliminates the main pathologies found in previous simple
analytical approaches for the polaronic regime. The results for the spectral
and transport properties are compared with those from several other approaches
for a wide range of parameters. The method can be formulated in a simple way to
obtain the full counting statistics. Results for the shot and thermal noise are
presented.Comment: 11 pages, 11 figures. Accepted for publication in Physical Review
Low-temperature anomalies of a vapor deposited glass
We investigate the low temperature properties of two-dimensional
Lennard-Jones glass films, prepared in silico both by liquid cooling and by
physical vapor deposition. We identify deep in the solid phase a crossover
temperature , at which slow dynamics and enhanced heterogeneity emerge.
Around , localized defects become visible, leading to vibrational
anomalies as compared to standard solids. We find that on average,
decreases in samples with lower inherent structure energy, suggesting that such
anomalies will be suppressed in ultra-stable glass films, prepared both by very
slow liquid cooling and vapor deposition.Comment: 10 pages including appendices, 8 figures. Version accepted for
Physical Review Material
O papel das populaçÔes tradicionais na conservação da biodiversidade.
bitstream/CNPF-2009-09/42622/1/Doc153.pdf1 CD-ROM
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