5,601 research outputs found
Quantitative analyses of empirical fitness landscapes
The concept of a fitness landscape is a powerful metaphor that offers insight
into various aspects of evolutionary processes and guidance for the study of
evolution. Until recently, empirical evidence on the ruggedness of these
landscapes was lacking, but since it became feasible to construct all possible
genotypes containing combinations of a limited set of mutations, the number of
studies has grown to a point where a classification of landscapes becomes
possible. The aim of this review is to identify measures of epistasis that
allow a meaningful comparison of fitness landscapes and then apply them to the
empirical landscapes to discern factors that affect ruggedness. The various
measures of epistasis that have been proposed in the literature appear to be
equivalent. Our comparison shows that the ruggedness of the empirical landscape
is affected by whether the included mutations are beneficial or deleterious and
by whether intra- or intergenic epistasis is involved. Finally, the empirical
landscapes are compared to landscapes generated with the Rough Mt.\ Fuji model.
Despite the simplicity of this model, it captures the features of the
experimental landscapes remarkably well.Comment: 24 pages, 5 figures; to appear in Journal of Statistical Mechanics:
Theory and Experimen
Muon Spin Relaxation Studies of Superconductivity in a Crystalline Array of Weakly Coupled Metal Nanoparticles
We report Muon Spin Relaxation studies in weak transverse fields of the
superconductivity in the metal cluster compound,
Ga[N(SiMe)]-LiBr(thf)2toluene. The temperature and field dependence of the muon spin relaxation
rate and Knight shift clearly evidence type II bulk superconductivity below
K, with T,
T, and weak flux pinning. The data
are well described by the s-wave BCS model with weak electron-phonon coupling
in the clean limit. A qualitative explanation for the conduction mechanism in
this novel type of narrow band superconductor is presented.Comment: 4 figures, 5 page
Chiral two-loop pion-pion scattering parameters from crossing-symmetric constraints
Constraints on the parameters in the one- and two-loop pion-pion scattering
amplitudes of standard chiral perturbation theory are obtained from explicitly
crossing-symmetric sum rules. These constraints are based on a matching of the
chiral amplitudes and the physical amplitudes at the symmetry point of the
Mandelstam plane. The integrals over absorptive parts appearing in the sum
rules are decomposed into crossing-symmetric low- and high-energy components
and the chiral parameters are finally related to high-energy absorptive parts.
A first application uses a simple model of these absorptive parts. The
sensitivity of the results to the choice of the energy separating high and low
energies is examined with care. Weak dependence on this energy is obtained as
long as it stays below ~560 MeV. Reliable predictions are obtained for three
two-loop parameters.Comment: 23 pages, 4 figures in .eps files, Latex (RevTex), our version of
RevTex runs under Latex2.09, submitted to Phys. Rev. D,minor typographical
corrections including the number at the end of the abstract, two sentences
added at the end of Section 5 in answer to a referee's remar
Identification of a non-purple tartrate-resistant acid phosphatase: an evolutionary link to Ser/Thr protein phosphatases?
Ocorrência de fotossensibilização em equinos mantidos em pastagem de Brachiaria humidicola.
bitstream/item/138780/1/COT-40.pdfCNPGC
Electrostatic extraction of cold molecules from a cryogenic reservoir
We present a method which delivers a continuous, high-density beam of slow
and internally cold polar molecules. In our source, warm molecules are first
cooled by collisions with a cryogenic helium buffer gas. Cold molecules are
then extracted by means of an electrostatic quadrupole guide. For ND the
source produces fluxes up to molecules/s with
peak densities up to molecules/cm. For
HCO the population of rovibrational states is monitored by depletion
spectroscopy, resulting in single-state populations up to .Comment: 4 pages, 4 figures, changes to the text, updated figures and
reference
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