273,230 research outputs found
Dependence of folding rates on protein length
Using three-dimensional Go lattice models with side chains for proteins, we
investigate the dependence of folding times on protein length. In agreement
with previous theoretical predictions, we find that the folding time grows as a
power law with the chain length N with exponent for the
Go model, in which all native interactions (i.e., between all side chains and
backbone atoms) are uniform. If the interactions between side chains are given
by pairwise statistical potentials, which introduce heterogeneity in the
contact energies, then the power law fits yield large values that
typically signifies a crossover to an underlying activated process.
Accordingly, the dependence of folding time is best described by the stretched
exponential \exp(\sqrt{N}). The study also shows that the incorporation of side
chains considerably slows down folding by introducing energetic and topological
frustration.Comment: 6 pages, 5 eps figure
Magnetic effects in heavy-ion collisions at intermediate energies
The time-evolution and space-distribution of internal electromagnetic fields
in heavy-ion reactions at beam energies between 200 and 2000 MeV/nucleon are
studied within an Isospin-dependent Boltzmann-Uhling-Uhlenbeck transport model
IBUU11. While the magnetic field can reach about G which is
significantly higher than the estimated surface magnetic field (
G) of magnetars, it has almost no effect on nucleon observables as the Lorentz
force is normally much weaker than the nuclear force. Very interestingly,
however, the magnetic field generated by the projectile-like (target-like)
spectator has a strong focusing/diverging effect on positive/negative pions at
forward (backward) rapidities. Consequently, the differential
ratio as a function of rapidity is significantly altered by the magnetic field
while the total multiplicities of both positive and negative pions remain about
the same. At beam energies above about 1 GeV/nucleon, while the integrated
ratio of total to multiplicities is not, the differential
ratio is sensitive to the density dependence of nuclear symmetry
energy . Our findings suggest that magnetic effects should
be carefully considered in future studies of using the differential
ratio as a probe of the at supra-saturation
densities.Comment: 12 pages including 8 figures and 1 tabl
Baryon enhancement in high-density QCD and relativistic heavy ion collisions
We argue that the collinear factorization of the fragmentation functions in
high energy nuclear collisions breaks down at transverse momenta due to high parton densities in the colliding hadrons and/or nuclei. We
find that gluon recombination dominates in that region. We calculate the
inclusive cross-section for meson and nucleon production using the low
energy theorems for the scale anomaly in QCD, and compare our quantitative
baryon-to-meson ratio to the RHIC data.Comment: 4 pages, 2 figure; Contribution to Quark Matter 2008 in Jaipur,
India; submitted to J. Phys.
Reward modulates spatial neglect
Copyright @ 2012 The Authors. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and 85 reproduction in any medium, provided the original author and source are credited. The article was made available through the Brunel University Open Access Publishing Fund.BACKGROUND: Reward has been shown to affect attention in healthy individuals, but there have been no studies addressing whether reward influences attentional impairments in patients with focal brain damage. METHODS: Using two novel variants of a widely-used clinical cancellation task, we assessed whether reward modulated impaired attention in 10 individuals with left neglect secondary to right hemisphere stroke. RESULTS: Reward exposure significantly reduced neglect, as measured by total targets found, left-sided targets found and centre of cancellation, across the patient group. Lesion analysis showed that lack of response to reward was associated with damage to the ipsilateral striatum. CONCLUSIONS: This is the first experimental evidence that reward can modulate attentional impairments following brain damage. These results have significant implications for the development of behavioural and pharmacological therapies for patients with attentional disorders.PM is supported by a HEFCE Clinical Senior Lectureship Award and this research was funded by grants from the UK Academy of Medical Sciences/Wellcome Trust and the NIHR Biomedical Research Centre at Imperial College London. DS is supported by a grant from the UK Medical Research Council (89631). CR is supported by a Brunel Research Initiative Award (BRIEF) and a scientific bursary from the Bial foundation, Portugal
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Plasma fluctuations as Markovian noise
Noise theory is used to study the correlations of stationary Markovian fluctuations that are homogeneous and isotropic in space. The relaxation of the fluctuations is modeled by the diffusion equation. The spatial correlations of random fluctuations are modeled by the exponential decay. Based on these models, the temporal correlations of random fluctuations, such as the correlation function and the power spectrum, are calculated. We find that the diffusion process can give rise to the decay of the correlation function and a broad frequency spectrum of random fluctuations. We also find that the transport coefficients may be estimated by the correlation length and the correlation time. The theoretical results are compared with the observed plasma density fluctuations from the tokamak and helimak experiments.Physic
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