18,496 research outputs found
Chemical-potential flow equations for graphene with Coulomb interactions
We calculate the chemical potential dependence of the renormalized Fermi
velocity and static dielectric function for Dirac quasiparticles in graphene
nonperturbatively at finite temperature. By reinterpreting the chemical
potential as a flow parameter in the spirit of the functional renormalization
group (fRG) we obtain a set of flow equations, which describe the change of
these functions upon varying the chemical potential. In contrast to the fRG the
initial condition of the flow is nontrivial and has to be calculated
separately. Our results confirm that the charge carrier density dependence of
the Fermi velocity is negligible, validating the comparison of the fRG
calculation at zero density of Bauer et al., Phys. Rev. B 92, 121409 (2015)
with the experiment of Elias et al., Nat. Phys. 7, 701 (2011).Comment: 7 pages, 4 figure
Non-equilibrium diagrammatic approach to strongly interacting photons
We develop a non-equilibrium field-theoretical approach based on a systematic
diagrammatic expansion for strongly interacting photons in optically dense
atomic media. We consider the case where the characteristic photon-propagation
range is much larger than the interatomic spacing and where the
density of atomic excitations is low enough to neglect saturation effects. In
the highly polarizable medium the photons experience nonlinearities through the
interactions they inherit from the atoms. If the atom-atom interaction range
is also large compared to , we show that the subclass of diagrams
describing scattering processes with momentum transfer between photons is
suppressed by a factor . We are then able to perform a self-consistent
resummation of a specific (Hartree-like) diagram subclass and obtain
quantitative results in the highly non-perturbative regime of large single-atom
cooperativity. Here we find important, conceptually new collective phenomena
emerging due to the dissipative nature of the interactions, which even give
rise to novel phase transitions. The robustness of these is investigated by
inclusion of the leading corrections in . We consider specific
applications to photons propagating under EIT conditions along waveguides near
atomic arrays as well as within Rydberg ensembles.Comment: 72 pages, 36 figure
Diagonalization of a bosonic quadratic form using CCM: Application on a system with two interpenetrating square lattice antiferromagnets
While the diagonalization of a quadratic bosonic form can always be done
using a Bogoliubov transformation, the practical implementation for systems
with a large number of different bosons is a tedious analytical task. Here we
use the coupled cluster method (CCM) to exactly diagonalise such complicated
quadratic forms. This yields to a straightforward algorithm which can easily be
implemented using computer algebra even for a large number of different bosons.
We apply this method on a Heisenberg system with two interpenetrating square
lattice antiferromagnets, which is a model for the quasi 2D antiferromagnet
Ba_2Cu_3O_4Cl_2. Using a four-magnon spin wave approximation we get a
complicated Hamiltonian with four different bosons, which is treated with CCM.
Results are presented for magnetic ground state correlations.Comment: 4 pages, 2 Postscript figures, to be published in acta physica
polonica A (European Conference 'Physics of Magnetism 99'
Quantifying the behavioural relevance of hippocampal neurogenesis
Few studies that examine the neurogenesis--behaviour relationship formally
establish covariation between neurogenesis and behaviour or rule out competing
explanations. The behavioural relevance of neurogenesis might therefore be
overestimated if other mechanisms account for some, or even all, of the
experimental effects. A systematic review of the literature was conducted and
the data reanalysed using causal mediation analysis, which can estimate the
behavioural contribution of new hippocampal neurons separately from other
mechanisms that might be operating. Results from eleven eligible individual
studies were then combined in a meta-analysis to increase precision
(representing data from 215 animals) and showed that neurogenesis made a
negligible contribution to behaviour (standarised effect = 0.15; 95% CI = -0.04
to 0.34; p = 0.128); other mechanisms accounted for the majority of
experimental effects (standardised effect = 1.06; 95% CI = 0.74 to 1.38; p =
1.7 ).Comment: To be published in PLoS ON
The WD40 protein Caf4p is a component of the mitochondrial fission machinery and recruits Dnm1p to mitochondria
The mitochondrial division machinery regulates mitochondrial dynamics and consists of Fis1p, Mdv1p, and Dnm1p. Mitochondrial division relies on the recruitment of the dynamin-related protein Dnm1p to mitochondria. Dnm1p recruitment depends on the mitochondrial outer membrane protein Fis1p. Mdv1p interacts with Fis1p and Dnm1p, but is thought to act at a late step during fission because Mdv1p is dispensable for Dnm1p localization. We identify the WD40 repeat protein Caf4p as a Fis1p-associated protein that localizes to mitochondria in a Fis1p-dependent manner. Caf4p interacts with each component of the fission apparatus: with Fis1p and Mdv1p through its NH2-terminal half and with Dnm1p through its COOH-terminal WD40 domain. We demonstrate that mdv1{Delta} yeast contain residual mitochondrial fission due to the redundant activity of Caf4p. Moreover, recruitment of Dnm1p to mitochondria is disrupted in mdv1{Delta} caf4{Delta} yeast, demonstrating that Mdv1p and Caf4p are molecular adaptors that recruit Dnm1p to mitochondrial fission sites. Our studies support a revised model for assembly of the mitochondrial fission apparatus
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