430 research outputs found
Offspring social network structure predicts fitness in families.
addresses: Centre for Ecology and Conservation, Biosciences, College of Life and Environmental Sciences, University of Exeter, Cornwall Campus, Penryn, Cornwall TR10 9EZ, UK. [email protected]: PMCID: PMC3497231types: Journal Article; Research Support, Non-U.S. Gov'tSocial structures such as families emerge as outcomes of behavioural interactions among individuals, and can evolve over time if families with particular types of social structures tend to leave more individuals in subsequent generations. The social behaviour of interacting individuals is typically analysed as a series of multiple dyadic (pair-wise) interactions, rather than a network of interactions among multiple individuals. However, in species where parents feed dependant young, interactions within families nearly always involve more than two individuals simultaneously. Such social networks of interactions at least partly reflect conflicts of interest over the provision of costly parental investment. Consequently, variation in family network structure reflects variation in how conflicts of interest are resolved among family members. Despite its importance in understanding the evolution of emergent properties of social organization such as family life and cooperation, nothing is currently known about how selection acts on the structure of social networks. Here, we show that the social network structure of broods of begging nestling great tits Parus major predicts fitness in families. Although selection at the level of the individual favours large nestlings, selection at the level of the kin-group primarily favours families that resolve conflicts most effectively
Vortex Charging Effect in a Chiral -Wave Superconductor
Quasiparticle states around a single vortex in a -wave
superconductor are studied on the basis of the Bogoliubov-de Gennes (BdG)
theory, where both charge and current screenings are taken into account. Due to
the violation of time reversal symmetry, there are two types of vortices which
are distinguished by their winding orientations relative to the angular
momentum of the chiral Cooper pair. The BdG solution shows that the charges of
the two types of vortices are quite different, reflecting the rotating Cooper
pair of the -wave paring state.Comment: 10 pages, 5 figures, revtex, to be published in Phys. Rev.
Ginzburg-Landau Theory for a p-Wave Sr_2RuO_4 Superconductor: Vortex Core Structure and Extended London Theory
Based on a two dimensional odd-parity superconducting order parameter for
Sr_2RuO_4 with p-wave symmetry, we investigate the single vortex and vortex
lattice structure of the mixed phase near H_{c1}. Ginzburg-Landau calculations
for a single vortex show a fourfold structure with an orientation depending on
the microscopic Fermi surface properties. The corresponding extended London
theory is developed to determine the vortex lattice structure and we find near
H_{c1} a centered rectangular vortex lattice. As the field is increased from
H_{c1} this lattice continuously deforms until a square vortex lattice is
achieved. In the centered rectangular phase the field distribution, as
measurable through \mu-SR experiments, exhibits a characteristic two peak
structure (similar to that predicted in high temperature and borocarbide
superconductors).Comment: 12 pages, 7 figure
Ferromagnetism in the two dimensional t-t' Hubbard model at the Van Hove density
Using an improved version of the projection quantum Monte Carlo technique, we
study the square-lattice Hubbard model with nearest-neighbor hopping t and
next-nearest-neighbor hopping t', by simulation of lattices with up to 20 X 20
sites. For a given R=2t'/t, we consider that filling which leads to a singular
density of states of the noninteracting problem. For repulsive interactions, we
find an itinerant ferromagnet (antiferromagnet) for R=0.94 (R=0.2). This is
consistent with the prediction of the T-matrix approximation, which sums the
most singular set of diagrams.Comment: 10 pages, RevTeX 3.0 + a single postscript file with all figure
Coupling to optical phonons in the one-dimensional t-J model: Effects on superconducting fluctuations and phase separation
The one-dimensional (1D) - Holstein model is studied by exact
diagonalization of finite rings using a variational approximation for the
phonon states. Due to renormalization effects induced by the phonons, for
intermediate electron-phonon coupling, the phase separation (PS) boundary, and
with it the region of dominating superconducting fluctuations is shifted
substantially to smaller values of as compared to the pure - model.
Superconducting correlations are weakened through charge density wave
interactions mediated by the phonons. Possible consequences for the high
oxides are discussed.Comment: 4 pages, Latex2
Numerical Study of Impurity Effects on Quasiparticles within S-wave and Chiral P-wave Vortices
The impurity problems within vortex cores of two-dimensional s-wave and
chiral p-wave superconductors are studied numerically in the framework of the
quasiclassical theory of superconductivity and self-consistent Born
approximation under a trial form of the pair potential. The dispersion and
impurity scattering rate (the inverse of the relaxation time) of the Andreev
bound state localized in vortex cores are deduced from the angular-resoloved
local density of states. The energy dependence of the impurity scattering rates
depends on the pairing symmetry; particularly, in the chiral p-wave vortex core
where chirality and vorticity have opposite sign and hence the total angular
momentum is zero, the impurities are ineffective and the scattering rate is
vanishingly small. Owing to the cancellation of angular momentum between
chirality and vorticity, the chiral p-wave vortex core is similar to locally
realized s-wave region and therefore non-magnetic impurity is harmless as a
consequence of Anderson's theorem. The results of the present study confirm the
previous results of analytical study (J. Phys. Soc. Jpn. {\bf 69} (2000) 3378)
in the Born limit.Comment: 8pages, 9figures, submitted to J. Phys. Soc. Jp
Vortex dynamics of a -wave superconductor
The vortex dynamics of a d+is-wave superconductor is studied numerically by
simulating the time-dependent Ginzburg-Landau equations. The critical fields,
the free flux flow, and the flux flow in the presence of twin-boundaries are
discussed. The relaxation rate of the order parameter turns out to play an
important role in the flux flow. We also address briefly the intrinsic Hall
effect in d- and d+is-wave superconductors.Comment: 5 pages, 5 figure
Spontaneous plaquette dimerization in the Heisenberg model
We investigate the non magnetic phase of the spin-half frustrated Heisenberg
antiferromagnet on the square lattice using exact diagonalization (up to 36
sites) and quantum Monte Carlo techniques (up to 144 sites). The spin gap and
the susceptibilities for the most important crystal symmetry breaking operators
are computed. A genuine and somehow unexpected `plaquette RVB', with
spontaneously broken translation symmetry and no broken rotation symmetry,
comes out from our numerical simulations as the most plausible ground state for
.Comment: 4 pages, 5 postscript figure
Low Temperature Behavior of the Vortex Lattice in Unconventional Superconductors
We study the effect of the superconducting gap nodes on the vortex lattice
properties of high temperature superconductors at very low temperatures. The
nonlinear, nonlocal and nonanalytic nature of this effect is shown to have
measurable consequences for the vortex lattice geometry and the effective
penetration depth in the mixed state as measured by muon-spin-rotation
experiments.Comment: 3 figures and extensive discussion added, Version to appear in
September 1 issue of PR
Singlet Stripe Phases in the planar t-J Model
The energies of singlet stripe phases in which a plane is broken up into spin
liquid ladders by lines of holes, is examined. If the holes were static then
patterns containing spin liquids with a finite spin gap are favored. The case
of dynamic holes is treated by assembling t-J ladders oriented perpendicular to
the stripes. For a wide region around the hole-hole
correlations in a single ladder are found to be predominantly charge density
wave type but an attraction between hole pairs on adjacent ladders leads to a
stripe phase. A quantum mechanical melting of the hole lines at smaller
values leads to a Bose condensate of hole pairs, i.e. a superconducting phase.Comment: 5 pages, uuencoded compressed PostScript file including 5 figures,
ETH-TH/942
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