1,025 research outputs found
Enhanced Two-Channel Kondo Physics in a Quantum Box Device
We propose a design for a one-dimensional quantum box device where the charge
fluctuations are described by an anisotropic two-channel Kondo model. The
device consists of a quantum box in the Coulomb blockade regime, weakly coupled
to a quantum wire by a single-mode point contact. The electron correlations in
the wire produce strong back scattering at the contact, significantly
increasing the Kondo temperature as compared to the case of non-interacting
electrons. By employing boundary conformal field theory techniques we show that
the differential capacitance of the box exhibits manifest two-channel Kondo
scaling with temperature and gate voltage, uncontaminated by the
one-dimensional electron correlations. We discuss the prospect to
experimentally access the Kondo regime with this type of device.Comment: EPL style, 5 pages, 1 figure, final published versio
The effect of multiple paternity on genetic diversity during and after colonisation
In metapopulations, genetic variation of local populations is influenced by
the genetic content of the founders, and of migrants following establishment.
We analyse the effect of multiple paternity on genetic diversity using a model
in which the highly promiscuous marine snail Littorina saxatilis expands from a
mainland to colonise initially empty islands of an archipelago. Migrant females
carry a large number of eggs fertilised by 1 - 10 mates. We quantify the
genetic diversity of the population in terms of its heterozygosity: initially
during the transient colonisation process, and at long times when the
population has reached an equilibrium state with migration. During
colonisation, multiple paternity increases the heterozygosity by 10 - 300 % in
comparison with the case of single paternity. The equilibrium state, by
contrast, is less strongly affected: multiple paternity gives rise to 10 - 50 %
higher heterozygosity compared with single paternity. Further we find that far
from the mainland, new mutations spreading from the mainland cause bursts of
high genetic diversity separated by long periods of low diversity. This effect
is boosted by multiple paternity. We conclude that multiple paternity
facilitates colonisation and maintenance of small populations, whether or not
this is the main cause for the evolution of extreme promiscuity in Littorina
saxatilis.Comment: 7 pages, 5 figures, electronic supplementary materia
PAR14: ASSESSMENT OF THE RELATIONSHIP BETWEEN DISEASE SEVERITY, QUALITY OF LIFE AND WILLINGNESS TO PAY IN ASTHMA
A universal mechanism generating clusters of differentiated loci during divergence-with-migration
Genome-wide patterns of genetic divergence reveal mechanisms of adaptation under gene flow. Empirical data show that divergence is mostly concentrated in narrow genomic regions. This pattern may arise because differentiated loci protect nearby mutations from gene flow, but recent theory suggests this mechanism is insufficient to explain the emergence of concentrated differentiation during biologically realistic timescales. Critically, earlier theory neglects an inevitable consequence of genetic drift: stochastic loss of local genomic divergence. Here we demonstrate that the rate of stochastic loss of weak local differentiation increases with recombination distance to a strongly diverged locus and, above a critical recombination distance, local loss is faster than local 'gain' of new differentiation. Under high migration and weak selection this critical recombination distance is much smaller than the total recombination distance of the genomic region under selection. Consequently, divergence between populations increases by net gain of new differentiation within the critical recombination distance, resulting in tightly-linked clusters of divergence. The mechanism responsible is the balance between stochastic loss and gain of weak local differentiation, a mechanism acting universally throughout the genome. Our results will help to explain empirical observations and lead to novel predictions regarding changes in genomic architectures during adaptive divergence. This article is protected by copyright. All rights reserved
Measuring Luttinger Liquid Correlations from Charge Fluctuations in a Nanoscale Structure
We suggest an experiment to study Luttinger liquid behavior in a
one-dimensional nanostructure, avoiding the usual complications associated with
transport measurements. The proposed setup consists of a quantum box, biased by
a gate voltage, and side-coupled to a quantum wire by a point contact. Close to
the degeneracy points of the Coulomb blockaded box, and in the presence of a
magnetic field sufficiently strong to spin polarize the electrons, the setup
can be described as a Luttinger liquid interacting with an effective Kondo
impurity. Using exact nonperturbative techniques we predict that the
differential capacitance of the box will exhibit distinctive Luttinger liquid
scaling with temperature and gate voltage.Comment: REVTeX, 4 pages, 1 figure included. Final version, two references
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The Fine-Structure of the Net-Circular Polarization in a Sunspot Penumbra
We present novel evidence for a fine structure observed in the net-circular
polarization (NCP) of a sunspot penumbra based on spectropolarimetric
measurements utilizing the Zeeman sensitive FeI 630.2 nm line. For the first
time we detect a filamentary organized fine structure of the NCP on spatial
scales that are similar to the inhomogeneities found in the penumbral flow
field. We also observe an additional property of the visible NCP, a
zero-crossing of the NCP in the outer parts of the center-side penumbra, which
has not been recognized before. In order to interprete the observations we
solve the radiative transfer equations for polarized light in a model penumbra
with embedded magnetic flux tubes. We demonstrate that the observed
zero-crossing of the NCP can be explained by an increased magnetic field
strength inside magnetic flux tubes in the outer penumbra combined with a
decreased magnetic field strength in the background field. Our results strongly
support the concept of the uncombed penumbra
Two-Species Reaction-Diffusion System with Equal Diffusion Constants: Anomalous Density Decay at Large Times
We study a two-species reaction-diffusion model where A+A->0, A+B->0 and
B+B->0, with annihilation rates lambda0, delta0 > lambda0 and lambda0,
respectively. The initial particle configuration is taken to be randomly mixed
with mean densities nA(0) > nB(0), and with the two species A and B diffusing
with the same diffusion constant. A field-theoretic renormalization group
analysis suggests that, contrary to expectation, the large-time density of the
minority species decays at the same rate as the majority when d<=2. Monte Carlo
data supports the field theory prediction in d=1, while in d=2 the
logarithmically slow convergence to the large-time asymptotics makes a
numerical test difficult.Comment: revised version (more figures, claim on exactnes of d=2 treatment
removed), 5 pages, 3 figures, RevTex, see related paper Phys. Rev. E, R3787,
(1999) or cond-mat/9901147, to appear in Phys. Rev.
Transporting ideas between marine and social sciences: experiences from interdisciplinary research programs.
The oceans comprise 70% of the surface area of our planet, contain some of the world’s richest natural resources and are one of the most significant drivers of global climate patterns. As the marine environment continues to increase in importance as both an essential resource reservoir and facilitator of global change, it is apparent that to find long-term sustainable solutions for our use of the sea and its resources and thus to engage in a sustainable blue economy, an integrated interdisciplinary approach is needed. As a result, interdisciplinary working is proliferating. We report here our experiences of forming interdisciplinary teams (marine ecologists, ecophysiologists, social scientists, environmental economists and environmental law specialists) to answer questions pertaining to the effects of anthropogenic-driven global change on the sustainability of resource use from the marine environment, and thus to transport ideas outwards from disciplinary confines. We use a framework derived from the literature on interdisciplinarity to enable us to explore processes of knowledge integration in two ongoing research projects, based on analyses of the purpose, form and degree of knowledge integration within each project. These teams were initially focused around a graduate program, explicitly designed for interdisciplinary training across the natural and social sciences, at the Gothenburg Centre for Marine Research at the University of Gothenburg, thus allowing us to reflect on our own experiences within the context of other multi-national, interdisciplinary graduate training and associated research programs
What explains rare and conspicuous colours in a snail? A test of time-series data against models of drift, migration or selection
It is intriguing that conspicuous colour morphs of a prey species may be maintained at low frequencies alongside cryptic morphs. Negative frequency-dependent selection by predators using search images ('apostatic selection') is often suggested without rejecting alternative explanations. Using a maximum likelihood approach we fitted predictions from models of genetic drift, migration, constant selection, heterozygote advantage or negative frequency-dependent selection to time-series data of colour frequencies in isolated populations of a marine snail (Littorina saxatilis), re-established with perturbed colour morph frequencies and followed for >20 generations. Snails of conspicuous colours (white, red, banded) are naturally rare in the study area (usually <10%) but frequencies were manipulated to levels of ~50% (one colour per population) in 8 populations at the start of the experiment in 1992. In 2013, frequencies had declined to ~15-45%. Drift alone could not explain these changes. Migration could not be rejected in any population, but required rates much higher than those recorded. Directional selection was rejected in three populations in favour of balancing selection. Heterozygote advantage and negative frequency-dependent selection could not be distinguished statistically, although overall the results favoured the latter. Populations varied idiosyncratically as mild or variable colour selection (3-11%) interacted with demographic stochasticity, and the overall conclusion was that multiple mechanisms may contribute to maintaining the polymorphisms.Heredity advance online publication, 21 September 2016; doi:10.1038/hdy.2016.77
Hidden Kondo Effect in a Correlated Electron Chain
We develop a general Bethe Ansatz formalism for diagonalizing an integrable
model of a magnetic impurity of arbitrary spin coupled ferro- or
antiferromagnetically to a chain of interacting electrons. The method is
applied to an open chain, with the exact solution revealing a ``hidden'' Kondo
effect driven by forward electron scattering off the impurity. We argue that
the so-called ``operator reflection matrices'' proposed in recent Bethe Ansatz
studies of related models emulate only forward electron-impurity scattering
which may explain the absence of complete Kondo screening for certain values of
the impurity-electron coupling in these models.Comment: 5 pages, RevTex; to appear in Phys. Rev. Let
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