1,027 research outputs found
Current facilitation by plasmon resonances between parallel wires of finite length
The current voltage (IV) characteristics for perpendicular transport through
two sequentially coupled wires of finite length is calculated analytically. The
transport within a Coulomb blockade step is assisted by plasmon resonances that
appear as steps in the IV characteristics with positions and heights depending
on inter- and intrawire interactions. In particular, due to the interwire
interactions, the peak positions shift to lower voltages in comparison to the
noninteracting wires which reflects the facilitation of current by
interactions. The interwire interactions are also found to enhance the
thermally activated current.Comment: 5 pages, 1figur
Cross-Over between universality classes in a magnetically disordered metallic wire
In this article we present numerical results of conduction in a disordered
quasi-1D wire in the possible presence of magnetic impurities. Our analysis
leads us to the study of universal properties in different conduction regimes
such as the localized and metallic ones. In particular, we analyse the
cross-over between universality classes occurring when the strength of magnetic
disorder is increased. For this purpose, we use a numerical Landauer approach,
and derive the scattering matrix of the wire from electron's Green's function.Comment: Final version, accepted for publication in New Journ. of Physics, 27
pages, 28 figures. Replaces the earlier shorter preprint arXiv:0910.427
Prevalence, risk factors, and clinical patterns of chronic venous disorders of lower limbs: A population-based study in France
ObjectivesThe goals of this study were to document the prevalence of varicose veins, skin trophic changes, and venous symptoms in a sample of the general population of France, to document their main risk factors, and to assess relationships between them.MethodsThis cross-sectional epidemiologic study was carried out in the general population of 4 locations in France: Tarentaise, Grenoble, Nyons, and Toulon. Random samples of 2000 subjects per location were interviewed by telephone, and a sub-sample of subjects completed medical interviews and underwent physical examination, and the presence of varicose veins, trophic changes, and venous symptoms was recorded.ResultsPrevalence of varicose veins, skin trophic changes, and venous symptoms was not statistically different in the 4 locations. In contrast, sex-related differences were found: varicose veins were found in 50.5% of women versus 30.1% of men (P < .001); trophic skin changes were found in 2.8% of women versus 5.4% of men (P = NS), and venous symptoms were found in 51.3% of women 51.3% versus 20.4% of men (P < .001). Main risk factors for varicose veins were age and family history in both sexes, and pregnancy in women. Female sex was a significant factor only for non-saphenous varicose veins. Varicose veins, age, and pitting edema were the most significant risk factors for trophic skin changes. The risk factors for venous symptoms were female sex, varicose veins, and prolonged sitting or standing. A negative relationship with age was found in women.ConclusionOur results show a high prevalence of chronic venous disorders of the lower limbs in the general population of France, with no significant geographic variations. They also provide interesting insights regarding the association of varicose veins, skin trophic changes, and venous symptoms
Free fatty acids link metabolism and regulation of the insulin-sensitizing fibroblast growth factor-21
OBJECTIVEâFibroblast growth factor (FGF)-21 improves insulin
sensitivity and lipid metabolism in obese or diabetic animal
models, while human studies revealed increased FGF-21 levels in obesity and type 2 diabetes. Given that FGF-21 has been suggested to be a peroxisome proliferatorâactivator receptor (PPAR) âdependent regulator of fasting metabolism, we hypothesized that free fatty acids (FFAs), natural agonists of PPAR, might modify FGF-21 levels.
RESEARCH DESIGN AND METHODSâThe effect of fatty
acids on FGF-21 was investigated in vitro in HepG2 cells. Within a randomized controlled trial, the effects of elevated FFAs were studied in 21 healthy subjects (13 women and 8 men). Within a clinical trial including 17 individuals, the effect of insulin was analyzed using an hyperinsulinemic-euglycemic clamp and the effect of PPAR activation was studied subsequently in a rosiglitazone
treatment trial over 8 weeks.
RESULTSâOleate and linoleate increased FGF-21 expression
and secretion in a PPAR-dependent fashion, as demonstrated
by small-interfering RNAâinduced PPAR knockdown, while
palmitate had no effect. In vivo, lipid infusion induced an
increase of circulating FGF-21 in humans, and a strong correlation between the change in FGF-21 levels and the change in FFAs was observed. An artificial hyperinsulinemia, which was induced to delineate the potential interaction between elevated FFAs and
hyperinsulinemia, revealed that hyperinsulinemia also increased FGF-21 levels in vivo, while rosiglitazone treatment had no effect.
CONCLUSIONSâThe results presented here offer a mechanism
explaining the induction of the metabolic regulator FGF-21 in the fasting situation but also in type 2 diabetes and obesity
Two dimensional Dirac fermions in the presence of long-range correlated disorder
We consider 2D Dirac fermions in the presence of three types of disorder:
random scalar potential, random gauge potential and random mass with long-range
correlations decaying as a power law. Using various methods such as the
self-consistent Born approximation (SCBA), renormalization group (RG), the
matrix Green function formalism and bosonisation we calculate the density of
states and study the full counting statistics of fermionic transport at lower
energy. The SCBA and RG show that the random correlated scalar potentials
generate an algebraically small energy scale below which the density of states
saturates to a constant value. For correlated random gauge potential, RG and
bosonisation calculations provide consistent behavior of the density of states
which diverges at zero energy in an integrable way. In the case of correlated
random mass disorder the RG flow has a nontrivial infrared stable fixed point
leading to a universal power-law behavior of the density of states and also to
universal transport properties. In contrast to uncorrelated case the correlated
scalar potential and random mass disorders give rise to deviation from the
pseudodiffusive transport already to lowest order in disorder strength.Comment: 17 pages, 8 figures, revtex
Glassy trapping of manifolds in nonpotential random flows
We study the dynamics of polymers and elastic manifolds in non potential
static random flows. We find that barriers are generated from combined effects
of elasticity, disorder and thermal fluctuations. This leads to glassy trapping
even in pure barrier-free divergenceless flows
(). The physics is described by a new RG fixed point at finite
temperature. We compute the anomalous roughness and dynamical
exponents for directed and isotropic manifolds.Comment: 5 pages, 3 figures, RevTe
Superconducting instability in 3 band metallic nanotubes
Motivated by recent experiments on small radius nanotubes, we study the
superconducting instabilities of cylindrical (5,0) nanotubes. According to band
structure calculations, thesenanotubes possess three bands at the Fermi energy.
Using a fermionic renormalization group approach and a careful bosonization
treatment,we consider the effect of different attractive interactions, mediated
by phonons, within the Luttinger Liquid framework. We particularly focus on a
superconducting instability specific to the three bands model we consider for
the description of these
(5,0) cylindrical nanotubes.Comment: RevTeX 4, 17 pages, 10 EPS figure
Particle-hole symmetric localization in two dimensions
We revisit two-dimensional particle-hole symmetric sublattice localization
problem, focusing on the origin of the observed singularities in the density of
states at the band center E=0. The most general such system [R. Gade,
Nucl. Phys. B {\bf 398}, 499 (1993)] exhibits critical behavior and has
that diverges stronger than any integrable power-law, while the
special {\it random vector potential model} of Ludwiget al [Phys. Rev. B {\bf
50}, 7526 (1994)] has instead a power-law density of states with a continuously
varying dynamical exponent. We show that the latter model undergoes a dynamical
transition with increasing disorder--this transition is a counterpart of the
static transition known to occur in this system; in the strong-disorder regime,
we identify the low-energy states of this model with the local extrema of the
defining two-dimensional Gaussian random surface. Furthermore, combining this
``surface fluctuation'' mechanism with a renormalization group treatment of a
related vortex glass problem leads us to argue that the asymptotic low
behavior of the density of states in the {\it general} case is , different from earlier prediction of Gade. We also
study the localized phases of such particle-hole symmetric systems and identify
a Griffiths ``string'' mechanism that generates singular power-law
contributions to the low-energy density of states in this case.Comment: 18 pages (two-column PRB format), 10 eps figures include
Density of states for the -flux state with bipartite real random hopping only: A weak disorder approach
Gade [R. Gade, Nucl. Phys. B \textbf{398}, 499 (1993)] has shown that the
local density of states for a particle hopping on a two-dimensional bipartite
lattice in the presence of weak disorder and in the absence of time-reversal
symmetry(chiral unitary universality class) is anomalous in the vicinity of the
band center whenever the disorder preserves the sublattice
symmetry. More precisely, using a nonlinear-sigma-model that encodes the
sublattice (chiral) symmetry and the absence of time-reversal symmetry she
argues that the disorder average local density of states diverges as
with some non-universal
positive constant and a universal exponent. Her analysis has been
extended to the case when time-reversal symmetry is present (chiral orthogonal
universality class) for which the same exponent was predicted.
Motrunich \textit{et al.} [O. Motrunich, K. Damle, and D. A. Huse, Phys. Rev. B
\textbf{65}, 064206 (2001)] have argued that the exponent does not
apply to the typical density of states in the chiral orthogonal universality
class. They predict that instead. We confirm the analysis of
Motrunich \textit{et al.} within a field theory for two flavors of Dirac
fermions subjected to two types of weak uncorrelated random potentials: a
purely imaginary vector potential and a complex valued mass potential. This
model is believed to belong to the chiral orthogonal universality class. Our
calculation relies in an essential way on the existence of infinitely many
local composite operators with negative anomalous scaling dimensions.Comment: 30 pages, final version published in PR
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