458 research outputs found
Multiscaling in passive scalar advection as stochastic shape dynamics
The Kraichnan rapid advection model is recast as the stochastic dynamics of
tracer trajectories. This framework replaces the random fields with a small set
of stochastic ordinary differential equations. Multiscaling of correlation
functions arises naturally as a consequence of the geometry described by the
evolution of N trajectories. Scaling exponents and scaling structures are
interpreted as excited states of the evolution operator. The trajectories
become nearly deterministic in high dimensions allowing for perturbation theory
in this limit. We calculate perturbatively the anomalous exponent of the third
and fourth order correlation functions. The fourth order result agrees with
previous calculations.Comment: 14 pages, LaTe
Statistical geometry in scalar turbulence
A general link between geometry and intermittency in passive scalar
turbulence is established. Intermittency is qualitatively traced back to events
where tracer particles stay for anomalousy long times in degenerate geometries
characterized by strong clustering. The quantitative counterpart is the
existence of special functions of particle configurations which are
statistically invariant under the flow. These are the statistical integrals of
motion controlling the scalar statistics at small scales and responsible for
the breaking of scale invariance associated to intermittency.Comment: 4 pages, 5 figure
Mapping liver fat female-dependent quantitative trait loci in collaborative cross mice
Non-alcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease in the western world, with spectrum from simple steatosis to non-alcoholic steatohepatitis, which can progress to cirrhosis. NAFLD developments are known to be affected by host genetic background. Herein we emphasize the power of collaborative cross (CC) mouse for dissecting this complex trait and revealing quantitative trait loci (QTL) controlling hepatic fat accumulation in mice. 168 female and 338 male mice from 24 and 37 CC lines, respectively, of 18-20 weeks old, maintained on standard rodent diet, since weaning. Hepatic fat content was assessed, using dual DEXA scan in the liver. Using the available high-density genotype markers of the CC line, QTL mapping associated with percentage liver fat accumulation was performed. Our results revealed significant fatty liver accumulation QTL that were specifically, mapped in females. Two significant QTLs on chromosomes 17 and 18, with genomic intervals 3 and 2 Mb, respectively, were mapped. A third QTL, with a less significant P value, was mapped to chromosome 4, with genomic interval of 2 Mb. These QTLs were named Flal1-Flal3, referring to Fatty Liver Accumulation Locus 1-3, for the QTLs on chromosomes 17, 18, and 4, respectively. Unfortunately, no QTL was mapped with males. Searching the mouse genome database suggested several candidate genes involved in hepatic fat accumulation. Our results show that susceptibility to hepatic fat accumulations is a complex trait, controlled by multiple genetic factors in female mice, but not in male
Statistical conservation laws in turbulent transport
We address the statistical theory of fields that are transported by a
turbulent velocity field, both in forced and in unforced (decaying)
experiments. We propose that with very few provisos on the transporting
velocity field, correlation functions of the transported field in the forced
case are dominated by statistically preserved structures. In decaying
experiments (without forcing the transported fields) we identify infinitely
many statistical constants of the motion, which are obtained by projecting the
decaying correlation functions on the statistically preserved functions. We
exemplify these ideas and provide numerical evidence using a simple model of
turbulent transport. This example is chosen for its lack of Lagrangian
structure, to stress the generality of the ideas
A Bivariate Measure of Redundant Information
We define a measure of redundant information based on projections in the
space of probability distributions. Redundant information between random
variables is information that is shared between those variables. But in
contrast to mutual information, redundant information denotes information that
is shared about the outcome of a third variable. Formalizing this concept, and
being able to measure it, is required for the non-negative decomposition of
mutual information into redundant and synergistic information. Previous
attempts to formalize redundant or synergistic information struggle to capture
some desired properties. We introduce a new formalism for redundant information
and prove that it satisfies all the properties necessary outlined in earlier
work, as well as an additional criterion that we propose to be necessary to
capture redundancy. We also demonstrate the behaviour of this new measure for
several examples, compare it to previous measures and apply it to the
decomposition of transfer entropy.Comment: 16 pages, 15 figures, 1 table, added citation to Griffith et al 2012,
Maurer et al 199
Site-Dilution in quasi one-dimensional antiferromagnet Sr2(Cu1-xPdx)O3: reduction of Neel Temperature and spatial distribution of ordered moment sizes
We investigate the Neel temperature of Sr2CuO3 as a function of the site
dilution at the Cu (S=1/2) sites with Pd (S=0), utilizing the muon spin
relaxation (muSR) technique. The Neel temperature, which is Tn=5.4K for the
undoped system, becomes significantly reduced for less than one percent of
doping Pd, giving a support for the previous proposal for the good
one-dimensionality. The Pd concentration dependence of the Neel temperature is
compared with a recent theoretical study (S. Eggert, I. Affleck and M.D.P.
Horton, Phys. Rev. Lett. 89, 47202 (2002)) of weakly coupled one-dimensional
antiferromagnetic chains of S=1/2 spins, and a quantitative agreement is found.
The inhomogeneity of the ordered moment sizes is characterized by the muSR time
spectra. We propose a model that the ordered moment size recovers away from the
dopant S=0 sites with a recovery length of \xi = 150-200 sites. The origin of
the finite recovery length \xi for the gapless S=1/2 antiferromagnetic chain is
compared to the estimate based on the effective staggered magnetic field from
the neighboring chains.Comment: 10 pages, 9 figures, submitted to PR
Doping and temperature dependence of electron spectrum and quasiparticle dispersion in doped bilayer cuprates
Within the t-t'-J model, the electron spectrum and quasiparticle dispersion
in doped bilayer cuprates in the normal state are discussed by considering the
bilayer interaction. It is shown that the bilayer interaction splits the
electron spectrum of doped bilayer cuprates into the bonding and antibonding
components around the point. The differentiation between the bonding
and antibonding components is essential, which leads to two main flat bands
around the point below the Fermi energy. In analogy to the doped
single layer cuprates, the lowest energy states in doped bilayer cuprates are
located at the point. Our results also show that the striking
behavior of the electronic structure in doped bilayer cuprates is intriguingly
related to the bilayer interaction together with strong coupling between the
electron quasiparticles and collective magnetic excitations.Comment: 9 pages, 4 figures, updated references, added figures and
discussions, accepted for publication in Phys. Rev.
Muon Spin Relaxation and Susceptibility Studies of Pure and Doped Spin 1/2 Kagom\'{e}-like system (CuZn)VO(OH) 2HO
Muon spin relaxation (SR) and magnetic susceptibility measurements have
been performed on the pure and diluted spin 1/2 kagom\'{e} system
(CuZn)VO(OH) 2HO. In the pure
system we found a slowing down of Cu spin fluctuations with decreasing
temperature towards K, followed by slow and nearly
temperature-independent spin fluctuations persisting down to = 50 mK,
indicative of quantum fluctuations. No indication of static spin freezing was
detected in either of the pure (=1.0) or diluted samples. The observed
magnitude of fluctuating fields indicates that the slow spin fluctuations
represent an intrinsic property of kagom\'e network rather than impurity spins.Comment: 4 pges, 4 color figures, Phys. Rev. Lett. in pres
Scotland, Catalonia and the “right” to self-determination: a comment suggested by Kathryn Crameri’s “Do Catalans Have the Right to Decide?
No abstract available
Active and passive fields face to face
The statistical properties of active and passive scalar fields transported by
the same turbulent flow are investigated. Four examples of active scalar have
been considered: temperature in thermal convection, magnetic potential in
two-dimensional magnetohydrodynamics, vorticity in two-dimensional Ekman
turbulence and potential temperature in surface flows. In the cases of
temperature and vorticity, it is found that the active scalar behavior is akin
to that of its co-evolving passive counterpart. The two other cases indicate
that this similarity is in fact not generic and differences between passive and
active fields can be striking: in two-dimensional magnetohydrodynamics the
magnetic potential performs an inverse cascade while the passive scalar
cascades toward the small-scales; in surface flows, albeit both perform a
direct cascade, the potential temperature and the passive scalar have different
scaling laws already at the level of low-order statistical objects. These
dramatic differences are rooted in the correlations between the active scalar
input and the particle trajectories. The role of such correlations in the issue
of universality in active scalar transport and the behavior of dissipative
anomalies is addressed.Comment: 36 pages, 20 eps figures, for the published version see
http://www.iop.org/EJ/abstract/1367-2630/6/1/07
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