3,536 research outputs found
Novel dynamical effects and glassy response in strongly correlated electronic system
We find an unconventional nucleation of low temperature paramagnetic metal
(PMM) phase with monoclinic structure from the matrix of high-temperature
antiferromagnetic insulator (AFI) phase with tetragonal structure in strongly
correlated electronic system . Such unconventional
nucleation leads to a decease in resistivity by several orders with relaxation
at a fixed temperature without external perturbation. The novel dynamical
process could arise from the competition of strain fields, Coulomb
interactions, magnetic correlations and disorders. Such competition may
frustrate the nucleation, giving rise to a slow, nonexponential relaxation and
"physical aging" behavior.Comment: 5 pages, 4 figure
Absence of Fragmentation in Two-Dimensional Bose-Einstein Condensation
We investigate the possibility that the BEC-like phenomena recently detected
on two-dimensional finite trapped systems consist of fragmented condensates. We
derive and diagonalize the one-body density matrix of a two-dimensional
isotropically trapped Bose gas at finite temperature. For the ideal gas, the
procedure reproduces the exact harmonic-oscillator eigenfunctions and the Bose
distribution. We use a new collocation-minimization method to study the
interacting gas in the Hartree-Fock approximation and obtain a ground-state
wavefunction and condensate fraction consistent with those obtained by other
methods. The populations of the next few eigenstates increase at the expense of
the ground state but continue to be negligible; this supports the conclusion
that two-dimensional BEC is into a single state.Comment: 6 pages, 1 figur
Giant viscosity enhancement in a spin-polarized Fermi liquid
The viscosity is measured for a Fermi liquid, a dilute He-He mixture,
under extremely high magnetic field/temperature conditions ( T, mK). The spin splitting energy is substantially greater than
the Fermi energy ; as a consequence the polarization tends to unity
and s-wave quasiparticle scattering is suppressed for . Using a
novel composite vibrating-wire viscometer an enhancement of the viscosity is
observed by a factor of more than 500 over its low-field value. Good agreement
is found between the measured viscosity and theoretical predictions based upon
a -matrix formalism.Comment: 4 pages, 4 figure
Anisotropic Spin Diffusion in Trapped Boltzmann Gases
Recent experiments in a mixture of two hyperfine states of trapped Bose gases
show behavior analogous to a spin-1/2 system, including transverse spin waves
and other familiar Leggett-Rice-type effects. We have derived the kinetic
equations applicable to these systems, including the spin dependence of
interparticle interactions in the collision integral, and have solved for
spin-wave frequencies and longitudinal and transverse diffusion constants in
the Boltzmann limit. We find that, while the transverse and longitudinal
collision times for trapped Fermi gases are identical, the Bose gas shows
diffusion anisotropy. Moreover, the lack of spin isotropy in the interactions
leads to the non-conservation of transverse spin, which in turn has novel
effects on the hydrodynamic modes.Comment: 10 pages, 4 figures; submitted to PR
Maximal length of trapped one-dimensional Bose-Einstein condensates
I discuss a Bogoliubov inequality for obtaining a rigorous bound on the
maximal axial extension of inhomogeneous one-dimensional Bose-Einstein
condensates. An explicit upper limit for the aspect ratio of a strongly
elongated, harmonically trapped Thomas-Fermi condensate is derived.Comment: 6 pages; contributed paper for Quantum Fluids and Solids, Trento
2004, to appear in JLT
On the decay of turbulence in plane Couette flow
The decay of turbulent and laminar oblique bands in the lower transitional
range of plane Couette flow is studied by means of direct numerical simulations
of the Navier--Stokes equations. We consider systems that are extended enough
for several bands to exist, thanks to mild wall-normal under-resolution
considered as a consistent and well-validated modelling strategy. We point out
a two-stage process involving the rupture of a band followed by a slow
regression of the fragments left. Previous approaches to turbulence decay in
wall-bounded flows making use of the chaotic transient paradigm are
reinterpreted within a spatiotemporal perspective in terms of large deviations
of an underlying stochastic process.Comment: ETC13 Conference Proceedings, 6 pages, 5 figure
Characterisation of genetic regulatory effects for osteoporosis risk variants in human osteoclasts.
BACKGROUND: Osteoporosis is a complex disease with a strong genetic contribution. A recently published genome-wide association study (GWAS) for estimated bone mineral density (eBMD) identified 1103 independent genome-wide significant association signals. Most of these variants are non-coding, suggesting that regulatory effects may drive many of the associations. To identify genes with a role in osteoporosis, we integrate the eBMD GWAS association results with those from our previous osteoclast expression quantitative trait locus (eQTL) dataset. RESULTS: We identify sixty-nine significant cis-eQTL effects for eBMD GWAS variants after correction for multiple testing. We detect co-localisation of eBMD GWAS and osteoclast eQTL association signals for 21 of the 69 loci, implicating a number of genes including CCR5, ZBTB38, CPE, GNA12, RIPK3, IQGAP1 and FLCN. Summary-data-based Mendelian Randomisation analysis of the eBMD GWAS and osteoclast eQTL datasets identifies significant associations for 53 genes, with TULP4 presenting as a strong candidate for pleiotropic effects on eBMD and gene expression in osteoclasts. By performing analysis using the GARFIELD software, we demonstrate significant enrichment of osteoporosis risk variants among high-confidence osteoclast eQTL across multiple GWAS P value thresholds. Mice lacking one of the genes of interest, the apoptosis/necroptosis gene RIPK3, show disturbed bone micro-architecture and increased osteoclast number, highlighting a new biological pathway relevant to osteoporosis. CONCLUSION: We utilise a unique osteoclast eQTL dataset to identify a number of potential effector genes for osteoporosis risk variants, which will help focus functional studies in this area
How does flow in a pipe become turbulent?
The transition to turbulence in pipe flow does not follow the scenario
familiar from Rayleigh-Benard or Taylor-Couette flow since the laminar profile
is stable against infinitesimal perturbations for all Reynolds numbers.
Moreover, even when the flow speed is high enough and the perturbation
sufficiently strong such that turbulent flow is established, it can return to
the laminar state without any indication of the imminent decay. In this
parameter range, the lifetimes of perturbations show a sensitive dependence on
initial conditions and an exponential distribution. The turbulence seems to be
supported by three-dimensional travelling waves which appear transiently in the
flow field. The boundary between laminar and turbulent dynamics is formed by
the stable manifold of an invariant chaotic state. We will also discuss the
relation between observations in short, periodically continued domains, and the
dynamics in fully extended puffs.Comment: for the proceedings of statphys 2
The Entrainment-Limited Evolution of FR II Sources: Maximum Sizes and A Possible Connection to FR Is
We construct a simple theoretical model to investigate how entrainment
gradually erodes high-speed FR II jets. This process is described by embedding
a mixing-layer model developed originally to describe FR I objects in a
self-similar model for the lobe structure of classical FR II sources. Following
the classical FR II models, we assume that the lobe is dominated by the
particles injected from the central jet. The entrainment produces a boundary
shear layer which acts at the interface between the dense central jet and the
less denser surrounding lobe, and the associated erosion of the jet places
interesting limits on the maximum size of FR II sources. The model shows that
this limit depends mainly on the initial bulk velocity of the relativistic jet
triggered. The bulk velocities of FR IIs suggested by our model are in good
agreement with that obtained from direct pc-scale observations on ordinary
radio galaxies and quasars. Finally, we discuss how FR IIs may evolve into FR
Is upon reaching their maximum, entrainment-limited sizes.Comment: 9 pages, 5 figures, accepted for publication in MNRA
Localization of the relative phase via measurements
When two independently-prepared Bose-Einstein condensates are released from
their corresponding traps, the absorbtion image of the overlapping clouds
presents an interference pattern. Here we analyze a model introduced by
Javanainen and Yoo (J. Javanainen and S. M. Yoo, Phys. Rev. Lett. 76, 161
(1996)), who considered two atomic condensates described by plane waves
propagating in opposite directions. We present an analytical argument for the
measurement-induced breaking of the relative phase symmetry in this system,
demonstrating how the phase gets localized after a large enough number of
detection events.Comment: 8 pages, 1 figur
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