2,308 research outputs found
Strain-induced Evolution of Electronic Band Structures in a Twisted Graphene Bilayer
Here we study the evolution of local electronic properties of a twisted
graphene bilayer induced by a strain and a high curvature. The strain and
curvature strongly affect the local band structures of the twisted graphene
bilayer; the energy difference of the two low-energy van Hove singularities
decreases with increasing the lattice deformations and the states condensed
into well-defined pseudo-Landau levels, which mimic the quantization of massive
Dirac fermions in a magnetic field of about 100 T, along a graphene wrinkle.
The joint effect of strain and out-of-plane distortion in the graphene wrinkle
also results in a valley polarization with a significant gap, i.e., the
eight-fold degenerate Landau level at the charge neutrality point is splitted
into two four-fold degenerate quartets polarized on each layer. These results
suggest that strained graphene bilayer could be an ideal platform to realize
the high-temperature zero-field quantum valley Hall effect.Comment: 4 figure
Determining the structure of Ru(0001) from low-energy electron diffraction of a single terrace
While a perfect hcp (0001) surface has three-fold symmetry, the diffraction
patterns commonly obtained are six-fold symmetric. This apparent change in
symmetry occurs because on a stepped surface, the atomic layers on adjacent
terraces are rotated by 180 degrees. Here we use a Low-Energy Electron
Microscope to acquire the three-fold diffraction pattern from a single hcp Ru
terrace and measure the intensity-vs-energy curves for several diffracted
beams. By means of multiple scattering calculations fitted to the experimental
data with a Pendry R-factor of 0.077, we find that the surface is contracted by
3.5(+-0.9) at 456 K.Comment: 10 pages, 4 figures. Corrected some typos, added more details.
Accepted for publication in Surface Science (Letters
Faraday waves on a viscoelastic liquid
We investigate Faraday waves on a viscoelastic liquid. Onset measurements and
a nonlinear phase diagram for the selected patterns are presented. By virtue of
the elasticity of the material a surface resonance synchronous to the external
drive competes with the usual subharmonic Faraday instability. Close to the
bicriticality the nonlinear wave interaction gives rise to a variety of novel
surface states: Localised patches of hexagons, hexagonal superlattices,
coexistence of hexagons and lines. Theoretical stability calculations and
qualitative resonance arguments support the experimental observations.Comment: 4 pages, 4figure
Long-Lived Localized Field Configurations in Small Lattices: Application to Oscillons
Long-lived localized field configurations such as breathers, oscillons, or
more complex objects naturally arise in the context of a wide range of
nonlinear models in different numbers of spatial dimensions. We present a
numerical method, which we call the {\it adiabatic damping method}, designed to
study such configurations in small lattices. Using 3-dimensional oscillons in
models as an example, we show that the method accurately (to a part in
10^5 or better) reproduces results obtained with static or dynamically
expanding lattices, dramatically cutting down in integration time. We further
present new results for 2-dimensional oscillons, whose lifetimes would be
prohibitively long to study with conventional methods.Comment: LaTeX, 8 pages using RevTeX. 6 PostScript figures include
Square to stripe transition and superlattice patterns in vertically oscillated granular layers
We investigated the physical mechanism for the pattern transition from square
lattice to stripes, which appears in vertically oscillating granular layers. We
present a continuum model to show that the transition depends on the
competition between inertial force and local saturation of transport. By
introducing multiple free-flight times, this model further enables us to
analyze the formation of superlattices as well as hexagonal lattice
Crumpling a Thin Sheet
Crumpled sheets have a surprisingly large resistance to further compression.
We have studied the crumpling of thin sheets of Mylar under different loading
conditions. When placed under a fixed compressive force, the size of a crumpled
material decreases logarithmically in time for periods up to three weeks. We
also find hysteretic behavior when measuring the compression as a function of
applied force. By using a pre-treating protocol, we control this hysteresis and
find reproducible scaling behavior for the size of the crumpled material as a
function of the applied force.Comment: revtex 4 pages, 6 eps figures submitted to Phys Rev. let
Isolation of a novel aquaglyceroporin from a marine teleost (Sparus auratus) Function and tissue distribution
The aquaporins (formerly called the major intrinsic
protein family) are transmembrane channel proteins. The
family includes the CHIP group, which are functionally
characterised as water channels and the GLP group,
which are specialised for glycerol transport. The present
study reports the identification and characterisation of a
novel GLP family member in a teleost fish, the sea bream
Sparus auratus. A sea bream aquaporin (sbAQP) cDNA of
1047·bp and encoding a protein of 298·amino acids was
isolated from a kidney cDNA library. Functional
characterization of the sbAQP using a Xenopus oocyte
assay revealed that the isolated cDNA stimulated osmotic
water permeability in a mercury-sensitive manner and
also stimulated urea and glycerol uptake. Northern
blotting demonstrated that sbAQP was expressed at high
levels in the posterior region of the gut, where two transcripts were identified (1.6·kb and 2·kb), and in
kidney, where a single transcript was present (2·kb). In
situ hybridisation studies with a sbAQP riboprobe
revealed its presence in the lamina propria and smooth
muscle layer of the posterior region of the gut and in
epithelial cells of some kidney tubules. sbAQP was also
present in putative chloride cells of the gill. Phylogenetic
analysis of sbAQP, including putative GLP genes from
Fugu rubripes, revealed that it did not group with any of
the previously isolated vertebrate GLPs and instead
formed a separate group, suggesting that it may be a novel
GLP member.This work was supported by project PRAXIS
XXI/2/2.1/BIA/211/94 from the Portuguese National Science
and Technology Foundation (FCT), co-financed by EU
structural funds, DG-Fisheries Project Q5RS-2002-00784
(CRYOCYTE) and an EU Biotech grant (QLRT2000-00778).
C.R.A.S., J.C.R.C. and J.F. were in receipt of FCT
fellowships PRAXIS XXI/BPD/22040/99, PRAXIS
XXI/BD/19925/99BPD/22033/99, respectively
Nomenclature for renal replacement therapy and blood purification techniques in critically ill patients: practical applications
This article reports the conclusions of the second part of a consensus expert conference on the nomenclature of renal replacement therapy (RRT) techniques currently utilized to manage acute kidney injury and other organ dysfunction syndromes in critically ill patients. A multidisciplinary approach was taken to achieve harmonization of definitions, components, techniques, and operations of the extracorporeal therapies. The article describes the RRT techniques in detail with the relevant technology, procedures, and phases of treatment and key aspects of volume management/fluid balance in critically ill patients. In addition, the article describes recent developments in other extracorporeal therapies, including therapeutic plasma exchange, multiple organ support therapy, liver support, lung support, and blood purification in sepsis. This is a consensus report on nomenclature harmonization in extracorporeal blood purification therapies, such as hemofiltration, plasma exchange, multiple organ support therapies, and blood purification in sepsis
A Continuum Description of Vibrated Sand
The motion of a thin layer of granular material on a plate undergoing
sinusoidal vibrations is considered. We develop equations of motion for the
local thickness and the horizontal velocity of the layer. The driving comes
from the violent impact of the grains on the plate. A linear stability theory
reveals that the waves are excited non-resonantly, in contrast to the usual
Faraday waves in liquids. Together with the experimentally observed continuum
scaling, the model suggests a close connection between the neutral curve and
the dispersion relation of the waves, which agrees quite well with experiments.
For strong hysteresis we find localized oscillon solutions.Comment: paper has been considerably extended (11 instead of 6 pages; 6
instead of 4 figures) much better agreement with experiment. obtain now
oscillons in 1 dimensio
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