754 research outputs found
Jamming, two-fluid behaviour and 'self-filtration' in concentrated particulate suspensions
We study the flow of model experimental hard sphere colloidal suspensions at
high volume fraction driven through a constriction by a pressure
gradient. Above a particle-size dependent limit , direct microscopic
observations demonstrate jamming and unjamming--conversion of fluid to solid
and vice versa--during flow. We show that such a jamming flow produces a
reduction in colloid concentration downstream of the constriction.
We propose that this `self-filtration' effect is the consequence of a
combination of jamming of the particulate part of the system and continuing
flow of the liquid part, i.e. the solvent, through the pores of the jammed
solid. Thus we link the concept of jamming in colloidal and granular media with
a 'two-fluid'-like picture of the flow of concentrated suspensions. Results are
also discussed in the light of Osborne Reynolds' original experiments on
dilation in granular materials.Comment: 4 pages, 3 figure
BiFeO3/La0.7Sr0.3MnO3 heterostructures deposited on Spark Plasma Sintered LaAlO3 Substrates
Multiferroic BiFeO3 (BFO) / La0.7Sr0.3MnO3 heterostructured thin films were
grown by pulsed laser deposition on polished spark plasma sintered LaAlO3 (LAO)
polycrystalline substrates. Both polycrystalline LAO substrates and BFO films
were locally characterized using electron backscattering diffraction (EBSD),
which confirmed the high-quality local epitaxial growth on each substrate
grain. Piezoforce microscopy was used to image and switch the piezo-domains,
and the results are consistent with the relative orientation of the
ferroelectric variants with the surface normal. This high-throughput synthesis
process opens the routes towards wide survey of electronic properties as a
function of crystalline orientation in complex oxide thin film synthesis.Comment: 10 pages, 4 figures, Submitted to Applied Physics Letter
Bulk Fermi surface coexistence with Dirac surface state in BiSe: a comparison of photoemission and Shubnikov-de Haas measurements
Shubnikov de Haas (SdH) oscillations and Angle Resolved PhotoEmission
Spectroscopy (ARPES) are used to probe the Fermi surface of single crystals of
Bi2Se3. We find that SdH and ARPES probes quantitatively agree on measurements
of the effective mass and bulk band dispersion. In high carrier density
samples, the two probes also agree in the exact position of the Fermi level EF,
but for lower carrier density samples discrepancies emerge in the position of
EF. In particular, SdH reveals a bulk three-dimensional Fermi surface for
samples with carrier densities as low as 10^17cm-3. We suggest a simple
mechanism to explain these differences and discuss consequences for existing
and future transport studies of topological insulators.Comment: 5 mages, 5 figure
The surface-state of the topological insulator BiSe revealed by cyclotron resonance
To date transport measurements of topological insulators have been dominated
by the conductivity of the bulk, leading to substantial difficulties in
resolving the properties of the surface. To this end, we use high magnetic
field, rf- and microwave-spectroscopy to selectively couple to the surface
conductivity of BiSe at high frequency. In the frequency range of a few
GHz we observe a crossover from quantum oscillations indicative of a small 3D
Fermi surface, to cyclotron resonance indicative of a 2D surface state
Correlation length by measuring empty space in simulated aggregates
We examine the geometry of the spaces between particles in diffusion-limited
cluster aggregation, a numerical model of aggregating suspensions. Computing
the distribution of distances from each point to the nearest particle, we show
that it has a scaled form independent of the concentration phi, for both two-
(2D) and three-dimensional (3D) model gels at low phi. The mean remoteness is
proportional to the density-density correlation length of the gel, xi, allowing
a more precise measurement of xi than by other methods. A simple analytical
form for the scaled remoteness distribution is developed, highlighting the
geometrical information content of the data. We show that the second moment of
the distribution gives a useful estimate of the permeability of porous media.Comment: 4 page
Quantum oscillations in the parent pnictide BaFeAs : itinerant electrons in the reconstructed state
We report quantum oscillation measurements that enable the direct observation
of the Fermi surface of the low temperature ground state of \ba122. From these
measurements we characterize the low energy excitations, revealing that the
Fermi surface is reconstructed in the antiferromagnetic state, but leaving
itinerant electrons in its wake. The present measurements are consistent with a
conventional band folding picture of the antiferromagnetic ground state,
placing important limits on the topology and size of the Fermi surface.Comment: 5 pages, 3 figure
Doping dependence of femtosecond quasi-particle relaxation dynamics in Ba(Fe,Co)_2As_2 single crystals: possible evidence for normal state nematic fluctuations
We systematically investigate the photoexcited (PE) quasi-particle (QP)
relaxation and low-energy electronic structure in electron doped
Ba(Fe_{1-x}Co_{x})_{2}As_{2} single crystals as a function of Co doping, 0<= x
<=0.11. The evolution of the photoinduced reflectivity transients with
proceeds with no abrupt changes. In the orthorhombic spin-density-wave (SDW)
state a bottleneck associated with a partial charge-gap opening is detected,
similar to previous results in different SDW iron-pnictides. The relative
charge gap magnitude decreases with increasing x. In the superconducting (SC)
state an additional relaxational component appears due to a partial (or
complete) destruction of the SC state proceeding on a sub-0.5-picosecond
timescale. From the SC component saturation behavior the optical SC-state
destruction energy, U_p/k_B=0.3 K/Fe, is determined near the optimal doping.
The subsequent relatively slow recovery of the SC state indicates clean SC
gaps. The T-dependence of the transient reflectivity amplitude in the normal
state is consistent with the presence of a pseudogap in the QP density of
states. The polarization anisotropy of the transients suggests that the
pseudogap-like behavior might be associated with a broken point symmetry
resulting from nematic electronic fluctuations persisting up to T~200 K at any
x. The second moment of the Eliashberg function, obtained from the relaxation
rate in the metallic state at higher temperatures, indicates a moderate
electron phonon coupling, lambda <~0.3, that decreases with increasing doping
The Reactome BioMart
Reactome is an open source, expert-authored, manually curated and peer-reviewed database of reactions, pathways and biological processes. We provide an intuitive web-based user interface to pathway knowledge and a suite of data analysis tools. The Reactome BioMart provides biologists and bioinformaticians with a single web interface for performing simple or elaborate queries of the Reactome database, aggregating data from different sources and providing an opportunity to integrate experimental and computational results with information relating to biological pathways. Database URL: http://www.reactome.org
Dilatancy, Jamming, and the Physics of Granulation
Granulation is a process whereby a dense colloidal suspension is converted
into pasty granules (surrounded by air) by application of shear. Central to the
stability of the granules is the capillary force arising from the interfacial
tension between solvent and air. This force appears capable of maintaining a
solvent granule in a jammed solid state, under conditions where the same amount
of solvent and colloid could also exist as a flowable droplet. We argue that in
the early stages of granulation the physics of dilatancy, which requires that a
powder expand on shearing, is converted by capillary forces into the physics of
arrest. Using a schematic model of colloidal arrest under stress, we speculate
upon various jamming and granulation scenarios. Some preliminary experimental
results on aspects of granulation in hard-sphere colloidal suspensions are also
reported.Comment: Original article intended for J Phys Cond Mat special issue on
Granular Materials (M Nicodemi, Ed.
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