178 research outputs found
Failure of mean-field approach in out-of-equilibrium Anderson model
To explore the limitations of the mean field approximation, frequently used
in \textit{ab initio} molecular electronics calculations, we study an
out-of-equilibrium Anderson impurity model in a scattering formalism. We find
regions in the parameter space where both magnetic and non-magnetic solutions
are stable. We also observe a hysteresis in the non-equilibrium magnetization
and current as a function of the applied bias voltage. The mean field method
also predicts incorrectly local moment formation for large biases and a spin
polarized current, and unphysical kinks appear in various physical quantities.
The mean field approximation thus fails in every region where it predicts local
moment formation.Comment: 5 pages, 5 figure
Fluctuation-induced dynamics of multiphase liquid jets with ultra-low interfacial tension
postprin
Clogging by sieving in microchannels: Application to the detection of contaminants in colloidal suspensions
We report on a microfluidic method that allows measurement of a small
concentration of large contaminants in suspensions of solid micrometer-scale
particles. To perform the measurement, we flow the colloidal suspension through
a series of constrictions, i.e. a microchannel of varying cross-section. We
show and quantify the role of large contaminants in the formation of clogs at a
constriction and the growth of the resulting filter cake. By measuring the time
interval between two clogging events in an array of parallel microchannels, we
are able to estimate the concentration of contaminants whose size is selected
by the geometry of the microfluidic device. This technique for characterizing
colloidal suspensions offers a versatile and rapid tool to explore the role of
contaminants on the properties of the suspensions
Quantum teleportation by particle-hole annihilation in the Fermi sea
A tunnel barrier in a degenerate electron gas was recently discovered as a
source of entangled particle-hole excitations. The entanglement is produced by
elastic tunneling events, without requiring electron-electron interactions.
Here we investigate the inverse process, the annihilation of an electron and a
hole by elastic scattering. We find that this process leads to teleportation of
the (unknown) state of the annihilated electron to a second, distant electron
-- if the latter was previously entangled with the annihilated hole. We propose
an experiment, involving low-frequency noise measurements on a two-dimensional
electron gas in a high magnetic field, to detect teleportation of electrons and
holes in the two lowest Landau levels.Comment: 5 pages including 2 figures; [2017: fixed broken postscript figures
Stochastic analysis of a radial-inflow turbine in the presence of parametric uncertainties
This paper presents an uncertainty quantification study of the performance analysis of the high pressure ratio single stage radial-inflow turbine used in the Sundstrand Power Systems T-100 Multi-purpose Small Power Unit. A deterministic 3D volume-averaged Computational Fluid Dynamics (CFD) solver is coupled with a non-statistical generalized Polynomial Chaos (gPC) representation based on a pseudo-spectral projection method. One of the advantages of this approach is that it does not require any modification of the CFD code for the propagation of random disturbances in the aerodynamic and geometric fields. The stochastic results highlight the importance of the blade thickness and trailing edge tip radius on the total-to-static efficiency of the turbine compared to the angular velocity and trailing edge tip length. From a theoretical point of view, the use of the gPC representation on an arbitrary grid also allows the investigation of the sensitivity of the blade thickness profiles on the turbine efficiency. The gPC approach is also applied to coupled random parameters. The results show that the most influential coupled random variables are trailing edge tip radius coupled with the angular velocity
Competitive dynamics of two erosion patterns around a cylinder
We investigate experimentally the local erosion of a granular bed near a
fixed vertical cylinder that emerges from the bed. The onset of erosion arising
at the base of the cylinder and usually ascribed to the wrapping horseshoe
vortex is determined and rationalized by a flow contraction effect. We report a
new erosion pattern visible downstream of the cylinder that consists of two
side-by-side elongated holes. This pattern is observed for flow regimes close
to the horseshoe scour onset, whose growth usually inhibits its spatiotemporal
development.Comment: 6 pages, 6 figure
Experimental investigation of tsunami waves generated by granular collapse into water
The generation of a tsunami wave by an aerial landslide is investigated
through model laboratory experiments. We examine the collapse of an initially
dry column of grains into a shallow water layer and the subsequent generation
of waves. The experiments show that the collective entry of the granular
material into water governs the wave generation process. We observe that the
amplitude of the wave relative to the water height scales linearly with the
Froude number based on the horizontal velocity of the moving granular front
relative to the wave velocity. For all the different parameters considered
here, the aspect ratio and the volume of the column, the diameter and density
of the grains, and the height of the water, the granular collapse acts like a
moving piston displacing the water. We also highlight that the density of the
falling grains has a negligible influence on the wave amplitude, which suggests
that the volume of grains entering the water is the relevant parameter in the
wave generation.Comment: 23 pages, 16 figure
Spin current shot noise as a probe of interactions in mesoscopic systems
It is shown that the spin resolved current shot noise can probe attractive or
repulsive interactions in mesoscopic systems. This is illustrated in two
physical situations : i) a normal-superconducting junction where the spin
current noise is found to be zero, and ii) a single electron transistor (SET),
where the spin current noise is found to be Poissonian. Repulsive interactions
may also lead to weak attractive correlations (bunching of opposite spins) in
conditions far from equilibrium. Spin current shot noise can be used to measure
the spin relaxation time , and a set-up is proposed in a quantum dot
geometry.Comment: 5 pages, 4 Figures, revised version, added reference
Mechanical tuning of the evaporation rate of liquid on crossed fibers
We investigate experimentally the drying of a small volume of perfectly
wetting liquid on two crossed fibers. We characterize the drying dynamics for
the three liquid morphologies that are encountered in this geometry: drop,
column and a mixed morphology, in which a drop and a column coexist. For each
morphology, we rationalize our findings with theoretical models that capture
the drying kinetics. We find that the evaporation rate depends significantly on
the liquid morphology and that the drying of liquid column is faster than the
evaporation of the drop and the mixed morphology for a given liquid volume.
Finally, we illustrate that shearing a network of fibers reduces the angle
between them, changes the morphology towards the column state, and so enhances
the drying rate of a volatile liquid deposited on it
A coarse-grained multiscale model to simulate morphological changes of food-plant tissues undergoing drying
Numerical modelling has emerged as a powerful and effective tool to study various dynamic behaviours of biological matter. Such numerical modelling tools have contributed to the optimisations of food drying parameters leading to higher quality end-products in the field of food engineering. In this context, on of the most recent developments is the mesh-free based numerical models, which have demonstrated enhanced capabilities to model cellular deformations during drying, providing many benefits compared to conventional grid-based modelling approaches. However, the potential extension of this method for simulating bulk level tissues has been a challenge due to the increased requirement for higher computaional time and resources. As a solution for this, by incorporating meshfree features, a novel coarse-grained multiscale numerical model is proposed in this work to predict bulk level (macroscale) deformations of food plant tissues during drying
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