2,423 research outputs found
Beating the teapot effect
We investigate the dripping of liquids around solid surfaces in the regime of
inertial flows, a situation commonly encountered with the so-called "teapot
effect". We demonstrate that surface wettability is an unexpected key factor in
controlling flow separation and dripping, the latter being completely
suppressed in the limit of superhydrophobic substrates. This unforeseen
coupling is rationalized in terms of a novel hydro-capillary adhesion
framework, which couples inertial flows to surface wettability effects. This
description of flow separation successfully captures the observed dependence on
the various experimental parameters - wettability, flow velocity, solid surface
edge curvature-. As a further illustration of this coupling, a real-time
control of dripping is demonstrated using electro-wetting for contact angle
actuation.Comment: 4 pages; movies at http://lpmcn.univ-lyon1.fr/~lbocque
Space-time estimation of a particle system model
13 pagesLet X be a discrete time contact process (CP) on the discrete bidimensional lattice as define by Durett - Levin (1994) . We study estimation of the model based on space-time evolution on a finite subset of sites. For this, we make use of a marginal pseudo-likelihood. The estimator obtained is consistent and asymptoticaly normal for non-vanishing supercritical CP. Numerical studies confirm these results
Efficient simulation of non-crossing fibers and chains in a hydrodynamic solvent
An efficient simulation method is presented for Brownian fiber suspensions,
which includes both uncrossability of the fibers and hydrodynamic interactions
between the fibers mediated by a mesoscopic solvent. To conserve hydrodynamics,
collisions between the fibers are treated such that momentum and energy are
conserved locally. The choice of simulation parameters is rationalised on the
basis of dimensionless numbers expressing the relative strength of different
physical processes. The method is applied to suspensions of semiflexible fibers
with a contour length equal to the persistence length, and a mesh size to
contour length ratio ranging from 0.055 to 0.32. For such fibers the effects of
hydrodynamic interactions are observable, but relatively small. The
non-crossing constraint, on the other hand, is very important and leads to
hindered displacements of the fibers, with an effective tube diameter in
agreement with recent theoretical predictions. The simulation technique opens
the way to study the effect of viscous effects and hydrodynamic interactions in
microrheology experiments where the response of an actively driven probe bead
in a fiber suspension is measured.Comment: 12 pages, 2 tables, 5 figure
Zenithal bistability in a nematic liquid crystal device with a monostable surface condition
The ground-state director configurations in a grating-aligned, zenithally bistable nematic device are calculated in two dimensions using a Q tensor approach. The director profiles generated are well described by a one-dimensional variation of the director across the width of the device, with the distorted region near the grating replaced by an effective surface anchoring energy. This work shows that device bistability can in fact be achieved by using a monostable surface term in the one-dimensional model. This implies that is should be possible to construct a device showing zenithal bistability without the need for a micropatterned surface
Personalized Pancreatic Tumor Growth Prediction via Group Learning
Tumor growth prediction, a highly challenging task, has long been viewed as a
mathematical modeling problem, where the tumor growth pattern is personalized
based on imaging and clinical data of a target patient. Though mathematical
models yield promising results, their prediction accuracy may be limited by the
absence of population trend data and personalized clinical characteristics. In
this paper, we propose a statistical group learning approach to predict the
tumor growth pattern that incorporates both the population trend and
personalized data, in order to discover high-level features from multimodal
imaging data. A deep convolutional neural network approach is developed to
model the voxel-wise spatio-temporal tumor progression. The deep features are
combined with the time intervals and the clinical factors to feed a process of
feature selection. Our predictive model is pretrained on a group data set and
personalized on the target patient data to estimate the future spatio-temporal
progression of the patient's tumor. Multimodal imaging data at multiple time
points are used in the learning, personalization and inference stages. Our
method achieves a Dice coefficient of 86.8% +- 3.6% and RVD of 7.9% +- 5.4% on
a pancreatic tumor data set, outperforming the DSC of 84.4% +- 4.0% and RVD
13.9% +- 9.8% obtained by a previous state-of-the-art model-based method
Adaptive optics in high-contrast imaging
The development of adaptive optics (AO) played a major role in modern
astronomy over the last three decades. By compensating for the atmospheric
turbulence, these systems enable to reach the diffraction limit on large
telescopes. In this review, we will focus on high contrast applications of
adaptive optics, namely, imaging the close vicinity of bright stellar objects
and revealing regions otherwise hidden within the turbulent halo of the
atmosphere to look for objects with a contrast ratio lower than 10^-4 with
respect to the central star. Such high-contrast AO-corrected observations have
led to fundamental results in our current understanding of planetary formation
and evolution as well as stellar evolution. AO systems equipped three
generations of instruments, from the first pioneering experiments in the
nineties, to the first wave of instruments on 8m-class telescopes in the years
2000, and finally to the extreme AO systems that have recently started
operations. Along with high-contrast techniques, AO enables to reveal the
circumstellar environment: massive protoplanetary disks featuring spiral arms,
gaps or other asymmetries hinting at on-going planet formation, young giant
planets shining in thermal emission, or tenuous debris disks and micron-sized
dust leftover from collisions in massive asteroid-belt analogs. After
introducing the science case and technical requirements, we will review the
architecture of standard and extreme AO systems, before presenting a few
selected science highlights obtained with recent AO instruments.Comment: 24 pages, 14 figure
Influence of flow confinement on the drag force on a static cylinder
The influence of confinement on the drag force on a static cylinder in a
viscous flow inside a rectangular slit of aperture has been investigated
from experimental measurements and numerical simulations. At low enough
Reynolds numbers, varies linearly with the mean velocity and the viscosity,
allowing for the precise determination of drag coefficients and
corresponding respectively to a mean flow parallel and
perpendicular to the cylinder length . In the parallel configuration, the
variation of with the normalized diameter of the
cylinder is close to that for a 2D flow invariant in the direction of the
cylinder axis and does not diverge when . The variation of
with the distance from the midplane of the model reflects the
parabolic Poiseuille profile between the plates for while it
remains almost constant for . In the perpendicular configuration,
the value of is close to that corresponding to a 2D system
only if and/or if the clearance between the ends of the cylinder
and the side walls is very small: in that latter case,
diverges as due to the blockage of the flow. In other cases, the
side flow between the ends of the cylinder and the side walls plays an
important part to reduce : a full 3D description of the flow is
needed to account for these effects
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