7,426 research outputs found
Vibration-induced climbing of drops
We report an experimental study of liquid drops moving against gravity, when
placed on a vertically vibrating inclined plate, which is partially wetted by
the drop. The frequency of vibrations ranges from 30 to 200 Hz, and, above a
threshold in vibration acceleration, drops experience an upward motion. We
attribute this surprising motion to the deformations of the drop, as a
consequence of an up or down symmetry breaking induced by the presence of the
substrate. We relate the direction of motion to contact angle measurements.
This phenomenon can be used to move a drop along an arbitrary path in a plane,
without special surface treatments or localized forcing.Comment: 4 pages, 7 figure
From the stress response function (back) to the sandpile `dip'
We relate the pressure `dip' observed at the bottom of a sandpile prepared by
successive avalanches to the stress profile obtained on sheared granular layers
in response to a localized vertical overload. We show that, within a simple
anisotropic elastic analysis, the skewness and the tilt of the response profile
caused by shearing provide a qualitative agreement with the sandpile dip
effect. We conclude that the texture anisotropy produced by the avalanches is
in essence similar to that induced by a simple shearing -- albeit tilted by the
angle of repose of the pile. This work also shows that this response function
technique could be very well adapted to probe the texture of static granular
packing.Comment: 8 pages, 8 figures, accepted version to appear in Eur. Phys. J.
The electron's dance
A joint Fermilab/SLAC publicationParis' Trocadéro science exhibition allows science enthusiasts to see--and even control--a real electron accelerator
Conceptual Frameworks for Multimodal Social Signal Processing
This special issue is about a research area which is developing rapidly. Pentland gave it a name which has become widely used, âSocial Signal Processingâ (SSP for short), and his phrase provides the title of a European project, SSPnet, which has a brief to consolidate the area. The challenge that Pentland highlighted was understanding the nonlinguistic signals that serve as the basis for âsubconscious discussions between humans about relationships, resources, risks, and rewardsâ. He identified it as an area where computational research had made interesting progress, and could usefully make more
Influence of humidity on granular packings with moving walls
A significant dependence on the relative humidity H for the apparent mass
(Mapp) measured at the bottom of a granular packing inside a vertical tube in
relative motion is demonstrated experimentally. While the predictions of
Janssen's model are verified for all values of H investigated (25%< H <80%),
Mapp increases with time towards a limiting value at high relative humidities
(H>60%) but remains constant at lower ones (H=25%). The corresponding Janssen
length is nearly independent of the tube velocity for H>60% but decreases
markedly for H=25%. Other differences are observed on the motion of individual
beads in the packing. For H=25%, they are almost motionless while the mean
particle fraction of the packing remains constant; for H>60% the bead motion is
much more significant and the mean particle fraction decreases. The dependence
of these results on the bead diameter and their interpretation in terms of the
influence of capillary forces are discussed.Comment: 6 pages, 6 figure
A Compositional Deadlock Detector for Android Java
We develop a static deadlock analysis for commercial Android Java applications, of sizes in the tens of millions of
LoC, under active development at Facebook. The analysis runs
primarily at code-review time, on only the modified code and
its dependents; we aim at reporting to developers in under 15
minutes.
To detect deadlocks in this setting, we first model the real
language as an abstract language with balanced re-entrant locks,
nondeterministic iteration and branching, and non-recursive
procedure calls. We show that the existence of a deadlock in this
abstract language is equivalent to a certain condition over the
sets of critical pairs of each program thread; these record, for all
possible executions of the thread, which locks are currently held
at the point when a fresh lock is acquired. Since the critical pairs
of any program thread is finite and computable, the deadlock
detection problem for our language is decidable, and in NP.
We then leverage these results to develop an open-source
implementation of our analysis adapted to deal with real Java
code. The core of the implementation is an algorithm which
computes critical pairs in a compositional, abstract interpretation
style, running in quasi-exponential time. Our analyser is built in
the INFER verification framework and has been in industrial
deployment for over two years; it has seen over two hundred
fixed deadlock reports with a report fix rate of âŒ54%
Statistics at the tip of a branching random walk and the delay of traveling waves
We study the limiting distribution of particles at the frontier of a
branching random walk. The positions of these particles can be viewed as the
lowest energies of a directed polymer in a random medium in the mean-field
case. We show that the average distances between these leading particles can be
computed as the delay of a traveling wave evolving according to the Fisher-KPP
front equation. These average distances exhibit universal behaviors, different
from those of the probability cascades studied recently in the context of mean
field spin-glasses.Comment: 4 pages, 2 figure
Anderson transition on the Cayley tree as a traveling wave critical point for various probability distributions
For Anderson localization on the Cayley tree, we study the statistics of
various observables as a function of the disorder strength and the number
of generations. We first consider the Landauer transmission . In the
localized phase, its logarithm follows the traveling wave form where (i) the disorder-averaged value moves linearly
and the localization length
diverges as with (ii) the
variable is a fixed random variable with a power-law tail for large with , so that all
integer moments of are governed by rare events. In the delocalized phase,
the transmission remains a finite random variable as , and
we measure near criticality the essential singularity with . We then consider the
statistical properties of normalized eigenstates, in particular the entropy and
the Inverse Participation Ratios (I.P.R.). In the localized phase, the typical
entropy diverges as with , whereas it grows
linearly in in the delocalized phase. Finally for the I.P.R., we explain
how closely related variables propagate as traveling waves in the delocalized
phase. In conclusion, both the localized phase and the delocalized phase are
characterized by the traveling wave propagation of some probability
distributions, and the Anderson localization/delocalization transition then
corresponds to a traveling/non-traveling critical point. Moreover, our results
point towards the existence of several exponents at criticality.Comment: 28 pages, 21 figures, comments welcom
The Universal Gaussian in Soliton Tails
We show that in a large class of equations, solitons formed from generic
initial conditions do not have infinitely long exponential tails, but are
truncated by a region of Gaussian decay. This phenomenon makes it possible to
treat solitons as localized, individual objects. For the case of the KdV
equation, we show how the Gaussian decay emerges in the inverse scattering
formalism.Comment: 4 pages, 2 figures, revtex with eps
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