10,163 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
The branching Brownian motion seen from its tip
It has been conjectured since the work of Lalley and Sellke (1987) that the
branching Brownian motion seen from its tip (e.g. from its rightmost particle)
converges to an invariant point process. Very recently, it emerged that this
can be proved in several different ways (see e.g. Brunet and Derrida, 2010,
Arguin et al., 2010, 2011). The structure of this extremal point process turns
out to be a Poisson point process with exponential intensity in which each atom
has been decorated by an independent copy of an auxiliary point process. The
main goal of the present work is to give a complete description of the limit
object via an explicit construction of this decoration point process. Another
proof and description has been obtained independently by Arguin et al. (2011).Comment: 47 pages, 3 figure
How genealogies are affected by the speed of evolution
In a series of recent works it has been shown that a class of simple models
of evolving populations under selection leads to genealogical trees whose
statistics are given by the Bolthausen-Sznitman coalescent rather than by the
well known Kingman coalescent in the case of neutral evolution. Here we show
that when conditioning the genealogies on the speed of evolution, one finds a
one parameter family of tree statistics which interpolates between the
Bolthausen-Sznitman and Kingman's coalescents. This interpolation can be
calculated explicitly for one specific version of the model, the exponential
model. Numerical simulations of another version of the model and a
phenomenological theory indicate that this one-parameter family of tree
statistics could be universal. We compare this tree structure with those
appearing in other contexts, in particular in the mean field theory of spin
glasses
A uniform isotopic and chemical signature of dust exported from Patagonia: Rock sources and occurrence in southern environments
Patagonia is considered to be the most important source of dust from South America that is deposited in surrounding areas, and
we present here a systematic Sr and Nd isotopic study of sediment currently being exported. Eolian and suspended riverine
sediments from Patagonia have a homogeneous chemical and isotopic composition that results from the mixing of by-products
from explosive Andean volcanism, derived from the extensive Jurassic silicic Province of Chon Aike and pyroclastic materials
from the basic to intermediate southern Andean Quaternary arc, which are easily denudated and dispersed. The main Andean uplift
and the glaciations that began in the Late Tertiary account for the extensive distribution of these sediments in the extra-Andean
region. The present geochemical signature of Patagonian sediments was produced during the Pleistocene, along with the onset of
the southern Andean explosive arc volcanism. Previously published compositions of sediments from other southern South
American source regions, assumed to be representative of Patagonia, are distinct from our data. Considering the alleged importance
of Patagonia as a dust source for different depositional environments in southern latitudes, it is surprising to verify that the chemical
and isotopic signatures of Patagonian-sourced sediments are different from those of sediments from the Southern Ocean, the
Pampean Region or the Antarctic ice. Sediments from these areas have a crustal-like geochemical signature reflecting a mixed
origin with sediment from other southern South American sources, whereas Patagonian sediments likely represent the basic to
intermediate end-member composition
Controlling the composition of a confined fluid by an electric field
Starting from a generic model of a pore/bulk mixture equilibrium, we propose
a novel method for modulating the composition of the confined fluid without
having to modify the bulk state. To achieve this, two basic mechanisms -
sensitivity of the pore filling to the bulk thermodynamic state and electric
field effect - are combined. We show by Monte Carlo simulation that the
composition can be controlled both in a continuous and in a jumpwise way. Near
the bulk demixing instability, we demonstrate a field induced population
inversion in the pore. The conditions for the realization of this method should
be best met with colloids, but being based on robust and generic mechanisms, it
should also be applicable to some molecular fluids.Comment: 9 pages, 5 figure
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
Data sources for rescuing the rich heritage of Mediterranean historical surface climate data
10.1002/gdj3.4Availability of long-term and high-quality instrumental climate records is still insufficient and the rich heritage of meteorological surface observations is largely underexploited in many parts of the world. This is particularly striking over the Greater Mediterranean region (GMR), where meteorological observations have been taken since the 18th century at some locations. The lack of high quality and long series here is despite this region being regarded as a climate change hot spot. This article mainly assesses relevant sources containing Mediterranean historical climate data and metadata either from online repositories worldwide or physical archives, with the emphasis here on the rich holdings kept at French archives. A particular case study is the data rescue (DARE) program undertaken by the Algerian National Meteorological Service, as well as some of the past and ongoing projects and initiatives aimed at enhancing climate data availability and accessibility over the GMR. Our findings point to the high potential for undertaking DARE activities over the GMR and the need for bringing longer and higher quality climate time series to support a diverse number of scientific and technical assessments and policies
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