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