Rayleigh-Taylor instability under an inclined plane

We revisit the canonical Rayleigh-Taylor instability and investigate the case of a thin film of fluid upon the underside of an inclined plane. The presence of a natural flow along the plane competes with the conventional droplet forming instability. In particular, experiments reveal that no drops form for inclinations greater than a critical value. These features are rationalized in the context of the absolute/convective analysis conducted in this article

Elaboration of metallic compacts with high porosity for mechanical supports of SOFC

The development of third generation Solid Oxide Fuel Cells (SOFC) with metallic mechanical supports presents several advantages over that of ceramic stacks by offering a lower cost and longer lifetime of the stacks. As a consequence, it is necessary to prepare metallic porous compacts that remain stable at the operating temperature of the SOFC (700–800 C) under reductive atmosphere. This paper presents an innovative process to elaborate iron, nickel and cobalt porous compacts. The process is based on the thermal decomposition of metal oxalate precursors with controlled morphology into metallic powders with coralline shape. Uniaxial compaction of such powders (without binder addition to the powders) under low uniaxial pressures (rising from 20 to 100 MPa) gave rise to green compacts with high porosity and good mechanical properties. After annealing at 800 C under H2 atmosphere, the compacts still present interconnected porosity high enough to allow sufficient gas flow to feed a SOFC single cell in hydrogen: the porosity rises from 25 to 50% for iron compacts, from 20 to 50% for cobalt compacts, and is higher than 40% for nickel compacts. Results from physicochemical characterization (XRD, SEM, gas permeation, Hg porosimetry) corroborated the process for SOFC application

A new route to prepare anodic coatings on dense and porous metallic supports for SOFC application

Metallic cell supports have been developed for the new generation of fuel cells. Sol–gel process has been used to prepare anodic coatings on these supports at moderate thermal treatment temperature, in order to keep a good support mechanical behavior and limit metallic corrosion. Indeed, we take advantage of the numerous reaction routes that sol–gel method can offer to first synthesize NiO–YSZ (yttria-stabilized zirconia) homogeneous composites, and then to process films of different thicknesses on metallic supports by dipcoating. In this work, the metallic supports could be either dense or porous. To begin with, duplex microstructured anodes were prepared from both thin and thick layers, directly deposited on dense metallic supports. The interfacial anodic layer, around 100 nm thick, improves adhesion and accommodates stresses between metallic interconnect and active thick anode. Moreover, by dipping the substrate into an optimized slurry containing sol–gel composite powders, films of a few microns thick have been obtained and constituted the active anodic part. A heat treatment at only 800 °C leads to a coherent anodic duplex stacking which is continuous, homogeneous and adherent. Subsequently, thick anodic films have also been deposited on two different porous supports, with both dip-coating process and slurries routes. These thick anodic coatings were characterized after thermal treatment at 800 °C

Benefits and lessons learned from the Sentinel-3 tandem phase

During its commissioning phase, the Copernicus Sentinel-3B satellite has been placed in a tandem formation with Sentinel-3A for a period of 6 months. This configuration allowed a direct comparison of measurements obtained by the two satellites. The purpose of this paper was to present the range of analyses that can be performed from this dataset, highlighting methodology aspects and the main outcomes for each instrument. We examined, in turn, the benefit of the tandem in understanding instrument operational modes differences, in assessing inter-satellite differences, and in validating measurement uncertainties. The results highlighted the very good consistency of the Sentinel-3A and B instruments, ensuring the complete inter-operability of the constellation. Tandem comparisons also pave the way for further improvements through harmonization of the sensors (OLCI), correction of internal stray-light sources (SLSTR), or high-frequency processing of SRAL SARM data. This paper provided a comprehensive overview of the main results obtained, as well as insights into some of the results. Finally, we drew the main lessons learned from the Sentinel-3 tandem phase and provided recommendations for future missions

Tezos: the OCaml Crypto-Ledger

International audienceIn this talk, we will present the story of the Tezos project. Tezos is a crypto-ledger, i.e. a distributed blockchain with a language to express smart contracts, with two specific characteristics: the first one is its ability for self-amendment, that allows a majority of stake-holders to update the behavior of Tezos without risking a fork; the second one is a design and implementation (in OCaml) that took into account safety and security from the very beginning, and in particular the use of static typing and formal methods when possible. For example, Michelson, the smart contract language of Tezos, is the only such language with a formal semantics, a type system ensuring no runtime errors, and an implementation that uses OCaml GADTs to ensure its correctness. 1 Context A crypto-ledger is an append-only distributed data structure, with a consensus mechanism to avoid inconsistencies in the view of the most up-to-date version. It is also often called a Blockchain, popularized by the Bitcoin crypto-currency, and the tens of new crypto-currencies appearing every year. Among them, Ethereum was probably the most innovative one (and the main challenger for Bitcoin), with an expressive language to write smart contracts, i.e. programs that are executed when they are added to the blockchain or when they are called by other contracts. However, Ethereum is also famous for the hack of the TheDAO smart contract, on June 17, 2016, when an attacker stole around 50 Million dollars of Ether in a few minutes, using a known vulnerability in the smart contract code. Following this attack, the blockchain was updated to remove the attack, but the update was followed by only 85% of the miners, leading to a fork of the network in two separate networks, Ethereum and Ethereum classic. 2 The Tezos project The Tezos project was started in 2014, with the publication of a white paper on a self-amending crypto-ledger[1]. The paper showed, well before fork of Ethereum, the importance of governance in a crypto-ledger, and proposed a mechanism to avoid forks of the network