Current developments of nanoscale insight into corrosion protection by passive oxide films

Oxide passive films are a key for the durability of metals and alloys components as well as a central issue in corrosion science and engineering. Herein, we discuss current developments of the nanometer and sub-nanometer scale knowledge of the barrier properties and adsorption properties of passive oxide films brought by recent model experimental and theoretical investigations. The discussed aspects include (i) the chromium enrichment and its homogeneity at the nanoscale in passive films formed on Cr-bearing alloys such as stainless steel, (ii) the corrosion properties of grain boundaries in early intergranular corrosion before penetration and propagation in the grain boundary network, and (iii) the interaction of organic inhibitor molecules with incompletely passivated metallic surfaces. In all three cases, key issues are highlighted and future developments that we consider as most relevant are identified.Comment: Current Opinion in Solid State and Materials Science, Elsevier, final accepted preprin

Characterization of strychnine binding sites in the rodent spinal cord

The convulsant alkaloid strychnine is a selective and highly potent antagonist at postsynaptic receptor for the inhibitory neurotransmitter glycine. These properties have led to the extensive use of strychnine as a ligand to probe the postsynaptic glycine receptor. Despite the recent increased understanding of the molecular structure of this receptor protein there is still much dispute as to the nature of the interaction between glycine and strychnine. In an attempt to more clearly define this interaction the experiments described, combine the techniques of protein modification and ligand binding. These investigations also revealed a novel [3H]-strychnine binding site in the rodent CNS and attempts were made to characterize this phenomenon. The results described suggest that glycine is a fully competitive inhibitor of [3H]-strychnine binding and its reported action as a partial competitive inhibitor is an artefact of the assay conditions. The disruption of [3H]-strychnine binding by residue selective protein modifying reagents suggests some overlap in the strychnine and glycine binding sites at the receptor. Protection studies confirm this and the results are best explained by overlapping yet conformationally distinct recognition sites for strychnine and glycine. Experiments which describe protein modification and ligand protection of strychnine binding antisera highlight possible congruence in the molecular recognition at the antisera and the receptor. This is of interest in the light of proposed models of the strychnine binding site at the postsynaptic glycine receptor. Modification of spinal cord membranes by the arginine selective reagent 2,3-butanedione (BD) reveals a low affinity and high capacity [3H]-strychnine binding site which is not detectable in untreated membranes. This binding site showed a similar distribution in the CNS as the high affinity site. However, experiments using affinity purified glycine receptor and crude membrane preparations from the mutant mouse spastic indicated that the BD-induced binding site is not located on the postsynaptic glycine receptor. Competition studies revealed that [3H]-strychnine binding sites in untreated and BD-treated membranes have different structural determinants. The ability to effectively inhibit [3H]-strychnine binding to the BD-induced site by cation channel blockers is in accord with reports that strychnine can interact with various cation channels to open or block them. In addition several compounds that inhibit the BD-induced [3H]-strychnine binding can also modulate the reaction of BD with spinal cord membranes if present during the treatment, suggesting a conformational dependent modification. Upon exposure to ultraviolet light [3H]-strychnine is specifically incorporated into a low molecular weight peptide in BD-treated membranes in addition to the ligand binding subunit of the inhibitory glycine receptor, which is the only peptide photolabelled in untreated membranes. The significance of this biochemical and pharmacological characterization of this previously undescribed strychnine binding site is presently unclear. However, the uneven distribution in the CNS and the interaction with important therapeutic agents; local anaesthetics and anti-arrhythmics, indicate the possible biological importance of the novel strychnine binding site

An open question : How to solve efficiently 3D frictional contact problem ?

International audienceIn this talk, we want to discuss possible numerical solution procedures for the following discrete frictional contact problem. We will recall a result for the problem in (1) which ensures that a solution exists [3]. In this framework, we will list several algorithms that have been previously developed for solving the SOCCP (1) mainly based variational inequality and nonsmooth equations reformulations. On one hand, we will show that algorithms based on Newton methods for nonsmooth equations solve quickly the problem when they succeed, but suffer from robustness issues mainly if the matrix H has not full rank. On the other hand, the iterative methods dedicated to solving variational inequalities are quite robust but with an extremely slow rate of convergence. To sum up, as far as we know there is no option that combines time efficiency and robustness. To try to answer to this question, we develop an open collection of discrete frictional contact problems called FCLIB http://fclib.gforge.inria.fr in order to offer a large library of problems to compare algorithms on a fair basis. In this work, this collection is solved with the software Siconos and its component Siconos/Numerics http://siconos.gforge.inria.fr

Progress in corrosion science at atomic and nanometric scales

International audienceContemporary aspects of corrosion science are reviewed to show how insightful a surface science approach is to understand the mechanisms of corrosion initiation at the atomic and nanometric scales. The review covers experimental approaches using advanced surface analytical techniques applied to single-crystal surfaces of metal and alloys exposed to corrosive aqueous environments in well-controlled conditions and analysed in situ under electrochemical control and/or ex situ by scanning tunnelling microscopy/spectroscopy, atomic force microscopy and x-ray diffraction. Complementary theoretical approaches based on atomistic modeling are also covered. The discussed aspects include the metal-water interfacial structure and the surface reconstruction induced by hydroxide adsorption and formation of 2D (hyd)oxide precursors, the structure alterations accompanying anodic dissolution processes of metals without or with 2D protective layers and selective dissolution (i.e. dealloying) of alloys, the atomic structure, orientation and surface hydroxylation of ultrathin passive films, the role of step edges at the exposed surface of oxide grains on the dissolution of passive films and the effect of grain boundaries in polycrystalline passive films acting as preferential sites of passivity breakdown, the differences in local electronic properties measured at passive films grain boundaries, and the structure of adlayers of organic inhibitor molecules

Steering the Smart Grid

Increasing energy prices and the greenhouse effect lead to more awareness of energy efficiency of electricity supply. During the last years, a lot of technologies and optimization methodologies were developed to increase the efficiency, maintain the grid stability and support large scale introduction of renewable sources. In previous work, we showed the effectiveness of our three-step methodology to reach these objectives, consisting of 1) offline prediction, 2) offline planning and 3) online scheduling in combination with MPC. In this paper we analyse the best structure for distributing the steering signals in the third step. Simulations show that pricing signals work as good as on/off signals, but pricing signals are more general. Individual pricing signals per house perform better with small prediction errors while one global steering signal for a group of houses performs better when the prediction errors are larger. The best hierarchical structure is to use consumption patterns on all levels except the lowest level and deduct the pricing signals in the lowest node of the tree

Improved Heat Demand Prediction of Individual Households

One of the options to increase the energy efficiency of current electricity network is the use of a Virtual Power Plant. By using multiple small (micro)generators distributed over the country, electricity can be produced more efficiently since these small generators are more efficient and located where the energy is needed. In this paper we focus on micro Combined Heat and Power generators. For such generators, the production capacity is determined and limited by the heat demand. To keep the global electricity network stable, information about the production capacity of the heat-driven generators is required in advance. In this paper we present methods to perform heat demand prediction of individual households based on neural network techniques. Using different input sets and a so called sliding window, the quality of the predictions can be improved significantly. Simulations show that these improvements have a positive impact on controlling the distributed microgenerators