Bio-catalyzed electrode reactions: from biocorrosion to biofuel celles

International audienceWhereas corrosion of metallic materials by bacteria is a process dreaded by metallurgists, the mechanisms of such corrosion, involving specific biofilms or enzymes as they do, are of great interest as regards fuel cells. Indeed, developing biofilms or adding enzymes having the ability to reproduce biocorrosion phenomena enables enhanced rates to be achieved for the reactions occurring at the anode and cathode areas of metallic materials leading to biocorrosion. Bio-catalyzed reactions at the anode and cathode are nearly identical in microbial fuel cells leading to electricity production. Demonstration of such biocatalysis processes on conductor materials hints at new prospects, with the highlighting of an electrochemical connection between materials and microorganisms. Biofilms, owing to the bacteria and/or enzymes they contain, are electrochemically active, thus conferring on conducting materials unexpected behavior, including corrosion protection effects

Nuclear corrosion and materials: achievements and challenges

International audienceCorrosion and material sciences face challenges which involved and still need increases of knowledge and understanding in light water nuclear power plants.In pressurized water reactors (PWRs), the performances of the two first barriers for the plant safety (cladding for the fuel and steam generator tubing for the primary circuit) have key importance and their performances have been improved through the better knowledge of their corrosion behaviors. This leads for cladding to the evolution of zirconium alloy composition with addition of niobium. Stress corrosion cracking of nickel base alloys has been a great challenge for PWRs which has been solved progressively by evolutions of Alloy 600 from Meal Annelled (MA) to thermally treated (TT) materials and then to evolution of the alloy composition with less nickel and more chromium (Alloy 690), based on corrosion results. SCC mechanisms are still in progress for a better prediction of the nickel base alloy susceptibility, linked to the extension of the service time of nuclear power plants from 40 years, as initially planned, to 60 years and probably more as expected now, In secondary circuits of PWRs, like for boiling water reactors, flow accelerated corrosion (FAC) has been and is still an industrial challenge linked to the design of the apparatus, thermohydraulics and water chemistry. The chemical composition of low alloyed steels (chromium content) is a major parameter for FAC. These 3 corrosion phenomena (general corrosion of cladding alloys, stress corrosion cracking of nickel base alloys and flow accelerated corrosion) sustain researches and developments to model corrosion phenomena at various scales, from atoms to components

Methods for in-flight robustness evaluation

The goal of this program was to combine modern control concepts with new identification techniques to develop a comprehensive package for estimation of 'robust flutter boundaries' based on experimental data. The goal was to use flight data, combined with a fundamental physical understanding of flutter dynamics, to generate a prediction of flutter speed and an estimate of the accuracy of the prediction. This report is organized as follows: the specific contributions of this project will be listed first. Then, the problem under study will be stated and the general approach will be outlined. Third, the specific system under study (F- 18 SRA) will be described and a preliminary data analysis will be performed. Then, the various steps of the flutter boundary determination will be outlined and applied to tile F-18 SRA data and others

Analysis and Modeling of Ground Operations at Hub Airports

Building simple and accurate models of hub airports can considerably help one understand airport dynamics, and may provide quantitative estimates of operational airport improvements. In this paper, three models are proposed to capture the dynamics of busy hub airport operations. Two simple queuing models are introduced to capture the taxi-out and taxi-in processes. An integer programming model aimed at representing airline decision-making attempts to capture the dynamics of the aircraft turnaround process. These models can be applied for predictive purposes. They may also be used to evaluate control strategies for improving overall airport efficiency.This research was supported in part by Honeywell, by an MIT teaching fellowship, and by NASA under grant NAG 2-1128 and through the National Center of Excellence for Aviation Operations Research (NEXTOR)

Subspace Identification with Multiple Data Sets

Most existing subspace identification algorithms assume that a single input to output data set is available. Motivated by a real life problem on the F18-SRA experimental aircraft, we show how these algorithms are readily adapted to handle multiple data sets. We show by means of an example the relevance of such an improvement

Statistically designed experiments to screen chemical mixtures for possible interactions.

For the accurate analysis of possible interactive effects of chemicals in a defined mixture, statistical designs are necessary to develop clear and manageable experiments. For instance, factorial designs have been successfully used to detect two-factor interactions. Particularly useful for this purpose are fractionated factorial designs, requiring only a fraction of all possible combinations of a full factorial design. Once the potential interaction has been detected with a fractionated design, a more accurate analysis can be performed for the particular binary mixtures to ensure and characterize these interactions. In this paper this approach is illustrated using an in vitro cytotoxicity assay to detect the presence of mixtures of Fusarium mycotoxins in contaminated food samples. We have investigated interactions between five mycotoxin species (Trichothecenes, Fumonisins, and Zearalenone) using the DNA synthesis inhibition assay in L929 fibroblasts. First, a central composite design was applied to identify possible interactive effects between mycotoxins in the mixtures (27 combinations from 5(5) possible combinations). Then two-factor interactions of particular interest were further analyzed by the use of a full factorial design (5 x 5 design) to characterize the nature of those interactions more precisely. Results show that combined exposure to several classes of mycotoxins generally results in effect addition with a few minor exceptions indicating synergistic interactions. In general, the nature of the interactions characterized in the full factorial design was similar to the nature of those observed in the central composite design. However, the magnitude of interaction was relatively small in the full factorial design

A Scalable Safety Critical Control Framework for Nonlinear Systems

There are two main approaches to safety-critical control. The first one relies on computation of control invariant sets and is presented in the first part of this work. The second approach draws from the topic of optimal control and relies on the ability to realize Model-Predictive-Controllers online to guarantee the safety of a system. In the second approach, safety is ensured at a planning stage by solving the control problem subject for some explicitly defined constraints on the state and control input. Both approaches have distinct advantages but also major drawbacks that hinder their practical effectiveness, namely scalability for the first one and computational complexity for the second. We therefore present an approach that draws from the advantages of both approaches to deliver efficient and scalable methods of ensuring safety for nonlinear dynamical systems. In particular, we show that identifying a backup control law that stabilizes the system is in fact sufficient to exploit some of the set-invariance conditions presented in the first part of this work. Indeed, one only needs to be able to numerically integrate the closed-loop dynamics of the system over a finite horizon under this backup law to compute all the information necessary for evaluating the regulation map and enforcing safety. The effect of relaxing the stabilization requirements of the backup law is also studied, and weaker but more practical safety guarantees are brought forward. We then explore the relationship between the optimality of the backup law and how conservative the resulting safety filter is. Finally, methods of selecting a safe input with varying levels of trade-off between conservatism and computational complexity are proposed and illustrated on multiple robotic systems, namely: a two-wheeled inverted pendulum (Segway), an industrial manipulator, a quadrotor, and a lower body exoskeleton

As variedades de arroz vermelho brasileiras.

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Mathematic Models for Aircraft Trajectory Design: A Survey

Presented at the 2013 ENRI International Workshop on ATM/CNS (EIWAC2013), Tokyo, Japan, February 2013.Air traffic management ensure the safety of flight by optimizing flows and maintaining separation between aircraft. After giving some definitions, some typical feature of aircraft trajectories are presented. Trajectories are objects belonging to spaces with infinite dimensions. The naive way to address such problem is to sample trajectories at some regular points and to create a big vector of positions (and or speeds). In order to manipulate such objects with algorithms, one must reduce the dimension of the search space by using more efficient representations. Some dimension reduction tricks are then presented for which advantages and drawbacks are presented. Then, front propagation approaches are introduced with a focus on Fast Marching Algorithms and Ordered upwind algorithms. An example of application of such algorithm to a real instance of air traffic control problem is also given. When aircraft dynamics have to be included in the model, optimal control approaches are really efficient. We present also some application to aircraft trajectory design. Finally, we introduce some path planning techniques via natural language processing and mathematical programming