Which Broadcast Abstraction Captures k-Set Agreement?

It is well-known that consensus (one-set agreement) and total order broadcast are equivalent in asynchronous systems prone to process crash failures. Considering wait-free systems, this article addresses and answers the following question: which is the communication abstraction that "captures" k-set agreement? To this end, it introduces a new broadcast communication abstraction, called k-BO-Broadcast, which restricts the disagreement on the local deliveries of the messages that have been broadcast (1-BO-Broadcast boils down to total order broadcast). Hence, in this context, k=1 is not a special number, but only the first integer in an increasing integer sequence. This establishes a new "correspondence" between distributed agreement problems and communication abstractions, which enriches our understanding of the relations linking fundamental issues of fault-tolerant distributed computing

The unscripted image

This article examines realism in the films of Ken Loach and Mike Leigh, comparing and relating the two director's distinct processes to the procedure of making a painting that represents everyday life. In particular, the article positions painting from found photographs as akin to making a film based on a very tight script and predetermined narrative (Loach). Leigh's mode of arriving at narrative, subject and meaning through devising is compared to painting from memory and experience without a constraint on outcome. The article references Ricoeur's proposals that narrative structures impose linear histories and Carel Weight's narrative paintings

Organogel formation rationalized by Hansen solubility parameters: improved methodology

International audienceAn organogel is obtained when a low molar mass compound forms a network of anisotropic fibres in a liquid that is therefore transformed into a macroscopic solid. Various approaches have been proposed to correlate organogel formation and Hansen solubility parameters. These approaches are well adapted to specific experimental datasets but lack universality. A general method to determine the gelation domain from the solubility data of low molecular weight gelators is here reported

D.1.2 – Modular quasi-causal data structures

GDD_HCERES2020In large scale systems such as the Internet, replicating data is an essential feature in order to provide availability and fault-tolerance. Attiya and Welch proved that using strong consistency criteria such as atomicity is costly as each operation may need an execution time linear with the latency of the communication network. Weaker consistency criteria like causal consistency and PRAM consistency do not ensure convergence. The different replicas are not guaranteed to converge towards a unique state. Eventual consistency guarantees that all replicas eventually converge when the participants stop updating. However, it fails to fully specify the semantics of the operations on shared objects and requires additional non-intuitive and error-prone distributed specification techniques. In addition existing consistency conditions are usually defined independently from the computing entities (nodes) that manipulate the replicated data; i.e., they do not take into account how computing entities might be linked to one another, or geographically distributed. In this deliverable, we address these issues with two novel contributions. The first contribution proposes a notion of proximity graph between computing nodes. If two nodes are connected in this graph, their operations must satisfy a strong consistency condition, while the operations invoked by other nodes are allowed to satisfy a weaker condition. We use this graph to provide a generic approach to the hybridization of data consistency conditions into the same system. Based on this, we design a distributed algorithm based on this proximity graph, which combines sequential consistency and causal consistency (the resulting condition is called fisheye consistency). The second contribution of this deliverable focuses on improving the limitations of eventual consistency. To this end, we formalize a new consistency criterion, called update consistency, that requires the state of a replicated object to be consistent with a linearization of all the updates. In other words, whereas atomicity imposes a linearization of all of the operations, this criterion imposes this only on updates. Consequently some read operations may return outdated values. Update consistency is stronger than eventual consistency , so we can replace eventually consistent objects with update consistent ones in any program. Finally, we prove that update consistency is universal, in the sense that any object can be implemented under this criterion in a distributed system where any number of nodes may crash

DUCK : a deDUCtive Keyboard

Abstract This paper presents the deDUCtive Keyboard (DUCK), aiming to improve text entry for visually impaired users on AZERTY/QWERTY based layout on software keyboards. Relying on a predictive system, DUCK allows rapid text entry without any precision on keyboard hits. A preliminary study with a visually impaired user indicated that usability is improved when compared to a regular virtual keyboard with a vocal feedback

Evaluation of the DMX Process for Industrial Pilot Demonstration – Methodology and Results

The SP3 Subproject of the OCTAVIUS EU FP7 project was dedicated to the demonstration of the DMX CO2 capture process, developed by IFP Energies nouvelles (IFPEN) and licensed by PROSERNAT, on the 3.5 MWe equivalent industrial pilot of ENEL at Brindisi. The DMX process is based on the particular property of demixing solvents to form, for specific CO2 loadings and temperature conditions, two immiscible liquid phases. The light phase being almost free of CO2, only the high capacity heavy phase is sent to the stripper, which makes possible energy savings but also requires an adapted process flow scheme and extra equipment. Prior to launch the corresponding retrofit and perform the pilot tests, two conditions were settled. First, a quantitative evaluation of the process must show a significant interest in comparison with the benchmark MEA 30wt.%. To evaluate this first conditions, 24 criteria were considered. Second, an acceptable cost for the retrofit of the existing industrial pilot, determined from a Front End Engineering and Design (FEED) study must be obtained. Most of this paper deals with the evaluation of these two conditions which ended in November 2013 and a small section is dedicated to the FEED study. It is shown that most of the parameters considered for the process evaluation are in good agreement with the initial targets. The proposed evaluation methodology could be used for any new process prior to demonstration. © 2013 The Authors. Published by Elsevier Ltd. Selection and peer-review under responsibility of GHGT

Nouvelles classes de ligands et complexes métalliques pour la fonctionnalisation d'alcanes par activation C-H

Des catalyseurs homogènes efficaces pour la déshydrogénation d'alcanes cycliques et [1] linéaires ont été développés depuis 1996.Ils sont basés sur l'utilisation d'un complexe de l'iridium coordiné par un ligand tridente bis(phosphine) {Ir PCP} A ou bis(phosphinite) {Ir POCOP} B (Schéma 1). Le but de ce travail était de synthétiser les analogues carbènes N hétérocycliques (NHCs) de ces complexes (molécules cibles C, Schéma 1), de les caractériser et de les évaluer dans des réactions tests de déshydrogénation d'alcanes, réaction qui représente un enjeu scientifique et économique important. Les carbènes N hétérocycliques ont été choisis pour leurs caractéristiques électroniques particulières. En effet, ce sont des ligands à caractère fortement donneur capables de [2] stabiliser les ions métalliques de façon plus importante que les trialkylphosphines.Ainsi, [3]l énergie de dissociation de la liaison NHC métal est particulièrement élevée.Ces propriétés sont très importantes pour la catalyse : la présence de ligands NHCs dans la sphère de coordination d'un métal permet d'augmenter la densité électronique sur ce métal. Ceci peut faciliter le processus d'addition oxydante qui est une étape clé dans de nombreux systèmes catalytiques et notamment dans la fonctionnalisation d'alcanes. la liaison carbène métal est forte ce qui permet d'éviter des problèmes liés à la perte de ligands pendant la catalyse. Dans le cas des complexes de type {Ir PCP} et {Ir POCOP} le ligand se comporte comme une pince vis à vis du métal. Les ligands pince sont des ligands chélatants rigides qui sont connus pour stabiliser fortement les ions métalliques. Les complexes résultants sont thermostables ce qui permet leur utilisation sans dégradation à des températures élevées (200 à 250°C pour les complexes pince {Ir PCP} par exemple).Les complexes métalliques qui contiennent des ligands plans, rigides et tridentes incorporant au moins un motif NHC ont été intensivement étudiés durant les dix dernières années et possèdent des propriétés catalytiques uniques.Pourtant, au début du projet, aucun complexe de l'iridium de ce type n avait été reporté.Le travail réalisé a permis de développer une voie de synthèse de nouveaux complexes dicarbènes N hétérocycliques pince et hydrure de l'iridium(III) (Schéma 2, molécules 1 2).Hollis et al avaient reporté la synthèse du dimère à pont iode 3 (Schéma 2) en 2 étapes avec un rendement < 50%.Notre procédure est plus générale et permet d'obtenir les complexes attendus 1 2 en une seule étape depuis les sels de bis(imidazolium) correspondants avec un rendement d'environ 70%. Les analogues diiodures 4 6 ont été également isolés mais avec des rendements d'environ 30% (Schéma 2). Les conditions opératoires permettant de préparer les complexes 1 2 et 4 6 ont été étudiées de façon précise. Plusieurs paramètres [la nature du précurseur bis(imidazolium), la nature et la quantité de base, la température, la présence de KI et le temps de réaction] influencent fortement la quantité et la nature des complexes obtenus. Des intermédiaires réactionnels dans la synthèse des complexes pince 1 2 ont été isolés et un mécanisme réactionnel décrivant leur formation a été proposé. Le dicarbène libre 7, remarquablement stable à température ambiante, a été préparé et sa réactivité avec l'iridium a permis d'obtenir des complexes mononucléaires et dinucléaires dans lequel le ligand est pontant et non pas chélatant ou pince comme attendu a priori (Schéma 3).Le complexe hétérodinucléaire Ir(I) Rh(I) 8, qui constitue un exemple rare de complexe bimétallique porteur d'un ligand NHC, a été synthétisé en deux étapes depuis 7. La structure inattendue du complexe 9 révèle une topologie particulière en figure de huit,qui permet de remettre en cause des structures chélates proposées dans la littérature pour des complexes analogues (Schéma 3). L'influence de la nature de la base sur la synthèse de complexes NHC a été peu mentionnée dans la littérature.Nous avons montré que la formation de complexes mononucléaires et dinucléaires Ir NHC était plus rapide lorsque Cs2CO3 était utilisée à la place de NEt3 et donnait des rendements plus élevés pour un temps de réaction donné.Pour la synthèse du complexe 9, le choix de la base est encore plus crucial, puisque le complexe n est formé que lorsque Cs2CO3 est utilisé. Deux chemins réactionnels sont concevables pour la formation de la liaison Ir NHC dans ces complexes : soit un processus combiné d'addition oxydante de la liaison C(2) H de l'imidazolium sur le précurseur d'iridium suivi de l'élimination réductrice de HX assistée par la base soit formation du carbène libre et coordination in situ sur le centre d'Ir(I). Dans ce dernier cas, la basicité intrinsèque de Cs2CO3 est supérieure à celle de la NEt3 et représente un avantage pour engendrer le carbène libre. Autre avantage, la protonation du carbène libre par l'acide conjugué de Cs2CO3 est moins facile que la réaction entre le carbène libre et [HNEt3]+X. Comme mentionné plus haut, nous avons envisagé une application des nouveaux complexes pince de l'iridium synthétisés comme catalyseurs pour des réactions de fonctionnalisation d'alcanes. Dans un premier temps, nous avons calibré nos conditions opératoires à l'aide d'un précurseur de référence {Ir POCOP}. Nous avons ensuite testé les complexes 1 2 et 4 6, dans différentes conditions, mais aucune activité significative n a été observée pour le transfert déshydrogénant du cyclooctane en présence de tert butyléthylène comme oléfine acceptrice. Plusieurs pistes ont été envisagées pour la mise au point d'un nouveau catalyseur actif pour des réactions de fonctionnalisation d'alcanes. Le travail actuel s'oriente vers la synthèse d'un complexe NHC pince de l'iridium(III) à 16 électrons (et non 18 électrons comme dans les complexes 1 2, 4 6). Deux stratégies sont en cours d'étude au laboratoire : (a) la synthèse d'un complexe D (Schéma 4) possédant un ligand mixte NHC/donneur P dans lequel les groupements sur le phosphore viendraient apporter l'encombrement nécessaire à la stabilisation d'un complexe à 16 électrons,(b) l'augmentation de l'encombrement stérique des NHC en jouant sur la nature des groupements (par exemple un motif adamantyl) portés par les azotes (E, Schéma 4). Enfin, les perspectives du travail réalisé incluent l'utilisation des complexes NHC d'iridium synthétisés comme catalyseurs dans d'autres réactions telles que l'hydrogénation d'alcènes trisubstitués,le transfert hydrogénantou l'oxydation d'alcoolsde type Oppenauer. Des modifications au niveau du ligand doivent permettre d'envisager une utilisation en catalyse assymétrique (hydrogénation, transfert hydrogénant ou hydrosilylation).Des complexes NHC de Rh (hydroformylation et hydroaminomethylation des alcènes) et de Cr (oligomérisation de l'éthylène) ont également trouvés des applications importantes.Highly active homogeneous catalysts for the dehydrogenation of linear and cyclic alkanes have been developed since 1996. These iridium complexes contained a tridentate bis(phosphine) [for {Ir PCP}, A] or bis(phosphinite) ligand [for {Ir POCOP}, B] (Scheme 1).The goal of this work was to synthesize and characterize N heterocyclic carbenes (NHC) analogues of these complexes (target molecules C, Scheme 1) and to evaluate their activity in alkane dehydrogenation reactions. The transformation of alkanes into alkenes represents a very important reaction, both scientifically and economically. N heterocyclic carbenes were chosen for their unique stereroelectronic properties. Indeed, NHCs are even better donors than trialkylphosphines and can strongly stabilize metal ions.Thus, the dissociation energy of the M NHC bond is particularly high.The features of NHC ligands are important for catalytic applications: the presence of NHC ligands in the coordination sphere of the metal increases the electron density around the metal center. This facilitates the oxidative addition process which is a key step in numerous catalytic systems and notably in the functionalization of alkanes. the fact that the M NHC bond is strong limits the loss of ligand during the catalytic process. In {Ir PCP} and {Ir POCOP} complexes, the ligand acts as a pincer for the metal. Pincer ligands are rigid, chelating ligands which strongly stabilize metal ions. The resulting homogeneous complexes are thermostable and can be used at relatively high temperatures (200 250°C for {Ir PCP} pincer complexes for example) without degradation. Metal complexes with pincer, planar and rigid ligands which incorporate at least one NHC functionality have been intensively studied during the last ten years and exhibit unique catalytic properties.However, at the beginning of this project, no NHC pincer complex of iridium was reported in the literature.We have developed a synthetic route towards new hydrido, N heterocyclic dicarbene iridium(III) pincer complexes (Scheme 2, molecules 1 2). Hollis et al reported the preparation of the iodide bridged dimer CNHCCCNHC iridium complex 3 (Scheme 2) in 2 steps with a yield inferior to 50%.Our method provides a more direct route and allows the synthesis of the expected complexes 1 2 in one step from the corresponding bis(imidazolium) salts in almost 70% yield. The diiodide analogues 4 6 were also isolated in almost 30% yield (Scheme 2).Experimental conditions used to prepare complexes 1 2 and 4 6 were thoroughly investigated. The influence of several parameters [nature of the bis(imidazolium) precursor, nature and amount of base, temperature, addition of KI and reaction time] on the course of the formation of NHC complexes and on the nature of the complexes was demonstrated. Reaction intermediates in the synthesis of pincer complexes were isolated and a possible mechanism for their formation was suggested. The NHC dicarbene ligand 7, remarkably stable at room temperature, was prepared and its reaction towards several iridium precursors yielded mono and dinuclear iridium complexes in which the ligand acts as a bridge and no as a chelate or a pincer as might have been anticipated (Scheme 3).The heterodinuclear Ir(I) Rh(I) complex 8, which constitutes a rare example of heterobimetallic complex with a NHC ligand, was synthesized in two steps from 7. The unprecedented and unexpected structure of 9, which possesses a remarkable figure of eight topology,is useful in order to reconsider some chelate structures postulated in the literature for similar complexes (Scheme 3).Only a few comparative studies dealing with the influence of the nature of the weak base on the course of the formation of NHC complexes have been disclosed in the literature.We were able to demonstrate that higher yields of mono and dinuclear NHC complexes were obtained, for a given reaction time, when Cs2CO3 was used in place of NEt3. For the synthesis of the dinuclear complexes 9, the choice of the base is even more critical, because products are formed only when Cs2CO3 is used. Two different pathways are conceivable for the formation of the Ir NHC bond in our complexes: either a combined oxidative addition/HX base assisted elimination process or the formation of the fre carbene and its in situ coordination to the Ir(I) center. In the latter case, the higher intrinsic basicity of Cs2CO3 compared to NEt3 would represent an advantage for the generation of a fre carbene. Moreover, protonation of the fre carbene by the conjugate acid of Cs2CO3 is less likely than the reaction between fre carbene and [HNEt3]+X . As mentioned above, we envisaged to use our iridium pincer complexes as catalysts for the functionalization of alkanes. Firstly, we calibrated our experimental conditions with a precursor of reference {Ir POCOP}. Then, we tested 1 2 and 4 6, under different conditions, but no significant activity was observed for the transfer dehydrogenation of cyclooctane with tert butylethylene as olefin acceptor. Several pathways were envisaged to obtain an active catalyst. We are focusing on the synthesis of CNHCCCNHC 16 electron iridium(III) pincer complexes (in contrast to 18 electron complexes 1 2 and 4 6). We are currently studying in the laboratory: (a) the preparation of a complex D (Scheme 4) containing a mixed donor phosphorus NHC ligand in which the phosphorus substituents can provide the steric hindrance necessary to stabilize a 16 electron iridium(III) complex,(b) the increase of the steric hindrance of the NHC ligand by replacing, for example, the n butyl group by adamantyl groups on the nitrogen of the imidazole rings (E, Scheme 4). Finally, the perspectives of this work include the use of our Ir NHC complexes as catalysts for other reactions such as the hydrogenation of trisubstituted alkenes,transfer hydrogenationsor the Oppenauer type oxidationof alcohols. Modifications of the ligand architecture can lead to envisage applications of our complexes in asymmetric catalysis (hydrogenation, transfer hydrogenation or hydrosilylation).Rh NHC complexes (hydroformylation or hydroaminomethylation of alkenes) or Cr NHC complexes (ethylene oligomerisation) can also find outstanding applications