Creep behaviour of as received, aged and cold worked INCONEL 617 at 850 °C and 950 °C

The effect of initial microstructure on alloy 617 creep behaviour has been investigated at 850 °C and 950 °C. The solution treated material shows non-classical creep behaviour at both temperatures with a strain rate drop at the beginning of the tests followed by a creep rate increase to a plateau before the onset of the tertiary creep. The intragranular secondary carbides which precipitate early at test temperature are responsible of the strong initial hardening effect by pinning the dislocations. This effect is overpassed during the thermo mechanical ageing of the alloy which induces growth of these carbides. Prior 1000 h thermal ageing at the temperature test totally removes the strain rate drop and reduces the lifetime. The intragranular microstructure has evolved thanks to the prior thermal ageing before the creep tests. Microstructural examinations also show the presence of grain boundary migration and recrystallization in the material during creep tests of the as received and aged materials. Preliminary cold work treatment highly reduces the strain rate of Inconel 617 and enhances the lifetime at 850 °C while the opposite is observed at 950 °C

Saddle Points and Stark Ladders: Exact Calculations of Exciton Spectra in Superlattices

A new, exact method for calculating excitonic absorption in superlattices is described. It is used to obtain high resolution spectra showing the saddle point exciton feature near the top of the miniband. The evolution of this feature is followed through a series of structures with increasing miniband width. The Stark ladder of peaks produced by an axial electric field is investigated, and it is shown that for weak fields the line shapes are strongly modified by coupling to continuum states, taking the form of Fano resonances. The calculated spectra, when suitably broadened, are found to be in good agreement with experimental results.Comment: 9 pages Revtex v3.0, followed by 4 uuencoded postscript figures, SISSA-CM-94-00

Evidence-Based Treatment Options in Recurrent and/or Metastatic Squamous Cell Carcinoma of the Head and Neck.

The major development of the past decade in the first-line treatment of recurrent and/or metastatic squamous cell carcinoma of the head and neck (R/M SCCHN) was the introduction of cetuximab in combination with platinum plus 5-fluorouracil chemotherapy (CT), followed by maintenance cetuximab (the EXTREME regimen). This regimen is supported by a phase 3 randomized trial and subsequent observational studies, and it confers well-documented survival benefits, with median survival ranging between approximately 10 and 14 months, overall response rates between 36 and 44%, and disease control rates of over 80%. Furthermore, as indicated by patient-reported outcome measures, the addition of cetuximab to platinum-based CT leads to a significant reduction in pain and problems with social eating and speech. Conversely, until very recently, there has been a lack of evidence-based second-line treatment options, and the therapies that have been available have shown low response rates and poor survival outcomes. Presently, a promising new treatment option in R/M SCCHN has emerged: immune checkpoint inhibitors (ICIs), which have demonstrated favorable results in second-line clinical trials. Nivolumab and pembrolizumab are the first two ICIs that were approved by the US Food and Drug Administration. We note that the trials that showed benefit with ICIs included not only patients who previously received ≥1 platinum-based regimens for R/M SCCHN but also patients who experienced recurrence within 6 months after combined modality therapy with a platinum agent for locally advanced disease. In this review, we outline the available clinical and observational evidence for the EXTREME regimen and the initial results from clinical trials for ICIs in patients with R/M SCCHN. We propose that these treatment options can be integrated into a new continuum of care paradigm, with first-line EXTREME regimen followed by second-line ICIs. A number of ongoing clinical trials are comparing regimens with ICIs, alone and in combination with other ICIs or CT, with the EXTREME regimen for first-line treatment of R/M SCCHN. As we eagerly await the results of these trials, the EXTREME regimen remains the standard of care for the first-line treatment of R/M SCCHN

Effects of Age and Task Load on Drivers’ Response Accuracy and Reaction Time When Responding to Traffic Lights

International audienceDue to population aging, elderly drivers represent an increasing proportion of car drivers. Yet, how aging alters sensorimotor functions and impacts driving safety remains poorly understood. This paper aimed at assessing to which extent elderly drivers are sensitive to various task loads and how this affects the reaction time (RT) in a driving context. Old and middle-aged people completed RT tasks which reproduced cognitive demands encountered while driving. Participants had to detect and respond to traffic lights or traffic light arrows as quickly as possible, under three experimental conditions of incremental difficulty. In both groups, we hypothesized that decision-making would be impacted by the number of cues to be processed. The first test was a simple measure of RT. The second and third tests were choice RT tasks requiring the processing of 3 and 5 cues, respectively. Responses were collected within a 2 s time-window. Otherwise, the trial was considered a no-response. In both groups, the data revealed that RT, error rate (incorrect answers), and no-response rate increased along with task difficulty. However, the middle-aged group outperformed the elderly group. The RT difference between the two groups increased drastically along with task difficulty. In the third test, the rate of no-response suggested that elderly drivers needed more than 2 s to process complex information and respond accurately. Both prolonged RT and increased no-response rate, especially for difficult tasks, might attest an impairment of cognitive abilities in relation to aging. Accordingly, casual driving conditions for young drivers may be particularly complex and stressful for elderly people who should thus be informed about the effects of normal aging upon driving

Electronic structure of intentionally disordered AlAs/GaAs superlattices

We use realistic pseudopotentials and a plane-wave basis to study the electronic structure of non-periodic, three-dimensional, 2000-atom (AlAs)_n/(GaAs)_m (001) superlattices, where the individual layer thicknesses n,m = {1,2,3} are randomly selected. We find that while the band gap of the equivalent (n = m = 2) ordered superlattice is indirect, random fluctuations in layer thicknesses lead to a direct gap in the planar Brillouin zone, strong wavefunction localization along the growth direction, short radiative lifetimes, and a significant band-gap reduction, in agreement with experiments on such intentionally grown disordered superlattices.Comment: 10 pages, REVTeX and EPSF macros, 4 figures in postscript. e-mail to [email protected]

Multifractal analysis of the electronic states in the Fibonacci superlattice under weak electric fields

Influence of the weak electric field on the electronic structure of the Fibonacci superlattice is considered. The electric field produces a nonlinear dynamics of the energy spectrum of the aperiodic superlattice. Mechanism of the nonlinearity is explained in terms of energy levels anticrossings. The multifractal formalism is applied to investigate the effect of weak electric field on the statistical properties of electronic eigenfunctions. It is shown that the applied electric field does not remove the multifractal character of the electronic eigenfunctions, and that the singularity spectrum remains non-parabolic, however with a modified shape. Changes of the distances between energy levels of neighbouring eigenstates lead to the changes of the inverse participation ratio of the corresponding eigenfunctions in the weak electric field. It is demonstrated, that the local minima of the inverse participation ratio in the vicinity of the anticrossings correspond to discontinuity of the first derivative of the difference between marginal values of the singularity strength. Analysis of the generalized dimension as a function of the electric field shows that the electric field correlates spatial fluctuations of the neighbouring electronic eigenfunction amplitudes in the vicinity of anticrossings, and the nonlinear character of the scaling exponent confirms multifractality of the corresponding electronic eigenfunctions.Comment: 10 pages, 9 figure

Montagnes en bataille. Une géopolitique du refuge depuis la vallée de la Clarée

A la fin du xxe siècle, plusieurs grands projets d’aménagement du Briançonnais ont été mis en déroute par diverses mobilisations collectives. De nouvelles initiatives contestent désormais la ségrégation socio-spatiale des personnes exilées qui tentent de traverser la frontière en dépit de leur militarisation violente et dans un contexte de médiatisation sensationnaliste des évènements. Cet article étudie les discours produits autour de ces luttes ainsi que l’essor de certaines mémoires, et en particulier celle d’Émilie Carles (1900 - 1979). Il considère leur impact sur les perceptions de la « montagne » en faisant l’hypothèse qu’ils peuvent participer aux dynamiques d’essentialisation des espaces montagneux et de naturalisation de leurs habitant·es. Ses conclusions montrent que le thème de la « montagne-refuge » est réactivé et enrichi par le travail politique des mémoires locales. A travers une approche de géographie critique, cet article contribue aux réflexions sur le devenir des espaces montagneux en déployant une analyse politique des figures du refuge et en articulant les questions de l’exil et de l’écologie.Toward the end of the 20th century, several major development projects that had been proposed in the Briançon area were defeated thanks to collective mobilization efforts. New initiatives now challenge the socio-spatial segregation of exiled people who are trying to cross the border amid the latter’s heavy militarization and in the context of the sensationalist coverage of events by the media. This article examines the discourses produced around these struggles, as well as people’s memories –in particular, that of Émilie Carles (1900–1979). The article considers their impact on how the “mountain” is perceived and hypothesizes that it can play a role in the dynamics of how mountain spaces are essentialized and their inhabitants naturalized. We find that the theme of a “mountain-refuge” is reactivated and enriched by the political work done by local memories. Through a critical geographical approach, this article carries out a political analysis of the figures of the mountain-refuge and links the issues of exile and ecology in order to contribute to thinking on the future of mountain areas

Etude des évolutions microstructurales et comportement mécanique des alliages base nickel 617 et 230 à haute température

Dans le cadre du développement des Réacteurs à Haute Température (RHT), un des systèmes retenus pour la quatrième génération de centrale nucléaire, l’utilisation d’un cycle indirect est envisagée. Ce type d’installation, utilisant de l’hélium comme caloporteur, nécessite un échangeur intermédiaire de chaleur (Intermediate Heat eXchanger, IHX) le plus compact possible entre les circuits primaire et secondaire. Les contraintes imposées par la conception ainsi que les conditions sévères d’utilisation pour ce type d’installation (température maximale 850°C à 950°C, durée de vie 20000 h) ont orienté le choix des matériaux constitutifs de l’IHX vers deux alliages base nickel en solution solide : l’Inconel 617 et le Haynes 230. Le premier matériau a été largement étudié dans les années 1980 lors du projet allemand sur les RHT car possédant de bonnes propriétés mécaniques et en corrosion à haute température mais sa forte teneur en cobalt potentiellement activable est à considérer. Le Haynes 230, plus récent, possède des caractéristiques similaires à celles de l’alliage 617, le cobalt ayant été remplacé par du tungstène. L’objectif de cette thèse est d’étudier le comportement mécanique à haute température de ces deux alliages en relation avec les évolutions de leur microstructure. Les observations microstructurales à l’état de réception révèlent la présence de carbures primaires (M6C), la majorité étant répartie de manière homogène. Des carbures secondaires M23C6, peu nombreux, sont visibles à l’état de réception pour les deux matériaux. Les vieillissements thermiques imposés aux alliages à 850°C permettent une précipitation importante de carbures M23C6 sur les lignes de glissement et aux joints de grains, la taille de ces carbures augmentant et leur nombre réduisant avec la durée de traitement. A 950°C, l’évolution microstructurale conduit à une précipitation intragranulaire beaucoup plus limitée et à une évolution intergranulaire plus importante. Pour les deux matériaux, les observations de la microstructure et les résultats de dureté montrent que la majorité des évolutions microstructurales se produisent avant 1000 h aux deux températures étudiées. Les caractéristiques mécaniques de ces alliages ont été testées en traction, en fluage et en fatigue et fatigue relaxation. En particulier, les propriétés à 850°C et 950°C ont été étudiées pour différentes charges (en fluage), vitesses de déformation (en traction) et durées de relaxation (fatigue relaxation). Les effets d’un traitement initial ont également été étudiés, tels que l’effet d’un vieillissement thermique testé en fluage et traction et l’effet d’une prédéformation sur le fluage. Il ressort de cette étude que différents mécanismes de déformation sont mis en jeu successivement ou en parallèle au cours des essais réalisés. Ainsi, l’importance de la précipitation des carbures sur les propriétés mécaniques de l’Inconel 617 et du Haynes 230 a pu être démontrée, malgré leur statut d’alliages en solution solide. Par ailleurs, un même mécanisme thermiquement activé opère sur une très large gamme de vitesses de déformation, correspondant aux essais de traction, fluage et relaxation. Cette mise en relation entre microstructure et propriétés mécaniques permet de déterminer les avantages de chaque alliage ainsi que leurs limites d’utilisation dans le cadre de la fabrication d’un échangeur de chaleur de centrale nucléaire. ABSTRACT : High Temperature Reactors (HTR), is one of the innovative nuclear reactor designed to be inherently safer than previous generation and to produce minimal waste. The most critical metallic component in that type of reactor is the Intermediate Heat eXchanger (IHX). The constraints imposed by the conception and the severe operational conditions (high temperature of 850°C to 950°C, lifetime of 20,000 h) have guided the IHX material selection toward two solid solution nickel base alloys, the Inconel 617 and the Haynes 230. Inconel 617 is the primary candidate alloy thanks to its good high temperature mechanical and corrosion properties and the large data base developed in previous programs. However, its high cobalt content has to be considered as an issue (nuclear activation). The more recent alloy Haynes 230, in which most of the cobalt has been replaced by tungsten, present characteristics similar to the 617 alloy. The objective of this thesis is to study the high temperature mechanical behaviour of both alloys in relation with their microstructural evolutions. The as received microstructural observations have revealed primary carbides (M6C). Most of this precipitates are evenly distributed in the materials. Few M23C6 secondary carbides are observed in both alloys in the as received state. Thermal ageing treatments at 850°C lead to an important M23C6 precipitation on slip lines and at grain boundaries. The size of this carbides increases and their number decreases with increasing ageing duration. The intragranular precipitation of secondary carbides at 950°C is more limited and the intergranular evolution more important than at 850°C. The microstructural observations and the hardness evolution of both alloys show that the main microstructural evolutions occur before 1,000 h at both studied temperatures. The mechanical properties of the Inconel 617 and the Haynes 230 have been studied using tensile, creep, fatigue and relaxation-fatigue tests. Particularly, the properties at 850°C and 950°C have been evaluated using several stress levels (creep), strain rates (tensile) and relaxation duration (fatigue). The effects of initial treatments have also been studied, i.e.ageing treatments effects on creep and tensile properties and cold-work effects on creep properties. At high temperature, the as received Inconel 617 does not show classical creep behaviour. This study shows the importance of the fast carbides precipitation on their mechanical properties, despite the fact that the Inconel 617 and the Haynes 230 are listed as solid solution alloys. Low cycle fatigue tests with and without holding time have been performed at 850°C under air and under vacuum on both alloys. The results showed that cyclic hardening, cyclic stability and life time are closely related to the duration of the holding time. Furthermore, a single thermally activated mechanism operates over a very wide range of strain rates, corresponding to tensile tests, creep and relaxation. The link between microstructure and mechanical behaviour presented in this thesis helps to determine the advantages as the operation limits of each alloy in order to manufacture a nuclear power plant heat exchange

Mountains at Work. The Geopolitics of Refuge in the Clarée Valley

Toward the end of the 20th century, several major development projects that had been proposed in the Briançon area were defeated thanks to collective mobilization efforts. New initiatives now challenge the socio-spatial segregation of exiled people who are trying to cross the border amid the latter’s heavy militarization and in the context of the sensationalist coverage of events by the media. This article examines the discourses produced around these struggles, as well as people’s memories – in particular, that of Émilie Carles (1900–1979). The article considers their impact on how the “mountain” is perceived and hypothesizes that it can play a role in the dynamics of how mountain spaces are essentialized and their inhabitants naturalized. We find that the theme of a “mountain-refuge” is reactivated and enriched by the political work done by local memories. Through a critical geography approach, this article carries out a political analysis of the figures of the mountain-refuge and links the issues of exile and ecology in order to contribute to thinking on the future of mountain areas

Binding of biexcitons in GaAs/AlxGa1-xAs superlattices

Binding of the heavy-hole excitons and biexcitons in GaAs/Al0.3Ga0.7As superlattices is studied using linear and nonlinear optical techniques. High biexciton binding energies characteristic of quasi two-dimensional biexcitons are observed in superlattices with considerable miniband dispersion