Policy gradient methods for free-electron laser and terahertz source optimization and stabilization at the FERMI free-electron laser at Elettra

In this article we report on the application of a model-free reinforcement learning method to the optimization of accelerator systems. We simplify a policy gradient algorithm to accelerator control from sophisticated algorithms that have recently been demonstrated to solve complex dynamic problems. After outlining a theoretical basis for the functioning of the algorithm, we explore the small hyperparameter space to develop intuition about said parameters using a simple number-guess environment. Finally, we demonstrate the algorithm optimizing both a free-electron laser and an accelerator-based terahertz source in-situ. The algorithm is applied to different accelerator control systems and optimizes the desired signals in a few hundred steps without any domain knowledge using up to five control parameters. In addition, the algorithm shows modest tolerance to accelerator fault conditions without any special preparation for such conditions

Coping among Students: Development and validation of an exploratory measure

Students is a very specific population according to their manner to cope with stress. A coping questionnaire for students was developed and administered to 1100 French students at the beginning of the term (T1). Principal Component Analysis of responses, followed by varimax rotations, yielded three factors accounting for 50.5% of the total variance. Factors were identified as seeking social support, avoidance/emotion-focused coping and festive-addictive coping. Associations were observed between scores on these factors and a general coping scale (WCC-R), personal variables measured at the same time (T1), neuroticism, self-esteem, substance use, and four stress factors, as well as variables measured at the end of the term (T2), somatic symptoms, depressive symptoms, eating disorders, and life satisfaction. It would be very interesting to develop the students' personal competencies, so that they are learning how to adopt functional strategies of coping rather than of the harmful kind

Coupling multiphysics problems in transient regimes: application to liquid resin infusion process

Liquid resin infusion (LRI) process is widely considered in the aeronautics, due to its benefits (low void content and production of large parts), for high performance composite material forming. The main objective of the present work is to simulate nu- merically the LRI process, in a high performance computing framework, which consists in coupling fluid-solid mechanics. Hence, two fluid flow regimes are coupled with an ef- ficient ASGS stabilized monolithic finite element formulations: the resin flow in both a highly permeable distribution medium (Stokes) and low permeability fibrous orthotropic preforms (Darcy). Moreover, weak coupling algorithms are used along for coupling solid / fluid mechanics, solid / level-set problems and fluid / level-set problems; where the level-set method is used to capture the moving flow front and the Stokes-Darcy interface. To transfer the different physical variables between the above coupled problems, Message Passing Interface (MPI) library is chosen, to ensure the best data transfer performances

3D simulation of the matter transport by surface diffusion within a level-set context

International audienceWithin the framework of the sintering process simulation, this paper proposes a numerical strategy for the direct simulation of the matter transport by surface diffusion. A level-set method is used to describe the topological changes which arise at the free boundary of the sintering particles. The surface velocity is found to be proportional to the surface Laplacian of the curvature, that is, proportional to the fourth-order derivative of the level-set function. Consequently, both curvature and velocity must be computed carefully and with accuracy. Finally, three-dimensional simulations are shown and investigated

Rôle de certains facteurs psychosociaux dans la réussite universitaire d’étudiants de première année

En France, le taux d’échec en 1re année d’université est élevé (50 % environ), ce qui est dû probablement aux difficultés jalonnant ce passage. Nous avons évalué en T1 (rentrée universitaire) diverses caractéristiques psychosociales (prédicteurs) sur un échantillon de 421 étudiants entrant en première année dans les quatre universités de Bordeaux. Les étudiants ont été classés dans deux groupes (réussite ou échec) selon leurs résultats aux examens en T2 (critère mesuré en fin d’année). Les étudiants qui réussissent en T2 avaient en T1 un score plus élevé d’affectivité positive et un score plus faible d’impulsivité que ceux qui échouent. Des régressions logistiques multivariées ont été calculées entre prédicteurs et critères. Les étudiants qui réussiront ont plus d’affectivité positive et moins d’impulsivité ; ils utilisent moins, face aux problèmes de rentrée universitaire, un coping centré sur le problème.In France, the failure rate in first year at university is high (about 50%), which is probably due to the difficulties punctuating this transition. In T1 (beginning of the term), we assessed some psychosocial characteristics (predictors) in a sample of 421 freshmen of the four universities of Bordeaux. These students were classified in two groups (success or failure), according to their exams results in T2 (criterion measured at the end of the school year). Students who succeed in T2 had in T1 a higher score in positive affectivity and a lower score in impulsiveness than those who failed. Multivariate logistic regressions were calculated between predictors and criterion. The students who will pass their exams are less impulsive and experiment more positive affects; they use less focused-problem coping to face the beginning of the term

L’ajustement au stress professionnel chez les enseignants français du premier degré

Nous avons administré à 410 enseignants français en école élémentaire une adaptation française du questionnaire de Dewe (1985) au 1er trimestre d’une année scolaire (T1) pour évaluer leurs réponses de coping, ainsi que d’autres outils mesurant divers antécédents situationnels (fréquence des difficultés professionnelles) et personnels (auto-efficacité générale, caractéristiques socio-démographiques). Le burnout et les symptômes somatiques de 259 enseignants de la même cohorte ont été évalués pendant le 3e trimestre (T2). Une analyse factorielle des réponses de coping (T1) a permis d’isoler quatre facteurs : coping centré sur le problème, coping évitant, besoin de communiquer, adoption d’un style d’enseignement traditionnel. Ces facteurs sont similaires à ceux décrits dans d’autres études des stratégies de coping des enseignants. Chaque stratégie est associée à certains des antécédents mesurés en T1. La stratégie centrée sur le problème s’avère fonctionnelle (elle atténue le burnout en T2), alors que la stratégie évitante et l’adoption d’un style pédagogique traditionnel ont des effets dysfonctionnels (elles amplifient le burnout ultérieur). Ces résultats sont en accord avec ceux de la littérature. Ils suggèrent des prises en charge du stress et du burnout des enseignants.410 French primary school teachers were administered a French version of the Dewe questionnaire (1985) during the first term of the school year (T1) to assess their coping responses. We also used other tools to measure situational (frequency of professional difficulties) and personal (overall self-efficacy, socio-demographic data) antecedents. Burnout and somatic symptoms of 259 teachers in the same cohort were assessed during the third term (T2). A factorial analysis of coping responses (T1) yielded four factors: problem-focused coping, avoidance, need to communicate and adoption of a conservative teaching style. These factors are similar to those described in other studies of teacher coping. Each strategy was associated with some of the antecedents measured at T1. Problem-focused coping proved to be functional by attenuating burnout at T2, whereas avoidance and adoption of a conservative pedagogical style had a deleterious effect by worsening subsequent burnout. These results are in agreement with previous data. They suggest how to manage stress and burnout in teachers