Integer polyhedra for program analysis

Polyhedra are widely used in model checking and abstract interpretation. Polyhedral analysis is effective when the relationships between variables are linear, but suffers from imprecision when it is necessary to take into account the integrality of the represented space. Imprecision also arises when non-linear constraints occur. Moreover, in terms of tractability, even a space defined by linear constraints can become unmanageable owing to the excessive number of inequalities. Thus it is useful to identify those inequalities whose omission has least impact on the represented space. This paper shows how these issues can be addressed in a novel way by growing the integer hull of the space and approximating the number of integral points within a bounded polyhedron

The Initial Conceptions of Students in the Teaching Practice of Life and Earth Sciences Teachers in Morocco

This study aims to describe the learning environment that can influence the construction of scientific concepts among Moroccan students. It focuses on the role of students’ initial conceptions in the teaching practice of Life and Earth Science (LES) teachers in Morocco. To conduct this study, we performed a quantitative analysis of collected data using a multiple-choice questionnaire, which aimed to understand the characteristics of the target group and the techniques employed to gather students’ initial conceptions of the ecosystem, as well as their declared and actual teaching practices. To compare our results, we considered two contexts: rural and urban, where the teachers operate. The analysis of the obtained results revealed that a majority of the surveyed teachers start by identifying students’ initial conceptions before approaching the teaching process. Additionally, the study found that debate and diagnostic testing are the most commonly utilized techniques for identifying and addressing students’ initial conceptions of the ecosystem. Furthermore, this analysis revealed that teachers do not take students’ conceptions into account when preparing the ecosystem learning sequence

Towards a new relationship between: Innovative ideas and designs adopted by teachers for improving the study environment of life and earth sciences in Morocco

Science teaching requires not only the acquisition of scientific knowledge, but also the appropriation of scientific ways of thinking and the development of a scientific and technological culture. According to the constructivist model, the teacher must consider the classroom as a research laboratory, enabling learners to apply scientific approaches to the construction of knowledge. Adopting this model requires consideration of coherent methodological and epistemological options, as well as an understanding of key aspects of the nature of science, as the latter is an essential component in developing students’ scientific culture. This research aims to explore and analyze the idea of science among Moroccan teachers of life and earth sciences. We explored these ideas through semistructured interviews, followed by a qualitative content analysis. We found a certain heterogeneity of conceptions among the teachers. They share contrasting conceptions of science, sometimes adequate, sometimes erroneous. This study therefore highlights a profound lack of culture in terms of reflection on the nature of science and the ways in which scientific knowledge is developed. Hence, it is important to add epistemology in initial and in-service teacher training. Thus, training in the history of science appears desirable in order to emphasize the evolutionary and revolving character of science, and to ensure a positive impact on teachers, students, society and the environment

A global look at time: a 24-country study of the equivalence of the Zimbardo Time Perspective Inventory

In this article, we assess the structural equivalence of the Zimbardo Time Perspective Inventory (ZTPI) across 26 samples from 24 countries (N = 12,200). The ZTPI is proven to be a valid and reliable index of individual differences in time perspective across five temporal categories: Past Negative, Past Positive, Present Fatalistic, Present Hedonistic, and Future. We obtained evidence for invariance of 36 items (out of 56) and also the five-factor structure of ZTPI across 23 countries. The short ZTPI scales are reliable for country-level analysis, whereas we recommend the use of the full scales for individual-level analysis. The short version of ZTPI will further promote integration of research in the time perspective domain in relation to many different psycho-social processes

Analyse des contraintes dans la zone de contact Poinçon cylindrique à extrémités plates – couche élastique isotrope transverse

Le problème de contact se présente comme l’action d’un corps rigide sur un corps élastique lié à un support également rigide. Ce type de problème est une variante de problèmes mixtes aux valeurs aux limites. Dans cet article, nous résolvons le problème de contact d’une couche élastique isotrope transverse d’épaisseur (H), reposant sur une plate-forme également rigide. Le chargement qui est supposé parallèle à l’axe de symétrie de la couche est appliqué normalement à sa surface libre par un poinçon cylindrique à extrémités plates. Nous développons et proposons dans ce but une méthode semi analytique basée sur la transformation intégrale de Hankel prévue pour résoudre les équations différentielles gouvernant le problème. Un exemple pratique est étudié et les courbes de répartition de contraintes dans la zone de contact sont tracées

Shakedown within polycrystals: a direct numerical assessment

International audienceIt is well known that in high cycle fatigue (HCF), macroscopically, structures undergo elastic shakedown and the stress level commonly determines the lifetime. In this domain, the fatigue phenomena is due to local plasticity at the grain scale. Therefore, some multiscale HCF multiaxial fatigue criteria were proposed, among them the well-known Dang Van criterion. This criterion supposes that in a polycrystal, some misoriented grains can undergo plastic shakedown which conducts to crack initiation. The objective of this work is to validate this assumption by conducting numerical simulations on polycrystalline aggregates. As it is necessary to estimate the stabilized state in each grain of the polycrystal, classical incremental simulations are not the best way as it will be highly time-consuming because of the size of the aggregate. In the recent years, Pommier proposed a method called Direct Cyclic Algorithm to obtain the stabilized response of a structure under cyclic periodic loading, which it is shown to be more efficient compared to an incremental analysis in such situation. However, errors can be obtained in certain case with respect to the incremental solution. In this work, a Crystal Plasticity FEM model, based on dislocation densities, was used. As a first step, an aggregate of 20 grains of AISI 316L stainless steel under strain controlled cyclic loading was studied. Precise comparisons were conducted with incremental analysis and the results show that DCA seems to be an efficient solution in order to estimate the shakedown state of polycrystalline aggregates

Image-based stress field reconstruction in complex media

International audienceIn many instances in life, materials around or within us suffer deformation at high rates. This is the case when engineering structures undergo e.g. impact, crash, forming or pulsed welding. Another important area concerns biological tissues injuries. In those contexts, the transience and inhomogeneous aspect of such loadings as well as the strong multi-physic couplings induced by quasi-adiabatic conditions make both: the experimental capture of the mechanical response very challenging and all the potential assumptions regarding the constitutive relation of the deforming material extremely hazardous. To overcome both issues, we demonstrate in the following that experimental full-field measurements of accelerations can be directly used to inverse the local equilibrium equation and reconstruct fields of stress tensor with no assumption at all on the constitutive relation and its potential spatial and temporal variations. It is also demonstrated that both experimental stress and strain fields can be recombined to eventually identify the local tangent stiffness tensor of the material. The latest constitutes a first step in the field of "model identification", as opposed to parameters' model identification