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

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

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

In many instances in life, materials are subject to deformation at high rates, for example: impact, crash, metal forming or pulsed welding. In this context, the transient and inhomogeneous nature of such loading as well as the strong multi-physic couplings induced by quasi-adiabatic conditions make: the experimental capture of the mechanical response very challenging. Additionally, assumptions regarding the constitutive relation of the deforming material are generally required. To overcome both issues, we demonstrate that experimental full-field measurements of acceleration fields can be directly used to invert the local equilibrium equation and reconstruct fields of the stress tensor with no assumption on the constitutive relation and its spatial and temporal variations. We also demonstrate that both experimental stress and strain fields can be recombined to eventually identify the local tangent stiffness tensor of the material. This study constitutes a first step in the field of “direct model identification”, as opposed to standard parametric model identification.</p