Material standards design for minimum zone fitting of freeform optics

International audienceIn most cases, ultra-high-precision coordinate measuring machines (CMMs) are used to measure manufactured parts especially in the presence of freeform surfaces. The obtained data should be then processed to determine a quality measure of the surface. The least value of peak-to-valley (PV) is the widely used quality measure since it conforms to the ISO Geometrical and Product Specification (GPS) standards. To determine the minimum value of PV, a number of fitting methods exist but minimum zone fitting is the most suitable since it directly minimizes the PV. In the measurement process, fitting algorithms are essential elements. For this reason, their quality must be assessed as well; this could be achieved using either softgauges or material artefacts. In this paper, a design of a reference thermo-invariant material standard for minimum zone fitting is suggested and manufactured. The artefact was then measured by a number of partners participating to the FreeFORM 15SIB-01 project so as a comparison could be made in the light of gathered measurements

The Natal rift (South Mozambique, Africa): tectonic inheritance and magmatism

International audienceThe break-up of the Gondwana supercontinent started during the Early Jurassic and lead to the formation of the Mozambique passive margins, as Africa and Antarctica separated during the mid-Jurassic period. Albeit plate kinematics during the oceanic spreading stage are relatively well constrained, the initial fit of Africa and Antarctica, their earliest relative movements and the architecture of distinct margin segments from Mozambique to South Africa in relation to those from Antarctica remain sparsely known. While margins architecture has been recently evidenced along the central Mozambique, the spatial extent of rifting further south remains poorly documented.Based on detailed observations related to seismic reflection profiles and oil company wells, findings show the existence of a magma-rich segment with large volume of seaward dipping reflectors in the South Mozambique (i.e. the Natal segment). Such segment is defined by a rapid transition from continental to oceanic domains that differs from classical divergent margins. Such particular architecture may be related to a difference in lithosphere rheology (i.e. Archean vs. Neoproterozoic) that favored extension and upwelling from a deep thermomechanical anomaly, called Karoo superplume. In parallel, the birth of the Natal ocean occurred at ca. 165 - 160 Ma and bring new constrains on Gondwana breakup. Here, we inferred a simplified conceptual geodynamic model for the whole area, from the initiation of extension to the seafloor spreading. We summarize this evolution in three main steps. Stage T1 represents the first extensional event inducing crustal thinning during the Permo-Trias before the breakup of the Gondwana. It is characterized by an E-W extension trend responsible for the formation of large N-S fault-controlled basins. Stage T2 is marked by the onset of a plume activity at about 180 Ma. Characterized by large N-S trending basins and by seawards dipping reflectors infilling, deformation related to T2 is consistent with a NW-SE trending extension. Finally, Stage T3 corresponds to the continuation of the rift with a stress field rotation ranging from NW-SE to N-S, suggesting that Antarctica moving in a SSE direction with respect to Africa after 156 Ma. The entire region is then going through an episode of uplift related to mantle dynamics

Assessment of ventilatory thresholds from heart rate variability in well-trained subjects during cycling

The objective of the present paper is to analyse the dynamic recrystallization process occurring during the hot cutting of spheroidal graphite iron. In the first instance, hot cutting tests are performed with an orthogonal cutting test bench. The emergence of dynamic recrystallization is highlighted thanks to microstructural observations. Then, a finite element model of the hot cutting operation is introduced. The material behaviour is modelled with a specific constitutive model considering the influence of dynamic recrystallization on the plastic flow stress. Finally, the predictive response of this model is compared to the experimental observations

The ‘terril’ effect: coal mine spoil tips select for collembolan functional traits in post-mining landscapes of northern France

International audienceWe sampled collembolan communities in 11 coal mine spoil tips (locally called 'terrils') from the North of France, and their surroundings, in various stages of vegetation development (bare soil, herb, shrub and tree vegetation). We wondered whether species, functional trait (Community Weighted Mean trait or CWM) composition and trait diversity (Rao's quadratic entropy) responded to the particular environment of coal mine spoil tips (here called 'terril' effect) and to successional effects and which of these three sets was the best indicator of soil and vegetation effects, taking into account that spoil tips were spatially distant and idiosyncratic (e.g. varying in height, area, past history and surrounding environment). We showed that species, but not traits, were strongly influenced by site effects, while traits were influenced by both 'terril' and successional effects to a significant extent, making traits more robust than species when trying to discern patterns of community response to soil and vegetation changes. Functional diversity did not show any significant multi-trait response to either 'terril' or successional effects, but several functional traits showed an increase in diversity with succession. The overall response of trait diversity was intermediate between species and trait responses. The 'terril' effect was mainly mediated by a coarser soil texture (51% coarse sand compared to 14% in the surrounding environment) which, combined with harsher microclimate conditions, stems in a better representation of functional traits linked to subterranean life, such as shorter body length and increased representation of parthenogenesis. Successional effects (in particular the increase in diversity shown by several functional traits varying with vertical distribution) were mediated by the increasing development of organic horizons but other factors like microclimate were seemingly involved, too. More generally this study showed that shift to subterranean life was an adapted response of collembolan communities to harshness of the environment and that vertically stratified ecosystems allow a more complete expression of their functional diversity

New insight into the working mechanism of lithium–sulfur batteries: in situ and operando X-ray diffraction characterization

International audienceIn order to improve the electrochemical performances of lithium–sulfur batteries, it is crucial to understand profoundly their working mechanism and the limitation factors. This communication presents synchrotron-based in situ XRD studies of structural modifications occurring inside the cell upon cycling, since the active material changes constantly its form between solid and liquid phases.Graphical abstract: New insight into the working mechanism of lithium–sulfur batteries: in situ and operando X-ray diffraction characterizatio