La recherche présentée dans cette communication correspond à la première phase d’une recherche-formation qui s’intéresse aux outils développés et utilisés dans la formation en sciences des enseignants du premier degré. Nous présentons ici les résultats de la phase exploratoire de cette recherche, dans laquelle nous avons interrogé les usages d’un cahier de sciences par deux étudiantes. Les résultats montrent que l’outil a été perçu comme utile principalement en ce qui concerne les apprentissages en lien avec l’enseignement des sciences mais sans être perçu comme un outil potentiel pour les pratiques et de fait qu’il n’a très peu été utilisé dans les pratiques.

The nature of point defects in hexagonal boron nitride (hBN) is of current interest for the potential to alter its optical and electrical properties. The strong interaction between neutrons and the boron-10 isotope makes neutron irradiation a controllable way to introduce point defects in hBN. In this study, we perform Raman spectroscopy, photoluminescence, electron paramagnetic resonance (EPR), and optically detected magnetic resonance (ODMR) characterization of neutron-irradiated monoisotopic (hBN with a single boron isotope) 10 B-and 11 B-enriched hBN crystalline flakes and a pyrolytic BN (pBN) reference sample. In h 10 BN and pBN, neutron irradiation produced two new Raman bands at 450 and 1335 cm −1 , which could be associated with B-related vacancies or defects. The near-bandedge optical emission was also significantly impacted by the neutron irradiation. EPR measurements clarified the origin of a high-spin defect center due to negatively charged boron vacancies, which was recently reported for similar neutron-irradiated hBN crystals. The ODMR experiments further confirmed this assignment. High-temperature annealing partially recovered some of the hBN vibrational and optical properties. Our results are helpful to identify the nature of defects in hBN and enable defect-engineered applications such as quantum information and sensing.

We use the impact of drops on a small solid target as a tool to investigate the behavior of viscoelastic fluids under extreme deformation rates. We study two classes of transient networks: semidilute solutions of supramolecular polymers and suspensions of spherical oil droplets reversibly linked by polymers. The two types of samples display very similar linear viscoelastic properties, which can be described with a Maxwell fluid model, but contrasting nonlinear properties due to different network structure. Upon impact, weakly viscoelastic samples exhibit a behavior qualitatively similar to that of Newtonian fluids: A smooth and regular sheet forms, expands, and then retracts. By contrast, for highly viscoelastic fluids, the thickness of the sheet is found to be very irregular, leading to instabilities and eventually formation of holes. We find that material rheological properties rule the onset of instabilities. We first provide a simple image analysis of the expanding sheets to determine the onset of instabilities. We then demonstrate that a Deborah number related to the shortest relaxation time associated to the sample structure following a high shear is the relevant parameter that controls the heterogeneities in the thickness of the sheet, eventually leading to the formation of holes. When the sheet tears-up, data suggest by contrast that the opening dynamics depends also on the expansion rate of the sheet.

Background and purpose: Few data are available regarding the influence of the timing of ischemic stroke management, such as daytime and nighttime hours, on the delay of mechanical thrombectomy, the effectiveness of revascularization, and clinical outcomes. We aimed to investigate whether admission during nighttime hours could impact the clinical outcome (mRS at 90 days) of patients with acute ischemic stroke treated by mechanical thrombectomy.Materials and methods: We retrospectively analyzed 169 patients (112 treated during daytime hours and 57 treated during nighttime hours) with acute ischemic stroke in the anterior cerebral circulation. The main outcome was the rate of patients achieving functional independence at 90 days (mRS ≤2), depending on admission time.Results: In patients admitted during nighttime hours, the rate of mRS ≤ 2 at 90 days was significantly higher (51% versus 35%, P = .05) compared with those admitted in daytime hours. Patients in daytime and nighttime hours were comparable regarding admission and treatment characteristics. However, patients in nighttime hours tended to have a higher median NIHSS score at admission (P = .08) and to be younger (P = .08), especially among the mothership group (P = .09). The multivariate logistic regression analysis confirmed that patients in nighttime hours had better functional outcomes at 90 days than those in daytime hours (P = .018; 95% CI, 0.064-0.770; OR = 0.221).Conclusions: In a highly organized stroke care network, mechanical thrombectomy is quite effective in the nighttime hours among acute ischemic stroke presentations. Unexpectedly, we found that those patients achieved favorable clinical outcomes more frequently than those treated during daytime hours. Larger series are needed to confirm these results.