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Femtosecond Laser Irradiation of Ge-Rich Ge-Sb-Te in Thin Films and Multilayer Structures for Phase-Change Memory
No full textInternational audienceThis study demonstrates that femtosecond laser pulses can efficiently induce amorphization in Ge-rich Ge-Sb-Te (GGST) thin films and GST/GGST multilayer structures. Using cross-sectional scanning transmission electron microscopy (STEM), we examined the structural evolution of undoped and compositionally stabilized GGST films under different femtosecond laser fluences. In both type of samples, a single laser pulse triggered significant structural transformations, including grain dissolution, lattice disorder, and the formation of an amorphous matrix. Two distinct transformation mechanisms were identified: thermal melting followed by rapid quenching and non-thermal bond destabilization via electronic excitation. These findings are supported by high-resolution STEM imaging, SAED patterns, and elemental mapping. Furthermore, successful amorphization was achieved in complex multi-layered architectures composed of alternating GST and GGST layers, underscoring the applicability of femtosecond laser-induced amorphization in advanced phase-change memory (PCM) structures. These results validate the feasibility of ultrafast optical amorphization in GGST single layers and GST/GGST multilayer structures, and provide critical insights for the rational design of next-generation laser-programmable phase-change materials for practical memory device applications
Un modèle de turbulence RANS à deux échelles dédié à la prévision des couches limites turbulentes soumises à de forts taux de turbulence extérieure
No full textInternational audienceTurbulent boundary layers (TBLs) developing beneath a highly turbulent free stream are ubiquitous in turbomachinary flows and come along with a substantial increase in skin friction and wall heat transfer. A precise numerical prediction of this kind of flow is then of paramount importance in this context. Nevertheless, classical RANS (Reynolds-Averaged Navier-Stokes) turbulence models have shown to fail in this regard. The present paper presents the development process and rationale behind a multi-scale k − ω model designed to capture free-stream turbulence (FST) effects. Starting from an in-depth insight at the physical mechanisms characterising the development of TBLs under strong FST, in particular the scale separation and inactive character of the large scales, modelling guidelines are obtained. The multi-scale approach to turbulence modelling then appears to offer a sound framework for a faithful reproduction of the complex physics involved in the interaction between FST and TBLs as opposed to classical single-scale models. The two-scale k − ω model developed in this work is presented in detail and special attention is paid to how the experimental observations are transcribed in the model. Extensive testing of the two-scale model on various datasets about TBLs developing under strong FST environment is undertaken and it is shown that our modelling choices greatly improve the predictions when compared to a single-scale k − ω model
Assessing the integrity of SARS-CoV-2 and F-specific RNA bacteriophage RNA in raw wastewater (ANRS0160)
No full textInternational audienceRNA integrity is an essential parameter for analyzing the nature of viral particles, especially in environmental samples where assessing virus infectivity is often difficult or impossible. It is also an important factor in the effectiveness of virus sequencing in environmental matrices containing mixed viral populations composed of variants that differ from one another by only a limited number of mutations, such as in the case of SARS-CoV-2. This study introduces a multiplex Reverse Transcription Digital PCR (RT-dPCR) method for evaluating the RNA integrity of SARS-CoV-2 and F-specific RNA phages belonging to subgroup I (FRNAPH-I) using synthetic RNA, viral stocks, and then raw wastewater (WW) in which SARS-CoV-2 and FRNAPH-I were naturally present. An initial approach using one-step multiplex digital Reverse Transcription PCR (dRT-PCR) demonstrated unequal detection across the genomic regions of both FRNAPH and SARS-CoV-2. To overcome this methodological bias, a two-step method called Long-Range Reverse Transcription digital PCR (LR-RT-dPCR) was developed. This approach involves performing long-range reverse transcription at the 3′ end using a single specific reverse primer to generate contiguous cDNA that spans multiple targets of interest. Following cDNA synthesis, the sample is partitioned, and a multiplex amplification is carried out on targets located at the 3′ end, middle, and 5′ end of the sequence. The LR-RT-dPCR method enabled uniform detection with enhanced sensitivity and was validated using capillary electrophoresis on synthetic RNA of MS2, a phage which belongs to the FRNAPH-I subgroup. LR-RT-dPCR was employed in both triplex and quintuplex formats to analyze the MS2 phage genome (3,569 nucleotides (nt)) and SARS-CoV-2 genome (∼30,000 nt), respectively. Using this approach, viral RNA integrity was evaluated through the detection frequencies of genome fragments of the whole genome. The viral stocks of MS2 phages replicated in a laboratory and stored in phosphate-buffered saline (PBS) exhibited high RNA detection frequencies (> 50 %). In WW, RNA detection frequency was significantly lower, not exceeding 2 % even for the shortest fragment of the FRNAPH-I genome. On the other hand, SARS-CoV-2 RNA showed greater detection frequency than FRNAPH-I RNA in WW, with values exceeding 30 % for short fragments (<1,500 nt) and ranging from 0 % to 44 % for longer fragments (1,500 to 3,500 nt). The relationship between the detection frequency of a fragment and its length does not appear to be strictly linear, as factors other than length can influence genome integrity. These factors include the intrinsic properties of specific genomic regions. For example, the S3-ORF3a region of the SARS-CoV-2 genome appears particularly stable
Hydrolytic weakening controls Jurassic to early Cretaceous mylonitisation in the basement of the Pyrenees
No full textInternational audienceThe age of the mylonite belts in the basement rocks of the Pyrenees is a subject of debate in the structural geology and petrology communities because of its potential implication on the regional tectono-thermal history and on the tectonic evolution of SW Europe. Here we address when and how mylonitisation took place in two key areas of the Eastern Pyrenees, where shear zones are associated with Giant Quartz Veins (GQVs). We conducted zircon U-Pb and muscovite 40 Ar/ 39 Ar dating coupled with structural, textural, and crystallographic preferred orientation (CPO) analyses of mylonites from the Cap de Creus and Canigó Massifs. U-Pb zircon dating of a dacite porphyry dyke crosscut by GQVs and mylonitic bands yields a maximum shear zone and GQV formation age of ca. 292 ± 3 Ma. 40 Ar/ 39 Ar analyses of muscovite within mylonitised GQVs yield initial crystallisation ages between ca. 164 and 188 Ma, as well as younger recrystallisation ages of ca. 110-118 Ma. A qualitative assessment of the GQV history is inferred from stepheating spectra of muscovite and quartz CPOs. The results indicate that GQV formation and mylonitisation were coupled, coeval, and long-lasting processes that took place from early Jurassic to early Cretaceous times. A comparative evaluation of quartz CPOs reveals inconsistencies regarding the strain distribution, quartz slip systems activity, and deformation temperatures depending on the deformed rock type. Quartz mylonites have stronger CPOs dominated by basal <a>, prism <a> or prism <c> slip systems, whilst phyllonites and granite mylonites show weaker fabrics mostly dominated by mixed <a> slip. This apparently suggests higher deformation temperatures in quartz mylonites than those inferred from more reliable proxies, such as mineral assemblages, brittle behaviour of K-feldspar, and fluid inclusion data. We suggest that the water-weakening effect caused by coeval formation and deformation of GQVs enabled easier dislocation glide and creep, allowing strain localisation and transitions between slip systems at lower temperatures than commonly inferred due to enhanced ductility. U-Pb zircon dating further suggests the existence of an early Carboniferous (ca. 332 ± 4 Ma; Visean) magmatic episode in the Pyrenees, in agreement with a cyclic, rather than a progressive, geodynamic history of the region during Variscan times.The present work challenges classical interpretations stating that Pyrenean mylonite belts developed during the retrograde stages of the Variscan Orogeny, highlighting that the structural evolution of this region during Mesozoic times deserves further investigation. Results have implications for interpreting deformation localisation mechanisms and conditions in crustal rocks, for the formation mechanisms of GQVs in worldwide orogenic belts, and for the tectono-thermal history of the Pyrenees since late-Variscan times.</div
Phosphorylated lignin–cellulose nanofibrils for multifunctional PVA composites with UV-absorption and flame-retardancy
No full textInternational audienceComposite manufacturing often requires multiple additives to achieve desired properties in terms of strength, safety, and durability. Here, we produce multifunctional lignin-cellulose nanofibrils (PLCNFs) via a simple phosphorylation of giant reed using H3PO4/urea. The synergistic effects of cellulose, lignin, and phosphate in PLCNFs offer promising prospects for the manufacturing of multifunctional composites. Polyvinyl alcohol (PVA)/PLCNF nanocomposites were produced by solvent casting and comprehensively characterized using scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry, Fourier transform infrared (FTIR) spectroscopy, UV–vis spectroscopy, contact angle measurements, moisture uptake, and microscale combustion calorimetry. The reinforcing and flame-retardant potentials of PLCNF in the PVA matrix were revealed, along with additional UV-shielding and hydrophobicity imparted by lignin. These features highlight the potential applications of these nanocomposites as a safe substitute for flammable or hazardous materials. These multifunctional films are promising for sustainable food packaging and protective coating applications requiring UV-blocking and flame-retardant properties. In summary, this study demonstrates that underused lignocellulosic resources, when combined with benign phosphorylation chemistry, can serve as robust, reliable, and eco-friendly flame-retardant additives for enhanced nanocomposites
Homogenization model for a dense elastic medium of cylindrical scatterers and based on a realistic pair correlation function
No full textInternational audienceMultiple scattering effects due to a random distribution of identical cylindrical inclusions in an elastic medium are investigated. The approach is based on the analysis proposed by Fikioris and Waterman. The solution of the developed modal equations yields the effective wavenumbers of elastic coherent waves. Attention is made in this paper to a more realistic description of scatterers’ distribution in the host medium: this distribution is taken into account in modeling by introducing the notion of pair correlation function. The existing Conoir and Norris approach has been established by using the Hole Correction as pair correlation function, which simplifies the description of scatterers’ distribution and may lead to unphysical results for dense media. New formulas for the effective wavenumbers are proposed here by generalization of the latter theory and enable the use of any pair correlation function for possible application to dense media. The new generalized analytical model coupled to a realistic pair correlation function is compared to the previous approach in different materials configurations and validated for concrete structures by comparison to numerical simulations
Investigating the Influence of Training Difficulty on the Learning Outcomes of Medical Students
No full textInternational audienceBackground: Determining an optimal training difficulty level for the best learning outcome is a crucial goal for adaptive educational systems. The literature supports the Inverted U-shape Hypothesis, suggesting that the ideal challenge level for learning is neither too easy nor too difficult. However, this optimal point depends on the type of training and response modality and may vary across domains, necessitating thorough examination before implementing adaptive learning procedures.Objectives: This study aimed to investigate the influence of training difficulty on the learning outcomes of French medical students.Methods: Using data from a national educational platform, we explored the influence of the mean question difficulty encountered during training, relative to individual student ability, on the learning outcomes of medical students across diverse medical specialties. Importantly, the mean difficulty level varied randomly between students on this platform, mirroring a quasi-experimental design and enabling a thorough exploration of these effects. We first employed the Elo rating system to estimate the difficulty of platform questions and the evolution of students’ abilities. A linear mixed-effects model was then used, with final exam performance as the main outcome and mean relative question difficulty during training (linear and quadratic terms) as the main predictor.Results and Conclusions: Results showed a significant negative quadratic effect of mean relative difficulty on final exam performance, revealing optimal difficulty levels for each medical specialty. Additionally, the analysis demonstrated that students with high abilities displayed a more pronounced inverted U-shaped relationship between training difficulty and final exam scores. This study advances our understanding of optimal training difficulty in the complex realm of medical education by emphasizing the need to acknowledge variability across medical specialties and student abilities
Integrative assessment of biohydrogen and biomethane production from Brittany and Caribbean Sargassum (Ochrophyta, Fucales)
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Set-Valued Approaches to Control and Estimation of Uncertain Systems
No full textInternational audienceThis edited book presents recent advances in state estimation, robust control synthesis, system identification, fault detection, localization, and optimization, with a particular emphasis on interval-based methods and set-membership techniques. Covering both theoretical developments and practical applications, the book brings together contributions from recognized experts in these research areas.Topics include set-based state estimation in varied dynamical system settings, sliding-mode predictive and state-feedback control, innovative optimization algorithms, zonotopic fault detection and identification, as well as distributed moving horizon estimation. The proposed methods are illustrated through practical simulation studies in robotics, autonomous vehicles, fuel cell systems, and sensor networks.Intended for researchers, engineers, and graduate students in control systems, applied mathematics, and various engineering disciplines, this book offers both a rigorous foundation and cutting-edge approaches for addressing uncertainty in complex dynamical systems