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Le débaguage orthodontique, l'art de conclure sans abimer!
No full textNational audienceOften regarded as a mere formality marking the endof orthodontic treatment, bracket removal is in facta procedure with a high iatrogenic risk. This step,sometimes performed hastily or too quickly, can leadto irreversible damage to already weakened enamel- a paradox considering the patience required overmonths or even years of orthodontic treatment.Although data on the subject exist in the literature,a lack of information, training, or the underestimationof potential harm often results in quality beingunintentionally sacrificed in favor of speed. This articleaims to reestablish debonding as a central clinicalconcern, exploring the limitations of currentinstrumentation while opening avenues toward moreprecise, tissue-friendly tools that remain compatiblewith the time constraints of everyday clinical practice.Souvent considéré comme une simple formalité marquant la findu traitement, le débaguage orthodontique est en réalité une étapeà haut risque iatrogène. Réalisé parfois de manière « précipitée »,il peut entraîner des dommages irréversibles sur un émail fragilisé.Un paradoxe, compte tenu de la patience imposée durant desmois, voire des années de traitement. Bien que des donnéesexistent dans la littérature, le manque d’informations, de formationou la sous-estimation des dégâts potentiels conduisent à sacrifier,parfois involontairement, la qualité au profit de la rapidité. Cet articlepropose de replacer le débaguage au centre des préoccupationscliniques. Il s’intéresse aux limites des instruments actuellementdisponibles, tout en ouvrant des pistes vers une instrumentationplus précise, mieux tolérée par les tissus dentaires et compatibleavec les contraintes de temps de la pratique clinique quotidienne
Growth and optimization of N-polar GaN epilayers on silicon substrates using ammonia-MBE and a hybrid NbN/AlN buffer layer
No full textInternational audienceIII-Nitride based High Electron Mobility transistors (HEMTs), first developed in the early 90s, are gaining increasing attention in both scientific and industrial fields, to the point of being now mass-produced to meet the growing demand for wireless data transmission. These HEMTs are mostly grown following the III-N metal polarity (Ga-polar) but in recent years nitrogen polar (N-polar) heterostructures have enabled remarkable improvements.Indeed, in this fast-paced race towards higher frequencies and power densities, N-polar GaN HEMTs appear to be positioned to dominate due to the various intrinsic advantages they offer over their regular Ga-polar counterparts [1].However, the development of these devices requires high-quality N-polar epilayers. The growth of N-polar III-Nitrides on SiC (C-face), bulk GaN (N-polar face), and sapphire is progressing well and is already yielding promising results, especially using MOCVD. In contrast, there have been only a few attempts at growing N-polar nitrides on Si, typically involving Mg doping [2] or surface silicon nitridation [3], none of which have been followed up to the best of our knowledge.In this work, we demonstrate the reproducible fabrication of N-polar III-Nitride epilayers on Si using a hybrid AlN/NbN grown by ammonia-MBE (see Fig. 1). Niobium Nitride (NbN), best known for its high superconducting critical temperature (17K), belongs to the family of the “new nitrides” that has recently gained attention for its exotic properties [4], which nicely complement those of conventional semiconducting III-N materials. Interestingly in our system, NbN stabilizes the N-polarity of the nitride layer grown above it (Fig.1), as was demonstrated using transmission electron microscopy. However, in order to achieve the structure shown Fig. 1 several epitaxial challenges have to be understood and addressed. These challenges, including the NbN layer continuity and its roughness, the N-polar nucleation on this NbN layer and the adjustment of the growth conditions to optimize the quality and surface roughness of N-polar GaN epilayers, will be discussed in this presentation.Specifically, we have investigated the impact of growth temperature and substrate offcut angle on roughness, crystal quality (X-ray diffraction and photoluminescence), and impurity concentration (Secondary Ion Mass Spectroscopy). Additionally, we improve the architecture of the template itself, in particular by adjusting the composition of the N-polar AlGaN buffer layer grown on the NbN. Ultimately, we demonstrate a smooth N-polar GaN epilayer (only 300 nm thick) with crystalline quality comparable to a μm thick Ga-polar GaN layer, thereby paving the way for the growth of new N-polar III-N heterostructures on silicon substrates
AlN/NbN epitaxial heterostructures on Si: polytypes, strain and polarity
No full textInternational audienceThe combination of metal/superconductor NbN with III-N semiconductors opens the way to a wide range of innovative applications. Notably, it is possible to epitaxially integrate NbN and III-N. NbN can exist in different crystalline structures, commonly referred as polytypes. We found that by a fine-tunning of the growth conditions, a precise control of the NbN polytype formed on AlN can be obtained. This work focuses on a detailed analysis through advanced scanning transmission electron microscopy (STEM) of AlN/NbN/AlN heterostructures epitaxially-grown on Si (111) substrates by NH3-molecular beam epitaxy (MBE).Figure 1 (a) show a high angle annular dark field (HAADF) image of a δ-NbN layer viewed along the AlN[11-20] zone axis where the ABC cubic stacking is clearly observed. The epitaxial relationship is AlN<11-20>││δ-NbN<1-10> and AlN<0001>││δ-NbN<111>. Conversely, it is also possible to achieve a predominantly ε-NbN layer. Figure 2(a) show a HAADF image of such a layer observed along the AlN[11-20] zone axis. While the first monolayers adopt the δ-polytype, the majority of the NbN layer exhibit the AA-BB stacking corresponding to the ε-polytype. The observed epitaxial relationship is AlN<11-20>││ε-NbN<11-20> and AlN<0001>││ε-NbN<0001>.The lattice mismatches between AlN and NbN depends on the NbN polytype. Specifically, the in-plane lattice mismatches are -0.7% and -4.7% for δ- and ε-NbN respectively. Figure 1(b) and 2(b) show strain maps obtained using the geometrical phase analysis (GPA) method for both heterostructures, with the AlN lattice distance used as reference. These maps reveal that, due to the low mismatch, δ-NbN is fully strained on AlN without introduction of misfit dislocations. For the NbN layer consisting of δ-polytype at the bottom and ε-polytype at the top, the δ-region is strained on AlN whereas the ε-region is fully relaxed.A key distinction between wurtzite III-N and NbN is that III-N are polar materials whereas NbN is non-polar. Our observations using integrated differential phase contrast (iDPC) (figure (3)) confirm previous results: adding a thin epitaxial NbN layer reverses the polarity of AlN from Al-Polar to N-Polar.Our STEM study demonstrates that is possible to control the NbN polytype by adjusting the growth conditions. Whatever the polytype, the introduction of a thin NbN layer consistently reverses the polarity of the AlN top layer. Another interesting finding obtained from our analyses is that the AlN/δ-NbN/AlN heterostructures are pseudomorphic with no misfit dislocations paving the way for the realization of high crystalline quality hybrid semiconductor/superconductor heterostructures and also hybrid Al-Polar/N Polar AlN layers
On-sky demonstration of an ultra-fast intensity interferometry instrument utilizing hybrid single photon counting detectors
No full textInternational audienceIntensity interferometry is a reemerging astronomical technique for performing high angular resolution studies at visible wavelengths, benefiting immensely from the recent improvements in (single) photon detection instrumentation. Contrary to direct imaging or amplitude interferometry, intensity interferometry correlates light intensities rather than light amplitudes, circumventing atmospheric seeing limitations at the cost of reduced sensitivity. We developed an ultra-fast, single photon counting and highly stable intensity interferometry instrument for 1 m class optical telescopes. The instrument records on sky the expected stellar photon rates and reaches the temporal coherence times as measured in the laboratory. In addition, all components, especially the photon detection hardware, of the instrument are easily upgradeable with custom hardware currently being developed. The collimated telescope output is spectrally filtered via an ultra-narrow band pass of 2 nm at a central wavelength of 405 nm. We use hybrid photon detectors (HPDs) for single photon detection and a constant fraction discriminator (CFD) for signal conditioning. A timeto-digital converter (TDC) is used for time stamping. The combination of HPDs and CFDs is optimized for a large active area and high timing resolution. We successfully measured photon bunching of three bright A-type stars-Vega, Altair, and Deneb at the 1.04 m Omicron telescope of C2PU (Centre Pédagogique Planète Univers) at the Calern Observatory in the south of France. In all cases, the observed coherence time, bunching peak amplitude, and S/N fit well to both the pre-calculated expectations as well as the values measured in preceding laboratory tests. We obtained the previously estimated photon count rates at the telescope and achieved highly stable coupling of the starlight to the detectors
Air pollution and performances in outdoor sports: a systematic review and meta-analysis of short-terms associations
No full textInternational audienceLaboratory studies suggest that high concentrations of particles matter (diameter<2.5 mm [PM2.5]) and ozone (O3) may reduce sport performances at short term. However, a systematic review of literature examining whether air pollution has an effect on sport performances in real situations is missing.Seven databased were searched for articles which examined the association between particulate (PM2.5, PM10, PMCoarse), gaseous (O3, sulfur dioxide [SO2], nitrogen dioxide [NO2], carbon monoxide [CO], and index (Air Quality Index [AQI]) of air pollutants and sport performances in real context. We included observational studies with objective measures of air pollution and performances. They were categorized into endurance, power/speed, technical performances. Harvest plots were used to summarize the findings and guide narrative synthesis. Risk of bias was also assessed. When appropriate, meta-analyses were completed to evaluate the strength of the associations. Subgroup and sensitivity analyses were also conducted. Over 200 reported associations from 21 articles were examined. Participants were primarily elite athletes. The majority of studies examined football (n = 9), and endurance sports (n = 9). Overall, no evidence supported a negative association between performances and the AQI, PM2.5, and NO2 outdoor concentrations. We found that exposure to O3 was associated with reduced sports performance O3, (d = -0.33, 95%CI: -0.65 –0.02 [all performances]; d = -0.54, 95%CI: -1.02 -0.04) [endurance performances]). An absence of significant association between AQI, PM2.5, or NO2 exposure and sports performance is clearly supported by our systematic review and meta-analyses. Higher O3 concentration could impair sport performances in real context, but the evidence is less consistent. No firm conclusion can be drawn from our work for the short term levels of CO, PM10, or SO2 and their respective association with endurance and technical performances
Dysanapsis is a determinant of expiratory flow limitation during exercise in master athletes
No full textInternational audienceIntroductionPrevious research has identified expiratory flow limitation (EFL) as a limiting factor to exercise performance in older endurance athletes (i.e. master athletes), who represent a model of successful aging. A mismatch between airway size and lung size, termed dysanapsis, has been proposed as a contributor to EFL during exercise. We thus investigated whether dysanapsis determine the prevalence and severity of EFL in master athletes during exercise.MethodsFour female and fourteen male master athletes (age, 67 ± 5 years; V̇O2max, 50.9 ± 5.7 mL.min−1.kg−1) performed an incremental exercise test to exhaustion on a cycle ergometer. The maximal expiratory flow volume (MEFV) curve was assessed at rest and operational lung volumes were determined with participants performing inspiratory capacity maneuvers at each exercise workload. EFL severity was estimated as the percentage of the tidal expiratory volume that overlapped the MEFV curve. Dysanapsis was quantified using spirometry-derived indices.ResultsAll participants started experiencing EFL at workloads (WEFL) ranging from 40 % to 100 %PPO (WEFL = 68 ± 20 %PPO). EFL severity reached 46 ± 21 % at peak exercise. Lower values across dysanapsis indices, reflecting smaller airway size for a given lung volume, were correlated with lower WEFL (r²>0.490, P < 0.001) and greater EFL severity (r²>0.243, P < 0.038). Individuals experiencing EFL at lower intensities (i.e. lower WEFL) showed greater EFL severity (r²=0.571, P < 0.001).ConclusionOur results suggest that dysanapsis is a key determinant of EFL in master athletes, likely contributing to its earlier onset at lower workloads and to its increased severity. These findings have implications for understanding respiratory limitations during exercise in older adults
Entre désengagement et retrait : Analyser les réponses adaptatives des infirmiers à travers le prisme de la démission silencieuse
No full textInternational audienceMalgré sa pertinence croissante, la recherche sur de la démission silencieuse reste relativement rare, en particulier dans le secteur hospitalier. Cette étude propose un modèle conceptuel conçu pour servir de cadre analytique solide afin d'explorer les déterminants organisationnels et personnels de la démission silencieuse chez les infirmiers, ainsi que les comportements qui en découlent en milieu hospitalier. Les manifestations comportementales identifiées dans cette étude témoignent de l'importance d'interventions ciblées visant à restaurer le sentiment d'estime de soi des infirmiers, et la reconnaissance de leurs contributions, conditions indispensables pour assurer la pérennité des ressources humaines dans le secteur des soins de santé
Heterogeneous Multiscale Multivariate Autoregressive Model: existence, sparse estimation and application to functional connectivity in neuroscience
No full textInternational audienceIn neuroscience, functional connectivity is a concept that can be mathematically formulated as a graph of interactions between oscillatory brain rhythms and individual neuronal activity. Typically, each graph corresponds to a cognitive state and provides insight into higher cognitive processes, such as learning. However, a model or method to assess directed interactions within and across brain oscillations and individual neuronal activity is lacking. In this article, we propose a new model called HM-MVAR (Heterogeneous Multiscale Multivariate Autoregressive) that represents linear combinations of neural interaction patterns. These patterns include phase-locking, where the amplitude of one signal is modulated by the phase of another, and power-triggered phenomena, where the amplitude of one signal is modulated by the amplitude of another. Due to the multiscale structure, we use a block version of stationarity to exhibit conditions under which the process obeying the HM-MVAR model exists and is stationary. We also propose a data-driven weighted LASSO estimator based on martingale exponential deviation inequalities, which may have intrinsic interest in probability theory. We prove that our estimator satisfies an oracle inequality and present its strong performance in realistic simulations. Finally, applying our model and method on a publicly available multiscale electrophysiological data set, we recover interactions described in the literature but also uncover new phenomena of potential interest
Phase Characterization of Singular Metasurfaces
No full textInternational audienceThe controlled generation and accurate characterization of light beams carrying orbital angular momentum (OAM) are essential for emerging applications in optical communication, quantum information, and advanced imaging. Metasurfaces offer a versatile platform for tailoring such structured electromagnetic fields. However, the accurate measurement of wavefronts containing multiple phase singularities remains a significant metrological challenge. In this work, we employ quadriwave lateral shearing interferometry (QLSI) as a quantitative phase imaging technique to retrieve spatially resolved phase maps of OAM beams generated by metasurfaces. We demonstrate that QLSI enables robust reconstruction of perfect and imperfect singular phase profiles, providing a reliable tool for the characterization of complex optical fields. This methodology is applied to evaluate metasurfaces designed using two distinct phase encoding mechanisms: effective refractive index (ERI) modulation and Pancharatnam-Berry (PB) phase. Comparative analysis reveals superior phase accuracy and enhanced fabrication tolerance in PB-based metasurfaces relative to ERI counterparts. These results highlight the potential of QLSI as a diagnostic and validation tool for structured light generation in next-generation photonic devices.</div
