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Linear algebra and group theory
No full textThis is an introduction to linear algebra and group theory. We first review the linear algebra basics, namely the determinant, the diagonalization procedure, and more, and with the determinant being constructed as it should, as a signed volume. We discuss then the basic applications of linear algebra to questions in analysis. Then we get into the study of the closed groups of unitary matrices , with some basic algebraic theory, and with a number of probability computations, in the finite group case. In the general case, where is compact, we explain how the Weingarten integration formula works, and we present some basic applications
Electronic structure and transport in materials with flat bands: 2D materials and quasicrystals
No full textreviewInternational audienceIn this review, we present recent works on materials whose common point is the presence of electronic bands of very low dispersion, called "flat bands", which are due to specific atomic order effects without electron interactions. These states are always indicative of some form of confinement and have significant consequences on the electronic structure, transport properties and magnetism of these materials. A first part is devoted to the cases where this confinement is due to the long-range geometry of the defect-free structure. We have thus studied periodic approximant structures of quasiperiodic Penrose and octagonal tilings, and twisted bilayers of graphene or transition metal dichalcogenides (TMDs) whose rotation angle between the two layers assumes a special value, called "magic angle". In these materials, the flat bands correspond to electronic states distributed over a very large number of atoms (several hundreds or even thousands of atoms) and are very sensitive to small structural distortions such as "heterostrain". We have shown that their electronic transport properties cannot be described by usual Bloch-Boltzmann theories, because the interband terms of the velocity operator dominate the intraband terms as far as quantum diffusion is concerned. In the case of twisted bilayer graphene, flat bands can induce a magnetic state and other electron-electron correlation effects. The second part focuses on two-dimensional nanomaterials in the presence of local point defects that cause resonant electronic states (vacancies, adsorbed atoms or molecules). We present studies on monolayer graphene, twisted or Bernal bilayer graphene, carbon nanotubes, monolayer and multilayer black phosphorene, and monolayer TMDs. A recent result is the discovery that the selective functionalization of a Bernal bilayer graphene sublattice leads to a metallic or insulating behavior depending on the functionalized sublattice type. This result, which seems to be confirmed by very recent experimental measurements, suggests that functionalization can be a key parameter to control the electronic properties of two-dimensional materials
Single-Vehicle Trajectory Prediction: A Review and Experimental Embedded Assessment
No full textInternational audienceDue to technological advances in the automotive field, advanced driver assistance systems have attracted increasing interest from various research and development entities. Predicting road users' future trajectories remains an active research challenge for advanced driver assistance systems. Accurate Trajectory Prediction (TP) allows anticipation of surrounding road users' future motion, enabling timely safety-critical interventions such as speed regulation and emergency braking in unexpected driving situations. Recent advances in TP methods based on artificial intelligence have demonstrated remarkably accurate results compared to traditional methods. However, many of these models require a high computational burden, which makes their deployment on embedded architectures with constrained resources challenging. To overcome these constraints, TP models need to be lightweight and efficient to meet the real-time and power consumption requirements of advanced driver assistance systems. In other words, they must maintain high accuracy while guaranteeing low computational load and rapid inference. This paper presents a comparative and experimental review of state-of-the-art vehicle TP models. First, we propose a new taxonomy based on the operating environment, the trajectory output type, and the employed modeling approach to classify existing methods. Then, we evaluate representative approaches w.r.t the taxonomy in terms of accuracy, model complexity, computational performance, and real-time feasibility across a high-performance architecture and an embedded architecture. Finally, we discuss the evaluation results and present key conclusions and future directions
L'intrication, principe d'organisation de la réalité phénoménale
No full textLes propriétés de complémentarité et d'intrication peuvent être mises en évidence en dehors du strict domaine quantique et même au-delà du domaine matériel, en particulier pour le phénomène psychosomatique. Cette direction de recherche peut être développée rigoureusement dans le cadre d'une théorie quantique généralisée où toute référence a priori au monde physique a été éliminée. Un lien fondamental entre ces deux notions peut, en outre, y être établi comme le montre le théorème de Landeau. Nous proposons de considérer l'intrication comme un principe général d'organisation de notre expérience et de poser quelques jalons à l'élaboration d'une « logique de l'intrication »
Synchrotron-Assisted HPHT Annealing Of Quantum Nanodiamonds: In Situ Control Of Phase Stability
No full textInternational audienceGroup-IV color centers in nanodiamond, such as silicon-vacancy (SiV) defects, are promising quantum emitters for sensing and photonics due to their bright and narrow zero-phonon line (ZPL) emission, representing up to 80% of their total luminescence [1–3]. However, in as-grown CVD nanodiamonds, residual lattice strain induces significant spectral broadening, preventing access to the fine electronic structure of SiV centers even at cryogenic temperatures. To mitigate this effect, we carried out a controlled high-pressure and high-temperature (HPHT) annealing process using the Paris–Edinburgh press, performed in situ at the PSICHE beamline of Synchrotron SOLEIL [4]. The synchrotron X-ray diffraction and tomography measurements were crucial for the precise calibration of pressure and temperature conditions within the assembly, enabling us to finely tune the HPHT parameters to promote strain relaxation while avoiding the onset of graphitization. These in situ synchrotron investigations provided real-time insight into nanodiamond phase stability and strain-release mechanisms, which were confirmed ex situ by optical measurements, leading to the first observation of resolved fine-structure transitions in SiV centers after HPHT treatment. Importantly, the calibrated HPHT setup can now be reliably operated off-beam, enabling systematic post-annealing studies on different types of nanodiamonds and color centers. This methodology establishes a robust experimental reference for future off-beam HPHT annealing treatments and serves as a benchmark for the broader quantum diamond research community.REFERENCES 1. T. Muller et al., Nat. Commun. 5, 3328 (2014).2. M. De Feudis et al., Adv. Mater. Interfaces 7, 1901408 (2019).3. B. Vindolet et al., Phys. Rev. B 106, 214109 (2022).4. L. Henry et al., J. Synchrotron Rad. 29, 853-861 (2022)
Affects blancs et politiques de l’innocence
No full textInternational audienceDrawing on their respective work, Léna Dormeau and Félicien Faury explore the affective mechanisms through which whiteness is structured, legitimized, and reproduced. In this conversation, they revisit the notions of vulnerability, innocence, and liminality, and, through these, articulate the following question: what are white people afraid of ?À partir de leurs travaux respectifs, Léna Dormeau et Félicien Faury interrogent les mécaniques affectives permettant à la blanchité de se structurer, se légitimer et se perpétuer. Dans cette conversation, illes reviennent sur les notions de vulnérabilité, d’innocence ou de liminarité, et à travers elles dessinent la question suivante : de quoi les blancs ont-ils peur
Soil organic matter decomposition in semi-arid mangrove stands (New Caledonia)
No full textInternational audienceOrganic matter (OM) dynamics in mangrove forests have been studied extensively in terms of the capacity of their soils to store organic carbon. While δ13C, δ15N, and C/N values for mangrove soils and sources are well reported, other indicators of OM maturity and composition are lacking. In this study, soil OM decomposition processes were investigated for a semi-arid bay head mangrove forest in New Caledonia. Mangrove tissues and 20-cm soil cores were collected in monospecific stands of Avicennia marina and Rhizophora stylosa. The isotopic compositions of the samples were assessed, along with their molecular compositions (lignin-derived phenols and neutral carbohydrates). Rock-Eval analysis was also performed on the samples to investigate OM characteristics. Results showed that stable isotope ratios and Rock-Eval parameters followed similar vertical trends beneath both species indicating the influence of depth on OM state. However, the more anoxic conditions beneath R. stylosa limited OM decomposition as shown by the lower TpS2 values (indicator of OM thermal stability). Neutral carbohydrates and, surprisingly, lignin-derived phenols, were lost at higher rates than bulk organic carbon beneath both mangrove species. Selective degradation of individual compounds was observed, and species-dependent variations associated with the redox conditions and the OM sources were identified. We suggest that lignin was degraded, even in anoxic environments, because of the amount of labile lignocellulosic components in the soil. These findings enhance our understanding of OM dynamics in mangrove ecosystems, shedding light on the mechanisms underlying carbon cycling and their implications for global carbon storage and ecosystem management
Periodicities in radio emissions from Jupiter's magnetosphere and consequences for radio emissions from star─exoplanet systems
No full textInternational audienceContext. The search for radio signals from exoplanets or star-planet interactions is a topic of major scientific interest, as it is likely the best way to detect and measure a planetary magnetic field and, therefore, to probe the inner structure of exoplanets. However, detecting these radio emissions is challenging, since they are anisotropic by nature, sporadic, and of low intensity because of their great distances, and because the sky cannot be monitored continuously. Aims. The aim of this article is to demonstrate the relevance of using statistical tools to detect periodic radio signals in unevenly spaced observations and to identify the implications of the measured period. Methods. The identification of periodic radio signals was achieved here through a Lomb-Scargle analysis. The technique was first applied to simulated astrophysical observations with controlled simulated noise. This allowed us to characterise the origin of spurious detection peaks in the resulting periodograms - as well as to identify peaks corresponding to real periods in the studied system - and to combination or beat periods. Results. The method was validated using a real signal, with ∼1400 hours of data from observations of Jupiter's radio emissions by the NenuFAR radio telescope over more than six years, in order to detect the periodicities of Jovian radio emissions (auroral and induced by the Galilean moons). Conclusions. We demonstrate with the simulation that the Lomb-Scargle periodogram allows us to correctly identify periodic radio signals, even in a diluted signal. On real measurements, it correctly detects the rotation period of the strong signal produced by Jupiter and the beat period of the emission triggered by the interaction between Jupiter and its Galilean moon Io, but also possibly weaker signals, such as those produced by the interaction between Jupiter and Europa or between Jupiter and Ganymede. It is important to note that secondary peaks in the Lomb-Scargle periodogram appear at the beat and combination periods among all the detected signal periodicities (i.e. real signals, but also periodicities due to regular observation intervals). These secondary peaks can then be used to strengthen the detection of weak signals. Finally, the importance of the number of observation windows used in the Lomb-Scargle analysis is discussed, as well as the data's time and frequency resolutions in increasing its efficiency
Spatially resolved broad-line region in a quasar at z = 4
No full textInternational audienceWe present the first near-infrared interferometric data of a QSO at z = 4. The K -band observations were performed with GRAVITY+ on the VLTI using all four UTs, detecting a differential phase signal that traces the spatially resolved kinematics for both the H β and H γ lines in the broad-line region (BLR). We fit the two lines simultaneously with an updated model that includes distinct rotating and conical outflowing components. For the best-fit model, more than 80% of the H I line emission from the BLR originates in an outflow with a velocity up to 10 4 km s −1 . This is oriented so that our line of sight is along an edge of the conical structure, which produces the prominent blue wing on the line profile. A combination of anisotropic line emission and mid-plane opacity leads to the single-sided phase signal. The model is able to qualitatively match both the outflowing C IV line profile and the systemic O I fluorescent emission. The black hole mass of 8 × 10 8 M ⊙ that we derive is the highest redshift black hole mass measurement to date obtained directly from BLR dynamics. It is an order of magnitude lower than that inferred from various single epoch scaling relations, and it implies that the accretion is highly super-Eddington. With reference to recent simulations, the data suggest that this QSO is emitting close to its radiative limit in a regime where strong outflows are expected around a polar conical region
Cours d'Analyse de niveau L1, 2021-2024.
No full textDEUGVersion longue d'un cours d'analyse de niveau L1 donné en 2021-2024. Révision en 2026