Université Bordeaux 1
  • Talence, France
Recent publications
The main result of this paper states the subpolynomial growth of the number of integral points with bounded height of a variety over a number field whose fundamental group is large. This generalizes a recent paper of Ellenberg, Lawrence and Venkatesh and replies to two questions asked therein.
We extend our recent theoretical work on the bending relaxation of H2O in collisions with H2 by including the three water modes of vibration coupled with rotation, as well as the rotation of H2. Our full quantum close‐coupling method is combined with a high‐accuracy nine‐dimensional potential energy surface. The collisions of para‐H2O and ortho‐H2O with the two spin modifications of H2 are considered and compared for several initial states of H2O. The convergence of the results as a function of the size of the rotational basis set of the two colliders is discussed. In particular, near‐resonant energy transfer between H2O and H2 is found to control the vibrational relaxation process, with a dominant contribution of transitions with Δ j2=+2, +4 in H2. Finally, the calculated value of the H2O bending relaxation rate coefficient at 295K is found to be in excellent agreement with its experimental estimate.
In this note, we give a self-contained presentation of the POAV2 theory developed by Haddon to study the alignment of π-orbitals along a non-planar molecule. The classical POAV theory is purely geometric instead of the POAV2 which includes more physics in the computations. We compare the results obtained from the POAV2 and POAV theory. We prove that the difference between the two quantities is in most of the cases negligible. As a consequence, the POAV theory is sufficient for most of the purposes concerning the description of the local π-system of a molecule.
Plastic phases are constituted by molecules whose centers of mass form a long range ordered crystalline lattice, but rotate in a more or less constrained way. Pentachloronitrobenzene (PCNB) is a quasi-planar hexa-substituted benzene formed by a benzene ring decorated with a -NO2 group and five chlorine atoms that displays below the melting point a layered structure of rhombohedral (R3̄) planes in which the molecules can rotate around a six-fold-like axis. Dielectric spectroscopy [Romanini et al., The Journal of Physical Chemistry C, 2016, 120, 10614] of this highly anisotropic phase revealed a complex relaxation dynamics with two coupled primary α processes, initially ascribed to the in-plane and out-of-plane components of the molecular dipole. In this work, we perform a series of molecular dynamics simulations together with single crystal X-ray synchrotron diffraction experiments to investigate the puzzling dynamics of PCNB. We conclude that the molecule undergoes very fast movements due to the high flexibility of the -NO2 group, and two slower movements in which only the in-plane rotation of the whole ring is involved. These two movements are related to fast attempts to perform a 60° in-plane rotation, and a diffusive motion that involves the rotation of the molecule completely decorrelating the dipole orientation. We have also investigated whether a homogeneous or a heterogeneous scenario is better suited to describe the restricted orientational disorder of this anisotropic phase both from a structural and dynamical point of view.
Label‐free super‐resolution (LFSR) imaging relies on light‐scattering processes in nanoscale objects without a need for fluorescent (FL) staining required in super‐resolved FL microscopy. The objectives of this Roadmap are to present a comprehensive vision of the developments, the state‐of‐the‐art in this field, and to discuss the resolution boundaries and hurdles that need to be overcome to break the classical diffraction limit of the label‐free imaging. The scope of this Roadmap spans from the advanced interference detection techniques, where the diffraction‐limited lateral resolution is combined with unsurpassed axial and temporal resolution, to techniques with true lateral super‐resolution capability that are based on understanding resolution as an information science problem, on using novel structured illumination, near‐field scanning, and nonlinear optics approaches, and on designing superlenses based on nanoplasmonics, metamaterials, transformation optics, and microsphere‐assisted approaches. To this end, this Roadmap brings under the same umbrella researchers from the physics and biomedical optics communities in which such studies have often been developing separately. The ultimate intent of this paper is to create a vision for the current and future developments of LFSR imaging based on its physical mechanisms and to create a great opening for the series of articles in this field.
We find the generating function for the contributions of n-cylinder square-tiled surfaces to the Masur–Veech volume of \(\mathcal{H}(2g-2)\). It is a bivariate generalization of the generating function for the total volumes obtained by Sauvaget via intersection theory. Our approach is, however, purely combinatorial. It relies on the study of counting functions for certain families of metric ribbon graphs. Their top-degree terms are polynomials, whose (normalized) coefficients are cardinalities of certain families of metric plane trees. These polynomials are analogues of Kontsevich polynomials that appear as part of his proof of Witten’s conjecture.
Recycled fibre composites are made of discontinuous fibres that are not of the same length. Their mechanical behaviour depends on the load transfer between fibres and in particular on the overlaps between fibres of different lengths. The objective of the study is to show the influence of the architecture on the failure of a discontinuous reinforcement composite. A numerical model was developed to simulate different overlap lengths between fibres. The influence of defects, in this study small overlap length between fibres, and of their distribution in the architecture, was thus highlighted. Experimental tests allowed to validate the model. The model makes it possible to calculate a critical overlap length, length from which the composite strength reaches its maximum. In particular, simulations showed that discontinuous fibre architectures with small overlap lengths at the edge strongly decrease the strength of the composite. On the contrary, defects in the core of the architecture are tolerable. These results open perspectives for the choice of architectures based on recycled fibre in order to optimize the final properties of the composite.
Timing is a critical component of a wide range of sensorimotor tasks that can span from a few milliseconds up to several minutes. While it is assumed that there exist several distributed systems that are dedicated for production and perception [1], the neuronal mechanisms underlying precise timing remain unclear. Here, we are interested in the neural mechanisms of sub-second timing with millisecond precision. To this end, we study the control of song timing in male Zebra Finches whose song production relies on the tight coordination of vocal muscles. There, the premotor nucleus HVC (proper name) is responsible for the precise control of timing. Current models of HVC rely on the synfire chain, a pure feed-forward network. However, synfire chains are fragile regarding noise and are only functional for a narrow range of feed-forward weights, requiring fine tuning during learning. In the present work, we propose that HVC can be modelled using a ring attractor model [2], where recurrent connections allow the formation of an activity bump that remains stable across a wide range of weights and different levels of noise. In the case of asymmetrical connectivity, the bump of activity can “move” across the network, hence providing precise timing. We explore the plasticity of syllable duration in this framework using a reward-driven learning paradigm and a reward-modulated covariance learning rule applied to the network’s synaptic weights [3]. We show that the change in duration induced by the learning paradigm is specific to the target syllable, consistent with experimental data.
Inorganic metal halide perovskites such as CsPbI 3 are promising for high‐performance, reproducible and robust solar cells. However, inorganic perovskites are sensitive to humidity, which causes the transformation from the black phase to the yellow δ, non‐perovskite phase. Such phase instability has been a significant challenge to long‐term operational stability. Here, we report a surface dimensionality reduction strategy, using 2‐(4‐aminophenyl) ethylamine cation to construct a Dion‐Jacobson 2D phase that covers the surface of the 3D inorganic perovskite structure. The Dion‐Jacobson layer mainly grew at the grain boundaries of the perovskite, effectively passivating surface defects and providing favourable interfacial charge transfer. The resulting inorganic perovskite films exhibited excellent humidity resistance when submerged in an aqueous solution (Isopropanol: Water = 4: 1v/v) and exposed to a 50% humidity air atmosphere. The DJ 2D/3D inorganic perovskite solar cell (PSC) achieved a power conversion efficiency (PCE) of 19.5% with a V oc of 1.197 eV. It retained 83% of initial PCE after 1260 h of maximum power point tracking under 1.2 sun illumination. Our work demonstrates an effective way for stabilising efficient inorganic perovskite solar cells. This article is protected by copyright. All rights reserved
We propose in this paper a new nonlinear mathematical model of an oscillating water column (OWC). The one-dimensional shallow water equations in the presence of this device are reformulated as a transmission problem related to the interaction between waves and a fixed partially immersed structure. By imposing the conservation of the total fluid-OWC energy in the non-damped scenario, we are able to derive a transmission condition that involves a time-dependent air pressure inside the chamber of the device, instead of a constant atmospheric pressure as in Bocchi et al. (ESAIM Proc Surv 70:68–83, 2021). We then show that the transmission problem can be reduced to a quasilinear hyperbolic initial boundary value problem with a semi-linear boundary condition determined by an ODE depending on the trace of the solution to the PDE at the boundary. Local well-posedness for general problems of this type is established via an iterative scheme by using linear estimates for the PDE and nonlinear estimates for the ODE.
The defluorinative functionalization of allylic fluorides represents an attractive approach for the preparation of molecules containing a monofluoroalkene core. In that sense, introducing a “boryl nucleophile” is a powerful strategy to obtain polyvalent borylated intermediates as versatile synthetic precursors. To perform this reaction without the use of transition metals, the nucleophilic character of a diborane/fluoride system was exploited in a SN2′ type‐substitution reaction of gem‐difluoropropenes to install a pinacolborane group. The use of HMDS as a silylated additive is necessary to improve the reactivity. A direct oxidation of the intermediate boronates allowed the isolation of the corresponding β‐fluoroallyl alcohols in low to good yields (9−81%). Other synthetic transformations of a (2‐fluoroallyl)boronate are also illustrated.
In this contribution, we present a comparative study on top-down drilling in sodalime glass, with a femtosecond laser operating in single-pulse, MHz-burst and GHz-burst modes, respectively. We investigate the hole depth, drilling rate, and hole morphology for these three regimes while keeping the same experimental conditions. We demonstrate that, for both burst regimes, the burst length has to be adapted for optimizing the hole depth. In the GHz-burst regime, the lower the ablation rate the longer the holes. The three drilling regimes lead to different hole morphologies, where the GHz-burst mode results in the best hole quality featuring glossy inner walls and an almost cylindrical morphology. Furthermore, we obtain crack-free holes, the deepest measuring 3.7 mm in length and 25 µm in entrance diameter corresponding to an aspect ratio of 150, which is the highest aspect ratio reported thus far with femtosecond GHz-burst drilling to the best of our knowledge.
The aim of this study was to explore the adverse effects of a microplastic (MP) mixture obtained from litter accumulated in the Seine River (France) compared to those of their major co-plasticizer, dibutylphthalate (DBP), on the sentinel species Hediste diversicolor. A suite of biomarkers has been investigated to study the impacts of MPs (100 mg kg − 1 sediment), DBP (38 μg kg − 1 sediment) on worms compared to non-exposed individuals after 4 and 21 days. The antioxidant response, immunity, neurotoxicity and energy and respiratory metabolism were investigated using biomarkers. After 21 days, worms exposed to MPs showed an increasing aerobic metabolism, an enhancement of both antioxidant and neuroimmune responses. Energy-related biomarkers demonstrated that the energy reallocated to the defence system may come from proteins. A similar impact was depicted after DBP exposure, except for neurotoxicity. Our results provide a better understanding of the ecotoxicological effects of environmental MPs and their associated-contaminants on H. diversicolor.
We report, for the first time to the best of our knowledge, Bessel beam dielectrics cutting with a femtosecond laser in GHz-burst mode. The non-diffractive beam shaping is based on the use of an axicon and allows for cutting glasses up to 1 mm thickness with an excellent cutting quality. Moreover, we present a comparison of the cutting results with the state-of-the-art method, consisting of short MHz-bursts of femtosecond pulses. We further illustrate the influence of the laser beam parameters such as the burst energy and the pitch between consecutive Bessel beams on the machining quality of the cutting plane and provide process windows for both regimes.
We performed spin-, time- and angle-resolved extreme ultraviolet photoemission spectroscopy of excitons prepared by photoexcitation of inversion-symmetric 2H−WSe2 with circularly polarized light. The very short probing depth of XUV photoemission permits selective measurement of photoelectrons originating from the top-most WSe2 layer, allowing for direct measurement of hidden spin polarization of bright and momentum-forbidden dark excitons. Our results reveal efficient chiroptical control of bright excitons’ hidden spin polarization. Following optical photoexcitation, intervalley scattering between nonequivalent K−K′ valleys leads to a decay of bright excitons’ hidden spin polarization. Conversely, the ultrafast formation of momentum-forbidden dark excitons acts as a local spin polarization reservoir, which could be used for spin injection in van der Waals heterostructures involving multilayer transition metal dichalcogenides.
We introduce sequential and parallel decoders for quantum Tanner codes. When the Tanner code construction is applied to a sufficiently expanding square complex with robust local codes, we obtain a family of asymptotically good quantum low-density parity-check codes. In this case, our decoders provably correct arbitrary errors of weight linear in the code length, respectively in linear or logarithmic time. The same decoders are easily adapted to the expander lifted product codes of Panteleev and Kalachev. Along the way, we exploit recently established bounds on the robustness of random tensor codes to give a tighter bound on the minimum distance of quantum Tanner codes.
We here report theoretical triply differential cross sections (TDCS) for 250 eV electron and positron impact ionization of the methane molecule calculated within the second-order distorted-wave Born approximation (DWBA2) for various momentum transfer conditions. The experimental data taken from Işık et al. [J. Phys. B: At., Mol. Opt. Phys. 49, 065203 (2016)] will be compared with the current theoretical predictions as well as molecular three body distorted wave (M3DW) approximation and generalized Sturmian function (GSF) theoretical models in a non-coplanar geometry. In the low analyzer scattering plane, the results obtained within the DWBA2 theory show better agreement with the experimental results compared to the GSF results. The M3DW results also exhibit agreement with the experimental results, in particular in the perpendicular plane geometry. Furthermore, significant differences between electron and positron TDCS were observed.
Because the combination of chiral and magnetic properties is becoming more and more attractive for magneto-chiral phenomena, we here aim at exploring the induction of chirality to achiral magnetic molecules as a strategy for the preparation of magneto-chiral objects. To this end, we have associated free base- and metallo-porphyrins with silica nano helices, using a variety of elaboration methods, and have studied them mainly by electronic natural circular dichroism (NCD) and magnetic circular dichroism (MCD) spectroscopies. While electrostatic or covalent surface grafting uniformly yielded very low induced CD (ICD) for the four assayed porphyrins, a moderate response was observed when the porphyrins were incorporated into the interior of the double-walled helices, likely due to the association of the molecules with the chirally-organized gemini surfactant. A generally stronger, but more variable, ICD was observed when the molecules were drop casted onto the helices immobilised on a quartz plate, likely due to the different capacities of the porphyrins to aggregate into chiral assemblies. Electronic spectroscopy, electron microscopy and IR spectroscopy were used to interpret the patterns of aggregation and their influence on ICD and MCD. No enhancement of MCD was observed as a result of association with the nanohelices except in the case of the free base, 5,10,15,20-tetra-(4-sulfonatophenyl)porphyrin (TPPS). This nanocomposite demonstrated a large ICD in the Soret region and a large MCD in the Q-region due to J-aggregation. However, no induced MChD was observed, possibly due to the spectral mismatch between the ICD and MCD peaks.
Purpose: Coronal balance is a major factor impacting the surgical outcomes in adult spinal deformity (ASD). The Obeid coronal malalignment (O-CM) classification has been proposed to improve the coronal alignment in ASD surgery. Aim of this study was to investigate whether a postoperative CM < 20 mm and adherence to the O-CM classification could improve surgical outcomes and decrease the rate of mechanical failure in a cohort of ASD patients. Methods: Multicenter retrospective analysis of prospectively collected data on all ASD patients who underwent surgical management and had a preoperative CM > 20 mm and a 2-year follow-up. Patients were divided in two groups according to whether or not surgery had been performed in adherence to the guidelines of the O-CM classification and according to whether or not the residual CM was < 20 mm. The outcomes of interest were radiographic data, rate of mechanical complications and Patient-Reported Outcome Measures. Results: At 2 years, adherence to the O-CM classification led to a lower rate of mechanical complications (40 vs. 60%). A coronal correction of the CM < 20 mm allowed for a significant improvement in SRS-22 and SF-36 scores and was associated with a 3.5 times greater odd of achieving the minimal clinical important difference for the SRS-22. Conclusion: Adherence to the O-CM classification could reduce the risk of mechanic complications 2 years after ASD surgery. Patients with a residual CM < 20 mm showed better functional outcomes and a 3.5 times greater odd of achieving the MCID for the SRS-22 score.
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1,209 members
Vincent Lepetit
  • UMR LaBRI - Laboratoire Bordelais de Recherche en Informatique
Breysse Denys
  • Département de Génie Civil et Environnemental (GCE)
Bernard Veyret
  • UMR IMS - Laboratoire d'Integration du Materiau au Système (IMS)
Bruno Maureille
  • UMR PACEA - Laboratoire de la Préhistoire à l'Actuel : Culture, Environnement et Anthropologie
Nicole Mons
  • Aquitaine Institute for Cognitive and Integrative Neuroscience (INCIA)
351, cours de la libération, 33405, Talence, France