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Spatial Autoregressive Model on a Dirichlet Distribution
No full textInternational audienceCompositional data find broad application across diverse fields due to their efficacy in representing proportions or percentages of various components within a whole. Spatial dependencies often exist in compositional data, particularly when the data represents different land uses or ecological variables. Ignoring the spatial autocorrelations in modelling of compositional data may lead to incorrect estimates of parameters. Hence, it is essential to incorporate spatial information into the statistical analysis of compositional data to obtain accurate and reliable results. However, traditional statistical methods are not directly applicable to compositional data due to the correlation between its observations, which are constrained to lie on a simplex. To address this challenge, the Dirichlet distribution is commonly employed, as its support aligns with the nature of compositional vectors. Specifically, the R package DirichletReg provides a regression model, termed Dirichlet regression, tailored for compositional data. However, this model fails to account for spatial dependencies, thereby restricting its utility in spatial contexts. In this study, we introduce a novel spatial autoregressive Dirichlet regression model for compositional data, adeptly integrating spatial dependencies among observations. We construct a maximum likelihood estimator for a Dirichlet density function augmented with a spatial lag term. We compare this spatial autoregressive model with the same model without spatial lag, where we test both models on synthetic data as well as two real datasets, using different metrics. By considering the spatial relationships among observations, our model provides more accurate and reliable results for the analysis of compositional data. The model is further evaluated against a spatial multinomial regression model for compositional data, and their relative effectiveness is discussed
Strategies to achieve efficiencies of over 19% for organic solar cells
No full textInternational audienceOrganic solar cells are a promising system for generating clean energy. Recent advancements, particularly in non-fullerene acceptors such as Y6 and its derivatives, along with the development of innovative polymer donors, have significantly enhanced the power conversion efficiency of organic solar cells at the laboratory scale, with the expectation to reach 21% in the near future. The strategic engineering of these acceptors has expanded the pool of non-fullerene acceptor materials, providing excellent compatibility with a wide range of donor materials. Moreover, these advancements also foster research into solvent engineering, additive engineering, multicomponent devices, and device architectures. This review highlights the latest progress in terms of active material design, interface material development, device technology, and various proposed strategies aimed at achieving power conversion efficiencies above 19%. Finally, we propose future research directions to achieve high-efficiency organic solar cells. We also expect that this review will contribute to guiding large-scale construction and will pave the way for eventual commercialization
Domain wall dynamics in notched ferromagnetic nanowires
No full textInternational audienceWe study the dynamics of magnetization reversals, known as walls, in a notched ferromagnetic nanowire. The model used is the Landau-Lifschitz equation in dimension 1, with a weight representing the notch. Despite the pinning properties of notches, we establish in this article that when the applied field tends to push the wall far away from the notch, pinning effects are negligible, and wall dynamics are asymptotically close to those in an unnotched wire
"Le vilain qui vit un autre home od sa feme" de Marie de France - Édition et notes d'après le manuscrit York, Minster Library, XVI s. K-12 Pt. I
No full textÉdition et notes du "Vilain qui vit un autre home od sa feme" de Marie de France d'après le manuscrit York, Minster Library, XVI s. K-12 Pt.
"Le vilain et la femme felunesse" de Marie de France - Édition et notes d'après le manuscrit British Library Harley 978
No full textÉdition et notes du "Vilain et la femme felunesse" de Marie de France d'après le ms. BL Harley 97
Probing the structural and electronic heterogeneity of LiVPO4F and KVPO4F positive electrode materials by combined X-ray absorption and emission spectroscopy
No full textInternational audienceVanadium fluoride phosphates are highly intriguing due to their diverse crystal structures, which significantly influence their electrochemical properties, making them favorable candidates for Li-ion and post Li-ion battery applications. In this study, high-energy resolution fluorescence-detected X-ray absorption near-edge structure (HERFD-XANES) spectroscopy and X-ray emission spectroscopy (XES) are combined to describe and understand the distinctive features of Tavorite-type LiVPO4F and KTP-type KVPO4F, along with their deintercalated homeotypic phases. The HERFD-XANES spectra, featuring the 1s2p resonant inelastic X-ray scattering (RIXS) process at the pre-edge region, provide detailed information on the local structure, while a thorough interpretation of the XES signals, including Core-to-Core (CtC) Kα and CtC Kβ, offers complementary information about local structures and oxidation states, respectively. Furthermore, the occupied and unoccupied electronic states close to the Fermi level are described by combining the information from the XES Valence-to-Core (VtC) Kβ2,5 emission line and the HERFD-XANES pre-edge, respectively. The thorough understanding of these spectral signatures is made possible by the application of ab initio calculations. Overall, this comprehensive analysis of both local geometric and electronic structures provides valuable insights into these materials with distinct crystal structures which are applied as alkali ion positive electrodes
Uniform estimates for transmission problems in electromagnetism with high contrast in magnetic permeabilities
No full textInternational audienceWe consider the time-harmonic Maxwell equations set on a domain made up of two subdomains that represent a magnetic conductor and a non-magnetic material, and we assume that the relative magnetic permeability between the two materials is high. We prove uniform a priori estimates for Maxwell solutions when the interface between the two subdomains is supposed to be Lipschitz. Assuming smoothness for the interface between the subdomains, we prove also that the magnetic field possesses a multiscale expansion in powers of with profiles rapidly decaying inside the magnetic conductor
Trefftz methods for solving large-scale time-harmonic wave problems
No full textInternational audienceWave propagation is a complex physical phenomenon that makes the invisible visible by solving an inverse problem. The underlying mathematical model can be formulated in either the time or frequency regime, each with its own advantages and disadvantages. Here, we prefer the frequency domain, which makes it easier to take into account physical parameters such as attenuation. In this case, direct problem solving, crucial in the inversion algorithm, is very costly and the size of the system to be solved quickly reaches the limits of direct linear solvers. Here, we propose a numerical method that relaxes memory constraints by adopting an iterative approach. To this end, we construct an iterative method that belongs to the class of Discontinuous Galerkin Trefftz methods. By reducing calculations to the level of the mesh skeleton, these are known to use less memory than conventional finite element methods. The method is explained in detail in the 1D case, describing its main features, which are a legacy of Trefftz's idea of using approximation spaces composed of special functions, in this case plane waves. This leads to a wellposed discrete problem that can be solved by an iterative block Jacobi method. The method's performance is illustrated in 1D and 3D
Modelling of pheromone release from solid matrix dispenser for integrated pest management
No full textInternational audienceSex pheromones are introduced in the cultivated areas to create mating disruption and thus to protect crops from pests. This article deals with the release characteristics of a model pheromone (dodecyl acetate) encapsulated in a solid matrix developed as a passive dispenser. Released kinetics were obtained both in the field by extracting and quantifying the remaining pheromone in the dispenser over time and in laboratory by emission chamber tests under controlled conditions. Results showed that the release profiles follow pseudo-zero-order kinetics with a quasi-constant release rate of 1.53 mg day-1 under field conditions for the first sixty days. Emission data showed that two key parameters, i.e., the matrix/air partition coefficient (Kma) and the convective transfer coefficient in the gas phase (hm) govern the release rate of the dispenser. Estimates of Kma varied from 1×106 to 4.55×106 and hm from 3.2×10-3 to 5×10-3 m s-1 depending on the air velocity and temperature conditions. Temperature dependence of Kma was most significant and was addressed by estimating the enthalpy of the pheromone partitioning between the matrix dispenser and air (102 kJ mol-1). The results led to the development of a model based on Kma and hm as the main parameters describing pheromone release from the matrix dispenser. A good agreement was found between the measurements obtained in field and model predictions. This model could be an effective tool for adjusting the release rate of pheromone dispensers under practise conditions
Optimisation de forme de fonctionnelles polynomiales avec incertitudes sur le deuxième membre de l’équation d’état
No full textInternational audienceThe present paper is dedicated to a problem of shape optimization where the external loads applied to the structure are subject to uncertainties. The objective functional or the constraints can be written as the expected value of a polynomial functional of degree m. We provide a deterministic expression of the expectation of the polynomial as a function of the first m moments of the random variables modeling the uncertainties, as well as a method to compute its shape derivative according to Hadamard. In particular, no further assumptions on the distribution of the random variables are required, and the method presented in this article is not based on computationally expensive sampling techniques. The proposed method can be applied in different contexts, like the study of the variance of a quadratic functional, or the optimization of a functional approaching the L ∞-norm of a quantity in the structure