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The isometry of symmetric-Stratonovich integrals w.r.t. Fractional Brownian motion
No full textIn this work, we present a detailed analysis on the exact expression of the -norm of the symmetric-Stratonovich stochastic integral driven by a multi-dimensional fractional Brownian motion with parameter . Our main result is a complete description of a Hilbert space of integrand processes which realizes the -isometry where none regularity condition in the sense of Malliavin calculus is imposed. The main idea is to exploit the regularity of the conditional expectation of the tensor product of the increments onto the Gaussian space generated by as . The Hilbert space is characterized in terms of a random Radon -finite measure on off diagonal which can be characterized as a product of a non-Markovian version of the stochastic Nelson derivatives. As a by-product, we present the exact explicit expression of the -norm of the pathwise rough integral in the sense of Gubinelli
Concevoir un écosystème de formation à la transition socioécologique : le cas du projet HOLI-D Blue
No full textInternational audienceThis study focuses on the design and implementation of a training and research project, called HOLI-D Blue, which aims to develop a holistic training system for engineers to understand and respond to environmental and societal issues in the maritime fields. In practice, it is the creation of a cross-disciplinary and interdisciplinary specialisation, integrated into the curriculum of initial training of postgraduate students, starting with ENSTA Bretagne for the test device. Starting from a systemic approach, HOLI-D Blue is based on a transverse project pedagogy that seeks to link all the time-spaces and training modalities, both academic and non-academic, throughout a three-year curriculum, by involving a diversity of actors at different levels of the curriculum. At the halfway point of this project, this paper is an opportunity to present and question the modalities of co-construction of this pathway, as well as the first results of the implementation of the test device designed: the brakes and levers identified, the questions and perspectives raised. This reflective work focuses on two specific aspects: (1) the heuristic value of thinking and designing this type of training as ecosystems, (2) the contribution of this device to the accompaniment of students in their emancipation and their "power to act".Cette étude s’intéresse à la conception et la mise en œuvre d’un projet de formation et de recherche, dénommé HOLI-D Blue, qui a pour ambition de développer un dispositif holistique de formation d’ingénieurs pour comprendre et répondre aux enjeux environnementaux et sociétaux des domaines maritimes. En pratique, il s’agit de la création d’un parcours transversal et interdisciplinaire, intégré au cursus de formation initiale d’étudiants de 3ème cycle, à commencer par une école d'ingénieurs de la pointe Finistère pour le dispositif-test. Partant d’une approche systémique, HOLI-D Blue repose sur une pédagogie de projet transverse qui cherche à relier l’ensemble des espace-temps et des modalités de formation, académiques et non-académiques sur l’ensemble d’un cursus en trois ans, en impliquant une diversité d’acteurs à différentes échelles du curriculum. A mi-parcours de ce projet, cette communication est l’occasion de présenter et de questionner les modalités de co-construction de ce parcours, ainsi que les 1ers résultats de la mise en œuvre du dispositif-test conçu : les freins et leviers identifiés, les questions et perspectives soulevées. Ce travail réflexif se focalise sur deux aspects spécifiques : (1) la valeur heuristique de penser et concevoir ce type de formation comme des écosystèmes, (2) la contribution de ce dispositif à l’accompagnement des étudiants dans leur émancipation et leur« pouvoir d’agir »
The xanthate route to tetralones, tetralins, and naphthalenes. A brief account
No full textInternational audienceThe radical chemistry of xanthates allows numerous approaches to tetralones, tetralins, and naphthalenes
Palladium-Catalyzed ortho -C–H Alkoxycarbonylation of Aromatic Aldehydes via a Transient Directing Group Strategy
No full textInternational audienceTransient directing groups (TDGs) can be a powerful strategy to directly functionalized C−H bonds of aldehydes. We report a palladium-catalyzed ortho-C−H alkoxycarbonylation of benzaldehydes using catalytic amount of aromatic amine to form a transient imine which plays the role of monodentate TDG. The reaction conditions were applied to a broad range of aldehydes and corresponding 2-formyl benzoates were used as direct precursors for the synthesis of phthalides and 1-isoindolinones
Path-dependent Hamilton-Jacobi-Bellman equation: Uniqueness of Crandall-Lions viscosity solutions
No full textWe formulate a path-dependent stochastic optimal control problem under general conditions, for which weprove rigorously the dynamic programming principle and that the value function is the unique Crandall-Lions viscosity solution of the corresponding Hamilton-Jacobi-Bellman equation. Compared to the literature, the proof of our core result, that is the comparison theorem, is based on the fact that the valuefunction is bigger than any viscosity subsolution and smaller than any viscosity supersolution. It alsorelies on the approximation of the value function in terms of functions defined on finite-dimensionalspaces as well as on regularity results for parabolic partial differential equations
A hybrid shell-beam element for straight thin-walled tubular structures
No full textInternational audienceA novel beam model is proposed in order to consider deformations of its cross-section in the context of straight thin-walled tubes. For this purpose, the straight beam kinematics is enriched by addition of orthogonal shell-type displacement field of the tube section. The considered displacement field is composed of three contributions: classical linear beam and linear shell terms in conjunction with the non-linear coupling between local deformation of the section and its global rotation. Both Euler-Bernoulli and Love-Kirchhoff hypotheses for beam and shell kinematics, respectively, are adopted as well as the thin-walled assumption. First-order shear deformation for the radial variable and Fourier expansion in terms of the circumferential variable are also considered for the mid-surface displacement field. Then, the stress tensor is obtained under plane stress conditions. The virtual power principle is finally used to obtain the equations of motion satisfied by the corresponding generalized forces. Afterwards, an explicit updated Lagrangian Finite-Element approach using a lumped mass matrix is proposed for solving the tube governing equations and the stability condition of the time integration is given. Test-cases are then chosen to assess the present tube finiteelement. Both static and dynamic problems are considered. First, the proposed model is compared to analytical solutions. Finally, a tube subjected to a distributed patch loading is studied. The influence of the number of Fourier modes, of warping and coupling terms is examined. The proposed model makes it possible to retrieve classical shell solution of the cross-section deformation with significant computational savings
Reduced order modeling of rotating structures featuring geometric nonlinearity with the direct parametrisation of invariant manifolds method
No full textInternational audienceThe direct parametrisation method for invariant manifolds (DPIM) is applied to rotating structures. Reduced- order models of arbitrary order expansion can be derived for non-autonomous systems of nonlinear differential equations stemming from finite element models of continuous structures. The method is applied to a rotating simplified fan blade with comparisons to full order model simulations
Effect of the deposition direction on fracture propagation in a Duplex Stainless Steel manufactured by Directed Energy Deposition
No full textInternational audienceDense volumes of duplex stainless steel are manufactured by directed energy deposition. Compact tension specimens are machined from these volumes in order to evaluate the fracture toughness in two directions : parallel or perpendicular to the deposited layers. Different values are measured in the two cases. In order to understand this anisotropy, additional analyzes are performed on the cracked specimens post-mortem. A classical metallography analysis reveals the highly oriented structure of the material, as well as phase localization. The study of the fracture surface reveals several points. At the macroscale, while the crack surfaces are flat in the parallel case, pronounced shear lips cover half of the fracture surface in the perpendicular case. At the microscale, fracture is ruled by microvoid coalescence. The mesoscale, which is inherited from the deposition strategy, is found to pilot the crack growth. The border between the primary solidified melt pools and the heat-affected zones, which corresponds to the interface between the deposited layers, is the preferred area for crack growth. Analyzing the crack surface roughness confirms the dominance of the mesoscale, as its characteristic lengthscale is retrieved. This explains the differences observed for the two tested directions of fracture: in the parallel case, the crack is aligned with the weak interfaces between layers, which channel the crack growth; in the orthogonal one, out-of-plane excursion of the crack becomes possible allowing the crack to follow a tortuous three-dimensional path that results in a higher toughness than in the parallel situation
Water vapour monitoring over France using the low-cost GNSS collaborative network Centipede
No full textInternational audienceIn recent years, the significant growth of positioning applications has come with the development of low-cost dual frequency Global Navigation Satellite Systems (GNSS) receivers. Such receivers allow high precision positioning to be achieved. They are becoming increasingly popular for geosciences as they allow for large numbers of equipment at affordable prices.&#160;</p><p>Founded in 2019, the Centipede network is a collaborative permanent GNSS network that aims to offer free real-time centimetric positioning to any user. The network is currently made up of more than 330 low-cost reference stations located mainly in France and has nearly 500 regular users. Since July 2022, the GNSS raw data acquired by the stations forming this network have been archived by the R&#233;seau National GNSS (RENAG) scientific network data centre in order to evaluate their suitability for geosciences applications such as tectonic, sea-level monitoring, troposphere and ionosphere studies.&#160;</p><p>In this study, we present a first evaluation of the use of this dataset for the retrieval of integrated water vapour content (IWV) over five months in 2022. Troposphere delays are estimated from a PPP analysis and are converted to IWV using a standard procedure. Then, the IWV are compared with those retrieved for GNSS stations from the conventional French permanent GNSS networks, the R&#233;seau GNSS Permanent (RGP) and RENAG. The results of these comparisons are conclusive, with root mean square differences in the range of 0.5-2 kg/m2 and high correlations of the time series registered by nearby low-cost and geodetic-class receivers;These results confirm the high potential of low-cost GNSS networks. The development of such network is a real opportunity for geoscience applications, particularly in poorly instrumented areas. &#160;In such areas, their contribution could be especially significant for meteorological or climatological applications for which the monitoring of water vapour by GNSS is widely used
Gigue: A JIT Code Binary Generator for Hardware Testing
No full textNational audienceJust-in-time compilers are the main virtual machine components responsible for performance. They recompile frequently used source code to machine code directly, avoiding the slower interpretation path. Hardware acceleration and performant security primitives would benefit the generated JIT code directly and increase the adoption of hardware-enforced primitives in a high-level execution component.The RISC-V instruction set architecture presents extension capabilities to design and integrate custom instructions. It is available as open-source and several capable open-source cores coexist, usable for prototyping. Testing JIT-compiler-specific instruction extensions would require extending the JIT compiler itself, other VM components, the underlying operating system, and the hardware implementation. As the cost of hardware prototyping is already high, a lightweight representation of the JIT compiler code region in memory would ease prototyping and implementation of new solutions.In this work, we present Gigue, a binary generator that outputs bare-metal executable code, representing a JIT code region snapshot composed of randomly filled methods. Its main goal is to speed up hardware extension prototyping by defining JIT-centered workloads over the newly defined instructions. It is modular and heavily configurable to qualify different JIT code regions' implementations from VMs and different running applications. We show how the generated binaries can be extended with three custom extensions, whose execution is guaranteed by Gigue's testing framework. We also present different application case generation and execution on top of a fully-featured RISC-V core