École normale supérieure de Cachan

About: École normale supérieure de Cachan is a education organization based out in Cachan, Île-de-France, France. It is known for research contribution in the topics: Decidability & Finite element method. The organization has 2717 authors who have published 5585 publications receiving 175925 citations.

An automatic and modular stereo pipeline for pushbroom images

Abstract: . The increasing availability of high resolution stereo images from Earth observation satellites has boosted the development of tools for producing 3D elevation models. The objective of these tools is to produce digital elevation models of very large areas with minimal human intervention. The development of these tools has been shaped by the constraints of the remote sensing acquisition, for example, using ad hoc stereo matching tools to deal with the pushbroom image geometry. However, this specialization has also created a gap with respect to the fields of computer vision and image processing, where these constraints are usually factored out. In this work we propose a fully automatic and modular stereo pipeline to produce digital elevation models from satellite images. The aim of this new pipeline, called Satellite Stereo Pipeline and abbreviated as s2p, is to use (and test) off-the-shelf computer vision tools while abstracting from the complexity associated to satellite imaging. To this aim, images are cut in small tiles for which we proved that the pushbroom geometry is very accurately approximated by the pinhole model. These tiles are then processed with standard stereo image rectification and stereo matching tools. The specifics of satellite imaging such as pointing accuracy refinement, estimation of the initial elevation from SRTM data, and geodetic coordinate systems are handled transparently by s2p. We demonstrate the robustness of our approach on a large database of satellite images and by providing an online demo of s2p.

Experimental and numerical determinations of the initial surface of phase transformation under biaxial loading in some polycrystalline shape memory alloys

Abstract: Biaxial proportional loading such as tension (compression)–internal pressure and bi-compression tests are performed on a Cu-Zn-Al and Cu-Al-Be shape memory polycrystals. These tests lead to the experimental determination of the initial surface of phase transformation (austenite→martensite) in the principal stress space (σ1,σ2). A first “micro–macro” modeling is performed as follows. Lattice measurements of the cubic austenite and the monoclinic martensite cells are used to determine the “nature” of the phase transformation, i.e. an exact interface between the parent phase and an untwinned martensite variant. The yield surface is obtained by a simple (Sachs constant stress) averaging procedure assuming random texture. A second modeling, performed in the context of the thermodynamics of irreversible processes, consists of a phenomenological approach at the scale of the polycrystal. These two models fit the experimental phase transformation surface well.

Decidability of the termination problem for completely specified protocols

Abstract: In this paper, we present a new class of protocols called completely specified protocols. Each protocol is represented as a system of Communicating Finite State Machines. The class of completely specified protocols is such that each message that can be received by a Finite State Machine, can also be received in every local state of the Finite State Machine. These protocols are important because they allow for modelling unbounded fifo channels and make it possible to decide the Termination Problem, that is whether the reachability tree is finite or not. An example of our techniques is given using a practical problem concerning link protocols.

An expression for droplet evaporation incorporating thermal effects

Abstract: We propose a general theoretical expression for sessile droplets' evaporation, incorporating thermal effects related to the thermal resistance of the substrate and liquid properties. We develop an expression which accounts for thermal effects associated with evaporative cooling; the latter leads to a reduction in the rate of evaporation, which is not accounted for in the current theories, i.e. ‘isothermal diffusion theories’. The threshold for transition to a regime in which thermal effects start to be significant is identified through a dimensionless number which includes substrate and liquid properties as well as the kinetics of evaporation. The proposed theory is validated against experimental data in a very wide range of conditions and for a variety of systems. The developed expression extends the domain of use of diffusion-based models for droplet evaporation and accurately describes some aspects of the phenomenon which, to the best of our knowledge, are highlighted for the first time.

Scanning Nanospin Ensemble Microscope for Nanoscale Magnetic and Thermal Imaging.

Abstract: Quantum sensors based on solid-state spins provide tremendous opportunities in a wide range of fields from basic physics and chemistry to biomedical imaging. However, integrating them into a scanning probe microscope to enable practical, nanoscale quantum imaging is a highly challenging task. Recently, the use of single spins in diamond in conjunction with atomic force microscopy techniques has allowed significant progress toward this goal, but generalization of this approach has so far been impeded by long acquisition times or by the absence of simultaneous topographic information. Here, we report on a scanning quantum probe microscope which solves both issues by employing a nanospin ensemble hosted in a nanodiamond. This approach provides up to an order of magnitude gain in acquisition time while preserving sub-100 nm spatial resolution both for the quantum sensor and topographic images. We demonstrate two applications of this microscope. We first image nanoscale clusters of maghemite particles through ...