Statistics on Diffeomorphisms in a Log-Euclidean Framework

International audienceIn this article, we focus on the computation of statistics of invertible geometrical deformations (i.e., diffeomorphisms), based on the generalization to this type of data of the notion of principal logarithm. Remarkably, this logarithm is a simple 3D vector field, and can be used for diffeomorphisms close enough to the identity. This allows to perform vectorial statistics on diffeomorphisms, while preserving the invertibility constraint, contrary to Euclidean statistics on displacement fields

A Fast and Log-Euclidean Polyaffine Framework for Locally Affine Registration

Projet ASCLEPIOSIn this article, we focus on the parameterization of non-rigid geometrical deformations with a small number of flexible degrees of freedom . In previous work, we proposed a general framework called polyaffine to parameterize deformations with a finite number of rigid or affine components, while guaranteeing the invertibility of global deformations. However, this framework lacks some important properties: the inverse of a polyaffine transformation is not polyaffine in general, and the polyaffine fusion of affine components is not invariant with respect to a change of coordinate system. We present here a novel general framework, called Log-Euclidean polyaffine, which overcomes these defects. We also detail a simple algorithm, the Fast Polyaffine Transform, which allows to compute very efficiently Log-Euclidean polyaffine transformations and their inverses on regular grids. The results presented here on real 3D locally affine registration suggest that our novel framework provides a general and efficient way of fusing local rigid or affine deformations into a global invertible transformation without introducing artifacts, independently of the way local deformations are first estimated. Last but not least, we show in this article that the Log-Euclidean polyaffine framework is implicitely based on a Log-Euclidean framework for rigid and affine transformations, which generalizes to linear transformations the Log-Euclidean framework recently proposed for tensors. We detail in the Appendix of this article the properties of this novel framework, which allows a straightforward and efficient generalization to linear transformations of classical vectorial tools, with excellent theoretical properties. In particular, we propose here a simple generalization to locally rigid or affine deformations of a visco-elastic regularization energy used for dense transformations

Spatiotemporal Imaging of the Acoustic Field Emitted by a Single Copper Nanowire

International audienceThe monochromatic and geometrically anisotropic acoustic field generated by 400 nm and 120 nm diameter copper nanowires simply dropped on a 10 µm silicon membrane is investigated in transmission using three-dimensional time-resolved femtosecond pump-probe experiments. Two pump-probe time-resolved experiments are carried out at the same time on both side of the silicon substrate. In reflection, the first radial breathing mode of the nanowire is excited and detected. In transmission, the longitudinal and shear waves are observed. The longitudinal signal is followed by a monochromatic component associated with the relaxation of the nanowire's first radial breathing mode. Finite Difference Time Domain (FDTD) simulations are performed and accurately reproduce the diffracted field. A shape anisotropy resulting from the large aspect ratio of the nanowire is detected in the acoustic field. The orientation of the underlying nanowires is thus acoustically deduced

Vers un patient numérique personnalisé pour le diagnostic et la thérapie guidés par l'image [Towards a personalized digital patient for diagnosis and therapy guided by image].

National audienceRecent advances in computer science and medical imaging allow the design of new computational models of the patient which are used to assist physicians. These models, whose parameters are optimized to fit in vivo acquired images, from cells to an entire body, are designed to better quantify the observations (computer aided diagnosis), to simulate the evolution of a pathology (computer aided prognosis), to plan and simulate an intervention to optimize its effects (computer aided therapy), therefore addressing some of the major challenges of medicine of 21(st) century

Asclepios: a Research Project-Team at INRIA for the Analysis and Simulation of Biomedical Images

International audienceAsclepios1 is the name of a research project-team o cially launched on November 1st, 2005 at INRIA Sophia-Antipolis, to study the Analysis and Simulation of Biological and Medical Images. This research project-team follows a previous one, called Epidaure, initially dedicated to Medical Imaging and Robotics research. These two project teams were strongly supported by Gilles Kahn, who used to have regular scienti c in- teractions with their members. More generally, Gilles Kahn had a unique vision of the growing importance of the interaction of the Information Technologies and Sciences with the Biological and Medical world. He was one of the originators of the creation of a speci c BIO theme among the main INRIA research directions, which now regroups 16 di fferent research teams including Asclepios, whose research objectives are described and illustrated in this article

Nucleation of magnetisation reversal, from nanoparticles to bulk materials

We review models for the nucleation of magnetisation reversal, i.e. the formation of a region of reversed magnetisation in an initially magnetically saturated system. For small particles models for collective reversal, either uniform (Stoner-Wohlfarth model) or non-uniform like curling, provide good agreement between theory and experiment. For microscopic objects and thin films, we consider two models, uniform (Stoner-Wohlfarth) reversal inside a nucleation volume and a droplet model, where the free energy of an inverse bubble is calculated taking into account volume energy (Zeeman energy) and surface tension (domain wall energy). In macroscopic systems, inhomogeneities in magnetic properties cause a distribution of energy barriers for nucleation, which strongly influences effects of temperature and applied field on magnetisation reversal. For these systems, macroscopic material parameters like exchange interaction, spontaneous magnetisation and magnetic anisotropy can give an indication of the magnetic coercivity, but exact values for nucleation fields are, in general, hard to predict.Comment: 12 pages; Published in a Special Issue of the C. R. Physique devoted to nucleation. C.R. Physique 7, 977 (2006). Corrected version, as publishe

Propagation of Myocardial Fibre Architecture Uncertainty on Electromechanical Model Parameter Estimation: A Case Study

International audienceComputer models of the heart are of increasing interest for clinical applications due to their discriminative and predictive power. However the personalisation step to go from a generic model to a patient-specific one is still a scientific challenge. In particular it is still difficult to quantify the uncertainty on the estimated parameters and predicted values. In this manuscript we present a new pipeline to evaluate the impact of fibre uncertainty on the personalisation of an electromechanical model of the heart from ECG and medical images. We detail how we estimated the variability of the fibre architecture among a given population and how the uncertainty generated by this variability impacts the following personalisation. We first show the variability of the personalised simulations, with respect to the principal variations of the fibres. Then discussed how the variations in this (small) healthy population of fibres impact the parameters of the personalised simulations

Phonons in Slow Motion: Dispersion Relations in Ultra-Thin Si Membranes

We report the changes in dispersion relations of hypersonic acoustic phonons in free-standing silicon membranes as thin as \sim 8 nm. We observe a reduction of the phase and group velocities of the fundamental flexural mode by more than one order of magnitude compared to bulk values. The modification of the dispersion relation in nanostructures has important consequences for noise control in nano and micro-electromechanical systems (MEMS/NEMS) as well as opto-mechanical devices.Comment: 5 page

Localized Surface Plasmon Resonance of Metallic Nanoparticles--Optical Property Characterization for Rational Applications

在光的激发下金属纳米结构中的自由电子能够发生群体性的振荡，进而产生表面等离激元（SPP）。发生等离激元共振时，金属纳米结构会将光束缚在表面，并在表面产生极强的电场增强。表面等离激元有两种类型：一类具有传播的特点，其表面等离激元能够在表面传播，称之为propagatingSPP；另一类不具有传播性，共振局域在一个很小的金属结构中，称之为localizedSPP，即局域表面等离激元共振（LSPR）。金属纳米颗粒就具有很强的表面等离激元共振的（LSPR）性质，使其对光产生增强的吸收和增强的散射，并表现出相关的热、光电场增强和热电子等效应。近年，随着纳米科技的发展，金属纳米粒子的LSPR效应已经成为一...The collective oscillation of free electrons in metal nanostructures excited with light is called surface plasmon polaritons (SPP). The light will be confined to a small area on the surface under the resonance condition (SPR), thus a giant enhancement in the electric field will be produced. There are two kinds of surface plasmon polaritons (SPP): one is propagating plasmon polaritons (PSPP), which...学位：理学博士院系专业：化学化工学院_物理化学(含化学物理)学号：2052010015366