Parcellation of fMRI datasets with ICA and PLS: a data driven approach

Inter-subject parcellation of functional Magnetic Resonance Imaging (fMRI) data based on a standard General Linear Model (GLM) and spectral clustering was recently proposed as a means to alleviate the issues associated with spatial normalization in fMRI. However, for all its appeal, a GLM-based parcellation approach introduces its own biases, in the form of a priori knowledge about the shape of Hemodynamic Response Function (HRF) and task-related signal changes, or about the subject behaviour during the task. In this paper, we introduce a data-driven version of the spectral clustering parcellation, based on Independent Component Analysis (ICA) and Partial Least Squares (PLS) instead of the GLM. First, a number of independent components are automatically selected. Seed voxels are then obtained from the associated ICA maps and we compute the PLS latent variables between the fMRI signal of the seed voxels (which covers regional variations of the HRF) and the principal components of the signal across all voxels. Finally, we parcellate all subjects data with a spectral clustering of the PLS latent variables. We present results of the application of the proposed method on both single-subject and multi-subject fMRI datasets. Preliminary experimental results, evaluated with intra-parcel variance of GLM t-values and PLS derived t-values, indicate that this data-driven approach offers improvement in terms of parcellation accuracy over GLM based techniques

Assessment of Topography E-Learning with Exomatic

The Swiss Federal Institute of Technology in Lausanne (EPFL) has successfully integrated the Bologna reform process that standardizes the Bachelor and Master programmes across Europe. This reform particularly affects the curriculum offered by the EPFL schools of civil and environmental engineering that share students during the bachelor program. Geomatics, the branch which deals with the acquisition and management of geographical data, is one of these courses to be attended by the students from both schools. As we merge classes of many students, we decided to introduce e-learning in this changing educational context. The Geodetic Engineering Laboratory launched the concept of topography e-learning during its first year class gathering more than 150 students. The idea is mainly based on a set of personalized exercises on the Web, followed by automatic corrections. This allows a substantial increase of the number of students in the course while maintaining the same level of comprehension and computational rigour. This simple concept, called Exomatic, encourages the students to be autonomous in their learning. This paper is divided into two parts: the first presents the architecture of the software developed for the Exomatic concept that notably improves the management of the exercises and of their automated corrections. The second part focuses on the assessment of Exomatic by the students and by the teachers

Precise Road Geometry for Integrated Transport Safety Systems

A safer mobility is a key concern for the strategy of the European governments and automotive industries. At the moment, a new generation of Intelligent Integrated Transport Safety Systems (IITSS) offers a promising potential to address this issue. Such co-operative systems will enable safety-concerning information to be exchanged between the vehicles or between the vehicles and the infrastructure. IITSS mainly involves sensors for detection and interpretation of the driving environment. One of the most significant related methods is the so-called Lane Departure Warning (LDW) since the unintended cross of the lane boundary is one of the largest cause of highway fatalities. Implementation of LDW requires an accurate survey of the lane layout is necessary. The Geodetic Engineering Laboratory of the Swiss Federal Institute of Technology in Lausanne has designed a mobile mapping system (Photobus) that provides fast and accurate acquisition of the road geometry. Recent surveys carried out by Photobus in Switzerland provide good basis in establishing the optimal relation between the required point sampling and the model of the road geometry. This paper focuses on methods for an accurate modelling of the road geometry and the derived geometric features for Advanced Driver Assistance Systems (ADAS). This offers new perspectives for Lane Departure Warning since precise positioning provides sufficient information for computing the offset of a vehicle from the road centreline, or from the boundaries of the lane

Cartographie routière précise pour les systèmes d'assistance à la conduite

Jusqu'à présent, les autorités publiques et l'industrie automobile ont été impliquées dans l'amélioration des conditions de sécurité routière par la prévention des accidents et par la réduction du nombre de blessés sur la route. La plupart des mesures préventives se sont focalisées sur le conducteur, alors que la réduction des conséquences d'un accident s'est concentrée sur la sécurité des véhicules et sur celle de l'infrastructure routière. ..

Photobus: Towards Real-Time Mapping

The Geodetic Engineering Laboratory at EPFL has designed a mobile mapping system to determine the geometry of the road: the Photobus. This paper describes major steps that move the Photobus towards a real-time mapping system

Hydrolytic kinetic model predicting embrittlement in thermoplastic elastomers

A hydrolytic kinetic model predicting chains scissions of a polyurethane elastomer (TPU) containing an anti-hydrolysis agent (stabilization via carbodiimide) was developed. This model is based on four components: uncatalysed hydrolysis, acid-catalysed hydrolysis, carboxylic acid dissociation and competitive carbodiimide-based deactivation of acid. Protons were considered as the key catalyst responsible for the hydrolysis. Model parameters were determined by fitting experimental data measured on unstabilized and stabilized TPUs, aged in immersion from 40 to 90 °C. Scission kinetics were predicted for immersion and 50% relative humidity conditions, from 10 to 100 °C. Structure-failure property relationships were also investigated, between molar mass and elongation at break. A master curve was established for elongation at break with molar mass, including both TPUs at four ageing temperatures. By combining predictions for scission kinetics with the molar mass-elongation at break master curve and an embrittlement molar mass as the end-of-life criterion, non-Arrhenian lifetime predictions are proposed for all exposure conditions considered

Manifestation de l'effet Portevin-Le Châtelier en cisaillement simple

Les alliages d’aluminium de la série 5000 pourraient avantageusement remplacer les alliages de la série 6000, plus coûteux, notamment dans la fabrication des ouvrants automobiles. Cependant, l’effet Portevin-Le Châtelier (PLC) qui se manifeste dans ces alliages au cours de leur déformation plastique freine grandement leur utilisation pour les pièces d’aspects. En effet, il conduit notamment à une diminution de la formabilité et il est à l’origine de marques donnant un aspect rugueux aux pièces obtenues. Par exemple, les alliages Al-Mg sont connus pour présenter un effet PLC à température ambiante, caractérisé par des serrations sur la courbe d’écoulement et une déformation plastique localisée dans des bandes au cours de la déformation globale. Ce phénomène est dû au vieillissement dynamique, une interaction entre les atomes de soluté de magnésium et les dislocations mobiles. Bien que de nombreuses études de l'effet PLC aient déjà été réalisées, le phénomène a été observé principalement en traction. Compte tenu des différents trajets de déformation rencontrés dans les procédés de mise en forme des tôles, il semble intéressant d’élargir les connaissances sur les conditions d'apparition de l'effet PLC sous divers états de chargement. Dans ces travaux, les courbes d’écoulement d’un alliage AA 5754-O lors d’essais de cisaillement simple pour différentes vitesses de déformation et pour différentes températures sont étudiées. Il est montré que l'effet PLC peut être observé pour cet état de contrainte. Les observations directes de la surface des éprouvettes en utilisant une technique de corrélation d'images permettent l'étude de la nature et de la cinématique des bandes en fonction de la contrainte de cisaillement, de la vitesse de déformation et de la température. Enfin, des simulations numériques par éléments finis utilisant le modèle de McCormick [1] sont présentées pour expliquer la cinématique des bandes PLC observées expérimentalement. [1] McCormick P.G., Theory of flow localisation due to dynamic strain ageing, Acta Metallurgica, 1988, 36 (12) 3061-306

Relationships between molar mass and fracture properties of segmented urethane and amide copolymers modified by chemical degradation

This publication highlights the structure–property relationships in several thermoplastic elastomers (TPEs): one poly(ether-block-amide) and two thermoplastic polyurethane elastomers with ester and ether soft blocks. Structural changes are induced by chemical degradation from virgin samples through hydrolysis and oxidation. Molar mass measurements show an exclusive chain scission mechanism for all TPEs, regardless of the chemical modification condition. Mechanical behavior was nevertheless obtained from uniaxial tensile testing and fracture testing while considering the essential work of fracture (EWF) concept. During the macromolecular scission process, elongation at break shows a plateau followed by a drop, while stress at break decreases steadily. Once again, the trend is identical for all TPEs in all conditions considered. The βwp parameter determined using the EWF concept exhibits an interesting sensitivity to scissions (i.e., molar mas decrease). Plotting elongation at break as a function of molar mass reveals a strong correlation between these two parameters. This master curve is particularly remarkable considering the range of TPEs and chemical breakdown pathways considered (hydrolysis and oxidation at several temperatures). Relevant structure–property relationships are proposed, highlighting that molar mass is a predominant parameter for determining the mechanical properties of thermoplastic elastomers.We gratefully acknowledge the financial support pro-vided by ANRT (CIFRE N°2016/0796). Samples were processed with the kind help of Paulo Ferreira. We also acknowledge the assistance of Sylvie Tencé-Girault, Mickael Premel-Cabic and Nicolas Lacotte, as well as Thomas Bizien and the Synchrotron team

Correlation between crystallization and mechanical stress revealed by chain scission of segmented amide copolymer

By tuning hydrolysis duration of a segmented ether-amide copolymer (PEBA), a range of specimens presenting various macromolecular structures has been produced. Knowing that scissions occur predominantly at the bond between hard and soft blocks, for a given hard phase structure we study the impact of phase interconnection changes on strain-induced crystallization (SIC) occurring during tensile loading. The consequences of chain scissions on the structural reorganization involving SIC measured with in situ X-ray diffraction is considered here for the first time. A close correlation between stress and crystallinity induced under strain is highlighted whatever the chain scission number, i.e. the number of phase interconnections. As a result, the stress decrease observed at a given elongation can be interpreted as a consequence of a SIC weakening with the chain scission process