Cluster Detection Tests in Spatial Epidemiology: A Global Indicator for Performance Assessment

International audienceIn cluster detection of disease, the use of local cluster detection tests (CDTs) is current. These methods aim both at locating likely clusters and testing for their statistical significance. New or improved CDTs are regularly proposed to epidemiologists and must be subjected to performance assessment. Because location accuracy has to be considered, performance assessment goes beyond the raw estimation of type I or II errors. As no consensus exists for performance evaluations, heterogeneous methods are used, and therefore studies are rarely comparable. A global indicator of performance, which assesses both spatial accuracy and usual power, would facilitate the exploration of CDTs behaviour and help between-studies comparisons. The Tanimoto coefficient (TC) is a well-known measure of similarity that can assess location accuracy but only for one detected cluster. In a simulation study, performance is measured for many tests. From the TC, we here propose two statistics, the averaged TC and the cumulated TC, as indicators able to provide a global overview of CDTs performance for both usual power and location accuracy. We evidence the properties of these two indicators and the superiority of the cumulated TC to assess performance. We tested these indicators to conduct a systematic spatial assessment displayed through performance maps

Experimental Evidence of Pitch Control of an All-Terrain AGV during a Ballistic Phase

International audienceIn some conditions, four-wheeled high speed mobile robots designed for open-field applications may take off and land badly. In order to avoid this dead-end situation, it is possible to use the mechanical principle of angular momentum conservation for correcting the pitch angle of the vehicle during the ballistic phases of actual jumps. In this study, the mechanical model of pitch control has been verified in laboratory experiments with a prototype of all-terrain AGV called "RobCat". Two series of trials have been realized on a specific test bench in which RobCat was hanged on a transversal axis passing through its CoM. In each series, RobCat was equipped either with its original hollow rubber tyres or with solid wheels having equivalent inertial parameters. The results of these experiments validated the mechanical model of angular momentum conservation of RobCat during an airborne phase and the feasibility of controlling RobCat's orientation around its pitch axis by accelerating or braking its wheels. The conclusions of this experimental study are highly encouraging for building agile mobile robots able to roll at high velocities on irregular grounds and that will combine the speed of aerial drones with the large autonomy and interaction capacity of terrestrial robots

Performance Evaluations of Cryptographic Protocols Verification Tools Dealing with Algebraic Properties

International audienceThere exist several automatic verification tools of cryptographic protocols, but only few of them are able to check protocols in presence of algebraic properties. Most of these tools are dealing either with Exclusive-Or (XOR) and exponentiation properties, so-called Diffie-Hellman (DH). In the last few years, the number of these tools increased and some existing tools have been updated. Our aim is to compare their performances by analysing a selection of cryptographic protocols using XOR and DH. We compare execution time and memory consumption for different versions of the following tools OFMC, CL-Atse, Scyther, Tamarin, TA4SP, and extensions of ProVerif (XOR-ProVerif and DH-ProVerif). Our evaluation shows that in most of the cases the new versions of the tools are faster but consume more memory. We also show how the new tools: Tamarin, Scyther and TA4SP, can be compared to previous ones. We also discover and understand for the protocol IKEv2-DS a difference of modelling by the authors of different tools, which leads to different security results. Finally, for Exclusive-Or and Diffie-Hellman properties, we construct two families of protocols P xori and P dhi that allow us to clearly see for the first time the impact of the number of operators and variables in the tools' performances

Development of a stereovision-based technique to measure the spread patterns of granular fertilizer spreaders

Centrifugal fertilizer spreaders are by far the most commonly used granular fertilizer spreader type in Europe. Their spread pattern however is error-prone, potentially leading to an undesired distribution of particles in the field and losses out of the field, which is often caused by poor calibration of the spreader for the specific fertilizer used. Due to the large environmental impact of fertilizer use, it is important to optimize the spreading process and minimize these errors. Spreader calibrations can be performed by using collection trays to determine the (field) spread pattern, but this is very time-consuming and expensive for the farmer and hence not common practice. Therefore, we developed an innovative multi-camera system to predict the spread pattern in a fast and accurate way, independent of the spreader configuration. Using high-speed stereovision, ejection parameters of particles leaving the spreader vanes were determined relative to a coordinate system associated with the spreader. The landing positions and subsequent spread patterns were determined using a ballistic model incorporating the effect of tractor motion and wind. Experiments were conducted with a commercial spreader and showed a high repeatability. The results were transformed to one spatial dimension to enable comparison with transverse spread patterns determined in the field and showed similar results

Rupture et comportement mécanique couplé des matériaux : application au bois et aux composites Présentée par

La fissuration et le comportement couplé des matériaux et des structures sont abordés dans ce mémoire. Tout d’abord, la synthèse de mes activités d’enseignant-chercheur est présentée dans le premier chapitre. Les recherches effectuées ont donné lieu à 28 articles dans des revues internationales à comité de lecture. Le deuxième chapitre présente les travaux sur les comportements viscoélastique, mécanosorptif et hydromécanique du bois (Sapin blanc du Massif Central). L’existence du comportement hygroverrou du bois est justifiée par des essais expérimentaux, des calculs analytiques et numériques. Les approches développées sont ensuite généralisées à des cas 3D. Enfin, la méthode de la grille est utilisée pour l’étude du comportement hydromécanique du bois de printemps et d’été. Le troisième chapitre présente les travaux sur la fissuration des matériaux intelligents et composites, des matériaux et structures treillis en bois ainsi que la fissuration des rondelles de bois suite à la dessiccation. La rupture aux interfaces des bi- matériaux piézoélectriques est étudiée en calculant les facteurs d’intensité de contrainte et électrique. Egalement, l’éprouvette Mixed Mode Crack Growth (MMCG) est optimisée et adaptée à la méthode de grille en mode I. Aussi, la rupture et le comportement semi-rigide des poutres treillis sont étudiés par la méthode de la grille. La fissuration des rondelles bois lors du séchage est également analysée en comparant les données expérimentales et numériques. Dans ce cadre, l’effet de la viscoélasticité sur l’initiation de la fissure est démontré. Le dernier chapitre présente les travaux en cours liés en partie au projet ANR JCJC CLIMBOIS qui s’intéresse à la fissuration du bois en environnements variables couplée à la fiabilité. La validité des approches est assurée par l’indépendance du domaine d’intégration autour de la pointe de fissure statique et en propagation. Les résultats montrent la capacité du modèle à séparer les modes mixtes de rupture en environnements variables. Parallèlement, la fiabilité et les méthodes statistiques sont appliquées afin d’étudier la probabilité de ruine et connaître les paramètres les plus discriminants dans le processus de fissuration

DefSLAM: Tracking and Mapping of Deforming Scenes from Monocular Sequences

Monocular simultaneous localization and mapping (SLAM) algorithms perform robustly when observing rigid scenes; however, they fail when the observed scene deforms, for example, in medical endoscopy applications. In this article, we present DefSLAM, the first monocular SLAM capable of operating in deforming scenes in real time. Our approach intertwines Shape-from-Template (SfT) and Non-Rigid Structure-from-Motion (NRSfM) techniques to deal with the exploratory sequences typical of SLAM. A deformation tracking thread recovers the pose of the camera and the deformation of the observed map, at frame rate, by means of SfT processing a template that models the scene shape-at-rest. A deformation mapping thread runs in parallel with the tracking to update the template, at keyframe rate, by means of an isometric NRSfM processing a batch of full perspective keyframes. In our experiments, DefSLAM processes close-up sequences of deforming scenes, both in a laboratory-controlled experiment and in medical endoscopy sequences, producing accurate 3-D models of the scene with respect to the moving camera

ROBUSfT: Robust Real-Time Shape-from-Template, a C++ Library

Tracking the 3D shape of a deforming object using only monocular 2D vision is a challenging problem. This is because one should (i) infer the 3D shape from a 2D image, which is a severely underconstrained problem, and (ii) implement the whole solution pipeline in real-time. The pipeline typically requires feature detection and matching, mismatch filtering, 3D shape inference and feature tracking algorithms. We propose ROBUSfT, a conventional pipeline based on a template containing the object's rest shape, texturemap and deformation law. ROBUSfT is ready-to-use, wide-baseline, capable of handling large deformations, fast up to 30 fps, free of training, and robust against partial occlusions and discontinuity in video frames. It outperforms the state-of-the-art methods in challenging datasets. ROBUSfT is implemented as a publicly available C++ library and we provide a tutorial on how to use it in https://github.com/mrshetab/ROBUSfTComment: This is the arXiv version of an article published in Image and Vision Computing. Please cite the accepted version: M. Shetab-Bushehri, M. Aranda, E. Ozgur, Y. Mezouar and Adrien Bartoli "ROBUSfT: Robust Real-Time Shape-from-Template, a C++ Library," in Image and Vision Computing, doi: 10.1016/j.imavis.2023.10486