Quelques pièges cachés des méthodes de sélection de variables en régression linéaire multiple

La régression linéaire est une méthode d'analyse des données parmi les plus anciennes. On attribue à K. F. Gauss (vers 1809) le mérite d'avoir développé la méthode des moindres carrés afin d'ajuster une équation qui est linéaire du point vue de ses paramètres. Des développements impressionnants sont survenus au cours des 150 années qui ont suivies pour finalement stagner vers 1959 puisque la majorité des idées nouvelles nécessitait l'utilisation d'un ordinateur très performant pour éclore. Le perfectionnement des ordinateurs combiné à la réduction des coûts d'utilisation a permis à des méthodes telles que la sélection d'un sousensemble de variables, dont il sera question dans ce mémoire, de voir le jour. Dans le présent document, nous jetterons un regard à la fois descriptif et critique à l'égard des méthodes de sélection développées principalement au cours des trente dernières années. Nous étudierons un certain nombre de critères et de méthodes de sélection construites de façon à identifier un sous-ensemble de variables de qualité acceptable que l'on qualifiera de"meilleur" sous-ensemble de variables

The Role of Footwear, Foot Orthosis and Training-Related Strategies in the Prevention of Bone Stress Injuries: A Systematic Review and Meta-Analysis

International Journal of Exercise Science 16(3): 721-743, 2023. Objective: To evaluate the effectiveness of footwear, foot orthoses and training-related strategies to prevent lower extremity bone stress injury (BSI). Design: Systematic review and meta-analysis. Data sources: Four bibliographic databases (from inception until November 2021): Cochrane Central Register of Controlled Trials, MEDLINE, EMBASE and CINAHL. Eligibility criteria: Randomised controlled trials (RCTs) that assessed the risk of developing a BSI when using particular footwear, foot orthoses or training-related strategies such as muscle strengthening, stretching, and mechanical loading exercises. Results: Eleven studies were included in this systematic review. When wearing foot orthoses, the risk ratio of developing a BSI on any lower extremity bone is 0.47 (95% CI 0.26 to 0.87; p = 0.02). When doing pre-exercise dynamic stretching, the risk ratio of suffering a tibial BSI is 1.06 (95% CI 0.67 to 1.68; p = 0.79). No meta-analyses could be performed for footwear or training-related strategies. The quality of evidence for all these results is low considering the high risk of bias in each study, the low number of studies and the low number of cases in each study. Conclusion: This systematic review reveals the lack of high-quality studies in BSI prevention. Based on studies at high risk of bias, foot orthoses could potentially help prevent BSIs in the military setting. It is still unknown whether footwear and training-related strategies have any benefits. It is crucial to further investigate potential BSI prevention strategies in women and athletes. Research is also needed to assess the influence of running shoes and loading management on BSI incidence

Investigation of volatile mixture emit by human tissues degradation

Human rescue dog unit are the more efficient tool to locate cadaver or people trap after a natural disaster. However, the dog training process is long and expensive. Dog trainers are always looking for a better understanding of the dog olfaction matching to improve their training methods (1). During these training sessions, dogs are usually trained to locate body pieces due to the difficulty to obtain a full cadaver. Moreover, some training aid solution are available but their compositions and their efficiencies are not worldwide recognized (2). To answer these questions, this project is monitoring the headspace human organs during the decomposition process. Five different organs are used: heart, lung, liver, kidney and blood. Every organs are sampled in triplicates and let to decompose in glass jar. Regularly, the headspace of the jar is sample by dynamic pumping to sorbent tubes that will further be injected on comprehensive two-dimensional gas chromatography system (GC×GC). GC×GC is a powerful analytical tool that allows the complete resolution of “the smell of death”, i.e. the decomposition odor (3-4). The compounds identified in the organs headspace can be compared with the one coming from decomposition studies on full bodies to establish a biomarkers list that will further be used for dog training solution elaboration. References 1. Hoffman et al. FSI (2009) 186, 6-13. 2. Stadler et al. J. Chrom. A. 1255, 202-206. 3. Stefanuto et al. CPC (2014) 79, 786-789. 4. Perrault et al. J. Sep. Sci. (2015) 38, 73-80

Atlas-Free Surface Reconstruction of the Cortical Grey-White Interface in Infants

BACKGROUND: The segmentation of the cortical interface between grey and white matter in magnetic resonance images (MRI) is highly challenging during the first post-natal year. First, the heterogeneous brain maturation creates important intensity fluctuations across regions. Second, the cortical ribbon is highly folded creating complex shapes. Finally, the low tissue contrast and partial volume effects hamper cortex edge detection in parts of the brain. METHODS AND FINDINGS: We present an atlas-free method for segmenting the grey-white matter interface of infant brains in T2-weighted (T2w) images. We used a broad characterization of tissue using features based not only on local contrast but also on geometric properties. Furthermore, inaccuracies in localization were reduced by the convergence of two evolving surfaces located on each side of the inner cortical surface. Our method has been applied to eleven brains of one- to four-month-old infants. Both quantitative validations against manual segmentations and sulcal landmarks demonstrated good performance for infants younger than two months old. Inaccuracies in surface reconstruction increased with age in specific brain regions where the tissue contrast decreased with maturation, such as in the central region. CONCLUSIONS: We presented a new segmentation method which achieved good to very good performance at the grey-white matter interface depending on the infant age. This method should reduce manual intervention and could be applied to pathological brains since it does not require any brain atlas

Digital Holographic Interferometry in the Long-Wave Infrared for the Testing of Large Aspheric Space Reflectors

Digital holographic (DH) interferometry has been developed in the long-wave infrared spectral range with CO2 lasers and microbolometer arrays. This application has been driven by the European Space Agency’s constant need of techniques for monitoring large displacements of large structures. Here the study focuses on the case of aspheric mirrors, like parabola and ellipses. Usually they are tested through interferometric wavefront error measurements which require expensive null-lenses matching each of the reflectors considered. In the case of monitoring deformation a holographic technique can be considered where the wavefront is compared with itself at different instant. Therefore the optical can be quite simple and easily reconfigurable from one reflector to another. The advantage of using long wavelength is that large deformations can be measured at once, in addition to being more immune against environmental perturbations. Another advantage of DH at such wavelengths is that the ratio between the wavelength and the pixel size allows reconstructing objects 5 to 10 times larger than with DH in the visible. In this project we considered first the case of a 1.1 meter diameter parabola for submillimeter range observations. Such specimen shows strong specular reflectivity. We have developed several set-ups with different ways to illuminate the object and to collect rays to form the object beam: either through point source or through and extended diffuser working by reflection of the laser beam. Both possibilities have been compared in terms of fringe quality as well as measurement range. We selected the diffuser illumination for applying the set-up into a large vacuum facility for measuring the deformation of the parabola between 224 and 107 K. Results of this measurement campaign are presented. A further application has been shown by observation of off-axis ellipse. In this case interferometric testing is difficult to achieve and LWIR DHI with diffuser illumination is found quite simple to implement and gives straightforward results.GSTP HOLODI