Portail des publications scientifiques IMT Mines Alès
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The study of the hyper-parameter modelling the decision rule of the cautious classifiers based on the Fβ measure
No full textInternational audienceIn some sensitive domains where data imperfections are present, standard classification techniques reach their limits. To avoid misclassifications that have serious consequences, recent works propose cautious classification algorithms to handle this problem. Despite of the presence of uncertainty and/or imprecision, a point prediction classifier is forced to bet on a single class. While a cautious classifier proposes the appropriate subset of candidate classes that can be assigned to the sample in the presence of imperfect information. On the other hand, cautiousness should not be at the expense of precision and a trade-off has to be made between these two criteria. Among the existing cautious classifiers, two classifiers propose to manage this trade-off in the decision step by the mean of a parametrized objective function. The first one is the non-deterministic classifier (ndc) proposed within the framework of probability theory and the second one is “evidential classifier based on imprecise relabelling” (eclair) proposed within the framework of belief functions. The theoretical aim of the mentioned hyper-parameters is to control the size of predictions for both classifiers. This paper proposes to study this hyper-parameter in order to select the “best” value in a classification task. First the utility for each candidate subset is studied related to the values of the hyper-parameter and some thresholds are proposed to control the size of the predictions. Then two illustrations are proposed where a method to choose this hyper-parameters based on the calibration data is proposed. The first illustration concerns randomly generated data and the second one concerns the images data of fashion mnist. These illustrations show how to control the size of the predictions and give a comparison between the performances of the two classifiers for a tuning based on our proposition and the one based on grid search method
La fabrique des territoires post-miniers. Trois territoires en Cévennes au prisme de la littérature scientifique et médiatique
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LSG Attention: Extrapolation of pretrained Transformers to long sequences
No full textInternational audienceTransformer models achieve state-of-the-art performance on a wide range of NLP tasks. They however suffer from a prohibitive limitation due to the self-attention mechanism, inducing O(n2) complexity with regard to sequence length. To answer this limitation we introduce the LSG architecture which relies on Local, Sparse and Global attention. We show that LSG attention is fast, efficient and competitive in classification and summarization tasks on long documents. Interestingly, it can also be used to adapt existing pretrained models to efficiently extrapolate to longer sequences with no additional training. Along with the introduction of the LSG attention mechanism, we propose tools to train new models and adapt existing ones based on this mechanism
Rythmes ternaires et swing : comment la musique influence la synchronisation des bras et des doigts
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Consensus Paper: Ataxic Gait
No full textInternational audienceThe aim of this consensus paper is to discuss the roles of the cerebellum in human gait, as well as its assessment and therapy. Cerebellar vermis is critical for postural control. The cerebellum ensures the mapping of sensory information into temporally relevant motor commands. Mental imagery of gait involves intrinsically connected fronto-parietal networks comprising the cerebellum. Muscular activities in cerebellar patients show impaired timing of discharges, affecting the patterning of the synergies subserving locomotion. Ataxia of stance/gait is amongst the first cerebellar deficits in cerebellar disorders such as degenerative ataxias and is a disabling symptom with a high risk of falls. Prolonged discharges and increased muscle coactivation may be related to compensatory mechanisms and enhanced body sway, respectively. Essential tremor is frequently associated with mild gait ataxia. There is growing evidence for an important role of the cerebellar cortex in the pathogenesis of essential tremor. In multiple sclerosis, balance and gait are affected due to cerebellar and spinal cord involvement, as a result of disseminated demyelination and neurodegeneration impairing proprioception. In orthostatic tremor, patients often show mild-to-moderate limb and gait ataxia. The tremor generator is likely located in the posterior fossa. Tandem gait is impaired in the early stages of cerebellar disorders and may be particularly useful in the evaluation of pre-ataxic stages of progressive ataxias. Impaired inter-joint coordination and enhanced variability of gait temporal and kinetic parameters can be grasped by wearable devices such as accelerometers. Kinect is a promising low cost technology to obtain reliable measurements and remote assessments of gait. Deep learning methods are being developed in order to help clinicians in the diagnosis and decision-making process. Locomotor adaptation is impaired in cerebellar patients. Coordinative training aims to improve the coordinative strategy and foot placements across strides, cerebellar patients benefiting from intense rehabilitation therapies. Robotic training is a promising approach to complement conventional rehabilitation and neuromodulation of the cerebellum. Wearable dynamic orthoses represent a potential aid to assist gait. The panel of experts agree that the understanding of the cerebellar contribution to gait control will lead to a better management of cerebellar ataxias in general and will likely contribute to use gait parameters as robust biomarkers of future clinical trials
Quantification and Rehabilitation of Unilateral Spatial Neglect in Immersive Virtual Reality: A Validation Study in Healthy Subjects
No full textInternational audienceUnilateral spatial neglect is a common sensorimotor disorder following the occurrence of a stroke, for which prismatic adaptation is a promising rehabilitation method. However, the use of prisms for rehabilitation often requires the use of specific equipment that may not be available in clinics. To address this limitation, we developed a new software package that allows for the quantification and rehabilitation of unilateral spatial neglect using immersive virtual reality. In this study, we compared the effects of virtual and real prisms in healthy subjects and evaluated the performance of our virtual reality tool (HTC Vive) against a validated motion capture tool. Ten healthy subjects were randomly exposed to virtual and real prisms, and measurements were taken before and after exposure. Our findings indicate that virtual prisms are at least as effective as real prisms in inducing aftereffects (4.39° ± 2.91° with the virtual prisms compared to 4.30° ± 3.49° with the real prisms), but that these effects were not sustained beyond 2 h regardless of exposure modality. The virtual measurements obtained with our software showed excellent metrological qualities (ICC = 0.95, error = 0.52° ± 1.18°), demonstrating its validity and reliability for quantifying deviation during pointing movements. Overall, our results suggest that our virtual reality software (Virtualis, Montpellier, France) could provide an easy and reliable means of quantifying and rehabilitating spatial neglect. Further validation of these results is required in individuals with unilateral spatial neglect
Synthesis of a new pyrimidine-based sorbent for indium(III) removal from aqueous solutions – Application to ore leachate
No full textInternational audienceA new sorbent (TcTDG, pyrimidine derivative, with high content of N-based reactive groups and S-based sites) was successfully synthesized by the polycondensation of thiocarbazide and 2-thiobarbituric acid through reaction with formaldehyde. The material is characterized by FTIR, SEM and SEM-EDX analyses, titration, elemental analysis, BET, and TGA. After interacting with In(III), the FTIR spectrum of TcTDG shows the modification of the environment of N- and S-based reactive groups. The sorption of In(III) is first studied in synthetic solutions with TcTDG micro-particles through the evaluation of pH effect (optimum at pH 4), the uptake kinetics (equilibrium achieved in 20–30 min), the sorption isotherms and the selectivity properties from equimolar solution of different metal ions. The sorption capacity significantly decreases when increasing the temperature from 15 to 50 °C: In(III) sorption onto TcTDG is exothermic. Maximum sorption capacity at room temperature and at pH 4 reaches up to 1.87 mmol In g−1; the isotherm is equally fitted by the Langmuir and the Sips equations. Indium is fully eluted from metal-loaded sorbent using 0.3 M HCl solution (equilibrium reached in 20–30 min). The pseudo-first order rate equation fits well experimental kinetic profile; although the resistance to intraparticle diffusion plays a significant role in the control of In(III) sorption. The sorbent is highly stable at recycling: the FTIR spectrum is restored after five cycles and desorption remains complete along the cycles; after five re-uses, the sorption efficiency decreases by less than 4%. The study is extended to more complex solutions: first, with multi-component synthetic equimolar solutions before investigating the application of TcTDG to metal recovery from acidic leachate of ore sample (from Eastern Central Desert, Egypt). The sorbent shows a marked preference for In(III) at pH 4 against mono-, di- and tri-valent metal ions in synthetic solutions, the preference is also appreciable but the selectivity coefficient (SCIn/metal) is weaker for rare metals (between 3 and 6, vs. 10–35 for other metal ions). In the case of acidic leachate, the pH control to 4 leads to substantial precipitation of huge amounts of iron and the co-precipitation of other metal ions. The sorption capacity for In(III) (and Ga(III)) is significantly reduced by the complexity of the effluents; although the sorbent maintains a preference for these trivalent metal ions. The new sorbent shows promising sorption properties, although complementary investigation is required for optimizing the practical application of this material (conditioning, larger number of recycling steps, etc.)
Silazanes, a novel flax fibers functionalization: Effect on silicone-based composites
No full textInternational audienceThe natural fibers use as reinforcement for composites is a topical subject. Usually, chemical functionalization is used in order to improve the compatibility between natural fibers and polymer matrices, for cross-linkable systems, the grafting agent used for fiber modification can also participate in the three-dimensional network formation and therefore improve the composite mechanical properties. In this study, a silazane: 1,3-divinyltetramethyldisilazane (DVTS) was used for the first time as a flax fibers modification to introduce at their surface vinyl groups, via covalent bonds, that can react during the polysiloxane system cross-linking. The reaction conditions for the flax functionalization were investigated, especially the alkaline pre-treatment impact of the fibers before grafting and the nature of solvent used during the reaction. Scanning electron microscope (SEM) analyses shown a high interfacial adhesion functionalized fibers/matrix
Occurrences, distribution and risk assessment of polar pesticides in Niger River valley and its tributary the Mekrou River (Niger Republic)
No full textInternational audienceThe increase in food needs due to high population growth in Niger has led to the intensification of urban agriculture and the increased use of pesticides. The objective of this study is primarily to assess the polar pesticide contamination (mainly herbi-cides) of the Niger River and its tributary, the Mekrou River, in Niger, using both grab sampling and POCIS (Polar Organic Chemical Integrative Samplers), and then to evaluate the risk to the aquatic environment. Two water sampling campaigns were carried out during the wet and dry seasons. The polar pesticides were analyzed by liquid chromatography coupled with tandem mass spectrometry, which allowed the identification of compounds with concentrations in the grab samples above the WHO guide values and the EU directive: diuron with 2221 ng/L (EU quality guideline: 200 ng/L), atrazine with 742 ng/L (EU quality guideline: 600 ng/L) and acetochlor with 238 ng/L (EU quality guideline: 100 ng/L). The risk assess-ment study indicated that diuron and atrazine present a high risk for the aquatic environment during the wet season. The main source of water contamination is the intensive use of pesticides in urban agriculture near the city of Niamey, and the intensive cotton farming in the Benin. Moreover, the surveys (30 producers interviewed) showed that 70% of the pesticides used are not approved by the Interstate Committee for Drought Control in the Sahel (CILSS) and some are prohibited in Niger. The inventory of pesticides sold in the zone showed that active ingredients used by producers are 48% insecticides, 45% herbicides, and 7% fungicides