POMDP-based long-term user intention prediction for wheelchair navigation

This paper presents an intelligent decision-making agent to assist wheelchair users in their daily navigation activities. Several navigational techniques have been successfully developed in the past to assist with specific behaviours such as "door passing" or "corridor following". These shared control strategies normally require the user to manually select the level of assistance required during use. Recent research has seen a move towards more intelligent systems that focus on forecasting users' intentions based on current and past actions. However, these predictions have been typically limited to locations immediately surrounding the wheelchair. The key contribution of the work presented here is the ability to predict the users' intended destination at a larger scale, that of a typical office arena. The systems relies on minimal user input - obtained from a standard wheelchair joystick - in conjunction with a learned Partially Observable Markov Decision Process (POMDP), to estimate and subsequently drive the user to his destination. The projection is constantly being updated, allowing for true user-platform integration. This shifts users' focus from fine motor-skilled control to coarse control broadly intended to convey intention. Successful simulation and experimental results on a real wheelchair robot demonstrate the validity of the approach. ©2008 IEEE

A POMDP framework for modelling human interaction with assistive robots

This paper presents a framework for modelling the interaction between a human operator and a robotic device, that enables the robot to collaborate with the human to jointly accomplish tasks. States of the system are captured in a model based on a partially observable Markov decision process (POMDP). States representing the human operator are motivated by behaviours from the psychology of the human action cycle. Hierarchical nature of these states allows the exploitation of data structures based on algebraic decision diagrams (ADD) to efficiently solve the resulting POMDP. The proposed framework is illustrated using two examples from as-sistive robotics; a robotic wheel chair and an intelligent walking device. Experimental results from trials conducted in an office environment with the wheelchair is used to demonstrate the proposed technique. © 2011 IEEE

Wheelchair driver assistance and intention prediction using POMDPs

Electric wheelchairs give otherwise immobile people the free-dom of movement, they significantly increase independence and dramatically increase quality of life. However the physical control systems of such wheelchair can be prohibitive for some users; for example, people with severe tremors. Several assisted wheelchair platforms have been developed in the past to assist such users. Algorithms that assist specific behaviors such as door - passing, follow - corridor, or avoid - obstacles have been successful. Recent research has seen a move towards systems that predict the users intentions, based on the users input. These predictions have been typically limited to locations immediately surrounding the wheelchair. This paper presents a new assisted wheelchair driving system with large scale intelligent intention recognition based on POMDPs (Partially Observable Markov Decision Processes). The systems acts as an intelligent agent/decision-maker, it relies on minimal user input; to predict the users intention and then autonomously drives the user to his destination. The prediction is constantly being updated as new user input is received allowing for true user/system integration. This shifts the users focus from fine motor-skilled control to coarse control intended to convey intention. © 2007 IEEE

Intention driven assistive wheelchair navigation

This paper presents an intelligent decision-making agent to assist wheelchair users in their daily navigation activities. The system has the ability to predict the users intended destination at a larger scale, that of a typical office or home arena. This system relies on minimal user input - obtained from a standard wheelchair joystick - in conjunction with a learned Partially Observable Markov Decision Process (POMDP), to estimate and subsequently aid in driving the user to the destination. The projection is constantly being updated, allowing for true user-platform integration. This shifts users focus from fine motor-skilled control to coarse guidance, broadly intended to convey intention. Successful simulation and experimental results on a real automated wheelchair platform demonstrate the validity of the approach

Incidence du chlorure de sodium sur la dénitrification d'éluats de résines par une bactérie chimiautotrophe soufre-oxydante

L'épuration ou la destination finale des éluats de régénération des résines utilisées en dénitratation reste un problème mal résolu. De nouvelles voies sont recherchées; la dénitrification biologique semble très attrayante car elle peut être mise en oeuvre sous forme d'un réacteur de faible coût et d'exploitation facile. L'objectif de ce travail a été d'affiner la connaissance du procédé de dénitrification chimioautotrophe sur soufre en milieu salé, dirigé vers l'épuration et/ou la valorisation de ces éluats.Claus et Kutzner (1985) ont montré l'action inhibitrice de la dénitrification du chlorure de sodium à partir de 20 g/l. Une colonne contenant du soufre est alimentée en continu par une solution comportant des nitrates et des sels nutritifs. La première partie de l'étude permet de relier la charge volumique (Cv) au rendement de dénitrification. Le rendement de dénitrification est supérieur à 85 % pour Cv < 2 kg NO3-/m3.j ; il tombe à 50 % pour Cv ~ 3,5 kg NO3-/m3.j Des rapports stoechiométriques entre les nitrates réduits et les produits formés/consommés ont été établis. Ainsi : NO3- donne 0,98 SO42- et 1 NO3- consomme 0,90 HCO3-. L'incidence de la teneur en NaCl de la solution alimentaire permet de montrer l'inhibition non compétitive du chlorure vis-à-vis de la dénitrification. L'incidence de la concentration en NaCl sur le vitesse de dénitrification apparaît pour une charge de 1 kg NO3-/m3.j. On note que le rendement de 90 % ou plus est obtenu pour une concentration 2 30 g/l. La constante d'inhibition est de l'ordre de 40 g/l. L'examen de la répartition de la biomasse sur le matériau et une approximation simple d'écoulement en flux piston nous conduisent à prévoir le rendement d'élimination de NO3- par :r=1 - e[ - 143,5 ] (sur) CV (41+I)Cette équation traduit les rôles de la charge volumique (Cv) et de la concentration en NaCl (I).The treatment and ultimate disposal of saline eluates from ionic exchange resins remain a badly worked out problem. New approaches are needed and biological denitrification seems to be very attractive since it may be implemented in the form of an inexpensively and easily used reactor.The aim of the present work was to better understand the bacterial denitrification process on sulphur by a chemoautotrophic bacterium, Thiobacillus denitrificans, in a saline medium, and to apply this knowledge to the treatment and/or the recycling of these eluates. Claus and Kutzner (1985) reported an inhibitory effect of NaCl starting at a concentration of 20 g/L.A column containing elemental sulphur was continually fed by a solution containing nitrate and nutrient salts. In the first step of the study, a relationship between the volumetric load (Cv) and the denitrification efficiency was established. For Cv < 2 kg NO3-/m3/j, the denitrification efficiency was greater than 85%, whereas it decreased rapidly to 50% for Cv 3,5 kg NO3- /m3/j. Stoichiometric ratios between reduced nitrates and formed/consumed products were determined. For example, the reduction of 1 mole of NO3- induces the formation of 0,98 mole SO42- and requires 0,90 moles HCO3-. The effect of the NaCl concentration was investigated for a volumetric charge of 1 NO3-/m3/j. An uncompetitive inhibition of denitrification by the sodium chloride present in the feed solution was observed. The denitrification efficiency reaches at least 90% for NaCl concentrations up to 30 g/L. The inhibition constant is about 40 g/l. A model linking the denitrification efficiency (r) to the volumetric loading and to the sodium chloride concentration in the regeneration water was developed, based on an examination of the biomass distribution on the fill material and the assumption of plug-flow within the column:r=1 - e[ - 143,5 ] (over) CV (41+I

Élimination des cations métalliques divalents : complexation par l'alginate de sodium et ultrafiltration

Depuis quelques années la pollution par les métaux lourds et devenue un problème important pour la protection de l'environnement et de nombreuses méthodes ont été développées pour éliminer les métaux toxiques présents dans l'eau.Parmi les différents procédés utilisés, la complexation-ultrafiltration est bien connue et de nombreuses études sur ce sujet sont décrites dans la littérature. Cependant, le choix de nouveaux macroligands hydrosolubles demeure important pour développer cette technologie.L'un des objectifs de ce travail était de montrer que dans ce procédé un biopolymère peut remplacer un macroligand de synthèse. Les expériences ont été menées avec de l'alginate de sodium, polysaccharide extrait des algues brunes, et porteur de groupements carboxyliques et hydroxydes capables de complexer les cations.Notre étude se divise en trois parties. Après avoir décrit, dans la première, le matériau et les méthodes utilisées, nous étudions dans la seconde les conditions de l'ultrafiltration (seuil de coupure, pression appliquée, pH, concentration ), avant de discuter dans la troisième les résultats obtenus dans le traitement de solutions contenant Cd2+, Cu2+, Mn2+ and Pb2+.For some years past, pollution by heavy metals has become one of the main problems for environmental protection. A number of methods have been developed to remove toxic metals from water. Among the various processes used, complexation-ultrafiltration is well known and numerous studies on this subject are described in the literature. However, the choice of new water-soluble macroligands remains important for developing this technology.One aim of the present work was to prove that biopolymers can replace synthetic macroligands in the process. The experiments have been conducted with sodium alginate, a polysaccharide extracted from brown seaweeds and containing carboxylic and hydroxyl groups able to complex heavy cations. Filtration experiments were performed with a frontal system, equipped with a polysulfone membrane with a 20000 Daltons cut-off . The solutions studied were prepared by diluting in demineralized water either sodium alginate or "Titrisol Merck" for cations. Before filtration the two solutions were mixed and stirred for 20 min. The pH of the feed solutions was adjusted with HCl (or HNO3 for Pb) or NaOH and determined accurately using a calibrated probe.The molecular weight of sodium alginate was determined by liquid chromatography and the viscosity was measured with either a viscosimeter for low values or a capillary method for concentrated solutions. Cation concentrations were measured by atomic absorption spectrophotometryBoth permeate and retentate macroligands concentrations were estimated from measurements of total organic carbon (TOC). Following each experiment, chemical cleaning was performed by filtration of HCl, NaOH and water. This procedure was followed by demineralized water filtration, to ensure that the initial permeability was restored.In the first part of the work the ultrafiltration of sodium alginate solutions for different concentrations and various pressures was studied. Experimental results for macroligand retention, deduced from the TOC values, show a total rejection. All the curves, permeate flux versus time, present the same profile which indicates a significant concentration polarization. According to the obtained results we chose the value of 5 10-2 g L-1 for the ligand concentration and one bar for the applied pressure.In the second part of the study, the retention of cations (Cd2+, Cu2+, Mn2+ and Pb2+) was investigated. The observed results show that the removal rates are close to 100%. These values depend both on the total concentration of cation and on the pH value. The retention of cations is shown to depend strongly on pH: a variation of pH between 3 and 5 leads to changes in retention efficiency from 0 to 100%. This can be explained by the dissociation of alginic acid as a function of pH. For lower pH values the macroligand is in a molecular form and the metallic cation remains free; for higher values metal complexation is possible, increasing the rejection. If coordination number, rejection rate and pH are known, the various association constants can be determined using a graphical method. It can be seen from the results that the stability of the complexes formed decreases in the sequence Pb>Cu>Mn>Cd.In order to investigate the retention of these cations in a fresh water, the influence of calcium hardness was studied. The results indicate that cation removal decreases when the calcium concentration increases. This observation is an important restriction for fresh water treatment but does not affect the elimination of metals from a solution or an industrial waste containing cations

A note on the integrable discretization of the nonlinear Schr\"odinger equation

We revisit integrable discretizations for the nonlinear Schr\"odinger equation due to Ablowitz and Ladik. We demonstrate how their main drawback, the non-locality, can be overcome. Namely, we factorize the non-local difference scheme into the product of local ones. This must improve the performance of the scheme in the numerical computations dramatically. Using the equivalence of the Ablowitz--Ladik and the relativistic Toda hierarchies, we find the interpolating Hamiltonians for the local schemes and show how to solve them in terms of matrix factorizations.Comment: 24 pages, LaTeX, revised and extended versio

Simultaneous Material Type Classification And Mapping Data Acquisition Using A Laser Range Finder

This paper presents a method for single sensor simultaneous derivation of three-dimensional mapping data and material type data for use in an autonomous sandblasting system. A Hokuyo laser range finder s firmware has been modified so that it returns intensity data. A range error and return intensity analyzing algorithm allows the material type of the sensed object to be determined from a set of known materials. Empirical results have demonstrated the system s ability to classify material type (under alignment and orientation constraints) from a set of known materials common to sandblasting environments (wood, concrete, metals with different finishes and cloth/fabric) and to successfully classify objects both when static and when fitted to an in-motion 6-DOF anthropomorphic robotic arm