Bayesian Programming Multi-Target Tracking: an Automotive Application

A prerequisite to the design of future Advanced Driver Assistance Systems for cars is a sensing system providing all the information required for high-level driving assistance tasks. In particular, target tracking is still challenging in urban trafc situations, because of the large number of rapidly maneuvering targets. The goal of this paper is to present an original way to perform target position and velocity, based on the occupancy grid framework. The main interest of this method is to avoid the decision problem of classical multi-target tracking algorithms. Obtained occupancy grids are combined with danger estimation to perform an elementary task of obstacle avoidance with an electric car

Ultrasound to Enhance a Liquid–Liquid Reaction

Liquid–liquid mass transfer with ultrasound was investigated experimentally during the hydrolysis of n-amyl acetate. Power ultrasound is supposed to improve the yield and kinetics of such multiphase chemical reactions thanks to the mechanical effects of cavitation. Indeed, implosion of micro-bubbles at the vicinity of the liquid– liquid interface generates disruption of this surface, and enhances mixing in the liquid around the inclusion, thus improving mass transfer between the two phases. This effect has been demonstrated here on the hydrolysis of n-amyl acetate by sodium hydroxide, a rather slow reaction but influenced by mass transfer; the reaction is carried out in a glass jacketed reactor, 500 mL of volume, equipped with a Rushton turbine and a 20 kHz sonotrode dipping in the solution. The ester is initially pure in the organic dispersed phase, and sodium hydroxide has an initial concentration of 300 mol/m3; one of the products, pentanol partitions between the two phases and the sodium salt stays in the aqueous phase. The initial apparent reaction rate is measured from the record of the conductivity giving the concentration of alkali versus time. The reaction rate was always found to increase when ultrasound is superimposed to mechanical stirring (at 600 rpm), with a positive influence of input power (20 and 50 W). When varying initial concentration (300 and 600 mol/m3), temperature (36 and 45°C) and ultrasound emitter (sonotrode or cuphorn), the benefit of ultrasound over mechanical agitation was systematic. The only case of a weak influence of ultrasound was the sonication of a dense medium, containing 23% of organic phase and impeding the propagation of ultrasound

Modélisation d'une politique d'autocontrôle sur un réseau d'eau potable

Quel est le nombre d'échantillons à prélever pour analyse bactériologique dans un réseau de distribution d'eau potable afin réaliser un autocontrôle optimal du point de vue économique (coûts analytiques et coût des actions curatives), tout en limitant les risques de dégradation de la qualité ? Pour répondre à cette question, nous proposons un modèle probabiliste qui simule le choix de la décision curative lorsque les analyses indiquent des résultats insatisfaisants ainsi que l'effet de cette décision sur la qualité de l'eau du réseau. Les différentes actions curatives et leur efficacité ont été déterminées empiriquement à partir de l'expertise du gestionnaire du réseau de la Banlieue de Paris et des données collectées de 1992 à 1996. Le modèle s'appuie sur un schéma Markovien d'évolution du couple (Qualité de l'eau, Action curative). Par programmation dynamique, on calcule le coût moyen de la politique décisionnelle de la Banlieue de Paris et le risque généré par cette politique en terme de qualité de l'eau (fréquence des états dégradés), pour différents niveaux d'autocontrôle (nombre d'analyses d'autocontrôle). Le risque d'avoir un état dégradé diminue avec le nombre d'analyses jusqu'au seuil de 140 analyses (autocontrôle et contrôle réglementaire) puis reste quasiment constant, tandis que les coûts continuent d'augmenter.Drinking water quality is monitored regularly by state officers (DDASS), and also by the water distributor at a level of his own choice. A model has been constructed to simulate decision making after observations of one or more bacteriological-positive samples from the drinking water distribution system of suburban Paris (four million inhabitants in 144 boroughs). In cases of non-conformity, a curative action is taken (rinsing, chlorinating...) that tends to increase the level of water quality for the ensuing weeks. The model compares the trade-offs between the global cost of the policy and the risk of quality failure, based on various sampling plans of different intensity which the quality manager may design to get information from the distribution system. The more weekly analyses he makes, the more money he spends in control, but at the same time, the more valuable is the information that he receives with which to assess the appropriateness of curative actions to increase quality within the system.The state of quality in the distribution system is supposed to be homogeneous, with each sampling station representative of the overall water quality. Three discrete classes of quality (acceptable, poor, unsatisfactory) have been defined, corresponding respectively to an average frequency of 5%, 10% and 15% of coliform-positive samples from the control design. The set of alternatives is composed of eight curative actions presently in use in the distribution system when a defect sample is registered: (1) complementary checking of measurements of the quality parameters, such as chlorine and temperature; (2) additional analyses of bacteriological counts; (3) rinses (water is released during a few hours from certain pipes directly into the sewage system, to allow its replacement by fresh water supposedly of better quality); (4) purges (same as rinses, but for a longer period in larger zones); (5) disinfection (the defective zone is isolated and a specialized truck introduces a large amount of chlorine into the distribution pipes); (6) deep cleaning (a yearly cleaning of 3% of the distribution system); (7) chlorinating (the level of free chlorine injection is increased in the water treatment plant); (8) a change in the treatment plant mode of operation (the complete process is checked to prevent the possible transfer of bacteria from the river to the distribution system). It also includes the standard decision of "doing nothing," i.e., let the system evolve on its own. The cost of each decision has been evaluated according to the economic data available from the distribution company, taking mainly into account controllers' work hours and travel expenses. Water quality dynamics in the distribution system are modeled as a Markov chain controlled by the possible decisions at each stage. For each curative action a (3*3) transition matrix is empirically elicited, using both available data and expertise from the team of quality managers. The present control strategy of the distribution company is embedded in the model, by respecting the observed constraints in the sequence of decisions: for instance, if a previous rinse has not been followed by a decrease in the number of coliform-positive samples in the following week, a stronger action such as a purge or disinfection is enforced, rather than repeating the rinse. The strategy also mimics the empirical rules of the quality manager's behavior in facing bacteriological incidents: for example, a single occurrence of coliforms with no specific curative action taken in a previous week will generally dictate a rinse (84% of time), sometimes demand a purge (12%), and occasionally require a disinfection (1%). The Markov model is run in a simulation mode for the spring-summer period: for a given value of the sample size, the average cost of the quality monitoring policy and a failure index (average frequency in the two lowest quality states) can be evaluated by backward induction. Although the assessment of the parameters has been made empirically, the model exhibits realistic performances with regard to side criteria used as discrepancy measures for model rejection checking: the relative use of each curative action and the average time necessary to escape from a non-acceptable state (resiliency) are of the same order of magnitude as the corresponding real indices. A sensitivity analysis reveals that the results are fairly robust to small changes in the probabilities of transition, but do depend on the way the range of water qualities is divided into discrete classes. With the data chosen, the model showed a satisfactory cost/risk balance at 110-140 analyses per week, for the homogeneous subsystem under study. In the case of more data availability, this model could become a valuable decision tool. Provided that a criterion of joint global utility between risk and cost can be defined, it could be used to design a control policy with a weekly varying sample

The temperature dependence of the isothermal bulk modulus at 1 bar pressure

It is well established that the product of the volume coefficient of thermal expansion and the bulk modulus is nearly constant at temperatures higher than the Debye temperature. Using this approximation allows predicting the values of the bulk modulus. The derived analytical solution for the temperature dependence of the isothermal bulk modulus has been applied to ten substances. The good correlations to the experiments indicate that the expression may be useful for substances for which bulk modulus data are lacking

Geometric and Bayesian models for safe navigation in dynamic environments

Autonomous navigation in open and dynamic environments is an important challenge, requiring to solve several difficult research problems located on the cutting edge of the state of the art. Basically, these problems may be classified into three main categories: (a) SLAM in dynamic environments; (b) detection, characterization, and behavior prediction of the potential moving obstacles; and (c) online motion planning and safe navigation decision based on world state predictions. This paper addresses some aspects of these problems and presents our latest approaches and results. The solutions we have implemented are mainly based on the followings paradigms: multiscale world representation of static obstacles based on the wavelet occupancy grid; adaptative clustering for moving obstacle detection inspired on Kohonen networks and the growing neural gas algorithm; and characterization and motion prediction of the observed moving entities using Hidden Markov Models coupled with a novel algorithm for structure and parameter learnin

Appropriateness of internal digital phantoms for monitoring the stability of the UBIS 5000 quantitative ultrasound device in clinical trials

In bone status assessment, proper quality assurance/quality control is crucial since changes due to disease or therapeutic treatment are very small, in the order of 2-5%. Unlike for dual X-ray absorptiometry, quality control procedures have not been extensively developed and validated for quantitative ultrasound technology, limiting its use in longitudinal monitoring. While the challenge of developing an ideal anthropometric phantom is still open, some manufacturers use the concept of the internal digital phantom mimicking human characteristics to check the stability of their device. The objective of the study was to develop a sensitive model of quality control suitable for the correction of QUS patient data. In order to achieve this goal, we simulated a longitudinal device lifetime with both correct and malfunctioning behaviors. Then, we verified the efficiency of digital phantoms in detecting those changes and subsequently established the in vitro/in vivo relationship. This is the first time that an attempt to validate an internal digital phantom has made, and that this type of validation approach is used. The digital phantom (DP) was designed to mimic normal bone (BUAP2) and osteoporotic bone (BUAP1) properties. The DP was studied using the UBIS 5000 ultrasound device (DMS, France). Diverse malfunctions of the UBIS-5000 were simulated. Several series of measurements were performed on both BUAP1 and 2 and on 12 volunteers at each grade of malfunction. The effect of each simulated malfunction on in vivo and in vitro results was presented graphically by plotting the average BUA values against the percentage change from baseline. The change from baseline in BUA was modeled using linear regression, and the in vivo/in vitro ratio was obtained from the model. All experimentations influenced the measure of BUAP1 and 2 as well as the measure of our 12 volunteers. However, the degree of significance varied as a function of the severity of the malfunction, and the results also differed substantially in magnitude between in vivo and in vitro. Indeed, the DP was about 10 times more sensitive to variations of the transfer function than was the in vivo measurement, which is very reassuring. The sensitivity of the digital phantoms was reliable in the determination of simulated malfunctions of the UBIS-5000. The digital phantoms provided an accurate evaluation of the acoustic performance of the scanner, including the fidelity of transducers. In light of these results, the QC approach of the UBIS-5000 will be extremely simple to implement compared with other devices. Indeed, since the digital phantom was automatically measured during every patient measurement, the QC approach could be built on an individual level basis rather than on an average basi

Probabilistic Grid-based Collision Risk Prediction for Driving Application

International audienceIn the recent years, more and more modern cars have been equipped with perception capabilities. One of the key applications of such perception systems is the estimation of a risk of collision. This is necessary for both Advanced Driver Assistance Systems and Autonomous Navigation. Most approach for risk estimation propose to detect and track the dynamic objects in the scene. Then the risk is estimated as a Time To Collision (TTC) by projecting the object's trajectory in the future. In this paper, we propose a new grid-based approach for collision risk prediction, based on the Hybrid-Sampling Bayesian Occupancy Filter framework. The idea is to compute an estimation of the TTC for each cell of the grid, instead of reasoning on objects. This strategy avoids to solve the difficult problem of multi-objects detection and tracking and provides a probabilistic estimation of the risk associated to each TTC value. After promising initial results, we propose in this paper to evaluate the relevance of the method for real on-road applications, by using a real-time implementation of our method in an experimental vehicle

Experience with the LEP vacuum system at energies above 90 GeV and future expectations

The LEP storage ring has been operated at energies above 90 GeV for more than 1000 hours during 1997. Because of the rapid increase with the beam energy of the power radiated as synchrotron light, the vacuum system has been submitted to very stringent conditions as far as power evacuation and photon stimulated gas desorption are concerned. The operational experience acquired under these, up to now unexplored, conditions will be reviewed together with an outline of the limitations which were experienced at these high levels of radiation in the use of the available vacuum instrumentation. Based o n the available data detailed predictions concerning the beam lifetime, gas desorption and beam cleaning of the vacuum system under the impact of photons with a critical energy approaching 1 MeV will be formulated

Experimental two dimensional cellular flames

International audienceThe propagation of very unstable cellular flames (also called self-turbulent flames) is studied experimentally in a Hele-Shaw cell. This quasi-two dimensional configuration allows for quantitative image analysis. The dynamics of the premixed flame is controlled in these conditions by the creation or merging of the cusps that appear on the front