An Inverse Method for Cracks Characterization from Ultrasonic Bscan Images

Concern has been expressed about the capabilities of performing non destructive evaluation (NDE) of flaws located near to the outer surface in nuclear pressurized water reactor (PWR) vessels. The ultrasonic examination of PWR is accomplished from the inside with ultrasonic focused transducers working in the pulse echo mode. By recording the echoes as a function of time, the Ascan representation may be obtained. Many ultrasonic flaw detectors used for NDE are based on the simple Ascan concept involving measuring a time interval called “time of flight”. By combining the Ascan concept with synchronized transducer scanning, one can produce Bscan images that are two dimensional descriptions of the flaw interaction with the ultrasonic field

Real-time reconstruction of non uniformly sampled signals

The purpose of this paper is the presentation of methods of signal processing or numerical analysis for the real-time reconstruction of non uniformly sampled signal . Our approach is essentially based on the short term modelling of a signal and its prediction using the obtained model. This paper includes three parts . In the first one we use a Kalman filter with a given model. The second part corresponds to numerical analysis methods ; we present a prediction-correction algorithm . In the last part, two examples of modelisation are presented. The first one uses Taylor development and the second one uses an AR model.Nous proposons dans cet article des méthodes de traitement statistique ou d'analyse numérique pour reconstituer en temps réel un signal échantillonné non uniformément. Notre approche est essentiellement basée sur une modélisation du signal à court terme suivie d'une prédiction utilisant le modèle obtenu. Cet article comprend trois parties. Une première concerne l'utilisation d'un filtre de Kalman pour une reconstitution à partir d'un modèle donné. La deuxième partie correspond à des méthodes d'analyse numérique, nous y présentons un algorithme de prédiction-correction. Enfin, la troisième partie présente deux modélisations, l'une par un développement de Taylor et l'autre par les paramètres AR du signa

Digital filters for non-uniformly sampled signais

Nous traitons dans cet article de la conception et la réalisation temps réel de filtres numériques pour des signaux échantillonnés non uniformément sans reconstruction préalable du signal échantillonné de manière périodique. Nous proposons dans une première étape une méthode de filtrage fondée sur des approximations numériques de l'intégrale de convolution ou d'équations différentielles et applicable par exemple aux filtres à réponse impulsionnelle finie. La deuxième méthode utilise la discrétisation d'un filtre continu équivalent et s'applique au cas des filtres à réponse impulsionnelle infinie. Des exemples viennent enfin illustrer l'étude

Ecotoxicity and fungal deterioration of recycled polypropylene/wood composites: Effect of wood content and coupling

Polypropylene (PP)/wood composites were produced by homogenization in a twin-screw extruder and injection molding of tensile bars. Their mechanical properties were determined before and after exposure to biological treatment, and the effect of the treatment was assessed by various ways including visual inspection and the measurement of weight loss. The ecotoxicity of the materials was also evaluated by using the bioluminescent bacteria Vibrio fischeri. The results proved that wood facilitates biodeterioration (colonization) under the conditions used. The coupling agents do not have inhibitory effect, but seems to stimulate fungal growth (biodeterioration) at large loads of wood flour. PP/wood composites can be considered quite durable, but the influence of wood content on environmental resistance must be taken into account for materials intended for applications requiring long-term outdoor exposure as the time of exposure to microbial colonization increases. Direct ecotoxic effect on aquatic ecosystems cannot be expected from PP/wood composites

Real-time reconstruction of 2D signals with missing observations

In this paper, we propose a new real-time reconstruction method of two-dimensional uniformly sampled signals with missing observations. A two-dimensional autoregressive model (AR-2D) is adopted. Two cases of causality, Quarter of Plane (QP) and Non symetric Half Plane (NSHP) are tested. The criterion used to estimate the model parameters is quadratic, and defined when samples are availables. Due to missing observations, the gradient of the criterion becomes non-linear. The optimum is reached by means of LMS-like algorithms adapted to 2D non uniformly sampled signals. Two approximations of the criterion are proposed. They lead to two algorithms whose formal descriptions and compared performances are provided. The results obtained show the reconstruction performances of two-dimensional (stationary and non stationary) signals, as a function of the ratio and the distribution law of missing samples.Dans cet article nous proposons une nouvelle méthode de reconstruction en temps réel de signaux bidimensionnels à échantillons manquants. Un modèle autorégressif bidimensionnel est adopté. On considère deux causalités, quart de plan (QP) et demi-plan asymétrique (NSHP : Non Symetric Half Plane). Le critère à optimiser pour estimer les paramètres du modèle est quadratique en l'erreur d'estimation, et défini aux instants d'arrivées des échantillons. Du fait d'observations manquantes, le gradient du critère devient non linéaire en les paramètres. L'optimum est atteint à l'aide d'algorithmes de type LMS adaptés aux signaux bidimensionnels à échantillons manquants. Deux approximations du critère sont proposées. Elles conduisent à deux algorithmes dont la description formelle est fournie et les performances comparées. Les résultats présentés montrent les performances de la reconstruction (pour des signaux bidimensionnels stationnaires et non stationnaires) en fonction du pourcentage d'échantillons manquants ainsi que de la loi de distribution de ces échantillons

Properties of cellulose nanofibre networks prepared from never-dried and dried paper mill sludge

Paper mills yield large volumes of sludge materials which pose an environmental and economic challenge for disposal, despite the fact that they could be a valuable source for cellulose nanofibres (CNF) production. The aim of the study was to evaluate the production process and properties of CNF prepared by mechanical fibrillation of never-dried and dried paper mill sludge (PMS). Atomic force microscopy (AFM) showed that average diameters for both never-dried and dried paper sludge nanofibres (PSNF) were less than 50 nm. The never-dried and dried sludge nanofibres showed no statistical significant difference (p > 0.05) in strength ∼92 MPa, and ∼85 MPa and modulus ∼11 GPa and ∼10 GPa. The study concludes that paper mill sludge can be used in a dried state for CNF production to reduce transportation and storage challenges posed on industrial scale

Towards an easy-to-use D.S.P

The use of digital signal processors is not yet commonly widespread despite their obvious advantages . In this paper we present a certain number of ideas helping case their use. These ideas have been put to work by conceiving the architecture of a processor which is both optimal and easy to use .L'utilisation des processeurs de signaux n'est pas encore très courante, en dépit des avantages qu'ils procurent . Nous présentons ici un certain nombre de réflexions menées dans le sens d'une plus grande facilité d'utilisation de ces processeurs . Ces réflexions ont été concrétisées dans l'élaboration d'une architecture de processeur, à la fois optimisée et d'utilisation aisée

Properties of cellulose nanofibre networks prepared from never-dried and dried paper mill sludge

Paper mills yield large volumes of sludge materials which pose an environmental and economic challenge for disposal, despite the fact that they could be a valuable source for cellulose nanofibres (CNF) production. The aim of the study was to evaluate the production process and properties of CNF prepared by mechanical fibrillation of never-dried and dried paper mill sludge (PMS). Atomic force microscopy (AFM) showed that average diameters for both never-dried and dried paper sludge nanofibres (PSNF) were less than 50 nm. The never-dried and dried sludge nanofibres showed no statistical significant difference (p > 0.05) in strength ∼92 MPa, and ∼85 MPa and modulus ∼11 GPa and ∼10 GPa. The study concludes that paper mill sludge can be used in a dried state for CNF production to reduce transportation and storage challenges posed on industrial scale