Feasibility of thickness mapping using ultrasonic guided waves

Detection and sizing of corrosion in pipelines and pressure vessels over large, partially accessible areas is of growing interest in the petrochemical and nuclear industries. Traditionally, conventional ultrasonic thickness gauging and eddy current techniques have been used to precisely measure the thickness in structures. These techniques only allow the measurement of the local thickness under the probe. Consequently obtaining the remnant thickness of a specimen over a large area requires the probe to be scanned, which is a long and tedious process. Moreover, with these techniques, the scanning may become impossible when the area of inspection is inaccessible. There is therefore a need for a rapid, accurate, long range inspection technique to measure the remaining thickness in corrosion patches. Low frequency guided waves are now routinely used to screen large area of pipes and other structures for cracks and corrosion. Their detection and location capability is very good, but the standard screening technique only gives a rough estimate of the remaining wall thickness. Guided waves have multiple properties which can be used for thickness mapping over large partially accessible areas e.g. dispersion and cutoff frequency thickness product of the high order modes. The present work aims to demonstrate the potential of guided waves for thickness mapping over large partially accessible areas. It starts with a general introduction on ultrasonic guided waves and a literature review of the different techniques for the evaluation of thickness with guided waves. The severity of the errors introduced in time-of-flight tomography for thickness reconstruction by breaking the assumption of the ray theory are investigated. As these errors are significant, the possibility of using the cutoff property of the high order modes is investigated in a frequency range where the ray theory is valid. It is found that the attenuation due to the scattering of the waves in corrosion is too large for this technique to work. Finally the use of low frequency guided wave for diffraction tomography is examined. Finite element simulations of a 64 element circular array on a plate show that when the scattering mechanism of the object to be reconstructed satisfies the Born approximation the reconstruction of the thickness is accurate. However the practical implementation is more challenging when the incident field is not known. Experimental results demonstrate that ultimately the scattering from the array of transducer is a major source of error in the tomographic reconstruction, but when there is no scattering from the array of transducers the reconstructions are very similar to the finite element simulations

La reconnaissance des acquis expérientiels: étude de cas de la politique d'admission des adultes à l'Université Laval

Has the inclusion of experience as a criterion of admission for adult students raised significantly the chances of these students of being admitted? The authors analyse the new admission policy at Laval University (1980) and, from a sample of400 candidates' dossiers, its practice age and a fair amount of experience appear to be important factors opening the door of university. However, the effects of these factors are particularly enhanced if experience is close to academic or cognitive learning or combined with a CEGEP diploma and a grade higher than 65%. Thus, experience does not seem to be used as a basis of admission of its own, but mainly to corroborate academic ability already expressed by good grades.Les auteurs évaluent formellement la politique et le processus d'évaluation de la clientèle adulte qui ne rencontre pas les critères "normaux" d'admission aux programmes de premier cycle à l'Université Laval en 1980. L'étude de l'application de cette politique, tenant compte de l'expérience de vie ou des acquis expérientiels des candidats adultes en plus de leurs acquis scolaires antérieurs et l'analyse d'un échantillon de 400 dossiers de candidats adultes nous révèlent que l'âge et la durée de l'expérience constituent des facteurs favorisant l'admissibilité des candidats adultes. Elles démontrent aussi clairement que le profil de référence, lors de ce processus d'évaluation, est principalement la for- mation scolaire et sa dimension cognitive. En effet, le fait de posséder des expé- riences liées à l'apprentissage, au moins un diplôme de niveau collégial et des résultats scolaires supérieurs à 65%, augmente les chances d'un candidat d'être reconnu admissible. Le concept d'expérience de vie semble donc être utilisé de façon secondaire, comme confirmation au renforcement des succès scolaires antérieurs, plutôt que comme critère autonome

Random field spin models beyond one loop: a mechanism for decreasing the lower critical dimension

The functional RG for the random field and random anisotropy O(N) sigma-models is studied to two loop. The ferromagnetic/disordered (F/D) transition fixed point is found to next order in d=4+epsilon for N > N_c (N_c=2.8347408 for random field, N_c=9.44121 for random anisotropy). For N < N_c the lower critical dimension plunges below d=4: we find two fixed points, one describing the quasi-ordered phase, the other is novel and describes the F/D transition. The lower critical dimension can be obtained in an (N_c-N)-expansion. The theory is also analyzed at large N and a glassy regime is found.Comment: 4 pages, 5 figure

Estimation of angular velocity and acceleration from shaft encoder measurements

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Influence of Local Mechanical Properties of High Strength Steel from Large Size Forged Ingot on Ultrasonic Wave Velocities

In the metallurgical industry, ultrasonic inspection is routinely used for the detection of defects. For the nondestructive inspection of small high strength steel parts, the material can be considered isotropic. However, when the size of the parts under inspection is large, the isotropic material hypothesis does not necessarily hold. The aim of this study is to investigate the effect of the variation in mechanical properties such as grain size, Young\u27s modulus, Poisson’s ratio, chemical composition on longitudinal and transversal ultrasonic wave velocities. A 2 cm thick slice cut from a 40-ton bainitic steel ingot that was forged and heat treated was divided into 875 parallelepiped samples of 2x4x7 cm3. A metallurgical study has been performed to identify the phase and measure the grain size. Ultrasonic velocity measurements at 2.25 MHz for longitudinal and transversal waves were performed. The original location of the parallelepiped samples in the large forged ingot and the measured velocities were used to produce an ultrasonic velocity map. Using a local isotropy assumption as well as the local density of the parallelepiped samples calculated from the chemical composition of the ingot provided by a previously published study [1], Young’s modulus and Poisson’s ratio were calculated from the longitudinal and transversal wave velocities. Microtensile measurements were used to validate Young’s modulus obtained by the ultrasonic wave velocity and an excellent match was observed

Contribution of point sources to the soft gamma-ray Galactic emission

The nature of the soft gamma-ray (20-200 keV) Galactic emission has been a matter of debate for a long time. Previous experiments have tried to separate the point source contribution from the real interstellar emission, but with a rather poor spatial resolution, they concluded that the interstellar emission could be a large fraction of the total Galactic emission. INTEGRAL, having both high resolution and high sensitivity, is well suited to reassess more precisely this problem. Using the INTEGRAL core program Galactic Center Deep Exposure (GCDE), we estimate the contribution of detected point sources to the total Galactic flux.Comment: Proceedings of the 5th INTEGRAL Workshop, Munich 16-20 February 2004. ESA SP-55

Embedding intelligent image processing algorithms : the new safety enhancer for helicopters missions

International audienc

Unwanted sexual experiences among adolescents: shedding light on the gray zone between consensual and non-consensual sex

This study aimed at exploring adolescents' perceptions of unwanted sexual experiences (USE) in order to set up definitions, categories, and boundaries on the continuum between consensual and non-consensual sex. Methods: We conducted a qualitative thematic analysis of four focus group discussions gathering a total of 29 male and female adolescents aged 16-20 years. Results: Analysis of participants' discourse revealed three main characteristics that define USE, namely, regret, as most situations discussed were said to be acceptable or not in terms of whether there were regrets after the fact; misperception of sexual intent; and lack of communication between partners. Conclusions: Our findings revealed that health professionals should be aware of the subtle aspects identifying USE when screening for situations that can have adverse psychological consequences. Where prevention is concerned, it appears important to address these aspects of USE in sex education classe

Urinary And Breast Milk Biomarkers To Assess Exposure Ro Naphthalene In Pregnant Women: An Investigation Of Personal And Indoor Air Sources

Naphthalene exposures for most non-occupationally exposed individuals occur primarily indoors at home. Residential indoor sources include pest control products (specifically moth balls), incomplete combustion such as cigarette smoke, woodstoves and cooking, some consumer and building products, and emissions from gasoline sources found in attached garages. The study aim was to assess naphthalene exposure in pregnant women from Canada, using air measurements and biomarkers of exposure