Nonlinear shear wave interaction at a frictional interface: Energy dissipation and generation of harmonics

Analytical and numerical modelling of the nonlinear interaction of shear wave with a frictional interface is presented. The system studied is composed of two homogeneous and isotropic elastic solids, brought into frictional contact by remote normal compression. A shear wave, either time harmonic or a narrow band pulse, is incident normal to the interface and propagates through the contact. Two friction laws are considered and their influence on interface behavior is investigated : Coulomb's law with a constant friction coefficient and a slip-weakening friction law which involves static and dynamic friction coefficients. The relationship between the nonlinear harmonics and the dissipated energy, and their dependence on the contact dynamics (friction law, sliding and tangential stress) and on the normal contact stress are examined in detail. The analytical and numerical results indicate universal type laws for the amplitude of the higher harmonics and for the dissipated energy, properly non-dimensionalized in terms of the pre-stress, the friction coefficient and the incident amplitude. The results suggest that measurements of higher harmonics can be used to quantify friction and dissipation effects of a sliding interface.Comment: 17 pages, 10 figure

Automated screening of MRI brain scanning using grey level statistics

This paper describes the development of an algorithm for detecting and classifying MRI brain slices into normal and abnormal by relying on prior-knowledge, that the two hemispheres of a healthy brain have approximately a bilateral symmetry. We use the modified grey level co-occurrence matrix method to analyze and measure asymmetry between the two brain hemispheres. 21 co-occurrence statistics are used to discriminate the images. The experimental results demonstrate the efficacy of our proposed algorithm in detecting brain abnormality with high accuracy and low computational time. The dataset used in the experiment comprises 165 patients with 88 patients having different brain abnormalities whilst the remainder do not exhibit any detectable pathology. The algorithm was tested using a ten-fold cross-validation technique with 100 repetitions to avoid the result depending on the sample order. The maximum accuracy achieved for the brain tumours detection was 97.8% using a Multi-Layer Perceptron Neural Network

Integration of digital watermarking technique into medical imaging systems

This paper presents the process of integrating digital watermarking technique into medical imaging workflow to evaluate, validate and verify its applicability and appropriateness to medical domains. This is significant to ensure the ability of the proposed approach to tackle security threats that may face medical images during routine medical practices. This work considers two key objectives within the aim of defining a secure and practical digital medical imaging system: current digital medical workflows are deeply analyzed to define security limitations in Picture Archiving and Communication Systems (PACS) of medical imaging; the proposed watermarking approach is then theoretically tested and validated in its ability to operate in a real-world scenario (e.g. PACS). These have been undertaken through identified case studies related to manipulations of medical images within PACS workflow during acquisition, viewing, exchanging and archiving. This work assures the achievement of the identified particular requirements of digital watermarking when applied to digital medical images and also provides robust controls within medical imaging pipelines to detect modifications that may be applied to medical images during viewing, storing and transmitting

Instabilités de frottement : Approches temporelle et fréquentielle

International audienceThe vibrations generated at the interface between the two bodies in friction are responsible for various noises such as squealing, juddering, hammering, hooting, etc... In order to model and understand friction-induced vibration phenomenon, two approaches are compared in this article: temporal approach and modal approach. This analysis has been made on a simplified system composed of two beams in contact. The two different approaches have been programmed using Finite Element method. Assumptions on the contact calculation are different for the two approaches. Modal approach consists in calculating eigenvalues of the friction coupled system. Instabilities appear when a pair of modes merges. Eigenvalues with positive real parts are identified as potentially unstable modes. Temporal approach calculates the evolution of displacements, velocities, accelerations, forces ... One speaks about instabilities when stick or separation zones appear in the contact surfaces. With this approach frequencies which are excited during instability are obtained. Results have been compared and both methods give coherent and complementary results

ANETAC: Arabic named entity transliteration and classification dataset

In this paper, we make freely accessible ANETAC, our English-Arabic named entity transliteration and classification dataset that we built from freely available parallel translation corpora. The dataset contains 79, 924 instances, each instance is a triplet (e, a, c), where e is the English named entity, a is its Arabic transliteration and c is its class that can be either a Person, a Location, or an Organization. The ANETAC dataset is mainly aimed for the researchers that are working on Arabic named entity transliteration, but it can also be used for named entity classification purposes. This dataset was developed and used as part of a previous research study done by Hadj Ameur et al. [1]

Study of the propolis extract as a corrosion inhibitor of copper alloy in ethylene glycol/water 0.1 M NaCl

The effect of propolis extract as a corrosion inhibitor of copper alloy in ethylene glycol / water 0.1 M NaCl solution was studied by electrochemical measurements. The Tafel polarization curves showed that the propolis extract at different concentration acts as mixed inhibitor, and the maximum value of the inhibitory efficacy is 73.28% at optimum concentration of 1.25 g/L of propolis extract. The activation parameters reveal that the inhibitor molecules on copper surface are absorbed by physisorption and obey Langmuir isotherm adsorption. These results were supplemented by IR Spectroscopy, Scanning electron microscopy (SEM) and EDX spectrum of chemical composition. The metal solution interface is simulated as a physical model by using Electrochemical Impedance Spectroscopy (EIS).Keywords: Copper Alloy, Propolis extract, ethylene glycol; Corrosion inhibition; Adsorption, Electrochemical impedance Spectroscopy (EIS