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Search Results: 1 - 10 of 206306 matches for " N. Ben Kahla "
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A New Criterion for the Stabilization Diagram Used with Stochastic Subspace Identification Methods: An Application to an Aircraft Skeleton
E. Mrabet,M. Abdelghani,N. Ben Kahla
Shock and Vibration , 2014, DOI: 10.1155/2014/409298
Abstract: The modal parameters of a structure that is estimated from ambient vibration measurements are always subject to bias and variance errors. Accordingly the concept of the stabilization diagram is introduced to help users identify the correct model. One of the most important problems using this diagram is the appearance of spurious modes that should be discriminated to simplify modes selections. This study presents a new stabilization criterion obtained through a novel numerical implementation of the stabilization diagram and the discussion of model validation employing the power spectral density. As an application, an aircraft skeleton is used. 1. Introduction The vibration and acoustical behaviors of a mechanical structure are determined by its dynamic characteristics. This dynamic behavior is typically described with a linear system model. The procedure for the estimation of modal parameters of structures from measured data can be split into three distinct steps [1]: data collection, system identification, and determination of modal parameters from the identified system description. Stochastic identification methods for systems with unknown input have been introduced decades ago. Among the most robust and accurate system identification methods for output-only modal analysis of mechanical structures is the stochastic subspace identification method. Two types of implementation are available: the covariance-driven (SSI-cov) [2] implementation and the data-driven (SSI-data) [3] implementation. For the first one (SSI-cov), three methods can be implemented: the balanced realization (BR), the principal component (PC), and the canonical variate analysis (CVA). For dynamic structures such as the aircraft skeleton studied in this paper, the major setback in applying system identification for large-scale structures is the selection of the model order and the corresponding system poles. To address this problem, the concept of the “stabilization diagram” is introduced, overestimating the structure model order. Therefore, spurious modes are going to surface out and we have to discriminate them. For this matter, many stabilization criteria have been implemented. The most recent one was the modal transform norm [4]. In this paper, a new stabilization criterion is implemented and a validation method is discussed. The stochastic subspace identification method used is the balanced realization. 2. Stochastic State Space Models for Vibrating Structures The finite element method [4] is one of the most common tools for modeling mechanical structures. In the case of a linear
Numerical Study of the Active Tendon Control of a Cable-Stayed Bridge in a Construction Phase
M. H. El Ouni,N. Ben Kahla
Shock and Vibration , 2014, DOI: 10.1155/2014/937541
Abstract: This paper investigates numerically the active tendon control of a cable-stayed bridge in a construction phase. A linear Finite Element model of small scale mock-up of the bridge is first presented. Active damping is added to the structure by using pairs of collocated force actuator-displacement sensors located on each active cable and decentralized first order positive position feedback (PPF) or direct velocity feedback (DVF). A comparison between these two compensators showed that each one has good performance for some modes and performs inadequately with the other modes. A decentralized parallel PPF-DVF is proposed to get the better of the two compensators. The proposed strategy is then compared to the one using decentralized integral force feedback (IFF) and showed better performance. The Finite Element model of the bridge is coupled with a nonlinear cable taking into account sag effect, general support movements, and quadratic and cubic nonlinear couplings between in-plane and out-of-plane motions. Finally, the proposed strategy is used to control both deck and cable vibrations induced by parametric excitation. Both cable and deck vibrations are attractively damped. 1. Introduction In the past few decades, design and construction of civil structures showed a very deep evolution because of the technological progress in materials and devices. Cable-stayed bridges increased considerably their center span from 182.6?m (Stromsund Bridge in Sweden) to 1104?m (Russky Bridge in Russia). These structures are getting more slender, light, and flexible which makes them sensitive to vibrations induced by wind, traffic, waves, or even earthquakes. Consequently, vibration control has become a major issue in civil engineering. Vibrations in cable-stayed bridges may be reduced using passive [1–4], semiactive [5–12], and active methods [13]. Active control uses a set of actuators and sensors connected by feedback or feed forward loops. Among the proposed devices to control vibrations of cable-stayed bridges are the active mass dampers [14], active aerodynamic appendages [15], and active tendons. Several strategies have been proposed for the active tendon control of the global modes of bridges, as well as for the in-plane and out-of-plane cable vibrations. Yang and Giannopolous [16] were the first to propose active tendon control to reduce vibration induced by strong wind gusts. They studied the feedback control of a simple continuous beam model suspended by four stay cables using four active tendons equipped with servohydraulic actuators. With respect to the motion
Etude du comportement mécanique de liants binaires et ternaires à base de ciment Portland, de laitier de haut fourneau et de filler calcaire Study of the mechanical behavior of slag-limestone fillercement blended binders
Khalifa N.E.H.,Bouasker M.,Mounanga P.,Ben Kahla N.
MATEC Web of Conferences , 2012, DOI: 10.1051/matecconf/20120201009
Abstract: Le principal objectif de cette étude est de déceler l’influence de l’addition de fillers calcaires en pourcentages modérés (0%, 10% et 20%) sur les performances de formulations de liants contenant différents dosages en laitier de haut fourneau (variant de 20% à 80%), en considérant, comme paramètres d’analyse, la porosité accessible au mercure et les propriétés mécaniques. Les essais ont été réalisés sur 12 pates de liants composées avec un rapport Eau/Liant égal à 0,32. Les propriétés mécaniques des différentes pates ont été étudiées à plusieurs échéances (1 jour, 7 jours, 28 jours et 90 jours). Les résultats obtenus nous ont permis d’estimer la possibilité de bénéficier de la complémentarité et de la synergie des trois composants considérés sur les performances mécaniques (résistance à la compression et module d’Young dynamique) des liants ternaires étudiés au jeune age et à age mature. The main objective of this study is to detect the influence of the addition of limestone fillers in moderate percentages (0%, 10% and 20%) on the performance of binder formulations containing different dosages of blast furnace slag (ranging from 20% to 80%). The analysis parameters are mercury intrusion porosity and mechanical properties. The tests were performed on 12 blended pastes made with a water/cement ratio equal to 0.32. The mechanical properties of different pastes were investigated at several curing time (1 day, 7 days, 28 days and 90 days). The obtained results allowed estimating the possibility to benefit from the complementarity and synergy of the three components considered in the mechanical performance (compressive strength and dynamic Young’s modulus) of ternary binders studied at both early age and mature age.
Isolation and molecular characterisation of Mycobacterium bovis from raw milk in Tunisia
I Ben Kahla, ML Boschiroli, F Souissi, N Cherif, M Benzarti, J Boukadida, S Hammami
African Health Sciences , 2011,
Abstract: Background: Consumption of raw milk and unpasteurized dairy products is common in Tunisia where bovine tuberculosis remains enzootic. We herein investigated the frequency of M. bovis isolation from raw milk. Methods: Three hundred and six milk samples collected from 102 infected cows in different Tunisian regions were analysed. M. bovis isolates were further characterized by spoligotyping and variable number tandem repeat typing. Results: A total of five (4.9 %) M. bovis strains exhibiting three different genotypes were isolated. Conclusion: This study demonstrates that consumers of raw milk or derivatives in Tunisia are at high risk of zoonotic infection with M. bovis.
Mycobacterium abscessus multispacer sequence typing
Sassi Mohamed,Ben Kahla Imen,Drancourt Michel
BMC Microbiology , 2013, DOI: 10.1186/1471-2180-13-3
Abstract: Background Mycobacterium abscessus group includes antibiotic-resistant, opportunistic mycobacteria that are responsible for sporadic cases and outbreaks of cutaneous, pulmonary and disseminated infections. However, because of their close genetic relationships, accurate discrimination between the various strains of these mycobacteria remains difficult. In this report, we describe the development of a multispacer sequence typing (MST) analysis for the simultaneous identification and typing of M. abscessus mycobacteria. We also compared MST with the reference multilocus sequence analysis (MLSA) typing method. Results Based on the M. abscessus CIP104536T genome, eight intergenic spacers were selected, PCR amplified and sequenced in 21 M. abscessus isolates and analysed in 48 available M. abscessus genomes. MST and MLSA grouped 37 M. abscessus organisms into 12 and nine types, respectively; four formerly “M. bolletii” organisms and M. abscessus M139 into three and four types, respectively; and 27 formerly “M. massiliense” organisms grouped into nine and five types, respectively. The Hunter-Gaston index was off 0.912 for MST and of 0.903 for MLSA. The MST-derived tree was similar to that based on MLSA and rpoB gene sequencing and yielded three main clusters comprising each the type strain of the respective M. abscessus sub-species. Two isolates exhibited discordant MLSA- and rpoB gene sequence-derived position, one isolate exhibited discordant MST- and rpoB gene sequence-derived position and one isolate exhibited discordant MST- and MLSA-derived position. MST spacer n°2 sequencing alone allowed for the accurate identification of the different isolates at the sub-species level. Conclusions MST is a new sequencing-based approach for both identifying and genotyping M. abscessus mycobacteria that clearly differentiates formerly “M. massiliense” organisms from other M. abscessus subsp. bolletii organisms.
The Pancharatnam Phase of a Three-Level Atom Coupled to Two Systems of N-Two Level Atoms  [PDF]
D. A. M. Abo-Kahla
Journal of Quantum Information Science (JQIS) , 2016, DOI: 10.4236/jqis.2016.61006
Abstract: In this paper, we present the analytical solution for the model that describes the interaction between a three-level atom and two systems of N-two level atoms. The effects of the quantum numbers and the coupling parameters between spins on the Pancharatnam phase and the atomic inversion, for some special cases of the initial states, are investigated. The comparison between the two effects shows that the analytic results are well consistent.
Kohstall Florian et Vairel Frédéric (dir.), Fabrique des élections, égypte. Monde Arabe, n°7, 3e série, 2010-2011
Sarah Ben Néfissa
Revue des Mondes Musulmans et de la Méditerranée , 2012,
Abstract: Suite aux soulèvements et révolutions, un vaste chantier électoral attend les pays arabes. La légitimité des urnes va progressivement succéder à la légitimité de la rue , et la sociologie électorale est en bonne voie de réactualisation et de renouvellement de ses paradigmes avec les exemples des pays de la région. Cette étape historique particulière rehausse l’importance de la publication récente du numéro de la revue du CEDEJ, égypte-Monde arabe, intitulé Fabrique des élections, et di...
A new line element derived from the variable rest mass in gravitational field
N. Ben-Amots
Physics , 2008,
Abstract: This paper presents a new line element based on the assumption of the variable rest mass in gravitational field, and explores some its implications. This line element is not a vacuum solution of Einstein's equations, yet it is sufficiently close to Schwarzschild's line element to be compatible with all of the experimental and observational measurements made so far to confirm the three Einstein's predictions. The theory allows radiation and fast particles to escape from all massive bodies, even from those that in Einstein's general relativity framework will be black holes. The striking feature of this line element is the non-existence of black holes.
Electrochemical Investigation of P-Tert-Butylcalix[6]Arene Modified Gold Electrode for Ionic Detection  [PDF]
H. Sakly, H. Ben Ouada, N. Jaffrezic Renault
Materials Sciences and Applications (MSA) , 2014, DOI: 10.4236/msa.2014.58054
The aim of this work was to study the electrochemical behavior of gold electrode which was modified with p-tert-butylcalix[6]arene membrane and this in the presence of different nickel ions based concentrations in order to form a nickel electrochemical sensor. For that, impedance-spec- troscopy characteristics have been investigated. The obtained results were then modeled by appropriate equivalent circuit aiming at elucidating the electrical properties of the modified gold transducer. A correlation between the present impedimetric results and previous potentiometric ones was achieved traducing then a fast ionic transfer.
Pyrosequencing assay for rapid identification of Mycobacterium tuberculosis complex species
Imen Kahla, Mireille Henry, Jalel Boukadida, Michel Drancourt
BMC Research Notes , 2011, DOI: 10.1186/1756-0500-4-423
Abstract: We herein develop a pyrosequencing assay analyzing polymorphisms within glpK, pykA and gyrB genes to identify members of the M. tuberculosis complex at the species level. The assay was evaluated with 22 M. tuberculosis, 21 M. bovis, 3 M. caprae, 3 M. microti, 2 M. bovis BCG, 2 M. pinnipedii, 1 M. canettii and 1 M. africanum type I isolates. The resulted pyrograms were consistent with conventional DNA sequencing data and successfully identified all isolates. Additionally, 127 clinical M. tuberculosis complex isolates were analyzed and were unambiguously identified as M. tuberculosis.We proposed a pyrosequencing-based scheme for the rapid identification of M. tuberculosis complex isolates at the species level. The assay is robust, specific, rapid and can be easily introduced in the routine activity.The Mycobacterium tuberculosis complex (MTC) includes M. tuberculosis, M. bovis and BCG-derived clones, M. africanum, M. canettii, M. microti, M. caprae and M. pinnipedii [1]. Recently, an eight member named Mycobacterium mungi was identified in banded mongooses (Mungos mungo) in Botswana [2]. While there is variable host-specificity among the different MTC members, every species, but M. mungi, has been implicated in human tuberculosis with M. tuberculosis being the most common pathogen [3-6]. The exact contribution of each species in human disease may be underestimated due to the limited capacity of laboratories to identify MTC isolates at the species level in routine practice. Indeed, phenotypic methods are time-consuming and the results are difficult to interpret. Molecular assays are hampered by the high genetic similarity reflected by the complete conservation of the 16S rRNA and rpoB genes of the MTC members [7,8]. This situation indeed, led to propose that the various MTC species would be more accurately described as ecotypes [9]. Despite the high degree of nucleotide sequence homology, some genomic markers such as pncA, mpt40, hupB, gyrB and wbbl1genes in addition t
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