RANDOM MAGNETIC FIELD EFFECTS ON ELECTRONIC PROPERTIES IN SUBSTITUTIONALLY AND TOPOLOGICALLY DISORDERED ALLOYS

We numerically investigate the effects of the random static magnetic field on a variety of electronic properties (localization of electron wavefunctions, spectral correlations and electrical conductance) in substitutionally and topologically disordered alloys. For this, we generate two-dimensional substitutionally disordered alloys and simulate three-dimensional amorphous structures by a molecular dynamics algorithm. As Hamiltonian models, we use the usual Anderson tight-binding model for the  substitutional  disorder and  a  tight-binding model with a set of explicit s-type orbitals for the topological disorder. We particularly focus on the effect of the random magnetic field on the localization of electron wavefunctions. In the presence of the substitutional disorder, we establish that the random magnetic field tends to delocalize the electron wavefunctions at the band center less than does the uniform magnetic field and it enhances the localization at the band edges. But, in the presence of the topological disorder, we observe the opposite effect. We show that the random magnetic field tends to delocalize the electron wavefunctions more than does the uniform magnetic field. In this respect, we demonstrate that the effect of the random magnetic field on the electron wavefunctions depends on the nature of the disorder.We numerically investigate the effects of the random static magnetic field on a variety of electronic properties (localization of electron wavefunctions, spectral correlations and electrical conductance) in substitutionally and topologically disordered alloys. For this, we generate two-dimensional substitutionally disordered alloys and simulate three-dimensional amorphous structures by a molecular dynamics algorithm. As Hamiltonian models, we use the usual Anderson tight-binding model for the  substitutional  disorder and  a  tight-binding model with a set of explicit s-type orbitals for the topological disorder. We particularly focus on the effect of the random magnetic field on the localization of electron wavefunctions. In the presence of the substitutional disorder, we establish that the random magnetic field tends to delocalize the electron wavefunctions at the band center less than does the uniform magnetic field and it enhances the localization at the band edges. But, in the presence of the topological disorder, we observe the opposite effect. We show that the random magnetic field tends to delocalize the electron wavefunctions more than does the uniform magnetic field. In this respect, we demonstrate that the effect of the random magnetic field on the electron wavefunctions depends on the nature of the disorder

Robust Flux and Speed State Observer Design for Sensorless Control of a Double Star Induction Motor

In this paper, a robust flux and speed observer for sensorless control of a double star induction motor is presented. Proper operation of vector control of the double star induction motor requires reliable information from the process to be controlled. This information can come from mechanical sensors (rotational speed, angular position). Furthermore, mechanical flux and speed sensors are generally expensive and fragile and affect the reliability of the system. However, the control without sensors must-have performance that does not deviate too much from that which we would have had with a mechanical sensor. In this framework, this work mainly deals with the estimation of the flux and speed using a robust state observer in view of sensorless vector control of the double star induction motor. The evaluation criteria are the static and dynamic performances of the system as well as the errors between the reference values and those estimated. Extensive simulation results and robustness tests are presented to evaluate the performance of the proposed sensorless control scheme. Furthermore, under the same test conditions, a detailed comparison between the proposed state observer and the sliding mode-MRAS technique is carried out where the results of its evaluation are investigated in terms of their speed and flux tracking capability during load and speed transients and also with parameter variation. It is worth mentioning that the proposed state observer can obtain both high current quality and low torque ripples, which show better performance than that in the MRAS system

Numerical analysis of the elastic-plastic behavior of a tubular structure in FGM under pressure and defect presence

Given the field of application and the many advantages, the use of FGM (Functionally Graded Materials) materials has recently been extended in several components and more particularly in cylindrical structures, which have been the subject of several recent studies. Our work aims to use the finite element method to analyze a cylindrical structure in FGM with properties gradated in the direction of the radius (Thickness) solicited purely in internal pressure by the implementation of a UMAT subroutine in the calculation code ABAQUS. The elasto-plastic behavior of the FGM is described by the flow theory represented by the equivalent stress of Von Mises and an incremental hardening variable. The TTO model (Tamura-Tomota-Ozawa) was used only to determine the elastic-plastic properties of the FGM material. The radial, tangential and axial stresses according to the thickness were evaluated in the first part of our work. In the second part, these stresses are evaluated under the same conditions but with the presence of a micro-cavity. The results obtained show clearly that these stresses are in direct relation not only with the thickness and properties of the FGM tube but also with the presence of the cavity

Numerical Simulation of the Mechanical Response of the Tunnels in the Saturated Soils by Plaxis

The forecast of settlement and movements caused by tunneling represents a significant challenge of technology. The evaluation of these movements is indeed of primary importance in order to prevent them. The methods of calculation making it possible to evaluate displacements and deformations in the ground due to tunneling give only one approximation of the true amplitudes of the movements in the ground. It is one of the assets of the Finite Element Method (FEM) which makes it possible a priori to treat configurations more complex and closer to reality. Our objective in this study is to calculate numerically the various movements caused by the construction of a shallow tunnel using a shield using PLAXIS 2D, the behavior of the ground is described by a perfectly plastic elastic model based on the criterion of Mohr-Coulomb. A comparison between the various methods: empirical, analytical and numerical in terms of settlement on the surface was carried out. The validation of these results was made by using results drawn from literature. We have also carried out a parametric study in order to analyze the influence of various geometrical and geotechnical parameters on the behavior of grounds due to tunneling. Lastly, we have treated the same example by supposing the existence of structures near the tunnel in order to see the influence of the presence of other structures on the profile of the settlements caused by tunneling. Results of our work agreed with those in literature

PID vs LQR controller for tilt rotor airplane

The main thematic of this paper is controlling the main manoeuvers of a tilt rotor UAV airplane in several modes such as vertical takeoff and landing, longitudinal translation and the most important phase which deal with the transition from the helicopter mode to the airplane mode and visversa based on a new actuators combination technique for specially the yaw motion with not referring to rotor speed control strategy which is used in controlling the attitude of a huge number of vehicles nowadays. This new actuator combination is inspired from that the transient response of a trirotor using tilting motion dynamics provides a faster response than using rotor speed dynamics. In the literature, a lot of control technics are used for stabilizing and guarantee the necessary manoeuvers for executing such task, a multiple Attitude and Altitude PID controllers were chosen for a simple linear model of our tilt rotor airplane in order to fulfill the desired trajectory, for reasons of complexity of our model the multiple PID controller doesnt take into consideration all the coupling that exists between the degrees of freedom in our model, so an LQR controller is adopted for more feasible solution of complex manoeuvering, the both controllers need linearization of the model for an easy implementation

Spondylodiscite tuberculeuse compliquée d’une ischémie aigue des membres inférieurs - à propos d’un cas

Les complications thromboemboliques associées à l´infection par Mycobacterium tuberculosis ont été rapportées dans la littérature et ont eu lieu dans 1,5 à 3,4% de l´infection tuberculeuse. Nous rapportons le cas d’une fillette âgée de 4ans suivie pour spondylodiscite tuberculeuse, admise dans notre formation pour prise en charge d’une ischémie aigue des deux membres inférieurs consommée, ayant nécessité une amputation transtibiale d’un côté et trans-fémorale du coté contro-latéral. Nous discutons les aspects cliniques, physiopathologiques et le lien de causalité.Key words: Thrombose, artère, tuberculose, ischémi