Search results for "theory"
showing 10 items of 24627 documents
Investigation and reduction of losses on inverter-fed induction motors
2017
An electric motor is more effective and flexible when supplied by a frequency converter. The frequency converter not only produces the fundamental voltage but also a set of higher harmonics which cause additional losses in the motor. Losses in the frequency converter are normally neglected in the drive dimensioning due to insufficient data available from manufacturers. Motor's losses can be reduced by increasing the switching frequency of frequency converters. An increase of the switching frequency may result in higher losses in the frequency converter. This work investigates analytically and experimentally the dependence of the losses of modern motor and frequency converter on a switching …
Sensorless control of induction motors using an extended Kalman filter and linear quadratic tracking
2017
Induction motors are the most commonly used prime-movers in industrial applications. Many induction motors supplied by frequency converters are coupled with a physical angular rotor position/velocity sensor which makes the drive complex and require maintenance. This paper presents a sensorless control structure to avoid using a physical angular rotor position/velocity sensor. The proposed method estimates and control the angular rotor velocity using optimal control theory. The optimal controller used in this paper is based on linear quadratic tracking and the states of the machine are estimated using an extended Kalman filter. Both the controller and the estimator utilize the same internal …
Resistive communications based on neuristors
2017
Memristors are passive elements that allow us to store information using a single element per bit. However, this is not the only utility of the memristor. Considering the physical chemical structure of the element used, the memristor can function at the same time as memory and as a communication unit. This paper presents a new approach to the use of the memristor and develops the concept of resistive communication.
The helicoidal magnetic generator
2016
Recently helicoidal generator for the exploitation of sea wave energy has been proposed. This device can convert both the vertical and rotational movement of seawaves. The electrical energy generated by such a device must be converted and conditioned in order to match the instantaneous utility requirements and a power link from the sea to an interconnection is needed. In this paper, the authors propose a mathematical model of this device and preliminarily present a prototype of the machine.
New fine structures resolved at the ELNES Ti-L2,3 edge spectra of anatase and rutile: comparison between experiment and calculation.
2010
Abstract Anatase and rutile Ti- L 2,3 edge spectra were measured in electron energy loss spectroscopy (EELS) using a transmission electron microscope (TEM) coupled to a CEOS Cs-probe corrector, an omega-type monochromator and an in-column omega-type energy filter fully corrected for 2nd order aberrations. Thanks to the high energy resolution, high electron probe current and high stability achieved under this instrumental configuration, new fine structures, never reported before, were resolved at the L 3 band of both rutile and anatase. The data suggest that new peaks also exist in the L 2 e g band. The experimental spectra are compared with multichannel multiple scattering (MMS) calculation…
Exploring the transport properties of equatorially low coordinated erbium single ion magnets
2019
Single-molecule spin transport represents the lower limit of miniaturization of spintronic devices. These experiments, although extremely challenging, are key to understand the magneto-electronic properties of a molecule in a junction. In this context, theoretical screening of new magnetic molecules provides invaluable knowledge before carrying out sophisticated experiments. Herein, we investigate the transport properties of three equatorially low-coordinated erbium single ion magnets with C3v symmetry: Er[N(SiMe3)2]3 (1), Er(btmsm)3 (2) and Er(dbpc)3 (3), where btmsm=bis(trimethylsilyl)methyl and dbpc=2,6-di-tert-butyl-p-cresolate. Our ligand field analysis, based on previous spectros…
Electronic structure and magnetic order in Cu Zn(1−)O: A study GGA and GGA + U
2019
Abstract Based on density functional theory within GGA formalism, first-principles calculations were performed in order to study the structural, electronic, and magnetic properties of Cu-doped ZnO compound with dopant concentrations x = 0.028, 0.042, 0.056, and 0.125. It was found that CuxZn(1−x)O is ferromagnetic for both the closest and farthest impurity distances, but it is more stable energetically for the closest one. For all concentrations we obtained nearly half − metallic behavior. The calculations show that two substitutional Cu atoms introduce a magnetic moment of about 2.0 μB for all dopant concentrations. The results indicate that the magnetic ground state originates from the st…
Molecular dynamics simulations of nanometric metallic multilayers: Reactivity of the Ni-Al system
2011
The reactivity of a layered Ni-Al-Ni system is studied by means of molecular dynamics simulations, using an embedded-atom method type potential. The system, made of an fcc-Al layer embedded in fcc-Ni, is initially thermalized at the fixed temperature of 600 K. The early interdiffusion of Ni and Al at interfaces is followed by the massive diffusion of Ni in the Al layer and by the spontaneous phase formation of $B2$-NiAl. The solid-state reaction is associated with a rapid system heating, which further enhances the diffusion processes. For longer times, the system may partly lose some its $B2$-NiAl microstructure in favor of the formation of $L{1}_{2}$-${\mathrm{Ni}}_{3}\mathrm{Al}$. This st…
Ab initio calculations of the electronic structure for Mn2+-doped YAlO3 crystals
2020
The electronic structure of Mn2+ ion substituted for the host Y atom in orthorhombic bulk YAlO3 crystals has been calculated by means of hybrid exchange-correlation functional HSE within density functional theory. The supercell approach has been used to simulate in Pbnm YAlO3 crystal the point defects, Mn-dopant and compensated the F+ center (oxygen vacancy with one trapped electron), to make unit cell neutral. Large 2 × 2 × 2 supercells of 160 atoms allow us to simulate substitutional point defect with concentration of about 3%. Mn2+ ions substituting for host Y form covalent Mn–O bonds, in opposite to the mostly ionic Y–O bond. The F center inserted to compensate the Mn2+ dopant in YAlO3 …
Efficiency of H center stabilization in alkali halide crystals at low-temperature uniaxial deformation
2020
The efficiency of stabilization of H centers as well as its dependence on the degree of uniaxial deformation are considered within the framework of the modified geometric model of alkali halides. It is shown that stabilization of H centers is difficult in KI and RbI crystals, while in other NaCl-type crystals it becomes quite probable. Under uniaxial deformation, the interstitial space, in which the defect will be located, decreases, and the efficiency decrease. In the case of cesium halides, the orientation of the H centers takes place predominantly in the direction; therefore, the criteria for their stabilization differ from the NaCl-type alkali halide crystals. According to calculations,…