Search results for "linear"
showing 10 items of 7165 documents
Ab initio calculations of structural, electronic and vibrational properties of BaTiO3 and SrTiO3 perovskite crystals with oxygen vacancies
2020
The first-principles (ab initio) computations of the structural, electronic, and phonon properties have been performed for cubic and low-temperature tetragonal phases of BaTiO3 and SrTiO3 perovskite crystals, both stoichiometric and non-stoichiometric (with neutral oxygen vacancies). Calculations were performed with the CRYSTAL17 computer code within the linear combination of atomic orbitals approximation, using the B1WC advanced hybrid exchange-correlation functional of the density-functional-theory (DFT) and the periodic supercell approach. Various possible spin states of the defective systems were considered by means of unrestricted (open shell) DFT calculations. It was demonstrated that…
Mechanisms of Electron-Induced Single-Event Upsets in Medical and Experimental Linacs
2018
In this paper, we perform an in-depth analysis of the single-event effects observed during testing at medical electron linacs and an experimental high-energy electron linac. For electron irradiations, the medical linacs are most commonly used due to their availability and flexibility. Whereas previous efforts were made to characterize the cross sections at higher energies, where the nuclear interaction cross section is higher, the focus of this paper is on the complete overview of relevant electron energies. Irradiations at an electron linac were made with two different devices, with a large difference in feature size. The irradiations at an experimental linac were performed with varying en…
Non-Linearity Extremum in Niobium Doped Potassium Tantalate
1997
We report non-linear dielectric measurements in the KTaO 3 :Nb system (x Nb ≤ 0.05). The non-linear susceptibility diverges at low temperatures and reaches maximum values in the intermediate range (0.0075 ≤ x Nb ≤ 0.02). To account for this extremum non linearity, we propose a model of temperature dependent clusters which fits with a number of experimental reports. We also suggest that this model may be applied to the related compounds SrTiO 3 :Ca and KTaO 3 :Na.
A Simple Approach for Determination of Numerical Values of Ferrite Nonlinear Susceptibilities
2020
This article presents a straightforward approach for determination of numerical values of nonlinear susceptibilities of soft magnetic ferrites. It is shown that numerical values of susceptibilities can be calculated from the measured amplitudes of harmonics in the output voltage of ferrite core transformer. For this purpose, useful expressions for the susceptibilities are derived and as example, numerical values of the largest nonlinear susceptibilities those of the third and fifth orders are calculated. Additionally, errors of the measured susceptibilities also are determined. Based on the expressions obtained, the analysis of phase shifts between components of flux density on different fr…
Numerical values of MnZn ferrite nonlinear susceptibilities in a lossless approximation
2017
On the basis of expressions for nonlinear magnetic susceptibilities of soft ferrites obtained earlier the analysis of phase shifts between components of flux density on different frequencies and the magnetic field strength is carried out. Only the largest nonlinear susceptibilities those of third and fifth order are considered. It is shown that in the frequency range where losses are small and can be neglected the susceptibility of third order is negative but that of fifth order is positive. These statements allow explaining the shape of output voltage of toroidal transformer with soft ferrite core induced by strong harmonic field strength in the input. Numerical values of nonlinear suscept…
Double resonance response in nonlinear magnetic vortex dynamics
2013
We present experimental evidences for the dynamical bifurcation behavior of ac-driven magnetic vortex core gyration in a ferromagnetic disk. The dynamical bifurcation, i.e., appearance and disappearance of two stable dynamical states in the vortex gyration, occurring as the amplitude of the driving Oersted field increases to ${B}_{Oe}g{B}_{Oe}^{cr}$, manifests itself in a double resonance response in the dependence of homodyne the dc-voltage signal on the frequency $\ensuremath{\omega}$ of the applied microwave current. We find that the frequency range $\ensuremath{\delta}\ensuremath{\omega}$ between the two resonance features strongly increases with the excitation power. Our analysis based…
Electromagnetically induced switching of ferroelectric thin films
2007
We analyze the interaction of an electromagnetic spike (one cycle) with a thin layer of ferroelectric medium with two equilibrium states. The model is the set of Maxwell equations coupled to the undamped Landau-Khalatnikov equation, where we do not assume slowly varying envelopes. From linear-scattering theory, we show that low-amplitude pulses can be completely reflected by the medium. Large-amplitude pulses can switch the ferroelectric. Using numerical simulations and analysis, we study this switching for long and short pulses, estimate the switching times, and provide useful information for experiments.
A Planar Generator for a Wave Energy Converter
2019
This article presents a permanent magnet planar translational generator which is able to exploit multiple modes of sea wave energy extraction. Linear electrical generators have recently been studied for the exploitation of sea wave energy, but, to the best of our knowledge, no synchronous planar translational generator has been proposed. In this article, to maximize the energy extraction, we have considered all the potential modes of motion due to wave excitation and included them within the mathematical model of the proposed system. The principle of operation of the generator can be summarized as follows: the moving part (translator) of the generator is driven from the sea waves and induce…
Reversed polarized emission in highly strained a-plane GaN/AlN multiple quantum wells
2010
The polarization of the emission from a set of highly strained $a$-plane GaN/AlN multiple quantum wells of varying well widths has been studied. A single photoluminescence peak is observed that shifts to higher energies as the quantum well thickness decreases due to quantum confinement. The emitted light is linearly polarized. For the thinnest samples the preferential polarization direction is perpendicular to the wurtzite $c$ axis with a degree of polarization that decreases with increasing well width. However, for the thickest well the preferred polarization direction is parallel to the $c$ axis. Raman scattering, x-ray diffraction, and transmission electron microscopy studies have been p…
Identification of parameters and harmonic losses of a deep-bar induction motor
2017
High frequency harmonics from a frequency converter causes additional losses in a deep-bar induction motor. The harmonics have their own amplitude and phase with respect to the fundamental signal, but the harmonic loss is only dependent on the amplitude of harmonics. A deep-bar induction motor can be modelled by a triple-cage circuit to take skin effect into account. The triple cage circuit having many parameters could be estimated from a small-signal model of the machine by using Differential Evolution. The correctly estimated parameters make the triple-cage circuit valid in a wide range of frequencies. However, the triple-cage circuit is very complicated which makes it difficult to model …