Search results for "Control and Systems Engineering"
showing 10 items of 994 documents
Dielectric nonlinearity of the PBB′B″O3 ferroelectric solid solutions
2001
Abstract Obtaining of novel thin film materials for electrically tuneable capacities is one of the current problems of ferroelectric material application. Suitable ferroelectric compounds exhibiting broad phase transitions and small dielectric loss in the paraelectric phase have been searched for the purpose. Lead-containing niobates PbMg1/3Nb2/3O3 (PMN), PbNi1/3Nb2/3O3 (PNN) and PbZn1/3Nb2/3O3 (PZN) and their solid solutions have been found as most appropriate. Materials have been synthesized by solid phase reactions from the relevant oxides; ceramic samples were obtained by conventional ceramic technology. Results of the studies of thermal dependence of dielectric permeability and loss fa…
LEAD-FREE (Na0.5Bi0.5)1-xBaxTiO3 SINGLE CRYSTALS (0 ≤ x ≤ 0.05) AND THEIR DIELECTRIC AND PYROELECTRIC PROPERTIES
2009
ABSTRACT Lead-free single crystals of Na0.5Bi0.5TiO3-BaTiO3 (NBT-BT) system were prepared by Czochralski method and their dielectric and pyroelectric properties have been studied. The results were compared with these for pure NBT. The obtained samples show pure perovskite structure with rhombohedral symmetry at room temperature. Low frequency (100 Hz–100 kHz) investigations reveal the diffuse phase transitions. The obtained results are discussed in terms of local electric and strain fields caused by different ionic radius of (Na, Bi) and Ba ions. The NBT-BT system is expected to be a new promising candidate for lead-free electronic crystals.
Synthesis and Characterization of Lead-Free (1-x)(K0.5Na0.5)Nb1-ySbyO3-xBaTiO3
2011
In this study lead-free ceramics with a formula (1-x)(K0.5Na0.5)Nb1-ySbyO3-xBaTiO3 have been synthesized and studied. XRD studies showed that all compositions have perovskite structure with monoclinic or tetragonal cell depending on substitution level. KNN ceramics with BaTiO3 have more homogeneous structure and increased density in comparison with pure KNN or antimony substituted KNN. Dielectric measurements revealed diffuse phase transition.
Dielectric Response in (K0.5Na0.5) (Nb1-xSbx)O3+0.5 mol%MnO2Ceramics to Weak Sinusoidal Fields of Low and Infra-low Frequencies
2011
The thermal anomalies exhibited as “shoulders” at infra-low frequencies and maximums at low frequencies related to structural transitions in the polar phase of (K0.5Na0.5)(Nb1-xSbx)O3+0.5 mol%MnO2 are found to shift from T ∼ 185°C to T ∼ 140°C at changing concentration x from 0 to 0.05. The range of temperature ΔТ(х) corresponding to the difference between positions of the anomalies on the ϵ′(T) curve at frequencies 1000 Hz and 1 Hz changes from 0.5 degrees at x = 0 to 2.5 degrees at x = 0.05, which may point to relaxor properties of the given phase transition being present only at rather high concentrations of Sb.
A framework for sign language sentence recognition by common sense context
2007
This correspondence proposes a complete framework for sign language recognition that integrates a commonsense engine in order to deal with sentence recognition. The proposed system is based on a multilevel architecture that allows modeling and managing of the knowledge of the recognition process in a simple and robust way. The final abstraction level of this architecture introduces the semantic context and the analysis of the correctness of a sentence given in a sequence of recognized signs. Experimentations are presented using a set of signs from the Italian sign language (LIS) for domotic applications. The implemented system maintains a high recognition rate when the set of signs grows, c…
Design of Zero-Ripple-Current Coupled Inductors With PWM Signals in Continuous Conduction Mode
2021
Coupled inductors are widely used in multiple outputs and interleaved dc–dc converters. Also filters often use coupled inductors as their inductive part. A generalized design procedure is proposed in this article focused on current ripple minimization and applicable to coupled inductors exposed to pulsewidth modulation signals and in continuous conduction mode. The design provides a very large inductance for all windings but one. Compared to other designs, it adapts to the existing magnetic properties of the magnetic device changing only the inductance ratio, simplifying the design and manufacturing process. It is based on the equivalent inductance value and its divergences. The only assump…
STRUCTURAL INSTABILITY IN FERROELECTRICS: SUPERIMPOSING HAMILTONIAN AND STOCHASTIC DYNAMICS
2008
ABSTRACT Structural instability of ferroelectrics distinguished by appearance of coexisting phases and spatial inhomogeneity is at variance with the predictions of statistics in the canonical ensemble. A more refined description includes ergodicity breaking which become apparent at critical temperature when the system resides in metastable state and its development lead to one of possible minimum energy states. In this study the domain growth and switching is reproduced within the framework of Fokker-Planck approach. The mathematical technique is developed for empiric Landau Hamiltonians and improved for application to first principles effective Hamiltonians with supercells and elementary l…
Rich dynamics and anticontrol of extinction in a prey-predator system
2019
This paper reveals some new and rich dynamics of a two-dimensional prey-predator system and to anticontrol the extinction of one of the species. For a particular value of the bifurcation parameter, one of the system variable dynamics is going to extinct, while another remains chaotic. To prevent the extinction, a simple anticontrol algorithm is applied so that the system orbits can escape from the vanishing trap. As the bifurcation parameter increases, the system presents quasiperiodic, stable, chaotic and also hyperchaotic orbits. Some of the chaotic attractors are Kaplan-Yorke type, in the sense that the sum of its Lyapunov exponents is positive. Also, atypically for undriven discrete sys…
Dissipative soliton interactions inside a fiber laser cavity
2005
We report our recent numerical and experimental observations of dissipative soliton interactions inside a fiber laser cavity. A bound state, formed from two pulses, may have a group velocity which differs from that of a single soliton. As a result, they can collide inside the cavity. This results in a variety of outcomes. Numerical simulations are based either on a continuous model or on a parameter-managed model of the cubic-quintic Ginzburg-Landau equation. Each of the models provides explanations for our experimental observations. © 2005 Elsevier Inc. All rights reserved.
Modulational Instability and Stimulated Raman Scattering in Normally Dispersive Highly Birefringent Fibers
2001
Abstract The nonlinear interaction of two laser beams in normally dispersive highly birefringent optical fibers leads to a large set of fascinating physical effects such as modulational instability (MI) and stimulated Raman scattering (SRS). These two nonlinear phenomena have a positive role as a mechanism for the generation of short optical pulses and represent a drawback in fiber-optics transmissions. Indeed, we will show that an induced process of modulational instability may be exploited for the generation of THz train of vector dark solitons. The technique of frequency-resolved optical gating is used to completely characterize the intensity and phase of the dark soliton trains. On the …