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Discussion on: "Analysis of control relevant coupled nonlinear oscillatory systems"
Rudi Pušenjak, Maks Oblak, 2008, izvirni znanstveni članek

Opis: The paper by I. D. Landau et al. presents an analysis of two structures of coupled van der Pol oscillators done by using the Krylov-Bogoliubov (K-B) averaging method. They devise the K-B method to effectively compute self-excited and externally driven oscillations, respectively on systems presumably subjected to control, where amplitudes and phases are slowly varying functions of time. After they present feedback structures of single and coupled generalized van der Pol equations, respectively, they perform the K-B analysis of these equations, which results in explanation of various regimes of self-excited and externally driven oscillations including the analysis of the combustion instability model. Although the proposed K-B methodmay be considered as a step forward in modeling self-oscillating systems, this discussion wants to show, that problems solved by the K-B method can be treated also in an alternative way. Based on the paper [1], it is obvious that coupled van der Pol oscillators, driven by an external excitation with slowly varying frequency or amplitude, can be analyzed by using Extended Lindstedt- Poincare (EL-P) method with multiple time scales.
Ključne besede: van der Pol oscillators, external excitation, multiple time scales
Objavljeno: 31.05.2012; Ogledov: 711; Prenosov: 26
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Extended Lindstedt-Poincare method for non-stationary resonances of dynamical systems with cubic nonlinearit
Rudi Pušenjak, 2008, izvirni znanstveni članek

Opis: This paper presents the extended Lindstedt-Poincare (EL-P) method, which applies multiple time variables to treat non-stationary oscillations arising in dynamical systems with cubic nonlinearities due to the slowly varied excitation parameters. The method is applied extensively in research of non-stationary vibrations of clamped-hinged beams. Recognizing the aperiodic nature of non-stationary oscillations, the new formulation is presented by adding an additional, slow time scale beside time scales of the nonlinear system, which generally correspond to the incommensurate nonlinear frequencies of the response. Using this concept, a generalized approach of the study to the passage through fundamental, superharmonic and subharmonic resonances is presented in the paper. Effects of slowly varying excitation frequency and slowly varying excitation amplitude on the non-stationary oscillations are studied with the computation of deviations from the stationary response. Although the method is formulated for N-dof dynamical systems having weak cubic nonlinearities, it is applied for non-stationary vibrations, where two-mode shape approximation of damped and undamped clamped-hinged beam, respectively, is used and the simultaneous appearance of internal resonance is taken into account. Stability analysis of stationary solutions is performed and comparisons of stationary resonance curves by results obtained with the incremental harmonic balance (IHB) method show good agreement. The passage through the fundamental resonance of damped and undamped clamped-hinged beam, respectively, is investigated in detail.
Ključne besede: dynamical systems with cubic nonlinearities, nonlinear oscillations, nonstationary nonlinear oscillations, time scales, excitation frequency, resonance, Lindstedt-Poincare method
Objavljeno: 01.06.2012; Ogledov: 1091; Prenosov: 16
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Construction of the Scale of child's attachment to his/her kindergarten teacher (CAKT)
Zlatka Cugmas, 2009, izvirni znanstveni članek

Opis: In the theoretical part of this paper, the author gives answers to the question of whether a real attachment relationship can exist between a child and a non-maternal caretaker. She mentions the established methods of measuring the child's attachment to the kindergarten teacher. She presents The scale of child's attachment to his/her kindergarten teacher (CAKT), which is based on authors previous findings and the experience of other authors in the forming of psychological instruments of this type. The scale was tested in a research which involved twenty-five kindergarten teachers who participated in the evaluation of 178 children (49.4% boys). Children ranged in age from 3 to 6 years. The purpose of the study was to investigate the dimensionality and internal consistency of the Scale. It was established that the psychometric characteristics of the Scale were adequate. This paper also presents the limitations of the research, which should be considered in the interpretation of the obtained results. Replication studies using clinical groups and samples from different cultures will be needed to assess a possible generalization of the presented results.
Ključne besede: navezanost, predšolski otroci, vzgojiteljice, socialno vedenje, ocenjevalne lestvice, merjenje, psihometrična analiza, attachment behaviour, preschool children, kindergarten teachers, preschool teachers, social behavior, measurment, scales
Objavljeno: 10.07.2015; Ogledov: 586; Prenosov: 23
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