Dnipropetrovsk, Ukraine
Dnipropetrovsk, Ukraine

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Brankack J.,University of Heidelberg | Kukushka V.I.,Dniepropetrovsk National University | Vyssotski A.L.,University of Zürich | Draguhn A.,University of Heidelberg
Brain Research | Year: 2010

There is growing interest in sleep research and increasing demand for screening of circadian rhythms in genetically modified animals. This requires reliable sleep stage scoring programs. Present solutions suffer, however, from the lack of flexible adaptation to experimental conditions and unreliable selection of stage-discriminating variables. EEG was recorded in freely moving C57BL/6 mice and different sets of frequency variables were used for analysis. Parameters included conventional power spectral density functions as well as period-amplitude analysis. Manual staging was compared with the performance of two different supervised classifiers, linear discriminant analysis (LDA) and Classification Tree. Gamma activity was particularly high during REM (rapid eye movements) sleep and waking. Four out of 73 variables were most effective for sleep-wake stage separation: amplitudes of upper gamma-, delta- and upper theta-frequency bands and neck muscle EMG. Using small sets of training data, LDA produced better results than Classification Tree or a conventional threshold formula. Changing epoch duration (4 to 10 s) had only minor effects on performance with 8 to 10 s yielding the best results. Gamma and upper theta activity during REM sleep is particularly useful for sleep-wake stage separation. Linear discriminant analysis performs best in supervised automatic staging procedures. Reliable semi-automatic sleep scoring with LDA substantially reduces analysis time. © 2010 Elsevier B.V. All rights reserved.


Gaponov A.V.,Dniepropetrovsk National University | Glot A.B.,Technological University of Mixteca
Journal of Materials Science: Materials in Electronics | Year: 2010

Current-voltage characteristics, temperature dependences of the low-field dc conductivity and the relative dielectric permittivity of tin dioxide based SnO 2-Co 3O 4-Nb 2O 5-Cr 2O 3 ceramics with CuO addition in the range 0-8 mol% are studied. These materials exhibit non-Ohmic conduction (the varistor effect). If 0.5 mol% CuO is added, the nonlinearity coefficient is increased from 54 to 75 and the electric field at fixed current density is decreased from 628 to 390 kV m -1. Higher amounts of CuO substantially diminish non-Ohmic behaviour. Thickness dependence of the nonlinearity coefficient and the electric field at fixed current density in SnO 2 varistor ceramics is observed. Electrical properties are discussed in the frames of grain-boundary controlled conduction mechanism. © 2009 Springer Science+Business Media, LLC.


Syetov Y.,Dniepropetrovsk National University | Vdovin A.,Polish Academy of Sciences
Vibrational Spectroscopy | Year: 2010

Infrared spectra of solid state 2-(2′-hydroxyphenyl)benzoxazole, 2,5-bis(2-benzoxazolyl)phenol and 2,5-bis(2-benzoxazolyl)hydroquinone were studied in the region 400-4000 cm-1. The measured spectra were compared with the results of density functional theory calculations of normal modes performed for different conformations of the isolated molecules. The calculated frequencies and intensities are in good agreement with the experimental values except the region 670-780 cm-1 which comprises OH torsion modes, CH out-of-plane bending vibrations and torsions of the aromatic and oxazole rings. The experimental infrared spectra can be well simulated by the spectral patterns of rotamers possessing OH⋯N intramolecular hydrogen bonds. In the case of 2,5-bis(2-benzoxazolyl)phenol a number of bands are assigned to the vibrations of the conformer formed by rotation of the non-hydrogen-bridged benzoxazole moiety. © 2010 Elsevier B.V. All rights reserved.


Loboda V.,Dniepropetrovsk National University | Lapusta Y.,French Institute for Advanced Mechanics | Sheveleva A.,Dniepropetrovsk National University
International Journal of Solids and Structures | Year: 2010

A plane problem for two identical piezoelectric semi-infinite spaces adhered by means of a thin isotropic interlayer is considered. It is assumed that a crack of a limited electric permeability occurs in the interlayer parallel to its faces. Combined electromechanical loading is prescribed at infinity. It is assumed that the interlayer is softer than the adherent materials. To avoid the singularities, which are typical for the Griffith crack model, two distinct zones - a zone of mechanical yielding and a zone of electrical saturation - of unknown lengths are introduced as crack continuations. These lengths can be essentially different, with the zone of mechanical yielding significantly longer or shorter than the zone of electrical saturation. Assuming that the interlayer thickness tends to zero, a constant normal stress is prescribed in the zone of mechanical yielding and a saturated electrical displacement is prescribed in the zone of electrical saturation. Outside of these zones, the semi-infinite spaces are assumed to be perfectly bonded. This formulation results in a linear fracture mechanics problem with unknown pre-fracture zone lengths. The problem, formulated mathematically by a system of two equations of linear relationship, is solved exactly. The unknown yield and saturated zones lengths are found from the conditions of finiteness of stress and electrical displacement at the ends of these zones for the both cases when the electrical saturated zone is longer and shorter than the zone of mechanical yielding. It is shown that the same equation as for the Griffith crack model can be used for the determination of the electrical displacement in the crack region. The main results of the paper are obtained in the form of simple analytical equations which are convenient for engineering applications. Some numerical illustrations in graphical and tabular form show dependencies of the pre-fracture zone lengths, the energy release rate, the mechanical displacement and electrical potential jumps on the electromechanical loading and the electrical permeability of the crack medium. © 2010 Elsevier Ltd. All rights reserved.


Loboda V.,Dniepropetrovsk National University | Sheveleva A.,Dniepropetrovsk National University | Lapusta Y.,French Institute for Advanced Mechanics
International Journal of Solids and Structures | Year: 2014

A plane problem for an electrically conducting interface crack in a piezoelectric bimaterial is studied. The bimaterial is polarized in the direction orthogonal to the crack faces and loaded by remote tension and shear forces and an electrical field parallel to the crack faces. All fields are assumed to be independent of the coordinate co-directed with the crack front. Using special presentations of electromechanical quantities via sectionally-analytic functions, a combined Dirichlet-Riemann and Hilbert boundary value problem is formulated and solved analytically. Explicit analytical expressions for the characteristic mechanical and electrical parameters are derived. Also, a contact zone solution is obtained as a particular case. For the determination of the contact zone length, a simple transcendental equation is derived. Stress and electric field intensity factors and, also, the contact zone length are found for various material combinations and different loadings. A significant influence of the electric field on the contact zone length, stress and electric field intensity factors is observed. Electrically permeable conditions in the crack region are considered as well and matching of different crack models has been performed. © 2013 Elsevier Ltd. All rights reserved.


Glot A.B.,University of León | Gaponov A.V.,Dniepropetrovsk National University | Sandoval-Garcia A.P.,University of León
Physica B: Condensed Matter | Year: 2010

This paper outlines some details of the conduction mechanism in SnO2-based ceramic varistors. It is shown that the activation energy of electrical conduction Eσ (the barrier height φ{symbol}) in SnO2 varistor is weakly decreased at low electric field E and strongly decreased at high fields. The strong decrease in Eσ (E) at high fields is conditioning factor of highly nonlinear current-voltage characteristic. The conduction process is thermally activated not only at low (Eσ ≅ 0.8 - 1 eV) but also at high electric fields (Eσ ≅ 0.3 - 0.5 eV). The "negative capacitance" phenomenon at high fields in highly nonlinear SnO2 varistor is observed. The relation between the high nonlinearity, the high slope of Eσ (E) dependence at high fields, the "negative capacitance" and possible generation of the minority carriers (holes) at high fields is discussed. © 2009 Elsevier B.V. All rights reserved.


Filins'kyy L.A.,Dniepropetrovsk National University
2012 6th International Conference on Ultrawideband and Ultrashort Impulse Signals, UWBUSIS 2012 - Conference Proceedings | Year: 2012

In the summary the results of experimental research of the dielectric properties ε and tgδ, in microwave band 4.4 - 5.8 GHz foam specimens, which are located in sections of rectangular waveguides 48 x 24 mm are presented. The characteristics of reflection and absorption of electromagnetic waves of specimens were investigated. © 2012 IEEE.


Filins'Kyy L.A.,Dniepropetrovsk National University
International Conference on Mathematical Methods in Electromagnetic Theory, MMET | Year: 2014

In the summary the results of experimental research of the dielectric properties ε and tgδ, in microwave band 5.2-8.6 GHz foam specimens, which are located in sections of rectangular waveguides 35 × 15 mm are presented. The characteristics of reflection and absorption of electromagnetic waves of specimens were investigated. © 2014 IEEE.


Pashchenko V.,Dniepropetrovsk National University
International Conference on Mathematical Methods in Electromagnetic Theory, MMET | Year: 2014

With the help of the indirect version of boundary elements (BE) method the modelling theory of Cartesian-projection (= x,y) of the eddy currents density has been found in the skin of orthotropic composites. Eddy currents have been created by the rectangular magnetic antenna that is parallel to both the plane composite surface and the reinforcement direction. Such antenna has been presented by the set of point sources those are placed in knots of the corresponding above-surface layer of the discretization net. The transition to dimensionless coordinates has been performed separately for Cartesian x- and y-projections of eddy currents density however adequately for space and time axises. Discretization steps are inversely proportional to the composite conductivity along and crosswise to the reinforcement direction. Therefore Nyquist criterion for Fourier spectral functions of passage and reflection characteristics has been satisfied. The peculiarity analysis of spherical waves superposition allows to find point sources influence zones, those have been covered by nonintersected BE. © 2014 IEEE.


Lyashkov A.Yu.,Dniepropetrovsk National University | Tonkoshkur A.S.,Dniepropetrovsk National University
Materials Chemistry and Physics | Year: 2013

The sensitivity of electrical conductivity of ZnO-based ceramics to vapors of saturated monohydric alcohols was investigated. Its interconnection with physicochemical parameters of alcohols: molecular mass, entropy, Gibbs energy, enthalpy, the bond breaking energy of C-O and O-H molecular bonds was analyzed. The selectivity of gas-sensitive properties toward vapors of saturated monohydric alcohols, seen in temperature, kinetic and concentration dependences of response was found. A model linking the sensor response, entropy and molecular mass was proposed. © 2013 Elsevier B.V. All rights reserved.

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