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Modeling cardiac pacemakers with relaxation oscillators
No full textabstractEN: A modified van der Pol oscillator model was designed in order to reproduce the time series of the action potential generated by a natural pacemaker of the heart (i.e., the SA or the AV node). The main motivation was that the models published up to now were not altogether adequate for research on the heart. Based on either the classical van der Pol oscillator or other nonlinear oscillators, these models were interesting rather because of the physical phenomena that could be obtained (chaos and synchronization). However, they were unable to simulate many important physiological features of true physiological action potentials. We based our research on the experience of other groups which modeled neuronal oscillators. There complex nonlinear oscillators were used whose most important feature was a certain topology of the phase space. In our case, we modified the phase space of the classical van der Pol oscillator by adding two fixed points: a saddle and a node. In addition, a damping term asymmetric with respect to the voltage was introduced. Introduction of these new features into the van der Pol oscillator allowed to change the firing frequency of the pacemaker node without changing the length of the refractory period – an important physiological detail. We also show different ways of changing the pacemaker rhythm. A comparison of the properties of the signal obtained from our model with the features of the action potentials measured by other groups is made.score: 30collation: 153-16
Phase-shifting method contrast calculations in time-averaged interferometry: error analysis
No full textabstractEN: Numerical simulations of the influence of the phase step miscalibration and average intensity changes between the registered frames on the time-averaged interferogram contrast calculated using the temporal phase-shifting (TPS) method are presented. The amplitude of sinusoidal vibration studied by the time-averaged method is encoded in the interferogram contrast or intensity modulation described by the zero-order Bessel function. The properties of the TPS method used for contrast determination are established. Experimental studies of vibration mode patterns of silicon microelements with specular reflection surfaces provide corroboration of theoretical and numerical findings. © 2005 Society of Photo-Optical Instrumentation Engineers.score: 20collation: 065601-06560
Optimization of Atrioventricular Delay of Pacemaker by Impedance Cardiography and Plethyzmography
No full textabstractEN: In the presented study SV values taken by plethyzmographic device were related to the results given by impedance cardiography device. The 20 patients; 4 females and 16 males (age 74 +/- 7 years) with a history of predominant pacemaker driven rhythm were included in the study group. The stroke volume was assessed for atrioventricular delay settings in a range from 100 to 250 msec. with a step of 10 msec. The basic rhythm for all evaluated patients was 70 bpm. The AV was assumed to be optimal at the maximum value of SV. The obtained results have shown that the plethyzmographic method can be applied for the AV delay optimization. The differences of SV between an optimized and the recommended by the companies settings showed a strong need of tailoring of AV for each patient separately especially in the group of the patients with a predominant pacemaker driven rhythm.score: 3collation: 321-32
On the interpretation of space charge profiles in CIGSe-based solar cells in presence of deep metastable defects
No full textabstractEN: Experimental evidence is provided for the presence of large density of metastable defects in the Cu(In, Ga)Se2 (CIGSe) absorber layer which within the range of milliseconds to seconds are able to adjust their charge state to the actual electron and hole concentrations. It is shown that the concentration of these defects may exceed the net shallow acceptor concentration even by orders of magnitude. The consequences of this fact for the interpretation of space charge profiles are discussed. It is shown that the difference between capacitance - voltage (CV) and drive level (DL) profiles as well as their U-shape can be explained by the bi-stable behavior of these defect states.score: 10collation: 002837-00284
Possibility of using diverse plant litter in soil restoration processes
No full textabstractEN: We evaluated the effect of mulching degraded soil with plant litter composed of single or mixed species on humus accumulation and algal biomass in experimental field study. Sandy loam (sand mixed with loam) mesocosms were examined over the course of 2.5 years. Five litters composed of meadow plants; both grasses and herbs were used: single species (I - Dactylis glomerata, II -c Festuca rubra and III - Trifolium pratense) and species mixtures IV (mixture of 3 species I, II and III); V (mixture of 12 species -IV and 9 other grasses and herbs). The highest humus acid (sum of fulvic and humic acids) content and algal biomass were found under the most diverse litter (V) when compared to other treatments. In general, the results suggest that mulching with diverse plant litter is the most effective.score: 0collation: 169-17
Selective hydrogenation of α,β-unsaturated aldehydes over Pt catalysts deposited on monolayer supports
No full textabstractEN: New Pt catalysts deposited on monolayer supports containing TiO2 have been tested in the hydrogenation of α,β-unsaturated aldehydes. Enhancement of selectivity towards unsaturated alcohols has been observed in comparison to the commonly used Pt/SiO2 or Pt/TiO2 catalysts.score: 35collation: L1-L
Relative Error Indices for Comparison of Neural Models of Different Robots
No full textabstractEN: In the article there are proposed relative error indices that can be used to evaluate neural models of different robots. The model of robot is identified using artificial neural networks with structure of the mathematical robot model in a form of the Lagrange-Euler equation. As an example the proposed indices are calculated for neural models of three different robots. Proposed indices significantly simplify an analysis and comparison of models of robots with different degree of freedom.score: 10collation: 233-23
Interferometric investigations of elliptical-core liquid crystal fibers
No full textabstractEN: The paper presents a new approach to structural investigations of elliptical-core liquid crystal fibers (ECLCFs) by using the interferometric method. The method enables to confirm envisaged molecular distribution within the elliptical core previously observed in polarimetric configuration.score: 0collation: 423-42
Investigation of refractive index distribution in different photonic crystal fiber elements
No full textscore: 1
Mesophase development in coal-tar pitch modified with various polymers
No full textabstractEN: The effect of 10\% addition of various polymers to coal-tar pitch on its conversion into mesophase during isothermal treatment at 450 °C has been studied using polarized light optical microscopy. The additives appear to modify to a different extent the kinetics of the conversion and morphology of the developed mesophase. A common effect is an acceleration of mesophase unit growth in the early stage of transformation, the influence decreasing from polystyrene to cumarone–indene resin, and, at the advanced stage, an increase of proportion of areas of isotropic appearance in the optical texture. The addition of poly(vinyl chloride) leads to non homogeneous texture of mesophase pitch due to early separation of particulate matter and growth of mesophase in a way typical of pitch matrix which is free from quinoline insolubles. Poly(ethylene glycol) and unsaturated polyester resin tend to hinder the ability of mesophase to coalescence giving products of enhanced proportion of spherical mesophase. The cumarone–indene resin is the only additive that distinctly increases residue yield but does not affect its optical texture. Based on the results the behaviour of polymers within pitch matrix under carbonization conditions and possible interactions of polymer degradation products with pitch constituents are discussed.score: 30collation: 147-16