Fakulta elektrotechniky a informatiky / Faculty of Electrical Engineering and Informatics
Stálý URI pro tuto komunituhttps://hdl.handle.net/10195/3847
Práce obhájené před rokem 2008 jsou uloženy pouze v kolekci Vysokoškolské kvalifikační práce
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Článekpeer-reviewedpostprint Omezený přístup Verification and estimation of uncertainties of Tobias Mayer's 18th century astronomical observations(Elsevier Science BV, 2023) Marek, Jaroslav; Tuček, JiříPerceiving the uncertainty of the measurement has been changing over the past centuries, reflecting the advancement in the experimental techniques, the urge for reliable and reproducible measurement methodology, and development of mathematical data processing and evaluating algorithms. From the historical perspective, the concepts of considering the measurement uncertainty were firstly introduced with geographic and cartographic measurements. In this context, the works of Tobias Mayer on lunar landscape measurements are widely highlighted which, at that time, presented innovative approaches in data processing with the method of averages and pioneeringly addressed the issue of measurement error. In this study, we analyze in details the Mayer's set of 27 non-linear equations with 3 unknown parameters and discuss the effect of Mayer's linearization and subsequent mathematical procedures on the accuracy of the parameter values in contrast with the results from rigorous treatment of non-linear regression model involving the least-square method. In particular, we compare the values of the unknown parameters and their uncertainties in several variants in the linearized and nonlinearized model, providing monitoring of a small deviation of the Mayer's linearization. The results, presented here, show that despite the conceptual and computational simplification of the Mayer's method, such an approach to data processing can be exploited, with an acceptable level of accuracy, in several practical situations even today.Článekpeer-reviewedpostprint Omezený přístup Analysis and modelling of single domain core-shell (?FeNi/chromite) nanoparticles emitted during selective laser melting, and their magnetic remanence(Elsevier Science, 2023) Dvorsky, Richard; Kukutschova, Jana; Pagac, Marek; Svoboda, Ladislav; Simonova, Zuzana; Dedlkova, Katerina Peterek; Bednar, Jiri; Mendes, Rafael Gregorio; Matysek, Dalibor; Malina, Ondrej; Tuček, Jiří; Vilamova, Zuzana; Kiselev, Sergei; Gemming, Thomas; Filip, PeterDespite recent intense implementation of increasingly eco-friendly additive manufacturing, the properties of nanoparticulate pollutants emitted during Laser Powder Bed Fusion are still not fully understood, and have generally been overlooked. This study aims to fill this gap in current research by providing new insights into distinct metal/oxide core-shell nanoparticles (3-36 nm) that are produced during 3D printing using stainless steel. It also suggests possible ways for the removal of these potentially harmful by-products. Further, this research also provides a newly developed kinetic model that predicts a metal core growth time of below 200 mu s and confirms the predicted theory for the formation of these by-products. In the current study it was found that the cores produced during this process are purely metallic and consist of meteoroid phase kamacite (alpha FeNi). Within this study there was found to be a complete dominance of single-domain cores of kamacite with pre-vailing particles below the superparamagnetic threshold showing strong magnetic response and remanence. This new knowledge can be used to minimize potential health risks and reduce contamination of raw materials by this nanoparticulate pollutant, which can adversely affect the quality of printed metal parts, the environment, and the health of the operator. These findings also provide a new possibility of targeted efficient production of super-paramagnetic core-shell nanoparticles with a metallic kamacite core during laser powder bed fusion of austenitic steel 316L powder, which can be used in the production of sensors.Článekpeer-reviewedpostprint Omezený přístup Generalized first-principle model of magnetic levitation(2023) Dušek, František; Tuček, Jiří; Novotný, Aleš; Honc, DanielSince its first demonstration more than a half century ago, magnetic levitation (MagLev) has gained eminent scientific attention from both the fundamental and applied points of view. In essence, MagLev shows highly nonlinear dynamics, described with nonlinear differential equations. Thus, in order to exploit the MagLev phenomenon, both mathematical models and control algorithms must be constructed. Frequently authors use simplifications of the model, and in doing so, limit the application of the MagLev model around a nominal operating point. In these simplified cases, the MagLev models may contain parameters that are not represented by proper physical quantities. Thus, in this work, we revised the issue of MagLev modelling from the first-principle approach. More specifically, we theoretically derived expressions for the interaction between the magnetic fields of the solenoid and a small magnetic object. The behaviour of the inductance on a distance from the solenoid was then described. The suggested MagLev modelling concept was verified experimentally, confirming the validity and correctness of the proposed MagLev mathematical model. The results presented here could thus be regarded as highly beneficial for formulating more complex MagLev designs exploitable in the field of model predictive control of the position of a levitating object.Článekpeer-reviewedpublished Otevřený přístup Solving magnetic induction heating problem with multidimensional Fredholm integral equation methods: Alternative approach for optimization and evaluation of the process performance(AIP Publishing, 2022) Rak, Josef; Tuček, JiříInduction heating is a frequently used technology in both fundamental and applied research. It is heavily exploited in the industry for processing materials by heat treatments. In addition, it is viewed as a promising tool in medicine, particularly as a part of therapeutic strategies for treating cancer diseases. Thus, in order to optimize (i.e., enhance and tune) the performance of the induction heating process, several aspects must be considered, including the design of the magnetic coils, features of the magnetic fields applied, coupling of magnetic and thermal fields, and the material's characteristics. To tackle this complex problem, numerical mathematical models are often used. The results of which can help in understanding the role of the various parameters on the performance of the induction heating. Here, we present an alternative mathematical approach to solve the induction heating problem using Fredholm integral equations of the second kind with a singular kernel. To reduce the computation time, the Nystrom method has been adopted. As the kernel function shows a singularity, a singularity subtraction has been involved in the developed mathematical procedure. Furthermore, the error features of the Nystrom method with the singularity subtraction have been described, and convergence conditions of the proposed computational algorithm have been thoroughly identified. Although special conditions for the kernel function and the integration rule are needed, the method shows lower computing times, competing well with those of traditional finite-element based routines. The applicability of the developed methodology is demonstrated for the simulation of induction heating the body of a metal object.Článekpeer-reviewedpublished Omezený přístup An effect of scandium substitution on the phase purity and structural, magnetic, and electrochemical features of epsilon-Fe2O3 nanoparticle systems(Royal Society of Chemistry, 2022) Polaskova, Michaela; Malina, Ondrej; Tuček, Jiří; Jakubec, PetrA series of Sc-substituted epsilon-Fe2O3 nanoparticles embedded in a silica matrix were synthesized by a sol-gel process. It was found that the preparation of a pure epsilon-Fe2O3 phase without any other iron(iii) oxide phases as admixtures was achieved for epsilon-Sc0.1Fe1.9O3 (5 at% of Sc) as documented by analyses of X-ray powder diffraction (XRD) results. Extensive physicochemical characterization of the epsilon-Sc0.1Fe1.9O3 sample was performed employing transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), magnetization measurements, Fe-57 Mossbauer spectroscopy, and electrochemical impedance spectroscopy (EIS). Magnetization vs. temperature plots showed vanishing of the two-step magnetic transition for the Sc-doped epsilon-Fe2O3 sample; a decrease in the magnetization profile was observed only once upon the change in the temperature. The Sc3+ substitution was found to cause a constriction of the magnetic transition region and a shift of the onset of the magnetic transition to a higher temperature in comparison with the undoped epsilon-Fe2O3 system. Moreover, upon the introduction of Sc3+ ions in the epsilon-Fe2O3 crystal lattice, a magnetic hardness was altered accompanied by a decrease in the coercivity. With Fe-57 Mossbauer spectroscopy, it was identified that Sc3+ predominantly substitutes Fe3+ in the distorted octahedral A- and B-sites and with almost equivalent occupation probability at both positions. Moreover, the electrochemical measurements confirmed the increase in the resistivity in the Sc-doped epsilon-Fe2O3 systems. Thus, the results, achieved within the present study, demonstrated an effect of Sc3+ substitution on the preparation purity of epsilon-Fe2O3 systems without the presence of any other iron(iii) oxide admixtures and on the change in its magnetic and electrochemical features, proving their feasible tuning with respect to the requirements of potential future applications.Článekpeer-reviewedpublished version Otevřený přístup Novel Magnetic Nanohybrids: From Iron Oxide to Iron Carbide Nanoparticles Grown on Nanodiamonds(2020) Ziogas, Panagiotis; Bourlinos, Athanasios B.; Tuček, Jiří; Malina, Ondřej; Douvalis, Alexios P.The synthesis and characterization of a new line of magnetic hybrid nanostructured materials composed of spinel-type iron oxide to iron carbide nanoparticles grown on nanodiamond nanotemplates is reported in this study. The realization of these nanohybrid structures is achieved through thermal processing under vacuum at different annealing temperatures of a chemical precursor, in which very fine maghemite (γ-Fe2O3) nanoparticles seeds were developed on the surface of the nanodiamond nanotemplates. It is seen that low annealing temperatures induce the growth of the maghemite nanoparticle seeds to fine dispersed spinel-type non-stoichiometric ~5 nm magnetite (Fe3−xO4) nanoparticles, while intermediate annealing temperatures lead to the formation of single phase ~10 nm cementite (Fe3C) iron carbide nanoparticles. Higher annealing temperatures produce a mixture of larger Fe3C and Fe5C2 iron carbides, triggering simultaneously the growth of large-sized carbon nanotubes partially filled with these carbides. The magnetic features of the synthesized hybrid nanomaterials reveal the properties of their bearing magnetic phases, which span from superparamagnetic to soft and hard ferromagnetic and reflect the intrinsic magnetic properties of the containing phases, as well as their size and interconnection, dictated by the morphology and nature of the nanodiamond nanotemplates. These nanohybrids are proposed as potential candidates for important technological applications in nano-biomedicine and catalysis, while their synthetic route could be further tuned for development of new magnetic nanohybrid materials.