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Stabilization for optical receiver
Kolka, Z. ; Barcík, P. ; Novotný, Jan ; Biolková, V.
Free-Space Optics (FSO) is a wireless optical technology for line-of-sight communications. The front of the receiving optical fiber is located at the focus of the telescope. The relatively small diameter of the core puts extreme demands on receiver pointing under atmospheric turbulences and mounting bracket vibrations. To ensure stability, the beam is stabilized by a fine positioning system. A detection unit evaluates the position of the centre of the laser spot using photodiodes and compensates for deviations by changing the mirror angle.
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Analysis of vibration of rotors with a thick rigid disc on the overhanging end supported by hydrodynamic bearings and loaded by uncertain unbalance effects
Zapoměl, Jaroslav ; Ferfecki, P. ; Molčan, M. ; Kozánek, Jan
Rotors of some rotating machines consist of a shaft and a rigid disc attached to its overhanging end. Because of manufacturing and assembling inaccuracies, the disc is unbalanced. In general case, the disc principal axis of inertia deviates from the shaft axis (both axes are skew lines) and the disc center of gravity is not situated on the shaft center line. Then the disc inertia effects are the source inducing the rotor lateral vibration. As magnitude of parameters specifying the disc unbalance is uncertain, application of an adequate method is required to perform the analysis. In addition, if the rotor is supported by hydrodynamic bearings, their nonlinear properties lead to rising complexity of the system vibration and to reducing its predictability. In the presented paper, the motion equation of a rigid disc has been derived. The shaft was represented by a beam body that was discretized into finite elements. The stiffness and damping parameters of the hydrodynamic bearings were linearized in vicinity of the rotor equilibrium position. Then vibration of the rotor is governed by a set of linearized motion equations. The fuzzy numbers were applied to consider uncertainty of the disc unbalance parameters. The presented procedure provides the approach to computational analysis of rotating machines with the rotor having a disc attached to its overhanging end and the geometrical, mechanical, or technological parameters of which have uncertain values.
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Electron beam welding of AlCoCrFeNi2.1 eutectic high-entropy alloy
Rončák, Ján ; Adam, O. ; Müller, P. ; Zobač, Martin
Eutectic high-entropy alloys have become a significantly studied type of material due to their combination of strength and ductility. However, previous research has focused primarily on manufacture, solidification behaviour and mechanical properties. Only a small part of the research has been devoted to welding. This paper is focused on evaluating the weldability of eutectic high-entropy alloy AlCoCrFeNi2.1 in the as-cast state without further heat treatment. The electron beam welding process was performed twice at the same parameters, except for the beam current. Properties such as the depth of the remelted layer, the formation of the heat-affected zone, and the presence of undesirable defects in the welded joints were observed using light and electron microscopy. At the same time, material properties in the form of microstructural stability, chemical composition, and hardness of the welded joints were evaluated.
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On kernel-based nonlinear regression estimation
Kalina, Jan ; Vidnerová, P.
This paper is devoted to two important kernel-based tools of nonlinear regression: the Nadaraya-Watson estimator, which can be characterized as a successful statistical method in various econometric applications, and regularization networks, which represent machine learning tools very rarely used in econometric modeling. This paper recalls both approaches and describes their common features as well as differences. For the Nadaraya-Watsonestimator, we explain its connection to the conditional expectation of the response variable. Our main contribution is numerical analysis of suitable data with an economic motivation and a comparison of the two nonlinear regression tools. Our computations reveal some tools for the Nadaraya-Watson in R software to be unreliable, others not prepared for a routine usage. On the other hand, the regression modeling by means of regularization networks is much simpler and also turns out to be more reliable in our examples. These also bring unique evidence revealing the need for a careful choice of the parameters of regularization networks
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Application Of Implicitly Weighted Regression Quantiles: Analysis Of The 2018 Czech Presidential Election
Kalina, Jan ; Vidnerová, P.
Regression quantiles can be characterized as popular tools for a complex modeling of a continuous response variable conditioning on one or more given independent variables. Because they are however vulnerable to leverage points in the regression model, an alternative approach denoted as implicitly weighted regression quantiles have been proposed. The aim of current work is to apply them to the results of the second round of the 2018 presidential election in the Czech Republic. The election results are modeled as a response of 4 demographic or economic predictors over the 77 Czech counties. The analysis represents the first application of the implicitly weighted regression quantiles to data with more than one regressor. The results reveal the implicitly weighted regression quantiles to be indeed more robust with respect to leverage points compared to standard regression quantiles. If however the model does not contain leverage points, both versions of the regression quantiles yield very similar results. Thus, the election dataset serves here as an illustration of the usefulness of the implicitly weighted regression quantiles.
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Final report about research in Sokolov post mining sites in 2021 based on agreement between ENKI ops and Institute of Soil Biology BC CAS
Frouz, Jan ; Bartuška, Martin ; Oppong, J.C. ; Lišková, K. ; Houška, J. ; Červenka, J. ; Kučera, J. ; Bednářová, E. ; Reitschmiedová, E. ; Dvorščík, P. ; Mudrák, O. ; Šimáňová, D. ; Woś, B. ; Karimi Nezhad, Mohammad Tashin ; Mustafa, Adnan ; Pietrzykowski, M. ; Kopecký, T. ; Hovorková, M. ; Čápová, K.
The report brings main results of the research about soil and ecosystem recovery in post mining landscape near Sokolov based on agreement between ENKI ops and Institute of soil biology, BC CAS.
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Risk assessment and prediction of natural fires in the immediate vicinity\nsurface sources of drinking water.
Trnka, Miroslav ; Kudláčková, Lucie ; Čermák, P. ; Balek, Jan ; Novotný, Jan ; Homolová, Lucie ; Semerádová, Daniela ; Brovkina, Olga ; Štěpánek, Petr ; Zahradníček, Pavel ; Skalák, Petr ; Bláhová, Monika ; Benáček, Patrik ; Fischer, Milan ; Sedlák, Pavel ; Janouš, Dalibor ; Žalud, Zdeněk ; Marek, Michal V. ; Možný, M. ; Hájková, L. ; Chuchma, F. ; Knozová, G. ; Beranová, J. ; Zatloukal, V. ; Albert, J. ; Mašková, R. ; Cienciala, E. ; Vizina, A. ; Nesládková, M. ; Melišová, E. ; Hanel, M.
The methodology formulates a procedure for assessing the risks of the occurrence and spread of natural fires in the immediate vicinity of surface sources of drinking water. The methodology\nproposes methods for estimating the consequences of natural fires on surface water quality, forecasting the change in the risk of fires due to climate change and the procedure for determining the risk of secondary pollution of reservoirs due to changes in run off after a natural fire. On this basis, the methodology proposes and diversifies preventíve and operational measures.The measures were designed in connection to modeling results for the Hadce pilot síte near the Švihov reservoir and the experience with the adverse effects of extensive deforestation on the water quality in the Vranov and Vír reservoirs.
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Free-space optical link fro coherent transfer
Hrabina, Jan ; Čížek, Martin ; Barcík, P. ; Kolka, Z. ; Skryja, P. ; Wilfert, O.
The dissemination of precise optical frequencies and time has an irreplaceable role in many applications (scientific experiments in time and frequency metrology, security of critical infrastructures, synchronisation of navigation systems, sensors). We must deploy a different transmission type where optical fibre links cannot be used. The paper describes the possible distribution of stable optical frequencies by the free-space optical link between FEEC BUT Brno (responsible for development and operation of FSO units) and ISI CAS CR (responsible for optical laser source, optical fibre links, data processing).
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Development of autonomous experimental setup to investigate directional distortional hardening under biaxial loading
Svárovský, Jiří ; Parma, Slavomír ; Štefan, Jan ; Ciocanel, C. ; Feigenbaum, H. P. ; Klepač, Vilém ; Marek, René ; Plešek, Jiří
Plastic deformations alter the shape of the yield surface in the stress space. Models for predicting the shape of the yield surface according to the direction of loading are being developed. Experimental data are the key factor in development and validation of phenomenological models, such as the model of directional distortional hardening cited in this study. The objective of this paper is to present the experimental setup for investigation of the directional distortional hardening. A new autonomous method was developed using an axial-torsional testing machine and the Labivew 2017 graphical programming environment to monitor the yield surface in axial stress – shear stress space. A suitable yield condition in form of effective plastic strain was used for the determination of the yield points. Initial yield surface obtained by this method shows promising agreement with von Mises model of the yield surface. Several outstanding yield points were measured which disrupt the assumption of the yield surface convexity. Therefore, possible shortcomings caused by the methodology are being investigated.
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