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A Comparison of Methods Recovering Signals from Non-Uniform Samples
(Elsevier, 2024-08-14) Mihálik, Ondrej; Mesárošová, Michaela; Čelko, Jakub; Sýkora, Tomáš; Bradáč, Zdeněk
Band-limited signals play a vital role in signal acquisition, transmission, processing and storage for decades. However, their recovery from non-uniformly spaced samples is still subject to discussion. There are multiple authors advancing different approaches and the user has to deal with an abundance of literature. Therefore, this paper offers a brief theoretical review of the most promising reconstruction methods. We also consider the importance of regularisation if the signal samples are noisy, which, surprisingly, seems to be neglected by many authors. Subsequently, the suitability of the methods is illustrated using an example of a real-world signal. Assessment of accuracy and speed of the methods is repeated for varying noise levels in signal amplitude, and for increasing degree of non-uniformities in sampling time. Cubic spline methods and sinc function reconstruction offer the best compromise between speed and accuracy for the concrete signal tested in this paper.
Thermal stability of electron beam welded AlCoCrFeNi2.1 alloy
(IOP Publishing, 2024-09-30) Rončák, Ján; Jozefovič, Patrik; Müller, Peter; Adam, Ondřej; Judas, Jakub; Dupák, Libor; Zavdoveev, Anatoliy; Jan, Vít; Zobač, Martin
AlCoCrFeNi2.1 alloy, which belongs to the group of eutectic high-entropy alloys (EHEAs), possesses a combination of increased strength and ductility. It should retain these properties over a wide temperature range due to the high entropy effect of the system. At the same time, eutectic alloys are generally considered to have good castability, which increases the possibility of casting the alloy in larger volumes. One of the processes, that the alloy does not avoid when applied in industry, are the various joining techniques including electron beam welding. The weld area is often in a non-equilibrium state, which increases the risk of failure during operation. The paper therefore discusses the stability of the microstructure and mechanical properties of AlCoCrFeNi2.1 alloy when exposed to short-term elevated temperatures. The material heated at 900 degrees C for 1 h in a vacuum furnace was observed using light and electron microscopy, analyzed for chemical and phase composition and finally subjected to HV0.1 hardness measurement and tensile strength test. The resulting condition was compared with the welded joint before exposure to elevated temperature. The microstructure of the weld was formed by a fine lamellar eutectic over the entire observed area. EBSD analysis confirmed the presence of a combination of FCC and BCC phases. The material hardness reached an average value of 370 HV0.1. Maximum tensile strength of the weld joint was measured at 944 MPa with the corresponding displacement of the crosshead 6.1 mm. The welded joint demonstrated sufficient stability and the ability to withstand short-term severe elevated temperature conditions.
CNN Architecture for Posture Classification on Small Data
(Elsevier, 2024-08-14) Mesárošová, Michaela; Mihálik, Ondrej; Jirgl, Miroslav
A convolutional neural network is often mentioned as one of the deep learning methods that requires a large amount of training data. Questioning this belief, this paper explores the applicability of classification based on a shallow net structure trained on a small data set in the~context of patient posture classification based on data from a pressure mattress. Designing a CNN often presents a complex problem, especially without a universally applicable approach, allowing many diverse structural possibilities and training settings. We tested various training options and layer configurations to provide an overview of influential parameters for posture classification. Experiments show encouraging results with the leave-one-out cross-validation accuracy of 93.1% of one of the evaluated CNN structures and its hyperparameter settings.
Digital twin of heat exchange station
(Elsevier, 2024-08-14) Benešl, Tomáš; Husák, Michal; Mihálik, Ondrej; Vancl, Radim; Bradáč, Zdeněk
The article describes the identification of a heat exchanger system using PLC for measurement, followed by system model identification and reconstruction in Matlab Simulink and SIMIT. The root-mean-square error of the identified system was 2.49 % on training data and 5.33 % in the validation scenario. The system model is suitable for predicting and simulating errors and anomalies; it can be used for the optimisation of control processes or system parameters. Therefore, the model can serve as an educational tool, allowing training of students, operators and other experts. They can experiment without fear of damaging components and without having to wait for the long-time transients of a real system.
Fuzzy Logic-based Techniques for Human Driver Behavior Modelling during a Simple Lane-changing Task
(Elsevier, 2024-06-19) Jirgl, Miroslav; Mesárošová, Michaela; Fiedler, Petr; Arm, Jakub
The paper presents an experiment with fuzzy-logic-based models for approximating data representing human driver behavior during a simple lane-changing task. Data are acquired via the self-developed car driving simulator under defined conditions. Three fuzzy-logic-based models are considered: fuzzy Hammerstein model, fuzzy PD controller with a fixed structure (analogy to the linear PD controller) and fuzzy PD controller with an optimized structure. A comparison of the effectiveness of the individual approaches was evaluated using a criterion representing the fitness of the model output and the measured data. Although only one dataset was considered in the frame of this paper, the results indicate an investigative potential of the fuzzy models for this kind of task connected with the modelling of human behavior.

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