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Analyzing stochastic stability of a gyroscope through the stochastic Lyapunov function
Náprstek, Jiří; Fischer, Cyril
2023 - anglický
The text delves into the application of first integrals in the construction of Lyapunov functions for analyzing the stability of dynamic systems in stochastic domains. It emphasizes the distinct characteristics of first integrals that warrant the introduction of additional constraints to ensure the essential properties required for a Lyapunov function. These constraints possess physical interpretations associated with system stability. The general approach to testing stochastic stability is illustrated using the example of a 3-degrees-of-freedom system representing a gyroscope.
Klíčová slova:
stochastic stability; Lyapunov function; first integral; gyroscope
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Analyzing stochastic stability of a gyroscope through the stochastic Lyapunov function
The text delves into the application of first integrals in the construction of Lyapunov functions for analyzing the stability of dynamic systems in stochastic domains. It emphasizes the distinct ...
Experimental and numerical investigation of the frequency-modal properties of the switch box
Zolotarev, Igor; Pešek, Luděk; Bula, Vítězslav; Šnábl, Pavel; Gabriel, Dušan; Mračko, Michal; Masák, Jan
2023 - anglický
The research is linked to increase of seismic resistivity of data board switch boxes. Therefore we deal with numerical modelling of the box for finding the hot spots and designing appropriate modifications. This paper deals with numerical and experimental frequency-modal properties of the switch box and mutual comparison for numerical model validation.
Klíčová slova:
modal analysis; natural frequencies; eigen-modes of vibration
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Experimental and numerical investigation of the frequency-modal properties of the switch box
The research is linked to increase of seismic resistivity of data board switch boxes. Therefore we deal with numerical modelling of the box for finding the hot spots and designing appropriate ...
Conductive open-cell silicone foam for modulatable damping and impact sensing applications
Preuer, R.; Šleichrt, Jan; Kytýř, Daniel; Graz, I.
2023 - anglický
Nature has long served as a source of inspiration for the development of new materials, with foam-like structures in fruits such as oranges and pamelos serving as examples of efficient energy dissipation. In this study, we present the synthesis and characterization of a conductive silicone foam for potential impact sensing applications. By blending Sylgard 184 and Carbon Black, we create a highly porous structure capable of dissipating energy and modulating its resistance. To investigate the properties of the foam, we utilized both micro-computer tomography (μCT) and scanning electron microscopy (SEM) imaging techniques. The μCT imaging revealed the intricate pore network of the foam, reminiscent of the complex structure found in natural sponges. SEM imaging allowed for observation of the uniform distribution of Carbon Black particles within the foam, enabling the conductive properties of the foam. The foam’s mechanical behavior was characterized by a compression test under μCT imaging to measure the deformation behavior and changes in the foam’s resistance. Additionally, a ball drop test was conducted to investigate the foam’s damping behavior while simultaneously measuring the impact location by the local change in resistance. Remarkably, our results demonstrate the exceptional damping capabilities of the conductive silicone foam, with the damping ratio modulated by adjusting the degree of compression-induced deformation. This is attributed to the collapse of the foam’s porous structure, resulting in a significant increase in the foam’s contact area. Overall, our study provides valuable insights into the behavior of conductive silicone foams and their potential as an impact sensing material. The use of both CT and SEM imaging techniques allows for a comprehensive understanding of the foam’s properties, which can be optimized for a variety of applications. The foam’s ability to modulate its damping properties by adjusting the degree of deformation provides a promising avenue for future research in the field of materials science and engineering.
Klíčová slova:
silicone foam; conductive properties; deformation behaviour; damping
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Conductive open-cell silicone foam for modulatable damping and impact sensing applications
Nature has long served as a source of inspiration for the development of new materials, with foam-like structures in fruits such as oranges and pamelos serving as examples of efficient energy ...
The influence of first CNN layer initialization on training convergence
Krejsa, Jiří; Věchet, Stanislav; Chen, K.S.
2023 - anglický
During evaluation of convolution neural networks on the task of sign language single hand alphabet classification we have discovered that in small but not negligible number of cases the training of the network does not converge at all. This paper investigates the problem that we believe is independent of the application. While the true cause of training divergence was not discovered, we can offer the reader an easy solution from practical point of view – initialization of the first CNN layer using pretrained networks parameters.
Klíčová slova:
convolution neural networks; training; initialization
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
The influence of first CNN layer initialization on training convergence
During evaluation of convolution neural networks on the task of sign language single hand alphabet classification we have discovered that in small but not negligible number of cases the training of ...
Post-processing the results of the topology optimization with the level set technique
Ježek, Ondřej; Kopačka, Ján; Gabriel, Dušan
2023 - anglický
Topology optimization (TO) has come to the fore with the development of 3D printing. The most commonly used method is SIMP, a density-based approach, which outputs a per-element constant density field and thus requires post-processing to obtain the shape. Conventional post-processing methods extract optimized topologies in the form of brep models. It yields only C0 continuous geometries, which are usually not suitable for downstream applications such as prototyping, design validation, and design exploration. In this paper, we present a new post-processing method based on the level set principle that overcomes common post-processing issues, such as the lack of smoothness.
Klíčová slova:
topology optimization; post-processing; level-set; signed distance function
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Post-processing the results of the topology optimization with the level set technique
Topology optimization (TO) has come to the fore with the development of 3D printing. The most commonly used method is SIMP, a density-based approach, which outputs a per-element constant density field ...
Photo-active liquid crystalline materials: effect of lateral substitution far from the chiral center
Mironov, Sergei; Suchánek, T.; Marhoul, J.; Cigl, Martin; Hamplová, Věra; Bubnov, Alexej
2023 - anglický
Photosensitive liquid crystalline (LC) materials give a fascinating possibility to tune and control the optical properties of soft systems distantly by illumination by UV-Vis light. Lateral substitution on the molecular core is an effective tool to tune the behaviour of chiral LCs. The effect of lateral substitution (by F, Cl, Br and methyl group) on the self-assembling behaviour, several new LCs with substituents placed on the benzene ring far from the chiral centre are and studied. All compounds, with exception of Br-substituted one, possess the cholesteric phase. The photosensitive behaviour, in particular the conversion of the E-Z isomers, was studied in toluene solution by HPLC. The kinetics of the photo-isomerization was identified under illumination by UV light. Due to presence of a photo-active azo group these materials can be used as functional dopants for design of smart photo-active liquid crystalline mixtures targeted for various applications in optoelectronics.
Klíčová slova:
photosensitive chiral liquid crystal; lateral substitution; azobenzene; E-Z isomerization
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Photo-active liquid crystalline materials: effect of lateral substitution far from the chiral center
Photosensitive liquid crystalline (LC) materials give a fascinating possibility to tune and control the optical properties of soft systems distantly by illumination by UV-Vis light. Lateral ...
Surface acoustic wave microfluidic chip for rapid cell sorting
Vejrosta, Jakub; Maňka, Tadeáš; Plichta, Tomáš; Šerý, Mojmír
2023 - anglický
This work revolves around microfluidics and micro-objects manipulation in general. In our device, we are producing surface acoustic wave (SAW). The SAW can be used to sort particles by their size or physical properties and separate them. In medical analysis SAW on microfluidic chip can be used to pre-sorting of body fluids or blood serum for further optical or chemical analysis. The wave is produced by pair of interdigital transducers (IDTs), which are situated on opposite sides of microfluidic channel. As our active material we have used lithium niobate crystalline material for its great piezoelectric properties. This work is also the precursor for measuring the rheological properties of a medium, such as micro-viscosity, via the measurement of the trajectory of a flow trace.
Klíčová slova:
microfluidics; surface acoustic wave; light microscopy
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Surface acoustic wave microfluidic chip for rapid cell sorting
This work revolves around microfluidics and micro-objects manipulation in general. In our device, we are producing surface acoustic wave (SAW). The SAW can be used to sort particles by their size or ...
Modelling of pulse-triggered running waves on a blade cascade
Šnábl, Pavel; Pešek, Luděk
2023 - anglický
An experimental cascade of five NACA 0010 blades with pitch degrees of freedom is excited by a moment pulse to one of the blades. Depending on the flow conditions, such as wind speed and the angle of attack of the wind on the blades, the vibration of the excited blade is transmitted by the wind to the other blades. This can result in a running wave that diminishes over time or in a flutter running wave. A simplified spring-mass-damper model with inter-blade connections and non-linear van der Pol dampers is tuned to match experimentally obtained stability curves and tested to see if it can qualitatively model the response of the cascade to the pulse excitation.\n
Klíčová slova:
pulse-triggered running waves; blade cascade; NACA 0010
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Modelling of pulse-triggered running waves on a blade cascade
An experimental cascade of five NACA 0010 blades with pitch degrees of freedom is excited by a moment pulse to one of the blades. Depending on the flow conditions, such as wind speed and the angle of ...
Autonomous vehicles lane detection using particle filters
Věchet, Stanislav; Krejsa, Jiří; Chen, K.S.
2022 - anglický
Lane detection belongs among many others crucial tasks which an autonomous vehicles traveling in urban roads need to take care of. We present a lane detection method which uses particle filters combined with visual information from onboard camera to control the vehicles direction. Our initial experiments shows promising results as applied and tested in urban roads with focus on real-time data processing.
Klíčová slova:
mobile robot; signal processing; measurement
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Autonomous vehicles lane detection using particle filters
Lane detection belongs among many others crucial tasks which an autonomous vehicles traveling in urban roads need to take care of. We present a lane detection method which uses particle filters ...
Mobile Robot in the Elevator: What Floor Am i On?
Krejsa, Jiří; Věchet, Stanislav; Chen, K.S.; Havelka, M.; Černil, M.
2022 - anglický
Wheeled mobile robots in multiple stories buildings have to use elevator to access arbitrary floor of the building. To do so, the control system must be able to detect and access elevator controls and also determine on which floor the elevator stopped. The paper deals with the latter problem, using the fusion of relative floor change detected by onboard accelerometer and absolute floor number detected by the processing of elevator information screen panel image acquired by onboard camera. Bayesian filter is used for data fusion and convolution neural network for image processing. Field tests resulted in 97% correct detection.
Klíčová slova:
mobile robot; elevator floor determination; Bayesian filtering
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Mobile Robot in the Elevator: What Floor Am i On?
Wheeled mobile robots in multiple stories buildings have to use elevator to access arbitrary floor of the building. To do so, the control system must be able to detect and access elevator controls and ...
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