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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 ...
Applications of blade vibration measurements in the laboratory of rotational laser vibrometry
Maturkanič, Dušan; Procházka, Pavel; Hodboď, Robert; Mekhalfia, Mohammed Lamine; Voronova, Evgeniya
2023 - anglický
The Laboratory of Rotational Laser Vibrometry was established at the Institute of Thermomechanics AS CR, v.v.i. in 2015 and the first experiments were started the following year. The measurements are intended for the research of vibration of rotating blades. The paper includes a summary of measurement results using a special turbine model and their consequences in theoretical research, as well as measurements with a real compressor of aircraft engine and comparison with computational analysis. The paper also describes the complex system for measurement and analysis.
Klíčová slova:
laboratory; turbine; blade; vibration; precision method
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Applications of blade vibration measurements in the laboratory of rotational laser vibrometry
The Laboratory of Rotational Laser Vibrometry was established at the Institute of Thermomechanics AS CR, v.v.i. in 2015 and the first experiments were started the following year. The measurements are ...
The effect of the backfill on the integrity of a buried pipeline upon heavy-duty vehicle crossings
Gajdoš, Lubomír; Šperl, Martin; Slížková, Zuzana; Drdlová, M.
2023 - anglický
The aim of this work was to determine stresses in the wall of a buried empty gas pipeline caused by the weight of backfill as well as by heavy-duty vehicles crossing the pipeline, and, on their basis to assess the applicability of protective sleeves. A buried pipeline with zero internal pressure of transported medium (empty pipeline) differs from an unburied pipeline by the vertical load due to the weight of the backfill which causes an ovalness of the circular cross section of the pipeline. This leads to the rise of through-wall bending stresses with the tensile stress at the outside surface at the 3 and 9 o´clock positions and compressive stress at the inside surface. At the 6 and 12 o´clock positions the stresses are tensile at the inside surface and compressive at the outside surface. The current depth of soil cover above gas pipelines is 0.5 m. For pipes DN500, t ~ 6.5 mm the through-wall bending stress is found to be σb ≈ ±10 MPa. In comparison with the yield stress of pipeline material, this stress is negligible. The situation is changed when heavy-duty vehicles cross the pipeline. For example, when a MAN truck with the mass load 3270 kg acting on a single wheel of the front axle crosses this pipeline, the pressure transmitted to the pipe will cause the through-wall bending stress σb ≈ ±76 MPa. This stress is superimposed to that of the backfill to give the total value ±86 MPa. When dead loads, imposed by backfill cover, together with live loads, caused by truck-wheel loads, are excessive a crushing of side walls of the pipeline and/or ring buckling of the pipe cross section can happen.
Klíčová slova:
gas pipeline; pressure; buried pipeline
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
The effect of the backfill on the integrity of a buried pipeline upon heavy-duty vehicle crossings
The aim of this work was to determine stresses in the wall of a buried empty gas pipeline caused by the weight of backfill as well as by heavy-duty vehicles crossing the pipeline, and, on their basis ...
Experimental evaluation of aluminothermic welds
Zeman, L.; Valach, J.; Zlámal, P.; Krčmářová, N.; Koudelková, Veronika; Zeman, J.
2023 - anglický
The article presents a study of the mechanical processes occurring during the aluminother-mic reaction using experimental methods (strain gauges, digital image correlation, thermography,scanning electron microscopy, profilometry). The aluminothermic reaction is a highly efficient weldingmethod due to its exothermic behaviour, however, it places considerable demands not only on thewelding technique, but also on the capabilities of the experimental methods used - these limitationsare also discussed in the article. The aluminothermic reaction is associated with the formation of alocalised heat source with a time evolution dictated by the technological procedure, which manifestsitself in heat propagation to the surrounding weld material. The unequal evolution of the temperaturefield is the fundamental cause of the appearance of the heat affected zone or local deformations orsurface curvature, which was the focus of the experimental methods deployed above and the results ofwhich are shown in the article.
Klíčová slova:
aluminothermic reaction; train gauges; hardness; profilometry; scanning electron microscope
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Experimental evaluation of aluminothermic welds
The article presents a study of the mechanical processes occurring during the aluminother-mic reaction using experimental methods (strain gauges, digital image correlation, thermography,scanning ...
Fast continuous in-situ XCT of additively manufactured carbon fiber reinforced tensile test specimens
Glinz, J.; Maurer, J.; Holzleitner, M.; Pace, F.; Stamopoulos, A.; Vopálenský, Michal; Kumpová, Ivana; Eckl, M.; Kastner, J.; Senck, S.
2023 - anglický
The reinforcement of fused filament fabricated (FFF) components with continuous fibers allows for high versatility in the design of mechanical properties for a specific application’s needs. However, the bonding quality between continuous fibers and the FFF matrix material has high impact on the overall performance of the composite. In a recent study [1], additively manufactured (AM) continuous fiber reinforced tensile test specimens have been investigated regarding the effect of amount and material of the embedded continuous fibers on tensile strength and AM build quality. During these tensile tests, a sudden reduction in tensile stress, which most likely was not related to actual rupture of continuous fibers, was noticeable. Since X-ray computed tomography (XCT) scans were performed only prior to and after the tensile testing, a detailed investigation on the origin of these drops in tensile stress was not possible. Within this work, we will expand upon these findings and present results of fast on-the-fly in-situ investigations performed on continuous carbon fiber reinforced specimens of the same AM build. During these investigations, specimens are loaded under the same conditions while fast XCT scans, with a total scan time of 12 seconds each, were performed consecutively. The resulting three-dimensional image data reveals internal meso- and macro-structural changes over time/strain to find the cause of the aforementioned reduction in tensile stress.
Klíčová slova:
additive manufacturing; composites; X-ray computed tomography; in-situ tensile testing
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Fast continuous in-situ XCT of additively manufactured carbon fiber reinforced tensile test specimens
The reinforcement of fused filament fabricated (FFF) components with continuous fibers allows for high versatility in the design of mechanical properties for a specific application’s needs. However, ...
Acta Polytechnica CTU Proceedings. Vol. 42 (2023)
Kytýř, Daniel; Doktor, T.; Zlámal, Petr
2023 - anglický
The YSESM symposium provides a forum for young researchers and engineers, PhD students and students dealing with subjects of experimental mechanics. The Symposium concentrates on current work in all areas of experimental research and its application in solid and fluid mechanics. The topic will particularly concern to: Conventional and Advanced Experimental Methods in Solid and Fluid Mechanics, Non-Destructive Testing and Inspection, Measurements in Material Science, Computer Assisted Testing and Simulation, Engineering Design Simulation, Hybrid Methods, Experimental Techniques – Numerical Simulation, Optical Methods and Image Processing, Measurements in Biomechanics, Sensor Techniques for Micro- and Nano-Applications, Measurement Methods for Forensic Engineering.
Klíčová slova:
experimental mechanics; fluid mechanics; mechanics of solids
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Acta Polytechnica CTU Proceedings. Vol. 42 (2023)
The YSESM symposium provides a forum for young researchers and engineers, PhD students and students dealing with subjects of experimental mechanics. The Symposium concentrates on current work in all ...
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 ...
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