Ano (2929)
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Applying a two degree of freedom model for drive-by identification
Bayer, Jan
2024 - anglický
A new concept of drive-by identification is examined applying the analogy with a Two Degree Of Freedom (DOF) system where the bridge is considered the ground-supported spring-mass and the moving spring-mass the second DOF. The response of the moving spring-mass is simulated on a bridge model using different road profiles and compared to parameters of the corresponding two DOF system. The focus is the spectral shift that can be observed on the moving spring-mass during its passage along the bridge and could possibly be applied for drive-by identification. The accuracy mainly depends on the relation of the moving spring-mass to the bridge mass and the relation between the natural frequency of the spring-mass and those of the bridge. The simulations showed that road profile can significantly reduce the accuracy of identified results, which imposes limits on practical applications.
Klíčová slova:
drive-by identification; structural health monitoring; finite element analysis; road roughness; two DOF system
Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
Applying a two degree of freedom model for drive-by identification
A new concept of drive-by identification is examined applying the analogy with a Two Degree Of Freedom (DOF) system where the bridge is considered the ground-supported spring-mass and the moving ...
Solution methods for an aeroelastic problem with combined harmonic and stochastic excitation
Fischer, Cyril; Náprstek, Jiří
2024 - anglický
Assessing responses in slender engineering structures facing both deterministic harmonic and stochastic excitation is often based on an approximation by the single-degree-of-freedom van der Pol-type nonlinear model. Determining the response probability density function involves solving the Fokker-Planck equation, which is generally a challenging task. Hence, semi-analytical and numerical methods come into play. This contribution reviews several possible techniques and spotlights the exponential-polynomial-closure method. The shown results are limited, as the paper reflects an early stage of the relevant research direction.
Klíčová slova:
Fokker-Planck equation; stochastic averaging; numerical solution; Galerkin approximation; van der Pol-type oscillator; partial amplitudes; exponential-polynomial-closure method
Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
Solution methods for an aeroelastic problem with combined harmonic and stochastic excitation
Assessing responses in slender engineering structures facing both deterministic harmonic and stochastic excitation is often based on an approximation by the single-degree-of-freedom van der Pol-type ...
Galloping of insulated bundled overhead line simplified analysis
Hračov, Stanislav; Macháček, Michael
2024 - anglický
Our paper provides an analysis of the susceptibility of a particular bundled overhead line to galloping. It presents a case study of an aerial bundled cable, consisting of four conductors insulated by polyethylene, and used for low-voltage power lines. The susceptibility to loss of stability is analyzed for cable without and with simulated icing observed on similar real conductors. In the first case, the proneness to galloping was excluded based on the results of CFD simulation and the Den Hartog criterion. In latter case, the possible occurrence of galloping was confirmed. The critical wind velocity for the ice-covered cable was calculated utilizing quasi-steady theory. Finally, the amplitudes of limit cycle oscillation for supercritical wind speeds were estimated based on simplified numerical analysis.
Klíčová slova:
aerial bundled cable; wind effects; galloping; limit cycle oscillation
Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
Galloping of insulated bundled overhead line simplified analysis
Our paper provides an analysis of the susceptibility of a particular bundled overhead line to galloping. It presents a case study of an aerial bundled cable, consisting of four conductors insulated by ...
LES simulations of airflow around rectangle with side ratio 2:1 and their comparison with experiments
Ledvinková, Blanka; Hračov, Stanislav; Macháček, Michael
2024 - anglický
Our contribution is focused on the comparison of the experimental investigations and of the numerical 3D LES simulations of the airflow around sharply edged rectangle with side ratio 2:1. The rectangle object was exposed to the airflow having a given velocity at different angles of the wind attack in the wind tunnel with the aim to obtain the curves of the aerodynamic coefficients and Strouhal number depending on the impact angle. The comparative numerical 3D simulations of the wind tunnel testing were performed using COMSOL Multiphysics and OpenFoam both incorporating the Large Eddy Simulation (LES) method.
Klíčová slova:
rectangle 2:1; wind tunnel; LES simulation; aerodynamic characteristics
Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
LES simulations of airflow around rectangle with side ratio 2:1 and their comparison with experiments
Our contribution is focused on the comparison of the experimental investigations and of the numerical 3D LES simulations of the airflow around sharply edged rectangle with side ratio 2:1. The ...
Gas sensors based on diamond heterostructures for air quality monitoring
Kočí, Michal; Szabó, Ondrej; Izsák, T.; Sojková, M.; Godzierz, M.; Wróbel, P.; Husák, M.; Kromka, Alexander
2024 - anglický
Currently, great emphasis is placed on air quality and the presence of pollutants. Attention is therefore focused on new gas-sensing materials enabling detection even at low (up to room) temperatures with sufficient response and short reaction time. Here, we investigate the suitability of H-NCD films and their heterostructures with MoS2, GO, rGO, SH-GO, or Au NPs for gas sensing applications. Electrical properties are measured for oxidizing gas NO2, reducing gas NH3, and chemical vapor of ethanol, and at temperatures varied from room temperature to 125 °C. In contrast to the individual forms of employed materials with limited response to the exposed gases, the HNCD heterostructures revealed better sensing properties. In particular, the Au NPs/H-NCD heterostructures revealed a higher response at 125 °C in contrast to H-NCD, MoS2/H-NCD had quite good response even at room temperature and GO/H-NCD revealed high sensitivity to chemical vapor, which further improved for the SH-GO/HNCD.
Klíčová slova:
gas sensors; nanocrystalline diamond; heterostructures; air quality monitoring
Dokument je dostupný na externích webových stránkách.
Gas sensors based on diamond heterostructures for air quality monitoring
Currently, great emphasis is placed on air quality and the presence of pollutants. Attention is therefore focused on new gas-sensing materials enabling detection even at low (up to room) temperatures ...
The Influence of Geometric Parameters of 3D Printed Structured Beds on Hydrodynamic Characteristics of Trickle-Bed Reactor
Nyklíčková, Kateřina
2024 - anglický
The study examines a parametric set of POCS structures, where cubic cell is the basic element. The parameters such as strut diameter sd and cell size cs were varied1. These modifications are implemented with an emphasis on maintaining similar porosity and specific surface area for these structures.
Klíčová slova:
trickle-bed reactor; pressure dop; POCS structures
Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
The Influence of Geometric Parameters of 3D Printed Structured Beds on Hydrodynamic Characteristics of Trickle-Bed Reactor
The study examines a parametric set of POCS structures, where cubic cell is the basic element. The parameters such as strut diameter sd and cell size cs were varied1. These modifications are ...
Surface changes induced by plasma treatment and high temperature annealing of silicon dioxide microparticles
Babčenko, Oleg; Remeš, Zdeněk; Beranová, Klára; Kolářová, Kateřina; Lörinc, J.; Prošek, Z.; Tesárek, P.
2024 - anglický
Due to the high surface to volume ratio, the particles’ surface properties modification defines its properties in general, which is crucial for their use. From this point of view, plasma processing or high temperature annealing can be considered as the universal techniques for efficient modification of materials in the form of powder. In this study, the silicon dioxide microparticles have been treated in a hydrogen, oxygen or vacuum by low temperature plasma or annealing. The change of SiO2 microparticles properties was investigated by photoluminescence spectroscopy at room and low temperature. High temperature annealing in hydrogen induced under UV excitation photoluminescence in the near UV and visible light indicating the change of defect states on the surface of the microparticles. We believe that observed findings clearly demonstrate useful method for analysis of SiO2 microparticles surface modification attractive also for fundamental research.
Klíčová slova:
silicon dioxide; plasma treatment; annealing; photoluminescence; measuring setup
Dokument je dostupný na externích webových stránkách.
Surface changes induced by plasma treatment and high temperature annealing of silicon dioxide microparticles
Due to the high surface to volume ratio, the particles’ surface properties modification defines its properties in general, which is crucial for their use. From this point of view, plasma processing or ...
The U.S. low-wage structure: a McWage comparison
Ashenfelter, O.; Jurajda, Štěpán
2024 - anglický
Thanks to standardized work protocol and technology of McDonald’s restaurants, the hourly wage of McDonald’s Basic Crew enables wage comparisons under near-identical skill inputs and hedonic job conditions. McWages capture labor costs in entry-level jobs, while the Big Macs (earned) Per Hour (BMPH) index measures corresponding purchasing power of wages. We document large and growing geographical wage differences in standardized jobs using data covering most U.S. counties during 2016-2023. Before the Covid-19 pandemic, there was no BMPH growth where minimum wages stayed constant, but the pandemic wage increase, which diminished the importance of minimum wages, was stronger in these areas.
Klíčová slova:
wage comparisons; labor costs; purchasing power
Dokument je dostupný na externích webových stránkách.
The U.S. low-wage structure: a McWage comparison
Thanks to standardized work protocol and technology of McDonald’s restaurants, the hourly wage of McDonald’s Basic Crew enables wage comparisons under near-identical skill inputs and hedonic job ...
Development of Polymeric Enantioselective Membranes
Čížek, Jan
2024 - anglický
Enantiomers are molecules that share the same chemical formula but in space form mirror images of each other. Their reactions with other chiral molecules can be remarkably different, which is crucial mainly for pharmaceuticals and agrochemicals. However, industrialscale synthetic production of enantiomerically pure compounds is not always available. Therefore, the need for pure enantiomeric compounds drives the development and research on various separation methods. However, most methods used on the industrial scale are limited to specific compounds (diastereomeric recrystallization) or generally difficult and/or expensive to scale up (chromatography-related methods). Separation of enantiomers using membranes is promising\nthanks to the easy scalability and continuous operation of membrane processes. Various ideas about how the enantioselective membranes should look like have been published in the last thirty years. The mechanism of enantiomeric separation on a membrane is, however, highly specific, and still requires extensive research. In this work, four types of enantioselective polymeric membranes are presented.
Plné texty jsou dostupné v digitálním repozitáři NUŠL
Development of Polymeric Enantioselective Membranes
Enantiomers are molecules that share the same chemical formula but in space form mirror images of each other. Their reactions with other chiral molecules can be remarkably different, which is crucial ...
Synthesis of Fluorinated Methyl β-Lactosides
Krčil, Aleš
2024 - anglický
In my contribution, I will describe the synthesis of a complete series of mono-deoxyfluorinated methyl β-lactosides (1–7). Their affinity towards hgals will be determined by analytical method ELISA. The synthesis relies on monosaccharide building blocks, which serves as key intermediates that are transformed into the target products through glycosylation followed by final deprotection steps.
Klíčová slova:
flurinated carbohydrates; galectin; deoxyfluorination
Plné texty jsou dostupné v digitálním repozitáři NUŠL
Synthesis of Fluorinated Methyl β-Lactosides
In my contribution, I will describe the synthesis of a complete series of mono-deoxyfluorinated methyl β-lactosides (1–7). Their affinity towards hgals will be determined by analytical method ELISA. ...
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