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Identification of quasiperiodic processes in the vicinity of the resonance
Fischer, Cyril; Náprstek, Jiří
2023 - anglický
In nonlinear dynamical systems, strong quasiperiodic beating effects appear due to combination of self-excited and forced vibration. The presence of symmetric or asymmetric beatings indicates an exchange of energy between individual degrees of freedom of the model or by multiple close dominant frequencies. This effect is illustrated by the case of the van der Pol equation in the vicinity of resonance. The approximate analysis of these nonlinear effects uses the harmonic balance method and the multiple scale method.
Klíčová slova:
dynamical systems; quasiperiodic response; van der Pol equation
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Identification of quasiperiodic processes in the vicinity of the resonance
In nonlinear dynamical systems, strong quasiperiodic beating effects appear due to combination of self-excited and forced vibration. The presence of symmetric or asymmetric beatings indicates an ...
Laboratory X-ray imaging in material sciences
Koudelka_ml., Petr; Kytýř, Daniel; Jiroušek, O.
2023 - anglický
In recent decades, X-ray imaging and computed (micro)tomography (XCT) in particular have become common tools for volumetric inspection, visualization, and analysis of internal structure in materials from various fields [1]. In this lecture, we will explore various applications of laboratory X-ray imaging chains utilizing the combination of tomographical imaging with mechanical, thermal, or chemical loading of the irradiated sample in a so-called time-resolved imaging allowing for unprecedented insight into different phenomena driving fundamental processes encountered in various fields of material science. We will show that failure processes in engineering or geological materials [2] can be thoroughly studied by synergy of information from radiographical imaging and other methods including acoustic emission detection and optical measurements via high-speed visible-spectrum and thermal-imaging cameras, where the radiography provides important spatial information regarding deformation processes evolving within the tested samples that could not be obtained otherwise. The state-of-the-art the laboratory based imaging chains for investigation of dynamic response of materials under loading will be also discussed including high speed X-ray radiography utilizing a powerful X-ray source during high velocity impact as an approach suitable for inspection of an impacted sample. As an alternative to both conventional high-power sources and accelerator facilities, capabilities of a flash X-ray system developed primarily for in-situ ballistics research providing very short bursts of an extremely powerful intermittent X-ray radiation with a typical duration of dozens of nanoseconds will be shown.
Klíčová slova:
X-ray imaging; material characterization; mechanical properties
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Laboratory X-ray imaging in material sciences
In recent decades, X-ray imaging and computed (micro)tomography (XCT) in particular have become common tools for volumetric inspection, visualization, and analysis of internal structure in materials ...
Interpolation with restrictions -- role of the boundary conditions and individual restrictions
Valášek, Jan; Sváček, P.
2023 - anglický
The contribution deals with the remeshing procedure between two computational finite element meshes. The remeshing represented by the interpolation of an approximate solution onto a new mesh is needed in many applications like e.g. in aeroacoustics, here we are particularly interested in the numerical flow simulation of a gradual channel collapse connected with a~severe deterioration of the computational mesh quality. Since the classical Lagrangian projection from one mesh to another is a dissipative method not respecting conservation laws, a conservative interpolation method introducing constraints is described. The constraints have form of Lagrange multipliers enforcing conservation of desired flow quantities, like e.g. total fluid mass, flow kinetic energy or flow potential energy. Then the interpolation problem turns into an error minimization problem, such that the resulting quantities of proposed interpolation satisfy these physical properties while staying as close as possible to the results of Lagrangian interpolation in the L2 norm. The proposed interpolation scheme does not impose any restrictions on mesh generation process and it has a relatively low computational cost. The implementation details are discussed and test cases are shown.
Klíčová slova:
interpolation; Lagrange multiplier; Lagrange projection
Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
Interpolation with restrictions -- role of the boundary conditions and individual restrictions
The contribution deals with the remeshing procedure between two computational finite element meshes. The remeshing represented by the interpolation of an approximate solution onto a new mesh is needed ...
Dynamics of dissolved organic carbon in surface water during extreme rainfall-runoff events
Matoušková, M.; Fraindová, K.; Bejčková, M.; Kliment, Z.; Vlach, V.; Vlček, Lukáš
2023 - anglický
The release of a greater amount of natural organic matter (NOM) within climate change is registered in many catchments with peatbog areas. The aim of our research is to study the dynamics of releasing dissolved organic carbon (DOC) into surface water in headwater areas with peatbogs. DOC concentrations are analysed in relation to extreme rainfall-runoff (R-R) events and according to the hydrological preconditions of the basin. These preconditions are described using selected hydroclimatic variables (14 days before the R-R event). The source data comes from stations of the Faculty of Science, Charles University, and the Czech Hydrometeorological Institute. For the evaluation of relations and processes, the Principal component analysis (PCA), hysteresis loops or Pearson correlation coefficient was used. The lag time of DOCmax for Qmax, the dependence of DOCmax and groundwater levels were studied. The influence of flow rate on the decline and ascent phases of DOC\nconcentrations by hysteresis loops and the influence of the number of partial flow maximums on the amount of transported DOC during the R-R event was analysed. Our first results show that great influence on the dynamic of DOC concentration in surface water has the change in groundwater-levels in the peatbog and the outflow amount during the R-R event. The hydroclimatic preconditions of the basin have also a significant influence on the DOC release. Changes in concentrations during R-R events also occurred for other compounds that were studied additionally. Particularly significant was the increase in metals (mainly Fe, Al, Mn) and base cation (K) and decrease in nitrate nitrogen.
Klíčová slova:
natural organic matter; dissolved organic carbon; peatbog; surface water
Dokument je dostupný na externích webových stránkách.
Dynamics of dissolved organic carbon in surface water during extreme rainfall-runoff events
The release of a greater amount of natural organic matter (NOM) within climate change is registered in many catchments with peatbog areas. The aim of our research is to study the dynamics of releasing ...
Vowel length in infant-directed speech: the realisation of short-long contrasts in Czech IDS
Svoboda, Michaela; Chládková, Kateřina; Kocjančič Antolík, T.; Paillereau, Nikola; Slížková, P.
2023 - anglický
When interacting with young children, talkers across many languages use a speech style that reflects positive affect, draws infants' attention, and supposedly facilitates language acquisition. As for the latter, a well-documented feature of infant-directed speech is an exaggeration of spectrally-cued vowel contrasts. Here we tested whether talkers exaggerate also durationally cued contrasts. Sixty-three mothers, native speakers of Czech, were recorded while playing with their infant (4- to 10-month-olds, IDS) and while speaking to an adult (ADS). The durations of the five Czech phonemically short vowels were compared to their long counterparts. Vowel duration (normalised for word duration) was longer in IDS than in ADS more for phonemically long vowels at the younger infant ages, indicating a developmentally specific early exaggeration of length contrasts in Czech infant-directed speech. The present finding suggests that in a language with phonemic length, caregivers' realisation of speech sounds may go beyond merely being longer and slower overall.
Klíčová slova:
infant-directed speech; vowel length; development of early input; Czech
Plné texty jsou dostupné na vyžádání prostřednictvím repozitáře Akademie věd.
Vowel length in infant-directed speech: the realisation of short-long contrasts in Czech IDS
When interacting with young children, talkers across many languages use a speech style that reflects positive affect, draws infants' attention, and supposedly facilitates language acquisition. As for ...
Bohl-Marek decomposition applied to a class of biochemical networks with conservation properties
Papáček, Štěpán; Matonoha, Ctirad; Duintjer Tebbens, Jurjen
2023 - anglický
This study presents an application of one special technique, further called as Bohl-Marek decomposition, related to the mathematical modeling of biochemical networks with mass conservation properties. We continue in direction of papers devoted to inverse problems of parameter estimation for mathematical models describing the drug-induced enzyme production networks [3]. However, being aware of the complexity of general physiologically based pharmacokinetic (PBPK) models, here we focus on the case of enzyme-catalyzed reactions with a substrate transport chain [5]. Although our ultimate goal is to develop a reliable method for fitting the model parameters to given experimental data, here we study certain numerical issues within the framework of optimal experimental design [6]. Before starting an experiment on a real biochemical network, we formulate an optimization problem aiming to maximize the information content of the corresponding experiment. For the above-sketched optimization problem, the computational costs related to the two formulations of the same biochemical network, being (i) the classical formulation x˙(t) = Ax(t) + b(t) and (ii) the 'quasi-linear' Bohl-Marek formulation x˙M(t) = M(x(t)) xM(t), can be determined and compared.
Klíčová slova:
Mathematical modeling; Biochemical network; Pharmacokinetic (PBPK) models
Dokument je dostupný na externích webových stránkách.
Bohl-Marek decomposition applied to a class of biochemical networks with conservation properties
This study presents an application of one special technique, further called as Bohl-Marek decomposition, related to the mathematical modeling of biochemical networks with mass conservation properties. ...
Validation of numerical simulations of a simple immersed boundary solver for fluid flow in branching channels
Keslerová, R.; Lancmanová, Anna; Bodnár, Tomáš
2023 - anglický
This work deals with the flow of incompressible viscous fluids in a two-dimensional branching channel. Using the immersed boundary method, a new finite difference solver was developed to interpret the channel geometry. The numerical results obtained by this new solver are compared with the numerical simulations of the older finite volume method code and with the results obtained with OpenFOAM. The aim of this work is to verify whether the immersed boundary method is suitable for fluid flow in channels with more complex geometries with difficult grid generation.
Klíčová slova:
immersed boundary method; finite volume method; OpenFOAM
Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
Validation of numerical simulations of a simple immersed boundary solver for fluid flow in branching channels
This work deals with the flow of incompressible viscous fluids in a two-dimensional branching channel. Using the immersed boundary method, a new finite difference solver was developed to interpret the ...
The Prager musikalisches Album (1838) and the nineteenth-century salon as cultural practice
Bunzel, Anja
2023 - anglický
This article deals with a collection of songs and piano pieces, the Prager musikalisches Album, published in 1838, asking two central questions. Drawing on different concepts of the musical work (Werkbegriff), I explore whether the album can be considered a work rather than a loose collection of multiple works. Within the musicological discourse there have been many attempts at defining these terms, ranging from quite narrow categorisations based on aspects of instrumentation, musical form, or stylistic matters to more open approaches encompassing the communicative process and viewing the history of genre as cultural history. Drawing on the latter, I suggest that the Prager musikalisches Album is a prime example of collective authorship, which opens up a second question, namely that of authorship. Authorship may embrace aspects of agency that exceed the realms of the person who penned a musical, literary, or artistic work. Indeed, it may be shaped by performers, audiences, presses/ salespeople, dedicatees, critics, patrons, and anyone else who has an impact on any given work at the time of its creation and/or publicization. By taking this perspective, I suggest that the Prager musikalisches Album is both reflective and representative of nineteenth-century salon culture, within whose context the album was embedded. Offering a holistic analysis of the album and its context, I use this article as a springboard to advocate for a musical historiography that takes into account the full breadth of musical culture, and which embraces, besides composers and poets, a number of other cultural agents that are often overlooked within more traditional music-historical considerations.
Klíčová slova:
nineteenth-century salon; genre; work; Prague; authorship
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
The Prager musikalisches Album (1838) and the nineteenth-century salon as cultural practice
This article deals with a collection of songs and piano pieces, the Prager musikalisches Album, published in 1838, asking two central questions. Drawing on different concepts of the musical work ...
Rooting algebraic vertices of convergent sequences
Hartman, David; Hons, T.; Nešetřil, J.
2023 - anglický
Structural convergence is a framework for convergence of graphs by Nešetřil and Ossona de Mendez that unifies the dense (left) graph convergence and Benjamini-Schramm convergence. They posed a problem asking whether for a given sequence of graphs (Gn) converging to a limit L and a vertex r of L it is possible to find a sequence of vertices (rn) such that L rooted at r is the limit of the graphs Gn rooted at rn. A counterexample was found by Christofides and Král’, but they showed that the statement holds for almost all vertices r of L. We offer another perspective to the original problem by considering the size of definable sets to which the root r belongs. We prove that if r is an algebraic vertex (i.e. belongs to a finite definable set), the sequence of roots (rn) always exists.
Klíčová slova:
rooting; algebraic vertices; convergent sequences
Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
Rooting algebraic vertices of convergent sequences
Structural convergence is a framework for convergence of graphs by Nešetřil and Ossona de Mendez that unifies the dense (left) graph convergence and Benjamini-Schramm convergence. They posed a problem ...
Effect of aging on mechanical properties of 3D printed samples using stereolithography
Drechslerová, V.; Falta, J.; Fíla, T.; Dvořák, R.; Kytýř, Daniel
2023 - anglický
This paper focuses on stereolithography (an additive manufacturing technology working on the principle of curing liquid resins layer by layer using ultraviolet radiation) and the effect of aging on the mechanical properties of the material and printed samples. The aging of the material could be a problem for its subsequent use as the stability of the mechanical properties would not be maintained and unwanted deterioration of the material could occur. As part of the research, sets of samples were printed and subjected to different aging methods and subsequently subjected to quasi-static and dynamic uni-axial load tests. From the data obtained, the basic mechanical properties of the material were calculated and compared with each other. The aim of this paper was to investigate whether aging process causes significant changes in the mechanical properties of the materials used, which could have a consequential impact on their use in different industries.
Klíčová slova:
stereolithography; aging; mechanical properties
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Effect of aging on mechanical properties of 3D printed samples using stereolithography
This paper focuses on stereolithography (an additive manufacturing technology working on the principle of curing liquid resins layer by layer using ultraviolet radiation) and the effect of aging on ...
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