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On the problem of singular limit
Caggio, Matteo; Ducomet, B.; Nečasová, Šárka; Tang, T.
2023 - anglický
We consider the problem of singular limit of the compressible Euler system confined to a straight layer Ωδ = (0, δ)×R², δ > 0. In the regime of low Mach number limit and reduction of dimension the convergence to the strong solution of the 2D incompressible Euler system is shown.
Klíčová slova:
compressible Euler equations; dissipative measure-valued solutions; low Mach number; thin domain
Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
On the problem of singular limit
We consider the problem of singular limit of the compressible Euler system confined to a straight layer Ωδ = (0, δ)×R², δ > 0. In the regime of low Mach number limit and reduction of dimension the ...
Deep learning methods for the acoustic emission methods to evaluate an onset of plastic straining
Parma, Slavomír; Kovanda, Martin; Chlada, Milan; Štefan, Jan; Kober, Jan; Feigenbaum, H. P.; Plešek, Jiří
2023 - anglický
Development of phenomenological plasticity models, hardening rules, and plasticity theories relies on experimental data of plastic straining. The experimental data are usually measured as the stress–strain response of the material being loaded and do not provide any clues or information about the local response of\nmaterial. In this paper, we analyze the plastic deformation of the material using the acoustic emission method and current state-of-the-art neural network models such as the InceptionTime architecture.
Klíčová slova:
metal plasticity; strain hardening; acoustic emission; neural networks
Dokument je dostupný na externích webových stránkách.
Deep learning methods for the acoustic emission methods to evaluate an onset of plastic straining
Development of phenomenological plasticity models, hardening rules, and plasticity theories relies on experimental data of plastic straining. The experimental data are usually measured as the ...
Model order reduction for particle-laden flows: systems with rotations and discrete transport operators
Kovárnová, A.; Isoz, Martin
2023 - anglický
In the present work, we concentrate on particle-laden flows as an example of industry-relevant transport-dominated systems. Our previously-developed framework for data-driven model order reduction (MOR) of such systems, the shifted proper orthogonal decomposition with interpolation via artificial neural networks, is further extended by improving the handling of general transport operators. First, even with intrusive MOR approaches, the underlying numerical solvers can provide only discrete realizations of transports linked to the movement of individual particles in the system. On the other hand, our MOR methodology requires continuous transport operators. Thus, the original framework was extended by the possibility to reconstruct continuous approximations of known discrete transports via another artificial neural network. Second, the treatment of rotation-comprising transports was significantly improved.
Klíčová slova:
model order reduction; shifted POD; artificial neural networks; CFD-DEM; Open- FOAM
Dokument je dostupný na externích webových stránkách.
Model order reduction for particle-laden flows: systems with rotations and discrete transport operators
In the present work, we concentrate on particle-laden flows as an example of industry-relevant transport-dominated systems. Our previously-developed framework for data-driven model order reduction ...
Can extended bodies follow geodesic trajectories?
Lukes-Gerakopoulos, Georgios; Mukherjee, Sajal
2023 - anglický
We provide an extension of the analysis on whether an extended test body can follow a geodesic trajectory given by Mukherjee et al. (2022). In particular, we consider a test body in a pole-dipole-quadrupole approximation under the Ohashi-Kyrian-Semer´ak spin supplementary condition moving in the Schwarzschild and Kerr background. Using orbital setups under which a pole-dipole body can follow geodesic motion, we explore under which conditions this can also take place in the pole-dipole-quadrupole approximation when only the mass quadrupole is taken into account. For our analysis, we employ the assumption that the dipole contribution and the quadrupole contribution vanish independentlly.
Klíčová slova:
Mathisson–Papapetrou–Dixon equations; particle dynamics; black holes; chaos
Dokument je dostupný na externích webových stránkách.
Can extended bodies follow geodesic trajectories?
We provide an extension of the analysis on whether an extended test body can follow a geodesic trajectory given by Mukherjee et al. (2022). In particular, we consider a test body in a ...
Underground Spaces In Bosonožský Hájek Nature Reserve And Their Geoeducation Importance
Kirchner, Karel; Kuda, František; Baldík, V.; Kubalíková, Lucie
2023 - anglický
Bosonožský hájek Natural Reserve (Brno, South Moravia) is a very important site from the Earth Science point of view, however, its geodiversity values have been rather overlooked and omitted in the past (the object of legal protection is the occurrence of well-preserved forest ecosystems and endangered species). In the last decades, a series of field work and geophysical measurements has been carried out and the Earth Science phenomena have been identified and described here. These are represented by a dense network of gullies that developed in Pleistocene loess and that are both of natural and anthropogenic origin (some gullies probably developed along the old paths) and specific underground spaces (so called dugouts). Until now, the dugouts in South Moravia have been investigated mainly by archaeologists and those in Bosonožský hájek NR have not been described in detail yet. This brief contribution brings new information about three underground landforms and their possible relationship to the age and development of the gullies. The possibility of different interpretations of the origin of these specific landforms can be considered an opportunity in the field of Earth Science (geosciences) education and as an interesting complement of tourist and recreational activities on site.
Klíčová slova:
gully network; loess; dugouts; Earth Science education
Dokument je dostupný na externích webových stránkách.
Underground Spaces In Bosonožský Hájek Nature Reserve And Their Geoeducation Importance
Bosonožský hájek Natural Reserve (Brno, South Moravia) is a very important site from the Earth Science point of view, however, its geodiversity values have been rather overlooked and omitted in the ...
Some Robust Approaches to Reducing the Complexity of Economic Data
Kalina, Jan
2023 - anglický
The recent advent of complex (and potentially big) data in economics requires modern and effective tools for their analysis including tools for reducing the dimensionality (complexity) of the given data. This paper starts with recalling the importance of Big Data in economics and with characterizing the main categories of dimension reduction techniques. While there have already been numerous techniques for dimensionality reduction available, this work is interested in methods that are robust to the presence of outlying measurements (outliers) in the economic data. Particularly, methods based on implicit weighting assigned to individual observations are developed in this paper. As the main contribution, this paper proposes three novel robust methods of dimension reduction. One method is a dimension reduction within a robust regularized linear regression, namely a sparse version of the least weighted squares estimator. The other two methods are robust versions of feature extraction methods popular in econometrics: robust principal component analysis and robust factor analysis.
Klíčová slova:
dimensionality reduction; Big Data; variable selection; robustness; sparsity
Dokument je dostupný na externích webových stránkách.
Some Robust Approaches to Reducing the Complexity of Economic Data
The recent advent of complex (and potentially big) data in economics requires modern and effective tools for their analysis including tools for reducing the dimensionality (complexity) of the given ...
Statistical Method Selection Matters: Vanilla Methods in Regression May Yield Misleading Results
Kalina, Jan
2023 - anglický
The primary aim of this work is to illustrate the importance of the choice of the appropriate methods for the statistical analysis of economic data. Typically, there exist several alternative versions of common statistical methods for every statistical modeling task and the most habitually used (“vanilla”) versions may yield rather misleading results in nonstandard situations. Linear regression is considered here as the most fundamental econometric model. First, the analysis of a world tourism dataset is presented, where the number of international arrivals is modeled for 140 countries of the world as a response of 14 pillars (indicators) of the Travel and Tourism Competitiveness Index. Heteroscedasticity is clearly recognized in the dataset. However, the Aitken estimator, which would be the standard remedy in such a situation, is revealed here to be very inappropriate, regression quantiles represent a much more suitable solution here. The second illustration with artificial data reveals standard regression quantiles to be unsuitable for data contaminated by outlying values, their recently proposed robust version turns out to be much more appropriate. Both illustrations reveal that choosing suitable methods represent an important (and often difficult) part of the analysis of economic data.
Klíčová slova:
linear regression; assumptions; non-standard situations; robustness; diagnostics
Dokument je dostupný na externích webových stránkách.
Statistical Method Selection Matters: Vanilla Methods in Regression May Yield Misleading Results
The primary aim of this work is to illustrate the importance of the choice of the appropriate methods for the statistical analysis of economic data. Typically, there exist several alternative versions ...
Fractionally Isomorphic Graphs and Graphons
Hladký, Jan; Hng, Eng Keat
2023 - anglický
Fractional isomorphism is a well-studied relaxation of graph isomorphism with a very rich theory. Grebík and Rocha [Combinatorica 42, pp 365–404 (2022)] developed a concept of fractional isomorphism for graphons and proved that it enjoys an analogous theory. In particular, they proved that if two sequences of graphs that are fractionally isomorphic converge to two graphons, then these graphons are fractionally isomorphism. Answering the main question from ibid, we prove the converse of the statement above: If we have two fractionally isomorphic graphons, then there exist sequences of graphs that are fractionally isomorphic converge and converge to these respective graphons. As an easy but convenient corollary of our methods, we get that every regular graphon can be approximated by regular graphs.
Klíčová slova:
graph; graphon; graph fractional isomorphism
Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
Fractionally Isomorphic Graphs and Graphons
Fractional isomorphism is a well-studied relaxation of graph isomorphism with a very rich theory. Grebík and Rocha [Combinatorica 42, pp 365–404 (2022)] developed a concept of fractional isomorphism ...
Summary of the Liquid-Gas Ejector Hydraulic Behavior - Theory and Practice
Gebouský, Ondřej; Haidl, Jan
2023 - anglický
Liquid-gas ejectors (LGEs) are fascinating devices that use the kinetic energy of the liquid jet to entrain and eventually compress the gas. LGEs find applications in both industry and everyday life, e.g., as sprayers. However, a complex and reliable method for LGE design was not available in the open literature until recently. This contribution follows up on our recent works about the hydraulic behavior of LGE with undisturbed and destabilized liquid jets. This paper aims to summarize the device’s complicated hydraulics and characterize its optimal design for three industrially relevant applications - (a) LGE as the vacuum pump, (b) LGE as the gas purification equipment, and (c) LGE as the gas distributor for bioreactors.
Klíčová slova:
liquid-gas ejector; jet pump; design method
Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
Summary of the Liquid-Gas Ejector Hydraulic Behavior - Theory and Practice
Liquid-gas ejectors (LGEs) are fascinating devices that use the kinetic energy of the liquid jet to entrain and eventually compress the gas. LGEs find applications in both industry and everyday life, ...
Přístroje pro měření úhrnu srážek od historie po současnost
Lipina, P.; Procházka, J.; Tesař, Miroslav
2023 - český
Úhrn srážek patří mezi nejdůležitější meteorologické prvky. Má zásadní význam pro tvorbu klimatologických charakteristik, je základem vodní bilance a primárně sledovaným prvkem v předpovědní a výstražné službě. Měření srážek je dlouhodobě zatíženo mnoha nejistotami a je mu proto věnována soustavně náležitá pozornost. \nPrvní měření srážek v Evropě se datuje k 17. století. Pravidelná, ale neúplná, měření srážek na pražské klementinské hvězdárně byla zahájena v roce 1752 (nepřetržitá řada od roku 1804), v Brně to bylo v roce 1803. V roce 1817 M. A. David publikoval první německy psaný návod pro pozorování počasí v Čechách určený dobrovolným pozorovatelům. Zásadní vliv pro vznik meteorologických stanic a měření srážek měly aktivity institucí a různých spolků, například pražské Klementinum, Přírodozpytný spolek v Brně, Ústřední ústav pro meteorologii a zemský magnetismus a jiné. Hydrografická komise pro království české a její hydrometrická sekce byla pod vedením F. J. Studničky založena roku 1875, o významné rozšíření měření srážek se v té době zasloužil v rámci budování sítě lesnických srážkoměrných stanic E. Purkyně.\nJiž více než 200 let dochází k vývoji srážkoměrů a metodik měření srážek. V českých zemích dlouhodobě využívaný manuální srážkoměr Metra 886 byl vyvinut podle rakouského vzoru prof. Kostlivého. Od roku 1995 byla zahájena automatizace měření srážek nejprve klopnými srážkoměry, které jsou postupně nahrazovány srážkoměry váhovými. V odlehlých a lesnatých oblastech jsou testovány alternativní způsoby měření srážek. Tento příspěvek se snaží historii, standardy a vývoj v měření srážek u nás alespoň orientačně přiblížit. The precipitation amount is one of the most important meteorological elements. It is of fundamental importance for the creation of climatological characteristics, it is the basis of the water balance and the primarily monitored element in the forecasting and warning service. Precipitation measurement has been burdened with many uncertainties for a long time and is therefore consistently given due attention.\nThe first measurement of precipitation in Europe dates back to the 17th century. Regular but not complete measurements of precipitation at Prague's Klementine observatory began in 1752 (continuous series since 1804), in Brno in 1803. In 1817, M.A. David wrote the first guide for observing the weather in Bohemia, published in German, intended for volunteer observers. The activities of institutions and various associations, such as the Prague Klementinum, the Natural Research Society in Brno, the Central Institute for Meteorology and Earth Magnetism and others, had a fundamental influence on the establishment of meteorological stations and precipitation measurements. The Hydrographic Commission for the Kingdom of the Czech Republic and its hydrometric section were founded in 1875 under the leadership of F. J. Studnička E. Purkyně was responsible for the significant expansion of precipitation measurement at that time as part of the construction of a network of forest precipitation measuring stations. \nFor more than 200 years, rain gauges and precipitation measurements have been developed. The Metra 886 manual rain gauge, which has been used for a long time in the Czech lands, was developed according to the Austrian model of prof. Kostlivý. Since 1995, the automation of rainfall measurement was started, first with tipping bucket raingauges, which are gradually being replaced by weighing raingauges. Alternative methods of measuring precipitation are being tested in\nremote and forested areas. This post tries to bring the history, standards and development of precipitation measurement in our country at least as a guide.
Klíčová slova:
rain gauge; measurement date; measurement history; meteorological station; guide for observers
Dokument je dostupný na externích webových stránkách.
Přístroje pro měření úhrnu srážek od historie po současnost
Úhrn srážek patří mezi nejdůležitější meteorologické prvky. Má zásadní význam pro tvorbu klimatologických charakteristik, je základem vodní bilance a primárně sledovaným prvkem v předpovědní a ...
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