Number of found documents: 16108
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GA 19-07635S: Outputs and Results
Rehák, Branislav
2023 - English
This manuscript aims to deliver a survey of results obtained during the solution of the project No. GA19-07635S of the Czech Science Foundation. The timespan dedicated to the work on this project was 1.3.2019 - 30.6.2022. The main area dealt with were\nnonlinear multi-agent systems and their synchronization, further, attention was paid to some auxiliary results in the area of nonlinear observers. This Report briefly introduces the Project, provides a summary of the results obtained and also sketches an outline how these results will be applied and extended in future. Keywords: multi-agent systems; nonlinear multi-agent systems; synchronization Fulltext is available at external website.
GA 19-07635S: Outputs and Results

This manuscript aims to deliver a survey of results obtained during the solution of the project No. GA19-07635S of the Czech Science Foundation. The timespan dedicated to the work on this project was ...

Rehák, Branislav
Ústav teorie informace a automatizace, 2023

Some modifications of the limited-memory variable metric optimization methods
Vlček, Jan; Lukšan, Ladislav
2023 - English
Several modifications of the limited-memory variable metric (or quasi-Newton) line search methods for large scale unconstrained optimization are investigated. First the block version of the symmetric rank-one (SR1) update formula is derived in a similar way as for the block BFGS update in Vlˇcek and Lukˇsan (Numerical Algorithms 2019). The block SR1 formula is then modified to obtain an update which can reduce the required number of arithmetic operations per iteration. Since it usually violates the corresponding secant conditions, this update is combined with the shifting investigated in Vlˇcek and Lukˇsan (J. Comput. Appl. Math. 2006). Moreover, a new efficient way how to realize the limited-memory shifted BFGS method is proposed. For a class of methods based on the generalized shifted economy BFGS update, global convergence is established. A numerical comparison with the standard L-BFGS and BNS methods is given. Keywords: unconstrained minimization; variable metric methods; limited-memory methods; variationally derived methods; arithmetic operations reduction; global convergence Available in a digital repository NRGL
Some modifications of the limited-memory variable metric optimization methods

Several modifications of the limited-memory variable metric (or quasi-Newton) line search methods for large scale unconstrained optimization are investigated. First the block version of the symmetric ...

Vlček, Jan; Lukšan, Ladislav
Ústav informatiky, 2023

Turbine blade linkages in reduced modal synthesis model
Pešek, Luděk; Šnábl, Pavel
2022 - English
The paper is the first stage of our modelling turbine blade linkages in reduced modal synthesis model. The modal synthesis method is used for the dynamic behaviour studies of turbine bladed wheels with frictional inter-blade linkages and in case of the microslips the stiffening effect of the linkages play an important role in wheel dynamics. The paper presents the first results of modal analysis of the wheel when springs were used to substitute the linkages in the modal synthesis model. Keywords: bladed wheel; reduced model; tie-boss; shroud; stiffening Available at various institutes of the ASCR
Turbine blade linkages in reduced modal synthesis model

The paper is the first stage of our modelling turbine blade linkages in reduced modal synthesis model. The modal synthesis method is used for the dynamic behaviour studies of turbine bladed wheels ...

Pešek, Luděk; Šnábl, Pavel
Ústav termomechaniky, 2022

XXIV Czech-Polish seminar: Structural and ferroelectric phase transitions: Book of abstracts and program
Pokorný, Jan; Bubnov, Alexej; Janovská, Marie
2022 - English
This is the Book of Abstracts for the XXIV Czech-Polish Seminar (CPSEM-2022 conference) held in Harrachov (Czech Republic) on May 23 - 27, 2022. The special objective of the conference is expressed in the conference subtitle: Structural and Ferroelectric Phase Transitions. The continuous worldwide interest to this conference series is proving that it has a respected position within the series of International/European conferences covering all interdisciplinary field of the research related to structural and ferroelectric phase transitions. At the CPSEM-2022 conference there were about 100 participants from 10 countries delivered 8 tutorial lectures for early stage researchers, 8 invited lectures and selected 34 oral contributions. More than 55 posters were presented during two poster sessions. Keywords: Czech-Polish seminar; structural and ferroelectric phase transition Available at various institutes of the ASCR
XXIV Czech-Polish seminar: Structural and ferroelectric phase transitions: Book of abstracts and program

This is the Book of Abstracts for the XXIV Czech-Polish Seminar (CPSEM-2022 conference) held in Harrachov (Czech Republic) on May 23 - 27, 2022. The special objective of the conference is expressed in ...

Pokorný, Jan; Bubnov, Alexej; Janovská, Marie
Fyzikální ústav, 2022

Modeling the spread of loanwords in South-East Asia using sailing navigation software and Bayesian networks
Kratochvíl, F.; Kratochvíl, Václav; Saad, G.; Vomlel, Jiří
2022 - English
A loanword is a word permanently adopted from one language and incorporated into another language without translation. In this paper, we study loanwords in the South-East Asia Archipelago, home to a large number of languages. Our paper is inspired by the works of Hoffmann et al. (2021) Bayesian methods are applied to probabilistic modeling of family trees representing the history of language families and by Haynie et al. (2014) modeling the diffusion of a special class of loanwords, so-called Wanderw ̈orter in languages of Australia, North America, and South America. We assume that in the South-East Asia Archipelago Wanderwörter spread along specific maritime trade routes whose geographical characteristics can help unravel the history of Wanderwörter diffusion in the area. For millennia trade was conducted using sailing ships which were constrained by the monsoon system and in certain areas also by strong sea currents. Therefore rather than the geographical distances, the travel times of sailing ships should be considered as a major factor determining the intensity of contact among cultures. We use sailing navigation software to estimate travel times between different ports and show that the estimated travel times correspond well to the travel times of a Chinese map of the sea trade routes from the early seventeenth century. We model the spread of loanwords using a probabilistic graphical model - a Bayesian network. We design a novel heuristic Bayesian network structure learning algorithm that learns the structure as a union of spanning trees for graphs of all loanwords in the training dataset. We compare this algorithm with BIC optimal Bayesian networks by measuring how well these models predict the true presence/absence of a loanword. Interestingly, Bayesian networks learned by our heuristic spanning tree-based algorithm provide better results than the BIC optimal Bayesian networks. Keywords: loanwords; Bayesian methods; probabilistic graphical model Fulltext is available at external website.
Modeling the spread of loanwords in South-East Asia using sailing navigation software and Bayesian networks

A loanword is a word permanently adopted from one language and incorporated into another language without translation. In this paper, we study loanwords in the South-East Asia Archipelago, home to a ...

Kratochvíl, F.; Kratochvíl, Václav; Saad, G.; Vomlel, Jiří
Ústav teorie informace a automatizace, 2022

Approaches to dynamical analysis of rotors with parameters of uncertain magnitudes
Zapoměl, Jaroslav; Kozánek, Jan; Košina, Jan; Cibulka, Jan
2022 - English
In many cases, the rotor configuration or loading characteristics are described by parameters of uncertain magnitude. Several procedures were developed to analyse such systems. This paper deals with the approach based on application of the fuzzy numbers. The investigated mechanical system is a rotor supported by hydrodynamic bearings. The parameters of its loading have uncertain values. Keywords: rotors; uncertain parameters; fuzzy numbers approach Available at various institutes of the ASCR
Approaches to dynamical analysis of rotors with parameters of uncertain magnitudes

In many cases, the rotor configuration or loading characteristics are described by parameters of uncertain magnitude. Several procedures were developed to analyse such systems. This paper deals with ...

Zapoměl, Jaroslav; Kozánek, Jan; Košina, Jan; Cibulka, Jan
Ústav termomechaniky, 2022

100 years of the Friedmann equation
Křížek, Michal
2022 - English
In 1922, Alexander Friedmann applied Einstein’s equations to a three-dimensional sphere to describe the evolution of our universe. In this way he obtained a nonlinear ordinary differential equation (called after him) for the expansion function representing the radius of that sphere. At present, the standard cosmological ΛCDM model of the universe is based just on the Friedmann equation. It needs a significant amount of dark matter, about six times that of the usual baryonic matter, besides an even larger amount of dark energy to be consistent with the real universe. But to date, both dark matter and dark energy have remained without concrete evidence based on direct physical measurements. We present several arguments showing that such a claimed amount of dark matter and dark energy can only be the result of vast overestimation, incorrect extrapolations, and that it does not correspond to the real universe. The spatial part of our universe seems to be locally flat and thus it can be locally modeled by the Euclidean space. However, Friedmann did not consider the flat space with zero curvature. Therefore, in the second part of this paper we will derive a general form of the corresponding metric tensor satisfying Einstein’s equations with zero right-hand side. Keywords: Einstein's equations; modeling error; incorrect extrapolations; dark matter Fulltext is available at external website.
100 years of the Friedmann equation

In 1922, Alexander Friedmann applied Einstein’s equations to a three-dimensional sphere to describe the evolution of our universe. In this way he obtained a nonlinear ordinary differential equation ...

Křížek, Michal
Matematický ústav, 2022

Nová regionální reanalýza pro střední Evropu PERUN/Reanalysis
Pokorná, Lucie; Belda, M.; Beranová, Romana
2022 - Czech
Tento příspěvek se věnuje obecnému popisu atmosférických reanalýz, jejich koncepci a roli při výzkumu atmosféry a klimatu. Představuje regionální reanalýzu PERUN/Reanalysis, která vznikla s využitím numerického modelu ALADIN v ČHMÚ v letech 2021-2022. The contribution describes atmospheric reanalyses in general, their concept and role in atmospheric and climate research. The novel PERUN/Reanalysis regional reanalysis based on the ALADIN numerical model opreating at the Czech National Institute of Hydrometeorology is presented. Keywords: assimilation; model Fulltext is available at external website.
Nová regionální reanalýza pro střední Evropu PERUN/Reanalysis

Tento příspěvek se věnuje obecnému popisu atmosférických reanalýz, jejich koncepci a roli při výzkumu atmosféry a klimatu. Představuje regionální reanalýzu PERUN/Reanalysis, která vznikla s využitím ...

Pokorná, Lucie; Belda, M.; Beranová, Romana
Ústav fyziky atmosféry, 2022

Cosmology on Small Scales 2022: Dark Energy and the Local Hubble Expansion Problem
Křížek, Michal; Dumin, Y. V.
2022 - English
One hundred years ago, Russian mathematician and physicist Alexander A. Friedmann applied the system of Einstein equations to the three-dimensional sphere with a time varying radius. In this way, he obtained a nonlinear ordinary differential equation which is called the Friedmann equation after him and serves now as a cornerstone of the standard cosmological model. Unfortunately, it is well known that this model exhibits a number of paradoxes. Thus, the main goal of the CSS 2022 Conference Proceedings is to discuss whether and how the Friedmann equation can be applied at the various spatial scales, from our local cosmic neighborhood up to the whole Universe, and if the existence of dark matter and dark energy are merely artifacts of the excessive extrapolations. Keywords: Friedmann equation; dark matter; dark energy; local Hubble expansion Fulltext is available at external website.
Cosmology on Small Scales 2022: Dark Energy and the Local Hubble Expansion Problem

One hundred years ago, Russian mathematician and physicist Alexander A. Friedmann applied the system of Einstein equations to the three-dimensional sphere with a time varying radius. In this way, he ...

Křížek, Michal; Dumin, Y. V.
Matematický ústav, 2022

Současný stav geofyzikálních výzkumů a průzkumů v České republice
Kaláb, Zdeněk
2022 - Czech
Základní výzkum fyzikálních polí Země je v ČR řešen výzkumnou infrastrukturou CzechGeo/EPOS, což je ucelený systém pozorování geofyzikálních polí provozovaný geovědními institucemi České republiky. CzechGeo/EPOS je distribuovaná, vícevrstvá, mnohaoborová infrastruktura založená na sběru a poskytování dat z geofyzikálních monitorovacích sítí. V oblasti průzkumných geofyzikálních prací je patrně největší akcí průzkum potenciálních lokalit pro hlubinné úložiště jaderného odpadu. Nejedná se pouze o průzkum na potenciálních lokalitách, ale také aktivity prováděné v podzemním výzkumném pracovišti Bukov. Jedním z velkých úkolů, který na užitou geofyziku v krátké budoucnosti čeká, je podíl na průzkumech pro vysokorychlostní železniční trať. Aplikace geofyzikálních metod ale pronikají stále více do dalších oborů.\n\n The basic research of the Earth's physical fields in the Czech Republic is solved by the research infrastructure CzechGeo/EPOS, which is a comprehensive system for observing geophysical fields operated by geoscience institutions in the Czech Republic. CzechGeo/EPOS is distributed multilayer research infrastructure based on acquisition and distribution of data from geophysical monitoring networks. In the area of exploratory geophysical works, the survey of potential sites for the deep repository of nuclear waste is probably the biggest topic. This is not only a survey of potential sites, but also activities at the Bukov underground laboratory. One of the major challenges facing applied geophysics in the near future is to participate in surveys for the high-speed railway line. Applications of geophysical methods are increasingly penetrating also other fields.\n Keywords: geophysics; CzechGeo/EPOS; deep repository of nuclear waste; Bukov Underground Research Facility; geophysical survey Available on request at various institutes of the ASCR
Současný stav geofyzikálních výzkumů a průzkumů v České republice

Základní výzkum fyzikálních polí Země je v ČR řešen výzkumnou infrastrukturou CzechGeo/EPOS, což je ucelený systém pozorování geofyzikálních polí provozovaný geovědními institucemi České republiky. ...

Kaláb, Zdeněk
Ústav geoniky, 2022

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