Počet nalezených dokumentů: 402
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Excessive extrapolations of Einstein's equations
Křížek, Michal; Somer, L.
2020 - anglický
The standard cosmological model is surprisingly quite thoroughly investigated even though it possesses many paradoxes. We present several arguments indicating why excessive extrapolations of Einstein's equations to cosmological distances are questionable. First, we show how to express explicitly the first of Einstein's 10 partial differential equations to demonstrate their extremely large complexity. Therefore, it would be very difficult to find their solution for two or more bodies to model, e.g., the evolution of the Solar system. Further, we present some unexpected failures of the Schwarzschild and Friedmann solution of these equations. Then we explain why application of Einstein's equations to the whole universe represents incorrect extrapolations that lead to dark matter, dark energy, and several unrealistic situations. Finally, we give 10 further arguments showing why celebrated Einstein's equations do not describe reality well. Klíčová slova: Einstein's equations; Schwarzschild solution; Friedmann equation Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
Excessive extrapolations of Einstein's equations

The standard cosmological model is surprisingly quite thoroughly investigated even though it possesses many paradoxes. We present several arguments indicating why excessive extrapolations of ...

Křížek, Michal; Somer, L.
Matematický ústav, 2020

A critical review of paradoxes in the special theory of relativity
Křížek, Michal
2020 - anglický
We show that the Doppler effect and aberration of light can produce more dominant and entirely opposite effects for relativistic speeds than those predicted by the Special Theory of Relativity, in particular, the clock paradox, time dilatation, and length contraction. For instance, an observer will measure a higher frequency of an approaching clock than the same clock has at rest. We also prove that under certain conditions an approaching bar on a photo may seem to have a larger length for a relativistic speed than at rest. Klíčová slova: Lorentz transformation; theory of groups; inertial systems Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
A critical review of paradoxes in the special theory of relativity

We show that the Doppler effect and aberration of light can produce more dominant and entirely opposite effects for relativistic speeds than those predicted by the Special Theory of Relativity, in ...

Křížek, Michal
Matematický ústav, 2020

Note on the problem of compressible non-Newtonian fluids
Caggio, M.; Nečasová, Šárka
2019 - anglický
The aim of the paper is to consider the compressible non-Newtonian fluids of power law type when the viscosity coeffcients depend not only on invariants of velocity field but also on the density. We introduce approximation scheme using model of multipolar fluids. After then passing with higher viscosity to zero we get the measure valued solution of the problem. Klíčová slova: non-Newtonian fluid; compressible fluid; multipolar fluid; measure-valued solution Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
Note on the problem of compressible non-Newtonian fluids

The aim of the paper is to consider the compressible non-Newtonian fluids of power law type when the viscosity coeffcients depend not only on invariants of velocity field but also on the density. We ...

Caggio, M.; Nečasová, Šárka
Matematický ústav, 2019

Programs and Algorithms of Numerical Mathematics 19 : Hejnice, June 24-29, 2018 : proceedings of seminar
Chleboun, J.; Kůs, Pavel; Přikryl, Petr; Rozložník, Miroslav; Segeth, Karel; Šístek, Jakub; Vejchodský, Tomáš
2019 - anglický
These proceedings contain peer-reviewed papers that are based on the invited lectures, survey lectures, short communications, and posters presented at the 19th seminar Programs and Algorithms of Numerical Mathematics (PANM) held in the International Center for Spiritual Rehabilitation, Hejnice, Czech Republic, June 24-29, 2018. The seminar was organized by the Institute of Mathematics of the Czech Academy of Sciences under the auspices of EU-MATHS-IN.cz, Czech Network for Mathematics in Industry, and with the financial support provided by the RSJ Foundation. It continued the previous seminars on mathematical software and numerical methods held (biennially, with only one exception) in Alšovice, Bratříkov, Janov nad Nisou, Kořenov, Lázně Libverda, Dolní Maxov, and Prague in the period 1983-2016. The objective of this series of seminars is to provide a forum for presenting and discussing advanced topics in numerical analysis, computer implementation of numerical algorithms, new approaches to mathematical modeling, and single- or multi-processor applications of computational methods. Klíčová slova: numerical mathematics Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
Programs and Algorithms of Numerical Mathematics 19 : Hejnice, June 24-29, 2018 : proceedings of seminar

These proceedings contain peer-reviewed papers that are based on the invited lectures, survey lectures, short communications, and posters presented at the 19th seminar Programs and Algorithms of ...

Chleboun, J.; Kůs, Pavel; Přikryl, Petr; Rozložník, Miroslav; Segeth, Karel; Šístek, Jakub; Vejchodský, Tomáš
Matematický ústav, 2019

On the mechanisms of dimensional transition in stably stratified turbulent fluid layers
Caggio, M.; Bodnár, Tomáš; Schiavon, M.
2019 - anglický
The purpose of this short review communication is to present some recent results on the effects of stable density stratification on the three-dimensional turbulent dynamics of 'thin' fluid layers forced at intermediate scales. In particular, how the strati cation and the confinement affect the mechanism of kinetic and potential energy transfer between different scales. Results on two-dimensional vertically stratifed flows and possible applications for stably stratifed atmospheric boundary layer will be shortly discussed. Klíčová slova: stable density stratification; kinetic and potential energy transfer; atmospheric boundary layer Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
On the mechanisms of dimensional transition in stably stratified turbulent fluid layers

The purpose of this short review communication is to present some recent results on the effects of stable density stratification on the three-dimensional turbulent dynamics of 'thin' fluid layers ...

Caggio, M.; Bodnár, Tomáš; Schiavon, M.
Matematický ústav, 2019

Numerical tests of far-field boundary conditions for stably stratified flows
Bodnár, Tomáš; Fraunié, P.; Řezníček, Hynek
2019 - anglický
This numerical study presents the results of simulations of stably stratified wall-bounded flows. The effect of artificial far-field boundary conditions is studied in detail. The standard homogeneous Neumann condition for pressure is replaced by a non-homogeneous condition depending on local velocity and its gradient. The two-dimensional tests are performed for the case of flow over a low isolated hill. The simulations on computational domains with three different heights are discussed to evaluate the performance of the new far-field artifcial boundary condition. The model is based on Boussinesq approximation of non-homogeneous Navier-Stokes equations, solved using artificial compressibility method, looking for a steady solution. Klíčová slova: boussinesq approximation; stable stratification; far-field boundary condition Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
Numerical tests of far-field boundary conditions for stably stratified flows

This numerical study presents the results of simulations of stably stratified wall-bounded flows. The effect of artificial far-field boundary conditions is studied in detail. The standard homogeneous ...

Bodnár, Tomáš; Fraunié, P.; Řezníček, Hynek
Matematický ústav, 2019

Multivariate smooth interpolation that employs polyharmonic functions
Segeth, Karel
2019 - anglický
We study the problém of construction of the smooth interpolation formula presented as the minimizer of suitable functionals subject to interpolation constraints. We present a procedure for determining the interpolation formula that in a natural way leads to a linear combination of polyharmonic splines complemented with lower order polynomials therms. In general, such formulae can be very useful e.g. in geographic information systems or computer aided geometric design. A simple computational example is presented. Klíčová slova: data interpolation; smooth interpolation; polyharmonic spline; radial basis function Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
Multivariate smooth interpolation that employs polyharmonic functions

We study the problém of construction of the smooth interpolation formula presented as the minimizer of suitable functionals subject to interpolation constraints. We present a procedure for determining ...

Segeth, Karel
Matematický ústav, 2019

Analysis of the turbulence parameterisations for the atmospheric surface layer
Caggio, Matteo; Bodnár, Tomáš
2018 - anglický
The purpose of this short communication is to present a method that aims to express the turbulent variables in the atmospheric surface-layer in function of the stability of the atmosphere. The case of very stable conditions (strong strati cation), where theoretical approaches provide conflicting results (see Luhar et al. [11]), is analysed in detail to provide some insight into the limits of applicability for some of the most popular models of turbulence. The problem of the existence of the critical flux Richardson number is also taken into account. Klíčová slova: atmospheric boundary layer; Monin-Obukhov similarity theory; turbulence parameterisations; strong strati cation Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
Analysis of the turbulence parameterisations for the atmospheric surface layer

The purpose of this short communication is to present a method that aims to express the turbulent variables in the atmospheric surface-layer in function of the stability of the atmosphere. The case of ...

Caggio, Matteo; Bodnár, Tomáš
Matematický ústav, 2018

Classification of distances in cosmology
Křížek, Michal; Mészáros, A.
2018 - anglický
In cosmology many different distances are defined: angular, comoving, Euclidean, Hubble, light-year, luminosity, Minkowski, parallax, proper motion, redshift, ... distance. There is not one single natural distance, since the universe is expanding, curved, and we look back in time. In this survey paper we will concentrate on geometrical interpretations of the above-mentioned distances. Klíčová slova: standard cosmological model; cosmological principle; Friedmann equation; cosmological parameters; Einstein static universe Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
Classification of distances in cosmology

In cosmology many different distances are defined: angular, comoving, Euclidean, Hubble, light-year, luminosity, Minkowski, parallax, proper motion, redshift, ... distance. There is not one single ...

Křížek, Michal; Mészáros, A.
Matematický ústav, 2018

Parallel domain decomposition solver for flows in hydrostatic bearings
Hanek, Martin; Šístek, Jakub; Burda, P.; Stach, E.
2018 - anglický
We perform simulations of oil flow in hydrostatic bearings. Stationary incompressible three-dimensional flow governed by the Navier-Stokes equations is considered. The finite element method is used for discretization. The arising nonlinear system of algebraic equations is linearized using the Picard’s iteration, and the Balancing Domain Decomposition based on Constraints (BDDC) method is used to solve the linear systems of equations. The solver is first validated with an experiment for the case of a bearing without motion, and it is then applied to simulation of flow in a sliding bearing. Klíčová slova: hydrostatic bearings; BDDC Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
Parallel domain decomposition solver for flows in hydrostatic bearings

We perform simulations of oil flow in hydrostatic bearings. Stationary incompressible three-dimensional flow governed by the Navier-Stokes equations is considered. The finite element method is used ...

Hanek, Martin; Šístek, Jakub; Burda, P.; Stach, E.
Matematický ústav, 2018

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