Počet nalezených dokumentů: 389
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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

Neglected gravitational redshift in detections of gravitational waves
Křížek, Michal; Somer, L.
2018 - anglický
In 2016, the letter [1] about the first detection of gravitational waves was published. They were generated by two merging black holes that had approximately 36 and 29 Sun’s masses. However, the authors have not taken into account a large gravitational redshift of this binary system, which is a direct consequence of time dilation in a strong gravitational field. Thus the proposed masses are overestimated. In our paper we also give other arguments for this statement. Klíčová slova: gravitational redshift; time dilatation; black holes; wavelets Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
Neglected gravitational redshift in detections of gravitational waves

In 2016, the letter [1] about the first detection of gravitational waves was published. They were generated by two merging black holes that had approximately 36 and 29 Sun’s masses. However, the ...

Křížek, Michal; Somer, L.
Matematický ústav, 2018

Assessing a teacher’s competence for implementation of inquiry based mathematics education from a discussion of open geometrical situations
Roubíček, Filip
2017 - anglický
The study is focused on the possibility to assess and develop primary teachers’ abilities to implement some principles of inquiry based mathematics education into their teaching practice. The requirements on a primary teacher and their competence are assessed through a joint discussion of open geometrical situations presented through Concept Cartoons. Teachers’ written comments and notes and verbal statements expressed in the discussion of four geometrical problems were analysed and presented. Klíčová slova: inguiry based mathematics education; primary teacher; elementary geometry Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Assessing a teacher’s competence for implementation of inquiry based mathematics education from a discussion of open geometrical situations

The study is focused on the possibility to assess and develop primary teachers’ abilities to implement some principles of inquiry based mathematics education into their teaching practice. The ...

Roubíček, Filip
Matematický ústav, 2017

Sine-Gordon model in the homogeneous higher grading
Zuevsky, Alexander
2017 - anglický
A construction of equations and solutions for the sine-Gordon model in the homogeneous grading as an example of higher grading a ne Toda models are considered. Klíčová slova: soliton solutions; affine Toda modes; homogeneous sine-Gordon model Plné texty jsou dostupné na vyžádání prostřednictvím repozitáře Akademie věd.
Sine-Gordon model in the homogeneous higher grading

A construction of equations and solutions for the sine-Gordon model in the homogeneous grading as an example of higher grading a ne Toda models are considered.

Zuevsky, Alexander
Matematický ústav, 2017

Courant algebroid connections and string effective actions
Jurčo, B.; Vysoký, Jan
2017 - anglický
Courant algebroids are a natural generalization of quadratic Lie algebras, appearing in various contexts in mathematical physics. A connection on a Courant algebroid gives an analogue of a covariant derivative compatible with a given fiber-wise metric. Imposing further conditions resembling standard Levi-Civita connections, one obtains a class of connections whose curvature tensor in certain cases gives a new geometrical description of equations of motion of low energy effective action of string theory. Two examples are given. One is the so called symplectic gravity, the second one is an application to the the so called heterotic reduction. All necessary definitions, propositions and theorems are given in a detailed and self-contained way. Klíčová slova: Courant algebroid connections; low-energy effective actions; Levi-Civita connections Plné texty jsou dostupné na vyžádání prostřednictvím repozitáře Akademie věd.
Courant algebroid connections and string effective actions

Courant algebroids are a natural generalization of quadratic Lie algebras, appearing in various contexts in mathematical physics. A connection on a Courant algebroid gives an analogue of a covariant ...

Jurčo, B.; Vysoký, Jan
Matematický ústav, 2017

Genus two prime form formula for vertex operator characters
Zuevsky, Alexander
2017 - anglický
We find an expression for the self-sewn genus two Riemann surface counterpart of the torus formula for for an $n$-vertex operator character for the Heisenberg vertex operator algebra an $n$-point correlation function for a vertex operator algebra module with complex parameterization of corresponding states. Klíčová slova: prime forms; vertex operator algebras; correlation functions; prime form identities Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Genus two prime form formula for vertex operator characters

We find an expression for the self-sewn genus two Riemann surface counterpart of the torus formula for for an $n$-vertex operator character for the Heisenberg vertex operator algebra an $n$-point ...

Zuevsky, Alexander
Matematický ústav, 2017

On the boundary conditions in the numerical simulation of stably stratified fluids flows
Bodnár, Tomáš; Fraunié, P.
2017 - anglický
This paper presents the results of a numerical study of the stably stratified flow over a low smooth hill. The emphasize is on certain problems related to artificial boundary conditions used in the numerical simulations. The numerical results of three-dimensional simulations are shown for a range of Froude and Reynolds numbers in order to demonstrate the varying importance of these boundary issues in different flow regimes. The simulations were performed using the Boussinesq approximation model solved by a high-resolution numerical code. The in-house developed code is based on compact finite-difference discretization in space and Strong Stability Preserving Runge-Kutta time integration. Klíčová slova: Boussinesq approximation; stable stratification; compact finite-difference Plné texty jsou dostupné na vyžádání prostřednictvím repozitáře Akademie věd.
On the boundary conditions in the numerical simulation of stably stratified fluids flows

This paper presents the results of a numerical study of the stably stratified flow over a low smooth hill. The emphasize is on certain problems related to artificial boundary conditions used in the ...

Bodnár, Tomáš; Fraunié, P.
Matematický ústav, 2017

Problem posing in prospective primary school teachers´ education: Case of Concept Cartoons
Hošpesová, A.; Tichá, Marie
2017 - anglický
The presentation will discuss creation of Concept Cartoons as a possible way to support the development and refinement of prospective primary teachers' pedagogical concept knowledge. Klíčová slova: problem posing; Concept Cartoons; PCK of prospective teachers Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Problem posing in prospective primary school teachers´ education: Case of Concept Cartoons

The presentation will discuss creation of Concept Cartoons as a possible way to support the development and refinement of prospective primary teachers' pedagogical concept knowledge.

Hošpesová, A.; Tichá, Marie
Matematický ústav, 2017

On the motion of chemically reacting fluids through porous medium
Feireisl, Eduard; Mikyška, J.; Petzeltová, Hana; Takáč, P.
2017 - anglický
We consider a parabolic-hyperbolic system of nonlinear partial differential equations modeling the motion of a chemically reacting mixture through porous medium. The existence of classical as well as weak solutions is established under several physically relevant choices of the constitutive equations and relevant boundary conditions. Klíčová slova: chemically reacting fluid; porous medium; DiPerna Lions theory Plné texty jsou dostupné na vyžádání prostřednictvím repozitáře Akademie věd.
On the motion of chemically reacting fluids through porous medium

We consider a parabolic-hyperbolic system of nonlinear partial differential equations modeling the motion of a chemically reacting mixture through porous medium. The existence of classical as well as ...

Feireisl, Eduard; Mikyška, J.; Petzeltová, Hana; Takáč, P.
Matematický ústav, 2017

VSI electromagnetic fields
Ortaggio, Marcello; Pravda, Vojtěch
2017 - anglický
A p-form F is VSI (i.e., all its scalar invariants of arbitrary order vanish) in a n-dimensional spacetime if and only if it is of type N, its multiple null direction is "degenerate Kundt", and ...F = 0. This recent result is reviewed in the present contribution and its main consequences are summarized. In particular, a subset of VSI Maxwell fields possesses a universal property, i.e., they also solve (virtually) any generalized (non-linear and with higher derivatives) electrodynamics, possibly also coupled to Einstein's gravity. Klíčová slova: p-form electromagnetism; VSI fields Plné texty jsou dostupné na vyžádání prostřednictvím repozitáře Akademie věd.
VSI electromagnetic fields

A p-form F is VSI (i.e., all its scalar invariants of arbitrary order vanish) in a n-dimensional spacetime if and only if it is of type N, its multiple null direction is "degenerate Kundt", and ...F = ...

Ortaggio, Marcello; Pravda, Vojtěch
Matematický ústav, 2017

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