Počet nalezených dokumentů: 426
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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

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

Mathematical Thermodynamics of Viscous Fluids
Feireisl, Eduard
2017 - anglický
This course is a short introduction to the mathematical theory of the motion of viscous fluids. We introduce the concept of weak solution to the Navier-Stokes-Fourier system and discuss its basic properties. In particular, we construct the weak solutions as a suitable limit of a mixed numerical scheme based on a combination of the finite volume and finite elements method. The question of stability and robustness of various classes of solutions is addressed with the help of the relative (modulated) energy functional. Related results concerning weak-strong uniqueness and conditional regularity of weak solutions are presented. Finally, we discuss the asymptotic limit when viscosity of the fluid tends to zero. Several examples of ill- posedness for the limit Euler system are given and an admissibility criterion based on the viscous approximation is proposed. Klíčová slova: thermodynamics of viscous fluid; Navier-Stokes-Fourier system Plné texty jsou dostupné na vyžádání prostřednictvím repozitáře Akademie věd.
Mathematical Thermodynamics of Viscous Fluids

This course is a short introduction to the mathematical theory of the motion of viscous fluids. We introduce the concept of weak solution to the Navier-Stokes-Fourier system and discuss its basic ...

Feireisl, Eduard
Matematický ústav, 2017

Observing how future primary school teachers reason and generalize: the case of number triangles and Concept Cartoons
Samková, L.; Tichá, Marie
2017 - anglický
The contribution focuses on the possibility to use an educational tool called Concept Cartoons as a diagnostic instrument in problem solving and problem posing activities of future primary school teachers. The aim of the presented study is to observe which aspects of future primary school teachers' knowledge related to reasoning and generalization could be investigated through Concept Cartoons that are based on a substantial learning environment called "Number triangles". Klíčová slova: future primary school teachers; reasoning; generalization Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Observing how future primary school teachers reason and generalize: the case of number triangles and Concept Cartoons

The contribution focuses on the possibility to use an educational tool called Concept Cartoons as a diagnostic instrument in problem solving and problem posing activities of future primary school ...

Samková, L.; Tichá, Marie
Matematický ústav, 2017

Average contra-rotation and co-rotation of line segments for flow field analysis
Šístek, Jakub; Kolář, Václav
2017 - anglický
The earlier concept of the average co-rotation of infinitesimal radial line segments near a point is extended to the case of contra-rotation. The tensor of the contra-rotation is introduced and averaged over "all planar cross sections" going through the examined point. Both the average contra-rotation and co-rotation, representing shear-free quantities, are applied to describe a complex flow structure. Klíčová slova: fluid mechanics; contra-rotation Plné texty jsou dostupné na vyžádání prostřednictvím repozitáře Akademie věd.
Average contra-rotation and co-rotation of line segments for flow field analysis

The earlier concept of the average co-rotation of infinitesimal radial line segments near a point is extended to the case of contra-rotation. The tensor of the contra-rotation is introduced and ...

Šístek, Jakub; Kolář, Václav
Matematický ústav, 2017

Crandall-Rabinowitz type bifurcation for non-differentiable perturbations of smooth mappings
Recke, L.; Väth, Martin; Kučera, Milan; Navrátil, J.
2017 - anglický
We consider abstract equations of the type ..., where lambda is a bifurcation parameter and tau is a perturbation parameter. We suppose that ... for all lambda and tau, F is smooth and the unperturbed equation ... describes a Crandall-Rabinowitz bifurcation in lambda=0, that is, two half-branches of nontrivial solutions bifurcate from the trivial solution in lambda=0. Concerning G, we suppose only a certain Lipschitz condition; in particular, G is allowed to be non-differentiable. We show that for fixed small ... there exist also two half-branches of nontrivial solutions to the perturbed equation, but they bifurcate from the trivial solution in two bifurcation points, which are different, in general. Moreover, we determine the bifurcation directions of those two half-branches, and we describe, asymptotically as ..., how the bifurcation points depend on tau. Finally, we present applications to boundary value problems for quasilinear elliptic equations and... Klíčová slova: nonsmooth equation; Lipschitz bifurcation branch; formula for the bifurcation direction Plné texty jsou dostupné na vyžádání prostřednictvím repozitáře Akademie věd.
Crandall-Rabinowitz type bifurcation for non-differentiable perturbations of smooth mappings

We consider abstract equations of the type ..., where lambda is a bifurcation parameter and tau is a perturbation parameter. We suppose that ... for all lambda and tau, F is smooth and the unperturbed ...

Recke, L.; Väth, Martin; Kučera, Milan; Navrátil, J.
Matematický ústav, 2017

Clusterization of correlation functions
Zuevsky, Alexander
2017 - anglický
Using the Zhu recursion formulas for correlation functions for vertex operator algebras, we introduce a cluster algebra structure over a non-commutative set of variables. Klíčová slova: vertex algebras; correlation functions; cluster algebras Plné texty jsou dostupné na vyžádání prostřednictvím repozitáře Akademie věd.
Clusterization of correlation functions

Using the Zhu recursion formulas for correlation functions for vertex operator algebras, we introduce a cluster algebra structure over a non-commutative set of variables.

Zuevsky, Alexander
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 vyžádání prostřednictvím repozitáře Akademie věd.
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 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

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