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Growth of orbital resonances around a black hole surrounded by matter
Stratený, Michal; Lukes-Gerakopoulos, Georgios
2023 - anglický
This work studies the dynamics of geodesic motion within a curved spacetime around a Schwarzschild black hole, perturbed by a gravitational field of a far axisymmetric distribution of mass enclosing the system. This spacetime can serve as a versatile model for a diverse range of astrophysical scenarios and, in particular, for extreme mass ratio inspirals as in our work. We show that the system is non-integrable by employing Poincaré surface of section and rotation numbers. By utilising the rotation numbers, the widths of resonances are calculated, which are then used in establishing the relation between the underlying perturbation parameter driving the system from integrability and the quadrupole parameter characterising the perturbed metric. This relation allows us to estimate the phase shift caused by the resonance during an inspiral.
Klíčová slova:
geodesic motion; black holes; chaos
Dokument je dostupný na externích webových stránkách.
Growth of orbital resonances around a black hole surrounded by matter
This work studies the dynamics of geodesic motion within a curved spacetime around a Schwarzschild black hole, perturbed by a gravitational field of a far axisymmetric distribution of mass enclosing ...
Risk Assessment on Geodiversity Sites
Kubalíková, Lucie; Nováková, Eva; Kuda, František; Kirchner, Karel; Bajer, A.; Balková, M.
2023 - anglický
Geoconservation is an action of conserving and enhancing geological, geomorphological, hydrological and soil features and processes. Particular geoconservation measures are very often applied on the site-level to protect important geodiversity sites. Nevertheless, despite established legal protection and related geoconservation activities, threats to geodiversity sites related to the multiple use and human society demands can arise and reaching a compromise can be difficult. In this contribution, a two-level threat assessment is applied and discussed. The first level of threat assessment is based on the already used criteria within geosite/geomorphosite concept. The second level of threat assessment is represented by Risk Assessment Matrix, which may be considered a useful tool providing a complex view on the threats to geodiversity sites. The methods are applied on two different sites and their advantages and limits are discussed. Based on the assessment, specific management proposals may be implemented in order to balance conservation needs and demands resulting from human activities related to the sites.
Klíčová slova:
geoconservation; risk assessment matrix; degradation risk; geosites; geomorphosites
Dokument je dostupný na externích webových stránkách.
Risk Assessment on Geodiversity Sites
Geoconservation is an action of conserving and enhancing geological, geomorphological, hydrological and soil features and processes. Particular geoconservation measures are very often applied on the ...
Ceramic protection of anti-corrosion layers of 3-glycidyloxypropyl-triethoxysilane on steel
Pokorný, P.; Janata, Marek; Brožek, Vlastimil
2023 - anglický
There are various variations on the problem of steel reinforcement bond strength in concrete. Along with geometrical considerations, corrosion performance of steels with varying chemical compositions in interaction with variable chemical compositions of concrete are crucial. One approach is to cover steel surfaces with organosilane compounds, which increases the reinforcement resistance to corrosion in both acidic and alkaline conditions but, on the other hand, may weaken the reinforcement bond strength on concrete. The issue is resolved by intentionally forming a thin-walled, highly adhering corundum layer that is highly porous and impregnated with 3-glycidyloxypropyltriethoxysilane. This procedure also includes testing the adhesion properties between the ceramic and the metal and the cement prior to conducting a corrosion test in a chloride environment.
Klíčová slova:
ceramic protection; 3-glycidyloxypropyl-triethoxysilane; steel
Dokument je dostupný na externích webových stránkách.
Ceramic protection of anti-corrosion layers of 3-glycidyloxypropyl-triethoxysilane on steel
There are various variations on the problem of steel reinforcement bond strength in concrete. Along with geometrical considerations, corrosion performance of steels with varying chemical compositions ...
Determination of the initial stress tensor from deformation of underground opening-theoretical background and applications
Malík, Josef; Kolcun, Alexej
2023 - anglický
In this paper a method for the detection of initial stress tensor is proposed. The method is based on measuring distances between some pairs of points located on the wall of underground opening in the excavation process. This methods is based on the solution of eighteen auxiliary problems in the theory of elasticity with force boundary conditions. The optimal location of the pairs of points on the wall of underground work is studied. The pairs must be located so that the condition number of a certain matrix has the minimal value, which guarantees a reliable estimation of initial stress tensor.
Klíčová slova:
initial stress tensor; first boundary value problem of the theory of elasticity; condition number of matrices
Dokument je dostupný na externích webových stránkách.
Determination of the initial stress tensor from deformation of underground opening-theoretical background and applications
In this paper a method for the detection of initial stress tensor is proposed. The method is based on measuring distances between some pairs of points located on the wall of underground opening in the ...
Dynamics of a cantilever beam with piezoelectric sensor: Finite element modeling
Cimrman, Robert; Kolman, Radek; Musil, Ladislav; Kotek, Vojtěch; Kylar, Jaromír
2023 - anglický
An elastodynamical model of a cantilever beam coupled with a piezoelectric sensor is introduced and its discretization using the finite element method is presented. The mathematical model includes additional terms that enforce the floating potential boundary condition for keeping a constant charge on an electrode of the sensor. The behaviour of the model is illustrated using a numerical example corresponding to an experimental setup, where vibrations of the beam and the potential on the sensor are measured.
Klíčová slova:
finite element method; piezo-electricity; floating potential; dynamic simulation
Dokument je dostupný na externích webových stránkách.
Dynamics of a cantilever beam with piezoelectric sensor: Finite element modeling
An elastodynamical model of a cantilever beam coupled with a piezoelectric sensor is introduced and its discretization using the finite element method is presented. The mathematical model includes ...
Hidden symmetry in turbulence and analytic study of shell models
Caggio, Matteo
2023 - anglický
This short communication concerns symmetries in developed turbulence and analytic study of shell models. However scale-invariance is broken due to the intermittency phenomenon, is possible to established a hidden self-similarity in turbulent flows. Using a shell model, the author in [18] (see also [19]) addressed the problem deriving a scaling symmetry for the inviscid equations. Here, first we discuss the analysis presented in [18], then, from the mathematical perspective, we propose an analytic study for the shell model with the presence of the viscous terms. This brief paper should be understood as an introductory note to this new scaling symmetry with implications for mathematical analysis [5].
Klíčová slova:
turbulence; scale-invariance symmetry; intermittency; shell-models
Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
Hidden symmetry in turbulence and analytic study of shell models
This short communication concerns symmetries in developed turbulence and analytic study of shell models. However scale-invariance is broken due to the intermittency phenomenon, is possible to ...
Calibrated finite volume method-based simulation framework for laser shock peening
Isoz, Martin; Gruber, Pavel; Schmidt, Jaroslav; Kubíčková, Lucie; Štefan, Jan; Kaufman, Jan; Brajer, Jan; Gabriel, Dušan
2023 - anglický
Modern and highly competitive industry seeks components with high strength and fatigue resistance. Both of these properties may be improved by peening of the component surface and the standard peening processes, such as the shot peening, are widely used in both automotive and aerospace industries. The laser shock\npeening (LSP), i.e. hardening of the material surface by a laser-induced shock wave, is a modern alternative to the standard peening. Concurrently, the industrial applications of LSP are promoted by recently emerged affordable high power-density lasers. However, the nascent LSP applications are still mostly a trial-and-error\nprocesses based on an extensive experimental testing. Consequently, we focused on a highly application-driven development of a framework for LSP modeling, and the internal workings and results of which are the focus of the present contribution.
Klíčová slova:
laser shock peening; modeling; finite volume method; OpenFOAM
Dokument je dostupný na externích webových stránkách.
Calibrated finite volume method-based simulation framework for laser shock peening
Modern and highly competitive industry seeks components with high strength and fatigue resistance. Both of these properties may be improved by peening of the component surface and the standard peening ...
Mixing characteristics of a magnetically driven Rushton turbine in an unbaffled stirred tank reactor
Idžakovičová, Kristýna; Haidl, Jan; Gebouský, Ondřej; Isoz, Martin
2023 - anglický
The standard and well-researched stirred vessel configuration comprises a tank equipped with one or more impellers positioned in the vessel’s axis and multiple wall-mounted baffles preventing the central vortex creation. However, particular industries, such as biotechnology, have an increased need for a sterile environment that often results in the usage of atypical stirred vessel configurations. An example of a commonly equipped atypical stirred vessel is an unbaffled stirred tank with an eccentric magnetically driven impeller. However, there is only a little knowledge about the mixing characteristics of such designs. In this work, we list experimental results for both the standard and atypical stirred vessel configurations. Furthermore, we present a CFD model of the atypical configuration. The model is used to calculate its mixing characteristics that are subsequently compared against our experimental results. It is shown that for the liquid height (H) to the vessel diameter (T) ratio H/T ≲ 1.2, the characteristics of both the standard and atypical designs coincide. For higher liquid heights (i) the characteristics of the atypical design decrease dramatically, and (ii) the characteristics estimates based on approaches developed for the standard configuration become unreliable.
Klíčová slova:
stirred vessel; eccentric impeller; unbaffled tank; CFD; OpenFOAM; experiment
Dokument je dostupný na externích webových stránkách.
Mixing characteristics of a magnetically driven Rushton turbine in an unbaffled stirred tank reactor
The standard and well-researched stirred vessel configuration comprises a tank equipped with one or more impellers positioned in the vessel’s axis and multiple wall-mounted baffles preventing the ...
Average Reward Optimality in Semi-Markov Decision Processes with Costly Interventions
Sladký, Karel
2023 - anglický
In this note we consider semi-Markov reward decision processes evolving on finite state spaces. We focus attention on average reward models, i.e. we establish explicit formulas for the growth rate of the total expected reward. In contrast to the standard models we assume that the decision maker can also change the running process by some (costly) intervention. Recall that the result for optimality criteria for the classical Markov decision chains in discrete and continuous time setting turn out to be a very specific case of the considered model. The aim is to formulate optimality conditions for semi-Markov models with interventions and present algorithmical procedures for finding optimal solutions.
Klíčová slova:
controlled semi-Markov reward processes; long-run optimality; intervention of the decision maker
Dokument je dostupný na externích webových stránkách.
Average Reward Optimality in Semi-Markov Decision Processes with Costly Interventions
In this note we consider semi-Markov reward decision processes evolving on finite state spaces. We focus attention on average reward models, i.e. we establish explicit formulas for the growth rate of ...
Permutation Flip Processes
Hladký, Jan; Řada, Hanka
2023 - anglický
We introduce a broad class of stochastic processes on permutations which we call flip processes. A single step in these processes is given by a local change on a randomly chosen fixed-sized tuple of the domain. We use the theory of permutons to describe the typical evolution of any such flip process started from any initial permutation. More specifically, we construct trajectories in the space of permutons with the property that if a finite permutation is close to a permuton then for any time it stays with high probability is close to this predicted trajectory. This view allows to study various questions inspired by dynamical systems.
Klíčová slova:
permutation; permuton; sorting dynamics; flip process
Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
Permutation Flip Processes
We introduce a broad class of stochastic processes on permutations which we call flip processes. A single step in these processes is given by a local change on a randomly chosen fixed-sized tuple of ...
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