Digital Library University of West Bohemia
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Recent Submissions
Partial Discharge Behavior and Insulation Failures Detection in Electrical Devices Subjected to Pulsed Voltage Excitation
(Elsevier, 2025) Eckert , Manuel; Ballweg, Christof; Pihera, Josef
Nebeská sféra v Parmenidově kosmologii
(2025) Kočandrle, Radim
Vliv Parmenidova myšlení je zdůrazňován zejména v ontologii. Ačkoli v oblasti kosmologie není příliš akcentován, jeho průvodním jevem by mohla být koncepce nebeské sféry, která u Aristotela v podobě sféry stálic uzavírala univerzum. U Parmenida se totiž setkáváme s pevnou částí, která obklopovala „věnce“ tvořící strukturu univerza. Ačkoli nejsme o její povaze a tvaru informováni, v Parmenidově myšlení se kromě kruhového tvaru objevuje i tvar koule. Ten je spojen zejména s pravým jsoucnem, které mohlo v kosmologickém smyslu znamenat „nebe“. S ním analogicky souvisel kulový tvar Země, rovnovážně umístěné uprostřed univerza. V předsókratovských kosmologiích můžeme navíc identifikovat vývoj, který vycházel z nového pojetí prostoru a odpovídal zavedení sférického tvaru nebe a Země v 5. století př. Kr. Lze se proto domnívat, že právě Parmenidés uvedl do antické kosmologie koncepci nebeské sféry.
Thales’s Conception of the Earth
(2025) Kočandrle, Radim
Aristotle ascribes to Thales of Miletus the notion of the Earth resting on water. However, in archaic Ionian cosmologies the Earth was not viewed as a cosmic body resting on physical support. The very motif is likely to have originated in the Near East. If Aristotle claims that this was the oldest conception of stability of the Earth it is possible that Thales may have been associated with it anachronistically.
Internal contact phenomena between fuel rod bundle and shroud-tube in ducted hexagonal fuel assemblies
(2026) Zeman, Vladimír; Hlaváč, Zdeněk; Dyk, Štěpán
The paper is focused on internal contact phenomena between the fuel rod bundle and the shroud-tube in the ducted hexagonal fuel assemblies. Due to transverse clearances on all six sides of the hexagonal profile and the bowing of the fuel assembly (FA), contact may occur under operating conditions characterized by vibration excitation from coolant pressure pulsations. A comprehensive modelling approach is presented, which incorporates the effects of all relevant internal reactor components and interactions between the fuel rod bundle and the shroud-tube. This framework enables selecting the number of such bowed FAs, as well as the definition of FA bow shapes, clearances, modal properties of the FA components, and other key parameters. The practical implementation of the proposed method is demonstrated on PWRs, specifically VVER-440-type reactors, along with a broad range of analyses and results.
Perfect stationary solutions of reaction–diffusion equations on lattices and regular graphs
(2026) Švígler, Vladimír; Volek, Jonáš
In this work, we introduce a notion of perfect stationary solutions of reaction–diffusion differential equations on lattices and regular graphs and show its elementary properties. The perfect stationary solutions – a special class of finite-range solutions in which the neighborhood values are determined by the value of the central vertex – generalize periodic stationary solutions. The focus on the solution which attain a finite number of values enables us to reduce the stationary problem from a countable algebraic system of equations to a finite one. However, the possible absence of periodicity in the solutions allows for richer structure of the solutions and their abundance compared to the periodic stationary solutions. We further present results from the theory of perfect colorings in order to prove the existence of the solutions on the square, triangular, and hexagonal grid. As a byproduct, the existence of uncountable number of two-valued stationary solutions on these grids is shown. These two-valued solutions alone can form highly aperiodic and highly irregular patterns. Finally, an application to a bistable reaction–diffusion equation on the square grid is presented.