Zahlavi

Ústavní semináře

Ústavní semináře, obvykle vedené v anglickém jazyce, jsou vyhrazeny tématům, rozšiřujícím znalosti v oblastech zájmu jednotlivých oddělení: zejména jde o semináře významných hostů ÚJF AV ČR, referáty odborných skupin ÚJF a prezentace vynikajících výsledků.

Příští semináře:

20. listopadu, 10:00, zasedací místnosti ÚJF

  • Gergely Farkas (ONIM ÚJF): Line profile analysis of single crystals using 3D diffraction data

25 listopadu, 13:30, zasedací místnosti ÚJF

  • Alexander Turbiner ( ICN-UNAM, Mexico and Stony Brook University, US ): Helium atom and helium-like ions - where we are today

Abstrakty:

Line profile analysis of single crystals using 3D diffraction data

Gergely Farkas , Ph.D.
ONIM ÚJF

Abstract: Line profile (LP) analysis of diffraction data is a widely used technique for determining the microstructure of crystalline materials. Despite its indirect nature, LP analysis is a reliable and powerful method that provides valuable insights into various microstructural properties. For polycrystalline materials with near-random textures, LP analysis can be used to determine dislocation density, coherent domain size, stacking faults, the relative occurrence of different dislocation slip modes, and the arrangement of dislocations within the material. Although several profile fitting methods have been developed for powder diffraction data, the literature on single-crystal diffraction line profile fitting is notably sparse, with essentially only one method being documented. In this presentation, it will be demonstrated how this method can be effectively applied to in-situ measurements using synchrotron diffraction data. And how can be evaluated in a polycrystal each grain separately determining each grain dislocation density, partial dislocation densities and grain size. It will be shown how this approach can be used to evaluate each grain in a polycrystal individually, determining the dislocation density, partial dislocation densities, and grain size for each grain.

Helium atom and helium-like ions - where we are today

Alexander Turbiner
ICN-UNAM, Mexico and Stony Brook University, US

Z-Helium atom is the simplest atomic, 3-body system in Nature after hydrogen atom. As a result of enormous computational efforts during the last 90 years (∼150 calculations) unprecedented accuracy in 35-44 figures is reached for non-relativistic ground state energies (in static approximation). It looks like we approached to a moment to ask a famous question by Lev Landau: ”...and so what!?” (what we have learned out of all that, what is the physics behind?)

After the brief review of contemporary situation it will be shown that the physics extracted from perturbation theory at small and large nuclear charges Z allows us to get easily 12-13 figures in the energy for Z ≤ 20. Furthermore, the domain of applicability of non-relativistic Quantum Mechanics of Coulomb Charges (no photons; no relativistic, QED, mass corrections) of 4-5 figures is described by the 2nd degree polynomial in Z (it is from the recently recovered E. Majorana formula, c. 1930). First 3 figures of (mass+rel+QED) corrections vs Z contribute to 5-6-7 figures of the ground state energy: they are described by 4th degree polynomial in Z (!) for Z ≤ 20. Similar situation holds for excited states of helium-like and lithium-like ions. Generalizing Hylleraas-Kinoshita-Harris it will be presented the ultra-compact, 7-parametric trial function leading to 5 figures in the energy.

 

Archiv ústavních seminářů:

 

2023

 

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Statutární zástupce: Ing. Ondřej Svoboda, Ph.D.  •  IČ: 61389005  •  DIČ: CZ61389005  •  Číslo účtu: 671958383/0300  •  Elektronická podatelna: ujf@ujf.cas.cz  •  ID datové schránky: t8xmzqw
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