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Geometric resonances in reflectivity spectra of lead zirconate
Dočekalová, Zuzana ; Hlinka, Jiří
The paper deals with effects of domain boundaries on the THz–frequency range dispersion of the complex dielectric permitivity tensor of lead zirconate. In the case of a sufficiently narrow domain widths (in comparison to the wave–length of the light used in the experiment), the effective–medium average permittivity shows additional peaks identified as geometric resonances, i.e. extraneous excitations created by thematerial interface. Features of the far–infrared reflectivity spectra of the twinned lead zirconate crystal in the limit of narrow and wide domains are estimated with the\nhelp of the damped harmonic oscillator model with paramaters fully determined fromrecent experiments.
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Lead-based relaxor ferroelectrics by Raman scattering
Rafalovskyi, Iegor ; Hlinka, Jiří (advisor) ; Deluca, Marco (referee) ; Dubroka, Adam (referee)
Title: Lead-based relaxor ferroelectrics by Raman scattering Author: Iegor Rafalovskyi Institute: Institute of Physics of the Czech Academy of Sciences Supervisor: Ing. Jiří Hlinka, Ph.D., Department of Dielectrics, Institute of Physics of the Czech Academy of Sciences Abstract: The following work is dedicated to measurement and analysis of Raman scat- tering spectra of different perovskite ferroelectrics, mainly lead-based relaxors in the form of bulk and thin films. Investigation of single crystal MPB composition PMN-0.32PT has shown that procedure of zero-field heating of previously field-cooled sample leads to sta- bilization of heterophase pattern with 10-100 µm parallel stripes of alternating tetragonal and rhombohedral (rhombohedral-like) phases. Another point of interest investigated in PMN-0.32PT is rhombohedral to tetragonal phase transition induced by electric field. The domain structure with 90-degree domain walls has been observed in relaxor based composition PFN-0.38PT. Adjacent domains were investigated by polarized Raman scat- tering to confirm their structure and symmetry. Relaxor ferroelectric PSN has shown totally different behavior in polarized Raman spectra if studied in the form of single crystal or epitaxial thin film. The normalized cross-polarized intensity of 810 cm−1 band measured in...
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Studies of Relaxor Ferroelectrics with Spontaneous Polar Nanoregions
Ondrejkovič, Petr ; Hlinka, Jiří (advisor) ; Bell, Andrew (referee) ; Čermák, Petr (referee)
Title: Studies of Relaxor Ferroelectrics with Spontaneous Polar Nanoregions Author: Petr Ondrejkovič Institute: Institute of Physics of the Czech Academy of Sciences Supervisor: Ing. Jiří Hlinka, Ph.D., Institute of Physics of the Czech Academy of Sciences Abstract: The thesis is devoted to relaxor ferroelectrics with spontaneous polar nanoregions. We have investigated one of the canonical representatives, uniaxial strontium barium niobate, by means of neutron scattering, and also performed computer simulations with a model of a uniaxial ferroelectric with point defects. Neutron scattering studies of strontium barium niobate single crystals under a defined sequence of thermal and electric field treatments elucidate nature of distinct components of its transverse diffuse scattering. These components are associated mainly with the static ferroelectric nanodomain structure and the dynamic order-parameter (polarization) fluctuations. Moreover, high-resolution neutron backscattering experiments allowed us to resolve characteristic frequencies of the order-parameter fluctuations and prove that this component is caused by the same polar fluctuations that are responsible for the Vogel-Fulcher dielectric relaxation, the hallmark of relaxor ferroelectrics. The model system of a uniaxial ferroelectric with point...
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Modern Maintenance Procedures for Airframe Inspections for General Aviation Category Aircraft
Koštial, Rostislav ; Petrásek, Miloslav (referee) ; Třetina, Karel (referee) ; Hlinka, Jiří (advisor)
Aircraft scheduled maintenance requirements are rapidly extending and developing due to rapid evolution of small aircraft. This evolution leads to implementation of until recently exclusively airliner class maintenance standards. In the field of general aviation and FAR 23/ EASA CS-23 especially, preventive maintenance based on part replacing or repairing is still dominant. DAMAGE TOLERANCE philosophy implementation into an aircraft design influences maintenance procedures, which are adjusted to older SAFE LIFE philosophy. Aircraft manufactures are developing new ways, how to integrate requirements of damage tolerance application into scheduled maintenance procedures. Huge airliner manufactures (FAR 25/ CS-25) are using the ATA MSG-3 intelligent maintenance approach based on inspection. This dissertation thesis develops intelligent scheduled maintenance methodology, utilizing ATA MSG-3 procedures, expert knowledge and Multiple Criteria Decision Analysis (MCDA).
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Spectroscopic Investigation of Lattice Dynamics in Multidomain Ferroelectrics
John Vakkechalil, Elizabeth ; Hlinka, Jiří (advisor) ; Hlídek, Pavel (referee) ; Hehlen, Bernard (referee)
Title: Spectroscopic investigations of lattice dynamics in multidomain ferroelectrics Author: Elizabeth Vakkechalil John Department: Department of Condensed Matter Physics Institution: Department of Dielectrics, Institute of Physics, AVČR, Na Slovance 2, Praha 8, 182 21, Czech Republic. Supervisor: Ing. Jiří Hlinka, PhD., Department of Dielectrics, Institute of Physics, AVČR., Na Slovance 2, Praha 8, 182 21, Czech Republic. Consultants: RNDr. Stanislav Kamba CSc., Ing. Ivan Gregora CSc. Fyzikální ústav AVČR, Na Slovance 2, Praha 8, 182 21, Czech Republic. Abstract: Lead based ferroelectric perovskites exhibit attractive physical and structural properties. Ferroelectric domains are known to have a very essential impact on dielectric and piezoelectric properties of ferroelectrics. Tailoring of domain structures allows to change the macroscopic symmetry of the material and to purposely modify its average tensor properties. Ferroelastic domains play also a key role in physics of epitaxial ferroelectric films. Here we studied signature of domain structure in PbTiO3 thin film grown by metalorganic chemical vapor deposition technique on different substrates, namely LaAlO3, MgO, NdGaO3, SrTiO3 (100), SrTiO3 (110), SrTiO3 (111) doped with 0.5% Nb and LSAT. Certain aspects of domain structure can be...
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New Approaches in Numerical Aeroelasticity Applied in Aerodynamic Optimization of Elastic Wing
Navrátil, Jan ; Slavík, Svatomír (referee) ; Komárek,, Martin (referee) ; Hlinka, Jiří (advisor)
Aeroelasticita je nezbytná vědní disciplína zahrnuta do návrhu letounů. Zaměřuje se na předpovídání jevů, které vznikají vlivem interakce aerodynamických, elastických a setrvačných sil. Tyto jevy často vedou ke katastrofickým následkům, proto musí být prokázáno, že nevzniknou v rozsahu rychlostí ohraničujících letovou obálku. Aplikace moderních materiálů při konstrukci draku, spolu se snahou navrhnout aerodynamicky efektivní tvar křídel, vede ke zvyšování poddajnosti letounů. To má za následek změnu aerodynamických vlastností a také k výraznějšímu vliv na aeroelastické jevy, které mohou být vyvolány snadněji vlivem pohybů tuhého tělesa než v případě tužších konstrukcí. Aeroelastické jevy mohou vznikat v širokém rozsahu rychlostí zahrnujícím i transsonickou oblast. V této oblasti je ovlivněna zejména rychlost, při níž dochází k třepetání, a to vlivem nelineárních jevů v proudu. Běžné nástroje, které jsou založeny na lineárních teoriích, nejsou schopny tyto nelineární jevy popsat. Cílem práce je proto navrhnout, implementovat a otestovat nástroj pro výpočetní (numerickou) simulaci aeroelasticity. Nástroj má využívat řešič proudového pole, který je schopen předpovědět nelineární jevy. V práci je kladen důraz na simulaci statické aeroelasticity. V práci jsou popsány metody, které je nutno zahrnout do numerické simulace statické aeroelasticity. Dále je popsán vlastní nástroj a je provedeno zhodnocení konvergence statických aeroelastických výpočtů. Funkčnost nástroje byla ověřena na příkladech, kdy byly použity různé aerodynamické a strukturální modely. Nástroj byl také aplikován při aerodynamické tvarové optimalizaci poddajného křídla. Výsledky optimalizace a její výpočetní náročnost byly porovnány s případem optimalizace tuhého křídla. Na závěr je v práci prezentován příspěvek autora do výzkumu zaměřeného na zhodnocení vlivu časové synchronizace mezi CFD a CSM řešiči. Použitý testovací případ je transsonické obtékání křídla na začátku třepetání (flutteru). Výsledky byly srovnány s experimentálními daty poskytnutými NASA.
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