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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
31

Vibronové stavy v cérových krystalických sloučeninách / Vibron states in cerium crystalline compounds

Doležal, Petr January 2021 (has links)
This thesis is focused on study of the vibron state in Ce intermetallics. The presence of a vibron state is a consequence of an enhanced magneto-elastic interaction, between phonons and 4f electrons of the Ce ion. The magneto-elastic interaction is usually weak and can be neglected, but here in CeAl2, CePd2Al2, CeCuAl3 and CeAuAl3 is considered to be strong enough, which leads to a bound state called the vibron state. A well determined crystal structure of these compounds is a necessary prerequisite to discuss this unique behaviour. Therefore our investigation is performed on the following levels: A crystal structure study of (Ce,La)Pd2Al2-xGax and CePt2Al2, by low temperature and high temperature X-ray powder diffraction; Investigation of bulk and transport properties of a CePt2Al2 single crystal using the specific heat, magnetisation and electrical resistivity measurements; Symmetry analysis of phonon modes and angular momentum operators in the model Hamiltonian, based on group theory; And finally the study of phonon dispersion curves in CePd2Al2 and LaPd2Al2 single crystals using inelastic X-ray scattering. All these results and preformed analyses lead to the following conclusions: The CePd2Al2 and LaPd2Al2 are incongruently melting phases. We found and described the way which has allowed us to...
32

Štúdie zarovnania Belle II vrcholového detektoru a rýchla sin 2 phi analýza / The Belle II vertex detector alignment studies and prompt sin 2 phi analysis

Kandra, Jakub January 2021 (has links)
This thesis is focused on the alignment studies of the vertex detector during first years of the Belle II detector operation and the first prompt sin 2ϕ1 analysis using the first rel- evant data collected by the detector. Firstly, the Belle II detector and the SuperKEKB accelerator is introduced. Secondly, the software framework and tools operation is ex- plained, then the alignment procedure and developed validation procedures are described in detail. Fourth section reports about the first years of the detector operation. Next three sections are related to different alignment studies during thee different periods of the vertex detector operation: the Phase 2, VXD Commissioning and beginning of the Phase 3 early. The last section covers the time-dependent CP Violation and mixing measurements performed using the data collected prior to the 11en of May 2020. 1
33

Symmetry and pressure : a theoretical and experimental approach of the distortion under pressure.

Libotte, Hugues 11 September 2007 (has links)
See file appended.
34

Etude de mecanismes de migration d'orientation moleculaire dans des films minces sol-gel : deformation de surface et proprietes optiques non-lineaires quadratiques.

Darracq, Bruno 15 December 1999 (has links) (PDF)
Cette these a pour cadre l'optimisation de films minces (1-10 microns) polymeres hybrides pour la realisation de composants passifs et actifs de l'optique integree. Nous avons plus precisement etudie la mobilite de molecules d'azobenzene soumises a des excitations electriques et photoniques dans deux types de matrices sol-gel : - dans une matrice faiblement reticulee, le processus de photo-isomerisation conduit a des phenomenes de migration moleculaire pouvant provoquer des deformations de surface spectaculaires (> 1 micron). Notre etude a porte plus particulierement sur la reponse du materiau vis-a-vis du de l'intensite, de la polarisation et des frequences spatiales de la figure d'illumination (franges d'interferences). On decrit aussi la realisation d'un coupleur a reseau, qui constitue l'un des composants passifs de l'optique integree. - dans une matrice fortement reticulee, l'orientation thermo-assistee des molecules d'azobenzene par un champ electrostatique applique au film permet de briser la centrosymetrie du materiau et de lui conferer des proprietes non-lineaires quadratiques. Les mecanismes d'orientation ont ete plus finement etudies en analysant l'influence de la concentration moleculaire sur l'efficacite du doublage de frequence par le materiau. On montre qu'un moyen d'ecranter les interactions dipolaires et ainsi d'augmenter notablement la mobilite des molecules actives est d'incorporer dans le materiau des groupements steriques passifs. Appliquee a des molecules optimisees par l'ingenierie moleculaire, cette strategie supramoleculaire a permis d'obtenir de forts coefficients electro-optiques stables a temperature ambiante et depassant ceux des meilleurs materiaux inorganiques (> 50 pm/v a 832 nm). Si de plus, les groupements steriques presentent des proprietes de photoconduction, on realise un materiau photorefractif. Nous avons analyse les proprietes originales d'un systeme presentant un effet photorefractif sans champ applique. .
35

Aspekty nezachování baryonového a leptonového čísla ve Standardním modelu částicových interakcí a v jeho rozšířeních / Aspects of baryon and lepton number non-conservation in the Standard model of particle interactions and beyond

Hudec, Matěj January 2021 (has links)
This work is devoted to baryon and lepton number violation and flavour physics in theories beyond the Standard Model of particle interactions. First, the relations between the accidental and imposed symmetries are dis- cussed. For example, we argue that the Levi-Civita tensors in the color space may be understood as a unique spurion carrying the baryon number, and as such its absence in the Lagrangian of a specific model indicates baryon number conservation. Afterwards, the two minimal scenarios of quark-lepton unification are ana- lyzed in detail: the Minimal quark-lepton symmetry model and its extension by the inverse seesaw mechanism. We investigate if the observed anomalies in the B-meson decays could be to some extent accommodated within these models. Finally, possible low-energy effects of gauge leptoquarks are studied in the theory of quark-lepton unification and its simple extensions by vector-like leptons. Taking fully into account the freedom in the quark-lepton mixing, a catalogue of measurements currently forming the border of the excluded parameter space is found. We argue that, within the considered class of models, the gauge leptoquark can account for the discrepancies in the neutral-current B decays if and only if at least two extra generations of weak-isosinglet leptons exist. 1
36

Biometrie s využitím snímků duhovky / Biometry based on iris images

Tobiášová, Nela January 2014 (has links)
The biometric techniques are well known and widespread nowadays. In this context biometry means automated person recognition using anatomic features. This work uses the iris as the anatomic feature. Iris recognition is taken as the most promising technique of all because of its non-invasiveness and low error rate. The inventor of iris recognition is John G. Daugman. His work underlies almost all current public works of this technology. This final thesis is concerned with biometry based on iris images. The principles of biometric methods based on iris images are described in the first part. The first practical part of this work is aimed at the proposal and realization of two methods which localize the iris inner boundary. The third part presents the proposal and realization of iris image processing in order to classifying persons. The last chapter is focus on evaluation of experimental results and there are also compared our results with several well-known methods.
37

Zpracování snímků duhovky pro biometrické aplikace / Processing of iris images for biometric applications

Osičková, Kristýna January 2015 (has links)
Biometrics is a method of recognizing the identity of a person based on unique biological characteristics that are unique to each person. The methods of biometric identification is currently becoming increasingly widespread in various sectors. This work is focused on the identification of a person by iris images. The introductory section describes the principles of the well-known methods for biometric applications and the next part describes the design method and its implementation in Matlab. In the practical part, fast radial symmetry method is used for detection of pupil, from which it derives further image processing. Two dimensional discrete welvet transform is used here. The proposed algorithm is tested on databases CASIA-Iris- Interval and database IITD.
38

Souvislost mezi reaktivitou imunitního systému a atraktivitou obličeje / Relationship between reactivity of immune system and facial attractiveness

Slámová, Žaneta January 2018 (has links)
Previous studies have shown that physical attractiveness is one of important aspects in mate choice. Facial traits perceived as attractive may be linked to potential mate quality, or more precisely to their reproductive potential, health and ability to invest in his mate and offspring. Mating with individuals with more reactive immune system could lead to higher reproductive success and thus it is possible that visual cues facilitating detection of such traits may have evolved. The main aim of the present thesis was to test a possible association between the reactivity of the immune system response to foreign antigens (stimulated by vaccination) and facial attractiveness perceived by opposite sex individuals. Further, we investigated visual changes occurring during immune system activation. We did not find any association between measures of reactivity of immune system and perceived facial attractiveness. However, participants with activated immune system were rated as significantly less attractive and were significantly paler. Overall, our results suggest that people are sensitive to visual cues to current health status but not to overall quality of the individual. Key Words Facial attractiveness, mate choice, sexual selection; heterozygosity; symmetry; immune system, antigen; disease-avoidance,...
39

Schwarzschildovy-Bachovy černé díry / Schwarzschild-Bach black holes

Knoška, Šimon January 2021 (has links)
Šimon Knoška The spherically symmetric spacetimes represent one of the most important classes of solutions in general relativity. Therefore, it is very natural to study them also in the context of modified theories of gravity. We directly continue in the previous works in quadratic gravity, where the generalised solutions with the constant Ricci scalar were found in the form of power series expansion in the conformal coordinates. In this work, we have found an alternative expression of this solution in the Robinson-Trautman-like coordinates analogously in the form of power series expansion around the horizon. Al- though the prescribed recurrent power series solution is more complicated than that in the conformal-to-Kundt coordinates, it posses numerous advantages. Namely, the trans- formation to the Schwarzschild-like coordinates is considerable simple and the physical interpretation of the coordinates is more evident. These properties are demonstrated in the preliminary investigation of the geodesic motion of the test particles near the black hole with analysis of the effect of the so-called Bach parameter. In particular, we have observed that the Bach parameter together with the positive cosmological constant Λ > 0 has a significant impact on the global structure of the spacetime.
40

Narušení elektroslabé symetrie dynamickým generováním hmot kvarků a leptonů / Electroweak symmetry breaking by dynamically generated masses of quarks and leptons

Smetana, Adam January 2013 (has links)
Title: Electroweak symmetry breaking by dynamically generated masses of quarks and leptons Author: Adam Smetana Department: Institute of Particle and Nuclear Physics, Faculty of Mathematics and Physics, Charles University Supervisor: Ing. Jiří Hošek, DrSc., Department of Theoretical Physics, Nuclear Physics Institute, Academy of Sciences of the Czech Republic Abstract: The aim of the thesis is to study models of the electroweak symmetry breaking caused by dynamically generated masses of quarks and lep- tons. (1) We perform the basic analysis whether the main underlying idea, that the masses of only known fermions can provide the elec- troweak symmetry breaking, is actually feasible. For that we elaborate a two-composite-Higgs-doublet model of the top-quark and neutrino condensation. The model suggests rather large number, O(100), of right-handed neutrinos. (2) We analyze the model of strong Yukawa dynamics where the dynamical fermion mass generation is provided by exchanges of new elementary massive complex doublet scalar fields. We focus on solving the coupled Schwinger-Dyson equations for fermion and scalar self-energies by means of approximative methods. We doc- ument that strongly hierarchical mass spectra can be reproduced. (3) We elaborate the flavor gauge model where the dynamical fermion mass...

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