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1.
Teaching complex fields of soft matter, proposal of a new liquid crystal analogy
Uroš Jagodič, Jacob Staines, Samo Kralj, Robert Repnik, 2014, original scientific article

Abstract: The key reason behind the richness of different structures and patterns displayed in nature is the universal mechanism of symmetry breaking. It shapes configurations at all length scales encountered in universe. Structures reached via symmetry breaking transitions are commonly described in terms of order parameter fields. One of the simplest systems where symmetry breaking concepts have already been explored in detail, are various liquid crystal (LC) phases. The reason behind this is rich variety of structures exhibited by LCs and their convenient experimental accessibility. Consequently, a wide spectrum of different theoretical tools have been developed in LCs. In this contribution the orientational ordering of housing block in San Francisco, which we choose as a typical large-city representative, was studied. Following nematic LC analogy we determine the local degree of ordering. The structural pattern of the city displays a domain-type pattern. The average degree of ordering within a domain strongly correlates with crime rate within it. Therefore, the results confirm an intuitive expectation that structures define properties. This model can be used as a helpful tool in education as it provides a way of understanding complex topics with the help of well-known every day phenomena.
Keywords: education, liquid crystals, modelling, order parameter
Published in DKUM: 19.12.2017; Views: 1152; Downloads: 73
.pdf Full text (2,32 MB)
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2.
Smektična A struktura v prisotnosti vsiljene upogibne deformacije
Uroš Jagodič, 2014, master's thesis

Abstract: Superprevodne kovine lahko delimo na dva tipa, ki jih karakteriziramo s tipičnimi razdaljami sistema. V analogiji lahko tudi za smektične tekoče kristale uvedemo podobno delitev. Smektike tipa I in tipa II ločimo s t. i. Ginzburgovim parametrom. V magistrski nalogi bomo preučevali odziv obeh tipov smektikov na vsiljeno upogibno deformacijo. Ta je v sistemu povzročena s t. i. strukturo ribje kosti na površini. Z naklonom brazd strukture vsiljujemo lokalne napetosti v sistemu, kar posledično vpliva na urejanje molekul tekočega kristala znotraj posamezne smektične plasti. V teoretični obravnavi problema zapišemo prosto energijo sistema s pomočjo Landau – de Gennesovega fenomenološkega pristopa. Prosto energijo bomo enodimenzionalno parametrizirali za primer strukture ribje kosti in zapisali Euler – Lagrangeovi enačbi, ki ju rešujemo numerično. Raziskali bomo odziv smektikov tipa I in tipa II na vsiljeno upogibno deformacijo znotraj strukture ribje kosti.
Keywords: tekoči kristali, smektična A faza, topološki defekti, struktura ribje kosti, Ginzburgov smektični parameter, smektiki tipa I in tipa II
Published in DKUM: 09.10.2014; Views: 1768; Downloads: 142
.pdf Full text (2,55 MB)

3.
Temperaturno induciran fazni prehod nematičnega tekočega kristala
Uroš Jagodič, 2012, undergraduate thesis

Abstract: V diplomskem seminarju obravnavamo dogajanje ob temperaturno induciranem faznem prehodu tekočega kristala med nematično ter izotropno fazo. V ta namen smo sintetizirali tekoči kristal MBBA ter z invertnim polarizacijskim mikroskopom opazovali dogajanje ob faznem prehodu. Vzorec smo izpostavili hitri ter počasni temperaturni spremembi ter opazovali fazni prehod ter rast domenskih struktur pri prehodu. Pri hitri podhladitvi smo izmerili korelacijske dolžine domenskih struktur ter hitrost naraščanja le-teh. Dogajanje ob prehodu smo opisali z Landau – de Gennesovim fenomenološkim modelom.
Keywords: tekoči kristal, nematik, I – ¬N fazni prehod, Landau – de Gennesov fenomenološki model, nenadno spreminjanje temperature ob faznem prehodu, rast domenskih struktur, meritve korelacijske dolžine.
Published in DKUM: 27.09.2012; Views: 2242; Downloads: 97
.pdf Full text (1,49 MB)

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