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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.
1

The Study of Hexagonal Lattice Pattern Formation of Polystyrene Thin Films

Lin, Yu-Sung 10 February 2011 (has links)
In this study, we investigate and fabricate two-dimensional ordered lattice structure by breath figures method. The breath figures pattern was prepared with the solution of carbon disulfide (CS2) doped with 1% weight concentration of polystyrene. The temperature and the humidity were controlled at ~23¢J and ~60 %, respectively. The breath figures pattern began to expand while CS2 is under evaporation. We explored the relationship between self-assemble of the water droplet and ordered structure via the solution height, the temperature evolution, and the dynamical optical images in the formation process of breath figures pattern. It was found that the radius of the water droplets varying with time follows the power law, £l ~ t £go; £g0=0.76. The fast Fourier transformation and Voronoi Diagram were used to conform that the formation of the breath figures pattern varied form a disordered state to an ordered state with the evaporation of CS2. The understanding of the breath figures pattern provides us to fabricate the photonics with size from nano- to micro-scale and to improve the application of nano device.
2

Особенности прокатки металлов и сплавов с гексагональной решеткой : магистерская диссертация / Features of metals and alloys rolling with a hexagonal lattice

Абашев, Д. Ю., Abashev, D. Yu. January 2022 (has links)
В работе описаны процессы пластической деформации для наиболее распространённых металлов с ГПУ кристаллической решеткой, к числу которых относится титан, магний, цирконий. Рассматривается характеристика ГПУ металлов с точки зрения особенностей кристаллического строения и действующих механизмов пластической деформации, описана область применения. Описано поведение металлов с ГПУ решеткой при пластической деформации и при повышенных температурах, что накладывает требования к технологии производства изделий из данных металлов. Представлены основные условия текучести, применяемые для ортотропных металлов, отражающие различное поведение материала в разных направлениях. Методом конечных элементов выполнены расчеты и представлено сравнение параметров плоской прокатки циркониевого сплава Э125 при применении изотропного и ортотропного условий текучести. / The paper describes the processes of plastic deformation for the most common metals with an HCP crystal lattice, which include titanium, magnesium, and zirconium. The characteristics of HCP metals are considered from the point of view of the features of the crystal structure and the operating mechanisms of plastic deformation, and the scope is described. The behavior of metals with an HCP lattice under plastic deformation and at elevated temperatures is described, which imposes requirements on the technology for the production of products from these metals. The basic flow conditions used for orthotropic metals are presented, reflecting the different behavior of the material in different directions. The finite element method is used to perform calculations and compare the parameters of flat rolling of the E125 zirconium alloy using isotropic and orthotropic yield conditions.
3

Interplay of dynamics and network topology in systems of excitable elements

Tomov, Petar Georgiev 22 March 2016 (has links)
Wir untersuchen globale dynamische Phänomene, die sich von dem Zusammenspiel zwischen Netzwerktopologie und Dynamik der einzelnen Elementen ergeben. Im ersten Teil untersuchen wir relativ kleine strukturierte Netzwerke mit überschaubarer Komplexität. Als geeigneter theoretischer Rahmen für erregbare Systeme verwenden wir das Kuramoto und Shinomoto Modell der sinusförmig-gekoppelten "aktiven Rotatoren" und studieren das Kollektivverhalten des Systems in Bezug auf Synchronisation. Wir besprechen die Einschränkungen, die durch die Netzwerktopologie auf dem Fluss im Phasenraum des Systems gestellt werden. Insbesondere interessieren wir uns für die Stabilitätseigenschaften von Fluss-invarianten Polydiagonalen und die Entwicklungen von Attraktoren in den Parameterräume solcher Systeme. Wir untersuchen zweidimensionale hexagonale Gitter mit periodischen Randbedingungen. Wir untersuchen allgemeine Bedingungen auf der Adjazenzmatrix von Netzwerken, die die Watanabe-Strogatz Reduktion ermöglichen, und diskutieren verschiedene Beispiele. Schließlich präsentieren wir eine generische Analyse der Bifurkationen, die auf der Untermannigfaltigkeit des Watanabe-Strogatz reduzierten Systems stattfinden. Im zweiten Teil der Arbeit untersuchen wir das globale dynamische Phänomen selbstanhaltender Aktivität (self-sustained activity / SSA) in neuronalen Netzwerken. Wir betrachten Netzwerke mit hierarchischer und modularer Topologie , umfassend Neuronen von verschiedenen kortikalen elektrophysiologischen Zellklassen. Wir zeigen, dass SSA Zustände mit ähnlich zu den experimentell beobachteten Eigenschaften existieren. Durch Analyse der Dynamik einzelner Neuronen sowie des Phasenraums des gesamten Systems erläutern wir die Rolle der Inhibierung. Darüber hinaus zeigen wir, dass beide Netzwerkarchitektur, in Bezug auf Modularität, sowie Mischung aus verschiedenen Neuronen, in Bezug auf die unterschiedlichen Zellklassen, einen Einfluss auf die Lebensdauer der SSA haben. / In this work we study global dynamical phenomena which emerge as a result of the interplay between network topology and single-node dynamics in systems of excitable elements. We first focus on relatively small structured networks with comprehensible complexity in terms of graph-symmetries. We discuss the constraints posed by the network topology on the dynamical flow in the phase space of the system and on the admissible synchronized states. In particular, we are interested in the stability properties of flow invariant polydiagonals and in the evolutions of attractors in the parameter spaces of such systems. As a suitable theoretical framework describing excitable elements we use the Kuramoto and Shinomoto model of sinusoidally coupled “active rotators”. We investigate plane hexagonal lattices of different size with periodic boundary conditions. We study general conditions posed on the adjacency matrix of the networks, enabling the Watanabe-Strogatz reduction, and discuss different examples. Finally, we present a generic analysis of bifurcations taking place on the submanifold associated with the Watanabe-Strogatz reduced system. In the second part of the work we investigate a global dynamical phenomenon in neuronal networks known as self-sustained activity (SSA). We consider networks of hierarchical and modular topology, comprising neurons of different cortical electrophysiological cell classes. In the investigated neural networks we show that SSA states with spiking characteristics, similar to the ones observed experimentally, can exist. By analyzing the dynamics of single neurons, as well as the phase space of the whole system, we explain the importance of inhibition for sustaining the global oscillatory activity of the network. Furthermore, we show that both network architecture, in terms of modularity level, as well as mixture of excitatory-inhibitory neurons, in terms of different cell classes, have influence on the lifetime of SSA.

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