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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.
221

Facile synthesis of bowl-shaped nitrogen-doped carbon hollow particles templated by block copolymer “kippah vesicles” for high performance supercapacitors

Lin, Zhixing, Tian, Hao, Xu, Fugui, Yang, Xiangwen, Mai, Yiyong, Feng, Xinliang 17 July 2017 (has links) (PDF)
This paper reports a simple self-assembly strategy towards bowl-shaped carbon-containing hollow particles, as well as an unprecedented potential application for block copolymer vesicles in energy storage. Kippah vesicles (fully collapsed vesicles), formed by solution self-assembly of an amphiphilic polystyrene-block-poly(ethylene oxide) block copolymer, were employed as the template to guide the formation of bowl-shaped nitrogen-doped carbon hollow particles (BNCHPs). As electrode materials of supercapacitors, BNCHPs exhibit superior electrochemical performance. In particular, compared with their spherical counterpart, BNCHPs largely increase their volumetric packing density, leading to much higher volumetric capacitance or volume reduction of electrodes, which is desired for practical supercapacitor devices.
222

Anténní řada pro určování pozice letadel / Antenna array to determine positions of airplanes

Zelenka, Pavel January 2019 (has links)
The project is aimed to design an antenna array for an aircraft positioning system at an airport. The system operates at frequencies 1030 MHz and 1090 MHz. The antenna is also used by the DME/TACAN system operating in frequency range from 1025 MHz to 1150 MHz. The required impedance bandwidth of the antenna array is 125 MHz, i.ee from 1025 MHz to 1150 MHz. The theoretical part of the thesis analyses properties of different patch antennas and discusses the possibility of extending the impedance bandwidth. The practical part is focused on the development of the numerical model of the broadband stacked patch antennas. In addition, properties of the 3-element and 4-element antenna array are compared. At the end, results of the thesis are summarized.
223

Analysis of the English language produced by a Swedish 4-year-old child in the light of the innatist perspective : A case study

Wistrand, Ida January 2021 (has links)
This is a case study that focuses on the oral proficiency in English manifested by the 4-year-old sonof the author. He speaks Swedish as his L1 like his both parents but has been exposed to Englishsince he was one year old from using a tablet. The child’s spoken production was recorded andtranscribed with a focus on the plural-forms and the genitive. An important field that this case studyis motivated by is how child language development may be connected to the concept of innatism,that language is based on innate principles (Lightbown & Spada, 2013:20) as it has been found that anumber of languages are acquired according to predictable patterns and processes (Moskowitz,1994:621-627) such as a the u-shaped learning process and over-generalization which has beenfound when investigating both L1 and L2 acquisition (Abrahamsson, 2013:663). The aim of thisstudy is to find possible similarities within the learning process: whether L2 acquisition follows thesame developmental patterns as in L1 acquisition by analyzing the recordings mainly targeting theplural and the genitive morphemes produced by a 4-year-old L2 speaker of English. Findings in thisresearch revealed that the child demonstrated a similar developmental pattern in the form of theu-shaped learning process (Abrahamsson, 2013:663).
224

Studium vlastností betonu s rozptýlenou výztuží, určeného pro výrobu betonových vejčitých trub / Study of the properties of concrete with reinforcement, intended for the production of concrete egg-shaped tubes

Šťastný, Antonín January 2015 (has links)
This diploma thesis examines the properties of concrete with reinforcement, designed for the production of a concrete egg-shaped tubes . The stress is put on using various types of fiber reinforcements. Theoretical part is divided into 4 subsections. The topic of the first subsection is a concrete in general. Second subsection deals with various technology of production of concrete pipes. The third subsection is focused on description and summary of basic properties of concrete and reinforced concrete tubes. The last subsection deals with standardized procedures for testing concrete. Experimental part of this thesis is divided into two subsection. First subsection deals with design of a reference sample. Six different samples of a concrete were designed and their rheological properties were tested. Second subsection deals with the additi-on of various types of fiber reinforcement to the reference sample. Eight different admixtures of a concrete were added to the reference sample. Properties of these admixtures were tested in fresh and hardened state.
225

Návrh technologie výroby tvarového víka / Design of production technology of shaped cover

Doležal, Václav January 2013 (has links)
This thesis presents a design technology of forming a shaped lid focused on cutting, bending, drawing, as well as trimming and making the required holes. There is described several basic variants of sheet metal forming based on the literature. Production of holes of specified cover, for an annual production of 100 pieces of shaped lid, is solved by unconventional technologies. From subsequent economic evaluation of selected technologies is chosen an appropriate technology to minimize production costs.
226

Fabrication of Nano Josephson Junctions Using the Femtosecond Laser Technique on High Tc Superconducting YBCO Thin films

Umenne, Patrice 27 February 2018 (has links)
This PhD work involves the utilization of the femtosecond laser technique to fabricate the novel S-shaped Josephson Junctions on the high - T_C superconducting YBCO thin films. Initially, it was envisaged as the title states to fabricate nano sized Josephson Junctions using this femtosecond laser technique. However in this PhD work, micron sized (1 – 2 µm) and near nano sized (500 – 800 nm) Josephson Junctions where achieved. / University of South Africa / Electrical and Mining Engineering
227

Použití symbolů v minojské a mykénské ikonografii / The Use of Symbols in Minoan and Mycenaean Iconography

Matoušková, Monika January 2020 (has links)
This Master thesis deals with symbolic objects appearing in the Bronze Age Aegean art in the 3rd and especially the 2nd millennium BCE. Recurrent types of scenes and motifs speak for the fact that there must have existed a complex iconographic system of Minoan and Mycenaean art. An analytical method aiming at single elements of composite scenes may bring us closer to better understanding of this system and to its more objective interpretation. The study, therefore, focuses on the iconography of each individual symbol and also discusses its possible parallels in art of the neighbouring Bronze Age cultures. Nonetheless, the Aegean iconographic system was not strictly codified throughout the entire Bronze Age and some of the themes evolved or were specific only for certain eras. For that reason, the studied material is treated in a diachronic approach so as to stress the iconographic evolution of the symbols' use. The aim is to provide a profound analysis of the rules applied to the symbols in Minoan and Mycenaean art, to investigate their possible origins, and finally to examine their mutual interconnections.
228

Résolution par la méthode de Monte Carlo de formulations intégrales du problème de diffusion électromagnétique par une suspension de particules à géométries complexes / Resolution by Monte Carlo method of the electromagnetic scattering by a suspension of complex-shaped particles

Charon, Julien 12 December 2017 (has links)
L’étude du problème de la diffusion d’une onde électromagnétique par une suspension de particules non sphériques est une difficulté récurrente dans de nombreux domaines de la recherche et de l’ingénierie. Cela implique d’utiliser des dispositifs expérimentaux hautement spécialisés ou de résoudre les équations de Maxwell, ce qui représente un véritable défi lorsque les particules sont de géométries complexes et avec des distributions statistiques de taille, d’orientation et de forme. L’objectif de la présente thèse est d’explorer l’utilisation de la méthode de Monte Carlo pour résoudre des formulations intégrales du champ électromagnétique diffusé déduites des équations de Maxwell. En particulier, nous résolvons celles de l’approximation de Schiff, de l’approximation de Born ainsi que celle du développement en série de Born. Notre approche est basée sur un travail de reformulation intégrale permettant de concevoir des algorithmes incluant les avancées les plus récentes de la méthode. Cette approche originale, utilisant les outils de la synthèse d’image pour gérer n’importe quelle géométrie, permet de traiter des statistiques de particules ainsi que d’évaluer les sensibilités à des paramètres d’intérêts, sans augmentation significative du temps de calcul. Les outils développés répondent d’ores et déjà aux besoins d’optimisation des photobioréacteurs qui mettent en œuvre des particules à faible contraste d’indice (micro-algues). À l’issue de ce travail, des pistes de recherches ont émergé pour explorer le verrou bien identifié des grandes particules et des forts contrastes d’indice à partir du principe de zéro-variance. / The resolution of the problem of an electromagnetic wave scattered by non-spherical particles suspensions is a significant difficulty encountered in many fields of research and engineering. This implies to use highly specialized experiments or to solve Maxwell’s equations, which is a real challenge when weconsider particles with complex shapes and with statistical distributions of size, orientation and shape.The aim of this thesis is to investigate the use of the Monte Carlo method in order to solve the integral formulations of electromagnetic scattering deduced from Maxwell’s equations. In particular, we solvethose of Schiff’s approximation, Born’s approximation as well as the Born series expansion. Our approachis based on integral reformulation in order to design algorithms including the most recent advances of the method. This original approach, using computer graphics algorithms in order to manage arbitraryshape, permits treating any distributions of parameters as well as evaluating sensitivities to parameters ofinterest, without additionnal CPU time. The developed tools already meet the needs for the optimisation of photobioreactors which bring into play soft particles (micro-algae). From this work, some researchideas have emerged to explore the well-identified issue of large particles and large refractive indices from zero-variance principle.
229

Moderní mikroextrakční techniky pro analýzy plynovou chromatografií / Modern microextraction techniques for gas chromatographic analysis

Bursová, Miroslava January 2018 (has links)
The submitted thesis is focused on the development, optimization, testing and practical application of the new microextraction method called Bell Shaped Extraction Device assisted Liquid-Liquid Microextraction (BSED-LLME). The method is based on the application of a miniature bell-shaped extraction tool in which the extraction takes place, so that only minimal solvent losses can occur, and which allows a reproducible dosing and collection of a small volume of the extraction solvent. The BSED- LLME method was used to preconcentrate selected volatile and less volatile analytes from aqueous samples into organic solvents of a density lower than water. After the extraction, the analytes were determined by fast gas chromatography with flame ionization detection and gas chromatography with mass spectrometry. The statistical methods known as Design of Experiment (DOE) were used for determination of the optimal extraction conditions for BSED-LLME procedure. DOE is based on a mathematical description of the system and the prediction of the optimal setting of experimental parameters that may influence extraction efficiency. Factors such as extraction time, volume of extraction solvent, addition of sodium chloride (ionic strength), stirring rate and the diameter of the extraction vessel ect., have been tested....
230

Analysis of wedge-shaped waveguides and design of multipactor-resistant microwave bandpass filters. Análisis de guías de onda en forma de cuña y diseño de filtros de microondas paso-banda resistentes al efecto multipactor.

Hueso González, Jaime 19 November 2013 (has links)
El efecto multipactor de ruptura en RF ha sido objeto de numerosos estudios desde hace más de 80 años, a partir del desarrollo de los primeros aceleradores de partículas en la primera mitad del siglo XX. A mediados de ese siglo, con el desarrollo de fuentes de alta potencia para aplicaciones radar y la llegada de los satélites artificiales, la investigación del multipactor cobró una considerable relevancia, al convertirse este fenómeno en un riesgo determinante para costosos proyectos comerciales. Las guías de onda con secciones rectas canónicas, como las rectangulares o las coaxiales, han sido tradicionalmente las más utilizadas en dispositivos de microondas. Sus principales ventajas son que sus campos electromagnéticos pueden resolverse analíticamente, lo que permite su aplicación directa en diseños complejos, y la simplicidad de su fabricación. Pero las capacidades de computación y las prestaciones de los algoritmos se han multiplicado con los años, lo que ha permitido ampliar el espectro de posibles topologías a geometrías casi arbitrarias, ofreciendo al diseñador una mayor libertad creativa. En todo caso, gran parte de los dispositivos de microondas actuales siguen confiando en la madurez y fiabilidad de las tecnologías de guía de onda tradicionales, que no requieren una inversión adicional en equipos de fabricación. La supresión del efecto multipactor es la motivación para arriesgarse a probar topologías de guía de onda innovadoras, como la guía en forma de cuña. Es en este contexto donde este trabajo de doctorado pretende ofrecer una contribuci'on. En primer lugar, se ha desarrollado un modelo numérico para predecir el efecto multipactor de ruptura en guías de onda huecas en forma de cuña. Esta herramienta ha permitido la identificación de criterios óptimos de diseño. Así mismo, se ha adaptado un método de síntesis de filtros paso-banda en guía rectangular para poder realizar un diseño similar pero basado en la nueva topología. Como culminación, las estructuras diseñadas se han fabricado y medido, con el fin de comprobar sus prestaciones electromagnéticas y su sensibilidad al efecto multipactor. Se ha registrado además una patente para proteger estos nuevos filtros. En resumen, el trabajo ha abarcado el ciclo de actividades relacionadas con el desarrollo industrial completo de un dispositivo pasivo de microondas: investigación básica, análisis, diseño, fabricación y calificación con medidas en el laboratorio. Estas medidas han comprobado la mejora prevista en los umbrales de multipactor de los filtros de microondas con topología en forma de cu¿na, y han confirmado que pueden ofrecer respuestas en frecuencia similares a aquellas de filtros basados en una guía de onda rectangular equivalente. Las implicaciones de los resultados han sido evaluadas a fondo y resumidas en este documento. Como observación final, se ha intentado redactar esta investigación de manera que refleje el proceso natural de aprendizaje, mostrando los aciertos y errores experimentados en el camino, todos los cuales han conducido al resultado final. Este reto no hubiera sido posible sin el apoyo y compromiso de varios profesionales de diferentes centros de investigación e industrias europeas (Universidad Politécnica de Valencia, Universidad de Valencia, Agencia Espacial Europea, Thales Alenia Espacio Espa¿na, Technische Universit¿at Darmstadt, 'Ecole Polythecnique F'ed'erale de Lausanne, Tesat, Aurora Software and Testing y Val Space Consortium), a los cuales estoy agradecido. / The multipactor RF breakdown effect has been object of numerous studies for over 80 years, since the development of the first particle accelerators in the beginning of the 20th century. Around the middle of that century, with the development of high power sources for radar applications and with the emergence of the artificial satellites, a new impulse was given to the multipactor research, since it became a risk for expensive commercial projects. Traditionally, waveguides with canonical cross sections, like rectangular or coaxial ones, have been the building blocks of most microwave devices. Their main advantages are that their electromagnetic fields can be solved analytically, enabling their direct application in complex designs, as well as their manufacturing simplicity. But over the years the computation capabilities and algorithms have continuously evolved, which has broadened the spectrum of possible topologies to almost arbitrary geometries, offering the designer more room for creativity. However, most of the current microwave devices still trust on the mature canonical waveguide technologies, which do not require an additional investment in manufacturing equipment. The suppression of the multipactor effect is the motivation for considering an innovative waveguide topology, like the wedge-shaped waveguide. It is within this context where this PhD work aims to offer a contribution. On the one hand, a numerical model for predicting the multipactor breakdown effect in wedge-shaped hollow waveguides has been developed. This tool has aided in the derivation of optimised design criteria. On the other hand, a bandpass filter synthesis method for rectangular waveguide has been adapted in order to calculate a similar design based on the new topology. As a culmination, the designed structures have been manufactured and tested, in order to verify their electromagnetic performance and their multipactor sensibility. A patent was also filed to protect these new filters. In short, this work has comprised the cycle of activities related to the whole industrial development of a passive microwave device: basic research, analysis, design, manufacturing and qualification through testing. These measurements have verified the predicted improvement in the multipactor thresholds of microwave filters with wedge-shaped topology, and have confirmed that they can offer similar frequency responses to the equivalent rectangular waveguide ones. The implications of the results have been thoroughly evaluated and summarised in this document. As a final remark, this research document has been drafted to reflect the natural learning process, and to show the rights and wrongs experienced in the way, which all have led to the final result. Such an endeavour would not have been possible without the support and commitment of several professionals from different European research centres and industries (Universidad Polit'ecnica de Valencia, Universidad de Valencia, European Space Agency, Thales Alenia Espacio Spain, Technische Universit¿at Darmstadt, 'Ecole Polythecnique F'ed'erale de Lausanne, Tesat, Aurora Software and Testing and Val Space Consortium), for which I am grateful. / Hueso González, J. (2013). Analysis of wedge-shaped waveguides and design of multipactor-resistant microwave bandpass filters. Análisis de guías de onda en forma de cuña y diseño de filtros de microondas paso-banda resistentes al efecto multipactor [Tesis doctoral]. Editorial Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/33750 / Alfresco

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