Dissertations / Theses: 'Negative Structures'

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Postma, Tiemen Rudolf. "Innovative laminate structures for tubular elements." Thesis, University of Bath, 2012. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.579514.

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The performance of peristaltic pumps is mainly governed by their tubing or hose materials. Research and development in this area is therefore very important for peristaltic pump manufacturers to keep in front of the competition and to open up new applications to enable further market penetration. Another aspect of this is of course price; performance and cost have to be in balance. As an approach to fabricate a new tube material, the field of negative Poisson's ratio (or: auxetic) materials is explored. The combined deformations of tensile, compression and shear in a peristaltic pump tube may well benefit from the specific characteristics of auxetic materials. Materials can be designed to keep their dimensions constant in directions perpendicular to an applied load. This is referred to as “auxetic balancing”. Finite element modelling shows that lowering the Poisson's ratio will rapidly decrease the maximum stresses in the cross-section of an occluded tube. Optimum values for the Poisson's ratio are found to be between −0.1 and +0.1, preferentially being 0. The re-entrant honeycomb structure is selected for initial trials, but manufacturing of this structure at the desired dimension proved to be too difficult at this time. Instead, electrospun nanofibre membranes are selected as the reinforcement structure. A liquid silicone elastomer is used as the matrix material. Key characteristics for the new material are derived from baseline test results on existing tubing. Laminates are manufactured from electrospun nylon6 nanofibre membranes coated with a liquid silicone rubber. Compression moulding is used to cure the nylon6-silicone rubber laminate, to give two effects: it ensures impregnation of the membrane and the compression deforms the nanofibre structure in such a way that it will become auxetic through-the-thickness. Flat sheet laminates of 2 mm thickness are manufactured with 14 layers of reinforcement. A reinforcing effect and substantial lowering of the through-the-thickness Poisson's ratio is observed for the laminates at low strains. At higher strains (>50%) the effect of the reinforcement diminishes and the Poisson's ratio of the laminate and pure silicone rubber equalises. Finally, tubular laminates are manufactured and the resulting tubes are tested in a peristaltic pump with some promising results (>1 million occlusions before failure). Tube performance is not yet at the required level, but with further optimisation of the laminating process, mould design and (post-)curing large steps forward can be made.

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8

Fellinger, Tim-Patrick. "Hydrothermal and ionothermal carbon structures : from carbon negative materials to energy applications." Phd thesis, Universität Potsdam, 2011. http://opus.kobv.de/ubp/volltexte/2012/5782/.

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The needs for sustainable energy generation, but also a sustainable chemistry display the basic motivation of the current thesis. By different single investigated cases, which are all related to the element carbon, the work can be devided into two major topics. At first, the sustainable synthesis of “useful” carbon materials employing the process of hydrothermal carbonisation (HC) is described. In the second part, the synthesis of heteroatom - containing carbon materials for electrochemical and fuel cell applications employing ionic liquid precursors is presented. On base of a thorough review of the literature on hydrothermolysis and hydrothermal carbonisation of sugars in addition to the chemistry of hydroxymethylfurfural, mechanistic considerations of the formation of hydrothermal carbon are proposed. On the base of these reaction schemes, the mineral borax, is introduced as an additive for the hydrothermal carbonisation of glucose. It was found to be a highly active catalyst, resulting in decreased reaction times and increased carbon yields. The chemical impact of borax, in the following is exploited for the modification of the micro- and nanostructure of hydrothermal carbon. From the borax - mediated aggregation of those primary species, widely applicable, low density, pure hydrothermal carbon aerogels with high porosities and specific surface areas are produced. To conclude the first section of the thesis, a short series of experiments is carried out, for the purpose of demonstrating the applicability of the HC model to “real” biowaste i.e. watermelon waste as feedstock for the production of useful materials. In part two cyano - containing ionic liquids are employed as precursors for the synthesis of high - performance, heteroatom - containing carbon materials. By varying the ionic liquid precursor and the carbonisation conditions, it was possible to design highly active non - metal electrocatalyst for the reduction of oxygen. In the direct reduction of oxygen to water (like used in polymer electrolyte fuel cells), compared to commercial platinum catalysts, astonishing activities are observed. In another example the selective and very cost efficient electrochemical synthesis of hydrogen peroxide is presented. In a last example the synthesis of graphitic boron carbon nitrides from the ionic liquid 1 - Ethyl - 3 - methylimidazolium - tetracyanoborate is investigated in detail. Due to the employment of unreactive salts as a new tool to generate high surface area these materials were first time shown to be another class of non - precious metal oxygen reduction electrocatalyst. Die Notwendigkeit einer nachhaltigen Energiewirtschaft, sowie der nachhaltigen Chemie stellen die Motivation der vorgelegten Arbeit. Auf Grundlage separater Untersuchungen, die jeweils in engem Bezug zum Element Kohlenstoff stehen, kann die Arbeit in zwei Themenfelder geordnet werden. Der erste Teil behandelt die nachhaltige Herstellung nützlicher Kohlenmaterialien mit Hilfe des Verfahrens der hydrothermalen Carbonisierung. Im zweiten Teil wird die Synthese von Bor und Stickstoff angereicherten Kohlen aus ionischen Flüssigkeiten für elektrochemische Anwendungen abgehandelt. Insbesondere geht es um die Anwendung in Wasserstoff-Brennstoffzellen. Als Ergebnis einer sorgfältigen Literatur¬zusammenfassung der Bereiche Hydrothermolyse, hydrothermale Carbonisierung und Chemie des Hydroxymethylfurfurals wird ein chemisch-mechanistisches Modell zur Entstehung der Hydrothemalkohle vorgestellt. Auf der Basis dieses Modells wird ein neues Additiv zur hydrothermalen Carbonisierung von Zuckern vorgestellt. Die Verwendung des einfachen Additivs, genauer Borax, erlaubt eine wesentlich verkürzte und zu niedrigeren Temperaturen hin verschobene Prozessführung mit höheren Ausbeuten. Anhand des mechanistischen Modells wird ein Einfluss auf die Reaktion von Zuckern mit der reaktiven Kohlenvorstufe (Hydroxymethylfurfural) identifiziert. Die chemische Wirkung des Minerals Borax in der hydrothermalen Carbonisierung wird im Folgenden zur Herstellung vielfältig anwendbarer, hochporöser Kohlen mit einstellbarer Partikelgröße genutzt. Zum Abschluss des ersten Teils ist in einer Serie einfacher Experimente die Anwendbarkeit des mechanischen Modells auf die Verwendung „echter“ Biomasse in Form von Wassermelonenabfall gezeigt. Im zweiten Teil werden verschiedene cyano-haltige ionische Flüssigkeiten zur ionothermalen Synthese von Hochleistungskohlen verwendet. Durch Variation der ionischen Flüssigkeiten und Verwendung unterschiedlicher Synthesebedingungen wird die Herstellung hochaktiver, metallfreier Katalysatoren für die elektrochemische Reduktion von Sauerstoff erreicht. In der direkten Reduktion von Sauerstoff zu Wasser (wie sie in Brennstoffzellen Anwendung findet) werden, verglichen zu konventionellen Platin-basierten elektrochemischen Katalysatoren, erstaunliche Aktivitäten erreicht. In einem anderen Beispiel wird die selektive Herstellung von Wasserstoffperoxid zu sehr geringen Kosten vorgestellt. Abschließend wird anhand der Verwendung der ionischen Flüssigkeit 1-Ethyl-3-methylimidazolium-tetracyanoborat eine detaillierte Betrachtung zur Herstellung von graphitischem Borcarbonitrid vorgestellt. Unter Verwendung unreaktiver Salze, als einfaches Werkzeug zur Einführung großer inneren Oberflächen wird erstmals die elektrokatalytische Aktivität eines solchen Materials in der elektrochemischen Sauerstoffreduktion gezeigt.

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9

Gould, Rebecca J. "The Variable use of ne in Negative Structures: An Apparent-Time Variationist Study of Synchronous Electronic French Discourse." Thesis, University of North Texas, 2010. https://digital.library.unt.edu/ark:/67531/metadc33157/.

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This study of the variable use of ne in synchronous electronic French discourse follows the methodological guidelines and the theoretical framework proposed and subsequently elaborated by Labov for analyzing variable features of language. This thesis provides a quantitative variable rule (i.e., VARBRUL) analysis including age as a factor group (i.e., independent variable), thereby making a new contribution to this area of inquiry. The data (50,000 words from the vingtaine 'twentysomething' channel and 50,000 words from the cinquantaine 'fiftysomething' channel) are a subset of 100,000 words from a corpus of one million words collected in 2008 by the thesis director from the public chat server EuropNet. This study aims to answer the following overarching question: To what extent does age-compared to other factors-influence the variable use of ne in verbal negation in synchronous electronic French discourse? In order to answer this question, and possibly others, the VARBRUL analysis will include age, subject (e.g., noun vs. pronoun), type of second negative particle (e.g., pas 'not', jamais 'never', personne 'no one'/'nobody', and so forth), as well as verbal mood/tense.

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10

Chen, Da. "A Multi-Material Projection Stereolithography System for Manufacturing Programmable Negative Poissons Ratio Structures." Thesis, Virginia Tech, 2017. http://hdl.handle.net/10919/74961.

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Digital light Projection based Additive Manufacturing (AM) enables fabrication of complex three-dimensional (3D) geometries for applications ranging from rapid prototyping jet parts to scaffolds for cell cultures. Despite the ability in producing complex, three-dimensional architectures, the state of art DLP AM systems is limited to a single homogenous photo-polymer and it requires a large volume of resin bath to begin with. Extensible Multi-material Stereolithography (EMSL) is a novel high-resolution projection stereolithography system capable of manufacturing hybrid 3D objects. This system provides new capabilities, allowing more flexible design criteria through the incorporation of multiple feedstock materials throughout the structure. With EMSL manufacturing ability, multi-material programmable negative Poissons ratio honeycomb reentrant structures are realized. Researchers have been studying auxetic structures over decades, the mechanical property control of auxetic structure mainly relies on geometry design in previous studies. Now with the help of EMSL system, other design variables associated with auxetic structures, such as material properties of local structural members, are added into design process. The additional variables are then proved to have significant effects on the material properties of the auxetic structures. The ability to accurately manufacture multi-material digital design will not only allow for novel mechanical and material researches in laboratory, but also extend the additive manufacturing technology to numerous future applications with characteristics such as multiple electrical, electromechanical and biological properties. The design and optimization of EMSL system realizes novel structures have not been producible, therefore it will stimulate new possibilities for future additive manufacturing development. Master of Science

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11

Corsi, Marzia. "Design of experiment analysis of additively manufactured negative stiffness structures for shock absorber applications." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/20436/.

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Negative stiffness structures, as a branch of multi-stable mechanical metamaterials, exhibit multiple stable configurations. Their characteristics, such as bi-stability, snapthrough and negative stiffness, make them particularly suitable for shock absorber applications. The majority of NSS is designed in a cuboidal shape and only recently few studies focused on cylindrical negative stiffness structures. During this study, three types of special-shaped NSS have been designed, produced and tested. To determine the influence of dimension parameters and materials on the functionality of these flexible structures, for each one of three concepts, five different versions in two different materials and techniques have been realized. The specimens were fabricated in PEBA (PolyEther Block Amide) and TPU (Thermoplastic PolyUrethane) using, respectively, Selective Laser Sintering (SLS) and MultiJet Printing (MJP) technologies; the design freedom of Additive Manufacturing (AM), allows the production of complex structures and the possibility of functional integration like shock absorber functionality. Albite in different ways, in all the three structures unit cells are present pre-shaped curved beams to ensure snap-through and bi-stable mechanisms and are expected to exhibit exceptional energy dissipation properties. To investigate the mechanical and NS properties of these structures and their deformation mechanisms, quasi-static compression tests have been performed. The results analyzed through force-displacement curves, highlighted the energy recovery of the specimens during deformation and the influence of dimension parameters on the response to the applied loads. During the tests, it was also evident how the usage of different dimensions and materials can lead, for the same structure, to a symmetric or asymmetric buckling mode in the collapse of the layers and to prevent the structure to return to its original shape once the load has been removed.

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12

Jallais, Christophe. "EFFETS DES HUMEURS POSITIVE ET NEGATIVE SUR LES STRUCTURES DE CONNAISSANCES DE TYPE SCRIPT." Phd thesis, Université de Nantes, 2006. http://tel.archives-ouvertes.fr/tel-00163826.

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La majorité des travaux menés sur l'interaction entre cognition et émotion a porté sur l'étude de mots simples mais peu de recherches se sont intéressées à l'impact des variations émotionnelles sur l'activation et sa propagation au sein des structures de connaissances comme les scripts. L'objectif de cette recherche consiste à étudier l'impact d'humeurs obtenues par induction sur l'organisation des scripts en mémoire. Quatre expériences (production libre, évaluations, dénominations d'actions en conditions automatique et stratégique) ont été effectuées afin de tester les effets différentiels des humeurs positives et négatives sur ces bases de connaissances. D'une manière générale, les résultats mettent en évidence une différence dans l'accès et l'organisation des diverses actions composant le script selon la dimension centralité entre les humeurs positives et négatives. L'idée de réorganisation cognitive en humeur positive révélée pour les concepts est ici vérifiée pour les scripts.

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13

Rose, Alec Daniel. "All-angle negative refraction of photonic and polaritonic waves in three-dimensionally periodic structures." Thesis, Boston College, 2009. http://hdl.handle.net/2345/685.

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Thesis advisor: Krzysztof Kempa Though nature provides a plethora of materials to work with, their properties are very much restricted, forcing severe limitations on the devices that are built from them. A huge portion of current technology stands to be significantly advanced and even revolutionized by the emergence of a new class of “configurable” materials. This class, generally referred to as metamaterials, has become more feasible than ever due to advancements in nanotechnology and fabrication techniques. Notable among nature’s limitations is an ever-positive index of refraction. This barrier has only recently been broken, and the known paths to negative refraction are few and limited. This paper introduces two distinct three-dimensional crystals capable of all-angle negative refraction. One uses the familiar photonic band, while the other is the first of its kind to rely on polaritonic waves. Their mode structures are examined and a set of parameters are chosen at which a negative effective index of refraction can be harnessed for unrestricted sub-wavelength lensing, demonstrated via numerical simulation. This work is expected to enable experimental observation of polaritonic negative refraction and sub-wavelength lensing at microwave frequencies Thesis (BS) — Boston College, 2009 Submitted to: Boston College. College of Arts and Sciences Discipline: College Honors Program Discipline: Physics

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Ortuño, Molinero Rubén. "Extraordinary Transmission Filtering Structures based on Plasmonic Metamaterials." Doctoral thesis, Universitat Politècnica de València, 2012. http://hdl.handle.net/10251/14639.

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Esta tesis trata sobre el fascinante fenómeno de la transmisión extraordinaria a través de láminas metálicas nonoestructuradas periódicamente con aperturas al corte. Un efecto relacionado con la excitación de un tipo de ondas superficiales como son los plasmones de superficie. Además, en aquellas estructuras formadas por el apilamiento de dos o más láminas metálicas se consiguen nuevas funcionalidades, como magnetismo artificial que da lugar a resonancias magnéticas y por tanto la posibilidad de obtener un índice de refracción negativo.Mediante un estudio teórico y numérico se ha comprobado que este tipo de respuesta magnética efectiva se debe a la excitación de resonancias plasmónicas internas en la estructura. Obteniéndose, bajo incidencia normal, un índice de refracción efectivo negativo en la dirección de propagación en el caso de que dichas resonancias se produzcan en zonas del espectro donde se obtenga la permitividad negativa, conectando el mundo de la plasmónica con el de los metamateriales. Uno de los principales objetivos en el diseño de metamateriales es obtener un índice de refracción negativo en un gran ancho de banda. Sin embargo, este objetivo suele ser complicado de conseguier al basar los diseños en fenómenos resonantes. Es por ello que en esta tesis se ha propuesto un diseño basado en el apilamiento de estructuras fishnet con diferentes grosores de dieléctrico para conseguir aumentar el ancho de banda en el cual se consigue un índice negativo. Básicamente, la obtención de tal efecto se basa en la excitación de resonancias plasmónicas a distintas frecuencias al estar formada la celda unidad por difentes grososres de dieléctrico. La hibridación que se produce entre dichas resonancias permite aumentar el ancho de banda con índice negativo. Aunque la transmisión extraordinaria esta principalmente relacionada con excitación de plasmones de superficie, los resultados mostrados en la tesis demuestran que para el caso de láminas metálicas rodeadas por dieléctricos también se consigue transmisión extraordinaria debido a la adaptación de la luz incidente a los modos soportados por los medios dieléctricos siempre y cuando el metal se encuentre estructurado periódicamente. Ortuño Molinero, R. (2012). Extraordinary Transmission Filtering Structures based on Plasmonic Metamaterials [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/14639 Palancia

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Ates, Kazim Ozan. "Theoretical Investigation Of Metamaterials: Srr Structures And Periodic Arrays Of Thin Conducting Wires." Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609485/index.pdf.

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In recent years, there has been an increasing interest on left handed metamaterials because of their possible innovative applications. The pioneer study introducing such materials was brought out by V. G. Veselago in 1968 [1]. In his work, Veselago proposed a medium having simultaneously negative electric permittivity and magnetic permeability and investigated its electromagnetic characteristics. He found out that the electric field, magnetic field and the propagation vector form a left handed triplet, thus named such materials as &ldquo Left Handed Materials&rdquo . Despite the significance of Veselago&rsquo s inferences, the metamaterial theory stayed dormant for nearly 30 years. Towards the end of 1990s, the physically realizable left handed materials were built as the combination of two periodical structures Split Ring Resonators (SRRs) and metallic thin wire arrays [4-5]. In this thesis, electrical and magnetic characteristics of the left handed metamaterials are theoretically investigated by using the analytical models for their permittivity and permeability functions with respect to frequency. For this purpose, first, two basic metamaterial structures the Split Ring Resonators and Thin Metallic Wire Arrays are studied individually and their electrical and magnetic characteristics are examined. Finally, the composite left handed structure containing both SRRs and thin wires is studied to investigate the resulting simultaneous resonance properties and to estimate their overall effective permeability and permittivity functions.

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16

Tsui, Ho-yu, and 徐浩宇. "Families of polarized abelian varieties and a construction of Kähler metrics of negative holomorphic bisectional curvature on Kodairasurfaces." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B37053760.

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Tsui, Ho-yu. "Families of polarized abelian varieties and a construction of Kähler metrics of negative holomorphic bisectional curvature on Kodaira surfaces." Click to view the E-thesis via HKUTO, 2006. http://sunzi.lib.hku.hk/hkuto/record/B37053760.

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Salloum, Rogério [Verfasser], Tobias [Akademischer Betreuer] Melz, and Rinderknecht [Akademischer Betreuer] Stephan. "Optimization of shunt damped composite structures using negative capacitances / Rogério Salloum. Betreuer: Tobias Melz ; Rinderknecht Stephan." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2016. http://d-nb.info/1112141960/34.

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Rogaten, Jekaterina. "Adaptive-positive vs. maladaptive-negative structures and processes in learning : towards the comprehensive model of academic performance." Thesis, London Metropolitan University, 2014. http://repository.londonmet.ac.uk/694/.

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The goal of the Ph.D. research was to develop an empirical foundation suitable for designing educational interventions and programmes aiming to improve students' learning. In order to achieve this a series of studies was conducted that supported the development and test of a comprehensive, chained mediation model of academic performance. The proposed chained mediation model comprised of adaptive-positive and maladaptive-negative submodels. The adaptive-positive submodel hypothesised firstly that trait intrinsic motivation and adaptive metacognition would facilitate the use of creative cognition in studying (first-level mediator). Secondly, the mediator hypothesised that the use of creative cognition in studying would lead to the experience of positive affect in studying, and to the development of adaptive approaches to studying (second-level mediators). Finally, the submodel hypothesised that positive affect in studying and adaptive approaches to studying would facilitate academic performance. The maladaptive-negative submodel hypothesised firstly that trait intrinsic motivation and maladaptive metacognition would lead to evaluation anxiety (first-level mediator). Secondly, the model hypothesised that evaluation anxiety would lead to the experience of negative affect in studying, and to the development of a maladaptive approach to studying (second-level mediators). Finally, the model hypothesised that negative affect in studying and the maladaptive approach to studying would undermine academic performance. A total of five studies were conducted employing 2140 university students.

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Hodge, II John Adams. "Analysis of Periodic and Random Capacitively-Loaded Loop (CLL) Metamaterial Structures for Antenna Enhancement Applications." Thesis, Virginia Tech, 2014. http://hdl.handle.net/10919/49298.

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After being theorized by Veselago in 1967, recent developments in metamaterials over the last two decades have allowed scientists and researchers to physically demonstrate that artificial composite media can be engineered to exhibit exotic material properties, such as negative refractive index, by exploiting features in arrays of sub-wavelength unit inclusions. These unconventional electromagnetic properties are realized through the coupling of the microscopic unit inclusions, which govern the macroscopic properties of the structure. After demonstrating that a periodic array of capacitively-loaded loop (CLL) inclusions paired with continuous wire results in negative refraction, this study performs numerical simulations to characterize random metamaterial structures. These structures consist of CLLs that are randomized in both position and orientation. In addition, this thesis introduces an innovative antenna enhancing structure consisting of capacitively-loaded loop (CLL) metamaterial elements loaded radially around a standard dipole antenna at an electrically small distance. As a result of this innovative arrangement, the dipole antenna is easily transformed into a directive mechanically scanned antenna with high realized gain. The desired directivity and gain can be tuned based on the number of radial CLL fins placed around the dipole. Interactions between the antenna and metamaterial elements result in significant enhancement of the maximum radiated field amplitude and front-to-back ratio. This innovative CLL-loaded dipole antenna is compared to the conventional Yagi-Uda antenna. The structures presented in this thesis are modeled using full-wave simulation, and one antenna structure is experimentally verified as a proof-of-concept. Master of Science

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21

Greve, Benjamin K. "Exploring the thermal expansion of fluorides and oxyfluorides with ReO₃-type structures: from negative to positive thermal expansion." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/43753.

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This thesis explores the thermal expansion and high pressure behavior of some materials with the ReO₃ structure type. This structure is simple and has, in principle, all of the features necessary for negative thermal expansion (NTE) arising from the transverse thermal motion of the bridging anions and the coupled rotation of rigid units; however, ReO₃ itself only exhibits mild NTE across a narrow temperature range at low temperatures. ReO₃ is metallic because of a delocalized d-electron, and this may contribute to the lack of NTE in this material. The materials examined in this thesis are all based on d⁰ metal ions so that the observed thermal expansion behavior should arise from vibrational, rather than electronic, effects. In Chapter 2, the thermal expansion of scandium fluoride, ScF₃, is examined using a combination of in situ synchrotron X-ray and neutron variable temperature diffraction. ScF₃ retains the cubic ReO₃ structure across the entire temperature range examined (10-1600 K) and exhibits pronounced negative thermal expansion at low temperatures. The magnitude of NTE in this material is comparable to that of cubic ZrW₂O₈, which is perhaps the most widely studied NTE material, at room temperature and below. This is the first report of NTE in an ReO₃ type structure across a wide temperature range. Chapter 3 presents a comparison between titanium oxyfluoride, TiOF₂, and a vacancy containing titanium hydroxyoxyfluoride, Tiₓ(O/OH/F)₃. TiOF₂ was originally reported to adopt the cubic ReO₃ structure type under ambient conditions, therefore the initial goal for this study was to examine the thermal expansion of this material and determine if it displayed interesting behavior such as NTE. During the course of the study, it was discovered that the original synthetic method resulted in Tiₓ(O/OH/F)₃, which does adopt the cubic ReO₃ structure type. The chemical composition of the hydroxyoxyfluoride is highly dependent upon synthesis conditions and subsequent heat treatments. This material readily pyrohydrolyizes at low temperatures (~350 K). It was also observed that TiOF₂ does not adopt the cubic ReO₃ structure; at room temperature it adopts a rhombohedrally distorted variant of the ReO₃ structure. Positive thermal expansion was observed for TiOF₂ from 120 K through decomposition into TiO₂. At ~400 K, TiOF₂ undergoes a structural phase transition from rhombohedral to cubic symmetry. High pressure diffraction studies revealed a cubic to rhombohedral phase transition for Tiₓ(O/OH/F)₃ between 0.5-1 GPa. No phase transitions were observed for TiOF₂ on compression. In Chapter 4, an in situ variable pressure{temperature diffraction experiment examining the effects of pressure on the coefficients of thermal expansion (CTE) for ScF₃ and TaO₂F is presented. In the manufacture and use of composites, which is a possible application for low and NTE materials, stresses may be experienced. Pressure was observed to have a negligible effect on cubic ScF₃'s CTE; however, for TaO₂F the application of modest pressures, such as those that might be experienced in the manufacture or use of composites, has a major effect on its CTE. This effect is associated with a pressure-induced phase transition from cubic to rhombohedral symmetry upon compression. TaO₂F was prepared from the direct reaction of Ta₂O₅ with TaF₅ and from the digestion of Ta₂O₅ in hot hydro uoric acid. The effects of pressure on the two samples of TaO₂F were qualitatively similar. The slightly different properties for the samples are likely due to differences in their thermal history leading to differing arrangements of oxide and uoride in these disordered materials. In Chapter 5, the local structures of TiOF₂ and TaO₂F are examined using pair distribution functions (PDFs) obtained from X-ray total scattering experiments. In these materials, the anions (O/F) are disordered over the available anion positions. While traditional X-ray diffraction provides detailed information about the average structures of these materials, it is not suffcient to fully understand their thermal expansion. Fits of simple structural models to the low r portions of PDFs for these materials indicate the presence of geometrically distinct M{X{M (M = Ti, Ta; X = O, F) linkages, and a simple analysis of the TaO₂F variable temperature PDFs indicates that these distinct links respond differently to temperature.

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22

Fellinger, Tim-Patrick [Verfasser], and Markus [Akademischer Betreuer] Antonietti. "Hydrothermal and ionothermal carbon structures : from carbon negative materials to energy applications / Tim-Patrick Fellinger. Betreuer: Markus Antonietti." Potsdam : Universitätsbibliothek der Universität Potsdam, 2012. http://d-nb.info/1019254297/34.

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23

Hay, Nicole M. "Complex Filters as Cascade of Buffered Gingell Structures: Design from Band-Pass Constraints." DigitalCommons@CalPoly, 2017. https://digitalcommons.calpoly.edu/theses/1731.

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Complex filters are multi-input, multi-output networks designed to discriminate based upon the relative phase difference between input signals. Complex filters find application in modern wireless systems for single sideband transmission and image-reject reception. This thesis presents one active complex filter implementation using two operational amplifiers per stage, termed “type-II” topology. The “type-II” originates from the passive RC-CR polyphase topology presented by Gingell in his 1973 paper, “Single sideband modulation using sequence asymmetric polyphase networks.” This new topology gains several advantages over existing complex filter implementations, namely “cascadability” (multiple sections placed in series to create a higher-order response) without altering the characteristics of each individual stage. In addition to describing the derivation of the topology and its performance relative to existing topologies, this thesis investigates the passband characteristics of a general higher-order filter and provides a passband-centric design approach through derivations of closed form expressions for passband gain and bandwidth. The thesis includes a five-stage design example using this approach in addition to an implementation, its characterization, and its comparison to the derived expressions and simulations.

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24

Paramasivam, Nagarajan [Verfasser], and Dirk [Akademischer Betreuer] Linke. "Identification of Surface Structures Common to Gram-Negative Bacteria that are Suitable for Vaccine Development / Nagarajan Paramasivam ; Betreuer: Dirk Linke." Tübingen : Universitätsbibliothek Tübingen, 2012. http://d-nb.info/1162843438/34.

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PERETTI, JACQUES. "Photoemission et photoemission assistee par champ de structures metal/semi-conducteur en affinite electronique negative : structure de bandes et proprietes de transport electronique dans les semi-conducteurs." Paris 11, 1992. http://www.theses.fr/1992PA112066.

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L'idee directrice de ce travail est de determiner experimentalement les proprietes electroniques d'un semi-conducteur d'un point de vue structurel, c'est-a-dire de mesurer sa structure de bandes, et d'un point de vue dynamique, a savoir d'identifier et de caracteriser les phenomenes qui regissent le transport electronique dans ce materiau. La distribution en energie des electrons photoemis par une structure ag/inp en affinite electronique negative est mesuree pour differentes valeurs de l'energie d'excitation lumineuse. La dispersion des premieres bandes de valence et de conduction de inp est ainsi exploree. En particulier, des contributions a l'energie de ces bandes des interactions avec les bandes eloignees sont mesurees. Les positions des minima secondaires des premiere et deuxieme bandes de conduction sont egalement determinees. Le transport d'electrons chauds dans inp est etudie par photoemission assistee par champ electrique d'une diode schottky ag/inp en affinite electronique negative. La distribution en energie des electrons photoemis est mesuree, a energie d'excitation fixee, pour differentes valeurs de la tension inverse appliquee a la jonction. Les resultats fournissent une image spectroscopique directe du transport electronique a l'interieur du cristal d'inp qui met en evidence les phenomenes physiques dominants. L'interpretation, basee sur des modeles originaux et intuitifs, permet d'acceder aux temps caracteristiques de collision electron phonon, dans l'ensemble de la premiere bande de conduction. Des informations sur la structure des niveaux electroniques de conduction sont egalement obtenues

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26

Oltean, Gabriel. "From Current Collectors to Electrodes : Aluminium Rod Structures for Three-dimensional Li-ion Micro-battery Applications." Doctoral thesis, Uppsala universitet, Institutionen för kemi - Ångström, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-215482.

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The potential use of 3D aluminium nanorod structures as current collectors and negative electrodes for 3D Li-ion micro-batteries was studied based on the use of relatively simple and cost-effective electrochemical and sol-gel deposition techniques. Aluminium rod structures were synthesised by galvanostatic electrodeposition using commercial porous membranes as templates. It was shown that the use of a short (i.e., 50 ms long) potential pulse (i.e., -0.9 V vs. Al3+/Al) applied prior to a pulsed current electrochemical deposition gave rise to homogeneous deposits with more even rod heights. Electrophoretic and sol-gel deposition of TiO2 on the same substrates were also studied. The use of the sol-gel technique successfully resulted in a thin coating of amorphous TiO2 on the Al nanorod current collector, but with relatively small discharge capacities due to the amorphous character of the deposits. Electrophoretic deposition was, however, successful only on 2D substrates. Anodisation of titanium was used to prepare 3D TiO2 nanotube electrodes, with a nanotube length of 9 um and wall thickness of 50 nm. The electrodes displayed high and stable discharge capacities of 460 µAh/cm2 at a 0.1 C rate upon prolonged cycling with good rate capability. The 3D aluminium nanorod structures were tested as negative electrodes for Li-ion cells and the observed capacity fading was assigned to trapping of LiAl alloy inside the aluminium electrode caused by the diffusion of lithium into the electrode, rather than to pulverisation of the aluminium rods. The capacity fading effect could, however, be eliminated by decreasing the oxidation potential limit from 3.0 to 1.0 V vs. Li+/Li. A model for the alloying and dealloying of lithium with aluminium was also proposed. Finally, a proof-of-concept for a full 3D Li-ion micro-battery with electrodes of different geometries was demonstrated. The cell comprised a positive electrode, based on LiFePO4 deposited on a carbon foam current collector, with an area gain factor an order of magnitude larger than that for the Al nanorod negative electrode. This concept facilitates the balancing of 3D Li-ion cells as the positive electrode materials generally have significant lower specific energy densities than the negative electrodes.

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27

Bogdanov, Bogdan. "Structures, thermochemistry, and dynamics of negative gas phase cluster ions studied by pulsed-ionization high pressure mass spectrometry and computational quantum chemistry techniques." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/NQ65224.pdf.

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28

Belfiore, Laura <1994&gt. "“A comparison of Implicit and Explicit methods in English L2 : evidence from Interrogative and Negative structures in child , adolescents and adults beginner language learners”." Master's Degree Thesis, Università Ca' Foscari Venezia, 2018. http://hdl.handle.net/10579/13286.

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This experimental study wants to compare two L2 methods of acquisition: the implicit method and the explicit method. In particular, the data will be focused on the interrogative and negative structures, which seem to be more difficult than affirmative ones. In these years, a large number of studies, have always been focused on the explicit method because, as Karen Lichtman (2013) says, it is the only one which is proposed for adult students. Since this method doesn’t allow the student to reach the mother tongue level which a child does being exposed to a second language, the question is : if one proposes an implicit or a natural method, which doesn’t mean going abroad in the country of the language one wants to learn, is it possible to reach an higher level than the one reached with the explicit method? The data in the present study, comes from the monthly observation of the linguistic path of six students of an English school which proposes a natural method of acquisition. However, 3 of these students are attending the normal course. In this way, these two groups are compared. In one of his famous study, Naom Chomsky (1975,1981), proposes the nativist theory which says that the acquisition of the language is an active process of rules discovery and of hypothesis checking which is possible thanks to an innate nature of the language. Moreover, Pinker (1994) affirms that the language is an instinct. Superficially considering these statements, one can speculate that a human being, which is innately provided with this ability, can learn a language in respective whichever his/her age is. However, this ability is constrained by the effects of a “temporal window” a critical period (Lennerberg 1967) after which, the natural acquisition of a second language unavoidably decreases. Therefore, the positive expectations for this method are very low. The results will show that the effects of the implicit method are lower with respect to the explicit method which is the one that records the highest progress independently of the age of the subject. Moreover, this study will show the positive implicit group’s results after a more explicit path.

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29

Reddy, K. Siva Sankara. "Electrical Properties Of Diamond Like Carbon Films In Metal-Carbon-Silicon (MCS) Structure." Thesis, Indian Institute of Science, 1994. https://etd.iisc.ac.in/handle/2005/192.

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Amorphous carbon film with Diamond like properties is the subject of intense interest in the past one and half decade. The unusual properties of these diamond like carbon films arise from the preponderance of SP3 tetrahedral bonding of carbon in the film. Depending on the processing technique and the processing conditions used, the structure of the films can range from amorphous carbon to large grain polycrystalline diamond. These deposited amorphous carbon films, which are smooth, may find their use in optoelectronics, in dielectric films and in microelectronics. These films are found to be chemically inhomogeneous(containing SP3 hybridized carbon in a matrix of SP2 hybridized non-graphitic carbon). There is a possibility of using these films as substrates in microelectronics, provided the deposited films are structurally smooth, are chemically homogeneous and are dopable with both types of impurities. A host of other advantages of using diamond like carbon as a substrate material in microelectronics made it a topic of interest to many investigators. This prompted the author to take up investigations on diamond like carbon films from the point of examining the electrical properties of these films and on the possibility of conceiving devices based on these films. This investigation dealt with, sputter deposition of diamond like carbon films and their electrical characteristics in MCS device structures. In this, emphasis is given to the importance of processing parameters involved and the effect of each parameter on the electrical and structural properties of the film. Various substrate treatments were done prior to sputtering and found that the DLC nature of the film exists in all the films but differ from one another in electrical resistivity, in nucleation density and in their adherence to the substrate. Films deposited on substrates treated with low vapour pressure oil resulted in compressive strain in the film and lead to very poor adhesion. The nucleation density increased when the substrates are pretreated with ultrasonic agitation in hard SiC grit. The substrate temperature had a direct impact on the resistivity of the film: resistivity decreases with increase in substrate temperature. The constituents of the plasma modified the structural properties of the film, e.g. the Hydrogen content in the plasma has resulted in increasing the SP3 hybridization content of the film, by acting as SP2- SP2 network terminator. Ultra violet light focused onto the substrate, in general, enhanced the deposition rate. Inclusion of Nitrogen in the plasma substantially increased the conductivity of the material and this is used in doping of the DLC film. The carbon films deposited on silicon are used for electrical characterisation. Deposition of metal electrode on the carbon film lead to the basic (MCS) device structure. The I vs.V characteristics of the MCS structure resemble those of junction diodes. From the I vs.V characteristics at different temperatures, it has been found that the reverse current goes through a maximum, drops back to certain level and once again increases with gradual increase in temperature. This behaviour of the structure with A1 as well as Ag as top electrode materials is explained by the heterojunction formed at the C-pSi interface. The initial increase in the reverse current is dominated by the drift of minority carriers across the depletion width at the reverse biased junction. With increase in temperature, the depletion width reduces to a minimum above a certain temperature, where the diffusion of carriers controls the current across the device. From the constructed energy-band diagram of heterojunction, it is shown that the change in the transport phenomena from drift of minority carriers to diffusion of majority carriers at the junction, introduces a barrier at the critical temperature; This is responsible for the drop in current at the critical temperature. This explains the anomaly of drop in reverse current with increase in temperature. The C vs. v characteristics showed a bell shaped behaviour indicating the presence of two junctions connected back to back. This confirms the type of contact formed at the metal-carbon interface and the type of conductivity of the film, concluding that A1 makes a Schottky contact where as Ag makes an ohmic contact and the deposited film behaves like n-type material. The C vs. V behaviour with temperature is explained by the two types of contacts in the case of Al-GpSi, i.e. Schottky contact at Al-C; and heterojunction at C-pSi interface. These C vs. V and I vs.V changes with temperature are in tune with each other and the model proposed takes care of all the characteristics observed. In case of Ag-GpSi, C vs. V with temperature shows junction like behaviour at elevated temperatures and are explained by the presence of the interface at C-pSi. It has been observed that in some of the carbon films, when an electric field of the order of l06 V/cm is applied, the reflectance of the Aluminium metal dot is increased by 5 times, coupled with a 50 to 100 times increase in the associated capacitance of the MCS structure. The increase in reflectance is explained by considering the film to be inhomogeneous with a matrix of varying dielectric constants (SP3 hybridized carbon in a medium of SP2 bonded carbon). The transformed film, is homogeneous and enhances the reflectance of the Aluminium dot. This is termed as "homogeneity induced smoothness." The transformation of inhomogeneous material to homogeneous material is further confirmed by the Raman spectroscopy, in which the broad peak is converted to a sharp peak changing the FWHM from 93 cm-1 to 4 cm-1 ; denoting the structural order in the film. To the best of our knowledge, this is the first investigation reporting the crystalline nature of the DLC, with structural order and the corresponding FWHM of the Raman peak as low as 4 cm-1. The preparational conditions of the film to get this transformation and the influence of various process parameters are examined. Devices based on Metal-Carbon-Oxide- Silicon (MCOS) structure are realized by thermally grown oxide/sputter deposited oxide on silicon, prior to carbon deposition. These structures showed voltage controlled negative resistance(VCNR) characteristics. The applied voltage and its distribution across the reverse biased junction and across the oxide gives rise to a negative resistance region. With the number of V vs. I characteristics measured, it is observed that the negative resistance region also shifts. This is attributed to the trapped charges in the carbon changing the distribution of applied voltage. This is explained by modifying the energy-band diagram. A concept of the accumalated charges at the oxide barrier filling up the higher energy states in the carbon and silicon, to become hot carriers is used. As long a. more voltage is dropped across the oxide, these hot carriers can surmount the barrier at the reverse biased junction. The flow of these carriers is cut off when the additional voltage is dropped across the reverse biased junction leading to a drop in the current. A further increase in the applied voltage nominally increases the current due to increase in the leakage current. A new hybrid (electrical/optical) read only memory (ROM) element is conceived and the way in which the information can be written and read is discussed. A two terminal negative resistance device using MCOS structure is fabricated and tested for its VCNR property. An analog memory device is proposed using the MCOS structure as gate in an FET. The work reported in this thesis has been divided into nine chapters. The introductory remarks on the importance of the area of research and about the work reported in this thesis are given in chapter one. Chapter two deals with some of the basic concepts related to understand the reported work. In chapter three the research work done by other investigators covering different aspects of this work is reported and some of their investigations are reviewed. Chapter four dealt with the various preparative techniques to deposit films, their structural characterisation, and the experimental work carried out to electrically characterize these films. Chapter five presents the I vs.V & C vs. V analysis and a model to qualitatively explain them. In chapter six field induced transformation phenomena of some of these films and its impact on the reflectance of the metal dot is dealt. Chapter seven consists of the MCOS device structure, its I vs.V characteristics and a model to explain the behaviour. Chapter eight presents the application part of same of the phenomena observed in conceiving a new hybrid ROM element and a two terminal negative resistance device. The concluding ninth chapter itemizes the important results of the work and suggestions to carry forward this work which can open up new vistas in the diamond like carbon film based technology and its applications in microelectronics.

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30

Reddy, K. Siva Sankara. "Electrical Properties Of Diamond Like Carbon Films In Metal-Carbon-Silicon (MCS) Structure." Thesis, Indian Institute of Science, 1994. http://hdl.handle.net/2005/192.

Full text

Abstract:

Amorphous carbon film with Diamond like properties is the subject of intense interest in the past one and half decade. The unusual properties of these diamond like carbon films arise from the preponderance of SP3 tetrahedral bonding of carbon in the film. Depending on the processing technique and the processing conditions used, the structure of the films can range from amorphous carbon to large grain polycrystalline diamond. These deposited amorphous carbon films, which are smooth, may find their use in optoelectronics, in dielectric films and in microelectronics. These films are found to be chemically inhomogeneous(containing SP3 hybridized carbon in a matrix of SP2 hybridized non-graphitic carbon). There is a possibility of using these films as substrates in microelectronics, provided the deposited films are structurally smooth, are chemically homogeneous and are dopable with both types of impurities. A host of other advantages of using diamond like carbon as a substrate material in microelectronics made it a topic of interest to many investigators. This prompted the author to take up investigations on diamond like carbon films from the point of examining the electrical properties of these films and on the possibility of conceiving devices based on these films. This investigation dealt with, sputter deposition of diamond like carbon films and their electrical characteristics in MCS device structures. In this, emphasis is given to the importance of processing parameters involved and the effect of each parameter on the electrical and structural properties of the film. Various substrate treatments were done prior to sputtering and found that the DLC nature of the film exists in all the films but differ from one another in electrical resistivity, in nucleation density and in their adherence to the substrate. Films deposited on substrates treated with low vapour pressure oil resulted in compressive strain in the film and lead to very poor adhesion. The nucleation density increased when the substrates are pretreated with ultrasonic agitation in hard SiC grit. The substrate temperature had a direct impact on the resistivity of the film: resistivity decreases with increase in substrate temperature. The constituents of the plasma modified the structural properties of the film, e.g. the Hydrogen content in the plasma has resulted in increasing the SP3 hybridization content of the film, by acting as SP2- SP2 network terminator. Ultra violet light focused onto the substrate, in general, enhanced the deposition rate. Inclusion of Nitrogen in the plasma substantially increased the conductivity of the material and this is used in doping of the DLC film. The carbon films deposited on silicon are used for electrical characterisation. Deposition of metal electrode on the carbon film lead to the basic (MCS) device structure. The I vs.V characteristics of the MCS structure resemble those of junction diodes. From the I vs.V characteristics at different temperatures, it has been found that the reverse current goes through a maximum, drops back to certain level and once again increases with gradual increase in temperature. This behaviour of the structure with A1 as well as Ag as top electrode materials is explained by the heterojunction formed at the C-pSi interface. The initial increase in the reverse current is dominated by the drift of minority carriers across the depletion width at the reverse biased junction. With increase in temperature, the depletion width reduces to a minimum above a certain temperature, where the diffusion of carriers controls the current across the device. From the constructed energy-band diagram of heterojunction, it is shown that the change in the transport phenomena from drift of minority carriers to diffusion of majority carriers at the junction, introduces a barrier at the critical temperature; This is responsible for the drop in current at the critical temperature. This explains the anomaly of drop in reverse current with increase in temperature. The C vs. v characteristics showed a bell shaped behaviour indicating the presence of two junctions connected back to back. This confirms the type of contact formed at the metal-carbon interface and the type of conductivity of the film, concluding that A1 makes a Schottky contact where as Ag makes an ohmic contact and the deposited film behaves like n-type material. The C vs. V behaviour with temperature is explained by the two types of contacts in the case of Al-GpSi, i.e. Schottky contact at Al-C; and heterojunction at C-pSi interface. These C vs. V and I vs.V changes with temperature are in tune with each other and the model proposed takes care of all the characteristics observed. In case of Ag-GpSi, C vs. V with temperature shows junction like behaviour at elevated temperatures and are explained by the presence of the interface at C-pSi. It has been observed that in some of the carbon films, when an electric field of the order of l06 V/cm is applied, the reflectance of the Aluminium metal dot is increased by 5 times, coupled with a 50 to 100 times increase in the associated capacitance of the MCS structure. The increase in reflectance is explained by considering the film to be inhomogeneous with a matrix of varying dielectric constants (SP3 hybridized carbon in a medium of SP2 bonded carbon). The transformed film, is homogeneous and enhances the reflectance of the Aluminium dot. This is termed as "homogeneity induced smoothness." The transformation of inhomogeneous material to homogeneous material is further confirmed by the Raman spectroscopy, in which the broad peak is converted to a sharp peak changing the FWHM from 93 cm-1 to 4 cm-1 ; denoting the structural order in the film. To the best of our knowledge, this is the first investigation reporting the crystalline nature of the DLC, with structural order and the corresponding FWHM of the Raman peak as low as 4 cm-1. The preparational conditions of the film to get this transformation and the influence of various process parameters are examined. Devices based on Metal-Carbon-Oxide- Silicon (MCOS) structure are realized by thermally grown oxide/sputter deposited oxide on silicon, prior to carbon deposition. These structures showed voltage controlled negative resistance(VCNR) characteristics. The applied voltage and its distribution across the reverse biased junction and across the oxide gives rise to a negative resistance region. With the number of V vs. I characteristics measured, it is observed that the negative resistance region also shifts. This is attributed to the trapped charges in the carbon changing the distribution of applied voltage. This is explained by modifying the energy-band diagram. A concept of the accumalated charges at the oxide barrier filling up the higher energy states in the carbon and silicon, to become hot carriers is used. As long a. more voltage is dropped across the oxide, these hot carriers can surmount the barrier at the reverse biased junction. The flow of these carriers is cut off when the additional voltage is dropped across the reverse biased junction leading to a drop in the current. A further increase in the applied voltage nominally increases the current due to increase in the leakage current. A new hybrid (electrical/optical) read only memory (ROM) element is conceived and the way in which the information can be written and read is discussed. A two terminal negative resistance device using MCOS structure is fabricated and tested for its VCNR property. An analog memory device is proposed using the MCOS structure as gate in an FET. The work reported in this thesis has been divided into nine chapters. The introductory remarks on the importance of the area of research and about the work reported in this thesis are given in chapter one. Chapter two deals with some of the basic concepts related to understand the reported work. In chapter three the research work done by other investigators covering different aspects of this work is reported and some of their investigations are reviewed. Chapter four dealt with the various preparative techniques to deposit films, their structural characterisation, and the experimental work carried out to electrically characterize these films. Chapter five presents the I vs.V & C vs. V analysis and a model to qualitatively explain them. In chapter six field induced transformation phenomena of some of these films and its impact on the reflectance of the metal dot is dealt. Chapter seven consists of the MCOS device structure, its I vs.V characteristics and a model to explain the behaviour. Chapter eight presents the application part of same of the phenomena observed in conceiving a new hybrid ROM element and a two terminal negative resistance device. The concluding ninth chapter itemizes the important results of the work and suggestions to carry forward this work which can open up new vistas in the diamond like carbon film based technology and its applications in microelectronics.

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31

Yi, Kaijun. "Controlling guided elastic waves using adaptive gradient-index structures." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEC044/document.

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Les matériaux à gradient d'indice de réfraction (GRIN) présentent des propriétés mécaniques variant en temps ou/et en espace. Ils ont été testés pour des applications prometteuses dans de nombreuses applications d'ingénierie, comme pour le contrôle santé structurale ou la surveillance de structure (SHM), le contrôle des vibrations et bruit, la récupération d'énergie, etc. D'un autre côté, les matériaux piézoélectriques offrent la possibilité de réaliser des cellules composites dont les propriétés mécaniques peuvent être contrôlées en ligne. Motivé par ces deux approches, cette thèse étudie la mise en œuvre de structures GRIN adaptatifs pour le contrôle des ondes élastiques. Deux types de structures GRIN adaptatifs sont étudiés dans ce travail. Le premier exemple concerne la mise en œuvre d'une lentille piézoélectrique dans une plaque. Il est composé de patchs piézoélectriques shuntés, collés périodiquement en surface du guide d'ondes. Les circuits de shunt utilisés permettent d'émuler une capacité négative (NC). En accordant les valeurs de NC on peut ajuster l'indices de réfraction du milieu à l'intérieur de la lentille piézoélectrique et pour satisfaire une fonction sécante hyperbolique. Les résultats numériques montrent que les lentilles piézoélectriques peuvent alors focaliser les ondes de flexion de la plaque sur les points focaux. La lentille piézoélectrique est efficace dans une grande bande de fréquences et efficace dans une grande plage de fonctionnement. Ainsi elle peut focaliser des ondes sur différent points par simple ajustement des valeurs de NC réalisés par le circuit. Cette focalisation adaptative la rend très intéressante pour de nombreuses applications comme la récupération d'énergie ou le SHM. La mise en œuvre de ces techniques pour la récupération d'énergie est discutée dans cette thèse. Le second exemple concerne l'étude d'une structure dont les propriétés mécaniques sont contrôlées en temps et en espace. En particulier, une modulation périodique permet de créer une onde artificielle se propageant dans la structure. L'interaction avec des ondes mécaniques entraîne une rupture de réciprocité visible dans un diagramme de bande non symétrique. De nombreux phénomènes inhabituels sont observés dans ce type de structures variables : fractionnement des fréquences, conversion d'ondes et transmission unidirectionnelles. Deux types de conversion fréquentielle sont démontrés et expliqués. Le premier est induit par la transmission d'énergie entre les différents modes Bloch et le second type est dû à la diffusion de Bragg dans les structures modulées. La transmission unidirectionnelle des ondes pourrait être exploitée pour réaliser des diodes dans des systèmes infinis ou semi-infinis. Cependant, la transmission unidirectionnelle n'existe pas dans les systèmes finis en raison des phénomènes de conversion de fréquence GRadient INdex (GRIN) media are those whose properties smoothly vary in space or/and time. They have shown promising effects in many engineering applications, such as Structural Health Monitoring (SHM), vibration and noise control, energy harvesting, etc. On the other hand, piezoelectric materials provide the possibility to build unit cells, whose mechanical properties can be controlled on-line. Motivated by these two facts, adaptive GRIN structures, which can be realized using shunted piezoelectric materials, are explored in this dissertation to control guided elastic waves. Two types of adaptive GRIN structures are studied in this work. The first type is a piezo-lens. It is composed of shunted piezoelectric patches bonded on the surfaces of plates. To control the mechanical properties of the piezoelectric composite, the piezoelectric patches are shunted with Negative Capacitance (NC). By tuning the shunting NC values, refractive indexes inside the piezo-lens are designed to satisfy a hyperbolic secant function in space. Numerical results show that the piezo-lens can focus waves by smoothly bending them toward the designated focal point. The piezo-lens is effective in a large frequency band and is efficient in many different working conditions. Also the same piezo-lens can focus waves at different locations by tuning the shunting NC values. The focusing effect and tunable feature of piezo-lens make it useful in many applications like energy harvesting and SHM. The former application is fully discussed in this thesis. The focusing effect at the focal point results in a known point with high energy density, therefore harvesting at the focal point can yield more energy. Besides, the tunable ability makes the harvesting system adaptive to environment changes. The second type is the time-space modulated structure. Its properties are modulated periodically both in time and space. Particularly, the modulation works like a traveling wave in the structure. Due to the time-varying feature, time-space modulated structures break the reciprocity theorem, i.e., the wave propagation in them is nonreciprocal. Many unusual phenomena are observed during the interaction between waves and time-space modulated structures: frequency splitting, frequency conversion and one-way wave transmission. Two types of frequency conversion are demonstrated and explained. The first type is caused by energy transmission between different orders Bloch modes. The second type is due to the Bragg scattering effect inside the modulated structures. The one-way wave transmission could be exploited to realize one-way energy insulation in equivalent infinite or semi-inffnite systems. However, the one-way energy insulation fails in finite systems due to the frequency conversion phenomenon

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32

Oliveira, Daniela Cabral de. "Diagnóstico de falhas em estruturas isotrópicas utilizando sistemas imunológicos artificiais com seleção negativa e clonal /." Ilha Solteira, 2019. http://hdl.handle.net/11449/182151.

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Orientador: Fábio Roberto Chavarette Resumo: Este trabalho é dedicado ao desenvolvimento de uma metodologia baseada no monitoramento da integridade estrutural em aeronaves com foco em técnicas de computação inteligente, tendo como intuito detectar, localizar e quantificar falhas estruturais utilizando os sistemas imunológicos artificiais (SIA). Este conceito permite compor o sistema de diagnóstico apto a aprender continuamente, contemplando distintas situações de danos, sem a necessidade de reiniciar o processo de aprendizado. Neste cenário, foi empregado dois algoritmos imunológicos artificiais, sendo o algoritmo de seleção negativa, responsável pelo processo de reconhecimento de padrões, e o algoritmo de seleção clonal responsável pelo processo de aprendizado continuado. Também foi possível quantificar o grau de influência do dano para as cinco situações de danos. Para avaliar a metodologia foi montada uma bancada experimental com transdutores piezelétricos que funcionam como sensor e atuador em configurações experimentais, que podem ser anexadas à estrutura para produzir ou coletar ondas numa placa de alumínio (representando a asa do avião), sendo coletados sinais na situação normal e em cinco situações distintas de danos. Os resultados demonstraram robustez e precisão da nova metodologia proposta. Abstract: This work is dedicated to the development of a methodology based on the monitoring of structural integrity in aircraft with a focus on intelligent computing techniques, aiming to detect structural failures using the artificial immune systems (AIS). This concept allows to compose the diagnostic system capable of learning continuously, contemplating different situations of damages, without the need to restart the learning process. In this scenario, two artificial immunological algorithms were employed, the negative selection algorithm, responsible for the pattern recognition process, and the clonal selection algorithm responsible for the continuous learning process. It was also possible to quantify the degree of influence of the damage for the five damage situations. To assess the methodology, an experimental bench was mounted with piezoelectric transducers that act as sensors and actuators in experimental configurations, which can be attached to the structure to produce or collect waves on an aluminum plate (representing the wing of the airplane), being collected signals in the normal situation and in five different situations of damages. The results demonstrate the robustness and accuracy of the proposed new methodology. Doutor

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33

Heo, Hyeonu. "Programmable Mechanical Metamaterials with Negative Poisson's Ratio and Negative Thermal Expansion." Thesis, University of North Texas, 2016. https://digital.library.unt.edu/ark:/67531/metadc955088/.

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Programmable matter is a material whose properties can be programmed to achieve particular shapes or mechanical properties upon command. This is an essential technique that could one day lead to morphing aircraft and ground vehicles. Metamaterials are the rationally designed artificial materials whose properties are not observed in nature. Their properties are typically controlled by geometry rather than chemical compositions. Combining metamaterials with a programmable function will create a new area in the intelligent material design. The objective of this study is to design and demonstrate a tunable metamaterial and to investigate its thermo-mechanical behavior. An integrated approach to the metamaterial design was used with analytical modeling, numerical simulation, and experimental demonstration. The dynamic thermo-mechanical analysis was used to measure base materials' modulus and thermal expansion coefficient as a function of temperature. CPS, the unit cell of the metamaterial, is composed of circular holes and slits. By decomposing kinematic rotation of the arm and elastic deformation of a bi-material hinge, thermo-mechanical constitutive models of CPS were developed and it was extended to 3D polyhedral structures for securing isotropic properties. Finite element based numerical simulations of CPS and polyhedral models were conducted for comparison with the analytical model. 3D printing of multi-materials was used for sample fabrication followed by tests with uniaxial compressive mechanical tests and thermal tests at 50℃. From the analytical model of the metamaterial, the contour plots were obtained for the effective properties – Poisson's ratio, the effective coefficient of thermal expansion of the metamaterial as a function of geometry and materials. A controllable range of temperature and strain was identified associated with maximized thermal expansion mismatch and contact on the slit surface of CPS, respectively. This work will pave the road toward the design of programmable metamaterials with both mechanically- and thermally- tunable capability and provide unique thermo-mechanical properties with a programmable function.

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34

Thilleul, Olivia. "Negative lift generation in a tidal device structure." Thesis, Cranfield University, 2009. http://dspace.lib.cranfield.ac.uk/handle/1826/8292.

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Becoming aware of the impact of global warming, all countries of the European Union have agreed to produce 20% of their electricity from renewable energy by 2020. Hence, a new market emerged to develop more efficient technologies of sustainable power production. Cranfield University has been involved since 2006 in wave and tidal energy design projects through various government agencies funded partnerships with the emerging industry of marine renewable energy. This thesis is based on one of these projects called “DeltaStream” which was developed by Tidal Energy Ltd (TEL). The tidal stream turbine is one of the most efficient concepts in marine renewable energy, because of the high predictability of tidal streams compared to wave and wind energy. Many devices are currently being developed in the UK. Most of them are moored to the seabed using traditional methods used in the offshore oil industry, which means drilling the sea floor. The goal of this work is to avoid drilling the seabed by adding hydrofoils on the structure. Indeed, by setting a hydrofoil in the tidal stream, the goal is to prove that a downward lift force is created and is efficient enough to maintain the structure at its location, avoiding mooring costs and ecological issues relative to drilling the sea floor. Computational Fluid Dynamics (CFD) models have been performed, studying the sensitivity of mesh size compared to results quality, and testing then different hydrofoils to get the best downward lift force in local conditions. The main characteristics of the simulation are unsteady and one phase. The chosen geometry is a “quasi-2D” domain in order to minimize computational requirements. A validation case has been first performed on a well-known geometry of a circular cylinder, to compare analytical results and CFD data. Small variations between results validated the model to enable us to use the model on a less-known simulation such as a hydrofoil. Different parameters influencing the efficiency of the hydrofoil in terms of lift production and drag reduction have been tested. These results have been compared with tank tests undertaken by the OENA Group in June-July 2009 in IFREMER (France). And complementary studies have been performed to compare these results and CFD results.

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35

Lona, Jennifer S. "Negation and clausal structure /." Thesis, Connect to this title online; UW restricted, 2000. http://hdl.handle.net/1773/8387.

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Aylo, Rola. "Wave Propagation in Negative Index Materials." University of Dayton / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1280497573.

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Panten, Dietmar. "Spectroscopic properties of degenerate electronic states in negative ions." Université de Marne-la-Vallée, 2003. http://www.theses.fr/2003MARN0148.

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38

Kwok, Wai Yee Alice. "Negative affect structure of Chinese adolescents in Hong Kong." online access from Digital Dissertation Consortium, 2007. http://libweb.cityu.edu.hk/cgi-bin/er/db/ddcdiss.pl?3295081.

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39

Douma, Bambi M. "The bases and impacts of negative social relationships." Diss., The University of Arizona, 2003. http://hdl.handle.net/10150/289870.

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While there is a large amount of research on positive social relationships and their potential benefits and opportunities (social capital), negative social relationships and their potential social liabilities have been virtually ignored in the sociological and organizational literatures. Several researchers have identified this gap and made the call for research to examine both sides of social relationships to balance the "social ledger" (e.g., Brass & Labianca, 1999). This dissertation was designed as a first step into the investigation of negative social ties. Two studies were conducted to examine characteristics that might affect the valence of social relationships as well as the influence of these types of social ties on various outcomes. Homophily, or interactions with similar individuals, has been shown to positively influence social relationships in a variety of areas (McPherson, Smith-Lovin, & Cook, 2001) and heterophily, or interactions with dissimilar others, has been proposed to influence negative social relationships (Brass & Labianca. 1999; Labianca & Brass, 1997). Furthermore, Brass and Labianca theorized that there would be an asymmetric effect between these two types of social ties and that negative ties would have more of an impact on outcomes than positive ties. I test hypotheses about heterophily and negative asymmetry, yet go beyond Brass and Labianca to also test for differences between forms of negative ties. Data from three samples of undergraduate students in a male-dominated field of study were examined. Dissimilarities in age and differences in leadership preferences between dyad members were significantly related to negative ties. Older participants were more likely to have negative ties than younger participants, as older participants rated others negatively more often and were rated negatively more often. Participants who preferred to be leaders in their small groups did not want to work again with others who did not care who led the small group or others who definitely preferred someone else lead. There was little evidence to support Brass and Labianca's negative asymmetry theory. An expansion of this theory that includes distinguishing between self-directed and other-directed outcomes, as well as when to apply the different forms of negative ties is presented.

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Vinci, Natalia. "Multiphoton detachment of negative alkaline ions." Thesis, Queen's University Belfast, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.342985.

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41

Buchoud, Edouard. "Détection, localisation et quantification de déplacements par capteurs à fibre optique." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENU021/document.

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Pour l’auscultation d’ouvrages, les capteurs à fibre optique sont généralement utilisés puisqu’ils présentent l’avantage de fournir des mesures réparties. Plus particulièrement, le capteur basé sur la technologie Brillouin permet d’acquérir un profil de fréquence Brillouin, sensible à la température et la déformation dans une fibre optique sur une dizaine de kilomètres avec un pas de l’ordre de la dizaine de centimètres. La première problématique est d’obtenir un profil centimétrique sur la même longueur d’auscultation. Nous y répondons en s’appuyant sur des méthodes de séparation de sources, de déconvolution et de résolution de problèmes inverses. Ensuite, nous souhaitons estimer la déformation athermique dans l’ouvrage. Pour cela, plusieurs algorithmes de filtrage adaptatif sont comparés. Finalement, un procédé pour quantifier le déplacement de l’ouvrage à partir des mesures de déformation est proposé. Toutes ces méthodes sont testés sur des données simulées et réelles acquises dans des conditions contrôlées For structural health monitoring, optical fiber sensors are mostly used thanks their capacity to provide distributed measurements. Based on the principle of Brillouin scattering, optical fiber sensors measure Brillouin frequency profile, sensitive to strain and temperature into the optical fiber, with a meter spatial resolution over several kilometers. The first problem is to obtain a centimeter spatial resolution with the same sensing length. To solve it, source separation, deconvolution and resolution of inverse problem methodologies are used. Then, the athermal strain into the structure is searched. Several algorithms based on adaptative filter are tested to correct the thermal effect on strain measurements. Finally, several methods are developed to quantify structure displacements from the athermal strain measurements. They have been tested on simulated and controlled-conditions data

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Kunert, Aaron [Verfasser]. "Facial Structure of Cones of non-negative Forms / Aaron Kunert." Konstanz : Bibliothek der Universität Konstanz, 2014. http://d-nb.info/105323127X/34.

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Bilbe, Edward. "The structure and negative thermal expansion of low-dimensional compounds." Thesis, University of Reading, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.542068.

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Hu, Jiazhi. "UNDERSTANDING THE STRUCTURE-PROPERTY-PERFORMANCE RELATIONSHIP OF SILICON NEGATIVE ELECTRODES." UKnowledge, 2019. https://uknowledge.uky.edu/cme_etds/109.

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Rechargeable lithium ion batteries (LIBs) have long been used to power not only portable devices, e.g., mobile phones and laptops, but also large scale systems, e.g., electrical grid and electric vehicles. To meet the ever increasing demand for renewable energy storage, tremendous efforts have been devoted to improving the energy/power density of LIBs. Known for its high theoretical capacity (4200 mAh/g), silicon has been considered as one of the most promising negative electrode materials for high-energy-density LIBs. However, diffusion-induced stresses can cause fracture and, consequently, rapid degradation in the electrochemical performance of Si-based negative electrodes. To mitigate the detrimental effects of the large volume change, several strategies have been proposed. This dissertation focuses on two promising approaches to make high performance and durable Si electrodes for high capacity LIBs. First, the effect of polymeric binders on the performance of Si-based electrodes is investigated. By studying two types of polymeric binders, polyvinylidene fluoride (PVDF) and sodium alginate (SA) using peel tests, SEM, XPS, and FTIR, I show that the high cohesive strength at the binder-silicon interface is responsible for the superior cell performance of the Si electrodes with SA as a binder. Hydrogen bonds formed between SA and Si is the main reason for the high cohesive strength since neither PVDF nor SA bonds covalently with Si. Second, the fabrication of high performance Si/polyacrylonitrile (PAN) composite electrode via oxidative pyrolysis is investigated. We show that high performance Si/polyacrylonitrile (PAN) composite negative electrodes can be fabricated by a robust heat treatment in air at a temperature between 250 and 400oC. Using Raman, SEM, XPS, TEM, TGA, and nanoindention, we established that oxidation, dehydration, aromatization, and intermolecular crosslinking take place in PAN during the heat treatment, resulting in a stable cyclized structure which functions as both a binder and a conductive agent in the Si/PAN composite electrodes. With a Si mass loading of 1 mg/cm2, a discharge capacity of ~1600 mAh/g at the 100th cycle is observed in the 400oC treated Si/PAN composite electrode when cycled at a rate of C/3. These studies on the structure-property-performance relations of Si based negative electrode may benefit the LIB community by providing (1) a guide for the design and optimization of binder materials for Si electrodes and (2) a facile method of synthesizing Si-based composite negative electrodes that can potentially be applied to other Si/polymer systems for further increasing the power/energy density and lower the cost of LIBs for electric vehicle applications and beyond.

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Franchin, Giorgia. "Additive Manufacturing of Ceramics. Printing Beyond the Binder." Doctoral thesis, Università degli studi di Padova, 2017. http://hdl.handle.net/11577/3426205.

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This research project focuses on the production of ceramics via Additive Manufacturing (AM) techniques, with particular focus on extrusion-based technologies. The main advantage of AM is the ability to produce cellular structures with high complexity and controlled porosity, allowing to manufacture light but efficient stretch-dominated structures. The inspiration comes from nature: bone architectures are a great example, consisting of thin, solid skins attached to highly porous, cellular cores. Very few commercially available AM systems are suited for ceramic materials, and most of them use ceramic powders as feedstock. Residual pores and cracks are very hard to avoid and result in low strength, poor reliability and loss of unique material properties such as glass optical transparency. AM technologies employing polymers are at a much more advanced stage of development. The goal has been to exploit such advances and to provide alternatives to the ceramic powder-binder approaches. Three different material families were explored: preceramic polymers, geopolymers, and glass. The same preceramic polymer, a commercial polysilsesquioxane, was employed as a non sacrificial, reactive binder to develop inks for stereolithography (SL) and direct ink writing (DIW). The first technology allowed for production of dense, crack-free SiOC micro-components with strut size down to ~200 μm and optimal surface quality. No shape limitations were experienced, but porous structures or small dense parts are the best options in order to avoid residual pores and cracks. The second approach was employed for the fabrication of complex biosilicate scaffolds for tissue engineering with a rod diameter of 350 µm and unsupported struts. The preceramic polymer had the double role of source of silica and rheology modifier. Ceramic matrix composites (CMCs) were also fabricated; the preceramic polymer developed the ceramic matrix (SiOC) upon pyrolysis in inert atmosphere, whereas reinforcement was given by chopped carbon fibers. Geopolymer components with controlled porosity were designed and produced first by negative replica of PLA sacrificial templates and then by DIW. Highly porous ceramic components with features of ~800 μm and unsupported parts with very limited sagging were produced with the latter approach. A novel extrusion-based AM approach was finally developed for the production of objects starting from molten glass. The system processed glass from the molten state to annealed components of complex, digitally designed forms. Objects possessing draft angles and tight radii were fabricated. Within the design space it was possible to print with high precision and accuracy; parts showed a strong adhesion between layers, and high transparency through the layers. Questo progetto di ricerca riguarda la produzione di ceramici tramite tecniche di manifattura additiva (AM), con particolare focus su tecnologie estrusive. Il principale vantaggio dell’AM è la possibilità di produrre strutture cellulari ad elevata complessità e porosità controllata, consentendo di produrre reticoli stretch-dominated leggeri ma efficienti. L’ispirazione è offerta dalla natura: le strutture ossee sono un ottimo esempio, in quanto si compongono di un involucro esterno, denso e sottile, e di un cuore a struttura cellulare altamente porosa. I sistemi di AM disponibili in commercio per la produzione di componenti ceramici sono molto pochi, e la maggior parte di essi utilizza polveri ceramiche. È molto difficile evitare porosità residua e cricche, e di conseguenza si ottengono oggetti dalla resistenza limitata e privi delle peculiarità di alcuni materiali, come ad esempio la trasparenza del vetro. Le tecnologie di AM che utilizzano polimeri sono ad uno stadio di sviluppo molto più avanzato. L’obiettivo è di sfruttare tale vantaggio e di fornire alternative agli approcci polvere-legante. Sono stati esplorati tre diversi materiali: polimeri preceramici, geopolimeri, e vetro. Un unico polimero preceramico, un polisilsesquiossano commerciale, è stato utilizzato come legante reattivo, non sacrificale per lo sviluppo di inchiostri per stereolitografia (SL) e direct ink writing (DIW). La prima tecnologia ha consentito di produrre micro-componenti in SiOC densi e privi di cricche, con una dimensione dei pilastri fino a ~200 μm e ottima qualità superficiale. Non ci sono state limitazioni di forma, anche se strutture porose o oggetti densi di piccole dimensioni sono da preferire per evitare porosità residua e cricche. Il secondo approccio ha portato alla fabbricazione di scaffold bioceramici per ingegneria tissutale con filamenti di diametro 350 µm e parti non supportate. Il polimero preceramico ha il doppio ruolo di fonte di silice e di modificatore reologico. Sono stati prodotti anche compositi a matrice ceramica (CMCs); il polimero preceramico sviluppa la matrice (SiOC) tramite pirolisi in atmosfera inerte, mentre il rinforzo è dato da fibre di carbonio macinate. Componenti in geopolimero a porosità controllata sono stati progettati e prodotti prima tramite replica negativa di template sacrificali in PLA, e poi via DIW. Il secondo approccio ha portato alla produzione di reticoli ceramici con filamenti di ~800 μm e parti non supportate con deflessione molto limitata. È stato sviluppato infine un innovativo processo estrusivo a partire da vetro fuso. Un unico sistema è in grado di lavorare il vetro dallo stato fuso fino alla ricottura di componenti complessi progettati digitalmente. Sono stati realizzati oggetti comprendenti sporgenze di diversa entità e piccoli raggi di curvatura. All’interno dello spazio di progettazione è stato possibile stampare con elevata precisione e accuratezza; le parti stampate mostrano una forte adesione tra gli strati e un’elevata trasparenza attraverso di essi.

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46

McMellon, Hannah. "Structure-function studies on putative Gly1 homologues in gram-negative bacteria." Thesis, University of Sheffield, 2016. http://etheses.whiterose.ac.uk/12921/.

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47

Abd, El All Naglaa Fathy. "Negative Thermal Expansion in Zincblende Structure: an EXAFS study of CdTe." Doctoral thesis, Università degli studi di Trento, 2010. https://hdl.handle.net/11572/369152.

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To gain a deeper insight on the local origin of NTE in zincblende crystals, EXAFS measurements have been performed on CdTe, which has NTE properties intermediate between Ge and CuCl. In this work an accurate evaluation of the bond thermal expansion, parallel and perpendicular MSRDs and distribution asymmetry of the first shell of CdTe has been made, obtaining a good agreement between two different procedures of the data analysis (i) ratio method (ii) FEFF6-FEFFIT method. The values of the relevant parameters of CdTe were found intermediate between the corresponding values previously found for Ge and CuCl. The positive contribution to thermal expansion due to the bond stretching and the negative contribution due to the tension effects are disentangled and quatified in terms of the bond thermal expansion and the perpendicular MSRD, respectively, determined by the EXAFS analysis. A critical comparison of EXAFS and Bragg diffraction results; thermal expansion, thermal factors and correlation of atomic vibration, for the iso-structural crystals Ge, CdTe and CuCl has been performed. The correlation between several quantities measured by EXAFS and NTE properties is confirmed.

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48

Abd, El All Naglaa Fathy. "Negative Thermal Expansion in Zincblende Structure: an EXAFS study of CdTe." Doctoral thesis, University of Trento, 2010. http://eprints-phd.biblio.unitn.it/574/1/Thesis_Naglaa_Fathy.pdf.

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To gain a deeper insight on the local origin of NTE in zincblende crystals, EXAFS measurements have been performed on CdTe, which has NTE properties intermediate between Ge and CuCl. In this work an accurate evaluation of the bond thermal expansion, parallel and perpendicular MSRDs and distribution asymmetry of the first shell of CdTe has been made, obtaining a good agreement between two different procedures of the data analysis (i) ratio method (ii) FEFF6-FEFFIT method. The values of the relevant parameters of CdTe were found intermediate between the corresponding values previously found for Ge and CuCl. The positive contribution to thermal expansion due to the bond stretching and the negative contribution due to the tension effects are disentangled and quatified in terms of the bond thermal expansion and the perpendicular MSRD, respectively, determined by the EXAFS analysis. A critical comparison of EXAFS and Bragg diffraction results; thermal expansion, thermal factors and correlation of atomic vibration, for the iso-structural crystals Ge, CdTe and CuCl has been performed. The correlation between several quantities measured by EXAFS and NTE properties is confirmed.

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49

Todd, Michael. "One dimensional dynamics : cross-ratios, negative Schwarzian and structural stability." Thesis, University of Warwick, 2003. http://wrap.warwick.ac.uk/50608/.

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This thesis concerns the behaviour of maps with a unique critical point which is either a maximum or a minimum: so-called unimodal maps. Our first main result proves that for C2+η unimodal maps with non-flat critical point we have good control on the behaviour of cross-ratios on small scales. This result, an improvement on a result of Kozlovski in [K2], proves that in many cases the negative Schwarzian condition (which is not even defined if a map is not C3) is unnecessary. This result follows recent work of Shen, van Strien and Vargas. The main tools are standard cross-ratio estimates, the usual principal nest, the Koebe Lemma, the real bounds from [SV] and the 'Yoccoz Lemma'. Our second main result concerns questions of structural stability. Prompted by the final section of Kozlovski's thesis [K1], we prove that in some cases we can characterise those points at which a small local perturbation changes the type of the map. We prove for these cases that this set of 'structurally sensitive points' is precisely the postcritical set. The main tools are the Koebe Lemma, the real bounds of [LS1], and the quasiconformal deformation argument of [K3]. The thesis is arranged in the form of two chapters dealing with each of the main results separately, followed by an appendix to prove an auxiliary result. The chapters may be read independently of each other.

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Jesinoski, Mark S. "Young's Schema Theory: Exploring the Direct and Indirect Links Between Negative Childhood Experiences and Temperament to Negative Affectivity In Adulthood." DigitalCommons@USU, 2010. https://digitalcommons.usu.edu/etd/845.

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Young's schema theory offers a theoretical approach that relates negative childhood experiences, temperament, and early maladaptive schema, to the experience of negative affect and/or depression in adulthood. However, despite the widespread use of schema therapy in clinical practice, little research has explored the pathways theorized by Young. This study explored the pathways posited by Young and colleagues looking at the direct and indirect relationships among negative childhood experience, temperament, early maladaptive schema, and the experience of negative affect in adulthood. Self-report data were collected from 365 undergraduate students. Results demonstrated consistent and robust direct relationships between temperament and negative affect, as well as indirect relationships between temperament and/or NCE, schema, and the outcome of negative affect. Results, though mixed, reveal strengths of the schema therapy model and provide suggestions for future research.

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Dissertations / Theses on the topic 'Negative Structures'

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