Thesis (Ph. D.)--University of Wisconsin--Madison, 1972. / Typescript. Vita. Description based on print version record. Includes bibliographical references.

No description available.

Etableringen av köpcentra i Malmö har medfört en ökad konkurrens gentemot handeln i stadskärnan vilket märktes tydligt vid Emporias invigning 2012. Handeln i staden tappade kraft och problem med vakanser uppstod. Syftet med studien är att undersöka hur centrumhandeln har utvecklats och hur fastighetsägarna ser på problemet med vakanser idag och om man fortfarande har problem med vakanser.Studien har genomförts med en kvalitativ metod där totalt sex intervjuer genomförts med både fastighetsägare och en samverkansorganisation för att få en bild av hur man arbetar med gågatan. Studien har presenterat teorier kring utbud, efterfrågan, konkurrens, hyror och samverkan. Resultatet av studien visade att stadskärnans attraktivitet avgör om andra handelsplatser är ett hot eller inte och att attraktiviteten är direkt kopplad till vakansgraden. Det är därför viktigt att stadskärnan utvecklar sina starka egenskaper och skapar något unikt som de andra handelsalternativen inte kan uppnå. För att utveckla staden till en attraktivare plats krävs det att alla aktörer i området skapar gemensamma mål och arbetar tillsammans. Citysamverkan gör det möjligt för fastighetsägare, butiker och kommunen att samverka för att göra staden attraktivare. Fastighetsägarna har även en stor roll i hur staden utvecklas då valet av butiker är en välplanerad process som följer den gemensamma vision man har i de olika delområdena. Studien visar på att samverkan är helt avgörande för attraktiviteten och att attraktiviteten påverkar hur stora vakansproblem man får. / The establishment of shopping malls in Malmö has resulted in increased competition, which was clearly noted at Emporia's opening in 2012. The trade in the city lost power and problems with vacancies arose. The purpose of the study is to investigate how the center trade has evolved and how property owners look at the problem of vacancies today and if you still have problems with vacancies.The study has been conducted with a qualitative method where a total of six interviews were conducted with both property owners and a collaborative organization to get an idea of how to work with the street. The study has presented theories about supply, demand, competition, rents and collaboration. The result of the study showed that the city center's attractiveness determines whether other trading venues are a threat or not and that the attractiveness is directly linked to the vacancy rate.It is therefore important that the city center develops its strong qualities and creates something unique that the other trading options can not achieve. In order to develop the city into an attractive location, all actors in the area need to create common goals and work together. Citysamverkan enables property owners, shops and the municipality to work together to make the city more attractive. Real estate owners also play a major part in the development of the city, as the choice of stores is a well-planned process that follows the common vision of the various sub-areas.The study shows that collaboration is crucial for attractiveness and that the attractiveness affects how much vacancy problems one gets.

No description available.

Stabilised zirconias have a remarkable variety of technological and commercial applications, e.g., thermal barrier coatings, gas sensors, solid oxide fuel cells, ceramic knives and even fashion jewelry. This amazing versatility seems to originate from the creation of atomic defects (oxide ion vacancies) in the zirconia crystal. Indeed, these vacancies, and their interactions with other vacancies or cations, dramatically affect the structural, thermal, mechanical and electrical properties of zirconia. This thesis is concerned with the study of the role of the vacancy interactions on the conducting properties of these materials. This study was performed by using realistic, first-principles based molecular dynamics simulations. The first system studied in this thesis is Zr0:5 0:5xY0:5+0:25xNb0:25xO7. This has a fixed number of vacancies across the series but its conductivity changes by almost two orders of magnitude as a function of x. For this reason, Zr0:5 0:5xY0:5+0:25xNb0:25xO7 represents an ideal test-bed for the role of the cation species on the defect interactions and therefore on the ionic conductivity of these materials. Realistic inter-atomic potentials for Zr0:5 0:5xY0:5+0:25xNb0:25xO7 were developed on a purely first-principles basis. The observed trends of decreasing conductivity and increasing disorder with increasing Nb5+ content were successfully reproduced. These trends were traced to the influences of the cation charges and relative sizes and their effect on vacancy ordering by carrying out additional calculations in which, for instance, the charges of the cations were equalised. The effects of cation ordering were considered as well and their influence on the conductivity understood. The second part of this thesis deals with Sc2O3–doped (ScSZ) and Y2O3–doped (YSZ) zirconias. These systems are of great academic and technological interest as they find use in solid oxide fuel cells. Inter-atomic potentials were parametrised and used to predict the structural and conducting properties of these materials, which were found to agree very well with the experimental evidence. The simulations were then used to study the role of the vacancy interactions on the conducting properties of these materials. Two factors were found to influence the ionic conductivity in these materials: cation-vacancy and vacancy-vacancy interactions. The former is responsible for the difference in conductivity observed between YSZ and ScSZ. Vacancies, in fact, prefer to bind to the smaller Zr4+ ions in YSZ whereas there is not a strong preference in the case of ScSZ, since the cations have similar sizes in this case. This effect is observed at temperatures as high as T = 1500 K. Finally, it was found that vacancies tend to order so that they can minimise their mutual interaction and that this ordering tendency is what ultimately is responsible for the observed anomalous decrease of the ionic conductivity with increasing dopant concentration. The consequences of such a behaviour are discussed.

L’étude des défauts ponctuels (lacunes, impuretés) et des complexes (cavités, joints de grains, etc.) est un domaine important de la physique du solide. Les propriétés physiques et chimiques des matériaux (élasticité, plasticité, fragilité, etc.) sont très souvent corrélées à la présence de ces défauts. Les techniques expérimentales ne sont cependant pas toujours en mesure de fournir une compréhension suffisante de ceux-ci. Dans ce cas-là, les simulations numériques et la modélisation à l’échelle atomique sont des outils utiles pour interpréter les résultats expérimentaux. Mon travail de thèse se situe dans ce cadre. Le manuscrit comporte 4 principales parties. Dans la première et la deuxième partie, nous présentons les principes de la DFT et la méthodologie utilisée dans cette thèse. La troisième partie de ce manuscrit résume l’étude théorique par DFT de la formation, la migration et la diffusion de différentes configurations de multi-lacunes Vn(n=1-15) dans le fer cubique centré. Les configurations de Vn les plus stables y sont décrites en détail : les énergies de formation, de liaison et de piégeage. La migration de différentes multilacunes est discutée en détail d’un point de vue énergétique et configurationnelle. Dans la dernière partie, nous nous intéressons à l’absorption du soufre dans différents sites (interstitiel et substitutionnel) du massif de Ni et sa ségrégation vers les surfaces Ni (100) et Ni (111). L’étude du soufre en volume permet de clarifie sa position en solution solide. Nous discutons des interactions soufre-soufre et avec le métal de base. La ségrégation et l’absorption sur des surfaces libres du nickel est aussi abordée en détail. / The study of point defects (vacancies, impurity) and complex defects (cavities, grain boundary etc.) is a major challenge for solid state physics. The physical and chemical properties of materials (such elasticity, plasticity, embrittlement etc.) are correlated to the presence of these defects. The experimental study is not always able to bring sufficient information about them. In this way computational simulations and the modeling on the atomic level is efficient to interpret the experimental results and to obtain new informations. This PhD work consists also in a theoretical study of defects in metals. This manuscript is organized in four main parts. In the first and second part, we present the theoretical principles and the methodology used in this work. In the third part, we report a long discussion on the study of formation, migration and diffusion of multivacancies Vn in the bcc-iron system. The main objective of this study is to identify and to analyze most stable configurations of multivacancies for different sizes of Vn (n=1-15) in Fe. The migration is also investigated. In the last part, we present a study of S atoms in nickel. The different sites (interstitial and substitutional sites) in solid solution of nickel-fcc and the segregation of sulfur on and in the Ni(100) and Ni(111) surfaces are discussed. The study of sulfur in the bulk shows that the atoms S occupy the substitutional sites. The S-S and S-Ni interactions are also presented. We conclude by a discussion on the segregation and the adsorption on free surfaces.

O principal objetivo dessa dissertação de mestrado é o estudo das propriedades estruturais e eletrônicas de umdosmateriaismais promissores para a nanoeletrônica, os nanotubos de carbono, na presença de defeitos do tipo vacâncias. Os defeitos estudados neste trabalho são as monovacâncias e multivacâncias em nanotubos de carbono armchair (5, 5). Para isso, realizamos cálculos quânticos de primeiros princípios baseados na teoria do funcional da densidade. Primeiramente, foi realizado um estudo sistemático das monovacâncias variando a sua concentração, para que possamos entender qual é a influência da distância entre esses defeitos no sistema. A partir de 14.784Å o efeito do potencial inserido pela vacância praticamente é desprezível. Seguindo essa sistemática, observamos também que a partir de 19.712Å a interação elástica entre defeitos é desprezível. Em todas as estruturas de bandas ocorre o surgimento de bandas de impureza, caracterizadas por uma localização de carga no defeito, principalmente no \"dangling bond\". Utilizando o procedimento NEB (nudge elastic band) obtivemos um valor de 0.55eV para a barreira de migração da vacância. Esse valor fornece um tempo aproximado de 0.156ms a 300K, para que a vacância salte de um sítio para outro na rede do nanotubo. Tendo isso, determinamos que a monovacância é um defeito que apresenta uma grande mobilidade no sistema, o que pode eventualmente ocorrer de uma encontrar-se com outras, formando sistemas maiores, como clusters de monovacâncias ou multivacâncias. Seguindo o nosso objetivo, realizamos um estudo sistemático das multivacâncias. Determinamos todas as reconstruções desses defeitos, nas quais observamos que as multivacâncias de índice par, apresentavam somente pentágonos e uma região central, e em contrapartida as de índice ímpar apresentavam pentágonos, uma região central e um dangling bond na sua estrutura final. Definidas as estruturas e as energias das multivacâncias, calculamos suas propriedades eletrônicas, onde é notório que a influência desses defeitos é muito mais drástica que as monovacâncias, devido a sua grande extensão no sistema. Realizamos cálculos de transporte eletrônico para todos os sistemas, utilizando o método de funções de Green fora do equilíbrio (NEGF-DFT), desenvolvido no nosso grupo. A partir desses cálculos, observamos que todos os defeitos modificam a estrutura eletrônica do sistema, uns mais outros menos, mas até para as multivacâncias maiores como a hexavacância, o sistema mantém o seu caráter metálico. Através das técnicas de funções de Green, mostramos que quando estamos utilizando condições periódicas de contorno há uma surgimento de minigap\'s espúrios. Estes não aparecem quando o vínculo de simetria translacional é quebrado via técnicas de funções de Green. / The main purpose of this dissertation is the study of the electronic and structural properties in the presence of different types of vacancies, in one of the most promising materials for nanoelectronics, carbon nanotubes. The defects studied in this work are monovacancy and multivacancies in (5, 5) armchair carbon nanotubes. For that purpose perform quantum ab initio calculations based on density functional theory (DFT). Firstly, was made a systematic study of monovacancies varying its concentration, so we can understand what is the influence of the distance between these defects in the system. Undergoes reconstruction pentagon nonagon from14.784Å on words the effect of the potential created by the vacancy is practically negligible. Following this systematic approach, we also found that from 19.712Å the structural interaction between the defects tends to zero. In all band structures one observes impurity bands, characterized by charge localization in the defect, mainly in the dangling bond. Using the NEB (nudge elastic band) procedure we obtained a value of 0.55eV for the migration barrier of the monovacancy. This value provides an approximate time of 0.156ms at 300K for the vacancy to jump from one site to another on the nanotube network. Hence, we determined that the monovacancy presents a great mobility in the system, which may possibly inccur in two ore more vacancies merging with others to form a larger defect, such as clusters of monovacancies or a hole multivacancy. Following our goal, we conducted a systematic study of multivacancies. We determined all reconstructions of these defects. We observed that multivacancies with and even number of carbon atoms removed had only pentagons and a central region. In contrast the CNT with and odd numbers of carbon atoms removed have pentagons, a central region and a dangling bond in its final structure. Once we have defined the structures and the energies of the multivacancies, we calculated their electronic properties. It is clear that the influence of these defects is much more drastic than the monovacancy, due to the size of the defect in the system. We calculated the electronic transport for all systems, using a non-equilibrium Green\'s functions method (NEGF-DFT), developed in our group. From these calculations, we observed that all the defects alter the electronic structure of the system, but even for the largest multivacancy, the system maintains its metallic character. Using the Green\'s functions techniques, we show that the use of periodic boundary conditions leads to the emergence of spurious mini-gap\'s. These do not appear when the translational symmetry is broken using Green\'s function approach and a true open system is considered.

Neste trabalho se realiza a síntese e caracterização de nanofios de óxido de zinco. Adicionalmente se apresenta o processo de montagem de um dispositivo para medidas elétricas deste material. Estuda-se complementarmente o efeito do tratamento de plasma sobre as propriedades de fotoluminescência do material. Nanofios foram sintetizados pelo mecanismo vapor-líquido-sólido (VLS), utilizando ouro como catalizador e safira c-plane como substrato. As amostras foram caracterizadas utilizando microscopia eletrônica de varredura, fotoluminescência a temperatura ambiente, difração de raios X, e microscopia eletrônica de transmissão. Os nanofios obtidos têm seção transversal com formato quase hexagonal, e larguras de aproximadamente 46 nm. O comprimento deles varia de 3 a 10 μm. Os resultados de difração de raios x e microscopia eletrônica de transmissão mostram que eles são monocristalinos com rede cristalina tipo wurtzita, e com direção de crescimento no eixo c. Foram estudados os efeitos da potência de plasma de oxigênio (O2) na fotoluminescência dos nanofios a temperatura ambiente. A diferença na fotoluminescência após diferentes tratamentos de plasma de O2 mostra que a razão entre a emissão da região do band gap e da banda do visível pode ser modificada pelo tratamento. Este efeito corrobora com a hipótese de que a banda verde de luminescência está relacionada às vacâncias de zinco. A variação percentual da razão entre as duas regiões apresenta uma dependência linear com a potência do plasma. / In this work, we performed the synthesis and characterization of zinc oxide nanowires. We also report an assembly process to measure the electrical properties of this material. We study the plasma treatment effect on the photoluminescence spectra of the nanowires. Nanowires were synthesized via vapor-liquid-solid mechanism, using gold as catalyst and c-plane sapphire as substrate. The samples were characterized using scanning electron microscopy, room temperature photoluminescence, x-rays diffraction and transmission electron microscopy. Our nanowires show a quasi-hexagonal cross section, with diameters of approximately 46 nm. Their lengths ranged from 3 to 10 μm. Our results show monocrystalline wurtzite crystal nanowires with c growth direction. We also study the plasma power effect of oxygen (O2) plasma treatment on the room temperature photoluminescence spectra of the nanowires. Our results show that the deep level emission to near band emission ratio decreases with the plasma treatment. This effect supports the hypothesis that claims the green band luminescence is related to the oxygen vacancies. Furthermore, the relative ratio change depends linearly on the plasma power.

Low-temperature heat capacity data contain information on the physical properties of materials, and new models continue to be developed to aid in the analysis and interpretation of heat capacity data into physically meaningful properties. This work presents the development of two such models and their application to real material systems. Equations describing low-energy vibrational modes with a gap in the density of states (DOS) have been derived and tested on several material systems with known gaps in the DOS, and the origins of such gaps in the DOS are presented. Lattice vacancies have been shown to produce a two-level system that can be modeled with a sum of low-energy Schottky anomalies that produce an overall linear dependence on temperature in the low-temperature heat capacity data. These two models for gaps in the vibrational DOS and the relationship between a linear heat capacity and lattice vacancies and many well-known models have been applied to several systems of materials to test their validity and applicability as well as provide greater information on the systems themselves. A series of bulk and nanoscale Mn-Fe and Co-Fe spinel solid solutions were analyzed using the entropies derived from heat capacity data, and excess entropies of mixing were determined. These entropies show that changes in valence, cation distribution, bonding, and the microstructure between the mixing ions is non-ideal, especially in the nanoparticles. The heat capacity data of ten Al doped TiO2 anatase nanoparticle samples have also been analyzed to show that the Al3+ dopant ions form small regions of short-range order, similar to a glass, within the TiO2 particles, while the overall structure of TiO2 remains unchanged. This has been supported by X-ray diffraction (XRD) and electron energy-loss spectroscopy and provides new insights to the synthesis and characterization of doped materials. The final investigation examines nanocrystalline CuO using heat capacities, magnetization, XRD, and electron microscopy and compares the findings to the known properties of bulk CuO. All of these measurements show transitions between antiferromagnetic and paramagnetic states in the temperature range of about 150-350 K that are greater in number and higher in temperature than the transitions in bulk CuO. These changes are shown to cause an increase in the temperature range of multiferroicity in CuO nanoparticles.

<p><font size="2" face="Arial"><font size="2" face="Arial"> <p align="left">This research paper is a review of the assertion by some commentators that the regulation of the labour market is a cause of the high unemployment rate in South Africa. It starts by providing a historical background of statutory industrial relations in South Africa leading to the current labour dispensation. The discussion includes a review of the current labour legislation and assessment of its compliance with international law. The rating of the South African labour market by the Doing Business study is discussed. This study seeks to ascertain whether there is a causal relation between labour market regulation and the unemployment rate. The conclusion reached is that South African labour legislation complies with international law as espoused in International Labour Organisation (ILO) Conventions, is not excessively rigid and, most importantly, that there is no convincing evidence of a causal relation between labour market regulation and the unemployment rate.</p> </font></font><font size="2" face="Arial"><font size="2" face="Arial"> <p>&nbsp / </p> </font></font></p>