Orientador: Maurice de Koning / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-23T15:22:38Z (GMT). No. of bitstreams: 1 SilvaJunior_DomingosLopesda_D.pdf: 17651517 bytes, checksum: 27cb54e210fe4d9dd8c11581abe57d01 (MD5) Previous issue date: 2013 / Resumo: Usando a abordagem da Teoria do Funcional da Densidade (DFT), estudamos propriedades estruturais de falhas de empilhamento e discordâncias parciais na fase sólida mais comum da água, conhecida como gelo Ih. Uma das principais características do gelo Ih é o desordenamento protônico, que exerce forte influência nas estruturas destes defeitos extensos. O deslocamento relativo entre camadas para produzir as falhas de empilhamento no gelo Ih é responsável por criar uma série de violações nas regras do gelo conhecidas como defeitos Bjerrum. Nas otimizações de geometria por DFT observamos que as moléculas apresentaram uma forte tendência de reconstrução para eliminar os defeitos Bjerrum. Entretanto, a desordem protônica dificulta que todos os defeitos Bjerrum sejam corrigidos espontaneamente. Estes defeitos remanescentes são responsáveis por elevar consideravelmente a energia de formação da falha de empilhamento, contrariando as estimativas experimentais. Tal contradição sugere que não há concentrações significativas de defeitos Bjerrum em falhas de empilhamento no gelo Ih. De fato, os nossos resultados para as energias de formação de falhas de empilhamento sem defeitos Bjerrum são muito próximos de zero, concordando com as estimativas experimentais. Uma energia de formação de falha de empilhamento baixa indica que a dissociação de discordâncias perfeitas em discordâncias parciais é favorável. Nós investigamos propriedades estruturais de discordâncias parciais conhecidas como parciais 30° e 90°. Observamos uma semelhança muito grande entre as estruturas destas parciais no gelo Ih com o caso do silício. Assim como no silício, as moléculas de água presentes no caroço destas parciais apresentam uma ligação quebrada. Em ambas as parciais observamos uma forte tendência de reconstrução de caroço para restabelecimento desta ligação. Novamente, a desordem protônica dificulta o restabelecimento de todas as ligações quebradas espontaneamente criando defeitos de reconstrução conhecidos como defeitos de anti fase (APD) que também são observados no silício. Fizemos simulações que comparam as energias das parciais não-reconstruídas com as totalmente reconstruídas e os nossos resultados mostraram uma grande redução do excesso de energia com a reconstrução. Isto sugere que as discordâncias parciais no gelo Ih são reconstruídas. A discordância parcial 90° apresenta dois tipos de reconstrução um deles conhecido como período simples e o outro como período duplo. A diferença de energia entre estas reconstruções é tão pequena que é plausível que estas reconstruções coexistam em um mesmo caroço. Esta coexistência é mais uma das semelhanças entre o caso do gelo Ih e do silício. Os principais resultados desta Tese foram publicados em Physical Review B 85, 024119 (2012) / Abstract: Using the Density Functional Theory (DFT) approach, we studied the structural properties of stacking faults and partial dislocations in the most common solid phase of water, known as ice Ih. One of the main features of Ice Ih is the proton disorder, which has a strong influence on the structures of these defects. The relative displacement between layers to produce the stacking faults in ice Ih is responsible for creating violations of the ice rules known as Bjerrum defects. In DFT geometric optimizations we observed that molecules show a strong tendency to reconstruct to eliminate the Bjerrum defects. However, the proton disorder prevents the correction of all Bjerrum defects spontaneously. These remaining defects are responsible for higher stacking-fault energies, contradicting experimental estimates. This contradiction suggests that there is no significant concentration of Bjerrum defects in stacking faults in ice Ih. Indeed fact, our results for stacking fault energies without Bjerrum defects are almost zero, consistent with the experimental estimates. Low stacking fault energies suggest that dissociation of perfect dislocations into two partials is favorable. We investigated the structural properties of 30° and 90° partial dislocations. We observed that the structures of partial dislocations in ice Ih is very similar to the case of silicon. As in silicon, the water molecules in the partial dislocation core have one dangling bond. In both partials we observed a strong tendency of reconstruction to fix this dangling bond. Again, the proton disorder prevents the full correction of dangling bonds to occur spontaneously, creating reconstruction defects known as anti phase defects, that are also observed in silicon. We compare the nonreconstructed with fully reconstructed partial dislocations and observed a large reduction of excess energies associated with reconstruction. This suggests that partial dislocation in ice Ih are reconstructed. The 90° partial has two types of reconstruction. One is known as single period and another as double period. The energy difference between both is so small that it is plausible that these reconstructions coexist in the same core. This coexistence is yet another similarity between ice Ih and the silicon. The main results of this Thesis were published in Physical Review B 85, 024119 (2012) / Doutorado / Física / Doutor em Ciências

Sample grid s are essential when we want to represent the variation in chemical and physical properties of the soil, being essential to know its features. In this way, this study aimed to relate the efficiency and practicality of using soil sampling knits of rectangular and hexagonal type in a farm located countryside Ivorá- RS. In order to get features that help the researcher and producer in choosing the appropriate mesh to represent and diagnose their crops by means of fertility maps and application. The methodological procedures consisted of structuring the rectangular and hexagonal sampling knits of 1 ha in the CR Campeiro 7, without user interference in the point s distribution. Soil samples were collected in June 2015. So, after analysis of the spatial distribution of points in the area for each of the cases the fertility maps and application were structured. Among the main results, it is noted that both knits can represent similarly the trends that the soil presents nevertheless, the rectangular grid, due to a higher number of points, can represent the variability more expressively, but was found that when there is a change in the position and number of sampling points in a crop, the representations of the maps have differences, which at first, analyzing only the fertility maps, these differences seem small, but when structured a map of application, this difference becomes significant as it will result in greater or lesser purchase of inputs. It is emphasized that each mesh has characteristics that will inevitably vary from crop to crop, and a sampling grid should be, always, planned and adjusted according to each case, combining the knowledge of the producer and additional data available to define the same. / As malhas de amostragem são fundamentais quando desejamos representar a variação de atributos químicos e físicos do solo, sendo imprescindível conhecer suas características. Desta forma, este trabalho teve como objetivo relacionar a eficiência e a praticidade da utilização das malhas de amostragem de solo do tipo retangular e hexagonal, em uma lavoura localizada no município de Ivorá- RS. Com o propósito de buscar características que auxiliem o pesquisador e o produtor na escolha da malha adequada para representar e diagnosticar suas lavouras, através de mapas de fertilidade e de aplicação. Os procedimentos metodológicos consistiram em estruturar as malhas de amostragem retangular e hexagonal de 1 ha no Sistema CR Campeiro 7, sem a interferência do usuário na distribuição dos pontos. As respectivas coletas de solo ocorreram no mês de junho de 2015. Assim, após a análise da distribuição espacial dos pontos na área para cada um dos casos e estruturados os mapas de fertilidade e aplicação. Entre os principais resultados encontrados, salienta-se que ambas as malhas conseguem representar de forma similar as tendências que o solo apresenta, no entanto, a malha retangular, por apresentar maior número de pontos, consegue representar a variabilidade de forma mais expressiva, mas nota-se que quando há uma alteração na posição e no número de pontos amostrais em uma lavoura, as representações dos mapas apresentam diferenças, que num primeiro momento, analisando somente os mapas de fertilidade, essas diferenças parecem ser pequenas, mas quando estruturado um mapa de aplicação, essa diferença passa a ser significativa, pois resultará em maior ou menor aquisição de insumos. Salienta-se que cada malha apresenta características que, inevitavelmente, variam de lavoura para lavoura, e uma malha de amostragem deve ser, sempre, planejada e ajustada conforme cada caso, aliando o conhecimento do produtor e dados adicionais disponíveis para definição da mesma.

While current approaches to digital image processing within the context of machine learning and deep learning are motivated by biological processes within the human brain, they are, however, also limited due to the current state of the art of input and output devices as well as the algorithms that are concerned with the processing of their data. In order to generate digital images from real-world scenes, the utilized digital images' underlying lattice formats are predominantly based on rectangular or square structures. Yet, the human visual perception system suggests an alternative approach that manifests itself within the sensory cells of the human eye in the form of hexagonal arrangements. As previous research demonstrates that hexagonal arrangements can provide different benefits to image processing systems in general, this contribution is concerned with the synthesis of both worlds in the form of the biologically inspired hexagonal deep learning for hexagonal image processing. This contribution is therefore concerned with the design, the implementation, and the evaluation of hexagonal solutions to currently developed approaches in the form of hexagonal deep neural networks. For this purpose, the respectively realized hexagonal functionality had to be built from the ground up as hexagonal counterparts to otherwise conventional square lattice format based image processing and deep learning based systems. Furthermore, hexagonal equivalents for artificial neural network based operations, layers, as well as models and architectures had to be realized. This also encompasses the related evaluation metrics for hexagonal lattice format based representations of digital images and their conventional counterparts in comparison. Therefore, the developed hexagonal image processing and deep learning framework Hexnet functions as a first general application-oriented open science framework for hexagonal image processing within the context of machine learning. To enable the evaluation of hexagonal approaches, a set of different application areas and use cases within conventional and hexagonal image processing – astronomical, medical, and industrial image processing – are provided that allow an assessment of hexagonal deep neural networks in terms of their classification capabilities as well as their general performance. The obtained and presented results demonstrate the possible benefits of hexagonal deep neural networks and their hexagonal representations for image processing systems. It is shown that hexagonal deep neural networks can result in increased classification capabilities given different basic geometric shapes and contours, which in turn partially translate into their real-world applications. This is indicated by a relative improvement in F1-score for the proposed hexagonal and square models, ranging from 1.00 (industrial image processing) to 1.03 (geometric primitives) with single classes even reaching a relative improvement of over 1.05. However, possible disadvantages are also given by the increased complexity of hexagonal algorithms. This is evident by the present potential in regard to runtime optimizations that have yet to be realized for certain hexagonal operations in comparison to their currently deployed square equivalents.:1 Introduction and Motivation 2 Fundamentals and Methods 3 Implementation 4 Test Results, Evaluation, and Discussion 5 Conclusion and Outlook

The fundamental properties of hexagonal multiferric HoMnO3 films have been thoroughly investigated. The films are grown by pulsed laser deposition on Y:ZrO2(111) substrates. High quality epitaxial HoMnO3 films of 25 { 1000 nm thickness were successfully prepared. The film properties are compared to those of single-crystals. The magnetization measurements revealed that the films show a deviating magnetic behavior from the single-crystals in several ways. For instance, the films have a weakened antiferromagnetic Ho3+ order confirmed from magnetic susceptibility. The difierences are likely to be related to the modified (mostly larger) lattice parameters of films. An approximate phase diagram in comparison with the single-crystal's one is constructed. For multiferroicity investigations, Second Harmonic Generation (SHG; in collaboration with the group of M. Fiebig) has been employed. By SHG, the ferroelectric polar order of the films is obviously confirmed. The ferroelectric switching at room temperature could be clearly demonstrated, whereas leakage of films requires generally a more sophisticated approach. / Die fundamentalen Eigenschaften von hexagonalen multiferroischen HoMnO3 Schichten werden eingehend untersucht. Die dünnen Schichten wurden mittels gepulster Laserdeposition auf Y:ZrO2(111)-Substraten gewachsen. Hochwertige epitaktische HoMnO3-Dünnschichten von 25 { 1000 nm Dicke wurden erfolgreich hergestellt. Die Dünnschichteigenschaften werden mit denen von Einkristallen verglichen. Die Magnitisierungsmessungen ergeben, dass die dünnen Schichten ein von den Einkristallen in verschiedener Weise abweichendes magnetischen Verhalten zeigen. Zum Beispiel haben die dünnen Schichten eine abgeschwächte antiferromagntetische Ho3+ Ordnung, die durch die magnetische Suszeptibilität bestätigt wird. Die Unterschiede sind wahrscheinlich auf die veränderten (meistens grösseren) Gitterparameter der dünnen Schichten zurückzuführen. Ein Phasendiagramm wird zum Vergleich mit Einkristallen konstruiert. Durch Second Harmonic Generation (SHG; in Zusammenarbeit mit der Gruppe von M. Fiebig) wird die ferroelektrische Ordnung der dünnen Schichten eindeutig bestätigt. Das ferroelektrische Umschalten bei Raumtemperatur kann eindeutig nachgewiesen werden, wobei durch den Leckstrom der dünnen Schichten allgemein eine detailliertere Vorgehensweise benötigt wird.

Colloidal assemblies of surfactants and polymers in aqueous solutions have been used by human mankind for hundreds of years and they are of great importance in many of our technological processes, such as fabrication of soap and papermaking. Less than two decades ago the idea of using colloidal assemblies as templates of inorganic materials was borne. A new population of materials, referred to as surfactant templated materials, took form. These materials showed extraordinary properties such as monodisperse pore size distribution, large surface areas and pore volumes.   The main focus of this thesis has been on synthesis and functionalisation of spherical mesostructured silica particulate materials. In the first part of the work, mesostructured materials with expanded pores have been produced using a well established aerosol-based method as well as the newly developed emulsion and solvent evaporation (ESE) method. Increase in pore size was realized through using Pluronic block copolymer F127 together with a swelling agent poly(propylene glycol) as template. The influence of the swelling agent on pore size expansion was shown to have a roughly linear relationship. Furthermore, the impact of synthesis parameters on internal and exterior morphology has been investigated. Accessibility of the internal pore space, as well as the external surface roughness were shown to be highly dependent on synthesis temperature. Additionally, a very interesting well ordered 3D closed packed (P63/mmc) material was produced using the ionic surfactant C16TAB as template in the ESE method.   In the second part of the thesis work, mesoporous spheres with large pore size, having either hydrophilic or hydrophobic surface properties, were used as carriers of an enzyme, lipase. The enzymatic activity of lipase was increased onto the hydrophobic surface, compared to lipase immobilized into the hydrophilic support as well as for lipase free in solution. This effect was probably due to a combination of enhanced hydrophobic interactions preventing denaturation of the enzyme and interfacial activation of the enzyme.  This study generated an inorganic carrier material that is a promising candidate for biocatalysis applications. Additionally, mesoporous spheres were used as carriers of a model drug, Ibuprofen, to study the effect of polyelectrolyte multilayers on release properties. However, these layers were shown impermeable independent on pH and the substance was only released from uncoated particles. / <p>QC 20100811</p>

Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / In this work was performed a study based on density functional theory of the electronic and magnetic properties of the hexagonal multiferroic manganite HoMnO3. Were performed calculations with and without the inclusion of the spin-orbit interaction, using the full potential linearized augmented plane wave method. The exchange and correlation electronic effects were approximated via generalized gradient approximation (GGA) and the method "+ U" (or GGA + U). It is known that the magnetism in HoMnO3 is due to Mn 3d4- and Ho 4f10-states. In addition, exist a consensus that the magnetic order at Mn sub-lattice is non-collinear due to the triangular arranged of Mn magnetic moments () at a-b plane. In the case of Ho magnetic moments, the arrangement is collinear with parallel to c-axis. However, because of the complexity of crystalline symmetry and of the varieties of magnetic ions in the material, the literature has not yet reached a consensus on the magnetic ordering of them (antiferromagnetic-AFM, ferromagnetic-FM or a combination of the two), as well as the values. In this work, the main objectives were: (1) to determine the ground-state magnetic structure for Ho sub-lattice (2) to obtain the values of their respective , and (3) to describe the electronic structure of the compound. Considering the nine different magnetic structures simulated, four of them are shown with more details. These are the result of the combination of two possible configurations of spins collinear for the Mn (A type AFM, A-AFM, and G type, G-AFM) and two for the Ho (FM and AFM). It was observed that, among these, the lowest energy configuration is that for Mn is fixed according to the G – AFM type and the Ho in the A – AFM type. This result agrees with the prediction of experiments in respect of the order on the Ho sub-lattice, but the values of the magnetic moments did not agree. Was found that there is a close relationship between the simulated magnetic order and its electronic structure. In particular, the band gap for the magnetic orders less energetically favorable tends to leave the compound with metallic character which is not experimentally expected. The HoMnO3 is a semiconductor whose optical gap is about 1.7 eV. Using an U = 3.0 eV on 3d and 4f states of the Ho, we obtained an energy band gap of 1.29 eV. To analyze the electronic structure in more detail, was computed the total and partial states of compound, where it was possible to notice that the 4f states of Ho are localized predominantly at the top and bottom of conduction band which are hybridized with O’s 2p states. / Nesse trabalho foi realizado um estudo baseado na teoria do funcional da densidade das propriedades eletrônicas e magnéticas da manganita hexagonal multiferroica HoMnO3. Foram realizados cálculos com e sem a inclusão da interação spin-órbita utilizando o método full potential linearized augmented plane wave. Os efeitos de troca e correlação eletrônica foram aproximados via a generalized gradient approximation (GGA) e o método “+U” (ou GGA+U). É sabido que o magnetismo no HoMnO3 é devido aos estados 3d4 do Mn e 4f10 do Ho. Além disso, há consenso que a ordem magnética na sub-rede do Mn é não colinear devido aos momentos magnéticos () arranjados triangularmente no plano a-b do cristal. No caso dos dos átomos de Ho, o arranjo é colinear e com paralelos ao eixo c-cristalino. Porém, devido à complexidade da simetria cristalina e das variedades de íons magnéticos no material, a literatura ainda não chegou a um consenso quanto ao ordenamento magnético do estado fundamental deles (antiferromagnético – AFM, ferromagnético – FM ou uma combinação dos dois), bem como nas magnitudes dos . Neste trabalho, os principais objetivos foram: (1) avaliar a ordem magnética na sub-rede do Ho que corresponde ao estado fundamental magnético, (2) obter os valores dos respectivos atômicos e (3) descrever a estrutura eletrônica do composto. Das nove estruturas magnéticas diferentes que foram simuladas, quatro delas são apresentados com maiores detalhes. Essas são resultado da combinação de duas possíveis configurações de spins colineares para o Mn (AFM do tipo A, A-AFM, e do tipo G, G-AFM) e duas para o Ho (FM e A-AFM). Observou-se que, dentre essas, a configuração de menor energia é aquela onde o Mn está arranjado segundo o tipo G – AFM e o Ho no tipo A – AFM. Esse resultado concorda com a previsão de um dos experimentos no que diz respeito à ordem na sub-rede do Ho. Porém, os valores dos calculados para os átomos de Ho não concordaram. Verificou-se que existe uma estreita relação entre a ordem magnética simulada e a estrutura eletrônica. Em especial, o band gap para as ordens magnéticas menos favoráveis energeticamente tende a deixar o composto com caráter metálico o que não é esperado experimentalmente. O HoMnO3 em estudo é um semicondutor cuja energia de gap óptico é aproximadamente de 1,7 eV. Empregando um U = 3,0 eV nos estados 3d do Mn e 4f do Ho, obtém-se uma energia de band gap de 1,29 eV. Para avaliar a estrutura eletrônica mais detalhadamente, realizaram-se cálculos de densidade de estados total e parciais, onde foi possível notar que os estados 4f do Ho hibridizados com os 2p dos O’s predominam no top da banda de valência e fundo da banda de condução do material. / São Cristóvão, SE

Fundação de Apoio a Pesquisa e à Inovação Tecnológica do Estado de Sergipe - FAPITEC/SE / The RMnO3 (R=Y,Lu) compounds, members of the family of hexagonal manganites, are materials which exhibit strong magneto-electric coupling characteristic for multiferroic compounds. Despite the numerous studies with objective to reveal the origin of this phenomenon, the mechanism that is causing it is still not fully understood. The question that attracts special attention of scientific community is about the cause of ferroelectric distortion that occurs at certain temperatures in these materials. Although this issue is discussed in many papers, there is still no consensus what mechanism is responsible for it: (1) hybridization between the Mn dz2 orbital and O pz orbital (Mn d0 –ness model), (2) hybridization between the R dz2 orbital and O pz orbital (R d0 –ness model), (3) geometric effects or (4) charge transfer from Mn-O bonds to R-O bonds. Understanding of the mechanism that leads to ferroelectric polarization is necessary to speed application of these materials in ferroelectric memories or spintronics devices. Objective of the present work was to evaluate the first two possible mechanisms that might cause the ferroelectric distortion in RMnO3. Adopted strategy was to investigate what happens with the Mn-O and R-O chemical bonds after the structural phase transition from paraelectric to ferroelectric phase that occurs at high temperature, at which both phases are characterized by paramagnetic order of the Mn magnetic moments. For that purpose, the first-principles calculations based on density functional theory were carried on, with usage of the most modern exchange-correlation potentials. The chemical bonds were evaluated (1) qualitatively, by analysis of density of electronic states (DOS) and maps of electronic density along the bonds, and (2) quantitatively, in terms of topological analysis of Bader. The results revealed that no significant change occurred with Mn-O bonds, while the R-O bonds were affected by phase transition in the sense that R dz2 and O pz orbital exhibited enhanced hybridization in the ferroelectric phase. Therefore, the present study substantiates the R d0 –ness mechanism as the probable cause of ferroelectric distortions in RMnO3 compounds. / The RMnO3 (R=Y,Lu) compounds, members of the family of hexagonal manganites, are materials which exhibit strong magneto-electric coupling characteristic for multiferroic compounds. Despite the numerous studies with objective to reveal the origin of this phenomenon, the mechanism that is causing it is still not fully understood. The question that attracts special attention of scientific community is about the cause of ferroelectric distortion that occurs at certain temperatures in these materials. Although this issue is discussed in many papers, there is still no consensus what mechanism is responsible for it: (1) hybridization between the Mn dz2 orbital and O pz orbital (Mn d0 –ness model), (2) hybridization between the R dz2 orbital and O pz orbital (R d0 –ness model), (3) geometric effects or (4) charge transfer from Mn-O bonds to R-O bonds. Understanding of the mechanism that leads to ferroelectric polarization is necessary to speed application of these materials in ferroelectric memories or spintronics devices. Objective of the present work was to evaluate the first two possible mechanisms that might cause the ferroelectric distortion in RMnO3. Adopted strategy was to investigate what happens with the Mn-O and R-O chemical bonds after the structural phase transition from paraelectric to ferroelectric phase that occurs at high temperature, at which both phases are characterized by paramagnetic order of the Mn magnetic moments. For that purpose, the first-principles calculations based on density functional theory were carried on, with usage of the most modern exchange-correlation potentials. The chemical bonds were evaluated (1) qualitatively, by analysis of density of electronic states (DOS) and maps of electronic density along the bonds, and (2) quantitatively, in terms of topological analysis of Bader. The results revealed that no significant change occurred with Mn-O bonds, while the R-O bonds were affected by phase transition in the sense that R dz2 and O pz orbital exhibited enhanced hybridization in the ferroelectric phase. Therefore, the present study substantiates the R d0 –ness mechanism as the probable cause of ferroelectric distortions in RMnO3 compounds.

The superior advantage of a nodal method for reactor cores with hexagonal fuel assemblies discretized as cells consisting of equilateral triangles is its mesh refinement capability. In this thesis, a diffusion and a simplified P3 (or SP3) neutron transport nodal method are developed based on trigonal geometry. Both models are implemented in the reactor dynamics code DYN3D. As yet, no other well-established nodal core analysis code comprises an SP3 transport theory model based on trigonal meshes. The development of two methods based on different neutron transport approximations but using identical underlying spatial trigonal discretization allows a profound comparative analysis of both methods with regard to their mathematical derivations, nodal expansion approaches, solution procedures, and their physical performance. The developed nodal approaches can be regarded as a hybrid NEM/AFEN form. They are based on the transverse-integration procedure, which renders them computationally efficient, and they use a combination of polynomial and exponential functions to represent the neutron flux moments of the SP3 and diffusion equations, which guarantees high accuracy. The SP3 equations are derived in within-group form thus being of diffusion type. On this basis, the conventional diffusion solver structure can be retained also for the solution of the SP3 transport problem. The verification analysis provides proof of the methodological reliability of both trigonal DYN3D models. By means of diverse hexagonal academic benchmark and realistic detailed-geometry full-transport-theory problems, the superiority of the SP3 transport over the diffusion model is demonstrated in cases with pronounced anisotropy effects, which is, e.g., highly relevant to the modeling of fuel assemblies comprising absorber material.

Nanokompositfilmer med fem olika sammansättningar av hexagonala bornitrid nanosheet och TEMPO-CNF tillverkades med hjälp av vakuumassisterad filtreringsteknik. sond-ultraljudsteknik användes som en grön väg för exfoliering av bornitridpulver i vattenhaltigt medium. TEMPO-CNF spelade nyckelroller som både matris och dispergeringsmedel för stabilisering av bornitrid nanosheets i kompositen. Nanokompositfilmerna var flexibla och formbara och de visade höga mekaniska egenskaper inklusive hög draghållfasthet och god brottöjning. / Nanocomposite films with five different compositions of hexagonal boron nitride nanosheets and TEMPO-CNF were fabricated using vacuum-assisted filtration technique. probe-ultrasonication technique was applied as a green route for exfoliation of boron nitride powder in aqueous medium. TEMPO-CNF played key roles as both matrix and dispersant agent for stabilization of the boron nitride nanosheets in the composite. The nanocomposite films were flexible and ductile, and they showed high mechanical properties including high tensile strength and good elongation at break.

The queens graph Qn has the squares of then x n chessboard as its vertices; two squares are adjacent if they are in the same row, column or diagonal. A set D of squares of Qn is a dominating set for Qn if every square of Qn is either in D or adjacent to a square in D. If no two squares of a set I are adjacent then I is an independent set. Let 'J'(Qn) denote the minimum size of a dominating set of Qn and let i(Qn) denote the minimum size of an independent dominating set of Qn. The main purpose of this thesis is to determine new values for'!'( Qn). We begin by discussing the most important known lower bounds for 'J'(Qn) in Chapter 2. In Chapter 3 we state the hitherto known values of 'J'(Qn) and explain how they were determined. We briefly explain how to obtain all non-isomorphic minimum dominating sets for Q8 (listed in Appendix A). It is often useful to study these small dominating sets to look for patterns and possible generalisations. In Chapter 4 we determine new values for')' ( Q69 ) , ')' ( Q77 ), ')' ( Q30 ) and i (Q45 ) by considering asymmetric and symmetric dominating sets for the case n = 4k + 1 and in Chapter 5 we search for dominating sets for the case n = 4k + 3, thus determining the values of 'I' ( Q19) and 'I' (Q31 ). In Chapter 6 we prove the upper bound')' (Qn) :s; 1 8 5n + 0 (1), which is better than known bounds in the literature and in Chapter 7 we consider dominating sets on hexagonal boards. Finally, in Chapter 8 we determine the irredundance number for the hexagonal boards H5 and H7, as well as for Q5 and Q6 / Mathematical Sciences / D.Phil. (Applied Mathematics)