Orientadores: Pascoal José Giglio Pagliuso, Ricardo Rodrigues Urbano / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-09-24T14:58:04Z (GMT). No. of bitstreams: 1 Garitezi_ThalesMacedo_D.pdf: 27111125 bytes, checksum: d3a94f446fa3f67a500d9adc5f733dc0 (MD5) Previous issue date: 2014 / Resumo: Nesta tese, são abordadas duas principais classes de materiais: os supercondutores à base de ferro e arsênico (FeAs) e os isolantes topológicos tridimensionais. Os supercondutores à base de FeAs foram descobertos em 2008 e desde então despertaram grande interesse na comunidade científica como candidatos à supercondutividade não-convencional de alta temperatura. Dentre as várias estruturas à base de FeAs descobertas, em particular, a família BaFe2As2 (122) é uma das mais estudadas até o momento por ser um composto intermetálico possível de ser crescido com relativa facilidade e alta qualidade comparada às outras famílias. Este composto puro possui uma transição estrutural de tetragonal para ortorrômbica à uma temperatura Ts ? 139 K, e, diminuindo a temperatura, há uma transição magnética de paramagnético (PM) para uma ordem anti-ferromagnética tipo onda de densidade de spin (SDW, no inglês) em TSDW ? 134 K. Estas transições em Ts e TSDW são gradualmente suprimidas tanto por substituição química quanto por pressão aplicada, e, antes que sejam completamente suprimidas, supercondutividade é induzida. Nesta região onde a supercondutividade (SC) ainda está emergindo, há coexistência e/ou competição de SC e SDW, com a presença de momentos quase localizados do Fe. Estes momentos podem agir como centros eficientes de aprisionamento de vórtices (centros de pinning) que são suprimidos gradativamente por pressão aplicada, formando um efeito de pinning magnético que se manisfestaria na corrente crítica dessas amostras. Para estudar os possíveis efeitos de pinning magnético neste material, foram crescidas amostras com diferentes substituições químicas e realizados estudos de densidades de corrente crítica sob pressão e campos magnéticos aplicados. Enquanto observamos que a densidade de corrente crítica nas amostras estudadas é dominada pela evolução da temperatura crítica Tc, encontramos evidências indiretas para a presença de pinning magnético em nossas amostras, através da comparação da dependência com a pressão observada para a temperatura crítica supercondutora Tc e para a densidade de corrente crítica Jc. Quanto às transições estrutural e magnética, discute-se na literatura se nesses sistemas há dopagem eletrônica efetiva quando se realiza substituição química, ou se ocorre uma sintonização das propriedades pelo ajuste da geometria dos tetraedros de FeAs nos planos do material. Além disso, na faixa de temperatura entre Ts e TSDW, há certo debate se o material torna-se inteiramente ortorrômbico e PM, ou se há coexistência entre as fases tetragonal/PM e ortorrômbica/SDW. Neste trabalho, foram crescidos monocristais de Ba(Fe,M)2As2 (M = Co, Cu) e neles estudadas as transições estrutural e magnética e a fase entre elas utilizando técnicas de ressonância magnética nuclear (RMN), difração de raios-X e calor específico. Nossos resultados sugerem que, independente do substituinte, não há dopagem eletrônica e que a geometria nos planos de FeAs regula as propriedades do material. Além disso, mostramos que, de fato, existe coexistência entre as fases tetragonal/PM e ortorrômbica/SDW nas amostras. Estes resultados corroboram nossas próprias observações em amostras de (Ba,K)Fe2As2, o que também indica a independência dos resultados com o tipo, concentração e localização dos átomos substituintes na matriz 122. Os isolantes topológicos (ITs) são uma nova classificação da matéria proposta teoricamente e observada experimentalmente em 2006, e consistem de maneira simplificada em materiais que são isolantes de banda em seu volume, porém possuem estados de superfície metálicos robustos. As propriedades exóticas destes estados de superfície tornam estes materiais candidatos a aplicações em computação quântica e spintrônica. Muitas famílias foram propostas como ITs e estudadas recentemente, em particular a família 23 ((Bi,Sb)2(Se,Te)3) e a família dos half-Heuslers, que são o foco desta Tese. Porém, ainda há muitos aspectos destes materiais que não estão bem determinados, como por exemplo a penetração dos estados de superfície, e sua resposta a campos magnéticos e a radiações incidentes. Neste trabalho, sintetizamos cristais dos ITs da família 23 e o half-Heusler YBiPt, e os estudamos utilizando a técnica de ressonância de spin eletrônico (RSE). Para o YBiPt dopado com Nd3+, observamos um comportamento da forma de linha nãoconvencional do espectro de RSE do Nd3+, onde a forma da linha depende fortemente da potência da micro-ondas, das dimensões da amostra e da concentração de Nd3+. A este comportamento não convencional atribuímos a presença de um efeito de fônon bottleneck e à presença dos estados de superfície. Para o Bi2Se3, nossos resultados preliminares sugerem que os estados de superfície têm uma interação maior com as sondas de Gd3+ abaixo de 40 K, e que estes estados de superfície possuem caráter de orbitais p / Abstract: In this thesis, two main material classes are studied: the iron arsenide (FeAs) superconductors and the three-dimensional topological insulators. The FeAs based superconductors were discovered in 2008 and since then have aroused great interest in the scientific community as possible unconventional high-temperature superconductors. Amongst the many FeAs bases structures that were discovered until now, the BaFe2As2 (122) family is one of the most studied for being an intermetallic compound which can be grown with reasonable ease and high quality when compared to other families. This pure compound presents a structural transition at Ts ? 139 K from tetragonal to orthorhombic, and a magnetic transition at a lower TSDW ? 134 K from paramagnetic (PM) to a spin density wave (SDW) anti-ferromagnetic order. Both transitions at Ts and TSDW are gradually suppressed by either chemical substitution or applied pressure, and, before both are completely suppressed, superconductivity emerges. In this region where superconductivity (SC) is still emerging, there is coexistence and/or competition between SC and SDW order, with the presence of Fe quasi-localized magnetic moments. Those moments may act as efficient pinning centers that are gradually suppressed by applied pressure, producing a magnetic pinning effect that would manifest itself in the critical currents of such samples. To study magnetic pinning effects in the 122 family, samples with different chemical substitutions were grown, and critical current density studies were performed under applied pressure and magnetic fields. While the behavior of critical current densities is dominated by the evolution of critical temperature Tc with pressure, we have found indirect evidences for the presence of magnetic pinning in our samples. Regarding the structural and magnetic transitions, there are evidences that, in the 122 system, there is no effective electronic doping when a chemical substitution is performed but a tuning of the system properties by the geometric configuration of FeAs tetrahedra in the material. Also, there is some debate if in the temperature range between Ts and TSDW the material becomes completely orthorhombic and PM, or if there is coexistence of tetragonal/PM and orthorhombic/SDW phases. In this work, Ba(Fe,M)2As2 (M = Co, Cu) single crystals were grown and their structural and magnetic transitions were investigated by nuclear magnetic resonance (NMR), X-ray diffraction and specific heat. Our results show that there is no effective electronic doping induced by any of the substitutions, and that it is the geometric configuration of FeAs tetrahedra that tunes the system properties. Also, we have shown that there is coexistence between tetragonal/PM and orthorhombic/SDW phases in these samples. The results confirm our previous observations made in (Ba,K)Fe2As2, which also indicates that our results do not depend on the type, concentration and placement of substituted atoms in the 122 matrix. Topological insulators (TIs) are a new class of condensed matter which was proposed theoretically and experimentally observed in 2006. They are, in a simplified view, materials which are band insulators in the bulk, but possess roubst intrinsic metallic surface states. The exotic properties of those surface states make these materials possible candidates in quantum computing and spintronic applications. Many different materials were proposed as TIs and recently studied, in particular the 23 family ((Bi,Sb)2(Se,Te)3) and the half-Heusler family, which are the focus of this thesis. Yet, there are several aspects of these materials which are not yet fully understood, such as the penetration of the surface states, and their response to magnetic fields and incident radiation. In this work, single crystals of the 23 and half-Heusler families were grown, and were studied by electronic spin resonance (ESR). For YBiPt, we observed an anomalous lineshape behavior, to which we attribute a phonon bottleneck effect and the presence of the surface states. For Bi2Se3, our preliminary results indicate that the surface states have an enhanced exchange interaction with the Gd3+ magnetic probes below 40 K, and that those surface states have a p-orbital character / Doutorado / Física / Doutor em Ciências

Este trabalho tem como objetivo propor uma metodologia para a classificação da hidrofobicidade (HC) em isoladores elétricos poliméricos de alta tensão. Atualmente a HC esta baseada no guia da STRI (Swedish Transmission Research Institute) elaborado em 1992. Porém neste guia a hidrofobicidade das superfícies de isoladores e classificada de acordo com o angulo de contato e/ou a quantidade de superfície molhada com água de forma subjetiva, através de um operador dependurado em uma torre de transmissão. Desta forma, este trabalho contribuiu na classificação da hidrofobicidade de forma objetiva, onde a analise foi realizada através de processamento digital de imagens. Na metodologia proposta, a HC foi determinada utilizando a analise da textura de imagens obtidas para materiais de isoladores elétricos poliméricos. Essas análises foram avaliadas com base na morfologia matemática, dimensão fractal, entropia, energia, variância e homogeneidade. Foram simuladas imagens (imagens sintéticas) da textura das superfícies dos isoladores utilizando uma placa de silicone e soluções de álcool isopropílico e água destilada (AIA) em proporções que variaram de 0 ate 100% em volume de álcool. A partir destas soluções foram obtidas imagens de gotas sobre as superfícies, para determinação do angulo de contato, e imagens da superfície para a obtenção dos padrões das texturas, que serviriam de base para a aplicação dos métodos estudados. Na tentativa de analisar as imagens independentes do padrao de iluminação, inerente as condições ambientais, foi aplicado o equalização de histograma (EQU) e/ ou implementado um filtro do tipo White Top-Hat (WTH). Este filtro funciona como um passa-alta, reduzindo o gradiente de iluminação das imagens obtidas em condições naturais. Outro método analisado de forma a eliminar o efeito do gradiente de iluminação, foi através da segmentação usando detecção de borda. Os cálculos da dimensão fractal das imagens em escala de cinza foram realizados através do método do box-counting, com tamanho do cubo variando de 3 até 11. A morfologia matemática foi utilizada de forma a qualificar as formas presentes nas imagens. Foram analisadas as derivadas das curvas do volume das imagens de abertura, de forma a identificar o tamanho dos elementos presentes na imagem. Na classificação das texturas das imagens através dos descritores de textura, os valores obtidos com a entropia apresentaram menor dispersão dentre os resultados, alem de baixo tempo de processamento, se apresentando como uma metodologia apropriada para a classificação da hidrofobicidade. Alteração nos valores de gama das imagens foi feito de forma a observar a modificação dos valores de entropia em função do efeito da iluminação das imagens. Os valores apresentaram pouca variação deste parâmetro nos resultados. Como forma de avaliar a qualidade da imagem em termos de tamanho, aumento e resolução, diversas imagens foram geradas visando a modificação destes parâmetros e analisando sua influencia nos valores de entropia. A partir dos resultados obtidos foi possível obter uma relação matemática entre as ferramentas aplicadas e as imagens, sendo possível definir a HC. Utilizando estas técnicas foi determinado o desvio dos resultados e o tempo de processamento, visando a aplicação em dispositivos moveis, como por exemplo, celulares. Assim, foi elaborado um aplicativo embarcado em um smartphone para analisar uma imagem em campo de um isolador, mostrando ao operador o valor da classificação da hidrofobicidade em aproximadamente um minuto. / The aim of this study is to propose a new method to classify the hydrophobicity (HC) in high voltage polymer insulators. Currently the HC is based on the STRI guide (Swedish Transmission Research Institute) published in 1992, where the hydrophobicity is classified by contact angle and/or amount of wet surface. In the proposed method, the HC was analyzed by digital image processing using the textures of the images obtained from electric insulators polymeric materials. These analysis were evaluated using mathematical morphology, fractal dimension, entropy, energy, variance and homogeneity. Simulated texture images (synthetic Images) about the surfaces of the insulators were created using a silicon plate and isopropyl alcohol and distilled water solutions in proportions from 0 to 100% in volume of alcohol (AIA). From these solutions, images of drops on the insulator surfaces were obtained to measure the contact angle; and surfaces images using the AIA solutions were obtained and then employed in the analysis of the texture patterns, which were used as basis for the analyzed methods. To analyze the images regardless the illumination conditions, which is a serious problem in natural weather, histogram equalization (EQU) and/or a White Top-Hat filter (WTH) was applied. This filter works as a high-pass filter, reducing the illumination gradient from the images obtained in natural conditions. Another way to avoid the gradient illumination was the segmentation technique by edge detection. The fractal dimension calculations in grayscale images were performed by the box-count method, with box size ranging from 3 to 11. Mathematical morphology was used to quantify the shapes in the images. The derivate of the volume from the opening images was analyzed to identify the elements in the image. The classification of the image texture by the entropy revealed not only the lowest dispersion of the results, but also the shortest time processing, presenting as an appropriated method to classify the hydrophobicity. Gama alterations in the images was done to observe the entropy values modifications as a function of the illumination effects in the images. The values shown the low influence of this parameter in the results. To evaluate the image quality regarding to size, zoom and resolution, different images were produced to observe the modification of these parameters and analyze its influence in the entropy values. From this study was possible to propose a mathematical function which relates the surface hidrophobicity and the texture patterns obtained by the AIA images. Hence, the hidrophobicity classification could be embedded in mobile devices, as example, cell phones, and performed in loco. A smartphone software was then developed to analyze the surface image of an insulator, producing the hidrophobicity classification value in about one minute.

This thesis studies the physics of multilayer heterostructures grown from topological insulators (TIs), primarily bismuth selenide and antimony telluride, and other topologically trivial materials. This is done by extending a standard low-energy 3D TI Hamiltonian and varying its associated material parameters across the simulation domain. New results arising from the position-dependent TI interface model are found. For the first time, this method is incorporated into a density-functional theory (DFT) solver in order to study the self-consistent charge density in multilayer TI heterostructures due to the interface states. The thesis is structured as follows. The introduction (Ch. 1) presents a pedagogical review of the theory of 3D TIs and low-energy Hamiltonians used to study them, as well as typical methods in solid state physics that are made use of throughout the thesis. Chapter 2 presents the position-dependent Hamiltonian, showing new evidence for topological features of bulk states including varying degrees of band mixing and inversion; also, interface state tunnelling is shown to be affected by atomic layer orbital overlap, and incomplete localisation of surface states is demonstrated for antimony telluride. Chapter 3 presents a new DFT model of TI heterostructure interfaces and shows how conduction through TI interface states can be controlled with an electric field. Chapter 4 covers the extension of the model in Ch. 1 to 2D cross-sections of TI wires and heterostructures, showing for the first time evidence of localisation of conduction almost entirely within the inner interfaces of a 2D heterostructure wire. Chapter 5 presents our work with magnetic fields, demonstrating evolution of interface and bulk states with changing magnetic field and Landau level, as well as presenting new evidence for more complex spin structures in bismuth selenide arising from Landé factor signs. Our conclusions are presented in Chapter 6.

Le PRC (Polyéthylène réticulé chimiquement) est utilisé comme matériau de base pour la fabrication de l’enveloppe à isolation électrique des câbles HTA en raison de ces propriétés thermiques et diélectriques remarquables. Afin d’améliorer la fiabilité de ces câbles, des études de vieillissement sous différentes contraintes (thermique, humidité, tension) ont été réalisées sur les différentes couches du câble, et en particulier sur l’isolant en PRC.Dans un premier temps, nous avons identifié un certain nombre de marqueurs chimiques et physiques pouvant donner des informations sur le degré de vieillissement de l’isolant PRC des câbles HTA. Ces différents marqueurs sont caractéristiques d’une dégradation multi-échelle (moléculaire, microscopique et macroscopique) et peuvent être utilisés pour établir le diagnostic d’un câble électrique et ainsi évaluer son état de dégradation général. Parmi ces marqueurs, l’existence d’un phénomène de migration d’espèces polaires des semi-conducteurs vers l’isolant du câble aura particulièrement attiré notre attention. Des analyses supplémentaires ont donc été réalisées afin de mieux appréhender ce phénomène.Ensuite, nous avons déterminé l’impact de contraintes thermique et électrique simultanées sur les propriétés physico-chimiques et diélectriques d’un isolant en PRC. Les analyses physico-chimiques ont montré que l’ajout d’une forte tension ne semble affecter ni l’oxydation, ni la diffusion. Des vieillissements sous contraintes importantes ont néanmoins permis d’identifier un signal particulier en spectroscopie diélectrique. La détection de ce signal pourra être utilisée pour anticiper des claquages de câbles sur le réseau électrique. Nous avons également réussi à établir un lien entre certains marqueurs chimiques et la dégradation des propriétés diélectriques des isolants pour des mises sous contraintes particulièrement extrêmes. / Due to its outstanding thermal and dielectric properties, XLPE (Chemically Crosslinked Polyethylene) is commonly used as a base material for manufacturing the electrical insulating jacket of MV cables. With a view to improve the reliability of these cables, aging studies have been carried out under different stress conditions (temperature, humidity, tension) on the different constituting layers, and in particular on the XLPE insulating one.First of all, we have identified several chemical and physical markers that can provide information on the aging degree of the XLPE insulation from MV cables. These different markers are representative of a degradation at different scales (molecular, microscopic and macroscopic) and they can be used to establish a diagnosis on an electrical cable, and thus evaluate its general state of degradation. Among these markers, the existence of a polar species’ migration phenomenon from semiconductors to the insulating layer had particularly attracted our attention. Additional analyzes were thus conducted to gain more insight on this phenomenon.Then, we have determined the impact of simultaneous thermal and electrical stresses on physico-chemical and dielectric properties of the XLPE insulating material. The physico-chemical analyzes have demonstrated that the addition of an important tension did not affect the oxidation and diffusion phenomena previously identified. Aging under high stress allowed us to identify a special signal in dielectric spectroscopy. The identification of such a signal could be used to anticipate cable breakdowns on the power grid. In addition, we were successful in establishing a clear link between some chemical markers and the degradation of the insulator dielectric properties in the case of extreme ageing conditions.

A great deal of theoretical activity has resulted from blending the fields of computer science and quantum mechanics. Out of this work has come the concept of a quantum computer, which promises to solve problems currently intractable for classical computers. This promise has, in turn, generated a large amount of effort directed toward investigating quantum computing experimentally. ¶ Quantum computing is difficult because fragile quantum superposition states of the computer’s register must be protected from the environment. This is made more difficult by the need to manipulate and measure these states. ¶ This thesis describes work that was carried out both to investigate and to demonstrate the utility of rare earth ion dopants for quantum computation. Dopants in solids are seen by many as a potential means of achieving scalable quantum computing. Rare earth ion dopants are an obvious choice for investigating such quantum computation. Long coherence times for both optical and nuclear spin transitions have been observed as well as optical manipulation of the spin states. The advantage that the scheme developed here has over nearly all of its competitors is that no complex nanofabrication is required. The advantages of avoiding nano-fabrication are two fold. Firstly, coherence times are likely to be adversely effected by the “damage” to the crystal structure that this manufacture represents. Secondly, the nano-fabrication presents a very serious difficulty in itself. ¶ Because of these advantages it was possible to perform two-qubit operations between independent qubits. This is the first time that such operations have been performed and presents a milestone in quantum computation using dopants in solids. It is only the second time two-qubit operations have been demonstrated in a solid. ¶ The experiments performed in this thesis were in two main areas: The first was the characterisation of hyperfine interactions in rare earth ion dopants; the second, simple demonstrations directly related to quantum computation. ¶ The first experiments that were carried out were to characterise the hyperfine interactions in Pr[superscript 3]+:Y[subscript 2]SiO[subscript 5]. The characterisation was the first carried out for the dopants in a site of such low symmetry. The resulting information about oscillator strengths and transition frequencies should prove indispensable when using such a system for quantum computation. It has already enabled an increase in the coherence times of nuclear spin transitions by two orders of magnitudes. ¶ The experiments directly related to the demonstration of quantum computation were all carried out using ensembles. The presence of a significant distribution of resonant frequencies, or inhomogeneous broadening, meant that many different sub-ensembles could be addressed, based on their resonant frequencies. Furthermore, the properties of the sub-ensembles could be engineered by optically pumping unwanted members to different hyperfine states away from resonance with the laser. ¶ A previously demonstrated technique for realising ensembles that could be used as single qubits was investigated and improved. Also, experiments were carried out to demonstrate the resulting ensembles’ utility as qubits. Further to this, ions from one of the ensembles were selected out, based on their interaction with the ions of another. Elementary two qubit operations were then demonstrated using these ensembles.

Thesis (M.S.) -- Mississippi State University. Department of Electrical and Computer Engineering. / Title from title screen. Includes bibliographical references.

<p>A controlled and efficient coordination of gene expression is the key for normal development of an organism. In mammals, a subset of autosomal genes is expressed monoallelically depending on the sex of the transmitting parent, a phenomenon known as genomic imprinting.</p><p>The imprinted state of the <i>H19</i> and <i>Igf2</i> genes is controlled by a short stretch of sequences upstream of <i>H19</i> known as the imprinting control region (ICR). This region is differentially methylated and is responsible for the repression of the maternally inherited <i>Igf2</i> allele. It harbors hypersensitive sites on the unmethylated maternal allele and functions as an insulator that binds a chromatin insulator protein CTCF. Hence the <i>H19</i> ICR, which plays an important role in maintaining the imprinting status of <i>H19</i> and <i>Igf2</i>, was shown to lose the insulator property upon CpG methylation.</p><p>Another ICR in the <i>Kcnq1</i> locus regulates long-range repression of <i>p57Kip2</i> and <i>Kcnq1</i> on the paternal allele, and is located on the neighboring subdomain of the imprinted gene cluster containing <i>H19</i> and <i>Igf2</i>, on the distal end of mouse chromosome 7. Similarly to the <i>H19</i> ICR, the <i>Kcnq1</i> ICR appears to possess a unidirectional and methylation-sensitive chromatin insulator property in two different somatic cell types. Hence, methylation dependent insulator activity emerges as a common feature of imprinting control regions.</p><p>The protein CTCF is required for the interpretation and propagation of the differentially methylated status of the <i>H19</i> ICR. Work in this thesis shows that this feature applies genomewide. The mapping of CTCF target sites demonstrated not only a strong link between CTCF, formation of insulator complexes and maintaining methylation-free domains, but also a network of target sites that are involved in pivotal functions. The pattern of CTCF <i>in vivo</i> occupancy varies in a lineage-specific manner, although a small group of target sites show constitutive binding. </p><p>In conclusion, the work of this thesis shows that epigenetic marks play an important role in regulating the insulator property. The studies also confirm the importance of CTCF in maintaining methylation-free domains and its role in insulator function. Our study unravels a new range of target sites for CTCF involved in divergent functions and their developmental control.</p>

Chromatin insulators play a role in gene transcription regulation by defining chromatinboundaries. Genome-wide studies in Drosophila have shown that a large proportion of insulator sites are found in intergenic DNA sequences, supporting a role for these elements as boundaries. However, approximately 40% of insulator sites are also found in intragenic sequences, where they can potentially perform as yet unidentified functions. Here we show that multiple Su(Hw) insulator sites map within the 110 kb sequence of the muscleblind gene (mbl), which also forms a highly condensed chromatin structure in polytene chromosomes. Chromosome Conformation Capture assays indicate that Su(Hw) insulators mediate the organization of higher-order chromatin structures at the mbl locus, resulting in a barrier for the progression of RNA polymeraseII (PolII ), and producing a repressive effect on basal and active transcription. The interference of intragenic insulators in PolII progression suggests a role for insulators in the elongation process. Supporting this interpretation, we found that mutations in su(Hw) and mod(mdg4) also result in changes in the relative abundance of the mblD isoform, by promoting early transcription termination. These results provide experimental evidence for a new role ofintragenic Su(Hw) insulators in higher-order chromatin organization, repression of transcription, and RNA processing.

ABSTRACT Chromatin insulators are required for proper temporal and spatial expression of genes in metazoans. Insulators are thought to play an important role in the regulation of gene expression through the formation of higher-order chromatin structures. One of the best characterized insulators is the Drosophila gypsy insulator, which is located in the gypsy retrovirus. Several proteins are required for gypsy insulator function, including Su(Hw), Mod(mdg4), and CP190. In addition to the gypsy insulator, these proteins are located throughout the genome at sites which are thought to correspond to endogenous insulators. Analysis of the distribution of insulator proteins across a region of chromosome 2R in Drosophila polytene chromosomes shows that Su(Hw) is found in three structures differentially associated with insulator proteins: bands, interbands and domains of coexpressed genes. Bands are formed by condensation of chromatin within genes containing one or more Su(Hw) binding sites, while Su(Hw) sites in interbands appear to form structures normally associated with open chromatin. Bands characterized by the lack of CP190 and BEAF-32 insulator proteins are formed by clusters of coexpressed genes, and these bands correlate with the distribution of specific chromatin marks. Conservation of the band interband pattern, as well as the distribution of insulator proteins in nurse cells, suggests that this organization may represent the basic organization of interphasic chromosomes. We also show that, in addition to the gypsy insulator, sequence analysis predicts the presence of Su(Hw) binding sites within a number of transposable elements. Su(Hw) binds to predicted sites within gtwin and jockey, which possesses enhancer-blocking activity. Su(Hw) affects the tissue-specific expression of transposable elements, although this effect is unrelated to the presence of Su(Hw) binding sites within the element or control of the elements via the piRNA pathway. Additionally, the effect of Su(Hw) on transposable element expression often differs from that of Mod(mdg4). Taken together, these results suggest that insulator proteins associate specifically with, and may help to define, various levels of chromatin organization on polytene chromosomes. Also, gypsy insulator proteins may influence the expression of transposable elements in a way that does not depend on Su(Hw) binding sites within the elements themselves.

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 195-202).