A simplified model of a double quantum dot is presented and analyzed, with applications to spin-qubit quantum computation. The ability to trap single electrons in semiconductor nanostructures has led to the proposal of quantum computers with spin-based qubits coupled by the exchange interaction. Current theory predicts an exchange interaction with a -1 power-law dependence on the detuning ϵ, the energy offset between the two dots. However, experiment has shown a -3/2 power-law dependence on ϵ. Using WKB analysis, this thesis explores one possible source of the modified dependence, namely an ϵ-dependent tunnel coupling between the two wells. WKB quantization is used to find expressions for the tunnel coupling of a one-dimensional double-well, and these results are compared to the exact, numerical solutions, as determined by the finite difference method and the transfer matrix method. Small ϵ-dependent corrections to the tunnel coupling are observed. In typical cases, WKB correctly predicts a constant tunnel coupling at leading-order. WKB also predicts small ϵ-dependent corrections for typical cases and strongly ϵ-dependent tunnel couplings for certain exceptional cases. However, numerical simulations suggest that WKB is not accurate enough to analyze the small corrections, and is not valid in the exceptional cases. Deviations from the conventional form of the low-energy Hamiltonian for a double-well are also observed and discussed.

Made available in DSpace on 2014-12-17T15:32:31Z (GMT). No. of bitstreams: 1 RosileneCS.pdf: 376311 bytes, checksum: 8a0459347381c3b197002ddd72f02225 (MD5) Previous issue date: 2005-11-04 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Oral squamous cell carcinoma (OSCC) is the most common malignancy in oral cavity and human papillomavirus (HPV) may have an important role in its development. The aim of this experiment was to investigate the HPV DNA and viral types in 90 cases of OSCC. Moreover, a comparative analysis between the cases of OSSC with and without HPV DNA was performed by using cell cycle markers p21 and pRb in order to detect a possible correlation of these proteins and HPV infection. DNA was extracted from paraffin embedded tissue and amplified by PCR (polymerase chain reaction) with primers PCO3+ e PCO4+ for a fragment of human β-globin gene. After this procedure, PCR for HPV DNA detection was realized using a pair of generic primers GP5+ e GP6+. Immunohistochemical study was performed by streptoavidin-biotin technique and antibodies against p21 and pRb proteins were employed. Eighty-eight cases were positive for human β-globin gene and HPV DNA was found in 26 (29.5%) of then. It could not be detected significant correlation between HPV and age, sex and anatomical sites of the lesion. The most prevalent viral type was HPV 18 (80.8%). Regarding the immunohistochemical analysis, it was detected significant association between HPV presence and pRb immunoexpression (p=0,044), nevertheless, the same was not observed in relation to p21 protein (p =0,416). It can be concluded that the low detection of HPV DNA in OSCC by the present experiment suggests a possible role of the virus in the development and progression in just a subset of this disease / O carcinoma epiderm?ide oral ? a neoplasia maligna mais freq?ente da cavidade oral e o papilomav?rus humano (HPV) parece ter um relevante papel na indu??o desta les?o. Neste trabalho investigou-se o DNA do HPV e tipos virais em 90 casos de carcinoma epiderm?ide oral (CEO). Realizou-se tamb?m uma an?lise comparativa entre os grupos de CEO com DNA do HPV e sem o DNA do v?rus, empregando-se os marcadores do ciclo celular p21 e pRb, a fim de estabelecer poss?vel correla??o entre a express?o imuno-histoqu?mica dessas prote?nas e a infec??o pelo HPV. O DNA foi extra?do de tecido emblocado em parafina e amplificado por PCR (rea??o em cadeia da polimerase) com um par de primers designados PCO3+ e PCO4+ para um fragmento do gene da β-globina humana. Posteriormente, realizou-se PCR para detec??o do DNA de HPV utilizando-se um par de primers gen?ricos designados GP5+ e GP6+. A tipagem viral foi realizada pela hibridiza??o dot blot. No m?todo imuno-histoqu?mico utilizou-se a t?cnica da streptavidina-biotina com um painel de anticorpos monoclonais para as prote?nas p21 e pRb. Dos 88 casos positivos para o gene da β-globina humana, em 26 (29,5%) foi detectado o DNA do HPV. N?o houve associa??o significativa entre o HPV e as vari?veis idade e sexo dos pacientes e localiza??o anat?mica da les?o. O tipo viral prevalente foi o HPV 18 (80,8%). Quanto ? an?lise imuno-histoqu?mica, foi observada associa??o estatisticamente significativa entre a presen?a do HPV e a express?o imunohistoqu?mica de pRb (p=0,044), entretanto, n?o houve qualquer diferen?a estatisticamente significativa entre a express?o da prote?na p21 e a presen?a do v?rus (p =0,416). P?de-se concluir que o baixo percentual de detec??o do DNA do HPV no carcinoma epiderm?ide oral no presente trabalho, sugere uma poss?vel participa??o do HPV no desenvolvimento e progress?o de apenas um subgrupo dessas les?es

Magister Public Health - MPH / Background: Tuberculosis (TB) poses a major public health challenge in South Africa and in the Northern Cape Province. The province has the third highest in TB incidence rate in the country. Poor adherence to TB treatment impacts negatively on treatment outcomes. Siyanda district in the Northern Cape Province has the second highest number of TB defaulters in the province despite the fact that 79.9% of these patients are on Community Based Direct Observation of Treatment (CBDOT). Aim: To explore the reasons for defaulting of TB patients from TB treatment in the CBDOT Programme in the Siyanda district, Northern Cape Province Study design: This was a qualitative exploratory study. Study population and sampling: Two TB nurses with varying years of experience in the TB Control Programme serving as key informants were selected from the participating facilities in the study area. Ten TB defaulters who were on the CBDOT programme were selected from the Electronic TB Register. Two focus group discussions (FGDs) comprising of purposively selected DOT Supporters (five in one group and six in the other) from different NGOs in the community were selected for maximum variation. Data collection: Key informant interviews were conducted with the TB nurses. Records of all defaulters in the study population were reviewed including clinic progress notes and patient TB treatment cards. In-depth interviews were conducted with the TB patients. FGDs were conducted with DOT supporters. Analysis: Analysis commenced simultaneously with collection of data. This enabled the researcher to continuously review and reflect on the data collected. Thematic content analysis was done.Categories emerged through the inductive process of the data analysis. Notes that were kept during data collection, reflections, audiotapes and transcripts were used to support the thick description of the findings. Results: The participants generally appreciated the programme and mostly had a good relationship with the DOT supporters. However, the quality of care exacerbated by inadequate health services such as lack of adherence counselling training of health professionals, low levels of education amongst TB defaulters, were found to be major contributory factors to TB defaulting. The patients interrupted treatment several times before defaulting, were not counselled during the interruption phase and understood TB messages differently. TB defaulters in the Siyanda District face socio economic challenges which include alcohol abuse, a major historic ill in the district and the grape farming community in the region. The impact of the disability grant on TB treatment adherence remains anecdotal and requires further research as TB defaulters did not admit to defaulting so that they could continue benefiting from the disability grant although these statements were refuted by the DOT supporters and key informants. The attitude of employers and fear of losing employment were also contributing factors. Conclusion and recommendations: It has become evident that TB in the Siyanda District is a public health issue. The predominantly rural, impoverished and transient community that moves to the farms to seek employment requires a CBDOT programme that will address pertinent challenges in the district to achieve a positive reduction in the TB defaulter rate. It will require collaboration with stakeholders including farmers, to address the challenges posed by the disease. Improved staff allocation, staff capacity development and community education are also recommended to improve quality of care.

La dyskinésie ciliaire primitive (DCP) est une maladie génétique rare, autosomique récessive, résultant d'un dysfonctionnement des cils de l'épithélium respiratoire. Les patients atteints souffrent d'infections respiratoires chroniques accompagnées de complications évoluant vers l'insuffisance respiratoire, en dépit de traitements antibiotiques et de kinésithérapique à vie. Ils peuvent aussi présenter une hétérotaxie.La première partie de ma thèse a consisté à rechercher des gènes impliqués dans l'hétérotaxie et la DCP. Grâce au séquençage haut-débit, nous avons pu identifier deux nouveaux gènes - MMP21 et RSPH1 - responsables respectivement d'hétérotaxie et de DCP. L'identification de tous les gènes responsables est un préalable indispensable à toute thérapie génique. Dans la deuxième partie, nous avons cherché à développer une thérapie génique in vivo dans le but de restaurer un battement ciliaire normal et ainsi de stopper l'évolution de la maladie. Préalablement, notre laboratoire avait apporté la preuve du concept dans un essai de thérapie génique in vitro impliquant le gène DNAI1. Pour la démonstration in vivo, la lignée Dnahc11iv de souris ayant une mutation du gène Dnahc11 et ayant des cils déficients a été choisie. L'ADNc de DNAH11 (14 kb) a été cloné sous contrôle d'une partie de la séquence du promoteur FOXJ1, suffisante pour limiter l'expression du transgène aux cellules ciliées. Une autre construction a permis de produire des vecteurs dérivés du baculovirus. Un essai de délivrance par voies nasale et trachéale a été réalisé avec succès d'une part avec les vecteurs dérivés du baculovirus et d'autre part avec l'ADNc complexé à des nanoparticules / Primary ciliary dyskinesia (PCD) is a rare autosomal recessive genetic disorder, caused by airway epithelial cilia dysfunction. Patients suffer from chronic respiratory infections along with various organ defects evolving toward respiratory insufficiency, in spite of antibiotic treatment and lifelong physiotherapy. They can also have heterotaxy syndrome. The first part of this work aimed to identify mutations in genes implicated in heterotaxy and PCD. Thanks to next-generation sequencing method, two new genes were identified MMP21 and RSPH1 causing heterotaxy and PCD respectively. The discovery of all causal genes is the base of the development of a PCD therapy system. The second part describes the development and the characterization of tools needed to establish an in vivo gene therapy. The purpose is to restore a normal cilia beating to limit or even stop the disease. First, our laboratory demonstrated the proof-of-concept in an in vitro gene therapy assay for DNAI1. To do so, Dnahc11 deficient mouse model with immotile cilia and PCD symptoms was chosen. Then, to achieve the project, DNAH11 cDNA (14 kb) has been cloned under control of a part of the sequence of the specific promoter (FOXJ1), previously demonstrated as sufficient to limit transgene expression to ciliated cells. Another construction was made to produce baculovirus derived vectors. A cDNA delivery attempt through nasal and tracheal way was done with baculovirus derived vector or DNAH11 cDNA complexed with nanoparticles

This thesis deals with the impacts of information and communication technology investment surge on USA economic growth in the 1990s. Besides others, rapid development of these technologies also led to the creation of a stock market bubble, which affected the expansion phase of the economic cycle. Its burst in 2000-2001 resulted in economic slow-down and end of the longest recorded economic expansion in the history of the United States. Main part of the thesis discusses the benefits of information technology for economy and further evaluates the role of the speculative bubble in the development of consumption and investment expenditures. The thesis results suggest that the increase in capital intensity and sharp stock market price inflation significantly accelerated the dynamics of the economic growth in the second half of the described cycle.

PHD (Health Sciences) / Department of Advanced Nursing Sciences

In recent years, interest has grown in the research fields of semiconductor lasers and photonic crystals. This thesis looks at integrating photonic crystals into existing semiconductor laser technology to act as functional laser mirrors. The majority of the research is conducted on a quantum-dot material system. The surface recombination velocity of a GaAs based quantum-dot material is shown to be a similar value to InP material. This allows the creation of fine photonic crystal structures in the laser design without high threshold current penalties. The spectral reflection properties of a one dimensional photonic crystal is studied and found to be an unsuitable candidate for a stand-alone laser mirror, due to its low reflectivity. A two-dimensional photonic crystal W3 defect waveguide is successfully integrated as a quantum-dot laser mirror. Single fundamental mode output is achieved with a typically multi-mode 20 μm wide laser mesa, highlighting the mode selective property of the mirror. A similar two-dimensional mirror is studied for its potential as a dispersion compensating mirror for mode-locked lasers. Initial theoretical analysis shows pulse compression for a suitably designed mirror. Experimental continuous- wave results for the same mirror structure demonstrate the tuning of mirror reflectivity with photonic crystal hole radius. A hybrid silicon-organic photonic crystal laser is demonstrated with output in the visible spectrum. This design is a new type of silicon emitter.

This dissertation focuses on improving the division-by-convergence algorithm. While the division by convergence algorithm has many advantages, it has some drawbacks, such as a need for extra bits in the multiplier and a large ROM table for the initial approximation. To mitigate these problems, two new methods are proposed here. In addition, the research scope is extended to seek an efficient architecture for implementing a divider with Quantum-dot Cellular Automata (QCA), an emerging technology. For the first proposed approach, a new rounding method to reduce the required precision of the multiplier for division by convergence is presented. It allows twice the error tolerance of conventional methods and inclusive error bounds. The proposed method further reduces the required precision of the multiplier by considering the asymmetric error bounds of Goldschmidt dividers. The second proposed approach is a method to increase the speed of convergence for Goldschmidt division using simple logic circuits. The proposed method achieves nearly cubic convergence. It reduces the logic complexity and delay by using an approximate squarer with a simple logic implementation and a redundant binary Booth recoder. Finally, a new architecture for division-by-convergence in QCA is proposed. State machines for QCA often have synchronization problems due to the long wire delays. To resolve this problem, a data tag method is proposed. It also increases the throughput significantly since multiple division computations can be performed in a time skewed manner using one iterative divider. / text

In this thesis, we study persistent currents and quantum critical phenomena in the systems of mesoscopic physics. As an introduction in Chapter 1 we familiarize the reader with the area of mesoscopic physics. We explain how mesoscopic systems are different from quantum systems of single atoms and molecules and bulk systems with an Avogadro number of elements. We also describe some important mesoscopic phenomena. One of the mathematical tools that we extensively use in our studies is Random Matrix Theorty. This theory is not a part of standard physics courses and for educational purposes we provide the basics of Random Matrix Theory in Chapter 2. In Chapter 3 we study the persistent current of noninteracting electrons in quantum billiards. We consider simply connected chaotic Robnik-Berry quantum billiard and its annular analog. The electrons move in the presence of a point-like magnetic flux at the center of the billiard. For the simply connected billiard, we find a large diamagnetic contribution to the persistent current at small flux, which is independent of the flux and is proportional to the number of electrons (or equivalently the density since we keep the area fixed). The size of this diamagnetic contribution is much larger than the previously studied mesoscopic fluctuations in the persistent current in the simply connected billiard. This behavior of persistent current can ultimately be traced to the response of the angular-momentum l = 0 levels (neglected in semiclassical expansions) on the unit disk to a point-like flux at its center. We observe the same behavior for the annular billiard when the inner radius is much smaller than the outer one. We also find that the usual fluctuating persistent current and Anderson-like localization due to boundary scattering are seen when the annulus tends to a one-dimensional ring. We explore the conditions for the observability of this phenomenon. In Chapter 4 we study quantum critical phenomena in a system of two coupled quantum dots connected by a hopping bridge. Both the dots and connecting region are assumed to be in universal Random Matrix crossover regimes between Gaussian orthogonal and unitary ensembles (defined in Chapter 2). We exploit a diagrammatic approach appropriate for energy separations much larger than the level spacing, to obtain the ensemble-averaged one- and two-particle Greens functions. We find that two main components of the twoparticle Green’s function (diffuson and Cooperon) can be described by separate scaling functions. We then use this information to investigate a model interacting system in which one dot has an attractive s-wave reduced Bardeen-Cooper-Schrieffer interaction, while the other is noninteracting but subject to an orbital magnetic field. We find that the critical temperature TC of the mean-field transition into the superconducting state in the first dot is non-monotonic in the flux through the second dot in a certain regime of interdot coupling. Likewise, the fluctuation magnetization above the critical temperature is also non-monotonic in this regime, can be either diamagnetic or paramagnetic, and can be deduced from the Cooperon scaling function. We end this thesis with conclusion in Chapter 5.

Two-dimensional (2D) carrier systems built from semiconductor heterostructures have been at the center of a wide variety of experimental and theoretical research over the past decades. The quality improvement of GaAs/AlGaAs systems has allowed the observation of several peculiar ground states stabilized by the subtle interplay between carrier-carrier interaction, disorder and magnetic field. More recently, 2D systems in semiconductor heterostructures have also been used as a prime substrate for further confinement of the carriers to mesoscopic systems of major interest for the emerging fields of quantum computing and spintronics. This thesis addresses both magnetotransport measurements in hole open quantum dots (QDs) and thermopower studies of 2D holes in (311)A GaAs heterostructures. In the first part of this thesis, we describe the fabrication process for hole GaAs open QDs and investigate their magnetotransport properties at very low temperature T. Below 500 mK, the magnetoconductance of the open QDs exhibits clear signatures of coherent transport, namely magnetoconductance fluctuations and weak anti-localization. From these effects, we extract a T dependence for the dephasing time, together with an upper limit for the spin-orbit scattering time using the random matrix theory. Both the dephasing time and the spin-orbit scattering time are found to be much smaller than for electrons in similar systems. In the second part of this work, we report low-T thermopower measurements in the parallel magnetic field-induced metal-insulator transition (MIT) of 2D GaAs hole heterojunctions with different interface-dependent mobilities. When the magnetic field is increased, the diffusion thermopower decreases across the MIT. The reduction of the diffusion thermopower is more pronounced for the lower mobility sample where it reverses its sign. This behaviour indicates that the system does not undergo any ground state modification through the MIT but rather that the parallel magnetic field induces a dramatic change of the dominant hole scattering mechanisms. Finally, the last part of this thesis is devoted to the thermopower study of the insulating phase (IP) observed in 2D GaAs bilayer hole systems around the total Landau level filling factor n = 1. Our measurements show that the diffusion thermopower diverges with decreasing T in the IP. This divergence of the diffusion thermopower at low T indicates the opening of an energy gap in the system's ground state and suggests the formation of a pinned bilayer hole Wigner crystal around n = 1.