No description available.

No description available.

In this thesis the proposed exact results for low energy effective N = 2 supersymmetric SU(N) Yang-Mills gauge theory coupled to Nf fundamental matter multiplets in four dimensions are considered. The proposed exact results are based upon the work of Seiberg and Witten for low energy effective four dimensional M = 2 supersymmetric SU[2) Yang-Mills gauge theory coupled to Nf fundamental matter multiplets. The testing and matching of the proposed exact results via supersymmetric instanton calculus are the motivation for two studies. Firstly, we study the ADHM construction of instantons for gauge groups U(N) and SU(2) and for topological charge two and three. The ADHM constraints which implicitly specify instanton gauge field configurations are solved for the explicit exact general form of instantons with topological charge two and gauge group U[N). This is the first explicit and general multi-instanton configuration for the unitary gauge groups. The U[N) ADHM two-instanton configuration may be used in further tests and matching of the proposed exact results in low energy effective M =2 supersymmetric SU(iV) Yang-Mills gauge theories by comparison with direct instanton calculations. Secondly, a one-instanton level test is performed for the reparameterization scheme proposed by Argyres and Pelland matching the conjectured exact low energy results and instanton predictions for the instanton contributions to the prepotential of low energy effective M = 2 supersymmetric SU [N) Yang-Mills gauge theory with Nf = 2N mass-less fundamental matter multiplets. The constants within the reparameterization scheme which ensure agreement between the exact results and the instanton predictions for general N > 1 are derived for the entire quantum moduli space. This constitutes a non-trivial test of the proposed reparameterization scheme, which eliminates the discrepancies arising when the two sets of results are compared.

Many semiconductor devices, such as heterostructure lasers and silicon bipolar transistors, require large concentrations of free carriers in the conduction and/or valence band of an active region. Under these conditions the band gap of the material is reduced by the many-body interactions of the carrier gas. The band gap narrowing results from a lowering of the conduction and raising of the valence band edge energies and is evaluated for a range of carrier concentrations. (10(^17) - 10(^22) cm_^-3)) in p-type Si and P- and n-type GaAs, Ga(_0.47) In(_0.53) As and Ga(_0.28) In(_0.72) As(_0.6) P(_0.4) at T = OK. A plasmon-pole approximation for the carrier gas dielectric function is used in the calculations. For all these materials, the largest energy shift occurs in the band containing the free carriers. For comparison the band edge shifts in all four materials are evaluated at finite temperature (300 K). The band gap narrowing at finite and zero temperatures differ notably only for low carrier concentrations (p < 5 x 10(^19) cm (^-3) in p-type Si) where the thermal excitation of the carriers reduces their screening effect so producing smaller band gap reduction. High hole concentrations also lead to increased optical losses in semi-conductor lasers due to intervalence band absorption (IVBA) transitions. These losses, which are considered to be partially responsible for the temperature dependence of threshold current densities in some semiconductor lasers, are evaluated in bulk laser materials using a pseudopotential band structure model. The temperature dependencies of the IVBA coefficients in GaAs, Ga(_0.47) In(_0.53) As and Ga(_0.28) In(_0.72) As(_0.6) P(_0.4) are shown to be either small or the coefficients themselves are negligible. Intervalence band absorption is also calculated for a 100/200 A GaAs/Ga(_0.7) al(_0.3) As quantum well laser structure for which the electronic band structure is determined using a variational k^-p approach. The wavelength dependence of the IVBA coefficients differs notably from corresponding results derived using simpler effective mass and pseudopotential models. In particular the k.p model gives significant contributions to the total loss, from certain 'forbidden' transitions.

No description available.

No description available.

No description available.

No description available.

No description available.

<p>We live in a society that continually reinforces the connection between femininity and maternity and for the majority of women, attempts to experience motherhood are successful. However, for others the world of motherhood is not so easy to enter. To date, research regarding the needs and life satisfaction of women who are unsuccessful in becoming mothers, is fairly limited. The purpose of this study was to explore the transitional phase women endure from potential motherhood to non-motherhood and to highlight some of the complexities underpinning infertility and its impact on the lives of women in South Africa. The main objective was to gain deeper insight into how women incorporated this experience into their lives and relationships and how they began to create a future life without their own biological children. A secondary aim of this study was to investigate whether the women viewed aspects such as age and finances as having had an effect on their decision to discontinue treatment for infertility. Feminist standpoint theory served as a theoretical framework for the study that recognized that each individual voice be heard. This study was a qualitative exploration, utilizing a short demographic questionnaire and an in-depth semi-structured interview. Five interviews were conducted with women from diverse backgrounds. These interviews were recorded / transcribed verbatim and thematic analysis of the data was conducted.</p>