Unitary models in two dimensions

Unitary models in two dimensions are classes of low dimensional theories which provide us with a convenient theoretical laboratory for studying various aspects of the theory of elementary particles. In this thesis, purely bosonic U(N) sigma models with the Wess-Zuraino-Witten (WZW) term in two-dimensional Euclidean space and the supersymmetric (Susy) U(N) σ models with and without this term are discussed. Particular attention is paid to the classical solutions of the equations of motion of these models. Due to the integrabihty of these models, we can associate with them a Lax-pair formalism. We observe that solutions of the Lax-pair equations of the U(N) a model provide us with solutions of the U(N) a model with the WZW-term. This is also the case for solutions of the Susy U(N) a model with the WZW-term which can be constructed from solutions of the Lax-pair equations of the Susy U(N) σ model. We present also some explicit solutions of the Susy U(N) a model without the WZW-term. Many properties of the constructed solutions for both the purely bosonic and Susy models are explored. In particular, we calculate the values of the action for some solutions and study the stability properties of these solutions and find that all the constructed solutions of these models correspond to the saddle points of the action. Finally we consider the hnearized fermion equations in the fixed background of a bosonic field. Special attention is paid to the case when the background field is given by a solution of the U(N) σ model with and/or without the WZW-term. Some classes of solutions of this problem are presented and their properties are discussed. We observe that a class of these solutions is related to the components of the energy-momentum tensor of the purely bosonic σ model and prove that some of these solutions are traceless

The Effect of Distribution for a Moving Force

Many types of slender or thin walled structures experience forces which traverse across them. For example: vehicles passing over a bridge, overhead crane operations and liquid "slug" movement in spanning pipelines. This moving force can initiate a large dynamic stress within the structure and is often important for assessing structural fatigue. For many of these force/structure scenarios, modelling of the force as a concentrated point force would be an adequate simplifying approximation. In some cases, however, it may not be appropriate to simplify the distributed force into a single point force. For instance, slug lengths in pipelines can be significant in relation to span lengths. There is currently no guidance in the literature regarding the distribution effect of the force on the response of a structure under a moving force. This paper investigates the dynamic response of an elastic, simply supported beam under the influence of a moving distributed force, with varying distribution to span length ratios. In addition, it examines the speed of the traversing force, which is also highly influential on the dynamic response of the beam. This investigation is undertaken using an explicit transient dynamic finite element formulation of a simply supported beam. Guidelines are provided to discriminate between those scenarios when it is appropriate to simplify a distributed moving force as a concentrated force, and those when it must be modelled as the original distributed force

Determinants of Adherence to Antiretroviral Therapy among HIV-Infected Patients in Africa

Background. There are only a few comprehensive studies of adherence to ART and its challenges in Africa. This paper aims to assess the evidence on the challenges and prospects of ART adherence in sub-Saharan Africa. Methods. The authors reviewed original and review articles involving HIV-positive individuals that measured adherence to ART and its predictors in the past decade. Findings. Against expectations, sub-Saharan Africa patients have similar or higher adherence levels compared to those of developed countries. The challenges to ART adherence include factors related to patients and their families, socioeconomic factors, medication, and healthcare systems. Conclusion. Despite good adherence and program-related findings, antiretroviral treatment is challenged by a range of hierarchical and interrelated factors. There is substantial room for improvement of ART programs in sub-Sahara African countries

Recent trends in the timing of first sex and marriage among young women in Ethiopia

Ethiopia has been characterized by  high  population  growth.  Recent social  and  economic developments have the potential to alter reproductive patterns in the country. Some of these developments include sustained economic growth, urbanization, rapid growth in school enrollments, expansion of primary health care, and a rise in contraceptive access and use. In other national contexts, these developments have been associated with a gradual decoupling of the transition into sexual activity and marriage among young women. We investigate recent trends in the transition into first sex and marriage among three cohorts of Ethiopian women. Methods: Using data from the 2000, 2005, and 2011 Ethiopia Demographic and Health Surveys (DHS) we estimate survival curves and discrete-time hazards models to examine recent trends in age at first sex and first marriage among women ages 20-29. Results: Across the three survey years the median age at first sex has remained relatively stable at 17 years, although the median age at marriage has increased from 17 to 18 years between the 2005 and 2011 surveys. Net of the effects of education and place of residence, there is evidence of a slight trend away from premarital first sex to sexual initiation in the context of marriage. However, among the most educated women and women living in urban areas (who are a small minority of women), there is a much greater tendency to initiate sexual activity outside of marriage compared to women with little schooling and women living in rural areas, and once they have begun sexual activity they tend to wait longer before they get married. We also find evidence in the most recent survey that women who have first sexual intercourse before marriage are delaying marriage more than was the case among earlier cohorts