No abstract

A procedure is developed and applied for predicting ex ante impacts of agricultural research on aggregate poverty, using as an example the poverty-reducing impact of peanut research in Uganda. Market-level information on economic surplus changes is combined with a procedure for allocating income changes to individual households. Characteristics of farmers that affect their likelihood of technology adoption are used to create a technology adoption profile. Associated changes in poverty resulting from adoption are computed using poverty indices. Predicted income changes at the household level are aggregated to the market level and reconciled with calculations of economic surplus changes. Copyright 2007, Oxford University Press.

No abstract

Background: The incidence of HIV and AIDS continues to be a source of great concern within universities in South Africa. Furthermore, university students constitute an important community in the intervention against the HIV/AIDS epidemic. Students in the age group of 15–24 years are at a greater risk of HIV infection than any other group in the country; yet, little is known about why they continue to engage in risky sexual practices. Objectives: This study was designed to explore the sexual behaviour of students in a metropolitan Durban University of Technology in KwaZulu-Natal to understand the social factors underlying their risk of HIV infection. Methods: This is a qualitative study that used cluster sampling where the population was stratified by campus and faculty. The study population was selected using a standard randomization technique. This was a part of a multi-phased research project aimed at providing a sero-prevalence baseline and an analysis of risk-taking behaviour at a Durban University of Technology in the eThekwini Metropolitan Municipality area. Results: The study highlights peer pressure among students as an influence in promoting high-risk sexual behaviour. Within this context, the findings revealed that university students lack the ability to negotiate risk-aware decisions especially regarding sexual relationships. Conclusion: This study draws attention to the perspectives of African university students regarding their risk-taking sexual practices and selected factors which influence such behaviour. The findings are not exhaustive in exploring contextual antecedents that shape students’ sexual practices. However, they provide an important basis in understanding key factors which expose students to HIV infections. The study provides insights into opportunities for further studies as well as preventative implications.

The Riccati transformation is used in the reduction of order of second and third Ž . order ordinary differential equations of maximal symmetry. The sl 2, R subalgebra is preserved under this transformation. The Riccati transformation is itself associated with the symmetry that is annihilated in the reduction of order. The solution symmetries and the intrinsically contact symmetries become nonlocal symmetries under the Riccati transformation. We investigate the fate and origins of the contact symmetries arising from the Riccati transformation. The exceptional properties of the second and third order equations of maximal symmetry are indicated. In the context of generalised symmetries we express the solution symmetries, Ž . contact symmetries, and the sl 2, R elements in terms of a Jacobian. We show that a basis for the solution set of equations of maximal symmetry is given in terms of the solution set of a second order ordinary differential equation. ᮊ

We give a complete group classification of the general case of linear systems of two second-order ordinary differential equations. The algebraic approach is used to solve the group classification problem for this class of equations. This completes the results in the literature on the group classification of two linear second-order ordinary differential equations including recent results which give a complete group classification treatment of such systems. We show that using the algebraic approach leads to the study of a variety of cases in addition to those already obtained in the literature. We illustrate that this approach can be used as a useful tool in the group classification of this class of equations. A discussion of the subsequent cases and results is given.

The reaction-diffusion delay differential equation u(x, t), u(x, t − τ ) arises in many applications in the sciences. Group analysis is applied in the study of this equation. A new definition of an equivalence Lie group for delay differential equations is given. As for the Lie group theory of differential equations, the determining equations for the equivalence and admitted Lie groups are constructed. The general solutions of the determining equations are obtained. The complete group classification of the reaction-diffusion equation with delay is presented in the manuscript and the invariant solutions of this equation are constructed.

In the literature, the generalized Sundman transformation has been used for obtaining necessary and sufficient conditions for a single second-and third-order ordinary differential equation to be equivalent to a linear equation in the Laguerre form. As far as we are aware, the generalized Sundman transformation has not been applied to a system of equations. The motivation of this work is then to expand the application of the generalized Sundman transformation to a system of ordinary differential equations, in particular, to a system of two second-order ordinary differential equations.