Mach Stem Height and Growth Rate Predictions

A new, more accurate prediction of Mach stem height in steady flow is presented. In addition, starting with a regular reflection in the dual-solution domain, the growth rate of the Mach stem from the time it is first formed till it reaches its steady-state height is presented. Comparisons between theory, experiments, and computations are presented for the Mach stem height. The theory for the Mach stem growth rate in both two and three dimensions is compared to computational results. The Mach stem growth theory provides an explanation for why, once formed, a Mach stem is relatively persistent

3D Particle Tracking Velocimetry Method: Advances and Error Analysis

A full three-dimensional particle tracking system was developed and tested. By using three separate CCDs placed at the vertices of an equilateral triangle, the threedimensional location of particles can be determined. Particle locations measured at two different times can then be used to create a three-component, three-dimensional velocity field. Key developments are: the ability to accurately process overlapping particle images, offset CCDs to significantly improve effective resolution, allowance for dim particle images, and a hybrid particle tracking technique ideal for three-dimensional flows when only two sets of images exist. An in-depth theoretical error analysis was performed which gives the important sources of error and their effect on the overall system. This error analysis was verified through a series of experiments, which utilized a test target with 100 small dots per square inch. For displacements of 2.54mm the mean errors were less than 2% and the 90% confidence limits were less than 5.2 μm in the plane perpendicular to the camera axis, and 66 μm in the direction of the camera axis. The system was used for flow measurements around a delta wing at an angle of attack. These measurements show the successful implementation of the system for three-dimensional flow velocimetry

On imploding cylindrical and spherical shock waves in a perfect gas

The problem of a cylindrically or spherically imploding and reflecting shock wave in a flow initially at rest is studied without the use of the strong-shock approximation. Dimensional arguments are first used to show that this flow admits a general solution where an infinitesimally weak shock from infinity strengthens as it converges towards the origin. For a perfect-gas equation of state, this solution depends only on the dimensionality of the flow and on the ratio of specific heats. The Guderley power-law result can then be interpreted as the leading-order, strong-shock approximation, valid near the origin at the implosion centre. We improve the Guderley solution by adding two further terms in the series expansion solution for both the incoming and the reflected shock waves. A series expansion, valid where the shock is still weak and very far from the origin, is also constructed. With an appropriate change of variables and using the exact shock-jump conditions, a numerical, characteristics-based solution is obtained describing the general shock motion from almost infinity to very close to the reflection point. Comparisons are made between the series expansions, the characteristics solution, and the results obtained using an Euler solver. These show that the addition of two terms to the Guderley solution significantly extends the range of validity of the strong-shock series expansion

Critical Challenges Of The South African School System

The emphasis in the new curriculum after 1996 in South Africa was placed on the transition from the traditional aims and objectives approach to Outcomes-based education (OBE) and Curriculum 2005. This paradigm shift was interpreted as a prerequisite for achievement of the vision of an internationally competitive country. When analysing the school system in South Africa it became clear that the education system was flawed, with poorly performing teachers, poor work ethics, lack of community and parental support, poor control by education authorities, poor support for teachers and very low levels of accountability. These factors further spilled over into the morale of learners and could be seen in the lack of discipline, brutal violence in schools, low moral values, truancy, absenteeism, late coming and high dropout rates from Grade 1 to Grade 12 and very poor performance in essential areas such as Mathematics and Literacy. Citizens in historically disadvantaged areas tend to become victims of poverty, gangs and drug abuse. These factors further blend with the evil of politics in South African schools which are furthermore plagued by various forms of corruption and socio-economic challenges. Eighteen years after the end of the apartheid dispensation, apartheid is still blamed by many for any real or imagined ills in society, but the reality is that there is no political will to enforce the law or to meet public expectations of accountability, efficiency and delivery. In the light hereof, recommendations are proposed that will address these challenges. The critical message of this article will convey that the fact of the matter is that learner enrolment is not the same as attendance and attendance does not imply learning. Therefore, teaching in South Africa must become a profession of preference and pride as opposed to the present very lackadaisical attitude

Critical Challenges Of The South African School System

The emphasis in the new curriculum after 1996 in South Africa was placed on the transition from the traditional aims and objectives approach to Outcomes-based education (OBE) and Curriculum 2005. This paradigm shift was interpreted as a prerequisite for achievement of the vision of an internationally competitive country. When analysing the school system in South Africa it became clear that the education system was flawed, with poorly performing teachers, poor work ethics, lack of community and parental support, poor control by education authorities, poor support for teachers and very low levels of accountability. These factors further spilled over into the morale of learners and could be seen in the lack of discipline, brutal violence in schools, low moral values, truancy, absenteeism, late coming and high dropout rates from Grade 1 to Grade 12 and very poor performance in essential areas such as Mathematics and Literacy. Citizens in historically disadvantaged areas tend to become victims of poverty, gangs and drug abuse. These factors further blend with the evil of politics in South African schools which are furthermore plagued by various forms of corruption and socio-economic challenges. Eighteen years after the end of the apartheid dispensation, apartheid is still blamed by many for any real or imagined ills in society, but the reality is that there is no political will to enforce the law or to meet public expectations of accountability, efficiency and delivery. In the light hereof, recommendations are proposed that will address these challenges. The critical message of this article will convey that the fact of the matter is that learner enrolment is not the same as attendance and attendance does not imply learning. Therefore, teaching in South Africa must become a profession of preference and pride as opposed to the present very lackadaisical attitude

Mach Stem Height and Growth Rate Predictions

A new, more accurate prediction of Mach stem height in steady flow is presented. In addition, starting with a regular reflection in the dual-solution domain, the growth rate of the Mach stem from the time it is first formed till it reaches its steady-state height is presented. Comparisons between theory, experiments, and computations are presented for the Mach stem height. The theory for the Mach stem growth rate in both two and three dimensions is compared to computational results. The Mach stem growth theory provides an explanation for why, once formed, a Mach stem is relatively persistent

Present-Day Dillemas And Challenges Of The South African Tertiary System

The Education White Paper 3 on Higher Education aimed to transform the higher education system. Change within tertiary education included adjusting the size and shape of institutions, the meaning of autonomy and accountability, the nature of higher education, the character of student demographic distribution, management and governance, roles of student politics, models of delivery, the notion of higher education in terms of the relationship between free trade and public good, programme changes and the nature of the academic workplace. At this stage, transformation in higher education is leaping outwards to fulfil the criteria set by international competitiveness and related efficiency criteria that can be attributed to globalisation pressures and to deeper factors inherent in the nature of higher education, especially in terms of its resistance to change and modernization. In this regard, the tertiary higher education system in South Africa is faced with many multi-dimensional challenges that need to be addressed in this article. This includes stating whether Grade 12 results as the outcome of this exit point at school level are, internationally speaking, a reasonable predictor of first-year academic success at university. In South Africa, there is no benchmarking of the National Senior Certificate (NSC) examination; therefore, first-year students have difficulty in adapting to the university environment as they find themselves devoid of indispensable bases for the pursuit of their studies and the weakness of the level of education given at school level in a large number of instances. Furthermore, five universities were placed under administration in the 2011-2012 period because of appallingly poor levels of management, which adds extra layers of suspicion to the notion of the impact of higher education in South Africa. Many other challenges are facing the South African tertiary education system, which will be analysed and recommendations arrived at that will attempt to contribute to an enhancement of tertiary education in South Africa

Restructuring And Mergers Of The South African Post-Apartheid Tertiary System (1994-2011): A Critical Analysis

Socio-economic and vocational needs of communities, governments and individuals change over the years and these discourses served as a compass for restructuring of higher institutions in South Africa from 1994. Before 1994, the claim to legitimacy for government policies in higher education rested on meeting primarily the interests of the white minority. From 1996 onwards, the newly established government considered education a major vehicle of societal transformation. The main objective had been to focus on reducing inequality and fostering internationalisation. Therefore, the rationale for the restructuring of South African universities included a shift from science systems to global science networks. Various challenges are associated with restructuring and include access, diversity, equity and equality. Thus, the restructuring and mergers between former technikons and traditional universities were probably the most difficult to achieve in terms of establishing a common academic platform, as transitional conditions also had to be taken into account and had a twin logic: It was not only the legacy of apartheid that had to be overcome but the incorporation of South Africa into the globalised world was equally important as globalisation transforms the economic, political, social and environmental dimensions of countries and their place in the world. Initially, the post-apartheid higher education transformation started with the founding policy document on higher education, the Report of the National Commission on Higher Education and this report laid the foundation for the 1997 Education White Paper 3 on Higher Education in which a transformed higher education system is described. Restructuring and mergers also had a far-reaching impact, positive and negative, on the various tertiary institutions. This article also reflects on the impact of restructuring and mergers of higher education and reaches the conclusion that higher education faces many more challenges than initially anticipated prior to transformation