The generation of offshore tidal sand banks and sand waves

A simple morphological model is considered which describes the interaction between a tidal flow and an erodible bed in a shallow sea. The basic state of this model describes a spatially uniform tide over a flat bottom where the flow vector is represented as a tidal ellipse. The linear stability of this solution is analysed with respect to bed form perturbations. Results are presented for both a uni-directional and circular tide. In the former case the wave-length and the orientation of the fastest growing bed mode agree well with those of tidal sand banks. However, this model only predicts the growth of large-scale sand ridges. With a simplified numerical model we tentatively show that the effects of secondary currents on the sediment transport trigger the formation of instabilities at an essentially smaller scale, viz, sand waves. Another limitation of a model with uni-directional tides is that no selective modes found are the first to become unstable if the model parameters are varied. In the case of a circular tide, critical model parameters are found below which the basic state is stable. We conclude that this provides a starting point for the development of a weakly non-linear analysis, which will yield information on the amplitude behaviour of marginally growing bed forms

Partial-Wave Analyses of all Proton-Proton and Neutron-Proton Data Below 500 MeV

In 1993 the Nijmegen group published the results of energy-dependent partial-wave analyses (PWAs) of the nucleon-nucleon (NN) scattering data for laboratory kinetic energies below Tlab=350 MeV (PWA93). In this talk some general aspects, but also the newest developments on the Nijmegen NN PWAs are reported. We have almost finished a new energy-dependent PWA and will discuss some typical aspects of this new PWA; where it differs from PWA93, but also what future developments might be, or should be.Comment: Presentation at the 19th European Conference on Few-Body Problems in Physics, Groningen, The Netherlands, 23-27 August 2004. 4 pages REVTeX4, no figure

The Status of the Pion-Nucleon Coupling Constant

A review is given of the various determinations of the different piNN coupling constants in analyses of the low-energy pp, np, pbarp, and pi-p scattering data. The most accurate determinations are in the energy-dependent partial-wave analyses of the NN data. The recommended value is f^2 = 0.075 . A recent determination of f^2 by the Uppsala group from backward np cross sections is shown to be model dependent and inaccurate, and therefore completely uninteresting. We also argue that an accurate determination of f^2 using pp forward dispersion relations is not a realistic option.Comment: 19 pages, latex2e with a4wide.sty, more information is available at http://NN-OnLine.sci.kun.nl . Invited talk at FBXV, Groningen, The Netherlands, July 22-26, 1997. Invited talk at MENU97, Vancouver, B.C., Canada, July 28 - August 1, 199

Renormalization of the Deuteron with One Pion Exchange

We analyze the deuteron bound state through the One Pion Exchange Potential. We pay attention to the short distance peculiar singularity structure of the bound state wave functions in coordinate space and the elimination of short distance ambiguities by selecting the regular solution at the origin. We determine the so far elusive amplitude of the converging exponential solutions at the origin. All bound state deuteron properties can then be uniquely deduced from the deuteron binding energy, the pion-nucleon coupling constant and pion mass. This generates correlations among deuteron properties. Scattering phase shifts and low energy parameters in the 3S1-3D1 channel are constructed by requiring orthogonality of the positive energy states to the deuteron bound state, yielding an energy independent combination of boundary conditions. We also analyze from the viewpoint of short distance boundary conditions the weak binding regime on the light of long distance perturbation theory and discuss the approach to the chiral limit.Comment: 22 pages, 11 figure

Vector mesons in qqˉqˉq\bar q\bar q systems

A new selection rule is described for the vector mesons in the decuplet representations of flavor SU(3)Comment: 7 pages and 1 figur

The nucleon-sigma coupling constant in QCD Sum Rules

The external-field QCD Sum Rules method is used to evaluate the coupling constant of the light isoscalar-scalar meson (``$\sigma$'' or \epsilon) to the nucleon. The contributions that come from the excited nucleon states and the response of the continuum threshold to the external field are calculated. The obtained value of the coupling constant is compatible with the large value required in one-boson exchange potential models of the two-nucleon interaction.Comment: 11 pages, 4 figure

Design and development of practical instruction for freshmen engineering students in a renewable energy course

Conference ProceedingsTechnical competence and problem solving skills are key graduate attributes that engineering students must develop, especially within a practical laboratory. A new specialized course in renewable energy was introduced at the beginning of 2014 at the Central University of Technology, with the main purpose of addressing this goal. The purpose of this research is to describe the design and development of relevant practical instruction which was introduced into one of the solar energy modules, termed Solar Energy Systems II. This module forms part of the curriculum of the new renewable energy course. The backward curriculum design method was applied in developing the practical instruction. Five learning outcomes were specified while three assessment strategies were selected, including oral presentations, written laboratory reports (headings include the experimental question, hypothesis, materials, procedure, observations, data, conclusion and reflections) and a final written class test. Two main pedagogical methods were used involving authentic learning and computer-based learning, while lectures, group work, videos and a learning management system were also used. A questionnaire was finally used to obtain student feedback on the practical instruction. Students indicated that the practical work was enjoyable (92%), relevant to the theory (83%), and a valuable learning experience (97%). This practical instruction has given freshmen engineering students the opportunity to demonstrate their acquisition of important graduate attributes that may help them to contribute to the socio-economic development of South Africa

The impact of atmospheric conditions on the sustainability of a PV system in a semi-arid region: A case study from South Africa

Published Conference ProceedingVarying atmospheric conditions can exert a significant negative impact on the amount of energy that is produced by a photovoltaic solar system. The purpose of this research is to present empirical data contrasting the available daylight hours of two distinct sites in South Africa, one being a semi-arid region and the other a pollution intensive area. Daylight hours are defined in this paper as the amount of time in which energy equivalent to the STC conditions is being received by a PV module. Both these sites are reported to have the same annual global horizontal irradiation according to available sources. However, the empirical data from this study indicates an average difference of 53% between the daylight hours available for the two sites for March, April and May