The diet of Merino and Dorper wethers and ewes, castrated Boer goats and Afrikaner oxen and heifers was ascertained in order to determine whether the species selection by these animals, during the various seasons of the year could offer an explanation for the changes in the floristic composition of mixed karoo veld. This study was also undertaken to determine the influence of the growth cycles of the different plants on the selection pattern of the animals. The study was carried out over a period of two years, August 1975 to August 1977, in a camp of the Agricultural Research Institute of the Karoo Region, Middelburg Cape. The vegetation of the camp could be discribed as a mixed grass and Karoo bush veld. In order to realize the abovementioned objectives the following data were recorded: *the available plant material during the various seasons of the year, *the floristic composition of the veld during the various seasons of the year, and the floristic composition of the diet of the different kinds of animals during the various seasons of the year. *The availability of plant material was determined by means of three monthly clipping trials. The clipped material was separated into edible and inedible material in order to determine the actual amount available as a source of food. *The floristic composition of the veld was determined by means of three monthly surveys using the descending point method described by Roux (1963). The results of the clipping trials were also used to express the floristic composition of the veld on a mass basis. *Samples of the diet were collected over a two year period, August 1975 to August 1977, every three months on four consecutive days by means of oesophageal fistulated animals.The floristic composition of the diet was determined by means of the microscope point method of Heady (1963) and expressed on a mass basis. Characteristics of a number of diagnostic elements of the species in the study area were described for the identification of the plant fragments in the diet samples. The results were presented as follows: *Graphs were drawn to illustrate, during the different sampling dates, the contribution of the various components of karoo veld to: *the diet of animals the available plant material, and the floristic composition of the veld. *Variation in the diet of the animals was discussed in terms of: *the available plant material, *the growth cycles of the different components, and *• the climate. *Variation in the availibility of plant material and the floristic composition of the veld was discussed and accounted for in terms of: *the diet of the animals *the growth cycles of the different components, and *the climate. The results revealed the following tendencies in the selection pattern:*Both the palatable and unpalatable karoo bush components were selected mainly during their active growth stages, that is, autumn and spring. Within these active growth stages the selection pattern of the animals varied. The animals showed a preference for the palatable karoo bush component during autumn and winter and for the unpalatable component during spring. *The grass component was, in the case of the small stock, selected mainly during the summer, in other words, the active growth stage. The large stock concentrated mainly on the grass component as a source of food throughout the study period. *Ephemerals were selected in large amounts only during the autumn, winter and spring of 1976. *The geophyte component constituted a significant part of the diet of the animals only during the autumn of 1976. The floristic composition of the veld changed over the study period. The contribution of the two karoo bush components increased over the study period, while the contribution of the grass component decreased. Only the change in the contribution of the palatable karoo bush component was statistically signficant on a 10 percent level. The changes may be attributed mainly to the species selection by the animals, although, influence of the climate, especially rain, may not be ignored. Owing to the tendency of the animals to select active growing plant material, it is essential to incorporate rotational rest periods in a veld management system in order to provide an opportunity for each component of karoo veld to grow and reproduce. / DSc, PU vir CHO, 1981

The diet of Merino and Dorper wethers and ewes, castrated Boer goats and Afrikaner oxen and heifers was ascertained in order to determine whether the species selection by these animals, during the various seasons of the year could offer an explanation for the changes in the floristic composition of mixed karoo veld. This study was also undertaken to determine the influence of the growth cycles of the different plants on the selection pattern of the animals. The study was carried out over a period of two years, August 1975 to August 1977, in a camp of the Agricultural Research Institute of the Karoo Region, Middelburg Cape. The vegetation of the camp could be discribed as a mixed grass and Karoo bush veld. In order to realize the abovementioned objectives the following data were recorded: *the available plant material during the various seasons of the year, *the floristic composition of the veld during the various seasons of the year, and the floristic composition of the diet of the different kinds of animals during the various seasons of the year. *The availability of plant material was determined by means of three monthly clipping trials. The clipped material was separated into edible and inedible material in order to determine the actual amount available as a source of food. *The floristic composition of the veld was determined by means of three monthly surveys using the descending point method described by Roux (1963). The results of the clipping trials were also used to express the floristic composition of the veld on a mass basis. *Samples of the diet were collected over a two year period, August 1975 to August 1977, every three months on four consecutive days by means of oesophageal fistulated animals.The floristic composition of the diet was determined by means of the microscope point method of Heady (1963) and expressed on a mass basis. Characteristics of a number of diagnostic elements of the species in the study area were described for the identification of the plant fragments in the diet samples. The results were presented as follows: *Graphs were drawn to illustrate, during the different sampling dates, the contribution of the various components of karoo veld to: *the diet of animals the available plant material, and the floristic composition of the veld. *Variation in the diet of the animals was discussed in terms of: *the available plant material, *the growth cycles of the different components, and *• the climate. *Variation in the availibility of plant material and the floristic composition of the veld was discussed and accounted for in terms of: *the diet of the animals *the growth cycles of the different components, and *the climate. The results revealed the following tendencies in the selection pattern:*Both the palatable and unpalatable karoo bush components were selected mainly during their active growth stages, that is, autumn and spring. Within these active growth stages the selection pattern of the animals varied. The animals showed a preference for the palatable karoo bush component during autumn and winter and for the unpalatable component during spring. *The grass component was, in the case of the small stock, selected mainly during the summer, in other words, the active growth stage. The large stock concentrated mainly on the grass component as a source of food throughout the study period. *Ephemerals were selected in large amounts only during the autumn, winter and spring of 1976. *The geophyte component constituted a significant part of the diet of the animals only during the autumn of 1976. The floristic composition of the veld changed over the study period. The contribution of the two karoo bush components increased over the study period, while the contribution of the grass component decreased. Only the change in the contribution of the palatable karoo bush component was statistically signficant on a 10 percent level. The changes may be attributed mainly to the species selection by the animals, although, influence of the climate, especially rain, may not be ignored. Owing to the tendency of the animals to select active growing plant material, it is essential to incorporate rotational rest periods in a veld management system in order to provide an opportunity for each component of karoo veld to grow and reproduce. / DSc, PU vir CHO, 1981

Hydrogen production via the electrolysis of water has gained a lot of attention in the last couple of years. Research related to electrolysers is mostly aimed towards decreasing the noble–metal catalyst content. In this study the presently used catalyst application techniques were reviewed and critically examined to find commercially applicable and effective methods. Selected methods were then practically applied to determine their feasibility and to gain “know–how” related to the practical application of these techniques. The selected techniques were the hand paint, inkjet print, screen print and spray paint techniques. Meaningful comparisons were made between the methods in terms of parameters such as practicality, waste of catalyst and microstructure. The results point out that the hand paint and spray paint methods are feasible methods although there are improvements to be made. The hand paint method was improved by applying a carbon micro porous layer to the gas diffusion layer before the painting is carried out. The addition of the carbon layer reduced the soaking of the catalyst–containing ink through the gas diffusion layer. A method not initially investigated was identified an evaluated and showed promising results in lowering the mass of catalyst applied. This method comprised of sputtering a layer of catalyst material onto a prepared gas diffusion layer. It also came to light from the results that electrodes, and therefore membrane electrode assemblies, can be produced at a much lower cost than the commercial available membrane electrode assemblies. / Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2012.

Hydrogen production via the electrolysis of water has gained a lot of attention in the last couple of years. Research related to electrolysers is mostly aimed towards decreasing the noble–metal catalyst content. In this study the presently used catalyst application techniques were reviewed and critically examined to find commercially applicable and effective methods. Selected methods were then practically applied to determine their feasibility and to gain “know–how” related to the practical application of these techniques. The selected techniques were the hand paint, inkjet print, screen print and spray paint techniques. Meaningful comparisons were made between the methods in terms of parameters such as practicality, waste of catalyst and microstructure. The results point out that the hand paint and spray paint methods are feasible methods although there are improvements to be made. The hand paint method was improved by applying a carbon micro porous layer to the gas diffusion layer before the painting is carried out. The addition of the carbon layer reduced the soaking of the catalyst–containing ink through the gas diffusion layer. A method not initially investigated was identified an evaluated and showed promising results in lowering the mass of catalyst applied. This method comprised of sputtering a layer of catalyst material onto a prepared gas diffusion layer. It also came to light from the results that electrodes, and therefore membrane electrode assemblies, can be produced at a much lower cost than the commercial available membrane electrode assemblies. / Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2012.