Some aspects of the ecology and biology of two estuarine grapsoid crabs
- Authors: Warren, Stephanie Judith
- Date: 1964
- Subjects: Crabs -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5899 , http://hdl.handle.net/10962/d1013506
- Description: Extracted from Summary, p. 172. The semi-terrestrial grapsoid crabs Cyclograpsus punctatus and Sesarma catenata have been studied in two ways. Part I of this thesis gives an account of their distribution in the Kowie River estuary in relation to certain environmental factors. Part II deals with further aspects of their biology as well as the ecological relationship between the two species.
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- Date Issued: 1964
Some ionospheric effects observed at sunrise
- Authors: Baker, D C
- Date: 1964
- Subjects: Sun -- Rising and setting , Ionosphere -- Research
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5513 , http://hdl.handle.net/10962/d1009496 , Sun -- Rising and setting , Ionosphere -- Research
- Description: The study of the ionosphere over the sunrise period is necessary for an understanding of the vtiriations in layer structure with time and has been a topic of research of many workers. On the whole these investigations have been restricted to a study of critical frequency variations with relatively short intervals of a few minutes between successive records, of N-h curves deduced from ionograms with long intervals (15 minutes or so) between successive N-h curves or of continuously monitored single frequency reflections. Not one of the three techniques is entirely satisfactory for a detailed study of ionospheric behaviour over sunrise. The first two do not give a sufficiently clear indication of what happens in the initial stages of layer development, while from the third incomplete data is obtained as to what is happening at a specific electron-density level. For this reason a preliminary investigation of the ionosphere over sunrise was made at Rhodes University during August, 1959. The records were obtained at four-and-a-half minute intervals and scaled by the method of KELSO (1952 ). "Many of t he results were inconclusive but it appeared that records would have to be taken at approximately one minute intervals and reduced to N-h curves by a scaling technique which made full allowance for low-level ionization if useful results were to be obtained. An attempt has been made in this thesis to investigate the behaviour of the ionosphere over sunrise more fully than can be done by the three techniques referred to. A number of observed phenomena are also examined. Part I deals with the theoretical background to ionosphere physics in general and describes the equipment, equipment modifications and experimental procedure. Part II presents the results obtained. The records for a largescale travelling disturbance are analysed. Various observed phenomena are described and discussed. A simple method of obtaining production rates from experimental data is described. The implications of the observed variations of production rates with height and time are discussed. Suggestions for further research and improvement of the methods used arc made in Charter 9.
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- Date Issued: 1964
The north gap dyke of the Transkei
- Authors: Moore, Alan C
- Date: 1964
- Subjects: Petrology -- South Africa -- Transkei , Dikes (Geology) -- South Africa -- Transkei , Petrofabric analysis -- South Africa -- Transkei
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5031 , http://hdl.handle.net/10962/d1007087
- Description: Field work and mapping with the aid of aerial photographs have shown the north Gap Dyke to be a vertical intrusion 93½ miles long . It extends from a point about 4½ miles south of Cathcart to the coast where it enters the sea about 100 yards north of the Ngadla R lver mouth. It is composed of several rock types including dolerite pegmatite, granophyric dolerite, subophitic dolerite, and it has a more or less central core of mobilized sediment at the western end. The essential minerals of the dolerite types include zoned plagioclase, which is described in some detail, and augite. Less important are hornblende and micropegmatite. Accessories include apatite, ilmenite, magnetite, quartz, actinolite, prehnite, calcite and epidote. Iddingsite (?), saussurite and chlorite occur as alteration products. The mode of origin of the Gap Dyke magma remains an open question: it may have arisen as a result of normal crystal fractionation or as the result of hybridization in depth followed by differentiation.
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- Date Issued: 1964
The South Atlantic radiation anomaly
- Authors: Van Rooyen, H O
- Date: 1964
- Subjects: Terrestrial radiation , Atmospheric radiation , Geomagnetism , Electron precipitation , South Atlantic Ocean -- Radiation
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5546 , http://hdl.handle.net/10962/d1013427
- Description: Part I. (1) An elementary treatment of the motion of charged particles in a magnetic field is presented. The concept of guiding centre motion is introduced, and is used in outlining the theory of particle drifts. (2 ) The motion of charged particles in the geomagnetic field is discussed, and the concept of adiabatic invariance introduced. (3) Mc Iliwains coordinates for mapping the distribution of charged particles trapped in the geometric field are defined and briefly discussed. (4) A survey of present knowledge of the Van Allen radiation zones is made. Particular attention is given to the distribution, characteristics, and variability of the trapped radiation. (5) The Cape Town magnetic anomaly, the Brazil radiation anomaly and the South Atlantic radiation anomaly are discussed. The electrons entering the South Atlantic radiation anomaly are shown to be those monitored over Iowa by the US satellite Injun I. Part 11. (1) It is shown how the geomagnetic field can, at high altitudes and over relatively short distances, be approximated by the field of a monopole. A new method is developed which enables one to plot the energy absorbed from an electron (which moves in a monopole field in the atmosphere) against altitude, given the initial energy and pitch angle of the electron. Some numerical computations using this method are described, and the results discussed. These results are used, in conjunction with US satellite Injun I for the Iowa region, to estimate the energy inout to the atmosphere in the South Atlantic radiation anomaly. The main approximations and simplifying assumptions made in this treatment, are discussed. (2) Geophysical effects generally recognized to be connected with the precipitation of charged particles are discussed. In the course of this discussion the two main theories of the connection between the radiation zones and the auroras are examined. (3) A preliminary discussion, based on the work summarized in point (1) of detectable geophysical events associated with the precipitation of electrons into the South Atlantic radiation anomaly is given. It is concluded that auroral emission, X-ray bursts, and ionospheric ionization in the E region should be more frequent and pronounced in the South Atlantic radiation anomaly than in any other region of comparable invariant latitudes and that the effects of atmospheric heating by precipitated electrons should be detectable over the anomaly. (4) An assessment is made of the value of the method referred to in point (1). Suggestions for its modification and extension are put forward. It is suggested that if more extensive rocket and satellite data on the low energy component of the electron flux become available, this method can be employed in a rigorous theoretical investigation of the South Atlantic radiation anomaly. Summary, p. 98-100.
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- Date Issued: 1964