Advanced ionospheric chirpsounding
- Authors: Poole, Allon William Victor
- Date: 1984
- Subjects: Ionospheric sounds Ionosphere -- Research
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5446 , http://hdl.handle.net/10962/d1001999
- Description: This dissertation reports research into the theory and practical application of linear frequency modulated ionospheric sounding, as an alternative to the more usual technique of pulse modulation. A comparison of this technique with that of conventional pulse sounders is given, based on the concepts of matched filters and ambiguity functions for both modulations. A theory is developed to relate the group range and phase velocity of the ionospheric target to the phase and frequency of the difference signal at the receiver output. A method is then described whereby the group range and phase velocity of the reflection point as well as the amplitude, arrival angle and polarisation mode of the reflected energy can be measured. A description of the implementation of the technique is given together with some initial results. Finally, some suggestions for improvements are given
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Oblique incidence investigations of the ionosphere over the Southern Ocean
- Authors: Rash, Jonathan Paul Stuart
- Date: 1979
- Subjects: Ionosphere Ionosphere -- Antartctic Ocean
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5438 , http://hdl.handle.net/10962/d1001991
- Description: The region of the South Atlantic and Southern Oceans ... is of considerable interest in ionospheric and aeronomic research owing to the presence of several 'anomalies'. The most notable of these is the South Atlantic (or Brazilian) Anomaly associated with the global minimum of magnetic field intensity off the coast of Brazil (Introduction, p. 1)
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A new model of the IO-Controlled Jovian decametric radiation
- Authors: Goertz, Christoph K
- Date: 1972
- Subjects: Jupiter (Planet) Radiation Magnetosphere Ionosphere
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5521 , http://hdl.handle.net/10962/d1012043
- Description: Jupiter, the largest planet in the solar system, is not only an emitter of thermal radiation like any other planet. Jupiter also emits relatively high-intensity non-thermal radiation in two bands, the decimetre wavelength range and the decametre wavelength range (5 MHz< f < 40 MHz). The decimetric radiation is believed to be due to synchrotron radiation of electrons trapped in a kind of Jovian "Van Allen belt". This thesis deals almost exclusively with the decametric radiation. Although the decametric radiation has been observed for 15 years since its discovery by Burke and Franklin in 1955, there is no generally accepted theoretical model of its generation to be found in the literature as yet. This is not surprising, as there are many complex and confusing aspects of the radiation. And since our knowledge of the Jovian ionosphere, magnetosphere and magnetic field is very limited indeed, every theoretical model must be based on some more or less well justified assumptions. It is, however, possible to draw some conclusions from the observed properties of the decimetric and decametric radiation. The radiation in both bands is polarized. It has been shown that at least part of the polarization is an intrinsic property of the radiation source at Jupiter, This indicates the existence of a Jovian magnetic field. The magnitude and shape of the magnetic field, however, is open to discussion, although a dipole field does seem to be a good approximation at least for large distances from Jupiter. Intro. p. 1-2.
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Diurnal and seasonal variations of the F2 region of the Antarctic ionosphere
- Authors: Williams, Morgan Howard
- Date: 1972
- Subjects: Harmonic analysis , Ionosphere -- Antarctic Ocean
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5548 , http://hdl.handle.net/10962/d1013459
- Description: [From Introduction, p. 2] The first chapter of this thesis deals with an analysis of F2 critical frequency data first for SANAE and then for eleven other Antarctic and sub-Antarctic stations covering the period 1957 to 1969. This shows certain aspects of the F2 behaviour. Some of the results of this chapter have been reported in a paper by Gledhill and Williams. The two most important mechanisms thought to be responsible for the Antarctic f₀F2 behaviour are incoming corpuscular radiation and horizontal neutral winds. These two mechanisms together with two others (the temperature theory of Torr and Torr and the semi-annual variation of neutral atmospheric density) are discussed in detail in part 2 (Chapters 2 to 4) with a view to discovering which aspects of the f₀F2 behaviour over Antarctica can be explained by each theory. An attempt is made in Part 3 (Chapters 5 and 6) to explain the observed behaviour by solving the continuity equation of the ionosphere for high-latitude stations. Finally, besides the critical frequency, another parameter of importance in explaining the behaviour in the F2 region is the height at which the F2 maximum occurs. This quantity cannot be read directly from an ionogram and it is not an easy quantity to determine. In fact the way in which it is usually obtained is by "scaling" the ionogram in question and converting the virtual heights obtained into real heights. In Part 4 (Chapter 7 and 8) an outline is given of the two computer programs which were written to perform this conversion.
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A critical analysis of the teaching of fundamental physical concepts and principles, with particular reference to South African schools
- Authors: Helm, Hugh
- Date: 1970
- Subjects: Physics -- Study and teaching -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5541 , http://hdl.handle.net/10962/d1013345
- Description: From introduction: The main purpose of the present study is to give a detailed critical survey of possible teaching approaches to fundamental physical ooncepts and principles which could reasonably be taught at sohool, and to consider the implications of this survey for the teaching of physical science in South Africa
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An investigation into the decametric radio emission by the planet Jupiter
- Authors: Gruber, Georg M
- Date: 1967
- Subjects: Jupiter (Planet) , Radio astronomy , Radio sources (Astronomy)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5545 , http://hdl.handle.net/10962/d1013410
- Description: From introduction: Jupiter is the largest planet in the solar system. Its distance from the Sun is five times that of the Earth and its mass is nearly two and a half times that of all the other planets added together. Jupiter turns about its own axis rather rapidly, once in just under ten hours, and it completes one revolution about the Sun in just under twelve years. Thus Earth has to pass almost directly between the Sun and Jupiter once every thirteen months. When this happens Jupiter is said to be in "opposition", as its position is then opposite to that of the Sun, when viewed from Earth. Around this time the planet will be most favourably placed for observations, as it is at its closest to Earth and up in the sky for a large part of the night. During the day observations on radio frequencies are more difficult, as the Sun is a source of great interference. Besides being an emitter of thermal electromagnetic radiation, as one would expect, Jupiter also emits two kinds of non-thermal radiation, one in the decimetre wavelength range and the other in the decametre wavelength range. A large number of scientists have worked on the problems of decimetre and decametre radiation. This thesis deals with some aspects of decametre radiation.
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Ultraviolet specular reflectance, electronic absorption and the excitation of fluorescence in single crystals of anthracene
- Authors: Wright, W H
- Date: 1966
- Subjects: Anthracene crystals -- Fluorescence , Ultraviolet spectroscopy -- Absorption , Reflectance
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5544 , http://hdl.handle.net/10962/d1013366
- Description: From introduction: The Fluorescence Excitation Spectrum or anthracene is known to vary considerably with the age and condition or the crystal. This thesis represents an attempt to improve the understanding of these variations. To put the problem on a quantitative basis it was found necessary to know both the ultraviolet reflection and absorption spectra. Reports of the reflection spectrum appear to have been confined to the case of polarised incident light. In addition the reflectivity measurements are always reported for a freshly cleaved surface. For these reasons the reflectivity of anthracene for various conditions of the reflecting surface was measured with unpolarised light. These varying reflectivities were used to further knowledge of the chemical processes at the crystal surface, as well as being used directly in the calculation of fluorescence excitation spectra. Reflection spectra with a- and b- crystallographic axis polarisations were also obtained. Since such spectra are reported in the literature it was possible, by comparison, to conclude that the experimental methods used in this thesis yielded valid results. The polarised measurements were used to obtain optical constants for the crystal. In the interests of readability most of the complicated process of converting the reflectivities to optical constants is dealt with in three appendices to the thesis.
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Construction of a wide-frequency range double heterodyne conductance bridge and its use in the investigation of polarisation errors in conductance measurements
- Authors: Govinden, Herby Silvester
- Date: 1961
- Subjects: Electrodynamics Electrolytes -- Conductivity
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5522 , http://hdl.handle.net/10962/d1012074
- Description: (1) Developments in a.c. conductance techniques during the past ninety years have been reviewed, and a brief outline is given of the older theories regarding electrolytic polarisation. (2) A conductance bridge - incorporating the double heterodyne principle - has been constructed, capable of giving resistance readings to an accuracy of 0.01% over a range of frequencies covering the best part of 100 kc/s. It has also been found possible to calibrate the oscillator so that frequency settings can be guaranteed to an accuracy of , at least, 0.1% in the range: 2 kc/S to 50 kc/S. (3) The Wheatstone Bridge Network has been slightly modified to enable measurements at the high frequencies. (4) Resistances in the measuring arm of the bridge have been calibrated 'in situ' by the method of intercomparison. (5) A brief description is given of the modern theories regarding electrode processes and modern methods of eliminating electrode effects. (6) Two types of conductance cells, with bright Pt electrodes, have been used to carry out measurements on potassium chloride solutions: (a) Thomas- Gledhill Cell (b) Nichol-Fuoss Cell. The latter incorporates concentric, cylindrical electrodes with the lead to the outer electrode acting as an electrical shield for the lead to the inner electrode. This cell was constructed and used for the first time in this laboratory. (7) From resistance-frequency graphs plotted, it is shown that the Jones and Christian extrapolation procedure cannot be applied (with any degree of confidence) to obtain the true resistance, when measurements are effected over an extended range of frequencies. (8) The method of resistance-reactance diagrams is discussed and applied to various networks of resistances and capacitances. (9) By drawing resistance-reactance diagrams for the experimental readings obtained, equivalent circuits have been derived - for all the solutions investigated in the N-F cell, and for the approx. O.OlD solution in the T-G cell - which approximate to cell behaviour in the range: 500 c/s to 75 kc/s. The less concentrated solutions in the T-G cell show peculiar behaviour at the high frequencies. (10) Probable reasons are advanced for deviations from linearity on resistance-frequency graphs. (11) A new method is proposed for determining the true resistance of solutions measured in cells of the N-F type. Summary, p. 166-167.
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Ionospheric studies of the solar eclipse 25 December, 1954
- Authors: McElhinny, M W
- Date: 1959
- Subjects: Ionosphere -- Research , Solar eclipses
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5531 , http://hdl.handle.net/10962/d1012869
- Description: Since the Kennelly- Heaviside hypothesis in 1902 of the existence of a partially conducting layer in the upper atmosphere was proved to be true by the experiments of APPLETON and BARNETT (1925) and BREIT and TUVE (1926), this region has become known as the ionosphere. The ionosphere was soon discovered to consist of, not one but several layers (Fig. 1) (i) A layer at a height of just over 100 km. called the E layer. (ii) A layer at a height of approximately 300km. called the F₂ layer. (iii) A layer at a height of approximately 200 km. called the F₁ layer; this layer differs from the other two in that it is only present during the day time in Summer. (iv) Occasional intense reflections from a height of about 100 km. are found - these cannot be attributed to the normal E layer and have received the name "Sporadic E". The presence of two E layers (E₁ and E₂) has been suggested by HALLIDAY (1936) and BEST and RATCLIFFE (l978) but until recently most workers still seem to attribute these reflections to Sporadic E. Recent measurement by rockets of the electron density at E layer heights still do not confirm whether such bifurcation exists in the E region. The diurnal and seasonal variations of the first three layers indicate that the sun is the chief agent in their production. It is generally agreed that these layers consist of ionised molecules or atoms and free electrons produced by radiation from the sun. The origin of Sporadic E ionisation is still obscure, but it is thought that these sudden increases in ionisation which occur in E layer heights are due to passing meteors. Recently it has also been suggested by SEDDON, PICKAR and JACKSON (1954) from rocket measurements that Sporadic E might be due to a steep electron density gradient above the B layer.
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A conductimetric investigation of phenomena in extremely dilute aqueous solutions
- Authors: Faure, Pierre Knobel
- Date: 1957
- Subjects: Adsorption , Solution (Chemistry)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4524 , http://hdl.handle.net/10962/d1014891
- Description: 1. The apparatus used in this investigation is fully described, and a new method is outlined for the calibration of bridge resistances "in situ". 2. A chart is given for the accurate correction of weights in air to weights in vacuum for a range of temperatures extending from 10° to 28°C, and for pressures from 690 to 730 mm. 3. An automatic recycling still has been designed for the continuous production of "ultra-pure" water. This still is capable of delivering daily, in routine operation, 16 l. of water of conductivity less than 100 nm/cm after aeration with "C0₂- and NH₃-free" air. 4. A very soluble layer appears to form on the surface of' glass when it is dried; this layer is readily removed on contact with water. 5. The removal of carbon dioxide and of ammonia from aqueous solution by aeration with an indifferent gas has been fully investigated, and it has been shown that these gases can be completely eliminated by such a process. Whereas the carbon dioxide is removed fairly rapidly, however, the ammonia, whether present alone or together with carbon dioxide, only goes out of solution rather slowly. 6. It has been shown that ammonia is adsorbed from aqueous solution on the glass walls of the cell. 7. There does not appear to be any ammonium bicarbonate in the residual impurity left in the "ultra-pure" water obtained from the still; the impurity can, in fact, be regarded as neutral salt with sufficient accuracy for most purposes. 8. The resistance change which accompanies any variation in the rate of bubbling of the stirring gas through the water has been investigated, but no solution has been found as to the cause of this change. 9. A comparison has been made of the efficiency of different gases for stirring purposes, and it seems that, for general work, nitrogen is by far the most suitable of the common gases. 10. The extrapolation to be used for converting resistances to their values at infinite frequency appears ...
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Measurements of the solubilities of some silver halides in water by electrical methods
- Authors: Malan, George McPherson
- Date: 1955
- Subjects: Silver halides -- Solubility , Silver halides -- Analysis , Conductometric analysis , Potentiometry , Silver halides
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4515 , http://hdl.handle.net/10962/d1013502
- Description: [Introduction, p. 3] The solubilities of the silver halides cannot be determined by the conventional methods of analytical chemistry because they are too sparingly soluble (of the order 1 x 10⁻⁵ to 1 x 10⁻⁶ g . equiv./1. at 25°C.) However, electrical, and to a lesser extent optical methods, are admirably suited because of their greater sensitivity. The conductometric and potentiometric methods are the two most important electrical techniques for the measurement of the solubilities of sparingly soluble salts, and are the ones employed in this research. There are large discrepancies between the published values for the solubility of silver chloride. Results obtained by the conductometric and potentiometric methods disagree. In addition, figures quoted by independent authors using the same method differ by as much as 15%.
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