An investigation of the polarization of solar radio noise
- Authors: Verschuur, Gerrit L.,1937-
- Date: 1961
- Subjects: Solar radio emission , Polarimetry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5547 , http://hdl.handle.net/10962/d1013441
- Description: CHAPTER I A description of the sun and the type of radio radiation it emits is given. The relation that exists between this and other events occurring on the sun's surface is studied. CHAPTER II The literature dealing with the origin of solar radio noise is reviewed. CHAPTER III The method of specifying polarized radiation and the effect of a magneto- ionic medium on such radiation is discussed. The possible origin of the polarization of solar radio noise is examined and the literature relating to this and to the observations of polarization of solar noise is reviewed. A short outline of the methods used in measuring polarization is given. CHAPTER IV A detailed outline of the construction of a polarimeter is given together with full circuit diagrams and illustrative photographs. CHAPTER V A brief discussion of the operation of the polarimeter, the results obtained and suggestions for its future operation is given.
- Full Text:
- Date Issued: 1961
- Authors: Verschuur, Gerrit L.,1937-
- Date: 1961
- Subjects: Solar radio emission , Polarimetry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5547 , http://hdl.handle.net/10962/d1013441
- Description: CHAPTER I A description of the sun and the type of radio radiation it emits is given. The relation that exists between this and other events occurring on the sun's surface is studied. CHAPTER II The literature dealing with the origin of solar radio noise is reviewed. CHAPTER III The method of specifying polarized radiation and the effect of a magneto- ionic medium on such radiation is discussed. The possible origin of the polarization of solar radio noise is examined and the literature relating to this and to the observations of polarization of solar noise is reviewed. A short outline of the methods used in measuring polarization is given. CHAPTER IV A detailed outline of the construction of a polarimeter is given together with full circuit diagrams and illustrative photographs. CHAPTER V A brief discussion of the operation of the polarimeter, the results obtained and suggestions for its future operation is given.
- Full Text:
- Date Issued: 1961
A 22 GHz water maser radiometer
- Authors: Nunn, Brian J
- Date: 1975
- Subjects: Masers , Radiometers
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5535 , http://hdl.handle.net/10962/d1012987
- Description: This thesis describes the properties of interstellar water maser sources, and other sources near 22 GHz. Calculations based on manufacturer's specifications of the 22 GHz mixer, which was to be used in a water radiometer, and on the size antenna aperture of the proposed antenna aperture, show the viability of constructing such a radiometer for spectral line and continuum work. Various sections of the radiometer were constructed, including the Cassegrain feed system and its support, an intermediate frequency amplifier and buffer, a timing control unit, and a data processor. These units are part of the radiometer, which is almost ready for observations of sources.
- Full Text:
- Date Issued: 1975
- Authors: Nunn, Brian J
- Date: 1975
- Subjects: Masers , Radiometers
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5535 , http://hdl.handle.net/10962/d1012987
- Description: This thesis describes the properties of interstellar water maser sources, and other sources near 22 GHz. Calculations based on manufacturer's specifications of the 22 GHz mixer, which was to be used in a water radiometer, and on the size antenna aperture of the proposed antenna aperture, show the viability of constructing such a radiometer for spectral line and continuum work. Various sections of the radiometer were constructed, including the Cassegrain feed system and its support, an intermediate frequency amplifier and buffer, a timing control unit, and a data processor. These units are part of the radiometer, which is almost ready for observations of sources.
- Full Text:
- Date Issued: 1975
Effects of precipitating electrons in the ionosphere
- Authors: Haschick, Aubrey D
- Date: 1974
- Subjects: Electrons , Electron precipitation , Ionosphere , Ionospheric electron density
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5526 , http://hdl.handle.net/10962/d1012220
- Description: As early as 1896, around the time of the discovery of the electron by J.J. Thompson, Birkeland was led to propose that aurorae were caused by fast moving electrons or similarly charged particles emitted by the sun and 'sucked in towards' the auroral zones by the geomagnetic field. He later supported this idea by firing electrons at a dipole field surrounding a sphere covered with a fluorescent coating. Extensive ground based observations of auroral features eventually led, in 1950, to the initial direct evidence of the fact that auroral emissions are due to energetic charged particles, consisting partly of protons, entering the earth's atmosphere (Meinel, 1951). However, it was only in 1952 and 1953 that the first measurements of what was later interpreted as bremsstrahlung X- rays from precipitating electrons were made at auroral latitudes. (Meredith et aI, 1955) During the IGY, 1957 - 1958, a number of rockets were fired through and near, visible aurorae and large fluxes of low energy electrons were detected ... Intro., p. 1.
- Full Text:
- Date Issued: 1974
- Authors: Haschick, Aubrey D
- Date: 1974
- Subjects: Electrons , Electron precipitation , Ionosphere , Ionospheric electron density
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5526 , http://hdl.handle.net/10962/d1012220
- Description: As early as 1896, around the time of the discovery of the electron by J.J. Thompson, Birkeland was led to propose that aurorae were caused by fast moving electrons or similarly charged particles emitted by the sun and 'sucked in towards' the auroral zones by the geomagnetic field. He later supported this idea by firing electrons at a dipole field surrounding a sphere covered with a fluorescent coating. Extensive ground based observations of auroral features eventually led, in 1950, to the initial direct evidence of the fact that auroral emissions are due to energetic charged particles, consisting partly of protons, entering the earth's atmosphere (Meinel, 1951). However, it was only in 1952 and 1953 that the first measurements of what was later interpreted as bremsstrahlung X- rays from precipitating electrons were made at auroral latitudes. (Meredith et aI, 1955) During the IGY, 1957 - 1958, a number of rockets were fired through and near, visible aurorae and large fluxes of low energy electrons were detected ... Intro., p. 1.
- Full Text:
- Date Issued: 1974
Electron precipitation and ionospheric disturbance
- Authors: Torr, Marsha R
- Date: 1966
- Subjects: Electrons , Electron precipitation , Ionosphere , Ionospheric electron density
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5509 , http://hdl.handle.net/10962/d1007691
- Description: From Introduction: The minimum in the scalar magnitude of the geographic total field, which lies off the coast of Brazil, allows the mirror points of trapped particles to dip low into the atmosphere over the South Atlantic Ocean, resulting in two regions of maximum intensity of preciptated particles in that region, one from the inner belt and one from the outer. High charged particle fluxes have been observed at low altitudes over these regions by satellites Sputnik 5 and 6 (Ginsburg et al, 1961) and Discoverer 31 (Seward and Kornblum, 1963) amongst others. The more southerly of these two regions acts as a sink for electrons from the outer radiation belt and will be referred to in what follows as the Southern Radiation Anomaly. Gladhill and van Rooyen (1963) predicted that the energy deposited in the upper atmosphere by these charged particles would be sufficient to give rise to enhanced geophysical effects such as auroral emission, X-rays and ionization and heating of the upper atmosphere in this region. Although some of these effects have been correlated with precipitated electrons, no definite relation had until now been established between ionospheric effects and precipitated particles. The aim of this thesis was to investigate such a relationship and the results were extremely successful. It will be shown conclusively in what follows, that the precipitation of electrons can account for the ionospheric disturbances defined by a disturbance criterion at all stations around L=4. Part I describes the exploration of the radiation belts and the magnetosphere with rockets and satellites. The resulting theoretical models based on the observations are discussed. A brief review is given of the work that has been done to date to derive equations for the loss and replenishment of particles in the belts. Because of the complexity of these and the number of doubtful factors involved, a simple model of injection of electrons into the outer belt is devised, giving average values of trapped and precipitated electron fluxes at any point around L=4. In Part II, this model is employed together with the disturbance criterion of Gledhill and Torr (1965) to examine the relationship between ionospheric disturbances and electron fluxes. Also the energy range of the precipitated particles is examined.
- Full Text:
- Date Issued: 1966
- Authors: Torr, Marsha R
- Date: 1966
- Subjects: Electrons , Electron precipitation , Ionosphere , Ionospheric electron density
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5509 , http://hdl.handle.net/10962/d1007691
- Description: From Introduction: The minimum in the scalar magnitude of the geographic total field, which lies off the coast of Brazil, allows the mirror points of trapped particles to dip low into the atmosphere over the South Atlantic Ocean, resulting in two regions of maximum intensity of preciptated particles in that region, one from the inner belt and one from the outer. High charged particle fluxes have been observed at low altitudes over these regions by satellites Sputnik 5 and 6 (Ginsburg et al, 1961) and Discoverer 31 (Seward and Kornblum, 1963) amongst others. The more southerly of these two regions acts as a sink for electrons from the outer radiation belt and will be referred to in what follows as the Southern Radiation Anomaly. Gladhill and van Rooyen (1963) predicted that the energy deposited in the upper atmosphere by these charged particles would be sufficient to give rise to enhanced geophysical effects such as auroral emission, X-rays and ionization and heating of the upper atmosphere in this region. Although some of these effects have been correlated with precipitated electrons, no definite relation had until now been established between ionospheric effects and precipitated particles. The aim of this thesis was to investigate such a relationship and the results were extremely successful. It will be shown conclusively in what follows, that the precipitation of electrons can account for the ionospheric disturbances defined by a disturbance criterion at all stations around L=4. Part I describes the exploration of the radiation belts and the magnetosphere with rockets and satellites. The resulting theoretical models based on the observations are discussed. A brief review is given of the work that has been done to date to derive equations for the loss and replenishment of particles in the belts. Because of the complexity of these and the number of doubtful factors involved, a simple model of injection of electrons into the outer belt is devised, giving average values of trapped and precipitated electron fluxes at any point around L=4. In Part II, this model is employed together with the disturbance criterion of Gledhill and Torr (1965) to examine the relationship between ionospheric disturbances and electron fluxes. Also the energy range of the precipitated particles is examined.
- Full Text:
- Date Issued: 1966
Theoretical aspects of the generation of radio noise by the planet Jupiter
- Authors: Deift, Percy A
- Date: 1972
- Subjects: Jupiter (Planet) , Radio astronomy , Radio noise
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5516 , http://hdl.handle.net/10962/d1011051 , Jupiter (Planet) , Radio astronomy , Radio noise
- Description: Decameter radiation was first observed from Jupiter by Burke and Franklin (JGR 60, 213, 1955). In 1964 Bigg (Nature, 203, 1008, (1964)) found that 1o exerted a profound effect on the radiation. The majority of the early theories to explain the origin of the decameter emissions, attributed the radiation to an emission process occurring at or near the electron gyrofrequency or the plasma frequency. Intro., p. 1. The majority of the early theories to explain the origin of the decameter emissions, attributed the radiation to an emission process occurring at or near the electron gyrofrequency or the plasma frequency (for a review see eg. Warwick, Space Sci. Rev. &" 841 (1967)). More recent work centred around the question of how 10 modulates the emission (see the article of Carr and Gulkis (Annual Review of Astronomy and Astrophysics Vol 8 (1970)) for a detailed review).
- Full Text:
- Date Issued: 1972
- Authors: Deift, Percy A
- Date: 1972
- Subjects: Jupiter (Planet) , Radio astronomy , Radio noise
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5516 , http://hdl.handle.net/10962/d1011051 , Jupiter (Planet) , Radio astronomy , Radio noise
- Description: Decameter radiation was first observed from Jupiter by Burke and Franklin (JGR 60, 213, 1955). In 1964 Bigg (Nature, 203, 1008, (1964)) found that 1o exerted a profound effect on the radiation. The majority of the early theories to explain the origin of the decameter emissions, attributed the radiation to an emission process occurring at or near the electron gyrofrequency or the plasma frequency. Intro., p. 1. The majority of the early theories to explain the origin of the decameter emissions, attributed the radiation to an emission process occurring at or near the electron gyrofrequency or the plasma frequency (for a review see eg. Warwick, Space Sci. Rev. &" 841 (1967)). More recent work centred around the question of how 10 modulates the emission (see the article of Carr and Gulkis (Annual Review of Astronomy and Astrophysics Vol 8 (1970)) for a detailed review).
- Full Text:
- Date Issued: 1972
A comparative study of atmospheric dynamics in the mesosphere and lower thermosphere (MLT) near Grahamstown (South Africa) and Adelaide (Australia)
- Authors: Malinga, Sandile Bethuel
- Date: 2002
- Subjects: Atmospheric physics Atmospheric physics -- South Africa -- Eastern Cape Atmospheric physics -- Australia Dynamic meteorology
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5506 , http://hdl.handle.net/10962/d1007307
- Description: The observations made near Grahamstown (33 .3°S, 26.5°E), South Africa and Adelaide (34.5°S, 138.5°E), Australia over the years 1987 to 1994 are used to study the dynamics of the mesosphere and lower thermosphere (ML T) region with a focus on ∼ 90 km altitude. In particular this thesis deals with on the atmospheric mean flow and the solar diurnal and semi diurnal oscillations with a view to (i) deducing their patterns at the two sites, (ii) comparing the dynamic structures observed at the two sites with special emphases on longitudinal variations, and (iii) putting these observations in a global context by comparing with other ground-based observations, satellite observations and numerical simulations. The main findings are summarised below. The mean flow and the tides at Grahamstown and Adelaide are characteristically variable at planetary time scales. Wavelet spectral and multiresolution analyses reveal that the dominant planetary oscillation is the quasi-16-day oscillation. However, no apparent correlation in the 16-day waves of the mean flow, the diurnal tide and the semidiurnal tide was found. The short-term fluctuations were also investigated using complex demodulation and bispectral techniques and it was found that some of the observed variations in tides could be due to non-linear wave-wave interactions. The long-term trends of the mean flow and tides show patterns that are in broad agreement with theory, results from elsewhere (ground-based and satellite) and the results of the Global-Scale Wave Model and various models by Portnyagin and others. In general the mean flow, the amplitudes and phases of both tides were found to exhibit seasonal and interannual variations which are thought to be related to various factors including (i) changes in the atmospheric mean environment, (ii) thermotidal forcing (iii) gravity wave effects, (iv) planetary scale influence, (v) long-term (e.g. quasi-biennial oscillation) modulation, and (vi) solar activity. There are significant longitudinal differences in the dynamic structure between Grahamstown and Adelaide. More especially, Grahamstown tends to have stronger mean flow and tidal activity than Adelaide. For tides, these differences are thought to be partly due to nonmigrating tidal modes but, in general, migrating modes were found to be dominant.
- Full Text:
- Date Issued: 2002
- Authors: Malinga, Sandile Bethuel
- Date: 2002
- Subjects: Atmospheric physics Atmospheric physics -- South Africa -- Eastern Cape Atmospheric physics -- Australia Dynamic meteorology
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5506 , http://hdl.handle.net/10962/d1007307
- Description: The observations made near Grahamstown (33 .3°S, 26.5°E), South Africa and Adelaide (34.5°S, 138.5°E), Australia over the years 1987 to 1994 are used to study the dynamics of the mesosphere and lower thermosphere (ML T) region with a focus on ∼ 90 km altitude. In particular this thesis deals with on the atmospheric mean flow and the solar diurnal and semi diurnal oscillations with a view to (i) deducing their patterns at the two sites, (ii) comparing the dynamic structures observed at the two sites with special emphases on longitudinal variations, and (iii) putting these observations in a global context by comparing with other ground-based observations, satellite observations and numerical simulations. The main findings are summarised below. The mean flow and the tides at Grahamstown and Adelaide are characteristically variable at planetary time scales. Wavelet spectral and multiresolution analyses reveal that the dominant planetary oscillation is the quasi-16-day oscillation. However, no apparent correlation in the 16-day waves of the mean flow, the diurnal tide and the semidiurnal tide was found. The short-term fluctuations were also investigated using complex demodulation and bispectral techniques and it was found that some of the observed variations in tides could be due to non-linear wave-wave interactions. The long-term trends of the mean flow and tides show patterns that are in broad agreement with theory, results from elsewhere (ground-based and satellite) and the results of the Global-Scale Wave Model and various models by Portnyagin and others. In general the mean flow, the amplitudes and phases of both tides were found to exhibit seasonal and interannual variations which are thought to be related to various factors including (i) changes in the atmospheric mean environment, (ii) thermotidal forcing (iii) gravity wave effects, (iv) planetary scale influence, (v) long-term (e.g. quasi-biennial oscillation) modulation, and (vi) solar activity. There are significant longitudinal differences in the dynamic structure between Grahamstown and Adelaide. More especially, Grahamstown tends to have stronger mean flow and tidal activity than Adelaide. For tides, these differences are thought to be partly due to nonmigrating tidal modes but, in general, migrating modes were found to be dominant.
- Full Text:
- Date Issued: 2002
A computer-controlled tracking system
- Authors: Oberem, Graham Edmund
- Date: 1979
- Subjects: Artificial satellites -- Tracking
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5437 , http://hdl.handle.net/10962/d1001990
- Description: A computer-controlled tracking system has been designed and constructed for the two metre antenna of the 22 GHz radio telescope at Rhodes University. The control system has been tested and its step response has been analysed with a view to response time optimization. Computer programs for tracking the sun and the moon have been written. Initial results of tracking the sun have revealed linearity and temperature stability problems. These problems have been investigated and suggestions have been made as to how they might be removed
- Full Text:
- Date Issued: 1979
- Authors: Oberem, Graham Edmund
- Date: 1979
- Subjects: Artificial satellites -- Tracking
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5437 , http://hdl.handle.net/10962/d1001990
- Description: A computer-controlled tracking system has been designed and constructed for the two metre antenna of the 22 GHz radio telescope at Rhodes University. The control system has been tested and its step response has been analysed with a view to response time optimization. Computer programs for tracking the sun and the moon have been written. Initial results of tracking the sun have revealed linearity and temperature stability problems. These problems have been investigated and suggestions have been made as to how they might be removed
- Full Text:
- Date Issued: 1979
Static and ultrasonic elastic moduli of wool, mohair and kemp fibres
- Authors: King, Neville Edwin
- Date: 1969
- Subjects: Moduli theory , Mohair , Wool
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5528 , http://hdl.handle.net/10962/d1012640 , Moduli theory , Mohair , Wool
- Description: Fibres used in textiles can be classified broadly into natural fibres and synthetic fibres. Natural fibres can be either animal, such as wool, mohair and camel hair, or vegetable such as cotton, flax and hemp. In the development of synthetic fibres numerous polymers have emerged which have no real natural counterpart and are unique in their mechanical and chemical behaviour. Often the synthetic counterpart of a natural fibre has properties with certain advantages from the textile point of view, but, simultaneously, may exhibit other properties which have disadvantages. Nylon 6 and nylon 6-6, for exemple, are extremely strong and generally easier to dye than animal fibres. On the other hand, they absorb relatively little water vapour and therefore do not give the buffering action characteristic of hygroscopic fibres, once they are woven or knitted into cloth. All textile fibres belong to the chemical class of polymers, i.e. they are made up of repeating molecular units which are linked together to form long chains. In wool the chains are made up of amino-acids which cluster together to form protein chains. Three of these protein chains, coil around each other to form what is termed a proto-fibril. The proto-fibrils make up the micro-fibrils, each of these consisting of eleven of the three chain proto-fibrils. The micro-fibrils, in turn, pack together in bundles which run parallel to the length of the wool fibre and are termed macro-fibrils. Sulphur rich amino-acids fill up the spaces between the micro-fibrils forming a matrix which binds the system into a continuous material. Intro., p. 1.
- Full Text:
- Date Issued: 1969
- Authors: King, Neville Edwin
- Date: 1969
- Subjects: Moduli theory , Mohair , Wool
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5528 , http://hdl.handle.net/10962/d1012640 , Moduli theory , Mohair , Wool
- Description: Fibres used in textiles can be classified broadly into natural fibres and synthetic fibres. Natural fibres can be either animal, such as wool, mohair and camel hair, or vegetable such as cotton, flax and hemp. In the development of synthetic fibres numerous polymers have emerged which have no real natural counterpart and are unique in their mechanical and chemical behaviour. Often the synthetic counterpart of a natural fibre has properties with certain advantages from the textile point of view, but, simultaneously, may exhibit other properties which have disadvantages. Nylon 6 and nylon 6-6, for exemple, are extremely strong and generally easier to dye than animal fibres. On the other hand, they absorb relatively little water vapour and therefore do not give the buffering action characteristic of hygroscopic fibres, once they are woven or knitted into cloth. All textile fibres belong to the chemical class of polymers, i.e. they are made up of repeating molecular units which are linked together to form long chains. In wool the chains are made up of amino-acids which cluster together to form protein chains. Three of these protein chains, coil around each other to form what is termed a proto-fibril. The proto-fibrils make up the micro-fibrils, each of these consisting of eleven of the three chain proto-fibrils. The micro-fibrils, in turn, pack together in bundles which run parallel to the length of the wool fibre and are termed macro-fibrils. Sulphur rich amino-acids fill up the spaces between the micro-fibrils forming a matrix which binds the system into a continuous material. Intro., p. 1.
- Full Text:
- Date Issued: 1969
Photofluorescence decay times of organic phosphors
- Authors: Hamilton, T D S
- Date: 1957
- Subjects: Fluorescence , Phosphorescence
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5525 , http://hdl.handle.net/10962/d1012136 , Fluorescence , Phosphorescence
- Description: The absorption and emission of energy is a fundamental property of any atomic system.When the emission occurs in the visible or near visible region the phenomenon is usually referred to as luminescence or fluorescence. This must be distinguished from thermal radiation as it does not follow Kirchoff's law.
- Full Text:
- Date Issued: 1957
- Authors: Hamilton, T D S
- Date: 1957
- Subjects: Fluorescence , Phosphorescence
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5525 , http://hdl.handle.net/10962/d1012136 , Fluorescence , Phosphorescence
- Description: The absorption and emission of energy is a fundamental property of any atomic system.When the emission occurs in the visible or near visible region the phenomenon is usually referred to as luminescence or fluorescence. This must be distinguished from thermal radiation as it does not follow Kirchoff's law.
- Full Text:
- Date Issued: 1957
Part four of the Rhodes University Skymap Program
- Authors: Wright, Michael Robert
- Date: 1989
- Subjects: Southern sky (Astronomy) Radio astronomy
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5435 , http://hdl.handle.net/10962/d1001988
- Description: The results of the fourth part of the Rhodes University Skymap Program are presented. The observations cover the area of sky between right ascension 14h00m and 02h30m and declination -26⁰ and + 13⁰ at a frequency of 2.3 GHz. Contour maps of this region, with a resolution of 0.38⁰, are presented. Various methods of reducing the effect of the Galactic disc emission are analyzed. The results demonstrate the effectiveness of one of these methods in the production of a flat base level. The filamentary structure of the North Polar Spur is enhanced and results are obtained which support current theories of the origin of this object. The HII region surrounding Ophiuchi is examined in detail. A number of parameters are derived for the HII region. The spur associated with the HII region S54 is also examined. A listing of 1105 point sources appearing in the maps is presented. The limiting flux density of this listing is 0.5 Jy
- Full Text:
- Date Issued: 1989
- Authors: Wright, Michael Robert
- Date: 1989
- Subjects: Southern sky (Astronomy) Radio astronomy
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5435 , http://hdl.handle.net/10962/d1001988
- Description: The results of the fourth part of the Rhodes University Skymap Program are presented. The observations cover the area of sky between right ascension 14h00m and 02h30m and declination -26⁰ and + 13⁰ at a frequency of 2.3 GHz. Contour maps of this region, with a resolution of 0.38⁰, are presented. Various methods of reducing the effect of the Galactic disc emission are analyzed. The results demonstrate the effectiveness of one of these methods in the production of a flat base level. The filamentary structure of the North Polar Spur is enhanced and results are obtained which support current theories of the origin of this object. The HII region surrounding Ophiuchi is examined in detail. A number of parameters are derived for the HII region. The spur associated with the HII region S54 is also examined. A listing of 1105 point sources appearing in the maps is presented. The limiting flux density of this listing is 0.5 Jy
- Full Text:
- Date Issued: 1989
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
- Full Text:
- Date Issued: 1970
- 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
- Full Text:
- Date Issued: 1970
The design and construction of a recording spectrometer for the measurement of fluorescence excitation spectra in the vacuum ultra-violet region
- Authors: Davidson, A T
- Date: 1963
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:21177 , http://hdl.handle.net/10962/6761
- Description: Summary: A recording spectrometer for the measurement of fluorescence excitation spectra in the visible and ultra-violet regions of the spectrum is described. A direct method of modulating the hydrogen light source of the spectrograph is presented, whereby the discharge is driven by an A.C. power oscillator. The use of tuned amplifiers in the detecting unit is investigated as a means of eliminating the D.C. component of the dark current. Aspects of the modulation method are discussed. Fluorescence and energy transfer in aromatic hydrocarbon is discussed with particular regard to anthracene. Some absorption, fluorescence, excitation and reflection spectra of anthracene obtained by previous workers are presented9 together with Tables listing the wavelengths of principal maxima for the above spectra published in the literature. Features of the excitation spectrum of anthracene are discussed and are related to its absorption and fluorescence spectra. The role of surface effects, defects and impurities are discussed in relation to the fluorescence of anthracene. The method of A.C. detection was unable to resolve the excitation spectrum of anthracene due to the high noise level associated with the method. However, peaks in the ultra-violet region of the hydrogen molecular spectrum were recorded at a modulation frequency of 400 Kc/sec. The noise level is explained and ways of improving the signal to noise ratio of the A.C. detection system are suggested. It is concluded that D.C. detection is a simpler and more direct way of measuring excitation spectra. No modulated signals were detected when the hydrogen discharge was excited at 6·5 Mc/sec. Signals were recorded at modulation frequencies of 400 Kc/sec . The degree of modulation at 400 Kc/sec. increased with decrease in the pressure of the hydrogen discharge.
- Full Text:
- Date Issued: 1963
- Authors: Davidson, A T
- Date: 1963
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:21177 , http://hdl.handle.net/10962/6761
- Description: Summary: A recording spectrometer for the measurement of fluorescence excitation spectra in the visible and ultra-violet regions of the spectrum is described. A direct method of modulating the hydrogen light source of the spectrograph is presented, whereby the discharge is driven by an A.C. power oscillator. The use of tuned amplifiers in the detecting unit is investigated as a means of eliminating the D.C. component of the dark current. Aspects of the modulation method are discussed. Fluorescence and energy transfer in aromatic hydrocarbon is discussed with particular regard to anthracene. Some absorption, fluorescence, excitation and reflection spectra of anthracene obtained by previous workers are presented9 together with Tables listing the wavelengths of principal maxima for the above spectra published in the literature. Features of the excitation spectrum of anthracene are discussed and are related to its absorption and fluorescence spectra. The role of surface effects, defects and impurities are discussed in relation to the fluorescence of anthracene. The method of A.C. detection was unable to resolve the excitation spectrum of anthracene due to the high noise level associated with the method. However, peaks in the ultra-violet region of the hydrogen molecular spectrum were recorded at a modulation frequency of 400 Kc/sec. The noise level is explained and ways of improving the signal to noise ratio of the A.C. detection system are suggested. It is concluded that D.C. detection is a simpler and more direct way of measuring excitation spectra. No modulated signals were detected when the hydrogen discharge was excited at 6·5 Mc/sec. Signals were recorded at modulation frequencies of 400 Kc/sec . The degree of modulation at 400 Kc/sec. increased with decrease in the pressure of the hydrogen discharge.
- Full Text:
- Date Issued: 1963
An investigation of the spectra and decay times of some organic phosphors under ultraviolet and ionising radiation
- Authors: Little, W A
- Date: 1955
- Subjects: Phosphors -- Spectra
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5530 , http://hdl.handle.net/10962/d1012733
- Description: In this thesis I have given an account of the work carried out by me on the measurement of the spectra and decay times of a few selected organic phosphors under ultraviolet and ionising radiation. The purpose of the investigation has been to attempt to throw more light on the mechanism by which energy migrates within the crystalline lattice. A general introduction is given to the process of fluorescence and the various proposed theories by which the excitation energy, which eventually appears as fluorescence light, is able to move about in the crystalline lattice. Preface, p. 1.
- Full Text:
- Date Issued: 1955
- Authors: Little, W A
- Date: 1955
- Subjects: Phosphors -- Spectra
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5530 , http://hdl.handle.net/10962/d1012733
- Description: In this thesis I have given an account of the work carried out by me on the measurement of the spectra and decay times of a few selected organic phosphors under ultraviolet and ionising radiation. The purpose of the investigation has been to attempt to throw more light on the mechanism by which energy migrates within the crystalline lattice. A general introduction is given to the process of fluorescence and the various proposed theories by which the excitation energy, which eventually appears as fluorescence light, is able to move about in the crystalline lattice. Preface, p. 1.
- Full Text:
- Date Issued: 1955
Ionospheric effects in the Southern radiation anomaly
- Authors: Torr, Douglas G
- Date: 1966
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5540 , http://hdl.handle.net/10962/d1013305
- Description: From introduction: As ionosphericist on the 4th South African National Antarctic Expedition, I spent twelve months at Sanae (70°18'S, 2°2l'W, L= 4) in 1963. In the course of routine vertical incidence soundings, it was noticed with some surprise that the frequency of occurrence of ionospheric blackouts was unexpectedly high. Initially this aroused considerable concern about the reliability of the equipment. In fact it has been · observed that some stations lying in and near the Southern Radiation Anomaly report such occasions as records lost due to non-ionospheric reasons. Coincidently, however, Gledhill and van Rooyen (1963), also of Rhodes University, predicted ionospheric irregularities and other geophysical phenomena in a region around Sanae where Ginsburg et al. (1962) observed high intensities of charged particles with Sputniks 5 and 6.
- Full Text:
- Date Issued: 1966
- Authors: Torr, Douglas G
- Date: 1966
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5540 , http://hdl.handle.net/10962/d1013305
- Description: From introduction: As ionosphericist on the 4th South African National Antarctic Expedition, I spent twelve months at Sanae (70°18'S, 2°2l'W, L= 4) in 1963. In the course of routine vertical incidence soundings, it was noticed with some surprise that the frequency of occurrence of ionospheric blackouts was unexpectedly high. Initially this aroused considerable concern about the reliability of the equipment. In fact it has been · observed that some stations lying in and near the Southern Radiation Anomaly report such occasions as records lost due to non-ionospheric reasons. Coincidently, however, Gledhill and van Rooyen (1963), also of Rhodes University, predicted ionospheric irregularities and other geophysical phenomena in a region around Sanae where Ginsburg et al. (1962) observed high intensities of charged particles with Sputniks 5 and 6.
- Full Text:
- Date Issued: 1966
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.
- Full Text:
- Date Issued: 1966
- 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.
- Full Text:
- Date Issued: 1966
A new continuum mapping procedure at HartRAO
- Authors: Büchner, Sarah
- Date: 2012-06-19
- Subjects: Hartebeesthoek Radio Astronomy Observatory , Radio astronomy -- Methodology , Galactic cosmic rays
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5510 , http://hdl.handle.net/10962/d1007766 , Hartebeesthoek Radio Astronomy Observatory , Radio astronomy -- Methodology , Galactic cosmic rays
- Description: A basket weaving technique for making radio continuum maps has been developed at the Hartebeesthoek Radio Astronomy Observatory (HartRAO). This data reduction technique significantly reduces scanning effects by using independent maps scanned in orthogonal directions. The observation and data analysis procedures that were developed are presented. The technique was used to map the supernova remnant MSH 15-52 at frequencies of 5000 MHz and 8500 MHz. The flux spectral index for this supernova remnant was found to be 0.83 ± 0.02 in this frequency range. Two regions (A and B) of the Galactic plane were observed at 8500 MHz with a resolution of 6'. Region A covered the 5°x5° area 47.5°< k 52.5°, Ibl < 2.5°, and region B was the 4.2°x3° area 320.4°< I <334.6°, Ibl < 1.5°. Far infrared observations at 60 !lm were used in conjunction with the radio maps to separate the thermal and non-thermal components of the radio emission. The technique can be used to map the Galactic plane at 8500 MHz using dual polarisation once the receiver at HartRAO has been upgraded. This would fulfil a need for a medium resolution, high frequency survey of the southern Galactic plane. , Adobe Acrobat Pro 9.4.6 , Adobe Acrobat 9.46 Paper Capture Plug-in
- Full Text:
- Authors: Büchner, Sarah
- Date: 2012-06-19
- Subjects: Hartebeesthoek Radio Astronomy Observatory , Radio astronomy -- Methodology , Galactic cosmic rays
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5510 , http://hdl.handle.net/10962/d1007766 , Hartebeesthoek Radio Astronomy Observatory , Radio astronomy -- Methodology , Galactic cosmic rays
- Description: A basket weaving technique for making radio continuum maps has been developed at the Hartebeesthoek Radio Astronomy Observatory (HartRAO). This data reduction technique significantly reduces scanning effects by using independent maps scanned in orthogonal directions. The observation and data analysis procedures that were developed are presented. The technique was used to map the supernova remnant MSH 15-52 at frequencies of 5000 MHz and 8500 MHz. The flux spectral index for this supernova remnant was found to be 0.83 ± 0.02 in this frequency range. Two regions (A and B) of the Galactic plane were observed at 8500 MHz with a resolution of 6'. Region A covered the 5°x5° area 47.5°< k 52.5°, Ibl < 2.5°, and region B was the 4.2°x3° area 320.4°< I <334.6°, Ibl < 1.5°. Far infrared observations at 60 !lm were used in conjunction with the radio maps to separate the thermal and non-thermal components of the radio emission. The technique can be used to map the Galactic plane at 8500 MHz using dual polarisation once the receiver at HartRAO has been upgraded. This would fulfil a need for a medium resolution, high frequency survey of the southern Galactic plane. , Adobe Acrobat Pro 9.4.6 , Adobe Acrobat 9.46 Paper Capture Plug-in
- Full Text:
The response of pure organic crystals to ionising radiations
- Authors: King, J W
- Date: 1953
- Subjects: Inorganic scintillators , Crystals
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5529 , http://hdl.handle.net/10962/d1012641 , Inorganic scintillators , Crystals
- Description: The introduction contains introductory remarks on scintillation counters together with a brief description of the exciton theory believed to be the means of primary energy migration within organic crystals. Part I contains a review of the data published on the reletive responses of different organic crystals and the attempted correlations of these results with the molecular structures of the different phosphors. From data which may be accepted as being both reliable and suitable for comparison it is concluded that theories involving correlations between phosphor efficiencies and molecular structures may be tested only if the efficiency data has (i) been extrapolated to give results for crystals of very small thickness and {ii) been obtained at very low temperatures. Part II contains accurate calculations based on the exciton theory proposed by Birks (1951 ) to account for the response of crystals to different types of ionising radiations. Satisfactory agreement is obta1ned with all the avalable experimental data in the literature. In part III an account is given of the response of organic crystals observed by the author for low-energy ⋉particles, and of the similar behaviour found by Taylor et al, (1951 ) for low-energy electrons. A possible extension of the theory described in part II, allowing for the escape of excitons through the crystal surface is given accounting for this behaviour. An exciton mean free path in anthracene, terphenyl and stilbene of about 3 - 7/u is obtained. Results were obtained with strong ⋉-particle sources which could not be explained. in terms ot normal response of the phosphor used. This effect was inventigatea as described in part IV, and it is shown that photons are produced in air, glass and quartz when these materials are irradiated by ⋉particles. This luminescence was probably responsible for the "scintillations" which Richards and Cole (1951) have ascribed to thin films of various materials. Problems requiring further investigation are indicated.
- Full Text:
- Date Issued: 1953
- Authors: King, J W
- Date: 1953
- Subjects: Inorganic scintillators , Crystals
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5529 , http://hdl.handle.net/10962/d1012641 , Inorganic scintillators , Crystals
- Description: The introduction contains introductory remarks on scintillation counters together with a brief description of the exciton theory believed to be the means of primary energy migration within organic crystals. Part I contains a review of the data published on the reletive responses of different organic crystals and the attempted correlations of these results with the molecular structures of the different phosphors. From data which may be accepted as being both reliable and suitable for comparison it is concluded that theories involving correlations between phosphor efficiencies and molecular structures may be tested only if the efficiency data has (i) been extrapolated to give results for crystals of very small thickness and {ii) been obtained at very low temperatures. Part II contains accurate calculations based on the exciton theory proposed by Birks (1951 ) to account for the response of crystals to different types of ionising radiations. Satisfactory agreement is obta1ned with all the avalable experimental data in the literature. In part III an account is given of the response of organic crystals observed by the author for low-energy ⋉particles, and of the similar behaviour found by Taylor et al, (1951 ) for low-energy electrons. A possible extension of the theory described in part II, allowing for the escape of excitons through the crystal surface is given accounting for this behaviour. An exciton mean free path in anthracene, terphenyl and stilbene of about 3 - 7/u is obtained. Results were obtained with strong ⋉-particle sources which could not be explained. in terms ot normal response of the phosphor used. This effect was inventigatea as described in part IV, and it is shown that photons are produced in air, glass and quartz when these materials are irradiated by ⋉particles. This luminescence was probably responsible for the "scintillations" which Richards and Cole (1951) have ascribed to thin films of various materials. Problems requiring further investigation are indicated.
- Full Text:
- Date Issued: 1953
A 22 GHz radio telescope
- Authors: Mutch, Laurence Ian
- Date: 1976
- Subjects: Radio telescopes , Paraboloid , Radio astronomy
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5532 , http://hdl.handle.net/10962/d1012919
- Description: This thesis reports on the design, construction, testing and operation of the spectral line and continuum receivers built for the 22 GHz Radio Telescope. First results from 'the telescope were obtained and have been analysed to give an estimate of system efficiency. Tests have been performed on the front end and in particular on the 22 GHz mixer in order to determine the minimum detectable temperature. The Sun, Moon and major planets are sources suitable for antenna alignment and consequently a literature survey of emission at 22 GHz from elements of the Solar system has been made.
- Full Text:
- Date Issued: 1976
- Authors: Mutch, Laurence Ian
- Date: 1976
- Subjects: Radio telescopes , Paraboloid , Radio astronomy
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5532 , http://hdl.handle.net/10962/d1012919
- Description: This thesis reports on the design, construction, testing and operation of the spectral line and continuum receivers built for the 22 GHz Radio Telescope. First results from 'the telescope were obtained and have been analysed to give an estimate of system efficiency. Tests have been performed on the front end and in particular on the 22 GHz mixer in order to determine the minimum detectable temperature. The Sun, Moon and major planets are sources suitable for antenna alignment and consequently a literature survey of emission at 22 GHz from elements of the Solar system has been made.
- Full Text:
- Date Issued: 1976
An investigation of the profiles of bursts of solar radio noise
- Wild, Peter Anthony Thornton
- Authors: Wild, Peter Anthony Thornton
- Date: 1960
- Subjects: Solar radio emission , Radio noise , Solar noise storms , Radio astronomy
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5551 , http://hdl.handle.net/10962/d1013504
- Description: [Summary] Chapter I . The general characteristics of solar radiation at metre wavelengths are described, with reference to data published in the literature. A brief description of some aspects of solar physics relevant to the study of solar noise is given, and the literature relating to the correlation of radio effects with solar disturbances is reviewed. Chapter II. A concise description of the apparatus constructed for the continuous recording of the flux density of solar radio noise at a frequency of 300 Mc/s is given, with some mention of difficulties experienced, and how these were overcome. Full circuit diagrams of electronic apparatus, and illustrative photographs, are supplied. Chapter III. The development of theories of the origin and propagation of solar noise radiation is historically reviewed and the success of each theory in explaining or predicting observed phenomena, is assessed. A working model is chosen from among these theories, and reasons for its adoption are given. Chapter IV. Observations made by the author of solar radiation at a frequency of 300 Mc/s are described, together with a description of the objects and methods, of analysis of the records. Chapter V. Phenomena observed by the author are compared with those observed by other workers. It is concluded that storm bursts are caused by transients similar to those producing Type II and Type ITI bursts, and a model for the production of storm bursts is tentatively suggested. Chapter VI. Suggestions for further research, including suggestions for methods of testing the author's conclusions, are made.
- Full Text:
- Date Issued: 1960
- Authors: Wild, Peter Anthony Thornton
- Date: 1960
- Subjects: Solar radio emission , Radio noise , Solar noise storms , Radio astronomy
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5551 , http://hdl.handle.net/10962/d1013504
- Description: [Summary] Chapter I . The general characteristics of solar radiation at metre wavelengths are described, with reference to data published in the literature. A brief description of some aspects of solar physics relevant to the study of solar noise is given, and the literature relating to the correlation of radio effects with solar disturbances is reviewed. Chapter II. A concise description of the apparatus constructed for the continuous recording of the flux density of solar radio noise at a frequency of 300 Mc/s is given, with some mention of difficulties experienced, and how these were overcome. Full circuit diagrams of electronic apparatus, and illustrative photographs, are supplied. Chapter III. The development of theories of the origin and propagation of solar noise radiation is historically reviewed and the success of each theory in explaining or predicting observed phenomena, is assessed. A working model is chosen from among these theories, and reasons for its adoption are given. Chapter IV. Observations made by the author of solar radiation at a frequency of 300 Mc/s are described, together with a description of the objects and methods, of analysis of the records. Chapter V. Phenomena observed by the author are compared with those observed by other workers. It is concluded that storm bursts are caused by transients similar to those producing Type II and Type ITI bursts, and a model for the production of storm bursts is tentatively suggested. Chapter VI. Suggestions for further research, including suggestions for methods of testing the author's conclusions, are made.
- Full Text:
- Date Issued: 1960
Ray tracing at very low frequencies when the effects of heavy ions are considered
- Authors: Terry, Patrick D.
- Date: 1969
- Subjects: Ionospheric radio wave propagation , Ionosphere -- Graphic methods , Ray tracing algorithms
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5542 , http://hdl.handle.net/10962/d1013350
- Description: The behaviour of very low frequency (V.L.F.) radio waves propagating in an ionlzed medium, such as the ionosphere and exosphere, may exhibit markedly different characteristics from those of frequencies such as are used for communication in the short-wave bands. The anisotropy introduced into the medium by the presence of the earth's magnetic field has a significant effect, while at frequencies below about 5KHz the presence of heavy positive ions may further affect propagation. In particular it is found that, under suitable conditions, V.L.F. signals may propagate along paths closely following the lines of force of the earth's magnetic field. The study of such signals has a practical interest in that, from consideration of their propagation times and dispersion properties, they can provide an inexpensive method of determining electron densities at well beyond the range of satellite investigation. For this reason, if for no other, theoretical investigation of the paths traced in a model exosphere may indicate how closely the model exosphere approximates the true one. A powerful method of tracing out these paths is by the use of "ray-tracing", provided the properties of the medium vary slowly in space, a condition not always fulfilled in practice. It has been the subject of this thesis to carry out ray-tracing studies, in particular noting the effects of the positive ions in the exosphere; effects which have not received much notice before as they were thought to be unimportant. Intro., p. 1-2.
- Full Text:
- Date Issued: 1969
- Authors: Terry, Patrick D.
- Date: 1969
- Subjects: Ionospheric radio wave propagation , Ionosphere -- Graphic methods , Ray tracing algorithms
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5542 , http://hdl.handle.net/10962/d1013350
- Description: The behaviour of very low frequency (V.L.F.) radio waves propagating in an ionlzed medium, such as the ionosphere and exosphere, may exhibit markedly different characteristics from those of frequencies such as are used for communication in the short-wave bands. The anisotropy introduced into the medium by the presence of the earth's magnetic field has a significant effect, while at frequencies below about 5KHz the presence of heavy positive ions may further affect propagation. In particular it is found that, under suitable conditions, V.L.F. signals may propagate along paths closely following the lines of force of the earth's magnetic field. The study of such signals has a practical interest in that, from consideration of their propagation times and dispersion properties, they can provide an inexpensive method of determining electron densities at well beyond the range of satellite investigation. For this reason, if for no other, theoretical investigation of the paths traced in a model exosphere may indicate how closely the model exosphere approximates the true one. A powerful method of tracing out these paths is by the use of "ray-tracing", provided the properties of the medium vary slowly in space, a condition not always fulfilled in practice. It has been the subject of this thesis to carry out ray-tracing studies, in particular noting the effects of the positive ions in the exosphere; effects which have not received much notice before as they were thought to be unimportant. Intro., p. 1-2.
- Full Text:
- Date Issued: 1969