A feasibility study into the possibility of ionospheric propagation of low VHF (30-35 MHZ) signals between South Africa and Central Africa
- Authors: Coetzee, Petrus Johannes
- Date: 2009
- Subjects: Communications, Military -- South Africa , Communications, Military -- Africa, Central , Digital communications -- South Africa , Digital communications -- Africa, Central , Signals and signaling -- South Africa , Signals and signaling -- Africa, Central , Artificial satellites in telecommunication -- South Africa , Artificial satellites in telecommunication -- Africa, Central , Shortwave radio
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5465 , http://hdl.handle.net/10962/d1005250 , Communications, Military -- South Africa , Communications, Military -- Africa, Central , Digital communications -- South Africa , Digital communications -- Africa, Central , Signals and signaling -- South Africa , Signals and signaling -- Africa, Central , Artificial satellites in telecommunication -- South Africa , Artificial satellites in telecommunication -- Africa, Central , Shortwave radio
- Description: The role of the South African National Defence Force (SANDF) has changed considerably in the last decade. The emphasis has moved from protecting the country's borders to peacekeeping duties in Central Africa and even further North. Communications between the peacekeeping missions and the military bases back in South Africa is vital to ensure the success of these missions. Currently use is made of satellite as well as High Frequency (HF) communications. There are drawbacks associated with these technologies (high cost and low data rates/interference respectively). Successful long distance ionospheric propagation in the low Very High Frequency (VHF) range will complement the existing infrastructure and enhance the success rate of these missions. This thesis presents a feasibility study to determine under what ionospheric conditions such low VHF communications will be possible. The International Reference Ionosphere (IRI) was used to generate ionospheric data for the reflection point(s) of the signal. The peak height of the ionospheric F2 layer (hmF2) was used to calculate the required antenna elevation angle. Once the elevation angle is known it is possible to calculate the required F2 layer critical frequency (foF2). The required foF2 value was calculated by assuming a Maximum Useable Frequency (MUF) of 20% higher than the planned operational frequency. It was determined that single hop propagation is possible during the daytime if the smoothed sunspot number (SSN) exceeds 15. The most challenging requirement for successful single hop propagation is the need of an antenna height of 23 m. For rapid deployment and semi-mobile operations within a jungle environment it may prove to be a formidable obstacle.
- Full Text:
- Date Issued: 2009
- Authors: Coetzee, Petrus Johannes
- Date: 2009
- Subjects: Communications, Military -- South Africa , Communications, Military -- Africa, Central , Digital communications -- South Africa , Digital communications -- Africa, Central , Signals and signaling -- South Africa , Signals and signaling -- Africa, Central , Artificial satellites in telecommunication -- South Africa , Artificial satellites in telecommunication -- Africa, Central , Shortwave radio
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5465 , http://hdl.handle.net/10962/d1005250 , Communications, Military -- South Africa , Communications, Military -- Africa, Central , Digital communications -- South Africa , Digital communications -- Africa, Central , Signals and signaling -- South Africa , Signals and signaling -- Africa, Central , Artificial satellites in telecommunication -- South Africa , Artificial satellites in telecommunication -- Africa, Central , Shortwave radio
- Description: The role of the South African National Defence Force (SANDF) has changed considerably in the last decade. The emphasis has moved from protecting the country's borders to peacekeeping duties in Central Africa and even further North. Communications between the peacekeeping missions and the military bases back in South Africa is vital to ensure the success of these missions. Currently use is made of satellite as well as High Frequency (HF) communications. There are drawbacks associated with these technologies (high cost and low data rates/interference respectively). Successful long distance ionospheric propagation in the low Very High Frequency (VHF) range will complement the existing infrastructure and enhance the success rate of these missions. This thesis presents a feasibility study to determine under what ionospheric conditions such low VHF communications will be possible. The International Reference Ionosphere (IRI) was used to generate ionospheric data for the reflection point(s) of the signal. The peak height of the ionospheric F2 layer (hmF2) was used to calculate the required antenna elevation angle. Once the elevation angle is known it is possible to calculate the required F2 layer critical frequency (foF2). The required foF2 value was calculated by assuming a Maximum Useable Frequency (MUF) of 20% higher than the planned operational frequency. It was determined that single hop propagation is possible during the daytime if the smoothed sunspot number (SSN) exceeds 15. The most challenging requirement for successful single hop propagation is the need of an antenna height of 23 m. For rapid deployment and semi-mobile operations within a jungle environment it may prove to be a formidable obstacle.
- Full Text:
- Date Issued: 2009
The photo-fluorescence properties of some organic materials
- Authors: Cameron, Antony John Wesley
- Date: 1959
- Subjects: Hydrocarbons -- Spectra -- Fluorescence , Organic compounds , Energy transfer
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5514 , http://hdl.handle.net/10962/d1010041 , Hydrocarbons -- Spectra -- Fluorescence , Organic compounds , Energy transfer
- Description: In this thesis I have given an account of the experimental work carried out by me at Rhodes University from the beginning of 1954 to the end of 1955, and the analysis of the results which was completed during the following two years, 1956 and 1957. The dissertation is divided into two sections; Part I deals with the photo fluorescence spectra of a large group of organic compounds, and Part 2 describes an investigation of the photo-fluorescence properties of and energy transfer in liquid organic solutions.
- Full Text:
- Date Issued: 1959
- Authors: Cameron, Antony John Wesley
- Date: 1959
- Subjects: Hydrocarbons -- Spectra -- Fluorescence , Organic compounds , Energy transfer
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5514 , http://hdl.handle.net/10962/d1010041 , Hydrocarbons -- Spectra -- Fluorescence , Organic compounds , Energy transfer
- Description: In this thesis I have given an account of the experimental work carried out by me at Rhodes University from the beginning of 1954 to the end of 1955, and the analysis of the results which was completed during the following two years, 1956 and 1957. The dissertation is divided into two sections; Part I deals with the photo fluorescence spectra of a large group of organic compounds, and Part 2 describes an investigation of the photo-fluorescence properties of and energy transfer in liquid organic solutions.
- Full Text:
- Date Issued: 1959
Aspects of the symplectic and metric geometry of classical and quantum physics
- Authors: Russell, Neil Eric
- Date: 1993
- Subjects: Symplectic manifolds Geometry, Differential Geometric quantization Quantum theory Clifford algebras
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5452 , http://hdl.handle.net/10962/d1005237
- Description: I investigate some algebras and calculi naturally associated with the symplectic and metric Clifford algebras. In particular, I reformulate the well known Lepage decomposition for the symplectic exterior algebra in geometrical form and present some new results relating to the simple subspaces of the decomposition. I then present an analogous decomposition for the symmetric exterior algebra with a metric. Finally, I extend this symmetric exterior algebra into a new calculus for the symmetric differential forms on a pseudo-Riemannian manifold. The importance of this calculus lies in its potential for the description of bosonic systems in Quantum Theory.
- Full Text:
- Date Issued: 1993
- Authors: Russell, Neil Eric
- Date: 1993
- Subjects: Symplectic manifolds Geometry, Differential Geometric quantization Quantum theory Clifford algebras
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5452 , http://hdl.handle.net/10962/d1005237
- Description: I investigate some algebras and calculi naturally associated with the symplectic and metric Clifford algebras. In particular, I reformulate the well known Lepage decomposition for the symplectic exterior algebra in geometrical form and present some new results relating to the simple subspaces of the decomposition. I then present an analogous decomposition for the symmetric exterior algebra with a metric. Finally, I extend this symmetric exterior algebra into a new calculus for the symmetric differential forms on a pseudo-Riemannian manifold. The importance of this calculus lies in its potential for the description of bosonic systems in Quantum Theory.
- Full Text:
- Date Issued: 1993
A neural network based ionospheric model for the bottomside electron density profile over Grahamstown, South Africa
- Authors: McKinnell, L A
- Date: 2003
- Subjects: Neural networks (Computer science) Ionospheric electron density -- South Africa -- Grahamstown
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5477 , http://hdl.handle.net/10962/d1005262
- Description: This thesis describes the development and application of a neural network based ionospheric model for the bottomside electron density profile over Grahamstown, South Africa. All available ionospheric data from the archives of the Grahamstown (33.32ºS, 26.50ºE) ionospheric station were used for training neural networks (NNs) to predict the parameters required to produce the final profile. Inputs to the model, called the LAM model, are day number, hour, and measures of solar and magnetic activity. The output is a mathematical description of the bottomside electron density profile for that particular input set. The two main ionospheric layers, the E and F layers, are predicted separately and then combined at the final stage. For each layer, NNs have been trained to predict the individual ionospheric characteristics and coefficients that were required to describe the layer profile. NNs were also applied to the task of determining the hours between which an E layer is measurable by a groundbased ionosonde and the probability of the existence of an F1 layer. The F1 probability NN is innovative in that it provides information on the existence of the F1 layer as well as the probability of that layer being in a L-condition state - the state where an F1 layer is present on an ionogram but it is not possible to record any F1 parameters. In the event of an L-condition state being predicted as probable, an L algorithm has been designed to alter the shape of the profile to reflect this state. A smoothing algorithm has been implemented to remove discontinuities at the F1-F2 boundary and ensure that the profile represents realistic ionospheric behaviour in the F1 region. Tests show that the LAM model is more successful at predicting Grahamstown electron density profiles for a particular set of inputs than the International Reference Ionosphere (IRI). It is anticipated that the LAM model will be used as a tool in the pin-pointing of hostile HF transmitters, known as single-site location.
- Full Text:
- Date Issued: 2003
- Authors: McKinnell, L A
- Date: 2003
- Subjects: Neural networks (Computer science) Ionospheric electron density -- South Africa -- Grahamstown
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5477 , http://hdl.handle.net/10962/d1005262
- Description: This thesis describes the development and application of a neural network based ionospheric model for the bottomside electron density profile over Grahamstown, South Africa. All available ionospheric data from the archives of the Grahamstown (33.32ºS, 26.50ºE) ionospheric station were used for training neural networks (NNs) to predict the parameters required to produce the final profile. Inputs to the model, called the LAM model, are day number, hour, and measures of solar and magnetic activity. The output is a mathematical description of the bottomside electron density profile for that particular input set. The two main ionospheric layers, the E and F layers, are predicted separately and then combined at the final stage. For each layer, NNs have been trained to predict the individual ionospheric characteristics and coefficients that were required to describe the layer profile. NNs were also applied to the task of determining the hours between which an E layer is measurable by a groundbased ionosonde and the probability of the existence of an F1 layer. The F1 probability NN is innovative in that it provides information on the existence of the F1 layer as well as the probability of that layer being in a L-condition state - the state where an F1 layer is present on an ionogram but it is not possible to record any F1 parameters. In the event of an L-condition state being predicted as probable, an L algorithm has been designed to alter the shape of the profile to reflect this state. A smoothing algorithm has been implemented to remove discontinuities at the F1-F2 boundary and ensure that the profile represents realistic ionospheric behaviour in the F1 region. Tests show that the LAM model is more successful at predicting Grahamstown electron density profiles for a particular set of inputs than the International Reference Ionosphere (IRI). It is anticipated that the LAM model will be used as a tool in the pin-pointing of hostile HF transmitters, known as single-site location.
- Full Text:
- Date Issued: 2003
The search for an ionospheric model suitable for real-time applications in HF radio communications
- Mercer, Christopher Crossley
- Authors: Mercer, Christopher Crossley
- Date: 1994
- Subjects: Ionospheric radio wave propagation
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5488 , http://hdl.handle.net/10962/d1005274 , Ionospheric radio wave propagation
- Description: Statement of work: In essence the research work was to focus on the development of an ionospheric model suitable for real time HF frequency prediction and direction finding applications. The modelling of the ionosphere had to be generic in nature, sufficient to ensure that the CSIR could simultaneously secure commercial competitiveness in each of the three niche market areas aforementioned, while requiring only minimal changes to software architecture in the case of each application. A little research quickly showed that the development of an ionospheric model capable of driving a HFDFSSL system in "real time" would result in one having to make only slight re-structuring of the software to facilitate application of the same model in the areas of real time frequency prediction and spectrum management. The decision made at the outset of the project to slant the research toward the development of a model best suited for HF direction finding applications is reflected in the avenues followed during the course of the modelling process
- Full Text:
- Date Issued: 1994
- Authors: Mercer, Christopher Crossley
- Date: 1994
- Subjects: Ionospheric radio wave propagation
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5488 , http://hdl.handle.net/10962/d1005274 , Ionospheric radio wave propagation
- Description: Statement of work: In essence the research work was to focus on the development of an ionospheric model suitable for real time HF frequency prediction and direction finding applications. The modelling of the ionosphere had to be generic in nature, sufficient to ensure that the CSIR could simultaneously secure commercial competitiveness in each of the three niche market areas aforementioned, while requiring only minimal changes to software architecture in the case of each application. A little research quickly showed that the development of an ionospheric model capable of driving a HFDFSSL system in "real time" would result in one having to make only slight re-structuring of the software to facilitate application of the same model in the areas of real time frequency prediction and spectrum management. The decision made at the outset of the project to slant the research toward the development of a model best suited for HF direction finding applications is reflected in the avenues followed during the course of the modelling process
- Full Text:
- Date Issued: 1994
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
- Full Text:
- Date Issued: 1984
- 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
- Full Text:
- Date Issued: 1984
Dynamics of charge movement in ∞-Al2O3:C,Mg using thermoluminescence phototransferred and optically stimulated luminescence
- Authors: Lontsi Sob, Aaron Joel
- Date: 2022-04-08
- Subjects: Thermoluminescence , Optically stimulated luminescence , Phototransfer , Deep traps , Phototransferred thermoluminescence (PTTL)
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/294607 , vital:57237 , DOI 10.21504/10962/294607
- Description: The dosimetric features of ∞-Al2O3:C,Mg have been investigated for unannealed and annealed samples. The unannealed sample is referred to as sample A whereas the samples annealed at 700, 900 and 1200°C for 15 minutes each are referred to as samples B, C and D respectively. A glow curve of unannealed ∞-Al2O3:C,Mg measured at 1°C/s after irradiation to 2.0 Gy consists of peaks at 43, 73, 164, 195, 246, 284, 336 and 374°C respectively. For sample B (annealed at 700°C), a glow curve measured at 1°C/s after irradiation to 3.0 Gy has peaks at 46, 76, 100, 170, 199, 290, 330 and 375°C whereas the glow curve of sample C (annealed at 900°C) recorded under the same conditions consists of peaks at 49, 80, 100, 174, 206, 235, 290, 335 and 375°C respectively. Sample D (annealed at 1200°C) is the most sensitive of the four samples. A glow curve of sample D measured at 1°C/s after irradiation to 0.2 Gy has peaks at 52, 82, 102, 174, 234, 288 and 384°C respectively. The peaks are labelled I-VIII in order of appearance. The 100°C peak, labelled IIa, is induced by annealing at or above 700°C. The dose response of these peaks was studied for doses within 0.1-8.2 Gy. The reported peaks follow first-order kinetics irrespective of annealing temperature. Peaks I-III of each sample are reproduced under phototransfer for preheating up to 400°C. For the unannealed sample, the reproduced peaks are labelled A1-A3 whereas for the annealed samples, they are labelled B1-B3, C1-C3 and D1-D3 respectively. The annealing-induced peak at 100°C is reproduced as B2a, C2a and D2a for samples B, C and D respectively. A PTTL peak labelled C2b or D2b is also observed near 140°C in samples C and D. In addition to these PTTL peaks, a PTTL peak corresponding to peak IV is also found for sample D and for the unannealed sample. As the corresponding conventional peaks, the PTTL peaks of each sample follow first-order kinetics. Peak I and its corresponding PTTL peak for each sample are unstable and fade to a minimal level after 300 s of storage time. On the other hand, peak II of each sample and its corresponding PTTL peak could still be observed with delay up to 5000 s. Peak III of the unannealed sample remains stable with storage time up to 48 hours. Irrespective of annealing, the trap corresponding to peak III is the most sensitive to optical stimulation. Time-dependent profiles of PTTL from unannealed and annealed ∞-Al2O3:C,Mg were also studied. The mathematical analysis of the PTTL time-response profiles is based on experimental results. The role of various electron traps in PTTL was determined by using pulse annealing and by monitoring the dependence of peak intensity on duration of illumination for peaks not removed by preheating. The presence and role of deep traps were further demonstrated with thermally assisted optically stimulated luminescence. For the unannealed sample, the activation energy for thermal assistance is 0.033 ± 0.001 eV and the activation energy for thermal i quenching is 1.043 ± 0.001 eV. For sample C, the activation energy for thermal assistance is 0.044 ± 0.003 eV whereas that for thermal quenching is 1.110 ± 0.006 eV. The values for the activation energy for thermal assistance are lower than those reported in literature. Only the values for the activation energy for thermal quenching are somewhat comparable to values reported elsewhere. , Thesis (PhD) -- Faculty of Science, Physics and Electronics, 2022
- Full Text:
- Date Issued: 2022-04-08
- Authors: Lontsi Sob, Aaron Joel
- Date: 2022-04-08
- Subjects: Thermoluminescence , Optically stimulated luminescence , Phototransfer , Deep traps , Phototransferred thermoluminescence (PTTL)
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/294607 , vital:57237 , DOI 10.21504/10962/294607
- Description: The dosimetric features of ∞-Al2O3:C,Mg have been investigated for unannealed and annealed samples. The unannealed sample is referred to as sample A whereas the samples annealed at 700, 900 and 1200°C for 15 minutes each are referred to as samples B, C and D respectively. A glow curve of unannealed ∞-Al2O3:C,Mg measured at 1°C/s after irradiation to 2.0 Gy consists of peaks at 43, 73, 164, 195, 246, 284, 336 and 374°C respectively. For sample B (annealed at 700°C), a glow curve measured at 1°C/s after irradiation to 3.0 Gy has peaks at 46, 76, 100, 170, 199, 290, 330 and 375°C whereas the glow curve of sample C (annealed at 900°C) recorded under the same conditions consists of peaks at 49, 80, 100, 174, 206, 235, 290, 335 and 375°C respectively. Sample D (annealed at 1200°C) is the most sensitive of the four samples. A glow curve of sample D measured at 1°C/s after irradiation to 0.2 Gy has peaks at 52, 82, 102, 174, 234, 288 and 384°C respectively. The peaks are labelled I-VIII in order of appearance. The 100°C peak, labelled IIa, is induced by annealing at or above 700°C. The dose response of these peaks was studied for doses within 0.1-8.2 Gy. The reported peaks follow first-order kinetics irrespective of annealing temperature. Peaks I-III of each sample are reproduced under phototransfer for preheating up to 400°C. For the unannealed sample, the reproduced peaks are labelled A1-A3 whereas for the annealed samples, they are labelled B1-B3, C1-C3 and D1-D3 respectively. The annealing-induced peak at 100°C is reproduced as B2a, C2a and D2a for samples B, C and D respectively. A PTTL peak labelled C2b or D2b is also observed near 140°C in samples C and D. In addition to these PTTL peaks, a PTTL peak corresponding to peak IV is also found for sample D and for the unannealed sample. As the corresponding conventional peaks, the PTTL peaks of each sample follow first-order kinetics. Peak I and its corresponding PTTL peak for each sample are unstable and fade to a minimal level after 300 s of storage time. On the other hand, peak II of each sample and its corresponding PTTL peak could still be observed with delay up to 5000 s. Peak III of the unannealed sample remains stable with storage time up to 48 hours. Irrespective of annealing, the trap corresponding to peak III is the most sensitive to optical stimulation. Time-dependent profiles of PTTL from unannealed and annealed ∞-Al2O3:C,Mg were also studied. The mathematical analysis of the PTTL time-response profiles is based on experimental results. The role of various electron traps in PTTL was determined by using pulse annealing and by monitoring the dependence of peak intensity on duration of illumination for peaks not removed by preheating. The presence and role of deep traps were further demonstrated with thermally assisted optically stimulated luminescence. For the unannealed sample, the activation energy for thermal assistance is 0.033 ± 0.001 eV and the activation energy for thermal i quenching is 1.043 ± 0.001 eV. For sample C, the activation energy for thermal assistance is 0.044 ± 0.003 eV whereas that for thermal quenching is 1.110 ± 0.006 eV. The values for the activation energy for thermal assistance are lower than those reported in literature. Only the values for the activation energy for thermal quenching are somewhat comparable to values reported elsewhere. , Thesis (PhD) -- Faculty of Science, Physics and Electronics, 2022
- Full Text:
- Date Issued: 2022-04-08
Classical and quantum picture of the interior of two-dimensional black holes
- Authors: Shawa, Mark
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/3629 , vital:20531
- Description: A quantum-mechanical description of black holes would represent the final step in our understanding of the nature of space-time. However, any progress towards that end is usually foiled by persistent space-time singularities that exist at the center of black holes. From the four-dimensional point of view, black holes seem to resist quantization. Under highly symmetric conditions, all higher-dimensional black holes are two-dimensional. Unlike their higher-dimensional counterparts, two dimensional black holes may not resist quantization. A non-trivial description of gravity in two dimensions is not possible using Einstein’s theory of gravity alone. However, we may still arrive at a consistent description of gravity by introducing a scalar field known as the dilaton. In this thesis, we study both the classical and quantum aspects of the interior of two-dimensional black holes using a generalized dilaton-gravity theory. Classically, we will find that the interior of most two-dimensional black holes is not much different from that of four-dimensional black holes. But by introducing quantized matter into the theory, the fluctuations in space-time will give a different picture of the structure of interior of black holes. Using a low-energy effective field theory, we will show that it is indeed possible to identify quantum modes in the interior of black holes and perform quantum-mechanical calculations near the singularity.
- Full Text:
- Date Issued: 2016
- Authors: Shawa, Mark
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/3629 , vital:20531
- Description: A quantum-mechanical description of black holes would represent the final step in our understanding of the nature of space-time. However, any progress towards that end is usually foiled by persistent space-time singularities that exist at the center of black holes. From the four-dimensional point of view, black holes seem to resist quantization. Under highly symmetric conditions, all higher-dimensional black holes are two-dimensional. Unlike their higher-dimensional counterparts, two dimensional black holes may not resist quantization. A non-trivial description of gravity in two dimensions is not possible using Einstein’s theory of gravity alone. However, we may still arrive at a consistent description of gravity by introducing a scalar field known as the dilaton. In this thesis, we study both the classical and quantum aspects of the interior of two-dimensional black holes using a generalized dilaton-gravity theory. Classically, we will find that the interior of most two-dimensional black holes is not much different from that of four-dimensional black holes. But by introducing quantized matter into the theory, the fluctuations in space-time will give a different picture of the structure of interior of black holes. Using a low-energy effective field theory, we will show that it is indeed possible to identify quantum modes in the interior of black holes and perform quantum-mechanical calculations near the singularity.
- Full Text:
- Date Issued: 2016
Solar cycle effects on GNSS-derived ionospheric total electron content observed over Southern Africa
- Authors: Moeketsi, Daniel Mojalefa
- Date: 2008
- Subjects: Ionosphere -- Africa, Southern Electrons Ionospheric electron density -- Africa, Southern Ionosondes -- Africa, Southern Electromagnetic waves
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5489 , http://hdl.handle.net/10962/d1005275
- Description: The South African Global Navigation Satellite System (GNSS) network of dual frequency receivers provide an opportunity to investigate solar cycle effects on ionospheric Total Electron Content (TEC) over the South Africa region by taking advantage of the dispersive nature of the ionospheric medium. For this task, the global University of New Brunswick Ionospheric Modelling Technique (UNB-IMT) was adopted, modified and applied to compute TEC using data from the southern African GNSS Network. TEC values were compared with CODE International GNSS services TEC predictions and Ionosonde-derived TEC (ITEC) measurements to test and validate the UNB-IMT results over South Africa. It was found that the variation trends of GTEC and ITEC over all stations are in good agreement and show pronounced seasonal variations with high TEC values around equinoxes for a year near solar maximum and less pronounced around solar minimum. Signature TEC depletions and enhanced spikes were prevalently evident around equinoxes, particularly for a year near solar maximum. These observations were investigated and further discussed with an analysis of the midday Disturbance Storm Time (DST) index of geomagnetic activity. The residual GTEC – ITEC corresponding to plasmaspheric electron content and equivalent ionospheric foF2 and total slab thickness parameters were computed and comprehensively discussed. The results verified the use of UNB-IMT as one of the tools for ionospheric research over South Africa. The UNB-IMT algorithm was applied to investigate TEC variability during different epochs of solar cycle 23. The results were investigated and further discussed by analyzing the GOES 8 and 10 satellites X-ray flux (0.1 – 0.8 nm) and SOHO Solar Extreme Ultraviolet Monitor higher resolution data. Comparison of UNB-IMT TEC derived from collocated HRAO and HARB GNSS receivers was undertaken for the solar X17 and X9 flare events, which occurred on day 301, 2003 and day 339, 2006. It was found that there exist considerable TEC differences between the two collocated receivers with some evidence of solar cycle dependence. Furthermore, the daytime UNB TEC compared with the International Reference Ionosphere 2001 predicted TEC found both models to show a good agreement. The UNB-IMT TEC was further applied to investigate the capabilities of geodetic Very Long Baseline Interferometry (VLBI) derived TEC using the Vienna TEC Model for space weather monitoring over HartRAO during the CONT02 and CONT05 campaigns conducted during the years 2002 (near solar maximum) and 005 (near solar minimum). The results verified the use of geodetic VLBI as one of the possible instruments for monitoring space weather impacts on the ionosphere over South Africa.
- Full Text:
- Date Issued: 2008
Solar cycle effects on GNSS-derived ionospheric total electron content observed over Southern Africa
- Authors: Moeketsi, Daniel Mojalefa
- Date: 2008
- Subjects: Ionosphere -- Africa, Southern Electrons Ionospheric electron density -- Africa, Southern Ionosondes -- Africa, Southern Electromagnetic waves
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5489 , http://hdl.handle.net/10962/d1005275
- Description: The South African Global Navigation Satellite System (GNSS) network of dual frequency receivers provide an opportunity to investigate solar cycle effects on ionospheric Total Electron Content (TEC) over the South Africa region by taking advantage of the dispersive nature of the ionospheric medium. For this task, the global University of New Brunswick Ionospheric Modelling Technique (UNB-IMT) was adopted, modified and applied to compute TEC using data from the southern African GNSS Network. TEC values were compared with CODE International GNSS services TEC predictions and Ionosonde-derived TEC (ITEC) measurements to test and validate the UNB-IMT results over South Africa. It was found that the variation trends of GTEC and ITEC over all stations are in good agreement and show pronounced seasonal variations with high TEC values around equinoxes for a year near solar maximum and less pronounced around solar minimum. Signature TEC depletions and enhanced spikes were prevalently evident around equinoxes, particularly for a year near solar maximum. These observations were investigated and further discussed with an analysis of the midday Disturbance Storm Time (DST) index of geomagnetic activity. The residual GTEC – ITEC corresponding to plasmaspheric electron content and equivalent ionospheric foF2 and total slab thickness parameters were computed and comprehensively discussed. The results verified the use of UNB-IMT as one of the tools for ionospheric research over South Africa. The UNB-IMT algorithm was applied to investigate TEC variability during different epochs of solar cycle 23. The results were investigated and further discussed by analyzing the GOES 8 and 10 satellites X-ray flux (0.1 – 0.8 nm) and SOHO Solar Extreme Ultraviolet Monitor higher resolution data. Comparison of UNB-IMT TEC derived from collocated HRAO and HARB GNSS receivers was undertaken for the solar X17 and X9 flare events, which occurred on day 301, 2003 and day 339, 2006. It was found that there exist considerable TEC differences between the two collocated receivers with some evidence of solar cycle dependence. Furthermore, the daytime UNB TEC compared with the International Reference Ionosphere 2001 predicted TEC found both models to show a good agreement. The UNB-IMT TEC was further applied to investigate the capabilities of geodetic Very Long Baseline Interferometry (VLBI) derived TEC using the Vienna TEC Model for space weather monitoring over HartRAO during the CONT02 and CONT05 campaigns conducted during the years 2002 (near solar maximum) and 005 (near solar minimum). The results verified the use of geodetic VLBI as one of the possible instruments for monitoring space weather impacts on the ionosphere over South Africa.
- Full Text:
- Date Issued: 2008
A pilot wide-field VLBI survey of the GOODS-North field
- Authors: Akoto-Danso, Alexander
- Date: 2019
- Subjects: Radio astronomy , Very long baseline interferometry , Radio interometers , Imaging systems in astronomy , Hubble Space Telescope (Spacecraft) -- Observations
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/72296 , vital:30027
- Description: Very Long Baseline Interferometry (VLBI) has significant advantages in disentangling active galactic nuclei (AGN) from star formation, particularly at intermediate to high-redshift due to its high angular resolution and insensitivity to dust. Surveys using VLBI arrays are only just becoming practical over wide areas with numerous developments and innovations (such as multi-phase centre techniques) in observation and data analysis techniques. However, fully automated pipelines for VLBI data analysis are based on old software packages and are unable to incorporate new calibration and imaging algorithms. In this work, the researcher developed a pipeline for VLBI data analysis which integrates a recent wide-field imaging algorithm, RFI excision, and a purpose-built source finding algorithm specifically developed for the 64kx64k wide-field VLBI images. The researcher used this novel pipeline to process 6% (~ 9 arcmin2 of the total 160 arcmin2) of the data from the CANDELS GOODS- North extragalactic field at 1.6 GHz. The milli-arcsec scale images have an average rms of a ~ 10 uJy/beam. Forty four (44) candidate sources were detected, most of which are at sub-mJy flux densities, having brightness temperatures and luminosities of >5x105 K and >6x1021 W Hz-1 respectively. This work demonstrates that automated post-processing pipelines for wide-field, uniform sensitivity VLBI surveys are feasible and indeed made more efficient with new software, wide-field imaging algorithms and more purpose-built source- finders. This broadens the discovery space for future wide-field surveys with upcoming arrays such as the African VLBI Network (AVN), MeerKAT and the Square Kilometre Array (SKA).
- Full Text:
- Date Issued: 2019
- Authors: Akoto-Danso, Alexander
- Date: 2019
- Subjects: Radio astronomy , Very long baseline interferometry , Radio interometers , Imaging systems in astronomy , Hubble Space Telescope (Spacecraft) -- Observations
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/72296 , vital:30027
- Description: Very Long Baseline Interferometry (VLBI) has significant advantages in disentangling active galactic nuclei (AGN) from star formation, particularly at intermediate to high-redshift due to its high angular resolution and insensitivity to dust. Surveys using VLBI arrays are only just becoming practical over wide areas with numerous developments and innovations (such as multi-phase centre techniques) in observation and data analysis techniques. However, fully automated pipelines for VLBI data analysis are based on old software packages and are unable to incorporate new calibration and imaging algorithms. In this work, the researcher developed a pipeline for VLBI data analysis which integrates a recent wide-field imaging algorithm, RFI excision, and a purpose-built source finding algorithm specifically developed for the 64kx64k wide-field VLBI images. The researcher used this novel pipeline to process 6% (~ 9 arcmin2 of the total 160 arcmin2) of the data from the CANDELS GOODS- North extragalactic field at 1.6 GHz. The milli-arcsec scale images have an average rms of a ~ 10 uJy/beam. Forty four (44) candidate sources were detected, most of which are at sub-mJy flux densities, having brightness temperatures and luminosities of >5x105 K and >6x1021 W Hz-1 respectively. This work demonstrates that automated post-processing pipelines for wide-field, uniform sensitivity VLBI surveys are feasible and indeed made more efficient with new software, wide-field imaging algorithms and more purpose-built source- finders. This broadens the discovery space for future wide-field surveys with upcoming arrays such as the African VLBI Network (AVN), MeerKAT and the Square Kilometre Array (SKA).
- Full Text:
- Date Issued: 2019
The SKA's the limit : on the nature of faint radio sources
- Authors: McAlpine, Kim
- Date: 2013 , 2012-09-14
- Subjects: Radio telescopes -- South Africa Radio astronomy -- South Africa Square Kilometer Array (Spacecraft)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5504 , http://hdl.handle.net/10962/d1007271
- Description: From abstract: Within the next few years a large number of new and vastly more sensitive radio astronomy facilities are scheduled to come online. These new facilities will map large areas of the sky to unprecedented depths and transform radio astronomy into the leading technique for investigating the complex processes which govern the formation and evolution of galaxies. This thesis combines multi-wavelength techniques, highly relevant to future deep radio surveys, to study the evolution and properties of faint radio sources. , TeX , Adobe Acrobat 9.54 Paper Capture Plug-in
- Full Text:
- Date Issued: 2013
- Authors: McAlpine, Kim
- Date: 2013 , 2012-09-14
- Subjects: Radio telescopes -- South Africa Radio astronomy -- South Africa Square Kilometer Array (Spacecraft)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5504 , http://hdl.handle.net/10962/d1007271
- Description: From abstract: Within the next few years a large number of new and vastly more sensitive radio astronomy facilities are scheduled to come online. These new facilities will map large areas of the sky to unprecedented depths and transform radio astronomy into the leading technique for investigating the complex processes which govern the formation and evolution of galaxies. This thesis combines multi-wavelength techniques, highly relevant to future deep radio surveys, to study the evolution and properties of faint radio sources. , TeX , Adobe Acrobat 9.54 Paper Capture Plug-in
- Full Text:
- Date Issued: 2013
Finite element simulations of shear aggregation as a mechanism to form platinum group elements (PGEs) in dyke-like ore bodies
- Authors: Mbandezi, Mxolisi Louis
- Date: 2002
- Subjects: Platinum group , Magmas , Shear flow , Geophysics , Terrestrial heat flow
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5561 , http://hdl.handle.net/10962/d1018249
- Description: This research describes a two-dimensional modelling effort of heat and mass transport in simplified intrusive models of sills and their feeder dykes. These simplified models resembled a complex intrusive system such as the Great Dyke of Zimbabwe. This study investigated the impact of variable geometry to transport processes in two ways. First the time evolution of heat and mass transport during cooling was investigated. Then emphasis was placed on the application of convective scavenging as a mechanism that leads to the formation of minerals of economic interest, in particular the Platinum Group Elements (PGEs). The Navier-Stokes equations employed generated regions of high shear within the magma where we expected enhanced collisions between the immiscible sulphide liquid particles and PGEs. These collisions scavenge PGEs from the primary melt, aggregate and concentrate it to form PGEs enrichment in zero shear zones. The PGEs scavenge; concentrate and 'glue' in zero shear zones in the early history of convection because of viscosity and dispersive pressure (Bagnold effect). The effect of increasing the geometry size enhances scavenging, creates bigger zero shear zones with dilute concentrate of PGEs but you get high shear near the roots of the dyke/sill where the concentration will not be dilute. The time evolution calculations show that increasing the size of the magma chamber results in stronger initial convection currents for large magma models than for small ones. However, convection takes, approximately the same time to cease for both models. The research concludes that the time evolution for convective heat transfer is dependent on the viscosity rather than on geometry size. However, conductive heat transfer to the e-folding temperature was almost six times as long for the large model (M4) than the small one (M2). Variable viscosity as a physical property was applied to models 2 and 4 only. Video animations that simulate the cooling process for these models are enclosed in a CD at the back of this thesis. These simulations provide information with regard to the emplacement history and distribution of PGEs ore bodies. This will assist the reserve estimation and the location of economic minerals.
- Full Text:
- Date Issued: 2002
- Authors: Mbandezi, Mxolisi Louis
- Date: 2002
- Subjects: Platinum group , Magmas , Shear flow , Geophysics , Terrestrial heat flow
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5561 , http://hdl.handle.net/10962/d1018249
- Description: This research describes a two-dimensional modelling effort of heat and mass transport in simplified intrusive models of sills and their feeder dykes. These simplified models resembled a complex intrusive system such as the Great Dyke of Zimbabwe. This study investigated the impact of variable geometry to transport processes in two ways. First the time evolution of heat and mass transport during cooling was investigated. Then emphasis was placed on the application of convective scavenging as a mechanism that leads to the formation of minerals of economic interest, in particular the Platinum Group Elements (PGEs). The Navier-Stokes equations employed generated regions of high shear within the magma where we expected enhanced collisions between the immiscible sulphide liquid particles and PGEs. These collisions scavenge PGEs from the primary melt, aggregate and concentrate it to form PGEs enrichment in zero shear zones. The PGEs scavenge; concentrate and 'glue' in zero shear zones in the early history of convection because of viscosity and dispersive pressure (Bagnold effect). The effect of increasing the geometry size enhances scavenging, creates bigger zero shear zones with dilute concentrate of PGEs but you get high shear near the roots of the dyke/sill where the concentration will not be dilute. The time evolution calculations show that increasing the size of the magma chamber results in stronger initial convection currents for large magma models than for small ones. However, convection takes, approximately the same time to cease for both models. The research concludes that the time evolution for convective heat transfer is dependent on the viscosity rather than on geometry size. However, conductive heat transfer to the e-folding temperature was almost six times as long for the large model (M4) than the small one (M2). Variable viscosity as a physical property was applied to models 2 and 4 only. Video animations that simulate the cooling process for these models are enclosed in a CD at the back of this thesis. These simulations provide information with regard to the emplacement history and distribution of PGEs ore bodies. This will assist the reserve estimation and the location of economic minerals.
- Full Text:
- Date Issued: 2002
A study of why some physic concepts in the South African Physical Science curriculum are poorly understood in order to develop a targeted action-research intervention for Newton’s second law
- Authors: Cobbing, Kathleen Margaret
- Date: 2020
- Subjects: Physics -- Study and teaching (Secondary) -- South Africa , Physics -- Examinations, questions, etc. -- South Africa , Motion -- Study and teaching (Secondary) -- South Africa
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/146903 , vital:38575
- Description: Globally, many students show a poor understanding of concepts in high school physics and lack the necessary problem-solving skills that the course demands. The application of Newton’s second law was found to be particularly problematic through document analysis of South African examination feedback reports, as well as from an analysis of the physics examinations at a pair of well-resourced South African independent schools that follow the Independent Examination Board curriculum. Through an action-research approach, a resource for use by students was designed and modified to improve students’ understanding of this concept, while modelling problemsolving methods. The resource consisted of brief revision notes, worked examples and scaffolded exercises. The design of the resource was influenced by the theory of cognitive apprenticeship, cognitive load theory and conceptual change theory. One of the aims of the resource was to encourage students to translate between the different representations of a problem situation: symbolic, abstract, model and concrete. The impact of this resource was evaluated at a pair of schools using a mixed methods approach. This incorporated pre- and post-tests for a quantitative assessment, qualitative student evaluations and the analysis of examination scripts. There was an improvement from pre- to post-test for all four iterations of the intervention and these improvements were shown to be significant. The use of the resource led to an increase in the quality and quantity of diagrams drawn by students in subsequent assessments.
- Full Text:
- Date Issued: 2020
- Authors: Cobbing, Kathleen Margaret
- Date: 2020
- Subjects: Physics -- Study and teaching (Secondary) -- South Africa , Physics -- Examinations, questions, etc. -- South Africa , Motion -- Study and teaching (Secondary) -- South Africa
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/146903 , vital:38575
- Description: Globally, many students show a poor understanding of concepts in high school physics and lack the necessary problem-solving skills that the course demands. The application of Newton’s second law was found to be particularly problematic through document analysis of South African examination feedback reports, as well as from an analysis of the physics examinations at a pair of well-resourced South African independent schools that follow the Independent Examination Board curriculum. Through an action-research approach, a resource for use by students was designed and modified to improve students’ understanding of this concept, while modelling problemsolving methods. The resource consisted of brief revision notes, worked examples and scaffolded exercises. The design of the resource was influenced by the theory of cognitive apprenticeship, cognitive load theory and conceptual change theory. One of the aims of the resource was to encourage students to translate between the different representations of a problem situation: symbolic, abstract, model and concrete. The impact of this resource was evaluated at a pair of schools using a mixed methods approach. This incorporated pre- and post-tests for a quantitative assessment, qualitative student evaluations and the analysis of examination scripts. There was an improvement from pre- to post-test for all four iterations of the intervention and these improvements were shown to be significant. The use of the resource led to an increase in the quality and quantity of diagrams drawn by students in subsequent assessments.
- Full Text:
- Date Issued: 2020
An investigation of traveling ionospheric disturbances (TIDs) in the SANAE HF radar data
- Authors: Atilaw, Tsige Yared
- Date: 2022-04-07
- Subjects: Ionospheric storms Antarctica , Radar Antarctica , Range time-intensity (RTI) , South African National Antarctic Expedition (SANAE) , Super Dual Auroral Radar Network (SuperDARN)
- Language: English
- Type: Doctoral thesis , text
- Identifier: http://hdl.handle.net/10962/232377 , vital:49986 , DOI 10.21504/10962/232377
- Description: This thesis aims to study the characteristics of traveling ionospheric disturbances (TIDs) as identified in the radar data of the South African National Antarctic Expedition (SANAE) Super Dual Auroral Radar Network (SuperDARN) radar located in Antarctica. For this project, 22 TIDs were identified from visual inspection of range time-intensity (RTI) plots of backscattered power and Doppler velocity parameters of the SANAE radar between 2005âAS2015. These events were studied to determine their characteristics and driving mechanisms. Where good quality data were available, the SANAE HF radar data were supplemented by Halley radar data, which has large area of overlapping field of view (FOV) with the SANAE radar, and also by GPS TEC data. This provided a multi-instrument data analysis of some TID events. Different spectral analysis methods, namely the multitaper method (MTM), Fast Fourier transform (FFT) and the Lomb-Scargle periodogram were used to obtain spectral information of the observed waves. The advantage of using multiple windowing in MTM over the traditional windowing method was illustrated using one of the TID events. In addition, the analytic signal of the wave from the MTM method was used to estimate the instantaneous phase velocity and propagation azimuth of the wave, which was able to track the change in the characteristics of the medium-scale TID (MSTID) efficiently throughout the duration of the event. This is a clear advantage over other windowing techniques. The energy contribution by this MSTID through Joule heating was estimated over the region where spectral analysis of both SANAE and Halley data showed it to be present. The majority of the TIDs (65.4%) could be classified as MSTIDs with periods of 20–60 minutes, velocities of 50–333 ms1 and wavelengths of 129–833 km. The TID occurrence rate was high around the March equinox with 12 out of the 16 event days being during March–May. March had a particularly high number of occurrences of TIDs (46%). The majority of the TIDs observed during this month propagated northward or southeastward. In terms of prevailing geomagnetic conditions, 6 out of 16 event days were geomagnetically quiet, while 10 occurred during geomagnetic storms and substorms. During quiet conditions, TIDs could be linked to Es and polarised electric fields in 2 of these events. The other quiet time events could not be related to Es instability and polarised electric field either because their exact propagation direction could not be determined or data quality from the Es region scatter was too poor to perform spectral analysis. The storm-/substorm-related TIDs are possibly generated through Joule heating, the Lorentz force and energetic particle precipitation. , Thesis (PhD) -- Faculty of Science, Physics and Electronics, 2022
- Full Text:
- Date Issued: 2022-04-07
- Authors: Atilaw, Tsige Yared
- Date: 2022-04-07
- Subjects: Ionospheric storms Antarctica , Radar Antarctica , Range time-intensity (RTI) , South African National Antarctic Expedition (SANAE) , Super Dual Auroral Radar Network (SuperDARN)
- Language: English
- Type: Doctoral thesis , text
- Identifier: http://hdl.handle.net/10962/232377 , vital:49986 , DOI 10.21504/10962/232377
- Description: This thesis aims to study the characteristics of traveling ionospheric disturbances (TIDs) as identified in the radar data of the South African National Antarctic Expedition (SANAE) Super Dual Auroral Radar Network (SuperDARN) radar located in Antarctica. For this project, 22 TIDs were identified from visual inspection of range time-intensity (RTI) plots of backscattered power and Doppler velocity parameters of the SANAE radar between 2005âAS2015. These events were studied to determine their characteristics and driving mechanisms. Where good quality data were available, the SANAE HF radar data were supplemented by Halley radar data, which has large area of overlapping field of view (FOV) with the SANAE radar, and also by GPS TEC data. This provided a multi-instrument data analysis of some TID events. Different spectral analysis methods, namely the multitaper method (MTM), Fast Fourier transform (FFT) and the Lomb-Scargle periodogram were used to obtain spectral information of the observed waves. The advantage of using multiple windowing in MTM over the traditional windowing method was illustrated using one of the TID events. In addition, the analytic signal of the wave from the MTM method was used to estimate the instantaneous phase velocity and propagation azimuth of the wave, which was able to track the change in the characteristics of the medium-scale TID (MSTID) efficiently throughout the duration of the event. This is a clear advantage over other windowing techniques. The energy contribution by this MSTID through Joule heating was estimated over the region where spectral analysis of both SANAE and Halley data showed it to be present. The majority of the TIDs (65.4%) could be classified as MSTIDs with periods of 20–60 minutes, velocities of 50–333 ms1 and wavelengths of 129–833 km. The TID occurrence rate was high around the March equinox with 12 out of the 16 event days being during March–May. March had a particularly high number of occurrences of TIDs (46%). The majority of the TIDs observed during this month propagated northward or southeastward. In terms of prevailing geomagnetic conditions, 6 out of 16 event days were geomagnetically quiet, while 10 occurred during geomagnetic storms and substorms. During quiet conditions, TIDs could be linked to Es and polarised electric fields in 2 of these events. The other quiet time events could not be related to Es instability and polarised electric field either because their exact propagation direction could not be determined or data quality from the Es region scatter was too poor to perform spectral analysis. The storm-/substorm-related TIDs are possibly generated through Joule heating, the Lorentz force and energetic particle precipitation. , Thesis (PhD) -- Faculty of Science, Physics and Electronics, 2022
- Full Text:
- Date Issued: 2022-04-07
Statistical study of traveling ionospheric disturbances over South Africa
- Authors: Mahlangu, Daniel Fiso
- Date: 2019
- Subjects: Ionosphere -- Research , Sudden ionospheric disturbances , Gravity waves , Magnetic storms
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/76387 , vital:30556
- Description: This thesis provides a statistical analysis of traveling ionospheric disturbances (TIDs) in South Africa. The velocities of the TIDs were determined from total electron content (TEC) maps using particle image velocimetry (PIV). The periods were determined using Morlet function in wavelet analysis. The TIDs were grouped into four categories: daytime, twilight, nighttime TIDs, and those TIDs that occurred during magnetic storms. It was found that daytime medium scale TIDs (MSTIDs) propagated equatorward in all seasons (summer, autumn, winter, and spring), with velocities of about 114 to 213 m/s. Their maximum occurrence was in winter between 15:00 and 16:00 LT. The daytime large scale (TIDs) LSTIDs propagated equatorward with velocities of approximately 455 to 767 m/s. Their highest occurrence was in summer, between 12:00-13:00 LT. Most of the these TIDs (about 78%) were observed during the passing of the morning solar terminator. This implied that the morning terminator was more effective in instigating TIDs. Only a few nighttime TIDs were observed and therefore their behavior could not be statistically inferred. The TIDs that occurred during magnetically disturbed conditions propagated equatorward. This indicated that their source mechanism was atmospheric gravity waves generated at the onset of geomagnetic storms.
- Full Text:
- Date Issued: 2019
- Authors: Mahlangu, Daniel Fiso
- Date: 2019
- Subjects: Ionosphere -- Research , Sudden ionospheric disturbances , Gravity waves , Magnetic storms
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/76387 , vital:30556
- Description: This thesis provides a statistical analysis of traveling ionospheric disturbances (TIDs) in South Africa. The velocities of the TIDs were determined from total electron content (TEC) maps using particle image velocimetry (PIV). The periods were determined using Morlet function in wavelet analysis. The TIDs were grouped into four categories: daytime, twilight, nighttime TIDs, and those TIDs that occurred during magnetic storms. It was found that daytime medium scale TIDs (MSTIDs) propagated equatorward in all seasons (summer, autumn, winter, and spring), with velocities of about 114 to 213 m/s. Their maximum occurrence was in winter between 15:00 and 16:00 LT. The daytime large scale (TIDs) LSTIDs propagated equatorward with velocities of approximately 455 to 767 m/s. Their highest occurrence was in summer, between 12:00-13:00 LT. Most of the these TIDs (about 78%) were observed during the passing of the morning solar terminator. This implied that the morning terminator was more effective in instigating TIDs. Only a few nighttime TIDs were observed and therefore their behavior could not be statistically inferred. The TIDs that occurred during magnetically disturbed conditions propagated equatorward. This indicated that their source mechanism was atmospheric gravity waves generated at the onset of geomagnetic storms.
- Full Text:
- Date Issued: 2019
Modeling and measurement of torqued procession in radio pulsars
- Authors: Tiplady, Adrian John
- Date: 2005
- Subjects: Pulsars , Radio telescopes , Radio astronomy , Precession , Hartebeeshoek Radio Astronomy Observatory (HartRAO)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5475 , http://hdl.handle.net/10962/d1005260
- Description: The long term isolated pulsar monitoring program, which commenced in 1984 using the 26 m radio telescope at the Hartebeeshoek Radio Astronomy Observatory (HartRAO), has produced high resolution timing residual data over long timespans. This has enabled the analysis of observed spin down behaviour for 27 braking pulsars, most of which have dataspans longer than 14 years. The phenomenology of observed timing residuals of certain pulsars can be explained by pseudo periodic effects such as precession. Analytic and numerical models are developed to study the kinematic and dynamic behaviour of isolated but torqued precessing pulsars. The predicted timing residual behaviour of the models is characterised, and confronted with timing data from selected pulsars. Cyclic variations in the observed timing residuals of PSR B1642-03, PSR B1323-58 and PSR B1557-50 are fitted with a torqued precession model. The phenomenology of the observed timing behaviour of these pulsars can be explained by the precession models, but precise model fitting was not possible. This is not surprising given that the complexity of the pulsar systems is not completely described by the model. The extension of the pulsar monitoring program at HartRAO is used as motivation for the design and development of a new low cost, multi-purpose digital pulsar receiver. The instrument is implemented using a hybrid filterbank architecture, consisting of an analogue frontend and digital backend, to perform incoherent dedispersion. The design of a polyphase filtering system, which will consolidate multiple processing units into a single filtering solution, is discussed for future implementation.
- Full Text:
- Date Issued: 2005
- Authors: Tiplady, Adrian John
- Date: 2005
- Subjects: Pulsars , Radio telescopes , Radio astronomy , Precession , Hartebeeshoek Radio Astronomy Observatory (HartRAO)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5475 , http://hdl.handle.net/10962/d1005260
- Description: The long term isolated pulsar monitoring program, which commenced in 1984 using the 26 m radio telescope at the Hartebeeshoek Radio Astronomy Observatory (HartRAO), has produced high resolution timing residual data over long timespans. This has enabled the analysis of observed spin down behaviour for 27 braking pulsars, most of which have dataspans longer than 14 years. The phenomenology of observed timing residuals of certain pulsars can be explained by pseudo periodic effects such as precession. Analytic and numerical models are developed to study the kinematic and dynamic behaviour of isolated but torqued precessing pulsars. The predicted timing residual behaviour of the models is characterised, and confronted with timing data from selected pulsars. Cyclic variations in the observed timing residuals of PSR B1642-03, PSR B1323-58 and PSR B1557-50 are fitted with a torqued precession model. The phenomenology of the observed timing behaviour of these pulsars can be explained by the precession models, but precise model fitting was not possible. This is not surprising given that the complexity of the pulsar systems is not completely described by the model. The extension of the pulsar monitoring program at HartRAO is used as motivation for the design and development of a new low cost, multi-purpose digital pulsar receiver. The instrument is implemented using a hybrid filterbank architecture, consisting of an analogue frontend and digital backend, to perform incoherent dedispersion. The design of a polyphase filtering system, which will consolidate multiple processing units into a single filtering solution, is discussed for future implementation.
- Full Text:
- Date Issued: 2005
Assignment of spin and parity to states in the nucleus ¹⁹⁶T1
- Authors: Uwitonze, Pierre Celestin
- Date: 2015
- Subjects: Nuclear spin , Particles (Nuclear physics) -- Chirality
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5558 , http://hdl.handle.net/10962/d1017903
- Description: This work presents a study of high-spin states in the nucleus ¹⁹⁶Tl via γ-spectroscopy. ¹⁹⁶Tl was produced via the ¹⁹⁷Au(⁴He,5n) ¹⁹⁶Tl reaction at a beam energy of 63 MeV. The γ-γ coincidence measurements were performed using the AFRODITE γ-spectrometer array at iThemba LABS. The previous level scheme of ¹⁹⁶Tl has been extended up to an excitation of 4071 keV including 24 new γ-ray transitions. The spin and parity assignment to levels was made from the directional correlation of oriented nuclei (DCO) and linear polarization anisotropy ratios. An analysis of the B(M1)/B(E2) ratios was found to be consistent with the configuration of πh₉/₂♁vi₁₃/₂ for the ground state band. Although no chiral band was found in ¹⁹⁶TI and ¹⁹⁸TI.
- Full Text:
- Date Issued: 2015
- Authors: Uwitonze, Pierre Celestin
- Date: 2015
- Subjects: Nuclear spin , Particles (Nuclear physics) -- Chirality
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5558 , http://hdl.handle.net/10962/d1017903
- Description: This work presents a study of high-spin states in the nucleus ¹⁹⁶Tl via γ-spectroscopy. ¹⁹⁶Tl was produced via the ¹⁹⁷Au(⁴He,5n) ¹⁹⁶Tl reaction at a beam energy of 63 MeV. The γ-γ coincidence measurements were performed using the AFRODITE γ-spectrometer array at iThemba LABS. The previous level scheme of ¹⁹⁶Tl has been extended up to an excitation of 4071 keV including 24 new γ-ray transitions. The spin and parity assignment to levels was made from the directional correlation of oriented nuclei (DCO) and linear polarization anisotropy ratios. An analysis of the B(M1)/B(E2) ratios was found to be consistent with the configuration of πh₉/₂♁vi₁₃/₂ for the ground state band. Although no chiral band was found in ¹⁹⁶TI and ¹⁹⁸TI.
- Full Text:
- Date Issued: 2015
Radio observation of the Gum Nebula Region
- Authors: Woermann, Beate
- Date: 1997
- Subjects: Radio sources (Astronomy) Nebulae -- Observations Radio astronomy
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5485 , http://hdl.handle.net/10962/d1005271
- Description: This thesis describes the results of an investigation of the physical properties of the Gum Nebula. For this investigation a radio continuum map of the region was made at 2326 MHz and resolution ⅓° with the HartRAO antenna. This map was used to generate spectral index images and an infrared to radio flux density ratio (IRR) image. The latter image shows that the IRR of the nebula is in the range 20 to 250, identifying it as an old SNR. Several spectral index images of this region were generated using two different methods, one based on the isolation of the nebula from its background radiation, the other based on TT-plots (Turtle et al., 1962). The two methods yield similar results, which show that the nebula has a thermal shell with a non-thermal region in its interior. Below the galactic plane the thermal region dominates and above the plane the nonthermal region. These results suggest a model of an old SNR with an H II region shell. Spectral line observations of hydrogen recombination lines and hydroxyl (OH) were made with the HartRAO and the Mopra telescopes. The detection of hydrogen recombination lines at four positions in the thermal regions of the nebula give electron temperatures and emission measures in the ranges 4000 to 6000 K and 220 to 460 pc.cm⁻⁶ respectively. The turbulent velocities are of the order of 20 km/s. A search for shocked OH lines at 1667 MHz and 1720 MHz in the Gum Nebula gave results that were negative, but numerous unshocked 1667 MHz OH lines were detected. The latter were used in a test for an expansion of the nebula. The most plausible fit to the data gives an expansion centre at l = 260.5°, b = -2.5° and at a distance of 0.7 kpc from us. The front face angular radius and expansion velocity are 10.5° and 16 km/s respectively. The back face angular radius and expansion velocity are 8.50 and 7 km/s respectively.
- Full Text:
- Date Issued: 1997
- Authors: Woermann, Beate
- Date: 1997
- Subjects: Radio sources (Astronomy) Nebulae -- Observations Radio astronomy
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5485 , http://hdl.handle.net/10962/d1005271
- Description: This thesis describes the results of an investigation of the physical properties of the Gum Nebula. For this investigation a radio continuum map of the region was made at 2326 MHz and resolution ⅓° with the HartRAO antenna. This map was used to generate spectral index images and an infrared to radio flux density ratio (IRR) image. The latter image shows that the IRR of the nebula is in the range 20 to 250, identifying it as an old SNR. Several spectral index images of this region were generated using two different methods, one based on the isolation of the nebula from its background radiation, the other based on TT-plots (Turtle et al., 1962). The two methods yield similar results, which show that the nebula has a thermal shell with a non-thermal region in its interior. Below the galactic plane the thermal region dominates and above the plane the nonthermal region. These results suggest a model of an old SNR with an H II region shell. Spectral line observations of hydrogen recombination lines and hydroxyl (OH) were made with the HartRAO and the Mopra telescopes. The detection of hydrogen recombination lines at four positions in the thermal regions of the nebula give electron temperatures and emission measures in the ranges 4000 to 6000 K and 220 to 460 pc.cm⁻⁶ respectively. The turbulent velocities are of the order of 20 km/s. A search for shocked OH lines at 1667 MHz and 1720 MHz in the Gum Nebula gave results that were negative, but numerous unshocked 1667 MHz OH lines were detected. The latter were used in a test for an expansion of the nebula. The most plausible fit to the data gives an expansion centre at l = 260.5°, b = -2.5° and at a distance of 0.7 kpc from us. The front face angular radius and expansion velocity are 10.5° and 16 km/s respectively. The back face angular radius and expansion velocity are 8.50 and 7 km/s respectively.
- Full Text:
- Date Issued: 1997
Thermoluminescence and phototransferred phermoluminescence of synthetic quartz
- Authors: Dawam, Robert Rangmou
- Date: 2020
- Subjects: Thermoluminescence , Quartz
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/145849 , vital:38472
- Description: The main aim of this investigation is on thermoluminescence and phototransferred thermoluminescence of synthetic quartz. Thermoluminescence was one of the tools used in characterising the electron traps parameters. The samples of quartz annealed at various temperatures up to 900̊C and the unannealed were used. The thermoluminescence glow curve was measured at 1̊C s~ 1 following beta irradiation to 40 Gy from the samples annealed at 500̊C and the unannealed consist of main peak at 70̊C and secondary peaks at 110, 180 and 310̊C. In comparison, the thermoluminescence glow curve for the sample annealed at 900̊C have main peak at 86̊C and the secondary ones at 170 and 310̊C. The kinetic analysis was carried out only on the main peak in each case. The activation energy was found to be decreasing with increase in annealing temperatures. The samples annealed at 500̊C and the unannealed were found to be affected by thermal quenching while sample annealed at 900̊C shows an inverse quenching for irradiation dose of 40 Gy. However, when the dose was reduce to 3 Gy the effects of thermal quenching was manifested. The activation energy of thermal quenching was also found to decrease with increase in annealing temperature. Thermally assisted optically stimulated luminescence measurement was carried out using continuous wave optical stimulated luminescence (CW-OSL). The samples studied were those annealed at 500̊C for 10 minutes, 900̊C for 10, 30, 60 minutes and 1000̊C for 10 minutes prior to use. The CW-OSL is stimulated using 470 nm blue LEDs at sample temperatures between 30 and 200̊C. It is measured after preheating to either 300 and 500̊C. When the integrated OSL intensity is plotted as a function of measurement temperature, the intensity goes through a peak. The increase in OSL intensity as a function of temperature is associated to thermal assistance and the decrease to thermal quenching. The kinetic parameters were evaluated by fitting the experimental data. The values of activation energies of thermal quenching are the same within experimental uncertainties for all the experimental conditions. This shows that annealing temperature, duration of annealing and irradiation dose have a negligible influence on the recombination site of luminescence using OSL. Phototransferred thermoluminescence (PTTL) induced from annealed samples using 470 nm blue light was also investigated. The quartz were annealed at 500 _C for 10 minutes, 900̊C for 10, 30, 60 minutes and 1000̊C for 10 minutes prior to use. The glow curves of conventional TL measured at 1 _C s1 following irradiation to 200 Gy shows six peaks in each case labelled I-VI for ease of reference whereas peaks observed under PTTL are referred to as A1 onwards. Only the first three peaks were reproduced under phototransfer for the sample annealed at 900̊C for 60 minutes and 1000̊C C for 10 minutes. Interestingly, for the intermediate duration of annealing of 30 minutes, the only peak that appears under phototransfer is the A1. For quartz annealed at 900̊C for 10 minutes, the PTTL appears as long as the preheating temperature does not exceed 560̊C. All other annealing temperatures, PTTL only appears for preheating to 450 and below. This shows that the occupancy of deep electron traps at temperatures beyond 450̊C or 560̊C is low. The activation energy for peaks A1, A2 and A3 were calculated. The PTTL peaks were studied for thermal quenching and peaks A1 and A3 were found to be affected. The activation energies for thermal quenching were determined as 0.62 ± 0.04 eV and 0.65 ± 0.02 eV for peaks A1 and A3 respectively. The experimental dependence of PTTL intensity on illumination time is modelled using sets of coupled linear differential equations based on systems of donors and acceptors whose number is determined by preheating temperature.
- Full Text:
- Date Issued: 2020
- Authors: Dawam, Robert Rangmou
- Date: 2020
- Subjects: Thermoluminescence , Quartz
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/145849 , vital:38472
- Description: The main aim of this investigation is on thermoluminescence and phototransferred thermoluminescence of synthetic quartz. Thermoluminescence was one of the tools used in characterising the electron traps parameters. The samples of quartz annealed at various temperatures up to 900̊C and the unannealed were used. The thermoluminescence glow curve was measured at 1̊C s~ 1 following beta irradiation to 40 Gy from the samples annealed at 500̊C and the unannealed consist of main peak at 70̊C and secondary peaks at 110, 180 and 310̊C. In comparison, the thermoluminescence glow curve for the sample annealed at 900̊C have main peak at 86̊C and the secondary ones at 170 and 310̊C. The kinetic analysis was carried out only on the main peak in each case. The activation energy was found to be decreasing with increase in annealing temperatures. The samples annealed at 500̊C and the unannealed were found to be affected by thermal quenching while sample annealed at 900̊C shows an inverse quenching for irradiation dose of 40 Gy. However, when the dose was reduce to 3 Gy the effects of thermal quenching was manifested. The activation energy of thermal quenching was also found to decrease with increase in annealing temperature. Thermally assisted optically stimulated luminescence measurement was carried out using continuous wave optical stimulated luminescence (CW-OSL). The samples studied were those annealed at 500̊C for 10 minutes, 900̊C for 10, 30, 60 minutes and 1000̊C for 10 minutes prior to use. The CW-OSL is stimulated using 470 nm blue LEDs at sample temperatures between 30 and 200̊C. It is measured after preheating to either 300 and 500̊C. When the integrated OSL intensity is plotted as a function of measurement temperature, the intensity goes through a peak. The increase in OSL intensity as a function of temperature is associated to thermal assistance and the decrease to thermal quenching. The kinetic parameters were evaluated by fitting the experimental data. The values of activation energies of thermal quenching are the same within experimental uncertainties for all the experimental conditions. This shows that annealing temperature, duration of annealing and irradiation dose have a negligible influence on the recombination site of luminescence using OSL. Phototransferred thermoluminescence (PTTL) induced from annealed samples using 470 nm blue light was also investigated. The quartz were annealed at 500 _C for 10 minutes, 900̊C for 10, 30, 60 minutes and 1000̊C for 10 minutes prior to use. The glow curves of conventional TL measured at 1 _C s1 following irradiation to 200 Gy shows six peaks in each case labelled I-VI for ease of reference whereas peaks observed under PTTL are referred to as A1 onwards. Only the first three peaks were reproduced under phototransfer for the sample annealed at 900̊C for 60 minutes and 1000̊C C for 10 minutes. Interestingly, for the intermediate duration of annealing of 30 minutes, the only peak that appears under phototransfer is the A1. For quartz annealed at 900̊C for 10 minutes, the PTTL appears as long as the preheating temperature does not exceed 560̊C. All other annealing temperatures, PTTL only appears for preheating to 450 and below. This shows that the occupancy of deep electron traps at temperatures beyond 450̊C or 560̊C is low. The activation energy for peaks A1, A2 and A3 were calculated. The PTTL peaks were studied for thermal quenching and peaks A1 and A3 were found to be affected. The activation energies for thermal quenching were determined as 0.62 ± 0.04 eV and 0.65 ± 0.02 eV for peaks A1 and A3 respectively. The experimental dependence of PTTL intensity on illumination time is modelled using sets of coupled linear differential equations based on systems of donors and acceptors whose number is determined by preheating temperature.
- Full Text:
- Date Issued: 2020
A real time Fast Fourier Transform analyser
- Authors: Fisher, John Stanley
- Date: 1980
- Subjects: Fourier transformations Ionosondes Algorithms Computer simulation
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5439 , http://hdl.handle.net/10962/d1001992
- Description: From the requirements of the Ionosonde digitisation project, undertaken by Rhodes University Antarctic Research Group, it was decided to use the Fast Fourier Transform to compute the spectrum analysis. Several FFT algorithms are reviewed and properties discussed, and the Ccoley Tukey algorithm chosen for utilization. The hardware implementation of this algorithm, and the microprogram control of the whole system are discussed in detail, and such design aspects that required computer simulation are also treated in detail. The final testing of the analyser is shown, and includes a test using data from an ionosonde sounding. The conclusions contain details of extensions to the analysers present operation, required by plans to place the whole Chirpsounder under microprocessor control
- Full Text:
- Date Issued: 1980
- Authors: Fisher, John Stanley
- Date: 1980
- Subjects: Fourier transformations Ionosondes Algorithms Computer simulation
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5439 , http://hdl.handle.net/10962/d1001992
- Description: From the requirements of the Ionosonde digitisation project, undertaken by Rhodes University Antarctic Research Group, it was decided to use the Fast Fourier Transform to compute the spectrum analysis. Several FFT algorithms are reviewed and properties discussed, and the Ccoley Tukey algorithm chosen for utilization. The hardware implementation of this algorithm, and the microprogram control of the whole system are discussed in detail, and such design aspects that required computer simulation are also treated in detail. The final testing of the analyser is shown, and includes a test using data from an ionosonde sounding. The conclusions contain details of extensions to the analysers present operation, required by plans to place the whole Chirpsounder under microprocessor control
- Full Text:
- Date Issued: 1980