A wideband spectropolarimetry study of the spatially resolved radio galaxies: Cygnus A & Hydra A
- Sebokolodi, Makhuduga Lerato Lydia
- Authors: Sebokolodi, Makhuduga Lerato Lydia
- Date: 2022-04-04
- Subjects: Radio astronomy , Radio galaxies , Faraday effect , Astrophysical spectropolarimetry , Intracluster medium , Cosmic magnetic fields
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/454415 , vital:75342 , DOI 10.21504/10962/454415
- Description: This study presented results from our deep, wideband, high-spectral and high-spatial-resolution polarisation observations of the two most powerful radio galaxies, namely Cygnus A and Hydra A, with the Jansky Very Large Array (JVLA). The high surface brightness and strong polarisation of these radio sources enabled detailed polarimetric imaging, providing images at 0.75′′ resolution across 2−18 GHz and 2000 independent lines-of-sight across Cygnus A, and images at 1.5′′ (2 − 12 GHz) and 600 lines-of-sight across Hydra A. Our data revealed significant depolarisation and depolarisation structure, as well as deviations from a _2-law. We also found complicated structures in the Faraday spectra ranging from single-peaked to blended/resolved double- and multiple-peaked. The Faraday spectra of Hydra A were more multiple-peaked than Cygnus A. The fractional polarisation increased monotonically with increasing resolution, as expected. However, there were numerous lines-of-sight with complicated behaviour. We also found that the structure and complexity in the depolarisation increased at lower resolutions, suggesting substantial spatial structures across the lobes/tails. We fitted the 0.3′′ (6−18 GHz) and 0.50′′ (6−12 GHz) images of Cygnus A and Hydra A, respectively, with a simple model incorporating random, unresolved fluctuations in the cluster magnetic field to determine the high-resolution, high-frequency properties of the sources and the cluster. We found rotation measures (RM) between −5000 rad m−2 and +6400 rad m−2 across Cygnus A, and −2000 rad m−2 and +11900 rad m−2 across Hydra A, consistent with previous studies. From these derived properties, we generated predicted polarisation images of the sources at lower frequencies (< 6 GHz), convolved to 0.75′′ for Cygnus A and 1.5′′ for Hydra A. The predictions were remarkably consistent with the observed emission in both sources, providing strong support for the depolarisation being a result of unresolved fluctuations in the magnetic fields. We fitted various analytical models to the wideband data. We found that the data for both sources were inconsistent with a wholly mixed gas of thermal and synchrotron gas, particularly for regions withRM > 1000 rad m−2. Instead, the data required a dominant Faraday rotating screen in the foreground of the radio sources. The wideband modelling also showed preference towards models with at least two or more unresolved Faraday rotating patches. Single depolarising models fail to describe the data. This implies the presence of more than one depolarising screen in the vicinity of these sources. The observations were consistent with the lower-frequency depolarisation due to unresolved fluctuations on scales ≳ 300−700 pc in the magnetic field or the electron density superposed on a partially ordered field component. Both the large-scale magnetic fields and unresolved magnetic field fluctuations are external to the radio emission. The magnetic fields around Cygnus A are located in the ambient cluster gas, the shocked gas in the boundary of the lobes or both, while the magnetic fields around Hydra A are most likely located in the ambient cluster gas. , Thesis (PhD) -- Faculty of Science, Physics, 2022
- Full Text:
- Authors: Sebokolodi, Makhuduga Lerato Lydia
- Date: 2022-04-04
- Subjects: Radio astronomy , Radio galaxies , Faraday effect , Astrophysical spectropolarimetry , Intracluster medium , Cosmic magnetic fields
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/454415 , vital:75342 , DOI 10.21504/10962/454415
- Description: This study presented results from our deep, wideband, high-spectral and high-spatial-resolution polarisation observations of the two most powerful radio galaxies, namely Cygnus A and Hydra A, with the Jansky Very Large Array (JVLA). The high surface brightness and strong polarisation of these radio sources enabled detailed polarimetric imaging, providing images at 0.75′′ resolution across 2−18 GHz and 2000 independent lines-of-sight across Cygnus A, and images at 1.5′′ (2 − 12 GHz) and 600 lines-of-sight across Hydra A. Our data revealed significant depolarisation and depolarisation structure, as well as deviations from a _2-law. We also found complicated structures in the Faraday spectra ranging from single-peaked to blended/resolved double- and multiple-peaked. The Faraday spectra of Hydra A were more multiple-peaked than Cygnus A. The fractional polarisation increased monotonically with increasing resolution, as expected. However, there were numerous lines-of-sight with complicated behaviour. We also found that the structure and complexity in the depolarisation increased at lower resolutions, suggesting substantial spatial structures across the lobes/tails. We fitted the 0.3′′ (6−18 GHz) and 0.50′′ (6−12 GHz) images of Cygnus A and Hydra A, respectively, with a simple model incorporating random, unresolved fluctuations in the cluster magnetic field to determine the high-resolution, high-frequency properties of the sources and the cluster. We found rotation measures (RM) between −5000 rad m−2 and +6400 rad m−2 across Cygnus A, and −2000 rad m−2 and +11900 rad m−2 across Hydra A, consistent with previous studies. From these derived properties, we generated predicted polarisation images of the sources at lower frequencies (< 6 GHz), convolved to 0.75′′ for Cygnus A and 1.5′′ for Hydra A. The predictions were remarkably consistent with the observed emission in both sources, providing strong support for the depolarisation being a result of unresolved fluctuations in the magnetic fields. We fitted various analytical models to the wideband data. We found that the data for both sources were inconsistent with a wholly mixed gas of thermal and synchrotron gas, particularly for regions withRM > 1000 rad m−2. Instead, the data required a dominant Faraday rotating screen in the foreground of the radio sources. The wideband modelling also showed preference towards models with at least two or more unresolved Faraday rotating patches. Single depolarising models fail to describe the data. This implies the presence of more than one depolarising screen in the vicinity of these sources. The observations were consistent with the lower-frequency depolarisation due to unresolved fluctuations on scales ≳ 300−700 pc in the magnetic field or the electron density superposed on a partially ordered field component. Both the large-scale magnetic fields and unresolved magnetic field fluctuations are external to the radio emission. The magnetic fields around Cygnus A are located in the ambient cluster gas, the shocked gas in the boundary of the lobes or both, while the magnetic fields around Hydra A are most likely located in the ambient cluster gas. , Thesis (PhD) -- Faculty of Science, Physics, 2022
- Full Text:
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:
In-beam spectroscopy of ⁷²Ge
- Authors: Henninger, Katharine Rose
- Date: 2012
- Subjects: Nuclear shapes , Hyperfine structure
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5559 , http://hdl.handle.net/10962/d1018233
- Description: The high-spin states of the nucleus ⁷²Ge were populated via the ⁷°Zn(a,2n)⁷²Ge fusion-evaporation reaction at a beam-energy of 30 MeV. The ')'-decays were observed with the AFRODITE spectrometer array at iThemba LABS (Faure, South Africa). Twenty-seven new transitions, 18 new levels and 2 new bands were added to the ⁷²Ge level scheme, and several corrections were made to t he previously-known level scheme. Transitions were characterised using Directional Correlation from Oriented states (DCO) and polarisation measurements, and spin-parity assignments were made for 7 new levels. Spin and parity were also reassigned to a previously-known structure. One of the new bands was ident ified as part of an octupole-vibrational band. No tetrahedral states were observed in the scheme despite N = 40 and Z = 32 having been identified as tetrahedral magic numbers. The meaning of the new 14⁺ yrast level for the underlying structure of the ground state band is discussed
- Full Text:
- Authors: Henninger, Katharine Rose
- Date: 2012
- Subjects: Nuclear shapes , Hyperfine structure
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5559 , http://hdl.handle.net/10962/d1018233
- Description: The high-spin states of the nucleus ⁷²Ge were populated via the ⁷°Zn(a,2n)⁷²Ge fusion-evaporation reaction at a beam-energy of 30 MeV. The ')'-decays were observed with the AFRODITE spectrometer array at iThemba LABS (Faure, South Africa). Twenty-seven new transitions, 18 new levels and 2 new bands were added to the ⁷²Ge level scheme, and several corrections were made to t he previously-known level scheme. Transitions were characterised using Directional Correlation from Oriented states (DCO) and polarisation measurements, and spin-parity assignments were made for 7 new levels. Spin and parity were also reassigned to a previously-known structure. One of the new bands was ident ified as part of an octupole-vibrational band. No tetrahedral states were observed in the scheme despite N = 40 and Z = 32 having been identified as tetrahedral magic numbers. The meaning of the new 14⁺ yrast level for the underlying structure of the ground state band is discussed
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Validation of high frequency propagation prediction models over Africa
- Authors: Tshisaphungo, Mpho
- Date: 2010
- Subjects: Ionospheric radio wave propagation , Ionospheric radio wave propagation -- Forecasting , Radio meteorology , Radio wave propagation -- Africa , Ionosphere -- Africa -- Radio waves , Atmospheric physics -- Africa , Shortwave radio -- Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5553 , http://hdl.handle.net/10962/d1015239
- Description: The ionosphere is an important factor in high frequency (HF) radio propagation providing an opportunity to study ionospheric variability as well as the space weather conditions under which HF communication can take place. This thesis presents the validation of HF propagation conditions for the Ionospheric Communication Enhanced Profile Analysis and Circuit (ICEPAC) and Advanced Stand Alone Prediction System (ASAPS) models over Africa by comparing predictions with the measured data obtained from the International Beacon Project (IBP). Since these models were not developed using information on the African region, a more accurate HF propagation prediction tool is required. Two IBP transmitter stations are considered, Ruaraka, Kenya (1.24°S, 36.88°E) and Pretoria, South Africa (25.45°S, 28.10°E) with one beacon receiver station located in Hermanus, South Africa (34.27°S, 19.l2°E). The potential of these models in terms of HF propagation conditions is illustrated. An attempt to draw conclusions for future improvement of the models is also presented. Results show a low prediction accuracy for both ICEPAC and ASAPS models, although ICEPAC provided more accurate predictions for daily HF propagation conditions. This thesis suggests that the development of a new HF propagation prediction tool for the African region or the modification of one of the existing models to accommodate the African region, taking into account the importance of the African ionospheric region, should be considered as an option to ensure more accurate HF Propagation predictions over this region.
- Full Text:
- Authors: Tshisaphungo, Mpho
- Date: 2010
- Subjects: Ionospheric radio wave propagation , Ionospheric radio wave propagation -- Forecasting , Radio meteorology , Radio wave propagation -- Africa , Ionosphere -- Africa -- Radio waves , Atmospheric physics -- Africa , Shortwave radio -- Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5553 , http://hdl.handle.net/10962/d1015239
- Description: The ionosphere is an important factor in high frequency (HF) radio propagation providing an opportunity to study ionospheric variability as well as the space weather conditions under which HF communication can take place. This thesis presents the validation of HF propagation conditions for the Ionospheric Communication Enhanced Profile Analysis and Circuit (ICEPAC) and Advanced Stand Alone Prediction System (ASAPS) models over Africa by comparing predictions with the measured data obtained from the International Beacon Project (IBP). Since these models were not developed using information on the African region, a more accurate HF propagation prediction tool is required. Two IBP transmitter stations are considered, Ruaraka, Kenya (1.24°S, 36.88°E) and Pretoria, South Africa (25.45°S, 28.10°E) with one beacon receiver station located in Hermanus, South Africa (34.27°S, 19.l2°E). The potential of these models in terms of HF propagation conditions is illustrated. An attempt to draw conclusions for future improvement of the models is also presented. Results show a low prediction accuracy for both ICEPAC and ASAPS models, although ICEPAC provided more accurate predictions for daily HF propagation conditions. This thesis suggests that the development of a new HF propagation prediction tool for the African region or the modification of one of the existing models to accommodate the African region, taking into account the importance of the African ionospheric region, should be considered as an option to ensure more accurate HF Propagation predictions over this region.
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Finite element modelling of a magma chamber surrounded by country-rock, with particular reference to the groundwater flow in sections of different permeability
- Authors: Remsing, Carmen
- Date: 2003 , 2013-05-23
- Subjects: Magmas , Groundwater flow
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5508 , http://hdl.handle.net/10962/d1007537 , Magmas , Groundwater flow
- Description: This thesis presents results of two-dimensional finite element modelling of a magma chamber surrounded by country-rock containing a section of high permeability. The high permeability section in the country-rock simulates structure that is predominant in controlling the groundwater convection pattern and resulting mineral deposits. The models have analogies in nature: for instance the gold mines in the Massif Central of France, the Pogo mine in Alaska and the Pilgrim's Rest gold field in South Africa. This is a complicated coupled system involving fluid flow and heat transfer under extreme conditions. The magma in the chamber convects and as it cools the heat liberated causes convection in the groundwater contained in the surrounding country-rock. This convection in turn affects the rate of liberation of heat from the magma. The software used for the modelling, FLOTRAN, is the computational fluid dynamics component of the commercial ANSYS package. The results obtained describe in detail the flow pattern in the magma chamber, the country-rock and high permeability section thereof. During the cooling of the magma chamber the groundwater convects more vigorously in the high permeability section than elsewhere, and a convection cell is seen forming within this region. This provides a mechanism for hydrothermal formation of valuable mineral deposits in the structure near a magma chamber. It is found that the relationship between the velocity of the flow in the cell and the temperature of the magma chamber is well represented by a first order linear differential equation, providing a simple understanding of this process, , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
- Full Text:
- Authors: Remsing, Carmen
- Date: 2003 , 2013-05-23
- Subjects: Magmas , Groundwater flow
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5508 , http://hdl.handle.net/10962/d1007537 , Magmas , Groundwater flow
- Description: This thesis presents results of two-dimensional finite element modelling of a magma chamber surrounded by country-rock containing a section of high permeability. The high permeability section in the country-rock simulates structure that is predominant in controlling the groundwater convection pattern and resulting mineral deposits. The models have analogies in nature: for instance the gold mines in the Massif Central of France, the Pogo mine in Alaska and the Pilgrim's Rest gold field in South Africa. This is a complicated coupled system involving fluid flow and heat transfer under extreme conditions. The magma in the chamber convects and as it cools the heat liberated causes convection in the groundwater contained in the surrounding country-rock. This convection in turn affects the rate of liberation of heat from the magma. The software used for the modelling, FLOTRAN, is the computational fluid dynamics component of the commercial ANSYS package. The results obtained describe in detail the flow pattern in the magma chamber, the country-rock and high permeability section thereof. During the cooling of the magma chamber the groundwater convects more vigorously in the high permeability section than elsewhere, and a convection cell is seen forming within this region. This provides a mechanism for hydrothermal formation of valuable mineral deposits in the structure near a magma chamber. It is found that the relationship between the velocity of the flow in the cell and the temperature of the magma chamber is well represented by a first order linear differential equation, providing a simple understanding of this process, , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
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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:
- 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.
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Students' conceptions of simple D.C. electricity circuits: a study of primary, inappropriate conceptions, learning difficulties of physics students, and implications for instruction
- Authors: Jiya, Zindlovu
- Date: 1990
- Subjects: Physical sciences -- Study and teaching (Secondary) -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5441 , http://hdl.handle.net/10962/d1001994
- Description: The work attempts to identify the general conceptual problems of the generations of Black students who pass through flrst year physics courses at the University of Fort Hare. In particular the alternative conceptions of students in the area of direct current electricity are investigated, using various techniques including written diagnostic tests. The main method used in the investigation of the student frameworks is the personal interview. A varied number of inappropriate conceptions are identifled in the students in significantly large proportions, and these are found to be dependent on many factors; for example the socio-cultural background like language and its metaphors, and media images. It is established that some of these are exacerbated by student perceptions about the nature of physics and of the scientific enterprise in general. Certain proposals are made about how to remedy the situation; relying mainly on the recently established innovative instructional strategies like conceptual change and cognitive conflict, and on making proposals about restructuring certain forms of presentation of the subject matter, paying attention to how language is used to address the speciflc problems of the students. The importance of providing practical experiences for the students is also emphasised
- Full Text:
- Authors: Jiya, Zindlovu
- Date: 1990
- Subjects: Physical sciences -- Study and teaching (Secondary) -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5441 , http://hdl.handle.net/10962/d1001994
- Description: The work attempts to identify the general conceptual problems of the generations of Black students who pass through flrst year physics courses at the University of Fort Hare. In particular the alternative conceptions of students in the area of direct current electricity are investigated, using various techniques including written diagnostic tests. The main method used in the investigation of the student frameworks is the personal interview. A varied number of inappropriate conceptions are identifled in the students in significantly large proportions, and these are found to be dependent on many factors; for example the socio-cultural background like language and its metaphors, and media images. It is established that some of these are exacerbated by student perceptions about the nature of physics and of the scientific enterprise in general. Certain proposals are made about how to remedy the situation; relying mainly on the recently established innovative instructional strategies like conceptual change and cognitive conflict, and on making proposals about restructuring certain forms of presentation of the subject matter, paying attention to how language is used to address the speciflc problems of the students. The importance of providing practical experiences for the students is also emphasised
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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:
- 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
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An intelligent computer-based tutor for elementary mechanics problems
- Authors: Oberem, Graham Edmund
- Date: 1987
- Subjects: Physics -- Programmed instruction Physics -- Computer-assisted instruction
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5444 , http://hdl.handle.net/10962/d1001997
- Description: ALBERT, an intelligent problem-solving monitor and coach, has been developed to assist students solving problems in one-dimensional kinematics. Students may type in kinematics problems directly from their textbooks. ALBERT understands the problems, knows how to solve them, and can teach students how to solve them. The program is implemented in the TUTOR language and runs on the Control Data mainframe PLATO system. A natural language interface was designed to understand kinematics problems stated in textbook English. The interface is based on a pattern recognition system which is intended to parallel a cognitive model of language processing. The natural language system has understood over 60 problems taken directly from elementary Physics textbooks. Two problem-solving routines are included in ALBERT. One is goal-directed and solves the problems using the standard kinematic equations. The other uses the definition of acceleration and the relationship between displacement and average velocity to solve the problems. It employs a forward-directed problem-solving strategy. The natural language interface and both the problem-solvers are fast and completely adequate for the task. The tutorial dialogue system uses a modified version of the natural language interface which operates in a two-tier fashion. First an attempt is made to understand the input with the pattern recognition system, and if that fails, a keyword matching system is invoked. The result has been a fairly robust language interface. The tutorial is driven by a tutorial management system (embodying a tutorial model) and a context model. The context model consists of a student model, a tutorial status model and a dynamic dialogue model. ALBERT permits a mixed initiative dialogue in the discussion of a problem. The system has been tested by Physics students in more than 80 problemsolving sessions and the results have been good. The response of the students has been very favourable
- Full Text:
- Authors: Oberem, Graham Edmund
- Date: 1987
- Subjects: Physics -- Programmed instruction Physics -- Computer-assisted instruction
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5444 , http://hdl.handle.net/10962/d1001997
- Description: ALBERT, an intelligent problem-solving monitor and coach, has been developed to assist students solving problems in one-dimensional kinematics. Students may type in kinematics problems directly from their textbooks. ALBERT understands the problems, knows how to solve them, and can teach students how to solve them. The program is implemented in the TUTOR language and runs on the Control Data mainframe PLATO system. A natural language interface was designed to understand kinematics problems stated in textbook English. The interface is based on a pattern recognition system which is intended to parallel a cognitive model of language processing. The natural language system has understood over 60 problems taken directly from elementary Physics textbooks. Two problem-solving routines are included in ALBERT. One is goal-directed and solves the problems using the standard kinematic equations. The other uses the definition of acceleration and the relationship between displacement and average velocity to solve the problems. It employs a forward-directed problem-solving strategy. The natural language interface and both the problem-solvers are fast and completely adequate for the task. The tutorial dialogue system uses a modified version of the natural language interface which operates in a two-tier fashion. First an attempt is made to understand the input with the pattern recognition system, and if that fails, a keyword matching system is invoked. The result has been a fairly robust language interface. The tutorial is driven by a tutorial management system (embodying a tutorial model) and a context model. The context model consists of a student model, a tutorial status model and a dynamic dialogue model. ALBERT permits a mixed initiative dialogue in the discussion of a problem. The system has been tested by Physics students in more than 80 problemsolving sessions and the results have been good. The response of the students has been very favourable
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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
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- 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
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A re-examination of the Carter solutions of Einstein's field equations
- Authors: Kun, A Ah
- Date: 1979
- Subjects: Einstein field equations Space and time General relativity (Physics)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5442 , http://hdl.handle.net/10962/d1001995
- Description: The study of geodesics in space-time is essential to a comprehensive understanding of the physics of the field. Global properties, e.g. the singularity structure and completeness of space-time, can be related to the geodesic properties, thus it is through the solutions of the geodesic equation of motion that many of the global properties of space-time can be obtained in an easily interpretable form. However, it is usually very difficult to integrate the geodesic equations for the particle motion in the presence of a gravitational field (Introduction, p. 1)
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- Authors: Kun, A Ah
- Date: 1979
- Subjects: Einstein field equations Space and time General relativity (Physics)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5442 , http://hdl.handle.net/10962/d1001995
- Description: The study of geodesics in space-time is essential to a comprehensive understanding of the physics of the field. Global properties, e.g. the singularity structure and completeness of space-time, can be related to the geodesic properties, thus it is through the solutions of the geodesic equation of motion that many of the global properties of space-time can be obtained in an easily interpretable form. However, it is usually very difficult to integrate the geodesic equations for the particle motion in the presence of a gravitational field (Introduction, p. 1)
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Precipitation effects on atmospheric electron densities
- Authors: Huang, Cheryl Yu-Yin
- Date: 1977
- Subjects: Precipitation (Chemistry)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5527 , http://hdl.handle.net/10962/d1012441 , Precipitation (Chemistry)
- Description: In this thesis the effects of precipitated electrons on electron densities in the upper atmosphere are investigated. A method for solving the continuity equation has been developed , and this has been used to calculate electron density profiles under various conditions: daytime equilibrium conditions, with and without additional ionization by precipitated electrons; and nighttime conditions, with and without precinitation . This preliminary study seems to show that certain effects may be attributable to precipitation, and that these effects may be significant at night.
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- Authors: Huang, Cheryl Yu-Yin
- Date: 1977
- Subjects: Precipitation (Chemistry)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5527 , http://hdl.handle.net/10962/d1012441 , Precipitation (Chemistry)
- Description: In this thesis the effects of precipitated electrons on electron densities in the upper atmosphere are investigated. A method for solving the continuity equation has been developed , and this has been used to calculate electron density profiles under various conditions: daytime equilibrium conditions, with and without additional ionization by precipitated electrons; and nighttime conditions, with and without precinitation . This preliminary study seems to show that certain effects may be attributable to precipitation, and that these effects may be significant at night.
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The performance of a 22 GHz radio telescope
- Authors: Gaylard, Michael John
- Date: 1977
- Subjects: Radio telescopes , Paraboloid
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5520 , http://hdl.handle.net/10962/d1011946 , Radio telescopes , Paraboloid
- Description: The performance of the Rhodes 22 GHz radio telescope and its improvement are discussed in this thesis. The reflector surfaces of the Cassegrain antenna were surveyed and the surface errors minimised, while the magnitude of thermal and gravitational defomations was calculated. The design and operation of the microwave front end has been improved, and the mixer performance characterised. The continuum and spectral line receivers and their sensitivity are described. The aperture efficiency, which has been raised from 0,47 to 0,57, was deduced from solar and lunar observations and atmospheric attenuation measurements. The antenna beam pattern was also obtained from the observations, with the aid of a computer program, and is compared to that predicted for the telescope.
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- Authors: Gaylard, Michael John
- Date: 1977
- Subjects: Radio telescopes , Paraboloid
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5520 , http://hdl.handle.net/10962/d1011946 , Radio telescopes , Paraboloid
- Description: The performance of the Rhodes 22 GHz radio telescope and its improvement are discussed in this thesis. The reflector surfaces of the Cassegrain antenna were surveyed and the surface errors minimised, while the magnitude of thermal and gravitational defomations was calculated. The design and operation of the microwave front end has been improved, and the mixer performance characterised. The continuum and spectral line receivers and their sensitivity are described. The aperture efficiency, which has been raised from 0,47 to 0,57, was deduced from solar and lunar observations and atmospheric attenuation measurements. The antenna beam pattern was also obtained from the observations, with the aid of a computer program, and is compared to that predicted for the telescope.
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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.
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- 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.
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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.
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- 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.
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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.
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- 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.
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Atmospheric ionization by precipitated electrons
- Authors: Wulff, Annemarie
- Date: 1973 , 2013-10-31
- Subjects: Ionization , Electrons
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5503 , http://hdl.handle.net/10962/d1007229 , Ionization , Electrons
- Description: From Introduction: Precipitation of energetic particl es into the upper atmosphere is known to cause aurora at high latitudes. Sanae is situated in the vicinity of the South Atlantic Geomagnetic Anomaly (Gledhill and Van Rooyen (1963)) where the magnetic field intensity is very low and it is felt that this phenomenon may enhance the loss of particles from the trapping zone into the upper atmosphere. Previous work at Rhodes has shown that it is extremely likely that particle precipitation could be the cause of some ionospheric effects at Sanae. Gledhill and Torr (1966) found that a "disturbed" ionosphere at Sanae was linked with "high" fluxes of precipitated electrons in the area conjugate to Sanae. Later papers by Gledhill, Torr and Torr (1967), and Torr and Torr (1967a, 1968a) established that electrons are precipitated over a large part of the earth's surface and this phenomenon is probably responsible for an average of about 30% of F-layer disturbances. The frequency of precipitation and corresponding disturbances is most pronounced in the South Atlantic Geomagnetic Anomaly . , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
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- Authors: Wulff, Annemarie
- Date: 1973 , 2013-10-31
- Subjects: Ionization , Electrons
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5503 , http://hdl.handle.net/10962/d1007229 , Ionization , Electrons
- Description: From Introduction: Precipitation of energetic particl es into the upper atmosphere is known to cause aurora at high latitudes. Sanae is situated in the vicinity of the South Atlantic Geomagnetic Anomaly (Gledhill and Van Rooyen (1963)) where the magnetic field intensity is very low and it is felt that this phenomenon may enhance the loss of particles from the trapping zone into the upper atmosphere. Previous work at Rhodes has shown that it is extremely likely that particle precipitation could be the cause of some ionospheric effects at Sanae. Gledhill and Torr (1966) found that a "disturbed" ionosphere at Sanae was linked with "high" fluxes of precipitated electrons in the area conjugate to Sanae. Later papers by Gledhill, Torr and Torr (1967), and Torr and Torr (1967a, 1968a) established that electrons are precipitated over a large part of the earth's surface and this phenomenon is probably responsible for an average of about 30% of F-layer disturbances. The frequency of precipitation and corresponding disturbances is most pronounced in the South Atlantic Geomagnetic Anomaly . , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
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A new model of the IO-Controlled Jovian decametric radiation
- Authors: Goertz, Christoph K
- Date: 1972
- Subjects: Jupiter (Planet) Radiation Magnetosphere Ionosphere
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5521 , http://hdl.handle.net/10962/d1012043
- Description: Jupiter, the largest planet in the solar system, is not only an emitter of thermal radiation like any other planet. Jupiter also emits relatively high-intensity non-thermal radiation in two bands, the decimetre wavelength range and the decametre wavelength range (5 MHz< f < 40 MHz). The decimetric radiation is believed to be due to synchrotron radiation of electrons trapped in a kind of Jovian "Van Allen belt". This thesis deals almost exclusively with the decametric radiation. Although the decametric radiation has been observed for 15 years since its discovery by Burke and Franklin in 1955, there is no generally accepted theoretical model of its generation to be found in the literature as yet. This is not surprising, as there are many complex and confusing aspects of the radiation. And since our knowledge of the Jovian ionosphere, magnetosphere and magnetic field is very limited indeed, every theoretical model must be based on some more or less well justified assumptions. It is, however, possible to draw some conclusions from the observed properties of the decimetric and decametric radiation. The radiation in both bands is polarized. It has been shown that at least part of the polarization is an intrinsic property of the radiation source at Jupiter, This indicates the existence of a Jovian magnetic field. The magnitude and shape of the magnetic field, however, is open to discussion, although a dipole field does seem to be a good approximation at least for large distances from Jupiter. Intro. p. 1-2.
- Full Text:
- Authors: Goertz, Christoph K
- Date: 1972
- Subjects: Jupiter (Planet) Radiation Magnetosphere Ionosphere
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5521 , http://hdl.handle.net/10962/d1012043
- Description: Jupiter, the largest planet in the solar system, is not only an emitter of thermal radiation like any other planet. Jupiter also emits relatively high-intensity non-thermal radiation in two bands, the decimetre wavelength range and the decametre wavelength range (5 MHz< f < 40 MHz). The decimetric radiation is believed to be due to synchrotron radiation of electrons trapped in a kind of Jovian "Van Allen belt". This thesis deals almost exclusively with the decametric radiation. Although the decametric radiation has been observed for 15 years since its discovery by Burke and Franklin in 1955, there is no generally accepted theoretical model of its generation to be found in the literature as yet. This is not surprising, as there are many complex and confusing aspects of the radiation. And since our knowledge of the Jovian ionosphere, magnetosphere and magnetic field is very limited indeed, every theoretical model must be based on some more or less well justified assumptions. It is, however, possible to draw some conclusions from the observed properties of the decimetric and decametric radiation. The radiation in both bands is polarized. It has been shown that at least part of the polarization is an intrinsic property of the radiation source at Jupiter, This indicates the existence of a Jovian magnetic field. The magnitude and shape of the magnetic field, however, is open to discussion, although a dipole field does seem to be a good approximation at least for large distances from Jupiter. Intro. p. 1-2.
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Diurnal and seasonal variations of the F2 region of the Antarctic ionosphere
- Authors: Williams, Morgan Howard
- Date: 1972
- Subjects: Harmonic analysis , Ionosphere -- Antarctic Ocean
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5548 , http://hdl.handle.net/10962/d1013459
- Description: [From Introduction, p. 2] The first chapter of this thesis deals with an analysis of F2 critical frequency data first for SANAE and then for eleven other Antarctic and sub-Antarctic stations covering the period 1957 to 1969. This shows certain aspects of the F2 behaviour. Some of the results of this chapter have been reported in a paper by Gledhill and Williams. The two most important mechanisms thought to be responsible for the Antarctic f₀F2 behaviour are incoming corpuscular radiation and horizontal neutral winds. These two mechanisms together with two others (the temperature theory of Torr and Torr and the semi-annual variation of neutral atmospheric density) are discussed in detail in part 2 (Chapters 2 to 4) with a view to discovering which aspects of the f₀F2 behaviour over Antarctica can be explained by each theory. An attempt is made in Part 3 (Chapters 5 and 6) to explain the observed behaviour by solving the continuity equation of the ionosphere for high-latitude stations. Finally, besides the critical frequency, another parameter of importance in explaining the behaviour in the F2 region is the height at which the F2 maximum occurs. This quantity cannot be read directly from an ionogram and it is not an easy quantity to determine. In fact the way in which it is usually obtained is by "scaling" the ionogram in question and converting the virtual heights obtained into real heights. In Part 4 (Chapter 7 and 8) an outline is given of the two computer programs which were written to perform this conversion.
- Full Text:
- Authors: Williams, Morgan Howard
- Date: 1972
- Subjects: Harmonic analysis , Ionosphere -- Antarctic Ocean
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5548 , http://hdl.handle.net/10962/d1013459
- Description: [From Introduction, p. 2] The first chapter of this thesis deals with an analysis of F2 critical frequency data first for SANAE and then for eleven other Antarctic and sub-Antarctic stations covering the period 1957 to 1969. This shows certain aspects of the F2 behaviour. Some of the results of this chapter have been reported in a paper by Gledhill and Williams. The two most important mechanisms thought to be responsible for the Antarctic f₀F2 behaviour are incoming corpuscular radiation and horizontal neutral winds. These two mechanisms together with two others (the temperature theory of Torr and Torr and the semi-annual variation of neutral atmospheric density) are discussed in detail in part 2 (Chapters 2 to 4) with a view to discovering which aspects of the f₀F2 behaviour over Antarctica can be explained by each theory. An attempt is made in Part 3 (Chapters 5 and 6) to explain the observed behaviour by solving the continuity equation of the ionosphere for high-latitude stations. Finally, besides the critical frequency, another parameter of importance in explaining the behaviour in the F2 region is the height at which the F2 maximum occurs. This quantity cannot be read directly from an ionogram and it is not an easy quantity to determine. In fact the way in which it is usually obtained is by "scaling" the ionogram in question and converting the virtual heights obtained into real heights. In Part 4 (Chapter 7 and 8) an outline is given of the two computer programs which were written to perform this conversion.
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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:
- 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).
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