Part four of the Rhodes University Skymap Program
- Authors: Wright, Michael Robert
- Date: 1989
- Subjects: Southern sky (Astronomy) Radio astronomy
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5435 , http://hdl.handle.net/10962/d1001988
- Description: The results of the fourth part of the Rhodes University Skymap Program are presented. The observations cover the area of sky between right ascension 14h00m and 02h30m and declination -26⁰ and + 13⁰ at a frequency of 2.3 GHz. Contour maps of this region, with a resolution of 0.38⁰, are presented. Various methods of reducing the effect of the Galactic disc emission are analyzed. The results demonstrate the effectiveness of one of these methods in the production of a flat base level. The filamentary structure of the North Polar Spur is enhanced and results are obtained which support current theories of the origin of this object. The HII region surrounding Ophiuchi is examined in detail. A number of parameters are derived for the HII region. The spur associated with the HII region S54 is also examined. A listing of 1105 point sources appearing in the maps is presented. The limiting flux density of this listing is 0.5 Jy
- Full Text:
- Date Issued: 1989
- Authors: Wright, Michael Robert
- Date: 1989
- Subjects: Southern sky (Astronomy) Radio astronomy
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5435 , http://hdl.handle.net/10962/d1001988
- Description: The results of the fourth part of the Rhodes University Skymap Program are presented. The observations cover the area of sky between right ascension 14h00m and 02h30m and declination -26⁰ and + 13⁰ at a frequency of 2.3 GHz. Contour maps of this region, with a resolution of 0.38⁰, are presented. Various methods of reducing the effect of the Galactic disc emission are analyzed. The results demonstrate the effectiveness of one of these methods in the production of a flat base level. The filamentary structure of the North Polar Spur is enhanced and results are obtained which support current theories of the origin of this object. The HII region surrounding Ophiuchi is examined in detail. A number of parameters are derived for the HII region. The spur associated with the HII region S54 is also examined. A listing of 1105 point sources appearing in the maps is presented. The limiting flux density of this listing is 0.5 Jy
- Full Text:
- Date Issued: 1989
The selection and evaluation of grey-level thresholds applied to digital images
- Authors: Brink, Anton David
- Date: 1988
- Subjects: Image processing -- Digital techniques
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5443 , http://hdl.handle.net/10962/d1001996
- Description: Many applications of image processing require the initial segmentation of the image by means of grey-level thresholding. In this thesis, the problems of automatic threshold selection and evaluation are addressed in order to find a universally applicable thresholding method. Three previously proposed threshold selection techniques are investigated, and two new methods are introduced. The results of applying these methods to several different images are evaluated using two threshold evaluation techniques, one subjective and one quantitative. It is found that no threshold selection technique is universally acceptable, as different methods work best with different images and applications
- Full Text:
- Date Issued: 1988
- Authors: Brink, Anton David
- Date: 1988
- Subjects: Image processing -- Digital techniques
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5443 , http://hdl.handle.net/10962/d1001996
- Description: Many applications of image processing require the initial segmentation of the image by means of grey-level thresholding. In this thesis, the problems of automatic threshold selection and evaluation are addressed in order to find a universally applicable thresholding method. Three previously proposed threshold selection techniques are investigated, and two new methods are introduced. The results of applying these methods to several different images are evaluated using two threshold evaluation techniques, one subjective and one quantitative. It is found that no threshold selection technique is universally acceptable, as different methods work best with different images and applications
- Full Text:
- Date Issued: 1988
A computer-controlled tracking system
- Authors: Oberem, Graham Edmund
- Date: 1979
- Subjects: Artificial satellites -- Tracking
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5437 , http://hdl.handle.net/10962/d1001990
- Description: A computer-controlled tracking system has been designed and constructed for the two metre antenna of the 22 GHz radio telescope at Rhodes University. The control system has been tested and its step response has been analysed with a view to response time optimization. Computer programs for tracking the sun and the moon have been written. Initial results of tracking the sun have revealed linearity and temperature stability problems. These problems have been investigated and suggestions have been made as to how they might be removed
- Full Text:
- Date Issued: 1979
- Authors: Oberem, Graham Edmund
- Date: 1979
- Subjects: Artificial satellites -- Tracking
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5437 , http://hdl.handle.net/10962/d1001990
- Description: A computer-controlled tracking system has been designed and constructed for the two metre antenna of the 22 GHz radio telescope at Rhodes University. The control system has been tested and its step response has been analysed with a view to response time optimization. Computer programs for tracking the sun and the moon have been written. Initial results of tracking the sun have revealed linearity and temperature stability problems. These problems have been investigated and suggestions have been made as to how they might be removed
- Full Text:
- Date Issued: 1979
A 22 GHz water maser radiometer
- Authors: Nunn, Brian J
- Date: 1975
- Subjects: Masers , Radiometers
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5535 , http://hdl.handle.net/10962/d1012987
- Description: This thesis describes the properties of interstellar water maser sources, and other sources near 22 GHz. Calculations based on manufacturer's specifications of the 22 GHz mixer, which was to be used in a water radiometer, and on the size antenna aperture of the proposed antenna aperture, show the viability of constructing such a radiometer for spectral line and continuum work. Various sections of the radiometer were constructed, including the Cassegrain feed system and its support, an intermediate frequency amplifier and buffer, a timing control unit, and a data processor. These units are part of the radiometer, which is almost ready for observations of sources.
- Full Text:
- Date Issued: 1975
- Authors: Nunn, Brian J
- Date: 1975
- Subjects: Masers , Radiometers
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5535 , http://hdl.handle.net/10962/d1012987
- Description: This thesis describes the properties of interstellar water maser sources, and other sources near 22 GHz. Calculations based on manufacturer's specifications of the 22 GHz mixer, which was to be used in a water radiometer, and on the size antenna aperture of the proposed antenna aperture, show the viability of constructing such a radiometer for spectral line and continuum work. Various sections of the radiometer were constructed, including the Cassegrain feed system and its support, an intermediate frequency amplifier and buffer, a timing control unit, and a data processor. These units are part of the radiometer, which is almost ready for observations of sources.
- Full Text:
- Date Issued: 1975
Ultraviolet specular reflectance, electronic absorption and the excitation of fluorescence in single crystals of anthracene
- Authors: Wright, W H
- Date: 1966
- Subjects: Anthracene crystals -- Fluorescence , Ultraviolet spectroscopy -- Absorption , Reflectance
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5544 , http://hdl.handle.net/10962/d1013366
- Description: From introduction: The Fluorescence Excitation Spectrum or anthracene is known to vary considerably with the age and condition or the crystal. This thesis represents an attempt to improve the understanding of these variations. To put the problem on a quantitative basis it was found necessary to know both the ultraviolet reflection and absorption spectra. Reports of the reflection spectrum appear to have been confined to the case of polarised incident light. In addition the reflectivity measurements are always reported for a freshly cleaved surface. For these reasons the reflectivity of anthracene for various conditions of the reflecting surface was measured with unpolarised light. These varying reflectivities were used to further knowledge of the chemical processes at the crystal surface, as well as being used directly in the calculation of fluorescence excitation spectra. Reflection spectra with a- and b- crystallographic axis polarisations were also obtained. Since such spectra are reported in the literature it was possible, by comparison, to conclude that the experimental methods used in this thesis yielded valid results. The polarised measurements were used to obtain optical constants for the crystal. In the interests of readability most of the complicated process of converting the reflectivities to optical constants is dealt with in three appendices to the thesis.
- Full Text:
- Date Issued: 1966
- Authors: Wright, W H
- Date: 1966
- Subjects: Anthracene crystals -- Fluorescence , Ultraviolet spectroscopy -- Absorption , Reflectance
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5544 , http://hdl.handle.net/10962/d1013366
- Description: From introduction: The Fluorescence Excitation Spectrum or anthracene is known to vary considerably with the age and condition or the crystal. This thesis represents an attempt to improve the understanding of these variations. To put the problem on a quantitative basis it was found necessary to know both the ultraviolet reflection and absorption spectra. Reports of the reflection spectrum appear to have been confined to the case of polarised incident light. In addition the reflectivity measurements are always reported for a freshly cleaved surface. For these reasons the reflectivity of anthracene for various conditions of the reflecting surface was measured with unpolarised light. These varying reflectivities were used to further knowledge of the chemical processes at the crystal surface, as well as being used directly in the calculation of fluorescence excitation spectra. Reflection spectra with a- and b- crystallographic axis polarisations were also obtained. Since such spectra are reported in the literature it was possible, by comparison, to conclude that the experimental methods used in this thesis yielded valid results. The polarised measurements were used to obtain optical constants for the crystal. In the interests of readability most of the complicated process of converting the reflectivities to optical constants is dealt with in three appendices to the thesis.
- Full Text:
- Date Issued: 1966
The design and construction of a recording spectrometer for the measurement of fluorescence excitation spectra in the vacuum ultra-violet region
- Authors: Davidson, A T
- Date: 1963
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:21177 , http://hdl.handle.net/10962/6761
- Description: Summary: A recording spectrometer for the measurement of fluorescence excitation spectra in the visible and ultra-violet regions of the spectrum is described. A direct method of modulating the hydrogen light source of the spectrograph is presented, whereby the discharge is driven by an A.C. power oscillator. The use of tuned amplifiers in the detecting unit is investigated as a means of eliminating the D.C. component of the dark current. Aspects of the modulation method are discussed. Fluorescence and energy transfer in aromatic hydrocarbon is discussed with particular regard to anthracene. Some absorption, fluorescence, excitation and reflection spectra of anthracene obtained by previous workers are presented9 together with Tables listing the wavelengths of principal maxima for the above spectra published in the literature. Features of the excitation spectrum of anthracene are discussed and are related to its absorption and fluorescence spectra. The role of surface effects, defects and impurities are discussed in relation to the fluorescence of anthracene. The method of A.C. detection was unable to resolve the excitation spectrum of anthracene due to the high noise level associated with the method. However, peaks in the ultra-violet region of the hydrogen molecular spectrum were recorded at a modulation frequency of 400 Kc/sec. The noise level is explained and ways of improving the signal to noise ratio of the A.C. detection system are suggested. It is concluded that D.C. detection is a simpler and more direct way of measuring excitation spectra. No modulated signals were detected when the hydrogen discharge was excited at 6·5 Mc/sec. Signals were recorded at modulation frequencies of 400 Kc/sec . The degree of modulation at 400 Kc/sec. increased with decrease in the pressure of the hydrogen discharge.
- Full Text:
- Date Issued: 1963
- Authors: Davidson, A T
- Date: 1963
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:21177 , http://hdl.handle.net/10962/6761
- Description: Summary: A recording spectrometer for the measurement of fluorescence excitation spectra in the visible and ultra-violet regions of the spectrum is described. A direct method of modulating the hydrogen light source of the spectrograph is presented, whereby the discharge is driven by an A.C. power oscillator. The use of tuned amplifiers in the detecting unit is investigated as a means of eliminating the D.C. component of the dark current. Aspects of the modulation method are discussed. Fluorescence and energy transfer in aromatic hydrocarbon is discussed with particular regard to anthracene. Some absorption, fluorescence, excitation and reflection spectra of anthracene obtained by previous workers are presented9 together with Tables listing the wavelengths of principal maxima for the above spectra published in the literature. Features of the excitation spectrum of anthracene are discussed and are related to its absorption and fluorescence spectra. The role of surface effects, defects and impurities are discussed in relation to the fluorescence of anthracene. The method of A.C. detection was unable to resolve the excitation spectrum of anthracene due to the high noise level associated with the method. However, peaks in the ultra-violet region of the hydrogen molecular spectrum were recorded at a modulation frequency of 400 Kc/sec. The noise level is explained and ways of improving the signal to noise ratio of the A.C. detection system are suggested. It is concluded that D.C. detection is a simpler and more direct way of measuring excitation spectra. No modulated signals were detected when the hydrogen discharge was excited at 6·5 Mc/sec. Signals were recorded at modulation frequencies of 400 Kc/sec . The degree of modulation at 400 Kc/sec. increased with decrease in the pressure of the hydrogen discharge.
- Full Text:
- Date Issued: 1963
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