Synthesis and photophysical behavior of axially substituted phthalocyanine, tetrabenzotriazaporphyrin, and triazatetrabenzcorrole phosphorous complexes
- Antunes, Edith M, Nyokong, Tebello
- Authors: Antunes, Edith M , Nyokong, Tebello
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/264518 , vital:53741 , xlink:href="https://doi.org/10.1142/S1088424609000048"
- Description: The synthesis of phosphorous phthalocyanines, triazatetrabenzcorroles, and tetrabenzotriazaporphyrins with a variety of axial ligands is reported. The new complexes are: phosphorous dihydroxy tetrabenzotriazaporphyrin (5, PV(OH)2TBTAP), diphenyl phosphorous phthalocyanine (6, [PV(Ph)2Pc](OH)), diphenyl phosphorous triazatetrabenzcorrole (7, PV(Ph)2TBC), and dioctyl phosphorous triazatetrabenzcorrole (8, PV(C8H17)2TBC). The complexes are not aggregated in dimethylsulfoxide (DMSO) and pyridine. Upon axial coordination of a phenyl or octyl group, the complexes are soluble (and not aggregated) in dichloromethane (DCM) and tetrahydrofuran (THF). The triplet lifetimes range from 395 to 546 μs (for complexes 5 to 8), with the P(Ph)2TBC (7) complex showing the longest triplet lifetime (546 μs), while the smallest triplet quantum yield (ΦT = 0.27) was obtained for the [P(Ph)2Pc](OH) (6) complex. [P(OH)2Pc](OH) (3) showed the shortest triplet lifetime (113 μs) and the largest triplet quantum yield (ΦT = 0.52).
- Full Text:
- Authors: Antunes, Edith M , Nyokong, Tebello
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/264518 , vital:53741 , xlink:href="https://doi.org/10.1142/S1088424609000048"
- Description: The synthesis of phosphorous phthalocyanines, triazatetrabenzcorroles, and tetrabenzotriazaporphyrins with a variety of axial ligands is reported. The new complexes are: phosphorous dihydroxy tetrabenzotriazaporphyrin (5, PV(OH)2TBTAP), diphenyl phosphorous phthalocyanine (6, [PV(Ph)2Pc](OH)), diphenyl phosphorous triazatetrabenzcorrole (7, PV(Ph)2TBC), and dioctyl phosphorous triazatetrabenzcorrole (8, PV(C8H17)2TBC). The complexes are not aggregated in dimethylsulfoxide (DMSO) and pyridine. Upon axial coordination of a phenyl or octyl group, the complexes are soluble (and not aggregated) in dichloromethane (DCM) and tetrahydrofuran (THF). The triplet lifetimes range from 395 to 546 μs (for complexes 5 to 8), with the P(Ph)2TBC (7) complex showing the longest triplet lifetime (546 μs), while the smallest triplet quantum yield (ΦT = 0.27) was obtained for the [P(Ph)2Pc](OH) (6) complex. [P(OH)2Pc](OH) (3) showed the shortest triplet lifetime (113 μs) and the largest triplet quantum yield (ΦT = 0.52).
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Synthesis, photophysical and nonlinear optical properties of microwave synthesized 4-tetra and octa-substituted lead phthalocyanines
- Modibane, Desmond K, Nyokong, Tebello
- Authors: Modibane, Desmond K , Nyokong, Tebello
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/263452 , vital:53629 , xlink:href="https://doi.org/10.1016/j.poly.2009.03.013"
- Description: This work presents the photophysical and nonlinear optical behaviour of newly synthesized complexes: 2,(3)-tetrakis(4-benzyloxyphenoxyphthalocyaninato) lead (5a) and 2,3-octakis(4-benzyloxyphenoxyphthalocyaninato) lead (6a). The nonlinear optical behaviour of complexes 5a and 6a are compared with those of 2,(3)-tetraphenoxyphthalocyaninato lead (5b), 2,(3)-tetrakis(4-t-butylphenoxyphthalocyaninato) lead (5c), 2,3-octaphenoxyphthalocyaninato lead (6b) and 2,3-octakis(4-t-butylphenoxyphthalocyaninato) lead (6c). The synthesis of 5a and 6a was performed using microwave irradiation. Photophysical properties were studied for these complexes in dimethylsulfoxide, dimethylformamide, toluene, tetrahydrofuran and chloroform. The fluorescence spectra were different from excitation spectra due to demetallation upon excitation. High triplet quantum yields ranging from 0.80 to 0.86 (in DMSO, DMF and toluene) and low triplet lifetimes (20–50 μs in DMSO, and more than 10 μs in the rest of the solvents) were observed due to the presence of heavy atom. Nonlinear optical properties were studied in dimethylsulfoxide. The optical limiting threshold intensity (Ilim) for the PbPc derivatives were calculated and ranged from 2.1 to 6.6 W/cm2.
- Full Text:
- Authors: Modibane, Desmond K , Nyokong, Tebello
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/263452 , vital:53629 , xlink:href="https://doi.org/10.1016/j.poly.2009.03.013"
- Description: This work presents the photophysical and nonlinear optical behaviour of newly synthesized complexes: 2,(3)-tetrakis(4-benzyloxyphenoxyphthalocyaninato) lead (5a) and 2,3-octakis(4-benzyloxyphenoxyphthalocyaninato) lead (6a). The nonlinear optical behaviour of complexes 5a and 6a are compared with those of 2,(3)-tetraphenoxyphthalocyaninato lead (5b), 2,(3)-tetrakis(4-t-butylphenoxyphthalocyaninato) lead (5c), 2,3-octaphenoxyphthalocyaninato lead (6b) and 2,3-octakis(4-t-butylphenoxyphthalocyaninato) lead (6c). The synthesis of 5a and 6a was performed using microwave irradiation. Photophysical properties were studied for these complexes in dimethylsulfoxide, dimethylformamide, toluene, tetrahydrofuran and chloroform. The fluorescence spectra were different from excitation spectra due to demetallation upon excitation. High triplet quantum yields ranging from 0.80 to 0.86 (in DMSO, DMF and toluene) and low triplet lifetimes (20–50 μs in DMSO, and more than 10 μs in the rest of the solvents) were observed due to the presence of heavy atom. Nonlinear optical properties were studied in dimethylsulfoxide. The optical limiting threshold intensity (Ilim) for the PbPc derivatives were calculated and ranged from 2.1 to 6.6 W/cm2.
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Synthesis, photophysical and photochemical properties of novel soluble tetra [4-(thiophen-3yl)-phenoxy] phthalocyaninato zinc (II) and Ti (IV) O complexes
- Erdoğmuş, Ali, Nyokong, Tebello
- Authors: Erdoğmuş, Ali , Nyokong, Tebello
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/263318 , vital:53617 , xlink:href="https://doi.org/10.1016/j.ica.2009.07.015"
- Description: The synthesis, photophysical and photochemical properties of zinc and oxo-titanium phthalocyanine derivatives 4-(tetra[4-(thiophen-3yl)-phenoxy]phthalocyaninato)zinc(II), (2); and 4-(tetra[4-(thiophen-3yl)-phenoxy]phthalocyaninato)oxo-titanium(IV), (3), are described for the first time. These peripherally substituted complexes (2 and 3) have been synthesized and characterized by elemental analysis, IR, 1H NMR and electronic spectroscopy. The compounds (2 and 3) have good solubility in organic solvents such as CHCl3, DCM, DMSO, DMF, THF and toluene and are not aggregated within a wide concentration range. General trends are described for singlet oxygen, photodegradation, fluorescence quantum yields, triplet quantum yields and triplet life times of these complexes in DMSO, DMF and THF. Compound 2 has higher fluorescence quantum yields, triplet quantum yields and triplet life times than 3, however, the former has lower singlet oxygen quantum yields and photodegradation quantum yields than the latter.
- Full Text:
- Authors: Erdoğmuş, Ali , Nyokong, Tebello
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/263318 , vital:53617 , xlink:href="https://doi.org/10.1016/j.ica.2009.07.015"
- Description: The synthesis, photophysical and photochemical properties of zinc and oxo-titanium phthalocyanine derivatives 4-(tetra[4-(thiophen-3yl)-phenoxy]phthalocyaninato)zinc(II), (2); and 4-(tetra[4-(thiophen-3yl)-phenoxy]phthalocyaninato)oxo-titanium(IV), (3), are described for the first time. These peripherally substituted complexes (2 and 3) have been synthesized and characterized by elemental analysis, IR, 1H NMR and electronic spectroscopy. The compounds (2 and 3) have good solubility in organic solvents such as CHCl3, DCM, DMSO, DMF, THF and toluene and are not aggregated within a wide concentration range. General trends are described for singlet oxygen, photodegradation, fluorescence quantum yields, triplet quantum yields and triplet life times of these complexes in DMSO, DMF and THF. Compound 2 has higher fluorescence quantum yields, triplet quantum yields and triplet life times than 3, however, the former has lower singlet oxygen quantum yields and photodegradation quantum yields than the latter.
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Synthesis, photophysical and photochemical properties of octa-substituted antimony phthalocyanines
- Modibane, Desmond Kwena, Nyokong, Tebello
- Authors: Modibane, Desmond Kwena , Nyokong, Tebello
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/264226 , vital:53711 , xlink:href="https://doi.org/10.1016/j.poly.2008.11.052"
- Description: This work reports on the synthesis and photophysicochemical parameters of unsubstituted [SbIIIPc]+I3- and octa-phenoxy ([SbIIIOPPc]+I3-) and -4-t-butylphenoxy ([SbIIIOTBPPc]+I3-) substituted antimony phthalocyanines. Photophysical and photochemical properties were studied for these complexes in dimethylsulfoxide, dimethylformamide and toluene. The excitation spectra of oxidized antimony (Sb(V)Pc) derivates were similar to absorption spectra. Low fluorescence quantum yields, high triplet quantum yields and low triplet lifetimes were observed as the result of heavy atom (antimony ion).
- Full Text:
- Authors: Modibane, Desmond Kwena , Nyokong, Tebello
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/264226 , vital:53711 , xlink:href="https://doi.org/10.1016/j.poly.2008.11.052"
- Description: This work reports on the synthesis and photophysicochemical parameters of unsubstituted [SbIIIPc]+I3- and octa-phenoxy ([SbIIIOPPc]+I3-) and -4-t-butylphenoxy ([SbIIIOTBPPc]+I3-) substituted antimony phthalocyanines. Photophysical and photochemical properties were studied for these complexes in dimethylsulfoxide, dimethylformamide and toluene. The excitation spectra of oxidized antimony (Sb(V)Pc) derivates were similar to absorption spectra. Low fluorescence quantum yields, high triplet quantum yields and low triplet lifetimes were observed as the result of heavy atom (antimony ion).
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Synthesis, photophysical and photochemical studies of water soluble cationic zinc phthalocyanine derivatives
- Idowu, Mopelola, Nyokong, Tebello
- Authors: Idowu, Mopelola , Nyokong, Tebello
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/264245 , vital:53712 , xlink:href="https://doi.org/10.1016/j.poly.2008.11.021"
- Description: Peripherally and non-peripherally 2-diethylaminoethanethiol tetra-substituted zinc phthalocyanine (5a and 6a) and their quaternized derivatives (5b and 6b) have been synthesized and characterized. The quaternized derivatives (5b and 6b) show excellent solubility in aqueous medium. The photophysical and photochemical properties of the 2-diethylaminoethanethiol appended zinc phthalocyanine in dimethylsulfoxide (DMSO) for the non-ionic (5a and 6a) and in both DMSO and aqueous medium (phosphate buffered saline solution PBS, pH 7.4) (in the presence and absence of cremophore EL (CEL)) for the quaternized (5b and 6b) derivatives were studied and compared with that of the peripherally octa-substituted derivatives (7a and 7b). The complexes have intense absorption in the visible/near-IR region though the quaternized forms (5b, 6b and 7b) were slightly blue shifted and highly aggregate in aqueous solution. The triplet state quantum yields (ΦT) and the triplet lifetimes (τT) were found to be higher in DMSO (ΦT values ranged from 0.57 to 0.75 while τT values ranged from 190 to 220 μs in DMSO for all complexes) compared to aqueous medium (ΦT values ranged from 0.15 to 0.17 while τT values ranged from 20 to 70 μs in pH 7.4 buffer). Addition of cremophore EL in aqueous solution resulted in induced disaggregation leading to increased ΦT and τT.
- Full Text:
- Authors: Idowu, Mopelola , Nyokong, Tebello
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/264245 , vital:53712 , xlink:href="https://doi.org/10.1016/j.poly.2008.11.021"
- Description: Peripherally and non-peripherally 2-diethylaminoethanethiol tetra-substituted zinc phthalocyanine (5a and 6a) and their quaternized derivatives (5b and 6b) have been synthesized and characterized. The quaternized derivatives (5b and 6b) show excellent solubility in aqueous medium. The photophysical and photochemical properties of the 2-diethylaminoethanethiol appended zinc phthalocyanine in dimethylsulfoxide (DMSO) for the non-ionic (5a and 6a) and in both DMSO and aqueous medium (phosphate buffered saline solution PBS, pH 7.4) (in the presence and absence of cremophore EL (CEL)) for the quaternized (5b and 6b) derivatives were studied and compared with that of the peripherally octa-substituted derivatives (7a and 7b). The complexes have intense absorption in the visible/near-IR region though the quaternized forms (5b, 6b and 7b) were slightly blue shifted and highly aggregate in aqueous solution. The triplet state quantum yields (ΦT) and the triplet lifetimes (τT) were found to be higher in DMSO (ΦT values ranged from 0.57 to 0.75 while τT values ranged from 190 to 220 μs in DMSO for all complexes) compared to aqueous medium (ΦT values ranged from 0.15 to 0.17 while τT values ranged from 20 to 70 μs in pH 7.4 buffer). Addition of cremophore EL in aqueous solution resulted in induced disaggregation leading to increased ΦT and τT.
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Synthesis, photophysics and photochemistry of novel tetra (quinoxalinyl) phthalocyaninato zinc (II) complexes
- Erdoğmuş, Ali, Ogunsipe, Abimbola, Nyokong, Tebello
- Authors: Erdoğmuş, Ali , Ogunsipe, Abimbola , Nyokong, Tebello
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/263441 , vital:53628 , xlink:href="https://doi.org/10.1016/j.jphotochem.2009.04.007"
- Description: The syntheses and spectral, photophysical and photochemical properties of some zinc phthalocyanine derivatives – {2, (3)-tetra(quinoxalinyl)phthalocyaninato zinc(II), (β-ZnPc) and 1, (4)-tetra(quinoxalinyl)phthalocyaninato zinc(II), (α-ZnPc)} – are presented. The β-substituted complex is more fluorescent and exhibits lower tendencies to undergo intersystem crossing than its α-substituted counterpart, as judged by the former's higher fluorescence quantum yield (ΦF) and lower triplet quantum yield (ΦT) than the latter's in three solvents (DMSO, DMF and toluene). Singlet oxygen quantum yield (ΦΔ) values show the same trends as ΦT values. The differences in the spectral and photophysical properties of α-ZnPc and β-ZnPc are partly attributed to greater molecular distortions in the former. Studies of the interaction of the triplet states of α-ZnPc and β-ZnPc with triplet oxygen showed that α-ZnPc is more vulnerable to oxygen quenching than β-ZnPc. Also, the smallest quenching rate constants were observed in DMSO, which is attributed to the higher viscosity of DMSO than DMF and toluene.
- Full Text:
- Authors: Erdoğmuş, Ali , Ogunsipe, Abimbola , Nyokong, Tebello
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/263441 , vital:53628 , xlink:href="https://doi.org/10.1016/j.jphotochem.2009.04.007"
- Description: The syntheses and spectral, photophysical and photochemical properties of some zinc phthalocyanine derivatives – {2, (3)-tetra(quinoxalinyl)phthalocyaninato zinc(II), (β-ZnPc) and 1, (4)-tetra(quinoxalinyl)phthalocyaninato zinc(II), (α-ZnPc)} – are presented. The β-substituted complex is more fluorescent and exhibits lower tendencies to undergo intersystem crossing than its α-substituted counterpart, as judged by the former's higher fluorescence quantum yield (ΦF) and lower triplet quantum yield (ΦT) than the latter's in three solvents (DMSO, DMF and toluene). Singlet oxygen quantum yield (ΦΔ) values show the same trends as ΦT values. The differences in the spectral and photophysical properties of α-ZnPc and β-ZnPc are partly attributed to greater molecular distortions in the former. Studies of the interaction of the triplet states of α-ZnPc and β-ZnPc with triplet oxygen showed that α-ZnPc is more vulnerable to oxygen quenching than β-ZnPc. Also, the smallest quenching rate constants were observed in DMSO, which is attributed to the higher viscosity of DMSO than DMF and toluene.
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The both-and edition:
- Authors: Garman, Anthea
- Date: 2009
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/158817 , vital:40231 , https://hdl.handle.net/10520/EJC139955
- Description: I was driving down the N2 from Cape Town towards the airport recently and scanning the turn-offs for Vanguard Drive, when suddenly I noticed among the shacks that line the road some really interesting buildings. These were not the pale pink matchboxes that periodically spring up in rows alongside the derelict housing that millions of South Africans call home. They were multi-levelled, had large windows and looked like an architect might have had something to do with them. I was heartened at the sight of housing – at last – with humanity in mind. But as I reread the 2010 pieces in this edition, I’m reminded by Jane Duncan in particular (“Whose World Cup?” page 23) that prettifying the ghastly spaces in our world cup cities that will be visible to those international tourists is high on the agenda for our government. But then, I reason, at least someone will benefit from living along the noisy and congested airport route!.
- Full Text:
- Authors: Garman, Anthea
- Date: 2009
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/158817 , vital:40231 , https://hdl.handle.net/10520/EJC139955
- Description: I was driving down the N2 from Cape Town towards the airport recently and scanning the turn-offs for Vanguard Drive, when suddenly I noticed among the shacks that line the road some really interesting buildings. These were not the pale pink matchboxes that periodically spring up in rows alongside the derelict housing that millions of South Africans call home. They were multi-levelled, had large windows and looked like an architect might have had something to do with them. I was heartened at the sight of housing – at last – with humanity in mind. But as I reread the 2010 pieces in this edition, I’m reminded by Jane Duncan in particular (“Whose World Cup?” page 23) that prettifying the ghastly spaces in our world cup cities that will be visible to those international tourists is high on the agenda for our government. But then, I reason, at least someone will benefit from living along the noisy and congested airport route!.
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The challenges of education and development in twenty-first century South Africa
- Authors: Badat, Saleem
- Date: 2009
- Language: English
- Type: Conference paper , text
- Identifier: vital:7121 , http://hdl.handle.net/10962/d1006569
- Description: From the introduction: I have chosen to address the theme of The Challenges of Education and Development in the Twenty First Century. This is not only an extremely important theme but also one that is both complex and broad and can be approached in many different ways. With respect to complexity, the concepts of education and development, like the concepts of freedom and democracy, are defined in various ways and have a variety of meanings associated with them. Moreover, notions of education and development are not neutral in that they are embedded in different views of the world and society, including views on what constitutes a just and good society. Further, the choices, policies, actions and practices that are associated with particular conceptions of education and development are not benign in that they have real and differential effects on different social classes and groups in society. , Keynote Address at the 15th Annual Conference of the Headmasters of the Traditional State Boy’s Schools of South Africa’ Queens College, Queenstown, 26 August 2009.
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- Authors: Badat, Saleem
- Date: 2009
- Language: English
- Type: Conference paper , text
- Identifier: vital:7121 , http://hdl.handle.net/10962/d1006569
- Description: From the introduction: I have chosen to address the theme of The Challenges of Education and Development in the Twenty First Century. This is not only an extremely important theme but also one that is both complex and broad and can be approached in many different ways. With respect to complexity, the concepts of education and development, like the concepts of freedom and democracy, are defined in various ways and have a variety of meanings associated with them. Moreover, notions of education and development are not neutral in that they are embedded in different views of the world and society, including views on what constitutes a just and good society. Further, the choices, policies, actions and practices that are associated with particular conceptions of education and development are not benign in that they have real and differential effects on different social classes and groups in society. , Keynote Address at the 15th Annual Conference of the Headmasters of the Traditional State Boy’s Schools of South Africa’ Queens College, Queenstown, 26 August 2009.
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The evaluation of Eudragit microcapsules manufactured by solvent evaporation using USP Apparatus 1
- Khamanga, Sandile M, Parfitt, Natalie R, Nyamuzhiwa, Tsitsi, Haidula, Hendrina, Walker, Roderick B
- Authors: Khamanga, Sandile M , Parfitt, Natalie R , Nyamuzhiwa, Tsitsi , Haidula, Hendrina , Walker, Roderick B
- Date: 2009
- Language: English
- Type: text , Article
- Identifier: vital:6389 , http://hdl.handle.net/10962/d1006310
- Description: The objectives of this study were to prepare microcapsules containing verapamil and propranolol and to evaluate the kinetics and mechanism of drug release from the microcapsules using USP Apparatus 1. The effects of polymer concentration and polymer type on the cumulative amount of drug released were evaluated. The microcapsules were manufactured using Eudragit RS and RL polymers by solvent evaporation with the ultimate aim of prolonging drug release. Twenty-four formulations were prepared using different drug/polymer ratios. The effects of polymer type and polymer/drug ratios on the size, flow properties, surface morphology, and the release characteristics of the microcapsules were examined. The effects of drug inclusion methods on drug loading, encapsulation efficiency, and release properties of the complex microcapsules were also investigated. The formulations containing drug/polymer ratio 1:4 (w/w) were the most appropriate with respect to encapsulation efficiency (70%), flow properties (HR = 1.2), drug loading (15–20%), and drug release characteristics, in all cases. The release kinetics from the different formulations followed mainly a diffusion-controlled mechanism.
- Full Text:
- Authors: Khamanga, Sandile M , Parfitt, Natalie R , Nyamuzhiwa, Tsitsi , Haidula, Hendrina , Walker, Roderick B
- Date: 2009
- Language: English
- Type: text , Article
- Identifier: vital:6389 , http://hdl.handle.net/10962/d1006310
- Description: The objectives of this study were to prepare microcapsules containing verapamil and propranolol and to evaluate the kinetics and mechanism of drug release from the microcapsules using USP Apparatus 1. The effects of polymer concentration and polymer type on the cumulative amount of drug released were evaluated. The microcapsules were manufactured using Eudragit RS and RL polymers by solvent evaporation with the ultimate aim of prolonging drug release. Twenty-four formulations were prepared using different drug/polymer ratios. The effects of polymer type and polymer/drug ratios on the size, flow properties, surface morphology, and the release characteristics of the microcapsules were examined. The effects of drug inclusion methods on drug loading, encapsulation efficiency, and release properties of the complex microcapsules were also investigated. The formulations containing drug/polymer ratio 1:4 (w/w) were the most appropriate with respect to encapsulation efficiency (70%), flow properties (HR = 1.2), drug loading (15–20%), and drug release characteristics, in all cases. The release kinetics from the different formulations followed mainly a diffusion-controlled mechanism.
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The formation of self-assembled monolayers of thiophthalocyanine complexes of titanium, vanadium and manganese and their use in l-cysteine electrocatalysis
- Mbambisa, Gcineka, Nombona, Nolwazi, Nyokong, Tebello
- Authors: Mbambisa, Gcineka , Nombona, Nolwazi , Nyokong, Tebello
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/263375 , vital:53622 , xlink:href="https://doi.org/10.1016/j.microc.2009.04.009"
- Description: Self-assembled monolayers (SAMs) based on octapentylthiophthalocyanine complexes of oxovanadium (IV) (OVOPThPc), titanium(IV) (OTiOPThPc), and manganese (III) acetate (AcMnOPThPc), and of tetraphenylthiophthalocyanine complexes of hydroxo manganese(III) (OHMnTPPc) and oxotitanium(IV) (OTiTPPc) are described. The oxidation of l-cysteine was observed at potentials which ranged from 0.52 V to 0.67 V. The detection limits for l-cysteine analysis were of the order of 10− 7 to 10− 6 M.
- Full Text:
- Authors: Mbambisa, Gcineka , Nombona, Nolwazi , Nyokong, Tebello
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/263375 , vital:53622 , xlink:href="https://doi.org/10.1016/j.microc.2009.04.009"
- Description: Self-assembled monolayers (SAMs) based on octapentylthiophthalocyanine complexes of oxovanadium (IV) (OVOPThPc), titanium(IV) (OTiOPThPc), and manganese (III) acetate (AcMnOPThPc), and of tetraphenylthiophthalocyanine complexes of hydroxo manganese(III) (OHMnTPPc) and oxotitanium(IV) (OTiTPPc) are described. The oxidation of l-cysteine was observed at potentials which ranged from 0.52 V to 0.67 V. The detection limits for l-cysteine analysis were of the order of 10− 7 to 10− 6 M.
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The influence of cellular phone "speak" on isiXhosa rules of communication
- Kaschula, Russell H, Mostert, André
- Authors: Kaschula, Russell H , Mostert, André
- Date: 2009
- Subjects: Cell phones -- South Africa , Communication and culture -- Technological innovations , Language and culture -- South Africa , Xhosa (African people) -- Social life and customs
- Language: English
- Type: article , text
- Identifier: http://hdl.handle.net/10962/59401 , vital:27594 , doi: 10.5842/37-0-43
- Description: Cellular telephones have revolutionised the art of communication across all societies, and South Africa is no exception. Access to this form of communication has made personal contact easier, in both rural and urban contexts. Globally this form of communication has been readily embraced. However, cultural rules that pertain to face-to-face communication are often flouted by cellular phone users. This flouting holds true no doubt across many cultures, languages and contexts. Bloomer (2005:97-100) assesses this flouting of cultural maxims in relation to Grice's cooperative principle. This article attempts to assess how general rules of politeness in isiXhosa have been and are being transformed by what could be termed the "economics of speaking".
- Full Text:
- Authors: Kaschula, Russell H , Mostert, André
- Date: 2009
- Subjects: Cell phones -- South Africa , Communication and culture -- Technological innovations , Language and culture -- South Africa , Xhosa (African people) -- Social life and customs
- Language: English
- Type: article , text
- Identifier: http://hdl.handle.net/10962/59401 , vital:27594 , doi: 10.5842/37-0-43
- Description: Cellular telephones have revolutionised the art of communication across all societies, and South Africa is no exception. Access to this form of communication has made personal contact easier, in both rural and urban contexts. Globally this form of communication has been readily embraced. However, cultural rules that pertain to face-to-face communication are often flouted by cellular phone users. This flouting holds true no doubt across many cultures, languages and contexts. Bloomer (2005:97-100) assesses this flouting of cultural maxims in relation to Grice's cooperative principle. This article attempts to assess how general rules of politeness in isiXhosa have been and are being transformed by what could be termed the "economics of speaking".
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The role of higher education in society: valuing higher education
- Authors: Badat, Saleem
- Date: 2009
- Language: English
- Type: Conference paper , text
- Identifier: vital:7122 , http://hdl.handle.net/10962/d1006571
- Description: From the introduction: Arthur E. Levine, President of the Teachers College of Columbia University, writes that "In the early years of the Industrial Revolution, the Yale Report of 1828 asked whether the needs of a changing society required either major or minor changes in higher education. The report concluded that it had asked the wrong question. The right question was, What is the purpose of higher education?" Levine goes on to add that questions related to higher education “have their deepest roots in that fundamental question” and that “faced with a society in motion, we must not only ask that question again, but must actively pursue answers, if our colleges and universities are to retain their vitality in a dramatically different world”. I propose to speak about three issues: the first is about our changing world; the second is about the three purposes of higher education; the third is about what I consider to be the five key roles of higher education. Finally, I want to conclude by making some observations on the sometimes unrealistic expectations of higher education. , HERS‐SA Academy 2009, University of Cape Town Graduate School of Business, Waterfront, Cape Town, 14 September 2009. Stagnant universities are expensive and ineffectual monuments to a status quo which is more likely to be a status quo ante, yesterday’s world preserved in aspic (Ralf Dahrendorf, 2000:106‐7)
- Full Text:
- Authors: Badat, Saleem
- Date: 2009
- Language: English
- Type: Conference paper , text
- Identifier: vital:7122 , http://hdl.handle.net/10962/d1006571
- Description: From the introduction: Arthur E. Levine, President of the Teachers College of Columbia University, writes that "In the early years of the Industrial Revolution, the Yale Report of 1828 asked whether the needs of a changing society required either major or minor changes in higher education. The report concluded that it had asked the wrong question. The right question was, What is the purpose of higher education?" Levine goes on to add that questions related to higher education “have their deepest roots in that fundamental question” and that “faced with a society in motion, we must not only ask that question again, but must actively pursue answers, if our colleges and universities are to retain their vitality in a dramatically different world”. I propose to speak about three issues: the first is about our changing world; the second is about the three purposes of higher education; the third is about what I consider to be the five key roles of higher education. Finally, I want to conclude by making some observations on the sometimes unrealistic expectations of higher education. , HERS‐SA Academy 2009, University of Cape Town Graduate School of Business, Waterfront, Cape Town, 14 September 2009. Stagnant universities are expensive and ineffectual monuments to a status quo which is more likely to be a status quo ante, yesterday’s world preserved in aspic (Ralf Dahrendorf, 2000:106‐7)
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The syntheses, characterization and fluorescence spectra of novel, octakis (alkylthiophthalocyanato) nickel (II) and palladium (II) complexes
- Ogunbayo, Taofeek Babatunde, Ogunsipe, Abimbola, Nyokong, Tebello
- Authors: Ogunbayo, Taofeek Babatunde , Ogunsipe, Abimbola , Nyokong, Tebello
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/263386 , vital:53623 , xlink:href="https://doi.org/10.1016/j.dyepig.2009.03.009"
- Description: The syntheses, characterization and fluorescence studies of several {octakis(alkylthio)phthalocyanato} palladium(II) and nickel(II) complexes are presented. The absorption spectra of some of the complexes showed extra peaks which are attributable to non-planar distortion, the extent of which, was found to dependent on alkyl chain length. The fluorescence excitation spectra of the nickel(II) derivatives were not in agreement with their absorption spectra, owing to structural changes upon excitation. Fluorescence quantum yields were very low (more than 1%) for all complexes as a consequence of the open-shell electronic structures of nickel(II) and palladium(II).
- Full Text:
- Authors: Ogunbayo, Taofeek Babatunde , Ogunsipe, Abimbola , Nyokong, Tebello
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/263386 , vital:53623 , xlink:href="https://doi.org/10.1016/j.dyepig.2009.03.009"
- Description: The syntheses, characterization and fluorescence studies of several {octakis(alkylthio)phthalocyanato} palladium(II) and nickel(II) complexes are presented. The absorption spectra of some of the complexes showed extra peaks which are attributable to non-planar distortion, the extent of which, was found to dependent on alkyl chain length. The fluorescence excitation spectra of the nickel(II) derivatives were not in agreement with their absorption spectra, owing to structural changes upon excitation. Fluorescence quantum yields were very low (more than 1%) for all complexes as a consequence of the open-shell electronic structures of nickel(II) and palladium(II).
- Full Text:
The synthesis and photophysicochemical behaviour of novel water-soluble cationic indium (III) phthalocyanine
- Durmus, Mahmut, Erdoğmuş, Ali, Ogunsipe, Abimbola, Nyokong, Tebello
- Authors: Durmus, Mahmut , Erdoğmuş, Ali , Ogunsipe, Abimbola , Nyokong, Tebello
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/263419 , vital:53626 , xlink:href="https://doi.org/10.1016/j.dyepig.2009.01.008"
- Description: The syntheses and characterization of 2,3-octakis-(3-pyridyloxyphthalocyaninato) indium(III) and quaternized 2,3-octakis-(3-pyridyloxyphthalocyaninato) indium(III) are described. The ground state electronic absorption spectra, photophysics and photochemistry of both dyes in DMSO as well as that of the quaternized compound in aqueous solution are also presented. A comparison of the photophysical and photochemical parameters of the two dyes revealed that quaternized 2,3-octakis-(3-pyridyloxyphthalocyaninato) indium(III) was a better photosensitizer than its unquaternized counterpart. The quantum yield values of fluorescence (ΦF), triplet state formation (ΦT) and singlet oxygen formation (ΦΔ) for the cationic dye were found to be 0.03, 0.68 and 0.66 respectively in DMSO; these values were higher than those for 2,3-octakis-(3-pyridyloxyphthalocyaninato) indium(III), which exhibited values of 0.02, 0.66 and 0.63, respectively in DMSO. The values for the cationic dye in aq. solution were 0.02, 0.59 and 0.56 respectively, suggesting that the water-soluble quaternized 2,3-octakis-(3-pyridyloxyphthalocyaninato) indium(III) offers potential as a photosensitizer in photodynamic therapy treatment.
- Full Text:
- Authors: Durmus, Mahmut , Erdoğmuş, Ali , Ogunsipe, Abimbola , Nyokong, Tebello
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/263419 , vital:53626 , xlink:href="https://doi.org/10.1016/j.dyepig.2009.01.008"
- Description: The syntheses and characterization of 2,3-octakis-(3-pyridyloxyphthalocyaninato) indium(III) and quaternized 2,3-octakis-(3-pyridyloxyphthalocyaninato) indium(III) are described. The ground state electronic absorption spectra, photophysics and photochemistry of both dyes in DMSO as well as that of the quaternized compound in aqueous solution are also presented. A comparison of the photophysical and photochemical parameters of the two dyes revealed that quaternized 2,3-octakis-(3-pyridyloxyphthalocyaninato) indium(III) was a better photosensitizer than its unquaternized counterpart. The quantum yield values of fluorescence (ΦF), triplet state formation (ΦT) and singlet oxygen formation (ΦΔ) for the cationic dye were found to be 0.03, 0.68 and 0.66 respectively in DMSO; these values were higher than those for 2,3-octakis-(3-pyridyloxyphthalocyaninato) indium(III), which exhibited values of 0.02, 0.66 and 0.63, respectively in DMSO. The values for the cationic dye in aq. solution were 0.02, 0.59 and 0.56 respectively, suggesting that the water-soluble quaternized 2,3-octakis-(3-pyridyloxyphthalocyaninato) indium(III) offers potential as a photosensitizer in photodynamic therapy treatment.
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The synthesis and photophysicochemical properties of low-symmetry zinc phthalocyanine analogues
- Chidawanyika, Wadzanai J U, Nyokong, Tebello
- Authors: Chidawanyika, Wadzanai J U , Nyokong, Tebello
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/263397 , vital:53624 , xlink:href="https://doi.org/10.1016/j.jphotochem.2009.06.005"
- Description: The synthesis of a low-symmetry derivative, zinc mono-carboxy substituted phthalocyanine, ZnPc-COOH (4) has been reported. The photochemical and photophysical properties of ZnPc-COOH (4), ZnTMPyPc (5), ZnttbPc (6) and a previously synthesized low-symmetry derivative, ZnttbIPc (7), in various organic solvents are reported. The red-shifting of the spectra of 4 and 5 (relative to that of unsubstituted zinc phthalocyanine, ZnPc) is a function of the electron-donating sulfur-containing substituents attached to the periphery of the molecule. High triplet quantum yields (ФT) generally occur in response to substitution on the zinc phthalocyanine ring periphery. The highest ФT values and triplet lifetimes (τT) occur in DMSO for all derivatives as a result of the solvent's high viscosity. The strongly electron-withdrawing imido fused ring of ZnttbIPc (7) stabilizes it against photo-oxidative degradation relative to the other derivatives.
- Full Text:
- Authors: Chidawanyika, Wadzanai J U , Nyokong, Tebello
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/263397 , vital:53624 , xlink:href="https://doi.org/10.1016/j.jphotochem.2009.06.005"
- Description: The synthesis of a low-symmetry derivative, zinc mono-carboxy substituted phthalocyanine, ZnPc-COOH (4) has been reported. The photochemical and photophysical properties of ZnPc-COOH (4), ZnTMPyPc (5), ZnttbPc (6) and a previously synthesized low-symmetry derivative, ZnttbIPc (7), in various organic solvents are reported. The red-shifting of the spectra of 4 and 5 (relative to that of unsubstituted zinc phthalocyanine, ZnPc) is a function of the electron-donating sulfur-containing substituents attached to the periphery of the molecule. High triplet quantum yields (ФT) generally occur in response to substitution on the zinc phthalocyanine ring periphery. The highest ФT values and triplet lifetimes (τT) occur in DMSO for all derivatives as a result of the solvent's high viscosity. The strongly electron-withdrawing imido fused ring of ZnttbIPc (7) stabilizes it against photo-oxidative degradation relative to the other derivatives.
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The synthesis, cyclic voltammetry and spectroelectrochemical studies of Co (II) phthalocyanines tetra-substituted at the α and β positions with phenylthio groups
- Nombona, Nolwazi, Nyokong, Tebello
- Authors: Nombona, Nolwazi , Nyokong, Tebello
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/264529 , vital:53742 , xlink:href="https://doi.org/10.1016/j.dyepig.2008.06.002"
- Description: Non-peripherally substituted cobalt 1,(4)-(tetraphenylthiophthalocyaninato) and peripherally substituted cobalt 2,(3)-(tetraphenylthiophthalocyaninato) complexes were synthesized. Redox processes were observed at E1/2 = −1.44 V (I), −0.39 V (II), +0.37 V (III), +0.78 V (IV) and 1.15 V (V) for the non-peripherally substituted and at E1/2 = −1.42 V (I), −0.57, −0.39 V (II), +0.27 V (III), +0.79 V (IV) and +1.10 V (V) for the peripherally substituted complexes, respectively. The couples were assigned to CoIPc−2/CoIPc−3 (I), CoIIPc−2/CoIPc−2 (II), CoIIIPc−2/CoIIPc−2 (III), and CoIIIPc−1/CoIIIPc−2 (IV) using spectroelectrochemistry. The last process (V) could not be ascertained by spectroelectrochemistry but is associated with ring oxidation. Upon reduction or oxidation, the Q band of the non-peripherally substituted complex became less red shifted compared to that of its peripherally substituted counterpart.
- Full Text:
- Authors: Nombona, Nolwazi , Nyokong, Tebello
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/264529 , vital:53742 , xlink:href="https://doi.org/10.1016/j.dyepig.2008.06.002"
- Description: Non-peripherally substituted cobalt 1,(4)-(tetraphenylthiophthalocyaninato) and peripherally substituted cobalt 2,(3)-(tetraphenylthiophthalocyaninato) complexes were synthesized. Redox processes were observed at E1/2 = −1.44 V (I), −0.39 V (II), +0.37 V (III), +0.78 V (IV) and 1.15 V (V) for the non-peripherally substituted and at E1/2 = −1.42 V (I), −0.57, −0.39 V (II), +0.27 V (III), +0.79 V (IV) and +1.10 V (V) for the peripherally substituted complexes, respectively. The couples were assigned to CoIPc−2/CoIPc−3 (I), CoIIPc−2/CoIPc−2 (II), CoIIIPc−2/CoIIPc−2 (III), and CoIIIPc−1/CoIIIPc−2 (IV) using spectroelectrochemistry. The last process (V) could not be ascertained by spectroelectrochemistry but is associated with ring oxidation. Upon reduction or oxidation, the Q band of the non-peripherally substituted complex became less red shifted compared to that of its peripherally substituted counterpart.
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The unit-based sustainability assessment tool and its use in the UNEP mainstreaming environment and sustainability in African universities partnership
- Togo, Muchaiteyi, Lotz-Sisitka, Heila
- Authors: Togo, Muchaiteyi , Lotz-Sisitka, Heila
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , book chapter
- Identifier: http://hdl.handle.net/10962/437409 , vital:73376 , ISBN 978-1-4020-8194-1 , https://doi.org/10.1007/978-3-319-02375-5_15
- Description: This paper reports on the development and use of a Unit-based Sustainability Assessment Tool (USAT) for establishing the status of Education for Sustainable Development initiatives and sustainable development practices in universities. The tool was developed for use in the Swedish/Africa International Training Programme (ITP) on ‘Education for Sustainable De-velopment in Higher Education’ and complements the UNEP Mainstreaming Environment and Sustainability into African Universities (MESA) ‘Education for Sustainable Development Innovations Programmes for Universities in Africa’ materials. The USAT facilitates a quick assessment of the level of inte-gration of sustainability issues in university functions and op-erations, both to benchmark sustainability initiatives and identi-fy new areas for action or improvement. It is based on a unit-based framework which allows for sustainability assessments to be done per division, unit, department, or faculty within uni-versities. Collectively, the unit-based assessments provide for development of an institution wide picture of university sus-tainability.
- Full Text:
- Authors: Togo, Muchaiteyi , Lotz-Sisitka, Heila
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , book chapter
- Identifier: http://hdl.handle.net/10962/437409 , vital:73376 , ISBN 978-1-4020-8194-1 , https://doi.org/10.1007/978-3-319-02375-5_15
- Description: This paper reports on the development and use of a Unit-based Sustainability Assessment Tool (USAT) for establishing the status of Education for Sustainable Development initiatives and sustainable development practices in universities. The tool was developed for use in the Swedish/Africa International Training Programme (ITP) on ‘Education for Sustainable De-velopment in Higher Education’ and complements the UNEP Mainstreaming Environment and Sustainability into African Universities (MESA) ‘Education for Sustainable Development Innovations Programmes for Universities in Africa’ materials. The USAT facilitates a quick assessment of the level of inte-gration of sustainability issues in university functions and op-erations, both to benchmark sustainability initiatives and identi-fy new areas for action or improvement. It is based on a unit-based framework which allows for sustainability assessments to be done per division, unit, department, or faculty within uni-versities. Collectively, the unit-based assessments provide for development of an institution wide picture of university sus-tainability.
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The willingness to pay for dusky kob (Argyrosomus japonicus) restocking: using recreational linefishing licence fees to fund stock enhancement in South Africa
- Palmer, Ryan M, Snowball, Jeanette D
- Authors: Palmer, Ryan M , Snowball, Jeanette D
- Date: 2009
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/71322 , vital:29833 , https://doi.org/10.1093/icesjms/fsp075
- Description: The economic feasibility of stock enhancement of Argyrosomus japonicus in South Africa was investigated using a willingness-to-pay (WTP) survey. The pilot study provides a unique example of the use of the contingent valuation method as a valuation tool for a proposed stock enhancement programme. An increase in the cost of a recreational fishing permit is used as a potential vehicle of payment. The median value of the maximum that fishers were willing to pay for a recreational fishing permit was R155 (South African Rand) for frequent fishers and R100 for non-frequent fishers. Analysis showed that a fee of more than R100 excluded up to 50% of anglers from the fishery, but that a fee of R100 excluded only 28% of recreational anglers and would generate an additional R12 million annually from the sale of recreational fishing permits. The estimated costs of set-up and running of a stock enhancement programme are substantially lower than this, suggesting that stock enhancement may be an economically feasible management option that deserves more investigation. The WTP method itself produces robust results and is likely to be an effective tool in the management of the marine environment.
- Full Text:
- Authors: Palmer, Ryan M , Snowball, Jeanette D
- Date: 2009
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/71322 , vital:29833 , https://doi.org/10.1093/icesjms/fsp075
- Description: The economic feasibility of stock enhancement of Argyrosomus japonicus in South Africa was investigated using a willingness-to-pay (WTP) survey. The pilot study provides a unique example of the use of the contingent valuation method as a valuation tool for a proposed stock enhancement programme. An increase in the cost of a recreational fishing permit is used as a potential vehicle of payment. The median value of the maximum that fishers were willing to pay for a recreational fishing permit was R155 (South African Rand) for frequent fishers and R100 for non-frequent fishers. Analysis showed that a fee of more than R100 excluded up to 50% of anglers from the fishery, but that a fee of R100 excluded only 28% of recreational anglers and would generate an additional R12 million annually from the sale of recreational fishing permits. The estimated costs of set-up and running of a stock enhancement programme are substantially lower than this, suggesting that stock enhancement may be an economically feasible management option that deserves more investigation. The WTP method itself produces robust results and is likely to be an effective tool in the management of the marine environment.
- Full Text:
The writing circle by Rozena Maart
- Authors: Naidu, Samantha
- Date: 2009
- Language: English
- Type: Book review , text
- Identifier: vital:26374 , http://hdl.handle.net/10962/54017 , http://www.wasafiri.org/product/wasafiri-issue-57/ , https://orcid.org/0000-0001-9456-8657
- Description: Book review. The writing circle by Rozena Maart.
- Full Text: false
- Authors: Naidu, Samantha
- Date: 2009
- Language: English
- Type: Book review , text
- Identifier: vital:26374 , http://hdl.handle.net/10962/54017 , http://www.wasafiri.org/product/wasafiri-issue-57/ , https://orcid.org/0000-0001-9456-8657
- Description: Book review. The writing circle by Rozena Maart.
- Full Text: false
Towards a GPS-based TEC prediction model for Southern Africa with feed forward networks
- Habarulema, John B, McKinnell, Lee-Anne, Opperman, Ben D L
- Authors: Habarulema, John B , McKinnell, Lee-Anne , Opperman, Ben D L
- Date: 2009
- Language: English
- Type: text , Article
- Identifier: vital:6806 , http://hdl.handle.net/10962/d1004192
- Description: In this paper, first results from a national Global Positioning System (GPS) based total electron content (TEC) prediction model over South Africa are presented. Data for 10 GPS receiver stations distributed through out the country were used to train a feed forward neural network (NN) over an interval of at most five years. In the NN training, validating and testing processes, five factors which are well known to influence TEC variability namely diurnal variation, seasonal variation, magnetic activity, solar activity and the geographic position of the GPS receivers were included in the NN model. The database consisted of 1-min data and therefore the NN model developed can be used to forecast TEC values 1 min in advance. Results from the NN national model (NM) were compared with hourly TEC values generated by the earlier developed NN single station models (SSMs) at Sutherland (32.38°S, 20.81°E) and Springbok (29.67°S, 17.88°E), to predict TEC variations over the Cape Town (33.95°S, 18.47°E) and Upington (28.41°S, 21.26°E) stations, respectively, during equinoxes and solstices. This revealed that, on average, the NM led to an improvement in TEC prediction accuracy compared to the SSMs for the considered testing periods.
- Full Text:
- Authors: Habarulema, John B , McKinnell, Lee-Anne , Opperman, Ben D L
- Date: 2009
- Language: English
- Type: text , Article
- Identifier: vital:6806 , http://hdl.handle.net/10962/d1004192
- Description: In this paper, first results from a national Global Positioning System (GPS) based total electron content (TEC) prediction model over South Africa are presented. Data for 10 GPS receiver stations distributed through out the country were used to train a feed forward neural network (NN) over an interval of at most five years. In the NN training, validating and testing processes, five factors which are well known to influence TEC variability namely diurnal variation, seasonal variation, magnetic activity, solar activity and the geographic position of the GPS receivers were included in the NN model. The database consisted of 1-min data and therefore the NN model developed can be used to forecast TEC values 1 min in advance. Results from the NN national model (NM) were compared with hourly TEC values generated by the earlier developed NN single station models (SSMs) at Sutherland (32.38°S, 20.81°E) and Springbok (29.67°S, 17.88°E), to predict TEC variations over the Cape Town (33.95°S, 18.47°E) and Upington (28.41°S, 21.26°E) stations, respectively, during equinoxes and solstices. This revealed that, on average, the NM led to an improvement in TEC prediction accuracy compared to the SSMs for the considered testing periods.
- Full Text: