Implementation and applications of the distortion operator
- Authors: Bangay, Shaun D
- Date: 2001
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/433382 , vital:72966 , https://doi.org/10.1145/513867.513872
- Description: The distortion operator transforms 2D images in a manner similar to image warping or morphing, allowing source pixels to be mapped to any destination pixel. This operator can be implemented on current hardware, allowing at least one distortion per frame at interactive frame rates. Potential applications are numerous, but those described include re-mapping images for correct projection onto curved screens, correcting camera distortion from multiple sources simultaneously, and allowing constant time dynamic texturing and lighting of a static scene which is independent of geometric complexity.
- Full Text:
- Date Issued: 2001
- Authors: Bangay, Shaun D
- Date: 2001
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/433382 , vital:72966 , https://doi.org/10.1145/513867.513872
- Description: The distortion operator transforms 2D images in a manner similar to image warping or morphing, allowing source pixels to be mapped to any destination pixel. This operator can be implemented on current hardware, allowing at least one distortion per frame at interactive frame rates. Potential applications are numerous, but those described include re-mapping images for correct projection onto curved screens, correcting camera distortion from multiple sources simultaneously, and allowing constant time dynamic texturing and lighting of a static scene which is independent of geometric complexity.
- Full Text:
- Date Issued: 2001
Visiview: a system for the visualization of multidimensional data
- Authors: Bangay, Shaun D
- Date: 1998
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/433466 , vital:72972 , https://doi.org/10.1117/12.309530
- Description: Results generated by simulation of computer systems are often presented as a multi-dimensional data set, where the number of dimensions may be greater than 4 if sufficient system parameters are modelled. This paper describes a visualization system intended to assist in understanding the relationship between, and effect upon system behavior of, the different values of the system parameters. The system is applied to data that cannot be represented using a mesh or isosurface representation, and in general can only be represented as a cloud of points. The use of stereoscopic rendering and rapid interaction with the data are compared with regard to their value in providing insight into the nature of the data. A number of techniques are implemented for displaying projections of the data set with up to 7 dimensions, and for allowing intuitive manipulation of the remaining dimensions. In this way the effect of changes in one variable in the presence of a number of others can be explored. The use of these techniques, when applied to data from computer system simulation, results in an intuitive understanding of the effects of the system parameters on system behavior.
- Full Text:
- Date Issued: 1998
- Authors: Bangay, Shaun D
- Date: 1998
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/433466 , vital:72972 , https://doi.org/10.1117/12.309530
- Description: Results generated by simulation of computer systems are often presented as a multi-dimensional data set, where the number of dimensions may be greater than 4 if sufficient system parameters are modelled. This paper describes a visualization system intended to assist in understanding the relationship between, and effect upon system behavior of, the different values of the system parameters. The system is applied to data that cannot be represented using a mesh or isosurface representation, and in general can only be represented as a cloud of points. The use of stereoscopic rendering and rapid interaction with the data are compared with regard to their value in providing insight into the nature of the data. A number of techniques are implemented for displaying projections of the data set with up to 7 dimensions, and for allowing intuitive manipulation of the remaining dimensions. In this way the effect of changes in one variable in the presence of a number of others can be explored. The use of these techniques, when applied to data from computer system simulation, results in an intuitive understanding of the effects of the system parameters on system behavior.
- Full Text:
- Date Issued: 1998
Nonlinear optical response of a low symmetry phthalocyanine in the presence of gold nanoparticles when in solution or embedded in poly acrylic acid polymer thin films
- Bankole, Owolabi M, Nyokong, Tebello
- Authors: Bankole, Owolabi M , Nyokong, Tebello
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/188719 , vital:44779 , xlink:href="https://doi.org/10.1016/j.jphotochem.2015.12.014"
- Description: In this article, we explored the photophysical and nonlinear optical (NLO) characterizations of low symmetry phthalocyanine (ZnPc-NH2) covalently linked to MPA-capped AuNPs (ZnPc-NH2-AuNPs) and poly acrylic acid (ZnPc-NH2-PAA). Nonlinear optical (NLO) properties of the samples were evaluated using Z-scan technique at 532 nm and 10 ns pulsed duration. We observed enhanced photophysical and nonlinear optical behaviour for the ZnPc-NH2 in presence of AuNPs. By virtue of the magnitude of absorption coefficients and other NLO optical parameters estimated in this work, ZnPc-NH2-AuNPs was found to exhibit improved nonlinear optical response compared to the ZnPc-NH2 and ZnPc-NH2-PAA. Both ZnPc-NH2-AuNPs and ZnPc-NH2 doped in PAA possess strong nonlinear absorption coefficients and very low limiting thresholds than when measured in solution.
- Full Text:
- Date Issued: 2016
- Authors: Bankole, Owolabi M , Nyokong, Tebello
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/188719 , vital:44779 , xlink:href="https://doi.org/10.1016/j.jphotochem.2015.12.014"
- Description: In this article, we explored the photophysical and nonlinear optical (NLO) characterizations of low symmetry phthalocyanine (ZnPc-NH2) covalently linked to MPA-capped AuNPs (ZnPc-NH2-AuNPs) and poly acrylic acid (ZnPc-NH2-PAA). Nonlinear optical (NLO) properties of the samples were evaluated using Z-scan technique at 532 nm and 10 ns pulsed duration. We observed enhanced photophysical and nonlinear optical behaviour for the ZnPc-NH2 in presence of AuNPs. By virtue of the magnitude of absorption coefficients and other NLO optical parameters estimated in this work, ZnPc-NH2-AuNPs was found to exhibit improved nonlinear optical response compared to the ZnPc-NH2 and ZnPc-NH2-PAA. Both ZnPc-NH2-AuNPs and ZnPc-NH2 doped in PAA possess strong nonlinear absorption coefficients and very low limiting thresholds than when measured in solution.
- Full Text:
- Date Issued: 2016
Photophysical and nonlinear optical studies of tetraakynyl zincphthalocyanine and its “clicked” analogue
- Bankole, Owolabi M, Nyokong, Tebello
- Authors: Bankole, Owolabi M , Nyokong, Tebello
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/189325 , vital:44837 , xlink:href="https://doi.org/10.1016/j.molstruc.2015.01.048"
- Description: We report here for the first time on the photophysical and nonlinear optical behavior of tetra-substituted alkynyl zinc phthalocyanine and its “clicked” analogue (4 and 5). The compounds exhibited high triplet quantum yields in dimethylsulphoxide (DMSO). Nonlinear optical (NLO) properties were also evaluated for the two compounds at 532 nm and 10 ns in DMSO. We observed two-photon absorption (2PA) and strong reverse saturable absorption (RSA) as the dominant mechanisms at nanosecond laser excitation. The presence of electron acceptor groups fused with triazole linkers in the peripheral positions of 4 provide excellent coexistent features, such as enhanced triplet quantum yields and lifetimes compared to 5. Large third-order susceptibility (2.09 × 10−11 and 3.53 × 10−9 esu) and hyperpolarizability (1.09 × 10−30 and 9.13 × 10−29 esu) were estimated for complexs 4 and 5, respectively.
- Full Text:
- Date Issued: 2015
- Authors: Bankole, Owolabi M , Nyokong, Tebello
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/189325 , vital:44837 , xlink:href="https://doi.org/10.1016/j.molstruc.2015.01.048"
- Description: We report here for the first time on the photophysical and nonlinear optical behavior of tetra-substituted alkynyl zinc phthalocyanine and its “clicked” analogue (4 and 5). The compounds exhibited high triplet quantum yields in dimethylsulphoxide (DMSO). Nonlinear optical (NLO) properties were also evaluated for the two compounds at 532 nm and 10 ns in DMSO. We observed two-photon absorption (2PA) and strong reverse saturable absorption (RSA) as the dominant mechanisms at nanosecond laser excitation. The presence of electron acceptor groups fused with triazole linkers in the peripheral positions of 4 provide excellent coexistent features, such as enhanced triplet quantum yields and lifetimes compared to 5. Large third-order susceptibility (2.09 × 10−11 and 3.53 × 10−9 esu) and hyperpolarizability (1.09 × 10−30 and 9.13 × 10−29 esu) were estimated for complexs 4 and 5, respectively.
- Full Text:
- Date Issued: 2015
Comparative studies on photophysical and optical limiting characterizations of low symmetry phthalocyanine linked to Fe 3 O 4–Ag core–shell or hybrid nanoparticles
- Bankole, Owolabi M, Nyokong, Tebello
- Authors: Bankole, Owolabi M , Nyokong, Tebello
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/188788 , vital:44785 , xlink:href="https://doi.org/10.1039/C6NJ01511E"
- Description: Photophysical and nonlinear optical (NLO) behaviours of low symmetry zinc phthalocyanine (1) linked to Fe3O4/Ag core–shell (represented as Fe/Ag) or Fe3O4–Ag hybrid (represented as FeAg) nanoparticles were investigated in DMSO. Triplet quantum yields and NLO parameters of phthalocyanine improved due to the combined effects of magnetic–metallic nanoparticles. A direct relationship between the increased triplet excited state absorptions by already excited molecules and reverse saturable absorption (RSA) was established as the predominant mechanism responsible for nonlinearity of the samples. Our findings show that, at the same approximate concentrations and conditions, 1-FeAg enhanced the OL potentials of 1 more than 1-Fe/Ag.
- Full Text:
- Date Issued: 2016
- Authors: Bankole, Owolabi M , Nyokong, Tebello
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/188788 , vital:44785 , xlink:href="https://doi.org/10.1039/C6NJ01511E"
- Description: Photophysical and nonlinear optical (NLO) behaviours of low symmetry zinc phthalocyanine (1) linked to Fe3O4/Ag core–shell (represented as Fe/Ag) or Fe3O4–Ag hybrid (represented as FeAg) nanoparticles were investigated in DMSO. Triplet quantum yields and NLO parameters of phthalocyanine improved due to the combined effects of magnetic–metallic nanoparticles. A direct relationship between the increased triplet excited state absorptions by already excited molecules and reverse saturable absorption (RSA) was established as the predominant mechanism responsible for nonlinearity of the samples. Our findings show that, at the same approximate concentrations and conditions, 1-FeAg enhanced the OL potentials of 1 more than 1-Fe/Ag.
- Full Text:
- Date Issued: 2016
Azide-derivatized gold nanosphere “clicked” to indium and zinc phthalocyanines for improved nonlinear optical limiting
- Bankole, Owolabi M, Nyokong, Tebello
- Authors: Bankole, Owolabi M , Nyokong, Tebello
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/188249 , vital:44738 , xlink:href="https://doi.org/10.1016/j.molstruc.2017.01.088"
- Description: We report on the conjugation of azide-derivatized gold nanoparticles (AuNPs) to alkyne moieties of ZnPc and InPc via azide-alkyne Huisgen cycloaddition reaction to form phthalocyanines-AuNPs (MPc-AuNPs) conjugates. The detailed structural characterizations of the composites were in good agreement with the expected results. The nonlinear absorption coefficients and other nonlinear optical limiting parameters were almost two times larger for the conjugates compared to free phthalocyanines. We established direct relationship between improved photophysical characterizations and enhanced nonlinear effects of reverse saturable absorption mechanisms favoured by excited triplet absorption of the phthalocyanines in the presence of AuNPs. The combination of InPc with AuNPs resulted in the lowest limiting intensity value of 0.06 J/cm2, hence the best performance in terms of optical limiting.
- Full Text:
- Date Issued: 2017
- Authors: Bankole, Owolabi M , Nyokong, Tebello
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/188249 , vital:44738 , xlink:href="https://doi.org/10.1016/j.molstruc.2017.01.088"
- Description: We report on the conjugation of azide-derivatized gold nanoparticles (AuNPs) to alkyne moieties of ZnPc and InPc via azide-alkyne Huisgen cycloaddition reaction to form phthalocyanines-AuNPs (MPc-AuNPs) conjugates. The detailed structural characterizations of the composites were in good agreement with the expected results. The nonlinear absorption coefficients and other nonlinear optical limiting parameters were almost two times larger for the conjugates compared to free phthalocyanines. We established direct relationship between improved photophysical characterizations and enhanced nonlinear effects of reverse saturable absorption mechanisms favoured by excited triplet absorption of the phthalocyanines in the presence of AuNPs. The combination of InPc with AuNPs resulted in the lowest limiting intensity value of 0.06 J/cm2, hence the best performance in terms of optical limiting.
- Full Text:
- Date Issued: 2017
Nonlinear optical behavior of alkyne terminated phthalocyanines in solution and when embedded in polysulfone as thin films: effects of aggregation
- Bankole, Owolabi M, Yilmaz, Yusuf, Nyokong, Tebello
- Authors: Bankole, Owolabi M , Yilmaz, Yusuf , Nyokong, Tebello
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/189110 , vital:44817 , xlink:href="https://doi.org/10.1016/j.optmat.2015.11.041"
- Description: We report here for the first time, on the comparative studies of the photophysical and optical limiting behavior of our two novel phthalocyanines namely 2(3), 9(10), 16(17), 23(24)-tetrakis-(4-(5-methylhex-1-yn-3-yloxy)) phthalocyanines 2, and 2(3), 9(10), 16(17), 23(24)-tetrakis-(4-(5-methylhex-1-yn-3-yloxy)) phthalocyaninato zinc (II) (3) in solution and thin films. Nonlinear optical (NLO) properties of the samples in solution and contained in polysulfone (PSU) thin films were evaluated using Z-scan technique at 532 nm and 10 ns pulsed duration. Effects of aggregation and disaggregation on the NLO performance of metal-free phthalocyanine are reported in detail. Our findings showed that the prepared Pcs show larger nonlinear absorption coefficient and lower limiting thresholds when embedded in polysulfone films compared to in solutions. The values of nonlinear susceptibility and hyperpolarizability recorded for 3-PSU in this work are respectively, ∼2.09 × 10−8 esu and ∼1.02 × 10−26 esu. These values are among the largest values reported for phthalocyanines and other macrocycles doped on polymer matrices.
- Full Text:
- Date Issued: 2016
- Authors: Bankole, Owolabi M , Yilmaz, Yusuf , Nyokong, Tebello
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/189110 , vital:44817 , xlink:href="https://doi.org/10.1016/j.optmat.2015.11.041"
- Description: We report here for the first time, on the comparative studies of the photophysical and optical limiting behavior of our two novel phthalocyanines namely 2(3), 9(10), 16(17), 23(24)-tetrakis-(4-(5-methylhex-1-yn-3-yloxy)) phthalocyanines 2, and 2(3), 9(10), 16(17), 23(24)-tetrakis-(4-(5-methylhex-1-yn-3-yloxy)) phthalocyaninato zinc (II) (3) in solution and thin films. Nonlinear optical (NLO) properties of the samples in solution and contained in polysulfone (PSU) thin films were evaluated using Z-scan technique at 532 nm and 10 ns pulsed duration. Effects of aggregation and disaggregation on the NLO performance of metal-free phthalocyanine are reported in detail. Our findings showed that the prepared Pcs show larger nonlinear absorption coefficient and lower limiting thresholds when embedded in polysulfone films compared to in solutions. The values of nonlinear susceptibility and hyperpolarizability recorded for 3-PSU in this work are respectively, ∼2.09 × 10−8 esu and ∼1.02 × 10−26 esu. These values are among the largest values reported for phthalocyanines and other macrocycles doped on polymer matrices.
- Full Text:
- Date Issued: 2016
Nonlinear interactions of zinc phthalocyanine-graphene quantum dots nanocomposites: Investigation of effects of surface functionalization with heteroatoms
- Bankole, Owolabi M, Achadu, Ojodomo J, Nyokong, Tebello
- Authors: Bankole, Owolabi M , Achadu, Ojodomo J , Nyokong, Tebello
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/188474 , vital:44757 , xlink:href="https://doi.org/10.1007/s10895-016-2008-8"
- Description: This study reports the development of functional optical limiting materials composed of pristine graphene (GQDs), nitrogen-doped (NGQDs) and sulfur-nitrogen co-doped (SNGQDs) graphene quantum dots covalently linked to mono-amino substituted zinc phthalocyanine (Pc). Open aperture Z-scan technique was employed to monitor the behaviour of the conjugates under tightly focussed Gaussian laser beam using a mode-locked Nd:YAG laser delivering 10 nanosecond (FWHM) pulses at 532 nm wavelength. Nonlinear effect due to reverse saturable absorption was the predominant mechanism; and was attributed to the moderately enhanced triplet population. The major factor(s) responsible for the enhanced nonlinearities in the Pc-NGQDs and Pc-SNGQDs was fully described and attributed to the surface defects caused by the presence of heteroatoms of N and S.
- Full Text:
- Date Issued: 2017
- Authors: Bankole, Owolabi M , Achadu, Ojodomo J , Nyokong, Tebello
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/188474 , vital:44757 , xlink:href="https://doi.org/10.1007/s10895-016-2008-8"
- Description: This study reports the development of functional optical limiting materials composed of pristine graphene (GQDs), nitrogen-doped (NGQDs) and sulfur-nitrogen co-doped (SNGQDs) graphene quantum dots covalently linked to mono-amino substituted zinc phthalocyanine (Pc). Open aperture Z-scan technique was employed to monitor the behaviour of the conjugates under tightly focussed Gaussian laser beam using a mode-locked Nd:YAG laser delivering 10 nanosecond (FWHM) pulses at 532 nm wavelength. Nonlinear effect due to reverse saturable absorption was the predominant mechanism; and was attributed to the moderately enhanced triplet population. The major factor(s) responsible for the enhanced nonlinearities in the Pc-NGQDs and Pc-SNGQDs was fully described and attributed to the surface defects caused by the presence of heteroatoms of N and S.
- Full Text:
- Date Issued: 2017
Enhanced nonlinear optical responses of zinc diaminopyrimidin-2-ylthio phthalocyanine conjugated to AgxAuy alloy nanoparticles
- Bankole, Owolabi M, Osifeko, Olawale L, Nyokong, Tebello
- Authors: Bankole, Owolabi M , Osifeko, Olawale L , Nyokong, Tebello
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/240382 , vital:50829 , xlink:href="https://doi.org/10.1016/j.jphotochem.2016.06.025"
- Description: In this article, the photophysical and nonlinear optical (NLO) characterizations of diaminopyrimidin-2-ylthio phthalocyaninatozinc (II) (2) before and after conjugation to AgxAuy nano-alloys are discussed. Phthalocyanines-AgxAuy (2-AgxAuy) composites showed enhanced triplet state and nonlinear optical behaviour when compared to free phthalocyanine. Optical limiting (OL) responses of the samples were evaluated using Z-scan technique at 532 nm and 10 ns in dimethyl sulfoxide. Reverse saturable absorption (RSA), which is a direct consequence of triplet absorption of already excited molecules was observed as the dominant mechanism responsible for nonlinearity of the samples. By virtue of the magnitude of absorption coefficients and other NLO optical parameters estimated in this work, 2-AgxAuy composites were found to exhibit stronger optical limiting responses than unconjugated phthalocyanine. The large third-order susceptibilities of the composites make them suitable materials for attenuating modern laser radiations, and also found useful in various optical applications.
- Full Text:
- Date Issued: 2016
- Authors: Bankole, Owolabi M , Osifeko, Olawale L , Nyokong, Tebello
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/240382 , vital:50829 , xlink:href="https://doi.org/10.1016/j.jphotochem.2016.06.025"
- Description: In this article, the photophysical and nonlinear optical (NLO) characterizations of diaminopyrimidin-2-ylthio phthalocyaninatozinc (II) (2) before and after conjugation to AgxAuy nano-alloys are discussed. Phthalocyanines-AgxAuy (2-AgxAuy) composites showed enhanced triplet state and nonlinear optical behaviour when compared to free phthalocyanine. Optical limiting (OL) responses of the samples were evaluated using Z-scan technique at 532 nm and 10 ns in dimethyl sulfoxide. Reverse saturable absorption (RSA), which is a direct consequence of triplet absorption of already excited molecules was observed as the dominant mechanism responsible for nonlinearity of the samples. By virtue of the magnitude of absorption coefficients and other NLO optical parameters estimated in this work, 2-AgxAuy composites were found to exhibit stronger optical limiting responses than unconjugated phthalocyanine. The large third-order susceptibilities of the composites make them suitable materials for attenuating modern laser radiations, and also found useful in various optical applications.
- Full Text:
- Date Issued: 2016
Two new species of Prosopistomatidae (Ephemeroptera) from South Africa and Swaziland
- Authors: Barber-James, Helen M
- Date: 2010
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/452385 , vital:75124 , https://hdl.handle.net/10520/EJC32841
- Description: Three species of Prosopistoma Latreille, 1833 are currently described from Africa. The immature nymph of Prosopistoma deguernei Vayssière, 1893 was described from Senegal, and the nymph and winged stages of Prosopistoma africanum Gillies, 1954 are known from Tanzania. The southern African species Prosopistoma crassi Gillies, 1954, initially described as a nymph from KwaZulu-Natal, South Africa, has subsequently been collected in a number of South African rivers. Two further species from South Africa are described here, the nymph of Prosopistoma amanzamnyama sp. n., and the nymph and female subimago of Prosopistoma mccaffertyi sp. n.
- Full Text:
- Date Issued: 2010
- Authors: Barber-James, Helen M
- Date: 2010
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/452385 , vital:75124 , https://hdl.handle.net/10520/EJC32841
- Description: Three species of Prosopistoma Latreille, 1833 are currently described from Africa. The immature nymph of Prosopistoma deguernei Vayssière, 1893 was described from Senegal, and the nymph and winged stages of Prosopistoma africanum Gillies, 1954 are known from Tanzania. The southern African species Prosopistoma crassi Gillies, 1954, initially described as a nymph from KwaZulu-Natal, South Africa, has subsequently been collected in a number of South African rivers. Two further species from South Africa are described here, the nymph of Prosopistoma amanzamnyama sp. n., and the nymph and female subimago of Prosopistoma mccaffertyi sp. n.
- Full Text:
- Date Issued: 2010
Bearing Witness to ‘Irreparable Harm': Incorporating Affective Activity as Practice into Ethics
- Barker, Kim, Macleod, Catriona I
- Authors: Barker, Kim , Macleod, Catriona I
- Date: 2018
- Subjects: To be catalogued
- Language: English
- Type: text , book chapter
- Identifier: http://hdl.handle.net/10962/434185 , vital:73037 , ISBN 978-3-319-74720-0 , https://link.springer.com/chapter/10.1007/978-3-319-74721-7_12
- Description: Research with individuals who have experienced trauma requires careful consideration. In preparing the ethics protocol for an ethnographic study of an anti-rape protest, we gave careful consideration to the potential ethical challenges in accordance with the University ethics code. However, this process did not prepare the first author for the dynamic and reciprocal positioning she encountered in relationships in the field or the ‘ethically important’ moment-by-moment decision-making which this required of her. Drawing on the philosophy of Emmanuel Levinas, a feminist reading of the contemporary ‘turn to affect’, and examples from our research, we show how ethical decision-making in ethnographic research is always relational and dialogical, both in our direct interactions with participants and in the ways in which we approach our ‘data’.
- Full Text:
- Date Issued: 2018
- Authors: Barker, Kim , Macleod, Catriona I
- Date: 2018
- Subjects: To be catalogued
- Language: English
- Type: text , book chapter
- Identifier: http://hdl.handle.net/10962/434185 , vital:73037 , ISBN 978-3-319-74720-0 , https://link.springer.com/chapter/10.1007/978-3-319-74721-7_12
- Description: Research with individuals who have experienced trauma requires careful consideration. In preparing the ethics protocol for an ethnographic study of an anti-rape protest, we gave careful consideration to the potential ethical challenges in accordance with the University ethics code. However, this process did not prepare the first author for the dynamic and reciprocal positioning she encountered in relationships in the field or the ‘ethically important’ moment-by-moment decision-making which this required of her. Drawing on the philosophy of Emmanuel Levinas, a feminist reading of the contemporary ‘turn to affect’, and examples from our research, we show how ethical decision-making in ethnographic research is always relational and dialogical, both in our direct interactions with participants and in the ways in which we approach our ‘data’.
- Full Text:
- Date Issued: 2018
A Comparison Of The Resource Requirements Of Snort And Bro In Production Networks
- Barnett, Richard J, Irwin, Barry V W
- Authors: Barnett, Richard J , Irwin, Barry V W
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/430040 , vital:72661 , https://www.iadisportal.org/applied-computing-2009-proceedings
- Description: Intrusion Detection is essential in modern networking. However, with the increas-ing load on modern networks, the resource requirements of NIDS are significant. This paper explores and compares the requirements of Snort and Bro, and finds that Snort is more efficient at processing network traffic than Bro. It also finds that both systems are capable of analysing current network loads on commodity hardware, but may be unable to do so for higher bandwidth networks. This is ben-eficial in a South African context due to the increasing international bandwidth that will come online with the launch of the SEACOM Cable, and local projects such as SANREN.
- Full Text:
- Date Issued: 2009
- Authors: Barnett, Richard J , Irwin, Barry V W
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/430040 , vital:72661 , https://www.iadisportal.org/applied-computing-2009-proceedings
- Description: Intrusion Detection is essential in modern networking. However, with the increas-ing load on modern networks, the resource requirements of NIDS are significant. This paper explores and compares the requirements of Snort and Bro, and finds that Snort is more efficient at processing network traffic than Bro. It also finds that both systems are capable of analysing current network loads on commodity hardware, but may be unable to do so for higher bandwidth networks. This is ben-eficial in a South African context due to the increasing international bandwidth that will come online with the launch of the SEACOM Cable, and local projects such as SANREN.
- Full Text:
- Date Issued: 2009
Towards a taxonomy of network scanning techniques
- Barnett, Richard J, Irwin, Barry V W
- Authors: Barnett, Richard J , Irwin, Barry V W
- Date: 2008
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/430310 , vital:72682 , https://doi.org/10.1145/1456659.1456660
- Description: Network scanning is a common reconnaissance activity in network in-trusion. Despite this, it's classification remains vague and detection sys-tems in current Network Intrusion Detection Systems are incapable of detecting many forms of scanning traffic. This paper presents a classi-fication of network scanning and illustrates how complex and varied this activity is. The presented classification extends previous, well known, definitions of scanning traffic in a manner which reflects this complexity.
- Full Text:
- Date Issued: 2008
- Authors: Barnett, Richard J , Irwin, Barry V W
- Date: 2008
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/430310 , vital:72682 , https://doi.org/10.1145/1456659.1456660
- Description: Network scanning is a common reconnaissance activity in network in-trusion. Despite this, it's classification remains vague and detection sys-tems in current Network Intrusion Detection Systems are incapable of detecting many forms of scanning traffic. This paper presents a classi-fication of network scanning and illustrates how complex and varied this activity is. The presented classification extends previous, well known, definitions of scanning traffic in a manner which reflects this complexity.
- Full Text:
- Date Issued: 2008
Performance Effects of Concurrent Virtual Machine Execution in VMware Workstation 6
- Barnett, Richard J, Irwin, Barry V W
- Authors: Barnett, Richard J , Irwin, Barry V W
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/429966 , vital:72655 , https://doi.org/10.1007/978-90-481-3660-5_56
- Description: The recent trend toward virtualized computing both as a means of serv-er consolidation and as a powerful desktop computing tool has lead into a wide variety of studies into the performance of hypervisor products. This study has investigated the scalability of VMware Workstation 6 on the desktop platform. We present comparative performance results for the concurrent execution of a number of virtual machines. A through statistical analysis of the performance results highlights the perfor-mance trends of different numbers of concurrent virtual machines and concludes that VMware workstation can scale in certain contexts. We find that there are different performance benefits dependant on the ap-plication and that memory intensive applications perform less effective-ly than those applications which are IO intensive. We also find that run-ning concurrent virtual machines offers a significant performance de-crease, but that the drop thereafter is less significant.
- Full Text:
- Date Issued: 2009
- Authors: Barnett, Richard J , Irwin, Barry V W
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/429966 , vital:72655 , https://doi.org/10.1007/978-90-481-3660-5_56
- Description: The recent trend toward virtualized computing both as a means of serv-er consolidation and as a powerful desktop computing tool has lead into a wide variety of studies into the performance of hypervisor products. This study has investigated the scalability of VMware Workstation 6 on the desktop platform. We present comparative performance results for the concurrent execution of a number of virtual machines. A through statistical analysis of the performance results highlights the perfor-mance trends of different numbers of concurrent virtual machines and concludes that VMware workstation can scale in certain contexts. We find that there are different performance benefits dependant on the ap-plication and that memory intensive applications perform less effective-ly than those applications which are IO intensive. We also find that run-ning concurrent virtual machines offers a significant performance de-crease, but that the drop thereafter is less significant.
- Full Text:
- Date Issued: 2009
Multivariate analysis of honeybees, Apis mellifera Linnaeus (Hymenoptera: Apidae) of the northeastern and southern regions of Algeria.
- Barour, C, Tahar, A, Radloff, Sarah E, Hepburn, H Randall
- Authors: Barour, C , Tahar, A , Radloff, Sarah E , Hepburn, H Randall
- Date: 2005
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/451976 , vital:75092 , https://hdl.handle.net/10520/EJC32628
- Description: Morphometric characters of worker honeybees, Apis mellifera Linnaeus, were analysed by multivariate methods to characterize their populations in the northeastern and southern regions (ecological-climatological zones) of Algeria, from 36°55' to 32°25'N and 3°39' to 8°22'E. Three morphoclusters were identified by using principal components and linear discriminant analyses. The bees are identified as Apis mellifera intermissa Buttel-Reepen.
- Full Text:
- Date Issued: 2005
- Authors: Barour, C , Tahar, A , Radloff, Sarah E , Hepburn, H Randall
- Date: 2005
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/451976 , vital:75092 , https://hdl.handle.net/10520/EJC32628
- Description: Morphometric characters of worker honeybees, Apis mellifera Linnaeus, were analysed by multivariate methods to characterize their populations in the northeastern and southern regions (ecological-climatological zones) of Algeria, from 36°55' to 32°25'N and 3°39' to 8°22'E. Three morphoclusters were identified by using principal components and linear discriminant analyses. The bees are identified as Apis mellifera intermissa Buttel-Reepen.
- Full Text:
- Date Issued: 2005
Nutrient-mediated silica uptake from agricultural runoff in invasive floating macrophytes: implications for biological control
- Baso, Nompumelelo C, Delport, Garyn A, Coetzee, Julie A
- Authors: Baso, Nompumelelo C , Delport, Garyn A , Coetzee, Julie A
- Date: 2020
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/424803 , vital:72185 , xlink:href="https://doi.org/10.1007/s10750-020-04344-5"
- Description: Silica (Si) plays a significant role in alleviating the effects of biotic and abiotic stressors in many plants, especially in an agricultural context. With increased use of Si-based fertilisers, understanding plant responses to the addition of Si to their environment, particularly aquatic environments, is important. We investigated how two invasive macrophytes, Eichhornia crassipes and Pistia stratiotes, responded to different nutrient and Si concentrations, in the presence and absence of herbivory. Both species incorporated Si into their foliage, but uptake of Si did not increase under high nutrient availability but rather decreased, especially in P. stratiotes. Plant quality (i.e. C:N) for both weed species was affected more by nutrient concentrations than Si content, and the addition of Si had a negative effect on plant growth. Eichhornia crassipes increased daughter plant production under high Si conditions, while P. stratiotes plants showed no reproductive response to increased Si except in low nutrient conditions where reproduction was reduced. The addition of Si resulted in increased biomass of E. crassipes, while P. stratiotes was unaffected. These results highlight that runoff of Si from fertiliser alter aquatic plant–insect interactions, which has consequences for biological control.
- Full Text:
- Date Issued: 2020
- Authors: Baso, Nompumelelo C , Delport, Garyn A , Coetzee, Julie A
- Date: 2020
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/424803 , vital:72185 , xlink:href="https://doi.org/10.1007/s10750-020-04344-5"
- Description: Silica (Si) plays a significant role in alleviating the effects of biotic and abiotic stressors in many plants, especially in an agricultural context. With increased use of Si-based fertilisers, understanding plant responses to the addition of Si to their environment, particularly aquatic environments, is important. We investigated how two invasive macrophytes, Eichhornia crassipes and Pistia stratiotes, responded to different nutrient and Si concentrations, in the presence and absence of herbivory. Both species incorporated Si into their foliage, but uptake of Si did not increase under high nutrient availability but rather decreased, especially in P. stratiotes. Plant quality (i.e. C:N) for both weed species was affected more by nutrient concentrations than Si content, and the addition of Si had a negative effect on plant growth. Eichhornia crassipes increased daughter plant production under high Si conditions, while P. stratiotes plants showed no reproductive response to increased Si except in low nutrient conditions where reproduction was reduced. The addition of Si resulted in increased biomass of E. crassipes, while P. stratiotes was unaffected. These results highlight that runoff of Si from fertiliser alter aquatic plant–insect interactions, which has consequences for biological control.
- Full Text:
- Date Issued: 2020
The effects of elevated atmospheric CO2 concentration on the biological control of invasive aquatic weeds
- Baso, Nompumelelo C, Coetzee, Julie A, Ripley, Bradford S, Hill, Martin P
- Authors: Baso, Nompumelelo C , Coetzee, Julie A , Ripley, Bradford S , Hill, Martin P
- Date: 2021
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/419423 , vital:71643 , xlink:href="https://doi.org/10.1016/j.aquabot.2020.103348"
- Description: There has been a rapid increase in atmospheric CO2 concentration, from pre-industrial values of 280 ppm to more than 400 ppm currently, and this is expected to double by the end of the 21st century. Studies have shown that plants grown at elevated CO2 concentrations have increased growth rates and invest more in carbon-based defences. This has important implications for the management of invasive alien plants, especially using biological control which is mostly dependent on herbivorous insects. The aim of this study was to investigate the effects of elevated atmospheric CO2 on the biological control of four invasive aquatic weeds (Azolla filiculoides, Salvinia molesta, Pistia stratiotes and Myriophyllum aquaticum). These species are currently under successful control by their respective biological control agents (Stenopelmus rufinasus, Cyrtobagous salviniae, Neohydronomus affinis, and Lysathia sp.) in South Africa. The plant species were grown in a two factorial design experiment, where atmospheric CO2 concentrations were set at ambient (400 ppm) or elevated (800 ppm), and plants were either subjected to or not subjected to herbivory by their target biological control agents. There was an overall increase in biomass production and C:N across all species at elevated CO2, both in the absence and presence of biological control, although C:N of M. aquaticum and biomass of A. filiculoides with herbivory were not constant with this trend. Insect feeding damage was reduced by elevated CO2, except for S. molesta. Thus, we can expect that plants will respond differently to CO2 increase, but the general trend suggests that these species will become more challenging to manage through biological control in future.
- Full Text:
- Date Issued: 2021
- Authors: Baso, Nompumelelo C , Coetzee, Julie A , Ripley, Bradford S , Hill, Martin P
- Date: 2021
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/419423 , vital:71643 , xlink:href="https://doi.org/10.1016/j.aquabot.2020.103348"
- Description: There has been a rapid increase in atmospheric CO2 concentration, from pre-industrial values of 280 ppm to more than 400 ppm currently, and this is expected to double by the end of the 21st century. Studies have shown that plants grown at elevated CO2 concentrations have increased growth rates and invest more in carbon-based defences. This has important implications for the management of invasive alien plants, especially using biological control which is mostly dependent on herbivorous insects. The aim of this study was to investigate the effects of elevated atmospheric CO2 on the biological control of four invasive aquatic weeds (Azolla filiculoides, Salvinia molesta, Pistia stratiotes and Myriophyllum aquaticum). These species are currently under successful control by their respective biological control agents (Stenopelmus rufinasus, Cyrtobagous salviniae, Neohydronomus affinis, and Lysathia sp.) in South Africa. The plant species were grown in a two factorial design experiment, where atmospheric CO2 concentrations were set at ambient (400 ppm) or elevated (800 ppm), and plants were either subjected to or not subjected to herbivory by their target biological control agents. There was an overall increase in biomass production and C:N across all species at elevated CO2, both in the absence and presence of biological control, although C:N of M. aquaticum and biomass of A. filiculoides with herbivory were not constant with this trend. Insect feeding damage was reduced by elevated CO2, except for S. molesta. Thus, we can expect that plants will respond differently to CO2 increase, but the general trend suggests that these species will become more challenging to manage through biological control in future.
- Full Text:
- Date Issued: 2021
Optimal template removal from molecularly imprinted polymers by pressurized hot water extraction
- Batlokwa, Bareki Shima, Mokgadi, Janes, Nyokong, Tebello, Torto, Nelson
- Authors: Batlokwa, Bareki Shima , Mokgadi, Janes , Nyokong, Tebello , Torto, Nelson
- Date: 2011
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/247813 , vital:51620 , xlink:href="https://doi.org/10.1007/s10337-010-1884-3"
- Description: An optimal extraction method for the removal of templates from molecularly imprinted polymers (MIPs) is presented. The extraction method is based on pressurized hot water extraction (PHWE). PHWE was evaluated by application to three distinctly colored MIPs for chlorophyll (green), quercetin (yellow) and phthalocynine (dark blue) with subsequent monitoring of template removal and template bleeding by an ultraviolet spectrophotometer. The templates were washed-off and the extraction efficiency (EE) was compared to that of soxhlet and ultrasonic extraction methods. PHWE employed hot water at an optimal temperature of 220 °C, pressure of 50 bars and flow rate of 2 mL min−1 to thoroughly wash-off the respective templates from their MIPs. The EE evaluated for PHWE was over 99.6% for all the MIPs with no subsequent or minimal template bleeding (more than 0.01%). The washing procedure was simple and relatively fast as it was achieved in 70 min at the most. At 95% confidence level (n = 3), soxhlet and ultrasonic recorded EE that was not significantly different (more than 94.5% in all cases) from that of PHWE (less than 99.6% in all cases). Soxhlet and ultrasonic had washing procedures that were slower (over 18 h) and employed large quantities (400 mL) of organic solvents modified with acids. The percentage relative standard deviations (%RSD) for the EE and recovery results were less than 2.3% in all cases indicating the high reproducibility of the method. Overall, the three methods performed comparably in extracting templates. PHWE seems to be the method of choice as it employed water which poses no environmental threat.
- Full Text:
- Date Issued: 2011
- Authors: Batlokwa, Bareki Shima , Mokgadi, Janes , Nyokong, Tebello , Torto, Nelson
- Date: 2011
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/247813 , vital:51620 , xlink:href="https://doi.org/10.1007/s10337-010-1884-3"
- Description: An optimal extraction method for the removal of templates from molecularly imprinted polymers (MIPs) is presented. The extraction method is based on pressurized hot water extraction (PHWE). PHWE was evaluated by application to three distinctly colored MIPs for chlorophyll (green), quercetin (yellow) and phthalocynine (dark blue) with subsequent monitoring of template removal and template bleeding by an ultraviolet spectrophotometer. The templates were washed-off and the extraction efficiency (EE) was compared to that of soxhlet and ultrasonic extraction methods. PHWE employed hot water at an optimal temperature of 220 °C, pressure of 50 bars and flow rate of 2 mL min−1 to thoroughly wash-off the respective templates from their MIPs. The EE evaluated for PHWE was over 99.6% for all the MIPs with no subsequent or minimal template bleeding (more than 0.01%). The washing procedure was simple and relatively fast as it was achieved in 70 min at the most. At 95% confidence level (n = 3), soxhlet and ultrasonic recorded EE that was not significantly different (more than 94.5% in all cases) from that of PHWE (less than 99.6% in all cases). Soxhlet and ultrasonic had washing procedures that were slower (over 18 h) and employed large quantities (400 mL) of organic solvents modified with acids. The percentage relative standard deviations (%RSD) for the EE and recovery results were less than 2.3% in all cases indicating the high reproducibility of the method. Overall, the three methods performed comparably in extracting templates. PHWE seems to be the method of choice as it employed water which poses no environmental threat.
- Full Text:
- Date Issued: 2011
Understanding spatial variation in the drivers of nature-based tourism and their influence on the sustainability of private land conservation
- Baum, Julia, Cumming, Graeme S, de Vos, Alta
- Authors: Baum, Julia , Cumming, Graeme S , de Vos, Alta
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/416481 , vital:71352 , xlink:href="https://doi.org/10.1016/j.ecolecon.2017.05.005"
- Description: Protected areas connect socio-economic and ecological systems through their provision of ecosystem goods and services. Analysis of ecosystem services allows the expression of ecological benefits in economic terms. However, cultural services, such as recreation opportunities, have proved difficult to quantify. An important challenge for the analysis of cultural services is to understand the geography of service provision in relation to both human and ecological system elements. We used data on visitation rates and measures of context, content, connectivity, and location for 64 private land conservation areas (PLCAs) to better understand geographic influences on cultural service provision. Visitation to PLCAs was influenced by a combination of ecological and socio-economic drivers. Variance partitioning analysis showed that ecology explained the largest proportion of overall variation in visitation rates (26%), followed by location (22%). In tests using generalized linear mixed models, individual factors that significantly explained visitation rates included the number of mammal species, the number of Big 5-species (ecological variables), the number of facilities provided (infrastructure) and average accommodation charges (affordability). Our analysis has important implications for the economic sustainability of PLCAs and more generally for understanding the relevance of spatial variation for analyses of cultural services.
- Full Text:
- Date Issued: 2017
- Authors: Baum, Julia , Cumming, Graeme S , de Vos, Alta
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/416481 , vital:71352 , xlink:href="https://doi.org/10.1016/j.ecolecon.2017.05.005"
- Description: Protected areas connect socio-economic and ecological systems through their provision of ecosystem goods and services. Analysis of ecosystem services allows the expression of ecological benefits in economic terms. However, cultural services, such as recreation opportunities, have proved difficult to quantify. An important challenge for the analysis of cultural services is to understand the geography of service provision in relation to both human and ecological system elements. We used data on visitation rates and measures of context, content, connectivity, and location for 64 private land conservation areas (PLCAs) to better understand geographic influences on cultural service provision. Visitation to PLCAs was influenced by a combination of ecological and socio-economic drivers. Variance partitioning analysis showed that ecology explained the largest proportion of overall variation in visitation rates (26%), followed by location (22%). In tests using generalized linear mixed models, individual factors that significantly explained visitation rates included the number of mammal species, the number of Big 5-species (ecological variables), the number of facilities provided (infrastructure) and average accommodation charges (affordability). Our analysis has important implications for the economic sustainability of PLCAs and more generally for understanding the relevance of spatial variation for analyses of cultural services.
- Full Text:
- Date Issued: 2017
A critical appraisal of the recruitment and selection process of the Public Protector in South Africa
- Bazana, Sandiso, Reddy, Tayra
- Authors: Bazana, Sandiso , Reddy, Tayra
- Date: 2021
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/453707 , vital:75279 , xlink:href=" https://journals.co.za/doi/full/10.4102/sajhrm.v19i0.1207"
- Description: Orientation: The process of recruitment and selection the Public Protector (PP) needs to ensure that the most ‘fit and proper’ candidate is appointed. The process needs critical scrutiny for such a fit and proper candidate to be selected. Research motivation: South Africa’s superior courts, including the Constitutional court have recently (in 2019) labelled the current Public Protector; dishonest and Incompetent in carrying out the duties of the PP office. Research purpose: This article critically appraises the recent process that culminated in the appointment of Ms Busisiwe Mkhwebane as the fourth Public Protector in the democratic South Africa.
- Full Text:
- Date Issued: 2021
- Authors: Bazana, Sandiso , Reddy, Tayra
- Date: 2021
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/453707 , vital:75279 , xlink:href=" https://journals.co.za/doi/full/10.4102/sajhrm.v19i0.1207"
- Description: Orientation: The process of recruitment and selection the Public Protector (PP) needs to ensure that the most ‘fit and proper’ candidate is appointed. The process needs critical scrutiny for such a fit and proper candidate to be selected. Research motivation: South Africa’s superior courts, including the Constitutional court have recently (in 2019) labelled the current Public Protector; dishonest and Incompetent in carrying out the duties of the PP office. Research purpose: This article critically appraises the recent process that culminated in the appointment of Ms Busisiwe Mkhwebane as the fourth Public Protector in the democratic South Africa.
- Full Text:
- Date Issued: 2021