Surface modifications of InAs: effect of chemical processing on electronic structure and photoluminescent properties
- Eassa, Nahswa Abo Alhassan Eassa
- Authors: Eassa, Nahswa Abo Alhassan Eassa
- Date: 2012
- Subjects: Indium arsenide , Chemical processes , Photoluminescence
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/8714 , vital:26423
- Description: In this thesis, the effects of various chemical treatments on the surface modification of bulk InAs are investigated. The study focuses on the chemical processes that occur upon the exposure of the surface to sulphur-, chlorine- and bromine-containing solutions and oxygen, and the resulting changes to the electronic structure of the surface, as deduced from photoluminescence (PL) measurements, X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), Raman scattering and scanning electron microscopy (SEM). Three processing treatments were evaluated: i) treatment with sulphur-based solutions (Na2S:9H2O, (NH4)2S + S, [(NH4)2S / (NH4)2SO4] + S); ii) etching in halogen-based solutions (bromine-methanol and HCl: H2O); and iii) thermal oxidation. A significant overall enhancement in PL response was observed after chemical treatment or thermal oxidation, which is associated with a reduction in surface band bending. These changes correlate with the removal of the native oxide, in addition to the formation of well-ordered layers of In-S (or In-As)O as a passivating layer, indicating that electronic passivation occurs at the surface. The passivating effect on sulphide treated surfaces is unstable, however, with an increase in band bending, due to reoxidation, observed over periods of a few days. The lowest re-oxidation rate was observed for ([(NH4)2S / (NH4)2SO4] + S). Etching in HCl:H2O and Br-methanol solutions of appropriate concentrations and for moderate times (1 min) resulted in smooth and defect-free InAs surfaces. Etching completely removed the native oxides from the surface and enhanced the PL response. The adsorption of bromine and chlorine onto the InAs surface led to the formation of As-Brx , In-Brx, As-Clx and In-Clxcompounds (x = 1, 2, 3), as inferred from changes in the In 3d3/2; 5/2 and As 3d core level binding energies. The etch rate was found to decrease because of strong anisotropic effects. The improvements in surface properties were reversed, however, if the concentrations of the etchants increased or the etch time was too long. In the worst cases, pit formation and inverted pyramids with {111} side facets were observed. Surface treatments or thermal oxidisation significantly enhanced the PL intensity relative to that of the as-received samples. This was due to a reduction in the surface state density upon de-oxidation, or in some cases, to the formation of a well ordered oxide layer on the surface. The overall increase in PL intensity after treatment is ascribed to a reduction in band bending near the surface. This allows several welldefined peaks not observed or reported previously for bulk InAs (with a carrier concentration n~2x1016 cm-3), to be studied. A combination of PL and XPS measurements before and after the various treatments was used to identify the chemical nature of the impurities giving rise to bound exciton recombination in InAs (111).
- Full Text:
- Date Issued: 2012
- Authors: Eassa, Nahswa Abo Alhassan Eassa
- Date: 2012
- Subjects: Indium arsenide , Chemical processes , Photoluminescence
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/8714 , vital:26423
- Description: In this thesis, the effects of various chemical treatments on the surface modification of bulk InAs are investigated. The study focuses on the chemical processes that occur upon the exposure of the surface to sulphur-, chlorine- and bromine-containing solutions and oxygen, and the resulting changes to the electronic structure of the surface, as deduced from photoluminescence (PL) measurements, X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), Raman scattering and scanning electron microscopy (SEM). Three processing treatments were evaluated: i) treatment with sulphur-based solutions (Na2S:9H2O, (NH4)2S + S, [(NH4)2S / (NH4)2SO4] + S); ii) etching in halogen-based solutions (bromine-methanol and HCl: H2O); and iii) thermal oxidation. A significant overall enhancement in PL response was observed after chemical treatment or thermal oxidation, which is associated with a reduction in surface band bending. These changes correlate with the removal of the native oxide, in addition to the formation of well-ordered layers of In-S (or In-As)O as a passivating layer, indicating that electronic passivation occurs at the surface. The passivating effect on sulphide treated surfaces is unstable, however, with an increase in band bending, due to reoxidation, observed over periods of a few days. The lowest re-oxidation rate was observed for ([(NH4)2S / (NH4)2SO4] + S). Etching in HCl:H2O and Br-methanol solutions of appropriate concentrations and for moderate times (1 min) resulted in smooth and defect-free InAs surfaces. Etching completely removed the native oxides from the surface and enhanced the PL response. The adsorption of bromine and chlorine onto the InAs surface led to the formation of As-Brx , In-Brx, As-Clx and In-Clxcompounds (x = 1, 2, 3), as inferred from changes in the In 3d3/2; 5/2 and As 3d core level binding energies. The etch rate was found to decrease because of strong anisotropic effects. The improvements in surface properties were reversed, however, if the concentrations of the etchants increased or the etch time was too long. In the worst cases, pit formation and inverted pyramids with {111} side facets were observed. Surface treatments or thermal oxidisation significantly enhanced the PL intensity relative to that of the as-received samples. This was due to a reduction in the surface state density upon de-oxidation, or in some cases, to the formation of a well ordered oxide layer on the surface. The overall increase in PL intensity after treatment is ascribed to a reduction in band bending near the surface. This allows several welldefined peaks not observed or reported previously for bulk InAs (with a carrier concentration n~2x1016 cm-3), to be studied. A combination of PL and XPS measurements before and after the various treatments was used to identify the chemical nature of the impurities giving rise to bound exciton recombination in InAs (111).
- Full Text:
- Date Issued: 2012
Rhenium complexes with multidentate benzazoles and related N,X-donor (X = N, O, S) ligands
- Authors: Potgieter, Kim Carey
- Date: 2012
- Subjects: Rhenium , Benzimidazoles , Ligands (Biochemistry)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10438 , http://hdl.handle.net/10948/d1020773
- Description: The coordination behaviour of 4-aminoantipyrine (H2pap) and its Schiff base derivatives with the oxorhenium(V) and tricarbonyl rhenium(I) cores are reported. The reactions of trans-[ReOX3(PPh3)2] (X = Cl, Br) with H2pap were studied, and the complexes cis-[ReX2(pap)(H2pap)(PPh3)](ReO4) were isolated. The ligand pap is coordinated monodentately through the doubly deprotonated amino nitrogen as an imide, and H2pap acts as a neutral bidentate chelate, with coordination through the neutral amino nitrogen and the ketonic oxygen. The reactions of trans-[ReOBr3(PPh3)2] and cis-[ReO2I(PPh3)2] with -(2-aminobenzylideneamino)-1,2-dihydro-2,3-dimethyl-1-phenylpyrazol-5-one (H2nap) and 4-(2-hydroxybenzylideneamino)-1,2-dihydro-2,3-dimethyl-1-phenylpyrazol-5-one (Hoap) are also reported. The complexes cis-[Re(nap)Br2(PPh3)]Br, [ReO(OEt)(Hnap)(PPh3)]I and [ReO(OMe)(oap)(PPh3)]I were isolated and structurally characterized. The reactions of the Schiff base derivatives 1,2-(diimino-4’-antipyrinyl)ethane (dae) and 2,6-bis(4-amino-1,2-dihydro-2,3-dimethyl-1-phenylpyrazol-5-one)pyridine (bap) with [Re(CO)5X] (X = Br or Cl) produced fac-[Re(CO)3(dae)Cl] and fac-[Re(CO)3(bap)Br] respectively. A series of rhenium(I) tricarbonyl complexes containing bidentate derivatives of aniline was synthesized and structurally characterized. With 1,2-diaminobenzene (Hpda) the ‘2+1’ complex salt fac-[Re(CO)3(κ1-Hpda)(κ2-Hpda)]Br was isolated, but with 2-mercaptophenol (Hspo) the bridged dimer [Re2(CO)7(spo)2] was found. The neutral complex [Re(CO)3(ons)(Hno)] was isolated from the reaction of [Re(CO)5Br] with 2-[(2-methylthio)benzylideneimino]phenol (Hons; Hno = 2-aminophenol), with ons coordinated as a bidentate chelate with a free SCH3 group. In the complex [Re(CO)3(Htpn)Br] (Htpn = N-(2-(methylthio)benzylidene)benzene-1,2-diamine) the potentially tridentate ligand Htpn is coordinated via the methylthiol sulfur and imino nitrogen atoms only, with a free amino group. These rhenium(I) complexes, with the exception of [Re2(CO)7(spo)2], revealed broad emissions centred around 535 nm. The reactions of the rhenium(V) complex cis-[ReO2I(PPh3)2] with 2-aminothiophenol (H2atp), benzene-1,2-dithiol (H2tdt) and 2-hydroxybenzenethiol (H2otp) led to the formation of the rhenium(III) compounds [Re(Hatp)(ibsq)2].OPPh3, [Re(sbsq)3].OPPh3 and [Re(obsq)3].OPPh3 (ibsq = 2-iminothiobenzosemiquinonate, sbsq = 1,2-dithiobenzosemiquinonate, obsq = 2-hydroxothiobenzosemiquinonate) respectively. The complexes adopt a trigonal prismatic geometry around the rhenium centre with average twists angles between 3.20-26.10˚. The E1/2 values for the Re(III)/Re(IV) redox couple were found to be 0.022, 0.142 and 0.126 V for [Re(Hatp)(ibsq)2].OPPh3, [Re(sbsq)3].OPPh3 and [Re(obsq)3].OPPh3 respectively. The reactions of the benzoxazole ligands, 3-(benzoxazol-2-yl)pyridin-2-ol (Hbop) and 5-amino-2-(benzoxazol-2-yl)phenol (Habo) with a [ReO]3+ precursor led to the rhenium(III) complex, [ReCl2(bop)(PPh3)2], and the complex salt, [ReO(abo)I(PPh3)2]ReO4, respectively. A variety of benzothiazole and benzimidazole derivatives were reacted with [Re(CO)5Br]. In the case of bis(benzothiazol-2-ylethyl)sulfide (bts), the neutral complex fac-[Re(CO)3(bts)Br] was obtained. The dimeric complexes (μ-dbt)2[Re(CO)3]2 and (μ-mbt)2[Re(CO)3]2 were formed when 1,3-bis(benzothiazol-2-yl)thiourea (Hdbt) and 1-(benzothiazol-2-ylidene)-3-methylthiourea (Hmbt) were used as ligands. The reaction of 2,2’-(oxybis(methylene))bis(benzimidazole) (bmb) with [Re(CO)5Cl] resulted in the rhenium(I) complex salt fac-[Re(CO)3(bmb)]+, with the tri-μ-chlorohexacarbonyl dirhenate [Re2(CO)6Cl3]- as the counter anion. The neutral complex fac-[Re(CO)3(btp)Cl] was isolated from the reaction of the 2,9-bis(benzothiazol-2-yl)-1,10-phenanthroline (btp) ligand and [Re(CO)5Cl]. The reactions of trans-[ReOCl3(PPh3)2] with bis(benzimidazol-2-ylethyl)sulfide (btn) and 1-(benzothiazol-2-ylidene)-3-methylthiourea (Hmbt) led to the formation of the cationic compounds (μ-O)2[Re2O2(btn)2]I2 and [ReCl2(bte)(PPh3)2]Cl (bte = (benzothiazole-2-yl)-N-ethylidenemethanamine) respectively.
- Full Text:
- Date Issued: 2012
- Authors: Potgieter, Kim Carey
- Date: 2012
- Subjects: Rhenium , Benzimidazoles , Ligands (Biochemistry)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10438 , http://hdl.handle.net/10948/d1020773
- Description: The coordination behaviour of 4-aminoantipyrine (H2pap) and its Schiff base derivatives with the oxorhenium(V) and tricarbonyl rhenium(I) cores are reported. The reactions of trans-[ReOX3(PPh3)2] (X = Cl, Br) with H2pap were studied, and the complexes cis-[ReX2(pap)(H2pap)(PPh3)](ReO4) were isolated. The ligand pap is coordinated monodentately through the doubly deprotonated amino nitrogen as an imide, and H2pap acts as a neutral bidentate chelate, with coordination through the neutral amino nitrogen and the ketonic oxygen. The reactions of trans-[ReOBr3(PPh3)2] and cis-[ReO2I(PPh3)2] with -(2-aminobenzylideneamino)-1,2-dihydro-2,3-dimethyl-1-phenylpyrazol-5-one (H2nap) and 4-(2-hydroxybenzylideneamino)-1,2-dihydro-2,3-dimethyl-1-phenylpyrazol-5-one (Hoap) are also reported. The complexes cis-[Re(nap)Br2(PPh3)]Br, [ReO(OEt)(Hnap)(PPh3)]I and [ReO(OMe)(oap)(PPh3)]I were isolated and structurally characterized. The reactions of the Schiff base derivatives 1,2-(diimino-4’-antipyrinyl)ethane (dae) and 2,6-bis(4-amino-1,2-dihydro-2,3-dimethyl-1-phenylpyrazol-5-one)pyridine (bap) with [Re(CO)5X] (X = Br or Cl) produced fac-[Re(CO)3(dae)Cl] and fac-[Re(CO)3(bap)Br] respectively. A series of rhenium(I) tricarbonyl complexes containing bidentate derivatives of aniline was synthesized and structurally characterized. With 1,2-diaminobenzene (Hpda) the ‘2+1’ complex salt fac-[Re(CO)3(κ1-Hpda)(κ2-Hpda)]Br was isolated, but with 2-mercaptophenol (Hspo) the bridged dimer [Re2(CO)7(spo)2] was found. The neutral complex [Re(CO)3(ons)(Hno)] was isolated from the reaction of [Re(CO)5Br] with 2-[(2-methylthio)benzylideneimino]phenol (Hons; Hno = 2-aminophenol), with ons coordinated as a bidentate chelate with a free SCH3 group. In the complex [Re(CO)3(Htpn)Br] (Htpn = N-(2-(methylthio)benzylidene)benzene-1,2-diamine) the potentially tridentate ligand Htpn is coordinated via the methylthiol sulfur and imino nitrogen atoms only, with a free amino group. These rhenium(I) complexes, with the exception of [Re2(CO)7(spo)2], revealed broad emissions centred around 535 nm. The reactions of the rhenium(V) complex cis-[ReO2I(PPh3)2] with 2-aminothiophenol (H2atp), benzene-1,2-dithiol (H2tdt) and 2-hydroxybenzenethiol (H2otp) led to the formation of the rhenium(III) compounds [Re(Hatp)(ibsq)2].OPPh3, [Re(sbsq)3].OPPh3 and [Re(obsq)3].OPPh3 (ibsq = 2-iminothiobenzosemiquinonate, sbsq = 1,2-dithiobenzosemiquinonate, obsq = 2-hydroxothiobenzosemiquinonate) respectively. The complexes adopt a trigonal prismatic geometry around the rhenium centre with average twists angles between 3.20-26.10˚. The E1/2 values for the Re(III)/Re(IV) redox couple were found to be 0.022, 0.142 and 0.126 V for [Re(Hatp)(ibsq)2].OPPh3, [Re(sbsq)3].OPPh3 and [Re(obsq)3].OPPh3 respectively. The reactions of the benzoxazole ligands, 3-(benzoxazol-2-yl)pyridin-2-ol (Hbop) and 5-amino-2-(benzoxazol-2-yl)phenol (Habo) with a [ReO]3+ precursor led to the rhenium(III) complex, [ReCl2(bop)(PPh3)2], and the complex salt, [ReO(abo)I(PPh3)2]ReO4, respectively. A variety of benzothiazole and benzimidazole derivatives were reacted with [Re(CO)5Br]. In the case of bis(benzothiazol-2-ylethyl)sulfide (bts), the neutral complex fac-[Re(CO)3(bts)Br] was obtained. The dimeric complexes (μ-dbt)2[Re(CO)3]2 and (μ-mbt)2[Re(CO)3]2 were formed when 1,3-bis(benzothiazol-2-yl)thiourea (Hdbt) and 1-(benzothiazol-2-ylidene)-3-methylthiourea (Hmbt) were used as ligands. The reaction of 2,2’-(oxybis(methylene))bis(benzimidazole) (bmb) with [Re(CO)5Cl] resulted in the rhenium(I) complex salt fac-[Re(CO)3(bmb)]+, with the tri-μ-chlorohexacarbonyl dirhenate [Re2(CO)6Cl3]- as the counter anion. The neutral complex fac-[Re(CO)3(btp)Cl] was isolated from the reaction of the 2,9-bis(benzothiazol-2-yl)-1,10-phenanthroline (btp) ligand and [Re(CO)5Cl]. The reactions of trans-[ReOCl3(PPh3)2] with bis(benzimidazol-2-ylethyl)sulfide (btn) and 1-(benzothiazol-2-ylidene)-3-methylthiourea (Hmbt) led to the formation of the cationic compounds (μ-O)2[Re2O2(btn)2]I2 and [ReCl2(bte)(PPh3)2]Cl (bte = (benzothiazole-2-yl)-N-ethylidenemethanamine) respectively.
- Full Text:
- Date Issued: 2012
Finite element analysis of the heat transfer in friction stir welding with experimental validation
- Authors: Vosloo, Natalie
- Date: 2012
- Subjects: Finite element method , Heat -- Transmission , Friction welding
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10511 , http://hdl.handle.net/10948/d1019981
- Description: Friction stir welding is a relatively new joining process. The heat transfer involved is crucial in determining the quality of the weld. Experimenrtal data, though important, does not provide enough information about the heat transfer process and experiments can be costly and time consuming. A numerical model, using the finite element method, was developed to stimulate the heat transfer in the workpiece in which the heat generation due to friction and plastic deformation was modelled as a surface heat flux boundary condition. This model was applied to Aluminium AL6082-T6 and Titanium Ti6A1-4V for different welding condiitions. Results were validated with experimental results. The model was shown to give better predictions of the maximum temperatures at locations in the workpiece than the overall temperature trend. A parametric study was also performed on the Aluminium model in order o predict temperature fields of the workpiece for welding conditions that were additional to those undertaken experimentally. It was found that rotational speed had a larger effect on the change in temperature than the feed rate. From the parametric study it was also clear that lower rotational speeds (300 to 660 rpm) had a greater effect on the change in temperature than the higher rotational speeds (840 to 1200 rpm). It was concluded that the model was well suited for the estimation of temperatures involved in the FSw of Aluminium Al6082-T6 but was not as accurate when applied to the FSW of Titanium.
- Full Text:
- Date Issued: 2012
- Authors: Vosloo, Natalie
- Date: 2012
- Subjects: Finite element method , Heat -- Transmission , Friction welding
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10511 , http://hdl.handle.net/10948/d1019981
- Description: Friction stir welding is a relatively new joining process. The heat transfer involved is crucial in determining the quality of the weld. Experimenrtal data, though important, does not provide enough information about the heat transfer process and experiments can be costly and time consuming. A numerical model, using the finite element method, was developed to stimulate the heat transfer in the workpiece in which the heat generation due to friction and plastic deformation was modelled as a surface heat flux boundary condition. This model was applied to Aluminium AL6082-T6 and Titanium Ti6A1-4V for different welding condiitions. Results were validated with experimental results. The model was shown to give better predictions of the maximum temperatures at locations in the workpiece than the overall temperature trend. A parametric study was also performed on the Aluminium model in order o predict temperature fields of the workpiece for welding conditions that were additional to those undertaken experimentally. It was found that rotational speed had a larger effect on the change in temperature than the feed rate. From the parametric study it was also clear that lower rotational speeds (300 to 660 rpm) had a greater effect on the change in temperature than the higher rotational speeds (840 to 1200 rpm). It was concluded that the model was well suited for the estimation of temperatures involved in the FSw of Aluminium Al6082-T6 but was not as accurate when applied to the FSW of Titanium.
- Full Text:
- Date Issued: 2012
Phytoplankton associated with mesoscale eddies in the Mozambique Channel
- Authors: O'Reilly, Bevan James
- Date: 2012
- Subjects: Mozambique Channel. , Phytoplankton
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10622 , http://hdl.handle.net/10948/d1010967 , Mozambique Channel. , Phytoplankton
- Description: The study undertaken was an attempt to provide information on the effect that oceanographic features common in the Mozambique Channel have on primary production. Oligotrophic conditions dominated the Mozambique Channel at the time of sampling and the introduction of nutrients into the euphotic zone by upwelling processes were identified as cyclonic eddies. Differences in physico-chemical variables between surface and F-max across all sites proved to be stronger than the physico-chemical variables between 4 grouped oceanographic features. This was revealed by stronger variations in phytoplankton community structure and chlorophyll a concentration between surface and F-max compared to oceanographic features sampled. One of the hypotheses presented for the study was that diatoms would dominate phytoplankton communities within a cyclonic eddy. This was not the case as the coccolithophorid, Emiliania huxleyi Lohmann (Hay and Mohler 1967) dominated F-max and surface water in the cyclonic eddies and most other sites. Phytoplankton community structure did not differ significantly between the oceanographic features sampled which contradicted another one of hypotheses presented in the study. Chlorophyll a concentration in surface water of the cyclonic eddies was significantly higher than in surface waters within the anti-cyclonic eddy. F-max was not significantly different in phytoplankton biomass between these two system types. The cyclonic eddies and anti-cyclone had similar phytoplankton diversity which did not verify the hypothesis that there would be less phytoplankton species diversity within cyclonic eddies compared to the anti-cyclonic eddy. Phytoplankton community structure differed between F-max (depth at which maximum chlorophyll a is found) and the surface. This phytoplankton community difference was linked to differences in physico-chemical variables between the two depths. The diatoms Thalassionema nitzschioides, Pseudo-nitzschia sp.A, Pseudo-nitzschia sp.B, Thalassiosira sp.C, Thalassiosira sp.E, Bacteriastrum furcatum, Guinardia cylindrus, Nitzschia closterium, Hemiaulus hauckii, and Nitzschia braarudii revealed the only discernible ecological similarity amongst phytoplankton species across all sites and depths. This is important as it revealed that these species were regularly found occupying similar depths and potentially similar physico-chemical ranges in the water column which suggest these diatom species responded to a dominant source of variation. Distribution patterns of species and of ecologically defined groups support the hypothesis that diatom species and assemblages are good indicators of the changing character of an upwelling system. These statements lead to the assumption that the diatom grouping found in this study indicates areas of upwelling where water temperatures are reduced and nutrients are more readily available. One must keep in mind that ordination techniques are only descriptive and no significance is tested. The coccolithophorid D. anthos and the dinoflagellate Phalacroma spp. were noted as being most dissimilar to all other phytoplankton species with regards to their position in the water column and their response to physico-chemical variables. Finally, the dominance of E. huxleyi in the Mozambique Channel during November/December of 2009 reveals the potential vulnerability of phytoplankton in the channel to ocean acidification.
- Full Text:
- Date Issued: 2012
- Authors: O'Reilly, Bevan James
- Date: 2012
- Subjects: Mozambique Channel. , Phytoplankton
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10622 , http://hdl.handle.net/10948/d1010967 , Mozambique Channel. , Phytoplankton
- Description: The study undertaken was an attempt to provide information on the effect that oceanographic features common in the Mozambique Channel have on primary production. Oligotrophic conditions dominated the Mozambique Channel at the time of sampling and the introduction of nutrients into the euphotic zone by upwelling processes were identified as cyclonic eddies. Differences in physico-chemical variables between surface and F-max across all sites proved to be stronger than the physico-chemical variables between 4 grouped oceanographic features. This was revealed by stronger variations in phytoplankton community structure and chlorophyll a concentration between surface and F-max compared to oceanographic features sampled. One of the hypotheses presented for the study was that diatoms would dominate phytoplankton communities within a cyclonic eddy. This was not the case as the coccolithophorid, Emiliania huxleyi Lohmann (Hay and Mohler 1967) dominated F-max and surface water in the cyclonic eddies and most other sites. Phytoplankton community structure did not differ significantly between the oceanographic features sampled which contradicted another one of hypotheses presented in the study. Chlorophyll a concentration in surface water of the cyclonic eddies was significantly higher than in surface waters within the anti-cyclonic eddy. F-max was not significantly different in phytoplankton biomass between these two system types. The cyclonic eddies and anti-cyclone had similar phytoplankton diversity which did not verify the hypothesis that there would be less phytoplankton species diversity within cyclonic eddies compared to the anti-cyclonic eddy. Phytoplankton community structure differed between F-max (depth at which maximum chlorophyll a is found) and the surface. This phytoplankton community difference was linked to differences in physico-chemical variables between the two depths. The diatoms Thalassionema nitzschioides, Pseudo-nitzschia sp.A, Pseudo-nitzschia sp.B, Thalassiosira sp.C, Thalassiosira sp.E, Bacteriastrum furcatum, Guinardia cylindrus, Nitzschia closterium, Hemiaulus hauckii, and Nitzschia braarudii revealed the only discernible ecological similarity amongst phytoplankton species across all sites and depths. This is important as it revealed that these species were regularly found occupying similar depths and potentially similar physico-chemical ranges in the water column which suggest these diatom species responded to a dominant source of variation. Distribution patterns of species and of ecologically defined groups support the hypothesis that diatom species and assemblages are good indicators of the changing character of an upwelling system. These statements lead to the assumption that the diatom grouping found in this study indicates areas of upwelling where water temperatures are reduced and nutrients are more readily available. One must keep in mind that ordination techniques are only descriptive and no significance is tested. The coccolithophorid D. anthos and the dinoflagellate Phalacroma spp. were noted as being most dissimilar to all other phytoplankton species with regards to their position in the water column and their response to physico-chemical variables. Finally, the dominance of E. huxleyi in the Mozambique Channel during November/December of 2009 reveals the potential vulnerability of phytoplankton in the channel to ocean acidification.
- Full Text:
- Date Issued: 2012
Vapour phase dehydrogenation of cyclohexane on microstructured reactors
- Authors: Mpuhlu, Batsho
- Date: 2012
- Subjects: Dehydrogenation , Cyclohexane
- Language: English
- Type: Thesis , Doctoral , DTech (Chemistry)
- Identifier: http://hdl.handle.net/10948/8661 , vital:26418
- Description: The work that is described in this thesis forms part of the research and development projects at InnoVenton: NMMU Institute of Chemical Technology in collaboration with Sasol Technologies. The broader view of the project was testing on the so-called “Small Production Platforms” (SPP’s). In particular the main aim of this study was to investigate the effect of micro-structuring on the heterogeneous catalysed, vapour-phase oxidative dehydrogenation of cyclohexane in the presence of air. Ground work studies were done to provide a proper comparison of the micro-structured reactor with a traditional fixed-bed reactor. These included evaluation of a proper vanadium pyrophosphate catalyst for the reaction, testing of reaction parameters for the oxidative dehydrogenation reaction on a fixed-bed reactor and lastly comparing the performance of the micro-structured reactor to that of the fixed-bed reactor Various vanadium pyrophosphate catalysts that were tested for activity included: bulk (VO)2P2O7, bulk (VO)2P2O7 promoted with Fe, (VO)2P2O7 supported on -Al2O3 and Fe promoted (VO)2P2O7 supported on -Al2O3. These catalysts showed significant differences in TOF, however it was not conclusive from the results whether these differences may be traced to increased activity for dehydrogenation for different catalysts since all reactions were run under conditions of oxygen deficiency. It is, however, clear that Fe promotion significantly increase activity, irrespective of the relative degrees of oxidative dehydrogenation and normal dehydrogenation. The Fe promoted catalyst was further tested for long term stability in-view of using it as the catalyst in the micro-structured reactor. These studies showed the catalyst to have a high degree of stability with minimal structural changes under the reaction conditions used. Various response surface models describing the variation in each of the cyclohexane conversion, cyclohexene selectivity, and benzene selectivity, respectively when changing reaction condition, were derived by means of multiple regression. To obtain some idea of the degree and nature of the normal dehydrogenation reaction, the amount of deficit oxygen was estimated from the measured results for cyclohexane conversion and cyclohexene and benzene selectivities. These estimated values were also modelled as described above. The regression models were used to interpret specific trends in the responses for the oxidative dehydrogenation of cyclohexane and account for the oxygen deficit in the system. The performance of a fixed bed tubular reactor (FBR) and micro-structured sandwich reactor (MSSR) were compared over an Fe promoted vanadium pyrophosphate. Reactor performance was evaluated by varying specific reaction conditions (temperature and space velocity). Subsequently the turn-over frequencies, conversion and selectivities from the two reactors were compared. The conversion achieved in the micro-structured reactor was observed to be significantly higher than that achieved in the fixed-bed reactor at all reaction parameters. This is despite the fact that the total amount of catalyst in the micro-structured reactor is approximately 5 times less than that used in the fixed bed reactor. In addition, the contact time (1/MHSV) in the micro-structured reactor is also significantly shorter than in the fixed-bed reactor.
- Full Text:
- Date Issued: 2012
- Authors: Mpuhlu, Batsho
- Date: 2012
- Subjects: Dehydrogenation , Cyclohexane
- Language: English
- Type: Thesis , Doctoral , DTech (Chemistry)
- Identifier: http://hdl.handle.net/10948/8661 , vital:26418
- Description: The work that is described in this thesis forms part of the research and development projects at InnoVenton: NMMU Institute of Chemical Technology in collaboration with Sasol Technologies. The broader view of the project was testing on the so-called “Small Production Platforms” (SPP’s). In particular the main aim of this study was to investigate the effect of micro-structuring on the heterogeneous catalysed, vapour-phase oxidative dehydrogenation of cyclohexane in the presence of air. Ground work studies were done to provide a proper comparison of the micro-structured reactor with a traditional fixed-bed reactor. These included evaluation of a proper vanadium pyrophosphate catalyst for the reaction, testing of reaction parameters for the oxidative dehydrogenation reaction on a fixed-bed reactor and lastly comparing the performance of the micro-structured reactor to that of the fixed-bed reactor Various vanadium pyrophosphate catalysts that were tested for activity included: bulk (VO)2P2O7, bulk (VO)2P2O7 promoted with Fe, (VO)2P2O7 supported on -Al2O3 and Fe promoted (VO)2P2O7 supported on -Al2O3. These catalysts showed significant differences in TOF, however it was not conclusive from the results whether these differences may be traced to increased activity for dehydrogenation for different catalysts since all reactions were run under conditions of oxygen deficiency. It is, however, clear that Fe promotion significantly increase activity, irrespective of the relative degrees of oxidative dehydrogenation and normal dehydrogenation. The Fe promoted catalyst was further tested for long term stability in-view of using it as the catalyst in the micro-structured reactor. These studies showed the catalyst to have a high degree of stability with minimal structural changes under the reaction conditions used. Various response surface models describing the variation in each of the cyclohexane conversion, cyclohexene selectivity, and benzene selectivity, respectively when changing reaction condition, were derived by means of multiple regression. To obtain some idea of the degree and nature of the normal dehydrogenation reaction, the amount of deficit oxygen was estimated from the measured results for cyclohexane conversion and cyclohexene and benzene selectivities. These estimated values were also modelled as described above. The regression models were used to interpret specific trends in the responses for the oxidative dehydrogenation of cyclohexane and account for the oxygen deficit in the system. The performance of a fixed bed tubular reactor (FBR) and micro-structured sandwich reactor (MSSR) were compared over an Fe promoted vanadium pyrophosphate. Reactor performance was evaluated by varying specific reaction conditions (temperature and space velocity). Subsequently the turn-over frequencies, conversion and selectivities from the two reactors were compared. The conversion achieved in the micro-structured reactor was observed to be significantly higher than that achieved in the fixed-bed reactor at all reaction parameters. This is despite the fact that the total amount of catalyst in the micro-structured reactor is approximately 5 times less than that used in the fixed bed reactor. In addition, the contact time (1/MHSV) in the micro-structured reactor is also significantly shorter than in the fixed-bed reactor.
- Full Text:
- Date Issued: 2012
The effects of salinity and inundation on salt marsh plants in the context of climate change
- Authors: Tabot, Pascal Tabi
- Date: 2012
- Subjects: Salt marsh plants -- Climatic factors , Plant ecophysiology
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10637 , http://hdl.handle.net/10948/d1019919
- Description: Ecophysiology studies are needed to predict plant responses in relation to climate change. Variations in salinity and inundation are expected to influence the survival and distribution of salt marsh. The following species were chosen to study as they occur in most South African salt marshes and are representative of different tidal ranges; namely Triglochin buchenaui (lower intertidal), Bassia diffusa (upper intertidal succulent) and Limonium linifolium (upper intertidal non-succulent). To simulate climate change conditions as predicted for South Africa, a 3 x 5 controlled experiment of three inundation levels (tidal, submerged and drought) and five salinity levels (0, 8, 18, 35, 45 ppt) was conducted for each species. This resulted in 15 treatments per species. Plant responses were measured over a three month period. Triglochin buchenaui showed significant variation in height (7.57 ± 0.5 to 29 ± 1.55 cm, p < 0.005, DF = 55) with optimum growth at 0 ppt under tidal conditions; leaf area increments and relative growth rates which decreased with increasing salinity under all inundation states. There was almost a cessation of growth under submergence which reduces the plant’s regeneration potential under these conditions. Proline accumulation (1.84 ± 0.23 to 3.36 ± 0.38 mg l-1), response of photosynthetic pigments and electrolyte leakage (8.17 ± 0.80 to 38.36 ± 7.42 percent) were fundamental to osmotic and membrane response regulation. Plants survived in all inundation states at salinity up to 45 ppt, but the optimum range was 0 to 18 ppt, and best water state was the tidal condition. Viable rhizomes were produced under drought conditions. Bassia diffusa (Thunb.) Kuntze plants under submergence died within one month, irrespective of the salinity. Optimum growth occurred in plants of the tidal treatment at 18 ppt, and reduced with increased salinity and drought conditions. Plants in the tidal treatments were more succulent than the drought-treated plants. There was reduced leaf mass and high anthocyanin concentrations in drought-treated plants and these effects increased with salinity. Soil and leaf water potential were positively correlated with anthocyanin concentration in leaves and stems, suggesting anthocyanin accumulated in response to drought and could be an adaptation to lower the plant’s water potential under drought conditions. A shift of anthocyanin from leaves to stems was found in drought-treated plants, and this possibly enables the maximization of photosynthesis in leaves, to complement its role in osmotic balance and photo-protection. Growth of Limonium linifolium showed that the plant was tolerant to a wide range of salinity under both tidal and drought conditions, but was susceptible to complete submergence, with high membrane damage even in tidal-treated plants. Plants died within 2 weeks of complete submergence. Results further indicated that L. linifolium tolerates extreme drought by accumulating large quantities of proline and oxalic acid, which consequently lowers its water potential for uptake of soil water of high salinity. Excess salts were excreted through salt glands. This is an important adaptation for a plant that thrives in a highly variable saline habitat Further investigation of submergence effects on upper intertidal species using B. diffusa showed three key stages in the response. A drop in chlorophyll a+b within 6 hours (4.2 ± 0.2 to 2.4 ± 0.3 mg l-1) with a corresponding increase in carotenoid concentration (0.6 ± 0.1 mg l-1) indicated an immediate response to submergence. Oxalic acid concentration was highest on Day 4 (13.6 mM) as opposed to control levels, indicative of its role in submergence tolerance, thus Day 4 may be the peak of positive acclimation. The third phase was marked by a sharp increase in electrolyte leakage to 47.5 ± 2.6 percent on Day 10, from 9.4 ± 1.4 percent on Day 7, with a corresponding decrease in total dissolved solutes between Days 7 and 10. Results suggest that oxalic acid accumulates under submergence possibly as a stabilizing osmolyte. The threshold for tolerance of the species under submergence is 7 days with membrane damage thereafter. Bassia diffusa would not survive prolonged submergence (> 7 days) but could survive submergence of short duration (< 7 days) through continuous underwater photosynthesis, accumulation of osmolytes such as oxalic acid and carotenoid, and maintenance of relative water content and succulence within control levels. When considered together, results showed that the two upper intertidal species were sensitive to waterlogging and would not survive complete submergence, whereas the lower intertidal species could in addition to its natural range, thrive in conditions typical of the upper intertidal range, namely prolonged dry conditions and high sediment salinity. These results have important implications for the future management of salt marshes under predicted climate change conditions. In permanently open South African estuaries, a landward migration of salt marsh will be possible if coastal squeeze is limited and the rate of landward recruitment is on par with sea level rise. In this case salt marsh species would retain their current zonation while shifting inland. Increased sea storms and saltwater intrusion could lead to high salinity concentration in the sediment and significantly reduce growth of salt-sensitive plants. In estuaries that are temporarily open to the sea, reduced freshwater inflow will result in an increase in mouth closure, high water levels, prolonged submergence, and consequently die back of salt marsh vegetation. On the other hand increased abstraction and drought would result in low water levels and high sediment salinity which would decrease growth and survival of salt marsh. This research has provided new knowledge on the ecophysiology of salt marsh plants which can be used to predict the responses of plants to climate change.
- Full Text:
- Date Issued: 2012
- Authors: Tabot, Pascal Tabi
- Date: 2012
- Subjects: Salt marsh plants -- Climatic factors , Plant ecophysiology
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10637 , http://hdl.handle.net/10948/d1019919
- Description: Ecophysiology studies are needed to predict plant responses in relation to climate change. Variations in salinity and inundation are expected to influence the survival and distribution of salt marsh. The following species were chosen to study as they occur in most South African salt marshes and are representative of different tidal ranges; namely Triglochin buchenaui (lower intertidal), Bassia diffusa (upper intertidal succulent) and Limonium linifolium (upper intertidal non-succulent). To simulate climate change conditions as predicted for South Africa, a 3 x 5 controlled experiment of three inundation levels (tidal, submerged and drought) and five salinity levels (0, 8, 18, 35, 45 ppt) was conducted for each species. This resulted in 15 treatments per species. Plant responses were measured over a three month period. Triglochin buchenaui showed significant variation in height (7.57 ± 0.5 to 29 ± 1.55 cm, p < 0.005, DF = 55) with optimum growth at 0 ppt under tidal conditions; leaf area increments and relative growth rates which decreased with increasing salinity under all inundation states. There was almost a cessation of growth under submergence which reduces the plant’s regeneration potential under these conditions. Proline accumulation (1.84 ± 0.23 to 3.36 ± 0.38 mg l-1), response of photosynthetic pigments and electrolyte leakage (8.17 ± 0.80 to 38.36 ± 7.42 percent) were fundamental to osmotic and membrane response regulation. Plants survived in all inundation states at salinity up to 45 ppt, but the optimum range was 0 to 18 ppt, and best water state was the tidal condition. Viable rhizomes were produced under drought conditions. Bassia diffusa (Thunb.) Kuntze plants under submergence died within one month, irrespective of the salinity. Optimum growth occurred in plants of the tidal treatment at 18 ppt, and reduced with increased salinity and drought conditions. Plants in the tidal treatments were more succulent than the drought-treated plants. There was reduced leaf mass and high anthocyanin concentrations in drought-treated plants and these effects increased with salinity. Soil and leaf water potential were positively correlated with anthocyanin concentration in leaves and stems, suggesting anthocyanin accumulated in response to drought and could be an adaptation to lower the plant’s water potential under drought conditions. A shift of anthocyanin from leaves to stems was found in drought-treated plants, and this possibly enables the maximization of photosynthesis in leaves, to complement its role in osmotic balance and photo-protection. Growth of Limonium linifolium showed that the plant was tolerant to a wide range of salinity under both tidal and drought conditions, but was susceptible to complete submergence, with high membrane damage even in tidal-treated plants. Plants died within 2 weeks of complete submergence. Results further indicated that L. linifolium tolerates extreme drought by accumulating large quantities of proline and oxalic acid, which consequently lowers its water potential for uptake of soil water of high salinity. Excess salts were excreted through salt glands. This is an important adaptation for a plant that thrives in a highly variable saline habitat Further investigation of submergence effects on upper intertidal species using B. diffusa showed three key stages in the response. A drop in chlorophyll a+b within 6 hours (4.2 ± 0.2 to 2.4 ± 0.3 mg l-1) with a corresponding increase in carotenoid concentration (0.6 ± 0.1 mg l-1) indicated an immediate response to submergence. Oxalic acid concentration was highest on Day 4 (13.6 mM) as opposed to control levels, indicative of its role in submergence tolerance, thus Day 4 may be the peak of positive acclimation. The third phase was marked by a sharp increase in electrolyte leakage to 47.5 ± 2.6 percent on Day 10, from 9.4 ± 1.4 percent on Day 7, with a corresponding decrease in total dissolved solutes between Days 7 and 10. Results suggest that oxalic acid accumulates under submergence possibly as a stabilizing osmolyte. The threshold for tolerance of the species under submergence is 7 days with membrane damage thereafter. Bassia diffusa would not survive prolonged submergence (> 7 days) but could survive submergence of short duration (< 7 days) through continuous underwater photosynthesis, accumulation of osmolytes such as oxalic acid and carotenoid, and maintenance of relative water content and succulence within control levels. When considered together, results showed that the two upper intertidal species were sensitive to waterlogging and would not survive complete submergence, whereas the lower intertidal species could in addition to its natural range, thrive in conditions typical of the upper intertidal range, namely prolonged dry conditions and high sediment salinity. These results have important implications for the future management of salt marshes under predicted climate change conditions. In permanently open South African estuaries, a landward migration of salt marsh will be possible if coastal squeeze is limited and the rate of landward recruitment is on par with sea level rise. In this case salt marsh species would retain their current zonation while shifting inland. Increased sea storms and saltwater intrusion could lead to high salinity concentration in the sediment and significantly reduce growth of salt-sensitive plants. In estuaries that are temporarily open to the sea, reduced freshwater inflow will result in an increase in mouth closure, high water levels, prolonged submergence, and consequently die back of salt marsh vegetation. On the other hand increased abstraction and drought would result in low water levels and high sediment salinity which would decrease growth and survival of salt marsh. This research has provided new knowledge on the ecophysiology of salt marsh plants which can be used to predict the responses of plants to climate change.
- Full Text:
- Date Issued: 2012
The contribution of the trade in medicinal plants to urban livelihoods: a case study of the informal markets in Nelson Mandela Bay Municipality, Eastern Cape
- Ah Goo, Delia Felecia Stephanie
- Authors: Ah Goo, Delia Felecia Stephanie
- Date: 2012
- Subjects: Medicinal plants -- South Africa -- Port Elizabeth , Informal sector (Economics) -- South Africa -- Eastern Cape , Traditional medicine -- South Africa -- Port Elizabeth -- Markets
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10654 , http://hdl.handle.net/10948/d1011601 , Medicinal plants -- South Africa -- Port Elizabeth , Informal sector (Economics) -- South Africa -- Eastern Cape , Traditional medicine -- South Africa -- Port Elizabeth -- Markets
- Description: The commercialisation of natural resources such as medicinal plants is a strategy that is increasingly being employed by poor people in developing countries such as South Africa, as a means of generating an income. Increasing economic hardship and a lack of employment opportunities in the formal sector of the economy has led to many urban dwellers seeking alternative means of meeting their everyday livelihood needs. Although the contribution of natural resources to subsistence economies is widely recognised, there are few studies that have examined the significance of the trade in medicinal plants to the livelihoods of poor and marginalised people. Thirty informal street traders were interviewed to investigate the role of the medicinal plant trade in sustaining the livelihoods of the traders who operate in the informal sector of the Nelson Mandela Bay Municipality, South Africa. The findings of the research indicate that the sale and collection of medicinal plants is an activity which is exploited by people with limited resources, few skills, little or no education and often without any other source of household income. Middle-aged women from impoverished, single income households dominated the trade. Although income from the trade is modest, it contributed substantially to the total household cash income of the traders. Other benefits of the trade included independence and having a sense of purpose in life, as the traders felt that they were not only helping their families but also the wider community. However, without the income from the trade, many of the traders and their families would be destitute and thus the medicinal plant trade is vital to the wellbeing of these people.
- Full Text:
- Date Issued: 2012
- Authors: Ah Goo, Delia Felecia Stephanie
- Date: 2012
- Subjects: Medicinal plants -- South Africa -- Port Elizabeth , Informal sector (Economics) -- South Africa -- Eastern Cape , Traditional medicine -- South Africa -- Port Elizabeth -- Markets
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10654 , http://hdl.handle.net/10948/d1011601 , Medicinal plants -- South Africa -- Port Elizabeth , Informal sector (Economics) -- South Africa -- Eastern Cape , Traditional medicine -- South Africa -- Port Elizabeth -- Markets
- Description: The commercialisation of natural resources such as medicinal plants is a strategy that is increasingly being employed by poor people in developing countries such as South Africa, as a means of generating an income. Increasing economic hardship and a lack of employment opportunities in the formal sector of the economy has led to many urban dwellers seeking alternative means of meeting their everyday livelihood needs. Although the contribution of natural resources to subsistence economies is widely recognised, there are few studies that have examined the significance of the trade in medicinal plants to the livelihoods of poor and marginalised people. Thirty informal street traders were interviewed to investigate the role of the medicinal plant trade in sustaining the livelihoods of the traders who operate in the informal sector of the Nelson Mandela Bay Municipality, South Africa. The findings of the research indicate that the sale and collection of medicinal plants is an activity which is exploited by people with limited resources, few skills, little or no education and often without any other source of household income. Middle-aged women from impoverished, single income households dominated the trade. Although income from the trade is modest, it contributed substantially to the total household cash income of the traders. Other benefits of the trade included independence and having a sense of purpose in life, as the traders felt that they were not only helping their families but also the wider community. However, without the income from the trade, many of the traders and their families would be destitute and thus the medicinal plant trade is vital to the wellbeing of these people.
- Full Text:
- Date Issued: 2012
Network analysis of trophic linkages in two sub-tropical estuaries along the South-East coast of South Africa
- Authors: Vosloo, Mathys Christiaan
- Date: 2012
- Subjects: Estuaries -- South Africa -- Eastern Cape , Estuarine ecology , Network analysis (Planning)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10708 , http://hdl.handle.net/10948/d1010966 , Estuaries -- South Africa -- Eastern Cape , Estuarine ecology , Network analysis (Planning)
- Description: Estuaries are some of the most productive yet threatened ecosystems in the world. Despite their importance they face significant threats through changes to river flow, eutrophication, rapid population growth long the caost and harvesting of natural resources. A number of international studies have been conducted investigating the structure and functioning of an array of ecosystems using ecological network analysis. Energy flow networks have been contsructed for coastal, lagoonal, intertidial and, most notably, permantently open estuaries. Despite the valualble insights contributed by these and other studies, a lack of information on the majority of estuarine ecosystems exists.
- Full Text:
- Date Issued: 2012
- Authors: Vosloo, Mathys Christiaan
- Date: 2012
- Subjects: Estuaries -- South Africa -- Eastern Cape , Estuarine ecology , Network analysis (Planning)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10708 , http://hdl.handle.net/10948/d1010966 , Estuaries -- South Africa -- Eastern Cape , Estuarine ecology , Network analysis (Planning)
- Description: Estuaries are some of the most productive yet threatened ecosystems in the world. Despite their importance they face significant threats through changes to river flow, eutrophication, rapid population growth long the caost and harvesting of natural resources. A number of international studies have been conducted investigating the structure and functioning of an array of ecosystems using ecological network analysis. Energy flow networks have been contsructed for coastal, lagoonal, intertidial and, most notably, permantently open estuaries. Despite the valualble insights contributed by these and other studies, a lack of information on the majority of estuarine ecosystems exists.
- Full Text:
- Date Issued: 2012
Response of mangroves in South Africa to anthropogenic and natural impacts
- Hoppe-Speer, Sabine Clara-Lisa
- Authors: Hoppe-Speer, Sabine Clara-Lisa
- Date: 2012
- Subjects: Mangrove forests , Climatic changes , Forest resilience
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10630 , http://hdl.handle.net/10948/d1012123 , Mangrove forests , Climatic changes , Forest resilience
- Description: The total mangrove area cover in South Africa is 1631.7 ha, with the largest area cover in a few estuaries in the KwaZulu-Natal Province (1391.1 ha) and the remainder recorded in the Eastern Cape Province with 240.6 ha. This represents 0.05 percent of Africa‟s mangrove area cover and although small adds irreplaceable value to the biodiversity of South Africa. Mangroves are threatened by over-utilization through harvesting for firewood and building materials as well as excessive browsing and trampling by livestock. The objective of this study was to investigate the response of mangroves to different stressors from natural change as well as anthropogenic pressures. This was done by identifying pressures, measuring area cover, population structure and environmental parameters such as sediment characteristics. Mangroves in 17 estuaries along the east coast were investigated. Population structure and the area covered by mangroves in 2011/2012 were compared with data from the same area for 1999. Detailed studies were conducted in St. Lucia Estuary to investigate the response of mangroves to reduced tidal flooding; mangrove expansion at a latitudinal limit in a protected area at Nahoon Estuary was studied and the effect of cattle browsing on mangroves was measured at Nxaxo Estuary. The St. Lucia Estuary (28°S; 32°E) represented a unique study site as the mouth has been closed to the sea since 2002 and the mangrove habitats have been non-tidal. St. Lucia Estuary is both a Ramsar and World Heritage site and therefore understanding the response of mangroves to changes in the environment is important. In 2010 sediment characteristics and mangrove population structure were measured at four sites which were chosen to represent different salinity and water level conditions. The site fringing the main channel had the highest density of mangrove seedlings and saplings. The dry site had a lower density of mangroves with mostly only tall adult trees and few saplings. Mangrove tree height and density increased at sites with high sediment moisture and low surface sediment salinity. Few seedlings and saplings were found at sites with dry surface sediment and high salinity. Long term data are needed to assess the influence of mouth closure on recruitment and survival of the mangrove forest at St. Lucia Estuary; however this study has shown that sediment characteristics are unfavourable for mangrove growth at sites now characterized by a lack of tidal flooding. It is not known when exactly the mangroves were planted in Nahoon Estuary (32°S; 27° E), East London, but it is suspected that this was in the early 1970s. Avicennia marina (Forrsk.)Vierh. was planted first, followed a few years later by the planting of Bruguiera gymnorrhiza (L.) Lam. and Rhizophora mucronata (L.) among the larger A. marina trees. Surprisingly the mangrove population appears to be thriving and this study tested the hypothesis that mangroves have expanded and replaced salt marsh over a 33 year period. This study provides important information on mangroves growing at higher latitudes, where they were thought to not occur naturally due to lower annual average temperatures. It further provides insights on future scenarios of possible shifts in vegetation types due to climate change at one of the most southerly distribution sites worldwide. The expansion of mangroves was measured over a 33 year period (1978 - 2011) using past aerial photographs and Esri ArcGIS Desktop 10 software. In addition, field surveys were completed in 2011 to determine the population structure of the present mangrove forest and relate this to environmental conditions. The study showed that mangrove area cover increased linearly at a rate of 0.06 ha-1 expanding over a bare mudflat area, while the salt marsh area cover also increased (0.09 ha-1) but was found to be variable over time. The mangrove area is still small (< 2 ha) and at present no competition between mangroves and salt marsh can be deduced. Instead the area has the ability to maintain high biodiversity and biomass. Avicennia marina was the dominant mangrove species and had high recruitment (seedling density was 33 822 ± 16 364 ha-1) but only a few Bruguiera gymnorrhiza and Rhizophora mucronata individuals were found (< 10 adult trees). The site provides opportunities for studies on mangrove / salt marsh interactions in response to a changing climate at the most southern limit of mangrove distribution in Africa. This research has provided the baseline data, permanent quadrats and tagged trees to be used in future long-term monitoring of population growth and sediment characteristics. At Nxaxo Estuary (32°S; 28°E) the response of mangrove trees (Avicennia marina) to cattle browsing and trampling was investigated by using cattle exclusion plots. Exclusion plots were established by fencing in five 25 m2 quadrats and adjacent to each experimental quadrat a control quadrat (not fenced in, 25 m2) was set-up. Trees were tagged and measured annually from 2010 to 2012. Sediment salinity, pH, moisture, organic content, compaction as well as sediment particle size was also measured in each quadrat. Sediment characteristics did not vary between control and experimental plots but did show changes between the years. The mangrove trees in the cattle exclusion plots grew exponentially over a period of two years. There was a significant increase in mean plant height (5.41 ± 0.53 cm), crown volume (0.54 ± 0.01 m3) and crown diameter (7.09 ± 0.60 cm) from 2010 to 2012. Trees in the control plots had significantly lower growth (p < 0.05). There was a decrease in plant height (-0.07 ± 0.67cm1) and only small increases in crown volume (0.14 ± 0.1 m3) and crown diameter (2.03 ± 2.61 cm). The research showed that browsing on mangroves by cattle stunts growth and causes a shrubby appearance as a result of coppicing. The browsed trees were dwarfed with horizontal spreading of branches and intact foliage close to the ground while the plants in the cattle exclusion plots showed an increase in vertical growth and expansion. In the cattle exclusion plots there was a significantly higher percentage of flowering (67 percent) and fruiting (39 percent) trees in 2012 compared to the control sites where 34 percent of the plants were flowering and 5.4 percent of the plants carried immature propagules. Observations in the field also indicated that cattle had trampled a number of seedlings thus influencing mangrove survival. The study concluded that browsing changes the morphological structure of mangrove trees and reduces growth and seedling establishment. This is an additional stress that the mangroves are exposed to in rural areas where cattle are allowed to roam free. Seventeen permanently open estuaries provide habitat for mangrove forests along the former Transkei coast. This part of the Eastern Cape is mostly undeveloped and difficult to access. Mangrove area cover, species distribution, population structure and health of the mangrove habitat were compared with results from previous studies in 1982 and 1999. The mangrove Bruguiera gymnorrhiza had the densest stands and was widely distributed as it was present in 13 of the 17 estuaries. Avicennia marina was dominant in those estuaries which had the largest area cover of mangroves and was present in 10 estuaries, while Rhizophora mucronata was rare and only present in five estuaries. Anthropogenic and natural impacts were noted within the mangrove habitats in each of these estuaries. Harvesting of mangrove wood, livestock browsing and trampling and footpaths occurred in most of the estuaries (> 70 percent). It was observed that browsing on trees resulted in a clear browse-line and browsing on propagules mainly by goats resulted in reduced seedling establishment in most of the estuaries except those in protected areas. Mangroves had re-established in estuaries where they had been previously lost but mouth closure due to drought and sea storms resulted in the mass die back of mangroves in the Kobonqaba Estuary. There was a total loss of 31.5 ha in mangrove area cover in the last 30 years and this was a total reduction of 10.5 ha (11 percent) for every decade. This is high considering that the present total mangrove area cover is only 240.6 ha for all the Transkei estuaries. In this study it was concluded that the anthropogenic impacts such as livestock browsing and trampling as well as harvesting in these estuaries contributed most to the mangrove degradation as these are continuous pressures occurring over long periods and are expected to increase in future with increasing human population. Natural changes such as sea storms occur less frequently but could result in large scale destruction over shorter periods. Examples of these are mouth closure that result in mangrove mass mortality as well as strong floods which destroy forest by scouring of the banks.
- Full Text:
- Date Issued: 2012
- Authors: Hoppe-Speer, Sabine Clara-Lisa
- Date: 2012
- Subjects: Mangrove forests , Climatic changes , Forest resilience
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10630 , http://hdl.handle.net/10948/d1012123 , Mangrove forests , Climatic changes , Forest resilience
- Description: The total mangrove area cover in South Africa is 1631.7 ha, with the largest area cover in a few estuaries in the KwaZulu-Natal Province (1391.1 ha) and the remainder recorded in the Eastern Cape Province with 240.6 ha. This represents 0.05 percent of Africa‟s mangrove area cover and although small adds irreplaceable value to the biodiversity of South Africa. Mangroves are threatened by over-utilization through harvesting for firewood and building materials as well as excessive browsing and trampling by livestock. The objective of this study was to investigate the response of mangroves to different stressors from natural change as well as anthropogenic pressures. This was done by identifying pressures, measuring area cover, population structure and environmental parameters such as sediment characteristics. Mangroves in 17 estuaries along the east coast were investigated. Population structure and the area covered by mangroves in 2011/2012 were compared with data from the same area for 1999. Detailed studies were conducted in St. Lucia Estuary to investigate the response of mangroves to reduced tidal flooding; mangrove expansion at a latitudinal limit in a protected area at Nahoon Estuary was studied and the effect of cattle browsing on mangroves was measured at Nxaxo Estuary. The St. Lucia Estuary (28°S; 32°E) represented a unique study site as the mouth has been closed to the sea since 2002 and the mangrove habitats have been non-tidal. St. Lucia Estuary is both a Ramsar and World Heritage site and therefore understanding the response of mangroves to changes in the environment is important. In 2010 sediment characteristics and mangrove population structure were measured at four sites which were chosen to represent different salinity and water level conditions. The site fringing the main channel had the highest density of mangrove seedlings and saplings. The dry site had a lower density of mangroves with mostly only tall adult trees and few saplings. Mangrove tree height and density increased at sites with high sediment moisture and low surface sediment salinity. Few seedlings and saplings were found at sites with dry surface sediment and high salinity. Long term data are needed to assess the influence of mouth closure on recruitment and survival of the mangrove forest at St. Lucia Estuary; however this study has shown that sediment characteristics are unfavourable for mangrove growth at sites now characterized by a lack of tidal flooding. It is not known when exactly the mangroves were planted in Nahoon Estuary (32°S; 27° E), East London, but it is suspected that this was in the early 1970s. Avicennia marina (Forrsk.)Vierh. was planted first, followed a few years later by the planting of Bruguiera gymnorrhiza (L.) Lam. and Rhizophora mucronata (L.) among the larger A. marina trees. Surprisingly the mangrove population appears to be thriving and this study tested the hypothesis that mangroves have expanded and replaced salt marsh over a 33 year period. This study provides important information on mangroves growing at higher latitudes, where they were thought to not occur naturally due to lower annual average temperatures. It further provides insights on future scenarios of possible shifts in vegetation types due to climate change at one of the most southerly distribution sites worldwide. The expansion of mangroves was measured over a 33 year period (1978 - 2011) using past aerial photographs and Esri ArcGIS Desktop 10 software. In addition, field surveys were completed in 2011 to determine the population structure of the present mangrove forest and relate this to environmental conditions. The study showed that mangrove area cover increased linearly at a rate of 0.06 ha-1 expanding over a bare mudflat area, while the salt marsh area cover also increased (0.09 ha-1) but was found to be variable over time. The mangrove area is still small (< 2 ha) and at present no competition between mangroves and salt marsh can be deduced. Instead the area has the ability to maintain high biodiversity and biomass. Avicennia marina was the dominant mangrove species and had high recruitment (seedling density was 33 822 ± 16 364 ha-1) but only a few Bruguiera gymnorrhiza and Rhizophora mucronata individuals were found (< 10 adult trees). The site provides opportunities for studies on mangrove / salt marsh interactions in response to a changing climate at the most southern limit of mangrove distribution in Africa. This research has provided the baseline data, permanent quadrats and tagged trees to be used in future long-term monitoring of population growth and sediment characteristics. At Nxaxo Estuary (32°S; 28°E) the response of mangrove trees (Avicennia marina) to cattle browsing and trampling was investigated by using cattle exclusion plots. Exclusion plots were established by fencing in five 25 m2 quadrats and adjacent to each experimental quadrat a control quadrat (not fenced in, 25 m2) was set-up. Trees were tagged and measured annually from 2010 to 2012. Sediment salinity, pH, moisture, organic content, compaction as well as sediment particle size was also measured in each quadrat. Sediment characteristics did not vary between control and experimental plots but did show changes between the years. The mangrove trees in the cattle exclusion plots grew exponentially over a period of two years. There was a significant increase in mean plant height (5.41 ± 0.53 cm), crown volume (0.54 ± 0.01 m3) and crown diameter (7.09 ± 0.60 cm) from 2010 to 2012. Trees in the control plots had significantly lower growth (p < 0.05). There was a decrease in plant height (-0.07 ± 0.67cm1) and only small increases in crown volume (0.14 ± 0.1 m3) and crown diameter (2.03 ± 2.61 cm). The research showed that browsing on mangroves by cattle stunts growth and causes a shrubby appearance as a result of coppicing. The browsed trees were dwarfed with horizontal spreading of branches and intact foliage close to the ground while the plants in the cattle exclusion plots showed an increase in vertical growth and expansion. In the cattle exclusion plots there was a significantly higher percentage of flowering (67 percent) and fruiting (39 percent) trees in 2012 compared to the control sites where 34 percent of the plants were flowering and 5.4 percent of the plants carried immature propagules. Observations in the field also indicated that cattle had trampled a number of seedlings thus influencing mangrove survival. The study concluded that browsing changes the morphological structure of mangrove trees and reduces growth and seedling establishment. This is an additional stress that the mangroves are exposed to in rural areas where cattle are allowed to roam free. Seventeen permanently open estuaries provide habitat for mangrove forests along the former Transkei coast. This part of the Eastern Cape is mostly undeveloped and difficult to access. Mangrove area cover, species distribution, population structure and health of the mangrove habitat were compared with results from previous studies in 1982 and 1999. The mangrove Bruguiera gymnorrhiza had the densest stands and was widely distributed as it was present in 13 of the 17 estuaries. Avicennia marina was dominant in those estuaries which had the largest area cover of mangroves and was present in 10 estuaries, while Rhizophora mucronata was rare and only present in five estuaries. Anthropogenic and natural impacts were noted within the mangrove habitats in each of these estuaries. Harvesting of mangrove wood, livestock browsing and trampling and footpaths occurred in most of the estuaries (> 70 percent). It was observed that browsing on trees resulted in a clear browse-line and browsing on propagules mainly by goats resulted in reduced seedling establishment in most of the estuaries except those in protected areas. Mangroves had re-established in estuaries where they had been previously lost but mouth closure due to drought and sea storms resulted in the mass die back of mangroves in the Kobonqaba Estuary. There was a total loss of 31.5 ha in mangrove area cover in the last 30 years and this was a total reduction of 10.5 ha (11 percent) for every decade. This is high considering that the present total mangrove area cover is only 240.6 ha for all the Transkei estuaries. In this study it was concluded that the anthropogenic impacts such as livestock browsing and trampling as well as harvesting in these estuaries contributed most to the mangrove degradation as these are continuous pressures occurring over long periods and are expected to increase in future with increasing human population. Natural changes such as sea storms occur less frequently but could result in large scale destruction over shorter periods. Examples of these are mouth closure that result in mangrove mass mortality as well as strong floods which destroy forest by scouring of the banks.
- Full Text:
- Date Issued: 2012
The influence of nutrients on surf-zone phytoplankton
- Authors: Wolmarans, Karien
- Date: 2012
- Subjects: Phytoplankton , Algal blooms , Diatoms
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10608 , http://hdl.handle.net/10948/d1008080 , Phytoplankton , Algal blooms , Diatoms
- Description: The variability in surf-zone phytoplankton community composition together with variability in nutrient concentrations was studied at seven beaches along the coast near Port Elizabeth, South Africa over a one-year sampling period. The nutrient requirements of selected diatoms and dinoflagellates that co-occur at these beaches were studied. The highest nutrient concentrations were recorded at Brighton beach, with phosphate concentration being substantially higher than standards set out for both South African and European waters. Nitrate, ammonium and silicate concentrations were consistent (low variability) at all beaches. The species composition of beaches without surf diatoms was also not variable (except for King’s Beach – an artificial beach). Maitland beach was the only beach that could be identified as a surf diatom beach due to the presence of Anaulus australis. The surf diatom Anaulus australis was found to be a superior competitor compared to all other species tested: the other surf diatom Asterionellopsis glacialis, and the dinoflagellates Gonyaulax spinifera, Prorocentrum micans, and Scrippsiella trochoidea. Gonyaulax spinifera could possibly outcompete Anaulus australis in systems should nitrate become limiting.
- Full Text:
- Date Issued: 2012
- Authors: Wolmarans, Karien
- Date: 2012
- Subjects: Phytoplankton , Algal blooms , Diatoms
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10608 , http://hdl.handle.net/10948/d1008080 , Phytoplankton , Algal blooms , Diatoms
- Description: The variability in surf-zone phytoplankton community composition together with variability in nutrient concentrations was studied at seven beaches along the coast near Port Elizabeth, South Africa over a one-year sampling period. The nutrient requirements of selected diatoms and dinoflagellates that co-occur at these beaches were studied. The highest nutrient concentrations were recorded at Brighton beach, with phosphate concentration being substantially higher than standards set out for both South African and European waters. Nitrate, ammonium and silicate concentrations were consistent (low variability) at all beaches. The species composition of beaches without surf diatoms was also not variable (except for King’s Beach – an artificial beach). Maitland beach was the only beach that could be identified as a surf diatom beach due to the presence of Anaulus australis. The surf diatom Anaulus australis was found to be a superior competitor compared to all other species tested: the other surf diatom Asterionellopsis glacialis, and the dinoflagellates Gonyaulax spinifera, Prorocentrum micans, and Scrippsiella trochoidea. Gonyaulax spinifera could possibly outcompete Anaulus australis in systems should nitrate become limiting.
- Full Text:
- Date Issued: 2012
Incorporating prey demographics and predator social structure into prey selection and carrying capacity estimates for cheetah
- Authors: Clements, Hayley Susan
- Date: 2012
- Subjects: Carnivorous animals , Cheetah
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10754 , http://hdl.handle.net/10948/d1018606
- Description: There is a need for a refined understanding of large carnivore prey preference and carrying capacity (K). To date, K estimates for large carnivores have been developed from predictions of carnivore diet at a prey and predator species-level. These predictions therefore assume that all social classes within a carnivore species display similar prey preferences and that all demographic classes within a prey species are equally preferred or avoided. The objective of this study was to investigate the importance of including prey demographics and carnivore social class in carnivore diet descriptions and thereby K estimates, using cheetah Acinonyx jubatus as a study species. It was predicted that prey sex, prey age and cheetah social class influence cheetah prey preferences, when they influence the risk and ease of prey capture, and that their inclusion in a K model would improve its predictive strength. Based on an analysis of 1290 kills from South Africa, male coalition cheetah were found to prefer a broader weight range of prey than solitary cheetah. Prey demographics further influenced cheetah prey preference, when it corresponded to differences in prey size and the presence of horns. The current species-level K regression model for cheetah is based on preferred prey and thus omits highly abundant antelope that often comprise the majority of the diet, an artefact of the way in which preferences are calculated. A refinement of the species-level K regression model, to account for prey demographic- and cheetah social class-level differences in diet and the biomass of accessible prey (defined in this study as all non-avoided prey) instead of just preferred prey, doubled the predictive strength of the K model. Because group-hunting enabled predation on a broader weight range of prey, cheetah K was influenced by the ratio of male coalition cheetah to solitary cheetah in the population. The refined K regression model is derived from ecosystems supporting an intact carnivore guild. A mechanistic approach to estimating K, based on Caughley‟s (1977) maximum sustainable yield model, therefore better predicted cheetah K in systems devoid of lion Panthera leo and African wild dog Lycaon pictus, which were found to suppress cheetah density. This study improves our understanding of the relationships between prey demographics, cheetah social classes and intra-guild competition in determining cheetah prey preferences and K. This study therefore paves the way for similar work on other large carnivores.
- Full Text:
- Date Issued: 2012
- Authors: Clements, Hayley Susan
- Date: 2012
- Subjects: Carnivorous animals , Cheetah
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10754 , http://hdl.handle.net/10948/d1018606
- Description: There is a need for a refined understanding of large carnivore prey preference and carrying capacity (K). To date, K estimates for large carnivores have been developed from predictions of carnivore diet at a prey and predator species-level. These predictions therefore assume that all social classes within a carnivore species display similar prey preferences and that all demographic classes within a prey species are equally preferred or avoided. The objective of this study was to investigate the importance of including prey demographics and carnivore social class in carnivore diet descriptions and thereby K estimates, using cheetah Acinonyx jubatus as a study species. It was predicted that prey sex, prey age and cheetah social class influence cheetah prey preferences, when they influence the risk and ease of prey capture, and that their inclusion in a K model would improve its predictive strength. Based on an analysis of 1290 kills from South Africa, male coalition cheetah were found to prefer a broader weight range of prey than solitary cheetah. Prey demographics further influenced cheetah prey preference, when it corresponded to differences in prey size and the presence of horns. The current species-level K regression model for cheetah is based on preferred prey and thus omits highly abundant antelope that often comprise the majority of the diet, an artefact of the way in which preferences are calculated. A refinement of the species-level K regression model, to account for prey demographic- and cheetah social class-level differences in diet and the biomass of accessible prey (defined in this study as all non-avoided prey) instead of just preferred prey, doubled the predictive strength of the K model. Because group-hunting enabled predation on a broader weight range of prey, cheetah K was influenced by the ratio of male coalition cheetah to solitary cheetah in the population. The refined K regression model is derived from ecosystems supporting an intact carnivore guild. A mechanistic approach to estimating K, based on Caughley‟s (1977) maximum sustainable yield model, therefore better predicted cheetah K in systems devoid of lion Panthera leo and African wild dog Lycaon pictus, which were found to suppress cheetah density. This study improves our understanding of the relationships between prey demographics, cheetah social classes and intra-guild competition in determining cheetah prey preferences and K. This study therefore paves the way for similar work on other large carnivores.
- Full Text:
- Date Issued: 2012
Statistical tools for wind energy generation
- Authors: Ndzukuma, Sibusiso
- Date: 2012
- Subjects: Wind power , Wind turbines , Winds -- Speed
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10580 , http://hdl.handle.net/10948/d1020627
- Description: In this study we conduct wind resource assessment to evaluate the annual energy production of a wind turbine. To estimate energy production of a wind turbine over a period of time, the power characteristics of the wind turbine are integrated with the probabilities of the wind speed expected at a chosen site. The first data set was obtained from a wind farm in Denmark. We propose several probability density functions to model the distribution of the wind speed. We use techniques from nonlinear regression analysis to model the power curve of a wind turbine. The best fit distribution model is assessed by performing numeric goodness–of–fit measures and graphical analyses. Johnson’s bounded (SB) distribution provides the best fit model with the smallest Kolmogorov–Smirnov (K-S) test statistic . 15. The four parameter logistic nonlinear regression (4PL) model is determined to provide the best fit to the power curve data, according to the Akaike Information Criterion (AIC) and the Bayesian Information Criterion (BIC). The estimated annual energy yield is compared to the actual production of the wind turbine. Our models underestimate the actual energy production by a 1 difference. In Chapter Six we conduct data processing, analyses and comparison of wind speed distributions using a data set obtained from a measuring wind mast mounted in Humansdorp, Eastern Cape. The expected annual energy production is estimated by using the certified power curve as provided by the manufacturer of the wind turbine under study. The commonly used Weibull distribution is determined to provide the best fit distribution model to our selected models. The annual energy yield is estimated at 7.33 GWh, with a capacity factor of 41.8 percent.
- Full Text:
- Date Issued: 2012
- Authors: Ndzukuma, Sibusiso
- Date: 2012
- Subjects: Wind power , Wind turbines , Winds -- Speed
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10580 , http://hdl.handle.net/10948/d1020627
- Description: In this study we conduct wind resource assessment to evaluate the annual energy production of a wind turbine. To estimate energy production of a wind turbine over a period of time, the power characteristics of the wind turbine are integrated with the probabilities of the wind speed expected at a chosen site. The first data set was obtained from a wind farm in Denmark. We propose several probability density functions to model the distribution of the wind speed. We use techniques from nonlinear regression analysis to model the power curve of a wind turbine. The best fit distribution model is assessed by performing numeric goodness–of–fit measures and graphical analyses. Johnson’s bounded (SB) distribution provides the best fit model with the smallest Kolmogorov–Smirnov (K-S) test statistic . 15. The four parameter logistic nonlinear regression (4PL) model is determined to provide the best fit to the power curve data, according to the Akaike Information Criterion (AIC) and the Bayesian Information Criterion (BIC). The estimated annual energy yield is compared to the actual production of the wind turbine. Our models underestimate the actual energy production by a 1 difference. In Chapter Six we conduct data processing, analyses and comparison of wind speed distributions using a data set obtained from a measuring wind mast mounted in Humansdorp, Eastern Cape. The expected annual energy production is estimated by using the certified power curve as provided by the manufacturer of the wind turbine under study. The commonly used Weibull distribution is determined to provide the best fit distribution model to our selected models. The annual energy yield is estimated at 7.33 GWh, with a capacity factor of 41.8 percent.
- Full Text:
- Date Issued: 2012
The accelerated life cycle testing and modelling of Li-ion cells used in electric vehicle applications
- Authors: Rossouw, Claire Angela
- Date: 2012
- Subjects: Lithium Ions , Electric batteries , Energy storage , Electric vehicles -- Power supply
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10417 , http://hdl.handle.net/10948/d1012709 , Lithium Ions , Electric batteries , Energy storage , Electric vehicles -- Power supply
- Description: Li-ion batteries have become one of the chosen energy storage devices that are used in applications such as power tools, cellular phones and electric vehicles (EV). With the demand for portable high energy density devices, the rechargeable Li-ion battery has become one of the more viable energy storage systems for large scale commercial EVs because of their higher energy density to weight or volume ratio when compared to other current commercial battery energy storage systems. Various safety procedures for the use of Li-ion batteries in both consumer and EV applications have been developed by the international associations. The test procedures studied in this dissertation demonstrated the importance of determining the true capacity of a cell at various discharge rates. For this, the well known Peukert test was demonstrated. The study also showed that cells with different battery geometries and chemistries would demonstrate different thermal heating during discharge and slightly different Ragone results if different test methods were used as reported in the literature. Accelerated ageing tests were done on different cells at different Depth-of-Discharge (DoD) regions. The different DoD regions were determined according to expected stresses the electrode material in a cell would experience when discharged to specific DoD that follows the discharge voltage profile. Electrochemical Impedance Spectroscopy (EIS) was used to measure various electrochemical changes within these cells. The EIS results showed that certain observed modelled parameters would change similarly to the ageing of the cell as it aged due to the accelerated testing. EIS was also done on cells at different State-of-Charge (SoC) and temperatures. The results showed that EIS can be used as an effective technique to observe changes within a Li-ion cell as the SoC or temperature changed. For automotive vehicles that are powered by a fuel cell or battery, a supercapacitor can be coupled to a battery in order to increase and optimize the energy and power densities of the drive systems. A test procedure in the literature that evaluated the use of capacitors with Pb-acid batteries was applied to Li-ion type cells in order to quantify the increased power due to the use of a supercapacitor with a Li-ion cell. Both a cylindrical LiCoO2 cell and a VRLA Pb-acid cell showed some additional charge acceptance and delivery when connected to the supercapacitors. A LiMn2O4 pouch cell showed significant charge acceptance and delivery when connected to supercapacitors. The amount of additional charge acceptance and delivery of the different combinations could be explained by EIS, in particular, the resistance and capacitance of the cell in comparison to the combination of the cell and supercapacitor. A large capacity LiCoO2 cell showed high charge acceptance and delivery without connection with a supercapacitor. The study proved that EIS can be used to model the changes within cells under the different conditions and using different test procedures.
- Full Text:
- Date Issued: 2012
- Authors: Rossouw, Claire Angela
- Date: 2012
- Subjects: Lithium Ions , Electric batteries , Energy storage , Electric vehicles -- Power supply
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10417 , http://hdl.handle.net/10948/d1012709 , Lithium Ions , Electric batteries , Energy storage , Electric vehicles -- Power supply
- Description: Li-ion batteries have become one of the chosen energy storage devices that are used in applications such as power tools, cellular phones and electric vehicles (EV). With the demand for portable high energy density devices, the rechargeable Li-ion battery has become one of the more viable energy storage systems for large scale commercial EVs because of their higher energy density to weight or volume ratio when compared to other current commercial battery energy storage systems. Various safety procedures for the use of Li-ion batteries in both consumer and EV applications have been developed by the international associations. The test procedures studied in this dissertation demonstrated the importance of determining the true capacity of a cell at various discharge rates. For this, the well known Peukert test was demonstrated. The study also showed that cells with different battery geometries and chemistries would demonstrate different thermal heating during discharge and slightly different Ragone results if different test methods were used as reported in the literature. Accelerated ageing tests were done on different cells at different Depth-of-Discharge (DoD) regions. The different DoD regions were determined according to expected stresses the electrode material in a cell would experience when discharged to specific DoD that follows the discharge voltage profile. Electrochemical Impedance Spectroscopy (EIS) was used to measure various electrochemical changes within these cells. The EIS results showed that certain observed modelled parameters would change similarly to the ageing of the cell as it aged due to the accelerated testing. EIS was also done on cells at different State-of-Charge (SoC) and temperatures. The results showed that EIS can be used as an effective technique to observe changes within a Li-ion cell as the SoC or temperature changed. For automotive vehicles that are powered by a fuel cell or battery, a supercapacitor can be coupled to a battery in order to increase and optimize the energy and power densities of the drive systems. A test procedure in the literature that evaluated the use of capacitors with Pb-acid batteries was applied to Li-ion type cells in order to quantify the increased power due to the use of a supercapacitor with a Li-ion cell. Both a cylindrical LiCoO2 cell and a VRLA Pb-acid cell showed some additional charge acceptance and delivery when connected to the supercapacitors. A LiMn2O4 pouch cell showed significant charge acceptance and delivery when connected to supercapacitors. The amount of additional charge acceptance and delivery of the different combinations could be explained by EIS, in particular, the resistance and capacitance of the cell in comparison to the combination of the cell and supercapacitor. A large capacity LiCoO2 cell showed high charge acceptance and delivery without connection with a supercapacitor. The study proved that EIS can be used to model the changes within cells under the different conditions and using different test procedures.
- Full Text:
- Date Issued: 2012
The effectiveness of agricultural extension as perceived by small scale farm holders
- Authors: Olufayo, Ayowumi Motunrayo
- Date: 2012
- Subjects: Agricultural extension work -- South Africa , Agriculture -- South Africa
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10592 , http://hdl.handle.net/10948/d1019765
- Description: Empirical studies have suggested that agricultural extension can increase agricultural productivity. However, the increase in productivity is dependent on a number of issues. As a result, this particular study was conducted among farmers in order to examine the relationship between the provision of extension services and increased productivity in a regional context. The perceptions of vegetable home gardeners resident in the Nelson Mandela Metropolitan area, who participated in the Siyazondla Homestead Production Programme, formed the source of the primary data. The views of these farmers were analysed to determine how extension services affected their performance. The findings revealed that the farmers have a good perception of the extension services, although this negatively correlates with their level of performance. In addition, the data indicate that farmers who had a poor perception of extension services tend to achieve high production while those with a good impression of services had a poor performance. It was however observed that level of education, farming experience and exposure to print media influenced the responses that were captured in the study.
- Full Text:
- Date Issued: 2012
- Authors: Olufayo, Ayowumi Motunrayo
- Date: 2012
- Subjects: Agricultural extension work -- South Africa , Agriculture -- South Africa
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10592 , http://hdl.handle.net/10948/d1019765
- Description: Empirical studies have suggested that agricultural extension can increase agricultural productivity. However, the increase in productivity is dependent on a number of issues. As a result, this particular study was conducted among farmers in order to examine the relationship between the provision of extension services and increased productivity in a regional context. The perceptions of vegetable home gardeners resident in the Nelson Mandela Metropolitan area, who participated in the Siyazondla Homestead Production Programme, formed the source of the primary data. The views of these farmers were analysed to determine how extension services affected their performance. The findings revealed that the farmers have a good perception of the extension services, although this negatively correlates with their level of performance. In addition, the data indicate that farmers who had a poor perception of extension services tend to achieve high production while those with a good impression of services had a poor performance. It was however observed that level of education, farming experience and exposure to print media influenced the responses that were captured in the study.
- Full Text:
- Date Issued: 2012
Evaluation for harnessing low-enthalpy geothermal energy in South Africa based on a model pilot plant in the Limpopo Mobile Belt
- Authors: Dhansay, Taufeeq
- Date: 2012
- Subjects: Geothermal resources -- South Africa -- Limpopo , Renewable energy sources -- South Africa -- Limpopo , Climatic changes -- South Africa -- Limpopo
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10667 , http://hdl.handle.net/10948/d1019789
- Description: South Africa generates more than 90 percent of its total energy capacity through non-renewable sources. With coal forming the predominant energy source, South Africa became the leading carbon emissive nation in Africa, emitting 450 million tonnes of CO2 in 2011. In an international effort to restrict global average temperature rise to 2° C above the average prior the industrial revolution, the Kyoto Protocol has been extended for another 8-year commitment period. This is complementary to an expected resolution of a new legally binding climate change policy in 2015. This policy will aim to introduce financial penalties for nations failing to meet ascribed GHG emission targets by 2020. In an attempt to meet these climate change resolutions South Africa will research and develop cleaner, alternative forms of energy, including hydro, wind, and biomass forms of renewable energy, in addition to designating stringent building regulations for the Incorporation of solar energy. These measures form part of an Integrated evelopment Plan that aims to generate a target of 10,000 GWh of renewable energy in 2013. South Africa is also investigating the possibilities of extracting its shale gas reserves and implementing it as a major energy source. This energy mix has given little attention to geothermal energy. The reasons for this omission appears to be the lack of active volcanism and previous research that suggests South Africa, largely underlain by the Kaapvaal Craton, has a relatively low heat Flow profile, deemed insufficient for harnessing geothermal energy.
- Full Text:
- Date Issued: 2012
- Authors: Dhansay, Taufeeq
- Date: 2012
- Subjects: Geothermal resources -- South Africa -- Limpopo , Renewable energy sources -- South Africa -- Limpopo , Climatic changes -- South Africa -- Limpopo
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10667 , http://hdl.handle.net/10948/d1019789
- Description: South Africa generates more than 90 percent of its total energy capacity through non-renewable sources. With coal forming the predominant energy source, South Africa became the leading carbon emissive nation in Africa, emitting 450 million tonnes of CO2 in 2011. In an international effort to restrict global average temperature rise to 2° C above the average prior the industrial revolution, the Kyoto Protocol has been extended for another 8-year commitment period. This is complementary to an expected resolution of a new legally binding climate change policy in 2015. This policy will aim to introduce financial penalties for nations failing to meet ascribed GHG emission targets by 2020. In an attempt to meet these climate change resolutions South Africa will research and develop cleaner, alternative forms of energy, including hydro, wind, and biomass forms of renewable energy, in addition to designating stringent building regulations for the Incorporation of solar energy. These measures form part of an Integrated evelopment Plan that aims to generate a target of 10,000 GWh of renewable energy in 2013. South Africa is also investigating the possibilities of extracting its shale gas reserves and implementing it as a major energy source. This energy mix has given little attention to geothermal energy. The reasons for this omission appears to be the lack of active volcanism and previous research that suggests South Africa, largely underlain by the Kaapvaal Craton, has a relatively low heat Flow profile, deemed insufficient for harnessing geothermal energy.
- Full Text:
- Date Issued: 2012
Towards a methodology for identifying potential sites for cemeteries
- Authors: Judge, Richard David Eadie
- Date: 2012
- Subjects: Cemeteries , Environmental impact analysis , Groundwater , Pollution
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10649 , http://hdl.handle.net/10948/d1008048 , Cemeteries , Environmental impact analysis , Groundwater , Pollution
- Description: Due to death being an extremely sensitive issue, the topic of cemeteries and associated environmental impacts is often left outside the mainstream environmental critique. However, this is a topic becoming more prevalent as the population numbers and the death rate increases, while the amount of available land decreases. Recent research has indicated that poorly sited cemeteries may pose a significant threat to groundwater resources with the consequential potential for severe health hazards. This has resulted in the need for a method of determining the acceptability of a given area for the establishment of a cemetery in a South African context. Cemeteries should be sited in such a way as to mitigate potential public health and safety concerns, minimise associated environmental impacts and provide a method of body disposal that is economically viable. This study therefore provides an integrated methodology to identify and assess a given area and rank a number of potential sites, ultimately determining a single cemetery site which proves to be acceptable for the establishment of a cemetery. Cemetery site selection should be based on the factors affecting the pollution potential of a proposed cemetery. These factors were identified and quantified based on research into the mechanisms of cemetery site pollution resulting in a number of fatal flaws and criteria deemed decisive when selecting a potential cemetery site. The assessment of a site with regards to these criteria and fatal flaws is undertaken through the use of GIS analysis software utilising data layers containing information on the site selection criteria, by investigating existing studies, literature or reports relating to the relevant area, or through field investigations. Although these criteria are vital when determining the specific characteristics of a site in terms of its pollution potential, a method of assessing a number of potential sites with regards to these criteria is vital. To this end, a multi-criteria ranking matrix has been developed, allowing for an objective method of assessing individual sites and thus indicating which sites are more suited for the establishment of a cemetery. The ranking matrix identifies a range of values for each criterion, therefore identifying a minimum and maximum allowable value. A site is then assessed with regards to these criteria in relation to the values identified in the ranking matrix. Each criteria is assigned a score according to the site conditions. Once the criteria for each site has been assessed and scored, the results can be tallied allowing the sites to be ranked according to which site proved to be the most acceptable for a cemetery based on the findings of the application of the site selection criteria. The methodology developed in this study is unique to previous studies in that it provides an integrated and staged approach to identifying, assessing and applying the criteria affecting the pollution potential of a cemetery. The methodology also provides a means of ranking a number of potential sites so to determine the most suitable. Furthermore, the criteria deemed as decisive in previous investigations were in most cases not quantified by the relevant authors, therefore leaving many of the criteria values up for interpretation. For this methodology to be affective, all criteria must be quantified therefore identifying maximum and minimum allowable limits for each. This study applies minimum and maximum allowable limits to these criteria, therefore aiding in the ranking process. The integrated methodology developed was then applied to a case study where by the effectiveness in identifying a number of potential cemetery sites could be tested. Subsequent to the application of this methodology to a case study, it was concluded that an additional two criteria, not identified in previous investigations, needed to be assessed to more adequately determine the suitability or otherwise of a site for a cemetery. Ultimately, twelve major criteria have been proposed for use as the basis of the methodology. The methodology and pertinent criteria proposed in this study should be compiled as a standard for planning authorities and consultants to use as a method of determining a number of potential environmentally sound cemetery sites.
- Full Text:
- Date Issued: 2012
- Authors: Judge, Richard David Eadie
- Date: 2012
- Subjects: Cemeteries , Environmental impact analysis , Groundwater , Pollution
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10649 , http://hdl.handle.net/10948/d1008048 , Cemeteries , Environmental impact analysis , Groundwater , Pollution
- Description: Due to death being an extremely sensitive issue, the topic of cemeteries and associated environmental impacts is often left outside the mainstream environmental critique. However, this is a topic becoming more prevalent as the population numbers and the death rate increases, while the amount of available land decreases. Recent research has indicated that poorly sited cemeteries may pose a significant threat to groundwater resources with the consequential potential for severe health hazards. This has resulted in the need for a method of determining the acceptability of a given area for the establishment of a cemetery in a South African context. Cemeteries should be sited in such a way as to mitigate potential public health and safety concerns, minimise associated environmental impacts and provide a method of body disposal that is economically viable. This study therefore provides an integrated methodology to identify and assess a given area and rank a number of potential sites, ultimately determining a single cemetery site which proves to be acceptable for the establishment of a cemetery. Cemetery site selection should be based on the factors affecting the pollution potential of a proposed cemetery. These factors were identified and quantified based on research into the mechanisms of cemetery site pollution resulting in a number of fatal flaws and criteria deemed decisive when selecting a potential cemetery site. The assessment of a site with regards to these criteria and fatal flaws is undertaken through the use of GIS analysis software utilising data layers containing information on the site selection criteria, by investigating existing studies, literature or reports relating to the relevant area, or through field investigations. Although these criteria are vital when determining the specific characteristics of a site in terms of its pollution potential, a method of assessing a number of potential sites with regards to these criteria is vital. To this end, a multi-criteria ranking matrix has been developed, allowing for an objective method of assessing individual sites and thus indicating which sites are more suited for the establishment of a cemetery. The ranking matrix identifies a range of values for each criterion, therefore identifying a minimum and maximum allowable value. A site is then assessed with regards to these criteria in relation to the values identified in the ranking matrix. Each criteria is assigned a score according to the site conditions. Once the criteria for each site has been assessed and scored, the results can be tallied allowing the sites to be ranked according to which site proved to be the most acceptable for a cemetery based on the findings of the application of the site selection criteria. The methodology developed in this study is unique to previous studies in that it provides an integrated and staged approach to identifying, assessing and applying the criteria affecting the pollution potential of a cemetery. The methodology also provides a means of ranking a number of potential sites so to determine the most suitable. Furthermore, the criteria deemed as decisive in previous investigations were in most cases not quantified by the relevant authors, therefore leaving many of the criteria values up for interpretation. For this methodology to be affective, all criteria must be quantified therefore identifying maximum and minimum allowable limits for each. This study applies minimum and maximum allowable limits to these criteria, therefore aiding in the ranking process. The integrated methodology developed was then applied to a case study where by the effectiveness in identifying a number of potential cemetery sites could be tested. Subsequent to the application of this methodology to a case study, it was concluded that an additional two criteria, not identified in previous investigations, needed to be assessed to more adequately determine the suitability or otherwise of a site for a cemetery. Ultimately, twelve major criteria have been proposed for use as the basis of the methodology. The methodology and pertinent criteria proposed in this study should be compiled as a standard for planning authorities and consultants to use as a method of determining a number of potential environmentally sound cemetery sites.
- Full Text:
- Date Issued: 2012
Microalgae and macrophytes as indicators of ecological health in the Great Brak Estuary
- Authors: Nunes, Monique
- Date: 2012
- Subjects: Microalge -- South Africa -- Great Brak Estuary , Estuarine ecology -- South Africa , Aquatic plants -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10629 , http://hdl.handle.net/10948/d1012097 , Microalge -- South Africa -- Great Brak Estuary , Estuarine ecology -- South Africa , Aquatic plants -- South Africa
- Description: The Great Brak temporarily open/closed estuary was subjected to a drought during the spring and summer of 2009/2010 resulting in the mouth remaining closed for a prolonged period. According to the Great Brak Estuary management programme, the mouth of the estuary had to be open for a total of 308 days during spring and summer of 2009/2010, respectively, but was closed for almost the entire two years (693 days). The aim of this study was to assess monthly changes in the abiotic characteristics (salinity, temperature, oxygen, pH and nutrients) and the biotic responses of phytoplankton and macroalgae; identify sources of nutrient input into the estuary and determine the response of the salt marsh to water level and salinity changes. The results indicated that physico-chemical parameters were similar to that previously recorded during the closed mouth condition. However mouth closure combined with elevated nutrient concentrations led to a shift from rooted submerged macrophytes to one where either microalgae or macroalgae were dominant. Soluble reactive phosphorus concentrations were significantly higher in bottom compared with surface waters. There was a significant negative correlation with SRP and dissolved oxygen for the sampling period indicating potential release of phosphorus from the sediment during closed mouth conditions. Microalgal biomass increased in response to remineralised nutrients and freshwater pulses. Flagellates were the dominant microalgal group (21718 ± 3336 cells m l-1, p < 0.05) because of their morphological ability to migrate vertically within the water column. The macroalgal cover was highest during the closed mouth state but only during winter (August 2010) when temperatures were below 20 oC. Five major point sources of nutrient input into the Great Brak Estuary were identified during rainfall periods. Point sources 4 and 5 in the upper reaches of the estuary had the highest DIN input whereas point source 3 in the middle reaches of the estuary had the highest DIP input. As a result of the drought and low water level, the salt marsh was never inundated for longer than 3 months. Die-back of Sarcocornia decumbens (r 2= -0.62, p < 0.05) was related to smothering by dead macroalgae whereas dieback of Sporobolus virginicus was related to decreasing nutrient (r2 = 0.59, p < 0.05) and salinity (r2 = 0.55, p < 0.05) levels. The physico-chemical characteristics alone did not convey the true health status of the Great Brak Estuary for the duration of the sampling (April 2010-April 2011). The study showed that microalgae and macroalgae are valuable indicators of the status of the estuary. Therefore it is suggested that bio-indicators are incorporated into the management/monitoring plan in order to assist in improving the health assessment of the Great Brak Estuary.
- Full Text:
- Date Issued: 2012
- Authors: Nunes, Monique
- Date: 2012
- Subjects: Microalge -- South Africa -- Great Brak Estuary , Estuarine ecology -- South Africa , Aquatic plants -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10629 , http://hdl.handle.net/10948/d1012097 , Microalge -- South Africa -- Great Brak Estuary , Estuarine ecology -- South Africa , Aquatic plants -- South Africa
- Description: The Great Brak temporarily open/closed estuary was subjected to a drought during the spring and summer of 2009/2010 resulting in the mouth remaining closed for a prolonged period. According to the Great Brak Estuary management programme, the mouth of the estuary had to be open for a total of 308 days during spring and summer of 2009/2010, respectively, but was closed for almost the entire two years (693 days). The aim of this study was to assess monthly changes in the abiotic characteristics (salinity, temperature, oxygen, pH and nutrients) and the biotic responses of phytoplankton and macroalgae; identify sources of nutrient input into the estuary and determine the response of the salt marsh to water level and salinity changes. The results indicated that physico-chemical parameters were similar to that previously recorded during the closed mouth condition. However mouth closure combined with elevated nutrient concentrations led to a shift from rooted submerged macrophytes to one where either microalgae or macroalgae were dominant. Soluble reactive phosphorus concentrations were significantly higher in bottom compared with surface waters. There was a significant negative correlation with SRP and dissolved oxygen for the sampling period indicating potential release of phosphorus from the sediment during closed mouth conditions. Microalgal biomass increased in response to remineralised nutrients and freshwater pulses. Flagellates were the dominant microalgal group (21718 ± 3336 cells m l-1, p < 0.05) because of their morphological ability to migrate vertically within the water column. The macroalgal cover was highest during the closed mouth state but only during winter (August 2010) when temperatures were below 20 oC. Five major point sources of nutrient input into the Great Brak Estuary were identified during rainfall periods. Point sources 4 and 5 in the upper reaches of the estuary had the highest DIN input whereas point source 3 in the middle reaches of the estuary had the highest DIP input. As a result of the drought and low water level, the salt marsh was never inundated for longer than 3 months. Die-back of Sarcocornia decumbens (r 2= -0.62, p < 0.05) was related to smothering by dead macroalgae whereas dieback of Sporobolus virginicus was related to decreasing nutrient (r2 = 0.59, p < 0.05) and salinity (r2 = 0.55, p < 0.05) levels. The physico-chemical characteristics alone did not convey the true health status of the Great Brak Estuary for the duration of the sampling (April 2010-April 2011). The study showed that microalgae and macroalgae are valuable indicators of the status of the estuary. Therefore it is suggested that bio-indicators are incorporated into the management/monitoring plan in order to assist in improving the health assessment of the Great Brak Estuary.
- Full Text:
- Date Issued: 2012
Environmental cues and sensory preferences directing the nesting process in loggerhead turtles, caretta caretta, nesting in Maputaland, South Africa
- Authors: Brazier, Wayne
- Date: 2012
- Subjects: Sea turtles
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10721 , http://hdl.handle.net/10948/d1015688
- Description: Animals use their senses for everything on an immediate, and day to day fashion – detecting danger, finding food, finding mates among other activities. In sea turtles and other migratory species senses are used for long-distance migrations. Senses such as smell, vision and hearing, have been studied experimentally under laboratory conditions but seldom have been investigated in the field. This thesis takes a combination of field and laboratory experiments and investigates some of the hypotheses involved in natal homing and nest site selection. The loggerhead’s nesting distribution in Maputaland is distinct with characteristic high and low density nesting areas which are consistent from year to year. Investigations by earlier researchers on these beaches suggested that beach characteristics, such as beach morphodynamic type and beach width, do not appear to influence the beaches at which loggerheads emerge to nest. The high density nesting area (with approximately 440 loggerhead emergences/km) have similar beach characteristics as the low density nesting area (with <50 loggerhead emergences/km). It is therefore suggested that there is another cue that drives nest site selection. It can either be related to a physical characteristic not yet realised, or is a non-physical (but chemical or biological) cue. This dissertation aims to identify the sensory inputs received during the nest selection process, as well as sea-finding ability after nesting. To investigate the mechanism causing the high-density as opposed to the low-density nesting area, three potential drivers were investigated namely: chemical imprinting (as a natal beach cue), ambient and artificial light (as deterrents) and social facilitation (as a learned behaviour). It was also attempted to identify the strength of the most common senses – vision, hearing and smell. As animal ethics restricts interfering with emerging or nesting turtles, the strengths of these senses were tested during sea-finding by adult loggerheads. The results indicate that sulfide concentrations appear to be used as chemical cues for nesting as these concentrations are elevated (>150 percent) in the high density nesting beaches compared to the low density nesting beaches within and among seasons however further investigations are required. Artificial light (range: 0.045–0.5 lux) is an active deterrent of female emergences while ambient light, even under extreme conditions such as lightning during electric storms (up to 8.2 lux), appears to have no observable influence on the spatial or temporal distributions of emergences. Social facilitation appears unlikely as a primary nest site selection factor for loggerheads. It may however, play a minor secondary role to preferred areas or hotspots. Sea-finding in post-nesting female loggerheads appears to be driven exclusively by visual cues such as the light horizon, with minimal to no influence from other cues (the sound of the breakers, slope or smell of the ocean) which solidify the visual system’s use in sea-finding. This research on the nest site selection of loggerheads and the sensory systems involved in this process has added valuable information to the limited pool of knowledge already present and has created a solid framework on which further investigations can be based. Future work in this field should focus on integrating a suite of sensory stimuli and cues to receive a greater understanding of the sensory systems used in nest site selection.
- Full Text:
- Date Issued: 2012
- Authors: Brazier, Wayne
- Date: 2012
- Subjects: Sea turtles
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10721 , http://hdl.handle.net/10948/d1015688
- Description: Animals use their senses for everything on an immediate, and day to day fashion – detecting danger, finding food, finding mates among other activities. In sea turtles and other migratory species senses are used for long-distance migrations. Senses such as smell, vision and hearing, have been studied experimentally under laboratory conditions but seldom have been investigated in the field. This thesis takes a combination of field and laboratory experiments and investigates some of the hypotheses involved in natal homing and nest site selection. The loggerhead’s nesting distribution in Maputaland is distinct with characteristic high and low density nesting areas which are consistent from year to year. Investigations by earlier researchers on these beaches suggested that beach characteristics, such as beach morphodynamic type and beach width, do not appear to influence the beaches at which loggerheads emerge to nest. The high density nesting area (with approximately 440 loggerhead emergences/km) have similar beach characteristics as the low density nesting area (with <50 loggerhead emergences/km). It is therefore suggested that there is another cue that drives nest site selection. It can either be related to a physical characteristic not yet realised, or is a non-physical (but chemical or biological) cue. This dissertation aims to identify the sensory inputs received during the nest selection process, as well as sea-finding ability after nesting. To investigate the mechanism causing the high-density as opposed to the low-density nesting area, three potential drivers were investigated namely: chemical imprinting (as a natal beach cue), ambient and artificial light (as deterrents) and social facilitation (as a learned behaviour). It was also attempted to identify the strength of the most common senses – vision, hearing and smell. As animal ethics restricts interfering with emerging or nesting turtles, the strengths of these senses were tested during sea-finding by adult loggerheads. The results indicate that sulfide concentrations appear to be used as chemical cues for nesting as these concentrations are elevated (>150 percent) in the high density nesting beaches compared to the low density nesting beaches within and among seasons however further investigations are required. Artificial light (range: 0.045–0.5 lux) is an active deterrent of female emergences while ambient light, even under extreme conditions such as lightning during electric storms (up to 8.2 lux), appears to have no observable influence on the spatial or temporal distributions of emergences. Social facilitation appears unlikely as a primary nest site selection factor for loggerheads. It may however, play a minor secondary role to preferred areas or hotspots. Sea-finding in post-nesting female loggerheads appears to be driven exclusively by visual cues such as the light horizon, with minimal to no influence from other cues (the sound of the breakers, slope or smell of the ocean) which solidify the visual system’s use in sea-finding. This research on the nest site selection of loggerheads and the sensory systems involved in this process has added valuable information to the limited pool of knowledge already present and has created a solid framework on which further investigations can be based. Future work in this field should focus on integrating a suite of sensory stimuli and cues to receive a greater understanding of the sensory systems used in nest site selection.
- Full Text:
- Date Issued: 2012
An evaluation of programming assistance tools to support the learning of IT programming: a case study in South African secondary schools
- Authors: Koorsse, Melisa
- Date: 2012
- Subjects: Computer science , Computer literacy , Computer programming
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10472 , http://hdl.handle.net/10948/d1010581 , Computer science , Computer literacy , Computer programming
- Description: Worldwide, there is a decline in interest in the computer science profession and in the subject at secondary school level. Novice programmers struggle to understand introductory programming concepts and this difficulty of learning to program is contributing to the lack of interest in the field of computer science. Information Technology (IT) learners in South African secondary schools are novice programmers, introduced to introductory programming concepts in the subject which also includes topics on hardware and system software, e-communication, social and ethical issues, spreadsheets and databases. The difficulties faced by IT learners are worsened by the lack of suitably qualified teachers, a saturated learning programme that allocates very little time to the understanding of complex programming concepts and limited class time where practical examples can be implemented with the support of the IT teacher. This research proposes that IT learners could be supported by a programming assistance tool (PAT). A PAT is a software program that can be used by novice programmers to learn how to program and/or improve their understanding of programming concepts. PATs use different techniques to assist novice programmers. The main objective of this research was to determine whether the use of a PAT impacted IT learners’ understanding of programming concepts and motivation towards programming. The literature study and feedback from IT learners and teachers were used to identify novice programming difficulties and IT learner programming difficulties, respectively. Selection criteria were derived from the programming difficulties identified. The selection criteria were grouped into three categories, namely, programming concepts, programming knowledge and programming skills. Existing PATs were evaluated using the selection criteria and three PATs, namely, RoboMind, Scratch and B#, were selected as suitable for use by IT learners. RoboMind was adapted in this research study, allowing it to support the Delphi programming language. The three PATs were evaluated by participating IT learners at four schools. The findings of this research provided no conclusive evidence that IT learners who used a PAT had a significantly better understanding of programming concepts and motivation towards programming than learners who did not use a PAT. IT learner feedback was used to identify the strengths and shortcomings of the three PATs and to provide recommendations for the development of PATs specifically to support IT learners. This research study has provided several theoretical and practical contributions, including the research design, selection criteria, adaptations to RoboMind and the evaluation of the three PATs. In addition, IT teachers and learners have been made aware of PATs and the support that can be provided by these PATs. IT teachers have also been provided with a means of selecting PATs applicable to the IT curriculum. All the research contributions have formed the basis for future work, such as improving and extending RoboMind’s functionality and support of programming concepts, the refinement of the selection criteria and, ultimately, the development of a new PAT, specifically designed to support IT learner understanding of programming concepts and motivation towards programming.
- Full Text:
- Date Issued: 2012
- Authors: Koorsse, Melisa
- Date: 2012
- Subjects: Computer science , Computer literacy , Computer programming
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10472 , http://hdl.handle.net/10948/d1010581 , Computer science , Computer literacy , Computer programming
- Description: Worldwide, there is a decline in interest in the computer science profession and in the subject at secondary school level. Novice programmers struggle to understand introductory programming concepts and this difficulty of learning to program is contributing to the lack of interest in the field of computer science. Information Technology (IT) learners in South African secondary schools are novice programmers, introduced to introductory programming concepts in the subject which also includes topics on hardware and system software, e-communication, social and ethical issues, spreadsheets and databases. The difficulties faced by IT learners are worsened by the lack of suitably qualified teachers, a saturated learning programme that allocates very little time to the understanding of complex programming concepts and limited class time where practical examples can be implemented with the support of the IT teacher. This research proposes that IT learners could be supported by a programming assistance tool (PAT). A PAT is a software program that can be used by novice programmers to learn how to program and/or improve their understanding of programming concepts. PATs use different techniques to assist novice programmers. The main objective of this research was to determine whether the use of a PAT impacted IT learners’ understanding of programming concepts and motivation towards programming. The literature study and feedback from IT learners and teachers were used to identify novice programming difficulties and IT learner programming difficulties, respectively. Selection criteria were derived from the programming difficulties identified. The selection criteria were grouped into three categories, namely, programming concepts, programming knowledge and programming skills. Existing PATs were evaluated using the selection criteria and three PATs, namely, RoboMind, Scratch and B#, were selected as suitable for use by IT learners. RoboMind was adapted in this research study, allowing it to support the Delphi programming language. The three PATs were evaluated by participating IT learners at four schools. The findings of this research provided no conclusive evidence that IT learners who used a PAT had a significantly better understanding of programming concepts and motivation towards programming than learners who did not use a PAT. IT learner feedback was used to identify the strengths and shortcomings of the three PATs and to provide recommendations for the development of PATs specifically to support IT learners. This research study has provided several theoretical and practical contributions, including the research design, selection criteria, adaptations to RoboMind and the evaluation of the three PATs. In addition, IT teachers and learners have been made aware of PATs and the support that can be provided by these PATs. IT teachers have also been provided with a means of selecting PATs applicable to the IT curriculum. All the research contributions have formed the basis for future work, such as improving and extending RoboMind’s functionality and support of programming concepts, the refinement of the selection criteria and, ultimately, the development of a new PAT, specifically designed to support IT learner understanding of programming concepts and motivation towards programming.
- Full Text:
- Date Issued: 2012
A comparison of harvester productivity and stump volume waste in coppiced and planted eucalyptus grandis pulpwood compartments in the KwaZulu-Natal forestry region of South Africa
- Ramantswana, Mufhumudzi Muedanyi
- Authors: Ramantswana, Mufhumudzi Muedanyi
- Date: 2012
- Subjects: Forest productivity , Forest management
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10744 , http://hdl.handle.net/10948/d1019844
- Description: Over the past decade the South African forestry industry has gradually experienced the ramifications of labour scarcity, increases in labour costs, the effect of HIV and AIDS and increasing timber demand. Consequently, this has led to an increase in the mechanisation rate, especially in timber harvesting operations. Due to the labour challenges in South Africa, mechanised forestry equipment has increasingly been required to operate in complex forest conditions, such as coppiced compartments, where they have not operated before. It therefore occurs that harvesters are either used in certain coppiced compartments with uncertain productivity expectations, or the harvesters are not used in these compartments due to a lack of productivity knowledge. The influence that certain factors have on harvester productivity and stump volume loss – factors such as coppice regeneration practices and stem form – is poorly understood and has not been quantified. No scientific research exists regarding the effects of coppice compartments on the productivity of a harvester and the amount of stump volume waste. This research aimed at determining the influence of tree volume, tree form, stem felled first and distance between stems on the productivity of an excavator based harvester in coppiced double, coppiced single and planted Eucalyptus grandis pulpwood compartments. Furthermore, the research determined whether there was any stump volume waste, and quantified how much of it was due to excessive stump heights by the harvester. Through regression analysis, productivity equations were derived to make productivity predictions in both coppiced and planted compartments. All stumps were evaluated for waste and the average stump volume waste in coppiced double, coppiced single and planted trees was determined. The research results showed that planted trees had the highest productivity across all tree sizes, followed by coppiced single trees and then coppiced double stems. When harvesting a 0.2 m3 tree, the mean harvester productivity was 8.7 m3 per PMH in coppiced double trees, 13.8 m3 per PMH in coppiced single trees and 16.1 m3 per PMH in planted trees. In coppiced double stems the productivity was not significantly influence by the distance between stems. However, the productivity was significantly influenced by the stem felled first. The regression results showed that if the smaller stem was felled first, the productivity would increase if the larger stem’s volume was less than 0.18 m3; however where the larger stem was greater than 0.18 m3, the relationship was reversed. In addition, the productivity for both coppiced single trees and coppiced double stems were significantly influenced by stem form. The poorly formed trees had low productivity compared to the trees with good form. The stump volume findings showed that coppiced double stems had the highest average stump volume waste per stump, with 0.00307 m3 waste, followed by coppiced single trees (0.001954 m3) and planted trees (0.001650 m3). The average stump volume waste per stump with waste for the planted trees was negligible. This research provides forestry companies and harvesting contractors with information on the effect of tree volume, tree form and stem felled first on harvester productivity in E. grandis coppiced double, coppiced single and planted compartments. This information will assist in making equipment and system selection decisions and improve operational management and control. In addition, they will also be aware of stump volume losses that will occur in the three scenarios.
- Full Text:
- Date Issued: 2012
- Authors: Ramantswana, Mufhumudzi Muedanyi
- Date: 2012
- Subjects: Forest productivity , Forest management
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10744 , http://hdl.handle.net/10948/d1019844
- Description: Over the past decade the South African forestry industry has gradually experienced the ramifications of labour scarcity, increases in labour costs, the effect of HIV and AIDS and increasing timber demand. Consequently, this has led to an increase in the mechanisation rate, especially in timber harvesting operations. Due to the labour challenges in South Africa, mechanised forestry equipment has increasingly been required to operate in complex forest conditions, such as coppiced compartments, where they have not operated before. It therefore occurs that harvesters are either used in certain coppiced compartments with uncertain productivity expectations, or the harvesters are not used in these compartments due to a lack of productivity knowledge. The influence that certain factors have on harvester productivity and stump volume loss – factors such as coppice regeneration practices and stem form – is poorly understood and has not been quantified. No scientific research exists regarding the effects of coppice compartments on the productivity of a harvester and the amount of stump volume waste. This research aimed at determining the influence of tree volume, tree form, stem felled first and distance between stems on the productivity of an excavator based harvester in coppiced double, coppiced single and planted Eucalyptus grandis pulpwood compartments. Furthermore, the research determined whether there was any stump volume waste, and quantified how much of it was due to excessive stump heights by the harvester. Through regression analysis, productivity equations were derived to make productivity predictions in both coppiced and planted compartments. All stumps were evaluated for waste and the average stump volume waste in coppiced double, coppiced single and planted trees was determined. The research results showed that planted trees had the highest productivity across all tree sizes, followed by coppiced single trees and then coppiced double stems. When harvesting a 0.2 m3 tree, the mean harvester productivity was 8.7 m3 per PMH in coppiced double trees, 13.8 m3 per PMH in coppiced single trees and 16.1 m3 per PMH in planted trees. In coppiced double stems the productivity was not significantly influence by the distance between stems. However, the productivity was significantly influenced by the stem felled first. The regression results showed that if the smaller stem was felled first, the productivity would increase if the larger stem’s volume was less than 0.18 m3; however where the larger stem was greater than 0.18 m3, the relationship was reversed. In addition, the productivity for both coppiced single trees and coppiced double stems were significantly influenced by stem form. The poorly formed trees had low productivity compared to the trees with good form. The stump volume findings showed that coppiced double stems had the highest average stump volume waste per stump, with 0.00307 m3 waste, followed by coppiced single trees (0.001954 m3) and planted trees (0.001650 m3). The average stump volume waste per stump with waste for the planted trees was negligible. This research provides forestry companies and harvesting contractors with information on the effect of tree volume, tree form and stem felled first on harvester productivity in E. grandis coppiced double, coppiced single and planted compartments. This information will assist in making equipment and system selection decisions and improve operational management and control. In addition, they will also be aware of stump volume losses that will occur in the three scenarios.
- Full Text:
- Date Issued: 2012