Exploring the lexical and semantic access afforded by novice and experienced Namibian physical science teachers’ talk during electricity and magnetism lessons
- Authors: Muzambani, Efraim Hiamueze
- Date: 2022-10-14
- Subjects: Knowledge, Theory of , Education, Secondary Aims and objectives Namibia , Science Study and teaching (Secondary) Namibia , Systemic functional linguistics , Lexical density , Electricity Study and teaching (Secondary) Namibia , Magnetism Study and teaching (Secondary) Namibia
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/405346 , vital:70163
- Description: Challenges to learners’ meaning-making in the topic of electricity and magnetism contributes to underperformance in grade 10 Physical Science in Namibian schools. Teacher talk in content-based classrooms not only contributes to learners’ language development (Gibbons, 2003), but also facilitates meaning-making and cumulative knowledge-building (Halliday, 1999). However, it is possible that there are differences between the classrooms talk of novice and experienced Namibian Physical Science teachers. An understanding of differences between experienced and novice Namibian science teacher talk could inform teacher training and professional development and potentially help improve learners’ meaning-making in topics such as electricity and magnetism. However, no study could be found in the Namibian context which explored whether novice and experienced teacher talk afforded similar semantic and lexical access to meaning-making. This research gap provided a strong rationale for undertaking the study reported in this thesis. The study sought to investigate the extent to which novice and experienced grade 10 Namibian Physical Science teachers’ classroom talk provides semantic and lexical access to learners for the topic of electricity and magnetism. The research is informed by Legitimation Code Theory (LCT) and Systemic Functional Linguistics (SFL). Research has shown that the two theories are complementary and can be used to characterize teachers’ pedagogical practices (Maton, 2014). A quantitative case study methodology was followed in this study with LCT’s semantic density and SFL’s lexical density as analytical tools to analyze the two teachers’ classroom talk. The results from a t-test for semantic density show that there is a significant difference in the means for “semantic density waving” criterion (t-value of -2.331; p-value for 2 tail test at 95% level of 0.0040) and for the “linking downward escalators or single references” criterion (t-value of 4.649; p-value for 2 tail test at 95% level of 0.001) of teacher talk by the teachers. The overall results for semantic density indicate that the experienced teacher affords better epistemological access through semantic waves than the novice teacher, whereas the novice teacher affords better epistemological access through semantic range and semantic flow. In terms of lexical density, both teachers afforded similar access, characterized by their talk veering towards the level of information density associated with written text. The study makes a methodological contribution to science education research through its characterization of novice and experienced teachers’ talk in terms of semantic waves and lexical density. This study also provides empirical insight into the differences between language use by novice and experienced Namibian Physical Science teachers, which can inform the work of educational institutions, advisory and inspectorate services in the ministry of education, and school managers. Relevant Namibian stakeholders are encouraged to consider including the topics of semantic density and lexical density, in continuous professional development programmes towards improving the meaning-making affordances of science teachers’ talk. , Thesis (MEd) -- Faculty of Education, Education, 2022
- Full Text:
- Date Issued: 2022-10-14
- Authors: Muzambani, Efraim Hiamueze
- Date: 2022-10-14
- Subjects: Knowledge, Theory of , Education, Secondary Aims and objectives Namibia , Science Study and teaching (Secondary) Namibia , Systemic functional linguistics , Lexical density , Electricity Study and teaching (Secondary) Namibia , Magnetism Study and teaching (Secondary) Namibia
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/405346 , vital:70163
- Description: Challenges to learners’ meaning-making in the topic of electricity and magnetism contributes to underperformance in grade 10 Physical Science in Namibian schools. Teacher talk in content-based classrooms not only contributes to learners’ language development (Gibbons, 2003), but also facilitates meaning-making and cumulative knowledge-building (Halliday, 1999). However, it is possible that there are differences between the classrooms talk of novice and experienced Namibian Physical Science teachers. An understanding of differences between experienced and novice Namibian science teacher talk could inform teacher training and professional development and potentially help improve learners’ meaning-making in topics such as electricity and magnetism. However, no study could be found in the Namibian context which explored whether novice and experienced teacher talk afforded similar semantic and lexical access to meaning-making. This research gap provided a strong rationale for undertaking the study reported in this thesis. The study sought to investigate the extent to which novice and experienced grade 10 Namibian Physical Science teachers’ classroom talk provides semantic and lexical access to learners for the topic of electricity and magnetism. The research is informed by Legitimation Code Theory (LCT) and Systemic Functional Linguistics (SFL). Research has shown that the two theories are complementary and can be used to characterize teachers’ pedagogical practices (Maton, 2014). A quantitative case study methodology was followed in this study with LCT’s semantic density and SFL’s lexical density as analytical tools to analyze the two teachers’ classroom talk. The results from a t-test for semantic density show that there is a significant difference in the means for “semantic density waving” criterion (t-value of -2.331; p-value for 2 tail test at 95% level of 0.0040) and for the “linking downward escalators or single references” criterion (t-value of 4.649; p-value for 2 tail test at 95% level of 0.001) of teacher talk by the teachers. The overall results for semantic density indicate that the experienced teacher affords better epistemological access through semantic waves than the novice teacher, whereas the novice teacher affords better epistemological access through semantic range and semantic flow. In terms of lexical density, both teachers afforded similar access, characterized by their talk veering towards the level of information density associated with written text. The study makes a methodological contribution to science education research through its characterization of novice and experienced teachers’ talk in terms of semantic waves and lexical density. This study also provides empirical insight into the differences between language use by novice and experienced Namibian Physical Science teachers, which can inform the work of educational institutions, advisory and inspectorate services in the ministry of education, and school managers. Relevant Namibian stakeholders are encouraged to consider including the topics of semantic density and lexical density, in continuous professional development programmes towards improving the meaning-making affordances of science teachers’ talk. , Thesis (MEd) -- Faculty of Education, Education, 2022
- Full Text:
- Date Issued: 2022-10-14
The construction of phthalocyanine- carbon nanoparticle conjugates for applications in photodynamic therapy and non-linear optics
- Matshitse, Refilwe Manyama Stephina
- Authors: Matshitse, Refilwe Manyama Stephina
- Date: 2021-10-29
- Subjects: Phthalocyanines , Nanodiamonds , Photochemotherapy , Nonlinear optics , Quantum dots
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/188397 , vital:44750 , 10.21504/10962/188397
- Description: The syntheses and characterization of symmetric and asymmetric Pcs functionalized at the peripheral position and sometimes positively charged are reported. The Pcs had either H2, zinc or silicon as central metals and have pyridyloxy, benzothiozole phenoxy, and respective cationic analogues as ring substituents. The Pcs were linked to carbon based nanoparticles such as graphene quantum dots, carbon dots, and detonation nanodiamonds (DNDs) via an ester, amide bond and/or π - π stacking. The physicochemical characteristics of the Pcs were assessed when alone and when in a conjugated system. Both symmetrically and asymmetrically substituted benzothiozole Pcs when quaternised displayed higher triplet and singlet oxygen quantum yields than their unquaternised counterparts. Linkage to carbon nanoparticles (especially to detonation nanodiamonds) had an increasing effect on triplet and singlet oxygen quantum yield. However, a general decrease in singlet oxygen quantum yield on linkage to doped detonation nanodiamonds was associated with the screening effect of DNDs. Heteroatom doped DNDs-Pc nanohybrids have less singlet oxygen than Pcs alone due to molecular structural stability associated with strain that is relatively reduced upon linking Pcs. The In vitro dark cytotoxicity and photodynamic therapy of selected Pc complexes and conjugates against MCF-7 cells was tested. All studied Pc complexes and conjugates showed minimum dark toxicity making them applicable for PDT. When Pc complexes are alone, there is less phototoxicity with >22% cell viability at concentrations ≤ 50 μg/mL relative to conjugates with <22% cell viability at concentrations ≤ 50 μg/mL. There was no direct relationship between PDT and singlet oxygen quantum yields. Nonlinear optical characteristics of complexes was improved upon conjugation of DNDs. Absorbance, input energy, percentage loading, central metal, substituent of Pc and nature of interaction (covalent, noncovalent) are amongst some of the factors that influence nonlinear absorption properties of materials used in this study. All materials followed reverse saturable absorption through two photon absorption mechanism at the excitation wavelength of 532 nm. Aggregates reduce excited state lifetime and Beff under high concentrations/absorbance. A direct relationship between absorbance and Beff of DNDs nanoconjugated systems at low concentrations result in increased optical limiting characteristics of materials. The findings from this work show the importance of linking (nonlinear optics and photodynamic therapy) and doping (photodynamic therapy) photosensitisers such as phthalocyanines and sometimes boron dipyrromethenes onto carbon based nanoparticles for the enhanced characteristics in variable applications. , Thesis (PhD) -- Faculty of Science, Chemistry, 2021
- Full Text:
- Date Issued: 2021-10-29
- Authors: Matshitse, Refilwe Manyama Stephina
- Date: 2021-10-29
- Subjects: Phthalocyanines , Nanodiamonds , Photochemotherapy , Nonlinear optics , Quantum dots
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/188397 , vital:44750 , 10.21504/10962/188397
- Description: The syntheses and characterization of symmetric and asymmetric Pcs functionalized at the peripheral position and sometimes positively charged are reported. The Pcs had either H2, zinc or silicon as central metals and have pyridyloxy, benzothiozole phenoxy, and respective cationic analogues as ring substituents. The Pcs were linked to carbon based nanoparticles such as graphene quantum dots, carbon dots, and detonation nanodiamonds (DNDs) via an ester, amide bond and/or π - π stacking. The physicochemical characteristics of the Pcs were assessed when alone and when in a conjugated system. Both symmetrically and asymmetrically substituted benzothiozole Pcs when quaternised displayed higher triplet and singlet oxygen quantum yields than their unquaternised counterparts. Linkage to carbon nanoparticles (especially to detonation nanodiamonds) had an increasing effect on triplet and singlet oxygen quantum yield. However, a general decrease in singlet oxygen quantum yield on linkage to doped detonation nanodiamonds was associated with the screening effect of DNDs. Heteroatom doped DNDs-Pc nanohybrids have less singlet oxygen than Pcs alone due to molecular structural stability associated with strain that is relatively reduced upon linking Pcs. The In vitro dark cytotoxicity and photodynamic therapy of selected Pc complexes and conjugates against MCF-7 cells was tested. All studied Pc complexes and conjugates showed minimum dark toxicity making them applicable for PDT. When Pc complexes are alone, there is less phototoxicity with >22% cell viability at concentrations ≤ 50 μg/mL relative to conjugates with <22% cell viability at concentrations ≤ 50 μg/mL. There was no direct relationship between PDT and singlet oxygen quantum yields. Nonlinear optical characteristics of complexes was improved upon conjugation of DNDs. Absorbance, input energy, percentage loading, central metal, substituent of Pc and nature of interaction (covalent, noncovalent) are amongst some of the factors that influence nonlinear absorption properties of materials used in this study. All materials followed reverse saturable absorption through two photon absorption mechanism at the excitation wavelength of 532 nm. Aggregates reduce excited state lifetime and Beff under high concentrations/absorbance. A direct relationship between absorbance and Beff of DNDs nanoconjugated systems at low concentrations result in increased optical limiting characteristics of materials. The findings from this work show the importance of linking (nonlinear optics and photodynamic therapy) and doping (photodynamic therapy) photosensitisers such as phthalocyanines and sometimes boron dipyrromethenes onto carbon based nanoparticles for the enhanced characteristics in variable applications. , Thesis (PhD) -- Faculty of Science, Chemistry, 2021
- Full Text:
- Date Issued: 2021-10-29
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