title: The Functional Significance of Black-Pigmented Leaves: Photosynthesis, Photoprotection and Productivity in Ophiopogon planiscapus ‘Nigrescens’

authors: Hatier, Jean-Hugues B.

abstract: Black pigmented leaves are common among horticultural cultivars, yet are extremely rare across natural plant populations. We hypothesised that black pigmentation would disadvantage a plant by reducing photosynthesis and therefore shoot productivity, but that this trait might also confer protective benefits by shielding chloroplasts against photo-oxidative stress. CO2 assimilation, chlorophyll a fluorescence, shoot biomass, and pigment concentrations were compared for near isogenic green- and black-leafed Ophiopogon planiscapus ‘Nigrescens’. The black leaves had lower maximum CO2 assimilation rates, higher light saturation points and higher quantum efficiencies of photosystem II (PSII) than green leaves. Under saturating light, PSII photochemistry was inactivated less and recovered more completely in the black leaves. In full sunlight, green plants branched more abundantly and accumulated shoot biomass quicker than the black plants; in the shade, productivities of the two morphs were comparable. The data indicate a light-screening, photoprotective role of foliar anthocyanins. However, limitations to photosynthetic carbon assimilation are relatively small, insufficient to explain the natural scarcity of black-leafed plants.

text: The Functional Significance of Black-Pigmented Leaves: Photosynthesis, Photoprotection and Productivity in Ophiopogon planiscapus ‘Nigrescens’ Black pigmented leaves are common among horticultural cultivars, yet are extremely rare across natural plant populations. We hypothesised that black pigmentation would disadvantage a plant by reducing photosynthesis and therefore shoot productivity, but that this trait might also confer protective benefits by shielding chloroplasts against photo-oxidative stress. CO2 assimilation, chlorophyll a fluorescence, shoot biomass, and pigment concentrations were compared for near isogenic green- and black-leafed Ophiopogon planiscapus ‘Nigrescens’. The black leaves had lower maximum CO2 assimilation rates, higher light saturation points and higher quantum efficiencies of photosystem II (PSII) than green leaves. Under saturating light, PSII photochemistry was inactivated less and recovered more completely in the black leaves. In full sunlight, green plants branched more abundantly and accumulated shoot biomass quicker than the black plants; in the shade, productivities of the two morphs were comparable. The data indicate a light-screening, photoprotective role of foliar anthocyanins. However, limitations to photosynthetic carbon assimilation are relatively small, insufficient to explain the natural scarcity of black-leafed plants.

year: 2013

title: Tribological properties of thermally sprayed TiAl-Al₂O₃ composite coating

authors: Salman, Asma Siddiq

subjects: engineering

abstract: The use of thermal spray coatings provides protection to the surfaces operating in severe environments. The main goal of the current work is to investigate the possibility of using a high velocity oxy fuel (HVOF) thermally sprayed wear resistant TiAl/Al2O3 coating on tool steel (H13) which is used for making dies for aluminium high pressure die casting. A feedstock of TiAl/Al2O3 composite powder was produced from a mixture of Al and TiO2 powders by high energy mechanical milling, followed by a thermal reaction process. The feedstock was then thermally sprayed using a high velocity oxy-fuel (HVOF) technique onto H13 steel substrates to produce a composite coating. The present study describes and compares the tribological properties such as friction and sliding wear rate of the coating both at room and high temperature (700°C). The results showed that the composite coating has lower wear rate at high temperature (700°C) than the uncoated H13 sample. At Room temperature without using lubricant there is no much significant difference between the wear rate of the coated and uncoated samples. The experimental results showed that the composite coating has great potential for high temperature application due to its lower wear rate at high temperature in comparison with the uncoated sample at the same temperature. The composite coating was characterized using scanning electron microscopy (SEM), optical microscopy and X-ray diffractometry (XRD). This paper reports the experimental observations and discusses the wear resistance performance of the coatings at room and high temperatures.

text: Tribological properties of thermally sprayed TiAl-Al₂O₃ composite coating The use of thermal spray coatings provides protection to the surfaces operating in severe environments. The main goal of the current work is to investigate the possibility of using a high velocity oxy fuel (HVOF) thermally sprayed wear resistant TiAl/Al2O3 coating on tool steel (H13) which is used for making dies for aluminium high pressure die casting. A feedstock of TiAl/Al2O3 composite powder was produced from a mixture of Al and TiO2 powders by high energy mechanical milling, followed by a thermal reaction process. The feedstock was then thermally sprayed using a high velocity oxy-fuel (HVOF) technique onto H13 steel substrates to produce a composite coating. The present study describes and compares the tribological properties such as friction and sliding wear rate of the coating both at room and high temperature (700°C). The results showed that the composite coating has lower wear rate at high temperature (700°C) than the uncoated H13 sample. At Room temperature without using lubricant there is no much significant difference between the wear rate of the coated and uncoated samples. The experimental results showed that the composite coating has great potential for high temperature application due to its lower wear rate at high temperature in comparison with the uncoated sample at the same temperature. The composite coating was characterized using scanning electron microscopy (SEM), optical microscopy and X-ray diffractometry (XRD). This paper reports the experimental observations and discusses the wear resistance performance of the coatings at room and high temperatures.

year: 2009

title: The rhetorical organisation of Maori discourse: An illustration

authors: Crombie, Winifred

subjects: Māori medium education

abstract: Almost 20% all Māori students in New Zealand schools are involved in some form of Māori-medium education. These students need to develop competence in using the language for a wide range of purposes. They need, therefore, to understand a range of written discourse conventions. In seeking to assist them in this task, elders and scholars are turning to the works of major Māori figures of the past, works composed when the language was used widely in a range of discourse contexts. However, scholars need ways of analysing these texts and of communicating their findings to others. The primary aim of this paper is to demonstrate one such approach. A single letter of condolence written in Māori is analysed here in terms of rhetorical discourse structure. On the basis of the analysis, a number of hypotheses concerning epistolary discourse in Māori are put forward. The primary hypothesis is that letters of condolence written in Māori by highly competent users of the language are likely to be characterized by an overall Problem-Solution rhetorical prototype involving spiral multilayering.

text: The rhetorical organisation of Maori discourse: An illustration Almost 20% all Māori students in New Zealand schools are involved in some form of Māori-medium education. These students need to develop competence in using the language for a wide range of purposes. They need, therefore, to understand a range of written discourse conventions. In seeking to assist them in this task, elders and scholars are turning to the works of major Māori figures of the past, works composed when the language was used widely in a range of discourse contexts. However, scholars need ways of analysing these texts and of communicating their findings to others. The primary aim of this paper is to demonstrate one such approach. A single letter of condolence written in Māori is analysed here in terms of rhetorical discourse structure. On the basis of the analysis, a number of hypotheses concerning epistolary discourse in Māori are put forward. The primary hypothesis is that letters of condolence written in Māori by highly competent users of the language are likely to be characterized by an overall Problem-Solution rhetorical prototype involving spiral multilayering.

year: 2001-02