title: Latitudinal variation in nutrient stoichiometry and chlorophyll-nutrient relationships in lakes: A global study

authors: Abell, Jonathan Michael

subjects: Eutrophication

abstract: We present analysis of variations in relationships between nitrogen (N), phosphorus (P) and chlorophyll-a (chl-a) in lakes along a gradient of latitude inclusive of tropical, temperate and polar regions. Total nitrogen (TN), total phosphorus (TP), chl-a, latitude and depth data were collated for 1316 lakes situated between 70 degrees S and 83 N. Latitudinal variation was then analysed for three empirical measures of phytoplankton nutrient limitation and/or nutrient assimilation. Lastly, chl-a near-maxima conditional on TN and TP abundance were empirically defined for this global dataset using quantile regression. Mean TN:TP increases with distance from the equator. This relationship is independent of variation in either lake depth or trophic state, reflecting latitudinal variation in nutrient cycling processes and/or nutrient sources. There is a negative linear relationship between latitude and chl-a:TN which similarly suggests that N is less abundant relative to phytoplankton growth requirements at lower latitudes. Relative to temperate lakes, the statistical capability of TN and TP to predict chl-a is poor for both tropical and polar lakes, reflecting latitudinal variation in lake ecosystem functioning and the subsequent potential unsuitability of applying relationships derived for temperate lakes elsewhere. Chl-a near-maxima correspond to chl-a:TN and chl-a:TP yields of 0.046:1 and 0.87:1 respectively, although some observations greatly exceed near-maxima, suggesting possible physiologically plastic phytoplankton responses in these exceptional cases. Deficiencies in understanding the mechanisms that drive variation in macro-nutrient stoichiometry and phytoplankton biomass-nutrient relationships across large spatial scales necessitates further landscape-scale research on this topic, particularly in the tropics.

text: Latitudinal variation in nutrient stoichiometry and chlorophyll-nutrient relationships in lakes: A global study We present analysis of variations in relationships between nitrogen (N), phosphorus (P) and chlorophyll-a (chl-a) in lakes along a gradient of latitude inclusive of tropical, temperate and polar regions. Total nitrogen (TN), total phosphorus (TP), chl-a, latitude and depth data were collated for 1316 lakes situated between 70 degrees S and 83 N. Latitudinal variation was then analysed for three empirical measures of phytoplankton nutrient limitation and/or nutrient assimilation. Lastly, chl-a near-maxima conditional on TN and TP abundance were empirically defined for this global dataset using quantile regression. Mean TN:TP increases with distance from the equator. This relationship is independent of variation in either lake depth or trophic state, reflecting latitudinal variation in nutrient cycling processes and/or nutrient sources. There is a negative linear relationship between latitude and chl-a:TN which similarly suggests that N is less abundant relative to phytoplankton growth requirements at lower latitudes. Relative to temperate lakes, the statistical capability of TN and TP to predict chl-a is poor for both tropical and polar lakes, reflecting latitudinal variation in lake ecosystem functioning and the subsequent potential unsuitability of applying relationships derived for temperate lakes elsewhere. Chl-a near-maxima correspond to chl-a:TN and chl-a:TP yields of 0.046:1 and 0.87:1 respectively, although some observations greatly exceed near-maxima, suggesting possible physiologically plastic phytoplankton responses in these exceptional cases. Deficiencies in understanding the mechanisms that drive variation in macro-nutrient stoichiometry and phytoplankton biomass-nutrient relationships across large spatial scales necessitates further landscape-scale research on this topic, particularly in the tropics.

year: 2012

title: Evaluation of the mechanical properties of powder metallurgy Ti-6Al-7Nb alloy

authors: Bolzoni, Leandro

subjects: Titanium alloy

abstract: Titanium and its alloys are common biomedical materials owing to their combination of mechanical properties, corrosion resistance and biocompatibility. Powder metallurgy (PM) techniques can be used to fabricate biomaterials with tailored properties because changing the processing parameters, such as the sintering temperature, products with different level of porosity and mechanical performances can be obtained. This study addresses the production of the biomedical Ti-6Al-7Nb alloy by means of the master alloy addition variant of the PM blending elemental approach. The sintering parameters investigated guarantee that the complete diffusion of the alloying elements and the homogenization of the microstructure is achieved. The sintering of the Ti-6Al-7Nb alloy induces a total shrinkage between 7.4% and 10.7% and the level of porosity decreases from 6.2% to 4.7% with the increment of the sintering temperature. Vickers hardness (280–300 HV30) and tensile properties (different combination of strength and elongation around 900 MPa and 3%) are achieved.

text: Evaluation of the mechanical properties of powder metallurgy Ti-6Al-7Nb alloy Titanium and its alloys are common biomedical materials owing to their combination of mechanical properties, corrosion resistance and biocompatibility. Powder metallurgy (PM) techniques can be used to fabricate biomaterials with tailored properties because changing the processing parameters, such as the sintering temperature, products with different level of porosity and mechanical performances can be obtained. This study addresses the production of the biomedical Ti-6Al-7Nb alloy by means of the master alloy addition variant of the PM blending elemental approach. The sintering parameters investigated guarantee that the complete diffusion of the alloying elements and the homogenization of the microstructure is achieved. The sintering of the Ti-6Al-7Nb alloy induces a total shrinkage between 7.4% and 10.7% and the level of porosity decreases from 6.2% to 4.7% with the increment of the sintering temperature. Vickers hardness (280–300 HV30) and tensile properties (different combination of strength and elongation around 900 MPa and 3%) are achieved.

year: 2017-03

title: Rethinking English in Māori-medium education

authors: Hill, Richard Kenneth

subjects: Māori-medium

abstract: English language instruction in New Zealand's Māori-medium schools is controversial, with many schools either excluding it from their curriculum or adopting a tokenistic approach. Yet, how Māori-medium educators can best support their students' academic English language growth is still an under-researched and unresolved question. This paper reports on a project involving the English language transition programmes of three Māori-medium primary schools. Interviews and observations of key personnel within these schools revealed the components of their programmes, their perceptions of the need for English transition education and the issues they were facing in implementing English language instruction. The project found a direct relationship between levels of student language attainment and the quantity and quality of exposure to English instruction. Where an English programme occupied a significant place in a school's timetable and was staffed by teachers knowledgeable about the learning needs of bilingual students and how best to attend to these, the result was higher literacy scores and more satisfied students. This paper argues that planning English language outcomes for Māori-medium students is essential if becoming biliterate is an important aim. This planning must also be long-term, across all 13 years of the students' education.

text: Rethinking English in Māori-medium education English language instruction in New Zealand's Māori-medium schools is controversial, with many schools either excluding it from their curriculum or adopting a tokenistic approach. Yet, how Māori-medium educators can best support their students' academic English language growth is still an under-researched and unresolved question. This paper reports on a project involving the English language transition programmes of three Māori-medium primary schools. Interviews and observations of key personnel within these schools revealed the components of their programmes, their perceptions of the need for English transition education and the issues they were facing in implementing English language instruction. The project found a direct relationship between levels of student language attainment and the quantity and quality of exposure to English instruction. Where an English programme occupied a significant place in a school's timetable and was staffed by teachers knowledgeable about the learning needs of bilingual students and how best to attend to these, the result was higher literacy scores and more satisfied students. This paper argues that planning English language outcomes for Māori-medium students is essential if becoming biliterate is an important aim. This planning must also be long-term, across all 13 years of the students' education.

year: 2011