title: A study of self-training variants for semi-supervised image classification

authors: Sahito, Attaullah

subjects: Self-training

abstract: Artificial neural networks achieve state-of-the-art performance when trained on a vast number of labelled examples. Still, they can easily overfit training examples when few labelled examples are available. The requirement to have labels for all training examples is a strong limitation of standard supervised machine learning. This can be addressed by applying semi-supervised learning methods that extend supervised learning and use unlabelled examples. Self-training is the most basic and generic semi-supervised approach. In self-training, a model is trained iteratively on both labelled and pseudo-labelled examples obtained from previous iterations. This thesis focuses on the task of investigating different variants of self-training by applying metric learning, transfer learning, and self-supervised learning.
The first part of this thesis investigates how metric learning can be applied to self-training. This is achieved by applying several metric learning losses for the training of feedforward neural networks. Experimental results show that triplet loss – a metric learning loss – can achieve better results than cross-entropy loss with simple neural networks.
For improving the performance of self-training, the second part of the thesis investigates applying large neural networks and pretraining on various image sizes of ImageNet with different loss functions. Experimental results show that pretraining always improves the predictive performance of the model. Pretraining on smaller image sizes with cross-entropy loss provides the highest performance.
In the third part of this thesis, several self-training methods are developed using self-supervised learning. Geometric transformation-based self-supervised learning is applied to unlabelled examples. The experimental results indicate that applying self-supervised learning for only the first iteration achieves better performance than using it in all iterations of self-training.

text: A study of self-training variants for semi-supervised image classification Artificial neural networks achieve state-of-the-art performance when trained on a vast number of labelled examples. Still, they can easily overfit training examples when few labelled examples are available. The requirement to have labels for all training examples is a strong limitation of standard supervised machine learning. This can be addressed by applying semi-supervised learning methods that extend supervised learning and use unlabelled examples. Self-training is the most basic and generic semi-supervised approach. In self-training, a model is trained iteratively on both labelled and pseudo-labelled examples obtained from previous iterations. This thesis focuses on the task of investigating different variants of self-training by applying metric learning, transfer learning, and self-supervised learning.
The first part of this thesis investigates how metric learning can be applied to self-training. This is achieved by applying several metric learning losses for the training of feedforward neural networks. Experimental results show that triplet loss – a metric learning loss – can achieve better results than cross-entropy loss with simple neural networks.
For improving the performance of self-training, the second part of the thesis investigates applying large neural networks and pretraining on various image sizes of ImageNet with different loss functions. Experimental results show that pretraining always improves the predictive performance of the model. Pretraining on smaller image sizes with cross-entropy loss provides the highest performance.
In the third part of this thesis, several self-training methods are developed using self-supervised learning. Geometric transformation-based self-supervised learning is applied to unlabelled examples. The experimental results indicate that applying self-supervised learning for only the first iteration achieves better performance than using it in all iterations of self-training.

year: 2021

title: Studies on soil and microbial lipases

authors: Cooper, Alvin Bryce

abstract: The relative sensitivities of four methods for the determination of lipase activity was found to be dependent upon the source of the enzyme, when comparisons were made using commercial porcine pancreatic lipase and two partially-purified bacterial lipases. 

Lipase activity was dependent upon substrate surface area rather than substrate concentration per se. Long-chain insoluble fatty acids were inhibitory to lipase activity. A minimum concentration of fatty acid was required before inhibition of lipase activity occurred. This minimum inhibitory concentration was inversely related to the chain length of the fatty acid. Fatty acid inhibition of lipase activity could be partially reversed by the addition of Ca²⁺. 

A sensitive and precise assay for the determination of soil lipase activity was developed. The assay involves a 3h 0.1 M tetra-sodium pyrophosphate (pH 7.5) extraction of soil, followed by a 10 min. assay on the extract using the fluorogenic substrate 4-methyl umbelliferone nonanoate (4 MUN). Basal lipase activities of thirteen New Zealand topsoils ranged from 28 to 597 nmol 4-methyl umbelliferone (4 MU) produced min⁻¹ g⁻¹ of oven-dried soil and were not strongly correlated with soil pH, clay content, cation-exchange capacity, or organic matter. 

The addition of triacylglycerols to soil samples induced microbial production of lipase resulting in triacylglycerol degradation and associated oxygen consumption. With tallow applied to a Hamilton clay loam topsoil sample at the rate of 2.5 mg g⁻¹ and incubated at 25°C, lipase levels increased from 160 nmol 4 MU min⁻¹ g⁻¹ to 490 nmol 4 MU min⁻¹ g⁻¹ after 8 days and the majority of the triacylglycerol was degraded within 14 days. The time for significant triacylglycerol degradation to occur was related to the level of lipase induction upon amendment and not upon the basal lipase levels of the soil. The extent of lipase induction and, therefore, triacylglycerol degradation, was influenced by loading rate, type of triacylglycerol, soil type, temperature, and mineral nutrient additions. In synthetic mixtures of substrates the breakdown of triacylglycerol occurred after the microbial oxidation of alternative substrates. 

The lipolytic microbiota of both unamended and triacylglycerol-amended soils were isolated. The bacterial population demonstrated the greatest increase upon amendment with triacylglycerols. A bacterial isolate obtained by enrichment culture, and designated Pseudomonas 017, was capable of producing high levels of extracellular inductive lipase when grown upon triacylglycerols, long-chain fatty acids and hydrocarbons. Growth upon these substrates was accompanied by the production of an emulsifying agent. The lipase of Pseudomonas 017 was partially purified and characterised.

text: Studies on soil and microbial lipases The relative sensitivities of four methods for the determination of lipase activity was found to be dependent upon the source of the enzyme, when comparisons were made using commercial porcine pancreatic lipase and two partially-purified bacterial lipases. 

Lipase activity was dependent upon substrate surface area rather than substrate concentration per se. Long-chain insoluble fatty acids were inhibitory to lipase activity. A minimum concentration of fatty acid was required before inhibition of lipase activity occurred. This minimum inhibitory concentration was inversely related to the chain length of the fatty acid. Fatty acid inhibition of lipase activity could be partially reversed by the addition of Ca²⁺. 

A sensitive and precise assay for the determination of soil lipase activity was developed. The assay involves a 3h 0.1 M tetra-sodium pyrophosphate (pH 7.5) extraction of soil, followed by a 10 min. assay on the extract using the fluorogenic substrate 4-methyl umbelliferone nonanoate (4 MUN). Basal lipase activities of thirteen New Zealand topsoils ranged from 28 to 597 nmol 4-methyl umbelliferone (4 MU) produced min⁻¹ g⁻¹ of oven-dried soil and were not strongly correlated with soil pH, clay content, cation-exchange capacity, or organic matter. 

The addition of triacylglycerols to soil samples induced microbial production of lipase resulting in triacylglycerol degradation and associated oxygen consumption. With tallow applied to a Hamilton clay loam topsoil sample at the rate of 2.5 mg g⁻¹ and incubated at 25°C, lipase levels increased from 160 nmol 4 MU min⁻¹ g⁻¹ to 490 nmol 4 MU min⁻¹ g⁻¹ after 8 days and the majority of the triacylglycerol was degraded within 14 days. The time for significant triacylglycerol degradation to occur was related to the level of lipase induction upon amendment and not upon the basal lipase levels of the soil. The extent of lipase induction and, therefore, triacylglycerol degradation, was influenced by loading rate, type of triacylglycerol, soil type, temperature, and mineral nutrient additions. In synthetic mixtures of substrates the breakdown of triacylglycerol occurred after the microbial oxidation of alternative substrates. 

The lipolytic microbiota of both unamended and triacylglycerol-amended soils were isolated. The bacterial population demonstrated the greatest increase upon amendment with triacylglycerols. A bacterial isolate obtained by enrichment culture, and designated Pseudomonas 017, was capable of producing high levels of extracellular inductive lipase when grown upon triacylglycerols, long-chain fatty acids and hydrocarbons. Growth upon these substrates was accompanied by the production of an emulsifying agent. The lipase of Pseudomonas 017 was partially purified and characterised.

year: 1982

title: Huri whakatau: The call for Māori software requirements elicitation

authors: Brown, Tamahau

abstract: It is essential to consider specifications and design when examining the requirements for new software for stakeholders and software engineers. The Huri Whakatau project investigates current relevant requirements and design techniques to understand the Māori (Indigenous people of Aotearoa) demographic to identify any relevant gaps for examining requirements.

The process has been tested by investigating existing internationally accepted groups and their methodologies to attempt to adapt a new methodology for Māori groups. In the context of the research, an accepted group is defined as a group which is not from a developing country or Indigenous group. The research was able to identify three untested methodologies; this involved conducting an empirical study as a part of the experiment. The decision was to transform the internationally accepted soft systems methodology (SSM) with groups in a user study. Comparing previously recorded satisfaction using the technique and the use of Māori techniques determined that SSM would be the strongest candidate. When testing SSM with participants, overall, there was a higher level of satisfaction with Māori participants using the new proposed adapted Māori approach as opposed to the internationally accepted groups.

text: Huri whakatau: The call for Māori software requirements elicitation It is essential to consider specifications and design when examining the requirements for new software for stakeholders and software engineers. The Huri Whakatau project investigates current relevant requirements and design techniques to understand the Māori (Indigenous people of Aotearoa) demographic to identify any relevant gaps for examining requirements.

The process has been tested by investigating existing internationally accepted groups and their methodologies to attempt to adapt a new methodology for Māori groups. In the context of the research, an accepted group is defined as a group which is not from a developing country or Indigenous group. The research was able to identify three untested methodologies; this involved conducting an empirical study as a part of the experiment. The decision was to transform the internationally accepted soft systems methodology (SSM) with groups in a user study. Comparing previously recorded satisfaction using the technique and the use of Māori techniques determined that SSM would be the strongest candidate. When testing SSM with participants, overall, there was a higher level of satisfaction with Māori participants using the new proposed adapted Māori approach as opposed to the internationally accepted groups.

year: 2023