Electronic Theses and Dissertations (Masters)

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Browsing Electronic Theses and Dissertations (Masters) by Author "Bau, Hairong"

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    Improving Semi-Supervised Learning Generative Adversarial Networks
    (University of the Witwatersrand, Johannesburg, 2023-08) Moolla, Faheem; Bau, Hairong; Van Zyl, Terence
    Generative Adversarial Networks (GANs) have shown remarkable potential in generating high-quality images, with semi-supervised GANs providing a high classification accuracy. In this study, an enhanced semi supervised GAN model is proposed wherein the generator of the GAN is replaced by a pre-trained decoder from a Variational Autoencoder. The model presented outperforms regular GAN and semi-supervised GAN models during the early stages of training, as it produces higher quality images. Our model demonstrated significant improvements in image quality across three datasets - namely the MNIST, Fashion MNIST, and CIFAR-10 datasets - as evidenced by higher accuracies obtained from a Convolutional Neural Network (CNN) trained on generated images, as well as superior inception scores. Additionally, our model prevented mode collapse and exhibited smaller oscillations in the discriminator and generator loss graphs compared to baseline models. The presented model also provided remarkably high levels of classification accuracy, by obtaining 99.32% on the MNIST dataset, 92.78% on the Fashion MNIST dataset, and 83.22% on the CIFAR-10 dataset. These scores are notably robust as they improved some of the classification accuracies obtained by two state-of-the-art models, indicating that the presented model is a significantly improved semi-supervised GAN model. However, despite the high classification accuracy for the CIFAR-10 dataset, a considerable drop in accuracy was observed when comparing generated images to real images for this dataset. This suggests that the quality of those generated images can be bettered and the presented model performs better with less complex datasets. Future work could explore techniques to enhance our model’s performance with more intricate datasets, ultimately expanding its applicability across various domains.
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    Using Machine Learning to Estimate the Photometric Redshift of Galaxies
    (University of the Witwatersrand, Johannesburg, 2023-08) Salim, Shayaan; Bau, Hairong; Komin, Nukri
    Machine learning has emerged as a crucial tool in the field of cosmology and astrophysics, leading to extensive research in this area. This research study aims to utilize machine learning models to estimate the redshift of galaxies, with a primary focus on utilizing photometric data to obtain accurate results. Five machine learning algorithms, including XGBoost, Random Forests, K-nearest neighbors, Artificial Neural Networks, and Polynomial Regression, are employed to estimate the redshifts, trained on photometric data derived from the Sloan Digital Sky Survey (SDSS) Data Release 17 database. Furthermore, various input parameters from the SDSS database are explored to achieve the most accurate redshift values. The research incorporates a comparative analysis, utilizing different evaluation metrics and statistical tests to determine the best-performing algorithm. The results indicate that the XGBoost algorithm achieves the highest accuracy, with an R2 value of 0.94, a Root Mean Square Error (RMSE) of 0.03, and a Mean Absolute Average Percentage (MAPE) of 12.04% when trained on the optimal feature subset. In comparison, the base model achieved an R2 of 0.84, a RMSE of 0.05, and a MAPE of 20.89%. The study contributes to the existing literature by utilizing photometric data during model training and comparing different high-performing algorithms from the literature.