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Yayın A robust Gradient boosting model based on SMOTE and NEAR MISS methods for intrusion detection in imbalanced data sets(Işık Üniversitesi, 2022-01-18) Arık, Ahmet Okan; Çavdaroğlu Akkoç, Gülsüm Çiğdem; Işık Üniversitesi, Lisansüstü Eğitim Enstitüsü, Enformasyon Teknolojileri Yüksek Lisans ProgramıNovel technologies cause many security vulnerabilities and zero-day attack risks. Intrusion Detection Systems (IDS) are developed to protect computer networks from threats and attacks. Many challenging problems need to be solved in existing methods. The class imbalance problem is one of the most difficult problems of IDS, and it reduces the detection rate performance of the classifiers. The highest IDS detection rate in the literature is 96.54%. This thesis proposes a new model called ROGONG-IDS (Robust Gradient Boosting) based on Gradient Boosting. ROGONGIDS model uses Synthetic Minority Over-Sampling Technique (SMOTE) and Near Miss methods to handle class imbalance. Three different gradient boosting-based classification algorithms (GBM, LightGBM, XGBoost) were compared. The performance of the proposed model on multiclass classification has been verified in the UNSW-NB15 dataset. It reached the highest attack detection rate and F1 score in the literature with a 97.30% detection rate and 97.65% F1 score. ROGONG-IDS provides a robust, efficient solution for IDS built on datasets with the imbalanced class distribution. It outperforms state-of-the-art and traditional intrusion detection methods.Yayın Spatial-Temporary analysis of Istanbul air pollution during the pandemic using Google Earth Engine and Google community mobility reports(Gök, Murat, 2023-06-30) Çavdaroğlu, Gülsüm Çiğdem; Arık, Ahmet OkanThe Covid-19 pandemic has brought drastic changes to people's daily life and environmental characteristics. To control the pandemic, all governments have implemented particular policies for their countries and imposed restrictions that affect people's daily life. The traffic index has decreased in many countries and cities depending on the restrictions. Therefore, restrictions in many countries and cities have positively impacted air quality. However, the opposite has also been observed in metropolitan cities. In this study, the change in the air quality of Istanbul, which is accepted as Turkey's largest metropolitan city, has been examined. First, the spatio-temporal distribution of air pollutants (NO2, CO, and SO2) has been analyzed using Sentinel-5P NRTI satellite images. Then six independent variable groups (traffic index of Istanbul, daily deaths in Istanbul, Google community mobility reports of Istanbul, fuel prices, stringency index of Turkey, two logical attributes regarding the Covid-19 restrictions and in-class education) were collected and combined to analyze the correlations between these variable groups and air pollutant concentrations. According to the spatial distribution graphs, there is a tendency to decrease NO2, CO, and SO2 pollutant concentrations in Istanbul when the restrictions are applied in Turkey. There was no significant relationship between the decrease in community mobility in Istanbul and pollutant concentrations, although an increase in air quality has been observed in many cities due to the restrictions of the Covid-19 pandemic.Yayın An intrusion detection approach based on the combination of oversampling and undersampling algorithms(Istanbul University Press, 2023-06-14) Arık, Ahmet Okan; Çavdaroğlu, Gülsüm ÇiğdemThe threat of network intrusion has become much more severe due to the increasing network flow. Therefore, network intrusion detection is one of the most concerned areas of network security. As demand for cybersecurity assurance increases, the requirement for intrusion detection systems to meet current threats is also growing. However, network-based intrusion detection systems have several shortcomings due to the structure of the systems, the nature of the network data, and uncertainty related to future data. The imbalanced class problem is also crucial since it significantly negatively affects classification performance. Although high performance has been achieved in deep learning-based methodologies in recent years, machine learning techniques may also provide high performance in network intrusion detection. This study suggests a new intrusion detection system called ROGONG-IDS (Robust Gradient Boosting – Intrusion Detection System) which has a unique two-stage resampling model to solve the imbalanced class problem that produces high accuracy on the UNSW-NB15 dataset using machine learning techniques. ROGONGIDS is based on gradient boosting. The system uses Synthetic Minority Over-Sampling Technique (SMOTE) and NearMiss-1 methods to handle the imbalanced class problem. The proposed model's performance on multi-class classification was tested with the UNSW-NB15, and then its robust structure was validated with the NSL-KDD dataset. ROGONG-IDS reached the highest attack detection rate and F1 score in the literature, with a 97.30% detection rate and 97.65% F1 score using the UNSW-NB15 dataset. ROGONG-IDS provides a robust, efficient intrusion detection system for the UNSW-NB15 dataset, which suffered from imbalanced class distribution. The proposed methodology outperforms state-of-the-art and intrusion detection methods.Yayın Istanbul’s community mobility changes during the COVID-19 pandemic: a spatial analysis(Istanbul University Press, 2023-08-15) Arık, Ahmet Okan; Çavdaroğlu, Gülsüm ÇiğdemCOVID-19 was the most recent pandemic to strike humanity. Moreover, this pandemic occurred during the most active period of global interaction and mobility, unlike pandemics like cholera, plague, and flu in earlier centuries. Many countries restricted domestic mobility after suspending international mobility to prevent the pandemic from spreading. Although these policies differ from nation to nation, they have affected the mobility of communities. This study examined spatial and non-spatial independent variables that affected how the community’s mobility patterns changed in various locations, including parks, transit stations, workplaces, grocery and pharmacies, and residential areas in Istanbul, Türkiye. The impact of the independent spatial variables on the mobility changes was examined after identifying the non-spatial independent variables influencing the mobility changes in 6 different areas. It was determined that the altitude variable, expected to impact how mobility changed, had no overall impact on the dependent variable. On the other hand, the dependent variables representing the mobility changes were affected by the independent variables representing the county center’s latitude and longitude values and whether the county is located near the sea. Regression analysis across Türkiye will be performed in upcoming studies using an updated version of the methodology used in this study.
