Mühendislik Fakültesi / Faculty of Engineering

Permanent URI for this collectionhttps://hdl.handle.net/11727/1401

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    Involution Generators Of The Big Mapping Class Group
    (Başkent Üniversitesi Mühendislik Fakültesi, 2024-06-09) Altunoz, Tulin; Pamuk, Mehmetcik; Yildiz, Oguz
    Let S = S(n) denote the infinite-type surface with n ends, n is an element of N, accumulated by genus. For n >= 6, we show that the mapping class group of S is topologically generated by five involutions. When n >= 3, it is topologically generated by six involutions.
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    Joshi-Malafarina-Narayan Singularity In Weak Magnetic Field
    (Başkent Üniversitesi Mühendislik Fakültesi, 2024-06-07) Azreg-Ainou, Mustapha; Acharya, Kauntey; Joshi, Pankaj S.
    The importance and significance of magnetic fields in the astrophysical scenario is well known. Many domains of astrophysical black hole physics such as polarized shadow image, high energy emitting processes and jet formation are dependent on the behavior of the magnetic fields in the vicinity of the compact objects. In light of this, we determine the master equation and master differential equation that determine the spatial behavior of the magnetic field inside a matter distribution or vacuum region, of general spherically symmetric metric, which is immersed in a test magnetic field. We also investigate here the case of JMN-1 singularity immersed in a uniform weak magnetic field and determine the behavior of magnetic fields by defining electromagnetic four potential vector. We find that the tangential component of the magnetic field is discontinuous at the matching surface of the JMN-1 singularity with the external Schwarzschild metric, resulting in surface currents. We define the covariant expression of surface current density in this scenario. We also analyze the behavior of center-of-mass energy of two oppositely charged particles in the geometry of the magnetized JMN-1 singularity. We briefly discuss the possible scenarios which would possess a discontinuous magnetic field and implications of the same and future possibilities in the realm of astrophysics are indicated.
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    A Plasma Arc-Based Electromechanical System Designed for Microchannel Processing
    (Başkent Üniversitesi Mühendislik Fakültesi, 2024-05-31) Akin, Fevzi; Ersoy, Ece; Idil, Deniz; Ozsimitci, Melih; Serdaroglu, Dilek Cokeliler; Ic, Yusuf Tansel; Atalay, Kumru Didem; Kocum, Cengiz; Okat, Kemal
    Plasma technology is based on a simple physical principle. When more energy enters the gas, it ionizes and becomes the fourth state of matter, the energy-dense plasma. The studies carried out within the scope of this study were designed to create microchannels on lamellar glass using an improved redesign of the current plasma arc device, which is the main subject of the paper. The created microchannel is examined at the microscale. Experimental analysis was conducted considering the effect of plasma on the effect of microchannel quality. We performed an experimental design study to determine the optimal parameter levels for improving microchannel quality. The predicted results have been validated with the experimental results. An experimental design study provides useful results, such as information about the distance between the probes, pulse duration, and material temperature, which enhances the channel dimensions. The improved device can be utilized effectively to establish microchannel processing in practice.
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    Computer-Aided Colorectal Cancer Diagnosis: Ai-Driven Image Segmentation And Classification
    (Başkent Üniversitesi Mühendislik Fakültesi, 2024-05-31) Erdas, Cagatay Berke
    Colorectal cancer is an enormous health concern since it is among the most lethal types of malignancy. The manual examination has its limitations, including subjectivity and data overload. To overcome these challenges, computer -aided diagnostic systems focusing on image segmentation and abnormality classi fi cation have been developed. This study presents a two -stage approach for the automatic detection of fi ve types of colorectal abnormalities in addition to a control group: polyp, low-grade intraepithelial neoplasia, high-grade intraepithelial neoplasia, serrated adenoma, adenocarcinoma. In the fi rst stage, UNet3+ was used for image segmentation to locate the anomalies, while in the second stage, the Cross -Attention Multi -Scale Vision Transformer deep learning model was used to predict the type of anomaly after highlighting the anomaly on the raw images. In anomaly segmentation, UNet3+ achieved values of 0.9872, 0.9422, 0.9832, and 0.9560 for Dice Coef fi cient, Jaccard Index, Sensitivity, Speci fi city respectively. In anomaly detection, the Cross -Attention Multi -Scale Vision Transformer model attained a classi fi cation performance of 0.9340, 0.9037, 0.9446, 0.8723, 0.9102, 0.9849 for accuracy, F1 score, precision, recall, Matthews correlation coef fi cient, and speci fi city, respectively. The proposed approach proves its capacity to alleviate the overwhelm of pathologists and enhance the accuracy of colorectal cancer diagnosis by achieving high performance in both the identi fi cation of anomalies and the segmentation of regions.
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    Investigation of the Additional Powder Effect on the Strength of Joined Aluminum Alloy Plates in Friction Stir Welding Using the Topsis-Game Theory Model
    (Başkent Üniversitesi Mühendislik Fakültesi, 2024-05-03) Yurdakul, Mustafa; Ulke, Ibrahim; Tansel, Yusuf I. C.
    Friction stir welding (FSW) is a process that can join many materials by causing minimal internal stress without the need for a direct electric current, contrary to traditional welding methods. The effects of SiC and Al2O3 reinforcing powders on the joining of AA6061-T6 and AA7075-T6 plates, which are difficult to join with conventional welding methods by FSW, are investigated in this study. The metallurgical properties of the combined samples are examined in terms of strength characteristics to investigate the effects of the reinforcement powder. In addition, elemental analysis is carried out for the mixing behavior of the powders. Finally, we used the TOPSIS method to select the most appropriate powder types to improve welding quality. Furthermore, a game theory application is presented to determine which powder type is suitable considering the joined aluminum plate's strength expectations.
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    Comprehensive Data Analysis Of White Blood Cells With Classification And Segmentation By Using Deep Learning Approaches
    (Başkent Üniversitesi Mühendislik Fakültesi, 2024-04-05) Ozcan, Seyma Nur; Uyar, Tansel; Karayegen, Gokay
    Deep learning approaches have frequently been used in the classification and segmentation of human peripheral blood cells. The common feature of previous studies was that they used more than one dataset, but used them separately. No study has been found that combines more than two datasets to use together. In classification, five types of white blood cells were identified by using a mixture of four different datasets. In segmentation, four types of white blood cells were determined, and three different neural networks, including CNN (Convolutional Neural Network), UNet and SegNet, were applied. The classification results of the presented study were compared with those of related studies. The balanced accuracy was 98.03%, and the test accuracy of the train-independent dataset was determined to be 97.27%. For segmentation, accuracy rates of 98.9% for train-dependent dataset and 92.82% for train-independent dataset for the proposed CNN were obtained in both nucleus and cytoplasm detection. In the presented study, the proposed method showed that it could detect white blood cells from a train-independent dataset with high accuracy. Additionally, it is promising as a diagnostic tool that can be used in the clinical field, with successful results in classification and segmentation.
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    Examination of Speech Analysis to Predict Suicidal Behavior in Depression
    (Başkent Üniversitesi Mühendislik Fakültesi, 2024-10-12) Yunden, S.; Ak, M.; Sert, M.; Gica, S.; Cinar, O.; Acar, Y. A.
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    A Pilot Study on Comparison of Teaching Workloads of Academicians Based on Working Periods During and Before the COVID-19 Pandemic
    (Başkent Üniversitesi Mühendislik Fakültesi, 2025-01-25) Yorulmaz, Muhammed; Can, Gulin Feryal; Toktas, Pelin
    The COVID-19 pandemic has had a profound impact on society, greatly changing the structure of social and working lives. Educational institutions, especially in higher education, were forced to suspend face-to-face education and switch to distance education. This change inevitably affected the working styles and workloads of academics. This study aims to explore the effects of the COVID-19 pandemic on academic teaching workloads by examining transaction data for a one-year period before and during the pandemic. The data were obtained from the system logs of a learning management system platform, which was used extensively during the pre-pandemic and pandemic periods, and were analyzed in terms of transaction density, day, and time of transactions. The findings from the pre-pandemic period showed that the academic workload was higher on weekdays than on weekends. However, with the transition to distance education during the pandemic, the difference between weekday and weekend workloads diminished significantly. Additionally, the working hours shifted during the pandemic by approximately one hour to later hours in the day.
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    Observational Tests Of Asymptotically Flat r2 Spacetimes
    (Başkent Üniversitesi Mühendislik Fakültesi, 2024-04-07) Zhu, Tao; Nguyen, Hoang Ky; Azreg-Ainou, Mustapha; Jamil, Mubasher
    A novel class of Buchdahl-inspired metrics with closed-form expressions was recently obtained based on Buchdahl's seminal work on searching for static, spherically symmetric metrics in R-2 gravity in vacuo. Buchdahl-inspired spacetimes provide an interesting framework for testing predictions of R(2 )ravity models against observations. To test these Buchdahl-inspired spacetimes, we consider observational constraints imposed on the deviation parameter, which characterizes the deviation of the asymptotically flat Buchdahl-inspired metric from the Schwarzschild spacetime. We utilize several recent solar system experiments and observations of the S2 star in the galactic center and the black hole shadow. By calculating the effects of Buchdahl-inspired spacetimes on astronomical observations both within and outside of the solar system, including the deflection angle of light by the Sun, gravitational time delay, perihelion advance, shadow, and geodetic precession, we determine observational constraints on the corresponding deviation parameters by comparing theoretical predictions with the most recent observations. Among these constraints, we find that the tightest one comes from the Cassini mission's measurement of gravitational time delay.
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    A Robust Aluminum Material Selection Process in the Aviation Industry: A Linear Discrete System Stability Test Perspective for Fuzzy Multicriteria Decision-Making
    (Başkent Üniversitesi Mühendislik Fakültesi, 2024-04-10) Ic, Yusuf Tansel; Hamzaoglu, Burak Meric; Yurdakul, Mustafa
    Aluminum parts are used in the aviation industry because of the need for light. However, in addition to lightness, critical parts that must have high strength properties have also been developed. The corrosion resistance, resistance to high temperatures, and workability were investigated in this case. It becomes difficult to choose among many aluminum materials that can be alternatives to each other when these features are included. The developed approach, which considers many of the features listed above and ultimately recommends to the user the most suitable aluminum material for the relevant critical part, will be used in overcoming the difficulties in this process. A material selection model is proposed in this paper for this purpose, and the decision-making model is demonstrated with examples from the aviation industry. Therefore, the developed model, which will enable the selection of the most suitable materials among alternative materials, especially for critical parts in the aviation industry, will guide professionals working in this field. For this purpose, the fuzzy TOPSIS method is used in the study, and suitable alternatives are determined. Finally, a robustness analysis is proposed to determine the most suitable aluminum material for highly uncertain situations. We apply a stability evaluation study based on process control theory in the robustness analysis.