Welcome to the Koç University Institutional Academic Repository
The Koç University Institutional Academic Repository (KUHub Research) is a state-of-the-art academic repository that consolidates all academic outputs—such as articles, conference proceedings, theses, research data, and more—produced by the university since its establishment in 1993.
KUHub Research adheres to the principles of Open Access and FAIR (Findable, Accessible, Interoperable, Reusable), providing access to the bibliographic records, research data, and full texts of research outputs. Equipped with innovative features such as Author Profile pages and enhanced tools, KUHub Research aims to enhance the visibility of researchers both nationally and internationally. KUHub Research aims to preserve and maintain Koç University's valuable academic legacy for future generations while also serving the needs of today’s researchers.
For more information or inquiries please contact openaccess@ku.edu.tr
Recent Submissions
Polyurethane synthesis revisited: effect of solvent, stoichiometry, and temperature on the reaction of MDI with polyether glycols
(Elsevier, 2025-05-09) Yılgör, İskender; Yılgör, Emel; Yıldırım, Armen; Department of Chemistry; KUYTAM (Koç University Surface Science and Technology Center); Graduate School of Sciences and Engineering; College of Sciences; GRADUATE SCHOOL OF SCIENCES AND ENGINEERING; Graduate School of Sciences and Engineering; Research Center
Thermoplastic polyurethanes (TPU) are one of the most widely investigated polymeric systems due to their interesting structure-morphology-property behavior. They also find broad range of applications in various fields. Global TPU market is projected to grow about 7.3 % annually from $2.30 billion in 2021 to $3.80 billion in 2028. 4,4′-Diphenylmethane diisocyanate (MDI) is the most widely used diisocyanate for the preparation of TPUs both in academia and industry. When TPU synthesis is carried out in solution, a polar aprotic solvent is necessary to obtain high molecular weight polymers. Most preferred solvents for TPU synthesis are high boiling, polar, aprotic solvents, such as dimethylacetamide (DMAC), dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and N-methyl pyrrolidone (NMP). When MDI is used as the diisocyanate, depending on the solvent used and reaction temperature, extensive side reactions may be observed, which consume excess diisocyanate and affect reaction stoichiometry. Side reactions also strongly influence TPU structure, topology, microphase morphology, and properties. In this study influence of the solvent, initial [NCO]/[OH] stoichiometry and reaction temperature on the rate of isocyanate consumption and kinetics of the reactions between MDI and poly(tetramethylene oxide) glycol (PTMO) were investigated. Catalytic effect of DMF even at reactions conducted at room temperature were observed, resulting in significant excess MDI consumption due to extensive side reactions. During prepolymer formation in [MDI]/[PTMO] = 2.0 system at 50 °C, side reactions were minimized or eliminated by using THF/DMF or toluene/DMF (90/10 by volume) solvent mixtures.
Simple and green process for silk fibroin production by water degumming
(American Chemical Society, 2025-01-05) Atay, İpek; Yağcı, Mustafa Barış; Sürme, Saliha; Kavaklı, İbrahim Halil; Yılgör, Emel; Yılgör, İskender; KUYTAM (Koç University Surface Science and Technology Center); Department of Chemistry; Department of Chemical and Biological Engineering; Department of Molecular Biology and Genetics; College of Sciences; College of Engineering; Research Center
Silk fibroin (SF), a natural polymer with very desirable physicochemical and biological properties, is an ideal material for crafting biocompatible scaffolds in tissue engineering. However, conventional methods for removing the sericin layer and dissolving SF often involve environmentally harmful reagents and processes, requiring extensive dialysis procedures to purify the fibers produced. Such processes may also damage the surface and bulk properties of the SF produced. Here, we report a simple, green water degumming method, in which almost complete sericin removal of 30% by weight is achieved in 6 h in boiling water. The SF produced is easily dissolved in formic acid/orthophosphoric acid (90/10, 85/15, and 70/30) mixtures, eliminating the need for salts like LiBr and CaCl2 followed by dialysis and freeze-drying, thus simplifying the process significantly. Additionally, our findings demonstrate significantly enhanced cell viability in electrospun poly(lactic acid)/SF blends. Overall, SF production via water degumming offers an eco-friendly pathway for generating bioactive scaffolds in tissue engineering applications.
Backward behavior and determining functionals for chevron pattern equations
(Elsevier, 2025) Kalantarov, Varga; Kalantarova H. V.; Vantzos, O.; Department of Mathematics; College of Sciences
The paper is devoted to the study of the backward behavior of solutions of the initial boundary value problem for the chevron pattern equations under homogeneous Dirichlet's boundary conditions. We prove that, as t -> infinity , the asymptotic behavior of solutions of the considered problem is completely determined by the dynamics of a finite set of functionals. Furthermore, we provide numerical evidence for the blow-up of certain solutions of the backward problem in finite time in 1D.
A hybrid autoencoder and index modulation framework for OTFS modulation
(Springer, 2025) Başar, Ertuğrul; Tek, Yusuf İslam; Doğukan, Ali Tuğberk; Gevez, Yarkın; Pıhtılı, Mehmet Ertuğ; Department of Electrical and Electronics Engineering; CoreLab (Communications Research and Innovation Laboratory); College of Engineering; Laboratory
This paper presents an innovative approach to orthogonal time frequency space (OTFS) modulation by integrating autoencoder-based enhanced (AEE) joint delay-Doppler index modulation (JDDIM) techniques. The proposed AEE-JDDIM-OTFS framework leverages deep learning to optimize the mapping and demapping processes, significantly improving spectral and energy efficiency in high-mobility communication scenarios. The system's performance is further enhanced by the introduction of a low-complexity greedy detector that maintains robust detection accuracy, even under imperfect channel state information (CSI) conditions. Extensive simulation results demonstrate that the proposed scheme achieves superior bit error rate (BER) performance compared to conventional OTFS and other OTFS-based modulation schemes, even in imperfect channel state information situations. The findings suggest that the AEE-JDDIM-OTFS framework offers a practical, low-complexity solution with promising potential for next-generation wireless communication systems.
A centralized frost detection and estimation scheme for Internet-connected domestic refrigerators
(Elsevier Science Ltd, 2025) Lazoğlu, İsmail; Mehmood, Mussawir Ul; Ur Rahman, Hammad; Department of Mechanical Engineering; MARC (Manufacturing and Automation Research Center); Graduate School of Sciences and Engineering; College of Engineering; GRADUATE SCHOOL OF SCIENCES AND ENGINEERING; Research Center
Frost accumulation on heat exchange units is a significant problem in refrigeration systems, adversely affecting their operating performance and thereby leading to increased power consumption. Therefore, timely detection and accurate quantification of frost are crucial for effective defrosting strategies. This study presents a novel centralized cloud-based IoT scheme for frost detection and thickness estimation. The image processing is performed on the cloud server to process evaporator coil images for frost thickness quantification. Experiments were conducted on a domestic refrigerator to assess the effectiveness of the proposed image-processing approach and determine latency and processing time. The presented scheme effectively quantifies frost thickness on the evaporator in the 1-5 mm range with a 10.8% error margin. The total inference time, which includes image acquisition, pre-processing, transmission latency, and frost thickness estimation, is approximately 5.15 seconds. The results demonstrate that the proposed image processing method performs comparably to conventional sensors and similar image processing techniques. Moreover, the centralized cloud-based IoT architecture presented effectively meets the scalability demands of consumer refrigerators.