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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/3
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Publication Metadata only Influence of soft segment structure, hydrogen bonding, and diisocyanate symmetry on morphology and properties of segmented thermoplastic polyurethanes and polyureas(Tubitak Scientific & Technological Research Council Turkey, 2023) Department of Chemistry; Yılgör, Emel; Yılgör, İskender; Department of Chemistry; College of SciencesA comprehensive review of the structure-morphology-property relations in segmented thermoplastic polyurethanes and polyureas (TPU) is provided. Special emphasis is given to the influence of the soft segment structure, polarity, and molecular weight, diisocyanate symmetry and the nature, extent, and strength of hydrogen bonding on the morphology and thermal and mechanical properties of TPUs. Experimental results obtained on composition-dependent TPU morphology and properties by various techniques were also compared by the morphology profiles generated by computational methods such as quantum mechanical calculations and molecular dynamics simulations.Publication Metadata only Exploration of novel 6,8,9-trisubstituted purine analogues: synthesis, in vitro biological evaluation, and their effect on human cancer cells(Tubitak Scientific & Technological Research Council Turkey, 2024) Polat, Muhammed Fatih; Atalay, Rengul; Tuncbilek, Meral; N/A; Şahin, İrem Durmaz; Koç University Research Center for Translational Medicine (KUTTAM); School of MedicineCancer, a leading global cause of mortality, demands continuous advancements in therapeutic strategies. This study focuses on the design and synthesis of a novel series of purine derivatives, specifically 6 -(substituted phenyl piperazine)-8-(4-phenoxyphenyl)9-cyclopentyl purine derivatives (5-11). The motivation behind this endeavor lies in addressing acquired resistance mechanisms in cancer cells, a significant hurdle in current treatment modalities. The synthesis, starting from 4,6-dichloro-5-nitropyrimidine, involves a multi -step process, resulting in seven new purine derivatives. Biological evaluation against human liver, colon, and breast cancer cells (Huh7, HCT116, and MCF7, respectively) was performed using the SRB assay. Among the synthesized analogs, compounds 5 and 6, exhibited notable cytotoxic activity, surpassing clinically used positive controls 5-Fluorouracil and Fludarabine in terms of efficacy. This research underscores the potential of purine derivatives with a phenyl group at the C-8 position as a scaffold for developing compounds with improved anticancer properties. The findings offer insights for future exploration and development of novel agents in cancer pharmaceutical research.Publication Metadata only Dislocation activities in aluminum alloyed Hadfield steels(N/A, 2008) Şehitoğlu, Hüseyin; Department of Mechanical Engineering; Canadinç, Demircan; Faculty Member; Department of Mechanical Engineering; College of Engineering; 23433The work presented herein investigates the unusual strain hardening prevalent in Hadfield steel, which has not yet been linked to a clear cause, yet. The methodology adopted in this study is suppressing one of the dominant deformation mechanisms interactively dictating the work hardening of Hadfield steel, namely twinning and slip, and concentrating on the other. To achieve this end, Hadfield steel was alloyed with aluminium to increase the stacking fault energy, and thereby suppress twinning and give way to slip only. As a result of the thorough mechanical and micro structural analyses, we have concluded that the slip-related dislocation activities and the high-density dislocation walls brought about by slip in Hadfield steel significantly contribute to the work hardening of this material. / Öz: Bu çalışma, uzun bir süredir araştırılmasına rağmen, Hadfield çeliğinin henüz sebebi kesin olarak ortaya konulamayan olağan dışı sertleşme kapasitesine ışık tutmak amacıyla probleme değişik bir açıdan yaklaşmaktadır. Şimdiye kadar bu sertleşmenin sebebi olarak öne sürülen ve sertleşmeye olan katkıları birbirinden ayırt edilmesi güç olan ikiz ve kayma mekanizmalarından birini bastırarak diğerini inceleme yoluna gidilmiştir. Hadfield çeliği alüminyum ile alaşımlanarak dizim hatası enerji eşiği yükseltilmiş ve kayma mekanizmasının baskın olması sağlanmıştır. Yürütülen kapsamlı deneysel ve nümerik analizler sonucu varılan sonuç, aykırı yerleşim aktivitelerinin ve bunun doğal bir sonucu olan yüksek yoğunluklu aykırı yerleşim duvarlarının, Hadfield çeliğinin sertleşmesinde büyük katkı sahibi olduğunu ortaya koymuştur.Publication Metadata only A two-dimensional Monte Carlo polymerization of 5-membered rings(Scientific Technical Research Council Turkey, 1997) Esentürk, O.; Pamuk, H. A.; Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129A modification of the kinetic growth model in two dimensions for the polymerization of 5-membered rings is presented. The preliminary results reveal the validity of the modified model.Publication Metadata only Access pattern-aware data placement for hybrid DRAM/NVM(TUBITAKScientific and Technical Research Council Turkey, 2017) Department of Computer Engineering; Erten, Didem Unat; Faculty Member; Department of Computer Engineering; College of Engineering; 219274in recent years, increased interest in data-centric applications has led to an increasing demand for large capacity memory systems. Nonvolatile memory (NVM) technologies enable new opportunities in terms of process-scaling and energy consumption, and have become an attractive memory technology that serves as a secondary memory at low cost. However, NVM has certain disadvantages for write references, due to its high dynamic energy consumption for writes and low bandwidth compared to DRaM writes. in this paper, we propose an access-aware placement of objects in the application code for two types of memories. Given the desired power savings and acceptable performance loss, our placement algorithm suggests candidate variables for NVM. We present an evaluation of the proposed technique on two applications and study the energy and performance consequences of different placements.Publication Metadata only Enhanced ionic conductivity and mechanical strength in nanocomposite electrolytes with nonlinear polymer architectures(TÜBİTAK, 2023) N/A; Department of Chemical and Biological Engineering; N/A; Bakar, Recep; Şenses, Erkan; Darvishi, Saeid; PhD Student; Faculty Member; PhD Student; Department of Chemical and Biological Engineering; Koç University Boron and Advanced Materials Application and Research Center (KUBAM) / Koç Üniversitesi Bor ve İleri Malzemeler Uygulama ve Araştırma Merkezi (KUBAM); Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; College of Engineering; Graduate School of Sciences and Engineering; N/A; 280298; N/ASolvent-free polymer-based electrolytes (SPEs) have gained significant attention to realize safer and flexible lithium-ion batteries. Among all polymers used for preparing SPEs electrolytes, poly(ethylene oxide), a biocompatible and biodegradable polymer, has been the most prevalent one mainly because of its high ionic conductivity in the molten state, the capability for the dissolution of a wide range of different lithium salts as well as its potential for the environmental health and safety. However, linear PEO is highly semicrystalline at room temperature and thus exhibits weak mechanical performance. Addition of nanoparticles enhances the mechanical strength and effectively decreases the crystallization of linear PEO, yet enhancement in mechanical performance often results in decreased ionic conductivity when compared to the neat linear PEO-based electrolytes; new strategies for decoupling ionic conductivity from mechanical reinforcement are urgently needed. Herein, we used lithium bis(trifluoromethane-sulfonyl)-imide (LiTFSI) salts dissolved in various nonlinear PEO architectures, including stars (4-arms and 8-arms) and hyperbranched matrices, and SiO2 nanoparticles (approximately equal to 50 nm diameter) as fillers. Compared to the linear PEO chains, the room temperature crystallinity was eliminated in the branched PEO architectures. The electrolytes with good dispersion of the nanoparticles in the nonlinear PEOs significantly enhanced ionic conductivity, specifically by approximately equal to 40% for 8-arm star, approximately equal to 28% for 4-arms star, and approximately equal to %16 for hyperbranched matrices, with respect to the composite electrolyte with the linear matrix. Additionally, the rheological results of the SPEs with branched architectures show more than three orders of magnitude enhancement in the low-frequency moduli compared to the neat linear PEO/Li systems. The obtained results demonstrate that the solvent-free composite electrolytes made of branched PEO architectures can be quite promising especially for irregularly shaped and environmentally benign battery applications suitable for medical implants, wearable devices, and stretchable electronics, which require biodegradability and biocompatibility. © TÜBİTAK.Publication Metadata only In silico design of novel and highly selective lysine-specific histone demethylase inhibitors(Scientific Technical Research Council Turkey-Tubitak, 2011) Akdogan, Ebru Demet; Yelekci, Kemal; Department of Chemical and Biological Engineering; Erman, Burak; Faculty Member; Department of Chemical and Biological Engineering; College of Engineering; 179997Histone lysine-specific demethylase (LSD1) is involved in a wide range of epigenetic processes and plays important roles in gene silencing, DNA transcription, DNA replication, DNA repair, and heterochromatin formation. Its active site shows a resemblance to those of 2 homologous enzymes, monamine oxidase A and B (MAO-A and MAO-B.) In the present work, starting from suitable scaffolds and generating thousands of structures from them, 10 potential inhibitors were obtained with structural and physicochemical properties selectively suitable for inhibiting LSD1. iLib Diverse software was used to generate the diverse structures and 3 docking tools, CDOCKER, GOLD, and AutoDock, were used to find the most probable potential inhibitor based on its binding affinity. The dispositions of the candidate molecules within the organism were checked by ADMET_PSA_2D (polar surface area) versus ADMET_AlogP98 (the logarithm of the partition coefficient between n-octanol and water), and their suitability is discussed. The LSD1 inhibition activities of the candidates were compared with the properties of trans-2-phenylcyclopropylamine (tranylcypromine) and 2-(4-methoxy-phenyl) cyclopropylamine, which are the 2 known inhibitors of LSD1.Publication Metadata only Engineer CEOs and firm performance in BIST manufacturing firms(Muhasebe ve Finansman Öğretim Üyeleri Derneği (MUFAD), 2017) Department of Business Administration; Department of Industrial Engineering; Çelikyurt, Uğur; Dönmez, Banu Nur; Faculty Member; Undergraduate Student; Department of Business Administration; Department of Industrial Engineering; College of Administrative Sciences and Economics; College of Engineering; 47082; N/AWe study the relation between the educational background of chief executive officers (CEOs) and firm performance for 122 manufacturing firms traded on Borsa Istanbul (BIST) between 2009-2015. We analyze two different measures of performance, namely operating performance and market-based performance. We find that firms that have CEOs with an engineering background experience higher operating performance measured by return on assets (ROA) than firms that have CEOs with other educational background. Moreover, firms with engineer CEOs also experience better market-based performance measured by Tobin’s Q. The positive association between having CEOs with an engineering background and firm performance that we document is robust to the inclusion of several firm-level control variables in our multivariate analysis. We also find that this positive relation is more pronounced for public manufacturing firms of smaller size. / Öz: Bu çalışmada Borsa İstanbul’da 2009-2015 arası işlem gören 122 imalat firmasındaki icra kurulu başkanının (CEO) öğrenim geçmişi ile firma performansı arasındaki ilişki incelenmiştir. Faaliyet performansı ve piyasa bazlı performans olmak üzere iki farklı performans ölçüsü analiz edilmiştir. Bulgularımıza göre icra kurulu başkanı mühendislik kökenli olan firmalar, icra kurulu başkanı diğer öğrenim geçmişlerinden olan firmalara kıyasla varlıkların getirisi bakımından daha yüksek faaliyet performansı göstermektedir. Ayrıca, icra kurulu başkanı mühendis olan firmalar Tobin’s Q oranı bakımından da daha iyi piyasa bazlı performans göstermektedir. Mühendislik kökenli icra kurulu başkanı sahibi olma ile firma performansı arasında göstermiş olduğumuz pozitif ilişki, firma düzeyindeki çeşitli kontrol değişkenlerinin çok değişkenli analizimize dahil edilmesinden etkilenmemektedir. Ayrıca bu pozitif ilişki daha küçük boyutlu halka açık imalat firmaları için daha belirgindir.