Fen Bilimleri Enstitüsü / Science Institute

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    Effects of Repair Techniques and Scarf Angles on Mechanical Performance of Composite Materials
    (2023) Karaduman, Beyza Naz; Elaldi, Faruk; https://orcid.org/0000-0003-0592-6868; AAG-5060-2019
    Today, composite materials, which have the advantage of strength and lightness ratio, have gained great importance especially in the aeronautical industry and automotive sector. With widespread use of composites, the repair of damages caused by external factors has also become an important research topic. In this study, the effects of different repair methods and scarf angles on the mechanical performance of the material were investigated. Scarf angles of 20 degrees, 30 degrees, and 45 degrees have been selected in order not to create too many scarf areas and to find a quick repair method. Also, a comparison of single scarf and double scarf repair was made to find a more robust solution. The samples were produced from carbon fiber prepreg and with the [45/0/90/0/45](2s) fiber orientation. Tensile, compression, and flexural (3-point bending) tests according to ASTM standards were applied to composite samples prepared with single scarf and double scarf repair configurations at different angles. The stress-strain curves obtained as a result of the tests showed that the specimens repaired at 20 degrees had the highest strength. In addition, it has been determined that the samples repaired with double scarf withstand higher forces compared to the samples repaired with single scarf at the same angle.
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    Omics in Oxidative Stress Tolerance in Crops
    (2019) Kayihan, Ceyhun; Eyidogan, Fusun; https://orcid.org/0000-0003-1684-4147; Q-4515-2016; ACA-9644-2022
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    Comparison of Intelligent Classification Techniques by Practicing a Specific Technology Audit
    (2016) Berkol, A.; Kara, G.; Turk, A.
    Technology audit activities arc carried out for assessment of firms' technological requirements, capacity or management capability. The aim of these assessments is to define the weaknesses of firms and develop actions in order to improve firms' technological capacity and/or technology management capability. Generally these activities are implemented with survey questionnaires. These questionnaires can be filled by managers of firms or can be implemented as an interview by independent experts. However, evaluating surveys and preparing useful comments related to results can consume lots of time and also contain lots of biases/subjectivity. In accordance to ease the decision making process and provide more verified/accurate results, we develop a methodology based on an Artificial Neural Network (ANN) algorithm which is aimed to behave like a decision maker. And in this study, we use a synthetic data set which is prepared for assessment of technology management capability of selected 70 Turkish firms.
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    Detection of Resistance to Pyrethroid And Neonicotinoid Insecticides in the Greenhouse Whitefly, Trialeurodes Vaporariorum (Westw.) (Hemiptera: Aleyrodidae)
    (2021) Erdogan, Cem; Velioglu, A. Sibel; Gurkan, M. Oktay; Denholm, Ian; Moores, Graham D.
    In Turkey as elsewhere, control of the greenhouse whitefly, Trialeurodes vaporariorum (Westw.) (Hemiptera: Aleyrodidae), relies extensively on the use of insecticides, which can promote the development of insecticide resistance. In this study, resistance to commonly used pyrethroid and neonicotinoid insecticides was investigated using bioassays and biochemical analyses. Full dose-response bioassays using 11 samples of T. vaporariorum from three locations in Turkey disclosed resistance up to 8.1-fold, 16-fold and 11.4-fold for the neonicotinoids acetamiprid, imidacloprid and thiamethoxam, respectively. Corresponding figures for pyrethroids were 56.5-fold for cypermethrin and 116.4-fold for deltamethrin. All samples were characterized using polyacrylamide gel electrophoresis (PAGE) and by measuring non-specific esterase and glutathione-S-transferase (GST) activity. There is no positive relationship between esterase activity and resistance pyrethroid or neonicotinoid resistance. It is thought that esterase enzyme activity seen in T. vaporariorum may be at lest partially related to the resistance to insecticides, but it cannot be responsible as a single mechanism. No relationship has been determined between GST activity and resistance to pyrethroids or neonicotinoids. The practical implications of these results for control of whiteflies are discussed.
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    A Polydentate Ligand Based On 2,2 '-Dipyridylamine Unit Linked Benzo-15-Crown-5; Alkali And Transition Metal Complexes; Photoresponsive Ligand; Antimicrobial Evaluation Against Pathogenic Microorganisms
    (2021) Kocoglu, Serhat; Hayvali, Zeliha; Ogutcu, Hatice; 0000-0002-3590-9084; GMW-9869-2022
    New double-armed benzo-15-crown-5 compound (L) was successfully synthesized from 4',5'-bis(bromethyl)benzo-15-crown-5 with 2,2'-dipyridylamine. The synthesized host molecule (L), the dipyridylamine unit was able to coordinate Ni2+, Cu2+ and Ag+ metal cations, whereas the crown ether moiety bound with the alkali metal cations (Na+ and K+). The structures of the ligand (L), alkali metal complexes (NaL and KL2) and transition metal complexes ([NiLOAc], [CuLOAc] and [AgLNO3]) were characterized by spectroscopic methods. NMR and mass data provided exact evidence of complex formation through both coordination centers of the new ligand (L). Both parts (dipyridyl and crown ether) were linked to form a potential fluorescent-sensing compound (L) for metal cations. Therefore, to investigate the metal selectivity, different metal cations (Na+, Mg2+, K+, Ba2+, Cr3+, Fe3+, Co2+, Ni2+, Cu2+, Zn2+ and Ag+) and the new sensing compound (L) fluorescence spectra were recorded. Coordinations with Zn2+, Fe3+ and Cu2+ induced obvious changes on their increasing concentrations in fluorescence spectra. Crown ethers, as representatives of supramolecular compounds, are also promising antibacterial active compounds because of their ionophoric features. Synthesized ligand (L) and complexes (NaL, KL2, [NiLOAc], [CuLOAc] and [AgLNO3]) also proved to be adjuvants that helped to overcome antimicrobial resistance in a range of bacteria and yeast. The antimicrobial activity of compounds was screened in vitro against some pathogenic Gram-positive bacteria, some Gram-negative bacteria and yeast.
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    Effects of Repair Techniques on Mechanical Performance in Composite Materials
    (Başkent Üniversitesi Fen Bilimler Enstitüsü, 2022) Karaduman, Beyza Naz; Elaldı, Faruk
    Günümüzde kompozit malzeme kullanımı oldukça yaygınlaşmış ve giderek de artmaktadır. Mukavemet ve hafiflik oranı avantajına sahip olan bu malzemeler, özellikle havacılık sanayi ve otomotiv sektöründe büyük önem kazanmıştır. Kompozit malzemelerin bu yaygın kullanımı sonrasında, malzemelerde dış etkenlerden dolayı meydana gelen hasarların tamiri de önemli bir araştırma konusu olmuştur. Bu çalışmada farklı onarım yöntemlerinin, malzemenin mekanik performansı üzerindeki etkileri incelenmiştir. Fazla yontma alanı yaratmamak ve hızlı bir onarım yöntemi bulmak için 20°, 30° ve 45° yontma açıları üzerinde çalışılmıştır. Ayrıca, daha sağlam bir çözüm bulmak için tek yönlü yontma ve çift yönlü yontma onarımının karşılaştırılması yapılmıştır. Numuneler karbon elyaf prepregten ve [45/0/90/0/45]2s oryantasyonuna sahip üretilmiştir. Farklı açılarda tek yönlü yontma ve çift yönlü yontma onarım konfigürasyonları ile hazırlanmış kompozit numunelere ASTM standartlarına göre, çekme, basma ve 3-nokta eğme testleri uygulanmıştır. Testler sonucunda elde edilen gerinim-gerilim eğrileri, 20° ile onarılmış numunelerin en yüksek dayanıma sahip olduğunu göstermiştir. Ayrıca çift yönlü yontma ile onarılmış numunelerin aynı açıda tek yönlü yontma ile onarılmış numunelere kıyasla daha yüksek kuvvetlere dayandığı tespit edilmiştir.Today, the use of composite materials has become widespread and is increasing. These materials, which have the advantage of strength and lightness ratio, have gained great importance especially in the aeronautical industry and automotive sector. After this widespread use of composite materials, the repair of damages caused by external factors has also become an important research topic. In this study, the effects of different repair methods on the mechanical performance of the material were investigated. Scarf angles of 20°, 30° and 45° have been studied in order not to create too many scarf areas and to find a quick repair method. Also, a comparison of single scarf and double scarf repair was made to find a more robust solution. The samples were produced from carbon fiber prepreg and with the [45/0/90/0/45]2s ratio. Tensile, compression and 3-point bending tests according to ASTM standards were applied to composite samples prepared with single scarf and double scarf repair configurations at different angles. The stress-strain curves obtained as a result of the tests showed that the specimens repaired at 20° had the highest strength. In addition, it has been determined that the samples repaired with double scarf withstand higher forces compared to the samples repaired with single scarf at the same angle.