Fen Bilimleri Enstitüsü / Science Institute

Permanent URI for this collectionhttps://hdl.handle.net/11727/1392

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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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    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.