Fen Bilimleri Enstitüsü / Science Institute
Permanent URI for this collectionhttps://hdl.handle.net/11727/1392
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Item 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-5060-2019Today, 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.Item Omics in Oxidative Stress Tolerance in Crops(2019) Kayihan, Ceyhun; Eyidogan, Fusun; https://orcid.org/0000-0003-1684-4147; Q-4515-2016; ACA-9644-2022Item 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.Item Encryption and multi-share-based seganography methods on images with low spectral resolution(Başkent Üniversitesi Fen Bilimler Enstitüsü, 2023) Çiftçi, Efe; Sumer, EmreSteganography is the name given to secret communication methods that third parties cannot detect. This secret communication is performed by hiding the secret information to be transmitted on a carrier medium so that the carrier does not raise any suspicions. Steganography science, of which many examples can be presented from the past to the present, has gained new application areas with the development of digital technologies. This thesis aims to develop new steganography methods that hide secret messages in plain text format on binary images, which have a lower spectral resolution when compared to color or grayscale images, used in digital devices as carriers. It has been observed that all implemented methods can successfully hide considerable lengths of plaintext payloads on binary images generated by both thresholding and halftoning methods, and this finding has been reinforced with conducted objective and subjective evaluations. Steganografi, üçüncü şahıslar tarafından tespit edilmeyecek şekilde gizli iletişim kurma yöntemlerine verilen isimdir. Bu gizli iletişim, iletilmek istenen gizli bilginin şüphe uyandırmayacak bir şekilde bir taşıyıcı ortamın üzerine gizlenmesiyle gerçekleşir. Geçmişten günümüze bir çok örneği sunulabilen steganografi bilimi, dijital teknolojilerin gelişmesiyle yeni uygulama alanları kazanmıştır. Bu tezin amacı, düz metin biçimindeki gizli mesajları, taşıyıcı olarak dijital cihazlarda kullanılan renkli veya gri tonlu görüntülere kıyasla daha düşük spektral çözünürlüğe sahip ikili görüntüler üzerine gizleyecek olan yeni steganografi yöntemlerinin geliştirilmesidir. Geliştirilen tüm yöntemlerin hem eşikleme, hem de yarıtonlama yöntemleriyle üretilen ikili görüntülere büyük uzunluklarda düz metin türünde veriyi başarıyla gizleyebildikleri görülmüş ve yapılan objektif ile subjektif değerlendirmelerle de bu bulgu pekiştirilmiştir.Item Automated Audio Captioning with Acoustic and Semantic Feature Representation(Başkent Üniversitesi Fen Bilimleri Enstitüsü, 2023) Ozkaya Eren, AysegulToday, audio data is increasing rapidly with the developing technology and the increasing amount of data. Therefore, there is a need for understanding and interpretation of the content of audio data by human-like systems. Generally, audio processing studies have focused on speech recognition, audio event/scene, and tagging to process audio data. Speech recognition aims to translate a spoken language into text. Audio event/scene and tagging studies make single or few-word explanations of an audio recording. Unlike the previous studies, automatic audio captioning aims to explain an environmental audio record with a natural language sentence. This thesis explores the importance of using semantic information to improve audio captioning performance after a detailed literature study on audio processing, image/video, and audio captioning. In this context, computational models have been developed using linguistic knowledge (subject-verbs), topic model, knowledge graphs, and acoustic events for audio captioning. As a methodology, the contributions of different features, word embedding methods, deep learning architectures and datasets, and the contribution of semantic information to audio captioning were examined. Within the scope of the studies, two publicly open audio captioning datasets were used. The success of the models proposed in the thesis was compared with the studies using the same datasets. The results show that the proposed methods improve AAC performance and give results comparable to the literature. Günümüzde gelişen teknoloji ve artan veri miktarı ile birlikte ses verileri de hızla artmaktadır. Bu nedenle, ses verilerinin içeriğinin insan benzeri sistemler tarafından anlaşılmasına ve yorumlanmasına ihtiyaç duyulmaktadır. Genel olarak ses işleme çalışmaları konuşma tanıma, ses olay/sahne tanıma ve ses etiketlemeye odaklanmıştır. Konuşma tanıma, konuşulan bir dili metne çevirmeyi amaçlar. Ses olay/sahne tanıma ve etiketleme sistemleri, bir ses kaydına tek veya birkaç kelimelik açıklamalar yapar. Otomatik ses başlıklandırma ise önceki çalışmalardan farklı olarak çevresel bir ses kaydını doğal bir dil cümlesi ile açıklamayı amaçlar. Bu tez, ses işleme, görüntü/video ve ses başlıklandırma üzerine ayrıntılı bir literatür çalışmasının ardından ses başlıklandırma performansını iyileştirmek için anlamsal bilgileri kullanmanın önemini araştırmaktadır. Bu bağlamda, otomatik ses başlıklandırma için dilbilimsel (özne-fiiller), konu modeli, bilgi çizgesi ve akustik olaylar kullanılarak sayısal modeller geliştirilmiştir. Metodoloji olarak, farklı özniteliklerin, kelime gömme yöntemlerinin, derin öğrenme mimarilerinin ve veri kümelerinin katkıları ve semantik bilginin ses başlıklandırmaya katkısı incelenmiştir. Çalışmalar kapsamında iki adet ses başlıklandırma veri seti kullanılmıştır. Tezde önerilen modellerin başarısı, aynı veri setlerini kullanan çalışmalarla karşılaştırılmıştır. Sonuçlar, önerilen yöntemlerin otomatik ses başlıklandırma performansını iyileştirdiğini ve literatürle karşılaştırılabilir sonuçlar verdiğini göstermektedir.Item 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.Item 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-9869-2022New 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.