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Novel cardiac magnetic resonance imaging sequences used in congenital heart disease
Recent advancements in cardiac magnetic resonance imaging have significantly enhanced the diagnostic accuracy and management of congenital heart disease. Modern magnetic resonance imaging sequences, such as steady-state free precession, phase-contrast imaging, and late gadolinium enhancement, offer detailed anatomical and functional insights, which are crucial for precise diagnosis, surgical planning, and long-term follow-up. These sequences allow for comprehensive assessment of complex cardiac structures, hemodynamics, and myocardial tissue characterization, thereby improving patient outcomes and aiding in the effective treatment of congenital heart disease. The integration of advanced imaging techniques like phase-contrast magnetic resonance imaging, 3D printing, and computational fluid dynamics has revolutionized the evaluation and management of congenital heart disease. Phase contrast magnetic resonance imaging provides comprehensive hemodynamic data, enabling precise assessment of blood flow patterns and quantification of flow parameters. These detailed flow analyses are further enhanced by 3D printing, which creates patient-specific models for pre-surgical planning and education. Together, these technologies offer a multifaceted approach to congenital heart disease, improving diagnostic accuracy, surgical planning, and patient-specific care. The first part of this thesis investigates differences in functional and 3D morphological characteristics of the right ventricular outflow tract and branch pulmonary arteries in patients with surgically corrected tetralogy of Fallot, which is referred to as surgical or transcatheter pulmonary valve replacements. The study found the reduced circumferential and radial strain in the right ventricle in the surgical valve replacement group by using cardiac magnetic resonance imaging with multiplanar reconstructions, 3D volume rendering, and 3D printed models for pre-procedural assessment. A significant correlation was noted between right ventricular outflow tract types and strain parameters. This study addresses a critical gap in understanding the effects of transcatheter pulmonary valve replacement on myocardial strain in patients with surgically corrected tetralogy of Fallot. The second part of this thesis is dedicated to determining the effects of transcatheter pulmonary valve replacement on atrial and ventricular strain in patients with surgically corrected tetralogy of Fallot using feature-tracking strain evaluation of cardiac magnetic resonance imaging. By demonstrating that pulmonary valve replacement leads to significant changes not only in volume and function parameters but also in strain characteristics it provides a deeper understanding of myocardial function in these patients. The study suggests incorporating strain analysis into routine cardiac magnetic resonance imaging protocols for a more comprehensive assessment.
Novel over-the-air methods and practical approaches for reconfigurable intelligent surfaces system designs and analyses
The rapid evolution of wireless communication networks towards 6G and beyond requires innovative solutions to enhance spectral efficiency, improve system reliability, and manage the growing complexity of modern communication systems. This thesis explores the integration of reconfigurable intelligent surfaces (RIS) with communication systems to address fundamental challenges in wireless networks, such as challenges in the channel, overall system efficiency, system scalability, practicality and more. By leveraging RIS technology, the wireless propagation environment can be dynamically reconfigured to optimize signal transmission, mitigate interference, and enhance network performance. This thesis presents novel over-the-air (OTA) approaches to RIS-aided communication systems, considering both passive and active RIS architectures as well as their practical implications in real-world deployments. Chapter 2 investigates an virtual OTA equalization technique enabled by RIS, demonstrating how RIS phase alignment can effectively eliminate inter-symbol interference (ISI) and convert frequency-selective fading channels into frequency-flat channels. Chapter 3 includes a study proposing RIS-aided uplink non-orthogonal multiple access (NOMA) schemes, optimizing resource allocation and improving outage probability performance for two users. Chapter 4 introduces a hybrid RIS architecture for OTA index modulation (IM), integrating passive and active RIS elements to achieve superior spectral efficiency and reduced detection complexity. Chapter 5 focuses on network-independent RIS architectures, proposing a user-controlled RIS system that enhances practicality, signal quality and energy efficiency in a simple and practical manner without relying on centralized network control. Chapter 6 discusses RIS identification techniques in mobile networks, addressing critical challenges related to RIS security, authentication, and interference mitigation, introducing a new and important concept for RIS deployment to the literature. Chapter 7 presents a power-differentiated dual-code index modulation (RIS-PD-DCIM) scheme that improves spectral efficiency and performance through optimal RIS partitioning strategies. The contributions of this thesis provide a comprehensive framework for RIS-aided communication systems, addressing key limitations in existing wireless technologies and paving the way for the seamless integration of RIS into 6G networks. The proposed methodologies and system models demonstrate the potential of RIS to revolutionize wireless communications by offering enhanced system designs, improved spectral and energy efficiency, and robust performance in dynamic environments. These findings contribute to the ongoing efforts in the research community to develop practical, scalable, and intelligent wireless networks for the future.
İstinat duvarlarının farklı deprem tasarım koşulları için davranışlarının incelenmesi
İstinat duvarları; yapılan bir kazının, mevcut bir şevin veya yapılacak bir dolgu alanının desteklenmesinde, zeminin tutulmasında ya da farklı kotlarda yapıların yapılması gerektiğinde kullanılan mühendislik yapılarıdır. İstinat yapılarının tasarımında stabilite ve yapısal dayanım ihtiyaçları göz ününde bulundurulmalıdır. Ancak ülkemiz bilindiği üzere birçok fay hattının geçtiği bir bölgede bulunmaktadır. Bu fay hatlarının hareketliliği, Türkiye'yi yüksek deprem riskli bölge riskine sokmaktadır. Bu nedenle ülkemizde yapılan yapılarda statik etkiler dışında dinamik etkilerinde büyük etkisi bulunmaktadır. Bu nedenden dolayı ülkemizde gerçekleştirilen istinat duvarı tasarımlarında dinamik etkilerinde göz önünde bulunarak tasarımının tamamlanması gerekmektedir. Bu çalışma da ülkemizde oluşan deprem riski nedeniyle farklı deprem koşullarında istinat duvarlarının davranışının incelenmesi amacıyla yapılmıştır. Çalışma için 4 farklı depremin ivme ve spektral ivme değerleri kullanılmıştır. Deprem kayıtlarının seçiminde Türkiye Bina Deprem Yönetmeliği (TBDY) 2018'de tanımlanan yer hareketi düzeyleri dikkate alınmıştır. Bu depremler; 23 Ekim 2011 Van depremi (7.0), 20 Şubat 2023 Hatay depremi (6.4), 6 Şubat 2023 Kahramanmaraş depremi (7.6) ve 13 Mart 1992 Erzincan (6.6) depremleridir. Bu depremler Afet ve Acil Durum Yönetimi Başkanlığı (AFAD) üzerinden alınan değerler ile TBDY 2018'de tarif edilen ampirik yöntem yardımıyla istinat duvarlarına uygulanmış ve davranışları incelenmiştir. Ayrıca ampirik yöntem yardımıyla incelenen modellemeler Plaxis 2D programı üzerinde modellenmiş ve analizi yapılmıştır. Toplam 8 farklı modelin hesapları yapılarak davranışları incelenmiştir ve ampirik yöntem ile Plaxis 2D sonuçları karşılaştırılmıştır.
Farklı yönlendirma açılarına sahip kenaf elyaf takviyeli kompozitlerin delinmesinin araştırılması
Sentetik esaslı kompozit malzemeler birçok avantajlarından dolayı yaygın olarak kullanılmaktadır. Ancak bu kompozit malzemeler fosil yakıtların tüketimini ve sera gazı emisyonlarını arttırmaktadır. Bu yüzden mühendisler ve araştırmacılar ekolojik olarak uyumlu ve çevre dostu ürünlerin gelişimine yönelmişlerdir. Bunun neticesinde ise sentetik esaslı kompozitler yerine doğal elyaf takviyeli kompozitler tercih edilmeye başlanılmıştır. Doğal kompozitlerde kullanılan takviye elemanları bitkilerden, hayvanlardan ve minerallerden elde edilmektedir. Bitkisel kökenden elde edilen elyaflardan biride kenaftır. Bu tez çalışmamızda, farklı yönlendirme açılarına (0°/90°, 30°/-60° ve ±45°) sahip kenaf elyaf takviyeli polimer (KETP) kompozitler vakum infüzyon yöntemi kullanılarak üretildi. Üretilen kompozitlerin ilk önce çekme hasar yükü belirlendi. Daha sonra KETP kompozitlerin delinmesi araştırıldı. KETP kompozitlerin delinmesinde iş mili devri ve ilerleme gibi delme parametrelerinin kesme kuvveti, deformasyon faktörü ve kesme sıcaklığı üzerine etkilerini deneysel olarak araştırıldı. 0°/90°, 30°/-60° ve ±45° yönlendirme açısına sahip KETP kompozitlerin çekme deneylerinden, en yüksek çekme kuvveti 0°/90° KETP kompozitlerden elde edildi. KETP kompozitlerin delinmesinde oluşan kesme kuvvetleri, iş mili devrinden ve ilerleme değerlerinden etkilendiği belirlendi. İş mili devrinin artması ile kesme kuvvetleri düşerken, ilerlemenin artması ile kesme kuvvetleri artmıştır. En düşük kesme kuvveti 30°/-60° yönlendirme açısına sahip KETP kompozitlerin delinmesinden elde edilirken, en yüksek kesme kuvveti ise ±45° yönlendirme açısına sahip KETP kompozitlerin delinmesinden elde edilmiştir. Kesme sıcaklığı ve deformasyon faktörü, iş mili devrinin ve ilerlemenin artması ile artmaktadır. Yüksek ilerleme değerleri ve iş mili devri delik bölgesinde oluşan deformasyonun artmasına neden olmaktadır. Deformasyon faktörü, kompozit malzemelerin yönlendirme açısından da etkilenmektedir. En düşük deformasyon faktörü 30°/-60° yönlendirme açısına sahip KETP kompozitin delinmesinde elde edilmiştir.
Östenitik (304) ve ferritik (430) paslanmaz çeliklerin bakır aratabaka kullanılarak difüzyon kaynağı ile birleştirilmesi
Paslanmaz çelik malzemeler otomotiv parçaları, biyomedikal aletler, mutfak eşyaları, ısı eşanjörleri, nükleer santraller, uzay ve havacılık gibi daha birçok alanda sıklıkla kullanılan bir malzeme türüdür. Paslanmaz çeliklerin korozyona (paslanmaya) karşı dayanıklılığı, farklı sıcaklık aralıklarında çalışma imkanı sunması, uzun ömürlü ve üretiminin kolay olması gibi özellikleri nedeniyle tercih edilmektedirler. Paslanmaz çelik malzemeleri arasında östenitik (AISI 304) ve ferritik paslanmaz çelik (AISI 430) malzemeleri endüstride en çok kullanım ağına sahip iki türüdür. Östenitik paslanmaz çelikler yüzey kalitesi, iyi korozyon direnci, yüksek mukavemet ve iyi kaynaklanabilme özellikleri nedeniyle sıklıkla tercih edilmektedirler. Diğer sıklıkla kullanılan paslanmaz çelik grubu ise ferritik paslanmaz çeliklerdir. Östenitik paslanmaz çeliklere kıyasla maliyetleri daha düşük ve yüksek korozyon direncine sahiptir. Ayrıca ferritik paslanmaz çelikler mıknatıslanma özelliğine de sahiptir. Bu çalışmada östenitik paslanmaz çelik (AISI 304) ve ferritik paslanmaz çelik (AISI 430) malzemeler, 200 μm kalınlığında bakır folyo aratabaka kullanılarak difüzyon kaynağı tekniği ile birleştirilmiştir. Difüzyon kaynağı, 960, 980 ve 1000°C sıcaklıklarda, 45, 60 ve 75 dakika sürelerde,1,2 ve 3 Mpa basınç altında argon gazı atmosferinde birleştirilmiştir. Malzemelerin mekanik mukavemetlerini belirlemek için mikro sertlik ve çekme testleri uygulanmıştır. Ayrıca deneylerde Taguchi optimizasyon yöntemi ile Varyans (Anova) analizleri yapılıp en etkili parametreler bulunmuş ve deneyin güvenilirlik seviyesi tespit edilmiştir. Sertlik değerleri incelendiğinde 430 paslanmaz çelik tarafında 75 dakika bekleme süresinde 1000 °C sıcaklığında birleştirilmiş numunede 279 HV olarak ölçülmüştür. Ara kesit bölgesinde en yüksek sertlik değeri de aynı sıcaklık ve süredeki numunede 125 HV olarak ölçülmüştür. Çekme testi gerçekleştirilen tüm numuneler incelendiğinde artan sıcaklık ve bekleme sürelerinde çekme dayanımlarında artışın olduğu gözlemlenmiştir. En yüksek çekme mukavemeti 75 dakika ve 1000°C sıcaklığındaki numunede 491,582 MPa olarak ölçülmüştür. Ayrıca tüm numuneler de sorunsuz kaynak bağlantıları gözlenmiştir.
Coğrafi bilgi sistemi (CBS) kullanılarak sıvılaşma potansiyelinin belirlenmesi
Geoteknik açıdan, deprem sırasında en önemli zemin hasarlarından biri olan sıvılaşma, suya doygun kumlu, siltli zeminlerde depremin dinamik etkisi ile ya da ani yüklenme ile zemin direncinin azaldığı durumda oluşan ve zeminin adeta bir sıvı gibi davrandığı olaydır. Bu çalışmada, Van ili İpekyolu, Edremit ve Tuşba ilçelerinin zemin sıvılaşma potansiyelinin belirlenmesi amaçlanmıştır. Çalışma alanında yapılan 43 adet sondajdan elde edilen SPT sonuçları ve alınan zemin numuneleri üzerinde laboratuvar deneyleri yapılarak zemin fiziksel özellikleri belirlenmiş ve analizler için bir veri tabanı oluşturularak, her 1.5 metre derinlikteki zemin tabakaları için sıvılaşma emniyet faktörü hesaplanmıştır. Böylece elde edilen sonuçları değerlendirilerek çalışma alanın sıvılaşma potansiyeli ortaya konulmuştur. Sıvılaşma analizi için ofis programı olan Microsoft Excel kullanılarak Seed ve İdriss (1971) tarafından önerilen "Basitleştirilmiş'' yönteme göre her bir ilçenin verileri için ayrı tablolar oluşturularak dört farklı deprem büyüklükleri (Mw=6,0; 6,5; 7,0; 7,5) için çalışma kapsamında olan sondajların her 1,5 m derinlikteki sıvılaşma emniyet faktörünün değerlerini hesaplanarak çalışma alanının sıvılaşma risk potansiyelini ortaya konulmuştur. Bunun sonucunda dört farklı deprem büyüklükleri için sıvılaşma potansiyeli haritaları, Coğrafi Bilgi Sistemleri (CBS) Global Mapper (20.1) programını kullanılarak oluşturulmuştur. Sıvılaşma potansiyeline ilişkin elde edilen sonuçlara göre çalışma alanının İpekyolu, Edremit ve Tuşba ilçelerinin deprem büyüklükleri (Mw= 6,5; 7,0; 7,5) için sıvılaşma riski taşıdığını görülmüştür. Deprem büyüklüğü (Mw= 6,0) için ise sıvılaşma riski birçok sondaj kuyusunda görülmezken, bazılarında sıvılaşma riski tespit edilmiştir. Ancak, çalışma alanın yer altı suyu ve kumlu siltli zeminlerin varlığında, bölgenin sismik özellikleri nedeniyle daha kapsamlı araştırmaların yapılması gerekmektedir. Anahtar Kelimeler: Sıvılaşma, SPT, Microsoft Excel, Mw, Global Mapper.
Capacity model araçlarda can hattından km verisinin alınması
Bu çalışmada, İstanbulda Metrobüs güzergahında çalışmakta olan Capacity model araçların Can-Bus sistemi üzerinde dolaşmakta olan araç toplam km verisinin araç ile eş zamanlı, uzaktan erişim ile alınabilmesi çalışması yer almaktadır. Can-Bus sistemi üzerinde dolaşmakta olan veri demetlerinin anlamlı hale getirilebilmesi için uluslararası standart olarak yolcu taşıyan araçlarda kullanılan J1939 standardı yardımıyla km veri kodlarının tespit edilmesi ve anlandırılması sağlanmıştır. Can-Bus sistemi üzerinden veri alınmasının sağlanabileceği devre tasarımı gerçekleştirilmiş ve veri demetinden km verisinin yazılım yardımı ile araç ile eş zamanlı olarak okunabilmesi sağlanmıştır. Çalışmanın sonucu, araç üzerinden km verisinin %100 doğruluk ile eş zamanlı olarak alınabildiğini göstermiştir.
Determination of antibacterial activity mechanism of red rose petal extract
Roses have been celebrated for centuries for their beauty, fragrance, and potential health benefits. Among the many bioactive compounds in red rose petals, anthocyanins stand out for their vibrant color and wide range of physiological effects. Anthocyanins, known for their antiatherogenic, anticancer, antidiabetic, anti-inflammatory, and antioxidant activities, are the primary pigments in red rose petals. Extracting these compounds can provide a visually appealing natural coloring agent suitable for various food products. Each component of a plant encompassing the trunk, bark, stems, leaves, fruits, roots, flowers, and seeds harbors a variety of chemical compounds, including phenolic acids, flavonoids, anthocyanins, and carotenoids. These compounds function as natural antioxidants, thereby mitigating the risk of plant diseases by delaying or preventing oxidative processes. This study focuses the antimicrobial properties of red rose petal extract and it is potential as natural preservative in the food industry. The extraction process involved freeze-drying the petals to preserve their bioactive constituents, followed by 70% ethanol extraction to obtain the desired extract. Frozen leaves were subjected to the vacuum freeze-dryer for a duration of 48 h. Moisture content was determined and the moisture content of the rose petal powder obtained in this study was found to be 4.65±0.05%. The antioxidant properties of red rose petal extract contribute to preserving food quality by preventing oxidative degradation and extending shelf life. Rose extract is used in medicinal chemistry to treat bacterial illnesses, targeting both Gram-positive and Gram-negative bacteria. This study assesses the antimicrobial activity and antioxidant potential of the extracted red rose petal extract. Through well diffusion assays and determination of Minimum Inhibitory Concentration (MIC) values, the study aims to identify susceptibilities of common foodborne pathogens against the extract as well as its antibacterial activity mechanism. The inherent antimicrobial properties of the rose extract position it as a promising candidate for utilization as a preservative in food products, thereby diminishing the risk of spoilage and ensuring food safety. Utilizing well diffusion assays, the efficacy of the extract against a spectrum of foodborne pathogens, including S. Typhimurium (31 mm), S. Enteritidis (23 mm), B. cereus (23 mm), S. aureus (25 mm), E. coli O157:H7 (23.5 mm), E. coli Biotype I (25mm), and L. monocytogenes (32.5 mm), was assessed. The discernible formation of zones of inhibition around the extract-treated discs signified inhibition of microbial growth, underscoring the extract's potential as an antimicrobial agent. Furthermore, MIC (Minimum Inhibition Concentration) values ranged from 114.07 mg/mL to 57.03 mg/mL. The determination of MIC values revealed S. Typhimurium and E. coli Biotype I had the highest MIC values and S. Enteritidis and B. cereus had the lowest MIC values. The petals of flowers are known as an ideal natural source of antioxidants from plant fiber due to their high flavonoid compound element level which includes anthocyanins.the red coloration of roses is attributed to the presence of carotenoids and anthocyanin. Plant based anthocyanins and carotenoids are valuable for food, nutrition, and pharmaceutical preparations due to low toxicity. The extract's total phenolic content (23.10 ± 0.81 mg GAE/g) and antioxidant activity were determined using established methods, including the FCR and DPPH assay, respectively. The observed antiradical activity ranged from 16.60 % to 74.15 %, indicating a dose-dependent response. The potential applications of red rose petal extract in food preservation are diverse. Its antioxidant activity can help retard lipid oxidation and preserve the quality of fats and oils in food products. Several studies were carried out to assess the time-dependent decrease in bacterial cell viability in the presence of rose petal extract. Initially, 24-hour bacterial cultures were prepared and supplemented with the rose petal extract, followed by incubation at 37°C to simulate optimal bacterial growth conditions. Sampling was conducted at predetermined intervals (0, 2, 4, 6, 24, and 48 hours) to monitor changes in bacterial cell viability over time. Each sampled culture was plated onto a Tryptic Soy Agar (TSA) medium to facilitate bacterial enumeration. A control group consisting of extract-free bacterial cultures was maintained to establish baseline bacterial growth patterns without the extract. The number of viable cells in the control tubes increased during the 24-hour incubation period for all bacterial cultures. In contrast, in the extract-added culture tubes, the number of viable cells reduced gradually, revealing the bactericidal effect of the red rose extract. A series of experiments assessed the potential damage to bacterial cytoplasmic membranes induced by rose petal extract. The extract was added to bacterial cultures at twice the Minimum Inhibitory Concentration (MIC × 2) and then incubated at 37°C for 24 hours. After the incubation period, the number of viable cells was determined by seeding onto two types of agar media: Tryptic Soy Agar (TSA) and TSA supplemented with 3% NaCl. Adding 3% NaCl to TSA created an osmotically stressful environment to challenge bacterial growth. Petri dishes containing the seeded agar were subsequently incubated at 37°C for 48 hours to facilitate colony formation. Following the incubation period, colonies were manually counted, and the difference in colony counts between TSA and TSA with 3% NaCl represented the number of cells with damaged membranes. The reduction percentages varied significantly among the tested strains: E. coli O157:H7 exhibited the highest reduction percentage at (80.83%), followed by S. Enteritidis at (64.52%), S. aureus at (34.51%), E. coli Biotype I at (14.86%), L. monocytogenes at (19.38%), S. Typhimurium at (11.5%) and B. cereus (6.72%). The investigation into the impact of rose petal extract on the tricarboxylic acid (TCA) cycle activity of pathogenic bacteria involved a series of experimental procedures. The extract was subsequently introduced into the suspension, adjusting bacterial cell concentration to 108 colony-forming units per ml (CFU/mL) during the logarithmic growth phase. Following a one-hour incubation period at 37°C, the mixture underwent centrifugation at 8000×g for ten minutes, forming a pellet. This pellet was then re- suspended in a 0.9% NaCl solution. Iodonitrotetrazolium chloride (INT) was then added to the suspension at a concentration of 1 mmol/L, and the mixture was further incubated for 30 minutes at 37°C. After the incubation, the maximum absorbance at 630 nm was measured using a spectrophotometer. By quantifying the maximum absorbance at 630 nm, changes in metabolic activity associated with the TCA cycle could be determined. Of note, the extract had a relatively minimal impact on the xxi metabolic activity of E. coli O157:H7. However, it demonstrated a more pronounced effect on the TCA cycle of Salmonella Typhimurium. Roses are emblematic of beauty, bravery, passion, and love, often revered as the king or queen of flowers. Their extensive range of applications offers significant advantages over most other flowers. The polyphenols from rose petals can enhance the value of by-products in fruit processing. Utilizing an enzyme-assisted extraction followed by spray drying, this green technology offers an eco-friendly alternative to traditional methods like organic solvent extraction. This natural oil and its constituents offer safe alternatives for incorporation into various applications within the food sector. Specifically, they may serve as additives in dietary supplements or functional food products. This study emphasizes the potential of red rose petal extract as a natural preservative and antimicrobial agent in food products. It highlights its promising applications in the food industry, suggesting it as a natural and health-promoting ingredient. Further research is needed to explore its effectiveness in different food matrices and ensure its safety for consumption, paving the way for its integration into various food products.
Modifiye riske maruz değer ve beklenen kayıp modellerinin geriye dönük testi: Lineer olmayan portföylerde uygulaması
The banks have to measure the market risk daily for the calculation of their capital adequacy. According to the Fundamental Review of Trading Book (FRTB) market risk revision, which was released in 2016 by the Basel Committee on Banking Supervision (BCBS), the expected shortfall (ES) will replace the value-at-risk (VaR) approach in order to capture the tail risks. In this paper, various risk management methodologies have been compared based on their performances using both the VaR and the ES. The data are based on three different currencies (USD/TRY, EUR/TRY, and EUR/USD) for the period from Jan 2nd, 2007 to Jan 4th, 2017. The methodologies have been applied to several portfolios of assets, ranging from a linear one (pure FX Position) to highly non-linear one (complex derivative securities on FX). The binomial backtest method is used for comparing backtesting performance and the empirical results indicate that the ES method, in lieu of the VaR methods, ensures the significant reduction in the capital adequacy for the semi-parametric models. In addition, the ES yields a considerable capital adequacy reduction compared to the VaR in linear portfolios. The reduction in loses strengths as the portfolios get more non-linear. These findings mainly highlight the importance of the convexity and the subadditivity features of the non-linear portfolios.
Hashgraph consensus algoritması kullanarak ıot cihazının sınıflandırılması için dağıtık karalisteleme protokolü
Industrial applications require highly reliable, secure, low-power and low-delay communications. However, wireless communication links in the industrial environment suffer from various channel impairments which can compromise these requirements. This thesis presents a new reliable blacklisting protocol for ensuring the Internet of Things (IoT) network security and mitigating the effects of interference caused by multipath Rayleigh fading using a distributed approach. The proposed blacklisting protocol is simulated over a distributed IoT network setup where flat Rayleigh fading disrupts Message Queuing Telemetry Transport (MQTT) communications. Distributed servers jointly decide in real-time whether to blacklist a device after individually performing anomaly detection and submitting their results to the hashgraph network. The IoT devices are classified by a device fingerprinting method using various machine learning (ML) algorithms that are trained with real-time packet capture data. The proposed blacklisting protocol is shown to increase the accuracy of blacklisting malignant devices from 42% to 82% as the number of servers increases from one to five for mixed attacks. It also achieves higher accuracies ranging between 47.2%-97.6% versus 47.4%-90.7% compared to the related work for Denial of Service (DoS) attacks. For this simulation with multiple servers, a novel solution for reducing the PER in a Rayleigh fading environment by searching optimal distributed server locations with a hybrid approach is also provided. The proposed protocol and the server location optimization algorithm are particularly suitable for the Industrial IoT (IIoT) in mitigating the effects of harsh communication environments in manufacturing facilities.
Modifikasyon yapılmış düz dişliler için kontak analizi
Gears are subjected to high speed and high power especially in critical applications. It is known that these high power gears are mostly subjected to main failure modes due to contact stress, bending stress, and fatigue. In this thesis, a new analytical model is developed for contact stress in selected gear pairs. The new analytical method is built by combining the Weber Banaschek Method with the Sainsot Method for mesh stiffness and gear foundation stiffness, respectively. Results obtained from the newly developed method are compared to the results obtained from available transmission tools (MASTA and KISSsoft). Combination of these two analytical methods yielded accurate results. It is also seen that the analytical solutions are more close to KISSsoft results than the MASTA solutions. The contact stress calculations according to the new method resulted close to ISO standard and compared to the FEM module of MASTA. The results obtained from the new analytical method are close to experimental results by 96%. The MASTA Programme tends to give higher results on contact pressure compared to KISSsoft solutions. Finally, calculations according to AGMA 2001-C95 standard yielded in lower safety factors compared to the ISO 6336 standard.
Kemik doku mühendisliği için doğal kökenli silika takviyeli çift fiberli matrisler
Graft therapy is used to treat bone tissue loss, which has drawbacks; donor scarcity, risk of disease transmission and immune reaction. Tissue engineering scaffolds can overcome these drawbacks. In this study, a 3D scaffold that will support tissue regeneration at defect site was developed using mainly natural materials. Scaffold was produced by co-electrospinning and had two fiber phases; first phase was produced from a bacterial origin polymer, Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), and small amount of Polycaprolactone to support fiber structure, second phase was formed by pullulan (PUL) and diatom silica shells (DS) from single cell algae origin. Also, in the study, PHBV production by Cupriavidus necator bacterial strain was optimized and used to produce scaffolds. PHBV/PCL/CA:PUL/DS scaffold group was produced as dual fiber matrix and new crosslinking method for PUL was developed for crosslinking through electrospinning. Cefuroxime Axetil antibiotic was loaded into hydrophobic PHBV fibers. Characterization studies revealed that, in aqueous environment scaffold degrade slowly, take less water and has stable structure, support controlled release of antibiotic and improved compressive strength due to incorporated DS and double fiber structure. In vitro studies revealed that DS bearing groups improved Saos-2 cell viability and co-electrospun groups that have hydrophilic PUL fibers supported L929 cell viability. Scanning electrone microscopy and confocal laser scanning microscopy analyses showed that cells distributed through co-electrospun scaffold with healthy morphology. In the study, a novel, 3D, dual fiber scaffold was produced with natural origin base materials and has potential to be used for bone tissue engineering applications.
Deprem yalıtımlı binalarda eğri yüzeyli kayıcı yalıtım birimlerindeki tasarım sürtünme katsayısının gerçek dağılımı dikkate alınarak yapının burulma davranışının incelenmesi
In this study, torsional response of seismic isolated buildings with curved surface slider (CSS) isolators are investigated considering actual distribution of design coefficient of friction in the CSS isolator. For this purpose, experimental results are used to characterize frictional properties of CSS isolator. Then, nonlinear response history analyses are performed using three-dimensional model of 3 structures that are developed based on a hospital structure. Torsional response of the structures and the parameters that influence the torsion are investigated. The analyses revealed that if the effect of contact pressure and heating on the friction coefficient is not taken into account, the additional displacements in the CSS isolators due to torsion are significantly underestimated. It is also found that increasing the number of groups within isolation system is an effective way to reduce torsion, if the isolators are seperated into groups based on axial loads on them.
Deprem yalıtımlı binalar için eşdeğer doğrusal analiz yönteminin doğruluğunun değerlendirilmesi
Earthquakes have been the leading cause of loss of lives and properties since the beginning of human history. After major earthquakes, we see that even the buildings constructed using modern engineering solutions suffer severe damage or even collapse. Seismic base isolation systems are used to minimize earthquake-induced damage. This thesis focuses on evaluating the accuracy of the equivalent linear analysis method in the analysis of seismic base-isolated buildings. In order to do that, certain buildings with different story numbers, widths, and isolator parameters were analyzed by using a set of ground motions selected for different soil properties, and results were compared with the results obtained from the equivalent linear analysis method.
Deprem yalıtmlı köprülerin salınım davranışının karşılaştırmalı irdelenmesi
In this thesis study a comprehensive roadmap is proposed for detailed modeling of rocking behavior of superstructure deck. Furthermore, a parametric study is conducted to determine effect of the superstructure rocking in enhancing the seismic performance of the box girder type bridge structures. For this purpose, various nonlinear models varying based on one chosen parameter are designed. Nonlinear boundary time history analysis (NTHA) of the models are then conducted being exposed to a set of ground motions scaled with reference to response spectra obtained for a specified coordinate in Canakkale region of Turkey. In the analysis, the effect of different parameters such as number of spans, eccentricity (e) of the bearing lines with respect to pier axis, pier height, span length, friction coefficient of the Friction Pendulum Sliding (FPS) Isolators, radius of curvature of FPS and ground motion scale and intensity are considered. The results of NTHA are then used to discuss the effects of these parameters on the seismic performance of box girder bridges in terms of pier moment and base shear.
Kemik hatalarında dolgu olarak potansiyel kullanım için grafen oksit / lanthanum katkılı kalsiyum fosfat kemik çimentoları
In this thesis, mesoporous particles of β-tricalcium phosphate (βTCP, βCa3(PO4)2) and lanthanum (La) doped βTCP were synthesized by wet precipitation method attached with a microwave refluxing system. Pure dicalcium phosphate (DCP) and La modified dicalcium phosphate (La-DCP) bone cements were prepared based on acid/base reaction between βTCP (or La- βTCP) and monocalcium phosphate monohydrate (MCPM) in the presence of water. DCP bone cements were also mixed with 1.5-3.5wt.% of graphene oxide (GO). The obtained materials were characterized by XRD, FTIR, SEM, ICP-OES, BET, and helium pycnometer. The loading /releasing analysis of proteins on/from βTCP and La- βTCP disks surfaces were evaluated using Fetal bovine serum (FBS) proteins. In vitro cell culture studies were performed with the human osteosarcoma cell line (Saos-2). Upon incorporating La3+ ions, expansion in lattice parameters of βTCP crystal was observed along with inhibition of growth rate. βTCP and La- βTCP materials were mesoporous in nature. Pore diameter and pore volume were expanded with the incorporation of La3+ ions. The outcomes confirmed that all La-βTCP materials were cytocompatible, and strict dose dependent effect of La3+ ions was observed on cell viability and alkaline phosphatase (ALP) activity. In DCP bone cements, the pure phase of brushite transformed into monetite with minimum addition of La3+ ions (0.090 mole), and the plate-like crystals of brushite turned into spheroid particles. The results of in vitro experiments on proliferation, adhesion, and osteogenic differentiation of Saos-2 cells indicated that the addition of 0.225 mole of La3+ ions promoted these properties compared to pure DCP. With the addition of GO to DCP bone cements, the mechanical properties of 2La-DCP cements improved. As the GO/2La-DCP bone cements were biocompatible, proliferation and differentiation properties of cells were significantly improved with the addition of GO.
Giyilebilir kardiyovasküler takip için grafen tekstil tabanlı akıllı giysi
Giyilebilir elektronik, son zamanlarda tüketici elektroniği pazarına başarılı ticari ürünler sunmaya başlayan hızla büyüyen bir alandır. Biyogeribildirim veya kontrol komutları gibi giyilebilir sistemlerde biyopotansiyel sinyallerin istihdam edilmesinin, bakım noktası sağlık izleme sistemleri, rehabilitasyon cihazları, insan-bilgisayar / makine arayüzleri (HCI / HMI'ler) ve beyin-bilgisayar arayüzleri (BCI'ler) dahil olmak üzere birçok teknolojide devrim yaratması beklenmektedir. Elektrotlar bu tür ürünlerin belirleyici bir parçası olarak görüldüğünden, neredeyse on yıldır incelenmiş ve tekstil elektrotlarının ortaya çıkmasına neden olmuştur. Bu çalışma, kişiselleştirilmiş sağlık izleme uygulamaları için giyilebilir elektrokardiyografi (EKG) sensörlerinin geliştirilmesi için grafen nanotekstillerin sentezi ve uygulaması hakkında rapor vermektedir. Bu çalışmada ilk kez elektrokardiyogramın tek bir kola yerleştirilen grafen tekstillerle başarılı bir şekilde elde edildiğini gösterdik. Sadece bir elastik kol bandı ve "tüm tekstil yaklaşımı" kullanımı, kullanıcının kesintisiz kalp izleme sağlamasını kolaylaştırır. Daldırma kaplama ve şablon baskı teknikleri kullanılarak üretilen grafen tekstillerinin işlevselliği, EKG sinyallerinin invaziv olmayan ölçümü, geleneksel ön jelleşmiş, ıslak, gümüş / gümüş-klorür (Ag / AgCl) ile grafen elektrotlatr karşılaştırıldığında % 98'e kadar mükemmel korelasyon ile gösterilmiştir. Farklı durumlarda güçlü bir şekilde elde edilen EKG sinyalleriyle kalp atış hızı oranları başarıyla belirlenmiştir. Burada sunulan sistem düzeyinde entegrasyon ve bütünsel tasarım yaklaşımı, giyilebilir kalp izleme cihazlarında en son teknolojinin geliştirilmesinde etkili olacaktır.
Etan ve metan saflaştırma süreçlerinde kullanılmak üzere metal-organik gözenekli yapılarin gaz ayırma performansının kapsamlı hesaplamalı taraması
Ethane purification and natural gas purification are two energy-intensive processes which can advantage from better separation techniques. Metal organic frameworks (MOFs) are a recent group of nanoporous materials which can be obtained through the combination of metal nodes and organic linkers on different topologies. Considering the large number of available MOFs, it is not possible to fabricate and test the gas separation performance of every single MOF adsorbents and membranes using purely experimental manners. Therefore, the C2H6/C2H4, C2H6/CH4, and CO2/CH4 separation performances of MOFs were investigated using high-throughput computational screening methods in this thesis. In the first part, molecular simulations were used to assess membrane-based C2H6/C2H4 and C2H6/CH4 separation performances of 175 different MOF structures. Results showed that a significant number of MOF membranes is C2H6 selective for C2H6/C2H4 separation in contrast to the traditional nanoporous materials. Several MOFs were identified to exceed the upper bound established for polymeric membranes and many MOF membranes exhibited higher gas permeabilities than zeolites and carbon molecular sieves. In the second part, a multi-level high-throughput computational screening methodology was used to examine the most recent MOF database for membrane-based CO2/CH4 separation. 8 promising MOF membranes offering the best combination of CO2 permeability (>106 Barrer) and CO2/CH4 selectivity (>80) were identified by combining grand canonical Monte Carlo (GCMC) and equilibrium molecular dynamics (EMD) simulations. Permeabilities and selectivities of the mixed matrix membranes (MMM) in which the best MOF candidates were incorporated as filler particles were also investigated. Many MOF membranes could outperform polymeric membranes for CO2/CH4 separation and MOF-based MMMs can have significantly higher CO2 permeabilities and moderately higher selectivities than pure polymers. Computational identification of the promising MOF candidates for CO2 separation depends on the accurate description of electrostatic interactions between CO2 molecules and MOFs. In the last part, role of partial charge assignment methods in high-throughput computational screening of MOFs for CO2/CH4 separation was examined. A quantum based, density-derived electrostatic and chemical charge method (DDEC) and an approximate charge equilibration method (Qeq) were used to compute the adsorption of CO2/CH4 mixture in 1500 MOFs at two different operating conditions. Results showed that the identity of the best performing MOF candidates, which were selected based on the regenerability and adsorbent performance score of MOFs, can change based on the type of the charge assignment method used in simulations. Overall, results showed that high-throughput screening approaches introduced in this thesis can be used to predict gas separation performance of MOF adsorbents and membranes and MOFs can perform better than commercially used materials. The results of this thesis will be useful to guide the experiments to the most promising MOF candidates and to accelerate the development of new MOFs with high performances.