IYTE GCRIS Database (Izmir Institute of Technology)
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Magnetism in Twisted Triangular Bilayer Graphene Quantum Dots
No full textUsing a tight-binding model along with the mean-field Hubbard method, we investigate the effect of twisting angle on the magnetic properties of twisted bilayer graphene (tBLG) quantum dots (QDs) with triangular shape and zigzag edges. We consider such QDs in two configurations: when their initial untwisted structure is a perfect AA- or AB-stacked BLG, referred to as AA- or AB-like dots. We find that AA-like dots exhibit an antiferromagnetic spin polarization for small twist angles, which transits to a ferromagnetic spin polarization beyond a critical twisting angle theta c. Our analysis shows that theta c decreases as the dot size increases, obeying a criterion, according to which once the maximum energy difference between electron and hole edge states (in the single-particle picture) is less than (U/gamma 0) t0, the spin-polarized energy levels are aligned ferromagnetically [U is the Hubbard parameter and gamma 0 (t0) the graphene intralayer (interlayer) hopping]. Unlike AA-like dots, AB-like dots exhibit finite magnetization for any twist angle. Furthermore, in the ferromagnetic polarization state, the ground net spin for both dot configurations agrees with the prediction from Lieb's theorem
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No full text12-14 Mayıs 2025 tarihleri arasında Japonya, Tokyo'da gerçekleştirilen COAR Annual Conference 2025'te gerçekleştirilen sunumdur.This is the presentation delivered at the COAR Annual Conference 2025, held in Tokyo, Japan, between May 12–14, 2025
Synthesis and Characterization of Doped Defective Titania Based Photocatalysts for Hydrogen Generation
No full textSera gazlarındaki artış, sürdürülemez fosil yakıtların yaygın kullanımıyla yoğunlaşarak sera etkisini artırmış ve bu da küresel ısınma ve iklim değişikliğine yol açmıştır. Yapay fotosentez, küresel CO2 seviyelerini azaltırken metan, metanol ve hidrojen gibi yenilenebilir, sürdürülebilir yakıtlar üretmek için umut verici bir tekniktir. Benzersiz optik ve kimyasal özellikleriyle bilinen titanyum bazlı fotokatalitik malzemeler, yapay fotosentezde yaygın olarak kullanılmakta olup, yakın zamanda sentezlenen siyah nano titanya malzemeleri de dahil olmak üzere nano tasarımlı hatalı TiO2 yapıları, UV veya güneş ışığı ile çalışan fotokatalitik hidrojen üretimi için en umut verici adaylardan bazıları olarak ortaya çıkmaktadır. Bu çalışmada, hatalı TiO2 bazlı fotokatalizörler sentezlenmiş ve geliştirilmiş fotokatalitik verimlilik potansiyellerini araştırmak için karakterize edilmiştir. Saf TiO2, hidrosol ve çöktürme yöntemleri kullanılarak sentezlenmiş, ardından kusurların oluşturulması için NaBH4 indirgeme maddesi ile indirgenmiştir. Hidrosol yöntemiyle üretilen hatalı TiO2 nanomalzemeler, indirgeme sıcaklığı ve TiO2-NaBH4 ağırlık oranı gibi indirgeme koşullarının optimize edilmesine odaklanırken, çöktürme yöntemi ön ısıtma işlemi ve indirgeme stratejileri içermektedir. Malzemelerin yapısal/optik özelliklerini analiz etmek için XRD, SEM, BET, ATR-FTIR, PL, UV-Vis spektroskopisi ve GC analizi gibi gelişmiş karakterizasyon teknikleri uygulanmıştır. Hidrosol yöntemiyle üretilen hatalı TiO2 nanomalzemeler, 325°C indirgeme sıcaklığında ve TiO2-NaBH4 (1:1) ağırlık oranıyla en yüksek hidrojen verimini elde etmiştir. Çökeltme yöntemiyle üretilen hatalı TiO2 nanomalzemeler ise 500°C'de ön ısıtma sonrasında optimum aktivite göstermiştir. Zr/Nd katkı maddesiyle yapılan katkılama çalışmaları, katkılanmamış fotokatalizörlere kıyasla hidrojen üretim verimliliğini artırmıştır.The increase in greenhouse gases caused by the extensive use of nonsustainable fossil fuels has intensified the greenhouse effect, leading to global warming and climate change. Artificial photosynthesis is a promising technique for producing renewable, sustainable fuels like methane, methanol, and hydrogen while reducing global CO2 levels. Titania-based photocatalytic materials, known for their unique optical and chemical properties, are widely utilized in artificial photosynthesis, with nano-designed defective TiO2 structures, including recently synthesized black nano titania materials, emerging as some of the most promising candidates for UV or solar light-driven photocatalytic hydrogen production. In this study, defective TiO2-based photocatalysts were synthesized and characterized to investigate their potential for enhanced photocatalytic efficiency. Pure TiO2 was synthesized using the hydrosol and precipitation methods, followed by reduction with NaBH4 as the reducing agent to introduce defects. The defective TiO2 nanomaterials via the hydrosol method focused on optimizing reduction conditions, including reduction temperature and TiO2-to-NaBH4 weight ratio, while the precipitation method involved preheat treatment and reduction strategies. Advanced characterization techniques such as XRD, SEM, BET, ATR-FTIR, PL, UV-Vis spectroscopy, and GC analysis were conducted to analyze the structural/optical properties of the materials. The defective TiO2 nanomaterials via the hydrosol method achieved the highest hydrogen yield at a reduction temperature of 325°C with a TiO2-to-NaBH4 weight ratio of (1:1). The defective TiO2 nanomaterials via precipitation method demonstrated optimal activity after preheating at 500°C. Doping studies were conducted with Zr/Nd as dopants, synthesized via the hydrosol method. These dopants enhanced hydrogen production efficiency compared to undoped photocatalysts
Redundancy Resolution Options for the Twin-It Robotic Hybrid Manufacturing System
No full textThe Twinnig Iztech in Robotics Manufacturing System (TWIN-IT-ROMANS) project funded by EU Horizon -Widera-2023-Access-02-01 aims to develop a hybrid manufacturing system that can perform additive and subtractive manufacturing processes and inline quality control using a robotic system. The system will incorporate a 6-degree-of-freedom robot arm and a positioner with 2-degree-of-freedom, which will operate synchronously. This manipulation system is to be designed for performing different manufacturing operations with different degrees-of-freedom requirements. In order to reveal alternative trajectory planning scenarios for this system, this paper presents an initial review of redundancy resolution approaches for kinematically redundant robotic manipulators. First, the four main approaches for redundancy resolution techniques are introduced. Then main studies on energy minimization and stiffness maximization for kinematically redundant robotic manipulators are reviewed. Similar or new approaches are planned to be generated and implemented for the redundant system for hybrid manufacturing. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2025
Design of Transformable Doubly Curved Surface Composed of Scissor Linkage Mechanisms
No full textThis study focuses on obtaining multi-loop scissor linkages capable of defining doubly curved surfaces that can transform from an initial form to a desired final form. A review of the existing literature reveals a limited number of studies addressing curvature transformation between different states. Most transformable designs are restricted to planar movements, while three-dimensional forms are typically achieved through the translational repetition of planar scissor linkages. Additionally, when scissor linkages are arranged in a grid, they often exhibit multiple degrees of freedom, making controlled transformations challenging. To address these limitations, this research introduces a novel geometric design method for multi-loop planar scissor linkages that enables transformation between predefined curves. The proposed approach utilizes quadrilateral loops to construct planar scissor linkages capable of achieving distinct curved forms. Furthermore, the study extends this concept to spatial scissor linkages that can dynamically alter their curvature between predefined surface geometries. The research employs simulation and modeling as primary methods. Computer simulations are used to develop the proposed models, while 3D-printed prototypes are produced to analyze their geometric behavior. These tools facilitate a comprehensive investigation of the transformability and structural performance of the designed mechanisms.Bu çalışma, başlangıç formundan istenen nihai forma dönüşebilen ve çift eğrilikli yüzeyler tanımlayabilen, çok döngülü makas mekanizmaları elde etmeye odaklanmaktadır. Mevcut literatür incelendiğinde farklı durumlar arasındaki eğrilik dönüşümünü ele alan sınırlı sayıda çalışma ortaya çıkmaktadır. Tek serbestlik derecesine sahip dönüştürülebilir tasarımların çoğu düzlemsel hareketlerle sınırlı iken üç boyutlu formlar ise genellikle düzlemsel makas mekanizmalarının ötelemeli tekrarı yoluyla elde edilebilmektedir. Buna ek olarak, düzlemsel makas mekanizmalarıyla ızgarada düzeninde bir yüzey tanımlayabilen formlar oluşturulduğunda, genellikle birden fazla serbestlik derecesine sahip olmaktadır ve bu da form dönüşümlerinin kontrolünü zorlaştırır. Bu tezde, belirtilen eksikliklerden yola çıkarak, önceden tanımlanmış eğriler arasında dönüşüme olanak tanıyan düzlemsel makas mekanizmaları için yeni bir geometrik tasarım yöntemi sunulmaktadır. Önerilen yaklaşım, farklı kavisli formlar elde edebilen düzlemsel makas mekanizmalarını oluşturmak için dörtgen döngülerden yararlanmaktadır. Bu çalışma, belirtilen yöntemden yola çıkarak, önceden tanımlanmış yüzey geometrileri arasında eğriliklerini dinamik olarak değiştirebilen uzaysal makas mekanizmalarını bu konsepte dahil etmektedir. Araştırma, birincil yöntemler olarak simülasyon ve modellemeyi kullanmaktadır. Önerilen modelleri geliştirmek için bilgisayar simülasyonları kullanılırken, geometrik davranışlarını analiz etmek için 3 boyutlu yazdırılmış prototipler üretilmiştir. Bu araçlar, tasarlanan mekanizmaların dönüştürülebilirliğinin ve yapısal performanslarının kapsamlı bir şekilde incelenmesini kolaylaştırmaktadır
Mesenchymal Stem Cells in Cancer Therapy
No full textThe mesenchymal stem/stromal cells (MSCs) are multipotent cells that were initially discovered in the bone marrow in the late 1960s but have so far been discovered in almost all tissues of the body. The multipotent property of MSCs enables them to differentiate into various cell types and lineages, such as adipocytes, chondrocytes, and osteocytes. The immunomodulation capacity and tumor-targeting features of MSCs made their use crucial for cell-based therapies in cancer treatment, yet limited advancement could be observed in translational medicine prospects due to the need for more information regarding the controversial roles of MSCs in crosstalk tumors. In this review, we discuss the therapeutic potential of MSCs, the controversial roles played by MSCs in cancer progression, and the anticancer therapeutic strategies that are in association with MSCs. Finally, the clinical trials designed for the direct use of MSCs for cancer therapy or for their use in decreasing the side effects of other cancer therapies are also mentioned in this review to evaluate the current status of MSC-based cancer therapies. © 2024. The Author(s), under exclusive license to Springer Nature Switzerland AG
Year-To Differentiation of Black Tea Through Spectroscopic and Chemometric Analysis
No full textThe compositions of food products such as tea can vary significantly from one harvest year to another, primarily due to factors such as shifting climatic conditions, and plant periodicity. These fluctuations in composition can significantly affect the overall product quality. Spectral methods combined with chemometric techniques can provide efficient tools to monitor and assess these variations. In this study, 205 black tea samples from two consecutive harvest years were analyzed using mid-infrared, UV–visible, and fluorescence spectroscopy. Mid-infrared spectra were collected for both infused and powdered samples, while only the infused samples were used for the other spectroscopic methods. The study used partial least-square discriminant (PLS-DA) and orthogonal partial least-square discriminant analyses (OPLS-DA) to differentiate samples by harvest year. These models, applied after various data transformations, achieved high correct classification rates. Mid-infrared spectroscopic data yielded rates of 93.33% and 90.33% for powdered and infused samples, respectively. Fluorescence and UV–visible spectra also showed excellent prediction accuracy, with success rates of 98.3% and 100%. The results indicate that these spectroscopic methods, combined with chemometric differentiation, are valuable tools for monitoring year-to-year changes in black tea. © The Author(s) 2024
Challenges Faced by Closed Basins From the Perspective of Water Resources: Case Studies From Türkiye
No full textClosed basins form important hydrological systems that provide a variety of benefits to both the environment and humans. This chapter examines the current status of closed basins in Turkiye and analyzes the natural and anthropogenic environmental stressors affecting these regions. Two distinct case studies are covered in this chapter: the Konya Closed Basin (KCB) and the Karakuyu region. Konya Closed Basin has experienced severe drought and sinkhole issues as a result of misapplications and excessive water consumption. The severity and frequency of water-related problems are increasing day by day due to the impact of climate change in the region. Agricultural activity and irrigation needs are high in the Karakuyu region, which is considered a second case study and is a small part of the Kucuk Menderes River Basin. It is hoped that with improved management practices, Karakuyu will not experience the condition of KCB in the future. The final section outlines the recommended practices and precautionary measures for addressing issues associated with closed basins