Scopus İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/395
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Article Citation - WoS: 1Citation - Scopus: 1Tailoring Quantum Dot Shell Thickness and Polyethylenimine Interlayers for Optimization of Inverted Quantum Dot Light-Emitting Diodes(MDPI, 2024-07-11) Yazici, Ahmet F.; Ocal, Sema Karabel; Bicer, Aysenur; Serin, Ramis B.; Kacar, Rifat; Ucar, Esin; Mutlugun, EvrenQuantum dot light-emitting diodes (QLEDs) hold great promise for next-generation display applications owing to their exceptional optical properties and versatile tunability. In this study, we investigate the effects of quantum dot (QD) shell thickness, polyethylenimine (PEI) concentration, and PEI layer position on the performance of inverted QLED devices. Two types of alloyed-core/shell QDs with varying shell thicknesses were synthesized using a one-pot method with mean particle sizes of 8.0 +/- 0.9 nm and 10.3 +/- 1.3 nm for thin- and thick-shelled QDs, respectively. Thick-shelled QDs exhibited a higher photoluminescence quantum yield (PLQY) and a narrower emission linewidth compared to their thin-shelled counterparts. Next, QLEDs employing these QDs were fabricated. The incorporation of PEI layers on either side of the QD emissive layer significantly enhanced device performance. Using PEI on the hole transport side resulted in greater improvement than on the electron injection side. Sandwiching the QD layer between two PEI layers led to the best performance, with a maximum external quantum efficiency (EQE) of 17% and a peak luminance of 91,174 cd/m2 achieved using an optimized PEI concentration of 0.025 wt% on both electron injection and hole injection sides. This study highlights the critical role of QD shell engineering and interfacial modification in achieving high-performance QLEDs for display applications.Article Citation - WoS: 25Citation - Scopus: 28Passive Flow Control Application Using Single and Double Vortex Generator on S809 Wind Turbine Airfoil(MDPI, 2023-07-12) Ozden, Mustafa; Genc, Mustafa Serdar; Koca, KemalThe current study is aimed at investigating the influences of vortex generator (VG) applications mounted to the suction and pressure surfaces of the S809 wind turbine airfoil at low Reynolds number flow conditions. Both single and double VG applications were investigated to provide technological advancement in wind turbine blades by optimizing their exact positions on the surface of the airfoil. The results of the smoke-wire experiment for the uncontrolled case reveal that a laminar separation bubble formed near the trailing edge of the suction surface, and it was moved towards the leading edge as expected when the angle of attack was increased, resulting in bubble burst and leading-edge flow separation at & alpha; = 12 & DEG;. The u/U-& INFIN;, laminar kinetic energy and total fluctuation energy contours obtained from the numerical study clearly show that both the single and double VG applications produced small eddies, and those eddies in the double VG case led the flow to be reattached at the trailing edge of the suction surface and to gain more momentum by energizing. This situation was clearly supported by the results of aerodynamic force; the double VG application caused the lift coefficient to increase, resulting in an enhancement of the aerodynamic performance. A novel finding is that the VG at the pressure surface caused the flow at the wake region to gain more energy and momentum, resulting in a reattached and steadier flow condition.Article Citation - WoS: 4Citation - Scopus: 3Optimization of the Recycling Process for Aligned Short Carbon Fiber TuFF Composites(MDPI, 2025-04-01) Balaga, Uday Kiran; Gunes, Aydin; Ozdemir, Tekin; Blackwell, Chris; Davis, Mark; Sauerbrunn, Steven; Heider, DirkRecycling of carbon fibers enables a sustainable feedstock for industrial applications of high-performance composite materials. This allows light weighting with recycled carbon fibers due to their superior mechanical properties while reducing the high embodied energy and cost of virgin carbon fiber composites. This study optimizes a pyrolysis cycle for fiber recovery of an aerospace-grade thermoset prepreg and a cleaning (oxidation) step to minimize fiber degradation and left-over resin residue, enabling dispersion and alignment of the recycled, discontinuous fibers in the Tailorable Universal Feedstock for Forming alignment process. The study balances the influence of the optimized thermal cycle (pyrolysis + oxidation step) on recycled carbon fiber strength retention with the ability to disperse at the filament level to create aligned, recycled carbon fiber composite samples with high fiber volume fraction. The optimized thermal cycle for efficient fiber recovery applied a pyrolysis step at 500 degrees C for 4 h in an inert gas environment and an additional oxidation step at the same temperature for 100 min. This resulted in similar to 20% strength degradation of the fiber compared to the virgin fiber. The processed recycled composite achieved 44% fiber volume fraction with full modulus translation (similar to 128 GPa) compared to the virgin continuous composite with strength translation (similar to 870 MPa), reaching similar to 50%.Article Citation - WoS: 4Citation - Scopus: 4Mesoscale Morphologies of Nafion-Based Blend Membranes by Dissipative Particle Dynamics(MDPI, 2021-06-02) Sen, Unal; Ozdemir, Mehmet; Erkartal, Mustafa; Kaya, Alaattin Metin; Manda, Abdullah A.; Oveisi, Ali Reza; Tokumasu, TakashiPolymer electrolyte membrane (PEM) composed of polymer or polymer blend is a vital element in PEM fuel cell that allows proton transport and serves as a barrier between fuel and oxygen. Understanding the microscopic phase behavior in polymer blends is very crucial to design alternative cost-effective proton-conducting materials. In this study, the mesoscale morphologies of Nafion/poly(1-vinyl-1,2,4-triazole) (Nafion-PVTri) and Nafion/poly(vinyl phosphonic acid) (Nafion-PVPA) blend membranes were studied by dissipative particle dynamics (DPD) simulation technique. Simulation results indicate that both blend membranes can form a phase-separated microstructure due to the different hydrophobic and hydrophilic character of different polymer chains and different segments in the same polymer chain. There is a strong, attractive interaction between the phosphonic acid and sulfonic acid groups and a very strong repulsive interaction between the fluorinated and phosphonic acid groups in the Nafion-PVPA blend membrane. By increasing the PVPA content in the blend membrane, the PVPA clusters' size gradually increases and forms a continuous phase. On the other hand, repulsive interaction between fluorinated and triazole units in the Nafion-PVTri blend is not very strong compared to the Nafion-PVPA blend, which results in different phase behavior in Nafion-PVTri blend membrane. This relatively lower repulsive interaction causes Nafion-PVTri blend membrane to have non-continuous phases regardless of the composition.Article Citation - WoS: 10Citation - Scopus: 11Investigation of the Mechanical Behavior of a New Generation Wind Turbine Blade Technology(MDPI, 2023-02-16) Ciftci, Cihan; Erdogan, Ayse; Genc, Mustafa SerdarWind turbine blades are one of the largest parts of wind power systems. It is a handicap that these large parts of numerous wind turbines will become scrap in the near future. To prevent this handicap, newly produced blades should be recyclable. In this study, a turbine blade, known as the new generation of turbine blade, was manufactured with reinforced carbon beams and recycled, low-density polyethylene materials. The manufacturing addressed in this study reveals two novelties: (1) it produces a heterogeneous turbine blade; and (2) it produces a recyclable blade. In addition, this study also covers mechanical tests using a digital image correlation (DIC) system and modeling investigations of the new generation blade. For the mechanical tests, displacement and strain data of both new generation and conventional commercial blades were measured by the DIC method. Instead of dealing with the modeling difficulty of the new generation blade's heterogeneity we modeled the blade structural system as a whole using the moment-curvature method as part of the finite element method. Then, the behavior of both the new generation and commercial blades at varying wind speeds and different angles of attack were compared. Consequently, the data reveal that the new generation blades performed sufficiently well compared with commercial blades regarding their stiffness.Article Citation - WoS: 37Citation - Scopus: 47Enhancing Cybersecurity in Smart Grids: False Data Injection and Its Mitigation(MDPI, 2021-05-06) Unsal, Derya Betul; Ustun, Taha Selim; Hussain, S. M. Suhail; Onen, Ahmet; Suhail Hussain, S.M.Integration of information technologies with power systems has unlocked unprecedented opportunities in optimization and control fields. Increased data collection and monitoring enable control systems to have a better understanding of the pseudo-real-time condition of power systems. In this fashion, more accurate and effective decisions can be made. This is the key towards mitigating negative impacts of novel technologies such as renewables and electric vehicles and increasing their share in the overall generation portfolio. However, such extensive information exchange has created cybersecurity vulnerabilities in power systems that were not encountered before. It is imperative that these vulnerabilities are understood well, and proper mitigation techniques are implemented. This paper presents an extensive study of cybersecurity concerns in Smart grids in line with latest developments. Relevant standardization and mitigation efforts are discussed in detail and then the classification of different cyber-attacks in smart grid domain with special focus on false data injection (FDI) attack, due to its high impact on different operations. Different uses of this attack as well as developed detection models and methods are analysed. Finally, impacts on smart grid operation and current challenges are presented for future research directions.Article Citation - WoS: 4Citation - Scopus: 6Enhanced Energy Savings With Adaptive Watchful Sleep Mode for Next Generation Passive Optical Network(MDPI, 2022-02-23) Butt, Rizwan Aslam; Akhunzada, Adnan; Faheem, Muhammad; Raza, BasitA single watchful sleep mode (WSM) combines the features of both cyclic sleep mode (CSM) and cyclic doze mode (CDM) in a single process by periodically turning ON and OFF the optical receiver (RX) of the optical network terminal (ONT) in a symmetric manner. This results in almost the same energy savings for the ONTs as achieved by the CSM process while significantly reducing the upstream delays. However, in this study we argue that the periodic ON and OFF periods of the ONT RX is not an energy efficient approach, as it reduces the ONT Asleep (AS) state time. Instead, this study proposes an adaptive watchful sleep mode (AWSM) in which the RX ON time of ONT is minimized during ONT Watch state by choosing it according to the length of the traffic queue of the type 1 (T1) traffic class. The performance of AWSM is compared with standard WSM and CSM schemes. The investigation reveals that by minimizing the RX ON time, the AWSM scheme achieves up to 71% average energy saving per ONT at low traffic loads. The comparative study results show that the ONT energy savings achieved by AWSM are 9% higher than the symmetric WSM with almost the same delay and delay variance performance.Article Citation - WoS: 31Citation - Scopus: 40Disaster-Resilient Optical Network Survivability: A Comprehensive Survey(MDPI, 2018-10-12) Ashraf, Muhammad Waqar; Idrus, Sevia M.; Iqbal, Farabi; Butt, Rizwan Aslam; Faheem, MuhammadNetwork survivability endeavors to ensure the uninterrupted provisioning of services by the network operators in case of a disaster event. Studies and news reports show that network failures caused by physical attacks and natural disasters have significant impacts on the optical networks. Such network failures may lead to a section of a network to cease to function, resulting in non-availability of services and may increase the congestion within the rest of the network. Therefore, fault tolerant and disaster-resilient optical networks have grasped the attention of the research community and have been a critical concern in network studies during the last decade. Several studies on protection and restoration techniques have been conducted to address the network component failures. This study reviews related previous research studies to critically discuss the issues regarding protection, restoration, cascading failures, disaster-based failures, and congestion-aware routing. We have also focused on the problem of simultaneous cascading failures (which may disturb the data traffic within a layer or disrupt the services at upper layers) along with their mitigating techniques, and disaster-aware network survivability. Since traffic floods and network congestion are pertinent problems, they have therefore been discussed in a separate section. In the end, we have highlighted some open issues in the disaster-resilient network survivability for research challenges and discussed them along with their possible solutions.Article Citation - WoS: 9Citation - Scopus: 10Anhedonia in Relation to Reward and Effort Learning in Young People With Depression Symptoms(MDPI, 2023-02-17) Frey, Anna-Lena; Kaya, M. Siyabend; Adeniyi, Irina; McCabe, CiaraAnhedonia, a central depression symptom, is associated with impairments in reward processing. However, it is not well understood which sub-components of reward processing (anticipation, motivation, consummation, and learning) are impaired in association with anhedonia in depression. In particular, it is unclear how learning about different rewards and the effort needed to obtain them might be associated with anhedonia and depression symptoms. Therefore, we examined learning in young people (N = 132, mean age 20, range 17-25 yrs.) with a range of depression and anhedonia symptoms using a probabilistic instrumental learning task. The task required participants to learn which options to choose to maximize their reward outcomes across three conditions (chocolate taste, puppy images, or money) and to minimize the physical effort required to obtain the rewards. Additionally, we collected questionnaire measures of anticipatory and consummatory anhedonia, as well as subjective reports of "liking", "wanting" and "willingness to exert effort" for the rewards used in the task. We found that as anticipatory anhedonia increased, subjective liking and wanting of rewards decreased. Moreover, higher anticipatory anhedonia was significantly associated with lower reward learning accuracy, and participants demonstrated significantly higher reward learning than effort learning accuracy. To our knowledge, this is the first study observing an association of anhedonia with reward liking, wanting, and learning when reward and effort learning are measured simultaneously. Our findings suggest an impaired ability to learn from rewarding outcomes could contribute to anhedonia in young people. Future longitudinal research is needed to confirm this and reveal the specific aspects of reward learning that predict anhedonia. These aspects could then be targeted by novel anhedonia interventions.