WoS İndeksli Yayınlar Koleksiyonu / WoS Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7150
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Article Citation - WoS: 1Citation - Scopus: 1Spiral-Shaped Dual-Port Microstrip Antenna for 5G/6G Applications With Wideband-To Transition Using Shape-Memory Alloy(Iop Publishing Ltd, 2025) Atac, Enes; Karatay, AnilWe propose a compact, thermally reconfigurable dual-port microstrip antenna featuring a spiral-shaped design and shape-memory alloy (SMA) that enable switching between wideband and narrowband operation for 5G/6G communication systems. The SMA's thermally induced shape-memory behavior allows reconfiguration in response to temperature changes without the need for electronic or optical control circuits, thus avoiding issues such as self-interference problem, high costs, regular maintenance requirements, and durability concerns. In the wideband mode, measured results show that Port 1 covers 4.7-10.5 GHz and Port 2 covers 4.5-8.3 GHz, which closely agrees with simulations. When the SMA is activated by heat, the antenna switches to the narrowband mode, where Port 1 operates at 7.6 and 9.5 GHz, and Port 2 operates at 8.9 GHz. A ground-plane isolation element ensures low coupling between the ports, with the envelope correlation coefficient remaining below 0.1 across all configurations. The antenna reaches a peak gain of 5.2 dBi and maintains consistent performance through repeated switching. By combining spiral-shaped geometry with a responsive smart material, this work presents a novel and efficient approach for designing reconfigurable dual-port antennas suitable for future wireless technologies.Article The Curvature Perturbation Generated by Thermal Fluctuations During Thermal Inflation(Iop Publishing Ltd, 2025) Bae, Jeong-Myeong; Mohammad, Hammam Raihan; Stewart, Ewan D.; Zoe, HeeseungDuring thermal inflation, the temperature determines the number of e-folds of expansion of the universe and so thermal fluctuations are magnified into curvature perturbations. We use classical thermodynamics to calculate the subhorizon thermal fluctuations and trace their evolution into superhorizon temperature perturbations. We convert the temperature perturbations into curvature perturbations using the delta N-formalism, or equivalently the junction condition of curvature perturbations at the end of thermal inflation, denoted by subscript c, and show that the late-time power spectrum is PR= 15 Hc 3 k3 4 pi 4 g & lowast;T 3 kc 3 . cArticle Citation - WoS: 2Citation - Scopus: 4Injectable Nanocomposite Hydrogels With Co-Delivery of Oxygen and Anticancer Drugs for Higher Cell Viability of Healthy Cells Than Cancer Cells Under Normoxic and Hypoxic Conditions(Iop Publishing Ltd, 2025) Kehr, Nermin SedaInjectable nanocomposite hydrogels (NC hydrogels) have the potential to be used for minimally invasive local drug delivery. In particular, pH-sensitive injectable NC hydrogels can be used in cancer treatment to deliver high doses of anticancer drugs to the target site in cancer tissue without damaging healthy tissue. Recent studies have shown that in addition to stimuli-responsive delivery of anticancer drugs to cancer cells, oxygen delivery to the hypoxic environment of cancer tissue can lead to advanced effects, as hypoxia and an acidic pH are common characteristics of cancer tissue. However, few studies have investigated the effects of simultaneous administration of oxygen (O2) and pH-dependent anticancer drugs via injectable NC hydrogels on the viability of healthy and cancer cells under normoxic and hypoxic conditions. In this context, we describe the synthesis of injectable NC hydrogels composed of pH-responsive nanomaterials carrying oxygen and anticancer drugs. Our system provides sustained O2 release and pH-responsive sustained release of anticancer drugs for 15 and 30 d, respectively. Moreover, O2 delivery and/or simultaneous delivery of O2 and anticancer drug resulted in higher cell survival of healthy fibroblast cells than malignant Colo-818 cells under hypoxic conditions (1% O2) after 7 d of incubation.Review Citation - WoS: 1Citation - Scopus: 1Colloidal Quantum Dots as Solution-Based Nanomaterials for Infrared Technologies(Iop Publishing Ltd, 2024) Sevim Ünlütürk, S.; Taşcıoğlu, D.; Özçelik, S.This review focuses on recent progress of wet-chemistry-based synthesis methods for infrared (IR) colloidal quantum dots (CQD), semiconductor nanocrystals with a narrow energy bandgap that absorbs and/or emits IR photos covering from 0.7 to 25 micrometers. The sections of the review are colloidal synthesis, precursor reactivity, cation exchange, doping and de-doping, surface passivation and ligand exchange, intraband transitions, quenching and purification, and future directions. The colloidal synthesis section is organized based on precursors employed: toxic substances as mercury- and lead-based metals and non-toxic substances as indium- and silver-based metal precursors. CQDs are prepared by wet-chemical methods that offer advantages such as precise spectral tunability by adjusting particle size or particle composition, easy fabrication and integration of solution-based CQDs (as inks) with complementary metal-oxide-semiconductors, reduced cost of material manufacturing, and good performances of IR CQD-made optoelectronic devices for non-military applications. These advantages may allow facile and materials' cost-reduced device fabrications that make CQD based IR technologies accessible compared to optoelectronic devices utilizing epitaxially grown semiconductors. However, precursor libraries should be advanced to improve colloidal IR quantum dot synthesis, enabling CQD based IR technologies available to consumer electronics. As the attention of academia and industry to CQDs continue to proliferate, the progress of precursor chemistry for IR CQDs could be rapid. © 2024 IOP Publishing Ltd. All rights, including for text and data mining, AI training, and similar technologies, are reserved.Article Citation - Scopus: 1Genetic Algorithm Optimization of Langevin Thermostat and Thermal Properties of Graphene-Aluminum Nanocomposites: a Molecular Dynamics(Iop Publishing Ltd, 2024) Toprak, KasimThe thermal properties of a laminated structure of graphene-coated aluminum composite nanomaterial were investigated through non-equilibrium molecular dynamics (NEMD) simulations to address the problem of temperature deviation in the thermostat volume applied. This paper presents a new insight into the best values of timestep and Langevin thermostat damping parameters for each atom in the nanomaterial with different size configurations using the genetic algorithm (GA) method by considering the timestep and thermostat damping parameters for each atom type, as well as the thickness of the nanomaterial, the thermostat, buffer, and heat flow lengths. The initial population results indicate that the thermostat temperature deviation increases with higher thermostat damping coefficients and timestep. However, the deviation decreases significantly with increased heat flow and thermostat lengths. Variations in buffer length and aluminum thickness do not have a significant effect on temperature. The application of a GA for optimization leads to a decrease in thermostat temperature deviation. The optimized parameters resulted in better thermostat temperature deviations when analyzing the temperature, aluminum thickness, and both buffer and thermostat lengths. Additionally, the thermal conductivity of aluminum-graphene nanomaterial decreases with increasing temperature, buffer length, and aluminum thickness, but increases by up to 9.85% with increasing thermostat length.Article Citation - WoS: 3Citation - Scopus: 6Large-Area (50 Cm X 50 Cm) Optically Transparent Electromagnetic Interference (emi) Shielding of Zto/Ag an Analytical/Numerical and Experimental Study of Optoelectrical and Emi Shielding Properties(Iop Publishing Ltd, 2024) Astarlioglu, Aziz Taner; Oz, Yahya; Unal, Emre; Kilic, Nail Bugra; Celikli, Cenkay; Ozdemir, Mehtap; Erdogan, NursevTransparent conducting oxides (TCOs), exhibiting both high optical transparency and low electrical resistivity, are commonly employed in optoelectronic devices. However, acquiring a balance between these optical and electrical properties in a uniform way over large areas has been a pending challenge, which is essential to achieving optically transparent electromagnetic interference (EMI) shielding surfaces. In this study, we propose and demonstrate a stratified thin film structure consisting of zinc-doped tin oxide (Zn2SnO4, ZTO) as TCO along with a metal layer of silver (Ag) deposited on a large area of 50 cm x 50 cm polycarbonate (PC) substrate enabled by a scanning magnetron sputtering gun. We achieved high EMI shielding of 99.9% at the optical transparency of 68% in the visible spectrum by engineering the stratified architecture of ZTO/Ag/ZTO. The Ag layer of 18 nm in thickness with a sheet resistance of 10 Omega/sq yields shielding effectiveness (SE) of 27 dB in a wide frequency range of 2-20 GHz. The bottom and top ZTO layers, 20 and 40 nm thick, respectively, provide the lowest optical loss of 13% across 400-700 nm. The structure's EMI shielding, optical and structural performances were systematically characterized through a free-space focused-beam system, UV-Vis spectrophotometer, ellipsometry, focused ion-beam cross-sectional sampling and imaging, transmission electron microscopy, atomic force microscopy and secondary ion mass spectroscopy. EMI shielding and optical performances were validated by CST Microwave Studio and the transfer matrix method, respectively. These findings indicate that the proposed multi-layer architecture holds great promise for large-area EMI shielding and other optoelectronic applications.Article Citation - WoS: 4Citation - Scopus: 4Ultra-Thin Double-Layered Hexagonal Cui: Strain Tunable Properties and Robust Semiconducting Behavior(Iop Publishing Ltd, 2024) Demirok, A. C.; Sahin, H.; Yagmurcukardes, M.In this study, the freestanding form of ultra-thin CuI crystals, which have recently been synthesized experimentally, and their strain-dependent properties are investigated by means of density functional theory calculations. Structural optimizations show that CuI crystallizes in a double-layered hexagonal crystal (DLHC) structure. While phonon calculations predict that DLHC CuI crystals are dynamically stable, subsequent vibrational spectrum analyzes reveal that this structure has four unique Raman-active modes, allowing it to be easily distinguished from similar ultra-thin two-dimensional materials. Electronically, DLHC CuI is found to be a semiconductor with a direct band gap of 3.24 eV which is larger than that of its wurtzite and zincblende phases. Furthermore, it is found that in both armchair (AC) and zigzag (ZZ) orientations the elastic instabilities occur over the high strain strengths indicating the soft nature of CuI layer. In addition, the stress-strain curve along the AC direction reveal that DLHC CuI undergoes a structural phase transition between the 4% and 5% tensile uniaxial strains as indicated by a sudden drop of the stress in the lattice. Moreover, the phonon band dispersions show that the phononic instability occurs at much smaller strain along the ZZ direction than that of along the AC direction. Furthermore, the external strain direction can be deduced from the predicted Raman spectra through the splitting rates of the doubly degenerate in-plane vibrations. The mobility of the hole carriers display highly anisotropic characteristic as the applied strain reaches 5% along the AC direction. Due to its anomalous strain-dependent electronic features and elastically soft nature, DLHC of CuI is a potential candidate for future electro-mechanical applications.Article Citation - WoS: 3Citation - Scopus: 3Understanding Neural Network Tuned Langevin Thermostat Effect on Predicting Thermal Conductivity of Graphene-Coated Copper Using Nonequilibrium Molecular Dynamics Simulations(Iop Publishing Ltd, 2024) Toprak, KasimCopper has always been used in thermoelectric applications due to its extensive properties among metals. However, it requires further improving its heat transport performance at the nanosized applications by supporting another high thermal conductivity material. Herein, copper was coated with graphene, and the neural network fitting was employed for the nonequilibrium molecular dynamics simulations of graphene-coated copper nanomaterials to predict thermal conductivity. The Langevin thermostat that was tuned with a neural network fitting (NNF), which makes up the backbone of deep learning, generated the temperature difference between the two ends of the models. The NNF calibrated the Langevin thermostat damping constants that helped to control the temperatures precisely. The buffer and thermostat lengths were also analyzed, and they have considerable effects on the thermostat temperatures and a significant impact on the thermal conductivity of the graphene-coated copper. Regarding thermal conductivity, the four different shapes of vacancy defect concentrations and their locations in the graphene sheets were further investigated. The vacancy between the thermostats significantly decreases the thermal conductivity; however, the vacancy defect in thermostats does not have a similar effect. When the graphene is placed between two copper blocks, the thermal conductivity decreases drastically, and it continues to drop when the sine wave amplitude on the graphene sheet increases.Article Citation - WoS: 3Citation - Scopus: 4Cost-Effective Experiments With Additively Manufactured Waveguide and Cavities in the S-Band(Iop Publishing Ltd, 2023) Karatay, Anıl; Yilmaz, Hasan Önder; Özkal, Ceren; Yaman, FatihThis study demonstrates the applicability of additively manufactured components that are metalized with conductive tape for two different microwave experiments. We focus on dielectric measurements and prototyping elliptical accelerator cavities at a low power regime for 2.45 GHz. To illustrate the accuracy of our results for the commonly used solid/liquid materials in engineering and to compare the fundamental accelerator cavity parameters with previous research rectangular and elliptic 3D-printed cavities coated with aluminum-type tape were employed in the experiments. Results reported for the complex-valued permittivities and specific design parameters for the cavity prototype are consistent with the literature. Various approaches to obtain the conductivity value of the tape and the effect of the roughness/thickness of the coating on the reflection parameter are discussed in detail. We confirm the effectiveness of the proposed approach, which reduces costs and provides a high degree of accuracy for investigated applications.