Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Impact of Titania Phase Structure and Surface Reactivity on the Photocatalytic Degradation of Various Dyes and Textile Wastewater(National Institute of Science Communication and Policy Research, 2023) Yurtsever, Hüsnü Arda; İloğlu, Onur; Çiftçioğlu, MuhsinTitania (TiO2) powders have been prepared by precipitation method in different precipitation media which contain sulfate, nitrate or organic species. Photocatalytic degradation of different dyes and a real textile wastewater have been conducted with these powders along with commercial powder Degussa P25 for comparison. Ethyl alcohol (organic medium), sulfuric acid (sulfate medium) and nitric acid (nitrate medium) have been used to dissolve titanium precursor for the precipitation of TiO2 in ammonia solution. UV-Vis DRS and XPS results indicate that S doping in sulfate medium precipitated powder and N doping in nitrate medium precipitated powder has been occurred and the presence of S or N containing impurities on the grain boundaries have been improved light absorption of TiO2 significantly. However, these powders have exhibited low surface reactivities. The highest surface reactivity has been obtained with the powder precipitated in organic medium which also has the highest crystallite sizes (76 nm rutile and 34 nm anatase crystallites) with relatively low rutile weight percentage (10.0%). The surface-normalized rate constants of this powder are 0.02038 min-1.m-2 in real textile wastewater degradation and 0.0161 min-1.m-2 in methyl orange degradation, which are 0.01563 and 0.0091 min-1.m-2, respectively, for Degussa P25. Results have shown that this powder show 30-70% higher surface reactivities compared to Degussa P25. The main structural difference of organic medium precipitated powder and Degussa P25 has been found to be the anatase-rutile weight ratio and crystallite size of rutile phase whereas band gap energy of Degussa P25 is lower and other properties are not significantly different.Article Citation - WoS: 1Citation - Scopus: 1Thermodynamic Re-Assessment of a Geothermal Binary Power Plant Operated in a Moderate-Temperature Geothermal Field(Inderscience, 2023) Özcan, Zeynep; Gökçen Akkurt, GüldenAn existing organic rankine cycle power plant which uses isobutane as working fluid is re-evaluated for different working fluids. The plant is first modelled by EES software; then the model is simulated for different working fluids obtaining heat transferred through the heat exchanger, net work output, energy and exergy efficiencies, and mass flowrate of the working fluid. Two parametric studies are conducted to evaluate the thermodynamic performance of the plant under a range of turbine inlet temperature (130°C–155°C) and geothermal resource temperature (152°C–161°C) for each working fluid. The study reveals that the highest cycle energy and exergy efficiencies are observed for R-152a at any geothermal resource temperature. R-152a resulted with 13.1% and 58.2% cycle energy and exergy efficiency, respectively at operation condition, whilst the lowest efficiency and net work output is calculated under n-butane presence.Article Citation - WoS: 2Citation - Scopus: 3The Green-Tao Theorem and the Infinitude of Primes in Domains(Taylor & Francis, 2022) Göral, Haydar; Özcan, Hikmet Burak; Sertbaş, Doğa CanWe first prove an elementary analogue of the Green-Tao Theorem. The celebrated Green-Tao Theorem states that there are arbitrarily long arithmetic progressions in the set of prime numbers. In fact, we show the Green-Tao Theorem for polynomial rings over integral domains with several variables. Using the Generalized Polynomial van der Waerden Theorem, we also prove that in an infinite unique factorization domain, if the cardinality of the set of units is strictly less than that of the domain, then there are infinitely many prime elements. Moreover, we deduce the infinitude of prime numbers in the positive integers using polynomial progressions of length three. In addition, using unit equations, we provide two more proofs of the infinitude of prime numbers. Finally, we give a new proof of the divergence of the sum of reciprocals of all prime numbers.Article Citation - WoS: 1Citation - Scopus: 2Preparation and Photocatalytic Performances of Zno Nanostructures: Effects of Anodization Voltage and Time(Wiley, 2022) Öksüz, Ahmet Emrecan; Yurddaşkal, Metin; Doluel, Eyyup Can; Kartal, Uğur; Dikici, TuncayIn this study, ZnO nanostructures with different morphologies were produced by varying anodizing parameters (time and voltage), and the photocatalytic activities of these structures were examined. ZnO nanostructures were fabricated through different voltage and duration consisting of nine samples with KHCO3 solution as an electrolyte. The produced ZnO nanostructures were investigated by using X-ray diffraction (XRD), scanning electron microscopy, X-ray photoelectron spectroscopy, and UV–vis spectrophotometer. It was found that the morphology of ZnO was formed as nanosponge, nanoflower, nanowire, heterogeneous structures. ZnO nanostructures were identified by matching XRD peaks due to the ICDD database. Experiments on photocatalytic degradation of methylene blue demonstrated the photocatalytic activity of ZnO samples. The best photocatalytic performance of the samples was observed by S1 sample, which was anodized for 30 min in 0.05 M of KHCO3 electrolyte at 20 V, after 420 min exposure of the UV–vis light source with the degradation rate of 87.3%. Such ZnO nanostructures exhibit unique properties and have high potential for wastewater treatment.Article Citation - WoS: 1Citation - Scopus: 1Design of Demountable Reciprocal Frames With New Geometric Properties(Int. Association for Shell and Spatial Structures, 2022) Özen, Gülçin; Kiper, Gökhan; Korkmaz, KorayThis study aims to develop missing geometric knowledge for demountable reciprocal frames (RF). While designing a demountable RF, one should know the initial, in-process and final form of the RF. These processes require some specific geometric knowledge. There are some deficiencies about geometric properties in the previous studies about demountable RFs. In this study, the positions and the orientations of the nexors are found by using the Denavit-Hartenberg parameters. This information gives where the joints are placed, how they are oriented and take position according to one another. Besides, the influence of engagement length on the fan height and the base edge are analyzed. Thereby one will be able to find out how much space the RF covers with the known base edge. With the geometric knowledge obtained from this study, demountable RFs having different engagement lengths can be produced with the same nexors.Article A Novel Design Method of Deployable Semi-Regular Tessellated Surfaces With Plano-Spherical Units(Int. Association for Shell and Spatial Structures, 2022) Maral, Mesude Oraj; Korkmaz, Koray; Kiper, GökhanThe design of movable systems gives an opportunity to create transformable designs which respond to the environmental, functional, cultural, and aesthetical needs of today's architecture. This paper proposes a method for designing a family of deployable structures which can be applied to semi-regular tessellated planar surfaces such as roofs, walls, and shading devices. The generated modular approach and adaptability provides a wide usage area and various combinations for these designs. The regular convex polygon modules are designed as a network of the triangular units. The triangular unit is designed using Bennett's overconstrained plano-spherical linkage topology. The polygonal modules are assembled to each other in one-uniform semi-regular tessellations. The assembly of adjacent regular convex polygons in each tessellation is examined to find a proper solution for no collision during deployment and to properly fit a surface without any gaps or overlaps in the deployed position. The assembly method for creating 1-DoF deployable surfaces and mobility calculations for a unit, the polygonal modules, and the assemblies are computed, and motion studies are demonstrated with CAD models and exemplified for a square module for motion tests in a prototype.Article Citation - WoS: 3Citation - Scopus: 3Reconstructions of Effective Parameters for a Metamaterial Antenna Via 3d-Printed Components(Taylor & Francis, 2022) Yılmaz, Hasan Önder; Yaman, FatihThis study presents the reconstruction of effective medium parameters for a double negative metamaterial slab from the knowledge of the measured/simulated S-matrix. The structure initially has been designed to embed into a patch antenna for a radar application. To observe the medium characteristics, we locate the slab in a rectangular waveguide for various orientations. The waveguide-based retrieval method is applied to find parameters regarding the biaxial anisotropic medium. Fundamental mode is used for the excitation. Additive printing technology is employed to manufacture a rectangular waveguide and its adapters for the experiments. The metallization is achieved by coating the printed structures with conductive thin layers. Experimental setups for each orientation are simulated as well. We illustrate good agreements between simulation and measurements under the fabrication tolerances. The feasibility and applicability of the additive printing technology for the investigations of the metamaterial anisotropic/bianisotropic nature is reported.Article Citation - WoS: 4Citation - Scopus: 4A Symmetrical Self-Diplexing Microstrip Antenna With Eight-Shaped Defects(Taylor & Francis, 2022) Karatay, AnılThis article aims to demonstrate the simulation and measurement results of a two-port and symmetrical microstrip antenna operating at 6.6 and 7 GHz frequencies. The essential advantages of the antenna in terms of numerical electromagnetism are that the geometry has a small electrical length at both frequencies, does not use a structure that requires extra computational load such as substrate integrated waveguide, and is symmetrical, thus reducing the mesh requirement by half. The proposed antenna was manufactured with the chemical etching method and the measurement results were presented. In addition, varying operating frequencies are shown with the aid of liquid metal to experimentally demonstrate the independent redesign/reconfigurability feature of the antenna. To further reduce the fabrication cost, the manufacturing process of the proposed antenna with the help of a 3D printer is explained, and the performance parameters are compared. Good agreement between simulations and measurements has been reported.Article Citation - WoS: 1Citation - Scopus: 1Viability of 3t3-L1 Preadipocytes Is Modulated by the Applied Frequency but Not the Exposure Duration of Low Intensity Vibratory Stimulation(World Scientific Publishing, 2022) Baskan, Öznur; Özçivici, EnginMechanical forces are the integral determinants in cell and tissue homeostasis and regeneration, and they can affect numerous biological process from proliferation to fate determination. Mechanical forces that possess low magnitude and high frequency characteristics are also known as low intensity vibrations (LIVs). These signals were studied widely on many cell types for regenerative purposes, however most of these studies select components of LIV signals (e.g., magnitude, frequency, duration, etc.) arbitrarily. Here, we addressed the effect of LIV applied frequency, LIV daily exposure time and fate induction on the viability of preadipocyte 3T3-L1 cells. For this, we performed a frequency sweep that was ranging from 30Hz to 120Hz with 15Hz increments applied for 5, 10 or 20min during quiescent growth or adipogenesis for up to 10 days. Results suggest that the applied frequency and fate induction was an important determinant of cell viability while daily exposure time had no effect. These findings contribute to the effort of optimizing a relevant mechanical stimulus that can inhibit adipogenesis.Article Citation - WoS: 2Citation - Scopus: 6Towards Integration of the Finite Element Modeling Technique Into Biomedical Engineering Education(World Scientific Publishing, 2022) Mihçin, Şenay; Çıklaçandır, SametBiomedical engineering (BME) is a multidisciplinary field, resulting in a heavy course load from different fields. We hypothesize that the engineering curriculum be tailored according to the requirements of the BME profession. In this study, we focus on the teaching of the finite element modeling (FEM) technique by redesigning the course to address the needs of the BME profession by some custom-made changes to meet the unmet needs. After the completion of the course, evaluation methods of the students were analyzed and detailed over a survey providing feedback from the students. The surveys were related to the teaching the theory of FEM, the laboratory sessions, and the project sessions. The survey results were evaluated using statistical methods. The Pearson correlation coefficient showed a linear agreement between theoretical and practical sessions indicating efficient blending of skills because of the custom-made changes. The survey analysis showed that the students were in favour of the changes, allowing them to be more resourceful and confident with their skills. The positive results indicate a positive attitude among the students towards their profession. As the course design addresses the needs of the profession allowing students to fit in better, the students might follow their own profession after graduation. A wider follow-up study might be planned next to compare the results between who received tailor-designed courses and those who did not.