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- MakaleAçık Erişim2016Scopus SJRQ2Practical implementation and stability analysis of ALOHA-Q for wireless sensor networks
Kosunalp, Selahattin; Mitchell, Paul Daniel; Grace, David; Clarke, Tim
This paper presents the description, practical implementation, and stability analysis of a recently proposed, energy-efficient, medium access control protocol for wireless sensor networks, ALOHA-Q, which employs a reinforcement-learning framework as an intelligent transmission strategy. The channel performance is evaluated through a simulation and experiments conducted using a real-world test-bed. The stability of the system against possible changes in the environment and changing channel conditions is studied with a discussion on the resilience level of the system. A Markov model is derived to represent the system behavior and estimate the time in which the system loses its operation. A novel scheme is also proposed to protect the lifetime of the system when the environment and channel conditions do not sufficiently maintain the system operation.
AtıfScopus7WoS3OpenAlex8
İncele - MakaleAçık Erişim2017Scopus SJRQ2Efficiency improvement of gas turbine cogeneration systems; [Poboljšanje učinkovitosti kogeneracijskih sustava plinske turbine]
Karaali, Rabi; Öztürk, İlhan Tekin
In this study eight methods are evaluated for a gas turbine cogeneration cycle to improve the efficiency. These methods are increasing gas turbine inlet air temperature, cooling the inlet air of the compressor, air preheating, fuel preheating, increasing compressor inlet air pressure, increasing air excess rates, steam injection, and humidification of the inlet air of the compressor. These methods are studied in order to compare their effects on the performance of the systems. The effects of these methods on the exergetic efficiency depend on the kind of the cogeneration cycle. By combining recuperation, preheating fuel and steam injection methods high efficiency can be achieved. The combined methods give the best results under variable heat demands of the market. An appropriate combination of the efficiency improvement methods may increase the exergetic efficiency about 20 %. The results show that efficiency improvement methods must be applied together whenever it is possible.
AtıfScopus8WoS6OpenAlex15İncele - MakaleAçık Erişim2015Scopus SJRQ2The effect of fly ash to self-compactability of pumice aggregate lightweight concrete
Kurt, Murat; Aydin, Abdulkadir Cüneyt; Gül, Muhammed Said; Gül, Rüstem; Kotan, Türkay
This paper presents the results of an experimental study on the effects of fly ash, different water/(cement + mineral additive) ratios and pumice aggregates to some physical and mechanical properties of self-compacting lightweight aggregate concrete. In this study, pumice had been used as lightweight aggregates. Several properties of self-compacting pumice aggregate lightweight concretes like the unit weight, flow diameter, T50 time, flow diameter after an hour, V-funnel time, and L-box tests, 7, 28, 90 and 180-day compressive strength, 28-day splitting tensile strength, dry unit weight, water absorption, thermal conductivity and ultrasonic pulse velocity tests were investigated. For this purpose, 18 series of concrete samples were prepared in two groups. Pumice aggregate was used as a replacement of natural aggregate, at the levels of 0, 20, 40, 60, 80, and 100% by volume. Furthermore, a second series of 100% pumice aggregate was used for the production of self-compacting lightweight aggregate concrete with constant w/(c + m) ratios as 0.35, 0.40, and 0.45 by weight. The flow diameters, T50 times, paste volumes, 28-day compressive strengths, dry unit weights and thermal conductivities of self-compacting lightweight aggregate concrete were obtained in the range of 600–800 mm, 2–8 s, 471–572 lt/m 3, 9.2–53.26 MPa, 839–2156 kg/m 3 and 0.321–1.508 W/mk, respectively, which satisfies not only the strength requirement of semi-structural lightweight concrete but also the flowing ability requirements and thermal conductivity requirements of self-compacting lightweight aggregate concrete.
AtıfScopus30OpenAlex36İncele - BildiriYayıncıda açık erişim2017Thermal and Acoustic Properties of Aerogels: Preliminary Investigation of the Influence of Granule Size
Moretti, Elisa; Merli, Francesca; Cuce, Erdem; Buratti, Cinzia
The influence of granules size in silica aerogels is experimentally investigated in terms of thermal and acoustic performance characteristics. The transmission loss (TL) is measured at normal incidence in a traditional impedance tube, whereas the thermal conductivity (λ) is evaluated using a Hot Plate apparatus, setting up an appropriate methodology, due to the nature of the sample. The results reveal that the small granules (granules size in the 0.01-1.2 mm range), which have the highest density, have the best performance both in terms of thermal and acoustic properties. Depending on the granules size, λ varies in 19-22 mW/mK range at 10°C, whereas a TL equal to 13 dB at about 6400 Hz for 20 mm thickness is obtained for small granules.
AtıfScopus58WoS46OpenAlex63İncele - MakaleAçık Erişim2016Scopus SJRQ1Novel glazing technologies to mitigate energy consumption in low-carbon buildings: A comparative experimental investigation
Cuce, Erdem; Cuce, Pinar Mert; Riffat, Saffa
Buildings play a key role in total world energy consumption as a consequence of poor thermal insulation characteristics of facade materials. Among the elements of a typical building envelope, windows are responsible for the greatest energy loss because of their notably high overall heat transfer coefficients. About 60% of heat loss through the building fabric can be attributed to the glazed areas. In this respect, novel cost-effective glazing technologies are needed to mitigate energy consumption, and thus to achieve the latest targets toward low/zero carbon buildings. Therefore in this study, three unique glazing products called vacuum tube window, heat insulation solar glass and solar pond window which have recently been developed at the University of Nottingham are introduced, and thermal performance analysis of each glazing technology is done through a comparative experimental investigation for the first time in literature. Standardized co-heating test methodology is performed, and overall heat transfer coefficient (U-value) is determined for each glazing product following the tests carried out in a calibrated environmental chamber. The research essentially aims at developing cost-effective solutions to mitigate energy consumption because of windows. The results indicate that each glazing technology provides very promising U-values which are incomparable with conventional commercial glazing products. Among the samples tested, the lowest U-value is obtained from the vacuum tube window by 0.40W/m2K, which corresponds to five times better thermal insulation ability compared to standard air filled double glazed windows.
AtıfScopus35WoS33OpenAlex37İncele - BildiriAçık Erişim2017Scopus SJRQ3Effect of copper addition to aluminium alloys on surface roughness in terms of turning operation
Özen, F.; Fiçici, F.; Dündar, M.; Çolak, M.
Aluminium alloys have found usage in numerous industries due to some superior properties, such as high strength-to-weight ratios and high oxidation resistance. Aluminum alloys can be strengthened by some techniques. One of them, the most practical one, is precipitation hardening in aluminum alloys. By adding Cu, aluminum gains strength and hardness. In this work the machinability of unalloyed aluminum and aluminum alloyed with 4% and 8% of Cu have been investigated. Machinability assessment was executed in terms of surface roughness during turning operation. Specimens were manufactured by sand casting method, which is a commonly utilized casting operation. In machinability experiments, three different cutting tool materials were employed. Three different cutting speeds and three different feed rates have been used. Effect of these feeds, speeds and cutting tool materials on surface roughness has been studied. In addition, effect of Cu addition to aluminum alloys on surface roughness has been examined.
AtıfScopus9WoS6OpenAlex10İncele - BildiriYalnız künye2013Nonlinear analysis of structures by Total Potential Optimization using Metaheuristic Algorithms (TPO/MA)
Toklu, Y.C.; Bekdaş, G.; Temür, R.; Toklu, Ş.Ç.; Uzun, F.
Structural analysis problems can be formulized as either root finding problems, or optimization problems. The general practice is to choose the first option directly or to convert the second option again to a root finding problem by taking relevant derivatives and equating them to zero. The second alternative is used very randomly as it is and that only for some simple demonstrative problems, most probably due to difficulty in solving optimization problems by classical methods. The method called Total Potential Optimization using Metaheuristic Algorithms (TPO/MA) described in this study successfully enables handling structural problems with optimization formulation. Using metaheuristic algorithms provides additional advantages in dealing with all kinds of constraints.
AtıfScopus1İncele - MakaleAçık Erişim2016Scopus SJRQ1Effects of grain size on room temperature deformation behavior of Zn–22Al alloy under uniaxial and biaxial loading conditions
Cetin, M.E.; Demirtas, M.; Sofuoglu, H.; Cora, Ö.N.; Purcek, G.
Effects of grain size on room temperature (RT) deformation behavior of superplastic Zn–22Al alloy under uniaxial and biaxial loading conditions were investigated. Two–step equal channel angular pressing (ECAP) and subsequent annealing processes were applied to the alloy in order to obtain microstructures with various grain sizes ranging from submicron to micron sizes. Grain size of 200 nm was achieved after ECAP of the alloy, and it was increased up to ~2.60 µm by annealing at 250 °C for different time periods. Changes in deformation behaviors of the alloy with various grain sizes were found to be in good agreement under the uniaxial tensile and biaxial Erichsen test conditions. Increasing grain size decreased both the maximum elongation under uniaxial deformation and limiting dome height (LDH) under biaxial deformation. The high elongation to failure and LDH values for the samples with submicron grain size were attributed to their high strain rate sensitivity.
AtıfScopus20WoS19OpenAlex21İncele - MakaleYalnız künye2019Scopus SJRQ2An approach to neutrosophic graph theory with applications
Şahin, Rıdvan
Graph theory that can be used to describe the relationships among several individuals has numerous applications in diverse fields such as modern sciences and technology, database theory, data mining, neural networks, expert systems, cluster analysis, control theory, and image capturing. As a generalization of fuzzy set (FS) and intuitionistic fuzzy set (IFS), the concept of neutrosophic set is a more functional tool for handling indeterminate, inconsistent and uncertain information that exist in real life compared to FSs and IFSs. In this paper, we apply the graph theory to the single-valued neutrosophic sets and investigate a new kind of graph structure which is called single-valued neutrosophic graphs and is generalized the results concerning crisp graphs, fuzzy graphs and intuitionistic fuzzy graphs. Then we describe some of their theoretical properties, such as the Cartesian product, composition, union and join. By applying two different procedures to solve single-valued neutrosophic decision-making problems, a neutrosophic graph-based multicriteria decision-making model is developed to consider relationships among the multi-input arguments which cannot be handled well by means of the existing methods. Finally, two illustrative examples are given to demonstrate the applicability, feasibility, effectiveness and advantages of these two proposed approaches.
AtıfScopus38WoS21OpenAlex31İncele - MakaleAçık Erişim2014Scopus SJRQ2Identification of structural and spectral features of synthesized cyano-stilbene dye derivatives: A comparative experimental and DFT study
Karabacak, M.; Asiri, A.M.; Al-Youbi, A.O.; Qusti, A.H.; Cinar, M.
The synthesized three dye derivatives of cyano-stilbene monomer were identified by experimental spectroscopic techniques and density functional approach. The optimized geometrical structure, vibrational and electronic transitions along with the nonlinear optical (NLO) properties of those compounds were presented in this study. The vibrational spectra of investigated compounds were recorded in solid state with FT-IR and FT-Raman spectrometry in the range of 4000-400 cm-1 and 3600-50 cm-1, respectively. The theoretical ground state equilibrium conformations and vibrational wavenumbers were carried out by using density functional method with 6-311G(d,p) basis set. Assignments of the fundamental vibrational modes were examined on the basis of the measured data and total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanical (SQM) method. The UV absorption spectra of monomers were observed in the range of 200-600 nm in chloroform, acetonitrile and toluene, and time dependent DFT method was used to obtain the electronic properties. The linear polarizability and first hyperpolarizability of the studied molecules indicates that the title compounds can be used as a good nonlinear optical material. A detailed description of spectroscopic behaviors of compounds was given based on the comparison of experimental measurements and theoretical computations.
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İncele - MakaleAçık Erişim2015Scopus SJRQ1Improvement of high strain rate and room temperature superplasticity in Zn-22Al alloy by two-step equal-channel angular pressing
Demirtas, M.; Purcek, G.; Yanar, H.; Zhang, Z.J.; Zhang, Z.F.
The Zn-22Al alloy was subjected to equal-channel angular pressing (ECAP) to improve its high strain rate (HSR) superplasticity at room temperature (RT). A well-designed two-step ECAP process formed an ultrafine-grained (UFG) microstructure with an average grain size of 200nm as the lowest one obtained so far after ECAP processing of this alloy. Also, agglomerate- and texture-free microstructure with UFG Al-rich α- and Zn-rich η-grains separated mostly by high-angle grain boundaries (HAGBs) was produced by this process. The maximum RT elongation was achieved to be 400% with a strain rate sensitivity of 0.30 at a very high strain rate of 5×10-2s-1 after the two-step ECAP process. This elongation value is the highest one obtained at RT and at all strain rates for this alloy up to now. The current results demonstrate that such an improvement in superplasticity of Zn-22Al alloy after the two-step ECAP process can enhance its applications where RT and HSR superplasticity are strongly needed.
AtıfScopus48OpenAlex48İncele - MakaleYalnız künye2017Scopus SJRQ2Harvesting of microalgae via submerged membranes: Flux, fouling and its reversibility
Elcik, Harun; Cakmakci, Mehmet
The purpose of this study was to investigate membrane fouling caused by microalgal cells in submerged membrane systems consisting of polymeric and ceramic microfiltration membranes. In this study, one polymeric (flat-sheet, pore size: 0.2 μm) and two ceramic (flat-sheet, pore size: 0.2 μm and cylindrical, pore size: 1 μm) membranes were used. Physical cleaning was performed with water and air to determine the potential for reversible and irreversible membrane fouling. The study results showed that substantial irreversible membrane fouling (after four filtration cycles, irreversible fouling degree 27% (cleaning with water) and 38% (cleaning with air)) occurs in the polymeric membrane. In cleaning studies performed using water and air on ceramic membranes, it was observed that compressed air was more effective (recovery rate: 87-91%) for membrane cleaning. The harvesting performance of the membranes was examined through critical flux experiments. The critical flux values for polymeric membrane with a pore size of 0.20 μm and ceramic membranes with a pore size of 0.20 μm and 1 μm were ≤ 95 L/m2hour, ≤ 70 L/m2hour and ≤ 55 L/m2hour, respectively. It was determined that critical flux varies depending on the membrane material and the pore size. To obtain more information on membrane fouling caused by microalgal cells, the characterization of the fouled polymeric membrane was performed. This study concluded that ceramic membranes with a pore size of 0.2-1 μm in the submerged membrane system could be efficiently used for microalgae harvesting by cleaning the membrane with compressed air at regular intervals.
AtıfScopus9WoS7OpenAlex7İncele - MakaleYalnız künye2017Scopus SJRQ1An accurate model for photovoltaic (PV) modules to determine electrical characteristics and thermodynamic performance parameters
Cuce, Erdem; Cuce, Pinar Mert; Karakas, Ibrahim Hakki; Bali, Tulin
Accurate and reliable modelling of photovoltaic (PV) modules is necessary for design and performance estimation of PV systems. Manufacturers of PV modules usually provide some basic electrical parameters specified at only one single operating condition, which is commonly known as standard test conditions (STCs). However, PV systems operate over a wide range of outdoor conditions, and the manufacturers’ reports do not cover sufficient information about how the PV modules react with respect to changes in the two most important environment-oriented conditions, which are solar intensity and operating cell temperature. In this respect, an accurate and reliable tool is required by designers to predict electrical characteristics and thermodynamic performance parameters of PV modules. Therefore in this research, a novel mathematical model is developed to determine solar intensity and cell temperature dependency of PV module parameters and thermodynamic efficiency figures. A simple one-diode model is proposed considering series resistance and shunt conductance. Mitsubishi PV-UJ225GA6 225 W polycrystalline silicon PV module and Kyocera KD205GH-2P 205 W multicrystal PV module are utilised for model assessment. Model results are compared with environmental chamber tests and manufacturers’ performance reports, and a very good agreement is achieved.
AtıfScopus97WoS85OpenAlex110İncele - MakaleAçık Erişim2017Scopus SJRQ3Multiple small solutions for p(x)-Schrödinger equations with local sublinear nonlinearities via genus theory
Ayazoglu Mashiyev, Rabil; Ekincioglu, Ismail; Alisoy, Gulizar
In this paper, we deal with the following p(x)-Schrödinger problem: (Formula Presented) where the nonlinearity is sublinear. We present the existence of infinitely many solutions for the problem. The main tool used here is a variational method and Krasnoselskii’s genus theory combined with the theory of variable exponent Sobolev spaces. We also establish a Bartsch-Wang type compact embedding theorem for the variable exponent spaces.
AtıfScopus7WoS7OpenAlex4İncele - MakaleYalnız künye2018Scopus SJRQ1Influence of high pressure torsion-induced grain refinement and subsequent aging on tribological properties of Cu-Cr-Zr alloy
Purcek, G.; Yanar, H.; Shangina, D.V.; Demirtas, M.; Bochvar, N.R.; Dobatkin, S.V.
Effects of ultrafine grain formation via high pressure torsion (HPT) and precipitation during aging on the microstructure, mechanical and tribological properties of a Cu-Cr-Zr alloy have been investigated systematically. HPT results in the formation of ultrafine-grained (UFG) structure in the alloy with an average grain/subgrain size of 155 nm which leads to remarkable improvement in its hardness and strength along with a reduction in elongation to failure. Aging of UFG alloy brings about further strengthening due to the precipitation. UFG formation by HPT increases substantially the wear resistance of Cu-Cr-Zr alloy and reduces the friction coefficient. The highest wear resistance and the lowest friction coefficient are obtained on the sample processed by HPT and subsequent aging. The dominant wear mechanism of the alloy varies depending on the applied processes. Adhesion with smearing is the predominant wear mechanism for the initial (warm extruded) samples having coarse-grained (CG) structure. UFG samples show less adhesional effect with less smearing, and a higher tendency to the formation of cracks, abrasion and delamination seem to be dominant in those samples. Oxidative wear mechanism is also operative in both CG and UFG alloy samples. It may be concluded from this study that a combined process including UFG formation by HPT and subsequent precipitation by artificial aging provides a simple and effective processing procedure for improving the strength, hardness and wear resistance of Cu–Cr–Zr alloys without modification of the chemical composition.
AtıfScopus96WoS91OpenAlex99İncele - MakaleAçık Erişim2018Scopus SJRQ2Synthesis and characterization of Zn-doped Mn3O4 thin films using successive ionic layer adsorption and reaction technique: Its structural, optical and wettability properties
Bayram, Ozkan; Ertargin, Mehmet Emrah; Igman, Erdal; Guney, Harun; Simsek, Onder
In this study, it is aimed to obtain Zn doped Mn3O4 (manganese oxide) nanostructured thin films on the soda lime glass substrates by successive ionic layer adsorption and reaction technique. The tetragonal crystal structure of the all thin films was detected using XRD spectroscopy. The average crystallite size of undoped Mn3O4 thin films was calculated to be 29 nm and for Zn-doped thin films, this value decreased to 23 nm with increasing Zn concentration. Characteristic peaks for thin films were also confirmed by RAMAN spectroscopy. The morphological structures of zinc-doped manganese oxide nano-sheets thin films were revealed by SEM. Using UV–Vis spectroscopy, it was found that the optical band gap of Mn3O4 thin films decreased from 2.05 to 1.73 eV with Zn doping. It has also been understood from the wettability analyzes of thin films that all thin films have a hydrophilic character. From all these analyzes, it is thought that the Zn doped Mn3O4 thin films have the potential to be used in supercapacitor applications.
AtıfScopus25WoS22OpenAlex25İncele - MakaleAçık Erişim2017Scopus SJRQ3Comparison of writing anxiety and writing dispositions of sixth, seventh and eighth grade students
Berk, Rifat Ramazan; Ünal, Emre
The purpose of this study is to determine sixth, seventh and eighth grade students' writing anxiety and dispositions and to examine to what extent they predict each other. The basis of this study is to determine whether writing disposition is the significant predictor of writing anxiety or not and whether students' grade levels and genders are significant predictor of writing anxiety and dispositions or not. The research was designed according to survey model. The study group, selected through simple sampling method, is made up of 860 students studying at 6th, 7th and 8th grades in elementary schools of Sarkisla District, Sivas. While "Writing Anxiety Scale", adapted into Turkish by özbay and Zorbay (2011), was administered to determine the study group's writing anxiety level, "Writing Disposition Scale", adapted into Turkish by Iseri and ünal (2010), was used to determine the writing disposition level. At the end of the study, it was found that writing disposition is a significant predictor of writing anxiety and students' grade levels and genders are significant predictors of writing anxiety and dispositions. An education environment to create a strong writing disposition for students is recommended. Also, similar studies on different dimensions of the issue can be conducted.
AtıfScopus9WoS4İncele - MakaleAçık Erişim2019Scopus SJRQ2Some physical properties of nanostructured Al doped ZnO thin films synthesized by RF magnetron sputtering at room temperature
Şenay, Volkan
In this research, AZO thin films were deposited on glass substrates with 70 W, 100 W and 125 W RF powers at room temperature by RF magnetron sputtering technique. The structural, optical and surface properties of the produced thin films were investigated. According to the obtained results, the investigated thin films had a crystalline structure and they showed high transparency in the visible region. The increase of RF power produced thicker films. Relatively thicker AZO films produced with higher RF power exhibited greater number of interference fringes in the reflectance and transmittance spectra. The refractive index values of the film produced with 125 W RF power were considerably lower than those of the films produced with 70 W and 100 W due to the decreased packing density. The optical energy band gap values of the produced AZO thin films were higher than that of undoped ZnO films. This expansion resulted from the Burstein–Moss effect. However, the band gap energy value as well as the roughness of the film surface decreased like refractive index with an increase in RF power, especially after 100 W. As a result, the values corresponding to the optical and surface properties can be tuned and AZO thin films can be produced by RF magnetron sputtering technique as promising candidates for optoelectronic devices and transparent conductive oxide applications.
AtıfScopus14WoS14OpenAlex13İncele - BildiriYalnız künye2013Space applications of tensegric structures
Toklu, Y.C.; Temur, R.; Bekdas, G.; Uzun, F.
Tensile integrity (tensegrity, tensegric) structures are suggested for possible use in outer space and on space bodies because of their minimal need for structural materials, ease of transfer and mounting. Structurally their behavior is non-linear. It has been shown here that their structural analysis can successfully be performed by total potential optimization using meta-heuristic algorithms (TPO/MA). The named method is an emerging technique that combines minimum energy principle of mechanics with metaheuristic algorithms. The technique thus defined has been shown to be very efficient, accurate and robust in analyzing structures. The success of the technique is especially profound for non-linear structures. In this study the named technique is applied to tensile integrity (tensegrity, tensegric) structures which are known to be highly nonlinear, thus difficult to analyze.
AtıfScopus10İncele - MakaleAçık Erişim2015Scopus SJRQ3Selective separation, preconcentration and determination of Pd(II) ions in environmental samples by coprecipitation with a 1,2,4-triazole derivative
Ozdes, Duygu; Duran, Celal; Serencam, Huseyin; Sahin, Deniz; Gundogdu, Ali; Soylak, Mustafa
A simple, sensitive, facile and low cost methodology, combined with flame atomic absorption spectrometry (FAAS), was employed to evaluate the selective separation and preconcentration of Pd(II) ions in environmental samples by using a triazole derivative as an organic coprecipitating agent without a carrier element. The developed method was systematically investigated in different set of experimental parameters that influence the quantitative recovery of Pd(II) ions. The accuracy of the method was tested by analyzing certified reference material and spike tests. The developed coprecipitation procedure has been applied to road dust, anodic slime, industrial electronic waste materials and water samples to determine their Pd(II) levels.
AtıfScopus12WoS12OpenAlex16İncele
