Yayınlar
Koleksiyondaki öğeler
- MakaleAçık Erişim2014Scopus SJRQ3Free vibration analysis of a laminated composite beam with various boundary conditions
Balci, Murat; Nalbant, Mustafa Oǧuz; Kara, Ercan; Gündoǧdu, Ömer
This study presents a free vibration analysis of a laminated composite beam, based on the Euler-Bernoulli beam theory. A numerical model of the laminated composite beam was obtained for various boundary conditions based on different length-to-thickness ratios for a number of layers, using the finite element method. A planar beam bending element with two nodes, each having two degrees of freedom, was chosen according to Euler-Bernoulli beam theory. The natural frequencies of the laminated composite beam were obtained for each case, and presented in such a way as to display the effect of these changes on the natural frequencies. Eight natural frequencies of clamped-free, clamped-clamped (CC) and simple-simple (SS) composite beams were first obtained for different length-to-thickness ratios (Lx /h), numbers of layers, layer angles and for their different positions. It can be seen that natural frequencies decrease for all modes with increasing length-to-thickness ratio in all cases.
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İncele - MakaleYalnız künye2015Scopus SJRQ2Analytical solution of a contact problem and comparison with the results from FEM
Öner, Erdal; Yaylaci, Murat; Birinci, Ahmet
This paper presents a comparative study of analytical method and finite element method (FEM) for analysis of a continuous contact problem. The problem consists of two elastic layers loaded by means of a rigid circular punch and resting on semi-infinite plane. It is assumed that all surfaces are frictionless and only compressive normal tractions can be transmitted through the contact areas. Firstly, analytical solution of the problem is obtained by using theory of elasticity and integral transform techniques. Then, finite element model of the problem is constituted using ANSYS software and the two dimensional analysis of the problem is carried out. The contact stresses under rigid circular punch, the contact areas, normal stresses along the axis of symmetry are obtained for both solutions. The results show that contact stresses and the normal stresses obtained from finite element method (FEM) provide boundary conditions of the problem as well as analytical results. Also, the contact areas obtained from finite element method are very close to results obtained from analytical method; disagree by 0.03-1.61%. Finally, it can be said that there is a good agreement between two methods.
AtıfScopus84WoS84OpenAlex35İncele - MakaleAçık Erişim2014Scopus SJRQ1Microwave method for reference-plane-invariant and thickness-independent permittivity determination of liquid materials
Hasar, U.C.; Kaya, Y.; Bute, M.; Barroso, J.J.; Ertugrul, M.
An attractive transmission-reflection method based on reference-plane invariant and thickness-independent expressions has been proposed for accurate and unique retrieval of complex permittivity of dielectric liquid samples. The method uses both branch-index-independent expressions and a restricted solution set for determining unique and fast complex permittivities. A 2D graphical method has been applied to demonstrate the operation and validation of the proposed method. A uncertainty analysis has been performed to monitor how the accuracy of the proposed method can be improved by a correct selection of sample holder properties. Scattering parameter measurements of two tested reference liquids (distilled water and methanol) have been carried out for comparison of various techniques with the proposed one when the reference-planes and sample thickness are not precisely known. We note from the comparison that whereas other techniques are seriously affected by imprecise knowledge of both reference-planes and sample thickness, the proposed method removes this restriction.
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İncele - MakaleYalnız künye2016Scopus SJRQ1Melt Cleanliness Comparison of Chlorine Fluxing and Ar Degassing of Secondary Al-4Cu
Çolak, Murat; Kayikci, Ramazan; Dispinar, Derya
The treatment of liquid aluminum prior to casting typically consists of purging gas and/or fluxes through the melt. By the use of several chemicals during these operations, several environmental problems can occur. Therefore, in this study, the melt cleanliness of Al-4Cu secondary alloy was investigated by comparing the use of argon degassing with or without chlorine fluxing. Reduced pressure test was used to assess the melt quality. Highest quality melt was obtained by Ar degassing with preheated graphite lance without the need to use any chemicals.
AtıfScopus14WoS11OpenAlex13İncele - MakaleYalnız künye2018Scopus SJRQ1Determination of powder flow properties of skim milk powder produced from high-pressure homogenization treated milk concentrates during storage
Mercan, Emin; Sert, Durmuş; Akın, Nihat
The aim of this study was to determine effects of high-pressure homogenization (HPH) treatment to milk concentrates on powder flow properties of skim milk powders (SMP). For this purpose, SMP samples were produced from skim milk concentrates which were HPH treated at 0 (control), 50, 100 and 150 MPa. SMP samples were stored 180 days at 20 and 40 °C and caking, cohesion and powder flow speed dependency test (PFSD) were performed using a Powder Flow Analyzer. HPH treatment decreased cohesion and caking properties of SMPs. At the 0. day, cake strength of SMPs from HPH treated concentrates varied from 0.43-2.70 mN.m, whereas cake strength of SMP-0 (control) was 8.20 mN.m. Cohesion index (CI) of samples ranged from 6.80-15.74 mm during storage. Based on CI, SMPs from HPH treated concentrates showed free and easy flowing flow behavior during storage at 20 and 40 °C. In addition, cohesion index at four speeds indicated that SMP from HPH treated concentrates were more flowable at even lower flow speeds then SMP-0. PFSD test verified that all SMP samples showed more free-flowing characteristics with increasing flow speeds. Flow stability of samples ranged from 0.95-1.15 and also flow stability of SMP-0 increased during storage at both 20 and 40 °C. The results revealed that HPH treatment to milk concentrates could improve powder flow properties of skim milk powders.
AtıfScopus47WoS41OpenAlex51İncele - MakaleAçık Erişim2018Primary school teachers' practices and troubles with the students who they think have undiagnosed difficulties in verbal communication, reading and writing
Ergen, Yusuf; Elma, Cevat
The primary school Turkish program was basically built on three learning domains. These are the learning domains of verbal communication, reading and writing. The purpose of the present study is to determine primary school teachers’ practices and difficulties related to students considered to have undiognosed verbal communication, reading and writing difficulties. The study used the phenomenological research design, one of the qualitative research designs. The sample of the study was composed of a total of 21 primary school teachers servicing in the province of Bayburt during the 2016-2017 educational year. The sample of the study was determined by using the maximum variation sampling method, one of the purposeful sampling methods. The study data was collected through using the semi-structured interview form. In the analysis of the data, the content analysis method was used. Based on the study results, it was concluded that the primary school teachers more frequently carried out the practices of 'speaking in front the class about daily events' for the students having speaking difficulties, 'using the smart board' for the students with listening difficulties, 'one-to-one reading with the teacher' for the students with reading difficulties and 'one-to-one dictation work' for the students with writing difficulties; they more frequently had problems related to the 'timid behaviors' of the students with speaking difficulties, 'losing attention' of the students with listening difficulties and the 'poor time management skills' of the students with reading and writing difficulties; they also expected help from families in all the learning domains.
AtıfScopus2OpenAlex2İncele - MakaleAçık Erişim2019Scopus SJRQ2Optical, surface and magnetic properties of the Ti-doped GaN nanosheets on glass and PET substrates by thermionic vacuum arc (TVA) method
Pat, Suat; Korkmaz, Şadan; Özen, Soner; Şenay, Volkan
Room-temperature ferromagnetism of GaN and doped GaN materials has been reported in nanostructured form. Especially, nanoparticles show ferromagnetic properties at room temperature. In this paper, Ti-doped effects on GaN were deposited on glass and Polyethylene terephthalate (PET) substrates by thermionic vacuum arc and their room temperature magnetic properties are presented for the first time. The structure of the Ti-doped GaN was crystallized in a novel form, nano honeycomb formation. Optical and surface properties of the nano honeycombs and honeycomb nanosheets were determined. GaN and TiN phases were detected in X-ray diffraction patterns. Field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) device were used for imaging of the crystal structure. According to FESEM images, hexagonal crystal formations were detected for all samples. Crystal formations are very good oriented on PET substrates materials according to glass samples. The band gap value of the sample is changed by crystallization dimension. It was found that increasing crystallizations and decreasing crystal dimensions were increased the band gap of the Ti-doped GaN approximately 50 meV. Fourier transform infrared spectra and a vibrating sample magnetometer results were presented. These results confirm the Ti doped GaN honeycomb nanosheets and nano honeycombs show the room temperature ferromagnetic properties.
AtıfScopus8WoS6OpenAlex8İncele - MakaleYalnız künye2017Scopus SJRQ2Solar Pond Window Technology for Energy-Efficient Retrofitting of Buildings: An Experimental and Numerical Investigation
Cuce, Erdem; Cuce, Pinar Mert
Windows are responsible for an important proportion of heat loss from building envelope due to inadequate insulative characteristics of traditional glazing products. In this respect, advanced glazing solutions are of vital importance to mitigate energy demand of buildings, thus to reduce carbon emissions. Therefore, in this research, a novel glazing technology called solar pond window is introduced, and it is numerically and experimentally investigated for different design configurations. The optimum design of this novel glazing covers four 5-mm-thick glass panes, two 20-mm-thick water layers, and one 20-mm-thick Krypton layer in the middle. The average heat transfer coefficient (U-value) of the optimum case is found to be about 0.40 W/m 2 K. If air is used as insulative gas in the interlayer, the U-value of the glazing is determined to be around 0.90 W/m 2 K, which is still competitive with the U-value range of argon-filled triple-glazed windows with low-e coatings. The fabrication cost of the optimum design of solar pond window is around €120/m 2. Overall, solar pond window technology is a cost-effective and energy-efficient glazing, which has a great potential to be the future of fenestration products as well as being capable of meeting the latest building fabric standards.
AtıfScopus10WoS7OpenAlex9İncele - MakaleYalnız künye2016Scopus SJRQ2Examination of the 8th grade students' TIMSS mathematics success in terms of different variables1
Kaleli-Yılmaz, Gül; Hanci, Alper
The aim of this study is to determine how the TIMSS mathematics success of the 8th grade students differentiates according to the school type, gender, mathematics report mark, parents' education level, cognitive domains and cognitive domains by gender. Relational survey method was used in the study. Six-hundred fifty two 8th grade students studying in the same city in Turkey participated in this study. In this study, a 45 question test that was made up by choosing TIMSS 2011 mathematics questionnaire was used as a data collection tool. Quantitative data analysis methods were used in the data analysis, frequency, percentage, average, standard deviation, independent sample test, one-way analysis of variance and post-hoc tests were applied to data by using SPSS packaged software. At the end of the study, it was determined that the school type, mathematics school mark, parents' education level and cognitive domains influenced the students' TIMSS mathematics success but their gender was a neutral element. Moreover, it was seen that schools which are really successful in national exams are more successful in TIMSS exam; students whose mathematics school marks are 5 and whose parents graduated from university are more successful in TIMSS exams than others.
AtıfScopus12WoS11OpenAlex18İncele - MakaleAçık Erişim2015Scopus SJRQ1The effects of heat treatment on the synthesis of nickel ferrite (NiFe2O4) nanoparticles using the microwave assisted combustion method
Karcioʇlu Karakaş, Zeynep; Boncukcuoʇlu, Recep; Karakaş, Ibrahim Hakki; Ertuʇrul, Mehmet
NiFe2O4nanoparticles were synthesized using the microwave assisted combustion method based on metal nitrate salts and urea. To remain of organic matters and to stabilize the particles, samples were thermally treated at various temperatures from 300-800 °C. The prepared samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) thermogravimetric analysis (TGA) and vibrating sample magnetometry (VSM). The heat treated samples show the reflection planes of (111), (220), (222), (311), (400), (422), (511), and (440) which perfectly confirm to a cubic spinel phase of NiFe2O4and no secondary phases were detected in the XRD patterns of the samples. The crystallite sizes calculated using the Debye-Scherrer formula were found to increase with the heat treatment temperature, from about 4 nm at 300 °C-85 nm at 800 °C. EDX results verify that the compositional mass rations were relevant, as expected from the synthesis. The micrographs of SEM and TEM showed that all of the samples have nano-crystalline behavior and particles indication cubic shape. Magnetization measurements were obtained at room temperature by using a VSM, which demonstrated that the all of the samples synthesized with heat treatment exhibited ferromagnetic behaviors.
AtıfScopus96WoS86OpenAlex95İncele - MakaleYalnız künye2017Scopus SJRQ3Continuous contact problem of a functionally graded layer resting on an elastic half-plane
Öner, E.; Adiyaman, G.; Birinci, A.
In this study, the continuous contact problem of a functionally graded layer resting on an elastic half-plane and loaded by a rigid rectangular stamp is examined. The problem is solved assuming that the functionally graded (FG) layer is isotropic and the shear modulus and mass density vary exponentially throughout the layer's thickness. However, the body force of the elastic half-plane is neglected. In addition, it is assumed that all surfaces are frictionless and only compressive stress is transferred along the contact surfaces. The mathematical problem is reduced to a singular integral equation in which the contact stress under the rigid stamp is unknown using the Fourier integral transform and boundary conditions related to the problem. This singular integral equation is solved numerically using the Gauss-Chebyshev integration formula. The dimensionless contact stress under the rigid stamp, the initial separation loads and the initial separation distances between the FG layer and the elastic half-plane are obtained for various dimensionless quantities.
AtıfScopus26İncele - BildiriAçık Erişim2017Determination of K shell XRF parameters and K to L shell vacancy transfer probabilities of ferromagnetic 3d transition metals
Allm, Bünyamin; Uǧurlu, Mine; Han, Ibrahim; Demir, Lütfü
In this study, K shell X-ray fluorescence cross-sections (σKα, σKβ and σK), K shell fluorescence yields (ωK) and K to L shell vacancy transfer probabilities (ηKL) of ferromagnetic 3d transition metals (Fe, Co, Ni) were investigated to understand how the relationship between ferromagnetism and these values changes with atomic number by using energy dispersive X-ray fluorescence (EDXRF) technique. The all obtained experimental and theoretical results were comparatively given as a function of the atomic number. It was clearly observed that all of the investigated parameters depend on the atomic number and the ferromagnetism state of the atom.
AtıfScopus3WoS2OpenAlex5İncele - MakaleAçık Erişim2016Scopus SJRQ2Embedding analogical reasoning into 5E learning model: A study of the solar system
Devecioglu-Kaymakci, Yasemin
The purpose of this study was to investigate how the 5E learning model affects learning about the Solar System when an analogical model is utilized in teaching. The data were gathered in an urban middle school 7th grade science course while teaching relevant astronomy topics. The analogical model developed by the researchers was administered to 20 seventh grade students in a city of the Black Sea Region in Turkey. "The Solar System and Beyond: The space puzzle" unit was taught by using 5E learning model accompanied by analogical model during two class hours. In this case study, pre-experimental design with pre-test-post-test was used to collect data through questionnaire, reflective thinking scale, video recording, and informal observations. According to the findings of this study, the teaching intervention not only significantly increased the students' academic achievement but also improved their science process skills. The study suggests that analogies should be well-planned and deployed for teaching science courses. Furthermore, the number of the analogical models in textbooks should be increased to enrich meaningful learning for students' transition levels between concrete and abstract operational terms.
AtıfScopus16OpenAlex23İncele - MakaleYalnız künye2014Scopus SJRQ1Purification and characterization of an alkaline pectin lyase produced by a newly isolated brevibacillus borstelensis (p35) and its applications in fruit juice and oil extraction
Demir, Nazan; Nadaroglu, Hayrunnisa; Demir, Yasar; Isik, Ceyhun; Taskin, Esen; Adiguzel, Ahmet; Gulluce, Medine
An alkaline pectin lyase (Pnl) (EC 4.2.2.10) secreted by Brevibacillus borstelensis P35 (genBank number: FJ417406) was purifed using ammonium sulfate fractionation, anion exchange chromatography on DEaE-cellulose and gel fltration chromatography on Sephadex g-150. The pH and temperature optima of the enzyme were found to be 8.0 and 60 °C. The enzyme does not loose activity up to 60 °C if exposed for 1 h. The values of Kmand Vmax of the enzyme were 0.625 mg/ml and 126.32 s-1, respectively. The molecular weight was found to be 36 ± 01 kDa. The presence of 10 mM concentration of Ca2+, Cu2+, Mn2+, Mg2+, Zn2+, Hg2+, Fe2+ and EDTa, L-cystein, ascorbic acid signifcantly enhanced the Pnl of the purifed enzyme. In the course of the laboratory trials, it was demonstrated that Pnl from B. borstelensis (P35) could be successfully applied to the production and clarif-cation of fruit juice and oil extraction.
AtıfScopus36WoS31OpenAlex35İncele - MakaleAçık Erişim2015The effect of dynamic geometry software and physical manipulatives on candidate teachers’ transformational geometry success
Yılmaz, Gül Kaleli
This study aims to investigate the effects of using Dynamic Geometry Software (DGS) Cabri II Plus and physical manipulatives on the transformational geometry achievement of candidate teachers. In this study, the semiexperimental method was used, consisting of two experimental and one control groups. The samples of this study were 117 students. A 30-question test which was prepared based on the relative literature and expert opinion was used as a data collection tool. The test includes sections on recognition, features, and construction, and each section consists of ten questions. The data obtained from the pre- and post-tests were analyzed using the SPSS program. As a result of the statistical analysis, success levels of all groups were found to be the same before the applications, but after the applications, students’ transformational geometry success was found to significantly increase. When group success was analyzed, it was seen that the Computer Group placed first, the Manipulatives Group placed second, and the Traditional Group placed third in the sections of recognition and features. In the construction section, the Computer and Manipulatives Groups’ success levels were equal, and both groups were significantly more successful than the Traditional Group. The exercises performed with all groups increased their success levels significantly, thus showing that the applications were effective.
AtıfScopus7OpenAlex9İncele - MakaleYalnız künye2019Scopus SJRQ1Rotation invariant curvelet based image retrieval & classification via Gaussian mixture model and co-occurrence features
Engin, M. Alptekin; Cavusoglu, Bulent
Demand for better retrieval methods continue to outstrip the capabilities of available technologies despite the rapid growth of new feature extraction techniques. Extracting discriminatory features that contain texture specific information are of crucial importance in image indexing. This paper presents a novel rotation invariant texture representation model based on the multi-resolution curvelet transform via co-occurrence and Gaussian mixture features for image retrieval and classification. To extract these features, curvelet transform is applied and the coefficients are obtained at each scale and orientation. The Gaussian mixture model (GMM) features are computed from each of the sub bands and co-occurrence features are computed for only specific sub band. Rotation invariance is provided by applying cycle-shift around the GMM features. The proposed method is evaluated on well-known databases such as Brodatz, Outex_TC_00010, Outex_TC_00012, Outex_TC_00012horizon, Outex_TC_00012tl84, Vistex and KTH-TIPS. When the feature vector is analyzed in terms of its size, it is observed that its dimension is smaller than that of the existing rotation-invariant variants and it has a very good performance. Simulation results show a good performance achieved by combining different techniques with the curvelet transform. Proposed method results in high degree of success rate in classification and in precision-recall value for retrieval.
AtıfScopus8WoS5OpenAlex6İncele - MakaleAçık Erişim2014Scopus SJRQ2Solution of a receding contact problem using an analytical method and a finite element method
Öner, Erdal; Yaylaci, Murat; Birinci, Ahmet
In this study, a receding contact problem for two elastic layers supported by a Winkler foundation is handled using two different methods such as an analytical method and a finite element method. Firstly, the problem is solved analytically using linear elasticity theory. Then, in order to solve the same problem in a different way, a finite element model of the problem is created by ANSYS software, and finite element analysis of the problem is performed. The contact stresses and the contact areas at the interfaces between punch-Layer 2 and Layer 1-Layer 2 are obtained for both solutions, and it is shown that the finite element method indicates a good agreement with the analytical method.
AtıfScopus36WoS37OpenAlex25İncele - MakaleYalnız künye2015Scopus SJRQ1A novel approach based on DEMATEL method and patent citation analysis for prioritizing a portfolio of investment projects
Altuntas, Serkan; Dereli, Türkay
The aim of this article is to propose a novel approach based on a method called Decision-Making Trial and Evaluation Laboratory (DEMATEL) and patent citation analysis for prioritizing the portfolio of investment projects. The proposed approach reflects the government's perspective and takes into account two important prioritization criteria. They are: (i) the decreasing rate of foreign trade deficits in the country and (ii) the potential to attract new investments which are not considered in the literature before. A case study from Turkey is presented to demonstrate the benefits of the proposed approach. The findings show that the proposed approach can be used easily and efficiently to prioritize investment projects among available project proposals.
AtıfScopus118WoS92İncele - MakaleAçık Erişim2017Scopus SJRQ3Debaryomyces hansenii as a new biocatalyst in the asymmetric reduction of substituted acetophenones
Şahin, Engin
Chiral secondary alcohols are convenient mediator for the synthesis of biologically active compounds and natural products. In this study fifteen yeast strains belonging to three food originated yeast species Debaryomyces hansenii, Saccharomyces cerevisiae and Hanseniaspora guilliermondii were tested for their capability for the asymmetric reduction of acetophenone to 1-phenylethanol as biocatalyst microorganisms. Of these strains, Debaryomyces hansenii P1 strain showed an effective asymmetric reduction ability. Under optimized conditions, substituted acetophenones were converted to the corresponding optically active secondary alcohols in up to 99% enantiomeric excess and at high conversion rates. This is the first report on the enantioselective reduction of acetophenone by D. hansenii P1 from pastırma, a fermented Turkish meat product. The preparative scale asymmetric bio reduction of 3-methoxy acetophenone 1g by D. hansenii P1 gave (R)-1-(3-methoxyphenyl) ethanol 2g 82% yield, and >99% enantiomeric excess. Compound 2g can be used for the synthesis of (+)-NPS-R-568 [3-(2-chlorophenyl)-N-[(1R)-1-(3-methoxyphenly) ethyl] propan-1-amine] which have a great potential for the treatment of primary and secondary hyper-parathyroidism. In addition, D. hansenii P1 successfully reduced acetophenone derivatives. This study showed that this yeast can be used industrially to produce enantiomerically pure chiral secondary alcohols, which can be easily converted to different functional groups.
AtıfScopus25WoS24OpenAlex26İncele - MakaleAçık Erişim2016Scopus SJRQ1Effects of in situ exopolysaccharide production and fermentation conditions on physicochemical, microbiological, textural and microstructural properties of Turkish-type fermented sausage (sucuk)
Dertli, Enes; Yilmaz, Mustafa Tahsin; Tatlisu, Nevruz Berna; Toker, Omer Said; Cankurt, Hasan; Sagdic, Osman
In this work, the role of in situ exopolysaccharide (EPS) production under different fermentation conditions on physicochemical, microbiological, textural and microstructural properties of sucuk was determined. For this purpose, the effect of EPS producing strains (control, strain 1, strain 2 and mixture) and fermentation conditions (fermentation temperature; 14, 16 and 18 °C and time; 8, 12 and 16 days) on physicochemical, microbiological, textural and microstructural properties were investigated using response surface methodology. In situ EPS production was observed to remarkably affect these properties while fermentation conditions were also seen to dominantly influence the physicochemical properties of sucuk, revealing that the ripening temperature appeared to be more determinant factor. EPS producing cultures enhanced the textural properties of sucuk which became harder, less adhesive and tougher. The microstructural analysis revealed the formation of web-like structure by in situ EPS production in sucuk mix during fermentation process. This study revealed the importance of in situ EPS production on final technological properties of sucuk.
AtıfScopus48WoS43OpenAlex54İncele
