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Bulunan: 37 Adet 0.001 sn
Koleksiyon [12]
Tam Metin [2]
Yayın Türü [2]
Yazar [20]
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Konu Başlıkları [20]
Yayıncı [1]
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Experimental investigation of optimum thermal performance and pressure drop of water-based Al2O3, TiO2 and ZnO nanofluids flowing inside a circular microchannel

Topuz A. | Engin T. | Alper Özalp A. | Erdoğan B. | Mert S. | Yeter A.

Article | 2018 | Journal of Thermal Analysis and Calorimetry131 ( 3 ) , pp.2843 - 2863

This paper presents thermal performance and pressure drop characteristics of water-based nanofluids flowing through a horizontal circular microchannel under the constant surface temperature condition, experimentally. Al2O3 (13 nm), TiO2 (10–25 nm) and ZnO (18 nm) nanoparticles with 0.5, 0.7 and 1.0% volume concentrations were used in order to prepare nanofluid. The thermal conductivity and viscosity values needed for the calculations were obtained by measuring separately. For the experiments, the microchannels made by both the different materials (Stainless steel, PEEK) and the different inner diameter (400, 750, 1000 µm) were teste . . .d for the different surface temperatures (283, 298, 313 K). In the tests, the nanofluids had the different inlet temperature (323–333 K), the volume flow rates (20, 35, 50 mL min-1) and the concentrations. Heat transfer rate, Nusselt number, pressure drop and friction factor results were calculated. The optimum conditions were determined by using Taguchi approach. The thermal performance and the pressure drop of the fluids were compared. The results showed that the best thermal performance was obtained for Al2O3 nanofluid with 1.0% vol. concentration. A heat transfer enhancement of 15.3% was achieved using nanofluid instead of deionized water as the base fluid. Moreover, it has been seen no considerable pressure drop. © 2017, Akadémiai Kiadó, Budapest, Hungary Daha fazlası Daha az

Modeling and predicting seasonal ionospheric variations in Turkey using artificial neural network (ANN)

Inyurt S. | Sekertekin A.

Article | 2019 | Astrophysics and Space Science364 ( 4 ) , pp.2843 - 2863

The aim of this study was to model and predict seasonal ionospheric total electron content (TEC) using artificial neural network (ANN). Within this scope, GPS observations acquired from ANKR GPS station (Turkey) in 2015 were utilized to model TEC variations. Considering all data for each season, training and testing data were set as 80% and 10%, respectively, and the rest of the data were used to estimate TEC values using extracted mathematical models of ANN method. Day of Year (DOY), hour, F107 cm index (solar activity), Kp index and DsT index (magnetic storm index) were considered as the input parameters in ANN. The performances o . . .f ANN models were evaluated using RMSE and R statistical metrics for each season. As a result of the analyses, considering the prediction results, ANN presented more successful predictions of TEC values in winter and autumn than summer and spring with RMSE 3.92 TECU and 3.97 TECU, respectively. On the other hand the R value of winter data set (0.74) was lower than the autumn data set (0.88) while the RMSE values were opposite. This situation can be caused by the accuracy and precision of data sets. The results showed that the ANN model predicted GPS-TEC in a good agreement for ANKR station. © 2019, Springer Nature B.V Daha fazlası Daha az

Reactivity and characterisation of various rank turkish bituminous coal chars

Kizgut S. | Baran Y. | Cuhadaroglu D.

Article | 2003 | Journal of Thermal Analysis and Calorimetry71 ( 3 ) , pp.857 - 865

A set of seven bituminous coal chars has been characterised by IR spectroscopy (FTIR), thermogravimetry (TG) and elemental analysis. FTIR study provided suitable information to establish differences between coal samples according to their chemical compositions. The reactivity of these samples was also studied and correlated with the coal parameters of mean vitrinite reflectance, fuel ratio and H/C ratio. The data suggest that reactivity as determined can be correlated with the mean vitrinite reflectance, fuel ratio and H/C ratio (0.90). The order of reactivity of samples were; Amasra (S1) (Rm= 0.65)>Azdavay (S4) (Rm=0.99)?Armutcu . . .k (S2) (Rm=0.81)?Acenta (S3) (Rm=0.92)>Ac212k (S6) (Rm=1.11) Cay (S5) (Rm=1.03)>Sogutozu (S7) (Rm=2.14) Daha fazlası Daha az

Interaction Between Science Teaching Orientation and Pedagogical Content Knowledge Components

Demirdöğen B.

Article | 2016 | Journal of Science Teacher Education27 ( 5 ) , pp.495 - 532

The purpose of this case study is to delve into the complexities of how preservice science teachers’ science teaching orientations, viewed as an interrelated set of beliefs, interact with the other components of pedagogical content knowledge (PCK). Eight preservice science teachers participated in the study. Qualitative data were collected in the form of content representation, responses to an open-ended instrument, and semi-structured interviews. Preservice teachers’ orientation and PCK were analyzed deductively. Constant comparison analysis of how their orientation interacted with other PCK components revealed three major themes: . . .(1) one’s purpose for science teaching determines the PCK component(s) with which it interacts, (2) a teacher’s beliefs about the nature of science do not directly interact with his/her PCK, unless those beliefs relate directly to the purposes of teaching science, and (3) beliefs about science teaching and learning mostly interact with knowledge of instructional strategies. Implications for science teacher education and research are discussed. © 2016, The Association for Science Teacher Education, USA Daha fazlası Daha az

Thermal characterization of Er-doped and Er–Gd co-doped ceria-based electrolyte materials for SOFC

Ozlu Torun H. | Çakar S.

Article | 2018 | Journal of Thermal Analysis and Calorimetry133 ( 3 ) , pp.1233 - 1239

Ce1-xErxO2 and Ce1-2xErxGdxO2 co-doped ceria electrolyte nanopowder materials were successfully prepared by sol–gel method. Depending on the temperature, the crystal structure changes were analyzed by X-ray diffraction. It was observed that the crystal size of the electrolytes decreased depending on the temperature and the time. X-ray diffraction results confirmed cubic fluorite structure in the samples. The microstructural properties of the samples were analyzed by scanning electron microscopy, and thermal stability measurement was performed by thermogravimetric and differential thermal analyses. The total electrical conductivity o . . .f the nanopowder electrolytes was determined by the dc four-point probe technique in air at temperatures ranging from room temperature to 1373 K. The four-probe conductivity results revealed that Ce0.8Er0.1Gd0.1O2 has a higher ionic conductivity compared to Ce0.83Er0.17O2 at 1123 K. The four-probe conductivity results show that both Ce1-xErxO2 and Ce1-2xErxGdxO2 solid electrolytes have potential application to oxide ionic conductor for solid oxide fuel cells. © 2018, Akadémiai Kiadó, Budapest, Hungary Daha fazlası Daha az

Kinetics of formation, dissociation and equilibrium constants of pentacyanoaquoruthenate(II) with heterocycles

Baran Y.

Article | 2000 | Transition Metal Chemistry25 ( 1 ) , pp.41 - 44

The kinetics of formation and dissociation reactions of [Ru(CN)5L]3- with a series of heterocyclic ligands were studied in aqueous media. In this presence of an excess of heterocycle, the observed second order rate constants were calculated from the kobs versus [ligand] plot at µ = 0.100 M NaClO4. Activation parameters for the formation reactions (?H‡ = 28 ± 7 kJ mol-1 and ?S‡ = 140 ± 35 J K-1 mol-1) are comparable for all systems, indicating a common mechanism. The kinetics of exchange of coordinated heterocycles for 1,3,5-triazine yielded a rate saturation typical of a limiting dissociative mechanism. Activation parameters of the . . .limiting first order specific rate of dissociation reactions were ?H‡ = 85 ± 7 kJ mol-1 and ?S‡ = 18 ± 4 J K-1 mol-1. Equilibrium constants were calculated from the second order rates of formation and pseudo-first order rates of dissociation reaction Daha fazlası Daha az

A constraint-based operation sequencing for a knowledge-based process planning

Göloğlu C.

Conference Object | 2004 | Journal of Intelligent Manufacturing15 ( 4 ) , pp.463 - 470

Process planning is a decision-making process. Decisions on machining operations for a particular feature have to be made on various independent conditions such as which operation should be performed with which tools and under what cutting parameters. An integrated knowledge-based CAPP system called ProPlanner has been developed. The system has five modules namely information acquisition, feature recognition, machining operation planning and tool selection, set-up planning, and operation sequencing. Most process-planning systems do not produce alternative process plans. Usually, a fixed sequence created by a process plan is not nece . . .ssarily the best possible sequence, Therefore, the aim should be to generate all possible operation sequences and use some optimality criteria to obtain the best sequence for the given operating environment. This paper presents an efficient heuristic algorithm, belongs to the system's operation sequencing module, for finding near-optimal operation sequences from all available process plans in a machining set-up. The costs of the various machining schemes are calculated and the machining scheme with the lowest cost is chosen. All feasible cutting tools are identified for each particular feature and the corresponding machining operations. This process is repeated for all the features in the machining set-up. All possible feature sequence combinations allowed by the current feature constraints are then generated. Appropriate cutting tools are identified and assigned to different operations. The feature sequence with the smallest number of tool changes is adopted Daha fazlası Daha az

Molybdenum and tungsten(0) tetracarbonyl complexes with pyridyl amine Schiff base ligands

Mentes A.

Article | 1999 | Transition Metal Chemistry24 ( 1 ) , pp.77 - 80

Molybdenum and tungsten tetracarbonyl compounds of the cis-[M(CO)4L2] (M = Mo, L2 = apmi, appi, apmi-Ph, appi-2-OMe, apmi-1-Me-1-Ph, bpmi, bppi, bpmi-Ph, bppi-2-OMe, bpmi-1-Me-1-Ph, bpai, M = W, L2 = apmi, appi, appi-2-OMe, bppi, bppi-2-OMe)† type have been prepared and characterised by 1H n.m.r., i.r., FAB-MS spectroscopy and by microanalysis.

Hereditary haemochromatosis gene (HFE) H63D mutation shows an association with abnormal sperm motility

Gunel-Ozcan A. | Basar M.M. | Kısa U. | Ankaralı H.C.

Article | 2009 | Molecular Biology Reports36 ( 7 ) , pp.1709 - 1714

The aim of this study was to screen infertile men for HFE H63D mutation in correlation with clinical characteristics of infertile men (sperm concentration, sperm motility, morphology, testicular volume, Follicle Stimulating Hormone (FSH), Luteinizing Hormone (LH) and total Testosterone levels) and find out if the HFE H63D mutation has an effect on male infertility. After excluding hormonal treatment, any scrotal pathology, having any systemic diseases such as diabetes mellitus, sickle cell anemia and microdeletions of the Y chromosome, a total of 148 infertile men with age range between 17 and 52-years-old (average age 29.6 ± 7.2) w . . .ere enrolled into the study. Our analysis indicates that the mean FSH levels are significantly higher (6.3 ± 4.6 mIU/ml, P = 0.03), whereas sperm motility is significantly lower (36.6 ± 28.1%, P = 0.01) in the infertile men with the HFE H63D mutation compared with subjects lacking this mutation. Comparison of allele frequencies of the infertile men with Ts < 50% versus the infertile men with Ts > 50% revealed a significant difference as expected (P = 0.001, OR = 0.14, %95 CI = 0.04-0.44). Comparison of allele frequencies of infertile men with abnormal sperm motility versus infertile men with normal sperm motility revealed a highly significant difference (P = 0.005, OR = 3.11, %95 CI = 1.41-6.86). Thus, the HFE H63D mutation seems to be an important risk factor for impaired sperm motility and is clinically associated with male infertility. © 2008 Springer Science+Business Media B.V Daha fazlası Daha az

Bond-coating in plasma-sprayed calcium-phosphate coatings

Oktar F.N. | Yetmez M. | Agathopoulos S. | Goerne T.M.L. | Goller G. | Ipeker I. | Ferreira J.M.F.

Conference Object | 2006 | Journal of Materials Science: Materials in Medicine17 ( 11 ) , pp.1161 - 1171

The influence of bond-coating on the mechanical properties of plasma-spray coatings of hydroxyatite on Ti was investigated. Plasma-spray powder was produced from human teeth enamel and dentine. Before processing the main apatite coating, a very thin layer of Al2O3/TiO2 was applied on super clean and roughened, by Al2O3 blasting, Ti surface as bond-coating. The experimental results showed that bond-coating caused significant increase of the mechanical properties of the coating layer: In the case of the enamel powder from 6.66 MPa of the simple coating to 9.71 MPa for the bond-coating and in the case of the dentine powder from 6.27 MP . . .a to 7.84 MPa, respectively. Both tooth derived powders feature high thermal stability likely due to their relatively high content of fluorine. Therefore, F-rich apatites, such those investigated in this study, emerge themselves as superior candidate materials for calcium phosphate coatings of producing medical devices. The methods of apatite powder production and shaping optimization of powder particles are both key factors of a successful coating. The methods used in this study can be adopted as handy, inexpensive and reliable ways to produce high quality of powders for plasma spray purposes. © 2006 Springer Science + Business Media, LLC Daha fazlası Daha az

Evaluation of macular and peripapillary choroidal thickness, macular volume and retinal nerve fiber layer in acromegaly patients

Yazgan S. | Arpaci D. | Celik H.U. | Isik I.

Article | 2018 | International Ophthalmology38 ( 2 ) , pp.617 - 625

Purpose: To evaluate macular volume, retinal nerve fiber layer, and macular and peripapillary choroidal thickness in acromegaly patients. Method: In this prospective, case–control study, 31 patients with acromegaly and 32 healthy subjects were recruited. Only right eyes were evaluated. Macular choroidal thickness (CT) was measured at three points, peripapillary CT was measured at eight points, and macular volume was measured at nine areas in the central 6 mm circle zone by spectraldomain optical coherence tomography (OCT). Retinal nerve fiber layer (RNFL) was measured automatically at six segments by OCT. Results: The mean macular a . . .nd peripapillary CT at all measuring points were significantly higher in acromegaly group (p Daha fazlası Daha az

Synthesis and characterization of novel rod-coil (tadpole) poly(linoleic acid) based graft copolymers

İnce, Özge | Akyol, Elvan | Sulu, Elvan | Şanal, Timur | Hazer, Baki

Article | 2016 | Journal of Polymer Research23 ( 1 ) , pp.1 - 10

Synthesis of novel poly (styrene)-g-poly(linoleic acid)-g-poly(ethylene glycol) amphiphilic rod-coil tadpole and poly (styrene)-g-poly(linoleic acid)-g-poly (dimethyl siloxane) double hydrophobic rod-coil tadpole graft copolymers have been reported. In the first step, poly(linoleic acid) peroxide macro initiator (PLina) was prepared by exposing linoleic acid to air at room temperature for three weeks, in view of the autoxidation process. In the second step, poly styrene-g-poly linoleic acid graft copolymer (PLinaS) was prepared by the polymerization of styrene initiated by PLina. In the third step, PS-g-PLina-g-PEG rod-coil tadpole . . .amphiphilic graft copolymer and PS-g-PLina-g-PolyPDMS rod-coil tadpole double hydrophobic graft copolymers were obtained by the reaction of carboxylic ends of PLinaS with polyethylene glycol (PEG) with primary amine terminal and poly (dimethyl siloxane) (PDMS) with primary amine terminals. The target copolymers and all intermediates were well characterized by GPC, FTIR, 1H NMR, DSC, and TGA in detail. © 2015, Springer Science+Business Media Dordrecht Daha fazlası Daha az

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