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Koleksiyondaki öğeler
- MakaleYalnız künye2014Scopus SJRQ1Microstructural, mechanical and tribological properties of Al-7Si-(0-5)Zn alloys
Alemdaǧ, Yasin; Beder, Murat
A series of Al-7Si-(0-5)Zn alloys were produced by permanent mould casting and their microstructure, mechanical and tribological properties were investigated in as-cast state. The microstructure of Al-7Si alloy consisted of α-Al dendrites surrounded by eutectic Al-Si mixture and a small amount of primary silicon particles. Addition of zinc into Al-7Si alloy resulted in the formation of α-solid solution and an increase in size and volume fraction of primary silicon particles. Moreover, these particles gathered inside interdendritic regions of the ternary Al-7Si-Zn alloys. The density, strength and hardness of Al-7Si-Zn alloys increased continuously with increasing zinc content, but their elongation to fracture and impact energy showed a reverse trend. It was also observed that zinc had no significant effect on the friction coefficient of the alloys, but their wear volume decreased with increasing zinc content up to 4%, above which the trend reversed. The wear surfaces of the alloys were characterized mainly by smearing layer with some degree of oxidation. In addition, delamination and fine scratches were observed on the worn surface. It was concluded that the addition of zinc up to 4% improves both mechanical and wear behaviour of Al-7Si alloy.
AtıfScopus48WoS41OpenAlex54
İncele - MakaleYalnız künye2015On the solutions of time-fractio3nal generalized hirota-satsuma coupled-KDV equation with modified riemann-liouville derivative by an analytical technique
Merdan, Mehmet
In this paper, the fractional variational iteration method (FVIM) was implemented to solve timefractional generalized Hirota-Satsuma coupled-KDV equation with modified Riemann-Liouville derivative. A new application of fractional variational iteration method (FVIM) was extended to derive analytical solutions in the form of a series for these equations. It is indicated that the solutions obtained by the FVIM are reliable and effective method for strongly nonlinear couple partial equations with modified Riemann-Liouville derivative. The effects of different fractional derivative for the coupled system are investigated.
AtıfScopus13WoS13İncele - MakaleYalnız künye2015Scopus SJRQ1Accident analysis with the random parameters negative binomial panel count data model
Coruh, Emine; Bilgic, Abdulbaki; Tortum, Ahmet
We analyzed factors affecting the frequency of accident counts in 81 cities over a three-year period (2008-2010) with monthly data using random-parameters negative binomial panel count data models. Among models considered, the random parameters model with the correlated coefficients outperformed the other models and was found to fit the data best with almost a perfect prediction of the conditional mean level. Most of variables used to control for the variation in the frequency of accident counts play crucial role with higher significance levels. Also, marginal effects and elasticity estimates were derived to get more insight into the effects of percent and unit changes in the dependent variable in response to changes in the exogenous variables.
AtıfScopus104WoS98OpenAlex99İncele - Kitap BölümüYalnız künye2013Geophysical approach for the detection and evaluation of geothermal energy potential stimulated from geology and tectonics in Cappadocia Region (Central Turkey)
Maden, Nafiz
Geothermal energy, which is a renewable energy source, can be used to heat buildings or generate electricity and does not contribute to air pollution when used properly, and it is heat continuously produced inside the earth that generates geological phenomena on a planetary scale. Central Anatolia is a triangular region which is limited by North Anatolian Fault Zone (NAFZ) to the north, East Anatolian Fault Zone (EAFZ) to the east, Dead sea FZ and Cyprus FZ to the south. The tectonic structure of the Cappadocia region is composed of NW trending Salt Lake Fault Zone extending approximately 220 km in length, Salanda fault zone extending 140 km, and NE trending Central Anatolian Fault zone more than 700 km in length. There are 82 geothermal regions having 171 sources with low and high temperatures due to the young volcanism and tectonic activities in this region. These geothermal regions caused by fault and fracture zones extending to the mantle parallel to the tectonic zones of the region and are situated on the areas having low Curie, high heat flow values. The Curie point depth, heat flow and geothermal gradient values determined from geophysical data of the region are correlated with tectonics and geothermal potential of the region. While the minimum crustal thickness is 38 km, the maximum crustal thickness is 41 km in Mt. Hasan and Mt. Erciyes. The Curie point depth value is computed as 13.7 km determined from magnetic anomaly data of the region. The geothermal gradient and heat flow values are estimated to be 42.3 °Ckm-1, 88.8 mWm-2, respectively. Geothermal systems and reservoir temperature of geothermal sources should be understood clearly to provide sustainability of the project with respect to the economical conditions. Various geothermometers methods have been used to determine the reservoir temperature in order to estimate the field of usage of the thermal water before the drilling stage because of the high price of the borehole. Silica geothermometers method applied to the SiO2 content of the sources gives the best information about the reservoir temperature. The maximum temperatures and depth to reservoir of the geothermal sources located in the Kayseri region are estimated as 131.8 °C, 1.14 km, respectively, in Kayseri region. It is concluded from these values that the Cappadocia region has very high geothermal potential caused by tectonic activities after the Late Triassic and partial melting of the lower crust.
- MakaleYalnız künye2013Scopus SJRQ2A statistical assessment of current seismic quiescence along the North Anatolian fault zone: Earthquake precursors
Öztürk, Serkan
The variations of the current seismicity rate on the North Anatolian Fault Zone in the beginning of 2009 have been analyzed based on the phenomenon of precursory seismic sequence before crustal main shocks. For this purpose, a statistical assessment is made to detect the seismic quiescence situation by using the standard normal deviate Z-value. Eight seismic quiescence regions are observed and quiescence anomalies in these regions have been observed since the beginning of 2005. On the Marmara part of the North Anatolian Fault Zone, four quiescence areas have been found on Silivri, in the Black Sea, around Izmit region and Çanakkale, Saros Gulf. On the Anatolian part of the North Anatolian Fault Zone, two quiescence areas have been observed on the Düzce fault and around the city of Amasya. Other anomalies have been observed around Erzincan, Elaziǧ and Bingöl regions on the eastern part of the North Anatolian Fault Zone. Due to the occurrences of the last strong earthquakes "MW = 6.0-Elaziǧ earthquake, 2010 March 08; MW = 5.2 - Çanakkale (Saros Gulf) earthquake, 2010 November 03; MW = 5.5-Erzincan earthquake, 2011 September 22 and MW = 5.1-Marmara Ereǧlisi (Tekirdaǧ) earthquake, 2012 June 07", other seismic quiescence regions may contribute to the forecasting of impending main shocks. Spatial and temporal estimates of the future seismic hazard of the North Anatolian Fault Zone are provided based on the results.
AtıfScopus14WoS10İncele - MakaleYalnız künye2012Scopus SJRQ3Synthesis and characterisation of new metallophthalocyanines containing four 12-membered diazadithia-macrocyclic moieties
Kaya, Elif Çelenk; Kantekin, Halit; Kaya, Afşin Ahmet; Dakoǧlu, Asuman; Öksüz, Sümeyra; Şişik, Hanife
Tetrasubstituted zinc, cobalt, nickel, copper and lead phthalocyanines bearing four 12-membered diazadithia macrocyclic moieties on peripheral positions have been synthesised by cyclotetramerisation reaction of 1,10-ditosyl-1,2,3,5,6,8,9,10-octahydrobenzo[h][1,4,7,10] dithiadiazacyclododecine-12,13-dicarbonitrile and corresponding anhydrous metal salts under microwave irradiation. The thermal stabilities of the phthalocyanine compounds have determined by thermogravimetric analysis.
AtıfScopus1WoS2OpenAlex1İncele - MakaleYalnız künye2012Scopus SJRQ3Yield and quality characteristics of sunflower silages in highlands
Guney, Erdal; Tan, Mustafa; Yolcu, Halil
This research was carried out to compare the yield and quality characteristics of four sunflower (Helianthus annuus L.) genotypes (i.e., confectionery Tekirdag landrace, confectionery Erzurum landrace, oilseed Sirena and oilseed C70165 hybrids) and one corn (Zea mays L.) genotype (i.e., SZE TC-S13 hybrid) in the Agriculture Faculty of Ataturk University in the east of Turkey during the period between 2005 and 2006. The study was designed in a randomized complete block design with five treatments replicated three times. The genotypes were evaluated in terms of forage properties as well as chemical and physical properties of silages in both years. According to the results, the corn genotype had better yield and silage qualities than sunflower genotypes. But crude protein contents of silages of sunflower genotypes were superior in comparison to the corn genotype. Also amongst sunflower genotypes, confectionery Tekirdag and Erzurum landraces had slightly higher silage qualities than oilseed sunflower hybrids.
AtıfScopus6WoS7İncele - MakaleYalnız künye2010Scopus SJRQ1Finite element model updating of an arch type steel laboratory bridge model using semi-rigid connection
Altunişik, Ahmet Can; Bayraktar, Alemdar; Sevlm, Bariş; Kartal, Murat Emre; Adanur, Süleyman
This paper presents finite element analyses, experimental measurements and finite element model updating of an arch type steel laboratory bridge model using semi-rigid connections. The laboratory bridge model is a single span and fixed base structure with a length of 6.1 m and width of 1.1m. The height of the bridge column is 0.85 m and the maximum arch height is 0.95 m. Firstly, a finite element model of the bridge is created in SAP2000 program and analytical dynamic characteristics such as natural frequencies and mode shapes are determined. Then, experimental measurements using ambient vibration tests are performed and dynamic characteristics (natural frequencies, mode shapes and damping ratios) are obtained. Ambient vibration tests are performed under natural excitations such as wind and small impact effects. The Enhanced Frequency Domain Decomposition method in the frequency domain and the Stochastic Subspace Identification method in the time domain are used to extract the dynamic characteristics. Then the finite element model of the bridge is updated using linear elastic rotational springs in the supports and structural element connections to minimize the differences between analytically and experimentally estimated dynamic characteristics. At the end of the study, maximum differences in the natural frequencies are reduced on average from 47% to 2.6%. It is seen that there is a good agreement between analytical and experimental results after finite element model updating. Also, connection percentages of the all structural elements to joints are determined depending on the rotational spring stiffness.
AtıfScopus18WoS17OpenAlex9İncele - BildiriYalnız künye2014Numerical solutions of linear differential-algebraic equation systems via Hartley series
Ünal, Emrah; Yalçin, Numan; Çelik, Ercan
In this paper, Hartley series are presented first. Then, the operational matrix of integration together with the product and coefficient matrices are presented. They are used to transform linear differential equation systems to a set of linear algebraic equations. Finally, numerical examples are given.
- MakaleAçık Erişim2013Scopus SJRQ1A numeric-analytic method for time-fractional Swift-Hohenberg (S-H) equation with modified Riemann-Liouville derivative
Merdan, Mehmet
In this paper, the fractional variational iteration method (FVIM) was applied to obtain the approximate solutions of time-fractional Swift-Hohenberg (S-H) equation with modified Riemann-Liouville derivative. A new application of fractional variational iteration method (FVIM) was extended to derive analytical solutions in the form of a series for these equations. Numerical results showed the FVIM is powerful, reliable and effective method when applied strongly nonlinear equations with modified Riemann-Liouville derivative.
AtıfScopus27WoS20OpenAlex25İncele - MakaleYalnız künye2010Scopus SJRQ3Optimum design of planar beams based on sensitivity analysis
Uysal, H.; Asci Demiröz, N.; Uzman, U.
In this study, the size optimization problem of a beam, in which the beam heights are determined along the beam axis, is considered as a shape optimization problem of a plate in plane elasticity. To achieve the shape optimization, different principles such as structural analysis, sensitivity analysis and mathematical programming are interrelated. The ANSYS that is a reliable finite element package programme is used only for the static analysis. The objective of this optimization problem is to minimize the volume of the beam under the constraints that the maximum value of the von Mises stress in each node do not exceed a predefined value and the beam axis is to remain straight. Design variables are the vertical coordinates of the corner nodal points of design elements. The design sensitivities are calculated through the finite, difference method and linear programming technique is used for obtaining the final shape of a beam. Several examples are solved under different loadings and boundary conditions. The obtained optimum beam volumes and the design variables are given in tables and the optimum beam shapes are plotted. One of the results given is compared with the literature.
- MakaleYalnız künye2013Scopus SJRQ3Application of carrier element free coprecipitation (CEFC) method for determination of Co(II), Cu(II) and Ni(II) ions in food and water samples
Serencam, Huseyin; Duran, Celal; Ozdes, Duygu; Bektas, Hakan
A simple and highly sensitive separation and preconcentration procedure, which has minimal impact on the environment, has been developed. The procedure is based on the carrier element free coprecipitation (CEFC) of Co(II), Cu(II), and Ni(II) ions by using 2-{4-[2-(1H-indol-3-yl)ethyl]-3-(4-methylbenzyl)-5-oxo- 4,5-dihydro-1H-1,2,4-triazol- 1-yl}-N'-(pyridin-2-yl methylidene)acetohydrazide (IMOTPA), as an organic coprecipitant. The levels of analyte ions were determined by flame atomic absorption spectrometry (FAAS). The detection limits for Co(II), Cu(II) and Ni(II) ions were found to be 0.40, 0.16 and 0.17 μg L-1, respectively, and the relative standard deviations for the analyte ions were lower than 3.0%. Spike tests and certified reference material analyses were performed to validate the method. The method was successfully applied for the determination of Co(II), Cu(II) and Ni(II) ions levels in sea and stream water as liquid samples and red pepper, black pepper, and peppermint as solid samples.
AtıfScopus10WoS10
İncele - MakaleYalnız künye2015Scopus SJRQ2Tectonic evolution of the northern shelf of the Marmara Sea (Turkey): interpretation of seismic and bathymetric data
Tur, Huseyin; Hoskan, Nihan; Aktas, Gulten
This study is based on the geological interpretation of 250 km2 of multibeam bathymetric data coupled with 300 km of seismic profiles recorded on the northern shelf of the Marmara Sea offshore Büyükçekmece and Küçükçekmece Lagoons. The sea bottom morphology has a highly chaotic structure at the exit of the Büyükçekmece and Küçükçekmece lagoons. This chaotic surface structure is controlled by a basin-ridge system lying in the NE–SW direction at the exit of the Büyükçekmece Lagoon and by a relatively deep entrance observed at the exit of the Küçükçekmece Lagoon. In addition, the linear submarine slope parallel to the shoreline between the Istanbul Strait and the Küçükçekmece Lagoon is an important morphological structure of this area. The Istanbul Strait’s canyon on the northern shelf of the Marmara Sea and the elevated submarine plain west of this canyon are other important morphological structures observed at the sea bottom. The geologic interpretation of seismic profiles has allowed us to distinguish two seismo-stratigraphic units. The lower one is separated from the overlying units by a seismic sequence having a seismic facies from chaotic to parallel and the top represented by a high amplitude seismic reflector. Since these units get close to the sea bottom rising landwards, they are inferred to be the seaward continuation of the Oligocene–Upper Miocene units widely exposed on land. The upper unit, overlying the acoustic basement, whose parallel internal reflections onlap and downlap on the top of the acoustic basement, is interpreted as a Quaternary basin fill. Two groups of faults have been identified on seismic profiles and identified based on their characteristics in the study area. The first group consists of dip-slip faults trending NNE–SSW. These faults border the western slope of the Bosporus and the NNE–SSW trending basins offshore of the Büyükçekmece Lagoon. The second group of faults consists of NW–SE oriented strike-slip faults. These faults have created the linearities in the same direction at the sea bottom. As the result of comparison of these NW–SE-faults to the North Anatolian Fault Zone (NAFZ), this group of faults is likely to have a relation with the NAFZ. Therefore, it is considered that the mentioned faults may be reactivated in the region due to the stress created by the NAFZ.
AtıfScopus12WoS11OpenAlex16İncele - MakaleYalnız künye2010Scopus SJRQ3Insight into magma genesis at convergent plate margins a case study from the eastern Pontides (NE Turkey)
Kaygusuz, Abdullah; Siebel, Wolfgang; Ilbeyli, Nurdane; Arslan, Mehmet; Satir, Muharrem; Şen, Cüneyt
Convergent plate margins are the most intense areas of granitoid magmatism on Earth. The Eastern Pontide Magmatic Belt in NE Turkey represents a paleo-arc with numerous quartz diorite to syenite intrusions, ranging in age from 142 to 56 Ma and being composed of K-feldspar, plagioclase, quartz, pyroxene, hornblende, biotite, and Fe-Ti oxides. The granitoids exhibit low- to high-K calc-alkaline, metaluminous to slightly peraluminous I-type features and contain abundant mafic magmatic enclaves (MME). They are characteristically enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE) relative to high field strength elements (HFSE). Chondrite-normalized REE patterns are fractionated (LaN/LuN= 1.49-17.4) with pronounced negative Eu anomalies (Eu/Eu* = 0.46-1.77). Initial 87SrZ86Sr values are between 0.7056 and 0.7079, and εNd(1) values between -5.3 and 1.6. Fractional crystallization, magma mixing/mingling and crustal contamination played an important role during magma evolution. All these characteristics, combined with the low values of K2O/Na2O, Mg-number, ASI and ratios Of Al 2O3/ (FeOT+MgO+TiO2) and (Na 2O+K2O)/(FeOT+MgO+TiO2), suggest an origin by dehydration melting of mafic (amphibolitic) or tonalitic lower crustal source rocks.
AtıfScopus54WoS49OpenAlex53İncele - MakaleYalnız künye2011Scopus SJRQ3Effects of kale (Brassica oleracea L. var. acephala DC) leaves extracts on the susceptibility of very low and low density lipoproteins to oxidation
Kural, Birgül Vanizor; Küçük, Nurçin; Yücesan, Fulya Balaban; Örem, Asim
Of Brassicaceous plants, kale (Brassica oleraceae L. var. acephala DC) contains polyphenols, flavonoids, isoflavones and glucosinolates and so has antioxidant and anticarcinogenic properties. Antioxidants inhibit negative effects of free radicals and may, therefore, protect tissues against oxidative damage. Oxidation of lipoproteins is a key event in the development of atherosclerosis. In the current study, the levels of total phenolic and flavonoid contents and total antioxidant capacity of methanolic and aqueous extracts of kale leaves were determined. In addition, the susceptibility of isolated lipoproteins - very low density lipoprotein (VLDL) and low density lipoprotein (LDL) to the Cu 2+-induced oxidation with various concentrations of metanolic and aqueous extracts was evaluated as t-lag values. Although aqueous extract had higher total antioxidant capacity, methanolic extract had higher total phenolic and flavonoid content (P<0.05). On the other hand, both extracts inhibited lipid peroxidation in both isolated VLDL and LDL. Inhibitory effect of extracts or increasing t-lag values, mainly in methanolic extract was found to be related to increasing the concentration of extracts. It was concluded that because of high antioxidant capacity and phenolic content, kale showed a protective effect on the oxidation of lipoproteins. Therefore, it may be speculated that kale consumption may play an important protective role in the cardiovascular and other related diseases resulting from imbalance of oxidant and antioxidant status.
AtıfScopus16WoS13İncele - MakaleAçık Erişim2011Scopus SJRQ3The first record of the genus Odiellus (opiliones, phalangiidae) in Turkey with some SEM studies on its morphology
Kurt, K.; Erman, O. Köksal
The harvestmen species Odiellus lendli (Soerensen, 1894), with its genus Odiellus Roewer, 1923, was found in Anatolia. It represents a new record of Turkish harvestmen fauna. The characteristic features of this species are described and illustrated. Scanning electron microscopy (SEM) studies on the dorsal integument, ventral habitus, chelicerae, pedipalpus, trident, the ocularium and legs of female specimens are also presented. Localities of the collecting sites are photographed and plotted on a map.
AtıfScopus4WoS4OpenAlex2İncele - MakaleAçık Erişim2014Scopus SJRQ3Synthesis and spectral and thermal characterization of new metal-free and metallophthalocyanines: Investigation of their photophysical, photochemical, and thin film properties
Kaya, Elif Çelenk; Durmuş, Mahmut; Yanmaz, Ekrem; KantekiN, Halit
Novel tetrasubstituted metal-free (2), zinc (II) (3), cobalt (II) (4), and copper (II) (5) phthalocyanines bearing 2-phenylethanolate groups on the peripheral positions were synthesized by the cyclotetramerization reaction of the phthalonitrile derivative 1. The new compounds were characterized by a combination of IR, 1H NMR, 13 C NMR, UV-Vis, elemental analysis, and MS spectra data. The thermal stabilities of the phthalocyanine compounds were determined by thermogravimetric analysis. For metal-free (2) and zinc (3) phthalocyanines, photochemical (photodegradation and singlet oxygen quantum yields) and photophysical (fluorescence quantum yields and fluorescence lifetimes) properties were analyzed in dimethylsulfoxide (DMSO). The cobalt (4) and copper (5) phthalocyanines were not evaluated for this purpose because of their paramagnetic behavior. The metal-free (2) and zinc (3) phthalocyanines' fluorescence quenching behaviors were also investigated. The new phthalocyanine compounds' fluorescence emissions were effectively quenched by 1,4-benzoquinone in DMSO. The thin films of the cobalt phthalocyanine compound (4) were grown by electron beam evaporation technique. Crystalline CoPc (4) thin films were investigated by X-ray diffraction spectroscopy. Surface morphology of the CoPc (4) thin films was characterized by SEM.
AtıfScopus13WoS11OpenAlex15
İncele - MakaleYalnız künye2012Scopus SJRQ2Chaotic systems via multi-step differential transformation method
Yildirim, Ahmet; Gökdoǧan, Ahmet; Merdan, Mehmet
In this article, the multi-step differential transform method is implemented to give approximate and analytical solutions of nonlinear fractional order ordinary differential equation systems, such as Chen, Lorenz, Arneodo-Coullet, Genesio, Lui, and Rikitake chaotic systems. The numerical solutions obtained from the proposed method indicate that the approach is easy, simple, and accurate when applied to systems of fractional differential equations. Numerical simulations are given to verify the reliability and effectiveness of this method.
AtıfScopus20WoS11OpenAlex19İncele - MakaleYalnız künye2013Scopus SJRQ2A multistage variational iteration method for solution of delay differential equations
Gökdoǧan, Ahmet; Merdan, Mehmet; Ertürk, Vedat Suat
In this paper, the approximate solution of delay differential equations is obtained by a reliable algorithm based on an adaptation of the classical variational iteration method (VIM), which is called the multi-stage variational iteration method (MSVIM). Examples are carried out and numerical results with comparison to exact solutions, VIM and MATLAB dde23 solver are given. The comparison reveals that the MSVIM is a promising tool to solve delay differential equations.
AtıfScopus3WoS2OpenAlex4İncele - MakaleAçık Erişim2015Scopus SJRQ3Synthesis and biological evaluation of a new series of 4-alkoxy-2-arylquinoline derivatives as potential antituberculosis agents
Tosun, Gonca; Arslan, Tayfun; Iskefiyeli, Zeynep; Küçük, Murat; Karaoʇlu, Şengül Alpay; Yayli, Nurettin
Three new series of 33 quinolone compounds, 2-(2-, 3-, and 4-fluorophenyl)-4-O-alkyl(C5-15)quinolines (7a-k, 8a-k, and 9a-k), were synthesized from 2-(2-, 3-, and 4-fluorophenyl)-2,3-dihydroquinolin-4(1H )-one (4, 5, and 6) by the reaction of alkyl halides under basic conditions in DMF. The new compounds 7a-k, 8a-k, and 9a-k were synthesized from flavonones 4-6, which can be considered new precursors for quinoline synthesis through a one-step reaction. All the target compounds (7a-k, 8a-k, and 9a-k) were evaluated for their in vitro antimicrobial activity against nine test microorganisms. They showed the most activity against Mycobacterium smegmatis with minimum inhibitory concentrations (MIC) of 62.5-500 μg/mL, indicating their potential uses as antituberculosis agents. Among them 8a-k (m-fluoride) were the most active compounds against M. smegmatis (MIC, 62.5-125 μg/mL). The newly synthesized title compounds were also evaluated for their in vitro antioxidant activities using DPPH• radical scavenging and FRAP tests. They showed at a low concentration (mg/mL) a range of SC50 values of 0.03-12.48 mg/mL (DPPH•) and 0-722 μM (FRAP), respectively. The antioxidant results of compounds 7a-k, 8a-k, and 9a-k revealed that the length of the alkyl chain was negatively correlated with antioxidant capacity.
AtıfScopus7WoS7OpenAlex11İncele
