Scopus İndeksli Yayınlar Koleksiyonu
https://hdl.handle.net/20.500.12403/1302
2024-03-29T10:13:24Z
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Leaded brass alloys for gamma-ray shielding applications
https://hdl.handle.net/20.500.12403/295
Leaded brass alloys for gamma-ray shielding applications
Şakar E.; Büyükyıldız M.; Alım B.; Şakar B.C.; Kurudirek M.
The leaded brasses show high machinability and atmospheric corrosion resistance. Hence, they are being used in different applications such as machine parts, valves, fittings etc. Besides, they can serve as radiation shields as they contain lead and their radiation shielding properties were not investigated so far. Thus, the aim of this study is to determine the radiation shielding properties of leaded brasses. Standard (CuZn) and leaded (CuZnPb) brasses were prepared and their mass attenuation coefficients (?/?), half-value layers (HVL), tenth-value layers (TVL), mean free paths (MFP) and effective atomic numbers (Z eff ) were determined. Linear attenuation coefficients (?) of the alloys were measured first at 53, 276, 302, 356 and 383 keV using a HPGe detector and a 133 Ba radioactive source. These values were then used to obtain other parameters. A good agreement was observed between experimental and theoretical results for HVL, TVL and MFP (Dif. ? 9%). Photon buildup through the present materials was studied in terms of exposure buildup factor (EBF). Results were presented and discussed regarding the photon energy and penetration depths. Fast neutron removal cross sections were also calculated for the given alloys. Some alloys were also evaluated morphologically by using EDX mapping. The leaded brasses were compared with standard shielding concretes and superior shielding properties against gammas and fast neutrons were obtained when compared with concretes. © 2019 Elsevier Ltd
2019-01-01T00:00:00Z
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Optimization of design parameters for heat transfer and friction factor in a heat sink with hollow trapezoidal baffles
https://hdl.handle.net/20.500.12403/296
Optimization of design parameters for heat transfer and friction factor in a heat sink with hollow trapezoidal baffles
Sahin B.; Ates I.; Manay E.; Bayrakceken A.; Celik C.
The aim of this study is to optimize the design parameters of a heat sink on which hollow trapezoidal baffles are mounted on the bottom surface by using Taguchi experimental-design method. The Nusselt number and the friction factor are considered as performance parameters. An orthogonal array is selected as experimental plan for the six parameters: the corner angle (?), the inclination angle (?), the baffle height (H), the baffle length (L), the baffle width (S) and Reynolds number. First of all, each goal has been optimized, separately. Then, all the goals have been optimized together, considering the priority of the goals. The length of the baffle is found to be the most influential parameter on the friction factor. This can be attributed the enhanced effect of longitudinal vortices with baffle length in flow direction. Likewise, it is demonstrated that the most effective parameter on the heat transfer is Reynolds number. The results show that the baffle width (S) and the corner angle (?) have insignificant effect on Nusselt number. The maximum heat transfer was obtained at Re = 17,000, H = 36 mm, L = 45 mm, S = 26 mm, ? = 0°, ? = 0°. The inclination angle (?) and the baffle height (H) have nearly no effect on the friction factor. The minimum friction factor was obtained at Re = 17,000, H = 20 mm, L = 25 mm, S = 26 mm, ? = 16°, ? = 0°. The inclination angle (?) and the baffle height (H) have nearly no effect on the friction factor. It can be concluded that the higher heat transfer rates can be achieved with lower pressure drop penalty with this type of vortex generator in particular configurations. © 2019 Elsevier Ltd
2019-01-01T00:00:00Z
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Purification and biochemical characterization of a novel copper, zinc superoxide dismutase from liver of camel (Camelus dromedarius): An antioxidant enzyme with unique properties
https://hdl.handle.net/20.500.12403/302
Purification and biochemical characterization of a novel copper, zinc superoxide dismutase from liver of camel (Camelus dromedarius): An antioxidant enzyme with unique properties
Chafik A.; Essamadi A.; Çelik S.Y.; Mavi A.
A novel copper, zinc superoxide dismutase (CuZnSOD) was purified to homogeneity from the liver of an animal well adapted to the stressful living conditions of the desert, the camel (Camelus dromedarius). The biochemical properties of camel liver CuZnSOD were examined. The purified enzyme had a native molecular weight of 28 kDa, as judged by gel filtration chromatography, and showed a single band at 27 kDa on SDS-PAGE, indicating that it is a monomeric protein. Optimal activity of the purified enzyme occurred at 43 °C and pH 6.0, and the activation energy was 1.42 kJ/mol. CuZnSOD activity was strongly inhibited by ?-ME, DTT, H 2 O 2 and SDS and slightly inhibited by EDTA, NaN 3 and PMSF. Al 3+ , Ca 2+ , Cd 2+ , Mg 2+ and Zn 2+ stimulated CuZnSOD activity, whereas Ba 2+ , Co 2+ , Fe 2+ and Ni 2+ inhibited it. The purified enzyme contained 0.010 µg of Cu and 0.69 µg of Zn per mg of protein. K m , V max , k cat and k cat /K m values for NBT and riboflavin were 16.27 and 0.16 µM, 20.85 and 21.54 U/mg, 9.65 and 9.97 s ?1 , and 0.59 and 62.33 s -1 µM ?1 , respectively. Camel liver CuZnSOD exhibited unique biochemical properties compared to those of other CuZnSODs, including lower molecular weight with a monomeric structure, higher optimum temperature, very low E a , very low optimum pH, very low contents of Cu and Zn, and higher affinity, turnover number and catalytic efficiency for riboflavin. These unique properties of camel liver CuZnSOD might be related to the ability of this animal to inhabit stressful desert conditions. © 2019 Elsevier Inc.
2019-01-01T00:00:00Z
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Optical, surface and magnetic properties of the Ti-doped GaN nanosheets on glass and PET substrates by thermionic vacuum arc (TVA) method
https://hdl.handle.net/20.500.12403/303
Optical, surface and magnetic properties of the Ti-doped GaN nanosheets on glass and PET substrates by thermionic vacuum arc (TVA) method
Pat S.; Korkmaz Ş.; Özen S.; Şenay V.
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. © 2017, © 2017 Taylor & Francis.
2019-01-01T00:00:00Z