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Orak, Milad,Sajedi, Fathollah Techno-Press 2021 Advances in nano research Vol.11 No.2
Today, the tendency to use self-compacting concrete (SCC) is expanding because of its significant benefits. In this study, SCC was made by using native materials and then different pozzolans were replaced instead of a part of cement and the rheological and mechanical properties and microstructure of the concrete were investigated. The pozzolans containing of metakaolin (15%, 25% and 35%), silica fume (6%, 12% and 18%) and fly ash (20%, 35% and 50%) were replaced instead of a part of cement separately or simultaneously. Self-compaction tests including slump flow, T500, L-box, U-box, and J-ring as well as mechanical tests including compressive strength, splitting tensile strength, and static modulus of elasticity were performed on the specimens. The results showed that the pozzolans improved the microstructure of the SCC and the secondary reactions improved the mechanical properties of the concrete containing the pozzolans at older ages than the reference concrete. At 15% replacement, metakaolin increased the 180-day compressive strength up to 106 MPa that was about 18% more than reference concrete. In ternary mixtures the maximum and minimum rate were 29% and 19%, respectively, and in quaternary mixtures the rates were significant and increased up to 46%, while the rate for reference concrete was 20%. This significant growth was probably due to the secondary reaction of pozzolans with calcium hydroxide residue from cement hydration.
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The electrical characterizations and illumination response of Co/N-type GaP junction device
Ikram Orak,Kadir Ejderha,Abdulmecit Turut 한국물리학회 2015 Current Applied Physics Vol.15 No.9
The manuscript describes characterization of a Co/n-GaP junction device. The currentevoltage etemperature (I-V-T), capacitanceefrequencyetemperature (C-f-T) measurements of the device were analyzed in the temperature range of 60e320 K by the steps of 20 K under dark condition, and light condition at room temperature. The characteristic parameters such as barrier height (BH), ideality factor (n) have been determined from the forward bias IeV characteristics on the basis of standard thermionic emission. The BH and n were found to be 0.98 eV and 1.05 at room temperature, respectively. The ideality factor increased and BH decreased with a decrease in temperature. The BH and n were found to be linear dependent on each other at two different regions, and these values are predicted with existence of Gaussian distribution (GD). For the two different methods the BH is seen in good agreement with each other. Especially, the homogeneous BH for the first region is found to around 1.02 eV. The homogeneous BH values are found to be good agreement for 3 different methods such as the linear correlations of BH versus n plot, GD of BHs and Norde's function. Interface states (Nss) and their time constant (t) were calculated from the C-f-T measurements and as sample temperature was increased, the Nss value increased and t decreased in dark conditions. Photovoltaic parameters such as fill factor (FF), power conversion efficiency (ηp), open circuit voltage (Voc) and short circuit current (Isc) were calculated. According to these, it was been seen that the semiconductor device under light illumination showed photovoltaic behavior.
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Evaluation of Antioxidant and Antimicrobial Potential of Strawberry Tree (Arbutus Unedo L.) Leaf
Hakime Hülya Orak,Hülya Yagar,Sebnem Selen Isbilir,Ahmet Şükrü Demirci,Tuncay Gümüş,Neslihan Ekinci 한국식품과학회 2011 Food Science and Biotechnology Vol.20 No.5
In present study, antioxidant and antimicrobial activities of strawberry tree (Arbutus unedo L.) leaves were investigated. Antioxidant activity was determined by methods of DPPH scavenging, β-carotene bleaching,reducing power, metal chelating, superoxide anion scavenging, and hydrogen peroxide scavenging activity. Total phenolic content were determined to be 197.16±1.43mg GAE/g extract in aqueous extract. The EC_50 value of methanolic extracts was found to be 0.423 mg/mL. The extracts of leaves showed nearly 1/4 metal chelating capacity of standard EDTA, high reducing power,superoxide anion scavenging, and hydrogen peroxide scavenging activities. While the strawberry tree leaves exhibited antibacterial activity against Staphylococcus aureus, there was no inhibitory effect against Escherichia coli and Salmonella enteritidis. The strawberry tree leaves exhibited antifungal effect against 2 aflatoxigenic molds namely Aspergillus parasiticus NRRL 2999 and NRRL 465. These results suggest that the strawberry tree leaves may be used as an antioxidant source for pharmaceutical application, nutraceutical and functional food industries.
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Hakime Hulya Orak,Sebnem Selen Isbilir,Hulya Yagar 한국식품과학회 2012 Food Science and Biotechnology Vol.21 No.4
The objective of this study was to compare the antioxidant activities of lyophilized olive leaf water extracts (OLWExtracts) from 21 different olive tree cultivars. The highest total phenolic content (102.69±1.63 μg GAE/mg extract) was found in cultivar ‘Esek Zeytini’ and the lowest content (78.52±2.18 μg GAE/mg extract) was in ‘Uslu’. The highest total flavonoid content (12.47±0.12 μg QE/mg extract) obtained from ‘Frantoio’. According to EC50values, ‘Domat’ have the highest DPPH scavenging activity (EC50 =59 μg/mL), reducing power (EC50 =180 μg/mL),and superoxide radical scavenging capacity (EC50=44 μg/mL). While, ‘Ascolana’ showed the highest metal chelating capacity (EC50=163 μg/mL), ‘Memecik’ showed the highest hydrogen peroxide (H2O2) scavenging capacity. Research results exhibited that OLWExtracts are comparable to synthetic antioxidants. The correlation study showed that while total phenolic content correlated with DPPH scavenging activity and reducing power (p<0.01), total flavonoid content correlated with metal chelating and superoxide radical scavenging capacity (p<0.05).
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Hakime Hulya Orak,Hulya Yagar,Sebnem Selen Isbilir 한국식품과학회 2012 Food Science and Biotechnology Vol.21 No.2
In this study, the antioxidant activities of juice,peel, and seed parts of pomegranate were investigated by using DPPH scavenging activity, β-carotene bleaching method, reducing power, and metal chelating activity. Sample of pomegranates which are named Punica granatum L. cv. Hicaznar, genotype 19-121, genotype 17-67, and genotype 19-66 obtained from BATEM (West Mediterranean Agricultural Research Institute) in Anlalya. The EC50values of DPPH scavenging activities in peel extracts (PE)had 23.4-fold higher than the juice extracts (JE), and the seed extracts (SE) had 2.3-fold higher than JE. The reducing power in peel extracts was found to be 4.7-fold higher than SE and 10.5-fold higher than the JE. The highest metal chelating capacity (37.22%) was determined in peel, while the lowest (7.151%) in seed. Generally, in peel, the total polyphenol, flavonoid, tannin contents, and in juice, the total polyphenol, anthocyanin, tannin contents,and acidity significantly affected to antioxidant activities.
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Mustafa Kutanis,Elif Orak Boru,Ercan Işık 대한토목학회 2017 KSCE JOURNAL OF CIVIL ENGINEERING Vol.21 No.5
The outcomes of the ambient vibration measurements carried out to evaluate the dynamic characteristics of the reinforced concrete field test structure were presented. The test building was designed according to Turkish Seismic Code and constructed for this research study at the field laboratory in Sakarya University. The first aim is to conduct ambient vibration tests on a full-scale field test structure to measure its modal properties for the cross-validation of a finite element model of the test structure. The second aim is to optimize the instrumentation schemes from cost and quality of data point of view. Six tri-axial accelerometers were situated in different configurations on the test structure. For every configuration ambient vibrations were recorded to measure the dynamic characteristics of the test structure. For the system identification with ambient vibration signals Enhanced Frequency Domain Decomposition (EFDD) method was used. A satisfactory match between theoretical and experimental modal parameters was deduced for certain instrumentation scheme.
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The structural analysis of MWCNT-SiO2 and electrical properties on device application
Adem Kocyigit,Ikram Orak,Ibrahim Karteri,Serhan Urus 한국물리학회 2017 Current Applied Physics Vol.17 No.9
Al/MWCNT-SiO2/p-Si device were obtained using chemical techniques and characterized using the I-V (under dark and light conditions) and C-V measurements depending on various frequency. MWCNT-SiO2 composite layer of the device were also characterized using XRD, FTIR, SEM, TEM and TGA measurements. These all results indicated that the MWCNT-SiO2 layer synthesized successfully on Si wafer as a composite form with chemical processes and spin coating. I-V measurements showed that device has good rectifying properties, small saturation current and good photodiode properties. Solar cell conversion efficiency (hp) and fill factor (FF) values of the device also were calculated as 0.12% and 47.6%, respectively. It could be seen from C-V measurements that capacitance and conductance properties of the device strongly depended on frequency and voltage. It may be used and improved this device as rectifier, photodiode and capacitor in the future.
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Effect of plastic media blasting method on mechanical properties of Al 2024-T6 alloy
Ümit Üner,Sezan Orak,Mehmet Alper Sofuoğlu 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.10
We investigated the effect of Plastic media blasting (PMB) method on mechanical properties of Al 2024-T6 alloy for aircraft body coatings. Painting-stripping process with three cycles was performed using PMB for three different thicknesses. The relationship between surface morphology-deformation and defects was characterized. PMB affects the fatigue life and surface morphology of specimens. The fatigue life decreases when the specimen thickness decreases. In contrast, this method does not significantly affect the fatigue life of thick specimens. The surface roughness was between 0.30-0.65 Ra for processed specimens. The study will determine proper sheet metal thickness which is not affected seriously because of the method for Al 2024-T6 alloy.
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