Person: GÜLLÜOĞLU, ARİF NİHAT
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GÜLLÜOĞLU
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ARİF NİHAT
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Publication Metadata only Effect of irradiation by 140 Mev Ag11+ ions on the optical and electrical properties of polypropylene/TiO2 composite(ELSEVIER, 2009) GÜLLÜOĞLU, ARİF NİHAT; Qureshi, Anjum; Singh, Dolly; Singh, N. L.; Ataoglu, S.; Gulluoglu, Arif N.; Tripathi, Ambuj; Avasthi, D. K.Changes in the optical, structural, dielectric properties and surface morphology of a polypropylene/TiO2 composite due to swift heavy ion irradiation were studied by means of UV-visible spectroscopy, X-ray diffraction, impedance gain phase analyzer and atomic force microscopy. Samples were irradiated with 140 MeV Ag11+ ions at fluences of 1 x 10(11) and 5 x 10(12) ions/cm(2). UV-visible absorption analysis reveals a decrease in optical direct band gap from 2.62 to 2.42 eV after a fluence of 5 x 10(12) ions/cm(2). X-ray diffractograms show an increase in crystallinity of the composite due to irradiation. The dielectric constants obey the Universal law given by epsilon proportional to integral(n-1), where n varies from 0.38 to 0.91. The dielectric constant and loss are observed to change significantly due to irradiation. Cole-cole diagrams have shown the frequency dependence of the complex impedance at different fluences. The average surface roughness of the composite decreases upon irradiation. (C) 2009 Elsevier B.V. All rights reserved.Publication Metadata only Synthesis, characterization, thermal, and antibacterial activity studies on MgO powders(SPRINGER, 2021) GÜLLÜOĞLU, ARİF NİHAT; Demirci, Selim; Yildirim, Bercem Kiran; Tuncay, Mehmet Masum; Kaya, Nusret; Gulluoglu, Arif NihatIn this study, MgO particles were synthesized via sol-gel technique and calcined at 600 degrees C for 2 h with heating rates of 2, 5, 10, and 20 degrees C/min, respectively, for the first time. Comprehensive characterizations were performed by TGA-DTA, XRD, SEM, Raman spectroscopy, BET analysis, photoluminescence techniques. The kinetic parameters were determined by employing four popular model-free methods: Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sonuse (KAS), Starink, and Tang methods. MgO powders had a high crystalline structure regardless of different heating rates based on XRD results. Surface morphologies and surface areas of MgO powders did not change with heating rates. Surface morphologies of MgO powders were found to be nearly spherical with some rounded shape and exhibiting faceted edges in some regions. The specific surface area of MgO powders was found to be 5.9179, 5.6883, 3.6617, and 4.1942 m(2)/g with increasing heating rate, respectively. According to Raman analysis, MgO particles produced at 2 degrees C/min possessed higher surface defects like oxygen vacancies. The PL emission signals for MgO particles were observed at similar to 500 nm consisting of broad peaks, which might be attributed to oxygen defects on the surface of particles. The antibacterial performances of MgO particles were carried out against gram-negative E. coli and gram-positive B. subtilis by means of the agar disc diffusion method. MgO particles produced at a heating rate of 2 degrees C/min possessed the biggest inhibition zone against gram-positive B. subtilis. Having better antibacterial performances for MgO particles produced at 2 degrees C/min heating rate might be attributed to surface oxygen vacancies and surface area, which led to the generation of more reactive oxygen species (ROS). [GRAPHICS] .Publication Open Access The similar and dissimilar spot welding of 304 and 316l austenitic stainless steels(2017-11-01) ÇINAR, ÖZGÜR; ÇETİNER, BURCU NİLGÜN; GÜLLÜOĞLU, ARİF NİHAT; EKİCİ, BÜLENT; ÇINAR Ö., ÇETİNER B. N., TOPCU İ., GÜLLÜOĞLU A. N., EKİCİ B.Publication Open Access Strategy Development Process in Higher Education: The Case of Marmara University(ELSEVIER SCIENCE BV, 2016-11) GÜLLÜOĞLU, ARİF NİHAT; Bakoglu, Refika; Oncer, Ayla Zehra; Yildiz, Muge Leyla; Gulluoglu, Arif Nihat; Ozsahin, MStrategic planning in higher education has become one of the most important factors of today's education system. State of the Republic of Turkey, which is aware of importance of this trend in the world, made the preparation and implementation of five-year strategic plans mandatory for higher education institutions. However, when examining the strategic plans made by universities in Turkey in general, it draws attention that strategy development techniques are not used in development processes. Strategies at different levels in universities are not taken in consideration, and strategies are not determined by high participation and not formed and implemented in a conscious way. Marmara University has developed a different and unique approach by considering these facts when doing researches to develop strategies to be effective in the next five-year period. In this notification, it is aimed to reveal strategical approach developed exclusive to universities in 2017-2021 strategic plan of Marmara University, and strategy development process model formed for the purpose of being internalized of strategy in institution. In this respect, in study; it is mentioned how participation of academic and administrative personnel is provided, in which way it is focused on creating value for all stakeholders, how internal and external environment analysis are made with which scientific research projects and how corporate learning is supported in every stage of the process. This paper tries to highlight a case from Marmara University's strategy development process indicating how strategic plan on the paper can be changed into internalized strategy creating change, momentum and dynamism trough the both implementation of a new approach to strategy and strategy development process. (C) 2016 The Authors. Published by Elsevier Ltd.Publication Metadata only Effect of surface geometry on low-velocity impact behavior of laminated aramid-reinforced polyester composite(SAGE PUBLICATIONS LTD, 2016) GÜLLÜOĞLU, ARİF NİHAT; Ayten, Ali Imran; Ekici, Bulent; Gulluoglu, Arif NihatThe aim of this study is to investigate the effect of surface geometry for low-velocity impact applications. To achieve this purpose, aramid fiber-reinforced laminated polyester composite with various geometries such as cylindrical, elliptical, and spherical were prepared, and low-velocity impact properties were investigated numerically and experimentally. All properties such as orientation, fiber volume fraction, matrix material, and average thickness are the same in all samples. Experimental low-velocity impact behaviors of structure were determined by drop weight tester at low velocity 2.012 m/s. Simulations were carried out by LS-Prepost 4.2 and LS-Dyna v971 software. By this way, results of impact tests were verified and modeled with finite element method. Results of the impact tests showed that the elliptical samples have the highest energy absorption capability due to effective stress transfer capacity. According to experimental results, maximum energy absorption rate difference is 17% between elliptical 10mm and cylindrical 5mm geometries.Publication Open Access Investigation of wear behavior of Ti-6Al-4V/CNT composites reinforced with carbon nanotubes(GAZI UNIV, FAC ENGINEERING ARCHITECTURE, 2018-09-12) GÜLLÜOĞLU, ARİF NİHAT; Topcu, Ismail; Gulluoglu, Arif N.; Bilici, M. Kemal; Gulsoy, H. OzkanIn this study, the effects of different production conditions and different sintering conditions on microstructure, density and wear resistance of Multi-wall carbon nanotubes (CNTs) powders reinforced with Titanium (Ti-6Al-4V) powder by mechanical alloying were examined. The powders produced by mechanical alloying were compressed with a Cold Isostatic Press die under a pressure of 250 MPa in this molding machine to obtain cylindrical composite specimens. These raw specimens were extruded at 1275 degrees C for 60 minutes in a high purity argon atmosphere and high vacuum (1.2 10-5 mbar). The erosive wear behavior of the Ti-6Al-4V / CNTs metal matrix composite was studied using a pin-on-disc wear tester. The abrasion behavior of a Ti-6Al-4V / CNTs alloy after various heat treatments has been studied on abrasive wear. Under appropriate conditions it has been shown that reinforced CNTs can reduce the wear rate by more than two orders of magnitude. Various investigations have been carried out detailing the reinforcement rates of this improved wear performance. The friction and wear data show a clear surplus value added to the composite Ti-6Al-4V wear modes. As a result, in the experimental studies made, it is seen that the wear resistance increase according to the v/v % CNTs ratio which is directly supplemented to the volume. However, this properties had been decrease with the % 5 CNTs ratio.Publication Metadata only Processing and mechanical properties of B4C reinforced Al matrix composites(ELSEVIER SCIENCE SA, 2009) GÜLLÜOĞLU, ARİF NİHAT; Topcu, I.; Gulsoy, H. O.; Kadioglu, N.; Gulluoglu, A. N.Aluminum matrix composites are emerging as advance engineering materials due to its high specific strength and stiffness, good wear resistance and high temperature properties. Properties of Al reinforced with Al2O3 and SiC are widely investigated. In the present study, mechanical properties of B4C reinforced Al matrix is investigated due to higher hardness and lower density properties than SiC and Al2O3. The high temperature deformation behavior of 5, 10, 15 and 20wt% B4C powder having an average particle diameter of about 10 mu m aluminum matrix composite sintered at 650 degrees C was investigated by creep tests at temperatures ranging from 400 to 450 degrees C and creep resistance of Al alloy is enhanced by the presence of B4C particles. Measurement of impact and hardness properties of composites showed that impact values decrease and hardness values increased with increase in weight fraction of reinforcement. (C) 2009 Elsevier B.V. All rights reserved.Publication Metadata only Dielectric properties of polymer composites filled with different metals(TAYLOR & FRANCIS INC, 2008) GÜLLÜOĞLU, ARİF NİHAT; Qureshi, Anjum; Mergen, Ayhan; Eroglu, Mehmet S.; Singh, N. L.; Gulluoglu, ArifElectrically conductive composite systems based on polyvinyl chloride (PVC) and polymethyl methacrylate (PMMA) filled with metal powders of Al and Cu have been studied. The composite preparation conditions allow the formation of a random distribution of metallic particles in the polymer matrix. Dependence of the dielectric and conductivity properties of the PVC and PMMA/fillers was studied over a broad range of frequency and volume fraction of metal fillers. The experimental results could be explained by means of the conductivity of fillers and the interface polarization between polymers and fillers. Percolation was also seen in this study when the volume fraction of conducting fillers was close to critical value, in which the composites undergo an insulator-conductor transition. The relation among the dielectric property and the fillers with different conductivity was proposed.Publication Metadata only Effect of surface modifications of additively manufactured Ti-6Al-4V alloys on apatite formation ability for biomedical applications(ELSEVIER SCIENCE SA, 2021) GÜLLÜOĞLU, ARİF NİHAT; Demirci, Selim; Dalmis, Ramazan; Dikici, Tuncay; Tuncay, Mehmet Masum; Kaya, Nusret; Gulluoglu, Arif NihatIn this study, Ti-6Al-4V alloys were additively manufactured (AM) with different laser powers. The goal was to investigate the effect of different surface modifications on apatite formation ability. Four types of surface modifications, namely, sandblasting (S), acid etching (E), anodic oxidation (AO) and anodic spark oxidation (ASO), were achieved on the Ti-6Al-4V samples. The microstructure, phase, morphology, roughness and wettability properties were examined by optical microscope (OM), scanning electron microscope (SEM), Xray diffraction (XRD), surface profilometer and contact angle techniques. The bioactivity analysis was performed in simulated body fluid (SBF) for 2 weeks. The results indicated that the microstructure, surface topography, roughness and wettability influenced the apatite formation were affected by the production laser power. Generally, the samples 3 showed higher Ca and P ion ratio value because of percentage of beta phase amount, the presence of bioactive phases on the surfaces. The E3 sample resulted in the best apatite formation theoretically. The etching procedure of AM Ti-6Al-4V in the acidic solution can be applied to improve the apatite formation ability of Ti-6Al-4V alloys. (c) 2021 Elsevier B.V. All rights reserved.Publication Metadata only Radiation induced modification of dielectric and structural properties of Cu/PMMA polymer composites(ELSEVIER SCIENCE BV, 2010) GÜLLÜOĞLU, ARİF NİHAT; Singh, Dolly; Singh, N. L.; Qureshi, Anjum; Kulriya, P.; Tripathi, Ambuj; Avasthi, D. K.; Gulluoglu, Arif N.In this study, composite films consisting of an insulating polymethyl methacrylate (PMMA) polymer matrix and metal powder (Cu) additive were prepared by solution costing method. These films were irradiated with 140 MeV silver ions at the fluences of 1 x 10(11) ions/cm(2) and 1 x 10(12) ions/cm2. The radiation induced changes in dielectric, structural and surface properties of PMMA/Cu composites were studied using impedance/gain phase-analyzer, X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). It was observed that the dielectric properties and ac electrical conductivity increased significantly with the concentration of dispersed metal powder (Cu) and also with the fluence. This reveals that ion beam irradiation creates free radicals, unsaturation etc. due to emission of hydrogen and/or other volatile gases, which makes the polymer more conductive. XRD analysis of the pristine and irradiated samples shows that the crystallinity improved upon irradiation at low fluence and deteriorated on further increase of the fluence, which could be attributed to cross linking of polymer chains at low fluence and degradation at higher fluence. High energy ion beam irradiation of semicrystalline polymer composite films changes its Tg behavior as observed from DSC analysis. This result is also corroborated with the results of XRD. The average surface roughness and topography of surfaces changed with the concentration of filler and also with the ion fluence as revealed from AFM/SEM analysis. (C) 2010 Elsevier B.V. All rights reserved.