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EKREN, NAZMİ

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EKREN

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NAZMİ

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2008 - 200922010 - 201922
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Now showing 1 - 10 of 24
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    Fabrication and characterization of pla/sa/ha composite nanofiber by electrospinning for bone tissue engineering applications
    (2018-07-18) CESUR, SÜMEYYE; EKREN, NAZMİ; KILIÇ, OSMAN; OKTAR, FAİK NÜZHET; BİLĞİÇ ALKAYA, DİLEK; AYAZ SEYHAN, SERAP; GÜNDÜZ, OĞUZHAN; Cesur S., Ekren N., Kılıç O., Oktar F. N., Bilğiç Alkaya D., Ayaz Seyhan S., Ege Z. R., Gündüz O.
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    Continuous wavelet transform for ferroresonance phenomena in electric power systems
    (ELSEVIER SCI LTD, 2013) EKREN, NAZMİ; Akinci, Tahir Cetin; Ekren, Nazmi; Seker, Serhat; Yildirim, Sezen
    The common characteristics of a nonlinear system are multiple equilibrium points, limit cycles, jump resonance and sub-harmonic generation. Ferroresonance is also a nonlinear electrical phenomenon, which occurs frequently in power systems including no-load saturable transformers, transmission lines and single/three phase switching. In this work, we modeled the 380 kV West Anatolian Electric Power Network of Turkey, by performing numerical simulations using MATLAB-Simulink Power System Block-set. We generated the signals that are characteristics to the ferroresonance in order to exhibit the emergence of the nonlinear phenomenon. In addition, using the continuous wavelet transform (CWT), we observed the behavior of the ferroresonance both in time and frequency domains. Using the results of the CWT and Power Spectral Density (PSD) applications, the ferroresonance is determined from the emergence of the over voltage changes and the inter-harmonics of between +/- Delta integral Wand +/- Delta integral depending on frequency resolution +/- Delta integral. (C) 2012 Elsevier Ltd. All rights reserved.
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    Cell studies on Electrohydrodynamic (EHD)-3D-bioprinted Bacterial Cellulose\Polycaprolactone scaffolds for tissue engineering
    (ELSEVIER SCIENCE BV, 2019) EKREN, NAZMİ; Altun, Esra; Ekren, Nazmi; Kuruca, Serap Erdem; Gunduz, Oguzhan
    The application of three-dimensional (3D) printed scaffolds for tissue engineering have gained significant attention in recent years. The biological activity of scaffolds used in tissue engineering applications depends on fabricating high-resolution patterns with fiber orientation and scale. In this study, Bacterial Cellulose (BC) and Polycaprolactone (PCL) composite scaffolds with the line spacing of 100 mu m are produced using Electrohydrodynamic (EHD)-3D-bioprinting technique. The composite scaffolds exhibit enhanced biocompatibility with facilitated cell attachment and proliferation in vitro. The results of this work have demonstrated that EHD-3D-bioprinting method shows great potential for the preparation of BC/PCL composite scaffold and patterns for tissue engineering with enhanced bioactivity. (C) 2018 Published by Elsevier B.V.
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    Production and Characterization of Antimicrobial Electrospun Nanofibers Containing Polyurethane, Zirconium Oxide and Zeolite
    (SPRINGER, 2018) OKTAR, FAİK NÜZHET; Aydogdu, Mehmet Onur; Oprea, Alexandra Elena; Trusca, Roxana; Surdu, Adrian Vasile; Ficai, Anton; Holban, Alina Maria; Iordache, Florin; Paduraru, Andrei Viorel; Filip, Diana Georgiana; Altun, Esra; Ekren, Nazmi; Oktar, Faik Nuzhet; Gunduz, Oguzhan
    In this study, electrospinning technique has been utilized to prepare composite nanofiber mats of polyurethane (PU)/zirconium dioxide (ZrO2) and PU/zeolite, consisted by antimicrobial properties. Tensile strength measurement test was performed for the mechanical analysis of the nanofibers. Scanning electron microscopy (SEM) were performed for displaying the morphological features of the fiber structure. XRD tests were performed for revealing the chemical structure. Antimicrobial tests were also performed to display antimicrobial effects of the produced materials. In vitro test was also performed to determine cytotoxicity and biocompatibility. The present PU/ZrO2 and PU/zeolite composite nanofibers resulted with improved mechanical properties and good antimicrobial properties against either their pure forms or other studies. Cell proliferation and viability also increased significantly with increase in zeolite and ZrO2 ratio. It is concluded that this composition provides a novel alternative as an antimicrobial material which can be suitable as a wound dressing or a coating material for various healthcare engineering applications.
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    Energy saving in lighting system with fuzzy logic controller which uses light-pipe and dimmable ballast
    (ELSEVIER SCIENCE SA, 2013) EKREN, NAZMİ; Gorgulu, Sertac; Ekren, Nazmi
    Approximately, 20% of the electricity consumed in the world is spent for lighting. More efficient utilization of the sun, as a natural source of light, for lighting would save electricity used for lighting. The aim of this study is to illuminate a windowless room via a light-pipe and dimmable electronic ballasts. Light-pipe is used for the illumination of the space during the daytime. In case of inadequate daylight, artificial lighting is made via dimmable electronic ballasts and fluorescence lamps. Artificial lighting is supervised by a fuzzy logic control system to keep the illumination level at 350 lux. When there is a motion in the room, the system works with the message of the motion sensor, which, thereby, enables energy saving. Additionally, dimming the lamps result in conversation of the electrical energy used for illumination. After the experimental studies, 350 lux value targeted in the work plane is achieved with +/- 10 lux error. (c) 2013 Elsevier B.V. All rights reserved.
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    Effect of yttria-doping on mechanical properties of bovine hydroxyapatite (BHA)
    (SAGE PUBLICATIONS LTD, 2008) OKTAR, FAİK NÜZHET; Gunduz, O.; Daglilar, S.; Salman, S.; Ekren, N.; Agathopoulos, S.; Oktar, F. N.
    Sintered bodies of hydroxyapatite, derived from calcinated bovine bone (BHA) and doped with 0.5 and 1wt% Y2O3, were prepared. Measurements of density, compression strength, and microhardness, along with scanning electron microscopy (SEM) and X-ray diffraction (XRD) were carried out. The experimental results showed that BHA doping with yttria favors formation of glassy phase, which advances sintering and results in a dense and reinforced BHA matrix. The best mechanical properties were achieved after sintering at 1200 degrees C for compressive strength (82 MPa) and 1300 degrees C for microhardness (672 HV). These results are better than pure BHA or composites of hydroxyapatite with Y2O3-stablized zirconia, qualifying yttria (as dopant of BHA) for further in vitro and in vivo experimentation.
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    Production of the biomimetic small diameter blood vessels for cardiovascular tissue engineering
    (TAYLOR & FRANCIS AS, 2019) TOKSOY ÖNER, EBRU; Aydogdu, Mehmet Onur; Chou, Joshua; Altun, Esra; Ekren, Nazmi; Cakmak, Selami; Eroglu, Mehmet; Osman, Asila A.; Kutlu, Ozlem; Oner, Ebru Toksoy; Avsar, Gulben; Oktar, Faik Nuzhet; Yilmaz, Ismail; Gunduz, Oguzhan
    A novel biomimetic vascular graft scaffolds were produced by electrospinning method with the most superior characteristics to be a proper biomimetic small diameter blood vessel using Polycaprolactone(PCL), Ethyl Cellulose(EC) and Collagen Type-1 were used to create the most convenient synergy of a natural and synthetic polymer to achieve similarity to native small diameter blood vessels. Scanning Electron Microscopy(SEM), Fourier Transform Infrared Spectroscopy(FTIR), Differential Scanning Calorimetry Analysis(DSC), tensile measurement tests, and in-vitro and in-vivo applications were performed. Results indicated significant properties such as having 39.33 nm minimum, 104.98 nm average fiber diameter, 3.2 MPa young modulus and 135% relative cell viability. [GRAPHICS] .
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    Developments of 3D polycaprolactone/beta-tricalcium phosphate/collagen scaffolds for hard tissue engineering
    (SPRINGER, 2019) İNAN, AHMET TALAT; Aydogdu, Mehmet O.; Mutlu, Bilcen; Kurt, Mustafa; Inan, Ahmet T.; Kuruca, Serap E.; Erdemir, Goekce; Sahin, Yesim M.; Ekren, Nazmi; Oktar, Faik N.; Gunduz, Oguzhan
    3D bioprinting provides an innovative strategy to fabricate a new composite scaffold material consisted in a porous and rough structure with using polycaprolactone (PCL), beta-tricalcium phosphate (beta-TCP), and collagen as a building block for tissue engineering. We investigated the optimization of the scaffold properties based on the beta-TCP concentration using 3D bioprinting method. Computer-aided drawing was applied in order to digitally design the scaffolds while instead of solid filaments, materials were prepared as a blend solution and controlled evaporation of the solvent during the bioprinting was enabled the proper solidification of the scaffolds, and they were successfully produced with well-defined porous structure. This work demonstrated the feasibility of complex PCL/beta-TCP/collagen scaffolds as an alternative in the 3D bioprinting engineering to the fabrication of porous scaffolds for tissue engineering.
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    Controlling of grid connected photovoltaic lighting system with fuzzy logic
    (PERGAMON-ELSEVIER SCIENCE LTD, 2010) ERDAL, HASAN; Saglam, Safak; Ekren, Nami; Erdal, Hasan
    In this study, DC electrical energy produced by photovoltaic panels is converted to AC electrical energy and an indoor area is illuminated using this energy. System is controlled by fuzzy logic algorithm controller designed with 16 rules. Energy is supplied from accumulator which is charged by photovoltaic panels if its energy would be sufficient otherwise it is supplied from grid. During the 1-week usage period at the semester time, 1.968 kWh energy is used from grid but designed system used 0.542 kWh energy from photovoltaic panels at the experiments. Energy saving is determined by calculations and measurements for one education year period (9 months) 70.848 kWh. (C) 2009 Elsevier Ltd. All rights reserved.
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    Fabrication and characterization of hazelnut shellpowder with reinforced polymer compositenanofibers
    (2018-09-14) KARTAL, İLYAS; OKTAR, FAİK NÜZHET; EKREN, NAZMİ; İNAN, AHMET TALAT; GÜNDÜZ, OĞUZHAN; CESUR, SÜMEYYE; Şengör İ., Cesur S., Kartal İ., Oktar F. N., Ekren N., İnan A. T., Gündüz O.