Yazar "Uslu, İbrahim" seçeneğine göre listele
Listeleniyor 1 - 13 / 13
Sayfa Başına Sonuç
Sıralama seçenekleri
Öğe The Au/polyvinyl alcohol (Co, Zn-doped)/n-type silicon Schottky barrier devices(ELSEVIER SCIENCE SA, 2011) Dökme, İlbilge; Tunç, Tuncay; Uslu, İbrahim; Altındal, ŞemsettinMetal/polyvinyl alcohol/n-type silicon Schottky barrier (SB) devices have been fabricated in this study. The importance of this study is that PVA (Co, Zn doped) nanofiber film as an interfacial layer was formed by the electrospinning technique on n-type silicon substrate. The forward and reverse bias current-voltage (I-V) characteristics of this device were measured at room temperature. The Phi(Bo) value of about 0.749 eV obtained from I-V characteristics indicates that the contact potential barrier exists at the interface between organic and inorganic semiconductor layer, that is, PVA/n-Si interface. The variation in the capacitance-voltage (C-V) and conductance-voltage (G/omega-V) characteristics of the Au/PVA (Co. Zn doped)/n-Si SB devices have been systematically investigated as a function of frequencies in the frequency range of 2 kHz-2 MHz at room temperature. The effects of density of interface states (N-ss) and series resistance (R-s) on I-V, C-V and G/omega-V characteristics were investigated. The high-frequency capacitance (C-m) and conductance (G(m)/omega) values measured under reverse bias were corrected to decrease the effects of series resistance. These results show that the locations of interface states between Si/PVA and series resistance have a significant effect on electrical characteristics of the Au/PVA (Co, Zn doped)/n-Si SB devices. (C) 2011 Elsevier B.V. All rights reserved.Öğe Characterization of boron doped Cobalt/Zinc acetate composite fibers(2009) Uslu, İbrahim; Gökmeşe, Faruk; Atakol, Orhan; Aksu, Mehmet LeventPVA/cobalt acetate/zinc acetate doped with boron composite fibers were prepared by electrospinning technique. Electrospinning was performed by putting solutions at different applied voltage in a range from 13 to 18 kV. The fibers were measured and characterized by viscometer, conductiometer (with fourpoint probe), Fourier transformed infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). The viscosity of the Boron doped solution was higher and favoring the formation of thinner and uniform nanofibers. DSC analysis shows that when boron is added to the polymer it increases the crosslinking and amorphous structure of PVA/ cobalt and zinc acetate composite polymer is increased.Öğe Coal an Impure Fuel Source: Radiation Effects of Coal-fired Power Plants in Turkey(2010) Uslu, İbrahim; Gökmeşe, FarukTurkish coal is generally poor quality and the levels of chemical and radiological toxic trace elements in it are higher with respect to mean values of activity concentrations given in United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) Report. The main pathways through which the population living around soal-fired power plant (CFPP) is exposed to natural radionuclides are external and internal (ingestion and inhalation) dose and fly ash particles are the major component of the risk. It is estimated that the people working or living near the CFPP in Turkey receive a dose in between 0.1 mSv to 1 mSv extra from CFPP because nearly all the region of Turkey uranium (U) and thorium (Th) content in the coal are higher than 5 ppm to 7 ppm and around 25 ppm to 40 ppm respectively. Continuous monitoring is essential to determine occupational exposure levels in all stages of the coal fuel-cycle and proper measures should be taken to prevent direct contact of the ash pile with the top soil and local drainage systems.Öğe Elmada hasat, nakliye ve depolama sırasında meydana gelen zedelenmelerin patolojik bozulmaya etkileri(Selçuk Üniversitesi Fen Bilimleri Enstitüsü, 2012-01-27) Uslu, İbrahim; Boyraz, NuhBu tez çalışması ile 2010?2011 yılları arasında Isparta ili Eğirdir ilçesi soğuk hava depolarındaki elmalarda hasat, nakliye ve depolama sırasında meydana gelen zedelenmelerin patolojik bozulmaya etkileri tespit edilmeye çalışılmıştır. Yapılan çalışma sonucunda zedelenen meyvelerde patolojik bozulmaların daha hızlı ve daha yoğun olarak meydana geldiği tespit edilmiştir.Bu patolojik bozulmalardan sorumlu 7 adet fungal organizma tespit edilmiştir.Bunlar; Penicillium expansum (Mavi Küf), Gloeosporium album (Acı çürüklük), Botrytis cinerea (Gri küf), Venturia inaequalis (Karaleke), Rhizopus spp. (Rhizopus Çürüklüğü), Aspergillus spp. (Siyah Küf), Alternaria mali (Siyah Çürüklük) dir. Bunlardan en çok görüleni Penicillium expansum olup, 6.ayın sonundaki sayım değerlerine göre toplam enfekteli meyvelerin %25`inde Penicillium expansum tespit edilmiştir. Penicillium expansum`u %12.4'lük oranla Gloeosporium album takip etmiştir. Tespit edilen diğer fungal etmenlerden Botrytis cinerea %11.1, Venturia inaequalis %8.1, Rhizopus spp%5.3, Aspergillus spp %3.1, Alternaria mali %2.6 `lık oranlarla Gloeosporium album `u takip etmiştir.Öğe Fabrication and characterisation of boron doped barium stabilised bismuth cobalt oxide nanocrystalline ceramic composite(TAYLOR & FRANCIS LTD, 2013) Uslu, İbrahim; Çınar, Emre; Koçyiğit, Serhat; Aytimur, Arda; Akdemir, AhmetIn this paper, the fabrication and characterisation processes of both boron doped and undoped barium stabilised bismuth cobalt oxide nanocrystalline ceramic powders using polymeric precursor were reported. Obtained boron doped barium stabilised bismuth cobalt oxide nanocrystalline ceramic powders, which have been synthesised by polymeric precursor technique at temperatures below 900 degrees C and at atmospheric condition, were characterised by X-ray diffraction, Fourier transform infrared and scanning electron microscopy techniques. According to X-ray results, fcc and bcc phases coexist in the samples of the nanocrystalline ceramic powders. Crystallite sizes for body centred cubic structure were calculated using Scherrer equation for both boron doped and undoped samples. In addition, lattice parameters were calculated for all samples.Öğe Fabrication and Characterization of Boron Supported YBCO Superconductive Nanofibers by Electrospinning(Bentham Science Publ Ltd, 2010) Uslu, İbrahim; Öztürk, Mustafa Kemal; Aksu, Mehmet Levent; Gökmeşe, FarukThis study is related to the preparation of boron supported YBa(2)Cu(3)O(7) (YBCO) superconducting material. The first step was the preparation of a composite formed by mixing yttrium, barium, and copper acetates with polyvinyl alcohol (PVA) at a suitable temperature. The resulting composite polymer was electrospun to produce nanofibers. Finally, the obtained nanofibers were subjected to thermal treatments at 500 degrees C, 600 degrees C and 1000 degrees C to elucidate their morphological properties. The conductivity of the nanofibers was measured by the four probe techniques, and the boron supported polymer was found that it had a higher conductivity. Differential Scanning Calorimetry (DSC) data for the boron doped material revealed that the addition of boron increased the thermal resistance of the fibers. Scanning electron microscopy (SEM) images of the fibers showed that they were homogeneously electrospun, and there was no beading or heaping on them.Öğe Frequency and Temperature Dependence of Dielectric Properties of Au/Polyvinyl Alcohol (Co, Ni-doped)/n-Si Schottky Diodes(Taylor & Francis As, 2010) Tunç, Tuncay; Uslu, İbrahim; Dökme, İlbilge; Altındal, Şemsettin; Uslu, HabibeThe dielectric properties and AC conductivity of Au/polyvinyl alcohol (Co, Ni-doped)/n-Si Schottky diodes (SDs) were investigated in the frequency range 1kHz-1MHz and in the temperature range 80-400K. The frequency and temperature dependence of dielectric constant (epsilon'), dielectric loss (epsilon''), loss tangent (tan ), AC electrical conductivity (sigma ac) and the real and imaginary parts of the electric modulus (M' and M'') were found to be a strong function of frequency and temperature. The values of epsilon', epsilon'' and tan decrease with increasing frequency, while they increase with increasing temperature, especially above 275K. The values of sigma ac increase with both increasing frequency and temperature. Such temperature-related behavior of sigma ac can be attributed to the high mobility of free charges at high temperature. Electric modulus formalism was also analyzed to obtain experimental dielectric data. The values of M' and M'' increase with increasing frequency, while they decrease with increasing temperature. The interfacial polarization, which more easily occurs at low frequencies and high temperatures, consequently contributes to the improvement of the dielectric properties of SDs.Öğe Nanofibers by electrospinning of nylon 6 doped with boron(2009) Uslu, İbrahim; Altaş, Ayşenur; Aksu, Mehmet Levent; Gökmeşe, FarukIn this study, Nylon 6 was successfully cross-linked with boron using formic acid as solution. Electrospinning process was performed by putting hybrid nylon 6/boric acid solutions at different applied voltage in a range from 20 to 25 kV using a high voltage power supply. Nylon has been widely used in industry because of its good mechanical properties. The use of boron improves the strength, flame retardant characteristics and flexibility of the nylon 6 fibers. The structures of the nanofibers synthesized are characterized by the Fourier transformed infrared spectroscopy (FTIR), thermo gravimetric and differential thermal analysis (TG/DTA), differential scanning calorimetry (DSC), atomic force microscopy (AFM), and scanning electron microscopy (SEM). DSC and TGA analysis revealed that stability of electrospun nylon 6 fiber is higher than non spun sample and increase of boric acid content increases the stability of the polymer. It is observed from the SEM images that the diameters of the fibers decreased with boron content increased. FTIR analysis revealed that all characteristic N-H structures are observed and consistent with literature.Öğe Preparation and characterization of PVA/Boron polymer produced by an electrospinning technique(EUROPEAN POLYMER FEDERATION, 2007) Uslu, İbrahim; Daştan, H.; Altaş, Ayşenur; Yaylı, Ahmet; Atakol, Orhan; Aksu, Mehmet LeventIn this study, poly(vinyl alcohol) were cross-linked with boron in varying concentrations and blend fibers were obtained with diameters ranging from 0.3 mu to 4.0 mu m with the use of electrospinning process. The resulting product was characterized by SEM, DSC, and FT-IR techniques. There is no beading tendency in either boron doped or undoped fibers. When the amount of boric acid in PVA solutions was increased the conductivity of the polymer decreased. The data indicated the existence of boron oxide in the polymeric structure and the formation of B-O-C bond. SEM micrographs reveal that higher viscosity favors the formation of thicker fibers. Boron addition seems to disturb the easy detachment of the fibers from the tip of the Taylor Cone.Öğe Preparation and characterization of PVA/zinc acetate/boron composite fiber(2007) Uslu, İbrahim; Başer, Burcu; Yaylı, Ahmet; Aksu, Mehmet LeventThe objective of this work was to synthesize boron incorporated PVA/Zinc acetate nano precursor composite polymer fibers using electrospinning technique. Produced fibers, are useful reagents in organic synthesis of zinc oxide nano structures which have gained wide interest because of their potential applications in the fabrication of microelectronic devices. Boron incorporated PVA/Zinc acetate not only improve the electrical properties of ZnO films but also has an influence on the crystal structure of ZnO films. The fibers were measured and characterized by conductiometer (with four-point probe), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The formation of boron incorporated PVA/Zinc acetate hybrid polymer was confirmed by FT-IR spectra. SEM micrographs clearly reveal that there are random-growth oriented fibers on aluminum foil with diameters ranging from 0.5 to 1 ?m. According to the TGA analysis decomposition of zinc acetate from the PVA chain was observed around 273°C, 368°C and 447°C. Boron incorporated PVA/Zinc acetate nano composite polymer fibers have been successfully synthesized for the first time using electrospinning technique and characterized in detail as precursor material for ZnO. Electrospinning process has been a widely used, simple and versatile method and in future may be used for large-scale preparation of nanofibers of ZnO.Öğe Preparation and Properties of Electrospun Poly(vinyl alcohol) Blended Hybrid Polymer with Aloe vera and HPMC as Wound Dressing(2010) Uslu, İbrahim; Keskin, Selda; Gül, Ali; Karabulut, Tutku Ceren; Aksu, Mehmet LeventA series of poly(vinyl alcohol) (PVA)/poly(vinyl pyrrolidone) (PVP)/poly(ethylene glycol) (PEG) hybrid nanofibers were fabricated by an electrospinning method, in order to be used as a potential wound dressing material. The effect of Aloe vera was investigated in terms of solution properties such as viscosity, conductivity, pH and surface tension. The nanofibrous wound dressing materials were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) and differential scanning calorimetry (DSC). SEM results revealed that the fiber diameters ranged between 200-500 nm and they were linear, homogenous and free of beads. DSC thermograms indicated that the addition of Aloe vera affects the crystal structure and efficiently cross-links the hybrid polymer, forming an amorphous structure with a melting temperature (Tm) of 219°C at an Aloe vera concentration of 3%. FTIR results clearly resolved the hybrid polymer structure of nanofibers obtained.Öğe Preparation of Gadolina Stabilized Bismuth Oxide Doped with Boron via Electrospinning Technique(SPRINGER, 2012) Tunç, Tuncay; Uslu, İbrahim; Durmuşoğlu, Şenol; Keskin, Selda; Aytimur, Arda; Akdemir, AhmetIn this study, boron doped and undoped poly (vinyl) alcohol/bismuth-gadolina acetate (PVA/Bi-Gd) nanofibers were prepared using electrospinning technique then calcinated at 800 degrees C for 2 h. The originality of this study is the addition of boron to metal acetates. The effects of boron doping were investigated in terms of solution properties, morphological changes and thermal characteristics. The characteristics of the fibers were investigated with FT-IR, XRD, SEM and BET. The addition of boron did not only increase the thermal stability of the fibers, but also their diameters, which yielded stronger fibers. XRD analyses showed that boron doping increased the peak intensities and indicated that the boron doping enhanced the crystallite size. Moreover, no shifts were noticed in diffraction angles for boron doped and undoped samples. Therefore, boron doping did not significantly alter the lattice spacing. The SEM micrograph of the fibers showed that the addition of boron resulted in the formation of cross-linked bright-surfaced fibers. The average fiber diameter for boron doped and undoped fiber mats were 204 and 123 nm, respectively. Also, grain diameters of boron doped and undoped nanocrystalline sintered powders were measured as 140 and 118 nm, respectively. The BET results showed that boron undoped and doped Bi2O3-La2O3 nanocrystalline powder ceramic structures sintered at 800 degrees C have surface areas of 59.72 and 39.80 m(2)/g, respectively.Öğe Preparation of PVA/Chitosan Doped With Boron Composite Fibers and Their Characterization(2008) Uslu, İbrahim; Çelikkan, Hüseyin; Atakol, Orhan; Aksu, Mehmet LeventIn this study, chitosan and poly(vinyl alcohol) were cross-linked with boron in varying concentrations and chitosan and poly(vinyl alcohol) blend fibers were obtained with electrospinning process. Viscosity and electrical conductivity results revealed that the increase in chitosan and boron content increased the viscosity of the solution and but decreased the electrical conductivity of the fibers. The peaks obtained with FT-IR analyses were in good agreement with literature. SEM micrographs also showed that wavy and curly fibers with relatively small diameters were obtained as the chitosan and boron concentrations were increased. Thermogravimetric data revealed that the formation of a more stable polymer structure as a result of the cross linking with boron.
