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Öğe Ultrasonically sprayed cobalt oxide thin films: Enhancing of some physical properties by nickel doping(Elsevier B.V., 2021) Kuş, Esra; Küçükkarslan, Ayşe; Demirselçuk, Barbaros; Sarıca, Emrah; Akyüz, İdris; Bilgin, VildanIn this study, the effect of Ni doping (3, 6, 9 at%) on structural, optical, electrical and magnetic properties of Co3O4 films was reported. Films were grown at 300 ± 5 °C substrate temperature via ultrasonic spray pyrolysis (USP) technique. The structural analyses showed that undoped and Ni (3%) doped films exhibit an amorphous structure. Ni doping at higher ratios caused the films to have improved crystallinity. Optical band gap values the films were found to be between 2.03 and 2.08 eV with an additional sub-band corresponding to energies varying between 1.35 and 1.46 eV. The electrical conductivity values of the films increased significantly depending on the Ni doping. The hysteresis curves of the films showed that the films have weak ferromagnetic properties. Ni doping significantly improved the structural and electrical properties of Co3O4 films making them suitable materials for technological applications.Öğe New photometric analysis of hot Jupiter: WASP-135b(Elsevier B.V., 2021) Öztürk, Oğuz; Erdem, AhmetWe report photometric follow-up observations of WASP-135b obtained using the 1.23-m telescope at Calar Alto Observatory and 1.00-m telescope at TÜBİTAK National Observatory during the 2017 and 2018 observational seasons. Eight new transit light curves of WASP-135b were analyzed with JKTEBOP code. The ratio of the planet radius to radius of host star, fractional radius of host star, and orbital inclination of WASP-135b were found to be 0.138 ± 0.002, 0.181 ± 0.008 and 82.44 ± 0.64 degrees, respectively. Planetary radius of WASP-135b was derived from transit parameters to be 1.075 ± 0.150 RJ. The transit ephemeris of WASP-135b was also updated using the maximum likelihood method (MLM). 165 well-known hot Jupiters (HJs) were selected from the Exoplanet Data Explorer database and the classification of these HJs together with WASP-135b, based on their equilibrium temperatures and Safronov numbers, is discussed.Öğe Einstein-Rosen universe with scalar field in f(R,T) theories(Elsevier B.V., 2021) Taṣer, Dog̃ukan; Dog̃ru, Melis UluNon-static Einstein–Rosen universe with scalar field is examined via two different selection of f(R,T) models. Firstly, we analyzed Einstein–Rosen universe with scalar field in f(R,T)=R+2f(T) model. Then, we constructed field equations for f(R,T)=f1(R)+f2(R)f3(T) model, as well. For both models, exact solutions of field equations have been attained without considering any approximation or restriction. Whether scalar field corresponds to phantom and/or quintessence scalar field are investigated for each models.Öğe Sol-gel derived ZnO:Sn thin films and fabrication of n-ZnO:Sn/p-Si heterostructure(Elsevier B.V., 2021) Sarıca, Emrah; Güneş, İbrahim; Akyüz, İdris; Bilgin, Vildan; Ertürk, KadirIn this work ZnO:Sn thin films were deposited onto glass and p-Si substrates by spin coating of prepared sols which contains different amounts of Zn(CH3COO)2·2H2O and SnCl2 (0, 5, 10 and 15%). Physical properties of ZnO films were examined as a function of SnCl2 in prepared sols. In addition to that, heterostructure examinations were also carried out by depositing all films on p-Si substrates as well. XRD studies revealed that all films have c-axis orientation with crystallite sizes between 38 and 47 nm. AFM and SEM images showed that morphology of the films remarkably deteriorated with the increase in amount of SnCl2 in sol. Optical transmittance and absorbance spectra showed that films have high transmittance and low absorbance in the visible region. Besides, optical band gap increased from 3.27 eV to 3.37 eV. Additional band gap energies were determined for 10% and 15% Sn doped ZnO films. Room temperature photoluminescence spectra for all films were deconvoluted for the evaluation of all emission bands and it was noted that incorporation of SnCl2 into sol led to enhancement of UV-blue emission bands and caused emission bands related to oxygen vacancies to diminish. Four-point-probe measurements revealed that electrical resistivity of ZnO:Sn films increased from 3.20 × 100 Ωcm to 2.82 × 104 Ωcm and diode ideality factor of Ag/ZnO:Sn/p-Si/Au heterostructure was calculated to be in the range of 2.14–4.59 while zero-bias barrier height is in the range of 0.63–0.78 eV.Öğe Design of EM-artifact-free earphone based on the photoacoustic effect(Elsevier GmbH, 2021) Muşdal, Bengi Derya; Kurt, MustafaElectromagnetic interactions between conventional earphones and the electroencephalography (EEG) electrodes used for analyzing brain waves give rise to efficiency problems in neurophysiological studies of auditory perception. Currently used speakers and headphones are electromagnetic devices based on strong magnets. In spite of intensive use of such systems, there has been no effective way to eliminate the electromagnetic artifacts produced by such audio transmitting devices to date. The ability for transferring audible sounds without the use of electromagnetic devices that can affect the EEG signal would open up many innovative possibilities in Audio Technologies. Audible sound transfer over long distances is possible by the photoacoustic effect. In such studies, the modulated optical signal can be converted into an audible signal arising from the absorption of the light energy of relevant molecules. In this study, we propose an earphone based on the photoacoustic effect, and calculated the dB SPL (Sound Pressure Level) values for a spherical cell filled with olive pomace. By the use of the method of Diebold and Westervelt, we theoretically calculated the sound pressure levels for our cell and determined a 60 dB SPL at a sound frequency of 1000 Hz for our preliminary earphone design.Öğe Improvement of electrical characteristics of SnSe/Si heterostructure by integration of Si nanowires(Elsevier B.V., 2021) Coşkun, Emre; Güllü, H. H.; Emir, C.; Parlak, M.In this study, the effects of the nanowire geometry on Si wafer substrate were investigated for the SnSe/Si-nanowire heterojunction device and the obtained results were compared with the one fabricated on planar Si surface. Nanowires on Si surface were produced by metal-assisted etching method and the SnSe film layer was deposited by thermal evaporation technique. On both Si and glass surfaces, deposited film shows polycrystalline and single SnSe phase. From optical transmission measurements, optical band gap of this film was determined as 1.36 eV in a good agreement with the literature. All SnSe/Si heterostructures were found in a p-n diode behavior and the ideality factor and series resistance values were calculated as 2.40, 547 Ω, and 3.71, 1.57 × 103 Ω, for SnSe/Si-nanowire and SnSe/Si heterojunctions, respectively. As a result, an improvement in device characteristics concerning the planar Si structure was found by utilizing Si nanowire structure.Öğe Electronic Spectra of C60Films Using Screened Range Separated Hybrid Functionals(American Chemical Society, 2021) Chakravarty, Chandrima; Aksu, Hüseyin; Maiti, Buddhadev; Dunietz, Barry D.We study computationally the electronic spectra of C60thin films using the recently developed density functional theory (DFT) framework combining a screened range separated hybrid (SRSH) functional with a polarizable continuum model (PCM). The SRSH-PCM approach achieves excellent correspondence between the frontier orbital’s energy levels and the ionization potential and electron affinity of the molecular systemat the condensed phaseand consequently leads to high quality electronic excitation energies when used in time-dependent DFT calculations. Our calculated excited states reproduce the experimentally main reported spectral peaks at the 3.6-4.6 eV energy range and when addressing excitonic effects also reproduce the red-shifted spectral feature. Notably, we analyze the low-lying peak at 2.7 eV and associate it to an excitonic state.Öğe Domain wall solutions with quark matter in higher dimensional space-times(Amer Inst Physics, 2007) Aktaş, Can; Yılmaz, İhsan; Baysal, Hüsnü; Aygün, Melis; Demirel, CananIn this paper, we have examined quark matter in the perfect form attached to domain walls in the higher dimensional spherical symmetric space-time admitting one-parameter group of conformal motions. For this purpose, we have solved Einstein's field equations for higher dimensional spherical symmetric space-time via conformal motions. Also, we have discussed the features of the obtained solutions.Öğe Strange quark matter solutions for Marder's universe in f (R, T) gravity with Λ(Springer, 2016) Aygün, Sezgin; Aktaş, Can; Yılmaz, İhsanIn this paper, we investigate homogeneous cylindrically symmetric Marder's universe in the presence of strange quark matter (SQM) source in f (R, T) gravity with cosmological constant Lambda. For this aim we have used the anisotropy feature (sigma(x)(x)/theta) of Marder type universe and equation of state (EoS) strange quark matter to obtain solutions in two classes f (R, T) gravity (Harko et al. in Phys. Rev. D 84:024020, 2011). Finally, some physical and kinematical properties are discussed.Öğe Quark and strange quark matter solutions for higher dimensional FRW universe in Lyra geometry(Springer Heidelberg, 2015) Aygün, Sezgin; Çağlar, Halife; Taşer, Doğukan; Aktaş, CanIn this study, we have investigated the higher dimensional flat Friedmann-Robertson-Walker (FRW) universe for a cloud of string with perfect fluid attached quark and strange quark matter (SQM) in Lyra geometry. Generalized (n + 2) dimensional flat FRW universe solutions have been achieved with the aid of equation of states (EOS) and deceleration parameter (q). From the field equations, we have obtained that the cloud of string with perfect fluid does not survive. Since the string tension density vanishes (lambda = 0) for this model, as a result, the cloud of string with perfect-fluid-attached quark and strange quark matter energy-momentum tensor is automatically transformed into a perfect-fluid-attached quark and strange quark matter energy-momentum tensor. Also, our solutions agree with Halford's study. beta(2) behaves like a cosmological constant. When t -> infinity the pressure of quark matter and the density go to zero, then, the quark matter transforms into another matter with time. Also our quark matter solutions are in agreement with the present idea.Öğe Magnetized strange quark matter solutions in f(R, T) gravity with cosmological constant(Elsevier Science Bv, 2017) Aktaş, Can; Aygün, SezginIn this research, we have studied magnetized strange quark matter (SQM) solutions for Friedmann-Robertson-Walker (FRW) universe in f(R, T) gravity. To obtain exact solutions of modified field equations we have used f(R, T) = R + 2 f(T) and f(R, T) = f(1)(R) + f(2)(T) models given by Harko et al. (Harko et al. in Phys. Rev. D 84: 024020, 2011) and f(R, T) = R + f(3)(T) model (here f(3) is an arbitrary function) with cosmological constant Lambda. For t -> 8 we obtain p = -rho dark energy situation with small constant values of cosmological constant in three different f (R, T) gravitation models. In our solutions magnetic field does not observe also we have transformed our solutions from FRW universe to Static Einstein Universe (SEU) and we get f(R, T) gravity results for SEU universe. Finally we discussed our physical solutions. (C) 2016 The Physical Society of the Republic of China (Taiwan). Published by Elsevier B.V. All rights reserved.Öğe Relationship between magnetic field and anisotropy parameter in gravitation theories(World Scientific Publ Co Pte Ltd, 2018) Aktaş, Can; Aygün, Sezgin; Sahoo, Pradyumn KumarThe magnetized strange quark matter (MSQM) solutions are obtained for a Marder type universe using constant deceleration parameter. The exact solutions of field equations are obtained for f(R,T) = R 2f(T) model given by [T. Harko et al., Phys. Rev. D 84, 024020 (2011)] with cosmological term. Also, we have obtained General Relativity (GR) solutions for MSQM distributions. For t -> infinity, we get the dark energy model, i.e. p -> -B-c, rho -> B-c and omega = -1. However, for t -> infinity, we find the cosmological constant A as negative in f (R, T) theory and GR. These results agree with [S. Aygun et al., Astrophys. Space Sci. 361, 380 (2016); C. Aktas and S. Aygun, Chinese T. Phys. 55, 71 (2017); P. K. Sahoo et al., Mod. Phys. Lett. A 32, 1750105 (2017)] in f(R,T) theory. The physical consequences of our obtained models are discussed at the end.Öğe Facile synthesis and characterization of trimesic acid-Cu based metal organic frameworks(Elsevier, 2014) Şahiner, Nurettin; Sel, Kıvanç; Öztürk, Ömer Faruk; Demirci, Şahin; Terzi, GözdeMetal-organic frameworks based on trimesic acid (TMA) as organic linker and Cu (II) as metal ions from different metal salts such as CuCl2, Cu(NO3)(2), CuSO4 and Cu(CH3COOH)(2) were prepared in relatively environmentally friendly media e.g., at room temperature in DI water and at the boiling point of ethanol. The prepared TMA-Cu MOFs showed very interesting porosity and optical coloring based on the source of the used metal salts and preparation medium. The prepared MOFs were characterized in terms of their porosity with BET measurements and it was found that about 850 m(2)/g for the MOF prepared from Cu(NO3)(2) salt in ethanol. The amounts of metal ions connected to TMA were determined by atomic absorption spectroscopy measurements (AAS) after dissolution of TMA-Cu MOFs by concentrated HCl treatments. From MS measurements the mole ratio of Cu(II) to TMA was found to vary between 1.5 and 2, depending on the source of metal ions and the solvent used during preparation. The structural analysis and thermal characterization of the prepared MOFs were done by using FT-IR and TGA analysis, respectively. Additionally, TMA-Cu based MOF disks were prepared and their conductivities were determined by I V measurements. The conductivity of TMA-Cu MOFs was calculated to be between 8.26E-08 and 5.29E-11 S/cm. (C) 2014 Elsevier B.V. All rights reserved.Öğe Benign Preparation of Metal-Organic Frameworks of Trimesic Acid and Cu, Co or Ni for Potential Sensor Applications(Springer, 2015) Sel, Kıvanç; Demirci, Şahin; Meydan, Engin; Yıldız, Sema; Öztürk, Ömer Faruk; Al-Lohedan, Hamad; Şahiner, NurettinMetal-organic frameworks (MOFs) have been constructed using trimesic acid (TMA) as organic linker and Co(II), Ni(II) or Cu(II) metal ions from their corresponding aqueous chloride salts at room temperature. The prepared TMA-M (M: Co, Ni, and Cu) MOFs have been characterized in terms of their porosity and optical, thermal, electrical, and structural properties. The prepared MOFs were characterized in terms of their porosity through Brunauer-Emmett-Teller measurements, yielding a value of 330 m(2)/g for the TMA-Cu MOF. Structural analysis and thermal characterization of the prepared MOFs were done by using Fourier-transform infrared (FT-IR) spectroscopy, x-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA), respectively. The optical properties were analyzed by fluorescence spectroscopy. Additionally, TMA-M MOF disks were prepared and their conductivities determined by room-temperature I-V measurements. The conductivity of the TMA-M MOFs was calculated to be between 7.97 x 10(-7) S/cm and 5.39 x 10(-9) S/cm.Öğe Magnetized quark and strange quark matter in the spherical symmetric space-time admitting conformal motion(Springer/Plenum Publishers, 2007) Aktaş, Can; Yılmaz, İhsanIn this paper, we have examined magnetized quark and strange quark matter in the spherical symmetric space-time admitting one-parameter group of conformal motions. For this purpose, we have solved Einstein's field equations for spherical symmetric space-time via conformal motions. Also, we have discussed the features of the obtained solutions.Öğe Ionic liquid colloids based on PEI for versatile use(Elsevier Science Bv, 2015) Demirci, Şahin; Sel, Kıvanç; Şahiner, NurettinThe PEI microgels were synthesized by micro-emulsion polymerization technique, and protonated with 0.1 M HCl acid treatment due the existence of abundant number of tertiary, secondary and primary amine groups on the PEI network. Then, the protonated PEI microgels (Q-PEI) were exposed to anion exchange reaction with differ ionic liquid forming salts, such as with sodium dicyanamide (SDCA), ammonium hexafluorophosphate (AHFP), and sodium tetrafluoroborate (STFB) in aqueous medium for the preparation of PEI-based ionic liquid colloidal microgels. Finally, the anion exchanged PEI based ionic liquid colloids (ILCs) were used as template for in situ metal nanoparticles preparation such as Co, Ni, and Cu to generate ILC composite (PEI-M) (M: Co, Ni, and Cu). Then, PEI-M composites were used in hydrolysis of NaBH4 for H-2 generation. Various parameters affecting the H-2 production rate such as the metal types, and the temperature were investigated, and the activation parameters were evaluated. Additionally, PEI-M metal composites were also shown to very effective catalyst in reduction of 4-nitophenol (4-NP) to 4-aminophenol (4-AP). (C) 2015 Elsevier B.V. All rights reserved.Öğe Conductivity of p(AAc) Cryogel and Its Li+, Na+, and K+ Salts for NH3 Sensing(Springer, 2016) Şahiner, Nurettin; Demirci, Şahin; Sel, KıvançPoly(acrylic acid) [p(AAc)] cryogel has been synthesized by a cryopolymerization technique under cryogenic conditions. The synthesized p(AAc) cryogel was treated with LiOH, NaOH, and KOH to generate corresponding salt forms of carboxylic acid groups within the p(AAc) cryogel network for activation as p(AAc)-Li+, p(AAc)-Na+, and p(AAc)-K+, respectively. The synthesized p(AAc)-based cryogels were characterized via Fourier-transform infrared (FT-IR) spectroscopy, thermogravimetric analysis, and scanning electron microscopy. The room-temperature electrical conductivity of the p(AAc), p(AAc)-Li+, p(AAc)-Na+, and p(AAc)-K+ cryogels was measured as 10(-11) S cm(-1), 10(-10) S cm(-1), 10(-9) S cm(-1), and 10(-8) S cm(-1), respectively. Furthermore, the p(AAc) cryogel and its salt forms were tested as sensor materials for NH3 gas by exposing them to NH3 vapor for 60 min under ambient conditions. Upon exposure to NH3 vapor, it was found that the conductivity of the bare p(AAc) and p(AAc)-K+ cryogels increased by up to 10(5)- and 10(2)-fold, respectively, compared with their NH3 unexposed states. The increase in conductivity for the other salt forms of p(AAc) cryogel was about 60-fold compared with their bare form. The conductivity increase for the p(AAc) and p(AAc)-K+ cryogels was therefore further investigated by changing the NH3 vapor exposure time, revealing that these materials could be used as sensors for NH3. It was further found that a 5 min NH3 gas exposure time was sufficient for p(AAc)-K+ cryogel to generate a detectable response via a change in the conductivity of the matrix.Öğe Covalent organic framework based on melamine and dibromoalkanes for versatile use(Springer, 2016) Şahiner, Nurettin; Demirci, Şahin; Sel, KıvançCovalent organic frameworks (COFs), based on melamine and dibromoalkanes [Br(CH2)(n)Br] with n = 2, 4, 6, and 8 for 1,2-dibromoethane, 1,4-dibromobutane, 1,6-bibromohexane and 1,8-dibromooctane as COF-1,2, COF-1,4, COF-1,6, COF-1,8, were synthesized in dimethyl sulfoxide at 150 A degrees C. The COFs had distinct color depending on the number of C atoms (n) in the dibromoalkanes e.g., light-yellow, intense yellow, brown and dark brown for COF-1,2, COF-1,4, COF-1,6, and COF-1,8, respectively. Furthermore, it was demonstrated that COF-1,2 and COF-1,4 COFs can be used as a template for in situ Co metal nanoparticle preparation by loading CoCl2 salt from ethanol solution into COFs and then treating with NaBH4 solution. Then the prepared catalyst systems of COF-1,2-Co and COF-1,4-Co were tested for H-2 generation from hydrolysis of NaBH4. The COF-1,2-Co composite materials showed better catalyst performance than COF-1,4-Co composite in the hydrolysis of NaBH4. The hydrogen generation rates (HGR) and turnover frequency values were calculated as 1589 and 594 ml H-2/(g of catalyst) x (min) HGR values, and 3.75 and 1.41 mol H-2/(mol catalyst min) for COF-1,2-Co and COF-1,4-Co composite materials, respectively. The room temperature conductivities were measured and the highest conductivity was measured as 2.26E-07 S cm(-1) for COF-1,2-(CoCl2). The COF also had fluorescent properties and their emission wavelengths reduced in the presence of Co nanoparticles depending on the n values of the dibromoalkanes.Öğe Synthesis and characterization of new microgel from tris(2-aminoethyl)amine and glycerol diglycidyl ether as poly(TAEA-co-GDE)(Elsevier, 2015) urRehman, Saif; Şahiner, Mehtap; Sel, Kıvanç; Siddiq, Mohammed; Şahiner, NurettinHere, we report a new microgel preparation from tris(2-aminoethyl)amine (TAEA) and glycerol diglycidyl ether (GDE) as p(TAEA-co-GDE) via simple microemulsion polymerization/crosslinking by using L-a lecithin as surfactant and gasoline as organic phase. The p(TAEA-co-GDE) microgels were visualized using optical microscopy and scanning electron microscopy (SEM) with size ranges <10 mu m. The prepared particles were found to be positively charged, 23.61 +/- 1.2 mV at pH similar to 4.5, according to zeta-potential measurements, and the charge of particles decreased with increase in pH of the medium and become negatively charged after pH 10. The microgel particles were protonated (quaternized) or deprotanated by HCl and NaOH treatments, changing their zeta potential to 33 +/- 1.3 mV and 14.53 +/- 1.8 mV, respectively. Thermal properties of the prepared particles were observed by TG analysis before and after quaternization, and also after Co(II), Cu(II) and Cd(II) metal ion absorption. Here, we also demonstrated in situ CdS quantum dot (Q-dots) preparation within p(TAEA-co-GDE) microgels. The peak energy of 2.5 eV was observed in the fluorescence spectrum of p(TAEA-co-GDE)-CdS microgel by applying an excitation wavelength of 300 nm. Furthermore, the prepared p(TAEA-co-GDE) particles showed antibacterial characteristics against common bacteria such as Escherichia coli ATCC 8739, Staphylococcus aureus ATCC 6538, Bacillus subtilis ATCC 6633 and Pseudomonas aeruginosa ATCC 10145 and have great potential for biomedical use. Additionally, p(TAEA-co-GDE) particles are found to be biocompatible against L929 Fibroblast cells. (C) 2015 Elsevier B.V. All rights reserved.Öğe Hydrogel templated CdS quantum dots synthesis and their characterization(Elsevier, 2011) Şahiner, Nurettin; Sel, Kıvanç; Meral, Kadem; Onganer, Yavuz; Bütün, Sultan; Özay, Özgür; Sılan, CoşkunThis work reports a facile method for preparation of CdS quantum dots (Q-dots), using a crosslinked hydrophilic p(AMPS) hydrogel network by absorption of Cd(II) ions and sequential precipitation with aqueous Na2S within the network at room temperature. The TEM images revealed that prepared CdS Q-dots were distributed throughout the p(AMPS) hydrogel network and their sizes were about 5 nm. The amount of inorganic material inside p(AMPS) hydrogel was determined by TGA measurements to be 16.9% by weight. Additionally, the Cd and S amounts inside the p(AMPS) network were determined by dissolution of particles with HCl (three treatments with 3 M HCl) and by using ICP-AES (for Cd) and an elemental analyzer (for S). From UV-visible absorbance measurements, optical energy gap values of 5.1 +/- 0.1 eV for p(AMPS) and 2.4 +/- 0.05 eV for p(AMPS)-CdS were determined. From the fluorescence spectrum of the p(AMPS)-CdS hydrogel, the peak energy was observed at 2.30 eV. The in situ prepared Q-dots were recovered from hydrogel matrices by placing the p(AMPS)-CdS composite in purified water. (C) 2011 Elsevier B.V. All rights reserved.
