Ortak Dersler Bölümü

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Citation - WoS: 1
Citation - Scopus: 1
Effect of Estimation Under Nonnormality on the Phase Ii Performance of Linear Profile Monitoring Approaches
(Wiley, 2019) Aytacoglu, Burcu; Bayrak, Ozlem Turker
The number of studies about control charts proposed to monitor profiles, where the quality of a process/product is expressed as function of response and explanatory variable(s), has been increasing in recent years. However, most authors assume that the in-control parameter values are known in phase II analysis and the error terms are normally distributed. These assumptions are rarely satisfied in practice. In this study, the performance of EWMA-R, EWMA-3, and EWMA-3(d(2)) methods for monitoring simple linear profiles is examined via simulation where the in-control parameters are estimated and innovations have a Student's t distribution or gamma distribution. Instead of the average run length (ARL) and the standard deviation of run length, we used average and standard deviation of the ARL as performance measures in order to capture the sampling variation among different practitioners. It is seen that the estimation effect becomes more severe when the number of phase I profiles used in estimation decreases, as expected, and as the distribution deviates from normality to a greater extent. Besides, although the average ARL values get closer to the desired values as the amount of phase I data increases, their standard deviations remain far away from the acceptable level indicating a high practitioner-to-practitioner variability.
Citation - WoS: 3
Citation - Scopus: 3
Temperature and Excitation Intensity Tuned Photoluminescence in Ga0.75in0.25se Crystals
(Elsevier Science Bv, 2013) Isik, M.; Guler, I.; Gasanly, N. M.
Photoluminescence (PL) spectra of Ga0.75In0.25Se layered single crystals have been studied in the wavelength range of 580-670 nm and temperature range of 7-59 K. Two PL emission bands centered at 613 nm (2.02 eV, A-band) and 623 nm (1.99 eV, B-band) were revealed at T = 7K. The excitation laser intensity dependence of the emission bands have been studied in the 0.06-1.40 W cm(-2) range. Radiative transitions from shallow donor levels located at E-A = 0.11 and E-B = 0.15 eV below the bottom of conduction band to single shallow acceptor level located at 0.01 eV above the valence band are suggested to be responsible for the observed A- and B-bands. A simple model was proposed to interpret the recombination processes in Ga0.75In0.25Se single crystals. (c) 2012 Elsevier B.V. All rights reserved.
Estimation of AR(1) Model Having Generalized Logistic Disturbances
(2020) Akkaya, Ayşen; Türker Bayrak, Özlem
Non-normality is becoming a common feature in real life applications. Using non-normal disturbances in autoregressive models induces non-linearity in the likelihood equations so that maximum likelihood estimators cannot be derived analytically. Thus, modified maximum likelihood estimation (MMLE) technique is introduced in literature to overcome this difficulty. However, this method assumes the shape parameter to be known which is not realistic in real life. Recently, for unknown shape parameter case, adaptive modified maximum likelihood estimation (AMMLE) method that combines MMLE with Huber estimation method is suggested in literature. In this study, we adopt AMMLE method to AR(1) model where the disturbances are Generalized Logistic distributed. Although Huber M-estimation is not applicable to skew distributions, the AMMLE method extends Huber type work to skew distributions. We derive the estimators and evaluate their performance in terms of effici
Citation - WoS: 9
Optical Analysis of Tlins2xse2(1-X) Mixed Crystals
(Amer inst Physics, 2014) Guler, I.
The ellipsometry measurements were carried out on TlInS2xSe2(1-x) mixed crystals in the spectral range of 1.5-6.0 eV at room temperature. The refractive index, extinction coefficient, real and imaginary parts of dielectric function were found as a result of ellipsometric measurements. The energies of interband transitions (critical point energies) of the TlInS2xSe2(1-x) mixed crystals were obtained by means of the second derivative of the real and imaginary parts of dielectric function. The variation of the critical point energies with the isomorphic anion substitution that is sulfur for selenium atoms was established. (C) 2014 AIP Publishing LLC.
Citation - WoS: 2
Citation - Scopus: 2
Thermoluminescence Characterization of (Ga2se3)0.25 - (Ga2s3)0.75 Single Crystal Compounds
(Elsevier Sci Ltd, 2020) Guler, I; Gasanly, N. M.; Isik, M.
Ga2Se3 and Ga2S3 compounds take attention due to their potential applications in photovoltaics. Defects and impurities may affect the quality of optoelectronic devices. Therefore, it is worthwhile to determine the parameters (activation energy, order of kinetics, frequency factor) of traps associated with the defects and/or impurities. The aim of the present paper is to investigate the trapping parameters of (Ga2Se3)(0.25) - (Ga2S3)(0.75) single crystal which is one of the member of (Ga2Se3)(x) - (Ga2S3)(1-x) mixed crystals. For this purpose, thermoluminescence (TL) experiments were performed on (Ga2Se3)(0.25) - (Ga2S3)(0.75) single crystals in the 10-300 K region. TL spectra were also recorded using various heating rates in between 0.2 and 1.0 K/s and stopping temperatures from 30 to 60 K to get the detailed information about the characteristics of the trapping parameters. TL glow curves exhibited the overlapped peaks. The stopping temperature experimental data indicated that traps present quasi-continuous distribution within the band gap. Initial rise method analyses were applied to get the activation energies of quasi-continuously distributed revealed traps. Thermal activation energies of distributed traps were found as increasing from 108 to 246 meV as stopping temperature was increased from 30 to 60 K. The structural characteristics (lattice constants and atomic compositions of constituent elements) of used compound were also reported in the present study.
Citation - WoS: 2
Citation - Scopus: 1
Inter-Laboratory Comparison Scheme for Fuel Sector, Labkar in Turkey
(Springer, 2009) Bayrak, Ozlem Turker; Okandan, Ender; Uckardes, Hale
Fuel sector is one of the powerful sectors in Turkish industry. The implementation of a new law for regulating the fuel sector had enforced the quality control of fuels sold to public. This resulted in several accredited fuel-testing laboratories to emerge. Thus, a scheme to evaluate their proficiency in measurements became an important requirement. The inter-laboratory comparison scheme LABKAR for gasoline, diesel oil, LPG, lubricating oil and biodiesel samples have evolved to fulfill this need. In this paper, LABKAR is introduced; the results obtained from the program are analyzed and discussed. The kernel densities of the participants' results show that the use of robust mean as a consensus value is appropriate for fuel samples. Although the number of rounds is not enough to derive strict conclusions, it is seen that the performance of the scheme based on the standard deviations and coefficient of variations is improving in each round. It has been observed that the number of laboratories receiving "action" or "warning" is decreasing, which indicates that they are benefiting from the scheme.
Citation - WoS: 2
Citation - Scopus: 3
A Phenomenological Study on Ferroelectric Β-Glycine
(Taylor & Francis Ltd, 2021) Kiraci, A.
The anomalous behavior of the specific heat for beta-glycine was analyzed in terms of the compressible Ising model approximately 5 K below and above the ferrelectric-paraelectric phase transition temperature of T-C =252 K. The obtained value of the critical exponent alpha =0.12 in the ferroelectric phase (T < TC) was consistent with that predicted from the 3-d Ising model (alpha =0.13), while the obtained value of alpha =0.32 in the paraelectric phase (T > TC) was consistent with that predicted from the 2-d potts model (alpha =0.30). Some thermodynamic quantities such as the internal energy, the entropy and the free energy of beta-glycine were then predicted in terms of these extracted values of the critical exponents close to the phase transition temperature of TC. Our calculated values of the thermodynamic quantities are in good agreement with the observed data.
Tarihten Günümüze Taşınanlar
(Etimesgut Belediye Başkanlığı Kültür Yayınları, 2019) Atıcı, Tüzel
Citation - WoS: 3
Citation - Scopus: 4
Development of a Selective Wet-Chemical Etchant for Precise 3d Sculpting of Silicon Enabled by Infrared Non-Linear Laser Modification
(Elsevier Sci Ltd, 2024) Borra, Mona Zolfaghari; Radfar, Behrad; Nasser, Hisham; Colakoglu, Tahir; Tokel, Onur; Turnali, Ahmet; Bek, Alpan
Recently-demonstrated high-quality three-dimensional (3D) subsurface laser processing inside crystalline silicon (c-Si) wafers opens a door to a wide range of novel applications in multidisciplinary research areas. Using this technique, novel maskless micro-pillars with precise control on the surface reflection and coverage are successfully fabricated by etching the laser-processed region of the c-Si wafer. To achieve this, a particular selective wet chemical etching is developed to follow subsurface laser processing of c-Si to reveal the desired 3D structures with smooth surfaces. Here, we report the development of a novel chromium-free chemical etching recipe based on copper nitrate, which yields substantially smooth surfaces at a high etch rate and selectivity on the both laserprocessed Si surface and subsurface, i.e., without significant etching of the unmodified Si. Our results show that the etch rate and surface morphology are interrelated and strongly influenced by the composition of the adopted etching solution. After an extensive compositional study performed at room temperature, we identify an etchant with a selectivity of over 1600 times for laser-modified Si with respect to unmodified Si. We also support our findings using density functional theory calculations of HF and Cu adsorption energies, indicating significant diversity on the c-Si and laser-modified surfaces.
Citation - WoS: 4
Citation - Scopus: 4
Characterization of N Rich-Silicon Nitride Thin Films Deposited by Pecvd
(Electrochemical Soc inc, 2023) Guler, I.
Silicon nitride thin films are very important for their possible use in semiconductor industry and electronic applications. Changing the deposition parameters, silicon nitrides which have many varying optical properties can be produced. In this work, silicon nitride (SiNx) thin films were deposited on silicon substrates using Plasma enhanced chemical vapor deposition (PECVD) technique. The silane (SiH4) and ammonia (NH3) were used as reactant gases. Using these reactant gases, nitrogen (N) rich SiNx films were obtained. In order to get information about absorption and bond types in the films, films were analyzed by the help of Fourier transform infrared spectroscopy (FTIR) was performed. The refractive index, extinction coefficient and band gap energy of the films were changed from 1.86, 0 and 5.38 eV to 2.05, 0.0048 and 4.26 eV, respectively. Using the refractive index, composition of the films were estimated that is [N]/[Si] ratio of the films varied from 1.38 to 1.62. For possible applications of the SiNx films, learning the origin of the light-emission of the films is very important so the photoluminescence (PL) measurements were also used to see the luminescent of the SiNx films which is related to the electronic transitions between the K-center level and the conduction band tail states.
Türk Romanında Gayrimüslime Bakış (1900-1960)
(Libra Yayınevi, 2018) Atabağsoy, Naim
Türk romanında 1900–1960 yılları arasında yayımlanan eserlerden seçilen örnekler yoluyla gayrimüslim karakterlerin ele alınışına odaklanan bu çalışma, aynı süreçte gayrimüslimler bağlamında öne çıkan siyasi, toplumsal ve ekonomik gelişmeleri de irdelemekte, böylelikle edebî ürünlerin tarihsel bağlam içerisinde anlamlandırılmasını amaçlamaktadır. Osmanlı İmparatorluğu’nun birçok alanda avantajlı konumda gösterilen gayrimüslim tebaası, Cumhuriyet’in ilan edilmesiyle birlikte azınlık statüsüne yerleştirilirken bu statünün hukuki zeminini oluşturan Lozan Antlaşması bu noktada dikkat çekici hâle gelir. Bu bakımdan bu çalışma, Antlaşma’nın imzalandığı 1923 yılını teorik olarak merkezine almaktadır. Çalışma, 1923 yılını hazırlayan süreçte ve Cumhuriyet dönemindeki iktidar değişimleriyle geçirilen 1960’a kadarki evrelerde öne çıkan gelişmeleri ve gayrimüslimler bakımından kırılma noktası niteliği taşıyan toplumsal olayları göz önüne alarak roman türündeki eserlerin, içerdiği gayrimüslim karakterler ve gayrimüslim kimliğine ilişkin söylemler üzerinden bu dönüşüm süreçlerinde nasıl reaksiyonlar gösterdiğini ortaya koyma gayreti taşımaktadır.
Citation - WoS: 7
Citation - Scopus: 7
Exploring the Linear and Nonlinear Optical Behavior of (Tlins2)0.75 Insights From Ellipsometry Measurements
(Elsevier, 2023) Guler, I.; Gasanly, N.; Isik, M.
The search for layered structured new semiconductor materials with remarkable optical properties has become a driving force, especially for materials science. Tl2In2S3Se [(TlInS2)0.75(TlInSe2)0.25], a fascinating compound, holds great promise for advanced photonic and optoelectronic applications. In the present study, the linear and nonlinear optical properties of Tl2In2S3Se layered single crystals were studied by ellipsometry measurements. The variation of refractive index, extinction coefficient, absorption coefficient and skin depth with energy were investigated. Applying the derivative analysis technique to the absorption spectrum, indirect bandgap was found as 2.19 eV. The refractive index data was analyzed considering single-effective-oscillator model. The lattice dielectric constant, plasma frequency, carrier density to the effective mass ratio and zero-frequency refractive index were found. Moreover, the change in optical conductivity with energy yielded to determine the direct bandgap as 2.40 eV. The optical parameters of nonlinear refractive index, first-and third-order nonlinear susceptibilities were also reported.
Citation - WoS: 3
Citation - Scopus: 3
N-Phosphorylation of Pyrroles: an Intramolecular Migration Reaction
(Pergamon-elsevier Science Ltd, 2018) Unaleroglu, Canan; Tasgin, Dilek Isik
A new synthetic method is reported for the N-phosphorylation of pyrroles via intramolecular migration of a phosphonate diester group. The reaction proceeds under mild conditions and produces N-phosphorylated pyrrole derivatives in moderate to good yields. (C) 2018 Elsevier Ltd. All rights reserved.
Citation - WoS: 12
Citation - Scopus: 13
Implementing Bring Your Own Device (Byod) Model in Flipped Learning: Advantages and Challenges
(Springer, 2020) Gunduz, Abdullah Yasin; Akkoyunlu, Buket; Kibar, Pinar Nuhoglu
Flipped learning is a type of blended learning that reverses traditional conceptions about pre-class and in-class activities. This pedagogical approach offers students the opportunity to exert more control over their learning. However, teachers should monitor whether in-class activities deepen pre-learning. In this paper, we present students' experiences regarding the advantages, challenges and future preferences of using BYOD in flipped learning. According to students, being allowed to use their own devices in classroom activities provided them a more comfortable learning environment. The model increased their productivity because they were familiar with their personal devices. Students reported that the BYOD model made storing and retrieving files easier, which enabled them to continue studying without remembering settings. However, students identified challenges, such as being required to carry heavy devices and dealing with poor classroom infrastructure. A few students decided they would rather not bring their own devices again due to weight, but the others indicated that they would prefer to participate in BYOD-embedded flipped learning in the future.
Citation - WoS: 4
Citation - Scopus: 4
Impaired Redox Homeostasis in the Heart Left Ventricles of Aged Rats Experiencing Fast-Developing Severe Hypobaric Hypoxia
(Springer, 2019) Agascioglu, Eda; Colak, Ridvan; Demirel, Haydar; Cakatay, Ufuk
Despite its rare occurrence, humans and animals have been prone to getting fast developing severe hypobaric hypoxia. Understanding the redox homeostasis related response of an aging heart to this type of hypoxia are crucially important, since the metabolism of myocardial tissue depends on the redox status of proteins. Rodents can tolerate hypoxic stress better than human subjects. This study was aimed at investigating the effects of fast developing severe hypobaric hypoxia on redox status biomarkers; such as, advanced oxidation protein products (AOPP), lipid hydroperoxides (LHPs), protein carbonyl groups (PCO), protein thiol groups (P-SH), and total thiol groups (T-SH) on the myocardial left ventricles of young and aged Wistar rats. The rats were gradually ascended and exposed to an 8000-meter hypobaric hypoxia. While AOPP levels showed no difference, the TSH and PSH concentrations decreased, and the PCO and LHP increased in both of the hypoxic groups than the controls. The TSH and PSH were lower, and AOPP, PCO and LHP were found to be higher in the elderly hypoxic groups than in the young ones. The significant outcome of the study represents that an 8000-meter hypobaric hypoxia could be considered as a severe hypoxic stress, but not life-treating for the rats and would affect both the young and aged left ventricles similarly in respect to impaired redox status. However, if the percentage increases are taken into consideration, it seems that the higher rate of protein oxidation occurs in young hearts; meanwhile aged hearts are more prone to T-SH oxidation.
Bilimsel iletişim becerilerini değerlendirmeye yönelik bir rubrik geliştirme çalışması
(2018) Menzi Çetin, Nihal; Akkoyunlu, Buket
Citation - WoS: 4
Citation - Scopus: 6
Structural and Optical Properties of (Tlins2)0.75 Thin Films Deposited by Thermal Evaporation
(Springer, 2023) Guler, I.; Isik, M.; Gasanly, N.
Layered semiconductor materials have become a serious research topic in recent years, thanks to their effective optical properties. In this article, the thin-film structure of Tl2In2S3Se [(TlInS2)(0.75)(TlInSe2)(0.25)] material with layered structure was grown by thermal evaporation method. The structural, morphological, and optical properties of the deposited thin films were examined. X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS) and atomic force microscopy (AFM) techniques were used to get information about structural and morphological properties of the thin films. XRD pattern presented well-defined peaks associated with monoclinic crystalline structure. The crystallite size, dislocation density, and lattice strain of the films were also obtained from the analyses of XRD pattern. EDS analysis showed that atomic compositional ratios of the Tl, In, S, and Se elements are consistent with chemical formula of Tl2In2S3Se. The optical characterization of thin film was performed using transmission and Raman spectroscopy techniques. Raman spectrum offered information about the vibrational modes of the thin film. The analyses of the transmission spectrum presented the indirect and direct band gap energies of the Tl2In2S3Se thin film as 2.23 and 2.52 eV, respectively. The further analyses on the absorption coefficient resulted in Urbach energy of 0.58 eV.
Analysis and Mathematical Computation of Some Dynamic Function for Strontium Stannate
(Taylor & Francis Ltd, 2021) Askun, Ali Riza
The frequency and full width at half maximum (FWHM) data of the A(g) Raman modes (95.4, 231.4 and 263.2 cm(-1)) in strontium stannate crystal have been analyzed using the Balkanski model and the fitting parameters were determined. Also, the isobaric Gruneisen parameter of A(g) Raman modes studied here was computed below the room temperature. This computation was performed from the unit cell volume and the observed frequency data of this crystal. Finally, values of the activation energy were extracted close to the structural phase transition temperatures of 160 and 265 K using the observed FWHM data of strontium stannate.
Pandemi Döneminin Ardından: Türkiye'de Yürütülen Acil Uzaktan Eğitim Araştırmalarının Değerlendirilmesi
(Nobel Akademi, 2021) Akkoyunlu, Buket; Bardakçı, Salih; Dağhan, Gökhan
Klasik Dönem Osmanlı Şiirinde Patronaj ve Şairin Üretim Süreci İlişkisine Bir Bakış
(2014) Atabağsoy, Naim

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