Ortak Dersler Bölümü

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Citation - WoS: 8
Citation - Scopus: 8
Analysis of the Specific Heat and the Free Energy of [N(ch3)4]2znbr4 Close To the Ferro-Paraelastic Phase Transition
(Taylor & Francis Ltd, 2019) Kiraci, A.; 42475; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
A power-law formula deduced from the Ising model was used to analyze the temperature dependence of the specific heat and the Gibbs free energy of [N(CH3)(4)](2)ZnBr4 compound in the vicinity of the phase transition temperature of T-C = 287.2 K. Obtained values of the critical exponents from the Gibbs free energy were consistent with that predicted from 2-d potts model ( = 0.3), while obtained values of from the specific heat in both ferroelastic and paraelastic phases were consistent with that predicted from the mean field theory ( = 0) in the vicinity of the phase transition temperature. This is an indication of that [N(CH3)(4)](2)ZnBr4 compound undergoes a second order type phase transition. Also, the enthalpy () and the entropy () of this crystal were calculated in terms of the extracted values of the critical exponent in both ferroelastic and paraelastic phases.
Citation - WoS: 3
Citation - Scopus: 3
Characterization of N Rich-Silicon Nitride Thin Films Deposited by Pecvd
(Electrochemical Soc inc, 2023) Guler, I.; 101531; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
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.
Citation - WoS: 5
Citation - Scopus: 5
Determination of Trapping Parameters of Tl2in2s3se Layered Single Crystal by Thermoluminescence
(Wiley-v C H verlag Gmbh, 2018) Gasanly, Nizami; Guler, Ipek; 101531; 01. Çankaya Üniversitesi; 09. Rektörlük; 09.01. Ortak Dersler Bölümü
Thermoluminescence (TL) measurements are performed to evaluate the trap states in Tl2In2S3Se layered single crystals. TL experiments are conducted with varying temperature from 10 to 300 K and warming rates from 0.2 to 1.0 K s(-1). From the analysis of both initial rise and curve fitting methods, the activation energy of the traps is obtained as 23 meV. The Chen's method is also used to find activation energy. By means of this technique, the activation energy of the TL glow curve is calculated as 25 meV. From both Chen's method and curve fitting method, the existence of mixed order of kinetics in Tl2In2S3Se crystal is found. The cross section to capture of the trap center is found out from the results of curve fitting method. The trap distribution of the crystals is investigated with different temperatures of illumination at a constant warming rate of 0.8 K s(-1). The temperatures of illumination change from 10 to 22 K. As a result of the increase in temperatures of illumination, the peak maximum values move to higher temperatures and intensity of the TL curves decreases. This behavior shows us that quasicontinuous traps distribution is present in Tl2In2S3Se layered single crystals.
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; 56416; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
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 - Scopus: 1
Inference of Autoregressive Model With Stochastic Exogenous Variable Under Short-Tailed Symmetric Distributions
(Springer international Publishing Ag, 2018) Bayrak, Ozlem Tuker; Akkaya, Aysen Dener; 56416; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
In classical autoregressive models, it is assumed that the disturbances are normally distributed and the exogenous variable is non-stochastic. However, in practice, short-tailed symmetric disturbances occur frequently and exogenous variable is actually stochastic. In this paper, estimation of the parameters in autoregressive models with stochastic exogenous variable and non-normal disturbances both having short-tailed symmetric distribution is considered. This is the first study in this area as known to the authors. In this situation, maximum likelihood estimation technique is problematic and requires numerical solution which may have convergence problems and can cause bias. Besides, statistical properties of the estimators can not be obtained due to non-explicit functions. It is also known that least squares estimation technique yields neither efficient nor robust estimators. Therefore, modified maximum likelihood estimation technique is utilized in this study. It is shown that the estimators are highly efficient, robust to plausible alternatives having different forms of symmetric short-tailedness in the sample and explicit functions of data overcoming the necessity of numerical solution. A real life application is also given.
Citation - Scopus: 1
Linear Contrasts in One-Way Classification Ar(1) Model With Gamma Innovations
(Hacettepe Univ, Fac Sci, 2016) Senoglu, Birdal; Bayrak, Ozlem Turker; 56416; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
In this study, the explicit estimators of the model parameters in oneway classification AR(1) model with gamma innovations are derived by using modified maximum likelihood (MML) methodology. We also propose a new test statistic for testing linear contrasts. Monte Carlo simulation results show that the MML estimators have higher efficiencies than the traditional least squares (LS) estimators and the proposed test has much better power and robustness properties than the normal theory test.
Citation - WoS: 3
Citation - Scopus: 3
N-Phosphorylation of Pyrroles: an Intramolecular Migration Reaction
(Pergamon-elsevier Science Ltd, 2018) Unaleroglu, Canan; Tasgin, Dilek Isik; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
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.
Pyrrolizine-3 Synthesis and Evaluation of Photophysical Properties
(Taylor & Francis inc, 2024) Tasgin, Dilek Isik; Bayraktar, Irem; 169107; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
We describe a synthetic approach for pyrrolizine-3-one derivatives and their photophysical properties. These compounds are prepared by a series of reactions employing the substituted pyrroles in one-pot, two-step oxidation, and intramolecular cyclization processes. The photophysical properties of the synthesized compounds were studied by using UV-Vis and fluorescence spectroscopy in different solvents. Maximum absorbance peaks were observed around 306-416 nm and maximum fluorescence emission around 603-614 nm and 465-498 nm for pyrrolyl and N-methyl pyrrolyl substituents, respectively. The introduction of a pyrrolyl substituent had a significant impact on the Stokes shifts (192-206 nm) and quantum yield values ranged from 0.002 to 0.046.
Citation - WoS: 5
Citation - Scopus: 6
Ring Annulation Versus Alkylation of Pyrrole With Α-Phosphoryl Ketones
(Pergamon-elsevier Science Ltd, 2016) Tasgin, Dilek Isik; Unaleroglu, Canan; 16910; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
In this study; novel aryl, heteroaryl, pyrrolyl and phosphoryl groups containing pyrrolizines were synthesized by the ring annulation reaction of aryl or heteroaryl substituted alpha-phosphoryl-alpha,beta-unsaturated ketones with pyrrole under mild reaction conditions. This domino reaction involves scandium triflate catalyzed addition of pyrrole to the double bond of alpha-phosphoryl-alpha,beta-unsaturated ketones, carbonyl group and finally ring annulation sequences. The presented work provided a convenient way for the synthesis of novel bispyrrolic compounds. (C) 2016 Elsevier Ltd. All rights reserved.
Citation - WoS: 13
Citation - Scopus: 14
Structural and Optical Properties of Ga2se3 Crystals by Spectroscopic Ellipsometry
(Springer, 2019) Isik, M.; Gasanly, N. M.; Gasanova, L. G.; Babayeva, R. F.; Guler, I.; 101531; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
Optical and crystalline structure properties of Ga2Se3 crystals were analyzed utilizing ellipsometry and x-ray diffraction (XRD) experiments, respectively. Components of the complex dielectric function (epsilon=epsilon(1)+i epsilon(2)) and refractive index (N=n+ik) of Ga2Se3 crystals were spectrally plotted from ellipsometric measurements conducted from 1.2eV to 6.2eV at 300K. From the analyses of second-energy derivatives of epsilon(1) and epsilon(2), interband transition energies (critical points) were determined. Absorption coefficient-photon energy dependency allowed us to achieve a band gap energy of 2.02eV. Wemple and DiDomenico single effective oscillator and Spitzer-Fan models were accomplished and various optical parameters of the crystal were reported in the present work.
Citation - WoS: 4
Citation - Scopus: 6
Structural and Optical Properties of Thermally Annealed Thallium Indium Disulfide Thin Films
(Elsevier Science Sa, 2020) Gasanly, N.; Guler, I; 101531; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
Structural and optical properties of thallium indium disulfide (TlInS2) thin films, deposited by thermal evaporation technique and thermally annealed at different temperatures, were analyzed. Crystallite size, dislocation density and lattice strain of the thin films were found from X-ray diffraction experiments. The atomic compositions of the films were determined from energy dispersive spectroscopy analysis. Surface morphology of the films was analyzed using atomic force microscopy. From room temperature transmittance spectrum, the band gap energies of the films were identified. The decrease in band gap energies of the films with the annealing temperature up to 300 degrees C was observed due to increase in crystallite size and decrease in lattice strain. From Raman measurements, it was observed that the Raman shifts of the films were well correlated with those of TlInS2 bulk crystal.
Citation - WoS: 7
Citation - Scopus: 7
A Theoretical Investigation: Effect of Structural Modifications on Molecular, Electronic, and Optical Properties of Phosphonate Substituted Bodipy Dyes
(Wiley-v C H verlag Gmbh, 2021) Tasgin, Dilek Isik; Sirin, Pinar Seyitdanlioglu; 169107; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
Phosphonates are important organophosphorus compounds which exhibit versatile properties in organic chemistry, medicinal chemistry, materials and biological applications. Phosphonate groups have appeared in a very few examples of BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) compounds that are important florescent dyes in these areas. The deficiency in the area motivated us to investigate how the phosphonate substituent(s) affect the structural, electronic, and optical properties of meso, alpha, or alpha, alpha '-substituted BODIPYs using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods. We have identified the suitable method as HSEH1PBE functional in combination with the basis set 6-31+G** by comparing the theoretical results with the experimental studies. Structural, electronic and optical parameters of a series of designed phosphonate substituted 12 BODIPYs (1-4) have been investigated. The alpha, and alpha, alpha '-vinyl phosphonate substituted BODIPYs (3,4) compared to meso-substituted BODIPYs (1,2) have both lower HOMO/LUMO electronic energies [(-5.57)-(-6.19)/(-3.16)-(-3.91)] and lower electronic energy gaps (E-gap) (2.11-2.42). Electrostatic potential analysis was performed for all BODIPYs to characterize their electron distribution and TD-DFT analysis was used for the absorption spectral analysis. The presented theoretical approach can be a practical guide for experimental studies for the design of new BODIPY compounds with desired properties.

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