DERIVATIVE FORMULAE FOR MODULAR FORMS AND THEIR PROPERTIES

Aygunes, Aykut Ahmet Korean Mathematical Society 2015 대한수학회지 Vol.52 No.2

In this paper, by using the modular forms of weight nk ($2{\leq}n{\in}\mathbb{N}$ and $k{\in}\mathbb{Z}$), we construct a formula which generates modular forms of weight 2nk+4. This formula consist of some known results in [14] and [4]. Moreover, we obtain Fourier expansion of these modular forms. We also give some properties of an operator related to the derivative formula. Finally, by using the function $j_4$, we obtain the Fourier coefficients of modular forms with weight 4.

Does the Addition of a Dynamic Pedicle Screw to a Fusion Segment Prevent Adjacent Segment Pathology in the Lumbar Spine?

Aygun Hayati,Yaray Osman,Mutlu Muren 대한척추외과학회 2017 Asian Spine Journal Vol.11 No.5

Study Design: Retrospective clinical cohort study. Purpose: To investigate whether the combined use of dynamic pedicle screws and polyaxial pedicle screws was effective on adjacent segment pathology (ASP). Overview of Literature: Various screw and rod models have been recently developed for preventing adjacent segment disease, and hybrid systems have been described along with posterior instrumentation in the fusion segment. In the literature, although the success of dynamic systems has been demonstrated in non-fusion posterior instrumentation, it remains unclear whether the addition of a screw-based dynamic system to a fusion segment would successfully prevent ASP in the long term. Methods: The study included 101 patients who underwent surgery for degenerative spine diseases between 2007 and 2014 with lumbar stabilization that used either polyaxial pedicle screws alone or polyaxial pedicle screws plus dynamic stabilization screws (with hinged screw heads). These two patient groups were compared using retrospectively obtained postoperative new clinical findings, Oswestry disability index (ODI) scores, visual analog scale (VAS) scores, and radiological data. Results: The proportion of patients with ASP who were radiologically assessed was low (p <0.01) in the group that underwent lumbar stabilization along with dynamic screws. Treatment outcomes were clinically successful in both groups according to ODI and VAS scores, and no significant difference was determined between the groups in terms of clinical ASP (p >0.05). Conclusions: Although the combined use of dynamic screws and the static system was radiologically found to be effective for preventing ASP in patients who underwent lumbar fusion with posterior instrumentation, it did not completely eliminate ASP or result in a significant improvement in clinical ASP.

A FAMILY OF FUNCTIONS ASSOCIATED WITH THREE TERM RELATIONS AND EISENSTEIN SERIES

Aygunes, Aykut Ahmet Korean Mathematical Society 2016 대한수학회보 Vol.53 No.6

Abstract. In this paper, for $a{\in}C$, we investigate functions $g_a$ and ${\psi}_a$ associated with three term relations. $g_a$ is defined by means of function ${\psi}_a$. By using these functions, we obtain some functional equations related to the Eisenstein series and the Riemann zeta function. Also we find a generalized difference formula of function $g_a$.

High alloyed new stainless steel shielding material for gamma and fast neutron radiation

Aygun, Bunyamin Korean Nuclear Society 2020 Nuclear Engineering and Technology Vol.52 No.3

Stainless steel is used commonly in nuclear applications for shielding radiation, so in this study, three different types of new stainless steel samples were designed and developed. New stainless steel compound ratios were determined by using Monte Carlo Simulation program Geant 4 code. In the sample production, iron (Fe), nickel (Ni), chromium (Cr), silicium (Si), sulphur (S), carbon (C), molybdenum (Mo), manganese (Mn), wolfram (W), rhenium (Re), titanium (Ti) and vanadium (V), powder materials were used with powder metallurgy method. Total macroscopic cross sections, mean free path and transmission number were calculated for the fast neutron radiation shielding by using (Geant 4) code. In addition to neutron shielding, the gamma absorption parameters such as mass attenuation coefficients (MACs) and half value layer (HVL) were calculated using Win-XCOM software. Sulfuric acid abrasion and compressive strength tests were carried out and all samples showed good resistance to acid wear and pressure force. The neutron equivalent dose was measured using an average 4.5 MeV energy fast neutron source. Results were compared to 316LN type stainless steel, which commonly used in shielding radiation. New stainless steel samples were found to absorb neutron better than 316LN stainless steel at both low and high temperatures.

Electrocoagulation of Disperse Dyebath Wastewater: Optimization of Process Variables and Sludge Production

Aygun, Ahmet,Nas, Bilgehan,Sevimli, Mehmet Faik The Korean Electrochemical Society 2021 Journal of electrochemical science and technology Vol.12 No.1

This study was conducted to investigate the effect of initial pH, current density, and electrolysis time on process performance in terms of decolorization and chemical oxygen demand (COD) removal from disperse dyebath wastewater (DDW) by mono-polar parallel laboratory scale electrocoagulation (EC) process. COD reduction of 51.3% and decolorization of 92.8% were obtained with operating cost of 0.19 €/㎥ treated wastewater for Al-Al electrode pair, while 90.5% of decolorization and 49.2% of COD reduction were obtained with operating cost of 0.20 €/㎥ treated wastewater for an Fe-Fe electrode pair. The amount of sludge production were highly related to type of the electrode materials. At the optimum conditions, the amount of sludge produced were 0.18 kg/㎥ and 0.28 kg/㎥ for Al-Al and Fe-Fe electrode pairs, respectively. High decolorization can be explained by the hydrophobic nature of the disperse dye, while limited COD removal was observed due to the high dissolved organic matter of the DDW based on auxiliary chemicals. Energy, electrode, and chemical consumptions and sludge handling were considered as major cost items to find a cost-effective and sustainable solution for EC. The contribution of each cost items on operating cost were determined as 10.0%, 51.1%, 30.5% and 8.4% for Al-Al, and they were also determined as 9.0%, 38.0%, 40.5% and 12.5% for Fe-Fe, respectively. COD reduction and decolorization were fitted to first-order kinetic rule.

LMC-based DTC for efficiency improvement of IM drives and their electric vehicle applications

Aygun, Hilmi,Aktas, Mustafa The Korean Institute of Power Electronics 2020 JOURNAL OF POWER ELECTRONICS Vol.20 No.5

Electric vehicles (EVs) with induction motor (IM) drives require energy optimization due to their limited energy storage capacity. Among the energy optimization methods currently available, a loss model-based controller (LMC) is a satisfactory technique, since it converges rapidly to an optimal operating point. Some of the simplifications applied to LMCs, such as neglecting the core loss and leakage inductances, affect IM drive performance negatively in terms of loss minimization. To overcome this problem, this paper presents an efficient LMC combined with direct torque control (DTC). The proposed method is based on the idea that the magnetizing current is much higher than the core loss current. Using the sum of the stator current and the rotor current instead of the magnetizing current, modelling the losses is simplified and the optimal stator flux is determined easily. A simulation study is carried out to evaluate the performance of the proposed scheme with an EV application during an FTP-75 urban driving cycle. A prototype 3 kW IM drive with a TMS320F28335 digital signal processor (DSP) is built to validate the simulation results. A significant efficiency improvement is obtained at low loads. Both simulation and experimental results demonstrate that the proposed DTC improves efficiency and decreases torque ripple.

Treatment of reactive dyebath wastewater by electrocoagulation process: Optimization and cost-estimation

Ahmet Aygun,Bilgehan Nas,Mehmet Faik Sevimli 한국화학공학회 2019 Korean Journal of Chemical Engineering Vol.36 No.9

Reactive dyestuff is commonly used in the textile industry. Reactive dyebath wastewater (RDW) was treated with a batch, monopolar, parallel lab scale electrocoagulation process (EC) having 0.042m2 effective electrode area. The effects of process parameters, such as initial pH, current density and electrolysis period on COD and color removal efficiency, were investigated by using response surface methodology (RSM). At the optimal conditions, 85.8% color and 76.9% COD removal were obtained with 1.84 €/m3 operating cost for Al electrode, while 92.0% decolorization and 80.9% COD removal were obtained with 1.56 €/m3 operating cost for an iron electrode. The iron electrode was found superior to aluminum as a sacrificial anode material in terms of COD and color removal with low cost. The cost of electrical energy, electrode, and chemical consumptions for electrocoagulation were considered to find an optimum and feasible solution. As a result, the operating cost consists of approximately 2% for energy, 28% for electrode and 70% for chemical consumption for both electrodes. Based upon the data, it is clearly seen that operating cost covers mostly for HCI to adjust pH due to the high pH and alkalinity of RDW, which was neglected in many studies. The first-order reaction kinetics with a higher slope for the color were well fitted, resulting in faster color removal than that of COD for both electrodes.

Removal of sulphate from landfill leachate by crystallization

Ahmet Aygun,Selim Dogan,Mehmet Emin Argun,Havva Ates 대한환경공학회 2019 Environmental Engineering Research Vol.24 No.1

The present study explores the applicability of response surface methodology (RSM) in conjunction with central composite design (CCD) matrix to statistically optimize ettringite crystallization process for the removal of sulphate from landfill leachate. A three factor-five coded level CCD with 20 runs, was performed to estimate the best fitted model. The RSM results indicated that the fitted quadratic regression model could be appropriate to predict sulfate removal efficiency. The pH was identified as the most dominant parameter affecting sulphate removal. 61.6% of maximum sulphate removal efficiency was obtained at pH of 11.06 for a 1.87 of Ca/SO₄ and 0.51 of Al/SO₄ molar ratios. The operating cost for ettringite crystallization at optimized conditions was calculated to be 0.52 $/m³. The significance of independent variables and their interactions were tested by analysis of variance. Scanning electron microscope (SEM) and SEM coupled with energy dispersive X-Ray spectroscopy results confirmed the formation of ettringite crystal and were used to describe its morphology features.

Effects of Chromium Nitrate on Phytohormone Content and Mitotic Activity in Maize (zea Mays L.)Seedlings

Filiz Aygun Erturk,Guleray Agar,Esra Arslan,Medine Gulluce,Metin Turan,Fikrettin Sahin 한국토양비료학회 2014 한국토양비료학회 학술발표회 초록집 Vol.2014 No.6

Validity and Reliability of Sun Protection Behavior Scale among Turkish Adolescent Population

Ozcan Aygun,Ayse Ergun 한국간호과학회 2015 Asian Nursing Research Vol.9 No.3

Purpose: The aim of this research was to adapt the Sun Protection Behavior Scale (SPBS) to Turkish and to perform validity and reliability analyses. Methods: The scale was administered to a total of 900 adolescents, the retest to 91 adolescents. The construct validity of the scale was evaluated using exploratory (EFA) and confirmatory factor analysis (CFA). The EFA and CFA were applied to sample groups of 449 and 451 people, respectively. Results: The Cronbach alpha coefficients for the Turkish form of the SPBS (a = .74) and its sunscreen (a = .88) and hat use (a = .70) subscales were found to be .70 while the sun avoidance subscale was calculated to be .67. The item-total score correlation between the scale and its subscales was .26 and the test-retest correlations were found to be .51. The CFA results verified the 8-item, 3-factor Turkish version of the SPBS. The confirmatory factor loadings for the scale were .45e.80 for sun avoidance, .72 e.93 for sunscreen use, and .66e.83 for hat use. In particular, SPBS and sunscreen use (p < .001) exhibited significantly high mean scores among girls and economically better backgrounds (p= .007, p < .001, respectively). In addition, SPBS (p = .004) and hat use (p < .001) revealed that the mean scores were significantly high in younger adolescents. Conclusions: The SPBS was found to be valid and reliable and its psychometric characteristics acceptable. The scale can be used to measure the behavior of Turkish adolescent populations with respect to sun protection.