Thermo-Electrical Properties in Pb-Sb Hypereutectic Alloy

M. ¸Sahin,E. Çadırlı,Y. Sürme,D. Özkır 대한금속·재료학회 2013 METALS AND MATERIALS International Vol.19 No.3

Pb-17 wt% Sb hypereutectic alloy was directionally solidified upward with three different growth rates (8μm/s, 18 μm/s, 42 μm/s, 166 μm/s and 497 μm/s) at a constant temperature gradient (3.6 K/mm) in the Bridgman-type growth apparatus. The dependence of characteristic microstructure parameters such as primary dendrite arm spacing (λ1) and secondary dendrite arm spacing (λ2) on the growth rate (V) were determined by using a linear regression analysis. Variations of electrical resistivity (ρ) for cast samples for temperatures in the range of 300-550 K were measured by using a standard dc four-point probe technique. The variations of thermal conductivity with temperature for the same alloys were determined from the WiedemannFranz and SmithPalmer equations by using the measured values of electrical resistivity. The enthalpy of fusion for the same alloys were determined by means of a differential scanning calorimeter from a heating trace during the transformation from solid to liquid. The corrosion resistance was analyzed by Tafel extrapolation and linear polarization resistance methods conducted in a 5% sodium chloride solution in contact with air maintained at room temperature. Effects of the growth rate on the electrical resistivity and corrosion resistance were also investigated.

Approximate and Three-Dimensional Modeling of Brightness Levels in Interior Spaces by Using Artificial Neural Networks

Sahin, Mustafa,Oguz, Yuksel,Buyuktumturk, Fuat The Korean Institute of Electrical Engineers 2015 Journal of Electrical Engineering & Technology Vol.10 No.4

In this study, artificial neural networks were used to determine the intensity of brightness in interior spaces. The illumination elements to illuminate indoor spaces were considered, not individually, but as a system. So, during the planned maintenance periods of an illumination system, after its design and installation, simple brightness level measurements must be taken. For a three-dimensional evaluation of the brightness level in indoor spaces in a speedy and accurate manner, the obtained brightness level measurement results and artificial neural network model were used. Upon estimation of the most suitable brightness level for indoor spaces by using the artificial neutral network model, the energy demands required by the illumination elements decreased. Consequently, in this study, with estimations of brightness levels, the extent to which the artificial neutral networks become successful was observed and more correct results have been obtained in terms of both economy and usage.

Symmetric bi-$\left( \sigma ,\tau \right) $ derivations of prime and semi prime gamma rings

Sahin Ceran,Mustafa A 대한수학회 2006 대한수학회보 Vol.43 No.1

The purpose of this paper is to define the symmetric bi-left(sigma ,tau right) derivations on prime and semi prime Gammarings and to prove some results concerning symmetric bi-left(sigma ,tau right) derivations on prime and semi prime Gammarings.

Protective Effects of the Nuclear Factor Kappa B Inhibitor Pyrrolidine Dithiocarbamate on Experimental Testicular Torsion and Detorsion Injury

Sahin Kabay,Hilmi Ozden,Gul Guven,Dilek Burukoglu,Mehmet Cengiz Ustuner,Fatma Topal,Hasan Veysi Gunes,Derya Ustuner,Cansu Ozbayer 대한약리학회 2014 The Korean Journal of Physiology & Pharmacology Vol.18 No.4

Testicular torsion results with the damage of the testis and it is a surgical emergency. Pyrrolidinedithiocarbamate (PDTC) is a low-molecular-weight antioxidant and potent inhibitor of nuclear factorkappa B (NF-κB) activation. In this study, we aimed to investigate the effects of PDTC to testiculartorsion-detorsion (T/D) injury. Forty adult male Sprague-Dawley rats were separated into four groups. A sham operation was performed in group I. In group II, torsion is performed 2 hours by 720 degreeextravaginally testis. In group III, 4 h reperfusion of the testis was performed after 2 h of testiculartorsion. In group IV, after performing the same surgical procedures as in group III, PDTC (100 mg/kg,intravenous’s) was administered before 30 min of detorsion. The testes tissue malondialdehyde (MDA),superoxide dismutase (SOD) catalase (CAT) level was evaluated. Histological evaluations were performedafter hematoxylin and eosin staining. Testicular tissue MDA levels were the highest in theT/D groups compared with treatment group. Administration of PDTC prevented a further increase inMDA levels. Significant decrease occurred in CAT and SOD levels in treatment group compared withthe control group. The rats in the treatment group had normal testicular architecture. The resultssuggest that PDTC can be a potential protective agent for preventing the biochemical and histologicalchanges related to oxidative stress in testicular injury caused by testis torsion.

CIRCLES ALONG A RIEMANNIAN MAP AND CLAIRAUT RIEMANNIAN MAPS

Sahin, Bayram Korean Mathematical Society 2017 대한수학회보 Vol.54 No.1

We first extend Yano-Nomizu's theorem, which characterizes extrinsic spheres in a Riemannian manifold, for Riemannian maps. Then we introduce Clairaut Riemannian maps, give an example and obtain necessary and sufficient conditions for a Riemannian map to be Clairaut type.

A Novel Soft Switching PWM·PFC AC·DC Boost Converter

Sahin, Yakup The Korean Institute of Electrical Engineers 2018 Journal of Electrical Engineering & Technology Vol.13 No.1

This study introduces a novel Soft Switching (SS) Pulse Width Modulated (PWM) AC-DC boost converter. In the proposed converter, the main switch is turned on with Zero Voltage Transition (ZVT) and turned off with Zero Current Transition (ZCT). The main diode is turned on with Zero Voltage Switching (ZVS) and turned off with Zero Current Switching (ZCS). The auxiliary switch is turned on and off with ZCS. All auxiliary semiconductor devices are turned on and off with SS. There is no extra current or voltage stress on the main semiconductor devices. The majority of switching energies are transferred to the output by auxiliary transformer. Thus, the current stress of auxiliary switch is significantly reduced. Besides, the proposed converter has simple structure and ease of control due to common ground. The theoretical analysis of the proposed converter is verified by a prototype with 100 kHz switching frequency and 500 W output power. Furthermore, the efficiency of the proposed converter is 98.9% at nominal output power.

Investigation of flexural strength and cytotoxicity of acrylic resin copolymers by using different polymerization methods

Sahin, Onur,Ozdemir, Ali Kemal,Turgut, Mehmet,Boztug, Ali,Sumer, Zeynep The Korean Academy of Prosthodonitics 2015 The Journal of Advanced Prosthodontics Vol.7 No.2

PURPOSE. The aim of this study was to appraise the some mechanical properties of polymethyl methacrylate based denture base resin polymerized by copolymerization mechanism, and to investigate the cytotoxic effect of these copolymer resins. MATERIALS AND METHODS. 2-hydroxyethyl methacrylate (HEMA) and isobutyl methacrylate (IBMA) were added to monomers of conventional heat polymerized and injection-molded poly methyl methacrylate (PMMA) resin contents of 2%, 3%, and 5% by volume and polymerization was carried out. Three-point bending test was performed to detect flexural strength and the elasticity modulus of the resins. To determine the statistical differences between the study groups, the Kruskall-Wallis test was performed. Then pairwise comparisons were performed between significant groups by Mann-Whitney U test. Agar-overlay test was performed to determine cytotoxic effect of copolymer resins. Chemical analysis was determined by FTIR spectrum. RESULTS. Synthesis of the copolymer was approved by FTIR spectroscopy. Within the conventional heat-polymerized group maximum transverse strength had been seen in the HEMA 2% concentration; however, when the concentration ratio increased, the strength decreased. In the injection-molded group, maximum transverse strength had been seen in the IBMA 2% concentration; also as the concentration ratio increased, the strength decreased. Only IBMA showed no cytotoxic effect at low concentrations when both two polymerization methods applied while HEMA showed cytotoxic effect in the injection-molded resins. CONCLUSION. Within the limitations of this study, it may be concluded that IBMA and HEMA may be used in low concentration and at high temperature to obtain non-cytotoxic and durable copolymer structure.

Computational finite element model updating tool for modal testing of structures

Sahin, Abdurrahman,Bayraktar, Alemdar Techno-Press 2014 Structural Engineering and Mechanics, An Int'l Jou Vol.51 No.2

In this paper, the development of a new optimization software for finite element model updating of engineering structures titled as FemUP is described. The program is used for computational FEM model updating of structures depending on modal testing results. This paper deals with the FE model updating procedure carried out in FemUP. The theoretical exposition on FE model updating and optimization techniques is presented. The related issues including the objective function, constraint function, different residuals and possible parameters for FE model updating are investigated. The issues of updating process adopted in FemUP are discussed. The ideas of optimization to be used in FE model updating application are explained. The algorithm of Sequential Quadratic Programming (SQP) is explored which will be used to solve the optimization problem. The possibilities of the program are demonstrated with a three dimensional steel frame model. As a result of this study, it can be said that SQP algorithm is very effective in model updating procedure.

A Data Path Design Tool for Automatically Mapping Artificial Neural Networks on to FPGA-Based Systems

Sahin, Ibrahim,Saritekin, Namik Kemal The Korean Institute of Electrical Engineers 2016 Journal of Electrical Engineering & Technology Vol.11 No.5

Determination of displacement distributions in welded steel tension elements using digital image techniques

Sahin Sozen 국제구조공학회 2015 Steel and Composite Structures, An International J Vol.18 No.5

It is known that material properties, connection quality and manufacturing methods are among the important factors directly affecting the behavior of steel connections and hence steel structures. The possible performance differences between a fabricated connection and its computer model may cause critical design problems for steel structures. Achieving a reliable design depends, however, on how accurately the material properties and relevant constitutive models are considered to characterize the behavior of structures. Conventionally, the stress and strain fields in structural steel connections are calculated using the finite elements method with assumed material properties and constitutive models. Because the conventional strain gages allow the measurement of deformation only at one point and direction for specific time duration, it is not possible to determine the general characteristics of stress-strain distributions in connections after the laboratory performance tests. In this study, a new method is introduced to measure displacement distribution of simple steel welded connections under tension tests. The method is based on analyzing digital images of connection specimens taken periodically during the laboratory tension test. By using this method, displacement distribution of steel connections can be calculated with an acceptable precision for the tested connections. Calculated displacements based on the digital image correlation method are compared with those calculated using the finite elements method.