On positive solutions of a reciprocal differenceequation with minimum } \iitem{}{\sc By and

Cengiz \c Cinar,Stevo Stevic,Ibrahim Yal\c cinkaya 한국전산응용수학회 2005 Journal of applied mathematics & informatics Vol.17 No.1-2

In this paper we consider positive solutions of the following difference equation xn+1 = min A xn , B xn−2 , A,B>0. We prove that every positive solution is eventually periodic. Also, we present here some results concerning positive solutions of the difference equation xn+1 = min( A xnxn−1...xn−k , B xn−(k+2)....xn−(2k+2)), A,B>0.

Chemical Composition, Antioxidant, and Enzyme Inhibitory Activities of the Essential Oils of Three Phlomis Species as well as Their Fatty Acid Compositions

Cengiz Sarikurkcu,Mehmet Cemil Uren,Mehmet Sefa Kocak,Mustafa Cengiz,Bektas Tepe 한국식품과학회 2016 Food Science and Biotechnology Vol.25 No.3

This study aimed to investigate the chemical composition, antioxidant, and enzyme inhibitory activities of the essential oils of Phlomis armeniaca WILLD., P. nissolii L., and P. pungens WILLD. var. pungens as well as their fatty acid contents. Germacrene D was found as the major compound in the oils (24.7, 15.1, and 7.2%, respectively). Additionally, n-hexadecanoic acid, hexahydrofarnesyl acetone, β-caryophyllene, and linalool were the other main compounds in the oils. Among the fatty acids, C18:3 ω3 and C18:2 ω6 were determined in high quantities in P. armeniaca (23.14 and 18.01%, respectively) and P. pungens var. pungens (24.64 and 17.51%, respectively). The essential oils of P. armeniaca and P. pungens var. pungens showed remarkable antioxidant and metal chelating activities as well as great reducing power potentials. These oils also showed a moderate scavenging effect on ABTS radicals. The oils also exhibited various degrees of inhibitory activities on AChE, BChE, α-amylase, α-glucosidase, and tyrosinase.

Phenolic composition, enzyme inhibitory, and antioxidant activity of Bituminaria bituminosa

Cengiz Sarikurkcu,Mustafa Cengiz,Mehmet Cemil Uren,Olcay Ceylan,Tuba Orenc,Bektas Tepe 한국식품과학회 2016 Food Science and Biotechnology Vol.25 No.5

This study aimed to evaluate the in vitro antioxidant and enzyme inhibitory activities of ethyl acetate, methanol, and water extracts of Bituminaria bituminosa. In phosphomolybdenum assay, the methanol extract showed the highest activity (166.78 μmol TEs/g dry plant). The water extract exhibited the highest scavenging activity on 1,1-diphenyl-2-picrylhydrazyl (DPPH•) and 2,2-azino-bis (3- ethylbenzothiazloine-6-sulphonic acid) (ABTS•+). In addition, it exhibited the highest activity in cupric ion reducing (CUPRAC) and ferric reducing antioxidant power (FRAP) assays (41.26 and 46.82 μmol TEs/g dry plant). The extracts did not show cholinesterase and tyrosinase inhibitory activity. However, α-glucosidase inhibition assay resulted in the superiority of water extract (1233.86 μmol ACEs/g dry plant). In the case of α-amylase inhibitory assay, the ethyl acetate extract showed the highest activity (53.65 μmol ACEs/g dry plant). The water extract exhibited the highest phenolic content (31.70 μmol GAEs/g dry plant). In contrast, the methanol extract was found rich in flavonoid compounds (5.29 μmol REs/g dry plant). The water extract contained considerable amounts of rosmarinic acid, luteolin, quercetin, and rutin. Therefore, it can be used as a source of new and alternative antioxidant and enzyme inhibitory agents.

Phenolic composition, enzyme inhibitory, and antioxidant activity of Bituminaria bituminosa

Sarikurkcu, Cengiz,Cengiz, Mustafa,Uren, Mehmet Cemil,Ceylan, Olcay,Orenc, Tuba,Tepe, Bektas 한국식품과학회 2016 Food Science and Biotechnology Vol.25 No.5

This study aimed to evaluate the in vitro antioxidant and enzyme inhibitory activities of ethyl acetate, methanol, and water extracts of Bituminaria bituminosa. In phosphomolybdenum assay, the methanol extract showed the highest activity ($166.78{\mu}mol\;TEs/g$ dry plant). The water extract exhibited the highest scavenging activity on 1,1-diphenyl-2-picrylhydrazyl ($DPPH^{\bullet}$) and 2,2-azino-bis (3-ethylbenzothiazloine-6-sulphonic acid) ($ABTS^{{\bullet}+}$). In addition, it exhibited the highest activity in cupric ion reducing (CUPRAC) and ferric reducing antioxidant power (FRAP) assays (41.26 and $46.82{\mu}mol\;TEs/g$ dry plant). The extracts did not show cholinesterase and tyrosinase inhibitory activity. However, ${\alpha}$-glucosidase inhibition assay resulted in the superiority of water extract ($1233.86{\mu}mol\;ACEs/g$ dry plant). In the case of ${\alpha}$-amylase inhibitory assay, the ethyl acetate extract showed the highest activity ($53.65{\mu}mol\;ACEs/g$ dry plant). The water extract exhibited the highest phenolic content ($31.70{\mu}mol\;GAEs/g$ dry plant). In contrast, the methanol extract was found rich in flavonoid compounds ($5.29{\mu}mol\;REs/g$ dry plant). The water extract contained considerable amounts of rosmarinic acid, luteolin, quercetin, and rutin. Therefore, it can be used as a source of new and alternative antioxidant and enzyme inhibitory agents.

Use of geopolymer-derived leucite as a reinforcement in dental bioceramic composites

Cengiz Bagci 한양대학교 청정에너지연구소 2023 Journal of Ceramic Processing Research Vol.24 No.4

Leucite (K2O·Al2O3·4SiO2) converted from geopolymers as a sustainable approach, was used as an alternative to feldspar, oneof the three components of dental ceramics. Leucite crystals were obtained from a dried potassium geopolymer of thecomposition K2O·Al2O3·4SiO2·11H2O by heating at 1200 oC for 3 h in an open-air furnace. Produced leucite was crushed intosmall parts, powdered in a planetary mill and then sieved to sub-63 micron size. Leucite crystals were then replaced byfeldspars at a range from 0-100 (wt.%) in all three parts of dental ceramic slurries. The slurries were molded to 1 cm3 andsubsequently heat-treated at 1300 oC-1450 ºC/4.5 h with a heating rate of 10 ºC/min. Final products were microstructurallycharacterized with XRD, SEM-EDS and mechanically based on Weibull analysis of compressive tests. Due to the phasetransformation occurring in leucite, it was determined that the amount of leucite had a significant effect on the structuralintegrity and therefore the mechanical properties of the final dental material. Results of the statistical analysis showed that thereplacement of 50% leucite exhibited the highest compressive strength of (49.3±10.5 MPa) compared to the other samplesconsistent with microstructural analysis.

Determination of collapse safety of shear wall-frame structures

Cengiz, Emel Yukselis,Saygun, Ahmet Isin Techno-Press 2007 Structural Engineering and Mechanics, An Int'l Jou Vol.27 No.2

A new finite shear wall element model and a method for calculation of 3D multi-storied only shear walled or shear walled - framed structures using finite shear wall elements assumed ideal elasto - plastic material are developed. The collapse load of the system subjected to factored constant gravity loads and proportionally increasing lateral loads is calculated with a method of load increments. The shape functions over the element are determined as a cubic variation along the story height and a linear variation in horizontal direction because of the rigid behavior of the floor slab. In case shear walls are chosen as only one element in every floor, correct solutions are obtained by using this developed element. Because of the rigid behavior of the floor slabs, the number of unknowns are reduced substantially. While in framed structures, classical plastic hinge hypothesis is used, in nodes of shear wall elements when vertical deformation parameter is exceeded ${\varepsilon}_e$, this node is accepted as a plastic node. While the system is calculated with matrix displacement method, for determination of collapse safety, plastic displacements and plastic deformations are taken as additional unknowns. Rows and columns are added to the system stiffness matrix for additional unknowns.

Clinical Marker of Platelet Hyperreactivity in Diabetes Mellitus (Diabetes Metab J 2013;37:423-8)

Cengiz Beyan,Esin Beyan 대한당뇨병학회 2014 Diabetes and Metabolism Journal Vol.38 No.2

Investigation of the effect of pressure on thermodynamic properties and thermoelastic phase transformation of CuAlNi alloys: A molecular dynamics study

Cengiz Tatar,Sefa Kazanc 한국물리학회 2012 Current Applied Physics Vol.12 No.1

Thermoelastic phase transformations and thermodynamic properties of CuAlNi alloys at 0, 1, 2 and 3 GPa pressures were investigated by using MD simulation in this study. The interactions between atoms were modelled by SuttoneChen type of embedded atom method (SCEAM) that is based on many-body interaction. It was observed that thermoelastic phase transformation in the ternary alloy system occurred at the end of thermal process. Radial distribution function (RDF) was used in order to analysis the structures obtained from MD simulation using the simulation techniques’ thermodynamic parameters. The transformation temperatures, enthalpy and entropy of the ternary alloy system have been observed to be changing with the applied pressure. In addition, it was found that the elastic energy has been decreased about 22% by applied pressure whereas Gibbs free energy has been increased about 60% by applied pressure. The values of the thermodynamical parameters obtained in this study were observed to be in close agreement with the experimental study. Thermoelastic phase transformations and thermodynamic properties of CuAlNi alloys at 0, 1, 2 and 3 GPa pressures were investigated by using MD simulation in this study. The interactions between atoms were modelled by SuttoneChen type of embedded atom method (SCEAM) that is based on many-body interaction. It was observed that thermoelastic phase transformation in the ternary alloy system occurred at the end of thermal process. Radial distribution function (RDF) was used in order to analysis the structures obtained from MD simulation using the simulation techniques’ thermodynamic parameters. The transformation temperatures, enthalpy and entropy of the ternary alloy system have been observed to be changing with the applied pressure. In addition, it was found that the elastic energy has been decreased about 22% by applied pressure whereas Gibbs free energy has been increased about 60% by applied pressure. The values of the thermodynamical parameters obtained in this study were observed to be in close agreement with the experimental study.

RPSL and Routing Policy

Cengiz Alaettinoglu 정보통신정책연구원 2000 세미나및공청회 Vol.2000 No.

Strength of biaxially loaded high strength reinforced concrete columns

Cengiz Dundar,Serkan Tokgoz 국제구조공학회 2012 Structural Engineering and Mechanics, An Int'l Jou Vol.44 No.5

An experimental research was conducted to investigate the strength of biaxially loaded short and slender reinforced concrete columns with high strength concrete. In the study, square and L-shaped section reinforced concrete columns were constructed and tested to obtain the load-deformation behaviour and strength of columns. The test results of column specimens were analysed with a theoretical method based on the fiber element technique. The theoretical ultimate strength capacities and the test results of column specimens have been compared and discussed in the paper. Besides this, observed failure mode and experimental and theoretical load-lateral deflection behaviour of the column specimens are presented.