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.

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.

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

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.

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.

Investigation of Mass Transfer of Ozone in Jet Loop Reactor

Cengiz Ibrahim,Değermenci Nejdet,Yildiz Ergun,Barlak Melahat Semin 한국화학공학회 2024 Korean Journal of Chemical Engineering Vol.41 No.4

Mass transfer of ozone in a jet loop reactor was investigated in this study. Diff erent parameters such as ozone gas concentration, gas fl ow rate, circulation fl ow rate, and spray nozzle diameter were examined for their eff ect on mass transfer. In experiments with ozone gas concentrations ranging from 3.83 to 17.1 g/m 3 , the K L a values remained unchanged, with an average of 28.7 ± 2.2 h −1 . As the ozone gas concentration increased, the saturation values of ozone in the liquid phase also increased. Experiments were carried out with gas fl ow rates ranging from 50 to 250 L/h in the jet loop reactor, and increasing gas fl ow rates increased the K L a value up to fi ve times. When the eff ect of the liquid circulation fl ow rate was examined for a spray nozzle diameter of 15.5 mm, increasing the fl ow rate from 40 L/min to 80 L/min increased the K L a value by approximately 41%. However, the power consumed per reactor volume for this process increased 8 times and reached 2.65 kW/m 3 . K L a values in the JLR vary between 6.1 and 37.3 h −1 depending on operating parameters and it has been concluded that it performs well compared to its counterparts.

The effects of high amounts of Al and Zn on the structural properties of hydroxyapatite prepared by sol-gel method

Cengiz Tatar,Dilek Bagci,Omer Kaygili 한양대학교 세라믹연구소 2016 Journal of Ceramic Processing Research Vol.17 No.5

In the present study, the effects of high amounts of Al and Zn additives on the crystal structure, phase composition andmicrostructure of hydroxyapatite (HAp) samples synthesized by sol-gel route were investigated by X-ray diffraction (XRD),Fourier transformation infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) techniques. The values of thecrystallinity percent, crystallite size, lattice parameter of a and volume of the unit cell decrease gradually with increasingamount of the co-additives. The formation of the new phases is observed and these phases become dominant with increasingamount of Al and Zn. The morphology of HAp, shape and size of the particles are also affected by the amount of Al and Zn. As expected, a gradual decrease in the Ca/P molar ratio is observed.

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.

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.

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