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      • KCI등재SCOPUS

        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.

      • KCI등재

        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.

      • KCI등재SCOPUS

        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.

      • SCIESCOPUSKCI등재

        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.

      • KCI등재SCOPUS

        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.

      • KCI등재SCOPUS

        Investigation of Degradative Signals on Outdoor Solid Insulators Using Continuous Wavelet Transform

        Cengiz,Polat,Uzunoglu 대한전기학회 2016 Journal of Electrical Engineering & Technology Vol.11 No.3

        Most outdoor solid insulators may suffer from surface degradations due to non-stationary currents that flow on the insulator surface. These currents may be classified as leakage, discharge and tracking currents due to their disturbing potencies respectively. The magnitude of these currents depends on the degree of the contamination of surface. The leakage signals are followed by discharge signals and tracking signals which are capable of forming carbonized tracking paths on the surface between high voltage and earth contacts (surface tracking). Surface tracking is one of the most breakdown mechanisms observed on the solid insulators, especially polymers which may cause severely reduced lifetime. In this study the degradations observed on polyester resin based insulators are investigated according to the IEC 587 Inclined Plane Test Standard. The signals are monitored and recorded during tests until surface tracking initiated. In order to prevent total breakdown of an insulator, early detection of tracking signals is vital. Continuous Wavelet Transform (CWT) is proposed for classification of signals and their energy levels observed on the surface. The application of CWT for processing and classification of the surface signals which are prone to display high frequency oscillations can facilitate real time monitoring of the system for diagnosis.

      • FUTURE ASPECTS OF TEACHING TOURISM BUSSINES ENGLISH

        Cengiz,,K 세계문화관광학회 2007 Conference Proceedings Vol.8 No.0

        '스콜라' 이용 시 소속기관이 구독 중이 아닌 경우, 오후 4시부터 익일 오전 7시까지 원문보기가 가능합니다.

        In today's world technology develops and changes quickly. If we do not consider future in this highly changing world we would fall behind our competitors. Those changes force people renew themselves in education as well. This is another aspect of globalization. Our world is becoming a global village, and people are able to get in touch with each other quickly and easily. This interaction plays a vital role in tourism which is a comer stone of Service Industry. Also the share of tourism export increases nearly to 30% in the world economy. (http://www.world-tourism.org/facts/menu.html) Having a good communication will lead to better and high quality service in Tourism Industry. And good communication can be maintained by good Tourism Business English education. The methods that are used to teach foreign language in today's classes are not up to date and were developed under the conditions which were totally different from today. In this study, how should the Tourism Business English education be carried out in the future will be explained in the light of developments around the world. Education and language is as old as human history. People interacted and get in touch with each other in every pace of their lives. As the societies developed and got bigger the level of interaction increased as well. Also when prosperity level of people increased the life standards of people become better. As a result of this people's view changed on their life styles. People began to spare more time for themselves, and began to travel to the other countries for their holidays. Tourism is one of the important elements in economy of most countries. Countries try to attract more tourists every year. Every year many people travel around the world for different reasons. Those reasons include, holiday, business, health, religion etc. Each year number of those people who travel around the world reaches 763, 9 million. As mentioned above share of tourism export increases to nearly 30% in the world economy (http://www.world-tourism.org/facts/menu.html). As a result of this the need for qualified and educated staff increases rapidly. Tourism Business English is as important as job qualifications for a person who works in Tourism Industry. The need for foreign language in different sectors can be seen at Figure 1. English has been the most used language all over the world. It is one of the most taught and learnt languages in the world. English is everywhere. Some 380 million people speak it as their first language and another 600 million speak it as their second. A billion are learning it, about a third of the world's population is in some sense exposed to it and by 2030, it is predicted almost half of the world will be more or less proficient in it. It is the language of globalization - of international business, politics and diplomacy. It is the language of computers and the Internet. You'll see it on posters in Beijing, you'll hear it in pop songs in Tokyo, and you'll read it in official documents in Prague. Deutsche Welle broadcasts in it. Bjork, an Icelander, sings in it. French business schools teaching it. It is the medium of expression in cabinet meetings in Bolivia. English is now the global language. (20,000 Teaching Jobs (English) Oxford Seminars. Retrieved on 2007-02-18.) Business English must be seen in the overall context of English for Specific Purposes (ESP), as it shares the important elements of needs analysis, syllabus design, materials selection and development which are common to all fields of work in ESP. As with other varieties of ESP, Business English implies the definition of a specific language corpus and emphasis on particular kinds of communication in a specific context.

      • SCIESCOPUSKCI등재후보

        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.

      • KCI등재SCOPUS

        The dispersion of the flexural waves in a compound hollow cylinder under imperfect contact between layers

        Cengiz,Ipek 국제구조공학회 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.55 No.2

        The influence of the interface imperfect bonding on the flexural wave dispersion in the bilayered hollow circular cylinder is studied with utilizing three-dimensional linear theory of elastodynamics. The shear-spring type model is used for describing the imperfect bonding on the interface between the layers and the degree of the imperfectness is estimated through the dimensionless shear-spring parameters which enter the mentioned model. The method for finding the analytical expressions for the sought values and dispersion equation are discussed and detailed. Numerical results on the lowest first and second modes are presented and analyzed. These results are obtained for various values of the shear-spring parameters. According to these results, in particular, it is established that as a results of the imperfection of the bonding between the layers the new branches of the dispersion related the first fundamental mode arise and the character of the dispersion curve related to the second mode becomes more complicated.

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