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        • KCI등재

          Geochemistry of Çamardl Formation sediments, central Anatolia (Turkey): implication of source area weathering, provenance, and tectonic setting

          Seref,Keskin 한국지질과학협의회 2011 Geosciences Journal Vol.15 No.2

          The upper Cretaceous-Eocene ‚amardl Formation is exposed along the northern edge of the Ulukl la Basin (central Anatolia) and consists of turbiditic sediments. The sediment geochemistry has been studied in order to understand the provenance, source area weathering, and tectonic setting of the basin. ‚amardl Formation sediments are characterized by low to moderate SiO_2 contents, variable abundances of major elements, and a relatively high proportion of ferromagnesian elements. Evidence from discrimination diagrams of sedimentary provenance, tectonic setting, major element geochemistry and Sc/Th, Cr/Th, Co/Th, Zr/Sc, La/Sc, La/Co, Cr/Sc, Y/Ni, and K/Rb values show that the ‚amardl Formation sediments were derived from mafic, felsic, and intermediate sources. The chemical index of alteration (CIA: 57.63–78.11) revealed moderately weathered source rocks. Then major and trace element concentrations indicated deposition in an active continental margin and continental island arc settings.

        • KCI등재SCOPUS

          Some Pyridazinone and Phthalazinone Derivatives and Their Vasodilator Activities

          Seref,Demirayak,Ahmet,Cagri,Karaburun,Ismail,Kayagil,Kevser,Erol,Basar,Sirmagul 대한약학회 2004 Archives of Pharmacal Research Vol.27 No.1

          In this study, 6-[(4-arylidene-2-phenyl-5-oxoimidazolin-1-yl)phenyl]-4,5-dihydro-3(2H)-pyridazinone and 4-[(4-arylidene-2-phenyl-5-oxoimidazolin-1-yl)phenyl]-1(2H)-phthalazinone derivatives were synthesized by reacting 6-(4-aminophenyl)-4,5-dihydro-3(2H)-pyridazinone or 4-(4- aminophenyl)-1(2H)-phthalazinone compound with different 4-arylidene-2-phenyl-5(4H)- oxazolone derivatives. The vasodilator activities of the compounds were examined both in vitro and in vivo. Some pyridazinone derivatives showed appreciable activity.

        • KCI등재SCOPUS

          Forced vibration analysis of viscoelastic nanobeams embedded in an elastic medium

          Seref,D.,Akbas 국제구조공학회 2016 Smart Structures and Systems, An International Jou Vol.18 No.6

          Forced vibration analysis of a simple supported viscoelastic nanobeam is studied based on modified couple stress theory (MCST). The nanobeam is excited by a transverse triangular force impulse modulated by a harmonic motion. The elastic medium is considered as Winkler-Pasternak elastic foundation.The damping effect is considered by using the Kelvin–Voigt viscoelastic model. The inclusion of an additional material parameter enables the new beam model to capture the size effect. The new non-classical beam model reduces to the classical beam model when the length scale parameter is set to zero. The considered problem is investigated within the Timoshenko beam theory by using finite element method. The effects of the transverse shear deformation and rotary inertia are included according to the Timoshenko beam theory. The obtained system of differential equations is reduced to a linear algebraic equation system and solved in the time domain by using Newmark average acceleration method. Numerical results are presented to investigate the influences the material length scale parameter, the parameter of the elastic medium and aspect ratio on the dynamic response of the nanobeam. Also, the difference between the classical beam theory (CBT) and modified couple stress theory is investigated for forced vibration responses of nanobeams.

        • KCI등재

          Linear and Nonlinear Cointegration of Purchasing Power Parity: Further Evidence from Developing Countries

          SEREF,BOZOKLU,SINEM,KUTLU 연세대학교 동서문제연구원 2012 Global economic review Vol.41 No.2

          In this study, we search for evidence of empirical validity of long-run purchasing power parity (PPP) in case of eight developing countries. We consider both a linear and nonlinear model of PPP based on cointegration analysis and apply firstly Johansen's linear approach and then conduct Breitung's rank and score tests to search for any non-linear cointegrating relationship. The results obtained from Breitung's rank test suggest that once the sources of nonlinearities are taken into account, the results provide stronger evidence on the empirical fulfillment of PPP.

        • KCI등재SCOPUS

          Post-buckling analysis of Timoshenko beams with temperature-dependent physical properties under uniform thermal loading

          Seref,Doguscan,Akbas,Turgut,Kocatürk 국제구조공학회 2012 Structural Engineering and Mechanics, An Int'l Jou Vol.44 No.1

          Post-buckling behavior of Timoshenko beams subjected to uniform temperature rising with temperature dependent physical properties are studied in this paper by using the total Lagrangian Timoshenko beam element approximation. The beam is clamped at both ends. In the case of beams with immovable ends, temperature rise causes compressible forces end therefore buckling and post-buckling phenomena occurs. It is known that post-buckling problems are geometrically nonlinear problems. Also, the material properties (Young's modulus, coefficient of thermal expansion, yield stress) are temperature dependent: That is the coefficients of the governing equations are not constant in this study. This situation suggests the physical nonlinearity of the problem. Hence, the considered problem is both geometrically and physically nonlinear. The considered highly non-linear problem is solved considering full geometric non-linearity by using incremental displacement-based finite element method in conjunction with Newton-Raphson iteration method. The beams considered in numerical examples are made of Austenitic Stainless Steel (316). The convergence studies are made. In this study, the difference between temperature dependent and independent physical properties are investigated in detail in post-buckling case. The relationships between deflections, thermal post-buckling configuration, critical buckling temperature, maximum stresses of the beams and temperature rising are illustrated in detail in post-buckling case.

        • SCIESCOPUSKCI등재후보

          Large post-buckling behavior of Timoshenko beams under axial compression loads

          Akbas,,Seref,D. Techno-Press 2014 Structural Engineering and Mechanics, An Int'l Jou Vol.51 No.6

          Large post-buckling behavior of Timoshenko beams subjected to non-follower axial compression loads are studied in this paper by using the total Lagrangian Timoshenko beam element approximation. Two types of support conditions for the beams are considered. In the case of beams subjected to compression loads, load rise causes compressible forces end therefore buckling and post-buckling phenomena occurs. It is known that post-buckling problems are geometrically nonlinear problems. The considered highly non-linear problem is solved considering full geometric non-linearity by using incremental displacement-based finite element method in conjunction with Newton-Raphson iteration method. There is no restriction on the magnitudes of deflections and rotations in contradistinction to von-Karman strain displacement relations of the beam. The beams considered in numerical examples are made of lower-Carbon Steel. In the study, the relationships between deflections, rotational angles, critical buckling loads, post-buckling configuration, Cauchy stress of the beams and load rising are illustrated in detail in post-buckling case.

        • Nonlinear static analysis of functionally graded porous beams under thermal effect

          Akbas,,Seref,D. Techno-Press 2017 Coupled systems mechanics Vol.6 No.4

          This paper deals with the nonlinear static deflections of functionally graded (FG) porous under thermal effect. Material properties vary in both position-dependent and temperature-dependent. The considered nonlinear problem is solved by using Total Lagrangian finite element method within two-dimensional (2-D) continuum model in the Newton-Raphson iteration method. In numerical examples, the effects of material distribution, porosity parameters, temperature rising on the nonlinear large deflections of FG beams are presented and discussed with porosity effects. Also, the effects of the different porosity models on the FG beams are investigated in temperature rising.

        • Modal analysis of viscoelastic nanorods under an axially harmonic load

          Akbas,,Seref,D. Techno-Press 2020 Advances in nano research Vol.8 No.4

          Axially damped forced vibration responses of viscoelastic nanorods are investigated within the frame of the modal analysis. The nonlocal elasticity theory is used in the constitutive relation of the nanorod with the Kelvin-Voigt viscoelastic model. In the forced vibration problem, a cantilever nanorod subjected to a harmonic load at the free end of the nanorod is considered in the numerical examples. By using the modal technique, the modal expressions of the viscoelastic nanorods are presented and solved exactly in the nonlocal elasticity theory. In the numerical results, the effects of the nonlocal parameter, damping coefficient, geometry and dynamic load parameters on the dynamic responses of the viscoelastic nanobem are presented and discussed. In addition, the difference between the nonlocal theory and classical theory is investigated for the damped forced vibration problem.

        • SCIESCOPUSKCI등재후보

          Large deflection analysis of edge cracked simple supported beams

          Akbas,,Seref,Doguscan 국제구조공학회 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.54 No.3

          This paper focuses on large deflection static behavior of edge cracked simple supported beams subjected to a non-follower transversal point load at the midpoint of the beam by using the total Lagrangian Timoshenko beam element approximation. The cross section of the beam is circular. The cracked beam is modeled as an assembly of two sub-beams connected through a massless elastic rotational spring. It is known that large deflection problems are geometrically nonlinear problems. The considered highly nonlinear problem is solved considering full geometric non-linearity by using incremental displacement-based finite element method in conjunction with Newton-Raphson iteration method. There is no restriction on the magnitudes of deflections and rotations in contradistinction to von-Karman strain displacement relations of the beam. The beams considered in numerical examples are made of Aluminum. In the study, the effects of the location of crack and the depth of the crack on the non-linear static response of the beam are investigated in detail. The relationships between deflections, end rotational angles, end constraint forces, deflection configuration, Cauchy stresses of the edge-cracked beams and load rising are illustrated in detail in nonlinear case. Also, the difference between the geometrically linear and nonlinear analysis of edge-cracked beam is investigated in detail.

        • Post-buckling analysis of aorta artery under axial compression loads

          Akbas,,Seref,Doguscan,Mercan,,Kadir,Civalek,,Omer Techno-Press 2020 Advances in nano research Vol.8 No.3

          Buckling and post-buckling cases are often occurred in aorta artery because it affected by higher pressure. Also, its stability has a vital importance to humans and animals. The loss of stability in arteries may lead to arterial tortuosity and kinking. In this paper, post-buckling analysis of aorta artery is investigated under axial compression loads on the basis of Euler-Bernoulli beam theory by using finite element method. It is known that post-buckling problems are geometrically nonlinear problems. In the geometrically nonlinear model, the Von Karman nonlinear kinematic relationship is employed. Two types of support conditions for the aorta artery are considered. The considered non-linear problem is solved by using incremental displacement-based finite element method in conjunction with Newton-Raphson iteration method. The aorta artery is modeled as a cylindrical tube with different average diameters. In the numerical results, the effects of the geometry parameters of aorta artery on the post-buckling case are investigated in detail. Nonlinear deflections and critical buckling loads are obtained and discussed on the post-buckling case.

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