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          • KCI등재SCIESCOPUS

            Sintering and Microstructure Characteristics of 42CrMo4 Steel Processed by Spark Plasma Sintering

            Ridvan,Yamanoglu,William,Bradbury,Eugene,A.,Olevsky,Randall,M.,German 대한금속·재료학회 2013 METALS AND MATERIALS International Vol.19 No.5

            Rapidly solidified micron sized 42CrMo4 steel powder with a size range of 150-250 μm produced by plasma rotating electrode process was consolidated using a recently developed spark plasma sintering (SPS) process. The relationship between sintering parameters (temperature and soaking time) and microstructural properties was investigated. The effect of slow and high heating regimes on the consolidation of sintered compacts has been also investigated. Maximum relative density (99.2%) was obtained at 1000 °C, under 50 MPa pressure, with 8 min holding time and 200 °C/min heating rate. The microstructure of sintered steel was influenced by carburization occuring inside the graphite SPS process die. The diffusion of carbon produced martensite structure near the surface region and hardened the surface. This effect was investigated in detail using optical microscopy and hardness measurement. Scanning electrone microscopy was also used to examine the fracture surface of sintered compacts. High heating rate promoted the relative density at low temperature compared to high temperature.

          • KCI등재SCOPUS

            In-plane vibrations of cracked slightly curved beams

            H.,Ridvan,Oz 국제구조공학회 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.36 No.6

            In-plane vibrations of slightly curved beams having cracks are investigated numerically and experimentally. The curvature of the beam is circular and stays in the plane of vibration. Specimens made of steel with different lengths but with the same radius of curvature are used in the experiments. Cracks are opened using a hand saw having 0.4 mm thickness. Natural frequencies depending on location and depth of the cracks are determined using a Brüel & Kjaer 4366 type accelerometer. Then the beam is assumed as a Rayleigh type slightly curved beam in finite element method (FEM) including bending,extension and rotary inertia. A flexural rigidity equation given in literature for straight beams having a crack is used in the analysis. Frequencies are obtained numerically for different crack locations and depths. Experimental results are presented and compared with the numerical solutions. The natural frequencies are affected too much due to larger moments when the crack is around nodes. The effect can be neglected when it is at the location of maximum displacements. When the crack is close to the clamped end, the decrease in the frequencies in all modes is very high. The consistency of the results and validity of the equations are discussed.

          • KCI등재SCOPUS

            In-plane vibrations of cracked slightly curved beams

            Oz,,H.,Ridvan Techno-Press 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.36 No.6

            In-plane vibrations of slightly curved beams having cracks are investigated numerically and experimentally. The curvature of the beam is circular and stays in the plane of vibration. Specimens made of steel with different lengths but with the same radius of curvature are used in the experiments. Cracks are opened using a hand saw having 0.4 mm thickness. Natural frequencies depending on location and depth of the cracks are determined using a Bruel & Kjaer 4366 type accelerometer. Then the beam is assumed as a Rayleigh type slightly curved beam in finite element method (FEM) including bending, extension and rotary inertia. A flexural rigidity equation given in literature for straight beams having a crack is used in the analysis. Frequencies are obtained numerically for different crack locations and depths. Experimental results are presented and compared with the numerical solutions. The natural frequencies are affected too much due to larger moments when the crack is around nodes. The effect can be neglected when it is at the location of maximum displacements. When the crack is close to the clamped end, the decrease in the frequencies in all modes is very high. The consistency of the results and validity of the equations are discussed.

          • KCI등재

            ENERGY ON A PARTICLE IN DYNAMICAL AND ELECTRODYNAMICAL FORCE FIELDS IN LIE GROUPS

            ( Talat Korpinar ), ( Ridvan Cem Demirkol ) 호남수학회 2018 호남수학학술지 Vol.40 No.2

            In this study, we firstly define equations of motion based on the traditional model Newtonian mechanics in terms of the Frenet frame adapted to the trajectory of the moving particle in Lie groups. Then, we compute energy on the moving particle in resultant force field by using geometrical description of the curva-ture and torsion of the trajectory belonging to the particle. We also investigate the relation between energy on the moving particle in different force fields and energy on the particle in Frenet vector fields.

          • KCI등재

            A New Approach On The Curvature Dependent Energy For Elastic Curves in a Lie Group

            Talat,Korpinar,Ridvan,Cem,Demirkol 호남수학회 2017 호남수학학술지 Vol.39 No.4

            Elastica is known as classical curve that is a solution of variational problem, which minimize a thin inextensible wire's bending energy. Studies on elastica has been conducted in Euclidean space firstly, then it has been extended to Riemannian manifold by giving different characterizations. In this paper, we focus on energy of the elastic curve in a Lie group. We attepmt to compute its energy by using geometric description of the curvature and the torsion of the trajectory of the elastic curve of the trajectory of the moving particle in the Lie group. Finally, we also investigate the relation between energy of the elastic curve and energy of the same curve in Frenet vector fields in the Lie group.

          • SCIESCOPUSKCI등재

            CONTACT CR-WARPED PRODUCT SUBMANIFOLDS IN KENMOTSU SPACE FORMS

            ARSLAN,,KADRI,EZENTAS,,RIDVAN,MIHAl,,ION,MURATHAN,,CENGIZHAN Korean Mathematical Society 2005 대한수학회지 Vol.42 No.5

            Recently, Chen studied warped products which are CR-submanifolds in Kaehler manifolds and established general sharp inequalities for CR-warped products in Kaehler manifolds. In the present paper, we obtain sharp estimates for the squared norm of the second fundamental form (an extrinsic invariant) in terms of the warping function for contact CR-warped products isometrically immersed in Kenmotsu space forms. The equality case is considered. Some applications are derived.

          • KCI등재

            ENERGY ON A PARTICLE IN DYNAMICAL AND ELECTRODYNAMICAL FORCE FIELDS IN LIE GROUPS

            Korpinar,,Talat,Demirkol,,Ridvan,Cem The Honam Mathematical Society 2018 호남수학학술지 Vol.40 No.2

            In this study, we firstly define equations of motion based on the traditional model Newtonian mechanics in terms of the Frenet frame adapted to the trajectory of the moving particle in Lie groups. Then, we compute energy on the moving particle in resultant force field by using geometrical description of the curvature and torsion of the trajectory belonging to the particle. We also investigate the relation between energy on the moving particle in different force fields and energy on the particle in Frenet vector fields.

          • KCI등재SCIESCOPUS

            Intestinal Obstruction Due to a Mesenteric Cyst

            Ibrahim,Barut,Omer,Ridvan,Tarhan,Metin,Ciris,Yusuf,Akdeniz,Mahmut,Bulbul 연세대학교의과대학 2004 Yonsei medical journal Vol.45 No.2

            Mesenteric cysts are rarely thought of, may be difficult to diagnose, and are usually asymptomatic except when complicated. Intestinal obstruction is a rarely reported complication of these cysts. A case of mesenteric cyst that was causing obstruction of the large bowel is presented, along with a review of the literature.

          • KCI등재

            A NEW APPROACH ON THE CURVATURE DEPENDENT ENERGY FOR ELASTIC CURVES IN A LIE GROUP

            Korpinar,,Talat,Demirkol,,Ridvan,Cem The Honam Mathematical Society 2017 호남수학학술지 Vol.39 No.4

            Elastica is known as classical curve that is a solution of variational problem, which minimize a thin inextensible wire's bending energy. Studies on elastica has been conducted in Euclidean space firstly, then it has been extended to Riemannian manifold by giving different characterizations. In this paper, we focus on energy of the elastic curve in a Lie group. We attepmt to compute its energy by using geometric description of the curvature and the torsion of the trajectory of the elastic curve of the trajectory of the moving particle in the Lie group. Finally, we also investigate the relation between energy of the elastic curve and energy of the same curve in Frenet vector fields in the Lie group.

          • Biological responses of a non-target aquatic plant (Nasturtium officinale) to the herbicide, tribenuron-methyl

            Duman,,Fatih,Urey,,Erkan,Temizgul,,Ridvan,Bozok,,Fuat The Korean Society of Weed Science and The Turfgra 2010 Weed Biology and Management Vol.10 No.2

            To assess its response to the herbicide, tribenuron-methyl, samples of Nasturtium officinale were exposed to 0, 0.01, 0.05, 0.1, and 0.5 $mg\;L^{-1}$ of tribenuron-methyl for 1, 2, 4 and 7 days. The influence of this herbicide on the relative growth rate, electrolyte leakage, lipid peroxidation, photosynthetic pigmentation, protein content, and performance of anti-oxidant enzymes, such as superoxide dismutase (SOD), catalase, and ascorbate peroxidase (APX), was examined. The results indicated that tribenuron-methyl, applied at 0.5 $mg\;L^{-1}$, affected plant growth negatively. It also was determined that chlorophyll a is the most responsive photosynthetic pigment to tribenuron-methyl exposure. Under stress conditions, the anti-oxidant enzymes were up-regulated compared to the control. The SOD activity was significantly stimulated, while the activity of APX was inhibited. A significant correlation was found between lipid peroxidation and SOD activity. The exposure period and herbicide concentration had significant effects on the biological responses against tribenuron-methyl stress. These results may be useful for clarifying the effect of herbicides on non-target aquatic plants.

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