Browsing by Publisher "Verlag der Zeitschrift fur Naturforschung"
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Item The analysis approach of boundary layer equations of power-law fluids of second grade(Verlag der Zeitschrift fur Naturforschung, 2008) Abbasbandy S.; Yürüsoy M.; Pakdemirli M.A powerful analytic technique for nonlinear problems, the homotopy analysis method (HAM), is employed to give analytic solutions of power-law fluids of second grade. For the so-called second-order power-law fluids, the explicit analytic solutions are given by recursive formulas with constant coefficients. Also, for the real power-law index in a quite large range an analytic approach is proposed. It is demonstrated that the approximate solution agrees well with the finite difference solution. This provides further evidence that the homotopy analysis method is a powerful tool for finding excellent approximations to nonlinear equations of the power-law fluids of second grade. © 2008 Verlag der Zeitschrift für Naturforschung, Tübingen.Item Optimum path of a flying object with exponentially decaying density medium(Verlag der Zeitschrift fur Naturforschung, 2009) Abbasbandy S.; Pakdemirli M.; Shivanian E.In this paper, a differential equation describing the optimum path of a flying object is derived. The density of the fluid is assumed to be exponentially decaying with altitude. The equation is cast in to a dimensionless form and the exact solution is given. This equation is then analyzed by homotopy analysis method (HAM). The results showed in the figures reveal that this method is very effective and convenient. © 2009 Verlag der Zeitschrift für Naturforschung, Tübingen.Item Analytical and numerical solutions of a generalized hyperbolic non-newtonian fluid flow(Verlag der Zeitschrift fur Naturforschung, 2010) Pakdemirli M.; Sari P.; Solmaz B.The generalized hyperbolic non-Newtonian fluid model first proposed by Al-Zahrani [J. Petroleum Sci. Eng. 17, 211 (1997)] is considered. This model was successfully applied to some drilling fluids with a better performance in relating shear stress and velocity gradient compared to power-law and the Hershel-Bulkley model. Special flow geometries namely pipe flow, parallel plate flow, and flow between two rotating cylinders are treated. For the first two cases, analytical solutions of velocity profiles and discharges in the form of integrals are presented. These quantities are calculated by numerically evaluating the integrals. For the flow between two rotating cylinders, the differential equation is solved by the Runge-Kutta method combined with shooting. For all problems, the powerlaw approximation of the model is compared with the generalized hyperbolic model, too. © 2010 Verlag der Zeitschrift für Naturforschung, Tübingen.Item Symmetry analysis of boundary layer equations of an upper convected Maxwell fluid with magnetohydrodynamic flow(Verlag der Zeitschrift fur Naturforschung, 2011) Deǧer G.; Pakdemirli M.; Aksoy Y.Steady state boundary layer equations of an upper convected Maxwell fluid with magnetohydrodynamic (MHD) flow are considered. The strength of the magnetic field is assumed to be variable with respect to the location. Using Lie group theory, group classification of the equations with respect to the variable magnetic field is performed. General boundary conditions including stretching sheet and injection are taken. Restrictions imposed by the boundary conditions on the symmetries are discussed. Special functional forms of boundary conditions for which similarity solutions may exist are derived. Using the symmetries, similarity solutions are presented for the case of constant strength magnetic field. Stretching sheet solutions with or without injection are presented. Effects of physical parameters on the solutions are depicted. © 2011 Verlag der Zeitschrift für Naturforschung, Tübingen.Item Extremely high boron tolerance in Puccinellia distans (Jacq.) Parl. related to root boron exclusion and a well-regulated antioxidant system(Verlag der Zeitschrift fur Naturforschung, 2016) Hamurcu M.; Hakki E.E.; Sert T.D.; Özdemir C.; Minareci E.; Avsaroglu Z.Z.; Gezgin S.; Kayis S.A.; Bell R.W.Recent studies indicate an extremely high level of tolerance to boron (B) toxicity in Puccinellia distans (Jacq.) Parl. but the mechanistic basis is not known. Puccinellia distans was exposed to B concentrations of up to 1000 mg B L-1 and root B uptake, growth parameters, B and N contents, H2O2 accumulation and ·OH-scavenging activity were measured. Antioxidant enzyme activities including superoxide dismutase (SOD), ascorbate peroxidase, catalase, peroxidase and glutathione reductase, and lipid peroxidation products were determined. B appears to be actively excluded from roots. Excess B supply caused structural deformations in roots and leaves, H2O2 accumulation and simultaneous up-regulation of the antioxidative system, which prevented lipid peroxidation even at the highest B concentrations. Thus, P. distans has an efficient root B-exclusion capability and, in addition, B tolerance in shoots is achieved by a well-regulated antioxidant defense system. © 2016 Walter de Gruyter GmbH, Berlin/Boston.