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Article Citation - WoS: 3Citation - Scopus: 4New Methods for Approximating Square Roots(Elsevier Science inc, 2006) Ozban, Ahmet YasarSome new higher order iterative methods are obtained to approximate the positive square root of a positive real number. Moreover some numerical tests are performed to demonstrate the performances and accuracies of the new methods. The numerical results show that the methods we obtain are competitive with the existing ones. (c) 2005 Published by Elsevier Inc.Article Citation - WoS: 26Citation - Scopus: 28On Idempotency of Linear Combinations of Idempotent Matrices(Elsevier Science inc, 2004) Özdemir, H; Özban, AYP-1, P-2 and P-3 being any three different nonzero mutually commutative n x n idempotent matrices, and C-1 C-2 and C-3 being nonzero scalars, the problem of characterizing some situations, where a linear combination of the form P = c(1)P(1) + c(2)P(2) or P = c(1)P(1) + c(2)P(2) + c(3)P(3), is also an idempotent matrix has been considered. Moreover two interesting results about the idempotency of linear combinations of 2 x 2 idempotent matrices and 3 x 3 idempotent matrices have been given. A statistical interpretation of the idempotency problem considered in this study has also been pointed out. (C) 2003 Elsevier Inc. All rights reserved.Article Citation - WoS: 96Citation - Scopus: 100Effect of Progesterone on Dppc Membrane: Evidence for Lateral Phase Separation and Inverse Action in Lipid Dynamics(Elsevier Science inc, 2005) Korkmaz, F; Severcan, FInteractions of progesterone with zwitterionic dipalmitoyl phosphatidylcholine (DPPC) triultilamellar liposomes were investigated as a function of temperature and progesterone concentration by using three non-invasive techniques namely Fourier transform infrared spectroscopy, turbidity at 440 nm, and differential scanning calorimetry. The results reveal that progesterone changes the physical properties of DPPC bilayers by decreasing the main phase-transition temperature, abolishing the pre-transition, broadening the phase-transition profile, disordering the system both in gel and liquid crystalline phase, increasing the dynamics at low concentrations whereas stabilizing the membrane at high concentrations, and inducing phase separation. Progesterone does not change the hydration of the C=O groups, while it strengthens the hydrogen bonding between the PO (2) over bar groups of lipids and the water molecules around. (c) 2005 Elsevier Inc. All rights reserved.Article Citation - WoS: 39Citation - Scopus: 38On Oscillation of Second Order Neutral Type Delay Differential Equations(Elsevier Science inc, 2004) Sahiner, YOscillation criteria are obtained by using the so called H-method for the second order neutral type delay differential equations of the form (r(t)psi(x(t))z'(t))' + q(t)f(x(sigma(t))) = 0, t greater than or equal to t(0), where z(t) = x(t) +p(t)x(tau(t)), r, p, q, tau, sigma, is an element of C([t(0), infinity), R) and f, psi is an element of C(R, R). The results of the paper contains several results obtained previously as special cases. Furthermore, we are also able to fix an error in a recent paper related to the oscillation of second order nonneutral delay differential equations. (C) 2003 Elsevier Inc. All rights reserved.Article Citation - WoS: 8Citation - Scopus: 9Improved convergence criteria for Jacobi and Gauss-Seidel iterations(Elsevier Science inc, 2004) Özban, AY; MathematicsSome simple criteria for the convergence of the Jacobi, Gauss-Seidel and SOR iterations have been proposed in the work of Huang [ZAMM 76-1 (1996) 57-58]. In this study we present some modified forms of the criteria introduced in Huang's work. The new criteria also allow for the norms of the Jacobi iteration matrices to be greater than unity. Numerical examples are also given which show the effectiveness of the criteria. (C) 2003 Elsevier Inc. All rights reserved.Article Citation - WoS: 3Citation - Scopus: 5Higher Order Isoparametric Finite Element Solution of Stokes Flow(Elsevier Science inc, 2005) Eid, RA finite element method of the penalization type, using higher order shape functions with rectangular elements, is presented for the solution of the Stokes flow. The fluid is viscous and the flow is slow, steady and incompressible. The solution has been obtained in terms of velocity field while the pressure terms are eliminated using the penalty function approach. The degree of the finite element approximation can be increased as much as one needs with this higher order shape function formulation. The method is tested in a lid-driven square cavity and it is found that there is a relationship between the viscosity and penalty parameter. From one solution one can obtain all the other solutions only by arranging one of the parameters since the product of these parameters has been shown that is a fixed constant. Selected graphs of the velocity field are given showing these behaviors. (C) 2004 Elsevier Inc. All rights reserved.Conference Object Citation - WoS: 3Citation - Scopus: 2Our Experience in Cardiac Transplantation in Baskent University(Elsevier Science inc, 2006) Sezgin, A; Gültekin, B; Özkan, S; Akay, T; Uguz, E; Tokalak, I; Aslamaci, SRecently cardiac transplantation has an important place in treatment of end-stage cardiac failure. In Turkey between 2003 and 2005 at 10 centers 64 cardiac transplantations were performed including five at our facility. Herein we have presented our results. All patients were men of mean age 34.2 +/- 10.7 (17 to 44) years. Upon preoperative echocardiography their mean ejection fraction was 18% +/- 3.27% (17% to 23%). Pulmonary vascular resistance was 4.47 wood unit in one patient and in one case, there was Rh incompatibility between donor and recipient. We used HTK solution for protection of donor hearts. Mean ischemia time was 251.2 +/- 62.7 minutes (155 to 314). Mean aortic clamping time was 84 +/- 4.7 minutes (80 to 90). In all patients we performed a biatrial anastomosis technique. Hemofiltration was used to prevent hemodilution during operation. In the postoperative period four patients had acute renal dysfunction; one, a minor cerebrovascular accident; two, reoperated because of bleeding; one, cholestasis; one, temporary atrio-ventricular block; and one, mediastinitis. Mean follow-up time was 15.6 +/- 19.7 months (2 to 50). Neither early nor late mortality has occurred. All patients are in New York Heart Association class I. In all cases we used triple immunosuppressive therapy. In the follow-up period the mean number of cardiac biopsies per patient was 4.2 +/- 3.03 (2 to 8). Two cases had cardiac catheterization. As a complication of cardiac biopsy, pericardial tamponade developed in one patient; in another one we observed a right ventricular aneursym after cardiac biopsy. Cardiac transplantation was performed with low mortality and morbidity rates in end-stage cardiac failure patients with longer life expectancy and higher life quality. Unfortunately in our country, because of difficulties to find donor hearts, cardiac transplantations were small in number. For better results, we need a larger series.
