Faculty Publications
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Item Long-term influence of concrete degradation on dam-foundation interaction(2011) Burman, A.; Maity, D.; Sreedeep, S.; Gogoi, I.The dam-foundation interaction behavior under the application of seismic load has been investigated in the present paper using finite element technique in the time domain. Since the dam face is in constant contact with water, concrete degradation due to hygromechanical loading is inevitable and should be considered in the analysis procedure. This ageing process of concrete leads to loss of stiffness and strength of the material. Therefore, to assess the behavior of the dam at a later stage of its life, it is important to determine the proper strength of the concrete at a certain age. An approach to include the time-dependent degradation of concrete owing to environmental factors and mechanical loading in terms of isotropic degradation index is presented. An iterative scheme has been developed to model the dam-foundation interaction effects of the coupled system. The strains and the displacements are observed to increase if the ageing procedure of the gravity dam is taken into account. The long-term behavior of the aged concrete gravity and foundation interaction has been observed by using a developed ageing model for concrete. © 2011 World Scientific Publishing Company.Item Adaptive non-local level-set model for despeckling and deblurring of synthetic aperture radar imagery(Taylor and Francis Ltd. michael.wagreich@univie.ac.at, 2018) Padikkal, P.; Banothu, B.In this article, we modify Mumford–Shah level-set model to handle speckles and blur in synthetic aperture radar (SAR) imagery. The proposed model is formulated using a non-local regularization framework. Hence, the model duly cares about local gradient oscillations (corresponding to the fine details/textures) during the evolution process. It is assumed that the speckle intensity is gamma distributed, while designing a maximum a posteriori estimator of the functional. The parameters of the gamma distribution (i.e. scale and shape) are estimated using a maximum likelihood estimator. The regularization parameter of the model is evaluated adaptively using these (estimated) parameters at each iteration. The split-Bregman iterative scheme is employed to improve the convergence rate of the model. The proposed and the state-of-the-art despeckling models are experimentally verified and compared using a large number of speckled and blurred SAR images. Statistical quantifiers are used to numerically evaluate the performance of various models under consideration. © 2018, © 2018 Informa UK Limited, trading as Taylor & Francis Group.Item Extended Newton-type iteration for nonlinear ill-posed equations in Banach space(Springer Verlag service@springer.de, 2019) Sreedeep, C.D.; George, S.; Argyros, I.K.In this paper, we study nonlinear ill-posed equations involving m-accretive mappings in Banach spaces. We produce an extended Newton-type iterative scheme that converges cubically to the solution which uses assumptions only on the first Fréchet derivative of the operator. Using general Hölder type source condition we obtain an error estimate. We also use the adaptive parameter choice strategy proposed by Pereverzev and Schock (SIAM J Numer Anal 43(5):2060–2076, 2005) for choosing the regularization parameter. © 2018, Korean Society for Computational and Applied Mathematics.Item Convergence analysis for single point Newton-type iterative schemes(Springer, 2020) Argyros, I.K.; George, S.The aim of this article is to present a convergence analysis for single point Newton-type schemes for solving equations with Banach space valued operators. The equations contain a non-differentiable part. Although the convergence conditions are very general, they are weaker than the corresponding ones in earlier works leading to a finer convergence analysis in both the local as well as the semi-local convergence analysis. Therefore, the applicability of these iterative schemes is extended. © 2019, Korean Society for Informatics and Computational Applied Mathematics.Item Computing the Moore-Penrose inverse using its error bounds(Elsevier Inc. usjcs@elsevier.com, 2020) Stanimirovi?, P.S.; Roy, F.; Gupta, D.K.; Srivastava, S.A new iterative scheme for the computation of the Moore-Penrose generalized inverse of an arbitrary rectangular or singular complex matrix is proposed. The method uses appropriate error bounds and is applicable without restrictions on the rank of the matrix. But, it requires that the rank of the matrix is known in advance or computed beforehand. The method computes a sequence of monotonic inclusion interval matrices which contain the Moore-Penrose generalized inverse and converge to it. Successive interval matrices are constructed by using previous approximations generated from the hyperpower iterative method of an arbitrary order and appropriate error bounds of the Moore-Penrose inverse. A convergence theorem of the introduced method is established. Numerical examples involving randomly generated matrices are presented to demonstrate the efficacy of the proposed approach. The main property of our method is that the successive interval matrices are not defined using principles of interval arithmetic, but using accurately defined error bounds of the Moore-Penrose inverse. © 2019 Elsevier Inc.Item Derivative Free Iterative Scheme for Monotone Nonlinear Ill-posed Hammerstein-Type Equations(International Association of Engineers, 2021) Erappa, S.M.; George, S.An iterative scheme which is free of derivative is employed to approximately solve nonlinear ill-posed Hammer-stein type operator equations )TG(x) = Y, where G is a non-linear monotone operator and ) is a bounded linear operator defined on Hilbert spaces X,Y,Z. The convergence analysis adapted in the paper includes weaker Lipschitz condition and adaptive choice of Perverzev and Schock(2005) is employed to choose the regularization parameter U. Furthermore, order optimal error bounds are obtained and the method is validated by a numerical example. © 2021, IAENG International Journal of Applied Mathematics. All Rights Reserved.Item Convergence criteria of three step schemes for solving equations(MDPI, 2021) Regmi, S.; Argyros, C.I.; Argyros, I.K.; George, S.We develop a unified convergence analysis of three-step iterative schemes for solving nonlinear Banach space valued equations. The local convergence order has been shown before to be five on the finite dimensional Euclidean space assuming Taylor expansions and the existence of the sixth derivative not on these schemes. So, the usage of them is restricted six or higher differentiable mappings. But in our paper only the first Frèchet derivative is utilized to show convergence. Consequently, the scheme is expanded. Numerical applications are also given to test convergence. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.Item On the complexity of convergence for high order iterative methods(Academic Press Inc., 2022) Argyros, I.K.; George, S.; Argyros, C.Lipschitz-type conditions on the second derivative or conditions on higher than two derivatives not appearing on these methods have been employed to prove convergence. But these restrictions limit the applicability of high convergence order iterative methods although they may converge. That is why a new semi-local analysis is presented using only information taken from the derivatives on these methods. The new results compare favorably to the earlier ones even if the earlier conditions are used, since the latter use tighter Lipschitz parameters. Special cases and applications test convergence criteria. © 2022 Elsevier Inc.Item Secant-type iteration for nonlinear ill-posed equations in Banach space(De Gruyter Open Ltd, 2023) George, S.; Sreedeep, C.D.; Argyros, I.K.In this paper, we study secant-type iteration for nonlinear ill-posed equations involving m-accretive mappings in Banach spaces. We prove that the proposed iterative scheme has a convergence order at least 2.20557 using assumptions only on the first Fréchet derivative of the operator. Further, using a general Hölder-type source condition, we obtain an optimal error estimate. We also use the adaptive parameter choice strategy proposed by Pereverzev and Schock (2005) for choosing the regularization parameter. © 2022 Walter de Gruyter GmbH, Berlin/Boston 2023.Item An apriori parameter choice strategy and a fifth order iterative scheme for Lavrentiev regularization method(Institute for Ionics, 2023) George, S.; Saeed, M.; Argyros, I.K.; Padikkal, J.In this paper, we propose a new source condition and introduce a new apriori parameter choice strategy for Lavrentiev regularization method for nonlinear ill-posed operator equation involving a monotone operator in the setting of a Hilbert space. Also, a fifth order iterative method is being proposed for approximately solving Lavrentiev regularized equation. A numerical example is illustrated to demonstrate the performance of the method. © 2022, The Author(s) under exclusive licence to Korean Society for Informatics and Computational Applied Mathematics.