The Experts below are selected from a list of 138 Experts worldwide ranked by ideXlab platform
Kelechi C Ogbuehi - One of the best experts on this subject based on the ideXlab platform.
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Smith Method assessment of anterior chamber depth for screening for narrow anterior chamber angles
Indian Journal of Ophthalmology, 2006Co-Authors: Turki M Almubrad, Kelechi C OgbuehiAbstract:Purpose: To compare the axial anterior chamber depth (ACD) using the Smith Method, in patients under treatment for primary open-angle glaucoma (POAG) and primary angle-closure glaucoma (PACG), with an age-matched control group. Materials and Methods: Triplicate just-touching-slit-length (JTSL) measurements of the axial anterior chamber depth were determined in 198 eyes of 99 patients (39 control; 36 POAG; and 24 PACG) recruited from King Saud University clinics, Riyadh, Saudi Arabia. Goldmann tonometry and gonioscopy were carried out as a part of the patient's routine examination. Subjects with a history of intraocular surgery for glaucoma or any other anterior segment disease were excluded form the study. The average ACD estimate by the JTSL Method were compared among the various groups. Results: The average JTSL estimates were: Control group 2.33±0.68 mm (axial ACD estimate = JTSL estimate ´ 1.4); POAG group 1.98±0.97 mm; PACG group 0.65±0.41 mm. There was no significant reduction ( P = 0.068) of the JTSL estimate in the POAG group, compared to the control group. There was a statistically significant ( P Conclusion: The Smith-Method JTSL technique may be used for non-invasive rapid screening, to help identify patients at risk of developing angle-closure, during routine examination of patients in the ophthalmology clinic.
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intra observer repeatability and inter observer agreement of the Smith Method of measuring the anterior chamber depth
Ophthalmic and Physiological Optics, 2000Co-Authors: Ebi Peter Osuobeni, K A Oduwaiye, Kelechi C OgbuehiAbstract:The Smith (1979) Method provides a means of estimating the anterior chamber depth without additional attachments to the slit lamp [Smith, R. J. H. (1979). A new Method of estimating the depth of the anterior chamber. Br. J. Ophthalmol. 63, 215-220]. In this study, the 95% intra-observer limits of repeatability and the 95% inter-observer limits of agreement of this Method have been determined. The intra-observer limits of repeatability were determined by plotting the difference vs the mean of the estimated anterior chamber depth obtained in two different sessions by each of two examiners, while the inter-observer limits of agreement are represented by a plot of the difference vs the mean estimated anterior chamber depth between the two examiners. For one examiner, the 95% intra-observer limits of repeatability was -0.36 to 0.58 mm, while for the other examiner the 95% intra-observer limits of repeatability was -0.25 to 0.37 mm. The 95% inter-observer limits of agreement were -0.31 to 0.23 mm and -0.41 to 0.25 mm for the first and second sessions respectively. The intra-observer limits of repeatability are comparable with those reported for A-scan ultrasonographic measures of the anterior chamber depth. These results imply that the Smith Method can be used with a high degree of repeatability and agreement to clinically monitor longitudinal changes in anterior chamber depth.
Peter Benner - One of the best experts on this subject based on the ideXlab platform.
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Structure preserving iterative Methods for periodic projected Lyapunov equations and their application in model reduction of periodic descriptor systems
Numerical Algorithms, 2017Co-Authors: Peter Benner, Mohammadsahadet HossainAbstract:In this paper, we develop structure preserving iterative schemes to solve the periodic discrete-time projected Lyapunov equations associated to analysis and design of discrete-time descriptor systems exploiting the reflexive generalized inverses of the periodic matrices associated with these systems. In particular, we extend the Smith Method to solve the large-scale projected periodic discrete-time algebraic Lyapunov equations in lifted form. A low-rank version of this Method is also presented, avoiding the explicit lifted formulation and working directly with the periodic matrix coefficients. Moreover, we consider an application of the Lyapunov solvers in balanced truncation model reduction of periodic discrete-time descriptor systems. Numerical results are given to illustrate the efficiency and accuracy of the proposed Methods.
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low rank iterative Methods for periodic projected lyapunov equations and their application in model reduction of periodic descriptor systems
Numerical Algorithms, 2014Co-Authors: Peter Benner, Mohammadsahadet Hossain, Tatjana StykelAbstract:We discuss the numerical solution of large-scale sparse projected periodic discrete-time Lyapunov equations in lifted form which arise in model reduction of periodic descriptor systems. We extend the alternating direction implicit Method and the Smith Method to such equations. Low-rank versions of these Methods are also presented, which can be used to compute low-rank approximations to the solutions of projected periodic Lyapunov equations in lifted form with low-rank right-hand side. Moreover, we consider an application of the Lyapunov solvers to balanced truncation model reduction of periodic discrete-time descriptor systems. Numerical results are given to illustrate the efficiency and accuracy of the proposed Methods.
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on the squared Smith Method for large scale stein equations
Numerical Linear Algebra With Applications, 2014Co-Authors: Peter Benner, Grece El Khoury, Miloud SadkaneAbstract:SUMMARY A squared Smith type algorithm for solving large-scale discrete-time Stein equations is developed. The algorithm uses restarted Krylov spaces to compute approximations of the squared Smith iterations in low-rank factored form. Fast convergence results when very few iterations of the alternating direction implicit Method are applied to the Stein equation beforehand. The convergence of the algorithm is discussed and its performance is demonstrated by several test examples. Copyright © 2013 John Wiley & Sons, Ltd.
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On the numerical solution of large-scale sparse discrete-time Riccati equations
Advances in Computational Mathematics, 2011Co-Authors: Peter Benner, Heike FaßbenderAbstract:We discuss the numerical solution of large-scale discrete-time algebraic Riccati equations (DAREs) as they arise, e.g., in fully discretized linear-quadratic optimal control problems for parabolic partial differential equations (PDEs). We employ variants of Newton’s Method that allow to compute an approximate low-rank factor of the solution of the DARE. The principal computation in the Newton iteration is the numerical solution of a Stein (aka discrete Lyapunov) equation in each step. For this purpose, we present a low-rank Smith Method as well as a low-rank alternating-direction-implicit (ADI) iteration to compute low-rank approximations to solutions of Stein equations arising in this context. Numerical results are given to verify the efficiency and accuracy of the proposed algorithms.
Ebi Peter Osuobeni - One of the best experts on this subject based on the ideXlab platform.
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intra observer repeatability and inter observer agreement of the Smith Method of measuring the anterior chamber depth
Ophthalmic and Physiological Optics, 2000Co-Authors: Ebi Peter Osuobeni, K A Oduwaiye, Kelechi C OgbuehiAbstract:The Smith (1979) Method provides a means of estimating the anterior chamber depth without additional attachments to the slit lamp [Smith, R. J. H. (1979). A new Method of estimating the depth of the anterior chamber. Br. J. Ophthalmol. 63, 215-220]. In this study, the 95% intra-observer limits of repeatability and the 95% inter-observer limits of agreement of this Method have been determined. The intra-observer limits of repeatability were determined by plotting the difference vs the mean of the estimated anterior chamber depth obtained in two different sessions by each of two examiners, while the inter-observer limits of agreement are represented by a plot of the difference vs the mean estimated anterior chamber depth between the two examiners. For one examiner, the 95% intra-observer limits of repeatability was -0.36 to 0.58 mm, while for the other examiner the 95% intra-observer limits of repeatability was -0.25 to 0.37 mm. The 95% inter-observer limits of agreement were -0.31 to 0.23 mm and -0.41 to 0.25 mm for the first and second sessions respectively. The intra-observer limits of repeatability are comparable with those reported for A-scan ultrasonographic measures of the anterior chamber depth. These results imply that the Smith Method can be used with a high degree of repeatability and agreement to clinically monitor longitudinal changes in anterior chamber depth.
K A Oduwaiye - One of the best experts on this subject based on the ideXlab platform.
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intra observer repeatability and inter observer agreement of the Smith Method of measuring the anterior chamber depth
Ophthalmic and Physiological Optics, 2000Co-Authors: Ebi Peter Osuobeni, K A Oduwaiye, Kelechi C OgbuehiAbstract:The Smith (1979) Method provides a means of estimating the anterior chamber depth without additional attachments to the slit lamp [Smith, R. J. H. (1979). A new Method of estimating the depth of the anterior chamber. Br. J. Ophthalmol. 63, 215-220]. In this study, the 95% intra-observer limits of repeatability and the 95% inter-observer limits of agreement of this Method have been determined. The intra-observer limits of repeatability were determined by plotting the difference vs the mean of the estimated anterior chamber depth obtained in two different sessions by each of two examiners, while the inter-observer limits of agreement are represented by a plot of the difference vs the mean estimated anterior chamber depth between the two examiners. For one examiner, the 95% intra-observer limits of repeatability was -0.36 to 0.58 mm, while for the other examiner the 95% intra-observer limits of repeatability was -0.25 to 0.37 mm. The 95% inter-observer limits of agreement were -0.31 to 0.23 mm and -0.41 to 0.25 mm for the first and second sessions respectively. The intra-observer limits of repeatability are comparable with those reported for A-scan ultrasonographic measures of the anterior chamber depth. These results imply that the Smith Method can be used with a high degree of repeatability and agreement to clinically monitor longitudinal changes in anterior chamber depth.
Miloud Sadkane - One of the best experts on this subject based on the ideXlab platform.
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on the squared Smith Method for large scale stein equations
Numerical Linear Algebra With Applications, 2014Co-Authors: Peter Benner, Grece El Khoury, Miloud SadkaneAbstract:SUMMARY A squared Smith type algorithm for solving large-scale discrete-time Stein equations is developed. The algorithm uses restarted Krylov spaces to compute approximations of the squared Smith iterations in low-rank factored form. Fast convergence results when very few iterations of the alternating direction implicit Method are applied to the Stein equation beforehand. The convergence of the algorithm is discussed and its performance is demonstrated by several test examples. Copyright © 2013 John Wiley & Sons, Ltd.
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a low rank krylov squared Smith Method for large scale discrete time lyapunov equations
Linear Algebra and its Applications, 2012Co-Authors: Miloud SadkaneAbstract:Abstract The squared Smith Method is adapted to solve large-scale discrete-time Lyapunov matrix equations. The adaptation uses a Krylov subspace to generate the squared Smith iteration in a low-rank form. A restarting mechanism is employed to cope with the increase of memory storage of the Krylov basis. Theoretical aspects of the algorithm are presented. Several numerical illustrations are reported.
