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Wave Modes (wave + mode)

Distribution by Scientific Domains

Engineering	60%

Selected Abstracts

Significance of autofluorescence in choriocapillaritis

ACTA OPHTHALMOLOGICA, Issue 2009
A MANTOVANI
Purpose To investigate the autofluorescence findings associated with choriocapillaritis Methods Illustrative cases of Primary Inflammatory Choriocapillaropathies(PICCPs)including Multiple Evanescent White Dot Syndrome (MEWDS), Acute Placoid Multifocal Pigment Epitheliopathy (APMPPE) or Multifocal Choroiditis (MFC), where Fundus Autofluorescence(FAF) images were obtained in the short wave mode(488nm), lipofuscin-related, or in near-infrared mode(787), melanin-related. Results In the groups of MEWDS and MFC patients, the more striking FAF alteration is an increase in autofluorescence. The areas of FAF do not strictly correspond to areas of ICGA hypofluorescence, with less FAF in areas of more pronounced ICGA hypofluorescence. The areas of increased FAF regress almost totally in the convalescent stage. In the APMPPE group, the placoid lesions are very often hypoautofluorescent except the margins that can be hyperautofluorescent. In the convalescent stage, altered FAF regresses, but bright FAF is often seen in the center of chorioretinal scars, corresponding to accumulation of fluorophores debris. Conclusion FAF is a complementary imaging technique in PICCPs indicating RPE cell dysfunction, but the information we have so far is scarce and has to be elucidated. In less severely hypoperfused areas,such as MEWDS and MFC, FAF488 is increased because the metabolism of the RPE cell is affected, which explains the accumulation of lipofuscin in its lysosomes. In conditions with severely nonperfused areas, such as APMPPE, FAF488 is very often decreased because RPE cell metabolism is probably affected to such a degree that it does not ingest any more lipofuscin and does not cause autofluorescence. [source]

Comparison of two wave element methods for the Helmholtz problem

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 1 2009
T. Huttunen
Abstract In comparison with low-order finite element methods (FEMs), the use of oscillatory basis functions has been shown to reduce the computational complexity associated with the numerical approximation of Helmholtz problems at high wave numbers. We compare two different wave element methods for the 2D Helmholtz problems. The methods chosen for this study are the partition of unity FEM (PUFEM) and the ultra-weak variational formulation (UWVF). In both methods, the local approximation of wave field is computed using a set of plane waves for constructing the basis functions. However, the methods are based on different variational formulations; the PUFEM basis also includes a polynomial component, whereas the UWVF basis consists purely of plane waves. As model problems we investigate propagating and evanescent wave modes in a duct with rigid walls and singular eigenmodes in an L-shaped domain. Results show a good performance of both methods for the modes in the duct, but only a satisfactory accuracy was obtained in the case of the singular field. On the other hand, both the methods can suffer from the ill-conditioning of the resulting matrix system. Copyright © 2008 John Wiley & Sons, Ltd. [source]

On the spectrum of the electric field integral equation and the convergence of the moment method

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 1 2001
Karl F. Warnick
Abstract Existing convergence estimates for numerical scattering methods based on boundary integral equations are asymptotic in the limit of vanishing discretization length, and break down as the electrical size of the problem grows. In order to analyse the efficiency and accuracy of numerical methods for the large scattering problems of interest in computational electromagnetics, we study the spectrum of the electric field integral equation (EFIE) for an infinite, conducting strip for both the TM (weakly singular kernel) and TE polarizations (hypersingular kernel). Due to the self-coupling of surface wave modes, the condition number of the discretized integral equation increases as the square root of the electrical size of the strip for both polarizations. From the spectrum of the EFIE, the solution error introduced by discretization of the integral equation can also be estimated. Away from the edge singularities of the solution, the error is second order in the discretization length for low-order bases with exact integration of matrix elements, and is first order if an approximate quadrature rule is employed. Comparison with numerical results demonstrates the validity of these condition number and solution error estimates. The spectral theory offers insights into the behaviour of numerical methods commonly observed in computational electromagnetics. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Lamb Wave Interactions with Non-symmetric Features at Structural Boundaries

PROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2008
M. R. Mofakhami
The paper initially describes on a numerical basis how a Lamb wave would have to perform that has been initiated in a pure mode (either symmetric or anti,symmetric) and what the wave would have to anticipate in terms of mode conversion when being reflected at a surface not perpendicular to its traveling direction. The effects of changing in geometric specifications of non,symmetric artificial features like angle of sloping edge or partially sloping edges are studied. The results obtained from these studies are presented as the reflected and converted parts of the incident wave versus angle of the edge or percentage of the sloped edge. It has been further shown that Lamb waves being generated experimentally by a finite size transducer into a plate like structure thus most likely result in a combination of modes. Reflection of these combined modes at structural boundaries will therefore generate an even more complex coupling of modes. This situation is further aggravated if the structural boundary is not purely perpendicular to the traveling wave but has a slightly varying angle such as it might have to be anticipated at a countersunk rivet, a notch or even more extreme a crack in a metallic component. However from understanding the background of Lamb wave generation, mode separation and superposition, a systematic approach can be established that allows complex Lamb waves, such as they are observed when monitoring true structures, to be interpreted and understood. This approach has been explained on the basis of numerical result obtained from finite element analyses first before proving the findings by some fundamental experiments performed with variable angle beam transducers which demonstrates the difficulties in de,coupling Lamb wave modes and how to handle those coupled modes in terms of structural condition monitoring. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Spin-wave resonance and magnetization studies in La0.7Mn1.3O3 films

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2003
P. Aleshkevych
Abstract Spin-wave resonance (SWR) in high quality epitaxial La0.7Mn1.3O3 films prepared by dc-magnetron sputtering was studied at a frequency of 9.25 GHz. SQUID magnetometry was used to study the film magnetization. A well-resolved structure of the SWR spectrum consists of surface and bulk spin waves modes. The experimentally found SWR spectra are in good agreement with the theory of SWR based on the surface-inhomogeneity model. Using the SWR and magnetization data, the spin-wave stiffness constant and the values of the bulk anisotropies were deduced. [source]