| 1. |
- Boström, Anders E, 1951, et al.
(författare)
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Scattering by two penny-shaped cracks with spring boundary conditions
- 1993
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Ingår i: Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences. - 1471-2946 .- 1364-5021. ; 443, s. 183-201
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Tidskriftsartikel (refereegranskat)abstract
- The elastodynamic scattering by a penny-shaped crack with spring boundary conditions is investigated. The transition (T) matrix of the crack is determined and the usefulness of this is illustrated by considering also the scattering by two cracks. The T matrix of a single crack is first determined by a direct integral equation method which gives the crack-opening displacement and the integral representation which subsequently gives the scattered field expanded in spherical waves. Two cracks are considered by a multi-centred T matrix approach where matrix inverses are expanded in Neuman series. Rotation matrices are employed so that the cracks may have an arbitrary rotation. The back-scattered longitudinal far field amplitude is computed both in the frequency and time domain in a few cases and the effects due to multiple scattering are in particular explored.
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| 2. |
- Eriksson, Arne S., 1961
(författare)
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Elastic Wave Scattering by Closed Cracks and Thin Flaws - Multiple Scattering and Resonances
- 1992
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis we study elastic wave scattering by thin flaws and closed cracks, which finds applications in ultrasonic testing and evaluation of materials. First we consider the scattering of an SH-wave by a thin finite elastic layer between two elastic half-spaces. The layer, thin compared to the wavelengths involved, is modelled by spring boundary conditions extended with terms accounting for inertia forces. A direct integral equation method is used, with the discontinuity of displacement and traction over the thin layer as the unknowns. Numerical results are given for the scattered energy and the far field amplitude. We also investigate the elastodynamic scattering by two penny-shaped cracks with spring boundary conditions in the fully three-dimensional case. The transition matrix of a single crack is first determined by a direct integral equation method which gives the crack-opening displacement (COD) and the integral representation which subsequently gives the scattered field expanded in spherical waves. Two cracks are considered by a multi-centered T matrix approach where the matrix inverses are expanded in Neumann series. Rotation matrices are employed so that the cracks may have an arbitrary orientation. The numerical procedures are very stable and it has been possible to go to quite high frequencies. The back-scattered longitudinal far field amplitude is computed both in the frequency and time domain in a few cases and the effects due to multiple scattering are in particular explored. The natural frequencies of one partially closed penny-shaped crack are calculated for the symmetric part of the problem. The natural frequencies are given as the complex SEM (singularity expansion method) poles of the symmetric part of the T matrix. A clear correlation is shown between the migration of the poles, as the crack gets more closed, and the frequencies at which the scattering cross section has its peaks.
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| 3. |
- Eriksson, Arne S., 1961, et al.
(författare)
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Ultrasonic wave propagation through a cracked solid
- 1995
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Ingår i: Wave Motion. - 0165-2125. ; 22, s. 297-310
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Tidskriftsartikel (refereegranskat)abstract
- The propagation of ultrasonic waves through a perfectly elastic medium containing a random distribution of equally-sized penny-shaped cracks with spring boundary conditions across the crack faces are considered. As limiting cases results for open and fluid-filled cracks are derived also. The medium with the crack distribution is modelled as an effective viscoelastic medium, using the non-interecting scatterer approximation and Foldy's thery. For this purpose the scattering by a single crack is solved by an integral equation method. Distributions of both randomly oriented and parallel cracks are considered. Numerical results are presented for the phase velocity and attenuation. For parallel cracks when the effective medium becomes transversely isotropic two further issues are investigated.The first is the extension of a static result due to Kachanov, who showed the transverse isotropy to be of a very special kind. The second is consistency of the wave speeds obtained by using Foldy's theory, with the fact that the effective material is transversely isotropic. In particular, the vertically polarized shear wave should have the same wave speeds in directions parallel and normal to the cracks. It is found that the relations established by Kachanov and the consistency requirements are satisfied by the phase velocity for all frequencies considered.
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| 4. |
- Hägg, Daniel, 1974, et al.
(författare)
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Expression profiling of macrophages from subjects with atherosclerosis to identify novel susceptibility genes.
- 2008
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Ingår i: International journal of molecular medicine. - 1107-3756. ; 21:6, s. 697-704
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Tidskriftsartikel (refereegranskat)abstract
- Although a number of environmental risk factors for atherosclerosis have been identified, heredity seems to be a significant independent risk factor. The aim of our study was to identify novel susceptibility genes for atherosclerosis. The screening process consisted of three steps. First, expression profiles of macrophages from subjects with atherosclerosis were compared to macrophages from control subjects. Secondly, the subjects were genotyped for promoter region polymorphisms in genes with altered gene expression. Thirdly, a population of subjects with coronary heart disease and control subjects were genotyped to test for an association with identified polymorphisms that affected gene expression. Twenty-seven genes were differentially expressed in both macrophages and foam cells from subjects with atherosclerosis. Three of these genes, IRS2, CD86 and SLC11A1 were selected for further analysis. Foam cells from subjects homozygous for the C allele at the -765C-->T SNP located in the promoter region of IRS2 had increased gene expression compared to foam cells from subjects with the nonCC genotype. Also, macrophages and foam cells from subjects homozygous for allele 2 at a repeat element in the promoter region of SLC11A1 had increased gene expression compared to macrophages and foam cells from subjects with the non22 genotype. Genotyping of 512 pairs of subjects with coronary heart disease (CHD) and matched controls revealed that subjects homozygous for C of the IRS2 SNP had an increased risk for CHD; odds ratio 1.43, p=0.010. Immunohistochemical staining of human carotid plaques showed that IRS2 expression was localised to macrophages and endothelial cells in vivo. Our method provides a reliable approach for identifying susceptibility genes for atherosclerosis, and we conclude that elevated IRS2 gene expression in macrophages may be associated with an increased risk of CHD.
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