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- Klarbring, Anders, 1957-, et al.
(författare)
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Residual Stress Fields in Soft Tissues
- 2004
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Ingår i: 21st International Congress of Theoretical and Applied Mechanics,2004. ; , s. 20-20
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Konferensbidrag (refereegranskat)
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| 3. |
- Olsson, Mats, 1960, et al.
(författare)
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Haldane rules: costs of outbreeding at production of daughters in sand lizards
- 2004
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Ingår i: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 7:10, s. 924-928
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Tidskriftsartikel (refereegranskat)abstract
- Haldane's rule is one of the most widely applicable paradigms in evolutionary biology, stating that in species crossings, the heterogametic sex will suffer more severely in terms of sterility and inviability. We address this in a within-species outbreeding situation by assessing the risk of producing inviable offspring depending on the sex ratio of the clutch produced in between-population crossings in the laboratory. In crossings between male and female sand lizards (Lacerta agilis) from two different sampling regions, one in Sweden, one in central Europe, risk of gametic incompatibility is unaffected by outbreeding, but offspring from between-population crossings show 300% higher malformation frequency and 10% lower hatching success. The risk of having inviable offspring increases with the production of daughters, i.e. the hemizygous sex in this species (ZW). Such sex-specific genetic costs of offspring production need to be incorporated into life history ecology, e.g. sex allocation theory.
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| 5. |
- Olsson, Tobias, 1977-, et al.
(författare)
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Boundary Value Problems of an Initially Stressed Body
- 2004
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The initial strain in a body can be described by a two-point tensor that maps tangent vectors between a local stress free configuration (manifolds) and the initially strained configuration. The initial strain tensor can be used to form a metric tensor and this metric can be used to induce a third manifold. The boundary value problem of an elastic body is in this paper formulated on these three manifolds: the induced manifold, the initially strained configuration and the local stress free configuration. Moreover, we consider a hyperelastic body with incompressible properties and we show that in that case, the divergence of the first Piola- Kirchhoff stress tensor defined on the initially strained configuration and on the induced manifold coincide. There-fore, we conclude that for an incompressible material, the boundary value problems stated on the initially strained configuration and on the induced manifold are the same.
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| 6. |
- Olsson, Tobias, 1977-
(författare)
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Modeling Residual Stress Fields in Soft Tissues : with Application to Human Arteries
- 2004
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Biomechanics or Mechanics of Biology comprises many different fields. This thesis deals with soft tissues or living tissues and the fact that these materials live in a pressurized environment. This means that an unloaded tissue may not be stress free. The stress in an unloaded body is usually called residual stress. This thesis consist of an introduction to continuum mechanics and to soft tissues, and three research papers.The first paper deals with a zero stress configuration and the question of compatibility. It is shown that the zero stress configuration not necessarily constitutes a compatible body. The condition for compatibility is analyzed and exemplified on a cylinder and a sphere.In the second paper a model for residually stressed arteries based on local deformations is developed. The material properties for a human aorta is identified by the solution to an optimization problem. The resulting initial strains show a non constant behavior and this behavior cannot be described by the commonly used opening- angle model.The last paper is about formulating boundary value problems for initially stressed bodies in three different reference configurations. Firstly, the equilibrium equation and constitutive relation are stated on the unloaded residually stressed body. Secondly, all material points are relieved from stress by a tangent map and the new stress free configuration, which may be incompatible, is used to state the boundary value problem. Thirdly; we use the relieving tangent map to induce a new metric on the body. This induced metric is in general non Euclidean. Finally, we formulate the boundary value problem on this manifold.
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| 8. |
- Uller, Tobias, 1977, et al.
(författare)
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Ectoparasite susceptibility in lizards from populations sympatric and allopatric with ticks
- 2004
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Ingår i: Ecoscience. - 1195-6860. ; 11:4, s. 428-432
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Tidskriftsartikel (refereegranskat)abstract
- Theory suggests that host-parasite interaction should lead to local adaptation of parasites to their hosts and vice versa. The degree of local adaptation depends on, for example, migration, relative generation time of host and parasite, and the number of host species. Furthermore, in any coevolutionary process, local adaptation of one species is dependent on the evolution of sympatric and allopatric populations of the other species, and the degree of gene flow. The tick Ixodes ricinus is a generalist tick feeding on hosts of a variety of taxa. We contrasted populations of common lizards (Lacerta vivipara) differing in their evolutionary history of exposure to ticks. Juvenile lizards were raised in a common garden experiment. We monitored growth rate, physiological performance, and aspects of immune function in tick-exposed and control offspring. There were no differences in response to tick infestation between host populations, with both sympatric and allopatric hosts showing impaired growth and endurance under parasite exposure. Ticks were marginally more engorged on allopatric hosts (P = 0.06); hence, our results do not support the hypothesis of local adaptation of parasites.
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