359 research outputs found
Complete assessment of elastic properties of trabecular bone architecture from 3D reconstruction images
A method is presented that allows for a complete mechanical evaluation of trabecular bone architecture directly from three-dimensional computer reconstruction images. With this method, the reconstruction images are used as a basis for microstructural FE-analyses. From the results of these analyses the full stiffness matrix of bone specimens is obtained, using a standard mechanics approach. An optimization procedure is then used to find the best orthotropic representation and principal directions of this matrix. The method is demonstrated here relative to two trabecular bone specimens. With the development of in vivo reconstructions and the methods demonstrated here, even in vivo measurements will be possibl
The role of trabecular architecture in the anisotropic mechanical properties of bone
As yet, no unique relationship between mechanical and structural parameters has been established for trabecular bone. A possible explanation for the variability in the relationships obtained so far is that the results of mechanical tests represent more parameters than those of trabecular morphology alone. In the present study, the results of such a mechanical test are compared to results of a numerical experiment, from which the isolated mechanical role of the trabecular architecture of a bone specimen is obtained. A mechanically tested bone specimen was reconstructed in a computer and converted to a microstructural FE-model. The results of experiment and FE-simulation were, obviously, not identical. It is hypothesized that experimental artifacts are the most important factors affecting the mechanical test results, thus causing variability in the relationships. More accurate relationships are expected when these artifacts can be excluded, for example, by using microstructural FE-models
Benthic foraminiferal assemblages and test accumulation in coastal microhabitats on San Salvador, Bahamas
Benthic foraminiferal populations were studied in a shallow bay of San Salvador
Island, the Bahamas. Surface sediments and marine macrophytes were collected
from 14Â sample sites along a 500 m transect at Grahams Harbour to
investigate the foraminiferal assemblage in each microhabitat and to test the
link between dead foraminiferal test accumulation patterns and living
epiphytic and sedimentary foraminiferal assemblages, macrophyte distribution,
and environmental gradients. The analyses include grain size measurements,
macrophyte biomass quantification, and qualitative and quantitative
studies of benthic foraminifera. The foraminifera found attached to
macrophytes differed between macrophyte habitats. However, a correlation
between these living communities and the dead assemblages in the sediments at
the same sites could not be observed. Principal component analysis (PCA) and
redundancy analysis (RDA) suggest that the presence of the macroalgae
Halimeda explains 16 % of the residual faunal variation in the dead
foraminiferal assemblage after the effects of sorting according to fall speed
are
partialled out. The RDA also reflects a positive correlation between
foraminifera larger than 1.0 mm in diameter and the 0.25–0.5 mm sediment
grain size, indicating sedimentological processes as the main factor
controlling the sedimentary epiphytic foraminiferal assemblages. These
sedimentary processes overprint most effects of ecological features or
macrophyte-specific association.</p
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