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- Almqvist, Nils, et al.
(författare)
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Micromechanical and structural properties of a pennate diatom investigated by atomic force microscopy
- 2001
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Ingår i: Journal of Microscopy. - : Wiley. - 0022-2720 .- 1365-2818. ; 202:3, s. 518-532
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Tidskriftsartikel (refereegranskat)abstract
- The mechanisms behind natural nanofabrication of highly structured silicas are increasingly being investigated. We have explored the use of a standard Nanoscope III Multimode atomic force microscope (AFM) to study the silica shell of diatoms. The delicate structures of the shell surface of the diatom Navicula pelliculosa (Breb.) Hilse were imaged and the shell's micromechanical properties were measured semi-quantitatively with a resolution down to approximately 10 nm. The technique to measure elasticity and hardness with the AFM was demonstrated to be useable even on these hard glass-like surfaces, Different experimental configurations and evaluation methods were tested, They gave a consistent result of the shell micromechanical properties, The first results showed that the diatom shell's overall hardness and elasticity was similar to that of known silicas. However, regions with different mechanical proper ties were distinguished. The elastic modulus varied from 7 to 20 GPa, from 20 to 100 GPa and from 30 to hundreds of GPa depending on the location. In general, the hardness measurements showed similar spatial differences, The hardness values ranged from 1 to 12 GPa but one specific part of the shell was even harder. Hence, certain localized regions of the shell were significantly harder or more elastic. These regions coincide with known characteristic features and mechanisms appearing at the different stages of the shell's growth. These results show that this method serves as a complementary tool in the study of silica biomineralization, and can detect eventual crystalline phases.
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| 2. |
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| 3. |
- Thomson, Elizabeth, et al.
(författare)
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Childbearing in stepfamilies : how parity matter
- 2002. - 2
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Ingår i: Dynamics of fertility and partnership in Europe<em></em>. - New York ; Geneva: United Nations. : United Nations. Economic Commission for Europe.. - 9211168090 ; , s. 87-99
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Bokkapitel (refereegranskat)abstract
- We investigate potential effects of stepfamily status on births in unions in Austria, Finland, France, and West Germany. In all four countries, we find support for the value of a first union birth to signal the couple’s commitment. Birth rates are higher if the couple has no shared children, net of their total (hers + his) parity. Unexpectedly, couples in which one of the partners is not a parent had lower birth risks than those in which both partners brought children to their union, contrary to the value of a first birth to establish parental status. We also find support for the value of a second shared birth to provide a full sibling. Net of their combined parity, stepfamily couples with one shared child had a higher risk than families without stepchildren of having a second shared birth. Some of these results were not consistent in analyses of men’s reports, in part due to the smaller male samples and, possibly, to the poorer reports of men about their children from previous unions.
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