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- Kron, J., et al.
(författare)
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Comparison of numerical simulation models for predicting temperature in solidification analysis with reference to air gap formation
- 2004
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Ingår i: International Journal of Cast Metals Research. - : Maney Publishing. - 1364-0461 .- 1743-1336. ; 17:5, s. 295-310
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Tidskriftsartikel (refereegranskat)abstract
- As a result of its influence on heat transfer between cast part and mould, air gap formation is an important problem for many casting processes. The general explanation for gap formation is that, as a result of stresses and distortions that are created from inhomogeneous cooling, shrinkage of the casting and expansion of the mould occur. In this paper, different thermomechanical approaches are applied to a well defined casting process using three commercial and one in-house codes and their predictions are compared with experimental findings. The experimental data were obtained from the solidification and subsequent cooling of cylindrical castings of eutectic Al-13% Si and ternary Al-7% Si-0.3% Mg alloys. Based on these findings, the major differences between the predictions of the models and the actual formation of the air gap are discussed.
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| 3. |
- Lövkvist Wallström, E, et al.
(författare)
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Importance of the 3' untranslated region of ornithine decarboxylase mRNA in the translational regulation of the enzyme
- 2001
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Ingår i: The Biochemical journal. - : Portland Press Ltd.. - 0264-6021 .- 1470-8728. ; 356:2, s. 34-627
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Tidskriftsartikel (refereegranskat)abstract
- Translational regulation of ornithine decarboxylase (ODC), which catalyses the first step in the biosynthesis of polyamines, appears to be an important mechanism in the strong feedback control as well as in the hypotonic induction of the enzyme. However, the exact mechanisms are not yet understood. The ODC mRNA has long 5' and 3' untranslated regions (UTRs) which may be involved in the translational control of the enzyme. In the present study we have used a series of stable transfectants of Chinese Hamster ovary cells expressing ODC mRNAs with various truncations in the 5' and 3' UTRs to investigate the importance of these regions. It is demonstrated that neither the 5' UTR nor the 3' UTR appears to be involved in the polyamine-mediated feedback control of ODC synthesis. The hypotonic induction of ODC, on the other hand, was shown to be highly dependent on the presence of the 3' UTR, but not on the 5' UTR, of ODC mRNA. Cells expressing ODC mRNAs lacking the 3' UTR showed no, or only a very slight, induction of ODC whether the 5' UTR was present or not, whereas the cell lines expressing ODC mRNAs containing the 3' UTR (with or without the 5' UTR) markedly induced ODC after a hypotonic shock. The present finding of a role for the ODC mRNA 3' UTR in the hypotonic induction of ODC is the first demonstration of a specific effect of the 3' UTR in the regulation of ODC.
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| 7. |
- Wendt, M., et al.
(författare)
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Localization of the High Frequency Field in a Beam-Plasma Diode Due to Density Gradients
- 2001
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Ingår i: Physica Scripta. - 0281-1847. ; 63, s. 62-69
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Tidskriftsartikel (refereegranskat)abstract
- An experimental study of the high frequency (hf) interaction of a strong, warm electron beam with an inhomogeneous, bounded plasma is presented and compared with particle-in-cell simulations. The density is highest in the center of the diode and decreases towards the boundaries. The electric field in the center is dominated by the unstable slow-space-charge wave, but experimental evidence is found, that reflected waves are present near the beam injection grid, where the oscillation frequency f is higher than the local plasma frequency f(pe)(x). The strong field at the resonance point (f = f(pe)(x)) is proposed to excite the unstable beam mode. Simulations confirm this picture by showing a concentration of the spectral power of the beam waves to the frequencies of the trapped Langmuir waves. Linear growth and Landau damping concentrate the beam wave to a 1.5-2 wavelengths wide region. Trapped Langmuir waves can accordingly determine the frequencies and position of the hf-field even for moderate density gradients and field strengths below the threshold for Langmuir collapse.
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