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- Allen, D.H., et al.
(författare)
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Modeling the viscoelastic response of GMT structural components
- 2001
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Ingår i: Composites Science And Technology. - 0266-3538 .- 1879-1050. ; 61:4, s. 503-515
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Tidskriftsartikel (refereegranskat)abstract
- A glass-mat-reinforced thermoplastic (GMT) composite material has been fabricated from randomly oriented continuous glass fibers embedded in a polypropylene matrix. The mechanical constitution of this composite has been characterized by using a linear viscoelastic micromechanically based material model. This material model has subsequently been implemented to several finite-element computer codes for analysis of structural components fabricated from polypropylene GMT. In this paper several example problems have been studied in order to determine the applicability of this modeling approach to predicting time-dependent deformations due to creep in GMT components. These example problems have been solved by utilizing two commercially available codes: ABAQUS, and ANSYS. Furthermore, results obtained with the codes have been compared to both analytic and experimental results, with varying degrees of success. The paper details these results for each of the example problems considered herein. © 2001 Elsevier Science Ltd. All rights reserved.
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- Enfors, Sven-Olof, et al.
(författare)
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Physiological responses to mixing in large scale bioreactors
- 2001
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Ingår i: Journal of Biotechnology. - 0168-1656 .- 1873-4863. ; 85:2, s. 175-185
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Tidskriftsartikel (refereegranskat)abstract
- Escherichia coli fed-batch cultivations at 22 m(3) scale were compared to corresponding laboratory scale processes and cultivations using a scale-down reactor furnished with a high-glucose concentration zone to mimic the conditions in a feed zone of the large bioreactor. Formate accumulated in the large reactor, indicating the existence of oxygen limitation zones. It is suggested that the reduced biomass yield at large scale partly is due to repeated production/reassimilation of acetate from overflow metabolism and mixed acid fermentation products due to local moving zones with oxygen limitation. The conditions that generated mixed-acid fermentation in the scale-down reactor also induced a number of stress responses, monitored by analysis of mRNA of selected stress induced genes. The stress responses were relaxed when the cells returned to the substrate limited and oxygen sufficient compartment of the reactor. Corresponding analysis in the large reactor showed that the concentration of mRNA of four stress induced genes was lowest at the sampling port most distant from the feed zone. It is assumed that repeated induction/relaxation of stress responses in a large bioreactor may contribute to altered physiological properties of the cells grown in large-scale bioreactor. Flow cytometric analysis revealed reduced damage with respect to cytoplasmic membrane potential and integrity in cells grown in the dynamic environments of the large scale reactor and the scale-down reactor.
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