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  • 1
    Electronic Resource
    Electronic Resource
    A hybrid representation approach for modelling complex dynamic bioprocesses (2000)
    Springer
    Bioprocess engineering 22 (2000), S. 547-556 
    Details
    ISSN: 0178-515X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract This paper considers the use of hybrid models to represent the dynamic behaviour of biotechnological processes. Each hybrid model consists of a set of non linear differential equations and a neural model. The set of differential equations attempts to describe as much as possible the phenomenology of the process whereas neural networks model predict some key parameters that are an essential part of the phenomenological model. The neural model is obtained indirectly, that is, using the prediction errors of one or more state variables to adjust its weights instead of successive presentations of input-output data of the neural network. This approach allows to use actual measurements to derive a suitable neural model that not only represents the variation of some key parameters but it is also able to partly include dynamic behaviour unaccounted for by the phenomenological model. The approach is described in detail using three test cases: (1) the fermentation of glucose to gluconic acid by the micro-organism Pseudomonas ovalis, (2) the growth of filamentous fungi in a solid state fermenter, and (3) the propagation of filamentous fungi growing on a 2-D solid substrate. Results for the three applications clearly demon- strate that using a hybrid model is a viable alternative for modelling complex biotechnological bioprocesses.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004499900110
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  • 2
    Electronic Resource
    Electronic Resource
    Thermodynamics of yeast cell osmoregulation: Passive mechanisms (1996)
    Springer
    Journal of biological physics 22 (1996), S. 73-86 
    Details
    ISSN: 1573-0689
    Keywords: Cell volume ; Osmotic pressure ; Osmotic stress ; Yeasts
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract The response of yeast cells to osmotic pressure variations of the medium were studied through the kinetics of cell-volume modifications corresponding to the mass transfer of water and solutes. Osmotic variations were made by modification of the concentration of an external binary solution (polyol/water) without nutritive components. Two phases were distinguished in the thermodynamic response. A transient phase following an osmotic shift, which is characterised by rapid water transfer across the cell membrane and whose kinetics determine cell viability; then, a steady-state phase is reached when the cell volume becomes quasi-constant. The response of the cell during the transient phase depends on the level of the osmotic stress, and hence of the osmotic pressure of the medium. In the range of weak osmotic pressures, the metabolism of the cell is preserved through the maintenance of the intracellular turgor pressure. On the other hand in the range of high osmotic pressures of the medium, yeast cells behave as osmometers and no further metabolism occurs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00954456
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    A neural network estimator for total biomass of filamentous fungi growing on two dimensional solid substrate (1998)
    Springer
    Biotechnology techniques 12 (1998), S. 515-519 
    Details
    ISSN: 1573-6784
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract A neural network dynamic model is proposed for the on-line estimation of total biomass during filamentous fungi cultures on two dimensional solid substrate. The neural network provides an accurate and robust estimation of biomass from macroscopic measurements of the colony radius evolution. Experiments were performed on Gibberella fujikuroi growing on Petri dishes under different conditions of temperature and water activity. © Rapid Science Ltd. 1998
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008895212814
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  • 4
    Electronic Resource
    Electronic Resource
    Influence of the water activity of a solid substrate on the growth rate and sporogenesis of filamentous fungi (1988)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 31 (1988), S. 457-463 
    Details
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The water activity (aw) of substrates has been related to the mycelial growth and the sporogenesis of two molds. In the absence of other limiting factors, optimal aw values were determined for growth and sporogenesis as 0.99 and 0.98, respectively, for Trichoderma viride TS and 0.97 and 0.96 for Penicillium roqueforti. In all cases, the accuracy of the optimal value would justify the regulation of this parameter. A model was proposed which establishes a relationship between the mycelial growth and the water activity value of the substrate.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260310510
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  • 5
    Electronic Resource
    Electronic Resource
    Effects of the kinetics of osmotic pressure variation on yeast viability (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 40 (1992), S. 1435-1439 
    Details
    ISSN: 0006-3592
    Keywords: osmotic pressure ; osmotic stress ; osmotolerance ; physiological state ; yeasts ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The variation rate of the osmotic pressure increase was found to have a great effect on the viability of yeasts subjected to hyperosmotic stress. A low intensity of the increase rate of osmotic pressure could maintain an important viability of the cells (about 90 to 100%) even for very high levels of osmotic pressure (about 108 Pa). The viability level was found to be highly dependent on the physiological state of the cells: Variations in the properties of the cell membrane were supposed to be involved in such a dependence. © 1992 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260401119
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  • 6
    Electronic Resource
    Electronic Resource
    Determination of cells' water membrane permeability: Unexpected high osmotic permeability of Saccharomyces cerevisiae (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 62-70 
    Details
    ISSN: 0006-3592
    Keywords: osmotic shock ; water permeability ; mixing time constant ; mathematical model ; yeast ; leukemia K562 cells ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Water permeability (Lp), calculated from the volume variations of cells subjected to an osmotic shock, is classically used to characterize cell membrane properties. In this work, we have shown the importance of the kind of mixing reactor used to measure the Lp parameter. A mathematical model including the mixing time constant has been proposed allowing an accurate Lp estimation even though the mixing time constant is higher than the cell time constant obtained in response to a perfect shock. The estimated Lp values of human leukemia K562 cells were found to be the same whatever the mixing time constant. The Lp value of Saccharomyces cerevisiae could not be exactly estimated. However, S. cerevisiae has unexpectedly high water permeability, implying that this yeast may contain water channels in the membrane. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 62-70, 1997.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
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