293 research outputs found
Dynamics and Control of Oscillatory Bioreactors
Bioreactors are widely used in many industries to generate a range of
products using various host cells e.g., yeast, insect, and mammalian cells.
Depending on the process, product, and host cell, some bioreactors exhibit
sustained periodic behavior in key process variables such as metabolite
concentrations, biomass, and product titer. Such dynamical behavior can arise
from different mechanisms, including predator-prey dynamics, substrate
inhibition, and cell sub-population synchrony. Oscillatory dynamical behavior
is undesirable as it can impact downstream processes, especially in a
continuous operation, and can make process operations and product quality
control more challenging. This article provides an overview of oscillatory
dynamics. The mechanisms that give rise to the oscillations and process control
strategies for suppressing the oscillations are discussed, while providing
insights that go beyond past studies. Alternative process configurations are
proposed for bypassing the mechanisms that generate oscillations.Comment: Submitted to Biotechnology Progress, ICB V Special Issue (invited).
Pavan Inguva and Krystian Ganko contributed equally to this work.
Corresponding author: Richard D. Braat
Electrical coupling of neuro-ommatidial photoreceptor cells in the blowfly
A new method of microstimulation of the blowfly eye using corneal neutralization was applied to the 6 peripheral photoreceptor cells (R1-R6) connected to one neuro-ommatidium (and thus looking into the same direction), whilst the receptor potential of a dark-adapted photoreceptor cell was recorded by means of an intracellular microelectrode. Stimulation of the photoreceptor cells not impaled elicited responses in the recorded cell of about 20% of the response elicited when stimulating the recorded cell. This is probably caused by gap junctions recently found between the axon terminals of these cells. Stimulation of all 6 cells together yielded responses that were larger and longer than those obtained with stimulation of just the recorded cell, and intensity-response curves that deviated more strongly from linearity. Evidence is presented that the resistance of the axon terminal of the photoreceptor cells quickly drops in response to a light flash, depending on the light intensity. Incorporating the cable properties of the cell body and the axon, the resistance of the gap junctions, and the (adapting) terminal resistance, a theoretical model is presented that explains the measurements well. Finally, it is argued that the gap junctions between the photoreceptor cells may effectively uncouple the synaptic responses of the cells by counteracting the influence of field potentials.
Quantum and Semiclassical Calculations of Cold Atom Collisions in Light Fields
We derive and apply an optical Bloch equation (OBE) model for describing
collisions of ground and excited laser cooled alkali atoms in the presence of
near-resonant light. Typically these collisions lead to loss of atoms from
traps. We compare the results obtained with a quantum mechanical complex
potential treatment, semiclassical Landau-Zener models with decay, and a
quantum time-dependent Monte-Carlo wave packet (MCWP) calculation. We formulate
the OBE method in both adiabatic and diabatic representations. We calculate the
laser intensity dependence of collision probabilities and find that the
adiabatic OBE results agree quantitatively with those of the MCWP calculation,
and qualitatively with the semiclassical Landau-Zener model with delayed decay,
but that the complex potential method or the traditional Landau-Zener model
fail in the saturation limit.Comment: 21 pages, RevTex, 7 eps figures embedded using psfig, see also
http://www.physics.helsinki.fi/~kasuomin
Biomanufacturing and testbed development for the continuous production of monoclonal antibodies
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