Individual cells of cyanobacteria or algae are supplied with light in a highly irregular fashion when grown in industrial-scale photobioreactors (PBRs). These conditions coincide with significant reductions in growth rate compared to the static light environments commonly used in laboratory experiments. We grew a dense culture of the model cyanobacterium Synechocystis sp. PCC 6803 under a sinusoidal light regime in a bench-top PBR (the Phenometrics environmental PBR [ePBR]). We developed a computational fluid dynamics model of the ePBR, which predicted that individual cells experienced rapid fluctuations (;6 s) between 2,000 and ,1 mmol photons m 22 s 21 , caused by vertical mixing and self-shading. The daily average light exposure of a single cell was 180 mmol photons m 22 s 21. Physiological measurements across the day showed no in situ occurrence of nonphotochemical quenching, and there was no significant photoinhibition. An ex situ experiment showed that up to 50% of electrons derived from PSII were diverted to alternative electron transport in a rapidly changing light environment modeled after the ePBR. Collectively, our results suggest that modification of nonphotochemical quenching may not increase cyanobacterial productivity in PBRs with rapidly changing light. Instead, tuning the rate of alternative electron transport and increasing the processing rates of electrons downstream of PSI are potential avenues to enhance productivity. The approach presented here could be used as a template to investigate the photophysiology of any aquatic photoautotroph in a natural or industrially relevant mixing regime.
Hypersonic rarefied flow of nitrogen over a sphere is simulated by the Direct Simulation Monte Carlo (DSMC) calculations to study the drag coefficient under Lord's diffuse scattering modelwith incomplete energy accommodation. The flow field and drag results from free-molecule flow to transition regime flow are obtained for extreme cases of complete energy accommodation and zero accommodation (diffuse elastic reflection). Available wind tunnel experimental data agree with the complete energy accommodation limit. But incomplete energy accommodation may have remarkable influence on orbital drag of a satellite. The parameters needed for this incomplete energy accommodation model are usually determined by the analysis on the result of the experiment.
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