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61.
It has been reported that flashing light enhances microalgal biomass productivity and overall photosynthetic efficiency. The
algal growth kinetics and oxygen production rates under flashing light with various flashing frequencies (5 Hz-37 kHz) were
compared with those under equivalent continuous light in photobioreactors. A positive flashing light effect was observed with
flashing frequencies over 1 kHz. The oxygen production rate under conditions of flashing light was slightly higher than that
under continuous light. The cells under the high frequency flashing light were also observed to be healthier than those under
continuous light, particularly at higher cell concentrations. When 37 kHz flashing light was applied to an LED-based photobioreactor,
the cell concentration was higher than that obtained under continuous light by about 20%. Flashing light may be a reasonable
solution to overcome mutual shading, particularly in high-density algal cultures. 相似文献
62.
Naohiro?Yoshimoto Toru?SatoEmail author Yutaka?Kondo 《Journal of applied phycology》2005,17(3):207-214
For a photobioreactor for mass-culturing microalgae, it is known that flashing light effect enhances the efficiency of photosynthesis. A dynamic model for photosynthesis was developed to elucidate this effect. A particular feature of the model is that discrete RuBP particles circulate in the Calvin cycle and their speeds in the cycle are determined by the amount of ATP generated in the photon reception process. This can realise the light saturation under continuous light and the flashing light effect under fluctuating illumination. Laboratory experiments were conducted to obtain model parameters by curve-fitting for Chaetoceros calcitrans. The present model demonstrates the light flashing effect moderately well and elucidates its mechanism reasonably. 相似文献
63.
Yonghong Wang Yuanguang Li Dingji Shi Guomin Shen Binggen Ru Siliang Zhang 《Biotechnology letters》2002,24(19):1593-1597
Synechocystis sp. PCC 6803 was grown in a 2.5 l enclosed photobioreactor on medium with or without glucose. The incident light intensities ranged from 1.5 klux to 7 klux. The highest average specific growth rates of mixotrophic culture and photoautotrophic culture were, respectively, 1.3 h–1 at a light intensity of 7 klux on 3.2 g l–1 glucose and 0.3 h–1 at both light intensities of 5 klux and 7 klux. The highest cell density 2.5 g l –1 was obtained at both of light intensities 5 klux and 7 klux on 3.2 g glucose l–1. Glucose consumption decreased with decreasing light intensity. The energy yields of mixotrophic cultures were 4 to 6 times higher than that of photoautotrophic cultures. Light favored mixotrophic growth of Synechocystis sp. PCC 6803, especially at higher light intensities (5–7 klux). 相似文献
64.
Priede MA Vanags JJ Viesturs UE Tucker KG Bujalski W Thomas CR 《Biotechnology and bioengineering》1995,48(3):266-277
The influence of two mixing geometries (at the same scale) with different flow energy distributions on the performance of the gibberellic acid fermentation and on the morphology of the producing fungus Fusarium moniliforme was investigated. Fermentations were performed using a turbine mixing system (TMS) and a counterflow mixing system (CMS), which were high and low power number mixing systems, respectively. Different agitator speed rate profiles were maintained to obtain equal specific power inputs to both mixing systems. Substantial differences in morphology and productivity of F. moniliforme were found. To investigate the causes of these differences, local values and spectra of the kinetic energy of flow fluctuations were measured during the fermentations using a stirring intensity measuring device (SIMD) and a frequency spectrum analyzer. Biomass and gibberellic acid concentrations were found to be higher in the TMS, where the energy distribution was less even, and Vi/here the main part of the energy was at small frequencies (large eddies). An automated image analysis method was used for quantitative characterization of F. moniliforme freely dispersed mycelia and clump morphology. A higher proportion of clumped mycelia with clumps of larger area, perimeter, and roughness was observed in the TMS. A correlation between the morphology and productivity was found, and TMS favored the development of more productive mycelia with longer and thinner hyphae. Introduced power was not a good parameter to characterize different impellers, even at a given scale. (c) 1995 John Wiley & Sons, Inc. 相似文献
65.
Baby hamster kidney (BHK) cell aggregates grown in stirred vessels with different working volumes and impeller sizes were characterized. Using batch cultures, the range of agitation rates studied (25-100 rpm) led to aggregates with maximum sizes of 150 mum. Necrotic centers were not observed and cell specific productivity was independent of aggregate size. High cell viability was found for both single and adherent cells without an increase in cell death when agitation rate was increased. The increase in agitation rate affected aggregates by reducing their size and increasing their concentration and cell concentration in aggregates, while increasing the fraction of free cells in suspension. The experimental relationship between aggregate size and power dissipation rate per unit of mass was close to -1/4, suggesting a correlation with a critical turbulence microscale; this was independent of vessel scale and impeller geometry over the range investigated. Viscous stresses in the viscous dissipation subrange (below Kolmogoroff eddies) appear to be responsible for aggregate breakage. Under intense agitation BHK cells grown in the absence of microcarriers existed as aggregates without cell damage, whereas cells grown on the surface of microcarriers were largely reduced. This is a clear advantage for scaleup purposes if aggregates are used as a natural immobilization system in stirred vessels. (c) 1995 John Wiley & Sons, Inc. 相似文献
66.
Studies in chiral symmetry breaking crystallization I: The effects of stirring and evaporation rates
Chiral symmetry breaking can be realized in stirred crystallization of Na-ClO3. We present experimental and theoretical studies of the random distribution of crystal enantiomeric excess (cee) for various stirring and solvent evaporation rates. For a fixed solvent evaporation rate, as the stirring RPM is increased, the probability distribution of cee initially broadens and subsequently develops a sharp peak close to cee = 1. On further increase of stirring rate, the probability distribution once again broadens. This broad probability distribution becomes narrow, with a sharp peak near cee = 1, if the solvent evaporation rate is decreased. Thus we show some ways in which the probability distribution of cee can be controlled in stirred crystallization. In particular, our study shows that the stirring rate and the solvent evaporation rate can be adjusted to maximize crystal enantiomeric excess. © 1995 Wiley-Liss, Inc. 相似文献
67.
Giuseppe Torzillo Paola Accolla Edoardo Pinzani Jiři Masojidek 《Journal of applied phycology》1996,8(4-5):283-291
A chlorophyll fluorescence technique was applied to anin situ study on the effects of low temperature and high light stresses onSpirulina cultures grown outdoors in controlled tubular photobioreactors at high (1.1 g L–1) and low (0.44 g L–1) biomass concentrations. Diurnal changes in PSII photochemistry (F
v/F
m) after 15 min of darkness, or in the light (dF/F
m), and non-photochemical (qN) quenching were measured using a portable, pulse-amplitude-modulated fluorometer. The depression of theF
v/F
m ratio ofSpirulina cultures grown outdoors at 25°C (i.e. 10°C below optimum for growth) and 0.44 g L–1, reached 30% at the middle of the day. At the same time of the day thedF/F
m ratio showed a reduction of up to 52%. The depression of bothF
v/F
m anddF/F
m was lower in the cultures grown at 1.1 g L–1. Photoinhibition reduced the daily productivity of the culture grown at 0.44 g L–1 and 25°C by 33% with respect to that grown at 35°C. Changes in the growth yields of the cultures grown under different temperatures and growth rates correlate well with analogous changes in photon yield (dF/F
m). Simple measurements of photochemical yield (F
v/F
m) can be used to test the physiological status ofSpirulina cultures. The results indicate that the saturating pulse fluorescence technique, when usedin situ, is a powerful tool for assessment of the photosynthetic characteristics of outdoor cultures ofSpirulina. 相似文献
68.
Ex vivo expansion of hematopoietic stem cells in a proliferation chamber with external stirred conditioning tank: Sequential optimization of growth factors
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Younes Beygi Khosrowshahi Ali Baradar Khoshfetrat Karim Shamsasenjan 《Engineering in Life Science》2016,16(3):254-262
The insufficient number of hematopoietic stem cells (HSCs) extracted from various cell sources creates the need for the use of growth factors in the culture systems. Numerous types and concentrations of growth factors have been reported in the literature. In this study, we investigated the effect of three important hematopoietic growth factors thrombopoietin (TPO), stem cell factor (SCF), and Fms‐like tyrosine kinase‐3 ligand (Flt‐3) as well as cell‐seeding density on ex vivo expansion of human HSCs using a factorial design. Sequential optimization was then followed by methods of steepest ascent and central composite design. The optimum concentrations of growth factors were 50, 90, and 34 ng/mL for SCF, TPO, and Flt‐3, respectively, at an initial cell density of 2.5 × 105 cells/mL. Effective expansion factor value (EEF) of HSCs increased considerably and revealed almost similar results when the cells were cultured in a 24‐well plate (EEF = 4.54 ± 0.43) and a proliferation chamber with an external stirred conditioning tank (PC‐ESCT; EEF = 5.1 ± 0.35) at seeding density of 2.5 × 105 cells/mL after 7 days. The cells did not show considerable changes in proliferation when they were cultured in medium containing serum or in a commercial serum‐free medium at the optimum concentrations of the growth factors. The present study demonstrated the optimum condition of hematopoietic growth factors as well as the potential of PC‐ESCT for ex vivo expansion of HSCs. 相似文献
69.
Outdoor experiments carried out in Florence, Italy (latitude 43.8° N, longitude 11.3° E), using tubular photobioreactors have
shown that in summer the average net productivity of a Spirulina platensis culture grown at the optimal temperature of 35 °C was superior by 23% to that observed in a culture grown at 25 °C. The rates
of night biomass loss were higher in the culture grown at 25 °C (average 7.6% of total dry weight) than in the one grown at
35 °C (average 5%). Night biomass loss depended on the temperature and light irradiance at which the cultures were grown,
since these factors influenced the biomass composition. A net increase in carbohydrate synthesis occurred when the culture
was grown at a low biomass concentration under high light irradiance or at the suboptimal temperature of 25 °C. Excess carbohydrate
synthesized during the day was only partially utilized for night protein synthesis. 相似文献
70.
Photosynthetic activity and growth physiology of Spirulina platensis (Nordstedt) Geitler cultures maintained at ultrahigh cell densities (i.e. above 100 mg chlorophyll-L?1) in a newly designed photobioreactor were investigated. Nitrogen (NaNO3) in standard Zarouk medium was characterized as a major nutrient-limiting factor in such cultures. The effect of ultrahigh cell density on photoinhibition of photosynthesis, as reflected by chlorophyll fluorescence and photosynthetic oxygen evolution, was studied: elevating the population density may arrest photoinhibition induced by high photon flux density, as well as low temperature. The relationship between incident irradiance and oxygen production rate was linear in situ for cultures at the optimal cell density, indicating that light limitation rather than light saturation or photoinhibition is the dominant condition outdoors in cultures of ultrahigh cell densities. In contrast with other reports, the extent of biomass loss at night due mainly to dark respiration was found to be relatively small when cell density was optimal, exerting only a minor effect on overall net productivity. Measurements of oxygen consumption at night revealed low rates of respiration, which may be explained by the low value of the volumetric mass transfer coefficient (KLa) of oxygen. Hence, reduced oxygen tension may play a role in preventing full expression of the respiratory potential in ultrahigh cell density cultures in which photoadaptive strategy may explain cell composition. Ultrahigh cell densities optimized with respect to the intensity of the light source, the length of the light path, and the extent of stirring represent the key for obtaining high output rates of cell mass and some natural products. 相似文献