• Biotechnology and Bioprocess Engineering:BBE
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• 제6권3호
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• pp.189-193
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• 2001

Critical cell density (CCD), the maximum cell concentration without mutual shading in algal cultures, can be used as a new operating parameter for high-density algal cultures and for the application of the flashing light effect on illuminated algal cultures. CCD is a function of average cell volume and light illumination area. The CCD is thus proposed as an index of estimation of mutual shading in algal cultures. Where cell densities are below the CCD, all the cells in photobioreactors can undergo photosysnthesis at their maximum rate. At cell densities over CCD, mutual shading will occur and some cells in the illumination chamber cannot grow photoautotrophically. When the cell concentration is higher than the CCD, specific oxygen production rates under flashing light were higher than those under continuous light. The CCD was found to be a useful engineering parameter for the application of flashing light, particularly in high-density algal cultures.

• Biotechnology and Bioprocess Engineering:BBE
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• 제5권3호
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• pp.186-190
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• 2000

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 (5Hz-37 kHz) were compared with those under equivalent continuous light in photobioreactors. A positive flashing light effect was observed with flashing frequencies over 1kHz. The oxygen production rate under conditions of flashing light was slightly higher than that under continuius ligth. The cells under the hight, particularly at higher cell concentrations. When 37kHz flashing light was applied to an LED-based photobioreactor, the 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.

• 한국생물공학회:학술대회논문집
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• 한국생물공학회 2000년도 춘계학술발표대회
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• pp.189-192
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• 2000

광합성 홍색세균의 light harvesting complex II (LHC II)발현 유전자가 제거된 돌연변이종을 halogen 램프 하에서 거리에 따라 광도를 달리하며 배양하여 wild type과 생산성을 비교한 결과 낮은 광도(34 ${\mu}E/m^2/s$)에서는 wild type가 높은 광도 (376, 118 ${\mu}E/m^2/s$)에서는 mutant가 높은 세포농도를 나타내었다. 특히 118 ${\mu}E/m^2/s$에서 LHC $II^-$ mutant가 56% 높은 세포생산량을 보였다. 이는 세포내 pigment양의 감소로 mutual shading effect가 감소하였기 때문으로 판단되었다.

• Biotechnology and Bioprocess Engineering:BBE
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• 제4권1호
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• pp.78-81
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• 1999

Light penetration depth in high-density Chlorella cultures can be successfully estimated by Beer-Lambert's law. The efficiency of light energy absorption algal cultures was so high that algal cells near the illuminating surface shade the cells deep in the culture. To exploit the potential of high-density algal cultures, this mutual shading should be eliminated or minimized. However, providing more light energy will not ease the situation and it will simply drop the overall light utilization efficiency.

• Journal of Microbiology and Biotechnology
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• 제10권6호
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• pp.817-822
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• 2000

A proper flashing light is expected to enhance microalgal biomass productivity and photosynthetic efficiency. The effect of flashing light on high-density Chlorella kessleri (UTEX 398) cultures was studied using light-emitting diodes. A frequency modulator was designed to flash LEDs, and the device successfully provided wide range of frequencies and various duty cycles of flashing. A relatively high frequencies of 10, 20 and 50 kHz were used in this study. These frequencies have very short flashing time ($2-50{\mu}s$), which corresponded to the time constant of the light reaction of photosynthesis. The specific oxygen production rates of photosynthesis under flashing light were compared with those under an equivalent continuous light in specially designed illumination cuvette. The specific oxygen production rates under flashing light were 5-25% higher than those under the continuous light. A range of cell concentration was discovered, where the benefit of flashing light was maximized. The photosynthetic efficiency was also higher under flashing light with frequencies of over 1 kHz, which was a clear indication of flashing light effect and the degree of mutual shading could by overcome by flashing lights, particularly at high-density algal cultures.

• Journal of Microbiology and Biotechnology
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• 제14권3호
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• pp.442-449
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• 2004

Improving the light utilization efficiency of photosynthetic cells in photobioreactors (PBRs) is a major topic in algal biotechnology. Accordingly, in the current study we investigated the effect and suitability of photosynthetic pigment reduction for improving light utilization efficiency. The light-harvesting complex II (LH-II) genes of Rhodobacter sphaeroides were removed to construct a mutant strain with less pigment content. The mutant strain exhibited a slower growth rate than the wild-type under a low light intensity, while the mutant grew faster under a high light intensity. In addition, the specific absorption coefficient was lower in the mutant due to its reduced pigment content, thus it seemed that light penetrated deeper into its culture broth. However, the distance (light penetration depth) from the surface of the PBR to the compensation point did not increase, due to an increase in the compensation irradiance of the mutant strain. Experimental data showed that a reduced photosynthetic pigment content, which lessened the photoinhibition under high-intensity light, helped the volumetric productivity of photosynthetic microorganisms.

• 한국토양비료학회지
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• 제1권1호
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• pp.125-128
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• 1968

엽(葉)의 차광(遮光)을 피(避)하고, 근부(根腐)를 피(避)하는 일방(一方) 양분(養分)을 적정(適正)히 공급(供給)할 수 있는 수경재배(水耕栽培)의 조건하(條件下)에서 출수이후(出穗以後)의 엽(葉)의 잔존수(殘存數)가 후기생육(後期生育) 및 탄수화물(炭水化物)의 전류(轉流)에 미치는 영향을 검토(檢討)하였으며 그 결과(結果)를 요약(要約)하면 다음과 같다. 1. 출수기(出穗期)에 전엽전엽(全葉剪葉), 지엽(止葉) 1 매잔류(枚殘留), 토위엽(土位葉) 2 매잔류(枚殘留) 및 토위엽(土位葉) 3 매잔류(枚殘留) 등 처리(處理)에 있어 등숙비율(登熟比率)은 각각(各各) 38.8, 74.7, 83.9 및 87.0%이였으며 정조천립중(精租千粒重)은 전엽전엽(全葉剪葉)이 21.3g로 가장 낮고 기타처리(基他處理)는 28.7g로 차이(差異)가 없었다. 2. 전엽수(剪葉數)의 증가(增加)에 따라 출수기(出穗期)에 축적(蓄積)된 탄수화물(炭水化物)의 전류(轉流)는 증가(增加)되며 간기중(稈基重)은 감소(減少)된다. 3. 출수기(出穗期) 이후(以後) 지엽(止葉)과 차엽(次葉)2매(枚)가 건재(健在)하면 등숙비율(登熟比率) 80% 정도(程度)로 유지(維持)시킬 수 있으리라 추정(推定)된다.