Browsing by Author "Tsai, Ming-Ta"

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Characterization of the thermal-tolerant mutants of Chlorella sp with high growth rate and application in outdoor photobioreactor cultivation
(2010-04-01)
Ong, Seow-Chin
;
Kao, Chien-Ya
;
Chiu, Sheng-Yi
;
Tsai, Ming-Ta
;
Lin, Chih-Sheng
In this study, two thermal-tolerant mutants of Chlorella sp. MT-7 and MT-15, were isolated. In indoor cultivation, specific growth rate (mu, d(-1)) of the mutants were 1.4 to 1.8-fold at 25 degrees C and 3.3 to 6.7-fold at 40 C higher than those of wild type. The carbon dioxide fixation rate of both microalgal mutants was also significantly higher than that of wild type. In outdoor closed cultivation, where the temperature of culture broth was 41 +/- 1 degrees C, the mu of mutant strain MT-15 was 0.238 d(-1) during an 8-day cultivation. Whereas, the growth of wild type was inhibited in the outdoor cultivation. Our results show that the isolated microalgal strains are adaptable to be applied in outdoor cultivation in subtropical zones. (C) 2009 Elsevier Ltd. All rights reserved.
High performance 380-nm ultraviolet light-emitting-diodes with 3% efficiency droop by using free-standing GaN substrate manufacturing from GaAs substrate
(2014-07-07)
Shieh, Chen-Yu
;
Tsai, Ming-Ta
;
Li, Zhen-Yu
;
Kuo, Hao-Chung
;
Chang, Jeng-Yang
We investigated the influence of free-standing GaN (FS-GaN) substrates on the performance of ultraviolet light-emitting-diodes (UV-LEDs) grown on top by atmospheric pressure metal-organic chemical vapor deposition. High-resolution double-crystal x-ray diffraction (HRDCXD) analysis demonstrated high-order satellite peaks and clear fringes between them for UV-LEDs grown on the FS-GaN substrate, from which the interface roughness was estimated. In addition, the full width at half maximum of the HRDCXD rocking curve in the (0002) and the (1012) reflections were reduced to below 90 arc sec. The Raman results indicated that the GaN-based epilayer of strain free was grown. Additionally, the effect of the FS-GaN substrate on the crystal quality of the UV-LEDs was examined in detail by transmission electron microscopy (TEM). The TEM characterizations revealed no defects and V-pits were found in the scanned area. Based on the results mentioned above, the light output power of UV-LEDs on the FS-GaN substrate can be enhanced drastically by 80% and 90% at 20 and 100 mA, respectively. Furthermore, an ultralow efficiency degradation of about 3% can be obtained for the UV-LEDs on the FS-GaN substrate at a high injection current. The use of an FS-GaN substrate is suggested to be effective for improving the emission efficiency and droop of UV-LEDs grown thereon.
High-efficiency and low assembly-dependent chip-scale package for white light-emitting diodes
(2015-04-21)
Huang, Che-Hsuan
;
Chen, Kuo-Ju
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Tsai, Ming-Ta
;
Shih, Min-Hsiung
;
Sun, Chia-Wei
This article presents a chip-scale package (CSP) with conformal and uniform structures for white light-emitting diodes used in lighting and backlight unit (BLU) applications. The CSP structures produce higher light extraction efficiency and lower assembly-dependent packaging compared with conventional surface-mounted devices (SMDs). Simulation results show that compared with SMDs, the luminous efficiency of CSP structures is 8.81% higher in lighting applications and 9.43% higher in BLU applications. This is likely due to light loss in the light bowl of the SMDs. Moreover, CSPs with a conformal phosphor structure exhibit low assembly dependence and redundancy, and rb-CSPs with a conformal structure are a more effective light source in both lighting and BLU applications. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)
Lipid accumulation and CO(2) utilization of Nannochloropsis oculata in response to CO(2) aeration
(2009-01-01)
Chiu, Sheng-Yi
;
Kao, Chien-Ya
;
Tsai, Ming-Ta
;
Ong, Seow-Chin
;
Chen, Chiun-Hsun
In order to produce microalgal lipids that can be transformed to biodiesel fuel, effects of concentration of CO(2) aeration on the biomass production and lipid accumulation of Nannochloropsis oculata in a semicontinuous culture were investigated in this study. Lipid content of N. oculata cells at different growth phases was also explored. The results showed that the lipid accumulation from logarithmic phase to stationary phase of N. oculata NCTU-3 was significantly increased from 30.8% to 50.4%. In the microalgal cultures aerated with 2%, 5%, 10% and 15% CO(2), the maximal biomass and lipid productivity in the semicontinuous system were 0.480 and 0.142 g L(-1) d(-1) with 2% CO(2) aeration, respectively. Even the N. oculata NCTU-3 cultured in the semicontinuous system aerated with 15% CO(2), the biomass and lipid productivity could reach to 0.372 and 0.084 g L(-1) d(-1), respectively. In the comparison of productive efficiencies, the semicontinuous system was operated with two culture approaches over 12 d. The biomass and lipid productivity of N. oculata NCTU-3 were 0.497 and 0.151 g L(-1) d(-1) in one-day replacement (half broth was replaced each day), and were 0.296 and 0.121 g L(-1) d(-1) in three-day replacement (three fifth broth was replaced every 3 d), respectively. To optimize the condition for long-term biomass and lipid yield from N. oculata NCTU-3, this microalga was suggested to grow in the semicontinuous system aerated with 2% CO(2) and operated by one-day replacement. (C) 2008 Elsevier Ltd. All rights reserved.
The air-lift photobioreactors with flow patterning for high-density cultures of microalgae and carbon dioxide removal
(2009-06-01)
Chiu, Sheng-Yi
;
Tsai, Ming-Ta
;
Kao, Chien-Ya
;
Ong, Seow-Chin
;
Lin, Chih-Sheng
A photobioreactor containing microalgae is a highly efficient system for converting carbon dioxide (CO(2)) into biomass. Using a microalgal photobioreactor as a CO(2) mitigation system is a practical approach to the problem Of CO(2) emission from waste gas. In this study, a marine microalga, Chlorella sp. NCTU-2, was applied to assess biomass production and CO(2) removal. Three types of photobioreactors were designed and used: (i) without inner column (i.e. a bubble column), (ii) with a centric-tube column and (iii) with a porous centric-tube column. The specific growth rates (it) of the batch cultures in the bubble column, the centric-tube and the porous centric-tube photobioreactor were 0.180, 0.226 and 0.252 day(-1), respectively. The porous centric-tube photobioreactor, operated in semicontinuous culture mode with 10% CO(2) aeration, was evaluated. The results show that the maximum biomass productivity was 0.61 g/L when one fourth of the culture broth was recovered every 2 days. The CO(2) removal efficiency was also determined by measuring the influent and effluent loads at different aeration rates and cell densities of Chlorella sp. NCTU-2. The results show that the CO(2), removal efficiency was related to biomass concentration and aeration rate. The maximum CO(2) removal efficiency of the Chlorella sp. NCTU-2 culture was 63% when the biomass was maintained at 5.15 g/L concentration and 0.125 vvm aeration (volume gas per volume broth per min; 10% CO(2) in the aeration gas) in the porous centric-tube photobioreactor.
The effect of free-standing GaN substrate on carrier localization in ultraviolet InGaN light-emitting diodes
(2014-12-13)
Tsai, Ming-Ta
;
Chu, Chung-Ming
;
Huang, Che-Hsuan
;
Wu, Yin-Hao
;
Chiu, Ching-Hsueh
In this study, we have grown 380-nm ultraviolet light-emitting diodes (UV-LEDs) based on InGaN/AlInGaN multiple quantum well (MQW) structures on free-standing GaN (FS-GaN) substrate by atmospheric pressure metal-organic chemical vapor deposition (AP-MOCVD), and investigated the relationship between carrier localization degree and FS-GaN. The micro-Raman shift peak mapping image shows low standard deviation (STD), indicating that the UV-LED epi-wafer of low curvature and MQWs of weak quantum-confined Stark effect (QCSE) were grown. High-resolution X-ray diffraction (HRXRD) analyses demonstrated high-order satellite peaks and clear fringes between them for the UV-LEDs grown on the FS-GaN substrate, from which the interface roughness (IRN) was estimated. The temperature-dependent photoluminescence (PL) measurement confirmed that the UV-LEDs grown on the FS-GaN substrate exhibited better carrier confinement. Besides, the high-resolution transmission electron microscopy (HRTEM) and energy-dispersive spectrometer (EDS) mapping images verified that the UV-LEDs on FS-GaN have fairly uniform distribution of indium and more ordered InGaN/AlInGaN MQW structure. Clearly, the FS-GaN can not only improve the light output power but also reduce the efficiency droop phenomenon at high injection current. Based on the results mentioned above, the FS-GaN can offer UV-LEDs based on InGaN/AlInGaN MQW structures with benefits, such as high crystal quality and small carrier localization degree, compared with the UV-LEDs on sapphire.