• KOREAN JOURNAL OF CROP SCIENCE
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• v.8 no.1
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• pp.83-89
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• 1970

Investigation was made to know the effects of the time of transplanting and harvesting, fertilizer, soil texture and period of storage on tuber yield and starch content of sweet potato. Variety used was Shin-mi, one or the leading varieties in Korea. Late transplanting, early harvesting, and balanced application of nitrogen, phosphorous and potassium, and loam and coarse sandy loam were more effective in increasing starch content than early planting, late harvesting, and more application of potassium and none application of phosphorous, and light clay respectively. Long storage period resulted in reducing starch content.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2018.10a
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• pp.35-38
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• 2018

This paper describes a low-power MPPT interface for DC-type energy harvesting sources. The proposed circuit consists of an MPPT controller, a bias generator, and a voltage detector. The MPPT controller consists of an MPG (MPPT Pulse Generator) with a schmitt trigger, a logic gate operating according to energy type (light, heat), and a sample/hold circuit. The bias generator is designed by employing a beta multiplier structure, and the voltage detector is implemented using a bulk-driven comparator and a two-stage buffer. The proposed circuit is designed with $0.35{\mu}m$ CMOS process. The simulation results show that the designed circuit consumes less than 100nA of current at an input voltage of less than 3V and the maximum power efficiency is 99.7%. The chip area of the designed circuit is $1151{\mu}m{\times}940{\mu}m$.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2014.10a
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• pp.278-281
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• 2014

This paper presents the performance comparison of three types of full-wave rectifiers for vibration energy harvesting. The first rectifier is consisted of two active diodes and two MOSFETs, and the comparators of the active diodes are powered from the output of the rectifier. The second one is a 2-stage full-wave rectifier. It comprises the basic rectifier consisted of four MOSFETs and an active diode. The comparator is also powered from the output of the rectifier. The third one is an input powered rectifier. It has the same structure as the second rectifier, but the comparator is powered from the input of the rectifier. These rectifiers have been designed using a 0.35um CMOS process and their performances have been compared through simulations. In terms of efficiency, the first rectifier shows the best performance at heavy loads, but the second one is suitable at light loads. When the power consumption during absence of vibration is more important than efficiency, the input-powered rectifier is proper.

• Journal of Sensor Science and Technology
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• v.22 no.5
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• pp.364-368
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• 2013

Vibrational energy harvester based on piezoelectricity has been expected to be the dominant energy harvesting technology due to the advantages of high conversion efficiency, light weight and small size, night operation, etc. Its commercialization is just around the corner but the integration with power management electronics should be solved in advance. In this paper, therefore, fully-integrated design environment for piezoelectric energy harvesting systems is presented to assist co-design with the power management electronics. The proposed design environment is capable of analyzing the energy harvester including the package-induced damping effects and simulating the device and its power management electronics simultaneously. When the developed design environment was applied to the fabricated device, the simulated resonant frequency matched well with the experimental result with a difference of 2.97% only. Also, the complex transient response was completed in short simulation time of 3,001 seconds including the displacement distribution over the device geometry. Furthermore, a full-bridge power management circuit was modeled and simulated with the energy harvester simultaneously. Therefore the proposed, fully-integrated design environment is accurate and fast enough for the contribution on successful commercialization of piezoelectric energy harvester.

• Transactions on Electrical and Electronic Materials
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• v.18 no.4
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• pp.190-194
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• 2017

Present-day solar panels incorporate inverters as their core components. Switching devices driven by specialized power controllers are operated in a transformerless inverter topology. However, some challenges associated with this configuration include the absence of isolation, causing leakage currents to flow through various components toward ground. This inevitably causes power losses, often being also the primary reason for the power inverters' analog equipment failure. In this paper, various aspects of the leakage currents are studied using different circuit analysis methods. The primary objective is to convert the leakage current energy into a usable DC voltage source. The research is focused on harvesting the leakage currents for producing circa 1.1 V, derived from recently developed rectifier circuits, and driving a $200{\Omega}$ load with a power in the milliwatt range. Even though the output voltage level is low, the harvested power could be used for charging small batteries or capacitors, even driving light loads.

• Journal of Korean Society of Water and Wastewater
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• v.27 no.5
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• pp.621-629
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• 2013

Since algae had been issued an environmental problem, water blooms, deepened due to increase of retention water basin in Korea as well as a biomass resource for producing biofuel, this study conducted a series of experiments for Spirulina platensis using the flotation process with micro-bubble. To elevate utilization of collected-algae, this study focused on omitting or minimizing coagulant's doses as changing a cultivation period and condition affected on physical property change of algae. Two coagulants, PAC and Chitosan, were used to test the collecting rate of algae and the result found no difference between two rates. For flotation experiments without adding the coagulant, dried algae weight (passing 14 days after cultivation for 20 days) detected high separation efficiency 98.2 % and it (passing 7 days after long-term cultivation for 28 days) presented good separation efficiency 91.9 %. Chlorophyll's separation efficiency showed a similar tendency with the case of the dried algae weight. In endogeny conditions, a light source and a carbon source were not considerably affected on the flotation separation efficiency. Thus, this study confirms that algae biomass may be collected without the coagulant during the endogeny condition period after enough cultivation time, 3 weeks.

• Journal of Sensor Science and Technology
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• v.30 no.6
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• pp.364-368
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• 2021

We developed a highly efficient organic photovoltaic (OPV) cell with a poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b']dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl)]:[6,6]-phenyl-C71-butyric acid methyl ester active layer for harvesting lower-intensity indoor light energy to power various self-powered sensor systems that require power in the microwatt range. In order to achieve higher power conversion efficiency (PCE), we first optimized the thickness of the active layer of the OPV cell through optical simulations. Next, we fabricated an OPV cell with optimized active layer thickness. The device exhibited a PCE of 12.23%, open circuit voltage of 0.66 V, short-circuit current density of 97.7 ㎂/cm², and fill factor of 60.53%. Furthermore, the device showed a maximum power density of 45 ㎼/cm², which is suitable for powering a low-power (microwatt range) sensor system.

• Journal of Photoscience
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• v.9 no.2
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• pp.350-352
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• 2002

We examined the bacteriochlorophyill/bacteriopheophytin ratios in several species of purple bacteria containing only LHI. The pigment ratios depended greatly on species. Further, Rhodospirillum rubrum showed wide variation when grown under different light intensity, and Rhodobium marinum showed significant variation from culture to culture even under the same light conditions. The protein ratios of a/RC and $\beta$/RC estimated by SDS-PAGE of chromatophores of Rsp. rubrum and Rbi. marinum exhibited the ratio of $\beta$/$\alpha$ > 1. These findings gave us the novel idea that there are two types of LHl; one is a C-shaped open antenna composed by $\alpha$$\beta$ units surrounding a RC, and another is a small closed ring antenna composed by $\alpha$$\beta$ units located peripherally in a variable ratio to the core complex like LH2.

• Proceedings of the Ginseng society Conference
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• 1980.09a
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• pp.39-47
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• 1980

The harvesting and export of Canadian ginseng from the cool, shady hardwood forests of southern Canada can be traced to 1796. Because of its high dollar value and diminishing woodland supplies it was decided in 1896 that it should be cultivated under wood lath screens. Present day economics dictate changes in production techniques to allow for a decreasing supply of expensive labour. Traditional wooden lath screens have a surface area of wood of 70 per cent and permit light penetration of only about 18 per cent. Experimental woven black polypropylene shade has an estimated surface area of 72 per cent and permits light pentration of about 28 per cent. While differences in air and leaf temperatures under the two shade structures can be measured it is doubtful if these are great enough to cause differences in plant growth under the two structures. Shade grown ginseng had a low fresh and dry weight and total chlorophyll content (ratio of a to b was 3 to 1) comparable to other shade species. There was no differences in fresh and dry weight and chlorophyll content of leaves from plants grown under the two shade structures. Maximum net photosynthesis of leaves was 0.175 g $CO_2\;m^{-2}\;hr^{-1}$ and light saturation level was about $200{\mu}E\;m^{-2}\;s^{-1},$ or about 10 per cent of full sunlight.

• Current Photovoltaic Research
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• v.11 no.3
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• pp.96-102
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• 2023

Sn-Pb narrow-bandgap perovskite solar cells, which is a light-harvesting layer thicker than 1.3 micrometers, is needed to enhance the low photocurrent. The fabrication of such a thick film through solution processing is a key challenge. Here, we studied and characterized the film by using a precursor solution of increased concentration, comparing it with the universally used 1-micrometer Sn-Pb perovskite film. The increase in molar concentration clearly induced thickness enhancement, but we observed that it also created numerous voids at the interface with bottom charge transporting layer. We hypothesized that these voids might hinder the increase in photocurrent associated with thickness enhancement. By introducing methylammonium chloride (MACl), we successfully fabricated Sn-Pb perovskite film with a thickness of 1.3 micrometer and no voids. Void-controlled Sn-Pb perovskite solar cells not only demonstrated superior short-circuit current density compared to those with voids but also operated smoothly under light exposure.