• 한국기계가공학회지
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• 제16권1호
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• pp.70-76
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• 2017

The pollution problem of fossil energy sources has caused the development of green energy harvesting systems. Piezoelectric energy harvesting technology has been developed under those external environmental factors. A piezoelectric energy harvester can be defined as a device which transforms mechanical vibration or impact energy into electrical energy. Most researches have focused on bender structures. However, these have a limitation on energy efficiency because of the small effective electromechanical coupling factor, around 10%. Therefore, we should look for a new design for energy harvesting. A cymbal energy harvester can be a good candidate for the high-power energy harvester because it uses a high amplification mechanism using endcaps while keeping a higher electromechanical coupling factor. In this research, we focused on energy efficiency improvements of the cymbal energy harvester by changing the polarization direction, because the electromechanical coupling factor of the k33 mode and the k15 mode is larger than that of the k31 mode. Theoretically, we checked the cymbal harvester with radial polarization and it could obtain 6 times larger energy than that with the k31 direction polarization. Furthermore, we verified the theoretical expectation using the finite element method program. Consequently, we could expect a more efficient cymbal harvester with the radial polarization by comparing two polarization directions.

• 한국의류학회지
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• 제32권8호
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• pp.1286-1298
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• 2008

This study was attempted to examine the indigo dyeing technique in the latter Joseon Dynasty, and to find diachronic specifics in the indigo dyeing method from 17C to 19C. The results are as follows: First, There were 2 kinds of indigo species-Yoram(Polygonum tinctorium Lour.) and Sungram(Isatis tinctoria L.)-in the latter Joseon Dynasty. Dangram was preferred in particular among Yoram species because of its high dyeing efficiency. Sungram was mainly used for making Jeon(indigo sediment). Second, Yoram cultivation took the following order: Sowing in April${\rightarrow}$planting out in June${\rightarrow}$harvesting leaves in August${\rightarrow}$collecting seeds in September. Sungram had more harvesting times and wider harvesting period than Yoram. Third, all indigo dyeing methods were grouped into two categories, one was temporary dyeing method, the other was permanent dyeing method. Mixture dyeing of the boiled and the raw, raw leaves dyeing, and fermentation dyeing belonged to the temporary dyeing. Jeon dyeing and Gaeogi dyeing belonged to the permanent dyeing. Finally, diachronic specifics from 17C to 19C were as follows: Decline in the mixture dyeing of the boiled and the raw, development in the raw leaves dyeing, continuance of the fermentation dyeing, and naturalization of Jeon dyeing technique.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2018년도 학술발표회
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• pp.485-485
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• 2018

Rainwater harvesting system (RWH) can provide a relief for the household and farmers especially in areas with intense water scarcity during the long lull of rainy season. However, much attention has not been given to this alternative water source in Nigeria. This paper estimates the per capita water demand for 1,950 inhabitants and rainwater potential in Ojonbodu Estate, Oyo State, Nigeria, using data from detailed questionnaires, water consumption calculator software, and 20-year rainfall data. The potential rainwater estimation was based on amount of precipitation, size of catchment and runoff coefficient. Consequently, using estimated values of $39420m^3$ and $6.5114{\times}10^7m^3$ for per capita consumption and potential rainwater respectively, the rainwater harvesting system was designed for rainwater collection, and storage. The harvested rainwater was $450, 000m^3$ with collection efficiency of 69.16 %, which exceeded the household water consumption requirement. Thus, the harvested rainwater was able to meet the estimated water demand of the Ojonbodu Estate households during the period of water scarcity.

• Elastomers and Composites
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• 제58권1호
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• pp.11-16
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• 2023

Electronic skin (e-skin), devices that are mounted on or attached to human skin, have advanced in recent times. Yet, the development of a power supply for e-skin remains a challenge. A stretchable thermoelectric generator is a promising power supply for the e-skin patches. It is a safe and semi-permanent energy harvesting device that uses body heat for generating power. Carbon nanotube (CNT) clays are used in energy-harvesting e-skin patches. In this study, we report improved thermoelectric performance of CNT clays by using chemical doping and physical blending of thermoelectric enhancers. The n-type and p-type thermoelectric enhancers increase electrical conductivity, leading to increased power factors of the thermoelectric CNT clays. The blend of CNT clays and enhancers is intrinsically stretchable up to 50% while maintaining its thermoelectric property.

• Smart Structures and Systems
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• 제32권6호
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• pp.383-391
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• 2023

Energy harvesting in trams may become a prevalent source of passive energy generation due to the high density of vibrational energy, and this may help power structural health monitoring systems for the trams. This paper presents a broadband vibrational energy harvesting device design that utilizes a varied frequency from a tram vehicle using a 2 DOF vibrational system combined with electromagnetic energy conversion. This paper will demonstrate stepwise optimization processes to determine mechanical parameters for frequency tuning to adjust to the trams' operational conditions, and electromagnetic parameters for the whole system design to maximize power output. The initial optimization will determine 5 important design parameters in a 2 DOF vibrational system, namely the masses (m₁, m₂ (and spring constants (k₁, k₂, k₃). The second step will use these parameters as initial guesses for the second optimization which will maintain the ratios of these parameters and present electrical parameters to maximize the power output from this system. The obtained values indicated a successful demonstration of design optimization as the average power generated increased from 1.475 mW to 17.44 mW (around 12 times).

• 한국작물학회지
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• 제61권3호
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• pp.215-221
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• 2016

바이오에너지용 억새의 트랙터 부착 수확기 등 중장비 동원 늦은 수확에 따른 부작용을 구명하기 위해 전년도 생육 줄기의 늦은 수확 시기별 당년 생육특성과 마른줄기 수량을 구명한 결과는 다음과 같다. 1. 시험포장의 지하 10 cm 토양 경도는 맹아시, 맹아기, 맹아종 수확에서 각각 650, 793, 735 kPa로 일정한 경향이 없었으나 지하 20 cm에서는 각각 741, 915, 1,045 kPa로 늦게 수확할수록 단단해 졌다. 2. 이질 3배체에 비해 거대1호가 생육시기별 경수의 변이폭이 컸다. 거대 1호는 수확 시기별로 가장 늦은 맹아종에서 생육중기(5월 22일)에 169개/$m^2$로 가장 많았으나 생육 최성기(7월 22일)에 70개/$m^2$로 급격히 감소하였다. 3. 수확시기가 늦을수록 당년 생성된 지하경이 전년의 것에 비해 가늘어져 맹아종 수확에서 전년, 당년생성 지하경태가 거대 1호는 각각 9.2 mm, 6.7 mm 이질 3배체는 각각 8.5 mm, 8.0 mm였다. 4. 수확시기가 늦을수록 경장이 작아지고 아울러 줄기수량도 감소하였다. 거대1호와 이질3배체의 경장은 맹아시 수확에서 각각 308 cm, 374 cm였으나 맹아종 수확에서는 각각 268 cm, 341 cm로 작아졌다. 줄기 수량 또한 맹아시 수확에서는 각각 1,440 kg/10a, 1,777 kg/10a였으나 맹아종 수확에서는 각각 847 kg/10a, 963 kg/10a로 크게 감소하였다. 5. 출수율은 거대 1호의 경우 맹아시 수확에서 3.9%로 극히 낮았고, 맹아기 및 맹아종 수확에서는 거의 출수되지 않았다. 이질3배체는 맹아시 수확에서 49.6%였고, 맹아기, 맹아종에서도 각각 40.6%, 21.8% 수준을 유지하였다.

• 한국작물학회지
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• 제45권2호
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• pp.79-82
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• 2000

Tuberous root of yacon (Polymnia sonchifolia Poeppig ＆ Endlicher) has not starch, and its brix degree changes during the curing. Therefore its chemical composition changes were investigated according to different curing conditions. Tuberous root contained 87.1% moisture at harvesting, that was decreased to 84.1-86.0% at 30 days after curing in different curing conditions. Brix degree was increased from 5.7 to 14.2-15.8% at 30 days after curing in comparison to at harvesting. Free sugars were detected from tuberous root in yacon by HPLC; that were fructose, glucose and sucrose. Fructose contents were increased from 0.09 to 1.04-1.79% during 30 days in five curing conditions. Glucose contents were shown to increase from 0.03 to 1.04-1.37 %. Sucrose contents were shown to increase from 0.04 to 0.13-0.43%. Tuberous root contained fructose, glucose and sucrose in order of amount that were highest in single-polyethylene film covered green house. Sucrose was little as comparison with fructose and glucose. Fructose and glucose were increased to 16.7 and 40.7 times, respectively, but sucrose was increased little about 6.8 times.

• 한국전기전자재료학회논문지
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• 제24권5호
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• pp.416-421
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• 2011

Nowadays, the increasing demands upon mobile devices such as wireless sensor networks and the recent advent of low power electrical devices such as MEMS make such renewable power sources attractive. A vibration-driven MEMS lead zirconate titanate $Pb(Zr,Ti)O_3$ (PZT) cantilever device is developed for energy harvesting application. This paper presents a piezoelectric based energy harvester which is suitable for power generating from conventional vibration and has in providing energy for low power electron ic devices. The PZT cantilever is used d33 mode to get the electrical power. The PZT cantilever based energy harvester with the dimension of 7 mm${\times}$3 mm${\times}$0.03 mm is fabricated using micromachining technologies. This PZT cantilever has the mechanical resonance frequency with a 900 Hz. With these conditions, we get experimentally the 37 uW output power from this device with the application of 1g acceleration using the 900 Hz vibration. From this study, we show the feasibility of one of energy harvesting candidates using PZT based structure. This PZT energy harvester could be used for various applications such a batteryless micro sensors and micro power generators.

• Safety and Health at Work
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• 제9권1호
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• pp.71-74
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• 2018

Background: Green tobacco sickness (GTS), an occupational disease in tobacco harvesters, is a form of acute nicotine intoxication by nicotine absorption through the skin from the wet green tobacco plant. We carried out a questionnaire survey and measured cotinine concentration, the metabolic product of nicotine, to determine the prevalence, incidence, and risk factors of GTS in Korean tobacco harvesters. Methods: We measured cotinine concentrations, and administered a questionnaire survey to tobacco harvesters in Cheongsong-gun, Gyeongsangbuk-do, Korea. We repeatedly measured urine cotinine concentration five times with a questionnaire survey. Results: Cotinine concentration at dawn was significantly higher than that at other times; it was significantly lower during the nonharvesting period than during the harvesting period. However, little change in cotinine concentration was detected in the daytime during the harvesting period. Study participants included 20 men and 20 women. The prevalence of GTS was 37.5% and was significantly higher in women than in men (55.0% vs. 20.0%, p < 0.01). GTS incidence according to number of workdays was 3.4 occurrences/100 person days. Conclusion: In this study, nicotine exposure and metabolism were experimentally determined from the time of cotinine exposure, and biological monitoring was performed in each season. In the future, this information may be valuable for medical decision-making in GTS prevention.

• 한국전기전자재료학회논문지
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• 제26권11호
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• pp.831-835
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• 2013

In this study, we fabricated a micro $Pb(Zr,Ti)O_3$ (PZT) film piezoelectric cantilever with a Si proof mass and dual beams through MEMS process. The size of the beam and the integrated Si proof mass were about $4,320{\mu}m{\times}290{\mu}m{\times}12{\mu}m$ and $1,380{\mu}m{\times}880{\mu}m{\times}450{\mu}m$ each. To reduce the air damping and have the larger displacement of dual beams was used for design. After mounting micro PZT film piezoelectric cantilever on shaker, we measured the resonance frequency and a output voltage while making resonant frequency changed. The resonant frequency and the highest average power of the cantilever device were 110.2 Hz and 0.36 ${\mu}W$ each, at 0.8 g acceleration and 23.7 $k{\Omega}$ load resistance, respectively.