• Journal of the Microelectronics and Packaging Society
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• v.23 no.4
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• pp.113-117
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• 2016

Recently, hydrogen is regarded as important energy in the future, because it is clean and renewable. The photoelectrochemical (PEC) system, which produce hydrogen using water splitting by solar energy, is one of the most promising energy systems because it has abundant energy sources and good theoretical efficiency. GaN has recently been regarded as suitable photoelectrode that could be used to split water to generate hydrogen without extra bias because its band edge position include water redox potential ($V_{redox}=1.23$ vs. SHE). GaN also shows considerable corrosion resistance in aqueous solutions and it is possible to control its properties, such as structure, band gap, and catalyst characteristics, in order to improve solar energy conversion efficiency. But, even if the band edge position of GaN make PEC reaction facilitate without bias, the overpotential of oxygen evolution reaction could reduce the efficiency of system. One of the ways to decrease overpotential is introduction of co-catalyst on photoelectrode. In this paper, we will investigate the effect of manganese dioxide ($MnO_2$) as a co-catalyst. $MnO_2$ particles were dispersed on GaN photoelectrode by spincoater and analyzed properties of the PEC system using potentiostat (PARSTAT4000). After coating $MnO_2$, the flat-band potential ($V_{fb}$) and the onset voltage ($V_{onset}$) were moved negatively by 0.195 V and 0.116 V, respectively. The photocurrent density increased on $MnO_2$ coated sample and time dependence was also improved. These results showed $MnO_2$ has an effect as a co-catalyst and it would enhance the efficiency of overall PEC system.

• KOMUNHWA
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• no.70
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• pp.133-161
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• 2007

It is judged that celadons with '○' pattern and '⊙' pattern have the indication of manufacturer by engraving mark at the internal center of the bottom. These celadons were produced at No.8.23.27 kiln sites located at Sadang-ri(사당리), Daegu-myon(대구면), Gangjin-gun(강진군), Jeollanamdo(전라남도), Korea and '⊙’ patterned celadon porcelain was found only at No. 23 and 27 kiln sites, so it is assumed that its production sites were limited. Kinds of celadons included bowl, dish, cup, bottle, case and vessel for emptied wine and there were a lot of dishes with a variety of patterns. These celadons were engraved by molded design technique using the same ceramic design as the pattern of celadons in the period of their prosperity and it was appropriate method to produce celadons of a good quality with production method to keep decorative design like pattern or size uniformly. It was also found that inlay method was not universalized in this period and similar celadons were produced with molded design in large quantities. These celadons had partially fire clay temper, but most of them were burnt by supporting the inner bottom of U-type base with quartzite after whole glazing. It was known through relics excavated at Seokreung(석릉) royal tomb of King Heejong(희종) at Ganghwa(강화) and Hyeeumwon(혜음원) temple site at Paju(파주) and military house at Wakamiyaoji(약궁대로) avenue Kamakura(겸창)-city, Japan(일본) that these celadons were manufactured at two quarters of the 13th century centering around 1230s. Therefore, these celadons will be significant materials to fill the gap of the celadons in the 13th century resulted from the record chronologically that green celadons were manufactured in the 12th century. And this period was invaded by Mongolia(몽고), but central control was achieved and green celadons were continuously produced. It was also considered that these celadons were excavated at Gabgot-ri(갑곶리) and Gwanchung-ri(관청리), Ganghwa(강화), Hyeeumwon temple, Paju which played the role of temporary palace, Bu1guksa(불국사) temple at Gyeongju(경주), Silsangsa(실상사) temple at Namwon(남원) and relics of Jangheung(장흥) adjacent to Daeguso(대구소) and these were produced for high class.

• Korean Journal of Agricultural and Forest Meteorology
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• v.12 no.1
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• pp.36-44
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• 2010

In order to rehabilitate forest sites damaged by wildfire via natural or artificial restoration, it is important to determine right tree species, which can acclimate to biogeoclimatic environment at the sites. The objectives of this study were to develop site index equation of different tree species for estimating forest productivity and to provide information on species selection for post-wildfire restoration. Site index equation was developed based on environmental information from wildfire damaged areas in Gangneung, Goseong, Donghae, and Samcheok, where were located in east coastal areas of South Korea. Despite the small numbers (4~5) of environmental variables used for the development of the site index equations, statistical analysis (e.g. mean difference, standard deviation of difference, and standard error of difference) showed relatively low bias and variation, suggesting that those equations can provide relatively high capability of estimation and practical applicability with high effectiveness. The small numbers of the variables enabled the model to be applied in a wide range of usages including determination of appropriate tree species for post-wildfire restoration. The estimation of forest site productivity showed the possibility of large distribution in east coastal region as the best site for Korean ash (Fraxinus rhynchophylla) and original oak (Quercus variabilis) that can be used for firebreak in the region. These results imply that damages by forest fire can be reduced significantly by replacing existing pure coniferous forests in the area with ones dominated by broad-leaved deciduous stands, which can play an important role as fire break and/or prevent a transition from surface fire to crown fire.