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Optimal Energy Management of the Electric Excavator using Super Capacitor
Hyeon-Seop Yi,Suk Won Cha 한국정밀공학회 2021 International Journal of Precision Engineering and Vol.8 No.1
Recently, petrol engines have been removed and replaced with fuel cells, batteries, and super capacitors as alternative power sources, in vehicles and construction machinery. Electric vehicles driven by batteries have been the only mass-produced vehicle with an alternative power source, while fuel cell vehicles have been developed in which the fuel cell and the battery are hybridized. For excavators, research and development are being done in a similar direction. Some excavators are equipped with a super-capacitor, which regenerates the upper braking energy to increase the efficiency of the engine. This paper deals with the energy management of environmentally friendly electric excavators using super capacitors. The power distribution profile of the fuel cell, battery, and super capacitor was examined with the optimal control theory of the required power profile of an existing engine excavator. The optimal control theory is based on dynamic programming. It was confirmed that the fuel cell efficiency of an excavator with a super capacitor was-higher than the fuel cell efficiency of a fuel cell-battery electric excavator. The simulation method used in this and its conclusions provide basic research that will help to massproduce electric excavators in the future.
Hyeon-Beom Seo,Seung Seop Kim,Hyeon-Yong Lee,정경환 한국생물공학회 2009 Biotechnology and Bioprocess Engineering Vol.14 No.5
In this study, we utilized a unique strategy for fed-batch fermentation using ethanol-tolerant Saccharomyces cerevisae toachieve a high-level of ethanol production that could be practically applied on an industrial scale. During this study, theaeration rate was controlled at 0.0, 0.13, 0.33, and 0.8 vvm to determine the optimal aeration conditions for the productionof ethanol. Additionally, non-sterile glucose powder was fed during fed-batch ethanol fermentation and corn-steepliquor (CSL) in the medium was used as an organic N-source. When aeration was conducted, the ethanol productionand productivity were superior to that when aeration was not conducted. Specifically, the maximum ethanol productionreached approximately 160 g/L, when the fermentor was aerated at 0.13 vvm. These findings indicate that the use of amuch less expensive C-source may enable the fermentation process to be directed towards the improvement of overallethanol production and productivity in fermentors that are aerated at 0.13 vvm. Furthermore, if a repeated fed-batchprocess in which the withdrawal and fill is conducted prior to 36 h can be employed, aeration at a rate of 0.33 and/or 0.8vvm may improve the overall ethanol productivity
박현섭 ( Hyeon Seop Park ),송인만 ( In Man Song ) 한국회계학회 2005 會計學硏究 Vol.30 No.2
본 연구는 외환위기 이후 신뢰성 있는 신용등급에 대한 수요가 확대되는 상황에서 회사채 신용등급 변경에 대한 주식시장의 반응을 상향 및 하향집단으로 구분해서 검토하고 있다. 구체적으로 첫째, 등급변경에 대한 주가반응이 등급변경정도에 따라 차이가 존재하는지 여부를 분석 하였다. 둘째, 동일한 등급변경정도에도 무형자산비중에 따라 시장반응에 차이가 존재하는지 여부와 외환위기 전후의 등급변경 공시에 질적 차이가 있는지를 분석하였다. 분석결과 등급하향의 경우에만 등급변경정도에 따른 정보효과가 존재하는 것으로 나타났다. 이처럼 등급하향의 경우에만 정보효과가 나타나는 이유로는 등급변경의 시기적절성, 발행자 우위의 시장구조, 경영자의 비대칭적 정보공시 유인 등이 제시될 수 있다. 특히 무형자산비중이 큰 기업일수록 등급변경에 따른 시장반응이 큰 것으로 나타났다. 또한 외환위기 전후의 등급변경공시도 시장반응에 차이가 있는 것으로 나타났다. 본 연구를 통해서 신용등급의 유용성이 확인되었다. 또한 지식정보화 사회의 도래와 함께 기업의 무형자산에 대한 효과적인 측정과 보고가 어려워 전통적인 재무제표의 역할이 감소되고 있는 상황에서 무형자산과 관련된 또 하나의 실증적 증거를 제공하고 있다는데 큰 의의를 찾을 수 있다. This study examines bond rating changes. The objectives of this study are a) whether stock price reactions for the rating changes differ depending on the degree of the rating change, and b) the market reactions differ according to the portion of intangible assets out of total assets, given the same degree of the rating change. The results show that the rating change is informative only for the downgrading. This seems to be attributable to the timeliness of rating changes, the market structure in which issuers are in dominant position, and asymmetric announcement of information by management. In cross-sectional analysis, the downgrading samples showed a statistically significant market reaction to the degree of the grade change. In addition, the percentage of intangible assets and the announcement of rating changes after foreign exchange crisis appear to significantly affect the market reaction. For the upgrading change, however, the explanatory power of model is not meaningful. Overall, this study confirms "information contents of credit rating change". In particular, this analysis provides another empirical evidence on the importance of intangible assets when the role of the traditional financial statement has become weak due to the difficulty of effectively assessing and reporting intangible assets.