• Journal of Mechanical Science and Technology
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• 제19권10호
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• pp.1902-1909
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• 2005

A process for production of ethyl ester for use as biodiesel has been studied. The sodium hydroxide catalyzed transesterification of soybean oil with ethanol was carried out at different molar ratio of alcohol to oil, reaction temperature and catalyst amount for a constant agitation in two hours of reaction time. Central composite design and response surface methodology were used to determine optimum condition for producing biodiesel. It was found that ethanol to oil ratio and catalyst concentration have a positive influence on ester conversion as well as interaction effects between the three factors considered. An empirical model obtained was able to predict conversion as a function of ethanol to oil molar ratio, reaction temperature and catalyst concentration adequately. Optimum condition for soybean ethyl ester production was found to be moderate ethanol to oil ratio (10.5: 1), mild temperature range ($70^{\circ}C$) and high catalyst concentrations ($1.0\%$wt), with corresponding ester conversion of $93.0\%$.

• 한국수소및신에너지학회논문집
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• 제18권1호
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• pp.85-94
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• 2007

Rice straw, produced as an agricultural by-product, is usable biomass as fuels if depolymerized to monomer unit, because the chemical structure are similar to high octane materials found in gasoline. In this study, parameters of thermochemical degradation by solvolysis reaction of rice straw such as the effect of reaction temperature, reaction time and type of solvent on conversion yield and degradation products were investigated. It was found that the effectiveness of the solvent on the solvolysis reaction was as follows; acetone>cresol>butanol. When acetone was used as a solvent, the highest rice straw conversion was observed to be 91.5% at $500^{\circ}C$, 40 min. Combustion heating value of liquid products from thermochemical conversion processes was in the range of 7,380 cal/g. The energy yield and mass yield in acetone-solvolysis of rice straw was as high as 69.0% and 38.2 g-oil/100g-raw material after 40 min of reaction at $350^{\circ}C$. Various aliphatic and aromatic compounds were detected in the rice straw solvolysis products. The major components of the solvolysis products, that could be used as fuel, were 4-methyl-2-pentanone, 3,5,5-trimethyl-2-cyclopentan-1-one as ketones.

• 전력전자학회논문지
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• 제20권5호
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• pp.389-394
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• 2015

This paper proposes a series-connected power conversion system that integrates a photovoltaic power conditioner and a charge-balancing circuit. In conventional methods, a photovoltaic power conditioner and a cell-balancing circuit are needed for photovoltaic systems with energy storage devices, which results in a complex configuration and high cost. To overcome these problems, a series-connected DC-DC power conditioning system that integrates a photovoltaic power conditioner with a charge-balancing circuit is proposed. During the generation, the system operates as power conditioner only, whereas it operates as a cell balancing circuit during the rest time. For the analysis, the operating principle of the circuit and the controller design are done by PSIM simulation. For verification, a hardware prototype with 48-W photovoltaic modules has been implemented. Results verified that the modularized photovoltaic power conversion system with a series-connected storage successfully works with the proposed method.

• 대한약침학회지
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• 제23권2호
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• pp.79-87
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• 2020

Objectives: Ginsenosides found in ginseng, and the hydrolysates derived from their conversion, exhibit diverse pharmacological characteristics [1]. These have been shown to include anti-cancer, anti-angiogenic, and anti-metastatic effects, as well as being able to provide hepatic and neuroprotective effects, immunomodulation, vasodilation, promotion of insulin secretion, and antioxidant activity. Therefore, the purpose of this study was to examine how quickly the ginsenosides decompose and what kinds of degradation products are created under physicochemical processing conditions that don't involve toxic chemicals or other treatments that may be harmful. Methods: The formation of ginsenoside-Rg2 and ginsenoside-Rg3 was examined. These demonstrated diverse pharmacological effects. Results: We also investigated physicochemical factors affecting their conversion. The heating temperatures and times yielding the highest concentration of ginsenosides (-Rb1, -Rb2, -Rc, -Rd, -Rf, -Rg1, and -Re) were examined. Additionally, the heating temperatures and rates of conversion of these ginsenosides into new 'ginseng saponins', were examined. Conclusion: In conclusion, obtained provide us with effective technology to control the concentration of both ginsenosides and the downstream converted saponins (ginsenoside-Rg2, Rg3, Rg5, and Rk1 etc.), as well as identifying the processing conditions which enable an enrichment in concentration of these compounds.

• 한국수소및신에너지학회논문집
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• 제21권5호
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• pp.470-477
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• 2010

The IGCC (Integrated gasification combined cycle) is known for one of the highest efficiency and the lowest emitting coal fueled power generating technologies. As the core technology of this system is the gasifier to make the efficiency and the continuous operation time increase, the research about different coal's gasification has been conducted. Our research group had set-up the coal gasifier for the pilot test to study the effect of different coals-Shenhua and Adaro coal- on gasification characteristics. Gasification conditions like temperature and pressure were controlled at a fixed condition and coal feed rate was also controlled 30 kg/h to retain the constant experimental condition. Through this study we found effects of coal composition and $O_2$/coal ratio on the cold gas efficiency, carbon conversion rate. The compounds of coal like carbon and ash make the performance of gasifier change. And carbon conversion rate was decreased with reduced $O_2$/coal ratio. The optical $O_2$/coal ratio is 0.8 for the highest cold gas efficiency approximately. At those operating conditions, the higher coal has the C/H ratio, the lower syn-gas has the $H_2$/CO ratio.

• Journal of Electrical Engineering and Technology
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• 제13권3호
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• pp.1156-1165
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• 2018

This paper presents a detailed realization of direct torque controlled induction motor drive for elevator applications. The drive is controlled according to the well-known space vector modulated direct control scheme (SVM-DTC). As the elevator drives are usually equipped with speed sensors, flux estimation is carried out using a current model where two stator currents are measured and accurate instantaneous rotor speed measurement is used to overcome the need for measuring stator voltages. Speed profiling for a comfortable elevator ride and other supervisory control activities to provide smooth operation are also explained. The drive performance is examined and controllers' parameters are fine-tuned using MATLAB/SIMULINK. The blocks used for flux and torque estimation and control in the offline simulation are compiled for real-time using dSPACE Microlabox. The performance of the drive has been verified experimentally. The results show good performance under transient and steady state conditions.

• 한국조경학회지
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• 제21권4호
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• pp.1-14
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• 1994

This study attempted to characterize conflict frames of environmental disputes by examining twelve actual wetland permitting cases in Ohio. The participants consisted of such interested parties as applicants, technical, legal or environmental consultants to applicants, U.S.Army Corps of Engineers, U.S.Environmental Protection Agency, U.S.Fish and Wildlife Service, Ohio Environmental Protection Agency, Ohio Department of Natural Resoures, local agencies, the environmental community, and citizens who have been involved of the permitting process. The purpose of this study is to provide empirical evidence of how different perceptual frames existed in the wetland conversion disputes, and to understand different environmental conflict frames that influenced disputants' perception relating to dispute resolution. The vehicles used to collect the necessary data were three survey instruments : Open-ended questionnaires, Likert-type questionnaires, and ranking questionnaires. Forty-three subjects were contacted for open fact-to-fact interviews, 53 subject for Kikert-type mail survey and 54 subjects for ranking instrument mail survey. Analyses of survey results revealed that six different types of frames were clearly identified from all the parties involved in Ohio wetland conversion disputes. It revealed that disputants had statistically significantly different levels of perception to the frames based on the participants' role (i.e. regulator, applicant, commentor), the number of involved parties in the process, processing time and the issuance of a permit. The findings also revealed that information sharing among disputants played a significant role in the process of froming and reframing. The alternative idea, building cooperation through negotiation, was proposed to provide new insight into the resolution of the dispute.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2010년도 춘계학술대회
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• pp.809-811
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• 2010

3차원 그래픽 응용이 가능한 소형 모바일 기기에서의 부동소수점 연산 처리는 전력소모가 많고 하드웨어 비용이 많이 들며 연산 해상도가 너무 정확한 연산보다는 적절한 해상도를 확보하되 하드웨어 자원을 적게 소모하고 전력소모가 낮을수록 바람직하다. 비용이 많이 소요되는 부동소수점 연산은 곱셈과 나눗셈이며, 로그 변환을 이용하면 곱셈과 나눗셈을 덧셈과 뺄셈으로 변환하여 고속 동작을 구현할 수 있으며, 이는 로그 함수값을 얼마나 실제값에 근사화 시킬 수 있는지에 따라 성능이 좌우된다. 본 연구에서는 이러한 고속 부동소수점 연산에 적용될 수 있는 로그변환 회로에 대한 동향을 조사하되, 설계 시 중요하게 고려해야 할 점과 로그변환 회로가 어떻게 근사화되고 적용될 수 있는지에 대하여 상세히 분석한다.

• 융합신호처리학회논문지
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• 제1권2호
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• pp.131-137
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• 2000

본 논문은 소프트웨어 무선에 적합한 전송장치로써 로직회로에 의해 생성되어지는 디지털신호를 직접 무선으로 변환시킬 수 있는 디지털-무선 변환장치를 제안한다. 이러한 회로가 실현되어지면 변조회로, RF회로와 안테나를 1개의 간단한 디바이스로 실현할 수 있어 소프트웨어무선의 본질인 소프트웨어처리에 의한 무선의 제어를 직접 수행할 수 있게 된다. 본 논문의 디지털-무선 변환장치는 채널화용 PN코드가 부여하는 위상각도에 의해 무수히 많은 채널화를 기할 수 있으며 디지털화에 의하여 설계에 유연성을 주게 되므로 하드웨어의 비중을 최소화시키고 소프트웨어 베이스의 유연한 기능을 갖는다.

• 정보처리학회논문지D
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• 제10D권2호
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• pp.343-350
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• 2003

본 연구는 음성 인터넷 서비스를 위하여 기존의 HTML 컨텐츠를 자동으로 VXML 컨텐츠로 변환하여 사용하는 방법에 관한 것이다. 문서 변환은 HTML 문서의 해석과 내용 분리에 앞서 컨텐츠의 선택이 필수적으로 요구되지만, 이미 알고 있고, 관심이 있는 내용의 집단적 선택에 대하여는 아직까지 좋은 해법이 없어 보인다. 본 논문에서는 비구조적 데이터로 구성된 웹 문서로부터 필요한 정보 묶음을 선택하기 위하여 웹 문서에 포함된 문자열, 구조에 대한 사용자의 사전 지식을 상호 반응적으로 사용하는 방법을 제안하며, 이를 구현하여 그 타당성을 입증하였다. 제안하는 방식은 기존의 구조적 방식에 의한 선택보다 사용자의 의도를 정확히 반영하며, 문서 표현의 구현 기법의 변화에 강건한 장점이 있다. 또한 컨텐츠 분리 측면에서는 XML또는 XHTML 문서변환을 중간 과정으로 사용하는 방식에 비하여 시간적으로 빠르며, 변환 과정의 부담이 작다.