• Journal of Korean Elementary Science Education
• /
• v.35 no.2
• /
• pp.181-193
• /
• 2016

We examined the inquiry activities in the material domain of the elementary science textbooks and experimental workbooks based on 2009 revised curriculum. The analysis framework was SEP (Science and Engineering Practices) - 'Asking questions and defining problems', 'developing and using models', 'planning and carrying out investigations', 'analyzing and interpreting data', 'using mathematics and computational thinking', 'constructing explanations and designing solutions', 'engaging in argument from evidence', and 'obtaining, evaluating, and communicating information'. Sub-SEP of each grade band were also used. The results showed that the $3^{rd}{\sim}5^{th}$ grade science textbooks and workbooks mainly emphasized 'make observations and/or measurements', 'represent data in tables and/or various graphical displays', or 'use evidence to construct or support an explanation or design a solution to a problem' among around 40 sub-SEP. In the case of the inquiry activities for $6^{th}$ grade, majority of sub-SEP included were also only 'collect data to produce data to serve as the basis for evidence to answer scientific questions or test design solutions', 'analyze and interpret data to provide evidence for phenomena' or 'construct a scientific explanation based on valid and reliable evidence obtained from sources'. The type of 'asking questions and defining problems', 'using mathematics and computational thinking' or 'obtaining, evaluating, and communicating information' were little found out of 8 SEP. Educational implications were discussed.

• Journal of Environmental Impact Assessment
• /
• v.18 no.2
• /
• pp.69-78
• /
• 2009

In order to provide fundamental data for developing greenhouse gas emission factor, we investigated power plants in Korea using B-C oil as Energy source. The power plant is a major source of greenhouse gases among the sectors of fossil fuel combustion, thus information of its emission factors is very essential to the establishment of control strategies for the greenhouse gas emissions. The caloric value of fuel was analyzed using calorimeter and the calorific value was 10,419 kcal/kg. The $CO_2$ concentration of flue gas and elemental analysis were conducted using GC-FID and elemental analyzer. The $CO_2$ emission factors from fuel analysis was 75,410 kg/TJ and that from $CO_2$ gas analysis was 94,265 kg/TJ. When compared with IPCC values, the emission factors by the fuel analysis was 2.5% lower, and that by $CO_2$ gas analysis was about 21.85% higher.

• 한국신재생에너지학회:학술대회논문집
• /
• 2010.11a
• /
• pp.163.1-163.1
• /
• 2010

2030년까지 신재생에너지발전 비중을 11%로 높이겠다는 정책목표 달성을 위한 정부의 지원방안이 현행 발전차액지원제도(FIT)에서 2012년부터는 신재생에너지의무할당제(RPS)로 전환된다. 전원별로 정해진 발전량에 대해 정부가 일정한 가격으로 구매해주는 현행 제도 하에서 신재생에너지발전사업자는 중장기 가격을 보장받음으로써 수익성을 초기에 확정할 수 있는 장점이 있는 반면 정부 입장에서는 보급이 확대될수록 막대한 재정부담이 발생하고 경쟁을 통해 생산 비용을 낮추기 위한 유인이 부족한 단점이 있다. 이러한 단점을 보완하기 위해 도입되는 의무할당제는 일정 설비규모 이상의 발전사업자에게 신재생에너지발전 의무량을 부과하고 의무대상자가 의무이행의 수단으로 공급인증서(REC)를 발급받거나 구매하여 의무를 이행토록 하는 제도로서 공급인증서 가격 결정을 시장기능에 맡김으로써 신재생에너지 사업자간 경쟁을 촉진시켜 생산비용을 절감하고 정부의 재정부담을 완화하는 장점이 있는 반면 신재생에너지발전사업자 입장에서는 수익성 분석이 복잡해지고 리스크가 증가하는 문제점이 있다. 특히 발전용 연료전지를 활용한 발전사업의 경우 다른 신재생에너지원과 달리 설비투자비용(CAPEX) 외에 가스요금 및 핵심부품의 주기적인 교체 등을 위한 운영비용(OPEX)의 비중이 작지 않기 때문에 더욱 정밀한 분석이 필요하다. 본 연구에서는 신재생에너지발전사업자 입장에서 비용과 편익에 영향을 미치는 각 요소와 그 영향을 파악함으로써 발전용 연료전지의 경제성 분석을 시도해 보았다.

• Clean Technology
• /
• v.7 no.3
• /
• pp.179-185
• /
• 2001

Some companies are trying to develop the microfiltration membranes because most of them used as a prefilter is imported in Korea. However, they are faced with much difficulty such as characterization of membrane and controlling of pore size on development. In this study, a microfiltration membrane developed by a company was evaluated for applicability to use as a prefilter before reverse osmosis membrane process in production of ultra pure water. The optimum feed pressure for the raw water was obtained at 0.2 to 0.4 atm. At that time, turbidity of the treated water was 0.4 NTU and flux was 6,000 to $9,000L/m^2/hr$. In case of the conventionally treated water, it showed the very stable flux and turbidity at 90% of recovery rate. The chemical cleaning was helpful to reduce the TMP for treated water. The turbidity was improved from 0.3 NTU to 0.1 NTU after chemical cleaning.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.33 no.1
• /
• pp.56-59
• /
• 2020

Porcelain insulators are typically exposed to surface discharge and lightning impulse in service. This study investigates the insulation characteristics of the external and internal discharges of a porcelain insulator with respect to its flashover for a 154 kV transmission line. The experiments are also conducted using a wet flashover test and an impulse test based on the external discharge and the internal penetration, to classify the flashover voltage-time curve of the porcelain insulator. When an impulse with a strength of 2,500 kV/㎲ was applied three times to 6.5 mm ceramic samples, electrical penetration of approximately 70% occurred. The impulse experiment confirmed that the electrical penetration inside the porcelain insulator coincided with the area where the electric field was concentrated. The wet flashover voltage test revealed that the flashover threshold voltage increases by approximately 7% after cleaning of the surface.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.33 no.1
• /
• pp.50-55
• /
• 2020

Porcelain insulators have been used for a long time in 154 kV power transmission lines. They are likely to be exposed to sudden failure because of product deterioration. This study was conducted to evaluate the quality of porcelain insulators. After stresses were applied, the damaged regions of aged insulators were investigated in terms of chemical composition, material structure, and other properties. For porcelain insulators that were in service for a long time, the mechanical failure load was 126 kN, whereas the average mechanical failure load was 167.3 kN for new products. It was also determined that corrosion occurred at the metal pin part due to the penetration of moisture into the gap between the pin and the ceramic. Statistical analyses of failure were performed to identify the portion of the insulators that were broken. Cristobalite porcelain insulators fabricated without alumina additives had a high failure rate of 54% for the porcelain component. In the case of the addition of Alumina (Al₂O₃) to the porcelain insulators to improve the strength of the ceramic component, a more frequent damage rate of the cap and pin of 73.3% and 27%, respectively, was observed. This study reports on the material component of SiO₂ and the percentage of alumina added, with respect to the mechanical properties of porcelain insulators.

• Journal of Korea Society of Industrial Information Systems
• /
• v.20 no.2
• /
• pp.85-96
• /
• 2015

Despite the growth of body-related industry has generated considerable interest in this topic among both academics and practitioners, there has been lack of studies that explore body esteem toward online fashion products leads to purchase intentions, which self-monitoring moderates the relationship between body esteem toward online fashion products and purchase intentions. To fill this gap, this study aim to propose a research model where body esteem influences on the purchase intentions, with self-monitoring as a moderator. In order to test hypotheses, response from 172 consumers were achieved, and the proposed model was estimated by using hierarchical moderated regression analysis. The empirical results showed that body esteem negatively related to purchase intentions toward online fashion products. Additionally, this study indicated that the moderating effects of self-monitoring exist between body esteem and purchase intentions toward online fashion products, thereby implying the importance of contingent role of self-monitoring in managing online channels.

• Journal of Energy Engineering
• /
• v.29 no.3
• /
• pp.57-63
• /
• 2020

In this paper, we reported that the global trend of cement production and utilization as raw materials and as a fuel. As we know, cement is one of the significant materials required for the construction industry. The recent trend of rising urbanization, both the cement and construction industry played a vital role. The cement industry is a major sustainable infrastructure for the countries. Currently, China producing cement half of the world's cement production. During the year 2018, Korea producing cements nearly 57.5 million metric tons. Waste materials are used as circular resources and also having tremendous benefits for cement production. Another important use of these circular resources is fuel for the cement industry. There is a large potential benefit of the cement industry, but it's creating a severe environmental threat. The cement industry contributes to the major emissions of CO2. This leads the global warming. As per the Paris agreement, the Korean government initiated the recycling policy of waste materials and also the utilization of circular resources for the prevention of limited natural resources and also the global warming effect.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.19 no.6
• /
• pp.1333-1340
• /
• 2015

IEEE 802.11 MAC(Media Access Control) defines DCF(Distributed Coordination Function) for data transmission control. BEB(Binary Exponential Backoff) algorithm of DCF has a problem that if the number of stations connected are over a certain threshold, it degrades network performance because of packet collisions caused from the minimum contention window size. To cope with this problem, we proposed a novel algorithm, named as VBS(Variable Backoff Stage) algorithm, which adjusts the rate of backoff stage increment depending on the number of stations associated with an AP(Access Point). Analytic model of proposed algorithm was derived and simulations on the BEB and the VBS algorithms have been conducted on the OFDM (Orthogonal Frequency Division Multiplexing) method. Simulation results showed that when the rate of backoff state increment was 5 and 10, the number of retransmission were reduced to 1/5 and 1/10 comparing to that of BEB, respectively. Our algorithm showed improvement of 19% and 18% in network utilization, respectively. Packet delay was reduced into 1/12.

• Korean Journal of Pharmacognosy
• /
• v.48 no.1
• /
• pp.70-76
• /
• 2017

Dendranthema spp are distributed in various regions in Korea. This report is the quantitative results of phenolic compounds on the 5 resources collected from all over the country. It was known that it has phenolic compounds, as an anticoagulant activities and immunoadjuvant activity of contribute to the cardiovascular effects. This was used for quantitative analysis of chlorogenic acid(CA), 3,5-Dicaffeoylquinic acid(3,5-DCA), 4,5-Dicaffeoylquinic acid(4,5-DCA) and linarin, with UPLC-PDA and LC-IT-TOF-MS. Extraction efficiency of compounds was compared by using ultrasonic extraction and reflux extraction with different extraction conditions (methods and time). In 50% MeOH extracs (30 mins) of Dendranthema zawadskii (Herb.) Tzvelev (SDZ), Dendranthema zawadskii var. yezoense (Maek.) Y.M.Lee & H.J.Choi (NDZ), Dendranthema zawadskii (Herb.) Tzvelev var. teuisectum (Kitag.) J. H. Pak (GDZ), Dendranthema careanum (H. $L{\acute{e}}v$. & Vaniot) Vorosch. (HDC) and Dendranthema zawadskii var. tenuisectum Kitag (PDZ), chlorogenic acid contents were 1.14‰, 6.95‰, 7.27‰, 1.47‰ and 2.64‰, 3,5-dicaffeoylquinic acid contents were 3.30‰, 5.60‰, 10.81‰, 2.67‰ and 1.50‰, 4,5-dicaffeoylquinic acid contents were 0.74‰, 1.93‰, 3.36‰, 0.61‰ and 0.43‰ and linarin contents were 3.90‰, 10.15‰, 0.15‰, 0.73‰ and 0.21‰, respectively.