• Journal of ILASS-Korea
• /
• v.28 no.2
• /
• pp.55-61
• /
• 2023

Natural gas is a high-octane fuel that is effective in controlling knocking combustion. In addition, as a low-carbon fuel with a high hydrogen-carbon ratio, it emits less carbon dioxide and almost no particulate matter compared to conventional fossil fuels. Stoichiometric combustion engines equipped with a three-way catalyst are useful in various fields such as transportation and power generation because of their excellent exhaust emission reduction performance. However, stoichiometric combustion engines have a disadvantage of lower thermal efficiency compared to lean combustion engines. In this study, a combination of high compression ratio and Atkinson cycle was implemented in a 11 liter, 6-cylinder, spark-ignition engine to improve the thermal efficiency of the stoichiometric engine. As a result, pumping and friction losses were reduced and the operating range was extended with optimized Atkinson camshaft. Based on the exhaust gas limit temperature of 730℃, the maximum load and thermal efficiency were improved to BMEP 0.66 MPa and BTE 35.7% respectively.

• The Transactions of the Korean Institute of Electrical Engineers A
• /
• v.48 no.1
• /
• pp.16-21
• /
• 1999

The analysis of distribution line faults is essential to the proper protections of the power system. A high impedance fault test, which was carried in Korean electric power systems, it was found that a arcing phenomenon occurred during the high level portion of conductor voltage in each cycle. In this paper, we propose a new method for detection of high impedance faults, which uses the arcing fault current difference during high voltage and low voltage portion of conductor voltage waveform. To extract this difference, we diveded one cycle fault current into equal spanned four data windows according to the magnitude of voltage waveform and applied fast fourier transform(FFT) to each data window. The frequency spectrum of current wavefrom in each portion are used as the inputs of neural network and is trained to detect high impedance faults. The proposed method shows improved accuracy when applied to staged fault data and fault-like load.

• Journal of the Korean Society of Earth Science Education
• /
• v.4 no.2
• /
• pp.126-133
• /
• 2011

This study explored different concepts by handing out the questionnaires asking the 6 students of the second year of junior high school who had no lesson on cycle "which words related to cycle are suggested?" In regard to the stimulation of the word 'cycle', students relate it to different fields that they learn at school such as biology, environmentology, and earth science. The analyzed results from the answers by students are as follows. First, it resulted in from analysis on the questionnaire and the half-structured interviews that students were unable to expand the concept of cycle to the scientific concept, and perceived it fragmentarily. Secondly, their understanding on the system of the earth was low and they understood the concept of cycle with a unilinear thought rather than a systematic thought. Therefore, we need to synthesize the students' unilinear thoughts on cycle shown through this study and an effective educational strategy for their continuous, systematic thoughts, is essential.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.17 no.4
• /
• pp.285-296
• /
• 2005

In order to reduce the compression power and to use the overall energy contained in LNG effectively, a combined cycle is devised and simulated. The combined cycle is composed of two cycles; one is an open cycle of liquid/solid carbon dioxide production cycle utilizing LNG cold energy in $CO_2$ condenser and the other is a closed cycle gas turbine which supplies power to the $CO_2$ cycle, utilizes LNG cold energy for lowering the compressor inlet temperature, and uses the heating value of LNG at the burner. The power consumed for the $CO_2$ cycle is investigated in terms of a production ratio of solid $CO_2$. The present study shows that much reduction in both $CO_2$ compression power (only $35\%$ of power used in conventional dry ice production cycle) and $CO_2$ condenser pressure could be achieved by utilizing LNG cold energy and that high cycle efficiency ($55.3\%$ at maximum power condition) in the gas turbine could be accomplished with the adoption of compressor inlet cooling and regenerator. Exergy analysis shows that irreversibility in the combined cycle increases linearly as a production ratio of solid $CO_2$ increases and most of the irreversibility occurs in the condenser and the heat exchanger for compressor inlet cooling. Hence, incoming LNG cold energy to the above components should be used more effectively.

• Journal of the Korean Society of Costume
• /
• v.63 no.8
• /
• pp.156-170
• /
• 2013

The purpose of this research is to scrutinize the cyclist's consumer behavior by analyzing the eWOM information search behavior of cycle-wear according to benefits sought and involvement. The research was conducted through an online survey and the respondents were 291 men who wore cycle-wear and searched information via online. The results of this research are as following. First, the benefits sought from wearing cycle apparel are composed of five sub-factors such as, ideal body figure, brand ostentation, comfort ease, personality, and economic feasibility. In addition, the cycle-wear involvement consisted of two sub-factors: cycling involvement and fashion involvement. Second, the eWOM information search behavior of cyclists was different depending on the benefits sought by the cyclists. When the cyclists pursued ideal body figure they searched more information of design and color, while cyclists put more weight on the information of design, color, and brand when they sought brand ostentation. Moreover, the valence and the type of the information were dissimilar depending on the benefits sought. Third, the sub-factors of eWOM information search behavior affected the eWOM effect distinctively. The price information was the only factor that influenced the eWOM effect among the contents of the information. The valence of the information influenced the eWOM effect, and the effect of positive information was stronger than negative information. Additionally, the subjective information also affected the eWOM effect. Lastly, the effect of the benefits sought influencing the eWOM information search behavior varied by the difference of the cycle-wear involvement. For example, when they are both high in the involvement there were various benefits sought affecting the eWOM information search behavior. However, when only the cycling involvement was high, and they pursued personality, the price information was not important to them.

• Journal of the Institute of Electronics and Information Engineers
• /
• v.49 no.12
• /
• pp.45-55
• /
• 2012

The energy efficiency is extremely significant in Wireless Sensor Networks (WSN) which deliver the data sensed in the sensor field, using wireless communications. Under the characteristics of WSN, many MAC protocols employ the Duty Cycle mechanism which continuously operates Wakeup and Sleep periods, for the energy efficiency. However, constant Wakeup period in general Duty Cycle incurs the limited performance of the energy efficiency and the receiving ratio. For addressing this, we design and propose a new scheme called Variable Wakeup Period, considering local traffic conditions. Our scheme enhances receiving ratio by increasing Wakeup period under the high traffic condition, and makes high energy efficiency by decreasing Wakeup period under the otherwise condition. In addition, we evaluate the performance of our scheme by performing the simulation, which experiments the previous synchronous and asynchronous MAC protocols, and which also experiments the same protocols with the proposed scheme, for comparative evaluations.

• Asian Pacific Journal of Cancer Prevention
• /
• v.16 no.10
• /
• pp.4357-4361
• /
• 2015

Thunbergia Laurifolia Linn. (TL) is one of the most familiar plants in Thai traditional medicine that is used to treat various conditions, including cancer. However, the antitumor activity of TL or its constituents has never been reported at the molecular level to support the folklore claim. The present study was designed to investigate the antitumor effect of an aqueous extract of TL in human breast cancer cells and the possible mechanism(s) of action. An aqueous crude extract was prepared from dried leaves of TL. Folin-Ciocalteu colorimetric assays were used to determine the total phenolic content. Antiproliferative and cell cycle effects were evaluated in human breast adenocarcinoma MCF-7 cells by MTT reduction assay, cell growth inhibition, clonogenic cell survival, and flow cytometric analysis. Free radical generation by the extracts was detected using electron paramagnetic resonance spectroscopy. The exposure of human breast adenocarcinoma MCF-7 cells to a TL aqueous extract resulted in decreases in cell growth, clonogenic cell survival, and cell viability in a concentration-dependent manner with an $IC_{50}$ value of $843{\mu}g/ml$. Treatments with extract for 24h at $250{\mu}g/ml$ or higher induced cell cycle arrest as indicated by a significant increase of cell population in the G1 phase and a significant decrease in the S phase of the cell cycle. The capability of the aqueous extract to generate radical intermediates was observed at both high pH and near-neutral pH conditions. The findings suggest the antitumor bioactivities of TL against selected breast cancer cells may be due to induction of a G1 cell cycle arrest. Cytotoxicity and cell cycle perturbation that are associated with a high concentration of the extract could be in part explained by the total phenolic contents in the extract and the capacity to generate radical intermediates to modulate cellular proliferative signals.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.25 no.5
• /
• pp.225-232
• /
• 2013

Heat pump systems have been widely adopted in buildings for cooling and heating, due to their higher energy efficiency. Recently, the demand for hot water supply from the heat pump system has been increasing. To increase the water supply temperature with higher system efficiency and reliability, a heat pump water heater adopting cascade cycle was investigated in this study. The cascade heat pump water heater consisted of a low-stage cycle using R410A, and a high-stage cycle using R134a. A simulation program for the cascade heat pump water heater was developed, and verified by comparison with experimental data. The performance of the cascade heat pump water heater was optimized, by varying the compressor rotating speeds of the low- and high-stage cycles. At low ambient temperatures, the performance of the cascade cycle was compared with that of the single-stage cycle. The system efficiency of the cascade cycle was higher than that of the single-stage cycle, showing a lower compression ratio and compressor discharge temperature.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.31 no.2A
• /
• pp.86-96
• /
• 2006

In recent year, EPON(Ethernet PON) system is expected to be more attractive solutions for high speed, broadband access networks in next generation access networks due to the conversionce of low-cost ethernet equipment and low-cost fiber infrastructure. Upstream channel control algorithm is essential to hare upstream bandwidth in EPON. In this paper, we suggest HUHG(High Utilization and Hybrid Granting) algorithm for supporting high bandwidth utilization and QoS for different service class. This algorithm improves bandwidth utilization as removing or diminishing idle time of upstream channel using characteristics of fixed EF(Expedited Forwarding) sub-cycle. The proposed algorithm also minimizes the packet delay and delay variation of EF class. We conduct detailed simulation experiments using OPNET to study the performance and validate the effectiveness of the proposed algorithm.

• Proceedings of the KIEE Conference
• /
• 1989.07a
• /
• pp.3-8
• /
• 1989

Recent research activities for open and closed cycle MHD electrical power generations are reviewed. World first full scale 500MWe natural gas fired open cycle MHD is now under construction in USSR. Coal-fired open cycle MHD researches are in the stage of proof of concept and retrofitting of old coal power stations with MHD is planned in US and other countries. Basic research for closed MHD is most actively pursued in Japan, which potentially can provide a very high efficiency and a simple and reliable system.