• Journal of Sensor Science and Technology
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• v.5 no.2
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• pp.29-36
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• 1996

With the three dimensional magnetic field measuring system dealt with in this paper, accurate measurements and analyses of extremely low frequency(ELF) magnetic fields caused by starting and/or operating electric devices and power installations can be conducted. To obtain high performance for lower frequency and spatial components without any distortion, the measuring system is designed as three dimensionally including the multiturn loop-type magnetic field sensors, differential amplifiers and active integrators. As the results of calibration experiments, the frequency response characteristics of the measuring system range from 8[Hz] to about 53[kHz] for each direction of x, y, z axes, and the response sensitivities are 9.54, 9.21, $10.89[mV/{\mu}T]$, respectively. The actual survey experiments by using an oscillating impulse current generator confirm a reliability of the proposed measuring system. Also, through the other experiments by using small-sized induction motors, the magnetic field intensities when starting and steady-state operating mark 15.8, $8.61[{\mu}T]$ as maximum value, respectively. And those intensities decrease steeply according as the measuring distance increases.

• Korean journal of food and cookery science
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• v.23 no.4 s.100
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• pp.452-460
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• 2007

As a preliminary study for developing cooking techniques to improve cooked rice flavor, we surveyed consumer perceptions on purchasing rice and the consumption of cooked rice. The quantity of rice purchased by consumers was in the range of $1O{\sim}20$ kg. The purchase criterion for 50% of the subjects was the taste of the cooked rice, and half of the subjects bought their rice at a supermarket. A majority (90%) of the subjects consumed the rice within 1 to 4 months, storing it raw in the package (32.4%) or in a container at room temperature. The rice was cooked for 2 to 5 persons (65%), 1 to 2 times a day (70%) with a pressure cooker (76%). The rice and water volume were measured by eye. The cooked rice was eaten immediately (41.8%) or in 1 to 2 days (48.6%) by keeping it in an electric cooker (63.6%). The subjects perceived the rice cultivar (37.9%) as the major factor for the cooked rice flavor, as well as the region of origin (21.3%), and storage period (11.9%); the cultivars of Ilmi, Ilpoom and Chuchung were preferred. In conclusion, the consumers regard rice as a principal food; however, the methods to measure rice and water are not standardized. To improve the taste of cooked rice, consumers depend on cooking equipment and the rice cultivar.

• Journal of the Korean earth science society
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• v.31 no.6
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• pp.563-572
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• 2010

Both multi-channel temperature monitoring and geophysical electric survey were performed together for an embankment to assess the leakage zone. Temperature variation according to space and time on the inner parts of engineering constructions (e.g.: dam and slope) can be basic information for diagnosing their safety problem. In general, as constructions become superannuated, structural deformation (e.g.: cracks and defects) could be generated by various factors. Seepage or leakage of water through the cracks or defects in old dams will directly cause temperature anomaly. This study shows that the position of seepage or leakage in dam body can be detected by multi-channel temperature monitoring using thermal line sensor. For that matter, diverse temperature monitoring experiments for a leakage physical model were performed in the laboratory. In field application of an old earth fill dam, temperature variations for water depth and for inner parts of boreholes located at downstream slope were measured. Temperature monitoring results for a long time at the bottom of downstream slope of the dam showed the possibility that temperature monitoring can provide the synthetic information about flowing path and quantity of seepage of leakage in dam body. Geophysical data by electrical method are also added to help interpret data.

• Journal of the Korean Institute of Landscape Architecture
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• v.36 no.3
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• pp.52-62
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• 2008

By analyzing specific plant distributions and physicochemical characteristics of topsoil in a reclaimed dredging area, baseline data was found of natural landscape planting sites, and developing dredged fill ground. The reclaimed dredging area is five different stands (1, 2, 3, 4 and 5) which were examined in this research. They are located from sea level to 15 meters in altitude and exhibited typical characteristics of the salt marsh in Gwangyang Bay. Species with high constancy in the vegetation on the reclaimed soil were classified into four stages. A total of 12, 15, 22, 27 and 35 different plant species were found and also increased in stands 1, 2, 3, 4 and 5, respectively. Moving from stand 1 to 5, halophytes decreased and non-halophytes increased. Desalination at each stage of the reclaimed dredging area was a driving force affecting the performance and distribution of halophytes and non-halophytes. Overall, 35 quadrats of soil were selected and analyzed for specific physicochemical characteristics of topsoil between O${\sim}$20cm. Results of the physicochemical analysis such as altitude, slope, vegetation and kind of reclaimed dredging soil, exhibited irregular increases or decreases. As survey areas moved from stand 1 to 4, desalination areas, soil acidity, electric conductions, content of salinity, available phosphorus, potassium, chlorine, calcium, and magnesium indicated decreasing patterns; however, total nitrogen, silt, and clay content increased. Cluster analysis and PCA by environmental data within the stands clearly showed five distinct vegetation patterns on the tested reclaimed area. These results indicate that the differences of performance and distribution of vegetation are due to the SAR in the reclaimed soil and related to the natural survival strategy at the given hostile habitat.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.16 no.2
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• pp.81-89
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• 2002

The Battery Energy Storage System (BESS) has lots of advantages such as load leveling, quick response emergency power (spinning reserve), frequency and voltage control, improvement of reliability, and deferred generation and transmission construction. However, it is very critical that economic feasibility requires justification from the customer side of meter to promoting the dissemination of BESS in nation widely. In this paper, we proposed the economic assessment model of customer owned BESS which is complemented and improved the existing model. The proposed model is applied to the typical customer types, i.e. light industrial, commercial, and residential, which are taken from the statistical analysis on the load profile survey of Korea Electric Power COmpany (KEPCO). The economic viability performed for each customer load type to justifying their economic feasibility of BESS installation from the economic measures such as payback period, Net Present Worth (NPW), Rate Of Return (ROR). The results show that the BESS has economic benefits to the specific customer type, i.e. residential customer. Therefore, the government and the energy agency should be committing the support program, such as tax incentive, financial support, to disseminate the BESS nation widely. The results of this paper are useful to the customer investment decision-making and the national energy policy & strategy in Korea.

• The Journal of Engineering Geology
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• v.30 no.3
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• pp.289-302
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• 2020

To determine the shallow subsurface structure and sliding surface of land creeping in 2016 at Hadong-gun, Gyeongsangnam-do, geophysical surveys (electric resistivity, and refraction seismic methods, borehole televiewer) and slope stability analysis were conducted. The subsurface structure delineated with borehole lithologies and seismic velocity structures provided the information that the sediment layer on the top of the slope was rather as thick as 20 m and the underlying weathered rock (anorthosite) was thinner than 1 m. Based on the tension cracks observed during the geological mapping, televiewer scanning was performed at the borehole BH-2 and detected the intensive fracture zones at the ground-water level, associated with the slip weak zones mapped in dipole-dipole electrical resistivity section. Downslope sliding and slightly upward pushing at the apex of high resistive bedrock explains the curved slip plane of the land creeping. Such a convex structure might play a role of natural toe abutment for preventing the downward development of slip weak zones. In slope stability analysis, the safety factors of the slip weak zone are calculated with varying the groundwater levels for dry and rainy seasons and the downslope is founded to be unstable with safety factor of 0.89 due to fully saturated material in rainy season.

• Environmental and Resource Economics Review
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• v.15 no.4
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• pp.693-712
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• 2006

A pre-feasibility test is done for renewable energy hybrid power systems at off~grid islands in which the current power supply is provided only by diesel generation. We apply Homer (Hybrid Optimization Model for Electric Renewables) which was developed by the National Renewable Energy Laboratory (NREL) for the analysis to identify the cost-minimizing combination of power generating facilities for the given load profiles. Chuja-Do, Geomun-Do and Youngsan-Do have been selected for our analysis considering the wind resources data of the Korea Institute of Energy Research (KIER). Information on wind speed, solar radiation and temperature is also used for the analysis. System component cost information from overseas market has been used due to the lack of domestic information. Site specific Load profile for electricity demand for those islands are reconstructed based on the partial survey results obtained form other sources. The LCOE of the least cost hybrid power systems for Chuja-Do, Geomun-Do and Youngsan-Do are $0.278/kWh, $0.234/kWh and $0.353/kWh, respectively Considering the fact that diesel generation is being subsidized at the price of $0.300/kWh by the government, first 2 cases are economically feasible for the introduction of renewable energy hybrid systems to those islands. But the third case of Youngsan-Do does not meet the criteria. The basic differences of these pre-feasibility test results are from the differences of the site specific renewable energy conditions, especially wind resources. In summary, promoting hybrid systems in the off-grid remote island should be based on the economic feasibility test results. Not all the off-grid islands are feasible for introducing this renewable energy hybrid system.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.6
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• pp.2629-2635
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• 2011

This study carried out questionnaire survey and experiment on oral hygiene effects according to the actual condition of using oral care products and the amount of toothpaste used targeting 40 freshmen and sophomores in dental hygienics in some universities from November 8, 2010 to November 26. The collected data was analyzed by using SPSS WIN 15.0 program. The following conclusions were obtained. 1. The result of actual condition of toothbrushing is as follows. As the answer of a question about whether or not toothbrushing after every meal at ordinary times, the largest was 47.5% of being average. The occasion of toothbrushing before going to bed at ordinary times was the largest with 47.5%. The daily toothbrushing frequency was 3 times mostly and the general toothbrushing method at ordinary times was a rolling method. The frequency of exchanging toothbrushes for the past 1 year was 3 times, which is the largest with 45.0%. 2. As a result of the actual condition of using oral care products, the majority of students don't use electric toothbrush, interdental brush, or mouth-rinse except dental floss. Accordingly, there need to be education and promotion with diverse methods so that a patient oneself can prevent oral disease by selecting and using oral care products that are proper for each individual. Also, it was indicated that there is no big difference in oral hygiene effects depending on the amount of toothpaste used. Thus, to avoid wasting toothpaste, we need to educate and promote to use the amount of toothpaste under 0.3g.

• Geophysics and Geophysical Exploration
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• v.9 no.1
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• pp.10-18
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• 2006

We measured the changes in P-wave velocity that occur when injecting $CO_2$ in gaseous, liquid, and supercritical phases into water-saturated anisotropic sandstones. P-wave velocities were measured in two cylindrical samples of Tako Sandstone, drilled along directions normal and parallel to the bedding plane, using a piezo-electric transducer array system. The velocity changes caused by $CO_2$ injection are typically -6% on average, with maximum values about -16% for the case of supercritical $CO_2$ injection. P-wave velocity tomograms obtained by the differential arrival-time method clearly show that $CO_2$ migration behaviour is more complex when $CO_2$ flows normal to the bedding plane than when it flows parallel to bedding. We also found that the differences in P-wave velocity images were associated both with the $CO_2$ phases and with heterogeneity of pore distribution in the rocks. Seismic images showed that the highest velocity reduction occurred for supercritical $CO_2$ injection, compared with gaseous or liquid $CO_$ injection. This result may justify the use of the seismic method for $CO_2$ monitoring in geological sequestration.

• Journal of The Korean Association For Science Education
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• v.37 no.2
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• pp.253-262
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• 2017

This study aims at investigating the perceptions of science teachers about the role of visual representations in the teaching of electromagnetism, and finding out how science teachers use visual representations in their teaching of electromagnetism and the difficulties they experience in dealing with those representations. A total of 121 science teachers responded to the online survey. The results showed that most of the teachers agreed to the significance of using visual representations in the classroom but regarded their role as means of simply delivering science knowledge rather than constructing or generating knowledge. For the three visual representations widely used in teaching of electromagnetism in secondary schools (electrostatic induction on electroscope, magnetic field around current carrying wire, structure and principle of electric motor), the teachers preferred teacher-centered use of visual representations rather than student-centered and teacher's construction of representations were the most frequent among four types of use; interpretation, construction, application, and evaluation. The difficulties of teaching with these three visual representations were categorized into several factors; teachers, students, the characteristics of the representations, and lack of resources and classroom environment. Teachers' limited perceptions about the role of visual representations were associated with the ways of using visual representations in their teaching. Implications for the effective use of visual representations for science learning and teaching were discussed.