• Journal of Radiation Protection and Research
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• v.44 no.4
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• pp.128-148
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• 2019

Massive environmental monitoring has been conducted continuously since the Fukushima Daiichi Nuclear Power accident in March of 2011 by different monitoring methods that have different features together with migration studies of radiocesium in diverse environments. These results have clarified the characteristics of radiological environments and their temporal change around the Fukushima site. At three months after the accident, multiple radionuclides including radiostrontium and plutonium were detected in many locations; and it was confirmed that radiocesium was most important from the viewpoint of long-term exposure. Radiation levels around the Fukushima site have decreased greatly over time. The decreasing trend was found to change variously according to local conditions. The air dose rates in environments related to human living have decreased faster than expected from radioactive decay by a factor of 2-3 on average; those in pure forest have decreased more closely to physical decay. The main causes of air dose rate reduction were judged to be radioactive decay, movement of radiocesium in vertical and horizontal directions, and decontamination. Land-use categories and human activities have significantly affected the reduction tendency. Difference in the air dose rate reduction trends can be explained qualitatively according to the knowledge obtained in radiocesium migration studies; whereas, the quantitative explanation for individual sites is an important future challenge. The ecological half-lives of air dose rates have been evaluated by several researchers, and a short-term half-life within 1 year was commonly observed in the studies. An empirical model for predicting air dose rate distribution was developed based on statistical analysis of an extensive car-borne survey dataset, which enabled the prediction with confidence intervals. Different types of contamination maps were integrated to better quantify the spatial data. The obtained data were used for extended studies such as for identifying the main reactor that caused the contamination of arbitrary regions and developing standard procedures for environmental measurement and sampling. Annual external exposure doses for residents who intended to return to their homes were estimated as within a few millisieverts. Different forms of environmental data and knowledge have been provided for wide spectrum of people. Diverse aspects of lessons learned from the Fukushima accident, including practical ones, must be passed on to future generations.

• Proceedings of the KSEEG Conference
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• 2002.04a
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• pp.59-61
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• 2002

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.4
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• pp.495-507
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• 1998

The transient characteristics of a 4.0㎾ inverter driven heat pump was investigated by theoretical and experimental studies. The heat pump used in this study consists of a high side scroll compressor and $\Phi$7 compact heat exchangers with two capillary tubes. A series of tests was peformed to examine the transient characteristics of heat pump in heating and cooling mode when the operating speed was varied from 30Hz to 102Hz. One of the major issues that has not been addressed so far is transient characteristics during speed modulation. A cycle simulation model has been developed to predict the cycle performance under frequency rise-up conditions, and the results of theoretical study were compared with the results of experimental study. The theoretical model was driven from mass conservation and energy conservation equations to predict the operation points of refrigerant cycle and the performances at various operating speeds. For transient conditions, the simulated results are in good agreement with the experimental results within 10%. The transient cycle migration of the liquid state refrigerant causes a significant dynamic change in system. Thus, the migration of refrigerant is the most important factor whenever An experimental analysis is performed or A simulation model is developed.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.277-278
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• 2002

Magnetron and Ion beam sputtering were used to texture the air-bearing surface of magnetic recording sliders. Flying height measurements and Laser-Doppler interferometry were used to compare the 'flyability' of textured and untextured sliders. Lubricant redistribution on the disk surface caused by slider/disk interactions was investigated using scanning ellipsometry (Surface Reflectance Analyzer (SRA)). The results show that slider surface texture causes only small changes in the flying height of sliders but reduces slider in-plane and out-of-plane vibrations. Textured sliders were found to cause less lubricant depletion on the disk surface than untextured sliders.

• Proceedings of the KSME Conference
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• 2001.06c
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• pp.246-250
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• 2001

In resin transfer molding (RTM), resin is forced to flow through the fiber perform of inhomogeneous permeability. This inhomogeneity is responsible for the mismatch of resin velocity within and between the fiber tows. The capillary pressure of the fiber tows exacerbates the spatial variation of the resin velocity. The resulting microscopic perturbations of resin velocity at the flow front allow numerous air voids to form. In this study, a mathematical model was developed to predict the formation and migration of micro-voids during resin transfer molding. A transport equation was employed to account for the migration of voids between fiber tows. Incorporating the proposed model into a resin flow simulator, the volumetric content of micro-voids in the preform could be obtained during the simulation of resin impregnation.

• Journal of the Korean Ceramic Society
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• v.29 no.11
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• pp.888-892
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• 1992

The chemically induced grain-boundary migration has been studied in MgAl2O4 spinel under ZnO atmosphere. MgAl2O4 compacts been prepared by sintering powder mixture of Al2O3 and MgO at 1$600^{\circ}C$ for 60 h in air. The sintered MgAl2O4 has been heat-treated at 150$0^{\circ}C$ in a ZnO atmosphere. During the heat-treatment grain boundaries have become curved or faceted, and the total area of grain boundaries have increased. In the migrated region, the ZnO content is higher by 6 wt% than that in other regions, indicating that the migration was induced by addition of ZnO. In some shrinking grains, the faceted planes of different grain boundaries for the same grain are parallel to each other. This result provide an experimental support for the coherency strain energy in diffusion layer of the shrinking grain as being the major driving force. Calculated coherency strain energy of MgAl2O4 shows the maximum at {111} planes and the minimum at {100} planes. Although the minimum surface energy is at {111} planes, the faceted moving boundaries are expected to be {100} planes because of lowest driving force for the grain-boundary migration.

• Journal of the Korean Regional Science Association
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• v.39 no.4
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• pp.111-125
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• 2023

China's rapid economic growth and accelerated urbanization have significantly increased labor force mobility. The choice of city residence and long-term residence intentions of migrants will have significant consequences on both economic output and societal dynamics. This paper investigates the impact of air quality on the long-term residence intention of migrants. By matching an individual-level survey on willingness to stay in the long run and the city-level air quality, represented by PM2.5, we find that the willingness to stay in the long run increases with better air quality. This implies that public policy to maintain good air quality is crucial in keeping those who moved to the city.

• Journal of Navigation and Port Research
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• v.34 no.10
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• pp.787-792
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• 2010

It is necessary to predict the penetration of chloride ions for designing RC construction in marine environments. However, it takes a long time to obtain chloride migration coefficients. Therefore, the rapid chloride penetration test (RCPT) is generally used to shorten the test time. But there is a difference between chloride migration coefficients determined by rapid chloride penetration tests and those based on exposure in marine environments. In this study, we evaluated the effect on the chloride ion migration coefficient caused by a change in voltage and NaCl concentration. We also compared the relationship between the chloride ion migration coefficient by RCPT and that by exposure in marine environments. As a result of the experiments, we found that there is only a small change in the experimental factors based on changes in voltage and NaCl concentration and since they are so small, we can conclude that they are in the range of experimental error and test results from chloride ion migration coefficients by RCPT and exposure were very different from each other. In the exposure experiments, when the water-cement ratio was increased, the smaller fine air gaps in concrete affected the chloride ion migration coefficient.

• Korean Journal of Environment and Ecology
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• v.23 no.1
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• pp.50-55
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• 2009

To understand the status of the migrating Oriental Honey Buzzard(Pernis ptilorhynchus) in Korea, we carried out a preliminary study on the number and local movements of the Honey Buzzard from September 2005 to October 2007 at Hongdo Island, Jeonnam Province, Korea. A total of 702 Honey Buzzards in 2005, 404 individuals in 2006, and 659 individuals in 2007 were recorded during the fall migration season, but during the spring migration season only two and eight birds were observed in 2006 and 2007 respectively. The migrating Honey Buzzard showed peak numbers from 20 September to 5 October at the study site. According to observation of arrival time of538 Honey Buzzard in October 2007, a total of 2l6 birds(40.l %) were passing over Hongdo Island between 7:00 AM to 8:00 AM, rising skyward on columns of warm air. This suggests the use of thermal currents and avoidance of nocturnal movement for crossing water. They preferred moderate winds(<5 m/s in speed) from northwest, but the migrating number apparently decreased in case of strong winds (${\geqq}5 m/s$). This suggests that wind speed and direction are important environmental factors for migration of the Oriental Honey Buzzard. At present, it is unclear which breeding population(from north-eastern China or Japan) passes over Hongdo Island. Moreover, it is difficult to prove migration route and to understand migratory behaviors of the Oriental Honey Buzzard in Korea. To prove the breeding sites and routes of the migrants over the study site, we need more detailed and further studies such as satellite tracking researches.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.3 no.1
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• pp.22-36
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• 1993

This study was conducted to evaluate the charcoal tube sampling method for carbon disulfide in the air. Breakthrough was investigated according to flow rate, sampling time and air volume. Also the storage stability by storage method and time was investigated. The results are summarized as follows. 1. The samples stored at room temperature($28.2^{\circ}C$), refrigerator($3.8^{\circ}C$) and freezer($-15.6^{\circ}C$) were analyzed every week to five weeks. At one week storage at room temperature, 3.5% of $CS_2$ in the front section of the charcoal tube migrated into the back section and 57.7% at five weeks. The amount of $CS_2$ in the back section of the charcoal increased continuously by storage time. Migration of $CS_2$ was slow at refrigerator, and stopped occur at freezer. Recovery rate $CS_2$ was 52-82% at room temperature and 92-101% at refrigerator, based on the amount at freezer as a reference value. Thus loss was observed at room temperature. 2. When 6-48 L of fresh air were passed through tubes with spiked amounts of 0.379 and 0.759mg sample, the amounts of $CS_2$ in the back section of charcoal were 5.7-132.4 and 0-92% of the amount in the front section, respectively. The total recovery rates of$CS_2$ from 0.379 and 0.759mg spiked sample were 35.7-101.0% and 9l.3-100.1%, respectively. $CS_2$ loss was observed in 0.379mg spiked sample, but not in 0.759mg spiked sample. In the spiked samples, the amount of $CS_2$ in the back section of charcoal was not affected by flow rate when the air volume was controlled. The amount of $CS_2$ in the back section of charcoal increased over sampling time. And the faster the flow rate, the more the migration amount when the sampling time was the same. 3. A known concentration, 10 ppm of $CS_2$, was produced in a 200 L Tedlar bag. When the air volume was 24, 36, 48 L, breakthrough was 5.8, 16.9, 47.4%, respectively. The sampling flow rate of 0.05, 0.1, 0.2 Lpm did not change the breakthrough rate. Breakthrough increased over sampling time. And the faster the flow rate, the more the breakthrough, when the sampling time was the same.