• Honam Mathematical Journal
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• v.41 no.4
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• pp.799-812
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• 2019

We introduce flat e-covers of modules and define e-perfect rings as a generalization of perfect rings. We prove that a ring is right perfect if and only if it is semilocal and right e-perfect which generalizes a result due to N. Ding and J. Chen. Moreover, in the light of the fact that a ring R is right perfect if and only if flat covers of any R-module are projective covers, we study on the rings over which flat covers of modules are (generalized) locally projective covers, and obtain some characterizations of (semi) perfect, A-perfect and B-perfect rings.

• Atmosphere
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• v.27 no.4
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• pp.399-409
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• 2017

The impact of land cover changed by tidal flats on local meteorology in Gyeonggi Bay was quantitatively evaluated based on a numerical modeling approach during 18 days (21 June to 9 July 2013). The analysis was carried out using three sets of simulation scenarios and the land cover of tidal flats for each simulation was applied as follows: (1) the herbaceous wetland representing coastal wetlands (i.e., EXP-BASE case), (2) the barren or sparsely vegetated representing low tide (i.e., EXP-LOW case), (3) the water bodies representing high tide (i.e., EXP-HIGH case). The area of tidal flats was calculated as about $552km^2$ (the ratio of 4.7% for analysis domain). During the daytime, the change (e.g. wetlands to water) of land cover flooded by high tide indicated the decrease of temperature (average $3.3^{\circ}C$) and the increase of humidity (average 13%) and wind speed (maximum $2.9m\;s^{-1}$). The changes (e.g. wetlands to barren or sparsely vegetated) of land cover induced by low tide were smaller than those by high tide. On the other hands, the effects of changed land cover at night were not apparent both high tide and low tide. Also, during the high tide, the meteorological change in tidal flats affected the metropolitan area (about 40 km from the tidal flat).

• Bulletin of the Korean Mathematical Society
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• v.40 no.1
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• pp.167-176
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• 2003

In [3］, Del Valle, Enochs and Martinez studied flat envelopes over rings and they showed that over rings as in the title these are very well behaved. If we replace flat with injective and envelope with the dual notion of a cover we then have the injective covers. In this article we show that these injective covers over the commutative noetherian rings with global dimension at most 2 have properties analogous to those of the flat envelopes over these rings.

• Journal of The Korean Astronomical Society
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• v.35 no.2
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• pp.87-95
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• 2002

We have conducted VI CCD photometry of the open cluster NGC 6819 in order to understand the effects of dynamical evolution in old open clusters. Our photometry covers 18' $\times$ 18' on the sky, centered on the cluster, which seems to cover the whole cluster field. Our photometry reaches down to V $\approx$ 20.5, which allows us to analyze the luminosity function and spatial distribution of stars brighter than Mv $\approx$ 8.5. There is a clear evidence for mass segregation in NGC 6819, i.e., the giants and upper main-sequence stars are concentrated in the inner regions, whereas the lower main-sequence stars distribute almost uniformly throughout the cluster. The luminosity function of the main-sequence stars of NGC 6819 is almost flat. The flat luminosity function indicates that a large number of low mass stars has escaped from the cluster unless its initial mass function is much different from the Salpeter type (${\phi}(m){\propto} m^{-(1+x)},x = 1.35$).

• Spatial Information Research
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• v.11 no.2
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• pp.101-117
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• 2003

High resolution satellite image analysis has been recognized as an effective technique for monitoring local land-cover and atmospheric changes. In this study, a new high resolution map for land-cover was generated using both high-resolution IKONOS image and conventional land-use mapping. Fuzzy classification method was applied to classify land-cover, with minimum operator used as a tool for joint membership functions. In separateness analysis, the values were not great for all bands due to discrepancies in spectral reflectance by seasonal variation. The land-cover map generated in this study revealed that conifer forests and farm land in the ground and tidal flat and beach in the ocean were highly changeable. The kappa coefficient was 0.94% and the overall accuracy of classification was 95.0%, thus suggesting a overall high classification accuracy. Accuracy of classification in each class was generally over 90%, whereas low classification accuracy was obtained for classes of mixed forest, river and reservoir. This may be a result of the changes in classification, e.g. reclassification of paddy field as water area after water storage or mixed use of several classification class due to similar spectral patterns. Seasonal factors should be considered to achieve higher accuracy in classification class. In conclusion, firstly, IKONOS image are used to generated a new improved high resolution land-cover map. Secondly, IKONOS image could serve as useful complementary data for decision making when combined with GIS spatial data to produce land-use map.

• Journal of Environmental Science International
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• v.28 no.3
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• pp.341-356
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• 2019

In this study, the impacts of local meteorology caused by tidal changes in the West Sea on ozone distributions in the Seoul Metropolitan Area (SMA) were analyzed using a meteorological model (WRF) and an air quality (CMAQ) model. This study was carried out during the day (1200-1800 LST) between August 3 and 9, 2016. The total area of tidal flats along with the tidal changes was calculated to be approximately $912km^2$, based on data provided by the Environmental Geographic Information Service (EGIS) and the Ministry of Oceans and Fisheries (MOF). Modeling was carried out based on three experiments, and the land cover of the tidal flats for each experiment was designed using the coastal wetlands, water bodies (i.e., high tide), and the barren or sparsely vegetated areas (i.e., low tide). The land cover parameters of the coastal wetlands used in this study were improved in the herbaceous wetland of the WRF using updated albedo, roughness length, and soil heat capacity. The results showed that the land cover variation during high tide caused a decrease in temperature (maximum $4.5^{\circ}C$) and planetary boundary layer (PBL) height (maximum 1200 m), and an increase in humidity (maximum 25%) and wind speed (maximum $1.5ms^{-1}$). These meteorological changes increased the ozone concentration (about 5.0 ppb) in the coastal areas including the tidal flats. The increase in the ozone concentration during high tide may be caused by a weak diffusion to the upper layer due to a decrease in the PBL height. The changes in the meteorological variables and ozone concentration during low tide were lesser than those occurring during high tide. This study suggests that the meteorological variations caused by tidal changes have a meaningful effect on the ozone concentration in the SMA.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.4
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• pp.343-352
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• 2013

In this study, a smooth flat surface, low fin, Turbo-B, and Thermoexcel-E surfaces are used to examine the effect of the flow velocity on the pool boiling heat transfer coefficients (HTCs) and critical heat fluxes (CHFs). HTCs and CHFs are measured on a smooth square heater of $9.53{\times}9.53mm^2$ at $60^{\circ}C$ in a pool of pure water at various fluid velocities of 0, 0.1, 0.15, and 0.2 m/s. Test results show that for all surfaces, CHFs obtained with flow are higher than those obtained without flow. CHFs of the low fin surface are higher than those of the Turbo-B and Thermoexcel-E surfaces due largely to the increase in surface area and sufficient fin spaces for the easy removal of bubbles. CHFs of the low fin surface show even 5 times higher CHFs as compared to the plain surface. On the other hand, both Turbo-B and Thermoexcel-E surfaces do not show satisfactory results because their pore sizes are too small and water bubbles easily cover them. At low heat fluxes of less than $50kW/m^2$, HTCs increase as the flow velocity increases for all surfaces. In conclusion, a low fin geometry is good for application to steam generators in nuclear power plants.

• Journal of Animal Science and Technology
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• v.64 no.3
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• pp.564-573
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• 2022

In this study, considering the difficulties for all farms to convert farm styles to animal welfare-based housing, an experiment was performed to observe the changes in the behavior and welfare of sows when the slat floor was changed to a collective breeding ground. Twenty-eight sows used in this study were between the second and fifth parities to minimize the influence of parity. Using a flats floor cover, the flattening rates were treated as 0%, 20%, 30%, 40%, and 50%. Data collection was the behavior of sows visually observed using a camera (e.g., standing, lying, fighting and excessive biting behaviors, and abnormal behaviors) and the animal welfare level measured through field visits. Lying behavior was found to be higher (p < 0.01) as the flattening rate increased, and sows lying on the slatted cover also increased as the flattening rate increased (p < 0.01). Fighting behavior wasincreased when the flattening rate was increased to 20%, and chewing behavior was increased (p < 0.05) as the flattening rate increased. The animal welfare level of sows, 'good feeding', it was found that all treatment groups for body condition score and water were good at 100 (p < 0.05). 'Good housing' was the maximum value (100) in each treatment group. As the percentage of floor increased, the minimum good housing was increased from 78 in 0% flattening rate to 96 in 50% flattening rate. The maximum (100) 'good health' was achieved in the 0% and 20% flattening rates, and it was 98, 98, and 99 in the 30%, 50%, and 40% flattening rate, respectively. 'Appropriate behavior' score was significantly lower than that of other paremeters, but when the flattening ratio was 0% and 20%, the maximum and minimum values were 10. At 40% and 50%, the maximum values were 39 and 49, respectively, and the minimum values were analyzed as 19 for both 40% and 50%. These results will be used as basic data about sow welfare for farmers to successfully transition to group housing and flat floors.