• Structural Engineering and Mechanics
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• v.86 no.4
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• pp.443-459
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• 2023

This study investigates the theoretical thermal buckling analyses of thick porous rectangular functionally graded (FG) plates with different geometrical boundary conditions resting on a Winkler-Pasternak elastic foundation using a new higher-order shear deformation theory (HSDT). This new theory has only four unknowns and involves indeterminate integral variables in which no shear correction factor is required. The variation of material properties across the plate's thickness is considered continuous and varied following a simple power law as a function of volume fractions of the constituents. The effect of porosity with two different types of distribution is also included. The current formulation considers the Von Karman nonlinearity, and the stability equations are developed using the virtual works principle. The thermal gradients are involved and assumed to change across the FG plate's thickness according to nonlinear, linear, and uniform distributions. The accuracy of the newly proposed theory has been validated by comparing the present results with the results obtained from the previously published theories. The effects of porosity, boundary conditions, foundation parameters, power index, plate aspect ratio, and side-to-thickness ratio on the critical buckling temperature are studied and discussed in detail.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.9
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• pp.116-121
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• 2020

In recent times, fuel economy enhancement and environmental regulation compliance have become the main topics of interest in the automobile industry. Electric vehicles are desirable alternatives to the existing cars that employ internal combustion engines. Specifically, electric vehicles are equipped with inverters, motors, and a gearbox instead of engines and transmission mechanisms. The gearbox is a key component, used to transmit power from the electric motor to the wheel. Therefore, the design of the gearbox is critical. However, most engineers design gears based only on their experience because no standards pertaining to the design factor exist, other than those for the gear ratios. To overcome this problem, the structural stabilities must be examined considering the design factors of the gears. In this study, we considered the module and number of teeth as the main factors. The constraints corresponded to the final gear ratio and fixed distance between each axle of the shafts. Moreover, a structural analysis was conducted, and the variation trend of the maximum equivalent stress against changes in the gear module and number of teeth was examined. By performing such an analysis, the structural stability in the design of a gear system could be effectively investigated.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.62 no.3
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• pp.166-171
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• 2017

For high-quality colored rice production, the cultivation environment is a critical factor. The major environmental factor is temperature, which includes the accumulated and average temperature during vegetative and reproductive stages. Generally, during the cultivation period, the temperature can be controlled by shifting the transplanting date. This study was carried out to determine the optimum transplanting date for high-quality red-colored rice production. Four red-colored rice varieties (Jeokjinju, Jeokjinjuchal, Hongjinju, and Gunganghongmi) were used as test materials. The transplanting dates were May 20 and June 5, 20, and 30 in 2015~2016. The most variable factor controlled by the transplanting date was the grain filling rate. The varieties transplanted on June 30 showed low yields owing to the decrease in the grain filling rate. In contrast, the polyphenol content increased with increasing delay in the transplanting date. Collectively, these two results indicate that the optimum transplanting date was June 20. The average temperature for 30 days after the heading date (30DAH) highly affected the polyphenol content. A lower temperature during the 30DAH induced higher polyphenol contents but also caused low yield. The optimum 30DAH temperature for obtaining a higher yield and polyphenol content was $22{\sim}23^{\circ}C$. Using the average 30DAH and accumulated temperatures, the optimum transplanting date was calculated as June 18 to 24 in Miryang region. The optimum transplanting date of Kyeungsangnamdo region was approximately mid-June to early July, and that of Kyeungsangbukdo region was approximately early to mid-June.

• Korean Journal of Environmental Agriculture
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• v.23 no.3
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• pp.142-147
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• 2004

Dissipation pattern of tebuconazole was evaluated by establishing application methods of the fungicide, paper-bagging of grape during growth and washing of grape after harvest. Application times increased from three to five resulted in high levels of residues in grape. Tebuconazole in grapes was present in different residual patterns with periods after final treatment ranging from 7 to 25 days. Significant differences in the residual patterns were also found when tebuconazole was treated during three different application periods, possibly due to meteorological condition and/or grape growth during each period. At the range from 2.5 g to 7.5 g of grape granules, residues were higher in small-sized grape than in big-sized grape and were mostly distributed on the peel of the grapes. Paper-bagging was a critical factor for reducing the fungicide residue on the peel. flesh of bagged and no-bagged grape had very low level of residues, 0.01 mg/kg and 0.05 mg/kg, respectively. Residues on grape was effectively eliminated with the washing methods suggested, a consecutive sinking-washing system Using of detergent solution during washing showed maximum residue reduction from grape. The washing methods showed effective action on the removal of lower content providing complete elimination, or almost, of the residues.

• Korean Journal of Agricultural and Forest Meteorology
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• v.13 no.2
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• pp.48-55
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• 2011

Solar radiation components reflected by the sea surface ($R_{ss}\uparrow$) are additional energy sources comprising the solar radiation regime. Previous studies, based on observational approaches, indicated that $R_{ss}\uparrow$ is an available climatological resource. However, an estimation process for $R_{ss}\uparrow$ has not been established. In this case study over Jeju Island in South Korea, we applied a new estimation process to solar radiation modeling and discussed the spatial distribution of $R_{ss}\uparrow$ and its seasonal variation. Our results showed that the illuminated area and the intensity of $R_{ss}\uparrow$ became greatest at the winter solstice and least at the summer solstice. We estimated the illuminated area of $R_{ss}\uparrow$ as it expanded over the southern slope of Jeju Island. At the winter solstice, on a daily basis, the area and intensity of illumination by $R_{ss}\uparrow$ were $182.3km^2$ and $0.41\;MJ\;m^{-2}\;day\;{-1}$, respectively. Comparing the daily accumulative and instantaneous values of $R_{ss}\uparrow$ intensity, the difference was about 20 times greater in daily cases than in instantaneous cases. On the other hand, for instantaneous values, the $R_{ss}\uparrow$ intensity accounted for up to 33% of the three components, i.e., direct, diffuse and reflected radiation in winter solstice. In addition, it was estimated that the sea surface reflectance depended on the wind speed. Therefore, in a practical use of this revised model, wind conditions should be considered as a critical factor in estimating $R_{ss}\uparrow$.

• Korean Journal of Ecology and Environment
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• v.37 no.2 s.107
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• pp.180-192
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• 2004

This study was carried out to assess the seasonal variation of water quality and the effect of pollutant loading from watershed in a shallow eutrophic reservoir (Shingu reservoir) from November 2002 to February 2004, Stable thermocline which was greater than $1^{\circ}C$ per meter of the water depth formed in May, and low DO concentration (< 2 mg $O_2\;L^{-1}$) was observed in the hypolimnion from May to September, 2003. The ratio of euphotic depth to mixing depth ($Z_{eu}/Z_{m}$) ranged 0.2 ${\sim}$ 1.1, and the depth of the mixed layer exceeded that of the photic layer during study period, except for May when $Z_{eu}$ and $Z_{m}$ were 4 and 4.3 m, respectively. Most of total nitrogen, ranged 1.1 ${\sim}$ 4.5 ${\mu}g\;N\;L^{-1}$, accounted for inorganic nitrogen (Avg, 58.7%), and sharp increase of $NH_3$-N Hand $NO_3$-N was evident during the spring season. TP concentration in the water column ranged 43.9 ${\sim}$ 126.5 ${\mu}g\;P\;L^{-1}$, and the most of TP in the water column accounted for POP (Avg. 80%). During the study period, DIP concentration in the water column was &;lt 10 ${\mu}g\;P\;L^{-1}$ except for July and August when DIP concentration in the hypolimnion was 22.3 and 56.7 ${\mu}g\;P\;L^{-1}$, respectively. Increase of Chl. a concentration observed in July (99 ${\mu}g\;L^{-1}$) and November 2003 (109 ${\mu}g\;L^{-1}$) when P loading through two inflows was high, and showed close relationship with TP concentration (r = 0.55, P< 0.008, n = 22). Mean Chl. a concentration ranged from 13.5 to 84.5 mg $L^{-1}$ in the water column, and the lowest and highest concentration was observed in February 2004 (13.5 ${\pm}$ 1.0 ${\mu}g\;L^{-1}$) and November 2003 (84.5 ${\pm}$29.0 ${\mu}g\;L^{-1}$), respectively. TP concentration in inflow water increased with discharge (r = 0.69, P< 0.001), 40.5% of annual total P loading introduced in 25 July when there was heavy rainfall. Annual total P loading from watershed was 159.0 kg P $yr^{-1}$, and that of DIP loading was 126.3 kg P $yr^{-1}$ (77.7% of TP loading. The loading of TN (5.0ton yr-1) was 30 times higher than that of TP loading (159.0 kg P yr-1), and the 78% of TN was in the form of non-organic nitrogen, 3.9 ton $yr^{-1}$ in mass. P loading in Shingu reservoir was 1.6 g ${\cdot}$ $m^{-2}$ ${\cdot}$ $yr^{-1}$, which passed the excessive critical loading of Vollenweider-OECD critical loading model. The results of this study indicated that P loading from watershed was the major factor to cause eutrophication and temporal variation of water quality in Shingu reservoir Decrease by 71% in TP loading (159 kg $yr^{-1}$) is necessary for the improvement of mesotrophic level. The management of sediment where tine anaerobic condition was evident in summer, thus, the possibility of P release that can be utilized by existing algae, may also be considered.

• Korean Journal of Ecology and Environment
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• v.36 no.2 s.103
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• pp.181-190
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• 2003

An investigation was conducted on the aquatic environment of the Okchon Stream watershed six times from May to September 2002. The results of investigation revealed that variation of environmental factors were quite significant for each stream and reach, showing a significant difference between running water and stagnant water. Aquatic nutrients were relatively low in the upstream, gradually increasing as the influx of treated wastewater into the stream increased. This suggests that the point source definitely affected the nutrient content of the stream. In particular, the variations of SRP and $NH_4$ were very distinct in the watershed compared to other nutrients. Thus, it can be considered as a major factor in evaluating the effect of treated wastewater. Immediately after the influx of treated waste-water, the average content of SRP rose to 919.3 ${\mu}g$ P/l. This was a very effective level in the watershed, suggesting that the percentage of the nutrients in the water was controlled by the content of P. The constant supply of treated wastewater was found to be a critical factor in triggering the increase in chl-a in the embayment of the stream. With the proliferation of the blue-green algae, the content of chl- a ranged 234.5${\sim}$1,692.2 ${\mu}g/l$. The maximum standing crops exceeded $1.0{\times}10^6$ cells/ml in August, which was more than 200 times the level for red tide in the freshwater. This result was well reflected in other environmental factors, with 100% of AFDM/TSS reflecting the severity of water pollution by algae. Therefore, the reduction of P and N con-tents in the treated wastewater is critical in improving the aquatic environment of the stream as well as water quality management for the reservoir.

• Korean Journal of Environment and Ecology
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• v.32 no.3
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• pp.342-350
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• 2018

The purpose of this study was to identify the environmental factors that affect the beginning and end of calling by Hyalessa fuscata and Cryptotympana atrata, which are dominant cicada species in the central urban areas of Korea. The study area was Banpo Apartments in Seoul. The research period included two months, being from the end of July to the end of August 2015. We analyzed the start and end time of cicada calling, and on average H. fuscata started calling at 5:21 am and C. atrata started at 7:40 am. The average end time of calling was 6:31 pm for H. fuscata and 7:51 pm for C. atrata. From the scatter plot and box plot results, H. fuscata started calling at 05:00 am, whereas C. atrata consistently stopped calling at 20:00 pm compared to H. fuscata. Multiple regression analysis of the start and end time of cicada calling showed that sunrise time was a factor affecting the start of H. fuscata calling. The end time of H. fuscata calling was affected by sunset time and total cloud cover. The starting time of C. atrata calling was mostly affected by temperature and sunrise time. The effect of temperature was greater than that of sunrise time. The end time of C. atrata calling was strongly affected by sunset time, whereas peak temperature was also shown to affect the end time. From the above results, sunrise and sunset are thought to be the critical factor affecting the start and end time of H. fuscata calling. Therefore, H. fuscata started calling with sunrise, and the end time was also affected by sunset. Temperature was the factor most affecting the start of C. atrata calling and sunset was identified as the factor affecting the end time. Therefore, the start time of C. atrata calling shows variation with daily temperature changes, and C. atrata stop calling simultaneously with sunset.

• Journal of Korea Water Resources Association
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• v.47 no.9
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• pp.767-776
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• 2014

Changes in climate have largely increased concentrated heavy rainfall, which in turn is causing enormous damages to humans and properties. Floods are one of the most deadly and damaging natural disasters known to mankind. The flood forecasting and warning system concentrates on reducing injuries, deaths, and property damage caused by floods. Therefore, the exact relationship and the spatial variability analysis of hydrometeorological elements and characteristic factors is critical elements to reduce the uncertainty in rainfall-runoff model. In this study, grid resolution depending on the topographic factor in rainfall-runoff models presents how to respond. semi-distribution of rainfall-runoff model using the model GRM simulated and calibrated rainfall-runoff in the Gamcheon and Naeseongcheon watershed. To run the GRM model, input grid data used rainfall (two event), DEM, landuse and soil. This study selected cell size of 500 m(basic), 1 km, 2 km, 5 km, 10 km and 12 km. According to the resolution of each grid, in order to compare simulation results, the runoff hydrograph has been made and the runoff has also been simulated. As a result, runoff volume and peak discharge which simulated cell size of DEM 500 m~12 km were continuously reduced. that results showed decrease tendency. However, input grid data except for DEM have not contributed increase or decrease runoff tendency. These results showed that the more increased cell size of DEM make the more decreased slope value because of the increased horizontal distance.

• Korean Journal of Ecology and Environment
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• v.56 no.2
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• pp.151-160
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• 2023

Cyanobacteria Pseudanabaena strains are known to produce 2-MIB(odorous material) in freshwater systems, thereby causing problems in water use. However, their physiological responses to environmental factors in relation with 2-MIB production is not well explored. This study was conducted to evaluate the effect of temperature on the growth and 2-MIB production of Pseudanabaena redekei. The experimental cyanobacteria strains were separated from the Uiam Reservoir (North Han River) and cultured in the BG-11 medium. Temperature was set to 10, 15, 20, 25, and 30℃ for the experiment, in the reflection of the seasonal water temperature variation in situ. For each temperature treatment, cyanobacterial biomass(Chl-a) and 2-MIB concentration (intra-cellular and extra-cellular fractions) were measured every 2 days for 18 days. Both maximal growth and total 2-MIB production of P. redekei appeared at 30℃. While intra-cellular 2-MIB contents were similar (26~29 ng L^-1) regardless of treated temperatures, extra-cellular 2-MIB concentration was higher only in high temperature conditions (25~30℃), indicating that the extents of 2-MIB biosynthesis and release by P. redekei vary with temperature. The 2-MIB productivity of P. redekei was much higher in low-temperature conditions (10~15℃) than high temperature conditions (25~30℃). This study demonstrated that temperature was a critical factor contributing to 2-MIB biosynthesis and its release in cell growth (r=0.605, p<0.01). These results are important to understand the dynamics of 2-MIB in the field and thereby provide basic information for managing odorous material in drinking water resources.