• Journal of The Korean Society of Agricultural Engineers
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• v.62 no.1
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• pp.1-16
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• 2020

The APEX model has been developed for assessing agricultural management efforts and their effects on soil and water at the field scale as well as more complex multi-subarea landscapes, whole farms, and watersheds. Recently, a key component of APEX application, named APEX-Paddy, has been modified for simulating water quality by considering paddy rice management practices. In this study, the performance of the APEX-Paddy model was evaluated using field data at Iksan experimental paddy sites in Korea. The discharge and pollutant load data during 2013 and 2014 were used to both manually and automatically calibrate the model. The APEX auto-calibration tool (APEX-CUTE 4.1) was used for model calibration and sensitivity analysis. Results indicate that APEX-Paddy reasonably performs in predicting runoff discharge rate and nitrogen yield. However, sediment and phosphorus yield is not correctly predicted due to the limitation of model schemes. With APEX-Paddy, the performance in reproducing the discharge and nitrogen yield is found to be a satisfactory level after manual calibration. The manually calibrated model performed better than the automatically calibrated model in nearly all comparisons. For runoff, manual calibration reduced PBIAS while R² and NSE values of the automatically calibrated model were the same as the manual calibration. For T-N, NSE and PBIAS were reduced when using manual calibration, whereas R² value was the same as manual calibration. The limitation of the APEX-Paddy model for predicting sediment, as well as the phosphorous yield, was discussed in this study.

• Microbiology and Biotechnology Letters
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• v.32 no.2
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• pp.123-127
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• 2004

Pseudomonas sp. MBEL21 was newly isolated from soil samples and found to accumulate medium-chain-length Polyhydroxyalkanoates(MCL-PHAs) using oleic acid as a sole carbon source. Among the various nutrient limiting conditions examined, including nitrogen, sulfur and phosphorus, only phosphorus limitation supported the accumulation of MCL-PHAs up to 15 wt％ of dry cell weight in flask cultures. MCL-PHAs produced by Pseudomonas sp. MBEL21 was mainly composed of 3-hydroxy-5-cis-tetradecenoate. Fed-batch culture of Pseudomonas sp. MBEL21 by novel feeding strategies based on cell growth charcteristics was carried out under phosphorus limitation using oleic acid as a sole carbon source. The final cell concentration and PHA content of 82 g/L and 28 wt％, respectively, were obtained. Furthermore, PHA consisted of MCL-hydroxyalkanoates and 3-hydroxybutyrate could be produced using olive oil as a sole carbon source.

• Journal of The Korean Society of Grassland and Forage Science
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• v.39 no.2
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• pp.75-80
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• 2019

Oilseed rape is known to crop having low nitrogen use efficiency (NUE) but requires high levels of N fertilizer. NUE is associated with N remobilization from source to sink organ, consequently affects seed yield. Remobilization of leaf N is also related to transport of C/N metabolites in phloem. However, interaction between seed yield and phloem transport was not fully documented. In response to seed yield, N and C metabolites and their transport into seed from bolting to pod filling stage investigated in two contrasting genotypes (Capitol and Pollen) cultivated under ample (HN) or limiting nitrate (LN) supply. Seed yield was significantly reduced in N limitation and its reduction rate was much lower in Capitol than in Pollen compared to HN treated plants. Amino acid and protein content was higher in Capitol than in Pollen at bolting stage. They gradually decreased during plant development but not significant between two cultivars and/or two treatments. Glucose, fructose and sucrose content were 1.8-,1.6- or 1.25-fold higher in LN condition than in HN condition, respectively. Amino acid and sucrose content in phloem were largely higher in Capitol than in Pollen under LN condition. These results indicate that the higher seed yield might be related to greater transport ability of amino acid and sucrose in phloem under LN condition.

• Journal of Korean Society of Water and Wastewater
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• v.8 no.2
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• pp.1-11
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• 1994

This study was conducted to develop a new RBC process available for the effective removal of organic matters and nitrogen in sewage. The RBC process for the oxidation organic compounds and nitrification was designed to occur at the 1st-stage and next-stage RBC respectively. Then nitrified water was recycled to the denitrifying RBC located at the lower part of the 1st-stage RBC. Some results were summarized as follows. 1. The loading limitation was represented as $60g{\cdot}COD/gm^2/day$ in experiment of simultaneous removal of organic matter and nitrogen. The maxmum COD % removal was 85% at the load $35g{\cdot}COD/m^2/day$. 2. The $NO_3-N$ % removal was approximately 80% at the load $60g{\cdot}COD/m^2/day$ and the maximum $NO_3-N$ remaval rate was $3.9g{\cdot}COD/m^2/day$ and the overall C/N ratio of 11.0 as required to achive 80% of $NO_3-N$% removal. 3.$NO_3-N$ removal rate was rapidly decreased above the load $7g{\cdot}NH_4{^+}-N/m^2/day$ and the maximum $NO_3-N$ removal rate was $3.7g{\cdot}NO_3-N/m^2/day$. 4. Irrespective of the recycle ratio, the COD % removal at the system of 2-stage RBC unit was nearly constant as 89% while the maximum one in the 1st-stage unit was 77% in the case of 50% recycle. 5. The maximum COD % removal in the 3-stage RBC system was 93% while 1st-stage one being 80%, under the $NH_4{^+}-N$ load of $7.4g/m^2{\cdot}d$. Also maximum percentage of nitrification and denitrification was 69% and 41% respectively, under the same $NH_4{^+}-N$ load.

• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.3
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• pp.59-70
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• 2020

Obtaining external forced convection heat transfer from bubble boiling and validating it with experimental results using cryogenic liquids are suggested to derive total heat transfer coefficient with pool boiling condition in the case of coil type heat exchanger with a bundle of tubes and to overcome the limitation of using the empirical correlation. Experiment is conducted with pool boiling heat transfer of saturate liquid nitrogen with helical coil type heat exchanger using liquid oxygen as hot stream fluid. Experimentally measured heat transfer coefficient is well-agreed with the estimated curve considering nucleate boiling and forced convection induced by bubble rise.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.8 no.3
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• pp.251-261
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• 2003

As a part of an on-going project investigating flux of materials in Gomso Tidal Flat, we have monitored temporal and spatial distribution of nitrogen components(TN, PON, DON, DIN) and have sought the relationships with the freshwater input(tidal range, salinity), the biological activities(chlorophyll-${\alpha}$, TP, DIP, silicate) and the resuspended bottom sediment in seawater(SPM) from 1999 to 2000. TN in seawater was 39.05 $\mu\textrm{m}$ol 1$\^$-1/ (31.03∼42.93 $\mu\textrm{m}$ol 1$\^$-1/) without any statistical difference(p<0.05) between the studied periods. Organic nitrogen (DON and PON) occupied 75％, 95％, 73％, and 75％ in April, August, September and November, respectively. DON and PON have been found within the narrow concentration ranges of 11.30∼16.38 $\mu\textrm{m}$ol 1$\^$-1/ and 13.16∼20.04 $\mu\textrm{m}$ol 1$\^$-1/ in spite of severe environmental differences through the studied periods. Dissolved fractions of nitrogen(DON and DIN) occupied 53∼65％ of TN. Only DIN varied with an evident temporal variability: low concentrations(1.325∼1.616 $\mu\textrm{m}$ol 1$\^$-1/) in August and high enrichment(8.377∼14.65 $\mu\textrm{m}$ol 1$\^$-1/) in September. High consumption rate of DIN by phytoplankton and a long-lasted drought probably induced such low concentration of DIN in August. Eventually heavy precipitation probably introduced plenty of new nitrogen sources into Gomso Bay in September. The portion of PON, DON and DIN in the total nitrogen was 40％, 38％ and 22％, respectively. Their contents were in the order of DON>PON>DIN for the year round except PON>DON>DIN only in September. The highest DON portion in August probably due to the active microbial decomposition of organic material in summer. Only in April, some evident negative correlations have been found between chlorophyll-${\alpha}$ and DIN mostly nitrate(-0.64, p<0.01), phosphate(-0.46, p<0.01) and silicate(-0.55, p<0.01). The Si(OH)$_4$/DIN/DIP ratios in the water column suggests the limitation of DIN for the growth of phytoplankton during the dry summer in Gomso Bay, which was the case of August in this work. Even with some difference between the studied periods, the primary factors on the distribution of nitrogen components in seawater overlying the Gomso Tidal Flat have been the tidal range and the freshwater input, but the additional variations were due to the biological activities.

• Journal of Korean Society of Environmental Engineers
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• v.30 no.2
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• pp.181-189
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• 2008

Phosphate is the limiting factor leading to the eutrophication in nature and has been usually removed by the luxury uptake of PAOs(Phosphate accumulating organisms). The purpose of this study was the control of wastewater treatment removing phosphorus. The control of wastewater treatment process was performed by optimal and adaptive control. They were performed as followings. Firstly the inflow phosphate concentration was measured and the optimal aeration time was calculated by simplified ASM No. 2 for the phosphate to be 1.0 mg/L in effluent. It was optimal control. But when the phosphate concentration in effluent was not 1.0 mg/L, adaptive control was necessary to coincide the objective of control with real value. Then it was performed as the objective phosphate concentration in effluent was changed according to calculation of errors and it was adaptive control. The wastewater treatment process had been controlled by them for about one month. The range of phosphate concentration in effluent 0.2$\sim$3.2 mg/L and the average of it was 1.0 mg/L. The limitation of luxury uptake occurred two times while wastewater treatment process was running. After the analysis of laboratory tests, we knew the reasons were the shortage of ammonia nitrogen and the excessive aeration.

• Korean Journal of Ecology and Environment
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• v.36 no.2 s.103
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• pp.139-149
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• 2003

This study was conducted to determine limiting nutrients and the physiological characteristics of phytoplankton in response of nutrients in Lake Paldang from March 2002 to October 2002. A field research was conducted along with laboratory batch culture experiment to find the limiting nutrients and the growth kinetics. According the results of Chl. a TP relationship, TN/TP ratio, and nutrient addition bioassay, phosphorus appeared to be a major limiting nutrient in Lake Paldang and thus the lake productivity was greatly influenced by it. P limitation for the phytoplankton of Lake Paldang varied with season, and the possibility of limitation by nitrogen and silica also occurred. The degree of P limitation was greatest during spring when the concentration of dissolved phosphorus is relatively much lower than summer and autumn. The maximum growth rate (${\mu}_{max}$) and half saturation concentration ($K_u$) of Lake Paldang phytoplankton ranged from 0.8${\sim}$1.1$day^1$ and from 0.1${\sim}$O.8${\mu}M$, respectively. $K_u$ was highest during May ($0.8{\mu}M$) and the lowest during September ($0.1{\mu}M$). Such result may be induced by the phytoplankton cell quota that showed the lowest concentration ($0.13{\mu}gP/{\mu}gChl.$ a) during May. The growth kinetics showed that phytoplankton growth in Lake Paldang was faster during summer and autumn than spring, suggesting that the Potential of algal bloom is high after the summer monsoon season.

• ALGAE
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• v.19 no.3
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• pp.271-276
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• 2004

One hundred and fifty four micro algal strains, newly isolated from nationwide freshwaters in Korea, were screened for their anticancer, ant diabetic, and antibiotic activities. The micro algal strains were cultured with different nutritional conditions that were divided into 4 groups as follows; a normal Allen medium, nitrogen (N)-limited medium, phosphorus (P)-limited medium, and N and P-limited medium. Algal biomass was extracted with a mixture of acetone:H₂O (1:1, v:v) and the extracts were used for the screening of bioactive materials. Anticancer, ant diabetic, and antibiotic materials were screened by the methods of vaccinia Hl-related protein tyrosine phosphates (VHR DS-PTPase) inhibition, protein tyrosine phosphates 1B (PTP1B) inhibition, and paper disk. The inhibition activity of VHR DS-PTPase was observed in 18 strains, having a maximum 79% inhibition from Anabaena affinis and the inhibition activity of PTP1B was observed in 9 strains, having a maximum 97% from Sphaerocystis schroeteri. Microcystis aeruginosa incubated in an N and P-limited medium showed antibiotic activity in 8 species out of 13 pathogenic bacteria. As a whole, it seemed that the stressed condition such as N and/or P limitation increased the production of bioactive materials in micro algae.

• Journal of The Korean Society of Grassland and Forage Science
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• v.9 no.2
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• pp.68-76
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• 1989

The effect of characteristic of mixture sowing combination on the development of botanical composition was conducted for 12 years on the meadow experiment. The results of this study were summarized as follows. 1. Festuca pratensis lost the expected position of a dominant species. Its vegetation ratio decreased gradually until the last survey year. 2. Arrhenatherum elatius, known as a typical 2-cutting grasss, developed to a dominant species only in the 3- cutting plot without limitation. 3. Alopecurus pratensis, whose feeding value diminishes rapidly, developed to a dominant species regardless of N-fertilization under the condition of 3-cutting, even though the same small amount of seeding was introduced as usual. 4. Trisetum flavescens which causes calcinose exceeded the 40% of vegetation ratio which was the approved rate for feeding at the high N-level (2OOKgIha). 5. Among the introduced, the species showed the significance in quantity were Lotus corniculafus solely in the 2-cutting plot, and Trifolium repens solely in the 3-cutting plot. In the 3-cutting plot legume yet remained under N-fertilization. 6. The appropriate ratio of vegetation for the subordinate species in the mixture sowing combination was easily attained from the least amount of seeding (Gramineae with max. 3Kg/ha, Leguminosae with max. 2kgIha). 7. Into the mixture sowing combination, infiltrated unintroduced species marked more noticeably in the 2- cutting plot than in the 3-cutting plot.