• Journal of Korean Society on Water Environment
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• v.33 no.5
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• pp.538-545
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• 2017

The purpose of this study is to investigate growth response and toxigenicity under various temperature and nutritional conditions, in order to understand the physioecological characteristics of Aphanizomenon flos-aquae, which is a bloom-forming cyanobacterium in the Nakdong River. The strain was inoculated into media under combinations of four temperatures (4, 12, 21, $30^{\circ}C$) and three nutrients (modified CB medium, P-depleted CB medium, N-depleted CB medium) for 28 days. The algae-inhibition tests were performed to assess the potential allelopathic effects of the strains' filtrates on the growth of four algae strains (Microcystis aeruginosa, Aulacoseria ambigua f. spiralis, Aphanizomenon flos-aquae, Scenedesmus obliquus). Toxin production of a strain was measured by Enzyme-Linked ImmunoSolbent Assay (ELISA). The optimal growth temperature (Topt) of strains was $19.9^{\circ}C$ ($18.3-21.2^{\circ}C$), and the temperature range for growth was from $-0.3^{\circ}C$ to $34.3^{\circ}C$. Specific growth rate (${\mu}$) in modified CB medium varied from 0.10 to $0.16day^{-1}$, and the maximum growth rate (${\mu}_{max}$) was $0.17day^{-1}$. Although growth curves under N-existed and N-depleted conditions were almost the same, growth under N-depleted condition was relatively slowed (${\mu}=0.09$ to $0.14day^{-1}$), with a decreased maximum cell density. However, growth under the P-depleted condition was restricted for all temperatures, Two stains of Aphanizomenon flos-aquae were confirmed as not producing toxins, because saxitoxin and cylindrospermopsin were not detected by ELISA. The exudates or filtrates from the Aphanizomenon flos-aquae (DGUC003) resulted in significant inhibition of algal growth on the Aulacoseira ambigua f. spiralis (DGUD001) and Aphanizomenon flos-aquae (DGUC001) (p < 0.01).

• Geomechanics and Engineering
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• v.17 no.4
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• pp.393-403
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• 2019

The cycling impact test of red sandstone soil under different axial pressure and different impact loads are conducted to reveal the mechanical properties and energy consumption mechanism of red sandstone soil with static-dynamic coupling loading. The results show that: Under the action of different axial pressure and different impact loads, the peak stress of the specimen increases, and then tends to be stable with the times of impact. With the increase of impact times, the specific energy absorption value of the red sandstone soil specimen is increased first and then gentle development trend. When the impact loads are certain, the larger the axial pressure is, the smaller the peak value of energy absorption, which indicates that the energy utilization rate is not high under the condition of large axial pressure. Through the analysis of energy utilization, it is found that the smaller the impact load, the higher the energy utilization rate. The greater the axial pressure, the lower the energy utilization rate. when the axial pressure is large, the impact loads corresponding to the maximum values of reflectivity, transmissivity and absorptivity are the same. The relationship between reflectivity and transmissivity is negatively correlated.

• Journal of Korean Society of Water and Wastewater
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• v.12 no.4
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• pp.78-85
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• 1998

Strains degrading and decolorizing reactive dyes, Procion blue HEGN and Procion red HE7B were isolated from water system, are named as RBK1 and RRK, the growth characteristics of which were investigated. Decolorization efficiencies after 42 hrs in batch culture were 95% and 77%, respectively. and the optimal culture condition of temperature and pH were $30^{\circ}C$, 7.0. Decolorization efficiencies in condition of aerobic shaking culture by strains RBK1 and RRK conspicuously increased, and culture by strain RBK1 was found as 95% after 42 hrs, while standing culture was 64%, Optimum nitrogen source was peptone, and It was found that decolorization efficiencies by strains RBK1 and RRK increased up to 4,000mg/l of peptone concentration as nitrogen source, but peptone concentration did' nt influence the decolorization efficiency in above 4,000mg/l. When the concentration of dyes were more than 800 mg/l and 400 mg/l respectively, the strains RBK1 and RRK, which degrade Procion bule HEGN and Procion red HE7B, showed a sharply decreased decolorization efficiencies; then the specific growth rate were $0.25hr^{-1}$ and $0.09hr^{-1}$.

• 한국생물공학회:학술대회논문집
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• 2001.11a
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• pp.762-766
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• 2001

The nar promoter of Escherichia coli was known to induce maximally under anaerobic or microaerobic conditions in the presence of nitrate. In this study, the nar promoter was tested to see whether the expression level of a reporter gene which fused lacZ gene at nar promoter's downstream, in the some gram negative host strains(Agrobacterium, Pseudomonas and Rhizobium). A nar promoter system(Combination of nar promoter and gram negative strain) was grown under aerobic conditions to absorbance at 600 nm of nearly 2.0 and then, the nar promoter was induced by lowering DO to 1-2% with alternating microaerobic and aerobic condition in the fermentor cultures, using different gram negative hosts. For a wild type nar promoter (pNW61), it was possible to maintain production of ${\beta}-galactosidase$ activity per cell(specific ${\beta}-galactosidase$ activity) at 14,000, 9600, 45 Miller units in the presence of 1% nitrate. and for a nitrate - independent nar promoter (pNW618) at 12,000, 10,400 and 58 Miller units in the absence of nitrate ion, respectively.

• Tribology and Lubricants
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• v.9 no.1
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• pp.38-44
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• 1993

The present study was undertaken to investigate the dry wear characteristics of die steel STD 11 for cold molding. The wear test was experimentally carried out under different conditions using a wear device, which was made in laboratory, and in which annular surfaces of wear testing specimens wear rubbed in dry sliding condition with varying the sliding speed, contact pressure, and sliding distance. The wear loss by variation of sliding speed was much in 0.3 m/sec and less in higher speed range above its sliding speed according to formation of the boundary lubrication film. The critical sliding speed with maximum value of the specific wear rate switched over to lower speed side according. as contact pressure increased. The critical sliding distance was increased with decrease in oxidation reaction velocity. The depth below subsurface showing maximum hardness (Hv) came out at the position, $60 \mu m$, of the maximum shear stress due to strain hardening.

• Journal of the Korean Society of Food Science and Nutrition
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• v.28 no.5
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• pp.1010-1016
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• 1999

Protease related mold was isolated and selected as a starter culture for commercial production of meju. Isolated microorganism was identified as Syncephalastrum racemosum PDA 132 2. To obtain basic data about protease for production of soybean peptides and application of the strain in meju fermentation, we extrated and purified protease and charateristics of the enzyme were investigated. The optimum condition for the production of enzyme was pH 4.0, 30oC, 5 days. The protease was purified 19.7 folds by gel filtration and ion exchange chromatography and specific activity was 12.4unit/mg. The purified enzyme was 34kDa in size, thiol protease(100% inhibited by PCMB), and was acidic protease(stable between pH 2.0~5.0). Vmax of the enzyme was 2.14 g/min which was lower(1/50) than that of by Asp. wentti and B. subtilis.

• Microbiology and Biotechnology Letters
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• v.36 no.2
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• pp.165-172
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• 2008

To find the optimum growth and metal removal condition of isolated strain LH2, effects of the environmental factors such as medium pH, growth temperature, and metal concentrations were investigated. Based on the 18S rDNA analysis, the isolated strain was identified to Exophiala sp. with 100% homology. Isolated strain Exophiala sp. LH2 showed maximum removal efficiency of metals at the shaking conditions of pH 7 and $25^{\circ}C$. When the concentration of metal was under 200ppm, the specific metal removal velocity at pH 7 increased from 0.01 to 4.43 mg-metal $L^{-1}{\cdot}d^{-1}{\cdot}mg{\cdot}DCW^{-1}$ as the concentration of metal increased from 10 ppm to 200 ppm. When 200 ppm of each metal was contained in the culture medium adjusted with pH 7, metal removal efficiencies Cr, Cu, Ni, Pb and Zn were 99.28%, 97.67%, 91.94%, 99.77%, 99.61%, respectively.

• KSBB Journal
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• v.32 no.2
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• pp.124-132
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• 2017

A methane-oxidizing bacterium was isolated from rice paddy field soil around Jeollanam-do province, Korea, and characterized. The isolate was gram-negative, orange pigmented and short rod ($1.1-1.2{\times}1.6-1.9{\mu}m$). It was catalase and urease-negative but oxidase-positive. The strain utilized methane and methanol as sole carbon and energy sources. It had an ability to grow with an optimum pH 7.0 and an optimum growth temperature $30^{\circ}C$. The strain was resistant to antibiotic polymyxin B but sensitive to streptomycin, kanamycin, ampicillin, chloramphenicol and rifampicin. The isolate required copper for their growth with concentration range of $2-25{\mu}M$, with an optimum of $10{\mu}M$. Under optimal culture condition, specific cell growth rate and generation time were found to be $0.046hr^{-1}$ and 15.13 hr, respectively. Phylogenetic analysis based on 16S rDNA sequences indicated that the strain formed a tight phylogenetic lineage with Methylomonas koyamae with a value of 99.4% gene sequence homology. So, we named the isolate as Methylomonas sp. SM4. 8.6 mM methanol was accumulated in the reaction mixture containing 70 mM sodium formate and 40 mM $MgCl_2$ (MDH inhibitor) under atmosphere of methane:air (40:60) mixture for 24 hr at $30^{\circ}C$.

• KSBB Journal
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• v.21 no.2
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• pp.85-89
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• 2006

Typical property of the white-rot fungi is their ability to degrade lignin and other aromatic compounds with non-specific extracellular enzyme. In this work, the modification of the strain(Funalia trogii ATCC 200800) and the culture condition was performed to enhance enzyme productivity. Single cell was separated by the protoplasts formation and several putative laccase and manganese peroxidase inducers were tested. By adopting the modified strain, enzyme productivity increased comparing with that of the original strain. Extracellular enzyme formation was highly stimulated by the addition of copper and various aromatic compounds in the glucose-based culture medium.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.3
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• pp.624-635
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• 1990

Analytical study based on linear fracture mechanics was conducted on propagation behavior of inclined surface crack in semi-infinite elastic body. The analytical model was assumed to be inclined surface crack under plane strain condition upon which Hertzian stress was superimposed. Supposing continuous distribution of dislocation and applying Erdogan-Gupta's method to this crack problem, the stress intensity factors $K_{I}$ and $K_{II}$) at the crack-tip were obtained for various Hertzian contact positions. Analytic results have shown that driving force for crack growth is $K_{I}$ for non-lubricated condition and $K_{II}$ for fluid and boundary lubricated condition. The coefficient of friction at the hertzian contact and crack surfaces plays an important role in predicting the direction of crack propagation. It is also found that the maximum effective stress intensity factor exists at cracks of a certain specific length depending on lubricated condition.ion.n.