• Korean Journal of Materials Research
• /
• v.22 no.11
• /
• pp.591-597
• /
• 2012

For heat exchanger applications, 2-ply clad materials were fabricated by rolling of aluminum (Al) and mild steel sheets. Effects of annealing temperature on interface properties, especially on inter-layer formation and softening of strain hardened mild-steel, for Al/mild steel clad materials, were investigated. To obtain optimum annealing conditions for the Al/mild steel clad materials, annealing temperature was varied from room temperature to $600^{\circ}C$. At the annealing temperature about $450^{\circ}C$, an inter-layer was formed in an island-shape at the interface of the Al/mild steel clad materials; this island expanded along the interface at higher temperature. By analyzing the X-ray diffraction (XRD) peaks and the energy dispersive X-ray spectroscopy (EDX) results, it was determined that the exact chemical stoichiometry for the inter-layer was that of $Fe_2Al_5$. In some samples, an X-layer was formed between the Al and the inter-layer of $Fe_2Al_5$ at high annealing temperature of around $550^{\circ}C$. The existence of an X-layer enhanced the growth of the inter-layer, which resulted in the delamination of the Al/mild-steel clad materials. Hardness tests were also performed to examine the influence of the annealing temperature on the cold deformability, which is a very important property for the deep drawing process of clad materials. The hardness value of mild steel gradually decreased with increasing annealing temperature. Especially, the value of hardness sharply decreased in the temperature range between $525^{\circ}C$ and $550^{\circ}C$. From these results, we can conclude that the optimum annealing temperature is around $550^{\circ}C$ under condition of there being no X-layer creation.

• Korean Journal of Microbiology
• /
• v.46 no.3
• /
• pp.270-277
• /
• 2010

In order to manufacture Bacillus cereus-free fermented soybean products, an antimicrobial agentproducing isolate against B. cereus was obtained from 150 traditionally fermented soybean products. The morphological and biochemical tests and the phylogenetic relationship among 16S rRNA gene sequences indicated that the isolate named as the strain SCK 121057 was most closely related to Bacillus licheniformis. The B. licheniformis isolate began to produce the antimicrobial agent after 48 h of incubation. The agent was nonproteinaceous and insensitive to heat, long term storage and protease K. Electron microscopic observation indicated that the agent attacked the membrane of B. cereus, leaving the ghost cell. The isolate inhibited growth of B. subtilis, Lactobacillus brevis and various types of pathogenic strains including Escherichia coli, E. faecalis, Micrococcus luteus, Staphylococcus aureus, Aspergillus flavus, A. ochraceus, and A. parasiticus as well as B. cereus. After coinoculation of B. licheniformis SCK 121057 and B. cereus in the ratio (as the basis of CFU/g sample) of 10 to 1 on the surface of cooked soybeans, cell numbers of B. cereus had been dramatically reduced after 31 days of incubation compared to those of single inoculation of B. cereus.

• Applied Biological Chemistry
• /
• v.19 no.3
• /
• pp.139-144
• /
• 1976

In order to investigate the properties of enzymes from two strains of mold, reported in the previous paper, (1) studies have been made concerning the characteristics of cellulase of Aspergillus niger-SM6 and Trichoderma viride-SM10, and summarized as follows. 1. In the semi-purification the recovery of ${\beta}-glucosidase$ was the highest when 80-90% ethanol was used and 0.8 saturation of $(NH_4)_2SO_4$. 2. The characteristics of the semi-purified enzyme were as follows. Aspergillus niger-SM6 Trichoderma viride-SM10 Optimum pH 3.5 4.0 pH stability 3.0-6.0 3.0-6.0 Optimum temperature $60^{\circ}C$ $60^{\circ}C$ Heat stability below $60^{\circ}C$ below $50^{\circ}C$ Optimum reaction time 30 min. 60 min. Optimum CMC concentration 3% 3% 3. The Km values of CMCase were 0.8% and 1.01 for Aspergillus niger-SM6 and Trichoderma viride-SM10, respectively. 4. In the strain of Aspergillus niger-SM6, there were high activity of xylanase and pectinase.

• Microbiology and Biotechnology Letters
• /
• v.3 no.2
• /
• pp.63-68
• /
• 1975

A biological active substance was isolated from the cultured medium of Streptomyces sp. and its biochemical characteristics were investigated. Isolation process of the substance was as follows; the pH of filterate of the cultured medium was adjusted to 3.0 with N-hydrochloric acid and saturated with sodium chloride, then chloroform was added to this filterate in one fifth portions and stirred vigorously. After extracting the active substance with chloroform in 3 stages, the chloroform layer combined and evaporatea after dehydrating with sodium sulfate. The substance was found to be to be toxic to various fresh water fishes; the lethal dose for an average size Pseudorasbora parva T. et. S. was 50ug per ml. In the acidic condition, the toxicity of the substance remained fora long time, while in the alkaline state, the toxicity was decreased very fast. This substance was found to be stable to organic solvents, but labile to heat treatment. The maximal revival time of Pseudorasbora parva T. et. S. was about 20 minutes in 25 ug/ml of the substance solution.

• International Journal of Industrial Entomology and Biomaterials
• /
• v.25 no.1
• /
• pp.99-110
• /
• 2012

Comparison on the genomic structure and phylogenetic relationship of the Hsp88 genes from P. tenuipes Jochoen-1, P. tenuipes, C. militaris and C. pruinosa was described. The Hsp88 genes from the three entomopathogenic strains, P. tenuipes Jocheon-1(strain), P. tenuipes(original species), and C. militaris contain the identical genomic structure, namely 5 introns and 6 exons with the length of 13, 62, 32, 1,438, 306, 288 nucleotides encoding 713 amino acid residues, whereas in case of C. pruinosa, it contains 4 introns and 5 exons with the length of 13, 62, 32, 1,744, 288 nucleotides encoding 713 amino acid residues. The genomic DNA length of the Hsp88 genes from P. tenuipes Jocheon-1 and P. tenuipes are both 2,600 nucleotides long in size. The Hsp88 genes from C. militaris and C. pruinosa are 2,582, 2,576 nucleotides long in size, respectively. Hsp88 genes of the P. tenuipes Jochoen-1, P. tenuipes, C. militaris and C. pruinosa also contain the conserved ATP-binding domain. Phylogenetic analysis of the Hsp genes of the four strains tested in this study showed that the fungal Hsp88 is divided into two separate clades, ascomycetes and deutromycete. Within the ascomycetes fungal clade, the P. tenuipes Jochoen-1 and P. tenuipes formed a subgroup, on the other hand, C. militaris and C. pruinosa formed another subgroup. Pair-wise comparison of P. tenuipes Jocheon-1 Hsp88 with those of P. tenuipes, C. militaris and C. pruinosa Hsp88s revealed significant identity in deduced amino acid sequence among these strains. The P. tenuipes Jocheon-1 Hsp88 showed 99% identity with the P. tenuipes, 97% identity with the C. militaris, and 98% identity with the C. pruinosa.

• Journal of the Korean Society of Food Science and Nutrition
• /
• v.22 no.6
• /
• pp.664-672
• /
• 1993

The purpose of this study was to investigate the effect of alcohol administration on selenium concentration and cell morphology in tissurs of rats fed with the different levels of selenium (Se) and vitamin E. Seventy two male rats of Sprague-Dawley strain weighing about 58~62g were divided into 12 groups. The dietary Se levels were 0mg(L-), 0.4mg(C-) and 10mg(H-), and the dietary vitamin E levels were 0mg(-L) and 150mg(-C) per kg diet, respectively. Alcohol-adminstrated groups(--A) received the triple distilled potable water solution containing 10% of ethanol from the 3rd week of experimental periods. The obtained experimental results are summarized as follows. Se concentration in blood and urine made difference in accordance with Se level in diet and tended to be low in alcohol administrated groups. Se concentration in liver and kidney was also directly proportional to the dietary Se level, and it tended to be low in each alcohol group, but Se concentration in kidney tended to be increased by alcohol administration. Myocardium in rats showed lysosome increasing, fat droplet, mitochondrial swelling, and in particular, bad intracellular edema, in H-group fed with high Se and in L-group with low Se. It also showed such phenomena in the alcohol administrated group. In HC-group fed with excessive Se and normal vitamin E. there appeared no noticeable change in liver tissue. However, in the alcohol administrated HCA-group, there came out fat droplet. Especially, in the alcohol administrated LLA-group, not fed with sufficient Se and vitamin, E, there were found lysosome increasing and a number of fat droplet.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2010.02a
• /
• pp.273-273
• /
• 2010

고열부하 환경에 노출되는 핵융합로의 플라즈마 대향부품은 주로 낮은 원자번호 물질-열전도가 좋은 물질-구조체의 순으로 다층 구조를 이루고 있으며, 이들 간의 우수한 접합성은 부품의 성능을 좌우하는 핵심 요소이다. 이러한 플라즈마 대향부품의 건전성을 평가하기 위해서는 고열속의 열부하를 반복적으로 인가하는 시험이 요구되며, 이를 위해 본 연구원에서는 KoHLT-1, 2의 시험시설을 운용하고 있다. 본 시설에서는 열부하원으로서 그라파이터 히터를 사용하며, 히터는 두 개의 시험 대상부품 사이에 설치되고, 히터에 고전류를 인가하여 복사열에 의해 시험 부품에 열부하를 가하게 된다. 고열부하 환경에서 열피로 시험을 위해 히터에 인가되는 전류를 시간에 따라 일정한 패턴으로 반복적으로 ON-OFF 하게 된다. 본 논문에서는 이러한 고열부하시험을 수행함에 있어 고려해야 할 여러 가지 요소에 대해 논의하였다. 우선 인가하는 열유속(heat flux) 값은 일차적으로 시험시설의 최대 출력에 의해 좌우되며, 시험대상물의 운전조건 및 열부하 반복횟수에 의해 결정된다. 열부하 반복횟수는 주어진 열유속 값에 대해 total strain이 파단에 이르는 수준에 의해 결정된다. 열부하를 인가하는 시간은 히터에 전류를 인가했을 때 요구되는 온도로 상승하는 데 걸리는 시간과 시험대상물의 온도가 더 이상 증가하지 않는데 걸리는 시간에 의해 좌우된다. 냉각시간은 길수록 시험대상물의 온도가 냉각수의 온도에 접근하게 되나 너무 길어지면 시험시간이 급격히 증가하게 되므로, 온도 감소 곡선을 검토하여 적절한 시간을 정하게 된다. 열유속 측정은 냉각수의 온도 상승값과 유량으로부터 계산하게 되며, 정확한 측정을 위해서는 열부하를 인가하는 시간이 충분히 길어야 한다. 또한 시험대상 부품에서 열부하가 인가되는 면적을 정확히 정의해야 하며, 냉각관로에 열부하가 인가되어서는 않된다. 또한 시험대상부품을 지지하는 지지구조체를 통한 열손실을 최소화해야 정확한 열유속을 측정할 수 있다. 시험대상부품을 설치할 때 히터와의 간격 또한 결정해야 할 중요한 요소이며, 간격이 좁을수록 최대 열유속 값을 증가시킬 수 있으나, 너무 가까운 경우 히터의 열변형에 의한 접촉 및 아크 방전의 가능성이 있으며, 이 경우 히터와 시험대상부품의 손상을 가져오게 된다. 시험대상물이 국제열핵융합로(ITER)의 일차벽과 같이 베릴륨이 포함되어 있는 경우 방전에 의한 손상은 인체에 유해한 오염의 원인이 될 수 있다. 또한 순간적인 방전은 고가의 고전류전원의 고장을 유발할 수도 있다. 열부하 시험 중 시험대상물의 온도를 정확히 측정하는 것은 필수적이며, 온도 변화 곡선으로부터 시험대상물의 건전성 여부를 판단할 수 있다. 이를 위해 변화를 가장 잘 탐지 할 수 있는 위치에 온도 센서를 설치하는 것이 관건이며, 이는 사전 분석을 통해 알 수 있다.

• Korean Journal of Materials Research
• /
• v.11 no.2
• /
• pp.104-114
• /
• 2001

To investigate the effects of the addition of Nb and Sn on the recrystallization of Zr- Sn-Nb alloys, both Vickers micro-hardness test and TEP measurement were carried out on cold-worked specimens annealed at various temperatures from $300^{\circ}C$ to 75$0^{\circ}C$. The microstructures of heat treated specimens were analyzed by optical microscope, SEM, and TEM. The study of microhardness and microstructures showed that both recrystallization process and grain growth were retarded as the activation energy was increased by the addition of Nb and Sn. Especially, the addition of Sn was more effective on retarding recrystallization. Precipitates were formed more easily when Nb was added because the solubility of Nb into Zr is lower than that of Sn. However, the recrystallization process was affected more by Sn than Nb because the strain field formed by substitutional Sn repressed the dislocation movement. TEP was increased due to the decrease of electron scattering as recovery and recrystallization were proceeded and saturated when the recrystallization completed. However, when precipitates formed, TEP was increased because the decrease of solute concentration near the precipitates caused the decrease of electron scattering.

• Korean Journal of Food Science and Technology
• /
• v.34 no.3
• /
• pp.472-479
• /
• 2002

The antimicrobial effects of metabolites from isolated strains from feces of Korean newborn baby and from Dongchimi against six food-borne microorganisms, and characteristics of the metabolites were investigated.. The metabolites from isolated strains adjusted pH to 3.5, 4.0, and 4.5 showed strong growth inhibition against S. Typhimurium, and S. Enteritidis. The metabolites has kept its inhibition activities to the pathogens after catalase, trypsin or pepsin treatment. In addition, antimicrobial activity of metabolites was not decreased by heat treatment at $121^{\circ}C$ for 15 min. D2 and F35-2 strains were confirmed homofermentative and F20-3 was heterofermentative bacteria identified by final organic acid and gas production. The amount of lactic acid produced by D2 and F35-2 strains after 24 h of incubation was 1.84 and 1.85% respectively, but F20-3 strain produced acetic acid (0.22%) and lactic acid (0.91%).

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.24 no.1
• /
• pp.97-107
• /
• 2020

In this study, finite element analysis was carried out through the finite element analysis program (ANSYS) to investigate the fire resistance of composite columns in fire. Transient heat transfer analysis and static structural analysis were performed according to ASTM E 119 heating curve and axial force ratio 0.7, 0.6, 0.5 by applying stress-strain curves according to temperature, and loading heating experiments were carried out under the same conditions. In addition, the nominal compressive strength of the composite column according to the heating time according to the standard(Eurocode 4) was calculated and expressed as the axial force ratio and compared with the analytical and experimental values. Through the analysis, As a result of finite element analysis, the fire resistance time was 180 minutes and similar value to the experimental value was obtained, whereas the fire resistance time 150 minutes and 60 minutes were derived from the axial force ratios 0.6 and 0.7. In addition, it was confirmed that the fire resistance time according to the axial force ratio calculated according to the reference equation (Eurocode 4) was lower than the actual experimental value. However, it was confirmed that the standard(Eurocode 4) was higher than the experimental value at the axial force ratio of 0.7. Accordingly, it is possible to confirm the fire resistance characteristics(time-axial force ratio relationship) of the SRC column at high axial force, and to use the experimental and anaylsis data of the SRC column as the data for verification based on Eurocode.