• 소성∙가공
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• 제19권6호
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• pp.357-362
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• 2010

Dry sliding wear behavior of pure Fe and Cu which have BCC and FCC crystal structure, respectively, was investigated. The wear characteristics of the pure metals with different crystal structure were compared. Dry sliding wear tests were carried out using a pin-on-disk wear tester at various loads under the constant sliding speed condition of 0.15 m/s against a silica ball at room temperature. Sliding distance was fixed as 600 m for all wear tests. Wear rate of a specimen was calculated by dividing the weight loss of the specimen after the test by the specific gravity and sliding distance. Worn surfaces and wear debris were analyzed by SEM. The wear of both pure Fe and Cu proceeded with surface deformation, resulting in similar wear rates despite of their structure difference under the current test conditions. Wear rates of both metals were low if the surface deformation due to wear forms thick surface-deformation layer that is strain hardened beneath the wearing surface. The pure Cu specimens showed a lot of oxides on the worn surface when tested at low loads less than 5 N, which resulted in very low wear rate.

• 생명과학회지
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• 제13권2호
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• pp.191-196
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• 2003

Arylsulfatase를 암호화하는 Neurospora crassa의 ars-1 유전자는 황의 결핍에 의해서 발현이 조절된다. lacZ 유전자에 연결된 ars-1 프로모터 (Pars)가 N. crassa RLM 35-35 a his-3 inl 균주에 형질전환되고, 유사 서열 재조합에 의한 단일 교차에 의해서 염색체의 his-3 부위로 도입이 되었다. 황이 결여된 Vogel의 배지에서 자란 균사로부터 $\beta$-galactosidase 활성이 측정되었다. $\beta$-galactosidase 활성은 derepression 조건으로 변환한지 14 시간 후에 최고치를 기록하였다. Microconidiation에 의해서 생산된 homokaryon에서 측정된 활성은 heterokaryon보다 17% 증가가 되었음을 보여주었다. 이 실험은 ars-1 프로모터의 발현율을 측정할 수 있는 한 방법을 제시한 것으로, 보다 수월한 ars-1 발현 조절 연구가 기능할 것이다.

• 한국미생물·생명공학회지
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• 제23권3호
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• pp.263-268
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• 1995

A screening was performed to isolate exoploysaccharide-producing microorganisms, which synthesized specific exopolysaccharide for the substitutive of commercial polysaccharides, from natural sources. Soil bacterium, one of 378 mucoid isolates, was finally selected as potential producer of polysaccharides which made the culture broth very viscous and thus examined in detail for optimal medium composition. Isolated strain was identified as Xanthomonas sp. EPS- 1 from the results of morphological and biochemical characteristics. The composition of optimal medium for exopolysaccharide production was as follows: 50 g sucrose, 1.5 g peptone, 2 g KH$_{2}$PO$_{4}$, 2 g MgSO$_{4}$, -7H$_{2}$O, 3 g NaCl, 0.05 g CaCO$_{3}$, 0.07 g FeSO$_{4}$-7H$_{2}$O and 0.05 g MnSO$_{4}$-7H$_{2}$O in 1 liter of distilled water. From the experiments of temperature and pH dependence, the optimal conditions for exopolysaccharide biosynthesis seemed to be 30$\circ$C and 8.0, respectively. About 14.9 gram of maximum exopolysaccharide per liter was obtained at the initial pH 8.0, 30$\circ$C and 250 rpm in a flask culture. The exopolysaccharide EPS-1 had such potential as an emulsifying agent and a gelling agent in comparision with commercial exopolysaccharide.

• Nuclear Engineering and Technology
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• 제53권3호
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• pp.901-910
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• 2021

KHNP recently has obtained the approval for the commercialization of the modified 37-element (or 37 M) fuel bundle and now is loading the 37 M fuel bundles in CANDU-6 reactors in KOREA. One of the main issues for approval was the burnup limit. Due to CANDU design and neutronic characteristics, there was no specific burnup restriction of a fuel bundle. The absence of a burnup limit does not mean that a fuel bundle can stay in the CANDU reactor without a time limit. However, the regulator requested traditional design values as well as the burnup limit reflecting the computer code uncertainty. The method for the PWR burnup limit was not applied to the CANDU fuel bundle. Since there was no approved methodology to build the burnup limit with uncertainties, KHNP introduced a Monte-Carlo method coupled with a 95/95 approach to determine the conservative burnup limit from the viewpoint of the centerline temperature, internal pressure, strain measurement deviation. Moreover, to consider the uncertainties of various computing models, a converted power uncertainty was introduced. This paper presents the methodology and puts forward the limits on burnup, evaluated for each of the existing and modified fuel bundles, in consideration of the pressure tube aging condition.

• The Plant Pathology Journal
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• 제40권1호
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• pp.83-97
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• 2024

Fusarium graminearum, the causal agent of Fusarium head blight (FHB) in cereal crops, employs the production of sexual fruiting bodies (perithecia) on plant debris as a strategy for overwintering and dissemination. In an artificial condition (e.g., carrot agar medium), the F. graminearum Z3643 strain was capable of producing perithecia predominantly in the central region of the fungal culture where aerial hyphae naturally collapsed. To unravel the intricate relationship between natural aerial hyphae collapse and sexual development in this fungus, we focused on 699 genes differentially expressed during aerial hyphae collapse, with 26 selected for further analysis. Targeted gene deletion and quantitative real-time PCR analyses elucidated the functions of specific genes during natural aerial hyphae collapse and perithecium formation. Furthermore, comparative gene expression analyses between natural collapse and artificial removal conditions reveal distinct temporal profiles, with the latter inducing a more rapid and pronounced response, particularly in MAT gene expression. Notably, FGSG_09210 and FGSG_09896 play crucial roles in sexual development and aerial hyphae growth, respectively. Taken together, it is plausible that if aerial hyphae collapse occurs on plant debris, it may serve as a physical cue for inducing perithecium formation in crop fields, representing a survival strategy for F. graminearum during winter. Insights into the molecular mechanisms underlying aerial hyphae collapse provides offer potential strategies for disease control against FHB caused by F. graminearum.

• 대한수의학회지
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• 제30권3호
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• pp.297-307
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• 1990

To establish an agar-gel immunodiffusion (AGID) test for detection of antibodies to Aujeszky's disease virus(ADV) in swine, the precipitating antigens were prepared by four procedures using the Aujeszky's disease virus, NYJ-1-87 strain isolated from the affected piglets in Korea. The optimal condition for AGID test and the properties of the antigens were investigated. To determine the optimal concentration of antigens, four antigens were experimentally prepared by concentrating the viral fluids by 1/30 to 1/200. It was proved that the antigen precipitated with ammonium sulfate at concentration of 1/100 was the most efficient to detect ADV antibodies by AGID test. When the relationship between the concentration of the antigens and the size of precipitating in radial immunodiffusion test was investigated, a high correlation coefficiency at r=0.95 (y=0.23x+23.4) was estimated, In study on the effects of various buffered salt solutions and agars on the sensitivity of AGID test by using the experimental ADV antigens, it was found that 0.05M tris buffer without sodium chloride at pH 7.2 induced the most distinctive precipitating lines, and that there was no significant differences in the sensitivity between the agarose and Noble's special agar. When the efficiency of AGID test was compared with serum neutralization(SN) test, the sensitivity of AGID test was 100% in SN titer over 1 : 16, 91.7% in SN titer of 1 : 8 and 57.1% in SN titer of 1 : 4. The specificity of AGID test compared with the sera with SN titer under 1 : 2 was 98.4%. Protein analysis of the antigens by SDS-PAGE indicated that antigen I and antigen III showed a specific band of polypeptides with molecular weight of 116 K in comparison with the control antigen. Antigen IV, treated with tween-80 and ammonium sulfate, revealed specific polypeptides bands at the molecular weights 45K, 98K and 150 K.

• Composites Research
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• 제16권6호
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• pp.41-47
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• 2003

복합재료는 비강성, 비강도가 높고 열팽창 계수가 낮으며 우수한 내열 특성 등 기계적, 열적 특성이 좋아 항공기, 인공위성을 비롯하여 여러 다른 구조물에 폭넓게 사용되고 있다. 하지만, 복합재료를 고온 환경에 사용하기 위해서는 고온 환경에서의 물성에 대한 검증이 필요하다. 본 연구에서는 FBG 센서가 삽입된 T700/Epoxy 복합재료 시편에 대해 온도에 따른 물성을 측정하였다 실험은 열챔버 내에서 수행하였고 온도 범위는 상온, $100^{\circ}$, $200^{\circ}$, $300^{\circ}$, $300^{\circ}$이다. 삽입된 광섬유의 예비 시험을 통해, 광섬유 센서의 삽입이 물성값에 미치는 영향을 확인하였다. 시험에는 [0/{0}/0]$_{T}$, [$90_2$/{0}/$90_2$] 와 같은 적층각을 갖는 두 종류의 시편을 사용하였다. 실험 결과로부터 온도에 따른 복합재료의 물성 변화를 성공적으로 측정하였으며 FBG 센서가 고온 환경의 변형률 측정 센서로 매우 적합함을 확인하였다.

• 한국해양환경ㆍ에너지학회지
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• 제12권2호
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• pp.91-95
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• 2009

저서성 미세조류의 성장에 미치는 부착기질의 영향을 알기 위해 서로 다른 크기의 glass bead를 첨가하여 저서성 미세조류 Nitzschia sp.(진해만 클론)의 성장을 조사하였다. 연구에 사용된 glass bead의 크기는 0.09-0.15 mm(G1), 0.25-0.50 mm(G2), 0.75-1.00 mm(G3) 그리고 1.25-1.65 mm(G4)이며, glass bead를 첨가하지 않는 대조구도 설정하였다. Nitzschia sp.의 가장 높은 성장속도(0.37/day)와 최대세포밀도($9,232{\pm}840$ cells/mL)는 가장 작은 크기의 glass bead를 첨가한 G1에서 나타났다. 그리고 성징속도와 최대세포밀도는 glass bead 크기의 증가와 함께 감소하였다(G4의 성장속도와 최대세포밀도는 각각 0.24/day와 $6,397{\pm}524$ cells/mL였다). 더욱이 대조구의 성장속도는 실험구 G1에서 G3의 성장속도보다 상당히 낮았다. 이 결과에서 Nitzschia sp.와 같은 저서성 미세조류를 위한 부착기질은 성장속도 뿐만 아니라 세포밀도에도 큰 영향을 주는 것으로 나타났다. 따라서 부착미세조류의 생리실험을 위해서는 예비실험으로 부착기질의 유무 및 대상 종에 적합한 부착입자의 크기의 고려가 필요할 것으로 보인다.

• 대한기계학회논문집A
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• 제27권5호
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• pp.823-832
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• 2003

To define the causes of cladding degradation which can take place during the operation of nuclear power plants, it is required to develop the new fracture toughness test of spent fuel cladding. The fracture toughness of Zircaloy-4 cladding was estimated using the recently developed KAERI embedded Charpy (KEC) specimen. Axially notched KEC specimens cut directly from unirradiated fuel claddings, were tested in a way similar to the standard toughness test method of a Single Edge Bending (SEB) specimen. The results of KEC fracture toughness test at room temperatures were discussed and compared with those of the previous other studies. In conclusions, even though the KEC fracture toughness test of nuclear fuel claddings was easier and more reliable than those developed earlier, the results from the cladding fracture tests were not the material characteristics but the specific fracture parameters which were deeply related to the specification of claddings. In addition, the phenomenon of a thickness yielding was not observed from the fracture surface. It was closely related to the fact that the plane strain condition of the KEC specimen was changed to the plane stress condition during crack advancing. It was also supported by the fractographic evidence that the formation of ductile dimples at the crack initiation became the similar appearance such as a quasi-cleavage after the sufficient crack advancing.

• 대한미생물학회지
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• 제17권1호
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• pp.75-85
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• 1982

In order to demonstrate the effect of specific serum IgG antibody on the adherence of Streptococcus mutans to smooth surface and the mechanism of effective adherence inhibition by IgG antibody, in the present study authors obtained purified IgG from different immunogen preparations of S. mutans NCTC 10449(serotype c) and observed the effect of each IgG preparation on the adherence of each S. mutans strain cultured in different conditions. In addition, the present study was undertaken to observe the cross-reactivity of IgG and the effect of sucrose concentration on the adherence of S. mutans in vitro non-growth condition. The adherence of S. mutans to glass surface was effectively inhibited by serum IgG antibody. At the same IgG concentrations, anti-2% fructose grown/1N NaCl washed S. mutans NCTC 10449 cell showed greater adherence inhibitory effect to S. mutans strains than anti-2% sucrose grown and anti-S. mutans NCTC 10449 cell wall, and the greater inhibitory effects of IgG preparations were observed in assay using 2% fructose grown S. mutans cell preparations than using 0.1% sucrose grown cell preparations. These results suggest that the more effective adherence inhibition by serum IgG antibody is due to the reaction with S. mutans cell surface antigens rather than glucan and cell-associated glucosyltransferase. The greatest adherence inhibitory effect of IgG to S. mutans strains was observed on homologous NCTC 10449 strain and the inhibition cross-reactivities were observed between serotype c, e, and f strains. More pronounced cross-reactivity of adherence inhibition of IgG to S. mutans was observed in assay using anti-2% fructose grown/1N NaCl washed cell than using other IgG preparations, and observed in assay using 2% fructose grown S. mutans cell preparations than 0.1% sucrose grown cell preparations. It was interested that low, but adequate concentration of reactive IgG antibody significantly increased the adherence ability of S. mutans. This result may be due to the formation of small cell aggregates resulted in a increase in the numbers of organisms which adhered to glass surface. The adherence of S. mutans to glass surface was possible in the absence of glucan-synthetic activity. Low level of sucrose significantly increased the adherence ability of S. mutans to glass surface, but excessive amount of sucrose induced large cell aggregates resulted in a decrease in the numbers of organism which adhered.