• 미생물학회지
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• 제24권3호
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• pp.197-203
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• 1986

Streptomyces lavendulae에서 생성된 원형질체 및 원형질체 융합과정에 대한 미세구조 및 행태학적 관찰을 투과 전자현미경과 주사전자현미경을 사용하여 행하였다. 생성된 원행질체들은 고장액에서 대체로 안정하였으나 간혹 변형된 원형질체들이 관찰되었다. 원형질체 융합은 접촉지역 융합지역, 분리지역 형성과정을 차례로 거치면서 선행되는 것이 관찰되었다. 이러한 사실은 세포막 구조의 변화와 이원형의 소실에 의하여 뒷받침이 될 수 있으으로 이러한 변화들을 융합과정에서의 각 단계로 해석하는 것이 가능하리라 사료된다.

• 한국레이저가공학회지
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• 제7권3호
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• pp.25-36
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• 2004

This study was performed to clarification of the formation of weld discontinuities in the dissimilar laser fusion zone. Welding parameters were beam power of 1300, 1430, 1560, and 1700 W and travel speed of 1, 1.3, and 1.7 m/min. Most cavities in the fusion zone were observed near the tip. Cavities in the fusion zone observed to be formed and grown from pores in the tip. More cavities were formed as the beam position moves to the tip side. Small cavities were decreased but large cavities were increased when the energy input increased. W content in the fusion zone was increased with heat input and as the beam position close to the tip. In the fusion zone, W content in the dendrite boundary was increased with heat input. Considering the propagation path and fracture morphology, cracks were solidification cracking, and were initiated and propagated along the dendrite boundaries. The formation of cracks might be related with the W rich ${\mu}$ phase which was formed in the grain boundaries and dendrite boundaries.

• Journal of Welding and Joining
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• 제31권1호
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• pp.58-64
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• 2013

The following results were obtained, microstructures and tensile properties in arc brazed joints of DP(dual phase) steel using Cu-5.3wt%Sn insert metal was investigated as function of brazing current. 1) The Fusion Zone was composed of ${\alpha}Fe+{\gamma}Cu$ and Cu23Sn2. The reason for the formation of these solid solutions. Despite, Fe & Cu were impossible to solid solution at room temperature. It's melting & reaction to something of insert metal & Base Metal (DP Steel) by Arc. Brazing Process has faster cooling rate then Cast Process, Supersaturated solid solution at room temperature. 2) The increase Hardness of Fusion Zone was directly proportional to the rise of welding current. Because, ${\alpha}Fe+{\gamma}Cu$ phase (higher hardness than the Cu23Sn2.(104.1Hv < 271.9Hv)) Volume fraction was Growth, due to increasing the amount of base metal melting by High current. 3) The results of tensile shear test by Brazing, All specimens happen to fracture in Fusion Zone. On the other hand, when Brazing Current increasing tend to rise tensile load. but it was very small, about 26-30% of the base metal. 4) The result of fracture analysis, The crack initiate at Triple Point for meet to Upper B.M/Under B.M/Fusion Zone. This Crack propagated to Fusion zone. So ruptured by tensile strength. The Reason to in the fusion zone fracture, Fusion zone by Brazing of hardness (strength) was very lower then the base metal (DP steel). In addition the Fusion Zone's thickness in triple point was thin than the base metal's thickness in triple point.

• Journal of Welding and Joining
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• 제34권5호
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• pp.70-76
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• 2016

In this study, Microstructure and tensile properties in arc brazed joints of 1000MPa grade DP steel using Cu-Si insert metal were investigated. The fusion zone was composed of Cu phase which solidified a little Fe and Si. The former phase formed due to dilute the edge of base material by arc, although Fe was not solid solution in Cu at the room temperature. Cu3Si particles formed by crystallization at $1100^{\circ}C$ during faster cooling. After the tensile shear test, there are no differences between the brazed joint efficiencies. The maximum joint efficient was about 37% compared to strength of base metal. It is better than that of arc brazed joint of DP steel using Cu-Sn filler metal. Fracture position of all brazing conditions was in the fusion zone. Crack initiation occurred at three junction point which was a stress singularity point of upper sheet, lower sheet and the fusion zone. And then crack propagated across the fusion zone. The reason why the fracture occurred at fusion zone was that the hardness of fusion zone was lower than that of base material and heat affected zone. The correlation among maximum load and hardness of fusion zone and EST at fractured position was $R^2=0.9338$. Therefore, this means that hardness and EST can have great impact on maximum load.

• Journal of Welding and Joining
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• 제14권3호
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• pp.93-104
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• 1996

This study evaluated relative hot cracking susceptibility of commercial aluminum alloy welds, and then suggested possible mechanisms operated in the weld fusion zone and in the heat affected zone based on the observed cracking morphologies, fractography and microstructural features. The fusion zone solidification cracking was found to be mainly due to a microsegregation of Cu, Si, and Mg in grain boundaries, while liquation cracking in the HAZ was by the incipient melting of the segregated grain boundaries and the consitutional liquation of large aging precipitates and intermetallic compounds in the partially melted zone adjacent to the fusion line which experienced a rapid thermal excursion during welding.

• Journal of Welding and Joining
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• 제31권6호
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• pp.96-106
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• 2013

In this study, the effect of laser source($CO_2$ and Nd:YAG) on the microstructure and tensile properties of laser welded Al-Si coated boron steel(1.2mmt) was investigated with before and after hot-stamping. In case of as welds condition, fracture occurred in base metal unrelated to the laser source. It could be explained that tensile strength of fusion zone composed of martensite and bainite is higher than that of base metal that contains a lot of ferrite despite dilution of Al and Si from coating layer to fusion zone. In case of hot-stamping condition, the fracture occurred in fusion zone irrelevant to laser source and the tensile strength was lower than hot stamped base metal. In the $CO_2$ laser welds, $Fe_3$(Al,Si) formed near the bond line was transformed into ferrite during hot-stamping. Therefore tensile strength of bond line is lower than that of base metal and center of fusion zone and the fracture occurred in the bond line. On the other hand, in the Nd:YAG laser welds, the higher concentration of Al formed the ferrite in the fusion zone during hot-stamping treatment. Also, the thickness of centerline was thinner than that of base metal. Therefore, it is considered that fracture occurred in centerline of fusion zone due to effect of concentration stress, and it leaded to a lower tensile strength and elongation.

• Journal of Welding and Joining
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• 제31권3호
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• pp.66-75
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• 2013

In this study, the effect of coating thickness($20{\mu}m$ and $30{\mu}m$) on microstructure and tensile properties in Yb:YAG disk laser welds of Al-Si-coated boron steel (1.2mmt) was investigated. In the case of as welds, the quantity of ferrite was found to be higher in base metal than that in HAZ (Heat Affected Zone) and fusion zone, indicating, fracture occurrs in base metal, and the fracture position is unrelated to the coating thickness. Furthermore, yield strength, tensile strength of base metal and welded specimens showed similar behavior whereas elongation was decreased. On the other hand, base metal and HAZ showed existence of martensite after heat treatment, the fusion zone indicated the presence of full ferrite or austenite and ferrite during heat treatment ($900^{\circ}C$, 5min), After water cooling, austenite was transformed to martensite, and the quantity of ferrite in fusion zone was higher as compared with in base metal, resulting in sharply decrease of yield strength, tensile strength and elongation, which leads to fracture occured at fusion zone. In particular, results showed that because the concentration of Al was higher in 30um coating layer specimen than that of 20um coating specimen, after heat treatment, producing a higher quantity of ferrite was higher after heat treatment in the fusion zone; howevers, it leads to a lower tensile property.

• Current Optics and Photonics
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• 제4권1호
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• pp.9-15
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• 2020

Fresnel zone plates have been widely used in many applications, such as x-ray telescopes, microfluorescence, and microimaging. To obtain an x-ray Fresnel zone plate, many fabrication methods, such as electron-beam etching, ion-beam etching and chemical etching, have been developed. Fresnel zone plates fabricated by these methods will inevitably lead to some nonideal factors, which have an impact on the focusing characteristics of the zone plate. In this paper, the influences of these nonideal factors on the focusing characteristics of the zone plate are studied systematically, by numerical simulations based on scalar diffraction theory. The influence of the thickness of a Fresnel zone plate on the absolute focusing efficiency is calculated for a given incident x-ray's wavelength. The diffraction efficiency and size of the focal spot are calculated for different incline angles of the groove. The simulations of zone plates without struts, with regular struts, and with random struts are carried out, to study the effects of struts on the focusing characteristics of a zone plate. When a Fresnel zone plate is used to focus an ultrashort x-ray pulse, the effect of zone-plate structure on the final pulse duration is also discussed.

• 한국균학회지
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• 제21권3호
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• pp.188-194
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• 1993

Rhizoctonia solani AG-1(IA), R. oryzae, R. oryzae-sativae의 다른 지역(地域) 및 포장분리균주(圃場分離菌株)들간의 균사융합형(菌絲融合型)과 배양(培養)에 의한 균사상호작용(菌絲相互作用)조사하였다. R. solani AG-1(IA)균주(菌株)들의 상호간(相互間) 균상융합(菌絲融合) 검정결과(檢定缺課), 세포질융합(細胞質融合)은 자기균사융합(自己菌絲融合)에서만 발생하였으며, 다른 균주(菌株)들 상호간(相互間)에는 비세포질융합(非細胞質融合)이 발생하였다. R. oryzae균주(菌株)들의 상호간(相互間) 균사융합(菌絲融合) 검정결과(檢定缺課), 세포질융합(細胞質融合)은 자기균사융합(自己菌絲融合)에서 뿐 만 아니라 다른 지역분리(地域分離) 균주(菌株)들간의 6조합(組合)과 같은 지역(地域)의 다른 포장분리(圃場分離) 균주(菌株)들간의 2조합(組合)에서 발생하였다. 이 경우에 이 균의 4균주(菌株) 상호간(相互間)에서는 세포질융합(細胞質融合)이 발생하였다. R. oryzae-sativae균주(菌株)들의 상호간(相互間) 균상융합(菌絲融合) 검정결과(檢定結果), 세포질융합(細胞質融合)은 자기균사융합(自己菌絲融合)에서만 발생하였으며, 다른 지역(地域) 및 포장분리(圃場分離) 균주(菌株)들간에는 비세포질융합(非細胞質融合)만이 발생하였다. R. solani의 비세포질융합균주(非細胞質融合菌株)들(NCFIs)을 PDA에서 대치배양(對峙培養)한 결과(結果), 치사대(致死帶)가 형성되었으며, R. oryzae의 NCFIs간에도 치사대(致死帶)가 형성되었다. R. oryzae의 세포질융합균주(細胞質融合菌株)들(CFIs)간에는 치사대(致死帶)가 형성되지 않았는데, 그 CFIs의 균사(菌絲)들은 어떤 경계선(境界線)도 형성하지 않고, 상호간(相互間)에 혼합(混合)되었다. R. oryzae-sativae의 NCFIs간에는 치사대(致死帶)가 형성되지 않고, 엉킴대가 형성되었다.

• Journal of Welding and Joining
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• 제30권2호
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• pp.76-80
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• 2012

In this study, the effect of the welding current on the hardness characteristics and microstructure in the resistance spot welding of 1GPa grade cold-rolled DP steel was investigated, Also, correlation between the hardness and microstructure was discussed. In spite of the change in the welding current, the hardness distributions near weld was similar. the hardness in the HAZ and the fusion zone was higher than that of the base metal and the hardness in the fusion zone was variated with the location. Especially, the hardness of HAZ adjacent to the base metal showed maximum value, and softening zone in the base metal adjacent to HAZ was found. With the increasing of welding current, there were no difference in maximum hardness and average hardness in the fusion zone were, but the hardness of the softening zone reduced. The difference in the hardness in each location of weld due to grain size of prior austenite. The softening of the base metal occurred by tempering of the martensite.