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윤영섭,윤덕용 대한금속재료학회(대한금속학회) 1977 대한금속·재료학회지 Vol.15 No.2
The effect of cold working and subsequent annealing on mechanical properties of W-Ni-Fe heavy alloy has been studied. The specimen composition was 90W-5Ni-5Fe by weight percent. The specimens were prepared by usual powder metallurgy techniques and sintered in liquid phase at 1460℃ for 30 minutes in hydrogen atmosphere. The specimens were then cold worked up to 60% by rolling. The observed UTS increases with cold working from about 94㎏/㎟ to 143㎏/㎟ at 50% deformation. The elongation decreases sharply from 20% to about 2% at 15% deformation. While the microhardness of the tungsten grains increases steadily with degree of cold work, the micro hardness of the matrix appears to increase rapidly with deformation initially. It is therefore suggested that at relatively small deformation the matrix phase work hardens rapidly and affects the deformation behavior of the composite alloy. The alloy specimen cold worked to 50% was annealed at temperatures from 400℃ to 1000℃ for an hour in hydrogen atmosphere and the mechanical properties were measured. Annealing of the cold worked specimen at 400˚increases UTS to 160㎏/㎟ from 143㎏/㎟ for the unannealed specimen, and with increasing annealing temperatures UTS decreases. The elongation begins to increase with annealing temperature at 800℃ and rises sharply to 4% at 1000℃. The microhardness of the tungsten grains remains unchanged with annealing temperature up to 600℃ and from 800℃ begins to decrease slowly. The microhardness of the matrix on the other hand shows maximum after annealing at 400℃ and decreases subsequently with higher annealing temperatures. These observations indicate that the increase of the UTS after annealing at 400℃ is largely due to the increased strength of the matrix. This increase in matrix strength with annealing is most likely caused by some, kind of precipitation hardening which is probably accelerated by cold work. The observed changes of mechanical properties at higher annealing temperatures are attributed mainly to the recovery and recrystallization of the matrix phase.
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윤영섭,이오영,박호용,한성희,양선영,전대원,전용철,한동수,최호순,윤병철 대한소화기내시경학회 2005 Clinical Endoscopy Vol.31 No.3
Colonoscopy is a relatively safe procedure with few complications. However, it may be accompanied with complications such as bleeding, perforation and, rarely, acute appendicitis. Acute appendicitis occurs when the appendiceal opening is obstructed by lymphoid hyperplasia, fecalith or foreign materials. In case of late detection, acute appendicitis can results in perforation and panperitonitis. Therefore early diagnosis and proper management is mandoctory. We experienced a 70-year-old female patient who visited for abdominal pain and tenderness after the diagnostic colonoscopy and was found to develop acute appendicitis. Herein, we report the case with the review of literatures. 진단 대장내시경 검사는 치료 대장내시경술에 비해 합병증이 드문 비교적 안전한 검사이다. 그러나 이러한 진단 대장내시경 검사 역시 출혈, 천공 등의 합병증이 동반될 수 있고 드물게 급성 충수염이 발생하기도 한다. 급성 충수염은 대개 림프조직의 비대, 대변, 이물질에 의해 충수돌기 입구가 막혀서 생기며 여러 검사 및 치료 술기 후 합병증으로 생길 수 있다. 급성 충수염은 진단이 늦어질 경우 천공이나 복막염 등의 심각한 합병증이 올 수 있으므로 빠른 진단 및 치료가 필요하다. 저자는 진단 대장내시경 검사를 시행한 뒤 발생한 복통과 압통으로 다시 내원하여 급성 충수염으로 진단된 예를 경험하였기에 문헌 고찰과 함께 보고한다.
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SEPOX (selective poly oxidation) process에서 Si-buffer layer에 발생하는 pinhole 현상에 대한 연구
윤영섭 대한전자공학회 1996 전자공학회논문지-A Vol.33 No.6
We propose a mechanism for the formation of pinholes in the Si-buffer layer, through the observations with varying the process- and structure variables in the SEPOX (selective poly-oxidation) process, an isolation method for sub-u DRAMs. Pinholes are formed through the accumulation of Si vacancies generated by the oxidation of Si, in which Si atoms leave the sites (vacancies) at the Si/SiO$_{2}$ interfaces and diffuse into the oxide to be oxidized near interface. In the course of the accumulation of Si-vacancies, the stress induced in the Si-buffer layer affects the migration of vacancies to result in the final size and distribution of pinholes. This paper may be, to our knowledge, the first report about the oxidation-induced pinhole in the Si/SiO$_{2}$ system.
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특정 산업에 집중된 펀드의 성과가 더 우수한가? : 한국 펀드시장에서의 증거
윤영섭,손판도,김성신 한국재무관리학회 2011 財務管理硏究 Vol.28 No.1
Many prior studies have suggested that fund managers can create superior performance by concentrating their holders in specific industries with informational advantage. We investigate whether fund managers are motivated to hold specific industry concentrated portfolios using Korea fund holding data from 2001 to 2007 because they have investment skills that are linked to specific industries. That is, we examine the relationship between the industry concentration of fund and performance using various fund performance measures. Our analysis finds as follows : First, it is found that using unconditional and conditional model in measuring the fund performance, more industry concentrated funds generate more abnormal returns, 0.4 percent and 0.2 percent per monthfor each models rather than less industry concentrated funds. These differences are significant even after controlling for characteristic variables. Second, we also find that more concentrated fund managers tend to have the superior industry selection ability and stock selection ability rather than less industry concentrated fund managers. Third, we document that the superior performances of concentrated fund manager are not due to fund size in testing the differential performance from fund size. Fourth, we identify that in testing the persistence of the superior performance in more concentrated funds, highly industry concentrated funds incline to have higher performance sustainably and persistently than low industry concentrated funds. This findings also indicates that industry concentrated funds are more successful in selecting stocks and industries than more diversified funds. Our results imply that the industry concentration of fund is positively related to fund performance. Our findings support to the hypothesis that investment ability of fund managers is linked to specific industries with informational advantage. 기존 논문에서 우월한 정보를 가진 산업에 집중된 투자를 하는 것이 분산된 투자보다 더 우수한 성과를 보인다는 사실을 이론적, 실증적으로 증명하고 있다. 본 논문에서도 2001~2007년에 걸친 한국 펀드자료를 가지고 이러한 산업에 집중된 투자가 과연 더 우수한 성과를 보이는가를 실증적으로 검증한다. 본 논문의 실증분석 주요 결과는 다음과 같다. 첫째, 비조건부 및 조건부 모형을 사용하여 펀드성과를 측정한 결과, 산업집중도가 높은 펀드가 산업집중도가 낮은 펀드에 비해 각각 월 0.4%와 0.2% 정도의 위험조정 초과수익률을 실현하는 것으로 나타났다. 이러한 차이는 통계적으로 유의할 뿐만 아니라 펀드관련 특성 변수를 통제한 후에도 비슷하게 나타났다. 둘째, 펀드운용자가 우월한 정보를 이용하여 미래성과가 좋은 특정 산업을 선택할 수 있으며 특정 산업 내에서 좋은 주식을 선택할 수 있는 능력을 가졌는가의 여부를 검증하였는데 산업이 집중된 펀드에서 그러한 사실을 발견할 수 있었다. 셋째, 펀드규모에 따라 성과가 달라지는가를 검증한 결과 기존의 실증결과는 펀드 규모에 영향을 받지 않음을 보였다. 넷째, 산업집중도에 따른 펀드성과가 지속성을 가지는 지를 검증한 결과 과거 산업집중도가 높은 펀드는 그렇지 않은 펀드에 비해 높은 운용성과를 보이며 지속성이 유지되고 있다. 이러한 결과는 펀드 초과수익률과 주식선택능력(CS)의 경우에서도 동일하게 성과 지속성을 보이고 있다. 따라서 본 논문의 의의는 우리나라에서도 펀드운용자가 정보우위를 가진 특정 산업에 집중적으로 투자할 경우 보다 우수한 운용성과를 투자자에게 가져다 줄 수 있음을 확인하였다.
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