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오진근 朝鮮大學校 經營經濟硏究所 2006 經營經濟硏究 = Management and economics research Vol.29 No.1
There is substantial evidence that stock prices do not follow random walks and that returns are predictable. Jegadeesh and Titman (1993) show that stock returns exhibit momentum behavior at intermediate horizons. A self-financing strategy that buys the top 10% and sells the bottom 10% of stocks ranked by returns during the past 6 months. and holds the positions for 6 months, produces profits of 1% per month. Moskowitz and Grinblatt(1999) argue that momentum in individual stock returns is driven by momentum in industry returns. DeBondt and Thaler (1985), Lee and Swaminathan (2000), and Jegadeesh and Titman (2001) document long-term reversals in stock returns. Stocks that perform poorly in the past perform better over the next 3 to 5 years than stocks that perform well in the past. In this paper, we find that a readily' available piece of information-the highest price in a month-largely explains the profits from investment strategies. The sample period chosen for this study is from June 1990 to June 2003. The purpose of this study is to test whether or not past stock prices can predict portfolio returns based on investment strategies using the highest price information in the Korean Stock Market and additional hypotheses are tested by using BE/ME ratio. The empirical results of this study can be summarized as follows: First, the past highest price seems to predict future portfolio returns. Second, joint test used by past monthly price high and BE/ME seems to predict future portfolio returns more than the monthly price high only.
정밀주조된 Ti-6Al-4V 합금 판재의 피로성질에 미치는 판재 두께의 영향
吳振根,李玎求,金洛俊,李星鶴,李義徽 대한금속재료학회 2002 대한금속·재료학회지 Vol.40 No.7
Effects of plate thickness on high-cycle fatigue properties and fatigue crack propagation behavior of investment-cast Ti-6Al-4V alloy plates having Widmansta¨tten structure were investigated in this study. High-cycle fatigue test and fatigue crack propagation test were conducted on three cast plates having different thickness, and then the test data were analyzed in relation with microstructures, tensile properties, and fatigue fracture mode. The high-cycle fatigue results indicated that fatigue strength of the three cast plates was quite similar because of their similar tensile strength. In the case of the fatigue crack propagation, the thicker cast plate composed of thinner α platelets had the slightly faster crack propagation rate than the other plates. The effective microstructural factor determining the fatigue crack propagation rate was found to be the thickness of a platelets because it was well matched with the reversed cyclic plastic zone size calculated in the threshold ΔK regime.
열간압연으로 제조된 Ti Aluminide 다층판재의 미세조직 : Ⅱ. 금속간화합물의 성장거동 Part Ⅱ: Growth Behavior of Intermetallic Phases
吳振根,表成奎,李聖鶴,金洛俊 대한금속재료학회 2002 대한금속·재료학회지 Vol.40 No.4
The present study is to investigate the growth behavior of intermetallic phases in multilayered Ti/TiAl_3 sheets fabricated by hot rolling. When these sheets were heat-treated at 1000℃, interfacial phases such as Ti_3Al, TiAl, and TiAl_2 were grown consuming Ti and TiAl_3. As the heat treatment proceeded, TiAl was grown consuming TiAl_2, thereby finally fabricating multilayered sheets composed of Ti_3Al and TiAl. Conventional lamellar structure composed of Ti_3Al and TiAl could also be fabricated by heat treatment of multilayered Ti/TiAl_3 sheets at 1400℃. The growth rate and activation energy of interfacial phases were obtained from their growth behavior. The results indicated that the growth of intermetallic phases was mainly controlled by volume diffusion than by grain boundary diffusion. The formation process of the multilayered sheets and the formation mechanism of interfacial phases were elucidated, and an idea to fabricate multilayered or bulk Ti aluminide sheets by hot rolling and heat treatment was eventually suggested in this study.
오진근(Jinkeun Oh),김낙준(Nack J. Kim),이성학(Sunghak Lee),이의휘(Eui W. Lee) 대한기계학회 2001 대한기계학회 춘추학술대회 Vol.2001 No.8
The effects of microstructural factors on high-cycle fatigue properties of welded regions of an investment cast Ti-6AI-4V alloy were investigated in this study. High-cycle fatigue were conducted for the welded regions, which were processed by two different welding methods, i.e. tungsten inert gas (TIG) welding and electron beam (EB) welding, and then the test data were analyzed in relation with microstructures, tensile properties, and fatigue fracture mode. The base metal was composed of a Widmanstatten structure, which was then transformed to a basket-weave structure having thin a platelets after welding and annealing. The high-cycle fatigue results indicated that fatigue strength of the EB weld was lower than that of the base metal or the TIG weld because of the existence of coarse micropores formed during welding, although it had highest yield strength.
Al-Si 도금층 두께가 22MnB5강의 핫스탬핑 공정 마모에 미치는 영향
지민기,손현성,오진근,김성우,김경목,전태성 대한금속·재료학회 2020 대한금속·재료학회지 Vol.58 No.8
Al-Si coated ultra-high strength steels (UHSS) are widely used in automotive applications because of their high strength-to-weight ratio, corrosion protection and good weldability. The hot stamping (also called hot press forming) process is an effective and suitable technique for producing automotive parts from Al-Si coated UHSS. However, critical issues, such as the transfer of the coating materials and the build-up of these materials on the tool surface, have been encountered. These defects affect tool life and product quality. The wear behaviour of Al-Si coated 22MnB5 and Cr coated SKD11 tool was investigated using a high temperature friction test which mimicked the actual hot stamping environment. Two kinds of Al-Si coated 22MnB5 with ~19.6 (AlSi-A) and ~29.3 (AlSi-B) μm coating thicknesses were used in this study. After the friction test the coated layer of AlSi-A was found to be worn up to the diffusion layer, while for AlSi-B, the coating layer mostly remained after the friction test. Adhesive wear predominantly occurred on the tool surface in both cases, but the wear increased significantly in case of AlSi-B. This suggests that the coating thickness and the associated surface roughness are critical factors affecting wear behaviour.