W 섬유강화 스테인레스강 복합재료의 열피로에 관한 연구

이지환 대한금속재료학회(대한금속학회) 1988 대한금속·재료학회지 Vol.26 No.1

In this paper was investigated the effect of thermal cycling on dimensional change and microstructural change of the interfacial region in W/stainless steel composites, which was hot pressed at 1100℃ and then exposed up to 200 h at 1200℃, with HfN coated and uncoated fibers. After thermal cycling, it was found that axial dilatation of the matrix in W/stainless steel composites with HfN coated fiber occurred conspicuously only in the early stage of cycling. However, the axial dilatation became nearly zero after several tens of cycles, which indicated that mechanical interactions exist between the matrix and the fiber did not exist any more. On the other hand, the matrix side of the interface in W/stainless steel composites with uncoated fiber became rough with increase of thermal cycling, and several voids were observed to be formed in the matrix.

최적화 및 머신러닝 기법을 활용한 다구간항공권 검색엔진 향상

이지환 대한산업공학회 2021 대한산업공학회 춘계학술대회논문집 Vol.2021 No.6

SiC 입자강화 Mg 합금기 복합재료의 제조에 관한 연구

이지환,이두면,이준서 대한금속재료학회(대한금속학회) 1995 대한금속·재료학회지 Vol.33 No.2

The aim of this paper was to optimize the fabrication of SiC_P/Mg alloy composite using AZ91D Mg alloy machined chips which have the difficulty of the recycling. The mixtures of Mg alloy machined chips and SiC particles were consolidated by vacuum hot pressing(pressing pressure : 100MPa, pressing temperature : 410℃). Extrusion was conducted at 300℃ with ram speed of 13㎝/min under hot extrusion ratios 25 : 1 and 40 : 1. Tε treatment was performed up to 150h at 170℃ after extrusion. Mg alloy chips was also extruded and heat-treated at the same condition as a reference material. Microstructural observation and tensile test were carried out to investigate the effects of extrusion on the microstructure and mechanical property of the composite. Microstructural observation showed that both extruded composite and extruded Mg alloy chips have fine grain sizes due to dynamic recrystallization during hot extrusion. It has been observed that tensile strength of extruded composite is superior than that of extruded Mg alloy machined chips. This may be attributable to the effect of SiC particles and the fine grain size along the periphery of SiC particle. In the T_6 condition, extruded Mg machined chips showed a small decrease of tensffe strength, whereas extruded composite showed an increase of tensile strength. This may be because SiC particles restricted the grain growth of the Mg matrix during solution treatment.

Differential expression of circulating microRNAs in lactating Holstein and Jersey cows exposed to heat stress

이지환,김두산,임병휘,유경림,백형욱,김주환,하승민,김상범,이승환,최태정,최인철 사단법인 한국동물생명공학회 2024 한국동물생명공학회지 Vol.39 No.4

Background: South Korea has recently faced record-high temperatures, which have adversely affected dairy production. Holstein cows, the primary dairy breed globally, are particularly sensitive to heat stress. In contrast, Jersey cows have shown greater heat tolerance, as demonstrated by phenotypic studies. Methods: We investigated physiological and molecular responses to heat stress in Holstein and Jersey cows by measuring rectal temperature, milk yield, and average daily gain, confirming Holstein cows’ greater vulnerability. To explore molecular mechanisms, we analyzed circulating microRNA profiles from whole blood samples collected under heat stress and normal conditions using microRNA-sequencing. Differential expression patterns were compared between the two breeds to identify biological pathways associated with heat stress. Results: Four microRNAs (bta-miR-20b, bta-miR-1246, bta-miR-2284x, and bta-miR- 2284y) were significantly differentially expressed in both breeds under heat stress (|FC| ≥ 2, p < 0.05). Notably, bta-miR-20b and bta-miR-1246 were linked to corpus luteum function and progesterone biosynthesis, while bta-miR-2284x and bta-miR- 2284y were associated with immune responses. A comparison of 11 potential heat stress-related microRNAs identified in previous studies of Holstein cows revealed consistent expression trends in Jersey cows, albeit with lower fold changes, suggesting their superior heat resilience. Conclusions: Our study highlights the physiological and microRNA-based differences in heat stress responses between Holstein and Jersey cows. Jersey cows exhibited greater resilience, supported by more stable microRNA expression profiles and improved heat stress indicators, making them a promising breed for dairy production in increasingly hot climates.

혁신적 제품-서비스 시스템 계획을 위한 비즈니스모델링 방법론

이지환,홍유석 대한산업공학회 2012 대한산업공학회 춘계학술대회논문집 Vol.2012 No.5

알루미나 나노유체의 유동 특성에 관한 연구

이지환,장석필 대한기계학회 2006 大韓機械學會論文集B Vol.30 No.6

이야기를 통한 탐구과정에 대한 기호학적 접근 - AT 706 <손 없는 색시>를 대상으로

이지환 한국기호학회 2023 기호학연구 Vol.74 No.-

이 연구는 퍼스 기호학적으로 <손 없는 색시>를 분석하였다. 그리고 퍼스 실용주의관점에서, 이야기기호에서 인물이 고난을 겪다가 평안에 도달하는 문답과정을, 어떤사고이자 탐구로 보았다. 그리고 이야기기호들의 도상기호인 다이어그램을 통한 추론을, 일종의 이야기에 대한 숙고이자 이야기를 통한 탐구들로 이해하였다. 그리고 이야기에 대한 기호학적 접근의 과정이나, 실용주의적 해석의 지침이나 적용을 구체적으로 서술하였다. 그리하여 어떤 문제나 탐구를 직간접적으로 제시하는 이야기에, 퍼스의 관점이 충분히 적용될 수 있다는 것을 보였다. <손 없는 색시> 유형의 설화들은 복합적인 문답과정과 다원적인 관계들을 보인다. 포괄적인 문답과정 하에 다양한 차이와 탐구 주체를 갖는 하위 문제나 임시 해결들이 제시된다. 그 문제상황들의 조건들과 인물의 행위 및 행위결과 등을 고려해서, 주된서사요소들에 대한 실용주의적 의미를 풍부하게 얻을 수 있었다. 이에 따라 색시 개인의 심리와 성장 도식에 집중했던 기존 연구와 달리, 문제 상황 속에서의 색시와 여러인물들의 다원적 관계를 파악할 수 있었다. 그리고 남편과 시어머니의 활동 등에 대하여 상세히 조명하였다. 그리고 색시의 손의 의미에 관하여, 실용주의적 관점에서의 해석을 통해, 색시의 습관 및 행동과의 관계 하에서

Business Model Mining: Analyzing a Firm’s Business Model with Text Mining of Annual Report

이지환,홍유석 대한산업공학회 2014 Industrial Engineeering & Management Systems Vol.13 No.4

As the business model is receiving considerable attention these days, the ability to collect business model related information has become essential requirement for a company. The annual report is one of the most important external documents which contain crucial information about the company’s business model. By investigating business descriptions and their future strategies within the annual report, we can easily analyze a company’s business model. However, given the sheer volume of the data, which is usually over a hundred pages, it is not practical to depend only on manual extraction. The purpose of this study is to complement the manual extraction process by using text mining techniques. In this study, the text mining technique is applied in business model concept extraction and business model evolution analysis. By concept, we mean the overview of a company’s business model within a specific year, and, by evolution, we mean temporal changes in the business model concept over time. The efficiency and effectiveness of our methodology is illustrated by a case example of three companies in the US video rental industry.

앙상블 기법을 활용한 선박 메인엔진 이상치 탐지

이지환 대한산업공학회 2020 대한산업공학회 추계학술대회논문집 Vol.2020 No.11

Experimental Investigation of Coupling Effects between Particle Size and Temperature on the Thermal Conductivity of Alumina Nanofluids

이지환,장석필,이승현,박용준,김동진,구자예 한국분무공학회 2014 한국액체미립화학회지 Vol.19 No.4

This study investigates the effects of nanoparticle size and temperature on the thermal conductivity enhancement of water-based alumina (Al2O3) nanofluids, using the centrifuging method and relative centrifugal forces of differing magnitude to produce nanofluids of three different particles without involving any dispersants or surfactants. We determined the coupling dependency in thermal conductivity enhancement relative to nanoparticle size and temperature of the alumina nanofluids and also experimentally showed that the effect of temperature on thermal conductivity is strongly dependent on nanoparticle size. Also, our experimental data presented that the effective medium theory models such as the Maxwell model and Hasselman and Johnson model are not sufficient to explain the thermal conductivity of nanofluids since they cannot account for the temperature- and size-dependent nature of water-based alumina nanofluids.