고온 코팅용 Cr-Al합금의 미세조직 및 특성에 미치는 Si 첨가의 영향

김정민,김일현,김현길,Kim, Jeong-Min,Kim, Il-Hyun,Kim, Hyun-Gil 한국재료학회 2019 한국재료학회지 Vol.29 No.1

Cr-Al alloys are attracting attention as oxidation resistant coating materials for high temperature metallic materials due to their excellent high temperature stability. However, the mechanical properties and oxidation resistance of Cr-Al alloys can be further enhanced, and such attempts are made in this study. To improve the properties of Cr-Al alloys, Si is added up to 5 wt%. Casting specimens with different amounts of Si content are prepared by a vacuum arc remelting method and isothermally heated under steam conditions at $1,100^{\circ}C$ for 1 hour. The as-cast microstructure of low Si alloys is mainly composed of only a Cr phase, while $Al_8Cr_5$ and $Cr_3Si$ phases are also observed in the 5 % Si alloy. In the high Si alloy, only Cr and $Cr_3Si$ phases remain after the isothermal heating at $1,100^{\circ}C$. It is found that Si additions slightly decrease the oxidation resistance of the Cr-Al alloy. However, the microhardness of the Cr-Al alloy is observed to increase with an increasing Si content.

레이저 표면 용융공정으로 Al-Cr 코팅한 Zr합금의 미세조직 특성

김정민,이재철,김일현,김현길,Kim, Jeong-Min,Lee, Jae-Cheol,Kim, Il-Hyun,Kim, Hyun-Gil 한국재료학회 2017 한국재료학회지 Vol.27 No.10

In this study, the coating of an Al-Cr layer on the surface of a Zircaloy-4 alloy was carried out through plasma pretreatment coating and a laser surface melting process. Two different conditions for laser treatment, severe or minimal surface melting of the Zr alloy substrate, were applied to form the final coating. When there was significant surface melting of the Zr alloy, the solidification microstructure of the newly formed coating layer was mainly composed of needle-shaped $Al_3Zr$, Al(Cr) and $Al_7Cr$ phases. On the other hand, the solidification microstructure of the coating layer was mainly composed of Al(Cr) and $Al_7Cr$ phases when there was minimal surface melting of Zr base in the laser process. However, when the coating was maintained at $1100^{\circ}C$ for 2 hours, significant inter-diffusion occurred between the phases in the coating. As a result, the upper part of the coating layer was observed to mainly consist of $Al_3Zr$ and $Al_8Cr_5$ phases, regardless of the laser treatment conditions.

음악과 음성 판별을 위한 웨이브렛 영역에서의 특징 파라미터

김정민,배건성,Kim, Jung-Min,Bae, Keun-Sung 대한음성학회 2007 말소리 Vol.61 No.-

Discrimination of music and speech from the multimedia signal is an important task in audio coding and broadcast monitoring systems. This paper deals with the problem of feature parameter extraction for discrimination of music and speech. The wavelet transform is a multi-resolution analysis method that is useful for analysis of temporal and spectral properties of non-stationary signals such as speech and audio signals. We propose new feature parameters extracted from the wavelet transformed signal for discrimination of music and speech. First, wavelet coefficients are obtained on the frame-by-frame basis. The analysis frame size is set to 20 ms. A parameter $E_{sum}$ is then defined by adding the difference of magnitude between adjacent wavelet coefficients in each scale. The maximum and minimum values of $E_{sum}$ for period of 2 seconds, which corresponds to the discrimination duration, are used as feature parameters for discrimination of music and speech. To evaluate the performance of the proposed feature parameters for music and speech discrimination, the accuracy of music and speech discrimination is measured for various types of music and speech signals. In the experiment every 2-second data is discriminated as music or speech, and about 93% of music and speech segments have been successfully detected.

Providencia Isolates Carrying blaPER-1 and blaVIM-2 Genes: Biofilm-Forming Capacity and Biofilm Inhibitory Concentrations for Carbapenem Antibiotics

김정민,Shukho Kim,Hee Woo Lee,Sung Min Kim,설성용 한국미생물학회 2011 The journal of microbiology Vol.49 No.3

Multidrug-resistant clinical isolates of Providencia carrying blaPER-1 and blaVIM-2 were evaluated for the abilities to form biofilm and high biofilm forming capacity was demonstrated in them. Minimum biofilm inhibitory concentrations (MBICs), minimum biofilm eradication concentrations (MBECs), and minimum inhibitory concentrations (MICs) for imipenem and meropenem were also determined. In all tested strains, the MBICs were higher than the MICs for both drugs. Interestingly, the MBICs and the MBEC50 for meropenem were lower than those for imipenem in the isolates producing high amounts of biofilm, suggesting that meropenem is superior to imipenem in the growth inhibition and eradication of biofilm forming Providencia strains.

일본뇌염바이러스의 Mutant M 단백질에 반응하는 다클론항체의 생산: 극성 아미노산 잔기의 바이러스 생산과정에서의 역할

김정민,윤상임,송병학,김진경,이영민,Kim, Jeong-Min,Yun, Sang-Im,Song, Byung-Hak,Kim, Jin-Kyoung,Lee, Young-Min 한국미생물학회 2010 미생물학회지 Vol.46 No.2

일본뇌염바이러스(Japanese encephalitis virus)는 모기 매개성 플라비바이러스에 속하며, 주로 동남아시아 지역에서 유행성 바이러스성 뇌염을 일으킨다. 일본뇌염바이러스는 외피를 가진 작은 바이러스로서, 양성가닥 RNA 게놈을 가지고 있다. 감염성을 띤 바이러스 입자는 capsid (C), membrane (M; prM 전구체로부터 생성), 및 envelope (E)과 같은 3개의 구조단백질로 이루어져 있다. 본 연구에서는 일본뇌염바이러스 생산과 정에 M 단백질의 N-말단부위에 위치한 극성 아미노산 잔기의 역할을 분석하였다. 일본뇌염바이러스의 infectious cDNA를 활용하여, M 단백질의 $E^9$와 $K^{15}K^{16}E^{17}$ 잔기를 알라닌으로 치환시킨 2개의 mutant cDNA (Mm1과 Mm2)를 각각 제작하였다. 각각의 cDNA로부터 합성된 mutant RNA를 세포에 트랜스펙션시킴으로써, 비록 세포 내에 축적된 3개의 구조단백질양은 변화가 없으나, 이들 세포로부터 생산된 바이러스의 양은 Mm2 RNA의 경우 ~1,000배 감소됨을 관찰하였다. 흥미롭게도, Mm2 RNA로부터 발현된 mutant M 단백질은 wild-type M 단백질을 인지하는 항혈청에는 반응하지 않았으나, mutant M 단백질을 항원으로 제작된 항혈청에는 반응하는 것을 알 수 있었다. 본 실험결과는 일본뇌염바이러스 M 단백질을 구성하는 3개의 극성 아미노산 잔기($K^{15}K^{16}E^{17}$)가 바이러스의 생산과정에 관여한다는 것을 암시한다. 앞으로, wild-type 또는 mutant M 단백질(Mm2)을 인식하는 2개의 항혈청은 이 단백질의 기능연구에 유용한 재료로 사용될 것으로 기대된다. Japanese encephalitis virus (JEV), a member of the mosquito-borne flaviviruses, causes epidemics of viral encephalitis in the Southeastern Asia. JEV is a small enveloped virus with a positive-sense RNA genome; the infectious virion consists of three structural proteins, namely capsid, membrane (M; a mature form of its prM precursor), and envelope proteins. Here, we investigated a role of the charged residues found at the N-terminus of the JEV M protein in virus production. Using an infectious JEV cDNA, we generated two mutant cDNAs, Mm1 and Mm2, by charged-to-alanine substitution for $E^9$ and $K^{15}K^{16}E^{17}$ residues of the M protein, respectively. By transfection of wild-type or each of the two mutant RNAs transcribed from the corresponding cDNAs, we found that Mm2, but not Mm1, had a ~3-log decrease in virus production, even though a comparable amount of all three structural proteins were produced in transfected cells. Interestingly, the prM protein expressed in Mm2 RNA-transfected cells was not recognized by the polyclonal antiserum raised against the N-terminal 44 amino acids of the wild type M protein, but reacted to the antiserum raised against the corresponding region of the mutant Mm2. Our results indicate that three charged residues ($K^{15}K^{16}E^{17}$) in JEV M protein play a role in virus production. Two polyclonal antisera specifically recognizing the wild-type or Mm2 version of the M protein would provide a useful reagent for the functional study of this protein in the virus life cycle.

단결정 반금속 비스무스 단일 나노선의 Shubnikov-de Haas 진동

김정민,함진희,심우영,이경일,전계진,정원용,이우영,Kim, Jeong-Min,Ham, Jin-Hee,Shim, Woo-Young,Lee, Kyoung-Il,Jeon, Kye-Jin,Jeung, Won-Young,Lee, Woo Young 한국재료학회 2008 한국재료학회지 Vol.18 No.2

The magneto-transport properties of an individual single crystalline Bi nanowire grown by a spontaneous growth method are reported. A four-terminal device based on an individual 400-nm-diameter nanowire was successfully fabricated using a plasma etching technique that removed an oxide layer that had formed on the surface of the nanowire. Large transverse ordinary magnetoresistance (1401%) and negative longitudinal ordinary magnetoresistance (-38%) were measured at 2 K. It was observed that the period of Shubnikov-de Haas oscillations in transverse geometry was $0.074^{T-1}$, $0.16^{T-1}$ and $0.77^{T-1}$, which is in good agreement with those of bulk Bi. However, it was found that the period of SdH oscillation in longitudinal geometry is $0.24^{T-1}$, which is larger than the value of $0.16^{T-1}$ reported for bulk Bi. The deviation is attributable to the spatial confinement arising from scattering at the nanowire surface boundary.

외모에 대한 사회문화적 요인, 신체질량지수 및 자아존중감이 신체상에 미치는 영향 - 발달단계별 차이를 중심으로 -

김정민,이세진,Kim, Jung-Min,Yi, Se-Jin 한국가정관리학회 2009 가정과삶의질연구 Vol.27 No.6

The purpose of the study is to investigate developmental changes in the effect of sociocultural factors towards appearance, body mass index and self-esteem on body image. Participants were 315elementary school, 305middle school students, 310hight school students and 346college students from Seoul and Gyeonggi Province. Collected data were analyzed through Cronbach's $\alpha$, Two-way ANOVA, Pearson's correlation, and stepwise multiple regression. The findings of the study were as follows: 1) Sociocultural factors towards appearance, body mass index, self-esteem and body image differed by grade and gender. 2) Peers, self-esteem, BMI and mass media were significant predictors of elementary school students' body image. Mass media, BMI and self-esteem were significant predictors of middle school students' body image. Self-esteem, peers, BMI, gender and mass media were significant predictors of high school students' body image. Self-esteem, mass media and BMI were significant predictors of college students' body image.

타워크레인 설치 및 해체

김정민,Kim, Jeong-Min 한국건설안전협회 1995 建設 安全技術 Vol.17 No.-

'항행의 자유 작전'의 전략적 접근

김정민,Kim, Jeong-Min 한국해양전략연구소 2021 해양안보 Vol.3 No.1

남중국해는 풍부한 해저 및 어로자원 뿐만 아니라 매년 4만여 척 이상의 선박이 통과하고, 세계 해양물류 50%, 원유 66%가 통과하는 중요한 해상교통로이다. 특히 대한민국의 수입 물동량의 30%, 에너지 수입량의 90%가 당 해역을 통과하고 있다. 미국과 중국은 이 해역의 중요성을 일찍이 깨달아 각각 '인도-태평양 전략', '일대일로(一帶一路) 전략'을 시행하는 등 국가전략적 차원에서 해양안보를 통한 국익을 구체화 하고 있다. 이런 지정학적 갈등은 남중국해에서 미국이 실시하는 '항행의 자유 작전'이라는 양상으로 드러나고 있다. 이러한 중요성에도 불구하고, 항행의 자유 작전에 대한 국내 연구는 미흡한 것이 사실이며, 기존 연구 대부분도 국제법과 국제 협약에 대한 분석을 중심으로 수행되었다. 본 논문은 항행의 자유 작전에 대한 전략적 인식을 통해 그 기원과 배경을 분석하고, 미·중 전략경쟁이 장기화되는 상황에서 한반도 안보에 주는 함의를 도출하고자 한다. The South China Sea is a significant maritime shipping route with abundant submarine and fishing resources. Over 40,000 ships pass through the South China Sea every year, constituting around 50% of global shipping and 66% of crude oil. In particular, 30% of Korea's import cargo and 90% of energy imports pass through this body of water. The US and China realized the significance of this sea area from early on and are embodying national interest through maritime security at the national strategic level by implementing the 'Indo-Pacific' and 'One Belt One Road' strategies, respectively. Such geopolitical conflicts are manifested in the 'freedom of navigation operations' by the US in the South China Sea. Despite its significance, there is a lack of studies in Korea on the freedom of navigation operations, and most previous studies only focus on analyzing international law and agreements. This article examines the origin and background of the strategic perception of the freedom of navigation operations and derives implications for the peace and security of the Korean Peninsula as the strategic competition between the US and China continues.

내산화성 Cr-Si-Al합금의 주조상태 및 고온가열 후의 미세조직 특성

김정민,김채영,양원철,박준식,Kim, Jeong-Min,Kim, Chae-Young,Yang, Won-Chul,Park, Joon-Sik 한국재료학회 2021 한국재료학회지 Vol.31 No.3

Cr-Si based alloys are not only excellent in corrosion resistance at high temperatures, but also have good wear resistance due to the formation of Cr3Si phase, therefore they are promising as metallic coating materials. Aluminum is often added to Cr-Si alloys to improve the oxidation resistance through which stable alumina surface film is formed. On the other hand, due to the addition of aluminum, various Al-containing phases may be formed and may negatively affect the heat resistance of the Cr-Si-Al alloys, so detailed investigation is required. In this study, two Cr-Si-Al alloys (high-Si & high-Al) were prepared in the form of cast ingots through a vacuum arc melting process and the microstructural changes after high temperature heating process were investigated. In the case of the cast high-Si alloy, a considerable amount of Cr3Si phase was formed, and its hardness was significantly higher than that of the cast high-Al alloy. Also, Al-rich phases (with the high Al/Cr ratio) were not found much compared to the high-Al alloy. Meanwhile, it was observed that the amount of the Al-rich phases reduced by the annealing heat treatment for both alloys. In the case of the high temperature heating at 1,400 ℃, no significant microstructural change was observed in the high Si alloy, but a little more coarse and segregated AlCr phases were found in the high Al alloy compared to the cast state.