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YBa₂(Cu_(1-x)Fe_(x))₃O_(9-y)계의 초전도성과 Mossbauer 효과
申榮男,金在慶,조현웅 大邱大學校附設 基礎科學硏究所 1990 基礎科學硏究 Vol.7 No.-
YBa₂(Cu_(1-x)Fe_(x))₃O_(9-y) superconductors are prepared and their physical characteristics are investigated by measuring the resistivity, X-ray diffraction pattens and Mossbauer spectra. At x=0.03, the crystal structure is transformed from orthorhombic to tetragonal system. Transition temperatures are not changed in the orthorhombic region, but linealy decreased with increasing x in the tetragonal region (80K at x=0.03 and 30K at x=0.1). The Mossbauer spectra are fitted to Lorentzian line shapes with two quadrupole doublets. Two main doublets and lattice parameters indicate that the valancy of Fe is +3. F2 site has typical square-pyramid coordination and F1 site has highly atypical (for Fe^(3+)) coorination of square-planar.
Development of indirect EFBEM for radiating noise analysis including underwater problems
Hyun-Wung Kwon,Suk-Yoon Hong,Jee-Hun Song 대한조선학회 2013 International Journal of Naval Architecture and Oc Vol.5 No.3
For the analysis of radiating noise problems in medium-to-high frequency ranges, the Energy Flow Boundary Element Method (EFBEM) was developed. EFBEM is the analysis technique that applies the Boundary Element Method (BEM) to Energy Flow Analysis (EFA). The fundamental solutions representing spherical wave property for radiating noise problems in open field and considering the free surface effect in underwater are developed. Also the directivity factor is developed to express wave’s directivity patterns in medium-to-high frequency ranges. Indirect EFBEM by using fundamental solutions and fictitious source was applied to open field and underwater noise problems successfully. Through numerical applications, the acoustic energy density distributions due to vibration of a simple plate model and a sphere model were compared with those of commercial code, and the comparison showed good agreement in the level and pattern of the energy density distributions.
권현웅(Hyun-Wung Kwon),홍석윤(Suk-Youn Hong),송지훈(Jee-Hun Song) 한국해양공학회 2012 韓國海洋工學會誌 Vol.26 No.4
Recently, the underwater radiated noises generated from large commerical ships have become a globally important issue. Countries with large ports and environmental protection organizations demand strict safety guidelines in relation to underwater radiated noise. In this paper, the coupled PFFE/PEBE method in used to investigate the vibration and underwater radiated noise of a commercial ship. PFFEM is employed to analyze the vibrational responses of the commercial ship, and PFBEM is applied to analyze the underwater radiation noise. The vibrational energy of the structure is treated as an acoustic intensity boundary condition of PFBEM to calculate the underwater radiation noise. Numerical simulations are presented for the commercial ship under various frequencies, and reliable results are obtained.
고부가가치선 선실의 소음 저감용 복합패널의 차음특성 해석
권현웅(Hyun-Wung Kwon),홍석윤(Suk-Youn Hong),길현권(Hyun-Gwon Kil),김화묵(Hwa-Muk Kim),송지훈(Jee-Hun Song) 한국해양공학회 2012 韓國海洋工學會誌 Vol.26 No.3
Recently, as the importance of the interior noise in a ship cabin has risen, ship builders have becomeconcerned about the use of noise reduction panels to reduce cabin noise. The results of previous researches have been based on analytical and experimental methods using simple sandwich panels. However, panel structures are becoming more complex to improve the transmission loss. Thus, researches that analyze the transmission loss of a panel are reaching the limit of study. This paper reports on research that was performed to determine the sound transmission characteristics of multi-complex panels applicable to high value-added vessels. It presents comparisons between analytical methods and experimental results by using a mini-reverberant chamber with components of sound attenuation panels, including the core and surface materials. The sound transmission loss of multi-complex panels are also analyzed in terms of the influences of the inside perforate plates and air gap thickness on the attenuation. Finally, the multi-complex panel with the highest noise attenuation is proposed based on the analysis results and experimental results in mini-reverberant chamber, which wereverified using a real-size reverberant chamber.
Analysis of the Predictive Validity of College Entrance Criteria
Bae, Hyun-Wung 한국데이터정보과학회 2007 한국데이터정보과학회지 Vol.18 No.4
Korea Military Academy has been using College Scholastic Ability Test(CSAT) and High School Grades(HSG) with other measures such as an Essay-type Test(ET), Physical Test(PT) and Personal Interview(PI) as criteria for entrance. The purpose of study is to investigate the properness of the criteria in admission decisions by examining the relationship between the college GPA and criteria, and the prediction of academic performance. The study showed that CSAT and HSG are significantly correlated with the college GPA, and these two criteria are better predictors for academic performance. Regression analysis also provided an important message that HSG is a better predictor than CSAT.
Development of indirect EFBEM for radiating noise analysis including underwater problems
Kwon, Hyun-Wung,Hong, Suk-Yoon,Song, Jee-Hun The Society of Naval Architects of Korea 2013 International Journal of Naval Architecture and Oc Vol.5 No.3
For the analysis of radiating noise problems in medium-to-high frequency ranges, the Energy Flow Boundary Element Method (EFBEM) was developed. EFBEM is the analysis technique that applies the Boundary Element Method (BEM) to Energy Flow Analysis (EFA). The fundamental solutions representing spherical wave property for radiating noise problems in open field and considering the free surface effect in underwater are developed. Also the directivity factor is developed to express wave's directivity patterns in medium-to-high frequency ranges. Indirect EFBEM by using fundamental solutions and fictitious source was applied to open field and underwater noise problems successfully. Through numerical applications, the acoustic energy density distributions due to vibration of a simple plate model and a sphere model were compared with those of commercial code, and the comparison showed good agreement in the level and pattern of the energy density distributions.