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오철민,오선택,나정열,이성욱 한국음향학회 2002 韓國音響學會誌 Vol.21 No.5
수심이 변하는 천해 환경에서 이동하는 선박방사소음의 광대역 간섭 유형을 고찰하였다. 수심 변화율이 일정한 음도파관에 대해 단열 모드 이론에 근거하여 거리-주파수 영역에서의 보강 (또는 상쇄) 간섭 발생 유형을 나타내는 음도파관 불변인자 (waveguide invariant index, β)를 유도하였다. 이를 이용하여 수심 변화에 의한 광대역 간섭 형태 변형을 해석하였다. 해석적 방법으로 고찰한 간섭 유형은 해상 실험과 수치 모델을 이용한 모의실험에서도 나타남을 확인하였다. Broadband interference patterns are studied using ship as an acoustic source in shallow waters with varying bathymetry. Waveguide invariant index (β) indicating the pattern of constructive (or destructive) interference in range-frequency domain is derived in a waveguide with constant bottom slope based on adiabatic mode theory. Using this invariant, changes of the interference patterns resulting from the variation of bottom bathymetry are analyzed. Results of the analytic interpretation is compared with those from sea experiments and numerical simulations.
Sn 휘스커 성장에 미치는 Air-HAST 조건의 영향
오철민,오상주,김다정,홍원식,김근수 대한용접접합학회 2019 대한용접·접합학회지 Vol.37 No.2
Sn whiskers are one of the major causes of failure in fine-pitch electronics because of the short distance between the leads in an electronic package. In various whisker mechanisms, it takes a long time to grow a whisker due to Sn corrosion because the temperature is limited to below 100℃ in high humidity. In the highly accelerated temperature and humidity stress test (HAST), the corrosion phenomenon rarely occurred because of the little air inside the chamber. Therefore, air is needed in the whisker accelerating test to meet the same whisker mechanism under high temperature and humidity conditions. In this study, an Air-HAST with air inputs in the chamber with highly temperature and humidity was introduced. Whisker growth was accelerated with temperatures at 130℃ and various air pressures using the thin quad flat package (TQFP) sample with Sn plating lead. The whisker growth in the Air-HAST, HAST, and high temperature and high humidity test (85℃, 85%R.H.) was compared by plotting each growth length and number of whiskers. The accelerated relationships of whisker growth under the various test conditions will help the electronic industry meet the short development cycles.
빌렘 플루서의 ‘無 의미’를 통해 본 디지털사진의 푼크툼 연구
오철민 현대사진영상학회 2022 현대사진영상학회논문집 Vol.25 No.2
Flusser regards human history as the historical change in codes of images, texts, and technical images. He says, “decoding the meanings of technical image is jumping into the empty universe and will never been decipherable.” This study is intended to find the clues that he left in hope of their being decoded and consider how the meaning of empty universe is decoded through photography, the first technical image. First, photography is a device based on gaps. The nature of thinking in text that has a desire for “personal narrative” is inherent in technical image. Taking Wolfgang Iser, an aesthetician of reception, as an example, it can be said that a work is reified by filling up the gaps and indeterminate elements through “personal narrative” of the recipient. Second, the symbol used for classifying the history of codes by Flusser is divided into ‘a sign agreed upon’ and ‘a sign to be agreed upon’ according to the consideration on Peirce, a semiotician. Decoding ‘a sign agreed upon’ is available through unilateral acceptance while decoding ‘a sign to be agreed upon’ is available through “metonymy by recipients.” Third, following the texts by Flusser, the character of empty universe is defined as “to have infinite potential, possibility and inevitability, no unchanging truth or objective meaning.” Here Flusser himself says: “The value of truth in photography is meaningless. Probability calculation and indeterminacy are dominant.” Based on Flusser’s theory, classical photography and digital one have the same position in ontology. It was observed that their principles and processes of decoding are identical, and therefore, digital photography also owns studium and punctum. Conclusionally, it can be seen that decoding technical image, especially photography, derives from the recipient-oriented interpretation and the recognition of potentials of its infinite meaning.
열충격 사이클에 따른 SnAgCu 솔더별 솔더 접합부의 신뢰성 및 계면반응
오철민 ( Chul Min Oh ),박노창 ( No Chang Park ),한창운 ( Chang Woon Han ),방만수 ( Man Soo Bang ),홍원식 ( Won Sik Hong ) 대한금속·재료학회 2009 대한금속·재료학회지 Vol.47 No.8
Pb-free solder has recently been used in electronics in efforts to meet environmental regulations, and a number of Pb-free solder alloy choices beyond the near-eutectic SnAgCu solder are now available. With increased demand for thin and portable electronics, the high cost of alloys containing significant amounts of silver and their poor mechanical shock performance have spurred the development of low Ag SnAgCu solder, which provides improved mechanical performance at a reasonable cost. Although low Ag SnAgCu solder exhibits significantly higher fracture resistance under high-strain rates, little thermal fatigue data exist for this solder. Therefore, it is necessary to investigate thermal fatigue reliability of low Ag SnAgCu solder under variation of thermal stress in order to allow its implementation in electronic products with high reliability requirements. In this study, the reliability of Sn0.3Ag0.7Cu(SAC0307), a low Ag solder alloy, is discussed and compared with that of Sn3Ag0.5Cu(SAC305). Three sample types and six samples size are evaluated. Mechanical properties and microstructure of the solder joint are investigated under thermal shock cycles. It was observed that the mechanical strength of SAC0307 dropped slightly with thermal cycling relative to that of SAC305. This reveals that the failure mode of SAC0307 is different from that SAC305 under this critical condition.