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Poling Study in the Composite Systems of Polymer and PZT Ceramics
Sa-gong, Geon 동아대학교 공과대학 부설 한국자원개발연구소 1986 硏究報告 Vol.10 No.1
Hydrophone응용에 PZT(Lead Zirconate Titanate)가 널리 이용되고 있으며, d ̄_(h) 및 g ̄_(h)계수가 큰 것이 요구되고 있다. 그러나 d ̄_(33) 및 d ̄_(31) 계수의 부호가 반대이므로 Figure of Merit(d ̄_(h)·g ̄_(h))가 적다. 이를 개선하기 위해 Phase Connectivity의 개념을 이용한 각종 형태의 Ceramic-Polymer Composite가 연구, 실용화 되고 있다. 그들 중 Hydrophone에 응용되고 있는 1-3, 1-3-0, 3-1, 3-2 및 3-3 Composite는 PZT보다 Figure of Merit가 우수한 특성을 보이나 만들기가 까다롭고 高價이다. 반면에 0-3 Composite는 값이 싸고, 만들기는 쉬우나, 분극시키는 데 상당한 電界와 장시간을 필요로 하므로 0-3 Composite를 제작, 이들의 分極條件(電界 및 시간)을 개선하였다. The topic of this study has been selected to give insight into the poling behavior which are important in processing of the composites which are of most interest for piezoelectric transducer applications, e g, Hydrophone, Biomedical Scanner. 0-3 composites made from PZT powder require a large field strength(100-150KV/㎝) and longer duration of time(1/2-1 hour) in order to achieve sufficient electrical poling In 0-3 composites the electrical field acting on the piezoelectric ceramic is controlled by the ratio of the electrical conductivity of the polymer to that of the piezoceramic. One approach to this poling difficulty is to increase the polymer conductivity To do this, 0-3 composites were prepared from PZT powder and different types of Eccogel polymer with small volume % of conduction phase such as carbon, germanium or silicon These composites had 0-0-3 type connectivity By adding a small amount of conductive phase, poling can be carned out at much lower voltages(30-40KV/cm) and for shorter duration(5-10 minutes), making these composites amenable to mass production The optimized figure of ment of PZT-Eccogel(1365-0) composite with carbon additive for Hydrophone was about 10 times larger than that of single solid PZT
Overall Illuminance Uniformity of IRED Lighting in Nighttime CCTV
Sa-Gong, Geon,Park, Yung-Jun,Park, Jung-Je,Lee, Suho The Korean Institute of Electrical and Electronic 2017 Transactions on Electrical and Electronic Material Vol.18 No.1
This study looks at optimizinge light redistribution to improve the overall illuminance uniformity of commercial IRED modules. To obtain uniform illumination over a prescribed rectangular area, a freeform surface lens was evaluated using TracePro. The LED light overall illuminance uniformity regulated in KSC 7658 was verified using Relux software. Experimental test results showed 0.81 overall illuminance uniformity for rectangular light distribution of LED lights having a radiation angle of $80^{\circ}$. After fabricating prototype IRED lights based on these simulation results, illuminance performance was observed when used as actual IRED lighting with a nighttime CCTV system. Image observation photographs of the prototype $80^{\circ}$ rectangular IRED lights confirmed that object images can be seen clearly owing to high overall illuminance uniformity, and that dark regions of the CCTV screen were not shown.
Sa Gong Min,Jin Seon Kim,Woo Hyok Chang 대한안과학회 2009 Korean Journal of Ophthalmology Vol.23 No.3
We report three cases of neovascular glaucoma secondary to central retinal artery occlusion (CRAO) which were effectively managed with intravitreal bevacizumab (IVB) followed by panretinal photocoagulation (PRP). Neovascular glaucoma without peripheral anterior synechiae developed between one and five weeks following CRAO onset. All patients received 0.75 mg (0.03 ml) IVB. In all patients, complete regression of the iris and anterior chamber angle neovascularization was confirmed within one week. PRP was applied two weeks after the injection. The follow-up period was four to seven months (average, five months). Intraocular pressure was controlled in all patients using topical antiglaucoma medications alone. However, one patient experienced a recurrence of neovascularization three months after the initial combination treatment. This patient received another IVB injection and additional PRP, and the recurrent neovascularization resolved. There were no local or systemic adverse events in any patients. Therefore, intravitreal bevacizumab may be an effective adjunct in the treatment of neovascular glaucoma associated with CRAO. Korean J Ophthalmol 2009;23:215-218
사공환(Sa gong Hwan) 고려대학교 글로벌일본연구원 2014 일본연구 Vol.22 No.-
한국인 일본어 학습자의 일본어 음성 습득 과정에서 어려움이 많은 항목의 하나로 모음의 장단 구분을 들 수 있다. 그래서 본 연구에서는 한국인 학습자에 의한 일본어 모음의 장단 지각시 나타나는 오류 경향에 대해, 학습자의 학습기간, 단어 내 장음 위치, 악센트형, 단어 길이라는 네 가지 요인을 관점으로 하여 이들이 지각에 미치는 영향에 대해 밝히는 것을 목적으로 하였다. 이를 위해 서울 방언 화자 88명을 학습기간에 따라 A군, B군, C군으로 나눈 피조사자군를 대상으로 청취조사를 실시하였다. 청취조사에서 학습자에게 단어 내 요인을 고려한 단어 음성을 듣고 단어 내 장음의 유무와 장음이 있는 경우 그 위치를 표시하도록 하였다. 그 결과 다음과 같은 사실을 밝힐 수 있었다. 먼저, 한국인 학습자는 학습 기간이 늘어날수록 일본어 모음의 지각변별 능력이 향상됨을 알 수 있었다. 또, 단어 내 장음 위치를 잘못 판단하기보다 장음을 단음으로 잘못인지하는 경향이 더 강했다. 둘째로, 한국인 학습자의 단어 내 장음 위치의 판단은 어두나 어중 보다 어말에서 더 어렵다는 것을 알 수 있었다. 생성면에서도 장음 발음이 어말에서 어렵다는 결과가 있어 지각면과의 상관성을 유추할 수 있다. 그리고 악센트형에서는 피치가 높은 HH형이나 LH형 장음의 청취가 용이하고 LL형 장음의 청취가 어렵다는 것을 알 수 있었다. 장음에서의 높은 피치가 학습자의 지각 판단에 영향을 미친 결과라 할 수 있겠다. 마지막으로, 장음의 지각보다는 단음의 지각이 더 용이하다는 결과를 얻을 수 있었다. The purpose of this study is to discover how Korean students who are learning Japanese perceive long and short vowels in Japanese. Eighty-eight students were divided into three groups for testing. The grouping was made according to the learning period. The perception of each student is measured with a listening test of 68 words that have different pitches, long vowel positions, and accent types. From this test, the following results emerged. First, as the learning period becomes longer, learners are able to perceive vowels better. This result should be obvious. But it is somewhat surprising that students have more trouble in perceiving the difference between long and short vowels than the positions of long vowels. Moreover, the factors boundary dividing the long and short vowels are different from those of native speakers. Second, it is more difficult to perceive long vowels when they are in a final position compared to in the initial or middle positions. Third, students can perceive more accurately in the HH accent type or LH accent type than the LL accent type. Finally, students have more difficulty perceiving long vowels than short vowels.