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과잉 PbO에 의한 (Pb,Y) $(Zr,Sn,Ti)O_3$세라믹스의 유전 및 전기장유기변형 특성
윤기현,김정희,강동헌,Yun, Gi-Hyeon,Kim, Jeong-Hui,Gang, Dong-Heon 한국재료학회 2000 한국재료학회지 Vol.10 No.1
디지털형 압전/전왜 액츄에이터 응용을 위하여 상경계(반강유전상/강유전상) 조성인 $Pb_{0.94}Y_{0.04}[(Zr_0.6Sn_0.4)_{0.915}Ti_0.085]O_3$ (PYZST) 계를 택하여 과잉 PbO의 첨가량 및 소결 조건 변화에 따른 상전이 특성, 유전 특성 및 전기장 유기변형 특성을 연구하였다. 사방정 구조를 갖는 PYZST 세라믹스에서 과잉 PbO 첨가에 따른 결정구조의 변화는 거의 확인되지 않았으나, 소결 후 입자가 약간 작아지며 둥근 형태로 변화하였고 첨가량 증가에 따라 적정 소결온도는 감소하였다. 과잉 PbO의 첨가량이 증가함에 따라, 분극측정시 반강유전상이 보다 안정되는 경향을 보였고, 전계유도변형 측정시 인가전기장 제거상태에서의 변형의 형상기억성이 감소하고 디지털형 변형곡선 특성이 강화되었다. 또한 최대 유전상수와 전계 유기변형량은 감소하였으나 반면 상전이(반강유전상$\leftrightarrow$강유전상) 전기장 및 비저항은 증가하는 경향을 나타냈다. 이러한 결과는 과잉으로 첨가된 PbO에 의한 격자 결함반응 및 분역벽 이동 거동 가능성과 연관시켜 설명하였다. The $Pb_{0.94}Y_{0.04}[(Zr_{0.6}Sn_{0.4})_{0.915}Ti_{0.085}]O_3$ ceramics which corresponded to the antiferroelectric-ferroelectric phase boundary composition were prepared for digital-type-piezoelectric/electrostrictive device application. Their dielectric, field-induced polarization (P) and strain (X) behaviors were studied with variations in sintering condition and excess PbO content. The orthorhombic structure of specimens was hardly affected either by excess PbO addition or sintering temperature. With increasing excess PbO content, grains tended to be smaller and rounded ones, and the optimum sintering temperature was lowered. Excess PbO addition stabilized the antiferroelectric phase of the specimen effectively, which was confirmed by P-E and X-E analyses. Also the digital-type-strain character was found to be enhanced despite of slight increase in phase transition (AFE-FE) field and electrical resistivity, and decrease in maximum strain. These results were explained in terms of possible lattice defects and domain wall motion.
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조영 경식도 심초음파에 의한 난원공개존 유병율 및 임상적 의의
이만영(Man Young Lee),전두수(Doo Soo Jeon),전승석(Seung Suk Cheon),이길환(Gil Hwan Lee),강동헌(Dong Heon Gang),김철민(Chul Min Kim),채장성(Jang Seong Chae),박인수(In Soo Park),홍순조(Soon Jo Hong),최규보(Kyu Bo Choi) 대한내과학회 1994 대한내과학회지 Vol.47 No.2
N/A Objectives: Most of patients with patent formen ovale have normal intracardiac pressure and no other abnormality during their life. But because of the high prevalence of clinically latent venous thrombosis, paradoxical embolism through a patent foramen ovale may occur. Although this is a rare complication, the result can be devastating. Previously, contrast transthoracic echocardiography was used to demonstrate patent foramen ovale but the prevalence rate was less than the expected one based on autopsy in general population. These low detection rates have discouraged the use of contrast transthoracic echocardiography to diagnose patent foramen ovale. But transesophageal echocardiography provides larger tomographic field and more clear views around the interatrial septum than transthoracic echocardiography, We tried this study to evaluate the incidence of patent foramen ovale and its role as a possible cause of paradoxical embolism in cerebral infarction patients. Methods: Contrast transesophageal echocardiographic examinations with indocyanine green were performed in 426 patients including 32 patients with cerebral infarction. The prescence of the patent forancen ovale was confirmed by demonstrating echogenic contrast crossing the interatrial septum. Result: 1) Contrast transesophageal echocardiography is a useful technique to evalute right to left shunt, 2) Patent foramen ovale was demonstrated in 73 of 426 patients and 6 of 32 two patients with cerebral infarction showed pakent formen ovale. But patent formen ovale was thought to be a cause of paradoxical embolism only in 3 patients without accompanying cardiovascular disease or risk factors. 3) The prevalence of patent foramen ovale increased progressively with increasing age. 4) There are no serious complications during and after contrast transesophageal echocardiography. Conclussion: Contrast transesophageal echocardiography is a safe, and reliable technique for evaluating interatrial shunt provoked with cough or Valsalva maneuver. This technique should be considered in cerebrovascualr disease patients without known risk factors to evaluate the possible paradoxical embolism.
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