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${La_{1-x}}{Sr_x}{MnO_{3-{\delta}}}$(0.19$\leq$x$\leq$0.31) 박막의 결정구조 및 전기전도 특성
허현,임세주,조남희,Heo, H.,Lim, S.J.,Cho, N-H. 한국재료학회 2000 한국재료학회지 Vol.10 No.6
기판온도, 박막조성 및 증착후 열처리 등의 조건에 따른 ${La_{1-x}}{Sr_x}{MnO_{3-{\delta}}}$(0.19$\leq$x$\leq$0.31) 박막의 결절구조와 전기전도 특성을 조사하였다. 스퍼터법을 이용하여 $500^{\circ}C$에서 증착된 박막은 강한 <001> 우선배향성과 유사정방정(pseudo-tetrag-onal, a/c-=0.97) 결정체를 나타냈다. 이러한 박막의 단위포는 산소분위기 내에서 증착후 열처리에 의하여 입장정 결정계로 변하였다. $La_{0.67}Sr_{0.33}MnO_3$ 조성의 주타겟과 $La_{0.3}Sr_{0.7}MnO_3$조성의 보조타겟을 동시에 이용하여 박막의 조성을 조절하였다. 보조타겟의 개수에 따라 박막내의 Sr 함량(x)은 0.19-0.31 범위의 값을 나타내었으며, x값이 0.19로부터 0.31로 증가시 금소-반도체의 전이 온도가 상승하였고, 전지비저항이 대체로 감소하였다. 0.18 T의 자기장 하에서, $La_{0.69}Sr_{0.31}MnO_3$조성의 박막의 자기저항변화 MR((%) = (${\rho}_o-{\rho}_H/{\rho}_H$)는 약 390% 이었다. We investigated the effect of substrate temperature, chemical composition and post-deposition heat-treatment on the crystal structure and electrical transport of $La_{1-x}Sr_xMnO_{3-{\delta}}$(0.19${\leq}x{\leq}$0.31) thin films. As-prepared $La_{1-x}Sr_xMnO_{3-{\delta}}$ films grown at $500^{\circ}C$ by sputter techniques were found to have the pseudo-tetragonal system(a/c=0.97) and a highly preferential <001> orientation. The films were changed to be of the cubic system by post-deposition annealing at around $900^{\circ}C$. A main target of $La_{0.67}Sr_{0.33}MnO_3$ as well as auxliary targets of $La_{0.3}Sr_{0.7}MnO_3$ ceramics were co-sputtered to control the chemical composition of the film. The Sr content(x) of the film ranged from 0.19 to 0.31, depending on the number of the auxiliary target. When x increased from 0.19 to 0.31, the electrical resistivity of the film decreased and the transition temperature between metal and semiconductor shifted to higher temperature. With a magnetic field of 0.18 T, the magneto-resistance ratio (MR(%) = (${\rho}_o-{\rho}_H/{\rho}_H$) of the $La_{0.69}Sr_{0.31}MnO_3$ thin film was about 390%.
기관 내관의 기낭을 팽창시키는 방법의 비교: 수동적 배출법과 최소 기낭 팽창법
허현,김경환,신동운,박준석,김훈,전우찬,신희준,김민정,박준민 대한응급의학회 2013 大韓應急醫學會誌 Vol.24 No.1
Purpose: Inflation of an endotracheal tube cuff with adequate pressure is an important procedure. Passive release technique (PRT) is a useful and convenient method for inflating the cuff. To date, no study comparing this method with minimal occlusive volume technique (MOVT), one of the most commonly used methods for inflating the cuff, has been reported. We conducted this study for comparison of effectiveness, difficulty, and preference between the two methods. Methods: We conducted a prospective, crossover, randomized study in which participants used each technique,one at a time. Participants inflated the cuff of an endotracheal tube inserted into a manikin after receiving brief education on use of the two methods. After inflating the cuff using each method, pressure and volume of the inflated cuff were measured using a portable manometer and syringes, respectively. Then, difficulty of each method was investigated using the visual analogue scale (VAS) and preference for each method was investigated. Results: A total of 47 participants were enrolled in the study. The mean pressure between the two methods was not statistically different (p=0.27). However, adequate pressure was achieved in 37 (78.7%) and 16 (34.0%) of participants in PRT and MOVT, respectively (p<0.01). The mean volume was 6.0±0.4 ml in PRT and 5.7±0.6 ml in MOVT (p<0.01). The VAS score for diffculty was 17.7±15.8 in PRT and 76.0±15.8 in MOVT (p<0.01). Preference for PRT was 46(97.9%) and that for MOVT was 1 (2.1%). Conclusion: PRT is an easier, more preferred, and more effective method for cuff inflation than MOVT.
끝나지 않은 전쟁: 북부와 남부의 차별적 위기 인식과 재건의 비극
허현 서울대학교 미국학연구소 2022 미국학 Vol.45 No.2
This study investigates the causes of the American Civil War and the failure of the Reconstruction by paying special attention to the Northern and Southern senses of crisis about “the impending crisis” of the 1850s. Whereas the North had a passive attitude towards slavery because of its obsession with Unionism, the South was desperate enough to secede from the Union in defense of slavery. The Southern perception of crisis was due to their feeling of impotence in the face of apparently crumbling slavery after the election of Lincoln. This Southern urgency enabled the Confederates, even after Appomattox, to continue the war against the freed but helpless blacks, which heralded the tragedy of the Reconstruction.
60Hz 전원동기를 이용한 스펙트럼 확산 전력선 통신에 관한 연구
許賢,潘在景 全北大學校 1996 論文集 Vol.41 No.-
Power line communication is very useful and economical for local area network, office automation, factory automation, and home automation. Electric power distribution circuits provide reasonably universal channels with a simple and standard interface in the from of a wall-socket plug. Disadvantages are limited bandwidth in comparison with ordinary communication links, high noise levels, and uncertain and varying levels of impedance. We presents the measurements of noise, attenuation, and impedance on the intrabuilding distribution circuits. Measurements were made at four different locations, such as laboratory, apartment, house, and hospital. These data are available for the design of communication systems. We consider pseudonoise(PN) modulation to overcome these impairments and present preliminary assessments of performance obtainable using a simple direct-sequence(DS) PN modem. Code synchronization is implemented by 60Hz zero crossing of the power frequency. The results have shown that data are transmitted and reconstructed well through power line up to 3kbps.