묘성증후군 환아 1예에서 관찰된 안과적 소견

김상균,김형석,김승현,Sang Kyoon Kim,Hyoung-Seok Kim,Seung Hyun Kim 대한안과학회 2008 대한안과학회지 Vol.49 No.11

방향계 폴리에테르이미드막의 물 - 알콜 혼합액의 투과증발 특성에 관한 연구 : Ⅰ . 구조 변화에 따른 투과증발

김상균,제갈종건,이규호 ( S . G . Kim,J . G . Jegal,K . H . Lee ) 한국공업화학회 1997 공업화학 Vol.8 No.6

방향계 폴리에테르이미드를 건/습 상분리방법으로 막을 만들고 imide group이 갖는 선택 투과 특성과 표면층의 구조를 변화시켜 이때 나타나는 물-알콜 혼합액의 투과 증발 특성에 대해 연구하였다. 막의 선택성은 구조 변화의 반응시간에 따라 일정 시간까지 선형적으로 증가하였으며 이때의 구조 변화는 미 반응 막보다 치밀한 구조로 변화됨에 따른 효과로 보이고 있다. 치밀 막의 경우엔 90% 에탄을 용액에서 160의 선택성을 보였고, 이소프로필알콜용액에서는 2000이 넘는 높은 선택성을 보여줌으로써 이미드재료가 높은 투과 선택성이 있음을 보여주고 있다. 막의 투과도에 대한 온도 의존성은 온도 증가에 따라 선형적으로 증가하였고 선택도 또한 증가함을 보여주었다. Aromatic polyetherimide membranes were prepared by dry/wet phase inversion method and investigated regarding the pervaporation characteristic of water-alcohol mixtures by using the permselective property of imide group and the structure modification of skin layer of the membrane. The membrane selectivity increased with the reaction time of surface-modification, to some extent, and the density of top layer tends to increases with increasing the reaction time. In the case of dense membrane, the separation factor was 160 and 2000 for 90wt% ethanol mixture and 90wt% isopropanol solution, respectively, which implies that aromatic polyetherimide has a high permselectivity. The temperature dependence of permeation flux seems to follow an Arrhenius type at the temperature range of(40℃-70℃).

조건 사후 최대 확률과 음성 스펙트럼 변이 조건을 이용한 통계적 모델 기반의 음성 검출기

김상균,장준혁,Kim, Sang-Kyun,Chang, Joon-Hyuk 한국음향학회 2011 韓國音響學會誌 Vol.30 No.6

본 논문에서는 조건 사후 최대 확률 (conditional maximum a posteriori, CMAP)과 음성 스펙트럼 변이 조건을 기반으로 한 새로운 음성 검출기 (voice activity detection, VAD)를 제안한다. 제안된 음성 검출기는 통계적 모델을 기반으로 한 우도비 테스트 (likelihood ratio test, LRT)의 문턱값을 결정하는데 조건 사후 최대 확률과 스펙트럼 변이의 상태 값을 조건부 확률로 부과한다. 제안된 알고리즘을 다양한 잡음 환경에서 기존의 CMAP 기반의 음성 검출기와 비교한 결과 전체적으로 향상된 성능을 보였으며 특히 SNR이 낮은 조건에서 향상 폭이 컸다. In this paper, we propose a novel approach to improve the performance of a statistical model-based voice activity detection (VAD) which is based on the conditional maximum a posteriori (CMAP) with deviation. In our approach, the VAD decision rule is expressed as the geometric mean of likelihood ratios (LRs) based on adapted threshold according to the speech presence probability conditioned on both the speech activity decisions and spectral deviation in the pervious frame. Experimental results show that the proposed approach yields better results compared to the CMAP-based VAD using the LR test.

IQ Imbalance와 위상 잡음을 고려한 OFDM 통신 시스템의 성능 분석

김상균,유흥균,강병수,이광천,Kim, Sang-Kyun,Ryu, Heung-Gyoon,Kang, Byung-Su,Lee, Kwang-Chun 한국전자파학회 2007 한국전자파학회논문지 Vol.18 No.7

OFDM(Orthogonal Frequency Division Multiplexing) 시스템은 이동성이 있는 고속 데이터 전송에 적합한 전송 방법으로 널리 알려져 있지만, 위상 잡음과 직교 불균형(IQ imbalance)에 매우 민감한 특성을 보이는 단점이 있다. 그러므로, 본 논문에서는 위상 잡음 특성에 따른 위상 잡음 분산을 계산한 다음, 직교 불균형이 있는 OFDM 시스템의 통신 성능을 분석하였다. 시뮬레이션 결과, 위상 잡음의 분산과 직교 불균형의 크기 변화에 따라 통신 성능이 변화하는 것을 분석하였다. 분석 결과, 진폭 불균형이 ${\varepsilon}$=0.2; 0.3; 0.4이고, 위상 불균형이 ${\phi}=10^0$이고, 위상 잡음의 분산 ${\sigma}^2=0.012$일 때, BER은 $10^{-5}$에서 각각 2.88 dB, 3.61 dB, 4.69 dB의 SNR penalty가 존재한다. OFDM system is an excellent high speed transmission method but it is seriously sensitive to the phase noise and IQ imbalance. Therefore, in this paper, we analyze the communication performance of the OFDM communication system with IQ imbalance and phase noise. Phase noise's variance can be calculated by integral calculus of phase noise power spectrum. From simulation results, it can be shown that the BER performances show different change according to the phase noise variance and IQ imbalance amount. When amplitude imbalance is ${\varepsilon}$=0.2; 0.3; 0.4 and phase imbalance is ${\phi}=10^0$, and distribution of phase noise is ${\sigma}^2=0.012$, BER is degraded by 2.88 dB, 3.61 dB, 4.09 dB in $10^{-5}$ in the respect of the SNR penalty.

에피라식 후 각막상피편 보존 여부에 따른 초기 통증 및 상피 창상 치유 기간의 비교

김상균,송종석,김효명,Sang Kyoon Kim,Jong Suk Song,Hyo Myung Kim 대한안과학회 2008 대한안과학회지 Vol.49 No.12

Purpose: To investigate the influence of preservation of an epithelial sheet in Epi-LASIK on postoperative pain and epithelial wound healing time. Methods: This prospective study included 34 eyes of 17 patients with myopia who received Epi-LASIK. An epithelial flap was created using the epikeratome (Centurion SES, Norwood Abbey EyeCare, Australia). After the stroma was ablated using the MEL 80 (Carl Zeiss Meditec. Germany) excimer laser, the epithelial sheet was replaced on the stromal bed in one randomly selected eye of each patient, and removed in the contralateral eye. The pain scores at postoperative day 0, 1, 2, 5 and the numbers of days for the complete epithelial wound healing were compared between the sheet-preserved and the sheet-removed eyes. At 1 month postoperative, uncorrected visual acuity (UCVA), refractive error and corneal haze were also compared. Results: Pain scores on the day of operation were lower in sheet-preserved group and statistically significant (p=0.01). On postoperative day 1, 2, and 5, pain scores did not reach statistical significance (p=0.24, 0.08, 0.56, respectively). The mean epithelial healing time was 4.88±0.93 days for the flap-preserved eyes and 4.29±0.77 days for the flap-removed eyes, which showed statistical significance (p=0.01). No significant difference was noted between the 2 groups for mean UCVA, corneal haze and refractive error at 1 month postoperative. Conclusions: A preserved epithelial sheet reduced early postoperative pain but did not accelerate epithelial wound-healing rate.

적응형 문턱값을 가지는 2차 조건 사후 최대 확률을 이용한 통계적 모델 기반의 음성 검출기

김상균,장준혁,Kim, Sang-Kyun,Chang, Joon-Hyuk 한국음향학회 2010 韓國音響學會誌 Vol.29 No.1

본 논문에서는 음성의 통계적 모델에 기반한 음성 검출기 (voice activity detection, VAD)의 성능 향상을 위해 2차 조건 사후 최대 확률 (second-order conditional maximum a posteriori, second-order CMAP)기법을 적용한 우도비 테스트 (likelihood ratio test, LRT)를 제안한다. 제안된 알고리즘은, 기존의 통계적 모델에 기반한 음성 검출기와 CMAP 기반의 음성 검출기를 분석한 다음, 직전 2 프레임에서 음성의 존재와 부재에 대한 조건부 확률에 따라 실시간으로 적응형 문턱값을 구하여 기하 평균한 우도비와 비교하는 음성검출 결정법 (decision rule)을 제시한다. 제안된 알고리즘을 비정상 (non-stationary) 잡음환경에서 기존의 통계적 모델에 기반한 음성 검출기, CMAP 기반의 음성 검출기와 비교하였으며, 향상된 성능을 보였다. In this paper, we propose a novel approach to improve the performance of a statistical model-based voice activity detection (VAD) which is based on the second-order conditional maximum a posteriori (CMAP). In our approach, the VAD decision rule is expressed as the geometric mean of likelihood ratios (LRs) based on adapted threshold according to the speech presence probability conditioned on both the current observation and the speech activity decisions in the pervious two frames. Experimental results show that the proposed approach yields better results compared to the statistical model-based and the CMAP-based VAD using the LR test.

재발된 간헐외사시에서 순응도에 따른 부분가림치료의 장기적 효과

김상균,이승태,김승현,조윤애,Sang Kyoon Kim,MD,Sung-Tae Yi,MD,Seung-Hyun Kim,MD,PhD,Yoonae A,Cho,MD,PhD 대한안과학회 2009 대한안과학회지 Vol.50 No.1

Purpose: To evaluate the reoperation rate and the change of exo-angle according to compliance level of part time occlusion therapy in recurrent intermittent exotropia. Methods: This retrospective study included 52 patients of recurrent intermittent exotropia who followed up more than 5 years after their first operation. They were ordered part time occlusion therapy for recurrent exotropia. The patients were divided into 4 groups according to the level of compliance of part time occlusion therapy (\'excellent\', \'good\', \'fair\', \'poor\'). We evaluated the reoperation rate in 5 years after the first operation and the change of exo-angle from the early recurrent time according to compliance levels. Results: The reoperation rate within 5 years after the first operation of \'excellent\' and \'good\' compliance groups was lower than that of \'fair\' and \'poor\' groups (33.3, 26.3, 73.7 and 45.5% respectively) and the degree of exo-angle progression from the early recurrent time of the \'excellent\' and \'good\' compliance groups was less than that of \'fair\' and \'poor\' compliance groups, both results of which were statistically significant (p=0.02, 0.03). Conclusions: Part time occlusion therapy in recurrent intermittent exotropia has good long-term effects of decreasingreoperation rates in patients with a high level of compliance.

Phase Change Characteristics of Sn_XSe_100-X Thin Films by RF-magnetron Sputtering

김상균,최세영,Kim, Sang-Kyun,Choi, Se-Young Materials Research Society of Korea 2009 한국재료학회지 Vol.19 No.4

$Sn_XSe_{100-X}$ (15|X|30) alloys have been studied to explore their suitability as phase change materials for nonvolatile memory applications. The phase change characteristics of thin films prepared by a Radio Frequency (RF) magnetron co-sputtering system were analyzed by an X-ray diffractometer and 4-point probe measurement. A phase change static tester was also used to determine their crystallization under the pulsed laser irradiation. X-ray diffraction measurements show that the transition in sheet resistance is accompanied by crystallization. The amorphous state showed sheet resistances five orders of magnitude higher than that of the crystalline state in $Sn_XSe_{100-X}$ (x = 15, 20, 25, 30) films. In the optimum composition, the minimum time of $Sn_XSe_{100-X}$ alloys for crystallization was 160, 140, 150, and 30ns at 15mW, respectively. The crystallization temperature and the minimum time for crystallization of thin films were increased by increasing the amount of Sn, which is correlated with the activation energy for crystallization.

위식도 역류 질환의 내과적 치료

김상균,정현채,Kim, Sang-Kyun,Jung, Hyun-Chae 대한기관식도과학회 2002 大韓氣管食道科學會誌 Vol.8 No.2

SET에 대한 이해

김상균,Kim, Sang-Gyun 한국데이터베이스진흥원 1997 디지털콘텐츠 Vol.12 No.-

전자상거래의 사실상의 보안표준 프로토콜로 부상하고 있는 SET에 대해 그 구체적인 모습과 역할, 구성요소에 대해 알아보도록 하겠다.