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권우현(Woo Hyun Kwon),이승화(Seung Wha Lee),채광표(Kwang Pyo Chae),이재광(Jae-Gwang Lee),서정철(Jung Chul Sur) 한국자기학회 2009 韓國磁氣學會誌 Vol.19 No.5
Fe₃O₄ particles, prepared by a sol-gel method, were examined for their structural characteristic, particle shapes and sizes, and their magnetic properties. Two different chemical compositions (using a mol rate Fe<SUP>2+</SUP>/Fe<SUP>3+</SUP> = 1/2 and only Fe<SUP>2+</SUP>) and 2-methoxyethanol were used for making proper solutions. And the solutions were refluxed and dry in a dry oven and the samples were fired at 200~600 ℃ in the N₂ atmosphere. The formation of single-phased spinel ferrite powders was identified with the X-ray diffraction measurement as they were fired at above 250 ℃. The result of scanning electron microscopy measurement showed the increase of annealing temperature yielded the particle size increased. The magnetic transition was observed using the Mossbaur spectroscopy measurement. As the ferrite, prepared with the chemical composition (Fe<SUP>2+</SUP>/Fe<SUP>3+</SUP> = 1/2), was fired at 250 ℃, 78% of the ferrite had a ferrimagnetic property and 22 % of the ferrite was non-magnetic. In case of preparing the sample with only Fe<SUP>2+</SUP> and annealed at 200 ℃, it had a single phased spinel structure but its particle size was too small to be ferrimagnetic. The annealing temperature above 250 ℃ made powders a spinel structure regardless of the preparation method. They had a typical soft magnetic property and their saturation magnetization and coercivity became larger as the annealing temperature increased.
고지질 식이 투여를 이용하여 상부위장관내시경 소견으로 진단된 원발성 장림프관 확장증
권우현,황진복,이영환,김용진,Kwon, Woo-Hyun,Hwang, Jin-Bok,Lee, Young-Hwan,Kim, Yong-Jin 대한소아소화기영양학회 1999 Pediatric gastroenterology, hepatology & nutrition Vol.2 No.1
전신 부종을 주소로 내원한 20개월된 남아에서 대변의 ${\alpha}_1$-antitrypsin clearance를 이용하여 단백상실성 장병증으로 진단하고, 상부위장관내시경을 시행하였으나 육안적 및 조직학적 소견상 특기할 만한 진단적 실마리가 관찰되지 않아, 고지질 식이를 투여 후 내시경을 시행하여 육안적, 조직학적 소견상 장림프관 확장증의 특징적인 소견이 확인되어 원발성 장림프관 확장증으로 진단된 증례이다. We experienced a case of primary intestinal lymphangiectasia in a 20-month-old boy, which was confirmed gastrofiberscopically and histologically only after a high-fat meal before the procedure. A characteristic endoscopic finding was the appearance of tiny white dots scattered in the duodenal mucosa, which were proved dilated lymph vessels in the lamina propria on histological examination. Treatment with low-fat diet and medium chain triglycerides supplementation was satisfactory.
여성의 긴장성 요실금의 치료로서 Burch수술, Pubovaginal Sling Operation, Tension-free Vaginal Tape의 수술성적 비교
손우현 ( Woo Hyun Sohn ),배상욱 ( Sang Wook Bai ),이웅희 ( Woong Hee Lee ),권자영 ( Ja Young Kwon ),권한성 ( Han Sung Kwon ),홍종욱 ( Jong Wook Hong ),노진래 ( Jin Lae Roh ),김세광 ( Se Kwang Kim ),박기현 ( Ki Hyun Park ) 대한산부인과학회 2003 Obstetrics & Gynecology Science Vol.46 No.4
Objective : The object of this study was to compare the cure rate and confirm the clinical efficacy of three most frequent surgical procedures for stress urinary incontinence (Burch colposuspension, pubovaginal sling operation, tension-free vaginal tape).
모바일 와이맥스에서의 효율적인 무선링크 대역폭 활용을 위한 헤더압축기법인 ROHC RTP 프로파일의 성능 분석
우현제,김주영,권정민,이미정,Woo, Hyun-Je,Kim, Joo-Young,Kwon, Jeong-Min,Lee, Mee-Jeong 한국정보처리학회 2008 정보처리학회논문지 C : 정보통신,정보보안 Vol.15 No.5
IP 기반 무선 광대역 서비스를 제공하는 모바일 와이맥스에서 물리적으로 제한적인 무선링크의 대역폭은 성능 저하의 큰 요인이 된다. 모바일 와이맥스 표준에서는 무선링크 대역폭의 효율적 활용을 위해 헤더 압축 기법인 PHS(Payload Header Suppression)를 정의하였으나, 제한적인 압축 가능 필드로 인해 PHS의 압축 효율성은 매우 낮다. 이에 본 논문에서는 높은 비트에러율과 긴 RTT(Round Trip Times) 및 제한적인 자원과 같은 특성을 지닌 무선 링크에 적절한 헤더 압축 기법으로 제안된 ROHC(Robust Header Compression)를 모바일 와이맥스에 적용하였을 때의 성능을 분석하고 PHS와 비교하였다. ROHC 성능에 대한 기존연구들은 무선링크에서의 비트에러에 대한 성능 분석에 초점을 맞추었으나, 맥 계층에서 에러 체크 기능을 제공하는 와이맥스와 같은 무선시스템의 경우 비트에러가 포함된 패킷이 상위 계층에 전달될 확률은 거의 없으므로 다른 측정 기준이 필요하다. 이에 본 논문에서는, 비트에러 대신 모바일 와이맥스 환경에서 발생할 수 있는 패킷 손실에 따른 ROHC의 성능 평가를 수행하였다. 다양한 ROHC 구현파라미터들이 ROHC 성능에 미치는 영향을 분석하고, ROHC와 기존의 방안인 PHS의 성능을 비교하였다. Mobile WiMAX provides wireless broadband services for data communication based on IP protocol. The limitation of physical bandwidth in the radio links may cause performance degradation in providing wireless broadband services in WIMAX. To enhance the efficiency of the radio link utilization, Payload Header Suppression (PHS) is defined as an optional header compression mechanism for mobile WiMAX. It has, however, a very limited compression capability since it has very restrictive compression fields. In this paper, hence, we assumed the application of Robust Header Compression (ROHC), a header compression scheme proposed for links characterized by high bit error ratios, long round-trip times (RTT), and scarce resource, to Mobile WiMAX, and studied its performance. Previous studies on ROHC performance merely focused on the impact of high bit error rate. However, bit error is virtually transparent to ROHC in the wireless systems like WiMAX, since the MAC provides the bit error checking function. In order to evaluate the performance of ROHC in the Mobile WiMAX environments, therefore, we evaluated the performance of ROHC with respect to the packet losses instead of bit error. We investigated the impact of the ROHC parameters that are recommended for the implementation in the ROHC and compared the performance of ROHC with PHS.
모바일 와이맥스 환경에서의 효율적인 무선링크 자원 활용을 위한 ROHC Optimistic 모드의 개선 방안
김주영,우현제,이미정,권정민,Kim, Joo-Young,Woo, Hyun-Je,Lee, Mee-Jeong,Kwon, Jeong-Min 한국정보처리학회 2009 정보처리학회논문지 C : 정보통신,정보보안 Vol.16 No.1
모바일 와이맥스에서 IP 기반의 무선 광대역 서비스를 효율적으로 제공하기 위해, 제한적인 무선링크의 대역폭을 보다 효율적으로 활용하는 방안이 필요하다. 모바일 와이맥스 표준에서 정의된 헤더 압축 기법인 PHS(Payload Header Suppression) 대신에 ROHC(RObust Header Compression) O(Bi-directional Optimistic) 모드를 사용할 경우, 압축효율성과 견고성 면에서 성능을 향상시킬 수 있으나[1, 2], 모바일 와이맥스의 음영서비스 지역이나 비트 에러로 인한 수신단에서의 연속적인 패킷의 손실이 발생할 경우 컴프레서와 디컴프레서가 유지하는 압축 정보가 비동기화되어 O 모드의 패킷 복구 실패율이 증가하게 되므로 이를 보완할 방안이 필요하다. 이에 본 논문에서는, 모바일 와이맥스 환경에서 패킷 손실에 대한 ROHC O 모드의 성능 향상을 위해 O 모드의 압축률과 견고성에 모두 영향을 미치는 Optimistic 파라미터의 값을 동적으로 조절하는 방안을 제안하고, OPNET 시뮬레이터를 사용하여 제안한 방안의 성능 분석을 하였다. In order to efficiently provide IP based Wireless Broadband services in Mobile WiMAX, schemes for more efficiently utilizing a limited bandwidth in radio links are needed. Robust Header Compression (ROHC), a standard header compression scheme proposed by IETF, Bi-directional Optimistic (O) mode provides higher compression efficiency and robustness compared with Payload Header Suppression (PHS) which is an optional header compression scheme for mobile WiMAX [1, 2]. However, if consecutive packet losses occur because of a Shadow Region of Mobile WiMAX or bit errors, header decompression failure rate of the ROHC O mode increases due to inconsistency of the compression information between the Compressor and the Decompressor. Therefore, a complementary mechanism is needed. In this paper, we propose an approach for the dynamic adjustment of an optimistic parameter, which has an effect on both the compression efficiency and the robustness, for improving the performance of ROHC O mode. We also analyze the performance of the proposed approach using an OPNET simulator.
윤경섭,이무영,김우현,권우현 ( Kyung Sup Yoon,Moo Young Lee,Woo Hyun Kim,Woo Hyen Kwon ) 한국센서학회 1997 센서학회지 Vol.6 No.4
The measure of motor speed using encoder is difficult to detect accurate speed and direction in very low speed because the intervals between an encoder pulse and pulse are long. So various speed estimation techniques were proposed to have the good dynamic performance in low speed. And direction detection is so important as speed measurement in very low speed. But because the conventional direction detection circuit check the direction only 1 time in 1 period of each encoder pulses, so it has long delayed detection time in very low speed, thus accurate detection of direction is difficult. In this paper, we propose a 2 way edge det~tion method which can detect at the rising and falling edge of each encoder pulses. So it can check the direction 4 times in I period of each encoder pulses. Therefore if we use proposed method, we can reduce the detection time as 1/4 than that of conventional circuit and can detect more accurate speed and direction. And computer simulation and experiment is performed to verify the perfomance and effect of proposed circuit and we analyze it`s results by comparing with that of conventional circuit.