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Pre-coding과 Antenna Subset Selection, AMC 기법을 적용한 최적의 4G 통신시스템
조인식 ( In Sik Cho ),서창우 ( Chang Woo Seo ),윤길상 ( Gil Sang Yoon ),이정환 ( Jeong Hwan Lee ),황인태 ( In Tae Hwang ),( Sherlie P. ) 전남대학교 전자통신기술연구소 2009 전자통신기술논문지 Vol.12 No.1
본 논문에서는 MIMO-OFDM 시스템에 여러 MIMO 기법을 적용한 후 모의실험을 통하여 성능을 비교 및 분석하였고, 또한 Pre-coding, Antenna Subset Selection, AMC 기법을 적용하여 시스템을 분석하였다. 그리고 최종적으로 최적의 MIMO-OFDM 시스템을 제안하고 성능을 분석하였다. 그 결과 4세대 이동통신 시스템에서 요구되고 있는 고속 데이터 전송과 고품질의 서비스의 Trade-off 관계를 최적의 MIMO-OFDM 시스템을 통해 개선할 수 있음을 확인하였다. In this paper, we have analyzed and compared the BER and the throughput performance through the computer simulation, after applying several MIMO schemes on the MIMO-OFDM system. Then, the thoughput performance of the proposed system is analyzed. As a result, the MIMO-OFDM proposed has a higher average data rate than Non AMC system through the improvement of Trade-off problem between throughput and SNR.
조인식(In Sik Cho),신충식(Choong shig Shin),김종엽(Jong Yup Kim),전용호(Yong ho Jeon) 대한기계학회 2012 大韓機械學會論文集A Vol.36 No.6
본 연구에서는 Ti-6Al-4V 합금에 대한 초고주기 피로시험 연구를 통하여 사이클에 따른 파단면 관찰결과 2가지 타입으로 명확히 구분되는 것을 확인할 수 있었다. 첫번째로 106사이클 범위에서 확인할 수 있는 것은 표면부에서 피로크랙 사이트가 시작된 전형적인 피로 파단면이다. 두번째는 107~109사이클에서는 확연히 다른 피로파단 양상으로, 표면으로부터 500 ㎛ 내부에서 피로크랙 사이트가 시작되어 크게 박리되어 나간 형상으로, 크랙 사이트 주변을 관찰한 결과 미세한 마이크로 크랙들이 입계파괴 양상으로 형성되어 있는 것을 확인 할 수 있었다. 이에 내부 크랙 사이트 피로거동에 대한 연구결과와 본 시험에서 사용된 초음파피로시험기술의 이론 및 적용사례를 소개하고 현재 활발히 진행중인 연구동향을 밝히고자 한다. Very high cycle fatigue (VHCF) behavior of aerospace components has emerged much attention due to their long service life. In this study, a piezoelectric ultrasonic fatigue testing (UFT) system has been developed by Mbrosiatec Co., Ltd. to study the high cycle fatigue (HCF) strength of Ti-6Al-4V alloy. Hourglass-shaped specimens have been investigated in the range from 10? to 10? cycles at room temperature under completely reversed R = ?1 loading conditions,. Scanning electron microscopy (SEM) analysis revealed that failures occurred in the entire range up to the gigacycle regime, and the fractures have beenfound to be initiated from the surface, unlike in steels. However, it was found from the SEM microgprahs that microcracks transformed into intergranular fractures. Thus, it can be concluded from according to the results that this test method can be applicable to commercialized automotive and railroad parts that require high cycle fatigue strength.
조인식(Cho In-Sik),유현조(You Hyun-Jo),신효필(Shin Hyo-Pil) 한국사전학회 2004 한국사전학 Vol.- No.3
The purpose of this study is to identify the properties of special-word, and to show the process of extracting special-words from a large corpus. A special-word corresponds to the notion of unknown words, which is a counterpart of the lexical database in Natural Language Process(NLP). Generally unknown words cause a lot of ambiguities and thus decline the accuracy of NLP systems. The special-word in this work includes various expressions about the events of the day or the fashions, abbreviated words and naturalized word. We came up with a semi-automatic procedure of constructing a special-word dictionary mainly based on the language-dependent heuristics. We, however, also feel that other statistical considerations including frequencies, and probability distributions may be required for unknown word extractions in a higher automatic fashion.
초음파 피로시험법을 이용한 엔지니어링 플라스틱(Polyoxymethylen ; POM)의 내구성 평가
조인식(In Sik Cho),황정호(Jung Ho Hwang),오주연(Joo Yeon Oh),김현창(Hyun Chang Kim),오세훈(Sae Hoon Oh),이창순(Chang Soon Lee),박인규(In Gyu Park) 대한기계학회 2015 大韓機械學會論文集A Vol.39 No.8
엔지니어링 플라스틱(Engineering Plastic ; EP)에 대한 내구성 평가를 위해 현재 새롭게 국내에서 개발한 초음파 피로시험법을 이용하여 EP 중에서도 결정화 속도가 빠르고 결정화도가 높은 범용 POM(Polyoxymethylene) 소재에 대한 초음파 가속피로시험 거동을 평가하고자 하였다. 이에 본 연구에서 사용된 POM 소재의 밀도는 1.37 g/㎤, 동탄성계수는 3.49 GPa 로 측정되었으며, 초음파피로시험 20kHz, 응력비 R= -1 의 판상시편 두께 (4t, 7t, 10t)에 따른 피로수명평가 결과 전체 응력진폭 5.0~6.0MPa 부위에서 피로한도를 확인하였다. 피로시험 후 파단 면을 관찰한 결과 7t, 10t 두께 시편의 크랙 시작위치에서 미소 공동들이 서로 연결된 형태의 잔금(crazing) 균열현상으로 파단된 dimple 구조형상을 전자현미경을 통해 확인할 수 있었다. In this study, a newly developed ultrasonic fatigue test was performed for durability assessment of polyoxymethylene engineering plastic, which has a high crystallization rate and degree of crystallization. Fatigue strength of POM (polyoxymethylene) was performed on a piezoelectric UFT developed by Mbrosia Co., Ltd(1), operating at a high frequency of 20 kHz. The test results showed a fatigue limit of 5.0~6.0 MPa under fatigue testing at R = -1, 20kHz; and, electron microscopy revealed the size effect by risk volume and fractured dimple structure after the coalescence of micro-voids through the crazing effect, which occurs during the failure of a polymer.
4G 통신시스템 기반의 Pre-coding과 Antenna Subset Selection, AMC 기법을 적용한 각 MIMO-OFDM 기법의 성능 분석 및 비교
조인식(In-sik Cho),서창우(Chang-woo Seo),윤길상(Gil-sang Yoon),이정환(Jeong-hwan Lee),황인태(In-tae Hwang) 大韓電子工學會 2010 電子工學會論文誌-TC (Telecommunications) Vol.47 No.3
본 논문에서는 MIMO-OFDM 시스템에 여러 MIMO 기법을 적용한 후 모의실험을 통하여 성능을 비교 및 분석하였고, 또한 Pre-coding, Antenna Subset Selection, AMC 기법을 적용하여 시스템을 분석하였다. 그리고 최종적으로 제안한 Adaptive-MCM(Adaptive-MIMO-Coding-Modulation) 기법의 성능을 분석하였다. 그 결과 4세대 이동통신 시스템에서 요구되고 있는 최대 전송률과 고품질 서비스의 Trade-off 관계를 개선할 수 있음을 확인하였다. In this paper, we have analyzed and compared the BER and the throughput performance through the computer simulation, after applying several MIMO schemes on the MIMO-OFDM system. Then, the thoughput performance of the proposed system, Adaptive-MCM, is analyzed. As a result, the MIMO-OFDM Adaptive-MCM system proposed has a higher average data rate than Non Adaptive-MCM system through the improvement of Trade-off problem between throughput and SNR.
용접부 수명향상을 위한 피닝기술 개발 동향 및 응용사례
김재성(Jae-Sung Kim),구병춘(Byeong-Choon Goo),송승현(Seong-Hyun Song),조인식(In-Sik Cho) 대한용접·접합학회 2021 대한용접·접합학회지 Vol.39 No.2
Welding processes in various industries such as shipbuilding, railroads, aircraft, and construction are inevitably accompanied by HAZ(Heat Affected Zone) deformation and metal structure changes around the toe of the welding bead. It is widely known that it is very weak in terms of structural strength because the tensile residual stress is introduced by welding, and the surface is also rough, causing the main cause of stress concentration to occur. It also becomes the damage initiation cite to the welded structure. Post-welding heat treatment, grinder, and TIG dressing methods were used to release residual stress and to eliminate defects in the welding part. Recently, various peening technologies using pulsed heat sources of laser, elastic vibration energy of ultrasonic waves, compressed air or cavitation have been developed and are being actively utilized as performance improvement and standardized safety technologies in the field. The local peening process on the surface of the welded part and the welded heat-affected part is not only easily portable by various technical methods, but is also being applied to robots or hybrid-3D printing technology. Therefore, in this technical paper, the technical analysis of the various advanced peening technologies that are currently being utilized and the device development trend are evaluated. The portable ultrasonic peening equipment was developed and the recently applied technologies that are newly grafted to improve mechanical properties are introduced.
치아 수복재에 의한 갈바닉 전류가 인체 타액에 미치는 영향
권혁춘,엄정문,조인식,류주희,손호현,Kwon, Hyuk-Choon,Um, Chung-Moon,Cho, In-Sik,Ryu, Ju-Hee,Son, Ho-Hyun 대한치과보존학회 1998 Restorative Dentistry & Endodontics Vol.23 No.2
The purpose of this study was to evaluate the effect of galvanic current between different metallic restorations on human saliva. The rate of salivary flow and concentrations of IgG, IgM, sIgA and lactoferrin were measured. In this study, unstimulated whole saliva collected before restoration was regarded as control group and unstimulated whole saliva collected 10 minutes, 1 day, 1 week, and 1 month after restoration were regarded as experimental groups. Following results were obtained from this study. 1. There were some differences in values of salivary flow rate between experimental groups, but the changes in values compared to those of the control group were not statistically significant(P>0.05). 2. Measurements of major antibacterial components of saliva showed that while the concentrations of IgG and IgM decreased significantly 1 week and 1 month after restoration(P<0.05), changes in values of sIgA and lactoferrin were not statistically significant(P>0.05). 3. In vitro measurements of galvanic currents decreased sharply in the first 20 seconds and thereafter decreased gradually. Galvanic current values measured in the early stages were greatly varied, but after 2 hours, the values in all groups approximated each other.