• 대한기계학회논문집A
• /
• 제24권5호
• /
• pp.1146-1154
• /
• 2000

Fatigue strength of NiAl and Ni$_3$Al particulate reinforced aluminum alloy composites fabricated by the diecasting method was examined at room and elevated temperatures. The results were compared wit h that of SiC particulate reinforced one. The particulate reinforced composites showed some improvement in the static and fatigue strength at elevated temperatures when compared with that of Al alloy. The composites reinforced by intermetallic compound particles showed good fatigue strengths at elevated temperatures especially $Ni_3AI_{p}/Al$ alloy composite showed good fatigue limit up to high temperature of 30$0^{\circ}C$. Adopting intermetallic compound particle as a reinforcement phase, it will be possible to develop MMC representing better fatigue property at elevated temperature.

• 한국표면공학회지
• /
• 제31권2호
• /
• pp.73-80
• /
• 1998

The aim of this study is to develop sintered stainless steels (SSS) with good mechanical strength, wear resistance, and corrosion resistance by nitrogen ion implantation on the Culated SSS surface. Stainless steel compacts containg Cu (2-10 wt%) were prepared by electroless Cu-pating method which results in the increased3 homogenization in alloying powder. Nitrogen ion implantation was carried out by using N2 gas as the ion source. Nitrogen ions were embedded by an acceleratol of 130keV with doese $3.0\times10^{17}\;ions/\textrm{cm}^2$ on the SSS at $25^{\circ}C$ in$2\times10^{-6}$ torr vacuum. The nitrogen ion implanted SSS obtained from anodic ploarization curves revealed higher corrosion potential than that of nitrogen ion unimplante one. And nitrogen ion implanted 316LSSS had good resistance to pitting corrosion due to the synergistic effect of Mo and N, and the inhibition of $NH_4\;^+$<\TEX>, against $CI^-$<\TEX>.

• 농업과학연구
• /
• 제37권3호
• /
• pp.393-398
• /
• 2010

Early pregnancy diagnosis of bovine is an essential component for efficient reproductive plan in farms because long term of non-pregnancy results in economic losses by failure of offspring production and low milk yield in dairy cattle. The major steroid hormones related with reproduction are known to be progesterone and estrogen in bovine pregnancy. To evaluate detection level of hormones in milk, plasma and milk progestrone and estrogen of Holstein cows was analyzed during artificial insemination (AI) and embryo transfer (ET). Progesterone concentration at 21 days postestrus was significantly different in plasma and milk between pregnant and non-pregnant cows. Estrogen concentration at estrus was higher in pregnant recipients than that in non-pregnant recipients. To analyze correlation between hormone levels and conception rates in Holstein, the conception and return rates were checked following AI, and the returned cows were on the track of pregnancy after consecutive AI. Pregnant cows following first AI were considered as high conception group while pregnant cows following third AI were rated as low conception group. Proportion of high and low conception groups in this study was 78.2% and 9.1%, respectively. Hormone analysis indicated that high conception group had higher estrogen level during estrus than low conception group ($26.45{\pm}3.32$ vs $19.017{\pm}2.97$). Progesterone level was not different between high and low conception groups during estrus but increased significantly after 21 days postestrus (21 day: $4.95{\pm}1.12$ vs $0.95{\pm}0.23$, 35 day: $12.47{\pm}3.82$ vs $2.41{\pm}1.21$). In conclusion, the pattern of progesterone and estrogen secretion in Holstein milk samples could be a good candidate for early pregnancy detection and selection of recipients during ET.

• 전기전자학회논문지
• /
• 제24권1호
• /
• pp.302-310
• /
• 2020

본 논문은 인공지능과 IoT 기반의 생활폐기물 모니터링 시스템을 구현하고, 이를 통하여 효율적인 쓰레기 처리와 관리 방안을 제안한다. 제주 지역은 타 지역에 비하여 대체로 정량적 추정과 운영 전략을 수립하는데 장점을 갖추고 있다. 특히, 상주인구 대비 사계절 관광객의 변화를 통하여 쓰레기 량의 변화를 알 수 있음으로써 쓰레기 종량제 연구의 좋은 사례가 되고 있다. 이에 클린하우스 현장에 기존 CCTV를 연동하여 정보를 제공할 수 있는 IoT 장치를 개발하고, 카메라의 쓰레기 영상데이터 셋을 분석하기 위하여 인공지능(AI) 알고리즘을 이용한다. 이를 통하여 쓰레기가 쓰레기통 밖에 잘못 투기되었는지, 쓰레기 처리를 위해 판단된 의사결정에 따라 쓰레기 차량이 수거해야 할지 정보를 전송함으로써 원활한 쓰레기 처리 및 홍보방송을 할 수 있도록 한다. 개발된 IoT 장치는 국가 공인 시험연구기관을 통해 전파적합성 시험과 환경시험을 하고, 다양한 쓰레기 대상을 제안한 인공지능 알고리즘으로 시뮬레이션하여 의사판단용 데이터 구축방법으로 활용하고자 한다.

• 수면정신생리
• /
• 제30권1호
• /
• pp.22-27
• /
• 2023

목 적: 본 연구에서는 불면증상 뿐만 아니라 과다수면, 하지불안증후군을 포함하여 수면 문제를 포괄적으로 평가하기 위한 수면 문제 선별 설문지(Sleep Problem Screening Questionnaire, SPSQ)를 개발하고, 신뢰도와 타당도를 검증하고자 하였다. 방 법: 불면증상(SPSQi), 과다수면(SPSQh), 하지불안증후군(SPSQr)의 세 가지 하위 영역을 포함하는 SPSQ를 개발하였다. 다음으로, 불면장애 임상군 222명 및 건강군 78명을 대상으로 SPSQ와 비교 척도인 불면증 심각도 척도(Korean version of Insomnia Severity Index)를 진행하고, 해당 데이터를 분석에 사용하였다. 결 과: SPSQ는 수용할만한 내적 일관성과 수렴·변별 타당도를 보여 수면장애의 측정에 타당한 도구로 평가되었다. ROC curve 분석 결과, 불면장애의 임상적 유의미성 판단을 위한 절단점은 SPSQi 6점, 민감도와 특이도는 각각 0.94, 0.96이었다. 결 론: 해당 연구결과는 SPSQ가 일반 성인 인구의 수면 문제를 선별하는데 있어 신뢰할 수 있고 유효한 도구임을 시사한다. 단, 하지불안증후군 및 과다수면 관련 척도와 비교 검증이 수행되지 못한 점을 고려해야겠다.

• Journal of Chest Surgery
• /
• 제12권4호
• /
• pp.355-360
• /
• 1979

Mitral and aortic valve replacement with tricuspid annuloplasty was undertaken in 5 patients out of 38 valvular surgery between the period from Jan. 1977 to May 1979 in the Dept. of Thoracic and Cardiovascular Surgery in Korea University Hospital. All were male patients with age ranging from 18 to 42 years, and preoperative evaluation revealed one case in Class IV, and four cases in Class III according to the classification of NYHA. Preoperative diagnosis was confirmed by routine cardiac study including retrograde aorto- and left ventriculography, and there were two cases with MSi+ASi+Ti, two cases with MSi+Ai+Ti, and one case with Mi+Ai+Ti. Double valve replacement was performed under the hypothermic cardiopulmonary bypass with total pump time of 247 min. in average ranging from 206 min. to 268 min. During aortic valve replacement, left coronary perfusion was done in the first two cases, and cardiac arrest with cardioplegic solution proposed by Bretschneider was applied in the remained three cases. Starr-Edwards, Bjork-Shiley prosthetic valves and Carpentier-Edwards tissue valve were replaced in the aortic area, and Carpentier-Edwards and Angell-Shiley tissue valves were replaced in the mitral area with each individual combination [three prosthetic and two tissue valves in the aortic, and five tissue valves in the mitral area respectively]. Postoperative recovery was uneventful in all cases except one case with hemopericardium, which was managed with pericardiectomy on the postoperative 10th day in good result. Follow-up after double valve replacement of the all five cases for the period from 6 months to 33 months revealed satisfactory adaptation in social activity and occupation with cardiac function of Class I according to the classification of NYHA In all five cases.

• 한국음향학회지
• /
• 제18권5호
• /
• pp.63-67
• /
• 1999

최근 들어 실내음향 특성의 측정과 평가를 위해 백색잡음을 이용한 잔향시간 측정법 대신에 임펄스응답을 이용한 측정법이 널리 이용되고 있다. 이 방법은 재현성이 우수하고 다양한 실내음향 특성치들을 한꺼번에 산출할 수 있어 전통적인 잔향시간 측정법에 비해 여러 가지 장점을 가지고 있다. 본 연구에서는 MLS(Maximum Length Sequence) 신호를 이용하여 실내에서의 임펄스 응답을 측정하고 이를 후처리(post-processing) 하여 잔향시간(EDT, RT), 명료도 지수(C50, C80, D, U50, U80, AI), 음의 크기 지수(G) 등, 주로 실의 음성음향 성능을 측정하는 시스템을 구축하였다. 본 연구에서는 측정시스템과 후처리 프로그램의 구성, 몇몇 실내공간에 대한 시험 측정의 결과 및 고찰 등에 대해 소개하고자 한다.

• International Journal of Internet, Broadcasting and Communication
• /
• 제9권3호
• /
• pp.44-58
• /
• 2017

The purpose of this study is to prove the Korean Internet company, Kakao's resilience capacity. For it, this paper reviews the previous literatures regarding Kakao's business models and discusses 'resilience' theory. Then, it organizes the research questions based on the theoretical background and explains the research methodology. It investigates the case of Kakao's business and organization. The case analysis shows that five levers of resilience are a good indicator for a successful platform business evolution. The five levers are composed of coordination, cooperation, clout, capability, and connection: First lever, coordination that makes the company to restructure its silo governance in order to respond to actual business flow starting from the basic asset like game and music content; second lever, cooperation where the firm provides creative people with playground for startups such as KakaoPage; third lever, clout where the company shares its data by opening its API of AI and chatbot to $3^{rd}$ party developers; fourth lever, capability where the firm establishes AI R&D center, KakaoBrain as the function of multi-domain generalist for developing diverse platforms tackling customer needs; and the last fifth lever, connection where the firm continues to expand its platform business to the peripheries, O2O businesses such as KakaoTaxi, KakaoOrder, KakaoPay, and KakaoBank. In conclusion, this study proposes Internet companies to be a resilient platform utilizing those five levers of resilience in order to form successful platform. This study contributes to the agile innovation of Internet platform with ecological sense.

• 한국동물생명공학회지
• /
• 제35권2호
• /
• pp.119-141
• /
• 2020

The Dromedary camel (Camelus dromedaries) is an important species because of its ability to produce good quality meat, milk, and fibers under harsh environmental conditions. Camels are also crucial for transportation, racing, and as draft animals in agriculture. Therefore, dromedary camels play a critical role in the economy for millions of people living in the arid part of the world. The inherent capability of camels to produce meat and milk is highly correlated with their reproductive performance. Compared with other domestic species, the reproductive efficiency in camelids is low. Although recent reproductive technologies such as in vitro fertilization (IVF) and somatic cell nuclear transfer (SCNT) have been successfully applied to camelids and the birth of live offspring following these technologies has been reported; in vitro embryo production (IVP) has lagged in this species. The development of the IVP system for dromedary camels may be a useful tool for the genetic improvement of this species. IVP in farm animals includes three main steps; in vitro maturation (IVM) of an oocyte, IVF of a matured oocyte, and in vitro culture (IVC) of fertilized oocyte up to the blastocyst stage. This review aims to summarize various factors that influence oocyte quality, IVM, and in vitro embryo development in dromedary camel.

• 터널과지하공간
• /
• 제25권2호
• /
• pp.210-219
• /
• 2015

본 연구에서는 설문조사 기법인 델파이 방법을 이용하여 RMR 분류법과 Q 분류법에 정성적인 지표로 제시되어 있는 불연속면의 거칠기 평가분류를 정량화하였다. 패널을 선정하고 웹상에 설문조사 사이트를 개설하여 불연속면의 거칠기에 대한 설문조사를 실시하였다. 총 3회의 걸쳐 설문조사를 수행하였으며, 설문조사에는 표준 프로파일과 몬테카를로 시뮬레이션 기법이 적용되어 표준 프로파일과 동일한 미소 평균거?각(Ai)을 갖는 프로파일을 이용하였다. 각 설문이 종료된 후에는 전체의 설문 결과를 배포하여 다음 설문 시에 전체의 의견과 자신의 의견을 비교하여 의사결정을 할 수 있도록 하였다. 설문 결과에 대하여 합의도와 수렴도를 나타내었으며, 설문조사가 회를 거듭할수록 합의도와 수렴도가 높아지는 경향을 보였다. 이에 3차 설문조사 결과를 일정한 합의의 수준에 도달하였다고 판단하고, 이를 이용하여 각 암반분류법의 거칠기 평가기준을 구분하고 분류의 범위를 정량화하였다.