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        Electrical Characteristics of AlxGa1-xN/GaN Heterostructure withIsoelectronic Al-Doped Channel for HFET Application

        이정희,Jae-Hee Park,Jae-Hoon Lee,Jae-Seung Lee,Jong-Wook Kim,Kye-Seok Lee,Sung-Bum Bae,Sung-Ho Hahm 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.III

        Based on investigating the effects of isoelectronic Al-doping on GaN film, a new layer structure is proposed for a heterostructure field effect transistor (HFET) including an isoelectronic Al-doped channel. The electron mobility measured at 77 (300) K significantly increased from 145 (130) cm$^2$/V$\cdot$s in the undoped sample to 823 (440) cm$^2$/V$\cdot$s in the Al-doped sample grown with a trimethylaluminum flow rate of 3 $\mu$mol /min, while maintaining the background doping concentration below $\sim$ 6 $\times$ 10$^{16}$ cm$^{-3}$. Two-dimensional electron gas mobilities of 1690 and 9280 cm$^2$/Vs were measured for a 25-nm Al$_{0.3}$Ga$_{0.7}$N/1-nm AlN/70-nm Al-doped channel/GaN heterostucture at 300 and 77 K, respectively. The improved results are explained based on a decrease in the compensating acceptors or other defects associated with the formation of screw dislocation due to the incorporation of Al in the channel layer, plus a decrease in the alloy disorder scattering in the heterostructure based on introducing a binary thin AlN layer between the Al$_{0.3}$Ga$_{0.7}$N and Al-doped channel layers.

      • SCOPUSKCI등재

        홀 형상이 막 냉각 유동에 미치는 효과에 대한 수치 해석적 연구

        이정희,최영기,Lee, Jeong-Hui,Choe, Yeong-Gi 대한기계학회 1997 大韓機械學會論文集B Vol.21 No.7

        In this study, the effect of hole geometry of the cooling system on the flow and temperature field was numerically calculated. The finite volume method was employed to discretize the governing equation based on the non-orthogonal coordinate with non-staggered variable arrangement. The standard k-.epsilon. turbulence model was used and also the predicted results were compared with the experimental data to validate numerical modeling. The predicted results showed good agreement in all cases. To analyze the effect of the discharge coefficient for slots of different length to width, the inlet chamfering and radiusing holes were considered. The discharge coefficient was increased with increment of the chamfering ratio, radiusing ratio and slot length to width and also the effect of radiusing showed better result than chamfering in all cases. In order to analyze the difference between the predicted results with plenum region and without plenum region, the velocity profiles of jet exit region for a various flow conditions were calculated. The normal velocity components of jet exit showed big difference for the low slot length to width and high blowing rate cases. To analyze the flow phenomena injected from a row of inclined holes in a real turbine blade, three dimensional flow and temperature distribution of the region including plenum, hole and cross stream with flow conditions were numerically calculated. The results have shown three-dimensional flow characteristics, such as the development of counter rotating vortices, jetting effect and low momentum region within the hole in addition to counter rotating vortex structure in the cross stream.

      • KCI등재후보

        얼굴 특징점 추적 및 움직임 측정도구

        이정희,이영희,차의영,Lee, Jeong-Hee,Lee, Young-Hee,Cha, Eui-Young 대한임베디드공학회 2011 대한임베디드공학회논문지 Vol.6 No.5

        This paper proposes facial feature tracking based on modified ART2 neural networks. And we also suggest new measurement devices such as 'Persistence Exponent' and 'Moving Space Exponent' for the criterion of input vector which consists features. The proposed methods have been applied to classify 48 students by 2-class (ADHD positive, ADHD negative). The results of the experiment have shown that the proposed methods are effective for ADHD Behavior Pattern Classification based on the Image Processing.

      • KCI등재

        Dynamic simulation and experimental verification for edge quality improvement in rotational electro-magnetic finishing process

        이정희,Se-Yeong Lee,곽재섭 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.12

        A rotational electro-magnetic finishing (REMF) was an effective way to minimize burr and improve edge quality on the surface. This study conducted two stages of explicit dynamic simulations: signle collision analysis and multiple collision analysis to verify the effect of abrasives’ behavior on the deburring processes. From observed results, successful deburring depended on the total amount of abrasives and the collision angle. Based on the simulated results and response surface methodology, it was found that the accuracy was reached approximately 95.4 %. Additionally, the maximum deburring area from the predictive model and simulation were similar to 2.27 mm 2 and 2.37 mm 2 , respectively, at rotational speed of 1800 rpm, abrasive diameter of 0.7 mm, and abrasive weight of 2.0 kg. In the experimental verification, the results were in good agreement with the experimental data, although specific values did not correspond exactly. Thus, the suggested approach adopting explicit dynamic simulations could effectively evaluate deburring performance in the REMF process.

      • 지식정보인프라 구축 선도를 위한 과학기술정보 정책연구 및 조사.분석

        이정희,Lee, Jeong-Hui 한국과학기술정보연구원 2003 지식정보인프라 Vol.12 No.-

        현재 우리나라는 지식정보인프라 관련 정책, 제도, 계획 등을 종합조정하고 체계적으로 연계, 지원할 수 있는 국가단위의 조정체계가 확립되어 있지 못하다. 또한 관련 기관간의 정책협의, 조정을 위한 기능이 매우 미약하다. 또한 새롭게 변화하는 지식정보유통의 패러다임의 변화에 대한 공공부문의 대응이 선진국에 비해 매우 뒤처지고 있다. 이러한 점에서 지식정보인프라의 구축을 선도하기 위한 관련 선행연구 및 방법론 개발과 이를 통한 개념정립과 전략개발이 매우 시급하다고 하겠다.

      • KCI등재
      • SCOPUSKCI등재

        터빈블레이드의 냉각에서 충돌제트에 의해 변화되는 유동 및 열전달 특성에 관한 수치해석적 연구

        이정희,김신일,유홍선,최영기,Lee, Jeong-Hui,Kim, Sin-Il,Yu, Hong-Seon,Choe, Yeong-Gi 대한기계학회 1996 大韓機械學會論文集B Vol.20 No.12

        A numerical simulation has been carried out for the jet impinging on a flat plate and a semi-circular concave surface. In this computation finite volume method was employed to solve the full Navier-Stokes equation based on a non-orthogonal coordinate with non staggered variable arrangement. The standard k-.epsilon. turbulent model and low Reynolds number k-.epsilon. model(Launder-Sharmar model) with Yap's correction were adapted. The accuracy of the numerical calculations were compared with various experimental data reported in the literature and showed good predictions of centerline velocity decay, wall pressure distribution and skin friction. For the jet impingement on a semi-circular concave surface, potential core length was calculated for two different nozzle(round edged nozzle and rectangular edged nozzle) to consider effects of the nozzle shape. The result showed that round edged nozzle had longer potential core length than rectangular edged nozzle for the same condition. Heat transfer rate along the concave surface with constant heat flux was calculated for various nozzle exit to surface distance(H/B) in the condition of same jet velocity. The maximum local Nusselt number at the stagnation point occurred at H/B = 8 where the centerline turbulent intensity had maximum value. The predicted Nusselt number showed good agreement with the experimental data at the stagnation point. However heat transfer predictions along the downstream were underestimated. This results suggest that the improved turbulence modeling is required.

      • Environment as an Indicator in the Buddhist Art of Asia

        이정희,Lee, Jung-Hee 한국조형예술학회 2008 조형예술학연구 Vol.13 No.1

        불교와 불교미술은 인도에서 발원하였지만, 그것들은 각 나라에 전파되면서 국제적인 환경을 만들어 냈다. 불교는 각 나라에 일종의 꾸러미의 형식으로 전파되었다. 예를 들면 불경, 불상과 불화의 도상과 양식, 건축과 그 기법, 복잡한 의식, 승려나 여승이 기거하는 사찰에서 건축적 요소와 그 기법들이 함께 소개되었다 불교의 시작은 인도의 아쇼카 왕조시기(reign of King Asoka)로 거슬러 올라가지만, 이후 각 나라의 정치적, 지적, 예술적, 종교적, 사회적, 자연적 환경, 지리적, 지질적 환경에 맞게 전개됐다. 불교미술은 토착화하면서 그 지역민을 닮은 상이 만들어 졌고, 또 지역마다 독특한 특색을 나타내면서 발전하기 시작했다. 스투파(stupa)와 차이챠 홀(chaitya hall)은 수도원의 독특한 분위기를 만들어 내곤 중앙아시아의 대상인들은 인도의 문화가 중국에 전해지는데 공헌했을 뿐만 아니라, 그들이 지나던 교역루트의 자연환경 덕분에 화려한 색채의 벽화들이 제작되고 보존될 수 있었다. 불교와 불교 미술이 중국과 한국, 일본에 전해졌을 때, 불교는 국가 제도와 사회적 조직의 일부가 되었다. 정치적 목적에 의해 거대한 불상들이 산속의 동굴에 만들어 지기도 했다. 중국은 스투파를 사각형의 기둥으로 변형시켰고, 기와를 얹은 지붕 형식의 탑을 만들어 냈다. 한국은 불교미술을 중국에서 일본으로 전파시켰을 뿐만 아니라, 고유한 방식으로 그것을 변형시켰다. 석굴암의 깊은 명상에 잠긴 듯한 보살상들의 이미지가 그 좋은 예이다. 중국에서는 신유교 철학이 국-가의 공식적인 이념이 되면서 선종의 부흥하기도 했으며, 일본의 선승들은 신도들의 명상을 북돋기 위해 선종 형식의 정원을 만들어 냈다. 티벳의 밀교에서도 불교미술의 중요한 발전양상을 확인할 수 있다. 밀교의 미술은 예술적 환경 뿐만 아니라, 지적이고 종교적인 것에도 속한다. 한편 티벳의 신들이 그들의 배우자를 안고 있는 모습은 신과 신자들의 융합을 상징하기도 한다. 불교미술은 독창적인 환경을 만들어 냈고, 여라 나라에 전파되면서, 상당한 변화를 낳았다. Buddhism and Buddhist art originated in India, but when they were introduced to different countries, they created an international environment. Buddhism was introduced as cultural package, with written texts, visual images, rituals, and the organization of monasteries. Buddhist art originated in India during the reign of King Asoka and then was developed under the political, intellectual, artistic, religious, social and natural environments of the regions. The stupa and the chaitya halls create monastic environment. The natural environment of the trade routes and caravans in the Central Asian deserts preserved brilliant-colored murals and helped spread tram India to China. When Buddhism and Buddhist art were introduced to China, Korea, and Japan, Buddhism became a part of government institution and social organization. Gigantic statues were carved in caves in mountains for political purposes. The Chinese transformed the stupa into a square pillar and created pagodas with tiled roofs in tower forms. Koreans not only transmitted the Buddhist art from China to Japan, but it also changed it with originality in the iconography of the pensive bodhisattva images and in the architecture of Seoggulam. The official ideology of Neo Confucian philosophy brought the rise of Chan Buddhism. Zen monasteries in Japan created unique environments by establishing the Zen Buddhist garden. to prompt believers to meditate. An important development in Buddhist art is the Esoteric Buddhist art in China and Tibet. This category belongs to the intellectual, religious as well as artistic environments. The Tibetan deities with consorts in their embrace symbolize the union of the god and the devotees. Buddhist art created a unique environment that was spread out to many nations and changed greatly over time.

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