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.

세계화와 상호공존의 시민정신: 하퍼 리의 『앵무새 죽이기』

이정희 ( Chung Hee Lee ) 한국현대영미소설학회 2004 현대영미소설 Vol.11 No.1

비접촉식 표면연마를 통한 디버링 효과 향상에 관한 연구

이정희,곽재섭,Lee, Jung-Hee,Kwak, Jae-Seob 한국기계가공학회 2022 한국기계가공학회지 Vol.21 No.6

The surface status of a workpiece determines its functionality, product quality, and manufacturing costs. Thus, several finishing technologies have been widely investigated and applied to improve surface characteristics. In this study, rotational electro-magnetic abrasive finishing (REMAF) was suggested as a non-contact finishing process to achieve high geometric precision. To verify the effects of the REMAF process on burr removal on the surface of Al6061, experiments were conducted using the Taguchi method. Based on the experimental results analyzed by the S/N ratio and ANOVA, the optimal conditions were defined as A₃B₂C₃D₃ that corresponded to 1,800 rpm of rotational speed, 1.5 kg of abrasive particle weight, 0.7 mm of abrasive diameter, and 15 min of working time. In addition, the particle weight was a key attribute for deburring, whereas the working time was less effective.

국내 쯔쯔가무시증의 감염자 분포와 유병자수 추정

이정희,박정수,Lee, Jung-Hee,Murshed, Sharwar,Park, Jeong-Soo 한국데이터정보과학회 2009 한국데이터정보과학회지 Vol.20 No.1

쯔쯔가무시증은 가을철 유행성 출혈열 중 80%이상을 차지하는 질병으로 1주에서 2주의 잠복기를 가지는 것으로 알려져 있다. 우리는 그 잠복기간의 확률분포가 감마분포라 가정하고 후향연산식을 이용하여, ${\hat{\mu}}=309.92$$, ${\hat{\sigma}}=14.154$인 정규분포를 따르는 감염자 분포를 추정하였다. 감염자는 10월에 집중적으로 분포하는 것으로 나타났다. 이러한 감염자 분포형태는 발병자 수가 11월동안 급격하게 증가하는 것에 기인한다. 본 연구에서 추정한 감염확률에 의해 미래의 유병자수를 계산한 결과 최대 1200명이었고 이는 매년 증가하는 발병자 수의 경향을 반영하지 못한 한계가 있다. 또한 우리는 전염병 모형으로 잘 알려져 있고 전염발전 단계간의 상호작용을 고려하는 SIRS 모형을 적용해 보았다. 모수는 초기값으로부터 잘 근사되어 수렴하는 값으로 추정하였다. Tsutsugamushi fever occupies more than 80% of total fall epidemic diseases and has an incubation period of 1 or 2 weeks as well. We have assumed that the incubation period distribution is gamma and therefore, reach an agreement that the infected distribution is normal with ${\hat{\mu}}=309.92$, ${\hat{\sigma}}=14.154$ by back calculation method. The infection cases are found severely large around the month of October. The infection case distribution demonstrates the incidence number increasing rapidly and progresses fast during the month of November. In this study, we have calculated the future prevalence number of maximum 1,200 people by inferred infection probability and incubation period distribution with some sort of limitation that the trend of increasing incidence number is not taking into an account. We considered the SIRS model which is also known as epidemic model, familiar to interaction between epidemiological classes. Our estimated parameters converged well with the initial parameter values.

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.

학교도서관발전을 위한 도서관정책

이정희,Lee, Jeong-Hui 한국도서관협회 1975 圖協月報 Vol.16 No.10

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.

학교도서관과 도서관법 개정방향

이정희,Lee, Jeong-Hui 한국도서관협회 1986 圖協會報 Vol.27 No.6

교류전위차법에 의한 강자성체의 응력확대계수 결정

이정희,Lee, Jeong-Hee 대한기계학회 1997 大韓機械學會論文集A Vol.21 No.9

In order to determine the Mode I stress intensity factor ($K_1$) experimentally by means of the alternating current potential drop(ACPD) technique, the change in potential drop due to load for a ferromagnetic material containing a two-dimensional surface crack was examined. The cause of the change in potential drop and the effect of the magnetic flux on the change in potential drop were clarified by using the measuring systems with and without removing the magnetic flux from the circumference of the specimen. To remove the magnetic flux, a new measuring system was made by utilizing the characteristic of coaxial transmission line. The change in potential drop in the case without magnetic flux in the air was caused by the change in electromagnetic properties near the crack tip due to magnetization. The relationship between the change in potential drop and the change in $K_I$ was linealized by demagnetization and was found to be independent of the crack length.

학교도서관과 독서지도의 문제

이정희,Lee, Jeong-Hui 한국도서관협회 1976 圖協月報 Vol.17 No.7