北漢江의 流砂量에 關한 硏究

劉漢烈,安相鎭(Ahan Sang Jin) 대한토목학회 1969 대한토목학회지 Vol.16 No.4

Large Enhancement of Extraction Efficiency in Thin-Film Photonic Crystal InGaN Light-Emitting Diode Structures

류한열 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.6

The light extraction efficiency in thin-film InGaN light-emitting diode (LED) structures having photonic crystal patterns is studied theoretically based on three-dimensional finite-difference timedomain (FDTD) simulations. The thin-film InGaN LED structures consist of p−i−n GaN/InGaN hetero-structures placed on a high-reflectance mirror. The extraction efficiency of an unpatterned LED structure has been found to be as high as 20 % at an appropriate quantum-well position for a GaN/InGaN film thickness of 1 µm. When square-lattice photonic crystal patterns are introduced in the optimized thin-film LED structure, a large increase in the extraction efficiency is observed as the air-hole depth increases. It is found that the extraction efficiency can be enhanced by more than 4 times, corresponding to an extraction efficiency of greater than 80 %. The light extraction efficiency in thin-film InGaN light-emitting diode (LED) structures having photonic crystal patterns is studied theoretically based on three-dimensional finite-difference timedomain (FDTD) simulations. The thin-film InGaN LED structures consist of p−i−n GaN/InGaN hetero-structures placed on a high-reflectance mirror. The extraction efficiency of an unpatterned LED structure has been found to be as high as 20 % at an appropriate quantum-well position for a GaN/InGaN film thickness of 1 µm. When square-lattice photonic crystal patterns are introduced in the optimized thin-film LED structure, a large increase in the extraction efficiency is observed as the air-hole depth increases. It is found that the extraction efficiency can be enhanced by more than 4 times, corresponding to an extraction efficiency of greater than 80 %.

Evaluation of the Internal Quantum Efficiency in Blue and Green Light-emitting Diodes Using the Rate Equation Model

류한열,류근환,이상호,김현중 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.2

We present a convenient and reliable method for the determination of the internal quantum efficiency (IQE) in GaN-based light-emitting diodes (LEDs) based on the carrier rate equation model. By using the peak point of the efficiency curve as the parameter of the rate equation analysis, we show the IQE of LEDs is unambiguously determined without any information on the recombination coefficients or LED structures. The theoretical analysis model was used to determine the IQE of LED samples. When the theoretical IQE model is applied to the measured external quantum efficiency (EQE) of a blue and a green LED, good agreements between the measured data and the theoretical-fit curves are found. From the measured EQE and the evaluated IQE values,the light extraction efficiency of the LED samples is obtained.

유한요소 영역/경계 분할법을 이용한 접촉 해석의 효율성 향상

류한열,신의섭 한국항공우주학회 2006 한국항공우주학회 학술발표회 논문집 Vol.- No.-

야산 기계화 개간공법에 관한 연구 -레이크 도저의 적정 이빨 간격의 선택과 발배근작업능률 시험(제1보)-

류한열,정하우박승우 한국농공학회 1975 한국농공학회논문집 Vol.17 No.3

This experiment was carried out to establish the mechanized methods in stumping and root-clearing, which were the most important works in the reclamation of sloping uplands. The determination of optimum teeth interval of rake blades and its operation methods to reduce the quantity of transported topsoil during the works, are the aims of this investigation. A newly designed rake blade, whose net teeth intervals could be regulated by three stages as 15cm, 25cm, and 35cm, was manufactured to attach to the bulldozer of 13ton. The experiments were carried out at Kilsang-Myon, Kwangwha-Gun, from Aug. 9 to Aug. 23, 1975. For each interval, 36 test plots of 50${\times}$10mn in size, which were regulated under three levels of land slopes of 10, 20, and 30% and two different tree stand density of high or medium values, were randomly chosen and arranged by two-replicated split-split plot design. Each stump classified by its diameter was stumped and cleared by the rake dozer to be related between diameter and stumping time. The results obtained in this experiment can be summarized as follows: 1. Stumping times for the diameters ranging from 6 to 18cm of stumps are almost the same and they are not varied by the difference of teeth intervals of rake dozer. 2. By back-ward stumping method, the number of stumps which can be stumped per hour ranges almost from 100 to 170, showing significant difference with respect to the teeth intervals. The working area is sharply varied with not only the stand density of stumps but the teeth intervals. 3. Optimum stumping distance for each teeth interval of rake dozer to minimize the quantity of transported topsoil are varied with such the rates as it is 15m or 20m for 15cm of teeth interval, but 25m for 25cm or 35cm, respectively. The clearing distance could be chosen almost double as long as the operating distance. 4. The working areas per hour of the simultaneous stumping and clearing methods are no significant difference among the various treatments of working conditions, but they are affected by the operating techniques. However, the influencing factors of the working conditions as classified before and the working directions are ranged from 10 to 15 per cent of total working area, respectively. 5. The residual rates of stumps which are not stumped by the rake dozer in each test plot are generally reduced as the teeth interval gets narrower, but there are no significant difference among them. The mean residual rates average to be about 4% for the simultaneous stumping and clearing method. The back-ward stumping method are recommended to be supervised and directed by more than one man, to show the operator where the stumps are located. 6. The results according to the stumping and clearing methods are summarized as Table IV-2. And the selection of working methods is recommended to follow as shown in Fig. IV-9 with respect to the stand density of the field. 7. Generally speaking, the narrower the teeth interval, the better become the working results, but the more the quantity of transported topsoil is increased. Therefore, it is recommended that the teeth interval should be reduced from the present distance of more than 30cm to 25cm or 15cm, by developing suitable working methods through more field works and experiments.

Extraction Efficiency in GaN Nanorod Light-emitting Diodes Investigated by Finite-difference Time-domain Simulation

류한열 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.58 No.41

The light extraction efficiency (LEE) in GaN-based nanorod light-emitting diode (LED) structures is investigated using a three-dimensional (3-D) finite-difference time-domain (FDTD) simulation. The LED structure is composed of a p-GaN layer, InGaN/GaN active layers, and an n-GaN layer grown on a sapphire substrate, and the active layers are positioned at the center of the rods. The LEE for top or bottom emission shows a periodic behavior as the radius of a rod varies, which can be interpreted by the creation of radial resonant modes inside the nanorod cavity. The LEE in a nanorod array is found to be quite high. For an optimized nanorod LED structure, it can be >90%, which is higher than that of current high-efficiency LED structures by around 10%. Due to the potential of very high LEE, the nanorod LED structure is expected to be a good candidate for future high-efficiency LEDs.

야산 기계화개간 공법에 관한 연구(II) -개간공사에 있어서 인력작업의 특성분석-

류한열,정하우박승우 한국농공학회 1975 한국농공학회논문집 Vol.17 No.4

In order primarily to establish the working stages in the reclamation works and to- analyze the working characteristics of man-power, the investigations for construction_ works were conducted on Echeon Largescale Reclamation Project Area. The results are summarized as follows; 1. The working chart on reclamation by man-power is Fig.IV-1. 2. The. ratio of actual working time to total varied with the total times, being 1.0 for less than 4 hours but about 0.9-0.83 for more than 5 hours. 3. Felling operations can be classified into three stages as truck-cutting, branch- cutting, and binding-up, of which results are in Table IV-2. The larger the diameter of stands, the more times for both the cutting operations are, but the moving time is constant to be about 15 sec. 4. Stumping and clearing works have the results prepared in Table IV-3. Between the stumping time and the diameter of stands d, there show highly significant positive correlations, expressed as t=2.212d -4.792. The more the ratio of small diameters to total, the more hastily the total hourly working results of each person are increased. 5. Working results for constructing drainage facilities and ridges are in Table IV-5. The labours for placing patches of grass are required more than twice or three times as much as those are showed in the established standards, and such the different results imply more investigation to be necessary. 6. Table IV-6 sholvs the results for plowing andh arrowing, that are less amount thant the standards. Therefore, more inverestigation should be prepared.

관개용 관정의 양수량과 영향인자들의 상관관계에 관한 연구

류한열,구자웅 한국농공학회 1974 한국농공학회논문집 Vol.16 No.2

The purpose of this study is to find out the correlation between pumping rates and influential factors in the tube wells for irrigation through the analysis of various statistical data of the existing tube wells for irrigation and pumping tests. Statistical data of the existing tube wells for irrigation were collected from the authorities concerned, and pumping tests were carried out for twelve tube wells. The results of this study are summarized as follows: 1. The drilled tube wells are the most useful among various tube wells in securing pumping rates. 2. The enlargement of well diameter or the improvement of pumping equipments is necessary in drilled tube wells with pumping rates more than 806 ㎥/day, and the adjustment of foot valves or the special control of pumping equipments is necessary in tube wells with pumping rates less than 300 ㎥/day. 3. The choking of aquifer and slits can be prevented by removing earth and sand piled in tube wells. 4. The increase of well loss and the destruction of aquifer can be prevented by determining the optimum pumping rates through the step draw down tests. 5. The thickness of gravel packing is rather thin in drilled tube tube wells. 6. High pamping rates can be gained by deepening the depth of tube wells in the place the ground water storage is abundant, the thickness of aquifer is thick. and the depth of tube wells is deep. 7. Higher pumping rates can be obtained by constructing tube wells in the place where the drawdown is little and the coefficient of transmissibility is large.

Investigation of the Radiative Efficiency and Threshold in InGaN Laser Diodes under the Influence of Efficiency Droop

류한열 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.5

Based on the rate equation model of semiconductor lasers, the radiative efficiency and threshold current density of InGaN-based blue laser diodes (LDs) are theoretically investigated, including the effect of efficiency droop in the InGaN quantum wells. The peak point of the radiative efficiency versus current density relation is used as the parameter of the rate equation analysis. The threshold current density of InGaN blue LDs is found to depend strongly on the maximum radiative efficiency at low current density, implying that improving the maximum efficiency is important to maintain a high radiative efficiency at a large current density and to achieve a low-threshold lasing action under the influence of efficiency droop.

Internal quantum efficiency of GaN-based light-emitting diodes grown on silicon substrates determined from rate equation analyses

류한열,Ki-Seong Jeon,Jun-Ho Sung,Min-Woo Lee,Euna Lee,Hooyoung Song,Min-Gu Kang,Yoonho Choi,Jeong-Soo Lee 한국물리학회 2013 Current Applied Physics Vol.13 No.8

We present a convenient and reliable method for determining the internal quantum efficiency (IQE) in GaN-based blue light-emitting diodes (LEDs) grown on Si(111) substrates based on the carrier rate equation model. By using the peak point of the efficiency curve in photoluminescence (PL) measurements as the parameter of the rate equation analysis, the IQE can be unambiguously determined without any pre-assumed parameters. The theoretical IQE model is used to fit the measured PL efficiency curves and the IQE of LED samples are determined. The maximum IQE of the LED sample grown on the Si substrate was obtained to be 0.74, which is found to agree well with the results obtained by conventional temperature-dependent PL measurements.