• Journal of the Korean Vacuum Society
• /
• v.9 no.2
• /
• pp.110-115
• /
• 2000

Deposition conditions of diamond thin films were optimized using hot-filament chemical vapor deposition (HFCVD). Boron-doped diamond thin films with varying boron densities were then fabricated using B4C solid pellets. Current-voltage responses and field emission currents were measured to test the characteristics of field emission display (FED). With the increase of boron doping, the crystal size of diamond decreased slightly, but its quality was not changed significantly in case of small doping. The I-V characterization was performed for Al/diamond/p-Si, and the current of doped diamond film was increased $10^4\sim10^5$ times as compared with that of undoped film. In the field emission properties, the electrons were emitted with low electric field with the increase of doping, while the emission current increased. The onset-field of electron emission was 15.5 V/$\mu\textrm{m}$ for 2 pellets, 13.6 V/$\mu\textrm{m}$ for 3 pellets and 11.1 V/$\mu\textrm{m}$ for 4 pellets. With the incorporation of boron, the slope of Fowler-Nordheim graph was decreased, revealing that the electron emission behavior was improved with the decrease of the effective barrier energy.

• Korean Journal of Materials Research
• /
• v.8 no.7
• /
• pp.601-606
• /
• 1998

The $SrTi0_3$:Al, Pr red phosphors were prepared by solid state reaction method. Phosphor preparation parameters such as sintering temperature and time were optimized for the photoluminescence(PU intensity and the cathodoluminescence(CL) intensity. Powder samples showed the characteristic X-ray diffraction patterns of the perovskite structure and the average particle size of 3~5/$\mu\textrm{m}$ for particle size distribution(PSD) analysis. Also, scanning electron microscopy for the powder samples showed that the particles are reasonably crystallized with spherical shape. Especially, higher low voltage CL properties of $SrTi0_3$:Al, Pr phosphors than commercial $Y_2O_3$:Eu phosphors are expected to be applied for a low voltage field emission display(FED).

• Journal of Advanced Marine Engineering and Technology
• /
• v.17 no.4
• /
• pp.38-48
• /
• 1993

A study on friction welding of stainless steel bar(SUS431) to chrome molybdenum steel bar(SCM21) was accomplished experimentally through analysis for relations among friction welding conditions, tension test, hardness test, microstructure test and acoustic emission test. The results obtained are summarized as follows ; 1. Through friction welding of SUS431 bar to SCM21 bar, the optimum welding condition by considering on strength and toughness was found to be the range of heating time of 3-5 sec when the number of rotating speed of 2000rpm, heating pressure of 10kg/$mm^2$, and upsetting time of 4 sec. 2. Quantitative ralationship was identified between heating time($T_1$, sec) and tensile strength (${\sigma},\;kgf/mm^2$) of the friction welded joint and the relation equation is $\sigma$=52.62$T_1{^{0.06}}$. 3. Through AE test, quantitative relationship was confirmed between heating time($T_1$, sec) and total AE(N, counts) during welding, and the relation is computed as follows ; N=30413.6$e^{0.06T1}$. 4. It was confirmed that the quantitative ralationship exists between the tensile strength of the welded joints and AE cumulative counts. And the relation is computed as the following ; ${\sigma}$=16.37(ln N)- 116.4. 5. When ONZ=36500-41500 counts by $OT_1Z$=3~5sec, it was identified by experiment that the range of welded joint tensile strength is 55.6-57.7kgf/$mm^2$/ whose joint efficiency is more than 100%, and it was experimentally confirmed that the real-time nondestructive quality(strength) evaluation for the friction welded joints could be possible by acoustic emission technique.

• Atmosphere
• /
• v.25 no.3
• /
• pp.529-541
• /
• 2015

Korea Institute of Atmospheric Prediction System (KIAPS) has been developing a global numerial prediction model and data assimilation system. We has implemented LETKF (Local Ensemble Transform Kalman Filter, Hunt et al., 2007) data assimilation system to NCAR CAM-SE (National Center for Atmospheric Research Community Atmosphere Model with Spectral Element dynamical core, Dennis et al., 2012) that has cubed-sphere grid, known as the same grid system of KIAPS Integrated Model (KIM) now developing. In this study, we have assimilated Global Positioning System Radio Occultation (GPS-RO) bending angle measurements in addition to conventional data within ensemble-based data assimilation system. Before assimilating bending angle data, we performed a vertical unit conversion. The information of vertical localization for GPS-RO data is given by the unit of meter, but the vertical localization method in the LETKF system is based on pressure unit. Therefore, with a clever conversion of the vertical information, we have conducted experiments to search for the best vertical localization scale on GPS-RO data under the Observing System Simulation Experiments (OSSEs). As a result, we found the optimal setting of vertical localization for the GPS-RO bending angle data assimilation. We plan to apply the selected localization strategy to the LETKF system implemented to KIM which is expected to give better analysis of GPS-RO data assimilation due to much higher model top.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.15 no.2
• /
• pp.175-180
• /
• 2015

In this paper, GPS / GLONASS receiving a small active antenna is proposed. A microstrip patch antenna which supports dual-band (GPS and GLONASS) was optimized. The antenna size is $13{\times}13{\times}3.6mm$. The jig was changed to confirm the proposed antenna characteristic size, was adjusted to feed gap of the patch antenna, it was confirmed by change in LNA shield case or not. The antenna jig size is $65.6{\times}13{\times}0.8mm$. The maximum gain of the GPS band is 3.78dBi, the maximum gain of the GLONASS bands is 4dBi. To amplify the Satellite reception signal level, one-stage low noise amplifier(LNA) was designed. The LNA chip was using the BGA715 N7, the LNA gain is 19.9dB. The utilization possibility of the GPS / GLONASS receiving a small active antenna could be confirmed according to compare and analyze the simulation and measurement data.

• Applied Chemistry for Engineering
• /
• v.31 no.4
• /
• pp.438-442
• /
• 2020

Studies on the recovery conditions and optimization process for valuable metal recovery through chemical treatment from detoxified asbestos-containing waste composed of calcium silicate, larnite, merwinite, and akermanite were conducted. The main components, Si, Ca, and Mg, of detoxified asbestos-containing waste (DACW) were separated and recovered in the form of SiO₂, CaSO₄, and Mg(OH)₂ compounds, respectively. Each separated component was confirmed through X-ray diffraction (XRD) and inductively coupled plasma spectrometer (ICP) analysis. The recovery conditions for each component were first treating them with an acid to separate SiO₂ and subsequently with H₂SO₄ to recover Ca in the form of sulfate, CaSO₄. The remaining Mg was recovered by precipitation with Mg(OH)₂ under strong basic conditions. This study suggested that it is possible to convert existing treatment process of asbestos waste by landfill through recovering the components into a resource-recycling green technology.

• Journal of the Korean Data and Information Science Society
• /
• v.28 no.6
• /
• pp.1447-1456
• /
• 2017

Accurate inference of parameters of a stochastic rainfall generation model is essential to improve the applicability of the rainfall generation model which modeled the rainfall process and the structure of rainfall events. In this study, the model parameters of a stochastic rainfall generation model, NSRPM (Neyman-Scott rectangular pulse model), were estimated using DFP (Davidon-Fletcher-Powell), GA (genetic algorithm), Nelder-Mead, and DE (differential evolution) methods. Summer season hourly rainfall data of 20 rainfall observation sites within the Nakdong river basin from 1973 to 2017 were used to estimate parameters and the regional applicability of inference methods were analyzed. Overall results demonstrated that DE and Nelder-Mead methods generate better results than that of DFP and GA methods.

• Journal of Advanced Marine Engineering and Technology
• /
• v.38 no.3
• /
• pp.262-268
• /
• 2014

This research introduces the structural design and the validation results of the flexible high speed coupling for 2MW class wind turbine which transmit and cut off torque between gear box and generator. The high speed coupling requires electrical insulation to prevent electrical surface damages on gear box. Therefore glass fiber reinforced plastics is applied to absorb the vibration and deformation of power train and to transmit required torque. Finite element analysis was performed to optimize the thickness and accumulation number of glass fiber reinforced plastics. Torque limiter which cut off the abnormal torque is designed in frictional disc type. The design of the coupling was validated with the performance test of prototype.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.18 no.10
• /
• pp.580-587
• /
• 2017

Recently, as the education population of Korea has been rapidly declining, many changes have been taking place in the university environment. Especially, community colleges linked to local communities have responded to these crises through various educational changes, such as three-year study transfers, work-parallelism, and employee commissioned education. However, such changes in the contents of education are causing a new type of classroom allocation problem, in which it is difficult to assign the limited number of classrooms to the major courses. In this paper, we classified the constraints involved in assigning classrooms into absolute constraints and relative constraints, mathematically modeled them, and allocated the classrooms optimally through optimization software. The results were satisfactory and enabled us to obtain superior results in terms of the various performance indices (classroom utilization rate, teacher satisfaction, etc.) than when assigning classrooms in the normal way.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2011.05a
• /
• pp.31-31
• /
• 2011

해마다 반복되는 수해를 대비하여 배수펌프장을 설치하고, 취수보를 철거하는 방법으로 수해예방시스템을 고도화 시키고 있지만, 증가하는 홍수량에 대한 대비책으로는 역부족이다. 따라서, 홍수 피해에 대한 선제적 대응방안으로 강변저류지를 설치하여 상습 침수구역에 대한 대비가 진행되고 있다. 강변저류지 설치를 통해 유역의 홍수량을 분담하고 인접지역의 침수피해를 예방하는 역할을 기대할 수 있다. 국내에서도 영월군의 상습침수구역에 대한 대비책 중 하나로 국토해양부 및 강원도가 함께 영월강변저류지 조성공사를 추진하고 있다. 영월군은 지난 2002년과 2003년에 태풍 '루사'와 '매미'로 인해 심각한 피해를 입었으며, 2006년 집중호우시에도 현재 저류지 예정지역인 방절리 일대와 영월읍 시가지, 북쌍리 등이 대규모로 침수피해를 입은 바 있다. 해당 저류지의 총 넓이는 68만 8천 $m^2$로 물 290만 $m^3$을 가두어 둘 수 있는 규모이다. 하지만, 영월 강변저류지의 저류용량이 290만 $m^3$에 불과해 홍수예방 효과가 미흡하다는 지적이 잇따르고 있다. 따라서, 적절한 수문운영을 통해 홍수저감량과 저류효과를 증대시키는 홍수예방 방안을 제안하고자 한다. 본 연구에서는 유전알고리즘의 적용을 통하여 강변저류지에 설치된 수문의 운영 방법을 개선함으로써 홍수저감량을 최대화하고자 하였다. 수리 수문학적 모형인 HEC-RAS, HEC-I 모형을 연계 운용하여 평창강 유역을 대상으로 수문분석, 홍수유출량 분석, 하류 하천의 홍수영향 분석 결과를 도출하였다. 강변저류지 설치로 인하여 저류지 직하류부를 기준으로 약 $131\;m^3/s$의 첨두홍수량 저감 효과가 발생하는 것으로 검토되었지만, 본 연구에서 제안된 최적화 기법이 적용된 수문운영 방법을 병행하여 운영한다면 추가적으로 $24\;m^3/s$를 저감하는 효과를 얻을 수 있다. 효율적으로 저류지를 운영하여 홍수피해를 사전에 방지하고 나아가 다른 저류지 유역에도 본 연구를 적용하여 홍수피해를 줄이고 합리적으로 용수를 이용하는데 기여할 수 있을 것으로 사료된다.