• Bulletin of the Korean Space Science Society
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• 2011.04a
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• pp.24.4-24.4
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• 2011

Frozen orbit concept is very useful in designing particular mission orbits including the Sun-synchronous and minimum altitude variation orbits. In this work, variety of frozen and Sun-synchronous orbit conditions around the Moon is investigated and analyzed. The first two zonal harmonics of the Moon, J2 and J3, are considered to determine mean orbital elements to be a frozen orbit. To check the long-term behavior of a frozen orbit, formerly developed YonSei Precise Lunar Orbit Propagator (YSPLOP) is used. First, frozen orbit solutions without conditions to be the Sun-synchronous orbit is investigated. Various mean semi-major axes having between ranges from 1,788 km to 1,938 km with inclinations from 30 deg to 150 deg are considered. It is found that a polar orbit (90 deg of inclination) having 100 km of altitude requires the orbital eccentricity of about 0.01975 for a frozen orbit. Also, mean apolune and perilune altitudes for this case is about 136.301 km and 63.694 km, respectively. Second, frozen orbit solutions with additional condition to be the Sun-synchronous orbit is investigated. It is discovered that orbital inclinations are increased from 138.223 deg to 171.553 deg when mean altitude ranged from 50 km to 200 km. For the most usual mission altitude at the Moon (100 km), the Sun-synchronous orbit condition is satisfied with the eccentricity of 0.01124 and 145.235 deg of inclination. For this case, mean apolune and perilune altitudes are found to be about 120.677 km and 79.323 km, respectively. The results analyzed in this work could be useful to design a preliminary mapping orbit as well as to estimate basic on-board payloads' system requirements, for a future Korea's lunar orbiter mission. Other detailed perturbative effects should be considered in the further study, to analyze more accurate frozen orbit conditions at the Moon.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.6
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• pp.1592-1602
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• 1990

Mixed mode surface crack in finite-width plate subjected to uniform tension and bending has been analyzed in 3-D problem by using boundary element method. The calculations were carried out for the surface crack angles(.a/pha.) of 0.deg., 15.deg., 30.deg., 45.deg., 60.deg., and 75.deg., and for the aspect ratio(a/c) of 0.2, 0.4, 0.6 and 1.0 to get stress intensity factors at the boundary points of the surface crack. For the aspect ratio of 1.0 and the surface crack angles, finite element method was used to check the results in this study. Comparison of the results from both methods showed good agreement.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.198.2-198.2
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• 2012

태양 전지판의 전개 여부는 저궤도 위성의 발사 성공 여부를 판단하는 가장 중요한 항목 중 하나이다. 태양 전지판이 성공적으로 전개되어야만 태양 지향 자세제어에 의해 위성 운용에 필요한 전력 생성이 가능하기 때문이다. 그러므로 발사 후 지상국 교신을 통해 최우선적으로 태양 전지판의 전개 여부를 판단한다. 태양 전지판의 전개 여부는 다양한 실패 상황에 가정해 총 5가지 조건을 통해 판단한다. 첫째, SAR1, SAR2의 입력 전류가 모두 0.8A보다 커야 한다. 만약 하나라도 0.8A 미만이라면 한 개 이상의 태양 전지판이 전개되지 않고 1번 태양 전지판이 태양 지향을 하지 못하는 상황이다. 둘째, SAR1 입력 전류와 SAR2 입력 전류의 값이 유사해야 한다. 만약 입력 전류 값이 크게 차이가 난다면 2번과 3번 태양 전지판 중 하나만 태양 지향을 하는 경우이다. 셋째, CSSA#5 출력 전류가 3.2mA보다 커야 한다. 만약 3.2mA보다 작다면 2번과 3번 태양 전지판의 전개가 실패하고 1번 태양 전지판이 태양 지향을 하는 경우 또는 1번 태양 전지판이 전개 실패하고 태양 지향을 하는 경우이다. 넷째, S/C Roll, Pitch, Yaw rate이 모두 0.2 deg/sec 보다 작아야 한다. 만약 body rate이 크다면 1번 태양 전지판의 전개 실패 상황을 예상할 수 있다. 다섯째, 각 태양 전지판의 온도 차이가 $35^{\circ}C$ 보다 작아야 한다. 만약 온도 차이가 크다면 1번 태양 전지판 전개 실패 상황에서 2번과 3번 태양 전지판이 태양 지향을 하는 경우이다. 총 다섯 가지의 조건을 모두 만족해야만 태양 전지판이 성공적으로 전개되었다고 판단한다. 태양 전지판의 전개 판단은 위성이 발사체에서 분리되고 약 4500초 이후 시점에 스발바드 지상국과의 교신을 통해 확인되었다. 이 시점의 SAR1 입력 전류는 약 2.00A, SAR2 입력 전류는 약 1.93A였기 때문에 모두 0.8A보다 크고 서로 유사한 값임을 확인했다. CSSA#5의 출력 전류는 약 3.5mA의 값을 나타냈다. S/C Roll rate은 -0.0084 deg/sec, Pitch rate은 -0.0072 deg/sec, Yaw rate은 -0.0303 deg/sec의 값을 나타냈다. 각 태양 전지판의 최대 온도 차이는 $7.7^{\circ}C$의 값을 나타냈다. 5가지 조건을 모두 만족함으로써 태양 전지판 전개는 성공적으로 수행된 것으로 판단했다.

• Electrical & Electronic Materials
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• v.3 no.3
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• pp.233-241
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• 1990

본 연구에서는 xPb(Zn$_{1}$3/Nb$_{2}$3/)O$_{3}$-yBa(Zn$_{1}$3/Nb$_{2}$3/)O$_{3}$-zPbTiO(0.50.leq.x.leq.0.60, 0.10.leq.y.leq.0.20, 0.20.leq.z.leq.0.40)세라믹을 1050.deg.C에서 2시간동안 유지시켜 일반소성법으로 제작하였다. 시편 제작시 조성은 조성변태 상경계부근을 선택하였으며 Ba(Zn$_{1}$3/ Nb$_{2}$3/)O$_{3}$ 고용량에 따른 purochlore상의 억제 및 그 영향을 조사하고 구조적, 유전적 및 압전적 특성을 측정하였다. X-선 회절분석 및 미세구조의 관찰 결과, Ba(Zn$_{1}$3/Nb$_{2}$3/)O$_{3}$의 고용량에 따라 pyrochlore상 및 미반응 물질등은 억제되어 0.20mol 고용된 시편에서는 균질한 perovskite상이 형성되었다. Ba(Zn$_{1}$3/Nb$_{2}$3/)O$_{3}$의 고용량이 증가함에 따라 유전상수는 증가하여 0.50PZN-0.20BZN-0.30PT시편의 경우 6880.9의 높은 값을 나타내었으며 정전용량의 온도계수는 감소하여 0.383[%/.deg.C]의 양호한 값을 나타내었다. 큐리온도는 PbTiO$_{3}$의 고용량이 0.20mol에서 0.40mol로 증가함에 따라 30.deg.C에서 170.deg.C로 증가하였다. 전기기계 결합계수 (K$_{p}$), 기계적 품질계수(Qm) 및 압전전하 계수 (d$_{33}$)는 조성변태 상경계 부근의 조성에서 크게 나타났으며 0.60PZN-0.15BZN-0.25PT 시편의 경우 각각 58.5%, 120.5, 150x$10^{-12}$[C/N]의 값을 나타내었다.다.다.

• Korean Journal of Optics and Photonics
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• v.12 no.1
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• pp.10-16
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• 2001

A new digital serrodyne (DS) signal processor for the close-loop fiber optic gyroscope was designed and implemented. It is based on a new algorithm that can solve the remaining problems of the existing digital serrodyne processing by utilizing a new modulation wavefonn. The algorithm was implemented in an FPGA and tested. Theoretical limit and experimental value of the random walk were measured to be 2.6 and 3.3 deg/hr/$\sqrt{Hz}$, respectively. And drift of the processor is smaller than that by Shupe's effect.effect.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.2
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• pp.290-301
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• 1992

An experimental study has been performed to investigate the characteristics of forced convective heat transfer in a rectangular duct with a 180.deg. bend. The Nusselt number of outer wall has maximum value near 105.deg. at which secondary flow is most active and the Nusselt number of inner wall has maximum value near the inlet of a duct. Near the outlet of a duct, the Nusselt number of outer wall decreases, the Nusselt number of inner wall increases and so those access each other through the influence of a straight duct attached to the end of a duct with a 180.deg. bend. Results of this experimental study would be the fundamental data when streamline curvature correction models are developed in the numerical study for forced convective heat transfer in a curved duct.

• Electrical & Electronic Materials
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• v.9 no.9
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• pp.911-917
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• 1996

Platinum thin films were deposited on Si-wafer by DC rnagnetron sputtering for RTD (resistance thermometer devices). We investigated the physical and electrical characteristics of these films under various conditions, the input power, working vacuum, temperature of substrate and also after annealing these films. The deposition rate was increased with increasing the input power but decreased with increasing Ar gas pressure. The resistivity and sheet resistivity were decreased with increasing the temperature of substrate and the annealing time at 1000.deg. C. At substrate temperature of >$300^{\circ}C$, input power of 7 w/cm$^{2}$, working vacuum of 5 mtorr and annealing conditions of 1000.deg. C and 240 min, we obtained 10.65.mu..ohm..cm, resistivity of Pt thin films and 3800-3900 ppm/.deg. C, TCR(temperature coefficient of resistance). These values are close to the bulk value. These results indicate that the Pt thin films deposited by DC magnetron sputtering have potentiality for the development of Pt RTD temperature sensor.

• 전기의세계
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• v.28 no.9
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• pp.43-50
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• 1979

Silicon nitride films were chemically deposited on silicon substrates by reacting SiCl$_{4}$ and NH$_{3}$ in a nitrogen atmosphere at 700~1100 .deg.C. The deposition rate increased rapidly with deposition temperature upto about 1000 .deg.C, and became less temperature dependent above this temperature. The etch rate of films in buffered HF solution decreased, with an increase of deposition temperature, and a heat treatment at a temperature higher than that of the deposition considerably reduced the etch rate. It indicates that the heat treatment resulted in a densification of the films. Surface charge density of 3~4 * 10$^{11}$ /cm$^{2}$ was determined from the C-V characteristics of MNS diode, and it was also found that surface charge density depended on deposition temperature, but not film thickness. The current-voltage characteristics displayed a logI-V$^{1}$2/ dependence in the temperature range of 300~500.deg.K. Measurement of the slope of this characteristics and its dependence on temperature and bias polarity suggest that conduction in sili con nitride films arises from the Poole-Frenkel mechanism.

• Korean Journal of Microbiology
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• v.9 no.1
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• pp.27-31
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• 1971

This experiment was carried out to research for the use of the mycelium and enzyme on the production of fermented feed. Among 354 strains isolated from natural sources, 3 strains of useful yeasts were selected and identified, and the cultural conditions of these strains were examined. The results obtained were as follows. 1) The strian No.55, No.112 and No. 340 selected were identified Endomycopsis fibuliger, Endomycopsis javanensis and Candida tropicalis, respectively. 2) The optimum pH and sugar concentration of the medium for the strain No.55, No.112 and 340 selected was around pH 6.5and Bllg.10.deg.. The optimum temperature for the growth of the strain No.55 and No.112 selected was 30.deg.C and was 25.deg.C of strain No.340. 3) The strain No.55 and No.112 were grown exceedingly well on the media containing 0.1 percent of (NH/sub 4/)/sub 2/SO/sub 4/.

• Journal of the Korean Vacuum Society
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• v.17 no.1
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• pp.34-39
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• 2008

We have investigated the characteristics of $Al_{0.55}Ga_{0.45}N$/GaN heterostructures with and without low-temperature (LT) AlN interlayer grown by metalorganic chemical vapor deposition. The structural and optical properties were systematically studied by Rutherford backscattering spectroscopy (RBS), X-ray diffraction (XRD), optical microscopy (OMS), scanning electron microscopy (SEM), and photoluminescence (PL). The Al content (x) of 55% and the structural properties of $Al_xGa_{1-x}N$/GaN heterostructures were investigated by using RBS and XRD, respectively. We carried out OMS and SEM experiments and obtained a decrease of the crack network in $Al_{0.55}Ga_{0.45}N$ layer with LT-AlN interlayer. A two-dimensional electron gas (2DEG)-related PL peak located at ${\sim}3.437eV$ was observed at 10 K for $Al_{0.55}Ga_{0.45}N$/GaN with LT-AlN interlayer. The 2DEG-related emission intensity gradually decreased with increasing temperature and disappeared at temperatures around 100 K. In addition, with increasing the excitation power above 3.0 mW, two 2DEG-related PL peaks were observed at ${\sim}3.411$ and ${\sim}3.437eV$. The observed lower-energy and higher-energy side 2DEG peaks were attributed to the transitions from the sub-band level and the Fermi energy level of 2DEG at the AlGaN/LT-AlN/GaN heterointerface, respectively.