• Journal of Astronomy and Space Sciences
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• 제5권2호
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• pp.111-122
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• 1988

지구의 비대칭 중력장 $J_2$와 $J_3$가 원궤도에 가까운 인공위성의 궤도요소에 미치는 장, 단주기 섭동과 영년섭동을 해석적 방법으로 구하였다. 이 때 궤도의 이심률이 작은 경우에 섭동방정식에서 발생하는 특이점은 Taff(1985)가 제시한 방법중 궤도요소 e, $\omega$, M을 $e_s$=$esin\omega$, $e_c=e\;cos\;\omega$, $\ell=\omega+M$으로 치환하는 방법을 사용하여 제거시켰다. Walter(1967)의 방법을 이용하여 기상위성 NOAA-10호의 평균궤도요소를 결정하였고 이를 NASA의 Brouwer 평균 궤도요소와 비교하였다. 평균 궤도요소 a, i, $\Omega$는 TBUS의 결과와 거의 일치하나 평균 궤도요소 e, $\omega$, M은 약간의 차이를 보였다. 그리고 특이점을 제거하기 위한 Taff의 방법 중 e, $\omega$, M 대신에 $e_s=e\;sin(\Omega+\omega)$, $e_c=e\;cos(\Omega+\omega)$, $L=\Omega+\omega+M$으로 치환하는 방법이 극궤도위성에는 부적합한 것으로 나타났다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1988년도 한국자동제어학술회의논문집(국제학술편); 한국전력공사연수원, 서울; 21-22 Oct. 1988
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• pp.943-946
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• 1988

A simple method is proposed for determining the frequency response function G(j.omega.) of a system using a pair of characteristic M-sequences (maximum length linear feed back shift register sequence). When a characteristic M-sequence is sampled with q$_{1}$ and q$_{2}$ both of which are coprime with N, where N is the period of the M-sequence, the obtained pair of sequences have conjugate complex frequency spectrum. Making use of this fact, two charcteristic M-sequences having conjugate complex frequency spectrum are applied to a system to be measured. Since the magnitude of spectrium of M-sequence is known, the gain of G(j.omega.) is directly obtained from the Fourier transform of the system output. The phase of G(j.omega.) is obtained simply by taking the average of the two phases of output spectrum.

• 대한수학회지
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• 제55권1호
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• pp.17-28
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• 2018

In this paper, we enlarge the ball of convergence of a uniparametric family of secant-like methods for solving non-differentiable operators equations in Banach spaces via using ${\omega}$-condition and centered-like ${\omega}$-condition meantime as well as some fine techniques such as the affine invariant form. Numerical examples are also provided.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.388-393
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• 2004

Creep behavior of Ti had been studied in a stress from 9.8 to 29.4 MPa and temperature rang from 873K to 973K with a special reference to tertiary creep. It was found that stress exponent of Ti was larger than that of the general pure metal and the compound metal. The relationship between true strain and strain rate in tertiary creep was appeared as the equation, $ln{\dot{e}}$ = $ln{\dot{e}}_{0}$ + ${\Omega}$ e Also, Apparent activation energy of was appeared as 274.92kJ/mol by using the equation ${\dot{\varepsilon}}_{0}$ = A ${\sigma }_{0}^{\ast_0}$ exp$(-Q_{0}/RT)$

• 대한전기학회:학술대회논문집
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• 대한전기학회 1992년도 하계학술대회 논문집 B
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• pp.649-652
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• 1992

ECR(Electron Cyclotron Resonance) occure at ${\omega}_c$=${\omega}$, ${\omega}_c$:electron cycltron frequency, ${\omega}$:electromagnetic wave frequency. ECR system have several merit, 1) power transefer efficiency 2) low neutral gas pressure (below 1 mTorr) 3) high plasma density($10^{12}$ $cm^{-3}$). It is applicated variously in the field of semiconductor and new materials as the manufacturing equipment. Magnetic field in ECR system contruct resonance layer (${\omega}$=2.45GHz, $B_z$=875 Gauss) and control plasma. Plasma is almost generated at resonance layer. If the distance between substrate and resonance layer is short, uniformity of plasma is related with profile of resonance layer. Plasma have the property "Cold in Field", so directonality of magnetic field is one of the control factors of anisotropic etching. In this study, we calculate B field and flux line distribution, optimize geometry and submagnet current and improve of magnetic field directionality (99.9%) near substrate. For the purpose of calculation, vector potential A(r,z) and magnetic field B(r,z), green function and numerical integration is used. Object function for submagnet optimization is magnetic field directionality on the substrate and Powell method is used as optimization skim.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 추계학술대회 논문집 Vol.14 No.1
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• pp.197-200
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• 2001

In this letter, we report on the investigation of Ni/Si/Ni Ohmic contacts to n-type 4H-SiC. Ohmic contacts have been formed by a vacuum annealing and $N_2$ gas ambient annealing method at $950^{\circ}C$ for 10 min. The specific contact resistivity ( $\rho_{c}$ ), sheet resistance($R_s$), contact resistance($R_c$), transfer length($L_T$) were calculated from resistance($R_T$) versus contact spacing(d) measurements obtained from 10 TLM(transmission line method) structures. The resulting average values of vacuum annealing sample were $\rho_{c}=3.8{\times}10^{-5}\Omega cm^{3}$, $R_{c}=4.9{\Omega}$, $R_{T}=9.8{\Omega}$ and $L_{T}=15.5{\mu}m$, resulting average values of another sample were $\rho_{c}=2.29{\times}10^{-4}\Omega cm^{3}$, $R_{c}=12.9{\Omega}$ and $R_{T}=25.8{\Omega}$. The physical properties of contacts were examined using X-Ray Diffraction and Auger analysis, there was a uniform intermixing of the Si and Ni, migration of Ni into the SiC.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 하계학술대회 논문집 A
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• pp.145-147
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• 2002

In this paper, the improved fault locating method using distributed parameter which calculating the reduced voltage and current according to the ground capacitance in long transmission line was proposed. For the purpose of the fault locating algorithm non influenced source impedance, the loop method was used in the system modeling analysis. To enhance the fault locating, zero sequence of the fault current which is variable according to ground capacitance was not used but positive and negative sequence. System model was simulated using EMTP software. To verify the accuracy of proposed method, in different cases 64 sampled data per cycle was used and 160km and 300km long transmission line has fault resistance $0{\Omega}\;and\;100{\Omega}$ respectively was compared.

• Journal of Astronomy and Space Sciences
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• 제23권1호
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• pp.55-70
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• 2006

한국의 역사서에 속에는 혜성을 관측한 기록이 많이 있다. 우리는 그 가운데 조선 현종 5년 1664년 겨울에 나타난 혜성을 관측한 기록을 <성변측후단자>, <천변등록>, <승정원일기>, <조선왕조실록>에서 수집 정리하였다. 우리는 올버스(Olbers)의 방법을 사용하여 혜성의 예비 궤도 요소를 구하고, 그것을 이전의 연구들과 비교하였다 올버스의 방법에서는 혜성 궤도의 이심율 e=1인 포물선 케도로 가정한다 관측 자료를 사용하여 궤도를 계산한 결과, 근일점 거리 (perifocal distance) $q=1.07\pm0.008AU$, 근일점 통과 시간 $T=2329165.50\pm0.72$일, 승교점과 근일점의 이각(argument of the perifocus) $\omega=318^{\circ}.2\pm2^{\circ}.29$, 승교점 경도(longitude of the ascending node) $\Omega=85^{\circ}.23\pm2^{\circ}53(J1665)$, 궤도 경사(inclination) $i=160^{\circ}.28\pm1^{|circ}.56$를 얻었다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2004년도 춘계 학술대회논문집
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• pp.139-145
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• 2004

A numerical study of underexpanded jet and impingement on a wall mounted at various distances from the nozzle exit is presented. The 3-dimensional Navier-Stokes equations and $\kappa-\omega$ turbulence equations are solved. The grids are constructed as overlapped grid systems to examine the distance effect. The DADI method is applied to obtain steady-state solutions. To avoid numerical instability such as the carbuncle that sometimes accompany approximate Riemann solver, the HLLE+ scheme is employed for the inviscid flux at the cell interfaces. A goal of this work is to apply a number of two-equation turbulence models based on the $\omega$ equation to the impinging jet problem.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2007년도 춘계 학술대회논문집
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• pp.3-7
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• 2007

The characteristics of asymmetric vortex and side force of tangent-ogive-cylinder flight vehicle at high angles of attack have been performed by using upwind Navier-Stokes method with the ${\kappa}-{\omega}$ turbulence model. And Asymmetric transition positions are considered for generation of asymmetric vortex.