• Journal of Astronomy and Space Sciences
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• v.5 no.2
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• pp.111-122
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• 1988

The short and long periodic perturbations and secular perturbation due to the geopotentials of degree $J_2$ and $J_3$ which affect orbital elements of a near-circular orbiting satellite are obtained by the analytical method. The singular points due to a small denominator e in the perturbation equations can be excluded using one of the methods introduced by Taff(1985), which substitutes $e_s=esin\omega,\;e_c=ecos\omega\;and\;\ell=\omega+M$ for the orbital elements e, $\omega$ and M. We determined the mean orbital elements of the meteorological satellite NOAA-10 using the Walter (1967)'s iterative procedure and compared with Brouwer's mean orbital elements determined at NASA. The mean orbital elements a, ⅰand $\Omega$ are consistent with those of NASA but the mean orgital elements e, $\omega$ and M have some deviations from those of NASA. According to the our results, it is not suitable for the polar orbiting satellites to use the Taff's proposal for excluding the singular points, which substitutes e, $\omega$ and M by $e_s=esin(\Omega+\omega),\;e_c=ecos(\Omega+\omega)\;and\;L=\Omega+\omega+M$.

• 제어로봇시스템학회:학술대회논문집
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• 1988.10b
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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.

• Journal of the Korean Mathematical Society
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• v.55 no.1
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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.

• Proceedings of the KSME Conference
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• 2004.11a
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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$(-Q_{0}/RT)$

• Proceedings of the KIEE Conference
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• 1992.07b
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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.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11b
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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.

• Proceedings of the KIEE Conference
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• 2002.07a
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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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• v.23 no.1
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• pp.55-70
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• 2006

There are many astronomical records of comets in Korean history books. We collected those of the comet that appeared in the winter of the year 1664. These records were written in Daily Reports of the Royal Observatory on Astronomical Events (星變測候單子), Final Reports of the Royal Observatory on An Astronomical Events (天變謄錄), the Daily Records of the Royal Secretariat of the Joseon Dynasty (承政院日記), and the Chronicle of the Joseon Dynasty (朝鮮王朝實錄). We used the Olbers' method for determination of preliminary orbit of the comet, and compared the result with the previous researches. In the Oblers' method the orbit is assumed to be parabolic (e=1). We obtained the following orbital elements: perifocal distance q=1.07\pm0.008AU, perifocal passage time $T=2329165.50\pm0.72$ days, argument of the perifocus $\omega=318^{\circ}.2\pm2^{\circ}.29$, longitude of ascending node $\Omega=85^{\circ}.23\pm2^{\circ}53(J1665)$(J1665), inclination $i=160^{\circ}.28\pm1^{|circ}.56$.

• 한국전산유체공학회:학술대회논문집
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• 2004.03a
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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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• 2007.04a
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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.