• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.7
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• pp.3191-3196
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• 2013

Ultrasonic transducer is the sensor which is measuring distance. Piezo ceramic of ultrasonic sensor and adhesive technique of matching layer are the most core techniques. With the study of relation on matching layer which takes off the ultrasonic wave into the air, this paper aims to find the second useful frequency as the results which can be changed are extracted in case piezo ceramic and matching layer are bonded. And the experiment is done with piezo ceramic as real piezoelectric element and matching layer of chemical wood. OD of piezo ceramic has designed by ${\Phi}50{\times}3T$ and OD of matching layer is designed by ${\Phi}62{\times}12t$ with ${\lambda}=1/4$. Acoustic impedance is generated at the most optimum resonant frequency of 53 Khz. As experimental result, more available frequency can be generated by using the adhesive close to solid than the flexible one.

• Korean Journal of Mathematics
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• v.24 no.3
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• pp.409-445
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• 2016

The class $\mathcal{W}^{\delta}_{\beta}({\alpha},{\gamma})$ defined in the domain ${\mid}z{\mid}$ < 1 satisfying $Re\;e^{i{\phi}}\((1-{\alpha}+2{\gamma})(f/z)^{\delta}+\({\alpha}-3{\gamma}+{\gamma}\[1-1/{\delta})(zf^{\prime}/f)+1/{\delta}\(1+zf^{\prime\prime}/f^{\prime}\)\]\)(f/z)^{\delta}(zf^{\prime}/f)-{\beta}\)$ > 0, with the conditions ${\alpha}{\geq}0$, ${\beta}$ < 1, ${\gamma}{\geq}0$, ${\delta}$ > 0 and ${\phi}{\in}{\mathbb{R}}$ generalizes a particular case of the largest subclass of univalent functions, namely the class of $Bazilevi{\check{c}}$ functions. Moreover, for 0 < ${\delta}{\leq}{\frac{1}{(1-{\zeta})}}$, $0{\leq}{\zeta}$ < 1, the class $C_{\delta}({\zeta})$ be the subclass of normalized analytic functions such that $Re(1/{\delta}(1+zf^{\prime\prime}/f^{\prime})+1-1/{\delta})(zf^{\prime}/f))$ > ${\zeta}$, ${\mid}z{\mid}$<1. In the present work, the sucient conditions on ${\lambda}(t)$ are investigated, so that the non-linear integral transform $V^{\delta}_{\lambda}(f)(z)=\({\large{\int}_{0}^{1}}{\lambda}(t)(f(tz)/t)^{\delta}dt\)^{1/{\delta}}$, ${\mid}z{\mid}$ < 1, carries the fuctions from $\mathcal{W}^{\delta}_{\beta}({\alpha},{\gamma})$ into $C_{\delta}({\zeta})$. Several interesting applications are provided for special choices of ${\lambda}(t)$. These results are useful in the attempt to generalize the two most important extremal problems in this direction using duality techniques and provide scope for further research.

• Journal of Astronomy and Space Sciences
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• v.24 no.4
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• pp.327-338
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• 2007

We estimate the momentum fluxes of short-period gravity waves which are observed in the OI 557.7 nm nightglow emission with all-sky camera at Mt. Bohyun ($36.2^{\circ}\;N,\;128.9^{\circ}\;E$) in Korea. The intrinsic phase speed ($C_{int}$), the intrinsic period (${\tau}_{int}$), and vertical wavelength (${\lambda}_z$) are also deduced from the horizontal wavelength (${\lambda}_h$), observed period (${\tau}_{ob}$), propagation direction (${\phi}_{ob}$), observe phase speed (${\upsilon}_{ob}$) of the gravity wave on the all-sky images. The neutral winds to deduce intrinsic wave parameters are measured with Fabry-Perot interferometer on Shigaraki ($34.8^{\circ}\;N,\;13.1^{\circ}\;E$) in Japan. We selected 5-nights of observations during the period between July 2002 and December 2006 considering of the weather and instrument conditions in two observation sites. The mean values of intrinsic parameter of gravity waves are $({\tau}_{int})\;=\;12.9\;{\pm}\;6.1\;m/s,\;({\lambda}_z)\;=\;12.9\;{\pm}\;6.5,\;and\;(C_{int})\;=\;40.6\;{\pm}\;11.6\;min$. The mean value of calculated momentum fluxes for four nights besides of ${\lambda}_z\;<\;6\;km$ is $12.0\;{\pm}\;15.2\;m^2/s^2$. It is needed the long-term coherent observation to obtain typical values of momentum fluxes of the mesospheric gravity waves using all-sky camera and the neutral wind measurements.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1656-1657
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• 2011

본 논문에서는 RF 프로브를 이용하여 평면 구조물의 RCS(Radar Cross Section)를 감쇄시키기 위한 방법을 제안하였다. 우선적으로, EM 시뮬레이터를 이용하여 제안한 방법에 대한 가능성을 증명한 후 실험을 수행하였다. x-band 에서 $10{\lambda}$의 알루미늄판 위에 FR4 기판을 이용하여 patch 형태로 제작된 RF 프로브를 설치하였으며, 그 후 알루미늄 판으로 입사되는 외부 전자파를 상쇄시키기 위하여 RF 프로브로부터 전자파를 방사하였다. 로테이터를 사용하여 알루미늄판을 phi 방향으로 회전하여 임의의 각도로 입사하는 평면파에 대해서도 반사파의 크기를 측정하였다. RF 프로브로부터 방사된 전자파의 세기와 위상은 신호 발생기와 위상 천이기를 이용하여 조절되었다. 결과적으로 무반향실에서의 실험을 통해, 알루미늄판에 의해 반사되는 전자파를 측정하여 외부 전자파의 상쇄 정도를 확인하였다.

• Communications of the Korean Mathematical Society
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• v.12 no.4
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• pp.935-950
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• 1997

When $\tau$ is a quasi-definite moment functional on P, the vector space of all real polynomials, we consider a symmetric bilinear form $\phi(\cdot,\cdot)$ on $P \times P$ defined by $$ \phi(p,q) = \lambad p(a)q(a) + \mu p(b)q(b) + <\tau,p'q'>, $$ where $\lambda,\mu,a$, and b are real numbers. We first find a necessary and sufficient condition for $\phi(\cdot,\cdot)$ and show that such orthogonal polynomials satisfy a fifth order differential equation with polynomial coefficients.

• Korean Journal of Mathematics
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• v.16 no.1
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• pp.41-49
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• 2008

We show the existence of a negative solution for the system of the following nonlinear wave equations with critical growth, under Dirichlet boundary condition and periodic condition $$u_{tt}-u_{xx}=au+b{\upsilon}+\frac{2{\alpha}}{{\alpha}+{\beta}}u_+^{\alpha-1}{\upsilon}_+^{\beta}+s{\phi}_{00}+f,\\{\upsilon}_{tt}-{\upsilon}_{xx}=cu+d{\upsilon}+\frac{2{\alpha}}{{\alpha}+{\beta}}u_+^{\alpha}{\upsilon}_+^{{\beta}-1}+t{\phi}_{00}+g,$$ where ${\alpha},{\beta}>1$ are real constants, $u_+={\max}\{u,0\},\;s,\;t{\in}R,\;{\phi}_{00}$ is the eigenfunction corresponding to the positive eigenvalue ${\lambda}_{00}$ of the wave operator and f, g are ${\pi}$-periodic, even in x and t and bounded functions.

• Honam Mathematical Journal
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• v.30 no.1
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• pp.197-203
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• 2008

We show the existence of the unique solution of the following system of the nonlinear wave equations with Dirichlet boundary conditions and periodic conditions under some conditions $U_{tt}-U_{xx}+av^+=s{\phi}_{00}+f$ in $(-{\frac{\pi}{2},{\frac{\pi}{2}}){\times}R$, ${\upsilon}_{tt}-{\upsilon}_{xx}+bu^+=t{\phi}_{00}+g$ in $(-{\frac{\pi}{2},{\frac{\pi}{2}}){\times}R$, where $u^+$ = max{u, 0}, s, t ${\in}$ R, ${\phi}_{00}$ is the eigenfunction corresponding to the positive eigenvalue ${\lambda}_{00}$ of the wave operator. We first show that the system has a positive solution or a negative solution depending on the sand t, and then prove the uniqueness theorem by the contraction mapping principle on the Banach space.

• Journal of applied mathematics & informatics
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• v.22 no.1_2
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• pp.557-562
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• 2006

We consider the relationship between absolute continuity for functions of a real variable and absolute continuity of functions of generalized bounded variation. Here, we obtain necessary and sufficient conditions between these two functions.

• 한국지구과학회:학술대회논문집
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• 2010.04a
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• pp.120-120
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• 2010

두 개의 별로 구성되었을 것이라고 여겨진 공생별은 밝기변화는 궤도운동에 따라 밝기가 변하는 것으로 알려졌다. 분광 관측 자료에는 이러한 궤도 변화 외에도 다양한 요소가 밝기 변화에 관여하는 것이 특성으로 나타난다. 또한 공생별은 밝기가 급격하게 증가하고 혹은 감소하기도 하는데, 이는 폭발에 기인하는 것으로 판단된다. 이러한 변화, 궤도 운동에 따라 기하학적 변화와 폭발 현상을 모두 볼 수 있는 대표적인 공생별이 Z And이다. 우리는 선행연구(MIKOLAJEWSKA & KENYON, 1996)에서 발표한 저분산 분광 자료를 이용하여 위상별로 변하는 상대적 선세기 변화를 조사하였다. MIKOLAJEWSKA & KENYON (1996)의 자료는 저분산 기기로(${\Delta\lambda\sim}3{\AA}$), HeI, HII, [OIII]5007, [NeV]등이 관측되었는데, 이러한 선들의 세기를 광이온 모델을 이용하여 예측한 후, 공생별 가스를 이온화시킨 중심별(WD)의 물리적 특성을 연구하였다. 또한 Hyung & Aller가 2002년 8월 12일 Lick Observatory에서 Hamilton Echelle Spectrograph (HES)를 사용하여 3600초 노출 관측한 고 분산 분광자료(${\Delta\lambda\sim}0.1{\AA}$)도 분석하였다. HES 관측 자료는 공생별의 위상이 $\Phi$=0.22이며, HES자료는 $3470{\AA}-9775{\AA}$에서 HI, HII, HeI, HeII, NII, NIII, OII, [OI], [OII], [OIII] 등이 있었다. 이 선들의 선 윤곽을 IRAF와 StarLink/Dipso를 이용하여 분석하고, 각 성분이 위상($\Phi$=0.22)인 상태에서의 관측자에 대해 어떠한 기하학적인 구조를 가지고 있는지 연구하였다. CLOUDY를 사용하여 광 이온 모형성운을 만들어 화학원소 및 성운가스의 물리적 조건을 연구하였다. Z And의 수소의 수밀도($N_H$)는 $10^{8.5}/cm^3$으로 가정하였다. 중심별 온도는 약 110,000K, 광도는 태양의 2000배로 추정되었다.

• Journal of the Korean earth science society
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• v.33 no.7
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• pp.608-617
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• 2012

The symbiotic nova Z Andromedae (And) was investigated, using the high dispersion spectra of spectral resolution, ${\Delta}{\lambda}{\sim}-0.1{\AA}$. The spectral observations were done with (1) the Hamilton Echelle Spectrograph (HES) and the high resolution spectra (exposures=1800s and 3600s) were obtained at Lick Observatory in 2001 August $30^{th}$ (phase ${\Phi}$=0.77), and 2002 August $12^{th}$ (phase ${\Phi}$=0.22), (2) with the Bohyunsan Echelle Spectrograph (BOES) at Bohyunsan Optical Astronomy Observatory and the high resolution spectra (exposure=1200s) were secured in 2009 October $21^{st}$ (phase ${\Phi}$=0.70). From both the HES and BOES spectral data in the $3600{\AA}-9500{\AA}$ wavelengths, we extracted the emission lines of HI, HeI, and HeII, which have been decomposed into double or triple Gaussian components for 3 consecutive phases. The emission zones responsible for these components appear to be closely related with the orbital motion of a white dwarf or a giant star. The presence of the Raman scattering $H{\alpha}$ broad wing feature and the kinematic characteristics of the line profile observed in each phase imply that the Z And emission lines are mostly from two Lagrangian points, $L_1$ and $L_2$, and the accretion disk around the white dwarf star. The Z And was most active in 2009 and 2001 during the outburst phase, while it remained quiescent in 2002 in spite of the complex line profiles.