• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.1
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• pp.47-52
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• 2007

Organic field-effect transistors (OFETS) are of interest for use in widely area electronic applications. We fabricated a copper phthalocyanine (CuPc) based field-effect transistor with varying channel length. The CuPc FET device was made a top-contact type and the channel length was a $100\;{\mu}m,\;50\;{\mu}m,\;40\;{\mu}m,\;and\;30\;{\mu}m$ and the channel width was a fixed at 3 mm. We observed a typical current-voltage (I-V) characteristics in CuPc FET with varying channel length (L) and we calculated the effective mobility. Also, we measured a capacitance-voltage (C-V) by applied bias voltage with varying frequency at 43, 100, 1000 Hz.

• Journal of The Korean Astronomical Society
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• v.42 no.6
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• pp.161-174
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• 2009

Observation of standard stars is of crucial importance in stellar photometry. We have studied the standard transformation relations of the UBV RI CCD photometric system at the Maidanak Astronomical Observatory in Uzbekistan. All observations were made with the AZT-22 1.5m telescope, SITe 2k CCD or Fairchild 486 CCD, and standard Bessell UBV RI filters from 2003 August to 2007 September. We observed many standard stars around the celestial equator observed by SAAO astronomers. The atmospheric extinction coefficients, photometric zero points, and time variation of photometric zero points of each night were determined. Secondary extinction coefficients and photometric zero points were very stable, while primary extinction coefficients showed a distinct seasonal variation. We also determined the transformation coefficients for each filter. For B, V, R, and I filters, the transformation to the SAAO standard system could be achieved with a straight line or a combination of two straight lines. However, in the case of the U filter and Fairchild 486 CCD combination, a significant non-linear correction term - related to the size of Balmer jump or the strength of the Balmer lines - of up to 0:08 mags was required. We found that our data matched well the SAAO photometry in V, B - V, V - I, and R - I. But in U - B, the difference in zero point was about 3.6 mmag and the scatter was about 0.02 mag. We attribute the relatively large scatter in U -B to the larger error in U of the SAAO photometry. We confirm the mostly small differences between the SAAO standard UBV RI system and the Landolt standard system. We also attempted to interpret the seasonal variation of the atmospheric extinction coefficients in the context of scattering sources in the earth's atmosphere.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.7
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• pp.604-610
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• 2003

The effects of sintering additives such as B $i_2$ $O_3$ and $V_2$ $O_{5}$ on the microwave dielectric and sintering properties of (Z $n_1$$_{-xM}$ $g_{x}$)Ti $O_3$ system were investigated. Highly dense samples were obtained for (Z $n_{0.8}$M $g_{0.2}$)Ti $O_3$ at the sintering temperature range of 870~90$0^{\circ}C$ with B $i_2$ $O_3$ and $V_2$ $O_{5}$ additions of 〈1 wt.%, respectively. The microwave dielectric properties of (Z $n_{0.8}$M $g_{0.2}$)Ti $O_3$ with 0.45 wt.%B $i_2$ $O_3$ and 0.55 wt.% $V_2$ $O_{5}$ sintered at 90$0^{\circ}C$ were as follows : Q$\times$ $f_{o}$ = 50,800 GHz, $\varepsilon$$_{r}$ = 22, and $\tau$$_{f}$ = -53 ppm/$^{\circ}C$. In order to improve temperature coefficient of resonant frequency, Ti $O_2$ was added to the above system. The optimum amount of Ti $O_2$ was 15 moi.% when sintered at 87$0^{\circ}C$, at which we could obtain following results: Q$\times$ $f_{o}$ = 32,800 GHz, $\varepsilon$$_{r}$ = 26, and$\tau$$_{f}$ = 0 ppm/$^{\circ}C$.EX>.EX>.EX>.EX>.EX>.EX>.EX>.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.7
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• pp.620-624
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• 2016

In this paper we designed a current mode logic frequency divider to transmit a baseband amplitude modulated signal. From simulation result, we studied input and output waveforms according to the variation of input bias voltage. For the purpose of the verification of the study, we designed a current mode logic frequency divider at 1,400 MHz. The designed frequency divider operates between 100 MHz and 3,000 MHz, for -33 dBm input power. The circuit draws $I_{total}=30mA$ from $V_{DD}=3V$ supply, and the simulation result shows that an amplitude modulated signal at 1,400 MHz with the modulation index of 0.5 was successfully downconverted to 700 MHz.

• Journal of The Korean Astronomical Society
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• v.37 no.4
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• pp.143-149
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• 2004

We present photometric results for four new variable stars discovered in the vicinity of the ZZ Ceti-type pulsating white dwarf BR Cam. Observations were performed on 5 nights in November 2003 using the 1.8m telescope at Bohyunsan Optical Astronomy Observatory with no filter, on 3 nights in December 2003 using the 0.61m telescope at Sobaeksan Optical Astronomy Observatory with V, I filters, and on 3 nights in October 2004 using the 1.0m telescope at Mt. Lemmon Optical Astronomy Observatory with V, I filters. We estimated their periods from the phase-match technique for one eclipsing binary and the multiple frequency analysis for three pulsating stars. By considering the light curve shape, period and amplitude difference between two passbands, we classified the objects by their variability types as follows: V1 (USNO-A2.0 1425-05691757) is a W UMa-type eclipsing binary with an orbital period of $0^d.4641$; V2 (USNO-A2.0 1425-05703335) is a multi-periodic $\delta$ Set-type pulsating star with a dominant period of $0^d.0649$; V3 (USNO-A2.0 1425-05699659) is also a $\delta$ Set-type pulsating star with a period of $0^d.1408$; and V 4 (USNO-A2.0 1425-05707705) is a RR Lyr-type pulsating star with a period of $0^d.2643$.

• Journal of Sensor Science and Technology
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• v.6 no.4
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• pp.290-297
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• 1997

In this study, the radiation monitoring system using CsI(TI) scintillation counter is developed for the measurement of radiation distribution in the field of high dose level. When the inner diameter of collimator is 8 mm, we have realized the optimum detecting efficiency and spatial resolution. At that time, the position resolution was 10 cm at 1 m from the system. And experimental results indicated that the energy resolution of the system were 10 % for 662 keV of Cs-137, 7.6 % for 1.17 MeV of Co-60, and 5.8 % for 1.33 MeV of Co-60. Also, we have shown that the real radiation distribution images may be obtained by our measurement system.

• Proceedings of the KIPE Conference
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• 2019.07a
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• pp.230-232
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• 2019

Light Triggerd Thyristor (LTT)는 HVDC 및 산업용 스위치 등에 사용되는 대전력 반도체소자이다. 일반적인 Thyristor가 전기적 신호에 의해 trigger 되는 것과는 다르게 LTT는 광신호에 의해 동작하는 소자이다. 본 논문에서는 5,000V, 2,200A 급의 4인치 LTT 소자의 제작 및 전기적인 특성평가 결과를 기술하였다. 4인치 LTT의 구조적인 특징은 전면부 중앙에 광신호가 주입되는 수광부가 위치해 있으며 입력 전류 증폭을 위한 4-단계 증폭 게이트 (gate) 구조를 가지도록 설계하였다. $400{\Omega}{\cdot}cm$ 비저항을 갖는 1mm 두께의 n-형 실리콘 웨이퍼에 boron 이온주입과 열처리 공정으로 약 $30{\mu}m$ 깊이의 p-base를 형성하였으며, 고내압 저지를 위한 edge termination은 VLD (variable lateral doping) 기술을 적용하였다. 제작된 4인치 LTT는 6,500 V의 순방향 항복전압 ($V_{DRM}$) 특성을 나타내었으며, 100V의 어노드전압 ($V_A$)과 20 mA의 게이트전류 ($I_G$)에 의하여 thyristor가 trigger 됨을 확인하였다. 제작한 LTT 소자는 disk형 press-pack 패키지를 진행한 후, LTT의 수광부에 $10{\mu}s$, 50 mW의 900 nm 광 펄스를 조사하여 전류 특성을 평가하였다. LTT 패키지 샘플에 60 Hz 주파수의 광 펄스를 조사한 경우 2,460 A의 순방향 평균전류 ($I_T$)와 $336A/{\mu}s$의 반복전류상승기울기 (repetitive di/dt)에 안정적으로 동작함을 확인하였다. 또한, 펄스 전류 시험의 경우 61.6 kA의 최대 통전 전류 (ITSM, surge current)와 $1,050A/{\mu}s$의 펄스전류 상승 기울기 (di/dt of on-state pulse current)에도 LTT의 손상 없이 동작함을 확인하였다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.7
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• pp.662-666
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• 2006

Microstructure and electrical properties of ZnO varistors as a function of sintering temperature and times were investigated. Sintering temperature and times greatly affected electrical properties and Bi-rich liquid phase of the microstructure. The varistor which were sintered at $1125^{\circ}C\sim1150^{\circ}C$, for 2 hr exhibited the varistor voltage$(V_c)$, nonlinear coefficient $(V_{10mA}/V_{1mA})$, leakage current$(I_L)$ dielectric constant and dissipation factor as $225\sim250V/mm,\;0.89\sim0.92,\;0.8\sim1.1{\mu}A,\;720\sim740\;and\;1.8\sim2.0%$, respectively.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.60.1-60.1
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• 2012

구경 3.6m의 캐나다-프랑스-하와이 망원경(Canada-France-Hawaii Telescope, CFHT)의 주 초점에 설치된 CFH12K CCD 카메라를 이용하여 늙은 산개성단 NGC 1245와 NGC 2506에 대한 V와 I필터를 이용한 CCD측광을 수행하였다. 관측된 영역은 NGC 1245는 84'${\times}$82', NGC 2506은 42'${\times}$81'이고, 한계등급 V ${\approx}$ 23등급까지 관측하였다. 이론적인 등연령곡선을 사용하여 NGC 1245와 NGC 2506에 대해 각각 물리량 E(B-V) = 0.2, 0.03, (V-M_V)_0 = 12.5, 12.5, log(age) = 9.0, 9.3으로 구하였다. 이로부터 MV ${\approx}$ 10등급까지의 광도함수와 질량함수를 구하였다. NGC 1245와 NGC 2506의 질량함수의 기울기를 각각 ${\Gamma}$ = -1.26${\pm}$0.04, ${\Gamma}$ = -1.27${\pm}$0.07로 얻었고, 이들의 기울기는 태양부근의 낱별의 질량함수의 기울기에 비해 완만하다. 이는 성단에서 질량이 작은 별들의 질량 증발에 의한 역학적 진화의 효과로 보인다. 본 발표에서는 관측 내용과 그 결과를 소개하고자 한다.

• Journal of the Korean Mathematical Society
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• v.54 no.6
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• pp.1801-1816
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• 2017

We study some spectral properties of Volterra-type integral operators $V_g$ and $I_g$ with holomorphic symbol g on the Fock-Sobolev spaces ${\mathcal{F}}^p_{{\psi}m}$. We showed that $V_g$ is bounded on ${\mathcal{F}}^p_{{\psi}m}$ if and only if g is a complex polynomial of degree not exceeding two, while compactness of $V_g$ is described by degree of g being not bigger than one. We also identified all those positive numbers p for which the operator $V_g$ belongs to the Schatten $S_p$ classes. Finally, we characterize the spectrum of $V_g$ in terms of a closed disk of radius twice the coefficient of the highest degree term in a polynomial expansion of g.