• Journal of Sensor Science and Technology
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• v.7 no.5
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• pp.350-355
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• 1998

We fabricated a photoconductive cell made of polycrystalline CdS thick film which has high photo-sensitivity using a print/sintering method. The resultant grain size is about $4\;{\mu}m$. When $CuCl_2$ of 0.06 to 0.12 mg is added, the sensitivity and the ratio of photocurrent to dark current are 0.8 and $10^5$, respectively. The response wavelength is 511 nm. The rise and decay response times are 50 and 20 ms, respectively. In addition, the maximum power dissipation is beyond 80mW. We noticed that the addition of $CuCl_2$ between 0.06 and 0.12 mg to 1g of CdS results in a reliable formation of photoconductive sensor.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.3
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• pp.589-597
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• 1992

The effect of pressure on soot formation in premixed propane-air combustion is investigated at high pressures over the pressure range of 1 to 5 MPa by using a specially designed constant volume combustion bomb. The combustiom chamber of disk type with eight spark plugs located on the circumference at an interval of 45deg is 100mm in diameter by 14mm thick. The end gases are compressed to high pressures by the eight converging flames. The soot volume fraction in the chamber center during the final stage of combustion at the highest pressure is measured by the in-situ laser extinction technique, and the burnt gas temperature during the same period is measured by the two-color method. It is found that the soot yield rises with 50 to 100% for the respective equivalence ratio range of 1.9-2.2 at an interval of 0.1 when the combustion pressure is increased from 1 to 5 MPa, and that the turbulent flames decrease in the soot yield as compared with the laminar flames because the burnt gas temperatures increase with the drop of heat loss.

• Korean Journal of Optics and Photonics
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• v.14 no.5
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• pp.545-554
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• 2003

Design of the optical modulator composed of a three-waveguide coupler and CPW traveling-wave electrodes was carried out. Switching phenomena of three-waveguide couplers were analyzed by using the coupled mode theory, and the coupling-lengths of the devices were calculated by means of the FDM. CPW traveling-wave electrodes were analysed by the CMM and SOR simulation technique in order to find the conditions of phase-velocity and impedance matching. Traveling-wave modulators were fabricated on z-cut LiNbO$_3$ substrate. Ti was in-diffused in LiNbO$_3$ to make waveguides and Au electrodes were built on the waveguides by the electrolyte technique. The fabricated modulator chip was end-polished, pig-tailed and packaged in a brass mount with K-connector. The insertion loss and the switching voltage of the optical modulator were about 4㏈ and 19V, respectively. Network analyzer was used to obtain the S parameter and the corresponding RF response. From the measurement, parameters of the traveling-wave electrodes were extracted to be Z$_{c}$= 45 Ω, N$_{eff}$=2.20, and $\alpha$$_{0}$=0.055/cm√GHZ. The measured optical response R($\omega$) was compared with the theoretically estimated one, showing both responses agree well. The measurement results revealed that 3㏈ bandwidth turned out to be about 13 GHz.

• Korean Journal of Optics and Photonics
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• v.15 no.4
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• pp.375-384
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• 2004

Switching phenomenon of a three-waveguide optical coupler was analyzed by using the coupled mode theory, and the coupling-length of the device was calculated by means of the FDM. CPW traveling-wave electrodes were designed by the CMM and SOR simulation techniques so as to satisfy the conditions of phase-velocity and impedance matching. Traveling-wave modulators were fabricated on a z-cut LiNbO$_3$ substrate. Ti was in-diffused in LiNbO$_3$ to make waveguides and Au electrodes were built on the waveguides by the electroplating technique. Insertion loss and switching voltage of the optical modulator were about 4 ㏈ and 15.6V. Network analyzer was used to obtain S parameters and corresponding RF response. From the measurement, parameters of the traveling-wave electrodes were extracted as such Z$_{c}$=39.2 $\Omega$, Neff=2.48, and a0=0.0665/cm((GHz) (1/2)). The measured optical response R(w) was compared with the theoretically estimated and both responses were shown to agree well. The measurement results revealed that the ㏈ bandwidth turned out to be about 13 GHz.

• Publications of The Korean Astronomical Society
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• v.36 no.3
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• pp.47-63
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• 2021

Variability is one of the major characteristics of Active Galactic Nuclei (AGN), and it is used for understanding the energy generation mechanism in the center of AGN and/or related physical phenomena. It it known that there exists a time lag between AGN light curves simultaneously observed at different wavelengths, which can be used as a tool to estimate the size of the area that produce the radiation. In this paper, We present long term near-infrared variability of optically bright type 1 AGN using the Wide-field Infrared Survey Explorer data. From the Milliquas catalogue v6.4, 73 type 1 QSOs/AGN and 140 quasar candidates are selected that are brighter than 18 mag in optical and located within 5 degree around the ecliptic poles. Light curves in the W1 band (3.4 ㎛) and W2 band (4.6 ㎛) during the period of 2010-2019 were constructed for these objects by extracting multi-epoch photometry data from WISE and NEOWISE all sky survey database. Variability was analyzed based on the excess variance and the probability P_var. Applying both criteria, the numbers of variable objects are 19 (i.e., 26%) for confirmed AGN and 12 (i.e., 9%) for AGN candidates. The characteristic time scale of the variability (τ) and the variability amplitude (σ) were derived by fitting the DRW model to W1 and W2 light curves. No significant correlation is found between the W1/W2 magnitude and the derived variability parameters. Based on the subsample that are identified in the X-ray source catalog, there exists little correlation between the X-ray luminosity and the variability parameters. We also found four AGN with changing W1-W2 color.

• Journal of radiological science and technology
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• v.29 no.3
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• pp.141-145
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• 2006

In this study, $Eu^{2+}$ ion was used as an activator in order to enhance the PL(photoluminescene) and PSL(photostimulated luminescence) intensity of $MCl_2:Eu^{2+}$(M = Ca, Sr, Ba)phosphors and the chracteristics of PL and PSL of the phosphors were investigated. The emission of $MCl_2:Eu^{2+}$(M = Ca, Sr, Ba) phosphors shows a shift wavelength when the host caution changes. The optimal preparing conditions of $CaCl_2:Eu^{2+}$ phosphor were 0.5 mol％ of $EuCl_2$ and the sintering temperature were $745^{\circ}C$, 45 min. in $H_2$ atmosphere. The PL and PSL spectra of $CaCl_2:Eu^{2+}$ locate in the range of $365{\sim}388\;nm$, peaking at 370 and 380 nm. The optimal preparing conditions of $BaCl_2:Eu^{2+}$ phosphor were 0.5 mol％ of $EuCl_2$ and the sintering temperature were $905^{\circ}C$, 45 min. in $H_2$ atmosphere. The PL and PSL spectra of $BaCl_2:Eu^{2+}$ locate in the range of $370{\sim}460\;nm$, peaking at 398 nm. The optimal preparing conditions of $SrCl_2:Eu^{2+}$ phosphor were 0.5mol％ of $EuCl_2$ and the sintering temperature were $840^{\circ}C$, 45min. in $H_2$ atmosphere. The PL and PSL spectra of $SrCl_2:Eu^{2+}$ locate in the range of $380{\sim}440\;nm$, peaking at 407 nm. The dose response of the $MCl_2:Eu^{2+}$(0.5 mol%)(M = Ba, Sr) phosphors were linear within $0.25{\sim}200\;mGy$ of 100 kV X-ray and the PSL intensity of the $SrCl_2:Eu^{2+}$ and $BaCl_2:Eu^{2+}$ phosphors faded to approximately 60 and 40% respectively after 120 min at room temperature.

• Applied Chemistry for Engineering
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• v.26 no.3
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• pp.319-325
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• 2015

Submicron-sized $CeO_2:Er^{3+}/Yb^{3+}$ upconversion phosphor particles were synthesized by spray pyrolysis, and their luminescent properties were characterized by changing the concentration of $Er^{3+}$ and $Yb^{3+}$. $CeO_2:Er^{3+}/Yb^{3+}$ showed an intense green and red emission due to the $^4S_{3/2}$ or $^2H_{11/2}{\rightarrow}^4I_{15/2}$ and $^4F_{9/2}{\rightarrow}^4I_{15/2}$ transition of $Er^{3+}$ ions, respectively. In terms of the emission intensity, the optimal concentrations of Er and Yb were 1.0 % and 2.0%, respectively, and the concentration quenching was found to occur via the dipole-dipole interaction. Upconversion mechanism was discussed by using the dependency of emission intensities on pumping powers and considering the dominant depletion processes of intermediate energy levels for the red and green emission with changing the $Er^{3+}$ concentration. An energy transfer from $Yb^{3+}$ to $Er^{3+}$ in $CeO_2$ host was mainly involved in ground-state absorption (GSA), and non-radiative relaxation from $^4I_{11/2}$ to $^4I_{13/2}$ of $Er^{3+}$ was accelerated by the $Yb^{3+}$ co-doping. As a result, the $Yb^{3+}$ co-doping led to greatly enhance the upconversion intensity with increasing ratios of the red to green emission. Finally, it is revealed that the upconversion emission is achieved by two photon processes in which the linear decay dominates the depletion of intermediate energy levels for green and red emissions for $CeO_2:Er^{3+}/Yb^{3+}$ phosphor.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.05b
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• pp.1011-1015
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• 2005

본 실험에서는 부력 조건이 달라질 때 단공방류구에서 정체수역으로 수평방류되는 부력제트의 거동을 규명하였다. LIF (Laser Induced Fluorescence) 시스템을 이용하여 수행하였는데, LIF 시스템은 고해상도의 이미지를 취득할 수 있어 데이터의 정확도가 높으며, 동시에 한 평면상의 농도장을 일시에 측정할 수 있는 장점이 있는 기술이다. LIF 시스템은 크게 세부분으로 구성되어 있는데 방출시스템, 포착시스템, 처리시스템이 그것이다. 실험 조건을 고려해서 온수를 이용하여 주변수와의 밀도차를 재현하였으며, LIF 시스템의 추적입자로 형광염료 Rhodamine B를 사용하였다. 또한, 실험 데이터 취득과정에서 필요한 검정과정을 수행하였는데, LIF 시스템에서 검정과정은 레이저 입사광의 강도가 불균등한 분포를 가지는 점과 주변수의 매질에 의한 근의 감쇠가 발생하는 문제를 해결하기 위한 것이다. LIF 시스템은 부력제트의 농도장을 매우 정밀하게 측정할 수 있는데, 방류밀도 Froude 수가 변함에 따라 측정된 순간이미지를 통해 제트의 진화과정을 상세하고 가시적으로 확인할 수 있었다. 검정과정을 거친 농도 종단면에서 중심선의 연장선이 LIF 시스템에 의해 측정된 순간이미지의 중심선 궤적과 거의 일치하는 것도 알 수 있었다. 또한 LIF 시스템을 통해서 취득된 단일수평부력제트의 궤적과 중심선 희석률을 기존의 상용모형인 VISJET과 CORMIX1에 의해 예측된 결과와 비교$\cdot$분석한 결과, 제트 중심선 궤적의 경우, LIF 시스템을 이용한 측정값은 대체로 VISJET 모형의 결과와 일치하는 것으로 밝혀졌다. 중심선 희석률의 경우, LIF 측정값은 대체로 CORMIX1 모형, Cederwall(1968)의 경험식과 일치하는 경향을 보였다.0\%$일 때가 밸브를 $60\%$와 $80\%$ 개폐시켰을 때보다 $0.3kg/cm^2,\;0.29kg/cm^2$ 낮게 나타나 밸브를 전체 개방 했을 때 관로내의 수압이 상수설계기준에 적합한 수압을 유지함을 알 수 있다. 상수관로 설계 기준에서는 관로내 수압을 $1.5\~4.0kg/cm^2$으로 나타내고 있는데 $6kg/cm^2$보다 과수압을 나타내는 경우가 $100\%$로 밸브를 개방하였을 때보다 $60\%,\;80\%$ 개방하였을 때가 더 빈번히 발생하고 있으므로 대상지역의 밸브 개폐는 $100\%$ 개방하는 것이 선계기준에 적합한 것으로 나타났다. 밸브 개폐에 따른 수압 변화를 모의한 결과 밸브 개폐도를 적절히 유지하여 필요수량의 확보 및 누수방지대책에 활용할 수 있을 것으로 판단된다.8R(mm)(r^2=0.84)$로 지수적으로 증가하는 경향을 나타내었다. 유거수량은 토성별로 양토를 1.0으로 기준할 때 사양토가 0.86으로 가장 작았고, 식양토 1.09, 식토 1.15로 평가되어 침투수에 비해 토성별 차이가 크게 나타났다. 이는 토성이 세립질일 수록 유거수의 저항이 작기 때문으로 생각된다. 경사에 따라서는 경사도가 증가할수록 증가하였으며 $10\% 경사일 때를 기준으로 $Ro(mm)=Ro_{10}{\times}0.797{\times}e^{-0.021s(\%)}$로 나타났다.천성 승모판 폐쇄 부전등을 초래하는 심각한 선천성 심질환이다. 그러나 진단 즉시 직접 좌관상동맥-대동맥 이식술로 수술적 교정을 해줌으로써 좋은 성적을 기대할 수 있음을 보여주었다.특히

• Journal of Korean Society of Environmental Engineers
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• v.30 no.6
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• pp.642-652
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• 2008

The aim of our research was to apply experimental design methodology in the optimization condition of Photo-Fenton oxidation of the residual livestock wastewater after the coagulation process. The reactions of Photo-Fenton oxidation were mathematically described as a function of parameters amount of Fe(II)($x_1$), $H_2O_2(x_2)$ and pH($x_3$) being modeled by the use of the Box-Behnken method, which was used for fitting 2nd order response surface models and was alternative to central composite designs. The application of RSM using the Box-Behnken method yielded the following regression equation, which is an empirical relationship between the removal(%) of livestock wastewater and test variables in coded unit: Y = 79.3 + 15.61x$_1$ - 7.31x$_2$ - 4.26x$_3$ - 18x$_1{^2}$ - 10x$_2{^2}$ - 11.9x$_3{^2}$ + 2.49x$_1$x$_2$ - 4.4x$_2$x$_3$ - 1.65x$_1$x$_3$. The model predicted also agreed with the experimentally observed result(R$^2$ = 0.96) The results show that the response of treatment removal(%) in Photo-Fenton oxidation of livestock wastewater were significantly affected by the synergistic effect of linear terms(Fe(II)($x_1$), $H_2O_2(x_2)$, pH(x$_3$)), whereas Fe(II) $\times$ Fe(II)(x$_1{^2}$), $H_2O_2$ $\times$ $H_2O_2$(x$_2{^2}$) and pH $\times$ pH(x$_3{^2}$) on the quadratic terms were significantly affected by the antagonistic effect. $H_2O_2$ $\times$ pH(x$_2$x$_3$) had also a antagonistic effect in the cross-product term. The estimated ridge of the expected maximum response and optimal conditions for Y using canonical analysis were 84 $\pm$ 0.95% and (Fe(II)(X$_1$) = 0.0146 mM, $H_2O_2$(X$_2$) = 0.0867 mM and pH(X$_3$) = 4.704, respectively. The optimal ratio of Fe/H$_2O_2$ was also 0.17 at the pH 4.7.