• Journal of the Korean Electrochemical Society
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• v.12 no.3
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• pp.234-238
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• 2009

In the excitation spectra of $YNbO_4$ : $Eu^{3+}$, the charge transfer (CT) band around 270 nm due to $[NbO_4]^{3-}$$-Eu^{3+}$ interaction and sharp excitation peaks by f-f transition of $Eu^{3+}$ strongly appeared simultaneously. CT band depended on the structural properties of powders, showing the red-shift with increasing the crystallinity, while the f-f transition peaks were independent of the crystallinity. For $YNb_{1-x}Ta_xO_4$ : $Eu^{3+}$ (x = 0.05.0.2), $[TaO_4]^{3-}$. configuration was locally constructed, leading to the blue-shift in CT band and the decrease in the red emission intensity with increasing the Ta content.

• Transactions on Electrical and Electronic Materials
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• v.16 no.1
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• pp.49-52
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• 2015

The change of the chemical structure of graphene oxide (GO) was investigated by periodical sampling of GO during exfoliation by using a sonicator. A significant amount of GO was exfoliated during up to 10 hr of sonication. Raman and Fourier transform infrared spectroscopy revealed a continuous increase of the G/D or C=C/C=O peak ratio of GO, as the sonication time increases. The photoluminescence (PL) intensity of each GO sample also decreased as a function of the sonication time. PL excitation spectra with three major peaks indicate that the sizes of $sp^2$ carbon clusters were enlarged by longer sonication. In addition, new excitation at around 300 nm proves the existence of newly developed small clusters of $sp^2$ carbons as the sonication time increased.

• Proceedings of the KOSOMBE Conference
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• v.1995 no.05
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• pp.42-44
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• 1995

The original DANTE sequence and its variations have limitation in excitation profile (a sinc function-like excitation) due to the finite duration of the DANTE pulsetrain. This sinc function-like selection profile excites only a small fraction of the spins in the pixel thereby results in poor signal to noise ratio (only about ${\sim}1%$ of normal MR imaging sequence). Therefore, this poor signal to noise ratio (SNR) has been the main drawback of the original DANTE sequence. To improve the signal to noise ratio, phases of individual RF pulses in the DANTE pulse train were modulated so that more spins in the object were excited ($1{\sim}3$). We have introduced a new FM (Frequency Modulation) DANTE sequence and analyzed the signal intensity and excitation profiles.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1997.10a
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• pp.155-159
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• 1997

We investigated the effect of mechanical backside damage in Czochralski silicon wafer. The intensity of mechanical damage were evaluated by minority carrier recombination lifetime by a laser excitation/microwave reflection photoconductance decay method, photo-acoustic displacement method, X-ray section topography, and wet oxidation/preferential etch methods. The data indicate that the higher the mechanical damage intensity, the lower the minority carrier lifetime, and the photoacoustic displacement values are also increased proportionally.

• Bulletin of the Korean Chemical Society
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• v.19 no.4
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• pp.471-475
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• 1998

Phase shift spectroscopy is applied to Eu(Ⅲ) luminescence from $Eu^{3+}$-exchanged Y zeolite. The phase shift and intensity modulation of luminescence following intensity-modulated excitation are measured as a function of modulation frequency and they are fitted into a double exponential decay. The fast decay component, compared with the slow one, has narrower spectral bandwidth and is emitted from the $Eu^{3+}$ that has more polar and definite environment with higher symmetry and that interacts more easily with hydrated water molecules. The fast decay component is attributed to $Eu^{3+}$ at site Ⅱ' while the slow one to $Eu^{3+}$ at sites Ⅰ' and Ⅰ.

• Journal of Korean Society of Environmental Engineers
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• v.28 no.2
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• pp.223-228
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• 2006

High-performance liquid chromatography(HPLC) and fluorescence derivatization were applied for a trace-level N-nitrosodimethylamine(NDMA) analysis of water samples. Fluorescence intensity was optimized with the excitation wavelength of 340 nm and the emission wavelength of 530 nm. pH adjustment after denitrosation was necessary to get a maximum intensity at pH between 9 and 12. Maximum intensity was found with a dansyl chloride concentration of 330 to 500 mg/L. Percentile error in the water sample analyses through solid phase extraction was 12-162% and 6-23% for the lower concentration level(10-200 ng/L NDMA) and the higher level(100-1000 ng/L NDMA), respectively, showing more discrepancy in lower level. However, the average ratios of estimated NDMA to the standard NDMA were close to 1 for both concentration ranges, presenting this HPLC method could detect from tens to hundreds nanograms NDMA per liter. Accurate determination of NDMA, which was injected to a wastewater effluent, revealed the selectivity of fluorescence derivatization for the target compound(NDMA) in the presence of complex interfering compounds. The HPLC with fluorescence derivatization may be applicable for determining NDMA of water and wastewater samples fur various research purposes.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1998.04a
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• pp.319-326
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• 1998

Structural intensity of plates experiencing bending vibration is analytically evaluated using the modal analysis based on the assumed mode method. In the analysis, material internal loss and localized damping are considered. The power obtained by structural intensity integration over the circle containing the excitation source is compared with the power injected into plates to verify the accuracy of the presented method and; to evaluate the convergence of mode superposition. The intensity integration is carried out varying the circle radius and the integral step to investigate their effects in case of the power estimation using structural intensities. In addition, the dominant component among internal forces in the energy transfer by the bending vibration of a stiffened plate is investigated.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.892-895
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• 2002

In this study, to grasp the effect of vibration intensity fur the laminated composite plate, the two-dimension plate was shaken by a harmonic point excitation with the natural frequency using the finite element method. As the result, it shows that the vibration intensity according to the change of angle-ply is various and it flows to the direction of length rather than width in the plate. Also this paper represents those results to the vector flow.

• Bulletin of the Korean Chemical Society
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• v.13 no.3
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• pp.325-331
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• 1992

By using the general theoretical framework proposed recently for treating the fluorescence quenching kinetics, we investigate the effect of light pulse intensity on the decay of fluorescence which follows excitation of fluorophors by the light pulse of very short but finite duration. It is seen that conventional theory breaks down when the exciting light pulse has a pulse width comparable to the fluorescent lifetime and its intensity is very high. We also find that even when the light intensity is not too high, conventional theory may fail in either of the following cases: (i) when the quencher concentration is high, (ii) when there is an attractive potential of mean force between the fluorophor and quencher, or (iii) when the energy transfer from the fluorophor to the quencher may also occur at a distance, e.g., via dipole-dipole interaction. The validity of the predictions of the present theory may thus be tested by fluorescence quenching experiments performed under such situations.

• Smart Structures and Systems
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• v.10 no.6
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• pp.557-572
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• 2012

This paper focuses on the vibration control of long-span reticulated steel structures under multi-dimensional earthquake excitation. The control system and strategy are constructed based on Magneto-Rheological (MR) dampers. The LQR and Hrovat controlling algorithm is adopted to determine optimal MR damping force, while the modified Bingham model (MBM) and inverse neural network (INN) is proposed to solve the real-time controlling current. Three typical long-span reticulated structural systems are detailedly analyzed, including the double-layer cylindrical reticulated shell, single-layer spherical reticulated shell, and cable suspended arch-truss structure. Results show that the proposed control strategy can reduce the displacement and acceleration effectively for three typical structural systems. The displacement control effect under the earthquake excitation with different PGA is similar, while for the cable suspended arch-truss, the acceleration control effect increase distinctly with the earthquake excitation intensity. Moreover, for the cable suspended arch-truss, the strand stress variation can also be effectively reduced by the MR dampers, which is very important for this kind of structure to ensure that the cable would not be destroyed or relaxed.