• Bulletin of the Korean Chemical Society
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• v.34 no.10
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• pp.2877-2882
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• 2013

Second-order rate constants ($k_{Ox^-}$) have been measured spectrophotometrically for nucleophilic substitution reactions of 4-nitrophenyl X-substituted-cinnamates (7a-7e) and Y-substituted-phenyl cinnamates (8a-8e) with butane-2,3-dione monoximate ($Ox^-$) in 80 mol % $H_2O$/20 mol % DMSO at $25.0{\pm}0.1^{\circ}C$. The Hammett plot for the reactions of 7a-7e consists of two intersecting straight lines while the Yukawa-Tsuno plot exhibits an excellent linearity with ${\rho}_X$=0.85 and r=0.58, indicating that the nonlinear Hammett plot is not due to a change in the rate-determining step but is caused by resonance stabilization of the ground state (GS) of the substrate possessing an electron-donating group (EDG). The Br${\o}$nsted-type plot for the reactions of Y-substituted-phenyl cinnamates (8a-8e) is linear with ${\beta}_{lg}$ = -0.64, which is typical of reactions reported previously to proceed through a concerted mechanism. The ${\alpha}$-nucleophile ($Ox^-$) is more reactive than the reference normal-nucleophile ($4-ClPhO^-$). The magnitude of the ${\alpha}$-effect (i.e., the $k_{Ox^-}/k_{4-ClPhO^-}$ ratio) is independent of the electronic nature of the substituent X in the nonleaving group but increases linearly as the substituent Y in the leaving group becomes a weaker electron-withdrawing group (EWG). It has been concluded that the difference in solvation energy between $Ox^-$ and $4-ClPhO^-$ (i.e., GS effect) is not solely responsible for the ${\alpha}$-effect but stabilization of transition state (TS) through a cyclic TS structure contributes also to the Y-dependent ${\alpha}$-effect trend (i.e., TS effect).

• Journal of Power Electronics
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• v.16 no.6
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• pp.2119-2128
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• 2016

Due to detection and control errors, some high-frequency harmonics with voltage-source characteristics cause circulating currents in modular inverters. Moreover, the circulating currents are usually affected by the output filters (OF) of each module due to their filter and resonance properties. The interaction among the circulating currents in the modules increase the power loss and reduce system stability and control precision. Therefore, this paper reports the results of a study on the SPWM high-frequency harmonics circulating currents for a double-module VSI. In the paper, an analysis of the circulating-current circuits is briefly described. Next, a mathematic model of the single-module output voltage based on the carrier frequency of SPWM is built. On this basis, through mathematic modeling of high-frequency harmonic circulating currents, the formation mechanism and distribution characteristics of circular currents and their influences are studied in detail. Finally, the influences of the OF on the circulating currents are studied by mainly taking an LC-type filter as an example. A theoretical analysis and experimental results demonstrate some important characteristics. First, the carrier phase shifting of the SPWM for each module is the major cause of the SPWM harmonic circulating currents, and the circulating currents are in an odd distribution around n-times the carrier frequency $n{\omega}_s$, where n = 1, 2, 3, ${\ldots}$. Second, the harmonic circular currents do not flow into the parallel system. Third, the OF can effectively suppress the non-circulating part of the high-frequency harmonic currents but is ineffective for the circulation part, and actually reduces system stability.

• Journal of Ginseng Research
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• v.38 no.3
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• pp.194-202
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• 2014

Background: Ginsenosides, the major ingredients of Panax ginseng, have been studied for many decades in Asian countries as a result of their wide range of pharmacological properties. The less polar ginsenosides, with one or two sugar residues, are not present in nature and are produced during manufacturing processes by methods such as heating, steaming, acid hydrolysis, and enzyme reactions. $^1H$-NMR and $^{13}C$-NMR spectroscopic data for the identification of the less polar ginsenosides are often unavailable or incomplete. Methods: We isolated 21 compounds, including 10 pairs of 20(S) and 20(R) less polar ginsenosides (1-20), and an oleanane-type triterpene (21) from a processed ginseng preparation and obtained complete $^1H$-NMR and $^{13}C$-NMR spectroscopic data for the following compounds, referred to as compounds 1-21 for rapid identification: 20(S)-ginsenosides Rh2 (1), 20(R)-Rh2 (2), 20(S)-Rg3 (3), 20(R)-Rg3 (4), 6'-O-acetyl-20(S)-Rh2 [20(S)-AcetylRh2] (5), 20(R)-AcetylRh2 (6), 25-hydroxy-20(S)-Rh2 (7), 25-hydroxy-20(S)-Rh2 (8), 20(S)-Rh1 (9), 20(R)-Rh1 (10), 20(S)-Rg2 (11), 20(R)-Rg2 (12), 25-hydroxy-20(S)-Rh1 (13), 25-hydroxy-20(R)-Rh1 (14), 20(S)-AcetylRg2 (15), 20(R)-AcetylRg2 (16), Rh4 (17), Rg5 (18), Rk1 (19), 25-hydroxy-Rh4 (20), and oleanolic acid 28-O-b-D-glucopyranoside (21).

• 전자공학회논문지 IE
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• v.48 no.2
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• pp.40-46
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• 2011

In this study, PZT-5A green sheet were prepared by using tape casting technique, and the piezoelectric properties of PZT-5A by variation of sintering temperature was investigated. After, design and piezoelectric properties of 2-2 piezocomposite ultrasonic transducers by menas of the FEA. The acoustic impedance and piezoelectric charge constant of the 2-2 type piezocomposite transducer decreased proportionally due to the density decrease caused by the PZT volume fraction decrease. The piezocomposite acoustic impedance were 7~3 MRayl between 0.6 and 0.2 allowing it to be used for a ultrasonic transducer. The resonance characteristics and the electro-mechanical coupling factor were the best when the volume fraction PZT was 0.6. The PZT volume fraction shows the fixed value, 0.6~0.65, approximately within the range between 0.2 and 0.6 while it is increased to decreased over the range. The result of the experiment above confirmed that the 2-2 piezoelectric composites could be used as the ultrasonic transducers.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.45 no.4
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• pp.60-67
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• 2008

This paper presents a new full-bridge soft switching PWM DC-DC converter circuit topology that adding two switcher, two lossless snubber quasi-resonance capacity, two diode to power source for general welding machine. This half bridge soft switching Is low voltage hight current output that first coil current is smaller than second coil current in high frequency transformer can be obtained with decreasing path loss in conventional DC bus line switcher. As it operate ZCS/ZVS in full range, high frequency, high efficiency and high output are implemented at low voltage and high DC current switching power supplies. All of this items are got from simulation and the result of experiment. If make up for the weak points of this proposed circuit, it will be used more easily for next generation TIG, MIG and MAG type of arc-welding machine.

• Polymer(Korea)
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• v.37 no.5
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• pp.625-631
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• 2013

Mucoadhesive property is the major function as an adhesive for medical devices, and therefore, these days many researches have conducted to develop polymers having this property. Recently, biomimetic technology has been used for developing mucoadhesive polymers. Among many technologies, mussel-inspired approaches have received noticeable attention because of its thread's strong adhesive characteristics. In this study, we synthesized mucoadhesive biomimetic polymers employing catechol structures which are abundant in mussel adhesive proteins, and their structures and molecular weights were characterized by using nuclear magnetic resonance spectroscopy and gel permeation chromatography. To evaluate in vitro mucoadhesive strength, the sheet type of the small intestinal porcine submucosa was prepared. Compared to commercial fibrin glue adhesives, catechol-containing mucoadhesive polymers showed enhanced adhesive strength. The study of adhesive strength with considering diverse factors, such as temperature, pressure, and oxidant amount indicated that mussel-inspired mucoadhesive polymer could be a promising candidate for an adhesive in various biomedical applications.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.14 no.4
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• pp.1-7
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• 2000

In this paper, we study a cause of malfunction of switch to control drive motor in DFMS(Digital Flux Mapping System) which can measure incore neutron flux of the nuclear plant, and develope a method to solve this problem. DFMS has the type of generating contact signal by mechanical switch lever, which is operated whenever thimble detector inserted or withdrawed through thimble Guide Tube. However the characteristics of the lever tend to be changed by mechanical degrade or bad environment and the lever finally generates errotic contact signal. Therefore we installed electric coil ass'yin the outside of Guide Tube instead of mechanical switch assy's. In addition we applied resonance effect to control circuit and installed condenser in the input of power supply to protect noise and interference. After completion of this improvement, we tested this improved device repetitively under the various conditions. In conclusion, we identified the generation of the desired contact signal and the prevention of detector failure through plant surveillance test during normal plant operation.

• Proceedings of the KIPE Conference
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• 2005.07a
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• pp.445-448
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• 2005

A new high efficiency phase shifted full bridge (PSFB) converter for sustaining power module of plasma display panel (PDP) is proposed in this paper .The proposed converter employs the rectifier of voltage doubler type without output inductor. Since it has no output inductor, the voltage stresses of the secondary rectifier diodes can be clamped at the level of the output voltage. Therefore, no dissipative resistor-capacitor (RC) snubber for rectifier diodes is needed and a high efficiency as well as low noise cutout voltage can be realized. In addition, due to elimination of the large output inductor, it features a simple structure, lower cost, less mass, and lighter weight. Furthermore, the proposed converter has wide zero voltage switching (ZVS ) ranges with low current stresses of the primary switches. Also the resonance between the leakage inductor of the transformer and the capacitor of the voltage doubler cell makes the current stresses of the primary switches and rectifier diodes reduced. In this paper, the operational principles, analysis of the proposed converter, and the experimental results are presented.

• Proceedings of the KSMRM Conference
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• 2002.11a
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• pp.103-103
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• 2002

목적：자화율 대조법을 사용한 관류 영상에서 동시획득 $T_{1}T_{2}^{*}$ 강조 경사 자장 펄스열을 사용하여 Gd-DTPA에 의한 $T_{1}T_{2}^{*}$ 감소 효과를 동시에 획득하여 종양의 치료 효과, 판정에 중요한 기준을 제시할 수 있는 정확한 관류 정보를 얻고자 한다. 대상 및 방법： Gd-DTPA에 의한 $T_{1}T_{2}^{*}$ 감소 효과를 동시에 획득하기 위하여 기존의 이중 경사자장 펄스열을 수정, 동시획득 $T_{1}T_{2}^{*}$ 강조 경사자장 펄스열을 개발하였고, 시간 해상도를 높이기 위하여 key-hole 방법을 사용하였다. 고정 phantom으로 Sephadex를 다양한 농도의 Gd-DTPA 용액에 swelling하여 사용하였고, 관류 phantom으로는 Sephadex와 Dialyzer를 사용하였다. Sephadex는 swelling 하였을 때 $T_1$, $T_2$값이 생체 조직의 값과 비슷하고, 물을 관류시킬 수 있어 생체 모형에 적합한 phantom이다 .관류 phantom은 정량 펌프에 연결하여 사용하였다. Sephadex 관류 phantom에서는 분당 약 4$m\ell$ 속도로 관류시키면서 25 mM Gd-DTPA을 0.1$m\ell$ 일시 주입하여 관류 방향에 수직인 coronal 영상을 약 15분 동안 얻었다. 투과도를 구하기 위한 phantom으로는 hollow fiber type Dialyzer를 사용하였고, in vivo에서 1차 관류 이후에 현관 밖에서의 Gd농도가 높고 혈관 내부의 농도가 낮은 상태를 만들기 위하여 fiber 바깥쪽으로 500 mM Gd-DTPA 2 ml를 미리 넣어두고 fiber 내부로 이보다 낮은 농도의 Gd 용액을 관류시키면서 약 1시간동안 영상을 얻었다. 관류 영상에서 $T_1$/$T_{2}^{*}$ 감소 효과를 구분하여 구한 $\DeltaR_1$, $\DeltaR_2$ 곡선의 적분값으로부터 관류량을 구하고, 2 구획 모델을 적용하여 투과도를 구했다.

• Proceedings of the KSMRM Conference
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• 2002.11a
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• pp.127-127
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• 2002

목적： 자화율 대조법을 사용한 관류 영상에서 동시획득 $T_{1}{/}T_{2}^{*}$ 강조 경사 자장 펄스열을 사용하여 Gd-DTPA에 의한 $T_{1}{/}T_{2}^{*}$ 감소 효과를 동시에 획득하여 종양의 치료 효과, 판정에 중요한 기준을 제시할 수 있는 정확한 관류 정보를 얻고자 한다. 대상 및 방법： Gd-DTPA에 의한 $T_{1}{/}T_{2}^{*}$ 감소 효과를 동시에 획득하기 위하여 기존의 이중 경사자장 펄스열을 수정, 동시획득 $T_{1}{/}T_{2}^{*}$ 강조 경사자장 펄스열을 개발하였고, 시간 해상도를 높이기 위하여 key-hole 방법을 사용하였다. 고정 phantom으로 Sephadex를 다양한 농도의 Gd-DTPA 용액에 swelling하여 사용하였고, 관류 phantom으로는 Sephadex와 Dialyzer를 사용하였다. Sephadex는 swelling 하였을 때 $T_1$, $T_2$값이 생체 조직의 값과 비슷하고, 물을 관류시킬 수 있어 생체 모형에 적합한 phantom이다. 관류 phantom은 정량 펌프에 연결하여 사용하였다. Sephadex 관류 phantom에서는 분당 약 4$m\ell$ 속도로 관류시키면서 25 mM Gd-DTPA을 0.1$m\ell$ 일시 주입하여 관류 방향에 수직인 coronal 영상을 약 15분 동안 얻었다. 투과도를 구하기 위한 phantom으로는 hollow fiber type Dialyzer를 사용하였고, in vivo에서 1차 관류 이후에 혈관 밖에서의 Gd 농도가 높고 혈관 내부의 농도가 낮은 상태를 만들기 위하여 fiber 바깥쪽으로 500mM Gd-DTPA 2$m\ell$를 미리 넣어두고 fiber 내부로 이보다 낮은 농도의 Gd 용액을 관류시키면서 약 1시간동안 영상을 얻었다. 관류 영상에서 $T_{1}{/}T_{2}^{*}$ 감소 효과를 구분하여 구한 $\Delta{R}_{1}$, $\Delta{R}_{2}^{*}$ 곡선의 적분값으로부터 관류량을 구하고, 2 구획 모델을 적용하여 투과도를 구했다.