• Journal of the Korean Chemical Society
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• v.17 no.1
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• pp.1-9
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• 1973

The purpose of this paper is to investigate the mechanism of Diels-Alder reaction by assuming pseudo molecular complex (PMC) which has characters both of ionic and radical bonds. We treated this complex quantum-chemically as an intermediate between the configuration without charge transfer (radical bond character) and the configuration corresponding to the charge transfer from Diene (R) to Dienophile (S) (ionic bond character). The wave function for the complex could be expressed as: ${\psi}_{complex} = {\psi}(R,S) +{ \rho}{\psi}(R^+,S^-)$ where ${\rho}$ is the extent of charge transfer which is a constant to measure the ionic character of PMC. It has been noticed that${\rho}$is related to the difference between Fr + Fr' and Fs + Fs' in free valence (F) when R is united to S through atom r in R to atom s in S and atom r' in R to atom s' in S, That is, ${\rho}{\alpha}$ ${\Delta}F = (Fr + Fr') - (Fs + Fs')$. We have calculated ${\Delta}F$values for more than forty Diels-Alder reactions. The calculated values of ${\Delta}F$ is reversely proportional to the values of Brown's paralocalization energy (Lp) as well as Dewar's differences of delocalization energy$({\Delta}Edeloc.)$ with good linearity. This approach also presents a way of predicting the possibility and the easiness of diene synthesis between any two conjugate compounds. According to the considerations, it could be concluded that Diels-Alder reaction takes place through the united ionic-radical mechanism rather than the separated ionic or radical mechanism.

• Journal of Life Science
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• v.30 no.10
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• pp.851-859
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• 2020

Saururus chinensis has white roots, leaves, and flowers and is known to have antibacterial activity and anti-cancer efficacy. The aim of this study was to investigate the effect of the ethyl acetate fraction of a methanol extract of Saururus chinensis (SCEA) on antioxidant activity and melanin synthesis. SCEA at 64 ㎍/ml showed 62% of the DPPH radical scavenging activity of vitamin C, and its reducing power was 33% greater than that of vitamin C. Tyrosinase activity was 26% higher and melanin synthesis was 44% higher in the presence of SCEA at 64 ㎍/ml than in a blank group in a dopa oxidation assay. MTT assay showed that SCEA displayed cytotoxicity above 0.5 ㎍/ml, and SCEA at 1 ㎍/ml increased melanin synthesis by 69% in live B16F1 cells. SCEA was also separated into 13 fractions by silica column chromatography, and fraction 2 (Fr. 2) showed the highest DPPH radical scavenging activity, reducing power, and melanin synthesis. SCEA also promoted melanin production in live cells. LC-MASS analysis showed that Fr.2 had a molecular weight of 239, and these findings suggest that SCEA could be available for the promotion of melanin synthesis in black hair.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.2
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• pp.779-783
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• 2012

In this paper, we studied the design and fabrication of $2{\times}2$ array-type microstrip patch antenna to be used in wireless communication systems operating at around 5GHz band. To obtain wide bandwidth and high gain, antenna parameters such as patch size, inter patch space are simulated by HFSS(High Frequency Structure Simulator). From these parameters, the $2{\times}2$ array-type microstrip patch antenna is fabricated using FR-4 substrate. The measured results of the antenna are as follows: The center frequency of 5.06GHz, insertion loss of -44dB, bandwidth of 200MHz, and VWSR of 1.1.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.5
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• pp.444-449
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• 2003

In this paper, a PCB(Printed Circuit Board) antenna for IMT-2000 is designed and analyzed. The antenna has a helical structure with via-holes and lines on FR-4($\varepsilon$$\sub$${\gamma}$/=4.6 ) PCB, and the type of feeding is GCPW(Grounded Co-Planar Waveguide). Using HFSS of Ansoft, the antenna was designed and the measured results of frequency and radiation characteristic,3 with VSWR<2.0 are satisfied within operating frequency band of 1.920∼2.170 GHz. And it has resonating frequency of 2.045 GHz and a bandwidth of 321 MHz. The radiation gain of the antenna was measured to be -1 dBi.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.1
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• pp.1-7
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• 2016

In this paper, the compact CPW-fed slot antenna for WLAN applications is proposed. While the proposed antenna with size of only $20{\times}18{\times}1mm^3$ is consisted of double stub and folded slot, the antenna for 2.4 GHz band and 5 GHz band is designed and fabricated with optimized parameters obtained by simulation. Proposed antenna is fabricated with FR-4 substrate to the thickness of 1.0 mm. By obtaining the measured return loss level of < -10 dB at dual-band, we showed that it is operated as antenna for WLAN applications, and then it is also expected to be usable as antenna for RFID.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.4
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• pp.241-246
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• 2018

In this study, we proposed a wideband frequency tunable metamaterial absorber using a switchable ground plane (SGP). We proposed two fire retardant or flame resistant 4 (FR4) substrate structures for the SGP. An SGP is placed at the middle layer, between the top pattern and the bottom ground plane. The SGP can either be made ground or reactive, by switching the PIN diode ON/OFF. As the frequency is determined by the substrate thickness, the frequency can be switched from the SGP. The proposed absorber is demonstrated by full-wave simulations and measurements. When the SGP is turned on, an absorptivity higher than 90% is achieved from 3.5 GHz to 11 GHz. When the SGP is turned off, an absorptivity higher than 90 % is achieved from 1.7 GHz to 5.2 GHz.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.7A
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• pp.678-682
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• 2011

In this paper, a compact log periodic dipole array (LPDA) antenna operating from 1 to 6 GHz is studied. Inverted-L shaped dipole elements are used to miniaturize the lateral size of an LPDA antenna and the spacing factor is also decreased to reduce the total length of the LPDA antenna. As the top-loading length of the inverted-L shaped dipole elements is increased, the width of the LPDA antenna is decreased but the bandwidth and the gain of the antenna are decreased. The fabricated compact LPDA antenna is printed on FR4 substrate With a dielectric constant of 4.4 and a thickness of 1.6 mm, and its size is reduced to 32% in width and 49% in length compared to a standard LPDA antenna.

• Transactions of the KSME C: Technology and Education
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• v.5 no.2
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• pp.81-87
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• 2017

315Fr compressor motor exceeds vibration specifications. To find the reason, first a modal impact test with free-free condition is done. Second a modal test with fixed condition is done. Thereafter the test results are compared with FEM simulation results. Using free-free condition modal impact test, FEM simulation conditions (boundary, mesh..) are modified. The motor has rolling motion around 120Hz. FEM simulation also shows same result. FEM simulation will be used to develop other series compressor motors. Using this, manufacturing test model and doing test will be useless.

• Proceedings of the Korea Information Processing Society Conference
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• 2008.05a
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• pp.721-724
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• 2008

무선 센서 네트워크(WSN)를 구성하는 각 센서 노드들의 에너지 관리는 네트워크 전체의 생명주기에 영향을 미치는 요소 중 가장 중요한 요소이다. 센서 노드들은 한번 설치된 이후 짧게는 수개월에서 길게는 몇 년에 걸쳐 동작해야 하기 때문에 배터리에 의존하고 있는 센서 노드들의 에너지를 효율적으로 관리할 수 있는 기술들이 필요하다. Directed Diffusion은 센서 노드에서 수집한 데이터를 네트워크 전체에 브로드캐스팅 하지 않고, 소스(Source)노드로부터 싱크(Sink)노드까지 강화(Reinforce)된 경로를 통해서만 데이터를 전송하여 경로 이외의 노드들의 불필요한 에너지 소모를 줄일 수 있는 라우팅 프로토콜이다. 그러나 기존의 Directed Diffusion에서는 전송 경로 상에 장애가 발생했을 경우 싱크에서 전송한 익스플로러터리 패킷을 기다려야 하며, 장애가 발견되고 재전송되기 전까지 전송된 데이터는 무의미한 데이터가 된다. 본 논문에서는 앞서 언급된 Directed Diffusion의 장애 경로 복구의 문제점을 보완하기 위해 Fast Repair(FR)를 제안한다. FR은 데이터 전송 경로 상에 장애 발생 시 데이터를 재전송 하고 경로를 재설정하는데 효율적이며, 성능평가 결과에서도 기존의 Directed Diffusion에 비하여 향상된 성능을 나타내고 있다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.20 no.5
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• pp.510-521
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• 2008

In the study, experiments are performed in the interaction region combined with wave and current to investigate the characteristics of local scour around submarine pipelines. Wave generator and current generator are used for the experiments and two current directions were used; co-direction and counter direction to the wave. The local scour depths around the pipeline are obtained according to the various pipe diameters(D), wave periods(T), wave heights(H), and current velocities(V). The experiments show that the maximum equilibrium local scour depth increases with pipe diameter, wave period, wave height, and current velocity. Using the experimental results, the correlations of scour depth and parameters such as Shields parameter($\theta$), Froude number(Fr), period parameter, Keulegan-Carpenter number(KC), Ursell number($U_R$), modified Ursell number($U_{RP}$) and ratio of velocities($U_{c}/(U_{c}+U_{m})$) are analyzed. In the interaction region combined with waves and currents, Froude number and Shields parameter are found the main parameters to cause the local scour around the submarine pipelines and this means that current governs the scour within any limits of the currents.