• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.2
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• pp.62-66
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• 2010

In this article, a oscillator at X-band with a double H-shape metamaterial resonator (DHMR) based on high-Q is proposed with metamaterial structure to improve Ihe phase noise and output power. The proposed oscillator is required low phase noise and high output power for the high performance frequency synthesizer. DHMR is designed to be high-Q at resonance frequency through strong coupling of E-field. This character makes phase noise excellent. The oscillator using DHMR is oscillated in X-band so as to apply frequency synthesizer of radar systems. The output power is 4.33 dBm and the phase noise is -108 dBc/Hz at 100 kHz offset of carrier frequency.

• Journal of the Korea Concrete Institute
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• v.16 no.2 s.80
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• pp.155-162
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• 2004

An analytical method to predict the time dependent flexural behavior of composite girder is presented based on sectional analysis. The time dependent constitutive relation accounting for the early-age concrete properties including maturing of elastic modulus, creep and shrinkage is derived in an incremental format by the first order Taylor series expansion. The sectional analysis calculates the axial and curvature strains based on the force and moment equilibriums. The deflection curve of the girder approximated by the quadratic polynomial function is calculated by applying to the proper boundary conditions in the consecutive segments. Numerical applications are made for the 3-span double composite steel box girder which is a composite bridge girder filled with concrete at the bottom of the steel box in the negative moment region. The calculated results are compared with those by finite element analysis results. Close agreement is observed between the two approaches.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.14 no.2
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• pp.63-67
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• 2004

The layered structure of cobalt dodecanesulfate was synthesized. A phase transition takes place at various temperature ranges and results in a drastic change of the layer distance. A monolayer structure of cobalt dodecanesulfate at room temperature transformed to a bilayer structure as a dehydrated form at high temperature.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.7 no.1
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• pp.137-142
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• 1997

We synthesized the intercalation compound between a layered double hydroxide and an ethyl orange. The orientation of the intercalated ethyl orange into the layered double hydroxide was investigated. The molecular plane of the ethyl orange and its N＝N axis lie nearly perpendicular to the hydroxide layers with an antiparallel pattern.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.32 no.6
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• pp.225-230
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• 2022

A new two-fold interpenetrating two-dimensional (2D) Tb(III) metal-organic framework (MOF), [Tb(p-XBP4)_2.5(H₂O)₂]·W(CN)₈ (1), was prepared using a p-XBP4 (N,N'-p-phenylenedimethylenbis(pyridin-4-one)), Cs₃[W(CN)₈], and Tb(NO₃)₃·6H₂O. The single crystal X-ray diffraction indicated that Tb-MOF exhibits a unique two-fold interpenetrating 2-D framework. It was also characterized through Fourier transform infrared spectroscopy (FTIR), and single and powder X-ray diffraction. To probe the molecular magnetic behavior, the magnetic properties of Tb-MOF were investigated by direct-current (DC) and alternating-current (AC) magnetic susceptibilities measurements and discussed.

• Applied Chemistry for Engineering
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• v.31 no.2
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• pp.187-192
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• 2020

(2S,3R)-3-hydroxyhomoserine lactone (HSL) has been used as a key intermediate for the synthesis of various biologically active compounds. In this study, we demonstrated an efficient synthesis of HSL via anti selective dihydroxylation of a protected vinyl glycine analog with an oxabicyclo[2.2.2]octyl orthoester (OBO) ester group. Because the acyclic conformation of the substrate was efficiently controlled by the bulky OBO ester group, a diastereoselectivity of > 10 : 1 was obtained in the dihydroxylation reaction without the use of a chiral reagent. By using this result, the target compound 1 can be obtained from commercially available N-Cbz-L-serine 2 in seven steps with an overall yeid of 34%. This result could be applied to the stereoselective synthesis of biologically active molecules containing a vicinal amino diol moiety.

• Journal of the Korea Concrete Institute
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• v.17 no.3 s.87
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• pp.445-454
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• 2005

Cracks due to low tensile strength in prestressed concrete (PC) beams may decrease rigidity and structural performance, resulting in excessive deflection. In an effort to solve this problem, in this research, prestressed dual concrete (PDC) has been proposed, consisting of normal strength concrete in compression zone, and high performance steel fiber reinforced concrete(HPSFRC) with a partial depth in tensile zone. Three PDC beams with different depths of HPSFRC and two PC beams were cast for experiments. Analytical models at each stage, i.e., precracking, postcracking, and ultimate, were proposed for analysis of flexural behavior in PDC beams. The experimental results agree well to the analytical ones. Crack formation and its propagation are controlled by the HPSFRC in PDC beams. The initial cracking and service limit loads are increased along with the load carrying capacity and flexural stiffness.

• 한국전자현미경학회:학술대회논문집
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• 2004.11a
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• pp.95-99
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• 2004

• Proceedings of the Korean Vacuum Society Conference
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• 2007.08a
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• pp.379-379
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• 2007

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.11a
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• pp.231-231
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• 2003

I-III-Ⅵ족 CuInGaSe$_2$(CIGS)계 화합물 태양전지는 1 eV 이상의 직접 천이형 에너지 밴드갭을 가지며, 전기 광학적으로 매우 안정하여 태양전지의 광흡수층으로 매우 이상적이다. CIGS 광흡수층제조를 위하여 용매열법 (solvothermal method)으로 CIGS나노입자를 합성하였다. 용매열법은 진공장비를 사용하던 기존의 방법에 비해 저온, 저압에서 저가로 합성할 수 있다는 장점을 가지고 있다. Copper, indium selenium 및 gallium 분말과 유기용매 ethylenediarnine을 autoclave안에서 반응시켜 CIGS 나노입자를 제조하였다. 280 에서 14시간동안 반응시켜 직경이 30-80 nm인 구형에 가까운 CIGS 나노입자를 얻었다. 이것은 용매열법에 의한 4성분계의 CIGS 나노입자의 최초 합성이다. diehyleneamine을 용매로 사용한 경우에 한하여 구형의 CIS 입자를 합성할 수 있다고 보고되었으나, Cu와 이중 N-chelation이 형성되는 ethylenediamine 용매임에도 불구하고 구형의 CIGS 나노분말이 형성된 것은 solution-liquid-solid (SLS) 기구로 설명할 수 있었다. HRSEM, TEM, XRD. EDS으로 나노분말의 형상 크기 및 조성을 조사하여 chalcopyrite 구조의 CuInGaSe$_2$ 임을 확인하였다.