• Journal of Powder Materials
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• v.27 no.6
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• pp.503-508
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• 2020

The mechanical properties and microstructures of hexagonal boron nitride (h-BN)-reinforced cement composites are experimentally studied for three and seven curing days. Various sizes (5, 10, and 18 ㎛) and concentrations (0.1%, 0.25%, 0.5%, and 1.0%) of h-BN are dispersed by the tip ultrasonication method in water and incorporated into the cement composite. The compressive strength of the h-BN reinforced cements increases by 40.9%, when 0.5 wt% of 18 ㎛-sized h-BN is added. However, the compressive strength decreases when the 1.0 wt% cement composite is added, owing to the aggregation of the h-BNs in the cement composite. The microstructural characterization of the h-BN-reinforced cement composite indicates that the h-BNs act as bridges connecting the cracks, resulting in improved mechanical properties for the reinforced cement composite.

• Proceedings of the Materials Research Society of Korea Conference
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• 1999.11a
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• pp.173-173
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• 1999

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2000.04a
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• pp.17-17
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• 2000

• Proceedings of the Korean Magnestics Society Conference
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• 1991.11a
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• pp.64-64
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• 1991

• Proceedings of the Korean Ceranic Society Conference
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• 2003.10a
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• pp.206.2-206
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• 2003

• 한국전산유체공학회:학술대회논문집
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• 2006.05a
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• pp.190-191
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• 2006

• Journal of Energy Engineering
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• v.25 no.1
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• pp.86-91
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• 2016

Convenient design guideline for Waveguide-below-cutoff (WBC) array is proposed to obtain the minimum waveguide length for electromagnetic pulse (EMP) shielding. The analysis includes circular, rectangular, and hexagonal WBC, determine the total length of the waveguide. When the unit side of rectangular WBC and the diagonal line of hexagonal WBC are given as 30 mm, the length of hexagonal WBC is 5 mm shorter than rectangular case with shielding effectiveness (SE) 80 dB. The length difference is deepened with SE of 100 dB, which shows approximately 30 mm shorter length for hexagonal case than others. In addition, hexagonal WBC requires much shorter length than circular WBC. In conclusion, hexagonal case is the most effective with respect to flow velocity and pressure loss for equivalent SE.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.10 no.5
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• pp.402-408
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• 2017

In this paper, we analyzed the frequency characteristics of hexagonal spiral thin-film inductor based on non-contact AC coupling for wireless signal transmission. We compared and analyzed the frequency characteristics of the rectangular spiral inductor and the hexagonal spiral inductor according to the number of turns, the line width and the line spacing of the conductor. Hexagonal spiral inductor has more number of turns to has the same inductance as rectangular spiral inductor, but the overall length of the conductors is shortened. This reduces the self inductance and increases the mutual inductance so that the overall inductance can have the same value. Also, since the overall length of the conductor is shortened and the magnetic resistance is reduced, the quality factor and the self-resonant frequency performance can be secured. The proposed hexagonal spiral thin-film inductor has the inductance of 3.54nH at 2GHz, the quality factor of max 14.00 at 5.0GHz and the self-resonant frequency at about 11.3GHz.

• Carbon letters
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• v.16 no.3
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• pp.192-197
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• 2015

In the present work, we propose a molecule (C₁₄H₁₄) that can be used as a building block of hexagonal diamond-type crystals and nanocrystals, including wurtzite structures. This molecule and its combined blocks are similar to diamondoid molecules that are used as building blocks of cubic diamond crystals and nanocrystals. The hexagonal part of this molecule is included in the C₁₂ central part of this molecule. This part can be repeated to increase the ratio of hexagonal to cubic diamond and other structures. The calculated energy gap of these molecules (called hereafter wurtzoids) shows the expected trend of gaps that are less than that of cubic diamondoid structures. The calculated binding energy per atom shows that wurtzoids are tighter structures than diamondoids. Distribution of angles and bonds manifest the main differences between hexagonal and cubic diamond-type structures. Charge transfer, infrared, nuclear magnetic resonance and ultraviolet-visible spectra are investigated to identify the main spectroscopic differences between hexagonal and cubic structures at the molecular and nanoscale. Natural bond orbital population analysis shows that the bonding of the present wurtzoids and diamondoids differs from ideal sp³ bonding. The bonding for carbon valence orbitals is in the range (2s^0.982p^3.213p^0.02)-(2s^0.942p^3.313p^0.02) for wurtzoid and (2s^0.932p^3.293p^0.01)-(2s^0.992p^3.443p^0.01) for diamantane.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.5 no.6
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• pp.558-561
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• 2004

The morphology of silica supported $MoO_{3}$ catalysts, which was prepared by impregnation of ammonium heptamolybdate(AHM) with various surface loadings up to 4 atoms $Mo/nm^{2}$, was studied using x-ray diffraction(XRD). All morphologies of silica supported $MoO_{3}$ appear to be thermodynamically driven. For high loaded catalysts there appeared three states: a sintered and well-dispersed hexagonal state at moderate temperature calcination($300^{\circ}C$), and a sintered orthorhombic state at high temperature calcination($500^{\circ}C$). Whereas the sintered orthorhombic phase is detected by XRD at loadings in excess of 1.1 atom $Mo/nm^{2}$, the well-dispersed hexagonal phase is not detected even until 4.0 $atomsMo/nm^{2}$. The higher apparent dispersion of the hexagonal phase may arise from some role of ammonia which results in a stronger $MoO_{3}-SiO_{2}$ surface interaction.