• 한국세라믹학회지
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• 제31권9호
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• pp.989-994
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• 1994

This study aims at finding the closest packings of regular shape particles such as sphere, circle rod and hexagonal rod type. As the ratio of particle size to container lowered to less than 1/10, the wall effect decreased gradually. The tap density of spherical particles with almost orthorhombic arrangement was 59.5%, while those of circle rod and hexagonal rod type particles were 63.5% and 63.0% respectively. And it was decreased with increasing the aspect ratio of regular particles. The tap density of binary mixtures was larger than that corresponding to the monosized particles packing by about 15%. The tap density of ternary mixtures was larger than that of corresponding to the packing of binary mixtures by about 9%. This work employed the binary mixture of 60% coarse particles and 40% fine particles with size ratio of 1.0 to 1/10 and the ternary mixture of 60% coarse particles, 20% medium and 20% fine particles with size ratio of 1:1/10:1/400 respectively.

• 한국전기전자재료학회논문지
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• 제25권2호
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• pp.110-113
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• 2012

ZnO crystals with a baseball bat shape were synthesized without any catalysts through a simple thermal oxidation of ZnS powder in alumina crucible under air atmosphere. SEM images demonstrated that the bat structure was composed of two pieces of ZnO crystals, i.e hexagonal-shaped rod and inverted cone-shaped rod. X-ray diffraction (XRD) pattern revealed that the ZnO crystals had wurtzite hexagonal structure. Energy dispersive X-ray (EDX) spectrum showed that the ZnO was of high purity. A strong green emission peak at 510 nm was observed in cathodoluminescece spectrum.

• 대한기계학회논문집A
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• 제20권7호
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• pp.2078-2086
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• 1996

This paper introduces two three-dimensional eight-node hexagonal elements obtained by using multivariable variational mehtod. Both of them are based on the modified hellinger-reissner principle to employ incompatible displacements and assumed stresses of assumed strains. The internal functions of element are introduced to as element formulation through two different methods : the first one uses the functions determined directly from the element boundary condition of the incompatible displacements ; while the second, being a kind of B-bar mehtod, employs the modification technique of strain-displacement matrix to pass the patch test. The elements are evaluated on the selective problems of bending and material incompressibility with regular and distorted meshes. The results show that the new elements perform with good accuracy in both of deformation and stress calculation and they are insensitive to distorted geometry of element.

• 대한산업공학회지
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• 제30권4호
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• pp.277-284
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• 2004

CDMA (Code Division Multiple Access) is a promising air interface technique for digital cellular systems. The soft handoff between base stations is one of many important features of CDMA for the mobile stations crossing the cell boundaries. The service areas of MSC's (Mobile Switching Centers) are defined as the unions of the service areas of the base stations connected to MSC's and are assumed to have hexagonal shapes. An analytical approach to the performance analysis of the link between MSC's for supporting the inter-MSC soft handoff scheme will be developed to obtain the probability that a soft handoff to an adjacent MSC will be blocked due to the shortage of the link capacity. Also, the rate of new connection establishments that are requested by the mobile stations moving to the service area of an MSC according to the inter-MSC soft handoff scheme will be obtained.

• 한국방송∙미디어공학회:학술대회논문집
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• 한국방송공학회 2011년도 하계학술대회
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• pp.602-605
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• 2011

자연현상이나 실제 상황을 담고 있는 비디오 시퀀스는 기본적으로 주위의 픽셀들과 높은 상관도를 가지고 있다. 따라서 움직임 벡터 정보도 주위 블록의 정보와 상관도가 높으며, 움직임 예측을 수행할 때의 계산 량을 줄이는데 용이하게 사용되어져 왔다. 본 논문에서도 이를 이용하여 움직임 벡터를 예측하는 방법을 제시한다. 현재 블록의 정확한 움직임 벡터 예측을 위하여, 참조 프레임의 움직임 벡터와 현재 프레임의 움직임 벡터 정보를 참조하여 시작점을 정확하게 재조정하였다. 더 정확해진 시작점 예측으로 인해 움직임 정보의 중앙으로 수렴하는 확률이 더 높아 졌으며, 이를 이용하여 enhanced hexagonal search의 첫 단계를 수정함으로써 search point를 줄였다. 실험결과에서는 제안한 알고리즘의 장점과 단점을 분석하고 각 테스트 시퀀스에 따른 성능을 비교하였다.

• 한국세라믹학회지
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• 제29권6호
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• pp.463-470
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• 1992

Corundum single crystals were grown in cryolite flux with the composition of Na3AlF6:Al2O3=80:20 wt%. This mixture was melted at 115$0^{\circ}C$, followed by slow cooling at a rate of 2$^{\circ}C$/hr to 96$0^{\circ}C$. And by adding of La2O3 to the flux, the change of crystal forms were observed. Crystal forms of corundum grown in cryolite flux had the habits of hexagonal plate which consist of well developed {0001} face and small {101} face. As La2O3 was added and its content was increased, {223} and {110} faces were developed, and crystal habits of equidimensional forms changed into hexagonal prism form. In a charge of 8 mole% B2O3, Al2O3:La2O3=15:1, transparent corundum single crystals of equent form were grown. As the content of B2O3 was increased, twineed crystals which have twin law of 2-fold parallel to [0001], and composition plane of (110) were grown.

• 한국세라믹학회지
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• 제16권2호
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• pp.89-98
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• 1979

In order to prepare ferroxplana ZnY $(Ba_2Zn_2Fe_{12}O_{22})$, which would be useful for GHz-band communication, the optimum coprecipitation condition of 1 $BaCl_{2-1} Zn(NO_3)_2-6FeCl_3$ in $NaOH-Na_2CO_3$ solution was investigated by use of a new apparatus invented in our laboratory. By freeze-drying and calcining the coprecitated hydroxide-carbonate, the very reactive powder was obtained, from which the synthesis process of ZnY and the other related crystals were investigated by means of X-ray diffraction. In results, it was found that the reactive powder containing ZnY as the major component can be prepared by this method, which may be used in manufacturing the various magnetic cores for the microwave communication.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2005년도 International Meeting on Information Displayvol.II
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• pp.1568-1571
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• 2005

We have evaluated thermal stability of a $BaAl_2Si_2O_8:Eu^{2+}$ $(BAS:Eu^{2+})$, which have polymorph property such as hexagonal, monoclinic structure depending upon firing temperature. When both polymorph $BAS:Eu^{2+}$ were baked in air at 500 $^{\circ}C$ for 30 min, the photoluminescence (PL) intensity of $monoclinic-BAS:Eu^{2+}$ was maintained of the initial intensity. However, the PL intensity of $hexagonal-BAS:Eu^{2+}$ decreased significantly, corresponding to about 34 %. From analyses of Rietveld refinement, the difference of thermal stability of both $BAS:Eu^{2+}$ can be ascribed to both crystal structure of host materials and the average interatomic distances between $Eu^{2+}$ ion and oxygen their crystal structure which plays a key role of shield for Eu2+ ions against oxidation atmosphere.

• 한국세라믹학회지
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• 제33권3호
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• pp.362-370
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• 1996

Kalsilite (KAlSiO4) system undergoes a displacive phase transition from hexagonal phase with p63 space group to the phase with P63mc at 886$^{\circ}C$. The flux composition having kalsilite :K2O:B2O3=1:2:2 has enabled the growth of hexagonal kalsilite with the size of 0.5~1 mm at a slow cooling rate (0.3$^{\circ}C$/hr). On decreasing the cooling rate the size has increased and pyramidal (1011) faces are newly developed with the shape of (0001) and (1010) faces. Upon stirring (1011) faces are degraded. The space group of O1 and O2 are P21221 and C2221 respectively. Their orthorombic modification O1 and O2 are synthesized at relatively low and high temperature respectively.

• 한국세라믹학회지
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• 제34권5호
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• pp.544-551
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• 1997

We tried to improve the coating capability of the coating material using an additive(hexagonal cystalline graphite) of 2%, 3%, 4% and 6% under various pouring temperature for the easy isolation of sand and coating material from the final product. As a result in case of using a 2% and 3% additive generally no burning state has been occurred under the low pouring temperature, but it has been gradually increased with the pouring temperature. On the other hand in case of using a 4% and 6% additive there has been no burning state through out the whole pouring temperature. From this result we could see that the best state of the final product without sand and coating material could generally be obtained if 4% and/or 6% of the crystalline graphite and the pouring temperature of 140$0^{\circ}C$$\pm$5$^{\circ}C$ would be used.