• Journal of electromagnetic engineering and science
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• 제10권1호
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• pp.28-34
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• 2010

This paper introduces a new U.S. ultra-wideband(UWB: 3.1~10.6 GHz) 1:2 power divider based on a single section Wilkinson type configuration. The divider provides very flat in-band power splitting, high isolation, low insertion loss, sharp roll-off bandpass filtering, and DC blocking characteristics. The circuit consists of a $\lambda$/4 Y resonator, three capacitively coupled $\lambda$/2 short-circuited lines, and a resistor between the two output ports. The circuit structure was simulated with ADS and HFSS, and realized with low-temperature co-fired ceramic(LTCC) green tape, which has a dielectric constant of 7.8. $|S_{11}|$ better than 10 dB, $|S_{21}|$ and $|S_{31}|$ less than 3.2 dB, with both $|S_{22}|$ and $|S_{32}|$ measured as better than 12 dB for the whole UWB band. Measurement results agree closely with HFSS simulation results. The power divider has a compact size of $4\times9\times0.6mm^3$.

• 한국분말재료학회지
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• 제18권6호
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• pp.488-495
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• 2011

This study was performed to fabricate the porous titanium foam by space holder method using NaCl powder, and to evaluate the effect of NaCl volume fractions (33.3~66.6 vol.%) on the porosities, compressive strength, Young's modulus and permeability. For controlling pore size, CP titanium and NaCl particles were sieved to different size range of 70~150 ${\mu}m$ and 300~425 ${\mu}m$ respectively. NaCl of green Ti compact was removed in water followed by sintered at $1200^{\circ}C$ for 2 hours. Total porosities of titanium foam were in the range of 38-70%. Pore shape was a regular hexahedron similar that of NaCl shape. Porous Ti body showed that Young's modulus and compressive strength were in the range of 0.6-6 GPa and 8-127 MPa respectively. It showed that pore size and mechanical properties of Ti foams was controllable by NaCl size and volume fractions.

• 한국세라믹학회지
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• 제29권6호
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• pp.419-430
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• 1992

Fabrication possibility of low-shrinkage alumina without oxidation and wetting agent was presented on the basis of observation about oxidation behavior, microstructure and physical characteristics of such reaction agents free Al2O3-Al system. The composition less than Al 10w/o where Al can act as a sintering agent for Al2O3 was excluded. Under the condition of present experiments oxidation of Al2O3-Al system was dependent not on holding time but mainly on oxidation temperature. In thes case of Al powder not comminuted effectively during powder mixing of Al2O3-Al, columnar structure which would act as a hindrance to the densification during sintering developed more during oxidation with higher Al contents, and which made the fabrication of low-shrinkage Al2O3 ceramics impossible. If Al powder was comminuted effectively due to co-mixed Al2O3 characteristics, densification was improved because of no columnar structure and made the fabrication of sintered body with -2.7% dimensional change and 81% relative density possible. As a result, it is possible to fabricate dense low-shrinkage Al2O3 ceramics without oxidation and wetting agent under conditions such as smaller particle size of Al, Al contents below 50v/o, higher green density of Al2O3-Al compact and the use of Al2O3 powder used for high-density ceramics.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 추계학술대회 논문집 Vol.17
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• pp.416-420
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• 2004

Varistors based on M.Matsuoka were prepared from ZnO nanopowders, every one of which had bar type and about less 100nm length. The compact green disks were conventionally sintered in air for 2 hours at a temperature of $1050^{\circ}C$. The Varistors with nonlinear coefficient ${\alpha}=45$, leakage current $I_{\ell}=2{\times}10^{-7}A/cm^2$, operating voltage 9000v/cm, and average grain size $3{\mu}m$ were obtained. The advantages of the samples were due to greater structural homogenity, higher density, smaller grain size.

• 한국세라믹학회지
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• 제17권2호
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• pp.80-88
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• 1980

The sintering phenomena and piezoelectric properties of PZT ceramics of composition $Pb(Zr_{0.54} Ti_{0.46})O_3$ were investigated when a small quantity of $La_2O_3$ , $LaMnO_3$, $LaCrO_3$ were added. The unwanted chemical composition change in PZT during sinterin porces du to PbO evaporation poses a severe problem in PZt manufacturinig. It is observed tat an addition of small amount of $LaMnO_3$ to PZT markedly decreases the evaporation of PbO during sintering . The green compact of (1-x) PZT.xLaMnO3(x=0.02~0.10) could be sintered of under O2 atmosphere alone with no significant loss of PbO. The planar coupling factor kp of the sintered $0.98Pb(Zr_{0.54} Ti_{0.46})O_{3.0.02}LaMnO}3$ is similar to that of commercial PZT 6A. Microstructure investigation shows that part of sintering process of $Pb(Zr, Ti)O_3$.$LaMnO_3$ system progresses via liquid phase sintering. It is believed that the evaporation of PbO in PZT sintering is restricted by the addition of $LaMnO_3$ due to the above phenomena. Furthermore the solid solution of $LaMnO_3$ in PZT causes diffuses phase transition.

• 한국세라믹학회지
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• 제20권1호
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• pp.63-69
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• 1983

It is know that $Si_3-N_4$ bonded SiC has almost all the valuable properties needed for the high temperature material and thus has bery wide range of applicability. Si powder and two different sized SiC powder were used as the raw mateials. Specimens were prepared by heating the green compact mode of the raw materials with polyvinyl alcohol binder in the nitrogen atmosphere. The bond-ing of SiC particles is brought about with the formation of reaction bonded silicon nitride phase between the particles he influences of the variation of the relative amounts of the raw materials and the amount of the organic binder on the density and the bend strength of the specimens were investigated. It was shown that the calculation of the amount of the nitridation of Si is somewhat complicated matter since some portion of the organic binder reacts with the Si during the firing process. Fixing the Si amount to 20w/o the distributions of the size of the SiC particles that gives the maximum density and the maximum strnegth were obtained through experiments. It was observed that the two distributions were not equal to each other. As the amount of Si increased the amount of Si reacted with nitrogen and the strength increased. The fracture mode was intergranular for the most part and the transgranular fracture was scarcely observed.

• 한국BIM학회 논문집
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• 제11권1호
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• pp.31-38
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• 2021

The design principles of new urbanism (NU) have been adopted for new towns-in town projects for inner city neighborhoods in Seoul, Korea Since 2000. Here, ten NU principles were matched to four urban design categories: streets, land use, housing and buildings, and public open spaces. These elements were analyzed for Eunpyung New Town project. Through the case, the applications and implications NU principles are explored. The principles of connectivity, quality architecture and urban design, increased density, green transportation, sustainability, and quality of life were positively and successively adopted for streets, land use, housing and buildings, and public open spaces. The principles of mixed-use and diversity and traditional neighborhood structure were only partially applied in land use, housing and buildings, and public open spaces. It should be note that the walkability principle is intended not for job-housing proximity, but for pedestrian-friendly street design.

• 한국조경학회지
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• 제33권5호통권112호
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• pp.69-82
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• 2005

These studies were carried out (1) to investigate the growth characteristics of Sedum album L. in the field, (2) to propose a suitable shallow peen roof system for this plant, and (3) to evaluate plant growth in the proposed system over the long term. The growth characteristics, such as morphological properties, growth habit, shade tolerance, and flowering, were surveyed. In experimental shallow green-roof systems, the effects of drainage type, substrate type, and soil depth on plant growth were investigated. Then drought tolerance was investigated. After planting Sedum album L. in the proposed system survival rate, cover, and resistance to insects, heal and cold were evaluated for about 2 years. The results of these studies are summarized below. 1. In the field, the aboveground part of Sedum album L. did not die back during the winter. Plant height was 4$\sim$7 cm. Roots were distributed to a depth of 5$\sim$7 cm. Sedum album L. is a compact ground-cover plant that spreads vigorously. Shading condition of less than $30\%$ of full sunlight didn't cause any trouble, but shading conditions above $87\%$ made the shape of the shoots and leaves abnormal. The plant bloomed from June to August and had a rather large compound umbel of white, star-shaped flowers. 2. Two systems, a drainage-blend-10 cm soil depth and a reservoir$\cdot$drainage-blend-15 cm soil depth, performed best in terms of cover, fresh weight, and dry weight. The first has an advantage for green roofs because it is lighter than the latter. 3. In drainage-blend-10 m soil depth and modified reservoir · drainage-blend-10 cm soil depth system no plants died for about 4 months after stopping the irrigation. The visual quality of the latter system was above 5 for 4 months and that of the former was under 5 after 2 months. In the field, however, the drought tolerance of Sedum album L. grown in the former would be enough to withstand the dry season. Considering the urban ecosystem and the importance of healthy growth the modified reservoir $\cdot$ drainage-blend-10 cm soil depth system was finally recommended. This system was composed of a 4 cm thick drainage layer and drain outlets placed at a height of 2.5 cm. 4. In the proposed system, the survival rate was $100\%$, and there was no injury induced by insects and heat. The leaf density decreased a little in winter. Cover increased throughout the year. Sedum album L. was planted with a cover of 72$cm^{2}$ on 3 April 2003; on 16 June 2003 and 15 June 2004, cover was $132.66\pm$5.87 $cm^{2}$(1.8 times) and $886.98\pm$63.51 $cm^{2}$(12.3 times), respectively.

• 식물조직배양학회지
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• 제26권2호
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• pp.127-132
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• 1999

4주 배양된 애기장대의 엽육조직으로부터 원형질체를 분리하여 2.0mg/L NAA, 0.5mg/L BAP및 9% mannitol이 포함된 MS 액체배지에서 $25^{\circ}C$, 암조건에서 배양하였다. 원형질체 유래 microcolonies를 dehydration시켜 배양하였을 때 non-dehydration에 비해 7배의 높은 캘러스 유도율을 나타내었다. Dehydrated microcolonies들 중에서 50개의 캘러스를 선별하여 0.05 mg/L NAA, 7mg/L 2-iP가 첨가된 MS배지에서 광조건으로 배양하였을 때 점차적으로 녹화되기 시작하였으며 배양 4주 후부터 전체적으로 녹화된 SF캘러스에서 green spots이 형성되었다 Shoot형성률은 식물생장조절물질의 종류에 따라 3.5%~56%로 나타났다. 재분화된 shoot는 식물생장조절물질이 첨가되지 않은 MS배지에서 뿌리를 유도하였으며 이들을 토양에 이식하여 완전한 재분화 식물체를 얻을 수 있었다. Shoot 형성과정을 조직학적인 측면에서 관찰한 결과, 배양초기에는 신장된 무정형의 세포가 대부분이었으나 배양이 진전됨에 따라 주위 세포들과 구별이 뚜렷한 도관요소 (tracheary element)와 분열조직군 (meristemoid)이 형성되면서 shoot primodia가 shoot로 발달되는 것을 관찰할 수 있었다. 재분화 식물체는 형태적으로 normal type이 78%이고 abnormal type이 22%였다.

• 한국세라믹학회지
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• 제42권1호
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• pp.69-75
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• 2005

고온자전연소법에 의한 질화알루미늄 합성에 있어서, 반응물(Al) 형상과 희석제(AlN) 입도 등의 형상학적 조건이 반응생성물에 미치는 영향을 조사하였다. 평균 입경(34$\mu$m)이 같은 두 종류의 Al 분말(입상, 편상)과 평균입경이 다른 4종류의 AM분말을 희석제로 사웅하여 반응 성형체를 준비하였다. 반응성형체의 충진밀도는 이론밀도의 $35\%로 고정하였고, 초기 질소압은 $1\~10MPa$, 희석을은 $0.4\~0.7$로 변화시키면서 반응을 실시하였다. 반응물과 희석제의 입도를 비슷하게 조절함으로써, 상대적으로 질소압이 낮은 1MPa의 조건에서도 순도 $98\% 이상, 입경 수십 $\mu$m의 AlN 합성이 가능함을 확인하였다. 이러한 고순도, 고입경화는 연소파 진행 후, 성형체 내부로 질소가스 투입 용이성의 차이에 의한 현상이라고 판단된다.