• Korean Journal of Crystallography
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• v.10 no.1
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• pp.76-82
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• 1999

융액인상법에 의하여 Garnet 구조내 결정학적 8면체 및 4면체의 양이온 자리에 전하 보상이온 Mg2+, 구조 수식이온 Sc3+ 및 laser 활성이온 Cr4+을 다양한 농도로 주입한 융액으로부터 Cr4+:YAG 단결정을 성장하고, 주입된 불순이온이 흡수계수에 미치는 영향을 규명하였다. 양질의 단결정을 성장하기 위한 인상속도와 회전속도는 각각 1.5 mm/h와 10 rmp이었으며, Cr4+:YAG 단결정은 <111> 방위로 성장하였다. 성장된 결정의 결정구조 동정 및 결정격자 상수를 측정하고, 1.064 ㎛에서의 결정화분율에 따른 흡수계수, 형광방출 스펙트럼, 유효편석계수(keff)를 보고하였다.

• Journal of the Korean Ceramic Society
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• v.31 no.12
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• pp.1459-1466
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• 1994

A novel technique for determining the oxygen tracer diffusion coefficients in oxides was developed. After the 16O-18O solid-gas exchange reactions between 16O in the oxides and 18O in the ambient gas, Raman spectra of the cross sections of oxide samples were measured in a spatial resolution of 5 ${\mu}{\textrm}{m}$. From thus obtained Raman spectra, depth profiles of 18O concentration in the oxide samples were calculated. The oxygen tracer diffusion coefficients and the surface exchange coefficients were determined under the assumptions that samples are semi-infinite slab and that the surface exchange reactionsare not negligible. The oxygen tracer diffusion coefficient of 2.8 mol% Y2O3-containing tetragonal ZrO2 polycrystals, 8 mol% Y2O3-containing ZrO2 polycrystals, and 10 mol% Y2O3-containing cubic ZrO2 single crystals (along the a axis) are as follows.

• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.1601-1604
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• 2006

A novel photo-alignment scheme using normally incident periodically intensity-modulated UV light has been developed and demonstrated to efficiently yield a stable pretilt angle of nematic liquid crystals by single exposure. The scheme, referred to as the "photo-rubbing", consists in unidirectional scan of the intensity-modulated UV light over the photo-alignment film, which causes asymmetrical photo-reactions in the film. We show here its successful application to multi-domain alignment processing. Thanks to the normal incidence, the photo-rubbing removes the instrumental disadvantages of the conventional oblique incidence technique, thereby providing a true practical solution for photo-alignment.

• Journal of the Korean Ceramic Society
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• v.29 no.3
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• pp.189-194
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• 1992

In order to grow a 127.86$^{\circ}$rotated LiNbO3 single crystal with good characteristics of surface acoustic wave (SAW) up to 80 mm in diameter, the temperature gradient of furnace, the growth rate and the rotation rate of crystal were changed. We could grow a crystal which had few macro defects at the conditions of temperature gradient as 30~6$0^{\circ}C$/cm, growth rate as 5 mm/hr and rotation rate as 8 rpm. The experimental ranges of the growth conditions are as follows. Temperature gradient was varied from 20 to 20$0^{\circ}C$/cm, growth rate as 5~7 mm/hr and crystal rotation rate as 6~12rpm.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2002.11a
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• pp.370-374
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• 2002

This paper describes the design and fabrication of distributed analog phase shifter circuit. The phase shifter consist of coplanar waveguide(CPW) lines that are periodically loaded with voltage tunable (Ba,Sr)TiO$_3$ thin film interdigital(IDT) capacitors deposited by the pulsed laser deposition(PLD) on (001) MgO single crystals. The phase velocity on these IDT loaded CPW lines is a function of applied bias voltage, thus resulting in analog phase shifting circuits. The measured differential phase shift is 48$^{\circ}$ and the insertion loss decreases from -5㏈ to -3㏈ with increasing bias voltage from 0 to 40 V at 100㎐.

• Proceedings of the Korean Magnestics Society Conference
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• 2003.06a
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• pp.152-153
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• 2003

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.5
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• pp.365-376
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• 2002

An experimental study has been conducted to measure the local film-cooling effectiveness and the heat transfer coefficient for a single row of rectangular-shaped holes. four different cooling hole shapes such ai a straight rectangular hole, a rectangular hole with laterally expanded exit, a circular hole and a two-dimensional slot are tested. A technique using thermochromic liquid crystals determine adiabatic film cooling effectiveness values and heat transfer coefficients on the test surface. Both film cooling effectiveness and heat transfer coefficient are measured for various blowing rates and compared with the results of the cylindrical ho1es and the two-dimensional slot. The flow patterns downstream of holes are calculated numerically using a cummercial package. The results show that the rectangular hopes provide better peformance than the cylindrical holes. For the rectangular holes with expanded exit, the penetration is reduced significantly, and the higher and more uniform cooling Peformance is obtained even at relatively high blowing rates.

• Proceedings of the Optical Society of Korea Conference
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• 2000.02a
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• pp.308-309
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• 2000

Nd:YAG 레이저의 수동적 Q-switching을 위해서는 대부분 유기물인 dye를 포화흡수체로 이용해 왔으나, 장시간 사용시 dye 분자의 결합이 끓어지면서 생기는 photodegradation으로 인하여 안정성에 많은 문제를 가지고 있다. 최근에 Cr$^{4+}$ :YAG 단결정의 물리적인 특성과 열적 안정성이 밝혀지면서 Nd:YAG 레이저의 Q-switching용 포화흡수체로 대치되고 있다[1]. 본 실험에서는 Z-Scan 방법을 이용하여 입사광의 세기에 따른 Cr$^{4+}$ :YAG 단결정의 흡수변화를 측정하였으며, 또한 Cr$^{4+}$ :YAG 단결정의 성장이 진행될수록 결정성장 길이에 따라 Cr 이온의 농도가 낮아지는 현상이[2] 발생하는데 두가지 서로 다른 결정화분률에 대해서 비선형 흡수를 비교하였다. (중략)

• Journal of Photoscience
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• v.6 no.4
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• pp.183-186
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• 1999

We have been prepared the porous silicon carbide (PSC) by electrochemical etching of silicon carbide single crystals. Samples of PSC have been studied by the methods of scanning electron microscope (SEM) and photoluminescence (PL). Two PL bands attributed to the blue and green light emission were observed in this study. According to the anodization conditions, the main source of emission in the oxidized layers of PSC lies in the different surface defect centers which consist of different geometrical structures due to the polytypes. It means that origin of these PL bands may be existed in different size pores simultaneously. The present results indicate that the high energy band comes from the top porous layers while the low energy band comes from the lower porous layers.

• Journal of the Korean Magnetic Resonance Society
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• v.19 no.3
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• pp.119-123
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• 2015

The thermodynamic properties and structural geometry of $KMgCl_3{\cdot}6H_2O$ were investigated using thermogravimetric analysis, differential scanning calorimetry, and nuclear magnetic resonance. The initial mass loss occurs around 351 K ($=T_d$), which is interpreted as the onset of partial thermal decomposition. Phase transition temperatures were found at 435 K ($=T_{C1}$) and 481 K ($=T_{C2}$). The temperature dependences of the spin-lattice relaxation time $T_1$ for the $^1H$ nucleus changes abruptly near $T_{C1}$. These changes are associated with changes in the geometry of the arrangement of octahedral water molecules.