• 설비공학논문집
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• 제12권10호
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• pp.901-907
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• 2000

The conceptual determination of mixed-refrigerant (MR) for a closed Joule-Thomson cryocooler is described in this paper. The thermodynamic cycle design was mainly considered to develop a cryocooler by using a compressor of domestic air-conditioning unit. The target cooling performance of the designed cryocooler is 10 W around 70 K with less than 5 kJ/kg enthalpy rise. The systematic approach of choosing a proper refrigerant among 20 different kinds of mixture for such cryogenic temperature was introduced in detail. The main components of the cryocooler are compressor, evaporator, oil separator, after-cooler, counterflow heat exchanger, and J-T expansion device. Due to the limitation of the compressor operation range, the temperature after the compression was limited below $117^{\circ}C$ (390 K) and the temperature before compression was restricted above $5^{\circ}C$ (278 K). 20 atm of discharging pressure (high pressure) and less than 3 atm suction pressure (low pressure) were the design conditions. The inlet temperature of a counterflow heat exchanger in the high Pressure side was about 300 K. The proper composition of the mixed refrigerant for the designed J-T cryocooler is 15% mol of$ N_2, 30% mol of $CH_4,\; 30% mol\; of C^2H^ 6,\; 10%\; mol\; of\; C_3H_8\; and \;15%\; mol\; of\; i-C_4H_10$.

• Archives of Pharmacal Research
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• 제28권2호
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• pp.220-226
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• 2005

Temperature and medium composition were changed with the aim of increasing growth and erythropoietin (EPO) production in EPO-producing Chinese hamster ovary (CHO) cells. We used the CHO cell line, IBE, and its derivative, CO5, which over-expresses the first two enzymes of the urea cycle, carbamoyl phosphate synthetase I (CPS I) and ornithine transcar-bamoylase (OTC). When supplements were added to the medium at $33\;^{\circ}C$, the growth of IBE and CO5 cells increased by $27\%\;and;26\%$, respectively and the maximum yield of EPO was increased by $40\%$ in both cell lines. The absolute EPO concentration in the CO5 cells was always $55{\sim}60\%$ higher than in the IBE cells. In addition, when the two cell lines were continuously cultured with supplements at $33\;^{\circ}C$ until their growth rates approached those at $37\;^{\circ}C$, the growth rates of both IBE and CO5 cells increased by $54\%$ and their maximum EPO levels increased by up to $73\%\;and\;56\%$, respectively. Therefore, the growth and EPO expression levels of CO5 cells increased 2.2-fold and 2.6-fold, respectively, compared to those of the IBE cells. These results indicate that adaptation to lower temperature as well as medium supplementation could be important for improving cell growth and EPO production.

• 대한화학회지
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• 제7권2호
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• pp.122-127
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• 1963

Pyrolysis fo polyethylene and polypropylene has been studied in order to clarify the mechanism of chain scission and effect of oxygen on degradation. Rate of weight decrease was measured under nitrogen and air atmosphere at constant temperature for the samples of high density polyethylene, low density polyethylene and isotactic polypropylene, and then gaseous hydrocarbons produced from pyrolysis were analysed by gas chromatography. Although there is little substantial difference between composition of hydrocarbon gases from pyrolysis of high density polyethylene and low density polyethylene except some difference in quantity of total gas produced, gas composition from polypropylene pyrolysis differs from that of polyethylene pyrolysis. Gases from pyrolysis under air contain much more unsaturated hydrocarbons than those from pyrolysis under inert gas.

• 자원리싸이클링
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• 제12권6호
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• pp.8-12
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• 2003

본 논문에서는 최근 고품위 TV 및 고정세도 디스플레이용으로 화상의 정세도를 향상시키기 위해 수평주파수를 높이려는 움직임이 있어, 편향 요크용 페라이트 코아에는 고주파수 영역에 있어서도 코아로스가 낮은 재료가 요구되고 있는 실정이다. Mg-Zn 페라이트에 있어서 화학조성 및 프로세스가 미세구조에 미치는 영향에 착안하여 저온 소결화를 하였다. 저손실인 Mg-Zn계 Ferrite에 Cu를 첨가하였다. MgO, ZnO, $Fe_2$$O_3$, CuO를 선택한 후 조성비의 변화를 두며 CuO를 MgO로 치환하였다. 이 시료를 $980∼1350^{\circ}C$까지 3시간 소결하였다. 측정은 투자율, 전력손실, 수축율, 코아로스를 측정하였다. 시료의 수축율을 개시하는 온도는 $900^{\circ}C$부근이며 Cu치환에 따라 수축율이 증가하였으며, Cu 치환에 따라 소성온도가 약 $-50∼-75^{\circ}C$ 낮아졌다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2011년도 제37회 추계학술대회논문집
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• pp.698-701
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• 2011

근래 추진제의 개발 동향은 온도 둔감 특성을 가지는 것을 목표로 온도에 둔감한 특성을 가진 DNDA-57을 활용한 개발이 이루어지고 있다. 이번 연구에서는 DNDA-57이 포함된 추진제에 대해 Closed Bomb Test 및 40MM 발사시험을 통해 온도 둔감 효과를 확인하였다. 현재 최적의 추진제 형상 및 조성, 그리고 작업 공정에 대한 연구가 진행 중이다. 향후 최적의 조성 및 공정을 수립하기 위한 연구를 지속적으로 수행할 계획이다.

• Journal of Korean Vacuum Science & Technology
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• 제4권3호
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• pp.81-85
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• 2000

The effects of $NH_3$ flow rate and reactor pressure on Al composition and the interface of AlGaN/GaN heterostructure were studied. Equilibrium partial pressure of Ga and Al over AiGaN alloy was calculated as a function of growth pressure, $NH_3$flow rate and temperature. It was found equilbrium vapor pressure of Al is significantly lower than that of Ga, thus, the alloy composition mainly controlled by Ga partial pressure. We believe that more decomposition of Ga occur at lower $NH_3$ flow rate and higher growth pressure leads to preferred Al incorporation into AlGaN. The alloy composition gradient became larger at AlGaN/GaN heterointerface at higher reactor pressures, higher Al composition and low $NH_3$ flow rate. This composition gradient lowered sheet carrier concentration and electron mobility as well. We obtained an AlGaN/GaN heterostructure with sheet carrier density of ${\sim}2{\times}10^{13}cm^{-2}$ and mobility of 1250 and 5000 $cm^2$/Vs at 300 K and 100 K, respectively.

• 기술표준
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• 통권12호
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• pp.67-78
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• 2003

In order to keep a characteristic corrugated fibreboard of fruits and flowers, temperature and humidity change of corrugated fibreboard are analyzed. According to relative humidity rises at fixed temperature, bursting strength of corrugated fibreboard was fallen and double wall corrugated fibreboard appeared greatly the bursting strength decline rate than double faced corrugated fibreboard and edgewise compressive strength of paper more than humidity 80% in rapidly fall. A column crush test of paper became decrease in the high temperature and ordinary temperature strength did over humidity 70% rapidly fallen and strength decrease happened by low temperature 80% slowly fallen and later rapidly. According to ISO standard temperature humidity conditioning (23$\pm$2 , 50$\pm$2%) change, pulp composition difference as to the ring crush strength of a physical strength and generally compare to KS standard increased 5∼8% for the compressive strength, and wet strength reagent was increased 4% inside and out.

• 한국응용과학기술학회지
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• 제35권1호
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• pp.80-88
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• 2018

본 연구에서는 투명도와 기계적 특성을 향상시키기 위해 저온 공정의 졸-겔 법을 이용하여 하이브리드 복합체의 코팅 박막을 제조하였다. 하이브리드 복합체로는 $ZrO_2/TiO_2/organosilane$을 사용하였으며, 그 중 organosilane은 3-(trimethoxysilyl)propyl methacrylate을 사용하였고 이는 저온 공정의 광경화 반응을 위해 도입되었다. 다양한 조성비로 합성된 복합체를 폴리 카보네이트 기판 위에 저온 공정의 졸-겔 법을 이용하여 광경화와 열처리 공정을 거처 코팅 박막을 제조하였고 이 코팅 박막의 광학 특성 및 기계적 강도를 확인하였다. 코팅 박막은 가시광선 영역에서 97.5 % 이상의 투과도를 가짐을 확인하였고 기계적 강도는 9H 이상의 연필 경도를 가진 것을 확인하였다. 특히 ZTS-2-1 코팅 박막의 나노 압입 경도는 1.14 GPa로 가장 높게 측정되었다.

• 한국전기전자재료학회논문지
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• 제29권7호
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• pp.404-407
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• 2016

In this study, to develop low temperature sintering capacitor composition ceramics with the good dielectric properties, $(Ba_{0.86}Ca_{0.14})(Ti_{0.85}Zr_{0.12}Sn_{0.03})O_3$ (BCTZ) ceramics were prepared by the conventional solid-state reaction method. The effects of $B_2O_3$ addition on the dielectric properties and microstructure was investigated. The XRD patterns demonstrated that all the specimens showed Perovskite phase, and secondary phases are indicated in the measurement range of XRD. And also, temperature coefficient of capacitance(TCC) of all the specimen sintered at $1,180^{\circ}C$ showed +3~-56% except for x=0.006. For all the specimens, observed one peak was tetragonal cubic difuse phase transition temperature(Tc), which is located in the vicinity of room temperature.

• 한국진공학회지
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• 제7권s1호
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• pp.85-99
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• 1998

A ultrahigh vacuum chemical vapor deposition(UHVCVD)/metalorganic chemical vapor deposition(MOMBE) system equipped with a radio frequency(RF)-plasma cell was employed to grow GaN layer on the sapphire at a low temperature. The x-ray photoelectron spectroscopy analysis of nitrogen composition on the nitridated sapphite surface indicated that a nitridation process is mostly affected by the RF power at low temperature. Atomic force microscope images of nitridated surface the protrusion density on the nitridated sapphire is dependent on the nitridation temperature. The crystallinity of GaN grown at $450^{\circ}C$ was found to be much improved when the sapphire was nitridated at low temperature prior to the GaN layer growth. Moreover, a strong photoluminescence spectrum of GaN grown by UHVCVD/MOMBE with a rf-nitrogen plasma was observed for the first time at room temperature.