• 생명과학회지
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• 제5권4호
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• pp.155-161
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• 1995

The effects of substrate concentration, enzyme concentration, reaction temperature, and water content were investigated in intramolecular esterification. This study used cyclohexane as organic solvent, power lipase as enzyme, and benzyl alcohol and octanoic acid as substrate. The initial reaction rate was found to be proportional to enzyme concentration; followed Michaelis-Menten equation for octanoic acid; and was inhibited by benzyl alcohol . The observed initial reaction rate first increased, then decreased with increasing reaction temperature, giving rise to the maximum rate at 20$\circ$. The drop in the reaction rate at higher temperature was to partition equilibrium change of substrate between organic solvent and hydration layer of enzyme molecule in addition to the deactivation by enzyme denaturation. Water layer surrounding enzyme molecule seemed to activate in organic solvent and the realistic reaction was done in the water layer. In the enzymatic reaction in organic solvent, the initial reaction rate was influenced by partition quilibrium of substrate, so the optimum condition of substrate concentration, enzyme concentration, reaction temperature, and water content would give a good design tool.

• 대기
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• 제17권2호
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• pp.171-183
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• 2007

Trends of daily maximum and minimum temperatures in major cities of South Korea (Seoul, Busan, Incheon, Daegu, and Ulsan) during the past 40 years (1961-2000) were investigated. Temperature records for the Chupungryeong station were compared with those of the large cities because of the rural environment of the station. There were distinct warming trends at all stations, although the warming rates depend on each station's local climate and environment. The warming rates in Korea are much greater than the global warming trends, by a factor of 3 to 4. The most increasing rate in daily maximum temperature was at Busan with $0.43^{\circ}C$ per decade, the most increasing rate in daily minimum temperature was at Daegu with $0.44^{\circ}C$ per decade. In general, the warming trends of the cities were most pronounced in winter season with an increasing rate of $0.5^{\circ}C$/decade at least. Diurnal temperature range shows positive or negative trends according to the regional climate and environmental change. The frequency distribution of the daily temperatures for the past 40 years at Seoul and Chupungryeong shows that there have been reductions in cold day frequencies at both stations. The results imply that the impacts on human health might be positive in winter and adverse in summer if the regional warming scenario by the current regional climate model reflects future climate change in Korea.

• Journal of Electrochemical Science and Technology
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• 제3권1호
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• pp.24-28
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• 2012

The electrocatalytic activities and surface roughness of indium-tin-oxide (ITO) electrodes have been investigated after thermal treatment at 100, 150, or $200^{\circ}C$ for 30 min, 2 h, or 8 h. To check electrocatalytic activities, the electrochemical behavior of four electroactive species (p-hydroquinone, $Ru(NH_3){_6}^{3+}$, ferrocenemethanol, and $Fe(CN){_6}^{4-}$) has been measured. The electron transfer rate for p-hydroquinone oxidation and ferrocenemethanol oxidation increases with increasing the incubation temperature and the incubation period of time, but the rate for $Ru(NH_3){_6}^{3+}$ is similar irrespective of the incubation temperature and period because $Ru(NH_3){_6}^{3+}$ undergoes a fast outer-sphere reaction. Overall, the electrocatalytic activities of ITO electrodes increase with increasing the incubation temperature and period. The surface roughness of ITO electrodes increases with increasing the incubation temperature, and the thermal treatment generates many towering pillars as high as several tens of nanometer.

• Tribology and Lubricants
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• 제33권2호
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• pp.37-44
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• 2017

A DE-side LBP tilting pad journal bearing of a 1-stage overhung heat-pump compressor in a propylene process exhibited abnormal high-temperature behavior. Its temperature had been relatively high at $78^{\circ}C$ from the beginning of operation. In 2014, after three years of operation, it increased suddenly and reached $103^{\circ}C$. Installing a varnish removal equipment and others managed to stabilize the temperature at $95^{\circ}C$. We undertook a troubleshooting approach for reviewing the comprehensive status and integrity of the temperature design of the bearing. We performed lubrication and heat-balance analysis, based on the design engineering data and documents supplied by the OEM. For the base design data of DE-side TPJB, evaluating the effects of key design variables on bearing metal temperature showed that firstly, increasing the bearing clearance and supply oil flow-rate, and next, changing the oil type, and finally, increasing the machined pad clearance and offset, are more effective in reducing the bearing metal temperature. Furthermore, a clarification meeting with the OEM revealed that an incorrect decision had been made to decrease the bearing clearance to eliminate the SSV harshness issue, while not maintaining a sufficient oil flow-rate. We conducted a detailed retrofit design analysis, wherein we increased the oil flow-rate and bearing clearance by decreasing the preload. We predicted that the bearing temperature would decrease to $63^{\circ}C$ from $75.7^{\circ}C$ even at the rerate condition. Finally, after installing and operating a retrofit replacement bearing in 2015, the bearing temperature stabilized at a low temperature of $65^{\circ}C$. Currently (January. 2017), two year later, the bearing metal temperature remains at $65^{\circ}C$. Therefore, we can conclude that the abnormal high-temperature behavior of the bearing has been resolved completely.

• Journal of Plant Biology
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• 제37권1호
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• pp.37-42
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• 1994

Correlative changes between photosynthetic O2 exchange rates and room temperature Chl fluorescence were investigated in wheat (Triticum aestivum L.) chloroplasts treated with high temperature for 5 min. With increasing treatment temperature, photosynthetic O2 evolution rate mediated by PSII was decreased, showing 50% inhibition at 38$^{\circ}C$ (I50). But PSI activity measured by O2 uptake rates was stimulated as a function of increasing temperature. Dark level fluorescence (Fo)-temperature (T) analysis showed that fluorescence rising temperature (Tr), critical temperature (Tc), and peak temperature (Tp) was 38, 43, and 52$^{\circ}C$, respectively. Quenching analysis of Chl fluorescence showed that both the oxidized fraction of plastoquinone (qQ) and degree of thylakoid membrane energization (qNP) increased up to 4$0^{\circ}C$ and then declined dramatically. These results suggest that Tr is correlated with temperature showing a 50% of inhibition of photosynthesis and under mild high temperature stress, qNP is worth regarding as indicator for heat-induced damage of photosynthesis.

• Current Optics and Photonics
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• 제2권5호
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• pp.468-473
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• 2018

We investigate the temperature dependence of efficiency droop in InGaN/GaN multiple-quantum-well (MQW) blue light-emitting diodes (LEDs) in the temperature range from 20 to $80^{\circ}C$. When the external quantum efficiency (EQE) and the wall-plug efficiency (WPE) of the LED sample were measured as injection current and temperature varied, the droop of EQE and WPE was found to be reduced with increasing temperature. As the temperature increased from 20 to $80^{\circ}C$, the droop ratio of EQE was decreased from 16% to 14%. This reduction in efficiency droop with temperature can be interpreted by a temperature-dependent carrier distribution in the MQWs. When the carrier distribution and radiative recombination rate in MQWs were simulated and compared for different temperatures, the carrier distribution was found to become increasingly homogeneous as the temperature increased, which is believed to partly contribute to the reduction in efficiency droop with increasing temperature.

• 태양에너지
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• 제16권2호
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• pp.65-77
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• 1996

동적형 빙축열 시스템의 빙축열조에서 세가지 얼음충진율에 대해 분산유체의 유온, 유량을 변화시켜 용융실험을 행하였다. 빙축열조에 분산되는 분산유체의 온도가 높고 유량이 많을수록 빙축열조 내의 온도성층화 현상도 뚜렸하였고 온도성층화에 돌입하는 시간이 단축되었다. 분산유체의 유량이 많을 때는 잠열이 방출되는 시기에 걸쳐서 빙축열조 내의 온도안정화 현상이 나타나고 온도안정화에 소요되는 시간도 단축되었다. 그러나 얼음의 용융이 끝난 후는 유량이 적을 때가 온도성층화 현상이 뚜렸하였다. 빙축열조 얼음충진율이 높을 때 온도성층화에 소요되는 시간이 길었으며 빙축열조 내 온도분포는 안정되었고 빙축열조의 벽면 영향으로 인해 빙축열조 상부의 온도가 높게 나왔다. 실험초기온도를 유지하는 기간은 빙축열조 내의 얼음이 존재하는 기간과 일치하였다. 빙축열조 내의 평균온도 상승은 분산유체의 유량이 많고 온도가 높을수록 일찍 상승하였다. 총방열에너지에 대한 잠열에너지($E/E_{ot}$)의 시간에 대한 변화비는 분산유체의 온도가 동일한 조건에서 유량이 많을수록, 분산유체의 온도가 높을수록 큰 값으로 나타났다.

• 한국표면공학회지
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• 제18권1호
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• pp.5-11
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• 1985

Titanium was deposited onto AISI-430 stainless steel by chemical vapor deposition from $TiI_4\;and\;H_2$ gas mixture. Effects of temperature, flow rate of the gas, and $TiI_4$ partial pressure on the deposition rate were thoroughly investigated. The deposition rate of Ti was found to be constant at the given temperature and was increased with increasing temperature. The rate is controlled by surface reaction at the flow rate of gas higher than 500 ml/min, whereas at the flow rate lower than that by diffusional process. It is also interesting to note that the reaction mechanism changes at 1050$^{\circ}C$, at temperatures lower than 1050$^{\circ}C$ the activation energy is 56.9 Kcal/mol, whilst at temperatures higher than that is 8.3 Kcal/mol.

• Journal of the Korean Wood Science and Technology
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• 제30권2호
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• pp.115-120
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• 2002

MDF를 페놀수지에 함침한 후 500, 650, 800, 1,000℃에서 소성하여 우드세라믹을 제조한 후 함침재 및 우드세라믹의 치수 변화와 휨강도를 측정하였다. 수지 함침율이 증가할수록 함침재의 치수 증가율 및 휨강도는 증가하였다. 소성온도에 따른 중량, 길이 및 두께감소율은 각각 소성온도 500℃일 때 59.9%, 19.4%, 26.3%이었으며, 소성온도 1,000℃일 때 65.3%, 22.5%, 31.6%로 소성온도가 증가함에 따라 증가하였으며, 휨강도 또한 함침율 40%일 때 소성온도 500℃에서 50.3 kgf/cm³, 800℃에서 0.79 g/cm³로 증가하였으나, 1,000℃에서는 0.75 g/cm³로 약간 감소하였다. 이상의 결과로 함침재 및 우드세라믹의 성질은 수지 함침율 및 소성온도의 영향을 받음을 알 수 있었다.

• 소성∙가공
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• 제3권4호
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• pp.427-439
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• 1994

The high temperature deformation behavior of $SiC_p/Al-Si$ composites and Al-Si matrix was studied by hot torsion test in a range of temperature from $270^{\circ}C$ to $520^{\circ}C$ and at strain rate range of $1.2{\times}10_{-3}~2.16{\times}10_{-1}/sec$. The hot restoration mechanisms for both matrix and composites were found to be dynamic recrystallization(DRX) from the investigation of flow curves and microstructural evolutions. The Si precipitates and SiC particles promoted DRX, and the peak strain$({\varepsilon}_p)$ of the composites was smaller than that of the matrix. Flow stresses of $SiC_p/Al-Si$ composites were found to be generally higher than the matrix, but the difference was quite small at higher temperature due to the decrease of capability of load transfer by SiC particles. With increasing temperature, failure strain of matrix and composites are inclined to increase, the increasing value of failure strain for the $SiC_p/Al-Si$ composites was small compared to that of matrix. The stress dependence of both materials on strain rate() and temperature(T) was examined by hyperbolic sine law, $\.{\varepsilon}=A_1[sinh({\alpha}{\cdot}{\sigma})]_n$exp(-Q/RT)