• 한국연소학회:학술대회논문집
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• 한국연소학회 2004년도 제29회 KOSCI SYMPOSIUM 논문집
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• pp.231-237
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• 2004

Vacuum carburizing continues to gain acceptance as an alternative to atmosphere carburizing particularly in the car industry. The advantages of low-pressure carburization over atmospheric gas carburization is not only the creation of a surface entirely free of oxide and the environmentally friendly nature of these methods but also an improvement in deformation behaviour achieved by combining carburization with gas quenching, a reduction in batch times by increasing the carburization temperature, low gas and energy consumption and the prevention of soot to a large extent. In present study, an improved vacuum carburizing method is provided which is effective to deposit carbon in the surface of materials and to reduce cycle time. Also LPC process simulator was made to optimize to process controls parameters such as pulse/pause cycles of pressure pattern, temperature, carburizing time, diffusion time. The carburizing process was simulated by a diffusion calculation program, where as the model parameters are proposed with help the experimental results and allows the control of the carburizing process with good accordance to the practical results. Thus it can be concluded that LPC process control method based on the theoretical simulation and experimental datas appears to provide a reasonable tool for prototype LPC system.

• 열처리공학회지
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• 제16권4호
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• pp.191-196
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• 2003

For improvement of the wear performance of Ti alloy, vacuum-carburizing technique was tried for the first time using propane atmosphere. During the low pressure carburizing carbide was formed at the surface and carbon transfer was occurred from the carbide to the matrix. It was found that: (i) surface hardness increased with the reduction of operating pressure and time; (ii) optimum hardness distribution could be obtained with the proper choice of temperature and carbon flux control; and, (iii) case depth was largely influenced not by time but by temperature. The two steps process was recommended for obtaining thick case depth and high surface hardness of Ti alloy. For the low oxygen partial pressure, it was necessary to introduce additional CO gas to the atmosphere.Grain boundary oxidation and non-uniformity could be prevented.

• 콘크리트학회논문집
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• 제17권5호
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• pp.853-856
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• 2005

A low water/cement ratio leads to autogenous shrinkage of cement paste at an early age. This autogenous shrinkage is related to the change of relative humidity in the pore structure that is formed during the hydration process. The relationship between autogenous shrinkage and relative humidity change are relatively well defined today, but the effects of temperature on autogenous shrinkage, relative humidity, and pore structures have been studied less systematically. This study focused on correlating alterations of these properties of cement paste hydrated at constant temperatures of 20, 40, and $60^{\circ}C$. The test results clearly indicate that increasing curing temperature resulted in increased porosity, particularly for pores between 5 to 50 nm as measured by MIP, and increased autogenous shrinkages, as a consequence of a reduction of relative humidity at early ages.

• 한국대기환경학회지
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• 제19권5호
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• pp.541-549
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• 2003

A basic experimental study was conducted in order to find the optimum combustion control technology to decrease the thermal NO$_{x}$, by applying the catalytic combustion method with natural gas. NO$_{x}$ emission increased with increasing space velocity due to temperature rising in the furnace. In order to overcome the low resistance to high temperature, secondary air was supplied to the CST combustor. The following secondary fuel formed combustible mixture in part, which resulted in steep increase of the exiting temperature of the 2nd catalyst bed. It led to the more generator of NO$_{x}$, 30∼60% of the 1 st catalyst bed. It might be due to the potential increase of thermal NO$_{x}$.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2006년도 춘계학술대회 논문집
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• pp.159-163
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• 2006

The effects of annealing temperature and time on mechanical properties and microstructures were studied in cold drawn pearlitic steel wires containing 0.84wt% Si. Annealing was performed from $200^{\circ}C$ to $450^{\circ}C$ with different time of 30sec, 1min, 15min and 1hr. The increase of tensile strength at low temperature was related with strain ageing. The decrease of tensile strength at high annealing temperature was related with spherodization of cementite and the occurrence of recovery of the lamellar ferrite in the pearlite. The improvement of ductility was connected with spherodization of cementite plate in pearlite and recovery process by reduction of high dislocation density at short time annealing temperature of $400^{\circ}C$.

• 대한기계학회논문집
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• 제19권2호
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• pp.402-407
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• 1995

The effects of room temperature and strain aging treatment are discussed on the critical condition for the onset of growth of non-propagating cracks on 0.15% C low carbon steel, with special emphasis on the length of the critical non-propagating crack and on the crack opening displacement(COD) at the crack tip. It is found from the experimental analysis that room temperature and strain aging of a fatigue pre-cracked specimen introduced the closure of a crack tip of the pre-crack and the reduction of crack opening displacement at the wake of crack, together with an improvement in crack growth resistance of the microstructure. This may cause an increase in the endurance limit of the specimen, through the enhancement of effective stress for the onset of growth of the critical non-propagating crack.

• 한국전기전자재료학회논문지
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• 제21권3호
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• pp.217-221
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• 2008

In this study, We have been investigated the effect of calcination temperature and high-energy ball-milling of powder influences the $BaTiO_3$-based PTCR(Positive Temperature coefficient Resistance) characteristics and microstructure. The mixed powder was obtained from $BaCO_3$, $TiO_2$, $CeO_2$ ball-milled in attrition mill. The mixed powder was calcine from 1000 $^{\circ}C$ to 1200 $^{\circ}C$ in air and then it was sintered in reduction- re-oxidation atmosphere. As a result, The room-temperature electrical resistivity decreased and increased with increasing calcination temperature. specially, Attrition milled powder could have low room-temperature resistivity and high PTC jump order at 1100 $^{\circ}C$. attrition milling had lower room-temperature resistivity than ball milling. Particle size decreased by Attrition milling of powder influences in calcination temperature and room-temperature resistivity.

• 대한기계학회논문집B
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• 제34권10호
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• pp.941-946
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• 2010

1.7L 커먼레일 직접분사 디젤엔진에 대하여 바이오 디젤 연료가 conventional 연소(PM-NOx 트레이드오프 존재)와 저온 연소(low temperature combustion, LTC)에서 배기가스 배출에 미치는 영향을 분석하였다. LTC 연소는 conventional 연소 대비 다량의 EGR 과 연료분사 조건 최적화를 통하여 이루어졌다. 실험에 사용한 두 가지 연료는 초저유황 디젤연료(ultra low sulfur diesel fuel, ULSD), ULSD 에 대두유를 20%(vol. base)혼합한 바이오 디젤 연료(B20)이다. 사용된 연료에 관계없이 LTC 연소를 통하여 conventional 연소 대비 PM 및 NOx 의 동시 저감이 가능하였다. 동일한 엔진작동 조건에 대하여 conventional 연소의 경우 B20 는 ULSD 보다 PM은 적게 배출되나, NOx 는 많이 배출되었다. LTC 연소의 경우 B20 는 ULSD 보다 PM 및 NOx 생성이 많았다.

• Ocean and Polar Research
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• 제37권3호
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• pp.201-209
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• 2015

To examine the effects of increased $CO_2$ concentration and seawater temperature on the photosynthesis and growth of forest forming Ecklonia cava (Laminariales, Phaeophyta), sporophytic discs and gametophytes were cultured under three $pCO_2$ concentrations (380, 750, 1000 ppm), four temperatures (5, 10, 15, $20^{\circ}C$ for sporophytes; 10, 15, 20, $25^{\circ}C$ for gametophytes), and two irradiance levels (40, $80{\mu}mol$ photons $m^{-2}s^{-1}$) for 5 days. Photosynthetic parameter values ($ETR_{max}$, $E_k$, and ${\alpha}$) were generally higher as sporophytic discs were grown under low temperature and increased $CO_2$ concentration at 750 ppm. However, photosynthesis of Ecklonia sporophytes was severely inhibited under a combination of high temperature ($20^{\circ}C$) and 1000 ppm $CO_2$ concentration at the two photon irradiance levels. The growth of gametophytes was maximal at the combination of 380 ppm (present seawater $CO_2$ concentration) and $25^{\circ}C$. Minimal growth of gametophytes occurred at enriched $pCO_2$ concentration levels (750, 1000 ppm) and high temperature of $25^{\circ}C$. The present results imply that climate change which is increasing seawater temperature and $pCO_2$ concentration might diminish Ecklonia cava kelp beds because of a reduction in recruitments caused by the growth inhibition of gametophytes at high $pCO_2$ concentration. In addition, the effects of increased temperature and $pCO_2$ concentration were different between generations - revealing an enhancement in the photosynthesis of sporophytes and a reduction in the growth of gametophytes.

• Annals of Clinical Neurophysiology
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• 제8권2호
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• pp.125-134
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• 2006

Among the various physiological factors that affect nerve conduction velocity (NCV), temperature is the most important. Because the influence of temperature is the most important source of error. It is known from animal experiments that conduction is eventually completely blocked at low temperatures, the myelinated A fibers being the first affected and the thin fibers of group C the last. Many studies showed that the NCV decreases linearly with lowering temperature within the physiological range. The distal motor latency increased by $0.2msec/^{\circ}C$ drop in temperature between $25^{\circ}C$and $35^{\circ}C$ in the median, ulnar and peroneal nerves. The temperature affect the neuromuscular transmission; The miniature endplate potential (MEPP) and endplate potential (EPP) are increase with increasing temperature. In myasthenia gravis, the reduction in the decremental response is observed following cooling. The lowering temperature make increase the amplitude of sensory compound action potential; make enlarge the surface area of compound muscle action potential with very little increase in amplitude; make diminish the fibrillation potential and increase the myotonia in needle electromyography (EMG). Because of these findings mentioned above, the skin temperature should be routinely monitored and controlled during nerve conduction tests and needle EMG and should be taken into account when interpreting the findings.