• 한국농림기상학회지
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• 제5권3호
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• pp.191-199
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• 2003

Optimum transplanting time for extremely early rice cultivation as an after-crop of fruit and vegetables under greenhouse conditions in the southern area was determined. Rice was transplanted on March 10, March 20, March 30, April 10 and April 20 far three years from 1998 to 2000. Meteorological computations for rice production were high for heading between early May and early July, but they were too low for heading between late July and early August. Especially the expected yield predicted with 35,000 spikelets, the average spikelets per $m^2$ for extremely early transplanting. Computation for heading between late July and early August was low by 106 kg/10a compared with that yield at heading during the same period in the field. As the transplanting date in extremely early rice cultivation was earlier) rice growth at early stages was more retarded by low temperature. Rice growth at heading stage recovered with high temperature, showing less difference for the transplanting date. Abnormal tillers occurred by 15.5∼22.2%. The contribution of 1,000 grain weight${\times}$ripened grain ratio to yield of the extremely early rice cultivation in the greenhouse was 50.6%, indicating 16% hi일or than the degree of panicle per $m^2$ on yield. The estimated optimum transplanting time on the basis of yield for the extremely early greenhouse rice cultivation ranged from March 19 to April 28, and the estimated critical transplanting date on the basis of accumulated effective temperature was March 12. Rice reduced the amount of NO$_3$-N by 97.1% and EC by 90.5% in greenhouse soil with continuous fruit/vegetables fer more than a 10-year period, and completely removed the root-knot nematodes.

• 한국재료학회지
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• 제17권1호
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• pp.37-42
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• 2007

The effects of immersion time in the liquid nitrogen and deformation-induced martensitic transformation on the behavior of austenite stainless steels used for the hydrogen storage tank of auto-mobile at cryogenic temperature were investigated. With increasing of immersion time in the liquid nitrogen, the tensile strength of all austenite stainless steels at cryogenic temperature was increased because the martensite transformation of unstable austenite. The restraint of crack generation ana transmission also increased the tensile strength by the active ${\alpha}'$ transformation. The elongation decreasing of 321 steel is not the mechanical deformation of austenite phase but the stress induced martensite phase during the tensile test.

• 제어로봇시스템학회논문지
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• 제12권12호
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• pp.1249-1255
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• 2006

This paper presents a constant power control logic for perfect starting a microtubine in vehicle. Under extremely low temperature, performance of the start-up system is severely dropped than that of room temperature because of increasing of load of mechanical parts including engine core and drop of the lead-acid battery capacity. Unfortunately, performance drop of lead-acid battery makes severe problems that cause a malfunction of fuel and lubrication system and power fail of digital devices. So we propose the new start-up logic by constant output power control of lead-acid battery using PWM inverter controller for preventing above problems and keeping good performance of start-up system for microturbine. Also, we prove usefulness of new start-up logic through experimental results under $-32^{\circ}C$ ambient temperature.

• 한국재료학회지
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• 제17권4호
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• pp.192-197
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• 2007

The effects of immersion time in the liquid nitrogen on the behavior of aluminum alloys used for the hydrogen storage tank of auto-mobile at cryogenic temperature were investigated. With increasing immersion time in the liquid nitrogen, the elongation of AI 5083 alloy at cryogenic temperature decreased because of non-uniform fracture of precipitates on the grain boundary, and the serration also occurred because of discontinuous slip due to rapid decreasing of the specific heat. The mechanical properties of AI 6061 alloy at cryogenic temperature were characterized by uniformed yield strength, tensile strength and elongation regardless of the immersion time in the liquid nitrogen. These mechanical properties of aluminum alloys at cryogenic temperature were interpreted by the strength of grain boundary and the slip deformation behavior.

• Tribology and Lubricants
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• 제31권1호
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• pp.28-34
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• 2015

This paper addresses the problems of using anti-freeze lubricants for different machines that must function at extremely low temperatures during winter operation in the Republic of Sakha (Yakutia). We discuss the possibility of obtaining anti-freeze base oils from Talakan crude oil, an area with major oil and gas deposits of the Republic of Sakha, and also provide the trade and technological classification of Talakan crude oil. We propose two different schemes for processing Talakan crude oil: the fuel scheme (obtaining light and heavy fractions as a fuel oil) and the base oil scheme (obtaining light fractions and base oils). We investigate the influence of pour point depressants on alkyl-methacrylate base on the low-temperature properties of the fractions obtained from Talakan crude oil and Korean base oils, and establish the optimal concentration of pour point depressants. We compare the properties of these fractions with the low-temperature properties of Korean base oils and find that the commercial oil "Ravenol 0W-40" provides optimistic results. We obtain oil with a pour point of minus $50^{\circ}C$ and a viscosity index greater than 100. The Design of Experiment was used to establish the optimum composition of the pour point depressants and the base oil S-8 to obtain lubricant oil with a kinematic viscosity of 17 cSt, viscosity index of 208, and a pour point of minus $64^{\circ}C$.

• 전기전자학회논문지
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• 제17권1호
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• pp.63-70
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• 2013

본 연구에서는 차량용 연료히터의 전기적 성능검사 챔버를 구현한다. 겨울철 저온환경의 영향을 받는 디젤 엔진이 냉각될 경우 일정한 온도 이하로 내려가면 파라핀과 같은 반고체 상태인 왁싱(Waxing)물질을 형성하여 엔진 시동이 잘 걸리지 않게 하는 원인이 된다. 히터내에 센서를 안착시켜 통합한 일체형 통합히터는 시동성 평가에 중요한 요소이며, 성능평가 시험 챔버 시스템을 통해 전기적인 특성을 시험한다. 최근 CRDI(커먼레일) 엔진을 주로 사용함에 따라 연료히터로 디젤오일을 가열하여 점화성능을 향상시키기 위한 연료히터 성능시험은 엔진의 시동성을 향상시키는 중요한 요소이다. 따라서 연료히터의 전기적 성능시험 검사항목은 상온, 극저온, 극고온에서 동작검사, 시험저항 설정에 따른 저항동작 지연시간 및 전류동작 지연시간, 온도변화에 따른 바이메탈 지연시간 검사, 블록히터의 전류 및 저항 검사, 히팅 운전검사 등을 수행하도록 설계한다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 하계학술대회 논문집 Vol.5 No.1
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• pp.63-66
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• 2004

The extraordinary intrinsic properties of SiC have made this material a suitable choice to use in high temperature, high frequency, and high voltage applications. In additional to these, SiC could be employed as the based material for nonvolatile memory applications, mainly due to its extremely low thermal-generation rate at room temperature. In this paper, the reasons of using this material in this particular application is presented and the development of the application over the past fifteen years is reviewed.

• 한국염색가공학회지
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• 제24권2호
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• pp.113-120
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• 2012

Jacquard floor covering could be prepared from low-melting/regular sheath-core hybrid polyester, where the fiber is dyed in yarn state. With regard that the expected high shrinkage of the hybrid polyester in water makes problems in yarn dyeing, low-temperature dyeing properties of the hybrid polyester were studied. The rate of shrinkage of low-melting hybrid polyester exceeds 9% in hot water above $90^{\circ}C$, at such condition, cheese yarn dyeing is very difficult. Although disperse dyes exhaust in a relatively high speed on low-melting hybrid polyester, diffusion of these dyes to the core regular polyester was extremely slow under $90^{\circ}C$. Foron Blue E-BL 150, an anthraquinone E-type disperse dye, showed appreciable diffusion after 48hrs dyeing at $90^{\circ}C$. The fastness to rubbing and drycleaning were improved by one grade after reduction cleaning.

• 한국세라믹학회지
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• 제50권3호
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• pp.226-230
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• 2013

We performed high pressure high temperature (HPHT) sintering for the 20 nm MgO powders at the temperatures from $600^{\circ}C$ to $1200^{\circ}C$ for only 5 min under 7 GPa pressure condition. To investigate the microstructure evolution and physical property change of the HPHT sintered MgO samples, we employed a scanning electron microscopy (SEM), density and Vickers hardness measurements. The SEM results showed that the grain size of the sintered MgO increased from 200 nm to $1.9{\mu}m$ as the sintering temperature increased. The density results showed that the sintered MgO achieved a more than 95% of the theoretical density in overall sintering temperature range. Based on Vickers hardness test, we confirmed that hardness increased as temperature increased. Our results implied that we might obtain the dense sintered MgO samples with an extremely short time and low temperature HPHT process compared to conventional electrical furnace sintering process.

• Journal of Magnetics
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• 제22권2호
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• pp.326-332
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• 2017

The effects of exposure to an extremely low-frequency magnetic field (25 Hz 20G) on animal cells have been studied. In some reports, stimulation was performed for fixed frequency and variations in magnitude; however, animal-cell experiments have established that both parameters play an important role. The present work undertook the modeling, simulation, and development of a uniform-magnetic-field generation system with variable frequency and stimulation intensity (0-60 Hz, 1-25G) for experimentation with cell cultures in situ. The results showed a coefficient of variation less than 1 % of the magnetic-field dispersion at the working volume, which is consistent with the corresponding simulation results demonstrating a uniform magnetic field. On the other hand, long-term tests during the characterization process indicated that increments of only $0.4^{\circ}C$ in the working volume temperature will not be an interfering factor when experiments are carried out in in situ cell cultures.