• Advances in concrete construction
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• 제5권1호
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• pp.17-29
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• 2017

Geopolymer concrete is environmentally friendly and could be considered as a construction material to promote the sustainable development. In this paper fly ash based geopolymer concretes with different percentages of alccofine were made by mixing sodium hydroxide and sodium silicate as an alkaline activator and cured at ambient as well as heat environment in an electric oven at $90^{\circ}C$. Effects of various parameters such as the percentage of alccofine, curing temperature, a period of curing, fly ash content, was studied on compressive strength as well as workability of geopolymer concrete. The study concludes that the presence of alccofine improves the properties of geopolymer concrete during a fresh and hardened state of concrete. Geopolymer concrete in the presence of alccofine can be used for the general purpose of concrete as required compressive strength can be achieved even at ambient temperature. The 28 days compressive strength of 73 MPa, when cured at 90-degree Celsius, confirmed that it is also very suitable for precast concrete components.

• Journal of Astronomy and Space Sciences
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• 제33권4호
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• pp.265-271
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• 2016

Interplanetary scintillation-driven (IPS-driven) ENLIL model was jointly developed by University of California, San Diego (UCSD) and National Aeronaucics and Space Administration/Goddard Space Flight Center (NASA/GSFC). The model has been in operation by Korean Space Weather Cetner (KSWC) since 2014. IPS-driven ENLIL model has a variety of ambient solar wind parameters and the results of the model depend on the combination of these parameters. We have conducted researches to determine the best combination of parameters to improve the performance of the IPS-driven ENLIL model. The model results with input of 1,440 combinations of parameters are compared with the Advanced Composition Explorer (ACE) observation data. In this way, the top 10 parameter sets showing best performance were determined. Finally, the characteristics of the parameter sets were analyzed and application of the results to IPS-driven ENLIL model was discussed.

• 원예과학기술지
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• 제32권3호
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• pp.318-329
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• 2014

본 연구는 온도구배터널에서 자라는 배추의 잎에서 광합성적 $CO_2$ 교환과 엽록소형광을 분석함으로써 배추의 생장에 미치는 고온의 영향을 정량적으로 분석하였다. 결구가 형성되기 전의 생육초기에는 대기온도보다 대기온도 $+4^{\circ}C$와 대기온도 $+7^{\circ}C$ 조건에서 생장한 배추가 엽수의 증가와 엽길이의 신장이 두드러지게 나타났다. $CO_2$ 고정률은 대기온도 $+4^{\circ}C$에서 자란 배추의 잎에서 $25.8{\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$로 다소 높았으나, 생육 온도에 따라 통계적으로 유의한 차이는 없었다. 반면에 호흡률은 대기온도에서 다소 높았으며 대기온도 $+4^{\circ}C$와 대기온도 $+7^{\circ}C$ 조건에서는 낮았다. 기공전도도와 증산률은 대기온도에서보다 대기온도 $+4^{\circ}C$와 대기온도 $+7^{\circ}C$ 조건에서 증가하고 수분이용효율은 감소하였다. 그리고, OKJIP 곡선의 패턴에서도 상승온도에서 $F_J$, $F_I$, $F_P$가 크게 낮아지고, 고온에서 특이적으로 나타나는 $F_K$의 증가와 $F_V/F_O$값의 감소 등을 확인할 수 있었다. RC/CS는 대조구에 비해 온도가 높아지면 크게 감소하였으며, ABS/CS, TRo/CS와 ETo/CS도 온도가 높아짐에 따라 점차 줄어들었다. 이에 반해 DIo/CS는 온도가 높아짐에 따라 증가하였다. 그리고 대조구인 대기온도에서는 정식 후 7주, 9주, 10주째에 수확한 배추 내부에서 병징이 나타나지 않았으나, 대기온도 $+4^{\circ}C$와 대기온도 $+7^{\circ}C$ 조건에서는 재배기간이 길어질수록 점차 무름병에 의한 피해가 두드러지게 나타났다. 이러한 결과는 급격하게 변화하는 미래의 기후 환경 하에서 배추가 고온 스트레스에 노출될 가능성을 암시하고 있다. 따라서 배추의 안정적인 생산을 위해서는 고온 적응성 품종, 특히 결구 시점에서 내고온성이 강한 품종을 육성하거나 고온의 피해를 최소화할 수 있는 재배기술이 확립되어야 할 것으로 보인다. 그리고 결구형성 시 고온 스트레스의 영향을 조기감별하기 위해서 OKJIP 곡선에서 $F_K$의 증가를 비롯하여 기존에 사용되고 있는 변수인 $F_O$, $F_V/F_M$와 $F_V/F_O$ 이외에도 $M_O$, $S_M$, RC/CS, ETo/CS, $PI_{abs}$, $SFI_{abs}$ 등의 형광변수들이 유용하게 활용될 수 있을 것으로 보인다.

• 한국생산제조학회지
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• 제21권2호
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• pp.337-343
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• 2012

This work investigates the vibrational characteristics of the underground gas pipelines. Experiments were conducted to analyze the effects of various parameters on the vibrational characteristics from the emergency detection point of view. Influences of the various types of impact exerted on the pipe, height of free fall and measuring locations were analyzed. Especially, the difference between the vibrational signal generated by the direct impact on the pipe and the ambient noise was successfully identified. To validate the experimental observation, computer simulation was also performed with constant properties(elasticity, fluid velocity and internal pressure) which are directly conjectured from the accompanying experiment with a real pipe system.

• Smart Structures and Systems
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• 제11권1호
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• pp.123-134
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• 2013

Identifying structural modal parameters, especially those modes within high frequency range, from ambient data is still a challenging problem due to various kinds of uncertainty involved in vibration measurements. A procedure applying an ensemble empirical mode decomposition (EEMD) method is proposed for accurate and robust structural modal identification. In the proposed method, the EEMD process is first implemented to decompose the original ambient data to a set of intrinsic mode functions (IMFs), which are zero-mean time series with energy in narrow frequency bands. Subsequently, a Sub-PolyMAX method is performed in narrow frequency bands by using IMFs as primary data for structural modal identification. The merit of the proposed method is that it performs structural identification in narrow frequency bands (take IMFs as primary data), unlike the traditional method in the whole frequency space (take original measurements as primary data), thus it produces more accurate identification results. A numerical example and a multiple-span continuous steel bridge have been investigated to verify the effectiveness of the proposed method.

• 한국대기환경학회지
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• 제2권3호
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• pp.45-51
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• 1986

The simple and precise model for the estimation of rain acidity from the ambient air quality was developed using the theory of wet scrubber and the chemical equilibria of $SO_2, CO_2, and H_2O$ system. From the measured mixing height, and from the developed relationship between NTU (=number of transfer units) and the concentration of $SO_2$(aq) in rain drops, the HTU (= height equivalent to one transfer unit, i.e. mass transfer resistance) was estimated, and validated with the field-measured data. In Seoul, Korea where the effect of $SO_2$ on rainfall acidity is as high as 84% and the average mixing height is 1 km, the average HTU of $SO_2$ system was found to be 191.5m. The important parameters affecting HTU were identified as rainfall intensity and initial ambient concentration of $SO_2$, and their effects on the value of overall volumetric mass transfer coefficient were quantified.

• IEIE Transactions on Smart Processing and Computing
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• 제3권4호
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• pp.246-250
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• 2014

Large mutual capacitance touch screen panels (TSP) are susceptible to display and ambient noise. This paper presents a multi-touch detection algorithm using an efficient noise compensation technique for large mutual capacitance TSPs. The sources of noise are presented and analyzed. The algorithm includes the steps to overcome each source of noise. The algorithm begins with a calibration technique to overcome the TSP mutual capacitance variation. The algorithm also overcomes the shadow effect of a hand close to TSP and mutual capacitance variation by dynamic threshold calculations. Time and space filters are also used to filter out ambient noise. The experimental results were used to determine the system parameters to achieve the best performance.

• Earthquakes and Structures
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• 제7권6호
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• pp.1093-1118
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• 2014

A sophisticated story-wise stiffness identification method for a shear building structure is applied to the case where the shear building is subjected to an actual micro-tremor. While the building responses to earthquake ground motions are necessary in the previous method, it is shown that micro-tremors can be used for identification within the same framework. This enhances the extended usability and practicality of the previously proposed identification method. The difficulty arising in the limit manipulation at zero frequency in the previous method is overcome by introducing an ARX model. The weakness of small SN ratios in the low frequency range is avoided by using the ARX model together with filtering and introducing new constraints on the ARX parameters.

• 한국연소학회지
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• 제5권1호
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• pp.81-89
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• 2000

An experimental study has been carried on single fuel droplets of water-in-light oil emulsions in an electric furnace to elucidate the dominant factor for the occurrence of micro-explosions. The tests were carried out by changing the following four parameters; the surfactant, the ratio of water to light oil, ambient temperature in electric furnace, and four kinds of fuels having different viscosity(light-oil, kerosene, iso-octane, bunker fuel). The result shows that micro-explosion phenomena is dominated without surfactant and below 30% of water content. Explosion-time is affected by ambient temperature and viscosity of used fuel.

• 전기학회논문지P
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• 제55권4호
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• pp.190-195
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• 2006

In this paper, safety algorithm of transformer is introduced for the sake of MV/LV distribution customers by using fuzzy theory. The current-carrying capacity of transformer is usually determined by the maximum temperature at which the transformer is permitted to operate. Overload of transformer has an effect on transformer utilization rate and maximum temperature rises as well as maximum ambient temperature of insulating materials. Therefore, we proposed the safety algorithm considering the overload of transformer and ambient temperature in this paper. We introduced the correlational equations between each parameters using experimental data of IEEE std C57.91-1995, and deduced the result using fuzzy reasoning. We guessed the safety algorithm making a diagnosis for the safety status of oil-immersed transformer.