• Journal of the Korean Solar Energy Society
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• v.29 no.1
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• pp.44-49
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• 2009

Steam reforming of methane in the high temperature solar chemical reactor bas advantage in its heating method. Using concentrated solar energy as a heating source of the reforming reaction can reduce the $CO_2$ emission by 20% compared to hydrocarbon fuel. In this paper, the simulation result of methane-steam reforming on a high temperature solar chemical reactor(SCR) using Fluent 6.3.26 is presented. The high temperature SCR is designed for the Inha Dish-1, a Dish type solar concentrator installed in Songdo city. Basic SCR performance factors are referred to the former researches of the same laboratory. Inside the SCR porous metal is used for a receiver/reactor. The porous metal is carved like a dome shape on the incident side to increase the heat transfer. Also, ring-disc set of baffle is inserted in the porous metal region to increase the path length. Numerical and physical models are also used from the former researches. Methane and steam is mixed with the same mole fraction and injected into the SCR. The simulation is performed for a various inlet mass flow rate of the methane-steam mixture gas. The result shows that the average reactor temperature and the conversion rate change appreciably by the inlet mass flow rate of 0.0005 kg/s.

• The Korean Journal of Physiology
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• v.14 no.2
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• pp.21-28
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• 1980

In order to investigate the effect of cholinergic substance on the electrical and the mechanical activities of the stomach muscle, 10 isolated cat stomachs were studied. At various sites of a stomach muscle preparation, the electrical activity was monopolarly recorded by using capillary electrodes containing chlorided silver wires, and the isometric contractile activity was recorded simultaneously at the terminal portion of the antrum in Krebs solution$(36^{\circ}C)$ which was aerated with a gas mixture consisting of 95% $O_2$ and 5% $CO_2$. The recording of these activities were performed before (control period) and after acetylcholine$(10^{-5}M)$ and atropine $(10^{-6}M)$ administrations serially. Following results were obtained: 1) The mean frequency of the slow wave was $4.36{\pm}0.22\;cycles/min$ at all the various sites of the cat stomach. The slow wave was propagated caudad in sequence and its velosity of propagation increased as the slow wave approached the pylorus in normal Krebs solution. 2) After acetylcholine administration, the frequency of the slow wave increased transiently and the increase of slow wave frequency was followed by the isometric contraction of antral muscle in association with the second potential which succeeded the slow wave. 3) By atropine administration, the stimulatory effect of acetylcholine on the antral muscle contraction was abolished completely, and the frequency of the slow wave decreased significantly compared with that of the control period, which tendency was more prominent in the antrum. The above results suggest that the transient increase in the frequency of gastric slow wave by acetylcholine may have some influence upon the contraction mechanism of the cat antral muscle.

• Korean Journal of Weed Science
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• v.14 no.2
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• pp.156-162
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• 1994

To better understand the exact nature of the major toxic compound responsible for phytotoxicity of sorghum stem, the most toxic compound from the stem extract was isolated by rapid chromatography and subsequently purified by thin-layer chromatography(TLC) and high pressure liquid chromatography(HPLC). Of the eight fractions isolated by rapid chromatography, the fraction with solvent combinations of butanol (8) : acetic acid (1) : water (1) had the highest toxicity. Further separation of the fraction by TLC in a solvent mixture of butanol (24) : acetic acid (16.4) : water (7) : propanol (1) showed that the spot with an $R_f$ 0.71 had one major peak with retention time of 20.40 minutes. Upon subjecting gas chromatography and the HPLC fraction to the mass spectrometry, the toxic compound is probably one of the four compounds ; 1-methyl-1-(2-propynyl)-hydrazine, 1-aziridineethanol, 5-chloro-2-pentanone, and 2-(methylseleno)-ethanamine.

• KSBB Journal
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• v.26 no.5
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• pp.471-476
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• 2011

Nowadays biodiesel (fatty acid methyl ester, FAME) has been becoming an important issue as a desired alternative of energy products because of non-toxic, biodegradable properties, and lower exhaust emissions. During esterification of fatty acids or transesterification of oils and fats with short chain alcohols by the alkali-catalyzed methanolysis, FAME and unrefined glycerol are generated. Quantification of glycerol as a by-product is important because of a determinant of biodiesel quality. However, the glycerol analysis by gas chromatography (GC) method has laborious works with sample preparation, long time and cost of sample analysis. Thus, there is a need to analyze glycerol more simply. Herein we demonstrate that the colorimetric assay for glycerol analysis conducted by UV-vis spectrophotometer at the wavelength 617 nm whose peak is maximum intensity of malachite green, resulting in the red-shift occurred proportionally as a function of glycerol amount. Thus, it is considered the solvent media for malachite green fading for biodiesel production: (1) water, (2) MeOH, and (3) EtOH. The resulting findings show that the peak intensity at 617 nm in glycerol-malachite green mixture had a relationship between glycerol concentration and degree of peak shift as increase in pure glycerol concentration approximately at pH 7.0. However, when it was measured the unrefined glycerol concentration by diluting and adjusting with water to buffer (pH 7.0), it was not observed the absorption peak at 617 nm because of impurities and OH ions. In case of glycerol from biodiesel production factories, glycerol concentration could be successfully measured.

• Journal of Life Science
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• v.16 no.1
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• pp.1-5
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• 2006

This study investigated the optimal conditions of high yield production of cyclofructan (CF) using recombinant deletion mutant enzyme CFT108 which is constructed by N-terminal deletion from cycloinulooligosaccharide fructanotransferase (CFTase) gene of Penibacillus polymyxa. The production yield was dependent on reaction time, substrate concentration and enzyme concentration. The optimum reaction time for industrial purpose was achieved at 3 hr reaction. The optimal concentrations of substrate and enzyme were found to be $2\%$ inulin and 40 unit/ g inulin, respectively. At optimum condition, 9.5 g/l of maximum yield and $47.5\%$ of conversion efficacy were achieved. For purification of CF produced, the reaction mixture was treated with 1 unit/ml exoinulinase and then added $3\%$ CaO three times with blowing $CO_2$ gas, resulted in $95\%$ purity.

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.7 no.1
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• pp.21-29
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• 1993

In this paper, we studied the 50% flashover voltage of lightening impulse which affect the most serious damages on the insulation of the electric power network system. Also its V -t characteristics and corona process phenomena of pure $SF_6, N_2, SF_6-N_2$mixtures under the circumstances of nonuniform field gap are researched. Comparing the characteristics of pure $SF_6$ with that of $SF_6, N_2$mixtures, we discussed that breakdown processes and $SF_6, N_2$ mixture's application to economics.As a results, 50% flashover voltage of $SF_6$ 50% - $N_2$ 50% for impulse voltage is higher then that of 80% of pure SF6, measured data and calculated data by equal area law are almost equal from the points of view of V-t characteristics. Therefore, it has been known that $SF_6$ 50% - $N_2$ 50% mixtures can be used as an economic constitution gas of pure $SF_6$, it is verified that corona processes from Lichtenberg figure.

• Proceedings of the KIEE Conference
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• 2006.07c
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• pp.1438-1439
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• 2006

$Ge_{2}Sb_{2}Te_5$(GST) thin film at present is a promising candidate for a phase change random access memory (PCRAM) based on the difference in resistivity between the crystalline and amorphous phase. PCRAM is an easy to manufacture, low cost storage technology with a high storage density. Therefore today several major chip in manufacturers are investigating this data storage technique. Recently, A. Pirovano et al. showed that PCRAM can be safely scaled down to the 65 nm technology node. G. T Jeonget al. suggested that physical limit of PRAM scaling will be around 10 nm node. Etching process of GST thin ra films below 100 nm range becomes more challenging. However, not much information is available in this area. In this work, we report on a parametric study of ICP etching of GST thin films in $Cl_2$/Ar chemistry. The etching characteristics of $Ge_{2}Sb_{2}Te_5$ thin films were investigated using an inductively coupled plasma (ICP) of $Cl_2$/Ar gas mixture. The etch rate of the GST films increased with increasing $Cl_2$ flow rate, source and bias powers, and pressure. The selectivity of GST over the $SiO_2$ films was higher than 10:1. X-ray photoelectron spectroscopy(XPS) was performed to examine the chemical species present in the etched surface of GST thin films. XPS results showed that the etch rate-determining element among the Ge, Sb, and Te was Te in the $Cl_2$/Ar plasma.

• Journal of the Korean Society of Combustion
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• v.18 no.2
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• pp.32-41
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• 2013

This study presents both experimental and numerical investigation of ignition delay time of n-heptane and n-butanol binary fuel. The $O_2$ concentration in the mixture was set to 9-10% to make high exhaust gas recirculation( EGR) rate condition which leads low NOx and soot emission. Experiments were performed using a rapid compression machine(RCM) at compressed pressure 20bar, several compressed temperature and three equivalence ratios(0.4, 1.0, 1.5). In addition, a numerical study on the ignition delay time was performed using CHEMKIN codes to validate experimental results and predict chemical species in the combustion process. The results showed that the ignition delay time increased with increasing the n-butanol fraction due to a decrease of oxidation of n-heptane at the low temperature. Moreover, all of the binary fuel mixtures showed the combustion characteristics of n-heptane such as cool flame mode at low temperature and negative-temperature-coefficient(NTC) behavior. Due to the effect of high EGR rate condition, the operating region is reduced at lean condition and the ignition delay time sharply increased compared with no EGR condition.

• International Journal of Automotive Technology
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• v.8 no.2
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• pp.137-147
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• 2007

Homogenous Charge Compression Ignition (HCCI) combustion systems can be broadly divided for the process applied to 4-stroke and 2-stroke engines. The former process is often referred to as simply HCCI combustion and the latter process as Active Thermo-Atmosphere Combustion (ATAC). The region of stable engine operation tends to differ greatly between the two processes. In this study, it was shown that the HCCI combustion process of a 4-stroke engine, characterized by the occurrence of autoignition under a high compression ratio, a lean mixture and wide open throttle operation, could be simulated by operating a 2-stroke engine at a higher compression ratio. On that basis, a comparison was made of the combustion characteristics of high-compression-ratio HCCI combustion and ATAC, characterized as autoignited combustion in the presence of a large quantity of residual gas at a low compression ratio and part throttle. The results showed that one major difference between these two combustion processes was their different degrees of susceptibility to the occurrence of cool flame reactions. Compared with high-compression-ratio HCCI combustion, the ignition timing of ATAC tended not to change in relation to different fuel octane numbers. Furthermore, when internal EGR was applied to high-compression-ratio HCCI combustion, it resulted in combustion characteristics resembling ATAC. Specifically, as the internal EGR rate was increased, the ignition timing showed less change in relation to changes in the octane number and the region of stable engine operation also approached that of ATAC.

• Resources Recycling
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• v.26 no.1
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• pp.16-21
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• 2017

This paper relates to the synthesis of a source powder for SiC crystal growth. ${\beta}-SiC$ powders are synthesized at high temperatures (>$1400^{\circ}C$) by a reaction between silicon powder and carbon powder. The reaction is carried out in a graphite crucible operating in a vacuum ambient (or Ar gas) over a period of time sufficient to cause the Si+C mixture to react and form poly-crystalline SiC powder. End-product characterizations are pursued with X-ray diffraction analysis, SEM/EDS, particle size analyzer and ICP-OES. The purity of the end-product was analyzed with the Korean Standard KS L 1612.