• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.39.1-39.1
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• 2013

We use high-resolution hydrodynamic simulations to study nonlinear gas responses to imposed non-axisymmetric stellar potentials in barred-spiral galaxies. The gas is assumed to be infinitesimally thin, isothermal, and unmagnetized. We consider various spiral-arm models with differing strength and pattern speed, while fixing the bar parameters. We find that the extent and shapes of spiral shocks as well as the related mass drift depend rather sensitively on the pattern speed. In models where the arm pattern is rotating more slowly than the bar, the gaseous arms extend from the bar ends all the way to the outer boundary, with a pitch angle slightly smaller than that of the stellar counterpart. The arms drive mass inflows at a rate of ${\sim}0.5-2.5M{\odot}/yr$ to the bar region to which the shock dissipation, external torque, and self-gravitational torque contribute about 50%, 40%, and 10%, respectively. About 85% of the inflowing mass is added to bar substructures such as an inner ring, dust lanes, and a nuclear ring. while the remaining 15% encircles the bar region. On the other hand, models where the arms corotate with the bar exhibit mass outflows, rather than inflows, over most of the arm region. In these models, spiral shocks are much more tightly wound than the stellar arms and cease to exist in the region where $M{\bot}/sinp*{\geq}25-40$, where $M{\bot}$ denotes the Mach number of a rotating gas perpendicular to the arms with pitch angle p*. We demonstrate that the distributions of line-of-sight velocities and densities can be a useful diagnostic tool to distinguish if the arms and bar corotate or not.

• Journal of Environmental Health Sciences
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• v.34 no.1
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• pp.42-48
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• 2008

The objectives of this study were to measure ambient TGM concentrations in Seoul Korea, to determine the temporal variation of TGM, and to analyze the relationships among TGM, meteorological data and PM2.5 measured at the same time. Ambient TGM and PM2.5 concentrations were measured at the roof of the Graduate School of Public Health building in Seoul, Korea for the period of January to October 2004. Average TGM concentration was $3.43{\pm}1.17ng/m^3$. The average TGM was at a low concentration similar to those of background sites in other countries. The temporal variations and meteorological phenomena of TGM were not statistically significant. There was a positive link between TGM and PM2.5. It didn't indicate that reduction of $Hg^{2+}$ to Hg0 had occurred in liquid water contained in smog as in a previous study, but it shows that PM2.5 and TGM could be emitted from the same sources such as power plants and combustion engines. Also, the strong correlation between TGM and $SO_2$ concentrations indicated that the source of TGM was from fossil fuel combustions including coal combustion. Specifically, $SO_2\;and\;SO_4{^2-}$ concentrations correlated to TGM concentrations could be linked to TGM emitted from local and regional sources as well.

• Journal of Environmental Health Sciences
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• v.36 no.1
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• pp.33-43
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• 2010

Atmospheric ammonia is a very important constituent of the environment because it is the dominant alkaline gaseous species present in the atmosphere. Ammonia is known to affect ecosystems at relatively low concentration. In this study flux profiles of ammonia emitted from the cattle housing were evaluated using a dynamic flux chamber (DFC). We have developed the emission factor of $NH_3$ from the cattle housing. Analysis of ammonia flux variation was made with respect to such variables as manure surface temperature, pH, and ammonium concentration. Ammonia flux has been measured up to summer in 2007 at calf and cattle housing. In the fall, average ammonia flux from calf and cattle housing was estimated as 1.406 (${\pm}0.947$) and 1.534 ((${\pm}0.956$) $mg\;m^2\;min^1$, respectively. In the winter, average ammonia flux was estimated 1.060 ((${\pm}0.569$) from the calf housing and 1.216 ((${\pm}0.655$) $mg\;m^2\;min^1$ from the cattle housing. The correlation coefficient (R=0.732) between ammonia flux and manure surface ammonium concentration exhibited stronger relationship than manure surface pH and temperature. In the fall, ammonia emission factor from calf and cattle housing was estimated as 3.94 ((${\pm}2.66$) and 11.41 ((${\pm}5.86$) kg-$NH_3$ animal$^1\;yr^1$, respectively. In the winter, ammonia average flux was estimated as 2.89 ((${\pm}1.59$) from the calf housing and 6.51 ((${\pm}3.67$) kg-$NH_3$ animal$^1\;yr^1$ from the cattle housing.

• Journal of Environmental Health Sciences
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• v.46 no.5
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• pp.555-564
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• 2020

Objectives: To identify and investigate through qualitative and quantitative analysis the hazardous substances generated when compressed wood was burned at a live fire-training center. Methods: Four types of compressed wood that are actually used in live fire training were burned in a chamber according to KS F2271. The gaseous material was sampled with a gas detector tube and conventional personal samplers. Results: 1,3-butadiene, benzene, toluene, xylene, formaldehyde, hydrogen chloride, hydrogen cyanide, ammonia, carbon monoxide, and nitric acid were detected. In particular, 1,3-butadiene (497.04-680.44 ppm), benzene (97.79-125.02 ppm), formaldehyde (1.72-13.03 ppm), hydrogen chloride (4.71-15.66 ppm), hydrogen cyanide (3.64-8.57 ppm), and sulfuric acid (3.85-5.01 ppm) exceeded the Korean Occupational Exposure Limit as measured by sampling pump according to the type of compressed wood. Conclusions: We found through the chamber testing that firefighters could be exposed to toxic substances during live fire training. Therefore, firefighter protection is needed and more research is required in the field.

• Asian-Australasian Journal of Animal Sciences
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• v.30 no.2
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• pp.275-283
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• 2017

Objective: An experiment was conducted to investigate the environment of the deep litter system and provided theoretical basis for production. Methods: The bedding samples were obtained from a pig breeding farm and series measurements associated with gases concentrations and the bacterial diversity as well as the quantity of Escherichia coli, Lactobacilli, Methanogens were performed in this paper. Results: The concentrations of $CO_2$, $CH_4$, and $NH_3$ in the deep litter system increased with the increasing of depth while the $N_2O$ concentrations increased fiercely from the 0 cm to the -10 cm depth but then decreased beneath the -10 cm depth. Meanwhile, the Shannon index, the dominance index as well as the evenness index at the -20 cm layer was significantly different from the other layers (p<0.05). On the other hand, the quantity of Escherichia coli reached the highest value at the surface beddings and there was a significant drop at the -20 cm layer with the increasing depth. The Lactobacilli numbers increased with the depth from 0 cm to -15 cm and then decreased significantly under the -20 cm depth. The expression of Methanogens reached its largest value at the depth of -35 cm. Conclusion: The upper layers (0 cm to -5 cm) of this system were aerobic, the middle layers (-10 cm to -20 cm) were micro-aerobic, while that the bottom layers (below -20 cm depth) were anaerobic. In addition, from a standpoint of increasing the nitrification pathway and inhibiting the denitrification pathway, it should be advised that the deep litter system should be kept aerobic.

• Bulletin of the Korean Chemical Society
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• v.23 no.2
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• pp.205-214
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• 2002

The reaction of gas-phase atomic hydrogen with hydrogen atoms chemisorbed on a silicon surface is studied by use of the classical trajectory approach. Especially, we have focused on the mechanism changes with the hydrogen surface coverage difference. On the sparsely covered surface, the gas atom interacts with the preadsorbed hydrogen atom and adjacent bare surface sites. In this case, it is shown that the chemisorption of H(g) is of major importance. Nearly all of the chemisorption events accompany the desorption of H(ad), i.e., adisplacement reaction. Although much less important than the displacement reaction, the formation of $H_2(g)$ is the second most significant reaction pathway. At gas temperature of 1800 K and surface temperature of 300 K, the probabilities of these two reactions are 0.750 and 0.065, respectively. The adsorption of H(g) without dissociating H(ad) is found to be negligible. In the reaction pathway forming $H_2$, most of the reaction energy is carried by $H_2(g)$. Although the majority of $H_2(g)$ molecules are produced in sub-picosecond, direct-mode collisions, there is a small amount of $H_2(g)$ produced in multiple impact collisions, which is characteristic of complex-mode collisions. On the fully covered surface, it has been shown that the formation of $H_2(g)$ is of major importance. All reactive events occur on a subpicosecond scale, following the Eley-Rideal mechanism. At gas temperature of 1800 K and surface temperature of 300 K, the probability of the $H_2(g)$ formation reaction is 0.082. In this case, neither the gas atom trapping nor the displacement reaction has been found.

• Bulletin of the Korean Chemical Society
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• v.23 no.2
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• pp.225-228
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• 2002

Amorphous $Ga_2O_3$ films have been grown on Si(100) substrates by metal organic chemical vapor deposition (MOCVD) using gallium isopropoxide, $Ga(O^iPr)_3$, as single precursor. Deposition was carried out in the substrate temperature range 400-800 $^{\circ}C$. X-ray photoelectron spectroscopy (XPS) analysis revealed deposition of stoichiometric $Ga_2O_3$ thin films at 500-600 $^{\circ}C$. XPS depth profiling by $Ar^+$ ion sputtering indicated that carbon contamination exists mostly in the surface region with less than 3.5% content in the film. Microscopic images of the films by scanning electron microscopy (SEM) and atomic force microscopy (AFM) showed formation of grains of approximately 20-40 nm in size on the film surfaces. The root-mean-square surface roughness from an AFM image was ${\sim}10{\AA}$. The interfacial layer of the $Ga_2O_3$/Si was measured to be ${\sim}35{\AA}$ thick by cross-sectional transmission electron microscopy (TEM). From the analysis of gaseous products of the CVD reaction by gas chromatography-mass spectrometry (GC-MS), an effort was made to explain the CVD mechanism.

• Transactions of the Korean hydrogen and new energy society
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• v.21 no.6
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• pp.587-594
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• 2010

Hydrogen is an alternative fuel for the future energy which can reduce pollutants and greenhouse gases. Synthesis gas has played an important role of synthesizing the valuable chemical compounds, for example methanol, DME and GTL chemicals. Renewable biomass feedstocks can be potentially used for fuel and chemicals. Current thermal processing techniques such as fast pyrolysis, slow pyrolysis, and gasification tend to generate products with a large slate of compounds. Lignocellulose feedstocks such as forest residues are promising for the production of bio-oil and synthesis gas. Pyrolysis and gasification was investigated using thermogravimetric analyzer (TGA) and bubbling fluidized bed gasification reactor to utilize forest woody biomass. Most of the materials decomposed between $320^{\circ}C$ and $380^{\circ}C$ at heating rates of $5{\sim}20^{\circ}C$/min in thermogravimetric analysis. Bubbling fluidized bed reactor was used to study gasification characteristics, and the effects of reaction temperature, residence time and feedstocks on gas yields and selectivities were investigated. With increasing temperature from $750^{\circ}C$ to $850^{\circ}C$, the yield of char decreased, whereas the yield of gas increased. The gaseous products consisted of mostly CO, $CO_2$, $H_2$ and a small fraction of $C_1-C_4$ hydrocarbons.

• Transactions of the Korean hydrogen and new energy society
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• v.28 no.2
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• pp.174-180
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• 2017

Recently, the world faces the environmental problem such as air pollution due to harmful gas discharged from car and abnormal climate due to the green-house gases increased by the discharge of $CO_2$. Compressed Natural Gas (CNG), one of alternative for this problem, is less harmful, compared to the existing fossil fuel, as gaseous fuel, and less carbon in fuel ingredients and carbon dioxide generation rate relatively favorable more than the existing fuel. However, CNG fuel has the weakness of slow flame propagation speed and difficult fast burn. On the other hand, hydrogen does not include carbon in fuel ingredients, and does not discharge harmful gas such as CO and HC. Moreover, it has strength of quick burning velocity and ignition is possible with small ignition energy source and it's has wide Lean Flammability Limit. If using this hydrogen with CNG fuel, the characteristics of output and discharge gas is improved by the mixer's burning velocity improved, and, at the same time, is possible to have stable lean combustion with the reduction of $CO_2$ expected. Therefore, this research tries to identify the characteristics of engine and emission gas when mixing CNG fuel and hydrogen in each portion and burning them in spark igniting engine, and grasp the lean combustion limit and emission gas characteristics according and use it as the basic data of hydrogen-CNG premixed engine.

• Journal of Energy Engineering
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• v.19 no.3
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• pp.195-202
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• 2010

A third of primary energy is lost as a waste heat. To improve this inefficient use of energy, systems using chemical reaction have been suggested and studied. In this study, methanol decomposition/synthesis reaction as a chemical reaction was selected for long time heat storage and long distance heat transport system because of safe, cheap and gaseous product. The purpose of this study is to find the optimal conditions in the methanol decomposition and synthesis reactions for long distance heat transport. Several parameters such as reaction temperature, pressure, $H_2$/CO ratio, space velocity, catalyst particle size were tested to find the effects on the reaction rates for the methanol synthesis. And the reaction temperature, space velocity, catalyst particle size were tested to find the effects on the production concentration for the methanol decomposition.