• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
• /
• v.4 no.4
• /
• pp.338-348
• /
• 1999

Physical properties of mudbelt sediments in the southeastern inner shelf of Korea are studied from 14 cores. Physical properties, compressional wave velocity, and sediment texture for core sediments are analyzed. The major source of sediment in the study area is the Nakdong River. Fine-grained sediments from the river are transported northeastward by coastal circulation and the Tsushima Current, resulting in a gradual northeastward increase in porosity and a decrease in wet bulk density and velocity. The trend matches well with the bathymetry. The mean grain size appears to be the most important variable to determine the physical properties and velocity. The variations of physical properties with burial depth are dependent more strongly on sediment texture than compaction and/or consolidation. Correlations between the physical properties and the sediment texture show slight deviations from those of the continental terrace sediment in the North Pacific and inner shelf sediment in the South Sea of Korea. The velocity is higher than that of the North Pacific and the South Sea sediments between these areas. This is probably due to differences in sedimentary, environment and mineral compositions. The higher sediment velocity in the study area may also be attributed to the escape of gas from pore space which decreases void ratio.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
• /
• v.5 no.4
• /
• pp.335-345
• /
• 2000

Physical and acoustic properties of the Southeastern Yellow Sea Mud (SEYSM) of Korea were studied by using 10 piston cores. The data were also compared with mudbelt sediments in the South Sea and the East Sea (southeastern inner shelf) of Korea. The sediments were mainly composed of homogeneous silt. Sandy mud and mud were minor components. The major source of sediment in the study area is probably the Keum River. Finegrained sediments discharged from the river are transported southward by coastal current, resulting in a gradual southward increase in porosity and a decrease in wet bulk density and sound velocity. The mean grain size especially appears to be the most important variable to determine the physical properties and velocity. The variations of physical properties with burial depth are dependent more strongly on sediment texture (especially, silt content) than compaction and/or consolidation. Correlations between the physical properties and the sediment texture show slight deviations from those of the East Sea and the South Sea of Korea in spite of similar pattern within the limiting values. This is probably due to the differences in silt contents, sedimentary environments, mineral compositions, and gas contents.

• Korean Journal of Crystallography
• /
• v.12 no.4
• /
• pp.197-206
• /
• 2001

A stoichiometric mixture of evaporating materials for AgInS₂ single crystal thin films was prepared from horizontal electric furnace. To obtain the single crystal thin films. AgInS₂ mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the Hot Wall Epitaxy(HWE)system. The source and substrate temperatures were 680℃ and 410℃, respectively. The crystalline structure of the single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction(DCXD). The carrier density and mobility of AgInS₂ single crystal thin film mea-sured from Hall effect by van der Pauw method are 9.35×10/sup 16/㎤ and 294㎠/V·s at 293K respectively. The temperature dependence of the energy band gap of the AgInS₂ obtained from the absorption spectra was well described by the Varshni's relation , E/sub g/(T)=2.1365eV-(9.89×10/sup-3/eV/K/)T²(T+2930K). The crystal field and the spin-orbit splitting energies for the valence band of the AgInS₂ have been estimated to be 0.1541eV and 0.0129 eV, respectively, by means of the photocur-rent spectra and the Hopfield quasicubic model. These results indicate that the splitting of the Δso definitely exists in the Γ/sub 5/ states of the valence band of the AgInS₂ /GaAs epilayer. The three photo-current peaks ovserved at 10K are ascribed to the A₁-, B-₁and C₁-exction peaks for n=1.

• Journal of the Korean Society for Marine Environment & Energy
• /
• v.6 no.2
• /
• pp.46-53
• /
• 2003

In order to analyze the movement characteristics of suspended solid(SS) in harbor construction, we investigate the generation and movement processes of the SS for the landfill construction by direct casting method and the grab dredging construction which is the most frequent process in harbor construction. We find that the SS is generated into a very high concentration right after the direct casting of landfill soil and continued up to 60 minutes in the landfill construction using the direct casting method with dredged materials by a ship of 700-tonnage. In the grab dredging construction, the SS is generated in a high density of concentration near at its source regardless of water depth, formed belt and diffused up to 700m along the trajectory of tidal current. Based on the result of the present study, it is recommended for the mitigation of SS generation that the silt protector be deployed near at construction site close enough to block the diffusion of SS and the body length of silt protector be long enough to mitigate the SS diffusion in the bottom layer.

• Journal of Aerospace System Engineering
• /
• v.17 no.6
• /
• pp.1-8
• /
• 2023

Research, such as developing alternative energy in the transportation field, including aviation, is being actively conducted to solve the issue of current climate change. Interest in ammonia fuel as a carbon free energy (CFE) source is increasing due to the ease of liquefaction and transportation and similarity in energy density to that of methanol. However, explosiveness and toxicity of ammonia make it difficult to handle. Therefore, in this study, stable ammonia production was attempted using relatively easy-to-handle urea water solution (UWS). High temperature steam was used to promote the hydrolysis of ammonia. In order to determine the causes for ammonia production below the theoretical equivalent ratio, it was suggested that there were not enough collisions to promote the hydrolysis based on the kinetic theory of gases. The hydrolysis of unreacted isocyanic acid (HNCO) was tested according to the change in water supply. As a result, an increased amount of ammonia produced was confirmed. The increased amount of ammonia produced in a certain section was dependent on the steam temperature and the flow rate of water supplied.

• Proceedings of the Materials Research Society of Korea Conference
• /
• 2011.05a
• /
• pp.5-5
• /
• 2011

The research and development of hybrid electric vehicle (HEV), plug-in hybrid electric vehicle (PHEV) and electric vehicle (EV) are intensified due to the energy crisis and environmental concerns. In order to meet the challenging requirements of powering HEV, PHEV and EV, the current lithium battery technology needs to be significantly improved in terms of the cost, safety, power and energy density, as well as the calendar and cycle life. One new technology being developed is the utilization of composite cathode by mixing two different types of insertion compounds [e.g., spinel $LiMn_2O_4$ and layered $LiMO_2$ (M=Ni, Co, and Mn)]. Recently, some studies on mixing two different types of cathode materials to make a composite cathode have been reported, which were aimed at reducing cost and improving self-discharge. Numata et al. reported that when stored in a sealed can together with electrolyte at $80^{\circ}C$ for 10 days, the concentrations of both HF and $Mn^{2+}$ were lower in the can containing $LiMn_2O_4$ blended with $LiNi_{0.8}Co_{0.2}O_2$ than that containing $LiMn_2O_4$ only. That reports clearly showed that this blending technique can prevent the decline in capacity caused by cycling or storage at elevated temperatures. However, not much work has been reported on the charge-discharge characteristics and related structural phase transitions for these composite cathodes. In this presentation, we will report our in situ x-ray diffraction studies on this mixed composite cathode material during charge-discharge cycling. The mixed cathodes were incorporated into in situ XRD cells with a Li foil anode, a Celgard separator, and a 1M $LiPF_6$ electrolyte in a 1 : 1 EC : DMC solvent (LP 30 from EM Industries, Inc.). For in situ XRD cell, Mylar windows were used as has been described in detail elsewhere. All of these in situ XRD spectra were collected on beam line X18A at National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory using two different detectors. One is a conventional scintillation detector with data collection at 0.02 degree in two theta angle for each step. The other is a wide angle position sensitive detector (PSD). The wavelengths used were 1.1950 ${\AA}$ for the scintillation detector and 0.9999 A for the PSD. The newly installed PSD at beam line X18A of NSLS can collect XRD patterns as short as a few minutes covering $90^{\circ}$ of two theta angles simultaneously with good signal to noise ratio. It significantly reduced the data collection time for each scan, giving us a great advantage in studying the phase transition in real time. The two theta angles of all the XRD spectra presented in this paper have been recalculated and converted to corresponding angles for ${\lambda}=1.54\;{\AA}$, which is the wavelength of conventional x-ray tube source with Cu-$k{\alpha}$ radiation, for easy comparison with data in other literatures. The structural changes of the composite cathode made by mixing spinel $LiMn_2O_4$ and layered $Li-Ni_{1/3}Co_{1/3}Mn_{1/3}O_2$ in 1 : 1 wt% in both Li-half and Li-ion cells during charge/discharge are studied by in situ XRD. During the first charge up to ~5.2 V vs. $Li/Li^+$, the in situ XRD spectra for the composite cathode in the Li-half cell track the structural changes of each component. At the early stage of charge, the lithium extraction takes place in the $LiNi_{1/3}Co_{1/3}Mn_{1/3}O_2$ component only. When the cell voltage reaches at ~4.0 V vs. $Li/Li^+$, lithium extraction from the spinel $LiMn_2O_4$ component starts and becomes the major contributor for the cell capacity due to the higher rate capability of $LiMn_2O_4$. When the voltage passed 4.3 V, the major structural changes are from the $LiNi_{1/3}Co_{1/3}Mn_{1/3}O_2$ component, while the $LiMn_2O_4$ component is almost unchanged. In the Li-ion cell using a MCMB anode and a composite cathode cycled between 2.5 V and 4.2 V, the structural changes are dominated by the spinel $LiMn_2O_4$ component, with much less changes in the layered $LiNi_{1/3}Co_{1/3}Mn_{1/3}O_2$ component, comparing with the Li-half cell results. These results give us valuable information about the structural changes relating to the contributions of each individual component to the cell capacity at certain charge/discharge state, which are helpful in designing and optimizing the composite cathode using spinel- and layered-type materials for Li-ion battery research. More detailed discussion will be presented at the meeting.

• Journal of The Korean Society of Grassland and Forage Science
• /
• v.30 no.2
• /
• pp.151-158
• /
• 2010

This study was conducted to evaluate the feed value and growth characteristics of Sasa quelpaertensis Nakai by horse grazing in the woodland of Jeju. Crude protein (CP), NDF, ADF and minerals contents at different growth stages of Sasa quelpaertensis were analyzed. The apparent digestibilities of DM, CP, NDF and ADF were determined by total collection method using 5 Jeju horses. The yield and growth characteristics of S. quelpaertensis Nakai by horse grazing were investigated. CP contents in the currentand the previous-year-sprouted leaves of S. quelpaertenisis were $16.6{\pm}1.0%$ and $12.2{\pm}1.1%$, respectively. The digestibility of DM, CP, NDF and ADF in the current-year-sprouted leaves of S. quelpaertenisis were $47.2{\pm}1.2$, $67.8{\pm}1.0$, $47.0{\pm}1.3$ and $47.1{\pm}1.1%$, respectively. The current-year-sprouted S. quelpaertenisis tended to have high nutritional values and digestibilities compared to those of the previous-year-sprouted. The dry matter yield, plant length, leaf width and density of S. quelpaertensis Nakai were clearly decreased by horse grazing. These results show that considering the feed value and growth characteristics, the natural S. quelpaertenisis Nakai can be used as a feed source for horses.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.18 no.5
• /
• pp.217-224
• /
• 2008

A stoichiometric mixture of evaporating materials for $ZnIn_2Se_4$ single crystal thin films was prepared from horizontal electric furnace. To obtain the single crystal thin films, $ZnIn_2Se_4$ mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the Hot Wall Epitaxy (HWE) system. The source and substrate temperatures were $630^{\circ}C$ and $400^{\circ}C$, respectively. The crystalline structure of the single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD). The carrier density and mobility of $ZnIn_2Se_4$ single crystal thin films measured from Hall effect by van der Pauw method are $9.41\times10^{16}cm^{-3}$ and $292cm^2/v{\cdot}s$ at 293 K, respectively. The temperature dependence of the energy band gap of the $ZnIn_2Se_4$ obtained from the absorption spectra was well described by the Varshni's relation, $E_g(T)=1.8622eV-(5.23\times10^{-4}eV/K)T^2/(T+775.5K)$. The crystal field and the spin-orbit splitting energies for the valence band of the $ZnIn_2Se_4$ have been estimated to be 182.7 meV and 42.6 meV, respectively, by means of the photocurrent spectra and the Hopfield quasicubic model. These results indicate that the splitting of the ${\Delta}so$ definitely exists in the ${\Gamma}_5$ states of the valence band of the $ZnIn_2Se_4/GaAs$ epilayer. The three photo current peaks observed at 10 K are ascribed to the $A_{1}-$, $B_{1}-exciton$ for n = 1 and $C_{27}-exciton$ peaks for n = 27.

• Journal of Energy Engineering
• /
• v.28 no.3
• /
• pp.65-79
• /
• 2019

The study attempted to estimate the optimal facility capacity by combining renewable energy sources that can be connected with gas CHP in industrial complexes. In particular, we reviewed industrial complexes subject to energy use plan from 2013 to 2016. Although the regional designation was excluded, Sejong industrial complex, which has a fuel usage of 38 thousand TOE annually and a high heat density of $92.6Gcal/km^2{\cdot}h$, was selected for research. And we analyzed the optimal operation model of CHP Hybrid System linking fuel cell and photovoltaic power generation using HOMER Pro, a renewable energy hybrid system economic analysis program. In addition, in order to improve the reliability of the research by analyzing not only the heat demand but also the heat demand patterns for the dominant sectors in the thermal energy, the main supply energy source of CHP, the economic benefits were added to compare the relative benefits. As a result, the total indirect heat demand of Sejong industrial complex under construction was 378,282 Gcal per year, of which paper industry accounted for 77.7%, which is 293,754 Gcal per year. For the entire industrial complex indirect heat demand, a single CHP has an optimal capacity of 30,000 kW. In this case, CHP shares 275,707 Gcal and 72.8% of heat production, while peak load boiler PLB shares 103,240 Gcal and 27.2%. In the CHP, fuel cell, and photovoltaic combinations, the optimum capacity is 30,000 kW, 5,000 kW, and 1,980 kW, respectively. At this time, CHP shared 275,940 Gcal, 72.8%, fuel cell 12,390 Gcal, 3.3%, and PLB 90,620 Gcal, 23.9%. The CHP capacity was not reduced because an uneconomical alternative was found that required excessive operation of the PLB for insufficient heat production resulting from the CHP capacity reduction. On the other hand, in terms of indirect heat demand for the paper industry, which is the dominant industry, the optimal capacity of CHP, fuel cell, and photovoltaic combination is 25,000 kW, 5,000 kW, and 2,000 kW. The heat production was analyzed to be CHP 225,053 Gcal, 76.5%, fuel cell 11,215 Gcal, 3.8%, PLB 58,012 Gcal, 19.7%. However, the economic analysis results of the current electricity market and gas market confirm that the return on investment is impossible. However, we confirmed that the CHP Hybrid System, which combines CHP, fuel cell, and solar power, can improve management conditions of about KRW 9.3 billion annually for a single CHP system.