• Journal of the Korean Crystal Growth and Crystal Technology
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• v.28 no.2
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• pp.57-62
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• 2018

In this study, we investigated the impurity effect of $Ga_2O_3$ doped thin film by simple doping method using Mg acetate solution. Both undoped $Ga_2O_3$ thin films and Mg-doped $Ga_2O_3$ thin films were grown on Si substrates at 600 and $900^{\circ}C$ for 30 minutes by means of a customized MOCVD method. As a result of the surface analysis, there were no obvious morphological differences by Mg impurity implantation. The surface of the thin film grown at $900^{\circ}C$ was rougher than those grown at $600^{\circ}C$ and polycrystallization was achieved. As a result of the optical property analysis, in the case of the doped sample, the overall emission peak was red shifted and the UV radiation intensity was increased. As a result of the I-V curve, the leakage current of the $600^{\circ}C$ growth thin film decreased by the Mg impurity and the photocurrent of the growth thin film of $900^{\circ}C$ increased.

• Korean Chemical Engineering Research
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• v.52 no.3
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• pp.279-288
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• 2014

Nuclear energy is expected to meet the growing energy demand while avoiding CO2 emission. However, the problem of accumulating spent fuel from current nuclear power plants which is mainly composed of uranium oxides should be addressed. One of the most practical solutions is to reduce the spent oxide fuel and recycle it. Next-generation fuel cycles demand innovative features such as a reduction of the environmental load, improved safety, efficient recycling of resources, and feasible economics. Pyroprocessing based on molten salt electrolysis is one of the key technologies for reducing the amount of spent nuclear fuel and destroying toxic waste products, such as the long-life fission products. The oxide reduction process based on the electrochemical reduction in a LiCl-$Li_2O$ electrolyte has been developed for the volume reduction of PWR (Pressurized Water Reactor) spent fuels and for providing metal feeds for the electrorefining process. To speed up the electrochemical reduction process, the influences of the feed form for the cathode and the type of anode shroud on the reduction rate were investigated.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.10 no.1
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• pp.9-16
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• 1990

The safety of concrete nuclear containment structures should be secured against all kinds of loading due to various natural disasters or extraordinary accidental loads. The current design criteria of concrete containment structures are not based on the reliabillty-based design concept but rely on the conventional design concept. In this paper, a probabillty-based reliability analysis were proposed based on a FEM-based random vibration analysis and serviceability limit state of structures. The limit state model defined for the study is a serviceability limit state in terms of the more realistic crack failure that might cause the emission of radioactive materials, and the results are compared with those of the strength limit state. More accurate reliability analyses under various dynamic loads such as earthquake loads were made possible by incorporation the FEM and random vibration theory, which is different from the conventional reliability analysis method. The uncertainties in loads and resistance available in Korea and the refernces were adapted to the situation of Korea, and especially in the case of earthquake, the design earthquake was assessed based on the available re ports on probabilistic description of earthquake ground acceleration in the Korea peninsula.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.6
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• pp.577-583
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• 2011

To meet the requirements of the Tier 4 interim regulations for off-road vehicles, emissions of particulate matter (PM) and nitrogen oxides (NOx) must be reduced by 95% and 30%, respectively, compared to current regulations. In this research, both the DPF and HPL EGR systems were investigated, with the aim of decreasing the PM and NOx emissions of a 56-kW off-road vehicle. The results of the experiments show that the DOC-DPF system is very useful for reducing PM emissions. It is also found that the back pressure is acceptable, and the rate of power loss is less than 5%. By applying the HPL EGR system to the diesel engine, the NOx emissions under low- and middle-load conditions are reduced effectively because of the high differential pressure between the turbocharger inlet and the intake manifold. The NOx emissions can be decreased by increasing the EGR rate, but total hydrocarbon (THC) emission increases because of the increased fuel consumption needed to compensate for the power loss caused by EGR and DPF.

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

• Economic and Environmental Geology
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• v.48 no.1
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• pp.65-75
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• 2015

The CBM(Coalbed Methane) development technology being developed in mid 1980s is the technology to produce the methane gas absorbed in the coal bed. CBM is easy to be developed and its coal deposit is abundant. Therefore, the CBM industry has a large potential as an energy source as well as to deal with the global regulations for reducing greenhouse gas emission. In order to produce coal, the CBM should first be developed as a preliminary action for mine security. So CBM is advantageous in reducing the global greenhouse gas as well as its advantage not being influenced by the changes in gas market. The ECBM (Enhanced Coalbed Methane) is a new technique producing the methane gas which is substituted and disorbed from coal by injecting $CO_2$ or $N_2$ gas into a coal bed. Especially, $CO_2$-ECMB is a low-carbon, green-growth technology, so can expect to the effect of green gas reduction as well as the improved productivity of methane gas. CBM technology is being developed in about 40 nations including Canada, Australia, China, India, Indonesia and Viet Nam, and the coal output using this technology is continually being increased. The CBM is expected to contribute in changing the energy source paradigm from current coal & petroleum energy to unconventional gas.

• Journal of Energy Engineering
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• v.25 no.4
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• pp.251-258
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• 2016

This article reports current status of micro fuel cell-combined heat and power (${\mu}FC$-CHP) systems which utilize both power and heat generated by fuel cells. There are several options for constructing CHP systems and among them, fuel cells are the most useful and their total energy efficiency combining heat and power can reach up to about 90%. Fuel cells are classified as five types based on the electrolyte, but the most suitable fuel cell types for the ${\mu}FC$-CHP system are proton exchange membrane fuel cells (PEMFCs) and solid oxide fuel cells (SOFCs). ${\mu}FC$-CHP systems have several advantages such as decrease of the transmission-distribution loss, reduced costs of electricity due to distributed power generation, and environmental-friendliness owing to zero emission. The main drawback of the ${\mu}FC$-CHP systems is the high initial investment, however, it keeps decreasing as the technology development reduces production costs. Currently, Japan is the most leading country of the ${\mu}FC$-CHP market, however, Korea tries to expand the market by planning the deployment of 1 million units of ${\mu}FC$-CHP systems and governmental subsidiary supporting of half of the install price. In this report, integration technologies for connecting FC and CHP, and technology trends of leading countries are presented as well.

• Journal of environmental and Sanitary engineering
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• v.7 no.2
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• pp.1-10
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• 1992

Since 1960's along with industrialization and urbanization, economic growth has been . achieved, however, at the same time, environmental condition has been seriously deteriorated. . Currently, volume of wastewater has been increasing at annual rate of 7% in sewage and 20% in industrial wastewater. However, the nation's sewage treatment serves only 33% of the municipal wastewater as of 1991. Major portion of air pollutants comes from combustion of oil and coal which comprise 81% of total energy use and emission gases from motor vehicles increasing at an accelerated rate. It is known that Korea generates the highest amount of waste per capta. Nevertheless, it is not sufficient to reduce the volume of waste by means of resources recovery and recycling. Recognizing the importance of global environmental problems such as ozone layer depletion, global warming and acid rain, international society has been making various efforts since the 1972 Stockholm conference. In particular, it is expected that the Rio conference which has adopted the Rio declaration and Agenda 21 will form a crucial turning point of the emerging new world order after the Cold War confrontation. To cope with such issues as domestic pollution and global environmental problems, the fundamental national policy aims at harmonizing "environmental protection and sustainable development". The Ministry of Environment has recently set up a mid-term comprehensive plan which includes annual targets for environmental protection. According to the government plan, gradual improvement of various environmental conditions and specific measures to achieve them is planned in time frame. Additional sewage treatment plants will be constructed in urban areas with the target to treat 65% of the nation's municipal sewage by 1996. Supply of clean fuels such as LNG will also be expanded starting from large cities as a cleaner substitute energy for coal and oil. In parallel with expansion of LNG, emphasis will be placed on installation of stack monitoring system. Due to the relatively limited land, government's basic policy for solid waste treatment is to develop large scale landfill facilities rather than small sized ones. Thirty three regional areas have been designated for the purpose of waste management. For each of these regions, big scale landfill site is going to be developed. To increase the rate of waste recycling the government is planning to reinforce separate collection system and to provide industries with economic incentives. As a part of meeting the changing situation on global environmental problems after UNCED, and accommodation regulatory measures stipulated in the global environmental conventions and protocols, national policy will try to alter industrial and economic structure so as to mitigate the increasing trends of energy consumption, by encouraging energy conservation and efficiency. In this regard, more attention will be given to the policy on the development of the cleaner technology. Ultimately, these policies and programs will contribute greatly to improving the current state of national public health.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.64.1-64.1
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• 2018

SNe light curves have been used to understand the expansion history of the universe, and a lot of efforts have gone into understanding the overall shape of the radioactively powered light curve. However, we still have little direct observational evidence for the theorized SN progenitor systems. Recent studies suggest that the light curve of a supernova shortly after its explosion (< 1 day) contains valuable information about its progenitor system and can be used to set a limit on the progenitor size, R*. In order to catch the early light curve of SNe explosion and understand SNe progenitors, we are performing a ~8hr interval monitoring survey of nearby galaxies (d < 50 Mpc) with 1-m class telescopes around the world. Through this survey, we expect to catch the very early precursor emission as faint as R=21 mag (~0.1 Rsun for the progenitor). In this poster, we outline this project, and present a few scientific highlights, such as the early light curve of SN 2015F in NGC 2442.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.22 no.5
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• pp.233-240
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• 2012

White LEDs (light-emitting diodes) are promising new-generation light sources which can replace conventional lamps due to their high reliability, low energy consumption and eco-friendly effects. This paper briefly reviews recent progress of oxy/nitride host phosphor and quantum dot materials with broad excitation band characteristics for phosphor-converted white LEDs. Among oxy/nitride host materials, $M_2Si_5N_8$ : $Eu^{2+}$, $MAlSiN_3$ : $Eu^{2+}$ M-SiON (M = Ca, Sr, Ba), ${\alpha}/{\beta}$-SiAlON : $Eu^{2+}$ are excellent phosphors for white LED using blue-emitting chip. They have very broad excitation bands in the range of 440~460 nm and exhibit emission from green to red. In this paper, In this review we focus on recent developments in the crystal structure, luminescence and applications of the oxy/nitride phosphors for white LEDs. In addition, the application prospects and current trends of research and development of quantum dot phosphors are also discussed.