• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.124-124
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• 2010

Much interest has been focused on InGaN-based materials and their quantum structures due to their optoelectronics applications such as light emitting diode (LED) and photovoltaic devices, because of its high thermal conductivity, high optical efficiency, and direct wide band gap, in spite of their high density of threading dislocations. Build-in internal field-induced quantum-confined Stark effect in InGaN/GaN quantum well LED structures results in a spatial separation of electrons and holes, which leads to a reduction of radiative recombination rate. Therefore, many growth techniques have been developed by utilizing lateral over-growth mode or by inserting additional layers such as patterned layer and superlattices for reducing threading dislocations and internal fields. In this work, we investigated various characteristics of InGaN multiple quantum wells (MQWs) LED structures grown on selectively wet-etched porous (SWEP) GaN template layer and compared with those grown on non-porous GaN template layer over c-plane sapphire substrates. From the surface morphology measured by atomic force microscope, high resolution X-ray diffraction analysis, low temperature photoluminescence (PL) and PL excitation measurements, good structural and optical properties were observed on both LED structures. However, InGaN MQWs LED structures grown on SWEP GaN template layer show relatively low In composition, thin well width, and blue shift of PL spectra on MQW emission. These results were explained by rough surface of template layer, reduction of residual compressive stress, and less piezoelectric field on MQWs by utilizing SWEP GaN template layer. Better electrical properties were also observed for InGaN MQWs on SWEP GaN template layer, specially at reverse operating condition for I-V measurements.

• Tunnel and Underground Space
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• v.20 no.6
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• pp.446-454
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• 2010

CAES-G/T (Compressed Air Energy Storage - Gas Turbine) power generation is a likely option for the buffer facility stabilizing the fluctuation of the renewable powers, such as wind and solar powers. Considering the geological conditions, the underground CAES facility is most probable if the CAES-G/T generation is planed in Korea. In this kind of facility, a concrete plug is installed to seal the compressed air in the container, so that the selection of the shape and dimension of concrete plug could be a critical design factor. The stability evaluation of two types of plug was carried out by investigating the distribution of the factor of safety in the plugs and the distribution of contact pressure over the contact surface. The analysis result shows that the taper-shaped plug is more structurally stable than the wedge-shaped plug for the given geological condition. Possible separation of the rock-concrete interface around the spring line of the wedge-shaped plug is anticipated, which means the possible leakage of compressed air through the side wall and also means the poor mobilization of frictional resistance on that area.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.12
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• pp.1065-1072
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• 2014

The shape of an impeller splitter for a dual-inlet centrifugal blower was optimized to enhance the blower performance. Two design variable, the normalized chord and pitch of a splitter, were used to evaluate the blower performance and internal flow fields based on the three-dimensional flow analysis. The blower performance obtained using this numerical simulation had a maximum error of 4 percent compared to that in an experiment at the design flow condition. The shape optimization of the splitter successfully increased the blower efficiency and pressure by 3.65 and 1.14 percent compared to the reference values. The blower performance was increased by reducing the flow separation near the blade suction surface by optimizing the shape of the splitter, which produced a pressure increase at the outlet of the volute casing.

• Journal of the Korean Institute of Intelligent Systems
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• v.22 no.6
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• pp.700-705
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• 2012

This paper addresses an intelligent digital redesign (IDR) technique for observer-based output-feedback control systems, in order to efficiently convert a pre-designed Takagi-Sugeno fuzzy model-based analog controller into a sampled-data one in the sense of state matching. A delta operator is used to get an asymptotic relation between the analog and the sampled-data control systems. The IDR problem is viewed as a minimization problem of the norm distances between linear operator to be matched. The condition is represented as linear matrix inequalities, and the separation principle on the IDR is shown.

• Resources Recycling
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• v.28 no.5
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• pp.68-73
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• 2019

Ilmenite is one of the principal ores for the production of titanium dioxide. To produce titanium dioxide with purity higher than 99.9% from ilmenite, Ti(IV) should be separated from the dissolved impurities such as Fe(III), Si(IV), and Mn(II) present in ilmenite. In this work, a hydrometallurgical process was investigated to recover pure titanium dioxide from ilmenite by HCl leaching followed by separation and hydrolysis of Ti(IV). An optimum leaching condition was obtained by investigating the effect of HCl concentration, pulp density, and leaching time on the leaching percentage of Ti(IV), Fe(III), Si(IV), and Mn(II). Ammonium hydroxide and sodium hydroxide solutions were employed as neutralizing agents to hydrolyze Ti(IV) from the stripping solution of Ti(IV). Titanium dioxide of the anatase phase was obtained by calcination of the hydrolyzed precipitates with $NH_4OH$ solution. A hydrometallurgical process can be developed to produce pure $TiO_2$ powders from ilmenite.

• YAKHAK HOEJI
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• v.29 no.2
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• pp.62-69
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• 1985

The isomeric intermediates, $3{\alpha}$and $3{\beta}-amino-5{\alpha}-cholestane required for the synthesis of N-nitrosoureas, N-(2-chloroethyl)-N-nitrosocarbamoyl-$3{\alpha}-amino-5{\alpha}$-cholestane (9), N-methyl-N-nitrosocarbamoyl-3${\alpha}-amino-5{\alpha}-cholestane$ (10), N-(2-chloroethyl)-N-nitrosocarbamoyl-$3{\beta}-amino-5{\alpha}-cholestane$: (7), and N-methyl-N-nitrosocarbamoyl-$3{\beta}-amino-5{\alpha}-cholestane$ (8) were obtained through the $LiAlH_{4}$ reduction of $5{\alpha}$-cholestan-3-one oxime, followed by the chromatographic separation: the assignment of the stereochemistry of both isomers were based on the shape and chemical shift of $C_{3}$-proton resonances on their NMR spectra and on the elution mobility on the TLC. The urea intermediates, N-(2-chloroethyl) carbamoyl-3.alpha.-amino-5.alpha.-cholestane (13), N-methylcarbamoyl-$3{\alpha}-amino-5{\alpha}-cholestane$ (14), N-(2-chloroethyl) carbamoyl-$3{\beta}-amino-5{\alpha}-cholestane (11) and N-methyl-$3{\beta}-amino-5{\alpha}$-cholestane (12) were prepared by the treatment of each isomers ($3{\alpha}$-amino-and $3{\beta}-amino-5{\alpha}$-cholestane) with alkyl isocyanates in anhydrous $CHCl_{3}$, and the corresponding nitrosoureas, 7-10 were obtained by the nitrosation of the ureas, 11-14, with AcOH (or HCOOH)/$NaNO_{2}$ in ice-cold condition. The inhibitory activity of the nitrosoureas, 7-10, and their intermediates, 12-14 towards the growth of L1210 murine leukemia cells, were examined. Among them, the compounds 9 and 10 exhibited high activity having $ED_{50}$ to be 5.5g/ml and 6.1g/ml, respectively.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.2
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• pp.655-661
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• 2019

This study examined the change in driving performance according to the starting position of the rear diffuser of a vehicle. To accomplish this, the CATIA 3D design program was used to model the vehicle with reference to a commercial SUV vehicle and design the rear diffuser to start from 300, 400, and 500 mm from the rear tire. The flow and drag change were analyzed and the change in air flow was confirmed using Fluent, a flow analysis program at a vehicle traveling speed of 60, 100, and 140 km/h. The rear diffuser reduced the lift and drag forces compared to no diffuser regardless of the starting position. This is because if there is a rear diffuser, it will reduce the vortex phenomenon by suppressing the flow separation that occurs when air is drawn out from the rear portion of the vehicle. In this study, the starting point SP 400 was determined to be the optimal condition because the lift force was the smallest at SP 400 and the lift reduction effect was the best.

• Transactions of the Korean hydrogen and new energy society
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• v.30 no.1
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• pp.83-94
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• 2019

LPG is increasingly being used as a clean energy source due to the continuous strengthening of environmental regulations. In addition, the demand of propane which is the basic compound for petrochemicals is increasing for propylene production. In the study, a divided wall column was used as de-propanizer and de-butanizer, which is expected to save large amount of energy among the four conventional distillation columns used for processing LPG. The simulation results showed a decrease of energy duty with ESI by 30.30% using two divided wall columns. Furthermore, simulation case studies were carried out with respect to design and operation condition. The main column tray and withdrawal tray were determined from the design case studies while the internal liquid flow and vapor flow were decided from the operating case studies. Also, ESI of 1.06% could be achieved from the case studies. According to the results, the simulation method used showed that it is greatly helpful to the design and evaluate a highly efficient divided wall column.

• Journal of Radiation Protection and Research
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• v.44 no.2
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• pp.53-63
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• 2019

Background: As neutron fields are always accompanied by gamma rays, it is essential to distinguish neutrons from gamma rays in the detection of neutrons. Neutrons and gamma rays can be separated by pulse shape discrimination (PSD) methods. Recently, we performed characterization of a stilbene scintillator detector and an EJ-301 liquid scintillator detector with a high-speed digitizer DT5730 and investigated optimized PSD variables for both detectors. This study is for providing a basis for developing fast neutron/gamma-ray dual-particle imager. Materials and Methods: We conducted PSD experiments using stilbene scintillator and EJ-301 liquid scintillator and evaluated neutron and gamma ray discriminability of each PSD method with a $^{137}Cs$ gamma source and a $^{252}Cf$ neutron source. We implemented digital signal processing techniques to apply two PSD methods - the charge comparison (CC) method and the constant time discrimination (CTD) method - to distinguish neutrons from gamma rays. We tried to find optimized PSD variables giving the best discriminability in a given experimental condition. Results and Discussion: For the stilbene scintillator detector, the charge comparison method and the constant time discrimination method both delivered the PSD FOM values of 1.7. For the EJ-301 liquid scintillator detector, both PSD methods delivered the PSD FOM values of 1.79. With the same PSD variables, PSD performance was excellent in $300{\pm}100keVee$, $500{\pm}100keVee$, and $700{\pm}100keVee$ energy regions. This result shows that we can achieve an effective discrimination of neutrons from gamma rays using these scintillator detector systems. Conclusion: We applied both PSD methods to a stilbene and a liquid scintillator and optimized the PSD performance represented by FOM values. We observed a good separation performance of both scintillators combined with a high-speed digitizer and digital PSD. These results will provide reference values for the dual-particle imager we are developing, which can image both fast neutrons and gamma rays simultaneously.

• The Journal of the Korea institute of electronic communication sciences
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• v.16 no.4
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• pp.643-652
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• 2021

Accidents or faults in the transmission and distribution system are never completely avoidable, and short-circuit and earth faults are occurs despite the efforts of the TSO and DSO. Recently, the connection to the transmission and distribution system of large-capacity new and renewable distributed power has increased rapidly and has various effects on the operation of the system. In order to minimize this, connection standards such as FRT (Fault-Ride-Through) have been established to provide wind turbines or solar inverters. In the event of a major faults of the power system, the operation support shall be provided so that the operator can stably operate the system by smoothly performing connection maintenance or rapid system separation. In this paper, in order to appropriately determine whether the FRT condition, which is the grid connection criterion for a representative DERs, is sufficient, a detection system using a PMU (Phasor Measurement Unit) that measures a synchro-phasors was designed and deployment and a system accident due to a generator step-out to analyze and evaluate the proposed system based on the case.