• Journal of the Korean Society of Hazard Mitigation
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• v.10 no.1
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• pp.89-102
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• 2010

Future uncertainty on water demand caused by future climate condition and water consumption leads a difficulty to determine the reservoir operation rule for supplying sufficient water to users. It is, thus, important to operate reservoirs not only for distributing enough water to users using the limited water resources but also for preventing floods and drought under the unknown future condition. In this study, the reservoir storage is determined in the first stage when future condition is unknown, and then, water distribution to users and river stream is optimized using the available water resources from the first stage decision using 2-stage stochastic linear programming (2-SLP). The objective function is to minimize the difference between target and actual water storage in reservoirs and the water shortage in users and river stream. Hedging rule defined by a precaution against severe drought by restricting outflow when reservoir storage decreases below a target, is also applied in the reservoir operation rule for improving the model applicability to the real system. The developed model is applied in a system with five reservoirs in the Han River basin, Korea to optimize the multi-reservoir system under various future water demand scenarios. Three multi-purposed dams - Chungju, Hoengseong, and Soyanggang - are considered in the model. Gwangdong and Hwacheon dams are also considered in the system due to the large capacity of the reservoirs, but they are primarily for water supply and power generation, respectively. As a result, the water demand of users and river stream are satisfied in most cases. The reservoirs are operated successfully to store enough water during the wet season for preparing the coming drought and also for reducing downstream flood risk. The developed model can provide an effective guideline of multi-reservoir operation rules in the basin.

• Journal of Energy Engineering
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• v.21 no.4
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• pp.402-410
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• 2012

A two-loop Rankine cycle for engine waste heat recovery of gasoline vehicle has been investigated. Water-steam cycle as a high-temperature (HT) loop for exhaust gas heat recovery and R-134a cycle as a low-temperature (LT) loop for both heat recovery of the engine coolant and the residual heat from the HT loop were considered. Energy and exergy analysis was performed to investigate the performance of the system. Because two volumetric expanders are used for the HT and LT loop, the sizes of two expanders are very important for the optimization of the system. The effects of pressure ratio of the HT loop, considering the size of the HT expander, and the condensation temperature of LT loop on the performance of the system at a target engine condition were investigated. This study shows that about 20% of additional power from the engine waste heat recovery can be obtained at the target engine condition.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.1
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• pp.688-695
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• 2017

This paper deals with characteristics analysis of a permanent magnet (PM) linear generator using analytical methods for wave energy harvesting. The wave energy is carried out from the movement of a yo-yo system. A linear generator using permanent magnets to generate a magnetic force itself does not require a separate power supply and has the advantage of simple maintenance. In addition to the use of a rare earth, a permanent magnet having a high-energy density can be miniaturized and lightweight, and can obtain high energy-conversion efficiency. We derived magnetic field solutions produced by the permanent magnet and armature reaction based on 2D polar coordinates and magnetic vector potential. Induced voltage is obtained via arbitrary sinusoidal input. In addition, electrical parameters are obtained, such as back-EMF constant, resistance, and self- and mutual-winding inductances. The space harmonic method used in this paper is confirmed by comparing it with finite element method (FEM) results. These facilitate the characterization of the PM-type linear generator and provide a basis for comparative studies, design optimization, and machine dynamic modeling.

• Microbiology and Biotechnology Letters
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• v.39 no.2
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• pp.153-160
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• 2011

In this study, we have developed taste and other functional enhancements of yam chips, from tasteless and flavorless yam slices, through the process of soaking freeze-dried yam in different commercially available juices, including apple, omija (fruit of Maximowiczia typica), grape, wild grape, orange, tomato, red ginseng, and black garlic juice. The analyses of color (brightness, redness and yellowness), pH, brix, acidity, total polyphenol, total flavonoids, total sugar and reducing sugar, DPPH and ABTS scavenging activity, reducing power and nitrite scavenging activity, of the different yam chips showed that the freeze-dried yam slices absorb various components of fruit juices, such as flavonoids, sugars, organic acids and flavors, during the soaking process. These changes resulted in increased taste (both sweet and sour tastes), flavor and antioxidant activity in the yam chips. The soaking time for yam slices in juice is considered to be a crucial factor for the taste and bioactivity of yam chips. In the case of grape juice-yam chips, which had the highest preference among the 8 different chips, the optimum soaking time was noted as 120 seconds. The optimization of the soaking process is necessary for various juices. These results suggest that taste, and other functional enhancements, in yam chips can be developed by juice-soaking and freeze-drying methods.

• Journal of the Korean Vacuum Society
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• v.21 no.1
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• pp.29-35
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• 2012

The Hydrogenated silicon nitride (SiNx:H) using plasma enhanced chemical vapor deposition is widely used in photovoltaic industry as an antireflection coating and passivation layer. In the high temperature firing process, the $SiN_x:H$ film should not change the properties for its use as high quality surface layer in crystalline silicon solar cells. Initially PECVD-$SiN_x:H$ film trends were investigated by varying the deposition parameters (temperature, electrode gap, RF power, gas flow rate etc.) to optimize the process parameter conditions. Then by varying gas ratios ($NH_3/SiH_4$), the hydrogenated silicon nitride films were analyzed for its optical, electrical, chemical and surface passivation properties. The $SiN_x:H$ films of refractive indices 1.90~2.20 were obtained. The film deposited with the gas ratio of 3.6 (Refractive index=1.98) showed the best properties in after firing process condition. The single crystalline silicon solar cells fabricated according to optimized gas ratio (R=3.6) condition on large area substrate of size $156{\times}156mm$ (Pseudo square) was found to have the conversion efficiency as high as 17.2%. Optimized hydrogenated silicon nitride surface layer and high efficiency crystalline silicon solar cells fabrication sequence has also been explained in this study.

• Journal of Korea Water Resources Association
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• v.41 no.4
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• pp.433-444
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• 2008

In recent, the integrated water resources management should consider not only existing management objects such as water supply, power generation, and instream flows but also new management objects such as water quantity, water quality, and water habitats which management system is large and complex. Moreover, integrated basin plan or operation are needed for solving conflicts problems between basins and between water usages and to maximize water resources usages. To increase use of optimization method for actual operation and apply various objects, a reservoir operation rule was developed and the KModSim's hydrologic states for integrated water resources management were tested in this study. The simulation results show that the developed operation rules applied in hydrologic states good represent the actual storages of both the Yongdam and the Daecheong Reservoirs so, it is possible to improve the water allocation method usually used in the basin management and manage the integrated basin water resources if new operating rules are applied in optimized programming.

• Progress in Medical Physics
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• v.18 no.1
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• pp.35-41
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• 2007

In this work practical considerations of a pulsed arterial spin labeling MRI are presented to reliable multi-slice perfusion measurements In the human brain. Three parameters were considered in this study. First, In order to improve slice profile and Inversion efficiency of a labeling pulse a high power Inversion pulse of adiabatic hyperbolic secant was designed. A $900^{\circ}$ rotation of the flip angle was provided to make a good slice profile and excellent Inversion efficiency. Second, to minimize contributions of a residual magnetization be4ween Interleaved scans of control and labeling we tested three different conditions which were applied 1) only saturation pulses, 2) only spotter gradients, and 3) combinations of saturation pulses and spotter gradients Applications of bo4h saturation pulses and spoiler gradients minimized the residual magnetization. Finally, to find a minimum gap between a tagged plane and an imaging plane we tested signal changes of the subtracted image between control and labeled Images with varying the gap. The optimum gap was about 20mm. In conclusion, In order to obtain high quality of perfusion Images In human brain It Is Important to use optimum parameters. Before routinely using In clinical studios, we recommend to make optimizations of sequence parameters.

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.993-994
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• 2008

Electrochromic (EC) devices are capable of reversibly changing their optical properties upon charge injection and extraction induced by the external voltage. The characteristics of the EC device, such as low power consumption, high coloration efficiency, and memory effects under open circuit status, make them suitable for use in a variety of applications including smart windows and electronic papers. Coloration due to reduction or oxidation of redox chromophores can be used for EC devices (e-paper), but the switching time is slow (second level). Recently, with increasing demand for the low cost, lightweight flat panel display with paper-like readability (electronic paper), an EC display technology based on dye-modified $TiO_2$ nanoparticle electrode was developed. A well known organic dye molecule, viologen, was adsorbed on the surface of a mesoporous $TiO_2$ nanoparticle film to form the EC electrode. On the other hand, ZnO is a wide bandgap II-VI semiconductor which has been applied in many fields such as UV lasers, field effect transistors and transparent conductors. The bandgap of the bulk ZnO is about 3.37 eV, which is close to that of the $TiO_2$ (3.4 eV). As a traditional transparent conductor, ZnO has excellent electron transport properties, even in ZnO nanoparticle films. In the past few years, one-dimension (1D) nanostructures of ZnO have attracted extensive research interest. In particular, 1D ZnO nanowires renders much better electron transportation capability by providing a direct conduction path for electron transport and greatly reducing the number of grain boundaries. These unique advantages make ZnO nanowires a promising matrix electrode for EC dye molecule loading. ZnO nanowires grow vertically from the substrate and form a dense array (Fig. 1). The ZnO nanowires show regular hexagonal cross section and the average diameter of the ZnO nanowires is about 100 nm. The cross-section image of the ZnO nanowires array (Fig. 1) indicates that the length of the ZnO nanowires is about $6\;{\mu}m$. From one on/off cycle of the ZnO EC cell (Fig. 2). We can see that, the switching time of a ZnO nanowire electrode EC cell with an active area of $1\;{\times}\;1\;cm^2$ is 170 ms and 142 ms for coloration and bleaching, respectively. The coloration and bleaching time is faster compared to the $TiO_2$ mesoporous EC devices with both coloration and bleaching time of about 250 ms for a device with an active area of $2.5\;cm^2$. With further optimization, it is possible that the response time can reach ten(s) of millisecond, i.e. capable of displaying video. Fig. 3 shows a prototype with two different transmittance states. It can be seen that good contrast was obtained. The retention was at least a few hours for these prototypes. Being an oxide, ZnO is oxidation resistant, i.e. it is more durable for field emission cathode. ZnO nanotetropods were also applied to realize the first prototype triode field emission device, making use of scattered surface-conduction electrons for field emission (Fig. 4). The device has a high efficiency (field emitted electron to total electron ratio) of about 60%. With this high efficiency, we were able to fabricate some prototype displays (Fig. 5 showing some alphanumerical symbols). ZnO tetrapods have four legs, which guarantees that there is one leg always pointing upward, even using screen printing method to fabricate the cathode.

• Korean Chemical Engineering Research
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• v.43 no.5
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• pp.595-602
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• 2005

In order to purify diethylene glycol as main impurity included in p-dioxanone, SLE (solid-liquid equilibria) and mixture density on two components system of p-dioxanone and diethylene glycol were measured and a layered melt crystallization with seed has been applied. The SLE of p-dioxanone and diethylene glycol were a simple eutectic system and the temperature and PDX concentration at eutectic point were 0.08 and 246 K, respectively. Densities of their binary mixtures were well fitted by the best correlation equation, ${\rho}_l=0.405+1.361x+0.002T-0.004xT$. In the melt crystallization, the growth rate (G) was proportional to the 1.5th power of the subcooling degree. The effective distribution coefficient ($K_{eff}$) as the degree of impurity removal was observed to increase with increasing the growth rate and initial p-dioxanone concentration. And also, $K_{eff}$ was correlated with Z function using Wintermantel's model such as $K_{eef}=-0.0604+6.392{\times}Z$. Finally, PDX purity through the optimization of this process can be obtained over 99%.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.8
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• pp.1105-1111
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• 2010

The Korea Atomic Energy Research Institutes has been developing the SMART (System integrated Modular Advanced ReacTor), an environment-friendly nuclear reactor for the generation of electricity and to perform desalination. SMART reactors can be exposed to various external and internal loads caused by seismic and coolant flows. The CRDM(control rod drive mechanism), one of structures of the SMART, is a component which is adjusting inserting amount of a control rod, controlling output of reactor power and in an emergency situation, inserting a control rod to stop the reactor. The purpose of this research is performing the analysis of dynamic characteristic to ensure safety and integrity of structure of CRDM. This paper presents two FE-models, 3-D solid model and simplified Beam model of the CRDM in the coolant, and then compared the results of the dynamic characteristic about the two FE-models using a commercial Finite Element tool, ABAQUS CAE V6.8 and ANSYS V12. Beam 4 and beam 188 of simplified-model were also compared each other. And simplified model is updated for accuracy compare to 3-D solid.