• Journal of Korea Water Resources Association
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• v.31 no.6
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• pp.727-739
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• 1998

The main objectives o reservoir optimal operation can be described as follows : maximization of the benefits through optimal allocation of the limited water resources for various purpose; minimization of t도 costs by the flood damage in potential damaging regions and risk of dam failure, etc. through safe drainage of a bulky volume of excessive water by a proper reservoir operation. Reviewing the past research works related to reservoir operation, we can find that the study on the matter of the former has been extensively carried out in last decades rather than the matter of the latter. This study is focused on developing a methodology of optimal reservoir operation for flood control, and a case study is performed on the Chungju multipurpose reservoir in Korea. The final goal of the study is to establish a reservoir optimal operation system which can search optimal policy to compromise two conflicting objectives: downstream flood damage and dam safety-upstream flood damage. In order to reach the final goal of the study, the following items were studied : (1)validation of hydrological data using HYMOS: (2)establishment of a downstream flood routing model coupling a rainfall-runoff model and SOBEK system for 1-D hydrodynamic flood routing; (3)replication of a flood damage estimation model by a neural network; (4)development of an integrated reservoir optimization module for an optimal operation policy.

• Journal of the Korean Society of Marine Environment & Safety
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• v.21 no.6
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• pp.759-769
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• 2015

Diode rectifiers are very popular in industry. However, they include large low-order harmonics in the input current and do not satisfy harmonic current content restrictions. To reduce the harmonics to the power system, several methods have been introduced. It is heavy and expensive solution to use passive filters as the solution for high power application. Another solution for the harmonic filter is utilization of active filter, but it is too expensive solution. Diode rectifiers with configurations using switching device have been introduced, but they are very complicated. The combined 12-pulse diode rectifier with the square auxiliary voltage supply has been introduced. It has the advantages that auxiliary circuit is simple and inexpensive compared to other strategies. The advanced auxiliary voltage supply in this thesis is presented as a new solution. When the square auxiliary voltage supply applied, the improvement of THD is 6~60[%] in whole load range. But when the advanced auxiliary voltage supply applied, it shows stable and excellent reduction effect of THD as 57~71[%]. Especially, for the case with 10[%] load factor, reduction effect of THD has little effect as 6[%] in the case of inserting a square auxiliary voltage supply. But when the proposed new solution applied, reduction effect has excellent effect as 71[%]. Theoretical analysis of the combined 12-pulse diode rectifier with the advanced auxiliary voltage supply is presented and control methods of the auxiliary supply is proposed. The reduction in the input current harmonics is verified by simulation using software PSIM.

• Nuclear Engineering and Technology
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• v.48 no.5
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• pp.1273-1279
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• 2016

Production of iodine-131 by neutron activation of tellurium in tellurium dioxide ($TeO_2$) material requires a target that meets the safety requirements. In a radiopharmaceutical production unit, a new lid for a can was designed, which permits tight sealing of the target by using tungsten inert gaswelding. The leakage rate of all prepared targets was assessed using a helium mass spectrometer. The accepted leakage rate is ${\leq}10^{-4}mbr.L/s$, according to the approved safety report related to iodine-131 production in the TRIGA Mark II research reactor (TRIGA: Training, Research, Isotopes, General Atomics). To confirm the resistance of the new design to the irradiation conditions in the TRIGA Mark II research reactor's central thimble, a study of heat effect on the sealed targets for 7 hours in an oven was conducted and the leakage rates were evaluated. The results show that the tightness of the targets is ensured up to $600^{\circ}C$ with the appearance of deformations on lids beyond $450^{\circ}C$. The study of heat transfer through the target was conducted by adopting a one-dimensional approximation, under consideration of the three transfer modes-convection, conduction, and radiation. The quantities of heat generated by gamma and neutron heating were calculated by a validated computational model for the neutronic simulation of the TRIGA Mark II research reactor using the Monte Carlo N-Particle transport code. Using the heat transfer equations according to the three modes of heat transfer, the thermal study of I-131 production by irradiation of the target in the central thimble showed that the temperatures of materials do not exceed the corresponding melting points. To validate this new design, several targets have been irradiated in the central thimble according to a preplanned irradiation program, going from4 hours of irradiation at a power level of 0.5MWup to 35 hours (7 h/d for 5 days a week) at 1.5MW. The results showthat the irradiated targets are tight because no iodine-131 was released in the atmosphere of the reactor building and in the reactor cooling water of the primary circuit.

• Korean Journal of Plant Resources
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• v.27 no.4
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• pp.365-370
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• 2014

This study was conducted to determine the effects of seed storage methods ($-20^{\circ}C$, stratification, $2^{\circ}C$ dry, $2^{\circ}C$ wet and room temperature) and $GA_3$ application (control, $dH_2O$, 10, 100, 1000 ppm) on seed germination and seedling growth of S. lyratum. As a result seed germination rate of S. lyratum was the highest at 91% when seeds were stored at room temperature and then soaked for 24 hours in $GA_3$ 10 ppm. And seedlings of S. lyratum showed the best quality when seed were stored at $2^{\circ}C$ dry and then soaked for 24 hours in $GA_3$ 1000 ppm, with the growth characteristics of plant height (47 mm), number of leaves (8), leaf width (12 mm), leaf length (19 mm), fresh weight (aerial/root part; 471/476 mg), dry weight (aerial/root; 106/41 mg) and seedling quality indices (106). Therefore, S. lyratum seed were stored at $2^{\circ}C$ dry, and then soaked for 24 hours in $GA_3$ 1000 ppm, seed germination rate was more than 80% and production of superior quality container seedlings.

• Archives of Pharmacal Research
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• v.28 no.3
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• pp.335-342
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• 2005

The effects of ginsenosides Rg$_3$(R) , Rg$_3$(S) and Rg$_5$/Rk$_1$ (a mixture of Rg$_5$ and Rk$_1$ 1:1, w/w), which are components isolated from processed Panax ginseng C.A. Meyer (Araliaceae), on memory dysfunction were examined in mice using a passive avoidance test. The ginsenosides Rg3(R), Rg3(S) or Rg$_5$/Rk$_1$, when orally administered for 4 days, significantly ameliorated the memory impairment induced by the single oral administration of ethanol. The memory impairment induced by the intraperitoneal injection of scopolamine was also significantly recovered by ginsenosides Rg3(S) and Rg$_5$/Rk$_1$. Among the three ginsenosides tested in this study, Rg$_5$/Rk$_1$ enhanced the memory function of mice most effectively in both the ethanol­and scopolamine-induced amnesia models. Moreover, the latency period of the Rg$_5$/Rk$_1$­treated mice was 1.2 times longer than that of the control (no amnesia) group in both models, implying that Rg$_5$/Rk$_1$ may also exert beneficial effects in the normal brain. We also evaluated the effects of these ginsenosides on the excitotoxic and oxidative stress-induced neuronal cell damage in primary cultured rat cortical cells. The excitotoxicity induced by glutamate or N­methyl-D-aspartate (NMDA) was dramatically inhibited by the three ginsenosides. Rg$_3$(S) and Rg$_5$/Rk$_1$ exhibited a more potent inhibition of excitotoxicity than did Rg$_3$(R). In contrast, these ginsenosides were all ineffective against the H$_2$O$_2$- or xanthine/xanthine oxidase-induced oxidative neuronal damage. Taken together, these results indicate that ginsenosides Rg$_3$(S) and Rg$_5$/Rk$_1$ significantly reversed the memory dysfunction induced by ethanol or scopolamine, and their neuroprotective actions against excitotoxicity may be attributed to their memory enhancing effects.

• Journal of rehabilitation welfare engineering & assistive technology
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• v.9 no.3
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• pp.195-201
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• 2015

In this study, IT education contents have been developed based on the u-Learning approach for people with hearing impairment, focusing on allowing the user to learn from anywhere and anytime. Specifically, this study applies HTML5 to implementing IT education contents(JSP, Oracle) for the deaf because HTML5 enables the learner to access the contents through both web and mobile device on various platforms including android, Mac OS, and PC etc. The results of this study are as follows: First, the online computer courses are mostly supposed to be compatible with diverse types of mobile devices. However, some of the contents could not be run on applications residing in web and mobile devices because the contents tend to be developed using FLASH. HTML5 is the effective way to overcome the compatibility problem. Second, FLASH and HTML5 contents authoring tools have been compared in terms of their strong and weak points by applying the developed contents to those tools. The study also suggests that the future work would be needed in order to implement wide variety of event functions with HTML5. Lastly, design strategies enabling access through web and mobile devices have been analyzed in accordance with u-Learning design guidelines for the deaf and mobile application accessibility guidelines. However, in the latter case, the future work regarding design guidelines needs to be conducted to improve the educational accessibility depending on the level of impairment.

• Korean Journal of Agricultural Science
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• v.45 no.2
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• pp.197-203
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• 2018

Biochar is the carbon solid produced through the pyrolysis of a biomass from organic sources such as agricultural waste, animal manure, and sludge under limited or anaerobic conditions. Biochar has the effect of reducing greenhouse gases through the carbon sequestration method; additionally, biochar is known to function as a soil amendment. This experiment was conducted to evaluate the application of biochar on the growth characteristics of Chinese cabbage at Chungnam National University in Daejeon, Korea. The Chinese cabbage was grown for 50 days in a glasshouse in pots. A pruning branch was used to produce the bead and pellet forms of biochar through pyrolysis. The biochar was added to the soil at 0, 2, and 5% by weight. The Chinese cabbage with the 2% treatment of the bead form of biochar had the highest fresh weight ($149.43{\pm}15.92g\;plant^{-1}$) which was increased by 10% compared to the control ($136.91{\pm}31.46g\;plant^{-1}$). Moreover, for the 5% treatment of the bead form of biochar ($60.91{\pm}9.82g\;plant^{-1}$), the growth decreased by 57% compared to the control. As the content of the bead form of biochar increased, the shoot dry weight, leaf number, leaf length and lead width that appeared decreased. An increase in the total organic matter, Avail. $P_2O_5$, Ex. cation and EC was observed when the biochar content was increased. Our results support the application of 2% biochar in the bead form for increased growth of Chinese cabbage.

• Clean Technology
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• v.19 no.4
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• pp.476-480
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• 2013

The growth behavior of $CH_4$ and $SF_6$ mixture gas hydrate has been investigated by a combined approach of Raman spectroscopy and molecular modeling. Raman spectroscopy results presented that when $CH_4$ is used only, $CH_4$ guest molecule is inserted first into the large cavity of the host structure built by $H_2O$ molecules and then into the small cavity to stabilize the whole gas hydrate structure. In the other hand, when $SF_6$ is mixed together, $SF_6$ is favored over (or competing with) $CH_4$ in being inserted into the large cavity and the small cavity still prefers $CH_4$ insertion. The calculations of binding energies clearly supported this. While $SF_6$ has a binding energy of -26.9 kcal/mol a little lower than -24.2 kcal/mol of $CH_4$ in the large cavity, $SF_6$ and $CH_4$ has 1.2 kcal/mol and -22.0 kcal/mol, respectively, in the small cavity. It indicates that the sizable $SF_6$ is not preferred in the small cavity but has a relative energetic advantage over $CH_4$ in the large cavity.

• Korean Journal of Agricultural Science
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• v.4 no.1
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• pp.26-33
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• 1977

We have studied the responce of nitrogen on the newly bred varieties, Yusin and Milyang #23, and the effects of defoliation at maturing stage on the rate of ripened grains under different nitrogen levels. The results obtained are summarized as follows : 1. Milyang #23 as well as Tongil was found to be highly nitrogen responsive variety and showed good grain maturing percentage. The number of grain per unit area affected the total yield under the high levels of nitrogen application. The variety, Yusin, was less responsive to nitrogen and had also less leaf area than other varieties under the high level of nitrogen application. Yusin also seemed to have low maturing percentage due to unbalanced ratio between photosynthetic area and size of storage. 2. The low internodes and leaf blade of Yusin and Milyang #15 were grown too much under high levels of nitrogen and these caused more lodging and less light penetration in pant canopy. 3. The effects of defoliation at maturing stage on yield was high under the high levels of nitrogen application, especially when defoliation was done early stage of maturing. The effects of defoliation appeared to be greates in Tongil than in Milyang #15.

• Journal of the Society of Naval Architects of Korea
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• v.50 no.5
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• pp.324-333
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• 2013

Recently, rudder erosion due to cavitation has been frequently reported on a semi-spade rudder of a high-speed large ship. This problem raises economic and safety issues when operating ships. The semi-spade rudders have a gap between the horn/pintle and the movable wing part. Due to this gap, a discontinuous surface, cavitation phenomenon arises and results in unresolved problems such as rudder erosion. In this study, we made a rudder model for 2-D experiments using the NACA0020 and also manufactured gap flow blocking devices to insert to the gap of the model. In order to study the gap flow characteristics at various rudder deflection angles($5^{\circ}$, $10^{\circ}$, $35^{\circ}$) and the effect of the gap flow blocking devices, we carried out the velocity measurements using PIV(Particle Image Velocimetry) techniques and cavitation observation using high speed camera in Seoul National University cavitation tunnel. To observe the gap cavitation on a semi-spade rudder, we slowly lowered the inside pressure of the cavitation tunnel until cavitation occurred near the gap and then captured it using high-speed camera with the frame rate of 4300 fps(frame per second). During this procedure, cavitation numbers and the generated location were recorded, and these experimental data were compared with CFD results calculated by commercial code, Fluent. When we use gap flow blocking device to block the gap, it showed a different flow character compared with previous observation without the device. With the device blocking the gap, the flow velocity increases on the suction side, while it decreases on the pressure side. Therefore, we can conclude that the gap flow blocking device results in a high lift-force effect. And we can also observe that the cavitation inception is delayed.