• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.4
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• pp.25-32
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• 2020

A numerical study on combustion instabilities in a model combustor was conducted with various momentum flux ratios. Five ratios are calculated based on an actual operating condition of rocket engine. As momentum flux ratio increases, the spreading angle on the injector outlet decreases. And, as increase of axial momentum flux, pressure fluctuation decreases inside the combustor. By using dynamic mode decomposition method, the acoustic modes inside the combustor are identified. Combustion stabilities are analyzed by comparing the damping coefficient of the 2^nd longitudinal mode.

• Explosives and Blasting
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• v.40 no.1
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• pp.17-28
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• 2022

Electrical pulse disintegration(ED) is known as an efficient technology for recovering valuable resources by inducing dielectric breakdown in solids to separate mineral interfaces in ores among the crushing technologies by high voltage discharge. In this study, ED crushing experiment and mechanical crushing experiment of sulfide minerals were performed, and SEM analysis and Microfocus X-Ray CT of the crushed product were performed in order to analyze the disintegration characteristics of zinc minerals exist in the sulfide minerals by the shock wave generated in the solid by high voltage discharge.

• Proceedings of the Korea Information Processing Society Conference
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• 2010.04a
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• pp.892-895
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• 2010

무선 기기의 소형화와 무선 통신 기술의 발달, 그리고 센서의 환경 정보 측정 기술 및 센서 네트워크의 확산으로 홍수, 태풍, 지진, 환경 오염, 등 재난의 피해를 줄이고자 재해 방지 시스템에 대한 연구가 활발하게 진행되고 있다. 그리고 이러한 재해는 특정한 시간에 특정 지점에만 발생하는 특징이 있으며, 이 발생 시간을 제외한 나머지 시간대에서는 정상적인 상황을 유지한다. 이와 같은 특성은 센서 네트워크 응용에서 센서의 배터리 전력 유지 및 환경 정보 획득 방법을 설계할 때, 주요한 사안으로 고려되고 있다. 이 논문에서는 센서의 전력소비를 줄이고 대기 오염에 대한 정보를 오염 발생 시간에 따라 적절히 획득하기 위하여, 대기 오염 방지 시스템에서의 센서 샘플링 주기 조정 기법을 제안한다. 제안된 기법은 대기 오염의 현재와 가까운 미래의 상태를 기반으로 센서의 샘플링 주기가 변화하는 규칙과 경계, 가중치를 설정한다. 그리고 매 샘플링 주기마다 센서 데이터 값과 이전에 저장된 오염 레벨을 고려하여 다음 샘플링 주기를 갱신한다. 이렇게 변화하는 샘플링 주기로 인해 대기 오염 감지 시스템은 측정 데이터의 정확도와 센서의 배터리 전력 소비의 균현을 적절히 유지할 수 있다. 제안된 샘플링 주기 기법은 다양한 환경 감시 응용에 활용될 수 있다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.3A
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• pp.533-538
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• 2006

This study deals with the static and dynamic stability analyses of simple tapered columns with constant volume. The crosssections of column taper are the regular polygons whose depths are varied with the parabolic functional fashion. The hingedhinged end constraint is chosen as the boundary condition of the column. The non-dimensional ordinary differential equation governing free vibrations of such column subjected to an axial load is derived and solved numerically. From numerical results, the relationships between natural frequencies and section ratios are obtained, from which the configurations of dynamic optimal shapes of columns and the strongest columns are extracted.

• Journal of the Korean earth science society
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• v.36 no.1
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• pp.82-89
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• 2015

In this study, the characteristics of sea ice initial conditions generated from a global ocean and sea ice prediction system, the Nucleus for European Modeling of the Ocean (NEMO) - Los Alamos Sea Ice Model (CICE)/NEMOVAR were analyzed for the period June 2013 to May 2014 over the Arctic region. For the purpose, the observed and reanalyzed data were used to compare with the sea ice initial conditions. Results indicated that the variability of the monthly sea ice extent and thickness in model initial conditions were well represented as compared to the observation, while it was found that the extent and thickness of Arctic sea ice in initial data were narrower and thinner than those in reanalysis and observation for the period. The reason for the narrower sea ice extent in model initial conditions seems to be due to the fact that the initial sea ice concentration at the boundary area of sea ice was about 20 percent less than the reanalysis data. Also, the reason for the thinner sea-ice thickness in the Arctic region is due to the underestimation of Arctic sea ice thickness (about 60 cm) of the model initial conditions in the Arctic Ocean area adjacent to Greenland and Arctic archipelago where thick sea ice appears all the year round.

• Journal of the korean academy of Pediatric Dentistry
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• v.35 no.2
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• pp.259-267
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• 2008

This in vitro study aimed to investigate the influence of flowable composite lining with different thicknesses on the marginal quality. One hundred twenty cavities, each preparated with proximal boxtype( 3mm of bucco-lingual width, 2mm of mesio-distal depth and gingival margin of 1mm supra-CEJ) were randomly dived into four groups. group I : Tetric ceram filling alone(control group) group II: 0.5mm thickness Tetric flow + Tetric ceram filling group III: 1.5mm thickness Tetric flow + Tetric ceram filling group IV: 2.5mm thickness Tetric flow + Tetric ceram filling The followings are the results: 1. Group II showed significantly less microleakage compared to group I(control group)(p<0.05). 2. There was no statistically significant difference between group III, IV and group I(p>0.05). 3. Group II showed significantly less microleakage compared to group III, IV(p<0.05). 4. There was microleakage more or less in all group. It was concluded that 0.5mm flowable composite lining improved cavity adaptation and marginal sealing.

• Korean Journal of Animal Reproduction
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• v.17 no.4
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• pp.339-346
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• 1994

An understanding of the structure and function of mammalian spermatozoa requires the iso-lation of these components. In this study, frozen-thawed bovine spermatozoa were treated by physical treatments (vortexing, 26 gauge needle, strained 26 gauge needles and freezing-thawing) or chemical treatments (trypsin, dithiothreitol, sodium dodecylsulfate and $\beta$-mercaptoethanoJ) to yield free heads and tails. The most effective treatment was repeated pumping of sperm suspension through a strained 26 gauge needle conneted to a syringe. Spermatozoa by this treatment were mainly broken at the junction of the head and the tail, resulting in 90-100% yields. Also, sperm head surface did not modify during strained 26 gauge needle treatment when either spermatozoa or sperm heads were incubated in 250${\mu}\textrm{g}$/ml of FITC-UEA 1 for 1 h at room temperature to detect the modification of sperm surface components. Other physical treatments were less efficient for the breakdown of spermatozoa. The effects of chemical treatments on bovine spermatozoa are not noticeable. Dissected sperm heads and tails should be fractional leading to nearly pure components by sucrose gradient centrifugation at 1,000 rpm for 15 min. The result suggest that the established method may be useful for the biochemical study of spermatozoal components, and the understanding of oocyte activation mechanism either by spermatozoal components during fertilization or microinjection of isolated components.

• Geophysics and Geophysical Exploration
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• v.26 no.1
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• pp.18-30
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• 2023

Submarine mud volcanos are topographic features that resemble volcanoes, and are formed due to eruptions of fluidized or gasified sediment material. They have gained attention as a source of subsurface heat, sediment, or hydrocarbons supplied to the surface. In the continental slope of the Canadian Beaufort Sea, mud volcano exists at various water depths. The MV420, is an active mud volcano erupting at a water depth of 420 meters, and it has been the subject of extensive study. The Korea Polar Research Institute(KOPRI) collected high-resolution seismic data and heat flow data around the caldera of the mud volcano. By analyzing the multi-channel seismic data, we confirmed the reverse-polarity reflector assumed by a gas hydrate-related bottom simulating reflector(BSR). To further elucidate the relationship between the BSR and gas hydrates, as well as the thermal structure of the mud volcano, a numerical geothermal model was developed based on the steady-state heat equation. Using this model, we estimated the base of the gas hydrate stability zone and found that the BSR depth estimated by multi-channel seismic data and the bottom of the gas hydrate stability zone were in good agreement., This suggests the presence of gas hydrates, and it was determined that the depth of the gas hydrate was likely up to 50 m, depending on the distance from the mud conduit. Thus, this depth estimate slightly differs from previous studies.

• Journal of Intelligence and Information Systems
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• v.16 no.3
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• pp.77-97
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• 2010

Market timing is an investment strategy which is used for obtaining excessive return from financial market. In general, detection of market timing means determining when to buy and sell to get excess return from trading. In many market timing systems, trading rules have been used as an engine to generate signals for trade. On the other hand, some researchers proposed the rough set analysis as a proper tool for market timing because it does not generate a signal for trade when the pattern of the market is uncertain by using the control function. The data for the rough set analysis should be discretized of numeric value because the rough set only accepts categorical data for analysis. Discretization searches for proper "cuts" for numeric data that determine intervals. All values that lie within each interval are transformed into same value. In general, there are four methods for data discretization in rough set analysis including equal frequency scaling, expert's knowledge-based discretization, minimum entropy scaling, and na$\ddot{i}$ve and Boolean reasoning-based discretization. Equal frequency scaling fixes a number of intervals and examines the histogram of each variable, then determines cuts so that approximately the same number of samples fall into each of the intervals. Expert's knowledge-based discretization determines cuts according to knowledge of domain experts through literature review or interview with experts. Minimum entropy scaling implements the algorithm based on recursively partitioning the value set of each variable so that a local measure of entropy is optimized. Na$\ddot{i}$ve and Booleanreasoning-based discretization searches categorical values by using Na$\ddot{i}$ve scaling the data, then finds the optimized dicretization thresholds through Boolean reasoning. Although the rough set analysis is promising for market timing, there is little research on the impact of the various data discretization methods on performance from trading using the rough set analysis. In this study, we compare stock market timing models using rough set analysis with various data discretization methods. The research data used in this study are the KOSPI 200 from May 1996 to October 1998. KOSPI 200 is the underlying index of the KOSPI 200 futures which is the first derivative instrument in the Korean stock market. The KOSPI 200 is a market value weighted index which consists of 200 stocks selected by criteria on liquidity and their status in corresponding industry including manufacturing, construction, communication, electricity and gas, distribution and services, and financing. The total number of samples is 660 trading days. In addition, this study uses popular technical indicators as independent variables. The experimental results show that the most profitable method for the training sample is the na$\ddot{i}$ve and Boolean reasoning but the expert's knowledge-based discretization is the most profitable method for the validation sample. In addition, the expert's knowledge-based discretization produced robust performance for both of training and validation sample. We also compared rough set analysis and decision tree. This study experimented C4.5 for the comparison purpose. The results show that rough set analysis with expert's knowledge-based discretization produced more profitable rules than C4.5.

• Journal of the Korea Society of Computer and Information
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• v.19 no.10
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• pp.63-70
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• 2014

Process of recognizing objects in binary images consists of image segmentation and pattern matching. If binary objects in the image are assumed to be separated, global features such as area, length of perimeter, or the ratio of the two can be used to recognize the objects in the image. However, if such an assumption is not valid, the global features can not be used but local features such as points or line segments should be used to recognize the objects. In this paper points with large curvature along the perimeter are chosen to be the feature points, and pairs of points selected from them are used as local features. Similarity of two local features are defined using elastic deformation energy for making the lengths and angles between gradient vectors at the end points same. Neighbour support value is defined and used for robust recognition of partially occluded binary objects. An experiment on Kimia-25 data showed that the proposed algorithm runs 4.5 times faster than the maximum clique algorithm with same recognition rate.