• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.524-527
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• 2004

Hybrid rocket had many advantage with compared to solid and liquid rockets. However, the engines have not yet been used in practical rocket systems, due mainly to the disadvantage of hybrid combustion, such as low fuel regression rate. In this study, lab-scale hybrid motor was designed and manufactured. And the methods of regression rate improvement were considered. Test firings with thrusts up to 300 N were conducted with GOX and transparent PMMA. Thrust was calculated with the pressure of the combustion chamber and the regression rate was measured in with variation of oxidizer flow rate. The regression rates showed a strong dependency on GOX mass flux. The frequency analysis technique of the bulk-mode oscillation of motor was applied to a hybrid rocket motor and was based on the principle that this frequency was inversely proportional to the square root of the chamber volume. Several problems and solutions of operating hybrid rocket were presented.

• International Journal of Fuzzy Logic and Intelligent Systems
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• v.8 no.2
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• pp.132-139
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• 2008

This paper proposes a scatternet topology formation, self-healing, and self-routing path optimization algorithm based on Relative Neighborhood Graph. The performance of the algorithm using ns-2 and extensible Bluetooth simulator called blueware shows that even though RNG-FHR does not have superior performance, it is simpler and easier to implement in deploying the Ad-Hoc network in the distributed dynamic environments due to the exchange of fewer messages and the only dependency on local information. We realize that our proposed algorithm is more practicable in a reasonable size network than in a large scale.

• Journal of the Korean Vacuum Society
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• v.4 no.S2
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• pp.139-147
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• 1995

The mechanism of the ionized cluster beam deposition has been studied using Molecular Dynamics Simulation. The Embedded Atom Method(EAM) potential were used in the simulation. The impact of a Au95-cluster on Au(100) substrate was studied for the impact energies 0.15-10eV/atom. The dependency of the impact energy of cluster beam was observed. For the cluster energy impact of 10eV per atom, the defects on surface were created and the cluster embedded into substrate as an amorphous state. For the energy of 0.5eV per atom, the defect free homoepitaxial growth was observed and atomic scale nucleation was formated, which are in good agreement with experiment. Thus molecular dynamics simulation is very useful to study the mechanism of the ionized cluster beam deposition.

• Structural Engineering and Mechanics
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• v.69 no.6
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• pp.637-649
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• 2019

In the current research paper, a quasi-3D beam theory is developed for free vibration analysis of functionally graded microbeams. The volume fractions of metal and ceramic are assumed to be distributed through a beam thickness by three functions, power function, symmetric power function and sigmoid law distribution. The modified coupled stress theory is used to incorporate size dependency of micobeam. The equation of motion is derived by using Hamilton's principle, however, Navier type solution method is used to obtain frequencies. Numerical results show the effects of the function distribution, power index and material scale parameter on fundamental frequencies of microbeams. This model provides designers with guidance to select the proper distributions and functions.

• Journal of Apiculture
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• v.34 no.2
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• pp.141-147
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• 2019

Pollinators play important roles for crop production as well as maintenance of wild plants' reproduction. Pollinator dependency in Korean agriculture have increased, but the degradation of habitat quality pose significant threats to pollination in agroecosystem. Provisioning flower habitat is one of the major activities to increase pollinator abundance and richness. We tested the effect of flower habitat supplementation on the pollinator, pest and natural enemy abundance in pepper field. Results showed that Hymenopteran pollinators were more abundant in the pepper plots close to the flower habitat. Among natural enemies, the similar pattern from pollinators was observed to parasitoids in the family of Eulophidae, but not to those of Ichneumonidae. There were no statistically significant differences of insect pests like aphids and thrips, as well as pepper production among plots in the pepper field. Even limited spatial scale, this study showed supplementing the flowering plant habitat to the agricultural landscape could conserve and boost pollinators and natural enemies, and possibly resulting better fruit production by pollination service.

• Ocean and Polar Research
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• v.44 no.2
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• pp.179-190
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• 2022

Data missing in optical satellite images caused by natural variations have been a crucial barrier in observing the status of marine surfaces. Although there have been many attempts to fill the gaps of non-observation, there is little research to analyze the ratio of missing grids to overall sea grids and their seasonal patterns. This report introduces the method of quantifying the distribution of missing points and then shows how the missing points have spatial correlation and seasonal trends. Both temporal and spatial integration methods are compared to assess the effectiveness of reducing missing data. The temporal integration shows more outstanding performance than the spatial integration. Moran's I and K-function with statistical hypothesis testing show that missing grids are clustered and there is a non-random distribution from daily integration. The result of the seasonality test for Moran's I through a periodogram shows dependency on full-year, half-year, and quarter-year periods respectively. These analysis results can be used to deduce appropriate integration periods with permissible estimation errors.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.1
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• pp.58.1-58.1
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• 2021

At the University of Seoul, we are investigating the following topics in cosmology: comparing traditional clustering algorithms to our new Mulguishin algorithms, analysis of 2-body Fuzzy Dark Matter 2-body collision, 2- and 3-point clustering statistics and its dependency on the cosmological model, and dynamics of dark-matter halos around the large-scale filamentary structures. In the following sections we present a brief introduction to our studies.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.1
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• pp.93-100
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• 2013

The objective of present study is to investigate the sensitivity of aerostatic force coefficients of twin box girder of Yi Sun-sin Bridge according to the Reynolds numbers. This paper presents the 1:30 scale sectional model tests conducted at high speed wind tunnel in Korea Air Force Academy. Comparison with results at low Reynolds number obtained in KOCED Wind Tunnel Center in Chonbuk National University is also provide. The Reynolds number dependency of aerodynamic force coefficients were observed at present streamlined twin box girder. The drag coefficient revealed significant decrease of nearby 23% at supercritical region. The boundary layer trip strip was found to reduce the Reynolds number dependency of aerodynamic forces by fixing the location of flow transition.

• Journal of the Korean Geographical Society
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• v.42 no.2 s.119
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• pp.177-195
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• 2007

The central aim of this paper is to identify the distributional pattern of poverty and to investigate the spatial relationship between poverty and welfare service providers in Busan, Korea. It is intended to explain how the relationship of service-dependency between impoverished people and social welfare services leads to uneven social geography. Welfare services controlled by public or private agencies may support the impoverished people in different ways, generating social outcomes. By exploiting the spatial variations in the incidence of poverty and the provisions of social welfare services, this paper is to understand the dynamics of the geography of poverty from a local scale so that it can help us understand how various governmental and nongovernmental area-based service providers are spatially uneven when they are compared to the distribution of service dependency group such as impoverished people. From this research, it is finally argued that the implications of locational interdependence between such needed groups and social welfare services for their support demand a paradigm for urban social geography that centers on the changing welfare provision structure and the linkages between population and service-provision.

• Journal of Oral Medicine and Pain
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• v.41 no.2
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• pp.54-60
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• 2016

Purpose: Mandibular advancement devices (MAD) are used effectively and widely for the treatment of obstructive sleep apnea (OSA) and rapid-eye-movement (REM) dependency of the patients can affect the treatment outcome of OSA. The aim of this study was to compare treatment outcomes of MAD between REM-related and not-REM-related OSA patients. Methods: Fifty-six consecutive patients with OSA who received MAD therapy were evaluated using full night polysomnography before and after insertion of the MADs. The patients were divided into REM-related (REM apnea-hypopnea index [AHI] at least two times higher than their non-REM AHI) and not-REM-related (REM AHI less than two times higher than their non-REM AHI) OSA groups. Results: MAD is used for the treatment of OSA effectively. In respect of AHI, MAD therapy were effective both in REM-related OSA and not-REM-related OSA, but MAD therapy was more effective in not-REM-related OSA than REM-related OSA in overall sleep and non-REM sleep. $SpO_2$ saturations were improved after MAD therapy, but were not different between two groups. Epworth sleepiness scale scores were not improved after MAD therapy. Percentage of REM sleep was increased after MAD therapy but was not different between two groups. Conclusions: MAD therapy was more effective in not-REM-related OSA than REM-related OSA and REM dependency can be a predictive factor of treatment outcome of oral appliance for OSA patients.