• Journal of the Korean earth science society
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• v.36 no.7
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• pp.649-660
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• 2015

This study aimed at the correlation analysis of geomagnetic variations related to earthquakes which occurred in and around the Korean Peninsula from 2012 to 2014. The wavelet-based semblance technique was used to confirm the geomagnetic variations related to earthquakes. As a result, a pattern of consistent geomagnetic variations in total magnetic has been found from the earthquakes occurred within 100 km radius around the observation site. A similar correlation between earthquake location and Z-field geomagnetic data was also confirmed by the wavelet-based semblance analysis. We mainly used the high quality geomagnetic measurements from the Cheongyang Observatory and additionally used the data from the Bohyunsan Observatory in order to validate the correlation between earthquake and Z-field geomagnetic data.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.8
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• pp.4068-4076
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• 2013

The wheel-rail interaction forces are influenced by the velocity of vehicle, wheel load, alignment (curve radius, cant etc). For the safety of track structure, it is required to evaluate the influences for track and influential factors. Recently, the HEMU 430-X, which was developed by Next Generation High-Speed Rail Development R&D Project, achieved 421.4km/h in a test run of Daegu.Busan section of the Gyeongbu high speed rail on March in 2013. In the case of additional speed-up test on Test-Bed Section(Gongju.Jeongeup: KP 100~128km Osong starting point), the analysis of track forces is required for outer rail by the increase of dynamic force and centrifugal force of vehicle. In this paper, the vehicle speed variation on HSL line is evaluated by TPS analysis considering the tractive effort of HEMU 430-X, tested running resistance and alignment of Honam HSR. And the track forces are evaluated by centrifugal force and impact factor on curved track.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.7
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• pp.38-45
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• 2020

A magnetically levitating capsule train, which runs inside the sub-vacuum tube, can reach ultra-fast speeds by dramatically reducing the aerodynamic drag and friction. The capsule train uses the superconductor electrodynamic suspension (SC-EDS) method for levitation. The SC-EDS method has advantages, such as a large levitation gap and free of gap control, which could reduce the infra-construction cost. On the other hand, disadvantages, such as the large variation of the levitation-guidance gap and small damping characteristics in levitation-guidance force, could degrade the running stability and ride comfort of the capsule train. In this study, a dynamic analytical model of a capsule train based on the SC-EDS was developed to analyze the running dynamic characteristics. First, as important factors in the capsule train dynamics, the levitation and guidance stiffness in the SC-EDS system were derived, which depend non-linearly on the velocity and gap variation. A 3D dynamic analysis model for capsule trains was developed based on the derived stiffness. Through the developed model, the effects of the different running speeds on the ride comfort were analyzed. The effects of a disturbance from infrastructure, such as the curve radius, tube sag, and connection joint difference, on the running stability of the capsule train, were also analyzed.

• Journal of the Korean Ceramic Society
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• v.30 no.7
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• pp.535-542
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• 1993

It was investigated in this study that a preparation method, activation energy, surface area, pore volume, pore size distribution and DTA analysis of the dry gel in process of producing monolithic porous gel in Li2O-Al2O3-TiO2-SiO2 system by the sol-gel technique using metal alkoxides. Activation energy for gellation according to the variation of water concentration and the kind of catalysts ranged from 10 to 20kcal/mole. Monolithic dry gels were prepared after drying at 9$0^{\circ}C$ when the amount of water for gellation was 4~8 times more than the stoichiometric amount, that was necessary for the full hydrolysis of the mixed metal alkoxide. The specific surface area, the pore volume, the average pore radius of the dried gel at 18$0^{\circ}C$ according to the various kinds of catalyst were about 348~734$m^2$/g, 0.35~0.70ml/g and 10~35$\AA$, respectively. It showed that the dry gels were porous body. As a result ofthe analysis of DTA, it was confirmed that the exothermaic peaks at 715$^{\circ}C$ and 77$0^{\circ}C$ was clue to the crystallization of dried gel.

• Proceedings of the KOSOMBE Conference
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• v.1997 no.11
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• pp.511-514
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• 1997

The objective of this study is to propose a finite element based design of the dental implant replacing unction and shape of natural teeth. For this, geometric actors were varied to investigate stress distribution of the alveolar bone around dental implant. In this study, the results were obtained based on the theory of linear elastic, with geometrically axisymmetric assumption. Geometric actors determining implant shape are ranged as 0.2mm-0.6mm, 0.04mm-0.1mm, 0.46mm-0.84mm or height of thread, radius of curvature of thread, and pitch, respectively. The stresses in the alveolar bone caused by biting force playa major role in determining implant stability. Especially, the stress concentration in the cortical bone causes bone resorption and finally makes the implant unstable. Therefore, the stress distributions were investigated on the side of the alveolar bone focusing on the area of cortical bone. The maximum von Mises stress was found to increase up to 6% as the height of thread increases, while its value was to decrease to 19% when the radius of curvature increase within the assigned ranges. For the variation of pitch, the larger size of pitch results in greater maximum von Mises stress when the length of the implant under consideration is fixed. The existence of the neck below the shoulder did not affect the stress distribution in the region of alveolar bone. However, the stresses on the side of the implant near the neck were found to be different by 20% approximately. Therefore, the neck can provide the stability of the implant against continuing biting movement. As a conclusion, the finite element based study shows a potential in designing the dental implant systematically.

• The Journal of the Acoustical Society of Korea
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• v.32 no.1
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• pp.32-42
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• 2013

Typical underwater piezoelectric spherical sensors are omni-directional, thus can measure the scalar quantity sound-pressure-magnitude only with the limitation not being able to measure the direction of the incoming wave. This paper proposes a method to simultaneously measure both the magnitude and direction of the sound wave with the spherical sensor. The method divides the piezoceramic sphere of the sensor into eight elements, and distinguishes the magnitude and direction of the sound pressure by combining the output voltage of the elements in a particular manner. Further, through the analysis of the sensitivity variation in relation to the structural parameters like radius and thickness of the piezoceramic sphere, we have suggested the way to improve the sensitivity of the vector sensor.

• Journal of Korean Society for Atmospheric Environment
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• v.27 no.2
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• pp.152-167
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• 2011

MODIS/Terra level 3 and NCEP/NCAR Reanalysis data from 2001 to 2008 have been analyzed to understand long-term aerosol and cloud optical properties, and their relationships around Korea. Interestingly, cloud fraction(CF) has the similar annual variation to aerosol optical depth (${\tau}_a$) without any temporal significant trend. Horizontal distributions of ${\tau}_a$ showed the substantial horizontal gradient from China to Korea, especially with the strong difference over the Yellow Sea, which could represent the evidence of the anthropogenic influence from China in the perspective of long-term average. Specifically the negative correlations between ${\tau}_a$ and liquid-phase cloud effective radius ($r_e$) were shown on the monthly-average basis, only in summer with significant associations over the Yellow Sea, but not in the other seasons and/or specific regions. Relationship between ${\tau}_a$ and CF for the low-level liquid-phase clouds exhibited the overall positive correlation, being consistent with cloud lifetime effect. Meanwhile static stability showed no deterministic relationships with ${\tau}_a$ as well as CF. The dependence of aerosol-cloud relationship on the meteorological conditions should be examined more in detail with the satellite remote sensing and reanalysis data.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.6-9
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• 2008

Analyzing the characteristics of blood flow in the blood vessels is very important to diagnose the circulatory diseases. In order to investigate the hemodynamic characteristics in vivo, the measurements of blood flows inside the extraembryonic arterial and venous blood vessels of chicken embryos were carried out using an in vivo micro-PIV technique. The circulatory diseases are closely related with the formation of abnormal hemodynamic shear stress regions, thereby it is important to get blood velocity and vessel's morphological information according to the vessel configuration and the flow conditions. In this study, the flow images of RBCs in blood vessels were obtained using a high-speed CMOS camera with a spatial resolution of approximately 14.6${\mu}$m${\times}$14.6${\mu}$m in the whole circulation network of blood vessels. The blood flows in the veins and arteries show steady laminar and unsteady pulsatile flow characteristics, respectively. The mean blood flows merged (in veins) and bifurcated (in arteries) smoothly into the main blood vessel and branches, respectively, without any flow separation or secondary flow which accompanying large variation of shear stress. Vorticity was high in the inner regions for both types of vessels, where the radius of curvature varied greatly. The instantaneous flows in the arterial blood vessels showed noticeable pulsatility due to the heart beat, and the main features of the velocity waveforms, including pulsatile shape, retrograde flow, mean velocity, maximum velocity and pulsatile frequency, were significantly dependent on the pulsatile condition which dominates the arterial blood flow. In near future, these in vivo experimental results of blood flow measured in various extraembryonic blood vessels would be very useful to understand the hemodynamic characteristics of human blood flows and various blood flow researches for clinically useful hemodynamic discoveries as well.

• Journal of Navigation and Port Research
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• v.34 no.6
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• pp.435-440
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• 2010

A numerical model, which can compute deformation of rubble mound structures composed with various size materials, was proposed. In the numerical model, wave field into the mound structures was computed by CADMAS-SURF and the deformations of mound structures were computed by DEM. Interaction between wave field and sectional deformation of structure was considered and to present the variation of behaviors caused by various properties of materials, computation was carried out with random coefficients by Monte Carlo simulation method for contact stiffness and friction angle. The experiments were carried out with rubbles and glass balls with radius of 2.9cm, 2.6cm and 1.5cm. And the deformation characteristics of rubble mounds composed with various size materials were clarified. Furthermore the validity and the applicability of the model were discussed by comparing with the experimental results.

• Journal of the Korean earth science society
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• v.38 no.1
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• pp.1-10
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• 2017

The symbiotic star AG Peg is a nebulous binary system that consists of giant star (GS) and white dwarf (WD). We investigated the HI Balmer emission lines of the symbiotic nova AG Peg, observed in 1998, 2001, and 2002 at Lick Observatory. The $H{\alpha}$ and $H{\beta}$ line profiles consist of blue-shifted, red-shifted, and broad components of which intensities and width showed notable changes. The HI emission line profiles that represent the kinematics of the gaseous nebula appear to be mainly from an accretion disk in relatively large radius from the WD. Considering the line of an observer's sight, both GS and WD are located at the sky plane side by side during the 1998 observation, while the WD is in front of GS during 2002 but the WD in rear during 2001. Such a relative position and the spectral line intensity variation imply that a fairly constant outflow occurs into WD from GS which caused to maintain the rotating thick accretion disk structure responsible for the observed spectral lines.