• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.539-542
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• 2005

In this study, we investigated the influence of vibrational stimulation on postural control. To study the effect, the sway of the center of pressure was observed fur two different visual conditions and for three different patterns of vibrational stimulation on plantar area. The two visual conditions were normal condition with visual feedback and blind condition with both eyes closed. The three vibrational stimulations were white noise, constant vibration, and vibration with amplitude modulations (sine curve modulation). The experimental results showed that the sway of the center of pressure distinctively reduced with white noise vibrational stimulation. This result showed that it's possible to use vibrational stimulation for improving the ability of postural control.

• Nuclear Engineering and Technology
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• v.55 no.12
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• pp.4504-4517
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• 2023

After a loss of coolant accident (LOCA) in the prestressed concrete containment vessels (PCCVs) of nuclear power plants, the coupling of temperature and pressure can significantly affect the mechanical properties of the PCCVs. However, there is no consensus on how this coupling affects the failure mechanism of PCCVs. In this paper, a simplified finite element modeling method is proposed to study the effect of temperature and pressure coupling on PCCVs. The experiment results of a 1:4 scale PCCV model tested at Sandia National Laboratory (SNL) are compared with the results obtained from the proposed modeling approach. Seven working conditions are set up by varying the internal and external temperatures to investigate the failure mechanism of the PCCV model under the coupling effect of temperature and pressure. The results of this paper demonstrate that the finite element model established by the simplified finite element method proposed in this paper is highly consistent with the experimental results. Furthermore, the stress-displacement curve of the PCCV during loading can be divided into four stages, each of which corresponds to the damage to the concrete, steel liner, steel rebar, and prestressing tendon. Finally, the failure mechanism of the PCCV is significantly affected by temperature.

• The Journal of Korean Obstetrics and Gynecology
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• v.15 no.4
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• pp.45-60
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• 2002

Mouse calvarial osteoblast cells were isolated and cultured. To examine whether the cells produce active gelatinases in culture medium or not,the cells were analyzed using by zymograsphic analysis on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). We show that mouse calvarial osteoblasts in culture constitutively synthesize progelatinase- A. Then, mouse osteoblasts, which were stimulated by PTH, $1,25(OH)_2D_3$, mononuclear cell conditioned medium (MCM) and IL-1 as bone resorption agent's, showed increased collagenolysis by producing the active gelatinase. However, treatment of indomethacin and dexamethasone significantly decreased those effects of collagenolysis in mouse osteoblastic cells. On the other hand, IL-1 in stimulating bone resorption was examined using fetal mouse long bone organ culture. IL-1 stimulated bone resorption and produced marked resorption when present simultaneously. Furthermore, when it was examined the effects of indomethacin and dexamethasone on the dose dependent responses of $IL-1{\alpha}$, indomethacin and dexametasone produced a rightward shift in the IL-1 dose response curve. The results of in vitro cytotoxicities showed that Taeyoungjon-Jahage water extracts(T.Y.J-J.H.G extracts) have no any cytotoxicities in concentrations of $1-200\;{\mu}g/ml$ and furthermore there is no any cytotoxicity even in concentration of $300\;{\mu}g/ml$ on mouse calvarial bone cells. T.Y.J.-J.H.G. extracts had protective activity against PTH (2 units/mI), or MCM (5%, v/v), or $rhIL-1{\alpha}$ (1 ng/mI) or $1,25(OH)_2D3$ (10 ng/ml) , $IL-1{\alpha}$ and $IL-1{\beta}-induced$ collagenolysis in the mouse calvarial cells. Pretreatment of the T.Y.J.-J.H.G.extracts for 1 h, which by itself had little effect on cell survival, did not enhance the collagenolysis, nor significantly reduced the collagenolysis by pretreatment. Furthermore. the medicinal extracts were shown to have the protective effects against collagenolysis induced by $IL-1{\alpha}$ and $IL-1{\beta}$. Pretreatment of the extracts for 1 h significantly reduced the collagenolysis. Interestingly, the T.Y.J.-J.H.G. extracts were shown to have the inhibiting effects against gelatinase enzyme and processing activity induced by the bone resortion agents of PTH, $1,25(OH)_2D_3$, $IL-1{\beta}$ and $IL-1{\alpha}$, with strong protective effect in pretreatment with the extracts. T.Y.J.-J.H.G. extracts were shown to have the inhibiting effects against $IL-1{\alpha}-$ and $IL-1{\beta}-stimulated$ bone resorption and the effect of the pretreatment with a various concentrations of the medicinal extracts were significant. The inhibition extent and phenomena of IL-1 stimulated bone resorption by nonsteroidal anti-inflammatory agents of indomethacin and dexamethasone were similar to those obtained by T.Y.J.-J.H.G. extracts treatment in the mouse calvarial tissue culture system. These results indicated that the T.Y.J.-J.H.G.-water extracts are highly stable and applicable to clinical uses in osteoporosis.

• Journal of the Korean Society for Heat Treatment
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• v.13 no.1
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• pp.1-9
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• 2000

The microstructural characteristics and low temperature tensile properties between $25^{\circ}C$ and $-196^{\circ}C$ for as-welded and age hardened specimen by using Al 5083-H321 for base metal, 5083-5356 and 5083-4043 weldments have been investigated. The hardness of 5083-5356 weldment decreases with aging treatment, whereas the weld region of 5083-4043 weldment shows remarkable increase in hardness after aging due to the precipitation of fine Si particle at the grain boundaries and interiors. Low temperature tensile properties of 5083 AI base metal, 5083-5356 and 5083-4043 weldments appear to be the increment of tensile strengths and elongations at the room temperature and $-196^{\circ}C$, while the decrement of tensile properties around $-50^{\circ}C$ is shown. Through the observation of fine serration to fracture in the stress-strain curve and tensile fractography, the increment of localized deformation leading to promote the neck initiation and the increment of the dimple size cause to decrease in tensile strengths and elongations around $-50^{\circ}C$. For the tensile specimen of the 5083 base metal, 5083-5356 and 5083-4043 weldments, the reason to increase in elongation after solution and aging treatment is the diminishment of fine pit, the resolution of Mg into the matrix and the spheridization of the eutectic Si.

• Journal of Navigation and Port Research
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• v.26 no.4
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• pp.435-440
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• 2002

The quantitative assessment of the effect of the residual stress on fracture behavior was executed by some experiment and numerical analysis. First of all, artificial residual stresses were imposed on CT(Compact Tension) specimens by local heating using gas torch, and an appropriate distribution of residual stresses was obtained by thermal elastic-plastic FE analysis. To certify the result of the FE analysis, an experimental measurement was performed in accordance with ASTM standard. Fracture toughness test was executed on the several types of specimens. The first type was the specimen without residual stresses, and the others had different peak value of compressive residual stress at crack front via controlling the heat flux. All the test results were presented on th J resistance(JR) curves and discussed to verify the effect of compressive residual stresses on fracture behavior.

• Steel and Composite Structures
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• v.37 no.2
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• pp.117-136
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• 2020

Curved steel-concrete composite box girder has been widely adopted in urban overpasses and ramp bridges. In order to investigate its mechanical behavior under complicated and combined bending, shear and torsion load, two large-curvature composite box girders with interior angles of 25° and 45° were tested under static hogging moment. Based on the strain and deflection measurement on critical cross-sections during the static loading test, the failure mode, cracking behavior, load-displacement relationship, and strain distribution in the steel plate and rebar were investigated in detail. The test result showed the large-curvature composite box girders exhibited notable shear lag in the concrete slab and steel girder. Also, the constraint torsion and distortion effect caused the stress measured at the inner side of the composite beam to be notably higher than that of the outer side. The strain distribution in the steel web was approximately linear; therefore, the assumption that the plane section remains plane was approximately validated based on strain measurement at steel web. Furthermore, the full-process non-linear elaborate finite element (FE) models of the two specimens were developed based on commercial FE software MSC.MARC. The modeling scheme and constitutive model were illustrated in detail. Based on the comparison between the FE model and test results, the FE model effectively simulated the failure mode, the load-displacement curve, and the strain development of longitudinal rebar and steel girder with sufficient accuracy. The comparison between the FE model and the test result validated the accuracy of the developed FE model.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.71.1-71.1
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• 2013

Among quadruples or higher multiplicity stars, only a few binary systems have been discovered. They are important targets to understand the formation and evolution of multiple stellar systems because we can obtain accurate stellar parameters from photometric and spectroscopic studies. We present the observational results of this kind of rare object 1SWASP J093010.78+533859.5, for which the doubly eclipsing feature had been detected previously from the SuperWASP photometric archive. Individual PSF photometry for two objects with a separation of about 1.9 arcsec was performed for the first time in this study. Our time-series photometric data show that the brighter object A is an Algol-type detached eclipsing binary with an orbital period of 1.3 days and the fainter B is a W UMa-type contact eclipsing binary with a period of 0.23 days. Using the high-resolution optical spectra, we obtained well-defined radial velocity variations of the system A. Furthermore, stationary spectral lines were detected and should have originated from the other stellar component, which was confirmed by the third object contribution from the light curve analysis. No spectral feature of the system B was detected, probably due to its faintness. We obtained the binary parameters and the absolute dimensions from each light curve synthesis. The primary and secondary components of the system A have a spectral type of K1 and K5 main sequences, respectively. Two components of system B have nearly the same type of K3 main sequence. Light variations at out of eclipses were appeared in both systems, interpreting as the effect of stellar spots on these late spectral type stars. We estimated the distances to the systems A and B individually. They may have similar distances of about 70 pc and seem to be gravitationally bound with a separation of about 130 AU. In conclusion, we suggest that 1SWASP J093010.78+533859.5 is a quintuple stellar system with a hierarchical structure of a triple system A(ab)c and a binary system B(ab).

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.49.1-49.1
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• 2021

We carried out simultaneous monitoring observations of five maser lines, H₂O (22 GHz), SiO 𝝊 =1, 2, J =1-0 (43.1, 42.8 GHz), and SiO 𝝊 =1, J=2-1, J =3-2 (86.2, 129.3 GHz), toward the Mira variable star WX Serpentis with the 21-m antennas of the Korean VLBI Network (KVN) in 2009-2021 (~12 years). Most spectra of the H₂O maser are well separated into two parts of two blue- and one redshifted features within ± 10 km s-1 of the stellar velocity. All detected SiO masers are generally concentrated within ± 5 km s-1 of the stellar velocity, and sometimes appear split into two components. Overall, the profiles of SiO and H₂O masers detected in WX Serpentis illustrate typical characteristics of the Mira variable. In addition, flux variations of both SiO and H₂O masers are well correlated with the optical light curve of the central star, showing a phase lag of ~ 0.1 for SiO masers and ~ 0.2 for H₂O maser. This phenomenon is considered to be the direct effect of propagating shock waves generated by the stellar pulsation, because SiO and H₂O masers are sequentially distributed at different positions with respect to the central star. In addition, we analyzed long-term trends and characteristics of maser velocities, maser ratio, and the velocity extents (the full width at zero power; FWZP). We also investigated a spectral energy distribution (SED) ranging from 1.2 to 240 ㎛ obtained using several infrared data: 2MASS, WISE, IRAS, ISO, COBE DIBRE, RAFGL, and AKARI (IRC and FIS). From the IRAS LRS and ISO SWS spectra of this star, we identified 9.7 and 12 ㎛ silicate emission features consistent with the SE6 spectrum model, corresponding to the typical AGB phase.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.32.2-32.2
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• 2012

Gamma Ray Bursts (GRBs) are the most energetic events in the universe, and are known to arise from the death of massive stars in many cases. Their extreme brightness makes it possible to detect them at very high redshift (z > 6.5), well into the epoch of re-ionization, providing us with an opportunity to investigate the deaths of the first stars when the universe was much younger than 1 Gyr. Here, we report the discovery of GRB 100905A, a GRB at $z$ - 7.5 (age of the universe at 700 Myr). Our observation revealed a strong spectral break between z and J band, allowing us to estimate its photometric redshift. Its gamma-ray light curve shows a very short duration of about 0.7 sec, the shortest duration event at z > 5. Investigation of this and three other known GRBs at z > 6.5 reveals that they are all short duration bursts. This is puzzling, considering that GRBs from death of massive stars do not show short duration. We suggest two possible explanations for this: (i) the BAT light curves of the high redshift GRBs suffered from observational selection effect where we are only observing the very tip of the light curve; (ii) the stars in the early universe had a peculiar nature that are different from ordinary stars at lower redshifts.

• Journal of the Korean Society for Railway
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• v.13 no.6
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• pp.552-558
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• 2010

Ride comfort of railway vehicles is affected by many factors, such as vibration, noise, smell, temperature, visual stimuli, humidity and a seat design. In general, vibration, which originates from vehicle motion, is considered as the primary concern. In evaluating the ride comfort, relationship between passenger's feeling and vibration characteristics is very important because human feeling is dependent on frequency spectrum of vibration. Therefore, the weighing functions in frequency domain are used to evaluate the ride comfort of railway vehicles. In the present paper, we have analyzed the characteristics of the frequency weighting curves defined in many standards and reviewed the effect resulting from their difference on the ride comfort.