• International Journal of Aeronautical and Space Sciences
• /
• v.3 no.1
• /
• pp.95-104
• /
• 2002

Numerical solution of the full Navier-Stokes equation as well as the energy equation has been obtained for the unsteady natural convection in a rectangular enclosure. One side wall was maintained at very high temperature simulating fires. Especially the effect of surface radiation was taken into account. While the enclosed air was assumed to be transparent, the internal walls directly interacted one another through the surface radiation. Due to a significant temperature difference in the flow field, the equation of state was used instead of the Boussinesq approximation. It was found that the rapid heating of the adiabatic ceiling and floor by the incoming radiation from the hot wall made the evolution at thermo-fluid field highly unstable in the initial period. Therefore, the secondary cells brought about at the floor region greatly affected the heat transfer mechanism inside the enclosure. The heat transfer rate was augmented by the radiation, resulting in requiring less time for the flow to reach the steady state. At the steady state neglecting radiation two internal hydraulic jumps were clearly observed in upper/left as well as in lower/right comer. However, the hydraulic jump in the lower/right comer could not be observed for the case including radiation due to its high momentum flow over the bottom wall. Radiation resulted in a faster establishment of the steady state phenomena.

• Proceedings of the Korea Association of Crystal Growth Conference
• /
• 2000.06a
• /
• pp.151-163
• /
• 2000

A polymerized organic-inorganic complexation route is introduced for the synthesis of oxide ceramic powders. Polyvinyl alcohol was used as the organic carrier for precursor ceramic gel. Porous and soft powders, which have a high specific surface area, were obtained after calcinating the aerated precursors. The PVA content and its degree of polymerization had a significant influence on the homogeneity of the final powder. In particular, attrition milling process with the porous powder resulted in ultra-fine particles. In the case of the preparation of cordierite powder, nano-size powder, which has a high specific surface area of 181 ㎡/g, was obtained by the milling process. The complexation route was also applied to the synthesis of unstable phase in room temperature like beta-cristobalite, high temperature form of silica.

• Journal of Korean Association for Spatial Structures
• /
• v.3 no.4 s.10
• /
• pp.77-84
• /
• 2003

Tensegrity systems are stable structures which are reticulated spatial structures composed of compressive straight members, struts and cables. But there are some difficulties concerning surface stability, surface formation and construction method. One of the ways to solve this problem reasonably is combination of tesile members and rigid members. This structure is a type of flexible strutural system which is unstable initially because the cable material has little initial rigidity. Therefore tensegrity structure need to be introduced to the Initial stress for the self-equilibrated system having stable state. The rigidification of tensegrity systems is related to selfstress states which can be achieved only when geometrical and mechanical requirements are simultaneously satisfied. In this paper, for the stabilization of tesnsegrity structure it is proposed the modified self-equilibrated equation and the range of the various geometrical parameter about unit system. And we generate the model of double layed single curvature arch using the new squew quadruplex unit system.

• Journal of the Korean Society of Physical Medicine
• /
• v.8 no.4
• /
• pp.533-538
• /
• 2013

PURPOSE: This study was performed to investigate the effect of Low-dye Taping on muscle activity during single-leg standing in subjects with flexible flatfoot. METHODS: Thirteen able-body volunteers who had flexible flatfoot were recruited for this study. Subjects were measured navicular drop test to evaluate pronation of foot and muscle activity during single-leg standing before and after taping. The muscle activity was recorded using surface EMG from the tibialis anterior and the peroneus longus during single-leg standing on stable and unstable surface. RESULTS: The results show that the navicular drop height and the tibialis anterior muscle activity were significantly decreased after Low-dye taping. CONCLUSION: The results suggest that Low-dye taping could be useful in managing overuse of the tibialis anterior by reducing their level of activation during single-leg standing.

• Proceedings of the Korea Water Resources Association Conference
• /
• 1992.07a
• /
• pp.133-141
• /
• 1992

A three water-intake structure designed to built along the right bank of the Missouri River near Chesterfield, Missouri was model-tested at an undistorted scale of 1:5. Although the discharge capacity of each of six pumps to be installed is only 21,000 gpm, the model indicated strong flow circuation and unstable free-surface conditions as flow entered the two-pump bay through a narrow sluice opening at an angle. Strong free-surface vartices were also observed in the model. The sump modifications developed in the study included an array of baffle bars, a perforated plate, floor splitters, and floor-corner fillets. The solutions developed in this study could be applied to other pump sumps with multiple pump units.

• Journal of the Korean Society for Precision Engineering
• /
• v.21 no.4
• /
• pp.103-108
• /
• 2004

Carbon fiber reinforced composites(CFRP) were fabricated with phenolic resin matrix by hot press molding, and its surface was modified by the ion-assisted reaction process. When we tested the friction coefficient and wear rate variation and observed the effect of fibers with respect to friction and wear characteristics, the amount of pitch based carbon fiber was 45wt% and the average friction coefficient was the lowest at 0.12. When the amount of ion-irradiation was $1\times10^{l6}ions/cm^2$, the friction coefficient of the composites was about 0.12 and the wear mode was stable, whereas, the friction coefficient of the non-treated composites was about 0.16 and the wear mode was very unstable. But if the amount of ion-irradiation was $5\times10^{l6}ions/cm^2$$1\times10^{l6}ions/cm^2$ion-irradiation case.

• Journal of Korean Society for Atmospheric Environment
• /
• v.23 no.2
• /
• pp.242-249
• /
• 2007

Deposition fluxes of polycyclic aromatic hydrocarbons (PAHs) were measured at the Chonbuk National University located in Jeonju between June and November 2002. Fluxes of gaseous and particulate PAHs were separately obtained using a water surface sampler (WSS) and a dry deposition plate (DDP). Most of PAHs were deposited in the gaseous form since the low molecular weight PAHs dominates in the atmosphere. The deposition velocity of particulate PAHs was higher than that of gaseous PAHs when the molecular weight was low, but substantially decreased as the fine particle fraction increased with molecular weight. The deposition velocity was generally higher at high wind speeds. However, increase in the deposition velocity in unstable atmospheric conditions was also observed for gaseous PAHs of intermediate molecular weight.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.15 no.2
• /
• pp.126-131
• /
• 2003

Convective instability driven by surface tension is analyzed in an initially quiescent water absorbing ammonia gas with heat transfer using the linear stability analysis. The propagation theory is adapted to find the critical conditions of the onset of Marangoni convection. In this theory, the solutal penetration depth is chosen as the length scale factor. The results show that the liquid layer becomes more stable with decreasing the Schmidt number and increasing the Lewis number. It is also found that there is a critical Biot number to make the liquid layer be most unstable, and there is a linear relationship between the thor-mal Marangoni number and the solutal Marangoni number.

• Tribology and Lubricants
• /
• v.14 no.1
• /
• pp.45-53
• /
• 1998

Friction and wear test for two kinds of Cu-based sintered metallic friction material against cast iron disk was carried out by plate-on-disk type friction and wear tester to investigate the friction and wear characteristics of brake system in severe condition. In this experimental study, the counter specimen was cast iron which is being used generally in brakes of heavy duty equipments. Test friction materials were A type which was manufactured by foreign company and B type by domestic company. Friction coefficient and wear volume were measured and compared with each other. The experiment was performed under room temperature. The worn surface of cast iron disk and friction material were observed by scanning electron microscope. The temperature of surface of disk was measured continuously by the non-contacting thermometer. It was found that A type friction material had stable friction coefficient over the wide range of sliding condition, but B type friction material had unstable friction coefficient and lower value of 0.2 under the severe sliding condition.

• Proceedings of the Korea Association of Crystal Growth Conference
• /
• 1996.06a
• /
• pp.19-37
• /
• 1996

Scanning electron microscopy (SEM) has been applied to observe directly the {{{{ SQRT { 19} }}}}${\times}${{{{ SQRT { 19} }}}} and (1${\times}$1)HT reconstructions and the transition associated step bunching on the GaAs (111)B surfaces under As pressure. Close to the transition point, {{{{ SQRT { 19} }}}}${\times}${{{{ SQRT { 19} }}}}an d (1${\times}$1)HT reconstructions are observed in dark and bright domains by SEM and determined by micro-probe reflection high-energy electron diffraction (${\mu}$-RHEED). The reconstruction diagram shows hyster-esis. The stepped surface morphology during the reconstruction transition was unstable. Heavy step bunching with rough macrostep edges was observed.