• Korean Journal of Plant Resources
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• v.24 no.4
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• pp.343-350
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• 2011

A medicinal herb, Stevia rebaudiana Bertoni which is grown under physical stresses such as simulated microgravity, shaking, and low temperature for 4 days, showed fresh weight decrease of 3.6%, 21% and 8.7% compared with the respective control. On control plants, the radical scavenging value of DPPH represented 86% and 55%, respectively in the leaves and stems extracts. Relatively weak antioxidant activities of 22% and 27% were measured respectively in AA (ascorbic acid) and BHA (beta-hydroxyacetic acid) known as synthetic antioxidants. The radical scavenging effect of DPPH (2,2-diphenyl-1-picryl hydazal) in stevia plants under a simulated microgravity was observed to be consistently higher relative to the control, whereas those effects of shaking and low temperature treatments rapidly increased and then reduced after 6 hours in case of shaking process and 24 hours in case of low temperature treatment, which results had similar levels of scavenging effects to the control. The plants under simulated microgravity showed the highest level of activity with the value of 147% and the shaking and low temperature treatments showed the increases of SOD activity by 121% and 125%, respectively. From the above results, it is clarified that the simulated microgravity is more effective to the antioxidant activity than those of other abiotic stresses.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1996.06a
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• pp.325-350
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• 1996

• Proceedings of the Optical Society of Korea Conference
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• 2005.07a
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• pp.296-297
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• 2005

• Journal of computational fluids engineering
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• v.3 no.1
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• pp.100-107
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• 1998

A numerical analysis of thermal stress over temperature variations near the crystal-melt interface is carried out for a floating-zone growth of Cadmium Telluride (CdTe). Thermocapillary convection determines crystal-melt interfacial shape and signature of temperature in the crystal. Large temperature gradients near the crystal-melt interface yield excessive thermal stresses in a crystal, which affect the dislocations of the crystal. Based on the assumption that the crystal is elastic and isotropic, thermal stresses in a crystal are computed and the effects of operating conditions are investigated. The results show that the extreme thermal stresses are concentrated near the interface of a crystal and the radial and the tangential stresses are the dominant ones. Concentrated heating profile increases the stresses within the crystal, otherwise, the pulling rate decreases the stresses.

• Journal of Advanced Marine Engineering and Technology
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• v.28 no.2
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• pp.338-346
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• 2004

Experimental data on the effect of the variable gravity magnitude, namely microgravity, normal gravity and hyper-gravity, on flow pattern and frictional pressure drop were obtained during co-current air-water flow in a horizontal tube, The flow patterns were found to depend strongly on the gravity magnitude and certain flow pattern were found to depend on the gas superficial velocity. The effect of the gravity magnitude had an effect on the frictional pressure drop only at low flow rates. The present data are used to evaluate some of existing flow pattern transition and pressure drop models and correlations.

• Animal cells and systems
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• v.4 no.3
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• pp.201-214
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• 2000

Two quite different types of plant cells are analysed with regard to transduction of the gravity stimulus: (i) Unicellular rhizoids and protonemata of characean green algae; these are tube-like, tip-growing cells which respond to the direction of gravity. (ii) Columella cells located in the center of the root cap of higher plants; these cells (statocytes) perceive gravity. The two cell types contain heavy particles or organelles (sataoliths) which sediment in the field of gravity, thereby inducing the graviresponse. Both cell types were studied under microgravity conditions ($10^{-4}$/ g) in sounding rockets or spacelabs. From video microscopy of living Chara cells and different experiments with both cell types it was concluded that the position of statoliths depends on the balance of two forces, i.e. the gravitational force and the counteracting force mediated by actin microfilaments. The actomyosin system may be the missing link between the gravity-dependent movement of statoliths and the gravity receptor(s); it may also function as an amplifier.

• Korean Chemical Engineering Research
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• v.57 no.2
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• pp.289-300
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• 2019

We have conducted a preliminary numerical analysis to understand the effects of double-diffusive convection on the molar flux at the crystal region during the growth of mercurous bromide ($Hg_2Br_2$) crystals in 1 g and microgravity (${\mu}g$) conditions. It was found that the total molar fluxes decay first-order exponentially with the aspect ratio (AR, transport length-to-width), $1{\leq}AR{\leq}10$. With increasing the aspect ratio of the horizontal enclosure from AR = 1 up to Ar = 10, the convection flow field shifts to the advective-diffusion mode and the flow structures become stable. Therefore, altering the aspect ratio of the enclosure allows one to control the effect of the double diffusive natural convection. Moreover, microgravity environments less than $10^{-2}g$ make the effect of double-diffusive natural convection much reduced so that the convection mode could be switched over the advective-diffusion mode.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.376-383
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• 2005

In this study, we conducted geophysical investigations for the organization of integrated geophysical methods to detect underground cavities of ground subsidence area at the field test site, located at Yongweol-ri, Muan-gun. We examined the applicability of geophysical methods such as electrical resistivity, electromagnetic, and microgravity to cavity detection with the aid of borehole survey results. Underground cavities are widely present within the limestone bedrock overlain by the alluvial deposits in the area of the test site where the ground subsidences have occurred in the past. The limestone cavities are mostly filled with groundwater and clays in the test site. Thus, cavities have low electrical resistivity and density compared to the surrounding host bedrock. The results of the study have shown that the zones of low resistivity and density correspond to the zones of the cavities identified in the boreholes at the site, and that the geophysical methods used are very effective to detect underground cavities. Furthermore, we could map the distribution of cavities more precisely with the test results incorporated from the various geophysical methods. It is also important to notice that the microgravity method is a very promising tool since it has rarely used for the cavity detection in korea. Beyond the investigation of underground cavities, the geophysical methods are required to provide useful information for the reinforcement design for the ground subsidence areas. It is, therefore, necessary to develop integrated geophysical technique incorporating different geophysical methods to precisely map underground cavities and image the subsurface of the ground subsidence areas.

• Journal of Advanced Marine Engineering and Technology
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• v.30 no.3
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• pp.403-412
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• 2006

The effect of a wall temperature on the soot deposition process from a diffusion flame to a solid wall was investigated in a microgravity environment to attain in-situ observations of the process. The fuel for the flames was an ethylene ($C_2H_4$). The surrounding oxygen concentration was 35% with surrounding air temperatures of $T_a=600K$. In the study, three different wall temperatures. $T_w$=300, 600, 800K, were selected as major test conditions. Laser extinction was adopted to determine the soot volume fraction distribution between the flame and burner wall. The experimental results showed that the maximum soot volume fractions at $T_w$=300, 800 K were $8.8{\times}10^{-6},\;9.2{\times}10^{-6}$, respectively. However, amount of soot deposition on wall surface was decreased because of lower temperature gradient near the wall with increasing wall temperature. A numerical simulation was also performed to understand the motion of soot particles in the flame and the characteristics of the soot deposition to the wall. The results from the numerical simulation successfully predicted the differences in the motion of soot particles by different wall temperature near the burner surface and are in good agreement with observed soot behavior that is, the 'soot line', in microgravity.

• Journal of the Korean Society of Safety
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• v.19 no.3 s.67
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• pp.124-129
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• 2004

To evaluate the numerical method in simulation of diffusion flames and to see the effects of strain rate and fuel concentration on the flame radius and thickness, the nonpremixed methane-air counterflow flames in microgravity were simulated axisymmetrically by using the MST Fire Dynamics Simulator (FDS). The $1000^{\circ}C$ based flame radius and thickness were investigated for the mole fraction of methane in the fuel stream, $X_m=20,\;50,\;and\;80\%$ and the global strain rates $a_g=20,\;60,\;and\;90s^{-1}$ for each mole fraction. The flame radius increased with the global strain rate while the flame thickness decreased linearly as the global strain rate increased. The flame radius decreased as the mole fraction increased, but it was not so sensitive to the mole fraction compared with the global strain rate. Since there was good agreement in the nondimensional flame thickness obtained with OPPDIF and FDS respectively, it was confirmed that FDS is capable of predicting well the counterflow flames in a wide range of strain rate and fuel concentration.