• Biomolecules & Therapeutics
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• v.26 no.4
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• pp.380-388
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• 2018

Neural stem cells (NSCs) have the ability to self-renew and differentiate into multiple nervous system cell types. During embryonic development, the concentrations of soluble biological molecules have a critical role in controlling cell proliferation, migration, differentiation and apoptosis. In an effort to find optimal culture conditions for the generation of desired cell types in vitro, we used a microfluidic chip-generated growth factor gradient system. In the current study, NSCs in the microfluidic device remained healthy during the entire period of cell culture, and proliferated and differentiated in response to the concentration gradient of growth factors (epithermal growth factor and basic fibroblast growth factor). We also showed that overexpression of ASCL1 in NSCs increased neuronal differentiation depending on the concentration gradient of growth factors generated in the microfluidic gradient chip. The microfluidic system allowed us to study concentration-dependent effects of growth factors within a single device, while a traditional system requires multiple independent cultures using fixed growth factor concentrations. Our study suggests that the microfluidic gradient-generating chip is a powerful tool for determining the optimal culture conditions.

• Journal of Korean Society of Forest Science
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• v.71 no.1
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• pp.50-54
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• 1985

The effect of relations parameters on the declination gradient of trees was studied in natural forest of Quercus variabilis, Quercus ${\times}$ grosseserrata, Quercus aliens, and Quercus dentata grown at various slope gradient. The declination gradients of trees were effected by the species, slope gradient, and direction of slope, but not effected by density and height in all species. The species shows a superior factor effecting declination gradient of trees compared with other relations parameters, and next effective factor was slope gradient. Especially in all of slope gradient, the declination gradient of Quercus ${\times}$ grossesserrata was highest.

• Journal of the Korean Ceramic Society
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• v.56 no.6
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• pp.589-595
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• 2019

The top-seeded solution growth (TSSG) method is an effective approach for the growth of high-quality SiC single crystals. In this method, the temperature gradient in the melt is the key factor determining the crystal growth rate and crystal quality. In this study, the effects of the aperture at the top of the hot-zone on the growth of the SiC single crystal obtained using the TSSG method were evaluated using multiphysics simulations. The temperature distribution and C concentration profile in the Si melt were taken into consideration. The simulation results showed that the adjustment of the aperture at the top of the hot-zone and the temperature gradient in the melt could be finely controlled. The surface morphology, crystal quality, and polytype stability of the grown SiC crystals were investigated using optical microscopy, high-resolution X-ray diffraction, and micro-Raman spectroscopy, respectively. The simulation and experimental results suggested that a small temperature gradient at the crystal-melt interface is suitable for growing high-quality SiC single crystals via the TSSG method.

• Korean Journal of Crystallography
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• v.7 no.1
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• pp.30-35
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• 1996

Calcite(CaCO3) single crystals were grown hydrothermally and transmittance of as grown crystals was measured. Instead of platinium, teflon was lined onto the wall of autoclave to prevent the corrosion of autoclave wall by acidic NH4Cl solution. Spontaneous nucleation and growth of calcite crystal on teflon was reduced considerably by addition of NaCl and /or CH3COOH and applying low temperature gradient. When the temperature gradient exceeded to a few degrees from the critical temperature gradient(6-7℃), spontaneous nucleation and growth was rapidly increased in any hydrothermal solutions. Precise temperature control is thought to be the most important factor for the growth of calcite single crystal by hydrothermal technique. As grown calcite single crytal showed high transmittance compared to natural one by UV-visible analysis.

• Journal of Industrial Technology
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• v.19
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• pp.269-278
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• 1999

When a variety of repeated loads are given, most steel structures failed in much lower level of loads than static failure loads. In addition, bridge always includes the internal defects or discontinuities. from these, fatigue cracks initiates and can lead to sudden failure. Thus, in this study, tensile specimens by the cover plate shapes were used as the test specimens. The fatigue test was performed by constant amplitude fatigue loading and beach mark. From the results of this study, each specimen's fatigue section was observed. in addition, stress intensity factor at crack tip was calculated by using the Green's function which applied to discontinuous section where causing stress concentration. Therefore, the fatigue life of structural detail was investigated by adopting the theories of fracture mechanics. each specimen's crack shape is a semi-elliptical surface crack or center crack sheet, stress gradient correction factor, Fg is the most subjective of all stress intensity correction factors and fatigue life should be predicted by previous proposed function and finite element analysis.

• Journal of Industrial Technology
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• v.20 no.A
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• pp.169-178
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• 2000

The 4-point bending tests have been performed In order to estimate the effect of TIG-dressing on fatigue strength and fatigue characteristics quantitatively for non load-carrying fillet welded joints subjected to pure bending. As a result of fatigue tests, fatigue strengths of as-welded specimens have satisfied the grade of fatigue strength prescribed in specifications of korea, AASHTO and JSSC. Fatigue strength at 2 million cycles of TIG-dressing specimens have increased compared with as-welded specimens. As the result of beachmark tests, fatigue cracks occurred at several points, where the radius of curvature and flank angle in the weld bead toes were low, and grew as semi-elliptical cracks, then approached to fracture. As a result of finite element analysis, stress concentration factor in weld bead toes has closely related to the flank angle and radius of curvature, and between these, the radius of curvature has more largely affected in stress concentration factor than flank angle. As a result of fracture mechanics approaches, the crack correction factor of test specimens has largely affected on stress gradient correction factor in case a/t is below 0.4. From the relations between stress intensity factor range estimated from FEM analysis and fatigue crack growth rate, fatigue life has been correctly calculated.

• The Korean Journal of Ecology
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• v.21 no.5_2
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• pp.491-499
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• 1998

An investigation was performed to establish the mathematical theories of a vibration for the plant growth and a wave distribution of a plant population on the boundary condition of a limiting factor in the environment. The mathematical theories of the plant growth vibration and wave distribution had been elucidated by the plant growth and the timber line on the middle slope of the west side of Mt. Paektu. The Betula ermaruii composes the timber line on about 2,060 m elevation of sea label, has a growth vibration on the ground surface and takes a wave distribution due to a boundary condition of alpine temperature gradient.

• YAKHAK HOEJI
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• v.40 no.6
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• pp.646-652
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• 1996

Epidermal Growth Factor (EGF), discovered by Stanley Cohen in 1960, has a potential healing effect for wounds and bums. Considering wound care, in order to avoid physical stress at the wound surface and efficiently apply EGF, the need for viscous spraying solutions was essential. Viscous spraying solutions containing EGF were prepared by utilizing viscosity-building polymer, poloxamer 407, and by introducing liposome systems. On the other hand, EGF is purified on reverse HPLC gradient program with the mobile solvent of acetonitrile. It is necessary to observe liposomal EGF changes as the acetonitrile contents varied in order to introduce liposome systems at the step of EGF solution (at the time of EGF purifying). By evaluating the size distribution and entrapment efficiency of EGF liposome, it was possible to detemine the limit contents of acetonitrile and establish the optimal conditions for solution formulations. It has been revealed that, as the acetonitrile content increases, mean diameter of EGF liposomes increased and the width of size distribution tends to decrease. The limit contents of acetonitrile were 10%, since there was little difference to the acetonitrile free liposomes.

• Journal of Veterinary Clinics
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• v.11 no.1
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• pp.389-392
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• 1994

To purify transforming growth factor type beta(TGF-$\beta$) in canine platelets, Sephadex G-75 gel filtration and semipreparative HPLC were carried out. The column of $2.0 {\times}120cm$ was used for gel filtration and one inch semipreparative column filled with SP-Toyopeal for HPLC. Electrophoresis and bioassay using African green monkey kidney cell were used for identification of TGF-$\beta$ Crude TGF-$\beta$ of 2.75mg was extracted from 5.2g of the platelets by the treatment of acid/ethanol. In gel filtration of crude TGF-$\beta$, 4 peaks were observed at the detection of spectrophotometer at 280nm. Electrophoresis and bioassay identified the 3rd peak TGF-$\beta$. Linear gradient elution from 0 to 3M NaCl in sornipreparative HPLC showed TGF-$\beta$ at 1.5M NaCl. Gel filtration was less expensive and useful method for the purification of TGF-$\beta$.

• Structural Engineering and Mechanics
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• v.18 no.6
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• pp.759-768
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• 2004

The torsion of a penny-shaped crack in a transversely isotropic strip is investigated in this paper. The shear moduli are functionally graded in such a way that the mathematics is tractable. Hankel transform is used to reduce the problem to solving a Fredholm integral equation. The crack tip stress field is obtained by taking the asymptotic behavior of Bessel function into account. The effects of material property parameters and geometry criterion on the stress intensity factor are investigated. Numerical results show that increasing the shear moduli's gradient and/or increasing the shear modulus in a direction perpendicular to the crack surface can suppress crack initiation and growth, and that the stress intensity factor varies little with the increasing of the strip's height.