• Journal of Korean Neurosurgical Society
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• 제64권3호
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• pp.367-373
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• 2021

Secondary neurulation (SN) is a critical process to form the neural tube in the posterior region of the body including the tail. SN is distinct from the anteriorly occurring primary neurulation (PN); whereas the PN proceeds by folding an epithelial neural plate, SN precursors arise from a specified epiblast by epithelial-to-mesenchymal transition (EMT), and undergo self-renewal in the tail bud. They finally differentiate into the neural tube through mesenchymal-to-epithelial transition (MET). We here overview recent progresses in the studies of SN with a particular focus on the regulation of cell lineage, self-renewal, and EMT/MET. Cellular mechanisms underlying SN help to understand the functional diversity of the tail in vertebrates.

• 대한화학회지
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• 제29권5호
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• pp.533-538
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• 1985

Spermine에 의하여 誘發되는 凝縮 DNA 構造의 安定化에 있어서 hydrophobic interaction의 重要性을 試驗하기 위하여 spermine-DNA 複合體의 異例的 吸光度-溫度 樣相에 미치는 urea의 效果를 調査하였다. 그 結果 異例的 吸光度-溫度 樣相의 downward peak(trough) 領域에 이르는 相變移에 對한 cooperativity, enthalpy, midpoint의 값들이 Tm 領域의 값들 보다 urea에 敏感한 影響을 받았으며, urea의 濃度 增加에 따라 downward peak가 점차 사라졌다. 이 data는 異例的 吸光度-溫度 樣相을 構成하는 downward peak가 spermine에 의하여 誘發되는 hydrophobic interaction에 의한 凝縮된 tertiary structure의 形成을 나타내고 있다고 불 수 있다.

• Advances in materials Research
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• 제8권4호
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• pp.337-359
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• 2019

Shape Memory Polymer Composites (SMPC) have gained popularity over the last few decades due to its flexible shape memory behaviour over wide range of strains and temperatures. In this paper, non-linear bending analysis has been carried out for SMPC beam under the application of uniformly distributed transverse load (UDL). Simplified C⁰ continuity Finite Element Method (FEM) based on Higher Order Shear Deformation Theory (HSDT) has been adopted for flexural analysis of SMPC. The numerical solutions are obtained by iterative Newton Raphson method. Material properties of SMPC with Shape Memory Polymer (SMP) as matrix and carbon fibre as reinforcements, have been calculated by theory of volume averaging. Effect of temperature on SMPC has been evaluated for numerous parameters for instance number of layers, aspect ratio, boundary conditions, volume fraction of carbon fiber and laminate stacking orientation. Moreover, deflection profile over unit length and behavior of stresses across thickness are also presented to elaborate the effect of glass transition temperature (T_g). Present study provides detailed explanation on effect of different parameters on the bending of SMPC beam for large strain over a broad span of temperature from 273-373K, which encompasses glass transition region of SMPC.

• Bulletin of the Korean Chemical Society
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• 제18권7호
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• pp.743-749
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• 1997

Local structure refinement of the BaFe1-xSnxO3-y system (x=0.00-0.50) has been carried out with Fe K-edge x-ray absorpion spectroscopic studies. It is found out that the Fe ions are placed in two different symmetric sites such as tetrahedral and octahedral sites in the compounds by comparison with Fe K-edge x-ray absorption near edge structure (XANES) spectrum of the γ-Fe2O3 compound as a reference. Small absorption peaks of dipole-forbiden transitions appear at a pre-edge region of 7111 eV due to the existence of Fe ions in the tetrahedral and octahedral sites. The peak intensity decreases with the substitution amount of Sn ion. Three different absorption peaks of 1s→4p dipole-allowed transition appear on the energy region between 7123 and 7131 eV. The peaks correspond to 1s→4p main transition of Fe ions in tetrahedral and octahedral sites and 1s→4p transition followed by the shakedown process of ligand to metal charge transfer. The bond distances between Fe ions in the tetrahedral site and nearest neighboring oxygen atom (Fe-4O), and those in octahedral site (Fe-6O) are determined with the extended x-ray absorption fine structure (EXAFS) analysis. Two different interatomic distances increase with the substitution amount of Sn ion and also the bond lengths of Fe-4O are shorter than those of Fe-6O in all compounds.

• 물과 미래
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• 제27권2호
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• pp.85-96
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• 1994

자연하천의 부정류에 Preissmann 기법을 적용시 나타나는 수치 불안정성의 원인을 규명하고 불안정성을 극복하기 위한 적절한 대책을 제시하였다. 주된 불안정성의 원인으로는 천이류, 하도단면의 급격한 변화, 부적절한 조도계수, 계산시간 및 거리간격, 급격하게 증가하는 유입수문곡선, 그리고 마른 하상 등이다. 이런 불안정성의 주된 원인은 천이류의 발생과 관계가 있으며 상류-사류가 공존하는 자연 하도에서 천이류를 해석할 수 있는 모형을 제안하였다. 가상하도를 통하여 모의 수치실험을 수행한 결과 전하도구간에 대하여 안정성있게 수렴하고 있었으며, 일관성있는 유량, 수위자료를 얻을 수 있었다. 본 연구의 모형은 앞으로 실제 하천자료를 통해 적용성의 검증이 이루어진다면 천이류로 발생하는 수치계산의 어려움의 해결에 기여할 수 있다고 판단된다.

• Journal of Mechanical Science and Technology
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• 제14권1호
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• pp.11-18
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• 2000

Fracture toughness JIC and KIC tests were performed on A516 Gr70 carbon steel plate at the temperature ranging from -$160^{\circ}C$ to $600^{\circ}C$, and test results were analyzed according to ASTM E 813 and ASTM E 399. Unloading compliance J-integral tests were performed on 1TCT specimens. The relation between the $J_{IC}$ value and the test temperature was obtained. It was concluded that the temperature ranging from $-15^{\circ}C$ to $600^{\circ}C$ is the upper shelf region of ductile-brittle transition temperature, and in this temperature range, fracture toughness $J_{IC}$ values decreased with increasing temperature. The ductile brittle transition temperature of the material may be around $-30^{\circ}C$. In the region near $-30^{\circ}C$, the tendency of $J_{IC}$ to decrease with decreasing temperature was significant.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1996년도 춘계학술발표회논문집(2)
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• pp.331-336
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• 1996

The effects of a mixing vane on air-water mixed flow have been experimentally studied in this work, to investigate the basic mechanisms that the mixing vane affects critical heat flux (CHF). Experiment was performed for various flow rates focusing on bubbly flow and annular flow patterns. Acrylic tube (1.7m long, 11 mm I.D.) and the split vane type mixing vane were used, and ring-type conductance probes were used to measure the liquid film thickness in annular flow. Experimental results show that, (a) bubbly-to slug flow transition and churn-to-annular flow transition occur respectively near the mixing vane compared to the tests without mixing vane, (b) in bubbly flow region, the mixing vane breaks the bubbles into smaller ones and forwards bubbles to the center region of the tube by the centrifugal force, (c) the liquid film thickness in annular flow is decreased near the mixing vane for mass fluxes.

• Journal of Astronomy and Space Sciences
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• 제28권1호
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• pp.13-16
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• 2011

The $CH_3OH$ $4_2-5_1$ E transition was observed toward the Sgr B2 region, including the Principal Cloud and its surroundings. This methanol transition shows an extended emission along the 2'N cloud, which is believed to be colliding with the Principal Cloud and may trigger the massive star formation in this cloud. This extended methanol emission may also suggest that the 2'N cloud is under shocks. We derive total methanol column density $N(CH_3OH)\;=\;2.9{\pm}0.3{\times}10^{14}\;cm^{-2}$ toward the peak position of the extended emission. The fractional abundance of methanol is about 10.9, relative to the estimated total $H_2$ abundance, which is similar to the methanol abundances in quiet gas phase.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1996년도 춘계학술발표회논문집(3)
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• pp.111-116
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• 1996

IGSCC(Intergranular stress corrosion cracking) behaviors of Alloy 600 were studied by the electrchemical ten methods of controlling specimens electrode potentials in the active-passive transition region of anodic polarization curve. Anodic polarization and static potential tests of stressed C-ring type MA Alloy 600 were carried out in 10% NaOH at 300 $^{\circ}C$ for 7days. It was confirmed that IGSCC of Alloy 600 was accellerated by maintaining the specimen potential in the susceptible active-passive transition region of anodic polarization curve. An intergranular crack was initiated on the surface area of C-ring specimens where protective oxide layer was broken down. And the depth of the crack growth was about 100 ${\mu}$m during the testing periods.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2006년 제4회 한국유체공학학술대회 논문집
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• pp.401-402
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• 2006

The turbulent flow around a sphere was investigated using two experimental techniques: smoke-wire flow visualization in wind tunnel at Re=5300, 11000 and PIV measurements in a circulating water channel. The smoke-wire visualization shows flow separation points near an azimuthal angle of $90^{\circ}$, recirculating flow, transition from laminar to turbulent shear layer, evolving vortex roll-up and fully turbulent eddies in the sphere wake. The mean velocity field measured using a PIV technique in x-y center plane demonstrates the detailed near-wake structure such as nearly symmetric recirculation region, two toroidal vortices, laminar separation, transition and turbulent eddies. The PIV measurements of turbulent wake in y-z planes show that a recirculating vortex pair dominates the near-wake region.