• Journal of Magnetics
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• 제17권4호
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• pp.242-244
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• 2012

We report on the basis of experiments that magnetic domain structures exhibit a transition between single and dendrite domains with respect to the width of ferromagnetic nanowires. This transition is directly observed in CoFe/Pt multilayered nanowires having a width in the range of 580 nm to 4.2 ${\mu}m$ with a magnetic force microscope. Nanowires wider than 1.5 ${\mu}m$ show typical dendrite domain patterns, whereas the nanowires narrower than 690 nm exhibit single domain patterns. The transition occurs gradually between these widths, which are similar to the typical widths of the dendrite domains. Such a transition affects the strength of the domain wall propagation field; this finding was made by using a time-resolved magneto-optical Kerr effect microscope, and shows that the domain wall dynamics also exhibit a transition in accordance with the domain configuration.

• 대한기계학회논문집B
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• 제22권9호
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• pp.1335-1348
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• 1998

Flow characteristics in transitional boundary layers on a flat plate were experimentally investigated under three different freestream conditions i. e. uniform flow with 0.1 % and 3.7% freestream turbulent intensity and cylinder-wake with 3.7% maximum turbulent intensity. Instantaneous streamwise velocities in laminar, transitional and turbulent boundary layers were measured by I-type hot-wire probe. For estimation of wall shear stresses on the flat plate, measured mean velocities near the wall were applied to the principle of Computational Preston Tube Method (CPM). Distributions of skin friction coefficients were reasonably predicted in all developed boundary layers. Intermittency profiles, which were estimated using Conditional Sampling Technique in transitional boundary layers, were also consistent with previously published data. It was predicted that the incoming turbulent intensity had more influence on transition onset point and transition process than freestream turbulent intensity existed just over the transition region. It was also confirmed that non-turbulent and turbulent profiles in transitional boundary layers could not be simply treated as Blasius and fully turbulent profiles.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2000년도 제18회 학술발표회 논문개요집
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• pp.213-213
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• 2000

Direct laser vaporization of transition-metal(Co, Ni)/graphite composite pellet produced single wall carbon naotubes(SWNT) in the condensing vapor in a heated flow cylinder-type tube furnace, Transition metal/graphite composite pellet target was made by mixing graphite, Co, and Ni in 98:1:1 atomic weight ratios, pressing the mixed powder, and curing it. The target was placed in a tube furnace maintained at 1200$^{\circ}C$ and Ar inert collision gas continuously flowed into the tube. The 2nd harmonic, 532nm wavelength light from Nd-YAG laser was used to vaporize the tube. The carbon nanotubes produced by the laser vaporization were accumulated on quartz tube wall. The raw carbon nanotube materials were purified with surfactants(Triton X-100) in a ultrasonicator. These carbon nanotubes were analyzed using SEM, XRD, and Raman spectroscopic method. The carbon nanotube growth on the Ni-patterned Si substrate was investigated by the CVD process. Transition-metal, Ni and CH4 gas were used as a catalyst and a reactant gas, respectively. The structure and the phonon frequencies of the carbon nanotubes formed on the patterned Si substrate were measured by SEM and Raman spectrometer.

• Journal of Ship and Ocean Technology
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• 제8권4호
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• pp.10-16
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• 2004

A response of a swept wing boundary layer to a single free-stream stationary axial vortex of a limited spanwise extent is considered as an example of typical problems that one can find in laminar-turbulent transition research and control. The response is dominated by streamwise velocity perturbations that grow quasi-exponentially downstream. It is shown that the formation of the boundary layer disturbance occurs for the most part close to the leading edge. The disturbance represents itself a wave packet consisted of the waves with characteristics specific for cross-flow instability. However, an admixture of growing disturbances whose origin can be attributed to transient effects and to a distributed receptivity mechanism is also identified.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2005년도 후기학술대회논문집
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• pp.242-243
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• 2005

The SrS:Ag, Cl thin films have been grown by the hot wall technique with S furnace placed on the outside of the growth chamber in order to investigate the crystallographic and optical characteristics. The XRD patterns indicate a strongly preferential orientation in the [200] direction. The PL spectrum has an emission peak of about 398nm which is assigned by the transition from $4d^{95}s^1$ to $4d^{10}$ of$Ag^+$ center.

• 대한기계학회논문집B
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• 제38권7호
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• pp.639-646
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• 2014

난류모델에서 벽면처리법이 터빈 노즐 베인의 열전달 예측에 미치는 영향을 비교 분석하였다. 본 연구를 위해 NASA의 C3X 터빈 노즐 베인을 사용하였다. 벽함수 방법, 저레이놀즈수 방법, 천이모델을 사용하여 베인 표면에서의 압력 및 온도를 해석하였다. 해석 결과 터빈 노즐 베인의 중간 압력분포는 각 벽면처리법에 따른 차이 없이 실험값과 잘 일치하였다. 그러나 터빈 노즐 베인의 온도와 열전달 계수는 각 벽면처리법에 따라 큰 차이를 보였다. 전반적으로 저레이놀즈수 방법과 천이모델은 벽함수 방법에 비해 온도 및 열전달 계수 예측에 특별한 이점을 보이지 않았으며, 벽함수 방법을 적용한 레이놀즈응력 난류모델이 터빈 노즐 베인 표면의 온도 및 열전달 계수를 비교적 잘 예측하였다.

• 한국실내디자인학회논문집
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• 제22권3호
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• pp.33-42
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• 2013

The purpose of this study was to analyze the design trend of the vertical garden design in the indoor space through the examples of green wall in the lobby space. For the analysis, this study looks into the 'Guide for the Building Greening System' to understand the technical consideration for the green wall. After that, the key design elements was drawn from existing green walls through the literature review and field survey and field-survey. The study picked six green walls which was completed after 2000 in the lobby space in Seoul. The major findings of this study were as follows: First, the design factors mainly depend on the plant selection, which leads to the outlook and texture of the vertical walls. The texture is expressed by the two-dimensional or three-dimensional planting methods which is related to the selection of plant species. Second, the vertical walls in the lobby area should be planned for the function of space which could be transition, human traffic, mood and attraction. Third, the vertical wall should be integrated with the surroundings in order to reinforces the dynamic or static space experience.

• 천문학회보
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• 제40권2호
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• pp.45.3-46
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• 2015

Space weathering agents such as micrometeoroids and solar wind particles continuously age the uppermost regolith of the lunar surface by comminuting as well as darkening and reddening. Among several maturity indices, we investigate median grain size () and optical maturity (OMAT) of the crater rim walls. Crater rim wall is the most immature place among the impact crater features because the vertical mixing process by mass-movement can enhance the gardening of regolith and the supply of immature materials in the deeper layer to the surface. More than 140 simple and complex craters were considered. Both and OMAT values of the inner rim wall initially increase as the crater size increases until ~10-20 km, then decrease. This transition crater size happens to correspond to the transition diameter from simple to complex craters. For larger craters, i.e., complex craters, it is clear that the inner rim wall of the craters formed in recent eras tend to remain fresh and become mature along with time. For the simple crater case, smaller craters are more mature, which is opposite to the case of complex craters. This is thought to be because smaller craters become flattened more quickly, thus have smaller vertical mixing in the regolith due to mass-movement. We will also discuss on the maturity indices of the crater rim walls at high latitudes as a function of the position angle to see the latitude dependence of the space weathering process.

• 대한기계학회논문집B
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• 제26권5호
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• pp.685-694
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• 2002

Effects of wake-passing orientation and frequency on the wake-induced boundary layer transition on a NACA0012 airfoil are investigated. The wakes are generated by rotating cylinders clockwise (CW) and counterclockwise (CCW) around the airfoil. Time- and phase-averaged streamwise mean velocities and turbulent fluctuations are measured with a single hot-wire probe. Wall skin frictions are estimated by the Computational Preston Tube Method (CPM). The pressure distribution on the airfoil is different according to the wake-passing orientation and frequency. Turbulent patches are generated in the laminar boundary layer due to the passing wake and the boundary layer becomes temporarily transitional. The transition process is significantly affected by the pressure gradient and the turbulent patches. For the receding wake, the turbulent patches propagate more rapidly than those for the approaching wake because adverse pressure gradient becomes larger. As the frequency increases, onset location of transition moles upstream and the boundary layer near the trailing edge becomes more transitional.

• 대한기계학회논문집B
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• 제28권9호
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• pp.1058-1065
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• 2004

In the present study, characteristics of steady state laminar flows of a straight duct connected to a 180$^{\circ}$ curved duct were examined in the entrance region through experimental and numerical analyses. For the analysis, the governing equations of laminar flows in the Cartesian coordinate system were applied. Flow characteristics such as velocity profiles, and secondary flows were investigated numerically and experimentally in a square cross-sectional straight duct by the PIV system and a CFD code(STAR CD). For the PIV measurement, working fluid produced from mosquito coils smoke. The experimental data were obtained at 9 points dividing the test sections by 400 mm. Experimental and numerical results can be summarized as follows. Critical Reynolds number, Recr which indicates transition from laminar steady flow to transition steady flow was 2,150. As Reynolds number, Re, was increased, dimensionless velocity profiles at the outer wall were increased due to the effect of the centrifugal force and the secondary flows. The intensity of a secondary flow became stronger at the inner wall rather than the outer wall regardless of Reynolds number.