• 한국결정성장학회지
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• 제17권4호
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• pp.160-164
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• 2007

Carbon nanofibers were deposited on silicon oxide substrate by thermal chemical vapor deposition method. For the enhancement of the characteristics of carbon nanofibers, the source gases ($C_2H_2,\;H_2$) flows were intentionally manipulated as the cyclic on/off modulation of $C_2H_2$ flow. By the cyclic modulation process during the initial deposition stage, the formation density of carbon nanofibers on the substrate could be much more enhanced. The diameter of as-grown carbon nanofibers was also reduced by the cyclic modulation process. The cause for the variation in the characteristics of carbon nanofibers by the cyclic modulation process was discussed in association with the hydrogen gas etching ability.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2005년도 춘계 학술발표회 논문집
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• pp.1554-1561
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• 2005

Geotextiles form one of the two largest groups of geosynthetics and it is consisted two major types of synthetic material (Woven, Non-woven). The functions of geotextiles are separation, reinforcement, filtration, drainage and as a moisture barrier. Within these functions, however, there are a large number of applications or use areas. Although the many research scholar and engineer developed and established the design criteria and construction methodology of geosynthetics filter layer, because the lack of suitable design terminology and uncertainty of long term durability, sustainable research still needed for optimum design methodology to the complicate field conditions. Especially, more intensive research needed about under the cyclic flow condition and fine silty sand base material. In this paper, the filter model test performed under cyclic flow with various boundary conditions (period and frequency of cyclic flow, types of geosynthetic filter material, surcharge etc.).

• Journal of Korean Vacuum Science & Technology
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• 제4권1호
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• pp.18-22
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• 2000

For the enhancement of the nucleation density of the diamond film, we introduced the cyclic process. The cyclic process was carried out by the on/off control of CH$_4$ flow rate for a relatively short time (10 min), compared with the total reaction time (6 h). Prior to depositing the diamond film, we made the pretreated glass substrate via the unidirectional scratch using ∼l $\mu\textrm{m}$ size diamond powders. Diamond films were deposited on the pretreated glass substrate in a microwave plasma enhanced chemical vapor deposition (MPECVD) system. We observed the enhancement of the nucleation density of the diamond films caused by the cyclic process. Detailed surface morphologies of the substrate were investigated after the cyclic process. Based on these results, we discussed the cause for the enhancement of the nucleation density on the pretreated glass substrate by the cyclic process.

• Geomechanics and Engineering
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• 제34권5호
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• pp.481-489
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• 2023

Drained cyclic triaxial tests were conducted on a saturated sand to examine its deformation characteristics under either axial or lateral cyclic loading condition. To apply lateral cyclic loading, the cell pressure was cycled while maintaining a constant vertical stress. The strain accumulations and flow direction in the soil were presented and discussed considering various initial stress ratios (η₀), cyclic stress amplitudes and cyclic stress paths. The results indicate that axial strain accumulation shows an exponential increase with the maximum stress ratio (η^max). The initial deviatoric stress has comparable effects with lateral cyclic stress amplitude on the accumulated axial strain. In contrast, the accumulated volumetric strain is directly proportional to the lateral cyclic stress amplitude but not much affected by η₀ values. Due to the anisotropy of the soil, the accumulated axial and lateral bulging strains are greater in lateral cyclic loading when compared to axial cyclic loading even though η^max is the same. It is also found that η^max affects soil's lateral deformation and increasing the ratio could change the lateral deformation from contraction to bulging. The flow direction depends on η^max in the sand under lateral cyclic loading, regardless of η₀ values and the cyclic stress amplitudes, and a large η^max could lead to great deviatoric strain but a little volumetric strain accumulation.

• 대한기계학회논문집B
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• 제28권12호
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• pp.1511-1520
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• 2004

A flow visualization of the two-dimensional rigid fling-clap motions of the flat-plate wing are performed to gain knowledge of butterfly mechanisms that might be employed by butterflies during flight. In this numerical visualization, the time-dependent Navier-Stokes equations are solved for cyclic fling and clap types of wing motion. The separation vortex pair that is developed in the fling phase of the cyclic fling and clap motion is observed to be stronger than those of the fling followed by clap and pause motion(1st cycle motion). This stronger separation vortex pair in the fling phase is attributable to the separation vortex pair of the outside space developed in the clap phase as it moves into the opening in the following fling phase. Accordingly, higher lift and power expenditure coefficients in the fling after clap phase is caused by the stronger separation vortex pair.

• 한국지반환경공학회 논문집
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• 제12권11호
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• pp.65-70
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• 2011

모래지반의 액상화 발생 가능성 및 측방유동 평가 방법에 대한 연구는 많이 알려져 있다. 최근에는 비소성 실트의 액상화 발생 가능성에 대해서도 연구하고 있다. 그러나 비소성실트의 동적하중이 작용하는 동안과 그 이후의 거동에 대해서는 세계적으로도 다소 알려져 있을 뿐이다. 특히 비소성실트의 측방유동에 대한 평가방법에 대해서는 거의 알려져 있지 않다. 이에 본 연구에서는 비소성실트지반에서의 액상화 발생 가능성 및 측방유동량의 평가 방법을 제안하는 것을 목적으로 하였다. 연구방법은 정적 및 동적 시험을 수행할 수 있는 직접단순전단시험기를 이용하여 동적하중을 받은 비소성실트의 액상화 가능성을 평가하였으며, 그 후 정적 시험을 수행하여 잔류강도를 측정하였다. 이 시험결과 비소성실트는 유효응력이 완전이 소멸되는 것은 곤란하지만 액상화에 거의 가깝게 발생하는 것을 확인하였다. 특히, 전단응력의 증가에 따른 강도저하는 매우 현저한 것을 확인하였다. 이 시험결과를 이용하여 액상화 발생 가능성 및 측방유동량을 추정할 수 있는 방법을 제안하였다.

• 한국진공학회지
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• 제18권6호
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• pp.481-487
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• 2009

탄소나노필라멘트의 직경크기를 조절하기 위하여 증착 반응초기에 $SF_6$를 증착원료기체($C_2H_2$, $H_2$)에 주입하였다. 증착 원료 기체와 $SF_6$를 열화학기상증착시스템에서 시간에 따라 싸이클릭 유량 변조시켰다. 싸이클릭 유량 변조 프로세스와 기판의 온도에 따라 기판위에 증착된 탄소나노필라멘트들의 특성을 조사하였다. 싸이클릭 에칭기간에 $SF_6$를 투입하자 탄소나노필라멘트의 직경크기는 급격히 감소하였다. 이러한 탄소나노필라멘트 직경의 크기 감소 원인은 $SF_6$ 기체의 주입에 따른 에칭능력 향상에 기인하는 것으로 이해되었다.

• 한국농공학회지
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• 제40권5호
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• pp.43-51
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• 1998

In design and management of sea0dikes, engineers need to study various transient seepage conditions through dikes not only for the sea water infiltration into dikes due to cyclic rises of sea water level also for the seepage flow out from dikes toward the sea due to cyclic drawdown of sea water level. Characteristics of seepage flow toward the sea from dikes are more complicated than as known and remained unclearly. The case of such seepage flow may be explained by figuring out seepage characteristics in filter as a part of sea-dikes. Filters in most sea-dikes in Korea are inevitably placed with reversely inclined shape due to field construction conditions. Most computer programs for seepage analysis based on the various numerical methods give practically acceptable results, but for the case of reversely inclined section of filters any verification to apply them might be needed. In this study, large scaled model tests were executed to verify and understand seepage flow through earth-filled sea-dikes. The results from numerical analysis and model tests show some remarkable differences in pore pressure distribution under cyclic changes of see level, and some of the results need to be considered in design and construction practices with further study.

• 한국유체기계학회 논문집
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• 제2권1호
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• pp.64-72
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• 1999

CSCM upwind flux difference splitting compressible Navier-Stokes method has been used to predict the transonic flows in a centrifugal compressor diffuser. The modified cyclic. TDMA and the mass flux boundary conditions were used as boundary conditions of the diffuser analysis. Broad flow separation on the suction surface near the hub and shroud was observed from the results of the mass flow rates 5.8, 6.0 and 6.2kg/s at 27000 rpm. The three-dimensional flow analysis predicted successfully that the static pressure increased and the total pressure decreased through the flow passage of the channel diffuser when compared to two-dimensional analysis due to the strong effect of the three-dimensional flow. The mass averaged loss coefficients and pressure coefficients were also studied.

• 한국결정성장학회지
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• 제22권5호
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• pp.213-217
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• 2012

Carbon coils could be synthesized on nickel catalyst layer-deposited silicon oxide substrate using $C_2H_2$ and $H_2$ as source gases under thermal chemical vapor deposition system. By the incorporation of $SF_6$ additive in cyclic modulation manner, the dominant formation of the nanosized carbon coils could be achieved with maintaining the minimized sulfur additive amount. The geometry variation of the as-grown carbon coils, such as linear type, microsized coil type, wavelike nanosized coil type, and nanosized coil type, were investigated according to the different cyclic modulation manner of $SF_6$ flow. $SF_6$ gas incorporation develops the coil-type geometry. Furthermore, the higher flow rate of $SF_6$ gas increased the amount of the nanosized carbon coils. The slightly increased etching ability by $SF_6$ addition seems to be the cause for these results.