• 한국인쇄학회지
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• 제20권1호
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• pp.65-78
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• 2002

The suspension polymerization of styrene was carried out to obtain the narrow-size distribution of particle by using poly(vinyl alcohol) (PVA) as suspension stabilizer according to the degree of hydrolysis and the molecular weight. The stabilizing properties of suspension are also dependent on the interfacial tension of aqueous solution when PVA is added. When the polymerization process was carried out with low hydrolyzed PVA, it gave single, well-defined particles, while high hydrolyzed PVA gave clusters. The size of particle produced in this study ranged between 5${\mu}{\textrm}{m}$ and 10${\mu}{\textrm}{m}$. The suspending agent, PVA, influences on the drop size and drop stability, When the molecular weight of PVA is increased, the drop size decreases and the drops become more stable toward coalescence. An increase in the PVA concentration decreases the mean drop size and narrows the drop size distribution.

• 대한기계학회논문집A
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• 제25권4호
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• pp.695-702
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• 2001

In this paper, the drop/impact simulation for a mobile phone has been carried out with the explicit code LS-DYNA and its validation has been experimentally verified. The small size of this kind of electronics products makes it time-consuming, and difficult to conduct drop tests to detect the failure mechanism and identify their drop behaviors. Strict drop/impact performance criteria of such hand held electronic products as mobile phones play an important role in their design because these products must withstand both normal and unexpected shock. Usually, the product durability on drop impact depends on designers experience. The present reliable methodology of drop/impact simulation provides an efficient and powerful vehicle to improve the design quality and reduce the design period.

• International Journal of Air-Conditioning and Refrigeration
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• 제12권2호
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• pp.70-78
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• 2004

An experimental study on the pressure drop during flow boiling for pure refrigerants Rl34a and R123, and their mixture was carried out in a uniformly heated horizontal tube. Tests were run at a pressure of 0.6㎫ and in the ranges of heat flux 5-50㎾/$m^2$, vapor quality 0-100 percent and mass velocity of 150-600 kg/$m^2$s. Generally, the two-phase frictional multiplier is used to predict the frictional pressure drop during the two-phase flow boiling. The obtained results have been compared to the existing various correlations for the two-phase multiplier. Also, the frictional pressure drop was compared to a few available correlations; The Lockhart-Martinelli correlation considerally overpredicted the frictional pressure drop data for mixture as well as pure components in the entire mass velocity ranges employed in the present study, while the Chisholm correlation underpredicted the present data. The Friedel correlation was found to satisfactorily correlate the frictional pressure drop data except for a low quality region.

• 전기전자학회논문지
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• 제23권2호
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• pp.552-556
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• 2019

본 논문에서는 전류 제어 회로를 이용하여 load Transient response 특성을 향상시킨 capless LDO(low drop-out) 레귤레이터를 제안하였다. LDO 레귤레이터 내부의 오차증폭기와 패스 트랜지스터 사이에 전류 조절 회로를 두어 전압 라인에 들어오는 전류특성을 개선시켜 기존의 LDO 레귤레이터보다 향상된 transient 응답특성을 갖는다. 제안된 회로는 cadence의 virtuoso, spectre 시뮬레이터를 이용하여 0.18 um 공정에서 특성을 분석하였다. 실험 결과에 따르면, 제안된 회로 구성을 이용한 LDO의 load transient response는 기존 LDO과 비교하여 부하 전류가 rising time인 경우 1.954 us에서 1.378 us, falling time인 경우 19.48 us에서 13.33 us으로 약 29%, 28% 개선된 응답속도를 가진다.

• 한국심리학회지 : 문화 및 사회문제
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• 제14권1호_spc
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• pp.299-317
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• 2008

2000년대를 전후로 급증한 청소년들의 학업중단을 실태와 기존의 연구들을 통해 종합적으로 조망하였다. 용어, 실태, 원인과 과정 및 학업중단 이후 과정으로 나누어 우리나라 청소년의 학업중단을 이해하고, 이를 다시 12가지 특성으로 정리하였다. 그리고 이러한 특성들을 생태학적 모형으로 재구조화하였다. 1990년대 중반에 시작된 사회적 안정구조의 흔들림과 1998년의 IMF 사태는 청소년들의 1차 환경인 가정과 학교에 영향을 미쳤다. 가정은 이혼 등의 갈등이 표면화되면서 청소년에 대한 심리적 지지와 경제적 지원을 약화시켰고, 학교에서는 교권과 교칙이 약화되면서 교사와의 갈등, 학업의 목적과 흥미 상실로 나타났다. 청소년들은 우울, 무력감, 공격성과 같은 정서적 반응, 미래의 불투명성, 학업적 의미 상실과 같은 인지적 반응 및 부적절한 성행동, 폭력과 같은 표면화된 비행행동반응을 보였다. 이러한 심리적 상태는 가출과 학업중단이라는 표면화된 행동으로 드러나게 되었고, 이후 이들의 학업 유지 의도에도 불구하고 준비되어 있지 않은 사회에 의해 비행화가 가속되었다. 이들에 대한 국가적 대처에 대한 제안과 제한점들이 논의에 첨가되었다.

• Nuclear Engineering and Technology
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• 제51권3호
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• pp.922-929
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• 2019

This paper presents the drop performance test of the control rod assembly which is one of the main components strongly related to the safety of the prototype generation IV sodium-cooled fast reactor. To investigate the drop performance, a real-sized control rod assembly that was recently modified based on the drop analysis results was newly fabricated, and several free drop tests under different flow rate conditions were carried out. Then the results were compared with those obtained from the previous tests conducted on the conceptually designed control rod assembly to demonstrate the improvement in performance. Moreover, the drop performance tests under several types and magnitudes of seismic loadings were also conducted to investigate the effect of the seismic loading on the drop performance of the modified control rod assembly. The results showed that the effects of the type and magnitude of the seismic loading on the drop performance of the modified control rod assembly were not significant. Also, the drop time requirement was successfully satisfied, even under the seismic loading conditions.

• 한국분무공학회지
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• 제1권1호
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• pp.44-54
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• 1996

A theoretical and experimental study was carried out on the prediction of drop size distribution of the pressure swirl atomizer. Drop size distribution was obtained by using maximum entropy formal ism. Several constraints in the form of the definition of mean diameter were used in this formulation in order to avoid the difficulties of the estimating source terms. In this study $D_{10}$ was only introduced into the formulation as a constraint. A drop size obtained by using linear Kelvin-Helmholtz instability theory was considered as an unknown characteristic length scale. As a result, the calculated drop size was agreed well with measured mean diameter, particularly with $D_{32}$. The predicted drop size distribution was agreed welt with experimental data measured wi th Malvern 2600.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2995-3000
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• 2008

Understanding of the impinging behavior of an electrically charged spray is essential in determining appropriate operating conditions for electro-spraying of paints, surface coating materials and insecticides. In the present work, the wall impact behavior of an electrically charged drop has been investigated and compared with that of a neutral drop experimentally. The critical Sommerfeld number representing the spread-splash boundary for the charged drop impacting on the dielectric substrate turned out to be larger compared to that for the neutral drop with the same surface condition. The change of the transition boundary is due to the increase in the surface wettability of the drop on the substrate. However, with the electrically conducting substrates, the charging effect on the transition boundary appeared negligible. This is because the electric discharging time is much shorter than the time required for the flattened drop to reach its maximum extent.

• 한국소음진동공학회논문집
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• 제17권6호
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• pp.484-490
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• 2007

A reciprocating compressor used in domestic refrigerators can be subjected to many different forms of shock. These shocks are usually experienced during transporting the products from a manufacturer to customers. The hermetic structure of this kind of compressor makes it difficult to conduct drop tests for identifying the failure mechanism and their drop behaviors. The drop/impact simulation for a reciprocating compressor has been carried out with the explicit code LS-DYNA and its validation has been experimentally verified. Simulation results are in good agreement with those of drop test. The present method of drop/impact simulation provides an efficient and powerful solution to improve the design quality and reduce the design period.

• 디지털융복합연구
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• 제12권8호
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• pp.61-66
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• 2014

이 연구는 한국 유학생의 grit 수준과 잠재적 중도탈락 및 대학생활적응과의 관계를 규명하고자 하였다. 연구의 대상은 335명의 한국에 있는 유학생이었다. 첫째, grit는 잠재적 중도탈락과는 부적 상관관계를 보였고, 정서적응과 사회적응, 대학생활 만족 및 학업적응과는 정적 상관관계를 보였다. 둘째, grit는 중간 점수보다 높았고 잠재적 중도탈락은 매우 낮았다. 정서적응과 대학만족은 대학적응보다 높았으나 사회적응은 하위 영역 중 가장 낮았다. 셋째, grit 수준이 높고 중간인 군집이 낮은 군집보다 잠재적 중도탈락은 낮았으나, 대학생활적응의 전체 하위영역은 높았다. 끝으로 유학생의 대학생활 적응을 위한 제언을 하였다.