• The Journal of Asian Finance, Economics and Business
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• 제7권8호
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• pp.407-417
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• 2020

Entrepreneurship has become an important topic for governments to shape and influence the quantity and quality of entrepreneurship and improve policy toward the entrepreneurial economy. This study investigates the factors affecting the entrepreneurial decision of nascent entrepreneurs belonging to Generation Y in Vietnam. A mixed-method including both qualitative and quantitative methodologies was utilized. A focus group was carried out with 11 participants for exploring, reviewing, and testing content validity of constructs and measurement items. The conceptual model and hypotheses were developed using data collected by a questionnaire survey. The cross-sectional survey method was applied. A sample of 221 respondents was constituted, by both electronic and paper surveys with non-probability and convenience sampling techniques. SmartPLS 3 software was employed to analyze the data collected. The results show that nine factors were affecting the entrepreneurial decision of nascent entrepreneurs belonging to Generation Y in Vietnam, including entrepreneurial education, family background, entrepreneurial ecosystem, perceived behavioral control, social valuation, perceived opportunity, attitude, entrepreneurial self-efficacy, and entrepreneurial intention. The findings show the importance of entrepreneurial education, social value, and ecosystems. Therefore, in order to promote successful entrepreneurship, it is necessary to strengthen entrepreneurship education and have a strategy for the improvement of the entrepreneurship ecosystem.

• 한국철도학회:학술대회논문집
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• 한국철도학회 1998년도 창립기념 춘계학술대회 논문집
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• pp.604-611
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• 1998

High-speed railway trains entering and leaving tunnels generate finite amplitude pressure wave which propagate back and forth along the tunnels, reflecting at the open ends of the tunnels and at other discontinuities such as ventilation shafts and the train themselves. In present day railways, the magnitudes of the pressure waves are much too small to cause structual damage, but they are a serious potential source of aural discomport for passengers on unsealed trains. Almost always do the pressure waves propagating along the tunnels lead to a hazardous impulse noise near the exit portal of the tunnel. In order to alleviate such undesirable phenomena, some control strategies have been applied to the compression wave propagating inside the tunnel. The objective of the current work is to investigate the effect of tunnel entrance hoods on the entry compression wave at the vicinity of the tunnel entrance. Three types of entrance hoods were tested by the numerical method using the characteristics of method for a wide range of train speeds. The results show that the maximum pressure gradient of compression wave can be considerably reduced by the tunnel entrance hood. Desirable hood shape for reduction of the pressure transients and impulse noise was found to be of abrupt type hood with its cross-sectional area 2.5times the tunnel area.

• Advances in Computational Design
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• 제3권2호
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• pp.165-190
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• 2018

In this article, the static behavior of non-prismatic sandwich beams composed of functionally graded (FG) materials is investigated for the first time. Two types of beams in which the variation of elastic modulus follows a power-law form are studied. The principle of minimum total potential energy is applied along with the Ritz method to derive and solve the governing equations. Considering conventional boundary conditions, Chebyshev polynomials of the first kind are used as auxiliary shape functions. The formulation is developed within the framework of well-known Timoshenko and Reddy beam theories (TBT, RBT). Since the beams are simultaneously tapered and functionally graded, bending and shear stress pushover curves are presented to get a profound insight into the variation of stresses along the beam. The proposed formulations and solution scheme are verified through benchmark problems. In this context, excellent agreement is observed. Numerical results are included considering beams with various cross sectional types to inspect the effects of taper ratio and gradient index on deflections and stresses. It is observed that the boundary conditions, taper ratio, gradient index value and core to the thickness ratio significantly influence the stress and deflection responses.

• 대한기계학회논문집B
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• 제31권12호
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• pp.986-993
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• 2007

The microchannel heat sink is promising heat dissipation method far high density electronic devices. The cross-sectional shape of MEMS based microchannel heat sink is limited to triangular, trapezoidal, and rectangular due to their fabrication method. And heat is added to one side surface of heat source. Therefore, those specific conditions make some complexity of heat transfer in microchannel heat sink. Though many previous research of conjugate heat transfer in microchannel was conducted, most of them did not consider heat loss. In this study, numerical investigation of conjugate heat transfer in rectangular microchannel was conducted. The method of heat loss evaluation was verified numerically. Heat distribution was different for each wall of rectangular microchannel due to thermal conductivity and distance from heat source. However, the ratio of heat from each channel wall was correlated. Therefore, the effective area correction factor could be proposed to evaluate accurate heat flux in one side heating condition.

• 전자공학회논문지A
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• 제31A권8호
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• pp.91-99
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• 1994

Damage induced by Si ion implantation and its annealing behavior during rapid thermal annealing were investigated by cross-sectional TEM (transmission electron microscopy) and RB ( Rutherford backscattering) spectrum. 150keV and 50keV Si ions were implanted in Si (100) at room temperature with doses of 2${\times}10^{15}cm^{-2}$. And 100keV Si ions were implanted in Si with doses from 1${\times}10^{14}cm^{-2}$. A variety of damage structures were generated by Si ion implantation such as continuous amorphous layer extending to the surface buried amorphous layer and damage clusters. Damage clusters are annealed out at the lower annealing temperature of 550 $^{\circ}C$. However, event at the temperature of 110$0^{\circ}C$ end of range loops remain in the original lower amorphous/crystal interface in the case of continuous and buried amorphous layer formation. Extended defects in the shape of zipper dislocations are also observed at the middle of the recrystallized region in the buried amorphous layer.

• 한국결정성장학회지
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• 제5권1호
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• pp.44-49
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• 1995

6H - SiC를 승화법(Sublimation Process)으로 성장하였으며, 성장 결정의 표면에서 나타난 양상에 대하여 광학 현미경을 이용하여 관찰하였다. 6H-SiC는 측면방향(Hexagonal system에서 a축 방향)으로 성장하는 속도가 seed 방향인 c축 방향보다 빠르고, 따라서 많은 성장 step을 관찰할 수 있었다. 또한, SiC 결정의 주된 결함인 micropipe는 성장 후 결정의 표면까지도 형성되고 있어, 거대한 void로 관찰되어졌다. 이것은 pore와는 다르게 구별되며, 완전한 구형의 단면을 가진다. 본 연구에서는 micropipe 및 면결함, 그리고 결정성장시의 step 형성등의 현상에 대하여 광학 현미경으로 조사형 그 결과를 보고하기로 한다.

• 한국진공학회지
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• 제18권1호
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• pp.44-48
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• 2009

전기로에서 공급하는 열을 통해 주변 반응 기체와 기판이 열적 평형 상태를 이루고 있는 기존의 박막 성장 방식과 달리, 외부에서 주입시킨 공기를 이용하여 기판 홀더를 냉각시켜 기판과 기판 주변 반응 기체 사이에 온도 차이(temperature gradient)를 발생시키고, 그 온도 차이가 변함에 따라 사파이어 r-면 기판 위에 성장된 질화갈륨 나노 구조체의 구조적 특성이 어떻게 바뀌는지에 대한 연구를 수행하였다. 온도 차이의 크기에 따라 다족(multipod) 형태로 자란 나노 막대의 직경과 밀도, 그리고 길이가 변화함을 확인하였다. 또한, 동일한 온도 차이(temperature gradient)가 있더라도 기판 자체의 온도에 따라 나노막대 끝 단면의 모양이 변화됨을 발견하였다.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2013년도 춘계학술대회
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• pp.136-138
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• 2013

현재 해상교통안전시설인 표준등부표의 종류는 10가지이며, 가장 작은 등부표가 4.4m로 대형인 것이 현실이다. 따라서 제작, 교체 및 수리가 용이한 부유형의 소형 등부표를 제안하고자 하였다. 한편 부유형의 경우 환경적 외력에 의한 위치 신뢰도가 떨어지며, 특히 유실 등의 사고에 대비하기 위한 안정성 검토가 필요하다. 이 논문에서는 새로운 등부표의 운동성(Heave, Sway, Pitch)을 상용프로그램을 사용하여 Encounter Frequency별 분석하고, 2차원 경계요소법(Boundary Element Method, BEM)을 이용하여 부유체의 단면형상에 따른 유체력을 수치시뮬레이션하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
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• pp.274.2-274.2
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• 2013

We described a simple and efficient fabrication method for generating microfluidic channels with a circular-cross sectional geometry by exploiting the reflow phenomenon of a thick positive photoresist. Initial rectangular shaped positive photoresist micropatterns on a silicon wafer, which were fabricated by a conventional photolithography process, were converted into a half-circular shape by tuning the temperature to around $105^{\circ}C$. Through optimization of the reflow conditions, we could obtain a perfect circular micropattern of the positive photoresist, and control the diameter in a range from 100 to 400 ${\mu}m$. The resultant convex half-circular photoresist was used as a template for fabricating a concave polydimethylsiloxane (PDMS) through a replica molding process, and a circular PDMS microchannel was produced by bonding two half-circular PDMS layers. A variety of channel dimensions and patterns can be easily prepared, including straight, S-curve, X-, Y-, and T-shapes to mimic an in vivo vascular network. To inform an endothelial cell layer, we cultured primary human umbilical vein endothelial cells (HUVECs) inside circular PDMS microchannels, and demonstrated successful cell adhesion, proliferation, and alignment along the channel.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2006년도 추계학술대회 논문집
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• pp.96-101
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• 2006

3-D visualization using confocal laser scanning microscopy (CLSM) in a chaotic micromixer was performed as a reproduction experiment and the feasibility of 3-0 imaging technique in the microscale was confirmed. For diagonal micromixer (DM) and two types of staggered herringbone micromixers (SHM) designed by Whitesides et al., to verify the evolution of mixing, cross sectional images are reconstructed at the end of every cycle. In a DM, clockwise rotational flow motion generated by diagonal ridges placed on the floor of micromixer is observed and this motion makes the fluid commingle. On the contrary, there are two rotational flow structures in the SHM and the centers of rotation exchange their position each other every half cycle because of the V shape of ridges varying their orientation every half cycle. Local rotational flow and local extensional flow generated by the complicate ridge pattern make the flow be chaotic and accelerate the mixing of fluid. The dominant parameter that influences on the mixing characteristic of SHM is not the length of micromixer but the number of ridges under the same flow configurations.