• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.12
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• pp.4053-4061
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• 1996

Internal flow characteristics within Y-jet atomizers and the local drop size distribution and cross-sectional averaged drop size at the outside were investigated with the liquid and air injection pressures, mixing port length of atomizers, and the liquid properties taken as parameters. To examine the effect of the liquid viscosity, glycerin-water mixtures were used in this study. The liquid viscosity plays only a minor role in determining the internal flow pattern and the spatial distribution shape of drops, but the drop sizes themselves generally increase with increasing of the liquid viscosity. An empirical correlation for the liquid discharge coefficient at the liquid port was deduced from the experimental results; the liquid discharge coefficient strongly depends on the liquid flow area at the mixing point which is proportional to the local volumetric quality(.betha.$_{Y}$), and the volumetric quality was included in the correlation. Regardless of the value of the liquid viscosity, the compressible flow through the gas port was well represented by the polytropic expansion process(k=1.2), and the mixing point pressure could be simply correlated to the aspect ratio( $l_{m}$/ $d_{m}$) of the mixing port and the air/liquid mass flow rate ratio( $W_{g}$/ $W_{f}$) as reported in the previous study.udy.udy.y.

• Textile Coloration and Finishing
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• v.11 no.1
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• pp.34-41
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• 1999

To examine the increase of paper strength by solvent-bonding using N-methylmorpholine N-oxide (NMMO), a paper was treated with aqueous solutions of NMMO, concentrated at $90^\circ{C}$ for selected periods of time, and pressed for 5 seconds followed by washing and drying. The effect of the increasing NMMO concentration on bonding state and some important properties of samples were mainly investigated. With increasing concentration of NMMO, the degree of bonding between fibers was increased, the fiber cross-sectional shape was changed from 'thin ribbonlike' to 'round rodlike' by swelling with solvent, and the longitudinal waves (crimp) were introduced to fibers, hence the shrinkage, weight per unit area, and thickness of paper were increased. Consequently, the tensile strength and elongation, under standard and wet conditions, and the stiffness were increased, and the water absorption was decreased generally with increasing concentration of NMMO. The moisture regain of treated samples was lower than that of the untreated sample, because of the reduction of space between fibers. But the moisture regain was increased a little with increasing concentration of NMMO due to the fiber swelling with NMMO followed by structural relaxation.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.04a
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• pp.627-635
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• 1997

In general, the booming noise intensity at tunnel exit is strongly related to the gradient of the compression wave front created by high speed train entering the tunnel. This paper presents some results in relation with the compression wave front produced when the high speed train enters a tunnel. Four kinds of tunnel entrance shape with real dimensions were studied to investigate the formation of compression wave front inside tunnel by train entering tunnel. Computations were carried out using three-dimensional compressible Euler equation with vanishing viscosity and conductivity of fluid. According to the reslts, the flow disturbance occured at tunnel entrance were eliminated by tunnel hood with same cross sectional area. The compression wave front is formed completely at 30-40m from tunnel entrance. The maximum pressure gradient of compression wave front is reduced by 29.8% for the inclined tunnel hood and reduced by 21.5% for the tunnel hood with holes at the top face with tunnel without hood. The length of the inclined hood is 15m and the length of the hood with holes is 20m.

• Carbon letters
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• v.4 no.4
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• pp.168-174
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• 2003

Silver nitrate ($AgNO_3$) powder was mixed into a reformed pitch precursor. Then, the silver-containing pitch was melt spun to form round and "C" shape fibers. A wire mesh was inserted prior to the nozzle to improve the spinnability of the silvercontaining precursor pitch. Silver particles in the carbon fibers (CFs) were detected by XRD and TEM. These tests showed that silver particles were uniformly distributed and the total amount of silver remained constant during stabilization and carbonization. Next, the silver-containing CFs were activated by steam diluted in nitrogen gas. Silver particles accelerated the activation rate, but the specific surface areas of the silver-containing ACFs were similar to those of non-silver containing ACFs at the same burn-off levels. The specific surface area of the C-shaped activated carbon fibers was larger than that of the round activated carbon fibers. The likely reason is that the surface area of a C-shaped CF is about two times larger than that of a round CF when equivalent cross-sectional areas are compared. A small amount of silver particles in the periphery of the CFs was removed during the activation, but the remainder of silver was stayed within the ACFs.

• The Journal of Asian Finance, Economics and Business
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• v.7 no.8
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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.

• Proceedings of the KSR Conference
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• 1998.05a
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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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• v.3 no.2
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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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.12
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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.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.31A no.8
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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.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.5 no.1
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• pp.44-49
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• 1995

Abstract The surface of 6H - SiC bulk crystal grown by sublimation process was investigated by optical microscope observation. Since, in the 6H crystal growing, the crystal had the habitual step growth attitude such that the lateral growth rate along the random a - axis orientation was higher than that along the c - axis of the growth direction, then many steps were developed. There were, also, many micropipes on the surface in the form of as-like large voids. However, they were differenciated with pores and cross- sectional shape of them were close to the circle. In this study, many micropipes, planar defects and the growth steps appeared on the grown crystal surface were investigated.