• Annual Conference of KIPS
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• 2003.05a
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• pp.145-148
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• 2003

본 논문은 단일 VOD 환경에서의 서버/클라이언트 간 데이터 서비스 모델을 분석하고 이를 병렬 VOD 환경에 적용함으로써 보다 나은 사용자 QoS(Quality of Service)를 제공하고자 한다. 이를 위해 단일 VOD 환경에서는 클라이언트가 데이터를 요청하고 서버가 전달해주는 Client Pull 모델과 서버 측에서 일방적으로 데이터를 전달해주는 Server Push 모델을 네트워크상 전달지연 측면에서 분석하고 위 두 모델.을 통합한 IPP(Interleaving Pull & Push) 서비스 모델과 Client Pull 모델을 전달지연과 클라이언트 버퍼 내 데이터 잔여량 측면에서 병렬 VOD 환경에서 적용 및 비교하였다. 시뮬레이션을 통해 병렬 VOD 환경에서 IPP 서비스 모델이 가장 적은 전달지연과 보다 안정적인 클라이언트 버퍼를 유지함을 알 수 있으며 이를 동해 사용자에게 보다 나은 서비스를 제공할 수 있다.

• Proceedings of the KIPE Conference
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• 2008.10a
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• pp.103-105
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• 2008

DC-DC 컨버터, DC-AC (계통연계형)인버터, 입 출력 필터 등으로 구성된 연료전지용 PCS에서 DC-DC 컨버터가 전체 효율에 가장 많은 영향을 미친다고 할 수 있는데 본 논문에서는 Push-Pull 컨버터를 선정하여 손실에 관하여 해석하였다.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2000.11a
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• pp.18-22
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• 2000

An experimental study was carried out to investigate the effect of nano-contact condition on the nano-adhesion phenomena. SPM(scanning probe microscope) tips with different radius of curvature were fabricated by a series of masking and etching processes. DLC(diamond-like carbon) and W-DLC (tungsten-incorporated diamond-like carbon) were coated on (100) silicon wafer by PACVD(plasma assisted chemical vapor deposition). Pull-off forces of Pure Si-wafer, DLC and W-DLC were measured with SPM(scanning probe microscope). Also, the same series of tests were carried out with the tips with different radius of curvature. Results showed that DLC and W-DLC showed much lower pull-off force than Si-wafer and Pull-off force increased with the tip radius.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2001.06a
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• pp.49-54
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• 2001

Monolayers such as self-assembled monolayer (SAM) have received considerable attention to reduce stiction and friction in micro-devices and microelectromechanical systems (MEMS). Various organic molecular films were investigated to obtain better understanding of their tribological behaviors and adhesion property. The organic molecular films studied in this work are: epoxysilane SAMs, octadecyltricholosilane (OST), multi-layers composed of epoxysilane SAMs, poly〔styrene-b-(ethylene-co-butylene)-b-styrene〕(SEBS) and compound of epoxy resin and poly (paraphenylene) (EP/PPP). The pull-off forces of these films were also obtained from force-distance curves measured in static mode of operation of atomic force microscope (AFM). Tribological tests were conducted with a ball-on-flat reciprocating friction tester. The OST showed the lowest pull-off force, indicating its low adhesion property. It was revealed that, the OST, EP/PPP and the multi-layer of epoxysilane SAMs, SEBS and EP/PPP exhibited good tribological properties at the lower load (0.3 N) whereas the OST showed best performance at the higher load (1.8 N).

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.6
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• pp.1023-1030
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• 2001

The tensile properties of short nylon6 fiber reinforced NR and SBR have been investigated as functions of diameter ratio(DR), interphase condition, fiber aspect ratio(AR), and fiber content. The short-fiber(DR=3 and AR=2) reinforced SBR did not show the dilution effect for all interphase conditions. And the short-fiber(DR=3 and AR=2) reinforced NR did not show the dilution effect except for the no-coating. The better interphase condition, the lower dilution effect at same DR. The tensile moduli are significantly improved due to fiber content and diameter ratio at same interphase condition. The pull-out force increased with the DR. The better interphase condition, the higher pull-out force at same DR. It is found that the DR and AR have an important effect on tensile properties.

• Journal of the Korea institute for structural maintenance and inspection
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• v.6 no.4
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• pp.201-207
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• 2002

An advanced fiber sheet has been widely used for strengthening of the concrete structures due to its excellent properties such as high strength and light weight. Bond strength is very important in strengthening the concrete structures using an advanced fiber sheet. This research examines the bond behavior between fiber sheet and concrete, investigates the bond strength by the direct pull-out test and the tensile-shear test. To obtain the tensile-shear strength a double-face shear type bond test is conducted. The primary test variables are the types of concrete surface roughness (disk-grinding/chipping) and retrofitting methods (bonding/injection). Thirty specimens were tested to evaluate the bond strength. It is shown that the average bond strength between fiber sheet and concrete by the direct pull-out test and the tensile-shear test is $22.3{\sim}23.1kgf/cm^2$ $17.92{\sim}19.75kgf/cm^2$, respectively.

• Coupled systems mechanics
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• v.2 no.3
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• pp.215-230
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• 2013

This paper investigates the pull-in instability of functionally graded poly-SiGe micro-beams under the combined electrostatic and intermolecular forces and temperature change. The exponential distribution model and Voigt model are used to analyze the functionally graded materials (FGMs). Principle of virtual work is used to derive the nonlinear governing differential equation which is then solved using differential quadrature method (DQM). A parametric study is conducted to show the significant effects of material composition, geometric nonlinearity, temperature change and intermolecular Casimir force.

• Computers and Concrete
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• v.23 no.3
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• pp.155-160
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• 2019

The use of recycled aggregate concrete for the purpose of environmental and resource conservation has gained increasing interest in construction engineering. Nevertheless, few studies have reported on the bonding performance of the bars in recycled aggregate concrete after exposed to high temperatures. In this paper, 72 pull-out specimens and 36 cubic specimens with different recycled coarse aggregate content (i.e., 0%, 50%,100%) were cast to evaluate the bond behavior between recycled aggregate concrete and steel bar after various temperatures ($20^{\circ}C$, $200^{\circ}C$, $400^{\circ}C$, $600^{\circ}C$). The results show that the recycled aggregate concrete pull-out specimens exhibited similar bond stress-slip curves at both ambient and high temperature. The bond strength declined gradually with the increase of the temperature. On the basis of a regression analysis of the experimental data, a revised bond strength mode and peak slip ratios relationship model were proposed to predict the post-heating bond-slip behavior between recycled aggregate concrete and steel bar.

• The Journal of Korea Robotics Society
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• v.14 no.3
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• pp.221-227
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• 2019

This paper studies an effect of vibration on twisted string actuation inside conduit at high curvature angles. In our previous work. we have mentioned that twisted string actuators can be used to transmit power even at significant curvature angles of the conduit. However, several undesirable effects, namely pull-back, hysteresis, and chattering, were present during actuation due to friction between strings and the internal sheath of the conduit. This paper reports the results of experimental study on effects of vibration on twisted string actuation inside curved conduits. We have demonstrated that applying vibration generated near natural frequency of the system during the stages of twisting and untwisting cycles helped reduce pull-back and hysteresis and increase string contraction. In case when sheath was deflected by $180^{\circ}$ under a constant load of 3 kg, we were able to achieve over 40% decrease in pull-back and 30% decrease in hysteresis, compared with no vibration case.

• Structural Engineering and Mechanics
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• v.76 no.5
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• pp.619-629
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• 2020

In current study, surface/interface effects for pull-in voltage and viscous fluid velocity effects on dimensionless natural frequency (DNF) of fluid-conveying piezoelectric nanosensor (FCPENS) subjected to direct electrostatic voltage DC with nonlinear excitation, harmonic force and also viscoelastic foundation (visco-pasternak medium and structural damping) are investigated using Gurtin-Murdoch surface/interface (GMSIT) theory. For this analysis, Hamilton's principles, the assumed mode method combined with Lagrange-Euler's are used for the governing equations and boundary conditions. The effects of surface/interface parameters of FCPENS such as Lame's constants (λI,S, μI,S), residual stress (τ0I,S), piezoelectric constants (e31psk,e32psk) and mass density (ρI,S) are considered for analysis of dimensionless natural frequency respect to viscous fluid velocity u̅f and pull-in voltage V̅DC.