• Bulletin of the Korean Chemical Society
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• 제32권12호
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• pp.4371-4376
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• 2011

In this work, we investigate the growth behavior of silicon oxide nanowires via a solid-liquid-solid process. Silicon oxide nanowires were synthesized at $1000^{\circ}C$ in an Ar and $H_2$ mixed gas. A pre-oxidized silicon wafer and a nickel film are used as the substrate and catalyst, respectively. We propose two distinctive growth modes for the silicon oxide nanowires that both act as a unique solid-liquid-solid growth process. We named the two growth mechanisms "grounded-growth" and "branched-growth" modes to characterize their unique solid-liquid-solid growth behavior. The two growth modes were classified by the generation site of the nanowires. The grounded-growth mode in which the grown nanowires are generated from the substrate and the branchedgrowth mode where the nanowires are grown from the side of the previously grown nanowires or at the metal catalyst drop attached at the tip of the nanowire stem.

• 한국레이저가공학회지
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• 제2권3호
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• pp.11-18
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• 1999

This paper describes the weldability of carbon steel and stainless steel using 5㎾ $CO_2$ laser system with nearly multi-mode beam and a parabolic focusing mirror. In the laser welding of steels, major welding parameters are focal point, travel speed, beam power, shield gas and gap tolerance, etc.. Two kinds of gases(Ar, He) were used as a assist gas and supplied through the external nozzle. It is very important for optimum condition to remove plasma plume which absorbs laser beam and to obtain deep penetration and sound weld bead. Bead-on-plate welding tests were carried out for the experiments. Penetration data were obtained with various welding parameters and the effects of welding parameters were discussed. Butt welding tests were performed with various conditions. Only the optimum laser parameters assured good weld quality As a result of this study, We achieve the fundamental weldabilities using a high power $CO_2$ laser for carbon steel and stainless steel.

• 한국레이저가공학회지
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• 제8권1호
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• pp.9-18
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• 2005

The laser direct writing method using a UV Argon-ion laser is studied for fabrication of waveguide. The laser direct writing system is constructed with a vision camera, a xy-stage, a motion controller and the delivery components of a laser beam. The UV Argon-ion laser has wavelength range of $333.6\~363.8$ nm. A photo-active UV curable polymer for a planar light-wave circuit(PLC) of single mode is used. This polymer is irradiated by Argon-ion laser and developed by a solvent after a post-baking. The optimum laser direct writing condition is obtained experimentally by changing various process parameters such as laser power, writing speed and focal length. The propagation and coupling loss of a optical waveguide was measured as 1dB/cm and 0.6dB/cm, respectively. Also, the minimum width of waveguide of $100{\mu}m$(ZPLW-207) is obtained. Finally, the waveguides of line, bend and branch type are successfully fabricated.

• 대한교통학회:학술대회논문집
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• 대한교통학회 2003년도 제43회 학술발표회논문집
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• pp.127-150
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• 2003

This research presents a novel application of static traffic assignment methods, but with a variable time value, for estimating the market share of a high-speed rail (HSR) in the NW-SE corridor of Korea which is currently served by the airline (AR), conventional rail (CR), and highway (HWY) modes. The proposed model employs the time-space network structure to capture the interrelations among all competing transportation modes, and to reflect their supply- and demand-sides constraints as well as interactions through properly formulated link-node structures. The embedded cost function for each network link offers the flexibility for incorporating all associated factors, such as travel time and fare, in the model computation, and enables the use of a distribution rather than a constant to represent the time-value variation among all transportation mode users. To realistically capture the tripmakers' value-of-time (VOT) along the target area, a novel method for VOT calibration has been developed with aggregate demand information and key system performance data from the target area. Under the assumption that intercity tripmakers often have nearly "perfect" travel information, one can solve the market share of each mode after operations of HSR for each O-D pair under the time-dependent demand with state-of-the-art traffic assignment. Aside from estimating new market share, this paper also investigated the impacts of HSR on other existing transportation modes.

• Journal of Welding and Joining
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• 제16권2호
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• pp.93-99
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• 1998

The effects of welding conditions of gas metal arc welding on the elements loss of solid wire, oxygen content and impact toughness of weld metals were studied. Deoxidizing elements loss was increased with increase of arc voltage in both short-circuit transfer mode and globular transfer mode. It is believed that increase of arc voltage results in increase of reaction time between elements in the droplet and surrounding gas at the end of wire and in the arc column. Based on the thermodynamic equilibrium model, the oxygen content of weld metal can be predicted with the content of silicon and manganese as following : [%O] = $K([%Si][%Mn])^{-0.25}$, K = -15518/T+6.01. The equilibrium temperature was dependent on shielding gas, and it was 187$0^{\circ}C$ for $CO_2$ gas and 180$0^{\circ}C$ for 20%$CO_2$-80%Ar gas. The oxygen content of weld metal which shows maximum impact toughness was varied with deoxidizing alloy system of wires, 0.041 wt% for Si-Mn type wire and 0.026 wt% for Si-Mn-Ti type wire.

• International Journal of Aeronautical and Space Sciences
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• 제12권4호
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• pp.305-317
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• 2011

This paper presents an overview on flutter boundary prediction in tests which is principally based on a system stability measure, named Jury's stability criterion, defined in the discrete-time domain, accompanied with the use of autoregressive moving-average (AR-MA) representation of a sampled sequence of wing responses excited by continuous air turbulences. Stability parameters applicable to two-, three- and multi-mode systems, that is, the flutter margin for discrete-time systems derived from Jury's criterion are also described. Actual applications of these measures to flutter tests performed in subsonic, transonic and supersonic wind tunnels, not only stationary flutter tests but also a nonstationary one in which the dynamic pressure increased in a fixed rate, are presented. An extension of the concept of nonstationary process approach to an analysis of flutter prediction of a morphing wing for which the instability takes place during the process of structural morphing will also be mentioned. Another extension of analytical approach to a multi-mode aeroelastic system is presented, too. Comparisons between the prediction based on the digital techniques mentioned above and the traditional damping method are given. A future possible application of the system stability approach to flight test will be finally discussed.

• 대한본초학회지
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• 제22권2호
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• pp.97-102
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• 2007

Objectives : This study presents a high performance liquid chromatography - electrospray ionization-mass spectrometer (HPLC-MS/MS) methods for the quantitative and qualitative analysis of various active components in Samul-tang, which is composed of four crude herbs. Methods : HPLC-ESI-MS/MS for the determinations of paeoniflorin and 5-HMF (5-hydroxymethyl 2-furaldehyde) in the Samul-tang, the separation method was performed on an COSMOS1L 5C18-AR-Il (2.0 X 150 mm I.D.) column by gradient elution with 0.1% acetic acid and 5% CH3CN in water (A)-0.1% acetic acid and 5% H20 in CH3CN (B) as the mobile phase at a flow-rate of 300 ${\mu}L/min$ with detection at quadrupole mass spectrometer. The all marker substances were always detected as the base peaks in the positive ion mode. Results : The paeoniflorin of Paeoniae Radix in Samul-tang showed a strong base peak [M+H2O]+ in the positive detection mode to give the following as; paeoniflorin (498.109 [M+H2O]+, 479.8 [M]+, 301 [M-glucose]+, 179.3 [glucose]+). Based on the HPLC retnetion time and MS of standard compounds confirmed the identity of active compounds in Rehmanniae Radix Preparata as follows; 5-HMF (127.0[M+H]+, 109.3 [M-OH]+) in the positive ion mode. Conclusion : According to the above results, HPLC-ESI-MS method permits assignment of tentative structures such as paeoniflorin and 5-HMF in the Samul-tang.

• 한국광학회지
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• 제10권5호
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• pp.430-438
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• 1999

근적외선 파장영역에서 시분해 분광용 레이저 광원개발을 위해 발진파장이 반사경의 파장 선폭에 의해 제한된 수십 펨토초 펄스폭의 고출력 티타늄 사파이어 레이저를 개발하였다. 한쪽 프리즘 끝에 미세 stepping-motor로 제어되는 kniff-edge slits를 사용하여 발진파장을 선택하였으며, 파장가변영역은 770nm~870nm이었고, 이 파장영역에서 얻은 펄스폭은 40 fs 미만이었다. 가장 짧은 펄스폭은 약 17 fs 이었으며 이때의 파장중심은 820nm이고 선폭은 72nm이었다. 약 5W 출력의 아르곤 레이저 여기광을 사용하여 위의 파장영역에서 얻은 평균출력은 440 mW~580 mW 이었다. 연속발진 경우와 Kerr-lens mode locking 경우의 이득매질에서의 빔의 크기를 계산하여 이득변조값 ${\lambda}=2.5{\times}10_{-8}$ W을 수치적으로 얻었고, 이로부터 Ginzberg Landau 방정식을 사용하여 40 fs 미만의 펄스폭이 발생됨을 보였다.

• 한국마이크로전자및패키징학회:학술대회논문집
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• 한국마이크로전자및패키징학회 2001년도 추계 기술심포지움
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• pp.226-229
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• 2001

현재 초소형 정밀기계(MEMS;Microelectromechanical System) 소자의 가장 큰 문제점으로 대두되고 있는 점착현상을 방지하기 위하여 불화유기박막을 증착하였다. Octafluorocyclobutane(C$_4$F$_{8}$)을 소스가스를 PECVD (Plasma Enhanced CVD)와 ICP (Inductively Coupled Plasma)를 이용하여 증착하였다. 여기에 Ar을 첨가하여 플라즈마의 반응성을 높여주었다. 형성된 불화유기박막의 나노트라이볼러지 특성을 살펴보기 위하여 AFM을 통하여 증착시킨 시편의 topography를 살펴보았다. 그리고 박막의 antiadhesion의 정도를 살펴보기 위하여 cantilever와 박막의 표면 사이에 존재하는 interaction force를 측정 하였고 AFM의 force curve mode를 이용하였다 PECVB를 이용하여 증착된 박막은 ICP를 이용한 박막보다 균일하지 못한 박막을 보였으며 attractive force가 강한 것으로 사료된다.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2004년도 Asia Display / IMID 04
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• pp.1155-1158
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• 2004

Various inorganic alignment layers of nematic liquid crystal (NLC) molecules were investigated. Ar ion beam (IB) irradiation was utilized for alignment method and homogenous and homeotropic orientations with tilt angle were obtained on the suitable inorganic thin films. Proper doping materials were added to diamond-like carbon (DLC) films. In the case of homogeneous alignment, nitrogen doping affected the increase of pretilt angle, while the fluorine bonding in the DLC films was induced the tilted homeotropic alignment cause its extreme hydrophobic property. These results showed that ion beam irradiation method could be applied to the various alignment mode of NLC such as IPS, TN and MVA.