• Proceedings of the Optical Society of Korea Conference
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• 2003.02a
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• pp.38-39
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• 2003

The GaAs semiconductor whispering gallery modes, produced in the peripheral Rayleigh band region of W／sub Rayleigh／ ＝ (${\Phi}$／2)( 1-n／sub eff／n), exhibit novel properties of ultralow thresholds open to nano-ampere regime associated with photonic quantum ring (PQR) production (Fig 1 (a)). The PQR phenomena are associated with a photonic field-driven phase transition of quantum well(QW)-to-quantum wire (QWR) and hence the photonic (non-de Broglie) quantum corral effects, on the Rayleigh cavity confined carriers in dynamic steady state, occur as schematically shown in Fig 1. (omitted)

• International Journal of Naval Architecture and Ocean Engineering
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• v.11 no.2
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• pp.688-698
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• 2019

If heave motion in the platform causes horizontal parametric vibration of a Compliant Vertical Access Riser (CVAR), the riser may become unstable. A combination of riser parameters lies in the unstable region aggravates vibrational damage to the riser. Change of axial tensile stress in the riser combined with its natural frequency and mode shape change results in mode coupling. In accordance with the state transition matrices of the riser in the coupled and uncoupled states, the stable and unstable regions were obtained by Floquet theory, and the vibration response under different conditions was obtained. The parametric excitation of the CVAR is shown to occur mainly in first-order unstable regions. Mode coupling may cause parametric excitation in the least stable regions. Damping reduces the extent of unstable regions to a certain extent.

• Proceedings of the KWS Conference
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• 1994.05a
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• pp.39-43
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• 1994

The effects of ageing treatment on the mechanical properties of two Cu-bearing HSLA(High Strength Low Alloy) steels, HSLA-A and HSLA-B ,were studied by means of SEM, TEM, tensile, charpy impact and hardness tests. These steels showed excellent combination in strength and toughness at an ageing of $650^{\circ}C$ by the precipitation of $\varepsilon$-Cu and low carbon alloying. The peak strength was achieved at an ageing of 50$0^{\circ}C$ in both steels, while the impact energy was very low in this peak strength. With ageing temperature above this temperature, strength was decreased whereas impact energy increased. A marked increase in hardness above 675$^{\circ}C$ was associated with the formation of “M-A constituents” which forms during cooling from austenite-ferrite two phase region. The impact transition temperature of HSLA-A and HSLA-B steels were -l$25^{\circ}C$ and -145$^{\circ}C$, respectively.

• Solar Energy
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• v.19 no.3
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• pp.93-100
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• 1999

The objective of this experimental study was to investigate the characteristics of heat transfer and air flow in two-dimensional impinging jet system, in which hybrid rods have been set up in front of heating surface in order to increase heat transfer. The shape of hybrid rods had a cross section made with a half of circular cross section and that of rectangular. This time, the clearance from hybrid rod to heating surface(C=1, 2, 4mm) and the pitch between each hybrid rods(P=30, 40, 50mm) changed for the transition region(H/B=10). And this result compared with the experimentation without hybrid rod. As a result, heat transfer performance was best under the condition of C=1mm, in case clearance changed, and as the pitch is 30mm, it is largely influenced by eddies and acceleration in case pitch of hybrid rod changed.

• Journal of Institute of Control, Robotics and Systems
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• v.14 no.3
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• pp.213-220
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• 2008

The object of this paper is to propose a method to deal with the problem of modeling user specifications in approaches based on supervisory control and Petri nets. However, most of Petri Net approaches are based on forbidden states specifications, and these specifications are suitable the use of tool such as the reachability graph. But these methods were not able to show the user specification easily and these formalisms are generally limited by the combinatorial explosion that occurs when attempting to model complex systems. Herein, we propose a new efficient method using FSSTP (Forbidden Sequences of State-Transitions Problem) and theory of region. Also, to detect and avoid the deadlock problem in control process, we use DAPN method (Deadlock Avoidance Petri nets) for solving this problem in control model.

• Journal of Ocean Engineering and Technology
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• v.2 no.1
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• pp.150-162
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• 1988

The dynamic fracture toughness, $K_{Id}$,is measured in the heat-treated and ion-nitrided Cr-Mo, Ni-Cr-Mo steel using standard and Precracked Charpy specimens an imstrumented impact machine. The value of $K_{Id}$and both the energy of initiate fracture, and the total energy of fracture. Since the $K_{Id}$values of the precraked impact specimens are in accord with their theoretical ones, this testing method is sufficently practical. The effect of ion-nitriding are found to be larger than the heat-treaded specimen.

• Publications of The Korean Astronomical Society
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• v.14 no.2
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• pp.79-81
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• 1999

We have made an extensive mapping of the $^{13}CO$ J=1-0 transition line in the dark cloud L1535. We also constructed the $100{\mu}m$ IRAS map in the region. We found a semi-detached cloud component of $^{13}CO$ in the northeast direction of the $^{13}CO$ main cloud which forms a dumbbell-like structure. This additional component with an angular size of $20'\times16'$ has not been observed before in any molecular surveys of the cloud. The IRAS map shows a similar structure with two intensity peaks whose positions coincide with those of the $^{13}CO$ clouds.

• Journal of Power Electronics
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• v.11 no.6
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• pp.846-855
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• 2011

This paper proposes a control mode switching scheme between vector control and constant V/f control for induction machine (IM) drives for maximum torque utilization in a higher speed region. For the constant V/f scheme, a smooth transition method from the linear range of PWM up to the six-step mode is applied, by which the machine flux and torque can be kept constant in a high-speed range. Also, a careful consideration of the initial phase angle of the voltage in the transient state of the control mode change between the vector control and V/f schemes is described. The validity of the proposed strategy is verified by the experiment result for a 3-kW induction motor drives.

• Journal of Power Electronics
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• v.14 no.5
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• pp.926-936
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• 2014

A simplified and effective space vector pulse-width modulation (SVPWM) algorithm with two and three levels for three-phase voltage-source converters is proposed in this study. The proposed SVPWM algorithm only uses several linear calculations on three-phase modulated voltages without any complicated trigonometric calculations adopted by conventional SVPWM. This simplified SVPWM also avoids choosing the vector sector required by conventional SVPWM. A two-level overmodulation scheme is integrated into the proposed two-level SVPMW to generate the output voltage that increases from a linear region to a six-step state with a smoothly linear transition characteristic and a simple overmodulation process without a lookup table and complicated nonlinear functions. The three-level SVPWM with a proportional-integral controller effectively balances the neutral point potential of the neutral point clamped converter. Results from the simulation in MATLAB/Simulink and the experiment based on a digital signal processor are provided to clearly demonstrate the validity and effectiveness of the proposed strategies.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.544-547
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• 1999

To develop the better insulants. the zeolite particle, which is aluminosilicate mineral, was filled In the DGEBA/MDA/SN epoxy resin system. Dynamic DSC curves of cured specimens with various contents of zeolite were observed and the glass transition temperature(T$_{g}$) was obtained. According to this result, we could carry out the experiment concerned with the dielectric breakdown strength around T$_{g}$ and find the limit temperature for the application of the DDEBA/MDA/SN system filled with natural zeolite. T$_{g}$ increased with the content of zeolite. As the temperature increased, the dielectric breakdown strength decreased rapidly, in the region of T$_{g}$. At the high temperature, the deterioration by electrical stress was activated. The diameter of puncture at the high temperature was larger 7han that at the room temperature.erature.