Browsing by Author "Chung, WC"

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Effects of thermal annealing on Ni/Ta/n-GaN Schottky diodes
(2001-03-15)
Chen, GL
;
Chang, FC
;
Chung, WC
;
Huang, BR
;
Chen, WH
The thermal effects of Ni/Ta/n-GaN Schottky diodes have been investigated for the first time using current-voltage, X-ray photoemission spectroscopy and Auger electron spectroscopy (AES) methods. Their barrier height is found to increase monotonously with increasing annealing temperature up to 800 degreesC. Preliminary results indicate that when a Th intermediate layer is added into the Ni/GaN diodes, it can prevent the metal-semiconductor interdiffusion and Ni accumulation adjacent to GaN substrate to a large extent so that a more thermally stable device can be obtained.
Long-term photocapacitance decay behavior in undoped GaN
(2000)
Chung, HM
;
Pan, YC
;
Chung, WC
;
Chen, NC
;
Tsai, CC
We have employed the photocapacitance measurement to examine the physical properties of GaN Schottky diode made from the undoped epilayer grown by metalorganic vapor phase epitaxy. The resulted transient capacitance spectrum shows that the diode exhibits a characteristic of long-term logarithmic-type decaying behavior, which, we believe, is correlated closely to the linear arranged traps close to the core of the threading edge dislocations.
New synthesis of tacamonine.
(2003-09-01)
Ho, TL
;
Chung, WC
;
應用化學系
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Department of Applied Chemistry
Nonlinear control of longitudinal flight dynamics
(2003)
Liaw, DC
;
Song, CC
;
Chung, WC
;
電控工程研究所
;
Institute of Electrical and Control Engineering
This paper presents the nonlinear analysis and control of a third-order model for longitudinal flight dynamics. Bifurcation analysis using numerical study for F-8 aircraft reveals that Hopf bifurcations may occur at some critical values of the elevator commands. These results agree with the well-known nonlinear phenomena existed in longitudinal flight dynamics. Furthermore, bifurcation control using both washout filter and direct state feedback are applied to develop the stabilizing laws for system equilibria and periodic solutions emerged from bifurcation points. Numerical simulations are provided to demonstrate these main results.
Surge control of axial flow compression systems via linear and nonlinear designs
(2002)
Liaw, DC
;
Ren, SM
;
Chung, WC
;
Abed, EH
;
電控工程研究所
Based on Moore and Greitzer's model (1986), the surge behavior is found to be attributed to the appearance of Hopf bifurcation. A Lyapunov function based control is proposed to provide the asymptotic stability of the post-surge operating point for the compressor with uncertain axisymmetric characteristic. Though the robust stabilization can be achieved by Lyapunov function based design, however, such an approach strongly relies on the explicit knowledge of the operating point. A washout filter type linear controller is proposed to delay and suppress the occurrence of Hopf bifurcation in compressor dynamics, which does not require the knowledge of system equilibria. Numerical results demonstrate the effectiveness of the proposed designs.
Two-parameter bifurcation analysis of longitudinal flight dynamics
(2003-07-01)
Liaw, DC
;
Song, CC
;
Liang, YW
;
Chung, WC
;
電控工程研究所
The bifurcation analysis of longitudinal flight dynamics is presented, emphasizing the influence of elevator deflection and aircraft mass. Based on a mathematical model proposed by Garrard and Jordan (1977), a rich variety of bifurcation phenomena such as saddle-node bifurcation, Hopf bifurcation, and cycle fold bifurcations are observed in the numerical simulations of longitudinal flight dynamics of the F-8 aircraft. The occurrence of saddle-node bifurcation and Hopf bifurcation may result in jump behavior and pitch oscillations of flight dynamics. The analysis leads to a division of the longitudinal flight space into several maneuvering regions, and may provide more understanding of the longitudinal flight dynamics.