Browsing by Issue Date, starting with "2001-02-16"

Now showing 1 - 20 of 76716

Fuzzy approaches for fault diagnosis of transformers
(2001-02-16)
Chen, AP
;
Lin, CC
;
資訊管理與財務金融系註：原資管所+財金所
;
Department of Information Management and Finance
Dissolved gas analysis has been used as a diagnostic method to determine the conditions of transformers for a long time. The criteria used in dissolved gas analysis are based on crisp value norms. Due to the dichotomous nature of crisp criteria, transformers with similar gas-in-oil conditions may lead to very different conclusions of diagnosis especially when the gas concentrations are around the crisp norms. To deal with this problem, gas-in-oil data of failed transformers were collected and treated in order to obtain the membership functions of fault patterns using a fuzzy clustering method. All crisp norms are fuzzified to linguistic variables and diagnostic rules are transformed into fuzzy rules. A fuzzy system originally proposed by Takagi and Sugeno is used to combine the rules and the fuzzy conditions of transformers to obtain the final diagnostic results. It is shown that the diagnosing results from the combination of several simple fuzzy approaches are much better than traditional methods especially for transformers which have gas-in-oil conditions around the crisp norms. (C) 2001 Elsevier Science B.V. All rights reserved.
Using fuzzy set to model the stability region on the bicycle derailleur system
(2001-02-16)
Lin, TY
;
Tseng, CH
;
機械工程學系
;
Department of Mechanical Engineering
In designing the bicycle derailleur system, designers can use the results from the "stability region test" to determine many parameters. Experimentation is the most accurate way to find a stability region because it is very difficult to derive a mathematical expression for the stability region. In this paper, a fuzzy set is used to determine the stability region of the bicycle derailleur system. The database of the fuzzy set model is created from the experimental results. The relationship between the experimental data and fuzzy set model will be described. Many properties of the stability region can be derived from this model. The existence of the stability region, the reduction of experimental noise, the determination of indexed points, and other techniques in designing an indexed derailleur system will also be introduced. This approach can simplify the previous representations of the stability region and the mechanical characteristics. Finally, a case study of the market product is presented. (C) 2001 Elsevier Science B.V. All rights reserved.
Fuzzy ARIMA model for forecasting the foreign exchange market
(2001-02-16)
Tseng, FM
;
Tzeng, GH
;
Yu, HC
;
Yuan, BJC
;
管理學院
Considering the time-series ARTMA (p,d,q) model and fuzzy regression model, this paper develops a fuzzy ARIMA (FARIMA) model and applies it to forecasting the exchange rate of NT dollars to US dollars. This model includes interval models with interval parameters and the possibility distribution of future values is provided by FARIMA. This model makes it possible for decision makers to forecast the best- and worst-possible situations based on fewer observations than the ARIMA model. (C) 2001 Elsevier Science B.V. All rights reserved.
Low dark current quantum-dot infrared photodetectors with an AlGaAs current blocking layer
(2001-02-19)
Wang, SY
;
Lin, SD
;
Wu, HW
;
Lee, CP
;
電子工程學系及電子研究所
Low dark current InAs/GaAs quantum-dot infrared photodetectors (QDIPs) are demonstrated. The dark current is reduced by over three orders of magnitude by using a thin AlGaAs current blocking layer. This thin AlGaAs layer reduces the dark current much more than the response signal. The responsivity at 0.5 V is 0.08 A/W with a peak detection wavelength at 6.5 mum. The corresponding detectivity is 2.5x10(9) cm Hz(1/2)/W-1/2, which is the highest detectivity reported for a QDIP at 77 K. (C) 2001 American Institute of Physics.
請問東阿王曹子健先生
(2001-02-22)
管管
管管作品十三首
(2001-02-25)
管管
管管作品十三首
(2001-02-25)
管管
管管作品十三首
(2001-02-25)
管管
管管作品十三首
(2001-02-25)
管管
管管作品十三首
(2001-02-25)
管管
Special issues on multimedia communication services
(2001-03-01)
Hang, HM
;
Rao, KR
;
電信研究中心
;
Center for Telecommunications Research
Characterization of p-type InxGa1-xN grown by metalorganic chemical vapor deposition
(2001-03-01)
Wen, TC
;
Lee, WI
;
Sheu, JK
;
Chi, GC
;
友訊交大聯合研發中心
This study investigates the electrical and optical characteristics of Mg-doped InxGa1-xN grown by metalorganic chemical vapor deposition. All the Mg-doped InxGa1-xN layers show p-type conduction after thermal annealing. Room temperature (RT) carrier concentration increases exponentially with an In mole fraction increase. The highest hole concentration of bull; Mg-doped InxGa1-xN is 1.65 x 10(19) cm(-3). Also, the RT photoluminescence (PL) spectra of Mg related emissions in InxGa1-xN are displayed. However, the PL peak intensity becomes weak after the post-annealing process on Mg-doped InxGa1-xN. This degradation might be created by the surface dissociation during the post-annealing process. (C) 2001 Elsevier Science Ltd. All rights reserved.
Hydrogen bonding and mechanical properties in segmented montmorillonite/polyurethane nanocomposites of different hard segment ratios
(2001-03-01)
Tien, YI
;
Wei, KH
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Hydrogen bonding in the hard segments of the synthesized montmorillonite/polyurethane nanocomposites of various hard segment ratios was found to decrease with the increasing amount of montmorillonite regardless of the hard segment ratios, but reached plateau values at 5 wt% montmorillonite concentration. The maximal reductions of the hydrogen bonding in the polyurethane nanocomposites ranged from 20 to 37%, depending on the hard segment ratios as compared to that in the pure polyurethane. The maximal strength and the elongation at break of the polyurethane nanocomposites increased dramatically as compared to that of pristine polyurethane, and the maximal values occurred at 1 wt% montmorillonite concentration. (C) 2001 Elsevier Science Ltd. All rights reserved.
Phase transformations in an Fe-8Al-30Mn-1.5Si-1.5C alloy
(2001-03-01)
Lee, JW
;
Liu, TF
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The phase transformations in an Fe-8Al-30Mn-1.5Si-1.5C alloy has been investigated by means of transmission electron microscopy. In the as-quenched condition, the microstructure of the alloy was austenite phase containing fine (Fe,Mn)(3)AlC carbides. The fine (Fe,Mn)(3) AlC carbides were formed during quenching by a spinodal decomposition. When the as-quenched alloy was aged at temperatures ranging from 550 to 1000 degreesC, the phase transformation sequence as the aging temperature increased was found to be (Fe,Mn)(3)AlC carbide + D0(3) --> (Fe, Mn)(3)AlC carbide + B2 --> (Fe, Mn)(3)AlC carbide + alpha --> gamma. This transformation has never before been observed in the Fe-Al-Mn-C and Fe-Al-Mn-Si-C alloys. (C) 2001 Elsevier Science B.V. All rights reserved.
請問東阿王曹子建先生-曹家豆子店外史
(2001-03-01)
管管
Variable structure control scheme for landing on a celestial object
(2001-03-01)
Liaw, DC
;
Cheng, CC
;
電控工程研究所
;
Institute of Electrical and Control Engineering
This paper considers the landing of a space vehicle on a celestial object. By assuming the air drag in two specific forms and th uncertainty in matching type, their effects are studied. Through the construction of a time-varying boundary layer, a new guidance control law for landing on a celestial object is proposed via the variable structure control (VSC) technique to guarantee that tracking performance is achieved at an exponential convergence rate. The proposed guidance law is continuous and alleviates chattering drawback by classic VSC design. Finally, simulation results are presented to illustrate the use of the main design.
Fabrication and characterization of phosphorus-doped diamond field emitters in triode-type field emission arrays
(2001-03-01)
Chen, CF
;
Tsai, CL
;
Lin, CL
;
材料科學與工程學系
;
Department of Materials Science and Engineering
In this work, we present a novel scheme that involves a new fabrication process for gate-structured metal-insulator-semiconductor (MIS) diodes using IC technology. Using a bias-assisted microwave-plasma chemical vapor deposition (BAMPCVD) system to synthesize P-doped emitters completes this process. A comparison of the held emission characteristics of two types of non-doped dendrite-like and P-doped nanotube-like diamond emitters with a 4-mum gate aperture is made. Phosphorus doping can enhance the electrical characteristics by reducing the turn-on voltage and enhancing the emission current density. The turn-on voltage of non-doped and P-doped emitters is 15 and 5 V, respectively. Phosphorus doping can enhance the electrical properties by increasing the emission current, since the field emission current (I-a) of non-doped and P-doped emitters is 4 muA (at V-gc = 45 V) and 322 muA (at V-gc = 120 V), respectively. The emission current of P-doped emitters is approximately 80-fold larger than that of non-doped diamond emitters. (C) 2001 Elsevier Science B.V. All rights reserved.
Effect of gravity on particle collection efficiency of inertial impactors
(2001-03-01)
Huang, CH
;
Tsai, CJ
;
環境工程研究所
;
Institute of Environmental Engineering
This study has investigated the effect of gravitational force on particle collection efficiency in inertial impactors numerically and experimentally. In the numerical study, two-dimensional flow field in the inertial impactor was simulated by solving the Navier-Stokes equations with the control volume method. Particle trajectories were then calculated to obtain the collection efficiency at different Reynolds numbers, which are based on nozzle diameter. This study shows that gravitational force increases the particle collection efficiency when the Reynolds number is below about 1500. The numerical results were found to be in good agreement with the experimental data of Marple et al. (JAPCA, 37, 1303) (1987), Rubow et al. (American Industrial Hygiene Association Journal, 48, 532) (1987) and those obtained in the present study. (C) 2001 Elsevier Science Ltd. All rights reserved.
Tracking control of unicycle-modeled mobile robots using a saturation feedback controller
(2001-03-01)
Lee, TC
;
Song, KT
;
Lee, CH
;
Teng, CC
;
電機資訊學士班
The tracking control problem with saturation constraint for a class of unicycle-modeled mobile robots is formulated and solved using the backstepping technique and the idea from the LaSalle's invariance principle. A global result is presented in which several constraints on the linear and the angular velocities of the mobile robot from recent literature are dropped. The proposed controller can simultaneously solve both the tracking and regulation problems of a unicycle-modeled mobile robot. With the proposed control laws, the robot can globally follow any path specified by a straight line, a circle or a path approaching the origin using a single controller. As demonstrated, the circular and parallel parking control problem are solved using the proposed controller. Computer simulations are presented which confirm the effectiveness of the proposed tracking control law Practical experimental results validate the simulations.
Sol-gel synthesis and the effect of boron addition on the phosphorescent properties of SrAl2O4 : Eu2+,Dy3+ phosphors
(2001-03-01)
Chen, IC
;
Chen, TM
;
應用化學系
;
Department of Applied Chemistry
The effects of boron addition on the microstructure and afterglow properties of the long-phosphorescent SrAl2O4:Eu2+,Dy3+ (SAED), synthesized via a novel sol-gel route, were systematically investigated. Significant improvement on luminescence intensity and the lengthening of afterglow persistent time in boron-added SAED (BSAED) phases were observed, as compared to those without boron addition and commercial phosphors. Typical bluish-green emissions attributed to the doublet phosphorescence with wavelengths peaking at 412 and 501 nm for BSAED phase and 398 and 486 nm for the pristine SAED phase were observed. Afterglow with wavelengths peaking at 403 and 485 nm was observed for BSAED phase, whereas that with wavelengths peaking at 486.5 nm was found for the pristine SAED phase, as indicated by time-dependent afterglow decay profiles. Results from scanning electron microscopic morphological studies were used to investigate the modification of microstructure of the BSAED phases.