Browsing by Author "Tsai, HM"

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Characteristics and electrochemical performance of supercapacitors with manganese oxide-carbon nanotube nanocomposite electrodes
(2005)
Lee, CY
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Tsai, HM
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Chuang, HJ
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Li, SY
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Lin, P
Supercapacitor characteristics of manganese oxide/nickel (MnOx/Ni) and manganese oxide/carbon nanotubes/nickel (MnOx/CNTs/Ni) nanocomposite electrodes were investigated in this study. The CNTs were deposited on the Ni substrate by electrophoresis in a 0.5 mg CNT/1 mL dimethylformamide solution, whereas the MnOx were synthesized by anodic deposition in a 0.16 M manganese sulfate pentahydrate aqueous solution on substrates. The crystallinity and surface morphology of these electrodes were determined by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The capacitive properties of these electrodes were demonstrated by cyclic voltammetry with scan rates ranging from 5 to 100 mV/s. The specific capacitances of the MnOx/CNT/Ni nanocomposite electrode were 415 and 388 F/g with scan rates of 5 and 100 mV/s, respectively. After 1000 cycles of operation, this electrode can maintain 79% of its original capacitance. These MnOx/CNT/Ni nanocomposite electrodes possessing good electrochemical reversibility and high capacitance may be appropriate for supercapacitor application in the future. (c) 2005 The Electrochemical Society.
Comparison of the electronic structures of AIN nanotips grown on p- and n-type Si substrates
(2005-12-07)
Chiou, JW
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Tsai, HM
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Pao, CW
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Dong, CL
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Chang, CL
At and N K-edge x-ray absorption near-edge structure (XANES), scanning photoelectron microscopy (SPEM) and x-ray emission measurements were performed on AIN nanotips grown on p- and n-type Si substrates (p-AIN and n-AIN). Features and intensities in the Al and N K-edge XANES spectra of these AIN nanotips overall are similar. In contrast, the intensities of the valence-band SPEM spectra of p-AIN are apparently larger than those of n-AIN, which indicates that the valence-band density of states of p-AIN exceeds that of n-AIN. This result may be related to the observed enhancement of field-emission intensity of AIN nanotips grown on the p-type Si substrate.
Design and implementation of an OA&M system for WLL network
(2000-09-01)
Huang, JY
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Tsai, HM
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Lin, YB
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Tseng, CC
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資訊工程學系
This paper describes the design and implementation of an OA&M system for DECT-based WLL network. This system follows the client-server architecture that enables remote management through the Internet, Object-oriented design is used to yield quality software, where the entire WLL network is treated as a hierarchical collection of objects. The "plug-in" mechanism provides the capabilities of replacing and extending OA&M functionalities in run-time, Design patterns are applied to improve the reusability of software components. Two types of user interfaces are implemented in different platforms to provide access to the OA&M system, Although our design is tailored for the WLL network, it is also appropriate to serve as the OA&M system for other small-scale telecommunication systems.
Development of an on-line diagnosis system for rotor vibration via model-based intelligent inference
(2000-01-01)
Bai, MSR
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Hsiao, I
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Tsai, HM
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Lin, CT
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機械工程學系
An on-line fault detection and isolation technique is proposed for the diagnosis of rotating machinery. The architecture of the system consists of a feature generation module and a fault inference module. Lateral vibration data are used for calculating the system features. Both continuous-time and discrete-time parameter estimation algorithms are employed for generating the features. A neural fuzzy network is exploited for intelligent inference of faults based on the extracted features. The proposed method is implemented on a digital signal processor. Experiments carried out for a rotor kit and a centrifugal fan indicate the potential of the proposed techniques in predictive maintenance. (C) 2000 Acoustical Society of America. [S0001-4966(00)03201-X].
Direct experimental evidence of hybridization of Pb states with O 2p states in ferroelectric perovskite oxides
(2005-07-04)
Jan, JC
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Tsai, HM
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Pao, CW
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Chiou, JW
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Asokan, CK
This work presents the O K- and Ti L-3,L-2-edge x-ray absorption near-edge structure (XANES) spectra of PbxSr1-xTiO3 (PxSTO) and BaxSr1-xTiO3 (BxSTO) compounds with various Pb and Ba concentrations. The result provides direct evidence that the Pb-O bonding strongly affects O 2p-Ti 3d hybridization in the TiO6 octahedron of PxSTO. In contrast, the Ba-O bonding does not substantially affect O 2p-Ti 3d hybridization in BxSTO. The Ti L-3-edge XANES spectra show the splitting of the e(g) band for PxSTO with x greater than or similar to 0.5, which provides an evidence of Pb-induced tetragonal distortion in the TiO6 octahedron. In contrast, e(g) band splitting is absent in BxSTO. (c) 2005 American Institute of Physics.
Effect of bismuth content on the properties of Sr0.8BixTa1.2 Nb0.9O9+y ferroelectric thin films
(1999-01-15)
Tsai, HM
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Lin, P
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Tseng, TY
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材料科學與工程學系
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電子工程學系及電子研究所
This study investigates the effect of bismuth content on the ferroelectric properties of Sr0.8BixTa1.2Nb0.9O9+y (SBTN, x = 1.7, 2.0, 2.5, 2.7, 2.9, and 3.2) thin film capacitors. SBTN films are in situ grown on Pt/SiO2/Si substrates by using two-target off-axis radio-frequency magnetron sputtering at a substrate temperature of 600 degrees C. The films are crystallized with a high (115) diffraction intensity and exhibit a columnar microstructure. Experimental results indicate that the root mean square surface roughness of the film increases with an increase of the bismuth content. In addition, the ferroelectric properties of the films heavily rely on the bismuth content. Moreover, the 440-nm-thick Sr0.8Bi2.5Ta1.2Nb0.9O9+y films exhibit maximum remanent polarization (2Pr) of 52 mu C/cm(2) and minimum coercive field (2Ec) of 28 kV/cm at an applied voltage of 1.5 V. X-ray photoelectron spectral studies reveal that except for Bi+3, no lower valence state bismuth exists in the Sr0.8Bi2.5Ta1.2Nb0.9O9+y film and bismuth substituted in the strontium site still remains in its +3 valence state. (C) 1999 American Institute of Physics. [S0021-8979(99)06302-1].
Effect of the Ca content on the electronic structure of Pb1-xCaxTiO3 perovskites
(2003-10-20)
Jan, JC
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Kumar, KPK
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Chiou, JW
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Tsai, HM
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Shih, HL
This study performs O K- and Ti L-3,L-2-edge x-ray absorption near-edge structure (XANES) measurements and first-principles pseudopotential calculations for the electronic structures of ABO(3)-type Pb1-xCaxTiO3 (x=0-1) perovskites. The features in the O K-edge XANES spectra are found to be contributed primarily by hybridization between O 2p and Ti 3d, Pb 6p, and Ca 3d orbitals. The O K-edge XANES spectra reveal that partial substitution of A cations, Pb, by Ca not only decreases O 2p-Pb 6p but also O 2p-Ti 3d hybridization. The Ti L-3,L-2-edge measurements find that the off-center displacement of Ti, and hence, ferroelectricity persist up to a Ca concentration between 0.3 and 0.4. (C) 2003 American Institute of Physics.
Modeling wireless local loop with general call holding times and finite number of subscribers
(2002-07-01)
Tsai, HM
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Lin, YB
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資訊工程學系
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Department of Computer Science
This paper proposes an analytic model to compute the loss probability for Wireless Local Loop (WILL) with a finite number of subscribers. The number of trunks between the WILL concentrator and the base station controller is less than the total number of radio links in the WILL. This model is validated against the simulation results. The execution of our model is efficient compared with simulation. However, its time complexity is higher than several existing analytic models that approximate the loss probability for WILL. Therefore, we design an efficient WLL network planning procedure (in terms of time complexity and accuracy) that utilizes the approximate analytic models to provide small ranges for selecting the values of system parameters. Our model is then used to accurately search the operation points of WILL within the small ranges of the system parameter values. This paper proves that the performance of WILL with limited trunk capacity and finite subscriber population is not affected by the call holding time distributions. Based on our model, we illustrate WLL design guidelines with several numerical examples.
Moisture-induced material instability of porous organosilicate glass
(2003-04-01)
Chang, TC
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Chen, CW
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Liu, PT
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Mor, YS
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Tsai, HM
The mechanism of leakage current of porous organosilicate glass (POSG) with O-2 plasma ashing is investigated. The O-2 plasma ashing often deteriorates the POSG film, causing moisture uptake. We find that the leakage-current mechanism of POSG transforms from Schottky emission into ionic conduction after O-2 plasma treatment. The mobile ions (H+,OH-) supported by absorbing moisture move easily when an external electric field is applied to POSG film, which leads to the ionic conduction leakage current across the moisture-absorbing POSG film. Hence, the leakage current density is drastically increased about four to five orders of magnitude compared with untreated POSG film. (C) 2003 The Electrochemical Society.
Repacking on demand for hierarchical cellular networks
(2005-11-01)
Tsai, HM
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Pang, AC
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Lin, YC
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Lin, YB
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資訊工程學系
In mobile telecommunications operation, radio channels are scarce resources and should be carefully assigned. One possibility is to deploy the hierarchical cellular network (HCN). This paper studies a HCN channel assignment scheme called repacking on demand (RoD). RoD was originally proposed for wireless local loop networks. We expend this work to accommodate mobile HCN. A simulation model is proposed to study the performance of HCN with RoD and some previously proposed schemes. Our study quantitatively indicates that RoD may significantly outperform the previous proposed schemes.
Repacking on demand for speed-sensitive channel assignment
(2005-01-14)
Tsai, HM
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Pang, AC
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Lin, YC
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Lin, YB
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資訊工程學系
In mobile telecommunications networks, radio channels are limited resources that should be carefully allocated. To increase network capacity, channel assignment can be exercised in a hierarchical cellular network (HCN). By considering the speeds of MSs, we propose an HCN channel assignment approach called repacking on demand (RoD). A simulation model is developed to investigate the performance of RoD and some previously proposed approaches for HCN. Our study quantitatively shows that RoD significantly outperforms the previous proposed approaches. (C) 2004 Elsevier B.V. All rights reserved.
Repacking on demand for two-tier wireless local loop
(2004-05-01)
Hung, HN
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Lin, YB
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Peng, NF
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Tsai, HM
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統計學研究所
This paper proposes a radio channel assignment scheme called repacking on demand (RoD) for two-tier wireless local loop (WLL) networks. A two-tier WLL overlays a macrocell with several microcells. When a new call arrives at a two-tier WLL with RoD, if no idle channel is available in both the microcell and the macrocell, repacking is performed (i.e., a call in the macrocell is moved to its corresponding microcell), and then the reclaimed macrocell channel is used to serve the new call. An analytic model is proposed to compute the call blocking probability of the two-tier WLL with repacking. This analytic model is validated against simulation experiments.We prove that the blocking probability is not affected by the call holding time distributions, but is only dependent on the mean of the call holding times. Compared with some previous proposed schemes, RoD has low blocking probability and significantly reduces repacking rate.
Sr0.8Bi2.5Ta1.2Nb0.9O9+x ferroelectric thin films prepared by two-target off-axis radio frequency magnetron sputtering
(1998-04-06)
Tsai, HM
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Lin, P
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Tseng, TY
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材料科學與工程學系
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電子工程學系及電子研究所
Ferroelectric Sr0.8Bi2.5Ta1.2Nb0.9O9+x thin films on a Pt/SiO2/Si substrate were prepared by using two-target off-axis radio frequency magnetron sputtering, and their structural and electrical properties were investigated. The films crystallized with high (115) diffraction intensity at a substrate temperature of 600 degrees C, and showed columnar microstructure. The 600 degrees C sputtered films with a thickness of 440 nm exhibited remanent polarization (2P(r)) of 52 mu C/cm(2) and coercive field (2E(c)) 28 kV/cm at an applied voltage of 1.5 V. The leakage current density was about 6 X 10(-6) A/cm(2) at an electric field of 50 kV/cm. The films demonstrated fatigue free characteristics up to 1.0 X 10(10) switching cycles under a 3 V bipolar 1 MHz square wave. (C) 1998 American Institute of Physics. [S0003-6951(98)04014-5].