Browsing by Issue Date, starting with "2002-04-01"

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Miscibility and hydrogen bonding in blends of poly(vinyl acetate) with phenolic resin
(2002-04-01)
Huang, MW
;
Kuo, SW
;
Wu, HD
;
Chang, FC
;
Fang, SY
The miscibility of phenolic resin and poly(vinyl acetate) (PVAc) blends was investigated by differential scanning calorimeter (DSC), Fourier transform infrared spectroscopy (FT-IR) and solid state C-13 nuclear magnetic resonance (NMR). This blend displays single glass transition temperature (T-g) over entire compositions indicating that this blend system is miscible in the amorphous phase due to the formation of hydrogen bonding between hydroxyl groups of phenolic resin and carbonyl groups of PVAc. Quantitative measurements on fraction of hydrogen-bonded carbonyl group using both C-13 solid-state NMR and FT-IR analyses result in good agreement between these two spectroscopic techniques. According to the proton spin-lattice relaxation time in the rotating frame (T-lp(H)), the phenolic/PVAc blend is intimately mixed on a scale less than 2-3 nm. Furthermore, the inter-association equilibrium constant and its related enthalpy of phenolic/PVAc blends were determined as a function of temperatures by infrared spectra based on the Painter-Coleman association model. (C) 2002 Elsevier Science Ltd. All rights reserved.
Effects of the relationship between resistivity and additive chemistries in electrochemically deposited copper films
(2002-04-01)
Chen, CF
;
Lin, KC
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The room-temperature electrical resistance of copper films on silicon wafers deposited from acid-copper sulfuric solutions is a function of grain size and impurity content. These properties were examined by a series of additive chemistries used in plating baths. The trapped impurities and the functional characteristics of additives were analyzed by X-ray photoelectron spectroscopy (XPS) and cyclic voltammetric stripping (CVS) measurements, The impurity scattering effect on the resistances depends on the charge factor for different dopants. On the other hand, the effect of grain-boundary scattering on the resistances will depend on the extent of activation overpotential of various additive chemistries. Evidence suggests that additive chemistries with a higher overpotential would create a higher resistivity due to larger grain-boundary scattering and greater impurity incorporation into copper films.
Applicability of perturbative QCD and NLO power corrections for the pion form factor
(2002-04-01)
Yeh, TW
;
物理研究所
;
Institute of Physics
As is well recognized, the asymptotic of the perturbative QCD prediction for the pion form factor is much smaller than the upper end of the data. We investigate this problem. We first evaluate the next-to-leading-order (NLO) power correction for the pion form factor. The corrected form factor contains nonperturbative parameters which are determined from a chi(2) fit to the data. Interpreting these parameters leads to the fact that the involved strong interaction coupling constant should be identified as an effective coupling constant under a nonperturbative QCD vacuum. If the scale associated with the effective coupling constant is identified as (2)Q(2), then Q(2), the momentum transfer square for the pion form factor to be measured, can have a value about 1 GeV2, and , the averaged momentum fraction variable, can locate around 0.5. This circumstance is consistent with the asymptotic model for the pion wave function.
Subcooled flow boiling heat transfer of R-134a and the associated bubble characteristics in a vertical plate heat exchanger
(2002-04-01)
Hsieh, YY
;
Chiang, LJ
;
Lin, TF
;
機械工程學系
;
Department of Mechanical Engineering
Subcooled Row boiling heat transfer characteristics of refrigerant R-134a in a vertical plate heat exchanger (PHE) are investigated experimentally in this study. Besides, the associated bubble characteristics are also inspected by visualizing the boiling flow in the vertical PHE. In the experiment two vertical counterflow channels are formed in the exchanger by three plates of commercial geometry with a corrugated sinusoidal shape of a chevron angle of 60degrees. Upflow boiling of subcooled refrigerant R-134a in one channel receives heat from the downflow of hot water in the other channel. The effects of the boiling heat flux, refrigerant mass flux, system pressure and inlet subcooling of R-134a on the subcooled boiling heat transfer are explored in detail. The results are presented in terms of the boiling curves and heat transfer coefficients. The measured data showed that the slopes of the boiling curves change significantly during the onset of nucleate boiling (ONB) especially at low mass flux and high saturation temperature. Besides, the boiling hysteresis is significant at a low refrigerant mass flux. The subcooled boiling heat transfer coefficient is affected noticeably by the mass flux of the refrigerant. However, increases in the inlet subcooling and saturation temperature only show slight improvement on the boiling heat transfer coefficient. The photos from the flow visualization reveal that at higher imposed heat flux the plate surface is covered with more bubbles and the bubble generation frequency is substantially higher, and the bubbles tend to coalesce to form big bubbles. But these big bubbles are prone to breaking up into small bubbles as they move over the corrugated plate, producing strong agitating flow motion and hence enhancing the boiling heat transfer. We also note that the bubbles nucleated from the plate are suppressed to a larger degree for higher inlet subcooling and mass flux. Finally, empirical correlations are proposed to correlate the present data for the heat transfer coefficient and the bubble departure diameter in terms of boiling, Froude, Reynolds and Jakob numbers. (C) 2002 Elsevier Science Ltd. All rights reserved.
The ANNIGMA-wrapper approach to fast feature selection for neural nets
(2002-04-01)
Hsu, CN
;
Huang, HJ
;
Schuschel, D
;
資訊工程學系
;
Department of Computer Science
This paper presents a novel feature selection approach for backprop neural networks (NNs). Previously, a feature selection technique known as the wrapper model was shown effective for decision trees induction. However, it is prohibitively expensive when applied to real-world neural net training characterized by large volumes of data and many feature choices. Our approach incorporates a weight analysis-based heuristic called artificial neural net input gain measurement approximation (ANNIGMA) to direct the search in the wrapper model and allows effective feature selection feasible for neural net applications. Experimental results on standard datasets show that this approach can efficiently reduce the number of features while maintaining or even improving the accuracy. We also report two successful applications of our approach in the helicopter maintenance applications.
Global optimal fuzzy tracker design based on local concept approach
(2002-04-01)
Wu, SJ
;
Lin, CT
;
電控工程研究所
;
Institute of Electrical and Control Engineering
In this paper, we propose a global optimal fuzzy tracking controller, implemented by fuzzily blending the individual local fuzzy tracking laws, for continuous and discrete-time fuzzy systems with the aim of solving, respectively, the continuous and discrete-time quadratic tracking problems with moving or model-following targets under finite or infinite horizon (time). The differential or recursive Riccati equations, and more, the differential or difference equations in tracing the variation of the target are derived. Moreover, in the case of time-invariant fuzzy tracking systems, we show that the optimal tracking controller can be obtained by just solving algebraic Riccati equations and algebraic matrix equations. Grounding on this, several fascinating characteristics of the resultant closed-loop continuous or discrete time-invariant fuzzy tracking systems can be elicited easily. The stability of both closed-loop fuzzy tracking systems can be ensured by the designed optimal fuzzy tracking controllers. The optimal closed-loop fuzzy tracking systems cannot only be guaranteed to be exponentially stable, but also be stabilized to any desired degree. Moreover, the resulting closed-loop fuzzy tracking systems possess infinite gain margin; that is, their stability is guaranteed no matter how large the feedback gain becomes. Two examples are given to illustrate the performance of the proposed optimal fuzzy tracker design schemes and to demonstrate the proved stability properties.
Possible evidence for the existence of the Fehrenbacher-Rice band: O K-edge XANES study on Pr1-xCaxBa2Cu3O7
(2002-04-01)
Hong, IP
;
Lin, JY
;
Chen, JM
;
Chatterjee, S
;
Liu, SJ
X-ray absorption near edge structure (XANES), resistivity, and thermoelectric power have been measured on Pr1-xCaxBa2Cu3O7. These data reveal an intriguing electronic structure in Pr-doped cuprates. The absorption peak in XANES associated with the Fehrenbacher-Rice (FR) band has been identified. The Ca-doped holes in Pr1-xCaxBa2Cu3O7 go to both the Zhang-Rice (ZR) and FR bands. Comparative studies on the related samples suggest that the FR band is partially filled and highly localized. Implications of these results on other recent experiments, such as the observation of superconductivity in PrBa2Cu3O7 single crystals, are discussed.
Improvement on Peyravian-Zunic's password authentication schemes
(2002-04-01)
Hwang, JJ
;
Yeh, TC
;
資訊管理與財務金融系註：原資管所+財金所
;
Department of Information Management and Finance
Peyravian and Zunic (2000) presented two schemes for protecting password transmission and password change respectively. Like the traditional authentication scheme using passwords, the two new schemes are also vulnerable to attacks like guessing attacks, server spooling, and server data eavesdropping, This paper will give demonstrations on what have caused to these drawbacks, and more of that, two improved schemes are also proposed which are free from worries of those possible attacks.
On automatic-verification pattern generation for SoC with port-order fault model
(2002-04-01)
Wang, CY
;
Tung, SW
;
Jou, JY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Embedded cores are being increasingly used in the designs of large system-on-a-chip (SoC). Because of the high complexity of SoC, the design verification is a challenge for system integrators. To reduce the verification complexity, the port-order fault (POF) model has been used for verifying core-based designs (Tung and Jon, 1998). In this paper, we present an automatic-verification pattern generation (AVPG) for SoC design verification based on the POF model and perform experiments on combinational and sequential benchmarks. Experimental results show that our AVPG can efficiently generate verification patterns with high POF coverage.
High-density MIM capacitors using Al2O3 and AlTiOx dielectrics
(2002-04-01)
Chen, SB
;
Lai, CH
;
Chin, A
;
Hsieh, JC
;
Liu, J
We have investigated the electrical characteristics of Al2O3 and AlTiOx MIM capacitors from IF (100 KHz) to RF (20 GHz) frequency range. Record high capacitance density of 0.5 and 1.0 muF/cm(2) are obtained for Al2O3 and AlTiOx MIM capacitors, respectively, and the fabrication process is compatible to existing VLSI backend integration. However, the AlTiOx MIM capacitor has very large capacitance reduction as increasing frequencies. In contrast, good device integrity has been obtained for Al2O3 MIM capacitor as evidenced from the small frequency dependence, low leakage current, good reliability, small temperature coefficient, and low loss tangent.
Characteristics of transmission of electrons in a quantum wire tangentially attached to a superconductor ring threaded by magnetic flux
(2002-04-01)
Gu, BY
;
Lu, Y
;
Yang, TJ
;
電子物理學系
;
Department of Electrophysics
We present numerical investigations of the transmission properties of electrons in a normal quantum wire tangentially attached to a superconductor ring threaded by magnetic flux. A point scatterer with a delta-function potential is placed at node to model scattering effect. We find that the transmission characteristics of electrons in this structure strongly depend on the normal or superconducting state of the ring. The transmission probability as a function of the energy of incident electrons, in the case of a superconductor ring threaded by one quantum magnetic flux, emerges one deep dip, imposed upon the first broad bump in spectrum. This intrinsic conductance dip originates from the superconductor state of the ring. When increasing the magnetic flux from one quantum magnetic flux to two, the spectrum shifts toward higher energy region in the whole. This conductance dip accordingly shifts and appears in the second bump. In the presence of a point-scatterer at the node, the spectrum is substantially modified. Based on the condition of I he formation of the standing wave functions in the ring and the broken of the time-reserve symmetry of Schrodinger equation after switching magnetic flux, the characteristics of transmission of electrons in this structure can be well understood.
Observation of dislocation etch pits in epitaxial lateral overgrowth GaN by wet etching
(2002-04-01)
Wen, TC
;
Lee, WI
;
Sheu, JK
;
Chi, GC
;
電子物理學系
This work investigates dislocation etch pits in epitaxial lateral overgrowth (ELO) GaN by wet etching. A mixture of H2SO4 and H3PO4 was used as an etching solution. SEM and AFM were employed to observe the surface topography. For the as-grown sample, SEM images show the flat, smooth surface without any pits or hillocks. After the chemical etching, hexagonal shaped etch pits were observed at the edge of ELO GaN. AFM observation of etched ELO GaN displayed high densities of etch pits clustered in the "window" region and the coalescent line of two growing fronts. In contrast, the overgrowth region was nearly free of etch pits. Moreover, we observed that different sizes of etch pits dominated in "window" region and coalescent region. This implied different types dislocations dominated in these regions. (C) 2002 Elsevier Science Ltd. All rights reserved.
Hot carrier induced degradation in the low temperature processed polycrystalline silicon thin film transistors using the dynamic stress
(2002-04-01)
Chang, KM
;
Chung, YH
;
Lin, GM
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The dynamic stress on low-temperature processed polycrystalline silicon thin-film transistors (poly-Si TFTs) is studied under two different stress conditions. As compared to static stress. the enhanced degradation in poly-Si TFT can be observed in dynamic stress. The enhanced degradation in dynamic stress (V-g = 0-20 V, V-ds = 22 V) is due to (1) the impact ionization effect in the ON state (V-gs = 20 V, V-ds = 22 V), (2) the drain avalanche hot carrier effect in the OFF state (V-gs = 0 V, V-ds = 22 V), and (3) the transient current stressing effect (at the switching period), However, in the stress condition of V-gs = -20 V to 20 V, V-ds = 0 V. both the source and drain regions are equally damaged. As the falling time becomes shorter, the transient current will increase to cause more device degradation near drain. It is also found that the degradation is more serious in short channel device than that in long channel device. As the stress frequency increases, the degradation will be enhanced. Moreover, the reduced degradation under high stress temperature is clue to reduced hot carrier effect under high temperature stressing.
A neural fuzzy network for word information processing
(2002-04-01)
Lin, CT
;
Duh, FB
;
Liu, DJ
;
電控工程研究所
;
Institute of Electrical and Control Engineering
A neural fuzzy system learning with fuzzy training data is proposed in this study. The system is able to process and learn numerical information as well as word information. At first, we propose a basic structure of five-layered neural network for the connectionist realization of a fuzzy inference system. The connectionist structure can house fuzzy logic rules and membership functions for fuzzy inference. The inputs, outputs, and weights of the proposed network can be fuzzy numbers of any shape. Also they can be hybrid of fuzzy numbers and numerical numbers through the use of fuzzy singletons. Based on interval arithmetics, a fuzzy supervised learning algorithm is developed for the proposed system. It extends the normal supervised learning techniques to the learning problems where only word teaching signals are available. The fuzzy supervised learning scheme can train the proposed system with desired fuzzy input-output pairs. An experimental system is constructed to illustrate the performance and applicability of the proposed scheme. (C) 2002 Elsevier Science B.V. All rights reserved.
Frequency-dependent capacitance reduction in high-k AlTiOx and Al2O3 gate dielectrics from IF to RF frequency range
(2002-04-01)
Chen, SB
;
Lai, CH
;
Chan, KT
;
Chin, A
;
Hsieh, JC
We have characterized the capacitance and loss tangent for high-k Al2O3 and AlTiOx gate dielectrics from IF (100 KHz) to RF (20 GHz) frequency range. Nearly the same rate of capacitance reduction as SiO2 was demonstrated individually by the proposed Al2O3 and AlTiOx gate dielectrics as frequency was increased. Moreover, both dielectrics preserve the higher k better than SiO2 from 100 KHz to 20 GHz. These results suggest that both Al2O3 and AlTiOx are suitable for next generation MOSFET application into RF frequency regime.
Fault-tolerant hamiltonicity of twisted cubes
(2002-04-01)
Huang, WT
;
Tan, JJM
;
Hung, CN
;
Hsu, LH
;
資訊工程學系
The twisted cube TQ(n), is derived by changing some connection of hypercube Q(n) according to specific rules. Recently, many topological properties of this variation cube are studied. In this paper, we consider a faulty twisted n-cube with both edge and/or node faults. Let F be a subset of V(TQ(n)) boolean AND E(TQ(n)), we prove that TQ(n) - F remains hamiltonian if F less than or equal to n - 2. Moreover, we prove that there exists a hamiltonian path in TQ, - F joining any two vertices u, v in V(TQ(n)) - F if F less than or equal to n-3. The result is optimum in the sense that the fault-tolerant hamiltonicity (fault-tolerant hamiltonian connectivity respectively) of TQn is at most n-2 (n-3 respectively). (C) 2002 Elsevier Science (USA).
Earthquake devastation and recovery in tourism: the Taiwan case
(2002-04-01)
Huang, JH
;
Min, JCH
;
管理科學系
;
經營管理研究所
;
Department of Management Science
The most serious earthquake in Taiwan of the 20th century struck the central region of the island on September 21, 1999. The so-called September 21 Earthquake, measuring 7.3 on the Richter scale, dealt a sharp blow to the Taiwanese tourism industry, with the worst impact being suffered by the international tourism sector. To revitalize the dramatic decline in inbound tourist flows, the government of Taiwan implemented a series of swift countermeasures. The purpose of this study is to evaluate whether Taiwan tourism has rebounded completely from the crisis. This research establishes a model for Taiwan's inbound demand to predict the volume of visitor arrivals after the quake (September 1999 to July 2000). The forecasts are based on the seasonal autoregressive integrated moving average (SARIMA) model which are then compared with the actual volume of visitor arrivals to analyze the recovering status. Empirical results indicate that the island's inbound arrivals have not yet fully recovered from the earthquake's devastation after 11 months. (C) 2002 Elsevier Science Ltd. All rights reserved.
Minimum redundancy for ISI free FIR filterbank transceivers
(2002-04-01)
Lin, YP
;
Phoong, SM
;
電控工程研究所
;
Institute of Electrical and Control Engineering
There has been great interest in the design of filter-bank transceivers. Usually, with proper time domain equalization, the channel is modeled as an FIR filter. It is known that for FIR channels, the introduction of certain redundancy allows the receiver to cancel intersymbol interference (ISI) completely, and channel equalization is performed implicitly using FIR transceivers. This scheme allows us to trade bandwidth for ISI cancellation. In this paper, we will derive the minimum redundancy required for the existence of FIR transceivers for a given channel. We will see that the minimum redundancy is directly related to the zeros of the channel and to the Smith form of an appropriately defined channel matrix.
Reduction of off-state leakage current in Schottky barrier thin-film transistors (SBTFT) by a field-induced drain
(2002-04-01)
Yeh, KL
;
Lin, HC
;
Huang, RG
;
Tsai, RW
;
Huang, TY
Detailed conduction mechanisms in a conventional Schottky barrier thin-film transistor (SBTFT) and a recently proposed novel SBTFT with field-induced drain (FID) extension have been studied. The new SBTFT device with FID extension shows excellent ambipolar performance with effective suppression of gate-induced drain leakage (GIDL)-like off-state leakage that plagues conventional SBTFT devices. By characterizing the activation energy of the conduction process in the off-state for conventional SBTFT devices, it is suggested that field emission of carriers from the drain junction is the major conduction mechanism. While for the FID SBTFT devices, owing to the effect of Fermi level pinning in the FID region, thermionic emission rather than field emission becomes the dominant conduction mechanism, resulting in the effective suppression of the undesirable GIDL-like leakage current.
Building a CAL expert system based upon two-phase knowledge acquisition
(2002-04-01)
Tsai, CJ
;
Tseng, SS
;
資訊工程學系
;
Department of Computer Science
With the fast growing and globally accepted e-learning technology, Computer-Assisted Learning (CAL) system, which can provide the individualized materials, becomes a matter of great importance. In this paper, we propose a CAL Expert System (CAL-ES), in which teachers can provide their teaching strategy as guidance to students' learning. Because the knowledge hierarchy and the knowledge itself are both important in CAL domain, and the teaching strategy can be considered as rule-format, Two-phase Knowledge Acquisition is proposed to acquire the knowledge hierarchy and the rule-based knowledge by the cooperation of teachers and knowledge engineers. The prototype of CAL-ES is constructed of the mathematical teaching materials. The CAL-ES is useful for student learning and is easy for teachers maintaining. (C) 2002 Elsevier Science Ltd. Ail rights reserved.