Browsing by Issue Date, starting with "2003-02-07"

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Polymer blends of poly(ethylene-2,6-naphthalate) with polystyrene compatibilized by styrene-glycidyl methacrylate copolymers. I. Rheology, morphology, and mechanical properties
(2003-02-07)
Huang, JM
;
Ju, MY
;
Hung, CJ
;
Luoh, WC
;
Chang, FC
The compatibilization of blends of poly(ethylene-2,6-naphthalate) (PEN) with polystyrene (PS), through the styrene-glycidyl methacrylate copolymers (SG) containing various glycidyl methacrylate (GMA) contents, was investigated in this study. SG copolymers are able to react with PEN terminal groups during melt blending, resulting in the formation of desirable SG-g-PEN copolymers in the blend. These in situ formed copolymers tend to reside along the interface preferentially as the result of interfacial reaction and thus function as effective compatibilizers in PEN/PS blends. The compatibilized blends exhibit higher viscosity, finer phase domain, and improved mechanical properties. It is found that the degree of grafting of the in situ formed SG-g-PEN copolymer has to be considered as well. In blends compatibilized with the SG copolymer containing higher GMA content, heavily grafted copolymers would be produced. The length of the styrene segment in these heavily grafted copolymers would be too short to penetrate deep enough into the PS phase to form effective entanglements, resulting in the lower compatibilization efficiency in PEN/PS blends. Consequently, the in situ formation of SGg-PEN copolymers with an optimal degree of grafting is the key to achieving the best performance for the eventually produced PEN/PS blends through SG copolymers. (C) 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 967-975, 2003.
Conservation constraints on random matrices
(2003-02-07)
Ma, WJ
;
Wu, TM
;
Hsieh, J
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物理研究所
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Institute of Physics
We study the random matrices constrained by the summation rules that are present in the Hessian of the potential energy surface in the instantaneous normal mode calculations, as a result of momentum conservation. In this paper, we analyse the properties related to such conservation constraints in two classes of real symmetric matrices: one with purely row-wise summation rules and the other with the constraints on the blocks of each matrix, which underscores partially the spatial dimension. We show explicitly that the constraints are removable by separating the degrees of freedom of the zero-eigenvalue modes. The non-spectral degrees of freedom under the constraints can be realized in terms of the ordinary constraint-free orthogonal symmetry but with the rank deducted by the block dimension. We propose that the ensemble of real symmetric matrices with full randomness, constrained by the summation rules, is equivalent to the Gaussian orthogonal ensemble (GOE) with lowered rank. Independent of the joint probability distribution, the Jacobian contributed by the transformation from the matrix coordinates to the spectral coordinates, possesses the same spectral-variable dependence in these two cases. We verify numerically that the small-separation asymptotic in the nearest-neighbour level spacing distribution is indeed governed by the same symmetry power factor, beta = 1, as that of the GOE, under conservation constraints and other underlying spatial correlations.
Observation of vector vortex lattices in polarization states of an isotropic microcavity laser
(2003-02-07)
Chen, YF
;
Huang, KF
;
Lai, HC
;
Lan, YP
;
電子物理學系
We experimentally investigate the formation of a vector polarization pattern from an isotropic microcavity laser. It is found that the orthogonal components of the observed pattern are localized on the geometrical rays. The connection between eigenfunctions and geometrical rays is analytically constructed by using the SU(2) coherent states. With the analytical function form, the observed vector pattern is completely reconstructed and the vector vortex lattice is apparent.
Synthesis of hyperbranched aromatic poly(amide-imide): Copolymerization of B ' B-2 monomer with A(2) monomer
(2003-02-11)
Chang, YT
;
Shu, CF
;
應用化學系
;
Department of Applied Chemistry
A hyperbranched aromatic poly(amide-imide) was prepared by the copolymerization of 4-(3,5-dicarboxyphenoxy)phthalic anhydride, a B'B2 type monomer, and 1,4-phenylenediamine, an A(2) type monomer. The rapid reaction between the anhydride and amino group led to the formation of the dominant imide intermediate which can be regarded as a new AB(2) type of monomer. The intermediate, without isolation, was subjected to further polymerization in the presence of TPP/pyridine, as condensing agents, to give the hyperbranched poly(amide-imide), containing carboxylic acid chain ends. In comparison, the AB(2) monomer was prepared separately, and the conventional self-polymerization of this monomer was also studied. The structures of the obtained polymers were characterized by FTIR and H-1 NMR spectroscopy. The spectral data showed that these two polymers, prepared from two different synthetic approaches, have nearly identical structures. The degree of branching of the hyperbranched poly(amideimide)s was estimated to be 60-61%. The terminal carboxylic acid groups were modified by reaction with a variety of aromatic amines to give the corresponding amide derivatives. The nature of the chain ends was shown to have a significant effect on the solubility and T, of the hyperbranched poly(amideimide)s.
Characteristics and stress-induced degradation of laser-activated low temperature polycrystalline silicon thin-film transistors
(2003-02-15)
Peng, DZ
;
Chang, TC
;
Chang, CY
;
Tsai, ML
;
Tu, CH
The characteristics and reliability of laser-activated polycrystalline silicon thin-film transistors (poly-Si TFTs) under the stress condition of drain voltage (V-d)=12 V and gate voltage (V-g)=15 V have been investigated. In spite of reducing the source/drain resistivity by using laser activation method, the leakage current (V-g<0) is larger for laser-activated poly-Si TFTs in comparison with traditional furnace-activated counterparts. It is also found that the post-stress leakage and on/off current ratio degrade much faster for laser-activated poly-Si TFTs, while the degradation rates of threshold voltage and subthreshold swing are comparable to those of traditional furnace-activated TFTs. The laser activation modifies the grain structure between drain and channel region and causes grain discontinuity extending from the drain side to the channel region. The grain discontinuity near drain side in the polysilicon film has been investigated by transmission electron microscopy analysis. The effective trap state density calculated from typical I-V curve has been compared for laser-activated and furnace-activated TFTs. As a result, an inferior reliability with extra trap state density and larger leakage current was observed in the laser-activated poly-Si TFTs. (C) 2003 American Institute of Physics.
Low temperature sintering and crystallisation behaviour of low loss anorthite-based glass-ceramics
(2003-02-15)
Lo, CL
;
Duh, JG
;
Chiou, BS
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Anorthite-based glass-ceramics including TiO2 as nucleating agent were melted and quenched in this study. The effect of particle size on the sintering behaviour of glass powders was investigated in order to obtain low-temperature sintered glass-ceramics. Anorthite glass-ceramic starts to densify at the transition temperature of glass (T-g = 770degreesC) and is fully sintered before the crystallisation occurrence (880degreesC). Therefore, a dense and low-loss glass-ceramic with predominant crystal phase of anorthite is achieved by using fine glass powders (D-50 = 0.45 mum) fired at 900degreesC. The as-sintered density approaches 99% theoretical density and the apparent porosity is as low as 0.05 Vol%. The dense and crystallized anorthite-based glass-ceramic exhibits a fairly low dielectric loss of 4 x 10(-4) at 1 MHz and a thermal expansion coefficient of 4.5 x 10(-6)degreesC(-1). Furthermore, the microwave characteristics were measured at 10 GHz with the results of K = 9.8, Of = 2250, and temperature coefficient of resonant frequency tau(f) = -30 ppm/degreesC. (C) 2003 Kluwer Academic Publishers.
Comparison of p-side down and p-side up GaN light-emitting diodes fabricated by laser lift-off
(2003-02-15)
Chu, CF
;
Yu, CC
;
Cheng, HC
;
Lin, CF
;
Wang, SC
The performance characteristics of laser lift-off (LLO) freestanding InGaN/GaN multiple quantum well (MQW) light-emitting diodes (LEDs) mounted on a Cu substrate with p-side up, and p-side down configurations were determined and compared. The InGaN/GaN MQW LED structures, which were originally fabricated on a sapphire substrate, were transferred to a Cu substrate by the LLO process into two different configurations, namely p-side up and p-side down with the same Ni/Pd/Au p-contact metallizations. Both p-side down and p-side up LLO-LEDs showed a higher current operation capability up to 400 mA than the original LEDs on the sapphire substrate. The p-side down LLO-LEDs showed a nearly eightfold increase in the light output power compared to the p-side up LLO-LEDs. The p-side down LLO-LEDs also showed a more stable wavelength emission spectrum than the p-side up ones.
Phase transformations in a Cu-142Al-15.0Ni alloy
(2003-02-17)
Chen, CH
;
Liu, TF
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材料科學與工程學系
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Department of Materials Science and Engineering
In the as-quenched condition, the microstructure of the Cu-14.2Al-15.0Ni alloy was D0(3) phase containing extremely fine L-J precipitates. Since both fine D0(3) domains with a/2(100) anti-phase boundaries (APBs) and small B2 domains with a/4(111) APBs could be observed, the D0(3) phase existing in the as-quenched alloy should be formed by an A2 --> B2 --> D0(3) continuous ordering transition during quenching. It is worthwhile to note that the a/4(111) APBs have never been observed by other workers in the Cu-Al-Ni ternary alloys before. When the as-quenched alloy was aged at temperatures ranging from 400 to 1000 degreesC for longer times, the phase transformation sequence as the aging temperature increased was found to be (alpha + B2 precipitate) --> (B2 + B2 precipitate) --> B2 --> A2. This transformation has also never been observed by other workers in the Cu-Al-Ni ternary alloys before. (C) 2002 Elsevier Science B.V. All rights reserved.
Electrical and structural characteristics of PbTiO3 thin films with ultra-thin Al2O3 buffer layers
(2003-02-17)
Sun, CL
;
Chen, SY
;
Yang, MY
;
Chin, A
;
材料科學與工程學系
Polycrystalline PbTiO3 thin films have been prepared on Si substrates with ultra-thin SiO2 and Al2O3 buffer layers by chemical solution deposition, respectively. Although capacitance-voltage characteristics show hysteresis loops in both cases, the memory window of PbTiO3/Al2O3 stacked dielectric is 3.3V larger than that on SiO2. In addition, well-behaved capacitance-voltage characteristics are only obtained in PbTiO3/Al(2)o(3) and the PbTiO3 films on Al2O3 have the dielectric constant of 116 larger than 42 of PbTiO3 films on SiO2. The leakage current density of PbTiO3/Al2O3 dielectric is 1.3 x 10(-7) A cm(-2) at -2.5 V, which is low enough for deep sub-mum application. (C) 2002 Elsevier Science B.V. All rights reserved.
A computational study of regioselectivity in a cyclodextrin-mediated Diels-Alder reaction: Revelation of site selectivity and the importance of shallow binding and multiple binding modes
(2003-02-17)
Li, WS
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Chung, WS
;
Chao, I
;
應用化學系
;
Department of Applied Chemistry
The use of a cyclodextrin . Diels-Alder transition structure complex (CD . TS) as a model in molecular dynamics simulations has enabled us to gain insight into the controlling factors in the cyclodextrin-mediated Diels-Alder reaction of methyl-p-benzoquinone with isoprene. MD Simulations were carried out with multiple binding configurations of the CD . TS (TS = meta-TS, para-TS) complexes at the top and bottom rims of beta-CD. We discovered that i) only shallow binding with the CD is necessary for the regioselectivity, and multiple binding geometries are possible: ii) the narrow bottom rim. with the primary hydroxyl groups, of the CD binds both regio-TSs better than at the wider top rim (secondary hydroxyl groups), which was unexpected from the perspective of shape complementarity that governs the stability of most CD . guest complexes. Overall, the bottom rim of the CD exhibits higher regioisomer discrimination for the meta-TS; iii) structural clustering analyses of the CD . TS configurations (sampled during MD simulations) have enabled us to evaluate the binding energies of the different binding configurations. The result indicates that there is a direct correlation between meta-product selectivity and a higher number of binding configurations favoring the formation of the CD . meta-TS complex, The main forces of stabilization in the CD . TS complexes are the van der Waals interactions when the TS is bound at the top rim. At the bottom rim, closer contacts between polar functional groups of the TS and CD have increased the importance of electrostatic interactions, We found that van der Waals, solvation, and torsional forces are less favorable for complexation at the bottom rime however, this is compensated by large favorable electrostatic interactions. With insights obtained from the study of CD . TS complexes and MD simulations of the modified heptakis-[6-O-(2-hydroxyl)propyl]-beta-CD, we were able to explain why a low selectivity was observed when the Diels-Alder reaction was carried out in this modified CD. Two types of search method [Monte Carlo and multiple minimum (MCMM) and molecular dynamics (MD)] to explore and evaluate the different possible binding geometries of the TS within beta-CD, were discussed.
Characterization of BaPbO3 and Ba(Pb1-xBix)O-3 thin films
(2003-02-17)
Sun, CL
;
Wang, HW
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Chang, MC
;
Lin, MS
;
Chen, SY
BaPbO3 and Ba(Pb1-xBix)O-3 films made from barium 2-ethylhexanoate, lead 2-ethylhexanoate and bismuth acetate were prepared by metal-organic deposition (MOD) method on Pt/Ti/SiO2/Si substrate. The phase transition and the physical properties of these films were studied. The polycrystalline BaPbO3 phase starts to form above 600 degreesC and the Pb-excess addition would enhance the formation of single perovskite BaPbO3 phase. With increasing annealing temperature, the optimum sheet resistance 1.6 Omega sq(-1) (resistivity approximate to 1.07 x 10(-4) Omega cm) could be obtained at 750 degreesC. However, an annealing temperature over 800 degreesC causes reactions between substrate and BaPbO3 phase and results in sharp increase of resistance. On the other hand, the substitution of Pb by Bi in the Ba(Pb1-xBix)O-3 films could stabilize the perovskite phase, though the sheet resistance is raised over 10 Omega sq(-1) at x = 0.3. (C) 2002 Elsevier Science B.V. All rights reserved.
A novel approach for optimizing the optical performance of the broadband tap coupler
(2003-02-20)
Hsu, CM
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Su, CT
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Liao, D
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工業工程與管理學系
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Department of Industrial Engineering and Management
An integrated approach using neural networks, exponential desirability functions and genetic algorithms to optimize parameter design problems with multiple responses is presented. The proposed approach aims to identify the input parameter settings to maximize the overall minimal satisfaction level with respect to all the responses. The proposed approach is illustrated by optimizing the fused process parameters created during fused biconic taper coupler development to improve the performance and reliability of a 1% (1/99) single-window broadband tap coupler. The proposed solution procedure was implemented on a Taiwanese manufacturer of fibreoptic passive components. The implementation results demonstrate the practicability of the method. Comparison analysis revealed that the proposed procedure outperformed the traditional Taguchi method in resolving multi-response parameter design problems.
Ab initio studies of ClOx reactions. 3. Kinetics and mechanism for the OH plus OClO reaction
(2003-02-20)
Xu, ZF
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Zhu, RS
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Lin, MC
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交大名義發表
;
National Chiao Tung University
The mechanism for the OH + OClO reaction on the singlet and triplet surfaces and its rate constants for formation of various products have been investigated by means of ab initio molecular orbital theory and variational RRKM theory calculations. The geometric parameters of stationary points were optimized at the B3LYP level of theory with the 6-311G(d,p) and 6-311+G(3df,2p) basis sets, and the potential energy surfaces were evaluated at the G2M(CC2)//B3LYP/6-311+G(3df,2p) level of theory. Three main product channels, all located on the singlet PES, have been identified: (1) HOO + ClO, (2) HOCl + O-1(2), and (3) HOClO2, the association product. The predicted results show that the rate constants for channels 1 and 2 are pressure-independent up to 1000 atm and that for channel 3 is strongly pressure dependent. Below 1000 K, all rate constants were found to vary negatively with temperature. The individual and total rate constants in the temperature range from 200 to 1000 K at 1 Torr He pressure can be represented by k(1)(T) = 1.22 x 10(-22)T(2.75) exp(1682/T), k(2)(T) = 5.47 x 10(-20)T(2.07) exp(2064/T), k(3)(T) = 1.37 x 10(4)T(-6.61) exp(-536/T) (200-500 K) and 4.99 x 10(54)T(-22.36) exp(-9807/T) (500-1000 K), and k(tot)(T) = 1.78 x 10(-20)T(2.25) exp(2100/T) in units of cm(3) molecule(-1) s(-1). The predicted rate constant, with the HOCl + O-1(2) as the major products in the 300-500 K range, agrees well with available experimental data obtained at 1 Torr He pressure. The high- and low- pressure limits of k(3) can be effectively given by k(3)(infinity)(T) = 3.24 x 10(-11) T-0.28 exp(- 18/T) cm(3) molecule(-1) s(-1) in 200-2500 K and k(3)degrees(T) = 1.28 x 10(-13)T(-6.36) exp(-635/T) for 200-800 K, 7.37 x 10(84)T(-36.02) exp(-22134/T) for 800-1000 K, and 2.91 x 10(-13)T(-8.42) exp(11500/T) for 1000-2500 K in units of cm(6) molecule(-2) s(-1) with N-2 as the third body.
Metallic percolation in La0.67Ca0.33MnO3 thin films
(2003-02-24)
Chen, SF
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Lin, PI
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Juang, JY
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Uen, TM
;
Wu, KH
Phase separation in La0.67Ca0.33MnO3 thin films was investigated by scanning tunneling microscopy. The correlation between the grain structure and the spatial distribution of the coexisting metallic and insulating phases was evidently established. At temperatures not far below the metal-insulator transition, the spatial variation of the coexisting metallic and insulating phases is susceptible to magnetic field in an irreversible manner. The irreversibility suggests that the metallic percolation paths can be affected randomly by magnetic field. However, the variation becomes insensitive to magnetic field at lower temperatures. (C) 2003 American Institute of Physics.
A note on unscrambling address lines
(2003-02-28)
Lu, CC
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Tsai, SC
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資訊科學與工程研究所
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Institute of Computer Science and Engineering
A writer stores some data in memory accessible via address lines. If an adversary permutes the address lines after the writer leaves the message, then how can a reader find the permutation? This is the so-called unscrambling address lines problem of Broder et al. [SODA'99, 1999, pp. 870-871]. By a divide-and-conquer approach, we give a very simple algorithm to recover the permutation. Our method is much easier to understand than Broder et al.'s previous ad hoc solution. (C) 2002 Elsevier Science B.V. All rights reserved.
Sortability of vector partitions
(2003-02-28)
Hwang, FK
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Lee, JS
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Liu, YC
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Rothblum, UG
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應用數學系
Some combinatorial properties of partitioning points in R-1 have recently been well studied. We extend this study to points in R-d with the hope to benefit clustering and optimal partition problems in R-d. (C) 2002 Elsevier Science B.V. All rights reserved.
Using a conflict map as an instructional tool to change student alternative conceptions in simple series electric-circuits
(2003-03-01)
Tsai, CC
;
教育研究所
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師資培育中心
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Institute of Education
;
Center of Teacher Education
Research in science education has revealed that students have alternative conceptions when learning various domains in science. The conflict map uses a series of discrepant events, critical events, relevant scientific conceptions and perceptions to promote student conceptual change. This study was conducted to examine the effects of using a conflict map on eighth graders' conceptual change and ideational networks about simple series electric circuits. Through a quasi-experimental research design, 93 of Taiwan's eighth graders were assigned to a control group, receiving traditional instruction, while 97 eighth graders were assigned to an experimental group, which used a conflict map as an instructional tool. Research data gathered from a two-tier test revealed that the conflict map could help students overcome alternative conceptions about simple series electric circuits. Student interview data, analysed through a flow map method, also showed that the use of conflict map could help students construct greater, richer and more integrated ideational networks about electric circuits.
All-planar dual-mode asymmetric filters at Ka-band
(2003-03-01)
Chen, HC
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Tzuang, CKC
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電信工程研究所
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Institute of Communications Engineering
All-planar dual-mode inductive asymmetric filters utilizing new planar microstrip to dielectric-loaded rectangular waveguide transitions at Ka-band were presented and built in this letter. The conventional, three-dimensional metallic rectangular waveguide dual-mode filters can be implemented into mature PCB technology with a much easier and lower-cost fabrication process on the basis of the all-planar feature of the transition. This work demonstrates two Ka-band filter examples with center frequency at 31 GHz and bandwidth at 1 GHz and 2 GHz. The measured minimum insertion loss of each case was, respectively, 2.68 and 1.12 dB, with greater than 10 dB return loss in the passband. Moreover, the measured side-band attenuation (near passband) is larger than 30 dB due to the transmission zeros at each side of the passband.
Effect of Zr/Ti ratios on characterization of Pb(ZrxTi1-x)O-3 thin films on Al2O3 buffered Si for one-transistor memory applications
(2003-03-01)
Sun, CL
;
Hsu, JJ
;
Chen, SY
;
Chin, A
;
材料科學與工程學系
Pb(ZrxTi1-)O-3 (PZT) thin films have been prepared on Al2O3/Si and PbTiO3/Al2O3/Si substrates, respectively. On Al2O3/Si substrates, Ti-rich PZT thin films had lower perovskite transformation temperatures than those of Zr-rich PZT films. Therefore, PbTiO3 was used as the seeding layer on Al2O3/Si to form a PbTiO3/Al2O3/Si substrate. The threshold voltage shift of a PZT(53/ 47)/PbTiO3/Al2O3/Si capacitor reaches 9 V with +/-10 V writing voltages, which is much larger than the 2 V of the PZT(0/100)/PbTiO3/Al2O3/Si capacitor. Different memory mechanisms in the capacitance-voltage characteristics of capacitors were further examined and discussed in this paper. (C) 2003 The Electrochemical Society.
An embedding algorithm for multiple watermarks
(2003-03-01)
Shieh, CS
;
Huang, HC
;
Wang, FH
;
Pan, JS
;
電子工程學系及電子研究所
A new algorithm for embedding several watermarks into the same original source is proposed in this paper. Instead of conventional watermark embedding algorithms that embed one watermark in one specific domain, we propose algorithms for embedding multiple watermarks into different compression domains to protect the ownership of the original images. The proposed schemes for embedding and extraction in different domains vary from the existing methods reported in the literature. Simulation results show their robustness for surviving intentional attacks and, hence, their effectiveness in protecting copyrights. They are also easy to implement.