Browsing by Issue Date, starting with "2003-02-17"

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Phase transformations in a Cu-142Al-15.0Ni alloy
(2003-02-17)
Chen, CH
;
Liu, TF
;
材料科學與工程學系
;
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
;
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
;
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
;
Su, CT
;
Liao, D
;
工業工程與管理學系
;
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
;
Zhu, RS
;
Lin, MC
;
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
;
Lin, PI
;
Juang, JY
;
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
;
Tsai, SC
;
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
;
Lee, JS
;
Liu, YC
;
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
;
師資培育中心
;
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
;
Tzuang, CKC
;
電信工程研究所
;
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.
THz radiation emission properties of multienergy arsenic-ion-implanted GaAs and semi-insulating GaAs based photoconductive antennas
(2003-03-01)
Liu, TA
;
Tani, M
;
Pan, CL
;
光電工程學系
;
Department of Photonics
We compare the performance of THz photoconductive (PC) emitter antennas fabricated on multienergy arsenic ion implanted GaAs (multi-GaAs:As+) and semi-insulating GaAs. High damage threshold biasing (>60 kV/cm) and large saturation optical-pumping power (similar to20 mW) for multi-GaAs:As+ based PC antennas are reported. Carrier mobility in the As ion implanted layer of GaAs:As+ was estimated to be about 150 cm(2)/V/s, which was comparable to that of. low,temperature GaAs. (C) 2003 American Institute of Physics.
Free-space electrooptic sampling of terahertz radiation from optically excited superconducting YBa2Cu3O7-delta thin films
(2003-03-01)
Lin, PI
;
Wu, KH
;
Juang, JY
;
Lin, JY
;
Uen, TM
The characteristics of photogenerated terahertz radiation from a current-biased superconducting YBa2Cu3O7-delta (YBCO) bow-tie antenna were investigated using a free-space electrooptic sampling technique. Picosecond electromagnetic pulses about 450 fs wide were obtained. The frequency spectrum derived by Fourier transforming the picosecond pulses spans over 0.1-4 THz. The dynamics of the quasi-particles optically induced by the ultrafast laser pulse primarily determines the performances of the transient terahertz radiation generated under different operating parameters. The results indicate a characteristic quasi-particle relaxation time of about 2.5 ps close to the critical temperature T-c, and a faster time at lower temperatures.
Narrow-band interference rejection in DS/CDMA systems using adaptive (QRD-LSL)-based nonlinear ACM interpolators
(2003-03-01)
Yuan, JT
;
Lee, JN
;
電信工程研究所
;
Institute of Communications Engineering
An Mth order adaptive lattice filter automatically generates all M of the outputs that would be provided by M separate transversal filters. This feature may effectively suppress the narrow-band interference (NBI) of either unknown or time-varying bandwidth (or number of frequency bands) in direct-sequence code-division multiple access systems for which the order of the interference rejection filter that achieves the optimal performance is unknown or constantly changing. Moreover, a lattice filter may significantly outperform its transversal counterpart in complex jamming environments in which the adaptive lattice filter must suppress multiple jammers, since each stage of a lattice filter adapts to suppress an orthogonal component of the NBI. This paper,develops a computationally efficient and numerically stable adaptive QR-decomposition-based least squares lattice (QRD-LSL)-based nonlinear approximate conditional mean interpolator to suppress NBI effectively. Simulation results demonstrate that both the signal-to-noise ratio improvements and the convergence rate achieved by the proposed interpolators outperform those of other existing prediction-based techniques.
Phase transformations in a Cu-14.2Al-7.8Ni alloy
(2003-03-01)
Chen, CH
;
Liu, TF
;
工學院
;
材料科學與工程學系
;
College of Engineering
In the as-quenched condition, the microstructure of the Cu-14.2 wt pct Al-7.8 wt pet Ni alloy was D0(3) phase containing extremely fine L-J precipitates with two variants. The L-J precipitate has an orthorhombic structure with lattice parameters a = 0.413 nm, b = 0.254 nm and c = 0.728 nm, which was a new phase found firstly by the present workers. The orientation relationship between the L-J phase and the matrix is (100)(L-J)//(011)(m), (010)(L-J)//(111) and (001)(L-J)//(211)(m). The rotation axis and rotation angle between two variants of the L-J phase are [021] and 90 deg. When the alloy was aged at 500 degreesC for short times and then quenched, gamma(2) particles started to precipitate within the D0(3) matrix at the aging temperature and the remaining D0(3) matrix would transform to gamma(1)' martensite during quenching. This is similar to that observed by other workers in a Cu-14Al-4Ni alloy. However, when the alloy was aged at 500 degreesC for longer times, the remaining D0(3) matrix would transform to a mixture of (B2 + alpha) phases. This feature has never been observed by other workers in the Cu-Al-Ni alloys.
Microlens array fabricated by excimer laser micromachining with gray-tone photolithography
(2003-03-01)
Tien, CH
;
Chien, YE
;
Chiu, Y
;
Shieh, HPD
;
光電工程學系
We demonstrate the fabrication of a refractive microlens array by using 249nm excimer laser micromachining with coded gray-tone mask photolithography. With pre-corrections to the nonlinear exposure process, the maximum deviation from the designed shape was below 5%. The fabricated hemispherical lens of 30 mum radius was used as a solid immersion lens (SIL) and combined with a 0.54 numerical aperture (NA) objective to achieve a 0.87 effective NA through the knife-edge scanning test. The. experimental results agreed with those of the simulation. Unlike the methods such as the thermal melting process, this one-step optical exposure method with a coded mask provides a relatively fast and cost-effective way to realize a microlens array in optical data storage, information processing, and optical interconnection applications.
A combination logic design for a high speed IEEE 802.11 MAC controller
(2003-03-01)
Li, RZ
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Huang, SP
;
Lin, FS
;
Hong, MT
;
Chen, PN
In this paper, we propose a pure combinational logic design for the implementation of IEEE802.11 Medium Access Control (MAC) protocol, in contrast to firmware implementation based on an embedded micro-engine. In order to have a timely response, a Control Frame Handler is also included in our MAC controller. A further improvement for timely manipulation on the time-critical management frames (such as Beacon, ATIM and Probe Response) is subsequently developed in our revised edition. Equipped with a self-developed PCMCIA unit, the functions of our MAC controller have been verified using two Altera EPF 10K-100 ARC240-2 FPGAs in an on-line MAC-to-MAC data exchange fashion. Experimental results show that a pure combinational logic design can easily achieve a baseband-interfacing throughput of over-100Mbps with a cost-effect gate count of 21702.
Sources of sampling error for field measurement of nitric acid gas by a denuder system
(2003-03-01)
Bai, H
;
Lu, C
;
Chang, KF
;
Fang, GC
;
環境工程研究所
Field measurements of atmospheric HNO3 gas by a denuder system equipped with four annular denuders were conducted in Taiwan. The positive errors from interfering N-compounds as well as the negative errors from incompleteness of the apparent absorption of the HNO3 gas. as sampled by one NaCl-denuder, were quantitatively determined and the error sources were identified. It is found that the concentrations of positive error and negative error might cancel each other resulting in less difference between the measured and the true HNO3 concentrations. The atmospheric HNO3 concentration and the ambient temperature were the major factors that influence the degree of negative errors. The apparent absorption efficiency might decrease to less than 80% if the HNO3 gas concentration were lower than 0.3 mug m(-3) or the ambient temperature were over 28degreesC. There are also evidences showed that the positive errors were from both interfering N-containing gases and nitrate-containing particles. (C) 2003 Elsevier Science Ltd. All rights reserved.