Browsing by Issue Date, starting with "1999-01-03"

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Transesterification in homogeneous poly(epsilon-caprolactone)-epoxy blends
(1999-01-03)
Chen, JL
;
Huang, HM
;
Li, MS
;
Chang, FC
;
應用化學系
Transesterification has been investigated in poly(epsilon-caprolactone) (PCL)-epoxy blends. In the hot melt process, the hydroxyl on diglycidyl ether of bisphenol-il (DGEBA) monomers is too low to give a noticeable transesterification reaction. In the postcure process, model reactions reveal that the hydroxyls from a ring-opening reaction are able to react with the esters of PCL. In the meantime, the PCL molecular weight decrease and its distribution becomes broader. Nuclear magnetic resonance spectra reveal that fraction of the tertiary hydroxyls converts to secondary hydroxyls. In the cured DGEBA-3,3'-dimethylmethylene-di(cyclohexylamine)-PCL blend, a homogeneous morphology is achieved. PCL segments are grafted onto the epoxy network after postcuring and result in the lower T-g observed in the differential scanning calorimetry thermogram. A higher transesterification extent also results in broader transition peaks by dynamic mechanical analysis. (C) 1999 John Wiley & Sons, Inc.
An efficient algorithm for finding the D-stability bound of discrete singularly perturbed systems with multiple time delays
(1999-01-10)
Hsiao, FH
;
Pan, ST
;
Teng, CC
;
電控工程研究所
;
Institute of Electrical and Control Engineering
In this paper, we present an original work on the D-stabilization problem of discrete singularly perturbed systems with multiple time delays. A new robust D-stability criterion in terms of stability radius is first derived to guarantee that all poles of the discrete multiple time-delay systems remain inside the specific disk D(alpha, r) in the presence of parametric uncertainties. Then, by using the technique of time-scale separation, we derive the corresponding slow and fast subsystems of a discrete multiple time-delay singularly perturbed system. The state feedback controls for the D-stabilization of the slow and the fast subsystems are separately designed and a composite state feedback control for the original system is subsequently synthesized from these state feedback controls. Thereafter, we derive a frequency domain epsilon-dependent D-stability criterion for the original discrete multiple time-delay singularly perturbed system under the composite state feedback control. If any one of the conditions of this criterion is fulfilled, D-stability of the original closed-loop system is thus investigated by establishing that of its corresponding slow and fast closed-loop subsystems. Finally, an efficient algorithm is proposed to obtain a less conservative D-stability bound of the singular perturbation parameter and to reduce the computation time.
Interlayer cross talk in dual-layer read-only optical disks
(1999-01-10)
Yang, BW
;
Shieh, HPD
;
光電工程學系
;
Department of Photonics
Volumetric optical disks comprising multiple data layers have been proposed to multiply recording density. Owing to the presence of out-of-focus data layers, interlayer cross talk is induced in readout. An optical model was developed to study the readout process and the effect of interlayer cross talk on the readout of dual-layer read-only optical disks. Schemes to improve the readout characteristics by suppression of the interlayer cross talk were proposed. Experiments that agreed well with the simulation resulted. (C) 1999 Optical Society of America.
Majority- and minority-carrier traps in Te-doped AlInP
(1999-01-11)
Wu, YR
;
Sung, WJ
;
Lee, WI
;
電子物理學系
;
友訊交大聯合研發中心
The properties of deep levels found in Te-doped AlInP grown by metal-organic chemical vapor deposition have been studied. By using pn-junction structure, both minority- and majority-carrier traps can be observed. Two deep levels are found in Te-doped AlInP: one majority-carrier trap and one minority-carrier trap. The activation energies of majority- and minority-carrier traps are 0.24+/-0.05 and 0.25+/-0.03 eV, respectively. The majority-carrier trap is uniformly distributed, indicating that this level belongs to some kind of bulk defect. (C) 1999 American Institute of Physics. [S0003-6951(99)05202-X].
Onset of entanglement
(1999-01-12)
Lin, YH
;
Juang, JH
;
應用化學系
;
Department of Applied Chemistry
The onset of entanglement was determined from studying the viscoelastic spectra of the blends consisting of two nearly monodisperse polystyrene polymers: component one having a molecular weight slightly less than the entanglement molecular weight M-e (=4 rho RT/5G(N)), whereas that of component two being greater than M-e (such a blend is referred to as the blend solution). It is shown that because of the absence of the hydrodynamic interaction the viscoelastic spectrum of the blend solution can be described by applying the Rouse theory to both components in the entanglement-free region. As entanglements among the chains of component two occur, when its weight fraction, W-2, increases above a critical point, the viscoelastic response of component one remains described by the Rouse theory. With the Rouse viscoelastic response of component one as the internal reference, the onset of chain entanglement among the chains of component two can be determined by monitoring the deviation of the viscoelastic response of component two from being described by the Rouse theory as a function of increasing mil. According to the study, entanglement starts to occur in the close neighborhood of M-e' (the entanglement molecular weight of the blend solution and M-e' = MeW2-1) for the polymer blend solution or equivalently M-e for the monodisperse polymer melt well below M-c' or M-c (M-c' = McW2-1, where M-c is the critical molecular weight of the zero shear viscosity of the polymer melt).
Hyperbranched poly(ether ketone) with carboxylic acid terminal groups: Synthesis, characterization, and derivatization
(1999-01-12)
Shu, CF
;
Leu, CM
;
應用化學系
;
Department of Applied Chemistry
A new procedure is described for the formation of a hyperbranched poly(ether ketone) with carboxylic acid terminal groups. This preparation was based on the one-step synthesis of an AB(2)-type monomer 5-phenoxyisophthalic acid using phosphorus pentoxide/methanesulfonic acid as the condensing agent and solvent. The electrophilic aromatic substitution reaction led to the formation of the al yl ketone linkage. With the help of model compounds, H-1 NMR studies revealed that the degree of branching of the poly(ether ketone) was about 55%. The terminated carboxylic acid groups were readily functionalized, yielding hyperbranched polymers with a variety of different functional chain ends. The nature of the chain ends was shown to dramatically affect physical properties of the hyperbranched macromolecules. The ammonium derivative was soluble in water and behaved as a unimolecular micelle.
Optimal assignment of mobile agents for software authorization and protection
(1999-01-15)
Shieh, SP
;
Lin, CT
;
Wu, SY
;
資訊工程學系
;
Department of Computer Science
In this paper, a model for software authorization and protection in mobile code systems is proposed. In the model, a software is partitioned into objects, called mobile agents, and the privileges to access these agents are separated and distributed to the user's local system and a number of trusted servers called trusted computational proxies. The execution of a program (software) is conducted by cooperation of the agents and the proxies that contain them. Two agents are dependent if there is a message passing between them. To reduce the risk of software being attacked,dependent agents are distributed to different proxies. In this way, if a proxy is compromized, minimal information of the software will be disclosed. Methods for assigning agents to proxies are also proposed to minimize, under the security constraints, computation load of the proxies as well as communication load between the user's local system and proxies. (C) 1999 Elsevier Science B.V. All rights reserved.
Effect of bismuth content on the properties of Sr0.8BixTa1.2 Nb0.9O9+y ferroelectric thin films
(1999-01-15)
Tsai, HM
;
Lin, P
;
Tseng, TY
;
材料科學與工程學系
;
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].
Correlation of countercurrent extraction with countercurrent chromatography in aqueous matrixes. An improved model
(1999-01-15)
Yu, TI
;
Liang, CS
;
Luo, SK
;
應用化學系
;
Department of Applied Chemistry
A mathematical model was employed to simulate supercritical fluid extraction (SFE) efficiency in aqueous matrixes with supercritical fluid chromatography (SFC) data in a previous study. The SFE extraction vessel, i.e., the column for the SFC, was mathematically divided into limited layers. The analyte mass was uniformly distributed in the vessel before extraction. However, it changed when the fluid flowed through the aqueous sample and reached the column outlet. The mass redistribution as a function of the layer was computed using a countercurrent distribution approach. Afterward, each layer was considered to undergo a chromatographic process simultaneously. Each layer's chromatographic capacity factor and peak width were calculated using the true SFC experimental data, and the sum of all these peak distributions as a function of time gave the extraction efficiency, In this work, the mass redistribution was calculated through a chromatographic approach, which predicted the extraction recovery better than the previous approach,,Both the previous SFE and the newly acquired liquid/liquid extraction data using a countercurrent chromatographic apparatus were examined to demonstrate the upgrading of the model using this new chromatographic approach. Significant improvements were observed, especially for analytes with small capacity factors. The simulation deviations came mainly from the fact that analyte molecules in the individual layers would shift away from Gaussian shapes that were assumed in the model.
The effects of shallow germanium halo doping on N-channel metal oxide semiconductor field effect transistors
(1999-01-15)
Wang, MF
;
Chien, CH
;
Chao, TS
;
Lin, HC
;
Jong, FC
In this paper, we report the use of shallow germanium halo doping on improving the short-channel effects of deep submicron n-channel metal-oxide-semiconductor field effect transistors. It is demonstrated that by adding a shallow (i.e., 10 keV) germanium large-angle-tilt implant (LATID), V-th lowering in short-channel transistors is significantly improved. The improvement is found to increase with increasing germanium dose. A low germanium dose (e.g., 5 x 10(12) cm(-2)) is also found to effectively improve the drain-induced barrier lowering (DIBL) of the short-channel transistors. Our results also show that junction leakage degradation, which has been previously reported to accompany germanium implants using higher energy, can be minimized by the shallow low-dose implant used in this study.
Determination of built-in field by applying fast Fourier transform to the photoreflectance of surface-intrinsic n(+)-type doped GaAs
(1999-01-18)
Wang, DP
;
Wang, KR
;
Huang, KF
;
Huang, TC
;
Chu, AK
Photoreflectance spectroscopy of surface-intrinsic n(+)-doped (s-i-n(+)) GaAs has been measured at various power densities (P-pu) of a pump beam. Many Franz-Keldysh oscillations (FKOs) were observed above the band-gap energy, which will enable the electric-field strength (F) to be determined from the periods of the FKOs. Field F thus obtained is subject to photovoltaic effects. In order to reduce the photovoltaic effects from the pump beam, P-pu was kept below 10 mu W/cm(2) in the previous experiments. Here, we demonstrate that the built-in field can be determined at a larger P-pu by using fast Fourier transform techniques. (C) 1999 American Institute of Physics. [S0003-6951(99)02803-X].
High birefringence and wide nematic range bis-tolane liquid crystals
(1999-01-18)
Wu, ST
;
Hsu, CS
;
Shyu, KF
;
應用化學系
;
Department of Applied Chemistry
Several dialkyl and fluoro bis-tolane liquid crystals were synthesized and their physical properties evaluated. These highly conjugated liquid crystals exhibit a wide nematic range, small heat fusion enthalpy, high birefringence, and relatively low viscosity. Their excellent compatibility with commercial cyano mixtures makes these liquid crystals attractive for many electro-optic applications. (C) 1999 American Institute of Physics. [S0003-6951(99)02103-8].
Contributions of CuO2 planes and CuO chains on the transport properties of YBa2Cu4O8
(1999-01-20)
Chatterjee, S
;
Weng, SS
;
Hong, IP
;
Chang, CF
;
Yang, HD
We have investigated the contributions of CuO2 planes and CuO chains on the transport properties of YBa2Cu4O8 by measuring the electrical resistivity and thermoelectric power (S) of Y1-xPrxBa2(Cu1-yZny)(4)O-8, Y1-xCaxBa2Cu4O8 and YBa2(Cu1-xGax)(4)O-8. Pr reduces the mobile carrier concentration in the CuO2 planes in YBa2Cu4O8, as a consequence, the superconducting transition temperature is progressively decreased with increasing Pr. The S(T) data suggest that the metallic behavior at lower temperature of the Pr and Zn doped compounds is contributed by the double CuO chains. On the other hand, the S(T) behavior of Ca doped samples is opposite to that of the Pr doped samples because the doping of Ca in Y-site introduces holes in the CuO2 planes. However, the substitution of Ga in Cu(1)-site suppresses the carrier concentration in CuO chains and increases the normal-state resistivity revealing the important contribution from CuO chains on the metallic behavior of YBa2Cu4O8 and PrBa2Cu4O8. (C) 1999 Published by Elsevier Science B.V. All rights reserved.
An effective three-dimensional model for UHF radio propagation into multistory office buildings
(1999-01-20)
Tarng, JH
;
Chang, YC
;
Chen, CM
;
電信工程研究所
;
Institute of Communications Engineering
An effective three-dimensional (3-D) direct-transmitted model combined with a patched-wall model is proposed to explore UHF radio propagation into multistory buildings in a microcellular environment. The model is verified by comparing the computed path loss with the measured one of 1.7 and 2.44 GHz radio waves propagating at different sites. The comparison demonstrates that the model has reasonably accurate prediction when the number of floor levels between the transmitting and the receiving antennas is no more than four.
Improved CMAC neural network control scheme
(1999-01-21)
Lin, CC
;
Chen, FC
;
電控工程研究所
;
Institute of Electrical and Control Engineering
The cerebellar model articulation controller (CMAC) neural network control scheme is a powerful tool for practical real-time nonlinear control applications. However, despite its initial outstanding performance, the CMAC control system can suddenly diverge after a long period of stable tracking. The authors propose a modification to the CMAC control scheme in order to improve stability while preserving the original good performance.
Microstrip leaky-wave antenna fed by short-end CPW-to-slot transition
(1999-01-21)
Chen, TL
;
Lin, YD
;
傳播研究所
;
Institute of Communication Studies
Single and dual-beam microstrip leaky-wave antennas fed by a short-end coplanar waveguide (CPW)-to-slot transition are presented. The radiation bands of the antennas are deduced from the leaky-wave propagation characteristics of the microstrip line first higher order leaky mode. The measured reflection coefficients of the radiation band confirm the predicted leaky band and the measured radiation paffems exhibit. the frequency-scanning feature of the leaky-wave antenna. The short-end CPW-to-slot transition feeding method simplifies the circuit layout and is more suitable for different band design than the CPW-fed microstrip first higher order leaky-wave antennas presented in the literature.
A note on breaking and repairing a secure broadcasting in large networks
(1999-01-25)
Sun, HM
;
Shieh, SP
;
Sun, HM
;
資訊工程學系
;
Department of Computer Science
In this note, we show that a proposed secure broadcasting scheme is insecure. We also present a modified scheme to overcome this weakness. The modified scheme has the extra advantage that each participant can derive his group keys from group identities without the need of knowing other information. (C) 1999 Elsevier Science BV. All rights reserved.
The effect of native oxide on epitaxial SiGe from deposited amorphous Ge on Si
(1999-01-25)
Wu, YH
;
Chen, WJ
;
Chin, A
;
Tsai, C
;
電子工程學系及電子研究所
We have investigated the effect of native oxide on the epitaxial SiGe from deposited amorphous Ge on Si. Instead of epitaxial growth by molecular beam epitaxy or ultrahigh-vacuum chemical vapor deposition, the SiGe layer is formed by this simple process followed by an annealing step. As observed by transmission electron microscopy, the suppression of native oxide plays an important role to achieve epitaxial SiGe. The SiGe quality degrades with increasing native oxide thickness and becomes polycrystalline with a similar to 20 Angstrom interfacial native oxide. On the other hand, single crystalline SiGe can be routinely formed from a HF-vapor treated Si surface. (C) 1999 American Institute of Physics. [S0003-6951(99)04504-0].
藝術家進駐鄉野創傳奇大道藝術館開先例
(1999-01-26)
賴素鈴
An efficient algorithm for computing quantiles of the noncentral chi-squared distribution
(1999-01-28)
Ding, CG
;
管理科學系
;
Department of Management Science
An efficient algorithm is provided for computing quantiles of the noncentral chi-squared distribution. Newton's method, which requires the evaluations of both of the noncentral chi-squared distribution function and the density, is used. A close relationship between their recursive computing formulas is noted to allow concurrent evaluation of the distribution function and the density. Newton's iterative computation can therefore be greatly speeded up. An example is given to illustrate the usefulness of the algorithm. (C) 1999 Elsevier Science B.V. All rights reserved.