Browsing by Author "Wu, JY"

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A convenient modular approach of functionalizing aromatic polyquinolines for electrooptic devices
(1999-08-01)
Ma, H
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Jen, AKY
;
Wu, JY
;
Wu, XM
;
Liu, S
A versatile and generally applicable synthetic method for making second-order nonlinear optical (NLO)side-chain aromatic polyquinolines has been developed. This approach emphasizes the ease of incorporating NLO chromophores onto the pendent phenyl moieties of parent polyquinolines at the final stage via a mild Mitsunobu reaction, which provides the synthesis of NLO polyquinolines with a broad variation of polymer backbones and great flexibility in the selection of chromophores. The synthesized NLO side-chain polyquinolines possess high glass transition temperature (T-g > 200 degrees C), good processability, and excellent thermal stability. The promising results of electrooptic (EO) activity (up to 35 pm/V at 830 nm and 22 pm/V at 1300 nm), optical loss (1.5-2.5 dB/cm), and long-term stability of the poling-induced polar order (r(33) values retained > 90% of their original values at 85 degrees C for more than 1000 h) have demonstrated the advantages of this design approach. The excellent combination of these properties in the resulting polymers have also provided a great promise in the development of EO devices.
A near-optimal low-complexity transceiver for CP-free multi-antenna OFDM systems
(2006-01-01)
Lin, CY
;
Wu, JY
;
Lee, TS
;
資訊工程學系
;
電信工程研究所
Conventional orthogonal frequency division multiplexing (OFDM) system utilizes cyclic prefix (CP) to remove the channel-induced inter-symbol interference (ISI) at the cost of lower spectral efficiency. In this paper, a generalized sidelobe canceller (GSC) based equalizer for ISI suppression is proposed for uplink multi-antenna OFDM systems without CP. Based on the block representation of the CP-free OFDM system, there is a natural formulation of the ISI suppression problem under the GSC framework. By further exploiting the signal and ISI signature matrix structures, a computationally efficient partially adaptive (PA) implementation of the GSC-based equalizer is proposed for complexity reduction. The proposed scheme can be extended for the design of a pre-equalizer, which pre-suppresses the ISI and realizes CP-free downlink transmission to ease the computational burden of the mobile unit (MU). Simulation results show that the proposed GSC-based solutions yield equalization performances almost identical to that obtained by the conventional CP-based OFDM systems and are highly resistant to the increase in channel delay spread.
A novel approach of combining thin-layer chromatography with surface-assisted laser desorption/ionization (SALDI) time-of-flight mass spectrometry
(2002-01-01)
Wu, JY
;
Chen, YC
;
應用化學系
;
Department of Applied Chemistry
A novel means of combining thin-layer chromatography (TLC) with laser desorption/ionization mass spectrometry using a liquid matrix is proposed. Surface-assisted laser desorption/ionization (SALDI) mass spectrometry, which uses a mixture of a micrometer-sized carbon powder (graphite or activated carbon, the SALDI solid) and 13% sucrose/glycerol, dissolved in an equal volume of methanol (SALDI liquid) as a SALDI matrix, is used for laser desorption mass analysis. The ablation of carbon powder from a pencil drawing was used as an alternative to the SALDI solid. The liquid matrix resembled that used in a conventional SALDI matrix system. A line was drawn before separation with a pencil on the track of the sample developed on the TLC plate. After TLC separation, similar to0.1 mul of SALDI liquid was directly applied to the chromatographic spots on the TLC plate. Porphyrins were used to demonstrate this combination owing to the visible colors of this type of compound. The analyte signal can be easily detected by irradiating the laser along the pencil line on the TLC plate. An additive, p-toluenesulfonic acid, is added to the SALDI liquid to enhance the signal's intensity. This additive dramatically improves the signal-to-noise ratio. A detection limit of similar to500 pg is demonstrated for porphines, which is 50 times better than that corresponding to conventional TLC SALDI Copyright (C) 2001 John Wiley Sons, Ltd.
Analysis of small organics on planar silica surfaces using surface-assisted laser desorption/ionization mass spectrometry
(2001)
Chen, YC
;
Wu, JY
;
應用化學系
;
Department of Applied Chemistry
This study demonstrates the feasibility of directly obtaining analyte signals from a planar silica gel surface by using laser desorption mass spectrometry (LDMS). The surface of the planar silica gel was pretreated using a line drawn by a soft carbon pencil, and 0.3 muL of a liquid matrix (15% sucrose/glycerol-methanol 1:1, v/v) was applied to it (width similar to 1mm) before sample deposition. The laser was then used to directly irradiate the sample spot on the pencil line (similar to2 mm). Carbon powder ablated from the pencil residue is used to couple the laser UV energy into a liquid solution in LDMS. This sample preparation method is related to surface-assisted laser desorption/ionization (SALDI) mass spectrometry, which uses a suspension of mum-sized carbon powder (SALDI solid) mixed with a viscous liquid (SALDI matrix) as the matrix. In the present approach, the ablated carbon powder from the pencil drawing on a planar silica gel surface was used as an alternative to the SALDI solid. The liquid matrix was that used in conventional SALDI matrix systems, and the sample preparation applied herein is simpler than conventional SALDI. The matrix background remains quite low in this approach, which significantly assists the analysis of small organics such as methylephedrine and cytosine. PEG (polyethylene glycol) 400 and PEG 2000 were also used for demonstration purposes. Copyright (C) 2001 John Wiley & Sons, Ltd.
Blind identification with periodic modulation: A time-domain approach
(2002-11-01)
Lin, CA
;
Wu, JY
;
電控工程研究所
;
Institute of Electrical and Control Engineering
We propose a method for blind identification of finite impulse response (FIR) channels with periodic modulation. The time-domain formulation in terms of block signals is simple compared with existing frequency-domain formulations. It is shown that the linear equations relating the products of channel coefficients and the autocorrelation matrix of the received signal can be further arranged into decoupled groups. The arrangement reduces computations and improves accuracy of the solution; it also leads to very simple identiflability conditions and a very natural formulation of the optimal modulating sequence selection problem. The proposed optimal selection minimizes the effects of channel noise and error in autocorrelation matrix estimation; it results in a consistent channel estimate when the channel noise is white. Simulation results show, that the method yields good performance: It compares favorably with an existing subspace modulation-induced-cyclostationarity method, and it is robust with respect to channel order overestimation. The effect of modulation period and threshold of the modulating sequence are also discussed.
Block based symbol detection for high rate space-time coded systems
(2004)
Ho, CL
;
Wu, JY
;
Lee, TS
;
電信工程研究所
;
Institute of Communications Engineering
A new block based symbol detection scheme is proposed for a class of high data rate space-time coded systems reported in the literature. We here adopt the vertical Bell labs layered space-time (V-BLAST) detection algorithm to defect the transmitted symbols at the receiver end, since it yields reasonable trade-off between performance and computational complexity with respect to the optimal maximum likelihood detection. By exploiting the distinctive structures resulting front the space-time block coded systems, we show that the associated V-BLAST detection can be performed in a block-by-block manner: in each iteration stage, a block of symbols is simultaneously defected. Compared with the conventional symbol-by-symbol based V-BLAST, the block based detection tends to reduce computations and decoding delays since it involves less iterations. Computer simulations show that the proposed block based symbol detection can achieve nearly the same performance of the symbol-by-symbol based one.
Growth competition between crystalline silicon carbon nitrides and silicon nitrides deposited on Si wafer by MPCVD
(2001-11-01)
Wu, JY
;
Kuo, CT
;
Yang, PJ
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The Si-C-N films were synthesized on Si wafer by microwave plasma chemical vapor deposition with CH4, N-2, 0.0-8.3 vol.% H-2 and the additional Si chips, as the sources. The growth competition on Si wafer between crystalline ternary Si-C-N and binary silicon nitrides was examined. Based merely on the results of ESCA, XRD and SEM analyses on the film surface, it might often give false impression of forming ternary silicon carbon nitride crystalline films, as reported in the literature, though their volume fractions of H-2 were from 35 to 77%. One of the possible reasons for a false impression is due to the fact that carbon often settles on the deposited films during cooling period. The further examinations on the cross-section of the films by TEM + EDS + ED, and on the film surface by FTIR and Raman spectroscopy clarify that the films essentially consist of similar to2 mum. binary silicon nitride crystals on top of similar to 100 nm ternary Si-C-N crystallites. This is in agreement with the ESCA depth profile examinations and the substrate scratching experiment by Si3N4 powders, which greatly enhance nucleation rate of binary silicon nitride crystals. Under a higher temperature and a longer deposition time, growth competition between crystalline Si-C-N and silicon nitrides will generally result in forming a film covered with silicon nitrides. The crystal structure of the silicon nitrides on the films is much close to alpha -Si3N4 than beta -Si3N4 and tetragonal Si3N4 type structures, but silicon content is higher. (C) 2001 Elsevier Science B.V. All rights reserved.
GSC-based frequency-domain equalizer for CP-Free OFDM systems
(2005)
Lin, CY
;
Wu, JY
;
Lee, TS
;
電信工程研究所
;
Institute of Communications Engineering
A multi-antenna generalized sidelobe canceller (GSC) based equalizer for inter-symbol interference (ISI) suppression is proposed for high-rate single-input multiple-output (SIMO) orthogonal frequency division multiplexing (OFDM) systems without cyclic prefix (CP). The proposed method relies on the block representation of the OFDM transmission and exploits the ISI subspace structure in the associated multi-antenna system model. A computationally efficient partial adaptivity (PA) implementation of the GSC equalizer is also provided for reducing the receiver complexity. Simulation results show that the proposed GSC-based solution yields an equalization performance almost identical to that obtained by the conventional CP-based OFDM system and is highly resistant to the increase of channel delay spread.
Internal stresses and microstructures of commercial thick diamond films deposited by different deposition methods
(2001-11-01)
Kuo, CT
;
Wu, JY
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Lin, CH
;
Lu, TR
;
Sung, CM
Structures and stress state of six commercial freestanding thick diamond films (> 300 mum) were analyzed by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and Raman spectroscopy. These films represent the typical samples synthesized by three different chemical vapor deposition (CVD) methods, including DC are, microwave plasma, and hot filament. It was found that the higher diamond deposition rate it reaches, the more non-diamond carbons it contains, and the larger the residual compressive stress it possesses. Moreover, the samples with the highest degree of optical transparency are under the lowest compressive stress. These crystal characteristics can be manipulated by selecting different deposition methods and parameters that affect nucleation rate and growth rate of diamond. The present results show that the DC are method gives poorly developed crystals, and its residual compressive stress of the films is the highest due to the fastest diamond nucleation and crystal growth rates. (C) 2001 Elsevier Science B.V. All rights reserved.
Nondestructive characterization of the film quality and stress states in diamond films on various substrates
(2000)
Kuo, CT
;
Wu, JY
;
Chou, SL
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材料科學與工程學系
;
Department of Materials Science and Engineering
Diamond films deposited on various substrates were characterized nondestructively by Raman spectroscopy and X-ray diffraction (XRD) to evaluate their stress states and film quality. The X-ray diffraction method is further divided into two methods, i.e., the low incident beam angle X-ray diffraction (LIBAD), and Clemens-Bain method for the textured films. The whole-pattem-fitting structure refinement method, or called "Rietveld method" was adapted in XRD method to improve its accuracy. The film adhesion, film morphology and film structures including its non-diamond carbon content, crystal size, texture coefficient, film thickness and surface roughness were also examined. The correlations between structure and residual stress of the films on various substrates and under various deposition and pretreatment conditions were analyzed. The feasibility of nondestructive evaluation the Blm quality and stress states, and the origins of the residual stress of the films were discussed.
Optimal approximate inverse of linear periodic filters
(2004-09-01)
Wu, JY
;
Lin, CA
;
電控工程研究所
;
電信工程研究所
;
Institute of Electrical and Control Engineering
We propose a method for constructing optimal causal approximate inverse for discrete-time single-input single-output (SISO) causal periodic filters in the presence of measurement noise. The analysis is based on block signals and multi-input multi-output (MIMO) time-invariant models for periodic filters. The objective function to be minimized is the asymptotic block mean square error. The optimization problem is formulated in terms of transfer matrices as an optimal model-matching problem with nonsquare model and plant. Based on an inner-outer factorization on the transpose of the plant rational matrix, it is shown that the problem can be further reduced to one with a lower dimensional square model and plant, which is then solved in the time-domain, and a closed-form solution is obtained. A lower bound on the objective function is given. It is shown that the lower bound can be asymptotically achieved as the order of the optimal transfer matrix increases. The proposed method is extended to MIMO periodic systems. Numerical examples are used to illustrate the performance of the proposed approximate inverse.
Optimal finite impulse response approximate inverse of linear periodic filters
(2006-04-01)
Wu, JY
;
Lin, CA
;
電控工程研究所
;
電信工程研究所
;
Institute of Electrical and Control Engineering
A method to construct an optimal finite impulse response (FIR) approximate inverse for discrete-time causal FIR periodic filters in the presence of measurement noise is proposed. The objective function to be minimised is the sum-of-mean-square errors over one period. On the basis of the matrix impulse response of the multi-input multi-output time-invariant representation of periodic filters, the optimisation problem is formulated as one that minimises the summed equation errors of a set of over-determined linear equations. It is shown that the problem is equivalent to a set of least-squares problems from which a simple, closed-form solution is obtained. Numerical examples are used to illustrate the performance of the proposed FIR approximate inverse.
Optimal FIR approximate inverse of linear periodic filters
(2004)
Wu, JY
;
Lin, CA
;
電控工程研究所
;
Institute of Electrical and Control Engineering
We propose a method for constructing FIR approximate inverse for discrete-time causal FIR periodic filters in the presence of measurement noise. The objective function to be minimized is the sum of the error variance over one period. The optimization problem is formulated based on the matrix impulse response of the multi-input multi-output (MIMO) time-invariant representation of periodic filter as one that minimizes the sum of equation errors of a set of over-determined linear equations. It is shown that the problem is equivalent to a set of least squares problems and a simple closed-form solution is obtained Numerical examples are used to illustrate the performance of the proposed FIR approximate inverse.
Path-time coding for downlink multi-user CDMA over multipath channels
(2003)
Ho, CL
;
Wu, JY
;
Lee, TS
;
電信工程研究所
;
友訊交大聯合研發中心
A new BLAST MIMO transceiver is proposed for the downlink of high data rate CDMA systems over frequency-selective multipath channels. We consider the scenario in which multiple antennas are used at both the base station (BS) and each mobile station (MS). The high data-rate stream is first demultiplexed into multiple substreams, which are then encoded across different paths and time delays by a set of "path-time" encoders for achieving path diversity, and spread by a set of precoders designed to suppress the multiple access interference (MAI) and equalize the multipath channels without the use of channel information. These coded substreams are transmitted simultaneously by multiple antennas for an increased spectral efficiency. At each MS, the received data is passed through a simple matched filter (MF) with a modified code sequence to blindly suppress the residual ISI. A multi-user detection scheme is then employed to separate the mutually interfering signals from the multiple transmit antennas and restore the diversity gain due to path-time coding (PTC). The proposed scheme can effectively provide spatial multiplexing and diversity gain at the same time. Moreover, significant enhancement in performance can be achieved at the receiver by incorporating suitable iterative interference cancellation strategies.
Periodic-modulation based blind channel identification for single-carrier block transmission with frequency-domain equalization
(2005)
Wu, JY
;
Lee, TS
;
電信工程研究所
;
Institute of Communications Engineering
We propose a periodic-modulation based blind channel identification scheme for single-carrier block transmission with frequency-domain equalization. The proposed approach relies on the block system model and exploits the circulant channel matrix structure after the cyclic prefix is removed. It is shown that the set of linear equations relating the autocorrelation matrix of the block received signal and the product channel coefficients can, he rearranged into one with a distinctive block circulant structure. The identification equations thus obtained lead to a very simple identifiability condition, as well as a natural formulation of the optimal modulating sequence design problem which, based on the block circulant data structure, can be cast as a constrained quadratic problem that allows for a simple closed-form solution. The optimal sequence is shown to result in a consistent channel estimate irrespective of white noise perturbation. Simulation results are used for illustrating the performance of the proposed method.
Periodic-modulation-based blind channel identification for single-carrier block transmission with frequency-domain equalization
(2006-03-01)
Wu, JY
;
Lee, TS
;
電信工程研究所
;
Institute of Communications Engineering
This paper proposes a periodic-modulation-based blind channel identification scheme for single-carrier (SC) block transmission with frequency-domain equalization (FDE). The proposed approach relies on the block system model and exploits the circulant channel matrix structure after the cyclic prefix is removed. It is shown that the set of linear equations relating the autocorrelation matrix of the block received signal and the product channel coefficients can be rearranged into one with a distinctive block circulant structure. The identification equations thus obtained lead to a very simple identifiability condition, as well as a natural formulation of the optimal modulating sequence design problem which, based on the block circulant signal structure, can be cast as a constrained quadratic problem that allows for a simple closed-form solution. The impact of the optimal modulating sequence on the peak-to-average power ratio (PAPR) is investigated. Also, it is shown that the optimal sequence results in a consistent channel estimate irrespective of white noise perturbation. Pairwise error probability analysis is used to examine the equalization performance and based on which several design tradeoffs are discussed. Simulation results are used for illustrating the performance of the proposed method.
Preparation and characterization of polystyrene-clay nanocomposites by free-radical polymerization
(2002-08-15)
Tseng, CR
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Wu, JY
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Lee, HY
;
Chang, FC
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應用化學系
The polymerizable cationic surfactant, vinylbenzyldimethylethanolammouium chloride (VBDEAC), was synthesized to functionalize montmorillonite (MMT) clay and used to prepare exfoliated polystyrene-clay nanocomposites. The organophilic MMT was prepared by Na(+) exchanged montmorillonite and ammonium cations of the VBDEAC in an aqueous medium. Polystyrene-clay nanocomposites were prepared by free-radical polymerization of the styrene containing intercalated organophilic MMT. Dispersion of the intercalated montmorillonite in the polystyrene matrix determined by X-ray diffraction reveals that the basal spacing is higher than 17.6 nm. These nanocomposites were characterized by differential scanning calorimetry (DSC), transmission electron micrograph (TEM), thermal gravimetric analysis (TGA), and mechanical properties. The exfoliated nanocomposites have higher thermal stability and better mechanical properties than the pure polystyrene. (C) 2002 Wiley Periodicals, Inc.
Preparation and crystallization behavior of syndiotactic polystyrene-clay nanocomposites
(2001-12-01)
Tseng, CR
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Wu, JY
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Lee, HY
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Chang, FC
;
應用化學系
Syndiotactic polystyrene/modified-clay nanocomposites have been prepared by solution blending by mixing pure s-PS and organophilic clay with adsorbed cetyl pyridium chloride (CPC) in dichlorobenzene. The dispersability of the clay in syndiotactic polystyrene/modified-clay nanocomposites was studied using X-ray and transmission electron microscopy. The clay is well dispersed into the s-PS matrix using solution blending with scale in 1-2 nm or in a few tenths similar to 100 nm depending on surfactant treatment. The CPC is partially compatible with s-PS and allows syndiotactic polystyrene chains intercalating into clay layers. The crystallization behavior of alpha- and beta -crystals for syndiotactic polystyrene nanocomposite has been thoroughly examined using the Fourier transform infrared and differential scanning calorimetry. Our results further demonstrate that the presence of the clay plays a vital role in facilitating the formation on the thermodynamically more favorable beta form crystal when the s-PS is melt- or cold-crystallized. (C) 2001 Elsevier Science Ltd. All rights reserved.
Space-path spreading for high rate MIMO MC-CDMA systems with transmit diversity
(2003)
Deng, JH
;
Wu, JY
;
Lee, TS
;
電信工程研究所
;
Institute of Communications Engineering
A new MIMO transceiver is proposed for the downlink of high data rate multicarrier CDMA (MC-CDMA) systems over frequency-selective multipath channels. The design of the transceiver involves the following procedure. First, the data stream is demultiplexed into multiple substreams, which are then encoded by a set of space time block codes (STBC) for achieving spatial diversity. Second, the coded substreams are spread by a set of "space-path" spreading (SPS) codes which is designed to achieve path multiplexing by exploiting independent multipath channels and pre-suppress the multiple access interference (MAI) without the use of channel state information (CSI). These substreams; are then transmitted simultaneously from multiple antennas. At each mobile station, a simple matched filter (MF) is used to despread the received data. Linearly combining the MF outputs with the aid of CSI and employing a multi-user detection scheme can then separate the mutually interfering signals from the multiple transmit antennas and restore the diversity gain due to SPS and STBC. An increased spectral efficiency and diversity gain can thus be achieved at the same time. Simulation results confirm that the proposed transceiver offers better performance than the conventional BLAST transceiver, and achieves nearly the performance of STBC and space-time spreading BLAST transceiver.
Structures and properties of the SiNC films on Si wafer at different deposition stages
(2001-11-01)
Wu, JY
;
Kuo, CT
;
Liu, TL
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材料科學與工程學系
;
Department of Materials Science and Engineering
The films were deposited on Si wafer by a microwave plasma chemical vapor deposition (MPCVD) system with CH4, N-2, up to 8.3 vol.% HZ and additional Si chips as the sources. The films were examined at different deposition times to explore different growth stages of deposition. Examination indicated the deposition can be roughly divided up to three stages, depending on deposition time and based on their structure and property. In the early deposition stages, the films consist of two layers, i.e. Si-oxide and SiNC layers. The SiNC layer consists essentially of nano-crystals embedded in ternary SiNC amorphous matrix with crystal structure close to SiC. In contrast, in the later stage, the films are further covered by a layer of the binary SiN crystalline phases with crystal structures much closer to alpha -Si3N4 than beta -Si3N4 and tetragonal Si3N4 type structures. The band gaps, as revealed by CL (cathodoluminescence) spectra, are similar to3.88 eV (320 nm) for SiN layer and similar to2.82 eV (440 nm) for SiNC layer. Depending on the deposition conditions, the growth competitions among SiC, Si-N and SiNC crystalline phases may result in different morphologies, compositions and properties of the films. (C) 2001 Elsevier Science B.V All rights reserved.