Browsing by Issue Date, starting with "2001-04-01"

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Luminescence intensity reduction in Mg-doped GaN grown by metalorganic chemical vapor phase epitaxy
(2001-04-01)
Shu, CK
;
Chen, HH
;
Lee, WH
;
Pan, YC
;
Huang, HY
Photoluminescence dynamic responses of a heavily Mg-doped GaN grown by metalorganic chemical vapor phase epitaxy have been investigated. As the probe power density increased from 2.5 to 925 W/cm(2), a Mg-related emission band shifted from 2.82 to 3.16 eV revealing characteristics of donor-acceptor pair recombination. The intensity evolution also showed slow decay that suggests the metastable emission behavior. A simple potential barrier model was proposed to occur between the Mg related deep levels and common Mg acceptor level, which impedes electron relaxation and thus slows down the luminescence decay. From the variation of decay time constant with temperature. a barrier energy was deduced to be about 69 meV which is very close to the electrical result of 68 meV.
Numerical and experimental study of internal flow field for a carbon fiber tow pneumatic spreader
(2001-04-01)
Chen, JC
;
Chao, CG
;
材料科學與工程學系
;
Department of Materials Science and Engineering
In this study, a three-dimensional (3-D) mathematical model of a fiber pneumatic spreader was successfully developed in the physical phenomena of the internal flow field by a far-field treatment at boundary conditions. The 3-D numerical analysis was carried out on incompressible fluid flows in the pneumatic spreader by using finite volume method combined with the k-epsilon turbulence model which solves Reynolds-averaged Naiver-Stokes equations. Characteristics of the flow field in the spreader at different service conditions are investigated by velocity and pressure distributions. Comparisons of numerical results with measured velocity and pressure distributions were made to determine the accuracy of the employed method. A good agreement was found in both qualitative and quantitative analysis. Fibers were spread on 1:1-scale model of the pneumatic spreader at various fiber transporting rates and air flow rates. Photography techniques were simultaneously used to record the procedures of fibers spread. The carbon fiber tow was easily spread out at service conditions. The performance was better than prior studies in one-dimensional orifice formulation. The results revealed details of the fiber spreading processes. Agreement among those results validated the assumptions inherent to the computational calculation and gave confidence to more complex geometries as well as flow fields. In other words, the use of numerical analysis in the internal flow field was useful for the fiber pneumatic spreader design.
Possibilistic programming in production planning of assemble-to-order environments
(2001-04-01)
Hsu, HM
;
Wang, WP
;
工業工程與管理學系
;
Department of Industrial Engineering and Management
For the sake of alleviating the influences of demand uncertainty in assemble-to-order (ATO) environments, the strategies of regulating dealers' forecast demands, determining appropriate safety stocks, and deciding the numbers of key machines are usually adopted by manufacturers. In this paper, we propose a possibility linear programming model to manage these production planning problems. The proposed model accomplishes forecasting adjustments, material management, and production activities. Because of price fluctuations, material obsolescence, and the time value of, capital. the ambiguity of cost is considered in the objective function of the model. We substituted the fuzzy objective function with three crisp objectives: minimizing the most possible cost, maximizing the possibility of obtaining lower cost, and minimizing the risk of obtaining higher cost. Zimmermann's fuzzy programming method is then applied for achieving an overall satisfactory compromise solution. Finally, an example is given to illustrate our model. (C) 2001 Elsevier Science B.V. All rights reserved.
Integration of thin film transistor controlled carbon nanotubes for field emission devices
(2001-04-01)
Cheng, HC
;
Hong, WK
;
Tarntair, FG
;
Chen, KJ
;
Lin, JB
A new field emission device composed of carbon nanotubes and a thin film transistor (TFT) has been successfully demonstrated to significantly improve emission stability. Carbon nanotubes are directly integrated in the drain region of the TFT and the emission current from the carbon nanotubes is controlled via the TFT drain current. The fluctuation of the emission current of the TFT-controlled carbon nanotubes can be suppressed to less than 2%, below the fluctuation of uncontrolled carbon nanotubes. The novel field emission device exhibits low-voltage controllability, good emission stability, and structural simplicity, making it promising for application to future field-emission display. (C) 2001 The Electrochemical Society.
A framework for temporal similarity measures of content-based scene retrieval
(2001-04-01)
Shan, MK
;
Lee, SY
;
資訊科學與工程研究所
;
Institute of Computer Science and Engineering
The distinguished features of video retrieval lie in the similarity measures and content-based retrieval. Most research on content-based video retrieval represents the content of video as a set of frames, leaving out the temporal ordering of frames in the shot. In this paper, the similarity measures of video content are investigated. We propose a series of similarity measures based on the similarity of frame sequence which take temporal ordering into consideration. All the algorithms corresponding to the similarity measures are based on the approach of dynamic programming. (C) 2001 Published by Elsevier Science B.V.
Ordered lookup with bypass matching for scalable per-flow classification in layer 4 routers
(2001-04-01)
Lin, YD
;
Wei, HY
;
Wu, KJ
;
資訊工程學系
;
Department of Computer Science
In order to provide different service treatments to individual or aggregated hows, layer 4 routers in Integrated Services networks need to classify packets into different queues. The classification module of layer 4 routers must be fast enough to support gigabit links at a rate of millions of packets per second. In this work, we present a new software method OLBM to lookup multiple fields of a packet, in a dynamically pre-defined order, against the classification database. This algorithm also uses a technique called bypass matching and can classify packets at a rate of well over one million packets per second while scaling to support more than 300k flows. Complexity analysis and experiment measurements are also presented in this study. (C) 2001 Elsevier Science B.V. All rights reserved.
On-chip ESD protection design by using polysilicon diodes in CMOS process
(2001-04-01)
Ker, MD
;
Chen, TY
;
Wang, TH
;
Wu, CY
;
電子工程學系及電子研究所
A novel on-chip electrostatic discharge (ESD) protection design by using polysilicon diodes as the ESD clamp devices in CMOS process is first proposed in this paper, Different process splits have been experimentally evaluated to find the suitable doping concentration for optimizing the polysilicon diodes for both on-chip ESD protection design and the application requirements of the smart-card ICs. The secondary breakdown current (It2) of the polysilicon diodes under the forward- and reverse-bias conditions has been measured by the transmission-line-pulse (TLP) generator to investigate its ESD robustness, Moreover, by adding an efficient VDD-to-VSS clamp circuit into the IC, the human-body-model (HBM) ESD robustness of the IC with polysilicon diodes as the ESD clamp devices has been successfully improved from the original similar to 300 V to become greater than or equal to3 kV, This design has been practically applied in a mass-production smart-card IC.
Analysis and DSP implementation of a broadband duct ANC system using spatially feedforward structure
(2001-04-01)
Bai, MR
;
Lin, YJ
;
機械工程學系
;
Department of Mechanical Engineering
The active control technique for broadband attenuation of noise in ducts, using spatially feedfoward structure. is investigated from the viewpoints of both acoustic analysis and exists an ideal controller for this problem. The ideal controller is a function of the finite control engineering. According to the previous work by Munjal and Eriksson [1], there source impedance and is thus independent of the boundary conditions. Despite the simplicity the ideal controller cannot be practically implemented due to the difficulty of calibration of electro-mechanical parameters. To overcome the problem, the controller is implemented via an equivalent formulation modified from the controller originally proposed by Roure [2]. The modified controller is implemented on a DSP platform, using a FIR filter, an IIR filter and a hybrid filter. The experimental results showed that the system achieved 17.2 dB maximal attenuation in the frequency band 300 similar to 600 Hz. Physical insights and design considerations in implementation phase are also discussed in the paper.
A beamspace-time blind RAKE receiver for sectored CDMA systems
(2001-04-01)
Lee, TS
;
Tsai, TC
;
Chen, CH
;
電信工程研究所
;
友訊交大聯合研發中心
A beamspace-time (BT) RAKE receiver is proposed for multiple access interference (MAT) suppression and multipath diversity reception in sectored wireless CDMA communications. The scheme involves three stages. First, a set of adaptive beamformers encompassing a prescribed angular sector is constructed on an antenna array, each providing effective suppression of out-of-sector MAI and reception of in-sector signal. Second, a set of adaptive correlators is attached to each beam to combat in-sector MAI. Finally, the beamspace correlator output data are combined to capture the signal multipaths coherently. The above three-stage operation is performed in a blind mode in that no training signal is needed. The only information required is the signature, timing and a rough estimate of the angle of arrival (AOA) of the desired signal.
Analysis and design of large leaky-mode array employing the coupled-mode approach
(2001-04-01)
Hu, CN
;
Tzuang, CKC
;
電信工程研究所
;
Institute of Communications Engineering
This paper presents the coupled-mode approach to the analysis and design of a large leaky-mode array, in which an N-element microstrip array above a common ground plane supports N coupled leaky modes (leaky EH1 modes) at the first higher order, Following a brief description of a conventional full-wave nonstandard eigenvalue problem for solving the complex propagation constants, we present the detailed formulation of the coupled-mode approach, clearly showing the transformation of the nonstandard eigenvalue problem into a standard one. Thus, all the eigenvalues (complex propagation constants) and eigenvectors (modal current distributions) are solved simultaneously, regardless of the size of the array (N). Two key issues pertinent to the successful implementation of the proposed coupled-mode approach are addressed: the determination of the coupling coefficients and the uniqueness of the isolated uncoupled leaky mode, which represents the leaky modal solution of a single microstrip, but is derived from a system of coupled leaky-mode solutions provided the coupled microstrips have equal width and spacing, Closed-form expressions for obtaining the coupling coefficients of orders two, three, and four are presented. Theoretical studies of closely coupled microstrip arrays of two, three, and four elements show that the magnitude of the coupling coefficient C-i,C-i+j between elements i and i + j decreases at the order of 10(-j). These theoretical case studies also lead to the same isolated uncoupled leaky-mode solution as predicted. Furthermore, the dispersion characteristics of the microstrip array at the first higher order obtained by the coupled-mode approach and the full-wave approach agree excellently for all the case studies, Error analyses indicated that at least two coupling coefficients (C-i,C-i+1 and C-i,C-i+2) are required for obtaining accurate complex propagation constants with rms errors less than 1% for most of the leaky region of the particular array under investigation. An example of applying the proposed coupled-mode approach for analyzing a corporate-fed leaky-mode array of eight elements is reported, revealing that only four out of the eight leaky modes are excited. The coupled-mode theory predicts the far-field radiation pattern in the main beam region in excellent agreement with the measured results.
Low cost CMOS on-chip and remote temperature sensors
(2001-04-01)
Weng, MC
;
Wu, JC
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
This paper describes the design and results of low cost integrated CMOS local and remote temperature sensors with digital outputs. No trimming is needed to obtain good temperature linearity, so that only one-temperature calibration is needed which greatly reduces testing cost. The base-emitter voltage of the parasitic substrate bipolar transistor is used to measure the local temperature. A diode-connected external bipolar transistor is used to measure the remote temperature. Chopper techniques were used to cancel the offset voltage of the op-amp, so that a precise bandgap voltage call be obtained without resistance trimming. A first order Sigma Delta ADC was used to produce the digital output. The local and remote temperature sensors were realized in a 0.6 mu cm single-poly triple-metal CMOS technology with active area of 0.61 nm(2) and 0.65 mm(2), respectively. After calibration, the error is +/-1 degreesC for the local temperature sensor over the temperature range of -20 to 130 degreesC, and +/-2 degreesC for tile remote temperature sensor over the range of 0 to 120 degreesC. The supply currents of tile local and remote temperature sensors are 3.5 muA and 38 muA at 8 samples/s, respectively.
Approaches to tacamonine.
(2001-04-01)
Ho, TL
;
Su, CY
;
Gorobets, E
;
應用化學系
;
Department of Applied Chemistry
Sidelobe suppression of spectral response in holographic optical filter
(2001-04-01)
Zajtsev, AK
;
Lin, SH
;
Hsu, KY
;
電子物理學系
;
光電工程學系
In order to suppress sidelobes of holographic filter's spectral response we propose to use weighting of grating intensity distribution along light propagation. This can be realized in photorefractive material (for example in LiNbO3:Fe) by using spatial selective decaying of conventional uniform grating by illumination of light through some transparent mask. Experimental results show that it is able to obtain 8 dB improvement of sidelobe level compared to uniform grating. But it is accompanied by 1.7 times expansion of main lobe and two times decrease of diffraction efficiency. (C) 2001 Elsevier Science B.V. All rights reserved.
Schottky barrier thin-film transistor (SBTFT) with silicided source/drain and field-induced drain extension
(2001-04-01)
Lin, HC
;
Yeh, KL
;
Huang, RG
;
Lin, CY
;
Huang, TY
A novel Schottky barrier thin-film transistor (SBTFT) with silicided source/drain and field-induced drain (FID) extension is proposed and demonstrated. In the new device configuration, a metal field-plate (or sub-gate) lying on the passivation oxide is employed to induce a sheet of carriers in a channel offset region located between the silicided drain and the active channel region underneath the main-gate. The new device thus allows ambipolar device operation by simply switching the polarity of the bias applied to the field plate. In contrast to the conventional SBTFT that suffers from high GIDL (gate-induced drain leakage)-like off-state leakage current, the new SBTFT with FID is essentially free from the GIDL-like leakage current. In addition, unlike the conventional SBTFT that suffers from the low on-off current ratio, the new device exhibits high on/off current ratio up to 10(6) for both n- and p-channel modes of operation. Moreover, the implantless feature and the ambipolar capability of the new device also result in extra low mask count for CMOS processes integration. These excellent device characteristics, coupled with its simple processing, make the new device very promising for future large-area electronic applications.
Providing service differentiation in wireless networks
(2001-04-01)
Lee, CL
;
Chen, YC
;
Chen, JR
;
資訊工程學系
;
Department of Computer Science
Differentiated services: (Diffserv) model is one of the possible solutions for providing quality of service (QoS) on the Internet. Most existing approaches assume that the packet loss is an indication of network congestion and thus reduce the sending rates: of sources. For wireless networks, the assumption is not proper since packet losses may he caused by other reasons, such as fading and interference of the signal. Therefore, these approaches do not work well in wireless networks. In this paper, we propose an approach which is able to provide service differentiation in wireless environments. In our approach, the rate share of a connection is determined by the associated weight. By keeping a proper amount of extra data in the network, the proposed approach can achieve weighted proportional fairness, which can provide selective QoS without any particular support, from the network. We use the ns simulator to evaluate our approach. Simulation results show the validity of the proposed approach.
Effect of temperature and illumination on the instability of a-Si : H thin-film transistors under AC gate bias stress
(2001-04-01)
Huang, CY
;
Teng, TH
;
Yang, CJ
;
Tseng, CH
;
Cheng, HC
This work investigates the temperature and illumination effects on the a-SM thin-film transistors (a-SiH TFTs) under AC gate bias stress to find the larger threshold voltage shift and subthreshold swing change for the bias-temperature-stress (BTS) and bias-illumination-stress (BIS). Excess carriers from thermal-generation electron-hole pairs or photoexcited electron-hole pairs may significantly influence the instability of a-SM TFTs during bias stress. The instability mechanisms originate from the carrier-induced defect Creation enhanced by thermal generation in the BTS case and also emphasized by photoexcitation for the BIS case. Both stress conditions will induce a larger threshold voltage shift and higher cutoff frequency than those for simple bias stresses.
Unsupervised fuzzy neural network structural active pulse controller
(2001-04-01)
Hung, SL
;
Lai, CM
;
土木工程學系
;
Department of Civil Engineering
Applying active control systems to civil engineering structures subjected to dynamic loading has received increasing interest. This study proposes an active pulse control model, termed unsupervised fuzzy neural network structural active pulse controller (UFN-SAP controller), for controlling civil engineering structures under dynamic loading. The proposed controller combines an unsupervised neural network classification (UNC) model, an unsupervised fuzzy neural network (UFN) reasoning model, and an active pulse control strategy. The UFN-SAP controller minimizes structural cumulative responses during earthquakes by applying active pulse control forces determined via the UFN model based on the clusters, classified through the UNC model, with their corresponding control forces. Herein, we assume that the effect of the pulses on structure is delayed until just before the next sampling time so that the control force can be calculated in time, and applied. The UFN-SAP controller also averts the difficulty of obtaining system parameters for a real structure for the algorithm to allow active structural control. Illustrative examples reveal significant reductions in cumulative structural responses, proving the feasibility of applying the adaptive unsupervised neural network with the fuzzy classification approach to control civil engineering structures under dynamic loading. Copyright (C) 2001 John Wiley & Sons, Ltd.
Forced symmetry-breaking via boundary conditions
(2001-04-01)
Mei, Z
;
Shih, CW
;
應用數學系
;
Department of Applied Mathematics
Shape matching and recognition using a physically based object model
(2001-04-01)
Chuang, JH
;
Sheu, JF
;
Lin, CC
;
Yang, HK
;
資訊工程學系
We present a novel approach of shape matching and recognition of 3D objects using artificial potential fields. The potential model assumes that boundary of every 3D template object of identical Volume is uniformly charged. An initially small input object placed inside a template object will experience repulsive force and torque arising from the potential field. A better match in shape between the template object and the input object can be obtained if the input object translates and reorients itself to reduce the potential while growing in size. The template object which allows the maximum growth of the input object corresponds to the best match and thus represents the shape of the input object. The above repulsive force and torque are analytically tractable for an input object represented by its boundary samples. which makes the shape matching efficient. The proposed approach is intrinsically invariant under translation: rotation and size changes of the input object. (C) 2001 Elsevier Science Ltd. All rights reserved.
Low dielectric polyimide/poly(silsesquioxane)-like nanocomposite material
(2001-04-01)
Tsai, MH
;
Whang, WT
;
材料科學與工程學系
;
Department of Materials Science and Engineering
A new type of low dielectric polyimide/poly(silsesquioxane)-like (PI/PSSQ-like) hybrid nanocomposite material is successfully prepared from the polyimide (ODA-ODPA) precursor containing phenyltrialkoxysilane IPTS) at two chain ends and monoaryltrialkoxysilane with a self-catalyzed sol-gel process. We employ p-aminophenyltrimethoxysilane (APTS) to provide bonding between the PTS and ODPA-ODA phase, It is shown by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) that the PSSQ-like domain sizes with uniform size are fairly well separated in the hybrid films. The silica domain sizes of 5000-PIS and 5000-PIS-50-PTS films are in the range of 30-100 nm, of 5000-PIS-100-PTS and 10000-PIS-100-PTS in the range of 80-200 and 300-600 nm, respectively. The dielectric constant can be 2.79 for 5000-PIS-140-PTS with fairly good mechanical properties. The PI/PSSQ-like hybrid films have higher onset decomposition temperature and char yield in thermogravimetric analysis (TGA) and higher T-g in differential scanning calorimetry (DSC) than the pure PI. Moreover, the PI/PSSQ-like hybrid films have excellent transparency even under high PTS content. In the series of X-PIS hybrid films, the coefficient of thermal expansion (CTE) below T-g increases with the PI block chain length, but in the series of X-PIS-y-PTS films, it slightly increases with the PTS content. However, above T-g the CTE of X-PIS and X-PIS-24-PTS is much lower than that of the pure PI. The dielectric constant and water absorption of X-PIS-V-PTS films decrease with the PTS content because of the higher free volume and hydrophobicity. (C) 2001 Elsevier Science Ltd. All rights reserved.