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收集所有交通大學研究人員與學生個人或團體所發表之各項學術著作，涵蓋期刊論文、教師專書、學位論文等項。;;Collections of Publications of NCTU Researchers and Students Like Journal Papers and Thesis.

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Now showing 1 - 10 of 12

A video information system for sport motion analysis
(1997-06-01)
Chang, CW
;
Lee, SY
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資訊科學與工程研究所
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Institute of Computer Science and Engineering
In this paper, we present several important methods in a video information system for sport motion analysis. We first describe an efficient method for computing the position of one or more moving objects in a video sequence. We utilize computer vision routines for both target object tracking and feature value extraction. Then, we propose a multiple subsequence matching mechanism for comparing the difference in object motion between two video sequences. A mapping function, penalty table and the overall distance between two video sequences have been defined. We use the prominent feature points as our segmentation positions and separate the sequence into several subsequence groups. After an alignment process, we can find the mapping of the best matching and get an evaluation report between the two video sequences for motion analysis. The video information system described in this paper has successfully analysed several examples of sport motion, and is representative of techniques commonly used in practice. (C) 1997 Academic Press Limited.
Automatic cel painting in computer-assisted cartoon production using similarity recognition
(1997-07-01)
Chang, CW
;
Lee, SY
;
資訊科學與工程研究所
;
Institute of Computer Science and Engineering
The task of painting each eel of an animated sequence has always been a tedious work using traditional methods. In order to simplify and speed up the process, the development of an automatic eel painting system is desired. This paper presents a method for assisting the production of cartoon animation using computers in order to reduce the production expense and to improve the overall quality. It signals a great improvement in the working environment where 2-D animation Is produced. The basic idea of our automatic eel painting mechanism is to extract both statistical and topological features of regions from input animation drawings, and to search for similar corresponding regions in the previous drawing, If the similarity measures are within the accepted thresholds, the corresponding colour will be inherited. A new integrated labelling algorithm constructing statistical region and topological graph features is proposed. Furthermore, a similarity measure of regions is defined and an algorithm of partial matching of attribute graphs is presented. The experimental result shows the feasibility and practicability of the proposed approach. (C) 1997 by John Wiley & Sons, Ltd.
Determination of dynamic elastic constants of transversely isotropic rocks using a single cylindrical specimen
(1997-10-01)
Liao, JJ
;
Hu, TB
;
Chang, CW
;
土木工程學系
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Department of Civil Engineering
A new experimental procedure and its associated interpretation theories are proposed to determine the five dynamic elastic constants of a transversely isotropic rock. Using Christoffel's equations, the elastic constants can be uniquely determined based on ultrasonic wave velocity measurements on a single cylindrical specimen. The new method requires that the orientation of planes of elastic symmetry by parallel to its longitudinal axis. The wave velocity measuring devices (i.e. transducers) can be mounted on the sides or ends of the specimen. The new method has been implemented in the laboratory on a transversely isotropic rock, argillite. Wave velocity measurements were taken on specimens with and without a tensile load applied at the ends. Consistent results were obtained in both cases. This paper describes details of the analytical background and the proposed experimental procedure. Available test results are presented to demonstrate the efficacy of the new method. (C) 1997 Elsevier Science Ltd.
Femtosecond fluorescence dynamics of trans-azobenzene in hexane on excitation to the S-1(n,pi*) state
(2002-10-01)
Lu, YC
;
Chang, CW
;
Diau, EWG
;
應用化學系
;
Department of Applied Chemistry
Femtosecond fluorescence dynamics of trans-azobenzene in hexane have been investigated on excitation to the S-1(n,pi*) state at 432 nm using the up-conversion technique. Two transient components were observed to represent the fast and the slow S-1 fluorescence dynamics in the wavelength range of 550-732 nm. Based on the results obtained from recent ab initio calculations (Ishikawa, T.; Noro, T.; Shoda, T., J. Chem. Phys. 2001, 115, 7503), a dynamical picture is given in the following. Upon initial excitation to the S, state, the excited molecule is moving away from the first detection window within the observed 200-300 fs. The structural relaxation from the Franck-Condon region may be responsible for the observed fast S-1 dynamics with the driving force being the CNNC twisting motion along the rotational coordinate. For the rest of the motion on the S-1 global potential surface, the excited molecule may search for the S-0/S-1 conical intersection for an efficient internal conversion to the ground state. The nuclear motions for the observed slow S-1 dynamics not only involve the CNNC torsional coordinate but also the other degrees of freedom such as the CNN bending coordinate on the multidimensional S-1 potential energy surface. The whole electronic relaxation process occurs within the observed 1-2 ps. The slow S-1 dynamics were found to vary with the fluorescence wavelengths due to the influence of the solvent-induced vibrational relaxation in the S-1 state; the vibrational relaxation should occur on a time scale comparable to the time scale of the electronic relaxation (S-1-->S-0 internal conversion).
Resolution of the inversion-rotation controversy of azobenzene in solution via femtosecond fluorescence anisotropy on S1 excitation.
(2004-08-22)
Diau, EWG
;
Chang, CW
;
應用化學系
;
應用化學系分子科學碩博班
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Department of Applied Chemistry
Image Smoothing of liquid crystal display by a high-efficiency grating
(1999)
Chang, CW
;
Ko, FJ
;
Shieh, HPD
;
光電工程學系
;
Department of Photonics
The black matrix of Liquid Crystal Displays (LCDs) degrades image quality of projection system and Head Mount Displays (HMDs) by appearing as dark boundaries around each pixel. Therefore, an image smoothing technique is required to suppress these boundaries. With proposed image smoothing grating, not only the horizontal but also vertical parts of black matrix fade away into the first order diffraction beams. Moreover, the contrast of the smoothed image is close to the original value, because the second order beams can be designed to be negligible.
Error statistics of closed-loop power control in multirate DS-CDMA cellular systems
(2002)
Wang, LC
;
Chang, CW
;
電信工程研究所
;
Institute of Communications Engineering
In this paper, we investigate the error statistics of the close-loop power control scheme with variable spreading factors for the multi-rate services in the third generation wideband CDMA (WCDMA) system. We demonstrate that the long scrambling pseudo-noise code, besides its well known feature in differentiating users and base stations, can improve power control false command over a frequency-selective fading channel as well. Our computer simulation results indicate that the SIR measurement error can be reduced by 3 dB in a typical case, and the power control false command can be reduced from 27 % to 10 % in comparison to using pure short Walsh codes. It will be shown that the close-loop power control error is a composite function of spreading factor, target E-b / N-o and Doppler frequency. The statistics of closed loop power control false command can be easily characterized by a Bernoulli distribution with a parameter provided by our results.
Impact of measurement errors on the closed loop power control for CDMA systems
(2003)
Wang, LC
;
Chang, CW
;
交大名義發表
;
National Chiao Tung University
In this paper we present a simple analytical model to evaluate the impact of measurement errors on the closed-loop power control for code division multiple access (CDMA) systems. By introducing a new performance measurement, the probability of false command in power control, P-FC, a closed form formula for calculating P-FC with consideration of measurement errors is presented. Furthermore, we drive a bit error rate (BER) performance bound in terms of P-FC for the CDMA system with the closed-loop power control (CLPC). The proposed analytical approach can quantitatively evaluate the performance of the CLPC taking into account of the effects of measurement errors and Doppler frequency under a Rayleigh fading channel. Through simulation and analysis, we show that the proposed analytical BER bound can accurately estimate the BER performance of the CLPC under the impact of measurement errors. Interestingly, we find that the CLPC is less sensitive to measurement errors due to the non-linear operation in the one step up/down power control scheme compared with the variable-step size power control.
Gap-processing time analysis of stall avoidance mechanisms for high speed downlink packet access with parallel HARQ schemes
(2005)
Wang, LC
;
Chang, CW
;
電信工程研究所
;
Institute of Communications Engineering
The parallel multi-channel stop-and-wait (SAW) hybrid. automatic repeat request (HARQ) mechanism is one of key technologies for high speed downlink packet access in the wideband code division multiple access system. However, this parallel HARQ mechanism may encounter a serious stall problem, resulted from the error of the negative acknowledgement (NACK) changing to the acknowledgement (ACK) in the control channel. In the stall situation, the receiver waits for a packet that will be no longer sent by the transmitter and stops delivering the medium access control (MAC) layer packets to the upper layer. The stall issue seriously degrades the quality of service for the high speed mobile terminal owing to the high probability of NACK-to-ACK errors. In this paper, we present an analytical approach to compare three stall avoidance schemes: the timer-based, the window-based, and the indicator-based schemes. To this end, we first define a new performance metric - the gap-processing time the duration for a nonrecoverable gap appearing in the MAC layer re-ordering buffer until it is recognized. Second, we derive the closed-form expressions for the average gap-processing time of these three stall avoidance schemes. It will be shown that our analytical results match the simulations well. Further, by analysis we demonstrate that the indicator-based stall avoidance scheme outperforms the. timer-based and the window-based schemes. The developed analytical approaches provide important insight into determining a proper number of processes in the parallel SAW HARQ mechanism when applying the indicator-based stall avoidance scheme. Moreover, our analysis can facilitate the physical/MAC/radio link control cross-layer design because the gap-processing time is closely related to packet error rate in the physical layer, reordering buffer size in the MAC and RLC layer.
Gap-processing time analysis of an indicator-based stall avoidance mechanism for high speed downlink packet access
(2005)
Wang, LC
;
Chang, CW
;
Chang, CJ
;
電信工程研究所
;
Institute of Communications Engineering
For supporting high speed downlink packet access (HSDPA) in the wideband code division multiple access (WCDMA) system, an indicator-based stall avoidance mechanism was recently proposed to remove the nonrecoverable gap in the received out-of-sequence packets. The stall of delivering medium access control (MAC) layer data to the upper layer is a serious problem when a negative acknowledgement (NACK) control signal becomes an acknowledgement (ACK) signal in the multiprocess stop-and-wait (SAW) hybrid automatic repeat request (HARQ) mechanism. This paper presents an analytical model to calculate the gap-processing time of the indicator-based stall avoidance mechanism. Instead of time-consuming simulations, the gap-processing time of the indicator-based stall avoidance in the multi-process SAW HARQ mechanism in the HSDPA system can be calculated easily by the proposed method for different packet error rates, various numbers of allowable users, and different numbers of parallel processes in the SAW HARQ mechanism. Numerical results are performed in a Rayleigh fading channel to demonstrate the effectiveness of the proposed method in understanding the performance tradeoffs of the multi-process HARQ mechanism in HSDPA.

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