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Now showing 1 - 10 of 48

An accuracy enhancement algorithm for hierarchical radiosity
(1998-03-01)
Chang, CC
;
Shih, ZC
;
資訊工程學系
;
Department of Computer Science
In this research, we propose an algorithm to enhance the accuracy of the hierarchical radiosity. The proposed approach particularly creates links on the hierarchy in a bottom-up fashion according to both a user-specified error tolerance and the minimum patch area. It differs from the original hierarchical method that creates the links in a top-down manner. In our approach, the upper-level patches have more accurate estimates of the kernel. More accurate error bounds can be obtained for the upper-level patches. These error bounds make the creation of links on the hierarchy more accurate. Furthermore, more accurate form factors can also be obtained for the upper-level patches. Thus, we enhance the accuracy of hierarchical radiosity. (C) 1998 Elsevier Science Ltd. All rights reserved.
Tighter error bounds and weighted error metrics for hierarchical radiosity
(1998-04-01)
Chang, CC
;
Shih, ZC
;
資訊工程學系
;
Department of Computer Science
In this paper we first derive a tighter error bound on form factors as a subdivision criterion for the hierarchical radiosity algorithm. Such an error bound can reduce more unnecessary links and improve the performance of the hierarchical radiosity algorithm to meet a user-specified error tolerance. We then propose a weighted error metric in form factor computation such that more effort is automatically applied to shadow boundaries. Evaluating form factors along shadow boundaries with a higher degree of precision should enhance the quality of human perception. Using the proposed tighter error bound on the weighted error metric, we not only improve the performance but also increase the accuracy of the hierarchical radiosity algorithm. (C) 1998 John Whey & Sons, Ltd.
Elimination of dynamic instabilities in the plus c-face incident photorefractive BaTiO3 mutually pumped phase conjugator
(1999-05-15)
Chang, CC
;
Chen, TC
;
Tang, LC
;
Yau, HF
;
光電工程學系
Experimental observations of the dynamic instabilities in the +c-face incident mutually pumped phase conjugator (MPPC) of a BaTiO3 crystal are reported for the first time. Experiments show that it is possible to stabilize the phase-conjugate output by choosing a proper geometry formed from the crystal and two incident beams. By choosing the proper geometry the essential configuration of the MPPC attained is a "kite" rather than a "fish head". Data also indicate that the phase-conjugate output can reach a very steady state with a high value (similar to 32%) and is insensitive to angular and positional variations.
Navigation integration of a mobile robot in dynamic environments
(1999-07-01)
Song, KT
;
Chang, CC
;
電機資訊學士班
;
Undergraduate Honors Program of Electrical Engineering and Computer Science
This article presents a design and experimental study of navigation integration of an intelligent mobile robot in dynamic environments. The proposed integration architecture is based on the virtual-force concept, by which each navigation resource is assumed to exert a virtual force on the robot. The resultant force determines how the robot will move. Reactive behavior and proactive planning can both be handled in a simple and uniform manner using the proposed integration method. A real-time motion predictor is employed to enable the mobile robot to deal in advance with moving obstacles. A grid map is maintained using on-line sensory data for global path planning, and a bidirectional algorithm is proposed for planning the shortest path for the robot by using updated grid-map information. Therefore, the mobile robot has the capacity to both learn and adapt to variations. To implement the whole navigation system efficiently, a blackboard model is used to coordinate the computation on board the vehicle. Simulation and experimental results are presented to verify the proposed design and demonstrate smooth navigation behavior of the intelligent mobile robot in dynamic environments, (C) 1999 John Wiley & Sons, Inc.
Reliable determination of object pose from line features by hypothesis testing
(1999-11-01)
Chang, CC
;
Tsai, WH
;
資訊工程學系
;
Department of Computer Science
To develop a reliable computer vision system, the employed algorithm must guarantee good output quality. In this study, to ensure the quality of the pose estimated from line features, two simple test functions based on statistical hypothesis testing are defined. First, an error function based on the relation between the line features and some quality thresholds is defined. By using the first test function defined by a lower bound of the error function, poor input can be detected before estimating the pose. After pose estimation, the second test function can be used to decide if the estimated result is sufficiently accurate. Experimental results show that the first test function can detect input with low qualities or erroneous line correspondences and that the overall proposed method yields reliable estimated results.
Reactive navigation in dynamic environment using a multisensor predictor
(1999-12-01)
Song, KT
;
Chang, CC
;
電控工程研究所
;
Institute of Electrical and Control Engineering
A reactive navigation system for an autonomous mobile robot in unstructured dynamic environments is presented. The motion of moving obstacles is estimated for robot motion planning and obstacle avoidance. A multisensor-based obstacle predictor is utilized to obtain obstacle-motion information. Sensory data from a CCD camera and multiple ultrasonic rangefinders are combined to predict obstacle positions at next sampling instant. A neural network, which is trained off-line, provides the desired prediction on-line in real lime. The predicted obstacle configuration is employed by the proposed virtual-force-based navigation method to prevent collision with moving obstacles. Simulation results are presented to verify the effectiveness of the proposed navigation system in an environment with multiple mobile robots or moving objects. This system was implemented and tested on an experimental mobile robot at our laboratory. Navigation results in real environment are presented and analyzed.
Minimization of the life cycle cost for a multistate system under periodic maintenance
(2000-02-01)
Su, CT
;
Chang, CC
;
工業工程與管理學系
;
Department of Industrial Engineering and Management
Although preventive maintenance policies have received extensive interest, limited attention has been paid to implementing multiple maintenance actions for a multistate system over a finite horizon in continuous time. Therefore, this study closely ex-amines such maintenance actions by viewing a coherent multicomponent system as a multistate system and assuming that the necessary maintenance action and cost which move the current state to an extremely better state depends on the current state. The above problem is also formulated as a periodic maintenance model. In addition, the model's characteristics are elucidated to obtain the optimal cycle time of maintenance actions, thereby minimizing the life cycle cost over a specific finite horizon.
A semantic differential study of designers' and users' product form perception
(2000-04-01)
Hsu, SH
;
Chuang, MC
;
Chang, CC
;
應用藝術研究所
;
工業工程與管理學系
This study investigated the differences in the product form perception of designers and users. The semantic differential (SD) method was employed to examine the relationship between the subjects' evaluation of telephone samples and form design elements. The authors used 14 image-word pairs for the evaluation of telephone design. The format for a measurement scale was constructed by a projection method in order to extract design attributes for an SD test. Twenty-four real telephone samples were presented to 40 subjects (20 designers and 20 users) for subjective evaluation. Multivariate analyses were performed to analyze the subject's perceptions and to build conceptual models for telephone design. The result revealed that many differences exist between designers' and users' perceptions of the same real objects and their interpretations of the same image-words. Users are not clear regarding the meaning of the image-words. Moreover, they are very concerned about whether a telephone looks new. Designers tend to value telephone samples with an elegant style while users prefer modern and sleek designs. The conceptual models of the two subject groups are made up of different components. Creative, mature, delicate design images play a greater role in affecting the designers' preference while the users' preference is affected mainly by images of delicacy. The implications of differences in preference and the relationship between image-word and actual design elements for the two subject groups are discussed. Relevance to industry It is the users' needs and preferences, not those of the designers, that should be taken into consideration during the product design process. Due to the fact that many differences exist between designers and users, it is a challenge for designers to transfer the consumer's needs into technical and design specifications. Quantitative data on the relationship between design elements and user evaluations is useful to product designers and managers in formulating design strategies. (C) 2000 Elsevier Science B.V. All rights reserved.
Purification and characterization of neutral sphingomyelinase from Helicobacter pylori
(2000-04-25)
Chan, EC
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Chang, CC
;
Li, YS
;
Chang, CA
;
Chiou, CC
Phospholipase activities of human gastric bacterium, Helicobacter pylori , are regarded as the pathogenic factors owing to their actions on epithelial eel membranes. In this study, we purified and characterized neutral sphingomyelinase (N-SMase) from the superficial components of H. pylori strains for the first time. N-SMase was purified 2083-fold with an overall recovery of 37%. The purification steps included acid glycine extraction, ammonium sulfate precipitation, CM-Sepharose, Mono-Q, and Sephadex G-75 column chromatography. Approximate molecular mass for the native N-SMase was around 32 kDa. When N-omega-trinitrophenylaminol auryl sphingomyelin (TNPAL-SM) was used as a substrate, the purified enzyme exhibited a K-m of 6.7 mu M and a V-max of 15.6 nmol of TNPAL-sphingosine/h/mg of protein at 37 degrees C in 50 mM phosphate-buffered saline, pH 7.4. N-SMase I-caches optimal activity at pH 7.4 and has a pi of 7.5. The enzyme activity is magnesium dependent and specifically hydrolyzed sphingomyelin and phosphatidylethanolamine. The enzyme also exhibits hemolytic activity on human erythrocytes. According to Western blot analysis, a rabbit antiserum against purified N-SMase from H. pylori cross-reacted with SMase from Bacillus cereus. Sera from individuals with H, pylori infection but not uninfected ones recognizing the purified N-SMase indicated that it was produced in vivo. In enzyme linked immunosorbent assays, the purified N-SMase used as an antigen was as effective as crude protein antigens in detecting human antibodies to H. pylori.
Multiaction maintenance subject to action-dependent risk and stochastic failure
(2000-08-16)
Su, CT
;
Wu, SC
;
Chang, CC
;
工業工程與管理學系
;
Department of Industrial Engineering and Management
Although Markov maintenance problems have received extensive attention, relatively few studies have addressed multiple nonreplacement maintenance actions for a multistate system with action-dependent risk and stochastic failure. In this study, we closely examine such multiple maintenance actions by viewing a coherent multicomponent system as a multistate system and assuming that each maintenance action regarding state improvement has a probabilistic risk which is ineffective. The above problem is also modeled as a Markov maintenance problem, demonstrating that the optimal maintenance policy has easily computed and implemented control limit rule. More specially, results in this study confirm the practical nature of the proposed model with respect to its ability than most conventional Markov maintenance models for some particular systems. (C) 2000 Elsevier Science B.V. All rights reserved.

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