Browsing by Author "Yeh, C"

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A reference standard of defect compensation for leather transactions
(2005-06-01)
Yeh, C
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Perng, DB
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工業工程與管理學系
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Department of Industrial Engineering and Management
Defects exist on natural leather surfaces and they usually cannot be eliminated during processing. No international criterion specifies the compensatory counting for calf leather surface defects. So complicated negotiation causes additional cost and argument between suppliers and purchasers. The objective of this article is to establish a compensatory standard of leather defects for finished leather transactions. We start by collecting 170 samples of defective leather and classify the leather defects into seven types. By using digital image processing techniques, we can identify the defects and group nearby defects into a larger scrap area. The area of leather falling into disuse can be calculated. The compensatory standard corresponding to each type of leather defect is then defined. The established compensatory standard for finished leather transactions is evaluated for simulated practical leather transaction. Simulation results showed that the proposed approach is useful and beneficial for practical leather transactions.
Effects of porosity change of gas diffuser on performance of proton exchange membrane fuel cell
(2003-09-15)
Chu, HS
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Yeh, C
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Chen, F
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機械工程學系
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Department of Mechanical Engineering
An investigation is made of the effects of the change of the porosity of the gas diffuser layer (GDL) on the performance of a proton exchange membrane (PEM) fuel cell. The analysis of fuel cell performance with non-uniform porosity of GDL is a necessity because the presence of liquid water in the GDL leads to a non-uniformly distributed porosity in the GDL. To implement this performance analysis, a half-cell model which considers the oxygen mass fraction distribution in the gas channel, the GDL and the catalyst layer, and the current density and the membrane phase potential in the catalyst layer and the membrane is investigated. Four continuous functions of position are employed to describe the porosity, and differential equations are derived based on oxygen transportation and Ohm's law for proton migration and solved numerically. Results show that a fuel cell embedded with a GDL with a larger averaged porosity will consume a greater amount of oxygen, so that a higher current density is generated and a better fuel cell performance is obtained. This explains partly why fuel cell performance deteriorates significantly as the cathode is flooded with water (i.e. to give a lower effective porosity in the GDL). In terms of the system performance. a change in GDL porosity has virtually no influence on the level of polarization when the current density is medium or lower, but exerts a significant influence when the current density is high. This finding supports the scenario proposed by previous studies that the polarization at high current density corresponds mainly to mass transfer through (or the concentration activation of) the membrane assembly. (C) 2002 Elsevier Science B.V. All rights reserved.
Establishing a demerit count reference standard for the classification and grading of leather hides
(2001)
Yeh, C
;
Perng, DB
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工業工程與管理學系
;
Department of Industrial Engineering and Management
Leather hide, as a natural material, may have many types of undesirable surface defects. No analytical method has been devised for classifying and grading wet blue hide surface defects. A high return rate and disputes between the customer and manufacturing company usually cause additional costs. This paper proposes a semi-automatic machine vision method to measure the unusable surface defect areas in wet blue hides and a clear reference standard for the demerit count for graders to classify and grade wet blue hides. A statistical comparative evaluation of the grade deviation rate and a practical demerit count method for tannery performance are given to show the usefulness of the proposed approach.
Identify the centerline of tubular structure in medical images
(2005)
Ching, YT
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Yeh, C
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資訊工程學系
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Department of Computer Science
Finding the centerline of the tubular structure helps to segment or analyze the organs such as the vessels or neuron fibers in medical images. This paper described a semi-automatic method using the minimum cost path finding and Hessian matrix analysis in scale space to calculate the centerline of tubular structure organs. Unlike previous approaches, exhaustive search for tine-like shapes in every scale is prevent. Centerline pixels candidates and the width of the vessel are extracted by analyzing the intensity profile along the gradient vectors in the image. A verification procedure using Hassian matrix analysis with the scale obtained from the gradient analysis is applied to those candidates. Results obtained from the Hessian matrix analysis are used to construct a weighted graph. Finding the minimum cost path in the graph gives the centerline of the tubular structure. The method is applied to find the centerline of the vessels in the 2D angiogram and the neuron fibers in the 3D confocal microscopic images.
Switching level optimization for adaptive modulation
(2004)
Lai, L
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Yeh, C
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Chang, WT
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電信工程研究所
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Institute of Communications Engineering
Two formulations that are commonly used in the determination of the switching levels are the Torrance cost function and the Lagrangian optimization. From the Lagrangian optimization, it can be seen that the switching levels can be each separately related to the target bit error rate with the constraint that the average bit error satisfies the target bit error requirement. This provides a search direction for the optimum solution of the Torrance formulation. Also, it is verified that if the target bit error is neglected, the Torrance formulation can find the optimum solution for the possible lowest bit error rate. In this case, each switching level is only related to two adjacent modulation modes. Based on this relation, we approximate the Torrance formulation with a two-mode one-dimensional search problem. From this decomposition, we further develop a one mode cost function to evaluate the cost of using one specific modulation mode as a function of instantaneous SNR. Switching levels can be determined by simply comparing these one mode cost function.