Browsing by Author "Chen, HM"

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Design of nearest neighbor classifiers: multi-objective approach
(2005-07-01)
Chen, JH
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Chen, HM
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Ho, SY
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生物資訊及系統生物研究所
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Institude of Bioinformatics and Systems Biology
The goal of designing optimal nearest neighbor classifiers is to maximize classification accuracy while minimizing the sizes of both reference and feature sets. A usual way is to adaptively weight the three objectives as an objective function and then use a single-objective optimization method for achieving this goal. This paper proposes a multi-objective approach to cope with the weight tuning problem for practitioners. A novel intelligent multi-objective evolutionary algorithm IMOEA is utilized to simultaneously edit compact reference and feature sets for nearest neighbor classification. Three comparison studies are designed to evaluate performance of the proposed approach. It is shown empirically that the IMOEA-designed classifiers have high classification accuracy and small sizes of reference and feature sets. Moreover, IMOEA can provide a set of good solutions for practitioners to choose from in a single run. The simulation results indicate that the IMOEA-based approach is an expedient method to design nearest neighbor classifiers, compared with an existing single-objective approach. (c) 2005 Elsevier Inc. All rights reserved.
Efficient gene selection for classification of microarray data
(2005)
Ho, SY
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Lee, CC
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Chen, HM
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Huang, HL
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生物資訊及系統生物研究所
Microarray is a useful technique for measuring expression data of thousands of genes simultaneously. One of challenges in classification of microarray data is to select a minimal number of relevant genes which can maximize classification accuracy. Many gene selection methods as well as their corresponding classifiers have been proposed. One of existing analysis methods is the hybrid approach based on genetic algorithm and maximum likelihood classification (GA/MLHD). In this paper, an intelligent genetic algorithm (IGA) using control genes and an improved fitness function is proposed to determine the minimal number of relevant genes and identify these genes, while maximizing classification accuracy simultaneously. The experimental results show that our approach is superior to the existing method GA/MLHD in terms of the number of selected genes, classification accuracy, and robustness of selected genes and accuracy, especially for the datasets which have numerous categories and a large number of testing genes inside.
I/O clustering in design cost and performance optimization for flip-chip design
(2004)
Chen, HM
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Liu, IM
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Wong, MDF
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Shao, MZ
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Huang, LD
I/O placement has always been a concern in modern IC design. Due to flip-chip technology, I/O can be placed throughout the whole chip without long wires from the periphery of the chip. However, because of I/O placement constraints in design cost and performance, I/O buffer planning becomes a pressing problem. During the early stages of circuits and packaging co-design, I/O layout should be evaluated to optimize design cost and to avoid product failures. In this paper, our objective is to better an existing/initial standard cell placement by I/O clustering, considering design cost reduction and signal integrity preservation. We formulate it as a minimum cost flow problem minimizing alphaW + betaD, where W is the I/O wirelength of the placement and D is the total voltage drop in the power network. The experimental results on some MCNC benchmarks show that our method achieves better timing performance and averagely over 30% design cost reduction when compared with the conventional design rule of thumb popularly used by circuit designers.
Persistent photoconductivity in n-type GaN
(1997-07-15)
Chen, HM
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Chen, YF
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Lee, MC
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Feng, MS
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材料科學與工程學系
Results of photoconductivity measurements in undoped n-type and Se-doped GaN epitaxial thin films are presented. Similar to the photoluminescence spectra, the photoconductivity also shows a broad yellow band centered around 2.2 eV. It is found that persistent photoconductivity (PPC) does exist in all the studied thin films. In addition, the PPC effects can be observed for the pumping photon energy down to the yellow band. The results reveal that the origin of the PPC effect and yellow luminescence may arise from the same intrinsic defect. It is shown that the most probable candidate of the intrinsic defect is nitrogen antisite. (C) 1997 American Institute of Physics.
Scoring method for tumor prediction from microarray data using an evolutionary fuzzy classifier
(2006)
Ho, SY
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Hsieh, CH
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Chen, KW
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Huang, HL
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Chen, HM
In this paper, we propose a novel scoring method for tumor prediction using an evolutionary fuzzy classifier which can provide accurate and interpretable information. The merits of the proposed method are threefold. 1) The score ranged in [0, 100] can further illustrate the degree of tumor status in contrast to the conventional tumor classifier. 2) The derived score system can be used as a tumor classifier using a system-suggested or human-specified threshold value. 3) The derived classifier with a compact fuzzy rule base can. generate an interpretable and accurate prediction result. The effectiveness of the proposed method is evaluated and compared using two well-known datasets from microarray data and an existing tumor classifier. It is shown by computer simulation that the proposed scoring method is effective using ROC curves of classification.
Simultaneous power supply planning and noise avoidance in floorplan design
(2005-04-01)
Chen, HM
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Huang, LD
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Liu, IM
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Wong, MDF
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電子工程學系及電子研究所
With today's advanced integrated circuit manufacturing technology in deep submicron (DSM) environment, we can integrate entire electronic systems on a single system on a chip. However, without careful power supply planning in layout, the design of chips will suffer from local hot spots, insufficient power supply, and signal integrity problems. Postfloorplanning or postroute methodologies in solving power delivery and signal integrity problems have been applied but they will cause a long turnaround time, which adds costly delays to time-to-market. In this paper, we study the problem of simultaneous power supply planning and noise avoidance as early as in the floorplanning stage. We show that the problem of simultaneous power supply planning and noise avoidance can be formulated as a constrained maximum flow problem and present an efficient yet effective heuristic to handle the problem. Experimental results are encouraging. With a slight increase of total wirelength, we achieve almost no static IR (voltage)-drop requirement violation in meeting the current and power demand requirement imposed by the circuit blocks compared with a traditional floorplanner and 45.7% of improvement on a Delta I noise constraint violation compared wit the approach that only considers power supply planning.
Yellow luminescence in n-type GaN epitaxial films
(1997-09-15)
Chen, HM
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Chen, YF
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Lee, MC
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Feng, MS
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材料科學與工程學系
Photoluminescence, resonant Raman scattering, and photoconductivity measurements have been employed to study the yellow; emission in undoped n-type and a set of Se-doped GaN epitaxial films. It is best described by a transition from the conduction-band edge to a deep acceptor. Unlike the donors and accepters used in most previous studies that substitute Ga sires, Se atoms can replace N sites. With this unique fact, we identify that the origin of the yellow emission involves the nitrogen antisite. In addition, it is found that persistent photoconductivity can be observed after the yellow; band excitation, We further suggest that the nitrogen antisite exhibits a metastable behavior similar to the arsenic antisite in GaAs.