Browsing by Author "Chen, CM"

Now showing 1 - 20 of 47

A discrete region competition approach incorporating weak edge enhancement for ultrasound image segmentation
(2003-02-01)
Chen, CM
;
Lu, HHS
;
Chen, YL
;
統計學研究所
;
Institute of Statistics
Ultrasound images are inherently difficult to analyze due to their echo texture, speckle noise and weak edges. Taking into account these characteristics, we present a new region-based approach for ultrasound image segmentation. It is composed of two primary algorithms, discrete region competition and weak edge enhancement. The discrete region competition features four techniques, region competition, statistical modeling of speckle, early vision modeling, and discrete concepts. In addition, to prevent regions from leaking out of the desired area across weak edges, edges located on the slowly varying slope are enhanced according to their position on the slope and the length of the slope. This new approach has been implemented and verified on clinical ultrasound images. (C) 2002 Elsevier Science B.V. All rights reserved.
A dual-snake model of high penetrability for ultrasound image boundary extraction
(2001-12-01)
Chen, CM
;
Lu, HHS
;
Hsiao, AT
;
統計學研究所
;
Institute of Statistics
Most deformable models require the initial contour to be placed close to the boundary of the object of interest for boundary extraction of ultrasound (US) images, which is impractical in many clinical applications. To allow a distant initial contour, a new dual-snake model promising high penetrability through the interference of the noises is proposed in this paper. The proposed dual-snake model features a new far-reaching external force, called the discrete gradient flow, a connected component-weighted image force, and an effective stability evaluation of two underlying snakes. The experimental results show that, with a distant initial contour, the mean distance from the derived boundary to the desired boundary is less than 1.4 pixels, and most snake elements are within 2.7 pixels of the desired boundaries for the synthetic images with CNR greater than or equal to 1. For the clinical US images, the mean distance is less than 1.9 pixels, and most snake elements are within 3 pixels of the desired boundaries. (E-mail: chung@lotus.mc.ntu.edu.tw) (C) 2002 World Federation for Ultrasound in Medicine Biology.
A novel concept for finding proper orthogonal wavelets effectively to solve a large object scattering problem
(2003-04-18)
Chen, CM
;
Tarng, JH
;
Huang, JM
;
電信工程研究所
;
友訊交大聯合研發中心
[1] A novel concept of "visible energy" is proposed, and its magnitude is shown to be valuable information for determining whether the chosen orthogonal wavelet is proper in solving a large object scattering problem. With the properly chosen wavelets for the targeting problem the ( transformed) wavelet-domain impedance matrix can be sparsified effectively for solving electromagnetic integral problems. Visible energy is defined as the energy of all dilations of a single mother wavelet for an arbitrary translation in the spectral domain over the entire "visible region." It is found that for large matrix sizes, using wavelets with smaller visible energy will lead to a greater sparsification of the matrix. Numerical examples considering various scatterers with different shapes such as a circular cylinder, an L-shaped scatterer, and a duct show the validity of our findings.
A novel method for net-shape forming of hypereutectic Al-Si alloys by thixocasting with powder preforms
(2005-08-25)
Chen, CM
;
Yang, CC
;
Chao, CG
;
材料科學與工程學系
;
Department of Materials Science and Engineering
This work presents a novel and feasible method for net-shape forming of hypereutectic A1-Si alloy parts. This method, briefly termed as powder thixocasting in this paper, combines the techniques of thixocasting and conventional powder metallurgy. Consolidated preforms made of gas-atomized and pre-alloyed A1-25Si-2.5Cu-1Mg-0.5Mn powder were used as the feedstock for thixocasting. The alloy powder was preheated under protection of argon atmosphere and then was compacted to form powder preforms. The powder preforms were quickly heated into semi-solid state by induction coils and were immediately thixocast using a die-casting machine. A die with a center gate, a long runner and plate-shaped cavities was designed to examine the feasibility of this process. Results demonstrated that the powder preforms exhibits very good formability by this unique process. The powder thixocast products have satisfied strength and substantial structure with uniform distribution of fine Si particles, while the processing temperature is suitably controlled. This novel process was also successfully used to fabricate compressor scrolls for demonstration. (c) 2004 Elsevier B.V. All rights reserved.
A textural approach based on Gabor functions for texture edge detection in ultrasound images
(2001-04-01)
Chen, CM
;
Lu, HHS
;
Han, KC
;
統計學研究所
;
Institute of Statistics
Edge detection is an important, but difficult, step in quantitative ultrasound (US) image analysis. In this paper, we present a new textural approach for detecting a class of edges in US images; namely, the texture edges with a weak regional mean gray-level difference (RMGD) between adjacent regions. The proposed approach comprises a vision model-based texture edge detector using Gabor functions and a new texture-enhancement scheme. The experimental results on the synthetic edge images have shown that the performances of the four tested textural and nontextural edge detectors are about 20%-95% worse than that of the proposed approach. Moreover, the texture enhancement may improve the performance of the proposed texture edge detector by as much as 40%, The experiments on 20 clinical US images have shown that the proposed approach can find reasonable edges for real objects of interest with the performance of 0.4 +/- 0.08 in terms of the Pratt's figure. (C) 2001 World Federation for Ultrasound in Medicine & Biology.
Activation of carbon nanotube emitters by using supercritical carbon dioxide fluids with propyl alcohol
(2006)
Liu, PT
;
Tsai, CT
;
Chang, TC
;
Kin, KT
;
Chang, PL
This paper explores the application of supercritical carbon dioxide fluids on the field emission enhancement for vertically aligned carbon nanotubes. The typical heating process cannot effectively activate the deionized-water-rinsed carbon nanotube emitters, exhibiting poorer field emission performance, due to residual moisture uptake in the carbon nanotubes. In contrast, the field emission enhancement can be achieved significantly by applying the supercritical carbon dioxide fluids associated with 3 to 9 vol % propyl alcohol. It is found the cosolvent propyl alcohol plays a critical role in the activation efficiency of supercritical carbon dioxide fluids. A physical model is also deduced to clarify the observation. (c) 2006 The Electrochemical Society.
Adaptive symmetric mean filter: A new noise-reduction approach based on the slope facet model
(2001-10-10)
Huang, HC
;
Chen, CM
;
Wang, SD
;
Lu, HHS
;
統計學研究所
Two new noise-reduction algorithms, namely, the adaptive symmetric mean filter (ASMF) and the hybrid filter, are presented in this paper. The idea of the ASMF is to find the largest symmetric region on a slope facet by incorporation of the gradient similarity criterion and the symmetry constraint into region growing. The gradient similarity criterion allows more pixels to be included for a statistically better estimation, whereas the symmetry constraint promises an unbiased estimate if the noise is completely removed. The hybrid filter combines the advantages of the ASMF, the double-window modified-trimmed mean filter, and the adaptive mean filter to optimize noise reduction on the step and the ramp edges. The experimental results have shown the ASMF and the hybrid filter are superior to three conventional filters for the synthetic and the natural images in terms of the root-mean-squared error, the root-mean-squared difference of gradient, and the visual presentation. (C) 2001 Optical Society of America.
An adaptive snake model for ultrasound image segmentation: Modified trimmed mean filter, ramp integration and adaptive weighting parameters
(2000-10-01)
Chen, CM
;
Lu, HHS
;
統計學研究所
;
Institute of Statistics
The snake model is a widely-used approach to finding the boundary of the object of interest in an ultrasound image. However, due to the speckles, the weak edges and the tissue-related textures in an ultrasound image, conventional snake models usually cannot obtain the desired boundary satisfactorily. In this paper, we propose a new adaptive snake model for ultrasound image segmentation. The proposed snake model is composed of three major techniques, namely, the modified trimmed mean (MTM) filtering, ramp integration and adaptive weighting parameters. With the advantages of the mean and median filters, the MIM filter is employed to alleviate the speckle interference in the segmentation process. The weak edge enhancement by ramp integration attempts to capture the slowly varying edges, which are hard to capture by conventional snake models. The adaptive weighting parameter allows weighting of each energy term to change adaptively during the deformation process. The proposed snake model has been verified on the phantom and clinical ultrasound images. The experimental results showed that the proposed snake model achieves a reasonable performance with an initial contour placed 10 to 20 pixels away from the desired boundary. The mean minimal distances from the derived boundary to the desired boundary have been shown to be less than 3.5 (for CNR greater than or equal to 0.5) and 2.5 pixels, respectively, for the phantom and ultrasound images.
An anomalous crossover in Vth roll-off for indium-doped nMOSFETs
(2000-09-01)
Chang, SJ
;
Chang, CY
;
Chen, CM
;
Chou, JW
;
Chao, TS
The effects of indium channel implant energy on short-channel effect (SCE) and narrow channel effect (NCE) were studied on NMOS devices down to 0.1 mu m channel length. An anomalous crossover in Vth roll-off curves was observed, for the first time, on indium-implanted splits with different implant energies. This intriguing finding, together with the observed reduction in reverse narrow channel effect (RNCE) and effective channel length with reducing indium implant energy, can be consistently explained by the suppression of transient enhanced diffusion (TED) of channel impurity due to indium deactivation.
An early vision-based snake model for ultrasound image segmentation
(2000-02-01)
Chen, CM
;
Lu, HHS
;
Lin, YC
;
統計學研究所
;
Institute of Statistics
Due to the speckles and the ill-defined edges of the object of interest, the classic image-segmentation techniques are usually ineffective in segmenting ultrasound (US) images. In this paper, we present a new algorithm for segmenting general US images that is composed of two major techniques; namely, the early-vision model and the discrete-snake model, By simulating human early vision, the early-vision model can capture both grey-scale and textural edges while the speckle noise is suppressed. By performing deformation only on the peaks of the distance map, the discrete-snake model promises better noise immunity and more accurate convergence. Moreover, the constraint for most conventional snake models that the initial contour needs to be located very close to the actual boundary has been relaxed substantially. The performance of the proposed snake model has been shown to be comparable to manual delineation and superior to that of the gradient vector flow (GVF) snake model. (C) 2000 World Federation for Ultrasound in Medicine & Biology.
An effective three-dimensional model for UHF radio propagation into multistory office buildings
(1999-01-20)
Tarng, JH
;
Chang, YC
;
Chen, CM
;
電信工程研究所
;
Institute of Communications Engineering
An effective three-dimensional (3-D) direct-transmitted model combined with a patched-wall model is proposed to explore UHF radio propagation into multistory buildings in a microcellular environment. The model is verified by comparing the computed path loss with the measured one of 1.7 and 2.44 GHz radio waves propagating at different sites. The comparison demonstrates that the model has reasonably accurate prediction when the number of floor levels between the transmitting and the receiving antennas is no more than four.
Analysis of ATSC field test results in Taiwan
(2002-03-01)
Lin, CC
;
Chen, CM
;
Tarng, JH
;
Hang, HM
;
Yu, HC
Field tests of the transmission performance of the ATSC DTV system have been conducted in Taiwan. The test results as well as comparisons against the NTSC system performance are reported and analyzed. From the measured results the reception characteristics of the DTV can be deduced and can provide guidelines for television stations to design transmission system, schedule equipment deployment, plan service coverage areas, and improve the reception quality of the digital signal.
Catalyzed growth model of carbon nanotubes by microwave plasma chemical vapor deposition using CH4 and CO2 gas mixtures
(2003-10-01)
Chen, M
;
Chen, CM
;
Koo, HS
;
Chen, CF
;
材料科學與工程學系
Catalyst growth carbon nanotubes (CNTs) have been synthesized successfully by microwave plasma chemical vapor deposition using CH4-CO2 gas sources, and Fe, Ti, Fe/Ti as catalysts. Significant difference of morphology in the carbon deposition was observed between Fe and Ti catalyst. By adjusting growth parameters of CH4 to CO2, a high yield of vertically aligned CNTs can be found in an Fe-deposited substrate. Ti is shown to be not suitable as a catalyst in CNT production. In the present work, we investigated the effect of H-2 plasma pretreatment on the CNT growth from the viewpoint of catalyst morphology, using Fe as the catalyst. After the H-2 pretreatment, significant catalyst particle sintering was observed and resulted in a broad size distribution of catalyst particles. The diameter of CNTs was governed by the catalyst particle size. The diameter of CNTs thus increased as the H-2 plasma pretreated time increased. The CNT diameters were distributed in the range approximately 10-20 nm when Fe-deposited substrate was not pretreated. However, the diameter of CNTs increased from 30 to 300 nm when Fe-deposited substrate was pretreated from 1 to 15 min. The CNT growth model in catalysts, as a function of a gas environment of CH4-CO2 gas mixture, was investigated. (C) 2003 Elsevier Science B.V. All rights reserved.
Cell-based dual snake model: A new approach to extracting highly winding boundaries in the ultrasound images
(2002-08-01)
Chen, CM
;
Lu, HHS
;
Huang, YS
;
統計學研究所
;
Institute of Statistics
Two common deficiencies of most conventional deformable models are the need to place the initial contour very close to the desired boundary and the incapability of capturing a highly winding boundary for sonographic boundary extraction. To remedy these two deficiencies, a new deformable model (namely, the cell-based dual snake model) is proposed in this paper. The basic idea is to apply the dual snake model in the cell-based deformation manner. While the dual snake model provides an effective mechanism allowing a distant initial contour, the cell-based deformation makes it possible to catch the winding characteristics of the desired boundary. The performance of the proposed cell-based dual snake model has been evaluated on synthetic images with simulated speckles and on the clinical ultrasound (US) images. The experimental results show that the mean distances from the derived to the desired boundary points are 0.9 +/- 0.42 pixels and 1.29 +/- 0.39 pixels for the synthetic and the clinical US images, respectively.
Competence set expansion for obtaining scheduling plans in intelligent transportation security systems
(2003)
Hu, YC
;
Chiu, YJ
;
Chen, CM
;
Tzeng, GH
;
資訊管理與財務金融系註：原資管所+財金所
In this paper; to reach safe driving, a new method is proposed to acquire project schedules by competence set expansion for developing intelligent transportation systems (ITSS), that can promote security, efficiency and comfort for drivers. Since for each decision problem, there is a competence set consisting of ideas, knowledge, information, and skills needed to solve that problem, this paper treats ITSS as the needed competence set to attain the goal of safe driving. Schedules can be further obtained by using a known method proposed by Li (1999) for expanding competence sets. An empirical study is utilized to demonstrate the usefulness of the proposed method.
CPn model on fuzzy sphere
(2002-03-18)
Chan, CT
;
Chen, CM
;
Lin, FL
;
Yang, HS
;
電子物理學系
We construct the CPn model on fuzzy sphere. The Bogomolny bound is saturated by (anti-)self-dual solitons and the general solutions of BPS equation are constructed. The dimension of moduli space describing the BPS solution on fuzzy sphere is exactly the same as that of the commutative sphere or the (noncommutative) plane. We show that in the soliton backgrounds, the number of zero modes of Dirac operator on fuzzy sphere, Atiyah-Singer index, is exactly given by the topological charge of the background solitons. (C) 2002 Elsevier Science B.V. All rights reserved.
Cross-reference weighted least square estimates for positron emission tomography
(1998-02-01)
Lu, HHS
;
Chen, CM
;
Yang, IH
;
統計學研究所
;
Institute of Statistics
An efficient new method, termed as the crossreference weighted least square estimate (WLSE) [CRWLSE], is proposed to integrate the incomplete local smoothness information to improve the reconstruction of positron emission tomography (PET) images in the presence of accidental coincidence events and attenuation. The algebraic reconstruction technique (ART) is applied to this new estimate and the convergence is proved. This numerical technique is based on row operations. The computational complexity is only linear in the sizes of pixels and detector tubes, Hence, it is efficient in storage and computation for a large and sparse system. Moreover, the easy incorporation of range limits and spatially variant penalty will not deprive the efficiency. All this makes the new method practically applicable. An automatically data-driven selection method for this new estimate based on the generalized cross validation is also studied, The Monte Carlo studies demonstrate the advantages of this new method.
Deployment of personalized e-catalogues: An agent-based framework integrated with XML metadata and user models
(2001-07-01)
Liu, DR
;
Lin, YJ
;
Chen, CM
;
Huang, YW
;
資訊管理與財務金融系註：原資管所+財金所
In e-commerce applications, supporting electronic catalogues (e-catalogues) to provide product-search services on the Internet is emerging as an important function of electronic brokers ( e-brokers). However, as the Internet expands, an increasing number of virtual stores are selling products on-line. The explosive growth of information is creating difficulties for customers searching for the product information they desire. In this work, an integrated framework is proposed to develop personalized e-catalogues. The proposed framework integrates XML-based metadata models, user models and agents. The XML-based metadata model can facilitate resource-discovery and format translation, and can flexibly model the definitions of diverse product attributes in heterogeneous data resources. The proposed user model can model a user's shopping interests to resources, categories and products. This work integrates the agent technology with the proposed metadata model and user model to develop a personalized e-catalogue system. The novel system effectively provides an integrated search for heterogeneous product information, as well as supporting personalized product search and browsing for each user based upon their profiles. (C) 2001 Academic Press.
Dry sliding wear behaviors of Al-25Si-2.5Cu-1Mg alloys prepared by powder thixocasting
(2005-04-25)
Chen, CM
;
Yang, CC
;
Chao, CG
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The wear performance of an Al-25Si-2.5Cu-1Mg alloy prepared by powder thixocasting was studied using a pin-on-disc machine. LM13 and an Al-25Si-2.5Cu-lMg alloy prepared by conventional ingot metallurgy were also investigated for comparison. The sliding tests were performed under ambient conditions and without lubricant. During the tests, the applied load was increased stepwise until wear seizure occurred. Experimental data reveal that the powder thixocast alloys exhibit better wear performance than that of conventional alloys, especially under heavy load conditions and following T6 treatment. This work demonstrates the potential of the new method, powder thixocasting, for fabricating hypereutectic Al-Si-X alloys with a high wear resistance. Moreover, the variation in the wear rate with the applied load for the alloy can be divided into three regions. The mechanisms associated with these wear regions were discussed based on the investigations of the worn subsurface and the wear debris. (c) 2005 Elsevier B.V. All rights reserved.
Electromagnetic absorption in human brains by using fast wavelet transform methods
(2001)
Chen, CM
;
Tarng, JH
;
Huang, JM
;
電信工程研究所
;
Institute of Communications Engineering
An application of fast wavelet transform methods including discrete wavelet transform (DWT) and discrete wavelet packet (DWP) methods to the electromagnetic absorption in the human brains is presented. The total induced electric field inside the brain determined from the tensor integral-equation (TIE) is solved by the method of moments (MoM), DWT and DWP, respectively. It is found that using the wavelet transform methods especially using the DWP method in the targeted problems will lead to very sparsely moment matrices and relatively reduced computational complexities and memory requirements. Numerical examples are given to show the validity and effectiveness of the method.