Browsing by Author "Chen, Chih-Ming"

Now showing 1 - 19 of 19

A novel and efficient neuro-fuzzy classifier for medical diagnosis
(2006)
Hong, Chin-Ming
;
Chen, Chih-Ming
;
Chen, Shyuan-Yi
;
Huang, Chao-Yen
;
電控工程研究所
This study attempts to propose a novel neuro-fuzzy network which can efficiently reason fuzzy rules based on training data to solve the medical diagnosis problems. First, this study proposes a refined K-means clustering algorithm and a gradient-based learning rules to logically determine and adaptively tuned the fuzzy membership functions for the employed neuro-fuzzy network. In the meanwhile, this study also presents a feature reduction scheme based on the grey-relational analysis to simplify the fuzzy rules obtained from the employed neuro-fuzzy network. Experimental results indicated that the proposed neuro-fuzzy network with feature reduction can discover very simplified and easily interpretable fuzzy rules to support medical diagnosis.
A Novel Evaluation Function for LT Codes Degree Distribution Optimization
(2014-01-01)
Tsai, Pei-Chuan
;
Chen, Chih-Ming
;
Chen, Ying-Ping
;
資訊工程學系
;
Department of Computer Science
Luby transform (LT) codes implements an important property called ratelessness, meaning a fixed code rate is unnecessary and LT codes can complete the transmission without channel status. The property is advantageous to transmit over certain environments such as broadcasting in heterogeneous networks or transmitting data over unknown channels. For this reason, improving LT codes is a crucial research issue in recent years. The performance of LT codes is decided by the code length and a probability mass function, called degree distribution, used in the encoding process. To improve the performance of LT codes, many studies proposed to optimize the degree distribution by using methods in evolutionary computation. One of the key steps in the evolutionary process is to evaluate decision variables for comparing the fitness of each individual. In the optimization of LT codes, it needs to repeatedly simulate the encoding/decoding process with a given distribution and evaluate the performance over a sufficient number of runs. Hence, a lot of computational resource is necessary for the optimization of LT codes. In this paper, we propose a heuristic function to evaluate the performance of LT codes. The evaluation function estimates the expected fraction of unsolved symbols with the specified code length, reception overhead, and degree distribution. Based on the proposed function, a huge number of evaluations is possible for searching for better degree distributions. We first verify the practicality of the proposed function and then employ it in a multi-objective evolutionary algorithm to investigate the tradeoff of LT codes between the computational cost and decoding performance.
A Practical Optimization Framework for the Degree Distribution in LT Codes
(2013-11-01)
Chen, Chih-Ming
;
Chen, Ying-Ping
;
Shen, Tzu-Ching
;
Zao, John K.
;
資訊工程學系
LT codes are the first practical rateless codes whose reception overhead totally depends on the degree distribution adopted. The capability of LT codes with a particular degree distribution named robust soliton has been theoretically analyzed; it asymptotically approaches the optimum when the message length approaches infinity. However, real applications making use of LT codes have finite number of input symbols. It is quite important to refine degree distributions because there are distributions whose performance can exceed that of the robust soliton distribution for short message length. In this work, a practical framework that employs evolutionary algorithms is proposed to search for better degree distributions. Our experiments empirically prove that the proposed framework is robust and can customize degree distributions for LT codes with different message length. The decoding error probabilities of the distributions found in the experiments compare well with those of robust soliton distributions. The significant improvement of LT codes with the optimized degree distributions is demonstrated in the paper.
Connection Choice Codes
(2014-07-01)
Chen, Chih-Ming
;
Chen, Ying-ping
;
交大名義發表
;
資訊工程學系
;
National Chiao Tung University
Luby Transform (LT) codes are the first practical implementation of digital fountain codes. In LT codes, encoding symbols are independently generated so as to realize the universal property which means that performance is independent of channel parameters. The universal property makes LT codes able to provide reliable delivery simultaneously via channels of different quality while it may also limit the flexibility of LT codes. In certain application scenarios, such as real-time multimedia transmission, most receivers have tolerable channels whose erasure rates are not fixed, and channels of high erasure rate are outside the design box. In this paper, Connection Choice (CC) codes are proposed to trade the universal property for better performance. The key to CC codes is replacement of random selection with tournament selection. Tournament selection can equalize the frequency of input symbols to join encoding and change the degree distribution of input symbols. Our study indicates that CC codes with appropriate degree distributions provide better performance than the best known LT code when channels of high erasure rate can be ignored. CC codes enable system designers to customize digital fountain codes by taking into account the distribution of the erasure rate and create a new possibility for setting trade-offs between performance and erasure rate.
Effect of polyimide baking on bump resistance in flip-chip solder joints
(2014-03-01)
Cheng, Hsi-Kuei
;
Feng, Shien-Ping
;
Lai, Yi-Jen
;
Liu, Kuo-Chio
;
Wang, Ying-Lang
The effect of polyimide (PI) thermal process on the bump resistance of flip-chip solder joint is investigated for 28 nm technology device with aggressive extreme low-k (ELK) dielectric film scheme and lead-free solder. Kelvin structure is designed in the bump array to measure the resistance of single solder bump. An additional low-temperature pre-baking before standard PI curing increases the bump resistance from 9.3 m Omega to 225 m Omega. The bump resistance increment is well explained by a PI outgassing model established based on the results of Gas Chromatography-Mass Spectrophotometer (GC-MS) analysis. The PI outgassing substances re-deposit on the Al bump pad, increasing the resistance of interface between under-bump metallurgy (UBM) and underneath Al pad. The resistance of interface is twenty-times higher than pure solder bump, which dominates the measured value of bump resistance. Low-temperature plasma etching prior to UBM deposition is proposed to retard the PI outgassing, and it effectively reduces the bump resistance from 225 m Omega to 10.8 m Omega. (C) 2013 Published by Elsevier Ltd.
Efficiency enhancement of regular-type perovskite solar cells based on Al-doped ZnO nanorods as electron transporting layers
(2017-02-01)
Huang, Zheng-Lun
;
Chen, Chih-Ming
;
Lin, Zheng-Kun
;
Yang, Sheng-Hsiung
;
光電工程學系
In this paper, we first incorporated Al(NO3)(3 center dot)9H(2)0 as the Al source into ZnO nanorods (NRs) lattice via the hydrothermal method to modify nature properties of ZnO NRs for the fabrication of perovskite solar cells (PSCs). The X-ray diffraction (XRD) pattern of Al-doped ZnO NRs exhibits higher 20 values and stronger intensity of (002) plane. Larger optical band gap and higher electrical conductivity of Al-doped ZnO NRs are also observed relative to non-doped ZnO ones. The steady-state photoluminescence shows effective charge extraction and collection at the interface between Al-doped ZnO NRs and perovskite layer. The optimized PSC based on Al-doped ZnO NRs showed an open-circuit voltage of 0.84 V, a short-circuit current density of 21.93 mA/cm(2), a fill factor of 57%, and a power conversion efficiency of 10.45% that was 23% higher than the non-doped ZnO ones. (C) 2016 Elsevier Ltd. All rights reserved.
Enhancing MOEA/D with Guided Mutation and Priority Update for Multi-objective Optimization
(2009)
Chen, Chih-Ming
;
Chen, Ying-ping
;
Zhang, Qingfu
;
資訊工程學系
;
Department of Computer Science
Multi-objective optimization is an essential and challenging topic in the domains of engineering and computation because real-world problems usually include several conflicting objectives. Current trends in the research of solving multi-objective problems (MOPs) require that the adopted optimization method provides an approximation of the Pareto set such that the user can understand the tradeoff between objectives and therefore make the final decision. Recently, an efficient framework, called MOEA/D, combining decomposition techniques in mathematics and optimization methods in evolutionary computation was proposed. MOEA/D decomposes a MOP to a set of single-objective problems (SOPs) with neighborhood relationship and approximates the Pareto set by solving these SOPs. In this paper, we attempt to enhance MOEA/D by proposing two mechanisms. To fully employ the information obtained from neighbors, we introduce a guided mutation operator to replace the differential evolution operator. Moreover, a update mechanism utilizing a priority queue is proposed for performance improvement when the SON obtained by decomposition are not uniformly distributed on the Pareto font Different combinations of these approaches are compared based on the test problem instances proposed for the CEC 2009 competition. The set of problem instances include unconstrained and constrained MOPs with variable linkages. Experimental results are presented in the paper, and observations and discussion are also provided.
Interfacial reactions between Cu and SnAgCu solder doped with minor Ni
(2015-02-15)
Cheng, Hsi-Kuei
;
Huang, Chin-Wen
;
Lee, Hsuan
;
Wang, Ying-Lang
;
Liu, Tzeng-Feng
The interfacial reactions between Cu and SnAgCu-based solders were investigated. Two types of SnAgCu-based solders were used, one was Sn-1.0Ag-0.5Cu (SAC105) and the other was Sn-1.2Ag-0.5Cu-0.05Ni (LF35), where the composition was in wt.%. The addition of Ni in the SnAgCu-based solder was found to have significant effects on the morphological evolution and growth of the Cu6Sn5 and Cu3Sn phases formed at the solder/Cu interfaces. At the Ni-added LF35/Cu interface after liquid/solid reaction at 260 degrees C,the Cu6Sn5 phase presented a microstructure with a much smaller grain size. During subsequent solid/solid reaction at 150 and 200 degrees C, the growth of the Cu6Sn5 phase was significantly enhanced at the LF35/Cu interface but that of the Cu3Sn phase was inhibited. A potential mechanism was proposed to explain the effects of Ni addition on the solder/Cu interfacial reactions. (C) 2014 Elsevier B. V. All rights reserved.
Microstructural and thermal characterizations of light-emitting diode employing a low-temperature die-bonding material
(2016-08)
Wang, Tzu-Hao
;
Lee, Hsuan
;
Chen, Chih-Ming
;
Chen, Ming-Guan
;
Hu, Chi-Chang
A Sn/Bi bilayer was deposited on a hot air solder leveling (HASL)-treated metal-core printed circuit board (MCPCB) using electroplating as a low-temperature die-bonding material for light-emitting diode (LED). The eutectic feature of the Sn/Bi contact enabled the die-bonding process to accomplish through a liquid/solid reaction at 185 degrees C with a proper compression force. A high-temperature die-bonding structure composed of a Bi layer sandwiched by two intermetallic compounds (IMCs) formed after thermocompression. Employment of the Sn/Bi bilayer for low-temperature die-bonding prevented the LEDs from thermal stress problems, and the resulting high-temperature IMC/Bi/IMC die-bonding structure was capable of withstanding multiple bonding reactions and high temperature/current operation environment. Durability tests including mechanical, thermal, and optical performance were systematically performed and compared with other commercially available die-bonding materials (Ag paste and solder alloys). (C) 2016 Elsevier Ltd. All rights reserved.
Microstructural Evolution of Cu/Solder/Cu Pillar-Type Structures with Different Diffusion Barriers
(2016-08)
Cheng, Hsi-Kuei
;
Lin, Yu-Jie
;
Chen, Chih-Ming
;
Liu, Kuo-Chio
;
Wang, Ying-Lang
Microstructural evolution of the Cu/solder/Cu pillar-type bonding structures with a reduced solder volume subjected to thermal aging at 423 K to 473 K(150 A degrees C to 200 A degrees C) was investigated. In a bonding structure employing a Ni single layer as the diffusion barrier, solder was consumed with formation of the Ni3Sn4 phase at the bonding interfaces due to an usual Sn/Ni interfacial reaction. However, an unusual Sn/Cu reaction occurred with formation of the Cu6Sn5 (and Cu3Sn) phase on the periphery of the Cu pillar due to out-diffusion of Sn toward the pillar periphery. Consumption of solder was accelerated by the above two reactions which led to the formation of a continuous gap in the bonding structure. Employment of a thicker Ni layer plus a Cu cap layer as the diffusion barrier in the bonding structure effectively blocked out-diffusion of Sn toward the periphery of the Cu pillar and therefore retarded the gap formation. The retardation effect was attributed to an increment of diffusion distance on the pillar periphery due to an effective diffusion barrier composed by Ni and thicker Cu-Sn (Cu6Sn5 + Cu3Sn) phase layers. Detailed phase identification and microstructural evolution in the bonding structures were also investigated using scanning electron microscopy and transmission electron microscopy.
On the Optimization of Degree Distributions in LT Code with Covariance Matrix Adaptation Evolution Strategy
(2010)
Chen, Chih-Ming
;
Chen, Ying-ping
;
Shen, Tzu-Ching
;
Zao, John K.
;
資訊工程學系
Luby Transform code (LT code) has been a popular and practical technique in the field of channel coding since its proposal. One of the key components of LT code is a degree distribution which is used to determine the relationship between source data and codewords. Luby in his proposal suggested two general methods to construct feasible degree distributions. Such general designs work appropriately in typical situations but not optimally in most cases. To explore the full potential of LT code, in this work, we make the first attempt to introduce evolutionary algorithms to optimize the degree distribution in LT code. Degree distributions are encoded as real-valued vectors and evaluated by numerical simulation of LT code. For applications of different natures, two objectives are implemented to search good degree distributions with different decoding behavior. Compared with the original design, the experimental results are quite promising and demonstrate that the degree distribution can be customized for different purposes. In addition to manually adjusting the degree distribution as the common practice, the work presented in this paper provides an efficient alternative approach to use and adapt LT code for both practitioners and researchers.
Optimizing Degree Distributions in LT Codes by Using The Multiobjective Evolutionary Algorithm Based on Decomposition
(2010)
Chen, Chih-Ming
;
Chen, Ying-ping
;
Shen, Tzu-Ching
;
Zao, John K.
;
資訊工程學系
Luby Transform code (LT code) is the first practical digital fountain code and has been widely used as basic components in many communication applications. The coding behavior of LT code is mainly decided by a probability distribution of codeword degrees. In order to customize a degree distribution for different purposes, multi-objective evolutionary algorithm is introduced to optimize degree distributions in this paper. Two critical performance indicators of LT code are considered in our experiments. Some applications hope to minimize the overhead of extra packets and some require to limit the computational cost of the coding system. To handle this problem, MOEA/D is applied to optimize two objectives simultaneously. We expect to obtain the Pareto front (PF) formed by partial optimal solutions and provide those available degree distributions to different LT code applications. Not only promising results are represented in this paper but also the behavior of LT code is thoroughly explored by optimizing the degree distribution according to multi-objectives.
Particle Swarm Guided Evolution Strategy
(2007)
Hsieh, Chang-Tai
;
Chen, Chih-Ming
;
Chen, Ying-ping
;
資訊工程學系
;
Department of Computer Science
Evolution strategy (ES) and particle swarm optimization (PSO) are two of the most popular research topics for tackling real-parameter optimization problems in evolutionary computation. Both of them have strengths and weaknesses for their different search behaviors and methodologies. In ES, mutation, as the main operator, tries to find good solutions around each individual. While in PSO, particles are moving toward directions determined by certain global information, such as the global best particle. ill order to leverage the specialties offered by both sides to our advantage, this paper combines the essential mechanism of ES and the key concept of PSO to develop a new hybrid optimization methodology, called particle swarm guided evolution strategy. We introduce swarm intelligence to the ES mutation framework to create a new mutation operator, called guided mutation, and integrate the guided mutation operator into ES. Numerical experiments are conducted on a set of benchmark functions, and the experimental results indicate that, PSGES is a promising optimization methodology as well as an interesting research direction.
Performance Characterization of Dye-Sensitized Photovoltaics under Indoor Lighting
(2017-04-20)
Chen, Chia-Yuan
;
Jian, Zih-Hong
;
Huang, Shih-Han
;
Lee, Kun-Mu
;
Kao, Ming-Hsuan
Indoor utilization of emerging photovoltaics is promising; however, efficiency characterization under room lighting is challenging. We report the first round-robin interlaboratory study of performance measurement for dye-sensitized photovoltaics (cells and mini-modules) and one silicon solar cell under a fluorescent dim light. Among 15 research groups, the relative deviation in power conversion efficiency (PCE) of the samples reaches an unprecedented 152%. On the basis of the comprehensive results, the gap between photometry and radiometry measurements and the response of devices to the dim illumination are identified as critical obstacles to the correct PCE. Therefore, we use an illuminometer as a prime standard with a spectroradiometer to quantify the intensity of indoor lighting and adopt the reverse-biased current voltage (I-V) characteristics as an indicator to qualify the I-V sampling time for dye-sensitized photovoltaics. The recommendations can brighten the prospects of emerging photovoltaics for indoor applications.
PSO-Based Evacuation Simulation Framework
(2014-01-01)
Tsai, Pei-Chuan
;
Chen, Chih-Ming
;
Chen, Ying-ping
;
資訊工程學系
;
Department of Computer Science
Evacuation simulation is a critical and important research issue for people to design safer building layouts or plan more effective evacuation routes. Many studies adopted methodologies in evolutionary computation into the evacuation simulation systems for finding better solutions. To simulate human behavior or crowd motion is one key factor to the practicality of the system. Particle swarm optimization algorithm (PSO), which is originated from the inspiration of bird flocking, is commonly applied to model human behavior. Based on the PSO-based human behavior simulation, many studies have got good results on evacuation simulation. However, the configurations of describing the experiment environment in the literature are complicated and specialized for certain specific scenarios. Observing the fact, we propose a new PSO-based simulation framework in order to provide a simple and general way to configure various simulation scenarios. This work adopts our previously proposed PSO-based crowd movement controlling mechanism and introduces new mechanisms to make the simulation fitting into evacuation circumstance more real. In the proposed framework, all people, obstacles, exits, and even the evacuation guide indicators are modeled as the original component of the PSO algorithm. It is convenient to setup the simulation environment upon the framework. Therefore, taking the proposed work as a research tool will be advantageous when the issue of evacuation simulation is investigated.
Sparse Degrees Analysis for LT Codes Optimization
(2012)
Tsai, Pei-Chuan
;
Chen, Chih-Ming
;
Chen, Ying-ping
;
資訊工程學系
;
Department of Computer Science
Luby Transform (LT) codes are a new member in the family of forward error correction codes without a fixed code rate. The property called rateless is attractive to researchers in last decade, and lots of studies have been proposed and attempted to improve the performance of LT codes. One variation is the use of a sparse degree distribution instead of a full one referred to in the encoding process of LT codes to reduce the search space. Observing a fact that the ability of a sparse degree distribution is limited by the nonempty degrees, we introduce a tag selection scheme to choose reasonable sparse degrees for LT codes in this paper. We firstly investigate the influence of different degrees on the error rate of LT codes and then propose a general selection algorithm based on our observations. After that, the covariance matrix adaptation evolution strategy (CMA-ES) is applied to find the optimal sparse degree distributions of which the degrees are defined by our selection algorithm. Finally, the experimental results are presented as evidence to show the proposed scheme is effective and practical.
Thermal and angular dependence of next-generation photovoltaics under indoor lighting
(1970-01-01)
Chen, Chia-Yuan
;
Kuo, Ting-Yang
;
Huang, Chien-Wu
;
Jian, Zih-Hong
;
Hsiao, Po-Tsung
Next-generation photovoltaic technologies such as dye-sensitized solar cells, organic thin-film photovoltaics and perovskite solar cells are promising to efficiently harvest ambient light energy. However, more and deeper understanding of their photovoltaic characteristics is essential to create new applications under room light illumination. In this study, for the first time, the difference in temperature coefficients and angular dependence of photovoltaic parameters for the large-area devices are investigated systematically under the compact fluorescent lamp and light-emitting diode light. These emerging photovoltaic devices, compared with the single crystalline silicon solar cells, not only have higher open-circuit voltage (up to approximate 1 V) and better power conversion efficiency (in the range of 9.2% similar to 22.6%) but also exhibit less temperature dependent voltage and output power (< -0.6% degrees C-1), as well as broader angular response (over 75 degrees). The state-of-the-art dye-sensitized and organic thin-film devices also show advantageously positive temperature coefficients of current, and the latter even has positive thermal dependence of fill factor. These features suggest the next-generation photovoltaic devices are more favorable than the conventional crystalline silicon solar cells for real-life indoor applications.
Unusual Morphological Evolution of the Cu Pillar/Solder Micro-joints During High-Temperature Annealing
(2015-05-01)
Cheng, Hsi-Kuei
;
Lin, Yu-Jie
;
Chang, Hou-Chien
;
Liu, Kuo-Chio
;
Wang, Ying-Lang
The morphological evolution of Cu pillars capped with Sn-1.8 wt pct Ag solder during high-temperature annealing was investigated. Two intermetallic compounds (Cu6Sn5 + Cu3Sn) formed at the Cu/solder interface which changed the pillar\'s morphology. Surface diffusion enhanced the growth of Cu6Sn5 + Cu3Sn around the pillar brim and transformed the pillar top from a plane into a truncated cone. Bulk diffusion dominated after long-term annealing and the pillar top became hemispherical shaped. A mechanism was proposed to explain the unusual morphological evolution. (C) The Minerals, Metals & Materials Society and ASM International 2015
WO3 Nanoparticles or Nanorods Incorporating Cs2CO3/PCBM Buffer Bilayer as Carriers Transporting Materials for Perovskite Solar Cells
(2016-10-18)
Chen, Chih-Ming
;
Lin, Zheng-Kun
;
Huang, Wei-Jie
;
Yang, Sheng-Hsiung
;
照明與能源光電研究所
In this work, we demonstrate a novel carrier transporting combination made of tungsten trioxide (WO3) nanomaterials and Cs2CO3/PCBM buffer bilayer for the fabrication of perovskite solar cells (PSCs). Two different types of WO3, including nanoparticles and nanorods, were prepared by sol-gel process and hydrothermal method, respectively. Cs2CO3/PCBM buffer bilayer was inserted between WO3 and perovskite layers to improve charge transfer efficiency and formation of pinhole-free perovskite layer. Besides, the leakage current of the devices containing Cs2CO3/PCBM buffer bilayer was significantly suppressed. The optimized device based on WO3 nanoparticles and Cs2CO3/PCBM bilayer showed an open-circuit voltage of 0.84 V, a short-circuit current density of 20.40 mA/cm(2), a fill factor of 0.61, and a power conversion efficiency of 10.49 %, which were significantly higher than those of PSCs without Cs2CO3/PCBM buffer bilayer. The results revealed that the combination of WO3 nanomaterials and Cs2CO3/PCBM bilayer provides an effective solution for improving performances of PSCs.