Browsing by Issue Date, starting with "2008-02-11"

Now showing 1 - 20 of 56226

Electrical and thermal transport in single nickel nanowire
(2008-02-11)
Ou, M. N.
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Yang, T. J.
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Harutyunyan, S. R.
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Chen, Y. Y.
;
Chen, C. D.
The thermal conductivity and electrical resistivity of a suspended nickel nanowire have been measured for T=15-300 K. The temperature dependence of the thermal conductivity and the Lorenz number strongly differ from the bulk. The comparison of the transports in the Ni nanowire shows, that at temperatures 75 < T < 300 K Wiedemann-Franz (WF) law holds, whereas at temperatures T < 75 K the WF law is violated, indicating that thermal current in this material is suppressed more than electrical current. The results are explained by combined effect of confined dimension, enhanced disorder, and grown contribution of N-processes. (C) 2008 American Institute of Physics.
Terahertz air-core microstructure fiber
(2008-02-11)
Lu, Ja-Yu
;
Yu, Chin-Ping
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Chang, Hung-Chung
;
Chen, Hung-Wen
;
Li, Yu-Tai
A low-loss terahertz air-core microstructure fiber is demonstrated for terahertz waveguiding. Substantially low attenuation constant less than 0.01 cm(-1) has been achieved and the guiding wavelength is found to be tunable by linear scaling the fiber size. The experimental results well agree with the simulation based on the finite-difference frequency-domain method, which interprets the guiding mechanism as the antiresonant reflecting waveguiding. The simulated modal pattern shows that most terahertz field is concentrated inside the central hollow air core and is guided without outside interference, which has high potential for guiding intense terahertz waves with minimized loss. (C) American Institute of Physics.
Nonvolatile memory characteristics influenced by the different crystallization of Ni-Si and Ni-N nanocrystals
(2008-02-11)
Chen, Wei-Ren
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Chang, Ting-Chang
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Yeh, Jui-Lung
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Chang, Chun-Yen
;
Chen, Shih-Ching
The formation of Ni-Si and Ni-N nanocrystals by sputtering a Ni(0.3)Si(0.7) target in argon and nitrogen environment were proposed in this paper. A transmission electron microscope analysis shows the nanocrystals embedded in the nitride layer. X-ray photoelectron spectroscopy and x-ray diffraction also offer the chemical material analysis of nanocrystals with surrounding dielectric and the crystallization of nanocrystals for different thermal annealing treatments. Nonvolatile Ni-Si nanocrystal memories reveal superior electrical characteristics for charge storage capacity and reliability due to the improvement of thermal annealing treatment. In addition, we used energy band diagrams to explain the significance of surrounding dielectric for reliability. (c) 2008 American Institute of Physics.
Enhanced green laser activation by antireflective gate structures in panel transistors
(2008-02-11)
Shieh, Jia-Min
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Chen, Chih
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Lin, Yu-Ting
;
Pan, Ci-Ling
;
材料科學與工程學系
Antireflective gate structures of polycrystalline silicon (poly-Si) and silicon dioxide films enable postimplantation green continuous-wave laser annealing of all Si regions of green laser-crystallized panel Si transistors. About 40% of the incident laser-energy penetrates to the channels, owing to antireflective gate structures with the absorptive gate poly-Si, while 65% of the incident laser-energy enters the source/drain regions because of Fresnel reflections at the air/source (drain) interfaces. Such inverted laser-energy profiles and ascendant defect distributions along the channels/junctions/contact regions, yielded continuous, improved epilike Si microstructures over the entire active layer. The electron mobility of the transistors, 620 cm(2)/V s, approaches that of integrated-circuits transistors. (C) 2008 American Institute of Physics.
Centralized versus decentralized decision-making for recycled material flows
(2008-02-15)
Hong, I-Hsuan
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Ammons, Jane C.
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Realff, Matthew J.
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工業工程與管理學系
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Department of Industrial Engineering and Management
A reverse logistics system is a network of transportation logistics and processing functions that collect, consolidate, refurbish, and demanufacture end-of-life products. This paper examines centralized and decentralized models of decision-making for material flows and associated transaction prices in reverse logistics networks. We compare the application of a centralized model for planning reverse production systems, where a single planner is acquainted with all of the system information and has the authority to determine decision variables for the entire system, to a decentralized approach. In the decentralized approach, the entities coordinate between tiers of the system using a parametrized flow function and compete within tiers based on reaching a price equilibrium. We numerically demonstrate the increase in the total net profit of the centralized system relative to the decentralized one. This implies that one may overestimate the system material flows and profit if the system planner utilizes a centralized view to predict behaviors of independent entities in the system and that decentralized contract mechanisms will require careful design to avoid losses in the efficiency and scope of these systems.
Using the nonstationary spectral method to analyze asymptotic macrodispersion in uniformly recharged heterogeneous aquifers
(2008-02-15)
Chang, Ching-Min
;
Yeh, Hund-Der
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環境工程研究所
;
Institute of Environmental Engineering
This paper describes an investigation of the influence of uniformly distributed groundwater recharge on asymptotic macrodispersion in two-dimensional heterogeneous media. This is performed using a nonstationary spectral approach [Li, S.-G., McLaughlin, D., 1991. A nonstationary spectral. method for solving stochastic groundwater problems: unconditional analysis. Water Resour. Res. 27 (7), 1589-1605; Li, S.-G., McLaughlin, D., 1995. Using the nonstationary spectral method to analyze flow through heterogeneous trending media. Water Resour. Res. 31 (3), 541-551] based on Fourier-Stieltjes representations for the perturbed quantities. To solve the problem analytically, focus is placed on the case where the local longitudinal dispersivity alpha(L) is much smaller than the integral scale of log transmissivity A (i.e., alpha(L)/lambda << 1). The closed-form expressions are obtained for describing the spectrum of flow velocity, the variability of flow velocity and asymptotic macrodispersion, in terms of the statistical properties and the integral scale of log transmissivity, local transport parameters and a parameter beta [Rubin, Y., Bellin, A., 1994. The effects of recharge on flow nonuniformity and macrodispersion. Water Resour. Res. 30 (4), 939-948] used to characterize the degree of flow nonuniformity due to the groundwater recharge. The impact of beta on these results is examined. (c) 2007 Elsevier B.V. All rights reserved.
Information-conveying approaches and cognitive styles of mental modeling in a hypermedia-based learning environment
(2008-02-15)
Lee, Jiunde
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Boling, Elizabeth
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傳播研究所
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Institute of Communication Studies
The increasing spread of Internet technology has highlighted the need for a better understanding of the fundamental issues concerning human users in a virtual space. Despite the great degree of navigational freedom, however, not all hypermedia users have the capability to locate information or assimilate internal knowledge. Research findings suggest that this type of problem could be solved if users were able to hold a cognitive overview of the hypermedia structure. How a learner can acquire the correct structural knowledge of online information has become an important factor in learning performance in a hypermedia environment. Variables that might influence learners' abilities in structuring a cognitive overview, such as users' cognitive styles and the different ways of representing information, should be carefully taken into account. The results of this study show that the interactions between information representation approaches and learners' cognitive styles have significant effects on learners' performance in terms of structural knowledge and feelings of disorientation. Learners' performance could decline if a representational approach that contradicts their cognitive style is used. Finally, the results of the present study may apply only when the learner's knowledge level is in the introductory stage. It is not clear how and what type of cognitive styles, as well as information representation approaches, will affect the performance of advanced and expert learners.
Thermally evaporated In2O3 nanoloquats with oxygen flow-dependent optical emissions
(2008-02-15)
Chu, Chia-Pu
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Ko, Tsung-Shine
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Chang, Yu-Cheng
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Lu, Tien-Chang
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Kuo, Hao-Chung
We report the synthesis of the In2O3 nanoloquat grown at different oxygen flow rates by using the thermal evaporation method. The gold nanoparticles were used as the catalyst and were dispersed on the silicon wafer to facilitate the growth Of In2O3 nanoloquats. The nanostructures of the In2O3 nanoloquats were characterized by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The photoluminescence (PL) study reveals that In2O3 nanoloquats could emit different luminescence peaks in the range of 500-600 nm with broad bands by adjusting different oxygen flow rates. The coverage of the wavelength tuning in the emission peaks of the In2O3 nanoloquats could be beneficial for possible applications in white light illumination through manipulating the ratio of each wavelength component. (c) 2007 Published by Elsevier B.V.
Developing recommender systems with the consideration of product profitability for sellers
(2008-02-15)
Chen, Long-Sheng
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Hsu, Fei-Hao
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Chen, Mu-Chen
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Hsu, Yuan-Chia
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運輸與物流管理系註：原交通所+運管所
In electronic commerce web sites, recommender systems are popularly being employed to help customers in selecting suitable products to meet their personal needs. These systems learn about user preferences over time and automatically suggest products that fit the learned model of user preferences. Traditionally, recommendations are provided to customers depending on purchase probability and customers' preferences, without considering the profitability factor for sellers. This study attempts to integrate the profitability factor into the traditional recommender systems. Based on this consideration, we propose two profitability-based recommender systems called CPPRS (Convenience plus Profitability Perspective Recommender System) and HPRS (Hybrid Perspective Recommender System). Moreover, comparisons between our proposed systems (considering both purchase probability and profitability) and traditional systems (emphasizing an individual's preference) are made to clarify the advantages and disadvantages of these systems in terms of recommendation accuracy and/or profit from cross-selling. The experimental results show that the proposed HPRS can increase profit from cross-selling without losing recommendation accuracy. (c) 2007 Elsevier Inc. All rights reserved.
Tonic and phasic electroencephalographic dynamics during continuous compensatory tracking
(2008-02-15)
Huang, Ruey-Song
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Jung, Tzyy-Ping
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Delorme, Amaud
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Makeig, Scott
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腦科學研究中心
Tonic and phasic dynamics of electroencephalographic (EEG) activities during a continuous compensatory tracking task (CTT) were analyzed using time-frequency analysis of EEG sources identified by independent component analysis (ICA). In I-hour sessions, 70-channel EEG data were recorded while participants attempted to use frequent compensatory trackball movements to maintain a drifting disc close to a bulls-eye at screen center. Disc trajectories were converted into two moving-average performance measures, root mean square distance of the disc from screen center in 4-s ('local') and in 20-s ('global') moving time windows. Maximally independent EEG processes and their equivalent dipole source locations were obtained using the EEGLAB toolbox (http://sccn.ucsd.edu/eeglab). Across subjects and sessions, independent EEG processes in occipital, somatomotor, and supplementary motor cortices exhibited tonic power increases during periods of high tracking error, plus additional phasic power increases in several frequency bands before and after trackball movements following disc 'perigees' (moments at which the disc began to drift away from the bulls-eye). These phasic activity increases, which were larger during high-error periods, reveal an intimate relation between EEG dynamics and top-down recognition of responding to threatening events. Thus during a continuous tracking task without impulsive stimulus onsets, sub-second scale EEG dynamics related to visuomotor task could be dissociated from slower spectral modulations linked to changes in performance and arousal. We tentatively interpret the observed EEG signal increases as indexing tonic and phasic modulations of the levels of task attention and engagement required to maintain visuomotor performance during sustained performance. (c) 2007 Elsevier Inc. All rights reserved.
Growth of a-plane ZnO thin films on LaAlO3(100) substrate by metal-organic chemical vapor deposition
(2008-02-15)
Tian, Jr-Sheng
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Liang, Mel-Hui
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Ho, Yen-Teng
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Liu, Yuan-An
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Chang, Li
ZnO(1 1 (2) over bar 0) thin films were successfully grown on LaAlO3 (lanthanum aluminate) (10 0) substrate by atmospheric pressure metalorganic chemical vapor deposition. X-ray diffraction, atomic force microscopy, and scanning electron microscopy showed that ZnO films formed at 450 degrees C were composed of almost all (1 1 (2) over bar 0) oriented grains while (0 0 0 2) oriented ZnO grains started to appear at temperature above 550 degrees C. The a-plane ZnO films consisted of two types of domains with their c-axis perpendicular to each other due to LaAlO3(1 0 0) symmetry with low lattice mismatch along < 1 1 0 >. (C) 2007 Elsevier B.V. All rights reserved.
Elastic properties of the Abrikosov lattice near the upper critical field and peak effect in the critical current
(2008-02-15)
Rosenstein, B.
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Zhuravlev, V.
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電子物理學系
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Department of Electrophysics
Abrikosov vortices in type II superconductors under magnetic field form highly correlated configurations with well defined elasticity, like regular atomic solids. While in the London limit vortices can be considered as line-like objects, when the field approaches the upper critical field H-c2(T) the core structure becomes important for elastic properties. Taking into account the deformation of the shape of the current distribution leads to significant increase in the shear modulus of the vortex lattice compared to previous estimates. The elastic properties determine the response to vortex matter pinning. The modified value of the elastic modulus is used to support a recent theory of the discontinuous "peak effect" in the critical current. It is argued that the critical current of the vortex lattice decreases monotonously as a function of the magnetic field, jumping to a high value in the homogeneous amorphous phase. (c) 2007 Published by Elsevier B.V.
Fabrication and characterization of poly(methyl methacrylate) photopolymer doped with 9,10-phenanthrenequinone (PQ) based derivatives for volume holographic data storage
(2008-02-15)
Lin, Shiuan-Huei
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Chen, Po-Lin
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Hsiao, Yi-Nan
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Whang, Wha-Tzong
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材料科學與工程學系
We present our studies on the photopolymer of poly(methyl methacrylate) (PMMA) doped with 9,10-phenanthrenequinone based derivatives for volume holographic storage. By introducing different functional groups on the side-chain of 9,10-phenanthrenequinone molecule, the holographic characteristics of the material can be modified. The photoreaction involved with the holographic recording in the samples was investigated by measuring UV-Vis absorption spectrum and mass spectrum. The experimental results show that the similar behaviors were exhibited in these photopolymers. It is found that phase hologram recording in our PQ derivatives doped PMMA photopolymer involves a structure change of the quinone based molecule, which induces a strong change of the refractive index. Experimental characterizations on holographic data storage, including material sensitivity, dynamic range (M#) and bit-error-rate have been performed. We found that, by selecting appropriate functional groups, an improvement in sensitivity and M# for holographic data storage can be achieved. (c) 2007 Elsevier B.V. All rights reserved.
Effectiveness of Si thin buffer layer for selective SiGe epitaxial growth in recessed source and drain for pMOS
(2008-02-15)
Chenga, P. L.
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Liao, C. I.
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Chien, C. C.
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Yang, C. L.
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Ting, S. F.
Locally strained Si technology using embedded SiGe has been used to improve pMOSFET device performance through hole mobility enhancement. Embedded SiGe is achieved by selectively growing epitaxial SiGe film in recessed Si pMOSFET source and drain areas. Prior to selective SiGe epi growth, a thin layer of Si seed was employed to help nucleate following low-temperature selective SiGe epitaxial film in recessed. source and drain areas. In combination with pre-epi wet clean and low-temperature chemical bake, use of Si seed resulted in improved SiGe film morphology and micro-loading effect, and further improved device performance. (c) 2007 Elsevier B.V. All rights reserved.
Investigations of organic light emitting diodes with CdSe(ZnS) quantum dots
(2008-02-15)
Lee, C. W.
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Chou, C. H.
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Huang, J. H.
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Hsu, C. S.
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Nguyen, T. P.
In this study, we report results on investigation of bilayer light emitting diodes made of organic capped CdSe(ZnS) core/shell type nanocrystals and poly [2-phenyl-3-(9,9-dihexyl-fluoren-2-yl) phenylene vinylene]-co-[2-methoxy-5-(2'-ethylhexyloxy) phenylene vinylene] (FP-PPV-co-MEH-PPV) electroluminescent co-polymer. Light emitting diodes of structure: indium-tin-oxide (ITO)/polyethylene dioxythiophene: polystyrene sulfonate (PEDOT:PSS)/FP-PPV-co-MEH-PPV/Ca/Al devices have been fabricated and studied. The co-polymer device emits a yellow light with a maximum brightness of 3949 cd/m(2) and a maximum external quantum efficiency of 0.27 cd/A at 10 V. Incorporation of CdSe(ZnS) quantum dots into the active polymer film resulted in an increase in device brightness, which reached 8192 cd/m(2) and in external quantum efficiency, which became 1.27 cd/A at 7 V with a lower turn-on voltage. The results indicate that CdSe(ZnS) quantum dots improved significantly the emission of the devices by modifying the injection and transport of the charge carriers. We suggest a non-uniform dispersion of QDs in the co-polymer layer with carrier blocking process by the particles, which produced a balanced charge distribution inside the co-polymer, and thus increased the emission efficiency. (c) 2007 Elsevier B.V. All rights reserved.
Fault-tolerant hamiltonian connectedness of cycle composition networks
(2008-02-15)
Kueng, Tz-Liang
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Lin, Cheng-Kuan
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Liang, Tyne
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Tan, Jimmy J. M.
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Hsu, Lih-Hsing
It is important for a network to tolerate as many faults as possible. With the graph representation of an interconnection network, a k-regular hamiltonian and hamiltonian connected network is super fault-tolerant hamiltonian if it remains hamiltonian after removing up to k - 2 vertices and/or edges and remains hamiltonian connected after removing up to k - 3 vertices and/or edges. Super fault-tolerant hamiltonian networks have an optimal flavor with regard to the fault-tolerant hamiltonicity and fault-tolerant hamiltonian connectivity. For this reason, a cycle composition framework was proposed to construct a (k + 2)-regular super fault-tolerant hamiltonian network based on a collection of n k-regular super fault-tolerant hamiltonian networks containing the same number of vertices for it n >= 3 and k >= 5. This paper is aimed to emphasize that the cycle composition framework can be still applied even when k = 4. (c) 2007 Elsevier Inc. All rights reserved.
消除分頻多工系統中因通道時變產生載波間干擾的方法
(2008-02-16)
吳文榕
;
許兆元
正交分頻多工(OFDM)系統於高速移動的環境下,通道在一OFDM符元(symbol)內具有時變特性,此時變特性會造成載波間正交性喪失而互相干擾,降低系統效能,因此本發明即在提供一種消除分頻多工系統中因通道時變產生載波間干擾的方法,其係利用線性時變通道之干擾矩陣本身的特殊結構,配合牛頓疊代(iteration)法化簡反矩陣運算,並使用快速傅立葉轉換降低運算量,不需使用額外電路即可達到消除載波間干擾之目的。
消除分頻多工存取系統中載波頻率偏移干擾之方法
(2008-02-16)
吳文榕
;
許兆元
本發明提供一種消除分頻多工存取系統中,因震盪器的頻率不精確產生載波頻率偏移所引起之載波間干擾的方法,其係利用牛頓疊代法以疊代方式計算載波頻率偏移干擾矩陣之反矩陣與接收頻域訊號的乘積,並利用干擾矩陣的特殊結構,發展出以快速傅立葉轉換為主之演算法,使得運算複雜度大幅降低,並且不需使用額外電路即可有效消除載波間干擾。
Genetic algorithms for portfolio selection problems with minimum transaction lots
(2008-02-16)
Lin, Chang-Chun
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Liu, Yi-Ting
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資訊管理與財務金融系註：原資管所+財金所
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Department of Information Management and Finance
Conventionally, portfolio selection problems are solved with quadratic or linear programming models. However, the solutions obtained by these methods are in real numbers and difficult to implement because each asset usually has its minimum transaction lot. Methods considering minimum transaction lots were developed based on some linear portfolio optimization models. However, no study has ever investigated the minimum transaction lot problem in portfolio optimization based on Markowitz' model, which is probably the most well-known and widely used. Based on Markowitz' model, this study presents three possible models for portfolio selection problems with minimum transaction lots, and devises corresponding genetic algorithms to obtain the solutions. The results of the empirical study show that the portfolios obtained using the proposed algorithms are very close to the efficient frontier, indicating that the proposed method can obtain near optimal and also practically feasible solutions to the portfolio selection problem in an acceptable short time. One model that is based on a fuzzy multi-objective decision-making approach is highly recommended because of its adaptability and simplicity. (c) 2007 Published by Elsevier B.V.
Note on "Wash criterion in analytic hierarchy process"
(2008-02-16)
Lin, Jennifer Shu-Jen
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Chou, Shuo-Yan
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Chouhuang, Wayne T.
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Hsu, C. P.
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科技管理研究所
The paper of Finan and Hurley - published in Computers and Operations Research (2002) - was re-examined, where they discussed a seemingly contradictory phenomenon resulting from the ignoring of wash criteria in the analytic hierarchy process (AHP). With that, they raised a serious challenge to the AHP methodology. However, by reviewing their arguments and example data, analyses regarding to their propositions and numerical example are presented in this paper to counter their challenge. (c) 2007 Elsevier B.V. All rights reserved.