Browsing by Issue Date, starting with "1998-07-15"

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Representations and characterizations of vertices of bounded-shape partition polytopes
(1998-07-15)
Hwang, FK
;
Onn, S
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Rothblum, UG
;
應用數學系
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Department of Applied Mathematics
Consider a finite set whose elements are associated with vectors of common dimension. A partition of such a set is associated with a matrix whose columns are the sums of the vectors corresponding to each part. The partition polytope associated with a class of partitions (that share the number of parts) is then the convex hull of the corresponding matrices. We derive representations and characterizations of these polytopes and their vertices, (C) 1998 Elsevier Science Inc, All rights reserved.
Persistent photoconductivity in SiGe/Si quantum wells
(1998-07-15)
Tsai, LC
;
Huang, CF
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Fan, JC
;
Chang, YH
;
Chen, YF
Persistent photoconductivity (PPC) has been observed in boron-doped Si1-xGex/Si quantum wells. The decay kinetics of the PPC effect can be well described by a stretched-exponential function, I-ppc(t) = I-ppc(0)exp[-(t/tau)(beta)](0 < beta < 1), which is usually observed in many disorder materials. Through the studies of the PPC effect under various conditions, such as different temperature, different photon energy of photoexcitation, and different Ge content, we identify that the alloy potential fluctuations induced by compositional disorder are the origin of the PPC effect in Si1-xGex/Si quantum wells. (C) 1998 American Institute of Physics. [S0021-8979(98)00914-1].
抱不夠的鹽
(1998-07-16)
管管
A data-parallel algorithm for minimum-width tree layout
(1998-07-16)
Lang, W
;
資訊工程學系
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Department of Computer Science
The tree-layout problem is to compute the coordinates of nodes of a tree so that the tree, when drawn on a piece of paper, appeals to human understanding. The tree-layout problem, which seems inherently sequential at the first glance, can be solved with a data-parallel algorithm. It takes O(height x log width) time on width processors when proper communication links between processors are available, where height and width are the height and width of the tree, respectively. The layout calculated by the algorithm has the minimum width. (C) 1998 Elsevier Science B.V. All rights reserved.
管管第二春開花結果
(1998-07-17)
蘇嫻雅
Low-complexity, perfect reconstruction FIR QMF bank
(1998-07-23)
Chen, SG
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Kao, MC
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
A low-complexity, perfect reconstruction quadrature mirror filter (QMF) bank is proposed, which requires only 50% of the multiplications and additions of the existing QMF banks per output sample. In addition, the new QMF bank only needs to solve a set of linear equations instead of the commonly required nonlinear optimisation technique for the prototype filter.
Intramolecular Diels-Alder reaction of furans with allenyl ethers followed by sulfur and silicon atom-containing group rearrangement
(1998-07-24)
Wu, HJ
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Yen, CH
;
Chuang, CT
;
應用化學系
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Department of Applied Chemistry
The intramolecular Diels-Alder reactions of a furandiene with an allenyl ether dienophile followed by the alkylthio, alkylsulfinyl, alkylsulfonyl, and trimethylsilyl group rearrangements are reported. Refluxing the propargyl ether 3 with t-BuOK in t-BuOH at 85 degrees C gave the 1,4-rearrangement product 4 exclusively. The alkylthio group 1,4-rearrangement may proceed intramolecularly via the tight; ion pairs. Refluxing the 5-(alkylsulfinyl)-2-furfuryl propargyl ethers 9a-e and the 5-(alkylsulfonyl)-2-furfuryl propargyl ethers 19a-e under the same reaction conditions gave the alkylsulfinyl group and the alkylsulfonyl group 1,2-rearrangement products 10a-e and 20a-e, respectively. No detectable amount of the corresponding 1,4-rearrangement products 11a-e and 21a-e was obtained. In the cases of 9b and 19b, which possess two furfurylic hydrogen atoms, no detectable amount of the furan ring-transfer reaction products was obtained. Refluxing the 5-(trimethylsilyl)-2-furfuryl propargyl ethers 25a-d with t-BuOK in t-BuOH at 85 degrees C for 10 h gave the trimethylsilyl group 1,2-rearrangement products 26a-d and Brook rearrangement products 27a-d. The reaction mechanisms for these novel intramolecular Diels-Alder reactions are discussed. In the case of 37, which possesses two furfurylic hydrogen atoms, compound 38 was obtained via an intramolecular Diels-Alder reaction followed by the furan ring-transfer reaction and Brook rearrangement.
Enacting object-oriented methods by a process environment
(1998-07-30)
Chen, JYJ
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Chou, SC
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資訊工程學系
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Department of Computer Science
This paper describes modeling and enactment of two object-oriented methods, namely the OMT method and the Booch method, using the concurrent software process language (CSPL). CSPL is a process-centered environment using Ada95-like syntax to model a method as a process program which is then compiled to C-shell executing in UNIX. A method can thus be enacted (executed) using this approach. Experiences of the approach are depicted. It is demonstrated that CSPL is feasible and appropriate for modeling and enacting methods, including object-oriented methods. Additionally, partial CSPL program modeling the Booch method is included in the Appendix. (C) 1998 Elsevier Science B.V.
Canonical gauge equivalences of the sAKNS and sTB hierarchies
(1998-07-31)
Shaw, JC
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Tu, MH
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應用數學系
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Department of Applied Mathematics
We study the gauge transformations between the supersymmetric AKNS (sAKNS) and supersymmetric two-boson (sTB) hierarchies. The Hamiltonian nature of these gauge transformations is investigated, which turns out to be canonical. We also obtain the Darboux-Backlund transformations for the sAKNS hierarchy from these gauge transformations.
A novel structural design for force/torque fingertip sensors
(1998-08-01)
Chang, YH
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Huang, YC
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Liu, YP
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Tsay, SM
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電子工程學系及電子研究所
This work presents a novel structural design of force/torque fingertip sensors for sensing planar forces. The resolution can be increased by reducing the condition number of the calibration matrix and the sensitivity can be enhanced by placing strain gauges at specified positions. Moreover, the interaction from off-axis loads is intrinsically negligible in our design. A relatively simple and accurate calibration method for performance evaluation is introduced. Some experimental results are presented to demonstrate the capability of the proposed design.
Texture classification using fuzzy uncertainty texture spectrum
(1998-08-01)
Lee, YG
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Lee, JH
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Hsueh, YC
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資訊工程學系
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Department of Computer Science
A new method using fuzzy uncertainty, which measures the uncertainty of the uniform surface in an image, is proposed for texture analysis. A grey-scale image can be transformed into a fuzzy image by the uncertainty definition. The distribution of the membership in a measured fuzzy image, denoted by the fuzzy uncertainty texture spectrum (FUTS), is used as the texture feature for texture analysis. To evaluate the performance of the proposed method, supervised texture classification and rotated texture classification are applied. Experimental results reveal high-accuracy classification rates and show that the proposed method is a good tool for texture analysis. (C) 1998 Elsevier Science B.V. All rights reserved.
Design of the coupling schemes for the AC-3 coder in stereo coding
(1998-08-01)
Liu, CM
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Lee, WC
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Juang, SY
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資訊工程學系
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Department of Computer Science
When applying the Dolby AC-3 coder for the stereo music compression, the coupling scheme that combines the two channels stereo audio signals in high frequency into one channel is the key technology for the Dolby AC-3 to achieve the bit rates lower than 96x2 kbits/sec while preserving high stereo audio quality. This paper proposes four coupling methods for the AC-3 encoder. These four methods vary with the complexity and performance. These four methods are compared through both subjective and objective tests. These four coupling methods are also combined with the dithering scheme and examined through subjective and objective tests. The result shows that the dithering scheme can effectively ease the coupling artifacts and enhance the audio quality.
Image contrast enhancement based on a histogram transformation of local standard deviation
(1998-08-01)
Chang, DC
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Wu, WR
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電信工程研究所
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Institute of Communications Engineering
The adaptive contrast enhancement (ACE) algorithm, which uses contrast gains (CG's) to adjust the high-frequency components of images, is a well-known technique for medical image processing. Conventionally, the CG is either a constant or inversely proportional to the local standard deviation (LSD), However, it is known that conventional approaches entail noise overenhancement and ringing artifacts, In this paper, we present a new ACE algorithm that eliminates these problems. First, a mathematical model for the LSD distribution is proposed by extending Hunt's image model. Then, the CG is formulated as a function of the LSD. The function, which is nonlinear, is determined by the transformation between the LSD histogram and a desired LSD distribution. Using our formulation, it can be shown that conventional ACE's use linear functions to compute the new CG's, It is the proposed nonlinear function that produces an adequate CG resulting in little noise overenhancement and fewer ringing artifacts. Finally, simulations using some X-ray images are provided to demonstrate the effectiveness of our new algorithm.
Multi-objective machine-part cell formation through parallel simulated annealing
(1998-08-01)
Su, CT
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Hsu, CM
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工業工程與管理學系
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Department of Industrial Engineering and Management
Group technology (GT) is a manufacturing philosophy which identifies and exploits the similarity of parts and processes in design and manufacturing. A specific application of GT is cellular manufacturing (CM). The first step in the preliminary stage of cellular manufacturing system (CMS) design is cell formation, generally known as a machine-part cell formation (MPCF) or a machine-component grouping (MCG) problem. Simulated annealing (SA) is not only a highly effective and general random search method to obtain near-global optimal solutions for optimization problems, but also quite appropriate for the MPCF problem which is an NP complete, complex problem. In this study, we introduce modified SA with the merits of a genetic algorithm (GA), call parallel SA (PSA), and propose a PSA-based procedure to solve the MPCF problem. More specifically, this study aims to minimize (1) total cost which includes intercell and intracell part transportation cost and machine investment cost, (2) intracell machine loading unbalance and (3) intercell machine loading unbalance under many realistic considerations. The illustrative example, comparisons and analysis demonstrate the effectiveness of this procedure. The proposed procedure is extremely adaptive, flexible, efficient and can be used to solve real MPCF problems in factories by providing a robust manufacturing cell formation in a short execution time.
Performance evaluation of an API Aerosizer (TM)
(1998-08-01)
Tsai, CJ
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Chein, HM
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Chang, ST
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Kuo, JY
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環境工程研究所
A numerical method was developed to simulate the compressible flow field and particle trajectory in an API Aerosizer(TM). Experimental particle time-of-flights (tau(TOF)) data using mono-disperse solid and liquid particles were also obtained. Theoretical particle tau(TOF) results were compared with the present experimental data and those of Cheng er al. (1993, J. Aerosol Sci. 26, 501-514). Good agreement was found for solid particles. The original tau(TOF) calibration for the API Aerosizer(TM) was found to underestimate measured tau(TOF) mainly because of the assumption of one-dimensional flow in the nozzle, and incorrect use of the particle drag coefficient in the supersonic flow field. Effects of decreasing ambient pressure and increasing particle density on increasing tau(TOF) were found to be important. (C) 1998 Elsevier Science Ltd. All rights reserved.
Video data indexing by 2D C-trees
(1998-08-01)
Hsu, FJ
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Lee, SY
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Lin, BS
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資訊工程學系
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Department of Computer Science
Video data contains a large amount of spatial and temporal information. The changes of video frames are quite useful for motion analysis and cannot be provided by other media easily. Chang et al: had proposed an effective 2D string approach for spatial indexing of image data. In this paper, we extend this iconic approach and apply it to video data indexing. We propose 2D C-trees to represent the spatial content within individual frames. A video sequence can then be represented and indexed by a temporal set or an ordering set of 2D C-trees. The similarity retrieval of video matching problem becomes the problem of video sequence matching by computing the similarity, or the minimum cost of matched frames. We present three schemes, full-sequence matching, segment matching and subsequence matching, for video information retrieval. The matching schemes can be modified and extended to approximate sequence matching by computing the partial distance for providing a comprehensive retrieval of video data. A prototype video information system is also developed to validate the effectiveness of video data indexing by 2D C-trees. (C) 1998 Academic Press.
The recognition of double Euler trails in series-parallel networks
(1998-08-01)
Ho, TY
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Sung, TY
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Hsu, LH
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Tsai, CH
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Hwang, JY
Given a series-parallel network (network, for short) N,its dual network N' is given by interchanging the series connection and the parallel connection of network N. We usually use a series-parallel graph to represent a network Let G[N] and G[N'] be graph representations of N and N', respectively. A sequence of edges e(1), e(2),...,e(k) is said to form a common trail on (G[N],G[N']) if it is a trail on both G[N] and G[N']. If a common trail covers all of the edges in G[N] and G[N'], it is called a double Euler trail. However, there are many different graph representations for a network. We say that a network N has a double Euler trail (DET) if there is a common Euler trail for some G[N] and some G[N']. Finding a DET in a network is essential for optimizing the layout area of a complementary CMOS functional cell. Maziasz and Hayes (IEEE Trans. Computer-Aided Design 9 (1990), 708-719) gave a linear time algorithm for solving the layout problem in fixed G[N] and G[N'] and an exponential algorithm for finding the optimal cover in a network without fixing graph representations. In this paper, we study properties of subnetworks of a DET network. According to these properties, we propose an algorithm that automatically generates the rules for composition of trail cover classes. On the basis of these rules, a linear time algorithm for recognizing DET networks is presented. Furthermore, we also give a necessary and sufficient condition for the existence of a double Euler circuit in a network. (C) 1998 Academic Press.
Global derivation of marine gravity anomalies from Seasat, Geosat, ERS-1 and TOPEX/POSEIDON altimeter data
(1998-08-01)
Hwang, C
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Kao, EC
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Parsons, B
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土木工程學系
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Department of Civil Engineering
Marine gravity anomalies over the area 82 degrees S to 82 degrees N and 0 degrees E to 360 degrees E on a 2' x 2' grid have been derived from Seasat, Geosat, ERS-1 and TOPEX/POSEIDON altimeter data. The inverse Vening Meinesz formula with a 1-D FFT method was used to compute gravity anomalies from gridded north-south and west-east geoid gradients, in a remove-restore procedure with the EGM96 gravity model as the reference field. This paper presents a new gridding technique and an altimeter data management system that help to extract date efficiently. In the 12 areas where ship-measured gravity and satellite-derived gravity were compared, rms agreements of 5-14 mgal were obtained. Special discussions of the gravity anomalies over selected inland seas, the Arctic, Antarctica and coastal waters are presented. The derived gravity anomalies show detailed tectonic structures of the world ocean. The global data set will be continuously updated with more altimeter data included in the derivation.
Subband Kalman filtering for speech enhancement
(1998-08-01)
Wu, WR
;
Chen, PC
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電信工程研究所
;
Institute of Communications Engineering
Kalman filtering is an effective speech-enhancement technique, in which speech signals are usually modeled as autoregressive (AR) processes and represented in the state-space domain. Since AR coefficients identification and Kalman filtering require extensive computations, real-time implementation of this approach is difficult. This paper proposes a simple and practical scheme that overcomes these obstacles. Speech signals are first decomposed into subbands. Subband speech signals are then modeled as low-order AR processes, such that low-order Kalman filters can he applied. Enhanced fullband speech signals are finally obtained by combining the enhanced subband speech signals. To identify AR coefficients, prediction-error filters adapted by the LMS algorithm are applied. Due to noisy inputs, the LMS algorithm converges to biased solutions. The performance of the Kalman filter with biased parameters is analyzed, It is shown that accurate estimates of AR coefficients are not required when the driving-noise variance is properly estimated. New methods for making such estimates are proposed. Thus, we can tolerate biased AR coefficients and take advantage of the LMS algorithm's simple structure. Simulation results show that speech enhancement in the subband domain not only greatly reduces the computational complexity, but also achieves better performance compared to that in the fullband domain.
Preparation and electronic properties of YBa2Cu3Ox films with controlled oxygen stoichiometries
(1998-08-01)
Wu, KH
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Hsieh, MC
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Chen, SP
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Chao, SC
;
Juang, JY
We describe a novel technique capable of controlling the oxygen content of YBa2Cu3Ox (YBCO) films in a precise and reversible manner. The temperature dependence of resistivity and the distinct two-plateau behavior in critical temperature T-CO versus oxygen content plot of these films are consistent with those observed in the bulk and single crystals of YBCO. The O 1s and Cu 2p absorption spectra of these films were measured by polarization-dependent X-ray absorption spectroscopy (XAS). The intensity variations of the pre-edge peaks as a function of oxygen content are discussed. We also used these films to systematically study the electron-phonon coupling strength and the position of Fermi level by using a femtosecond pump-probe technique. A clear sign-reversal of the transient reflectivity, which was consistently explained by the thermomodulation model, was observed. Both of these optical measurements support the idea that the electronic structure of YBCO cuprates is based on the charge transfer model with hybridization between the Cu and O sites.