Browsing by Issue Date, starting with "2004-05-01"

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Adaptive asymptotic Bayesian equalization using a signal space partitioning technique
(2004-05-01)
Chen, RJ
;
Wu, WR
;
電信工程研究所
;
Institute of Communications Engineering
The Bayesian solution is known to be optimal for symbol-by-symbol equalizers; however, its computational complexity is usually very high. The signal space partitioning technique has been proposed to reduce complexity. It was shown that the decision boundary of the equalizer consists of a set of hyperplanes. The disadvantage of existing approaches is that the number of hyperplanes cannot be controlled. In addition, a state-search process, that is not efficient for time-varying channels, is required to find these hyperplanes. In this paper, we propose a new algorithm to remedy these problems. We propose an approximate Bayesian criterion that allows the number of hyperplanes to be arbitrarily set. As a consequence, a tradeoff can be made between performance and computational complexity. In many cases, the resulting performance loss is small, whereas the computational complexity reduction can be large. The proposed equalizer consists of a set of parallel linear discriminant functions and a maximum operation. An adaptive method using stochastic gradient descent has been developed to identify the functions. The proposed algorithm is thus inherently applicable to time-varying channels. The computational complexity of this adaptive algorithm is low and suitable for real-world implementation.
Schottky-barrier S/D MOSFETs with high-K gate dielectrics and metal-gate electrode
(2004-05-01)
Zhu, SY
;
Yu, HY
;
Whang, SJ
;
Chen, JH
;
Shen, C
This letter presents a low-temperature process to fabricate Schottky-barrier silicide source/drain transistors (SSDTs) with high-kappa gate dielectric and metal gate. For p-channel SSDTs (P-SSDT) using PtSi source/drain (S/D), excellent electrical performance of I-on/I-off similar to 10(7) - 10(8) and subthreshold slope of 66 mV/dec have been achieved. For n-channel SSDTs (N-SSDTs) using DySi2-x S/D, I-on/I-off can reach similar to 10(5) at V-ds of 0.2 V with two subthreshold slopes of 80 and 340 mV/dec. The low-temperature process relaxes the thermal budget of high-kappa dielectric and metal-gate materials to be used in the future generation CMOS technology.
Blind and semiblind detections of OFDM signals in fading channels
(2004-05-01)
Chang, MX
;
Su, YT
;
電信工程研究所
;
Institute of Communications Engineering
This paper considers the problem of blind joint channel estimation and data detection for orthogonal frequency-division multiplexing (OFDM) systems in a fading environment. Employing a regression model for a time-varying channel, we convert the problem into one that finds the data sequence x whose associated least-squares'(LS) channel estimate z(x) is closest to the space of some regression curves (surfaces). We apply the branch-and-bound principle to solve the nonlinear integer programming problem associated with finding the curve that fits a subchannel in the LS sense. A recursive formula for fast metric update is obtained by exploiting the intrinsic characteristic of our objective function. The impacts of reordering the data sequence and selective detection are addressed. By employing a preferred order along with a selective detection method, we greatly reduce the detector complexity while giving up little performance loss. Both the complete and the reduced-complexity algorithms can be used for blind and semiblind detections of OFDM signals in a subchannel-by-subchannel manner. To further reduce the complexity and exploit the frequency-domain channel correlation, we suggest a two-stage approach that detects a few selected positions in some subchannels first, and then, treating the detected symbols as pilots, determines the remaining symbols within a properly chosen time-frequency block by a two-dimensional model-based pilot-assisted algorithm. The proposed methods do not require the information of the channel statistics like signal-to-noise ratio or channel correlation function. Performance of differential modulations like differential quaternary phase-shift keying and STAR 16-ary quadrature amplitude modulation are provided. Both blind and semiblind schemes yield satisfactory performance.
一種鐵電層電極結構及製造方法
(2004-05-01)
曾俊元
;
李顯億
本案係指一種鐵電層電極結構及製造方法，其製造方法係包含下列步驟：(a)提供一基板；(b)形成一絕緣層於該基板上；(c)形成複數個氧化物電極於該絕緣層之上；(d)形成一鐵電層於該絕緣層及該複數個氧化物電極之上；以及(e)相對於該複數個氧化物電極形成複數個金屬電極於該鐵電層之上。
GEMDOCK: A generic evolutionary method for molecular docking
(2004-05-01)
Yang, JM
;
Chen, CC
;
生物科技學系
;
Department of Biological Science and Technology
We have developed an evolutionary approach for flexible ligand docking. This approval, GEMDOCK, uses a Generic Evolutionary Method for molecular DOCKing and an empirical scoring function. The former combines both discrete and continuous global search strategies with local search strategies to speed up convergence, whereas the latter results in rapid recognition of potential ligands. GEMDOCK was tested on a diverse data set of 100 protein-ligand complexes from the Protein Data Bank. In 79% of these complexes, the docked lowest energy ligand structures had root-mean-square derivations (RMSDs) below 2.0 Angstrom with respect to the corresponding crystal structures. The success rate increased to 85% if the structure water molecules were retained. We evaluated GEMDOCK on two cross-docking experiments in which each ligand of a protein ensemble was docked into each protein of the ensemble. Seventy-six percent of the docked structures had RMSDs below 2.0 Angstrom when the ligands were docked into foreign structures. We analyzed and validated GEMDOCK with respect to various search spaces and scoring functions, and found that if the scoring function was perfect, then the predicted accuracy was also essentially perfect. This study suggests that GEMDOCK is a useful tool for molecular recognition and may be used to systematically evaluate and thus improve scoring functions. (C) 2004 Wiley-Liss, Inc.
Single- and multiepoch analyses of global positioning system baseline network: Application to coordinate and velocity determinations in Central Taiwan
(2004-05-01)
Hwang, CW
;
Lee, LH
;
Yu, SB
;
Chen, HY
;
土木工程學系
Theories and computer programs are developed for single- and multiepoch analyses of a global positioning system (GPS) baseline network using the datum-free and weighted constraint solutions. Single-epoch analysis is for evaluating data quality, removing outliers, examining network precision, and estimating coordinates. Multiepoch analysis is for simultaneously determining epoch coordinates and station velocities. The datum-free solution yields estimable data residuals and relative coordinates and is suitable for adjusting data only and for detecting changes of relative coordinates. The weighted constraint solution allows a lower-order network to be attached to an existing, higher-order network. The analysis methods are applied to a multiepoch GPS baseline network in central Taiwan, which was hit by the 1999 Chi-Chi earthquake measuring 7.3 on the Richter scale. The velocities computed by the methods developed in this study are consistent with those from the Bernese GPS software. The result of the multiepoch analysis indicates that, in the first year after the Chi-Chi earthquake, the crust east of the Chelungpu Fault moved northwestwards at a mean rate of about 10 cm/year, while the crust west of the Chelungpu Fault moved in the opposite direction at a much lower speed.
Magnetism and electronic structure of Fe chains and nano-wires
(2004-05-01)
Yang, TJ
;
Zhao, YJ
;
Freeman, AJ
;
電子物理學系
;
Department of Electrophysics
The electronic and magnetic structures of an Fe linear chain and FCC and BCC nano-wires were determined by accurate first-principles self-consistent full potential linearized augmented plane wave calculations. The one-dimensional nature of the systems results in dramatic changes in their properties-as expected from the early predictions of Weinert and Freeman (J. Mag. Magn. Mater. 38 (1983) 23) for linear transition metal chains: a high density of states arising from van Hove singularities, large s-d-exchange splittings (larger in the chain than in the wires) and filled majority d bands (i.e., a "strong Stoner" ferromagnet) and strikingly enhanced Fe magnetic moments that depend on their coordination number. These unusual and distinctive properties are expected to invite somewhat unique experimental characterizations. (C) 2004 Elsevier B.V. All rights reserved.
Electronic-based procedure for managing unbalanced bids
(2004-05-01)
Wang, WC
;
土木工程學系
;
Department of Civil Engineering
Construction lump sum lowest bid procurement is one of the most prevalent methods of awarding construction contracts. For a lump sum bidding practice in Taiwan, after the lowest bidder is awarded a construction project contract, the contractual unit price for each cost item is taken as the product of the owner's estimated unit price and a discounting ratio equal to the total bid price divided by the owner's project cost estimate. This owner-based approach is inequitable because the bidder is denied the right to allocate the risks associated with the costs of performing the work. In U.S. practice, while the unit prices submitted by the bidder are usually considered as the contractual ones, unbalanced bids may occur. This work presents a bidder-based quantitative procedure, built on an electronic-based bidding process for effectively and efficiently supporting reviewing and adjusting the bidder's proposed unit prices for a lump sum procurement project. The advantages of this procedure include that the unit prices electronically obtained front the owner and all qualified bidders are included in analyses during unit-price evaluation, and that rules for unit-price adjustment along with maintaining the total contractual price are included. The novel procedure has been successfully applied to several construction projects in Taiwan and the results have been greatly appreciated by both governments and contractors.
Matching effect and flux pinning force in a Nb superconducting thin film with a triangular lattice of artificial pinning centers
(2004-05-01)
Horng, Lance
;
Wu, J. C.
;
Kang, P. C.
;
Wu, T. C.
;
Yang, T. J.
A strong pinning force in a Nb superconducting thin film is formed by a triangular lattice of defects due to the structural corrugation that acts as pinning centers. The magnetoresistance measurement close to the transition temperature shows a set of minima of magnetoresistance at equal external field intervals. A crossover in current-voltage relations with matching field and half-integer matching field occurs for currents exceeding a certain threshold value. The phenomenon is related to the presence of pinning structures at matching fields. (C) 2003 Elsevier B.V. All rights reserved.
Ballistic transport through coupled T-shaped quantum wires
(2004-05-01)
Lin, YK
;
Lin, KC
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
The ballistic conductance of a coupled T-shaped semiconductor quantum wire (CTQW) is studied. Two types of CTQW are considered, one of which is a H-shaped quantum wire (PiQW) which consists of two vertical arms on the same side of the horizontal arm and the other a Pi-clone quantum wire (PiCQW) which consists of two vertical armes on the opposite sides of the horizontal arm. The mode matching method and Landauer-Buttiker theory are employed to study the energy dependence of the ballistic conductance. Most of transmission profiles of PiQW and PiCQW are found to be distinguishable for large separation d between the two vertical arms. The transmission probability manifests oscillatory behavior when d is increased. When a potential is applied to the connection region, it results in decoupling or coupling effects between the two T-shaped quantum wires according to whether it is positive or negative. When magnetic field is applied to CTQW, the transmission profiles are found to be affected prominently even if the electron passes through the field free region only. (C) 2003 Elsevier B.V. All rights reserved.
Repacking on demand for two-tier wireless local loop
(2004-05-01)
Hung, HN
;
Lin, YB
;
Peng, NF
;
Tsai, HM
;
統計學研究所
This paper proposes a radio channel assignment scheme called repacking on demand (RoD) for two-tier wireless local loop (WLL) networks. A two-tier WLL overlays a macrocell with several microcells. When a new call arrives at a two-tier WLL with RoD, if no idle channel is available in both the microcell and the macrocell, repacking is performed (i.e., a call in the macrocell is moved to its corresponding microcell), and then the reclaimed macrocell channel is used to serve the new call. An analytic model is proposed to compute the call blocking probability of the two-tier WLL with repacking. This analytic model is validated against simulation experiments.We prove that the blocking probability is not affected by the call holding time distributions, but is only dependent on the mean of the call holding times. Compared with some previous proposed schemes, RoD has low blocking probability and significantly reduces repacking rate.
Numerical range of a normal compression
(2004-05-01)
Gau, HL
;
Wu, PY
;
應用數學系
;
Department of Applied Mathematics
Let N be an n-by-n diagonal matrix whose distinct eigenvalues form corners of their convex hull, let x be a vector in with nonzero components, and let A be the compression of N to the orthogonal complement of x . In this article, we study the properties of the eigenvalues and the numerical range of A and show that in many ways they are analogous to the ones for unitary N . The approach via the diagonal form of N yields a much simpler proof for some of the main results in this area.
Special issue on mobile computing
(2004-05-01)
Tseng, YC
;
Lai, TH
;
Sadayappan, P
;
Lin, YB
;
資訊工程學系
Andreev scattering in semiconductor-superconductor junctions containing a finite width semiconductor region applied by magnetic fields
(2004-05-01)
Hsue, YC
;
Yang, TJ
;
Gu, BY
;
Wang, J
;
電子物理學系
We present numerical studies of conductance of quasi-particles (QPs) in junctions consisting of semiconductor (Sm) two-dimensional electronic gas (2DEG) and superconductor (S) containing a finite width 2DEG region (referred to magnetic barrier) applied by a magnetic field perpendicular to the 2DEG plane. Total conductance as a function of beta = mu(N)/homega(c), (where mu(N) is the chemical potential of semiconductor and omega(c) = eB/cm(N)(*) is the cyclotron frequency) strongly depends on the normal or superconducting state of the superconductor. It demonstrates that the Andreev reflection (AR) plays a dominant role. The total conductance of G((NBN)) or G((NBS)) as a function of beta for the NBN or NBS junction displays monotonically increasing behavior with different rising slopes. We observe the existence of a critical magnetic field for switching off the conductance. This critical field of G((NBS)) is a half of that of G((NBN)) in the matching case of the Fermi level and effective mass of QPs in materials forming the junctions. G((NBS)) is usually larger than G((NBN)) for a given magnetic field. The 3D plot of the conductance G((NBN)) and G((NBS)) as functions of beta and the incident angle theta of the QPs displays a flat plateau over a finite domain region of [beta,theta]. However, in the mismatching case of the Fermi energy and effective mass of QPs, G((NBS)) is lower than G((NBN)) because the AR of the holelike QPs now becomes incomplete and normal reflection (NR) of the electronlike QPs is considerably enhanced. The corresponding 3D plot of conductance against beta and theta exhibits heavy spike oscillations around its occupied boundary. We present explicit analytic expressions of the conductance of QPs for this model junction on the basis of classical cyclotron orbit of the QPs in magnetic fields and the quantum mechanical calculation. The characteristics of conductance can be well interpreted by this phenomenological physical picture.
A low-power ASIC design for cell search in the W-CDMA system
(2004-05-01)
Li, CF
;
Chu, YS
;
Sheen, WH
;
Tian, FC
;
Ho, JS
This paper presents a low-power ASIC design for cell search in the wideband code-division multiple-access (W-CDMA) system. A low-complexity algorithm that is able to work satisfactorily under the effect of large frequency and clock errors is designed first. Then, a set of low-power measures are employed in the design of hardware architecture and circuits. Finally, through power analysis, critical blocks are identified and redesigned so as to further reduce the power consumption. The final design shows that the power is reduced by 51 % from the original design of 133.6 mW to 65.49 mW, and its core area is also reduced by 31.9% from 3.4 x 3.4 mm(2) to 2.8 x 2.8 mm(2). The design is implemented and verified in a 3.3-V 0.35-mum CMOS technology with clock rate 1 36 MHz.
Fuzzy discriminant analysis with outlier detection by genetic algorithm
(2004-05-01)
Lin, CC
;
Chen, AP
;
資訊管理與財務金融系註：原資管所+財金所
;
Department of Information Management and Finance
This paper proposes a method for performing fuzzy multiple discriminant analysis on groups of crisp data and determining the membership function of each group by minimizing the classification error using a genetic algorithm. Euclidean distance is used to measure the similarity between data points and defining membership functions. A numerical example is provided for illustration. The numerical example indicates that the classification obtained by fuzzy discriminant analysis is more satisfactory than that obtained by crisp discriminant analysis and is less fuzzy than that obtained by fuzzy cluster analysis. Moreover, the proposed fuzzy discriminant analysis is also a good approach to identifying outliers, of which the degree of membership to each group is zero. (C) 2003 Elsevier Ltd. All rights reserved.
Superradiant and Aharonov-Bohm effect for the quantum ring exciton
(2004-05-01)
Chen, YN
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
The Aharonov-Bohm and superradiant effect on the radiative decay rate of an exciton in a quantum ring is studied. With the increasing of ring radius, the exciton decay rate is enhanced by superradiance, while the amplitude of AB oscillation is decreased. The competition between these two effects is shown explicitly and may be observable in time-resolved experiments. (C) 2004 Elsevier Ltd. All rights reserved.
Product modelling to support case-based construction planning and scheduling
(2004-05-01)
Dzeng, RJ
;
Tommelein, ID
;
土木工程學系
;
Department of Civil Engineering
Many human schedulers create schedules by reusing past similar schedules. The retrieval and reuse of similar schedules are subjective and experience-based. This paper explores different notions of similarity required when performing different scheduling tasks. It describes the CasePlan system that helps schedulers retrieve and reuse parts of existing schedules based on a generic product model, and apply case-based reasoning to generate new schedules. The validation experiment demonstrated CasePlan's accuracy in determining individual subnetworks and activity durations, but weak performance in determining interlinks between subnetworks, which highly depends upon the availability of pertinent cases and the level of detail of project information. (C) 2004 Elsevier B.V. All rights reserved.
Simulation study of carbon nanotube field emission display with under-gate and planar-gate structures
(2004-05-01)
Lan, YC
;
Lee, CT
;
Hu, Y
;
Chen, SH
;
Lee, CC
Recently, two new CNTs-based triode structures, i.e., under-gate and planar-gate structures, for field emission display were proposed and exhibited good characteristics. In this paper, we will investigate how the current density distributed on anode plate and how the display's resolution affected by the bias conditions of the emitter and the gate electrode via computer simulation. Our simulation results exhibit that the gate voltage has a strong effect on display's resolution. For the planar triode structure, the good resolution is achieved when the gate voltage is adjusted to converge the electron beams on an anode plate. For the under-gate structure, the display has a good resolution provided that the gate voltage is not too large to pull the electrons striking on other pixels. In general, the under-gate structure has a wider gate-biased operating condition, but the planar triode structure has a higher light efficiency under the same resolution. Due to the lack of field effect in the y-direction, the spot size of the current density on anode plate looks like strips instead of points. And the resolution of the display will be affected by this factor. (C) 2004 American Vacuum Society.
Adaptive backstepping motion control of induction motor drives
(2004-05-01)
Lin, SK
;
Fang, CH
;
電控工程研究所
;
Institute of Electrical and Control Engineering
In this paper, an adaptive backstepping controller is proposed for position tracking of a mechanical system driven by an induction motor. The mechanical system is a single link fixed on the shaft of the induction motor such as a single-link robot. The backstepping methodology provides a simpler design procedure for an adaptive control scheme and provides a method to define the sliding surface if the robust sliding-mode control is applied. Thus, the backstepping control can be easily extended to work as an adaptive sliding-mode controller. The presented position control system is shown to be stable and robust to parameter variations and external disturbances. The effectiveness of the proposed controllers is demonstrated in experiments.