Browsing by Issue Date, starting with "2000-05-15"

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Liquid crystal alignment with a photo-crosslinkable and solvent-soluble polyimide film
(2000-05-15)
Lee, WC
;
Hsu, CS
;
Wu, ST
;
應用化學系
;
Department of Applied Chemistry
A new photo-crosslinkable and solvent-soluble polyimide containing cinnamate side chains (PICA) was developed for aligning nematic liquid crystals (LCs). Good LC alignment was achieved by exposing a long-wave linearly polarized ultraviolet (LPUV) light to the PICA film. The LC alignment direction is found perpendicular to the polarization axis of the incident LPUV light. The uniform alignment of LC molecules induced by PICA Films remains intact after being heated at 85 degreesC for 450 hours. A small pretilt angle on the PICA film was generated by the double exposure method.
A micromachined silicon-submount package for vertical emission of edge emitting laser diodes
(2000-05-15)
Shie, JS
;
Yu, SH
;
光電工程學系
;
Department of Photonics
A silicon-submount package structured with vertical emission of edge emitting laser diodes (LDs) is addressed. Utilizing the micromachining technique, a (100) silicon wafer can be engraved into a batch of submount structures having 45 degrees-slant mirrors for light deflection, and mesas for precise die dwelling. The mirrors are fabricated by deep V-groove etching with the etching window aligned to [100] crystal direction, and by multiple cycles of oxidation-and-isotropic etching processes. The initial ridged surface can thus be polished to a final roughness below 30 nm, with 100-mu m depth, sufficient to accommodate the vertically extended angle of a laser beam. Gold plating on the surface is patterned to form reflective mirrors on the slopes individually, and to provide the bases, which are connected to common electrode, for electroplating of thick indium pads selectively on the mesa areas. Self-alignment of LD bars or dice soldered right on the mesas can be achieved by the surface-tension mechanism that existed between the LD gold electrodes and the indium pads during melting. With simple TO-5 package, a vertically emitted beam has been observed on a stacked LD-submount device, as expected. (C) 2000 Elsevier Science S.A. All rights reserved.
On estimation and prediction for temporally correlated longitudinal data
(2000-05-15)
Lee, JC
;
Hwang, RC
;
統計學研究所
;
Institute of Statistics
In this paper, from a Bayesian point of view, we consider estimation of parameters and prediction of future Values for the longitudinal model proposed by Diggle (1988. Biometrics 44. 959-971). This model, called the repeated measures linear model, incorporates group mean, variability among individuals, serial correlation within an individual, and measurement error. Two different: priors are employed by the Bayesian approach, one is the noninformative prior and the other is composed of inverse gamma distributions. Given the noninformative prior, it is shown that the resulting approximate estimates of the regression coefficients are the same as those derived by the restricted maximum likelihood estimation. Markov chain Monte Carlo methods are also used to obtain more accurate Bayesian inference for parameters as well as prediction of future values. For parameter estimation and prediction of future values, the advantages of the Bayesian approach over the maximum likelihood method and the restricted maximum likelihood method are demonstrated by both real and simulated data. (C) 2000 Elsevier Science B.V. All rights reserved. MSC: 62F15; 62F10.
資深作家聚首,期盼繼續寫作
(2000-05-15)
蔡美娟
Applying stack simulation for branch target buffers
(2000-05-15)
Shiu, RM
;
Lu, NP
;
Chung, CP
;
資訊科學與工程研究所
;
Institute of Computer Science and Engineering
Branch target buffer (BTB) is widely used in modern microprocessor designs to reduce the penalties caused by branches. To evaluate the performance of a BTB, trace-driven simulation is often used. However, as the trace of a typical program is very large, the simulation time is often too long. To reduce the simulation time, we developed a stack simulation technique for BTB to evaluate many sets of design parameters in one simulation pass. Due to the fact that the prediction information in the BTB does not have the inclusion property - a property which makes the stack simulation work, we propose a state vector method to enumerate the prediction information for different sets of BTB design parameters to mimic the inclusion property. Simulation results show that the state vector method greatly reduces the simulation time. The speedup of the stack simulation for BTB proposed in this paper over the traditional BTB simulation is 4.68 in terms of simulation time when 13 sets of BTB design parameters are simulated in one simulation pass. (C) 2000 Elsevier Science Inc. All rights reserved.
資深作家書展文學風華再現
(2000-05-15)
陳文芬
Primitive spatial relations based on SKIZ
(2000-05-15)
Jan, SR
;
Hsueh, YC
;
資訊工程學系
;
Department of Computer Science
Spatial relations between objects or regions in an image play important roles in scene understanding. However, it is difficult to define these relations for automation. Most existing methods for defining spatial relations depend on angle measurements between points of the two objects of interest. In this study, we propose a new approach based on the concept of skeleton by zones of influence (SKIZ) for recognizing the primitive spatial relations between objects or regions in a segmented image. The approach is compared with the aggregation and compatibility methods. The experimental result shows the proposed approach is effective and fast. (C) 2000 Elsevier Science B.V. All rights reserved.
A GA-based fuzzy adaptive learning control network
(2000-05-16)
Chung, IF
;
Lin, CJ
;
Lin, CT
;
電控工程研究所
;
Institute of Electrical and Control Engineering
This paper addresses the structure and an associated learning algorithm of a feedforward multilayered connectionist network for realizing the basic elements and functions of a traditional fuzzy logic controller. The proposed fuzzy adaptive learning control network (FALCON) can be contrasted with the traditional fuzzy logic control systems in their network structure and learning ability. A structure/parameter learning algorithm, called FALCON-GA, is proposed for constructing the FALCON automatically. The FALCON-GA is a three-phase hybrid learning algorithm. In the first phase, the fuzzy ART algorithm is used to do fuzzy clustering in the input/output spaces according to the supervised training data. In the second phase, the genetic algorithm (GA) is used to find proper fuzzy logic rules by associating input clusters and output clusters. Finally, in the third phase, the backpropagation algorithm is used for tuning input:output membership functions. Hence, the FALCON GA combines the backpropagation algorithm for parameter learning and both the fuzzy ART and GAs for structure learning. It can partition the input/output spaces, tune membership functions and find proper fuzzy logic rules automatically. The proposed FALCON has two important features. First, it reduces the combinatorial demands placed by the standard methods for adaptive linearization of a system. Second, the FALCON is a highly autonomous system. In its learning scheme, only the training data need to be provided from the outside world. The users need not give the initial fuzzy partitions, membership functions and fuzzy logic rules. Computer simulations have been conducted to illustrate the performance and applicability of the proposed system. (C) 2000 Elsevier Science B.V. All rights reserved.
Integrating membership functions and fuzzy rule sets from multiple knowledge sources
(2000-05-16)
Wang, CH
;
Hong, TP
;
Tseng, SS
;
資訊工程學系
;
Department of Computer Science
Ln this paper, we propose a GA-based fuzzy knowledge-integration framework that can simultaneously integrate multiple fuzzy rule sets and their membership function sets. The proposed two-phase approach includes fuzzy knowledge encoding and fuzzy knowledge integration. In the encoding phase, each fuzzy rule set with its associated membership functions is first transformed into an intermediary representation, and further encoded as a string. The combined strings form an initial knowledge population which is then ready for integration. In the knowledge-integration phase. a genetic algorithm is used to generate an optimal or nearly optimal set of fuzzy rules and membership functions from the initial knowledge population. The hepatitis diagnostic problem was used to show the performance of the proposed knowledge-integration approach. Results show that the fuzzy knowledge-base resulting from using our approach performs better than every individual knowledge base. (C) 2000 Elsevier Science B.V. All rights reserved.
Nucleotide binding and sulfation catalyzed by phenol sulfotransferase
(2000-05-19)
Lin, ES
;
Yang, YS
;
生物科技學系
;
Department of Biological Science and Technology
The sulfation of a nucleotide is an indispensable step for the sulfuryl group transfer in a biological system. The product and cosubstrate of sulfotransferase in physiological condition are adenosine 3',5'-bisphosphate (PAP) and 3'-phospho adenosine 5'-phosphosulfate (PAPS), respectively. We find that ribose and adenine, two major parts of the adenosine nucleotide, bind tightly to phenol sulfotransferase (PST) separately, and various nucleotides also bind tightly to PST. We determine the dissociation constants of a variety of nucleotides and examine their potential as cofactors or cosubstrates of PST. Using 4-nitrophenyl sulfate as the sulfuryl group donor, three nucleotides, adenosine 5'-monophosphate (AMP), adenosine 2',5'-bisphosphate (2',5'-PAP), and adenosine 2':3' cyclic phosphate 5'-phosphate (2':3'-cyclic PAP), are shown here for the first time to be sulfated at 5'-phopho position by a PST catalyzed reaction. Spectrophotometry, HPLC, and P-31 NMR are used to determine the activity of PST and identify the sulfated nucleotides. The V-max of PST and K-m of these nucleotides are determined when they are used as cofactors or cosubstrates for the sulfuryl group transfer. The existence and possible physiological significance of these newly reported binding and sulfation of nucleotides by PST in biology is yet to be discovered. (C) 2000 Academic Press.
Distribution of dangling bond pairs on partially hydrogen-terminated Si(100) surface observed by scanning tunneling microscopy
(2000-05-20)
Chen, RP
;
Lin, DS
;
物理研究所
;
Institute of Physics
Hydrogen recombinative desorption from a Si2H2 monohydride dimer on the Si(100) surface regenerates a dangling bond (DB) pair on the dimer. In this paper, we investigated the spatial distribution of the regenerated DB pairs on the Si(100)-2 x 1:H and disilane-passivated Si(100) surface using elevated temperature scanning tunneling microscopy (HT-STM) in the temperature range between 590 and 622 K. Experimental results indicate that the ends of one-dimensional (1D) monohydride dimer islands are preferred sites for DB pairs and a repulsive interaction occurs between two neighboring DB pairs in the same dimer row. (C) 2000 Elsevier Science B.V. All rights reserved.
Mesh independence of matrix-free methods for path following
(2000-05-21)
Ferng, WR
;
Kelley, CT
;
應用數學系
;
Department of Applied Mathematics
In this paper we consider a matrix-free path following algorithm for nonlinear parameter-dependent compact fixed point problems. We show that if these problems are discretized so that certain collective compactness and strong convergence properties hold, then this algorithm can follow smooth folds and capture simple bifurcations in a mesh-independent way.
Dielectric relaxation and defect analysis of Ta2O5 thin films
(2000-05-21)
Ezhilvalavan, S
;
Tsai, MS
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The presence of defects in thin-film dielectrics often leads to dielectric relaxation as a function of frequency, in which the dielectric constant decreases and the loss tangent increases with increasing frequency. Dielectric relaxation results in charge storage capacity reduction under dynamic random access memory operating conditions. In this work, the dielectric relaxation behaviour of de reactive sputtered Ta2O5 thin film was investigated. Using dielectric dispersion measurements as a function of frequency (100 Hz less than or equal to f less than or equal to 10 MHz) and temperature (27 degrees C less than or equal to T less than or equal to 150 degrees C), we determined the dielectric relaxation and defect quantity of the films and propose an equivalent circuit on the basis of complex capacitance, admittance and impedance spectral studies.
Time-resolved photoluminescence study of isoelectronic In-doped GaN films grown by metalorganic vapor-phase epitaxy
(2000-05-29)
Huang, HY
;
Shu, CK
;
Lin, WC
;
Chuang, CH
;
Lee, MC
Time-resolved photoluminescence spectra were used to characterize isoelectronically doped GaN:In films. Our results indicate that the recombination lifetime of the donor-bound-exciton transition of undoped GaN exhibits a strong dependence on temperature. When In is doped into the film, the recombination lifetime decreases sharply from 68 to 30 ps, regardless of the measured temperature and In source flow rate. These observations might be related to the isoelectronic In impurity itself in GaN, which creates shallow energy levels that predominate the recombination process. (C) 2000 American Institute of Physics. [S0003- 6951(00)02622-X].
Depth-averaged two-dimensional curvilinear explicit finite analytic model for open-channel flows
(2000-05-30)
Hsu, CT
;
Yeh, KC
;
Yang, JC
;
土木工程學系
;
Department of Civil Engineering
A depth-averaged two-dimensional model has been developed in the curvilinear co-ordinate system for free-surface flow problems. The non-linear convective terms of the momentum equations are discretized based on the explicit-finite-analytic method with second-order accuracy in space and first-order accuracy in time. The other terms of the momentum equations, as well as the mass conservation equation, are discretized by the finite difference method. The discretized governing equations are solved in turn, and iteration in each time step is adopted to guarantee the numerical convergence. The new model has been applied to various flow situations, even for the cases with the presence of sub-critical and supercritical flows simultaneously or sequentially. Comparisons between the numerical results and the experimental data show that the proposed model is robust with satisfactory accuracy. Copyright (C) 2000 John Wiley & Sons, Ltd.
An aperture-coupled linear microstrip leaky-wave antenna array with two-dimensional dual-beam scanning capability
(2000-06-01)
Hu, CC
;
Jou, CF
;
Wu, JJ
;
傳播研究所
;
Institute of Communication Studies
This paper describes an X-band 4 x 1 aperture-coupled series-fed electronically steerable microstrip leaky-wave antenna (LWA) array design, which has dual-beam radiation pattern and two-dimensional (2-D) beam-scanning capability. The LWA array is operated in the first higher order mode and excited by center-fed aperture coupled for dual-beam operation. The varactor-tuned phase shifters are placed between the antenna elements. The measured half-power beamwidth of the H-plane and quasi-E-plane radiation patterns are less than 30 degrees. By tuning the reverse de bias of the varactor diodes, the main beam can be scanned in azimuth plane from -13 degrees to +13 degrees off broadside. In the elevation plane, the beam-scanning angle is close to 20 degrees as the operating frequency tuned from 11.58-12.5 GHz. Taking into account each phase-shifter insertion loss and phase progression, the measured results compared closely with the theoretical prediction, The proposed antenna array is suitable for wireless communication and collision warning radar systems.
Thermocapillary effect on drying of a polymer solution under non-uniform radiant heating
(2000-06-01)
Chen, JJ
;
Lin, JD
;
機械工程學系
;
Department of Mechanical Engineering
This theoretical investigation analyzes the two-dimensional heat and mass transfer characteristics arising from the cion-uniform radiant incidence in polymer solutions whose motion is governed by combined thermocapillary/ buoyancy laminar flow. Also considered herein is the evaporation of solvent at solution surface. The effects of various radiation input, external convective parameters, and important physical properties of solutions on the drying characteristics are investigated and results are presented in terms of flow, thermal, and concentration fields, and rate of water removal. In addition, the influence of thermocapillary effect on drying features is also examined. Numerical results indicate that absorbed energy and distribution of the solvent concentration dominate the drying rate. At larger surface tension Reynolds number, more mass concentration can be transferred by thermocapillary flow from the interior region to the surface, which then increases drying rate. Furthermore, removing the solid wall effect reduces the drying time required for a solution film with two sides of symmetric surfaces, which is irradiated by an array of infrared radiant heaters. (C) 2000 Elsevier Science Ltd. All rights reserved.
Thickness dependent gate oxide quality of thin thermal oxide grown on high temperature formed SiGe
(2000-06-01)
Wu, YH
;
Chin, A
;
Chen, WJ
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
For thin oxides grown on high temperature formed Si0.3Ge0.7, the gate oxide quality is strongly dependent on oxide thickness and improves as thickness reduces from 50 to 30 Angstrom. The thinner 30 Angstrom oxide has excellent quality as evidenced by the comparable leakage current, breakdown voltage, interface-trap density and charge-to-breakdown with conventional thermal oxide grown on Si. The achieved good oxide quality is due to the high temperature formed Si0.3Ge0.7 that is strain relaxed and stable during oxidation, The possible reason for strong thickness dependence may be due to the lower GeO2 content formed in thinner 30 Angstrom oxide rather than strain relaxation related rough surface or defects.
Study of linear and nonlinear optical properties of distorted Ti-O-6 perovskite structure in BaxSr1-xTiO3
(2000-06-01)
Chen, WK
;
Cheng, CM
;
Huang, JY
;
Hsieh, WF
;
Tseng, TY
We report the linear and nonlinear optical properties of sol-gel prepared BaxSr1-xTiO3 (BST) crystalline powders. The results from powder X-ray diffraction, birefringence, and second-order optical nonlinearity measurements indicate that the paraelectric-ferroelectric phase transition of Ba0.75Sr0.25TiO3 occurs near room temperature. The second-order optical nonlinearity of the ferroelectric BST is about 7.9 pm/V. The index of refraction, n = 2.2, and birefringence, Delta n(B) similar to 0.05, are also appropriate for practical nonlinear optical applications. (C) 2000 Elsevier Science Ltd. All rights reserved.
Effect of growth temperature on the electric properties of In0.12Ga0.88As/GaAs p-i-n multiple-quantum-well diodes
(2000-06-01)
Chen, JF
;
Wang, PY
;
Wang, JS
;
Wong, HZ
;
電子物理學系
The electric properties of In0.12Ga0.88As/GaAs p-i-n multiple-quantum-well (MQW) diodes, with the MQW layer grown at different temperatures by molecular beam epitaxy, have been investigated. Temperature-dependent current-voltage studies reveal a trap-filled limit current at a low temperature and a generation-recombination current via deep levels at high temperature for a 300 degrees C-grown sample. Frequency-dependent capacitance and deep-level transient spectroscopy reveal one majority trap at 0.73 eV and two minority traps at 0.71 and 0.43 eV. The 0.73 eV trap is also detected in 550 degrees C-grown samples, suggesting that it is a common defect in relaxed InGaAs/GaAs MQWs and probably originates from the defect states related to the strain relaxation. The 0.71 eV trap is believed to be the dominating deep level that governs the current conduction due to the activation energy observed in the current-voltage characteristics. (C) 2000 American Institute of Physics. [S0021-8979(00)00711-8].