Browsing by Issue Date, starting with "2000-06-01"

Now showing 1 - 20 of 78337

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].
Personal rules generation for intelligent e-mail service system
(2000-06-01)
Tsai, CJ
;
Tseng, SS
;
Cheng, HT
;
資訊工程學系
;
Department of Computer Science
As E-mail becomes more popular over network, the problem of receiving a lot of undesired E-mails arise. All of the previous systems, which have been developed to solve this problem, may be divided into two different categories, client-side, and server-side, from the view of location of filter. The former case always causes waste of network traffic and the latter case results that ail users may only share a small predefined set of filtering rules. In this paper, we propose a new architecture of E-mail service system, called Intelligent E-mail Service System (IESS), integrating client-side and server-side to help users manage their E-mails. A data mining approach is used in client to find managing rules from user's behavior of reading E-mail automatically. Then these rules would be stored in rule base for predicating E-mail at server. The prediction of the E-mail is made before transferring it to client; therefore, the undesired E-mails can be filtered at server to save network traffic. In addition, the feedback mechanism is provided to refine the prediction accuracy based on each user's decisions for reading E-mails. Experimental results show that IESS can infer E-mail reading preference of individual users correctly up to the accuracy about 80%. We may conclude that IESS can help users manage their E-mails effectively.
Comments on "Reliability and component importance of a consecutive-k-out-of-n system" by Zuo
(2000-06-01)
Hwang, FK
;
Cui, LR
;
Chang, JC
;
Lin, WD
;
應用數學系
Zuo claimed that the comparison of Birnbaum importance between two components for a consecutive-k-out-of-n:G system is the same as that for the F-system. We show that this is not the case and give a correct relation between the two systems. (C) 2000 Elsevier Science Ltd. All rights reserved.
A FIFO-based buffer management approach for the ATM GFR services
(2000-06-01)
Chan, CT
;
Hu, SC
;
Wang, PC
;
Chen, YC
;
資訊工程學系
We investigate the TCP packet transmission over the ATM Guaranteed Frame Rate (GFR) service using a selective packet-discard with buffer vacancy tracking strategy and a packet-based push-out buffering scheme. Our approach is based on FIFO queueing discipline, it features fair sharing of available resources as well as feasibility in hardware implementation.
Interfacial reactions of Ni/Si0.76Ge0.24 and Ni/Si1-x-yGexCy by vacuum annealing and pulsed KrF laser annealing
(2000-06-01)
Luo, JS
;
Lin, WT
;
Chang, CY
;
Shih, PS
;
電子工程學系及電子研究所
Interfacial reactions of Ni on Si0.76Ge0.24 and Si1-x-yGexCy. films by vacuum annealing and pulsed KrF laser annealing were studied by transmission electron microscopy (TEM) in conjunction with energy dispersive spectrometry (EDS) and X-ray diffraction (XRD). For the Ni/Si0.76Ge0.24 and Ni/Si1-x-yGexCy films annealed at a temperature of 200-600 degrees C Ge segregation and agglomeration occurred at an extent becoming more severe at higher temperatures. Upon pulsed KrF laser annealing the agglomeration structure was improved. The retardation of phase transformation in the Ni/Si1-x-yGexCy system was observed upon either vacuum annealing or pulsed laser annealing. Multiple-pulse annealing is an effective method to fabricate smooth Ni(Si0.76Ge0.24)(2) and Ni(Si1-x-yGexCy)(2) films without inducing Ge segregation to the remaining substrates and strain relaxation. (C) 2000 Elsevier Science B.V. All rights reserved.
Analogical process in hypothesis-testing skill acquisition: The modulatory effect of language
(2000-06-01)
Huang, LF
;
Horng, RY
;
工業工程與管理學系
;
Department of Industrial Engineering and Management
唱詩
(2000-06-01)
管管
Correlates of sex-role egalitarianism on employment: A study in Taiwan
(2000-06-01)
Horng, RY
;
Chen, PH
;
交大名義發表
;
National Chiao Tung University
High capacity image steganographic model
(2000-06-01)
Lee, YK
;
Chen, LH
;
資訊工程學系
;
Department of Computer Science
Steganography is an ancient art of conveying messages in a secret way that only the receiver knows the existence of a message. So a fundamental requirement for a steganographic method is imperceptibility; this means that the embedded messages should not be discernible to the human eye. There are two other requirements, one is to maximise the embedding capacity, and the other is security. The least-significant bit (LSB) insertion method is the most common and easiest method for embedding messages in an image. However, how to decide on the maximal embedding capacity for each pixel is still an open issue. An image steganographic model is proposed that is based on variable-size LSB insertion to maximise the embedding capacity while maintaining image fidelity. For each pixel of a grey-scale image, at least four bits can be used for message embedding. Three components are provided to achieve the goal. First, according to contrast and luminance characteristics, the capacity evaluation is provided to estimate the maximum embedding capacity of each pixel. Then the minimum-error replacement method is adapted to find a grey scale as close to the original one as possible. Finally, the improved grey-scale compensation, which takes advantage of the peculiarities of human visual system, is used to eliminate the false contouring effect. Two methods, pixelwise and bitwise, are provided to deal with the security issue when using the proposed model. Experimental results show effectiveness and efficiency of the proposed model.
Analysis of dielectric breakdown patterns in parallel-plate capacitors
(2000-06-01)
Sheu, CR
;
Cheng, CY
;
Wang, PS
;
Lee, CY
;
Pan, RP
The parallel-plate capacitor cells are used as model systems for studying the dielectric breakdown (DB) patterns. Air, a liquid crystal and several kinds of oils are used as the dielectric material sandwiched between the plates. We study the types of patterns formed with different materials, voltages and cell thickness. The fractal dimensions and the conditions for getting each type of DB pattern are obtained for the first time. In addition, the fractal dimensions of patterns simulated by using the active walker model (AWM) are also analyzed and compared with the experimental DB patterns.
Construction of complex-valued wavelets and its applications to scattering problems
(2000-06-01)
Leou, JL
;
Huang, JM
;
Jeng, SK
;
Li, HJ
;
電信工程研究所
This paper introduces the construction of a Family of complex-valued scaling functions and wavelets with symmetry/antisymmetry, compact support, and orthogonality from the Daubechies polynomial, and applies them to solve electromagnetic scattering problems. For simplicity, only two extreme cases in the family, maximum-localized complex-valued wavelets and minimum-localized complex-valued wavelets are investigated. Regularity of root location of the Daubechies polynomial in spectral Factorization are also presented to construct these two extreme genus of complex-valued wavelets. When wavelets are used as basis functions to solve electromagnetic scattering problems by the method of moment (MoM), they often lead to sparse matrix equations. We will compare the sparsity of MoM matrices by the real-valued Daubechies wavelets, minimum-localized complex-valued Daubechies and maximum-localized complex-valued Daubechies wavelets. Our research summarized in this paper shows that the wavelets with smaller signal width will result in a more sparse MoM matrix, especially when the scatterer is with many corners.
Convergence of a dual-porosity model for two-phase flow in fractured reservoirs
(2000-06-01)
Yeh, LM
;
應用數學系
;
Department of Applied Mathematics
A dual-porosity model describing two-phase, incompressible, immiscible hows in a fractured reservoir is considered. Indeed, relations among fracture mobilities, fracture capillary presure, matrix mobilities, and matrix capillary presure of the model are mainly concerned. Roughly speaking, proper relations for these functions are (1) Fracture mobilities go to zero slower than matrix mobilities as fracture and matrix saturations go to their limits, (2) Fracture mobilities times derivative of fracture capillary presure and matrix mobilities times derivative of matrix capillary presure are both integrable functions. Galerkin's method is used to study this problem. Under above two conditions, convergence of discretized solutions obtained by Galerkin's method is shown by using compactness and monotonicity methods. Uniqueness of solution is studied by a duality argument. Copyright (C) 2000 John Wiley & Sons, Ltd.
Effects of thermal boundary condition on buoyancy driven transitional air flow in a vertical cylinder heated from below
(2000-06-01)
Cheng, TC
;
Li, YH
;
Lin, TF
;
機械工程學系
;
Department of Mechanical Engineering
A three-dimensional unsteady numerical computation was carried out here to investigate the effects of the thermal boundary condition on the convection flow in a vertical, bottom heated cylinder containing air. The thermal condition at the sidewall of the cylinder is assumed to be thermally well insulated or perfectly conducting. Results were obtained for air in a cylinder of finite aspect ratio (Gamma = 2) for various thermal Rayleigh numbers. The predicted results indicate that the flow in the sidewall insulated cylinder is highly asymmetric even at steady state and contains multicellular vortices. The flow formation processes leading to the above structures are relatively complicated. In the early transient two axisymmetric circular vortex rolls, one on top of another, appear. Then the rods merge asymmetrically. In the late stage the flow deflection by the cylinder top and bottom results in a very complex flow. In the cylinder with a perfectly conducting sidewall the transition from a steady to a time dependent flow is subcritical. However, in the cylinder with an insulated sidewall the flow transition is supercritical.
Relationships between student scientific epistemological beliefs and perceptions of constructivist learning environments
(2000-06-01)
Tsai, CC
;
師資培育中心
;
Center of Teacher Education
This study was conducted to explore the interplay between students' scientific epistemological beliefs and their perceptions of constructivist learning environments. Through analysing 1,176 Taiwanese tenth-graders' (16-year-olds) questionnaire responses, this study found that students tended to perceive that actual learning environments were less constructivist orientated than what they preferred. Students having epistemological beliefs more orientated to constructivist views of science (as opposed to empiricist views about science) tended to have a view that actual learning environments did not provide sufficient opportunities for social negotiations (p < 0.01) and prior knowledge integration (p < 0.01); and moreover, they show significantly stronger preferences to learn in the constructivist learning environments where they could (1) interact and negotiate meanings with others (p < 0.001), (2) integrate their prior knowledge and experiences with newly constructed knowledge (p < 0.001) and (3) meaningfully control their learning activities (p < 0.001). The main thrust of the findings drawn from this study indicates that teachers need to be very aware of students' epistemological orientation towards scientific knowledge, and to complement these preferences when designing learning experiences, especially to provide constructivist-based lessons to enhance science learning for students who are epistemologically constructivist orientated.
Effects of calcination temperature and A/B ratio on the dielectric properties of (Ba,Ca)(Ti,Zr,Mn)O-3 for multilayer ceramic capacitors with nickel electrodes
(2000-06-01)
Lee, WH
;
Tseng, TY
;
Hennings, DFK
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The electrical performance of multilayer ceramic capacitors (MLCCs) with Ni inner electrodes, made from (Ba,Ca)-(Ti,Zr,Mn)O-3 (BCTZM), is closely related to the calcination temperature and the A/B ratio of the powder. For materials showing A/B = 1.000, the lifetime, the breakdown voltage, and the RC increase with higher calcination temperatures. No significant effect of the calcination temperature on RC and lifetime was found for materials showing A/B = 0.991, The isoelectric point of BCTZM is shifted toward higher pH values when the calcination temperature is decreased. The above results are attributed to the colloidal stability of aqueous BCTZM suspensions and the resulting green density of powder compacts.
AlSixNy as an embedded layer for attenuated phase-shifting mask in 193 nm and the utilization of a chemically amplified negative resist NEB-22 for maskmaking
(2000-06-01)
Loong, WA
;
Lin, CM
;
應用化學系
;
Department of Applied Chemistry
AlSixNy (x similar to 0.31, y similar to 0.45) thin film as a new embedded material for AttPSM in 193 nm lithography was presented. With the good controlling of plasma sputtering of Al (100 similar to 130 W) and Si (20 similar to 50 W) under Ar (75 seem), and nitrogen (2.5 similar to 5 seem), AlSixNy has enough deposition latitude to meet the requirements as an embedded layer. For required phase shift 180 degree, the calculated thickness d(180) of AlSixNy films is in the range of 87 similar to 100 nm. The T% in 365 and 488 nm for optical inspection and alignment is below 40%. Its sheet resistance R-s, is less than 0.8 k Omega/square. Helicon wave plasma etcher and Taguchi design of experiment have been applied to the study of the etching selectivity of AlSixNy over substrate fused silica and negative resist NEB-22. Under chamber pressure 3 mtorr, BCl3 45 sccm, Cl-2 7 seem, plasma source power 1400 W and substrate bias RF power 30 W for the selectivity of AlSixNy over NEB-22 was found to be 4.8:1. The selectivity of AlSixNy over fused silica was 12.3:1 under chamber pressure 9 mtorr, BCl3 13 seem, Cl-2 45 seem, O-2 8 seem, plasma source power 1400 W and substrate bias RF power 30 W. A 0.3 mu m line/space etched pattern using AlSixNy as embedded layer was successfully fabricated.