Browsing by Issue Date, starting with "2003-07-15"

Now showing 1 - 20 of 72502

Formation of transverse modes with Y-junction structures in broad-area oxide-confined vertical-cavity surface-emitting laser
(2003-07-15)
Kou, RJ
;
Pan, CL
;
光電工程學系
;
Department of Photonics
We performed experimental and theoretical investigations on the transverse-mode emission behavior of a broad-area oxide-confined vertical-cavity surface-emitting laser (VCSEL). The far-field emission pattern with y-junction structures is observed in the VCSEL with a 20-mum-diameter aperture when the injection current is significantly above the thermal roll-over point. In order to provide a quantitative understanding of these emission characteristics, we present a numerical simulation to model and fit the experimental results. The numerical simulation adopts the high-order Laguerre-Gaussian mode due to the assumptions of a parabolic refractive-index profile and ring-shaped carrier distribution in the laser. From the numerical simulation results, the formation of y-junction structures is inferred to be caused by the superposition of two high-order Laguerre-Gaussian modes. The results of this numerical simulation are in good agreement with the experimental findings.
A feedback-injected Fabry-Perot laser diode filtering technique for side-mode suppression and linewidth reduction of erbium-doped fiber lasers
(2003-07-15)
Lin, GR
;
Lee, SK
;
光電工程學系
;
Department of Photonics
By adding a fiber-pigtailed Fabry-Perot laser diode (FPLD) into a close-loop erbium-doped fiber amplifier (EDFA) ring cavity. and feedback-injecting the FPLD biased at just below threshold and the EDFA each other via directional couplers, we demonstrate a low-cost band-pass filtering technique for constructing narrow linewidth erbium-doped fiber laser (EDFL) with ultrahigh side-mode suppression ratio (SMSR). Under an output coupling ratio of 90%, the mutually injection-locked EDFL-FPLD link exhibits a maximum output power and SMSR of up to 98.6 mW and 49.6 dB at wavelength 1561.37 nm,. respectively. Wavelength tuning of up to 6 nm can be achieved by tuning the temperature and fine adjusting the below threshold driven current of FPLD. The minimum spectral linewidth at 3dB-decay of as small as 0.017 nm measuring by commercial optical spectrum analyzer with limited resolution bandwidth of 0.01 nm are observed. The stabilities in power, SMSR, peak wavelength of +/-0.01 mW, +/-0.5 dB, and +/-0.025 nm, respectively, are also determined. (C) 2003 Elsevier Science B.V. All rights reserved.
System integration of WAP and SMS for home network system
(2003-07-15)
Wu, CH
;
Jan, RH
;
資訊工程學系
;
Department of Computer Science
This paper proposes a Home Network System (HNS) architecture integrated with Wireless Application Protocol and Short Message Service to support the connectivity between home and Internet/Global System for Mobile Communication (GSM) networks. The HNS architecture includes an HNS gateway and three home network subsystems, i.e., home appliance, security and messaging subsystems. The main objective of the integrated system is to remotely monitor and control the devices in the HNS via laptop computer or a GSM mobile terminal. In addition to responding to remote queries, the managed devices (e.g., home appliances or burglar alarm system) can actively send alerting messages to a mobile terminal when an abnormal state occurs. Through the HNS gateway, the monitoring and control information is diffused to the Internet/GSM network. An implementation of the HNS system is described in this paper as an illustration of the feasibility of the proposed architecture. (C) 2003 Elsevier Science B.V. All rights reserved.
OS portal: an economic approach for making an embedded kernel extensible
(2003-07-15)
Chang, DW
;
Chang, RC
;
資訊工程學系
;
Department of Computer Science
With the rapid development of embedded system techniques and Internet technologies, network-enabled embedded devices have grown in their popularity. One critical design trend of such devices is that they are shifting from static and fixed-function systems to more dynamic and extensible ones, which are capable of running various kinds of applications. To support the diversity of the applications, kernels on these devices must be extensible. However, making embedded kernels extensible is challenging due to the shortage of resources on these devices. In this paper, we propose the operating system portal framework, which makes embedded kernels become extensible while keeping the added overheads minimal. By storing kernel modules on a resource-rich server and loading them on demand, the need for equipping a local storage on the device is eliminated. In addition, we propose mechanisms for reducing the memory requirements and performing on-line module replacement on the embedded devices. According to the performance evaluation, our approach requires only 1% of the resource requirements, compared to the traditional approaches. This allows our framework to be applied on a wide range of embedded devices. (C) 2002 Elsevier Science Inc. All rights reserved.
Mutual injection locking of an erbium-doped fiber laser and a fiber-pigtailed Fabry-Perot laser diode
(2003-07-15)
Lin, GR
;
光電工程學系
;
Department of Photonics
Mutual injection locking of a fiber-pigtailed Fabry-Perot laser diode (FPLD) and a closed-loop erbium-doped fiber-amplifier-based laser (EDFL) system are studied. A single FPLD longitudinal mode can be lasing in the EDFL-FPLD link, with a reduced linewidth of <0.017 ran and an improved sidemode-suppressing ratio of 50 dB. The FPLD's optimized current range is below threshold within 10%, and its required feedback-injecting power is 12.4 muW (corresponding to 0.03% of the EDFL output power). The maximum detuning ranges of the current and temperature of the FPLD that preserve the narrow linewidth and the highest sidemode-suppressing ratio of the EDFL-FPLD link are 2.4 mA and 2.2degreesC, respectively. The power dissipated by the EDFL-FPLD link is 20% more than that of the free-running EDFL. (C) 2003 Optical Society of America.
Finite Blaschke products of contractions
(2003-07-15)
Gau, HL
;
Wu, PY
;
應用數學系
;
Department of Applied Mathematics
Let A be a contraction on Hilbert space H and phi a finite Blaschke product. In this paper, we consider the problem when the norm of phi(A) is equal to 1. We show that (1) parallel tophi(A)parallel to = 1 if and only if parallel toA(k)parallel to = 1, where k is the number of zeros of phi counting multiplicity, and (2) if H is finite-dimensional and A has no eigenvalue of modulus 1, then the largest integer I for which parallel toA(l)parallel to = 1 is at least m/(n - m), where n = dim H and m = dim ker(I - A*A), and, moreover, l = n - 1 if and only if m = n - 1. (C) 2003 Elsevier Science Inc. All rights reserved.
Effect of hydrolysis on the strength of hydrogen bonds and T-g of poly(vinylphenol-co-acetoxystyrene)
(2003-07-15)
Kuo, SW
;
Liu, WP
;
Chang, FC
;
應用化學系
;
Department of Applied Chemistry
A series of poly(vinylphenol-co-acetoxystyrene) (PVPh-co-PAS) copolymers were prepared by partial hydrolyses of poly(acetoxystyrene) (PAS) in acidic and basic solutions. Higher glass transition temperature, higher fraction of hydrogen-bonded carbonyl group, and higher interassociation equilibrium constant were observed for copolymers with same composition prepared from the acidic hydrolysis than from the basic hydrolysis because the sequence distribution of the former is relatively more random than the latter. Infrared spectra provide positive evidence in terms of sequence distribution, glass transition temperature, and hydrogen-bonding strength in poly(vinylphenol-co-acetoxystyrene) by prepared these two hydrolysis methods.
A new key authentication scheme based on discrete logarithms
(2003-07-15)
Lee, CC
;
Hwang, MS
;
Li, LH
;
資訊工程學系
;
Department of Computer Science
In this article, we propose a new public key authentication scheme for cryptosystems with a trusty server. The scheme is based on discrete logarithms. In the scheme, the certificate of the public key is a combination of user's password and private key. The scheme not only resolve the problems appeared but also is secure for the others public-key authentication. (C) 2002 Elsevier Science Inc. All rights reserved.
Vortex structure. of quantum eigenstates and classical periodic orbits in two-dimensional harmonic oscillators
(2003-07-18)
Chen, YF
;
Huang, KF
;
電子物理學系
;
Department of Electrophysics
The connection between the wavefunctions and the classical periodic orbits in a 2D harmonic oscillator is analytically constructed by using the representation of SU(2) coherent states. It is found that the constructed wavefunction generally corresponds to an ensemble of classical trajectories and its localization is extremely efficient. With the constructed wavefunction, we also analyse the property of the probability current density associated with the classical periodic orbit. The appearance of vortex structure in the quantum flow. is clearly found to arise from the wave interference.
Fourth-order finite difference scheme for the incompressible Navier-Stokes equations in a disk
(2003-07-20)
Lai, MC
;
應用數學系
;
Department of Applied Mathematics
We develop an efficient fourth-order finite difference method for solving the incompressible Navier-Stokes equations in the vorticity-stream function formulation on a disk. We use the fourth-order Runge-Kutta method for the time integration and treat both the convection and diffusion terms explicitly. Using a uniform grid with shifting a half mesh away from the origin, we avoid placing the grid point directly at the origin; thus, no pole approximation is needed. Besides, on such grid, a fourth-order fast direct method is used to solve the Poisson equation of the stream function. By Fourier filtering the vorticity in the azimuthal direction at each time stage, we are able to increase the time step to a reasonable size. The numerical results of the accuracy test and the simulation of a vortex dipole colliding with circular wall are presented. Copyright (C) 2003 John Wiley Sons, Ltd.
Preparing titanium oxide with various morphologies
(2003-07-20)
Chen, YF
;
Lee, CY
;
Yeng, MY
;
Chiu, HT
;
應用化學系
Titanium oxide powder was prepared by hydrolyzing titanium tetraisopropoxide (TTIP) in aqueous solutions at pH 2, using TMC and NP-204 as surfactants. The anatase phase was formed when the precipitants were dried at 373 K. When the calcination temperature was below 773 K, all the powders were crystalline in the anatase phase. The powders changed to the rutile phase when the calcination temperature exceeded 1173 K. The powder calcined at 673 K has spherical primary particles with diameters of approximately 8 nm. When the powders calcined at 673 K were heated in NaOH solutions of various concentrations at 423 K for 20 h, titanium oxide powders with different morphologies were obtained. After the powders were refluxed in 5 M NaOH solutions, flower-like titanium oxide particles were formed. Nanotubes of titanium oxide about 8 run in diameter and over 600 rim long were obtained when the powders were refluxed in 10 M NaOH solution. (C) 2003 Elsevier Science B.V. All rights reserved.
A Stop-or-Move Mobility model for PCS networks and its location-tracking strategies
(2003-07-21)
Tseng, YC
;
Chen, LW
;
Yang, MH
;
Wu, JJ
;
資訊工程學系
This paper considers the location-tracking problem in PCS networks. Solutions to this problem in fact highly depend on the mobility patterns of mobile subscribers [ACM DIAL-M (1999) 72]. In the literature, many works have assumed a simple random walk model, where mobile subscribers always stay in a roaming state and can move in any direction with equal probability. In this paper, we propose a new Stop-or-Move Mobility (SMM) model, which is characterized by the following features: 'transition between stop and move', 'infrequent transition', 'memory of roaming direction', and 'oblivious in different moves'. Based on this mobility model, a static and an adaptive location-tracking Scheme are developed. The schemes only need to keep very little information for each user. Analyses and simulations are provided, which show that the proposed schemes are quite prospective. (C) 2003 Elsevier Science B,V. All rights reserved.
在溫度分佈量測中達到改善空間解析度的訊號處理方法
(2003-07-21)
祁甡
;
李健仲
;
蔣博文
本發明係提出一種在溫度分佈量測中達到改善空間解析度的訊號處理方法，其係使用短取樣間隔及寬脈波寬度的雷射光源，並結合分解布里淵頻譜的訊號處理方法，將量取光脈波進入感測光纖及過渡重疊區域時之頻譜資料，並利用該等頻譜與加重因子值之關係式求得該脈波真正進入感測光纖中的長度，進而推算出實際溫度變化的位置；最後再利用該位置推導得到一對應於實際感測溫度之布里淵頻譜之頻率漂移值，以藉此得到一感測溫度分佈。本發明不需要短脈波寬度即可達到高空間及高溫度解析度之功效，並同時適用於短或長感測範圍的分佈型溫度量測。
Synthesis of t-butylated diphenylanthracene derivatives as blue host materials for OLED applications
(2003-07-21)
Balaganesan, B
;
Shen, WJ
;
Chen, CH
;
應用化學系
;
資訊工程學系
This paper describes the cost-effective synthesis and the photoluminescence of diphenylanthracene derivatives, which are found to be potential blue host materials for organic light emitting diode (OLED) technology. (C) 2003 Elsevier Ltd. All rights reserved.
Electrooptical properties of GaNAs/GaAs multiple quantum well structures
(2003-07-25)
Lee, JR
;
Chen, YY
;
Lu, CR
;
Lee, WI
;
Lee, SC
The electrooptical properties of the GaNAs/GaAs multiple quantum well structures have been studied using the photoreflectance spectroscopy from 20 K to room temperature. Above the band gap energy of GaAs, Franz-Keldysh oscillations were observed. The period of the Franz-Keldysh oscillations decreased slightly with decreasing temperature, and indicated that the corresponding space charge distribution varied slowly with temperature. The modulated quantum well transition features were observed below the band gap energy of GaAs. A matrix transfer algorithm was used to calculate the quantum well subband energies numerically. The band gap energy and the electron effective mass of the GaNAs/GaAs system were adjusted to obtain the subband energies to best fit the observed quantum well transition energies. (C) 2003 Elsevier Science B.V. All rights reserved.
Correlation between N 1s XPS binding energy and bond distance in metal amido, imido, and nitrido complexes
(2003-07-28)
Wu, JB
;
Lin, YF
;
Wang, JL
;
Chang, PJ
;
Tasi, CP
Synchrotron-based X-ray photoelectron spectroscopy is used to measure N 1s binding energies of several metal amido, imido, and nitrido complexes of group 5 and 6 metals. The N 1s binding energy decreases as the formal M-N bond order increases. A simple correlation between the contraction of the M-N bond and the lowering of binding energy is also observed. This correlation supports a notion that the bonding character of a linear metal-imido linkage resembles that of a metal-nitrido linkage closely.
Bright red-emitting electrophosphorescent device using osmium complex as a triplet emitter
(2003-07-28)
Kim, JH
;
Liu, MS
;
Jen, AKY
;
Carlson, B
;
Dalton, LR
A series of efficient and bright double-layer light-emitting devices have been fabricated using the osmium (Os) complex as the triplet emissive dopant in both a blue-emitting polyfluorene derivative (PF-TPA-OXD) containing hole-transporting triphenylamine (TPA) and electron-transporting oxadiazole (OXD) as side chains and a blend of 2-(4-t-butylphenyl)-5(4-biphenylyl)-1,3,4-oxadizole (PBD) in poly(N-vinylcarbazole) (PVK). Due to a balanced charge injection and transport in PF-TPA-OXD and very efficient energy transfer from this polymer to the Os complex, the resulting device (indium tin oxide/HTL/OsCF3:PF-TPA-OXD/Ca/Ag) reaches a maximum external quantum efficiency of 2.1% with a peak brightness of 2920 cd/m(2). These results are significantly higher than those obtained from the commonly used host, PVK:PBD (0.49% and 1270 cd/m(2)). (C) 2003 American Institute of Physics.
Selective distribution of surface-modified TiO2 nanoparticles in polystyrene-b-poly (methyl methacrylate) diblock copolymer
(2003-07-29)
Weng, CC
;
Wei, KH
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Ordered aggregates of surfactant-modified TiO2 nanoparticles in the selective block of lamellar assemblies of the diblock copolymer PS-b-PMMA have been prepared. The hydrophobic or hydrophilic nature of the tethered surfactant determines the location of TiO2 nanoparticles in the corresponding block, as confirmed by transmission electron microscopy, differential scanning calorimetry, and Fourier transform infrared spectroscopy. The modes of dispersion of TiO2 in the blocks depend on the type of bonding between the surfactant and TiO2. Photoluminescence studies of these nanocomposites demonstrate that the location of TiO2 nanoparticles affect the block copolymer's luminescence at different wavelengths.
Bipanconnectivity and edge-fault-tolerant bipancyclicity of hypercubes
(2003-07-31)
Li, TK
;
Tsai, CH
;
Tan, JJM
;
Hsu, LH
;
資訊工程學系
A bipartite graph is bipancyclic if it contains a cycle of every even length from 4 to I V(G) I inclusive. It has been shown that Q(n) is bipancyclic if and only if n greater than or equal to 2. In this paper, we improve this result by showing that every edge of Q(n) - E' lies on a cycle of every even length from 4 to V(G) inclusive where E' is a subset of E(Q(n)) with E' less than or equal to n - 2. The result is proved to be optimal. To get this result, we also prove that there exists a path of length I joining any two different vertices x and y of Qn when h (x, y) less than or equal to l less than or equal to V(G) - 1 and l - h (x, y) is even where It (x, y) is the Hamming distance between x and y. (C) 2003 Elsevier Science B.V. All rights reserved.
Design and implementation of electromagnetic active control actuators
(2003-08-01)
Bai, MR
;
Ou, KY
;
機械工程學系
;
Department of Mechanical Engineering
We present the modeling, parameter identification and design procedure of a linear voice-coil motor. A numerical simulation has been carried out to facilitate system integration. In particular, we use electromechanical analogy and the time-domain identification procedure with the eigensystem realization algorithm to predict the system response. In order to evaluate the performance of the voice-coil motor, we conducted an experimental investigation. Voice-coil motors mounted on a ball bearing housing are used for generating counter forces to cancel the transverse vibrations of a shaft. A controller is designed by using generalized predictive control. Multiple channel active control systems are implemented on the platform of a digital signal processor. Numerical and experimental results indicated that the designed actuators were effective in suppressing the periodic disturbances in rotors.