Browsing by Issue Date, starting with "2000-05-01"

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Excitation of ''rotation'' collective modes in vortex lattice of clean type II superconductors
(2000-05-01)
Kasatkin, A
;
Rosenstein, B
;
電子物理學系
;
Department of Electrophysics
In superclean limit, the Magnus force on Abrikosov vortices is stronger than friction. Due to this nondissipative force, vortex segments rotate around pinning centers. Waves of such rotations under certain conditions are only weakly damped (not overdamped as is usually the case) and lead to resonances in ac response. Excitation of such waves by applied ac field near the surface is considered. Surface impedance, ac resistivity and magnetic permeability are calculated using elasticity theory of the vortex lattice. (C) 2000 Published by Elsevier Science B.V. All rights reserved.
Feedforward active noise controller design in duets without independent noise source measurements
(2000-05-01)
Hu, JS
;
Lin, JF
;
電控工程研究所
;
Institute of Electrical and Control Engineering
Feedforward control architectures have been widely used in active noise control systems to achieve broad-band noise reductions. The basic principle of the control algorithm requires that the feedforward signal, usually the noise source, be independent from the actuator's output. Failure to meet this requirement implies that the overall system contains an acoustic feedback loop and stability and robustness issues become important. This paper investigates this problem in a one-dimensional sound field (e.g., ducts) using a unidirectional sound wave as the feedforward signal. Controller design based on a distributed parameter model is studied. Several experiments are conducted to illustrate the design procedure as well as verify the effectiveness of broad-band noise reductions.
Design and analysis of traffic control for guaranteed services on the Internet
(2000-05-01)
Wang, PC
;
Chan, CT
;
Chen, YC
;
資訊工程學系
;
Department of Computer Science
Real-time communications services will be one of the most promising applications on the Internet. Real-time traffic usually utilizes a significant amount of resources while traversing through the network. To provide guaranteed service for delay-sensitive real-time applications, both resource reservation and effective traffic control are necessary. The resource reservation protocol (RSVP) was developed to deal with the former problem while various approaches have been proposed to solve the latter one. It is crucial for guaranteed services to maintain satisfactory performance through effective traffic control, which must be implemented in a feasible way and be able to work with RSVP. In this article, we present a flexible and effective traffic-control approach with a resource reservation scheme to accommodate delay-sensitive services on the Internet. We demonstrate that our approach features proven bounded end-to-end queueing delay for delay-sensitive applications and good resilience for resource allocation. In addition, our packet transmission discipline achieves significant improvement in end-to-end delay control.
A direction-based location update scheme with a line-paging strategy for PCS networks
(2000-05-01)
Hwang, HW
;
Chang, MF
;
Tseng, CC
;
資訊工程學系
;
Department of Computer Science
On the problem of location update and terminal paging, many schemes using ring-paging strategies have been proposed, However, sequentially paging the rings surrounding the mobile user's last updated location may cause large paging cost. In this letter, we propose a direction-based location update (DBLU) scheme using a line-paging strategy to reduce the paging cost. A moving direction identification mechanism using only simple computations detects the change of moving direction and updates the mobile's location. The numerical results show that our DBLU scheme achieves good performance when the paging cost is high.
Using NH3 plasma treatment to improve the characteristics of hydrogen silsesquioxane for copper interconnection application
(2000-05-01)
Chang, KM
;
Deng, IC
;
Yeh, SJ
;
Tsai, YP
;
電子工程學系及電子研究所
Hydrogen silsesquioxane, a material with low dielectric constant, can successfully suppress Cu diffusion without using a barrier metal by implementing a NH3 plasma treatment. Lower leakage current and better barrier capability can be achieved by hydrogen silsesquioxane film after NH3 plasma treatment. Having been treated with different plasma exposure rimes. this film can still maintain its original dielectric constant with few changes. The decrease in leakage current with increasing exposure time can be attributed to the following mechanisms: dielectric film becomes denser, dangling bonds are passivated, nitride film is formed on the hydrogen silsesquioxane, and the bulk damage of hydrogen silsesquioxane is annealed out. A thin layer of nitride formed on the dielectric is the cause for having better capability. The thickness of the nitride layer on hydrogen silsesquioxane is about 35 nm, and it can prevent the Cu diffusion/migration into the underlying dielectric. The role of our nitride film is to act as a passive diffusion barrier. (C) 2000 The Electrochemical Society. S0013-4651(99)10-093-4. All rights reserved.
A new blind adaptive interference suppression scheme for acquisition and MMSE demodulation of DS/CDMA signals
(2000-05-01)
Hwang, HC
;
Wei, CH
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
In this paper, we present an efficient blind algorithm for estimating the code timing of a desired user in an asynchronous direct-sequence code-division multiple-access (DS/CDMA) system over frequency-nonselective-fading channels. The proposed algorithm acquires the code timing explicitly and results in a near-far resistant minimum mean-squared error (MMSE) demodulation without requiring the knowledge of the timing information, amplitudes, and transmitted symbols of all transmissions, The only required knowledge is the information of the signature sequence used by the desired transmission. Several computer simulations are done for additive white Gaussian channels, Rayleigh fading channels, and two-ray Rayleigh fading multipath channels, respectively. Numerical results show that the new algorithm is near-far resistant to the multiple-access interference (MAI) in the DS/CDMA system.
Anisotropic peak effect due to structural phase transition in the vortex lattice
(2000-05-01)
Rosenstein, B
;
Knigavko, A
;
電子物理學系
;
Department of Electrophysics
The recently observed new peak effect in YBCO is explained by softening of the vortex lattice (VL) due to a structural phase transition in the VL. At this transition, square lattice transforms into a distorted hexagonal one. While conventional peak effect is associated with softening of shear modes at melting, in this case the relevant mode is the point. The squash mode is highly anisotropic and we point out some peculiar effects associated with this feature. (C) 2000 Published by Elsevier Science B.V. All rights reserved.
Construction schemes for fault-tolerant Hamiltonian graphs
(2000-05-01)
Wang, JJ
;
Hung, CN
;
Tan, JJM
;
Hsu, LH
;
Sung, TY
In this paper, we present three construction schemes for fault-tolerant Hamiltonian graphs. We show that applying these construction schemes on fault-tolerant Hamiltonian graphs generates graphs preserving the original Hamiltonicity property. We apply these construction schemes to generate some known families of optimal 1-Hamiltonian graphs in the literature and the Hamiltonicity properties of these graphs are the direct consequence of the construction schemes. In addition, we can use these construction schemes to propose new family of optimal 1-Hamiltonian graphs. (C) 2000 John Wiley & Sons, Inc.
A fully digital noncoherent and coherent GMSK receiver architecture with joint symbol timing error and frequency offset estimation
(2000-05-01)
Huang, YL
;
Fan, KD
;
Huang, CC
;
電信工程研究所
;
Institute of Communications Engineering
We propose a fully digital noncoherent and coherent Gaussian minimum shift keying (GMSK) receiver architecture with joint frequency offset compensation and symbol timing recovery in this paper. Carrier phase offset ran be estimated if the coherent demodulation mode is adopted. The converted base-band complex signal is first frequency discriminated and then passed through a digital filter which performs a fast Fourier transform (FFT), The frequency offset can be estimated from the de component of the FPT, and the symbol timing error can be estimated from the phase angle of the FFT at a specified frequency which is equal to an integral multiple of half the bit rate. These two estimated parameters are then used for frequency offset compensation and symbol timing recovery during a preamble period. Coarse carrier phase can be estimated by averaging sampled in-phase and quadrature-phase signals and finding its phase angle within the preamble period after carrier frequency offset is estimated and compensated. The bit error rate (BER) performance of this GMSK receiver architecture is assessed for an additive white Gaussian noise (AWGN) channel by computer simulation.
PBX based mobility manager for wireless local loop
(2000-05-01)
Lin, YB
;
資訊工程學系
;
Department of Computer Science
In a typical wireless local loop (WLL) system, a user can only access the wireless services at fixed locations. This paper proposes a private branch exchange (PBX) based mobility manager for WLL, which allows users to receive wireless service at any locations within the WLL service area. We show how the mobility manager can be implemented in a PBX environment where the base stations are connected to the PBX using standard line or trunk interfaces. The proposed mobility manager can be tailored to connect wireless system such as DECT or PACS. Copyright (C) 2000 John Wiley & Sons, Ltd.
The influence of Mg on creep properties and fracture behaviors of Mar-M247 superalloy under 1255 K/200 MPa
(2000-05-01)
Bor, HY
;
Chao, CC
;
Ma, CY
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The effects of Mg microadditions on the high-temperature/low stress (1255 K/200 MPa) creep properties and fracture behavior of a Mar-M247 superalloy were investigated in this study. The results of quantitative statistical analyses showed that when Mg microadditions up to 50 ppm were made, the MC carbides located at grain boundaries (designated GB MC) were significantly refined and spheroidized and the number of MC carbides decreased. In addition, the M23C6 carbides present on GBs dramatically increased with increasing Mg contents up to 50 ppm, and the creep resistance was enhanced under the test condition of 1255 K/200 MPa. However, the creep performance of a Mar-M247 superalloy containing 80 ppm Mg deteriorated due to the formation of an extremely large amount of MC carbide and a decrease in the number of M23C6 carbides at GBs. The cracks mainly initiated and propagated along GBs in both the Mg-free and Mg-containing Mar-M247 superalloys under 1255 K/200 MPa, and the finial rupture was caused by intergranular fracture. Under the present creep condition, the optimal Mg microaddition to a Mar-M247 superalloy should be 30 to 50 ppm.
A project model for software development
(2000-05-01)
Liang, BS
;
Chen, JN
;
Wang, FJ
;
資訊科學與工程研究所
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Institute of Computer Science and Engineering
Uncertainty and dynamic changes in a software project cause iterations during development and the need for decision-making in planning and controlling a project. This paper presents a Software Project Review and Evaluation Model, SPREM, a superset of CPM/PERT which extends CPM/PERT's notation to four types of vertices (AA, AX, XA, and XX vertices) to express the non-deterministic and iterative behaviors of software engineering projects. Several behavioral properties of SPREM and analysis of them are discussed. For example, the enaction capability can be used to evaluate the possibility that a vertex will enact processes beforehand. Project managers can revise a SPREM graph to rescue dead vertices before project execution. Furthermore, enaction ordering allows project managers to calculate the dependency between processes to be enacted. This might help in computing important information such as critical paths among these processes.
Field emission from quasi-aligned SiCN nanorods
(2000-05-01)
Tarntair, FG
;
Wen, CY
;
Chen, LC
;
Wu, JJ
;
Chen, KH
We report on the preparation and field emission properties of quasi-aligned silicon carbon nitride (SiCN) nanorods. The SiCN nanorods are formed by using a two-stage growth method wherein the first stage involves formation of a buffer layer containing high density of nanocrystals by electron cyclotron resonance plasma enhanced chemical vapor deposition and the second stage involves using microwave plasma enhanced chemical vapor deposition for high growth rate along a preferred orientation. It should be noted that growth of the SiCN nanorods is self-mediated without the addition of any metal catalyst. Scanning electron microscopy shows that the SiCN nanorods are six-side-rod-shaped single crystals of about 1-1.5 mu m in length and about 20-50 nm in diameter. Energy dispersive x-ray spectrometry shows that the nanorod contains about 26 at. % of Si, 50 at. % of C, and 24 at. % of N. Characteristic current-voltage measurements indicate a low turn-on field of 10 V/mu m. Field emission current density in excess of 4.5 mA/cm(2) has been observed at 36.7 V/mu m. Moreover, SiCN nanorods exhibited rather stable emission current under constant applied voltage. (C) 2000 American Institute of Physics. [S0003-6951(00)01117-7].
Influence of energy-transfer upconversion on the performance of high-power diode-end-pumped CW lasers
(2000-05-01)
Chen, YF
;
Lan, YP
;
Wang, SC
;
電子物理學系
;
光電工程學系
The influence of energy-transfer upconversion (ETU) on the performance of diode-end-pumped lasers is studied by including ETU effects into the space-dependent rate equations. The dependence of ETU rates on the mode-to-pump size ratio and on the output mirror transmission is derived. Experiments for Nd:YAG and Nd:YVO4 crystals are performed to validate the present model. It is found that the ETU process increases the sensitivity of the output power to the output mirror transmission but its influence on the output power is not significant for low output transmission.
Improvements of amorphous-silicon inverted-staggered thin-film transistors using high-temperature-deposited Al gate with chemical mechanical polishing
(2000-05-01)
Shih, PS
;
Chang, TC
;
Liang, CY
;
Huang, TY
;
Chang, CY
Chemical mechanical polished Al (CMP-Al) films deposited at various temperatures were explored as the gate electrodes of amorphous- silicon (a-Si:H) inverted-staggered thin-film transistors (TFTs) for the first time. Although the surface roughness of the as-deposited Al films increased with increasing deposition temperature, Al films deposited at higher temperature were more robust to hillock formation during subsequent annealing. To take advantage of the better hillock suppression properties, CMP is employed to reduce the inherently large surface roughness of these high-temperature-deposited Al films. Our results show that the electrical characteristics of the TFTs are significantly improved. Specifically, the threshold voltage is reduced from 2.37 to 1.43 V, the mobility is improved from 0.32 to 1.36 cm(2)/V s, and the subthreshold swing is improved from 0.72 to 0.58 V/decade as the Al deposition temperature is increased from 25 to 400 degrees C. (C) 2000 The Electrochemical Society. S1099-0062(99)10-107-X. All rights reserved.
The design and implementation of a multi-threaded object request broker
(2000-05-01)
Lo, W
;
Chang, YS
;
Yuan, SM
;
Liang, D
;
資訊工程學系
Multi-threaded programming is a well-known technique for improving the performance of applications. In a CORBA environment, clients can invoke shared remote objects. If these objects are single-threaded, the performance of the system in the large distributed applications is affected. This paper presents a detailed description of the design and implementation of a multi-threaded Object Request Broker (ORB) on CORBA. The ORE was implemented on top of Windows NT and the underlying TCP protocol. The system's performance in both one-way and two-way requests is compared with that of a well-known commercial product, the IONA Orbix.
Vegas plus: Improving the service fairness
(2000-05-01)
Chen, JR
;
Chen, YC
;
資訊工程學系
;
Department of Computer Science
TCP Vegas is a congestion avoidance scheme designed to prevent the periodic packet loss which occurs in traditional schemes. Since Vegas successfully avoids such packet loss, it achieves much higher throughput than TCP Reno. However, it does not concern the fairness among source-destination pairs with different round-trip times (RTT's). In this letter, we propose a different mechanism to adjust the window size, this allows TCP to provide much better fairness regardless the large variation of RTT's.
Ultrafast response of multi-energy proton-bombarded GaAs photoconductors
(2000-05-01)
Lin, GR
;
Pan, CL
;
光電工程學系
;
Department of Photonics
We have investigated the ultrafast optical and optoelectronic characteristics of multi-energy proton-bombarded GaAs (GaAs:H+) material and devices in some detail. Photo-excited carrier lifetimes of GaAs:H+ were observed to be as low as 350 +/- 50 fs. Photoconductive switches (PCS) fabricated on GaAs:H+ were found to exhibit lower dark currents (15 nA at a bias of 10 V) and higher breakdown voltage (> 100 kV/cm) than PCS's fabricated on semi-insulating (S.I.) GaAs. The temporal response of the GaAs:H+ PCS was about 2 ps at full-wave half minimum. Optically excited terahertz (THz) radiation from GaAs:H+ was reported for the first time to our knowledge. The temporal response and spectral bandwidth of the emitted THz radiation were 0.7 ps and 1.25 THz, respectively. The field strength of the THz signal was about 20 mV/cm. From the THz data, we are able to deduce that the effective carrier mobility of GaAs:H+ was less than 1 cm(2)/V-sec.
High current density field emission from arrays of carbon nanotubes and diamond-clad Si tips
(2000-05-01)
Tarntair, FG
;
Chen, LC
;
Wei, SL
;
Hong, WK
;
Chen, KH
Arrays of carbon nanotubes (CNT) and diamond-clad Si tips were grown by microwave plasma-enhanced chemical vapor deposition. The former ones were grown directly on prepatterned cobalt-coated silicon substrate, while the latter ones were grown on Si-tip arrays. Each array contains 50 x 50 emitting cells and each individual cell is 3 mu m square. A maximum effective emission current density of about 17 A/cm(2) (at a macroscopic field of 17.5 V/mu m) has been demonstrated, while a macroscopic emission current density of 10 mA/cm(2) with operating fields around 10 V/mu m can be routinely achieved from an an ay of CNT emitters. In contrast, operating fields above 20 V/mu m were needed to draw a comparable emission current density from all of the diamond-clad Si tips arrays. Emission stability test performed at 40 mA/cm(2) for CNT arrays also showed little sign of degradation. Due to the high efficiency of electron emission, simple sample process, and large area growth capability, field emitter arrays based on CNT are attractive for flat panel display applications. (C) 2000 American Vacuum Society. [S0734-211X(00)08003-3].
Very low bit rate color image compression by using stack-run-end coding
(2000-05-01)
Tsai, MJ
;
資訊管理與財務金融系註：原資管所+財金所
;
Department of Information Management and Finance
A low complexity wavelet based image coding algorithm for color image compression is presented in this paper. The key renovation of this algorithm is that a small number of symbol set was designed to convert the information from the wavelet transform domain into a compact data structure for each subband. The scheme works first by color space conversion, followed by uniform scalar quantization and data conversion where raster scanning order is performed for individual subband and quantized coefficients are converted into the symbol stream according to the designed symbol representation. Two different context lists in each subband are specified from the symbol stream and alternatively compressed by adaptive arithmetic coder with high efficiency. Unlike zerotree coding or its variations which utilize the intersubband relationship into its own data representation, our work is a low complexity intrasubband based coding method which only addresses the information within the subband. The only extension is the termination symbols which carry the zero value information towards the end of the subband or across the subbands till the end of the image. Compared with the zerotree refined schemes. this algorithm results in competitive PSNR values and perceptually high quality images at the same compression ratio for color image compression.