Browsing by Issue Date, starting with "2003-05-15"

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A novel numerical approach to heterojunction bipolar transistors circuit simulation
(2003-05-15)
Li, YM
;
Huang, KY
;
電子工程學系及電子研究所
;
友訊交大聯合研發中心
;
Department of Electronics Engineering and Institute of Electronics
In this paper we present a novel computational method for calculating the heterojunction bipolar transistor (HBT) physical characteristics in the time domain. To calculate the HBT high frequency properties, the Gummel-Poon equivalent circuit model is applied to replace the HBT in the circuit and a set of governing ordinary differential equations (ODEs) is formulated. We directly decouple the system ODEs and solve each decoupled ODE with the monotone iterative method in the time domain. This solution methodology proposed here has been applied to semiconductor device simulation by us earlier, and we find this method for the HBT simulation has good accuracy and converges globally. Compared with the HSPICE circuit simulator results, our results present the accuracy, efficiency, and robustness of the method. (C) 2002 Elsevier Science B.V. All rights reserved.
High interfacial exchange energy in TbFeCo exchange-bias films
(2003-05-15)
Lin, CC
;
Lai, CH
;
Jiang, RF
;
Shieh, HPD
;
光電工程學系
The exchange-bias films of ferrimagnetic/ferrimagnetic, ferromagnetic/ferromagnetic, and ferromagnetic/antiferromagnetic bilayers were fabricated to investigate their interfacial exchange energy Deltasigma. Deltasigma of TbFeCo bilayers is larger than 5 erg/cm(2) at room temperature. By varying the composition of TbFeCo layers, both positive and negative exchange bias have been observed. A highly uncompensated-spin interface model was proposed to explain the strong exchange interaction in TbFeCo bilayers. Due to the characteristics of highly uncompensated-spin interface at TbFeCo bilayers, the exchange coupling field in TbFeCo bilayers exhibited less dependence on interfacial roughness than that in IrMn/NiFe bilayers. In addition, by adjusting the composition of TbFeCo, the anisotropy of pinning layer can be manipulated and exhibits strong effects on exchange bias of TbFeCo bilayers. (C) 2003 American Institute of Physics.
3-disjoint gamma interconnection networks
(2003-05-15)
Chen, CW
;
Lu, NP
;
Chung, CP
;
資訊工程學系
;
Department of Computer Science
In this paper, we propose a new multistage interconnection network, called 3-disjoint gamma interconnection network (3DGIN). The 3DGIN is a modified gamma interconnection network that provides 3-disjoint paths to tolerate two switch or link faults between any source and destination pairs. The 3DGIN has lower hardware cost than GIN; furthermore, the routing and rerouting tags to generate 3-disjoint paths can be obtained in O(logN) time. To show the advantage features of 3DGIN, we also make a comparison between the gamma-related networks, the GIN, enhanced IADM, and 3DGIN. (C) 2002 Elsevier Science Inc. All rights reserved.
Mapping spatial variations of the coercivity on patterned magneto-optical materials
(2003-05-15)
Wu, TH
;
Ye, LX
;
Lee, JM
;
Wu, JC
;
Shieh, HPD
The spatial variation of coercivity on patterned magneto-optical (MO) materials has been studied with a Kerr microscope. Our results show that the coercivity values on arrays made by holes are larger than those observed on the land regions. In contrast with nonpatterned MO media, which present a sharp Gaussian-like distribution, the coercivity distribution in the patterned material is much wider and shows an exponential-type distribution. This article maps the spatial variation of the coercivity on patterned magnetic materials with a spatial resolution of 0.1x0.1 mum(2). (C) 2003 American Institute of Physics.
Variable-size data item placement for load and storage balancing
(2003-05-15)
Ma, YC
;
Chiu, JC
;
Chen, TF
;
Chung, CP
;
資訊工程學系
The rapid growth of Internet brings the need for a low cost high performance file system. Two objectives are to be pursued in building such a large scale storage system on multiple disks: load balancing and storage minimization. We investigate the optimization problem of placing variable-size data items onto multiple disks with replication to achieve the two objectives. An approximate algorithm, called LSB Placement, is proposed for the optimization problem. The algorithm performs bin packing along with MMPacking to obtain a load balanced placement with near-optimal storage balancing. The key issue in deriving the algorithm is to find the optimal bin capacity for the bin packing to reduce storage cost. We derive the optimal bin capacity and prove that LSB Placement algorithm is asymptotically 1-optimal on storage balancing. That is, when the problem size exceeds certain threshold, the algorithm generates a load balanced placement in which the data sizes allocated on disks are almost balanced. We demonstrate that, for various Web applications, a load balanced placement can be generated with disk capacity not exceeding 10% more than the balanced storage space. This shows that the LSB Placement algorithm is useful in constructing a low cost and high performance storage system. (C) 2002 Elsevier Science Inc. All rights reserved.
Transport spectroscopy in a time-modulated open quantum dot
(2003-05-15)
Tang, CS
;
Tan, YH
;
Chu, CS
;
電子物理學系
;
Department of Electrophysics
We have investigated the time-modulated coherent quantum transport phenomenon in a ballistic open quantum dot. Conductance G and the electron dwell time in the dots are calculated by a time-dependent mode-matching method. Under high-frequency modulation, the traversing electrons are found to exhibit three types of resonant scatterings. They are intersideband scatterings into quasibound states in the dots, into true bound states in the dots, and into quasibound states just beneath the subband threshold in the leads. Dip structures or fano structures in G are their signatures. Our results show structures due to 2 (h) over bar omega intersideband processes. At the above scattering resonances, we have estimated, according to our dwell time calculation, the number of round-trip scatterings which the traversing electrons undertake between the two dot openings.
Growth of high-quality Ge epitaxial layers on Si(100)
(2003-05-15)
Luo, GL
;
Yang, TH
;
Chang, EY
;
Chang, CY
;
Chao, KA
A method of growing high-quality epitaxial Ge layers on a Si(100) substrate is reported. In this method, a 0.8 mum Si0.1Ge0.9 layer was first grown. Due to the large lattice mismatch between this layer and the Si substrate, many dislocations form near the interface and in the lower part of the Si0.1Ge0.9 layer. A 0.8 mum Si0.05Ge0.95 layer and a 1.0 mum top Ge layer were subsequently grown on the Si0.1Ge0.9 layer. The formed interfaces of Si0.05Ge0.95/Si0.1Ge0.9 and Ge/Si0.05Ge0.95 can bend and terminate the upward-propagated dislocations very effectively. The in situ annealing process was also performed for each individual layer. Experimental results show that the dislocation density in the top Ge layer can be greatly reduced, and the surface is very smooth, while the total thickness of the structure is only 2.6 mum.
Reducing the energy consumption caused by flooding messages in mobile ad hoc networks
(2003-05-15)
Wang, SY
;
資訊工程學系
;
Department of Computer Science
The message flooding method is an important and useful operation for several applications. However, if a network has a large number of mobile nodes and these nodes use the flood operation often, a mobile node's scarce battery energy will be quickly consumed due to flooding too many messages. In this paper, we propose an approach to reducing the energy consumption caused by flooding messages. The energy saving is achieved by (1) merging several small flood messages into a larger one, and (2) limiting the scope of a flood message. Our simulation results show that, at the cost of an increased message forwarding delay, the proposed approach can substantially reduce flood messages' energy consumption without increasing their delivery failure rates. (C) 2003 Elsevier Science B.V. All rights reserved.
Ab initio studies of ClOx radical reactions: V. Evidence for a new path in the Cl+ClOOCl reaction
(2003-05-15)
Zhu, RS
;
Lin, MC
;
交大名義發表
;
National Chiao Tung University
The mechanism for the reaction Cl + ClOOCl has been investigated by ab initio molecular orbital and transition-state theory calculations. The result shows that the reaction can produce both Cl-2 + ClOO and Cl2O + ClO. The former product pair can be formed by direct and indirect abstraction paths. The direct abstraction path, which dominates at low temperatures, takes place barrierlessly with the rate constant k(1) = 1.53 x 10(-13)T(1.1) exp(118/T) cm(3) molecule(-1) s(-1) in the temperature range of 200-1000 K. The rate constant of the indirect path, which occurs via the two isomers of the Cl-O(Cl)OCl complex lying 3 kcal/mol below the reactants, k(1)' = 7.14 x 10(-12)T(0.86) exp(-2370/T) cm(3) molecule(-1) s(-1), accounting for less than 0.1% of the Cl-2 yield at 298 K but increasing to about 46% at 1000 K. The new Cl2O + ClO products can be produced by the fragmentation of the two complexes; the rate constant for their formation was found to be pressure-independent and can be expressed by k(2) = 2.19 x 10(-14)T(0.70) exp(-1110/T) cm(3) molecule(-1) s(-1) covering the temperature range of 200-1000 K. Above room temperature, Cl2O formation becomes competitive; for example, its branching ratios, k(2)/k(t), are predicted to be 0.19, 0.55, and 0.62 at 298, 500, and 1000 K, respectively. The predicted total rate constant agrees closely with available experimental results. The heat of formation of ClOOCl has been examined in detail using different reactions and computational methods. The results of these calculations converge to Delta(f)Hdegrees(0)(ClOOCl) = 30 +/- 2 kcal/mol.
Spin-orbit interaction and electron elastic scattering from impurities in quantum wells
(2003-05-15)
Huang, HC
;
Voskoboynikov, O
;
Lee, CP
;
交大名義發表
;
National Chiao Tung University
We present a theoretical study of the spin-dependent scattering of electrons from screened impurities in III-V semiconductor quantum wells. Our calculation is based on the effective one-electronic-band Hamiltonian and the spin-orbit coupling with the Coulombic potential of the impurities. We demonstrate that the spin-orbit interaction can lead to recognizable magnitudes of spin asymmetry in the elastic-scattering cross section. Fairly large values of the Sherman function (about 0.01) are obtained for repulsive and attractive impurities in quantum wells of narrow gap semiconductors.
Optimization of TQFP molding process using neuro-fuzzy-GA approach
(2003-05-16)
Chiang, TL
;
Su, CT
;
工業工程與管理學系
;
Department of Industrial Engineering and Management
This paper focuses on an integated optimization problem that involves multiple qualitative and quantitative responses in the thin quad flat pack (TQFP) molding process. A fuzzy quality loss function (FQLF) is first applied to the qualitative responses., since the molding defects cannot be simply represented by the relationship between molding conditions and mathematical models. Neural network is then used to provide a nonlinear relationship between process parameters and responses. A genetic algorithm together with exponential desirability function is employed to determine the optimal parameter setting for TQFP encapsulation. The proposed method was implemented in a semiconductor assembly factory in Taiwan. The results from this study have proved the feasibility of the proposed approach. (C) 2002 Elsevier Science B.V. All rights reserved.
Piezoelectric-transducer-based optoelectronic frequency synchronizer for control of pulse delay in a femtosecond passively mode-locked Ti : sapphire laser
(2003-05-20)
Lin, GR
;
Chang, YC
;
Liu, TA
;
Pan, CL
;
光電工程學系
We propose a piezoelectric transducer- (PZT-) based optoelectronic frequency synchronizer to control simultaneously changes in the repetition rate, the relative pulse delay, and the phase noise of a passively mode-locked femtosecond Ti:sapphire laser with an intracavity saturable Bragg reflector absorber with respect to an electronic frequency reference. An optoelectronic phase-locked-loop-based PZT feedback controller with a proportional, integral, and differential (PID) circuit and a tunable voltage regulator is designed to achieve frequency synchronization, phase-noise suppression, and delay-time tuning. When the controlling voltage is tuned from -2.6 to 2.6 V, the maximum pulse-delay range, tuning slope, and tuning resolution of the laser pulse-train are 11.3 ns, 2.3 ps/mV, and 1.2 ps, respectively. Setting the gain constant of the PID circuit at 10 or larger causes the delay-time tuning function to be linearly proportional to the controlling voltage. In the delay-time tuning mode the uncorrelated single-side-band phase-noise density of the frequency-synchronized laser is approximately -120 dBc/Hz at an offset frequency of 5 kHz, which is only 7 dBc/Hz; higher than that of the electrical frequency reference. The proposed system also supports linear, continuous switching, and programmable control of the delay time of Ti:sapphire laser pulses when they are frequency synchronized to external reference clocks. (C) 2003 Optical Society of America.
最短偏小展
(2003-05-24)
管管
The microstructure and the thermal expansion characteristics of Cu/SiCp composites
(2003-05-25)
Shu, KM
;
Tu, GC
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Copper/silicon carbide composites (Cu/SiCp) were made by the powder metallurgy method. Electroless plating was employed to deposit a copper film on SiCp powder before mixing with Cu powder in order to improve the bonding status between Cu and SiC particles during sintering. Thermal expansion property of as-formed product was measured in the temperature range from 50 to 550 degreesC. The results showed that copper coating on silicon carbide particles could render uniform distribution of SiCp in the copper matrix. The composites exhibited positive thermal hysteresis behavior when cooled down from the peak temperature to room temperature, which can be explained in terms of the residual stresses and the interfacial bonding between copper and silicon carbide. The magnitude of this strain was a function of the SiCp volume fraction and the number of thermal cycles. The thermal expansion property of composites was measured and compared with those predicted from various theoretical models. (C) 2002 Published by Elsevier Science B.V.
Robust control of non-linear affine systems
(2003-05-25)
Liang, YW
;
Liaw, DC
;
電控工程研究所
;
Institute of Electrical and Control Engineering
Issue of robust control for non-linear affine systems with uncertainties appearing in both drift and non-drift terms are presented. Based on Lyapunov function approach, control laws are proposed to guarantee uniformly asymptotic stability of the equilibrium point. To facilitate the design and simplify the checking procedure, stabilization control for the uncertain systems possess asymptotic stabilizable nominal time-invariant driftness terms are proposed for the demonstration of robust design. (C) 2002 Elsevier Science Inc. All rights reserved.
The linear-exponential-quadratic-Gaussian control for discrete systems with application to reliable stabilization
(2003-05-25)
Liaw, DC
;
Chen, CH
;
電控工程研究所
;
Institute of Electrical and Control Engineering
In this paper, we derive the discrete linear-exponential-quadratic-Gaussian (LEQG) controller which can take both the system and measurement noise covariances into consideration. Comparing with the traditional linear-quadratic-Gaussian (LQG) design, the LEQG has the wilder design freedom. The proposed discrete LEQG control scheme is then applied to the study of reliable control which can tolerate abnormal operation within some pre-specified set of actuators. This is achieved by suitable modification of the algebraic Riccati equation for the design of the controller. The bounds of gain margins for the feedback control gains of reliable stabilization are also derived. The stability of the overall system is preserved despite the abnormal operation of actuators within a pre-specified subset in the bounds of gain margins. (C) 2002 Elsevier Science Inc. All rights reserved.
The growth mechanism of micron-size V defects on the hydride vapor phase epitaxy grown undoped GaN films
(2003-05-26)
Lin, PY
;
Wu, YCS
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Micron-size V defects were found on the hydride vapor phase epitaxy grown GaN films. When the film thickness increased, the diameter of V defects increased, but the density of the defects decreased. The defect has six {1 1 0 1} facets, which encircle to form a concave hexagonal pyramid. Its shape is similar to that of epitaxial lateral overgrowth (ELO) GaN crystal grown on a dot-patterned GaN underlying layer. Through the analysis of the growth mechanism of ELO GaN, the growth mechanism of the V defects was investigated. (C) 2003 Elsevier Science B.V. All rights reserved.
古硯
(2003-05-28)
管管
Surface acidity over vanadia/titania catalyst in the selective catalytic reduction for NO removal - in situ DRIFTS study
(2003-05-28)
Lin, CH
;
Bai, H
;
環境工程研究所
;
Institute of Environmental Engineering
An in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) study of the selective catalytic reduction (SCR) of NO with NH3 in the presence of O-2 was carried out over vanadia-based catalysts. Vanadia-based catalysts were prepared by impregnation method. The results indicated that the strength of Bronsted acidity positively increased with V2O5 loading, whereas Lewis acidity remained almost constant at a typical SCR operating temperature. Water vapor does not affect the adsorption of Lewis ammonia, but the formation of Bronsted acidity has to be accompanied by water vapor adsorption. Bronsted acidity is decreased with increasing temperature and disappeared at a temperature of around 500degreesC for all testing catalysts, while Lewis acidity slightly decreased with increasing temperature. The disappearance of Bronsted acidity at a high temperature was related to the loss of adsorbed water vapor. (C) 2002 Elsevier Science B.V. All rights reserved.
Generalized honeycomb torus
(2003-05-31)
Cho, HJ
;
Hsu, LY
;
運輸與物流管理系註：原交通所+運管所
;
Department of Transportation and Logistics Management
Stojmenovic introduced three different honeycomb tori by adding wraparound edges on honeycomb meshes, namely honeycomb rectangular torus, honeycomb rhombic torus, and honeycomb hexagonal torus. These honeycomb tori have been recognized as an attractive alternative to existing torus interconnection networks in parallel and distributed applications. In this paper, we propose generalized honeycomb tori. The three different honeycomb tori proposed by Stojmenovic are proved to be special cases of our proposed generalized honeycomb tori. We also discuss the Hamiltonian property of some generalized honeycomb tori. (C) 2003 Published by Elsevier Science B.V.