Browsing by Author "Lo, SC"

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A self-consistent dynamic traffic flow model part I: modeling and analysis
(2001)
Cho, HJ
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Lo, SC
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運輸與物流管理系註：原交通所+運管所
;
Department of Transportation and Logistics Management
Traffic flow theory can provide real time prediction and evaluation of traffic management strategies. Lightwill, Whitham and Richards applied a fluid mechanism to traffic flow and proposed a dynamic model (LWR model) in 1955 first. However, the LWR model needs to couple with a specific speed-density relation to be solved. Sometimes the assumption of such a relationship is not consistent with the whole model. In this study, we develop a dynamic traffic flow model based on the continuity equation (LWR model) and second-order model. The assumptions of the system equations are consistent with each other. Therefore, a self-consistent system is proposed herein. The existence and uniqueness of the solution is also illustrated in this work. Numerical simulations are left for further studies.
A study of oxide patterning on titanium thin films using scanning probe microscopy
(2001)
Tsai, HR
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Hsieh, TE
;
Lo, SC
;
Lin, HH
;
材料科學與工程學系
This work studies the fabrication of oxide patterns on titanium (Ti) thin films using scanning probe microscopy (SPM). We employed three different SPM techniques, namely, AFM in contact mode, lift mode incorporated with contact mode AFM, and STM. It was found that bias voltages.. scanning speed, scanning height of the probe (for lift mode), and setpoint current (for STM) play important roles in forming the attainable oxide features. Among these three methods, contact mode AFM exhibited the best patterning efficiency and stability and this method was adopted to oxidize the I-shaped Ti films. The resistance of I-shaped specimen after anoxidization raised from 10(4)Omega to 10(8)_10(9)Omega which evidenced the occurrence of oxidation in Ti.
A study of the threshold voltage variations for ultrathin body double gate SOI MOSFETs
(2004)
Tang, CS
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Lo, SC
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Lee, JW
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Tsai, JH
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Li, YM
Silicon on insulator (SOI) devices have been of great interest in these years. In this paper, simulation with density-gradient transport model is performed to examine the variation of threshold voltage (VTH) for double gate SOI MOSFETs. Different thickness of silicon (Si) film, oxide thickness, channel length and doping concentration are considered in this work. According to the numerical study, both drift-difftision (DD) and density gradient (DG) models demonstrate that the thickness of Si film greatly affects the threshold voltage (5 similar to 15% variation). It is found that the thickness of Si film decreases, VTH variation increases; and the dependence relation is nonlinear. Therefore, this effect must be taken into account for the realization of double gate SOI ULSI circuit.
Chaos and control of discrete dynamic traffic model
(2005-11-01)
Lo, SC
;
Cho, HJ
;
運輸與物流管理系註：原交通所+運管所
;
Department of Transportation and Logistics Management
This study discusses chaotic traffic flow. The discrete dynamic model proposed herein is derived from both the flow-density-speed fundamental diagram and Greenshield's model. The model employs occupancy as its variable and the ratio of free flow and average speed as its control parameter. The function form of the model is equal to logistic map that bifurcates when the value of the control parameter increases. Chaotic traffic means that traffic becomes unstable and unpredictable, which is dangerous for driving. Therefore, this study considers the implementation of chaotic control in signal or ramp metering design so as to stabilize the chaotic traffic phenomena. These results are illustrated by numerical examples. (c) 2005 The Franklin Institute. Published by Elsevier Ltd. All rights reserved.
Four-dimensional dielectric property image obtained from electron spectroscopic imaging series
(2001)
Lo, SC
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Kai, JJ
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Chen, FR
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Chang, L
;
Chen, LC
We have demonstrated a new quantitative method to characterize two- dimensional distributions of energy-dependent dielectric function of materials from low loss electron spectroscopic image (ESI) series. Two problems associated with extracted image-spectrum from the low-loss image series, under-sampling and loss of energy resolution, were overcome by using fast Fourier transformation (FFT) interpolation and maximum entropy deconvolution method. in this study, Black Diamond(TM)/Si3N4/SiO2/Si-substrate dielectric layer designed for copper metallization was used as the sample. We show that the reconstructed (FFT interpolated and maximum entropy deconvoluted) image-spectrum obtained from ESI series images can be quantified with the same accuracy as conventional electron energy-loss spectroscopy spectra. Since the analysis of the dielectric function is sensitive to the local thickness of the specimen using Kramers-Kronig analysis, we also developed a new method to quantitatively determine the dielectric constant for low-k materials. We have determined the thickness of the Black Diamond using the extrapolated thickness method from the materials of known dielectric constants. Using Kramers-Kronig formula, the dielectric function map can be deduced front two-dimensional reconstructed single scattering spectra with providing the information of thickness. We proposed a four-dimensional data presentation for revealing the uniformity of the energy dependent property. The accuracy of our methods depends on the thickness determination and on the quality of the reconstructed spectra from the image series.
HRTEM and EFTEM studies of the evolution of Cu/Ta/SiO2/Si interfaces in ULSI devices
(1999)
Yin, KM
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Chang, L
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Chen, FR
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Kai, JJ
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Chuang, CCCG
The Cu/Ta/SiO2/Si films have been annealed at temperatures from 500 degreesC to 600 degreesC in various vacuum conditions. Transmission electron microscopy has been used to characterize the microstructure of the films after annealing. It shows that different thicknesses of amorphous interlayer were formed between Cu and Ta under various vacuum conditions. Energy dispersive spectroscopy confirmed this interlayer to be tantalum oxide. It has also found that tantalum oxidation is caused by oxygen from the outside atmosphere diffusing along grain boundaries in copper films.
Modeling of nonlinear stochastic dynamic traffic flow
(2001)
Jou, YJ
;
Lo, SC
;
運輸與物流管理系註：原交通所+運管所
;
Department of Transportation and Logistics Management
Most dynamic flow models are developed under deterministic assumptions or simple linear models. Although these models can describe dynamic phenomena, they cannot adapt a variance of the real world. However, in the developing trend of intelligent transportation systems, operators have to understand and accurately predict traffic flow to predict, evaluate, and manage the performance of present and future systems. Thus, a model capable of describing variant traffic phenomena, which encompasses both nonlinearity and stochasticity, is necessary. This study formulates nonlinear stochastic dynamic traffic flow models based on conventional macroscopic models; the nonlinear terms are decomposed by polynomials to reduce the complexity of the models. Then, the 116 equation is introduced to convert the deterministic model to a stochastic one. Also considered here is the traffic flow model with a diffusion effect.
Modeling self-consistent multi-class dynamic traffic flow
(2002-09-15)
Cho, HJ
;
Lo, SC
;
運輸與物流管理系註：原交通所+運管所
;
Department of Transportation and Logistics Management
In this study, we present a systematic self-consistent multiclass multilane traffic model derived from the vehicular Boltzmann equation and the traffic dispersion model. The multilane domain is considered as a two-dimensional space and the interaction among vehicles in the domain is described by a dispersion model. The reason we consider a multilane domain as a two-dimensional space is that the driving behavior of road users may not be restricted by lanes, especially motorcyclists. The dispersion model, which is a nonlinear Poisson equation, is derived from the car-following theory and the equilibrium assumption. Under the concept that all kinds of users share the finite section, the density is distributed on a road by the dispersion model. In addition, the dynamic evolution of the traffic flow is determined by the systematic gas-kinetic model derived from the Boltzmann equation. Multiplying Boltzmann equation by the zeroth, first- and second-order moment functions, integrating both side of the equation and using chain rules, we can derive continuity, motion and variance equation, respectively. However, the second-order moment function, which is the square of the individual velocity, is employed by previous researches does not have physical meaning in traffic flow. Although the second-order expansion results in the velocity variance equation, additional terms may be generated. The velocity variance equation we propose is derived from multiplying Boltzmann equation by the individual velocity variance. It modifies the previous model and presents a new gas-kinetic traffic flow model. By coupling the gas-kinetic model and the dispersion model, a self-consistent system is presented. (C) 2002 Elsevier Science B.V. All rights reserved.
Monotone iterative simulation of the multilane traffic dispersion model
(2002-11-01)
Cho, HJ
;
Lo, SC
;
運輸與物流管理系註：原交通所+運管所
;
Department of Transportation and Logistics Management
In this study, the multilane traffic flow is modeled as a nonlinear Poisson equation in a two-dimensional space. The model is derived from the interaction among vehicles and the assumption that vehicles will tend toward the equilibrium state under a given traffic condition. A monotone iterative scheme for the nonlinear model, which is a finite difference approximation of the model, is presented. The convergency is also discussed herein. At last, a numerical example is employed to explain the model. (C) 2002 Elsevier Science B.V. All rights reserved.
Search of optimum bias voltage for oxide patterning on Si using scanning tunneling microscopy in air
(2000-03-01)
Tseng, KS
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Hsieh, TE
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Lo, SC
;
Lin, HF
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材料科學與工程學系
Nanometer-scale oxide patterns were fabricated on H-passivated Si using a scanning tunneling microscopy (STM) in air. We found that the optimum bias voltage to generate clean and uniform oxide patterns depends on the composition of the tip material rather than on the tip head sharpness. For tungsten tips, oxide patterns with the desired geometrical features can be obtained at bias voltages ranging from -0.8 to -1.2 V, while for platinum-iridium tips, the bias voltages lie between -1.5 and -2.5 V at a fixed tunneling current of 2.0 nA. These biases correspond to the working voltage generating the oxide pattern with the lowest apparent depth. Beyond these voltage ranges, tip scratching on the sample surface or field-induced mass transfer from the tip might occur, as evidenced by tip wearing and the contamination of debris of tip material in the vicinity of the patterns. On the other hand, the tip head sharpness affects the width and the height of line patterns. When extremely fine oxide lines were desired, a sharp tip has to be used for STM patterning. (C) 2000 American Vacuum Society. [S0734-211X(00)08202-0].