Browsing by Author "Chen, CS"

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A Contention Access Protocol with Dynamic Bandwidth Allocation for wireless ATM networks
(2000)
Yuang, MC
;
Tien, PL
;
Chen, CS
;
資訊工程學系
;
Department of Computer Science
In this paper, we propose a new Contention Access Protocol (CAP) augmented with a Dynamic Bandwidth Allocator (DBA) for wireless ATM networks supporting ABR and Signaling Control (SCR) traffic. CAP incorporates a dynamic tree-splitting collision resolution algorithm parameterized by an optimal Splitting Depth (SD). DBA performs estimation and on-line prediction of ABR self-similar traffic characteristics. It in turn determines the optimal SD per every frame, satisfying ABR throughput and SCR blocking probability requirements while retaining maximal aggregate throughput. Simulation results postulate the optimal SD's under various ABR and SCR traffic conditions. These results are then off-line trained and constructed by a Back Propagation Neural Network (BPNN), which is used on-line for optimal bandwidth allocation.
A distributed intrusion detection model for the domain name system
(2002-11-01)
Chen, CS
;
Tseng, SS
;
Liu, CL
;
資訊工程學系
;
Department of Computer Science
We have investigated the problem of detecting DoS-like DNS anomalies in DNS system. In this paper, we propose a distributed Two-phase DNS anomaly detection model for solving the problem. Three sets of algorithms corresponding to different configurations are proposed, including one sequential algorithm and two distributed algorithms, each with an increasing level of parallelism. The complexity of these algorithms have been found to be O (n l(og)n). The distributed algorithms show at least a constant (1-1/C-k), C-k > 1, improvement over the sequential one. To evaluate the performance, we have implemented the algorithms and applied them to a number of examples. The experimental result shows a speed up of about 1.68 on the test example for running on an enhanced distributed architecture with C-IDS over the sequential one. A higher speedup might be common because DNS anomalies will make the traffic distribution more concentrated on the outliers, and the computation will usually converge much more quickly.
A Laplace transform solution for tracer tests in a radially convergent flow field with upstream dispersion
(1996-09-01)
Chen, JS
;
Liu, CW
;
Chen, CS
;
Yeh, HD
;
環境工程研究所
When tracers are introduced into an injection borehole, noticeable concentration gradients at the injection well may cause a backward spreading of the initial plume during radially convergent tracer tests. Based on this concept a non-rigorous mathematical model is developed to estimate the effect of backward spreading. The injection well with an instantaneous slug input is treated as a mathematical source and the initial plume at the injection well is allowed to move upstream. The model assumes that advection and longitudinal dispersion are the transport mechanisms in a radially converging how field. The Laplace transform solution for solute concentration in an infinite porous medium is obtained using the method of Green's function. Breakthrough curves are computed by numerically inverting the Laplace transform solution. As compared with the solution of Moench, it is concluded that the presence of backward movement of initial plume yields a decrease of peak concentration and spreading out of breakthrough curve tails. This effect is significant for small Peclet numbers and can be neglected for large Peclet numbers. A field tracer test is carried out to demonstrate the applicability of the model. The experimental data are fitted with the type curves of this study, and those of Moench's study, to determine dispersivity and aquifer porosity. The results show that dispersivity values estimated by matching the two type curves are different. Because it neglects backward dispersion, Moench's solution overestimates the dispersivity and effective aquifer porosity.
A Laplace transform solution for tracer tests in a radially convergent flow field with upstream dispersion
(1996-09-01)
Chen, JS
;
Liu, CW
;
Chen, CS
;
Yeh, HD
;
環境工程研究所
When tracers are introduced into an injection borehole, noticeable concentration gradients at the injection well may cause a backward spreading of the initial plume during radially convergent tracer tests. Based on this concept a non-rigorous mathematical model is developed to estimate the effect of backward spreading. The injection well with an instantaneous slug input is treated as a mathematical source and the initial plume at the injection well is allowed to move upstream. The model assumes that advection and longitudinal dispersion are the transport mechanisms in a radially converging how field. The Laplace transform solution for solute concentration in an infinite porous medium is obtained using the method of Green's function. Breakthrough curves are computed by numerically inverting the Laplace transform solution. As compared with the solution of Moench, it is concluded that the presence of backward movement of initial plume yields a decrease of peak concentration and spreading out of breakthrough curve tails. This effect is significant for small Peclet numbers and can be neglected for large Peclet numbers. A field tracer test is carried out to demonstrate the applicability of the model. The experimental data are fitted with the type curves of this study, and those of Moench's study, to determine dispersivity and aquifer porosity. The results show that dispersivity values estimated by matching the two type curves are different. Because it neglects backward dispersion, Moench's solution overestimates the dispersivity and effective aquifer porosity.
A method for calibrating a motorized object rig
(2006)
Huang, PH
;
Tsai, YP
;
Lo, WY
;
Shih, SW
;
Chen, CS
Object Movies (OMs) have been successfully used in many applications. However, the techniques for acquiring OMs still need to be improved if high-quality and efficient OMs are desired. In this paper, we present a method for calibrating a motorized object rig to facilitate the acquisition of OMs. We first apply the CPC kinematic model to formulate the 3D configuration of the device, and then propose a method to estimate the parameters of the CPC model of the device. Furthermore, a visual tool is provided for users to adjust the controllable axes of the rig according to the estimated results. After this calibration, more accurate camera parameters can be obtained and then be used for different purposes. In this work, we use the parameters to reconstruct, from an OM, the 3D model of the object, and then adjust the OM according to the center of the 3D model so that a high-quality OM can be obtained for rendering.
A novel cross-coupling control design for Bi-axis motion
(2002-11-01)
Shih, YT
;
Chen, CS
;
Lee, AC
;
機械工程學系
;
Department of Mechanical Engineering
A new structure of cross-coupling controller for precise tracking in motion control is proposed in this paper. When compared with the conventional cross-coupling system, this new structure has the advantage that the compensators in CCC have a simpler design process than conventional ones and so does its stability analysis. The proposed compensator (or controller) is evaluated and compared experimentally with a traditional uncoupled controller on a microcomputer controlled dual-axis positioning system. The experimental results show that the new structure of cross-coupling controller remarkably reduces contour error. In addition, this new controller can be implemented easily on a majority of motion systems in use today via reprogramming the reference position command subroutine. (C) 2002 Elsevier Science Ltd. All rights reserved.
A unifying framework for intelligent DNS management
(2003-04-01)
Chen, CS
;
Tseng, SS
;
Liu, CL
;
資訊技術服務中心
;
Information Technology Services Center
The Domain Name System (DNS) is a special kind of distributed directory service for people to create and access the network information systems by (1) allowing local control of its segments and (2) making each segment's data available on the Internet using a client-server scheme. However, few administrators have the expertise to do the jobs well since this distributed mechanism is a double-edged sword; it allows DNS not only to scale to Internet size but also allows for incredible mis-configurations. The presented study is an analysis of what problems and difficulties most DNS administrators might encounter and provides the insights into how various DNS assistant sub-systems could be designed and deployed to solve the complex problems or alleviate these DNS administration job loadings. Ontologies become an important mechanism to build information systems. The role of ontologies is to capture domain knowledge and provide a commonly agreed upon understanding of a domain. The advantages include the sharing and re-use of knowledge, and the better engineering of knowledge-based systems with respect to acquisition, verification and maintenance. In this paper, we propose a unifying framework (e.g. including configuration, outstanding traffic monitoring and analysis, planning and management, tutoring, etc.) for supporting intelligent DNS management using web interface and expert system technology to help inexperienced administrators in insuring the smooth operation of their DNS systems. To help extract knowledge, we propose an efficient DNS Ontology Construction Algorithm to fast conceptualize DNS domain knowledge through a hybrid method of brainstorming and use cases modeling. While some sub-systems are still under development, others have been prototyped and deployed for everyday use. As our experience with a first simple prototype has shown, the paradigm of using DNS ontology to build a unifying framework for intelligent DNS management works good and effective. It is supposed that all these might become an integral part of the DNS administration activities of an organization in the near future. (C) 2003 Elsevier Science Ltd. All rights reserved.
Dependence of luminescence efficiency on dopant concentration and sintering temperature in the erbium-doped Ba0.7Sr0.3TiO3 thin films
(2002-08-15)
Kuo, SY
;
Chen, CS
;
Tseng, TY
;
Chang, SC
;
Hsieh, WF
We found the dependence of luminescence efficiency on Er3+ concentration and sintering temperature in the Er-doped Ba0.7Sr0.3TiO3 (BST) thin films is governed by crystallinity and ion-ion interaction. X-ray diffraction and Raman studies of the sol-gel prepared samples show that the BST polycrystalline phase occurred when the sintering temperature reaches 700 degreesC, whereas, it becomes worse for temperature above 700 degreesC resulting from phase separation and the Er3+ concentration exceeding 3 mol % due to charge compensation mechanism. The observed green emission reaches maximum at sintering temperature 700 degreesC and 3 mol % Er3+ ions concentration. We also showed the Er dopant does not affect the dielectric property of BST thin films in C-V measurement and the Ba0.7Sr0.3TiO3 films doped with Er3+ ions may have potential use for electroluminescence devices. (C) 2002 American Institute of Physics.
Design of acceleration/deceleration profiles in motion control based on digital FIR filters
(1998-07-01)
Chen, CS
;
Lee, AC
;
機械工程學系
;
Department of Mechanical Engineering
In motion control, the reference commands should pass through the acceleration/deceleration (Acc/Dec) processor before being fed into the servo loop. Consequently, not only can a smooth motion profile be obtained but undesirable vibration can be avoided. In this study, we develop a systematic design procedure for the Acc/Dec processor based on the discrete time finite-impulse-response (FIR) filter design technique with some necessary conditions. Compared with the conventional Acc/Dec scheme, the FIR Acc/Dec scheme poses the advantage that the contouring error can be analyzed. Also, the contouring error caused by the conventional Acc/Dec scheme is evaluated by demonstrating a mapping technique from the conventional Acc/Dec scheme to the FIR Acc/Dec scheme. The proposed Acc/Dec algorithm is quite flexible and efficient, creating space for users to use more sophisticated profiles to more efficiently match the system constraints with minimum contouring errors. Simulation and experimental results verify that the proposed Acc/Dec processor can effectively improve the motion accuracy. (C) 1998 Elsevier Science Ltd. All rights reserved.
Effects of channel width on electrical characteristics of polysilicon TFTs with multiple nanowire channels
(2005-10-01)
Wu, YC
;
Chang, TC
;
Liu, PT
;
Chen, CS
;
Tu, CH
This brief studies the electrical characteristics of a series of polysilicon thin-film transistors (poly-Si TFTs) with different numbers of multiple channels of various widths, with lightly doped drain (LDD) structures. The nanoscale TFT with ten 67-nm-wide split channels (M10) has superior and more uniform electrical characteristics than other TFTs. Additionally, experimental results reveal that the electrical performance of proposed TFTs enhances with each channel width decreasing, yielding a profile from a single-gate to tri-gate structure.
Electrical properties of ZnO varistors prepared by microwave sintering process
(1996-09-01)
Chen, CS
;
Kuo, CT
;
Lin, IN
;
機械工程學系
;
材料科學與工程學系
Microwave sintering processes were observed to substantially enhance the densification rate for ZnO varistor materials. Samples microwave sintered at 900-1200 degrees C for 10 min reached the same high density as those conventionally sintered at the same temperature for 60 min. A similar tendency was observed for the grain size. Prolonged microwave sintering, however, resulted in fast grain growth and degraded electric field-current density (E-J) properties. Capacitance-voltage (C-V) analysis indicated that the degradation in E-J behavior primarily resulted from the decrease in grain boundary barrier height. The modification of the grain boundary electrical properties, in turn, is ascribed to the loss of volatile Bi species along the grain boundaries.
Enhancing precision of global positioning system using short-range distance baseline field
(2002-02-01)
Chen, CS
;
Yeh, TK
;
土木工程學系
;
Department of Civil Engineering
This paper presents two novel concepts to improve the precision of global positioning system (GPS). First, observations of the low cutoff angle are applied to GPS positioning for obtaining more information to enhance precision. However, unequal weight P = cos(2)(z) is used, where z denotes the zenith distance, since the noise of the GPS observations is increased following the increase of the zenith distance. Second, a short-range baseline field is used as the test area. In addition, the external precision of the GPS baseline is evaluated using the distance obtained with a precise telemeter to replace the conventional method, which uses internal precision, i.e., baseline repeatability or standard deviation. The analysis results indicate that the best precision of GPS positioning is obtained at a cutoff angle of 15degrees. Moreover, using unequal weight to receive low cutoff angle GPS observation data to positioning can improve the precision average 3 mm for our test baselines.
High performance and high reliability polysilicon thin-film transistors with multiple nano-wire channels
(2004)
Wu, YC
;
Chang, CY
;
Chang, TC
;
Liu, PT
;
Chen, CS
We have investigated the lightly-doped drain (LDD) polysilicon thin-film transistors (poly-Si TFTs) with a series of multi-channel with different widths. The ten 67 nm-wide split channels TFT has best gate control due to its tri-gate structure, and has lowest poly-Si grain boundary defects, which were passivated by NH3 plasma effectively due to its split nano-wires structure. The proposed TFT exhibits high performance electrical characteristics, such as a high ON/OFF current ratio (>10(9)), a steep subthreshold slope (SS) of 137 mV/decade, an absence of drain-induced barrier lowering (DIBL), suppressed kink-effect, and superior reliability.
High-performance polycrystalline silicon thin-film transistor with multiple nanowire channels and lightly doped drain structure
(2004-05-10)
Wu, YC
;
Chang, TC
;
Chang, CY
;
Chen, CS
;
Tu, CH
This investigation examines polycrystalline silicon thin-film transistors (TFTs) with multiple nanowire channels and a lightly doped drain (LDD). A device with an LDD structure exhibits low leakage current because the lateral electrical field is reduced in the drain offset region. Additionally, multiple nanowire channels can generate fewer defects in the polysilicon grain boundary and have more efficient NH3 plasma passivation than single-channel TFTs, further reducing leakage current. They exhibit superior electrical characteristics to those of single-channel TFTs, such as a higher ON/OFF current ratio (>10(8)), a better subthreshold slope of 110 mV/decade, an absence of drain-induced barrier lowering, and suppressed kink-effect. Devices with the proposed TFTs are highly promising for use in active-matrix liquid-crystal display technologies. (C) 2004 American Institute of Physics.
Impact of a large earthquake on a GPS network: The case of the 1999 Chi-Chi, Taiwan earthquake
(2002-04-01)
Kuo, LC
;
Yu, SB
;
Hsu, VJ
;
Hou, CS
;
Lee, YH
On 20 September 1999, Taiwan was hit by the largest inland earthquake (M-w = 7.6) in the last century resulting in an 80-kilometre thrust rupture almost directly along the existing Chelungpu fault. Here, we estimated the coordinates of the GPS stations by using the annual epoch-observed and permanent continuously-recorded GPS data covering the 1992-1999 period Taking into account the effects of secular motion and post-deformation, we calculated the corrected coseismic displacements. Relatively large coseismic displacements of 8-9 in in the horizontal and vertical components were found in the northern part of the fault. Stations on the hanging wall shifted horizonatly 2-9 in in the NW direction and decreased in magnitude from west to east. On the other hand, displacements on the footwall were less than 2 in in the SE direction hid increased from west to east. The size of the zone overlapping the hanging wall and the foowall showed a decrease of 796 ppm in 494 km(2). This is in direct contrast to areas near the fault which increased in size from 13 to 23 7 ppm. Significant postseismic deformations were also observed in data from the existing 44 permanent stations and 7 temporary stations. Additionally, large postseismic deformations of 10-20 cm were found at stations SUAM, 100 7 and YUSN within 10 months.
Improvement on the degradation of microwave sintered ZnO varistors by postannealing
(1998-06-01)
Chen, CS
;
Kuo, CT
;
Lin, IN
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The microwave sintering process not only densified the ZnO materials in a higher rate, but also resulted in significantly better varistor characteristics. Large nonlinear coefficient and low leakage current density were attained by cooling the samples under a rate of 80 degrees C/min after sintering, followed by 600 degrees C postannealing for 60 min under oxygen atmosphere. Inappropriate annealing deteriorated the varistor characteristics that can either be attributed to the insufficient reoxidation along grain boundaries when annealed in N-2 (or air) or loss of Zn species in these regions when annealed at 750 degrees C (900 degrees C). By contrast, the degradation behavior of these materials can be improved by the annealing process regardless of the annealing atmosphere or temperature.
Low power CMOS wideband receiver design
(2004)
Sung, CC
;
Chou, MF
;
Wu, CC
;
Chen, CS
;
Wen, KA
A low power CMOS receiver for ultra-wideband (UWB) wireless applications is presented. The low-noise amplifier (LNA) building block employing stagger tuning technique consists of two common-source stages with different resonance frequencies to achieve low power consumption and wide operating bandwidth. In addition, the variable gain amplifier (VGA) follows the passive mixer employs a novel wide-range pseudo-exponential circuit topology. This work was implemented in 0.18-mu m CMOS process exhibits 280-MHz bandwidth and draws 27.4 mA on average from a 1.8-V supply. The receiver has a minimum noise figure of 2.6 dB, and maximum IIP3 of -33 dBm across the UWB group 1 bands.
Microstructure and nonlinear properties of microwave-sintered ZnO-V2O5 varistors: I, effect of V2O5 doping
(1998-11-01)
Kuo, CT
;
Chen, CS
;
Lin, IN
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The modification of the densification behavior and the grain-growth characteristics of the microwave-sintered ZnO materials, caused by the incorporation of V2O5 additives, have been systematically studied. Generally, the addition of V2O5 markedly enhances the densification rate, such that a density as high as 97.9% of the theoretical density and a grain size as large as 10 mu m can be attained for a sintering temperature as low as 800 degrees C and a soaking time as short as 10 min. Increasing the sintering temperature or soaking time does not significantly change the sintered density of the ZnO-V2O5 materials but it does monotonously increase their grain size. Varying the proportion of V2O5 in the range of 0.2-1.0 mol% does not pronouncedly modify such behavior. The leakage current density (J(L)) of these high-density and uniform-granular-structure samples is still large, which is amended by the incorporation of 0.3 mol% of Mn3O4 in the ZnO materials, in addition to 0.5 mol% of the V2O5 additives. Samples that are obtained using such a method possess good nonohmic characteristics (alpha = 23.5) and a low leakage current density (J(L) = 2.4 x 10(-6) A/cm(2)).
Microstructure and nonlinear properties of microwave-sintered ZnO-V2O5 varistors: I, effect of V2O5 doping
(1998-11-01)
Kuo, CT
;
Chen, CS
;
Lin, IN
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The modification of the densification behavior and the grain-growth characteristics of the microwave-sintered ZnO materials, caused by the incorporation of V2O5 additives, have been systematically studied. Generally, the addition of V2O5 markedly enhances the densification rate, such that a density as high as 97.9% of the theoretical density and a grain size as large as 10 mu m can be attained for a sintering temperature as low as 800 degrees C and a soaking time as short as 10 min. Increasing the sintering temperature or soaking time does not significantly change the sintered density of the ZnO-V2O5 materials but it does monotonously increase their grain size. Varying the proportion of V2O5 in the range of 0.2-1.0 mol% does not pronouncedly modify such behavior. The leakage current density (J(L)) of these high-density and uniform-granular-structure samples is still large, which is amended by the incorporation of 0.3 mol% of Mn3O4 in the ZnO materials, in addition to 0.5 mol% of the V2O5 additives. Samples that are obtained using such a method possess good nonohmic characteristics (alpha = 23.5) and a low leakage current density (J(L) = 2.4 x 10(-6) A/cm(2)).
Microstructure and nonlinear properties of microwave-sintered ZnO-V2O5 varistors: II, effect of Mn3O4 doping
(1998-11-01)
Kuo, CT
;
Chen, CS
;
Lin, IN
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The microstructure and nonlinear current-voltage characteristics of Mn3O4-doped ZnO-V2O5 ceramics, microwave-sintered at 800 degrees-1200 degrees C for 10 min, have been investigated. A high density (96% of the theoretical density) has been achieved. The incorporation of Mn3O4 additives does not significantly alter the densification behavior of the ZnO-V2O5 materials, but rather pronouncedly increases the non-linear coefficient (alpha = 23.5) and markedly suppresses their leakage current density (J(L) = 2.4 x 10(-6) A/cm(2)). On the other hand, the intrinsic properties of the materials, including the Schottky barrier height (Phi(b)) and the donor density (N-d), are only moderately modified; that is, Phi(b) = 1.16 eV and N-d = 5.4 x 10(17)/cm(3). X-ray diffractometry analyses and energy-dispersive X-ray microanalyses (via scanning electron microscopy) indicate that the V2O5 species facilitate the densification and the development of microstructure via the formation of a liquid phase (Zn-3(VO4)(2)) along the grain boundaries, whereas the Mn3O4 species markedly enhance the nonohmic behavior of the ZnO-V2O5 materials by forming the surface states along the grain boundaries.