Browsing by Issue Date, starting with "2000-08-28"

Now showing 1 - 20 of 78153

The dependence of initial states on the excitation of NO molecules by chirped infrared laser pulses
(2000-08-28)
Lin, JT
;
Jiang, TF
;
物理研究所
;
Institute of Physics
We study the effect of initial states on the chirping excitation of NO molecules in order to interpret recent experimental data. The results show that excitation is efficient when the probability density localizes along the polarization direction of the external field. Therefore, the thermal effect on the density distribution must be taken into account for the experimental case of 15 K. Furthermore, as the adiabatic limit is fully satisfied, the interference pattern of excited state populations disappears. This becomes a limiting factor under experimental conditions. We also find that excitation can be enhanced significantly when the pulse intensity is increased to fit the adiabatic criterion.
An intelligent buffer management approach for GFR services in IP/ATM internetworks
(2000-08-30)
Wang, PC
;
Chan, CT
;
Chen, YC
;
資訊工程學系
;
Department of Computer Science
In ATM networks, the Guaranteed Frame Rate (GFR) service has been proposed to accommodate non-real-time traffic with packet size not exceeding a maximum length, such as TCP/IP based traffic. The GFR service not only guarantees a minimum throughput at the frame level, but also supports a fair share of available resources. In this article, we propose a buffering strategy called Intelligent Fair Buffer Allocation (IFBA) that provides minimum cell rate (MCR) guarantees and fair sharing to GFR virtual circuits (VCs). From the simulation results, we demonstrate that IFBA fulfills the requirements of GFR service as well as improves the TCP throughput using the FIFO scheduling. (C) 2000 Elsevier Science B.V. All rights reserved.
Spur gear generation by shaper cutters
(2000-08-31)
Tsay, CB
;
Liu, WY
;
Chen, YC
;
機械工程學系
;
Department of Mechanical Engineering
This paper proposes the computerized tooth profile generation of spur gears cut with shaper cutters. A complete geometrical mathematical model of a spur shaper cutter is proposed, including the protuberance, the involute region and semi-topping. The profiles of standard or non-standard spur gears cut with the shaper cutter are obtained based on the theory of gearing. In addition, the effects of the cutter parameters on the generated tooth profile are investigated and illustrated with computer simulation, while the appropriate shaper cutter parameters corresponding to the required gear profile, are also determined using an optimization method. (C) 2000 Elsevier Science S.A. All rights reserved.
The design and development of a hydrostatic extrusion apparatus
(2000-08-31)
Hung, JC
;
Hung, CH
;
機械工程學系
;
Department of Mechanical Engineering
The purpose of this research is to design and construct an experimental hydrostatic extrusion apparatus which has a maximum working pressure of 10 000 kg/cm(2). and to reduce the cost of this extrusion apparatus. The high-pressure extrusion container has been designed with two-layer pyramidal cylinders, and the material used was SKD61 which is cheap and readily available. Different materials and designs for high-pressure seals were tested and analyzed for the best combination performance. Problems in the extrusion processes using this device a ere analyzed and solved, which increased the reliability of the device. The results of extrusion experiments have established that this device is practicable, (C) 2000 Published by Elsevier Science S.A.
Active cancellation of noise in a car cabin using the zero spillover controller
(2000-08-31)
Bai, MSR
;
Chen, HH
;
機械工程學系
;
Department of Mechanical Engineering
In active noise control problems, spillover will occur because of the Bode integral constraint if the performance sensors and measurement sensors are collocated, or if the control speakers and the noise sources are collocate, This paper is focused on the implementation of a multiple-channel zero-spillover ANC controller using a spatially feedforward structure for a car cabin. The plant model is realized by using a frequency-domain procedure. The linear-quadratic-Gaussian algorithm is used in controller design. Experiments are carried out to verify the proposed technique, where random noise and engine noise are chosen as the primary noise. The results indicate that the proposed controller yields a broadband attenuation for the random noise. The proposed method is also effective in attenuating the engine noise if an assumed model of the noise is incorporated into controller design. (C) 2000 Academic Press.
Synthesis of substituted poly (arylene vinylene) films by vapor deposition polymerization
(2000-09-01)
Li, AK
;
Janarthanan, N
;
Hsu, CS
;
應用化學系
;
Department of Applied Chemistry
An efficient method for the synthesis of PPV based polymers, poly (2,5-dimethyl-1,4-phenylene vinylene) (DMe-PPV) and poly (2,5-dimethoxy-1,4-phenylene vinylene) (DOMe-PPV) were developed using 2,5-dimethyl-1,4-bis (chloromethyl) benzene and 2,5-dimethoxy 1,4-bis (chloromethyl) benzene via vapor phase pyrolysis and followed by vapor deposition polymerization. The structure of polymer films were confirmed by FT-IR, solid state NMR and elemental analysis. Thermal gravimetry analysis reveals that the precursor polymer films form a conjugated polymer after thermal conversion at 250 degrees C. The optical and electrical properties of the polymer films were investigated by UV-Vis absorption and photoluminescence spectroscopies. Electroluminescent devices were fabricated using these polymers.
Improving the spectral sharpness of an apodized fibre grating
(2000-09-01)
Yang, C
;
Lai, Y
;
光電工程學系
;
Department of Photonics
We fabricate a steep skirt fibre Bragg grating (FBG) by employing an apodized phase mask. Gaussian UV beams with different FWHM are used on the mask to derive better spectral responses. The ratio of the FBG reflection bandwidth at -0.5 to -20 dB is improved from 0.35-0.55.
Recovery of Giardia and Cryptosporidium from water by various concentration, elution, and purification techniques
(2000-09-01)
Hsu, BM
;
Huang, C
;
環境工程研究所
;
Institute of Environmental Engineering
The performances of different concentration and elution techniques, as well as two purification methods, were evaluated in terms of their recovery efficiencies of Giardia cysts and Cryptosporidium oocysts from seeded deionized water, treated water, and raw water samples. Out of the three concentration techniques, the Envirochek capsule filtration followed by the membrane filtration consistently gave the highest recovery efficiencies for both protozoan parasites. Although the cartridge filtration is the most suitable technique for handling large quantities of water, it also brought the greatest loss of protozoan parasites. For elution and centrifugation, both the membrane filter with hand-kneading and Envirochek capsule with wrist-action shaking attained higher recovery efficiencies for cysts and oocysts. Immunomagnetic separation (IMS), the purification procedure in Method 1623, had a much higher recovery efficiency for both Giardia and Cryptosporidium than the Percoll-sucrose density gradient purification, which was the notation procedure of the Information Collection Requirements Rule (ICR) protozoan method. Recovery efficiencies of IMS were 78.6% (SD = 13.7%) and 69.3% (SD = 13.3%) for cysts and oocysts, respectively, in contrast to the 22.7% (SD = 14.5%) for cysts and 29.9% (SD = 20.3%) for oocysts by using Percoll-sucrose density gradient purification. In general, Giardia cysts attained a higher recovery efficiency. The recovery efficiencies of Method 1623, due to the use of Envirochek capsule filtration combined with the IMS, were 48.0% and 37.2% higher for Giardia and Cryptosporidium, respectively, than the ICR protozoan method for the three types of water.
A new multi-search engine for querying data through an Internet search service on CORBA
(2000-09-01)
Chang, YS
;
Yuan, SM
;
Lo, W
;
資訊工程學系
;
Department of Computer Science
Search engines are important but generally far from ideal tools of the World Wide Web (WWW). Many researchers therefore prefer to use meta-brokers to construct multi-search engines (MSE). However, these have no uniform programming interfaces, which makes tying them with other search engines difficult. Moreover, for an application that needs a search service capability, querying them is difficult. To reduce that difficulty, we propose in this paper an Internet search service (ISS) based on common object request broker architecture (CORBA) that follows the style of common object service specification (COSS). We design a multi-search engine based on ISS, which we term Octopus. For a system developer, because of its uniformity of interface, Octopus easily ties with any search engine. Equally, for an application programmer, the ISS offers a clear interface for application programs to search for information or mine data from the Internet. We demonstrate our approach to designing multi-search engines through ISS by tying two search engine agents, Yahoo and Alta Vista, with Octopus and show how CORBA clients query them. Programmers may use this interface to construct their search engine agents or query a search engine agent in their applications. (C) 2000 Elsevier Science B.V. All rights reserved.
Intelligent medium access for mobile ad hoc networks with busy tones and power control
(2000-09-01)
Wu, SL
;
Tseng, YC
;
Sheu, JP
;
資訊工程學系
;
Department of Computer Science
In mobile ad hoc networks (MANETs), one essential issue is how to increase channel utilization while avoiding the hidden-terminal and the exposed-terminal problems. Several MAC protocols, such as RTS/CTS-based and busy-tone-based schemes, have been proposed to alleviate these problems. In this paper, we explore the possibility of combining the concept of power control with the RTS/CTS-based and busy-tone-based protocols to further increase channel utilization. A sender will use an appropriate power level to transmit its packets so as to increase the possibility of channel reuse. The possibility of using discrete, instead of continuous, power levels is also discussed. Through analyses and simulations, we demonstrate the advantage of our new MAC protocol. This, together with the extra benefits such as saving battery energy and reducing cochannel interference, does show a promising direction to enhance the performance of MANET's.
On-wafer electrooptic probing using rotational deformation modulation
(2000-09-01)
Chen, WH
;
Kuo, WK
;
Huang, SL
;
Huang, YT
;
電子工程學系及電子研究所
On-wafer electrooptic probing of two-dimensional electric-field vector (E-vector) is demonstrated by using one laser beam and one electrooptic prober. This technique utilizes both compressed-stretched deformation and rotational deformation on the index ellipsoid of the electrooptic crystal. Both experiment and simulation were performed to map the E-vector on a circuit hoard, and the measurement error is within 2.2%.
The minimum distance diagram of double-loop networks
(2000-09-01)
Chen, CY
;
Hwang, FK
;
應用數學系
;
Department of Applied Mathematics
It is well-known that the minimum distance diagram of st double-loop network yields an L-shape. It is important to know, for a given L-shape, whether there exists a double-loop network realizing it. Necessary and sufficient conditions were given before, but were said to be cumbersome. They also need some clarification. We give new conditions and a simple proof. We also prove that all double-loop networks realizing the same L-shape are isomorphic as the existing proof was given in a Spanish dissertation.
Significant improvement on the electroluminescence characteristics of MEH-PPV by blending with PMMA
(2000-09-01)
Chao, CS
;
Whang, WT
;
Chuang, KR
;
材料科學與工程學系
;
Department of Materials Science and Engineering
A significant improvement on the electroluminescence threshold voltage from 5.5 volts down to 2.9 volts of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene vinylene] (MEH-PPV) in the Ca/polymer/ITO diode is observed by incorporating a non-conjugated PMMA into MEH-PPV. The threshold voltage of the material decreases with the poly(methyl methacrylate) (PMMA) content. Near-field scanning absorption and photoluminescence micrographs show that the PMMA domains dispersed in the continuous MEH-PPV phase appear to be similar to sesame seeds embedded in the MEH-PPV pancakes. The resistivity of PMMA is two orders lower than that of MEH-PPV. The excellent electrical conduction of PMMA in Ca/PMMA/ITO glass devices is not due to a pin-hole defect mechanism but may result from the electron hopping from Ca through the carbonyl groups in the PMMA. The significant improvement in the threshold Voltage may be due to the combination of the electron hopping in the thin PMMA sesame seeds and the thinner thickness effect of MEH-PPV in the light emitting layer.
Multiple access control with intelligent bandwidth allocation for wireless ATM networks
(2000-09-01)
Yuang, MC
;
Tien, PL
;
資訊工程學系
;
Department of Computer Science
Two major challenges pertaining to wireless asynchronous transfer mode (ATM) networks are the design of multiple access control (MAC), and dynamic bandwidth allocation. While the former draws more attention, the latter has been considered nontrivial and remains mostly unresolved, In this paper, we propose a new intelligent multiple access control system (IMACS) which includes a versatile MAC scheme augmented with dynamic bandwidth allocation, for wireless ATM networks. IMACS supports four types of traffic-CBR, VER, ABR, and signaling control (SCR), It aims to efficiently satisfy their diverse quality-of-service (QoS) requirements while retaining maximal network throughput. IMACS is composed of three components: multiple access controller (MACER), traffic estimator/predictor (TEP), and intelligent bandwidth allocator (IBA), MACER employs a hybrid-mode TDMA scheme, in which its contention access is based on a new dynamic-tree-splitting (DTS) collision resolution algorithm parameterized by an optimal splitting depth (SD), TEP performs periodic estimation and on-line prediction of ABR self-similar traffic characteristics based on wavelet analysis and a neural-fuzzy technique. IBA is responsible for static bandwidth allocation for CBR/VBR traffic following a closed-form formula. In cooperation with TEP, IBA governs dynamic bandwidth allocation for ABR/SCR traffic through determining the optimal SD. The optimal SD's under various traffic conditions are postulated via experimental results, and then off-line constructed using a back propagation neural network (BPNN), being used on-line by IBA, Consequently, with dynamic bandwidth allocation, IMACS offers various QoS guarantees and maximizes network throughput irrelevant to traffic variation.
Predictive classifier for image vector quantization
(2000-09-01)
Tai, SC
;
Wu, YG
;
Kuo, IS
;
資訊工程學系
;
Department of Computer Science
A new scheme for a still image encoder using vector quantization (VQ) is proposed. The new method classifies the block into a suitable class and predicts both the classification type and the index information. To achieve better performance, the encoder decomposes images into smooth and edge areas by a simple method. Then, it encodes the two kinds of region using different algorithms to promote the compression efficiency. Mean-removed VQ (MRVQ) with block sizes 8 x8 and 16x16 pixels compress the smooth areas at high compression ratios. A predictive classification VQ (CVQ) with 32 classes is applied to the edge areas to reduce the bit rate further. The proposed prediction method achieves an accuracy ratio of about 50% when applied to the prediction of 32 edge classes. Simulation demonstrates its efficiency in terms of bit rate reduction and quality preservation. When the proposed encoding scheme is applied to compress the "Lena" image, it achieves the bit rate of 0.219 bpp with the peak SNR (PSNR) of 30.59 dB. (C) 2000 Society of Photo-Optical Instrumentation Engineers. [S0091-3286(00)00908-9].
Explicit solution of partitioning problems over a 1-dimensional parameter space
(2000-09-01)
Hwang, FK
;
Onn, S
;
Rothblum, UG
;
應用數學系
;
Department of Applied Mathematics
We consider a class of partitioning problems where the partitioned set is a finite set of real numbers and the objective function of a partition is a function of the vector whose coordinates are the sums of the elements in each part of the given partition (the number of such parts is assumed given). We obtain an explicit solution of such partitioning problem with polynomial complexity bounds. (C) 2000 John Wiley & Sons, Inc.
Fabrication of very high resistivity Si with low loss and cross talk
(2000-09-01)
Wu, YH
;
Chin, A
;
Shih, KH
;
Wu, CC
;
Liao, CP
We have used proton and As+ implantation to increase the resistivity of conventional Si (10 Omega-cm) and Si-on-quartz substrates, respectively. High resistivity of 1.6 M Omega-cm is measured that is close to intrinsic Si and semi-insulating GaAs, Very low loss and cross coupling of 6.3 dB/cm and -79 dB/cm (10 mu m gap) at 20 GHz are measured on these samples, respectively. The very high resistivity and improved rf performance are due to the extremely fast similar to 1 ps carrier lifetime stable even after a 400 degrees C annealing for 1 h, Little negative effect on gate oxide integrity is also observed as evidenced by the comparable stress-induced leakage current and charge-to-breakdown for 30 Angstrom oxides.
Crosstalk-driven interconnect optimization by simultaneous gate and wire sizing
(2000-09-01)
Jiang, IHR
;
Chang, YW
;
Jou, JY
;
資訊工程學系
;
電子工程學系及電子研究所
Noise, as well as area, delay, and power, is one of the most important concerns in the design of deep submicrometer integrated circuits. Currently existing algorithms do not handle simultaneous switching conditions of signals for noise minimization. In this paper, we model not only physical coupling capacitance, but also simultaneous switching behavior for noise optimization. Based on Lagrangian relaxation, we present an algorithm which ran optimally solve the simultaneous noise, area, delay, and power optimization problem by sizing circuit components. Our algorithm, with linear memory requirement and linear runtime, is very effective and efficient. For example, for a circuit of 6144 wires and 3512 gates, our algorithm solves the simultaneous optimization problem using only 2.1-MB memory and 19.4-min runtime to achieve the precision of within 1% error on a SUN Spare Ultra-I workstation.
Quality management approaches in libraries and information services
(2000-09-01)
Hsieh, PN
;
Chang, PL
;
Lu, KH
;
經營管理研究所
;
Institute of Business and Management
The increasing expectations of users for better services have motivated libraries to view quality management as an effective means of incorporating quality improvement into their related services. Effectively implementing quality management in libraries requires an understanding of applying appropriate quality management concepts and techniques. This article reviews the quality management tools and techniques developed over the last five decades and, then, categorises them into three broad approaches. In addition, a framework of quality management approaches and techniques is developed and applied to assess and improve the service quality of libraries and information services.
A QoS-guaranteed fuzzy channel allocation controller for hierarchical cellular systems
(2000-09-01)
Lo, KR
;
Chang, CJ
;
Chang, C
;
Shung, CB
;
電信工程研究所
This paper proposes a fuzzy channel allocation controller (FCAC) for hierarchical cellular systems. The FCAC mainly contains a fuzzy channel allocation processor (FCAP) which is designed to be in a two-layer architecture that consists of a fuzzy admission threshold estimator in the first layer and a fuzzy channel allocator in the second layer. The FCAP chooses the handoff failure probability, defined as quality-of-service (QoS) index, and the resource availability as input linguistic variables for the fuzzy admission threshold estimator, where the Sugeno's position gradient-type reasoning method is applied to adaptively adjust the admission threshold for the fuzzy channel allocator. And the FCAP takes the mobility of user, the channel utilization, and the resource availability as input variables for the fuzzy channel allocator so that the channel allocation is finally determined, further based upon the admission threshold. Simulation results show that FCAC can always guarantee the QoS requirement of handoff failure probability for all traffic loads, Also it improves the system utilization by 31.2% while it increases the handoff rate by 12.9% over the overflow channel allocation (OCA) scheme [7]; it enhances the system utilization by 6% and still reduces the handoff rate by 6.7% as compared to the combined channel allocation (CCA) scheme [10], under a defined QoS constraint.