Browsing by Issue Date, starting with "1999-06-01"

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The application of laser metrology and resonant optical cavity techniques to the measurement of G
(1999-06-01)
Ni, WT
;
Liu, DK
;
Liu, TT
;
Mei, HH
;
Pan, SS
Our goal is to measure the gravitational constant G to within 1-10 ppm using a high-finesse Fabry-Perot optical cavity. The two high-reflectivity mirrors of the Fabry-Perot cavity will be suspended separately by two nearly identical simple pendulums of length about 1 m. For the source of attraction, we have built a rotating mass source with 12 lead bricks (each brick is of mass 11.5 kg) on each of two opposite sides of a rotating table. The period of rotation can be adjusted. We normally use a rotation period of 200 s. For this rotating mass, the relative equilibrium displacement of the two mirrors is over 10 nm and we are working for a preliminary measurement of this distance to one part in 10(4). Auxiliary quantities such as the positions of the test mass and the positions of Fabry-Perot cavity mirrors can be monitored using real-time laser metrology. The stability and real-time monitoring of the pendulums, building stability, and the compensation or averaging of mass inhomogeneity need special considerations.
Synthesis and characterization of liquid crystalline multiblock copolyesters of oxybenzoate and ethylene terephthalate
(1999-06-01)
Ho, JC
;
Lin, YS
;
Wei, KH
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Multiblock copoly(oxybenzoate-p-ethylene terephthalate) (POB-PET) was synthesized by a direct reaction of poly(hydroxybenzoic acid) (PHBA), acetoxybenzoic acid and poly(ethylene terephthalate). The synthesized multiblock POB-PET becomes more blocky and less soluble in the mixed solvent of trifluoroacetic acid and chloroform when the degree of polymerization of PHBA used in the synthesis is higher as evidenced in the solid-state and liquid-state nuclear magnetic resonance study. The thermal curves displayed by the synthesized multiblock 20/80 and 40/60 POB-PET contained distinctive contributions from both PET blocks and POB blocks in the copolymers when the degree of polymerization of PHBA used in the synthesis is seven. Only 20 mol% of POB is needed to form liquid crystalline phase in these multiblock POB-PET as opposed to a minimum of 40 mol% of POB is required to form liquid crystalline phases for random POB-PET. (C) 1999 Elsevier Science Ltd. All rights reserved.
Obstacle avoidance for autonomous land vehicle navigation in indoor environments by quadratic classifier
(1999-06-01)
Ku, CH
;
Tsai, WH
;
資訊工程學系
;
Department of Computer Science
A vision-based approach to obstacle avoidance for autonomous land vehicle (ALV) navigation in indoor environments is proposed. The approach is based on the use of a pattern recognition scheme, the quadratic classifier, to find collision-free paths in unknown indoor corridor environments. Obstacles treated in this study include the walls of the corridor and the objects that appear in the way of ALV navigation in the corridor. Detected obstacles as well as the two sides of the ALV body are considered as patterns, A systematic method for separating these patterns into two classes is proposed. The two pattern classes are used as the input data to design a quadratic classifier, Finally, the two-dimensional decision boundary of the classifier, which goes through the middle point between the two front vehicle a heels, is taken as a local collision-free path, This approach is implemented on a real ALV and successful navigations confirm the feasibility of the approach.
A 2-V, 1.8-GHz BJT phase-locked loop
(1999-06-01)
Chen, WZ
;
Wu, JT
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
This paper describes the design of a bipolar junction transistor phase-locked loop (PLL) for Sigma Delta fractional-N frequency-synthesis applications. Implemented in a 0.8-mu m BICMOS technology, the PLL can operate up to 1.8 GHz while consuming 225 mW of power from a single -2-V supply. The entire LC-tuned negative-resistance variable-frequency oscillator is integrated on the same chip. A differential low-voltage current-mode logic circuit configuration is used in most of the PLL's functional blocks to minimize phase jitter and achieve low-voltage operation. The multimodulus frequency divider is designed to support multibit digital modulation. The new phase and frequency detector and loop filter contain only npn transistors and resistors and thus achieve excellent resolution in phase comparison. When phase locked to a 53.4-MHz reference clock, the measured phase noise of the 1.6-GHz output is -91 dBc/Hz at 10-kHz offset, The frequency switching time from 1.677 to 1.797 GHz is 150 mu s. Die size is 4300 x 4000 mu m(2), including the passive loop filter.
Application of selective liquid-phase deposition to fabricate contact holes without plasma damage
(1999-06-01)
Yeh, CF
;
Liu, CH
;
Su, JL
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
This work develops an alternative method, selective liquid-phase deposition (S-LPD), to fabricate contact holes instead of reactive ion etching. In preliminary experiments, deep n(+)/p junction diodes with contact holes prepared by S-LPD exhibit much less reverse current, unity ideality factor, larger forward current, lower contact resistance, and higher thermal stability than those prepared by reactive ion etching. Further superiority of plasma damage-free near-surface regions is also investigated using Schottky and ultrashallow junction diodes. Experimental results indicate that S-LPD can be applied to the submicron contact-hole process. The data after reverse bias temperature stress reveals the satisfactory reliability of S-LPD contact holes. This work demonstrates that the S-LPD technology is a highly promising means of replacing reactive ion etching processes to form submicron contact holes as reliably as those by wet-etching. (C) 1999 The Electrochemical Society. S0013-4651(98)08-119-1. All rights reserved.
One-loop Vilkovisky-DeWitt effective potential for scale-invariant gravity
(1999-06-01)
Lin, SY
;
Ng, KW
;
電子物理學系
;
物理研究所
;
Department of Electrophysics
For a pure gravity theory without matter, the scale symmetric phase represents an equivalent class of gravity theories, to which the Einstein gravity plus a cosmological constant belongs under a special gauge choice. The one-loop quantum correction of this scale-invariant theory is calculated by using Vilkovisky-DeWitt's method. It is shown that the resulting effective potential is gauge-independent as expected. Some discussions of the Vilkovisky-DeWitt method through this calculation are given.
Effects of BF2+ implantation on the oxidation resistance of copper films
(1999-06-01)
Wu, ZC
;
Liu, YL
;
Chen, MC
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
This work investigates the effects of BF2+ implantation on the oxidation resistance of copper films. The BF2+ ions were implanted into Cu films through a 1000 Angstrom thick screen SiO2 layer. We found that the oxidation resistance of Cu films can be significantly improved by BF2+ implantation at appropriate conditions. In particular, BF2+ implantation at 35 to 40 keV to a dose of 1 - 8 x 10(14) cm(-2) made the Cu films capable of resisting oxidation at temperatures up to 250 degrees C. At these BF2+ implantation energies, boron atoms of peak concentration were projected near the Cu surface; thus the diffusion paths of oxidizing species were efficiently blocked. Implantation at too high energy would result in greater depth of projection, thus a lower concentration of boron at the Cu surface; moreover, it generally leads to increased implantation defects that might serve as diffusion paths for the oxidation species. On the other hand, too high dosage implantation would also have an adverse effect on the capability of oxidation resistance for Cu films owing to the higher density of implantation damage as well as the formation of reactive fluorine compound (CuF2) near the Cu surface. (C) 1999 Elsevier Science S.A. All rights reserved.
CSO distortions due to the combined effects of self- and external-phase modulations in long-distance 1550-nm AM-CATV systems
(1999-06-01)
Wu, MC
;
Wang, CH
;
Way, WI
;
電信工程研究所
;
Institute of Communications Engineering
We found that the combined effects of self- and external-phase modulations must be considered in order to precisely predict the composite second-order distortions in a long-distance 1550-nm externally modulated AM-cable TV (CATV) system, especially when the applied phase modulation index and modulating tone frequency to the integrated phase modulator are high, This result has important implications to the optimum design of 1550-nm transmitter for long-distance Am- and QAM-CATV systems.
Electromigration in sputtered copper films on polyimide
(1999-06-01)
Wang, HW
;
Chiou, BS
;
Jiang, JS
;
電子物理學系
;
電子工程學系及電子研究所
Electromigration damage (EMD) is one of the major causes for the failures of interconnects. In this study, the electromigration of Cu on polyimide is investigated. An empirical formula is used to evaluate the EMD of Cu film. The activation energy (Q) obtained is significantly less than those of lattice and grain boundary diffusion. This suggests that the electromigration in copper proceeds via an interfacial diffusion path. The geometry of the metallization also affects the activation energy. Any abrupt change in the interconnect direction and metal width causes current crowding and should be avoided. The current exponents (n), calculated from EMD data, are 3.58 and 3.35 for straight and zig-zag Cu films, respectively.
The distributed program reliability analysis on a star topology: Efficient algorithms and approximate solution
(1999-06-01)
Chang, MS
;
Chen, DJ
;
Lin, MS
;
Ku, KL
;
資訊科學與工程研究所
A distributed computing system consists of processing elements, communication links, memory units, data files, and programs. These resources are interconnected via a communication network and controlled by a distributed operating system. The distributed program reliability (DPR) in a distributed computing system is the probability that a program which runs on multiple processing elements and needs to retrieve data files from other processing elements will be executed successfully. This reliability varies according to 1) the topology of the distributed computing system, 2) the reliability of the communication edges, 3) the data files and programs distribution among processing elements, and 4) the data files required to execute a program. In this paper, we show that computing the distributed program reliability on a star distributed computing system is #P-complete. A polynomially solvable case is developed for computing the distributed program reliability when some additional file distribution is restricted on the star topology. We also propose a polynomial time algorithm for computing the distributed program reliability with approximate solutions when the star star topology has no the additional file distribution.
Analysis of AC electrical response for radio-frequency sputtered (Ba0.5Sr0.5)TiO3 thin film
(1999-06-01)
Wang, YP
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Through the measurement of dielectric dispersion as a function of frequency (100 Hz less than or equal to f less than or equal to 1 MHz), we investigated the trapping dielectric relaxation of r.f.-sputtered (Ba0.5Sr0.5)TiO3 film and proposed an equivalent circuit on the basis of the admittance and capacitance spectra. Admittance spectral studies in the temperature range of 200-420 K revealed the existence of a trap level. The trap, located at 0.05 eV, is envisaged to be responsible for the origin of dielectric relaxation and carrier concentration. The equivalent circuit, consisting of a series trapping resistance and capacitance combination in parallel with leakage resistance and high frequency limit capacitance, is adopted to explain satisfactorily the AC response and to identify the contribution of the shallow trap on the electrical properties of BST thin film. (C) 1999 Elsevier Science S.A. All rights reserved.
The feasibility study of transporting IS-95CDMA signals over HFC networks
(1999-06-01)
Lin, YM
;
Way, WI
;
電信工程研究所
;
Institute of Communications Engineering
This letter studies the feasibility of transmitting IS-95 code-division multiple-access (CDMA) wireless signals in hybrid-fiber-coax (HFC) networks, Capacity estimation of an HFC optical node-based CDMA cellular systems using a return-path channel model is provided. In addition to multiple-access interference in IS-95 CDMA networks, the return-path channel model takes into account ingress noise, impulsive noise, and microreflections in a coaxial cable transmission system; and laser diode clipping-induced intermodulation noise in an optical fiber link.
Partition polytopes over 1-dimensional points
(1999-06-01)
Gao, B
;
Hwang, FK
;
Li, WCW
;
Rothblum, UG
;
應用數學系
We consider partitions of a finite set whose elements are associated with a single numerical attribute. For each partition we consider the vector obtained by taking the sums of the attributes corresponding to the elements in the parts (sets) of the partition, and we study the convex hulls of sets of such vectors. For sets of all partitions with prescribed number of elements in each set, we obtain a characterizing system of linear inequalities and an isomorphic representation of the face lattice. The relationship of the resulting class of polytopes to that of generalized permutahedra is explored.
New methods for students' evaluation using fuzzy sets
(1999-06-01)
Chen, SM
;
Lee, CH
;
資訊工程學系
;
Department of Computer Science
In an earlier work, Biswas (1995) presented two methods for the application of fuzzy sets in students' answerscripts evaluation. In this paper, we extend his work to propose two new methods for evaluating students' answerscripts using fuzzy sets. The proposed methods can overcome the drawbacks in Biswas (1995) due to the fact that they do not need to perform the complicated matching operations and they can evaluate students' answerscripts in a more fair manner. (C) 1999 Elsevier Science B.V. All rights reserved.
Analyzing accelerated degradation data by nonparametric regression
(1999-06-01)
Shiau, JJH
;
Lin, HH
;
統計學研究所
;
Institute of Statistics
This paper presents a nonparametric regression accelerated life-stress (NPRALS) model for accelerated degradation data wherein the data consist of groups of degrading curve data. In contrast to the usual parametric modeling, a nonparametric regression model relaxes assumptions on the form of the regression functions and lets data speak for themselves in searching for a suitable model for data. NPRALS assumes that various stress levels affect only the degradation rate, but not the shape of the degradation curve. An algorithm is presented for estimating the components of NPRALS. By investigating the relationship between the acceleration factors and the stress levels, the mean time to failure estimate of the product under the usual use condition is obtained. The procedure is applied to a set of data obtained from an accelerated degradation test for a light emitting diode product. The results look very promising. The performance of NPRALS is further checked by a simulated example and found satisfactory. We anticipate that NPRALS can be applied to other applications as well.
Effect of the sensitizer on the properties of fully functionalized photorefractive epoxy polymers and their performance in the hologram image storage
(1999-06-01)
Chang, CJ
;
Whang, WT
;
Hsu, KY
;
Hsieh, ML
;
材料科學與工程學系
The 3-amino-9-ethyl carbazole (AEC)/Dispersed Orange 3 (DO3)/diglycidyl 1,2 cyclohexanedicarboxylate (DCD) main chain copolymers are synthesized and studied on their photorefractive (PR), photoconductive, and holographic characteristics. They are good hologram recording media because not only the stored hologram exhibits excellent fringe contrast with the resolution at about 20 mu m, but also the image can be stored, erased, and overwritten. The UV/Vis spectra shows that AEC segments may form charge transfer complexes with either DO3 segments or TNF sensitizers. By incorporating the sensitizer or increasing the charge transfer component concentration, the grating growth rate can be speeded up. Applying an electric field on the polymer film containing no sensitizer helps to elevate the grating growth speed, but it shows little influence on the grating growth speed of the films with sensitizers. More nonlinear optical (NLO) segments in the copolymer result in higher diffraction efficiency. The dark decay of the film depends on the dark conductivity. Incorporating sensitizers or more charge transport segments leads to more dark decay because of increasing dark conductivity. The dark decay of the PR properties at elevated temperature can also be evaluated by the thermal stimulated discharge current (TSDC) spectroscopy technique. (C) 1999 John Wiley & Sons, Inc.
Influence of design and operation parameters on bag-cleaning performance of pulse-jet baghouse
(1999-06-01)
Lu, HC
;
Tsai, CJ
;
環境工程研究所
;
Institute of Environmental Engineering
In this study, a filter test system with clean new fabric bags was used to measure the pulse pressure and acceleration of the filter bag. Fabric acceleration and pulse pressure were used as an index of bag-cleaning intensity. The jet pump curves, which relate the flow rate through the venturi to the average developed pressure by the venturi, were determined by the similar system. The intersection of the jet pump curve and the bag operating line, which relates the pressure drop to flow rate across the bag during pulse-jet cleaning, is the system operating point that was used to predict the average pulse pressure in the bag during pulse-jet cleaning. Experimental results of this study show that a higher pulse pressure can be achieved without the venturi at the top of the bag for bag materials with low resistance coefficient. For bags with higher resistance coefficients, higher pulse pressure is obtained with a venturi installed at the top of the bag. The predicted pressure values are in good agreement with experimental data. Dimensional analysis for jet pump performance was developed to reduce the experimental data. The results show that the jet pump curves obtained under different operating conditions can be reduced to the same nondimensional curve, which can be used to facilitate the design and operation of a pulse-jet cleaning system.
Hamiltonian structures of generalized Manin-Radul super-KdV and constrained super KP hierarchies
(1999-06-01)
Tu, MH
;
Shaw, JC
;
應用數學系
;
Department of Applied Mathematics
A study of Hamiltonian structures associated with supersymmetric Lax operators is presented. Following a constructive approach, the Hamiltonian structures of Inami-Kanno super-KdV hierarchy and constrained modified super-KP hierarchy are investigated from the reduced supersymmetric Gelfand-Dickey brackets. By applying a gauge transformation on the Hamiltonian structures associated with these two nonstandard super-Lax hierarchies, we obtain the Hamiltonian structures of generalized Manin-Radul super-KdV and constrained super-KP hierarchies. We also work out a few examples and compare them with the known results. (C) 1999 American Institute of Physics. [S0022-2488(99)02206-9].
Synthesis and characterization of nonlinear optical chromophores with conformationally locked polyenes possessing enhanced thermal stability
(1999-06-01)
Shu, YC
;
Gong, ZH
;
Shu, CF
;
Breitung, EM
;
McMahon, RJ
Dipolar NLO chromophores with an interposed conjugated tetraene segment in which all but four of the methine groups are incorporated into a tetrahydronaphthalene framework have been synthesized and characterized. This conformation-locking approach furnishes NLO chromophores possessing an enhanced thermal stability. X-ray crystallographic data indicate that the polyenic chain of these molecules exhibits a near-planar all-trans conformation in the solid state. EFISH measurements show that these conformationally locked tetraenic chromophores exhibit large second-order optical nonlinearities (mu.beta similar to 4000 x 10(-48) cm(6) at 1907 nm), although the nonlinearities of the corresponding "unlocked" analogues are slightly larger.
A probability model for reconstructing secret sharing under the internet environment
(1999-06-01)
Lee, CY
;
Yeh, YS
;
Chen, DJ
;
Ku, KL
;
資訊科學與工程研究所
Internet technologies have ushered in a new era for computer-related communications. Use of the Internet for commercial applications and resource sharing has accelerated in recent years as well. Owing to such developments, Internet security has become a critical issue for both academic and commercial sectors. Several studies have focused on areas involving network security such as authentication, privacy, and integrity. In some applications, an important message can be divided into pieces and allocated at several different sites over the Internet for security access concern. For example, an important map that can be used to access a military base, a vital key that can be used to give a military order or command. To access such an important message, one must reconstruct the divided pieces from different sites under the given Internet environment. In this paper, we present a novel probability model for reconstructing secret sharing under the Internet. Also, how to assign the divided shares into different sites over the Internet is studied. Also proposed herein are algorithms to perform shares assignment and to evaluate the probability of reconstructing the divided pieces into the original secret. Illustrative examples and simulation results demonstrate the feasibility of the proposed approach. (C) 1999 Elsevier Science Inc. All rights reserved.