Browsing by Issue Date, starting with "1999-01-15"

Now showing 1 - 20 of 80809

Optimal assignment of mobile agents for software authorization and protection
(1999-01-15)
Shieh, SP
;
Lin, CT
;
Wu, SY
;
資訊工程學系
;
Department of Computer Science
In this paper, a model for software authorization and protection in mobile code systems is proposed. In the model, a software is partitioned into objects, called mobile agents, and the privileges to access these agents are separated and distributed to the user's local system and a number of trusted servers called trusted computational proxies. The execution of a program (software) is conducted by cooperation of the agents and the proxies that contain them. Two agents are dependent if there is a message passing between them. To reduce the risk of software being attacked,dependent agents are distributed to different proxies. In this way, if a proxy is compromized, minimal information of the software will be disclosed. Methods for assigning agents to proxies are also proposed to minimize, under the security constraints, computation load of the proxies as well as communication load between the user's local system and proxies. (C) 1999 Elsevier Science B.V. All rights reserved.
Effect of bismuth content on the properties of Sr0.8BixTa1.2 Nb0.9O9+y ferroelectric thin films
(1999-01-15)
Tsai, HM
;
Lin, P
;
Tseng, TY
;
材料科學與工程學系
;
電子工程學系及電子研究所
This study investigates the effect of bismuth content on the ferroelectric properties of Sr0.8BixTa1.2Nb0.9O9+y (SBTN, x = 1.7, 2.0, 2.5, 2.7, 2.9, and 3.2) thin film capacitors. SBTN films are in situ grown on Pt/SiO2/Si substrates by using two-target off-axis radio-frequency magnetron sputtering at a substrate temperature of 600 degrees C. The films are crystallized with a high (115) diffraction intensity and exhibit a columnar microstructure. Experimental results indicate that the root mean square surface roughness of the film increases with an increase of the bismuth content. In addition, the ferroelectric properties of the films heavily rely on the bismuth content. Moreover, the 440-nm-thick Sr0.8Bi2.5Ta1.2Nb0.9O9+y films exhibit maximum remanent polarization (2Pr) of 52 mu C/cm(2) and minimum coercive field (2Ec) of 28 kV/cm at an applied voltage of 1.5 V. X-ray photoelectron spectral studies reveal that except for Bi+3, no lower valence state bismuth exists in the Sr0.8Bi2.5Ta1.2Nb0.9O9+y film and bismuth substituted in the strontium site still remains in its +3 valence state. (C) 1999 American Institute of Physics. [S0021-8979(99)06302-1].
Correlation of countercurrent extraction with countercurrent chromatography in aqueous matrixes. An improved model
(1999-01-15)
Yu, TI
;
Liang, CS
;
Luo, SK
;
應用化學系
;
Department of Applied Chemistry
A mathematical model was employed to simulate supercritical fluid extraction (SFE) efficiency in aqueous matrixes with supercritical fluid chromatography (SFC) data in a previous study. The SFE extraction vessel, i.e., the column for the SFC, was mathematically divided into limited layers. The analyte mass was uniformly distributed in the vessel before extraction. However, it changed when the fluid flowed through the aqueous sample and reached the column outlet. The mass redistribution as a function of the layer was computed using a countercurrent distribution approach. Afterward, each layer was considered to undergo a chromatographic process simultaneously. Each layer's chromatographic capacity factor and peak width were calculated using the true SFC experimental data, and the sum of all these peak distributions as a function of time gave the extraction efficiency, In this work, the mass redistribution was calculated through a chromatographic approach, which predicted the extraction recovery better than the previous approach,,Both the previous SFE and the newly acquired liquid/liquid extraction data using a countercurrent chromatographic apparatus were examined to demonstrate the upgrading of the model using this new chromatographic approach. Significant improvements were observed, especially for analytes with small capacity factors. The simulation deviations came mainly from the fact that analyte molecules in the individual layers would shift away from Gaussian shapes that were assumed in the model.
The effects of shallow germanium halo doping on N-channel metal oxide semiconductor field effect transistors
(1999-01-15)
Wang, MF
;
Chien, CH
;
Chao, TS
;
Lin, HC
;
Jong, FC
In this paper, we report the use of shallow germanium halo doping on improving the short-channel effects of deep submicron n-channel metal-oxide-semiconductor field effect transistors. It is demonstrated that by adding a shallow (i.e., 10 keV) germanium large-angle-tilt implant (LATID), V-th lowering in short-channel transistors is significantly improved. The improvement is found to increase with increasing germanium dose. A low germanium dose (e.g., 5 x 10(12) cm(-2)) is also found to effectively improve the drain-induced barrier lowering (DIBL) of the short-channel transistors. Our results also show that junction leakage degradation, which has been previously reported to accompany germanium implants using higher energy, can be minimized by the shallow low-dose implant used in this study.
Determination of built-in field by applying fast Fourier transform to the photoreflectance of surface-intrinsic n(+)-type doped GaAs
(1999-01-18)
Wang, DP
;
Wang, KR
;
Huang, KF
;
Huang, TC
;
Chu, AK
Photoreflectance spectroscopy of surface-intrinsic n(+)-doped (s-i-n(+)) GaAs has been measured at various power densities (P-pu) of a pump beam. Many Franz-Keldysh oscillations (FKOs) were observed above the band-gap energy, which will enable the electric-field strength (F) to be determined from the periods of the FKOs. Field F thus obtained is subject to photovoltaic effects. In order to reduce the photovoltaic effects from the pump beam, P-pu was kept below 10 mu W/cm(2) in the previous experiments. Here, we demonstrate that the built-in field can be determined at a larger P-pu by using fast Fourier transform techniques. (C) 1999 American Institute of Physics. [S0003-6951(99)02803-X].
High birefringence and wide nematic range bis-tolane liquid crystals
(1999-01-18)
Wu, ST
;
Hsu, CS
;
Shyu, KF
;
應用化學系
;
Department of Applied Chemistry
Several dialkyl and fluoro bis-tolane liquid crystals were synthesized and their physical properties evaluated. These highly conjugated liquid crystals exhibit a wide nematic range, small heat fusion enthalpy, high birefringence, and relatively low viscosity. Their excellent compatibility with commercial cyano mixtures makes these liquid crystals attractive for many electro-optic applications. (C) 1999 American Institute of Physics. [S0003-6951(99)02103-8].
Contributions of CuO2 planes and CuO chains on the transport properties of YBa2Cu4O8
(1999-01-20)
Chatterjee, S
;
Weng, SS
;
Hong, IP
;
Chang, CF
;
Yang, HD
We have investigated the contributions of CuO2 planes and CuO chains on the transport properties of YBa2Cu4O8 by measuring the electrical resistivity and thermoelectric power (S) of Y1-xPrxBa2(Cu1-yZny)(4)O-8, Y1-xCaxBa2Cu4O8 and YBa2(Cu1-xGax)(4)O-8. Pr reduces the mobile carrier concentration in the CuO2 planes in YBa2Cu4O8, as a consequence, the superconducting transition temperature is progressively decreased with increasing Pr. The S(T) data suggest that the metallic behavior at lower temperature of the Pr and Zn doped compounds is contributed by the double CuO chains. On the other hand, the S(T) behavior of Ca doped samples is opposite to that of the Pr doped samples because the doping of Ca in Y-site introduces holes in the CuO2 planes. However, the substitution of Ga in Cu(1)-site suppresses the carrier concentration in CuO chains and increases the normal-state resistivity revealing the important contribution from CuO chains on the metallic behavior of YBa2Cu4O8 and PrBa2Cu4O8. (C) 1999 Published by Elsevier Science B.V. All rights reserved.
An effective three-dimensional model for UHF radio propagation into multistory office buildings
(1999-01-20)
Tarng, JH
;
Chang, YC
;
Chen, CM
;
電信工程研究所
;
Institute of Communications Engineering
An effective three-dimensional (3-D) direct-transmitted model combined with a patched-wall model is proposed to explore UHF radio propagation into multistory buildings in a microcellular environment. The model is verified by comparing the computed path loss with the measured one of 1.7 and 2.44 GHz radio waves propagating at different sites. The comparison demonstrates that the model has reasonably accurate prediction when the number of floor levels between the transmitting and the receiving antennas is no more than four.
Improved CMAC neural network control scheme
(1999-01-21)
Lin, CC
;
Chen, FC
;
電控工程研究所
;
Institute of Electrical and Control Engineering
The cerebellar model articulation controller (CMAC) neural network control scheme is a powerful tool for practical real-time nonlinear control applications. However, despite its initial outstanding performance, the CMAC control system can suddenly diverge after a long period of stable tracking. The authors propose a modification to the CMAC control scheme in order to improve stability while preserving the original good performance.
Microstrip leaky-wave antenna fed by short-end CPW-to-slot transition
(1999-01-21)
Chen, TL
;
Lin, YD
;
傳播研究所
;
Institute of Communication Studies
Single and dual-beam microstrip leaky-wave antennas fed by a short-end coplanar waveguide (CPW)-to-slot transition are presented. The radiation bands of the antennas are deduced from the leaky-wave propagation characteristics of the microstrip line first higher order leaky mode. The measured reflection coefficients of the radiation band confirm the predicted leaky band and the measured radiation paffems exhibit. the frequency-scanning feature of the leaky-wave antenna. The short-end CPW-to-slot transition feeding method simplifies the circuit layout and is more suitable for different band design than the CPW-fed microstrip first higher order leaky-wave antennas presented in the literature.
A note on breaking and repairing a secure broadcasting in large networks
(1999-01-25)
Sun, HM
;
Shieh, SP
;
Sun, HM
;
資訊工程學系
;
Department of Computer Science
In this note, we show that a proposed secure broadcasting scheme is insecure. We also present a modified scheme to overcome this weakness. The modified scheme has the extra advantage that each participant can derive his group keys from group identities without the need of knowing other information. (C) 1999 Elsevier Science BV. All rights reserved.
The effect of native oxide on epitaxial SiGe from deposited amorphous Ge on Si
(1999-01-25)
Wu, YH
;
Chen, WJ
;
Chin, A
;
Tsai, C
;
電子工程學系及電子研究所
We have investigated the effect of native oxide on the epitaxial SiGe from deposited amorphous Ge on Si. Instead of epitaxial growth by molecular beam epitaxy or ultrahigh-vacuum chemical vapor deposition, the SiGe layer is formed by this simple process followed by an annealing step. As observed by transmission electron microscopy, the suppression of native oxide plays an important role to achieve epitaxial SiGe. The SiGe quality degrades with increasing native oxide thickness and becomes polycrystalline with a similar to 20 Angstrom interfacial native oxide. On the other hand, single crystalline SiGe can be routinely formed from a HF-vapor treated Si surface. (C) 1999 American Institute of Physics. [S0003-6951(99)04504-0].
藝術家進駐鄉野創傳奇大道藝術館開先例
(1999-01-26)
賴素鈴
An efficient algorithm for computing quantiles of the noncentral chi-squared distribution
(1999-01-28)
Ding, CG
;
管理科學系
;
Department of Management Science
An efficient algorithm is provided for computing quantiles of the noncentral chi-squared distribution. Newton's method, which requires the evaluations of both of the noncentral chi-squared distribution function and the density, is used. A close relationship between their recursive computing formulas is noted to allow concurrent evaluation of the distribution function and the density. Newton's iterative computation can therefore be greatly speeded up. An example is given to illustrate the usefulness of the algorithm. (C) 1999 Elsevier Science B.V. All rights reserved.
A consistent co-rotational finite element formulation for geometrically nonlinear dynamic analysis of 3-D beams
(1999-01-29)
Hsiao, KM
;
Lin, JY
;
Lin, WY
;
機械工程學系
;
Department of Mechanical Engineering
A co-rotational total Lagrangian finite element formulation for the geometrically nonlinear dynamic analysis of spatial Euler beam with large rotations but small strain, is presented. The nodal coordinates, displacements, rotations, velocities, accelerations, and the equations of motion of the structure are defined in a fixed global set of coordinates. The beam element has two nodes with six degrees of freedom per node. The element nodal forces are conventional forces and moments. The kinematics of beam element are defined in terms of element coordinates, which are constructed at the current configuration of the beam element. Both the element deformation nodal forces and inertia nodal forces are systematically derived by consistent linearization of the fully geometrically nonlinear beam theory using the d'Alembert principle and the virtual work principle in the current element coordinates. An incremental-iterative method based on the Newmark direct integration method and the Newton-Raphson method is employed here for the solution of the nonlinear equations of motion. Numerical examples are presented to demonstrate the accuracy and efficiency of the proposed method. (C) 1999 Elsevier Science S.A. All rights reserved.
Blind adaptive algorithm for demodulation of DS/CDMA signals with mismatch
(1999-02-01)
Hwang, HC
;
Wei, CH
;
電子工程學系及電子研究所
;
電信研究中心
;
Department of Electronics Engineering and Institute of Electronics
The minimum mean-squared error (MMSE) linear detector is known to be a near-far resistant strategy for direct-sequence code-division multiple access systems. The MMSE linear detector can be implemented adaptively by the MOE adaptation algorithm or the Griffiths' adaptation algorithm, which utilises the desired signal vector for initial adaptation instead of training sequences, The performance loss caused by the imprecise knowledge of the desired signal vector is investigated. A new blind adaptive algorithm is presented to mitigate the effect of the mismatch caused by the timing error in acquisition. Several;numerical results show that the new algorithm can provide a resistance to the effect of mismatch compared to the MOE and Griffiths' algorithms.
The behavior of a compressible silty fine sand
(1999-02-01)
Huang, AB
;
Hsu, HH
;
Chang, JW
;
土木工程學系
;
Department of Civil Engineering
Publications associated with sands are often limited to clean (i.e., little fines content), uniform, uncemented silica or quartz sand. On the other hand, the importance of mineral content, particle shapes, as well as gradation to the behavior of sand has long been recognized. Although systematic studies of sands ether than clean quartz sand have been limited, there is increasing attention being paid to sands with an appreciable fines content. Because of a major construction project, extensive field and laboratory experiments were performed on a silty fine sand from Mai-Liao, which is located on the central west coast of Taiwan. Results show that Mai-Liao Sand (MLS), a silty sand, can be significantly more compressible than clean quartz sand under static load. The particles of MLS have moderate strength, and significant crushing can be induced by triaxial shearing. As a result, MLS has low dilatancy and a relatively small range of peak friction angles. Cone penetration tests in MLS were conducted in a calibration chamber. Analyses of the data indicate that interpreting cone tip resistance in MLS using methods developed based on clean quartz sand without considering the differences of compressibility can be unrealistic. This paper documents results of the experimental studies on MLS.
Treatment of high strength hexamine-containing wastewater by Electro-Fenton method
(1999-02-01)
Chou, SS
;
Huang, YH
;
Lee, SN
;
Huang, GH
;
Huang, CP
A novel Electro-Fenton (EF-Fere) method, applied H2O2 and electrogenerated ferrous ion, was investigated for treating the hexamine-containing wastewater. The performance of Fe2+ generation in the electrolytic system was first evaluated, including the factors of the cathode material, initial pH, initial ferric concentration (Fe-i), and current density. When initial pH exceeded 2.5, the current efficiency dramatically decreased, which was due to the formation of Fe(OH)(3). Between 3000 and 10,000 mg/l of Fe-i, the initial current efficiency of Fe2+ generation was almost constant (85-87%), which dropped sharply to 39% at 1000 mg/l. In EF-Fere experiments, the COD removal efficiency attained above 94% after 5 h of reaction. The relationship between the temperature, dissolved oxygen, and COD was discussed. The changes in hexamine and its oxidation intermediates (methanol, formaldahyde, formate, ammonium and nitrate) during the reaction were also investigated. Three additional experiments using H2O2/Fe2+, H2O2/Fe3+, and direct electrolysis were also conducted to treat the hexamine-containing wastewater for comparison. The results showed that the EF-Fere method was the most efficient. (C) 1998 Elsevier Science Ltd. All rights reserved.
An explicit approximation to the wavelength of nonlinear waves
(1999-02-01)
Chang, HK
;
Lin, SC
;
土木工程學系
;
Department of Civil Engineering
An explicit and concise approximation to the wavelength in which the effect of nonlinearity is involved and presented in terms of wave height, wave period, water depth and gravitational acceleration. The present approximation is in a rational form of which Fenton and Mckee's (1990, Coastal Engng 14, 499-513) approximation is reserved in the numerator and the wave steepness is involved ill the denominator. The rational form of this approximation can be converted to an alternative form of a power-series polynomial which indicates that the wavelength increases with wave height and decreases with water depth. If the determined coefficients in the present approximation are fixed, the approximating formula can provide a good agreement with the: wavelengths numerically obtained by Rienecker and Fenton's (1981, J. Fluid Mech. 104, 119-137) Fourier series method, but has large deviations when waves of small amplitude are in deep water or all waves are in shallow water, The present approximation with variable coefficients can provide excellent predictions of the wavelengths for both long and short waves even, for high waves. (C) 1998 Elsevier Science Ltd. All rights reserved.
Finding inheritance hierarchies in fuzzy-valued concept-networks
(1999-02-01)
Horng, YJ
;
Chen, SM
;
資訊工程學系
;
Department of Computer Science
In this paper, we extend the works of [2] and [4] to present a new method for finding the inheritance hierarchies in fuzzy-valued concept-networks, where the relevant values (degrees of generalization or degrees of similarity) between concepts in a fuzzy-valued concept network are represented by fuzzy numbers. The proposed method is more flexible than the ones presented in [2] and [4] due to the fact that it allows the grades of similarity and the grades of generalization between concepts to be represented by fuzzy numbers rather than crisp real values between zero and one or interval values in [0, 1].