Browsing by Issue Date, starting with "1999-01-20"

Now showing 1 - 20 of 80803

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].
Design of dynamic-floating-gate technique for output ESD protection in deep-submicron CMOS technology
(1999-02-01)
Chang, HH
;
Ker, MD
;
Wu, JC
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
A novel dynamic-floating-gate technique is proposed to improve ESD robustness of the CMOS output buffers with small driving/sinking currents. This dynamic-floating-gate design can effectively solve the ESD protection issue which is due to the different circuit connections on the output devices. By adding suitable time delay to dynamically float the gates of the output NMOS/PMOS devices which are originally unused in the output buffer, the human-body-model (machine-model) ESD failure threshold of a 2-mA output buffer can be practically improved from the original 1.0 kV (100 V) up to greater than 8 kV (1500 V) in a 0.35-mu m bulk CMOS process. (C) 1998 Elsevier Science Ltd. All rights reserved.
Construct message authentication code with one-way hash functions and block ciphers
(1999-02-01)
Yeh, YS
;
Wang, CC
;
資訊科學與工程研究所
;
Institute of Computer Science and Engineering
We suggest an MAC scheme which combines a hash function and an block cipher in order. We strengthen this scheme to prevent the problem of leaking the intermediate hash value between the hash function and the block cipher by additional random bits. The requirements to the used hash function are loosely. Security of the proposed scheme is heavily dependent on the underlying block cipher. This scheme is efficient on software implementation for processing long messages and has clear security properties.
Quasi-two-dimensional simulation of scour and deposition in alluvial channels - Closure
(1999-02-01)
Lee, HY
;
Hsieh, HM
;
Yang, JC
;
Yang, CT
;
土木工程學系
An expert-system technique for object-oriented program testing
(1999-02-01)
Chen, WC
;
Chen, DJ
;
Chung, CG
;
資訊科學與工程研究所
;
Institute of Computer Science and Engineering
Data abstraction, information hiding, inheritance, and dynamic binding are four basic elements used in designing object-oriented (OO) programs. These four mechanisms enable programmers to write object-oriented programs that are easily extended, reused and maintained. Software implemented by OO methodologies has increased software quality and productivity.(1) However, this cannot be guaranteed without an appropriate software testing approach. Traditional testing approaches cannot be applied directly to the testing of OO programs due to the OO characteristics used in these programs. OO program testing strategies and methods are proposed continually, but fewer OO testing tools with flexibility are discussed.
Chromic acid removal by anion exchange
(1999-02-01)
Tan, HKS
;
應用化學系
;
Department of Applied Chemistry
The kinetics of dilute chromic acid removal by anion exchange was studied using a batch system. Rate model formulated for total Cr(VI) removal based on film diffusion control was applied. This rate model was shown to adequately fit the experimental rate data. In addition, column experimental runs were performed by using 20-50 mesh anion resin with feed solution containing 0.2 g/L CrO3. The bed heights of 15, 25 and 35 cm and flow rates ranging from 1.02 cm/s to 2.38 cm/s were employed in the experiments. Linear driving force rate expression based on film diffusion rate control was incorporated in the model equations for simulation of column performance. The kinetic parameter and equilibrium relation in the rate equation were obtained independently either by separate experiments or from data available in the literature. Satisfactory agreements between experimental and calculated breakthrough curves were obtained.
Recursive constructions for perfect secret sharing schemes
(1999-02-01)
Sun, HM
;
Shieh, SP
;
資訊工程學系
;
Department of Computer Science
A secret sharing scheme is a method which allows a secret to be shared among a set of participants in such a way that only qualified subsets of participants can recover the secret. A secret sharing scheme is called perfect if unqualified subsets of participants obtain no information regarding the secret. The information rate of a secret sharing scheme is defined to be the ratio between the size of secret and the maximum size of the shares. In this paper, we propose some recursive constructions for perfect secret sharing schemes with access structures of constant rank. Compared with the best previous constructions, our constructions have some improved lower bounds on the information rate. (C) 1999 Elsevier Science Ltd. All rights reserved.