Browsing by Issue Date, starting with "2000-02-05"

Now showing 1 - 20 of 78559

A back-to-back dual-beam active microstrip leaky-wave antenna array with mode-switching capability
(2000-02-05)
Hu, CC
;
Jou, CF
;
Wu, JJ
;
Peng, ST
;
傳播研究所
An X-band two-element back-to-back coupled-oscillator-driven spatial power-combining microstrip leaky-wave antenna array is developed, which has a dual-beam radiation pattern and mode-switching capability. Two Gunn diode CPW oscillators are placed on the back side of the substrate, each driving two back-to-back microstrip leaky-wave antenna pairs in opposite directions for dual-beam operation. This active antenna array is able to produce sum and difference patterns between the in-phase and 180 degrees out-of-phase mode by controlling the bias voltages of the Gunn diodes. (C) 2000 John Wiley & Sons, Inc.
雪年
(2000-02-08)
管管
Transmission coefficients in a narrow constriction threaded by two impenetrable magnetic flux tubes
(2000-02-10)
Liang, HC
;
電子物理學系
;
Department of Electrophysics
The transmission coefficients in a narrow constriction and their dependence on the Fermi energy and on the transverse positions of two impenetrable magnetic Bur tubes is studied. An overlapping integral L-mn can qualitatively represent the strength of interaction between incoming subband rn and outgoing subband n. The conductance G and its components exhibit oscillatory-like behavior as the transverse positions of the tubes change.
吃魚的忘刺
(2000-02-13)
管管
胭脂經給Y.C.L
(2000-02-14)
管管
Date attachable electronic cash
(2000-02-15)
Fan, CI
;
Chen, WK
;
Yeh, YS
;
資訊工程學系
;
Department of Computer Science
In this paper we propose a new untraceable electronic cash scheme which makes it possible for a payer to attach the desired date to his electronic cash during a transaction. With the aid of the date attachability property, the date on which an electronic cash is deposited in the bank cannot be forged in an electronic cash scheme. It is conducive to the unforgeability of the number of days for which the cash has been stored in the bank for some necessary purposes such as interest calculation. Our scheme not only keeps the attached date from being forged but also avoids two or more different dates being attached to the same electronic cash. Furthermore, the date attachment does not affect the untraceability property of electronic cash. Comparing with typical electronic cash schemes, the extra computation required for date attachment is just hashing. (C) 2000 Elsevier Science B.V. All rights reserved.
Mutation at non-cysteine positions eliminates the oxidation/reduction effect on the activity of phenol sulfotransferase.
(2000-02-15)
Yang, YS
;
生物科技學系
;
Department of Biological Science and Technology
Systematic tuning of the luminescent properties of self-activated ZnGa2O4 phosphors by Cd ion substitution
(2000-02-15)
Chen, TM
;
Chen, YW
;
應用化學系
;
Department of Applied Chemistry
The effect of host compositions on the luminescent properties of spinel-type ZnGa2O4 phosphors was investigated by systematic substitution of Cd2+ for Zn2+ in the host lattice. A continuous solid solution with the composition (Zn1-xCdx)Ga2O4 (0 less than or equal to x less than or equal to 1.0) was synthesized at 950 degrees C as self-activated phosphors, as indicated by X-ray diffraction (XRD) analysis. With increasing substitution of Cd2+ the emission and excitation wavelengths (lambda(cm) and lambda(exc)) of self-activated (Zn1-xCdx)Ga2O4 were observed to exhibit a red shift, as indicated by photoluminescence spectral analysis. Similar results were also confirmed by cathodoluminescence data. Our observations are attributed to the systematic narrowing of the energy gap of the host attributed to expanding lattice dimensions induced by Cd2+ substitution. A CIE: chromaticity diagram manifests the effect of Cd2+ doping on variation of hue for the (Zn1-xCdx)Ga2O4 gallate phosphors. (C) 2000 Academic Press.
The improvement of composite triple-beat distortion induced by cross-phase-modulation in wavelength-division-multiplexing CATV transmission systems with chirped fiber grating compensator
(2000-02-15)
Lee, CC
;
Chi, S
;
光電工程學系
;
Department of Photonics
Composite triple-beat (CTB) distortion induced by cross-phase modulation (XPM) in a 1.55 mu m wavelength-division multiplexing (WDM) CATV transport system has been effectively improved, theoretically and experimentally, from -55.4 dBc to -60.8 dBc by using the chirped fiber grating to compensate the fiber dispersion. (C) 2000 Elsevier Science B.V. All rights reserved.
On sums of three square-zero matrices
(2000-02-15)
Takahashi, K
;
應用數學系
;
Department of Applied Mathematics
Wang and Wu characterized matrices which are sums of two square-zero matrices, and proved that every matrix with trace-zero is a sum of four square-zero matrices. Moreover, they gave necessary or sufficient conditions for a matrix to be a sum of three square-zero matrices. In particular, they proved that if an n x n matrix A is a sum of three square-zero matrices, the dim ker(A - alpha I) less than or equal to 3n/4 for any scalar alpha not equal 0. Proposition 1 shows that this condition is not necessarily sufficient for the matrix A to be a sum of three square-zero matrices, and characterizes sums of three square-zero matrices among matrices with minimal polynomials of degree 2. (C) 2000 Elsevier Science Inc, All rights reserved.
Wide angle distributed Bragg reflectors for 590 nm amber AlGaInP light-emitting diodes
(2000-02-15)
Chiou, SW
;
Lee, CP
;
Huang, CK
;
Chen, CW
;
電子工程學系及電子研究所
A structure for high brightness light-emitting diodes (LEDs) is demonstrated. A distributed Bragg reflector (DBR) is used to enhance the quantum efficiency of the LEDs. This unique DBR uses a composite structure that consists of two DBRs to provide both high reflectivity and wide angle reflection. For 590 nm (amber range) AlGaInP LEDs, the quantum efficiency is increased to 5.05% by using this composite DBR structure. This result is much better than those obtained from conventional DBRs, and is comparable to that of wafer bonded AlGaInP LEDs. (C) 2000 American Institute of Physics. [S0021-8979(00)01704-7].
Higher derivative Weyl gravity
(2000-02-15)
Kao, WF
;
物理研究所
;
Institute of Physics
A higher derivative Weyl model is analyzed carefully. We show that there is a nontrivial constraint if a symmetry-breaking potential is added to the system. A rigorous proof for the constraint is presented. One, hence, studies the applications of this conformal theory in the inflationary universe.
Magnetic monopole in induced Einstein-Yang-Mills models
(2000-02-15)
Kao, WF
;
物理研究所
;
Institute of Physics
We show that a regular SO(3) non-Abelian monopole cannot exist in induced gravity models with a variety of symmetry breaking potentials. The no-hair theorem is also shown to be true in these models. We also analyze the global behavior of the gauge field in the presence of a black hole with a nonvanishing cosmological constant. It is shown that the nontrivial non-Abelian monopole solution exists only if the radius of the event horizon is smaller than the characteristic radius of the classical monopole.
Thiazole and thiophene analogues of donor-acceptor stilbenes: Molecular hyperpolarizabilities and structure-property relationships
(2000-02-16)
Breitung, EM
;
Shu, CF
;
McMahon, RJ
;
應用化學系
;
Department of Applied Chemistry
We calculate the first hyperpolarizability (beta) of several thiazole and thiophene analogues of donor-acceptor stilbene compounds using the ZINDO (sum-over-states) formalism. Because of the inherent dipolar nature of thiazole, in which C2 is electron-poor and C5 is electron-rich, the relative orientation of the thiazole subunit in the dipolar chromophore dramatically affects the nonlinear optical properties. In the "mismatched" case, the dipole of the thiazole ring opposes the molecular dipole created by the donor-acceptor substituents, while in the "matched" case, the dipole of the thiazole ring reinforces the molecular dipale. The hyperpolarizability of the "mismatched" monothiazole 2 (beta(mu) = 68 x 10(-30) cm(5) esu(-1)) exceeds that of stilbene 1 (beta(mu) = 34 x 10(-30) cm(5) esu(-1)) but is smaller than that of monothiophene 4 (beta(mu) = 90 x 10(-30) cm(5) esu(-1)). By contrast, the hyperpolarizability of the "matched" monothiazole 3(beta(mu) = 177 x 10(-30) cm(5) esu(-1)) exceeds not only that of the "mismatched" monothiazole 2, but also that of monothiophene 4. Substituting thiazole for both aryl rings of stilbene produces very large hyperpolarizabilities in the "matched-matched" case (e.g., bis-thiazole 24, beta(mu) = 254 x 10(-30) cm(5) esu(-1)). The nonlinear optical response of heterocyclic analogues of donor-acceptor stilbene derivatives is discussed in terms of the difference in aromatic delocalization energy between phenyl, thiophene, and thiazole, the electronic nature of the heteroaromatic rings, and conformational factors.
Studies of nonlinear absorption and refraction in C-60/toluene solution
(2000-02-18)
Wei, TH
;
Huang, TH
;
Wu, TT
;
Tsai, PC
;
Lin, MS
Nonlinear absorptive and refractive properties of C-60/toluene solution are studied using the Z-scan technique and a 532 nm laser delivering single picosecond (ps) pulses and trains of ps pulses separated by 7 nanoseconds (ns). With single ps pulses, reverse saturable absorption and positive nonlinear refraction are observed and attributed to population transitions among the singlet states. With ps pulse trains, a sign change of nonlinear refraction relative to that of single ps-pulse excitation is observed and is attributed to heat-induced temperature rise and population relaxing to triplet states. (C) 2000 Elsevier Science B.V. All rights reserved.
苔蘚詞
(2000-02-24)
管管
High-pressure phase transitions in Zn0.83Mn0.17Se thin film
(2000-02-28)
Lin, CM
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
The energy-dispersive X-ray-diffraction (EDXD) and Raman spectroscopy are used to study phase transitions of Zn0.83Mn0.17Se thin film up to 17.5 and 16.1 GPa, respectively. The EDXD results show that possible zinc blende(B3) to sodium chloride phase(B1) structure transition for Zn0.83Mn0.17Se thin film occurs at 10.0 GPa. The unloading run reveals a reversible phase transition existed in the Zn0.83Mn0.17Se thin film. For micro-Raman spectra at ambient pressure, three Raman peaks are distinct as LO, TO, and Mn local modes in Zn1-xMnxSe bulk. As the pressure is increased to 10.9 GPa, metallization occurs, the LO and Mn local phonon peaks disappear while the two unidentified Raman peaks of TO mode are still observable above the metallization pressure till 17.5 GPa. The phase transition pressure P-t obtained from the results of micro-Raman spectra seems to be in good agreement with that obtained by EDXD measurements. (C) 2000 Published by Elsevier Science B.V. All rights reserved.
Evaluation of cleaning efficiency with a radioactive tracer and development of a microwave digestion method for semiconductor processes
(2000-02-29)
Lu, JK
;
Ko, FH
;
Chu, TC
;
Sun, YC
;
Wang, MY
A radioactive tracer technique was applied to investigate the effectiveness of various wet cleaning recipes in removing metallic impurities such as sodium, iron and cesium. The effects of solution temperatures and substrate types were studied. The mechanisms of the electrochemical segregation of metallic impurities between the substrate and cleaning solution were examined. The enthalpy of oxide formation and the effect of adsorption were the two reasons for the presence of surface metal impurities in the cleaning solutions. Our results indicated that SC2 and DHF can effectively remove the metallic impurities at 47 and 82 degrees C, while SPM and BOE are only effective at 82 degrees C. The gravimetric method was successfully implemented to evaluate the open-focused microwave digestion efficiency for anti-reflective coating and photoresist (PR) samples. By following the established microwave digestion method and inductively coupled plasma mass spectrometric determination, the detection limits (DLs) obtained for multi-elements were in the ng ml(-1) and sub-ng ml(-1) levels. Except for calcium, the spike recoveries of the metals were in the range 82-121% for the lithographic samples. The analytical results were found to be in reasonably good agreement with literature values, and the lithographic sample throughput can achieve up to 3.5 samples per hour for the analysis of 13 elements. (C) 2000 Elsevier Science B.V. All rights reserved.
Forest leaves and four-cycles
(2000-03-01)
Fu, HL
;
Rodger, CA
;
應用數學系
;
Department of Applied Mathematics
In this article, we find necessary and sufficient conditions for the existence of a 4-cycle system of K-n - E(F) for any forest F of K-n. (C) 2000 John Wiley & Sons, Inc.
Enhancing science instruction: the use of 'conflict maps'
(2000-03-01)
Tsai, CC
;
師資培育中心
;
Center of Teacher Education
This paper proposes the use of 'conflict maps' as a way of enhancing science teaching and learning. The conflict map emphasizes not only the use of discrepant events, but also the resolution of the conflict between students' alternative conceptions and the scientific conception, using critical events or explanations and relevant perceptions and conceptions that explicate the scientific conception. The use of conflict maps is consistent with a conceptual change model suggested by science educators; hence, it is expected that the conflict map could help students overcome alternative conceptions and thus promote conceptual change. The conflict map, which clearly displays students' alternative conceptions and scientific conceptions, could be used as an instructional aid, helping science teachers construct or implement lesson plans, or as a metacognitive tool, helping learners monitor their ideas and the processes of conceptual change.