Browsing by Issue Date, starting with "2003-09-05"

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The full Steiner tree problem
(2003-09-05)
Lu, CL
;
Tang, CY
;
Lee, RCT
;
生物科技學系
;
Department of Biological Science and Technology
Motivated by the reconstruction of phylogenetic tree in biology, we study the full Steiner tree problem in this paper. Given a complete graph G = (V, E) with a length function on E and a proper subset R subset of V, the problem is to find a full Steiner tree of minimum length in G, which is a kind of Steiner tree with all the vertices of R as its leaves. In this paper, we show that this problem is NP-complete and MAX SNP-hard, even when the lengths of the edges are restricted to either I or 2. For the instances with lengths either I or 2, we give a 8/5-approximation algorithm to find an approximate solution for the problem. (C) 2003 Elsevier B.V. All rights reserved.
Cost-effective fabrication of a phase mask by direct etching of the laser-interference grating on fused silica substrate
(2003-09-05)
Lu, YT
;
Chen, YH
;
Chi, S
;
光電工程學系
;
Department of Photonics
A simple and cost-effective method to manufacture a phase mask with high diffraction efficiency for deep UV application is proposed. The deep rectangular grating fabricated by using laser interference is etched directly into a fused silica substrate, instead of the dielectric coating on a substrate (done in a previous method). Using the metal layer on a dielectric layer for masking in the deep, dry etching process is also unnecessary in our technique. A fabricated rectangular grating with high diffraction efficiency is presented in this paper. We also demonstrate the fabrication processes and show the optimum parameters for our proposed technology. (C) 2003 Wiley Periodicals, Inc.
Insights into dynamics of the F+CD4 reaction via product pair correlation
(2003-09-08)
Zhou, JG
;
Lin, JJ
;
Shiu, WC
;
Liu, KP
;
應用化學系
To unravel the "extra-atom" complexity of the title reaction, we exploit an experimental approach which, by taking advantage of the correlated information of coincident product pairs, allows us to peel off judiciously the intrinsic complications of a six-atom reaction, extracting the underlying backbone of three-atom dynamics. Examining the collisional energy dependencies of the pair-correlated attributes for a given state(s) of CD3 products from the title reaction, several of major observations can qualitatively be understood, whereas others await further theoretical investigations. An intriguing possibility for the existence of reactive resonances in this six-atom reaction is surmised. (C) 2003 American Institute of Physics.
Highly efficient blue-light-emitting diodes from polyfluorene containing bipolar pendant groups
(2003-09-09)
Shu, CF
;
Dodda, R
;
Wu, FI
;
Liu, MS
;
Jen, AKY
A highly efficient blue-light-emitting copolymer with bulky hole-transporting triphenylamine (TPA) and electron-transporting oxadiazole (OXD) pendant groups at the C-9 position of fluorene was synthesized. The results from photoluminescence and electrochemical measurements reveal that both the side chains and the polyfluorene main chain retain their own electronic characteristics in the copolymer. It shows a pure blue emission with no aggregates or excimers formed even after being annealed at 150 degreesC under nitrogen for 20 h. In addition, it also demonstrates improved charge injection and balanced charge transport in electroluminescence. The maximum external quantum efficiency of a single-layer device using this copolymer as the emitting layer is 1.21% (at a brightness of 354 cd/m(2) with driving voltage of 7.6 V). The maximum luminance of the device reaches 4080 cd/m(2) at a bias of 12.0 V and a current density of 640 mA/cm(2).
Cation substitution effects on structural, electronic and optical properties of nonlinear optical AgGa(SxSe1-x)(2) crystals
(2003-09-10)
Tang, LC
;
Lee, MH
;
Yang, CH
;
Huang, JY
;
Chang, CS
The structural, electronic and optical properties of tetragonal nonlinear optical (NLO) crystals, AgGa(SxSe1-x)(2) (x = 0.0, 0.25, 0.5, 0.75, and 1.0), were investigated theoretically and experimentally. The results obtained indicated that the electronic bandgaps, optical properties and bulk moduli of these compounds were linearly dependent on the substitution concentration of cations. From partial density of state analysis, it was found that the electronic states near the band edges of AgGa(SxSe1-x)(2) were a simple proportional mixture of the atomic orbitals of sulfur and selenium. A cell-volume effect was proposed as the major cause of the linear dependence of material properties on the substitution concentration. It was calculated that the second-order NLO susceptibilities were scaled with the cubic power of bandgap, although a minor deviation existed. This deviation arose from the optical transition moment products.
Assessment of conservative weighting scheme in simulating chemical vapour deposition with trace species
(2003-09-10)
Wu, JS
;
Hsiao, WJ
;
Lian, YY
;
Tseng, KC
;
機械工程學系
Low-pressure or ultra-high vacuum chemical vapour deposition often involves important trace species in both gas-phase and surface reactions. The conservative weighting scheme (J. Thermophys. Heat Transfer 1996; 10(4):579) has been used to deal with the trace species often involved in some non-reactive physical processes, which is otherwise considered computationally impossible using the conventional DSMC method. This conservative weighting scheme (CWS) improves greatly the statistical uncertainties by decreasing the weighting factors of trace-species particles and ensures the conservation of both momentum and energy between two colliding particles with large difference of weighting factors. This CWS is further extended to treat reactive processes for gas-phase and surface reactions with trace species, which is called extended conservative weighting scheme (ECWS). A single-cell equilibrium simulation is performed for verifying both the CWS and ECWS in treating trace species. The results of using CWS show that it is most efficient and accurate for weight ratio (trace to non-trace) equal to or less than 0.01 for flows with two and three species. The results of a single-cell simulation using ECWS for gas-phase reaction and surface reactions show that only ECWS can produce acceptable results with reasonable computational time. Copyright (C) 2003 John Wiley Sons, Ltd.
光纖布拉格光柵感測系統
(2003-09-11)
祁甡
;
曾弘毅
;
彭朋群
本發明係提供一種光纖布拉格光柵感測系統，係利用線性共振腔光纖雷射架構設計高解析度光纖感測系統，其中以光纖布拉格光柵感測元件當作光纖雷射反射端，另一端接上寬頻光放大器，並在此寬頻光放大器的另一端接上光纖迴路等效鏡，組合線性共振腔光纖雷射的基本架構，之後在雷射的輸出端並接兩個光纖布拉格光柵濾波器，由於光纖布拉格光柵感測元件，會受到溫度的變化造成雷射光頻譜飄移，因此可根據兩個光纖布拉格光柵濾波器的反射訊號得知感測元件受溫度的變化。
Heuristic PAC model for hybrid MTO and MTS production environment
(2003-09-11)
Chang, SH
;
Pai, PF
;
Yuan, KJ
;
Wang, BC
;
Li, RK
Two distinct types of semiconductor plants in Taiwan are integrated device manufacturing (IDM) plants and foundry plants. Most IDM plants are make-to-stock (MTS) operations, focusing on throughput and machine utilization. However, foundry plants are make-to-order (MTO) operations, focusing on due date and cycle time. Besides the challenge of different process technology, the mode of hybrid operation (a combination of MTO and MTS operations) is also a formidable task for these plants. This study develops a heuristic production activity control model to achieve the two different criteria in a hybrid wafer production environment. (C) 2003 Elsevier B.V. All rights reserved.
Phase separation and melting behavior in poly(epsilon-caprolactone)-epoxy blends cured by 3,3'-dimethylmethylene-di(cyclohexylamine)
(2003-09-12)
Chen, JL
;
Chang, FC
;
應用化學系
;
Department of Applied Chemistry
The morphology and the melting behavior of poly(E-caprolactone)/epoxy blends (PCL/epoxy) have been investigated by SEM and DSC. The mechanism of phase separation varies with the curing temperature and PCL content, which can be deduced from the cured morphology of the blend. Higher temperature leads to lower blend viscosity and a higher curing rate, and the final morphology is determined by the competition of these two factors. The PCL melting behavior of the blend is influenced by the extent of phase separation and crystallization during curing. The dual melting behavior of the PCL blend can be ascribed to the interference of the epoxy, which results in the formation of less perfect PCL crystallites melted at lower temperature. (C) 2003 Wiley Periodicals, Inc.
Effects of porosity change of gas diffuser on performance of proton exchange membrane fuel cell
(2003-09-15)
Chu, HS
;
Yeh, C
;
Chen, F
;
機械工程學系
;
Department of Mechanical Engineering
An investigation is made of the effects of the change of the porosity of the gas diffuser layer (GDL) on the performance of a proton exchange membrane (PEM) fuel cell. The analysis of fuel cell performance with non-uniform porosity of GDL is a necessity because the presence of liquid water in the GDL leads to a non-uniformly distributed porosity in the GDL. To implement this performance analysis, a half-cell model which considers the oxygen mass fraction distribution in the gas channel, the GDL and the catalyst layer, and the current density and the membrane phase potential in the catalyst layer and the membrane is investigated. Four continuous functions of position are employed to describe the porosity, and differential equations are derived based on oxygen transportation and Ohm's law for proton migration and solved numerically. Results show that a fuel cell embedded with a GDL with a larger averaged porosity will consume a greater amount of oxygen, so that a higher current density is generated and a better fuel cell performance is obtained. This explains partly why fuel cell performance deteriorates significantly as the cathode is flooded with water (i.e. to give a lower effective porosity in the GDL). In terms of the system performance. a change in GDL porosity has virtually no influence on the level of polarization when the current density is medium or lower, but exerts a significant influence when the current density is high. This finding supports the scenario proposed by previous studies that the polarization at high current density corresponds mainly to mass transfer through (or the concentration activation of) the membrane assembly. (C) 2002 Elsevier Science B.V. All rights reserved.
Device transfer technology by backside etching (DTBE) for poly-Si thin-film transistors on glass/plastic substrate
(2003-09-15)
Wang, SC
;
Yeh, CF
;
Huang, CK
;
Dai, YT
;
電子工程學系及電子研究所
This work presents a novel method entitled "device transfer by backside etching (DTBE)" for transferring thin-film devices from Si wafers to a glass or plastic substrate. First, high performance poly-Si thin-film transistors (TFTs) were fabricated on a Si wafer and then adhered to glass or plastic substrates. The remaining Si was removed delicately using wafer. backside chemical-mechanical polishing (CMP) and wet chemical etching. The devices after transferring exhibit comparable electrical characteristics to the original ones on Si substrates. The new transfer scheme has quite attractive applications for fabricating high-quality displays on low-cost substrates with low melting temperatures.
Energy spectrum of tau leptons induced by the high energy Earth-skimming neutrinos
(2003-09-15)
Tseng, JJ
;
Yeh, TW
;
Athar, H
;
Huang, MA
;
Lee, FF
We present a semianalytic calculation of the tau-lepton flux emerging from the Earth induced by incident high energy neutrinos interacting inside the Earth for 10(5)less than or equal toE(nu)/GeVless than or equal to10(10). We obtain results for the energy dependence of the tau-lepton flux coming from the Earth-skimming neutrinos, because of the neutrino-nucleon charged-current scattering as well as the resonant (nu) over bar (e)e(-) scattering. We illustrate our results for several anticipated high energy astrophysical neutrino sources such as the active galactic nuclei, the gamma-ray bursts, and the Greisen-Zatsepin-Kuzmin neutrino fluxes. The tau-lepton fluxes resulting from rock-skimming and ocean-skimming neutrinos are compared. Such comparisons can render useful information about the spectral indices of incident neutrino fluxes.
Linewidth reduction and wavelength tuning of an erbium-doped fiber laser by use of a single-mode-selected and side-mode-suppressed Fabry-Perot laser diode
(2003-09-20)
Lin, GR
;
Wu, JR
;
光電工程學系
;
Department of Photonics
A single-mode and highly side-mode-suppressed 1.55-mum Fabry-Perot laser diode (FPLD) is achieved by feedback injection with an erbium-doped fiber laser (EDFL). For selection of the strongest longitudinal mode from the gain spectrum of the FPLD for lasing in the EDFL, the FPLD is operated at just below the threshold condition and is feedback injected by 0.02% of the EDFL output power. The lasing mode and center wavelength of the proposed single-mode FPLD source are decided by cross-correlated gain profiles of the EDFL and the FPLD; however, the effect of FPLD injection modes is found to be more pronounced. The optimized lasing linewidth (system limitation) and side-mode suppression ratio of 0.01 nm and >49 dB are obtained, which are far better than those of a FPLD at free-running condition. The worst linewidths at 3- and 10-dB decay are observed to be at approximately 0.016 and 0.05 nm, respectively. Linear wavelength tuning of as much as 4.5 nm (from 1558.7 to 1563.2 nm) by adjustment of the temperature of the FPLD from 10 degreesC to 40 degreesC at just below threshold is reported. The wavelength-tuning slope is approximately 0.14 nm/degreesC under temperature accuracy of 0.1 degreesC. (C) 2003 Optical Society of America.
Diode-pumped passively mode-locked multiwatt Nd : GdVO4 laser with a saturable Bragg reflector
(2003-09-20)
He, JL
;
Lee, CK
;
Huang, JYJ
;
Wang, SC
;
Pan, CL
We report a first demonstration, to our knowledge, of a cw passively mode-locked Nd:GdVO4 laser (lambda = 1063 nm). A relaxed saturable Bragg reflector was used. The laser generates pulses of 9.2 ps at a repetition rate of 119 MHz. As much as 5.4 W of average power was realized with a slope efficiency of 25.7%. (C) 2003 Optical Society of America.
鐵電場效電晶體製造方法
(2003-09-21)
陳三元
;
孫嘉良
;
荊鳳德
本案係指一種鐵電場效電晶體製造方法，其係應用於金屬/鐵電薄膜/絕緣層/半導體(MFIS)結構的閘極電容元件製作上，該方法乃藉由在該絕緣層上沈積一鉍系鐵電薄膜，並經由一高溫熱處理後，再鍍上一上電極層於該鉍系鐵電薄膜上，俾得致該鐵電場效電晶體結構。
Effect of thermal annealing of Ni/Au ohmic contact on the leakage current of GaN based light emitting diodes
(2003-09-22)
Hsu, CY
;
Lan, WH
;
Wu, YS
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The effect of thermal annealing on current-voltage properties of GaN light emitting diodes (LEDs) has been studied. At annealing temperatures above 700 degreesC, the p-n junction of the diodes became very leaky and Ga-contained metallic bubbles were observed on the surface of Ni/Au p-ohmic contact. Transmission electron microscopy and energy dispersive x-ray spectrometer studies revealed that these metallic bubbles resided directly on top of the threading dislocations in GaN and both Ni and Au were indiffused into the LED structure along the cores of the TDs. The conducting paths formed by the metal containing dislocation cores are believed to be the cause for the observed short circuit behavior of p-n junctions at high annealing temperatures. (C) 2003 American Institute of Physics.
4-(Dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran doped red emitters in organic light-emitting devices
(2003-09-22)
Liu, TH
;
Iou, CY
;
Wen, SW
;
Chen, CH
;
應用化學系
We have studied the device optimization of red 4-(Dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) dye doped Alq(3) emitters in organic light-emitting devices (OLED). By varying the hole injection materials, thickness of hole-transport layer and by evaporation with rubrene as co-dopant, efficiencies of 3.24 cd/A and near saturated CIE color coordinates of x = 0.643, y = 0.354 was achieved without needing additional doping of hole-trap with NPB. From experiments with film thickness variation, it is concluded that the improved electrofluorescent (EL) performance and color saturation are due to the synergistic effects of microcavity, device structural optimization as well as optimal doping of DCJTB with rubrene. We believe this luminance efficiency for red is by far one of the best ever reported for dye-doped electrofluorescent OLEDs. (C) 2003 Elsevier B.V. All rights reserved.
Polyimide-side-chain tethered polyhedral oligomeric silsesquioxane nanocomposites for low-dielectric film applications
(2003-09-23)
Leu, CM
;
Chang, YT
;
Wei, KH
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Low-dielectric-constant nanoporous films (dielectric constant, k = 2.4) with thermal integrity and controllable mechanical strength have been prepared by covalently tethering nanoporous polyhedral oligomeric silsesquioxane (POSS) molecules, 1-nm size, to the side chains of polyimide. The tethered POSS molecules in the amorphous polyimide retain a nanoporous crystal structure, but form an additional ordered architecture due to microphase separation. With this approach, the dielectric constant of the film can be tuned by the amount of POSS molecules introduced in the nanocomposite film; the polyimide molecules offer additional advantages of maintaining certain thermal and mechanical strengths.
Blocking the dengue virus 2 infections on BHK-21 cells with purified recombinant dengue virus 2 E protein expressed in Escherichia coli
(2003-09-26)
Chiu, MW
;
Yang, YL
;
生物科技學系
;
Department of Biological Science and Technology
Dengue viruses (DVs) are mosquito-borne infectious pathogens. They have become an expanding public health problem in the tropics and subtropics. The dengue envelope (E) protein is one of the viral structure proteins responsible mainly for the virus attachment and entry onto host cells. It is also the major immunogen for virus neutralization. In this study, we have constructed a recombinant plasmid expressing a truncated E protein of DV-2 virus PL046 strain: The C-terminal hydrophobic domain of the E protein was removed and replaced with the sequence of S peptide to facilitate expression and purification. When expressed in Escherichia coli, the recombinant E proteins were found to be in the form of aggregated state. Through denaturation and dialysis processes, the receptor-interacting function of the purified recombinant E proteins was maintained, which was demonstrated by its ability to inhibit the DV-2 plaque-forming efficiency on mammalian BHK-21 host cells. (C) 2003 Elsevier Inc. All rights reserved.
Molecular sublayers beneath the air-sea interface relative to momentum, heat and gas transports
(2003-09-27)
Tsai, WT
;
Chen, SM
;
Lin, MY
;
Hung, LP
;
土木工程學系
Numerical simulations of the wind-driven aqueous turbulent flow and the underlying heat and dissolved gas transports are conducted with sufficiently fine grid resolution to resolve the molecular sublayers immediately beneath the air-water interface. The simulated mean distributions of velocity, temperature and gas concentration all exhibit exponential profiles across the sublayers in accordance with the theoretical postulation of Liu and Businger [1975] which they derived on the basis of the conceptual surface renewal model. The numerical results identify two major coherent renewal processes within the flow: intermittent upwellings induced by uprising horseshoe-like eddies in the well-mixed region, and elongated, high-speed, cool streaks within the sublayer reflecting the cool-skin thermal structure.