Browsing by Issue Date, starting with "2001-06-05"

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Miscibility and hydrogen bonding in blends of poly(vinylphenol-co-methyl methacrylate) with poly(ethylene oxide)
(2001-06-05)
Kuo, SW
;
Chang, FC
;
應用化學系
;
Department of Applied Chemistry
Blends of poly(vinylphenol-co-methyl methacrylate) (PVPh-co-PMMA) with poly(ethylene oxide) (PEO) were prepared by solution casting from tetrahydrofuran (THF) solution. The miscibility behavior and hydrogen bonding of blends were investigated by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and solid-state nuclear magnetic resonance (NMR). Experimental results indicate that PEO was miscible with PVPh-co-PMMA as shown by the existence of single composition-dependent glass transition temperatures over the entire composition range by DSC. In addition, a negative polymer-polymer interaction energy density "B" was calculated based on the melting depression of PEO using the Nishi-Wang equation. Solid-state NMR reveals single-exponential decay of proton spin-lattice relaxation times in the rotating frame (T-1p(H)) in the amorphous PVPh-co-PMMA phase. Furthermore, FTIR and solid-state NMR results reveal that at least three competing equilibria are present in the blend; self-association of PVPh-co-PMMA copolymer (hydroxyl-hydroxyl and hydroxyl-carbonyl) and hydroxyl-ether interassociation between PVPh and PEG. Quantitative results show that although the hydroxyl-ether interassociation is favored at room temperature, the hydroxyl-carbonyl self-association dominate's at higher temperatures (> 70 degreesC). The Painter-Coleman association model (PCAM) can predict three interacting functional groups based on our experimental results at various temperatures.
Giant Hall effect in nonmagnetic granular metal films
(2001-06-11)
Zhang, XX
;
Wan, CC
;
Liu, H
;
Li, ZQ
;
Sheng, P
Nearly 3 orders of magnitude enhancement in the Hall coefficient is observed in Cu-x -(SiO2)(1-x) granular films. This large enhancement of the Hall coefficient not only is significantly larger than the prediction of the classical percolation theory, but also occurs at a metal concentration identified to be the quantum percolation threshold. Measurements of the electron dephasing length and magnetoresistance, plus the TEM characterization of microstructures, yield a physical picture consistent with the mechanism of the local quantum interference effect.
Study of hydrogen-bonding strength in poly(epsilon-caprolactone) blends by DSC and FTIR
(2001-06-15)
Kuo, SW
;
Huang, CF
;
Chang, FC
;
應用化學系
;
Department of Applied Chemistry
The hydrogen-bonding strength of poly(epsilon -caprolactone) (PCL) blends with three different well-known hydrogen-bonding donor polymers [i.e., phenolic, poly(vinyl-phenol) (PVPh), and phenoxy] was investigated with differential scanning calorimetry and Fourier transform infrared spectroscopy. All blends exhibited a single glass-transition temperature with differential scanning calorimetry, which is characteristic of a miscible system. The strength of interassociation depended on the hydrogen-bonding donor group in the order phenolic/PCL > PVPh/PCL > phenoxy/PCL, which corresponds to the q value of the Kwei equation. Tn addition, the interaction energy density parameter calculated from the melting depression of PCL with the Nishi-Wang equation resulted in a similar trend in terms of the hydrogen-bonding strength. Quantitative analyses on the fraction of hydrogen-bonded carbonyl groups in the molten state were made with Fourier transform infrared spectroscopy for all systems, and good correlations between thermal behaviors and infrared results were observed. (C) 2001 John Wiley & Sons, Inc.
Time-resolved photoluminescence study of InGaAs/GaAs quantum wells on (111)B GaAs substrates under magnetic fields
(2001-06-15)
Tsai, FY
;
Lee, CP
;
Voskoboynikov, O
;
Cheng, HH
;
Shen, JX
The exciton dynamics in InxGa1-xAs/GaAs quantum wells grown on (111)B and (100) GaAs substrates were studied by time-resolved photoluminescence (PL) under magnetic fields in a Faraday configuration. We have found that the piezoelectric fields in (111)B samples affect the transient behavior of the PL spectra. Compared with the reference (100) sample, we have found that the strong piezoelectric fields, as well as the magnetic fields, cause a slower spin-flip process in (111)B strained quantum wells. (C) 2001 American Institute of Physics.
Friedmann equation and stability of inflationary higher derivative gravity
(2001-06-15)
Kao, WF
;
Pen, UL
;
Zhang, PJ
;
物理研究所
;
Institute of Physics
A stability analysis of the de Sitter universe in pure gravity theory is known to be useful in many aspects. We first show how to complete the proof of an earlier argument based on a redundant field equation. It is shown further that the stability condition applies to k not equal 0 Friedmann-Robertson-Walker spaces based on the nonredundant Friedmann equation derived from a simple effective Lagrangian. We show how to derive this expression for the Friedmann equation of pure gravity theory. This expression is also generalized to include scalar field interactions.
Collection efficiency and capacity of three samplers for acidic and basic gases
(2001-06-15)
Tsai, CJ
;
Huang, CH
;
Wang, SH
;
環境工程研究所
;
Institute of Environmental Engineering
This paper compares the collection efficiency and capacity of a coated porous metal disk with those of a silica gel tube and an impinger at the acid or basic aerosol concentration of two times the permissible exposure limitation (Taiwan IOSH, Institute of Occupational Safety and Health), relative humidity of 80 +/- 5%, and temperature of 30 +/- 3 degreesC in the laboratory. Using 5% sodium carbonate/glycerin coating, the collection efficiencies of the porous metal disk for nitric acid, hydrogen chloride, and hydrogen fluoride are found to be higher than those of the silica gel tube and the impinger when the sampling time is less than 3.0 h. The gas collection capacity of the porous metal disk coated with 5% sodium carbonate is calculated to be 3.9, 5.8, and >2.5 mg for nitric acid, hydrogen chloride, and hydrogen fluoride, respectively. For ammonia, the porous metal disk coated using 4% citric acid performs slightly better than the impinger, and the corresponding capacity is slightly greater than 33.6 mg.
Dynamic resizing of utilization target in measurement-based admission control
(2001-06-15)
Sun, YS
;
Chuang, CC
;
Lin, YD
;
資訊工程學系
;
Department of Computer Science
A major issue in design of measurement-based admission control (MBAC) algorithms relies on how to maximize link utilization while meeting applications' QoS constraints. Studies have claimed that many proposed MBAC algorithms would give the same performance if the parameters were properly tuned, In this paper, we study the effects of tuning two of the most important parameters in MBAC algorithms: Measurement Window and Utilization Target. We show that the measurement window is not a good tuning knob for enforcing rigid loss probability constraints. We propose a new parameter called Soft Utilization Target combined with a simple flow admittance policy called the Latch algorithm. The simulation results show that this scheme can achieve better enforcement of loss probability constraint while maintaining higher link utilization. (C) 2001 Elsevier Science B.V. All rights reserved.
Stream ciphers for GSM networks
(2001-06-15)
Lo, CC
;
Chen, YJ
;
資訊管理與財務金融系註：原資管所+財金所
;
Department of Information Management and Finance
With the advance of wireless communications technology, mobile communications has become more convenient than ever. However, because of the openness of wireless communications, how to protect the privacy between communicating parties is becoming a very important issue. In this paper, we focus on the security of transferring voice message on the Global System for Mobile communication (GSM) networks. Stream cipher is recommended for message encryption and decryption. First, a key generator is presented. Then, on the basis of the key generator, stream ciphers are designed with respect to different levels of securities of GSM networks. Simulation results indicate that the key generator always produces key strings of evenly distributed 0's and 1's and with a very long period; i.e. it is very unlikely that repeated patterns will appear. Cryptanalysis and operational analysis show that the proposed stream ciphers are secure and efficient; consequently, they provide a comprehensive set of message encryption/decryption algorithms for GSM networks. (C) 2001 Elsevier Science B.V. All rights reserved.
The finite element analysis on planetary rolling process
(2001-06-15)
Shih, CK
;
Hung, CH
;
Hsu, RQ
;
機械工程學系
;
Department of Mechanical Engineering
This paper is focused on using the finite element method to simulate and analyze the planetary rolling process. First, a basic geometric model of the planetary rolling mill that considers roll profiles and offset angle of the rolls was constructed. Then, a three-dimensional elastic-plastic finite element simulation was used to analyze both the deformation characteristics of this process and the distributions of stress and strain in the workpieces. During simulations, an algorithm called Equation of Meshing was proposed by which the initial contact conditions between the rollers and the workpiece were successfully derived. Finally, an optimum design method was integrated into this analysis for seeking the best design variables in order to reduce the cavity conditions in the leading end of milled steel rods. (C) 2001 Elsevier Science B.V. All rights reserved.
Comparison of thermal reactions of phosphine on Ge(100) and Si(100) by high-resolution core-level photoemission
(2001-06-20)
Tsai, HW
;
Lin, DS
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物理研究所
;
Institute of Physics
The thermal decomposition processes of phosphine (PH;) on a Ge(I 0 0)-2 x I surface at temperatures between 325 and 790 K were investigated and compared with those on Si(I 0 0)-2 x 1. High-resolution synchrotron radiation core-level photoemission spectra indicates that. at room temperature phosphine molecularly adsorbs on the Ge(I 0 0)-2 x I surface, however on the Si(1 0 0)-2 x I it partially dissociates into PH2 and H. Successive annealing of the PH3-saturated Si(1 0 0) and Ge(I 0 0) surfaces at higher temperatures similarly converts PH3 into PH2 and PH2 to P. P atoms form stable P-P and/or P-Si dimers on Si(I 0 0) above 720 K. but exhibit complex bonding configurations on Ge(1 0 0). (C) 2001 Elsevier Science B.V. All rights reserved.
Efficient and robust watermarking algorithm with vector quantisation
(2001-06-21)
Huang, HC
;
Wang, FH
;
Pan, JS
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
A new method for watermarking based on Vector quantisation is proposed. It is efficient for implementation with conventional techniques, and simulation results show its robustness under a variety of attacks. Tt also represents superiority over eng algorithms.
具高能隙偏移層結構之薄膜場效電晶體元件
(2001-06-23)
張俊彥
一種具高能隙偏移層結構之薄膜場效電晶體元件，係在基底上的源極/汲極和閘極底下閘極絕緣層之間,垂直疊放複數個不同能隙之半導體層,該複數個半導體層包含高-低-高-低能隙,低-高-低能隙,高-低-高能隙或低-高能隙結構的半導體層,其中低能隙半導體層鄰接閘極絕緣層,作為載子的通道層，在元件導通時能傳導載子，而鄰接通道層的高能隙偏移層,能在該元件關閉狀態下，阻擋傳導載子發生能帶到能帶的穿透傳輸，降低閘極感應之汲極漏電流,另外,鄰接高能隙偏移層的低能隙半導體層，形成半導體與金屬層之間的歐姆接觸區,當做源極/汲極的接觸層,而鄰接閘極的高能隙介面層，則是用來捕捉可能存在於通道層與閘極絕緣層之間的介面缺陷,使元件特性便不會受閘極絕緣層20的介面特性直接影響，並讓該元件在導通狀態下能維持相當大的導通電流，同時在關閉狀態下,能大幅降低元件之關閉電流,提高其開/關電流比，適合應用到液晶顯示器上,可以大幅提升其畫面品質。
Lower bounds for wide-sense nonblocking Clos network
(2001-06-28)
Tsai, KH
;
Wang, DW
;
Hwang, F
;
應用數學系
;
Department of Applied Mathematics
The 3-stage Clos network is generally considered the most basic multistage interconnecting network (MIN). The nonblocking property of such network has been extensively studied in the past. However, there are only a few lower bound results regarding wide-sense nonblocking. We show that in the classical circuit switching environment, to guarantee wide-sense nonblocking for large r, 2n - 1 center switches are necessary, where I is the number of input switches and n is the number of inlets of each input switch. For the multirate environment, we show that for large r, any 3-stage Clos network needs atleast 3n - 2 center switches to guarantee wide-sense nonblocking. Our proof works even for the two-rate environment. (C) 2001 Elsevier Science B.V. All rights reserved.
Synthesis of novel acetal thia-cage compounds
(2001-06-29)
Wu, CY
;
Lin, HC
;
Wang, ZY
;
Wu, HJ
;
應用化學系
The synthesis of novel acetal this-cage compounds has been accomplished by the direct substitution for the oxygen atom by the sulfur atom in the reaction of the acetal groups of era-cages with Lawesson reagent (LR). Reaction of the tetraoxa-cage compound 2 with LR in dichloromethane at 25 degreesC sequentially gave the monothia-, dithia-, trithia-, and tetrathia-cage compounds 3, 6, 7, and 9. The reaction mechanism for the conversion from era-cages into thia-cages was proposed. The diacetal trioxa-cages 18-20 and 24-26 were also transformed into the thia-cages 21-23 and 27-29, respectively. Reaction of the trioxa-cages 34 and 35 with LR under the same reaction conditions gave the thia-cages 36 and 37 with the carbonyl group intact. Treatment of the pentaoxa[5]-peristylane 40 with LR in chloroform under supersonic shaking at refluxing temperature gave the monothia[5]peristylane 41 and the dithia-[5] peristylane 42. Attempts to synthesize the thia[5]-peristylanes from the tetraoxa-cage 51 and the transformation from the parent (unsubstituted) pentaoxa[5]peristylane 46 to the thia-cages have been made. Reaction of the pentaoxa[5]-peristylane 40 with P2S5 in refluxing toluene gave 41, 42, and a rearrangement product 47. The synthesis of new heterocyclic cage compounds 59 and 60, which contain oxygen, nitrogen, and sulfur atoms in the same molecule, was also accomplished.
Frequency control in a low voltage, wide tuning VCO design at 2.4 GHz
(2001-07-01)
Kao, YH
;
Chien, CC
;
傳播研究所
;
Institute of Communication Studies
A low voltage and wide tuning rang voltage controlled oscillator (VCO)( at 2.4 GHz is developed for ISM applications. A design procedure wit the parasitics of packaged devices considered is offered A VCO with a 200 MHz tuning range for les than 2 V using a packaged varactor is demonstrated.
Vector quantization based on genetic simulated annealing
(2001-07-01)
Huang, HC
;
Pan, JS
;
Lu, ZM
;
Sun, SH
;
Hang, HM
Genetic algorithm (GA) has been successfully applied to codebook design for vector quantization (VQ). However, most conventional GA-based codebook design methods need long runtime because candidate solutions must be fine tuned by LBG. In this paper, a partition-based GA is applied to codebook design, which is referred to as genetic vector quantization (GVQ). In addition, simulated annealing (SA) algorithm is also used in GVQ to get more promising results and the corresponding method is referred to as GSAVQ. Both GVQ and GSAVQ use the linear scaling technique during the calculation of objective functions and use special crossover and mutation operations in order to obtain better codebooks in much shorter CPU time. Experimental results show that both of them save more than 71-87% CPU time compared to LEG. For different codebook sizes, GVQ outperforms LEG by 1.1-2.1 dB in PSNR, and GSAVQ outperforms LBG by 1.2-2.2 dB in PSNR. In addition, GVQ and GSAVQ need a little longer CPU time than, the maximum decent (MD) algorithm, but they outperform MD by 0.2-0.5 dB in PSNR. (C) 2001 Elsevier Science B.V. All rights reserved.
Energy-effectiveness of nonthermal plasma reactors for toluene vapor destruction
(2001-07-01)
Lin, CH
;
Bai, HL
;
環境工程研究所
;
Institute of Environmental Engineering
The energy-effectiveness of packed-bed and nonpacked-bed plasma reactors for the destruction of toluene vapors is evaluated on the basis of the power consumption of the reactor system. The operation and design parameters being evaluated include the applied voltage, inlet gas flow rate, and toluene concentration. The optimal operational conditions for the target destruction of toluene vapors, with minimum power consumption, are determined. The results showed that a packed-bed plasma reactor has a higher toluene destruction efficiency and a lower power consumption than a nonpacked-bed plasma reactor. The toluene destruction efficiency is increased as both the inlet gas flow rate and the toluene gas concentration are decreased. For a plasma reactor 2 cm in diameter and packed with 5-mm glass pellets, > 90% of toluene destruction can be reached at an applied voltage of 8.7 kV, inlet toluene concentrations <1,000 ppm, and gas flow rates of < 680 cm(3)/min. The corresponding energy-effectiveness is about 15 g toluene/kW (.) h.
A review and discussion of epistemological commitments, metacognition, and critical thinking with suggestions on their enhancement in internet-assisted chemistry classrooms
(2001-07-01)
Tsai, CC
;
師資培育中心
;
Center of Teacher Education
Heuristic algorithm for optimal design of the two-level wireless ATM network
(2001-07-01)
Din, DR
;
Tseng, SS
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資訊工程學系
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Department of Computer Science
In this paper, we investigate the optimal assignment problem of cells in PCS (Personal Communication Service) to switches in a wireless ATM network. Given cells and switches on an ATM network (whose locations are fixed and known), the problem is grouping cells into clusters and assigning these clusters to the switches in an optimum manner. This problem is modeled as a complex integer programming problem and finding an optimal solution of this problem is NP-complete. A three-phase heuristic algorithm MCMLCF (Maximum cell and minimum local communication first) consisting of Cell Pre-Partitioning Phase, Cell Exchanging Phase, and Cell Migrating Phase, is proposed. First, in the Cell Pre-Partitioning Phase, a three-step procedure (Clustering Step, Packing Step, and Assigning Step) is proposed to group cells into clusters. Second, Cell Exchanging Phase, is proposed to greatly improve the result by repeatedly exchanging two cells in different switches. Finally, Cell Migrating Phase is proposed to reduce cost by repeatedly migrating all cells in a used switch to an empty switch. Experimental results indicate that the proposed algorithm runs efficiently. Comparing the results of the algorithm to a naive heuristic called NSF, we have shown that the computation time is reduced by 30.1%. Experimental results show that Cell Exchanging and Cell Migrating phases can reduce the total cost by 34.1% on average. By comparing the results of the proposed algorithm to the genetic algorithm, the heuristic method came close to optimum - on average within 5%.
Seismic isolation of rigid cylindrical tanks using friction pendulum bearings
(2001-07-01)
Wang, YP
;
Teng, MC
;
Chung, KW
;
土木工程學系
;
Department of Civil Engineering
Storage tanks are vulnerable to earthquakes, as numerous major earthquakes have demonstrated. The trend of recent revisions to make seismic design criteria for large-scale industrial storage tanks increasingly stringent has made development of cost-effective earthquake-resistant design and retrofit techniques for industrial tanks imperative. This study assesses the feasibility of seismic base isolation for making liquid-filled storage tanks earthquake resistant. The sliding-type friction pendulum seismic (FPS) bearings are considered rather than the elastomeric bearings because the dynamic characteristics of an FPS-isolated tank remain unchanged regardless of the storage level. This work has devised a hybrid structural-hydrodynamic model and solution algorithm, which would permit simple, accurate and efficient assessment of the seismic response of rigid cylindrical storage tanks in the context of seismic isolation. Extensive numerical simulations confirm the effectiveness of seismic base isolation of rigid cylindrical tanks using FPS bearings. Copyright (C) 2001 John Wiley & Sons, Ltd.