Browsing by Issue Date, starting with "2003-08-08"

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Blends of poly(propylene) and polyacetal compatibilized by ethylene vinyl alcohol copolymers
(2003-08-08)
Huang, JM
;
Cheng, HJ
;
Wu, JS
;
Chang, FC
;
應用化學系
Polymer blends of poly(propylene) (PP) and polyacetal (polyoxymethylene, POM) with ethylene vinyl alcohol (EVOH) copolymers were investigated by differential scanning calorimetry (DSC), rheological, tensile, and impact measurements, Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The PP-POM-EVOH blends were extruded with a co-rotating twin-screw extruder. The ethylene group in the EVOH is partially miscible with PP, whereas the hydroxyl group in the EVOH can form hydrogen bonding with POM. The EVOH tends to reside along the interface, acting as a surfactant to reduce the interfacial tension and to increase the interfacial adhesion between the blends. Results from SEM and mechanical tests indicate that a small quantity of the EVOH copolymer or a smaller vinyl alcohol content in the EVOH copolymer results in a better compatibilized blend in terms of finer phase domains and better mechanical properties. (C) 2003 Wiley Periodicals, Inc.
An iterative method for adaptive finite element solutions of an energy transport model of semiconductor devices
(2003-08-10)
Chen, RC
;
Liu, JL
;
應用數學系
;
Department of Applied Mathematics
A self-adjoint formulation of the energy transport model of semiconductor devices is proposed. This new formulation leads to symmetric and monotonic properties of the resulting system of nonlinear algebraic equations from an adaptive finite element approximation of the model. A node-by-node iterative method is then presented for solving the system. This is a globally convergent method that does not require the assembly of the global matrix system and full Jacobian matrices. An adaptive algorithm implementing this method is described in detail to illustrate the main features of this paper, namely, adaptation, node-by-node calculation, and global convergence. Numerical results of simulations on deep-submicron diode and MOSFET device structures are given to demonstrate the accuracy and efficiency of the algorithm. (C) 2003 Elsevier Science B.V. All rights reserved.
Super-connectivity and super-edge-connectivity for some interconnection networks
(2003-08-10)
Chen, YC
;
Tan, JJM
;
Hsu, LH
;
Kao, SS
;
資訊工程學系
Let G = (V, E) be a k-regular graph with connectivity K and edge connectivity. G is maximum connected if kappa = k, and G is maximum edge connected if lambda = k. Moreover, G is super-connected if it is a complete graph, or it is maximum connected and every minimum vertex cut is {x(v,x) is an element of E} for some vertex v is an element of V; and G is super-edge-connected if it is maximum edge connected and every minimum edge disconnecting set is {(v,x)(v,x) is an element of E} for some vertex v is an element of V. In this paper, we present three schemes for constructing graphs that are super-connected and super-edge-connected. Applying these construction schemes, we can easily discuss the super-connected property and the super-edge-connected property of hypercubes, twisted cubes, crossed cubes, mobius cubes, split-stars, and recursive circulant graphs. (C) 2002 Elsevier Science Inc. All rights reserved.
Dynamical behavior of a bistable chiral quasihomeotropic liquid crystal cell
(2003-08-11)
Hsieh, CY
;
Chen, SH
;
光電工程學系
;
Department of Photonics
The dynamical behavior of the directors in a bistable chiral quasihomeotropic (BCQH) liquid crystal cell has been investigated. This cell can be switched from the initial quasihomeotropic configuration state at zero field to two static twisted states at 14 V by different switching processes. We studied the dynamic behavior of the BCQH cell based on the general nematohydrodynamic theory, and the detailed dynamical mechanism was illustrated by analyzing the director and velocity profiles obtained from the numerical simulation. We found that, in addition to the flow effect, the asymmetric polar-alignment condition is another important factor to achieve the switching bistability of our BCQH cell. The experimental and numerical results are reported in this letter. (C) 2003 American Institute of Physics.
Observation of a crossover of the inelastic electron scattering in Sc100-xAgx thick films
(2003-08-15)
Lee, TC
;
Lin, JJ
;
Chang, SF
;
電子物理學系
;
物理研究所
We have made a series of thick Sc films doped with different amounts of Ag, which results in a systematic decrease in the resistivities, i.e., disorder, of the films. From measurements of the low-field magnetoresistances and comparison with three-dimensional weak-localization theoretical predictions, the electron dephasing times are extracted in every film. We find a crossover of the inelastic electron process from the critical electron-electron scattering to the electron-phonon scattering as the disorder decreases and the system progressively moves away from the Anderson localization.
Reducing the alkali cation adductions of oligonucleotides using sol-gel-assisted laser desorptionionization mass spectrometry
(2003-08-15)
Chen, WY
;
Chen, YC
;
應用化學系
;
Department of Applied Chemistry
The alkali cation adductions of oligonucleotides dramatically degrade MALDI mass spectra and even affect the detection limit. Desalting is generally involved in MALDI sample preparation. This work demonstrates the feasibility of using 3,4-diaminobenzoic acid (DABA) and 3,5-DABA as the MALDI matrix for oligonucleotide analysis. Furthermore, sodium ion adducts of oligonucleotides were simultaneously reduced in the mass spectra when DABA was used as the MALDI matrix and sol-gel material was used as the sample support. However, depositing the sample on the sample support was very difficult, and the lack of homogeneity of analytes/matrix distribution on the sample support also led the analyte signals to be revealed only in "sweet spots". Alternatively, DABA was doped into sol-gel materials to generate homogeneous DABA/sol-gel hybrid film. The DABA/sol-gel hybrid film was used as the sample substrate to assist the desorption/ionization of analytes. The analyte signals were evenly found on the sample substrate. The sodium ion adductions of oligonucleotides were also effectively suppressed. The sample preparation used in this approach resembles that used in the authors' previous study, involving sol-gel-assisted laser desorption/ionization (SGALDI) mass spectrometry (Lin, Y.-S.; Chen, Y.-C. Anal. Chem. 2002, 74, 5793-5798.) The SGALDI approach was demonstrated to be effective in assisting the desorption/ionization of peptides and small proteins. Herein, the SGALDI material, DABA/sol-gel hybrid material, was successfully applied to oligonucleotide analysis, and good-quality mass spectra were obtained without extra desalting. Additionally, the presence of 0.1% SDS in the oligonucleotide sample solution was tolerated without degrading the mass spectra. The largest detectable molecular size for oligonucleotides was 72 mer. The detection limit for 24 mer of oligonucleotide was 20 fmol.
Phase transition in a Cu-14.1A1-9.0Ni alloy
(2003-08-15)
Chen, CH
;
Yang, CC
;
Liu, TF
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The phase transition of the Cu-14.1 wt.% Al-9.0 wt.% Ni alloy has been examined by transmission electron microscopy and energy-dispersive X-ray analysis. In the as-quenched condition, the microstructure of the alloy was Do(3) phase that contained extremely fine L-J precipitates. During the early stage of isothermal aging at 500 degreesC, a high density of the extremely fine B2 particles was observed within the extremely thin lamellar gamma(1)' martensite, which was formed by a D0(3) --> gamma(1)' martensitic transformation during quenching. With increasing aging time at 500 degreesC, the isothermal phase transition sequence was found to be D0(3) --> D0(3) --> B2 --> D0(3) + B2 + alpha --> B2 + alpha + gamma(2). This transition significantly differs from that observed by other researchers. Besides, both Kurdjumov-Sachs (K-S) and Nishiyama-Wassermann (N-W) orientation relationships between the B2 particle and the alpha phase could be detected in the aged alloy. (C) 2003 Elsevier Science B.V. All rights reserved.
Controlling access in large partially ordered hierarchies using cryptographic keys
(2003-08-15)
Hwang, MS
;
Yang, WP
;
資訊工程學系
;
Department of Computer Science
The problem of access control in a hierarchy is present in many application areas. Since computing resources have grown tremendously, access control is more frequently required in areas such as computer networks, database management systems, and operating systems. Many schemes based on cryptography have been proposed to solve this problem. However, previous schemes need large values associated with each security class. In this paper, we propose a new scheme to solve this problem achieving the following two goals. One is that the number of keys is reduced without affecting the security of the system. The other goal is that when a security class is added to the system, we need only update a few keys of the related security classes with simple operations. (C) 2002 Elsevier Inc. All rights reserved.
Charge transport in doped organic semiconductors
(2003-08-15)
Shen, YL
;
Diest, K
;
Wong, MH
;
Hsieh, BR
;
Dunlap, DH
We report an unusual transition in the conductivity of an organic semiconductor upon doping: For low doping levels, the conductivity of N,N,N-',N-'-tetra-p-tolyl-4-4(')-biphenyldiamine dispersed polycarbonate increases with doping in a nearly linear fashion, and shows an activation energy of 0.2 eV. At high doping levels, a superlinear increase of conductivity with doping is observed, and the activation energy decreases, reaching a low of 0.12 eV. This behavior is understood in terms of broadening of the transport manifold due to enhanced disorder coming from the dopants.
Rotational states of an adsorbed dipole molecule in an external electric field
(2003-08-15)
Shih, YT
;
Liao, YY
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
The rotational states of an adsorbed dipole molecule in an external electric field were investigated. The surface hindering potential was modeled as a finite conical well and a dipole-field interaction was added to the hindering potential. The molecular wave functions were expressed in terms of the eigenfunctions of molecular hindered rotation in the absence of electric field. Eigenenergies were determined by the matrix diagonalization procedures. Our results showed that, for both vertically and horizontally adsorbed molecules, there is avoided crossing between two adjacent rotational energy levels, as the field strength is increased, and finally all state energies decrease rapidly as the field strength is strong enough. The avoided crossing is due to the redistribution of wave function between different potential well regions. By employing the sudden unhindrance approximation, the rotational-state distributions of molecules desorbing from a solid surface in the presence of external electric field were calculated. Our results showed that the rotational-state distributions are significantly influenced by the external electric field. Since the electric field increases the ground-state energy of adsorbed molecule, the distribution shifts towards the high-J region if the electric field is applied to orient the molecular axis against the molecular preferred orientation. On the contrary, the distribution shifts towards the low-J region if the electric field is applied to orient the molecular axis towards molecular preferred orientation because the electric field decreases the ground-state energy of adsorbed molecule. The solutions to the finite conical well were also used to calculate the rotational alignment in the photodesorption of CO from Cr2O3(0001). Our results showed that at low-J values the CO molecules desorb like a helicopter, while at high-J values a cartwheel-like motion is preferred. This result is in qualitative agreement with the experimental observation.
Optimal replenishment for a periodic review inventory system with two supply modes
(2003-08-16)
Chiang, C
;
管理科學系
;
Department of Management Science
In this paper, we study periodic inventory systems with long review periods. We develop dynamic programming models for these systems in which regular orders as well as emergency orders can be placed periodically. We identify two cases depending on whether or not a fixed cost for placing an emergency order is present. We show that if the emergency supply mode can be used, there exists a critical inventory level such that if the inventory position at a review epoch falls below this critical level, an emergency order is placed. We also develop simple procedures for computing the optimal policy parameters. In all cases, the optimal order-up-to level is obtained by solving a myopic cost function. Thus, the proposed ordering policies are easy to implement. (C) 2002 Elsevier Science B.V. All rights reserved.
Ultrabroadband terahertz field detection by photoconductive antennas based on multi-energy arsenic-ion-implanted GaAs and semi-insulating GaAs
(2003-08-18)
Liu, TA
;
Tani, M
;
Nakajima, M
;
Hangyo, M
;
Pan, CL
The photoconductive antennas based on multi-energy arsenic-ion-implanted GaAs and semi-insulating GaAs are demonstrated to have a useful bandwidth beyond 20 THz for a gating laser pulse width of 15 fs. The bandwidth and signal-to-noise ratio are compared with those of reference photoconductive antennas based on low-temperature grown GaAs. (C) 2003 American Institute of Physics.
SiC-capped nanotip arrays for field emission with ultralow turn-on field
(2003-08-18)
Lo, HC
;
Das, D
;
Hwang, JS
;
Chen, KH
;
Hsu, CH
Silicon nanotips with tip diameter and height measuring 1 nm and 1 mum, respectively, and density in the range of 10(9)-3x10(11) cm(-2), were fabricated monolithically from silicon wafers by electron cyclotron resonance plasma etching technique at a temperature of 200 degreesC. Field emission current densities of 3.0 mA/cm(2) at an applied field of similar to1.0 V/mum was obtained from these silicon nanotips. High-resolution transmission electron microscope and Auger electron spectroscopy analyses concluded that the nanotips are composed of monolithic silicon and nanometer-size SiC cap at the top. A 0.35 V/mum turn-on field to draw a 10 muA/cm(2) current density was demonstrated, which is much lower than other reported materials. The excellent field emission property demonstrated by these nanotips, which were fabricated by a process integrable to the existing silicon device technology at low temperatures, is a step forward in achieving low-power field emission displays and vacuum electronic devices. (C) 2003 American Institute of Physics.
On the log-Sobolev constant for the simple random walk on the n-cycle: the even cases
(2003-08-20)
Chen, GY
;
Sheu, YC
;
應用數學系
;
Department of Applied Mathematics
Consider the simple random walk on the n-cycle Z(n). For this example, Diaconis and Saloff-Coste (Ann. Appl. Probab. 6 (1996) 695) have shown that the log-Sobolev constant alpha is of the same order as the spectral gap lambda. However the exact value of alpha is not known for n>4. (For n = 2, it is a well known result of Gross (Amer. J. Math. 97 (1975) 1061) that alpha is 1/2. For n = 3, Diaconis and Saloff-Coste (Ann. Appl. Probab. 6 (1996) 695) showed that alpha = 1/2 log 2 < lambda/2 = 0.75. For n = 4, the fact that alpha = 1/2 follows from n = 2 by tensorization.) Based on an idea that goes back to Rothaus (J. Funct. Anal. 39 (1980) 42; 42 (1981) 110), we prove that if ngreater than or equal to4 is even, then the log-Sobolev constant and the spectral gap satisfy alpha = lambda/2. This implies that alpha = 1/2(1 - cos 2pi/n) when n is even and ngreater than or equal to4. (C) 2003 Elsevier Inc. All rights reserved.
In situ generation of the silica shell layer - Key factor to the simple high yield synthesis of silver nanowires
(2003-08-20)
Hsia, CH
;
Yen, MY
;
Lin, CC
;
Chiu, HT
;
Lee, CY
利用N個皇后像素篩選之快速動態預測方法
(2003-08-21)
王俊能
;
楊心偉
;
劉啟民
;
蔣迪豪
本發明係在提出一種利用N個皇后像素篩選之快速動態預測方法，其係在視訊串列中選擇一參考區塊及欲處理之區塊後，使用N×N的皇后取樣圖案篩選像素，以進行區塊匹配，進而擷取出一足夠好之區塊差異值。本發明係以像素篩選法的方式結合減少搜尋點的快速動態預測方法，達到簡化動態預測法的計算複雜度之目的，因此不但能篩選出具有足夠代表性的像素，亦不會多出額外的計算複雜度。
Holographic spatial walk-off polarizer and its application to a 4-port polarization-independent optical circulator
(2003-08-25)
Chen, JH
;
Su, DC
;
光電工程學系
;
Department of Photonics
Based on the coupled-wave theory, a holographic spatial walk-off polarizer (HSWP) is designed. This HSWP is a transmission-type phase volume holographic grating on a substrate and its optical recording geometry can be derived from Chen's corrected methodology with a desired reconstruction condition. A pair of fabricated HSWPs with the splitting angle of 60degrees is applied to assemble a new type of 4-port polarization-independent optical circulator. The operating principles and the characteristics of the proposed HSWP and the prototype optical circulator are discussed. (C) 2003 Optical Society of America.
Effect of hydrogen bonding strength on the microstructure and crystallization behavior of crystalline polymer blends
(2003-08-26)
Kuo, SW
;
Chan, SC
;
Chang, FC
;
應用化學系
;
Department of Applied Chemistry
Combinations of differential scanning calorimetry, Fourier transform infrared spectroscopy, optical microscopy, and small-angle X-ray scattering were used to investigate the influence of hydrogen bonding strength on the crystallization kinetics and morphologies in poly(epsilon-caprolactone) (PCL) blends with three different well-known hydrogen bond donating polymers, i.e., phenolic, poly(vinylphenol) (PVPh), and phenoxy. The strength of the intercomponent interactions in the blend system depends on the hydrogen bond donor group and occurs, based on the Painter-Coleman association model, in the order phenolic/PCL > PVPh/PCL > phenoxy/PCL. Significantly reduced overall crystallization kinetics and crystal growth rate in PCL crystalline phase were also in the order phenolic/PCL > PVPh/PCL > phenoxy/PCL, which is consistent with the relative strengths of their intermolecular hydrogen bonding. Our experimental findings show that the hydrogen bonding strength has a greater effect on the rate of crystallization than does the influence of the blend's glass transition temperature, which is related to its chain mobility. In addition, values of the surface free energy of chain folding and crystalline thickness in PCL blends depend strongly on the relative ratio of the interassociation equilibrium constant and the self-association equilibrium constant (K-A/K-B). In phenolic/PCL and PVPh/PCL blends, the values of the surface free energies of chain folding in the PCL crystalline phase are increased with an increase in the content of the hydrogen bond donating polymer since the K-A is greater than the K-B in these two blend systems. In contrast, in the phenoxy/PCL blend system, the smaller K-A relative to the K-B induces a smaller value for the surface free energy of chain folding than that of pure PCL. Various miscible crystalline/amorphous binary polymer blends exhibiting either strong hydrogen bonding or weak interactions are also reviewed.
原來如此
(2003-08-28)
管管
Two-stage dynamic uplink channel and slot assignment for GPRS
(2003-09-01)
Hsu, YC
;
Lin, YD
;
Chiang, MY
;
資訊工程學系
;
Department of Computer Science
General packet radio service (GPRS) uses a two-stage mechanism to allocate uplink radio resource to mobile stations (MSs). In stage-1, the base station (BS) assigns several packet data channels (PDCHs) to an MS. Furthermore, a PDCH may be assigned to multiple MSs. In stage-2, therefore, the BS selects one of the multiplexed MSs in a PDCH to use the radio resource. In this paper, maintaining a load balance between PDCHs in stage-1 is examined and several selection schemes to lower the mis-selection rate in stage-2 are proposed. From our simulation results, the cost deduced from the poor load balancing and selection schemes render a lower system throughput and a non-negligible increase in packet queuing delay. Among the various stage-2 selection policies, round robin with linearly-accumulated adjustment (RRLAA) has the lowest mis-selection rate and outperforms the one without any heuristic by up to 50%.