Browsing by Issue Date, starting with "2006-11-05"

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A study of weldability and fracture modes in electron beam weldments of AZ series magnesium alloys
(2006-11-05)
Chi, Chao-Ting
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Chao, Chuen-Guang
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Liu, Tzeng-Feng
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Wang, Che-Chung
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材料科學與工程學系
Given the growing need for environmental protection and lightweight construction, electron beam welding (EBW) is becoming the most important welding technology because it can compensate for the poor formability of magnesium alloys. This paper examines interactions between the properties of three AZ series magnesium alloys and welding conditions. The EBW process can yield four kinds of defect in a weld: cavities, the heat-affected zone (HAZ), undercuts, and root concavities. These defects obviously induce stress concentrations in the weld, and may seriously damage its strength. Additionally, the distribution of precipitates (gamma phase, Mg17Al12) in the fusion zone (FZ) changes from a relatively small number of scattered particles to a dense population of dendrites as the Al content of the magnesium alloy increases. Under excessive tensile stress, alloy weldments break in one of two fracture modes: an irregular FZ fracture, or a regular HAZ fracture. AZ31B usually exhibits the former mode and AZ91D the latter, while AZ61A exhibits each mode half the time. The overall weldability, which depends on the random distribution of these precipitates and defects, is found to be greatest for the AZ61A alloy. The best process window, on the other hand, is found for the AZ91D alloy. Finally, we obtain optimum parameters for the EBW process and empirical formulae for the weldment strength as a function of these parameters. These results are closely related to each other. (c) 2006 Elsevier B.V. All rights reserved.
Analysis of the flow in grooved pumps with specified pressure boundary conditions
(2006-11-06)
Tsui, Yeng-Yung
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Jung, Shiaugh-Ping
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機械工程學系
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Department of Mechanical Engineering
In this study the numerical method is employed to examine the flow in pumps with spiral grooves. A methodology suitable for the use of unstructured grids is developed. In order to have the greatest feasibility, the governing equations are formulated in such a manner that the grids are allowed to rotate with the rotor. Different from common practices, pressures are specified on the inlet and the outlet boundaries. Therefore, special treatments are required to calculate the mass flow rate and the inlet and outlet velocities. The methodology developed here is assessed via comparison with existing measurements and good agreement is obtained. Examination of pump parameters reveals that in order to obtain maximum flow rate, both the spiral angle and the groove height need to be carefully determined. The force balance over the entire flow channel shows that for a fixed pressure rise across the pump, the pressure difference between side walls is proportional to tangent of the spiral angle and the groove width, but inversely proportional to the groove height and the rotor length. These relationships can roughly be seen in the calculated results. (c) 2005 Published by Elsevier Ltd.
Synthesis and characterization of amphiphatic carboxymethyl-hexanoyl chitosan hydrogel: Water-retention ability and drug encapsulation
(2006-11-07)
Liu, Tse-Ying
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Chen, San-Yuan
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Lin, Yi-g Lin
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Liu, Dean-Mo
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材料科學與工程學系
Carboxymethyl-hexanoyl chitosan (NOCHC) amphiphatic hydrogel with excellent water-absorption and water-retention abilities under neutral conditions was successfully synthesized for the first time and then employed as a carrier for delivering amphiphatic agents. NOCHCis a water-soluble chitosan derivative bearing the carboxymethyl (hydrophilic) group and the hexanoyl (hydrophobic) group, which was synthesized using N,O-carboxymethyl chitosan (NOCC) as the starting precursor. Water-absorption ability (W-c), water-retention ability, and drug encapsulation efficiency of the NOCHC hydrogel were investigated in terms of the degree of carboxymethyl and hexanoyl substitution. It was found that the amount of moisture uptake was dependent on the relative humidity as well as degree and nature of such substitution. The hexanoyl substitution affected significantly the water-absorption ability by altering the number of water-binding sites and the state of water under low humidity and the fully swollen state, respectively. In addition, the presence of hydrophobic hexanoyl substitution significantly retards water mobility during deswelling, causing better water-retention ability. Moreover, compared with that of pristine chitosan and NOCC, the encapsulation efficiency of ibuprofen (partially hydrophobic agent) was significantly enhanced with the incorporation of the hexanoyl group. These results demonstrate that the newly developed NOCHC amphiphatic hydrogel showed enhanced water-absorption ability, water-retention ability, and amphiphatic drug encapsulation efficiency compared with NOCC and chitosan.
A power-saving scheduling for infrastructure-mode 802.11 wireless LANs
(2006-11-08)
Lin, Hsiao-Po
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Huang, Shih-Chang
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Jan, Rong-Hong
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資訊工程學系
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Department of Computer Science
This paper presents a novel method to arrange wakeup schedule for sleeping stations such that the number of wakeup stations in each beacon interval is balanced in IEEE 802.11 wireless local area networks (WLANs). This method reduces the probability of collision and thus the station can save more power. Next, we consider how to poll the wakeup stations to send the PS-Poll frame to get back their buffered data so that the contention can be avoided. Three different access scheduling mechanisms are proposed for the contention avoidance. In the first mechanism, only one of wakeup stations is scheduled to access the buffered data. The second and third mechanisms based on the smallest association ID (AID) first and the smallest queue length first, respectively, arrange a subset of wakeup stations to get back their buffered data within a beacon interval. Simulation results show that the proposed methods are effective in the power-saving. (c) 2006 Elsevier B.V. All rights reserved.
Measuring the flexibility of immunoglobulin by gold nanoparticles
(2006-11-08)
Huang, G. Steven
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Chen, Yu-Shiun
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Yeh, Hsiao-Wei
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材料科學與工程學系奈米科技碩博班
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奈米科技中心
We measured the flexibility of Fab and Fc arms of immunoglobulin using gold nanoparticles (GNPs). Enzyme-linked immunosorbent assay was performed to measure the affinity of anti-5 nm GNP antiserum against various sizes of GNPs. The flexibility of Fc was also measured by electron microscopy. The restricted binding affinity indicated that only a very limited amount of freedom was allowed for the Fab-Fab hinge, while Fab-Fc showed a much larger degree of freedom.
Finding point correspondence using local similarity and global constraint under insignificant scaling and roll
(2006-11-09)
Kao, J. -H.
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Chuang, J. -H.
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Hsieh, M. -L.
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資訊工程學系
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Department of Computer Science
Establishing point correspondences is an important research topic in computer vision. Proposed is an algorithm using local similarity and global constraint to obtain point correspondence. The point correspondences are obtained by comparing their associated colour codes, which are computed by image gradients, and using spatial relationships among neighbouring feature points. The approach assumes insignificant scaling and roll, and is suitable for real-time applications.
Distribution of internal states of CO from O (D-1) + CO determined with time-resolved Fourier transform spectroscopy
(2006-11-09)
Chen, Hui-Fen
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Lee, Yuan-Pern
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應用化學系
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應用化學系分子科學碩博班
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Department of Applied Chemistry
Following collisions of O (D-1) with CO, rotationally resolved emission spectra of CO (1 e V e 6) in the spectral region 1800-2350 cm(-1) were detected with a step-scan Fourier transform spectrometer. O (D-1) was produced by photolysis of O-3 with light from a KrF excimer laser at 248 nm. Upon irradiation of a flowing mixture of O-3 (0.016 Torr) and CO (0.058 Torr), emission of CO (v <= 6) increases with time, reaches a maximum similar to 10 mu s. At the earliest applicable period (2-3 mu s), the rotational distribution of CO is not Boltzmann; it may be approximately described with a bimodal distribution corresponding to temperatures similar to 8000 and similar to 500 K, with the proportion of these two components varying with the vibrational level. A short extrapolation from data in the period 2-6 As leads to a nascent rotational temperature of similar to 10170 +/- 600 K for v = 1 and similar to 1400 +/- 40 K for v = 6, with an average rotational energy of 33 (6 kJ mol(-1). Absorption by CO (v = 0) in the system interfered with population of low J levels of CO (V) 1). The observed vibrational distribution of (v = 2):(v = 3):(v = 4):(v = 5):(v = 6) = 1.00: 0.64: 0.51: 0.32: 0.16 corresponds to a vibrational temperature of 6850 +/- 750 K. An average vibrational energy of 40 (4 kJ mol(-1) is derived based on the observed population of CO (2 e V e 6) and estimates of the population of CO (V) 0, 1, and 7) by extrapolation. The observed rotational distributions of CO (1 <= v <= 3) are consistent with results of previous experiments and trajectory calculations; data for CO (4 <= v <= 6) are new.
Measurement of the adhesive force between a single Klebsiella pneumoniae type 3 fimbria and collagen IV using optical tweezers
(2006-11-10)
Chang, Bo-Jui
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Huang, Ying-Jung
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Chan, Chia-Han
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Hsu, Long
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Peng, Hwei-Ling
Type 3 fimbriae are important adhesive filaments that assist Klebsiella pneumoniae to establish an infection. Different MrkD adhesin variants on the fimbriae are known to display distinct adherence capability for the bacteria to bind extracellular matrix proteins, although the difference has not been determined physically. For this reason, the adhesive force between type 3 fimbriae and collagen IV were measured using optical tweezers. The measured force data displayed a periodic histogram thus Fourier analysis was applied to group it to extract the adhesive force of a single molecular pair. Specifically, we showed that grouping should begin with an offset at the first half of the period. Finally, we first present the adhesive force between each mrkD(V2)-, mrkD(V3)-, and mrkD(V4)-expressed fimbriae and collagen IV is 2.03, 3.79, and 2.87 pN, respectively, This result can be referred to further research on mrkD allelic effect on bacteria infection. (c) 2006 Elsevier Inc. All rights reserved.
適用於超長指令字元之階層式指令編碼方法及其解碼器
(2006-11-11)
任建葳
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林泰吉
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張金祺
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趙至敏
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劉志尉
本發明提供一種適用於超長指令字元之階層式指令編碼方法及其對應之解碼器架構，編碼方法係將超長指令字元(VLIW)之各子指令依照需要轉換成長短不一之指令碼以縮短指令長度，接著將這些長度不固定的指令拆解成固定長度之頭及可變長度之尾欄位，最後加上控制資訊帽(cap)並依特有之排列方式置入一固定長度之指令包裹內，以方便程式記憶體之讀取及指令解碼。控制資訊帽中係包含一有效欄位來移除NOP指令，並同時解決一般可變長度VLIW需額外加入位置分配碼的問題；另外，本發明所特有之指令碼排列方式可採用對數移位器(logarithmic shifter)及漸進式移位器(incremental shifter)組成解碼器，具有簡易且高效率之優點。
Enhancement and inverse behaviors of magnetoimpedance in a magnetotunneling junction by driving frequency
(2006-11-13)
Chien, W. C.
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Lo, C. K.
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Hsieh, L. C.
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Yao, Y. D.
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Han, X. F.
The magnetoimpedance effect was employed to study magnetotunneling junction (MTJ) with the structure of Ru(5 nm)/Cu(10 nm)/Ru(5 nm)/IrMn(10 nm)/CoFeB(4 nm)/Al(1.2 nm)-oxide/CoFeB(4 nm)/Ru(5 nm). A huge change of more than +/- 17 000% was observed in the imaginary part of the impedance between the magnetically parallel and antiparallel states of the MTJ. The inverse behavior of the magnetoimpedance (MI) loop occurs beyond 21.1 MHz; however, the normal MI at low frequency and the inverse MI at high frequency exhibit the same magnetization reversal as checked by the Kerr effect. The reversal in MI was due to the dominance of magnetocapacitance at high frequency. (c) 2006 American Institute of Physics.
Extended microtunnels in GaN prepared by wet chemical etch
(2006-11-13)
Huang, Hsin-Hsiung
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Zeng, Hung-Yu
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Lee, Chi-Ling
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Lee, Shih-Chang
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Lee, Wei-I
It is demonstrated in GaN that microtunnels extended beyond hundreds of microns can be easily achieved using wet chemical etch. To obtain this result, specially designed structures of GaN layers are first grown on sapphire substrates with metal-organic chemical vapor deposition and subsequently with hydride vapor phase epitaxy techniques. The prepared samples are then chemically etched in molten KOH. With the designed structure of GaN layers, extended microtunnels with triangular cross sections are formed. The crystallographic planes of the triangular bevels belong to the {11(2) over bar 2} family. The etch rate of the tunnel can be as high as 10 mu m/min at proper etching conditions. (c) 2006 American Institute of Physics.
Helical morphologies of thermotropic liquid-crystalline chiral Schiff-based rod-coil amphiphiles
(2006-11-14)
Lin, Tz-Feng
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Ho, Rong-Ming
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Sung, Chien-Hung
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Hsu, Chain-Shu
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應用化學系
A series of Schiff-based rod-coil molecules possessing thermotropic liquid-crystalline (LC) character have been prepared whereas a sugar-based moiety was introduced to the chain end of the molecules so as to create chiral amphiphiles for self-assembly. The self-assembly of the chiral Schiff-based rod-coil amphiphiles gave rise to a variety of specific LC textures. A banded morphology under polarized light microscopy (PLM) can be observed; the appearance of the banded texture is strongly dependent upon the length of hydrophobic tail that determines the twisting power of self-assembled hierarchical superstructures with helical sense. As a result, the banded spherulites are identified as quaternary helical morphology with a collection of the tertiary chiral structures (i.e., helical twists) so as to give regular extinction in PLM attributed to zero-birefringence effect. Consistent with the observation of helical morphologies, the occurrence of chiral smectic C (SmC*) phase can only be found in samples with enough alkoxyl chain length, suggesting the existence of strong correlation for morphological evolution from molecular level to macroscopic object with the formation of SmC*. A hypothetic model about the bilayer structure within the SmC* structure is thus given to elucidate the morphological evolution. Consequently, the self-assembly of the chiral amphiphiles with thermotropic LC character represents the mechanism for the chirality transfer in different length scales.
H-bonded effects on novel supramolecular dendrimers containing electron-transporting donor dendrons and single/double H-bonded acceptor emitters
(2006-11-14)
Wu, Chung-Wen
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Lin, Hong-Cheu
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材料科學與工程學系
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Department of Materials Science and Engineering
Novel asymmetric/symmetric supramolecular dendrimers were constructed by two kinds of (single/double) H-bonded acceptor chromophores, i.e., pyridyl/bispyridyl acceptor emitters, encapsulated with (one or two) 1,3,4-oxadiazole (OXD) donor dendrons in proper acceptor/donor molar ratios. These acceptor emitters were also complexed with another type of dendritic donor cores to form exterior emitting shells reverse to the previous system (with emitting cores) via self-assembly of complementary H- bonded moieties. Because of the shielding effect of bulky OXD dendritic shells in H- bonded donors, the supramolecular dendrimers are able to prevent acceptor emitters from spatial aggregation, and thus to induce glass-forming properties (with T-g) and show stronger emission intensities via H-bonds. Besides, the dendritic donors act as efficient light-harvesting antennae capable of transferring light energy from their peripheral OXD arms to their emitting acceptors, where the chromophore luminance induced by energy transfer is more efficient than that by direct excitation of the emitting cores. Compared with analogous dendritic mixtures without H-bonds, higher quantum yields were observed in the supramolecular dendrimers because of better energy transfer from OXD units. Therefore, compared with acceptor emitters, not only can the emission wavelength be tuned (up to 100 nm of red-shift) by H- bonds, but also much higher emission efficiencies of the H- bonded complexes were induced by reduced aggregation and energy transfer from the OXD donor dendrons.
Fabrication, characterization and studies of annealing effects on ferromagnetism in Zn1-xCoxO nanowires
(2006-11-14)
Wu, Z. Y.
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Chen, F. R.
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Kai, J. J.
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Jian, W. B.
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Lin, J. J.
Diluted magnetic semiconductor Zn1-xCoxO ( x <= 0.11) nanowires with average diameter of similar to 40 nm were prepared by thermal evaporation, followed by high-energy Co ion implantation. Bombardment by Co ions produced a good number of structural defects (stacking faults and orientational variations) in the nanowires. The as-implanted nanowires were paramagnetic. We performed two types of thermal annealing, one in 1 atm argon flow and the other in a high vacuum, at 600 degrees C, and studied the effects of annealing on the magnetic properties of these nanowires. Argon annealing removed structural defects in the nanowires and the nanowires then revealed ferromagnetic ordering. This result suggests that structure defects are harmful to the occurrence of ferromagnetism in the Co- implanted ZnO. The structure of the as-implanted and the annealed nanowires was inspected in detail by using scanning electron microscopy, energy dispersive x-ray spectroscopy, maps of electron energy loss spectra, x-ray diffraction, and high-resolution transmission electron microscopy. Taken together, these studies suggested that no second phase existed on the scale down to the spatial resolution of similar to 0.5 nm. Noticeably, the nanowires even displayed largely enhanced ferromagnetism after annealing in a high vacuum. A subsequent annealing in oxygen has also been performed on those vacuum-annealed nanowires to study the roles played by the O vacancies in determining the ferromagnetic properties of the nanowires. Our results indicate that both the improved structural quality and the increased number of O vacancies are key factors for the occurrence of ferromagnetic ordering in the Zn1-xCoxO nanowires.
Simulations for the time evolution of instantaneous resonant modes: Creation, annihilation and mode exchange
(2006-11-15)
Wu, Ten-Ming
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Chang, S. L.
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Tsay, Shiow-Fon
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Tsai, K. H.
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物理研究所
In this paper, we simulate the time evolution of the instantaneous resonant modes (IRMs), which are quasilocalized, in a model of Ga liquid. Through the simulations, we have observed the whole process from creation to annihilation of each individual IRM, and its lifetime is, therefore, estimated. We also find the exchange in character between an IRM and a non-resonant instantaneous normal mode (INM). The exchange occurs as the two INMs have very close frequencies and share a common central particle. (c) 2006 Elsevier B.V. All rights reserved.
Use of modal interference for probing birefringence induced in a bent optical fiber
(2006-11-15)
Chen, Tien-Jung
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Lin, Yi-Hsin
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光電工程學系
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Department of Photonics
We report a novel method that utilizes two lowest-order modes, HE11 and TE01, to probe birefringence induced in a bent circular-core optical fiber. The interference patterns of the two modes are examined by using a polarizer at the fiber output end. The contrast that is extracted from the interference pattern is periodically modulated as a function of phase retardation between the two modes, while the shift of the contrast function shows a strong dependence on the fiber birefringence as the polarizer rotates. Theoretical description followed by the test results demonstrates the feasibility of the method. (c) 2006 Optical Society of America.
Strain study of self-assembled InAs quantum dots by ion channeling technique
(2006-11-15)
Wang, Hsing-Yeh
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Lee, Chien-Ping
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Niu, H.
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Chen, C. H.
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Wu, S. -C.
Ion channeling technique using MeV C++ ions was used to study strain in self-assembled InAs quantum dots (QDs) buried in GaAs matrix. Because of the use of heavy ions, we were able to observe an angular shift in the angular scan of the In signal relative to that of the Ga/As signal. This provided a direct evidence that the InAs lattice is larger than that of GaAs in the growth direction. Combining the channeling results in [100] and [110] directions and the photoluminescence emission spectrum, we conclude that the InAs QDs are under tensile strain in the growth direction and have the same lattice constant as that of GaAs in the lateral direction. Thermal annealing causes the strain to relax, first in the growth direction and then in the lateral direction as the annealing temperature increases. The photoluminescence spectra of the QDs before and after annealing indicate, however, that composition intermixing also takes place during annealing and is the dominant factor in determining the band gap energy of the QDs. (c) 2006 American Institute of Physics.
Atomistic modeling of dislocation activity in nanoindented GaAs
(2006-11-15)
Jian, Sheng-Rui
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Fang, Te-Hua
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Chuu, Der-San
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Ji, Liang-Wen
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電子物理學系
The mechanical behavior of GaAs was investigated by nanoindentation with the aid of molecular dynamics (MD) analysis based on the Tersoff potential. Particular attention was devoted to the evolution characterization of dislocation activity during deformation. The transition from elastic-to-plastic deformation behavior was clearly observed as a sudden displacement excursion occurring during the load-displacement curves of larger loads (single pop-in), faster impact velocity and higher temperature (multiple pop-ins). Even for an ultra-small penetration depth (< 3 nm), the MD simulation shows that GaAs deforms plastically and a good description is given in the results. The plastic deformation occurs due to the anticipated change in the twinning and/or dislocation motion. Dislocation nucleations occurred inside the material near the top of the surface and generated loops in the {111} slip planes. The MD analysis of the deformation behavior shows an agreement with that of previous atomic force microscopy (AFM) and transmission electron microscopy (TEM) experiments. (c) 2006 Elsevier B.V. All rights reserved.
Characterization and field-emission properties of carbon nanotube arrays in nanoporous alumina template and on blank Si substrate
(2006-11-15)
Yang, Ching-Jung
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Chen, Chih
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Shieh, Jia-Min
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材料科學與工程學系
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Department of Materials Science and Engineering
Ordered carbon nanotube (CNT) arrays were synthesized within anodized aluminum oxide template by thermal decomposition of hydrocarbon precursor with hydrogen ambient at growth temperature as low as 500 degrees C. Excess hydrogen in precursor mixture enables a steady supply of mobile hydrocarbon reactant which promotes facile solid-phase diffusion. The activation energy for CNT growth was determined to be 0.55 eV, a number smaller than 1.02 eV for similar precursor in nitrogen ambient. Moreover, CNTs grown in anodized aluminum oxide nanopores in this low temperature process were found to exhibit unusually high field-emission current of 100 mA/cm(2) at 8 V/mu m. (c) 2006 American Institute of Physics.
Two-phased meta-heuristic methods for the post-mapping yield control problem
(2006-11-15)
Su, C. -T.
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Yang, C. -H.
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工業工程與管理學系
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Department of Industrial Engineering and Management
Yield control plays an important role in the TFT-LCD manufacturing firms, and the post-mapping operation is a crucial step. The post-mapping operation combines one TFT plate and one CF plate to form a LCD. Each TFT and CF plate is divided into a number of panels. The LCD panel is acceptable only when both TFT and CF panels are good. The TFT-LCD manufacturing firms use the sorter, a kind of robot, to increase the yield for matching TFT and CF plates. Evidently, there will be a great loss if a random mapping policy is executed. In this study, we first apply two of the most popular meta-heuristic methods to solve the post-mapping problem: Genetic Algorithm (GA) and Simulated Annealing ( SA). However, when the number of matched cassettes is large, the number of ways for choosing different matched objects will become so enormous that the initial population in GA ( or initial solution in SA) should be selected with a proper procedure. That is, we propose a two-phased GA and SA to improve the performance of the initial population. The basic concept of phase one is to generate an efficient initial population ( or initial solution). In phase one, the initial population is created based on the optimal solution to the cassette-matching problem. In phase two, we perform GA ( or SA) with the initial population created in phase one. The four different heuristic algorithms are tested for the same data to compare the various ports in the post-mapping yield control problem. The result shows that proposed two-phased algorithms provide a more excellent solution than GA and SA.