Browsing by Issue Date, starting with "2006-07-25"

Now showing 1 - 20 of 62980

Evaluating performance of post-tensioned steel connections with strands and reduced flange plates
(2006-07-25)
Chou, Chung-Che
;
Chen, Jun-Hen
;
Chen, Yu-Chih
;
Tsai, Keh-Chyuan
;
土木工程學系
The seismic performance of post-tensioned steel connections for moment-resisting frames was examined experimentally and analytically. Cyclic tests were conducted on three full-scale subassemblies, which had two steel beams post-tensioned to a concrete-filled tube (CFT) column with high-strength strands to provide recentring response. Reduced flange plates (RFPs) welded to the column and bolted to the beam flange were used to increase the dissipation of energy. Test results indicated that (1) the proposed buckling-restrained RFP could dissipate energy in axial tension and compression, (2) the subassemblies could reach an interstorey drift of 4% without strength degradation, and (3) buckling of the beam occurred towards an interstorey drift of 5%, causing a loss of the strand force, the recentring response, and the moment capacity. A general-purpose non-linear finite element analysis program (ABAQUS) was used to perform a correlation study. The behaviour of the steel beam under both post-tensioning and flexural loadings was compared to the test results and predictions. Copyright (C) 2006 John Wiley & Sons, Ltd.
Holder continuity for two-phase flows in porous media
(2006-07-25)
Yeh, Li-Ming
;
應用數學系
;
Department of Applied Mathematics
This work is to prove the Holder continuity of the solutions of the degenerate differential equations describing two-phase, incompressible, immiscible flows in porous media. The differential equations allow degeneracy at two end points and the assumption on mild degeneracy is not required in this study. The regularity result is proved by an alternative argument. Uniqueness of the weak solutions of the differential equations is a direct consequence from this Holder continuity. Copyright (C) 2006 John Wiley & Sons, Ltd.
Method for web content filtering
(2006-07-25)
Lin
;
Po-Ching
;
Lin
;
Ying-Dar
;
Liu
The present invention provides a method of web content filtering, which can be applied to gateway devices at client ends. When an access request for a web page from a browser is sent, by analyzing the web page content returned from the web site, we can decide whether the page is allowed or not, by early blocking and early bypassing algorithms. It allows making the decision as early as we have enough confidence that the web content should belong to some forbidden category or a normal one. Therefore, the web content determination speed can be improved and users' waiting time can be reduced. Moreover, by the present method, the network gateway devices will be allowed to analyze more web content.
Defect states investigation in poly(2-methoxy,5-(2 ' ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV)
(2006-07-26)
Nguyen, T. P.
;
Le Rendu, P.
;
Gaudin, O.
;
Lee, A. J. T.
;
Jackman, R. B.
in this study, application of the charge based Deep Level Transient Spectroscopy (Q-DLTS) has been extended to poly(2-methoxy,5-(2ethylhexyloxy)-1,4-phenylene vinylene) (MEH-PPV) single layer diodes, whose cathode consisted of aluminium and anode of indium tin oxide (ITO). The results reveal a broad Q-DLTS spectrum, with at least two maxima, consistent with a complex distribution of trap states. Only the Q-DLTS maximum with the shortest relaxation time could be fully resolved over the temperature range used here (100-300 K), yielding activation energies and capture cross sections in the ranges 0.3-0.4 eV and 10(-20) 10(-18) cm(2), respectively. It will be shown that this energy level is likely related to a majority-carrier (hole) trap, consistent with a Poole-Frenkel injection mechanism and p-type doping of the MEH-PPV film. The origin of the second (non-resolved) Q-DLTS peak will also be discussed. (c) 2005 Elsevier B.V. All rights reserved.
Sub-5-fs spectroscopy of a thiophene derivative with a quinoid structure
(2006-07-26)
Kobayashi, Takayoshi
;
Wang, Haibo
;
Wang, Zhuan
;
Otsubo, Tetsuo
;
電子物理學系
Sub-5-fs spectroscopy of a thiophene derivative with an electron donative and an acceptive moieties and quinoid structure provided the experimental evidence of dynamic mode coupling. It was shown that two out-of-plane bending modes mediate the dynamic mode coupling between 1469 and 1379 cm(-1) and between 1603 and 1469 cm(-1). These couplings are considered to be associated with geometrical relaxation relevant to the neutral bipolaron formation in all-s-trans polyacetylene. (c) 2006 Elsevier B.V. All rights reserved.
An adaptive bluetooth packet selection and scheduling scheme in interference environments
(2006-07-26)
Shih, Chen-Han
;
Wang, Kuochen
;
Shih, Hung-Cheng
;
資訊工程學系
;
Department of Computer Science
Bluetooth is a new technology for Wireless Personal Area Networks (WPANs). It intends to eliminate the need of wires and connectors between a variety of devices, like PCs and their peripherals, walkmans and their earphones, etc. Bluetooth provides robust and secure wireless radio communication of both data and voice, even when the devices are not within line-of-sight. Bluetooth employs the 2.4 GHz ISM band, sharing the same band with the Wireless LAN (WLAN) implementing the IEEE 802.11 series standard. While WLANs and WPANs are complementary rather than competing technologies, the likelihood of mutual interference may occur unexpectedly, which may impact the performance of either severely. In this paper, we propose a Bluetooth channel state dependent data segmentation and reassembly (CSD-SAR) scheme and a queue state dependent priority (QSD-PR) scheduling policy. The CSD-SAR maintains a receiving frequency table to predict channel conditions and selects the best packet type and packet size to transmit data. In this way, it not only masks bad frequencies without delaying transmission but also leads to the best performance with high link utilization in error-prone environments. In addition, the QSD-PR also uses the receiving frequency table to avoid bad frequencies and gives a selected master-slave pair, which has more queued data to send between each other, a higher priority to eliminate the wastage of slots. The conventional scheduling policy, Round Robin (RR), yields poor performance with the time division duplex based MAC protocol and results in slot wastage and may not ensure fairness. Simulation results show that our proposed scheme achieves better link utilization and higher throughput with bounded delay compared to the RR scheme in error-free and error-prone environments. Our scheme can also eliminate interference to other wireless networks that share the same spectrum, such as WLANs, by avoiding selecting channels occupied by other networks. (c) 2006 Elsevier B.V. All rights reserved.
Unified semiclassical theory for the two-state system: An analytical solution for general nonadiabatic tunneling
(2006-07-28)
Zhu, Chaoyuan
;
Lin, Sheng Hsien
;
應用化學系
;
應用化學系分子科學碩博班
;
Department of Applied Chemistry
Unified semiclasical solution for general nonadiabatic tunneling between two adiabatic potential energy surfaces is established by employing unified semiclassical solution for pure nonadiabatic transition [C. Zhu, J. Chem. Phys. 105, 4159 (1996)] with the certain symmetry transformation. This symmetry comes from a detailed analysis of the reduced scattering matrix for Landau-Zener type of crossing as a special case of nonadiabatic transition and nonadiabatic tunneling. Traditional classification of crossing and noncrossing types of nonadiabatic transition can be quantitatively defined by the rotation angle of adiabatic-to-diabatic transformation, and this rotational angle enters the analytical solution for general nonadiabatic tunneling. The certain two-state exponential potential models are employed for numerical tests, and the calculations from the present general nonadiabatic tunneling formula are demonstrated in very good agreement with the results from exact quantum mechanical calculations. The present general nonadiabatic tunneling formula can be incorporated with various mixed quantum-classical methods for modeling electronically nonadiabatic processes in photochemistry. (c) 2006 American Institute of Physics.
Confined breather-type excitation in a quinoidal thiophene after sub-5 fs pulse excitation
(2006-07-28)
Kobayashi, Takayoshi
;
Wang, Haibo
;
Wang, Zhuan
;
Otsubo, Tetsuo
;
電子物理學系
A quinoidal thiophene molecule which is a prototype of the repeated unit of s-trans-cis-polyacetylene was studied by sub-5 fs spectroscopy. A breatherlike mode modulation of both the amplitude and frequency of the C = C stretching was observed for the first time. It generates two sidebands of 2238 and 700 cm(-1) with a separation of 769 cm(-1) corresponding to the modulation frequency. The latter mode is very close to the C-S-C ring deformation, which indicate that this mode mediates coupling between the breather mode and the C-beta-C-beta stretching mode. It was also found that the breather-type excitation has a longer lifetime (2-3 ps) than in all-trans-polyacetylene (50 fs) due to its confinement. (c) 2006 American Institute of Physics.
Dynamic behaviors of dual frequency liquid crystals in bistable chiral tilted-homeotropic nematic liquid crystal cell
(2006-07-31)
Hsu, Jy-Shan
;
Liang, Bau-Jy
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Chen, Shu-Hsia
;
光電工程學系
;
Department of Photonics
The switching behaviors of dual frequency liquid crystals (DFLC) in a bistable chiral tilted-homeotropic nematic (BHN) LC cell are simulated and compared with the observed results. This cell can be switched between tilted-homeotropic state and twisted state under the applied voltage as low as 5 V. The reason for the low switching voltage is attributed to the dielectric anisotropy character of DFLC. The analysis also shows that the switching wave form accelerates the switching behaviors of the directors which results in faster response in BHN LC cell. (c) 2006 American Institute of Physics.
Regioselectivity in the 1,3-dipolar cycloaddition of adamantylidenefulvene and its modification by inclusion in cyclodextrins' solutions
(2006-07-31)
Chu, Jean-Ho
;
Li, Wan-Sheung
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Chao, Ito
;
Lee, Gene-Hsiang
;
Chung, Wen-Sheng
The 1,3-dipolar cycloaddition of adamantylidenefulvene (1) with 2 equiv of nitrile oxides 2a-d gave 1/1 cycloadducts, 3a-d and 4a-d, as the major products, and four other 1/2 minor cycloadducts 5-8a,b. The ratios of 1/1 cycloadducts 3a-d to 4a-d in THF solution were about 1/1 in the four different nitrile oxides 2a-d studied and microwave was found to accelerate the reactions and enhance their yields. It is noteworthy that the regioselectivity of 3a/4a was enhanced to 71/29 in beta-cyclodextrin (beta-CD) aqueous solution compared to that of 40/60 in the absence of P-CD. The regioselectivity of 3b/4b was further enhanced to 99/1 when 4-tert-butylphenyl hydroximinoyl chloride (9b) was complexed with beta-CD and then proceeded to react with 1; this is in sharp contrast with that of 33/67 in the absence of beta-CD. The binding constant of 1 center dot beta-CD in acetone-d(6)/D2O (1/1) was determined to be 188 +/- 9 M-1 by H-1 NMR titration experiments. The binding mode of 1 center dot beta-CD was further determined by ROESY experiment. Furthermore, molecular dynamic simulations were carried out to provide information of the complexation modes of 1 center dot beta-CD, 3a center dot beta-CD, 4a center dot beta-CD, 9a center dot beta-CD, and 9b center dot beta-CD. It was found that both steric and electrostatic effects play important roles in determining the regio- and stereochemistry of 1,3-dipolar cycloaddition of 1. Finally, beta-CD is shown to serve as a chiral shift reagent to differentiate the enantiomers of 4a in H-1 NMR. (c) 2006 Elsevier Ltd. All rights reserved.
Bandwidth enhancement phenomenon of a high-speed GaAs-AlGaAs based unitraveling carrier photodiode with an optimally designed absorption layer at an 830 nm wavelength
(2006-07-31)
Shi, Jin-Wei
;
Li, Yu-Tai
;
Pan, Ci-Ling
;
Lin, M. L.
;
Wu, Y. S.
In this letter, the authors introduce a GaAs/AlGaAs based unitraveling carrier photodiode (UTC-PD) for a wavelength of around 830 nm. There is significant bias- and output-current-dependent bandwidth enhancement phenomena observed with this device. According to their microwave and optical-to-electrical measurement results, such distinct phenomena can occur under a much lower current density (0.3 mA/mu m(2) vs 0.05 mA/mu m(2)) than previously reported for InP-InGaAs UTC-PDs. This can be attributed to the self-induced field in the absorption region, made possible due to the optimized p-type doping profile. (c) 2006 American Institute of Physics.
愛情萬歲
(2006-07-31)
梁玉芳
Highly efficient and stable inverted bottom-emission organic light emitting devices
(2006-07-31)
Chu, Ta-Ya
;
Chen, Jenn-Fang
;
Chen, Szu-Yi
;
Chen, Chao-Jung
;
Chen, Chin H.
The authors report the development of highly efficient and stable C545T doped green fluorescent Alq(3) inverted bottom-emission organic light emitting device (OLED), with a device configuration of ITO/Mg/Cs(2)O:Bphen/Alq(3)/C545T:Alq(3)/NPB/WO(3)/Al, that achieved a maximum current efficiency of 23.7 cd/A and a power efficiency of 12.4 lm/W which are two times better than those of the conventional OLED. At a brightness level of 100 cd/m(2), the device required driving current density only as low as 0.5 mA/cm(2) at a driving voltage of only 5.0 V and its half-lifetime T(1/2) in excess of 104 000 h. (c) 2006 American Institute of Physics.
Enhancing luminescence efficiency of InAs quantum dots at 1.5 mu m using a carrier blocking layer
(2006-07-31)
Hsieh, Tung-Po
;
Chiu, Pei-Chin
;
Chyi, Jen-Inn
;
Chang, Hsiang-Szu
;
Chen, Wen-Yen
The authors report an effective way to enhance the optical efficiency of InAs quantum dots (QDs) on GaAs emitting at the wavelength of 1.5 mu m. It is found that the loss of holes from QDs to their proximity via the high indium composition InGaAs overgrown layer, which is necessary for achieving long wavelength emission, is the origin of photoluminescence intensity degradation at high temperature. Inserting a 4 nm thick Al0.45Ga0.55As layer, acting as a carrier blocking layer, into the GaAs capping matrix can improve the room temperature photoluminescence peak intensity by five and two times for the ground and first excited states, respectively.
Formation of germanium nanocrystals embedded in silicon-oxygen-nitride layer
(2006-07-31)
Tu, Chun-Hao
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Chang, Ting-Chang
;
Liu, Po-Tsun
;
Liu, Hsin-Chou
;
Tsai, Chia-Chou
The formation of germanium nanocrystals embedded in silicon-oxygen nitride with distributed charge storage elements is proposed in this work. A large memory window is observed due to isolated Ge nanocrystals in the SiON gate stack layer. The Ge nanocrystals were nucleated after high temperature oxidized SiGeN layer. The nonvolatile memory with the Ge nanocrystals embedded in SiON stack layer exhibits 4 V threshold voltage shift under 10 V write operation. Also, the manufacture technology using the sequent high-temperature oxidation of the a-Si layer acting as the blocking oxide is proposed to enhance the performance of nonvolatile memory devices. (c) 2006 American Institute of Physics.
Stable inverted bottom-emitting organic electroluminescent devices with molecular doping and morphology improvement
(2006-07-31)
Chen, Szu-Yi
;
Chu, Ta-Ya
;
Chen, Jenn-Fang
;
Su, Chien-Ying
;
Chen, Chin H.
Stable inverted bottom-emitting organic light-emitting diodes (IBOLEDs) have been investigated by inserting n-type Cs2O dopant between indium-tin oxide bottom cathode and Alq(3), the combination of which not only improved the morphology of organic layer but enhanced the lifetime of the IBOLED. This n-type doped IBOLED achieved efficiencies of 5.2 cd/A and 2.0 lm/W at 20 mA/cm(2). The 20% decay lifetime (t(80)) of Cs2O doped IBOLED is 270 h which is about 1.7 times more stable than that of the conventional OLED (160 h) and 2.5 times of Li doped IBOLED (104 h). (c) 2006 American Institute of Physics.
Influence of a holey cladding structure on spectral characteristics of side-polished endlessly single-mode photonic crystal fibers
(2006-08-01)
Chen, Nan-Kuang
;
Chi, Sien
;
光電工程學系
;
光電工程研究所
;
Department of Photonics
We experimentally investigate the spectral characteristics of side-polished endlessly single-mode photonic crystal fibers of different polishing depths and radii of curvature that are important to mode field diameter. evanescent coupling, waveguide losses, higher-order mode excitation, and dispersion slopes of photonic crystal fiber components. A polished photonic crystal fiber with a greater polishing depth or a larger radius of curvature shows a more dispersive characteristic. In contrast to conventional single-mode fibers, in photonic crystal fibers the evanescent field is more strongly localized, and the propagating light can be more efficiently guided within the deformed core. (c) 2006 Optical Society of America
Hafnium silicate nanocrystal memory using sol-gel-spin-coating method
(2006-08-01)
You, Hsin-Chiang
;
Hsu, Tze-Hsiang
;
Ko, Fu-Hsiang
;
Huang, Jiang-Wen
;
Lei, Tan-Fu
The authors fabricate the hafnium silicate nanocrystal memory for the first time using a very simple sol-gel-spincoating method and 900 degrees C 1-min rapid thermal annealing (RTA). From the TEM identification, the nanocrystals are formed as the charge trapping layer after 900 degrees C 1-min RTA and the size is about 5 mn. They demonstrate the composition of nanocrystal is hafnium silicate from the X-ray-photoelectron-spectroscopy analysis. They verify the electric properties in terms of program/erase (P/E) speed, charge retention, and endurance. The sol-gel device exhibits the long charge retention time of 10(4) s with only 6% charge loss, and good endurance performance for P/E cycles up to 10(5).
Process for fabricating supersphere solid immersion lens
(2006-08-01)
Hsu
;
Wensyang
;
Sun
;
Yi-Ting
The present invention relates to process for fabricating supersphere solid immersion lens (SSIL). The procedure of the present invention comprises the steps of: firstly, coating a positive photoresist layer on a substrate, followed by first exposure and second exposure with different exposure dose separately by first mask and second mask to form the positive photoresist structure with different dimensions and depths. The first exposure dose is supplied enough to make sure the patterns of the first mask can be observed on the positive photoresist layer during the alignment of the second exposure process. And the following reflow process forms a supersphere solid immersion lens (SSIL) structure.
Simulation for optimization of mask error enhancement factor by design of experiments in both dry and immersion ArF lithography
(2006-08-01)
Yeh, Kwei-Tin
;
Lin, Chih-Hung
;
Hu, Ji-Ren
;
Loong, Wen-An
;
應用化學系
Simulations for the optimization of the mask error enhancement factor (MEEF) by using Taguchi's design of experiment (DOE) method in both dry and immersion ArF lithography have been demonstrated here. By DOE, MEEF has been successfully reduced, and the process window hash also been enlarged. Furthermore, in immersion lithography, MEEF has been significantly reduced, and resolution is also enhanced. In this study, we determined the optimal process and optical parameters to enlarge the process window and reduce MEEFs for different types of mask by DOE.