Browsing by Issue Date, starting with "2007-08-24"

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Metallo-homopolymer and metallo-copolymers containing light-emitting poly (fluorene/ethynylene/(terpyridyl)zinc (II)) backbones and 1,3,4-oxadiazole (OXD) pendants
(2007-08-24)
Chen, Yi-Yu
;
Lin, Hong-Cheu
;
材料科學與工程學系
;
Department of Materials Science and Engineering
A series of novel metallo-polymers containing light-emitting poly(fluorene/ethynylene/(terpyridyl)zinc(II)) backbones and electrontransporting 1,3,4-oxadiazole (OXD) pendants (attached to the C-9 position of fluorene by long alkyl spacers) were synthesized by self-assembled reactions. The integrated ratios of H-1 NMR spectra reveal a facile result to distinguish the well-defined main-chain metallo-polymeric structures which were constructed by different monomer ligand systems (i.e. single, double, and triple monomer ligands with various pendants). Furthermore, UV-vis and photoluminescence (PL) spectral fitration experiments were carried out to verify the metallo-polymeric structures by varying the molar ratios of zinc(II) ions to monomers. As a result, the enhancement of thermal stability (T-d) and quantum yields were introduced by the metallo-polymerization, and their physical properties were mainly affected by the nature of the pendants. The photophysical properties of these metallo-polymers exhibited blue PL emissions (around 418 nm) with quantum yields of 34-53% (in DMF). In contrast to metallo-polymers containing alkyl pendants, the quantum yields were greatly enhanced by introducing 1,3,4-OXD pendants but reduced by carbazole (CAZ) pendants. Moreover, electrolumineseent (EL) devices with these light-emitting metallo-polymers as emitters showed green EL emissions (around 550 nm) with turn-on voltages of 6.0-6.5 V, maximum efficiencies of 1.05-1.35 cd A(-1) (at 100 mA/cm(-2)), and maximum luminances of 2313-3550 cd/m(2) (around 15 V), respectively. (c) 2007 Elsevier Ltd. All rights reserved.
Intramolecular Diels-Alder reaction of 2-diphenylphosphinyl-5-(propargyloxymethyl)furans followed by nucleophilic 1,2-rearrangement of the phosphinyl group
(2007-08-27)
Wu, Hsien-Jen
;
Liu, Chuan-Fang
;
Wang, Zhongyi
;
Lin, Hui-Chang
;
應用化學系
The base-catalyzed intramolecular Diels-Alder reactions of 2-diphenylphosphinyl-5-(propargyloxymethyl)furans 2a-e gave the tetrahydrofuran ring annulated o-diphenylphosphinophenols 3a-e in 70-80% yields, a novel reaction involving an intramolecular Diels-Alder reaction of furan diene with allenyl ether dienophile followed by a nucleophilic 1,2-rearrangement of the diphenylphosphinyl group. (C) 2007 Elsevier Ltd. All rights reserved.
Current injection and transport in polyfluorene
(2007-08-27)
Yang, Chieh-Kai
;
Yang, Chia-Ming
;
Liao, Hua-Hsien
;
Horng, Sheng-Fu
;
Meng, Hsin-Fei
A comprehensive numerical model is established for the electrical processes in a sandwich organic semiconductor device with high carrier injection barrier. The charge injection at the anode interface with 0.8 eV energy barrier is dominated by the hopping among the gap states of the semiconductor caused by disorders. The Ohmic behavior at low voltage is demonstrated to be not due to the background doping but the filaments formed by conductive clusters. In bipolar devices with low work function cathode it is shown that near the anode the electron traps significantly enhance hole injection through Fowler-Nordheim tunneling, resulting in rapid increases of the hole carrier and current in comparison with the hole-only devices. (c) 2007 American Institute of Physics.
Nano-ferrosponges for controlled drug release
(2007-08-28)
Hu, Shang-Hsiu
;
Liu, Ting-Yu
;
Liu, Dean-Mo
;
Chen, San-Yuan
;
材料科學與工程學系
Magnetic sponge-like hydrogels (ferrosponges) were fabricated by using an in-situ synthesis of magnetic nanoparticles (MNPs) in the presence of various concentrations of gelatin. The resulting ferrosponges show an interconnected nanopore structure which serves as a reservoir to accommodate therapeutic drugs and the nanoporous networks demonstrate magnetic sensitive behavior under the application of magnetic field. The ferrosponges showed high swelling ratios, together with excellent elasticity and hydrophilicity, allow them to response rapidly to an external magnetic stimulation for fast and repeatable swelling-deswelling (or expansion-contractile) operations. The ferrosponges with lower gelatin concentration exhibited good performance on magnetification. Furthermore, drug release from the ferrosponges is relatively magnetic-sensitive and is dominated by its magnetism and associated interaction between the magnetic nanoparticle and the gelatin matrix under an external magnetic field. Higher MNPs concentration in the ferrosponges exhibited higher degree of magnetic sensitive which is due to stronger interparticle forces. By taking these peculiar magnetic sensitive behaviors of the ferrosponges, a novel drug delivery system can be designed for medical uses. (C) 2007 Elsevier B.V. All rights reserved.
Algorithm for a memory-based Viterbi decoder
(2007-08-28)
Lee
;
Chen-Yi
;
Lin
;
Chien-Ching
;
Wu
A method of convolutional decoding with a memory-based Viterbi decoder employs the property of a trace-back path; that is, the similarity between two consecutive trace-back paths becomes higher as the data error rate goes down. Therefore, the method of the invention saves the previous trace-back path into a register, and as soon as the current trace-back path is found to be the same as the previous one, the demanded path is obtained. After that, the memory read operations will stop, thereby reducing the power consumption caused by memory read operations. Prior to path trace-back, the path prediction can be executed by utilizing the property that the minimum path metric and the path are consecutive. The invention reduces the number of memory access operations and power consumption by employing the mechanisms of path matching and path prediction.
Highly integrated automotive radar sensor
(2007-08-31)
Cheng, G. F.
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Ho, H.
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Wang, W. T.
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Chang, C. Y.
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Chung, S. J.
The design and measured results of the developed radar sensor for automotive applications are presented. The radar sensor is highly integrated with the transceiver module, antenna and baseband circuits. The proposed antenna is composed of a novel microstrip-line-fed hom antenna and a quasi-optic lens antenna.
Monolithic integration of well-ordered nanoporous structures in the microfluidic channels for bioseparation
(2007-08-31)
Kuo, Chiung-Wen
;
Shiu, Jau-Ye
;
Wei, Kung Hwa
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Chen, Peilin
;
材料科學與工程學系
Gel electrophoresis and capillary gel electrophoresis are widely used for the separation of biomolecules. With increasing demand in the miniaturized devices such as lab-on-a-chip, it is necessary to integrate such a separation component into a chip format. Here, we describe a simple approach to fabricate robust three-dimensional periodic porous nanostructures inside the microchannels for the separation of DNA molecules. In our approach, the colloidal crystals were first grown inside the microchannel using evaporation assisted self-assembly process. Then the void spaces among the colloidal crystals were filled with epoxy-based negative tone photoresist (SU-8). UV radiation was used to cure the photoresist at the desired area inside the microchannel. After subsequent development and nanoparticle removal, the well-ordered nanoporous structures inside the microchannel were obtained. Our results indicated that it was possible to construct periodic porous nanostructures inside the microchannels with cavity size around 300 nm and interconnecting pores around 30 nm. The mobility of large DNA molecules with different sizes was measured as a function of the applied electric field in the nanoporous materials. It was also demonstrated that I kilo-base pair (kbp) DNA ladders could be separated in such an integrated system within 10 min under moderate electric field. (c) 2007 Published by Elsevier B.V.
Evaluating the supply chain performance of IT-based inter-enterprise collaboration
(2007-09-01)
Chen, Mu-Chen
;
Yang, Taho
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Li, Hsin-Chia
;
運輸與物流管理系註：原交通所+運管所
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Department of Transportation and Logistics Management
With the use of IT, the nature of business processes has changed from intra- to cross-enterprise. This has significantly altered enterprise interactions with suppliers and customers. Collaboration is essential for successful supply chain performance. In recent years a variety of initiatives have been adopted by industries. These attempted to create efficiency and effectiveness through integration of the activities and processes. However, enterprises can only gain significant benefits by mass collaboration. Collaborative Planning, Forecasting and Replenishment (CPFR), which result in deeper partnerships, have become an important factor in supply chains. We investigated the performance of CPFR; it possesses formalized guidelines and is a relatively new initiative. By using simulation, we investigated four CPFR alternatives that are used in the adoption of collaboration strategies in industries. Retailers have traditionally played the hub role in supply chains in order to reduce the bullwhip effect, but our simulation confirmed that shifting the retailer (buyer-driven) collaboration to a manufacturer (supplier-driven) approach was a more viable option. (C) 2007 Elsevier B.V. All rights reserved.
Entanglement detection via the condition of quantum correlation
(2007-09-01)
Li, Che-Ming
;
Hsu, Li-Yi
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Chen, Yueh-Nan
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Chuu, Der-San
;
Brandes, Tobias
We develop a necessary condition of quantum correlation. It is utilized to construct a d-level bipartite Bell-type inequality which is strongly resistant to noise and requires only analyses of O(d) measurement outcomes compared to the previous result O(d(2)). Remarkably, a connection between the arbitrary high-dimensional bipartite Bell-type inequality and entanglement witnesses is found. Through the necessary condition of quantum correlation, we propose that the witness operators to detect truly multipartite entanglement for a generalized Greenberger-Horne-Zeilinger (GHZ) state with two local measurement settings and a four-qubit singlet state with three settings. Moreover, we also propose a robust entanglement witness to detect a four-level tripartite GHZ state with only two local measurement settings.
Interaction of AC magnetic field with Josephson vortices in high anisotropy superconductors Bi2212 and Bi2223
(2007-09-01)
Shaltiel, D.
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von Nidda, H.-A. Krug
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Shapiro, B. Ya.
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Shapiro, I.
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Loidl, A.
We show that in both high anisotropy superconductors Bi2212 (T-c = 90 K), and Bi2223 (T-c = 110 K), an AC magnetic field applied collinear to the DC field and parallel to the Cu layers induces strong microwave dissipation. It is theoretically predicted that the Josephson solitons are responsible for this absorption. Good qualitative agreement of experimental data with theoretical predictions is found. Differences observed in the experimental results between these two compounds are discussed. (c) 2007 Elsevier B.V. All rights reserved.
An innovative understanding of metal-insulator-metal (MIM)-capacitor degradation under constant-current stress
(2007-09-01)
Hung, Chi-Chao
;
Oates, Anthony S.
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Lin, Horng-Chih
;
Chang, Yu-En Percy
;
Wang, Jia-Lian
This paper provides a new understanding of metal-insulator-metal-capacitor-degradation behavior under a wide range of constant-current-stress conditions. It was found that capacitance degrades with stress, but the behavior of the degradation strongly depends on the stress-current density. At high stress levels, the capacitance increases logarithmically as the injection charge increases until dielectric breakdown occurs. At lower stress conditions, the degradation rate is proportional to the stress current and reverses after a certain period of time. A metal-insulator interlayer is observed using cross-sectional transmission-electron-microscopy micrographs, which possibly explains this reversal phenomenon.
A cross-layer investigation for the throughput performance of CSMA/CA-Based WLANs with directional antennas and capture effect
(2007-09-01)
Wang, Li-Chun
;
Chen, Anderson
;
Huang, Shi-Yen
;
電信工程研究所
;
Institute of Communications Engineering
In this paper, we develop a physical/medium-access-control (PHY/MAC) cross-layer analytical model to investigate the throughput performance of the wireless local-area network (WLAN) in a lossy wireless environment. From the PHY-layer perspective, the developed model incorporates the effects of capture and directional antennas, while from the MAC-layer perspective, our approach takes into account the carrier-sense multiple access with collision-avoidance (CSMA/CA) MAC protocol and the effect of the backoff process in the IEEE 802.11 WLAN. We derive explicit analytical expressions for the frame outage and capture probabilities of a directional antenna system in the presence of shadowing and Rayleigh fading. Applying this analysis, we can model the interaction between the PHY and MAC layers more accurately for the infrastructure-based WLAN. The numerical results show that our analytical model can approach that attained by simulations. The proposed cross-layer analytical model not only provides insights into the PHY layer impacts on the throughput of the CSMA/CA MAC protocol but also indicates to how directional antennas can improve the CSMA/CA-based WLAN in terms of antenna beamwidth and the number of radio transceivers.
Specific heat of Mn-doped NaxCoO2 center dot yH(2)O
(2007-09-01)
Lin, J.-Y.
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Chen, Y.-J.
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Liu, C.-J.
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Wang, J.-S.
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Sun, C. P.
C(T) of NaxCo0.99Mn0.01O2 center dot yH(2)O is studied to reveal more details on the nature of the doped Mn ions and the T-c suppression. The extra specific heat contribution in NaxCo0.99Mn0.01O2 center dot yH(2)O manifests the induced local magnetic moment due to Mn doping. The absence of the superconducting transition peak in C(T) of NaxCo0.99Mn0.01O2 center dot yH(2)O suggests a reduced superconducting volume fraction. (C) 2007 Elsevier B.V. All rights reserved.
Study of the gate-sensing and channel-sensing transient analysis method for monitoring the charge vertical location of SONOS-type devices
(2007-09-01)
Du, Pei-Ying
;
Lue, Hang-Ting
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Wang, Szu-Yu
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Lai, Erh-Kun
;
Huang, Tiao-Yuan
The gate-sensing and channel-sensing transient analysis method is studied in detail. This method introduces an additional gate-sensing capacitor to be compared with the conventional channel-sensing one. Sensing in both modes provides two equations that are suitable to solve for two variables-the charge density (Q) and the average charge vertical location (x). In this paper, the principle of this method is discussed in detail. Several factors that affect the measurement accuracy are also analyzed. The power of this method is demonstrated by program/erase cycling and data retention tests. This method is indeed a powerful tool for detailed understanding of trapping dynamics.
Efficient support for content-aware request distribution and persistent connection in Web clusters
(2007-09-01)
Liu, Ho-Han
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Chiang, Mei-Ling
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Wu, Men-Chao
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資訊工程學系
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Department of Computer Science
To support Web clusters with efficient dispatching mechanisms and policies, we propose a light-weight TCP connection transfer mechanism, TCP Rebuilding, and use it to develop a content-aware request dispatching platform, LVS-CAD, in which the request dispatcher can extract and analyze the content in requests and then dispatch each request by its content or type of service requested. To efficiently support HTTP/1.1 persistent connection in Web clusters, request scheduling should be performed per request rather than per connection. Consequently, multiple TCP Rebuilding, as an extension to normal TCP Rebuilding, is proposed and implemented. On this platform, we also devise fast TCP module handshaking to process the handshaking between clients and the request dispatcher in the IP layer instead of in the TCP layer for faster response times. Furthermore, we also propose content-aware request distribution policies that consider cache locality and various types of costs for dispatching requests in this platform, which makes the resource utilization of Web servers more effective. Experimental results of a practical implementation on Linux show that the proposed system, mechanisms, and policies can effectively improve the performance of Web clusters. Copyright (C) 2007 John Wiley & Sons, Ltd.
Dynamics of disordered type-II superconductors: Peak effect and the I-V curves
(2007-09-01)
Bel, G.
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Li, D. P.
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Rosenstein, B.
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Vinokur, V.
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Zhuravlev, V.
We quantitatively describe the competition between the thermal fluctuations and disorder by the Ginzburg-Landau approach using both the replica method in statics and the dynamical Martin-Siggia-Rose approach which allows generalization beyond linear response. The two methods are consistent in static, while the dynamical method allows calculation of the critical current as function of magnetic field and temperature. The surface in the J-B-T space defined by this function separates between a dissipative moving vortex matter regime and vortex glass. The non-Ohmic I-V curve is obtained. (c) 2007 Elsevier B.V. All rights reserved.
Optimal design of resonant piezoelectric buzzer from a perspective of vibration-absorber theory
(2007-09-01)
Bai, Mingsian R.
;
Chen, Rong-Liang
;
Chuang, Chung-Yuan
;
Yu, Cheng-Sheng
;
Hsieh, Huey-Lin
In this paper, an optimization technique is presented for the design of piezoelectric buzzers. This design technique aims at finding the optimal configuration of the coupled cavity and diaphragm structure to maximize the sound pressure output. Instead of measuring the material constants of the piezoelectric ceramic and the metal diaphragm, an "added-mass method" is developed to estimate the equivalent electromechanical parameters of the system on which an analogous circuit can be established. The electrical impedance and on-axis sound pressure level of the piezoelectric buzzer can be simulated by solving the loop equations of the electromechanoacoustical analogous circuit. An interesting finding of this research is that the nature of the piezoelectric buzzer bears remarkable resemblance to that in the dynamic vibration absorber theory. Much physical insight can be gained by exploiting this resemblance in search of the optimal configuration. According to the system characteristic equation, a design chart was devised to "lock" the critical frequency at which the system delivers the maximal output. On the basis of the analogous circuit and the vibration absorber theory, an optimal design was found with constrained optimization formalism. Experiments were conducted to justify the optimal design. The results showed that the performance was significantly improved using the optimal design over the original design. Design guidelines for the piezoelectric buzzers are summarized. (c) 2007 Acoustical Society of America.
The nanocomposite thin film applied to high-density write-once optical data storage
(2007-09-01)
Mai, Hung-Chuan
;
Hsieh, Tsung-Eong
;
材料科學與工程學系
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Department of Materials Science and Engineering
This work demonstrates the feasibility of producing composite thin films containing nano-scale recording particles for highdensity optical data storage. The nanocomposite recording layers were found to exhibit an ultrafast transition rate and a unique phase transition temperature compared with the bilayer recording systems. For type I disk samples containing a nanocomposite recording layer and a Ag reflection layer, modulations higher than 0.8 and 0.5 could be achieved when I IT and 4T signals were respectively written into the disk samples using a blue-laser dynamic tester. As for type 11 disk samples containing a sole nanocomposite recording layer, modulations better than 0.8 and 0.6 were obtained. Transmission electron microscopy (TEM) characterization attributed the main signal recording mechanism to the coalescence and coarsening of nano-recording particles, which, in turn, implies a sufficient reflectivity difference for signal readout. The reactions and/or redistribution of elements involved in the layer structure of optical disks also contributed to the signal recording. The nanocomposite recording layer provides various advantages including a fast phase transition rate, initialization-free, disk structure simplification, and a sputtering-compatible fabrication process and thus, promising applications to next-generation write-once optical data storage are expected.
High-power single-mode submonolayer quantum-dot photonic crystal vertical-cavity surface-emitting lasers
(2007-09-01)
Lai, Fang-I.
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Yang, H. P. D.
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Lin, G.
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Hsu, I. -Chen
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Liu, Jui-Nung
A high-power, wide operation-range single-fundamental-mode InGaAs submonolayer (SML) quantum dot (QD) photonic crystal vertical-cavity surface-emitting laser (VCSEL) for fiber-optic applications was demonstrated. Single-fundamental-mode with a threshold current (I-th) of 0.9 mA and maximum continue-wave (CW) output power of 3.8 mW at 28 mA has been achieved in the 990 nm range. A side-mode suppression ratio (SMSR) larger than 35 dB has been observed over the entire current operating range. The far field measurement shows that the beam divergence angle remains very small and almost unchanged between 6.7-6.9 degrees, with the operation range increasing from 3 to 20 mA.
The effects of group composition of self-efficacy and collective efficacy on computer-supported collaborative learning
(2007-09-01)
Wang, Shu-Ling
;
Lin, Sunny S. J.
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教育研究所
;
Institute of Education
Although research has suggested that group composition plays an important role in collaborative learning, the role of motivation in group composition has rarely been taken into account. This study investigates the effects of group composition of self-efficacy (e.g. low, high, and mixed self-efficacy) on group motivation (i.e. collective efficacy), collaborative learning behavior, and performance in a computer-supported collaborative learning environment. The results indicate that high self-efficacy groups have higher collective efficacy beliefs than low self-efficacy groups. Furthermore, high self-efficacy groups use more high-level cognitive skills during group discussion than low self-efficacy groups, despite no significant difference in usage of lowlevel cognitive skills among the three groups. This study also demonstrates that collective efficacy has positive effects on discussion behaviors and group performance. Students with higher collective efficacy not only use more high-level cognitive skills in group discussion, but also demonstrate better academic performance. Our research further indicates that students' use of high-level cognitive skills in group discussion has positive effects on group performance. Finally, implications and suggestions for future research are also provided. (c) 2006 Elsevier Ltd. All rights reserved.