Browsing by Issue Date, starting with "2004-02-18"

Now showing 1 - 20 of 70646

Electronic transport in insulating AlPdRe quasicrystals
(2004-02-18)
Rosenbaum, R
;
Murphy, T
;
Brandt, B
;
Wang, CR
;
Zhong, YL
Resistivity and magnetoresistance measurements have been performed on insulating icosahedral AlPdRe quasicrystal (QC) bar samples. At temperatures in the range 300 K greater than or equal to T greater than or equal to 50 K, the resistivities follow a simple inverse temperature law: rho(T) rho(0)/T(1.0+/-0.1). Below 1 K, the resistivity of a weakly insulating sample exhibited a simple inverse temperature law where rho(T) = rho0/T-0.33 and not an activated variable-range hopping (VRH) law. Strongly insulating samples exhibit saturation of their resistivities to finite values as T --> 0 K. These saturation resistivity values are believed to arise from the presence of a second metallic phase located within the quasicrystal's structure. By extrapolating the measured resistivities at 22 mK to absolute zero, the saturation conductivity values were estimated at T = 0 K and subtracted from the conductivity data points. These 'corrected' data, corresponding only to the QC phase, were found to follow activated VRH laws, having hopping exponents y that vary in the range 0.18 less than or equal to y less than or equal to 0.43. The activated VRH behaviours are observed only below 1 K. The magnetoresistances (MRs) of these samples are also anomalous. The MRs can be explained by including contributions from both the saturation conductivity values and from the QC MR ratios, estimated using the wavefunction shrinkage model.
Double-layer networks with holographic optical switches
(2004-02-20)
Deng, JS
;
Lu, MF
;
Huang, YT
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The double-layer networks have the advantages of being strictly nonblocking and having a simpler routing algorithm, the lowest system insertion loss, a zero differential loss, fewer drivers, fewer interconnection lines, fewer crossovers, and the best signal-to-noise-ratio characteristic compared with any nondilated network. Using holographic optical switches to construct these networks not only eliminates all interconnection lines and crossovers but also reduces the number of drivers. (C) 2004 Optical Society of America.
Multi-port polarization-independent optical quasi-circulators by using a pair of holographic spatial- and polarization-modules
(2004-02-23)
Chen, JH
;
Hsieh, PJ
;
Su, DC
;
Su, JC
;
光電工程學系
In this paper we proposed an alternative type of multi-port polarization-independent optical quasi-circulator by using a pair of holographic spatial- and polarization-modules. The prototype is fabricated and experimentally tested. In addition, the operating principles, the characteristics and the performances of this device are discussed. The merits of this design include polarization-independence, compactness, high isolation, low polarization mode dispersion, and easy fabrication. Furthermore, the number of ports can be scaled up easily. (C) 2004 Optical Society of America.
Sub femto-joule sensitive single-shot OPA-XFROG and its application in study of white-light supercontinuum generation
(2004-02-23)
Zhang, JY
;
Lee, CK
;
Huang, JY
;
Pan, CL
;
光電工程學系
We report a new design of single-shot cross-correlation frequency-resolved optical gating (XFROG) with sub femto-joule sensitivity for complete field characterization of ultrashort optical pulse using a 400-nm-pumped type-I noncollinear optical parametric amplifier. Optical parametric gain as high as 10(8) with 0.8-0.9 femto-joules sensitivity had been demonstrated with an un-cooled CCD in this study. The experimental FROG traces have been successfully retrieved with an error no worse than 0.0014. The device had been to be useful for studying the generation mechanism of white-light supercontinuum (WLS). (C) 2004 Optical Society of America.
Comparisons of InP/InGaAlAs and InAlAs/InGaAlAs distributed Bragg reflectors grown by metalorganic chemical vapor deposition
(2004-02-25)
Lu, TC
;
Tsai, JY
;
Kuo, HC
;
Wang, SC
;
光電工程學系
Long wavelength vertical cavity surface emitting lasers (VCSELs) are considered the best candidates for the low cost reliable light emitters in fiber communications. The low refractive index contrast in the conventional InP-based lattice-matched distributed Bragg reflectors (DBRs), InP/InGaAsP, impeded the development of 1.3-1.5 mum VCSELs. However, the monolithic InP-based lattice-matched DBRs are still most attractive and desirable. The InP/InGaAlAs and InAlAs/InGaAlAs DBRs with larger refractive index contrast than the conventional InP/InGaAsP DBRs have been demonstrated recently. In this report, we compare these two material systems in terms of optical and electrical properties of DBRs. We found the InP/InGaAlAs DBRs have better electrical and optical properties, while the InAlAs/InGaAlAs DBRs have much lower growth complexity. (C) 2003 Elsevier B.V. All rights reserved.
Transport of exogenous surfactants on a thin viscous film within an axisymmetric airway
(2004-02-26)
Tsai, WT
;
Liu, LY
;
土木工程學系
;
Department of Civil Engineering
The transport of exogenous surfactant in an axisymmetric pulmonary airway lining is analyzed using the model based on lubrication theory to understand the parameters involved in surfactant replacement therapy for neonatal respiratory distress syndrome, including the ratio of film thickness-to-airway radius epsilon, and the initial exogenous and endogenous surfactant distributions. Numerical simulation of the model indicates that the film disturbance induced by Marangoni flow in low generation airways (small epsilon, such as trachea) would be more significant than that in high generation airways (large epsilon, such as bronchioles) for the same amount of instilled surfactant. The non-dimensional transport properties of the exogenous surfactant, however, are virtually identical in various airway generations considered. Increasing the initial local exogenous concentration enhances the surfactant transport and also intensifies the film disturbance. The presence of endogenous surfactant tends to moderate the shock-like film disturbance and also prolongs the extent of surfactant monolayer front. This, however, does not mean that the spread of exogenous surfactant is enhanced with the presence of endogenous surfactant. The extended monolayer is attributed to the compression of endogenous surfactant concentration in regions ahead of the advancing exogenous surfactant front. (C) 2003 Elsevier B.V. All rights reserved.
Orbital ordering in La0.5Sr1.5MnO4 studied by soft x-ray linear dichroism
(2004-02-27)
Huang, DJ
;
Wu, WB
;
Guo, GY
;
Lin, HJ
;
Hou, TY
We found that the conventional model of orbital-ordering of 3x(2)-r(2)/3y(2)-r(2) type in the e(g) states of La0.5Sr1.5MnO4 is incompatible with measurements of linear dichroism in the Mn 2p-edge x-ray absorption, whereas these e(g) states exhibit predominantly cross-type orbital ordering of x(2)-z(2)/y(2)-z(2). LDA+U band-structure calculations reveal that such a cross-type orbital-ordering results from a combined effect of antiferromagnetic structure, Jahn-Teller distortion, and on-site Coulomb interactions.
A novel algorithm for computing the 2D split-vector-radix FFT
(2004-03-01)
Huang, HY
;
Lee, YY
;
Lo, PC
;
電控工程研究所
;
Institute of Electrical and Control Engineering
This paper presents a novel two-dimensional split-vector-radix fast-Fourier-transform (2D svr-FFT) algorithm. The modularizing feature of the 2D svr-FFT structure enables us to explore its characteristics by identifying the local structural property. Each local module is designated as a DFT (non-DFT) block if its output corresponds to DFT (non-DFT) values. The block attribute (DFT or non-DFT) directs the algorithm to construct the local module. We will show that the distribution of DFT blocks can be illustrated by the Sierpinski triangle-a class of fractals generated by IFS (iterated function system). The finding of the Sierpinski-triangle structural property enables us to actually implement the 2D svr-FFT algorithm. To the best of our knowledge, the 2D svr-FFT has never been realized in software. The computational efficiency of the proposed algorithm is considerably improved in comparison with that provided by Matlab. (C) 2003 Elsevier B.V. All rights reserved.
Building an identifiable latent class model with covariate effects on underlying and measured variables
(2004-03-01)
Huang, GH
;
Bandeen-Roche, K
;
統計學研究所
;
Institute of Statistics
In recent years, latent class models have proven useful for analyzing relationships between measured multiple indicators and covariates of interest. Such models summarize shared features of the multiple indicators as an underlying categorical variable, and the indicators' substantive associations with predictors are built directly and indirectly in unique model parameters. In this paper, we provide a detailed study on the theory and application of building models that allow mediated relationships between primary predictors and latent class membership, but that also allow direct effects of secondary covariates on the indicators themselves. Theory for model identification is developed. We detail an Expectation-Maximization algorithm for parameter estimation, standard error calculation, and convergent properties. Comparison of the proposed model with models underlying existing latent class modeling software is provided. A detailed analysis of how visual impairments affect older persons' functioning requiring distance vision is used for illustration.
An innovative piston retractor for bicycle hydraulic disc braking systems
(2004-03-01)
Mao, YJ
;
Tseng, CH
;
機械工程學系
;
Department of Mechanical Engineering
Hydraulic disc brake systems offer various advantages over other braking systems, including a good heat dissipation rate, a high force enlargement ratio and a constant braking force in various environments. However, they have an important defect as the lining pads remain at a small clearance from the disc rotor, occasionally producing judder, noise and power loss when freely running. This study proposes an innovative piston retractor by utilizing the theory of innovative problem solving. The prototype is manufactured and installed in a commercial brake caliper. Experimental results are obtained and demonstrate the feasibility of applying the proposed design in a bicycle hydraulic disc braking system. Retraction performance of the proposed design is superior to a current product with a ring seal as its retractor and another product with a retractor that does not contain an automatic adjustment mechanism. The clearance between the lining pad and disc rotor is successfully kept at a larger value than these products regardless of the pad wear.
Genetic watermaking based on transform-domain techniques
(2004-03-01)
Shieh, CS
;
Huang, HC
;
Wang, FH
;
Pan, JS
;
電子工程學系及電子研究所
An innovative watermarking scheme based on genetic algorithms (GA) in the transform domain is proposed. It is robust against watermarking attacks, which are commonly employed in the literature. In addition, the watermarked image quality is also considered. In this paper, we employ GA for optimizing both the fundamentally conflicting requirements. Watermarking with GA is easy for implementation. We also examine the effectiveness of our scheme by checking the fitness function in GA, which includes both factors related to robustness and invisibility. Simulation results also show both the robustness under attacks, and the improvement in watermarked image quality with GA. (C) 2003 Pattern Recognition Society. Published by Elsevier Ltd. All rights reserved.
Generally applicable self-masked dry etching technique for nanotip array fabrication
(2004-03-01)
Hsu, CH
;
Lo, HC
;
Chen, CF
;
Wu, CT
;
Hwang, JS
Well-aligned nanotip arrays were fabricated by electron cyclotron resonance (ECR) plasma process using gas mixtures of silane, methane, argon, and hydrogen. The resultant tips have nanoscale apexes (similar to1 nm) with high aspect ratios (similar to50), which were achieved by simultaneous SiC nanomask formation and dry etching during ECR plasma process. This technique was applied to a variety of substrates such as silicon, polycrystalline silicon, gallium nitride, gallium phosphide, sapphire, and aluminum, indicating its general applicability. High-resolutiontransmission electron microscopy and Auger depth profile analyses revealed that the SiC cap, with Si:C ratio of 1:1, exhibited 3C-SiC and 2H-SiC structure on Si and GaP, respectively, with heteroepitaxial relationship. This one-step self-masked dry etching technique enables the fabrication of uniform nanotip arrays on various substrates over large area at low process temperatures, thereby demonstrating a high potential for practical industrial application.
Design and implementation of the SNMP agents for remote monitoring and control via UML and Petri nets
(2004-03-01)
Lee, JS
;
Hsu, PL
;
電控工程研究所
;
Institute of Electrical and Control Engineering
For large-scale find long-distance distributed systems, this paper proposes a systematical multiparadigm approach to develop the simple network management protocol (SNMP) agents for remote monitoring and control. The standard unified modeling language (UML) is adopted for modeling the system, and then the Petri-net model is applied to achieve both qualitative and quantitative analyses for the system's dynamic behavior. In real applications, the present design can be further implemented with Java and ladder diagrams on programmable logic controllers (PLC). The developed system has been used successfully in a mobile switching center (MSC) of Taiwan Cellular Corporation for the remote monitoring and control, through the Internet, of its environmental conditions, including the temperature, humidity, power, and security, with a total of 316 sensors and 140 actuators.
A new DLL-based approach for all-digital multiphase clock generation
(2004-03-01)
Chung, CC
;
Lee, CY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
A new DLL-based approach for all-digital multiphase clock generation is presented. By-using the time-to-digital converter (TDC) with fixed-step search scheme, the proposed all-digital and cell-based solution can overcome the false-lock problem in conventional designs. Furthermore, the proposed all-digital multiphase clock generator (ADMCG) can easily be ported to different processes in a short time. Thus, it can reduce the design time and design complexity in many different applications. The test chip shows that our proposal demonstrates a wide frequency range to meet the needs of many digital. communication applications.
Sensitivity analysis of the optimal management policy for a queuing system with a removable and non-reliable server
(2004-03-01)
Pearn, WL
;
Ke, JC
;
Chang, YC
;
工業工程與管理學系
;
Department of Industrial Engineering and Management
The management policy of an M/G/1 queue with a single removable and non-reliable server is considered. The decision-maker can turn the single server on at any arrival epoch or off at any service completion. It is assumed that the server breaks down according to a Poisson process and the repair time has a general distribution. Arrivals form a Poisson process and service times are generally distributed. In this paper, we consider a practical problem applying such a model. We use the analytic results of the queueing model and apply an efficient Matlab program to calculate the optimal threshold of management policy and some system characteristics. Analytical results for sensitivity analysis are obtained. We carry out extensive numerical computations for illustration purposes. An application example is presented to display how the Matlab program could be used. The research is useful to the analyst for making reliable decisions to manage the referred queueing system. (C) 2003 Elsevier Ltd. All rights reserved.
Nanoindentation investigation of amorphous hydrogenated carbon thin films deposited by ECR-MPCVD
(2004-03-01)
Han, SR
;
Fang, TH
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
Nanomechanical properties of amorphous hydrogenated carbon thin films are performed by nanoindentation technique. The amorphous hydrogenated carbon films are produced on silicon substrate by electron cyclotron resonance microwave plasma chemical vapor deposition (ECR-MPCVD). The effect of negative bias voltage on amorphous hydrogenated carbon films is examined by Raman spectroscopy and the results showed that the intensity ratio of D-peak to G-peak (I-D/I-G) of amorphous hydrogenated carbon films at various bias voltages, increased as the bias voltage increased. The results also showed that Young's modulus and hardness also increased as the bias voltage increased. In addition, Young's modulus and hardness both decreased as the indentation depth increased. (C) 2003 Elsevier B.V. All rights reserved.
A family of low-complexity blind equalizers
(2004-03-01)
Hwang, CI
;
Lin, DW
;
電子工程學系及電子研究所
;
電信研究中心
;
Department of Electronics Engineering and Institute of Electronics
Two important topics in equalizer design are its complexity and its training. We present a family of blind equalizers which, by incorporating a decomposition finite-impulse response filtering technique, can reduce the complexity of the convolution operation therein by about one half. The prototype algorithm in this equalizer family employs the prevalent Godard cost function. Several simplified algorithms are proposed, including a sign algorithm which eliminates multiplications in coefficient adaptation and a few delayed versions. We also study the convergence properties of the algorithms. For the prototype algorithm, we show that, in the limit of an infinitely long equalizer and under mild conditions on signal constellations and channel characteristics, there are only two sets of local minima on the performance surface. One of the sets is undesirable and is characterized by a null equalized channel response. The other corresponds to perfect equalization, which can be reached with proper equalizer initialization. For the simplified algorithms, corresponding cost functions may not exist. Some understanding of their convergence behaviors are obtained via examination of their adaptation equations. Simulation results are presented to demonstrate the performance of the algorithms.
可調整位元流大小的影像編解碼裝置
(2004-03-01)
黃項群
;
王俊能
;
蔣迪豪
;
杭學鳴
一種可調整位元流大小的影像編碼裝置，包含一基層編碼器和一加強層編碼器。經由比較原始影像與基層編碼器和加強層編碼器中具運動補償之預測影像產生運動補償差異影像。以滲漏預測和部份預測為基礎，在加強層建造高品質參考影像以改進時間上的預測。在高品質參考影像的建造中，參數β控制使用的加強層差異係數的位元平面數，而另一個參數α控制預測滲漏的量。空間的可調整大小模組允許基層和加強層處理的圖形具有相同或不同的空間解析度。
Evolutionary-based virtual training in extracting fuzzy knowledge for deburring tasks
(2004-03-01)
Su, SF
;
Horng, TJ
;
Young, KY
;
電控工程研究所
;
Institute of Electrical and Control Engineering
In this research, the problems of how to teach a robot to execute skilled operations are studied. Human workers usually accumulate their experience after executing the same task repetitively. In the process of training, a worker needs to find ways of adjusting his/her execution. In our system, the parameters for an impedance control scheme are considered as the targets for adjustment in the training process. The way to make adjustments is represented as a set of fuzzy rules in our research. Furthermore, a training scheme, called the evolutionary-based virtual training scheme, is proposed to extract knowledge (a set of fuzzy rules) for robotic deburring tasks. In this approach. an evolutionary algorithm is employed to find the best set of fuzzy rules and a simulation system is built to evaluate the execution performances of candidates. This learning scheme has been applied in finding a set of fuzzy rules that can adjust the parameters of impedance controllers required in deburring operations with satisfactory performance in deburring tasks.
Morphological, thermal, barrier and mechanical properties of LDPE/EVOH blends in extruded blown films
(2004-03-01)
Huang, CH
;
Wu, JS
;
Huang, CC
;
Lin, LS
;
應用化學系
We have investigated the morphological, thermal, barrier, and mechanical properties of low-density polyethylene/ethylenevinyl alcohol blend (LDPE/EVOH; 85/15 wt%) in highly and biaxially oriented blown films. Maleic anhydride-grafted linear low-density polyethylene (LDPE-g-MAH) in various concentrations (from 0 to 10 phr) was used as the compatibilizer for the immiscible system. Thermal analysis of the blend films shows that their melting temperatures, crystallization temperatures, and heats of fusion stay almost constant upon varying the amount of compatibilizer. The addition of the compatibilizer did not adversely affect the inherent properties of the blends, especially their barrier properties, through constraint effects of the grafted EVOH (EVOH-g-LD). The heat of fusion of EVOH obtained during the first heating is much higher than that of the second as a result of stress-induced crystallization during the blown film process. Oxygen permeation measurements show that the oxygen barrier properties of both highly and biaxially oriented blown films decrease upon increasing the amount of compatibilizer. although morphological analysis showed that the blends exhibit better laminar dispersion of the EVOH phase in the LDPE matrix when LDPE-g-MAH is added. The increase in oxygen permeability results from the presence of microvoids at the interface between the two phases during the process. Mechanical measurements showed that there exists an optimal amount of LDPE-g-MAH for maximizing both the tensile and tear properties in both the machine and transverse directions.