Browsing by Issue Date, starting with "1996-03-30"

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Two-dimensional elastodynamic transient analysis by QL time-domain BEM formulation
(1996-03-30)
Wang, CC
;
Wang, HC
;
Liou, GS
;
土木工程學系
;
Department of Civil Engineering
A quadratic time-domain Boundary Element Method (BEM) for two-dimensional (2-D) elastodynamic transient wave analysis is presented. Emphasis is focused on developing time-domain fundamental convoluted kernels and methodology for quadratic temporal solution procedure which are never presented before. In the presented BEM method, the displacement temporal variation is assumed to be quadratic, the traction temporal variation is assumed to be linear (called QL method, a two-time-step piecewise continuity method), and the spatial variations are assumed to be quadratic variation. The QL method is compared with the LC method and the QC method by solving several example problems. Numerical study reveals that the QC and QL methods are more accurate and stable than the LC method, and the QL method is much better than the QC method for transient problems.
個性書店
(1996-03-30)
不詳
謁陵．感懷
(1996-03-31)
管管
謁陵．感懷
(1996-03-31)
管管
謁陵．感懷
(1996-03-31)
管管
謁陵．感懷
(1996-03-31)
管管
Derivation of the Glover-Doyle algorithms for general H-infinity control problems
(1996-04-01)
Hong, JL
;
Teng, CC
;
電控工程研究所
;
Institute of Electrical and Control Engineering
We show that the Glover-Doyle algorithm can be formulated simply by using the (J,J')-lossless factorization method and chain scattering matrix description. This algorithm was first stated by Glover and Doyle in 1988. Because the corresponding diagonal block of the (J,J')lossless matrix in the general 4-block H-infinity control problem of the Glover-Doyle algorithm is not square, a new type of chain scattering matrix description is developed. With this description in hand, we obtain two types of state-space solution, which are similar to each other. Thus a similarity transformation between these solutions in the 4-block H-infinity control problem can also be obtained. The main idea of the solution is illustrated by means of block diagrams.
Synthesis of novel tetraacetal oxa-cage compounds from 2-methylthiofurans
(1996-04-01)
Lin, CC
;
Huang, FJ
;
Lin, JC
;
Wu, HJ
;
交大名義發表
Several novel tetraacetal oxa-cage compounds 9a-9f were synthesized from the corresponding 2-methylthiofurans 1a-1f by a short sequence. The structures of these tetraoxa-cage compounds were deduced from their spectral data and proven by X-ray analysis of 9a. Ozonolysis of the endo adducts 5a-5f in CH2Cl2 at -78 degrees C followed by reduction with dimethyl sulfide gave the tetraoxa-cages 9a-9f in 65-75% yields, respectively. Ozonolysis of the exo adduct 6a under the same reaction conditions gave the tetracarbonyl compound 10. The phenylthio group substituted tetraoxa-cage 13 and the tetraacetal oxa-cage 17, with one more carbon atom on the apex position, were also synthesized in a similar sequence.
New nonlinear algorithms for estimating and suppressing narrowband interference in DS spread spectrum systems
(1996-04-01)
Wu, WR
;
Yu, FF
;
交大名義發表
;
電信工程研究所
;
National Chiao Tung University
It has been shown that the narrow-band (NB) interference suppression capability of a direct-sequence (DS) spread spectrum system can be enhanced considerably by processing the received signal via a prediction error filter, The conventional approach to this problem makes use of a linear filter. However, the binary DS signal, that acts as noise in the prediction process, is highly non-Gaussian, Thus, linear filtering is not optimal, Vijayan and Poor [11] first proposed using a nonlinear approximate conditional mean (ACM) filter of the Masreliez type and obtained significant results, This paper proposes a number of new nonlinear algorithms, Our work consists of three parts, 1) We develop a decision-directed Kalman (DDK) filter, that has the same performance as the ACM filter but a simpler structure, 2) Using the nonlinear function in the ACM and the DDK filters, we develop other nonlinear least mean square (LR IS) filters with improved performance, 3) We further use the nonlinear functions to develop nonlinear recursive least squares (RLS) filters that can be used independently as predictors or as interference identifiers so that the ACM or the DDK filter can be applied, Simulations show that our nonlinear algorithms outperform conventional ones.
An efficient construction of perfect secret sharing schemes for graph-based structures
(1996-04-01)
Sun, HM
;
Shieh, SP
;
資訊工程學系
;
Department of Computer Science
In this paper, we propose an efficient construction of perfect secret sharing schemes for graph-based access structures where a vertex denotes a participant and an edge does a qualified pair of participants. The secret sharing scheme is based on the assumptions that the pairs of participants corresponding to edges in the graph can compute the master key but the pairs of participants corresponding to nonedges in the graph cannot. The information rate of our scheme is 1/(n-1), where n is the number of participants. We also present an application of our scheme to the reduction of storage and computation loads on the communication granting server in a secure network.
On efficiency and optimization of C++ programs
(1996-04-01)
Wu, PC
;
Wang, FJ
;
交大名義發表
;
資訊工程學系
;
National Chiao Tung University
The efficiency of object-oriented programs has become a point of great interest, One necessary factor for program efficiency is the optimization techniques involved. This paper presents the performance of several variations of a given C++ program and compares them with a version that uses no object-oriented features, Our result indicates that some object-oriented features in C++ are not well optimized in current C++ compilers. We thus discuss some code optimization techniques that can improve the efficiency based on the given C++ program.
Dynamic range and switching speed limitations of an NxN optical packet switch based on low-gain semiconductor optical amplifiers
(1996-04-01)
Tai, C
;
Way, WI
;
交大名義發表
;
光電工程學系
;
National Chiao Tung University
Two important system performance limitations-dynamic range and switching speed-of an integrated packet switch fabric based on low-gain semiconductor optical amplifiers (SOA's) have been examined by using cascaded blocks of an SOA model, which includes transient effect, nonlinear pulse distortion effect, and amplified spontaneous emission (ASE) noise, Low-gain SOA's were used to minimize ASE noise considering that no optical filters can be integrated in an SOA-based switch fabric, The system performance with and without a narrowband optical filter at the receiver were both studied, By assuming fixed wavelength transmitters and no optical filter can be used at the receiving end owing to the unpredictability of arriving packet wavelengths, our simulation results indicate that the dynamic ranges of 4 x 4 and 8 x 8 SOA-based packet switches at 2.5 Gb/s can only be about 3.2 and 0.8 dB, respectively, However, at 155 Mb/s, even without a receiving-end optical filter, the dynamic range of each switch size can be increased by more than 17 dB as compared to the cases of 2.5 Gb/s, Note that the dynamic ranges were estimated under the conditions of a bit error rate (BER) less than or equal to 10(-9) and a pulse distortion ratio less than or equal to 30%. We have also shown that, when an optical filter with a 1 nm bandwidth was used at the receiving end to simulate 1) a circuit-switched condition where the center wavelength of the filter can be adjusted according to the established circuit, or 2) a packet-switched condition where each receiver has a wavelength demultiplexer and a detector array, the dynamic range of 4 x 4 and 8 x 8 switches can be increased to 16.3 and 14 dB, respectively, at 2.5 Gb/s.
Complementary-LVTSCR ESD protection circuit for submicron CMOS VLSI/ULSI
(1996-04-01)
Ker, MD
;
Wu, CY
;
Chang, HH
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
There are one LVTSCR device merged with short-channel NMOS and another LVTSCR device merged with short-channel PMOS in complementary style to offer effective and direct ESD discharging paths from the input or output pads to VSS and VDD power lines, The trigger voltages of LVTSCR devices are lowered to the snapback-breakdown voltages of short-channel NMOS and PMOS devices. This complementary-LVTSCR ESD protection circuit offers four different discharging paths to one-by-one bypass the four modes of ESD stresses at the pad, so it can effectively avoid the unexpected ESD damages on internal circuits, Experimental results show that it can perform excellent ESD protection capability in a smaller layout area as compared to the conventional CMOS ESD protection circuit, The device characteristics under high-temperature environment of up to 150 degrees C is also experimentally investigated to guarantee the safety of this proposed ESD protection circuit.
Fabrication and microstructure of the dc-magnetron-sputtered YBa2Cu3O7-x superconducting thin films
(1996-04-01)
Koo, HS
;
Tseng, TY
;
Chang, WR
;
Tu, GC
;
材料科學與工程學系
Systematic investigations were conducted to determine the effect of deposition conditions on the microstructure and superconducting properties of YBa2Cu3O7-x thin films produced by d.c. magnetron sputtering on (001) MgO substrate. The films were c-axis preferentially oriented with respect to the (001) MgO surface at substrate temperatures of 680-700 degrees C. X-ray diffraction patterns clearly indicated the existence of the c-axis alignment normal to the substrate surface and some second phases. The second phases, including a Cu-rich phase and Y2O3, were identified by energy dispersive X-ray spectrometer and the microstructures were analysed by electron and;atomic force microscopes.
Spread spectrum multiple-access with DPSK modulation and diversity for image transmission over indoor radio multipath fading channels
(1996-04-01)
Wang, BC
;
Chang, PR
;
交大名義發表
;
電信工程研究所
;
National Chiao Tung University
As demand for networked multimedia applications is increasing rapidly, it is important to provide the ubiquitous accessibility for these services in wireless communication environment, Such access allows users to share novel multimedia applications without any geographical restrictions. In this paper, we investigate the application of the well-known antimultipath spread spectrum code-division multiple access (SS-CDMA) techniques to image transmission related to the development of next-generation multimedia wireless local area networks within a building, SS-CDMA is particularly well suited to a subband coding scheme that divides the image information into multiple parallel data streams using an analysis filter bank, each of which is multiplied by its unique spreading code, All the product signals are then transmitted at the same time in the same radio channel, even though the total bandwidth of all the signals may exceed the channel bandwidth. Each received signal is independently recovered at the decoder by multiplying its spreading code and all the recovered subbands are then reassembled by a synthesis filter bank into a close reproduction to the original image, A forward error correction (FEC) scheme based on convolutional codes with interleaving is proposed to minimize the effect of bursty channel errors on the picture duality degradation, Better image quality can be achieved by using the predetection diversity combining in order to combat the indoor multipath distortion, In this paper, the image quality of subband image transmission via SS-CDMA indoor fading channels with differential phase shift keying (DPSK) modulation is evaluated and examined, Simulation results show that the image peak signal-to-noise (PSNR) ratio is inversely related to a logarithmic function of bit error rate when each subband employs equal protection channel coding.
Mathematical model and bearing contacts of the ZK-type worm gear set cut by oversize hob cutters
(1996-04-01)
Fang, HS
;
Tsay, CB
;
交大名義發表
;
機械工程學系
;
National Chiao Tung University
An oversize worm-type hob cutter is used to cut worm gears in this study. A mathematical model of the ZK-type worm gear set is developed based on the cutting mechanism and its tool parameters. Variations in bearing contact due to pitch diameter variations of oversize hob cutters and center distance variations of worm gear sets are also investigated. A numerical example is given to demonstrate the paths and dimensions of the bearing contacts of worm gear sets.
Transient three-dimensional convection of air in a differentially heated rotating cubic cavity
(1996-04-01)
Lee, TL
;
Lin, TF
;
機械工程學系
;
Department of Mechanical Engineering
Transient three-dimensional mixed convection of air in a differentially heated vertical cubic cavity rotating about a vertical axis through the cavity center is numerically investigated. The unsteady Navier-Stokes and energy equations were discretized by the power-law scheme and solved by the projection method. Results were obtained for the thermal and rotational Rayleigh and Taylor numbers all varied from 10(2) to 10(7). Effects of the centrifugal and Coriolis forces on the thermal buoyancy driven flow were examined in detail. Significant flow modification was noted when Ra-omega > Ra or Ta > Ra. It was noted in a rotational buoyancy dominated flow that after the initial transient the main flow structure is characterized by a symmetric pair of longitudinal rolls with their axes parallel with the rotating axis of the cavity. The increase in the Coriolis force decelerates the flow near the walls and reduces the heat transfer. The local Nusselt number distributions on the hot and cold plates were more sensitive to the change in the driving forces than the space average Nusselt numbers.
Effects of oxygen content on the penetration depth of pulsed laser deposited YBCO thin films
(1996-04-01)
Hsieh, MC
;
Tseng, TY
;
Wei, SM
;
Fu, CM
;
Wu, KH
By systematically varying the oxygen content of microstrip line resonators made of pulsed laser deposited YBa2Cu3O7-x films, the effect of oxygen deficiency on the effective penetration depth were studied. By using the two-fluid model, the zero-temperature penetration depths for the fully oxygenated (i.e. O=7) and oxygen deficient (O=6.8) states in the same strip are found to be 483.2 nm and 789.8 nm, respectively. The large values obtained are attributed to the granular nature of the YBCO films used. The correlation between the penetration depths and superconducting carrier densities as functions of the oxygen content are also discussed.
Investigation of hysteresis and transport critical current under field cycle for Bi-based multifilamentary tapes
(1996-04-01)
Horng, L
;
Chen, K
;
Lee, WD
;
Yang, TJ
;
電子物理學系
The transport properties of Hi-based multifilamentary tapes on magnetic field have been studied. The tapes were fabricated by powder-in-silver tubing technique followed by appropriate sintering. The hysteretic behavior of transport critical current of the tapes with bending strain has been investigated. The experimental data are obtained at 77 K under field cycling from 0 to 1000 G to 0. The critical current density under a field does not vary when bending strain is smaller than a critical bending strain, and then decreases gradually with increasing bending strain. The normalized values are unaffected by bending strain up to 1.31%. The remnant magnetic filed H-m associated with the flux pinning force is obtained by an empirical expression, which is similar to generalized critical state model. The H-m is almost a constant for all bending strain. This observation indicates that the intrinsic pinning properties are not varied with bending strain.
A genetic algorithm with disruptive selection
(1996-04-01)
Kuo, T
;
Hwang, SY
;
交大名義發表
;
資訊科學與工程研究所
;
National Chiao Tung University
Genetic algorithms are a class of adaptive search techniques based on the principles of population genetics. The metaphor underlying genetic algorithms is that of natural evolution. Applying the ''survival-of-the-fittest'' principle, traditional genetic algorithms allocate more trials to above-average schemata, However, increasing the sampling rate of schemata that are above average does not guarantee convergence to a global optimum; the global optimum could be a relatively isolated peak or located in schemata that have large variance in performance, In this paper we propose a novel selection method, disruptive selection. This method adopts a nonmonotonic fitness function that is quite different from traditional monotonic fitness functions, Unlike traditional genetic algorithms, this method favors both superior and inferior individuals. Experimental results show that GA's using the proposed method easily find the optimal solution of a function that is hard for traditional GA's to optimize, We also present convergence analysis to estimate the occurrence ratio of the optima of a deceptive function after a certain number of generations of a genetic algorithm, Experimental results show that GA's using disruptive selection in some occasions find the optima more quickly and reliably than GA's using directional selection, These results suggest that disruptive selection can be useful in solving problems that have large variance within schemata and problems that are GA-deceptive.