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201.
Yi-Chun Wang Jui-Cheng Hsu Ping-Chi Kuo Yung-Chun Lee 《International Journal of Heat and Mass Transfer》2009,52(1-2):328-336
The primary motivation for this work is to provide data on the loss characteristics and flow rectification performance of flat-walled microdiffuser valves for Reynolds numbers between 100 and 2000 which is considered deficient in literature. The diffusers are designed with a fixed slenderness of 15 and an aspect ratio of 0.92 and with diverging angles ranging from 4° to 120°. The total pressure loss coefficient of the diffuser flow is determined experimentally. Components of the loss are studied in detail by numerical simulations. Results from the computations are in satisfactory agreement with the measurements. Simulations are also carried out for nozzle flows. Based on the experimental and the computational results, efficiencies of the diffuser valves are calculated. It is shown that, for laminar flows, global flow separation plays a significant role in reducing the loss of the diffuser. Consequently, the diffuser angle corresponding to the optimum diffuser efficiency varies from 40° at Re = 100 to 20° for Re ?500. 相似文献
202.
Ching-Luh Hsu Jen-Tsai Kuo Chin-Wei Chang 《Microwave Theory and Techniques》2009,57(1):149-156
Branch-line and rat-race couplers are designed to have dual-band operation with arbitrary power division ratios. An elementary two-port is proposed to imitate the 90deg section at the two designated frequencies with different characteristic impedances. The two-port consists of a stepped-impedance section with open stubs attached to its two ends, and its circuit parameters are determined by the transmission line theory. The use of the stepped-impedance sections also leads to circuit miniaturization. By the standard microstrip technology, investigated also includes the realizable power division ratios and circuit bandwidths in the two bands, the upper limit of the ratio of the two designated frequencies and the miniaturization factor of the proposed circuit. Hybrid couplers operating at 2.45/5.2 GHz with various power division ratios are designed, fabricated and tested. Experiment results are compared with the theory and simulation. 相似文献
203.
Chien-Hung Kuo Tzu-Chien Hsueh Shen-Iuan Liu 《Analog Integrated Circuits and Signal Processing》2002,33(3):289-300
A four pointer data weighted averaging (FPDWA) algorithm is presented to reduce the nonlinearity of the feedback multi-bit digital-to-analog converter (DAC) for delta-sigma modulators. By utilizing the proposed algorithm, the noise power caused by element mismatch can be reduced. A nine-level second-order delta-sigma modulator has been implemented in a double-poly double-metal 0.35 m CMOS process. Experimental results indicate the peak SNDR reaches 86.59 dB within bandwidth of 22 kHz. The maximum input amplitude is –7 dB below the full scale with 10-kHz input frequency, the sampling frequency is 5 MHz, and the OSR is around 113. The power consumption is 6.27 mW for a power supply of 3.3 V. 相似文献
204.
205.
An image cryptosystem based on multiple phase-only masks is proposed. The proposed cryptosystem is a hierarchical security system that can use multiple phase keys to retrieve different amounts of data. In addition to the sequential order of the phase keys, the distance parameters among the phase keys are introduced to increase the system security. Even when an illegal user steals all the phase keys, the system cannot be broken without the correct sequential order and the distance parameters. However, the proposed system can verify the identities of the persons by the cascaded structure for the phase keys to generate different verification images. Simulation results are further demonstrated to verify the proposed method. 相似文献
206.
The technique of the multiple phase encoding for optical security and verification systems is presented in this paper. This technique is based on a 4-f optical correlator that is a common architecture for optical image encryption and verification systems. However, two or more phase masks are iteratively retrieved by use of the proposed multiple phases retrieval algorithm (MPRA) to obtain the target image. The convergent speed of the iteration process in the MPRA is significantly increased and the recovered image is much more similar to the target image than those in previous approaches. In addition, the quantization effects due to the finite resolution of the phase levels in practical implementation are discussed. The relationships between the number of phase masks and the quantized phase levels are also investigated. According to the simulation results, two and three phase masks are enough to design an efficient security verification system with 64 and 32 phase levels, respectively. 相似文献
207.
Alex Ching‐Wei Lin Ting‐Kuo Chang Chueh‐Kuei Jan Meng‐Hsun Hsieh Chung‐Yang Tsai James Shih‐Chang Chang Alan Yaw‐Ming Tsai 《Journal of the Society for Information Display》2006,14(4):353-362
Abstract— A 3.5‐in. QVGA‐formatted driving‐circuit fully integrated LCD has been developed using low‐temperature poly‐Si (LTPS) technology. This display module, in which no external ICs are required, integrates all the driving circuits for a six‐bit RGB digital interface with an LTPS device called a “FASt LDD TFT” and achieves a high‐quality image, narrow frame width, and low power consumption. The LTPS process, device, and circuit technologies developed for system‐on‐glass LCD discussed. The development phase of LTPS circuit integration for system‐on‐glass LCDs is also reviewed. 相似文献
208.
Single-mode 1.27-/spl mu/m InGaAs:Sb-GaAs-GaAsP quantum well vertical cavity surface emitting lasers
Hao-Chung Kuo Ya-Hsien Chang Yi-An Chang Lai F.-I. Jung-Tang Chu Min-Ying Tsai Shing-Chung Wang 《IEEE journal of selected topics in quantum electronics》2005,11(1):121-126
The 1.27-/spl mu/m InGaAs:Sb-GaAs-GaAsP vertical cavity surface emitting lasers (VCSELs) were grown by metalorganic chemical vapor deposition and exhibited excellent performance and temperature stability. The threshold current varies from 1.8 to 1.1 mA and the slope efficiency falls less than /spl sim/35% from 0.17 to 0.11 mW/mA as the temperature is raised from room temperature to 75/spl deg/C. The VCSELs continuously operate up to 105/spl deg/C with a slope efficiency of 0.023 mW/mA. With a bias current of only 5 mA, the 3-dB modulation frequency response was measured to be 8.36 GHz, which is appropriate for 10-Gb/s operation. The maximal bandwidth is estimated to be 10.7 GHz with modulation current efficiency factor of /spl sim/5.25GHz/(mA)/sup 1/2/. These VCSELs also demonstrate high-speed modulation up to 10 Gb/s from 25/spl deg/C to 70/spl deg/C. We also accumulated life test data up to 1000 h at 70/spl deg/C/10 mA. 相似文献
209.
210.
The development of large-area, Na--Al2O3 single-crystal films on sapphire substrates via vapor reaction is reported. The films form at the expense of the sapphire which reacts with the alkali-vapors generated from mixed (Na,Li)--Al2O3 powders occupying the same space as the sapphire. A number of -Al2O3 single-crystal, large area isomorphs have been synthesized via ion exchange and their refraction and luminescence properties are reported. Patterned luminescence has been achieved in Cu+-doped single-crystal films using an electrochemical cell with + electrolyte separator between aqueous-solution electrodes. Ag+ ions are injected into the -Al2O3 electrolyte and Na+ expelled. The distribution of luminescent and environment ions is controlled by electrical charge and the chemical potential of the ions in the solution electrodes. 相似文献