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101.
The synthesis of the first mesogenic hexaalkoxybenzo[b]triphenylene derivative is reported; this compound exhibits a broad columnar liquid crystal phase at temperatures only slightly above room temperature. 相似文献
102.
103.
We report on an intracavity optical parametric oscillator (OPO) placed within a compact diode-pumped Nd:YALO laser cavity. This OPO utilizes a pair of KTP crystals, which are diffusion bonded together in a walk-off-compensated configuration. We have generated up to 21.4 W of 2-mum radiation, operating in a few-kilohertz range. 相似文献
104.
A novel linearised bipolar amplifier topology, integrating both reduction of baseband distortion and self-adaptive biasing techniques, is presented. The linearising circuit suppresses more than 25 dB of the spectral regrowth for the first-order sidelobes and reduces up to 36% DC bias power of the amplifying transistor 相似文献
105.
Lau A.P.T. Kschischang F.R. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2007,53(4):1386-1400
In a system utilizing multiuser diversity, regular feedback of channel-quality predictions to the base station is required for each user. Typically, the measure of channel quality must be quantized at each mobile station before it can be sent back. In this paper, we present two distributed scalar quantization schemes that optimize two different performance criteria: a) the minimization of the probability P e of incorrectly identifying the user with the best channel quality and b) maximization of the resulting throughput R. For a typical Rayleigh-fading system with 30 users per sector, numerical optimization results show that the Pe and R realized by the uniform quantization strategy with 16 quantization levels for each user can be achieved by only three quantization levels using the two proposed strategies. A practical approximation of the proposed schemes is studied and is shown to provide near-optimal performance for both performance criteria as the number of quantization levels becomes large 相似文献
106.
Wang D.X. Yung E.K.N. Chen R.S. Lau P.Y. 《Antennas and Propagation, IEEE Transactions on》2007,55(7):1970-1980
A generalized volume integral equation method is formulated for electromagnetic scattering by arbitrarily shaped complex bodies with inhomogeneous bi-isotropy. Based on the volume equivalence principle, the integral equations are represented in terms of a pair of coupled bi-isotropic polarized volume electric and magnetic flux densities. Reduction of the integral equations into the corresponding matrix equations is obtained using the method of moments (MoM) combined with the tetrahedral mesh. In the MoM solution, the three-dimensional solenoidal function is incorporated as the basis function defined over each tetrahedral element and the details of implementation, particularly the treatment of integral singularities, will be elucidated. The efficiency and accuracy of the proposed method are validated by illustratively supported examples. 相似文献
107.
Wei Zhou Chak Wah Tang Jia Zhu Kei May Lau Zeng Y. Liu H.G. Tao N.G. Bolognesi C.R. 《Electron Device Letters, IEEE》2007,28(7):539-542
Good-quality metamorphic InP buffer layers have been successfully grown on GaAs substrates by metal-organic chemical vapor deposition. Characterization by atomic force microscope, transmission electron microscopy, high-resolution X-ray diffraction, and Hall measurements indicated that the layers are of high crystalline quality, good mobility, and excellent surface morphology. On this buffer, we demonstrated the first metamorphic InP/GaAsSb/InP double heterojunction bipolar transistors (DHBTs) with good material quality and device performance. Metamorphic DHBTs showed direct-current and radio-frequency characteristics that are comparable to those grown on lattice-matched InP substrates. 相似文献
108.
Peak-to-average ratio (PAR) of a signal is an important parameter to a linear amplifier because it determines the backoff factor needed to be applied to the amplifier in order to avoid clipping and hence spectral regrowth. In this paper, we analyzed the PAR of the downlink direct code-division multiple-access (DS-CDMA) signal for the IS-95 (2G) and the CDMA2000 (3G) systems. Both the single-carrier (SC) and the multi-carrier (MC) situations are considered. For MC systems, an analytical model is developed to describe the PAR distribution. Closed-form expressions are obtained. Results are compared with simulations, and a nearly exact match is found. This is very useful since simulations for PAR distribution are very costly. Finally, PAR control by synthesis methods are proposed, and their effectiveness are discussed 相似文献
109.
To improve the productivities of an automated container terminal, it is important to schedule different types of handling
equipment in an integrated way. A mixed-integer programming model, which considers various constraints related to the integrated
operations between different types of handling equipment, is formulated. A heuristic algorithm, called multi-layer genetic
algorithm (MLGA) is developed with a view to overcome the computation difficulty for solving the mathematical model. A numerical
experimentation is carried out in order to evaluate the performance of the algorithm. 相似文献
110.
The operation principles of a high-power high-efficiency GaAlAs superluminescent diode based on an internal absorber for lasing suppression is described. The absorber is based on an unpumped/reverse-biased section in the device, and the superluminescent diode characteristic depends heavily on the bias condition of the absorber section. The very high efficiency of the device arises from the strong waveguiding effect of the buried heterostructure. A theory which accurately describes the various device characteristics is described 相似文献