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991.
W. S. Holland P. A. R. Ade M. J. Griffin I. D. Hepburn D. G. Vickers C. R. Cunningham P. R. Hastings W. K. Gear W. D. Duncan T. E. C. Baillie E. E. Haller J. W. Beeman 《Journal of Infrared, Millimeter and Terahertz Waves》1996,17(4):669-692
We describe the design and construction of bolometric detectors for SCUBA - the Submillimetre Common-User Bolometer Array for the James Clerk Maxwell Telescope in Hawaii. The instrument contains 131 individual detectors, in two arrays, optimized for the submillimetre atmospheric transmission windows. The detectors are cooled by dilution refrigeration to a temperature of 100 mK, so that the receiver performance will be limited by photon noise from the sky and telescope background in all wavebands. A future paper will describe the performance of the detectors with reference to typical data obtained during the laboratory commissioning period. 相似文献
992.
Aigo T. Goto M. Ohta Y. Jono A. Tachikawa A. Moritani A. 《Electron Devices, IEEE Transactions on》1996,43(4):527-534
We report on DC and microwave characteristics for high electron-mobility transistors (HEMT's) grown on Si substrates by metal-organic chemical vapor deposition (MOCVD). Threshold voltage (V th) distribution in a 3-in wafer shows standard deviation of Vth (σVth) of 36 mV with Vth of -2.41 V for depletion mode HEMT's/Si and σVth of 31 mV with Vth of 0.01 V for enhancement mode, respectively. The evaluation of Vth in a 1.95×1.9 mm2 area shows high uniformity for as-grown HEMT's/Si with σVth of 9 mV for Vth of -0.10 V, which is comparable to that for HEMT's/GaAs. Comparing the Vth distribution pattern in the area with that for annealed HEMT's/Si, it is indicated that the high uniformity of Vth is obtained irrelevant of a number of the dislocations existing in the GaAs/Si. From microwave characteristic evaluation for HEMT's with a middle-(10~50 Ω·cm) and a high-(2000~6000 Ω·cm) resistivity Si substrate using a new equivalent circuit model, it is demonstrated that HEMT's/Si have the disadvantage for parasitic capacitances and resistances originated not from the substrate resistivity but from a conductive layer at the Si-GaAs interface. The parasitic parameters, especially the capacitances, can be overcome by the reduction of electrode areas for bonding pads and by the insertion of a dielectric layer under the electrode, which bring high cut-off frequency (fT) and maximum frequency of operation (fmax) of 24 GHz for a gate length of 0.8 (μm). These results indicate that HEMT's/Si are sufficiently applicable for IC's and discrete devices and have a potential to be substituted for HEMT's/GaAs 相似文献
993.
994.
Ohshima S. Nakamura M.S. Baba S. Tomioka T. Miyachi M. Shimomura Y. 《Lightwave Technology, Journal of》1995,13(9):1838-1846
This paper describes frequency control techniques for cold start and channel recognition functions in coherent multichannel local area networks. A Z-cut quartz etalon can be used to stabilize the optical transmitter frequencies. The capture range and the influence of humidity on a Fabry-Perot etalon are discussed. The frequency deviation of the optical transmitter was estimated to be less than ±1 GHz in the long term. A double AFC loop has been proposed for local LD frequency control. It showed a wide capture range of ±100 GHz. Coherent FDM receiver switching to the desired channel was demonstrated over a range from 0 to 40°C in an experiment 相似文献
995.
Pan J.S. McInnes F.R. Jack M.A. 《Vision, Image and Signal Processing, IEE Proceedings -》1996,143(1):67-71
A bound for a Minkowski metric based on Lp distortion measure is proposed and evaluated as a means to reduce the computation in vector quantisation. This bound provides a better criterion than the absolute error inequality (AEI) elimination rule on the Euclidean distortion measure. For the Minkowski metric of order n, this bound contributes the elimination criterion from the L1 metric to L n metric. This bound can also be an extended quadratic metric which can be a hidden Markov model (HMM) with a Gaussian mixture probability density function (PDF). In speech recognition, the HMM with the Gaussian mixture VQ codebook PDF has been shown to be a promising method 相似文献
996.
Estimation of locations of sudden changes in a steplike signal has many signal processing applications; e.g., well-log signal segmentation, ionic-channel signal classification, edge detection, and segmentation of images. In this work, the Cramer-Rao lower bound (CRLB) on locations of steps in one-dimensional (1-D) steplike signals is calculated. The calculation is based on the use of a sigmoidal function to model a sudden-change (step) in the signal. The introduced model has an adjustable parameter that can be used to fit the CRLB calculation to a particular class of steplike signals 相似文献
997.
998.
A simple and efficient method for using bipolar codes in noncoherent optical code-division multiple access systems is proposed. The proposed system requires only incoherent optical delay lines and direct detection receivers. Practical architectures for the encoder/decoder are given. The Letter shows that combining Gold codes of period M=127 and Barker code of period K=4 into composite sequences of period N=508 allows 20 simultaneous active users for Pe=10 -9, while requiring only four nonprogrammable delay lines 相似文献
999.
P. J. Wellmann W. V. Schoenfeld J. M. Garcia P. M. Petroff 《Journal of Electronic Materials》1998,27(9):1030-1033
We report the tunability of up to 150 meV of the ground state transition of self-assembled InAs quantum dots (QDs) using Mn
ion implantation and subsequent annealing. Because of the exciton localization in the quantum dots, the photoluminescence
efficiency (T=12K) of the quantum dot transition remains at 80% of its original value after implantation with a Mn dose of
1×1013 cm−2ions. Strong luminescence still remains at room temperature. At a high implantation dose (1×1015 cm−2) and rapid thermal annealing (700°C for 60s) about 25% of the QD luminescence intensity is recovered at T=12K. 相似文献
1000.
We investigate the wave propagation properties of nonuniform plane waves in an (unbounded homogeneous) anisotropic conducting material. Such waves (for which amplitudes vary across surfaces of constant phase) characterize the refracted field in an imperfect dielectric, like the earth when a uniform electromagnetic plane wave is incident from the air. The results, presented in terms of polar diagrams of the attenuation, slowness, energy velocity, and quality factor predict the existence of “stopbands” beyond a given degree of nonuniformity (i.e., combinations of propagation and attenuation directions where there is no wave propagation). This is a peculiar, effect due to the joint presence of anisotropy and conductivity that may have application in the design of synthetic materials acting as absorbers of electromagnetic radiation 相似文献