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991.
Nynke A. M. Verhaegh Jeroen S. van Duijneveldt Jan K. G. Dhont Henk N. W. Lekkerkerker 《Physica A》1996,230(3-4):409-436
Mixtures of colloidal silica spheres and polydimethylsiloxane in cyclohexane with a colloid-polymer size ratio of about one were found to phase separate into two fluid phases, one which is colloid-rich and one which is colloid-poor. In this work the phase separation kinetics of this fluid-fluid phase separation is studied for different compositions of the colloid-polymer mixtures, and at several degrees of supersaturation, with small angle light scattering and with light microscopy. The small angle light scattering curve exhibits a peak that grows in intensity and that shifts to smaller wave vector with time. The characteristic length scale that is obtained from the scattering peak is of the order of a few μm, in agreement with observations by light microscopy. The domain size increases with time as
, which might be an indication of coarsening by diffusion and coalescence, like in the case of binary liquid mixtures and polymer blends. For sufficiently low degrees of supersaturation the angular scattering intensity curves satisfy dynamical scaling behavior. 相似文献
992.
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
993.
Switched-current (SI) signal processing circuits with video frequency performance are presented. The delay cells employ negative feedback to produce a `virtual earth' at the input node to improve transmission accuracy. Fully differential structures with common-mode feedback are used to reduce charge injection errors and crosstalk from digital signals. An IC test circuit, in a 1 μm standard digital CMOS process, containing simple delay lines and an FIR filter section is described, and measured performance is given. Typically, a 2T delay line sampling at 13.3 MHz gave a low-frequency gain error of -54 dB, a settling error of -60 dB, a third-harmonic distortion of -40 dB with 75% modulation, and an S /N ratio of 60 dB. Scaling of the memory cell device dimensions and currents should permit SI operation at clock frequencies beyond 100 MHz 相似文献
994.
F. G. Johnson B. L. Olmsted Samuel Chen G. W. Wicks 《Journal of Electronic Materials》1993,22(3):331-334
The composition profile of an (AlAs)1/2(GaAs)1/2 tilted superlattice is characterized for the first time. The tilted superlattice sample is thermally disordered, and the
energy of the direct band gap photoluminescence peak is measured as a function of increasing layer interdiffusion. The shift
in the photoluminescence peak energy after completely disordering the tilted superlattice is 39 meV. A theoretical model is
used to simulate the change in band gap as a function of layer interdiffusion for several composition profiles. The profile
that gives the best fit to the experimental data is chosen. The tilted superlattice composition profile is found to be sinusoidal,
varying from Al0.40Ga0.60As to Al0.60Ga0.40As. 相似文献
995.
The temperature dependence of the Cd hyperfine field in a trivacancy complex in Ni between 25 and300 K is reported. It was found that, unlike the Cd substitutional field in Ni which follows the temperature dependence of the magnetization, the Cd hyperfine field in a trivacancy complex is essentially temperature independent. This temperature anomaly is compared with other temperature anomaly of impurity hyperfine fields in ferromagnetic hosts. 相似文献
996.
A new colour quantisation and quadtree based image compression scheme is proposed. The features of the new scheme are that colour palette ordering and requantisation of the decoded image for palette-based monitor displays are not required. Thus, fast decoding and displaying can be achieved 相似文献
997.
M.R.X. de Barros G. Nykolak D.J. DiGiovanni A. Bruce W.H. Grodkiewicz P.C. Becker 《Photonics Technology Letters, IEEE》1996,8(6):761-763
We report the gain, noise figure, output saturation power, and conversion efficiency of a highly concentrated Er/sup 3+/-doped alumino silicate fiber amplifier. We obtain a gain per unit length of 1.0 dB/cm, which corresponds to the highest gain per unit length obtained in an Er/sup 3+/-doped fiber amplifier. The pump power threshold ranges from 2 to 5 mW, depending on the fiber length. 相似文献
998.
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
999.
The use of block coding and errors-and-erasures decoding can enhance performance in frequency-hop (FH) communication systems, provided that a good scheme is employed to determine which symbols to erase. The problem of making erasure decisions from collections of receiver outputs is investigated in this paper. Methods to determine which received symbols to erase are derived from Bayesian decision theory. Decision rules are developed for a system with M-ary orthogonal signaling, noncoherent demodulation, and frequency-selective fading. One result is a class of Bayesian schemes in which erasure decisions are made independently from symbol to symbol. Within this class is a rule that uses signal amplitude estimates for improved performance. A second result is a Bayesian technique in which erasure decisions are mutually dependent and are made collectively for each codeword. These techniques are analyzed and compared with the performance of receivers that use erasure techniques that require multiple applications of bounded distance decoding. The performance of the Bayesian techniques for dependent erasures are also compared with the performance of receivers that do not permit erasures. It is found that each of the Bayesian techniques offers substantial performance gains over errors-only decoding, and the dependent erasure scheme provides the best performance among the techniques of lower complexity 相似文献
1000.
Liang W. Hygate G. Nye J.F. Gentle D.G. Cook R.J. 《Antennas and Propagation, IEEE Transactions on》1997,45(5):772-780
We describe an optically modulated scatterer as an electric-field probe for measuring radio-frequency and microwave fields. It has a high spatial resolution and the ability to operate very close to conducting and dielectric objects without appreciable distortion of the field to be measured. Thus, it can scan close to antennas and diffracting metal structures. We describe how the electric field is deduced from the measurements and present gain measurements and far-field patterns deduced from near-field scans of antennas. The results are tested by comparing them with those obtained by established measurement techniques 相似文献