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121.
Six months of data from the YSCAT94 experiment conducted at the CCIW WAVES research platform on Lake Ontario, Canada, are analyzed to evaluate a compound probability model. YSCAT was an ultrawideband small footprint (≈1 m) microwave scatterometer that operated at frequencies of 2-18 GHz, incidence angles from 0° to 60°, both h-pol and v-pol, and which tracked the wind using simultaneous weather measurements. The probability distribution function of the measured instantaneous backscattered amplitude (p(a)) is compared to theoretical distributions developed from-the composite model and a simple wave spectrum. Model parameters of the resulting Rayleigh/generalized lognormal distribution probability density function (pdf) (C, a1 , and a2) are derived directly from the data and are found to demonstrate relationships with wind speed, incidence angle, and radar frequency 相似文献
122.
We report on the first observation and studies of a weak delocalizing logarithmic temperature dependence of the conductivity,
which causes the conductivity of the 2D metal to increase as T decreases down to 16 mK. The prefactor of the logarithmic dependence is found to decrease gradually with density, to vanish
at a critical density n
c
, 2∼2×1012 cm−2, and then to have the opposite sign at n>n
c
,2. The second critical density sets the upper limit on the existence region of the 2D metal, whereas the conductivity at the
critical point, G
c
,2∼120e
2/h, sets an upper (low-temperature) limit on its conductivity.
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 6, 497–501 (25 September 1998)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
123.
124.
We predict that, for wavelength division multiplexing optical-network applications, an asymmetrically dilated configuration of a 2×2 cross-connect is significantly better in terms of overall crosstalk when the levels of the bar-port crosstalk and the cross-port crosstalk are significantly different from each other, as is the case with optical-frequency filters which utilize grating-assisted coupling. As a verification, we present a simulation study with 2×2 polarization-diversified acousto-optic tunable filters. We present a recursive method to extend the principle of asymmetric dilation to larger-size cross-connect switches, and make a recommendation for an asymmetrically dilated 4×4 cross-connect configuration 相似文献
125.
Neviani A. Meneghesso G. Zanoni E. Hafizi M. Canali C. 《Electron Device Letters, IEEE》1997,18(12):619-621
Impact ionization is a major limiting factor to the maximum operating voltage of InGaAs-based, high-speed transistors. In this work, data on the positive temperature dependence of the electron impact ionization coefficient αn in In0.53Ga0.47As at medium-low electric fields are reported for the first time. The increase of αn with temperature is opposite to the behavior normally observed in most semiconductors. This anomalous behavior implies the onset of a positive feedback between power dissipation and avalanche generation which may adversely affect the power handling capability of In0.53Ga 0.47As-based devices, and which should be taken into account in device thermal modeling. In the experimental procedure, based on the measurement of the multiplication factor M-1 in npn In0.53Ga 0.47As/InP Heterojunction Bipolar Transistors (HBT), particular care has been taken in order to rule out possible spurious, temperature-dependent contributions to the measured multiplication current 相似文献
126.
127.
128.
Fahmy H.I. Develekos G. Douligeris C. 《Selected Areas in Communications, IEEE Journal on》1997,15(2):226-237
Communication network design is becoming increasingly complex, involving making networks more usable, affordable, and reliable. To help with this, we have proposed an expert network designer (END) for configuring, modeling, simulating, and evaluating large structured computer networks, employing artificial intelligence, knowledge representation, and network simulation tools. We present a neural network/knowledge acquisition machine-learning approach to improve the END's efficiency in solving the network design problem and to extend its scope to acquire new networking technologies, learn new network design techniques, and update the specifications of existing technologies 相似文献
129.
Single-phase voltage source power converters (VSCs) under consideration are AC-DC current-controlled boost-type power converters with bidirectional power-handling capability. Equivalence between two series-connected two-level power converters and a single three-level power converter is considered here. Further considered is the series operation of three-level power converters. Simulation results and experimental verification for both are provided. Economical configurations of three-level power converters leading to multilevel waveforms are presented thereafter 相似文献
130.
The perfectly matched layer for use with the finite-difference time-domain method is adapted to our transmission-line matrix simulation as what we call a heaviside absorbing layer (HAL). It is shown that the reflection coefficient for the wave incident on a HAL is less than that of the wave incident on a matched-load termination at all angles of incidence. Furthermore, the dispersion relation of a transmission-line matrix mesh of a symmetrical condensed node with both electric and magnetic loss stubs is derived. It provides guidance on how to choose the losses of HAL and other simulation parameters properly 相似文献