Geometric properties of nonlinear networks containing capacitor-only cutsets and/or inductor-only loops. Part II: Symmetries

This paper is the last in a two-part sequence which studies nonlinear networks, containing capacitor-only cutsets and/or inductor-only loops, from the geometric coordinate-free point of view of the theory of differentiable manifolds. For such circuits, it is shown that (subject to certain assumptions) there is a naturally defined Lie group action of on the state space ofN, where ₀ is the sum of the number of independent capacitor-only cutsets and the number of independent inductor-only loops. Circuit theoretic sufficient conditions on the reactive constitutive relations are derived for the circuit dynamics to be invariant under this Lie group action.This work was supported by the Natural Sciences and Engineering Research Council of Canada, under Grant Number A7113, and by scholarships from the Natural Sciences and Engineering Research Council of Canada and the Ontario Provincial Government.     

Microbending loss evaluation in arbitrary-index single-mode optical fibers. Part I: Formulation and general properties

Microbending loss formula is derived for arbitrary-index profile optical fibers by using analytical curved fiber fields to the first-order perturbation theory. Relation between loss and fiber curvature power spectral statistics is studied in detail. Normalized frequency giving the minimum microbending loss value scarcely depends on the power spectrum. The larger the propagation constant difference between the guided and quasi-guided modes, the smaller the microbending loss is in regard to wavelength, relative index difference, and normalized frequency dependence. The obtained formulas for single-mode fiber show the same dependence as the graded-index multimode fiber, with respect to fiber structure and curvature statistical parameters.     

Fabrication of Germanosilicate glass optical fibers containing Tm/sup 2+/ ions and their nonlinear optical properties

Germanosilicate glass optical fibers incorporated with the Tm/sup 2+/ ions were fabricated to enhance optical nonlinearity by providing a strong reduction environment based on the solution doping technique in the modified chemical vapor deposition (MCVD) process. The incorporation of the Tm/sup 2+/ ions into the fiber core was identified by the electron paramagnetic resonance (EPR) spectrum in the fiber preform, and the absorption and emission properties between 350 and 1600 nm of the Tm/sup 2+/ ions in optical fibers and the fiber preform. A strong broad absorption band due to the Tm/sup 2+/ ions appeared from 350 to /spl sim/900 nm, and a broad emission from /spl sim/600 to /spl sim/1050 nm and the other emission from /spl sim/1050 to /spl sim/1300 nm, which were not shown in the Tm/sup 3+/ ions, were found upon Ar-ion laser pumping at 515 nm. Both absorption and emission results confirm that the Tm/sup 2+/ ions in the germanosilicate glass have the 4f-5d energy band from 350 to /spl sim/900 nm and the 4f-4f energy level at /spl sim/1115 nm. Also, the resonant nonlinearity at /spl sim/1310 and /spl sim/1530 nm due to the Tm/sup 2+/ ions in the fiber was measured upon the 515 nm optical pumping by using a long-period fiber grating (LPG) pair method. The nonlinear refractive index n/sub 2/ at /spl sim/1310 and /spl sim/1530 nm was found to be /spl sim/4/spl times/10/sup -15/ m/sup 2//W, where 70% and 30% of the n/sub 2/ are attributed to the nonradiative transitions and the radiative transitions, respectively.     

NLq theory: checking and imposing stability of recurrentneural networks for nonlinear modeling

It is known that many discrete-time recurrent neural networks, such as e.g., neural state space models, multilayer Hopfield networks, and locally recurrent globally feedforward neural networks, can be represented as NL_q systems. Sufficient conditions for global asymptotic stability and input/output stability of NL_q systems are available, including three types of criteria: (1) diagonal scaling; (2) criteria depending on diagonal dominance; (3) condition number factors of certain matrices. The paper discusses how Narendra's (1990, 1991) dynamic backpropagation procedure, which is used for identifying recurrent neural networks from I/O measurements, can be modified with an NL_q stability constraint in order to ensure globally asymptotically stable identified models. An example illustrates how system identification of an internally stable model corrupted by process noise may lead to unwanted limit cycle behavior and how this problem can be avoided by adding the stability constraint     

On the analysis and synthesis of active networks containing DVCCS/DVCVS

A signal-flow graph approach to the problem of analysis of networks containing resistors, capacitors, and DVCCS/DVCVS is given, and a flexible synthesis procedure is derived.     

System implications of 14/11 GHz path depolarization. Part I: Predicting the impairments

Exploitation of the international 14/11 GHz communications bands will probably follow the same pattern as that of the 6/4 GHz bands. First, the available monopolarized bandwidth will be filled. Next, multiple beams that use spatial isolation to provide frequency reuse will be developed. Finally, full dual-polarized operation will be employed. In the 14/11 GHz bands, rain can cause appreciable attenuation and depolarization. In some instances, dual polarized links will be depolarization limited. If up-link power control is implemented on attenuation dominated paths, depolarization can again dominate, owing to interference constraints. In both cases, a measure of depolarization compensation needs to be introduced to reduce the impact of interference. Part I of this paper quantifies this problem and establishes a set of reference statistics which can be used to assess the need for impairment restoration. Part II will discuss several ways of reducing the system impact of path depolarization.     

Experimental diamond photonics: Current state and prospects. Part I

In this review, we generalize and systematize the experimental data of the past few years concerning the implementation of solid-state photonic structures based on synthetic diamond materials. We list the physical properties and performances of the available devices and describe the technologies for their fabrication. The aim of the review is to establish whether the quality of the available quantum network elements, including various waveguide structures and microcavities interacting with the color centers, meets the concept of a solid-state photonic chip.     

Vacuum distillation of liquid metals: Part I. Theory and experimental study

The kinetics of vacuum distilling copper, tin, manganese, and sulfur from melted steel scrap have been measured. The experiments found that 70 to 90 pct of initial copper, 60 to 80 pet of initial tin, 80 to 100 pct of initial manganese, and 20 to 40 pct of initial sulfur can be eliminated in 30 minutes exposure to vacuum. Melt masses were in the range 10 to 60 kg, melt temperatures in the range 1850 to 2050 K, and chamber pressures in the range 3 to 400 pascals. Crucible diameter was 0.2 m. Mass transport has been described in terms of Machlin’s model for melt phase diffusion, Langmuir’s model for evaporation, and convective bulk flow for gas phase mass transport. Two preliminary criteria are shown to demonstrate the suitability of vacuum distillation to any particular system and a third operational criterion is developed to define the range of vacuum required to eliminate gas phase mass transport resistance effectively. Formerly with McGill University.     

Superconducting resonators and charge qubits: Spectroscopy and quantum operations. Part I

For the past few years, considerable progress has been made in the fabrication of quantum devices using mesoscopic semiconductor elements. These devices can represent the elemental base for a wide class of high-tech devices from supersensitive detectors of an electromagnetic field to reliable sources of single photons and quantum computers. The article reviews the main experimental results obtained to date with the participation of superconducting quantum devices.     

Stable identification of nonlinear systems using neural networks: theory and experiments

This paper presents an approach for stable identification of multivariable nonlinear system dynamics using a multilayer feedforward neural network. Unlike most of the previous neural network identifiers, the proposed identifier is based on a nonlinear-in-parameters neural network (NLPNN). Therefore, it is applicable to systems with higher degrees of nonlinearities. Both parallel and series-parallel models are used with no a priori knowledge about the system dynamics. The method can be considered both as an online identifier that can be used as a basis for designing a neural network controller as well as an offline learning scheme for monitoring the system states. A novel approach is proposed for the weight updating mechanism based on the modification of the backpropagation (BP) algorithm. The stability of the overall system is shown using Lyapunov's direct method. To demonstrate the performance of the proposed algorithm, an experimental setup consisting of a three-link macro-micro manipulator (M/sup 3/) is considered. The proposed approach is applied to identify the dynamics of the experimental robot. Experimental and simulation results are given to show the effectiveness of the proposed learning scheme.     

Analytical description of avalanche photodiode characteristics. An overview: Part I

The analytical model of avalanche photodiodes based on the different types of p–n structures is discussed. Formulas for avalanche breakdown voltage V _BD and the exponent in Miller’s relation for dependence between the carrier multiplication coefficient M and the applied voltage V are derived. The obtained results enable us to avoid time-consuming numerical calculations and develop an analytical method for optimizing the structural parameters of avalanche heterophotodiodes (its principles will be reported in Part II).     

Coarsening of three-dimensional droplets by two-dimensional diffusion: Part I. Experiment

An experimental study of diffusional coarsening, or Ostwald ripening, in a liquid-liquid two-phase system is described. An experiment performed at its isopycnic point, 42°C, allowed observations for the long times required to investigate coarsening. A holographic technique was instrumental in this work. Holograms takenin situ permit investigation of details regarding both the influence of local environmental conditions on individual droplet size histories and measurement of global averages. This study utilized a 100 μm pathlength test cell. The discrete phase was nucleated on one wall of the cell. This configuration resembles island formation in thin film growth. Observation of Ostwald ripening over a period of 1×10⁷ s (∼4 mo.) reveals that droplet number decays as t^−0.733 and the average radius increases as t^−0.247, in the asymptotic limit. This shows good agreement with theoretical predictions for diffusional growth of spherical caps on a two-dimensional substrate which is a valid approximation for the geometry of this experiment. Part I of this paper describes the experimental results. Part II discusses a numerical model for droplet growth in a comparison with the experimental results.     

Linear and nonlinear optical properties of ternary AIIBIVC2Vchalcopyrite semiconductors

The refractive indices of ZnSiAs2, CdGeP2, and CdGeAs2have been determined over a wide range of wavelengths and the optical nonlinear coefficient for second-harmonic generation from the 10.6-μ CO2laser have been measured. The absorption coefficient versus wavelength is given for the above materials as well as for ZnGeP2, a previously discussed material. Three-frequency phase-matched mixing is described for each material.     

Directional couplers made of nonidentical asymmetric slabs. Part I: Synchronous couplers

We discuss TE and TM mode directional couplers made of nonidentical asymmetric slab waveguides. Approximate expressions are provided for the coupling coefficients of synchronous (no grating) couplers and their accuracy is checked by comparison with exact solutions that are based on solving the guided mode problem of the total structure consisting of the two slabs considered to be a single waveguide.     

Photo- and Nanoelectronics Based on Two-Dimensional Materials. Part I. Two-Dimensional Materials: Properties and Synthesis

Journal of Communications Technology and Electronics - We review the synthesis methods, crystal parameters, and band structure of two-dimensional and quasi-two-dimensional materials, including...     

Joint estimation of the channel and I/Q imbalance for two-way relay networks

In modern day communication systems, the massive MIMO architecture plays a pivotal role in enhancing the spatial multiplexing gain, but vice versa the system energy efficiency is compromised. Consequently, resource allocation in-terms of antenna selection becomes inevitable to increase energy efficiency without having any obvious effect or compromising the system spectral efficiency. Optimal antenna selection can be performed using exhaustive search. However, for a massive MIMO architecture, exhaustive search is not a feasible option due to the exponential growth in computational complexity with an increase in the number of antennas. We have proposed a computationally efficient and optimum algorithm based on the probability distribution learning for transmit antenna selection. An estimation of the distribution algorithm is a learning algorithm which learns from the probability distribution of best possible solutions. The proposed solution is computationally efficient and can obtain an optimum solution for the real time antenna selection problem. Since precoding and beamforming are also considered essential techniques to combat path loss incurred due to high frequency communications, so after antenna selection, successive interference cancellation algorithm is adopted for precoding with selected antennas. Simulation results verify that the proposed joint antenna selection and precoding solution is computationally efficient and near optimal in terms of spectral efficiency with respect to exhaustive search scheme. Furthermore, the energy efficiency of the system is also optimized by the proposed algorithm, resulting in performance enhancement of massive MIMO systems.

     

Estimation of snow water equivalence using SIR-C/X-SAR. I. Inferring snow density and subsurface properties

Algorithms for estimating dry snow density and the dielectric constant and roughness of the underlying soil or rock use backscattering measurements with VV and HH polarization at L-band frequency (1.25 GHz). Comparison with field measurements of snow density during the first SIR-C/X-SAR overpass shows absolute accuracy of 42 kg m/sup -3/ (13% relative error). For the underlying soil, comparisons with the ground scatterometer measurements showed errors of 4% by volume for soil moisture estimation and 4 mm for the surface root mean square (RMS) height. Values of snow density and the properties of the underlying soil are necessary for the estimation of snow water equivalence.     

In situDiagnostics of Plasma Processes in Microelectronics: The Current Status and Immediate Prospects. Part I.

The necessity of in situmonitoring plasma processes in present-day microelectronics stems from the fact that they must provide high precision. New-generation micro- and nanodevices, which will have sharp interfaces and atomic-level sizes, demand continuous monitoring of process stages. Preference should be given to built-in monitoring facilities, which exploit highly sensitive physical effects and do not disturb particle fluxes from a plasma to a substrate. Part I covers advanced diagnostic and monitoring methods, as applied to plasmochemical processes used in microelectronics, with emphasis to optical spectral techniques. They are based on in-process measuring volume (nonlocal) parameters of a reactive plasma. Processes monitored may include etching and deposition of semiconductor, metal, and insulating layers, as well as resist stripping and surface cleaning.