Richard Vinter, (Imperial College,London, UK): Optimal ControlBirkhäuser Series on Systems & Control: Foundations & Applications

Open Systems and Information Dynamics -     

Multiple output differential OTA with linearizing bulk‐driven active‐error feedback loop for continuous‐time filter applications

A CMOS circuit realization of a highly linear multiple‐output differential operational transconductance amplifier (OTA) has been proposed. The presented approach exploits a differential pair as an input stage with both the gate and the bulk terminals as signal ports. For the proposed OTA, improved linearity is obtained by means of the active‐error feedback loop operating at the bulk terminals of the input stage. SPICE simulations of the OTA show that, for 0.35 µm AMS process, total harmonic distortion at 1.36Vpp is less than 1% with dynamic range equal to 60.1 dB at power consumption of 276 μW from 3.3 V supply. As an example, both single output and dual differential OTAs are used to design third‐order elliptic low‐pass filters. The cut‐off frequency of the filters is 1 MHz. The power consumption of the OTA‐C filter utilizing the dual output differential OTA is reduced to 1.24 mW in comparison to 2.2 mW consumed by the single output differential OTA‐C filter counterpart. Copyright © 2014 John Wiley & Sons, Ltd.     

Mechanism of particle formation in radical emulsion copolymerization of styrene with α-tert-butoxy-ω-vinylbenzyl-polyglycidol macromonomer

In the batch emulsion copolymerization of styrene and α-tert-butoxy-ω-vinylbenzyl-polyglycidol macromonomer, carried out at macromonomer concentrations exceeding the critical micelle concentration (c_mc), particles are formed by a two-step coagulative nucleation mechanism. This mechanism leaves its mark on morphology of particle interface, rate of polymerization and on molecular weight distribution of the obtained polymer. AFM studies revealed that the interface of particles is composed of objects with dimensions close to dimensions of the primary particles. Compartmentalization of styrene in the macromonomer micelles leads to the higher initial rate of styrene conversion than in the similar macromonomer free homopolymerization of styrene. The initial polymerization in the monomer-swollen macromonomer micelles, similar to the microemulsion polymerization, is responsible for the formation of the highest molecular weight component. In the mature particles there are two different polymerization loci: the interfacial layer and the core. This leads to bimodal molecular weight distribution of the formed polymer.     

A microstructural study of carbon–carbon composites impregnated with SiC filaments

Porous multidirectional carbon/carbon composite obtained by pulse chemical vapour infiltration (PCVI) was impregnated with silicon carbide (SiC) derived from pyrolysis of polymethylsiloxane resin (PMS). The impregnation process was made to improve oxidation resistance and mechanical properties of MD C/C composite. The resin was used as a source of silicon carbide component of the composite forming after heat treatment above 1000 °C. During this process SiC thin filaments were formed inside the porous carbon phase. The aim of this work was to investigate the structure and microstructure of the constituents of carbon composite obtained after pyrolysis of SiC PMS precursor. Microscopic observations revealed that during careful heat treatment of crosslinked polymethylsiloxane resin up to 1700 °C, the filaments (diameter 200–400 nm) crystallized within porous carbon phase. The filaments were randomly oriented on the composite surface and inside the pores. FTIR spectra and XRD analysis of the modified C/C composite showed that filaments had silicon carbide structure with the crystallite size of silicon carbide phase of about 45 nm. The Raman spectra revealed that the composite contains two carbon components distinctly differing in their structural order, and SiC filaments present nanocrystalline structure.     

BOOKS RECEIVED

As a result of modifications of BET model assumptions a new equation for sorption/desorption isotherms containing three constants was obtained. The proposed equation was verified successfully by means of measurements of sorption and desorption isotherms of water vapour for 29 substances and low-temperature adsorption of argon on 10 materials. Our own equation fits better, sometimes even much better, to the experimental points than the relations proposed by Harkins and Jura. Kühn, Halsey, Henderson, and Brunauer. Emmett and Teller (n = ∞).     

Finding all the DC solutions of a certain class of piecewise-linear circuits

The problem of finding all the DC solutions of a certain class of piecewise-linear electronic circuits containing locally passive and locally active one-ports is considered in this paper. An effective method enabling us to locate the solutions is developed. The method constitutes the crucial point of an algorithm based on the idea of successive contraction, division, and elimination that is capable of determining all the solutions. Several numerical examples are given, and some comparison analyses are performed confirming the usefulness of the proposed approach.This work was supported by the State Committee for Scientific Research (KBN) under grant 8T11B0911.     

Neural networks for constrained optimization problems

This paper is concerned with utilizing neural networks and analogue circuits to solve constrained optimization problems. We propose a novel neural network architecture for solving a class of non-linear programming problems. the proposed neural network is then used, and if necessary modified, to solve minimum norm problems subject to linear constraints. Minimum norm problems have many applications in various areas, but we focus on their applications to the control of discrete dynamic processes. the applicability of the proposed neural network is demonstrated on numerical examples.     

Reduced-order observer-based decentralised control of non-linear interconnected systems

The output feedback-based asymptotic stabilisation problem for a class of non-linear interconnected systems is considered, where the non-linear interconnections between subsystems satisfy quadratic constraints. A novel decentralised dynamic output feedback control strategy involving local projection operator-based reduced-order observers is proposed. This decentralised controller is characterised by the separation property. Two easily verifiable conditions that guarantee the asymptotic stability of the closed-loop system driven by the proposed decentralised controller are given. The effectiveness of the developed decentralised control strategy is illustrated with a numerical example and simulations.