About stabilization of non-minimum phase systems by output feedback

This thesis work has been motivated by an internal benchmark dealing with the output regulation problem of a nonlinear non-minimum phase system in the case of full-state feedback. The system under consideration structurally suffers from finite escape time, and this condition makes the output regulation problem very hard even for very simple steady-state evolution or exosystem dynamics, such as a simple integrator. This situation leads to studying the approaches developed for controlling Non-minimum phase systems and how they affect feedback performances. Despite a lot of frequency domain results, only a few works have been proposed for describing the performance limitations in a state space system representation. In particular, in our opinion, the most relevant research thread exploits the so-called Inner-Outer Decomposition. Such decomposition allows splitting the Non-minimum phase system under consideration into a cascade of two subsystems: a minimum phase system (the outer) that contains all poles of the original system and an all-pass Non-minimum phase system (the inner) that contains all the unavoidable pathologies of the unstable zero dynamics. Such a cascade decomposition was inspiring to start working on functional observers for linear and nonlinear systems. In particular, the idea of a functional observer is to exploit only the measured signals from the system to asymptotically reconstruct a certain function of the system states, without necessarily reconstructing the whole state vector. The feature of asymptotically reconstructing a certain state functional plays an important role in the design of a feedback controller able to stabilize the Non-minimum phase system.

Harmonic identification using parallel neural networks in single-phase systems

In this paper, artificial neural networks are employed in a novel approach to identify harmonic components of single-phase nonlinear load currents, whose amplitude and phase angle are subject to unpredictable changes, even in steady-state. The first six harmonic current components are identified through the variation analysis of waveform characteristics. The effectiveness of this method is tested by applying it to the model of a single-phase active power filter, dedicated to the selective compensation of harmonic current drained by an AC controller. Simulation and experimental results are presented to validate the proposed approach. (C) 2010 Elsevier B. V. All rights reserved.

Liquid-Liquid Equilibrium of Aqueous Two-Phase Systems Containing Some Synthetic Polyelectrolytes and Polyethylene Glycol

Experimental results are presented for the liquid-liquid equilibrium of aqueous two-phase systems containing a synthetic polyelectrolyte (polysodium acrylate, polysodium methacrylate, and polysodium ethylene sulfonate) and polyethylene glycol at (298.2 and 323.2) K. A total of 40 phase diagrams were obtained, comprising data both of the binodal curve (obtained through cloud-point measurements) and of equilibrium compositions. The influences of temperature, the nature of the polyelectrolyte monomer unit, and the chain length of both types of polymers are analyzed and discussed.

Extraction of Ascorbate Oxidase from Cucurbita maxima by Continuous Process in Perforated Rotating Disc Contactor Using Aqueous Two-Phase Systems

The ascorbate oxidase is the enzyme used to determine the content of ascorbic acid in the pharmaceutical and food industries and clinics analyses. The techniques currently used for the purification of this enzyme raise its production cost. Thus, the development of alternative processes and with the potential to reduce costs is interesting. The application of aqueous two-phase system is proposed as an alternative to purification because it enables good separation of biomolecules. The objective of this study was to determine the conditions to continuously pre-purify the enzyme ascorbate oxidase by an aqueous two-phase system (PEG/citrate) using rotating column provided with perforated discs. Under the best conditions (20,000 g/mol PEG molar mass, 10% PEG concentration, and 25% citrate concentration), the system showed satisfactory results (partition coefficient, 3.35; separation efficiency, 54.98%; and purification factor, 1.46) and proved suitable for the pre-purification of ascorbate oxidase in continuous process.

Separation and partitioning of Green Fluorescent Protein from Escherichia coli homogenate in poly(ethylene glycol)/sodium-poly(acrylate) aqueous two-phase systems

The partitioning of Green Fluorescent Protein (GFP) in poly(ethylene glycol)/Na-poly(acrylate) aqueous two-phase systems (PEG/NaPA-ATPS) has been investigated. The aqueous two-phase systems are formed by mixing the polymers with a salt and a protein solution. The protein partitioning in the two-phase system was investigated at 25 degrees C. The concentration of the GFP was measured by fluorimetry. It was found that the partitioning of GFP depends on the salt type, pH and concentration of PEG. The data indicates that GFP partitions more strongly to the PEG phase in presence of Na2SO4 relative to NaCl. Furthermore, the GFP partitions more to the PEG phase at higher pH. The partition to the PEG phase is strongly favoured in systems with larger tie-line lengths (i.e. systems with higher polymer concentrations). The molecular weight of PEG is important since the partition coefficient (K) of GFP gradually decreases with increasing PEG size, from K ca. 300-400 for PEG 400 to K equal to 1.19 for PEG 8000. A separation process was developed where GFP was separated from a homogenate in two extraction steps: the GFP is first partitioned to the PEG phase in a PEG 3000/NaPA 8000 system containing 3 wt% Na2SO4, where the K value of GFP was 8. The GFP is then re-extracted to a salt phase formed by mixing the previous top-phase with a Na2SO4 solution. The K-value of GFP in this back-extraction was 0.22. The total recovery based on the start material was 74%. (c) 2008 Elsevier B.V. All rights reserved.

Purification of alpha-toxin from Clostridium perfringens type A in PEG-phosphate aqueous two-phase systems: a factorial study

BACKGROUND: Purification of a-toxin produced by Clostridium perfringens type A in aqueous two-phase systems (ATPS) was studied with a full two-level factorial design on two factors (concentrations of 8000 g mol(-1) PEG and phosphate salt at pH 8.0), to estimate the influence of these factors on the purification results. RESULTS: The partition coefficient (K), purification factor (PF) and activity yield (Y) were strongly influenced by the PEG and phosphate concentrations. Raising the levels of the two factors increased these responses. The highest purification factor (5.7) was obtained with PEG and phosphate concentrations of 17.5% and 15%, respectively. CONCLUSION: These results support the proposal that polymer excluded volume and hydrophobic interactions are the factors that drive the alpha-toxin in PEG/phosphate aqueous two-phase systems. (c) 2008 Society of Chemical Industry

Protein partitioning in poly(ethylene glycol)/sodium polyacrylate aqueous two-phase systems

The partition of hemoglobin, lysozyme and glucose-6-phospate dehydrogenase (G6PDH) in a novel inexpensive aqueous two-phase system (ATPS) composed by poly(ethylene glycol) (PEG) and sodium polyacrylate (NaPA) has been studied. The effect of NaCl and Na2SO4, pH and PEG molecular size on the partitioning has been studied. At high pH (above 9), hemoglobin partitions strongly to the PEG-phase. Although some precipitation of hemoglobin occurs, high recovery values are obtained particularly for lysozyme and G6PDH. The partitioning forces are dominated by the hydrophobic and electrochemical (salt) effects, since the positively charged lysozyme and negatively charged G6PDH partitions to the non-charged PEG and the strongly negatively charged polyacrylate enriched phase, respectively. (c) 2007 Elsevier B.V. All rights reserved.

Polyethylene glycol 8000+ citrate salts aqueous two-phase systems: Relative hydrophobicity of the equilibrium phases

The Gibbs free energy of transfer of a methylene group, G*(CH2), is reported as a measure of the relative hydrophobicity of the equilibrium phases. Furthermore, G*(CH2) is a characteristic parameter of each tie-line, and for that reason can be used for comparing different tie-lines of a given aqueous two-phase system (ATPS) or even to establish comparisons among different ATPSs. In this work, the partition coefficients of a series of four dinitrophenylated-amino acids were experimentally determined, at 23 °C, in five different tie-lines of PEG8000(sodium or potassium) citrate ATPSs. G*(CH2) values were calculated from the partition coefficients and used to evaluate the relative hydrophobicity of the equilibrium phases. PEG8000potassium citrate ATPSs presented larger relative hydrophobicity than PEG8000sodium citrate ATPSs. Furthermore, the results obtained indicated that the PEG-rich phase (top phase) has higher affinity to participate in hydrophobic hydration interactions than the salt-rich phase (bottom phase).

Effect of NaCl additive on solute-solvent interactions in aqueous polyethylene glycol-sodium sulfate two-phase systems

Abstract Partition behavior of eight small organic compounds and six proteins was examined in poly(ethylene glycol)-8000-sodium sulfate aqueous two-phase systems containing 0.215 M NaCl and 0.5 M osmolyte (sorbitol, sucrose, TMAO) and poly(ethylene glycol)-10000-sodium sulfate-0.215 M NaCl system, all in 0.01 M sodium phosphate buffer, pH 6.8. The differences between the solvent properties of the coexisting phases (solvent dipolarity/polarizability, hydrogen bond donor acidity, and hydrogen bond acceptor basicity) were characterized with solvatochromic dyes using the solvatochromic comparison method. Differences between the electrostatic properties of the phases were determined by analysis of partitioning of sodium salts of dinitrophenylated (DNP-) amino acids with aliphatic alkyl side-chain. The partition coefficients of all compounds examined (including proteins) were described in terms of solute-solvent interactions. The results obtained in the study show that solute-solvent interactions of nonionic organic compounds and proteins in polyethylene glycol-sodium sulfate aqueous two-phase system change in the presence of NaCl additive.

Effect of sodium chloride on solutesolvent interactions in aqueous polyethylene glycolsodium sulfate two-phase systems

Partition behavior of eight small organic compounds and six proteins was examined in poly(ethylene glycol)-8000sodium sulfate aqueous two-phase systems containing 0.215 M NaCl and 0.5 M osmolyte (sorbitol, sucrose, TMAO) and poly(ethylene glycol)-10000sodium sulfate0.215 M NaCl system, all in 0.01 M sodium phosphate buffer, pH 6.8. The differences between the solvent properties of the coexisting phases (solvent dipolarity/polarizability, hydrogen bond donor acidity, and hydrogen bond acceptor basicity) were characterized with solvatochromic dyes using the solvatochromic comparison method. Differences between the electrostatic properties of the phases were determined by analysis of partitioning of sodium salts of dinitrophenylated (DNP-) amino acids with aliphatic alkyl side-chain. The partition coefficients of all compounds examined (including proteins) were described in terms of solutesolvent interactions. The results obtained in the study show that solutesolvent interactions of nonionic organic compounds and proteins in polyethylene glycolsodium sulfate aqueous two-phase system change in the presence of NaCl additive.

Interrelationship between partition behavior of organic compounds and proteins in aqueous dextran-Polyethylene glycol and Polyethylene glycol-sodium sulfate two-phase systems

Partition behavior of adenosine and guanine mononucleotides was examined in aqueous dextran-polyethylene glycol (PEG) and PEG-sodium sulfate two-phase systems. The partition coefficients for each series of mononucleotides were analyzed as a functions of the number of phosphate groups and found to be dependent on the nature of nucleic base and on the type of \ATPS\ utilized. It was concluded that an average contribution of a phosphate group into logarithm of partition coefficient of a mononucleotide cannot be used to estimate the difference between the electrostatic properties of the coexisting phases of ATPS. The data obtained in this study were considered together with those for other organic compounds and proteins reported previously, and the linear interrelationship between logarithms of partition coefficients in dextran-PEG, PEG-Na2SO4 and PEG-Na2SO4-0.215 M NaCl (all in 0.01 M Na- or K/Na-phosphate buffer, pH 7.4 or 6.8) was established. Similar relationship was found for the previously reported data for proteins in Dex-PEG, PEG-600-Na2SO4, and PEG-8000-Na2SO4 ATPS. It is suggested that the linear relationships of the kind established in \ATPS\ may be observed for biological properties of compounds as well.

Influence of the temperature and type of salt on the phase equilibrium of peg 1500 + potassium phosphate and peg 1500 + sodium citrate aqueous two-phase systems

The present work analyzed the effect of the temperature and type of salt on the phase equilibrium of aqueous two-phase systems (ATPS) formed by poly (ethylene glycol) (PEG) 1500 + potassium phosphate, from (278.15 to 318.15) K, and PEG 1500 + sodium citrate, from (278.15 to 298.15) K. The rise of the temperature normally increased the slope of the tie line (STL). With respect to the influence of the type of salt, sodium citrate showed better capability to induce phase separation, when compared to potassium phosphate.

Auto-weighted minimum-variance self-tuning controller

A self-tuning controller which automatically assigns weightings to control and set-point following is introduced. This discrete-time single-input single-output controller is based on a generalized minimum-variance control strategy. The automatic on-line selection of weightings is very convenient, especially when the system parameters are unknown or slowly varying with respect to time, which is generally considered to be the type of systems for which self-tuning control is useful. This feature also enables the controller to overcome difficulties with non-minimum phase systems.

Separation and partitioning of Green Fluorescent Protein from Escherichia coli homogenate in poly(ethylene glycol)/sodium-poly(acrylate) aqueous two-phase systems

The partitioning of Green Fluorescent Protein (GFP) in poly(ethylene glycol)/Na-poly(acrylate) aqueous two-phase systems (PEG/NaPA-ATPS) has been investigated. The aqueous two-phase systems are formed by mixing the polymers with a salt and a protein solution. The protein partitioning in the two-phase system was investigated at 25 degrees C. The concentration of the GFP was measured by fluorimetry. It was found that the partitioning of GFP depends on the salt type, pH and concentration of PEG. The data indicates that GFP partitions more strongly to the PEG phase in presence of Na2SO4 relative to NaCl. Furthermore, the GFP partitions more to the PEG phase at higher pH. The partition to the PEG phase is strongly favoured in systems with larger tie-line lengths (i.e. systems with higher polymer concentrations). The molecular weight of PEG is important since the partition coefficient (K) of GFP gradually decreases with increasing PEG size, from K ca. 300-400 for PEG 400 to K equal to 1.19 for PEG 8000. A separation process was developed where GFP was separated from a homogenate in two extraction steps: the GFP is first partitioned to the PEG phase in a PEG 3000/NaPA 8000 system containing 3 wt% Na2SO4, where the K value of GFP was 8. The GFP is then re-extracted to a salt phase formed by mixing the previous top-phase with a Na2SO4 solution. The K-value of GFP in this back-extraction was 0.22. The total recovery based on the start material was 74%. (c) 2008 Elsevier B.V. All rights reserved.

Plasmid DNA partitioning and separation using poly(ethylene glycol)/poly(acrylate)/salt aqueous two-phase systems

Phase diagrams of poly(ethylene glycol)/polyacrylate/Na2SO4 systems have been investigated with respect to polymer size and pH. Plasmid DNA from Escherichia coil can depending on pH and polymer molecular weight be directed to a poly(ethylene glycol) or to a polyacrylate-rich phase in an aqueous two-phase system formed by these polymers. Bovine serum albumin (BSA) and E. coil homogenate proteins can be directed opposite to the plasmid partitioning in these systems. Two bioseparation processes have been developed where in the final step the pDNA is partitioned to a salt-rich phase giving a total process yield of 60-70%. In one of them the pDNA is partitioned between the polyacrylate and PEG-phases in order to remove proteins. In a more simplified process the plasmid is partitioned to a PEG-phase and back-extracted into a Na2SO4-rich phase. The novel polyacrylate/PEG system allows a strong change of the partitioning between the phases with relatively small changes in composition or pH. (C) 2012 Elsevier B.V. All rights reserved.