Advances in PID Control

Since the foundation and up to the current state-of-the-art in control engineering, the problems of PID control steadily attract great attention of numerous researchers and remain inexhaustible source of new ideas for process of control system design and industrial applications. PID control effectiveness is usually caused by the nature of dynamical processes, conditioned that the majority of the industrial dynamical processes are well described by simple dynamic model of the first or second order. The efficacy of PID controllers vastly falls in case of complicated dynamics, nonlinearities, and varying parameters of the plant. This gives a pulse to further researches in the field of PID control. Consequently, the problems of advanced PID control system design methodologies, rules of adaptive PID control, self-tuning procedures, and particularly robustness and transient performance for nonlinear systems, still remain as the areas of the lively interests for many scientists and researchers at the present time. The recent research results presented in this book provide new ideas for improved performance of PID control applications

Pattern recognition in the nucleation kinetics of non-equilibrium self-assembly

Inspired by biology’s most sophisticated computer, the brain, neural networks constitute a profound reformulation of computational principles. Analogous high-dimensional, highly interconnected computational architectures also arise within information-processing molecular systems inside living cells, such as signal transduction cascades and genetic regulatory networks. Might collective modes analogous to neural computation be found more broadly in other physical and chemical processes, even those that ostensibly play non-information-processing roles? Here we examine nucleation during self-assembly of multicomponent structures, showing that high-dimensional patterns of concentrations can be discriminated and classified in a manner similar to neural network computation. Specifically, we design a set of 917 DNA tiles that can self-assemble in three alternative ways such that competitive nucleation depends sensitively on the extent of colocalization of high-concentration tiles within the three structures. The system was trained in silico to classify a set of 18 grayscale 30 × 30 pixel images into three categories. Experimentally, fluorescence and atomic force microscopy measurements during and after a 150 hour anneal established that all trained images were correctly classified, whereas a test set of image variations probed the robustness of the results. Although slow compared to previous biochemical neural networks, our approach is compact, robust and scalable. Our findings suggest that ubiquitous physical phenomena, such as nucleation, may hold powerful information-processing capabilities when they occur within high-dimensional multicomponent systems

Design of robust controllers for telecom power supplies

A Telecom power supply is studied and analyzed from control system viewpoint. It consists of three stages: AC/DC rectifier, a backup battery, and a Telecom load. The AC/DC rectifier stage can be composed of paralleled DC/DC converters preceded by paralleled AC/DC converters. However, paralleled DC/DC converters are only considered in this thesis because they constitute the main dynamics in practice. A system of paralleled DC/DC converters operating in continuous inductor current mode with either voltage mode control or peak current mode control are modeled and analyzed using state-space representation. The H∞ control design is used in order to guarantee the robust stability and robust performance of the system in spite of different uncertainties. Also the H∞ loop-shaping design is used to design robust controllers in the presence of uncertainties. μ-analysis is used to evaluate the robustness of the system. Simulation results are presented to demonstrate the control design procedure and to compare between the two approaches presented. A Telecom power system can be composed of voltage-loop and current-loop subsystems. The multi-input-multi-output proportional-integral-derivative (PID) controller is first designed achieving robust stability and robust performance of the voltage-loop. Then, the multi-input-multi-output proportional-integral (PI) controller for current-loop is designed to achieve robust stability and robust performance of the overall system. μ-analysis is used to evaluate the robustness of PID and PI controllers. Simulation results are also presented to demonstrate and validate the control design. The required output characteristic of a Telecom power system contains three modes of operation: constant-voltage, modified constant-power, and constant-current modes. This nonlinear operation can be achieved by using the fuzzy-logic approach. A fuzzy PID-like controller is implemented to achieve the robust output voltage in spite of load disturbances. A fuzzy PI-like controller is implemented to ensure the overload protection reaching the optimal output characteristic of a Telecom power system. Also the internal-model control (IMC) method is applied to basic DC/DC converters: buck, boost, and buck-boost converters. IMC scheme is used to improve the dynamic performance of basic converters by achieving a robust output voltage against line and load disturbances. Simulations show good dynamic performance of the IMC controller.reviewe

Proteotoxicity of polyglutamine expansion proteins: Cellular mechanisms and their modulation by molecular chaperones

Proteins are central to all biological processes. To become functionally active, newly synthesized protein chains must fold into unique three-dimensional conformations. A group of proteins, known as molecular chaperones, are essential for protein folding to occur with high efficiency in cells. Their main role is to prevent off-pathway reactions during folding that lead to misfolding and aggregation. A number of human diseases are known to result from aberrant folding reactions. The formation of insoluble protein aggregates in neurons is a hallmark of neurodegenerative diseases including Huntington’s disease (HD). These disorders are though to result from the acquisition of dominant, toxic functions of misfolded proteins. HD is caused by a CAG trinucleotide expansion that results in the expansion of a polyglutamine (polyQ) tract in the protein Huntingtin (Htt). The disorder is characterized by a progressive loss of specific neurons and the formation of inclusions containing aggregated Htt. Aggregate formation is causally linked to the progressive HD neuropathology, though it is not clear whether large insoluble, fibrillar structures or smaller assemblies of Htt are the toxic agents. Toxicity could arise from the recruitment of other polyQ-containing proteins, i.e. transcription factors, into the inclusions resulting in a loss of their normal cellular functions. Here, soluble Htt oligomers have been found to accumulate in the nucleus and to inhibit the function of the transcription factors TBP and CBP in cells. Aberrant interaction of toxic Htt with the benign polyQ repeat of TBP structurally destabilized the transcription factor, independent of the formation of insoluble coaggregates and caused transcriptional dysregulation. Chaperones of the Hsp70 family protect against this deactivation by modulating the conformation of Htt. This protective effect of Hsp70 was found to be based on a cooperation between Hsp70 and the chaperonin TRiC. Both chaperone systems cooperate in eliminating toxic polyQ oligomers, which may resemble the potentially pathogenic, prefibrillar states of other amyloidogenic disease proteins, and in stabilizing mutant Htt in a soluble, oligomeric state that is not associated with toxicity. TRiC and Hsp70 appear to be part of an effective chaperone network preventing the formation of harmful, amyloidogenic proteins species. They act synergistically on Htt, reminiscent of their sequential action in assisting the folding of newly-synthesized proteins

Analysis of chaperone function in multi-domain protein folding

Proteins are the central molecules of life. To become functionally active, newly synthesized polypeptide chains must fold into unique three-dimensional structures on a biologically relevant time scale. Although the information required for correct folding resides in the linear amino acid sequence of a protein, execution of the folding process under cellular conditions is critically dependent on the assistance of “helper proteins” termed molecular chaperones. This group of proteins shares the common function of binding to newly synthesized non-native proteins to prevent off-pathway reactions which otherwise would lead to misfolding and aggregation. Two major classes of chaperones, the Hsp70s and the chaperonins, have been implicated in de novo protein folding in the cytosol. While Hsp70s are primarily involved in stabilizing nascent chains until a complete domain has emerged from the ribosome and is competent for folding, the barrel-shaped chaperonins provide physically defined compartments inside which complete proteins or protein domains can fold unimpaired by aggregation. Proteins of eukaryotic origin which, on average, have a more complex architecture than their prokaryotic counterparts, often fold inefficiently upon expression in bacterial hosts. For many decades, this phenomenon placed great limitations on the recombinant production of proteins. In the present study, eukaryotic multi-domain proteins were synthesized in cell-free translation systems in order to investigate the contribution of individual chaperones to their de novo folding: Upon expression under chaperone depleted conditions in an Escherichia coli based lysate, the modular eukaryotic protein firefly luciferase was demonstrated to fold by a rapid default pathway, tightly coupled to translation. However, only a minor fraction of the translated protein chains folded correctly. In contrast, supplementation of the lysate with purified trigger factor and DnaK/DnaJ/GrpE increased the amount of native protein, but markedly delayed firefly luciferase folding relative to translation. Interestingly, while the bacterial multi-domain protein ß-galactosidase uses the endogenous chaperone machinery effectively (Agashe et al., 2004), the efficient co-translational domain folding of firefly luciferase observed in eukaryotes is not compatible with the prokaryotic chaperone system. Thus, important differences between bacterial and eukaryotic cells seem to exist in the coupling of translation and folding. Moreover, the bacterial lysate which did not contain any eukaryotic chaperones was further utilized to determine the minimum requirements for the folding of newly synthesized actin. By conducting in vitro translation reactions in the presence of purified components, the chaperonin TRiC was found to be the only eukaryotic chaperone absolutely necessary and sufficient for de novo actin folding. The actin thus produced bound DNase I and polymerized into filaments, hallmarks of its native state. Lysate supplementation with the bacterial chaperonin GroEL/GroES or the DnaK/DnaJ/GrpE chaperones led to mostly soluble actin, yet failed to facilitate its correct folding. Notably, actin folding in the TRiC-supplemented bacterial lysate occurred with slower kinetics when compared to the eukaryotic cytosol. Additionally, TRiC was demonstrated to be capable of mediating the domain-wise folding of modular proteins by their partial encapsulation in the chaperonin cavity. This was based on the fact that upon expression of actin multi-domain fusion proteins both in vivo and in vitro, the proteins properly integrated into yeast cytoskeleton structures as well as formed stable complexes with DNase I. The mechanism of how TRiC might promote the folding of individual protein domains is thereby reminiscent of the domain-wise endoproteolytical degradation of proteins by the proteasome, as reported recently (Liu et al., 2003)