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  • 11
    Electronic Resource
    Electronic Resource
    Analysis of decentralized control structures for nonlinear systems (1989)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989), S. 549-558 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Configuration of feedback loops between input and output variables of a given plant constitutes a subtask of control system synthesis. In the past, this subtask has been tackled through direct decomposition of either the process or the set of input-output variables. Linear interaction analysis has been used in both approaches to assess and minimize sub-system interactions. Since most chemical processes exhibit nonlinear behavior, it is evident that a measure is needed for assessment of interactions in the presence of system nonlinearities. In this paper we focus on input-output variable set decomposition and introduce the notion of nonlinear block relative gain (NBRG) as a nonlinear interaction measure. Both the statistic and dynamic versions of NBRG are discussed, and a computational procedure is presented for their evaluation. Direct simulations on a CSTR verify the interactions predicted by NBRG for different feedback configurations. Moreover, nonsymmetry of the effect of one loop on another, a fact not captured by the linear BRG, is accurately predicted by NBRG.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690350405
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  • 12
    Electronic Resource
    Electronic Resource
    Dynamic process modeling with recurrent neural networks (1993)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 39 (1993), S. 1654-1667 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A method of nonhlinear static and dynamic process modeling via recurrent neural networks (RNNs) is studied. An RNN model is a set of coupled nonlinear ordinary differential equations in continuous time domain with nonlinear dynamic node characteristics as well as both feedforward and feedback connections. For such networks, each physical input to a system corresponds to exactly one input to the network. The system's dynamics are captured by the internal structure of the network. The structure of RNN models may be more natural and attractive than that of feedforward neural network models, but computation time for training is longer. Our simulation results show that RNNs can learn both steady-state relationships and process dynamics of continuous and batch, single-input/single-output and multiinput/multioutput systems in a simple and direct manner. Training of RNNs shows only small degradation in the presence of noise in the training data. Thus, RNNs constitute a feasible alternative to layered feedforward back propagation neural networks in steady-state and dynamic process modeling and model-based control.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690391009
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  • 13
    Electronic Resource
    Electronic Resource
    Control of nonlinear dynamical systems modeled by recurrent neural networks (1993)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 39 (1993), S. 1890-1894 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690391116
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  • 14
    Electronic Resource
    Electronic Resource
    Design of robust constrained model-predictive controllers with volterra series (1995)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 41 (1995), S. 2098-2107 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Sufficient conditions are developed in this work for robust stability and pefformance of nonlinear model-predictive control systems that use an end-condition and second-order Volterra model with parametric uncertainty in the time domain. The robust stabilfly conditions involve the lengths of the prediction and control horizons, as well as the coefficients of the control move suppression terms in the on-line objective function. These conditions may be used for both analysis and synthesis purposes. A case study of a chemical reactor is presented to elucidate these issues.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690410909
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  • 15
    Electronic Resource
    Electronic Resource
    Robust stability analysis of constrained l1-norm model predictive control (1993)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 39 (1993), S. 1954-1965 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Sufficient conditions for robust closed-loop stability of a class of dynamic matrix control (DMC) systems are presented. The l1-norm is used in the objective function of the on-line optimization, thus resulting in a linear programming problem. The ideas of this work, however, are expandable to other DMC-type controllers. The keys to the stability conditions are: to use an end-condition in the moving horizon on-line optimization; to have coefficients of the move suppression term in the objective function of the on-line optimization satisfy certain inequalities; and to express the uncertainty as deviations in the unit pulse response coefficients of the nominal plant. These deviations and disturbances must also satisfy certain inequalities.An off-line tuning procedure for robust stability and performance of a class of DMC controllers is also included, which determines an optimal moving horizon length and optimal values for coefficients of the move suppression term. The applicability of our approach is elucidated through numerical simulations.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690391206
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  • 16
    Electronic Resource
    Electronic Resource
    A hybrid approach to nonlinear system stability and performance (1989)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989), S. 559-572 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The problems of stability and performance for nonlinear feedback systems are examined. A hybrid approach that combines input-output and state-space theories is proposed. Within this framework the notions of dynamic gain and dynamic incremental gain of a nonlinear operator are reexamined and their inability to accurately reflect the dynamic behavior of a physical system is demonstrated. The concepts of dynamic gain and dynamic incremental gain over sets are introduced and their connection to a physical system's dynamic behavior is established. Theorems are developed that allow the systematic computation of these gains through nonsmooth optimal control theory. Illustrative examples are provided throughout the paper.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690350406
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  • 17
    Electronic Resource
    Electronic Resource
    An approach to fault diagnosis of chemical processes via neural networks (1993)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 39 (1993), S. 82-88 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This article presents an approach to fault diagnosis of chemical processes at steadystate operation by using artificial neural networks. The conventional back-propagation network is enhanced by adding a number of functional units to the input layer. This technique considerably extends a network's capability for representing complex nonlinear relations and makes it possible to simultaneously diagnose multiple faults and their corresponding levels in a chemical process. A simulation study of a heptane-to-toluene process at steady-state operation shows successful results for the proposed approach.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690390109
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  • 18
    Electronic Resource
    Electronic Resource
    Performance bounds for robust quadratic dynamic matrix control with end condition (1995)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 41 (1995), S. 2083-2097 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Sufficient conditions for robust stability of multivariable quadratic dynamic matrix controllers with an end condition (EQDMC) are developed, and the effect of these conditions on closed-loop performance is examined. Hard and soft constraints on process inputs and outputs, and process modeling uncertainty are present Modeling uncertainty is quantified in the time domain as upper and lower bounds on the coefficients of a finite pulse response process model. The robust stability conditions that we develop involve the prediction and control horizon lengths, and a set of inequalities that the move-suppression coefficients in the on-line EQDMC objective function must satisfy. These conditions imply that for processes with modeling uncertainty, the move-suppression coefficients could be quite large and quite sensitive to the control horizon length and process modeling errors. This could make the EQDMC controller conservative, thus significantly deteriorating performance. To determine the optimal control horizon length corresponding to the best robust performance of the EQDMC controller for a class of disturbances, follow the proposed EQDMC controller design methodolo∼. To illustrate this methodology simulations on an SISO example and a 2 × 2 subsystem of the Shell Standard Control Problem are presented.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690410908
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  • 19
    Electronic Resource
    Electronic Resource
    Saccharification, fermentation, and protein recovery from low-temperature AFEX-treated coastal bermudagrass (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 44 (1994), S. 1122-1131 
    Details
    ISSN: 0006-3592
    Keywords: cellulase ; protein ; AFEX ; ethanol ; lignocellulose ; HCH-1 model ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Coastal bermudagrass was pretreated by a low-temperature ammonia fiber explosion (AFEX) process, which soaked the grass in liquid ammonia and then explosively released the pressure. Saccharifying enzymes were systematically applied to the AFEX-treated grass corresponding to low, medium, and high loadings of cellulase/hemicellulase (from Trichoderma reesei), cellobiase, glucoamylase, and pectinase. Three-day sugar yields linearly correlated with the logarithm of the cellulase loading. Supplemental enzymes (cellobiase, pectinase) caused upward shifts in the lines. The linearity and upward shifts are consistent with the HCH-1 model of cellulose hydrolysis. The hydrolysis sugars were converted to ethanol using yeast (Saccharomyces cerevisiae). The solid residues were treated with proteases to attempt recovery of valuable proteins. The low-temperature AFEX pretreatment was able o nearly double sugar yields. At the highest cellulase loadings (30 IU/g), the best reducing sugar and ethanol yields were 53% and 44% of the maximum potential, respectively. Protein recovery was, at most, 59% © 1994 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260440914
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  • 20
    Electronic Resource
    Electronic Resource
    Novel biodegradable copolyamides based on adipic acid, isophorone diamine and α-amino acids, 3Part 2, cf.13.. Synthesis, study of properties and evaluation of their biodegradability for food packaging applications (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 221 (1994), S. 67-90 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Neuartige biologisch abbaubare Copolyamide wurden durch Schmelzkondensation hergestellt. Durch den Einbau von α-Aminosäuren wurden statistische Copolymere erhalten, die zwar erhöhte Glasübergangstemperaturen, aber geringere Zugfestigkeiten und eine geringere alkalische Hydrolysebeständigkeit aufweisen, was aus GPC-Messungen hervorgeht. Die amorphe Struktur dieser neuen Copolyamide wurde durch Röntgenweitwinkelstreuung und Differentialthermoanalyse bestätigt. Durch FT-IR-Spektroskopie wurde das Vorhandensein der Aminosäuresegmente belegt. Diese neuartigen biologisch abbaubaren Copolyamide könnten für sich alleine oder auch als Bestandteil von Composites Anwendung finden, z. B. als Nahtmaterial bei der Fixierung von Implantaten.
    Notes: Novel biodegradable copolyamides were synthesized by melt polycondensation. Statistical copolymers were produced by the incorporation of α-amino acids showing a gradual increase in their Tg but a decrease in their tensile strength followed by higher susceptibility to alkali hydrolysis which was confirmed with GPC measurements. The amorphous nature of these novel copolyamides was confirmed with the aid of wide-angle X-ray diffraction patterns and differential thermal analysis. FT-IR spectra of the copolymers confirmed the existence of the amino acid moiety. These novel biodegradable copolyamides are expected to find application either on their own in the fields of food packaging and agriculture (disposable plastics) or as a part of composites, as sutures for fixation of macroscopic implants.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1994.052210107
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