A control-theoretic study of complex systems such as closed-loop neural prostheses exhibits several challenges, from the design of an optimal feedback control problem to its solution. In this paper we study one such s...
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ISBN:
(纸本)9781612848006;9781612848013
A control-theoretic study of complex systems such as closed-loop neural prostheses exhibits several challenges, from the design of an optimal feedback control problem to its solution. In this paper we study one such system, a closed-loop voluntary movement of a prosthetic finger using electrophysio-logical activities of a single cortical motor neuron. We develop an optimal feedback control problem in the nonlinear receding horizon based terminal set constraint framework. We analyze the feasibility and stability of the control problem. Further, we solve the control problem numerically by implementing a local optimum based nonconvex nonlinear programming algorithm. Finally, we study effects of visual and proprioceptive feedback pathways on the closed-loop system. Our results elucidate the importance of multiple feedback paths in designing a closed-loop neural prosthetic system.
Microbial dynamics in structured food products differ from microbial dynamics in liquids. In structured products, microorganisms are immobilised and constrained to grow as colonies, as opposed to liquid, where bacteri...
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Microbial dynamics in structured food products differ from microbial dynamics in liquids. In structured products, microorganisms are immobilised and constrained to grow as colonies, as opposed to liquid, where bacteria grow planktonically, i.e., dispersed or free-living. Little information is available on the displacement mechanisms within colony formation of non-motile bacteria. Three displacement mechanisms can be found in literature, i.e., (i) a discrete cellular automaton (CA) mechanism, (ii) a moving boundary mechanism, and (iii) a shoving mechanism. All three mechanisms are implemented in an individual-based modelling (IbM) environment. Advantages and disadvantages of each approach with respect to the individualbased modelling approach are summarised. The discrete CA results in the least realistic colony formation, but has the advantage of great computational speed. Both the moving boundary and the shoving mechanism produce biologically realistic results, albeit at a different level of detail for the representation of the environment. Both are suitable for IbM implementation and the choice depends on the level of detail necessary to describe the microbial phenomena under study.
The task of verifying the correct (with respect to a given specification) behaviour of discrete event controllers for continuous processes requires to combine model types of continuous and of discrete nature. In this ...
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The task of verifying the correct (with respect to a given specification) behaviour of discrete event controllers for continuous processes requires to combine model types of continuous and of discrete nature. In this contribution, the verification problem is treated by approximating the continuous dynamics using automata models, and by carrying out a reachability analysis in the discrete domain. The focus is on different methods to generate timed automata and hybrid automata from switched continuous systems. Furthermore, some model properties and their effects on the analysis results are discussed.
With intermittently operated municipal waste water plants the aeration switching sequence should be optimized under the constraints that the solved nitrogen concentration in effluent has to be kept within its environm...
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With intermittently operated municipal waste water plants the aeration switching sequence should be optimized under the constraints that the solved nitrogen concentration in effluent has to be kept within its environmental limits. This is a highly nonlinear control problem because of the nonlinear biological process model ASM1 (Activated Sludge Model 1), the on-off state of the manipulated sequence and the concentration constraints. The constrained optimization was transformed to the unconstrained optimization of the predictive on-off control, as the violations of the constraints were converted to their economical costs. Furthermore, the cost of the aeration was considered in the cost function.
Several steadystate design studies of distillation systems that combine complex configurations (prefractionators and sidestream columns) and heat integration have appeared in the literature and have shown the potentia...
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Several steadystate design studies of distillation systems that combine complex configurations (prefractionators and sidestream columns) and heat integration have appeared in the literature and have shown the potential for large reductions (50%) in energy consumption compared to conventional designs. However, the dynamics and control aspects of these highly interactive and multivariable systems have been virtually unexplored. This paper presents the results of computer simulation studies of the dynamic controllability of a complex heat-integrated distillation system for the ternary mixture of benzene, toluene and m-xylene. Both low and high-purity separations were explored. For the low-purity (95% product purities) separation, the complex heat-integrated system was found to be controllable and gave dynamic responses that were comparable to the simple conventional system. A diagonal multi-loop SISO controller structure was successful in controlling this 3x3 multivariable process. controlled variables were the three product purities. Manipulated variables were the flow rates of reflux, sidestream and reboiler steam. For the high-purity (99.9%) separation, the complex heat-integrated system was found to be controllable but could only handle small (<10%) feed composition disturbances and was dynamically worse than the conventional system. The control structure used in the low-purity separation did not work in the high-purity separation because of severe nonlinearity. To decrease the nonlinearity, a control structure was developed that maintained the two impurities in the toluene sidestream product instead of the toluene purity. The additional manipulated variable needed in this modified process (now a 4x4 multivariable process) was achieved by changing the sidestream drawoff-tray location.
An approach to the neural network-based feedforward control of a two-stage heat exchange process is presented. When pressure change occurs in the distillation column, the disturbance causes a variation of material bal...
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An approach to the neural network-based feedforward control of a two-stage heat exchange process is presented. When pressure change occurs in the distillation column, the disturbance causes a variation of material balance that produces undesirable material and heat imbalance. The task is fulfilled first by developing a mathematical model in a traditional way, followed by the implementation of a neural network multilayer feedforward-based controller. The dynamics and unsteady state are investigated.
Hydrogenation reactions are ubiquitous in the fine chemicals and pharmaceutical industries. The hydrogenation of o-nitroanisole to o-anisidine in methanol was selected as a model three-phase reaction for kinetics stud...
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ISBN:
(纸本)9781604235258
Hydrogenation reactions are ubiquitous in the fine chemicals and pharmaceutical industries. The hydrogenation of o-nitroanisole to o-anisidine in methanol was selected as a model three-phase reaction for kinetics study in a packed-bed microchannel reactor using Pd metal supported on zeolite as a catalyst. The kinetics of three-phase hydrogenation reactions in conventional slurry or batch reactors is often limited by mass transfer of hydrogen through the liquid due to the limited solubility of hydrogen in organic substrates and solvents. These reactions are also highly exothermic, therefore adequate temperature control is of primary importance to reduce side reactions and to prevent thermal runaway conditions. The use of a microchannel reactor for such reactions provides improved mass and heat transfer rates which may ensure that the reaction operates close to intrinsic kinetics. In the present study, the rate data in the intrinsic kinetic regime were analyzed and found to be well represented by L-H type rate equations. Kinetic experiments were also conducted in a semi-batch reactor under similar reaction conditions as the microchannel reactor. The performance of the packed bed microchannel reactor was compared to that of the semi-batch reactor by evaluating the mass transfer resistance in each system.
The implementation of a new estimation method with alternative process models for the state estimation of the baker’s yeast fermentation is presented. Some of the implementation issues are discussed using the data ob...
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The implementation of a new estimation method with alternative process models for the state estimation of the baker’s yeast fermentation is presented. Some of the implementation issues are discussed using the data obtained from simulation tests.
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